Isbn 3527305793

Contents

Preface XI

List of Contributors XIX

Part I Industrial Applications

1 Industrial Applications of Reactive Distillation 3

1.1 Introduction 3

1.2 Etherification: MTBE, ETBE, and TAME 14

1.3 Dimerization, Oligomerization, and Condensation 15

1.4 Esterification: Methyl Acetate and Other Esters 16

1.5 Hydrolysis of Esters 18

1.6 Hydration 20

1.7 Hydrogenation/Hydrodesulfurization/Hydrocracking 20

1.7.1 Benzene to Cyclohexane 21

1.7.2 Selective Hydrogenation of C4 Stream 21

1.7.3 Hydrogenation of Pentadiene 21

1.7.4 C4 Acetylene Conversion 22

1.7.5 Hydrodesulfurization, Hydrodenitrogenation, and Hydrocracking 22

1.7.6 Miscellaneous Hydrogenations 22

1.8 Chlorination 23

1.9 Acetalization/Ketalization 23

1.10 Recovery and Purification of Chemicals 24

1.11 Difficult Separations 25

1.12 Chemical Heat Pumps 26

1.13 RD with Supercritical Fluids 26

1.14 Conclusions 26

2 Reactive Distillation Process Development in the Chemical Process Industries 30

2.1 Introduction 30

2.2 Process Synthesis 32

2.3 Process Design and Optimization 35

2.4 Limitations of the Methods for Synthesis and Design: the Scale-Up Problem 37

2.5 Choice of Equipment 38

2.6 Some Remarks on the Role of Catalysis 46

2.7 Conclusions 46

2.8 Acknowledgments 47

2.9 Notation 47

3 Application of Reactive Distillation and Strategies in Process Design 49

3.1 Introduction 49

3.2 Challenges in Process Design for Reactive Distillation 51

3.2.1 Feasibility Analysis 51

3.2.2 Catalyst and Hardware Selection 51

3.2.3 Column Scale-Up 51

3.3 MTBE Decomposition via Reactive Distillation 52

3.3.1 Conceptual Design 52

3.3.2 Model Development 54

3.3.2.1 Catalyst Selection and Reaction Kinetics 55

3.3.2.2 Phase Equilibrium Model 55

3.3.2.3 Steady-State Simulation 56

3.3.3 Lab-Scale Experiments 57

3.3.4 Pilot-Plant Experiments 58

3.4 Conclusions 61

Part II Physicochemical Fundamentals

4 Thermodynamics of Reactive Separations 65

4.1 Introduction 65

4.2 Process Models for Reactive Distillation 66

4.2.1 Outline 66

4.2.2 Case Study: Methyl Acetate 66

4.3 Equilibrium Thermodynamics of Reacting Multiphase Mixtures 70

4.4 Fluid Property Models for Reactive Distillation 74

4.4.1 Outline 74

4.4.2 Examples 75

4.4.2.1 Hexyl Acetate: Sensitivity Analysis 75

4.4.2.2 Methyl Acetate: Prediction of Polynary Vapor-Liquid Equilibria 77

4.4.2.3 Butyl Acetate: Thermodynamic Consistency 81

4.4.2.4 Ethyl Acetate: Consequences of Inconsistency 82

4.4.2.5 Formaldehyde + Water + Methanol: Intrinsically Reactive Complex Mixture 83

4.5 Experimental Studies of Phase Equilibria in Reacting Systems 88

4.5.1 Outline 88

4.5.2 Reactive Vapor-Liquid Equilibria 90

4.5.2.1 Batch Experiments 90

4.5.2.2 Flow Experiments 91

4.5.2.3 Recirculation Experiments 92

4.6 Conclusions 92

4.7 Acknowledgments 93

4.8 Notation 93

5 Importance of Reaction Kinetics for Catalytic Distillation Processes 97

5.1 Introduction 97

5.2 Reactive Ideal Binary Mixtures 98

5.2.1 Reaction-Distillation Process with External Recycling 100

5.2.2 Distillation Column with Reactive Reboiler 103

5.2.3 Fully Reactive Distillation Column 106

5.3 Kinetic Effects on Attainable Products 109

5.3.1 Singular Point Analysis 110

5.3.2 Ideal Ternary Mixtures 112

5.3.3 Non-Ideal Mixtures 115

5.3.3.1 Synthesis of MTBE 115

5.3.3.2 Synthesis of TAME 117

5.3.4 Systems with Liquid-Phase Splitting 121

5.3.5 Systems with Interfacial Mass-Transfer Resistances 126

5.4 Determination and Analysis of Reaction Kinetics 129

5.4.1 Physicochemical Transport Phenomena 129

5.4.2 Process Evaluation by Dimensionless Numbers 131

5.4.3 Formulation of Reaction Rate Expressions 133

5.4.4 Importance of Transport Resistances for Column Operation 135

5.5 Conclusions 138

5.6 Acknowledgments 139

5.7 Notation 140

Part III Process Design

6 Feasibility and Process Alternatives for Reactive Distillation 145

6.1 Introduction 145

6.2 Motivation 147

6.3 Flash Cascade Model 153

6.4 Feasibility Hypothesis 156

6.5 Bifurcation Analysis of the Flash Cascade Model 160

6.6 Conclusions 165

6.7 Notation 165

7 Hardware Selection and Design Aspects for Reactive Distillation Columns 169

7.1 Introduction 169

7.2 Hardware for Homogeneous Reactive Distillation 169 7.2.1 Case Study for Methyl Acetate Production 173

7.3 Hardware for Heterogeneous Reactive Distillation 177

7.3.1 Different Hardware Configurations 177

7.3.2 Hardware Selection Aspects 183

7.4 The Side-Reactor Concept 185

7.5 Conclusions 187

7.6 Acknowledgments 188

8 Development of Unstructured Catalytic Packing for Reactive Distillation Processes 190

8.1 Introduction 190

8.2 Requirements for RD Catalytic Packing 190

8.3 State of the Art: Catalytic Packing for RD Processes 191

8.3.1 Commercial Packing 191

8.3.2 Alternative Concepts 193

8.3.2.1 Catalysts Made of Pure Catalytic Material 193

8.3.2.2 Catalysts Supported on Carrier Materials 194

8.4 New Catalyst Concept: Porous Polymer/Carrier Composite 195

8.4.1 Requirements for the Carrier Materials 198

8.4.2 Requirements for the Polymerization Process 199

8.5 Preparation of Sulfonated Ion-Exchange Polymer/Carrier Catalysts 200

8.6 Performance of Polymer/Carrier Catalysts 203

8.6.1 Influence of Polymer Content and Reactant Concentration 204

8.6.2 Influence of Reaction Temperature 205

8.6.3 Influence of Cross-Linking 207

8.6.4 Influence of Cross-Linking at Low Polymer Content 207

8.6.5 Influence of Cross-Linking at High Polymer Content 209

8.7 Outlook: Extension to Other Synthetic Processes With Integrated Separation 210

8.7.1 Reactive Stripping 210

8.7.2 Reactive Chromatography 211

8.7.3 Polymer-Assisted Solution-Phase Organic Synthesis 212

8.8 Conclusions 212

Part IV Modeling and Process Control

9 Modeling of Homogeneous and Heterogeneous Reactive Distillation Processes 217

9.1 Introduction 217

9.2 Equilibrium Stage Models 217

9.3 Non-equilibrium Stage Modeling 220 9.3.1 The Conventional NEQ Model 220

9.3.2 NEQ Modeling of Reactive Distillation 223

9.3.3 Homogeneous Systems 223

9.3.4 Heterogeneous Systems 225

9.3.5 NEQ Cell Model 227

9.3.6 Properties, Hydrodynamics, and Mass Transfer 232

9.4 Comparison of EQ and NEQ Models 232

9.5 A View of Reactive Distillation Process Design 237

9.6 Notation 238

10 Nonlinear Dynamics and Control of Reactive Distillation Processes 241

10.1 Introduction 241

10.2 Multiplicity and Oscillations in Chemical Process Systems 242

10.3 Methyl Formate Synthesis 245

10.3.1 Singularity Analysis of a One-Stage Column 246

10.3.3 Continuation Analysis of Lab-Scale Column 248

10.4 Ethylene Glycol Synthesis 249

10.4.1 Singularity Analysis of a One-Stage Column 250

10.4.2 Continuation Analysis of Industrial Size Distillation Column 251

10.5 MTBE and TAME Synthesis 257

10.5.1 MTBE Synthesis 257

10.5.2 TAME Synthesis 258

10.5.3 Kinetic Instabilities for Finite Transport Inside the Catalyst 260

10.5.4 Oscillatory Behavior 261

10.6 Classification 262

10.7 Nonlinear Wave Propagation 264

10.8 Control 271

10.8.1 Control Structure Selection 271

10.8.2 Control Algorithms 274

10.9 Conclusions 276

10.10 Acknowledgments 278

Index 283

Preface

In the chemical process industries, chemical reaction and the purification of the desired products by distillation are usually carried out sequentially. In many cases, the performance of this classic chemical process structure can be significantly improved by integration of reaction and distillation in a single multifunctional process unit. This integration concept is called 'reactive distillation' (RD); when heterogeneous catalysts are applied the term 'catalytic distillation' is often used.

As advantages of this integration, chemical equilibrium limitations can be overcome, higher selectivities can be achieved, the heat of reaction can be used in situ for distillation, auxiliary solvents can be avoided, and azeotropic or closely boiling mixtures can be more easily separated than in non-RD. Increased process efficiency and reduction of investment and operational costs are the direct results of this approach. Some of these advantages are realized by using reaction to improve separation; others are realized by using separation to improve reaction.

Most important industrial applications of RD are in the field of esterification processes such as the famous Eastman Chemical Co.'s process for the synthesis of methyl acetate [1]. This process combines reactive and non-reactive sections in a single hybrid RD column and thereby replaces a complex conventional flowsheet with 11 process units. With this RD technology investment and energy costs were reduced by factor five [2]. Another success story of RD was started in the 1980s by using this technology for the preparation of the ethers MTBE, TAME, and ETBE, which are produced in large amounts as fuel components because of their excellent antiknock properties [3],

Nowadays, many research and development activities are under way to introduce RD into other chemical processes. But despite the convincing success of RD in esterification and etherification applications, it is important to note that RD is not always advantageous. In some cases it is not even feasible. Therefore, the development of reliable tools for the conceptual design of RD processes is one of the most important fields of current research activities.

Due to the interaction of reaction and distillation in one single apparatus, the steady-state and dynamic operational behavior of RD can be very complex. Therefore, suitable process control strategies have to be developed and applied, ensuring optimal and safe operation. This is another very important area of current and future research and development.

Today, RD is discussed as one part of the broader area of reactive separation, which comprises any combination of chemical reaction with separation such as distillation, stripping, absorption, extraction, adsorption, crystallization, and membrane separation. In the next decade, unifying approaches to reactive separators should be developed allowing the rigorous selection of the most suitable type of separation to be integrated into a chemical reactor.

Despite the fact that the basic idea of combining reaction and distillation is old, there has been an enormously growing interest in the design and operation of RD processes in recent years. Fig. 1 shows the number of journal papers that have appeared on the subject during the last 30 years. It is worth noting that the total number of publications including the papers in conference proceedings and so on is a multiple of the number of publications in scientific journals. In an analogous manner, the industrial interest in applying this attractive process technology has increased continuously. This is reflected by the steadily growing number of patents applied since 1970.

Despite the large number of publications only a few review papers have been written on this topic so far. Podrebarac et al. [4] highlighted the advantages of RD and gave an overview on potential uses of catalytic distillation. The review by Taylor and Krishna [5] focused mainly on the modeling aspects of RD. Doherty and Malone [6] gave valuable commentaries on future trends and challenges in this field of research. Gorak and co-workers [7] summarized rate-based modeling techniques for RD and also for reactive absorption. Book chapters on RD are available in volumes on distillation technology by Stichlmair and Fair [8], and by Doherty and Malone [9], and also in a recent book on reactive separations [10].

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