The University of New South Wales School of Chemical
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THE UNIVERSITY OF NEW SOUTH WALES SCHOOL OF CHEMICAL ENGINEERING DIFFUSION AND KINETIC STUDIES IN THE CHLORINATION OF TOLUENE DISSERTATION Submitted in Partial Fulfilment of the Requirement for the Degree of Doctor of Philosophy in Chemical Engineering FONG SECK KONG B. Sc. Hons. I January 1970. 0F KE,^30/^' (, -x- KENSINGTON ) V * . <fJ Libram CANDIDATE'S CERTIFICATE This is to certify that the work presented in this thesis was carried out in the School of Chemical Engineering of the University of New South Wales, and has not been submitted to any other University or Institution for a Higher Degree. (Fong Seek Kong). 1 Acknowledgements The author wishes to record his sincere thanks to Professor J.S. Ratcliffe who suggested and supervised the work described in this thesis. His constant interest and discussions concerning the work have been an inspiration. The author is further thankful to Professor J.S. Ratcliffe and to Miss Chamberlain of the Commonwealth Office of Education and Science for their patient discussions and kind advice in difficult times. Thanks are due to the Commonwealth Government of Australia for the scholarship under the Commonwealth Scholarship and Fellowship Plan, and to the Government of Singapore for securing the award. Thanks are also due to the professional and technical staff of the School of Chemical Engineering for their assistance in the equipment construction and advice rendered, and to Mrs. V. Theodore for typing this thesis. Last, but not least, the author is greatly indebted to his family, whose days of austerity have to be prolonged, and to Miss Chew Ann Kheng for their encouragement and support. ii INDEX Page Acknowledgements i Abstract xv Nomenclature xvii Chapter One 1.1 Chemical Reaction Systems 1 1.2 Toluene and Its Reaction with Chlorine 6 1.3 Previous Investigations in Toluene Side-Chain Chlorination 13 1.4 Homogeneous and Heterogeneous Reaction Systems 19 1.5 Mass Transfer in Heterogeneous Systems 21 1.6 Mass Transfer and Chemical Reaction 28 Chapter Two 2.1 Gas-Liquid Contact Systems 57 2.1.1 Characteristics of the Gas Bubble Column 60 2.1.2 Mass Transfer Characteristics of the Gas Bubble Column 69 2.2 The Agitated Tank Reactor 75 2.2.1 Characteristics of the Agitated Tank 76 2.2.2 Mass Transfer and Interfacial Area in Agitated Tanks 79 iii Page Chapter Three 3.1 Experimental Programme and Equipment Design 84 3.2 Analytical Techniques 100 3.3 Experimental Procedure 110 Chapter Four Introduction 112 4.1 On a Gas-Liquid Absorption Followed by a First Order Reaction in the Liquid Reactant 114 4.2 Effect of Diffusion on Selectivity in Heterogeneous Consecutive Reactions 147 4.3 Unsteady State Chlorination of Toluene in a Laboratory Bubble Column Reactor 168 4.4 Bubble Behaviour in Chlorination of Toluene 169 4.5 Kinetics and Evaluation of Kinetic Data 180 4.6 Controlling Regime in Chlorine Absorption 214 4„7 Evaluation of Volumetric Mass Transfer Coefficients 220 4.8 Effect of Mass Transfer on Selectivity 243 4„9 An Evaluation of Specific Interfacial Area and Film Thickness 256 4.10 Chlorine Solubility Data - A Comparison of Experimental and Empirical Data 265 4.11 Experimental Investigation in the Agitated Batch Reactor 272 iv Page Chapter Five 5.1 Controlling Parameters on Conversion Rate 284 5.2 Effect of Diffusion on the Yield of the Intermediate in a Heterogeneous Consecutive Reaction 301 Chapter Six 6.1 Summary and Conclusions 318 6.2 Suggestions for Further Research 322 Appendix I A Computer Programme for Evaluation of Mole Fractions from Chromatogram 323 B Typical Result from Computer 327 II A Gas Liquid Heterogeneous Reaction-Solution of Differential Equations 328 B Selectivity in Heterogeneous Series Reaction-Solution of Differential Equations 331 C Selectivity in Homogeneous Series Reaction 336 D Maximum Yield of Intermediate in a Heterogeneous Series Reaction for S = 1.0 338 III A Evaluation of Diffusion Coefficients 341 B Estimation of Diffusion Parameter 345 V Page IV A Evaluation of Molar Chlorine Flow Rate 350 B Evaluation of Orifice Reynolds Number 352 V Concentration Units in the Evaluation of Data 353 VI Sample Calculations A Calculation of and k° 355 B Evaluation of Diffusion Regime Volumetric Mass Transfer Coefficient 357 C Evaluation of Gas/Liquid Interfacial Area and Film Thickness 358 VII Experimental Results Tables A1-A16 359 VIII References 378 vi List of Figures Page 101 Qualitative Effect of Chemical Reaction on the Profile of A in a Heterogeneous Pseudo First Order Reaction 29 1.2 Concentration Profile of A in a Fast Pseudo First Order Reaction 39 1.3a Concentration Profile of A in a Slow Pseudo First Order Reaction; High Interfacial Area 42 1.3b Concentration Profile of A in a Slow Pseudo First Order Reaction; Low Interfacial Area 43 1.4 Typical Concentration Profile of A and B in Infinitely Fast Chemical Reaction 49 3.1 G eneral Layout of Equipment 85 3.2 Sketch of Bubble Column Reactor 92 3.3 Sketch of Stirred Batch Reactor 95 3.4 Temperature Control-Electrical Circuit 97 3.5 Typical Gas-Liquid Chromatogram of Toluene, Benzyl, Benzal and Benzo-tri Chlorides 102 3.6 Calibration of Chromatographic Column 108 vii Page 4. la, Concentration Profiles at Interfacial Region. Slow 125, 4.1b Chemical Reaction 126 4.2af Concentration Profiles at Interfacial Region. Fast 129, Chemical Reaction 130 4.3 Concentration Profiles at Interfacial Region. Infinitely Fast Chemical Reaction 133 4.4a Effect of Diffusion Parameter on Chemical Acceleration Factor 141 g 4.4b Effect of 1/^ on Chemical Acceleration Factor 142 i 4.5 Typical Concentration Profile at Interfacial Region in a Heterogeneous Series Reaction 149 4.6 Effect of Diffusion of Selectivity. Slow Chemical Reaction 151 4.7 Effect of Diffusion on Selectivity. Fast Chemical Reaction 153 00 • Effect of Diffusion on Selectivity Fast Chemical Reaction 154 4.9 Effect of Diffusion on Selectivity. Fast Chemical Reaction 157 4.10 Effect of Diffusion of Selectivity. Infinitely Fast Chemical Reaction 159 4.11 Plot of Degree of Chlorination Against Time 184 4.12 Plot of Mole Fraction Toluene Against Time 185 viii Page 4.13 Time-Product Distribution Plot 190 4.14 Plot of log (Fraction Initial Benzal Chloride) Against Tim% 194 4.15 Plot of log (Fraction Initial Benzal Chloride) Against Time 197 4.16 Time-Product Distribution Plot 201 4.17 Arrhenius Equation Plot of and k^ 212 4.18 Deviation of Linear Absorption from Linearity 215 4.19 Plot of Degree of Chlorination Against Time in Diffusion Regime 222 4.20 Plot of Degree of Chlorination Against Time in Diffusion Regime 223 4.21 Typical Free Chlorine Accumulation Curve 228 4.22 Graphical Evaluation of Kinetic Regime Physical Volumetric Mass Transfer Coefficient 231 4.23 Plot of Physical Volumetric Mass Transfer Coefficient Against Molar Chlorine Flow Rate 237 4.24 Plot of Diffusion and Kinetic Regime Physical 241 Volumetric Mass Transfer Coefficient Against Temperature 4.25 Selectivity of Benzyl Chloride at 45°C 247 4.26 Selectivity of Benzyl Chloride at 80°C 249 4.27 Selectivity of Benzyl Chloride at 70°C 251 IX Page 4.28 Degree of Chlorination - Product Distribution Plot 254 4.29 Plot of Product Distribution Against Degree of Chlorination 255 4,30 Plot of Specific Interfacial Area and Film Thickness Against Temperature 261 4,31 Plot of Specific Interfacial Area and Film Thickness Against Chlorine Flow Rate 262 4.32 Comparison of Experimental and Empirical Chlorine Solubility Data 270 4.33 Plot of log (Fraction Initial Benzal Chloride) Against Time - Agitated Batch Reactor 273 4.34 Degree of Chlorination - Product Distribution Plot 275 4.35 Selectivity of Benzyl Chloride - Agitated Batch Reactor at 70°C 276 4.36 Effect of Agitation on Diffusion Regime Physical Volumetric Mass Transfer Coefficient 278 4.37 Effect of Agitation on Kinetic Regime Physical Volumetric Mass Transfer Coefficient 281 X Page 5.1 Determination of Transition Points 289 5.2 Effect of Chlorine Flow Rate on Free Chlorine Content 295 5.3 Effect of Chlorine Flow Rate on Chemical Acceleration Factor 2 96 5.4 Effect of Agitation on Free Chlorine Content 2 97 5.5 Effect of Agitation Rate on Chemical Acceleration Factor 298 5.6 Plot of Intermediate Yield Against (1-conversion) 305 5.7 Effect of Ratio of Reaction Rate Constants on Maximum Selectivity-limited Intermediate Yield 313 5.8 Effect of Ratio of Reaction Rate Constants on Maximum Yield of Intermediate 315 A1 Plot of Diffusion Coefficient Against Temperature 344 xi List of Tables Page Chapter Two 2.1 Summary of Some Published Literature on Bubble Columns 61 Chapter Four 4.1 Summary of Dye Dispersion Time and Orifice Reynolds Number for Bubble Column at 70°C 178 4.2 Specific Kinetic Constant, k at 70°C 196 O 4.3 Specific Kinetic Constant 199 4.4 Specific Kinetic Constants k^, k^, k^ 203 4.5 Analysis of Specific Kinetic Constant Variation with Temperature 211 4.6 Thermodynamic Constants of Reaction 213 4.7 Evaluation of Diffusion Regime Chlorine Physical Volu metric Mass Transfer Coefficient 225 4.8 Evaluation of Kinetic Regime Chlorine Physical Volumetric Mass Transfer Coefficient 230 4.9 Summary of Evaluated Kinetic Regime Chlorine Physical Volumetric Mass Transfer Coefficients and Chlorine Solubilities 233 4.10 Comparison of Diffusion Regime and Kinetic Regime Chlorine Physical Volumetric Mass Transfer Coefficients 235 4.11 Variation of Chlorine Volumetric Mass Transfer Coefficient with Temperature 240 xii Page 4.12 Theoretical Selectivity of Benzyl Chloride under Diffusion and Non-diffusion Limitation at 45°C 246 4.13 Theoretical Selectivity of Benzyl