Design and Application of a Catalytic Distillation Column

CATALYTIC DISTILLATION DESIGN AND APPLICATION OF A CATALYTIC DISTILLATION COLUMN

by JOSIAS JAKOBUS (JAKO) NIEUWOUDT

Thesis presented in partial ful…lment of the requirement for the Degree

of MASTER OF SCIENCE IN ENGINEERING (CHEMICAL ENGINEERING) in the Department of Process Engineering at the UNIVERSITY OF STELLENBOSCH

in co-operation with the UNIVERSITY OF CAPE TOWN CATALYSIS RESEARCH UNIT in the Department of Chemical Engineering

SUPERVISORS University of Stellenbosch Dr. L.H. CALLANAN

University of Cape Town A/Prof. K.P. MöLLER

GRADUATION DATE DECEMBER 2005

DECLARATION

I, the undersigned, hereby declare that the work contained in this thesis is my own original work and that I have not previously in its entirety or in part submitted it at any university for a degree.

______16th May 2005 J.J. Nieuwoudt Date ii iii

SUMMARY

Catalytic Distillation (CD) is a hybrid technology that utilizes the dynamics of simultaneous reaction and separation in a single process unit to achieve a more compact, economical, e¢ cient and optimized process design when compared to the traditional multi-unit designs. The project goal (and key question) is (how) to design a cost-e¤ective, simple and accurate laboratory-scale continuous CD system that will su¢ ciently and accurately supply useful data for model validation. The system to be investigated is the continuous

hydrogenation of an -ole…n C6 (1-hexene) feed stream to the corresponding alkane (n-hexane) product with simultaneous reactant/product separation. Hypothetically, a system can be constructured to determine whether hydrogenation will bene…t from the heat and mass transfer integration observed under CD conditions in terms of energy usage, temperature control and the catalyst’ssurface hydrogen concentration. System convergence with commercial distillation simulation packages were not attained and a dynamic design approach was followed based on the converged non-reactive solution. A simpli…ed McCabe-Thiele approach approximates the system’sbehavioural operational trends. The continuous computer control, monitoring, logging and emergency shutdown system is routed through LabVIEW 7.1 Express. Software and/or electronics is used to maintain constant feed ‡ow rates, reboiler heat duty, level and re‡ux ratio set-points and to generate transient temperature pro…les. A modi…ed push- pull system achieves pressure control and liquid compositional sampling is currently manual. It is concluded that the modularly commissioned system can supply much needed transiently monitored mass balances, energy balances and concentrations as required for non-equilibrium (NEQ) CD computer model validation. Its design addresses separation of close-boiling components, the system’s laboratory-scale size and issues introduced by a non-condensable gas. Hydrodynamic e¤ects must still be considered. There is additional capacity for on-line concentration measurements and for a side reactor. The designed system is a powerful, ‡exible tool to experimentally explore the potential of CD. iv v

OPSOMMING

Katalitiese distillasie (KD) gebruik gelyktydige reaksie-skeidingsdinamika in ’nenkele proseseenheid om ’nmerkbaar meer kompakte, ekonomiese, energie e¤ektiewe en prak- tiese sisteem daar te stel vergeleke met tradisionele multi-eenheid ontwerpsbenaderings. Die projekdoel (en gepaardgaande sleutelvraag) is (hoe) om ’n ekonomiese, een- voudige en akkurate laboratorium-grootte kontinue KD sisteem te ontwerp wat voldoende en akkurate data sal verskaf vir die geldigheidstoetsing van sisteemmodelle d.m.v. gevallestudies. Die sisteem wat ondersoek sal word behels die kontinue hidrogenering van ’n C6 -ole…ene (1-hekseen) voerstroom na die ooreenstemmende alkaanproduk- stroom (n-heksaan) terwyl reagens/produk skeiding gelyktydig plaasvind. Hipoteties gesproke kan ’n sisteeem gebou word wat kan toest of hidrogenering in terme van en- ergieverbruik, temperatuurbeheer en waterstof katalis-oppervlakkonsentrasie baatvind by die hitte- en massaoordrag integrasie wat onder KD toestande waargeneem word. Sisteemkonvergensie is nie bereik met ’nkommersiële distillasie simulasie pakket nie en ’ndinamiese ontwerpsbenadering, gebaseer op die konvergente oplossing vir die nie- reaktiewe sisteeem, is dus gevolg. ’nVereenvoudigde McCabe-Thiele model poog om die sisteem se operasionele neigings te antisipeer. Die kontinue rekenaarbeheer, -monitering, -leggering en -noodstop sisteem werk deur LabVIEW 7.1 Express. Sagteware en/of elektronika volhou ’nkonstante vloeitempo, opkokerdrywing, vlak en re‡uksverhouding setpunte and genereer ook tydafhanklike temperatuurpro…ele. ’n Trek-druk sisteem word vir drukbeheer toegepas en vloeistof komposisionele toetsing word met die hand gedoen. Die uiteindelike gevoltrekking is dat die deelsgewys inbedryfgestelde sisteem nodige, bruikbare tyd-afhanklik gemoniteerde massa-, energiebalanse en konsentrasies vir mod- elveri…ëring van nie-ekwilibrium KD rekenaarmodelle kan verskaf. Ontwerpskwessies met betrekking tot naby-kokende komponente, die klein skaal van die sisteem en die aanwesigheid van ’nsuperkritiese gas word aangespreek. Hidrodinamiese e¤ekte moet steeds oorweeg word. Daar is addisionele kapasiteit vir aanlyn konsentrasiemetings en die toevoeging van ’n kantreaktor. Die ontwerpte sisteem is dus ’n kragtige, buigbare instrument om die potensiaal van KD eksperimenteel te ondersoek. vi

[Watterson, 1993] May this NOT be true of this thesis! vii

ACKNOWLEDGEMENTS

The …rst two words of thanks must go to my supervisors Dr. Linda H. Callanan (University of Stellenbosch) and A/Prof. Klaus P. Möller (University of Cape Town, UCT) who helped and guided me through this project from grass roots to commissioning. I also gratefully acknowledge the additional classes, support, information and fa- cilities made available to me by the Catalysis Research Unit of the Chemical Engineering Department at the University of Cape Town where the system was constructed and where it now stands. Such collaboration between the Chemical Engineering Departments of the Universities of Stellenbosch and Cape Town is to be applauded and encouraged. The timely completion of the project would also not have been possible without the necessary support services. In this regard Marc Wüst (UCT catalysis technical o¢ cer), Bill Randall and Granville de la Cruz (UCT electronic workshop) and Jannie Barnard and Anton Cordier at the Stellenbosch mechanical workshop deserve special mention. The UCT mechanical workshop must also be included for the signi…cant amount of hours that they put into the system. Last, but certainly not least, a word of gratitude must also be given to Sasol who made this project possible with a generous post-graduate sponsorship. viii Contents

Contents ix

Nomenclature xv

List of Figures xix

List of Tables xxi

I LITERATURE REVIEW 1

1 INTRODUCTION 3 1.1 History and Background ...... 3 1.2 Advantages and criteria ...... 4 1.3 Existing and possible applications ...... 6 1.3.1 TheMTBEprocess...... 6 1.3.2 Selective hydrogenation ...... 7 1.4 Project goals, hypothesis, key questions and de…nitions ...... 8

2 REACTION KINETICS AND PROCESS CONDITIONS 11 2.1 Mechanism ...... 11 2.2 Reactionkinetics ...... 13 2.3 Processconditions ...... 15 2.3.1 Possible range for process conditions ...... 15

3 MODELLING THEORY 19 3.1 Residuecurvemaps ...... 20 3.2 Equilibrium (EQ) models ...... 22 3.3 Non-equilibrium (NEQ) models ...... 23 3.3.1 MESH equations for the non-reactive distillation section . . . . . 24 3.3.2 MESH equations for the reactive section ...... 26 3.4 Non-condensable gases ...... 27

ix x CONTENTS

4 MASS TRANSFER EQUATIONS 29 4.1 Phase hydrodynamics ...... 29 4.2 Fick’sLaw...... 30 4.2.1 Filmtheory ...... 32 4.2.2 Two-…lm theory ...... 33 4.3 The Stefan-Maxwell approach to mass transfer ...... 34 4.3.1 Interphase mass transfer ...... 35 4.3.2 Mass transfer within pores: the dusty ‡uid model ...... 36 4.4 Modellingtools ...... 38

5 LITERATURE REVIEW: CONCLUDING REMARKS 39

II PROCESS DESIGN 41

6 PROCESS DESIGN METHODOLOGY 43

7 EXISTING SYSTEM DESCRIPTION 45 7.1 Reaction investigated: Hydrogenation ...... 45 7.2 Experimental apparatus ...... 46 7.3 Previous column internals ...... 47 7.3.1 Catalyst speci…cations and reactive packing ...... 47 7.3.2 Non-reactive packing ...... 48

8 MASS AND ENERGY BALANCES 51 8.1 Simulation using distillation packages ...... 51 8.1.1 Non-reactive distillation ...... 51 8.1.2 Reactive distillation: adding a reaction ...... 51 8.2 Spreadsheet calculations and ProII veri…cations ...... 53 8.2.1 Revised design approach ...... 53 8.2.2 Excel spreadsheet ...... 53 8.3 McCabe-Thiele system trends ...... 54

9 MECHANICAL DESIGN 61 9.1 Materials of construction (MOC) ...... 61 9.2 Pipesystem ...... 63 9.3 Maincolumnbody ...... 63 9.4 Column internals and liquid distribution ...... 63 9.4.1 Column internals (non-reactive sections) ...... 64 9.4.2 Column internals (reactive section) ...... 64 9.4.3 Liquid distribution and redistribution ...... 66 CONTENTS xi

9.5 Reboiler ...... 67 9.6 Coolingloops ...... 69 9.6.1 Two-stage partial condenser ...... 69 9.6.2 Bottomscooler ...... 71

10 PROCESS CONTROL 73 10.1 Isobaric pressure control ...... 73 10.2 Gaseous and liquid feeds ...... 74 10.3 Re‡ux line con…guration ...... 76 10.3.1 Levelcontrol ...... 78

10.3.2 Re‡ux ratio (R = V_L=V_D)...... 81 10.4Reboiler ...... 83 10.4.1 Heat duty control ...... 83 10.4.2 Levelcontrol ...... 84 10.5 Resulting P&ID and control philosophy ...... 85

11 COMPUTER CONTROL SYSTEM 89 11.1 Basic software-hardware structure ...... 89 11.2 Program Launcher and Main Graphical User Interface (GUI) ...... 91 11.3 Start-up and Shutdown ...... 93 11.4 Data Acquisition (DAQ) ...... 94 11.5 Instrument control loops ...... 96 11.5.1 Gaseous and liquid feeds ...... 98 11.5.2 Reboiler heat duty control ...... 98 11.5.3 Optical level control ...... 100 11.5.4 Re‡ux ratio control ...... 100 11.6ErrorHandling ...... 100

12 OPERATION 103 12.1 Equipment frame locations ...... 103 12.2 Operating procedures ...... 104

III RESULTING SYSTEM 109

13 MODULAR COMMISSIONING 111 13.1 Pressure Testing And Gas Lines ...... 111 13.2 Simpli…ed start-up ...... 112 13.3 General observations ...... 114 13.3.1 Data acquisition and logging ...... 114 13.3.2 Thermal response ...... 115 xii CONTENTS

13.4Resultingsystem ...... 118

14 CONCLUSIONS 123

15 GEVOLGTREKKINGS 125

16 RECOMMENDATIONS 127

Bibliography 129

IV APPENDICES AND INDEX 133

A EXISTING AND FUTURE APPLICATIONS FOR CD 135

B THERMODYNAMIC, PHYSICAL PROPERTY AND MASS TRANS- FER MODELS 139

C DESIGN CALCULATIONS 141 C.1 PROIICalculations ...... 141 C.2 Excel Calculations ...... 151 C.3 Derivation of the McCabe-Thiele approximation ...... 156 C.3.1 Condenser...... 156 C.3.2 Recti…cation section ...... 157 C.3.3 ReactiveZone...... 158 C.3.4 Stripping section (reactive zone incorporated) ...... 159 C.3.5 Stripping section (reactive zone excluded) ...... 160 C.3.6 Reboiler ...... 161

D PYREX SAFE WORKING PRESSURE 163

E MECHANICAL DRAWINGS 165

F EQUIPMENT DATA SHEETS 173 F.1 Catalytic distillation column data sheet (CD-1) ...... 174 F.2 Two-stage partial condenser data sheet (C-DP) ...... 175 F.3 Refrigerator data sheet (E-1) ...... 177 F.4 Re‡ux pump data sheet (P-RD) ...... 178 F.5 Precisa balances data sheets (W-D and W-B) ...... 179

G STREAM INFORMATION 181

H OPERATING PROCEDURES 187 CONTENTS xiii

I GRAPHICAL KEY 195

Index 197 xiv CONTENTS Nomenclature

Normal letters Units a Interfacial area [m2] a Sutro weir geometric parameter (only used in eq. 10.3) [mm] A Area [m2] 2 B0 Permeability [m ] c Number of components [None] C Concentration [mol/m3] 3 Ci Concentration of component i [mol/m ] 3 CR Bulk concentration of an organic substrate [mol/m ] d Diameter [mm] 2 DAB Fick’sdi¤usivity of A (…rst letter) in B (second letter) [m /s] E Energy accumulated/Energy balance equation [W] 6 E Energy transfer rate [W] Eq Equilibrium [None] fi Feed ‡ow rate of component i [mol/s] F Feed ‡ow rate [mol/s] 2 3 FP Packing factor [Seader and Henley, 1998] [ft /ft ] g Gravitational acceleration (9.81 m/s2) [m/s2] H Speci…c enthalpy [J/mol] H 3 Hi Henry’sconstant for component i in the solvent mixture [Pa.m /mol] 2 Jiz Component i molar ‡ux in the z direction relative to bulk ‡ow [mol/m .s] k Intrinsic chemical rate constant [mol/s.gcat] kc Mass-transfer coe¢ cient - concentration (C) driving force [m/s] K Equilibrium constant [None] 2 Kg Overall vapour-liquid mass transfer rate [mol/s.m Pa] 2 Kl Overall liquid-solid mass transfer rate [mol/s.m Pa] L Liquid molar ‡ow rate [mol/s] ·m Mass ‡ow rate [kg/s]

xv xvi CONTENTS

M Moles accumulated/Component material balance equation [mol/s] n Number of di¤using species (equivalent to c in CD) [None] N Molar ‡ux relative to a stationary reference [mol/m2.s] P Pressure [Pa] Q Heat transferred added to (+) or removed from (-) system [W]

r Rate of reaction [mol/s.gcat]

rj Fraction of vapour or liquid leaving stage j that is drawn o¤ [None] R Ideal gas constant (8 314 J/kmol.K) [J/kmol.K] S Sum of components as de…ned in equations (3.10) and (3.11) [None] t Time [s] T Temperature [K] v Linear velocity [m/s] V Vapour molar ‡ow rate [mol/s] V· Volumetric ‡ow rate [m3/s] 3 Vi Partial molar volume of component i in mixture [m /mol] 3 VR Reaction volume of clear liquid [m ] w Mass of catalyst per unit volume of slurry [kg/m3] W· Work rate (Power) [W] x Molar fraction of subscripted component in liquid mixture [None] X Transformed liquid composition variable (see equation (3.1)) [None] y Molar fraction of subscripted component in vapour mixture [None] Y Transformed vapour composition variable (see equation (3.2)) [None] z Indicates z-direction in 3-dimensional space [m]

zi Charge on species i [None]

zF;j Molar composition of feed [None]

Subscripts Units b Indicates bulk liquid [None] cat Catalyst [None] F Feed to column [None] i Indicates component i in the mixture [None] I Interface [None] j Indicates stage j in the distillation system [None] k Reference component k in the mixture [None] p Catalyst particle [None] R Recti…cation section [None] S Stripping section [None] t or T Total –refers to the entire mixture [None] CONTENTS xvii

Superscripts Units I Indicates interface [None] L Indicates liquid phase [None] sat Indicates saturation [None] S Indicates solid (catalyst) phase [None] vap Refers to vaporization [None] V Indicates vapour phase [None]

Greek letters Units

i Viscous selectivity parameter [None] Indicates a large change [None] Molar ‡ow rate of vapour in the o¤-gas (McCabe-Thiele) [mol/s] ^ i Fugacity coe¢ cient of species i in solution [None] Electrostatic potential [V] Activity coe¢ cient [None] Dimensionless coordinate [None]

visc Fluid mixture viscosity [Pa.s] Mass transfer coe¢ cient [m/s] E¤ectiveness factor [None] Chemical potential [J/mol]

V vk vT yk Transformed time variable de…ned by d = dt [s] L vk vT xk i Stoichiometric coe¢ cient of component i [None]

Other Units 2 Ðij Stefan-Maxwell di¤usivity for the component pair i-j [m /s] e 2 Ðij E¤ective di¤usivity for the component pair i-j in a porous medium [m /s] e ÐiM E¤ective Knudsen di¤usivity for the component pair i-j in a porous medium [m2/s] Mathematical operator for “gradient” [None] r Frictional factor [J/kg] = Faraday constant (96 500 C/mol) [C/mol] F

Abbreviations BP or bp Boiling point (former used in …gures; latter in text) Cat. No. Catalogue Number CD Catalytic Distillation CFD Computational Fluid Dynamics DP Dew point xviii CONTENTS

EQ Equilibrium GUI Graphical User Interface HETP Height Equivalent of a Theoretical Plate HPLC High Pressure Liquid Chromatography KD Katalitiese Distillasie LM Levenberg-Marquardt MESH Set of equations including Material balance, Equilibria, Summation and Energy (H) balance equations MOC Materials of construction MTBE Methyl tertiary butyl ether NEQ Non-equilibrium NTP Normal Temperature and Pressure (273.15 K; 101 325 Pa) PID Proportional-integral-derivative RD Reactive Distillation STP Standard Temperature and Pressure (298 K; 101 325 Pa) UPS Uninterrupted power supply VI Virtual Instrument (main program in LabVIEW) VLE Vapour-liquid equilibrium List of Figures

1.1 Comparison between a traditional and CD process for MTBE production 7 1.2 CD column for selective butadiene hydrogenation ...... 8

2.1 Horiuti-Polanyi hydrogenation mechanism ...... 12 2.2 Speci…c liquid hold-up as a function of super…cial gas and liquid velocities 18

3.1 Applications of di¤erent design approaches in CD ...... 19 3.2 Residue curve - reactive ternary ideal system ...... 21 3.3 Residue curve showing the occurrence of a reactive azeotrope - reactive ternaryidealsystem ...... 21 3.4 Equilibrium stage model ...... 22 3.5 Non-equilibrium stage model for non-reactive distillation ...... 24 3.6 Non-equilibrium model with a solid catalyst phase ...... 27

4.1 Concentration pro…le in a unit cell ...... 30 4.2 Film theory concentration pro…le for two phases (phase I and an adjoining phase) ...... 32 4.3 Two-…lm theory concentration pro…le ...... 33

6.1 Block diagram of the CD system ...... 44

7.1 Comparison between the VLE’s of a 1-hexene/hexane system and a 1- hexene/1-heptene system (P = 2 bar(a)) ...... 46

8.1 Schematic of the ProII simulation for non-reactive distillation ...... 52 8.2 McCabe-Thiel approximation of the CD system ...... 56

9.1 Steel compositions required for prevention against hydrogen attack as a function of temperature and pressure ...... 62 9.2 "Tea-bag" approach used in the reactive zone with (a) the empty stainless

steel cylindrical disks and (b) the disk …lled with 21 g Ni/Al2O3 ..... 65 9.3 Various catalyst packing techniques for use in the reactive zone . . . . . 66

xix xx LIST OF FIGURES

10.1 Pressure control using (a) vapour product rate variations and (b) inerts pressurecontrol ...... 74 10.2 Pressure control in the CD system ...... 75 10.3 MFC calibration and error curve ...... 76 10.4 Main di¤erences between (a) forced ‡ow and (b) gravity lines ...... 77 10.5 Level control methods: (a) Over‡ow type, (b) ‡oat valve, (c) magnetic sensors and (d) optical sensors ...... 79 10.6 Two methods for re‡ux ratio control: (a) re‡ux splitter, (b) sutro weir . 81 10.7 Schematic representation of the PID feedback control loop used to main-

tain the reboiler temperature [C] or heat duty [W] set-point ...... 84

11.1 Block diagram of the overall control system ...... 90 11.2 Overall ‡ow diagram of control program ...... 92 11.3 The CD control system’smain graphical user interface ...... 93 11.4 SubVI start-up and shutdown methodologies ...... 95 11.5 Main body of the data acquisition subVI ...... 97 11.6 General algorithmic ‡ow diagram for the control loops ...... 99

12.1 Frame and dimensional layout of the CD system ...... 105

13.1 CD column temperature pro…le ...... 113 13.2 Start-up temperature pro…le and the related reboiler power setting for the CDsystem...... 114 13.3 Behaviour of the system based on the e¤ect of parameter changes on the temperaturepro…le ...... 119 13.4 Photo of CD system taken on 10 April 2005, showing the front and back views...... 120 13.5 Photo of CD system taken on 10 April 2005, showing the two side views . 121

D.1 Pyrex Safe Working Pressure ...... 164 List of Tables

2.1 Reaction between ethene and hydrogen over a Ni catalyst ...... 11 2.2 Horiuti-Polanyi alkene hydrogenation mechanism ...... 13 2.3 Hydrogenation reaction heats for 1-hexene and 1-heptene at STP - 298K and101325Pa ...... 15 2.4 E¤ect of Process Variables ...... 16

4.1 Phenomena observed between Fick’s…rst law in the form of equation 4.3 andexperimentaldata ...... 31

7.1 Equipment Speci…cations ...... 47 7.2 Information of catalyst used by Mphahlele [2003] ...... 48 7.3 Sulzer CY geometric data ...... 49 7.4 Comparison of types of packing ...... 49

9.1 Speci…cations of tubes used ...... 63 9.2 Speci…cations of Sulzer CY gauze type packing used in the CD system (information extracted from user manual) ...... 65

13.1 Mass and Energy balance classi…cations of the various control components 111 13.2 CD control program’sresponse to the eight possible signal combinations from the optical sensors ...... 116 13.3 Excerpt from the CD system’s logging …le (textual changes shown in italics)...... 117

A.1 Existing and future applications for CD ...... 136 A.2 Existing and future applications for CD continued...... 137

B.1 Thermodynamic, physical property and mass transfer models incorporated into the RD design program of Baur et al. [2000] ...... 140

xxi xxii LIST OF TABLES Part I

LITERATURE REVIEW

Chapter 1

INTRODUCTION

1.1 History and Background

Reactive distillation (RD) has existed from the beginning of distillation itself although it was not always viewed as advantageous [Doherty and Buzad, 1992]. Only in the early 1920’sdid the possible bene…ts of RD capture the imagination of scientists and engineers and by 1922 the …rst of four patents were taken out by Backhaus [Taylor and Krishna, 2000]. However, the …rst commercial-scale catalytic distillation (CD) column was not put into operation until 1981, nearly 60 years later [Rock et al., 1997]. It was used by Charter Oil’s Houston, Texas re…nery for production of methyl tertiary butyl ether (MTBE) which acts as an octane enhancer in fuels. The process was found to be so successful that by 1997 CD-based processes outnumbered rival installations [Prodebarac et al., 1997]. In 1992 Doherty and Buzad published a keynote paper that reviewed the literature up to that time. This sparked a renewed interest in the subject. In fact, in an update to this review by Taylor and Krishna [2000], they pointed out that over 150 of the 300 papers that they cited were written after 1992. But what are reactive and catalytic distillation? Simply stated they are systems in which reaction and distillation occur simultaneously. In reactive distillation (RD) a homogeneously catalyzed reaction is used while a heterogeneously catalyzed reaction is used in catalytic distillation (CD). These two terms are used almost interchangeably in literature, but for the purpose of this report the above de…nitions will be strictly maintained. Since the emphasis of this review lies on the investigation and modelling of a catalytic distillation column the rest of this introduction will focus on CD. CD is a complex …eld encompassing concepts from reactor design and distillation as well as some unique ones resulting from the simultaneous reaction-separation. This overlapping of disciplines implies that aspects from both must be considered in such

3 4 CHAPTER 1. INTRODUCTION systems. Proper choice of the reaction is critical in ensuring an e¤ective CD system. The reaction kinetics involved and their e¤ect on the system must be considered. In this regard the type of catalyst used, rate of reaction, heat of reaction and possible rate limiting step(s) are important parameters. Mass and heat transfer e¤ects are also pivotal to successfully describe CD systems. In fact, it is the dynamic transport between the gas, liquid and solid (catalyst) phases in the column that enhances separation via distillation and allows gaseous reactants to participate in the heterogeneous liquid phase reactions. Modelling of CD systems requires computer aided mathematical techniques that can solve large systems of equations. Taylor and Krishna [2000] additionally suggest the use of computational ‡uid dynamics (CFD) to enhance the current understanding of the e¤ects of hydrodynamics and mass transfer on CD. In general it is possible to state that, although the concept of simultaneous reaction-separation is simple, the modelling of CD is more complex. This is because the multitude of parameters that must be speci…ed, estimated and calculated ultimately results in a model consisting of a set of complex, interrelated equations, which then has to be solved simultaneously. Research in CD has thus far fallen mainly on modelling and Taylor and Krishna [2000] point out that there is a dire need for model validation from experimental data. The implicit aim of this work (see section 1.4) is to construct a properly designed and tested experimental tool that can add more depth to our understanding of CD and that may be used in future projects for model validation. Modelling will, however, still be considered in some detail in this review as a solid grasp of the mathematical description of CD is a prerequisite in order to understand the system’s dynamics and the various issues involved. In 2000 Taylor and Krishna start their review of reactive distillation with the following quote by Berman, Isbenjamin, Sedo¤ and Othmer (1948): “The versatility of the fractionating column in the dual role of continuous reactor and separator as applied to chemical processing is well established.” Ironically, even after the turn of the century the complex dynamics in CD systems are still not fully understood or predictable. In a world that is increasingly geared towards energy e¢ ciency, environmental protection and cost minimization CD has an integral role to play. It is the hope of this work that its small contribution will shed some more light on this technology.

1.2 Advantages and criteria

The advantages and qualitative criteria of CD are well established and quoted. Perhaps the best summary of the advantages of CD compared to …xed bed reactors is provided by Prodebarac et al. [1997] and is adapted hereafter. 1.2. ADVANTAGES AND CRITERIA 5

Heat integration The heat released in the exothermic reaction is used directly in the column to generate more vapour thus enhancing separation via distillation and increasing energy e¢ ciency - the synergistic e¤ect.

Reduced danger of hot spots Since the CD column contains boiling liquid the danger of hot spots is reduced, as the temperature of the liquid cannot exceed its boiling point. Additionally, as long as the catalyst is properly wetted it will have a similar temperature as the liquid.

Precise isothermal reaction control This is essentially an extension of the previous point and is achieved by keeping the catalyst particle temperature close to the liquid boiling point. Radial and axial temperature gradients are also minimized.

Reduced capital and operating costs Instead of having a reactor and subsequent separation units, one can achieve both product formation and separation in the same column thus cutting back on costs.

Reduced corrosion It is unnecessary to use corrosion resistant material to construct the column walls or internals when using corrosive or hazardous catalysts, as there is no contact between them in CD.

Increased conversion CD can e¤ectively “cheat” equilibrium and circumvent thermodynamic restrictions by immediately removing the products from the system upon formation. According to Le Chatelier’s principle this favours the forward reaction thus shifting the equilibrium to increase the product formation rate and subsequently the conversion.

Improved selectivity Consecutive reactions are minimized by the relatively fast removal of products from the CD column’sreactive zone.

Increased catalyst life Reduced catalyst poisoning is possible by correct placement of the reactive zone relative to the feed point.

Azeotropes can disappear Non-reactive azeotropes may disappear when a reaction takes place [Krishna and Wesselingh, 1997].

Since CD combines two chemical engineering concepts (heterogeneous reactions and distillation) that are complex …elds of study in their own right it makes sense that only very speci…c systems have the correct characteristics to be used in CD. The system must therefore satisfy the following criteria [Prodebarac et al., 1997]:

1. Distillation must be a viable method of separation.

2. The reaction must take place in the liquid phase. 6 CHAPTER 1. INTRODUCTION

3. Conditions within the column must preferably ensure both acceptable reaction and distillation performances. The boiling temperature within the column can be changed by changing the pressure, but at least one component must always be below its critical point.

4. The reaction must preferably be exothermic (or not too endothermic) otherwise the advantage of heat integration is lost as a signi…cant input of energy to the column is then required.

5. The catalyst must have a long lifespan (1 to 2 years for commercial viability) since its replacement is expensive and labour intensive.

1.3 Existing and possible applications

Table A.1 in Appendix A summarizes some of the existing and potential applications of CD from Armor [2001] and Prodebarac et al. [1997] and also lists some general advantages for each. Refer to Hiwale et al. [2004] for an excellent summary on recent developments. In this sub-section only two processes, namely the MTBE process and selective hydrogenation, will be brie‡y considered as examples.

1.3.1 The MTBE process

The MTBE (methyl tertiary butyl ether) process is generally viewed as a classic success story for CD and illustrates many of the advantages possible in a simultaneous reaction-distillation system. MTBE is used in gasoline as an environmentally friendly alternative to heavy metal octane enhancers1. Its ability to reduce automobile exhaust emissions coupled with increasingly strict global environmental awareness and legisla- tion has greatly increased its demand from an estimated annual world production of 11.6 million m3 (3,07 billion gallons) in 1990 to 26.1 million m3 (6,9 billion gallons) in 1995 [Prodebarac et al., 1997]. Figure 1.1 illustrates the di¤erence between the conventional and CD systems. The heat of reaction generated in the adiabatic reactor is used to preheat the feed to the CD column. A maximum isobutene conversion of 99,99% is possible in the CD column compared to the 95% in conventional systems. Additionally, the minimum boiling azeotrope in the MTBE-methanol system that complicates distillation in the conventional system is used in the CD system to enhance

1 Although MTBE inhalation at high concentrations and its ingestion through drinking water (preliminary 40ppb maximum concentration; no de…nitive conclusions are available) may be harmful to humans, the Environmental Protection Agency (EPA) reports that 87% of oxygenated gasoline (comprising 30% of the total) in America uses MTBE rather than ethanol due to economic reasons, its blending characteristics and its transportability through existing pipe lines (http://www.epa.gov/mtbe/). 1.3. EXISTING AND POSSIBLE APPLICATIONS 7

Spent C4

Cooling Distillation Distillation Distillation column column column Reactor Reactor 1 2 3 1 2

Mixed C4

MTBE

Methanol

Mixed C4

Methanol Spent C4

Reactor 1

Distillation Distillation CD column column column 1 2

MTBE

Figure 1.1: Comparison between a traditional (above) and CD process (below) for MTBE production the purity of the MTBE bottoms product. This occurs because, according to the VLE of the system, at the relatively high concentrations of MTBE (bp. 55C) found in the stripping section there is more gaseous than liquid methanol (bp. 64,5C). Unreacted liquid methanol is therefore vaporized and rises up the column back to the reaction zone for further conversion [Prodebarac et al., 1997].

1.3.2 Selective hydrogenation

In 1997 CDTech reported that they could install more than nine di¤erent CD selective hydrogenation units into a process [Rock et al., 1997]. The main applications include buta-, penta-, and hexadiene selective hydrogenation as well as benzene total hydrogenation. The selective hydrogenation of butadiene is of particular importance in industry. Diole…ns in hydrocarbon streams can deactivate downstream catalysts and participate in undesirable side reactions [Prodebarac et al., 1997]. It is also of special interest to re…ners who selectively hydrogenate C4 streams to increase the n-butane content available for alkylation, which in turn reduces acid consumption during alkylation. This reduces costs and environmental impacts due to e• uents from, for example, acid regeneration. Ultimately, it enhances the octane number of the fuel coming from the hydro‡uoric 8 CHAPTER 1. INTRODUCTION

Hydrogen recycle

Off•gas

Treated C4 (no diolefins)

CD column

C4+ Fraction

Hydrogen

C5+ Fraction

Figure 1.2: CD column for selective butadiene hydrogenation [Prodebarac et al., 1997]

alkylation units [Rock et al., 1997]. The CD system for selective hydrogenation of butadiene discussed by Prodebarac et al. [1997] was patented by E.M. Jones in 1985. The system depicted in Figure 1.2 achieves simultaneous selective hydrogenation of butadiene, separation of the C4 and C5+ fraction and hydrogenation of the light sulphur compounds to H2S, which is subsequently removed from the system through the o¤-gas stream. Consequently a sulphur-free C4 fraction is obtained and the heavier sulphur compounds exit with the C5+ bottoms product. As a point of interest, another commercial CD system that is manufactured by

CDTech combines selective hydrogenation of C4 diole…ns into mono-ole…ns and etheri…- cation of C4 and methanol to MTBE [Rock et al., 1997].

1.4 Project goals, hypothesis, key questions and de- …nitions

As hydrogenation is an exothermic reaction it should bene…t greatly from the heat and mass transfer integration observed under CD conditions in terms of energy usage, temperature control and enhanced hydrogen mass transfer from the gas to the liquid phase where the reaction occurs. In principle, a more economical energy usage should 1.4. PROJECT GOALS, HYPOTHESIS, KEY QUESTIONS AND DEFINITIONS 9

also be achieved as the exothermic heat released in the reaction contributes directly to the energy required for distillation. In this study, the e¢ ciency of 1-hexene hydrogenation under catalytic distillation conditions will be considered. In order to achieve this a laboratory-scale CD column must be constructed with a continuous computer control, monitoring, logging, report generation and emergency shutdown system. The system must supply the much needed mass balances, energy balances and concentrations as a function of time as required for validation of non-equilibrium (NEQ) CD computer models. It will thus be a powerful tool to experimentally explore the potential of CD. The system to be investigated is a laboratory-scale CD hydrogenation column that converts a simple, possibly mixed, reactant -ole…ns feed stream (consisting mainly, though not necessarily exclusively, of 1-hexene) to the corresponding product alkanes and simultaneously separates the products and residual reactants into a 1-hexene rich distillate and n-hexane rich bottoms product. It is hypothesized that a system can be constructed to test whether higher reaction e¢ ciencies in this type of system are due to increased hydrogen transfer from the gas to the liquid phase, which is the result of the higher vapour-liquid contact areas and better mixing of distillation. The project goal is to convert a batch CD system into a continuous computer controlled system that will closely approximate industrial-scale behaviour and yield accurate data that may be used for case studies in developing generic computer models for CD. In order to supply a guideline for the project, a general requirement for successful project completion must be satis…ed namely that the system must be completed and must function correctly reproducibly. In the sections that follow the key questions that must be asked are therefore:

1. What can be done to design a cost-e¤ective, simple and accurate pilot scale continuous CD system?

2. What system parameters and dynamics must be considered and/or measured to ensure that the system supplies useful data for case studies?

3. How does the ole…n conversion under CD conditions compare to that under conventional trickle bed conditions? 10 CHAPTER 1. INTRODUCTION Chapter 2

REACTION KINETICS AND PROCESS CONDITIONS

The reaction is the distinguishing factor between conventional and catalytic distillation. In this section aspects related to the reaction is therefore considered. The reaction mechanism and kinetics are investigated before a cursory glance is a¤orded to the possible process conditions that will be used in the experimental case studies.

2.1 Mechanism

During the 1930’s, extensive research was done on the hydrogenation of ole…ns over Ni catalysts and, more speci…cally, on the heterogeneous hydrogenation of ethene. Prior to the early 1930’sit was assumed that hydrogenation of alkenes over Ni and Pt catalysts occurred via direct addition of the hydrogen to the double bond. However, the discovery that hydrogen existed in its atomic form as a chemisorbed species on the metal surface questioned this hypothesis [Farkas et al., 1934]. To determine a more accurate mechanistic description, the above authors did experiments with a combination of hydrogen (H2 or light hydrogen) and deuterium (D2 or heavy hydrogen) in the hydrogenation of ethene over a Ni catalyst. In essence, by employing deuterium they “marked” a certain percentage of the hydrogen used in the reaction and were thus able to follow the reaction pathway of the hydrogen more closely. They found that two simultaneous reactions took place (Table 2.1)

Table 2.1: Reaction between ethene and hydrogen over a Ni catalyst No. Type of reaction Reaction (i) Exchange reaction C2H4 + HD C2H3D + H2 (ii) Addition reaction C2H4 + HD C2H5D

It was found that at low temperatures (below 20C) hydrogenation (hydrogen ad-

dition) occurred without exchange, while at higher temperature (20 - 100C) exchange

11 12 CHAPTER 2. REACTION KINETICS AND PROCESS CONDITIONS

R H Ni C H Ni Ni C H H H Ni

R H R H Ni C H* Ni Ni C H* Ni

Ni C H* Ni Ni C H* Ni H H H H

R H R H Ni C H* Ni Ni C H* Ni

Ni C H Ni Ni C H* Ni H H* H H

Figure 2.1: Horiuti-Polanyi hydrogenation mechanism [Horiuti and Polanyi, 1934] and addition took place simultaneously. Additionally, with relation to ethene, zero order kinetics was observed at low temperatures (20C) while …rst order kinetics was noted at higher temperatures (60C). The apparent independence of the reaction rate on the ethene and hydrogen partial pressures at low temperatures were explained by suggesting that, at these temperatures, the metal surface is completely covered by ethene. The reaction rate is thus rather dependant on the rate of desorption of the ethene and ethane from the surface, yielding an open metal site on which hydrogen can adsorb for further reaction. At higher temperatures the surface was found to be only partially covered with ethene. The work by Farkas et al. [1934] stimulated the research of Horiuti and Polanyi [1934] who investigated the exchange reactions between hydrogen and benzene and hydrogen and ethene over a platinum black1 catalyst and over a nickel catalyst. They suggested the reaction mechanism depicted in Figure 2.1 to account for the simultaneous addition/exchange reactions on Ni catalysts. Pines [1981] supplies a re…ned Horiuti-Polanyi mechanism (Table 2.2), which in-

1 According to Kieboom and Rantwijk [1977] “metal black”refers to the old catalysts that consisted of pure metal. 2.2. REACTION KINETICS 13

Table 2.2: Horiuti-Polanyi alkene hydrogenation mechanism [Pines, 1981] No. Type of reaction Reaction (i) Chemisorption of ole…n (AH2) AH2 + 2Ni Ni(AH2)Ni (ii) Chemisorption of H2 H2 + 2Ni 2HNi (iii) Half-hydrogenated state formation Ni(AH2)Ni + HNi Ni(AH2H) +2Ni (iv) Addition (hydrogenation) product Ni(AH2H) + HNi (AH2H2) + 2Ni !

dicates the reversibility and irreversibility of the various elementary reactions for the hydrogenation reaction. It is also indicated that the Horiuti-Polanyi mechanism is “generally accepted” and that the desorption of the alkane (step (iv)) is “almost irreversible at room temperature”. It must be pointed out that these statements are made without proof or references, but that it would appear that other references cited in this report concur [Rylander, 1994; Kieboom and Rantwijk, 1977]. Partial justi…cation that the last step is irreversible may also be obtained in a paper by Gonzo and Boudart [1978]. They cite references that indicate that cycloalkanes do not chemisorb dissociatively on palladium catalysts which would suggest that re-adsorption of the product alkane is unlikely to occur. Gonzo and Boudart [1978] also supplies references to prove that addition of the …rst hydrogen to the ole…n is also irreversible because of the large amount of exchanged alkenes observed in deuterium experiments. They lastly cite the existence of HD in these experiments as an indication that the hydrogen adsorption is also reversible. In 1939 Twiggs and Rideal predicted that, due to the exchange reaction, double-bond migration may also occur. Pines [1981] uses the Horiuti-Polanyi mechanism to explain how this is possible. Essentially, once the half-hydrogenated state is formed via transfer of the adsorbed hydrogen to the alkene either of the two carbon atoms adjacent to the remaining adsorbed carbon can adsorb on the metal and transfer its hydrogen to a metal site (reaction (iii) in (Table 2.2) is reversible). Moving back to the reactant alkene via reversible reactions (ii) and (i) thus means that the double bond may be shifted away from its original position. It must also be noted that the acid sites on the alumina support may contribute to isomerization.

2.2 Reaction kinetics

It has proven unexpectedly di¢ cult to obtain kinetic data for hydrogenation of 1-hexene over an alumina (Al2O3) supported Ni catalyst. This is especially curious when considering that Sabatier and Senderens discovered catalytic hydrogenation in the late 1800’s [Pines, 1981] and presented an article regarding their original hydrogenation and hy- 14 CHAPTER 2. REACTION KINETICS AND PROCESS CONDITIONS drogenolysis experiments over Ni as early as 18972 [Kieboom and Rantwijk, 1977]. It is generally observed that, above a certain substrate (say, ole…n) concentration, the hydrogenation rate is directly proportional to the gaseous hydrogen pressure and independent of (or thus zero order in) the ole…n concentration [Murthy, 1999]. This is called the zero-order3 zone. Campelo et al. [1982] also re-iterates that the reaction is independent of the ole…n concentration. This is not surprising since it is well-known that the reaction is usually not kinetically controlled, but mass transfer limited by the rate at which the hydrogen dissolves in the liquid phase. It is possible to explain this phenomenon with the hydrogenation reaction (or 1-hexene consumption) rate presented by [Murthy, 1999]:

VRPH2 rHydrogenation = r1 Hexene = H (2.1) sdpH 1 + H2 1 + 1 Kga 6w Kl kCR From the above equation it is clear that the reaction rate is directly proportional to the hydrogen partial pressure. Note the inverse of the substrate concentration (CR) appearing in the denominator. At very low CR the hydrogenation rate is kinetically controlled and a¤ected by both the substrate (say, ole…n) concentration and the hydrogen pressure (…rst-order region). With increasing CR the inverse CR term diminishes and a point is eventually reached where the reaction becomes mass-transfer controlled (zero- order region). Since the ole…n concentrations in the CD column will be relatively high it should be safe to assume that the reaction rate is …rst order with respect to the hydrogen partial pressure, lump the constants and, essentially, make k equivalent to the Henry’sconstant:

r1 Hexene = kPH2 (2.2)

The above may also be shown using a simple Langmuir-Henselwood approach and assuming a …rst order irreversible (at low temperatures and pressures) reaction:

kPHs C1 hexene r1 Hexene = (2.3) 1 + K1PHs + K2C1 hexene + K3Cn hexane

If C1 hexene.is very large K2C1 hexene 1+K1PHs +K3Cn hexane and eq. 2.3 reduces to eq. 2.2. From the previous discussion and from Murthy [1999], the following appears to be clear:

2 Although Sabatier and Senderens are credited as the founders of modern hydrogenation (focusing mostly on vapour hydrogenation) Debus is the …rst recorded person to have observed catalytic hydrogenation over platinum black in 1863 (http://www.thesoydailyclub.com/SFC/MSPproducts501.asp). 3 Conversely, below a certain substrate concentration the hydrogenation rate is also directly proportional to the substrate concentration: the …rst-order region. 2.3. PROCESS CONDITIONS 15

Table 2.3: Hydrogenation reaction heats for 1-hexene and 1-heptene at STP - 298K and 101 325Pa (http://webbook.nist.gov/chemistry/) Heat of reaction (H0) Reactant Product f [kJ/mol] 1-Hexene n-Hexane 125 3 1-Heptene n-Heptane 125 3

1. Hydrogenation reactions are exothermic (see Table 2.3)

2. The rate of reaction increases with increasing temperature

3. At high substrate (in this case ole…n) concentrations the hydrogenation rate is …rst-order in hydrogen; zero-order in the substrate.

4. Hydrogen dissolves only slightly in the liquid phase

2.3 Process conditions

Consider Table 2.4 that supplies the qualitative in‡uence of the reaction variables on the system as summarized from Murthy [1999] and Rylander [1994]. It is clear from the table that low surface hydrogen concentrations may lead to an increase in double bond migration and isomerization products. It is also apparent that a large hydrogen availability does not necessarily imply a high rate of reaction. For example, increasing the pressure enhances hydrogen mass transfer thus increasing the amount of hydrogen on the catalyst surface and hence the reaction rate. In contrast increasing the temperature increases the intrinsic reaction rate thereby increasing the mass transfer limitations and decreasing the surface coverage of hydrogen.

2.3.1 Possible range for process conditions

The …nal process conditions are to be determined during the experiments themselves, but it is possible to make a few general statements. Once a certain operating pressure has been chosen for a system the VLE immediately restricts the possible operating temperature range as it is necessary to remain within the phase change region of the VLE throughout the column – from the bottoms to the distillate. For example, for a 1-hexene/n-hexane system at 2 bar(a) this would be between 88 and 92C (see Figure 7.1). By increasing the operating pressure, the operating temperatures also increase. This will, however, also increase the reaction rate (Table 2.4), which would be tempting except for the repeated warning by Murthy [1999] that temperature control is the primary safety 16 CHAPTER 2. REACTION KINETICS AND PROCESS CONDITIONS • • • + + + + + Not supplied Isomerization • • • + + + + + Migration Effects on Not supplied Summary from Rylander (1994) • • • • • + + + availability 2 Not supplied H controlled Not supplied Not supplied Not supplied Not supplied considerations Disadvantages degradation issues Reduced selectivity reactor due to safety Increases reactor size Increase in reaction rate Increased material cost for Additional processing steps May reduce if selectivity May low reaction becomes kinetically eventually levels off as masseventually hydrogen availability required* availability hydrogen transfer•control diminishes and Introduces solvent make•up and Table 2.4: E¤ect of Process Variables Summary from Murthy (1999) solubility Not supplied Not supplied Not supplied Not supplied Advantages solvent evaporation rate before levelling off Increased reaction rate Increased reaction rate Moderate temperature via Dilutes reactants and thus and reaction rate increases At low rates hydrogen mass rates hydrogen At low reduces formation by•product if it has a higher hydrogenation transfer limitations are reduced At low levels increases reaction Can increase hydrogenation rate Can increase hydrogenation Increased variable Mass Activity Concentration Metal concentration Pressure Agitation Solvent Inhibitors Temperature Catalyst * This project focusesto reduce the two last mentioned products. This point may therefore be seen as an advantage in this on project. hydrogenation and thus attempts to minimize double bond migration and isomerization. Consequently, higher hydrogen availability is preferred in order 2.3. PROCESS CONDITIONS 17

issue in hydrogenation reactions. The heat removal rate must therefore be larger than the reaction heat generated. Fortunately, one of the advantages of the CD column is enhanced temperature control (cf. section 1.2). Additionally, though the heat of reaction augments the reboiler duty and is therefore advantageous, it actually increases the required condenser duty. One must also remember that the temperature through the column should always be lower than the bottoms temperature so that care must be taken that the reboiler can either supply su¢ cient energy or that the heat removal in the reactive zone is adequate to accomplish this. The packing can run dry in areas with a high heat density. It might therefore be prudent to start at a pressure of 2 bar(a). Ole…ns are hydrogenated very easily so this should not be a problem [Pines, 1981]. Now consider the feed point which can be a critical design parameter according to various authors including Taylor and Krishna [2000] and deduced from Prodebarac et al. [1997]. A qualitative discussion related to the VLE should su¢ ce as an initial decision. Should the hydrocarbon feed enter at the top of the reactive section, the 1- hexene may evaporate too quickly, decreasing its residence time in the reactive zone (or bypassing the zone completely) and reducing the column’se¢ ciency in terms of 1-hexene hydrogenation. However, it is also possible that the cooler 1-hexene feed may enhance the internal recycle of 1-hexene liquid back down the column depending on the reactive zone location along the column’s temperature and related compositional pro…le. The optimal relationship between the reactive zone location and 1-hexene feed point will have to be determined experimentally (refer to section 8.3 for further detail). As a …rst approximation, the 1-hexene feed will enter above the reactive zone. The hydrogen feed point must be located below the reactive zone as hydrogen is non-condensable and thus only rises - except for a small degree of expected backmixing. As a …rst approach it will enter at the bottom of the stripping section to avoid disrupting the VLE because of a varying hydrogen partial pressure through the section and the formation of a largely stagnant hydrogen volume below its feed point. Liquid hold-up is critical as it is required for both the liquid phase hydrogenation reaction (it is essentially the reactor volume) and also the VLE mass transfer in the non- reactive sections. Yet, in packed columns liquid hold-up can be a big problem. Consider Figure 2.2 4. In a packed column one commonly …nds that there exists a pre-loading region within which the super…cial gas velocity may be increased without changing the speci…c liquid hold-up. However, a point (termed the “loading point”) is eventually reached where liquid starts to accumulate in the column. The limiting case is the ‡ooding point where

4 Note: This type of graph is speci…c to a size and type of packing and has been adapted from one supplied by the reference for irrigated 25mm metal Bialecki rings. The goal of Figure 2.2 is not to supply numerical values (a graph for the speci…c system used in this project has not been found yet) but to illustrate the concept of ‡ooding and loading. 18 CHAPTER 2. REACTION KINETICS AND PROCESS CONDITIONS

] Increasing superficial 3 liquid velocity /m 3 [m/h]

Flooding line Specific liquid hold•up [m Loading line

Superficial gas velocity [m/s]

Figure 2.2: Speci…c liquid hold-up as a function of super…cial gas and liquid velocities (extrapolated from Seader and Henley [1998])

an increase the gas velocity causes the pressure drop to increase in…nitely. It is usually preferable to operate in the pre-loading region as it is more stable [Seader and Henley, 1998]. The latter authors supply the following correlation for calculation of the ‡ooding point: 0;7 Pflooding = 0:115FP (2.4)

Note that here Pflooding has units of inches water per foot of packed height. F p is 2 3 a packing factor speci…c to a certain type of packing. FP has the value of 70 ft /ft for Koch-Sulzer CY packing [Seader and Henley, 1998]. Substituting and converting to SI units Pflooding is calculated to be 1 840 Pa/m. Chapter 3

MODELLING THEORY

It is possible to distinguish between three main types of existing models for catalytic distillation. They are (in order of increasing complexity):

1. Residue curve maps

2. Equilibrium models (EQ)

3. Non-equilibrium models (NEQ)

Each of these models has its place in the design of a CD column. The design approach may be represented graphically as depicted in Figure 3.1. The focus of this project will lie on the NEQ model. However, in order to fully understand the reasons why NEQ is the focus and also to illustrate some interesting aspects of CD, residue curve maps and EQ models will also be considered brie‡y.

RESIDUE CURVE MAPS Initial screening and flow sheet development

EQUILIBRIUM (EQ) MODELS Preliminary design

NON•EQUILIBRIUM (NEQ) MODELS Final design and control strategies

Figure 3.1: Applications of di¤erent design approaches in CD (adapted from Taylor and Krishna [2000])

19 20 CHAPTER 3. MODELLING THEORY 3.1 Residue curve maps

Many attempts have been made over the years to mould thermodynamic models for CD operations into a set of equations that are similar to those observed in conventional non-reactive distillation. This was (and is) an attempt to make CD conform to recog- nizable, familiar models which, by now, can be manipulated quite e¤ectively. Barbosa and Doherty [1987, 1988] did pioneering work in this regard with the introduction of transformed composition variables for the representation of residue curves. Essentially, a residue curve for CD is analogous to a vapour-liquid (VLE) equilibrium diagram for non-reactive distillation. By choosing a reference component participating in the reaction it is possible to eliminate the reaction term from the mass balance equations. It is then possible to de…ne the following two transformed composition variables:

xi xk vi vk Xi = (3.1) (vk vT xk)

yi yk vi vk Yi = (3.2) (vk vT yk) where xi and yi are respectively the liquid and vapour mole fraction of component i, k indicates the reference component, v refers to the subscripted component’sstoichiometric c coe¢ cient and vT = vi. i=1 Using these variablesX the dynamics of a simple RD process may then be given as follows: dXi = Xi Yi (3.3) d

Integration of this for a ternary reaction mixture may yield the curve in Figure 3.2.

The dashed lines represent constant Xi. The axes are in normal liquid mole fractions. Assuming that a liquid with a certain composition enters the CD column and that instantaneous chemical equilibrium is reached the liquid composition will move immediately along a line of constant Xi (in the directions of increasing time indicated by the arrows) to the solid line representing the residue curve. In this case, the curve indicates that (for these speci…c conditions) a point in time will eventually be reached where the liquid phase consists of pure B. Compare this to the curve in Figure 3.3. Here the pure components A and B are both unstable. The arrows of increasing time eventually reach a point where the two directions intersect. This is a reactive azeotropic point representing a distillation boundary. Regardless the feed composition, the residual ‡uid’s composition will strive towards this point. Unlike in non-reactive distillation, reactive azeotropes can exist even in ideal mixtures. It is possible to show 3.1. RESIDUE CURVE MAPS 21

Figure 3.2: Residue curve - reactive ternary ideal system [Barbosa and Doherty, 1988]

Figure 3.3: Residue curve showing the occurrence of a reactive azeotrope - reactive ternary ideal system [Barbosa and Doherty, 1988] 22 CHAPTER 3. MODELLING THEORY

Vj Vapour side Lj•1 draw x yi,j i,j•1 V HL H j j•1 T Tj j•1

EQUILIBRIUM STAGE j Qj

zF,,j x Vj+1 i,j L HF H yi,j+1 j

TF,j HV T j+1 j Liquid side draw Tj+1

Figure 3.4: Equilibrium stage model [Taylor and Krishna, 1993]

that the reactive azeotrope corresponds to the following relation:

Xi = Yi (3.4)

This is strikingly similar to the condition for non-reactive azeotropes (xi = yi). As mentioned, this type of correlation between the non-reactive and RD models is one of the aims of the residue curve map approach. An interesting advantage of RD is that non-reactive azeotropes can disappear because of the chemical reaction. However, the striking similarities between the models using transformed compositions variables for CD and the conventional ones used for traditional non-reactive distillation is misleading. They are inherently di¤erent systems. Various authors including Taylor and Krishna [2000] emphasize that conventional wisdom is not always applicable to CD.

3.2 Equilibrium (EQ) models

Material and Energy balances together with equilibrium relations are the underlying building blocks of the EQ model [Taylor and Krishna, 1993], which may be represented as shown in Figure 3.4. The use of EQ models is a tried-and-tested technique used extensively in the design of non-reactive distillation columns. As its designation suggests, the crucial assumption 3.3. NON-EQUILIBRIUM (NEQ) MODELS 23

in EQ models is that the vapour and liquid phases leaving any stage in the column are in thermal equilibrium. This is clearly not always the case. For this reason, EQ models are usually co-used with an e¢ ciency estimation model to compensate for non-equilibrium conditions. The advantage of the EQ models is that, for modelling purposes, relatively little information regarding the inside of the theoretical stage is required and complex modelling of multicomponent di¤usion and interphase mass transfer is circumvented. To understand this advantage, consider Figure 3.4. In the EQ model the balanced equations are written around the stage. The assumption of vapour-liquid equilibrium is pivotal to EQ models because it is the only way to relate the compositions and energies of the exiting and entering vapour and liquid streams. Subsequently, very little (if any) information is required about exactly what happens inside the stage thus drastically reducing the complexity of the model. However, its strengths can also be its greatest weaknesses. There are mainly two disadvantages related to the EQ model. Firstly, the VLE data of the vapour-liquid streams entering and exiting a stage is required. Secondly, the accuracy of the EQ model is not only dependant on the validity of the vapour-liquid equilibrium assumption, but also on the accuracy of the e¢ ciency model. This dependency on the e¢ ciency model is emphasized by various authors including H. Sawistowski (1980) as quoted by Taylor and Krishna [1993]: “. . . the concept of plate e¢ ciency of individual components in a multicomponent mixture is of doubtful validity and is retained only because of its simplicity”. Taylor and Krishna [2000] also states that, to the best of their knowledge, “there are no fundamentally sound methods for estimating either e¢ ciencies or HETP in RD operations”. They continue by pointing out that the chemical reaction itself has an e¤ect on the component e¢ ciencies and that a complete understanding of RD is only possible if the interaction between mass transfer and chemical reaction is properly understood. This is where the NEQ model comes in.

3.3 Non-equilibrium (NEQ) models

In addition to mass and energy balances, and equilibrium relations, the NEQ model also incorporates mass and energy transfer models [Taylor and Krishna, 1993]. While it appears that there is little di¤erence between the EQ and NEQ models, there is a fundamental di¤erence in the way that the material and energy balances are calculated. This is illustrated by Figure 3.5. In the EQ model the vapour and liquid phases entering and leaving a stage are in equilibrium. As explained in the previous section it is unnecessary to model the complex multicomponent mass and energy transfer occurring within the stage. However, in the NEQ model this assumption of vapour-liquid equilibrium is not made. 24 CHAPTER 3. MODELLING THEORY

Vj Vapour side Lj•1 draw x yi,j i,j•1 V HL H j j•1 T Tj j•1

V L Q j STAGE j Q j

Vapour Liquid

NVL V L f j,j f j,j EVL V L H j H j x Vj+1 i,j HL yi,j+1 j HV T j+1 j Liquid side draw Tj+1

Figure 3.5: Non-equilibrium stage model for non-reactive distillation [Taylor and Krishna, 1993]

The balance equations are e¤ectively set up for each phase in the stage, instead of for the stage itself. It is now also critical to know whether a homogeneous or heterogeneous reaction is employed as this determines the equations to be used for calculating the inter-phase molar ‡ux.

3.3.1 MESH equations for the non-reactive distillation section

MESH equations are a set of equations comprising material (M) balances, equilibrium (E) relationships, summation (S) equations and energy (H) balances employed to model a section (or stage) within a separation system. The model developed here comes from Taylor and Krishna [1993]. The following assumptions are made here:

1. Figure 3.5 is an accurate description of mass transfer within a stage.

2. There is no accumulation of mass or energy within the system boundaries -i.e. the “accumulation”terms in the mole and energy balances are zero. 3.3. NON-EQUILIBRIUM (NEQ) MODELS 25

3. No reactions take place in the vapour or liquid phases and therefore the nett formation of any component is zero.

4. The work done on the system is negligible.

5. Vapour-liquid equilibrium exists at the vapour-liquid interface.

Firstly, it is necessary to do the material (M) balances for the stage j. The vapour phase mole balance for component i may be written as follows:

Accumulation = In Out + Nett formed Accumulation = Out - In - Nett formed V V VL V M = 1 + r yi;jVj + N yi;j+1Vj+1 + f [0] ij j ij ij V V VL 0 = 1 + rj yi;jVj yi;j+1Vj+1 fij + Nij (3.5) To …nd the total material mole balance it is necessary to sum the above equation for the component mole balance:

c c V V VL V Mij = 1 + rj yi;jVj + Nij yi;j+1Vj+1 + fij [0] i = 1 i = 1 X X V V V V Mtj = 1 + rj Vj Vj 1 Fj + Ntj = 0 (3.6)

c c Note that yi = 1 and fi = F . i = 1 i = 1 Similarly, the componentP and overallP material mole balances for the liquid phase may be calculated as follows:

L L L L Mij = 1 + rj xi;jLj xi;j 1Lj 1 fij Nij = 0 (3.7)

L L L L Mtj = 1 + rj Lj Lj 1 Fj Ntj = 0 (3.8) Secondly, it is assumed that vapour-liquid phase equilibrium (E) exists at the phase interface: I I (Eq) = y Ki;jx = 0 (3.9) i;j i;j i;j Thirdly, at the interface the di¤erence between one and the sum (S) of the mole fractions of the various components must be zero:

c VI I Sj = yij 1 = 0 (3.10) i = 1 X 26 CHAPTER 3. MODELLING THEORY

c LI I Sj = xij 1 = 0 (3.11) i = 1 X An overall energy balance (H ) is now set up for each stage. This looks as follows for the vapour and liquid phases respectively:

Accumulation = In Out + Work done on system + Energy put into system - Accumulation = Out - In - Work done on system - Energy put into system

V V V V V V (F ) V 0 = 1 + rj VjHj + Ej Vj 1Hj 1 + Fj Hj [0] Qj V V V V h V V (F ) V i V Ej = 1 + rj VjHj Vj 1Hj 1 Fj Hj + Ej + Qj (3.12) 6

L L L L L L L L Ej = 1 + rj LjHj Lj 1Hj 1 Fj Hj Ej + Qj = 0 (3.13) 6 The MESH equations represent a non-equilibrium stage model for the distillation column. However, the model is not yet complete. It is still necessary to …nd a way to calculate the molar ‡uxes (N) in the column and then a methodology is required to solve the resulting set of independent equations. The former will be discussed in the following section, while a note with regards to the latter is given in section 4.4.

3.3.2 MESH equations for the reactive section

In the reactive section of the CD column there is the added complication that there is not only interphase mass transfer between a liquid and solid (catalyst) phase which must be taken into account but also di¤usion within the catalyst particle itself. In this case the NEQ model is depicted in Figure 3.6. Only the liquid material and energy balances in the MESH equations have to be changed in this case to take the factors shown in the …gure into account. The liquid component balance now has an additional term, which is also re‡ected in the overall material balance:

L L L L S Mij = 1 + rj xi;jLj xi;j 1Lj 1 fij Nij + Nij = 0

L L L L S Mtj = 1 + rj Lj Lj 1 Fj Ntj + Ntj = 0 Lastly, the liquid energy balance must also be changed:

L L L L L L L S L Ej = 1 + rj LjHj Lj 1Hj 1 Fj Hj Ej + Ej + Qj = 0 6 The NEQ CD model is not yet complete as it is still necessary to …nd a way to calculate the molar ‡uxes (N) in the column and to solve the resulting set of independent equations. Chapter 4 addresses the development of the ‡ux equations and the solution 3.4. NON-CONDENSABLE GASES 27

Vj L Vapour side f j,j Lj•1 draw L L x Q j H j yi,j i,j•1 V HL H j j•1 T Tj j•1

V Q j STAGE j

Vapour Liquid Catalyst

NVL NLS V f j,j EVL ELS V H j x Vj+1 i,j HL yi,j+1 j HV T j+1 j Liquid side draw Tj+1

Figure 3.6: Non-equilibrium model with a solid catalyst phase methodology required for the models.

3.4 Non-condensable gases

Since super-critical gases have no saturated vapour pressure the presence of hydrogen in the system introduces additional considerations into estimation of the VLE. Consider the Gamma/Phi (modi…ed Raoult’s law) formulation that is normally used in VLE calculations:

P ^ sat ^sat Vi yiiP = xi iPi i dP P sat RT Z i V l(P P sat) = x P sat^sat exp[ i i ] (3.14) i i i i RT

The above method can clearly not be used where a saturation pressure does not exist, as in the case of non-condensable (supercritical) gases. In such cases Carroll [1991] suggests the use of the ensemble Henry’slaw:

P ^ H Vi yiiP = xi iHij dP (3.15) P sat RT Z j 28 CHAPTER 3. MODELLING THEORY where i indicates the solute (say, hydrogen) and j the solvent (say a 1-hexene/n-hexane mixture). The ensemble Henry’slaw is applicable over the entire range of compositions, unlike H the simple Henry’s law (P = Hij xi) and can be coupled with reaction equilibrium models if necessary. Unlike the modi…ed Raoult’slaw, which uses the pure component as the standard state, the ensemble Henry’slaw uses in…nite dilution of the solute in the solvent as the standard state. Consequently, the two laws also have di¤erent activity coe¢ cients - as indicated by the starred superscript [Carroll, 1999]. Accurate Henry’s constants are not easily found in literature or correlated and the best source for Henry’s constants remain experimental data. One problem is that Henry’s constants are dependant on two components and thus inherently di¤erent for each mixture. Vapour pressures for non-condensables may be extrapolated for use in the modi…ed Raoult’slaw, but this must be done with care [Carroll, 1999]. Lastly, as will be seen later (see, for example, the condenser design; chapter 9.6.1), mathematical descriptions of mass and energy transfer may have to compensate for the possibly signi…cant deleterious e¤ect of a supercritical gas. Inerts are thus a misnomer for non-condensables in this system as they can have a signi…cant impact on system performance. Chapter 4

MASS TRANSFER EQUATIONS

As mentioned in the previous sections mass transfer limitations play an integral part in the CD hydrogenation system. In this chapter the in‡uence of multicomponent mass transfer on the system will be considered and ways to model it will be investigated. There are two main methods to model mass transfer that will be considered here, namely Fick’sLaw and the Stefan-Maxwell approach. It will be shown that the Stefan- Maxwell approach is the preferred choice in this case. Multicomponent mass transfer is a well studied …eld and the reader is referred to some of the references cited at the end of this review including Seader and Henley [1998] and Taylor and Krishna [1993] for more detailed information on this subject. Only certain important aspects will be highlighted here.

4.1 Phase hydrodynamics

The mass transfer approaches just mentioned (and discussed in the following sections) must be used in conjunction with models describing the phase hydrodynamics. These include the …lm theory, two-…lm theory, penetration, …lm penetration and turbulent boundary layer models. For the purposes of this review only the …lm and two-…lm theories will be discussed and then also for illustrative purposes of the application of Fick’s law. It must be emphasized that these theories are simply ways to model the hydrodynamics of the phases and the concepts therefore remain equally applicable to both Fick’slaw and the Stefan-Maxwell approach. Higler et al. [2000] used the NEQ model and the Stefan-Maxwell approach with the unit cell depicted in Figure 4.1. From this …gure it is clear that the hydrodynamics between the vapour and liquid are modelled via the two-…lm theory while the …lm theory is used between the liquid and solid catalyst.

29 30 CHAPTER 4. MASS TRANSFER EQUATIONS

Vj L Vapour side f j,j Lj•1 draw L L x Q j H j yi,j i,j•1 V HL H j j•1 T Tj j•1

V Q j STAGE j Vapour Liquid Catalyst

NLS

ELS

V NVL f j,j V EVL H j x Vj+1 i,j HL yi,j+1 j HV T j+1 j Liquid side draw Tj+1

Figure 4.1: Concentration pro…le in a unit cell (modi…ed from Higler et al. [2000])

4.2 Fick’sLaw

Fick’s …rst law (1855) states that, for a binary mixture of components A and B, the molar ‡ux of, say, component A is directly proportional to the concentration gradient of A in the mixture : dCA JA = DAB (4.1) z dz

The proportionality constant D is called the di¤usivity. Note that JAz is the molar ‡ux relative to the bulk liquid ‡ow i.e. it is the molar ‡ux due only to the di¤usion and not due to the bulk liquid ‡ux. If the mixture is isotropic, the molar ‡ux is independent of direction and the z subscript may be dropped

Fick’s…rst law may also be seen as relating the molar ‡ux of a component to a driving force which is simply the di¤erence in concentration of the relevant component between two points in the mixture. In other words: the larger the di¤erence in concentration of a component, say A, between two …xed points in a mixture (i.e. the distance between the points is constant) the larger the driving force and the larger the molar ‡ux. 4.2. FICK’SLAW 31

Table 4.1: Inconsistencies between Fick’s…rst law in the form of equation 4.3 and experimental data (summarized from Krishna and Wesselingh [1997]) Type of system Inconsistency Osmotic di¤usion: A component di¤uses despite the absence of a driving force Di¤usion in an ideal Reverse di¤usion: A component di¤uses in a direction ternary gas mixture opposite to that dictated by the driving force Di¤usion barrier: A component’s di¤usional ‡ux is zero despite a very large driving force Di¤usion in a mixed ion Fick di¤usivity fails to describe transport of individual system ionic species Ultra…ltration of an Fick’sconstitutive relation fails to accurately predict this aqueous solution of system as it neglects the mutual interaction between polyethylene, glycol and the dextran and PEG which is required for accurately dextran modelling transport Transport of n-butane Selectivity reversal that may be observed when chang- and hydrogen across ing from a single component to binary mixture cannot be zeolite membrane modelled simply by Fick’s…rst law

Fick’slaw can also be re-written in the following form:

dxA JA = CDAB (4.2) dz

where xA is simply the molar fraction of A in the mixture. If it is further assumed that A is a very dilute species (i.e. A sees only the other component in the mixture) it is possible to further simplify this equation to Fick’s constitutive relation:

dxA JA = CDA (4.3) dz

The above equation therefore includes the assumptions that the mixture is a binary mixture in which A is dilute and that there are no external forces being applied to the system such as, for example, electrostatic or centrifugal forces [Krishna and Wesselingh, 1997]. Krishna and Wesselingh [1997] further refer to a classic paper by Toor (1957) in which he highlights several curious phenomena (cf. Table 4.1) between experimentally observed data and Fick’s…rst law. These phenomena are the result of choosing a concentration gradient as the driving force for di¤usion, which requires that the di¤usion coe¢ cient, rather than the driving force itself, must compensate for thermodynamic e¤ects. This makes prediction of the Fickian di¤usivity more di¢ cult and can, as shown, lead to initially counter-intuitive 32 CHAPTER 4. MASS TRANSFER EQUATIONS

Interface

Phase II Phase I Stagnant layer (adjoining phase)

CAI

CAb

z = 0 z = dL

Figure 4.2: Film theory concentration pro…le for two phases (phase I and an adjoining phase)

di¤usional e¤ects. In comparison, the Stefan-Maxwell approach to mass transfer, which will be discussed in section 4.3, uses a fundamentally more sound thermodymanic driving force. Nonetheless, Fick’s …rst law is still the basis of numerous techniques that are used in the design of mass transfer equipment. It is also a convenient way to illustrate the concepts of the …lm and two-…lm theories discussed in the following two sections. Note, however, that the …lm theories are not restricted to use in Fick’slaw, but are used in conjunction with Fick’slaw to model interphase mass transfer. These concepts are therefore equally applicable to the Stefan-Maxwell approach.

4.2.1 Film theory

The …lm theory was suggested by Nernst in 1904 and is depicted in Figure 4.2. The …lm theory essentially assumes that all the resistance to mass transfer lies in a single stagnant liquid …lm between the gas and liquid phases. Thus, integrating equation

4.3 between z = 0 and z = L:

CAI CAb J = D (4.4) A AB

Film theory would suggest that the mass transfer rate is directly proportional to the di¤usivity –a fact which is contradicted by experimental data. Using the Chilton- Colburn analogy it is possible to rewrite equation 4.4 so that the following equation 4.2. FICK’SLAW 33

Interface Stagnant Stagnant Bulk vapour Bulk liquid vapour layer liquid layer

Cvb,A

CvI,A

ClI,A

Clb,A

Figure 4.3: Two-…lm theory concentration pro…le holds: 2 DAB 3 kc = D (4.5) / AB

This has better agreement with the experimental data, however the exponent of DAB is seen to vary between 0.5 and 0.75. Despite this fact the …lm theory is still widely used in the design of mass transfer equipment, probably due to its simplicity. Although, it may prove to be very accurate for certain speci…c systems it is not generally applicable and is therefore deemed to have insu¢ cient accuracy for the purposes of this project.

4.2.2 Two-…lm theory

The two-…lm theory is simply an extension of the …lm theory and has found extensive application in modelling of steady-state gas-liquid and liquid-liquid mass transfer. Moreover, it is widely used for structured packing and is therefore very relevant to the CD column which uses Sulzer CY gauze type structured packing in the stripping and recti…cation section. Figure 4.3 illustrates the two-…lm theory. Consider component A which has a larger concentration in the vapour (or gas) phase than in the liquid phase. Its di¤usion from the bulk vapour to the bulk liquid is modelled in 5 steps:

1. The two-…lm theory assumes that the bulk concentration of A (Cvb;A) in the vapour phase is uniform. 34 CHAPTER 4. MASS TRANSFER EQUATIONS

2. Following the driving force A must di¤use through a stagnant (i.e. no bulk ‡ow) vapour …lm representing the resistance to mass transfer in the vapour phase.

3. There exists an interface (I) between the stagnant vapour …lm and a stagnant liquid …lm. The interface does not represent any additional resistance to mass transfer and the concentrations of the two ‡uids at the interface are in equilibrium. In most applications it is furthermore assumed that steady state conditions exist, i.e. there is no build up of A at the interface. The concentration of A on the vapour

…lm side of the interface is CvI;A and on the liquid …lm side it is ClI;A.

4. A continues to follow the driving force and di¤uses through the stagnant layer that represents the resistance to mass transfer in the liquid until it reaches the bulk liquid.

5. The concentration of A in the bulk liquid is assumed to be uniform and is denoted

by Clb;A.

As seen in Figure 4.3 the two-…lm theory provides a closer approximation of the more realistic concentration pro…le observed when separation of two contacting ‡uids is executed. Laminar and turbulent ‡ow of steady-state gas-liquid or liquid-liquid mass transfer may be modelled. The steady-state assumption holds for small mass transfer rates. In random or structured packing the two-…lm theory is used to write equations expressed in terms of overall mass transfer coe¢ cients. The goal is to generate relationships that can be used to calculate the HETP (height equivalent of a theoretical plate). The HETP essentially translates the convenient and traditional methods used to determine the number of trays required in a distillation column into a height of random or structured packing that will exhibit similar separation.

4.3 The Stefan-Maxwell approach to mass transfer

The Stefan-Maxwell approach is a popular technique to model mass transfer in multicomponent systems. Taylor and Krishna [2000] call it “the most fundamentally sound way to model mass transfer in multicomponent systems”in their review of reactive and catalytic distillation. This statement is justi…able as the driving force in the Stefan- Maxwell approach is the di¤erence in chemical potential () between two points. In other words, the very basis for the prediction of di¤usional ‡ux in the Stefan-Maxwell approach is a fundamentally sound thermodynamic driving force, whereas the Fickian use of concentration gradients, though intuitively logical and generally observable in practice, may yield initially unexpected phenomena as shown in section 4.2. 4.3. THE STEFAN-MAXWELL APPROACH TO MASS TRANSFER 35

The Stefan-Maxwell approach have the advantages that various ‡ow mechanisms are put under the same framework, that it is comprehensive for large pore spaces and more consistent with experimental data than Fick’slaw (Table 4.1) and that its constitutive ‡ux equations are applicable under non-isobaric and non-isothermal conditions [Do, 1998]. According to Do [1998] the main disadvantage of the method is that it is not as mature in terms of surface di¤usion as it is in the modelling of the ‡ow mechanism in the larger pores of the particle. It is, however, still possible to use the Stefan-Maxwell approach to model surface di¤usion. In any event, surface di¤usion only starts to play a signi…cant role in micropores (as observed in zeolites) which is not of consequence in the Ni catalyst used. With reference to Figure 3.6 (section 3.3) it is possible to discern that mass transfer models for interphase mass transfer from the vapour to the liquid phase as well as mass transfer within the porous catalyst structure are required. The above issues will now be addressed separately.

4.3.1 Interphase mass transfer

It must be reiterated here that there are two distinct types of zones in the CD column, namely the reactive zone and the non-reactive zones that comprise the recti…cation and stripping sections. By comparing Figure 3.5 and Figure 3.6 it is clear that the model for the reactive section is simply an extension of the model for the non-reactive section as it just entails addition of the solid catalyst phase in the reactive section and, consequently, modelling of interphase mass transfer between the liquid and solid phases. This discussion will therefore focus on the interphase mass transfer model for the reactive section. The equivalent model for the purely reactive sections is exactly the same except that interphase mass transfer between the liquid and solid (catalyst) phases and di¤usion within the porous catalyst structure are not taken into account Consider Figure 4.1 again. It would appear from Baur et al. [2000] that interphase mass transfer may be represented by equations 4.6 to 4.8. From vapour to liquid:

VL c VL VL y @ yi;jN yk;jN i;j i;j = k;j i;j (4.6) RT @ CVL VLa k = 1 t;j i;k j X From liquid to vapour:

LV c LV LV x @ xi;jN xk;jN i;j i;j = k;j i;j (4.7) RT @ CLV LV a k = 1 t;j i;k j X 36 CHAPTER 4. MASS TRANSFER EQUATIONS

Between liquid and solid:

LS c LS LS x @ xi;jN xk;jN i;j i;j = k;j i;j (4.8) RT @ CLS LSa k = 1 t;j i;k j X Note from Figure 4.1 that there are two …lms between the vapour and liquid phases, hence the two equations (4.6) and (4.7), while there is only one …lm between the liquid and solid, hence only equation (4.8).

4.3.2 Mass transfer within pores: the dusty ‡uid model

It is possible to discern mainly three di¤usion mechanisms within porous structures such as catalyst pellets [Krishna and Wesselingh, 1997; Fogler, 1999]:

Bulk di¤usion In bulk di¤usion the pores of the catalyst are so large that the number of collisions between the molecules and the pore wall are small compared to the collisions between di¤erent molecules. More descriptive synonyms include “free space”and “free molecular”di¤usion.

Knudsen di¤usion When the mean free path of a molecule becomes greater than the diameter of the catalyst pore, collisions between the molecules and the pore wall start to dominate and molecules of di¤erent species do not a¤ect each other anymore.

Surface di¤usion An adsorbed species moves along the surface of the solid (say, a catalyst). This type of di¤usion predominates in micropores or when a species adsorbs very strongly to the solid surface.

IUPAC de…nes the following three di¤erent sizes of pores:

1. Micropores: dpore < 2 nm

2. Mesopores: 2 nm < dpore < 50 nm

3. Macropores: dpore > 50 nm

From the above de…nitions it is clear that micropores are very small and in fact they are typically found in structures such as zeolite catalysts. Since the catalyst used in this project (section 7.3.1) does not have micropores, but rather mesopores and macropores it will therefore be assumed that surface di¤usion plays a negligible role in the system. According to Krishna and Wesselingh [1997] it is generally agreed that the dusty gas model is the “most convenient way to model combined bulk and Knudsen di¤usion”. The model approximates the pore walls, through which a species is di¤using, as consisting of large, uniformly distributed molecules or "dust". As a parallel to the dusty gas 4.3. THE STEFAN-MAXWELL APPROACH TO MASS TRANSFER 37

model Krishna and Wesselingh [1997] use the Stefan-Maxwell approach with the following assumptions to derive a general description of di¤usion of non-ideal ‡uid mixtures (“dusty ‡uid model”) inside a porous structure:

1. The dust concentration (CM ) is spatially uniform.

2. The dust is motionless and thus its molar ‡ux is zero (NN+1 = 0).

3. The molar mass of the dust particles tends to in…nity (Mn+1 ). ! 1 4. The solution and the solid matrix are electrically neutral.

5. Electrostatic potential is the only external body force acting on the system.

The subsequent equation then looks as follows:

n xi xi xi xjNi xiNj Ni T;P i Vi P zi = + (4.9) RT r RT r RT Fr C Ð C Ðe j=1 t ij t iM Xj=i 6 The dusty gas model was originally formulated by Mason and Malinauskas [1983]. It was assumed that viscous ‡ow was non-separative. Viscous ‡ow in a porous matrix occurs because of ‡uid phase pressure gradients [Krishna and Wesselingh, 1997]. To compensate for its separative nature the “viscous selectivity factor” was introduced. Ac- cording to Krishna and Wesselingh [1997] this leads to the following Mason formulation for intraparticle di¤usion:

n Ci Ci B0 xjNi xiNj Ni V P P C z F = + (4.10) RT T;P i RT i Ðe i i RT Ðe Ðe r r iM r r j=1 ij iM X

However, the above equation does not take into account that there is a heterogeneous chemical reaction taking place simultaneously with the molar ‡ux. Krishna and Wesselingh [1997] presents the following formula to account for reaction stoichiometry:

i n 1 N1 i=1 Ð e P = iM (4.11) ; x r 1 n i i 1 + ÐPviscous e RT i=1 Ð iM P

Ðviscous is de…ned as being directly proportional to the product of the total molar

concentration (CT ), the permeability of the structure (B0), the ideal gas constant (R)

and temperature (T ), but inversely proportional to the viscous ‡uid viscosity (visc):

CtB0RT Ðviscous (4.12) visc 38 CHAPTER 4. MASS TRANSFER EQUATIONS

By using equations 4.10 to 4.12 it is possible to describe the bulk and Knudsen di¤usion within the catalyst particle with simultaneous heterogeneous reactions taking place.

4.4 Modelling tools

In the previous sections the emphasis was on the information and models required to describe the CD system. In this section the focus must now shift towards the tools available to solve it. However, in-depth treatment of the techniques and tools involved to solve the resulting sets of independent equations fall outside the scope of this literature review and only some general comments will be made here. From chapters 3 and 4 it is clear that a model for CD consists of a relatively large interwoven set of equations that must be solved simultaneously. The computer aided distillation simulation packages that are currently readily available to the researcher are ProII, Aspen and Chemsep. These packages do have the functionality to handle homogeneous reactions with simultaneous separation and can thus also model a heterogeneous reaction system if a pseudo-homogeneous approach is assumed. However, these programmes are not ideally suited for CD as their main design mo- tivation is distillation simulation. One of main driving forces for the creation of a tool to describe CD is to contribute to an accurate, e¤ective model of such systems. In this regard, it should be possible to use, for example, FORTRAN1 or Mathcad to generate simpli…ed models, but given the already limited time available this is impractical and far less accurate than the available packages described above.

1 FORTRAN can be described as a number crunching programming language and also has an extensive set of libraries available. Chapter 5

LITERATURE REVIEW: CONCLUDING REMARKS

The advantages associated with catalytic distillation (CD), and mentioned in section 1.2, act as an incentive to investigate CD in more depth. The question that must be answered is whether the CD-type conditions have an advantageous e¤ect on reaction e¢ ciency and conversion even for reactions that are not equilibrium limited. To investigate this, a system that satis…es the de…nition of CD, namely that simultaneous heterogeneous reaction and separation must occur, has been chosen. As a …rst approach, hydrogenation of an -ole…n feed, consisting of 1-hexene, to the product alkane, hexane, will be investigated. In terms of modelling, a non-equilibrium (NEQ) model is preferred above the rival residue curve and equilibrium (EQ) model approaches as it a¤ords a more rigorous mathematical description of CD systems. To describe mass and heat transfer in the system the fundamental Stefan-Maxwell approach is recommended by Taylor and Krishna [2000]. This approach is fundamentally more sound than Fick’sLaw and is also used in the formulation of the dusty ‡uid model for mass transfer within catalyst pores. Using the foundation laid in this part, the next part will take the experimental apparatus from the design to the commissioning stage.

39 40 CHAPTER 5. LITERATURE REVIEW: CONCLUDING REMARKS Part II

PROCESS DESIGN

Chapter 6

PROCESS DESIGN METHODOLOGY

A signi…cant amount of time was spent on designing the CD system, obtaining the required quotes, procuring the relevant items, constructing the system and then commissioning it. These aspects of the project will now be discussed here. An attempt was made to follow the logical and largely chronological stages of the design process. This part can thus be divided into three main sub-parts:

1. The Mass and Energy Balances, Mechanical Design, and Process Con- trol chapters culminating in the Pipe and Instrumentation Diagram (P&ID) and control philosophy (section 10.5).

2. The Computer Control System chapter resulting in Figure 11.1.

3. The Construction and Operation chapter depicting a spatially consistent representation of the CD apparatus in Figure 12.1.

It may be prudent to give the above mentioned …gures a cursory glance after this introduction so as to get an overall feel of the system before reading its natural evolution from the basic block diagram (Figure 6.1) to the …nished product (…gures mentioned above). The common design criteria followed throughout this design may be summarized as follows:

Safety Safety was and must always be the most important consideration in any design.

Keep it straight and simple (KISS) The simple, viable, economical solution was always preferred and used where possible. Simplicity often equates to a more economical, safer system. Each unnecessary layer of complexity (in the mechanical

43 44 CHAPTER 6. PROCESS DESIGN METHODOLOGY

Partial Condenser Off•gas line

Reflux Drum

Hydrocarbon Feed Distillate product tank

CD column

Hydrogen Feed

Reboiler Bottoms product tank

Figure 6.1: Block diagram of the CD system

design, electronic system, computer control system, etc.) increases the opportunities for errors and failures to occur and thus decreases the e¢ ciency, accuracy and safety of the system.

Minimize heat loss Minimization of the heat losses in the column is paramount for the e¢ cient operation of the column and to draw accurate conclusions from the generated data. Structurally, this requires a minimization of the atmospheric contact area and in this regard it is best to use ‡anges as little as possible as they act as …ns for heat transfer.

Reduce ‡ow pulsation Pulsation is highly undesirable in a continuous system where a steady state must be reached. Anything that could cause or encourage pulsation was avoided if possible. If it had to be used, care was always taken to ensure a high enough pulsation frequency so as to have an overall smoothing e¤ect. Chapter 7

EXISTING SYSTEM DESCRIPTION

The existing batch CD column was chosen, designed, built and modi…ed by two previous researchers at the University of Cape Town (UCT): Tendekai Chaza and Geo¤ Mphahlele. This section critically considers the proposed continuous system vs. the existing batch system.

7.1 Reaction investigated: Hydrogenation

The hydrogenation of 1-hexene was chosen as the reactive system for a number of reasons. Firstly, it came as a natural extension of the work done by Mphahlele [2003] who also employed hydrogenation of 1-hexene to hexane in the reactive zone. However, he ran the CD column as a batch system (section 7.2) and not as a continuous system. Secondly, the system conforms to the requirements for a CD system (section 1.2). From Figure 7.1 it is clear that separation of 1-hexene and hexane via distillation is very di¢ cult (compare it to the 1-hexene/1-heptene VLE, which shows a much improved range for separation) because of the relatively narrow phase change region, but it is by no means impossible given a suitable packing in the non-reactive zones (see section 8). Note that the hydrogenation of 1-hexene is in no way thermodynamically limited. This means that one of the main advantages in doing CD is lost, namely that the reaction may be pushed beyond its thermodynamic limit – a limit that does not exist in this case (section 1.2). However, this simpli…es the system somewhat, does not compromise the objectives, hypothesis or key questions (referring to section 1.4) and facilitates the investigation of mass transfer integration.

45 46 CHAPTER 7. EXISTING SYSTEM DESCRIPTION

DP 1•Hexene/Hexane BP 1•Hexene/Hexane BP 1•Hexene/1•Heptene DP 1•Hexene/1•Heptene

120 120 118

115 115

110 110

105 105

100 100

95 95 Temperature, T [°C] T Temperature, 92

90 90 88

85 85

80 80 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Mole fraction 1•hexene [None]

Figure 7.1: Comparison between the VLE’sof a 1-hexene/hexane system and a 1-hexene/1-heptene system (P = 2 bar(a))

7.2 Experimental apparatus

The experimental system for the batch operation, as adapted from the schematic given by Mphahlele [2003] in his preliminary draft report, is presented at the end of this chapter. Note that, although this drawing is based on a schematic supplied by Mphahlele [2003], it has been amended by adding more detail from the actual system before com- mencement of alterations were implemented. Table 7.1 summarizes the equipment speci…cations given for the batch set-up. More detailed equipment speci…cations are supplied on the schematic. Batch systems can be used very e¤ectively in determining experimental mass transfer coe¢ cients and have less variables to control and monitor than continuous systems. The study of a continuous system is also signi…cantly more expensive due to the large modi…cations required to the existing system, cost of a process control system and the amount of 1-hexene feed required. The major characteristic of any batch system is that it’s behaviour it time-dependant and a skilled statistician can thus extract a relatively large amount of data from this transient response using data mining techniques. Unsteady state models capable of simulating time-dependant behaviour are also used in industry during systems’start-up and shutdown. However, unsteady state behaviour is more di¢ cult to model when compared to the 7.3. PREVIOUS COLUMN INTERNALS 47

Table 7.1: Equipment Speci…cations Unit Speci…cation Value/Description Units MOC Stainless steel type 316 [none] Column Diameter 50.0 [mm] Height 1700.0 [mm] Volume 0.5 [dm3] Reboiler Settings Voltac variable transformer [none] Volume 1.0 [dm3] Condenser Inlet pressure gauge (WIKA) 0 - 30 [bar(g)] Temperature controller RSA A Gefran 500 [none] Length 600.0 [mm] Tube to condenser Internal diameter 50.0 [mm] continuous (steady state) mode of operation and batch systems can be unpredictable and di¢ cult to control notwithstanding fewer process control variables. Most applications of industrial interest aim to produce a large, steady state quantity of products and limit transient responses to start-up, shutdown and set-point changes. Investigation of a continuous system would thus follow industry trends. Operating costs for the continuous system can also be minimized by carefully planning small set-point changes that will allow steady-state to be reached more quickly, thus reducing the amount of ole…ns fed to the column. Experimentation on such a system will also allow ‡exibility of design as it is relatively simple to operate a continuous system in batch mode, while the opposite can be di¢ cult or almost impossible without signi…cant modi…cations. Because a continuous system is more ‡exible and supplies industrially relevant data it was decided to convert the existing batch system to a steady state system regardless the higher cost and time involved.

7.3 Previous column internals

The previous column internals’ speci…cations are given and discussed in this section. Changes to these internals fall outside the scope of a literature review and will be considered in part II.

7.3.1 Catalyst speci…cations and reactive packing

The catalyst information is summarized in Table 7.2. Although not stated expressly by the previous researcher, it is assumed that Ni was chosen as it is cheaper than the other classically used hydrogenation catalysts (Pd, Rh, Ru, Os, Ir, Pt). This is despite the fact that it allows, relative to most of the other catalysts, more double bond migration [Rylander, 1994]. Since the main project focus is not catalyst synthesis and in order to 48 CHAPTER 7. EXISTING SYSTEM DESCRIPTION more closely approximate reality a Ni catalyst1 will again be used.

Table 7.2: Information of catalyst used by Mphahlele [2003] Subject Speci…cation Value [Units] Kata-Leuna, CRI, Manufacturer [none] Manufacturer Houston, Texas, USA Catalyst type KL6560-TL2.5 [none] Nickel content 18 [weight%] Composition Alumina content 82 [weight%] Bulk density 650 750 [kg/m3] Average length 3 5 [mm] Physical properties BET surface area 120 140 [m2/g] Pore volume 0:48 0:56 [cm3/g] Side crush length 12 [N/mm] Geometry Approximate diameter 2:5 [mm] Bags Total amount 5 [bags] MOC Stainless steel [none] Geometry Wire mesh sausage [none] Containment Diameter 20 [mm] stainless steel wire Length 200 [mm] mesh sausage bags Catalyst Amount 2 [bags] Weight 10 [g/bags] Inert glass beads 3 [bags]

The sausage bags used for catalyst containment were sewn closed at the top. As can be seen from Table 7.2 only two of the …ve sausage bags were …lled with catalyst. The remaining three were …lled with inert glass beads in order to decrease the pressure drop across, and enhance the ‡ow patterns within the reactive section. To further decrease the pressure drop the …ve sausage bags were wrapped in demister wire, bringing their e¤ective diameter up to 50 mm and increasing the internal gas voidage in the reactive section. No special activation procedures are necessary for the catalyst.

7.3.2 Non-reactive packing

A packed column, with its comparatively much lower HETP, is used rather than a trayed one as it yields the much shorter column preferred in space restricted laboratory- scale applications. A low HETP is also essential when working with close-boiling components (such as 1-hexene and n-hexane) to ensure adequate separation and to avoid a prohibitively tall column.

1 The detailed catalyst speci…cations are proprietary and cannot be disclosed here. 7.3. PREVIOUS COLUMN INTERNALS 49

Sulzer CY gauze type packing is used in the non-reactive stripping and recti…cation sections of the CD column. This type of structured packing is commonly used in many conventional distillation columns. Table 7.3 lists its geometric data.

Table 7.3: Sulzer CY geometric data Speci…cation Symbol Value Units Void fraction " 0.965 [none] 2 3 Packing surface area ap 708 [m /m ] Crimp height h 4.25 [mm] Channel base B 7.5 [mm] Channel side S 5.65 [mm] Channel ‡ow angle from horizontal None 45 []

The packing consists of parallel corrugated sheets which are inclined at an angle of

45 relative to the horizontal axis of the CD column. There are mainly two types of packing namely random (dumped) and structured. The reason for choosing the latter instead of the former becomes apparent when considering Table 7.42 - adapted from Seader and Henley [1998].

Table 7.4: Comparison of types of packing [Seader and Henley, 1998] Random packing Parameter Raschig rings and Structured "Through ‡ow" saddles Relative cost Low Moderate High Pressure drop Moderate Low Very low E¢ ciency Moderate High Very high Vapour capacity Fairly high High High Typical turndown ratio 2 2 2

It is clear that the higher costs for structured packing is compensated for by the advantages in pressure drop, e¢ ciency and vapour capacity. Additionally, the use of structured packing distributes down-coming liquid more uniformly over the catalyst in the reactive section. It is envisaged that this will mimic liquid distribution observed in large pilot-scale CD columns [Mphahlele, 2003]. In packed columns gravity causes the liquid phase to ‡ow downward over the packing as a …lm or as droplets while the gas phase rises upward, thus e¤ecting gas-liquid contact for mass transfer. Liquid channelling is always a potential problem in packed columns. Channelling occurs when the liquid ‡ows down mainly near the walls of the column while gas ‡ows up in the centre. Redistributors are used in industry to ensure a more uniform liquid distribution, although this should not be necessary given the size of the CD column. 2 The turndown ratio is de…ned as the ratio of maximum to minimum vapour capacity.

Chapter 8

MASS AND ENERGY BALANCES

The ProII and Chemsep distillation simulation packages were used in an attempt to do the mass and energy balances over the system. Not only are both well-known and used extensively by researchers and engineers to simulate non-reactive distillation, but they also have the ability to include reactions in simultaneous reaction-separation systems. It was decided to use a modular approach and gradually build up the simulation from a simple distillation problem to that of reactive distillation.

8.1 Simulation using distillation packages

8.1.1 Non-reactive distillation

It was relatively simple to make the system converge for the conventional non-reactive distillation case. The main results for the …nal case study are given in Appendix C.1. The ‡ow sheet, speci…cations and simulated results are given in Figure 8.1.

8.1.2 Reactive distillation: adding a reaction

The reaction was now added and the heterogeneous reaction kinetics found in literature converted to be pseudo-homogeneous. It is not surprising that it proved di¢ cult to make the reactive distillation system converge. From the literature review it is clear that accurate prediction, simulation and scale-up of RD and CD systems are still di¢ cult - some of the main motivations for this project. It was concluded that customization of the distillation packages is probably required in order for the simulation to converge to a solution. However, this was deemed impractical given the time constraints involved: a more dynamic approach was required to size the system.

51 52 CHAPTER 8. MASS AND ENERGY BALANCES

Figure 8.1: Schematic of the ProII simulation for non-reactive distillation 8.2. SPREADSHEET CALCULATIONS AND PROII VERIFICATIONS 53 8.2 Spreadsheet calculations and ProII veri…cations

8.2.1 Revised design approach

As mentioned, it is not surprising that it was not possible to make the reactive distillation system converge. In fact, this experimental system is being built for that exact purpose: to investigate those dynamics in CD that make it di¢ cult to predict, simulate and scale- up. To proceed, assumptions could be made until the system equations are manageable enough to solve, but in this case (given the mathematically complex interactions involved) the resulting model could be so simpli…ed that it may not represent reality at all - defeating the whole purpose. Alternatively, an EQ model and/or an NEQ model (complicated by the non-condensable hydrogen) could be used, but this will require anything from a year for a simple, non-reactive distillation system to decades for the level already reached by the researchers mentioned in the literature review. Writing and, in fact, re-inventing such a time-consuming model is not practical, nor is it the immediate aim of the project. The most reliable, least simpli…ed and apparently most realistic prediction at this point in time appeared to be that of the converged solution for the non-reactive section. It was therefore decided to use this as a basis for the design and to anticipate the missing reaction dynamics by following a conservative design approach. In other words, it was decided to create a robust experimental system with a wide range of possible operating conditions.

8.2.2 Excel spreadsheet

The …nal Excel spreadsheet used for the sizing is attached in appendix C. As shown on the spreadsheet, most of the physical properties calculated by ProII were veri…ed using experimentally determined properties and/or prediction correlations obtained from a variety of carefully selected sources. The speci…ed column pressure; molar feed ‡ow rates and compositions; feed temperatures and pressures were retained as well as the temperatures, pressures, molar ‡ow rates and molar compositions calculated by ProII for the distillate, o¤-gas and bottoms products. This was then used to calculate total and species molar and mass ‡ow rates, molar and mass stream densities, volumetric ‡ow rates and stream viscosities. When working with ‡ows in pipes Sinnot [2001] suggests 1 to 3 m/s linear velocity for non-viscous liquids and 15 to 30 m/s linear velocities for gases. Values of 1 m/s and 20 m/s were thus chosen for liquids and gases respectively. Using Bernoulli’sequation it was found that pipe inner diameters for transporting liquids could be as small as 0.23 mm ID without a prohibitive pressure loss and that of gases 0.381 mm ID. This 54 CHAPTER 8. MASS AND ENERGY BALANCES

1 would suggest the use of 16 " tubing for both gases and liquids. However, from a practical 1 view-point 16 " tubing is too ‡exible. Also, following a conservative design approach, it makes sense to increase the system’s liquid and gas ‡ow rate capacities and to take into consideration that the heat released in the exothermic reaction may increase the gas volumetric ‡ow rate above that predicted by the non-reactive model. For these 1 reasons, it was decided to use 8 " tubing as a standard for the liquids and gases and a 1 2 " tube at the top of the column where there is a high exiting gas volumetric ‡ow rate. This excludes the cooling loops and nitrogen pressure regulation, which will be discussed later.

8.3 McCabe-Thiele system trends

Before continuing with the design, it would be preferable to have a general idea of the expected behavioural trends observable in the system and also which parameters are important in the control strategy. As is clear from chapter 3, however, a rigorous approach will not yield a set of simple equations that will show trends easily and clearly. It was thus decided to use a simpli…ed McCabe-Thiele approach to get a feeling of the system’sbehaviour. It must be emphasized that this approach can, at best, only give a general idea of the system’s behaviour. Not only does the reactive zone disrupt the thermodynamic equilibrium, but its operating line is also non-linear and thus di¢ cult to use in McCabe-Thiele. Due to the di¢ culties involved in gleaming useful, clear trends from the system’soperating lines, an approach was used that focused on total ‡ow rates rather than a compositional pro…le of the column. This precludes the calculation of the required number of theoretical stages and the conversion in the reactive zone, which are both dependant on compositions. Firstly, n-hexane and 1-hexene have very similar liquid, vapour and vaporization enthalpies, which will be assumed equal. Consequently, the total liquid and vapour enthalpies are composition independent. n-hexane and 1-hexene are also very close- boiling and it is thus plausible to assume that the vapour and liquid enthalpies are constant between the trays of the column, and only di¤er by the vaporization enthalpy (this is especially true in the isothermal reactive zone). The McCabe-Thiele assumption vap vap of equimolar ‡ow thus also holds as Hj;1 hexene Hj;n hexane is assumed. The non-condensable hydrogen gas was assumed to have a negligible e¤ect on the VLE and to be insoluble except where a reactive driving force exists. In reality, since the system is assumed isobaric, the diminished hydrogen partial pressure in the recti…cation zone will have an e¤ect on the VLE, which will have to compensate for the vapour’s increased partial pressure. However, the hydrogen ‡ow rate is consequently assumed constant in the non-reactive recti…cation and stripping zones and is treated as a separate stream from the vapour and liquid ones. The speci…c molar enthalpy of hydrogen HG 8.3. MCCABE-THIELE SYSTEM TRENDS 55 only varies by approximately 2% over the temperature range in question and is thus also assumed constant. The most di¢ cult section to model accurately and simply is the reactive zone where reaction and separation occurs simultaneously. This zone in‡uences and is in‡uenced by both the recti…cation and stripping sections. Since the reactive zone is small relative to the non-reactive sections and not designed for separation, but rather reaction, it was assumed that the heat generated in the reaction is used to vaporize the liquid in the zone without a change in liquid composition. The zone was also assumed to be isothermal, with all the reaction heat generated used to vaporize the liquid. Due to the distillation hydrodynamics and the enhanced mixing it a¤ords, the zone was modelled as a CSTR. The reaction thus proceeds as follows:

C6H12(l) + H2(g) C6H14(l) ! with the C6H12/C6H14mixture vaporizing. Conversion is based on hydrogen, though the molar changes of the reactants and product are all equal from the reaction stoichiometry. The simplifying assumptions for the Mcabe-Thiele approximation may be summarized as follows1:

L L L 1. cp;j;1 hexene cp;j;n hexane (and thus Hj;1 hexene Hj;n hexane = Hj ) V V V 2. Hj;1 hexene Hj;n hexane = Hj vap vap vap V L 3. Hj;1 hexene Hj;n hexane = Hj Hj Hj 4. There is equimolar ‡ow between 1-hexene and n-hexane in the non-reactive sections vap vap as Hj;1 hexene Hj;n hexane 5. HG is constant (it actually varies by ca. 2% across the temperature range, which is comparable to the error introduced by the equimolar approximation

6. Inert gasses are insoluble in the liquid phase except where a reaction driving force exists

7. Reaction: C6H12(l) + H2(g) C6H12(l) !

8. From previous assumption and de…nition of conversion: GR = (1 X)G 9. The system is isobaric

10. The reactive zone is isothermal 1 Note: G refers to the hydrogen gas, V to the condensable vapour and L to the liquid. 56 CHAPTER 8. MASS AND ENERGY BALANCES

Figure 8.2: McCabe-Thiel approximation of the CD system 8.3. MCCABE-THIELE SYSTEM TRENDS 57

11. Due to the amount of subcooling no hydrocarbons exit through the o¤-gas (the derivations in Appendix C.3 do not assume this until the end) and = 0

Note that the rate of reaction is given by rA = kPH (eq. 2.2). Since a CSTR 2 is assumed the exiting hydrogen partial pressure should be used if the reaction rate equation is employed. Using the reaction rate equation and the de…nition that the partial pressure of i is the product of the fraction of i in the total vapour and gas space, and the total pressure:

rA = kPH 2 G1 rA = k PT (8.1) G1 + V1

Only the resulting simpli…ed McCabe-Thiele model equations will be considered here and the reader is referred to Appendix C.3 for the full derivation. Consider a system where the conversion (X) in the reactive zone is known. In application this is not the case, however calculation of X additionally requires a column composition pro…le, which signi…cantly increases the model complexity to a point where trends are not clearly visible. Assuming X is equivalent to hypothetically assuming that the catalyst mass may be varied to maintain a constant conversion. From a material and energy balance around the recti…cation zone (refer to …g. 8.2)

it is possible to derive relationships for the downwards ‡owing liquid (LR) and upwards

‡owing vapour (VR) streams:

V V V V V V (Hn Hj ) + D(Hn Hj ) + F (Hj HF ) + RD(Hn HD) LR = vap (Hj ) V V F (Hj HF ) + RD(Hn HD) = vap (8.2) (Hj )

V V V V V V (Hn Hj ) + D(Hn Hj ) + F (Hj HF ) + RD(Hn HD) VR = ( + D F ) + vap (Hj ) V V F (Hj HF ) + RD(Hn HD) = (D F ) + vap (8.3) (Hj )

As is intuitively logical, the equations indicate that an increase in R also increases the liquid and vapour ‡ow rates in the recti…cation section. Note that LR is more sensitive to the re‡ux ‡ow rate than VR, as the latter is also dependant on a second term that is not a¤ected by the re‡ux ratio. The degree of sub-cooling (indicated by a lower HD value) also increases both LR and VR as it increases the amount of liquid 58 CHAPTER 8. MASS AND ENERGY BALANCES being internally recycled. This internal recycle can also be manipulated by varying the temperature of the feed stream F . Consider the reactive zone:

XHrxn VS = VR LR Hvap XHrxn = ( + D F ) + LR(1 ) Hvap V V rxn F (H HF ) + RD(H HD) XH j n = (D F ) + vap (1 vap ) (8.4) (Hj ) H

XHrxn LS = LR(1 ) Hvap V V rxn F (H HF ) + RD(H HD) XH j n = vap (1 vap ) (8.5) (Hj ) H

An increase in X decreases the vapour and liquid ‡ow rates in the stripping section as the reaction heat transferred is absorbed into vaporizing the reaction mixture to the liquid stream (LR). The vapour ‡ow in the stripping section (VS) is thus also smaller than that in the recti…cation section (VR) which receives the vapourized liquid. It is Hvap important to note that there exists a conversion X = Hrxn 6 1 where there will be no downcoming liquid in the stripping section. At this point mass transfer in the stripping section ceases and, since VS must be zero if there is no liquid to be boiled up, everything entering at feedpoint F must exit through the distillate (i.e. D = F ) unless there is a feedpoint in the stripping section. Essentially, the reactive zone takes over the function of the reboiler.

To ensure that VS and LS is as calculated above it is necessary to control the boil-up ratio via the reboiler heat input (QB).

B = F + FS ( + D) = F + FS D (8.6)

rxn V V V XH Hw QB = F HB Hw + (Hj HF )(1 vap )[2 vap 1] + FS(HB HFS) f H (Hj ) g rxn V V V XH Hw + D(Hw HB) + RD(Hn HD)(1 vap )(2 vap 1) H (Hj ) (8.7) 8.3. MCCABE-THIELE SYSTEM TRENDS 59

As the conversion increases the required heat input decreases as more heat is being generated in the reactive zone (this is one of the advantages of CD; refer to section 1.2).

An increase in R or the re‡ux sub-cooling increases the required QB as both tend to cool down the streams at the top of the column. From the above equations it is not possible to determine the compositional pro…le in the column nor the number of stages. It thus also di¢ cult to make a conclusive decision regarding where the feed point must be placed relative to the reactive zone. From the last equation it would appear that putting the feed below the reactive zone (F = 0) will

make QB less dependant on the conversion and thus easier to control, though this is at best only an assumption. What is clear from eq. 8.2 is that introducing a liquid feed

stream in the recti…cation section (higher F ), especially a sub-cooled one (low HF ) will

increase LR and thus the amount of liquid recycled for further reaction in the reactive zone. The location of the reactive zone along the column’s distillation equilibrium temperature pro…le should be at a point where the 1-hexene fraction composition is at a maximum, but where the heat produced does not vaporize the entire liquid stream, bypassing the stripping section and thus reducing the n-hexane/1-hexene separation e¢ ciency. This point should be determine experimentally. It may be useful to de…ne the concept of a thermal location within the column more closely. For any location in the column the composition is set by the VLE if the temperature and pressure are known. In this system the pressure is set isobarically and is thus assumed to be known and constant through the column. Any disturbance that can thus signi…cantly a¤ect the temperature pro…le in the column, will thus also change the column’scompositional pro…le. The bottoms heat duty set-point is chosen as is the physical distance location of the reactive zone along the length of the column. If the temperature at the top of the column changes (due, for example, to a di¤erent re‡ux ratio) the temperature and compositional pro…les change. This will shift the reactive zone’sthermal (and hence compositional) location (as its physical location is …xed) - a thermal location that may not have the optimal 1-hexene liquid concentration in terms of conversion. This e¤ect is best illustrated by the following operating lines for the recti…cation and stripping sections respectively (see Appendix C.3 for the derivation):

V V vap (F (H HF ) + RD(H HD) xj + (xDD zF F )H f j n g j yj+1 = vap V V (8.8) H (D F ) + F (H HF ) + RD(H HD) j j n

V V vap FS(HFS Hw+1) + B(Hw+1 HB) + QB xw + Hw (zF sFS xBB) yw+1 = f vap V g V (8.9) Hw (FS B) + FS(HFS H ) + B(H HB) + QB w+1 w+1 The isothermal reactive zone is not included. Temperature in the above operating 60 CHAPTER 8. MASS AND ENERGY BALANCES lines is intrinsically represented by the enthalpies. In the equation, the composition of stage j or w is determined by the stream ‡ow rates, value of x and the enthalpies. In order to relate the above operating lines to a physical location along the length of the column it has to be combined with an xy equilibrium diagram. However, the thermal position can be chosen by calculating the enthalpies at that temperature. Chapter 9

MECHANICAL DESIGN

As estimated, the nominal conditions within the system should be 7 - 150C and 1 - 6 bar(g). To encompass these conditions with some built-in ‡exibility it was decided to

choose 0 - 200C and 1 to 10 bar(g) as the minimum mechanical and electrical design criteria. The general design criteria stated at the beginning of this part continue to apply.

9.1 Materials of construction (MOC)

Hydrogen under elevated temperatures and signi…cant partial pressures (such as those prevalent in the CD column) can pose a major safety risk to systems constructed from carbon steels and (certain) stainless steels. The risk is two-fold. Firstly, under these conditions the small hydrogen molecule penetrates the steel and removes the carbon by reaction to methane (decarburization) resulting in decreased steel strength. Secondly, the high pressure "causes a loss of ductility (hydrogen embrittlement) and failure by cracking of the steel" [Perry et al., 1997]. This is known as hydrogen attack and from

Figure 9.1 it is clear that the minimum design criteria within the CD column (150C and 6 bar(g)) does not fall within the region where it can occur. However anticipating future projects and considering the fact that (as will be seen) most of the system can operate

at conditions within this region (i.e. above 30 bar(g) and 400C) hydrogen attack must be considered possible. From the graph it is also clear that, in order to prevent hydrogen attack, it is necessary to use a 0.5 Mo steel alloy. The widely used stainless steel 316 (SS316) appears to be the best choice. It’s composition is 18% Cr, 12% Ni and 25%Mo [Perry et al., 1997]. Moreover, it is an austenitic stainless steel which (in general) has a better corrosion and pitting resistance. Lastly, Swagelok products (the standard used in the design) are readily available in SS316. It should be noted that the iron in stainless steel can also catalyze the reaction. As

61 62 CHAPTER 9. MECHANICAL DESIGN

Figure 9.1: Steel compositions required for prevention against hydrogen attack as a function of temperature and pressure (from …g. 28-1 in Perry et al. [1997]).

a …rst approach, it will be assumed that the catalyst has a much higher surface area than the packing, column and pipe walls so that this e¤ect is assumed negligible. From the values given in Tables 7.2 and 7.3 the catalyst has a minimum BET surface area of 78 x 106 m2/m3 compared to 708 m2/m3 for the Sulzer CY packing, translating to 2 520 m2 for 21 g of catalyst and 1.6 m2 for 1.12 m of packing. However, the catalyst’s active nickel-containing surface area is much lower and might well be comparable to that of the Sulzer CY packing. A dry run without the reactive zone is thus required to determine the validity of the above assumption. Stainless steel 316 has thus been used as the metal of preference throughout the system because of safety considerations, for practical reasons and for consistency. Te‡on was used as packing sealant between ‡anges and also preferentially when a hard plastic was required for any application – such as acting as an insulator and/or bu¤er between the CD column support legs and the column itself. Normal rubber absorbs the 1-hexene, swells up and then ruptures, making it unsuitable for the current application. Additionally, Te‡on has an upper service temperature of 260C - well within the design criterium of 200C. The type of glass to be used is Pyrex (a borosilicate). The chief problem with glass is its brittleness and weakness to shocks [Perry et al., 1997]. In terms of its softening temperature (550C) and resistance to most corrosive acids it is well within the design criteria. Glass’sresistance to pressure will be dealt with later, but the reader may refer 9.2. PIPE SYSTEM 63

Table 9.1: Speci…cations of tubes used Tube OD Wall thickness Working pressure [inch] [inch] [bar] 1/8 0.028 586 1/4 0.035 352 to Appendix D for data on the safe working pressure for a glass tube.

9.2 Pipe system

Consider the block diagram shown in Figure 6.1. The pipe size inner diameters were determined in chapter 8 and the MOC chosen in section 9.1. The various wall thicknesses of the pipes must now be chosen to handle the system’s design pressure of 10 bar(g). Perry et al. [1997] supplies ways to calculate minimum required wall thicknesses. How- ever, in this case it is better to trust the speci…cations supplied by the manufacturer (Swagelok). The chosen pipe speci…cations as well the allowable operating pressures are supplied in Table 9.1.

9.3 Main column body

The main column body is made from the chosen standard SS316 and consists of three interchangeable 49.25 mm ID pipe sections (5.54 mm wall thickness; 7.47 kg/m) tailored to contain a maximum combined packed height of 1280 mm. Currently the height comprises 2 x 416 mm and 1 x 500 mm long column segments. Flanges are used to …x the sections to each other and a Te‡on O-ring is used inbetween as sealant. The amount of ‡anges used were kept to a minimum to prevent excessive heat loss, although ‡anges were required for ‡exibility of design. Using the stainless steel with the relevant wall thickness also a¤orded ‡exibility in terms of adding and placing inlets, outlets, thermocouples, pressure gauges, etc. directly into the wall.

9.4 Column internals and liquid distribution

It is di¢ cult to over-emphasize the importance of high contact areas in both distillation and heterogeneous reactions. In the former e¤ort is directed into optimizing the gas-liquid interfacial area for maximum mass and heat transfer while in the latter op- timization of the catalyst surface area is vital for an e¢ cient reaction. E¢ cient gas and liquid distribution is therefore essential for e¢ cient column operation. It is therefore possible to identify three interconnected elements that require attention in the CD column design, namely uniform liquid distribution of the re‡ux entering the top of the 64 CHAPTER 9. MECHANICAL DESIGN column, maximization of the gas-liquid interfacial area in the non-reactive distillation zones and redistribution of the liquid phase ‡owing down the column. These elements will now be discussed in more detail.

9.4.1 Column internals (non-reactive sections)

The two previous UCT researchers working on the batch CD system used Sulzer CY gauze type structured packing in the non-reactive sections of the column and it consequently made economic sense to use the same if Sulzer did not have a signi…cantly more suitable product available. For economic and simplicity reasons it was decided to use packing made from standard materials with nominal diameter ranges that encompassed the 50 mm ID of the CD column, although non-standard packing speci…cations may be requested. The packing in the column must have a low HETP, low pressure drop and its MOC must be non- reactive with and non-catalytic towards the hydrocarbons and hydrogen present. Sulzer CY packing ful…lls these requirements best and compares favourably with the other Sulzer products for this application. It has the "maximum number of theoretical stages per meter" (lowest HETP) which is critical in maximizing the separation e¢ ciency in this relatively short column and also has a generally acceptable pressure drop. Unfor- tunately, the nominal MOC of the packing consists of a variety of metals that could, in principle, catalyze the 1-hexene hydrogenation reaction. However, although the packing is speci…cally designed for the maximum possible surface area, thus increasing the risk of a¤ecting the reaction dynamics signi…cantly, it is still much lower than that of the catalyst used and, as discussed before, the e¤ect should therefore be minimal although a dry run is de…nitely required for veri…cation. SS316L was thus chosen as the MOC to make the packing non-reactive to hydrogen, to minimize its catalytic e¤ect and to be consistent with the rest of the system (see section 9.1). The packing speci…cations are summarized in Table 9.2 and the geometric data in Table 7.3.

9.4.2 Column internals (reactive section)

The catalyst in the reactive zone must not only be uniformly distributed, but must also be arranged in such as way as to ensure the smallest possible resistance to ‡ow (pressure drop). A uniform distribution is necessary to prevent a radially asymmetrically occurring reaction, which can, for example lead to hot spots. The requirement of a low pressure drop across the zone is of particular importance here as a large drop will disrupt the distillation facet of the CD system. To facilitate a radially uniform catalyst distribution it was therefore opted not to employ the sausage bag method of the previous researcher, but to rather use cylindrical gauze disks (Figure 9.2). 9.4. COLUMN INTERNALS AND LIQUID DISTRIBUTION 65

Table 9.2: Speci…cations of Sulzer CY gauze type packing used in the CD system (information extracted from user manual) Technical speci…cations General Theoretical stages per meter Maximum [none] Most economical load range (F factor) 1.5 to 2 [Pa1=2] Minimum liquid load approximate 0.05 [m3/m2h] Hold-up Small [none] Fins for liquid redistribution Yes [none] System speci…c Material of construction SS316 [none] Type Gauze [none] Height per layer 160 [mm] Diameter 50 [mm] Additional information Preferred Applications Batch and continuous columns Pilot and laboratory scale (reliable scale-up) Limited suitability Fouling substances Non-wetting liquids

(a) (b)

Figure 9.2: "Tea-bag" approach used in the reactive zone with (a) the empty stainless steel cylindrical disks and (b) the disk …lled with 21 g Ni/Al2O3 66 CHAPTER 9. MECHANICAL DESIGN

(a) (b) (c) (d • top) (d • front)

Tea•bag configurations Catalyst bales (licensed by Chemical Research and Licensing)

(e) (f) (g) Horizontally disposed catalyst containing gauze Sulzer Katapak•SP configurations

Figure 9.3: Various catalyst packing techniques for use in the reactive zone ((a)-(f) from Taylor and Krishna [2000] and (g) from http://www.sulzerchemtech.com/ eprise/SulzerChemtech/Sites/products_services/reaction.html)

Figure 9.3 shows other documented techniques that can be explored once the system has been tested successfully. Of particular interest is the possibility of coating the catalyst onto the structured packing used in distillation. Commercially, Sulzer (for example) can already supply a hybrid catalyst-structured-packing product called Katapak. It may be of interest for future research to consider putting a thin layer of ZSM-5 on the Sulzer CY packing used in the column. Research on the synthesis of thin …lm ZSM-5 catalysts is available in literature [Hedlund et al., 2004].

9.4.3 Liquid distribution and redistribution

In general, liquid tends to want to ‡ow down the walls and gas to rise up through the centre of a distillation column thus negatively impacting the gas-liquid interfacial contact area and consequently also the interphase mass transfer - a critical goal of distillation. Column internals must therefore be carefully selected and designed to counteract this 9.5. REBOILER 67 e¤ect. The geometry of structured packing attempts to minimize this e¤ect, but cannot eliminate it completely as it must also optimize gas-liquid contact by spreading a thin layer of liquid on its surface in cross‡ow with the gas. This obviously demands that the liquid crisscrosses down the column and inevitably the liquid will be directed towards the column wall. Liquid re-distributors are then used to either re-direct the liquid to the centre of the column or to re-spread it uniformly over the column diameter. There are various types of re-distributors and the reader is referred to Kister [1990] for a more complete discussion of the subject. As a …rst approach to the CD column design it should be safe to assume that the three collars located on each layer of Sulzer CY packing are su¢ cient to achieve a good liquid distribution in the column. Naturally, the initial liquid distribution of the re‡ux onto the Sulzer packing at the top of the column is critical as it sets the pace for the distribution lower down. Once again a variety of options were considered. Kister [1990] identi…es two main types: pressure and gravity distributors. Given the high volumetric gas ‡ow rate and the height restriction imposed on the column, a pressure type perforated pipe distributor appears to be the preferred choice. Although it is prone to plugging and generally yields a slightly inferior distribution, it occupies less of the vapour ‡ow area and does not signi…cantly add to the column height as, say, the commonly used gravity type ori…ce distributor. It was decided not to employ a spray type distributor as it would tend to direct much of the liquid to the edge of the packing near the wall of the column. Rather, a perforated ring distributor was designed, but the ring proved impractical to make given the very small size concerned. The ring was removed and an angled perforation used to accommodate the areas that were covered by the ring - an angled perforated radial distributor. This design leaves 77% of the gas ‡ow area open (see appendix E).

9.5 Reboiler

Various options were considered for the reboiler and various sources were considered and consulted. There is an excellent comparison table of reboiler types in Kister [1990] that deals with the practical aspects of reboilers. Other literature sources include Sinnot [2001], Perry et al. [1997] and Seader and Henley [1998]. The two con…gurations that were most seriously considered were the heated oil circulation and kettle type reboiler. It was decided to use the latter as it is inherently simpler. Heated oil circulation requires additional heating equipment and ‡ow control. It is also moderately easier to calculate the power generated by a heating element compared to the heat exchanged by a heating loop. The former requires only the current through and potential di¤erence over the heating loop, while the latter requires the 68 CHAPTER 9. MECHANICAL DESIGN

oil ‡ow rate, temperature dependant heat capacity (cp (T )) and temperature di¤erence between the inlet and outlet. However, there is a risk that the heating element can overheat either itself and/or the heated medium - a problem not encountered with the heated oil circulation as the temperature of the heated medium cannot exceed that of the heating medium due to the second law of thermodynamics. This risk is easily reduced by implementing temperature monitoring and fuses that will respectively control or (if necessary) cut power to the heating element. The next question is whether to use a heating element located inside the vessel or on its external wall. From a safety perspective, mounting it outside on the wall of the vessel isolates it from the pressurized, high-temperature 1-hexene, n-hexane and hydrogen mixture inside. However, from a heat integration perspective, putting it inside the vessel will minimize heat losses as all the power generated must be used either for internal heating of the element or for heating of the ‡uid medium. It should be noted that the hydrocarbon-hydrogen mixture is not explosive unless it comes into contact with an oxygen source. Since neither oxygen nor an oxygen containing species is fed to the system and since the system is airtight and pressurized, thus preventing atmospheric gases from entering, it should be safe and energy e¢ cient to employ an internal heating element. The mechanical drawing of the reboiler is shown in appendix E. The liquid inventory was kept as low as possible to allow a fast response for set-point changes, although the physical limitations impressed by the heating element had to be taken in account as well. For a 1 kW (conservative design with 54% above the estimated 650 W) 8 mm OD element at least 80 mm height and 45 mm internal coil radius was required. Su¢ cient space then had to be left between the coiled element and the vessel wall as well as the top of the element and liquid surface. From a safety perspective it is paramount that the heating element does not run dry (i.e. stick out above the liquid into the vapour space) and a low level alarm (LLA) must be installed at a safe depth to switch the element o¤ if necessary. Care was taken to ensure ‡exibility in the design. The element is …xed to the reboiler’sbottom ‡ange for easy removal and use of a ‡at surface for the electrical connections. It was decided to locate the reboiler outlet in the centre of the bottom ‡ange as the ‡ow of liquid past the element minimizes surface fouling accumulation. Two holes were drilled in the bottom ‡ange to connect the external power connectors to the element and the element silver soldered to these stainless steel connectors. The element itself is made of Incoloy, which consists mainly of iron, nickel and chrome, and very small amounts of carbon, titanium and aluminium. The reboiler vessel is manufactured from SS 316, uses only a top and bottom ‡ange to minimize heat loss and is connected to the thinner column with a conical reducing connector to ensure smooth ‡ow patterns and prevent stagnant zones. The sightglass shown is part of the level control system and will be discussed in section 9.6.1. 9.6. COOLING LOOPS 69 9.6 Cooling loops

9.6.1 Two-stage partial condenser

The gas leaving the top of the column contains mainly residual, unreacted 1-hexene and hydrogen as well as n-hexane –as dictated by the VLE. As mentioned before, hydrogen is a non-condensable gas at the system’s operating conditions. Non-condensable gases can have a negative e¤ect on the heat transfer coe¢ cient as they tend to accumulate next to the condensing surface [Sideman and Moalem-Maron, 1982] forming a stagnant gas layer that acts as a resistance to heat transfer. Essentially, the rate at which the gas naturally convects and di¤uses away from the condensing surface equals that at which it is brought to the surface, increasing the amount of gas, reducing the vapour partial pressure and thus lowering its condensation temperature [Steinmeyer, 1972]. A higher cooling duty is thus required. If the cooled stream contains 0.5 - 70% non-condensables one should estimate heat transfer based on both the methods for total condensation and forced convection [Sinnot, 2001]. According to ProII, the gas stream leaving the top of the column thus falls in this region. Additionally, there are numerous warnings from literature regarding fog formation [Sinnot, 2001; LoPinto, 1982]. According to LoPinto [1982], when there is a high temperature di¤erential and non-condensable:condensable vapour ratio in a condenser a "suspension of …ne droplets" with a diameter anywhere between 1 to 10 m (fog) can form. This is of course undesirable as it is possible that these …ne droplets may be entrained by the gas phase and carried out of the condenser [Sinnot, 2001] resulting in a loss of the desired liquid product and causing downstream pollution. The gas-vapour- nuclei mixture that largely determines the existence or absence of fog formation in a condenser is, unfortunately, often uncontrollable by process engineering. Fortunately, "catastrophic fog formation is rare" [Steinmeyer, 1972]. It was therefore decided to verify whether fog formation is indeed a problem and, if so, to take the appropriate actions suggested by LoPinto [1982] and Steinmeyer [1972]. These include reducing temperature di¤erences in the condenser and increasing the heat exchange surface area, using mist eliminators, seeding with condensation nuclei to produce larger drops that can be separated out more easily, …ltering out the nuclei in the gas stream to attempt to prevent fog formation, and/or signi…cantly superheating the feed gas. The ProII simulation predicted a required condenser duty of ca. 650 W to cool the vapour-gas mixture from 150 to 7C. The refrigerator used by the previous researchers can be used to reach this low temperature, but can supply only 500 W of cooling. Clearly, some creative thinking is required. A simple, economical solution that uses the existing equipment is to construct a two-stage condenser. The …rst stage uses tap water as the cooling medium and the second the refrigerator’s water-glycol mixture. For a 70 CHAPTER 9. MECHANICAL DESIGN

conservative design a maximum tap water temperature of 40C, representing unusually hot ambient temperatures in Cape Town, was decided upon. This represents a signif- icant temperature gradient between the cooled gas and coolant and a short tap water cooling section achieving rapid cooling and using relatively little water can be expected. A refrigerator cooled section then brings down the temperature to the desired outlet temperature of 7C. There are various con…gurations for heat exchangers. Some of them include [Perry et al., 1997; Sinnot, 2001]:

1. Shell and tube heat exchangers

2. Plate heat exchangers

3. Spiral heat exchangers

4. Direct contact heat exchangers

5. Finned tubes

6. Double-pipe heat exchangers

The spiral heat exchangers and shell and tube heat exchangers were investigated in more detail, although variations on the double-pipe heat exchangers in the form of annuli were also considered. Many glass spiral heat exchangers are used in laboratories. However, due to the high pressure in the column it would have to be constructed from metal. The calculated required speci…cations of such an exchanger proved impractical from a manufacturing point of view as the metal can buckle when bent into such a small diameter. Shell and tube heat exchangers are widely used and are familiar to the researcher. It would also be simple to adapt it for two-stage operation. The design illustrated in appendix E was therefore used. The gas exiting the top of the CD column enters the gas inlet chamber and proceeds along the negative pressure gradient down small pipes. The hydrocarbons condense out of the hydrogen in the tap water and refrigerator cooled sections and drip down directly into the re‡ux chamber while the hydrogen exits through an o¤ gas line. As shown in Appendix E the relation between the exchanger tubes and o¤-gas outlet were chosen to encourage liquid to be ‡ung down and not be entrained by the hydrogen. Also, the initial gradient of the exit line is 30 to allow entrained liquid droplets to ‡ow back down into the re‡ux chamber. An integrated condenser-re‡ux drum was used for a simple, compact design with reduced opportunities for heat loss. Ba• es are used on the shell side to increase the heat transfer coe¢ cient. Countercurrent ‡ow is preferred here as (assuming the same overall resistance to heat mass transfer) it generally yields a higher 9.6. COOLING LOOPS 71

log mean temperature di¤erence (and thus a smaller required surface area for the same heat transferred) and allows for more ‡exibility (the cooling medium outlet temperature can exceed the heated medium outlet temperature) when compared to parallel ‡ow [Incropera and DeWitt, 1996]. Rules of thumb from Sinnot [2001] indicate that the ba• e cut must be 20-25% of the the ba• e disk diameter and that ba• e spacings must be 0.3-0.5 times the shell diameter. They also supply guidelines for the bundle diameter. Di¢ culties were encountered in accurately sizing the heat exchanger and quite a few assumptions had to be made. Estimation of the heat transfer coe¢ cient on the gas-vapour side is not only complicated by the non-condensable hydrogen and by the changing nature of the condensing hydrocarbon mixture due to its VLE, but prediction of the VLE itself is also complicated by the non-condensable hydrogen. Lastly, a sightglass is required to visually ascertain the hydrocarbon liquid height

in the re‡ux chamber. This is achieved by a¢ xing a glass tube between 90 swagelok …ttings connected to two outlets in the re‡ux chamber - one in the bottom liquid phase and one in the gas-vapour space above that. Graphite or Te‡on ferrules can be used for the glass-metal contact in the …tting. Pyrex tubing was used and the correct tube length, outer diameter and wall thickness had to be chosen for a safe working pressure. A 6 mm OD and 3 mm ID tube that can withstand a maximum pressure of 30 bar up to a length of 500 mm was chosen (Figure D.1). Lateral shocks from outside can break the glass and thus the tube was wrapped in gauze to contain the shards should the glass break.

9.6.2 Bottoms cooler

The function of the bottoms cooler is simply to cool down the bottoms product exiting the reboiler (ca. 132C) to prevent it from ‡ashing to atmospheric pressure across the sample point valve or the valve prior to the product tank. Both constitute a signi…cant safety risk and loss of product. The hydrocarbons must also be reduced to well below their normal boiling points or uneven vaporization can cause signi…cant inaccuracies in the measured liquid composition. For heat integration and water saving purposes the tap water exiting the partial condenser will be used as coolant and a thermocouple at the cooled down hydrocarbon outlet will check to make sure that it is below its normal boiling point. The heat exchanger that was previously used as the condenser in the batch CD system will be used as the bottoms cooler. 72 CHAPTER 9. MECHANICAL DESIGN Chapter 10

PROCESS CONTROL

One cannot su¢ ciently stress the importance of optimal, e¢ cient and accurate process control of a system. The previous chapter concentrated on the mechanical structures constituting the system. This chapter describes the control mechanisms imposed on the material inside these structures while chapter 11 will treat the electrical system and computer software driving some of these control mechanisms. The general design aims expressed at the beginning of this part still hold. The various control parameters are treated individually in the following sections and put into context by the control philosophy at the end of the chapter.

10.1 Isobaric pressure control

Isobaric pressure control is a critical design parameter in this system as the VLE, upon which the system design and separation is based, is strongly dependant on it. Fluctu- ations in pressure will cause boiling points to ‡uctuate and the column’s temperature pro…le to change, thus making reboiler temperature control di¢ cult and a¤ecting conversion by shifting the thermal (and thus compositional) position of the reactive zone and changing the hydrogen partial pressure. Kister [1990] supplies many options for isobaric pressure control. It appeared that the two options depicted in Figure 10.1, namely vapour product rate variations and inerts pressure control, were the most suitable to this application. The vapour product rate variation for pressure control is de…nitely the simplest and uses the presence of non-condensable hydrogen to its advantage. However, the second option is not solely dependant on hydrogen to regulate the pressure, which is advantageous considering the experimental nature of the system and the fact that the hydrogen is being consumed in the reaction. It is also simple to connect the existing N2 laboratory utility to the o¤-gas line. Although this method is relatively costly as it results in a loss of inerts, it has a fast response [Kister, 1990] and allows tight

73 74 CHAPTER 10. PROCESS CONTROL

Off•gas From top Inerts product of column Utility and inerts From top PC of column

Off•gas PC product

Liquid Liquid Reflux to Reflux to distillate distillate column column product product

(a) (b)

Figure 10.1: Pressure control using (a) vapour product rate variations and (b) inerts pressure control

control of the column pressure. Column pressure is therefore maintained via a type of push-pull system (Figure 10.2).

The inert nitrogen (N2) utility stream is set to the desired column pressure and connected to the o¤-gas stream exiting the partial condenser located at the top of the column. The nitrogen is available as a utility and a pressure regulator will be required to sustain a constant nitrogen pressure to the system. Due to safety considerations a pressure relief valve is located on the partial condenser to prevent over-pressurization. A non-return (or check) valve prevents o¤-gas from ‡owing into the utility line.

Lastly, the N2 utility can also easily be integrated with the hydrogen feed line for purging of the column before start-up.

10.2 Gaseous and liquid feeds

The 1-hexene and hydrogen feeds are convenient as they both have chosen ‡ow rates and precisely known compositions. However, from chapter 8.3, these ‡ow rates and compositions must be tightly controlled not only for an accurate experimental methodology, but also for process control. Fluctuations in the feed temperatures will be slow (the ambient room temperature is controlled at ca. 25C) and will have a minimal impact on the column’stemperature pro…le as both hydrogen and 1-hexene have low cp values and will not require much energy to be elevated to the column temperature at the feed points. Fluctuations in the 1-hexene feed ‡ow rate, though, could have a signi…cant e¤ect as it changes the vaporization heat required to transfer the 1-hexene into the internal gas 10.2. GASEOUS AND LIQUID FEEDS 75

Inerts Utility

PR Off•gas product and inerts From top of column

LC Liquid Reflux to distillate column product

Figure 10.2: Pressure control in the CD system

stream, changing the thermal and compositional pro…les through the column and possibly demanding more power from the reboiler. Analogously, pulsations in the hydrogen feed ‡ow rate (and thus pulsations in the hydrogen partial pressure) will directly a¤ect the conversion in the reactive zone and thus not only the heat generated, but also the conversion, changing the temperature and compositional pro…le. The reactant feed ‡ow rates are thus important control parameters. A Series I isocratic HPLC (high pressure liquid chromatography) pump that can handle the required ‡ow rate and supply a pressure from 0 to 172 bar(g) was chosen. It has a RS232 connection that makes it possible to control it remotely from a computer. A non-return valve (one-way valve) is installed after it to prevent damage from material pushing back up the line from the CD column. A Brooks 5850S smart mass ‡ow controller (MFC) will be used to regulate the hydrogen utility gas ‡ow rate. An RS485 cable can connect the Brooks MFC to a Brooks readout and control unit (power supply), which in turn communicates with the computer via RS232. The use of RS485 makes future expansion simple as it allows multiple MFC’s to be daisychained and connected to the same power supply. The MFC has an internal PID loop and the computer merely supplies it with a set-point and monitors compliance with the set-point. However this can be achieved with a simple analog I/O card (see chapter 11) rather than via the more costly readout and control unit. From a cost and practical perspective the readout and control unit was thus not used despite a small loss in the additional (in this case redundant) functionality that it provides The hydrogen utility inlet pressure to the MFC is controlled at 6 bar(a) by a pressure regulator as a pressure drop is required over the MFC. A 0.5 m stainless steel in-line 76 CHAPTER 10. PROCESS CONTROL

Flow rate Error Linear (F low rate)

3.50 3.50 3.44

3.00 3.00

CAL IBRATIO N CO NDITIO NS Parameter Value Units 2.50 2.50 G as name Nitrogen [none] T emp eratu re 20 [°C] Inlet pressure 10 [bar(g)] O utlet pressure 6 [bar(g)] 2.00 2.00 Full•scale flow 3.42 [nl/min] y = 0.0344x R2 = 1

1.50 1.50

Flow rate [nl/min] rate Flow Error [% of flow rate] 1.00 1.00

0.50 0.50

0.00 0.00 0 10 20 30 40 50 60 70 80 90 100 Percentage of maximum flow rate [% ]

Figure 10.3: MFC calibration and error curve

…lter is installed prior to the MFC to protect it from particulate matter and a non-return valve after it to prevent damage from material pushing back up the pipe from the CD column. It was asked that the MFC be calibrated as shown in Figure 10.3 with the ProII predicted volumetric ‡ow (at STP) at 71%. This ensures that the ‡ow rates required are located in the middle of the MFC’scalibrated range of 0 - 3.42 ln/min for accuracy and ease of use purposes. The MFC fails closed to cut o¤ hydrogen feed in emergencies. The nitrogen utility is also connected to the hydrogen feed line for purging purposes. For this purpose it was speci…cally requested that the MFC should be able to handle nitrogen as well.

10.3 Re‡ux line con…guration

There are various con…gurations for the re‡ux portion of the CD column [Kister, 1990]. Fundamentally, it can be divided into two options namely those that use gravity and those that use mechanical means to e¤ect liquid ‡ow and level control (Figure 10.4). Both have certain advantages and both were considered for this system. Using gravity lines is simple and elegant. However, it neccesitates a vent line, which complicates the system and which also requires very accurate sizing of the pipe diameters, that is in turn di¢ cult given the experimental nature of the system. It also 10.3. REFLUX LINE CONFIGURATION 77

PR PR Inerts Off•gas Inerts Off•gas Utility product Utility product and inerts and inerts

Drain (NC)

Liquid Liquid distillate distillate product product Drain (NC)

(a) (b)

Figure 10.4: Main di¤erences between (a) forced ‡ow and (b) gravity lines 78 CHAPTER 10. PROCESS CONTROL requires considerable head space, long piping (consequently increasing heat losses), accurate level control, accurate distillate mass ‡ow rate measurements and implementation of safeguards and/or design considerations to prevent vapour from ‡owing into the re‡ux instead of the column top exit stream. These disadvantages may be circumvented by using forced ‡ow lines. Although this con…guration involves more mechanical, instrumental and control issues it allows for better control of the re‡ux line and, as will be seen later, may be used in conjunction with the distillate mass ‡ow rate to maintain a constant re‡ux ‡ow rate.

10.3.1 Level control

Surprisingly enough, e¢ cient level control proved to be one of the most di¢ cult aspects of the design. Perry et al. [1997] names a few di¤erent types and [Kister, 1990] once again supplies excellent practical suggestions in their use. The following options were considered and are schematically presented in Figure 10.5:

1. An over‡ow type of control

2. Using a ‡oat valve

3. Magnetic level control

4. Optical level control

Using an over‡ow system would de…nitely adhere to the KISS principle set out at the beginning of this part. To achieve level control in this case is simple (as shown in Figure 10.5). Loop the distillate product line up making sure that its apex is at the exact level required for the liquid height in the condenser’s re‡ux chamber and then down to the pressurized distillate product tank. By equalizing the pressures between these three points (the re‡ux chamber vapour phase, distillate line apex and the product tank) to prevent siphoning, choosing a pipe that can handle large capacities and by ensuring that the product tank is below the re‡ux chamber the liquid should exit naturally through the elevated product line and simultaneously control the liquid height just as weirs do in equi-pressure atmospheric systems. However, there are three disadvantages to this system. Firstly, although it maintains the liquid below a certain high level, it does not achieve low level control to prevent the re‡ux line from running dry. The latter is highly undesirable and could cause serious damage to a re‡ux pump should one be used. Also, the available Precisa balance used to measure the distillate mass ‡ow rate (see appendix F) cannot handle a load larger than 4 200 g which precludes the use of a heavy, pressurized steel distillate product container. Lastly, it is relatively di¢ cult to re-set the height online as it entails re-bending the distillate product tube to change the apex height. 10.3. REFLUX LINE CONFIGURATION 79

Inerts Inerts Utility Utility

PR PR Off•gas Off•gas product product and inerts and inerts From top From top of column of column

PI PI

Reflux to Reflux to column column Liquid Liquid Distillate Distillate

(a) (b)

PI PI

LC LC

LLA LLA

Reflux to Reflux to column column Liquid Liquid Distillate Distillate

Figure 10.5: Level control methods: (a) Over‡ow type, (b) ‡oat valve, (c) magnetic sensors and (d) optical sensors 80 CHAPTER 10. PROCESS CONTROL

A ‡oat valve introduces mechanical di¢ culties. It is used with great success in especially large tanks, but will be di¢ cult to implement in the small CD system. Ad- ditionally, it also does not have low level control, cannot be re-set at a di¤erent level (it has to be inserted through a bored hole in the chamber wall) and there are certain minor sealing problems that have be overcome. Magnetic coupled devices for ‡ow control are also of the ‡oat actuated type [Perry et al., 1997] and uses a hollowed or light magnet on a ‡oat that moves along a vertical guide as the liquid level changes. Magnetic detection of the magnet position yields the liquid level, which can then be used either directly or indirectly to open or close valves. This type of detection is, however, apparently more e¢ cient in large scale applications. Optical level sensors appear to present the best solution for level control. An infrared LED transmitter shines a thin beam through a glass tube (connected to the interior of the liquid containing vessel) to an infrared transceiver (detector) located in the same horizontal plane in a straight line from the transmitter. Infrared light is used to prevent the visible light in the atmosphere from interference with the signal. When liquid passes through this infrared beam it either increases or decreases the intensity of the signal received by the transceiver and the optical sensors detect the liquid. Consider the latter case where a broken beam implies that liquid has been detected in the beam’s path and vice versa. A broken beam generates a 0 V and an unbroken beam a +5 V signal. This signal triggers a solenoid valve on the vessel’sselected outlet line to either open and drain the vessel (high level - HL), close and allow the liquid height to rise above the low level (LL) or shut down the system to protect peripheral equipment from running dry (low level alarm - LLA). The main advantages of this approach are that it executes non-invasive on/o¤ control by keeping the sensors outside the vessel, thus minimizing their interference on the system and making it easy to adjust the controlled heights if necessary. Additionally, it a¤ords the operator direct ocular veri…cation of the liquid level. The disadvantages are, …rstly, that if the glass is not kept clean the signal will be distorted or broken resulting in inaccurate control. Secondly, the glass represents a weak point in the system and tight sealing between glass and metal can be di¢ cult, whereas stainless steel may be used for a magnetic coupled device. Fortunately, the mechanical di¢ culties involved are not insurmountable - as discussed in section 9.1. Glass can handle relatively high pressures if the correct length and wall thickness is chosen, but it must be protected from lateral shock to prevent it from breaking. Optical level sensors will therefore be used to control the re‡ux chamber liquid level. Refer to subsection 11.5.3 for more detail regarding the related signals and software control. Mechanically, the optical transmitter and receiver of each sensor pair are diametrically aligned on opposite sides of the sightglass tube and housed in a movable Te‡on block. As explained previously there are three sensors pairs: high level, low level and low level alarm. The Te‡on blocks can slide up and down the tube to vary the 10.3. REFLUX LINE CONFIGURATION 81

Figure 10.6: Two methods for re‡ux ratio control: (a) re‡ux splitter, (b) sutro weir level height control parameter, but the spacing between the sensor pairs are limited to a minimum of 10 mm due to the size of the blocks. The glass tube is 110 mm in length, 6 mm in outer diameter with a 1.5 mm wall thickness and a safe working pressure of 30 bar(g).

10.3.2 Re‡ux ratio (R = V_L=V_D)

It is clear from equations 8.2 to 8.7 that disturbances in the re‡ux ratio propagates through the entire column and that e¤ectively controlling it is thus paramount to stable control. Kister [1990] suggested four methods of re‡ux control:

1. Internal re‡ux control

2. Gravity re‡ux control cycling

3. Sutro (proportional) weir dividers

4. Re‡ux splitters

"A re‡ux splitter is an on/o¤ solenoid valve operated device actuated by a timer. The timer setting corresponds to a …xed re‡ux distillate ‡ow ratio". A high frequency solenoid valve is required to achieve uninterrupted ‡ow. Kister [1990] recommends that 82 CHAPTER 10. PROCESS CONTROL the use of re‡ux splitters be restricted to batch and small distillation applications and suggests a sutro weir for continuous distillation. Figure 10.6 illustrates the concept of a sutro weir. Liquid enters the inside tank and over‡ows into the encapsulating tank at a ratio determined by the liquid height in the smaller tank and the geometrics of the weir opening.

Assuming v1 and v3 to be very small relative to v2 and v4 (because of the large dif- ference in diameter between the tank and pipes), negligible frictional losses and pressure drops between points 1,2,3, and 4 and then applying Bernoulli’sequation:

2 2 _ P1 P2 v1 v2 W + + g (z1 z2) = + 2 = m_ 2 v2 + g (z1 z2) = 0 2 _ ( VL )2 Apipe + g (c + h ) = 0 2 1

V_L = Apipe 2g (c + h1) (10.1) p From French [1985] the equation for a sutro-weir is:

1 V_sw = CDb 2ga h1 a (10.2) 3 p

However, in this case V_sw = V_D and it is thus possible to state the following:

V_ R = L V_D V_ = L V_sw

Apipe 2g (c + h1) = 1 CDbp2ga h1 a p 3 Apipe (c+ h1) = 1 CDbpa h1 a p 3 (c + h1) = constant 1 (10.3) h1 a p 3 There are quite a few advantages to using a sutro weir to control the re‡ux ratio. It is a simple, non-‡uctuating system that gives a uniform, consistent re‡ux ratio. Unfortu- nately, the disadvantages in using the sutro weir in this system outweigh the advantages. Firstly it entails narrow control of one height and monitoring of the other to prevent it from over‡owing, which is di¢ cult due to the small size of the column. Secondly it will be bulky compared to the rest of the system thus supplying more surface area for heat loss. Additionally, there are mechanical di¢ culties involved in making the 10.4. REBOILER 83

sutro weir ‡exible to easily and accurately supply a non-discreet range of re‡ux ratios - especially given the sealing (and subsequent safety) problems encountered to make the high-pressure, high-temperature system leak-free. Controlling the re‡ux ratio with a sutro weir is made di¢ cult due to the small size of the system. It was thus decided to use a forced circulation system rather than a gravity line. The re‡ux metering pump is controlled from the computer via an Emotron frequency inverter. The computer converts the distillate mass ‡ow rate (measured online by an electronic balance) to a volumetric ‡ow rate, multiplies it with the chosen re‡ux ratio to obtain the desired re‡ux volumetric ‡ow rate and outputs this ‡ow rate to the pump’s frequency inverter.

10.4 Reboiler

As in non-reactive distillation heat is added to the bottom of the system by a reboiler; lost to the atmosphere because of temperature gradients between the system’sinner and outer surfaces; and removed by a condenser at the top of the column. Additionally, in CD one must also consider the exothermic heat generated by the reaction.

10.4.1 Heat duty control

Any parameter signi…cantly a¤ecting temperature or pressure must be tightly controlled as it consequently also signi…cantly a¤ects the column’sVLE and compositional pro…le. The heating element power input into the system is thus a critical design parameter that must be controlled as tightly as possible as it directly a¤ects the temperature and indirectly the system pressure through vapour generation. Two options are available. Either the reboiler temperature or heat duty can be controlled as the set-point. Since 1-hexene and n-hexane are very close boiling, accurate temperature control will be very di¢ cult and since the reboiler temperature is essentially set by the boiling liquid (for a certain composition) the reboiler temperature should be relatively stable. It was thus decided to rather control the heat duty, but, since temperature control entails calculation of the heat duty in any event, the extension of the control philosophy to temperature control is thus simple and the control program was designed to accommodate both methods. Reboiler temperature control is achieved via a standard PID (proportional-integral- derivative) feedback loop that measures the bottoms liquid temperature and regulates the amount of power delivered to the heating element. Figure 10.7 shows that the reboiler thermocouple (T-R) is used to measure the temperature of the liquid (control variable) in the reboiler inventory. The temperature measuring point is in the centre of the reboiler diameter and below the low level alarm (thus between the heating coils). 84 CHAPTER 10. PROCESS CONTROL

Setpoint Computer PID Temperature [°C] Feedback Loop OR Heat Duty [W] Determines what power is required to satisfy the Connector block Computer card supplied setpoint TC Thermocouple Thermocouples and converts it to settings for the pulse width modulator (PWM) signal that Regulated power Heater regulates the Mains Computer card power supplied to power Solid state Relay Connector block 220V, Counter/Timer the heater by the SSR Counter/Timer 50Hz(AC) generates PWM SSR.

Computer power

Figure 10.7: Schematic representation of the PID feedback control loop used to maintain the reboiler temperature [C] or heat duty [W] set-point

The mV reading (optional control variable) from the thermocouple is converted into C and compared to the set-point. A LabVIEW PID control block then processes the input temperature and assigns the required heater power (manipulated variable) using a pulse width modulated (PWM) output via a solid state relay (SSR). A constant heat duty can also be forced by the user for heat duty control. The PWM signal is generated by the software itself (see section 11.5.2) and is transmitted to the SSR hardware which controls the percentage of the total power received by the heating element by switching it hard-on or hard-o¤.

10.4.2 Level control

The same methods used and discussed in subsection 10.3.1 for the re‡ux drum level control can, in principle, be used to control the reboiler level as well. There is one added complication namely that the liquid is boiling and thus the liquid surface height ‡uc- tuates erratically because of the rising gas bubbles (Kister [1990] makes the distinction between the "actual" and "apparent" liquid height) making control via the over‡ow and ‡oat valve level controllers more di¢ cult. Once again, the fact that the optical level sensors are located outside the vessel is an advantage. Also, the vapour does not bubble through or boil in the glass tube as it is located on the side of the vessel away from the heating element and cooled by the atmosphere. This a¤ords a more stable liquid level. Lastly, using the optical sensors simplify the design and computer control integration as it merely demands duplication of the system used at the re‡ux drum. 10.5. RESULTING P&ID AND CONTROL PHILOSOPHY 85 10.5 Resulting P&ID and control philosophy

The completed P&ID is given on the following fold-out page and summarizes the design situation thus far. A quick summary is warranted here before continuing to the detailed discussion of the control system in the next chapter. 1 8 " tubing liquid sampling points are supplied for the hydrocarbon feed, distillate product and bottoms product lines and for the reboiler inventory (should the system ever be run as a batch operation) for monitoring purposes. In the case of the bottoms product line a cooler is used for safety and practical purposes to reduce the pressurized liquid’stemperature to below its normal boiling point. It was considered to use a two- valve sampling system to prevent the potentially unsafe situation where the pressurized line shoots the liquid out of the sampling point. This entails opening the tube side valve, …lling the tube between the valves with the sample, closing the tube side valve and then opening the atmospheric side valve to obtain the sample. Such a system was not used as the chosen needle valves should supply su¢ cient control and tight shutt-o¤ (to prevent leakage) of the liquid sample’s‡ow. The feed ‡ow rate from the hydrocarbon tank is controlled by a HPLC pump and the hydrogen utility gas ‡ow rate by a mass ‡ow controller. Both set-points are …xed. A small pressure drop is required over the MFC and the inlet pressure is thus maintained by a pressure regulator, which reduces the 100 bar(g) utility pressure to the applicable range. An in-line 0.5micron …lter at its inlet protects the MFC from solid particulates and a non-return valve at its outlet prevents back pressure to force reverse ‡ow through the line. The hydrocarbon feed tank is slightly elevated above the HPLC pump to supply the necessary positive pressure to the pump. Pressure control is achieved by connecting the pressure regulated (inert) nitrogen utility to the o¤-gas line exiting the partial condenser in the previously described push- pull system. Once again a non-return valve prevents o¤-gas to push back up the nitrogen utility line. A connecting line and three-way ball valve allows the nitrogen utility to be routed through the MFC and into the system for purging purposes. Two 1l catch pots (one in both the nitrogen and hydrogen gas lines) serve as added protection against back-pressure forcing liquid into the gas lines. The retained liquid can either be drained or forced back into the column once the correct pressure gradient is re-established. The reboiler heat duty control variable is maintained at its set-point via a feedback loop that uses the amount of power supplied to a 1 kW heating element as the manipulated variable. This power regulation is accomplished with a software driven pulse width modulator (PWM). Heat is removed at the top of the column with a two-stage partial condenser that has two constant ‡ow cooling mediums: tap water and a refrigerated glycol-water mixture. The tap water ‡ow rate is …xed with a metering valve and that of the glycol-water mixture is set on the refrigerator and checked on a rotameter. 15 86 CHAPTER 10. PROCESS CONTROL

Thermocouples will supply a temperature pro…le across the entire system. Two sets of three optical sensors keep the liquid levels in the reboiler and partial condenser within tolerable limits. The high and low level infrared transmit-receive pairs respectively opens and closes the relevant product outlet solenoid valve, while a low level alarm pair re-a¢ rms that the valve is closed and additionally triggers an emergency shutdown. In the case of the reboiler the latter is a critical safety issue that prevents the reboiler from running dry, while in the case of the condenser the re‡ux pump may su¤er considerable damage if it should run dry. As for the distillate and bottoms product mass ‡ow rates, they are measured using balances. The distillate mass ‡ow rate is then used in a feed back loop to the re‡ux pump to control the re‡ux ratio. 6 5 4 3 2 1

T-HC HPLC-1 MFC-1 CD-1 P-RD C-DP E-1 T-DC6/TBC6 NOTES HYDROCARBON FEED TANK FEED PUMP MASS FLOW CONTROLLER CD COLUMN REFLUX PUMP PARTIAL CONDENSER REFRIGERATOR PRODUCT STORAGE TANKS Temperature Ambient [°C] Flow 0.01 - 10 [ml/min] Capacity 0 - 3670 [ml/min] Temperature < 240 [°C] Flow 0 - 14.2 [l/h] TypeShell and tube [-] Cooling (20°C) 415 [W] Temperature Ambient [°C] Pipe specifications Pressure 1.01325 [bar] Pressure 0 - 172 [bar] Press. (out) 1 - 6 [bar] Pressure 1 - 6 [bar] Press. (max) 20 [bar] Area 57453 [mm 2] Heater cap'ty 1000 [W] Pressure 1 [bar] Material prefixOD [inch] Pipe MOC Line number Orientation Horizon'l [-] Fluid density 662 [kg/m 3] Press. (max) 100 [bar] MOC SS316 [-] Fluid density ca. 662 [kg/m 3] Duty650 [W] Cooling med. Water-Glycol [-] Orientation Horizon'l [-] MOC Glass [-] Type HPLC [-] Temperature 70 [°C] Size Type Dosing [-] Shell Tube Type RTE-8 [-] MOC Glass [-] Size MOC SS [-] Valve MOC Viton [-] Height 2000 [mm] MOC SS316 [-] Temp. (tap) 30/40 124/60 [°C] Temp. (in) 10 [°C] Size Height 240 [mm] Remote RS232 [-] Valve norm. Closed [V] Inner diam. 47 [mm] Diaphragm PTFE [-] Temp. (refr.) 2/7 60/7 [°C] Temp. (out) 2 [°C] Height 240 [mm] H2 - 0.125 - SS316 - 01 Outer diam. 130 (base) [mm] Power 220/60 [V/Hz] Power 24 [V(dc)] Internals Sulzer CY [-] 230 [V] Pressure 1 6 [bar] Pump Outer diam. 130 (base) [mm] Motor Material Description Material Description D Internals N/A [-] Reboiler Kettle [-] 3/4 [ph/pole] Phase L G/V [-] Max. capacity 13 [l/min]Internals N/A [-] D (1C6) Mainly 1-hexene N2 Nitrogen N/A [-] 1000 [W] Power (shaft) 250 [W] MOC SS316 SS316 [-] Head 5.2 [m] N/A [-] 1C6 1-hexene (nC6) Mainly n-hexane Extractor fan G Glycol P Plastic T Atmosphere N2-0.125-SS316-18 5 H2 Hydrogen SS316 Stainless steel 316 Nitrogen outside T (H2/N2)-0.125-SS316-12 (H2) Mainly hydrogen TW Tap water NV-N2 1 CV-PE building PR-N2 CP-N2 FM-Off Abbreviations SV-1 SV-0.5-P-19 (FO) T-0 TI TW-0.5-P-01 Abbr. Description Abbr. Description Tap water H H H BV-CPN2 P-C C Condenser HF Hydrocarbon feed 1 2 NV-TW 3 TI T-E1 MTC B Bottoms HPLC HPLC pump (1C6)-0.875-SS316-07 U 11 PI T Catalytic distillation 7 C-DP 6 CD MFC Mass flow controller P-HF H5 column

TI T-1 H4 D Distillate NC Normally closed PI MTC 12 E Heat exchanger NO Normally open MTC 9 G-0.5-P-13 H 10 F Filter P Pump U H 6 TI 6 FI FC Fail closed RM Rotameter MC MTC H H 1 1 7 11 FO Fail open SV Safety valve T T-TWin G-0.5-P-14 MC 3 U HC Hydrocarbon T Tank CV-1C6 2 BV-SLD 14 E-1 L-OD1 RM-1 (NC) Instrument identification letters Description LC Letter TI T-2 First Second Third MTC 2 A Analysis Alarm LLA B Bottoms Bleed

(1C6)-0.25-SS316-09 C Control Control L-OD2 D Distillate Distillate / Drain

1C6-0.125-SS316-05 U11 U12 E Equilization C F Flow Feed C CV-RD TI 1C6-0.125-P-02 H High HPLC-1 TI T-3 NV-RD I Indicator U1 T2 MTC 3 T-C K Timer

Vent-0.25-P-20 L Level / Low Level O T Optical NV-SF 4 P Pressure Product (1C6)-0.125-SS316-15 R Reflux Reboiler T-HC S Sample 1800 1600 NV-SD T Temperature 1400 Sol-D FM-D V 1200 H Valve Valve 1000 12 800 (FO) (FO) W Weight 600 TI T-4 400 MTC X Miscellaneous 4 BV Ball valve Mixed P-RD CV Check valve 1C6-0.25-SS316-10 hydrocarbons FM Fine metering (1-Hexene) NV Needle valve PR Pressure regulator U U T-DC6 SL Seal loop 8 9 1800 1600 Sol Solenoid valve Ambient T 1400 1200 1000 C distillate 800 SCALE TI TI T-5 6 600 (Concentrated 1-hexene) 400 MTC 5 Thermometer Not drawn to scale W-D DRAWN BY: REVISED: N2-0.125-SS316-03

P-N2/H2 Pump TI T-6 ______MTC power PI 6 J.J. Nieuwoudt 13/05/2005 B FC B H2/N2-0.125-SS316-06 MC 3 APPROVED BY: DATE Hydrogen MC TI T-7 NV-H2 TV-HN F-HN U U CV-H2 4 MTC PR-H2 2 MFC-1 3 7 (FC) H2-0.125-SS316-04 CP-H2 L-OB1 ______TW-0.5-P-11 T-R CV-B LC L.H. Callanan (US) BV-CPH2 E-BP T TI 7 MTC 8 U10 H13 Sol-B FM-B LLA H NV-SB 8 (FC) (FC) MTC 13 T-EPB ______

U4 TC L-OB2 T-BC6 1800 K.P. Möller (UCT) NV-SR TI TI 1600 1400 1200 1000 U5 T-TWout C bottoms 800 MTC 15 6 600 400 (nC6)-0.125-SS316-08 (Concentrated hexane) Reboiler TI H MTC 9 P&ID power 14 (nC6)-0.125-SS316-16 W-B T-B U CATALYTIC DISTILLATION PROJECT 13 TW-0.5-P-17 Drain Continuous system

Stream numbers 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 CD SYSTEM Temperature [°C] Ambient 25 25 25 25 25 124 132 7 7 40 7 2 10 7 50 0 Ambient Pressure [bar] 3 1 6 6 6 6 5 5 5 5 3 5 1 1 5 5 3 5 DESCRIPTION Phase [-] L L G G L GG,V/LL L L L G L L L L L G A Mass flowrate [g/h] 21600 101.00 Purging 3.59 101.00 3.59 4142 46.67 4084 4083.64 21600 8.16 43200 43200 49.95 0.00 21600 Varies Pipe and instrumentation diagram of the catalytic A Molar flowrate [mol/h] 10693 1.19 Purging 1.78 1.19 1.78 51 0.54 49 48.56 10693 1.83 21386 21386 0.59 0.00 10693 Varies distillation system 1-Hexene [mol/mol] 0.00 0.50 0.00 0.00 0.50 0.00 0.87 0.01 0.90 0.90 0.00 0.03 0.00 0.00 0.90 0.01 0.00 0.00 DRAWING NUMBER REVISION NO. n-Hexane [mol/mol] 0.00 0.50 0.00 0.00 0.50 0.00 0.09 0.99 0.10 0.10 0.00 0.00 0.00 0.00 0.10 0.99 0.00 0.00 JJN/09112003-01 1 Hydrogen [mol/mol] 0.00 0.00 0.00 1.00 0.00 1.00 0.04 0.00 0.00 0.00 0.00 0.97 0.00 0.00 0.00 0.00 0.00 0.00 REFERENCE NUMBER SHEET Water [mol/mol] 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.00 0.00 1.00 1.00 0.00 0.00 1.00 0.00 1 OF 33

Composition Nitrogen [mol/mol] 0.00 0.00 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.00 6 5 4 3 2 1 88 CHAPTER 10. PROCESS CONTROL Chapter 11

COMPUTER CONTROL SYSTEM

This section considers the CD column’s continuous computer control, monitoring, logging, report generation and emergency shutdown system which is routed through the graphical programming language LabVIEW 7.1 Express. Safety considerations were once again interwoven with the design process.

11.1 Basic software-hardware structure

The entire process control system may be divided into 7 di¤erent parts as depicted in Figure 11.1 and summarized below:

1. User

2. Computer software

3. Computer cards

4. Terminal connector blocks

5. Electronic box

6. Power supply box

7. Instrument control receive/reply

The user manipulates certain control variables either through the software computer interface or directly via switches on the instruments themselves and/or electronic and power supply boxes. The software relays and retrieves information from the computer cards, which in turn exchanges information with the rest of the system through the terminal connector blocks. Signals sent or received by the latter are manipulated and/or converted in the electronic box. Some are connected to the power supply that controls

89 90 CHAPTER 11. COMPUTER CONTROL SYSTEM 25 Pin DB

25 Pin

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DIN B • l o S to to 48

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D • l o S 15 Pin 16

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15 Thermocouples

Channels 1•15 (+,•)

P S 25 Pin Electronic Box

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S 220 to 12V Transformer 2 e c n a l a B

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R S S

D • l o S Relay

Mechanical R S S

AC B • l o S Power Supply Box Wall socket 220V, 50Hz 11.2. PROGRAM LAUNCHER AND MAIN GRAPHICAL USER INTERFACE (GUI)91

220 V AC power ‡ow to the various instruments and that also contains an emergency shutdown mechanism. Various aims were set for the successful completion of the program. To make the program code robust it was decided to use a generic program structure that could, in principle, be used as a template for other similar control systems and which would also facilitate future expansion (e.g. the addition of a control loop) if necessary. This was achieved by using control loops encapsulated within independent subVI’s1 so that additions to the program would have a minimal impact on the existing code. The main subVI’scan be divided into the following basic groups:

1. System Con…guration

2. Graphical User Interface (GUI)

3. Data Acquisition (DAQ)

4. Instrument control loops

5. Error Handling

6. Shutdown and emergency shutdown

For safety reasons each instrument is controlled by a separate, independent control loop that is called (and initiated) only once by a program launcher. Thus, if one of the control loops should crash or execute incorrectly, the others would continue una¤ected. Data acquisition, error handling and shutdown is centralized and also handled by separate, independent subVI’s. To ensure this independence the main subVI’scommunicate by publishing data to datasockets and subscribing to datasockets to retrieve the stored data. It is impossible here to discuss the extensive volume of intricacies and safeguards built into a program that is intuitively structured. Rather, the focus here will be to consider the way in which it …ts into the larger control process while highlighting the salient facts regarding the more intricate programming.

11.2 Program Launcher and Main Graphical User Interface (GUI)

The graphical user interface’s(GUI’s) evolved form is shown in Figure 11.3 (see Appendix I for a graphical key). It is a representation analogous to the actual physical system.

1 A subVI in LabVIEW is analogous to a subroutine in FORTRAN. The VI or Virtual Instrument (LabVIEW equivalent of FORTRAN’s main program) calls and communicates with smaller blocks of code or subVI’s (LabVIEW equivalent of FORTRAN subroutines) that execute certain tasks and/or return information to the caller VI. 92 CHAPTER 11. COMPUTER CONTROL SYSTEM .txt Config STOPPED Balance Bottoms 3 4 2 1 5 6 12 7 11 8 10 9 execute ) Y/N Y/N Execute sequence Start•up/Shutdown Shutdown? or Emergency (Check whether Start•up?, (Check whether N Shutdown? is TRUE (Y) then (Y) TRUE Shutdown? is 3 4 2 1 5 6 12 7 11 8 10 9 Balance Distillate 3 4 2 1 5 Start•up? 6 12 7 11 Shutdown? 8 10 9 (Emergency) stopped? .txt Control loops Config Y Pump Reflux 3 4 2 1 5 6 12 7 11 8 .txt 10 9 Shutdown Sequence Reflux 3 4 2 Level Control 1 5 6 12 7 11 8 10 9 Errors Main GUI) Error Logger the various control and writes it to a text file and maintenance loops’ Error maintenance loops’ Handler reentrant SubVI’s; (Reads the error arrays from (Reads the error arrays Source 3 4 2 1 5 6 12 Reboiler 7 11 8 10 9 Create Timing 3 4 2 Level Control 1 5 6 12 7 11 8 10 9 3 4 2 1 5 6 12 7 11 8 10 9 .xls Control: 3 4 2 Temperature 1 5 6 12 7 11 8 10 9 .txt Config Data Acquisition 3 4 2 1 5 6 12 7 11 8 10 9 Pump HPLC 3 4 2 1 5 6 12 7 11 8 10 9 Figure 11.2: Overall ‡ow diagram of control program Data Main Front Panel Controller Mass Flow 3 4 2 1 5 6 12 7 11 8 10 9 3 4 2 1 5

6 12

7 11 8 10 s p o o L l o r t n o C 9

m a r g o r P n i a M 3 4 2 1 5 6 12 7 11 8 10 9 Front Panel Display N Y Y Y N RE• loops Stop? Display START Compile structure Configure? Configure? configurable Sequence of Front Panels Generate tree program loops pathname list of without executing

r e h c n u a L m a r g o r P 11.3. START-UP AND SHUTDOWN 93

Figure 11.3: The CD control system’smain graphical user interface

Except for start-up, shutdown and emergency shutdown control the main GUI supplies very little direct control as such, but rather functions as a monitoring station showing a summary of the system’sstatus and various settings, variables and conditions. More speci…c instrument control (such as settings of set-points) is realized by clicking on the instrument’sbutton to open its front panel, which contains a more comprehensive GUI of its sometimes unique controls and indicators.

11.3 Start-up and Shutdown

The aim of the start-up and shutdown system depicted in Figure 11.4 was to facilitate ‡exibility while still retaining safety during the critical periods of column operation at which the system behaves transiently and not at its designed steady state conditions. Start-up can be initiated only by the user while the shutdown and emergency shutdown can by triggered by either the user or the Error Handler VI. A user can select the sequence in which the main equipment is initiated and can also choose the delay between the various equipment start-ups. Shutdown o¤ers the same ‡exibility of design. Each timed or while loop has its own uniquely named start-up and shutdown boolean global variables, which act as equipment speci…c on and o¤ switches and which execute the 94 CHAPTER 11. COMPUTER CONTROL SYSTEM relevant piece of code when set to TRUE. In the start-up and shutdown cases the program checks equipment compliance with the relevant command. If con…rmation is not achieved before a certain time has elapsed the user is informed via a timed two-button message window which takes a prede…ned default action after 10 s if the user does not supply any response to the query. In the case of shutdown an emergency shutdown is triggered. Each piece of equipment has its own start-up and shutdown sequence embedded in its instrument control loop as will be discussed later in section 11.5. However, the emergency shutdown operates outside the control loops and uses a two-step safety procedure. As with shutdown an emergency shutdown can be triggered either by the user or the Error Handler. In both events the boolean emergency shutdown global variable is immediately set to TRUE and then read by the Toggle Pulse VI and the Start-up and Shutdown VI. The latter VI takes action by simultaneously setting the unique boolean global variable shutdowns of each of the VI’sto true to commence each VI’sshutdown. However, at about the same time the Toggle Pulse VI discontinues poling a digital pin which is routed through a small circuit to the mechanical relay located in the power supply box. If the circuit is not toggled TRUE-FALSE every 5 s it cuts power to the entire system via the mechanical relay. This excludes the computer which then has time to run its shutdown con…guration scripts and save the Excel datasheets and other logger text …les.

11.4 Data Acquisition (DAQ)

A PCI6014 Multipurpose DAQ card and NI4351 thermocouple card were bought from National Instruments for data acquisition purposes. These cards act as "interpreters" between the physical channels that communicate with the column hardware, sensors and other instrumentation, and the virtual channels with which LabVIEW in turn communicates. Their respective terminal block accessories were also designed to make it easier to connect individual signals to the cards. The main body of the DAQ Logger VI is contained within a timed loop: a while loop that executes on the beat of a periodic timing source. In this particular case the timing source is the oscillating counter/timer on the PCI 6014 card as it yields a much higher accuracy when compared to the Windows system clock. The timing source’s selected period sets the rhythm for the control program as it also determines the control loops’repetition rate. Thus, at …xed intervals (default 5 s) data is retrieved from the cards, time stamped and logged in an Excel …le. Note that the cards themselves operate at a much higher resolution. Information regarding the names and units of the various parameters are only extracted on the …rst iteration. 11.4. DATA ACQUISITION (DAQ) 95

Initialize variables (amongst other Start•up = False; Shutdown = False) CALLED Configure SubVI (load/save as default) Call Datasocket Open definitions subVI Datasockets START N While Loop

Assign as Y Assign as Default? Default

Y True Emergency Start•up = ? Shutdown? False N N Shutdown? Y

Y Start•up = ? Start•up = TRUE Shutdown = TRUE N Start•up sequence Shutdown sequence Emergency Shutdown Set the uniquely named start•up Set the uniquely named shutdown Simultaneously set all the control global variable (acts as an “on switch”) global variable (acts as an “off switch”) loops’ uniquely named shutdown of each control loop VI to TRUE in the of each control loop VI to TRUE in the global variables to TRUE and stop user specified sequence. user specified sequence. oscillating the digital pulse.

Start•up sequence Y All VI’s: VI Shutdown = TRUE completed? VI Shutdown = TRUE

N VI Start•up = TRUE

N Continuous N Achieved? loop? Discontinue digital pulsing Y This occurred immediately when the Error Handler set the Emergency Y Shutdown global variable to TRUE , but re•do for safety purposes. Y Y Note: The digital pulse switches high N Extricate from and low periodically. It is routed Last VI? Loop? through a circuit connected to a mechanical relay. When it stops, the mechanical relay cuts power to all the N equipment except the computer. Next VI

Error False Shutdown=? Re•loop Handler True

STOP While Loop Close configuration file reference Error STOPPED Handler SubVI Close Datasockets

Figure 11.4: SubVI start-up and shutdown methodologies 96 CHAPTER 11. COMPUTER CONTROL SYSTEM

The NI4351 cards are specially designed for high accuracy temperature measurements and its terminal block accessory contains in-built cold-junction compensation. Additionally, it has 8 DIO pins. K-type thermocouples were used. Upon each 5 s iteration the 15 thermocouples’mV signals are converted to temperatures, quickly read directly into the DAQ Logger VI, built into an array and saved to the Excel …le. Data from the PCI6014 card follows a slightly di¤erent route as the card does not only monitor, but also sends information. It can also utilize the new DAQmx function in LabVIEW, which makes it slightly easier to decentralize acquisition and control by assigning tasks to each channel. Each control loop thus communicates directly with its relevant channels. This is combined with any user set-points and other control parameters speci…c to that control loop and is then written to the loop’s own unique datasocket from where it is read by the DAQ Logger VI and added to the array that is saved to the Excel …le. The DAQ Logger VI is illustrated in Figure 11.5.

11.5 Instrument control loops

Figure 11.6 shows a ‡ow diagram of an instrument control loop’sstructure. As may be seen it is generally possible to discern seven di¤erent stages:

Con…guration The program opens, retrieves and loads the user or programmer’scho- sen default settings

Initialization Communication channels are opened (more speci…cally datasockets and DAQ channels) and variables initialized

Standby The control loop has been primed and is ready to initiate start-up on the user’scommand

Start-up A start-up command has been received and has triggered a start-up procedure unique to the relevant loop

Execution Start-up has been achieved and the loop now executes its main purpose

Shutdown A shutdown command has been received and the loop is running its prede- …ned shutdown script

Closure Open references are closed and the Error Handler does a …nal check before the VI code ends

The four program states Standby, Start-up, Execution and Shutdown comprise the main body of the loop and the other stages the peripheral code. The four states are 11.5. INSTRUMENT CONTROL LOOPS 97

11 12 1 10 2 9 3 8 4 7 6 5 Execute Control Algorithm section of the DAQ SubVI This is only the DAQ section of the complete subVI (see elsewhere for complete diagram) and does not depict e.g. the start•up and shutdown sequences or the configuration subVI. Note: timed loop termination is only possible upon the next loop iteration where the “Shutdown” case instead of this one will be executed.

Call Datasocket definitions subVI Read the data of When data written to a each datasocket Build datasocket is retrieved and then array (read) the data’s structure must be known unbundle the of data (e.g. Boolean, 32 bit data integer, word)

First Call? N Y

Extract headings and units for data

Initialize Initialize headings; data’s units to an empty array T Initialize Measured Initialize temperature data to an empty array temperatures

Build array of 11 12 1 10 2 9 3 8 4 7 5 data 6 DAQ card counter/timer Run information Researcher, Build array of Align array Experimental series’ headings rows; columns name Unique name.xls Compiled from experimental series’ .xls name and date•time

STOP Error Initialize Shutdown=? Initialize to NO ERROR Timed Loop Handler

Figure 11.5: Main body of the data acquisition subVI 98 CHAPTER 11. COMPUTER CONTROL SYSTEM encapsulated within the timed loop and are separated by TRUE/FALSE case structures with the Execution-Shutdown case inside the Standby-Start-up case. In the case of a control loop the execution mode personi…es the main purpose of the VI and maintains the steady state control of the equipment.

11.5.1 Gaseous and liquid feeds

The focus here is on the hardware-software interface of the equipment discussed in the previous chapter. The HPLC pump allows for RS232 serial communication with the computer and is controlled in this way. The Brooks 5850S MFC is usually connected to a Model 0152 or 0154 Readout and Control Unit which can control up to four MFC’svia RS232. However, …nancially the control unit costed approximately as much as the MFC itself and practically it simply supplies a 15 V(dc) power supply and a 4-20 mA set-point to the MFC with a 4-20 mA set-point return. The former is easily supplied with a 220 V(AC) mains to 15 V(dc) transformer followed by an AC to DC electronic circuit board converter, while the latter can easily be supplied and controlled by LabVIEW and the already purchased DAQ card. A calibrated 0-5 V(dc) analogue output ‡ow rate set-point is supplied by LabVIEW on the bought PCI6014 card, converted to 4-20 mA by an electronic circuit board housed in the electronic box and fed to the appropriate pin on the MFC’s15 pin DB connector. A 4-20 mA signal return (converted back to 0-5 V(dc) for compatibility with the DAQ card) is required for the PID control in LabVIEW to ensure that the actual ‡ow rate corresponds to the required set-point.

11.5.2 Reboiler heat duty control

If temperature control is employed, the reboiler temperature is measured by a thermocouple, relayed to LabVIEW through the NI4351 card and compared to the chosen set-point by a PID VI, which then manipulates the amount of power supplied to the heating element in order to maintain the temperature at the desired value. As explained in section 10.4.1, however, it is more likely that the power supplied to the heater will be set directly by the user rather than indirectly by the reboiler temperature. Power regulation is achieved with a pulse width modulator (PWM) connected to a solid state relay (SSR). LabVIEW generates a square wave signal with a chosen amplitude, frequency and duty cycle. The amplitude is set to 5 V(dc) and the pulse oscillates between 0 and 5 V(dc) to periodically switch the element’s 220 V(AC) power supply on and o¤ via the SSR. The percentage of power delivered at a certain frequency is essentially determined by the duty cycle, which is the intrinsic variable manipulated by LabVIEW. 11.5. INSTRUMENT CONTROL LOOPS 99 N SubVI STOP Y Error Handler Default Default? Assign as Assign as Error Handler Y Shutdown achieved? Close control Shutdown = True N Shutdown sequence Y Stop AO/AI/DIO tasks AND/OR Stop AO/AI/DIO Close reference(s) to RS232 ports RS232 reference(s) to Close Shutdown? Y Close Datasockets N Close configuration file reference True Write data Read data Executed? STOP Timed Loop Manipulate data Control algorithm N Start•up = ? Request information through RS232 Request information Manipulate read data and perform the digital outputs AND/OR RS232 device digital outputs AND/OR necessary operations and conversions Write to datasockets AND analogue/ Read analogue; digital inputs AND/OR False Open True Datasockets Shutdown=? Y Start•up Initialize variables False achieved? Start•up = True Start•up sequence Y N Open/configure control Start AO/AI/DIO tasks AND/OR Configure and reference RS232 ports (amongst other Start•up = False; Shutdown False) Call Datasocket definitions subVI Figure 11.6: General algorithmic ‡ow diagram for the control loops Start•up? N N Configure Y (load/save as default) Standby Shutdown? Start•up = False Shutdown = True SubVI CALLED 3 4 2 1 5 6 12 7 11 8 10 9 100 CHAPTER 11. COMPUTER CONTROL SYSTEM

For example, a duty cycle of 0.5 at 0.2 Hz implies that for 50% of each 5 s period of the square wave the heating element receives power. The square wave signal is generated by the counter/timer on the PCI6014 DAQ card and is connected to the SSR. A solid state relay was used as it does not contain movable parts (as opposed to a mechanical relay) which can be worn out by this relatively high frequency switching.

11.5.3 Optical level control

The optical level control system was explained in section 10.3.1 in some detail. The analogue signal from the optical sensors are sent through a small circuit which switches it hard on (0 V) or hard o¤ (+5 V) depending on whether it crossed a threshold voltage of 4,5 V or not.

11.5.4 Re‡ux ratio control

As mentioned previously, the determined distillate mass ‡ow rate and user supplied re‡ux rate (control variable) is used to speed up or slow down the rate at which the re‡ux pump recycles the distillate re‡ux to the column. Speci…cally, the CD control program retrieves the measured balance weight at regular time intervals, calculates the mass ‡ow rate, converts it to a volumetric ‡ow rate, sends out a scaled 0-5 V(dc) signal to the re‡ux metering pump’s Emotron Frequency Inverter (the pump’s control interface), which then changes the pump stroke speed accordingly. Note: the pump stroke length is set beforehand; the stroke speed is the manipulated variable as a variable speed drive is used. To convert the obtained mass ‡ow rate to a volumetric ‡ow rate the measured product temperature is used in a density correlation from Perry et al. [1997]. Because of the current unavailability of and costs involved in procuring an unit for on-line composition analysis it was assumed that nearly pure 1-hexene exits the top of the column so that the pure component correlation could be used. This should not introduce a signi…cant error as there is not a large density di¤erence between 1-hexene and n-hexane.

11.6 Error Handling

At each critical juncture in the program (usually at the end of a loop or VI) the Error Handler VI checks whether any errors occurred and compares the error’snumerical code to a prede…ned error array list in order to ascertain what type of action is required. Errors may be divided into three types. The …rst type indicates a system error which does not pose a threat to e¤ective control or misinterpretation of the system status and which may be ignored. The second, more serious error, is one in which e¢ cient control 11.6. ERROR HANDLING 101 is impaired or where a potentially unsafe situation is detected, but where a controlled shutdown is still possible. The third error is a fatal error where control is seriously, or totally, compromised or where a dangerous condition has been detected within the CD system, which demands an immediate and total shut down - an emergency shutdown. As explained previously, in the case of an emergency shutdown the error handler switches o¤ the toggler signal whose absence cuts power to all the electrical equipment except to the software heart of the control system: the computer itself. In fact, because the toggler’sdigital channel line must be physically switched hard on (TRUE) and hard o¤ (FALSE) on each of its loop iterations (it is not a continuous timed signal as in the case of the PWM, but simply a DIO line) an emergency shutdown will also be triggered if the program itself hangs. This illustrates the elegant way in which the software and hardware has been fused in order to enhance the safety features of the control system. The Error Handler VI itself is a reentrant VI, which means that each instance called executes separately and independently. Reentrant VI’sdi¤er from the normal execution mode where a VI that is called more than once and in various programs is essentially the same program called in sequence by its callers2 based on the priority the caller has on the relevant callee. A non-reentrant VI would be contrary to the control criteria set at the beginning of the chapter as each VI calling the Error Handler would then have to wait for the current caller to …nish with the Error Handler instance before the next could use it. This clearly violates the independence criteria. Even worse, the very VI responsible for detecting and acting on error information may itself be beset by an erroneous control loop and become incapable of taking the proper action. Also, with reentrant VI’sthe danger of inputted and outputted data being mixed up between di¤erent callers is eliminated. Once an error or an array of errors is detected it is written to a datasocket speci…c to the relevant caller, which is then read by the Error Logger VI. The latter then adds it to any errors detected by the other callers and writes the resulting accumulated array of errors to a text …le for later retrieval.

2 A caller is a VI or subVI that requests (calls) a subVI (callee) to execute. 102 CHAPTER 11. COMPUTER CONTROL SYSTEM Chapter 12

OPERATION

In this chapter, the modular designs detailed in the previous sections are combined to arrive at the holistic system. Refer to Appendix F for detailed equipment speci…cations.

12.1 Equipment frame locations

The dimensional layout of the system is shown in Figure 12.1. The CD column and all peripheral equipment were carefully measured and located such that the system did not exceed the allocated walk-in fume cupboard (or "hood") space of 700 x 800 x 2 000 mm (w x l x h). Each hood is accessed through a large glass sliding door, giving the system a "face" (front) showing to the outside observer. The system can easily be accessed from three sides, the fourth and right hand side being restricted by another apparatus. Hoods need only to be accessed for maintenance or manual changes on experiments. For practical reasons the liquid feeds enter the CD column (hanging in the large open volume on the right) from the back, the thermocouples enter from the left closest to the electrical system and the products exit at the front into the partial condenser and bottoms cooler. Vibration propagation through the frame structure and pipe system will have a deleterious e¤ect on system operations that require a stable base (for example the sensitive electronic balance, vertical alignment of the column, etc.) To dampen the main vibrational source, namely the metering pump, the pump is erected on two stainless steel baseplates bu¤ered in-between by rubber feet and also by rubber feet between the lower plate and the frame ‡oor. The system’scentre of gravity is kept low. The pump is placed on the ‡oor of the frame for this reason as well as to ensure su¢ cient liquid head at the inlet. The column and partial condenser are each supported by three ready rods (M10, threaded steel rods) inserted through their individual top ‡anges and a¢ xed at the top of the frame to a support plate. Vertical alignment of the column and condenser is

103 104 CHAPTER 12. OPERATION critical to ensure radially symmetric hydrodynamics and is achieved by adjusting the support nuts threaded onto the ready rods. 14 thermocouples are positioned across the system. 8 are positioned at pre-determined intervals down the column to supply a complete column temperature pro…le - 1 of which is located in the reboiler for temperature control purposes. 7 are situated on the cooling system (partial condenser, refrigerator loop and cooler) for temperature pro…le and energy balance purposes (exact placement is shown on the P&ID). Assuming a 5C temperature di¤erence (for close boilers) between the bottom and top of the column the achieved column temperature resolution (0.7C/thermocouple) pro…le is adequate given the 0.5C thermocouple accuracy. The column and piping is insulated to reduce excessive heat losses. Slow dynamics are also required in the re‡ux line. The distillate ‡ow rate is determined by the level control solenoid valve opening and closing. This in turn determines the re‡ux pump ‡ow rate set-point (to maintain the re‡ux ratio), which in turn a¤ects the re‡ux drum level. A low proportional PID response is subsequently necessary as an extreme pump response can make this interconnected system unstable or drain the re‡ux drum completely. The electrical control system was put on the topmost shelve to protect it from possible ‡uid leaks. The physical system comprises the computer, connector block box, electronics, power supply and the Emotron Frequency Inverter. Computer power is supplied from an uninterrupted power supply (UPS) to ensure constant control and monitoring. The rest of the system’spower is not uninterrupted, though it is connected to a back-up power supply as well. In the event of a power failure power it is per- manently cut to the entire system except the computer, which can then run emergency shutdown scripts.

12.2 Operating procedures

The operating procedures are supplied in Appendix H together with a note and/or discussion for each of the steps. Only the most important aspects will be highlighted here. Control in this system is slightly complicated because of mainly two issues. Firstly, as is intuitively obvious (and substantiated by Kister [1990]) it is best to pressurize the column to the operating pressure as early in the start-up procedures as possible. How- ever, parallel to this the latter source recommends against using an inert gas to achieve this pressurization because of the adverse thermal e¤ects involved1. This precludes the

1 When the system initially contains a pressurized inert gas the entering volatile liquid component ‡ashes because of its very low partial pressure, drawing energy from its environment and making metal overchilling possible. This continues until su¢ cient vapour is formed to reach a VLE. If the system 12.2. OPERATING PROCEDURES 105

800.00mm 700.00mm 452.50mm 272.50mm m m 0 m 5 . m 2 0 9 0 3 . 6 8 3

A A m G m T I 4 3 m . N 1 m R m 0 3 E 7 4 m . 0 E 2 0 2 m . M

1 144.64mm 5 H m 0 0 P

4 1800 1800 0 T I 1600 1600 .

1400 1400 0

1200 1200 8 U F 1000 1000 4 800 800 600 600 Q

O 400 400 E ) ” T

E 50.00mm U C m

210.00mm O m m A 0 m m H 0 0 F . m 0 0 . 0 T “ 0 2 0 I . ( 2 9

B 0 B m 2 9 2 1 m 1 W 0 2 m 0 W 1800 . 1600 m m 5 1400 0 E 2 m

1200 W 0 I 5 . 1000 0 0 800 2 . E 8 V 600 1 I

400 4 3 m 2 V T m HPLC 0 N 0 E .

2 (Front) 5 O D 1 I R S m F C C 460.00mm m 0 0 . 0 6 5 m m 0 0 . m 6 m 8 m 0 3

5 1800 m . 1600 0 2 Reflux pump 1400 0 2

. 1200 5 5 [Side View] 1000

4 800 600 4 Regrigerator (RTE•8) 400 [Front View] m m 7 1 . 8 5 2 m m 0 0 . 0 1 1 S E N

I Ni Cards L N N O I w O m m I e T i m m T C 0 0 V 0 0 . . E C 0 0 y p l S 0 0 7 7 o s E r p c T B e p i t • S u n C u B o S L p r N t r P m c e H o e W l w C o E A P R D m m E 0 1 . H 8 3

T 123.00mm M

MFC m m O 0 0

Reflux pump . 0 R 4 1 F 460.00mm N N N O O I I m m W T T m m C C 0 0 O 0 0 . . E E 0 0 D S S 0 0 m 7 7 m A C 0 G • • 0

. Refrigerator (RTE•8) 0 A C N 0 I 4 K O O L

Note The frame is constructed from square tubing with 25 mm sides Because the bottoms product tank is elevated above the reboiler outlet the column must be operated at >1 bar(a).

Figure 12.1: Frame and dimensional layout of the CD system 106 CHAPTER 12. OPERATION use of the push-pull pressure control system to be used during steady state. Instead, its is suggested to use one of the volatile components in vapour form to achieve the correct operating pressure before introducing the other components. Secondly, to exac- erbate this situation the bottoms liquid (high-boiler) required for the reboiler inventory is, unlike in non-reactive distillation, not available in the hydrocarbon feed, but must be formed as a product of the liquid feed reagent. There are two approaches available. Either the low-boiler (1-hexene) is initially loaded into the reboiler inventory or a mixture of the low and high-boiler (n-hexane) is loaded into the reboiler and heated to boiling point. The advantage of the former over the latter is that the mixture more closely resembles the eventual reactive distillation steady mixture, that it makes it possible to reach a non-reactive distillation steady state before initiating the reaction (instead of just boiling the pure component, separation is actually possible) and the fact that steady state will be reached more quickly as the reboiler inventory mixture that acts as a bu¤er to set-point changes is immediately closer to its steady state concentration. The system is thus pressurized to slightly below its desired steady state pressure by the volatile lighter boiling component. The critical point to remember is that the reboiler element must not run dry. The hydrogen is purposefully introduced when the system is operating as a controlled non-reactive distillation column as it causes a signi…cant disturbance. Most notably it increases the gas ‡ow rate in the column, puts pressure on the system temperature control due to the initiation of the exothermic reaction and could pose a safety risk should the rest of the system not be under control. As a case in point for the latter, apart from the possibility of it coming into contact with the exposed heating element, one must also consider that hydrogen could exit through the liquid product lines if they should be dry. This would be undesirable, but not completely unprepared for as the liquid product tank’s atmospheric equalization pressure lines are connected to the extraction system. The hydrogen is introduced into the closed system without pressure control and the pressure is allowed to increase to the operating pressure. If the hydrogen were introduced into a pressure controlled system, it would suddenly lower the partial pressure of the prior present vapour component and cause instantaneous liquid evaporation. It is critical to tightly monitor the column during the addition of this ‡ammable gas and the accompanying initiation of the exothermic reaction. Once the operating pressure is achieved control can be handed over to the nitrogen push-pull system. Shutdown is simpler than start-up in this case. It entails discontinuing all heat inputs (thus stopping the hydrogen feed to slowly halt the exothermic reaction and cutting power to the reboiler), allowing the system to cool down to below the components were initially …lled with a vapour the ‡ashingfeed’senergy would be supplied by condensing the vapour. 12.2. OPERATING PROCEDURES 107 normal boiling points, stopping the pressure control system and then shutting down the remaining equipment. 108 CHAPTER 12. OPERATION Part III

RESULTING SYSTEM

109

Chapter 13

MODULAR COMMISSIONING

An e¢ cient, autonomously controlled, safe, steady-state operation of the built CD system requires experience in system-speci…c behavioural trends that can only be determined with careful trial and error experimentation. The time required for this is left for future research. In this chapter the system will be shown to be modularly commissioned. This will be considered as achieved if the various control components (or parameters) can be controlled correctly, each on an individual basis, and be combined with su¢ cient monitored data to allow accurate calculation of the mass and energy balances (refer to Table 13.1).

Table 13.1: Mass and Energy balance classi…cations of the various control components Function Control Type Components Mass/Energy Pressure control Nitrogen feed line Feed rates HPLC, MFC Mass Balance Re‡ux rate Re‡ux pump Product rates Bottoms/distillate solenoid valves/balances Heat input Reboiler heating element Energy Balance Heat removal Refrigerator and tap water cooling lines Temperature pro…le Data acquisition and logging

13.1 Pressure Testing And Gas Lines

A pneumatic test was conducted with the dual function of a pressure and leak test. Leaks in the system were detected by using a simple soap bubble solution to detect escaping gas. Nitrogen was chosen as a safe, readily available and already connected system gas for this purpose. A maximum pressure of 6 bar(g) was used as a …rst approach, although it should, in fact, be capable of handling much higher pressures - refer to Appendix F. The limiting factors with regards to pressure are the partial condenser and reboiler sightglasses, which have a safe working pressure of 30 bar(g) - see Appendix D.

111 112 CHAPTER 13. MODULAR COMMISSIONING

The pressure in the column must be determined visually from analogue pressure gauges, but can also be read (manually and/or programmatically) from the HPLC feed pump.

13.2 Simpli…ed start-up

The refrigerator and ambient tap water cooling loop was activated, the former set to 0C and su¢ cient time given for the refrigerator temperature to reach a steady state. During the time required for the refrigerator to reach its set-point temperature, the reboiler was loaded with 1-hexene by using the 1-hexene HPLC feed pump set to its maximum value of 10 ml/min. It is suggested that a faster loading method be investigated in future. Once the refrigerator set-point was reached and the reboiler level attained a position half-way between the low and high level settings, the element was set to a heat duty value of 500 W. Since pure component 1-hexene was used it was observed, as expected, that a thermal wave with a temperature corresponding to the boiling point of 1-hexene, at the relevant pressure, moved up the length of the column from the reboiler heat source - refer to Figure 13.1. The drop in the reboiler inventory liquid level due to vaporization was detected correctly by the reboiler level sensors. The transient temperature change of the various thermocouples is shown as a function of time in Figure 13.2. There is the initial period during which the reboiler simply adds sensible heat to the reboiler inventory until it reaches its boiling point. A 1-hexene vapour wave then moves up through the column, rapidly heating the temperature at each point along the column from ambient (ca. 27C) to the boiling point. Above the tip of the rising thermal wave the 1-hexene pinches. As the 1-hexene vaporizes the pressure in the closed column increases, increasing the boiling point and thus the observed temperature. Once the 1-hexene vapour reaches the condenser it condenses and causes a slight drop in the re‡ux drum temperature. The re‡ux drum liquid level now starts to increase and is detected correctly by the three optical sensors. Once the re‡ux level reached its nominal position the re‡ux pump was activated programmatically and set to a constant pump rate. In this case there is su¢ cient head to prevent pump cavitation. For …rst approach purposes the pump rate was not linked to the scaled distillate ‡ow rate value. However, the balances are working and communicating satisfactorily with the computer via RS232 and allows easy calculation of the distillate and bottoms mass ‡ow rates. The distillate and bottoms solenoid valves, although kept closed here, responds correctly to programmatic commands. An iterative procedure was followed to reach steady liquid levels in the reboiler and re‡ux drum. This entailed trial and error changes to the reboiler heat duty and re‡ux pump ‡ow rates. A steady state was eventually reached twice between times 12 370 and 15 980 s and 18 635 and 22 820 s (Figure 13.3). 13.2. SIMPLIFIED START-UP 113

Figure 13.1: CD column temperature pro…le 114 CHAPTER 13. MODULAR COMMISSIONING

T•C T•0 T•1 T•2 T•3 T•4 T•5 T•6 T•7 T•R Power

100 1000

T•0 80 800

T•1

] T•2 °C [ T•3 T

, 60 600 T•5 T•4 Heating Element Power

T•7 T•6 Temperature 40 400 T•R Heating Element Power [W] Power Element Heating

T•C 20 200

0 0 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Time, t [s]

Figure 13.2: Start-up temperature pro…le and the related reboiler power setting for the CD system

13.3 General observations

The HPLC pump initially cavitated when pumping the 1-hexene feed into the column. An increase in the liquid head was limited by physical dimensions and pressurization of the feed tank was undesirable due to its material of construction (glass) and safety issues concerned with connecting to the existing gas pressure manifold. The simpler option of cooling down the pump head with cold liquid from the existing refrigerator was employed. The feed line is su¢ ciently long to allow the 1-hexene feed to regain its ambient temperature before entering the column. Vibration from the re‡ux pump appears to be su¢ ciently damped and the HPLC pump does not appear to be a signi…cant source. However, the refrigerator does contribute signi…cantly during start-up and shutdown and should also be put on a bu¤ering base. Over…lling of the re‡ux drum caused liquid to exit into the o¤-gas line and should preferably be avoided in future.

13.3.1 Data acquisition and logging

The Data Acquisition and Logging VI accurately logged set-points and other monitored values. Table 13.3 shows an excerpt from the programmatically generated logging …le 13.3. GENERAL OBSERVATIONS 115 that represents the system in an unsteady state mode. It illustrates the logging of set-points, such as the reboiler heat duty, the control status of the program and/or instruments (ON = TRUE = 1), it’sability to monitor data (temperatures, inventory levels and balance measurements) and its ability to interpret and manipulate that data (initiating an emergency shutdown or converting a balance measurement to a ‡ow rate). It should be noted that it currently takes several multiples of 5 s to receive a reading from the balances. This is due to the nature of the RS232 communication and with careful programming it should be possible to reduce this dead time. Also, a reduction in the vibration generated by the refrigerator will allow the balance to furnish a stable, accurate reading more quickly. It was observed that vibrational e¤ects introduce small, but signi…cant errors into the balance readings, though, the resulting mass ‡ow rate is calculated correctly from the read values. At the time of this excerpt, the bottoms solenoid valve was already opened manually, thus explaining the presence of a bottoms ‡ow rate. The bottoms cooler supplied su¢ cient cooling of the 1-hexene bottoms take- o¤ to cool it to below its normal boiling point and prevent ‡ashing. The re‡ux drum level control operates as programmed. Table 13.2 indicates its response to the eight di¤erent combinations of responses that it can get from the 3 pairs of optical sensors. At time 13 995 s the low level optical sensor indicates that it does not detect liquid and attempts to close the distillate solenoid valve, which, however, is currently set to manual control. The liquid level falls to below the low level alarm sensors and the control program correctly attempts to initiate an emergency shutdown1. There follows a period where apparently no command is sent to the solenoid valve. This corresponds to a boolean signal of 001 where the liquid level has again risen to the nominal position between the low and high level settings. However, at time 14 030 s it attempts another emergency shutdown, which is unlikely as it means that the re‡ux drum must drain empty from its nominal position within only 5 s. This second shutdown is thus probably due to the observed gas bubble that was trapped in the sightglass and slight changes may have to be made to the control program for it to anticipate this eventuality.

13.3.2 Thermal response

As already partially illustrated during start-up in section 13.2, the monitored temperature pro…le in itself can be a valuable analysis tool that can yield a signi…cant amount of direct data and inferred information. Consider Figure 13.3, illustrating the column temperature pro…le during the entire run. At …rst glance there is an apparent discrepancy between the temperature at the top

1 Emergency shutdown was disconnected during start-up as it would be triggered by the low level alarm during …lling of the empty re‡ux drum by condensation of the rising reboiler vapour. 116 CHAPTER 13. MODULAR COMMISSIONING

Table 13.2: CD control program’sresponse to the eight possible signal combinations from the optical sensors Boolean signal: LLA/Lo/Hi Response Comment (0 = Liquid Detected) 000 Open valve Liquid level is high 001 No action Liquid level within bounds 010 Warning Sensors may be malfunctioning 011 Close valve Liquid level is low 100 Warning Sensors may be malfunctioning 101 Emergency shutdown Alarm does not detect liquid 110 Emergency shutdown Alarm does not detect liquid 111 Emergency shutdown Vessel is running dry of the condenser (T-0) and the re‡ux drum temperature (T-C) as the former is initially lower than the latter. However, this can be explained by the fact that T-0 is positioned closer to the heat exchange areas of the condenser than T-C. The former’s proximity to the cooling areas also makes it more sensitive to changes in the reboiler heat input than thermocouples T-R to T-1 as it is quickly cooled by the condenser if the heat input is reduced. This is indicated by the sharp gradients of T-0 in the event of a change in the heating element power. It is interesting to note that, with no re‡ux, cooling does not proliferate through the column as quickly as heating, as is indicated by the unsymmetrical nature of the graph around ca. t = 5 000 s where the heater is switched o¤. From the positive and negative slopes around t = 5 000 s it is possible to respectively calculate the heating and cooling rates. T-2 exhibited relatively excessive noise when the re‡ux pump is switched on. This is probably because it is located in the vapour space above the packing, but below the re‡ux line outlet into the column, causing it to experience alternating warm, rising vapour and cold descending liquid. Note from Figure 13.1 that there is a very slight temperature gradient at steady state along the length of the column, signifying the cumulative e¤ect of heat losses and, probably, also pressure. The small change in temperature indicates that the aim of minimizing heat losses was at least partially achieved. This can also be seen on Figure 13.3 by noticing the close correlation between temperatures at the bottom and top of the column. Although it has not been done yet, the temperature pro…le can be used to estimate the rate of heat loss by using the drop in temperature as a function of time when there is no reboiler heating, condenser cooling or re‡ux. Steady state was achieved twice: between 12 370 and 15 980 s and 18 635 and 22 820 s. The temperature pro…le can thus show the movement of heat, the related movement 13.3. GENERAL OBSERVATIONS 117 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 W•B Status 1=TRUE Boolean Indicator 0=FALSE 1531.8 1531.8 1531.8 1366.2 1366.2 1366.2 1366.2 1339.2 1339.2 1339.2 1339.2 1283.4 1283.4 1283.4 1283.4 1101.6 1101.6 1101.6 1101.6 1216.8 1216.8 1216.8 g/h Rate W•B Flow BOTTOMS BALANCE BOTTOMS 140.42 140.42 140.42 148.01 148.01 148.01 148.01 155.45 155.45 155.45 155.45 162.58 162.58 162.58 162.58 168.70 168.70 168.70 168.70 175.46 175.46 175.46 g W•B Read Weight 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Status 1=TRUE Boolean 0=FALSE 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Initiate 1=TRUE Boolean 0=FALSE Shutdown Emergency 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Valve Close 1=TRUE Boolean 0=FALSE REFLUX DRUM LEVEL CONTROL REFLUX DRUM 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Open Valve 1=TRUE Boolean 0=FALSE 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1=TRUE Boolean Indicator 0=FALSE TR Status 900 900 900 900 900 900 900 900 900 900 900 900 900 900 900 900 900 900 900 900 900 900 W Power HEATING ELEMENT 93.7 93.5 93.3 93.2 93.3 93.2 93.2 93.2 93.0 93.1 93.0 93.0 92.8 92.9 92.8 92.7 92.7 92.7 92.6 92.6 92.7 92.5 Researcher: 10 T•R Jako Nieuwoudt Deg C Voltage 1•Hexene Hydrogenation in a CD column1•Hexene Hydrogenation (M.Sc.Eng) Table 13.3: Excerpt from the CD system’slogging …le (textual changes shown in italics) 92.9 92.8 92.7 92.6 92.6 92.5 92.5 92.5 92.4 92.4 92.4 92.3 92.2 92.2 92.1 92.2 92.1 92.0 92.1 92.1 92.0 91.8 2 T•1 TEMPERATURE 10:19 Deg C Time: Voltage 13995 14000 14005 14010 14015 14020 14025 14030 14035 14040 14045 14050 14055 14060 14065 14070 14075 14080 14085 14090 14095 14100 Time TIME Date: Seconds 05/04/2005 118 CHAPTER 13. MODULAR COMMISSIONING of material the system’s operational state, potential unsafe situations and the relative sensitivity of di¤erent parts of the column to set-point changes and/or disturbances.

13.4 Resulting system

From the previous sections it is clear that the various control components (as de…ned in Table 13.1) each function correctly on individual bases and allow calculation of the mass and energy balances. The system has thus been successfully modularly commissioned. Images of the completed system are shown in Figures 13.4 and 13.5. A few practical aspects that were not covered previously can be mentioned here. In general, care was taken to keep lines neat, tidy, short, out of the way and grouped according to type. This is best illustrated on Figure 13.4 showing the back of the system where the electronics (thermocouples), material (gas lines) and power lines are kept separate and grouped. It also shows that external supply sources (such as the electrical, water and gas supply) enter the frame from above to keep the walking area clear. Pressure control was put at the back on eye level to facilitate ease and e¢ ciency of use, and to shorten gas lines. The o¤-gas line enters the o¤-gas extraction pipe above the CD frame. A separate ‡exible pipe system connects the feed and product tank vent lines to another o¤-gas extraction point. A ‡exible Buna-N pipe is led from the nearby water point overhead to the partial condenser, down to the cooler and back over to the nearest drain line. Control valves and sampling points are easily reachable. The re‡ux pump is also visible on its bu¤ering base on the bottom shelve. The two electrical power supply points can also be seen from the back. As discussed previously the electrical control units are located on the top shelf, close to the power supplies and away from liquids. On each shelf electrical and electronic lines are suspended from the top shelf to keep it away from accumulating or ‡owing liquids (as, for example, in the event of a leak or excessive dripping condensation from the cooling lines) Control and digital readings on the HPLC pump, balances, and re‡ux pump frequency inverter as well as the power supply, computer and electronic box are clearly visible and accessible through the glass sliding doors (Figure 13.4). The refrigerator cooling lines and its branch wound around the HPLC piston head can also be seen here. 13.4. RESULTING SYSTEM 119

Figure 13.3: Behaviour of the system based on the e¤ect of parameter changes on the temperature pro…le 120 CHAPTER 13. MODULAR COMMISSIONING

Power supplies Electronics Tap Water (UPS right) Power supply Extraction

Thermocouples Gas Computer Feed

Frequency Inverter NI Partial Cards Condenser Liquid Feed Pressure control Rotameter

Bottoms CD Cooler Column HPLC

Distillate

Reboiler

Refrigerator

Bottoms Reflux Pump

Front View Back View

Figure 13.4: Photo of CD system taken on 10 April 2005, showing the front and back views 13.4. RESULTING SYSTEM 121

Left View Right View

Figure 13.5: Photo of CD system taken on 10 April 2005, showing the two side views 122 CHAPTER 13. MODULAR COMMISSIONING Chapter 14

CONCLUSIONS

The project goal and guideline have been achieved and satis…ed respectively as the converted batch to continuous system has been commissioned piecewise and appears to be operating correctly, reproducibly, and within design parameters. Complete commissioning of the system will require systematic investigation into the system’skey parameters as well as generic CD system behaviour and is left for future research. Material feed ‡ows can be tightly controlled and monitored using a program. How- ever, the o¤-gas ‡ow rate must currently still be measured using a bubble meter. The system can supply su¢ cient controlled heating, and cooling can be calculated by com- bining an accurate and complete temperature pro…le with the relevant cooling medium ‡ow rates. This should thus yield an accurate energy balance for the process. The exhaustive temperature pro…le supplies valuable information of especially the internal dynamics of the packed sections of the column. Re…nement of the control program is necessary, but the basic structure and operation is sound. Safety is integral to both the program and physical system design, and the heating element is correctly protected by the low level alarm, though a localized power cut to the element may be considered rather than a system wide shutdown. The total cost for the project is R127 000 - excluding the prior existing refrigerator, stainless steel column body, rotameter, solid state relays and 1-hexene feed material. The hypothesis and the key questions have been partially tested and answered as the system has been contructed, although they must still be considered with regards to mass transfer and conversion. However, the completed and modularly commissioned CD system could supply much needed transiently monitored mass balances, energy balances and manually measured concentrations for use in case studies to validate NEQ CD computer models. It is especially designed to address the separation of close-boiling components, to operate on a small-scale and to consider the complicating factor of non- condensable gases. The system meets the basic design requirements to be a powerful, ‡exible tool to experimentally explore the potential of CD.

123 124 CHAPTER 14. CONCLUSIONS Chapter 15

GEVOLGTREKKINGS

Die sisteem is deelsgewys inbedryfgestel en die projekdoel en -gids bevredig aangesien die sisteeem blykbaar korrek en binne die ontwerpskriteria funksioneer. Volledige inbedryf- stelling van die sisteem benodig meer tyd vir van-’n-kant ondersoeke om die sisteemspe- si…eke en algemene KD neigings te bepaal en verdere navorsing word dus vereis. Voervloeitempo’s kan streng beheer en produkvloeitempo’sprogramaties gemoniteer word. Die uitlaatgasvloeitempo moet huidiglik steeds met die hand gemeet word d.m.v. ’n borrelmeter. Die sisteem kan voldoende beheerde verhitting verskaf, en verkoeling kan bereken word deur die akkurate temperatuurlesings te kombineer met die verkoel- ingsmediumvloeitempo’s. ’n Akkurate energiebalans behoort dus suksesvol gelewer te kan word. Die temperatuurpro…el verskaf waardevolle informasie aangaande veral die interne dinamika van die gepakte dele van die kolom. Verfyning van die beheersisteem is nodig, maar die basiese struktuur en uitvoering daarvan is aanvaarbaar. Veiligheid is deurgaans in beide die program en …siese sisteem in ag geneem en die verhittingselement word korrek deur ’n lae-vlak alarm beskerm, alhoewel ’nonmiddellike gelokaliseerde kragonderbreking tot die element miskien bo ’n algehele sisteemstaking oorweeg moet word. Die totale koste van die projek beloop R127 000 - uitsluitend die voorafbestaande verkoeler, vlekvrye staal kolom, rotameter vastetoestandrelês en 1-hekseen voermateri- aal. Die hipotese en sleutelvrae is gedeeltelik getoets en beantwoord deurdat die sisteem voltooi is. Die voltooide en deelsgewys inbedryfgestelde KD sisteem het dus die ver- moë om tydafhanklik gemoniteerde massa balanse, energie balanse en handgeneemde konsentrasie-monsters te verskaf vir veri…ëring van nie-ekwilibrium KD rekenaarmodelle. Dit is spesi…ek ontwerp om nabykokende stowwe, die klein skaal van die sisteem en die kompliserende e¤ek van nie-kondenseerbare gasse in ag te neem. Die sisteem voldoen aan die basiese ontwerpsverwagtings van ’n kragtige, buigbare eksperimentele opstelling wat die potensiaal van KD kan ondersoek.

125 126 CHAPTER 15. GEVOLGTREKKINGS Chapter 16

RECOMMENDATIONS

The existing column represents a fully functional system, but it is still possible to identify a few areas in its design that my be improved upon or investigated in more detail. Accurate, continuous, on-line measurements of the o¤-gas line ‡ow rate and composition is such an area. It is currently assumed that, because of the large degree of subcooling of the distillate, the o¤-gas line contains mostly unreacted hydrogen gas - an assumption that may not remain accurate when the reaction system is changed. In fact, accurate, continuous, on-line compositional measurements of the product streams leaves a wide scope for improvement should the transient response of the system be of interest. For the purposes of an M.Sc.Eng it was di¢ cult to justify this functionality because of the time limitations involved, the large additional expenditure that would be required, the fact that this was a …rst approach to designing a fully operation CD system and because it is redundant when only steady state conditions are of interest. There is also scope to increase the operating range and conditions of the column. In general, the materials of construction used are robust and should be resistant to a wide range of materials - even corrosive materials, though each case will have to be considered separately. The internal electrical heating element may be of concern as it could pose an explosion hazard should it crack or cause a spark. With the current system it is not of critical concern as there are no oxygen or oxygen-containing components available to fuel such an explosion and because there is a positive pressure gradient between the inside of the system and the atmosphere. Should this not be true either the use of a heated oil circulation bath or an external electrical heater is suggested. In terms of pressure, the partial condenser and reboiler’ssightglass tubes dictate the upper pressure limit, which could be increased by using a di¤erent transparent material, such as quarts, for example. In the unlikely even that even higher pressures are required one of the other discussed level control techniques may be considered. The maximum operating temperature (assuming a large enough reboiler capacity) is determined by the Te‡on and other plastic items used. This can easily be increased by using di¤erent (though

127 128 CHAPTER 16. RECOMMENDATIONS more expensive) materials. In any event, with regards to temperature and pressure, operating separation and reactor systems outside (as a rule of thumb) 1 to 10 bar and 40 to 250C must be justi…able due to the high capital and operating costs involved [Turton et al., 1998]. As a matter of scale, because of practical considerations and because of the availability of other options to achieve separation the building of a high-pressure high- temperature distillation column and/or the retro…tting of an existing one is di¢ cult to justify when compared to a reactor where favourable reaction conditions dominate the design considerations. In such cases where favourable separation and reaction conditions do not match, the use of a side reactor may be a viable alternative [Bauer and Krishna, 2004b,a; Bisowarno et al., 2004]. Bibliography

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APPENDICES AND INDEX

133

Appendix A

EXISTING AND FUTURE APPLICATIONS FOR CD

135 136 APPENDIX A. EXISTING AND FUTURE APPLICATIONS FOR CD 4 Advantages No external through reactor cooling or recycle One less reactor lifeProlonged catalyst Heat of reaction used to preheat feed 99,99% isobutene conversion vs. 95% pure MTBENearly obtained (beyond equilibrium limit) Reverse process for de•etherification also possible and C Separation of close•boiling isobutylene available at refineries Reactant (propylene) readily thermodynamicConversion beyond equilibrium Higher conversion equilibrium (beyond limit) vs. operation with excessNo water recycle water pure TBANearly obtained Higher conversion equilibrium (beyond limit) ether Might be extended to dimethyl oligomerizationPropylene Prevention of hot spots life Increased catalyst savings due to heat integration 50% energy 25% lower capital costs of benzene large quantity Unnecessary to recycle Reduction of carcinogen reducedFormation of polyalkylbenzenes foulingPrevents catalyst and poisoning improve selectivityMay reduce paraffinMay recycling simplify process May Homogeneous corrosive catalysts and hazardous Higher conversion (80% vs. 20%) but variable composition, deactivation observed and catalyst reduced selectivity Does not require expensive refrigeration Possibility with little modification with to MTBE process Possibility Possibility with little modification with to MTBE process Possibility Status Possible Possible Possible expensive conducted Operational experiments Possible, but heterogeneous demand for TBA Laboratory•scale Possible, but low Future possibility Future possibility Possible, but good catalyst still requiredcatalyst TBA DAA fuels DIPE DIPE MTBE 1997)) gasoline Cumene (t•butyl alcohol) (t•butyl ethyl•t•butyl ether ethyl•t•butyl Product/Process (diisopropyl ether) (diisopropyl ether) (diisopropyl (diacetone alcohol) t•amyl methyl ether t•amyl methyl process has similar (methyl•t•butyl ether) (methyl•t•butyl Branched paraffinnic Benzene reduction in Benzene (existing ethylbenzene advantages (Rock et al., Table A.1: Existing and future applications for CD [Prodebarac et al., 1997] olefins benzene Alkylation Alkylation to Alkylation Etherification Dehydration of Dehydration Aldol condensation Aldol Hydration of olefins Hydration 1 2 3 4 5 6 No. Type of reaction 137 fraction and selective 5+ and C 4 Two less distillation required units theoretically of methyl acetate Reduced recycle Lower capital costs requirementEstimated 50% lower energy toward intermediateImproved (ethylene reaction selectivity formed • lessglycol glycol) diethylene Isothermal conditions in reaction zone Heat of reaction enhances distillation Can separate iso•olefins from linear olefins (e.g. separation of close•boiling and C4) isobutylene Isothermal conditions in reaction zone, but rapid catalyst and poor selectivity deactivation Simultaneous distillation of C Foulant and poisining ofprevented catalyst Isothermal temperature profile in reaction zone Reduced capital cost Simultaneous removal of trace sulphur compounds Equilibirum limitations overcome 99% conversion of (nearly methanol and formaldehyde) 99% pure Methylal External mass transfer problems minimized Simplified separation of these close boiling liquids Reaction driven to completion dehydrogenation of butadiene impurity dehydrogenation Possible Possible Possible Possible Computer conducted simulations experiments Tests conducted Tests Laboratory•scale 4 4 iso•olefins 5 acetate) Methylal Acetic acid Acetic hydrogenation Ethylene glycol Ethylene oligomerization and C from amine n•amyl Selective butadiene (hydrolysis of methyl (hydrolysis Oligomerization of C 1•butene and mixed C Separation of piperidine Table A.2: Existing and future applications for CD continued... [Prodebarac et al., 1997] Olefin epoxides hydrolysis to ketones to aldehydes Hydrolysis of Hydrolysis Hydrogenation oligomerization Esterification and Addition of amines Addition Addition of alcohols Addition 7 8 9 10 11 12 138 APPENDIX A. EXISTING AND FUTURE APPLICATIONS FOR CD Appendix B

THERMODYNAMIC, PHYSICAL PROPERTY AND MASS TRANSFER MODELS

139 140APPENDIX B. THERMODYNAMIC, PHYSICAL PROPERTY AND MASS TRANSFER MODELS

Table B.1: Thermodynamic, physical property and mass transfer models incorporated into the RD design program of Baur et al. [2000] Raoult's law Ideal solution Equation of state Scatchard•Hildebrand K•value Gamma•Phi Margules models Chao•Seader Van Laar Activity Polynomial Wilson coefficients Ideal gas NRTL Virial UNIQUAC Equations of Redlich•Kwong UNIFAC state Soave•Redlich•Kwong ASOG API•SRK Antoine Peng•Robinson Extended Antoine EOS based methods Vapour DIPPR polynomial Rackett equation pressure Riedel Yen•Woods Lee•Kesler Molar volume Thompson•Probst•Hankinson Cubic EOS DIPPR polynomial (gases and Amagat's law liquids) DIPPR polynomial (gases and Misic•Thodos (gases) liquids) Chapman•Enskog•Brokaw (gases) Stiel•Thodos (gases) Brokaw (gas mixtures) API procedure 12A1 (liquids) Viscosity Yoon•Thodos (gases) Thermal DIPPR procedure 9I (liquid mixtures) conductivity Letsou•Stiel (liquid mixtures) DIPPR DIPPR procedure 9B (gases) procedure 8H Wassiljewa•Mason•Saxena (gas DIPPR polynomial mixtures) Lielmezs•Herrick DIPPR procedure 9E (liquids) DIPPR procedure 9H (liquid Surface API method mixtures) tension Brock•Bird Kinetic theory (gases) Digulio•Teja Fuller•Schettler•Giddings (gases) McLeod•Sugden Wilke•Chang (dilute liquids) Winterfield•Scriven•Davis Binary Hayduk•Laudie (dilute liquids) Onda et al. Hayduk•Minhas (dilute liquids) diffusion Bravo•Fair Siddiqi•Lucas (dilute liquids) coefficients Billet Schultes Generalized Vignes (liquid mixtures) Mass transfer Sherwood number correlation Leffler•Cullinan (liquid mixtures) coefficients • Bravo•Rocha•Fair (1985) Rathbun•Babb (liquid mixtures) packings Bravo•Rocha•Fair (1992) AIChE method Zogg Mass transfer Hughmark Brunazzi Chan•Fair coefficients • Ronge Zuiderweg trays Zogg•Toor•Marachello Harris None Chen•Chuang Ideal Enthalpy Ideal + excess (from EOS or activity model) Appendix C

DESIGN CALCULATIONS

C.1 PRO II Calculations

141 142 APPENDIX C. DESIGN CALCULATIONS C.1. PRO II CALCULATIONS 143

COLUMN SUMMARY NET FLOW RATES PRESSURE HEATER TR AY TEMP DEG C LIQUID VAPOR BAR FEED PRODUCT DUTIES G•MOL/HR M*J/HR 1C 7.4 5 48.6 1.8V •2.3349 0.6L 2 123.6 5 94.6 51 3 124.8 5 95.6 97 4 124.9 5 95.6 98 5 125.1 5 95.6 98 6 125.2 5 95.6 98 7 125.4 5 95.6 98 8 125.5 5 95.6 98.1 9 125.7 5 95.7 98.1 10 125.9 5 95.7 98.1 11 126.1 5 95.7 98.1 12 126.3 5 95.7 98.1 13 126.6 5 95.8 98.2 14 126.8 5 95.8 98.2 15 127.1 5 95.8 98.2 16 127.3 5 95.9 98.2 17 127.5 5 95.9 98.3 18 127.8 5 95.9 98.3 19 128 5 96 98.4 20 128.3 5 96 98.4 21 128.5 5 96 98.4 22 128.7 5 96.1 98.5 23 128.9 5 96.1 98.5 24 129.1 5 96.2 98.6 25 129.3 5 98.5 98.6 1.2L 26 129.5 5 98.5 99.7 27 129.7 5 98.6 99.8 28 129.9 5 98.6 99.8 29 130.1 5 98.6 99.8 30 130.2 5 98.7 99.9 31 130.3 5 98.7 99.9 32 130.5 5 98.7 99.9 33 130.6 5 98.8 100 34 130.7 5 98.8 100 35 130.8 5 98.8 100 36 130.9 5 98.8 100 37 130.9 5 98.8 100.1 38 131 5 98.9 100.1 39 131.1 5 98.9 100.1 40 131.1 5 98.9 100.1 41 131.2 5 98.9 100.1 42 131.2 5 98.9 100.1 43 131.2 5 98.9 100.1 44 131.3 5 98.9 100.2 45 131.3 5 98.9 100.2 46 131.3 5 98.9 100.2 47 131.4 5 98.9 100.2 48 131.4 5 98.9 100.2 49 131.4 5 98.7 100.2 1.8V 50R 132.4 5 98.2 0.5L 2.3469 144 APPENDIX C. DESIGN CALCULATIONS

STREAM MOLAR RATES COMPONENT STREAM ID BOTTOMS B1 B2 B3 NAME Bottoms stream PHASE LIQUID LIQUID MIXED MIXED FLUID RATES, G•MOL/HR 1 1•HEXENE 7.66E•03 7.66E•03 7.66E•03 7.66E•03 2 HEXANE 0.534 0.534 0.534 0.534 3 HYDROGEN 6.12E•07 6.12E•07 6.12E•07 6.12E•07 TOTAL RATE, G•MOL/HR 0.5417 0.5417 0.5417 0.5417 TEMPERATURE, C 132.3718 132.3714 132.2354 132.2351 PRESSURE, BAR 5.001 5.001 4.986 4.9859 ENTHALPY, M*J/HR 0.0153 0.0153 0.0153 0.0153 MOLECULAR WEIGHT 86.1494 86.1494 86.1494 86.1494 MOLE FRAC VAPOR 0 0 1.48E•03 1.50E•03 MOLE FRAC LIQUID 1 1 0.9985 0.9985 STREAM ID DISTILLATE D1 D2 D3 NAME Distillate stream PHASE LIQUID LIQUID MIXED MIXED FLUID RATES, G•MOL/HR 1 1•HEXENE 0.5358 0.5358 0.5358 0.5358 2 HEXANE 0.0563 0.0563 0.0563 0.0563 3 HYDROGEN 1.91E•03 1.91E•03 1.91E•03 1.91E•03 TOTAL RATE, G•MOL/HR 0.594 0.594 0.594 0.594 TEMPERATURE, C 7.3872 7.3872 7.388 7.388 PRESSURE, BAR 5 5 4.985 4.9849 ENTHALPY, M*J/HR 3.47E•04 3.47E•04 3.47E•04 3.47E•04 MOLECULAR WEIGHT 84.0899 84.0899 84.0899 84.0899 MOLE FRAC VAPOR 0 0 1.01E•05 1.02E•05 MOLE FRAC LIQUID 1 1 1 1 STREAM ID HYDROCARBONS HYDROC1 HYDROC2 HYDROC3 NAME Hydrocarbon feed streams PHASE LIQUID LIQUID LIQUID LIQUID FLUID RATES, G•MOL/HR 1 1•HEXENE 0.594 0.594 0.594 0.594 2 HEXANE 0.594 0.594 0.594 0.594 3 HYDROGEN 0 0 0 0 TOTAL RATE, G•MOL/HR 1.188 1.188 1.188 1.188 TEMPERATURE, C 25 25 25 25 PRESSURE, BAR 6 5.9999 5.9849 5.9848 ENTHALPY, M*J/HR 4.93E•03 4.93E•03 4.93E•03 4.93E•03 MOLECULAR WEIGHT 85.1705 85.1705 85.1705 85.1705 MOLE FRAC VAPOR 0 0 0 0 MOLE FRAC LIQUID 1 1 1 1 C.1. PRO II CALCULATIONS 145

STREAM ID HYDROGEN HYDROG1 HYDROG2 HYDROG3 NAME Hydrogen feed stream PHASE VAPOR VAPOR VAPOR VAPOR FLUID RATES, G•MOL/HR 1 1•HEXENE 0 0 0 0 2 HEXANE 0 0 0 0 3 HYDROGEN 1.782 1.782 1.782 1.782 TOTAL RATE, G•MOL/HR 1.782 1.782 1.782 1.782 TEMPERATURE, C 25 25 24.9999 24.9999 PRESSURE, BAR 6 5.9999 5.9959 5.9957 ENTHALPY, M*J/HR 5.22E•03 5.22E•03 5.22E•03 5.22E•03 MOLECULAR WEIGHT 2.016 2.016 2.016 2.016 MOLE FRAC VAPOR 1 1 1 1 MOLE FRAC LIQUID 0 0 0 0 STREAM ID OFF•GAS O1 2 3 NAME

Off•gas stream mainly containing H2 PHASE VAPOR VAPOR VAPOR VAPOR FLUID RATES, G•MOL/HR 1 1•HEXENE 0.0505 0.0505 0.0505 0.0505 2 HEXANE 3.71E•03 3.71E•03 3.71E•03 3.71E•03 3 HYDROGEN 1.7801 1.7801 1.7801 1.7801 TOTAL RATE, G•MOL/HR 1.8343 1.8343 1.8343 1.8343 TEMPERATURE, C 7.3872 7.3872 7.3868 7.3868 PRESSURE, BAR 5 4.9998 4.9908 4.9907 ENTHALPY, M*J/HR 6.08E•03 6.08E•03 6.08E•03 6.08E•03 MOLECULAR WEIGHT 4.4482 4.4482 4.4482 4.4482 MOLE FRAC VAPOR 1 1 1 1 MOLE FRAC LIQUID 0 0 0 0 146 APPENDIX C. DESIGN CALCULATIONS

STREAM SUMMARY STREAM ID BOTTOMS B1 B2 B3 NAME Bottoms stream PHASE LIQUID LIQUID MIXED MIXED TOTAL STREAM RATE, G•MOL/HR 0.542 0.542 0.542 0.542 K*G/HR 4.67E•02 4.67E•02 4.67E•02 4.67E•02 STD LIQ RATE, M3/HR 7.03E•05 7.03E•05 7.03E•05 7.03E•05 TEMPERATURE, C 132.372 132.371 132.235 132.235 PRESSURE, BAR 5.001 5.001 4.986 4.986 MOLECULAR WEIGHT 86.149 86.149 86.149 86.149 ENTHALPY, M*J/HR 1.53E•02 1.53E•02 1.53E•02 1.53E•02 J/G 328.146 328.145 328.145 328.149 MOLE FRACTION LIQUID 1 1 0.9985 0.9985 REDUCED TEMP (KAYS RULE) 0.7994 0.7994 0.7991 0.7991 PRES (KAYS RULE) 0.1683 0.1683 0.1678 0.1678 ACENTRIC FACTOR 0.2943 0.2943 0.2943 0.2943 WATSON K (UOPK) 12.806 12.806 12.806 12.806 STD LIQ DENSITY, G/M3 663534.621 663534.621 663534.621 663534.621 SPECIFIC GRAVITY 0.6642 0.6642 0.6642 0.6642 API GRAVITY 81.542 81.542 81.542 81.542 VAPOR RATE, G•MOL/HR N/A N/A 8.03E•04 8.13E•04 K*G/HR N/A N/A 6.92E•05 7.00E•05 K*M3/HR N/A N/A 4.72E•09 4.77E•09 NORM VAP RATE(1), K*M3/HR N/A N/A 1.80E•08 1.82E•08 SPECIFIC GRAVITY (AIR=1.0) N/A N/A 2.974 2.974 MOLECULAR WEIGHT N/A N/A 86.135 86.135 ENTHALPY, J/G N/A N/A 602.51 602.51 CP, J/G•C N/A N/A 2.266 2.266 DENSITY, G/K*M3 N/A N/A 1.47E+07 1.47E+07 Z (FROM DENSITY) N/A N/A 0.8686 0.8686 TH COND, W/M•K N/A N/A 0.02271 0.02271 VISCOSITY, PAS N/A N/A 8.66E•06 8.66E•06

(1) NORMAL VAPOR VOLUME IS 22.414 M3/KG•MOLE (273.15 K AND 1 ATM) LIQUID RATE, G•MOL/HR 0.542 0.542 0.541 0.541 K*G/HR 4.67E•02 4.67E•02 4.66E•02 4.66E•02 M3/HR 8.63E•05 8.63E•05 8.62E•05 8.62E•05 GAL/MIN 3.80E•04 3.80E•04 3.79E•04 3.79E•04 STD LIQ RATE, M3/HR 7.03E•05 7.03E•05 7.02E•05 7.02E•05 SPECIFIC GRAVITY (H2O=1.0) 0.6642 0.6642 0.6642 0.6642 MOLECULAR WEIGHT 86.149 86.149 86.149 86.149 ENTHALPY, J/G 328.146 328.145 327.737 327.737 CP, J/G•C 3.048 3.048 3.048 3.048 DENSITY, G/M3 540633.561 540634.116 540811.768 540812.146 Z (FROM DENSITY) 0.0236 0.0236 0.0236 0.0236 SURFACE TENSION, N/M 7.37E•03 7.37E•03 7.39E•03 7.39E•03 THERMAL COND, W/M•K 0.08529 0.08529 0.08533 0.08533 VISCOSITY, PAS 1.35E•04 1.35E•04 1.35E•04 1.35E•04 C.1. PRO II CALCULATIONS 147

STREAM ID DISTILLATE D1 D2 D3 NAME Distillate stream PHASE LIQUID LIQUID MIXED MIXED TOTAL STREAM RATE, G•MOL/HR 0.594 0.594 0.594 0.594 K*G/HR 5.00E•02 5.00E•02 5.00E•02 5.00E•02 STD LIQ RATE, M3/HR 7.39E•05 7.39E•05 7.39E•05 7.39E•05 TEMPERATURE, C 7.387 7.387 7.388 7.388 PRESSURE, BAR 5 5 4.985 4.985 MOLECULAR WEIGHT 84.09 84.09 84.09 84.09 ENTHALPY, M*J/HR 3.47E•04 3.47E•04 3.47E•04 3.47E•04 J/G 6.938 6.938 6.938 6.938 MOLE FRACTION LIQUID 1 1 1 1 REDUCED TEMP (KAYS RULE) 0.558 0.558 0.558 0.558 PRES (KAYS RULE) 0.1617 0.1617 0.1613 0.1612 ACENTRIC FACTOR 0.2943 0.2943 0.2943 0.2943 WATSON K (UOPK) 12.515 12.515 12.515 12.515 STD LIQ DENSITY, G/M3 675511.243 675511.243 675511.243 675511.243 SPECIFIC GRAVITY 0.6762 0.6762 0.6762 0.6762 API GRAVITY 77.764 77.764 77.764 77.764 VAPOR RATE, G•MOL/HR N/A N/A 6.01E•06 6.03E•06 K*G/HR N/A N/A 2.68E•08 2.69E•08 K*M3/HR N/A N/A 2.82E•11 2.83E•11 NORM VAP RATE(1), K*M3/HR N/A N/A 1.35E•10 1.35E•10 SPECIFIC GRAVITY (AIR=1.0) N/A N/A 0.154 0.154 MOLECULAR WEIGHT N/A N/A 4.455 4.455 ENTHALPY, J/G N/A N/A 744.038 744.036 CP, J/G•C N/A N/A 7.086 7.086 DENSITY, G/K*M3 N/A N/A 950126.851 950122.411 Z (FROM DENSITY) N/A N/A 1.0021 1.0021 TH COND, W/M•K N/A N/A 0.15311 0.15311 VISCOSITY, PAS N/A N/A 8.15E•06 8.15E•06

(1) NORMAL VAPOR VOLUME IS 22.414 M3/KG•MOLE (273.15 K AND 1 ATM) LIQUID RATE, G•MOL/HR 0.594 0.594 0.594 0.594 K*G/HR 5.00E•02 5.00E•02 5.00E•02 5.00E•02 M3/HR 7.31E•05 7.31E•05 7.31E•05 7.31E•05 GAL/MIN 3.22E•04 3.22E•04 3.22E•04 3.22E•04 STD LIQ RATE, M3/HR 7.39E•05 7.39E•05 7.39E•05 7.39E•05 SPECIFIC GRAVITY (H2O=1.0) 0.6762 0.6762 0.6762 0.6762 MOLECULAR WEIGHT 84.09 84.09 84.091 84.091 ENTHALPY, J/G 6.938 6.938 6.938 6.938 CP, J/G•C 2.076 2.076 2.076 2.076 DENSITY, G/M3 683086.896 683086.891 683085.714 683085.71 Z (FROM DENSITY) 0.0264 0.0264 0.0263 0.0263 SURFACE TENSION, N/M 0.0199 0.0199 0.0199 0.0199 THERMAL COND, W/M•K 0.12661 0.12661 0.12661 0.12661 VISCOSITY, PAS 3.02E•04 3.02E•04 3.02E•04 3.02E•04 148 APPENDIX C. DESIGN CALCULATIONS

STREAM ID HYDROCARBONS HYDROC1 HYDROC2 HYDROC3 NAME Hydrocarbon feed streams PHASE LIQUID LIQUID LIQUID LIQUID TOTAL STREAM RATE, G•MOL/HR 1.188 1.188 1.188 1.188 K*G/HR 0.101 0.101 0.101 0.101 STD LIQ RATE, M3/HR 1.51E•04 1.51E•04 1.51E•04 1.51E•04 TEMPERATURE, C 25 25 25 25 PRESSURE, BAR 6 6 5.985 5.985 MOLECULAR WEIGHT 85.171 85.171 85.171 85.171 ENTHALPY, M*J/HR 4.93E•03 4.93E•03 4.93E•03 4.93E•03 J/G 48.681 48.681 48.681 48.681 MOLE FRACTION LIQUID 1 1 1 1 REDUCED TEMP (KAYS RULE) 0.5896 0.5896 0.5896 0.5896 PRES (KAYS RULE) 0.1974 0.1974 0.1969 0.1969 ACENTRIC FACTOR 0.2952 0.2952 0.2952 0.2952 WATSON K (UOPK) 12.647 12.647 12.647 12.647 STD LIQ DENSITY, G/M3 670190.474 670190.474 670190.474 670190.474 SPECIFIC GRAVITY 0.6709 0.6709 0.6709 0.6709 API GRAVITY 79.426 79.426 79.426 79.426 VAPOR RATE, G•MOL/HR N/A N/A N/A N/A K*G/HR N/A N/A N/A N/A K*M3/HR N/A N/A N/A N/A NORM VAP RATE(1), K*M3/HR N/A N/A N/A N/A SPECIFIC GRAVITY (AIR=1.0) N/A N/A N/A N/A MOLECULAR WEIGHT N/A N/A N/A N/A ENTHALPY, J/G N/A N/A N/A N/A CP, J/G•C N/A N/A N/A N/A DENSITY, G/K*M3 N/A N/A N/A N/A Z (FROM DENSITY) N/A N/A N/A N/A TH COND, W/M•K N/A N/A N/A N/A VISCOSITY, PAS N/A N/A N/A N/A

(1) NORMAL VAPOR VOLUME IS 22.414 M3/KG•MOLE (273.15 K AND 1 ATM) LIQUID RATE, G•MOL/HR 1.188 1.188 1.188 1.188 K*G/HR 0.101 0.101 0.101 0.101 M3/HR 1.53E•04 1.53E•04 1.53E•04 1.53E•04 GAL/MIN 6.72E•04 6.72E•04 6.72E•04 6.72E•04 STD LIQ RATE, M3/HR 1.51E•04 1.51E•04 1.51E•04 1.51E•04 SPECIFIC GRAVITY (H2O=1.0) 0.6709 0.6709 0.6709 0.6709 MOLECULAR WEIGHT 85.171 85.171 85.171 85.171 ENTHALPY, J/G 48.681 48.681 48.681 48.681 CP, J/G•C 2.179 2.179 2.179 2.179 DENSITY, G/M3 662583.209 662583.197 662581.258 662581.246 Z (FROM DENSITY) 0.0311 0.0311 0.031 0.031 SURFACE TENSION, N/M 0.0179 0.0179 0.0179 0.0179 THERMAL COND, W/M•K 0.1195 0.1195 0.1195 0.1195 VISCOSITY, PAS 2.73E•04 2.73E•04 2.73E•04 2.73E•04 C.1. PRO II CALCULATIONS 149

STREAM ID HYDROGEN HYDROG1 HYDROG2 HYDROG3 NAME Hydrogen feed stream PHASE VAPOR VAPOR VAPOR VAPOR

TOTAL STREAM RATE, G•MOL/HR 1.782 1.782 1.782 1.782 K*G/HR 3.59E•03 3.59E•03 3.59E•03 3.59E•03 STD LIQ RATE, M3/HR 5.14E•05 5.14E•05 5.14E•05 5.14E•05 TEMPERATURE, C 25 25 25 25 PRESSURE, BAR 6 6 5.996 5.996 MOLECULAR WEIGHT 2.016 2.016 2.016 2.016 ENTHALPY, M*J/HR 5.23E•03 5.23E•03 5.23E•03 5.23E•03 J/G 1454.359 1454.359 1454.359 1454.359 MOLE FRACTION LIQUID 0 0 0 0 REDUCED TEMP (KAYS RULE) 8.9669 8.9669 8.9669 8.9669 PRES (KAYS RULE) 0.4626 0.4626 0.4623 0.4623 ACENTRIC FACTOR •0.22 •0.22 •0.22 •0.22 WATSON K (UOPK) 47.444 47.444 47.444 47.444 STD LIQ DENSITY, G/M3 69930.982 69930.982 69930.982 69930.982 SPECIFIC GRAVITY 0.07 0.07 0.07 0.07 API GRAVITY 1889.929 1889.929 1889.929 1889.929 VAPOR RATE, G•MOL/HR 1.782 1.782 1.782 1.782 K*G/HR 3.59E•03 3.59E•03 3.59E•03 3.59E•03 K*M3/HR 7.39E•06 7.39E•06 7.39E•06 7.39E•06 NORM VAP RATE(1), K*M3/HR 3.99E•05 3.99E•05 3.99E•05 3.99E•05 SPECIFIC GRAVITY (AIR=1.0) 6.96E•02 6.96E•02 6.96E•02 6.96E•02 MOLECULAR WEIGHT 2.016 2.016 2.016 2.016 ENTHALPY, J/G 1454.359 1454.359 1454.359 1454.359 CP, J/G•C 14.296 14.296 14.296 14.296 DENSITY, G/K*M3 486437.805 486426.007 486102.9 486091.094 Z (FROM DENSITY) 1.0031 1.0031 1.0031 1.0031 TH COND, W/M•K 0.17562 0.17562 0.17562 0.17562 VISCOSITY, PAS 8.88E•06 8.88E•06 8.88E•06 8.88E•06

STREAM ID OFF•GAS O1 2 3 NAME

Off•gas stream mainly containing H2 PHASE VAPOR VAPOR VAPOR VAPOR TOTAL STREAM RATE, G•MOL/HR 1.834 1.834 1.834 1.834 K*G/HR 8.16E•03 8.16E•03 8.16E•03 8.16E•03 STD LIQ RATE, M3/HR 5.81E•05 5.81E•05 5.81E•05 5.81E•05 TEMPERATURE, C 7.387 7.387 7.387 7.387 PRESSURE, BAR 5 5 4.991 4.991 MOLECULAR WEIGHT 4.448 4.448 4.448 4.448 ENTHALPY, M*J/HR 6.08E•03 6.08E•03 6.08E•03 6.08E•03 J/G 744.633 744.633 744.633 744.633 MOLE FRACTION LIQUID 0 0 0 0 REDUCED TEMP (KAYS RULE) 5.9474 5.9474 5.9474 5.9474 PRES (KAYS RULE) 0.3703 0.3703 0.3696 0.3696 ACENTRIC FACTOR •0.2047 •0.2047 •0.2047 •0.2047 WATSON K (UOPK) 27.871 27.871 27.871 27.871 STD LIQ DENSITY, G/M3 140496.071 140496.071 140496.071 140496.071 SPECIFIC GRAVITY 0.1406 0.1406 0.1406 0.1406 API GRAVITY 874.653 874.653 874.653 874.653 VAPOR RATE, G•MOL/HR 1.834 1.834 1.834 1.834 K*G/HR 8.16E•03 8.16E•03 8.16E•03 8.16E•03 K*M3/HR 8.58E•06 8.58E•06 8.59E•06 8.59E•06 NORM VAP RATE(1), K*M3/HR 4.11E•05 4.11E•05 4.11E•05 4.11E•05 SPECIFIC GRAVITY (AIR=1.0) 0.154 0.154 0.154 0.154 MOLECULAR WEIGHT 4.448 4.448 4.448 4.448 ENTHALPY, J/G 744.633 744.633 744.633 744.633 CP, J/G•C 7.096 7.096 7.096 7.096 DENSITY, G/K*M3 951477.768 951448.234 949740.404 949710.816 Z (FROM DENSITY) 1.0021 1.0021 1.0021 1.0021 TH COND, W/M•K 0.15315 0.15315 0.15315 0.15315 VISCOSITY, PAS 8.15E•06 8.15E•06 8.15E•06 8.15E•06

(1) NORMAL VAPOR VOLUME IS 22.414 M3/KG•MOLE (273.15 K AND 1 ATM) LIQUID RATE, G•MOL/HR N/A N/A N/A N/A K*G/HR N/A N/A N/A N/A M3/HR N/A N/A N/A N/A GAL/MIN N/A N/A N/A N/A STD LIQ RATE, M3/HR N/A N/A N/A N/A SPECIFIC GRAVITY (H2O=1.0) N/A N/A N/A N/A MOLECULAR WEIGHT N/A N/A N/A N/A ENTHALPY, J/G N/A N/A N/A N/A CP, J/G•C N/A N/A N/A N/A DENSITY, G/M3 N/A N/A N/A N/A Z (FROM DENSITY) N/A N/A N/A N/A SURFACE TENSION, N/M N/A N/A N/A N/A THERMAL COND, W/M•K N/A N/A N/A N/A VISCOSITY, PAS N/A N/A N/A N/A C.2. EXCEL CALCULATIONS 151 C.2 Excel Calculations 152 APPENDIX C. DESIGN CALCULATIONS Test Test 2.45E•05 5 0.03 0.00 0.97 1.00 1.83 0.01 0.00 0.49 0.51 0.03 0.00 0.97 1.00 7.3872 • • • 0.0505 0.0037 1.7801 500000 1.40E•08 1.03E•09 4.94E•07 5.10E•07 280.5372 Off•gas 6 25 Gases 1.5 0.00 0.00 1.00 1.00 1.78 0.00 0.00 0.50 0.50 0.00 0.00 1.00 1.00 298.15 0.0000 0.0000 1.7820 • • • 600000 feed 4.95E•07 4.95E•07 0.00E+00 0.00E+00 Hydrogen 0.0 1.0 0.0 0.01 0.99 0.00 1.00 0.54 0.00 0.15 0.00 0.15 1.00 5.001 0.0077 0.5340 0.0000 • • • • 500100 2.13E•09 1.48E•07 1.70E•13 1.50E•07 132.3718 405.5218 Bottoms Streams 5 0.9 0.1 0.0 0.90 0.09 0.00 1.00 0.59 0.15 0.02 0.00 0.17 1.00 7.3872 0.5358 0.0563 0.0019 • • • • 500000 1.49E•07 1.56E•08 5.30E•10 1.65E•07 280.5372 Distillate Liquids 6 25 0.5 0.5 0.0 1.19 0.33 0.50 0.50 0.00 1.00 1.19 0.17 0.17 0.00 0.33 1.00 298.15 0.5940 0.5940 0.0000 600000 1.65E•07 1.65E•07 3.30E•07 • • 0.00E+00 feed Hydrocarbon [K] [°C] [Pa] [bar] Units/ [None] [None] [None] [None] [None] [mol/h] [mmol/s] [mole:mole] Component 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total i x Total [mol/h] [kmol/s] [mmol/s] 1•Hexene 1•Hexene n•Hexane Hydrogen Total Pressure Parameters Temperature Assumed overall conversion Molar flowrate Molar (mole fractions) :Hydrocarbon feed ratio feed :Hydrocarbon 2 H

Flow rates and compositions and rates Flow

T & P & T balance Mass C.2. EXCEL CALCULATIONS 153 Test 7.81E•10 7.81E•04 2.81E•03 1.18 0.09 1.00 2.27 4.25 0.32 3.59 8.16 0.52 0.04 0.44 1.00 0.21 0.21 0.21 0.21 0.13 0.01 4.53 4.66 0.43 18.04 18.47 0.953 0.029 0.002 1.018 1.049 1.18E•06 8.87E•08 9.97E•07 2.27E•06 0.00 0.00 1.00 1.00 0.00 0.00 3.59 3.59 0.00 0.00 1.00 1.00 0.24 0.24 0.24 0.24 0.00 0.00 4.13 4.13 0.49 20.37 20.86 0.488 0.000 0.000 2.049 2.049 9.98E•07 9.98E•07 0.00E+00 0.00E+00 0.18 0.00 0.64 0.00 0.01 0.99 0.00 1.00 6.51 6.31 0.15 6.31 0.30 12.78 12.96 46.02 46.66 0.002 0.156 0.000 0.158 0.000 0.002 0.000 0.002 548.31 543.94 543.97 1.79E•07 1.28E•05 3.43E•13 1.30E•05 1.35 0.00 4.85 0.00 0.90 0.10 0.00 1.00 8.15 7.79 0.21 7.26 0.43 12.53 13.87 45.09 49.95 0.111 0.012 0.015 0.138 0.001 0.000 0.000 0.002 686.09 671.59 610.23 1.25E•05 1.35E•06 1.07E•09 1.39E•05 0.00 0.00 0.49 0.51 0.00 1.00 7.95 7.61 0.24 7.78 0.49 13.89 14.22 28.11 49.99 51.19 0.063 0.066 0.000 0.129 0.001 0.001 0.000 0.002 101.18 669.19 656.02 662.46 1.39E•05 1.42E•05 2.81E•05 0.00E+00 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total ] 3 ] 3 i i / mi / i g/s] mi x /kmol] /kmol] x 3 3 [g/h] x [kg/s] [ [kg/m [kmol/m [m [m Density

Mass flow rate Mass Mass balance Mass 154 APPENDIX C. DESIGN CALCULATIONS 20 4.80 3.93 0.29 0.24 0.02 8.30 8.56 5.65 0.41 2.90 65.44 39.58 0.143 0.389 0.015 138.40 142.61 199.29 205.36 2306.60 2376.84 1395.03 1437.51 6.54E•08 4.80E•09 2.31E•06 2.38E•06 6.54E•05 4.80E•06 2.31E•03 2.38E•03 2.38E•06 3.89E•04 Off•gas 20 Gases 0.00 0.00 0.00 0.00 0.00 0.00 7.36 7.36 0.00 0.00 0.00 0.00 0.123 0.361 0.014 122.70 122.70 176.69 176.69 2045.03 2045.03 1236.83 1236.83 feed 2.05E•06 2.05E•06 2.05E•03 2.05E•03 2.05E•06 3.61E•04 0.00E+00 0.00E+00 0.00E+00 0.00E+00 Hydrogen 1 0.33 0.00 0.02 1.41 0.00 1.43 0.00 0.08 0.00 0.09 0.03 2.03 0.00 2.06 0.20 0.00 23.50 23.83 14.21 14.41 0.001 0.174 0.007 3.27E•10 2.35E•08 1.15E•12 2.38E•08 3.27E•07 2.35E•05 1.15E•09 2.38E•05 2.38E•08 1.74E•04 Bottoms Streams 1 2.01 2.47 1.10 0.12 0.15 1.36 0.07 0.01 0.01 0.08 1.58 0.17 0.21 1.96 1.21 1.50 18.26 22.74 11.04 13.75 0.001 0.170 0.007 1.83E•08 2.01E•09 2.47E•09 2.27E•08 1.83E•05 2.01E•06 2.47E•06 2.27E•05 2.27E•08 1.70E•04 Distillate Liquids 1 0.00 1.25 1.30 0.00 2.55 0.07 0.08 0.00 0.15 1.79 1.87 0.00 3.67 0.00 20.75 21.67 42.43 12.55 13.11 25.66 0.003 0.232 0.009 2.08E•08 2.17E•08 4.24E•08 2.08E•05 2.17E•05 4.24E•05 4.24E•08 2.32E•04 0.00E+00 0.00E+00 feed Hydrocarbon /s] 3 [m] [m/s] [mm] [l/min] [m Units/ [inches] Component 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total 1•Hexene n•Hexane Hydrogen Total /s] i /s] 3 v ol 3 l/s] u Q D Q [l/h] [ [m [l/day] [dm [l/week] [ml/min] Parameters Inner diameter Inner

Av. liquid Av. velocity

Volumetric flow rate Volumetric flow rate Mass balance Mass C.2. EXCEL CALCULATIONS 155 Solver Solver Solver Solutions Solutions Solutions Solutions 1 1 1 1 911 5.00 4.65 4.65 0.95 9.81 0.00 0.00 0.39 1.00 0.00 20.00 20.00 0.018 500000 465084 465084 8.15E•06 3.89E•04 36622.86 36622.86 36622.86 0.00E+00 1 1 1 1 397 6.44 6.44 6.00 0.49 9.81 0.00 0.00 0.36 1.00 0.00 20.00 20.00 0.040 643876 643876 600000 600000 8.88E•06 3.61E•04 89923.24 89923.24 89923.24 •1.00E•06 1 1 1 1 704 5.00 3.58 3.58 1.00 1.00 9.81 0.00 0.00 0.20 0.24 0.17 1.00 0.00 0.023 543.97 262.03 262.03 262.03 500100 357564 357564 1.35E•04 1.74E•04 0.00E+00 1 1 1 1 344 5.00 1.65 1.65 1.00 1.00 9.81 0.00 0.00 0.29 0.36 0.17 1.00 0.00 0.047 610.23 548.18 548.18 548.18 500000 165489 165489 3.02E•04 1.70E•04 •1.00E•06 1 1 1 1 563 7.64 7.63 6.00 1.00 1.00 9.81 0.00 0.00 0.25 0.30 0.23 1.00 0.00 0.028 662.46 245.70 247.36 245.70 763864 762766 600000 2.73E•04 2.32E•04 1.66E+00 ] ] 3 2 [m] [m] [m] [m] [W] [Pa] [Pa] [Pa] [Pa] [cP] [cP] [cP] [bar] [bar] [bar] [bar] [m/s] [m/s] [mm] [J/kg] [m/s [Pa.s] [None] [None] [None] [None] [None] [None] [None] [None] [None] [kg/m e c 2 1 2 1 T 2 1 x f 90° g z z P P v v Di •F W K K K Re K needle v alv e needle K 1•Hexene n•Hexane Hydrogen Mixture Valves diameter Viscosity Pipe inner Pipe Straight pipe Straight Reynolds no. Reynolds Fitting amounts Fitting Frictional losses Used inUsed Solver calculation RHS LHS Work Heights Densities Pressures Gravit. Acc. Linear velocities Solve losses Frictional

calculation

Required for Required Hydrodynamic calculations Hydrodynamic 156 APPENDIX C. DESIGN CALCULATIONS C.3 Derivation of the McCabe-Thiele approximation

The assumptions used in the derivation of these equations are given in section 8.3. Refer to Figure 8.2 for a schematic layout de…ning the variables used below.

C.3.1 Condenser

Overall Material Balance:

+ (1 + R)D = Vn

Vn = + (1 + R)D (C.1)

Component Balance:

y + (1 + R)xDD = ynVn

y + (1 + R)xDD = yn[ + (1 + R)D] y + (1 + R)x D y = D (C.2) n + (1 + R)D

Energy Balance:

V G V G H + (1 + R)DHD + GRH = VnH + GRH QC n n V G V G H + (1 + R)DHD + (1 X)GH = [ + (1 + R)D]H + (1 X)GH QC n n V G QC = [ + (1 + R)D]H + (1 X)GH n n V G [H + (1 + R)DHD + (1 X)GH ] V V V = (H H ) + (1 + R)D(H HD) n n + (1 X)G(HG HG) n V V V = (H H ) + (1 + R)D(H HD) (C.3) n n C.3. DERIVATION OF THE MCCABE-THIELE APPROXIMATION 157

C.3.2 Recti…cation section

Overall Material Balance:

+ D + LR = F + VR

VR = ( + D F ) + LR (C.4) V V V V V V (Hn Hj ) + D(Hn Hj ) + F (Hj HF ) + RD(Hn HD) = ( + D F ) + vap (Hj ) V V F (Hj HF ) + RD(Hn HD) = (D F ) + vap (Hj )

Component Balance:

Out = In + NettF ormed

y + xDD + xjLR = zF F + yj+1VR

yj+1VR = LRxj + (y + xDD zF F ) LR (y + xDD zF F ) yj+1 = xj + VR VR LR (y + xDD zF F ) = xj + (C.5) [( + D F ) + LR] [( + D F ) + LR] Energy Balance:

L V G LRH = FHF + VRH + Gj+1H + ( QC ) H + DHD + GRH j j j f g L V G LRH = FHF + VRH + (1 X)GH + ( QC ) H + DHD + (1 X)GH j j j f g L V G LRH = FHF + VRH [H + DHD + (1 X)G(H H ) + QC ] j j j L V G LRH = FHF + VRH [H + DHD + (1 X)G(H H ) + QC ] j j j L V G LRH = FHF + [( + D F ) + LR]H [H + DHD + (1 X)G(H H ) + QC ] j j j L V V G LR(H H ) = FHF + ( + D F )H [H + DHD + (1 X)G(H H ) + QC ] j j j j V L G V LR(H H ) = H + DHD + (1 X)G(H H ) + QC FHF ( + D F )H j j j j vap V V V G LR(H ) = (H H ) + D(HD H ) + F (H HF ) + (1 X)G(H H ) + QC j j j j j V V V G (H Hj ) + D(HD Hj ) + F (Hj HF ) + (1 X)G(H Hj ) + QC LR = vap (Hj ) V V V (H Hj ) + D(HD Hj ) + F (Hj HF ) + QC = vap (C.6) (Hj )

Substituting QC in from eq. C.3 and then assuming that no 1-hexene exits through 158 APPENDIX C. DESIGN CALCULATIONS the o¤-gas ( = 0):

V V V V V V V V (Hn Hj ) + D(Hn Hj ) + F (Hj HF ) + (Hn H ) + (1 + R)D(Hn HD) LR = vap (Hj ) V V F (Hj HF ) + RD(Hn HD) == vap (C.7) (Hj )

Substitute equations C.4 and C.4 into eq. C.5 to obtain the operating line:

V V V (H H )+D(HD H )+F (H HF )+QC j j j (Hvap) xj + y + xDD zF F j yj+1 = V V V (H H )+D(HD H )+F (H HF )+QC j j j ( + D F ) + (Hvap) j V V V vap (H Hj ) + D(HD Hj ) + F (Hj HF ) + QC xj + (y + xDD zF F )Hj = f vap V g V V H ( + D F ) + (H H ) + D(HD H ) + F (H HF ) + QC j j j j

V V V Substitute in for QC = (H H ) + (1 + R)D(H HD) form eq. C.3 and n n rearrange. Then cancel equivalent enthalpies and assume = 0:

V V V V vap ( + D)(H H ) + F (H HF ) + RD(H HD) xj + (y + xDD zF F )H f n j j n g j yj+1 = vap V V V V H ( + D F ) + ( + D)(H H ) + F (H HF ) + RD(H HD) j n j j n (C.8) V V vap F (H HF ) + RD(H HD) xj + (xDD zF F )H f j n g j = vap V V H ( + D F ) + F (H HF ) + RD(H HD) j j n C.3.3 Reactive Zone

XHrxn VS = VR LR Hvap XHrxn = ( + D F ) + LR(1 ) Hvap = ( + D F ) V V V V V V rxn (H H ) + D(H H ) + F (H HF ) + RD(H HD) XH n j n j j n + vap (1 vap ) (Hj ) H V V rxn F (H HF ) + RD(H HD) XH j n = (D F ) + vap (1 vap ) (C.9) (Hj ) H C.3. DERIVATION OF THE MCCABE-THIELE APPROXIMATION 159

XHrxn LS = LR(1 ) Hvap V V V V V V rxn (H H ) + D(H H ) + F (H HF ) + RD(H HD) XH n j n j j n = vap (1 vap ) (Hj ) H V V rxn F (H HF ) + RD(H HD) XH j n = vap (1 vap ) (C.10) (Hj ) H

C.3.4 Stripping section (reactive zone incorporated)

B = F + FS ( + D) = F + FS D (C.11)

G V L QB = BHB + GH + VSH (FSHFS + GHG + LSH ) w+1 w+1 w G V L = (F + FS ( + D))HB + G(H HG) FSHFS + VSH LSH w+1 w+1 w V vap V = (F + FS D)HB FSHFS + VSH LS(H H ) w+1 w w V vap V = (F + FS D)HB FSHFS + VSH LS(H H ) w w w vap V = (F + FS D)HB FSHFS LS(H ) + H [VS + LS] w w V V rxn F (H HF ) + RD(H HD) XH j n vap = (F + FS D)HB FSHFS vap (1 vap )(Hw ) (Hj ) H V V rxn F (H HF ) + RD(H HD) XH V j n + Hw [(D F ) + 2 vap (1 vap )] (Hj ) H rxn V V XH = (F + FS D)HB FSHFS [F (H HF ) + RD(H HD)](1 ) j n Hvap V V rxn F (H HF ) + RD(H HD) XH V j n + Hw [(D F ) + 2 vap (1 vap )] (Hj ) H rxn V V V XH Hw = F HB Hw + (Hj HF )(1 vap )[2 vap 1] + FS(HB HFS) f H (Hj ) g rxn V V V XH Hw + D(Hw HB) + RD(Hn HD)(1 vap )(2 vap 1) H (Hj ) (C.12) 160 APPENDIX C. DESIGN CALCULATIONS

C.3.5 Stripping section (reactive zone excluded)

Overall Material Balance:

B + VS = FS + LS

VS = (FS B) + LS (C.13) Component Balance:

Out = In + NettF ormed

xBB + yw+1VS = zF sFS + xwLS

yw+1VS = (zF sFS xBB) + LSxw LS (zF sFS xBB) yw+1 = xw + VS VS LS (zF sFS xBB) = xw + (C.14) [(FS B) + LS] [(FS B) + LS] Energy Balance:

G V L BHB + GHw+1 + VSHw+1 = FSHFS + GHG + LSHw + QB G V L G(H HG) + VSH = (FSHFS BHB) + LSH + QB w+1 w+1 w V L G VSH LSH = (FSHFS BHB) G(H HG) + QB w+1 w w+1 V L G [(FS B) + LS]H LSH = (FSHFS BHB) G(H HG) + QB w+1 w w+1 V L V V G LS(H H ) = FS(HFS H ) + B(H HB) G(H HG) + QB w+1 w w+1 w+1 w+1 vap V V G LS(H ) = FS(HFS H ) + B(H HB) G(H HG) + QB w w+1 w+1 w+1 V V G FS(HFS Hw+1) + B(Hw+1 HB) G(Hw+1 HG) + QB LS = vap Hw (C.15)

Operating line (substitute equations C.13 and C.15 into eq. C.14):

V V G FS (HFS Hw+1)+B(Hw+1 HB ) G(Hw+1 HG)+QB [ vap ]xw + (zF sFS xBB) Hw yw+1 = V V G FS (HFS Hw+1)+B(Hw+1 HB ) G(Hw+1 HG)+QB (FS B) + [ vap ] Hw V V G vap FS(HFS Hw+1) + B(Hw+1 HB) G(Hw+1 HG) + QB xw + Hw (zF sFS xBB) = f vap V V g G Hw (FS B) + FS(HFS Hw+1) + B(Hw+1 HB) G(Hw+1 HG) + QB V V vap FS(HFS Hw+1) + B(Hw+1 HB) + QB xw + Hw (zF sFS xBB) = f vap V g V Hw (FS B) + FS(HFS H ) + B(H HB) + QB w+1 w+1 (C.16) C.3. DERIVATION OF THE MCCABE-THIELE APPROXIMATION 161

C.3.6 Reboiler

Overall Material Balance:

B + Vm+1 = Lm

Vm+1 = Lm B (C.17) Component Balance:

xBB + ym+1Vm+1 = xmLm

ym+1Vm+1 = Lmxm xBB ym+1[Lm B] = Lmxm xBB Lm xBB ym+1 = xm (C.18) Lm B Lm B Energy Balance:

V L BHB + Vm+1Hm = LmHm + QB (C.19) V BHB + Vm+1HB = LmHB + QB V BHB + Vm+1HB = [B + Vm+1]HB + QB V Vm+1HB = Vm+1HB + QB vap Vm+1HB = QB 162 APPENDIX C. DESIGN CALCULATIONS Appendix D

PYREX SAFE WORKING PRESSURE

163 164 APPENDIX D. PYREX SAFE WORKING PRESSURE

Figure D.1: Pyrex Safe Working Pressure (graph obtained from university glass blower’sPyrex manual) Appendix E

MECHANICAL DRAWINGS

165 166 APPENDIX E. MECHANICAL DRAWINGS G C D H A B E F 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

467.25mm

10.00mm 419.00mm

10.00mm 139.00mm 3.00mm 180.00mm 60.00mm 0.875in 0.25in 84.50mm

100.00mm 3.00mm

8 .00mm 0.125in 22.00mm 13.69mm 25.00mm 11.31mm 1.00mm 0.25in 0.125in 30.0°

125.00mm Ø106.00mm 20.00mm 3.00mm Ø50.00mm Ø56.00mm Ø0.25in 5in J.J. NieuwoudtJ.J. ______2 20.00mm integrated reflux drum at the top of thetop of theat drum reflux integrated 0.1 DISTILLATE PARTIALDISTILLATE catalytic distillation column (CD-1) column distillation catalytic Distillate partial condenser and condenser partial Distillate

DRAWN BY:DRAWN 19.00mm 21.00mm CONDENSER 19.00mm 467.25mm DESCRIPTION (C-DP) 13/05/2005 ______

REVISED: 10.00mm 419.00mm

3.00mm 60.00mm 139.00mm 180.00mm 0.875in 0.500in 100.00mm 0 (Original drawing) (Original 0 REFERENCE NUMBERREFERENCE

JJN/09112003-01 0.049in DRAWING NUMBERDRAWING 10.00mm 20.00mm REVISION NO.REVISION 3.00mm 2 OF 33 OF 2 SCALE SHEET 1 :2 1 CATALYTIC DISTILLATION PROJECT DISTILLATION CATALYTIC DRAWING MECHANICAL 25.00mm Continuous system Continuous K.P. Möller (UCT) Möller K.P. (US) Callanan L.H. ______APPROVED BY:APPROVED 0.125in 1.00mm 0.25in ______

DATE 17.00mm G H D C E B A F 168 APPENDIX E. MECHANICAL DRAWINGS 6 5 4 3 2 1

100.00mm 100.00mm 50.00mm 50.00mm 3.00mm 20.00mm 3.00mm

D 10.00mm D

3.00mm 40.00mm 0.25in 25.00mm

C C 150.00mm 100.00mm 80.00mm(max.) 25.00mm 17.50mm

B Thread of 10.00mm B length 40mm 10.00mm Ø0.125in 0.125in 50.00mm 0.125in 100.00mm

Ø106.00mm Ø100.00mm

MECHANICAL DRAWING CATALYTIC DISTILLATION PROJECT REBOILER Continuous system

(Option 3) SCALE APPROVED BY: DATE A 1 :1 A DESCRIPTION DRAWING NUMBER JJN/06022004-01 ______Reboiler at the bottom of the catalytic L.H. Callanan (US) REVISION NO. distillation column 1

DRAWN BY: REVISED: SHEET 4 OF 33 ______K.P. Möller (UCT) REFERENCE NUMBER ______J.J. Nieuwoudt 05/05/2005 6 5 4 3 2 1 170 APPENDIX E. MECHANICAL DRAWINGS 2 1 SHORT DESCRIPTION TOP VIEW OF THE THE A-A SECTION 45.0° Perforation dimensions Diameter: 1mm Ø50.00mm Set on the nodes of a grid

containing squares with Ø4.93mm sides 4.5mm. Most of the holes are verticle.

B B Sideview:

B In each of the 8 legs there B is one 1mm perforation half-way between the last two at an angle of 45°with the horizontal. 12.00mm 12.00mm

1/4'' SS tube [SS-T4-S-035-6ME] Sideview:

The wall of the vessel already exists and is only included so that it can be seen how the shower head is supposed to fit R 20.00 into the vessel and how its inlet pipe should enter the vessel. 30mm Stainless Steel wall of the vessel

Tube has a threaded sleeve at the tip

Shower head's female NPT fitting

A A

40.00mm

3.18mm 50.00mm

SIDE VIEW OF THE B-B SECTION A A MECHANICAL DRAWING CATALYTIC DISTILLATION PROJECT LIQUID DISTRIBUTOR Continuous system SCALE APPROVED BY: DATE 1 :1

DESCRIPTION DRAWING NUMBER JJN/08032004-01 Liquid distributor for the reflux line ______REVISION NO. located at the top of the CD column. L.H. Callanan (US) 2

DRAWN BY: REVISED: SHEET 20 OF 33 ______REFERENCE NUMBER ______K.P. Möller (UCT) J.J. Nieuwoudt 13/05/2005

2 1 172 APPENDIX E. MECHANICAL DRAWINGS Appendix F

EQUIPMENT DATA SHEETS

173 174 APPENDIX F. EQUIPMENT DATA SHEETS F.1 Catalytic distillation column data sheet (CD-1)

Equipment No. (Tag) CD•1 CATALYTIC DISTILLATION COLUMN DATA SHEET Description (function) Simultaneous reaction•separation Sheet No. Operating data 1 No. required 1 [None] 2 Non•reactiv e section Structured packing [None] 3

Reactive section Ni/Al 2 O 3 catalyst [None] 4 Column shell 5 Sections Type 1 6 Amount available 3 [None] Length 480 [mm] 7 Types 2 [None] Amount available 1 [None] 8 Inner diameter 49.25 [mm] Type 2 9 Outer diameter 60.33 [mm] Length 416 [mm] 10 Thickness 5.54 [mm] Amount available 2 [None] 11 Corrosion allowance None [mm] Total height 1312 [mm] 12 3 Volume 2.5 [dm ] Material of construction SS AISI 316 [None] 13 Non•reactive structured packing 14 Type Sulzer CY [None] Channel 15 Void fraction 0.965 [None] Base 7.5 [mm] 16 2 3 Packing surface area 708 [m /m ] Side 5.65 [mm] 17 Crimp height 4.25 [mm] Flow angle from horiz. 45 [°] 18 Layer height 160 [mm] Packing height 1280 [mm] 19 Diameter 50 [mm] Material of construction SS316 [None] 20 Reactive section 21

Type "Tea bag" [None] Catalyst Ni/Al 2O 3 [None] 22 Reaction Hydrog enation [None] Catalyst weight 20 [g] 23 Reboiler 24 Type Kettle [None] Heating element 25 Vessel Geometry Coiled [None] 26 Diameter 100 [mm] Maximum power 1000 [W] 27 Height 150 [mm] Nominal power 650 [W] 28 3 Volume 1.18 [dm ] Outer diameter 8 [mm] 29 Material of construction SS AISI 316 [None] Height 80 [mm] 30 Material of construction Incoloy [None] 31 Glass level indicator 32 Location Side of section 4 [None] Glass tube 33 Metal connections Nominal pressure 2•6 [bar] 34 Inner diameter 0.194 [inch] Length 166.5 [mm] 35 Outer diameter 0.250 [inch] Outer diameter 6 [mm] 36 Thickness 0.028 [inch] Inner diameter 3 [mm] 37 Material of construction SS AISI 316 [None] Thickness 1.5 [mm] 38 W orking pressure (max.) 276 [bar] Material of construction Glass [None] 39 Glass•metal connection Graphite ferrules [None] Safe working pressure 30 [bar] 40 Other related equipment 41 Partial condenser C•DP [None] Storage tanks T•HC, T•DC6, T•BC6 [None] 42 Heat exchanger E•BP [None] Pumps P•HF, P•RD [None] 43 Refrigerator E•1 [None] 44 Office purposes 45 REMARKS: 46 47 48 F.2. TWO-STAGE PARTIAL CONDENSER DATA SHEET (C-DP) 175 F.2 Two-stage partial condenser data sheet (C-DP)

Equipment No. (Tag) C•DP PARTIAL CONDENSER SHEET Description (function) Partial condenser for distillate Sheet No. Operating data 1 No. of units required 1 [None] Sections (top to bottom) 2 Type Shell and tube [mm] Number 4 [None] 3 Shells per unit 2 [None] Section 1 Gas inlet chamber [None] 4 Surface area per unit 57453 [mm 2 ] Section 2 (shell) Tap water [None] 5 Surface area per shell [mm 2 ] Section 3 (shell) Glycol [None] 6 Total heat removed 650 [W] Section 4 Reflux chamber [None] 7 Performance of section 2 8 Shell side Tube side 9 Fluid circulating Tap water [None] Fluid circulating N/A • 10 N/A • 1•Hexene [None] 11 Vapour Vapour N/A • n•Hexane [None] 12 Liquid Water [None] Non•condensables Hydrog en [None] 13 Heat removed 250 [W] 14 Performance of section 3 15 Shell side Tube side 16 Fluid circulating Glycol [None] Fluid circulating N/A • 17 N/A • 1•Hexene [None] 18 Vapour Vapour N/A • n•Hexane [None] 19 Non•condensables N/A • Non•condensables Hydrog en [None] 20 Heat removed 400 [W] 21 Construction of section 1: Gas inlet chamber (top) 22 Material of construction SS AISI 316 [None] Baffles 23 Shell Amount 0 [None] 24 Number of shells 1 [None] Spacing N/A [mm] 25 Inner diameter 50 [mm] Diameter N/A [mm] 26 Outer diameter 56 [mm] Baffle cut N/A [mm] 27 Thickness 3 [mm] Thickness N/A [mm] 28 Length (excl. flanges) 21.44 [mm] Material of construction N/A [None] 29 Volume 42 [ml] Inlet and outlet 30 Flanges Outer diameter 0.875 [inch] 31 Outer diameter 106 [mm] Inner diameter 0.745 [inch] 32 Height 10 [mm] Thickness 0.083 [inch] 33 Total section height 34.44 [mm] 34 Construction of section 2: Tap water 35 Material of construction SS AISI 316 [None] Baffles 36 Shell Amount 2 [None] 37 Number of shells 1 [None] Spacing 19.33 [mm] 38 Inner diameter 50 [mm] Diameter 50 [mm] 39 Outer diameter 56 [mm] Baffle cut 15 [mm] 40 Thickness 3 [mm] Thickness 1 [mm] 41 Length (excl. flanges) 60 [mm] Material of construction SS AISI 316 [None] 42 Volume 118 [ml] Inlet and outlet 43 Flanges Outer diameter 0.500 [inch] 44 Outer diameter 106 [mm] Inner diameter 0.402 [inch] 45 Height 10 [mm] Thickness 0.049 [inch] 46 Total section height 80 [mm] 47 176 APPENDIX F. EQUIPMENT DATA SHEETS

Construction of section 3: Glycol 48 Material of construction SS AISI 316 [None] Baffles 49 Shell Amount 7 [None] 50 Number of shells 1 [None] Spacing 21.5 [mm] 51 Inner diameter 50 [mm] Diameter 50 [mm] 52 Outer diameter 56 [mm] Baffle cut 15 [mm] 53 Thickness 3 [mm] Thickness 1 [mm] 54 Length (excl. flanges) 180 [mm] Material of construction SS AISI 316 [None] 55 Volume 353 [ml] Inlet and outlet 56 Flanges Outer diameter 0.500 [inch] 57 Outer diameter 106 [mm] Inner diameter 0.402 [inch] 58 Height 10 [mm] Thickness 0.049 [inch] 59 Total section height 200 [mm] 60 Tubes 61 Number of tubes 12 [None] W orking pressure (max.) 276 [bar] 62 Configuration Staggered [None] Outer diameter 0.250 [inch] 63 Material of construction SS AISI 316 [None] Inner diameter 0.194 [inch] 64 Bundle diameter [mm] Thickness 0.028 [inch] 65 Shell bundle clearance 10.58 [mm] Length (excl. flanges) 66 Surface area Section 2 60 [mm] 67 Section 2 14363 [mm 2 ] Section 3 180 [mm] 68 Section 3 43090 [mm 2 ] Section 4 (from top) 17 [mm] 69 Total 57453 [mm 2 ] Pitch 8 [mm] 70 Section 4: Reflux chamber (bottom) 71 Total volume 273 [ml] Off•gas outlet 72 Liquid volume (nominal) 196 [ml] Outer diameter 0.125 [inch] 73 Liquid height (nominal) 100 [mm] Inner diameter 0.069 [inch] 74 Material of construction SS AISI 316 [None] Thickness 0.028 [inch] 75 Chamber dimensions Angle with horizontal 30 [°] 76 Inner diameter 50 [mm] Liquid outlets 77 Outer diameter 56 [mm] Amount 2 [None] 78 Thickness 3 [mm] Outer diameter 0.125 [inch] 79 Length (excl. flanges) 142 [mm] Inner diameter 0.069 [inch] 80 Flanges Thickness 0.028 [inch] 81 Outer diameter 106 [mm] 82 Height 10 [mm] 83 Total section height 155 [mm] 84 Glass level indicator 85 Location Side of section 4 [None] Glass tube 86 Metal connections Nominal pressure 2•6 [bar] 87 Inner diameter 0.194 [inch] Length 110 [mm] 88 Outer diameter 0.250 [inch] Outer diameter 6 [mm] 89 Thickness 0.028 [inch] Inner diameter 3 [mm] 90 Material of construction SS AISI 316 [None] Thickness 1.5 [mm] 91 W orking pressure (max.) 276 [bar] Material of construction Glass [None] 92 Glass•metal connection Graphite ferrules [None] Safe working pressure 30 [bar] 93 Other related equipment 94 Refrigerator E•1 [None] 95 Office purposes 96 REMARKS: 97 98 99 F.3. REFRIGERATOR DATA SHEET (E-1) 177 F.3 Refrigerator data sheet (E-1)

Equipment No. (Tag) E•1

REFRIGERATED CIRCULATING BATH (REFRIGERATOR) Description (function) Controls refrigeration liquid temperature Sheet No. Operating data 1 No. required 1 [None] Temperature 2 Neslab Instruments Inc. [None] Minimum •30 [°C] 3 Make Endocal [None] Maximum 100 [°C] 4 Type RTE•8 [None] Stability ±0.01 [°C] 5 Circulation Closed/Open loop [None] Nominal (input) 2 [°C] 6 Capacity Nominal (output) 10 [°C] 7 Cooling (@ 20°C) 415 [W] Electrical requirements 8 Heater 1000 [W] Voltage 230 [V] 9 43200 [g/h] Current 6.5 [A] 10 Fluid flow rate 0.72 [l/min] Frequency 50 [Hz] 11 Part number 15400401 [None] Serial number 84K15244•3 [None] 12 Main body 15 Unit Bath work area 16 Height 445.0 [mm] Length 209.0 [mm] 17 Width 406.0 [mm] Width 133.0 [mm] 18 Depth 432.0 [mm] Depth 229.0 [mm] 19 Cooling fluid options Bath v olume 10.0 [l] 20

50/50 (vol.) tap water + 50/50 (vol.) tap water + Below 7°C [None] Cooling fluid used [None] 21 lab. grade ethylene glycol lab. grade ethylene glycol

+7 to 80°C Filtered tap water [None] Filling requirements 22 Above 80°C User responsible [None] Filling 0.75'' of top plate [None] 23 Minimum bath level 2.5'' of top [None] 24 Internal pump 25 Capacity @ 13l/min Connections 26 0.0 [ft] MOC SS serrated [None] 27 Head (min.) 0.0 [m] Outer diameter (OD) 3/8 [inch] 28 17.0 [ft] 3/8 [inch] 29 Head (max.) Tubing accepted (ID) 5.2 [m] 5/16 [inch] 30 Safety characteristics 31 Material to be stored [None] Mass flow rate 32 Unit•rear/wall clearance 30 [cm] Cleaning Periodic [None] 33 External circulation Excessive heat [None] Plug RTE inlet line [None] 34 inoperative Avoid Moisture [None] Keep high enough [None] 35 Bath lev el Corrosive material [None] Avoid over•filling [None] 36 Dust [None] Visual inspection Monthly [None] 37 Office purposes 38 REMARKS: 39 40 41 178 APPENDIX F. EQUIPMENT DATA SHEETS F.4 Re‡ux pump data sheet (P-RD)

Equipment No. (Tag) P•RD Reflux Pump Description (function) Refluxes distillate to column Sheet No. Operating data 1 Number required 1 [None] Available NPSH 1 [m] 2 Type Metering pump [None] Required output 14.2 [l/h] 3 Fluid Operating pressures 5 [bar] 4 Viscosity 3.02E•04 [Pa.s] W orking temperature 7 [°C] 5 Density 683 [kg/m 3 ] Analysis None [None] 6 Electrical supply 230V (3phase) [None] 7 Technical data 8 Pump Lubricants 9

Drawing no. See manual [None] Pump case and gear box 10

Cucchi Hydraulic SAE140, 23°E (ca. Type [None] Type [None] 11 Diaphragm Pump 160mPa.s) Model CMP•2/12 X 118 [None] Volume 300 [ml] 12 Shell Spirax A85 W Maximum load 0•14.2 [l/h] Oil used [None] 13 140 Max. head 20 [bar] Oil chamber 14 Efficiency [None] Type 1 or 2 °E Pharma [ml] 15 Piston Volume 72 [ml] 16 Diameter 8 [mm] Oil used Glycerol [None] 17 str oke/ Max. stroke speed 118 W ater required 18 min Motor Cooling None [None] 19 Type H71A4•40050 [None] Sealing None [None] 20 Serial no. 4601 [None] Material of construction [None] 21 Year 2004 [None] Head SS316 [None] 22 Max. power delivered 0.25 [kW] Valv es SS316 [None] 23 Electrical power supply Diaphragm PTFE [None] 24 Voltage 230/380 [V] Phonometric 25 Phase 3 [None] Max. sound 76.6 dB(A) 26 Relief v alv e set pressure N/A [None] Av. surface pressure 73.2 dB(A) 27 Two•plate double Type of baseplates [None] Sound power 76.7 dB(A) 28 vibration dampener Dimensions (box) 29 Volume 23.52 [dm 3] 30 W idth 140.00 [mm] 31 Length 400.00 [mm] 32 Total Heigth 420.00 [mm] 33 Related equipment: Variable speed drive 34 Type Emotron [None] Model VSD•DFE23•02 [None] 35 DFE Freq uency 230V(1ph) to Description [None] Function [None] 36 Inverter 230V(3ph) Office purposes 37 REMARKS: When filling the oil chamber the stroke leng th must be set to 0% with the adjustment knob. Ensure that no 38 air remains in the poured oil. Gear box oil te be initially chang ed after 500hours and then 3000hours. 39 40 F.5. PRECISA BALANCES DATA SHEETS (W-D AND W-B) 179 F.5 Precisa balances data sheets (W-D and W-B)

Equipment No. (Tag) W•D and W•B ELECTRONIC BALANCES Description (function) Product balances for mass flow rates Sheet No. Operating data 1 No. required 2 [None] Ambient temperature 2 Input rate Minimum 5 [°C] 3 W •D 50 [g /h] Maximum 40 [°C] 4 W •B 47 [g /h] Relative humidity 5 Capacity (nominal) Minimum 25 [%] 6 W •D 2.5 [days] Maximum 85 [%] 7 W •B 2.5 [days] Criterium Non•condensing [None] 8 Technical data 9 Supplier Cape Scientific Services [None] W eighing pan 10 Make Precisa [None] Form Square [None] 11 Type XB 4200C [None] Length 170 [mm] 12 Minimum weight Breadth 170 [mm] 13 W eight 0.50 [g] Electrical 14 e 0.01 [g] Voltage 115 or 230 [V] 15 Maximum weight Voltage tolerance •20 to +15 [%] 16 W eight 4200.00 [g] Frequency 50 to 60 [Hz] 17 Readability (d) 0.10 [g] Power consumption 18 Linearity 0.15 [g] W ithout peripheral 6.0 [VA] 19 Reproducibility 0.10 [g] 20 Data transfer to peripheral devices 21 Interface RS232/V23 [None] 22 Safety characteristics 23 Maintenance period Regular [None] 24 Office purposes 25 REMARKS: 26 27 28 180 APPENDIX F. EQUIPMENT DATA SHEETS Appendix G

STREAM INFORMATION

181 182 APPENDIX G. STREAM INFORMATION

Relation to column Stream parameters Units Feed Number [None] 2 5 3 4 6 Hydrocarbon Pressurized Nitrogen Hydrogen Hydrogen/ Name [None] feed feed feed feed Nitrogen

Begin [None] T•HC HPLC•1 N 2 utility H 2 utility TV•HN

Description End [None] HPLC•1 CD•1 TV•HN TV•HN CD•1 [inch] N/A 0.125 0.125 0.125 0.125 Outer diameter [mm] N/A 3.175 3.175 3.175 3.175 [inch] 0.125 0.069 0.069 0.069 0.069 Inner diameter [mm] 3.175 1.753 1.753 1.753 1.753 [inch] N/A 0.028 0.028 0.028 0.028 Wall thickness [mm] N/A 0.711 0.711 0.711 0.711 MOC [None] Plastic SS 316 SS•316 SS 316 SS 316 Suitability of MOC [None] Moderate Excellent Excellent Excellent Excellent •29 to 37°C max. [bar] N/A 586 586 586 586 working pressure

Elevated Pipe [None] N/A 1.00 1.00 1.00 1.00 temperature factor

Allowable [°C] N/A •29 to 93 •29 to 93 •29 to 93 •29 to 93 temperature range

Max. working [bar] N/A 586 586 586 586 pressure

Flow sheet 1C6•0.125•P• 1C6•0.125• N2•0.125• H2•0.125• H2/N2•0.125• [None] description 02 SS316•05 SS316•03 SS316•04 SS316•06

Temperature [°C] 25 25 25 25 25 Pressure [bar] 1.01325 6 6 6 6 Phase [None] L L G G G [g/h] 101 101 Purging 3.593 3.593 Flow rate [mol/h] 1.188 1.188 Purging 1.782 1.782 Composition 1•Hexene [mol/mol] 0.50 0.50 0.00 0.00 0.00 n•Hexane [mol/mol] 0.50 0.50 0.00 0.00 0.00

Hydrogen [mol/mol] 0.00 0.00 0.00 1.00 1.00 Properties Water [mol/mol] 0.00 0.00 0.00 0.00 0.00 Nitrogen [mol/mol] 0.00 0.00 1.00 0.00 STD liquid [l/h] 0.15 0.15 Purging 7.36 7.36 volumetric flow rate [ml/min] 2.52 2.52 Purging 122.67 122.67 Density [kg/m 3] 670.2 670.2 6.781 0.488 0.488 183

Relation to column Top Bottom 7 9 10 12 15 8 16 Pressurized Cooled Overhead Reflux Off•gas Distillate Bottoms reflux bottoms CD•1 C•DP P•RD C•DP C•DP CD•1 C•BC6 C•DP P•RD CD•1 Atmosphere T•DC6 E•BP T•BC6 0.875 0.250 0.250 0.125 0.125 0.125 0.125 22.225 6.35 6.35 3.175 3.175 3.175 3.175 0.745 0.194 0.194 0.069 0.069 0.069 0.069 18.923 4.928 4.928 1.753 1.753 1.753 1.753 0.083 0.028 0.028 0.028 0.028 0.028 0.028 2.108 0.711 0.711 0.711 0.711 0.711 0.711 SS 316 SS 316 SS 316 SS 316 SS 316 SS 316 SS 316 Excellent Excellent Excellent Excellent Excellent Excellent Excellent

248 276 276 586 586 586 586

0.93 1.00 1.00 1.00 1.00 0.93 Variable

•29 to 204 •29 to 93 •29 to 93 •29 to 93 •29 to 93 •29 to 204 Variable

231 276 276 586 586 545 Variable

(1C6)•0.875• (1C6)•0.250• (1C6)•0.250• (H2)•0.125• (1C6)•0.125• (nC6)•0.125• (nC6)•0.125• SS316•07 SS316•09 SS316•10 SS316•12 SS316•01006 SS316•08 SS316•16

124 7 7 7 7 132 50 5 5 5 5 5 5 5 G,V/L L L G L L L 4142 4084 4084 8.159 49.950 46.670 Variable 51 49 49 1.834 0.594 0.542 Variable

0.87 0.90 0.90 0.03 0.90 0.01 0.01 0.09 0.10 0.10 0.00 0.10 0.99 0.99 0.04 0.00 0.00 0.97 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 295.70 6.04 6.04 8.56 0.07 0.07 Variable 4928.33 100.75 100.75 142.67 1.23 1.17 Variable 14.01 675.5 675.50 0.953 675.5 663.5 Variable 184 APPENDIX G. STREAM INFORMATION

Number [None] 1 11 17 13 14

Name [None] Tap water cooling loop Refrigeration loop

Begin [None] Tap C•DP E•BP E•1 C•DP

Description End [None] C•DP E•BP Drain C•DP E•1 [inch] N/A N/A N/A N/A N/A Outer diameter [mm] N/A N/A N/A N/A N/A [inch] 0.5 0.5 0.5 0.5 0.5 Inner diameter [mm] 12.7 12.7 12.7 12.7 12.7 [inch] N/A N/A N/A N/A N/A Wall thickness [mm] N/A N/A N/A N/A N/A MOC [None] Buna•N Buna•N Buna•N Buna•N Buna•N Suitability of MOC [None] Excellent Excellent Excellent Excellent Excellent •29 to 37°C max. [bar] N/A N/A N/A N/A N/A working pressure

Elevated Pipe [None] N/A N/A N/A N/A N/A temperature factor

Allowable [°C] •40 to 93 •40 to 94 •40 to 95 •40 to 96 •40 to 97 temperature range

Max. working 20 to 5.5 21 to 5.5 22 to 5.5 23 to 5.5 24 to 5.5 [bar] pressure (catalogue) (catalogue) (catalogue) (catalogue) (catalogue)

Flow sheet [None] TW•0.5•P•01 TW•0.5•P•11 TW•0.5•P•17 G•0.5•P•13 G•0.5•P•14 description

Temperature [°C] Ambient 40 Variable 2 10 Pressure [bar] 3 3 3 1 1 Phase [None] L L L L L [g/h] 21600 21600 21600 43200 43200 Flow rate [mol/h] 10693 10693 10693 21386 21386 Composition 1•Hexene [mol/mol] 0.00 0.00 0.00 0.00 0.00 n•Hexane [mol/mol] 0.00 0.00 0.00 0.00 0.00

Hydrogen [mol/mol] 0.00 0.00 0.00 0.00 0.00 Properties Water [mol/mol] 1.00 1.00 1.00 1.00 1.00 Nitrogen [mol/mol] 0.00 0.00 0.00 0.00 0.00 STD liquid [l/h] 22 22 Variable 43 43 volumetric flow rate [ml/min] 361.03 362.79 Variable 720.04 720.21 Density [kg/m 3] 997 992 Variable 1000 1000 185

Reboiler Distillate Bottoms Pressure Feed sample Seal loop sample sample sample control

5 Reboiler 9 16 9 N 2 utility Atmosphere Atmosphere Atmosphere Atmosphere CD•1 Of f •gas line 0.125 0.125 0.125 0.125 0.250 0.125 3.175 3.175 3.175 3.175 6.35 3.175 0.069 0.069 0.069 0.069 0.194 0.069 1.753 1.753 1.753 1.753 4.928 1.753 0.028 0.028 0.028 0.028 0.028 0.028 0.711 0.711 0.711 0.711 0.711 0.711 SS 316 SS 316 SS 316 SS 316 SS 316 SS 316 Excellent Excellent Excellent Excellent Excellent Excellent

586 Variable 586 Variable 276 586

1.00 Variable 1.00 Variable 1.00 1.00

•29 to 93 Variable •29 to 93 Variable •29 to 93 •29 to 93

586 Variable 586 Variable 276 586

N2•0.125• N/A N/A N/A N/A N/A SS316•18

N/A N/A N/A N/A 7 Ambient N/A N/A N/A N/A 5 5 G N/A N/A N/A N/A N/A Varies N/A N/A N/A N/A N/A Varies

N/A N/A N/A N/A N/A 0.00 N/A N/A N/A N/A N/A 0.00 N/A N/A N/A N/A N/A 0.00 N/A N/A N/A N/A N/A 0.00 N/A N/A N/A N/A N/A 1.00 N/A N/A N/A N/A N/A Variable N/A N/A N/A N/A N/A Variable N/A N/A N/A N/A N/A Variable 186 APPENDIX G. STREAM INFORMATION Appendix H

OPERATING PROCEDURES

187 188 APPENDIX H. OPERATING PROCEDURES

PRE•START•UP PROCEDURES

STEP TIME SEQUENCE DESCRIPTION ACTIVITIES 1 +00:00 Inspect extractor system Ensure that the extractor fans are working correctly and that non•reacted hydrogen leaving through the off•gas system will be vented to outside the building. 2 Inspect pressure relief valve For safety purposes it is vital to check that the safety valve SV•1 is functional and fitted correctly. 3 Close sample valves Sample valves NV•SF, NV•SD and NV•SB must be closed tightly prior to start•up to prevent leakage. 4 Open flow control valves Ensure that all the flow control needle valves are open

5 Open reflux valves Open the reflux valves NV•RD 6 Inspect the reflux pumps Ensure that the reflux pump is correctly and securely connected to the power source. However, at this point there must be no power supply to the pumps. 7 Check off•gas connections Ensure that the safety valve, off•gas lines and two product tanks are correctly and securely connected to the gas extraction system. 8 General electrical concerns All electrical cables must be well isolated and far away from water (or any other conductive material) as well as heat sources. This is especially important for the relatively high voltage cables connected to the 220V power supply plugs. Note that the cables must also be out of the way in the event of accidental spillage or other unusual occurrences. Signal cables and high voltage cables must be separated to prevent signal interference (not at issue with RS232). Use common sense.

9 Check N2 and H2 supply Check that there is sufficient N2 and H2 for the pressure experiment. 10 Purge the system See PURGE PROCEDURES 11 Switch on the computer Turn the red uninterrupted power supply (UPS) switch to the ON position and then switch on the computer.

12 Run control program Switch on the computer and run the control program executable. 13 Set start•up setpoints CRITICAL FOR A SAFE START•UP. All the setpoints must be zeroed. Thus no feed flows, BELOW AMBIENT REBOILER TEMPERATURE SETPOINT (20°C) and no reflux flow. 14 Set start•up and shutdown Initiate the control program by throwing the main sequences software switch. Check the current default setpoints for each controlled instrument and set the start•up and shutdown sequences as required (see Start• up/Shutdown Procedures for recommended). 15 Set refrigerator temperature Set the refrigerator setpoint temperature, but do not activate it yet. 16 Toggle switch off? Check that the toggle switch is off. 189

17 Supply power to the power Turn the blue power supply switch to the ON position in supply box order to supply power to the power supply box. NOTE: the following steps close the power supply circuits, but will not supply power as long as the toggle signal is not transmitting. WARNING: some of the power lines in the power supply box are now live. DO NOT EXECUTE THIS STEP IF THE BOX IS OPEN.

18 Close the power supply Close the power circuit to the electronic box by flipping circuit to the electronic box its switch on the power supply unit to ON.

19 Set switches on the Set the switches on the electronic box depending on the electronic box way in which the relevant instrument is controlled. The solenoid valves and heating element must be set to AUTO as their power supplies are software controlled. The HPLC pump, mass flow controller, reflux pump and balances must be set to MANUAL and their corresponding power switches to ON.

20 Close the power supply Set the refrigerator power supply to the ON position. circuit to the refrigerator

21 H2 Mass flow controller Set the mass flow controller to the correct H2 flow rate.

22 Check all the electrical Check that the electrical connections of the mass flow connections. controller, re•boiler, refrigerator and pumps are correct and secure. 23 Start•up Commence with start•up or purge procedures when pre• start•up procedures have been completed satisfactorily. 190 APPENDIX H. OPERATING PROCEDURES

START•UP PROCEDURES

STEP TIME SEQUENCE DESCRIPTION ACTIVITIES 1 Purge the system with N2 Purge the system with N2 at a pressure just slightly above atmospheric (purge instructions described in PURGE PROCEDURES). 2 Re•do pre•start•up It is possible that some settings or valve positions were procedures changed during the purging sequence. 3 Commence condenser Activate the refrigerator and use the rotameter to set the cooling coolant flow rate through the condenser as desired. Also set the desired tap water flow rate. Allow the refrigerator to reach its steady state setpoint (This could take some time).

4 Swing three•way valve open Swing the three•way (TV•NH) valve open to H2; closed

to H2 to N2. 5 Close all the outlet valves Close the off•gas, distillate product and bottoms product valves 6 Initiate standby control Initiate the control program by throwing the main software switch (if this has not been done in the pre•start• up already), re•check the setpoint values and choose to initiate standby control when prompted. 7 Push red toggle button Push the red button on the power supply box the moment that the toggle light starts flashing to indicate that the safety device is receiving the toggle signal. When the toggle signal stops, power is cut to the entire system excluding • the computer. 8 +00:00 Start•up Push the software start•up button when ready. 9 Monitor start•up Monitor the start•up procedure to ensure that all the equipment starts up correctly. The control program will inform the user if start•up verification was not timeously received. 10 Fill reboiler inventory Fill the reboiler inventory with the high boiler. For the 1• hexene/n•hexane mixture this is the n•hexane 11 Activate the re•boiler Allow the reboiler inventory fluid to heat up to the element relevant boiling temperature. 12 Initiate the start•up Set the HPLC pump to the required setpoint and feed hydrocarbon feed mixture the start•up mixture existing of a 50:50 mixture high• boiler:lower•boiler 13 Activate bottoms level Open the reboiler outlet valve and commence bottoms control level control via the solenoid valve.

14 Initiate H2 feed Set the MFC to the desired H2 flow rate. The reaction will start to occur, which will lead to an increase in temperature that must be monitored. Use the reflux ratio and condenser heat duty to control this temperature. 15 Commence pressure control Allow the vapour to fill and pressurize the system to the desired start•up pressure. Open the off•gas valve and

allow the N2 push•pull system to take over pressure control. NOTE: There will be a loss in some of the volatile component, which is to be expected. MONITOR THE SYSTEM PRESSURE FOR A WHILE TO ENSURE THAT IT HAS STABILIZED BEFORE CONTINUING TO THE NEXT STEP. 191

16 Activate distillate level Allow the reflux drum to reach the acceptable range control between the low and high level and start the reflux drum up at a flow rate half that of the feed rate. 17 Commence reflux drum Open the distillate outlet valve and commence reflux level control drum level control 18 Commence reflux ratio Switch the reflux pump programmatically to initiate reflux control ratio control. 19 Monitor the plant Monitor the plant until steady•state is reached and then continue with operational procedures.

PURGE PROCEDURES

STEP TIME SEQUENCE DESCRIPTION ACTIVITIES 1 +00:00 Close liquid sampling Close all the sampling valves. Only the valves product valves necessary to allow the gas to exit through the off•gas bottoms and distillate lines may be open.

2 Swing three•way valve open Swing the three•way (TV•NH) valve open to N2; closed

to N2 to H2. 3 Initiate standby control Initiate the control program by throwing the main software switch (if this has not been done in the pre•start• up already), re•check the setpoint values and choose to initiate standby control when prompted. 4 Push red toggle button Push the red button on the power supply box the moment that the toggle light starts flashing to indicate that the safety device is receiving the toggle signal. When the toggle signal stops, power is cut to the entire system excluding • the computer. 5 Display MFC control panel When the main GUI for the control panel is displayed, enter the MFC control program (DO NOT SELECT SYSTEM START•UP) to isolate control only to the MFC.

6 Initiate N2 feed Start•up the MFC and choose a purge flow rate setpoint.

7 Check that solenoid valves Check whether the bottoms and distillate solenoid valves are open are open or closed. If closed flip their control to manual and do it manually 8 Purge Purge the system. 9 Close the outlet valves Close all the outlet valves. 10 Cut power to the MFC Use the software control to stop the MFC. 11 Trigger a controlled A controlled shutdown can be triggered shutdown programmatically either by the operator or automatically by the software itself. 192 APPENDIX H. OPERATING PROCEDURES

SHUTDOWN PROCEDURES

STEP TIME SEQUENCE DESCRIPTION ACTIVITIES 1 00:00 Trigger a controlled A controlled shutdown can be triggered shutdown programmatically either by the operator or automatically by the software itself.

2 The H2 feed must be IT IS VITAL TO TERMINATE THE H2 FEED TO THE

terminated immediately. COLUMN. The MFC should terminate the H2 feed programmatically, but it can also be closed after the

MFC stops by using the H2 inlet valve (not recommended if the MFC is still controlling). 3 Deactivate reboiler Deactivate the reboiler 4 Relinquish level control Discontinue level control 5 Close bottoms valve Close the bottoms valve (Sol•B) once the hydrocarbon feed has been terminated. 6 Terminate hydrocarbon feed Stop the HPLC pump

7 Deactivate reflux pump Reduce the reflux pump rate to zero. 8 Close distillate valve Close the distillate valve (Sol•D) to minimize

hydrocarbon losses to product and to prevent H2 escaping through the distillate line if the condenser runs dry.

9 Discontinue pressure control Close the N2 pressure control valve when the column temperature has fallen to below the normal boiling point of the light boiler. 10 Monitor shutdown Monitor especially the column pressure and temperature until the former is atmospheric and the latter ambient. The control program will inform the user programmatically if an instrument's shutdown confirmation is not received. 11 Switch off Mains Set the blue mains power supply to the OFF position 12 Switch off the computer Shut down the computer once the control program has closed. 13 Switch off the UPS mains Turn the red UPS main power supply to the OFF position. 193

EMERGENCY SHUTDOWN PROCEDURES • General

STEP SEQUENCE DESCRIPTION ACTIVITIES 1 Initiate emergency shutdown Initiate the emergency shutdown. This can be (1) automatically triggered by the control program, (2) software initiated by the user and/or (3) achieved by flipping the main power switch on the power supply box to OFF and then also switching off the blue power supply socket. All three have the effect of CUTTING POWER to the system.

The H2 feed must be This should happen automatically via the fail closed terminated immediately. mass flow controller when power is suddenly cut. IT IS VITAL TO CHECK THAT THE H2 FLOW HAS BEEN TERMINATED. 2 Terminate hydrocarbon feed Close the hydrocarbon feed valve (NV•F) manually.

3 Close bottoms valve Close the bottoms valve (Sol•B) once the hydrocarbon feed has been terminated to minimize losses to product.

4 Close distillate valve Close the distillate valve (Sol•D) to minimize

hydrocarbon losses to product and to prevent H2 escaping through the distillate line if the condenser runs dry. 5 Deactivate main equipment Ensure that power has been cut to the main equipment pieces by checking that the toggle switch is not flashing

6 Institute emergency Remove all non•essential personnel from the laboratory procedures for their personal safety and to allow ease of access and freedom of movement. 7 Monitor shutdown Monitor especially the column pressure and temperature until the former is atmospheric and the latter ambient. 194 APPENDIX H. OPERATING PROCEDURES

EMERGENCY SHUTDOWN PROCEDURES • Power failure

STEP SEQUENCE DESCRIPTION ACTIVITIES

1 The H2 feed must be This should happen automatically via the fail closed terminated immediately. mass flow controller when power is cut. IT IS VITAL TO CHECK THAT THE H2 FLOW HAS BEEN

TERMINATED. Do it manually via the H2 inlet valve if not. 2 Terminate hydrocarbon feed This should happen automatically.

3 Check that the bottoms The bottoms solenoid valve (Sol•B) must fail closed valve is closed when the power is cut. When the electricity is cut off the pumps, reboiler and control systems go off•line. This means no level control (LC). It is better to flood the column than to let the reboiler run dry. 4 Check that the distillate The distillate solenoid valve (Sol•D) must fail closed valve is closed when power is cut to prevent the condenser from 5 Deactivate main equipment Check that power was cut to the reboiler and reflux pieces pump. When power is re•established the main equipment must be switched off or there will be an uncontrolled start•up. 6 Institute emergency Remove all non•essential personnel from the laboratory procedures for their personal safety and to allow ease of access and freedom of movement. Appendix I

GRAPHICAL KEY

195 196 APPENDIX I. GRAPHICAL KEY Index

Catalyst Fog formation, 69 speci…cations, 47 Heating element, 68 Catalytic distillation Hydrogen attack, 61 Advantages, 4 Hydrogenation Applications, 6 double-bond migration, 13 criteria, 5 mechanism, 11 Channeling, 49 process conditions, 15 Computer control reasons for choice, 45 computer cards, 94 safety, 15 data acquisition, 94 selective, 7 error handling, 100 zero-order zone, 14 feed, 98 graphical user interface, 91 Images of system, 118 heat duty, 98 instrument control loops, 96 Liquid distribution, 67 level control, 100 Liquid inventory, 68 re‡ux ratio control, 100 Loading point, 17 safety, 91, 94 Mason formulation, 37 shutdown, 93 Materials of construction (MOC) start-up, 93 Glass, 62 system breakdown, 89 Stainless Steel 316 (SS316), 61 Di¤usion mechanisms, 36 Te‡on, 62 Dusty ‡uid model, 36 Maxwell-Stefan approach, 34 dusty ‡uid model, 36 EQ model, 22 Interphase mass transfer, 35 Experimental MESH equations Current set-up, 46 non-reactive distillation, 24 logging, 114 reactive section, 26 start-up, 112 MTBE, 6, 8

Fick’s…rst law, 30 NEQ model, 23 Flooding point, 17 Non-condensable gas, 69

197 198 INDEX

Operation Reboiler, 67 dimensional layout, 103 Refrigerator, 69 operating procedures, 104 Residue curve maps, 20 vibration, 103 Sampling points, 85 Packing Sulzer CY, 64 speci…cations, 49 Synergistic e¤ect, 5 Partial condenser, 69 Temperature pro…le Phase hydrodynamics thermal response, 115 …lm theory, 32 thermal wave, 112 models, 29 thermocouple positions, 104 two-…lm, 33 thermal location, 59 Pressure testing, 111 Through ‡ow, 49 Process conditions feed point, 17 Viscous ‡ow, 37 liquid hold-up, 17 viscous selectivity factor, 37 pressure, 15 temperature, 15 Process control feed HPLC pump, 75 Mass ‡ow controller, 75 Isobaric, 73 level control ‡oat valve, 80 magnetic coupled devices, 80 optical level sensors, 80 over‡ow system, 78 re‡ux ratio forced circulation, 83 re‡ux splitter, 81 sutro weir, 82 Process design methodology, 43 Project goal, 9 guideline, 9 hypothesis, 9 system, 9

Reactive azeotropes, 20