Reactive Distillation Design and Control

William L. Luyben, PHD, is Professor of Chemical Engineering at Lehigh University. In addition to forty years of teaching, Dr. Luyben spent nine years as an engineer with Exxon and DuPont. He has written nine books and more than 200 papers. He was the 2004 recipient of the Computing Practice Award from the CAST Division of the AIChE and was elected in 2005 to the Process Automation Hall of Fame. CHENG-CHING YU, PHD, has spent sixteen years as a Professor at National Taiwan University of Science and Technology and four years at National Taiwan University. He has published over 100 technical papers in the areas of plant-wide process control, reactive distillation, control of microelectronic processes, and modeling of fuel cell systems.

• Preface xvii1 Introduction 11.1 History 21.2 Basics of Reactive Distillation 31.3 Neat Operation Versus Excess Reactant 71.4 Limitations 81.4.1 Temperature Mismatch 81.4.2 Unfavorable Volatilities 91.4.3 Slow Reaction Rates 91.4.4 Other Restrictions 91.5 Scope 91.6 Computational Methods 101.6.1 Matlab Programs for Steady-State Design 101.6.2 Aspen Simulations 101.7 Reference Materials 11Part I Steady-State Design of Ideal Quaternary System 152 Parameter Effects 172.1 Effect of Holdup on Reactive Trays 202.2 Effect of Number of Reactive Trays 222.3 Effect of Pressure 242.4 Effect of Chemical Equilibrium Constant 272.5 Effect of Relative Volatilities 292.5.1 Constant Relative Volatilities 302.5.2 Temperature-Dependent Relative Volatilities 302.6 Effect of Number of Stripping and Rectifying Trays 322.7 Effect of Reactant Feed Location 332.7.1 Reactant A Feed Location (NFA) 332.7.2 Reactant B Feed Location (NFB) 352.8 Conclusion 363 Economic Comparison of Reactive Distillation with a Conventional Process 373.1 Conventional Multiunit Process 383.1.1 Assumptions and Specifications 383.1.2 Steady-State Design Procedure 403.1.3 Sizing and Economic Equations 423.2 Reactive Distillation Design 433.2.1 Assumptions and Specifications 443.2.2 Steady-State Design Procedure 453.3 Results for Different Chemical Equilibrium Constants 473.3.1 Conventional Process 473.3.2 Reactive Distillation Process 543.3.3 Comparisons 613.4 Results for Temperature-Dependent Relative Volatilities 613.4.1 Relative Volatilities 623.4.2 Optimum Steady-State Designs 643.4.3 Real Chemical Systems 693.5 Conclusion 704 Neat Operation Versus Using Excess Reactant 714.1 Introduction 724.2 Neat Reactive Column 724.3 Two-Column System with Excess B 754.3.1 20% Excess B Case 764.3.2 10% Excess B Case 784.4 Two-Column System with 20% Excess of A 814.5 Economic Comparison 854.6 Conclusion 86Part II Steady-State Design of Other Ideal Systems 875 Ternary Reactive Distillation Systems 895.1 Ternary System without Inerts 905.1.1 Column Configuration 905.1.2 Chemistry and Phase Equilibrium Parameters 905.1.3 Design Parameters and Procedure 925.1.4 Effect of Pressure 945.1.5 Holdup on Reactive Trays 945.1.6 Number of Reactive Trays 945.1.7 Number of Stripping Trays 945.2 Ternary System with Inerts 995.2.1 Column Configuration 995.2.2 Chemistry and Phase Equilibrium Parameters 995.2.3 Design Parameters and Procedure 1005.2.4 Effect of Pressure 1025.2.5 Control Tray Composition 1035.2.6 Reactive Tray Holdup 1055.2.7 Effect of Reflux 1075.2.8 Chemical Equilibrium Constant 1095.2.9 Feed Composition 1095.2.10 Number of Reactive Trays 1135.2.11 Number of Rectifying and Stripping Trays 1135.3 Conclusion 1166 Ternary Decomposition Reaction 1196.1 Ternary Decomposition Reaction: Intermediate-Boiling Reactant 1206.1.1 Column Configuration 1206.1.2 Chemistry and Phase Equilibrium Parameters 1206.1.3 Design Parameters and Procedure 1216.1.4 Holdup on Reactive Trays 1236.1.5 Number of Reactive Trays 1246.1.6 Number of Rectifying and Stripping Trays 1266.1.7 Location of Feed Tray 1266.2 Ternary Decomposition Reaction: Heavy Reactant with Two-Column Configurations 1276.2.1 Column Configurations 1276.2.2 Chemistry and Phase Equilibrium Parameters 1286.2.3 Design Parameters and Procedure 1286.2.4 Reactive Holdup 1296.2.5 Number of Reactive Trays 1316.2.6 Number of Rectifying Trays 1326.3 Ternary Decomposition Reaction: Heavy Reactant with One-Column Configurations 1346.3.1 Feasibility Analysis 1346.3.2 Column Configuration 1396.3.3 Design Parameters and Procedure 1396.3.4 Reactive Tray Holdup 1396.3.5 Number of Reactive Trays 1396.3.6 Number of Rectifying Trays 1406.3.7 Location of Feed Tray 1436.3.8 Comparison Between These Two Flowsheets 1436.4 Conclusion 143Part III Steady-State Design of Real Chemical Systems 1457 Steady-State Design for Acetic Acid Esterification 1477.1 Reaction Kinetics and Phase Equilibria 1477.1.1 Reaction Kinetics 1477.1.2 Phase Equilibria 1497.2 Process Flowsheets 1537.2.1 Type I Flowsheet: MeAc 1537.2.2 Type II Flowsheet: EtAc and IPAc 1567.2.3 Type III Flowsheet: BuAc and AmAc 1577.3 Steady-State Design 1587.3.1 Design Procedure 1587.3.2 Optimized Design 1607.4 Process Characteristics 1687.4.1 Type I: MeAc 1687.4.2 Type II: EtAc and IPAc 1687.4.3 Type III: BuAc and AmAc 1707.5 Discussion 1757.6 Conclusion 1778 Design of Tame Reactive Distillation Systems 1798.1 Chemical Kinetics and Phase Equilibrium 1808.1.1 Chemical Kinetics 1808.1.2 Phase Equilibrium Using Aspen Plus 1818.1.3 Conceptual Design 1868.2 Component Balances 1948.3 Prereactor and Reactive Column 1958.3.1 Base Case Design of Reactive Column 1958.3.2 Effect of Design Parameters on Reactive Column 1998.4 Pressure-Swing Methanol Separation Section 2088.5 Extractive Distillation Methanol Separation Section 2098.6 Economic Comparison 2108.7 Conclusion 2129 Design of MTBE and ETBE Reactive Distillation Columns 2139.1 MTBE Process 2139.1.1 Phase Equilibrium 2149.1.2 Reaction Kinetics 2149.1.3 Aspen Plus Simulation Issues 2149.1.4 Setting up the Aspen Plus Simulation 2159.1.5 Effect of Design Parameters 2219.1.6 Chemical Equilibrium Model 2299.2 ETBE Process 2319.2.1 Kinetic Model 2319.2.2 Process Studied 2329.2.3 User Subroutine for ETBE 2329.2.4 Chemical Equilibrium Model 2349.2.5 Effects of Design Parameters 2369.3 Conclusion 237Part IV Control of Ideal Systems 23910 Control of Quaternary Reactive Distillation Columns 24110.1 Introduction 24210.2 Steady-State Design 24310.3 Control Structures 24510.4 Selection of Control Tray Location 24610.5 Closed-Loop Performance 24710.5.1 CS7-R Structure 24710.5.2 CS7-RR Structure 24810.6 Using More Reactive Trays 24910.6.1 Steady-State Design 24910.6.2 SVD Analysis 25010.6.3 Dynamic Performance of CS7-RR 25310.7 Increasing Holdup on Reactive Trays 25410.8 Rangeability 25610.9 Conclusion 25911 Control of Excess Reactant Systems 26111.1 Control Degrees of Freedom 26111.2 Single Reactive Column Control Structures 26311.2.1 Two-Temperature Control Structure 26511.2.2 Internal Composition Control Structure 27211.3 Control of Two-Column System 27811.3.1 Two-Temperature Control 27911.3.2 Temperature/Composition Cascade Control 28511.4 Conclusion 29212 Control of Ternary Reactive Distillation Columns 29312.1 Ternary System without Inerts 29312.1.1 Column Configuration 29312.1.2 Control Structure CS1 29612.1.3 Control Structure CS2 30012.1.4 Control Structure CS3 30312.2 Ternary System with Inerts 31012.2.1 Column Configuration 31012.2.2 Control Structure CS1 31012.2.3 Control Structure CS2 31412.2.4 Control Structure CS3 32012.2.5 Conclusion for Ternary A + B <=> C System 32212.3 Ternary A <=> B + C System: Intermediate-Boiling Reactant 32412.3.1 Column Configuration 32412.3.2 Control Structure CS1 32612.3.3 Control Structure CS2 32912.3.4 Control Structure CS3 33412.4 Ternary A <=> B + C System: Heavy Reactant with Two-Column Configuration 33412.4.1 Column Configuration 33412.4.2 Control Structure CS1 33412.4.3 Control Structure CS2 33512.5 Ternary A <=> B + C System: Heavy Reactant With One-Column Configuration 34212.5.1 Column Configuration 34212.5.2 Control Structure CS1 34212.5.3 Control Structure CS2 34412.5.4 Control Structure CS3 34512.5.5 Conclusion for Ternary A <=> B + C System 352Part V Control of Real Systems 35313 Control of Reactive Distillations for Acetic Acid Esterification 35513.1 Process Characteristics 35513.1.1 Process Studies 35513.1.2 Quantitative Analysis 35613.2 Control Structure Design 36213.2.1 Selection of Temperature Control Trays 36313.2.2 Control Structure and Controller Design 36613.2.3 Performance 36813.2.4 Alternative Temperature Control Structures 37613.3 Extension to Composition Control 38013.4 Conclusion 38814 Plantwide Control of Tame Reactive Distillation System 38914.1 Process Studied 38914.1.1 Prereactor 39014.1.2 Reactive Column C1 39114.1.3 Extractive Column C2 39114.1.4 Methanol Recovery Column C3 39714.2 Control Structure 39714.2.1 Prereactor 39714.2.2 Reactive Distillation Column C1 39914.2.3 Extractive Distillation Column C2 39914.2.4 Methanol Recovery Column C3 40114.3 Results 40314.4 Conclusion 40615 Control of MTBE and ETBE Reactive Distillation Columns 40715.1 MTBE Control 40715.1.1 Steady State 40715.1.2 Control Structure with C4 Feedflow Controlled 40815.1.3 Control Structure with Methanol Feedflow Controlled 41615.2 ETBE Control 41815.2.1 Control Structure with Flow Control of C4 Feed 41915.2.2 Control Structure with Flow Control of Ethanol Feed 424Part VI Hydrid and Nonconventional Systems 42916 Design and Control of Column/Side Reactor Systems 43116.1 Introduction 43116.2 Design for Quaternary Ideal System 43316.2.1 Assumptions and Specifications 43416.2.2 Reactor and Column Equations 43516.2.3 Design Optimization Procedure 43616.2.4 Results and Discussion 43716.2.5 Reactive Column with Optimum Feed Tray Locations 44516.3 Control of Quaternary Ideal System 44616.3.1 Dynamic Tubular Reactor Model 44616.3.2 Control Structures 44716.4 Design of Column/Side Reactor Process for Ethyl Acetate System 45816.4.1 Process Description 45816.4.2 Conceptual Design 45916.5 Control of Column/Side Reactor Process for Ethyl Acetate System 47416.5.1 Determining Manipulated Variables 47516.5.2 Selection of Temperature Control Trays 47916.5.3 Controller Design 48116.5.4 Performance 48116.5.5 Extension to Composition Control 48516.5.6 Comparison with Reactive Distillation Temperature Control 48516.6 Conclusion 48517 Effects of Boiling Point Rankings on the Design of Reactive Distillation 48717.1 Process and Classification 48717.1.1 Process 48717.1.2 Classification 49017.2 Relaxation and Convergence 49217.3 Process Configurations 49517.3.1 Type I: One Group 49617.3.2 Type II: Two Groups 50117.3.3 Type III: Alternating 50717.4 Results and Discussion 51117.4.1 Summary 51117.4.2 Excess Reactant Design 51417.5 Conclusion 51818 Effects of Feed Tray Locations on Design and Control of Reactive Distillation 51918.1 Process Characteristics 51918.1.1 Modeling 52118.1.2 Steady-State Design 52218.1.3 Base Case 52218.1.4 Feed Locations Versus Reactants Distribution 52318.1.5 Optimal Feed Locations 52718.2 Effects of Relative Volatilities 52918.2.1 Changing Relative Volatilities of Reactants 52918.2.2 Changing Relative Volatilities of Products 53018.2.3 Summary 53218.3 Effects of Reaction Kinetics 53318.3.1 Reducing Activation Energies 53318.3.2 Effects of Preexponential Factor 53618.4 Operation and Control 53818.4.1 Optimal Feed Location for Production Rate Variation 53818.4.2 Control Structure 53918.4.3 Closed-Loop Performance 54118.5 Conclusion 544Appendix Catalog of Types of Real Reactive Distillation Systems 545References 563Index 573