A Dissertation
entitled
Chemistry and Chemical Engineering Process for Making PET from
Bio Based Monomers
by
Damian Adrian Salazar Hernandez
Submitted to the Graduate Faculty as partial fulfillment of the requirements for the
Doctor of Philosophy Degree in Engineering
______
Dr. Saleh A. Jabarin, Committee Chair
______Dr. Maria Coleman, Committee Member
______Dr. Isabel Escobar, Committee Member
______Dr. Sridhar Viamajala, Committee Member
______Dr. Joseph Lawrence, Committee Member
______Dr. Patricia R. Komuniecki, Dean College of Graduate Studies
The University of Toledo
December, 2015
Copyright 2015, Damian Adrian Salazar Hernandez
This document is copyrighted material. Under copyright law, no parts of this document may be reproduced without the expressed permission of the author. An Abstract of
Chemistry and Chemical Engineering Process for Making PET from Bio Based Monomers
by
Damian Adrian Salazar Hernandez
Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Engineering
The University of Toledo
December, 2015
Polyethylene terephthalate (PET) is a semicrystalline polymer widely used for production of fibers, films and containers. The polymer is obtained from the reaction of ethylene glycol (EG) and terephthalic acid (PTA) in a two stage process involving esterification and polycondensation reactions. Historically, the raw materials have been obtained from petro sources through refining of oil. To alleviate the dependence on fossil energy resources, researchers have synthesized EG and PTA starting from biomass. The use of these bio monomers depends on their suitability to polymerization requirements and the quality of the polymer that can be produced.
In this research, PET was synthesized using both monomers obtained from a bio based source. Bio EG was obtained with a high purity and was used as received. Bio PTA was produced through a modified Amoco process using bio p-xylene separated through distillation and crystallization methods from a sample containing furans, aromatics and alkanes.
The analysis of the separation methods revealed that the side products present in the bio p-xylene sample do not have equilibrium limitations that prevent their removal iii through physical separation methods. Bio p-xylene was obtained with purity enough to be considered a high grade product (~99.8%), Low concentration impurities in the form of alkanes and a furan molecule were still present in the product.
The analysis of the production of PTA revealed that the furan impurity present in bio p-xylene did not oxidize under Amoco process conditions, the furan was recovered from the reaction media in the oxidation liqueur. When compared to the use of petro p- xylene, the PTA produced had similar characteristics evaluated through color measurements, optical density and product purity. Both materials were produced with concentration of monofunctional groups low enough for their use in the polymerization reaction.
In order to disclose the effect on polymerization of using bio derived monomers, the analyses of product composition, thermal stability, crystallization behavior and physical properties were done. It was found that when the purity of the bio derived monomers is comparable to that of a petro product a polymer with similar characteristics was obtained. Based on the characteristics of the polymers produced, there was no assignable difference to the use of either set of raw materials.
iv
To my wife, Alejandra, you are the most important part of my life, my support, my reality, my love, my friend and my partner in crime. Thank you for being with me in this journey and for being so passionate, caring, and dedicated in your life.
Para tí, por tí y contigo.
Acknowledgements
First, I would like to thank Dr. Saleh A. Jabarin for giving me this invaluable opportunity to be his student, for sharing his knowledge, for being always comprehensive and for his patience.
I would like to thank DAK Americas LLC for funding my Ph.D. program at the
University of Toledo. Special thanks to Dr. Peter Kezios for his continuous support and constructive criticism in my research work. Thank you to Alfredo Carrasco for believing in me and for his help in making this opportunity possible.
I would like to thank Elizabeth Lofgren for her enormous help in the analytical experiments and for reviewing this work. Thank you to Mike Mumford for his help with the processing equipment and with experiments.
Thank you to Dr. Maria Coleman, Dr. Joseph Lawrence, Dr. Isabel Escobar and Dr.
Sridhar Viamajala for serving on my dissertation committee.
Finally, I would like to thank my family for being there for me throughout these years and to all my friends at the University of Toledo for their support, friendship and for all those little details in our everyday that made these years so wonderful. ¡Gracias! vi
Table of Contents
Abstract ...... iii
Acknowledgments...... vi
Table of Contents ...... vii
List of Tables ...... xv
List of Figures ...... xxi
1 Introduction……………………………………………………………..………. 1
1.1 Polyethylene terephthalate (PET) overview ...... 1
1.2 Research significance ...... 5
1.3 Objectives ...... 6
1.3.1 Specific Objectives ...... 8
1.4 Organization of dissertation ...... 9
2 Literature Review ...... 12
2.1 PET synthesis – melt phase polymerization ...... 12
2.1.1 The role of catalyst on PET synthesis ...... 19
2.1.2 Formation of byproducts ...... 21
2.2 Degradation of PET ...... 23
2.2.1 Thermal degradation of PET ...... 23
2.2.2 Hydrolytic degradation of PET ...... 24
2.2.3 Thermal-oxidative degradation of PET ...... 25 vii
2.3 Production of petro based raw materials ...... 27
2.2.1 Petro ethylene glycol...... 27
2.3.2 Petro p-xylene ...... 29
2.3.3 Petro terephthalic acid...... 33
2.3.3.1 Amoco process ...... 34
2.4 Production of bio based raw materials ...... 42
2.4.1 Biomass composition ...... 42
2.4.2 Ethylene glycol ...... 45
2.4.2.1 Production from bio ethanol ...... 45
2.4.2.2 Production from sorbitol ...... 46
2.4.3 Terephthalic acid ...... 47
2.4.3.1 Production from oxygenated compounds ...... 47
2.4.3.2 Production from 5-hydroxymethylfurfural (HMF) ...... 49
2.4.3.3 Production from limonene ...... 52
2.4.3.4 Production from isobutanol...... 53
2.4.3.5 Production from muconic acid ...... 54
2.4.3.6 Production from ethylene ...... 55
2.4.3.7 Production from 2,5 furan dicarboxylic acid (FDCA) ...... 56
2.4.3.7.1 Polyethylene furanoate (PEF) ...... 57
2.4.3.8 Production from lignin ...... 59
3 Experimental ...... 60
3.1 Materials…...... 60
3.2 Analytical techniques ...... 63
viii
3.2.1 Gas Chromatography with flame ionization detector (GC-FID) ...... 62
3.2.2 Gas Chromatography mas spectroscopy (GC-MS)...... 64
3.2.3 Reversed phase liquid chromatography mass spectroscopy ...... 66
3.2.4 Acetaldehyde generation ...... 69
3.2.5 Residual acetaldehyde ...... 72
3.2.6 Color determination ...... 73
3.2.7 Inductively coupled plasma mass spectroscopy (ICP-MS) ...... 76
3.2.8 Differential scanning calorimetry ...... 78
3.2.9 Titration...... 82
3.2.10 Vinyl ester end group determination ...... 85
3.2.11 Melt viscosity measurements ...... 87
3.2.12 Refractive index ...... 89
3.2.13 Wide angle X-ray diffraction ...... 91
3.2.14 Thermogravimetric analysis (TGA) ...... 94
3.2.15 Fourier transformed infrared spectroscopy ...... 95
3.2.16 Ultraviolet spectroscopy ...... 96
4 Characterization of raw materials ...... 98
4.1 Diluted bio p-xylene…...... 99
4.1.1 Analysis by gas chromatography…...... 99
4.1.2 Color measurement…...... 102
4.1.3 Bio based content determination…...... 103
4.2 Bio ethylene glycol…...... 106
4.2.1 Color and refractive index measurement…...... 106
ix
4.2.2 Infrared spectroscopy ...... 107
4.2.3 Analysis by gas chromatography ...... 108
4.2.4 Bio based content determination ...... 111
4.3 Bio BTEX…...... 112
4.3.1 Analysis by gas chromatography ...... 112
4.3.2 Color measurement ...... 116
4.4 Summary…...... 117
5 Separation of p-xylene from bio based samples……………..………...... 119
5.1 Introduction…...... 119
5.2 Separation of p-xylene from the diluted bio p-xylene sample ...... 120
5.2.1 Experimental ...... 120
5.2.2 Preliminary experiments ...... 123
5.2.3 Process analysis ...... 125
5.2.4 Product quality ...... 131
5.2.5 Summary ...... 133
5.3 Separation of p-xylene from bio BTEX sample ...... 133
5.3.1 Experimental ...... 133
5.3.2 Preliminary experiments ...... 134
5.3.3 Process analysis ...... 137
5.3.4 Product quality ...... 141
5.3.5 Summary ...... 142
6 Production of terephthalic acid...... 144
6.1 Introduction…...... 144
x
6.2 Oxidation of p-xylene ...... 145
6.2.1 Experimental ...... 145
6.2.2 Preliminary experiments and process conditions rationale ...... 149
6.2.3 Process analysis ...... 155
6.2.4 Product composition ...... 159
6.2.5 Quality variables ...... 173
6.2.5.1 Color ...... 173
6.2.5.2 Optical density ...... 175
6.3 Purification of CTA ...... 177
6.3.1 Experimental ...... 179
6.3.2 Process conditions rationale ...... 184
6.3.3 Process analysis ...... 185
6.3.4 Product composition ...... 189
6.3.5 Quality variables ...... 194
6.3.5.1 Color ...... 194
6.3.5.2 Optical density ...... 197
6.4 Summary … ...... 198
7 Synthesis of PET using bio derived monomers ...... 199
7.1 Introduction…...... 199
7.1.1 Review of polymer properties ...... 200
7.2 Synthesis of PET using bio EG and petro PTA…...... 205
7.2.1 Experimental ...... 205
7.2.2 Preliminary experiments and process conditions rationale ...... 210
xi
7.2.3 Process analysis ...... 210
7.2.4 Physical properties ...... 220
7.2.4.1 Melt viscosity ...... 221
7.2.4.2 Color ...... 223
7.2.5 Product composition ...... 224
7.2.5.1 Residual catalysts ...... 225
7.2.5.2 Carboxyl end groups ...... 226
7.2.5.3 Copolymer content ...... 228
7.2.5.4 Residual acetaldehyde ...... 229
7.2.6 Thermal stability ...... 230
7.2.6.1 Acetaldehyde generation ...... 231
7.2.6.2 Vinyl end groups ...... 238
7.2.6.3 Thermogravimetric analysis ...... 241
7.2.7 Crystallization ...... 243
7.2.7.1 Isothermal crystallization ...... 245
7.2.7.2 Dynamic crystallization ...... 251
7.2.7.3 Crystal size ...... 258
7.2.8 Summary ...... 260
7.3 Synthesis of PET using bio PTA and petro EG…...... 261
7.3.1 Experimental ...... 261
7.3.2 Preliminary experiments and process conditions rationale ...... 265
7.3.3 Process analysis ...... 268
7.3.4 Physical properties ...... 273
xii
7.3.4.1 Solution viscosity ...... 273
7.3.4.2 Color ...... 275
7.3.5 Product composition ...... 276
7.3.5.1 Residual catalysts ...... 276
7.3.5.2 Carboxyl end groups ...... 277
7.3.5.3 Copolymer content ...... 278
7.3.6 Crystallization ...... 279
7.3.6.1 Isothermal crystallization ...... 279
7.3.6.2 Dynamic crystallization ...... 282
7.3.7 Summary ...... 286
8 Conclusions and future work recommendations ...... 288
8.1 Conclusions…...... 288
8.2 Future work recommendations…...... 293
References ...... 295
A Quantification of BTEX using GC-FID ...... 313
B Acetaldehyde generation – Calibration curve ...... 320
C Residual catalyst quantification for polymers made with petro EG ...... 321
D Normalization of NaOH solution for titration experiments ...... 326
E Melt viscosity calibration curve ...... 328
F Bio based determination report issued by Beta Analytic Inc...... 329
G Quantification of unreacted p-xylene in oxidation experiments ...... 331
H Product composition of samples obtained from physical separation methods ....333
I LC-MS calibration curves ...... 334
xiii
J Product composition of p-xylene oxidation and CTA purification samples...... 344
K Crystallization analysis of PET samples produced with petro/bio monomers ....346
xiv
List of Tables
2.1 Physical properties of aromatic compounds ...... 30
2.2 Organic impurities in terephthalic acid ...... 41
3.1 List of chemicals used during the research and their roles in the experiments ...... 62
3.2 Pump program used to create the solvent gradient during analysis ...... 68
3.3 Experimental conditions used for ionization and for the detector ...... 68
3.4 Mass ions and detection mode for specific analytes ...... 69
3.5 Melt viscosity testing conditions ...... 89
3.6 Principal x-ray diffraction peaks for PET ...... 93
3.7 Infrared absorption frequencies for some common bonds ...... 96
4.1 Peak assignation of compounds present in the diluted bio p-xylene sample ...... 100
4.2 Characteristics of peaks assigned for linear and branched alkanes ...... 101
4.3 CIELAB color indices for xylene and furan samples ...... 103
4.4 CIELAB color indices for ethylene glycol samples ...... 107
4.5 Bio ethylene glycol product composition and component characteristics ...... 110
4.6 Peak assignation on compounds present in bio BTEX sample ...... 113
4.7 Concentration of aromatics in Bio BTEX sample ...... 115
4.8 CIELAB color indices for BTEX samples...... 117
5.1 Mass distribution in first set of distillation experiments ...... 126
5.2 Mass distribution in second set of distillation experiments ...... 128 xv
5.3 Product composition in distillation and crystallization samples ...... 131
5.4 Color variations in reference materials and in samples ...... 132
5.5 Split-points used for distillation of the BTEX sample ...... 135
5.6 Mass distribution in the first set of distillation experiments of BTEX sample ....137
5.7 Product composition on samples obtained from processing of BTEX sample ....141
6.1 Operating conditions for p-xylene oxidation experiments ...... 153
6.2 Initial material balance for p-xylene oxidation ...... 156
6.3 Antoine equation parameters for different temperature ranges ...... 159
6.4 Boiling point of the liquid mixture inside the reactor at different pressures ...... 160
6.5 Solubility data in glacial acetic acid...... 163
6.6 Comparison of CTA production using petro and bio based p-xylene ...... 165
6.7 Calibration curves parameters and area of validity ...... 168
6.8 Comparison of yields and impurity content for oxidation experiments ...... 170
6.9 L* and b* values of CTA samples obtained from bio p-xylene oxidation ...... 174
6.10 L* and b* values of CTA samples obtained from petro p-xylene oxidation ...... 175
6.11 Crude terephthalic acid/deionized water slurry mass balance ...... 186
6.12 PTA / N,N-dimethylacetamide initial material balance for washing process ...... 187
6.13 Comparison of hydrogenation experiments using petro and bio CTA ...... 190
6.14 Comparison of PTA product quality after hydrogenation of CTA ...... 193
6.15 Comparison of OD measurements for petro and bio CTA and PTA ...... 197
7.1 Influence of side products on polymer properties and reactions ...... 202
7.2 Initial material balance for esterification reactions ...... 211
7.3 Comparison of yield for esterification reactions ...... 215
xvi
7.4 Initial material balance for polycondensation reactions ...... 218
7.5 Comparison of yield for polycondensation reactions ...... 220
7.6 Comparison of intrinsic viscosity for PET samples ...... 222
7.7 L* and b* values of PET samples in pellet form ...... 224
7.8 Residual catalyst concentration on PET samples ...... 226
7.9 Carboxyl end group concentration obtained from titration test ...... 227
7.10 Residual acetaldehyde data comparison for PET samples ...... 230
7.11 AA generation comparative data for PET samples ...... 235
7.12 Log values for AA generation rate and 1/T for PET samples ...... 237
7.13 Parameters for Arrhenius equation obtained from AA generation data ...... 237
7.14 Acetaldehyde generation data at 240 °C and different desorption times ...... 238
7.15 Results for the calculation of vinyl ester groups for PET samples ...... 240
7.16 Transition temperatures for TGA analysis of PET samples...... 242
7.17 Values for the Avrami exponent for various types of nucleation and growth .....244
7.18 Isothermal crystallization values k, n, t1/2 for petro/bio EG PET samples ...... 247
7.19 Physical parameters obtained from DSC analysis of PET samples ...... 254
7.20 Dynamic crystallization values k, n, t1/2 for petro/bio EG PET samples ...... 258
7.21 Crystallite sizes in the direction of 010 (depth) and 100 (width) ...... 260
7.22 Initial material balance for esterification reactions ...... 268
7.23 Comparison of yield for polycondensation reactions ...... 273
7.24 Comparison of solution viscosity measured at 30 °C ...... 275
7.25 L* and b* values of PET samples in powder form ...... 275
7.26 Residual catalyst concentration in PET samples ...... 277
xvii
7.27 Carboxyl end group concentration obtained from titration test ...... 278
7.28 Concentration of DEG in polymer samples ...... 279
7.29 Isothermal crystallization values k, n, t1/2 for petro/bio PTA PET samples ...... 280
7.30 Physical parameters obtained from DSC analysis of PET samples ...... 283
7.31 Dynamic crystallization values k, n, t1/2 for petro/bio PTA PET samples ...... 286
A.1 Concentration of aromatics in BTEX standard ...... 314
A.2 Area units from GC chromatograms of multiple BTEX standard injections ...... 314
A.3 Calibration factors used for quantification of aromatic components ...... 314
A.4 Area under the curve for different concentrations of toluene ...... 315
A.5 Area under the curve for different concentrations of ethylbenzene ...... 316
A.6 Area under the curve for different concentrations of m-xylene ...... 317
A.7 Area under the curve for different concentrations of p-xylene ...... 318
A.8 Area under the curve for different concentrations of o-xylene ...... 319
B.1 AA concentration and peak area for calibration curve standards ...... 320
B.2 Average calibration factor for AA quantification ...... 320
C.1 Residual catalyst concentration in PET samples made with bio and petro EG ...321
C.2 Residual catalyst concentration in PET samples made with bio and petro PTA .324
D.1 Standardization of NaOH solution titration of petro/bio EG PET samples ...... 326
D.2 Standardization of NaOH solution titration of petro/bio PTA PET samples ...... 326
D.3 Empirical degradation factors in eq/106 g for different heating times...... 327
E.1 Intrinsic vs melt viscosity calibration curve raw data ...... 328
G.1 Calculation of unreacted p-xylene for different oxidation experiments ...... 332
H.1 Area units obtained from GC chromatograms of selected samples ...... 333
xviii
H.2 Area units obtained from GC chromatograms of selected samples ...... 333
I.1 Preparation of individual samples for PTA calibration curve ...... 334
I.2 PTA calibration curve datapoints ...... 334
I.3 Preparation of 4-CBA stock solution ...... 336
I.4 Preparation of individual samples for 4-CBA calibration curve ...... 336
I.5 4-CBA calibration curve datapoints ...... 336
I.6 Preparation of 4-CBA stock solution ...... 338
I.7 Preparation of individual samples for 4-CBA calibration curve ...... 338
I.8 4-CBA calibration curve datapoints ...... 338
I.9 Preparation of individual samples for PTA calibration curve ...... 340
I.10 PTA calibration curve datapoints ...... 340
I.11 Preparation of p-tol stock solution ...... 342
I.12 Preparation of individual samples for p-tol calibration curve ...... 342
I.13 P-tol calibration curve datapoints ...... 342
J.1 Compilation of LCMS results for commercial, bio and petro terephthalic...... 344
J.2 Concentration of selected components in petro and bio PTA ...... 345
K.1 Raw data of isothermal crystallization at 220 °C of PET with petro PTA ...... 346
K.2 Raw data of isothermal crystallization at 220 °C of PET with bio PTA ...... 347
K.3 Raw data for non-isothermal crystallization of PET made with petro PTA ...... 348
K.4 Raw data for non-isothermal crystallization of PET made with bio PTA ...... 349
K.5 Raw data of isothermal crystallization at 220 °C of PET made with petro EG ...350
K.6 Raw data of isothermal crystallization at 220 °C of PET made with bio EG ...... 351
K.7 Raw data for non-isothermal crystallization of PET made with petro EG ...... 352
xix
K.8 Raw data for non-isothermal crystallization of PET made with bio EG...... 353
xx
List of Figures
2-1 AAC2 mechanism for esterification and transesterification ...... 14
2-2 Mechanism of PET formation by esterification reaction ...... 15
2-3 Mechanism of PET formation by polycondensation reaction ...... 17
2-4 Mechanism of antimony catalysis ...... 20
2-5 Formation of cyclic olygomers by “back-bitting” mechanism ...... 21
2-6 Mechanism for DEG formation ...... 22
2-7 Schematic of thermal degradation of PET by chain scission ...... 24
2-8 Schematic of hydrolytic degradation of PET ...... 25
2-9 Schematic of thermal-oxidative degradation of PET ...... 26
2-10 Reaction scheme for the oxidation of ethylene to ethylene oxide ...... 28
2-11 Reaction scheme to produce ethylene glycol from ethylene oxide ...... 29
2-12 Freezing point depression curves ...... 31
2-13 Intermediate products in p-xylene oxidation ...... 35
2-14 Free radical mechanism for the oxidation of p-xylene with Co/Mn/Br ...... 37
2-15 Catalyst oxidation/reduction reactions in radical process ...... 38
2-16 Byproducts obtained from p-xylene oxidation to PTA ...... 39
2-17 Biomass structure and composition ...... 43
2-18 Reaction scheme to produce ethylene from ethanol ...... 46
2-19 HMF hydrogenolysis to DMF over Cu:Ru catalyst bed ...... 50 xxi
2-20 Reaction scheme for production of p-xylene and hexanedione ...... 51
2-21 Schematic of -limonene transformation to PTA ...... 53
2-22 Schematic of isobutanol transformation to p-xylene ...... 54
2-23 Schematic of muconic acid transformation to PTA ...... 55
2-24 Schematic of ethylene transformation to p-xylene...... 56
2-25 Schematic of HMF transformation to FDCA ...... 57
2-26 Schematic of FDCA and EG transformation to PEF ...... 58
3-1 CIELAB index color ellipsoid ...... 74
3-2 Hunter Lab Model D25 Color Meter diagram ...... 75
3-3 Hunter Lab D25-P Optical sensor schematic diagram ...... 76
3-4 Refractive indices of aqueous ethylene glycol solutions at 25 °C ...... 91
4-1 Pictures of raw materials ...... 99
4-2 GC-FID of diluted bio p-xylene sample ...... 100
4-3 Mean proportions of bio vs fossil based 14C content in bio p-xylene sample ...... 105
4-4 Infrared radiation spectrum of glycol samples ...... 108
4-5 GC-FID chromatogram of petro EG and bio EG ...... 110
4-6 Mean proportions of bio vs fossil based 14C content in bio EG sample ...... 111
4-7 GC-MS chromatogram of bio BTEX ...... 113
4-8 GC-FID chromatogram of bio BTEX ...... 115
5-1 Schematic diagram of the fractional distillation set-up...... 122
5-2 Schematic diagram of the crystallization set-up ...... 123
5-3 Solid particles separated in the vacuum filtration unit ...... 125
5-4 GC-FID chromatograms of distillates and residue...... 127
xxii
5-5 GC-FID chromatograms of distillates and residue...... 129
5-6 GC-FID chromatograms of recovered liqueur and crystal phase ...... 130
5-7 Temperature diagram of the ternary xylene mixture...... 136
5-8 GC-FID chromatograms of distillates and residue...... 138
5-9 GC-FID chromatograms crystallization products ...... 140
6-1 Process diagram for the oxidation of p-xylene to crude terephthalic acid ...... 148
6-2 Reactants inside the glass liner used for oxidation ...... 149
6-3 Inside view of oxygen bubbling in reacting media ...... 149
6-4 Stoichiometric reaction for p-xylene oxidation...... 150
6-5 Temperature and pressure profiles during oxidation of petro p-xylene ...... 157
6-6 Temperature and pressure profiles during oxidation of bio p-xylene ...... 158
6-7 Model intermediate products obtained in p–xylene oxidation ...... 160
6-8 Concentration of reactants vs time ...... 162
6-9 LC-MS chromatogram of a product sample of p-xylene oxidation ...... 167
6-10 GC-FID chromatogram of DMF oxidation ...... 172
6-11 Comparison of OD for petro CTA, bio CTA and commercial PTA ...... 177
6-12 Process diagram for the purification of CTA to PTA ...... 182
6-13 CTA and palladium over activated carbon inside the reactor glass liner ...... 183
6-14 Separation of water from PTA and Pd using vacuum filtration ...... 183
6-15 Temperature and pressure profile during hydrogenation of petro CTA ...... 188
6-16 Temperature and pressure profile during hydrogenation or bio CTA...... 188
6-17 PTA after drying @ 110 °C for 8 hours ...... 191
6-18 b* color change for CTA and PTA products obtained from petro p-xylene ...... 195
xxiii
6-19 b* color change for CTA and PTA products obtained from bio p-xylene ...... 195
6-20 L* color change for CTA and PTA products obtained from petro p-xylene ...... 196
6-21 L* color change for CTA and PTA products obtained from bio p-xylene ...... 196
7-1 Process diagram for production of PET from petro PTA, petro EG and bio EG.209
7-2 Cumulative plot of water collected in buffer tank during esterification ...... 212
7-3 Temperature profiles in distillation column during esterification reactions ...... 213
7-4 GC-FID chromatogram (zoomed view) of liquid samples ...... 216
7-5 Torque variation during polycondensation reactions ...... 219
7-6 Melt viscosity vs shear rate at 270°C for PET samples ...... 222
7-7 AA at 280 °C for PET made with petro EG at multiple desorption times ...... 232
7-8 AA generation as function of time and temperature for petro EG PET ...... 233
7-9 AA generation as function of time and temperature for bio EG PET ...... 234
7-10 Arrhenius plot for AA generation of PET samples at 270, 280 and 290 °C ...... 237
7-11 Acetaldehyde generation at 240 °C for petro and bio PET samples ...... 239
7-12 Single stage mass loss curve for PET with bio EG ...... 242
7-13 Normalized heat flow profile for isothermal crystallization from the melt ...... 246
7-14 Comparative crystallization isotherms at 220 °C for PET samples ...... 247
7-15 Avrami plot for isothermal crystallization of PET from the melt at 220 °C ...... 248
7-16 Comparative DSC plot for PET samples. Second heating step ...... 252
7-17 Comparative DSC plot for PET samples. Cooling step ...... 252
7-18 Degree of crystallinity x(T) vs temperature for non-isothermal crystallization ..255
7-19 Degree of crystallinity x (T) at specific temperatures for PET samples ...... 256
7-20 Ozawa plot of petro EG PET from the melt at different temperatures ...... 256
xxiv
7-21 Ozawa plot of bio EG PET from the melt at different temperatures ...... 257
7-22 WAXD pattern for a PET sample made with petro EG glass crystallized ...... 259
7-23 Process diagram for PET production from bio EG, petro PTA and bio PTA ...... 264
7-24 Process conditions profiles during polymerization of petro PTA bio EG PET ...269
7-25 Process conditions profiles during polymerization of bio PTA bio EG PET ...... 270
7-26 Variation in torque during polycondensation of bio EG/ bio PTA prepolymer ...271
7-27 GC-FID chromatogram of liquid samples ...... 272
7-28 Comparative crystallization isotherms at 220 °C for PET samples ...... 280
7-29 Avrami plot for isothermal crystallization of PET from the melt at 220 °C ...... 281
7-30 Degree of crystallinity x (T) at specific temperatures for PET samples ...... 284
7-31 Ozawa plot of petro PTA PET from the melt at different temperatures ...... 285
7-32 Ozawa plot of bio PTA PET from the melt at different temperatures ...... 285
A-1 Certificate of analysis of BTEX standard ...... 313
A-2 Calibration curve for toluene ...... 315
A-3 Plot of residuals for toluene calibration data points ...... 315
A-4 Calibration curve for ethylbenzene ...... 316
A-5 Plot of residuals for toluene calibration data points ...... 316
A-6 Calibration curve for m-xylene ...... 317
A-7 Plot of residuals for toluene calibration data points ...... 317
A-8 Calibration curve for p-xylene ...... 318
A-9 Plot of residuals for toluene calibration data points ...... 318
A-10 Calibration curve for o-xylene ...... 319
A-11 Plot of residuals for toluene calibration data points ...... 319
xxv
E-1 Intrinsic vs melt viscosity calibration curve ...... 328
I-1 Calibration curve terephthalic acid ...... 335
I-2 Residual plot for terephthalic acid calibration ...... 335
I-3 Calibration curve 4-carboxybenzaldehyde ...... 337
I-4 Residual plot for 4-carboxybenzaldehyde calibration...... 337
I-5 Calibration curve 4-carboxybenzaldehyde ...... 339
I-6 Residual plot for 4-carboxybenzaldehyde calibration...... 339
I-7 Calibration curve terephthalic acid ...... 341
I-8 Residual plot for terephthalic acid calibration ...... 341
I-9 Calibration curve p-toluic acid ...... 343
I-10 Residual plot for p-toluic calibration ...... 343
xxvi
Chapter 1
Introduction
1.1 Polyethylene terephthalate (PET) overview
A polymer is a large molecule built up by the repetition of small, simple chemical units. In some cases the repetition in the chain is linear and in other cases the chains are branched or interconnected to form three-dimensional networks. The repeat unit of the polymer is usually equivalent or nearly equivalent to the monomer from which the polymer is formed. The length of the chain is specified by the number of repeat units in the chain. This is called degree of polymerization [1].
The processes of polymerization were divided by Carothers and Flory into two groups: condensation (step reaction) and addition (chain-reaction) polymerization. In the former one, condensation takes place between two polyfunctional molecules to produce one larger polyfunctional molecule, with the possible elimination of a small molecule such as water. This reaction continues until one of the reagents is used up. The equilibrium of the reaction can be shifted by increasing the temperature and controlling the amounts of reactants and products. Addition polymerization involves chain reactions in which the chain carrier may be an ion or a reactive substance with one unpaired
1
electron called a free radical. This free radical is formed by the decomposition of a relatively unstable material called an initiator. It is capable of reacting to open the double bond of the single unit and attach to it leaving an electron unpaired. In a matter of seconds or less, monomers are added to the growing chain increasing its length. Finally the chain is terminated when two radicals react by combination or disproportionation
[2,3].
Polyesters are one of the most important and versatile polymers in use today.
They are produced by the polycondensation reaction of a glycol or dialcohol with a difunctional carboxylic acid. Polyesters such as polyethylene terephthalate (PET) have been widely used to produce containers for different applications such as: water, soft drink bottles, clear drinking cups, films and clothing. The success of PET in these diverse markets is due to its clarity, barrier, recyclability, toughness, and the diverse ways it can be processed [3]. The versatility of PET is obtained through the various states of molecular arrangements that can be achieved through processing. The polymer has a linear molecular structure and can exist in either an amorphous or a semicrystalline state.
The amorphous state is characterized by an absence of the three-dimensional order present in crystalline polymers. Even in the amorphous state, the molecules can be highly ordered. The molecules of either amorphous or crystalline polymers can be uniaxially or biaxially oriented. The combination of these models of orientation result in a wide variety of physical properties, making the polymer adaptable to several practical applications.
Molecular arrangement is influenced by several parameters such as molecular weight, copolymer content, melting point, glass transition temperature, and also by processing parameters such as thermal and stress history [4].
2
PET is a polymer formed by reacting ethylene glycol (EG) and terephthalic acid
(PTA) in a step-growth polycondensation polymerization. The synthesis of PET by melt phase polymerization requires a two stage process. The first step, is the esterification of
PTA with EG, forming the monomer bis hydroxyethyl terephthalate (BHET), short chain oligomers and water. The latter is typically removed from the system through a condenser. Esterification is an equilibrium reaction with an equilibrium constant higher than two, therefore the reaction is not limited by the removal of byproducts. Esterification does not require the use of a catalyst. The PTA acts as reactant and catalyst providing the acidity needed for reaction to occurr.
The second step is polycondensation, transesterification takes place in the melt phase by reaction of chains with hydroxyl end groups to produce longer polymer chains and ethylene glycol. The byproduct is removed from the melt by vacuum. The reaction equilibrium constant is less than one, therefore an efficient removal of EG is required to shift the reaction towards products. As molecular weight increases, the viscosity of the melt also increases making the removal of EG more difficult. A higher viscosity PET grade is obtained by further polymerizing the PET in a solid-state process under vacuum or in an inert gas atmosphere. In this process a flow of preheated nitrogen passes through the solid polymer pellets removing byproducts such as: EG, acetaldehyde (AA) and others. Reactions take place in the solid phase and proceeds through reaction of end groups in the amorphous part of the polymer [5].
PET raw materials (EG and PTA) are currently obtained through reforming processes of oil and natural gas. Ethylene glycol is the most important industrial organic chemical derived from ethylene oxide. Its major application is in antifreeze mixtures for
3
automobile coolant systems and secondarily as a monomer for the production of polyesters. EG is a colorless, low-volatility, low-viscosity hygroscopic liquid, that is completely miscible with water and many organic solvents [6]. The most important commercial route to produce PTA is the liquid phase oxidation of p-xylene using a metal catalyst and with an upgrade step through hydrogenation. Its primary use is to produce
PET, but it is also used in the fiber and film industry [7].
Alternative ways to produce EG and PTA are being developed. The main difference with the current processes is the use of a different starting raw material, i.e. biomass. The justification for this technological development is based on two main ideas.
The first one is the understanding that fossil fuel availability is limited and current production technologies for EG and PTA will not be possible to use if the starting material is no longer available. Economics of production processes will be affected if the starting cost is increased due to difficulty with the supply of raw material. There is not a defined timeline for oil sources to run out, but it is known that they are finite. The second one is a growing concept of making products that inflict minimal or no harm to the environment (so called environmentally friendly) and the reduction in the product carbon footprint. This concept is defined as the total set of greenhouse gas emissions (GHG) caused by a product during its lifetime. Obtaining EG and PTA from a bio based source seems to fulfill the two requirements mentioned before: a new source to produce chemical products and the concept (yet to be proven) that the use of biomass will reduce the emission of GHG compared with existing petro production processes. Special care needs to be taken when selecting the starting biomass to be used and the treatment process to be followed. Technologies are under development and there is still not a total
4
understanding of the similarity and compatibility of a potential bio EG and bio PTA with petro based EG and PTA. PET produced with bio derived materials needs to be characterized and tested in order to determine if it has the same composition, morphology and performance as equivalent material produced from petro based monomers.
1.2 Research Significance
The conversion of biomass to chemicals provides researchers the option to produce key products and intermediates for the petrochemical industry. The use of these bio derived materials is acquiring more attention from companies, government, institutions, etc. as they can potentially be drop-in substitutions for petro based materials and be environmentally friendly.
Total polymer production in 2011 was reported to be 235 million tons with 1.5% being bio derived and a net PET production of 45 million tons. The projected scenario for
2020 expects a growth in total polymer production to 400 million tons with 3.0% being bio derived and a net PET production of 65 million tons [8]. Current bio based PET production is 200,000 tons. This polymer contains up to 30% of bio derived material as only EG is obtained from biomass. The projected scenario considers production of 5 million tons by 2020 with bio EG readily available and bio PTA available in some markets. There is a vast interest from companies in terms of large scale development of bio PTA. There are different chemical routes reported on how to transform biomass into this chemical, but most of them are for laboratory or small scale production. An example of this ongoing effort is the Plant PET Technology Collaborative (PTC) formed by Coca-
5
Cola Company, Ford Motor Company, H.J. Heinz Company, NIKE Inc. and Procter &
Gamble. This is a working group created to accelerate the development and use of 100% bio derived PET in their products/applications [9].
There is a justified market need for the implementation of bio derived EG and
PTA. To the best of our knowledge, no systematic study/analysis on the production of
PET from bio based monomers has been published. The following research work provides information to the PET value chain about the production of the polymer using bio derived monomers. In these bio raw materials there are impurities present. Identifying them, understanding their nature and showing if they have an impact in the final product will allow users to be aware of chemicals that may need to be eliminated or reduced in concentration from the bio based products.
1.3 Objectives
An increasingly important objective of the chemical and petroleum industries is the identification of feedstock based on renewable (biomass) rather than the depletion of petro sourced materials. The replacement of petroleum feedstock by biomass is limited by the lack of highly efficient methods to selectively convert carbohydrates to chemical compounds. Aromatic derivatives such as benzene, toluene, ethylbenzene, xylenes
(BTEX) have been synthesized by Chang [10] through catalytic pyrolysis of biomass using a powder particle fluidized bed. Virent Inc. [10] produce them using an aqueous phase reforming process (APR) on a catalytic bed. Antellotech Inc. [11] obtained BTEX
6
by heating biomass without the presence of oxygen and catalytically converting the effluent gases to aromatic products in a fluidized bed reactor.
Currently there are different chemical routes describing how to successfully transform the sugars obtained from biomass material into terephthalic acid and ethylene glycol. Yield of final product obtained is still in the range of low molecular weight material and effective separation represents a challenging step for researchers.
In this project, the main objective was to be able to produce PET polymer with comparable quality using both petro based and bio derived raw materials. The hypothesis is that bio derived raw materials with comparable purity as commercially available petro counterparts can be used in the same polymerization process to produce a polymer with the same characteristics. This research examined the critical areas in the separation and production of polymer precursors from bio derived samples, their use in the polymerization process to create PET, the effect (if any) of remaining low concentrations of impurities and the characterization of the polymer produced. The bio derived samples were donated by an Industrial Partner member of the PET Consortium. Bio EG was provided with a high purity grade and PTA precursor (p-xylene) was separated using distillation and crystallization from two bio based aromatic samples. These samples were identified as: bio based BTEX and diluted bio based p-xylene. The separated p-xylene was oxidized to PTA following a modified Amoco process. PET was produced through melt phase polymerization followed a two stage process involving esterification and polycondensation. The polymer produced with each set of raw materials was characterized and compared, identifying the main differences between them.
7
1.3.1 Specific Objectives
Characterization of the samples used in this research (petro EG/PTA, bio EG/p-
xylene) though analytical techniques (GC-FID, GC-MS, HPLC, FT-IR,
Colorimeter, Refractive index) to identify and quantify byproducts present in each
sample.
Separation/recovery of high purity bio p-xylene from bio derived samples via
filtration, fractional distillation and crystallization.
Lab scale production of PTA in a Parr reactor using a modified AMOCO process.
In the first stage p-xylene is transformed to CTA using liquid phase catalytic
oxidation and in the second stage PTA is produced by hydrogenation over a
palladium catalytic bed.
Lab scale production of PET in a small scale (~25 gr Parr reactor) and medium
scale (~1 kg RTI-International reactor) using petro based and bio based raw
materials with the same catalyst base and polymerization conditions for both
cases.
Characterization of PET polymers produced in terms of:
Physical properties
. Solution or melt viscosity (molecular weight)
. Color
Product composition
. Residual Catalysts
. Carboxyl end groups
8
. Copolymer content
. Residual acetaldehyde
Thermal stability
. Acetaldehyde generation
. Vinyl end groups
. Thermogravimetric analysis
Crystallization
. Isothermal crystallization
. Dynamic crystallization
. Crystal size
1.4 Organization of the dissertation
Chapter 1 provides a brief introduction to PET technology including the basis of the polymer synthesis and specific properties found in PET. The discussion is followed by introductory remarks to the production of PET raw materials (EG and PTA) from petro and bio based sources. The significance of this research is presented through an overview of current market needs in the PET business. Finally, the objectives and scope of the research are presented.
Chapter 2 contains a comprehensive review of melt phase polymerization to produce PET and the production of raw materials (EG and PTA) from a petro or a bio source. The mechanisms, effects of catalyst and formation of byproducts are explained in detail to understand the key variables that can affect the reaction process and the quality
9
of the polymer produced. The existing production processes to obtain EG and PTA from a petro source are discussed in terms of key production variables and possible impurities present in the material. Finally, a review of the different chemical pathways pursued to produce EG and PTA from bio based source are discussed in terms of their chemical route, type of product obtained and if there is any commercial implementation by companies.
Chapter 3 contains a list of the different chemicals used for this research in experiments and in sample analysis. The list contains detailed explanations of all the analytical techniques used, the conditions of each analysis and general guidelines on interpretation of the results obtained. For each technique, there is an explanation of its relevance, background information and the specific samples analyzed in this research.
Chapter 4 presents the results of the characterization of samples obtained from the
Industrial Partners, who are members of the PET Consortium. These bio derived samples were the raw materials for all the experiments reported in this thesis. The main focus was to determine the presence of impurities and in the case of some key impurities obtained their concentration. This information served as a reference for the selection of appropriate separation methods to obtain high purity p-xylene.
Chapter 5 presents the results obtained from the separation of bio p-xylene from the samples given. The separation methods were selected based on two principles: the results obtained from characterization of the samples and the equipment available in the
Polymer Institute laboratory. All separations were done attaining to obtain p-xylene with a high purity grade.
10
Chapter 6 discusses the results obtained from the lab scale production of PTA using p-xylene oxidation and hydrogenation with metal catalysts. The bio p-xylene
(separated by methods discussed in Chapter 5) and petro p-xylene acquired from a commercial source were the raw materials used for the experiments. A comparison between bio and petro performance was done based on process variables and the characteristics of the acid produced.
Chapter 7 discusses the production of PET using a set of raw materials including: bio EG, bio PTA, petro EG, petro PTA. The PTA samples were produced in this research
(Chapter 5), petro EG was obtained from a commercial source and bio EG was donated.
The PET polymer produced was analyzed for its crystallization behavior, physical properties, thermal stability and product composition. The interpretation of the results revealed differences and similarities on the use of bio or petro based raw materials for polymer production.
Chapter 8 shows the overall conclusions of this research and presents recommendations for future work that may expand or complement the findings in the production of PET from bio based sources.
11
Chapter 2
Literature Review
2.1 PET synthesis - melt phase polymerization
Polyethylene terephthalate is a thermoplastic material obtained by step-growth polymerization using ethylene glycol (EG) and terephthalic acid (PTA) as raw materials.
The overall production process has two stages: esterification and polycondensation. In esterification, PTA reacts with EG producing a prepolymer that contains the monomeric unit bis-hydroxyethyl terephthalate (BHET) and some short chain oligomers. The byproduct water is removed from the system using a distillation column. The reaction is acid catalyzed and it is considered that the concentration of carboxyl groups should be sufficiently high as to have an auto catalytic process [12]. Otton et al. [13] studied the esterification of different carboxylic acids by correlating the pKa with the rate constant, the value increases by a factor of two when comparing a double acid (PTA) with a single acid (p-toluic acid). The reaction order is considered as 2 with respect to acid and 1 with respect to alcohol, giving an overall reaction rate of 3. The acid behaves as both reactant and catalyst, as the acid is consumed the catalytic activity decreases [14]. The reaction temperature is usually between 230-260 °C and nitrogen is used inside the reactor to
12
maintain the operating pressure and to provide an inert environment that prevents degradation.
During the initial stage of esterification, the raw materials (PTA and EG) are mixed at a constant speed and temperature. This step called paste mixing incorporates the reactants to create a slurry. PTA is relatively insoluble in EG, at 190 °C thus 77 moles of
EG are required to dissolve 1 mole of PTA [15]. In PET production the molar ratio of reactants is between 1.2-1.5. The rate of esterification is much higher than the dissolution rate of PTA; therefore, the latter is the rate determining step for esterification.
Experimental studies to understand the dissolution rate are difficult to do at higher temperatures as there is a competing process with reaction. In an industrial operation,
PTA is usually dissolved in prepolymer. This material, with a certain number of carboxyl end groups, gives a much higher solubility for the acid [16]. Ravindranath [17] reported a constant solubility of 1.20 mol/kg in the range of 240-260 °C for PTA dissolution in glycol. Baranova [18] reported an increase in PTA solubility in BHET from 0.24 mol/kg at 180 °C to 0.95 mol/kg at 260 °C. It has also been found that particle size of the acid also has an influence on the esterification rate. A small particle can cause agglomeration and poor dispersion with the glycol, while a large particle has a lower mass transfer coefficient and requires more time to dissolve [15].
Esterification, hydrolysis (reverse reaction) and transesterification are equilibrium reactions with constants close to one. They proceed through an AAC2 mechanism
(Figure 2-1) meaning two molecules are involved and the reaction occurs by action of an acid. The acyl carbon of the carboxylic acid is protonated creating a charged intermediate. A nucleophile attacks the opposite side of the carbon by nucleophilic
13
substitution creating an intermediate that stabilizes by resonance in two slow steps to create a positive charged acyl carbon that contains both alkyl groups. The last step is the acyl cleavage on the carbonyl with the release of water as a byproduct [19].
+ H R2OH
slow
+ -H2O -H
Figure 2-1: AAC2 mechanism for esterification-hydrolysis and transesterification- glycolysis [19]
There are a number of reactions occurring during the esterification step.
Reimschuessel [20] proposed a comprehensive model containing 6 equations to describe the formation of PET through esterification (Figure 2-2). This mechanism was obtained by analysis of model systems containing ethylene glycol, benzoic acid, terephthalic acid and 2-(2-methoxyethoxy) ethanol. Reactions 1 and 3 are esterification reactions that produce an ester unit and water. Reactions 2 and 4 are transesterification reactions that produce a diester intermediate. Reaction 5 is the condensation reaction where diester and ethylene glycol are formed. Finally, reaction 6 is the transesterification-acydolisis where terephthalic acid and a biester are formed. Analyzing the overall mechanism, water is the main byproduct of the reactions. The diester group (Ed) is the contributor to small chain
14
oligomers produced from esterification. No degradation reactions where included in the analysis, only the ones that contribute to chain growth.
4푘 (1) + 퐸(11) 푘푡 G 퐻 T Et W
2푘 퐸(21) (2) + 𝑖 2푘퐻
T Et Ed W
2푘퐸(12)
(3) + 푡 푘퐻 Cp G Et W
푘퐸(22) (4) + 𝑖 2푘퐻 Et Cp Ed W
푘퐶 (5) +
4푘푔 Ed 2Et G
푘푇
(6) + 4푘퐴
2Cp T Eb
Nomenclature: T Terephthalic acid Eb Biester groups Cp Polymer carboxyl end groups Et Terminal ester groups E Total ester groups G Ethylene glycol Ed Diester groups W Water
Figure 2-2: Mechanism of polyethylene terephthalate formation by esterification reaction [20]
15
The kinetics of esterification has been studied by many researchers using model systems. Yamada [21] obtained a value of 2.5 at 260 °C for the esterification equilibrium constant considering reactivity of free EG and a value of 1.5 at 260 °C considering reactivity of EG end group. Reimschuessel [20] obtained values of 2.8 and 1.1 for the same considered reactivity and at the same temperature. The equilibrium constant value is more than one; the reaction towards products (esterification) is favored and not limited by the removal of the byproduct (water). Because of the high number of molecules of different chain length it is assumed that the reactions occur at the end groups and equal reactivity exist in all functional groups. This reactivity is independent of the length of the chain where a functional group is attached.
The second main reaction in melt phase polymerization is polycondensation process that proceeds via transesterification reactions. It is an equilibrium reaction with glycolysis being the reverse step. Both reactions follow the same AAC2 mechanism previously described for esterification. The main difference is the need for a catalyst to create an intermediate that facilitates the nucleophilic substitution on the carbon of the carboxyl group coordinated with the metal. The catalyst should be hydrolytically stable and should not provide a distinctive characteristic to the polymer, i.e. haze, yellowness.
Common metals used are: antimony (Sb), cobalt (Co), germanium (Ge) and titanium (Ti).
The process is carried out at 270–300 °C under full vacuum for the removal of gaseous products. In this stage of the reaction the polymer chain is built and ethylene glycol is obtained as a byproduct. Figure 2-3 shows the main chain propagation reaction during polycondensation.
16
+
Figure 2-3: Mechanism of polyethylene terephthalate formation by
polycondensation reaction [21]
The kinetics of polycondensation reactions are difficult to study as a sole step, because degradation reactions are likely to occur at the same time. Different authors have analyzed the reactions using antimony oxide as catalyst and different temperatures ranging from 212-250 °C. The values obtained for the equilibrium constants are: 0.5 [22],
0.36 [23], 0.5 [24], 1 [25]. The rate of reaction for glycolysis is in general higher than the rate of polycondensation. The overall reaction rate is limited by the efficiency of the removal of ethylene glycol, with an equilibrium constant of less than one and based on the Le Châtelier principle, it is imperative to remove the byproduct to shift the reaction towards products. The overall reaction order is 3, being 1 for ester, alcohol and catalyst.
Polycondensation proceeds in the presence of a three phase system that includes the remaining PTA and catalyst representing the solid phase, polymer melt and byproducts the liquid phase and gaseous byproducts the gas phase [26]. Once EG is formed, it must migrate through the polymer melt to the liquid-vapor interface. This step is diffusion controlled and becomes the rate determining step. As the reaction progresses, the viscosity of the melt increases (molecular weight increases) reducing the rate of diffusion. Aharoni [27] measured the melt viscosity, intrinsic viscosity (solution method) and the molecular weight (end groups method) of different PET samples. He determined that the molecular weight of entanglement for PET is at values of [] ≤ 0.18 (Mn≤ 3500).
17
At this point the melt viscosity changes gradually its power dependence on molecular weight from a value of 1 to a value of 3.4. Considering the molecular weight of a repeat unit as ~192 g/mol, the critical value is reached after a chain of ~18 units is formed.
These conditions can be reached in the early stages of the polymerization. At the interface, EG should migrate to the vapor phase to be removed from the reactor headspace. A full vacuum condition helps in reducing the boiling point temperature of
EG and serves as the driving force to remove the glycol. Different authors have extensively studied the phase equilibria system occurring in melt phase polymerization.
There is a general agreement that the diffusion coefficient of glycol is reduced as degree of polycondensation increases [28-30]. Rafler et al. [31] discussed the dependence of degree of polymerization on polymer melt thickness. In the experiment, the polycondensation of BHET (using antimony acetate as catalyst under full vacuum) was used as reference model. After 30 minutes of reaction time polycondensation rate increased by a factor of seven when the polymer melt thickness decreased by a factor of thirteen.
Once the polymer is formed, there are different quality control variables that must be analyzed. The molecular weight of the polymer, usually reported in terms of intrinsic viscosity (IV) measurement, allows us to get a sense of the extent of reaction reached during the production process. The measurements of color and acetaldehyde concentration are used as reference variable to review if thermal degradation occurred.
Traditionally diethylene glycol (DEG) and isophthalic acid (IPA) are used as copolymers, they modify the crystallization behavior, affect the melting point and the natural stretch characteristic of the polymer. In general three types of contaminants are identified in
18
industrial PET: yellow colored products from degradation reactions, high molecular weight cross-linked gels and metal particles in their elemental forms [32].
2.1.1 The role of catalyst on PET synthesis.
Different metals have been tested in the synthesis of PET including: germanium, antimony, cobalt, titanium, manganese and zinc. Tomita et al. [33] studied the catalytic activity of different metal compounds in the polycondensation of BHET. He obtained rate constants for propagation and degradation reactions at different times and did a correlation with the catalytic activity of the metals. This activity was determined by obtaining stability constants in the formation of metal complexes with dibenzoyl methane
(DBM). A higher constant value will indicate a better coordination of the metal with the carbon on the carbonyl group to facilitate nucleophilic substitution. Antimonium was found to have one of the highest stability and propagation rate constants and one of the lowest degradation rate constants.
Currently, antimony oxide (Sb2O3) is the major catalyst used in PET synthesis.
The rationale for its use is the low cost compared to other metals and its reduced effect in catalyzing side reactions. Typically, the catalyst is dissolved on warm EG to form antimony glycolate. If added in its solid form the metal will first react with free glycol in the system and then proceed with the coordination to the ester. The mechanism of antimony catalysis is shown on Figure 2-4. The metal in the form of glycolate (I) coordinates with the carbon on the carbonyl group (II) releasing ethylene glycol and creating activated hydroxyl end groups by metal complexation. In the next step a chain
19
with a hydroxyl end group (II) reacts with the carbon on the carbonyl group in the metal complex (III) by nucleophilic substitution regenerating the glycolate and creating a diester link (V) which forms part of the polymer chain [34, 35]. Hovenkamp [36] found a decrease in the catalytic activity of antimony in a glycol rich environment. The coordination of the carbonyl groups to the metal is suppressed by the preferred complexation with the hydroxyl end groups. An induction time is typically seen at the beginning of polycondensation. As hydroxyl end groups are incorporated into the chain,
(reducing their concentration), the coordination to the carbonyl proceeds and chain + growth is possible. I II
IV III +
I II
IV III
V
Figure 2-4: Mechanism of antimony catalysis [34]
V 20
2.1.2 Formation of by products
During the synthesis of PET short chain oligomers are formed accounting for
2-3% of the weight. These compounds can be linear or cyclic and have been identified
(with similar concentration values) by a number of researchers. It is considered that their formation is an equilibrium-controlled process. The oligomers cause problems in the processing of the polymer, because of distinctive properties, i.e. melting point. Among the oligomers, cyclic trimer is predominant. This could be either by a mechanism favoring its creation or because it has a lower energy of formation [37]. The concentration of oligomers has been found to increase to a limiting equilibrium value as residence time in the melt increases. The mechanism proposed for the formation of cyclic oligomers is shown on Figure 2-5.
Figure 2-5: Formation of cyclic olygomers by “back-bitting” mechanism [37]
Another important byproduct created during the synthesis of the polymer is DEG.
Almost all DEG is formed during esterification and in the low vacuum stages. The amount of DEG created depends on temperature, residence time, type of catalyst, etc.
Jabarin et al. [38] did a comprehensive study on the effect of DEG on the isothermal and 21
dynamic crystallization of PET. They found that an increased concentration of DEG reduces the Tg, the crystallization temperature, the melting point and the rate of crystallization. Kinetic studies on the formation of DEG show that the reaction is irreversible with an activation energy ~125 kJ/mol and that the rate constant is dependent on temperature following a typical Arrhenius relationship. Chen et al. [39] studied the formation of DEG at various temperatures of polymerization and different loadings of antimony oxide catalyst and found that the rate constant for DEG production increased as both variables also increased. Figure 2-6 shows the mechanism for DEG formation from hydroxyl end groups. This is not the only pathway to its formation, but it is used for illustrative purposes. The reaction between the two hydroxyl end groups follows a similar mechanism to that reported for the polycondensation reaction (AAC2). The main difference in the current process is that the activated hydroxyl end group reacts with the methylene carbon adjacent to the carboxyl group.
+
Figure 2-6: Mechanism for DEG formation [40]
22
2.2 Degradation of PET
There are three main degradation processes that are likely to occur during polymer synthesis or polymer processing at elevated temperatures: thermal degradation, hydrolytic degradation and thermal-oxidative degradation.
2.2.1 Thermal degradation of PET
Thermal degradation occurs from the exposure of PET to elevated temperatures.
The resulting chain scission leads to the formation of vinyl ester end groups and carboxyl end groups. Other effects caused by the thermal degradation were listed by Jabarin [41] and are included here as reference: reduction in molecular weight, formation of additional carboxyl end groups, discoloration, formation of volatile products i.e. acetaldehyde, formation of anhydride groups and formation of low molecular weight products such as terephthalic acid and oligomers.
There is not a complete understanding on the exact mechanism of degradation.
The main reason for this is the existence of different types of links in the polymer chain created by incorporation of copolymers, degradation products, byproducts, catalyst and impurities. The most accepted mechanism (chain scission) is shown in Figure 2-7. The breaking point of the chain is in the methylene of the ester link. The chains obtained have carboxyl and vinyl as the end groups. The vinyl end groups react with hydroxyl end groups producing a characteristic PET polymer chain and acetaldehyde or they can react with carboxyl end groups creating acetaldehyde and a polymer chain with an ether link
23
[41]. It is customary to monitor the concentration and generation of acetaldehyde in the polymer as a measurement of thermal degradation.
1
+
5
2 ℎ푦푑푟표푥푦푙 푒푛푑 푔푟표푢푝푠
4
3
퐶퐻 퐶퐻푂
3
Figure 2-7: Schematic of thermal degradation of PET by chain scission [41]
2.2.2 Hydrolytic degradation of PET
PET is a hygroscopic material that reacts with water at elevated temperatures causing a reduction in its molecular weight and the formation of chain segments with carboxyl and hydroxyl end groups. The reaction is catalyzed by carboxyl end groups and is reported to occur instantaneously at PET processing temperatures. This degradation process does not cause discoloration or creation of volatile byproducts. Figure 2-8 shows
24
the mechanism of hydrolytic degradation. Water reacts with the methylene carbon on the ester link producing a chain with a carboxyl end group and one with a hydroxyl end group. Because of this reducing molecular weight reaction, all PET material should be dried to a moisture content of 50 ppm before processing.
ℎ푒푎푡
+
Figure 2-8: Schematic of hydrolytic degradation of PET
2.2.3 Thermal-oxidative degradation of PET
Thermal-oxidative degradation occurs when oxygen reacts with the polymer chain at elevated temperatures. When compared with thermal degradation, the rate of reaction is higher and the activation energy is lower [31]. This type of degradation results in reduction of molecular weight, formation of branched chains, production of gaseous products (acetaldehyde) and discoloration [42]. The exact mechanism of oxidative degradation is not known. In Figure 2-9 an accepted radical reaction mechanism is shown. Oxygen reacts with the methylene carbon on the ester bond creating radical intermediates that react with hydroxyl end groups or peroxide radicals to create chains
25
with vinyl end groups and chains with carboxyl end groups. The formation of vinyl end groups ultimately leads to production of acetaldehyde.
O2
+ R
Figure 2-9: Schematic of thermal-oxidative degradation of PET [42]
Jabarin et al. [42] studied the kinetics of thermal and thermal-oxidative degradation of PET at melting conditions using samples dried in air or in vacuum. It was found that at the same temperature and time conditions, there is significantly more degradation in samples melted in air than in nitrogen environment. The amount of degradation is larger at melting conditions when samples were dried in air compared to
26
vacuum. This is attributed to the formation of peroxides during drying process and its subsequent effect at elevated temperatures during PET melting. This effect can be seen in the values of activation energy for thermal-oxidative degradation: 117 kJ/mol for samples dried in air and 159 kJ/mol for samples dried in vacuum. Zimmerman et al. [30] studied degradation PET samples with different catalyst systems using thermal analysis. The activation energy obtained was 86 kJ/mol for melting samples in air and 186 kJ/mol for melting samples in nitrogen. The general conclusion indicates that degradation is affected by the temperature, catalyst residue, or modification of the chain by byproducts or added components.
2.3 Production of petro based raw materials.
2.3.1 Petro ethylene glycol
The common process used to produce ethylene glycol starts with the oxidation of ethylene to ethylene oxide and the hydration of ethylene oxide to ethylene glycol. We will review some key information in each reaction step. Ethylene obtained through thermal pyrolysis of petroleum fractions or as a by-product of refinery catalytic cracking operations, is oxidized using air or oxygen. The difference between these processes relies on the amount of oxygen available for the oxidation in the active stream. An oxygen based process provides a higher amount of oxidant material, but its efficiency can be overcome by the economic cost of supplying it to the process [43]. Figure 2-10 shows the reactions that occur during the oxidation process at 600 K on a bed of silver catalyst.
27
Ethylene oxide, carbon dioxide, water and a negligible amount of formaldehyde are formed. Gong et al. [44] reports activation energies of 14.3 for the oxidation of ethylene to ethylene oxide and 21.4 kcal/mol for the oxidation of ethylene to carbon dioxide. The difference in these values lets us understand that as the temperature of the oxidation is increased the yield of carbon dioxide increase and the yield of ethylene oxide decreases.
An adequate temperature control over the reaction process is mandatory in order to limit the production of byproducts.
퐴푔 + 1/2 푂2
푒푡ℎ푦푙푒푛푒 표푥푦푔푒푛 푒푡ℎ푦푙푒푛푒 표푥𝑖푑푒
3 푂2 2 퐶푂2 2 퐻2푂
푐푎푟푏표푛 푑𝑖표푥𝑖푑푒 푤푎푡푒푟
푓표푟푚푎푙푑푒ℎ푦푑푒
5/2 푂 2
Figur e 2-10: Reaction scheme for the oxidation of ethylene to ethylene oxide [44]
Ethylene oxide and water follow a nucleophilic reaction, through which the ethylene oxide ring is opened with the addition of a proton to the oxygen atom and the addition of an anion to the adjacent carbon atom. Competing reactions involve the
28
production of diethylene glycol and high order glycols as the product reacts with the ethylene oxide. It is of primary concern to maintain a high ratio of water to ethylene oxide to favor the production of ethylene glycol and avoid the formation of byproducts
[43]. Matignon [45] reported the production of 82.3% ethylene glycol and 12.7% diethylene glycol when starting with a molar ratio of 1:10.5 ethylene to water and using palladium as catalyst. Figure 2-11 shows a reaction scheme used to obtain ethylene glycol and the formation of byproducts.
+
푒푡ℎ푦푙푒푛푒 표푥𝑖푑푒 푤푎푡푒푟 푒푡ℎ푦푙푒푛푒 푔푙푦푐표푙
푑𝑖푒푡ℎ푦푙푒푛푒 푔푙푦푐표푙
푡푟𝑖푒푡ℎ푦푙푒푛푒 푔푙푦푐표푙
Figure 2-11 : Reaction scheme to produce ethylene glycol from ethylene oxide [44]
2.3.2 Petro p-xylene
P-xylene is the aromatic precursor for the production of terephthalic acid. This chemical is obtained from the catalytic reforming of oil. A stream containing the
8-carbon-length aromatic is separated (primarily xylene isomers and ethylbenzene) from 29
the rest of the oil components in a fractional distillation unit. The separation into single products requires the use of separation techniques such as: fractional distillation, crystallization, membrane separation, etc. The difficulty of the separation relies on the similarity in the physical properties of the components. Table 2.1 shows the physical properties of some different aromatic compounds [46]. The first aromatic compounds
(benzene and toluene) have a significant difference in boiling point compared to the rest of the aromatic compounds. They can be obtained as an overhead condensate using fractional distillation.
The proximity of boiling points between xylene isomers and ethylbenzene requires the use of distillation columns with high numbers of plates and operation with high reflux values to increase the number of theoretical stages for separation and the number of contact points between flows to promote mass transfer. The xylene stream obtained from this process does not have enough purity to qualify as a pure product.
Table 2.1: Physical properties of aromatic compounds [46]
Compound Melting Point1 Boiling Point2 Refractive Index3 Density4 Benzene 5.5 78.8 1.523 0.873 Toluene -95.2 111.0 1.497 0.867 p-xylene 13.1 138.4 1.498 0.861 m-xylene -47.4 139.0 1.497 0.864 o-xylene -25.2 144.1 1.505 0.881 Ethylbenzene -94.9 136.2 1.496 0.867 1) °C at 760 torr 2) °C at 760 torr 3) 20 °C and wavelength: 589.3 nm 4) g cm-3 20 °C and 760 torr
30
Typically, the next step after distillation is crystallization. In this process the separation of xylene isomers is limited by the existence of ternary equilibrium points at
-65 °C (9% mol p-x, 30% mol o-x and 61% mol m-x) and the eutectic point between meta- and para-xylene at -53 °C (13% p-x, m-x 87% mole). Figure 2-12 shows the freezing point depression curves for ethylbenzene and xylene isomers. Four eutectic binary equilibrium conditions are identified along with one ternary eutectic for xylene isomers. The temperature difference between equilibrium conditions can be considered as the operating region for the crystallization process to obtain a single product in a crystal phase. These crystals must be separated by filtration and some byproduct can be carried over in the solid phase. Typically a multistage crystallization unit is used to purify the p- xylene crystals from its isomers.
Figure 2-12: Freezing point depression curves [47]
31
Berg et al. [48] reported the separation of m-xylene and p-xylene from o-xylene and ethylbenzene using dimethylformamide as an extractive agent. By adding this compound, the relative volatility changes to 1.3-1.4 making it possible to obtain a stream as a distillate with 55 weight percent p-xylene and m-xylene from an original mixture containing 25 weight percent p-xylene and m-xylene and 75 weight percent ethylbenzene, o-xylene and extractive agent. Lake et al. [49] used 2-methoxyethyl acetate to separate a mixture of equal parts by volume of o–xylene, m-xylene and p-xylene. The sample was introduced to a plate fractionating column and distillation was carried out at atmospheric pressure, obtaining a distillate at 138 °C, which was then condensed and extracted with water to separate the agent and get a substantially pure m-xylene and p-xylene mixture.
Garazi et al. [50] studied the crystallization of xylene isomers. They introduced equal parts of m-xylene, o-xylene, p-xylene, ethylbenzene and carbon tetrachloride
(CCl4) into a glass bulb submerged in a cooling bath. The temperature was kept constant for 2 hours and the liquid was analyzed using gas chromatography with a flame detector.
As the temperature of the cooling bath decreased, p-xylene crystallized alone until the binary eutectic point was reached. The addition of CCl4 creates a selective solid compound that enhances the rate of separation of p-xylene. The formed solid containing mainly xylene isomers and ethylbenzene is heated until complete dissolution is achieved, the separation of the remaining components is done using fractional distillation.
Mohameed et al. [51] studied the crystallization of p-xylene from a mixture of xylene isomers using a lab scale crystallizer. They determined that the separation of p-xylene strongly depends on the cooling profile of the mixture and the crystal size distribution that results from the formation of crystal nuclei. In U.S. Patent 2,435,792
32
McArdle [52] discussed that after removal of o-xylene via fractional distillation, the separation of p-xylene from m-xylene can be achieved with high yields by adding a volatile diluent (having a freezing point below the eutectic point of m-xylene and p- xylene) modifying the solid-liquid equilibrium and removing p-xylene from the formed crystals via filtration.
2.3.3 Petro terephthalic acid
Terephthalic acid can be obtained using different chemical pathways. Based on the similarity in the synthesis approach, all processes can be classified into three categories; these include the oxidation of p-xylene to PTA, hydrolysis of dimethyl terephthalate (DMT) and oxidation of toluene.
In the direct oxidation of p-xylene there are different technologies with specific conditions for operation. The Amoco process is described in detail in section 2.3.3.1. The
Toray process uses a liquid aldehyde as a medium and cobalt/manganese as catalyst. The reaction is done at 150 °C and 2000 kPa obtaining a high purity PTA. The Mitsubishi process is a spinoff of the Amoco process. A dual reaction system is used with a first stage operating at ~150 °C and a second stage operating at ~230 °C. The product obtained is a medium grade PTA. In all processes a separation step is required to recover the solid PTA from the oxidation liqueur. Different washing stages with water or solvents are used to separate byproducts from the acid [53].
In the hydrolysis of DMT, p-xylene is oxidized to produce p-toluic acid (an intermediate with a methyl group and a carboxylic acid). This material is esterified-
33
oxidized-esterified with methanol to produce dimethyl terephthalate. The final stage of the reaction is a two-step hydrolysis stage to produce PTA. This chemical approach was developed with different technologies by Dynamite-Nobel, Chemische and Sulzer
Chemtech [53].
In the oxidation of toluene, the aromatic compound reacts with oxygen to produce benzoic acid using cobalt acetate as catalyst. The acid reacts with KOH to produce potassium benzoate, a salt that follows a disproportionation solid phase reaction to produce dipotassium terephthalate. The final step is the reaction with sulfuric acid to produce PTA and dipotassium sulfate. A major drawback in this technology is the use of sulfuric acid, as specialized equipment is required to perform the reactions [7].
2.3.3.1 Amoco process
The most used technology worldwide was developed by Amoco Chemical Co. In general, it consists on the liquid phase oxidation of p-xylene to crude terephthalic acid
(CTA) and the subsequent upgrade step to produce the purified terephthalic acid (PTA).
Figure 2-13 shows the main intermediate products in the oxidation process. The names of the intermediates are: p-toluylaldehyde (p-TALD), p-toluic acid (TA) and 4- carboxybenzaldehyde (4-CBA).
34
PX p - TALD TA 4 - CBA PTA
Figure 2-13: Intermediate products in p-xylene oxidation
For the first stage of the process, p-xylene, glacial acetic acid, air and catalyst are fed into the reactor. Temperature is held at 175-225 °C and pressure at 15-30 atm. Air is fed in excess of stoichiometric requirements to minimize creation of byproducts. The catalyst used in the oxidation step is a combination of multivalent heavy metal, i.e. cobalt acetate and free radical provider i.e. sodium bromine. Cobalt has an important role in the oxidation of p-xylene to p-toluic acid. The total oxidation to CTA is possible by the action of bromine in the unreacted methyl group. P-xylene reaction with oxygen is highly exothermic. The heat of reaction is 2x108 J/kg p-xylene reacted [54]. This energy is removed by boiling/condensing acetic acid in the reaction vessel. The highly corrosive nature of this acid requires the use of titanium or titanium lined reactors. Conversion is usually > 98% with respect to p-xylene. The product is a slurry of CTA, water, acetic acid, byproducts and residual amounts of catalysts. The separation process uses crystallizers, surge vessels and filters to obtain a mother liquor (rich in acetic acid that is recycled to the reactor) and powder crude terephthalic acid with 4-CBA as the main impurity. Although PTA is obtained with ~99% purity, it cannot be used for the polymerization process as 4-CBA (a mono-functional reactant for esterification) is
35
present in the range of 350-400 ppm and will not allow the polymer reach the desire degree of polymerization [55].
The use of (Mn/Co/Br) catalyst is the core part of the Amoco process. The mechanism of oxidation using this catalytic system follows a radical process. Figure 2-14 shows the reaction steps in p-xylene oxidation. In the initiation step bromine ions are formed by oxidation of Co (III) or Mn (III) (1). These ions react with the methyl group in the aromatic ring creating a highly unstable radical by hydrogen atom abstraction (2).
During the propagation reaction the radicals follow oxidation with molecular oxygen, a cobalt or manganese ions and bromine radical (3, 5, 7, 9) in the expense of reducing hydroperoxides and radicals by cobalt or manganese ions (4, 6, 8, 10, 11). When the acid is formed (11) it imparts an electron-withdrawing effect on the molecule making the oxidation of the secondary methyl group more difficult. Heiba et al. [56] found that the rate of oxidation of p-toluic acid (single acid) is 26 times slower than the rate of p-xylene oxidation in a Co/acetic acid oxidation system. As with any radical reaction the termination can occur by disproportionation or combination producing the terephthalic acid and byproducts (12).
36
푀3+ + 퐵푟− → 푀2+ + 퐵푟 (1) 푎 + − 퐵푟 + 푅퐶퐻3 → 푅퐶퐻 + 퐻 + 퐵푟 (2) 푎 2 푅퐶퐻 + 푂2 → 푅퐶퐻2푂 (3) 2 푎 2 2+ 3+ − 푅퐶퐻2푂 + 푀 → 푅퐶퐻푂 + 푀 + 푂퐻 (4) 2 푎 푅퐶퐻푂 + 푀3+ → 푅퐶푂 + 푀2+ + 퐻+ (5) 푎 푅퐶퐻푂 + 퐵푟 → 푅퐶푂 + 퐵푟− + 퐻+ (6) 푎 푅퐶푂 + 푂2 → 푅퐶푂 (7) 푎 3 푅퐶푂 + 푅퐻 → 푅퐶푂3퐻 + 푅 (8) 3 푎 푅퐶푂3퐻 + 푅퐶퐻푂 → 2푅퐶푂푂퐻 (9) 푎 2+ 3+ − 푅퐶푂3퐻 + 푀 → 푅퐶푂 + 푀 + 푂퐻 (10) 푎 2 푅퐶푂 + 푅퐻 → 푅퐶푂푂퐻 + 푅 (11) 2 푎 퐼 + 퐼 → 퐼푖퐼푗 (12) 푖 푗 푎
Figure 2-14: Free radical mechanism for the oxidation of p-xylene with Co/Mn/Br catalyst system [57]
The molar ratio of Co/Mn/Br catalyst system plays a major role in the overall reaction kinetics. The interaction between them is shown on Figure 2-15. Bromine in the role of initiator acts as a promoter by performing hydrogen abstraction from hydrocarbons to produce bromide. The bromide ion is oxidized by Mn(III), obtaining the reduced Mn(II). Mn(II) is oxidized back to Mn(III) by reducing Co(III) obtaining the reduced Co(II). Co(II) is oxidized to Co(III) by reduction of peroxides to create the products. When bromine is used in the system, there is an increase in activity and selectivity due to the rapid electron transfer from cobalt to bromide [57].
At high temperatures (above 170 °C) cobalt participates in the decarboxylation of acetic acid causing a competition with the radical oxidation. Subramaniam et al. [58] studied the oxidation of p-xylene at a constant concentration of (Mn) and (Br) and increasing the concentration of cobalt (Co) from 33 mM to 66 mM. They found that the 37
yield and purity of PTA increases continuously to values ~90% for 33 mM and ~95% for
66 mM as temperature is increased from 120 to 145 °C. At higher temperatures there is no significant difference at different cobalt concentrations.
Wang et al. [59] studied the relationship of total catalyst feed in ppm to the catalyst ratio defined as [Br] / ([Co] + [Mn]) to obtain the same catalytic activity in the oxidation of 4-CBA to PTA. They found that below 0.3 there is a sharp increase in the amount of catalyst required to maintain activity. At values above 0.3 there is no difference. This behavior explains the need of bromine ions to initiate the radical reaction. Analysis of the ratio of cobalt and manganese [Co] / ([Co] + [Mn]) (in the absence of bromine) on the oxidation of p-toluic acid showed that the optimum ratio to obtain the highest rate decreases with increasing temperature. At 150 °C the ratio is ~1 and cobalt has the major role in catalytic activity. At 200 °C the ratio is ~0.3, this lower value is caused by the incremental amount of Mn needed due to its reduced activity at higher temperatures [59].
Figure 2-15: Catalyst oxidation/reduction reactions in radical process [59]
Side reactions occur during oxidation producing a set of byproducts other than the ones shown on Figure 2-13. These chemicals can co-precipitate with the terephthalic acid or remain soluble inside the oxidation liqueur. The nature and concentration of these
38
byproducts depends on the operating conditions of the process and the technology followed to do the oxidation. These impurities (4-CBA and p-toluic acid) can be mono- functional groups that limit the oxidation process or impart coloration to the acid formed.
A general relationship can be obtained by identifying the parent molecule for byproduct formation. The classification is as follows: benzoic acid derivatives, phenol derivatives, terephthalic acid derivatives, diphenyl derivatives, benzophenone derivatives, fluorenone derivatives, anthraquinone derivatives and esters [60]. The compounds that impair coloration are believed to be from the groups: biphenyl, fluorenone and anthraquinone.
Figure 2-16 shows the structure of a compound belonging to each group.
Figure 2-16: Byproducts obtained from p-xylene oxidation to PTA Left: biphenyl-4,4’- dicarboxylic acid Center: 9-oxo-9,10-dihydroanthracene-2,6-dicarboxylic acid Right: fluorine-2,6-dicarboxylic acid
Allen et al. [61] synthesized different compounds typically present in PTA to measure different properties such as: color, yellowness index, UV absorption at =340 nm and fluorescence. They correlated the results to obtain the amount of impurity required to increase the absorbance at =340 nm by 0.01 units. This wavelength was selected because chromophores (color causing products) have a transition at this value.
Table 2.2 shows some of the results obtained. For some compounds their typical
39
concentrations in TPA are reported. A lower number in the absorbance measurement indicates an increased effect on product discoloration. In agreement with the information presented before, fluorenone and anthraquinonce compounds have the lowest numbers.
The quality of the crude terephthalic acid obtained in the first stage does not satisfy the requirements for polyester production. Specifically the high concentration of
4-CBA (mono-functional group for esterification reactions) hinders the polymerization and the byproducts can impair an undesirable color to the polymer. To obtain a higher purity acid a second reaction is performed in which CTA is mixed with hot water to create a slurry with 13-18 weight percent of acid. This mixture is fed to the hydrogenation process along with hydrogen and palladium supported on carbon
(catalyst). The temperature is set at 260-290 °C and pressure at 1000 psi. In this reaction, the colored impurities are transformed into colorless products and 4-CBA is hydrogenated to p-toluic acid. The effluent is transferred to crystallizers in series that operate at a decreased pressure in each unit and finally to a centrifuge. The mother liquid obtained contains p-toluic acid and other impurities. The solids are dried and contain
PTA with ~25 ppm of 4-CBA. This concentration is acceptable for polymerization processes [62].
40
Table 2.2: Organic impurities in terephthalic acid [61]
Concentration ppm in CTA equivalent Compound name range in TA to 0.01 absorbance (ppm) increase at= 340 nm
p-Toluic acid 80–140 Benzoic acid <10 Isophthalic acid <10 4-Carboxybenzaldehyde <20 100 Fluorene-2,6-dicarboxylic acid 5–40 27 Anthracene-2,6-dicarboxylic acid 0.06–0.8 8 Trimellitic acid 20–40 10 000 4,4′-Diphenic acid 60–120 1250 Anthraquinone-2,6-dicarboxylic acid <0.5 6.3 Fluorenone-2,6-dicarboxylic acid n/d 15 Biphenylmethane-2,4′,5-tricarboxylic acid n/d 1180 Anthrone-2,6-dicarboxylic acid n/d 5.6
The efficiency of the transformation of colored compounds is measured by obtaining the b* index and the UV absorbance at 340 nm. In US Patent 4,626,598 [63]
Packer studied the hydrogenation of CTA using palladium catalyst at different temperatures and pressures. The average decrease in b* index was 1.8 units and the decrease in absorbance at 340 nm was 0.8 units. The difficulty in separating impurities from the purified products is the co-crystallization as temperature is reduced. P-toluic acid is soluble in water and maintains in the liquid phase at high temperatures. Typically a gradual cooling of the product slurry is done in different crystallizers to avoid precipitation of impurities. A secondary separation method to remove impurities is to dissolve the purified acid in a solvent, i.e. N,N-dimethylacetamide at moderate temperatures. Once the acid is dissolved the insoluble impurities are removed by
41
filtration and the liquid phase is cooled down to precipitate the purified terephthalic acid crystals. This process is repeated until desired acid purity is obtained.
2.4 Production of bio based raw materials.
2.4.1 Biomass composition
Plant biomass is a massive resource containing chemical compounds that are beneficial for existing markets. Its use on a regular basis is limited by two main factors.
The first of these is the technology implementation for biomass transformation and how it can differ from existing oil based technologies. Second, any implemented process should provide a product with an economic profile that can compete with its petro counterpart.
In the preferred scenario, industrial chemistry uses enzymology and molecular biology to overcome the transformation problems of the structural lignocellulose complex of plant cell wall (cellulose, hemicellulose and lignin) and plant material remaining after food crop harvesting, into a range of organic molecules that can be used to produce useful chemicals [64].
Lignocellulose is a structural unit in plants and represents the most abundant global polymer. Its synthesis rate is estimated at 1010-1011 tons per year. It is highly insoluble, organized into crystalline microscopic fibers mixed with other polysaccharides
(hemicellulose) and protected from enzyme attack in native woods by the physical presence of lignin. Figure 2-17 shows the structural arrangement of these components and their location in reference to the plant as a whole [65]. Cellulose is a structural
42
polysaccharide consisting of a long chain of glucose molecules connected by glycosidic bonds. The hydrogen bonds increase resistance of crystalline cellulose to degradation.
Hemicellulose is composed of various 5 and 6-carbon sugars such as arabinose, galactose, glucose, mannose and xylose. Lignin is composed of three major phenolic components: p-coumaryl alcohol (H), coniferyl alcohol (G) and sinapyl alcohol (S). The composition of these three major blocks in biomass is different for each material; therefore it is common to select the biomass depending on the type of sugar or single unit that is required for the production of a specific chemical.
Figure 2-17: Biomass structure and composition [65]
Due to the physical location of each major group in hemicellulose biomass, an effective process is required to breakdown the structures and access the single sugars.
43
The first step in such a process is called pretreatment and can be based on physical, thermal or chemical procedures. The main purpose of this stage is to break the arrangement of structural units and provide a higher contact area for chemicals to attack the crystalline structures. The effect of each pretreatment on the biomass blocks will be different depending on the method and the conditions (such as temperature, pressure, etc.) at which the process is conducted [66]. When the crystalline structure is exposed the saccarification step is responsible for breaking down the molecular array to the single sugar or sugars that it is made of. Historically acid hydrolysis with sulfuric acid provided an acceptable way for obtaining hexose and pentose using a two stage process with mild and harsh conditions [67].
Several routes are being examined to convert solid biomass to useful products. At low temperatures (e.g. 200-260 °C) diesel range alkanes can be produced by a multi-step aqueous-phase process involving dehydration, condensation and hydrogenation. At higher temperatures (~800 °C) synthesis gas is obtained from biomass by partial oxidation over catalyst. This gas can be fed to a secondary step to produce chemicals.
Another approach for chemical production is fast pyrolysis, which involves rapid heating to intermediate temperatures (~400 °C) followed by rapid cooling. Traditionally fast pyrolysis produces a thermally unstable liquid mixture called bio oils [68]. These components can be put in contact with a catalyst such as zeolite to convert oxygenated compounds (generated in the pyrolysis process) into aromatics, carbon monoxide, carbon dioxide, water and coke [69]. Comprehensive review articles on the transformation of biomass to chemicals have been published by different researchers [70-74].
44
2.4.2 Ethylene glycol
There are two main technologies implemented at an industrial scale to produce bio EG. The sources are bio ethanol or sorbitol. Many other technologies are being developed, but most of them are chemical pathways proven at a lab scale with no implementation for commercial production. In general, the line of work is to look for a one-step transformation of glucose to EG via hydrolysis-carbon cleavage-hydrogenation on a metal catalyst cluster. Section 2.4.2.1-2 discuss the existing commercial available technologies used to produce bio EG.
2.4.2.1 Production from bio ethanol
Ethylene glycol can be produced from dehydration of ethanol. This alcohol is obtained from the fermentation of sugars obtained from biomass. This is an ancient process in which sugar is put in contact with yeast to proceed with the fermentation. The principal yeast used in fermentation is Saccharomyces Cerevisiae. It can metabolize sugars such as glucose either to carbon dioxide and water given an adequate oxygen supply or generate large amounts of ethanol [75]. The first step in the fermentation process is the aerobic stage, where glucose is converted to pyruvate through the Embden-
Meyerhof-Parnas pathway (glycolysis). The second step is the anaerobic transformation of pyruvate to acetaldehyde and then ethanol [76].
One approach for the dehydration of bio ethanol is to mix the alcohol and sulfuric acid at a ratio of 1:2 and heat it to approximately 160 °C. The acid acts as a dehydrating
45
agent and removes a water molecule from the alcohol. This lost molecule allows the formation of the double bond to finally obtain bio ethylene. Figure 2-18 shows the reaction scheme for production of ethylene [77]. Once the bio ethylene is obtained the transformation into bio ethylene glycol follows the traditional oxidation-hydration process (Section 2.3.1). India Glycols is currently producing 440 million/lb of EG per year using Brazilian ethanol obtained from sugar cane. Its product is supplied to Coca-
Cola Company for their Plant Bottle business [78].
퐶표푛푐 . 퐻2푆푂4: 160 °퐶 + (−퐻2푂) 푒푡ℎ푎푛표푙 푒푡ℎ푦푙푒푛푒 푤푎푡푒푟
Figure 2-18: Reaction scheme to produce ethylene from ethanol [77]
2.4.2.2 Production from sorbitol
Glucose obtained from biomass is hydrogenated over a metal catalyst to produce sorbitol. This product is reacted with hydrogen over the metal catalyst at high temperatures and pressures to crack the molecule into three components: propylene glycol, ethylene glycol and 2,3 butanediol. Global Biochem uses this technology to obtain a combined production of 200,000 tons/year [79]. Zhang et al. [80] produced multiple samples of bio EG with different concentrations of 1,2-propylene glycol, 1,2- butanediol, 1-2, pentanediol and 1,2-hexanediol from glucose using a Ru:Ni catalyst.
These materials were used with petro based PTA to produce PET by melt phase polymerization. At concentration of 1,2-diols below 5% in the glycol, the molecular
46
weight, mechanical and thermal properties of the polymer produced were very similar to a control petro based PET. Above 5% there was a decrease of 2% in the tensile strength and flexural modulus. Analysis of the condensate show the presence of aldehydes and hemiacetals. It was concluded that the 1,2-diols does not readily incorporate into the chain and undergo degradation to these compounds.
2.4.3 Terephthalic acid
Currently, there are different reported chemical routes for obtaining terephthalic acid from biomass. Some of them are already implemented at industrial operations and others are demonstrated at a lab scale. In some cases the partner molecule p-xylene is obtained. It is assumed that upon separation it will follow the typical oxidation process to produce PTA. The following review discusses the core part of each process, its implementation and the type of products obtained.
2.4.3.1 Production from oxygenated intermediates
Thermochemical transformation of biomass uses heat and catalyst to transform plant components into chemicals. Among the different processes, catalytic fast pyrolysis
(CFP) has been studied by groups of researches for the production of BTEX starting with a biomass source. CFP is carried out in the absence of oxygen using high heating rates and temperatures around 500-600 °C. The effluent is rapidly cooled to obtain char, non- condensable gases and a condensable liquid called bio oil. The yield and composition of
47
this oil depends on many factors (starting biomass, temperature, residence time, etc), it contains the degradation products of cellulose and hemicellulose and water-insoluble lignin. It is not the purpose of this review to elucidate the pyrolysis of biomass, but to mention general characteristic and key products that have been obtained by other researchers.
Huber et al. [81] studied biomass pyrolysis in the presence of zeolite ZSM-5 as catalyst to upgrade bio oil and produce diesel fuel, heating oil and renewable chemicals such as BTEX. In a fluidized bed reactor, CFP was performed using wood chips as the starting material and activated ZSM-5 as the catalyst. The cellulose and hemicellulose part forms anhydrosugars which after dehydration produces furanic compounds such as, furan (F), 2-methyl furan (2MF), furfural (Fr), etc. These enter the zeolite pores and undergo transformation by several reactions, such as, decarbonylation, dehydration, oligomerization and decarboxylation producing aromatics, coke, olefins, water and gases.
At 600 °C, the carbon yield for aromatics is 17%, olefins 6%, coke 38% and gases 23%.
Selectivity for p-xylene in the aromatic group is 15%. It was previously discussed that temperature has an effect in the selectivity of aromatics. The higher it is the more benzene and toluene are produced. Also, as temperature rises the formation of coke in the system is reduced, while aromatic and olefin formation is favored.
Huber et al. [82] analyzed the effect in aromatic production by reacting furanic compounds and olefins via CFP in a fixed bed reactor. The effluent of the system is condensed in cool traps and analyzed using gas chromatography mass spectrometer
(GCMS). Furanic compounds enter the reactor via syringe pump, olefins are fed as carrier gas and ZSM-5 is placed inside the reactor in a quartz wool support. Temperature
48
is set at 600 °C, residence time is 3.5 seconds and partial pressure of reactant is 5 torr in average. Without feeding olefin to the system, selectivity to aromatics is 47.3% and selectivity to xylenes is 9.2%. The addition of 2% propylene in the carrier gas increased the values from 47.3% to 59.6% and 9.2% to 26.9%. The second most abundant product in the effluent stream is olefins, primarily ethylene. Anellotech Inc. produces BTEX and other chemicals by processing biomass in a pyrolysis unit and upgrading the effluent using a zeolite catalyst. The company operates under an exclusive license from the
University of Massachusetts for the core Catalytic Fast Pyrolysis (CFP) process technology developed in Dr. George Huber laboratory [83].
The product obtained in all the processes discussed is a mixture that contains aromatics, olefins, furans, coke, CO, CO2 and water. An initial approach to separate the components is to use stage condensation on the effluent obtained from CFP. A stream of aromatics could be obtained this way and its subsequent separation is required to obtain p-xylene as a product. This separation from aromatics is similar to the process described in section 2.3.2.
2.4.3.2 Production from 5-hydroxymethylfurfural (HMF)
In the process of transforming sugars to fuels, added value chemical intermediates are obtained. Such is the case of 5-hydroxymethylfurfural (HMF), a compound that can be obtained as a degradation product from the catalytic hydrolysis of sugars. HMF is a versatile platform chemical for the production of a broad range of products and fuels currently produced from petroleum. It is therefore desirable to be able to use cellulose
49
feedstock directly as a source of glucose to produce HMF. Zhang et al. [84] converted carbohydrates to HMF and other products by using ionic liquids and a catalyst comprising a preselected ratio of two metal halides. Dumesic et al. [85] produced HMF using a biphasic reactor containing a reactive aqueous phase and an organic extracting phase. Binder et al. [86] reported the transformation of a carbohydrate to a furan element in a polar aprotic solvent in the presence of chloride, bromide or iodide salt or a mixture of both. Once HMF is produced and isolated it can be transformed to the methylated furan: 2,5 dimethylfuran (DMF). Binder et al. [86] reported the synthesis of DMF from
HMF through hydrogenolysis. HMF is placed in a Parr reactor with Cu:Ru/carbon catalyst. The reactor is purged and pressurized with H2 to 7 bar, the temperature is raised to 220 °C and reaction is left to proceed for 10 hours. The conversion of HMF to DMF is reported at 69%. Figure 2-19 shows the reaction scheme for production of DMF.
퐻2,퐶푢:푅푢/퐶
220 °퐶, 100 푝푠𝑖
5 − ℎ푦푑푟표푥푦푚푒푡ℎ푦푙푓푢푟푓푢푟푎푙 2,5 − 푑𝑖푚푒푡ℎ푦푙푓푢푟푎푛
Figure 2-19: HMF hydrogenolysis to DMF over Cu:Ru catalyst bed [86]
Brandvolt et al. [87] reported the catalyzed cycloaddition of ethylene to DMF producing p-xylene. The mechanism followed is the cycloaddition of ethylene to the furan ring of DMF, followed by ring opening of the intermediate derivative with the
50
elimination of water to generate p-xylene. Figure 2-20 shows the reaction scheme for production of p-xylene and hexanedione. The reaction used acid activated carbon as catalyst, a temperature of 150 °C, pressure at 500 psig and reaction time of 5 hours.
Conversion to p-xylene is reported at 24%. It is discussed that water leads to hydrolysis of DMF producing the main byproduct: 2,5 hexanedione. This reaction limits the production of p-xylene. Williams et al. [88] used similar operating conditions to react p- xylene and ethylene using H-Y zeolite Si/Al=30 as catalyst and n-heptane as solvent in the reaction media. Brønsted sites catalyze the dehydration of intermediate products to p- xylene, making the cycloaddition rate determining. The solvent aids in minimizing the hydrolysis of dimethylfuran. Conversion of 98% for DMF is reported with 78% selectivity for p-xylene.
−퐻2푂 +
2,5 − 푑 𝑖푚푒푡ℎ푦푙푓푢푟푎푛 푒푡ℎ푦푙푒푛푒 1,4 푑𝑖푚푒푡ℎ푦푙 표푥푎푏𝑖푐푦푐푙표 ℎ푒푝푡푒푛푒 푝 − 푥푦푙푒푛푒
푤푎푡푒푟 2,5 ℎ푒푥푎푛푒푑𝑖표푛푒
Figure 2-20: Reaction scheme for production of p-xylene and hexanedione [88]
Virent Inc. produces bio p-xylene using a proprietary BioForming process.
Biomass is pretreated to obtain the C5 and C6 sugar. These molecules are transformed via hydrogenation or hydrogenolysis into polyhydric alcohols or short chain oxygenated
51
compounds. Aqueous phase reforming (APR), using a proprietary catalyst (Ru:Pt:Re), transforms the product into hydrogen, carbon dioxide, alcohols, ketones, aldehydes, byproduct alkanes, organic acids and furans. The upgrade of this mixture is done with a zeolite catalyst (ZSM-5) to promote reactions including but not limited to: dehydration of oxygenates, oligomerization of alkenes, cyclization and dehydrogenation to form aromatics and alkane isomerization. The final product contains aromatics (p-xylene), alkenes, alkanes and a minute concentration of oxygenates and hydrocarbons. A separation step involving distillation, centrifugation and crystallization is required to obtain p-xylene. The purity of the material depends on the success of the separation. It is important to mention that the feed of reactants can be selected to avoid formation of xylene isomers other than p-xylene [89].
2.4.3.3 Production from limonene
Terpenes are a specific type of hydrocarbons naturally occurring in plants and animals. They have a strong smell and are the main constituent of essential oils. Its structure is typically considered to be a number of isoprene units ordered in a regular pattern. SABIC Innovative Plastics published in US Patent 2010/0168371 the formation of PTA from -limonene. Figure 2-21 shows the chemical pathway of the transformation.
The terpene molecule is dehydrogenated with a metal (FeCl3) or amine (ethylenediamine) catalyst to produce p-cymene. This intermediate is oxidized in a two-step process, with the first step including mineral acid and the second one using a strong oxidizer, such as
KMnO4. There is no reported information on byproducts obtained from the reaction. This
52
process does not produce p-xylene as an intermediate to get the acid. In one example, bio
PTA is produced from limonene obtaining an overall yield of 85% and a molar relationship of one, this is, 1 mole of PTA produced for 1 mole of limonene consumed
[90].
푁퐻2퐶퐻2퐶퐻2푁퐻2 1) 퐻푁푂3, 푤푎푡푒푟 , ∆
퐹푒퐶푙3 + 푁푎 2) 퐾푀푛푂4, 푁푎푂퐻, 푤푎푡푒푟, ∆
훼 − 푙𝑖푚표푛푒푛푒 푝 − 푐푦푚푒푛푒 푃푇퐴
Figure 2-21: Schematic of -limonene transformation to PTA [90]
2.4.3.4 Production from isobutanol
Bio isobutanol is an alcohol that can be obtained from the fermentation of biomass using microorganisms through a process similar to sugar fermentation to produce ethanol. Gevo, Inc. developed a technology to produce bio p-xylene from isobutanol obtained from biomass. Figure 2-22 shows the chemical pathway of the reaction. Biomass pretreated to obtain monosaccharide units is fermented with a microorganism to produce isobutanol in an aqueous fermentation broth. The alcohol is dehydrated to isobutylene using a homogeneous catalyst such as: sulfuric acid, hydrogen fluoride, phosphoric acid and metal oxides. The product follows dimerization to diisobutylene using a catalyst such as: sulfonic acid, zeolites and phosphoric acid. The double molecule follows dehydrocyclization in the presence of a catalyst to produce
53
xylenes, unreacted C4 alkanes, 2,5-dimethylhexenes and 2,4,4-trimethylpentene. The separation of the effluent requires distillation to obtain p-xylene. In on example, for 100 kg of isobutanol fed to the system, ~18 kg of p-xylene and ~0.9 kg of xylene isomers were obtained [91].
푂2 푚푒푡푎푙 퐻2
𝑖푠표푏푢푡푎푛표푙 𝑖푠표푏푢푡푦푟푎푙푑푒ℎ푦푑푒 푑𝑖𝑖푠표푏푢푡푦푙푒푛푒 푝 − 푥푦푙푒푛푒
Figure 2-22: Schematic of isobutanol transformation to p-xylene [91]
2.4.3.5 Production from muconic acid
Muconic acid can be obtained from biomass via microbial synthesis. The carbohydrates (glucose) are transformed to a mixture of cis-, trans-, cis-trans-, trans-cis- muconic acid isomers using genetically modified bacteria. Isomerization to create trans- isomers of muconic acid is done using a metal catalyst. The trans- isomer precipitates from the solution upon cooling to room temperature obtaining ~90% yield. This isomer reacts with ethylene at 150 °C using a Lewis acid as catalyst to produce cyclohexa-2,5- diene-1,4-dicarboxylate as an intermediate through a Diels-Alder reaction. This cyclic compound follows hydrogenation with a metal catalyst to produce the terephthalic acid molecule [92]. Figure 2-23 shows the schematic pathway to obtain PTA from muconic acid. Amyris, Inc. and Michigan State University developed the technology for the transformation of muconic acid to PTA. The upscale of the process requires 3-5 days of
54
reaction time from glucose to PTA to obtain a yield of less than 50% [93]. In this process the tailoring of the enzyme for the transformation of glucose is key to minimize the production of unwanted isomers that may impose a restriction in the implementation at large scale.
∆ 푂2 +
푚푢푐표푛𝑖푐 푎푐𝑖푑 푒푡ℎ푦푙푒푛푒 푃푇퐴
Figure 2-23: Schematic of muconic acid transformation to PTA [93]
2.4.3.6 Production from ethylene
Bio ethylene is currently produced at an industrial scale by dehydration of bio ethanol over a silica-alumina catalyst. High conversions (up to ~99%) and high selectivity to ethanol up to (~95%) have been reported [94]. India Glycols Ltd and
Braskem are the major producers worldwide, with a combined installed capacity of 375 kTons/year [94]. Brookhart et.al [95] developed a method to transform ethylene into p- xylene. The ethylene molecule can be transformed to hexane using a known commercial process of catalytic trimerization. Hexene follows catalytic disproportionation via transfer dehydrogenation to produce hexadiene and hexane. Hexadiene and ethylene react via
Diels-Alder to produce 3,6-dimethylcyclohexene. This molecule is dehydrogenated using platinum as catalyst to produce p-xylene, ethylbenzene, and cyclic intermediates that can be transformed into aromatics in a secondary dehydrogenation step. Figure 2-24 shows
55
the schematic pathway to obtain p-xylene from ethylene. The products obtained are aromatic in nature; their separation can be done by fractional distillation. The equilibrium between p-xylene and ethylbenzene is the only thermodynamic limitation to consider for the separation. With the use of this technology and the existing transformation of ethylene to EG it would be possible to obtain both raw materials for PET from the same source.
푐푎푡푎푙푦푠푡
+
퐷𝑖푒푙푠 퐴푙푑푒푟
푒푡ℎ푦푙푒푛푒 푡푟𝑖푚푒푟𝑖푧푎푡𝑖표푛
퐷푒ℎ푦푑푟표푔푒푛푎푡𝑖표푛
2퐻2 ∆
Figure 2-24: Schematic of ethylene transformation to p-xylene [95]
2.4.3.7 Production from 2,5 furan dicarboxylic acid (FDCA)
FDCA can be produced as an oxidation product of 5-HMF. FDCA was recognized by the Department of Energy, USA. as a key bio derived platform chemical to produce ester and chlorides. The oxidation reaction has been analyzed using different
56
catalyst systems such as: Pt/C, Co/Mn/Br, KMnO4, Au/TiO2 and Pt/Al2O3, obtaining yields to FDCA that vary between 35-99% [96]. A Diels-Alder reaction between FDCA and ethylene, using a metal catalyst, produces a bicyclic ether molecule that upon dehydration (using an acid catalyst) produces PTA. The drawback in this approach is the low yields obtained (below ~20%). Figure 2-25 shows the schematic pathway to produce
PTA from FDCA.
푂 2
퐻푀퐹 퐹퐷퐶퐴
Figure 2-25: Schematic of HMF transformation to FDCA
2.4.3.7.1 Polyethylene furanoate (PEF)
An alternative use for FDCA is to use it as a monomer for the production of polyester. The chemical similarity with PTA (two carboxylic acids) makes it a viable option to produce a polymer following a traditional step-growth polymerization technique. Figure 2-26 shows the schematic approach to produce a polyester with FDCA and EG. Avantium produced polyethylene furanoate (PEF) using FDCA and EG in a high-throughput film reactor. Esterification was done in a single process at three different holding temperatures: 160 °C for one hour, 170 °C for 1 hour and 180 °C for 2 hours.
Titanium isopropoxide was added as catalyst, vacuum was gradually applied and
57
temperature increased to 230 °C. After two hours vacuum was stopped and nitrogen was introduced to avoid oxidative degradation. The product obtained had a Tg ~86 °C, a peak crystallization temperature of 160 °C and a melting point of ~211 °C. The polydispersity index measured by GPC was 2.63 [96]. These thermal properties differ substantially to values obtained for pure PET or PET copolymer with DEG and IPA.
Sbirrazzuoli et al. [97] analyzed the isothermal crystallization behavior of PEF samples using a DSC technique. The samples used were synthesized with a different catalyst system including: Ti(OPr)4, Sb2O3 and Ca(Ac)2. The Avrami exponent at temperatures between 140-190 °C varied from 3 to 4. The crystallization half time had its minimum value at ~165 °C. The equilibrium melting point was calculated as 247 °C 푐푎푡푎푙푦푠푡 + using Hoffman-Weeks technique. The glass transition temperature, determined in the
퐷
𝑖
푛
second heating step of the DSC was 70푒 °C. Further testing is required to determine if PEF
표
푙 푒
𝑖 푠
푡
푛
푒 푎 퐴
푙 푧
푙
𝑖 푦 푑
푟
is a viable material to be use in the packaging industry or in a copolymer formed with ℎ 푒
푒 푡 푟
푒 푚
𝑖
푟
푡
PET.
퐷푒ℎ푦푑푟표푔푒푛푎푡𝑖표푛
+ + 2퐻2 ∆
FDCA EG PEF
Figure 2-26: Schematic of FDCA and EG transformation to PEF
58
2.4.3.8 Production from lignin
Lignin molecules are a random polymer network with different type and concentrations of bonds. Lignin is typically separated and not processed in transformation methods of lignocellulosic biomass (it is often used to generate energy by combustion). It is a hydrophobic material with high resistance to biological or chemical degradation by nature. Biochemtex S.P.A. (part of M&G Company) developed a process to transform lignin into BTX components. Lignin is pretreated by soaking it in water followed by a steam-explosion process. The slurry containing the partially depolymerized lignin enters a bubble column reactor along with hydrogen and an elemental metal catalyst.
Deoxygenation takes place producing BTX among a variety of aromatics. Separation of p-xylene from the mixture is done by filtration, distillation and crystallization [98].
59
Chapter 3
Experimental
3.1 Materials
The materials used in this research are given below including: provider, name of the product and any special characteristic or grade. Table 3.1 shows the names of all chemicals and their use in this research.
Industrial Partner: 1) Bio BTEX obtained from thermochemical transformation of biomass. 2) Diluted bio p-xylene obtained from liquid phase transformation of biomass.
3) Bio ethylene glycol obtained from transformation of bio ethanol. The three products were donated to the Polymer Institute by members of the PET Industrial Consortium.
Dak Americas: 1) Purified terephthalic acid (PTA) % >99.8.
Mays Chemical Company: 1) Ethylene glycol polyester grade product (EG).
Airgas: 1) Oxygen UHP 99.99%. 2) Hydrogen 2% Nitrogen 98%. 3) Nitrogen industrial grade.
Fisher Scientific: 1) Antimony oxide 99.6%. 2) Cobalt acetate tetrahydrate 98+%. 3)
Triethylamine ≥ 99%. 3) Glacial acetic acid 99%. 4) Sodium bromide. 5) 10% Platinum on activated carbon. 6) N,N-dimethylacetamide. 7) Ethanol 99%. 8) p-xylene 99.99%. 9)
60
Methanol ACS grade. 10) Acetonitrile ACS grade. 12) Formic acid LCMS grade.
13) Manganese acetate tetrahydrate 99.99%. 14) Benzyl alcohol +98%. 15) Chloroform
ACS 99.8%. 16) Phenol red indicator. 17) 2-butanol 99.9%. 18) Benzoic acid +99.5%.
19) Sodium hydroxide 98%. 20) Ammonium hydroxide Certified ACS 14N. 21)
Phosphoric acid. 22) Triethylamine. 23) p-toluic acid. 24) 4-carboxybenzaldehyde. 25)
2,5 dimethylfuran.
Restek: 1) BTEX Standard 2000 ug/ml, Lot No. A089584.
Accustandard Inc.: 1) Acetaldehyde 1 mg/ml in water, Lot No. A8070315.
61
Table 3.1: List of chemicals used during the research and their roles in the experiments or laboratory analysis Name Use as Bio BTEX Raw material Diluted bio p-xylene Raw material Bio ethylene glycol Raw material Purified terephthalic acid Monomer for polymerization Ethylene glycol Monomer for polymerization Oxygen Reactant for oxidation Hydrogen 2% Nitrogen 98% Reactant for hydrogenation Nitrogen Inert gas for different reactions Glacial acetic acid Solvent for oxidation reaction Sodium bromide Catalyst for oxidation Manganese acetate Catalyst for oxidation Cobalt acetate Catalyst for polymerization and for oxidation Phosphoric acid Metal stabilizer for polymerization Triethylamine DEG suppressor for polymerization Antimony oxide Catalyst for polymerization 10% Pd on carbon Catalyst for hydrogenation N,N-dimethylacetamide Solvent to dissolve crude terephthalic acid p-xylene Solvent to dissolve purified terephthalic acid Ethanol Solvent for cooling bath Methanol Solvent for liquid chromatography Acetonitrile Solvent for liquid chromatography Formic acid Solvent for liquid chromatography Benzyl alcohol Solvent for titration Chloroform Solvent for titration Phenol red Indicator for titration 2-butanol Solvent for titration Benzoic acid Solvent for titration Sodium hydroxide Solvent for titration Ammonium hydroxide Solvent for UV spectroscopy p-toluic acid Standard for LCMS quantification 4-carboxybenzaldehyde Standard for LCMS quantification Purified terephthalic acid Standard for LCMS quantification 2,5 dimethylfuran Reference for GC identification Restek BTEX standard Standard for GC quantification Acetaldehyde standard Standard for AA quantification
62
3.2 Analytical Techniques
3.2.1 Gas chromatography with flame ionization detector (GC-FID)
Gas chromatography is a method of separation where the components to be separated are distributed between two phases; one is the stationary phase and the other is a mobile phase that passes through the former. Pressure gradients across the column are used to cause movement of the mobile phase. The information obtained is recorded on a chromatogram as a mass profile of the samples as a function of the movement of the mobile phase. Peak location and intensity allow qualitative and quantitative identification of certain components and the understanding of sample complexity [99].
The raw materials, intermediates and products obtained from specific experiments were analyzed and quantified using a gas chromatographer Shimadzu GC2010 equipped with a flame ionization detector. In all analysis helium was used as carrier gas and a mixture of air and hydrogen was used for the ignition of the flame. The GC column used for all analysis was Restek RTX-Wax 60 meter long, 0.25 mm ID, and 0.25 m of polyethylene glycol packing, a useful phase for the separation of a wide range of polar and hydrogen bonding solutes [100]. The installation and conditioning of the column was done according to guidelines provided by Restek [101].
The method used for all analysis was adapted from ASTM D6563 Standard test method for benzene, toluene, xylene (BTX) analysis by gas chromatography and is included here as reference [102]. Split ratio 200:1, make-up flow rate: 30 ml/min, injector temperature: 250 °C, detector temperature 300 °C, column program: 70 °C hold for 10
63
min, 5 °C/min to 200 °C hold for 24 min. Quantification and identification were done based on standards or calibration curves run with the same procedure. Detailed information is available in Appendix A.1-2.
Before injection all samples were diluted to 10% volume using LCMS grade methanol. To avoid carriage of suspended solids, a syringe filter luer/slip Phener-RC
4mm from Phenomenex was used for each draw. The vials with the diluted sample were homogenized by agitation at 3000 rpm using a vortex mixer. The syringe used for injection (5L SGE Analytical sample injector) was washed three times with fresh methanol before drawing the liquid from the vials, then it was filled with 1 L of sample followed by 0.5 L of air and the contents were immediately injected in the GC. Since the injection had to be done manually, extra care was taken to draw the volumes as precisely as possible.
The fitting of peak areas was done using the GC Post run program available through GC Solutions software. The system was set to do Gaussian peak fitting using the following parameters: width – 3 seconds, slope – 486.191, drift – 0 uV/min and minimum area/height – 1000 counts, also Baseline correction was activated. The area units obtained from the integration of each peak were taken as they were reported by the software.
3.2.2 Gas chromatography mass spectroscopy (GC-MS)
Mass spectrometry is used to identify components from their mass spectra. Each compound has a unique or nearly unique mass spectrum that can be compared with mass spectral databases and thus be identified. Through the use of standards, quantitation is
64
also possible. A mass spectrometer measures the mass to charge ratio (m/z) of gas phase ions [103]. In a typical sample analysis using a GCMS, the gas sample eluting from the
GC is ionized using Electron Ionization (EI) and the formed ions flow through the mass analyzer. The quadrupole mass analyzer uses oscillating electrical fields to selectively stabilize the paths of ions with a particular m/z passing through a radio frequency quadrupole field created between four metal rods. A quadrupole mass analyzer acts as a mass-selective filter. The ions finally reach the electron multiplier detector where they strike the semiconductor coating releasing electrons. The current from these electrons is amplified and processed by the system to create the chromatogram [104].
The raw materials and some intermediates were qualitatively analyzed using a
Bruker 320 GC Quadrupole Mass Spectrometer. All samples were filtered, diluted and homogenized as reported in Section 3.2.1. Samples were injected using an autosampler installed on the top of the GC. Before injection the syringe was rinsed 2 times with methanol, and then the sample was drawn and returned to the vial 5 times before taking the sample for analysis. Once the 1 L of sample was in the syringe, 0.5 L of air was introduced and the contents were injected into the GC. In all analysis helium was used as the carrier gas. The column used was Agilent DB-5MS-Ultra Inert 30 meter, 0.25 mm ID,
0.25 m. This column is capable of separating a long range of analytes; it has low bleed and high inertness performance. The program used for the analysis was: split ratio 100:1, column flow: 1 ml/min, column program: 30 °C hold for 10 min, increase to 150 °C at 5
°C/min then to 300 °C at 20 °C/min. The injector temperature was set at 300 °C and the detector was at a fixed voltage of 1650 V. To avoid interference with low concentration compounds due to the presence of a solvent peak of big intensity, the delay in acquisition
65
of mass spectroscopy data was set at 4 minutes.
For each chromatogram the peak identification was done using information reported on the NIST database. The software does a comparison of the MSMS breakdown of the peak selected against reference information on the database. Based on the comparative data it reports a Match index that can be used along with the individual
MSMS breakdown to decide if the information matches. In this way the compound is identified. For this work all compounds identified by GCMS had a Match of at least 700.
No quantification was done using the GCMS technique, only qualitative information was obtained.
3.2.3 Reversed phase liquid chromatography mass spectroscopy
Separation of components through liquid chromatography involves a combination of adsorption and partition. Conventional chromatographic techniques employ a polar stationary phase and a non-polar mobile phase [105]. In the case of high performance liquid chromatography (HPLC), it is common to use a non-polar chemically bonded stationary phase with an aqueous mobile phase containing different proportions of a miscible organic modifier. This method known as reversed phase chromatography is most often used in HPLC for the separation of both polar and non-polar organic molecules.
The variables that control the selectivity in HPLC are: separation mode, stationary phase structure and mobile phase composition.
Commercial PTA, crude and purified terephthalic acid produced as will be discussed in Chapter 6 were analyzed using a Varian 320-MS LC/MS. The LC flow rate
66
for the instrument is controlled by a dual pump system fed from two solvent reservoirs containing HPLC grade water and acetonitrile. Formic acid is added to the water at a concentration of 0.1% volume to correct for peak tailing. A solvent gradient technique is used to change the composition of the mobile phase throughout the separation to provide an incremental change in solvent strength that gives a convenient elution time and better peak shape [105]. The solvents were degassed and maintained under inert gas during the analysis. The pump program followed during the analysis of each sample is shown on
Table 3.2. These working conditions were adapted from the ones reported by Viola et.al.
[106] for analysis of p-xylene oxidation products. In each case the solvent profile migrates from polar to non-polar. After the end of each cycle the column was conditioned for 5 minutes before the next injection.
The reversed phase LC column used in all analysis was Phenomenex Zorbax®
Eclipse-XDB-C8, fully porous silica solid support, particle size 5 µm, pore size 80 Å, length 250 mm, internal diameter 4.6 mm. This column is particularly good for analysis of small molecules [107]. The effluent of the column is ionized via Electrospray Interface
(ESI) and fed to the quadrupole mass analyzer for detection.
67
Table 3.2: Pump program used to create the solvent gradient during analysis
Time Flow % Water % Acetonitrile min L/min 0 80 20 300 2 80 20 300 12 40 60 300 20 20 80 300 23 20 80 300 25 80 20 300 30 80 20 300
Before analysis, the mass and the voltage for each of the ions was determined.
Samples were precisely weighted and diluted with methanol to obtain solutions with concentrations of 5 ppm. Each sample was then injected directly into the ionization element. The MS is set to scan ions of mass 100-200. Once the analysis finishes, the ionization parameters and detector variables are recorded. Table 3.3 shows this information. Table 3.4 shows the mass and charge of the ions identified for each compound. This information is fed to the software so specific masses can be observed when analyzing an unknown sample.
Table 3.3: Experimental conditions used for ionization and for the detector
Parameter Units Value Needle voltage positive V 5000 Needle voltage negative V -4500 Spray shield voltage V 600 Spray chamber temperature °C 50 Drying gas temperature °C 200 Nebulizing gas pressure psi 55 Drying gas pressure psi 18
68
Table 3.4: Mass ions and detection mode for specific analytes
Compound Ion Mass Ion Voltage Ion Mode p-tolualdehyde 120.7 60 Positive p-toluic acid 134.7 -64 Negative 4-carboxybenzaldehyde 148.7 -76 Negative 2,5 furandicarboxylic acid 154.6 -48 Negative Terephthalic acid 164.0 -76 Negative
For all unknown and calibration curve samples a specific amount was precisely weighted in mg and mixed with a predetermined volume of methanol. The samples were placed in a sonicator for 40 minutes to have complete dissolution and mixed for one minute in a Vortex Genie Mixer to homogenize them. Sonicated samples were set aside for 40 minutes to allow temperature equilibration. Around 300 L were taken from each solution and placed in individual glass vials for analysis.
The fitting of peak areas was done using Varian Data Analysis software. The integration parameters were set as follows: peak width - 4 seconds, slope sensitivity – 20, tangent -10%, peak size reject – 2000 counts, smoothing – none, peak threshold value – none, noise – peak to peak. Baseline correction was activated and set to 7 points. The area units obtained for each peak were taken as they were reported by the software.
3.2.4 Acetaldehyde generation
During processing of PET at melting conditions, degradation is likely to occur.
Among the different types, thermal degradation (caused by heat) causes polymer chain scission, resulting in generation of vinyl end groups and carboxyl end groups. This ultimately results in reduction of molecular weight and generation of acetaldehyde. 69
Studies of acetaldehyde generation can be used to compare thermal stability of different
PET samples.
The method used to quantify the concentration of acetaldehyde generated at a specific temperature and time was adapted from the one reported by Kim and Jabarin
[108]. In this technique a Perkin-Elmer Automatic Thermal Desorption System
(ATD400) coupled to a Perkin-Elmer Autosystem XL Gas Chromatograph was used. The gas chromatograph used a Stabilwax, 30 m, 0.32 mm I.D. column and was equipped with a flame ionization detector. The oven was maintained at a constant temperature of 60 °C, the detector was set at 300 °C and a flow of 3 ml/min of helium was used as carrier gas.
For the ATD three desorption temperatures were used 270, 280 and 290 °C for different holding times up to 40 minutes. The transfer line was set at 160 °C and the collection trap used -30 °C as the minimum temperature and 300 °C as the maximum temperature. All sample tubes were preconditioned in the ATD before analysis by heating each one to 300
°C for 30 minutes.
For a typical run PET pellets were frozen with liquid nitrogen, grounded and sieved using a 40 mesh screen. The powder sample was dried at 110 °C overnight.
Approximately 90 mg of the dried sample was placed in Teflon sample tubes; quartz wool was lightly packed in each end of the tube to avoid sample loss. These tubes were then inserted inside individual metal tube holders and placed in the ATD sample rack.
The machine loaded the tube into the heating elements and a constant purge of inert gas at the preselected temperature passed through the sample for a predetermined time.
During the generation and desorption stages, an electrically cooled trap captures the volatile acetaldehyde generated. After generation, the trap is rapidly heated to deliver the
70
captured acetaldehyde to the capillary column in the GC oven. All samples were run in duplicate, and held for various desorption times at melting temperature. Multiple data points were obtained to create a plot of acetaldehyde generation vs time for each sample.
The quantification of acetaldehyde generated was done using a calibration curve.
Detailed information is shown on Appendix B. The standard use was obtained from
Accustandards; it contains a water based solution of acetaldehyde with a concentration of
1 mg/ml. Different volumes of this standard were taken to obtain five different data points. Each sample was placed (using a micro-syringe) inside a Teflon tube packed with
Tennex: an analyte adsorbing agent. These calibration samples were placed in the ATD and heated for 10 minutes at 250 °C, the process was repeated twice. The instrument calibration factor is the slope of the linear relationship between mg of acetaldehyde and instrument response. The value obtained was 1.116E-7 mg/(uV*sec). Integration parameters were considered as follows: sampling rate – 1 pts/s, bunching factor – 1 pts, noise threshold – 1 V and area threshold – 100 V. The concentration of acetaldehyde in the sample was determined using Equation 3.1.
퐶푎푙푖푏푟푎푡푖표푛 퐹푎푐푡표푟∗퐴푟푒푎∗106 푝푝푚퐴퐴 = (eqn. 3.1) 푚푔퐴퐴
where the Calibration Factor is the slope of the calibration curve reported in
Appendix B, Area is the numerical value in V*sec obtained from GC chromatograms at different temperatures and desorption times, mgAA is the amount in milligrams of powder polymer placed on the test vial.
71
3.2.5 Residual acetaldehyde
Acetaldehyde generated during the polymer synthesis can be found as the AA remaining inside the PET pellets. Its removal during production depends on the diffusion to the surface and the conditions of the environment to promote migration to the vapor phase. The quantification of residual acetaldehyde within the produced polymer can be used as indicative of thermal degradation during polymerization. The quantification of residual acetaldehyde was done by headspace analysis. A Perkin-Elmer TurboMatrix 40
Headspace Sampler was coupled with a Perkin-Elmer AutoSystem XL Gas
Chromatograph. The GC settings used were the same as the ones reported on Section
3.2.4. PET pellets were frozen with liquid nitrogen, grounded and sieved through a 40 mesh screen. The collected powder was placed on the freezer until analysis was done.
In a typical run, approximately 30 mg of PET powder was placed in a glass vial that was immediately sealed. The vials then were placed in the sample carrousel below the auto sampler. In each run the sample was heated for 60 minutes at 150 °C (at this temperature the polymer does not melt but it promotes diffusion and volatilization of acetaldehyde trapped). After 60 minutes a needle was inserted to extract a sample of the headspace inside the vial. The volatiles collected were then injected through a transfer line to the column of the GC for analysis.
The quantification of residual acetaldehyde was done in a similar manner as acetaldehyde generation. Different volumes of a standard sample were transferred to independent vials. Each vial was then heated for 15 minutes to 150 °C, the process was repeated twice. The instrument response factor was determined by the slope of the linear
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relationship between mg of acetaldehyde and instrument response. The value obtained was 1376 volts*sec/gramsAA. Finally, the concentration of residual acetaldehyde in
PET samples was calculated using Equation 3.1.
3.2.6 Color determination
Each color has its own distinct appearance, based on three elements: hue, chroma and lightness. To describe these elements, the International Commission on Illumination
(CIE) proposed a three coordinate system to locate a color in space using indices L*, a* and b*. This CIELAB technique is a color scale in which values L*, a* and b* are plotted using Cartesian coordinate system and it is based on opposite color principles. Value L* represents lightness; value a* represents the red/green axis; and value b* represents the yellow/blue axis. The scales a* and b* do not have a numerical limit, L* goes from 0 for black to 100 for white. CIELAB is a popular color space to use in measuring reflective and transmissive objects. Figure 3-1 is a schematic representation of CIELAB relationship and limits [109]. Color analysis is often used as an indirect way to check for presence of impurities, the absence of colored compounds or the effect of occurring reactions such as degradation. In PET for example, thermo-oxidative degradation causes yellowness as a result of the reaction of oxygen with polymer chains. By monitoring the b* index one can have an idea if such reaction is occurring or not.
Color measurements were done using a Hunter lab Digital Color and color difference meter, a Hunter Lab Optical Sensor and a Signal Processor. The latter can be connected to either instrument to obtain readings in CIELAB indices. To check for
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accuracy in the results a calibration was done using standards provided by Hunter
Associates Laboratory following their recommended procedure. White, black and colored tiles were used for this purpose. The results obtained showed a significant difference in readings for the a* index and within acceptable error for L* and b*. It was determined to discard a* readings in all measurements.
The analysis of solid samples (CTA, PTA and PET pellets) was done using the
Hunter LAB Model D25 Color and color difference meter. Figure 3-2 shows the unit and the name of its main parts. In a typical test, a cylindrical glass vial was packed and covered with black bond paper to avoid any reflectance from its surface, then the solid sample was placed on top making sure it was evenly distributed and it covered the whole surface. The vial was then placed in the specimen port and its top surface was aligned with the base of the instrument by operating the lab jack. The viewing aperture was used to corroborate the location of the sample was the same in all measurements. After some few seconds (to allow for equilibration), the readings for L* and b* were taken from the
Signal Processor display.
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In the case of liquid samples the Hunter Lab D-25 Optical Sensor was used. Figure 3-3 shows a schematic diagram of the instrument. In a typical run, the liquid samples were placed in rectangular glass vials, this shape was important as it allowed having a flat surface on the path of the incident light. The vials were then placed in a holder where the level could be adjusted as to make sure the liquid sample covered the whole area of the 3 cm circular opening in the spherical chamber. A white plate was located on the light trap position and the sphere was pivoted 8° off light path, this way we obtained measurement of transmitted color including specular reflectance [110]. After few seconds (to allow for equilibration), the readings for L* and a* were taken from the Signal Processor display.
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3.2.7 Inductively coupled plasma mass spectrometry (ICP-MS)
ICP-MS technique is typically used for elemental determinations. The sample is typically introduced into the ICP plasma as an aerosol, either by aspirating a liquid or dissolved solid sample into a nebulizer or using a laser to directly convert solid samples into an aerosol. Once the sample aerosol is introduced into the ICP torch, it is completely desolvated and the elements in the aerosol are converted first into gaseous atoms and then ionized. The ions are introduced into the mass spectrometer where they are separated by their mass to charge ratio [111]. In polymer science it is relevant to know the concentration of residual catalyst in the polymer as it can have an effect on multiple properties such as: color, crystallization, reheat, etc. The amount of catalyst is usually monitored in pellets, preforms and bottles to verify the possible leaching of the element outside the polymer network [112].
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An ICP-MS Xseries 2 Thermo Scientific was used to quantify the concentration of antimony, cobalt and phosphorous in the precursor and polymers produced in the lab.
Approximately 100 mg of PET in powder form, 10 ml of distilled water and 10 ml of
HNO3 were added to the EasyPrep Plus vial and agitated lightly with a glass rod, before putting them in a CEM Mars microwave digester. Two different mixtures were prepared for each sample as well as, two blanks with water and nitric acid. The digestion process was carried out by heating all the samples to 210 °C for 15 minutes and holding that temperature for an additional 20 minutes, while maintaining agitation at 500 rpms by spinning the central holder plate. At the end of the digestion time the samples were allowed to cool down to room temperature, before being removed from the machine. It was important to have the samples at room temperature to avoid splash when the vials are opened due to pressure build up during the heating and agitation of the mixture. The contents of each vial were transferred to a labeled glass container. When required for use
400 L were taken from each vial and diluted with 10 ml of distilled water to make a
~200 mg/L solution. This mixture was sampled and injected into the ICP-MS.
The quantification was done by using standards from Inorganic Ventures. The first standard was ICP-MS Complete Standard-IV-ICPMS-71A-125ML, it was a mixture of 71 elements including cobalt and phosphorous, the concentration of each element in the standard was 10 g/ml. The second standard was ICP-MS-MSSB-10PPM-125ML, a standard that contains antimony only at a concentration of 10 g/ml. Results were obtained using settings recommended by the ICP-MS manufacturer for the quantification of components using area under the curve readings. Appendix C shows the raw data of samples analyzed in the ICP machine.
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3.2.8 Differential scanning calorimetry
DSC thermal analysis technique is based upon the detection of changes in the specific heat of a sample with temperature. As temperature is increased the enthalpy increases according to the specific heat at the corresponding physical state. Upon transition there is a sudden change in enthalpy as reported in heat of reaction, heat of fusion, etc. In a DSC analysis the sample container and the reference container are heated separately by independent controllers. The power to these is adjusted in response to any thermal effects in the sample as to maintain identical temperatures in both containers. The differential power required to achieve this condition is recorded against temperature and plotted in a heat flow vs temperature chart called a chromatogram.
Thermoplastic materials such as PET exhibit different transitions as they are heated from room temperature to melting conditions or when cooled from the melt. These transitions depend on multiple factors related to the polymer such as molecular weight, composition, humidity level, catalyst concentration, impurities or end group balance, and to factors related to the method itself including rate, cooling capacity, thermal or oxidative degradation and recorder sensitivity [113].
The glass transition temperature (Tg) is the value at which the material becomes brittle as glass on cooling and soft on heating. It is a kinetic phenomenon, whose value depends on the cooling rate, the thermo mechanical history and conformation of the sample and the evaluation conditions. In many cases, an enthalpy relaxation peak overlaps the glass transition. This peak if present represents physical aging of the sample.
The Tg appears as a step in the curve showing a change in the specific heat capacity from
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solid to liquid. For Tg determination, the initial point is taken on the onset of the step change and the final point is the half point of the total step change in the baseline. Above
Tg as the polymer gains energy segmental mobility occurs allowing for cooperative rotational, translational and diffusional motions until the point where polymer chains have enough energy to move into ordered arrangements giving off heat. This process called crystallization is registered as an exothermic peak on the heat flow vs temperature curve. Integration of the peak area gives the latent heat of crystallization. The peak maximum reflects the point where the rate of crystallization achieves its maximum value.
The onset and endpoint temperatures are important values that provide insight on limits where polymer can be processed [114]. If enough energy is given the previously existing and the newly formed crystals fall apart. The polymer chains come out of their arrangement and begin to move freely. This endothermic process creates a peak whose broadness depends on the amount and size of the crystals present. The peak maximum is taken as the melting point of the material and the area under the curve is the latent heat of melting.
Typically in a DSC analysis multiple heating and cooling cycles are used to characterize the thermal properties of a polymer. The first heating cycle is used to eliminate the thermal history of the material and to obtain the original crystallinity percent of the sample. The cooling from the melt can be truncated at a specific value in the crystallinity region for a certain hold time as to allow for an isothermal crystallization process. The other option often used is to quench to room temperature to maintain the polymer in the amorphous phase. The second heating and second cooling are usually run
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at a specific rate and the transitions observed are caused by the true nature of the polymer.
DSC was used to compare the crystallization behavior of different polymer samples produced in this research. The isothermal and dynamic cases were analyzed and characterized using Avrami and Ozawa equations to understand the growth and type of nucleation. The polymer samples used were frozen with liquid nitrogen, grounded and sieved through a 20 mesh screen. The powder was dried for 12 hours at 110 °C in a vacuum oven. The weights of samples used for thermal experiments were between 5 mg to 10 mg. Industrial grade nitrogen was continuously flowing through the analysis chamber during the analysis and high purity nitrogen was introduced to the reference and sample containers to have an inert environment and avoid oxidative degradation.
For dynamic crystallization the programmed method steps were:
1. Heat from 30 °C to 300 °C at 10, 15, 20, 30 or 40 °C/min.
2. Hold for 5 minutes at 300 °C.
3. Cool from 300 °C to 30 °C at 300 °C/min.
4. Hold for 5 minutes at 30 °C.
5. Heat from 30 °C to 300 °C at 10, 15, 20, 30 or 40 °C/min.
6. Hold for 5 minutes at 300 °C.
7. Cool from 300 °C to 30 °C at 10, 15, 20, 30 or 40 °C/min.
8. Hold at 30 °C for 3 minutes.
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For the second heating step; in the melting transition the peak maximum was registered as the melting temperature (Tm) and the integration of the area under the curve as melting enthalpy (ΔHm). In the crystallization transition the peak maximum was registered as (Tch) and the area under the curve as the glass crystallization enthalpy
(ΔHch). The glass transition temperature (Tg) was taken as the middle point of the step change from the baseline to the maximum of the relaxation peak or to the new baseline value. On the cooling step at a controlled rate, the peak maximum on the crystallization transition was registered as the temperature of melt crystallization (Tcc) and the area under the curve as the melt crystallization enthalpy (ΔHcc).
For isothermal crystallization the programmed method steps were:
1. Heat from 30 °C to 300 °C at 10 °C/min.
2. Hold for 5 minutes at 300 °C.
3. Cool from 300 °C to 220 °C at 300 °C/min.
4. Hold for 80 or 140 minutes at 220 °C.
5. Cool from 220 °C to 30 °C at 300 °C/min.
6. Hold for 3 minutes at 30 °C.
7. Heat from 30 °C to 300 °C at 10 °C/min.
8. Hold for 5 minutes at 300 °C.
9. Cool from 300 °C to 30 °C at 10 °C/min.
10. Hold at 30 °C for 3 minutes.
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After quenching from the melt to 220 °C, the hold time was selected to be at least
10 times the crystallization half time of the polymer at that specific temperature. The second heating step was analyzed to verify there was no exothermic peak in the crystallization transition and therefore all crystallinity was developed during the isothermal step.
3.2.9 Titration
End group determination is a key part in the characterization of any poly ethylene terephthalate sample. Carboxyl and hydroxyl are the major end groups present in PET.
Once the concentration is known an analysis of the extent of polymerization can be made and intuitively make an assessment on the possible degradation of the material during production or processing. For carboxyl, acidimetric and potentiometric titration are used, and for hydroxyl, acetylation and other methods have been used. The key parameter in reliable titration determination is to have good solubility of PET in the solvent of choice [115].
The carboxyl contents of prepolymer and PET samples were determined by following an experimental procedure based on the work by Pohl’s [116] and used in the
Polymer Institute Laboratory. For this method a normalized NaOH solution, a phenol red indicator and a neutralized benzyl alcohol blank were used. For the NaOH solution, 100 ml of distilled water were mixed with 2 grams of NaOH to make it 0.1N. The solution was rinsed into a 500 ml volumetric flask with 50 ml of methanol and diluted to the mark with benzyl alcohol. The indicator was prepared by mixing 0.05 grams of phenol red
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indicator with 33 ml of 2-butanol and drops of the NaOH solution until the coloration was dark red color. The mixture was transferred to a 50 ml volumetric flask and diluted to the mark with 2-butanol. Benzyl alcohol was mixed with potassium carbonate to make an 80/20 weight percent solution. The mixture was vacuum distilled at 102 °C, the first distillate and the residue on the beaker where discarded. Only the middle condensed distillate was kept for titration.
The NaOH solution was normalized by titration; 10 ml of a solution made by mixing 0.1 grams of benzoic acid and 60 ml of chloroform was placed in a 100 ml volumetric flask and diluted to the mark with chloroform. Four 10 ml aliquots were placed in separate vials containing a small magnetic stirrer. Two more vials were filled with fresh chloroform to serve as blanks. Two drops of phenol red indicator were added to each of the six vials. The samples were titrated with the NaOH solution under a flow of nitrogen, the color changed from yellow through orange to a purple end point. The reading of the buret for each titration was recorded. A 1 mm change in the buret position was equal to 0.01 L of NaOH solution used. The detailed information of the readings are reported on Table D.1 and D.2. The average net ml of NaOH solution spent was obtained by subtracting the volume used for titrating the blanks from the volume used for titrating the vials with benzoic acid and chloroform. Finally, the normality was calculated by using Equation 3.2. For samples produced with petro and bio EG the normality of the solution was NNaOH = 0.061, and for samples produced with petro and bio PTA the normality of the solution was NNaOH = 0.058.
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푔푟푎푚푠 표푓 푏푒푛푧표푖푐 푎푐푖푑∗81.9 푁 = (eqn. 3.2) 푁푎푂퐻 푛푒푡 휇퐿 푁푎푂퐻
where grams of benzoic acid is the amount added on the solution used for neutralization, the conversion factor with value 81.9 is the result of the inverse of benzoic acid molecular weight multiply by 1000 to make units match and net L is the volume of solution used to titrate the samples minus the volume used in the benzoic acid and chloroform.
Before analysis PET powder samples sieved through mesh #20 were dried overnight at 110 °C. Approximately 100 mg of dried PET, 5 ml of neutralized benzyl alcohol and a small magnetic stirring bar were placed in a test tube. The latter was introduced in a boiling bath of benzyl alcohol and a timer was used to record the time in seconds until complete dissolution of polymer was achieved. The vial was quenched for 5 seconds in a water bath, and then 5 ml of chloroform were added with care to avoid splashing due to thermal difference. The cooling time should be long enough to avoid chloroform splashing but not long enough to cause gelation with the addition of the chloroform. This step was crucial and should be done with care to assure repetition in results. Two drops of indicator were added to the cooled vial and it was immediately titrated with the normalized NaOH solution to a pale red end point. A magnetic stirrer plate was placed below the vial to assure continuous agitation during titration. This procedure was repeated three times for each sample. A blank containing two drops of indicator, 5 ml of chloroform and 5 ml of benzyl alcohol was titrated using a heating time of 180 seconds. The reading for the blank was subtracted from the readings obtained for the samples to obtain net L spent. During all determinations a continuous flow of
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nitrogen was introduced to avoid reaction of the hot polymer with oxygen. Because of the thermal nature of the procedure it is possible that carboxyl end groups can be generated during testing, to correct for this an experimental correction factor (Cf) based on heating time to dissolve the sample is used. Values for this factor can be found in Table D.2.
The carboxyl content is expressed as equivalents per million grams of polymer and is calculated with Equation 3.3.
푛푒푡 휇퐿 푁푎푂퐻∗푁 퐶푂푂퐻 = 푁푎푂퐻 − 퐶 (eqn. 3.3) 푤푒푖푔ℎ푡 푃퐸푇 푖푛 푔푟푎푚푠 푓
where net L NaOH is the total volume used for titration in the samples minus the volume used in the blanks, NNaOH is the normality of the solution, Cf is the conversion factor used to account for carboxyl generation during heating and weight PET is the amount of dried powder added to the vial for carboxyl determination.
3.2.10 Vinyl ester end groups determination.
During the course of transesterification and polycondensation side reactions occur causing degradation of the polymer chains and generation of side products such as: cyclic ethyl terephthalate, diethylene glycol molecule and linkages, vinyl ester end groups, acetaldehyde, etc. In particular, the exposure of PET to temperatures above the melting point can lead to thermal degradation by chain scission. This reaction generates vinyl end groups and carboxyl end groups resulting in molecular weight reduction and the formation of acetaldehyde. Buxbaum [117] reported that the primary chain scission reactions are initiated and promoted by the ester unit in polyethylene terephthalate chains.
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Once the vinyl end group is formed it has been proposed that it reacts primarily with hydroxyl end groups and in some cases with carboxyl end groups to produce acetaldehyde [118]. Studies of acetaldehyde generation and vinyl end group concentration are usually paired to understand the thermal stability of the polymer and its susceptibility to degradation.
To calculate the vinyl end groups it was assumed that all the acetaldehyde measured during the test was produced from reaction of vinyl end groups at the test temperature of 240 °C. It was also assumed that all the chain end groups are located in the amorphous phase and reaction only takes place in this region. Using these assumptions an equation can be derived to relate the concentration of vinyl end groups based on the entire volume from the reaction rate equation of vinyl end groups and hydroxyl end groups assuming a first order reaction on each reactant.
Equation 3.4 shows how to calculate the concentration of vinyl end groups.
푟푎푡푒 푉퐸 = 1 − 푓 ∗ (eqn. 3.4) 푘∗[푂퐻]
where VE is the concentration of vinyl end groups, [OH] is the concentration of hydroxyl end groups, f is the volume fraction crystallinity, rate is the rate of acetaldehyde formation based on the entire volume (Figure 7-11) and k is the reaction kinetic constant calculated at the desorption temperature (240 °C) using Arrhenius equation and reported values by Ravindranath and Mashelkar [15] and Mallon et al. [119], in which A is
9.91*107 kg/(mol*hr) and Ea is 77.4 kJ/mol. The rate of generation was obtained using the same procedure reported on Section 3.2.4. In this test a unique temperature of 240 °C
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was used for three different desorption times of 20, 30 and 40 minutes. The quantification of acetaldehyde is also done using the calibration curve reported in Appendix B.
3.2.11 Melt viscosity measurement.
Rheology is the science of the deformation and flow of materials. With its fundamental equations the relationship between stress and strain applied to a polymer can be obtained and correlated to material characteristics. A polymer melt transitions through three different behaviors as the shear rate applied is increased. On the low end, the polymer behaves as a Newtonian fluid; therefore the typically called zero-shear viscosity remains constant. At intermediate shear rate the material behaves as a pseudo-plastic, the molecules untangle and align in the shear field reducing their resistance to slippage past another. On the high end there is a minimum resistance to flow as the chains are completely untangled and aligned, this regions is called upper Newtonian [120]. When testing for viscoelastic properties it is common to develop an empirical relationship between the zero shear rate complex viscosity (measured typically at 10 rad/s) and the inherent or intrinsic viscosity (measured from solution viscosity).
The complex viscosity at different shear rates was obtained from a RDA III
Parallel Plate Dynamic Analyzer. In this instrument a polymer sample is placed between a stationary plate and a plate that turns at different angular velocities. The stationary plate has a transducer that records the response or stress of the polymer. The typical response will include an in phase and an out of phase part; these represent the elastic and the viscous components. The former is used to account for the energy stored and is
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represented by the real part of the complex viscosity. The latter is used to account for energy lost and is represented by the imaginary part of the complex viscosity. Using these two components the complex viscosity can be calculated by using Equation 3.5 [121].
휂 = 휂′ − 𝑖휂" (eqn. 3.5)
where ’ is the real (dynamic) viscosity component and ” is the imaginary viscosity component.
Homopolymer samples of different molecular weight where analyzed by solution viscosity and melt viscosity to create a calibration curve. The solvent used to dissolve the sample for solution viscosity was composed of 60% phenol and 40% tetrachloroethane.
The procedure followed was based on ASTM D5225 Standard test method for measuring solution viscosity of polymers with a differential viscometer. The melt viscosity measurements were made using a parallel plate analyzer. The conditions followed during analysis are reported in Table 3.5.
The samples (previously dried at 150 °C for 12 hours) were placed between the rheometer plates. The gap was adjusted by lowering the moving plate until it touched the polymer, at that time the heating was started, taking the sample to 270 °C and holding it at that value for 3 minutes to assure complete melting of the polymer. The chamber of the analyzer was filled with nitrogen to have inert environment and avoid oxidative degradation. The reading of complex viscosity was taken at a frequency of 1 rad/s. Table
E.1 and Figure E-1 show the individual complex viscosity and the parameters obtained
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after linear fitting was done. The PET samples produced in this research were prepared and analyzed following the same procedure as the calibration samples.
Table 3.5: Melt viscosity testing conditions
Parameter Value Temperature 270 C Motor Dynamic Test delay 120 seconds Diameter of die 25 mm Gap 1mm Strain 15% Environment Nitrogen Shear rate 10 radians/second
3.2.12 Refractive index
The refractive index is a physicochemical property of a substance. It is equal to the velocity of light of a certain wavelength in vacuum divided by its velocity in a substance. It is used to identify a particular substance, to check for the purity or to measure the concentration in a mixture.
The Bausch&Lomb ABBE-3l refractometer used in this research consists of a refracting prism system, a measuring scale, a compensation system (which permits the use of white light) and an eyepiece with crosshairs which allows the borderline of total reflection to be observed and set with accuracy. In this unit light was applied to the outside surface of the illuminating prism, and it was transmitted to the refractive prism sitting horizontally and adjacent to the illuminating prism. A pivoted mirror was used to 89
move the total reflection. The observing eyepiece is located directly above the measuring prism.
In a typical run the liquid sample was placed in the space between the prisms.
Through the eyepiece the borderline was observed and adjusted by turning a knob until there was a faint blue and a faint red in opposite sides of the borderline. The crosshairs intersection was then adjusted to coincide with the dividing line. Once alignment was achieved the refractive index was read by depressing a switch that showed the measuring scale. Up to four significant figures can be obtained for each measurement. All analysis were done at 25 °C, an external water circulating system was attached to the refractometer to maintain that temperature.
Refractive index measurements were used to quantify the amount of ethylenglycol present in an ethylene glycol and water mixture. Samples analyzed were collected as the condensate product of the esterification reaction during polymer synthesis. A calibration curve was constructed by mixing different quantities of ethylene glycol and water.
Samples were agitated in a Vortex Mixer for 20 minutes before analysis. The intercept of the line is forced to be the value of refractive index for water. The calibration curve is shown on Figure 3-4.
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1.46
1.44 y = 0.001x + 1.3305 R² = 0.99 1.42 1.40
1.38 1.36 Index Refractive 1.34
1.32 0 10 20 30 40 50 60 70 80 90 100 Ethylene glycol, % by weight in water
Figure 3-4: Refractive indices of aqueous ethylene glycol solutions at 25 °C
3.2.13 Wide angle X-ray diffraction
X-ray diffraction techniques are used to obtain information about the spacing between layers of atoms, determine the orientation of a single crystal, find the crystal structure of an unknown material or measure the size, shape and internal stress of small crystalline regions. The incident x-ray is scattered by the atoms in the lattice of sample material. The scattered waves are interfered either constructively or destructively. When waves add up constructively the Brag condition is satisfied. Bragg’s law (Equation 3.6) is the general relationship between the angle of incidence, wavelength of incident x-rays and the spacing between crystal lattice planes of atoms.
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푛 휆 = 2 푑 푠𝑖푛휃 (eqn. 3.6)
where n is the order of reflection, is the wavelength of the incident X-ray, d is the interplanar spacing of the crystal and is the angle of incidence.
When the crystalline size is small enough the diffraction peaks will be broad, but still at the respective crystalline positions. A deconvolution step is required to extract the contribution of the crystal structure to the profile of the peak. It is customary to extract the instrumentation broadening component before deconvoluting the peaks. The final size values obtained are typically called apparent size because of this required step. The
Scherrer equation (Equation 3.7) is used to determine the apparent crystal size [114].
푘 휆 퐷ℎ푘푙 = (eqn. 3.7) 훽ℎ푘푙 푐표푠휃ℎ푘푙
where Dhkl is the crystal size in a specific hkl reflection, k is a constant of value
0.9, is the wavelength of radiation, is the width of the peak at half maximum for a specific hkl reflection and is the scattering angle at a specific hkl reflection. In general the planes 100, 010 and 001 are of interest since they represent the apparent width, depth and height of the crystallites. PET main x-ray diffraction peaks and its characteristics are shown on Table 3.6 [122].
The PET crystalline samples analyzed were sieved using a mesh #40. The powder samples were placed and evenly distributed across the hollow space on the glass holder.
Another glass piece was placed on top of the holder and pressed with fingers to pack the powder. Any material outside the hollow area was removed with a razor blade. The 92
process was repeated as many times as needed until the powder filled the space and was at the same horizontal level as the holder surface.
Table 3.6: Principal x-ray diffraction peaks for PET
Plane d spacing* 2 Relative Intensity 011 5.417 16.36 Strong 010 5.014 17.69 Strong 111 4.092 21.72 Medium 110 3.880 22.92 Strong 100 3.435 25.94 Very strong 111 3.164 28.20 Weak 101 2.699 33.20 Weak * d-spacing based on Cu radiation of 1.542 angstroms
X-ray diffraction patterns were obtained using a Rigaku Ultima III X-ray diffractometer. The generator is Cu target operated at 40 KV and 44 mA, with a wavelength of 1.54059 angstroms. The scan speed was 0.5 degrees/min and the range from 7 to 39°. Once the diffraction pattern was obtained the Jade software was used for deconvolution to obtain the crystalline and amorphous peaks. Three amorphous peaks were fitted with peak maximum locations at ~16°, 26° and 33°. The peak for plane 010 was located at 17.6° and the peak for plane 100 was located at 26.1°. The peak intensity of the 001 plane was too weak to discern and it was not included in the analysis. The initial selection of amorphous and crystalline peaks was done manually; the software used this information as reference to do the automatic adjustment of peak height and width. The final selection of the fitted peaks was done when the skew value had a minimum. PET samples analyzed by X-ray were distributed in the surface of cylindrical
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glass vials and were crystallized at 220 °C in a vacuum oven for 12 hours. This is the same temperature used for isothermal crystallization analysis in DSC.
3.2.14 Thermogravimetric analysis (TGA)
TGA is a dynamic technique through which the weight loss of a sample is measured as the temperature is increased at a predefined rate or the temperature is maintained constant and weight loss is computed as time increases. In polymers, TGA is used to study thermal decomposition, stability and material response to different environments. As the product is heated and transition or decomposition reactions happen weight loss occurs and effluents can be liberated, these compounds are usually analyzed with gas chromatography or mass spectroscopy coupled to the TGA unit. The heating rate, particle size, sample amount and heating time are parameters that affect the result obtained in TGA. The different material tested should be as similar as possible in size and quantity to avoid problems with inefficient heat transfer or diffusion of volatiles [114].
The SDT Q600 TGA, from TA instruments was used for this research. The instrument had a horizontal balance and furnace, the weight loss was registered by the comparison of the reference and empty beams. The PET samples produced in this research were weighted to values between 8-11 mg and were heated from room temperature to 600 °C at a rate of 10 °C/min. Each analysis was done under helium environment to avoid oxidative degradation and get an insight of the thermal stability of the sample. The total weight loss, induction and final temperature were recorded.
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3.2.15 Fourier transformed infrared spectroscopy
Infrared spectroscopy is a useful technique to determine the presence of specific functional groups or to quantify the concentration of a compound based on the interpretation of a specific peak. The portion of the IR spectral region between 4000 and
400 cm-1 provides information about the presence of organic groups in the sample. In an
IR spectrum the percentage of IR radiation that passes through the sample versus the wavenumber is plotted. Certain functional groups present in the sample produce particular absorption bands, these bands occur at the same frequency regardless of the structure of the rest of the molecule. It is possible then to identify the presence of a specific functional groups by correlating the position of the peaks of a given spectra with a reference table of absorption frequencies from literature. Table 3.7 shows IR band assignments for some functional groups [123].
A Perkin Elmer 1600 Series Fourier transform infrared spectroscopy (FTIR) instrument was used to compare the purity of ethylene glycol samples derived from bio based or petro based sources. The instrument was run on transmission mode; two KBr plates were attached to the holder and placed on the path of the incident radiation to record the background prior to sample analysis. After removing from the holder, a small amount of liquid sample was placed between the plates using a pipette. The plates were squeeze in together and visual inspection was done to assure the liquid was distributed in the surface of the plate. The plate arrangement was installed in the holder and positioned in the instrument for analysis. Sixty four scans were performed for each sample; the instrument resolution was 4 cm-1.
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Table 3.7: Infrared absorption frequencies for some common bonds
Wavenumber (cm-1) Bond (Stretch) Functional Group 2800-3000 −퐶 − 퐻 alkanes 1600-1680 −퐶 = 퐻 alkenes 2100-2270 −퐶 ≡ 퐻 alkynes 3200-3500 −퐶 − 푂퐻 alcohols, phenols 2500-3300 푂 = 퐶 − 푂퐻 carboxylic acids 3300-3500 푁 − 퐻 amines 1500-1700 −퐶 = 퐶 − aromatics 2720 and 2820 푂 = 퐶 − 퐻 aldehydes 2220-2260 퐶 ≡ 푁 nitriles 1600-1740 퐶 = 푂 ketones
3.2.16 Ultraviolet spectroscopy
This technique is often used to measure the concentration of compounds in a solution or to determine the presence of specific functional groups in a molecule based on known absorption reference information. The absorbance of a molecule is mathematically represented by Beer’s Law (Equation 3.8). Absorbance is directly proportional to the path length, the concentration of the compound and to a constant of proportionality called absorptivity. The latter is a numerical value characteristic of each compound.
퐴 = 휀 ∗ 푏 ∗ 푐 (eqn 3.8)
where is the absorptivity of the compound, b is the path length that light travels through the sample and c is the concentration of the compound.
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The absorption of ultra violet radiation occurs via excitation of outer electrons.
When a molecule receives energy the electrons are promoted from the ground state to an excited state (higher energy level). The magnitude of the change depends on the intensity of the excitation provided. In each of the energy levels there are segmental levels existing because of rotational and vibrational movement of the atoms. In organic molecules, the excitation at UV wavelengths happens in specific functional groups called chromophores.
These groups have valence electrons of low excitation energy that can undergo different transitions such as: n→*, n→*, →*, →*. Monitoring the absorption of a sample at a specific wavelength provides insight on the presence and concentration of specific compounds.
A Shimadzu UV Spectrometer was used for analysis of crude and purified terephthalic acid. A background with pure 4 N NH4OH solvent was analyzed before each sample. The scan wavelength range was 250-400 nm at a slow speed. The light source was set to 340 nm wavelength and the slit width at 0.5 nm.
Prior to analysis, the solvent was prepared by mixing 28 ml of 14.5 N NH4OH with 25 ml of deionized water, producing a 4 N NH4OH solution. 0.3 grams of solid CTA or PTA were mixed with 5 ml of the 4 N solution and agitated for 30 minutes until complete dissolution. For analysis in the UV spectrometer, 3 ml of the dissolved acid solution were placed in the cuvette and analyzed immediately. The overall spectra was compared between samples and the absorbance reading at 340 nm wavelength was registered for use in optical density determinations.
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Chapter 4
Characterization of Raw Material
Among the different technologies reported to produce terephthalic acid and ethylene glycol, there are significant differences in their stage of implementation and material quality. Any final product or intermediate obtained through these methods is representative of its unique production pathway and it is bound to a range of specific side-products or impurities. In an effort to investigate the separation processes required to obtain high purity monomers, their use in the production of PET and the characterization of the polymers produced, we obtained three different samples of bio derived products from Industrial Partners. These Partners are members of the PET Industrial Consortium at
The University of Toledo. Figure 4-1 show the three samples as received. The details and the names used in this research to refer to the samples are the following:
1. Bio BTEX - 1 liter sample with a strong yellow coloration and to the naked eye
no evidence of solid particles.
2. Diluted bio p-xylene - 8 liters sample with a strong brown coloration and
suspended black solid particles of fine size.
3. Bio EG - 5 liters sample of colorless liquid with no evidence of solid particles to
the naked eye.
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Figure 4-1: Left - Bio BTEX, Center - Diluted bio p-xylene, Right - Bio ethylene glycol. Raw materials are shown as received
Characterization of each sample was required in order to understand the composition and attributes of the components. This information was relevant as it was expected that a separation process would need to be done to obtain the chemical of interest from the Bio BTEX and diluted bio p-xylene. To gather this information
GC-FID, GC-MS and FTIR were done on the as received samples with no further treatment. Bio based testing was done on the received ethylene glycol and on the p- xylene separated from the original sample received.
4.1 Diluted bio p-xylene
4.1.1 Analysis by gas chromatography
Due to the uncertainty of the components present in the sample and the evidence of particles, a filtration step was done prior to injection into the GC. The sample was drawn from the container using an analytical syringe until the plunger was filled, then a
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syringe filter (Phener-RC, 4mm) was installed and the filtered sample was deposited in the analysis vial. To assure that there was no remaining material in the column, between each analysis the column was baked at 200 °C for 1 hour followed by a blank injection using the same program entered for the samples. Figure 4-2 and Table 4.1 show the chromatogram obtained, the identification of some peaks and the relative sample composition obtained through area normalization.
uV(x10,000)
6.0
5.0
4.0 C 3.0 B 2.0
A 1.0
0.0
10 20 30 40 50 min Figure 4-2: GC-FID of diluted bio p-xylene sample. Zoomed view to enhance visibility of peaks with small area
Table 4.1: Peak assignation and relative percentage composition of compounds present in the diluted bio p-xylene sample
Peak Compound Area Units % Composition A 2,5 Dimethylfuran 4567 0.2 B p-xylene 409018 20.1 C Branched/linear alkanes 1621267 79.6 -- Not determined 1063 0.1
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The assignment of peaks to a specific chemical was done following the Match index reported by the software using a NIST database as reference. Three major peak areas were identified; in the first one the major peak (A) is assigned to 2,5 dimethyl furan
(DMF), in the second one the major peak (B) corresponds to p-xylene and the third one
(C) is a number of peaks with a distribution of retention times that causes baseline to increase and return to zero value after the compounds have eluted. The latter were linear and branched alkanes according to the assignment done using the reference database.
Some details of these chemicals are reported on Table 4.2. Because of the high number of carbons of these molecules their respective boiling points are above the boiling point of p-xylene (138.4 °C) and their elution times come after the latter. Other peaks can be observed in the GC-FID chromatogram. It was not possible to get an assignment with a high Match index for these materials; therefore they are reported as not determined.
Table 4.2: Characteristics of peaks assigned for linear and branched alkanes
Name Conformation # of carbons Decane, 2,5,6 trimethyl- Branched 13 Dodecane, 2,6,10 trimethyl- Branched 15 Octane, 2,2,3 trimethyl- Branched 11 Hexadecane Linear 16 1-Octadecane Linear 18
As discussed in the literature review section, aqueous phase reforming (APR) is a tunable process that can produce a wide range of products depending on the configuration with the subsequent upgrade phase. The APR effluent contains a variety of compounds including: alcohols, ketones, aldehydes, alkanes, furans and others. This effluent can 101
undergo acid condensation by using a zeolite catalyst such as ZSM-5 to promote reactions including but not limited to: alkane isomerization, aromatization, alkane oligomerization and cracking [124]. A similar approach on the upgrade by zeolite has been used on the effluent of thermo chemical transformation of biomass. In this process a mixture of furans, anhydrous and deoxygenated sugars (among other compounds) are produced by the thermal degradation of biomass building blocks. The products from this reaction can include aliphatic and aromatic hydrocarbons, light alkanes and coke [125].
The products of the routes mentioned are similar in nature to the products identified by
GC-FID in the diluted bio p-xylene sample.
4.1.2 Color measurement
As seen in Figure 4-1 there is a distinctive brown coloration on the diluted bio p- xylene sample. A visual inspection revealed suspended particles of small size and the analysis by GC revealed the presence of at least one furan compound and different hydrocarbons. Even if not all the components on the mixture were identified, to get a better understanding on the color effect the analysis of pure samples of 2,5 DMF and p-xylene were performed to have a reference for comparison. The measurements were done with the Hunter Lab D-25 Optical Sensor; the results are reported on Table
4.3. The diluted bio p-xylene had the lowest L* value among the three. This is caused mainly by the presence of particles in the sample that scatter the light decreasing the transparency of the material. The b* value was in the positive side of the range towards the yellow color. This characteristic would be expected as 2,5 DMF (one of the products
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identified) has by nature a strong yellow/brown color [126]. Its b* index is significantly higher than the reference value of pure petro p-xylene. Removal of suspended particles and the reduction of 2,5 DMF concentration was needed to obtain a bio p-xylene product that could match the characteristics of the petro p-xylene.
Table 4.3: CIELAB color indices for xylene and furan samples
Sample L* b* Diluted bio p-xylene 33.3 0.8 Petro p-xylene1 62.7 -0.2 2,5 Dimethylfuran1 45.4 2.3 1) Obtained from Fisher Scientific
4.1.3 Bio based content determination
Bio based content analysis was done by Laboratory Beta Analytic Inc following the method B reported in ASTM D6866 Standard Test Methods for Determining the Bio based Content of Solid, Liquid and Gaseous Samples Using Radiocarbon Analysis. The key part in the ASTM procedure is the measurement of 14C on the samples tested. There are three types of carbon isotopes that occur naturally: 12C (98.98%), 13C (1.11%) and 14C
(1x10-10%). The unstable 14 isotope decays over time to 14N, the estimated half-time is reported as 5,568 years [127]. Biomass contains a known amount of this isotope that is well differentiated from other materials such as fossil fuels that do not have any 14C.
Radiocarbon dating using Accelerator Mass Spectroscopy (AMS) allows for a direct
14 measurement of C in the sample. In this technique the sample is first oxidized to CO2 by combustion in air, the water and non-combustible gases are separated by the use of
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cryogenic cooling traps. The CO2 produced is reduced to elemental carbon (graphitization reaction) in a two-step process by reacting with hydrogen over a pretreated carbon free cobalt catalyst surface. This reaction is done at 550 °C to 600 °C for 10-12 hours; the produced graphite is positioned in the AMS cathode for analysis. In general AMS dating involves the acceleration of negative ions produced from bombarding graphite with cesium ions to very high kinetic energies followed by ion counting in the detector region.
Not all the ions reach the detector, but ions from all isotopes are present so it is possible to calculate the ratio of 14C over 13C [128]. The measurement efficiency is determined by analyzing standards samples of known carbon ratio. The standards used by Beta
Analytical for reference, are samples obtained from NIST National Institute of Standards and Technology, they have a known radiocarbon content equivalent to the year AD 1950.
This date is selected as it represents the time before thermo-nuclear weapon testing occurred introducing excess of radiocarbon into the atmosphere [127].
As mentioned in the previous section the diluted bio p-xylene sample contains a mixture of furans, p-xylene and branched alkanes. From this mixture p-xylene was separated to the highest purity possible in a lab scale environment utilizing different methods such as: crystallization, distillation and filtration, the detailed discussion is presented in Chapter 5. The results of bio based content of the high purity separated p-xylene are shown on Figure 4-3. It can be seen that 63% of the total carbon present in the sample analyzed comes from a bio based source. The details of the report can be found in Appendix F. It is considered that because of the high purity achieved during the separation of p-xylene and the minimal presence of carbon containing byproducts, the contribution to carbon counting of any impurities present is not significant.
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Fossil
Carbon, Bio 37% Based Carbon, 63%
Figure 4-3: Mean proportions of bio vs fossil based indicated by 14C content in bio p-xylene sample
The p-xylene molecule consists of eight carbon atoms; and the 63% result indicates that 5 out of 8 carbons in the molecule were derived from biomass. As discussed in the literature review section, different technologies produce aromatic molecules by Diels-Alder reaction, aromatization, pyrolysis, dehydration, decarboxylation among others [68-72, 81-82, 88, 95]. The compounds that react to create the aromatics have different number of carbon units ranging in average from 3-6 units.
We can consider that the bio p-xylene present in the sample was obtained by reacting an intermediate containing five or less bio derived carbons with another intermediate containing at least three petro derived carbons. This idea is in agreement with the results obtained in the GC analysis. First, a mixture of linear and branched alkanes was identified. Even if the compounds suggested by the MS software have a chain length of more than 8 units, these are the result of reactions (i.e. oligomerization) that can occur during the synthesis of bio p-xylene. Based on information reported in literature, they were produced from units with low carbon number [124]. Second, a furan compound is 105
present in the mixture at low concentrations; it was presented in Chapter 2 the formation of furanic compounds as intermediate products of biomass transformation, presumably the bio based carbon atoms in the bio p-xylene molecule come from the transformation of bio 2,5 dimethylfuran into bio p-xylene. For example, a Diels-Alder reaction catalyzed by a zeolite of bio derived 2,5 dimethylfuran with a petro derived olefin can produce an aromatic compound such as p-xylene. Chang et.al. [129] used zeolite H-BEA as catalyst in the reaction of 2,5 DMF in heptane solvent with ethylene at 250 °C, the product had a
90% selectivity to p-xylene with no production of meta or ortho isomers, 9% selectivity to alkylated compounds and 1% selectivity to oligomers.
4.2 Bio ethylene glycol
4.2.1 Color and refractive index measurement
The as received bio ethylene glycol and the petro ethylene glycol from Fisher
Scientific were used for polymerization reactions to produce PET. Both materials were analyzed and compared using ASTM E202 “Standard test methods for analysis of ethylene glycols and propylene glycols” as general guideline. There was no evident difference in the physical appearance of either material and no signs of glycol degradation. If ethylene glycol is in contact with air for prolonged time, product discoloration and oxidation to glycolic acid occurs changing the acidity of the product (a quality variable that can affect esterification reaction in polymer production) [130]. Table
4.4 shows the results obtained for color and refractive index measurement. The difference
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in L* and b* indices is within the experimental error of the measurement. Both materials have the same color. A broad test to verify the presence of side products is to obtain the refractive index. Both samples were analyzed three times obtaining a difference within experimental error. These measurements showed similarity in both products and no evident presence of impurities.
Table 4.4: CIELAB color indices for ethylene glycol samples
Sample L* b* Refractive Index1 Bio ethylene glycol 60.9 -0.5 1.4350 Petro ethylene glycol 60.1 -0.4 1.4363 1) Measured at 25 °C
4.2.2 Infrared spectroscopy
To further analyze the ethylene glycol samples and determine if side products are present, a comparison of their infrared spectra was done. Between each sample analysis a new background was recorded to assure the initial condition before each test was the correct one. Figure 4-4 shows the spectra obtained for two samples of petro ethylene glycol from two different bottles and for one sample of bio ethylene glycol. Overall there is a similarity in the location and shape of the peaks obtained for all materials except for a small peak that was observed only in bio EG is at ~1650 cm-1. According to tables reported in literature (Table 3.7) there are different bonds from specific functional groups that produce a distinctive peak at this wavenumber such as: alkenes, ketones and 107
aromatics. To confirm the interpretation for the results, the bio EG IR spectrum was analyzed using Spectrum software from Perkin Elmer. The program assigns possible functional groups to peaks obtained based on database reference information. The suggested match is the presence of a carbonyl group in an aliphatic or aromatic compound. This information is in agreement with the information shown on Table 3.7.
1653.6
A
2000 1500
1929 1900 1800 1700 1600 1500 1400 1336 cm-1
A Name Description Oil EG Polyester grade Oil EG Polyester grade Bio EG 3 Bio EG 3
Oil EG ACS grade Oil EG ACS grade Absorbance
1657.1
3992 3500 3000 2500 2000 1500 1000 -1 492 3500 3000 2500 cm-1 2000 1500 1000 cm Name Description Oil EG Polyester grade Oil EG Polyester grade Bio EG 3 Bio EG 3 Figure Oil4 EG- ACS4 :grade InfraredOil EG ACS grade radiation spectrum of glycol samples. Top line - Bio based EG. Center and bottom: Petro based EG. Magnified region (2000-1500) showing a peak only in Bio based EG
4.2.3 Analysis by gas chromatography
The same samples used for IR measurements were further analyzed by GC-FID and GC-MS to confirm the presence of a byproduct in the bio EG sample, get an estimate of its relative concentration and obtain peak assignments using the NIST reference database. Figure 4-5 shows the GC-FID chromatograms of the three samples. The small
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peak at ~38 minutes retention time shown on the petro EG curve corresponds to diethylene glycol (DEG). This compound is a byproduct created during the formation of the glycol and it is typically found at small concentrations [130]. Other glycols of higher carbon number such as tri ethylene glycol and tetra ethylene glycol were not detected in any of the three samples. The sharp peak at ~30 minutes retention time corresponds to ethylene glycol (it is not shown completely on the chromatograms to distinguish small peaks near the baseline). At retention times between 26.5 and 29 minutes there are distinctive peaks only present in the bio EG samples. The compound-to-peak assignation was done by running the bio EG samples on the GC-MS and using the NIST database as reference. Only two peaks had a Match index above 700, the compounds assigned are hydroxyacetaldehyde and glycolic acid. Schnaidt et al. [131] reported the production of glyoxal, glycolic acid, glyoxilic acid, oxalic acid and hydroxyacetaldehyde from the oxidation of ethylene glycol on a Pt thin film electrode using a potentiostatic technique.
As reported in Section 2.4 .2, the different methods used to produce bio EG do not contain an oxidation step in the final reaction to form the molecule. Any oxidation must have occurred after bio EG was formed. Table 4.5 shows the formula, name and structure of the compounds identified. Two peaks were not considered because the Match index was below 700.
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Table 4.5: Bio ethylene glycol product composition and component characteristics
Formula Name Structure Area Units1 % Composition1
C2H4O2 Hydroxyacetaldehyde 637 0.003
C2H4O3 Glycolic acid 1144 0.006
C2H6O2 Ethylene glycol 14756933 99.991
1) Area units and relative composition obtained from GC-FID chromatogram
uV(x100)
6.5uV(x100) 6.56.0 uV(x1,000) 6.05.5 3.5 5.55.0
5.04.5 2 4.54.0 3.0 4.03.5 3.53.0
3.02.5 2.5 2.52.0 2.01.5
1.51.0 2.0 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 min 1.0 1 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 min
1.5
1.0
0.5 3
0.0
10 20 30 40 50 min
Figure 4-5: GC-FID chromatogram (zoomed view) of petro EG (bottom) and bio EG (middle, top). Base shift was used to distinguish individual baselines.
Peaks: Solvent (1), EG (2), DEG (3). Magnified region (26.5-29.0) showing distinctive peaks on bio EG samples
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4.2.4 Bio based content determination
The bio based content of bio ethylene glycol was analyzed by Laboratory Beta
Analytic Inc. following the experimental procedure reported in Section 4.1.3. The results show that all the carbons in the ethylene glycol molecule come from a bio based source
(Figure 4-6). The details of the report can be found in Appendix F. This result was expected based on the knowledge of existing commercial processes that produce bio EG.
If we analyze the production chemical pathways reported in Section 2.4.2, we can identify that the reactions followed to transform the original bio molecules (ethanol and sorbitol) do not involve the use of a carbon reactant. Oxygen, water, temperature and pressure are used to do the hydration of ethylene oxide or the catalytic cracking of sorbitol producing bio EG.
Bio Based Carbon, 100 %
Figure 4-6: Mean proportions of bio vs fossil based indicated by
14C content in bio ethylene glycol sample
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4.3 Bio BTEX
4.3.1 Analysis by gas chromatography
The bio BTEX sample components were identified using GC-MS and quantified using GC-FID. For both analysis the ASTM D6563-11a “Standard Test Method for
Benzene, Toluene, Xylene (BTX) Concentrates Analysis by Gas Chromatography” was used as a general guideline for how to identify aromatic components in a sample and to know the expected elution time of BTEX. Figure 4-7 and Table 4.6 show the peak assignation and name of the compounds identified by GC-MS. The bio BTEX sample contains a mixture of different aromatic compounds. At short elution times, benzene is the first chemical to elute, then mono, di and tri substituted rings appear. After 20 minutes of analysis polycyclic aromatics elute. We can presumably say that after formation of the benzene ring, alkylation reactions formed xylenes. The general classification of the identified components based on carbon content is: benzene, toluene
(mono substituted), xylenes (di substituted), trimethyl benzene (tri substituted), oxygenated compounds and naphthalene (double ring). The column used in the GC-MS unit does not separate xylenes to unit resolution. Benzene and toluene appear as wide peaks at short elution times.
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1 2 3
4 6 5 5
Figure 4-7: GC-MS chromatogram of bio BTEX.1) Toluene, 2) m/p-xylene, 3) o-xylene, 4) benzene, 1,2,4-trimethyl-, 5) benzofuran, 2-methyl-, 6) naphthalene
Table 4.6: Peak assignation on compounds present in bio BTEX sample
Compounds Benzene Benzene, 1,2,4,5-tetramethyl- Toluene 1-propenal, 3-phenyl- Ethylbenzene, m-p-xylene Benzofuran, 2-methyl- o-xylene Benzene, 4-ethenyl-1,2-dimethyl- Benzene-propyl 2-methylindene Benzene, 1-ethyl-3-methyl- 1H-Indene, 1-methyl- Benzene, (1-methylethyl)- Naphthalene Benzene, 1,2,4-trimethyl- Naphthalene, 1,2-dihydro-3-methyl Benzene, 1,3,5-trimethyl- Naphthalene, 1,2-dihydro-4-methyl Indane Naphthalene,2-methyl- Indene Naphthalene,2-ethyl- Benzene, (2-methyl-1-1propenyl)- Naphthalene,1,2-dimethyl-
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The GC-FID chromatogram obtained is shown on Figure 4-8. The location of peaks follows the same pattern obtained on GC-MS analysis. To quantify the amount of
BTEX present in the sample, an individual calibration curve was constructed for toluene, ethylbenzene and each xylene isomers. These chemicals were selected as they play a major role in the separation of high purity p-xylene. For each chemical 5 different concentrations were prepared using high purity reagent and methanol as solvent. Each sample was run three times to have significant data for the correlation. To verify the validity of the calibration curves obtained, the residuals were obtained and plotted, at all concentrations there is random error therefore the curves are valid. The calibration raw data, curves and plots of residuals are reported on Appendix A.2.
Sample quantification (Table 4.7) shows that 97 grams in the one liter sample of bio BTEX is p-xylene. This is the reference maximum amount used in the separation methods reported on Chapter 4. The m-xylene isomer has a higher concentration than p-xylene, because of its very similar physical properties the ratio of meta to para is always important as it dictates equilibrium limitations. The rest of the components of the mixture do not interfere with the separation of p-xylene.
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uV(x1,000,000) 5.0 Chromatogram
4.0
3.0 uV(x1,000,000) uV(x1,000,000) 5.0 5.0 Chromatogram Chromatogram 2.0
4.0 4.0 2 5 1.0 5 4 3.0 3.0 6 1 3 0.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 min 2.0 2.0
1.0 1.0
0.0 0.0
5.0 10.0 15.0 20.05.0 25.010.0 30.015.0 35.020.0 40.025.0 45.030.0 50.035.0 55.040.0 min45.0 50.0 55.0 min
Figure 4-8: GC-FID chromatogram of bio BTEX. Magnified region (13.0-15.0) showing high peak resolution for xylene isomers. 1) benzene, 2) toluene, 3) ethylbenzene, 4) p-xylene, 5) m-xylene, 6) o-xylene
Table 4.7: Concentration of aromatics in Bio BTEX sample
First Run Second Run Third Run Avg. Compound Slope Intercept Area Conc.1 Area Conc.1 Area Conc.1 Conc.1
Toluene 54363 -1859235 1.68E+07 344 1.71E+07 349 1.64E+07 335 343 Ethylbenzene 56417 -519321 4.11E+05 16 4.39E+05 17 4.31E+05 17 17 p-xylene 73830 -1251456 4.12E+06 73 4.63E+06 80 4.56E+06 79 77 m-xylene 95040 -1186564 7.81E+06 95 7.57E+06 92 7.47E+06 91 93 o-xylene 75384 -1147363 2.88E+06 53 2.89E+06 54 2.88E+06 53 53 1) mg/ml
Different researchers have reported the production of aromatic mixtures similar to
the bio BTEX sample by doing thermochemical transformation of biomass and upgrading
the effluent with a catalyst. Cheng et al. [82] produced a mixture of aromatics containing
but not limited to: BTEX, indenes, naphthalenes, styrenes, propylene and benzofuran by
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doing catalytic fast pyrolysis of furan using zeolite ZSM-5 as catalyst. The selectivity of aromatics was high for benzene (25.9%) and toluene (23.6%) and low for xylenes (4.3%).
Carlson et al. [132] studied the production of aromatics by doing pyroprobe experiments of cellulose, glucose and xylose using ZSM-5 as catalyst. For all raw materials the product distribution had naphthalene as the major component (45%), followed by toluene
(21%) and xylenes at (18%).
4.3.2 Color measurement.
The bio BTEX sample is a liquid with a strong yellow coloration (Figure 4-1).
The material did not contain any suspended solids or multiple liquid phases. The color analysis done with the Hunter Lab D-25 Optical Sensor (reported on Table 4.8) shows that b* index in the positive range of the scale toward the yellow limit and L* index close to the middle of the range towards white. Based on the GC analysis reported on the previous section a mixture of aromatics is present in the sample. P-xylene is the compound of interest and its effective separation may be limited by the presence of other xylene isomers, ethylbenzene or toluene. Color measurements on pure samples of these chemicals was done to have a reference of the reading that we could expect on a potential high purity bio p-xylene separated from the mixture.
The color indices of the four pure chemicals have a variation of 2.1 units for L* and 0.2 units for b*. There is a significant difference on color indices for BTEX sample and pure chemicals. The b* index for BTEX has value towards the yellow limit, this
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coloration is caused by the presence of components other than xylene isomers and toluene as their respective b* indices show values close to the neutral point.
Table 4.8: CIELAB color indices for BTEX samples
Sample L* b* Bio BTEX 55.2 3.4 Petro toluene 63.1 0.0 Petro p-xylene 62.7 -0.2 Petro o-xylene 61.0 0.0 Petro m-xylene 62.0 -0.1
4.4 Summary
Results obtained from analysis of the bio BTEX, diluted bio p-xylene and bio EG samples were presented in this section.
Bio BTEX sample contained a mixture of single aromatic, poly aromatic and small amount of oxygenated molecules. Toluene had the highest concentration, followed by xylene isomers. The presence of the isomers dictates the separation methods needed to obtain p-xylene as physical properties (Table 2.1) are very similar.
Through GC analysis, the presence of p-xylene in the bio BTEX and diluted bio p-xylene samples was confirmed. P-xylene concentration in the mixtures was determined to serve as reference on the theoretical maximum amount that can be recovered.
Diluted bio p-xylene sample contained side products that impair a strong coloration to the material. Based on physical properties, the components identified by GC
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do not seem to impair equilibrium limitations for the separation of p-xylene using physical methods.
Bio EG contained side products (at low concentration) not identified in the petro
EG. Their trace and effect (if any) on polymerization is discussed on Chapter 7.
The bio based content determination showed that bio EG was 100% obtained from biomass and the separated bio p-xylene was partially derived, obtaining a 63% biomass content.
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Chapter 5
Separation of P-xylene From Bio Based Samples
5.1 Introduction
P-xylene is an aromatic compound used for various commercial applications including: production of PTA, herbicides and as a solvent [48]. Depending on the application, the p-xylene purity required changes. For production of PTA, a high purity p- xylene is required. The composition requirements in the product to qualify for this grade are determined by the ASTM D5136 “Standard specification for high purity p-xylene”
[133]. The standard procedure specifies a required purity of at least 99.7% with 99.8% being a typical value obtained in the commercial product [134].
P-xylene is obtained from catalytic reforming of oil, it was obtained in a mixture with xylene isomers and other aromatic compounds. Many methods have been employed to separate p-xylene with high purity including: fractional distillation, crystallization, pervaporation, stripping crystallization, extractive distillation, etc. [47-52, 135]. The limitation in the effective separation of the chemical arises from the similarity in the physical properties of xylene isomers. Usually a combination of separation methods is employed to meet purity requirements.
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Recent efforts to produce p-xylene from alternative sources include the transformation of biomass into aromatics or precursors that ultimately can produce p- xylene (Section 2.4.3). This chapter describes a two-step laboratory scale procedure used to separate bio p-xylene from samples derived from biomass. The physical separation processes used were selected based on the information collected from characterization of the samples through gas chromatography (Chapter 4). Fractional distillation and crystallization were done multiple times to reduce the concentration of impurities in p- xylene and to obtain a product with enough purity to produce a PTA sample that could be used for polymerization (Chapter 7).
5.2 Separation of p-xylene from the diluted bio p-xylene sample
5.2.1 Experimental
The experimental set-up used for the separation consisted of a distillation column and a crystallization unit. For distillation, the sample to be separated was introduced into a three neck 50 ml round bottom 24/40 flask positioned inside a heating mantle. The port on the left of the flask head was sealed with a thermocouple port. The temperature reading at all times was used by a PID controller to regulate the heating output going to the mantle. This way, the temperature of the system could be modified by action of the controller. The port on the right of the flask head was plugged with a 24/40 stopper, this port was used as a safety feature in case of pressure build-up due to plugs in the plate column. An Oldershaw distillation column was installed in the port in the center of the
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head. The characteristics of the column are: 19mm I.D, vacuum jacketed, strip-silvered body, 24/40 joints, 5 perforated plates with a drain tube to direct condensed distillate to the next lower plate and a weir to maintain uniform liquid level. To reduce heat losses the column was covered with glass wool and wrapped with aluminum foil. A distilling head was connected to the top of the column. The characteristics of the head are: 24/40 joints,
10/30 thermometer port, two 4 mm stopcocks, a PTFE 0-3 mm metering valve and a cold finger condenser. A thermometer was installed to measure the temperature of the vapor phase eluting from the column. The metering valve was used to control the reflux of condensate. The service cooling water for the condenser was pumped from an auxiliary water bath set at 0 °C. Depending on the adjustment of the metering valve some condensate was obtained in a 50 ml round bottom flask installed in the exit port of the head. During operation, the reflux valve was opened only after a constant temperature reading in the thermocouple of the distilling head was obtained. Figure 5-1 shows the schematic diagram of the distillation unit.
For crystallization, the liquid distillate sample was placed inside a glass vial submerged in a cooling bath. Constant agitation was applied by using a magnetic stirrer.
The temperature of the cooling bath was established based on a correlation made by Lee
[136]. In his work a linear relationship was found between the cooling bath temperature and the volume fraction of ethylene glycol in a dry ice-ethanol-ethylene glycol mixture.
A thermocouple was placed inside the vial to measure the temperature of the sample.
Once the desired value was achieved, visual inspections were done to verify the formation of crystals.
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Temperature
Reflux Valve
Distillate Oldershaw Column
Thermocouple Heating Mantle
Figure 5-1: Schematic diagram of the fractional distillation set-up.
The sample was then passed through a fritted funnel to separate the formed crystals from the liqueur. The funnel with the crystals on the surface was placed on top of a clean beaker to allow for temperature equilibration. During this step the crystals melted and the product was recovered in a liquid phase. Due to the exposure to air during crystallization and the cold temperatures used in the process, some water condensed inside the beaker. The sample was separated using a liquid-liquid separating funnel.
Figure 5-2 shows the schematic diagram of the crystallization set-up.
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Temperature
Temperature
Cooling bath
Figure 5-2: Schematic diagram of the crystallization set-up.
5.2.2 Preliminary experiments
The GC-FID analysis of the sample (Section 4.1.1) revealed the presence of 2,5
DMF, p-xylene and linear/branched alkanes as the main constituents of the mixture.
Based on the elution times obtained and review of physical properties in literature, the difference in boiling points between them was determined to be high enough to separate them using distillation.
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To have a proper heating profile in the controller and to verify the temperature readings of the thermocouple during operation, a preliminary test was done. The sample was placed inside the vial and the set point was established at 200 °C. This temperature was above the normal boiling point of 2,5 DMF ~94°C [126] and p-xylene ~138.4 °C
[48]. The metering valve was closed completely to have full reflux during the test. After
~30 minutes, a vapor phase reached the thermometer in the distilling head and 25 minutes later there was a continuous flow of vapor eluting from the column and a liquid flow recirculating into the column. The temperature registered in the distilling head had a constant value of ~130 °C and the temperature on the thermocouple had a reading of
~188 °C. At this equilibrium condition one of the major components was eluting from the column at high concentrations, the temperature in the beaker at which this condition was established (called split-points) was used in subsequent experiments as the first set point for the controller. The reflux valve was opened to remove condensate from the system.
As the process continued the temperature in the beaker and in the thermometer increased until a second equilibrium condition was reached, the reflux valve was closed and the system was allowed to equilibrate for 10 minutes. After this time, the temperature in the beaker was ~202 °C and the temperature in the head was ~139 °C. The reflux valve was opened and more condensate was obtained. The temperature at the head remained at a value of ~139 °C for ~80 minutes while the temperature in the flask increased to a value of 244 °C. The split-points identified during this test were used as the set points for the controller and as reference on the appropriate moment to open the reflux valve and collect distillate from the head.
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5.2.3 Process analysis
As discussed in Section 4.1, the presence of suspended particles in the sample was evident. Due to potential problems with particles plugging the holes of the plates in the distillation column, the sample was filtrated in a vacuum filtration unit. Figure 5-3 shows the separated particles in the filter paper. Doing a mass balance of the product recovered, the solids represented 0.01 weight % of the original mixture. No further testing was done on these particles.
Figure 5-3: Solid particles separated in the vacuum filtration unit
The filtrated sample was distilled following the process rationale presented in the previous section. Three samples were collected in each experiment, two condensates (one at each split-point) and the remaining non-distilled material in the beaker. Due to volume constraints in the processing per batch, multiple distillations were done to separate
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sufficient sample for further processing. Table 5.1 shows the mass distribution for some representative experimental runs.
Table 5.1: Mass distribution in first set of distillation experiments
Original First distillate Second distillate Residue Material Lost Exp. # (g) (g) (g) (g) (g) 1 37.0 9.3 19.0 5.3 3.4 2 38.5 8.1 23.4 5.1 2.0 3 39.8 10.1 21.9 5.1 2.8 4 40.8 9.3 23.1 7.1 1.3 5 41.3 9.3 21.2 7.2 3.6 6 42.3 11.2 20.4 8.3 2.4 7 35.1 9.1 18.1 6.3 1.6
The samples collected were analyzed using GC-FID to verify the distribution of components in the samples. Figure 5-4 shows the combined chromatograms of samples obtained in one distillation experiment. The chromatograms are presented in a zoomed view to enlarge the area near the baseline and observe the small peaks present. The peak for 2,5 DMF appears at retention times ~ 7 min and the peak for p-xylene at ~13 min.
The first distillate contained a mixture of 2,5 DMF, p-xylene and some compounds at very low concentrations with boiling points close to that of 2,5 DMF. The second condensate was primarily composed of p-xylene with remaining 2,5 DMF and some of the branched/linear alkanes. The remaining material in the flask contained small amount of p-xylene and the rest was the mixture of alkanes.
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uV(x10,000) 5.0 Chromatogram
4.0
3.0 1 2.0
1.0
0.0
10 20 30 40 50 min uV(x10,000) 5.0 Chromatogram 4.0
3.0
2.0 2 1.0
0.0 10 20 30 40 50 min uV(x10,000) 5.0 Chromatogram
4.0
3.0 3 2.0
1.0
0.0
10 20 30 40 50 min uV(x100,000) 2.0 Chromatogram 1.5
1.0 4 0.5
0.0 10 20 30 40 50 min
Figure 5-4: GC-FID chromatograms of distillates and residue 1) Original sample
2) First distillate 3) Second distillate
4) Residue in beaker
Based on the relative areas observed on the chromatograms, it can be deduced that bio p-xylene was present as the major component in the second distillate. Multiple samples from different distillation experiments were mixed together to be reprocessed. In
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this case, no previous determination of the heat profile was done. The controller was set to 150 °C and the reflux valve was closes. The system reached equilibrium at temperatures of 136 °C in the head and 144 °C at the beaker. After 10 minutes at this condition, the valve was opened and the condensate was collected until the temperature at the head increased to 139 °C. At this time a new flask was used to collect the condensate.
The distillation was stopped when the temperature at the head increased above 141 °C.
Table 5.2 shows the mass distribution of representative runs.
Table 5.2: Mass distribution in the second set of distillation experiments
Exp. Original First distillate Second distillate Residue Material Lost # (g) (g) (g) (g) (g) 1 19.5 5.7 13.1 0.1 0.6 2 35.2 9.1 22.0 2.3 1.8 3 24.9 5.1 18.4 0.9 0.5
Figure 5-5 shows the combined chromatograms of samples obtained during the reprocessing of the second distillate from the initial set of distillations. The first distillate obtained contained p-xylene and most of the 2,5 DMF present in the sample. The second distillate was p-xylene with a high purity and the residue contained p-xylene and the remaining alkanes at low concentrations. The second distillate is the preferred material as the concentration of p-xylene is high, but the presence of impurities still needed to be reduced. The location and assignments of peaks is the same as in the previous example.
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uV(x100,000) 4.0 Chromatogram
3.0
2.0 1 1.0
0.0
5.0 10.0 15.0 20.0 25.0 30.0 min uV(x100,000) 4.0 Chromatogram
3.0
2.0
1.0 2 0.0
5.0 10.0 15.0 20.0 25.0 30.0 min uV(x100,000) 4.0 Chromatogram
3.0
2.0
1.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0 min 3 uV(x100,000) 4.0 Chromatogram
3.0
2.0
1.0
0.0
5.0 10.0 15.0 20.0 25.0 30.0 min
4 Figure 5-5: GC-FID chromatograms of distillates and residue
1) Initial sample (2nd distillate from first set) 2) First distillate
3) Second distillate 4) Residue in beaker
The second distillates collected from second runs of several distillation experiments were combined and uses in the crystallization unit. The cold bath solution
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was prepared to obtain a temperature of -5 °C. This temperature was below the melting point of p-xylene. All the material was crystallized in a single stage. The crystal phase separated was allowed to melt and the crystallization process was done for a second time obtaining the desired bio p-xylene, with high purity in the crystal phase. The total amount of product obtained after several experiments was 145 grams. This amount was sufficient to produce PTA for a polymerization reaction. Figure 5-6 shows the chromatogram of the liquid and crystal phases from the crystallization experiment. The concentration of p- xylene (main peak) increased in every stage of the crystallization experiments.
uV(x10,000) 2.5 Chromatogram
2.0
1.5
1.0 1 0.5
0.0
10 20 30 40 50 min uV(x10,000) 2.5 Chromatogram
2.0
1.5
1.0
0.5 2 0.0
10 20 30 40 50 min
Figure 5-6: GC-FID chromatograms of recovered liqueur (1) and crystal phase (2)
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5.2.4 Product quality
The concentration of p-xylene during the distillation and crystallization experiments was monitored through GC-FID analysis of the samples obtained. Table 5.3 shows the variations in the concentrations of p-xylene and 2,5 DMF throughout the separation procedure. The % composition values were obtained through area normalization. The detailed results obtained from each chromatogram can be found in
Appendix H. Most of the linear/branched alkanes were recovered in the residue during the distillation experiments. The first distillate contained most of the 2,5 DMF present in the sample and a high concentration of p-xylene. The second distillate had a high concentration of p-xylene but the purity was not in the range of a high-purity product.
The first and second stages of the crystallization process successfully reduced the concentrations of byproducts to obtain a high purity p-xylene. The p-xylene obtained as a crystal from the second stage was used to produce PTA. The results are shown in
Chapter 6.
Table 5.3: Product composition in distillation and crystallization samples1
2,5 branched/linear Not Stage Sample ID p-xylene DMF alkanes determined -- Original sample 20.13 0.214 79.63 0.024 1st distillate 93.56 2.857 2.149 1.432 1 2nd distillate 98.78 0.222 0.322 0.666 residue 0.80 0.111 98.23 0.854 liqueur 99.46 0.065 0.139 0.333 1 crystal 99.92 0.012 0.014 0.046 liqueur 99.58 0.056 0.075 0.284 2 crystal 99.98 0.010 0.005 0.002 1) Results reported as % composition obtained from area normalization
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As discussed in Section 4.1.2 the original sample had a distinctive brown coloration. This color was caused by the presence of colored compounds in the sample i.e. 2,5 DMF has by nature a strong yellow/brown color and it represents the main impurity in the separated bio p-xylene. Color determinations were done using different samples obtained through the separation in order to verify the effect in color and to compare the results with those obtained for a commercial p-xylene sample. Table 5.4 shows the results obtained. The samples containing a high concentration of 2,5 DMF had a b* index towards the yellow limit. After the first distillation, most of the branched/linear alkanes were separated on the residue. The compounds causing the brown coloration remained in these residue samples. The distillates obtained in the first and second distillation had little variation in their L* indices. The final high purity p- xylene sample has color values comparable to those of the commercial petro product.
Table 5.4: Color variations in reference materials and in samples obtained in distillation and crystallization experiments
Stage Sample ID L* b* -- Original sample 33.3 0.8 1st distillate 59.3 0.1 1 2nd distillate 58.2 0.0 residue 36.1 0.7 liqueur 60.6 -0.1 1 crystal 60.6 -0.1 liqueur 61.3 -0.1 2 crystal 61.9 -0.2 -- Commercial p-xylene 62.7 -0.2
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5.2.5 Summary
Results obtained from the separation of p-xylene from a mixture of furan, p- xylene and alkanes using distillation and crystallization were presented in this section.
Based on the purity of the intermediate and final samples obtained, the compounds present in the sample do not impose equilibrium limitations that may hinder their separation from the mixture using the described methods.
The main parts of the colored compounds in the original sample were removed during the first distillation. Samples with 2,5 DMF up to 0.310% composition, did not have a yellow coloration caused by the presence of this compound.
Using fractional distillation and crystallization, a p-xylene product that meets high-purity specifications was separated from a bio derived sample. This product is suitable for use in the production of bio terephthalic acid.
5.3 Separation of p-xylene from the Bio BTEX sample
5.3.1 Experimental
The experimental set-up used for the separation of bio p-xylene from distillation and crystallization was the same as that described in Section 5.1.1.
For distillation, a preliminary test was done to determine the split-points later used as set-point for the heating system. For crystallization, the cold bath temperature
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was continuously adjusted by changing the ratio of EG and ethanol to obtain the required cold temperature based on equilibrium.
5.3.2. Preliminary experiments
The GC-FID analysis of the sample (Section 4.3.1.) revealed the presence of oxygenated compounds and single, mono-substituted, di-substituted, tri-substituted and polycyclic compounds, all of aromatic nature. Based on the number of carbon units in each compound and information from literature (Table 2.1), it was expected that 3 different samples could be obtained through fractional distillation. One of them (desired product) would contain ethylbenzene and xylene isomers in high proportions. The separation of a sample with this composition through distillation and crystallization has been widely studied [47-54]. For distillation, the proximity in boiling points between m- xylene and p-xylene limits the separation of the isomers. In a lab scale environment, it is particularly difficult to achieve a good degree of separation; however, a modest purity is obtained in industry by employing distillation columns with multiple stages and operated at very high reflux [53]. Crystallization is usually done as a subsequent step to reduce the concentration of m-xylene. This process is thermodynamically limited as solid-liquid equilibrium conditions exist. Of particular interest, is the eutectic point formed between m-xylene and p-xylene. This equilibrium conditions occurs at -53 °C (13% p-x, m-x
87% mole) [47]. A quick interpretation of this condition is as follows. Depending on the initial concentration of the sample, the mixture would have a defined melting point. If the system is brought to this temperature p-xylene would start to crystalize. As this happens,
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the concentration of the liquid mixture is changing and a lower temperature is required to keep obtaining p-xylene in a crystal form. The limiting conditions are obtained at -53 °C, if the system temperature drops below this value, m-xylene would also crystalize with p- xylene. The difference in temperature between the eutectic point and the initial melting point for the mixture is the so called “process window” for crystallization. As the p- xylene crystals are formed, it is expected that some m-xylene or other aromatic present would be in the surrounding area of the crystals and would remain there after separation.
Multiple crystallization stages are therefore required to obtain p-xylene with high purity.
To obtain the split-points for the mixture, a sample was placed inside the flask and the set point for the heater was established at 260 °C. The iterative procedure to determine the split-point was previously described. The results obtained are presented on
Table 5.5. The product obtained up to a temperature in the head of 117 °C contained primarily benzene and toluene with small amount of xylenes. The product obtained between 117 °C and 137 °C contained the xylene isomers and some aromatics of higher carbon content (typically called C-9). The residue in the beaker contained the remaining
C-9 and oxygenated compounds.
Table 5.5: Split-points used for distillation of the BTEX sample
# T beaker ( °C) T head ( °C) 1 136 96 2 144 117 3 170 137
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For crystallization, depending on the GC results of the samples obtained after distillation, the temperature of the cold bath was determined depending on the estimated melting point of the mixture. Figure 5-7 shows the ternary equilibrium diagram used as reference. The solid lines inside the diagram represent the equilibrium region between isomers. The dashed lines are shown as temperature references. The temperature values at the intersection points of the solid lines and the axis are the binary eutectic points and the temperature in the center of the diagram (~65.3 °C) is the ternary equilibrium point.
o-x
-30 °C
-35 °C
-40 °C
-50 °C
-62 °C -60 °C -65.3 °C -55 °C
-50 °C
10 °C 0 °C -10 °C -20 °C -30 °C -53 °C
p-x m-x
Figure 5-7: Temperature projection diagram of the ternary xylene mixture assuming ideal behavior of liquid and solid phase. Prepared with information reported on Ref. [47]
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5.3.3 Process analysis
Due to volume constraints in the processing per batch, multiple distillations were done. Table 5.6 shows the mass balance of different distillation experiments. Figure 5-8 shows the GC-FID chromatogram of samples obtained from the reprocessing of the second distillate obtained during an initial distillation experiment. The peak location and assignments are the same as the ones presented in Figure 4.8. The peak for toluene is located at retention times at ~10 min, the peaks for xylene isomers are located at retention times at ~13 min and the rest of the peaks at higher retention times belong to C9 aromatics.
Table 5.6: Mass distribution in the first set of distillation experiments of BTEX sample
Original First distillate Second distillate Residue Material Lost Exp. # (g) (g) (g) (g) (g) 1 34.9 11.5 9.3 12.6 1.5 2 33.0 10.4 11.5 10.0 1.1 3 32.1 12.3 12.0 7.4 0.4 4 32.8 11.3 12.1 8.4 1.0 5 31.4 9.5 13.2 8.2 0.5
The original sample as a product of a first distillation experiment, contained a reduced amount of toluene and a high concentration of xylene isomers. The analysis of the second distillate obtained during reprocessing shows that the sample is primarily xylene isomers with low presence of other products. This sample was used for further purification in the crystallization unit. The residue obtained from distillation had a distinctive yellow coloration, this color was perceived in the original sample. The colored causing compounds remained in the liquid mixture after distillation. 137
uV(x10,000)
4.5
4.0 3.5 3.0
2.5 1 2.0
1.5
1.0
0.5
0.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 min uV(x10,000)
4.5Chromatogram
4.0 3.5 3.0 2
2.5 2.0 1.5
1.0
0.5
0.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 min uV(x10,000)
4.5Chromatogram
4.0 3.5 3.0 2.5 3 2.0 1.5
1.0
0.5
0.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 min uV(x10,000) 4.5Chromatogram
4.0
3.5
3.0 2.5 4 2.0 1.5
1.0 0.5 0.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 min
Figure 5-8: GC-FID chromatograms of distillates and residue 1) Original sample 2) First distillate 3) Second distillate 4) Residue in beaker
The cold bath solution for crystallization was prepared to obtain a temperature of
-25 °C. This temperature was below the melting point of the second distillate mixture
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obtained from distillation. All the material was crystallized in a single stage. The crystal phase separated was allowed to melt and recrystallization was done obtaining bio p- xylene. Analysis of the sample revealed the presence of residual amounts of m-xylene in the sample (up to 3%). Multiple crystallization experiments were needed to reduce its concentration and obtain p-xylene within specifications for a high purity product. Figure
5-9 shows the chromatogram of the crystal and liquid phases from the crystallization experiments. Using the chromatogram with label #3 as reference, from left to right, the first peak corresponds to ethylbenzene, the second to p-xylene, the third to m-xylene and the forth to o-xylene. In each crystallization experiment, the concentration of xylene isomers was reduced. The process was repeated until a product with the required high purity grade was obtained.
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uV(x100,000) 1.25Chromatogram
1.00
0.75 1
0.50
0.25
0.00 10.0 12.5 15.0 17.5 min uV(x100,000) 1.25Chromatogram
1.00
0.75 2
0.50
0.25
0.00 10.0 12.5 15.0 17.5 min uV(x100,000)
10.0Chromatogram 9.0 8.0
7.0 6.0 3 5.0 4.0 3.0
2.0 1.0 0.0
10.0 12.5 15.0 17.5 min uV(x100,000) 10.0
9.0 8.0 7.0 6.0 4 5.0
4.0 3.0 2.0
1.0 0.0 10.0 12.5 15.0 17.5 min Figure 5-9: GC-FID chromatograms crystallization products 1) Initial sample 2) First crystallization 3) Second crystallization 4) Third crystallization
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5.3.4 Product quality
The concentration of p-xylene during distillation and crystallization experiments was monitored through GC-FID analysis of the samples obtained. Table 5.7 shows the variation in the concentration of p-xylene in the different stages of the separation procedure. The % composition values were obtained through area normalization. The detailed results obtained in each chromatogram can be found in Appendix H. The distillation results correspond to the samples presented in Figure 5-8. The residue contained most of the C9 aromatics. The two distillates contained the xylene isomers in different proportions. The second distillate was used for the crystallization experiments.
At each stage of the crystallization experiments, the concentration of p-xylene in the crystal phase increased and the presence of xylene isomers decreased, in particular m- xylene concentration was reduced by operating the process above the equilibrium point.
The final product obtained from the separation meets specifications for a high purity product. Due to the multiple crystallization steps to achieve the desired purity, the yield of product was significantly affected. The amount of material obtained with high purity was less than ~5 grams. Due to this very limited amount of product, no further transformation into PTA was done. The study on the use of this sample was limited to the separation procedure to obtain p-xylene. The analysis made provides information on the key elements that must be monitored to obtain the desired product and the limitations that exist depending on the original composition of the sample available.
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Table 5.7: Product composition in samples obtained from the processing of the BTEX sample
Stage Sample ID % ethylbenzene % p-xylene % m-xylene % o-xylene % not determined 1st distillate 3.49 30.52 44.74 12.41 8.84 2 2nd distillate 2.57 29.01 44.85 19.06 4.51 residue 0.28 5.26 9.53 11.55 73.39 1 crystal 1.95 27.31 40.74 23.77 6.23 2 crystal 1.53 42.10 33.09 18.53 4.75 3 crystal 3.25 73.05 13.78 9.87 0.05 4 crystal 0.06 99.66 0.13 0.15 0.002 1) Results reported as % composition obtained through area normalization
5.3.5 Summary
Results obtained from the separation of p-xylene from a mixture of aromatics produced from biomass were presented in this section.
Based on the purity of the intermediate and final samples obtained, the presence of xylene isomers represent the major limiting step in the separation of p-xylene with high purity. These compounds impose equilibrium limitations that restrict the removal of p-xylene. According to the concentration of the sample, the conditions of the distillation and crystallization unit can be tuned to operate outside the equilibrium region.
The main parts of the colored compounds in the original sample were removed during the first distillation. This color was attributed to the oxygenated compounds present in the original sample.
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Using fractional distillation and crystallization, a p-xylene product that meets high-purity specifications was separated from a bio derived sample. This product is suitable for use in the production of bio terephthalic acid, but not enough quantity was obtained to pursue this next step.
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Chapter 6
Production of Purified Terephthalic Acid
6.1 Introduction
Terephthalic acid is an aromatic carboxylic acid essential to polyester fibers production. A large majority of the production of terephthalic acid is via catalytic oxidation of p-xylene with air in an acetic acid medium. The catalyst is a mixture of cobalt, manganese and bromine compounds. The solid product of this process is called crude terephthalic acid (CTA). A second stage is used to purify CTA, in which the solid acid reacts with hydrogen in a palladium catalytic bed to reduce the concentration of byproducts produced during oxidation and obtain a purified acid (PTA). This two stage process is commonly known as the AMOCO process.
This chapter describes a modified AMOCO process that was used to produce terephthalic acid using two different p-xylene products. The first one was a commercial high purity petro product acquired from Fisher Scientific, and the second one was bio p- xylene separated from a mixture of furan and alkanes (as explained in the previous chapter) with a purity of 99.98%. Both p-xylene samples were first oxidized and then purified using typical hydrogenation reaction to reduce the concentration of impurities in
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the form of p-tolualdehyde (p-tolu), p-toluic acid (p-tol), 4-carboxybenzaldehyde (4-
CBA), anthraquinone and fluorenone to polyester grade levels [61]. An assessment of the production processes and the quality variables of the acids produced allowed for a direct comparison of the use of a petro and a bio source for p-xylene. The effect of original impurities present in p-xylene on the production of the acid was evaluated by analyzing yield, process variables, product purity and physical properties of the final product obtained in each stage. These results are essential to determine product suitability for polyester production using typical two step polymerization techniques [20].
6.2 Oxidation of p-xylene
6.2.1 Experimental
The experimental set-up used for this experiments consisted of a 50 ml stainless steel reactor (4590 Micro Bench Top Parr Reactor) equipped with a 4-blade propeller stirrer, a pressure transducer installed on the head of the vessel, a thermocouple positioned to read the temperature of the reacting mixture, a dip tube leveled above the position of the stirrer blades used to bubble oxygen into the liquid, a safety release valve installed on the head with a burst pressure safety limit of 3000 psi, a gas feed line connected to the dip tube and a double tube condenser with a helix rod in the core tube installed on one of the ports in the head. The service cooling water for the condenser was pumped from an auxiliary water bath set at 0 °C. Due to the corrosive nature of the solvent, a glass liner was used to prevent attack to the inside surface of the reactor. The
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heating of the system was done using a band heater installed on the outside surface of the vessel. This heater was controlled by a PID unit calibrated with liquid acetic acid at the operating temperatures of the oxidation. The thermocouple and pressure transducer were connected to a main controller that continuously recorded the temperature and pressure of the system.
The product obtained from the oxidation reaction was transferred to a vacuum filtration system to recover the produced acid in solid form. This acid was washed with hot glacial acetic acid to dissolve remaining catalyst particles and obtain a clean solid product. The process diagram of the experimental set-up used in this work is shown in
Figure 6-1. The labels shown in the diagram are used to explain the experimental procedure.
In a typical experimental run, cobalt acetate (COAC), manganese acetate
(MNAC) and sodium bromide (NABR) were mixed in the glass liner until homogeneity was achieved (CATALYST). The liner was then placed inside the reactor and p-xylene
(P-XYLENE) and acetic acid (ACETICAF) were added, the contents were mixed at 200 rpm for 3 minutes. Figure 6-2 shows the glass liner with all the reactants inside. The vessel was closed and the system was flushed with nitrogen for 5 minutes, the flow of gas was set to a value that avoided carryover of the reactants to the head ports. After flushing, nitrogen was fed until the internal pressure of the vessel reached a value of 200 psig. At this point agitation was started and gradually increased, reaching a value of 250 rpm after
5 minutes.
The heater was set to a 20 minute ramp profile reaching 170 °C. After a 25 minute equilibration period at this temperature, the release valve was opened allowing nitrogen
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out of the system. The oxygen valve was then opened allowing gas into the dip tube
(OXYGEN). The supply of oxygen was regulated so as to have it bubbled in the liquid without causing splash to the head of the vessel. Figure 6-3 shows oxygen bubbling in a test solution inside the glass liner. After oxygen introduction, the release valve and gas feed line were closed and the reaction proceeded for 30 minutes. At the end of the process the heater was removed and temperature decreased gradually. When the system temperature was below the normal boiling point of acetic acid (118 °C) the reactor was opened and the glass liner was removed from the vessel. During the oxidation process any gas effluent from the reactor head was condensed and refluxed to the system
(ACETICAR).
The product recovered from the glass liner was transferred to a vacuum filtration unit. Filter paper #50 was selected for this process as it resists chemical attack from acetic acid and it allows recovery of fine crystalline phase. The solid crude terephthalic acid was retained in the filter (CTA) and the acetic acid and dissolved catalyst were separated as filtrate (CATRECYC). This first filtration was done immediately after removing the liner from the reactor to maintain the catalyst dissolved in the hot solvent. CTA was washed with fresh glacial acetic acid at 80 °C and filtered using vacuum filtration. This washing procedure was repeated 5 times until no dark coloration was visible to the naked eye on the recovered solid CTA and washing solvent. The product was then placed on a drying oven at 110 °C for 8 hours to evaporate any remaining solvent.
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COND
ACETICAR
OXYGEN P I T I COAC
MNAC CATALYST
NABR PXYLENE
ACETICAF
OX CTA
FILT CATRECYC
Figure 6-1: Process diagram for the oxidation of p-xylene to crude terephthalic acid
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Figure 6-2: Reactants inside the glass liner used for oxidation Figure 6-3: Inside view of oxygen bubbling in reacting media Left: Dip tube Center: Stirrer Right: Thermocouple
6.2.2 Preliminary experiments and process conditions rationale
The AMOCO technology used to produce terephthalic acid from p-xylene requires high amounts of acetic acid. This acid acts as a heat sink liquid, capturing the heat generated during the exothermal oxidation. It can be said that heat management during oxidation is done by evaporative cooling of the solvent [137]. The heat of p- xylene oxidation is 2.12x107 J/mol of reacted p-xylene [137] and the heat of evaporation for acetic acid is 2.12x104 J/mol [138]. The stoichiometric reaction for the oxidation of p- xylene is shown on Figure 6-4. Oxygen is typically provided in excess making p-xylene the limiting reactant. Theoretically, for each mol of reacted p-xylene, one mol of terephthalic acid and two moles of water are produced. At low concentrations of water
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the catalytic activity is favored as water interact with hydroperoxide molecules yielding more radicals. At high concentrations of water there is a decrease in the catalytic activity as it interacts with cobalt, reducing the rate of ligand formation [139].
Figure 6-4: Stoichiometric reaction for p-xylene oxidation
Considering complete oxidation of 1 kg of p-xylene, the required acetic acid to obtain a net zero in heat balance is 411 kg. This is a rough estimate as specific heat of the components in the mixture was not considered. This requirement for high amounts of acetic acid imparts a limitation to the amount of p-xylene that can be reacted per batch, as the acid will occupy most of the available volume in any reaction vessel. Furthermore the high concentration of acid and its highly corrosive nature at elevated temperatures require the use of titanium or titanium lined reactors that can withstand operating conditions without been attacked.
In this research a 316 stainless steel reactor was used for the production of terephthalic acid through oxidation and purification. This material has good corrosion resistance to acetic acid in solution at room temperatures, but it is corroded at elevated temperatures. To limit the attack of the acid to the walls of the vessel, a glass liner was used to contain the reactants during oxidation. The stirrer, dip tube, thermocouple and the surface of the top head of the reactor were exposed to the acid during all experiments.
After every run a visual inspection of the before mentioned elements was done to assure
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that stainless steel particles did not detach from their surface and remain in the reacting media. In case of severe attack, the parts were replaced by new ones of exactly the same type. It is considered that the use of new parts did not affect process performance in any way.
The potential corrosion reaction of the solvent with the vessel imposed a limitation to the maximum temperature that could be selected for oxidation. In general, an increase in temperature leads to an increase of the oxidation reaction rate constant, but it also accelerates the rate of corrosion. Different researchers have conducted lab scale p- xylene oxidation experiments (using titanium vessels) with operating temperatures between 160-230 °C [57,58,140,141]. No reported information was found for the use of stainless steel reactors in p-xylene oxidation experiments. An iterative process was followed to determine the operating conditions (temperature and pressure) that allowed oxidation to occur and caused the least possible corrosion effect on the stainless steel reactor. This effect was assessed by visual inspection of the reactor and accessories surfaces. The temperatures reported in the literature were taken as reference and as starting values for the experiments. The normal boiling point of acetic acid is 118 °C, the range of temperatures used for oxidation systems vary from 160-230 °C. The operating pressure of the system was preferably set to a value high enough to maintain the acid in liquid phase at the operating temperature of the process. Determination of this condition was done by using vapor-liquid equilibrium correlations such as the Antoine equation.
As discussed in Section 2.3.3.1 the basis of the AMOCO process is the use of a catalyst mixture containing bromine, cobalt and manganese. The bromide is usually fed in the form of acid (HBr) or in some cases as a salt with sodium (NaBr). The former has a
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higher catalytic activity as dissociation and oxidation to the radical form is relatively rapid. The drawback in its use is the highly corrosive nature of the chemical [54]. Cobalt and manganese are usually consumed as acetate salts tetrahydrated. Bromide, as an initiator of the radical reaction, has a major role at the beginning of the oxidation. A low concentration of bromide can lead to manganese precipitation in the form of MnO2.
Catalytic activity increases with a higher ratio of [Br] / ([Co] + [Mn]) until a value of 0.3 is reached, after this value a constant activity is obtained [59]. The rate constant of the determining step (oxidation of p-toluic acid [56]) increases with increasing [Co] / ([Co] +
[Mn]) ratio until an inflection point is reached [59]. This optimum ratio decreases with increasing temperature as manganese loses activity at incremental temperatures and more is needed to maintain activity. For 150 °C the optimum ratio is 0.95 and for 170 °C it is
0.65. This intricate relationship between activity, catalyst ratios and operating conditions requires the selection of process variables according to the experimental set-up available for oxidation reaction.
Preliminary tests were done using petro p-xylene as reactant, sodium bromide, cobalt acetate and manganese acetate as catalyst, oxygen as oxidizer and following the experimental procedure reported on Section 6.2.1. Table 6.1 summarizes the different operating conditions used in each experiment and includes reference information obtained from literature to serve as comparison. The goal for this set of experiments was to obtain the highest yield of solids possible after filtration, washing and drying with replicable operating conditions and consistent product quality.
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Table 6.1: Operating conditions for p-xylene oxidation experiments and reference information from literature
1 2 3 4 5 5 5 6 Run # Stirring speed T P Rxn time p-xylene Co Mn Br CTA RPM °C psig min grams mmol mmol mmol grams 1 100 140 45 3:00 2.6 8.3 0.0 3.3 0.20 2 120 140 45 3:00 2.5 8.3 0.0 3.3 0.30 3 200 140 40 3:00 1.8 8.3 0.0 3.3 0.30 4 250 140 200 1:30 1.8 8.3 0.0 3.3 0.50 5 500 170 230 0:40 1.6 6.3 6.2 8.9 1.02 6 500 190 230 1:00 1.6 6.3 6.2 8.9 0.72 7 500 170 230 0:40 1.6 6.3 6.2 8.9 1.00 8 500 170 230 0:40 1.6 6.3 6.2 8.9 1.00 Abrams [140]7 1000 195 8 (232) -- -- 6.0 17.0 10.0 -- Wang et al. [141] 800 191 6 (232) 0:40 -- 300 300 900 -- Li et al. [142] 1000 200 50 (232) 0:30 2.7 12.5 12.5 5.5 2.42 Zuo et al. [58] 1200 160 435 (450) 0:30 1.4 33.0 1.0 33.0 1.29 1) Target temperature before oxygen introduction
2) O2 pressure in the system. Values in () are system total pressure when pure O2 was not used 3) Effective reaction time after oxygen was introduced in the reactor 4) Total p-xylene fed to the reactor 5) Moles of metal elements fed to the reactor 6) Total solids obtained after oxidation. 7) Conditions used in an industrial process
In the first four runs, manganese was not used to avoid having a catalytic effect due to changes in pressure and reaction time. Constant concentrations of bromine and cobalt allowed having initiation and propagation of radical reactions. Zuo et al. [58] used equal amounts of [Co] and [Br] with no [Mn]. In our system the use of such a high bromine concentration was not possible because of corrosion. The concentration was set to a [Co] / [Br] molar ratio of 2.5; this value is close to the amounts used by Li et al.
[142].
In the first two runs, incremental changes in stirring speed were used to investigate if there was an effect on the dispersion of oxygen in the reacting media. The yield of CTA remained constant. In the third run, a decrease in fed p-xylene and an
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increase in rpm was tried to maximize oxygen utilization with a lower availability of reacting raw material. The yield did not have a big change. For the fourth run a decrease in reaction time was investigated, the time values tried up to this run are significantly higher than the ones found in literature; this is due to the idea that a lower reacting temperature (limited because of reactor material) would require more time of reaction.
The yield increased by 60%. This increase could have been caused by limiting the over oxidation of the solids formed at long reaction times. In the next run, manganese acetate was fed to the system in the same concentration as cobalt to obtain a [Co] / ([Co] + [Mn]) ratio of 0.5; this is in agreement with conditions used by Wang et al. [141] and Li et al.
[142] and is a lower value than the optimum reported for 170 °C. Stirring speed was increased due to the increased in solid material by addition of manganese acetate.
Reaction time was decreased to be consistent with information found in literature. The yield increased by 50% compared to the last run. An increased reaction time and temperature were tried on run #6. The yield was lower and there were evident signs of pitting corrosion in the stirrer and dip tube. The conditions used in run #5 were somewhat similar to some values reported in literature. They gave the highest solid yield and no signs of corrosion were seen at 170 °C. For run #7 and #8 the same conditions were tested to check for consistency. The yield of solids was the same and the product looked similar according to visual inspection with the naked eye.
The maximum yield obtained (~1 grams) was lower than the stoichiometric maximum product that could be produced (~2.4 grams). There were no further efforts to improve yield, since it was preferred to have operating conditions that gave consistency in the experimental procedure. These conditions were selected for the subsequent liquid
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phase oxidation of petro p-xylene and bio p-xylene.
6.2.3 Process analysis
After process conditions were determined by preliminary studies, the oxidations of petro and bio p-xylene were done on repeated occasions until enough material was available for polymerization with ethylene glycol. Ten oxidation reactions were performed for petro p-xylene and 40 for bio p-xylene. The product quality results presented in the following sections are representative of the materials that can be obtained through oxidation experiments. Not all the materials produced were tested in order to maximize the amount available at the end, since a complete characterization including product quality, color and optical density required ~0.4 grams of acid. This represents about 40% of the acid produced in each run.
The mass balance of the reactants fed to the system in each oxidation run is shown on Table 6.2. The total mass of reactants is 25.59 grams with acetic acid being the primary component. The total mass of catalyst is significantly higher than the feed of p- xylene. The heat of oxidation for total consumption of 1.6 grams of p-xylene is 3.18x105
J. Again using a rough estimate to obtain a net zero heat balance, 370 grams of acetic acid are required. In our experiments only 20 gr of acetic acid were used. It was expected that the acid would be evaporating and after contact with the condenser it would reflux back into the reacting mixture. The total amount of reactants was ~27 grams. The amount of acid was determined following recommendations of safe reactor operation determined by Parr Instruments. The reactor should be operated at 65% volume capacity.
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Table 6.2: Initial material balance for p-xylene oxidation in acetic acid media using metal catalyst
Compound M.W. (g/mol) mol grams p-xylene 106.1 0.015 1.59 Cobalt acetate 249.0 0.006 1.56 Manganese acetate 245.0 0.006 1.53 Sodium bromide 102.8 0.009 0.91 Glacial acetic acid 60.0 0.333 20.00
Process conditions (temperature and pressure) were continuously recorded in all oxidation experiments. Figure 6-5 and 6-6 show the temperature and pressure profiles for a typical run using petro p-xylene and bio p-xylene. In both cases the system was pressurized to 200 psig with nitrogen and the temperature was increased to 170 °C in 30 minutes and maintained at a constant value for an additional 30 minutes period. During the heating and holding step the pressure increased to values between 230-240 psig. After the holding time was completed, nitrogen was released from the reactor and the oxygen feed line was opened when the pressure decreased to a value of 120 psig. The pressure regulator on the cylinder was previously adjusted to supply an oxygen pressure of 190 psig. After oxygen introduction, evidence of oxidation reaction was confirmed by the instantaneous increase in temperature (as shown in the profiles). When nitrogen was released, temperature decreased to values between 158-162 °C and after oxygen introduction the temperature increased to values between 187-192 °C. The average temperature increment for petro and bio p-xylene oxidation was 31 °C. There was no significant difference in the average value between the two materials. As the temperature of the system is increased, the PID controller shuts down the heater to bring down the
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temperature to the set point of 170 °C. This continuous adjustment in the power output to the heater is the cause of the sinusoidal variation in temperature at ~ 55 minutes.
As the reaction proceeded the pressure in the system decreased, because of continuous oxygen consumption by radical intermediates. After 40 minutes the pressure decreased to a value between 160-170 psig. The heater was removed and temperature decreased gradually. When a value below 118 °C was obtained the reactor was opened and the contents collected. In all experiments some acetic acid was found between the wall of the glass liner and the wall of the reactor. As oxygen introduction was carefully done to avoid bubbling or carryover it was determined that this acid came from the condensation reflux line from the head of the reactor. This acid was added to the glass liner and the contents were weighted to obtain the total amount of material at the end of each run.
Figure 6-5: Temperature and pressure profiles during oxidation of petro p-xylene
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Figure 6-6 Temperature and pressure profiles during oxidation of bio p-xylene
At all stages of the oxidation it was mandatory to maintain both p-xylene and acetic acid in the liquid phase. The process variables recorded with the controller provided reference information to calculate and compare the theoretical boiling point of the mixture existing in the reactor. The Antoine equation (Equation 6.1) was used to calculate the boiling point of individual components using the corresponding parameters
(depending on temperature) shown on Table 6.3.
퐵 퐴 − 푃 = 10 퐶+푇 (eqn. 6.1)
where P is the absolute pressure in mmHg, T is the temperature in Celsius degrees and A, B, C are the Antoine constants values reported in Table 6.3.
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Table 6.3: Antoine equation parameters for different temperature ranges
Range Acetic acid [143] p-xylene [144] Water [145] °C 17-118 118 -227 27 -166 132 -284 1 -100 99 -374 A 7.5596 8.2674 6.9953 6.6579 8.0713 8.1402 B 1644.1 2258.2 1453.4 1172.5 1730.6 1810.9 C 233.524 300.97 215.3 171.2 233.426 244.485
The pressure of the system varied depending on the stage of the oxidation process.
The values recorded in each of the stages where used in the Antoine equation to calculate the boiling point of individual components at each specific pressure. These sets of values were used along with molar composition to calculate the boiling point of the liquid mixture inside the reactor using a simple additive rule. Table 6.4 shows the results obtained. The boiling point of the mixture was close to the individual boiling point of acetic acid, these results were expected as the moles of the acid are always the major component in the liquid mixture. At any stage of the process the boiling point of the liquid mixture was always above the process temperature. We can conclude that the selected operating pressure was adequate for this system to maintain reactant, product and solvent in the liquid phase.
6.2.4 Product composition
As discussed previously, the p-xylene oxidation to terephthalic acid involves a complicated free radical mechanism producing a vast number of intermediates with different oxygen content and colored compounds formed from side reactions of those 159
intermediates. Typically the kinetics and progress of the reaction are explained using the intermediates shown on Figure 6-7, these molecules are preferred for the analysis as the xylene molecule is consumed rapidly at the beginning of the reaction [141].
k k k k 1 2 3 4
p-xylene p-tolualdehyde p-toluic acid terephthalic 4-carboxy- benzaldehyde acid
Figure 6-7: Model intermediate products obtained in p–xylene oxidation
Table 6.4: Boiling point of the liquid mixture inside the reactor at different pressures
Pressure Acetic acid p-xylene Water Mixture psig x1 T°2 x3 T°2 x4 T°2 T°5 200 0.957 233 0.043 277 0.000 197 235 230 0.957 241 0.043 287 0.000 203 243 240 0.957 243 0.043 290 0.000 205 245 120 0.957 209 0.043 245 0.000 176 211 190 0.918 231 0.000 274 0.082 195 228 160 0.918 222 0.000 262 0.082 188 219 1) Constant mol composition considered throughout all the oxidation 2) Boiling point of individual components at each pressure. Obtained from Antoine correlations 3) Constant mol composition up to the point where oxygen is introduced 4) Calculated considering complete conversion of p-xylene
5) Boiling point of the liquid mixture. Calculated using additive rule T°=∑xi*Ti
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Different researchers [146-147] have determined the rate of reaction for each reaction step assuming pseudo-first order kinetics of the concentration of the intermediates. Individual rate laws are written for each intermediate and using experimental data of the concentration at different times a numerical method can be utilized to obtain the constants. In general, there is an agreement on the relative magnitude of the intermediates reaction constants in the following manner: k3 The determining step of the process is the oxidation of p-toluic acid to 4-CBA. The presence of a single carboxylic group in the molecule imparts an electron withdrawing effect retarding the reaction with oxygen [56]. Wang et al. [147] plotted the concentration vs time profiles for the intermediates in the liquid phase oxidation of p-xylene (Figure 6-8). The catalyst system was a mixture of cobalt, manganese and bromine. The experiment was done on a batch mode in a titanium unit. The concentration of terephthalic acid (TA) increased continuously until a constant value was obtained towards the end of the oxidation. The concentration of p- xylene decreased rapidly in the first third of the total reaction time. The intermediates had a bell-shape profile with different maxima and different broadness. The value for the maxima was determined by the effects of the ratio on the rate of production vs the rate of consumption. P-tolualdehyde (TALD) as the first intermediate, was rapidly consumed during the first third of the reaction. As discussed before, the rate of consumption of p- toluic acid (PT Acid) was the slowest step. This is reflected in the high value of the maxima compared with other intermediates and the tailing shape of the bell curve. The concentration of 4-CBA was the smallest among the intermediates at all times in the reaction. This was caused by the rapid reaction constant towards TA formation. 161 Figure 6-8: Concentration of reactants vs time [143] The final product obtained contained primarily TA and presence of some oxygenated remaining intermediates. PT acid and 4-CBA have a significantly higher solubility in acetic acid than TA. Table 6.5 shows solubility data reported by Li [148]. This difference is taken into account for the collection of the final product. Preferably, the separation of the solids is done at process temperature to have the highest solubility and limit co-precipitation of 4-CBA and PT acid with terephthalic acid. In this research it was not possible to obtain concentration data at intermediate reaction times as the reactor used did not have a sampling port/valve installed. The comparison on the use of different raw materials was done on quality variables of the final solid material obtained at the end of the oxidation. Based on the discussion found in 162 literature, it was expected that the oxidation would proceed through the reported intermediates and the final product would contain some impurities. Table 6.5: Solubility data in glacial acetic acid [148] ID T °C S (g PT/100 g Ac. Acid) 79 31.4 97 63.2 p-toluic acid 112 125.6 127 261.7 ID T °C S (g 4-CBA/100 g Ac. Acid) 112 6.23 124 10.18 4-CBA 148 23.09 179 45.25 196 68.71 ID T °C S (g TA/100 g Ac. Acid) 118 0.243 134 0.318 Terephthalic acid 153 0.392 171 0.646 202 1.618 The total conversion of p-xylene was calculated using Equation 6.2 for oxidation experiments using petro and bio based p-xylene. 푃푥 −푃푥 푋 = 표 푓 (eqn 6.2) 푃푥표 where Px0 is the initial mass of p-xylene fed to the reactor and Pxf is the mass of unreacted p-xylene. 163 The amount of unreacted p-xylene was determined by GC-FID analysis of the oxidation liqueur. This liqueur is the liquid obtained after the vacuum filtration step where CTA is recovered (solids produced). It is primarily acetic acid with dissolved catalysts and the soluble and partially soluble impurities. Appendix G shows the detailed calculation of the amounts of unreacted p-xylene. In summary, for each GC chromatogram the area under the curve for the p-xylene peak was obtained and using a calibration factor the amount of p-xylene present was calculated. Table 6.6 summarizes the results obtained for different oxidation experiments using both types of p-xylenes. The weight lost was obtained by comparing the total mass of material at the beginning of the reaction and at the end. This difference is primarily assigned to the production of gaseous compounds during oxidation. These are produced from over-oxidation of hydrocarbon reactants, intermediates and solvent [150]. The average conversion of bio p-xylene was 95.1% with a standard deviation of 3.4 and 95.4% for petro p-xylene with a standard deviation of 3.6. There is no significant difference in the conversion of p-xylene using either of the starting p-xylene products. These conversion values are just below the reported information on literature: 99% [58], 98% [142], 99% [151], 99% [57]. There are different factors related to process limitations in our experimental set-up that can explain the lower conversion values and the amounts of solids produced. These factors are: process temperature, volume of acetic acid used and concentration of initiator. 164 Table 6.6: Comparison of CTA production using petro and bio based p-xylene Total Total p-xylene Solids p-xylene initial p-xylene Material Run # weight unreacted produced conversion weight feed (g) lost (g) (g) (g) (%) (g) 1 25.6 0.83 1.60 0.035 1.00 98 2 24.8 0.86 1.61 0.028 0.98 98 3 25.1 1.04 1.58 0.183 0.96 88 4 25.9 0.97 1.59 0.027 1.10 98 5 25.9 0.90 1.60 0.108 0.99 93 6 28.0 0.87 1.60 0.164 1.00 90 7 27.4 0.79 1.58 0.033 0.92 98 Bio 8 25.4 0.47 1.61 0.035 0.96 98 p-xylene 9 24.9 0.71 1.60 0.144 0.94 91 10 23.7 0.52 1.60 0.025 1.00 98 11 25.7 0.61 1.57 0.033 0.93 98 12 25.6 0.56 1.60 0.152 0.99 91 13 25.7 0.58 1.60 0.057 1.00 96 14 25.9 0.72 1.59 0.069 1.01 96 15 25.1 0.93 1.64 0.078 1.10 95 Avg. 25.6 0.76 1.60 0.078 0.99 95.1 St. Dev. 1.0 0.17 0.02 0.055 0.05 3 1 24.2 1.23 1.64 0.044 1.00 97 2 25.3 1.21 1.59 0.030 1.00 98 Petro 3 25.1 0.59 1.62 0.185 0.98 89 p-xylene 4 26.7 0.46 1.61 0.085 1.04 95 5 24.9 0.79 1.58 0.027 1.01 98 Avg. 25.2 0.86 1.61 0.074 1.01 95.4 St. Dev. 0.8 0.32 0.02 0.059 0.02 4 The analysis of the product composition was done using reversed phase LCMS for the identification of known intermediates and UV spectroscopy for the indirect quantification of colored compounds. For the LCMS technique, the method reported by Viola et al. was used as reference [106]. The solid samples were mixed with methanol and placed in a sonicator bath until complete dissolution was achieved. A well-defined 165 volume (300 L) was injected into the LC column for each analysis. The column used has good performance for reversed phase experiments. A gradient elution technique was used for the complete separation of the analytes. The assignment of peaks was made by injecting a sample of each pure compound into the MS and determining the detection conditions for the produced ion. Quantification of the individual compounds was done using calibration curves. It was expected that the product obtained from oxidation experiments would contain a small concentration of the oxygenated intermediates and organic impurities produced from reactions that follow a different path than the one presented on Figure 6-7. For all analysis, the mass of: p-tolualdehyde, p-toluic acid, 4-carboxybenzaldehyde, terephthalic acid and 2,5 furandicarboxylic (FDCA) was searched for in the MS chromatograms. The latter is a possible oxidation product of the main impurity (2,5 dimethylfuran) present in the bio p-xylene produced as discussed in Chapter 5 [149]. The speculation was that this furan compound can follow radical oxidation by action of the metal catalysts used in p-xylene oxidation. The DMF molecule is a ring unit substituted with two methyl carbons at para position. This is similar to the molecule of p-xylene with a benzyl ring unit and substituted methyl groups in para position. A typical LCMS chromatogram is shown on Figure 6-9. The sample analyzed was crude terephthalic acid produced from oxidation of petro p-xylene. The ion for p- tolualdehyde (mass of 134.7) has a retention time of 21 minutes and the ion for FDCA (mass of 154.6) has a retention time of 12 minutes. These two products were not identified in the sample, therefore no peak is shown on the chromatogram. For p-toluic acid (mass of 134.7) the retention time is 16 minutes. For 4-CBA (mass of 148.7) the 166 retention time is 13 minutes and for terephthalic acid (mass of 164) the retention time is 16 minutes. In some ion chromatogram there are other peaks present. This can correspond to compounds of different mass, obtained after mass breakdown during the analysis. These peaks were not taken into account in the analysis. Figure 6-9: LCMS chromatogram of a product sample of p-xylene oxidation. Top curve (134.7 ion) is for to p-toluic acid. Middle curve (148.7 ion) is for 4-CBA.Bottom curve (164 ion) is for PTA 167 The concentration of each component in solution was calculated using the area under the curve for each peak and calibration curves prepared in the lab for this research. The detailed results obtained for calibration data points can be found in Appendix I. Table 6.7 summarizes the linear parameters used in each curve. To verify the validity of the calibration, the plots of the residuals were obtained confirming there is scattered error for all samples at all concentrations. The curves are therefore valid for the concentrations ranges used. The amount of each solid product in the sample analyzed with the LCMS was calculated using Equation 6.3. The concentration in ppm of the solid product obtained was calculated using Equation 6.4 and the mass yield using Equation 6.5. Table 6.7: Calibration curves parameters and area of validity Product Area range Slope Intercept 4-CBA 4.6x106-9.7x106 8.74E+05 2.46E+06 4-CBA 2.2x104-6.2x105 4.27E+05 -1.02E+05 PTA 6.18x107-1.88x108 4.58E+05 -1.25E+08 p-toluic 9.09x103-1.57x105 2.04E+05 -3.56E+04 푝푝푚 ∗휌∗푉 푚푔 = 푙 푀푒푂퐻 (eqn 6.3) 푠표푙𝑖푑 1000 where ppml is the concentration of the compound obtained using the calibration curves, is the density of methanol, VMeOH is the volume of methanol used to dissolve the sample prior to analysis and the numerical value is a correction factor. 168 푚푔𝑖 푝푝푚푠표푙푖푑 = (eqn 6.4) ∑ 푚푔𝑖 where mgi is the amount of solid product obtained for each individual compound. 푚푔 푠표푙𝑖푑 ∗푠표푙푖푑푠 푚푔 푝 푌𝑖푒푙푑 = 푠푎푚푝푙푒 (eqn 6.5) 푝푥푟푥푛 where mgsolid is the calculated value for each compound using Equation 6.3, mgsample is the total amount of material dissolved in methanol for the analysis, solidsp is the total amount of solids produced during each oxidation experiment and pxrxn is the amount of p-xylene reacted in each experiment (reported on Table 6.6). Table 6.8 summarizes the results obtained for different oxidation experiments. The details of the intermediate calculations can be found in Appendix J.1. Both materials showed high consistency in the amount of CTA produced. The average mass yield for bio p-xylene was 52.3% with a standard deviation of 3 and for petro xylene the average yield was 53.4% with a standard deviation of 2. There was no significant difference in the use of either p-xylene starting material. In general, the mass yield obtained is low compared to reported results in literature where reported yields range from 73-95% [58]. This is attributed in part to the low amount of solids recovered compared to the theoretical stoichiometric maximum and to process conditions that limit the propagation for the radical reaction. In all samples, p-tolualdehyde and FDCA were not identified in the solid product. For p-toluic acid there was a small peak in the chromatogram, but it was not considered as the ratio of signal/noise was low and could not be considered for 169 quantification. The concentration of 4-CBA is within reported values [53-55, 58] for crude terephthalic acid, but too high for this acid to be used in polymer synthesis. Table 6.8: Comparison of yields and impurity content for the liquid phase oxidation of bio and petro based p-xylene Impurities in solid phase Yield solid phase (%) Sample Run (ppm) CTA 4-CBA 4-CBA 1 50.7 0.6 1192 2 49.3 0.6 1210 3 53.6 0.6 1156 4 56.2 0.8 1374 5 53.4 0.9 1711 6 56.1 0.6 1027 7 45.7 0.6 1334 8 48.9 0.6 1242 Bio CTA 9 51.8 0.7 1420 10 51.6 0.8 1562 11 49.7 0.7 1317 12 55.5 0.7 1246 13 52.7 0.8 1519 14 53.8 0.9 1688 15 55.7 0.7 1289 Avg. 52.3 0.7 1352 St. Dev. 3.0 0.1 189 1 52.1 0.6 1155 2 50.2 0.5 1036 3 54.6 0.8 1446 Petro 4 55.8 0.9 1668 CTA 5 54.2 0.9 1568 Avg. 53.4 0.7 1374 St. Dev. 2.0 0.2 241 170 In the LCMS analysis of samples of solid crude terephthalic acid produced using bio based p-xylene, the oxidation product of DMF was not identified. To further investigate if this furan compound would follow oxidation using the AMOCO process, an oxidation experiment was done. P-xylene was substituted with pure DMF and the process conditions and concentrations of catalyst were the same as reported previously. After oxygen introduction, there was no increase in the temperature of the system. The temperature decreased because of the release in pressure and increased to the set point value by action of the PID controller. At the end of the experiment, the glass liner was removed from the reactor and vacuum filtration was done. There was no recovery of solid material in the filter. The liqueur obtained had the same dark (black) coloration obtained when oxidizing p-xylene. To verify if the DMF had remain unreacted or soluble byproducts were formed, GC-FID was done on the liqueur. Figure 6-10 shows the chromatograms obtained for analysis of the acetic acid used as solvent, liqueur from p-xylene oxidation and liqueur for DMF oxidation. The oxidation liqueurs for p-xylene and acetic acid have similar peak positions and numbers of peaks. The peaks at ~30 and ~35 minutes are believed to be degradation products of acetic acid [152]. They are also present in the pure sample of the acid, but with less intensity. The liqueur for DMF oxidation shows a significant difference in comparison with the other samples analyzed. It also contains the peaks of acetic acid and its degradation products. The characteristic peak for DMF appears at retention times ~7 minutes. In the analysis no such peak was identified, inferring that all the DMF reacted. The peak at retention times ~27 minutes corresponds to 2,5 hexanedione. This compound has been identified as a product of DMF reaction with 171 water [129,153,154]. The rest of the peaks were not identified but their presence provides insight that multiple products can be obtained from DMF oxidation. Brezonik [155] reported the production of diacetylethylene and hydrogen peroxide as the main oxidation products of DMF. Even if the furan molecule undergo oxidation to some extent, the products obtained do not seem to precipitate at the conditions used in our experimental set-up. The terephthalic acid produced most likely contained the typical impurities in the form of oxidation intermediates and no compounds produced from furan reactions. uV(x10,000) 5.0 Chromatogram 4.5 2 4.0 3.5 3.0 1 2.5 2.0 3 1.5 1.0 0.5 0.0 -0.5 10 20 30 40 50 min Figure 6-10: GC-FID chromatogram (zoomed view) of DMF oxidation liqueur (top), bio p-xylene oxidation liqueur (middle), acetic acid used in oxidation (bottom). Base shift was used to distinguish individual baselines. Identified peaks: solvent (1), acetic acid (2), 2,5 hexanedione (3) 172 6.2.5 Quality variables As reviewed in Section 2.3.3.1 side reactions of radical intermediates can produce a range of chemicals including: benzoic acid derivatives, phenol derivatives, terephthalic acid derivatives, diphenyl derivatives, benzophenone derivatives, fluorenone derivatives, anthraquinone derivatives and esters [60]. Some of these compounds impart a coloration to the acid or to the final polymer if the CTA were to be used without purification. As complementary analysis to characterize the quality of the produced terephthalic acid, color and optical density measurements were done. The former provides a numerical value to the effect color impurities have on the acid produced. The latter is often used as an indirect measurement to monitor the total concentration of organic impurities. 6.2.5.1 Color The CTA samples were analyzed using the Hunter Lab Color Meter D25. After calibration of the instrument using color standard tiles, the solid product was placed in glass vials and positioned in the opening port of the light chamber for measurement. The L* and b* indices readings were obtained after the readings shown on the Signal Processor Display were stable. Tables 6.9 and 6.10 show the results obtained for bio CTA and petro CTA respectively. Each data point represents a different experimental run. For both materials the average value for L* was in the middle, meaning a white coloration was observed. For b* the results were towards a zero value, meaning there was no distinction between blue and yellow in the sample. To have a point of comparison, color 173 analysis of commercial petro PTA was done. The material was a polyester grade purified terephthalic acid produced by DAK Americas LLC. The L* index obtained was 72 and the b * index was -1.0. There are significant differences in both indices compared to the crude petro and bio acid. The purified acid has a higher L* index towards the white and a b* index towards the blue. This differences observed for the crude acid comes from the presence of colored compounds and organic impurities in the petro and bio CTA produced. Table 6.9: L* and b* values of crude terephthalic acid samples obtained from bio p-xylene oxidation Run # L* b* 1 50.5 0.1 2 52.2 0.0 3 52.7 -0.1 4 52.3 -0.2 5 52.6 -0.2 6 52.1 0.0 7 52.0 -0.2 8 53.1 -0.4 9 52.2 -0.1 10 50.1 -0.1 11 52.6 -0.1 12 50.4 -0.3 13 51.4 0.1 14 51.5 0.0 15 53.5 -0.2 Avg. 51.9 -0.2 St. Dev. 0.9 0.1 174 Table 6.10: L* and b* values of crude terephthalic acid samples obtained from petro p-xylene oxidation Run # L* b* 1 50.8 -0.1 2 45.3 -0.1 3 52.6 0.1 4 47.1 0.1 5 50.1 0.2 6 52.7 0.0 7 51.7 0.0 8 51.1 -0.1 9 52.2 0.0 10 51.0 0.0 Avg. 50.5 0.0 St. Dev. 2.3 0.1 6.2.5.2 Optical density Crude terephthalic acid contains organic colored impurities produced from coupling side reactions occurring during the oxidation of p-xylene [61]. These yellow- colored compounds have structures of the benzyl, fluorenone and anthraquinone type [62]. The characteristic element in this compounds is the presence of chromophores that absorb light in the visible and ultraviolet range. Terephthalic acid does not absorb significantly in this range therefore measurement of the optical density (OD) can be used as an indirect indication of the concentration of colored impurities. OD is usually the reference variable used by researchers to assess the quality of the terephthalic acid produced and to monitor the reduction of organic impurities during the purification process of the acid (hydrogenation). Equation 6.6 shows the formula used to calculate OD. 175 퐴 푂퐷 = 340 (eq. 6.6) 340 퐿 where A refers to the absorbance at a wavelength of 340 nanometers and L refers to the distance in centimeters that light passes through the sample inside the cuvette. For all analysis, solid samples were dissolved in 4N NH4OH solution for 30 minutes. The correction in the absorption of the solvent was eliminated by running a background with pure solvent before each determination. The results obtained are shown in Figure 6-11. Due to the high amount of product required (~0.3 grams of the ~1.0 grams of material produced in each oxidation experiment) for this analysis, only selected samples of petro and bio CTA were analyzed. Commercial PTA produced by DAK Americas LLC. was analyzed to serve as reference. In average, the OD of the commercial product is 5 times smaller than the petro and bio CTA. This increased value in the acid samples produced in the lab confirms the presence of colored compounds in the acids produced. These results confirm the difference seen in the b* index measurement, where the numerical value showed a tendency towards the yellow color. Zuo et al. [58] measured OD340 values between 0.58-1.30 in CTA samples produced in lab scale oxidation of p-xylene with CO2 expanded acetic acid. Zeitlin et al. [156] obtained OD values ranging from 0.850-1.183 in samples recovered from sequential crystallizers in an industrial scale process. The CTA products obtained from petro and bio p-xylene have concentrations of organic impurities within the range found by other researchers. 176 0.90 Petro CTA 0.80 Bio CTA 0.70 0.60 Commercial PTA 0.50 0.40 0.30 Optical density Optical 0.20 0.10 0.00 Figure 6-11: Comparison of OD measurements for petro CTA, bio CTA and commercial PTA 6.3 Purification of CTA CTA is not suitable for use in polymerization due to the presence of impurities that can impart a coloration to the polymer produced and limit the maximum molecular weight attainable during polymerization. These impurities containing mono-functional groups can hinder the reaction rate and limit the build-up of molecular weight. For condensation polymerization, the functionality of the reactants should be the same. This is, the concentrations of end groups of different natures (i.e. hydroxyl and carboxyl) should be the same and this relationship should be maintained throughout the polymerization to attain high molecular weight polymer. The presence of mono- functional groups contribute terminal chain units incapable of reacting with other molecules. Flory [2] proposed a mathematical relationship to calculate the degree of 177 polymerization (DP) (Equation 6.7) based on the concentrations of functional groups (Equation 6.8). If only monomers with the same functionality are used (r=1) the attainable DP at conversion of 99% is 100, but if a mono functional group is present at a low concentration, i.e. 0.5 mol % (r=0.99) the DP at conversion of 99% drops to 67. This marked effect of monomer quality requires the use of reactants with very low concentrations of impurities to obtain high molecular weight polymers at high conversions. CTA should be purified to decrease the concentration of mono functional groups (i.e. 4-CBA) and to decrease the concentration of organic impurities and colored products. 1+푟 퐷푃 = (eqn. 6.7) 1+푟−2푟푝 where r is the ratio number of A and B groups present at the beginning and p is the degree of conversion. 푁 푟 = 퐴퐴 (eqn. 6.8) 푁퐵퐵+2푁퐵 where NAA is the total number of A groups initially present, NBB is the total number of B groups initially present and NB is the total number of monofunctional groups present. 178 6.3.1 Experimental The experimental set-up used for this research consisted of a 50 ml stainless steel reactor (4590 Micro Bench Top Parr Reactor) equipped with a 4-blade propel stirrer, a pressure transducer installed on the head of the vessel, a thermocouple that read the temperature of the reacting mixture, a safety release valve installed on the head (with a burst pressure safety limit of 3000 psi) and a gas feed line connected to the head of the vessel that introduced gas to the headspace of the reactor. The service cooling water for the condenser was pumped from an auxiliary water bath set at 0 °C. The heating of the system was done using a band heater installed on the outside surface of the vessel. This heater was controlled by a PID unit calibrated with liquid acetic acid at the operating temperatures of the oxidation. The thermocouple and pressure transducer were connected to a main controller that continuously recorded the temperature and pressure of the system. The product of the reaction was transferred to a vacuum filtration unit where water was separated from the solid phase containing the catalyst, the purified acid and any water insoluble impurities. The solids were mixed with a solvent and heated to a desired temperature to dissolve the purified acid and maintain the catalyst in solid form. The catalyst was removed using vacuum filtration and the filtrate containing the dissolved acid was placed in a cold bath. As the temperature decreased the purified acid and some impurities co-precipitated and they were removed from the solvent using vacuum filtration. The process diagram of the experimental set-up used in this work is 179 shown on Figure 6-12. The labels shown in the diagram are used to explain the experimental procedure. In a typical experimental run, crude terephthalic acid (CTA), Pd on activated carbon (CATALYST) and deionized water (WATER) were mixed in the glass liner until homogeneity was obtained. Figure 6-13 shows the glass liner with the CTA and Pd inside. The liner was placed inside the reactor and the vessel was closed. The system was flushed with nitrogen for 5 minutes; the flow of gas was set to a value that avoided carryover of the reactants. After flushing, a gas mixture containing 2% hydrogen and 98% nitrogen (HYDROGEN) was fed to the reactor until the internal pressure of the vessel reached a value of 600 psig. Agitation was gradually increased to a value of 250 rpm after 10 minutes and the heater was set to a ramp profile reaching 240 °C after 50 minutes. Once the temperature was achieved the system remained at constant temperature for 70 minutes before stopping the heater. The temperature decreased gradually and the reactor was opened when the temperature of the system was below the normal boiling point of water (100 °C). Once the reaction was completed, the contents of the glass liner were filtered using vacuum filtration. The purified acid and carbon were retained in the filter and the deionized water (WATERW) was collected on the flask. Figure 6-14 shows the separation in the vacuum filtration unit. The filtrate (TACAT) was then mixed with N,N- dimethylacetamide (SOLVENT) and homogenized using a magnetic stirrer. This mixture was heated to 80 °C for 30 minutes to dissolve the terephthalic acid in the solvent. After this time and while the mixture was at high temperature, the contents were separated using vacuum filtration. The solid phase consisted of catalyst and insoluble impurities 180 (CATALYSW). The filtrate containing the dissolved purified acid was cooled down using a cold bath to promote precipitation of the acid. The cold sample was separated using vacuum filtration. The solvent N-N-dimethylacetamide was obtained as filtrate (SOLVWAST) and the purified terephthalic acid was obtained as solid particles (PTA). The recovered acid was washed three times with fresh N-N-dimethylacetamide at room temperature. To remove any remaining solvent, the acid was dried at 110 °C for 8 hours in a drying oven. 181 HYDROGEN P I T I SOLVENT CTA T I CATALYST WATER PTACAT CATALYSW PUR FILT DISOL FILT2 WATERW PTA COOL FILT3 SOLVWAST Figure 6-12: Process diagram for the purification of crude terephthalic acid to purified terephthalic acid 182 Figure 6-13: Crude terephthalic acid and palladium over activated carbon inside the reactor glass liner Figure 6-14: Separation of water (filtrate) from PTA and palladium (solids) using vacuum filtration 183 6.3.2 Process conditions rationale A typical process used for the reduction of impurities in CTA is hydrogenation. This type of addition reaction usually done on a supported metal catalyst, such as Pd on carbon, is commonly used for hydrogenation of compounds with double bonds in some part of their molecules. The mechanism for the reaction includes three steps. First, the hydrogen attachment to the metal of the catalyst forming metal-hydrogen bonds and the metal ligand of the compound with the double bond to the surface of the catalyst. Second, the transfer of hydrogen atoms to the compound forming carbon-hydrogen bonds. Third, the detachment of the saturated compound from the surface of the catalyst [157]. Once the saturated compounds are formed the catalyst does not have any more ligand points and activity is decreased. Catalyst deactivation can be caused by metal sintering, palladium loss, poisoning, and deposition of metallic terephthalates or polymers [158]. These problems occur in industrial operation as the catalytic bed is used over a period of time. In this research, fresh catalyst was used in each experimental run, therefore it was expected that catalytic activity would be the same in all experiments. The produced petro and bio CTA contained 4-CBA and organic impurities (as determined by OD measurements) at determined concentrations and remaining catalyst metal particles at very low concentrations. During hydrogenation, the unsaturated part of these compounds transformed to saturated units. In the case of 4-CBA the product of a first hydrogenation is p-toluic acid. If allowed to continue p-tolualdehyde and ultimately p-xylene can be formed. This is an opposite trend in comparison to the intermediates 184 obtained during the oxidation reaction (Figure 6-7). The extent of hydrogenation of the molecule depends on the process conditions used during the experiments. Two moles of hydrogen react with 1 mole of 4-CBA to produce 1 mole of p-toluic acid. It is preferred to supply hydrogen at 3 times the stoichiometric amount [159]. In a typical process, water is used as solvent for the reaction. The solid reactant and catalysts are mixed to make slurries with 7-25 weight %. Water is used as solvent to maintain the formed products dissolved and to maintain the purified acid in solid phase. The temperature of the system is set at values between 170 and 300 °C. At higher temperatures than this range the catalytic activity decreases as the surface area is diminished by metal sintering due to thermal effect [160]. The pressure of the system is determined by the temperature of the hydrogenation (it should be high enough to maintain a liquid phase throughout the reaction). The process values are usually between 200 and 1500 psig. In this research, a process temperature of 240 °C and pressure of 600 psig were used. At this pressure the boiling point of water (calculated using the Antoine equation) is 250 °C, which is above the purification process temperature. Based on literature review the conditions selected for the experiment seem to fulfill the requirements for hydrogenation reaction. No preliminary testing was done as the amount of CTA available was limited. 6.3.3 Process analysis Hydrogenation reactions of petro and bio CTA were done until all the material was consumed and purified. 10 hydrogenation experiments were done for bio p-xylene 185 and 5 for petro p-xylene. The product quality results presented in the following sections are representative of the material that could be obtained at any oxidation experiments. Not all the materials produced were tested in order to maximize the amount available for polymerization. The mass balance of the reactants fed to the system in each hydrogenation run is shown on Table 6.11. The amount of acid purified in each run was dictated by recommendations of safe reactor operation determined by Parr Instruments. The number of CTA grams processed was calculated considering 30 grams as the maximum amount of reactants, 13.5 weight % as the concentration of the slurry and 4.5 as the molar ratio to catalyst. Table 6.11: Crude terephthalic acid/deionized water slurry mass balance Compound grams wt % CTA1 4.0 13.5% 10% Pd on carbon2 0.6 1.9% Deionized water 25.1 84.6% Total 29.6 1) Crude terephthalic acid obtained from bio or petro p-xylene oxidation 2) Molar ratio of 4.5:1 CTA:Pd/C In an industrial operation, the recovery of purified acid is typically done in a series of stage crystallizers operating at different temperatures, followed by a washing step to remove particles and drying to evaporate any remaining solvent. For this research, the product obtained from hydrogenation reactions was separated using vacuum filtration. The solid phase contained the PTA and the Pd/C catalyst. To recover the acid, a solvent with high PTA solubility and low Pd/C solubility is needed. N,N-dimethylacetamide was selected based on information found in literature [161]. Table 6.12 shows the mass balance used for the dissolution of the acid. 186 Table 6.12: Purified terephthalic acid / N,N-dimethylacetamide initial material balance for washing process Compound MW Mol Ratio mol Grams Terephthalic Acid 166.13 1 0.02 4.0 N-N-dimethylacetamide 87.12 5 0.12 10.5 Total 14.5 Process conditions (temperature and pressure) were continuously recorded in all hydrogenation experiments. Figure 6-15 and 6-16 show the temperature and pressure profiles for a typical run using petro and bio CTA. After flushing the system with pure nitrogen, a gas mixture of 2% hydrogen and 98% nitrogen was introduced in the system to set a pressure of 600 psig. The controlled heating increased the temperature to the operating condition of 240 °C in a period of ~50 minutes. Pressure increased due to the temperature increase reaching a value of ~780 psig at the end of the heating ramp. The temperature was held constant for 70 minutes to allow for reaction to occur. Hydrogenation is an exothermic reaction. During the experiments the thermocouple did not registered any unusual incremental change in temperature. This was due to the relatively small concentration of impurities (reactive molecules). At the end of the hold time, the heater was stopped and temperature decreased gradually. When the value was below 100 °C the reactor was opened and the glass liner with the products was removed from the reactor. All the materials were contained inside the glass liner, there was no liquid product in the wall between the liner and the reactor or condensation formed in the head of the reactor. We can conclude that the operating conditions used fulfilled the requirements for hydrogenation reaction. 187 400 1000 Temperature Pressure 350 900 800 300 700 250 600 C) 200 500 ° 150 400 300 100 200 50 100 (psig) Pressure ( Temperature 0 0 0 20 40 60 80 100 120 140 160 180 Time (min) Figure 6-15: Temperature and pressure profile during hydrogenation of petro CTA 400 Temperature Pressure 1000 350 900 800 300 700 250 600 C) 200 500 ° 150 400 300 100 200 50 100 (psig) Pressure Temperature ( Temperature 0 0 0 40 60 80 20 100 120 140 160 180 Time (min) Figure 6-16: Temperature and pressure profile during hydrogenation or bio CTA 188 6.3.4 Product composition The progress of hydrogenation reactions are typically monitored by measuring the concentrations of intermediates (i.e. p-toluic acid) with time and the optical density of the final purified acid produced. In this research, the effect of hydrogenation was determined based on purity and quality variables of the purified acid obtained. All the samples produced were analyzed in the same manner as the CTA obtained from oxidation experiments. Quantification in LCMS analysis was also done using the calibration curves reported in Appendix I. Table 6.13 summarizes the results obtained for different hydrogenation reactions using petro and bio CTA. The weight lost in each run was negligible and not considered in the material calculations. For both CTA materials, there was an average decrease of 1 gram after hydrogenation. This weight loss was attributed primarily to the solubility of compounds (p-toluic acid, 4-CBA, fluorenone derivatives, etc) in water. The original CTA had a certain concentration of these byproducts and as hydrogenation proceeds the colorless reduced compounds also became soluble. A second factor (of less effect) was related to the separation procedure, as not all the material was recovered during the filtration step. An additional loss of PTA occured during the filtration of the dissolved acid in N,N-dimethylacetamide. When the mixture was heated to high temperatures the acid became soluble and the solution was filtered using vacuum filtration. During filtration some of the acid precipitated due to the thermal difference between the solution and the filtering unit, some of this acid remained inside the filtration funnel mixed with catalyst particles. The average lost was 0.5 grams. The overall mass yield of recovered 189 bio PTA was 63% with a standard deviation of 6.5 and 57% for petro PTA with a standard deviation of 4.9. There was no distinctive difference in the production of PTA using either bio CTA or petro CTA. Figure 6-17 shows the PTA products obtained after drying to evaporate remaining solvent. Table 6.13: Comparison of hydrogenation experiments using petro and bio CTA Solids Total initial CTA feed Mass PTA Material Run # produced1 PTA2 (g) weight (g) (g) Yield % (g) 1 29.3 3.7 2.8 2.4 65 2 29.5 3.9 2.9 2.1 54 3 29.6 4.0 3.3 2.9 72 Bio 4 29.6 4.0 3.2 2.6 65 CTA 5 29.5 3.9 3.0 2.3 59 6 29.5 3.9 3.1 2.7 69 7 29.6 4.0 2.9 2.2 55 Avg. 29.5 3.9 3.0 2.5 63 St. Dev. 0.1 0.1 0.2 0.3 6.5 1 29.6 4.0 3.1 2.3 58 2 29.6 4.0 2.6 2.0 50 Petro 3 29.6 4.0 2.7 2.2 55 CTA 4 29.8 4.2 3.3 2.8 67 5 29.6 4.0 3.2 2.3 58 Avg. 29.6 4.0 3.0 2.3 57 St. Dev. 0.1 0.1 0.3 0.3 4.9 1) Solid product recovered after removal of water in vacuum filtration 2) Dried PTA recovered from cold N,N-dimethylacetamide using vacuum filtration 190 Figure 6-17: PTA after drying @ 110 °C for 8 hours The concentration of individual components was obtained from calibration curves and readings of area under the curve for each ion mass. Equation 6.9 shows the formula used to obtain the purity of the PTA. The mgsolid were calculated using Equation 6.3 and the concentration of impurities in ppm were calculated using Equation 6.4. 푝푝푚𝑖 푃푇퐴푝푢푟푖푡푦 = (eqn 6.9) ∑ 푝푝푚𝑖 where ppmi is the amount of each individual component present in the solid product. Table 6.14 summarizes the results obtained for different hydrogenation experiments. The details of the intermediate calculations can be found in Appendix J.2. As expected, in the LCMS analysis of the PTA samples no peaks for FDCA and p- tolualdehyde were detected. The concentration of 4-CBA in bio acid decreased from 191 1,352 ppm to 68 ppm and for petro CTA the concentration decreased from 1,374 to 84 ppm. This significant decrease in the concentration of 4-CBA proves the efficiency of the method to hydrogenate unsaturated compounds. To have a reference on the quality of the acid produced, commercial PTA was analyzed. The concentration of 4-CBA In the commercial product is lower than the average value in bio and petro PTA. This difference may limit the ultimate molecular weight obtained in polymerization of the produced PTA products. The purity of the material is consistent between experimental runs and no distinction is evident in the use of either CTA samples. 192 Table 6.14: Comparison of solid PTA product quality after hydrogenation over Pd catalyst of crude petro and bio terephthalic acid with commercial PTA Impurity in solid phase (ppm) Sample Run PTA purity (%) 4-CBA 1 99.79 85 2 99.78 61 3 99.80 63 4 99.79 63 Bio PTA 5 99.86 74 6 99.87 71 7 99.89 59 Avg. 99.83 68 St. Dev. 0.04 10 1 99.76 69 2 99.80 62 3 99.84 82 Petro PTA 4 99.86 96 5 99.82 111 Avg. 99.82 84 St. Dev. 0.03 17 1 99.95 50 2 99.95 53 3 99.95 53 4 99.95 50 Commercial PTA1 5 99.95 45 6 99.96 43 7 99.96 42 Avg. 99.95 48 St. Dev. 0.005 5 1) PTA produced by DAK Americas LLC 193 6.3.5 Quality variables The purified acids produced were analyzed for their color and optical density following the same procedures used for analysis of CTA samples. 6.3.5.1 Color The color measurements of bio and petro PTA samples were done using the Hunter Lab Color Meter D25. Figures 6-18 to 6-21 show the results obtained and the comparison with color readings of CTA material. Each data point represents a different CTA or PTA material. For the petro product the b* changed 0.17 units and for the bio product the change was 0.28. This change means both products have a color with tendency to the blue limit. The L* increased 13 units for the petro product and 10 units for the bio product. This increase means the products have a higher tendency to the white limit. The change in this color index is related to the removal of remaining catalyst particles from the oxidation process. During the dissolution of the acid in the amide solvent, the catalyst particles remained in solution and can be separated along with the Pd/C catalyst in the filter. The changes in color are in agreement with the reduction of concentration of 4-CBA and hydrogenation of polyaromatic colored compounds. 194 0.6 b* CTA Avg = 0.01 0.4 PTA 0.2 Avg = -0.18 0.0 -0.2 -0.4 -0.6 Figure 6-18: b* color change for CTA and PTA products obtained from petro p-xylene 0.8 b* CTA 0.6 Avg = -0.08 0.4 PTA 0.2 Avg = -0.36 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 Figure 6-19: b* color change for CTA and PTA products obtained from bio p-xylene 195 L* 75.0 65.0 55.0 45.0 CTA Avg = 50.5 35.0 PTA 25.0 Avg = 63.5 Figure 6-20: L* color change for CTA and PTA products obtained from petro p-xylene 75.0 L* 70.0 65.0 60.0 55.0 50.0 45.0 CTA 40.0 Avg = 51.9 35.0 PTA 30.0 Avg = 61.0 Figure 6-21: L* color change for CTA and PTA products obtained from bio p-xylene 196 6.3.5.2 Optical density The OD results obtained for petro and bio PTA are shown on Table 6.15. Only two samples of each material were analyzed to maximize the amount available for polymer synthesis. The average decrease in OD is 88% for petro PTA and 90% for bio PTA. This significant decrease is caused by the hydrogenation of colored compounds decreasing their concentration in the purified acid. Zeitlin et al. [156] reported a decrease of 90% in OD from 0.850 to 0.080 after hydrogenation of CTA at 282 °C in a continuous industrial process. The average OD of commercial product (Figure 6-11) is 0.12. This is a purified terephthalic acid, therefore a direct comparison can be made with the material produced in this research. The concentrations of petro and bio PTA are within values found in literature for purified products. Both materials followed hydrogenation producing PTA of comparable quality. Table 6.15: Comparison of OD measurements for petro and bio CTA and PTA Optical Density =340 Sample ID Run # CTA PTA 1 0.60 0.08 Petro 2 0.65 0.06 1 0.59 0.03 Bio 2 0.57 0.08 197 6.4 Summary Results obtained from the production of CTA and the purification to PTA using a modified AMOCO process were presented in this section. The discussion included the quality analyses of the materials produced and their comparison with commercially available PTA. A modified AMOCO process was successfully developed to produce crude and purified terephthalic acid using bio and petro p-xylene as the starting material. The acid produced in each stage was comparable in quality variables (color and optical density) to commercial product. Bio p-xylene at a concentration of 99.98% was used to produce crude and terephthalic acid with no identified difference in the processing and product quality against the petro counterpart (i.e. petro p-xylene). The furan (2,5 DMF) impurity in bio p-xylene at concentration of 0.1% does not affect the quality of PTA produced compared to a petro p-xylene counterpart. This compound does not oxidize to form 2,5 FDCA under a modified AMOCO process. 198 Chapter 7 Synthesis of PET using Bio Derived Monomers 7.1 Introduction Polyethylene terephthalate is a polyester used to produce containers for different applications such as: water, soft drink bottles, clear drinking cups, films and clothing. The versatility of PET is obtained through the various states of molecular arrangements that can be achieved through processing. PET produced through melt phase polymerization typically follows a two stage process, in the first part, PTA and EG react to create a monomer unit (BHET) in the esterification phase. This is an autocatalytic process done under nitrogen environment. In the second part, the monomer is mixed with metal catalysts in a full vaccum system to promote chain growth by removal of the side product EG. This is an equilibrium reaction limited by the efficient removal of the byproduct. This chapter describes the melt phase polymerization of bio and petro raw materials in a batch process. The petro EG is commercially available and was purchased from Fisher Scientific. The petro PTA was donated by DAK Americas LLC. The bio EG was donated by an Industrial Partner member of the PET Consortium (the material was 199 used as received). The bio PTA was produced in this research as described in detail in Chapter 6. The polymerization with bio EG and petro PTA was done in a kilogram-scale reactor as enough material was available. The polymerization with bio EG and bio PTA was done in a gram-scale Parr reactor, due to the limited amount of PTA available. The effects of using eitherof the raw materials were investigated by an assesment of the production processes and the characterization of the polymers produced. The results obtained and described in this section are expected to validate or disprove our hypotesis that bio derived raw materials (with purity comparable to that of commercially available petro counterparts) will produce a polymer with the same characteristics. 7.1.1 Review of polymer properties PET is a semi crystalline polymer widely used in different applications including fibers, packaging and films. For each application, certain characteristics of the polymer are exploited. During synthesis, the formation of side products from degradation or competing reactions modify the quality of the polymer obtained. In some cases, the side product does not interact with the polymer, but it is used to monitor degradation reactions (i.e. acetaldehyde). The change of end groups during polymerization is used to monitor the extent of reaction obtained and to verify the occurrence of degradation reactions. As a semi crystalline polymer, PET has different performance depending on the morphology of the sample. Molecular arrangement is influenced by several parameters such as molecular weight, copolymer content, melting point, glass transition temperature, and also by processing parameters such as thermal and stress history [4]. Molecular weight 200 and chain modifiers such as isophthalic acid (IPA), cyclohexanedimethanol (CHDM) and diethylene glycol (DEG) change the rate of crystallization of the material, the melting point and in some cases the glass transition temperature. Table 7.1 summarizes the interactions among end groups, side products, polymer properties, polymerization and degradation reactions. This information is presented to provide a general overview of the complex relationship between polymer properties and its formation and processing. A brief discussion of each effect is included immediately after the table. 201 Table 7.1: Influence of side products on polymer properties and polymerization/degradation reactions Thermal Melting Glass Crystallization Polymerization Variable / Compound Hydrolysis Discoloration stability point transition rate rate Acetaldehyde P E Diethylene glycol R E E E R Vinyl end groups R E Carboxyl end groups R P E E R Hydroxyl end groups R P R Water E R E E E R Molecular weight E E E E E R P Residual catalyst R E E R R P means the variable/compound is a product of the reaction R means the variable/compound is a reactant for the reaction E means the variable/compound has an effect on the listed property/reaction 202 For thermal stability, after chain scission occurs due to heat effects, the vinyl end groups generated can react with hydroxyl and carboxyl end groups producing acetaldehyde. The DEG linkage can also be ruptured due to reaction with oxygen at high temperatures producing vinyl end groups. These reactions are accelerated by the presence of catalyst. The molecular weight of the polymer determines the length of the chain. In the case of higher molecular weight polymers, the longer chains provide more potential links that may suffer degradation. Water present at elevated temperatures has a net positive effect in thermal stability as it reduces the rate of degradation; however, this is at the expense of increased hydrolytic degradation. For hydrolysis, water at elevated temperatures reacts immediately with the polymer chains causing a decrease in molecular weight and the formation of carboxyl and hydroxyl end groups. This reaction is acid catalyzed and is accelerated by the presence of residual catalyst. At any stage of polymer processing or during sample testing at elevated temperatures, the moisture level of the polymer should be maintained at a minimum (i.e. 25 ppm). For polymerization rate, esterification proceeds by the reaction of hydroxyl and carboxyl end groups in the raw materials producing a monomer unit (BHET). This unit reacts with itself or with chain modifiers (i.e. DEG) via a metal complex generated by the presence of metal catalyst. The concentration of catalyst should be high enough to accelerate polymerization, but not so high as to cause metal precipitation. As an equilibrium reaction, the removal of the byproduct (EG) is mandatory for the build-up of molecular weight. 203 For discoloration, the thermal and thermal oxidative degradation can produce intermediates (i.e. vinyl end groups and radical compounds) that produce colored compounds, which are typically formed by subsequent degradation of the products obtained from thermal and thermal oxidative degradation. In the case of melting point and crystallization rate, these physical properties are directly related to the ease with which polymer chains are able to align into ordered structures. The increase of the molecular weight of the polymer reduces the rate of crystallization and increases the melting point. During thermal analysis, the presence of carboxyl end groups and residual catalyst can cause an apparent increase in the molecular weight of the polymer, reducing the rate of crystallization. The presence of water as a disruptive chain element, modifies the molecular weight ultimately affecting crystallization and melting point. Any molecule that modifies the structure of the chain (i.e. DEG, IPA, CHDM), affects the alignment of the polymer under thermal effect or under stress. This limitation in the molecular arrangement affects the formation of crystals and the melting point. There is a multi-variable highly interrelated relationship among polymer properties, concentration of side groups, processing conditions, physical properties, polymerization conditions and degradation reactions. Due to these relationships, the characterization of a polymer cannot be done by a single test/analysis. The evaluation of polymer properties should be done considering all the factors previously mentioned and the interference some variables can have in the interpretation of the results. In this research, PET was synthesized using petro and bio raw materials. In both cases, the polymerization conditions were maintained the same (to the best of our 204 experimental capabilities), to minimize side reactions and to identify differences in polymerization caused by the use of a different raw material and not related to a polymer property. The polymers produced were tested for their physical properties by obtaining their molecular weight and color. For their product composition, by measuring residual catalyst, carboxyl end groups concentration, copolymer content and residual acetaldehyde. For their thermal stability, by monitoring acetaldehyde generation, vinyl end groups concentration and thermogravimetric analysis. Crystallization behavior was evaluated through isothermal crystallization, dynamic crystallization and by determination of crystallite size in crystalline materials. The cumulative analysis of these variables allowed us to do a comparison among the polymers and to determine if the use of different raw material had an effect in the polymer produced. 7.2 Synthesis of PET using bio EG and petro PTA 7.2.1 Experimental The experimental set-up used for this polymerization, consisted of two 3 liter reactors connected through a heated transfer line. The first vessel (used for esterification) was equipped with a double 4-blade propeller distanced 15 cm from each other over a central shaft, a thermocouple installed in a thermowell at the base of the reactor, a 10 cm feed port at the head of the vessel, a gas feed line connected to a port in the head of the vessel, a metering drain valve installed at the bottom of the vessel and connected to the transfer line, a pressure transducer installed in the head of the reactor and an exhaust line 205 for vapors installed on the head of the vessel. This exit line was insulated and connected to a distillation column. The column separated the water/glycol mixture obtaining a water rich stream in a buffer tank from the overhead and a glycol enriched reflux into the reactor. The product from the first vessel was transferred to the second vessel using a transfer line. This ¾” transfer line was wrapped with heating tapes and covered with insulation material to maintain temperature. The second vessel was equipped with a helix impeller, a thermocouple installed in a thermowell at the base of the reactor, a 10 cm feed port at the head of the vessel, a drain port at the bottom of the vessel, a pressure transducer installed in the head of the reactor and an exhaust line for vapors installed on the head of the vessel. This exit line was connected to a double tube condenser. The outlet was connected to a buffer tank and then to a cold trap operated with liquid nitrogen. The exit port of the cold trap was connected to a vacuum pump and any non- condensable products were removed from the system through this pump. The process diagram of the experimental set-up used in this work is shown in Figure 7-1. The labels shown in the diagram are used to explain the experimental procedure. In a typical experimental run, PTA (PTA), EG (EG) and trimethylamine (TEA) were introduced to the esterification unit through the feed port. The latter is used to control the production of diethylene glycol. It modifies the pH of the reacting medium limiting the formation of the byproduct. The reactor was flushed and pressurized to 17 psig with nitrogen (constant value throughout the reaction), the stirrer was set at 47 rpm and the contents were heated to 205 °C during 90 minutes. This step is usually called paste-mixing, the solid PTA was only dispersed in the liquid phase glycol as solubility is limited (see Section 2.1). Once the paste was homogeneous, the temperature of the 206 system was increased to 250 °C within a time period of two hours. During this time the formation of the monomer BHET occurred. As this molecule is formed the solubility of the PTA increases and its reaction with EG is favored [16]. The rpm of the system were increased to 188 (maximum setting) and the temperature was maintained at 250 °C until the reaction was finished. The progress of the reaction was monitored by temperature readings in the distillation column and the amount of water produced. The column was used to separate the water/glycol mixture produced during esterification. The temperature in the column was monitored by three thermocouples positioned at the bottom, middle and top. The gas effluent (primarily water) passed through a double tube condenser operated with cold water at ~10 °C and the condensate was directed to a three-way solenoid valve controlled by a timer. After 20 seconds, the valve opened the exit line for 2 seconds allowing liquid into a buffer tank (WATER). Once the valve closed a new timer was started, after 40 seconds the valve opened the reflux line for 2 seconds allowing liquid to recirculate into the top part of the column. The bottom liquid stream of the column with a higher concentration of glycol (EGR) was recycled back to the reactor. In this stage, monomer units (BHET) were obtained along with some small chain oligomers, called prepolymer. Due to the long reaction time for esterification, the product was collected from the vessel and allowed to cool down for 4 hours. After temperature equilibration, the material was crushed in small pieces and dry overnight in a vacuum oven. The dried product was introduced in into the second vessel (polycondensation unit) through the feed port at the head of the reactor (BHET). Nitrogen was introduced to maintain a pressure of 17 psig and the contents were heated to 285 °C to melt the 207 material. Once a uniform liquid phase was obtained, the system was depressurized and the catalyst solutions were added (SB2O3 and COAC) along with drops of phosphoric acid (H3PO4). The latter, is a thermal stabilizer used in polymer synthesis to reduce the occurrence of degradation reactions during synthesis. The phosphorous interacts with the metal-monomer transition complex retarding the reaction of end groups with carbon atoms in the polymer chain [35]. After catalyst introduction, the system was pressurized to 17 psig with nitrogen and allowed to react at 285 °C for 1 hour to promote coordination of the catalyst with the prepolymer. The pressure was then decreased gradually to atmospheric conditions over a period of 1 hour. After this time, the vacuum pump was started and the valve at the exit of the cold trap was slowly opened. Once full vacuum was obtained the system was allowed to react until a desired molecular weight was obtained. EG was continuously removed from the system (EGP) to shift the reaction towards products. The product was collected from the drain valve at the bottom of the vessel introducing a small positive pressure of nitrogen. The molten product (PET) extruding from the reactor was immediately quenched in a water bath and pulled by an external rotor to create strands of polymer. These strands were then processed in a pelletizer to obtain the polymer in pellet form. For esterification, the total mass of prepolymer produced and the amount of water collected in the buffer tank were used to analyze the extent of reaction in this stage. For polycondensation, the polymer pellets and the ethylene glycol recovered from the cold trap were used. 208 T I WATER T I T I P I T I T I EG EGR PTA P I T I TEA ES EGP BHET SB2O3 PC COAC PET H3PO4 Figure 7-1: Process diagram for the production of PET from petro PTA, petro EG and bio EG. 209 7.2.2 Preliminary experiments and process conditions rationale The reactor system used in this section has been widely studied by previous students in the Polymer Institute. The experimental method followed by them was used with minor modifications. The material balance was calculated to operate the system at 65% capacity as this was the recommended safe value provided by the manufacturer. Preliminary experiments were done to identify potential sources of error and verify consistency in the product obtained. The major problematic area was related to the addition of catalyst to the molten material. The catalysts were dissolved in hot EG (~100 °C) and added to the molten prepolymer (~285 °C) through the opening port at the top of the reactor. When the catalyst solution touched the product some of the glycol evaporated instantaneously due to the thermal difference. This caused the loss of some catalyst as the solution flashed to the walls of the reactor and to the stirrer shaft. To minimize variations from this source a funnel with a long stem was used for the addition of catalysts. 7.2.3 Process analysis After process conditions for polymerization were determined, the polymerization was done with two sets of raw materials. Petro PTA and petro EG were used for one batch and petro PTA with bio EG were used for the second one. Table 7.2 shows the mass balance of reactants used for the esterification reaction using the first vessel in the reactor set-up. As discussed in the introduction of Section 6.3, to attain high molecular weight material during polymerization the concentration of functional groups should be 210 the same at all times during reaction. Typically, an excess of EG in the range of molar ratio 1.2 to 1.5 is used to compensate for losses of EG in the distillation column or by degradation due to high temperatures [162]. For this research, a molar ratio of 1.5 [EG]/[PTA] was selected. In addition to the reactants shown in Table 7.2, 3 drops of TEA were added to the system to reduce the formation of DEG. Table 7.2: Initial material balance for esterification reactions ID M.W. mol1 grams PTA 166.1 6.02 1000 EG 62.0 9.03 560 1) Mol ratio [EG]/[PTA] = 1.5 The process conditions (temperature and pressures) were continuously monitored during the experiments. The reactor unit did not have an automatic recorder; therefore any reading obtained was recorded manually. The progress of the reaction was monitored by checking the temperature of the different stages in the distillation column and by the level of water collected in the buffer tank over time. Figure 7-2 shows the cumulative plot of water collected during esterification reactions. The reading was expressed in centimeters, as this was the level of water inside the vessel, 0.5 cm was the zero value. Figure 7-3 shows the temperatures of the three thermocouples in the distillation column during esterification reactions. 211 Petro EG Bio EG 4.0 3.5 3.0 2.5 2.0 1.5 (cm) Level water of 1.0 0.5 0.0 0 100 200 300 400 500 600 Time (min) Figure 7-2: Cumulative plot of water collected in buffer tank during esterification During the first 90 minutes of the reaction (paste mixing), the temperature of the system reached a value of 205 °C. In this step dissolution of PTA was the main change occurring in the reacting medium. As the temperature was increased to 250 °C, dissolution increased and esterification started to occur as seen by the increase of temperature in the bottom thermocouple of the distillation column at ~130 minutes. After 30 minutes, the temperature in the middle of the column registered an increase and the temperature at the bottom increased more. 212 Petro EG Bio EG C) 250 ° 200 150 100 Temperature ( bottom Temperature 50 0 160 C) ° 140 120 100 80 60 40 ( middle Temperature 20 0 140 C) ° 120 100 80 60 40 ( top Temperature 20 0 0 100 200 300 400 500 600 Time (min) Figure 7-3: Temperature profiles in distillation column thermocouples during esterification reactions. 213 The temperature at the top of the column started to increase at ~180 minutes. At this point, esterification was proceeding producing water as the main byproduct. This water along with some EG in vapor phase passed through the distillation column causing the rise in temperatures at the three sections. At ~220 minutes, the column temperatures readings stabilized at 206 °C for the bottom and 121 °C for the middle and top of the column. This value of 121°C can be calculated as the boiling point of water at the process pressure using the Antoine equation and parameters reported on Table 6.3. Esterification is a reversible reaction with an equilibrium constant higher than one. At this point in the reaction the removal of water was needed to accelerate the rate of reaction for esterification and overcome the equilibrium condition. The three way solenoid valve was started allowing water to pass to the buffer tank. At ~252 minutes the water level in the buffer tank started to increase gradually. At ~435 minutes, the temperature at the top of the column started to decrease. At this point the pressure of the system was released to continue esterification at atmospheric conditions and promote the removal of more water from the reacting media. The end of the reaction was considered when the temperature at the top of the column was below 100 °C and the level of water in the buffer tank remained constant. Table 7.3 shows the theoretical amount of prepolymer that can be produced from esterification and the real amount recovered from the reactor. When the reaction finished, the molten product had to pass through a transfer line into the second vessel and then it was drained from the bottom. Some of the material remained on the walls of the transfer line and the reactor, reducing the amount of material recovered. For both polymers produced, the amount of material recovered from the system was almost the same. 214 Table 7.3: Comparison of yield for esterification reactions Actual Yield (g) ID Theoretical Yield (g) Petro EG Bio EG BHET 1530 1100 1072 Water1 162 150 145 1) EG content: 12% Petro, 11% Bio The water collected in the buffer tank was comparable in both cases. During esterification, some of the EG leaves the system with the water stream obtained from the distillation column. Analysis of the refractive index of the water collected and a previously constructed calibration curve (Figure 3-4) were used to quantify the amount of glycol present. The results obtained are 12 weight % for PET made with petro EG and 11 weight % for PET made with bio EG. As discussed in Section 4.2.3, the bio EG sample contained small amounts of byproducts that were not present in the petro EG sample. According to literature, these chemicals could have been produced by oxidation of the EG molecule. To investigate the end point of these compounds, a GC-FID analysis of the recovered condensate (water/glycol mixture) from esterification was done. Figure 7-4 show the chromatograms obtained from the analysis of the samples and some reference curves included for discussion. Doing a direct comparison of the bio and petro EG, there is a distinctive set of peaks only present in the bio sample at retention times between 27 and 28.5 minutes. These peaks are only present in the condensate obtained from the esterification of petro PTA and bio EG. The compounds were not readily incorporated into the polymer chain and were removed from the system through the vapor water/glycol stream. A similar 215 observation was reported by Zhang et al. [80] where aldehydes and hemiacetals did not uV(x100) react with the polymer chain and were removed from the system through the vapor phase. 6.5 Even6.0 if these compounds were identified in the condensate, some remaining amount 5.5 could have been trapped in the polymer matrix like other low boiling point compounds 5.0 (i.e.4.5 acetaldehyde), the characterization of the polymer would reveal if these compounds have4.0 any effect on the produced polymer. 3.5 3.0 2.5 2.0 1.5 1.0 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 min 1 2 3 4 Figure 7-4: GC-FID chromatogram (zoomed view) of liquid samples. 1) Condensate from esterification of petro PTA and bio EG 2) Pure bio ethylene glycol 3) Pure petro ethylene glycol 4) Condensate from esterification of petro PTA and petro EG The temperature profiles for the different sections of the distillation column were very similar for both cases. The onset of temperature increase at the bottom of the column (related to the beginning of esterification), the constant temperature at the middle and top 216 plates (related to esterification equilibrium condition) and the time elapsed to reach a temperature below 100 °C at the top of the column (related to the end of esterification) were within numerical difference of 5 units (°C or minutes). The use of either set of raw materials does not show differences in the production of prepolymer through esterification reactions. The prepolymer obtained from esterification was dried overnight in a vacuum oven at 120 °C. It was important to have the same drying conditions as remaining moisture affects the rate of polycondensation by causing hydrolysis on polymer chains [41]. The prepolymer was melted at 285 °C in nitrogen environment inside the reactor. During this time, the catalyst solutions were prepared. Antimony oxide (Sb2O3) and cobalt acetate (CoAc) were mixed with fresh EG in separate vials and heated to ~110 °C until complete dissolution to form antimony and cobalt glycolate. The catalyst solutions were introduced into the molten prepolymer along with 3 drops of phosphoric acid (thermal stabilizer). After flushing, the system was pressurized with nitrogen to 14 psig and temperature was maintained at 285 °C for 1 hour. During this time, the metal catalyst coordinates with the carbon atoms of the carbonyl group creating a metal complex. The propagation reaction includes the reaction of a prepolymer molecule with the complex, producing a polymer chain and ethylene glycol as byproduct. This reaction, called polycondensation, is reversible with an equilibrium constant less than one, therefore removal of glycol is needed to shift the reaction towards products [22-24]. The pressure of the reactor was gradually reduced to atmospheric conditions over a period of 1 hour. After this time, vacuum was gradually applied by controlling a metering valve at the exit of the cold trap. When full vacuum was achieved the system 217 was allowed to react until reaction completion. As the polycondensation proceeds the molecular weight of the polymer increases causing an increase in the melt viscosity. After a critical molecular weight is reached (~Mn=3,500) the relationship of molecular weight 3.4 with melt viscosity is defined as: =KMn [27]. Taking advantage of this relationship, it is customary to monitor the build-up of molecular weight by recording the torque applied to the stirrer to maintain a constant stirring speed. In this research, the reaction was stopped when the torque (measured as % of motor output) reached a value of 0.8. The molten polymer was drained from the reactor into a water bath, due to the high viscosity of the material it was possible to pull the melt and create strands of polymer. These strands were then fed to a pelletizer to obtain the materials in pellet form. Table 7.4 shows the initial material balance used in polycondensation reactions. The grams of catalysts added were calculated using the theoretical amount of PET produced to give specific concentrations of metal ions in the final polymer. Table 7.4: Initial material balance for polycondensation reactions ID M.W. mol grams Prepolymer (BHET) 166.1 6.02 1000 1 Sb2O3 291.5 0.0017 0.2444 CoAc2 249.0 0.00046 0.1150 1) Calculated with theoretical yield of PET to give [Sb]=300 ppm in PET 1) Calculated with theoretical yield of PET to give [Co]=40 ppm in PET Figure 7-5 shows the change in torque during polycondensation reactions of prepolymer made with petro and bio EG. The zero time in the graph is the point of addition of catalyst solutions to the reactor. The initial reading of the torque was 0.04. It 218 can be seen that in both cases, after ~180 minutes the torque started to increase. During this time, the formation of the metal complex by coordination of the catalyst with the prepolymer occurred. The torque increased gradually until the final value of 0.8 was achieved, the difference on time for both materials to achieve this value was 20 minutes, with bio EG polymer being the fastest. Considering 180 minutes as the starting point a linear approximation of the torque increase up to a value of 0.80 was done. The slope for the polymer made with bio EG was 0.118 %motor output/hr and for the polymer made with petro EG was 0.116 %motor output/hr. There was a small difference in the build-up of molecular weight between the two materials. Petro EG Bio EG 0.9 0.8 0.7 0.6 0.5 Torque motor output) (% Torque 0.4 0.3 0 100 200 300 400 500 Time (min) Figure 7-5: Torque variation during polycondensation reactions 219 Table 7.5 shows the theoretical amount of polymer that can be produced from polycondensation and the real amount recovered from the reactor. For both polymers produced the amount of material recovered from the system was the same. Table 7.5: Comparison of yield for polycondensation reactions Actual Yield (g) ID Expected Yield (g)1 Petro EG Bio EG PET 680 620 600 EG 219 185 175 1) In both cases, 900gr of prepolymer were used for polycondensation 7.2.4 Physical properties The evaluation of physical properties on the polymers produced allowed to obtain product end characteristics and to identify if side reactions had occurred during polymerization. The melt viscosity of the polymer was obtained to understand the ultimate molecular weight produced in the polymerization system. This value can be affected by the presence of impurities in the monomers, degradation reactions, improper removal of glycol during synthesis, etc. The color measurement is an indirect measurement of degradation reactions during synthesis. 220 7.2.4.1 Melt viscosity Molecular weight determinations were done using a RDA III Parallel Plate Dynamic Analyzer. The pellets produced with both sets of raw materials were tested under the same conditions. The material was melted at 270 °C under a nitrogen environment in a gap space between the plates. After equilibration time (to assure all material is melted), the top plate of the apparatus started to rotate at different speeds. The sensor installed in the bottom plate recorded the in-phase viscosity (real part) and out-of- phase viscosity (imaginary part) response of the polymer. A subtraction of the two variables provides the melt viscosity of the sample (Equation 3.5). Through the use of a calibration curve (Appendix E), the intrinsic viscosity of the sample can be calculated using melt viscosity numbers. Figure 7-6 shows the change in melt viscosity with shear rate applied by the moving plate for a single analysis. At low shear rates, the polymer behaves as a Newtonian fluid obtaining a constant melt viscosity. As the shear rate increases the polymer chains untangle and resistance to flow decreases. This change is registered as a decrease in melt viscosity [120]. For both materials, the flow pattern was the same at all shear rates. To account for the intrinsic characteristic of the polymer the melt viscosity at 10 rad/s was used for calculation using the calibration curve. Table 7.6 shows the melt viscosity readings for samples of PET made with bio EG and petro EG. Both products have the same intrinsic viscosity, the variation of 0.1 is within the experimental error of the instrument. These results confirmed that for both polymers it was possible to build-up molecular weight (up to a reference value determined by torque measurements) with no marked limitations caused by the use of either raw materials. 221 Petro EG Bio EG 3000 s) - (Pa Viscosity 300 1 10 100 1000 Shear Rate (rad/s) Figure 7-6: Melt viscosity vs shear rate at 270°C for PET samples Table 7.6: Comparison of intrinsic viscosity for PET samples Sample I.V. (dl/g) Run # * (Pa*s)1 ID Calculated Avg. St. Dev. 1 1126 0.80 Petro 2 1198 0.81 0.80 0.004 EG 3 1130 0.80 1 1333 0.82 Bio 2 1265 0.81 0.81 0.005 EG 3 1213 0.81 1) Measured at 270°C and shear rate of 10 rad/sec. 222 7.2.4.2 Color Evaluation of the polymer color can provide information related to degradation during polymer synthesis or the presence of side products. The analysis of color in bio and petro EG (Section 4.2.1) showed similar results for L* and b* indices; therefore any difference identified on the polymer was not originated by a characteristic of the initial raw materials. Color analysis of PET pellets was done using the Hunter Lab D25 color meter. The pellets were poured in round glass vials and placed in the analysis port of the chamber. Table 7.7 shows the results obtained for polymer produced with petro and with bio EG. The results for amorphous material are reference of the quality of the material produced from the reactor. The b* indices for both products have a high value towards the yellow limit. This can be the result of degradation reactions during synthesis or during product recovery (Section 2.2.3). When the molten material was purged from the reactor it was exposed to air for a few seconds before falling into a water bath. Oxidative degradation could have occurred during this recovery step. The crystalline material was obtained after crystallizing amorphous pellets in a vacuum oven at 220 °C for 12 hours. The color measurement for crystalline material shows no difference in the polymers produced with bio or petro EG. To have a reference on how the synthesized material compares to commercial product, color analysis of Laser+B95A pellets (produced by DAK Americas LLC) was done. This product is produced through solid state polymerization and has an inherent level of crystallinity given by production conditions. The commercial product was analyzed as received. This material has a higher L* index 223 and a significantly lower b* index. This difference in color is attributed to controlled production conditions that minimize formation of colored side products through degradation reactions. Table 7.7: L* and b* values of PET samples in pellet form Amorphous Crystalline Sample L* b* L* b* Avg. St. Dev. Avg. St. Dev. Avg. St. Dev. Avg. St. Dev. Petro EG 56.7 0.4 9.7 1.1 69.5 0.3 6.3 1.0 Bio EG 57.3 0.3 8.3 0.8 69.3 0.5 5.9 0.9 Commercial -- -- 79.8 0.2 -3.1 0.9 7.2.5 Product composition The product composition of a polymer provides information about the structure of the polymer chain, the presence of byproducts, the concentration of end groups and remaining metal particles from catalyst. All these variables should be known to have a proper interpretation of polymer performance results. The residual amount of catalyst present in the polymer was used as reference information to indicate how much metal was involved in the polycondensation reaction. This number may not coincide with the theoretical amount fed to the system, as some side reactions may cause reduction of the metal to its elemental form causing precipitation and deactivation [163]. The carboxyl end groups are indications of the extent of reaction during polymerization and can also reflect if degradation occurred. As reviewed in Section 2.2, 224 degradation reactions (thermal, hydrolytic, oxidative) produce carboxyl end groups and other byproducts. Depending on the concentration of carboxyl end groups, this can also have an effect on crystallization kinetics or act as a catalyst in hydrolysis [164]. The bound copolymer (DEG) concentration was determined to understand the extent of modification of the polymer chains produced. During esterification, TEA was added to the system to limit the production of DEG, however it is not possible to completely impede its formation. The residual amount of acetaldehyde was obtained as reference for the thermal history of the materials during polymerization. 7.2.5.1 Residual catalysts Polymer samples were digested in a nitric acid + water solution at 210 °C to recover the catalyst from the polymer matrix. The liquid samples were analyzed in an ICP-MS Xseries instrument. Quantification was done using reference standards acquired from Organic Ventures. The instrument provides the result as concentration of metal in the liquid phase. Using the known amount of polymer digested, the concentration of the metal solid was calculated. Table 7.8 shows the catalyst concentration in the polymer samples. The detailed reports of the results obtained from ICP-MS can be found in Appendix C. The difference in the concentrations of cobalt and phosphorous are within experimental error of the measurement. Both of these elements are present at the same concentration. Antimony concentration is higher for the bio EG sample. This higher concentration did not affect 225 the color of the polymer as the L* index was the same, indicating that the difference in reduction to elemental antimony in both polymers was similar. The higher concentration of antimony explains why bio EG required a shorter time (~20 minutes) to achieve a torque measurement of 0.8 and a higher rate of change expressed as %motor output/hr (~0.118). The difference in catalyst concentrations is attributed to the inefficient procedure for addition to the molten polymer. Table 7.8: Residual catalyst concentration on PET samples Sb ppm Co ppm P ppm Sample Average St. Dev. Average St. Dev. Average St. Dev. Petro EG 237 3.2 35 0.4 29 0.4 Bio EG 309 5.3 36 0.3 33 1.7 7.2.5.2 Carboxyl end groups The carboxyl end group content was determined by titration. The powder polymer samples were dried overnight at 120 °C prior to analysis. Titration was done using phenol red as the indicator, benzyl alcohol and chloroform as the solvent for the polymer and a standardized solution of NaOH as the titrating media. Table 7.9 shows the carboxyl content of polymer samples. The detailed information of the normalization of the NaOH solution and the correction factors can be found in Appendix D. All determinations were done the same day to assure the normalization of the titrating solution was the same and no precipitation of NaOH had 226 occurred. The difference in the concentration of carboxyl end groups was within experimental error of the measurement, both polymers had the same carboxyl concentration. This results confirms the previous observations that both materials had the same thermal history during polycondensation. Degradation reactions that may have occurred during polymerization were similar in both cases. In relation to molecular weight, previous discussion showed the same intrinsic viscosity for both materials and a slight difference in polymerization rate. The concentration of carboxyl end groups as indicative of the extent of reaction also confirms similarity between the two sets of raw materials. Similar carboxyl end group concentrations have been reported by researchers for melt phase polymerization of PET. James et al. [165] reported values of 30.8 meq/g for polymer produced using antimony oxide as catalyst. Mazloom et al. [162] reported values of 28.5 and 33.1 meq/g for polymers produced with ~250 ppm of antimony oxide. Table 7.9: Carboxyl end group concentration obtained from titration test ID PET Time1 Reading (mm)3 Difference Net4 COOH Cf2 Sample mg sec. Initial Final ml ml meq/g Avg. St. Dev. 97 154 5.3 8930 15034 61.0 58.5 32 Petro 95 133 4.6 7350 13181 58.3 55.8 32 33 1.71 EG 94 160 5.5 10321 16804 64.8 62.3 36 97 145 5.0 3521 8909 53.9 51.4 28 Bio 97 150 5.1 10131 16010 58.8 56.3 31 30 1.72 EG 99 137 4.7 8235 14310 60.8 58.3 32 B.A.5 5 ml 180 -- 8115 8366 2.5 ------1) Heating time required to dissolve the sample in a benzyl alcohol bath 2) Correction factor for carboxyl generation during heating time 3) Difference in readings of titrating media inside the burette 4) Net volume consumed during titration of each sample 5) Blank sample containing benzyl alcohol, chloroform and indicator 227 7.2.5.3 Copolymer content Diethylene glycol is formed in a side reaction during polymer synthesis. This unit is bounded to the polymer chain creating a copolymer with PET. Its presence has an important impact in polymer properties. An increase in the concentration of DEG will reduce the rate of crystallization, reduce the melting point, increase the number of reactive points for degradation, etc. Its rate of formation is affected by the reaction temperature, reaction time, presence of pH modifiers, type of catalyst, etc. A higher concentration of antimony or a higher temperature of polymerization increases the rate of formation for EG [39]. The determination of DEG in the polymers produced was not done in the Polymer Institute. The samples were sent for analysis to a laboratory. The procedure followed to obtain the concentration was typical of analysis in polyesters, the highlights are: the polymer samples were depolymerized by saponification followed by neutralization, obtaining a solid phase of monomer units and a liquid phase containing the unbound DEG. Quantification through GC was done using an internal standard technique with benzyl alcohol as the reference compound [39]. For PET with bio EG the concentration of DEG was 2.62 weight % and for PET with petro EG was 2.51 weight %. The level of modification of the polymer chain caused by DEG was the same for both products. The effect of copolymer in crystallization behavior and melting conditions should be the same. 228 7.2.5.4 Residual acetaldehyde During polymerization, degradation reactions are likely to occur. Chain scission caused by thermal effect produces vinyl and carboxyl end groups. Vinyl end groups can react with hydroxyl end group producing AA (Section 2.2.1). Once it is formed it tends to migrate out of the polymer matrix. The high viscosity of the melt limits this diffusion process causing AA to be trapped inside the polymer. Determination of residual AA is an indication of the level of degradation that occurred during polymer synthesis and is typically monitored as a quality variable of importance for the beverage industry as AA may affect the taste of the product [55]. Residual acetaldehyde was calculated using Equation 3.1. Table 7.10 shows the residual acetaldehyde in PET samples produced with petro and bio EG. The difference in the concentration of AA is within the experimental error of the analysis. Both materials have the same concentration of residual acetaldehyde. This result indicates that both materials had a similar thermal history during polymerization and in both materials the removal of AA from the melt was done with comparable efficiency. 229 Table 7.10: Residual acetaldehyde data comparison for PET samples Sample Peak Area AA concentration (ppm)1 ID weight (mg) (units) Measured Average St. Dev. 30.12 2668 64.4 Petro EG 31.12 2523 58.9 64.5 4.6 30.16 2912 70.2 30.14 2515 60.6 Bio EG 30.02 2613 63.3 63.4 2.3 30.19 2751 66.2 1: Calibration factor = 1376 mvolts*sec/mgramsAA 7.2.6 Thermal stability PET is subject to degradation when exposed to high temperatures during polymerization or processing. The possible end results are the production of byproducts, discoloration and reduction of molecular weight. The mechanism for degradation is explained in terms of the breaking point in the polymer chain that leads to the formation of byproducts. Copolymer content, catalyst residue and carboxyl end groups have an important influence on the rate and course of degradation. The acetaldehyde generation studies were done to investigate how prone the polymers produced with both sets of raw materials are to thermal degradation. The tests were done with dried material and under an inert environment to avoid hydrolytic and thermal oxidative degradation. Replicating the test at different temperatures produced enough data to estimate activation energies for thermal degradation. The concentrations of vinyl end groups were obtained to quantify the presence of the reactive precursor that leads to the formation of acetaldehyde. These results along 230 with the residual amounts of catalyst, the carboxyl end group concentrations and the molecular weights provide a general overview of thermal stability in the polymers produced. The thermogravimetric analysis was done to verify the total rate, onset and end point of degradation for the polymers produced. The test was done in a nitrogen environment using dried samples. The maximum temperature was selected to achieve complete degradation of the polymer and compare total weight loss. 7.2.6.1 Acetaldehyde generation AA generation experiments are typically done at PET processing temperatures in order to predict polymer performance during processing. The technique used to quantify the concentration of AA generated at a specific temperature and time was adapted from the one reported by Kim and Jabarin [108]. A dried sample of PET was heated at different temperatures (270, 280 and 290 °C) for different desorption times (20, 30 and 40 minutes). The gas effluent was injected into a GC-FID instrument to record the amount of AA generated using calibration data. The quantification of AA was done using a calibration curve previously prepared. The samples used contained AA at different concentrations and were desorbed following the same method as for the PET samples. Details of the experimental procedure can be found in Section 3.2.4. The detailed information of the calibration curve data points can be found on Appendix B. The temperatures selected for AA generation experiments are typical values of those used in PET processing. The generation of acetaldehyde follows a linear 231 relationship with time, after a certain induction time has passed. Before this point, the slope is continuously changing until a constant linear value is obtained [55]. To verify that the selection of desorption time (20, 30 and 40 min) for AA generation experiments was correct, an extended test at 280 °C using shorter heating times (5 and 15 min) was done using PET made with petro EG. Figure 7-7 shows the result obtained. The generation of AA at heating times of 20, 30 and 40 min follows a linear relationship. These values are adequate for testing AA generation. 140 120 100 80 60 AA ppm AA 40 y = 3.31x - 16.17 R² = 0.99 20 0 0 10 20 30 40 50 Time min Figure 7-7: Acetaldehyde generation at 280 °C for PET made with petro EG at multiple desorption times 232 Table 7.11 shows the AA generation for PET samples made with petro and bio EG. Figure 7-8 shows the AA generation rates for PET with petro EG. Figure 7-9 shows the AA generation rates for PET with bio EG. For both polymers, the rate of generation increases with increasing temperature. This was expected as the reactions that lead to the formation of vinyl end groups and acetaldehyde are dependent on temperature [108]. The polymer produced with bio EG had higher AA generation rates at all temperatures. This difference can be explained by the higher concentration of vinyl end groups and higher concentration of residual catalyst in PET made with bio EG. 200 180 290 160 280 140 270 120 100 y = 4.84x - 19.65 80 R² = 0.99 (ppm) AA 60 y = 3.24x - 12.78 40 R² = 0.99 20 y = 2.04x - 10.58 0 R² = 1.00 0 10 20 30 40 50 Time (min) Figure 7-8: AA generation as function of time and temperature for PET made with petro EG 233 220 290 200 280 180 270 160 140 120 y = 5.64x - 26.11 R² = 1.00 100 AA (ppm) AA 80 y = 3.85x - 25.56 R² = 1.00 60 40 y = 2.74x - 12.99 R² = 0.99 20 0 0 10 20 30 40 50 Time (min) Figure 7-9: AA generation as function of time and temperature for PET made with bio EG 234 Table 7. 11: Acetaldehyde generation comparative data as a function of temperature and desorption times for PET samples Petro EG Bio EG Temperature Desorption Peak Area Peak Area (°C) time (min) ppm AA1 ppm AA1 (V*sec) (V*sec) 22678 28 31046 38 20 25753 32 31458 39 47183 58 55107 68 270 30 32762 41 60642 75 59797 74 84037 104 40 55478 69 69524 86 43819 54 41025 51 20 37329 46 41371 51 68064 84 74525 92 280 30 73136 91 71577 89 90342 112 96952 120 40 95188 118 109611 136 64375 80 69124 86 20 55912 69 70416 87 109582 136 106768 132 290 30 101558 126 124809 155 142806 177 164342 204 40 133717 166 157199 195 1) Calculated using calibration factor = 1.116E-7 mg/(uV*sec) AA generation rates were determined at three different temperatures (270, 280 and 290 °C) to calculate the activation energy and pre-exponential factor using the Arrhenius equation. Using logarithmic laws it can be expressed in a linear form as shown by Equation 7.4. 235 퐸 ln 푘 = ln 퐴 − 퐴 (eqn 7.4) 푅푇 where k is the rate constant in ppm/min, A is the pre-exponential factor in ppm/min, EA is the activation energy in J/mol, R is the gas constant in J/(mol*K) and T is the temperature of the experiment in Kelvin. The logarithmic value of the rate can be plotted against the inverse of temperature to obtain the activation energy from the slope and the pre-exponential factor from the intercept. Table 7.12 shows the individual values used for the linear relationship. Table 7.13 shows the parameters for the Arrhenius equation. Figure 7-10 shows the Arrhenius plot for PET samples. PET synthesized with bio EG has a lower activation energy for acetaldehyde generation compared to PET synthesized with petro EG. This difference exists because of the different amount of residual catalyst present in the samples. Degradation reactions that lead to the formation of AA are accelerated by the presence of catalyst [41]. PET with bio EG had a higher concentration of antimony according to ICP analysis (Section 7.2.5.1). As expected the activation energy for this material is lower. The activation energy values for both polymers are low compared to majority of values reported in literature. Jabarin et al. [42] reported 159 kJ/mol for overall thermal degradation, Tomita [33] reported 99 kJ/mol for overall degradation, Zimmerman [30] reported 178 kJ/mol for thermal degradation. These reported values were obtained by analysis of the reduction of molecular weight at a specific temperature overtime instead of monitoring the acetaldehyde generation. 236 Table 7.12: Logarithmic values for acetaldehyde generation rate and inverse of temperature as a function of melting temperature condition for PET samples Sample Temp °C Rate1 ln rate 1/T K^-1 1000/T K^-1 270 2.038 0.71 1.84E-03 1.84 Petro EG 280 3.310 1.20 1.81E-03 1.81 290 4.842 1.58 1.78E-03 1.78 270 2.737 1.01 1.84E-03 1.84 Bio EG 280 3.496 1.25 1.81E-03 1.81 290 5.641 1.73 1.78E-03 1.78 1) Expressed in ppm/min Table 7.13: Parameters for Arrhenius equation obtained from AA generation data Sample A Ea1 Petro EG 8.00E+10 110 Bio EG 1.75E+09 92 1) Activation energy expressed in KJ/mol 1.8 Petro Bio 1.6 1.4 1.2 ln k ln 1.0 0.8 0.6 1.76 1.78 1.80 1.82 1.84 1.86 1000 / T (1/K) Figure 7-10: Arrhenius plot for acetaldehyde generation of PET samples at 270, 280 and 290 °C 237 7.2.6.2 Vinyl end groups From all the degradation reactions that can occur in PET, thermal degradation has the greatest impact on the generation of AA. The formation of this byproduct is preceding by the formation of vinyl end groups primarily through polymer chain scission. These groups can react with either a carboxyl end group or hydroxyl end group to form AA. To investigate the rate of formation of vinyl end groups, the polymer samples were heated to a temperature just below their melting points (240 °C) and were maintained for different times to obtain AA generation rates. Table 7.14 shows the AA generation data at 240 °C. Figure 7-11 shows the generation rate for each polymer sample. Table 7.14: Acetaldehyde generation data at 240 °C and different desorption times Petro EG Bio EG Temperature Desorption Peak Area Peak Area (°C) time (min) ppm AA ppm AA (V*sec) (V*sec) 8633 11 12711 16 20 7424 9 13804 17 9907 12 16406 20 240 30 13489 17 21134 26 15098 19 21878 27 40 17231 21 22600 28 238 30 Petro Bio y = 0.56x + 5.72 25 R² = 0.98 20 y = 0.50x - 0.30 R² = 0.99 15 10 (ppm) concentration AA 5 10 20 30 40 50 Time (min) Figure 7-11: Acetaldehyde generation at 240 °C for petro and bio PET samples The concentrations of vinyl end groups were calculated using Equation 3.4. The number average molecular weight was calculated using Equation 7.5. The concentration of hydroxyl end groups was calculated using Equation 7.6, assuming equal presence of carboxyl and hydroxyl. 퐼. 푉. = 7.5 ∗ 10−4 ∗ 푀푛0.68 (eqn. 7.5) where I.V. is the intrinsic viscosity of the sample, the numerical factors are typical Mark-Houwink parameters used for PET and Mn is the number average molecular weight of the polymer. 239 2푥106 푀 = (eqn. 7.6) 푛 [푂퐻]+[퐶푂푂퐻] where I.V. is the intrinsic viscosity of the sample, the numerical factors are typical Mark-Houwink parameters used for PET and Mn is the number average molecular weight of the polymer. Table 7.15 shows the concentrations of vinyl end groups for both polymers and the different values used for Equation 3.4. As expected, the generation of AA at 240 °C is higher for the sample made with bio EG. This is the same trend observed at higher temperatures and is caused by the higher amount of residual catalyst. The concentration of vinyl end groups is higher for the PET sample made with bio EG. This difference is in agreement with the higher AA generation rate and lower activation energy. The difference in acetaldehyde generation is caused by the different content of vinyl end groups as the concentration of carboxyl and hydroxyl is very similar for both materials. Table 7.15: Results for the calculation of vinyl ester groups for PET samples Material AA rate1 I.V.2 Mn3 COOH4 OH5 VE6 Petro PET 0.504 0.800 28356 33 37 0.303 Bio PET 0.557 0.814 29087 32 39 0.323 1: AA generation rate at 240 °C. Obtained from the slope of data reported on Table 7.14 2: Melt viscosity obtained at 270 °C using parallel plate rheometer 3: Calculated from intrinsic viscosity using equation 7.5 4: Expressed in meq/g. Data obtained by titration 5: Expressed in meq/g, calculated using equation 7.6 6: Expressed in meq/g, calculated using equation 3.4 240 7.2.6.3 Thermogravimetric analysis Thermogravimetric analysis was done to investigate the degradation of the polymers samples exposed to temperatures higher than typical processing conditions. The analysis of the onset and end point of degradation provide information on the stability of the polymer. The total amount of weight loss provides insight on the extent of degradation obtained. All samples analyzed were dried in a vacuum oven to avoid hydrolytic degradation. The testing was done in a helium environment to avoid oxidative degradation. Figure 7-12 shows the weight loss profile for PET made with bio EG. Table 7.16 shows the relevant transitions observed during the testing. The temperatures at onset of and end of the main weight loss change are related to the overall degradation of the material. The temperature at 50% weight loss change is usually taken as reference for kinetic determinations. The peak temperature of the first derivative is used to identify inflexion points related to different transitions in the decomposition of the material. For both products only a single peak for the first derivative was obtained. The temperature transitions and the total weight loss were the same for both products. There was no indication of a different overall degradation process in PET produced with either materials. The values obtained are comparable to reported data in literature. Ray et al. [166] obtained an onset of degradation at 420 °C and a peak for first derivative at 440 °C. 241 Figure 7-12: Single stage mass loss curve for PET with bio EG Table 7.16: Transition temperatures for TGA analysis of PET samples Sample Variable Unit Petro EG Bio EG Texo1 °C 425 424 Texe2 °C 463 465 Tp3 °C 444 447 Th4 °C 448 448 Total weight loss % 83.8 85.2 1) Extrapolated onset temperature 2) Extrapolated end temperature 3) First derivative peak temperature 4) Temperature at 50% weight loss 242 7.2.7 Crystallization PET as a thermoplastic material can exist in different molecular arrangements depending on the exposure temperature. At temperatures up to 80 °C, the polymer behaves as a glass. As temperature is increased, segmental mobility starts to occur allowing chains to move into an ordered arrangement obtaining a crystallization phenomenon. For PET, crystallization occurs at temperatures between ~80 °C and ~240 °C, the maximum rate of crystallization is at ~170 °C. The crystallization rate is affected by many parameters such as: molecular weight, temperature, concentration of carboxyl end groups, moisture, copolymer content, concentration of residual catalyst and concentration of impurities. The study of crystallization with thermal analysis provides information on the type of nucleation and crystallization of the polymer. This information can be used to identify differences in polymer samples. Thermal analysis of crystallization can be done at a constant temperature (isothermal) or by modifying the cooling rate from the melt or glassy state (dynamic). In isothermal crystallization, the polymer is cooled from the melt to a specific temperature and held for at least ten times its half-time crystallization value. The polymer chains have time to arrange in ordered conformations creating crystals. In dynamic crystallization, the molten material is cooled down to room temperature using different cooling rates. The polymer crystallizes at different rates as it remains in the crystallization region for different times depending on the cooling rate. In both cases amorphous samples can be heated from the glassy state. 243 Crystallization under thermal effect proceeds through the formation of spherulitic structures growing radially outward and composed of lamella units containing folded polymer chains. The kinetic analysis of the course of isothermal crystallization was first proposed by Avrami [167]. In his theory, nucleation and growth are time dependent functions, nucleation can occur in a random fashion and growth takes place in one, two or three dimensions. Equation 7.7 shows the linearized form of the Avrami equation. Table 7.17 shows the values for the Avrami exponent. ln − ln 휃 = ln 푘 + 푛 ∗ 푙푛 푡 (eqn. 7.7) where is the fraction of amorphous material at a specific time, k is a constant related to nucleation and growth, t is the time and n is the Avrami exponent. Table 7.17: Values for the Avrami exponent for various types of nucleation and growth n Time dependent Dimensions Mechanism 4 Yes 3 Spherulitic growth from sporadic nuclei 3 No 3 Spherulitic growth from instantaneous nuclei 3 Yes 2 Disc-like growth from sporadic nuclei 2 No 2 Disc-like growth from instantaneous nuclei 2 Yes 1 Rod-like growth from sporadic nuclei 1 No 1 Rod-like growth from instantaneous nuclei For the case of dynamic crystallization, Ozawa [168] proposed a modification to the Avrami equation, including the cooling rate used for each analysis. Equation 7.8 shows the modification proposed by Ozawa in its linear form. 244 ln(− ln(1 − 훼 푇 )) = ln 푘 − 푛 ∗ 푙푛 푅 (eqn. 7.8) where is the amount of material transformed at temperature (T), k(T) is the rate of crystallization, R is the cooling rate and n is the Avrami exponent. The polymers produced were analyzed under isothermal and dynamic crystallization modes to identify differences in the materials. Avrami and Ozawa equations were used to understand the mechanism of crystallization and to obtain crystallization half times that relate to the crystallization rate of the materials. The analysis of crystal size was done to determine the dimensions of the crystals formed during isothermal crystallization. The results are indicative of differences in the modification of the polymer chain by the presence of side products. 7.2.7.1 Isothermal crystallization Both polymers were analyzed using a Perkin Elmer DSC 7, all determinations were done in nitrogen environment. The dried samples were heated from room temperature to 300 °C at 10 °C/min, held for 5 minutes and quenched to 220 °C using a cooling rate of 300 °C/min. The samples were held at this temperature for at least ten times their half-times of crystallization. After the holding time, the samples were cooled to room temperature. The heat profiles obtained during the hold time of each sample are shown in Figure 7-13. 245 Figure 7-13: Normalized heat flow profile for isothermal crystallization from the melt at 220 °C for PET samples For each material, the curves obtained were integrated obtaining a relationship between time and heat flow. Using the cumulative value of the area as the maximum of crystallinity, the fraction of crystallized material was calculated for different times by obtaining the ratio of the heat flow at a specific time over the cumulative value. The detailed information obtained from the integration and the values used for the Avrami equation can be found in Appendix K. Figure 7-14 shows the crystallization isotherms for both polymers. a is the fraction of amorphous material in the polymer at any time. Both isotherms have the typical sigmoidal shape. 246 1 0.9 0.8 0.7 0.6 0.5 a 0.4 Petro EG 0.3 0.2 Bio EG 0.1 0 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 ln (time) (seconds) Figure 7-14: Comparative crystallization isotherms at 220 °C for PET samples Using the individual values of a versus time and Equation 7.7, the Avrami plots were obtained for both materials. Figure 7-15 shows the results obtained. Table 7.18 shows the Avrami parameters for primary and secondary crystallization obtained from the slope and intercept of the linear relationships plotted on Figure 7-15. Table 7.18: Values of rate constant, k, Avrami exponent, n, and half time, t1/2, for PET samples when crystallized isothermally from the melt at 220 °C Petro EG Bio EG Crystallization 1 2 1 2 n k t 1/2 n k t 1/2 Primary 4.1 1.93E-12 686 3.2 2.89E-10 931 Secondary 1.8 5.05E-06 627 1.4 4.04E-05 1011 1: k, sec -n 2: t 1/2, sec 247 1 0.5 0 5.5 6.0 6.5 7.0 7.5 8.0 -0.5 a)) -1 ln( - ln( -1.5 Petro EG -2 Bio EG -2.5 -3 ln (time) (seconds) Figure 7-15: Avrami plot for isothermal crystallization of PET samples from the melt at 220 °C The difference in the crystallization stages is related to the formation of crystals at a specific time. At the beginning, a nuclei is formed after polymer chains get closer together by action of the thermal effect (primary nucleation). Upon its formation, crystalline arrangements starts to form on the surface of the nuclei (secondary nucleation), these arrangements grow radially outward (creating the spherulite) until impinging with a crystalline arrangement from a neighbor spherulite (primary crystallization). When the spherulites touch, there is no more free space for growth. The arrangement then starts to crystallize within the structure by reducing the amorphous 248 phase and perfecting the crystals (secondary crystallization). As shown in Table 7.17 the Avrami equation considers the geometrical planes where crystallinity occurs. During primary crystallization there is free space for the chains to grow and in the secondary phase crystallization is limited to the free space within spherulites. This difference is seen as a change of slope in the Avrami plots. For the results obtained, primary crystallization is considered at crystallization values up to 50%. For secondary crystallization, the values considered are the ones that give a distinctive constant slope (crystallinity above 75%). The Avrami exponent obtained for PET made with petro EG was 4, this is representative of a crystallization process creating spherulites with nuclei formation occurring sporadicly with time. For PET made with bio EG the exponent obtained was 3, this is representative of a crystallization process creating spherulites with instantaneous formation of nuclei (independent of time). An Avrami exponent of 3 often means that nuclei were formed due to the presence of impurities in the polymer (i.e. catalyst particles, contamination, etc) [167]. Considering the results presented before for the polymer characterizations, the molecular weight of the materials, the level of copolymer and the concentration of carboxyl end groups are all the same and the concentration of catalyst is different. It has been reported that catalyst particle may act as nucleating agents during crystallization [164]. The higher concentration in PET made with bio EG made it possible to have an Avrami exponent of 3, where the crystals grow in three dimensions starting from instantaneous nucleation, with the catalyst particles being the nucleating sites. Determination of the kinetics of crystallization is usually done by analyzing the time elapsed to achieve 50% crystallinity in the polymer. Care should be taken in the 249 interpretation of this result as the half time is dependent on the Avrami exponent of the process (as seen on Equation 7.7), since both materials have a different Avrami exponent no direct comparison can be made. An Avrami exponent of 4 considers a time dependent nucleation process, while an exponent of 3, considers no time dependence for nucleation (if growth is in spherulitic form). A more general analysis can be made by analyzing the rate constants. This variable includes the nucleation and growth constants. Comparing the rate constants for both polymers, the rate for PET made with bio EG is higher. Knowing that the nucleation process for this sample is not time dependent, we can presumably say that the growth constant is high enough to make a difference in the overall rate constant value. Avrami exponents of 3 and 4 have also been obtained by researchers in isothermal analysis of PET quenched from the melt. Jabarin et al. [38] obtained an exponent of 3 for PET samples produced with different DEG content. The samples were isothermally crystallized at temperatures between 210–225 °C. Kim [169] obtained exponent values of 3, for commercial grade PET samples isothermally crystallized at temperatures between 180-210 °C. The slope of the primary crystallization process for the PET sample made with bio EG seems to be changing with time as crystallization increased. This phenomenon has been studied by Kim [169] using samples isothermally crystallized from the melt. It was proposed that the Avrami exponent decreased over time due to a reduction in the growth rate of the spherulite as the point of impingement is reached. A second source of variation in the Avrami exponent is related to secondary crystallization competing with primary crystallization. These observations can explain the change in the slope of the 250 sample made with bio EG, particularly at values approaching 50% crystallinity, where the deviation is more pronounce. For secondary crystallization, the slopes of the lines are constant with increasing time. The Avrami exponents obtained were between 1 and 2. These values are in agreement with reported values in literature. The decrease in the exponent is related to the constricted space where crystallization is occurring inside the spherulite. Jabarin et al. [38] obtained values between 1-2 for the Avrami exponent in secondary crystallization of PET samples produced with different levels of DEG. 7.2.7.2 Dynamic crystallization For dynamic crystallization analysis, dried samples were heated to 300 °C at 10 °C/min, held for 5 minutes and quenched to 30 °C using a cooling rate of 300 °C/min. This first heating was done to erase any thermal history of the polymer and to have the material in the amorphous phase after the quench step. A second heating (same conditions as the first one) was done to obtain the transitions for both polymer samples followed by a cooling step. These second heating and cooling steps were done at different rates to obtain data for dynamic analysis. Figure 7-16 shows the second heating and Figure 7-17 shows the second cooling step, both were done at a rate of 10 °C/min. In both cases there is a difference in the crystallization region for petro and bio EG samples. 251 Figure 7-16: Comparative DSC plot for PET samples. Second heating step from 30 °C to 300 °C at a rate of 10 °C/min Figure 7-17: Comparative DSC plot for PET samples. Cooling step from 300 °C to 30 °C at a rate of 10 °C/min 252 Table 7.19 summarizes the results obtained for both samples using different heating and cooling rates. For all determinations and for both materials the Tg obtained was relatively the same. Small variations were observed along with a minimal increase with increasing rate, these are attributed to measurement error and not to a property of the polymer. The peak of melting was observed at ~245 °C, even if the heats of melting (related to the distribution in length of crystals formed) were not the same, the peak temperatures maintained constant in all determinations for both polymers. A comparable value of Tg and Tm reflects the similarity in the length and level of modification in the polymer chain of both samples. The glass crystallization and melting enthalpy reflect the formation and melting of crystals during the second heating step. The numerical value should be the same, meaning all the crystals formed during heating were melted. Variations in the magnitudes are caused by improper cooling in the quench step leaving some residual crystallization at the beginning of the second heating or from additional crystallization created when heating the sample during analysis. The peak crystallization temperature during heating or cooling exhibits a difference between the two polymers. As expected for a PET sample, in both cases, there is a decrease with increasing cooling rate when cooling for the melt and an increase with increasing cooling rate when heating from the glassy state. 253 Table 7.19: Physical parameters obtained from DSC analysis of PET samples Heating Cooling Crystallization Melting Crystallization Sample Rate 1 ID °C/min Tg2 Tch3 Hch4 Tm 5 Hm6 Tcc 7 Hcc8 (°C) (°C) (J/g) (°C) (J/g) (°C) (J/g) 10 78.7 131 -39 245 38 190 -40 15 79.2 135 -34 244 35 185 -34 Petro 20 79.5 138 -37 243 37 181 -31 EG 30 80.3 142 -25 242 30 174 -28 40 81.0 146 -31 241 32 169 -29 10 78.2 145 -31 244 31 188 -33 15 79.1 151 -29 243 27 181 -29 Bio 20 79.4 156 -31 243 46 177 -28 EG 30 80.2 162 -30 242 32 168 -27 40 81.0 167 -32 241 35 163 -24 1: Rates used for cooling from the melt or heating from glassy state 2: Glass transition temperature obtained from second heating step 3: Peak maximum temperature of glass crystallization 4: Glass crystallization enthalpy 5: Peak maximum temperature of melting 6: Melting enthalpy 7: Peak maximum temperature of melt crystallization 8: Melt crystallization enthalpy For each material, the second cooling curves were integrated obtaining a relationship between temperature and heat flow. Using the cumulative value of the area as the maximum of crystallinity, the fraction of crystallized material was calculated for different temperatures by obtaining the ratio of the heat flow at a specific time over the cumulative value. The detailed information obtained from the integration and the values used for the Ozawa equation can be found in Appendix K. Figure 7-18 shows the 254 illustrative crystallization curve for PET made with petro EG. For all cooling rates the curves have the typical sigmoidal shape. From this plot, a vertical line can be plotted at specific temperatures to obtain x(T) values for specific cooling rates. The readings were done on x(T) values below 50%. The results obtained are shown on Figure 7-19. The x(T) values at specific temperatures for different cooling rates were plotted according to Equation 7.8. Figure 7-20 and 7-21 show the results obtained for both samples. 1.0 0.9 0.8 0.7 0.6 0.5 10 x (T) x 0.4 15 0.3 20 0.2 30 40 0.1 0.0 135 145 155 165 175 185 195 205 Temperature °C Figure 7-18: Relative degree of crystallinity x(T) vs temperature for non- isothermal crystallization of PET made with petro EG from the melt. Cooling rates for each run is reported in °C/min 255 0.35 0.60 Petro PET Bio PET 0.30 CR 0.50 0.25 40 0.40 30 0.20 20 0.30 x(T) x (T) x 0.15 15 10 0.20 0.10 0.10 0.05 0.00 0.00 170 175 180 185 190 195170 175 180 185 190 195 Temperature °C Temperature °C Figure 7-19: Relative degree of crystallinity x (T) at specific temperatures (175, 186, 192 °C) for PET samples. Cooling rates (CR) reported in °C/min 6.0 175 4.0 186 2.0 x(T))) - 0.0 192 ln(1 -2.0 - ln( -4.0 -6.0 -8.0 2 2.5 3 3.5 4 ln (cooling rate) Figure 7-20: Ozawa plot for non-isothermal crystallization of PET made with petro EG from the melt at different temperatures 256 3.0 175 186 1.0 192 x(T))) -1.0 - ln(1 - -3.0 ln( -5.0 -7.0 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 ln (cooling rate) Figure 7-21: Ozawa plot for non-isothermal crystallization of PET made with bio EG from the melt at different temperatures From the linear relationships plotted in Figures 7-20 and Figure 7-21 the Avrami exponent can be obtained from the slope of the lines. Table 7.20 shows the results obtained. In agreement with the results obtained from isothermal crystallization, the Avrami exponent for PET made with petro EG is 4 and for PET made with bio EG is 3. These results confirm a difference in the crystallization behavior between the samples. This variation can be caused by the different amount of residual catalyst in the polymer, as an Avrami exponent of 3 is typically related to nucleation from particles [167], also other properties that affect crystallization were tested and found to be the same between products. 257 Table 7.20: Values of rate constant, k, and Avrami exponent, n, for PET samples when crystallized dynamically from the melt Temperature Petro EG1 Bio EG2 °C n K n K 175 4.0 26.7 3.1 17.2 186 4.0 12.6 3.1 10.3 192 4.0 7.6 3.1 6.5 1) Petro EG n = X ± 0.24, K=(min/deg)4 2) Bio EG n = X ± 0.35, K=(min/deg)3 7.2.7.3 Crystal size PET is known to have a triclinic crystal form, this means, all the angles and lengths of the crystalline unit are different. Typically, the determinations of crystal size are done through wide angle X-ray determinations. The main diffraction peaks for PET are reported in Table 3.6. If the chains in both polymers have the same level of modification the size of the crystals (caused by the presence of copolymer or chain modifier-compounds) should be the same. Polymer samples produced with both sets of raw materials were crystallized overnight at isothermal conditions (220 °C) in a vacuum oven. The samples were analyzed using a Rigaku Ultima III X-Ray diffractometer. The WAXD pattern obtained was following the method reported by Patcheack [122]. Three amorphous peaks were fitted obtaining 7 crystalline peaks. Figure 7-22 shows the WAXD pattern for PET sample produced with petro EG. 258 Figure 7-22: Typical WAXD pattern for a PET sample made with petro EG glass crystallized at 220 °C for 10 hours and peak deconvolution of the WAXD profile. Dashed line – Amorphous peaks. Dotted line – Crystalline peaks The 010 and 100 planes were selected for analysis of the crystal size. They represent the depth and width of the crystallites assuming the unit cell is cubic. From the WAXD pattern, the width of the deconvoluted peaks at half maximum for the selected reflections were obtained. These values along with the corresponding scattering angle were used in the Scherrer Equation (Equation 3.7) to calculate the crystallite dimensions in the 010 and 100 planes. The results obtained are reported in Table 7.21. The 259 dimensions of the crystals were very similar for PET samples produced with either raw materials. The results obtained are lower than values reported in literature. Patcheack [122] obtained 13.3 and 10.4 nm crystallite sizes for 010 and 100 reflections, the samples used were thin films isothermally crystallized in a hot stage. The small thickness of the film and the controlled heating environment in the hot stage can be a root cause for obtaining crystallites with larger dimensions. Table 7.21: Crystallite sizes in the direction of 010 (depth) and 100 (width) Plane (h k l ) Material d(Å) Centroid (°) FWHM Xs(nm) Petro EG 5.031 17.6 0.925 8.9 010 Bio EG 5.040 17.6 0.878 9.4 Petro EG 3.407 26.1 1.222 6.8 100 Bio EG 3.412 26.1 1.201 6.9 7.2.8 Summary Results obtained from the production of PET using petro PTA and bio/petro EG in a melt phase polymerization process, the discussion of the process conditions and the characterization of the polymers produced were presented in this section. PET was successfully synthesized with comparable quality using two sets of raw materials, petro EG/petro PTA and bio EG/petro PTA. Side products present in bio EG were identified in the condensate obtained from the esterification reaction. Analysis of the progress of reaction in esterification, variation of process conditions and total amount of material produced support the conclusion that 260 these side products did not participate in the polymerization reaction to create the polymer. The polymer produced with bio EG had distinctive characteristics in thermal stability and crystallization behavior. Polymer characterization including concentration of end groups, residual catalysts, molecular weight, kinetics of crystallization and crystallite dimensions revealed that a difference in the residual catalyst concentration was the root cause for the observed behavior and it was not related to the use of a different raw material. From the analysis of polymerization process conditions, physical properties, thermal stability and crystallization behavior of the polymers produced, we were able to determine that there was no difference in the use of either raw materials for the production of PET in the described melt phase polymerization processes. 7.3 Synthesis of PET using bio PTA and bio EG 7.3.1 Experimental The experimental set-up used for these experiments consisted of a 25 ml stainless steel reactor (4590 Micro Bench Top Parr Reactor) equipped with a 4-blade propeller stirrer, a pressure transducer installed on the head of the vessel, a thermocouple positioned to read the temperature of the reacting mixture, a gas feed line connected to a port in the head, a double tube condenser with a helix rod in the core tube installed on one of the ports in the head and a thermocouple reading the temperature of the vapor 261 phase heading towards the condenser. The transfer line connecting the reactor and the condenser was maintained at a high temperature using heating tapes. The service cooling water for the condenser was pumped from an auxiliary water bath set at 0 °C. The heating of the system was done using a band heater installed on the outside surface of the vessel. This heater was controlled by a PID unit calibrated with ethylene glycol at the operating temperatures of the polymerization. The thermocouple (on the line of the condenser) and pressure transducer were connected to a main controller that continuously recorded the temperature and pressure of the system. Esterification and polycondensation were done in a continuous manner in the same reactor. The process diagram of the experimental set-up is shown on Figure 7-23. The labels shown in the diagram are used to explain the experimental procedure. In a typical experimental run, PTA (PTA), EG (EG) and trimethylamine (TEA) were placed inside the reactor. The system was flushed with nitrogen for 5 minutes and the heating tapes were started to bring the transfer line to a temperature of 145 °C. The contents were heated to 240 °C over a period of 90 minutes, pressure was set at 48 psi and increased to ~51 psig at the end of the heating. This step was the paste mixing step. The temperature was increased to 265 °C over a period of 30 minutes and pressure was increased to a value of 58 psig. These conditions were maintained for 2 hours in order for esterification to proceed. The progress of the reaction was monitored with the temperature reading in the transfer line connecting the reactor and the condenser. An increase in this variable meant water was produced in the system and traveled towards the condenser. The pressure of the system was sequentially decreased to atmospheric conditions over a period of 60 minutes. Atmospheric esterification was continued for an 262 additional period of 60 minutes. At this point, the condensate produced during esterification was recovered from the condenser (WATER), the heater was removed from the reactor and the system was opened to add the solid catalyst (CATALYST) directly into the molten material. In an effort to minimize oxidative degradation a low pressure nitrogen flow was maintained during this step. The reactor was closed and flushed for 3 minutes. Nitrogen was introduced to obtain a pressure of 48 psig. The temperature of the reactor was increased to 285 °C over a period of 60 minutes and the stirring speed was set at 260 rpm. This step was used to allow the metal catalyst to first dissolve in the prepolymer and then to react and create the metal complex required for polycondensation. The pressure of the system was gradually reduced to atmospheric conditions over a period of 40 minutes and kept at this conditions for an additional 30 minutes. At this point of the reaction, the metal complex was formed and glycol removal was needed to promote polycondensation. Vacuum was gradually applied from the head of the vessel by adjusting a three way valve in the vacuum line. After 60 minutes the system was operating with full vacuum, at 285 °C and a stirring speed of 260 rpm. The temperature and vacuum were maintained constant throughout the rest of the polymerization. The stirring speed was increased to 362 rpm when full vacuum was applied. After 30 minutes the speed was decreased to 207 rpm and maintained at this value. The progress of the reaction was monitored by reading of the torque of the stirrer. When the reaction was completed, the system was opened and the contents (PET) were manually poured in a cold water bath. The solidified product was crushed and transformed into powder by freezing with liquid nitrogen and using a blender. 263 COLUMN VENT EGPROD P I WATER T I EG PTA CATALYST VACUUM COLDTRAP POLYM PET Figure 7-23: Process diagram for the production of PET from bio EG, petro PTA and bio PTA. 264 7.3.2 Preliminary experiments and process conditions rationale The Parr reactor used for polymerization is a recent acquisition in the Polymer Institute. No previous studies have been done with the unit and preliminary studies were conducted to determine the proper process conditions needed to produce polymer with consistent quality variables. The products produced were tested for their melt viscosity using the RDA Rheometer. The initial testing was done replicating the conditions used to evaluate materials prepared in the 3 L reactor used for polymerization of bio EG. Adjustments to the polymerization procedure were done based on the results obtained. The main difference in the two systems is the addition of catalyst. In the case of Parr reactor, the catalyst is added in a solid form directly to the molten material. It was found that if the catalyst is dissolved in EG and added to the reactor, at the moment of addition the thermal difference between the molten polymer and the solution is so high that precipitation of the catalyst was evident to the naked eye (reduction of antimony). The drawback with the method used in the Parr reactor is that the molten product is exposed to oxygen during catalyst addition. As reviewed in Section 2.2.3, the polymer reaction with oxygen produces radical compounds that create discoloration and reduction in molecular weight. This effect could not be avoided, but could be limited by the time the system was exposed to oxygen. For all experiments this detrimental factor was considered to be the same. The obtained product with the replicate experimental procedure was unreacted prepolymer with molecular weight below the limit of detection in the RDA. Most of the product was obtained as a transparent liquid, some was attached 265 to the stirrer and appeared to have a different viscosity due to formation of brittle strings when pulled. The total amounts of reactants were gradually decreased in different runs to investigate if the level of molten product had an effect in glycol removal and was limiting the build-up of molecular weight. The amount of reactants in the first experiments was determined based on the recommendation from Parr Instruments on safe operation of the system, in which 70% of the total volume was occupied by the reactants. Most of the initial experiments were unsuccessful, yielding products with low molecular weight and a distinctive yellow/brown coloration. This color was attributed to reaction of oxygen at the moment of catalyst addition. More positive results were obtained when the level of the total amount of reactants just barely covered the surface of the stirrer. The cylindrical design of the reactor vessel and the position of the propeller stirrer (at the bottom of the vessel) created a headspace above the stirrer that was not agitated in the same way as product in the bottom. This difference could have caused limitations in the diffusion of glycol through the molten material to the liquid-vapor interphase and in its removal from the system. If glycol was trapped in the reacting medium the reactions would be maintained at equilibrium conditions and no build-up of molecular weight could occur. When the level of reactants was minimal, a more uniform agitation profile was applied to the molten product and the path of diffusion for EG was reduced. Following this idea of improving the conditions for glycol removal, different stirring speed profiles were tested. In the 3 liter reactor and in most of industrial operation reactors, agitation is done with a helix impeller operated at low rpm (~50), this stirrer 266 design increases the interfacial area between the liquid-vapor phases. As molecular weight is built-up, the molten product travels upward through the coiled blade of the stirrer and falls back into the melt by the action of gravity. This process increases the interfacial area and produces a thin layer (shorter diffusion path) of polymer. In the Parr reactor, it was not possible to have a helix agitator due to geometrical constrains. The propeller impeller used provided agitation radially and axially but no movement of the molten product was possible. It was found that having a profile with high agitation speeds increased the build-up of molecular weight. The high stirring speed created a pronounced vortex reducing the thickness of the molten material and increasing the interfacial area. A shear effect with the wall of the reactor was also possible, creating a localized increase in temperature that may have caused thermal degradation. This effect was considered the same for all experiments as the stirring profile was the same. Using a profile with minimal amount of reactants and high stirring speed, it was possible to produce polymer obtained with a melt viscosity ~0.4 dl/g. This evidence of increase in molecular weight was also registered by an increased torque in the stirrer. The color of the material produced was yellow/brown. These experimental conditions were selected to produce polymer with bio EG/petro PTA and bio EG/bio PTA. It was known from the results presented in the previous section that the use of bio EG did not cause significant difference in polymer synthesis and characteristics. Any difference in the results obtained from samples produced for this section would be assignable to the use of a different terephthalic acid (petro or bio). 267 7.3.3 Process analysis After process conditions for polymerization were determined, the polymerization with two sets of raw materials was done. Petro PTA and bio EG were used for one batch and bio PTA with bio EG were used for the second one. Table 7.22 shows the mass balance of reactants used for the reaction. In addition to the reactants shown in Table 7.22, 1 drop of TEA was added to the system to reduce the formation of DEG. Table 7.22: Initial material balance for esterification reactions ID M.W. mol grams PTA1 166.1 2.107E-02 3.5 EG 62.0 2.839E-02 1.76 2 Sb2O3 291.5 3.368E-06 9.82E-04 1) Mol ratio [EG]/[PTA] = 1.35 2) [Sb] = 300 ppm in theoretical PET produced The pressure of the system and the temperature in the transfer line between the reactor and the condenser were continuously monitored. This temperature was used to monitor the progress of esterification. Figure 7-24 shows the recorded profiles for reaction of petro PTA/bio EG and Figure 7-25 shows the recorded profiles for reaction of bio PTA and bio EG. During the esterification reaction, the pressure of the system increased as the temperature in the reactor reached 265 °C. Once the temperature was constant the pressure stabilized at a value ~58 psig. At this value the boiling point of EG was 259 °C and that of water 154 °C. During this initial stage no evidence of water removal was seen, as the temperature in the transfer line remained constant. A stable 268 value of ~134 °C was obtained through the thermal effect of the heating tapes surrounding the line. When pressure was reduced to atmospheric conditions in stage changes, the temperature in the condenser increased rapidly for a few seconds and started to decrease to the equilibrium value at the specific pressure. This increase in temperature was caused by the removal of water/glycol from the reactor. After esterification was finished, nitrogen was introduced to flush any remaining water in the transfer line or in the walls of the condenser. This was registered as a sudden increase in temperature and pressure at ~405 minutes. The reactor was opened and the catalyst was added to the system. After flushing for 5 minutes to remove any oxygen from the system, the pressure was set to 49 psig at ~420 minutes to allow reaction of the prepolymer with the catalyst. After 60 minutes the pressure was reduced and full vacuum was gradually applied. 190 Temperature Pressure 110 170 150 90 130 70 C) ° 110 50 90 70 30 50 Temperature ( Temperature 10 30 (psig) Pressure -10 10 -10 0 -30 50 450 150 200 250 300 350 400 500 550 600 650 700 750 800 100 Time (min) Figure 7-24: Condenser temperature and system pressure profiles during polymerization of PET made with petro PTA and bio EG 269 200 Temperature 110 Pressure 180 90 160 70 140 C) ° 120 50 100 30 80 60 10 Temperature ( Temperature 40 -10 (psig) Pressure 20 0 -30 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 Time (min) Figure 7-25: Condenser temperature and system pressure profiles during polymerization of PET made with bio PTA and bio EG After catalyst complexation was completed and removal of glycol started, the build-up of molecular weight was registered as an increase in the motor output required to maintain a constant stirring speed. Figure 7-26 shows the variation of torque during the polycondensation of bio PTA and bio EG. Similar variations in torque measurements were seen for both sets of raw materials. Reaction was stopped after a torque reading of 30.8 %motor output was achieved. 270 31.5 31.3 31.1 30.9 30.7 30.5 30.3 30.1 29.9 Torque (%motor output) (%motor Torque 29.7 29.5 1 16 31 46 61 76 91 106 121 136 Time (min) Figure 7-26: Variation in torque during polycondensation of bio EG and bio PTA prepolymer. Time zero is considered when the catalyst was added As discussed in Section 7.2.3, the side products found in bio EG were identified through GC analysis of the condensate obtained from the esterification reaction. The same analysis was done on samples collected from esterification of bio EG with petro PTA and bio PTA. Figure 7-27 shows the results obtained. In both chromatograms the presence of their respective characteristic peaks at retention times ~23-25 minutes were observed. This indicates that side products from bio EG were removed from the system through the condensate. Similar unidentified peaks were also observed in both condensates, thus there is similarity in the products obtained with either set of raw materials. 271 Figure 7-27: GC-FID chromatogram (zoomed view) of liquid samples. Top: Condensate from esterification of petro PTA and bio EG Bottom: Condensate from esterification of bio PTA and bio EG Table 7.23 shows the product recovery in each polycondensation reaction. In both cases the recovery of glycol was not good due to the very low amount generated. It is likely than any EG molecules remained in the walls of the transfer line or fittings and were not able to travel to the condenser. Its removal from the reaction media was still possible as molecular weight increased during the reactions. For both sets of raw materials, there were losses due to product solidification in the walls of the reactor. This material was not scraped from the surface as it has been exposed to a higher thermal history than the rest of the product in the melt and may not have been representative of the characteristics obtained in the bulk product. 272 Table 7.23: Comparison of yield for polycondensation reactions Actual Yield (g) ID Expected Yield (g)1 Petro PTA Bio PTA PET 2.73 2.2 1.98 EG 0.88 0.15 0.19 1) Calculated from the stoichiometry Based on the information monitored during esterification and polycondensation, the analysis of condensate during esterification and the yield obtained in the polymerization, there was no difference in the use of commercial petro PTA or the produced bio PTA along with bio EG to synthesize PET. The polymer samples produced with bio and petro PTA were tested following the general principles used for analysis of samples synthesized with different EG products. The experimental procedure and the purpose for doing each test were the same. Due to limited quantity of sample available for testing, it was not possible to do the analysis for thermal stability, the rest of the tests are discussed in the next sections. 7.3.4 Physical properties 7.3.4.1 Solution viscosity Solution viscosity is a method typically used to obtain the intrinsic or the inherent viscosity of a polymer. In this test, the resistance to flow behavior of a polymer in solution is compared to that of the pure solvent. The difference in time to travel a specified distance in a viscometer is related to the viscosity of the polymer. 273 The measurements of solution viscosity in the polymers produced were not done in the Polymer Institute, the samples were sent for analysis to a laboratory. The procedure followed was based on an ASTM procedure [170]. Highlights of the procedure are included here as reference: the polymer sample was dissolved in a 60/40 phenol/1,1,2,2 tetrachloroethane solution to obtain a sample with concentration of 0.5%. The dissolved liquid passed through an Ubbelohde viscometer immersed in a water bath at 30 °C. The time elapsed for the sample to pass through two calibration marks was recorded and compared to that of the solvent. The Kraemer equation was used to calculate the viscosity of the sample [114]. Table 7.24 shows the results obtained. Prepolymer refers to material sampled from the reactor just before catalyst addition, this product is representative of the material obtained at the end of the esterification stage. Polymer refers to the final product obtained after polycondensation. The results obtained at each stage for both polymers produced were comparable. As seen before in the analysis of the process conditions, the increase in torque during polymerization led to the same maximum level. The similarity in the final I.V. of the polymer serves as confirmation that polycondensation proceeded in the same manner for both sets of raw materials. The final I.V. of the polymers are significantly lower than the values reported in the previous section. This could be caused by catalyst deactivation during polymerization, degradation reactions due to thermal effect (high stirring speed) or oxidative degradation due to exposure of the molten product to air at the moment of catalyst addition. 274 Table 7.24: Comparison of solution viscosity measured at 30 °C Sample Material I.V. Prepolymer 0.130 Petro PTA Polymer 0.414 Prepolymer 0.118 Bio PTA Polymer 0.410 7.3.4.2 Color The polymers obtained from the reactor were cut in small pieces of similar size. The pieces were placed in a vial and analyzed for their color. Table 7.25 shows the color measurement of the samples produced with petro and bio PTA. There was a slight difference in the L* index for the petro PTA sample, the b* indices were the same. In general, both materials had a strong color tendency towards yellow and black. This discoloration was caused by the creation of colored compounds as a result of oxidation degradation at the moment of catalyst addition. This unavoidable effect, seemed to be the same for both polymers. Table 7.25: L* and b* values of PET samples in powder form Amorphous Sample L* b* Avg. St. Dev. Avg. St. Dev. Petro PTA 43.2 0.8 11.3 0.7 Bio PTA 46.6 0.6 10.1 1.0 275 7.3.5 Product composition 7.3.5.1 Residual catalysts For polymerization reactions in the Parr reactor only antimony was used as catalyst. Table 7.26 shows the quantification of the metal in the polymer samples. There was a higher concentration in the sample prepared with petro PTA. This difference was attributed to the experimental procedure followed for the addition. The amount of catalyst added to the system was calculated to obtain a final concentration in the polymer of 300 ppm. The results obtained are clearly below this value. The causes for obtaining this reduced amount include: a reduction of the metal catalyst causing precipitation of elemental antimony and poor dispersion in the resulting molten product, improper incorporation of the solid particles into the molten product at the moment of addition causing the catalyst to remain in the walls of the reactor or the impeller and experimental error attributed to product recovery from the reactor. It was previously discussed that the material solidified in the wall of the reactor was not recovered for analysis. If the process of catalyst reduction occurred, it could explain the observed L* index towards black in both polymers. The low concentration of catalyst (compared to the desired amount) explains the relative low value obtained in solution viscosity. The increase in molecular weight is dependent on the concentration of catalyst available for polycondensation reactions [165]. 276 Table 7.26: Residual catalyst concentration in PET samples Sb ppm Sample Average St. Dev. Petro PTA 104 1.0 Bio PTA 94 0.3 7.3.5.2 Carboxyl end groups Table 7.27 shows the carboxyl determination results obtained for both polymers. For these analyses the NaOH solution was normalized again, detailed information can be found in Appendix D. The difference in the concentration of carboxyl end groups was within standard deviation of the measurement, both polymers had the same carboxyl concentration. It was evident from color determinations that degradation had occurred in the system. The carboxyl results confirmed that the effect of this degradation (reaction that produces more carboxyl) had the same impact in both polymers. The concentration of carboxyl end groups as indicative of the extent of reaction also confirms similarity between the two sets of raw materials, the higher value compared to the results obtained for polymers produced in a different reactor is indicative of differences in the degree of polymerization between polymers. This difference was also seen in the comparison of molecular weight. 277 Table 7.27: Carboxyl end group concentration obtained from titration test PET Time1 Reading (mm)3 Difference Net4 COOH ID Cf2 St. Sample mg sec. Initial Final ml L meq/g Avg. Dev. 98 142 4.90 6322 13714 73.9 72.1 38 Petro 99 160 5.50 4502 12476 79.7 77.9 40 41 2.99 PTA 98 139 4.80 3601 12172 85.7 83.9 45 98 153 5.20 7272 16021 87.5 85.7 46 Bio 97 141 4.80 6170 14273 81.0 79.2 43 43 2.08 PTA 98 147 5.00 3779 11624 78.5 76.6 41 B.A.5 5 ml 180 -- 4123 4304 1.8 ------1) Heating time required to dissolve the sample in a benzyl alcohol bath 2) Correction factor for carboxyl generation during heating time 3) Difference in readings of titrating media inside the burette 4) Net volume consumed during titration of each sample 5) Blank sample containing benzyl alcohol, chloroform and indicator 7.3.5.3 Copolymer content The copolymer contents in the PET samples were determined in a laboratory outside the Polymer Institute. Table 7.28 shows the results obtained. There was a higher concentration of DEG for the sample produced with petro PTA. Among the different reasons that affect the formation of DEG, the concentration of catalyst has been studied by researchers. Chen et al. [39] analyzed the formation of DEG at various temperatures and catalyst concentrations (antimony). They found that the rate of formation of DEG is linearly dependent on the concentration of catalyst and the rate of reaction increases with increasing temperature. As the time of reaction passes, the concentration of DEG increases until a constant (equilibrium) value is obtained. This could explain the higher 278 concentration of DEG in the sample produced with petro PET, since this sample contained a higher concentration of antimony. Table 7.21: Concentration of DEG in polymer samples DEG % weight Sample Avg. St. Dev. Petro PTA 2.12 0.13 Bio PTA 1.76 0.09 7.3.7 Crystallization 7.3.7.1 Isothermal crystallization The samples were analyzed using the same procedure reported on Section 7.2.7.1. The heat curve from the hold step was integrated to obtain the relationship of heat flow vs time for each material. Figure 7-28 shows the characteristic crystallization isotherms for both materials. The detailed information obtained from the integration and the values used for the Avrami equation can be found in Appendix K. 279 1.0 0.9 0.8 0.7 0.6 0.5 a 0.4 Petro PTA 0.3 0.2 Bio PTA 0.1 0.0 3.7 4.2 4.7 5.2 5.7 6.2 6.7 7.2 ln (time) (seconds) Figure 7-28: Comparative crystallization isotherms at 220 °C for PET samples Using the individual values of a versus time and Equation 7.7, the Avrami plots were obtained for both materials. Figure 7-29 shows the results obtained. Table 7.29 shows the Avrami parameters for primary crystallization obtained from the slope and intercept of the linear relationships plotted on Figure 7-29. Table 7.29: Values of rate constant, k, Avrami exponent, n, and half time, t1/2, for PET samples when crystallized isothermally from the melt at 220 °C Petro PTA Bio PTA Crystallization n Intercept k t 1/2 n Intercept k t 1/2 Primary 2.7 -15.9 1.1E-07 355 2.6 -15.7 1.5E-07 334 k, sec -n t 1/2, sec 280 0 4.5 5.0 5.5 6.0 -0.5 -1 -1.5 a)) ln( - -2 ln( -2.5 Petro PTA -3 Bio PTA -3.5 ln (time) (seconds) Figure 7-29: Avrami plot for isothermal crystallization of PET samples from the melt at 220 °C No secondary crystallization was observed. For both samples the slope had the same value, even at crystallization levels above 80%. The Avrami exponent obtained for these materials is close to a value of 3. This means that both polymers have nucleation independent of time and that the crystals grow in spherulitic structure. An exponent of 3 can also mean growth in two dimensions with nucleation dependent on time. Based on knowledge about PET crystallization, the first scenario is more likely to have occurred [38]. For the kinetics of crystallization, a direct comparison can be done between the polymers as the Avrami exponent was the same. It can be seen from Figure 7-28 and 7-29 that the sample produced with bio PTA required a lower crystallization time to achieve 281 the same level of crystallinity. The crystallization half times (calculated from the Avrami equation) have a difference of ~20 seconds. This time difference can be attributed to polymer characteristics previously described. The level of copolymer in the sample with bio PTA was lower. It has been determined that the less modification of the polymer chain the faster is the crystallization rate [38,167]. The sample made with petro PTA had a higher catalyst concentration that can cause an apparent increase in molecular weight of the polymer as the sample is heated during thermal analysis. It is known that a higher molecular weight reduces the rate of crystallization [164]. 7.3.7.2 Dynamic crystallization The samples were analyzed using the same procedure reported on Section 7.2.7.2. The second heating step was used to obtain the temperature and heat flow values for the thermal transitions and the second cooling step was used to obtain the Avrami exponent from Ozawa plots. The detailed information obtained from the integration and the values used for the Ozawa equation can be found in Appendix K. Table 7.30 summarizes the results obtained for both samples using different heating and cooling rates. The sample produced with petro PTA had a lower Tg at all cooling rates, this lower value could be caused by the increased level of DEG in the sample. The C-O-C linkage (attributed to DEG) in the chain provides more flexibility than the C-C linkage. Reduction in Tg by increasing DEG content has been reported in literature [38,171]. Another variable that is usually affected by the copolymer content is the melting point. In all determinations no important difference was seen between 282 samples. The peak of crystallization values obtained from the heating or the cooling steps show differences between samples. This is attributed to the difference identified in the kinetics of crystallization. As expected for a PET sample, in both cases, there is a decrease with increasing cooling rate, when cooling from the melt and an increase with increasing cooling rate when heating from the glassy state. Table 7.30: Physical parameters obtained from DSC analysis of PET samples Heating Cooling Sample Rate1 Crystallization Melting Crystallization ID °C/min Tg2 Tch3 Hch 4 Tm 5 Hm 6 Tcc 7 Hcc 8 (°C) (°C) (J/g) (°C) (J/g) (°C) (J/g) 10 76.4 139 -36 250.5 39 194 -37 15 76.9 141 -40 249.5 48 190 -45 Petro 20 77.0 152 -38 249.4 49 183 -47 PTA 30 79.0 158 -45 247.7 44 178 -50 40 77.9 161 -39 249.2 56 176 -38 10 81.0 148 -42 249.0 43 190 -41 15 80.2 153 -40 248.1 44 188 -43 Bio 20 80.7 160 -39 247.4 41 185 -40 PTA 30 80.8 163 -39 247.3 43 181 -44 40 80.6 165 -41 246.2 42 179 -38 1: Rates used for cooling from the melt or heating from glassy state 2: Glass transition temperature obtained from second heating step 3: Peak maximum temperature of glass crystallization 4: Glass crystallization enthalpy 5: Peak maximum temperature of melting 6: Melting enthalpy 7: Peak maximum temperature of melt crystallization 8: Melt crystallization enthalpy 283 As discussed previously, the peaks obtained from the second cooling step were integrated obtaining data points for the relative degree of crystallinity at different temperatures. Figure 7-30 shows the readings obtained for three different temperatures for both materials. The values were selected for crystallinity levels below 50%. The readings were used to create the Ozawa plots shown on Figure 7-31 and 7-32. Figure 7-30: Relative degree of crystallinity x (T) at specific temperatures (185, 192, 200 °C) for PET samples. Cooling rates (CR) reported in °C/min 284 2.0 185 192 1.0 200 0.0 x(T))) - -1.0 ln(1 - ln( -2.0 -3.0 -4.0 2 2.5 3 3.5 4 ln (cooling rate) Figure 7-31: Ozawa plot for non-isothermal crystallization of PET made with petro PTA from the melt at different temperatures 2.0 185 1.0 192 0.0 200 x(T))) - -1.0 ln(1 - -2.0 ln( -3.0 -4.0 -5.0 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 ln (cooling rate) Figure 7-32: Ozawa plot for non-isothermal crystallization of PET made with bio PTA from the melt at different temperatures 285 From the linear relationships plotted on Figures 7-31 and Figure 7-32 the Avrami exponent can be obtained from the slopes of the lines. Table 7.31 shows the results obtained. For both polymers the Avrami exponent is the same. It is not possible to determine with this sole result if the polymer nucleate and grow in the same fashion. As seen on Table 7.17 a value of two is assigned for two different morphologies and mechanism of nucleation. The exponent obtained is lower than the values reported as a result of isothermal crystallization indicating that the mechanism of crystallization is different. This difference in Avrami exponent on dynamic crystallization (typically a decrease) has also been obtained by other researchers [38,97]. Table 7.31: Values of rate constant, k, and Avrami exponent, n, for PET samples when crystallized dynamically from the melt Temperature Petro PTA1 Bio PTA2 °C n K n K 175 2.0 19.7 2.0 16.6 186 2.0 10.6 2.0 17.5 192 2.0 13.7 2.0 4.5 1:Petro PTA n = X ± 0.16, K=(min/deg)2 2:Bio PTA n = X ± 0.19, K=(min/deg)2 7.3.8 Summary Results obtained from the production of PET using bio EG and bio/petro PTA in a melt phase polymerization process, the discussion of the process conditions and the characterization of the polymers produced were presented in this section. 286 PET was successfully synthesized with comparable quality using two sets of raw materials, bio EG/petro PTA and bio EG/bio PTA. The analysis of esterification and polymerization process conditions, physical properties and crystallization behavior showed there was no difference in the synthesis and quality of the polymer produced with petro or bio PTA in the described melt phase polymerization process. The polymer produced with bio PTA showed a difference in the crystallization behavior. Polymer characterization including solution viscosity, concentration of end groups, kinetics of dynamic and isothermal crystallization and residual catalysts revealed that a reduced concentration of residual catalyst and a lower concentration of copolymer are the root cause for the observed behavior and it was not related to the use of a different raw materials. 287 Chapter 8 Conclusions and future work recommendations 8.1 Conclusions The broad purpose of this research was to produce PET polymer with comparable quality using petro and bio derived raw materials. This comprehensive study included the analysis of the initial raw materials to identify impurities present, the selection and engineering analysis of the required physical separation methods to obtain bio p-xylene with high purity grade, the modification of the AMOCO process to produce PTA with sufficient purity for polymer requirements, the synthesis of PET with bio and petro monomers using melt phase polymerization and a multi-variable characterization of the polymers produced. Through the knowledge obtained from these analyses, the suitability of using a bio derived monomer to produce PET polymer was evaluated. From the analysis of the initial bio derived samples used in this research. Bio EG contained a small concentration (0.01%<) of impurities not detected in the petro EG. The information obtained from literature suggested the formation of these compounds through the oxidation of the EG molecule at elevated temperatures [131]. The physical properties of the bio material evaluated through refractive index and color indices did not show any 288 difference when compared with the commercial EG product, the presence of the impurities had a negligible effect on the variables analyzed. The bio based content of the product was 100%. It was concluded that this material should have been produced following one of the reported methods in Section 2.4.2. The bio BTEX sample contained a mixture of aromatic compounds of different carbon content and degree of substitution. The main components were benzene, toluene and xylene isomers. It was found that some oxygenated compounds at low concentrations, caused a yellow coloration in the bio BTEX (b*=3.4). The diluted bio p-xylene sample contained a small concentration of 2,5 DMF (0.2%), branched/linear alkanes (79.6%) and p-xylene (20.1%). It was found that the alkanes caused the brown/yellow coloration in the original sample (L*=33.3, b*=0.8). The bio based content of the product was 63%, five of eight carbons in the molecule were obtained from biomass. This result along with the identification of 2,5 DMF in the sample are the basis to conclude that the sample was obtained through one of the methods reported on Section 2.4.3.1 and 2.4.3.2. P-xylene was successfully separated (with high purity grade) from the bio derived mixtures by using physical separation methods such as filtration, fractional distillation and crystallization. The preliminary experiments done to determine the appropriate heating profile during distillation, allowed to identify the split-points for each sample. For the diluted bio p-xylene sample, the condensate obtained at the second split-point (~202 °C) had a high concentration of p-xylene (~98.7%) and some remaining 2,5 DMF (~0.22%) and alkanes (~0.32%). For the bio BTEX sample, the condensate obtained in the second split-point (~137 °C) had a high concentration of xylene isomers (%95) and some residual toluene. For both samples, the impurities that cause a coloration in the 289 sample maintained in the residue inside the beaker. The condensates obtained had a reduced b* index towards the blue compared with the original sample. The effective separation in distillation experiments of high purity p-xylene from the bio BTEX sample was limited by the presence of xylene isomers. For the diluted bio p-xylene samples, the presence of 2,5 DMF and linear/branched alkanes did not impart any equilibrium limitations. The products obtained from distillation experiments did not meet requirements for high purity grade product. Crystallization in a cold bath was used to improve the purity. For the bio BTEX second condensate, the presence of xylene isomers limited the amount of p-xylene recovered in the crystal phase due to equilibrium conditions (Figure 5-7). Reprocessing of the purified material was done to achieve the desired grade. The concentration of p-xylene in the final product was high with a value of 99.7%. The final yield of material at this purity was low (~5 grams). This amount was not enough to produce PTA. For the diluted bio p-xylene second condensate, the impurities present did not limit the recovery of p-xylene in the crystal phase. The final product obtained had a concentration of 2,5 DMF (~0.01%) and p-xylene (~99.98%). This material meets requirements to be classified as high purity grade. PTA was produced using a modified AMOCO process obtaining a material with quality variables close to a commercial PTA product. The conditions for the oxidation and purification reactions were determined by preliminary studies. The separated bio p- xylene and commercial petro p-xylene were transformed using the same procedure to identify differences in performance and product quality. Both products produced CTA and PTA with comparable purity, color indices and concentration of side products. LC- MS analysis revealed the presence of the typical oxidation intermediates (i.e 4-CBA) in 290 the acids produced. The 2,5 DMF impurity present in bio p-xylene did not transformed to its oxidation product (2,5 FDCA). The GC analysis revealed that this molecule could have gone through degradation reactions by action of heat or by reaction with water produced during oxidation. The final quality of the acid was not affected by this transformation. The conversion of bio and petro p-xylene to CTA was lower than reported values in literature. This difference was caused primarily by the process conditions used during the experiments. The corrosion reaction between the stainless steel reactor and the acetic acid (solvent) limited the maximum temperature and pressure that could be used. The purification reaction reduced the concentration of impurities in the petro and bio CTA to quantities acceptable for the use of the acid in polymerization reactions (purity~99.8%). The optical density of the acids (petro=0.07, bio=0.05) and the color indices (petro L*=63 b*=-0.18, bio L*=61 b*=-0.36) indicate the effective reduction of impurities through the purification reaction and confirm the similarity in the product obtained with bio and petro p-xylene. In specific, bio p-xylene at a concentration of 99.98% was used to produce crude and purified terephthalic acid with no identified difference in the processing and product quality against the petro counterpart (i.e. petro p- xylene). The use of bio derived monomers in the production of PET was evaluated first, by using bio EG and petro PTA and then bio EG with bio PTA. In the first case, the impurities identified in the glycol molecule were detected (through GC analysis) in the water/glycol condensate obtained during esterification reactions. The characterization of the polymer through analysis of the physical properties, product composition, thermal stability and crystallization behavior, revealed that this impurities did not cause any 291 modification to the polymer produced during melt phase reaction. The polymerization conditions were also not affected as indicated by the monitoring of process conditions and molecular weight build-up during polycondensation. A direct comparison with a petro PET produced with the same system revealed a difference in the crystallization behavior of the polymer. Product characterization revealed that this difference was caused by a different concentration of residual catalyst in the material and was not related to the use of a bio derived monomer. The cumulative analysis of results determines that there was no difference in the use of bio or petro EG to produce PET. In the second case, the produced bio PTA was used with bio EG to synthesize PET. The polymer produced with bio PTA showed a faster crystallization rate. Polymer characterization including solution viscosity, concentration of end groups, kinetics of dynamic and isothermal crystallization and residual catalysts revealed that a reduced concentration of residual catalyst and a lower concentration of copolymer are the root cause for the observed behavior and it was not related to the use of a different raw materials. The analysis of esterification and polymerization process conditions, physical properties and crystallization behavior showed there was no difference associated to the use of a different raw material in the synthesis and quality of the product obtained with petro or bio PTA. In conclusion, the hypothesis was not rejected. It was possible to synthesize PET polymer with comparable quality using petro and bio derived monomers with similar purity. 292 8.2 Future work recommendations While this research provided a broad investigation towards understanding the overall effects of using bio derived monomers for the synthesis of PET, further work should be conducted to expand the analysis in each transformation stage and to evaluate the use of additional bio derived samples obtained from different biomass processing technologies. For this, the following recommendations are proposed: Extend the discussion of bio PET synthesis to include the production of the bio derived starting material in the scope of the analysis. In this research, the samples used were obtained from transformation of biomass through different technologies. If the process of production for these samples is included, a cause-effect relationship could be established between the type of impurities that can be present in the starting bio derived material (depending on the transformation process) and the effect on polymer production and characteristics. A second point of analysis regarding the use of a different bio derived starting material, using a sample produced with the same technology as the samples used in this research but obtained from a different type of biomass would provide valuable information on the effect of biomass in the production of monomers for polymerization. In this project, p-xylene was separated from bio derived samples to obtain a high purity grade product that is comparable in specifications to a commercial petro counterpart. A variation in the objective of the study can be done by obtaining bio p- xylene with different concentrations of impurities, the products will not meet high purity specifications but they can be used to analyze in more detail the maximum concentration of impurities that do not readily modified the characteristics of the PTA and ultimately 293 the PET produced. The number of experiments in the separation processes (outlined in this research) can be reduced to obtain a higher concentration of impurities in intermediate samples. The production of CTA in a stainless steel reactor is affected by the limitation in temperature and pressure caused by corrosion reaction of the solvent. To overcome this problematic area, an oxidation process with an alternative solvent can be investigated. The selection of the solvent should consider the solubility of the different intermediates obtained during oxidation and should have similar thermodynamic properties as acetic acid. The second option is to acquire a titanium reactor that can withstand the use of acetic acid. Having a system made with this material would allow to use the same process conditions used in industry and a direct comparison in production process and the terephthalic acid produced could be made. The build-up of molecular weight in the Parr reactor is somewhat restricted by the design of the vessel and limitations due to the experimental procedure. Further analysis can be done by modifying some of the features of the system (i.e. stirrer design, catalyst addition procedure) and evaluating the maximum molecular weight that can be attained. A second option is to follow the experimental procedure outline in this research to obtain a polymer with I.V. ~0.4 and do solid state polymerization on the product to increase the molecular weight. 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Polymer Engineering and Science, January 1991, Vol. 31, No.2, 110-115. 170 ASTM Standard D4603-91, “Standard test method for determining inherent viscosity of poly(ethylene terephthalate) (PET). ASTM International. West Conshohocken, PA, 2003, www.astm.org. 171 Amoco Chemicals. (1995). White paper on the effect of purified isophthalic acid modification on the thermal crystallization of PET. Chicago, IL. 312 Appendix A Quantification of BTEX using GC-FID A.1 Calibration curves using Restek BTEX standard Figure A-1: Certificate of analysis of BTEX standard use for the quantification of aromatic components using gas chromatography. 313 Calculation of calibration factors for BTEX components using Restek A089584 external standard for quantification. Standard - Restek Catalog No. 30213 Lot No. A089584 Table A.1: Concentration of aromatics in BTEX standard. Compound Concentration ug/ml Concentration ug/uL Benzene 2000 2 Toluene 2000 2 Ethylbenzene 2000 2 p-xylene 2000 2 m-xylene 2000 2 o-xylene 2000 2 Table A.2: Area units obtained from GC chromatograms of multiple BTEX standard injections. Sample # Area 1 2 3 4 5 Avg. Benzene 26157 25294 34128 49156 24463 31840 Toluene 31760 29185 49025 60778 32507 40651 Ethylbenzene 41678 36703 69168 74562 44186 53259 p-xylene 42638 37798 70009 75847 44818 54222 m-xylene 46125 40205 75173 82142 49070 58543 o-xylene 48343 41659 80021 83586 50991 60920 Concentration ug/uL Calibration Factor = Average area units Table A.3: Calibration factors used for quantification of aromatic components using gas chromatography. Compound Calibration Factor Benzene 6.28E-05 Toluene 4.92E-05 Ethylbenzene 3.76E-05 p-xylene 3.69E-05 m-xylene 3.42E-05 o-xylene 3.28E-05 314 A.2 Calibration curves using samples prepared in the laboratory A.2.1 Calibration curve for toluene obtained from gas chromatography. Table A.4: Area under the curve for different concentrations of toluene Concentration1 Area 1 Area 2 Area 3 Avg. Area 58 2.536E+06 2.485E+06 2.590E+06 2.200E+06 173 6.009E+06 8.071E+06 8.076E+06 7.386E+06 289 1.232E+07 1.523E+07 1.157E+07 1.272E+07 462 2.141E+07 2.389E+07 2.229E+07 2.253E+07 635 3.500E+07 3.120E+07 3.510E+07 3.377E+07 1) g/L 4.0E+07 3.5E+07 3.0E+07 Slope: 54363 2.5E+07 Intercept: -1859235 2.0E+07 2 Area 1.5E+07 R = 0.981 1.0E+07 5.0E+06 0.0E+00 0 200 400 600 800 Concentration g/L Figure A-2: Calibration curve for toluene 10% 5% 0% -5% Residuals -10% 0 100 200 300 400 500 600 700 Concentration g/L Figure A-3: Plot of residuals for toluene calibration data points 315 A.2.2 Calibration curve for ethylbenzene obtained from gas chromatography. Table A.5: Area under the curve for different concentrations of ethylbenzene Concentration1 Area 1 Area 2 Area 3 Avg. Area 29 1.503E+06 1.023E+06 1.520E+06 1.349E+06 57 3.130E+06 2.311E+06 2.786E+06 2.778E+06 115 4.698E+06 6.512E+06 5.090E+06 5.433E+06 172 8.852E+06 1.073E+07 8.055E+06 9.211E+06 287 1.485E+07 1.659E+07 1.593E+07 1.579E+07 1) g/L 2.0E+07 1.6E+07 1.2E+07 Slope: 56417 Slope: 54363 Intercept: -519321 Area 8.0E+06 Intercept: -1859235 R2 = 0.98 2 R 4.0E+06 = 0.981 0.0E+00 0 100 200 300 400 Concentration g/L Figure A-4: Calibration curve for ethylbenzene 20% 10% 0% Residuals -10% -20% 0 50 100 150 200 250 300 Concentration g/L Figure A-5: Plot of residuals for ethylbenzene calibration data points 316 A.2.3 Calibration curve for m-xylene obtained from gas chromatography. Table A.6: Area under the curve for different concentrations of m-xylene Concentration1 Area 1 Area 2 Area 3 Avg. Area 29 2.397E+06 2.366E+06 2.378E+06 2.033E+06 57 4.845E+06 3.830E+06 4.030E+06 4.134E+06 115 1.102E+07 9.859E+06 8.794E+06 9.598E+06 172 1.586E+07 1.362E+07 1.409E+07 1.445E+07 287 2.812E+07 2.583E+07 2.395E+07 2.648E+07 1) g/L 3.0E+07 2.5E+07 2.0E+07 Slope: 95040 1.5E+07 Intercept: -1186564 R2 = 0.984 Area 1.0E+07 5.0E+06 0.0E+00 0 100 200 300 400 Concentration g/L Figure A-6: Calibration curve for m-xylene 20% 10% 0% -10% Residuals -20% 0 50 100 150 200 250 300 Concentration g/L Figure A-7: Plot of residuals for m-xylene calibration data points 317 A.2.4 Calibration curve for p-xylene obtained from gas chromatography. Table A.7: Area under the curve for different concentrations of p-xylene Concentration1 Area 1 Area 2 Area 3 Avg. Area 29 1.768E+06 1.579E+06 1.990E+06 1.727E+06 58 3.106E+06 2.659E+06 2.613E+06 2.681E+06 115 6.339E+06 8.717E+06 7.430E+06 7.033E+06 173 1.033E+07 1.295E+07 1.114E+07 1.093E+07 289 2.232E+07 1.973E+07 2.089E+07 2.046E+07 1) g/L 2.5E+07 2.0E+07 1.5E+07 Slope: 73830 Intercept: -1251456 Area 1.0E+07 2 R = 0.974 5.0E+06 0.0E+00 0 100 200 300 400 Concentration ug/uL Figure A-8: Calibration curve for p-xylene 20% 10% 0% Residuals -10% -20% 0 50 100 150 200 250 300 Concentration g/L Figure A-9: Plot of residuals for p-xylene calibration data points 318 A.2.5 Calibration curve for o-xylene obtained from gas chromatography. Table A.8: Area under the curve for different concentrations of o-xylene Concentration1 Area 1 Area 2 Area 3 Avg. Area 29 2.281E+06 2.140E+06 2.324E+06 2.248E+06 59 4.086E+06 2.156E+06 2.180E+06 2.807E+06 117 5.111E+06 7.738E+06 6.973E+06 6.607E+06 176 1.108E+07 1.144E+07 1.323E+07 1.191E+07 293 2.243E+07 2.117E+07 2.023E+07 2.128E+07 1) g/L 2.5E+07 2.0E+07 Slope: 75384 1.5E+07 Intercept: -1147363 2 1.0E+07 R = 0.978 Area 5.0E+06 0.0E+00 0 100 200 300 400 Concentration ug/uL Figure A-10: Calibration curve for o-xylene 20% 10% 0% -10% Residuals -20% 0 50 100 150 200 250 300 Concentration g/L Figure A-11: Plot of residuals for o-xylene calibration data points 319 Appendix B Acetaldehyde generation – Calibration curve Table B.1: Acetaldehyde concentration and peak area for calibration curve standards ran on ATD machine. AA (mg) Peak area Peak area Sample Concentration of Tube in the Run 1 Run 2 amount AA solution injection V*sec V*sec Tenax05 2 ul 1 mg/ml 0.002 16296 16048 Tenax04 4 ul 1 mg/ml 0.004 32454 33422 Tenax03 6 ul 1 mg/ml 0.006 54821 56517 Tenax02 8 ul 1 mg/ml 0.008 69821 71556 Tenax01 10 ul 1 mg/ml 0.01 91280 90185 Table B.2: Average calibration factor for acetaldehyde quantification in AA generation experiments. Run # Calibration Factor 1 (mg/V*sec) 1 1.120E-07 2 1.112E-07 Average 1.116E-07 320 Appendix C Residual catalyst quantification for polymers made with petro and bio EG Table C.1: Residual catalyst concentration in PET samples made with bio and petro EG Sample ICP Results2 Metal concentration on PET3 Xc1 Sample weight Sb Co P Sb Co P mg mg/L ug/L ug/L ug/L ppm ppm ppm Petro 100.1 200.2 48.0 7.0 6.0 239.9 35.1 30.0 EG 100.4 200.8 46.9 6.9 5.8 233.4 34.3 28.9 Bio 100.6 201.1 61.0 7.2 6.4 303.3 35.9 31.7 EG 100.7 201.4 63.2 7.1 7.1 313.9 35.4 35.1 1: Polymer concentration in the injected sample to ICP MS. 2: Metal concentration in the injected sample, results reported in ppb. 3: Concentrations calculated using Xc and ICP results. 321 ICP report of antimony quantification for standard and PET samples. Sample Information Sample Information Run Blank Run Petro EG 1 x 0 x 48.04 s 0.003 s 2.276 %RSD 0 %RSD 4.738 Sample Information Sample Information Run Sb 50ppb Run Petro EG 2 x 50.06 x 46.88 s 1.106 s 1.17 %RSD 2.209 %RSD 2.495 Sample Information Sample Information Run Sb 200 ppb Run Bio EG 1 x 214.5 x 61.0 s 4.585 s 2.317 %RSD 2.138 %RSD 4.767 Sample Information Sample Information Run Sb 500 ppb Run Bio EG 2 x 493.1 x 63.2 s 10.8 s 2.066 %RSD 2.19 %RSD 4.301 Sample Information Run Sb 1000 ppb x 1001 s 16.79 %RSD 1.678 322 ICP report of cobalt and phosphorous quantification for standard and PET samples. Sample Information Sample Information Run Blank Run Petro EG 1 P Petro EG 1 Co x 0 x 4.458 7.037 s 0.001 s 1.141 0.007 %RSD 0 %RSD 25.59 0.1 Sample Information Sample Information Run QC 200 ppb P QC 200 ppb Co Run Petro EG 1 P Petro EG 1 Co x 175.6 178.4 x 4.327 6.894 s 1.119 0.507 s 0.502 0.036 %RSD 0.637 0.284 %RSD 11.61 0.528 Sample Information Sample Information Run QC 500 ppb P QC 500 ppb Co Run Bio EG 1 P Bio EG 1 Co x 509.7 508.6 x 6.368 7.229 s 0.674 0.807 s 0.965 0.023 %RSD 0.132 0.159 %RSD 15.16 0.317 Sample Information Sample Information Run QC 1000 ppb P QC 1000 ppb Run Bio EG 2 P Bio EG 2 Co Co x 1012 980.8 x 7.059 7.126 s 5.734 1.062 s 0.278 0.014 %RSD 0.567 0.108 %RSD 3.932 0.19 323 Residual catalyst quantification for polymers made with petro and bio PTA Table C.2: Residual catalyst concentration in PET samples made with bio and petro PTA Amount ICP Results2 Metal concentration on PET3 Xc1 Sample added Sb Sb mg mg/L ug/L ppm 101.0 202.00 21.2 105.1 Petro 101.0 202.00 21.0 104.2 PTA 101.0 202.00 20.8 102.8 100.6 201.20 18.9 94.1 Bio 100.6 201.20 18.9 93.9 PTA 100.6 201.20 18.8 93.3 1: Polymer concentration in the injected sample to ICP MS. 2: Results reported in ppb, metal concentration in the injected sample. 3: Concentrations calculated using Xc and ICP results. 324 ICP report of antimony quantification for standard and PET samples. Sample Information Sample Information Run Blank Run Petro PET 1 x 0 x 21.2 s 0.003 s 1.423 %RSD 0 %RSD 3.121 Sample Information Sample Information Run Sb 50ppb Run Petro PET 2 x 31.32 x 21.0 s 0.03 s 2.123 %RSD 0.096 %RSD 1.583 Sample Information Sample Information Run Sb 200 ppb Run Petro PET 3 x 197.8 x 20.8 s 0.351 s 2.89 %RSD 0.178 %RSD 4.321 Sample Information Sample Information Run Sb 500 ppb Run Bio PET 1 x 499.7 x 18.9 s 1.2 s 1.243 %RSD 0.24 %RSD 2.312 Sample Information Sample Information Run Sb 1000 ppb Run Bio PET 2 x 1002 x 18.9 s 2.636 s 2.321 %RSD 0.263 %RSD 3.805 Sample Information Run Bio PET 3 x 18.8 s 1.973 %RSD 4.192 325 Appendix D Normalization of NaOH solution for titration experiments. Table D.1: Standardization of NaOH solution used for COOH titration of PET samples made with petro and bio EG. Initial Final Difference Difference Sample ID Average1 reading (mm) reading (mm) (mm) (l) Chloroform1 1781 2000 219 0.0021 2.5 Chloroform2 1500 1781 281 0.0028 VF2 1 2000 15252 13252 0.1325 VF2 2 0 14092 14092 0.1409 135.3 VF2 3 300 13360 13060 0.1306 VF2 4 300 14022 13722 0.1372 1: Net ml = 135.3-2.5=132.8. Normality NNaOH = 0.1*81.9/132.8= 0.061 Table D.2: Standardization of NaOH solution used for COOH titration of PET samples made with petro and bio PTA. Initial Final Difference Difference Sample ID Average1 reading (mm) reading (mm) (mm) (l) Chloroform1 1984 2143 159 0.0016 2.1 Chloroform2 1104 1364 260 0.0026 VF2 1 723 14403 13680 0.1368 VF2 2 291 15006 14715 0.1472 142.6 VF2 3 75 13060 12985 0.1299 VF2 4 1341 17019 15678 0.1568 1: Net ml = 142.6-2.1=140.5. Normality NNaOH = 0.1*81.9/140.5= 0.058 326 Table D.3: Empirical degradation factors in eq/106 g for different heating times. Time 0 1 2 3 4 5 6 7 8 9 seconds 40 1.4 1.4 1.4 1.5 1.5 1.5 1.6 1.6 1.6 1.7 50 1.7 1.7 1.8 1.8 1.9 1.9 1.9 2.0 2.0 2.0 60 2.1 2.1 2.1 2.2 2.2 2.2 2.3 2.3 2.3 2.4 70 2.4 2.4 2.5 2.5 2.5 2.6 2.6 2.6 2.7 2.7 80 2.7 2.8 2.8 2.8 2.9 2.9 2.9 3.0 3.0 3.1 90 3.1 3.1 3.2 3.2 3.2 3.3 3.3 3.3 3.4 3.4 100 3.4 3.5 3.5 3.5 3.6 3.6 3.6 3.7 3.7 3.7 110 3.8 3.8 3.8 3.9 3.9 3.9 4.0 4.0 4.0 4.1 120 4.1 4.1 4.2 4.2 4.3 4.3 4.3 4.4 4.4 4.4 130 4.5 4.5 4.5 4.6 4.6 4.6 4.7 4.7 4.7 4.8 140 4.8 4.8 4.9 4.9 4.9 5.0 5.0 5.0 5.1 5.1 150 5.1 5.2 5.2 5.2 5.3 5.3 5.4 5.4 5.4 5.5 160 5.5 5.5 5.6 5.6 5.6 5.7 5.7 5.7 5.8 5.8 170 5.8 5.9 5.9 5.9 6.0 6.0 6.0 6.1 6.1 6.1 180 6.2 6.2 6.2 6.3 6.3 6.3 6.4 6.4 6.4 6.5 190 6.5 6.6 6.6 6.6 6.7 6.7 6.7 6.8 6.8 6.8 200 6.9 6.9 6.9 7.0 7.0 7.0 7.1 7.1 7.1 7.2 327 Appendix E Melt viscosity calibration curve Table E.1: Intrinsic vs melt viscosity calibration curve raw data. I.V.1 ln (*)2 Slope Intercept (dl/g) 0.821 3.12 0.755 2.92 0.707 2.80 0.33 -0.20 0.657 2.63 0.581 2.39 1: Intrinsic viscosity obtained from single data point dilute solution determination. 2: Melt viscosity at 270 °C measured at shear rate of 10 rad/sec. 0.85 0.80 0.75 y = 0.33x - 0.20 R² = 0.99 0.70 I.V. 0.65 0.60 0.55 0.50 2.20 2.40 2.60 2.80 3.00 3.20 ln * Figure E-1: Intrinsic vs melt viscosity calibration curve. 328 Appendix F Bio based determination report issued by Beta Analytic Inc. Analysis of the separated high purity bio p-xylene 329 Analysis of bio ethylene glycol 330 Appendix G Quantification of unreacted p-xylene in oxidation experiments The unreacted p-xylene was calculated using the Equation G.1 퐶푎푙푖푏푟푎푡푖표푛 푓푎푐푡표푟∗퐴푟푒푎∗푉표푙푢푚푒∗10 푢푛푟푒푎푐푡푒푑 푝푥 = (eqn. G.1) 1000 where Calibration factor has a value of 3.69x10-5, area is the area under the curve obtained from GC chromatogram and volume is the total volume at the end of the oxidation. The calibration factor was obtained from determinations reported on Appendix A.1 Table G.1 shows the retention times and areas under the curve obtained from GC chromatograms of oxidation liqueur obtained from multiple oxidation experiments. The total volume is the amount of material placed in the glass liner at the beginning of each experiment. The grams of unreacted p-xylene were calculated using Equation G.1 and the information presented in the table. 331 Table G.1: Calculation of unreacted p-xylene for different oxidation experiments Total Retention p-xylene Material Run Area Volume time (min) unreacted (g) (ml)1 1 12.766 4874 19.6 0.035 2 12.766 3773 20.4 0.028 3 12.79 24724 20.1 0.183 4 12.763 3854 19.2 0.027 5 12.786 14591 20.1 0.108 6 12.755 22751 19.6 0.164 7 12.781 4891 18.4 0.033 Bio p-xylene 8 12.78 4727 20.0 0.035 9 12.769 19939 19.6 0.144 10 12.773 3529 19.2 0.025 11 12.779 4063 22.2 0.033 12 12.767 20933 19.7 0.152 13 12.769 7910 19.7 0.057 14 12.779 9117 20.5 0.069 15 12.775 10300 20.5 0.078 1 12.777 5921 20.4 0.044 2 12.784 4266 19.2 0.030 Petro 3 12.755 26554 18.9 0.185 p-xylene 4 12.787 11348 20.3 0.085 5 12.787 3839 19.0 0.027 1) Total volume of liquid at the end of the oxidation 332 Appendix H Product composition of samples obtained from physical separation methods Table H.1: Area units obtained from GC chromatograms of selected samples Stage Sample ID 2,5 DMF p-xylene branched/linear alkanes Not determined 1st distillate 1345046 4.4E+07 1011871 674334 1 2nd distillate 162819 7.2E+07 236210 487766 residue 48620 349075 42840213 372242 liqueur 46865 7.1E+07 99731 238770 1 crystal 8647 7.5E+07 10706 34394 liqueur 41268 7.3E+07 54948 207590 2 crystal 7013 7.4E+07 3518 1188 1) Results reported as area units obtained from GC chromatograms Table H.2: Area units obtained from GC chromatograms of selected samples Stage Sample ID % ethylbenzene % p-xylene % m-xylene % o-xylene % not determined 1st distillate 33050 289297 424090 117590 83819 1 2nd distillate 33627 380163 587795 249718 59161 residue 5314 100596 182238 220976 1403800 1 crystal 22710 318204 474760 277001 72648 2 crystal 15590 429000 337232 188873 48408 3 crystal 187103 4208527 793866 568536 3069 4 crystal 42161 69187607 89313 101192 1552 1) Results reported as area units obtained from GC chromatograms 333 Appendix I LC-MS calibration curves Terephthalic acid (PTA) calibration curve range: 397 - 683 ppm Table I.1: Preparation of individual samples for PTA calibration curve Sample Methanol Final Amount volume added Concentration mg ml mg/ml ppm 27 50 0.540 683 24 50 0.484 612 21 50 0.428 541 18 50 0.364 460 16 50 0.314 397 Table I.2: PTA calibration curve datapoints Concentration Area ppm First run Second run Average St. Dev. 683 1.86E+08 1.89E+08 1.88E+08 1.38E+06 612 1.62E+08 1.62E+08 1.62E+08 1.50E+05 541 1.17E+08 1.15E+08 1.16E+08 1.15E+06 460 8.18E+07 8.26E+07 8.22E+07 3.90E+05 397 6.00E+07 6.36E+07 6.18E+07 1.81E+06 Calibration curve parameters Slope = 4.58E+05 Intercept = -1.25E+08 R2 = 0.98 334 2.E+08 y = 4.58E+05x - 1.25E+08 2.E+08 R² = 0.98 1.E+08 Area 8.E+07 4.E+07 0.E+00 0 200 400 600 800 ppm Figure I-1: Calibration curve terephthalic acid PTA Residual Plot 8.E+06 6.E+06 4.E+06 2.E+06 0.E+00 -2.E+06300 400 500 600 700 800 Residuals -4.E+06 -6.E+06 -8.E+06 ppm Figure I-2: Residual plot for terephthalic acid calibration 335 4-Carboxybenzaldehyde (4-CBA) calibration curve range: 2.9 - 8.4 ppm Table I.3: Preparation of 4-CBA stock solution Concentration stock 4-CBA Methanol solution mg g ml mg/ml ppm 10.6 79.1 100 0.106 134 Table I.4: Preparation of individual samples for 4-CBA calibration curve Original Methanol Sample volume Final concentration concentration volume added ml mg/ml ml mg/ml ppm 0.5 0.106 8 0.007 8.4 0.5 0.106 11 0.005 6.1 0.5 0.106 15 0.004 4.5 0.5 0.106 19 0.003 3.5 0.5 0.106 23 0.002 2.9 Table I.5: 4-CBA calibration curve datapoints Concentration Area ppm First run Second run Average St. Dev. 8.4 9.83E+06 9.73E+06 9.78E+06 5.15E+04 6.1 7.37E+06 7.86E+06 7.61E+06 2.46E+05 4.5 6.43E+06 6.60E+06 6.52E+06 8.35E+04 3.5 5.82E+06 6.01E+06 5.92E+06 9.35E+04 2.9 4.56E+06 4.68E+06 4.62E+06 6.10E+04 Calibration curve parameters Slope = 8.74E+05 Intercept = 2.46E+06 R2 = 0.97 336 1.E+07 y = 8.74E+05x + 2.46E+06 1.E+07 R² = 0.97 8.E+06 6.E+06 Area 4.E+06 2.E+06 0.E+00 0.0 2.0 4.0 6.0 8.0 10.0 ppm Figure I-3: Calibration curve 4-carboxybenzaldehyde 4-CBA Residual Plot 6.E+05 4.E+05 2.E+05 0.E+00 0.0 2.0 4.0 6.0 8.0 10.0 Residuals -2.E+05 -4.E+05 -6.E+05 ppm Figure I-4: Residual plot for 4-carboxybenzaldehyde calibration 337 4-Carboxybenzaldehyde (4-CBA) calibration curve range: 0.2 - 1.6 ppm Table I.6: Preparation of 4-CBA stock solution Concentration stock 4-CBA Methanol solution mg g ml mg/ml ppm 10.6 79.1 200 0.053 67 Table I.7: Preparation of individual samples for 4-CBA calibration curve Original Methanol Sample volume Final concentration concentration volume added ml mg/ml ml mg/ml ppm 0.5 0.053 20 0.0013 1.68 0.5 0.053 30 0.0009 1.12 0.5 0.053 50 0.0005 0.67 0.5 0.053 90 0.0003 0.37 0.5 0.053 160 0.0002 0.21 Table I.8: 4-CBA calibration curve datapoints Concentration Area ppm First run Second run Average St. Dev. 1.68 6.57E+05 5.96E+05 6.26E+05 3.06E+04 1.12 3.57E+05 3.94E+05 3.76E+05 1.84E+04 0.67 1.28E+05 1.61E+05 1.45E+05 1.66E+04 0.37 5.05E+04 4.58E+04 4.82E+04 2.35E+03 0.21 2.64E+04 1.81E+04 2.22E+04 4.16E+03 Calibration curve parameters Slope = 4.27E+05 Intercept = -1.02E+05 R2 = 0.98 338 7.E+05 6.E+05 y = 4.27E+05x - 1.02E+05 R² = 0.98 5.E+05 4.E+05 Area 3.E+05 2.E+05 1.E+05 0.E+00 0.00 0.50 1.00 1.50 2.00 ppm Figure I-5: Calibration curve 4-carboxybenzaldehyde 4-CBA Residual Plot 4.E+04 2.E+04 0.E+00 0.00 0.50 1.00 1.50 2.00 -2.E+04 Residuals -4.E+04 -6.E+04 ppm Figure I-6: Residual plot for 4-carboxybenzaldehyde calibration 339 Terephthalic acid (PTA) calibration curve range: 397 - 683 ppm Table I.9: Preparation of individual samples for PTA calibration curve Sample Methanol Final Amount volume added Concentration mg ml mg/ml ppm 27 50 0.540 683 24 50 0.484 612 21 50 0.428 541 18 50 0.364 460 16 50 0.314 397 Table I.10: PTA calibration curve datapoints Concentration Area ppm First run Second run Average St. Dev. 683 1.86E+08 1.89E+08 1.88E+08 1.38E+06 612 1.62E+08 1.62E+08 1.62E+08 1.50E+05 541 1.17E+08 1.15E+08 1.16E+08 1.15E+06 460 8.18E+07 8.26E+07 8.22E+07 3.90E+05 397 6.00E+07 6.36E+07 6.18E+07 1.81E+06 Calibration curve parameters Slope = 4.58E+05 Intercept = -1.25E+08 R2 = 0.98 340 2.E+08 y = 4.58E+05x - 1.25E+08 2.E+08 R² = 0.98 1.E+08 Area 8.E+07 4.E+07 0.E+00 0 200 400 600 800 ppm Figure I-7: Calibration curve terephthalic acid PTA Residual Plot 8.E+06 6.E+06 4.E+06 2.E+06 0.E+00 -2.E+06300 400 500 600 700 800 Residuals -4.E+06 -6.E+06 -8.E+06 ppm Figure I-8: Residual plot for terephthalic acid calibration 341 Table I.11: Preparation of p-tol stock solution p-toluic acid Methanol Concentration stock solution mg g ml mg/ml ppm 10 79.1 200 0.05 63 Table I.12: Preparation of individual samples for p-tol calibration curve Methanol Original Sample volume volume Final concentration concentration added ml mg/ml ml mg/ml ppm 0.5 0.05 35 0.0007 0.90 0.5 0.05 45 0.0006 0.70 0.5 0.05 60 0.0004 0.53 0.5 0.05 85 0.0003 0.37 0.5 0.05 140 0.0002 0.23 Table I.13: P-tol calibration curve datapoints Concentration Area ppm First run Second run Average St. Dev. 0.90 1.52E+05 1.62E+05 1.57E+05 4.95E+03 0.70 8.93E+04 9.92E+04 9.42E+04 4.96E+03 0.53 7.68E+04 6.00E+04 6.84E+04 8.41E+03 0.37 4.19E+04 5.64E+04 4.91E+04 7.28E+03 0.23 7.45E+03 1.07E+04 9.09E+03 1.63E+03 Calibration curve parameters Slope = 2.04E+05 Intercept = -3.56E+04 R2 = 0.97 342 2.E+05 y = 2.04E+05x - 3.56E+04 R² =0.97 1.E+05 Area 8.E+04 4.E+04 0.E+00 0.00 0.20 0.40 0.60 0.80 1.00 ppm Figure I-9: Calibration curve p-toluic acid p-toluic Acid Residual Plot 2.E+04 1.E+04 5.E+03 0.E+00 0.00 0.20 0.40 0.60 0.80 1.00 Residuals -5.E+03 -1.E+04 -2.E+04 ppm Figure I-10: Residual plot for p-toluic calibration 343 Appendix J Product composition of samples obtained from oxidation of p-xylene and purification of CTA Table J.1: Compilation of LCMS results for commercial, bio and petro terephthalic Area units ppm solution mg solid ppm solid Sample Run CTA 4-CBA CTA 4-CBA CTA 4-CBA CTA 4-CBA 1 5.88E+07 6.68E+06 401 5 15.9 0.19 9.88E+05 1192 2 5.92E+07 6.76E+06 402 5 15.9 0.19 9.88E+05 1210 3 5.59E+07 6.49E+06 395 5 15.6 0.18 9.88E+05 1156 4 6.00E+07 7.37E+06 404 6 16.0 0.22 9.86E+05 1374 5 6.15E+07 8.64E+06 407 7 16.1 0.28 9.83E+05 1711 6 6.17E+07 6.15E+06 408 4 16.1 0.17 9.90E+05 1027 7 5.32E+07 7.05E+06 389 5 15.4 0.21 9.87E+05 1334 Bio 8 6.11E+07 6.92E+06 406 5 16.1 0.20 9.88E+05 1242 CTA 9 6.10E+07 7.57E+06 406 6 16.1 0.23 9.86E+05 1420 10 6.32E+07 8.15E+06 411 7 16.2 0.26 9.84E+05 1562 11 6.54E+07 7.30E+06 415 6 16.4 0.22 9.87E+05 1317 12 6.31E+07 6.98E+06 410 5 16.2 0.20 9.88E+05 1246 13 6.35E+07 8.00E+06 411 6 16.3 0.25 9.85E+05 1519 14 6.27E+07 8.60E+06 410 7 16.2 0.28 9.83E+05 1688 15 5.83E+07 7.02E+06 400 5 15.8 0.21 9.87E+05 1289 1 6.77E+07 6.75E+06 421 5 16.6 0.2 9.88E+05 1155 2 5.64E+07 6.08E+06 396 4 15.7 0.2 9.90E+05 1036 Petro 3 6.03E+07 7.64E+06 404 6 16.0 0.2 9.86E+05 1446 CTA 4 6.47E+07 8.59E+06 414 7 16.4 0.3 9.83E+05 1668 5 6.81E+07 8.32E+06 421 7 16.7 0.3 9.84E+05 1568 344 Table J.2: Concentration of selected components in petro and bio PTA Area units ppm solution mg solid ppm solid Sample Run PTA 4-CBA p-tol PTA 4-CBA p-tol CTA 4-CBA p-tol Total CTA 4-CBA p-tol 1 1.55E+08 1.21E+05 1.24E+05 611 0.52 0.78 24.2 0.02 0.03 24.2 9.98E+05 85 128 2 1.33E+08 4.44E+04 1.43E+05 563 0.34 0.88 22.3 0.01 0.03 22.3 9.978E+05 61 155 3 1.38E+08 5.33E+04 1.30E+05 574 0.36 0.81 22.7 0.01 0.03 22.7 9.980E+05 63 141 Bio PTA 4 1.24E+08 4.43E+04 1.33E+05 544 0.34 0.83 21.5 0.01 0.03 21.6 9.979E+05 63 152 5 1.26E+08 7.06E+04 4.19E+04 548 0.40 0.38 21.7 0.02 0.02 21.7 9.986E+05 74 69 6 1.10E+08 5.41E+04 2.22E+04 513 0.37 0.28 20.3 0.01 0.01 20.3 9.987E+05 71 55 7 1.08E+08 2.69E+04 2.12E+04 507 0.30 0.28 20.1 0.01 0.01 20.1 9.989E+05 59 55 1 1.24E+08 5.84E+04 1.52E+05 543 0.38 0.92 21.5 0.015 0.04 21.5 9.976E+05 69 169 2 1.25E+08 4.37E+04 1.22E+05 546 0.34 0.78 21.6 0.013 0.03 21.6 9.980E+05 62 142 Petro PTA 3 1.34E+08 9.70E+04 5.93E+04 565 0.47 0.47 22.3 0.018 0.02 22.4 9.984E+05 82 82 4 1.56E+08 1.49E+05 1.48E+04 613 0.59 0.25 24.2 0.023 0.01 24.3 9.986E+05 96 40 5 1.05E+08 1.37E+05 3.47E+04 502 0.56 0.34 19.9 0.022 0.01 19.9 9.982E+05 111 69 1 1.79E+08 4.09E+04 0.00E+00 663 0.33 -- 26.2 0.013 -- 26.2 9.995E+05 50 -- 2 1.82E+08 4.97E+04 0.00E+00 671 0.36 -- 26.5 0.014 -- 26.5 9.995E+05 53 -- 3 1.70E+08 4.49E+04 0.00E+00 644 0.34 -- 25.5 0.014 -- 25.5 9.995E+05 53 -- PTA1 4 1.73E+08 3.66E+04 0.00E+00 650 0.32 -- 25.7 0.013 -- 25.7 9.995E+05 50 -- 5 1.67E+08 2.14E+04 0.00E+00 637 0.29 -- 25.2 0.011 -- 25.2 9.995E+05 45 -- 6 1.83E+08 2.15E+04 0.00E+00 671 0.29 -- 26.6 0.011 -- 26.6 9.996E+05 43 -- 7 1.84E+08 1.93E+04 0.00E+00 674 0.28 -- 26.6 0.011 -- 26.7 9.996E+05 42 -- 1) Commercial PTA from DAK Americas LLC 345 Appendix K Crystallization analysis of PET samples produced with petro and bio monomers Table K.1: Raw data of isothermal crystallization at 220 °C of PET with petro PTA Time Area a ln() ln(-ln()) ln (time) seconds J/g 0.75 0.00 -0.29 2.32 -1.87 0.95 -0.05 0.05 0.84 2.87 -3.74 0.90 -0.11 0.11 1.05 3.34 -5.61 0.85 -0.16 0.16 1.20 3.77 -7.48 0.80 -0.22 0.22 1.33 4.17 -9.35 0.75 -0.29 0.29 1.43 4.57 -11.22 0.70 -0.36 0.36 1.52 4.96 -13.09 0.65 -0.43 0.43 1.60 5.36 -14.96 0.60 -0.51 0.51 1.68 5.75 -16.83 0.55 -0.60 0.60 1.75 6.16 -18.70 0.50 -0.69 0.69 1.82 6.59 -20.57 0.45 -0.80 0.80 1.89 7.04 -22.44 0.40 -0.92 0.92 1.95 7.52 -24.31 0.35 -1.05 1.05 2.02 8.04 -26.18 0.30 -1.20 1.20 2.08 8.62 -28.05 0.25 -1.39 1.39 2.15 9.28 -29.92 0.20 -1.61 1.61 2.23 10.05 -31.79 0.15 -1.90 1.90 2.31 11.01 -33.66 0.10 -2.30 2.30 2.40 12.33 -35.53 0.05 -3.00 3.00 2.51 15.92 -37.40 0.00 2.77 346 Table K.2: Raw data of isothermal crystallization at 220 °C of PET with bio PTA Time Area a ln() ln(-ln()) ln (time) seconds J/g 0.67 1.00 -0.40 2.12 -2.32 0.95 -0.05 0.05 0.75 2.69 -4.65 0.90 -0.11 0.11 0.99 3.16 -6.97 0.85 -0.16 0.16 1.15 3.57 -9.30 0.80 -0.22 0.22 1.27 3.95 -11.62 0.75 -0.29 0.29 1.37 4.31 -13.94 0.70 -0.36 0.36 1.46 4.65 -16.27 0.65 -0.43 0.43 1.54 4.99 -18.59 0.60 -0.51 0.51 1.61 5.32 -20.92 0.55 -0.60 0.60 1.67 5.66 -23.24 0.50 -0.69 0.69 1.73 6.00 -25.56 0.45 -0.80 0.80 1.79 6.36 -27.89 0.40 -0.92 0.92 1.85 6.72 -30.21 0.35 -1.05 1.05 1.91 7.11 -32.54 0.30 -1.20 1.20 1.96 7.54 -34.86 0.25 -1.39 1.39 2.02 8.01 -37.18 0.20 -1.61 1.61 2.08 8.56 -39.51 0.15 -1.90 1.90 2.15 9.25 -41.83 0.10 -2.30 2.30 2.22 10.22 -44.15 0.05 -3.00 3.00 2.32 13.67 -46.48 0.00 2.61 347 Table K.3: Raw data for non-isothermal crystallization of PET made with petro PTA Petro 10 °C/min 15 °C/min 20 °C/min 30 °C/min 40 °C/min PET Temp Area Temp Area Temp Area Temp Area Temp Area x(T) C J/g C J/g C J/g C J/g C J/g 0.00 224.1 0.0 218.2 0.0 214.2 0.0 212.6 0.0 210.6 0.0 0.05 210.5 -1.8 206.4 -2.2 202.7 -2.4 198.5 -20.2 195.1 -1.9 0.10 208.1 -3.7 203.6 -4.5 199.2 -4.7 194.6 -40.4 191.7 -3.8 0.15 206.3 -5.5 201.6 -6.7 196.7 -7.1 191.8 -60.6 189.2 -5.7 0.20 204.9 -7.3 199.9 -8.9 194.7 -9.4 189.5 -80.8 187.0 -7.5 0.25 203.7 -9.1 198.6 -11.2 193.0 -11.8 187.5 -101.0 185.0 -9.4 0.30 202.6 -11.0 197.3 -13.4 191.5 -14.1 185.8 -121.2 183.1 -11.3 0.35 201.6 -12.8 196.2 -15.6 190.2 -16.5 184.3 -141.4 181.3 -13.2 0.40 200.6 -14.6 195.1 -17.9 188.9 -18.8 182.9 -161.6 179.5 -15.1 0.45 199.7 -16.4 194.1 -20.1 187.7 -21.2 181.7 -181.8 177.9 -16.9 0.50 198.8 -18.3 193.1 -22.3 186.5 -23.5 180.5 -202.0 176.3 -18.8 0.55 197.9 -20.1 192.1 -24.6 185.5 -25.9 179.5 -222.2 174.8 -20.7 0.60 197.0 -21.9 191.1 -26.8 184.4 -28.2 178.4 -242.4 173.3 -22.6 0.65 196.0 -23.7 190.1 -29.0 183.3 -30.6 177.4 -262.6 171.9 -24.5 0.70 195.0 -25.6 189.0 -31.3 182.3 -33.0 176.4 -282.8 170.4 -26.4 0.75 194.0 -27.4 187.9 -33.5 181.1 -35.3 175.3 -303.0 168.9 -28.2 0.80 192.9 -29.2 186.7 -35.7 180.1 -37.7 174.2 -323.2 167.2 -30.1 0.85 191.6 -31.0 185.4 -38.0 178.8 -40.0 172.9 -343.4 165.3 -32.0 0.90 190.0 -32.9 183.7 -40.2 177.2 -42.4 171.3 -363.6 162.8 -33.9 0.95 187.7 -34.7 181.4 -42.4 174.9 -44.7 169.0 -383.8 159.0 -35.8 1.00 174.1 -36.5 161.6 -44.7 160.8 -47.1 159.1 -404.0 138.1 -37.7 348 Table K.4: Raw data for non-isothermal crystallization of PET made with bio PTA Bio 10 °C/min 15 °C/min 20 °C/min 30 °C/min 40 °C/min PET Temp Area Temp Area Temp Area Temp Area Temp Area x(T) C J/g C J/g C J/g C J/g C J/g 0.00 220.5 0.0 214.6 0.0 212.5 0.0 209.0 0.0 204.5 0.0 0.05 207.3 -2.1 204.5 -2.2 200.8 -2.0 195.0 -17.6 191.5 -1.9 0.10 204.4 -4.1 201.9 -4.3 197.8 -4.0 191.3 -35.1 188.5 -3.8 0.15 202.3 -6.2 200.1 -6.5 195.6 -6.0 188.8 -52.7 186.3 -5.7 0.20 200.6 -8.2 198.5 -8.7 193.7 -7.9 187.1 -70.2 184.5 -7.6 0.25 199.1 -10.3 197.2 -10.8 192.1 -9.9 185.8 -87.8 183.0 -9.5 0.30 197.8 -12.4 196.0 -13.0 190.7 -11.9 184.9 -105.4 181.7 -11.4 0.35 196.5 -14.4 194.8 -15.2 189.5 -13.9 184.0 -122.9 180.6 -13.3 0.40 195.4 -16.5 193.7 -17.4 188.5 -15.9 183.3 -140.5 179.6 -15.2 0.45 194.3 -18.5 192.7 -19.5 187.6 -17.9 182.7 -158.0 178.8 -17.1 0.50 193.3 -20.6 191.7 -21.7 186.8 -19.8 182.1 -175.6 178.0 -19.0 0.55 192.4 -22.6 190.7 -23.9 186.2 -21.8 181.5 -193.2 177.2 -20.9 0.60 191.6 -24.7 189.8 -26.0 185.5 -23.8 180.9 -210.7 176.4 -22.8 0.65 190.9 -26.8 189.0 -28.2 184.9 -25.8 180.4 -228.3 175.6 -24.7 0.70 190.1 -28.8 188.2 -30.4 184.3 -27.8 179.8 -254.8 174.9 -26.6 0.75 189.4 -30.9 187.4 -32.5 183.7 -29.8 179.2 -263.4 174.1 -28.4 0.80 188.7 -32.9 186.6 -34.7 183.0 -31.8 178.5 -281.0 173.2 -30.3 0.85 187.9 -35.0 185.7 -36.9 182.3 -33.7 177.8 -298.5 172.2 -32.2 0.90 187.0 -37.1 184.6 -39.0 181.3 -35.7 176.8 -316.1 170.9 -34.1 0.95 185.7 -39.1 183.0 -41.2 179.8 -37.7 175.2 -333.6 168.8 -36.0 1.00 171.5 -41.2 162.1 -43.4 160.7 -39.7 160.5 -351.2 153.3 -37.9 349 Table K.5: Raw data of isothermal crystallization at 220 °C of PET made with petro EG Time Area a ln(a) ln(-ln(a)) ln (time) Seconds J/g 1.75 1.00 0.56 5.56 1.72 0.97 -0.03 0.03 1.72 6.48 3.44 0.94 -0.06 0.06 1.87 7.09 5.15 0.91 -0.09 0.09 1.96 7.57 6.87 0.88 -0.13 0.13 2.02 7.99 8.59 0.85 -0.16 0.16 2.08 8.37 10.31 0.82 -0.20 0.20 2.12 8.72 12.02 0.79 -0.24 0.24 2.17 9.05 13.74 0.76 -0.27 0.27 2.20 9.37 15.46 0.73 -0.31 0.31 2.24 9.68 17.18 0.70 -0.36 0.36 2.27 9.98 18.89 0.67 -0.40 0.40 2.30 10.28 20.61 0.64 -0.45 0.45 2.33 10.58 22.33 0.61 -0.49 0.49 2.36 10.88 24.05 0.58 -0.54 0.54 2.39 11.19 25.76 0.55 -0.60 0.60 2.41 11.50 27.48 0.52 -0.65 0.65 2.44 11.82 29.20 0.49 -0.71 0.71 2.47 12.15 30.92 0.46 -0.78 0.78 2.50 12.50 32.64 0.43 -0.84 0.84 2.53 12.88 34.35 0.40 -0.92 0.92 2.56 13.28 36.07 0.37 -0.99 0.99 2.59 13.71 37.79 0.34 -1.08 1.08 2.62 14.17 39.51 0.31 -1.17 1.17 2.65 14.69 41.22 0.28 -1.27 1.27 2.69 15.26 42.94 0.25 -1.39 1.39 2.73 15.92 44.66 0.22 -1.51 1.51 2.77 16.69 46.38 0.19 -1.66 1.66 2.81 17.63 48.09 0.16 -1.83 1.83 2.87 18.78 49.81 0.13 -2.04 2.04 2.93 20.15 51.53 0.10 -2.30 2.30 3.00 21.81 53.25 0.07 -2.66 2.66 3.08 24.11 54.96 0.04 -3.22 3.22 3.18 26.05 56.11 0.02 -3.91 3.91 3.26 32.73 57.25 0.00 350 Table K.6: Raw data of isothermal crystallization at 220 °C of PET made with bio EG Time Area a ln(a) ln(-ln(a)) ln (time) seconds J/g 1.50 0.00 0.41 6.41 3.17 0.97 -0.03 0.03 1.86 7.65 6.34 0.94 -0.06 0.06 2.03 8.48 9.51 0.91 -0.09 0.09 2.14 9.17 12.68 0.88 -0.13 0.13 2.22 9.77 15.85 0.85 -0.16 0.16 2.28 10.33 19.02 0.82 -0.20 0.20 2.34 10.87 22.19 0.79 -0.24 0.24 2.39 11.38 25.36 0.76 -0.27 0.27 2.43 11.90 28.53 0.73 -0.31 0.31 2.48 12.42 31.70 0.70 -0.36 0.36 2.52 12.96 34.87 0.67 -0.40 0.40 2.56 13.52 38.04 0.64 -0.45 0.45 2.60 14.13 41.21 0.61 -0.49 0.49 2.65 14.78 44.38 0.58 -0.54 0.54 2.69 15.48 47.55 0.55 -0.60 0.60 2.74 16.25 50.72 0.52 -0.65 0.65 2.79 17.11 53.89 0.49 -0.71 0.71 2.84 18.05 57.06 0.46 -0.78 0.78 2.89 19.08 60.23 0.43 -0.84 0.84 2.95 20.24 63.40 0.40 -0.92 0.92 3.01 21.48 66.57 0.37 -0.99 0.99 3.07 22.83 69.74 0.34 -1.08 1.08 3.13 24.23 72.91 0.31 -1.17 1.17 3.19 25.76 76.09 0.28 -1.27 1.27 3.25 27.46 79.26 0.25 -1.39 1.39 3.31 29.36 82.43 0.22 -1.51 1.51 3.38 31.45 85.60 0.19 -1.66 1.66 3.45 33.83 88.77 0.16 -1.83 1.83 3.52 36.62 91.94 0.13 -2.04 2.04 3.60 39.68 95.11 0.10 -2.30 2.30 3.68 43.06 98.28 0.07 -2.66 2.66 3.76 47.49 101.45 0.04 -3.22 3.22 3.86 52.25 103.56 0.02 -3.91 3.91 3.96 62.50 105.67 0.00 351 Table K.7: Raw data for non-isothermal crystallization of PET made with petro EG Petro 10 °C/min 15 °C/min 20 °C/min 30 °C/min 40 °C/min PET Temp Area Temp Area Temp Area Temp Area Temp Area x(T) C J/g C J/g C J/g C J/g C J/g 0.00 205.7 0.0 202.5 0.0 199.1 0.0 195.0 0.0 190.1 0.0 0.03 197.8 1.2 193.5 1.0 190.3 1.1 185.5 0.8 180.8 0.9 0.06 196.4 2.4 192.0 2.1 188.7 2.2 183.6 1.7 178.7 1.8 0.09 195.4 3.6 191.0 3.1 187.6 3.3 182.3 2.5 177.3 2.6 0.12 194.7 4.8 190.2 4.1 186.8 4.4 181.4 3.4 176.2 3.5 0.15 194.1 5.9 189.6 5.1 186.1 5.5 180.5 4.2 175.2 4.4 0.18 193.6 7.1 189.1 6.2 185.5 6.7 179.8 5.1 174.4 5.3 0.21 193.1 8.3 188.6 7.2 185.0 7.8 179.2 5.9 173.6 6.2 0.24 192.7 9.5 188.1 8.2 184.5 8.9 178.6 6.8 172.9 7.1 0.27 192.4 10.7 187.7 9.3 184.0 10.0 178.0 7.6 172.3 7.9 0.30 192.0 11.9 187.3 10.3 183.6 11.1 177.5 8.5 171.6 8.8 0.33 191.7 13.1 187.0 11.3 183.2 12.2 177.0 9.3 171.0 9.7 0.36 191.3 14.3 186.6 12.3 182.8 13.3 176.5 10.2 170.4 10.6 0.39 191.0 15.5 186.3 13.4 182.4 14.4 176.0 11.0 169.9 11.5 0.42 190.7 16.6 185.9 14.4 182.0 15.5 175.5 11.9 169.3 12.4 0.45 190.4 17.8 185.6 15.4 181.6 16.6 175.1 12.7 168.7 13.2 0.48 190.1 19.0 185.3 16.5 181.3 17.7 174.6 13.6 168.2 14.1 0.51 189.8 20.2 185.0 17.5 180.9 18.9 174.1 14.4 167.4 15.0 0.54 189.5 21.4 184.6 18.5 180.5 20.0 173.7 15.3 167.1 15.9 0.57 189.2 22.6 184.3 19.5 180.1 21.1 173.2 16.1 166.5 16.8 0.60 188.9 23.8 184.0 20.6 179.8 22.2 172.7 17.0 165.9 17.7 0.63 188.6 25.0 183.6 21.6 179.4 23.3 172.2 17.8 165.4 18.5 0.66 188.2 26.1 183.3 22.6 179.0 24.4 171.7 18.7 164.8 19.4 0.69 187.9 27.3 182.9 23.7 178.6 25.5 171.2 19.5 164.1 20.3 0.72 187.6 28.5 182.5 24.7 178.1 26.6 170.6 20.4 163.5 21.2 0.75 187.2 29.7 182.1 25.7 177.7 27.7 170.1 21.2 162.8 22.1 0.78 186.7 30.9 181.7 26.7 177.1 28.8 169.4 22.1 162.0 22.9 0.81 186.2 32.1 181.2 27.8 176.6 29.9 168.7 22.9 161.2 23.8 0.84 185.6 33.3 180.7 28.8 175.9 31.1 167.9 23.8 160.3 24.7 0.87 184.9 34.5 180.0 29.8 175.2 32.2 167.0 24.6 159.2 25.6 0.90 183.8 35.7 179.3 30.9 174.2 33.3 166.0 25.5 157.9 26.5 0.93 182.1 36.8 178.2 31.9 172.9 34.4 164.5 26.3 156.3 27.4 0.96 178.9 38.0 176.5 32.9 170.6 35.5 162.4 27.1 153.9 28.2 0.98 174.8 38.8 174.4 33.6 167.8 36.2 159.8 27.7 151.3 28.8 1.00 160.2 39.6 165.9 34.3 160.3 37.0 147.9 28.3 141.0 29.4 352 Table K.8: Raw data for non-isothermal crystallization of PET made with bio EG Bio 10 °C/min 15 °C/min 20 °C/min 30 °C/min 40 °C/min PET Temp Area Temp Area Temp Area Temp Area Temp Area x(T) C J/g C J/g C J/g C J/g C J/g 0.00 206.9 0.00 201.4 0.00 198.7 0.00 195.5 0.00 189.9 0.00 0.03 198.0 0.86 193.6 0.74 190.3 1.13 184.6 0.81 180.6 0.66 0.06 196.4 1.73 191.8 1.47 188.3 2.26 182.0 1.62 177.9 1.31 0.09 195.2 2.59 190.5 2.20 186.8 3.39 180.2 2.43 176.0 1.97 0.12 194.3 3.46 189.4 2.94 185.6 4.52 178.7 3.24 174.3 2.63 0.15 193.5 4.32 188.6 3.67 184.6 5.64 177.4 4.05 172.9 3.29 0.18 192.8 5.19 187.8 4.41 183.7 6.77 176.2 4.86 171.5 3.94 0.21 192.1 6.05 187.0 5.14 182.9 7.90 175.1 5.67 170.3 4.60 0.24 191.5 6.92 186.4 5.88 182.1 9.03 174.1 6.48 169.1 5.26 0.27 191.0 7.78 185.7 6.61 181.4 10.16 173.1 7.29 168.0 5.91 0.30 190.5 8.64 185.1 7.35 180.7 11.29 172.2 8.10 167.0 6.57 0.33 190.0 9.51 184.6 8.08 180.0 12.42 171.3 8.91 166.0 7.23 0.36 189.5 10.37 184.0 8.82 179.4 13.55 170.4 9.72 165.0 7.88 0.39 189.0 11.24 183.5 9.55 178.7 14.68 169.5 10.53 164.0 8.54 0.42 188.5 12.10 182.9 10.29 178.1 15.80 168.7 11.34 163.0 9.20 0.45 188.1 12.97 182.4 11.02 177.5 16.93 167.8 12.15 162.0 9.85 0.48 187.6 13.83 181.9 11.76 176.9 18.06 167.0 12.96 161.1 10.51 0.51 187.1 14.70 181.4 12.49 176.3 19.19 166.1 13.77 160.1 11.17 0.54 186.7 15.56 180.9 13.23 175.7 20.32 165.2 14.58 159.0 11.83 0.57 186.2 16.42 180.4 13.96 175.1 21.45 164.3 15.39 158.0 12.48 0.60 185.7 17.29 179.9 14.70 174.5 22.58 163.4 16.20 156.9 13.14 0.63 185.2 18.15 179.4 15.43 173.9 23.71 162.5 17.01 155.9 13.80 0.66 184.7 19.02 178.9 16.17 173.3 24.83 161.5 17.82 154.8 14.45 0.69 184.2 19.88 178.3 16.90 172.6 25.96 160.5 18.63 153.6 15.11 0.72 183.6 20.75 177.7 17.63 171.9 27.09 159.4 19.44 152.4 15.77 0.75 183.0 21.61 177.1 18.37 171.2 28.22 158.2 20.25 151.1 16.42 0.78 182.3 22.48 176.5 19.10 170.4 29.35 156.9 21.06 149.7 17.08 0.81 181.5 23.34 175.8 19.84 169.5 30.48 155.4 21.87 148.2 17.74 0.84 180.6 24.20 175.0 20.57 168.6 31.61 153.8 22.68 146.6 18.39 0.87 179.5 25.07 174.2 21.31 167.5 32.74 152.0 23.49 144.7 19.05 0.90 178.0 25.93 173.1 22.04 166.3 33.87 149.8 24.30 142.5 19.71 0.93 176.0 26.80 171.8 22.78 164.7 34.99 146.9 25.11 139.8 20.36 0.96 172.9 27.66 170.0 23.51 162.5 36.12 142.8 25.92 136.2 21.01 0.98 169.4 28.24 168.0 24.00 160.3 36.88 138.3 26.46 132.6 21.46 1.00 159.8 28.81 160.4 24.49 150.1 37.63 123.2 27.00 122.3 21.90 353