Ion-Exchange Membrane Separation Processes

361 Pages·2004·4.806 MB·English

by  Heiner Strathmann (Eds.)

ION-EXCHANGE MEMBRANE
SEPARATION PROCESSES
Membrane Science and Technology Series
Volume 1: Pervaporation Membrane Separation Processes
Edited by R.Y.M. Huang (1991)
Volume 2: Membrane Separations Technology, Principles and Applications
Edited by R.D. Noble and S.A. Stern (1995)
Volume 3: Inorganic Membranes for Separation and Reaction
By H.R Hsieh (1996)
Volume 4: Fundamentals of Inorganic Membrane Science and Technology
Edited by A.J. Burggraaf and L. Cot (1996)
Volume 5: Membrane Biophysics
Edited by H. Ti Tien and A. Ottova-Leitmannova (2000)
Volume 6: Recent Advances in Gas Separation by Microporous Ceramic Membranes
Edited by N.K. Kanellopoulos (2000)
Volume 7: Planar Lipid Bilayers (BLMs) and their Applications
Edited by H.T. Tien and A. Ottova-Leitmannova (2003)
Volume 8: New Insights into Membrane Science and Technology: Polymeric and
Biofunctional Membranes
Edited by D. Bhattacharyya and D.A. Butterfield (2003)
Volume 9: Ion-Exchange Membrane Separation Processes
By H. Strathmann (2004)
Membrane Science and Technology Series, 9
ION-EXCHANGE MEMBRANE
SEPARATION PROCESSES
Heiner Strathmann
Institut fElr Chemische Verfahrenstechnik
Universit~t Stuttgart, Stuttgart, Germany
2004
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Preface
Ion-exchange membranes and their application are not a recent development. Processes such
as electrodialysis have been used on a large industrial scale for more than half a century. The
literature covering various processes involving ion-exchange membranes and their applications is
very broad, extremely fragmented, and contained in a number of different scientific journals and
in various patents. This makes it difficult to gain a reasonably accurate overview of ion-exchange
membranes and their applications. While other membrane processes such as reverse osmosis or
micro- and ultrafiltration are described in great detail in a number of excellent text and reference
books there is hardly any comprehensive treatment of ion-exchange membrane separation
processes. Therefore, the time seems to be appropriate for a book that emphasizes the most
relevant aspects of this today already widely used technology.
The main difficulty confronted in such an endeavor is to find a balanced selection between the
fundamental theoretical background and practical applications necessary to provide the reader
with a sound understanding of the function of ion-exchange membranes and their importance for
solving difficult separation problems without getting lost in too many details. Therefore, the
objectives of this book are to give a comprehensive overview of ion-exchange membrane
separation processes covering the fundamentals as well as recent developments of the different
products and processes and their applications for a quite heterogeneous interest group including
plant managers and process engineers as well as research scientists and graduate students.
Reading this book the plant engineer might complain that too much emphasis is put on the
discussion of the theoretical background information, while on the other hand those in superior
command of thermodynamics and electrochemistry might express their concern about the
simplified approach of treating very complex phenomena. To facilitate the reading of the book I
have tried to separate the different topics. In the first chapter a very general overview of the
relevant electromembrane processes is given. In the second chapter some thermodynamic and
physicochemical fundamentals are described. This chapter can cheerfully be skipped by those
interested only in the various applications of the ion-exchange membrane separation processes
and their technical and commercial relevance compared to competing technologies. This is
discussed in the last chapter, which certainly can be missed by all those interested in the more
scientific aspects. The third chapter gives some information about ion-exchange membrane
preparation techniques, while in the fourth and fifth chapter the processes are discussed as unit
operations giving examples for the design of specific plants. These two chapters are probably of
interest mainly to the plant engineer and plant manager.
In a book of this kind it is impossible to mention all those who have contributed to the
development and understanding of ion-exchange membrane separation processes. Quotations and
literature references are restricted to publications, which are apt to illustrate the discussions in the
text. The choice of the literature references is arbitrary and a matter of personal preference, and I
apologize to all scientists and engineers whom I have not given due credit for their contribution
to the field.
My sincere thanks are due to many of my students and colleagues who have contributed to this
book with their work and many helpful suggestions. However, I am particularly indebted to Harm
Schmoldt for his valuable and constructive suggestions concerning the content of the book, my
vi
wife Monika who struggled valiantly with my English spelling and style while proofreading the
manuscript, and Andrej Grabowsky who spent many hours checking all the equations and
drawings very thoroughly and pointing out mistakes. His sound scientific background and
complete command of the computer was extremely helpful in writing this book. I thank both of
them for the many hours they have spent to improve the manuscript in the technical content and
in style.
Heiner Strathmann
vii
Contents
Chapter 1 Overview of Ion-Exchange Membrane Processes
1 Introduction .............................................................................................................. 1
2 Historical Development ........................................................................................... 1
3 The Structure of Ion-Exchange Membranes ............................................................ 4
4 Ion-Exchange Membrane Processes ........................................................................ 5
4.1 Ion-Exchange Membranes in Separation Processes ................................................. 6
4.1.1 Electrodialysis ..........................................................................................................6
4.1.2 Electrodialysis with Bipolar Membranes ................................................................. 7
4.1.3 Continuous Electrodeionization ............................................................................... 9
4.1.4 Diffusion Dialysis ....................................................................................................9
4.1.5 Donnan Dialysis ....................................................................................................... 11
4.1.6 Electrolytic Processes Using Ion-Exchange Membranes ......................................... 12
4.1.7 The Solid Polymer Electrolyte Fuel Cell ................................................................. 13
4.2 Technical Relevance of Ion-Exchange Membrane Processes .................................. 14
4.2.1 Desalination by Electrodialysis ................................................................................ 15
4.2.2 Concentration of Mineral Salts and Other Applications of Electrodialysis ............. 16
4.2.3 The Continuous Electrodeionization and the Use of Bipolar Membranes ............... 16
4.2.4 Diffusion Dialysis and Donnan Dialysis .................................................................. 17
4.3 Relevance of Electrolytic Production Processes and Fuel Cells .............................. 17
5 Recommended Further Reading: ............................................................................. 18
5.1 Ion-Exchange Membrane Preparation ...................................................................... 18
5.2 Electrodialysis .......................................................................................................... 18
5.3 Bipolar Membrane Electrodialysis ........................................................................... 18
5.4 Continuous Electrodeionization ............................................................................... 19
5.5 Electrolytic Chlorine and Alkaline Production ........................................................ 19
5.6 Fuel Cells and Electrochemical Synthesis ............................................................... 19
Literature: ............................................................................................................................2 0
Chapter 2 Electrochemical and Thermodynamic Fundamentals
1 Introduction ..............................................................................................................2 3
2 Basic Electrochemical Relations ............................................................................. 23
2.1 Electron and Ion Conductivity and Ohm's Law ...................................................... 24
2.2 The Electric Field and the Permittivity .................................................................... 26
2.2.1 The Electric Field .....................................................................................................2 7
2.2.2 The Debye-HiJckel Theory of Ionic Solutions ......................................................... 29
2.2.3 Electrical Dipoles and Intermolecular Forces .......................................................... 31
2.3 The Double Layer at the Surface of Ion-Exchange Membranes .............................. 33
2.3.1 The Principle of a Capacitor .................................................................................... 33
2.3.2 The Electrical Double Layer .................................................................................... 34
3 Basic Thermodynamic Relations ............................................................................. 37
3.1 Chemical and Electrochemical Equilibrium ............................................................ 43
viii
3.1.1 The Water Dissociation and the pH- and pK-Values of Acids and Bases ............... 43
3.1.2 The Ion-Exchange Equilibrium and the Donnan Potential ...................................... 47
3.1.3 The Electrochemical Equilibrium ............................................................................ 48
3.1.4 The Osmotic Equilibrium and the Osmotic Pressure ............................................... 53
3.1.5 Electroosmosis and Streaming Potential .................................................................. 57
3.2 The Electrochemical Cell and the Electromotive Force .......................................... 60
3.2.1 The Electrochemical Cell Reaction and the Gibbs Free Energy .............................. 63
3.2.2 The Standard Cell Potential and the Nernst Equation ............................................. 65
4 Transport of Ions in Solutions and Membranes ....................................................... 65
4.1 Mathematical Description of Transport Phenomena in Solutions ........................... 66
4.1.1 Phenomenological Description of Mass Transport .................................................. 67
4.1.2 Description of Mass Transport by the Stefan- Maxwell Approach ......................... 68
4.1.3 Description of Mass Transport by the Nernst-Planck Equation ............................... 69
4.1.4 Electrical Current and Ion Fluxes ............................................................................ 71
4.1.5 The Transport and Transference Numbers ............................................................... 72
4.1.6 Transport of Ions in an Aqueous Solution ............................................................... 73
4.1.7 Mass Transport in Ion-Exchange Membranes ......................................................... 75
4.1.8 Membrane Counterion Permselectivity ................................................................... 76
4.1.9 The Flux of Solvent Through an Ion-Exchange Membrane ..................................... 79
4.2 Membrane Permselectivity and the Donnan Exclusion ........................................... 80
4.3 The Membrane Potential .......................................................................................... 81
5 List of Symbols: ....................................................................................................... 84
Literature: 87
Chapter 3 Preparation and Characterization of Ion-Exchange Membranes
1 Introduction .............................................................................................................. 89
2 Preparation of Ion-Exchange Membranes ................................................................ 92
2.1 Preparation of Homogeneous and Microheterogeneous Membranes ....................... 93
2.1.1 Polymerization and Polycondensation of Monomers ............................................... 94
2.1.2 Introduction of Ionic Groups into a Preformed Solid Polymer Film ....................... 101
2.1.3 Introduction of Ionic Groups into a Dissolved Polymer .......................................... 102
2.2 Preparation Procedure of Heterogeneous Ion-Exchange Membranes ...................... 104
2.3 Special Property Ion-Exchange Membranes ............................................................ 105
2.3.1 Monovalent Ion Permselective Membranes ............................................................. 105
2.3.2 Proton Permselective Cation-Exchange Membranes ............................................... 106
2.3.3 Anion-Exchange Membranes of High Proton Retention ......................................... 106
2.3.4 Anti-Fouling Anion-Exchange Membranes ............................................................. 107
2.3.5 Alkaline Stable Anion-Exchange Membranes ......................................................... 108
2.3.6 Bipolar Membranes .................................................................................................. 109
2.3.7 Ion-Exchange Membranes for Diffusion Dialysis ................................................... 114
2.3.8 Other Special Property Ion-Exchange Membranes .................................................. 114
3 Characterization of Ion-Exchange Membranes ........................................................ 115
3.1 The Structure of Ion-Exchange Membranes and its Characterization ..................... 116
3.2 Mechanical Stability, Swelling, and Permeability of Membranes ........................... 117
3.2.1 The Membrane Water Content ................................................................................. 118
3.2.2 Hydraulic Permeability of Ion-Exchange Membranes ............................................. 119
3.2.3 Long-Term Chemical Stability of Membranes ........................................................ 120
3.3 Determination of Electrochemical Properties of Membranes .................................. 120
3.3.1 The Ion-Exchange Capacity of a Membrane ............................................................ 121
3.3.2 Electrical Resistance of Ion-Exchange Membranes ................................................. 121
3.3.3 Permselectivity of Ion-Exchange Membranes ......................................................... 131
3.3.4 Membrane Permeation Selectivity for Different Counterions ................................. 134
3.3.5 Diffusion Coefficients of Electrolytes in Ion-Exchange Membranes ...................... 134
3.3.6 Water Transport in Ion-Exchange Membranes ........................................................ 136
3.3.7 Characterization of Special Property Membranes .................................................... 138
4 List of Symbols ....................................................................................................... .140
Literature ............................................................................................................................. .141
Chapter 4 Operating Principle of Eiectrodialysis and Related Processes
1 Introduction .............................................................................................................. 147
2 The Principle of Conventional Electrodialysis ........................................................ 147
2.1 Mass Transport in an Electrodialysis Stack ............................................................. 149
2.1.1 Material Balance Between the Diluate and Concentrate Flow Streams .................. 152
2.2 Membrane Counterion Selectivity ........................................................................... 158
2.3 Concentration Polarization and Limiting Current Density ...................................... 159
2.4 The Limiting Current Density, Causes and Consequences ...................................... 163
2.4.1 Experimental Determination of the Limiting Current Density ................................ 164
2.4.2 The Overlimiting Current Density ........................................................................... 166
2.5 Membrane Fouling and Poisoning ........................................................................... 168
2.6 Energy Requirements in Electrodialysis .................................................................. 169
2.6.1 Minimum Energy Required for the Separation of a Molecular Mixture .................. 169
2.6.2 Practical Energy Requirements in Electrodialysis ................................................... 173
2.7 Processes Effecting the Efficiency of Electrodialysis .............................................. 181
2.7.1 Current Utilization ................................................................................................... 181
3 Electrodialysis with Bipolar Membranes ................................................................. 184
3.1 The Principle of Water Dissociation in Bipolar Membranes ................................... 185
3.1.1 Models for the Accelerated Water Dissociation in Bipolar Membranes ................. 187
3.1.2 Mass Transport in Electrodialysis with Bipolar Membranes ................................... 199
3.1.3 Energy Consumption in Electrodialysis with Bipolar Membranes .......................... 200
4 The Principle of Diffusion Dialysis ......................................................................... 205
4.1 The Mass Transport in Diffusion Dialysis ............................................................... 206
4.2 Complicating Factors in Dialysis Mass Transport Modeling ................................... 211
5 The Principle of Continuous Electrodeionization .................................................... 212
5.1 Mass Transfer in Continuous Electrodeionization ................................................... 213
5.2 Energy Requirements in Continuous Electrodeionization ....................................... 214
5.3 Complicating Factors in Continuous Electrodeionization Modeling ....................... 214
6 The Principle of Donnan Dialysis ............................................................................ 215
6.1 Mass Transport in Donnan Dialysis ......................................................................... 216
7 Other Ion-Exchange Separation Processes ............................................................... 218
8 List of Symbols ........................................................................................................ 218
Literature .............................................................................................................................. 222