MEMBRANE SEPARATION PROCESSES 1 1 %%^\^imte!#as#l=a^ Kaushik Nath Professor and Head Chemical Engineering Department GH Patel College of Engineering and Technology Vallabh Vidyanagar, Gujarat PHI Learning PnfaO Mmfei GBBr New Delhi-110001 2011
Contents Preface XI 1 Overview of Membrane Separation Processes 1-15 1.1 Equilibrium and Rate Governed Separation 1 1.2 What is a Membrane 2 1.3 Basic Principle of Membrane Separation 3 1.4 Historical Development of Membranes 4 1.5 Classification of Membrane Processes 5 1.6 Advantages of Membrane Processes 9 1.7 Disadvantages 10 1.8 Major Areas of Application 10 1.8.1 Chemicallndustry 12 1.8.2 Pharmaceutical Industry 12 1.8.3 Food and Dairy Industry 12 1.8.4 Biotechnology Industry 13 1.9 Future Prospects i4 Questions 15 2 Membrane Types, Materials, Preparation and Characterization 16-51 2.1 Types of Synthetic Membranes 16 2.1.1 Microporous Membranes 17 2.1.2 Asymmetric Membrane 18 2.1.3 Thin Film Composite 18 2.1.4 Electrically Charged 19 2.1.5 Inorganic Membrane 20 2.2 Membrane Modules 22 2.3 Typical Flow Patterns 28 2.4 Membrane Materials 29 2.5 Pore Characteristics 34 2.6 General Methods of Membrane Manufacture 35 2.6.1 Phase Inversion Process 35 iii
iv Contents 2.6.2 Track-etch Method 37 2.6.3 Sol-gel Peptisation Method 38 2.6.4 Interfacial Polymerization 38 2.6.5 Melt Pressing 39 2.6.6 Film Stretching 39 2.6.7 Template Leaching 40 2.6.8 Preparation of Ion-exchange Membranes 40 2.7 Measurement of Pore Size and Solute Rejection Properties 41 2.7.1 Visualization Methods 41 2.7.2 Hydraulic Permeability 42 2.7.3 Bubble Pressure or Point (Also Gas-Liquid Porosimetry) 42 2.1A Liquid Displacement (Also Liquid-Liquid Porosimetry) 43 2.7.5 Hg Porosimetry 43 2.1.6 Gas-Liquid Diffusion 44 2.7.7 Permporometry 44 2.7.8 Gas Adsorption-Desorption (Also BET Method) 45 2.7.9 Thermoporometry 45 2.7.10 Molecular Weight Cut Off (MWCO) 45 2.7.11 Microbial Challenge Test 47 2.8 Measurement and Interpretation of Surface Properties 48 Short Questions and Problems 49 3 Reverse Osmosis 52-88 3.1 Concept of Osmosis 52 3.1.1 Determination of Osmotic Pressure 54 3.1.2 Thermodynamic Consideration of Osmosis 55 3.1.3 Isotonic Solution 57 3.2 The Phenomenon of Reverse Osmosis 58 3.2.1 Pressure Requirement 59 3.2.2 High Pressure and Low Pressure RO 59 3.2.3 Advantages of Reverse Osmosis 59 3.2.4 Membrane Materials and Modules 60 3.2.5 Selection Criteria of RO Membrane 61 3.3 Models for Reverse Osmosis Transport 63 3.3.1 Kedem-Katchalsky Model 63 3.3.2 Spiegler-Kedem Model 64 3.3.3 Solution-Diffusion (SD) Model 64 3.3.4 Pore Transport Model 66 3.3.5 Modified Solution-Diffusion Model 66 3.4 Design and Operating Parameters 71 3.5 Concentration Polarization 72 3.5.1 Cake Enhanced Concentration Polarization (CECP) 73
Contents v 3.6 Membrane Plugging 74 3.7 Equivalent Work Requirement 75 3.8 Design of an RO Module 76 3.9 Reverse Osmosis for Non-aqueous System 78 3.10 Osmotic Pinch Effect 79 3.11 Forward Osmosis 79 3.12 Applications 80 Notations 83 Short Questions 84 Problems 86 Nanofiltration 89-100 4.1 Principle of Nanofiltration 89 4.2 Nanofiltration Membranes 90 4.2.1 Transport Mechanism in NF Membranes 90 4.2.2 Transport Mechanism of Charged Solutes 91 4.2.3 Parameters Affecting the Performance of NF Membranes 91 4.3 Mass Transfer in Nanofiltration 92 4.3.1 Fouling 4.4 Process Limitations 96 Model 93 4.5 Industrial Applications 97 Notations 99 Short Questions 100 5 Ultrafiltration 101-129 5.1 Basic Principle of Ultrafiltration 101 5.1.1 Advantages of Ultrafiltration 102 5.1.2 Ultrafiltration vis-a-vis Conventional Filtration 103 5.2 Ultrafiltration Membranes 103 5.2.1 Membrane Modules 104 5.2.2 Membrane Characterization 104 5.3 Configuration of UF Unit 105 5.4 Types of Devices in Ultrafiltration 106 5.4.1 Funnel 106 5.4.2 In-line Filters 107 5.4.3 Centrifuge Tube Devices 107 5.4.4 Diffusion Devices 108 5.4.5 Stirred Cell Modules 108 5.4.6 Cross Flow Modules 108 5.5 Factors Affecting the Performance of Ultrafiltration 109 5.6 Flux Equation for Ultrafiltration 110
VI Contents 5.7 Models for Solvent Flux 112 5.7.1 Resistance Model 112 5.7.2 Gel Polarization Model 113 5.8 Fouling and Flux Decline 117 5.9 Methods to Reduce Concentration Polarization 118 5.10 Energy Considerations 119 5.11 Micellar-enhanced Ultrafiltration 119 5.12 Affinity Ultrafiltration 121 5.12.1 Affinity Ultrafiltration in Protein Purification 122 5.13 Applications 123 Notations 126 Short Questions 127 Problems 127 6 Mlcroflltration 130-148 6.1 Basic Principle of Microfiltration 130 6.1.1 Cross Flow Microfiltration 131 6.1.2 Dead-end Microfiltration 131 6.2 Microfiltration Membranes 132 6.2.1 Membrane Pore Configuration 132 6.3 Mechanism of Transport 134 6.4 Retention Characteristics 137 6.5 Flow Characteristics 137 6.6 Membrane Plugging and Throughput 138 6.7 Fouling in Microfiltration Membranes 141 6.7.1 External Fouling 141 _' 6.7.2 Internal Fouling 142 6.7.3 Theoretical Models for Membrane Fouling 143 6.1 A Factors Affecting Membrane Fouling 144 6.7.5 Control of Fouling 145 6.7.6 Membrane Cleaning 145 6.8 Energy Consideration 145 6.9 Applications 146 Short Questions and Problems 147 7 Dialysis 149-165 7.1 Principle of Dialysis 149 7.2 Dialysis Systems 150 7.3 Dialysis Membranes 151 1.4 Mass Transfer in Dialysis 152 1.5 Applications 154 7.5.1 Hemodialysis 154 7.5.2 Removal of Alcohol From Beer to Produce a Reduced Alcohol Beer 159 7.5.3 Other Applications of Dialysis 159
Contents vii 7.6 Diffusion Dialysis 161 7.6.1 Advantages of Diffusion Dialysis 162 7.6.2 Application of Diffusion Dialysis 163 Notations 163 Short Questions 163 Problems 164 Gas Separation 166-199 8.1 Basic Principle 166 8.2 Membranes for Gas Separation 167 8.3 Membrane Modules 168 8.4 Fundamental Mechanism of Gas Transport 169 8.4.1 Knudsen Diffusion 169 8.4.2 Molecular Sieving 170 8.4.3 Solution-Diffusion 170 8.4.4 Dual Sorption Model 174 8.4.5 Facilitated Transport 175 8.4.6 Microscopic Models 177 8.5 Factors Affecting Gas Permeation 177 8.5.1 Temperature 177 8.5.2 Pressure 178 8.5.3 Plasticization 178 8.5.4 Permeant Condensability 179 8.5.5 Polymer Crystallinity 779 8.6 Complete Mixing Model 179 8.6.1 Solution of Equations 182 8.6.2 Equations for Multicomponent Mixtures 183 8.7 Cross Flow Model 184 8.8 Counter Current Model 187 8.9 Applications 192 Notations 195 Short Questions 196 Problems 197 Pervaporation 200-218 9.1 Basic Principle 200 9.2 Advantages of Pervaporation 201 9.3 Membrane Characteristics 202 9.4 Mass Transfer in Pervaporation 203 9.4.1 Permeation Through the Membrane 204 9.5 Thermodynamic Considerations 206 9.6 Design of a Pervaporation Module 208 9.7 Concentration Polarization 211 9.8 Factors Affecting Pervaporation 211
viii Contents 9.9 Temperature Drop at the Membrane Interface 212 9.10 Applications 213 Notations 217 Short Questions and Problems 218 10 Ion Exchange Membrane Process: Electrodialysis 219-238 10.1 Basic Principle 219 10.2 Ion Exchange Membranes 221 10.2.1 Ion Exchange Membranes in Chlor-Alkali Cells 223 10.2.2 Homogeneous and Heterogeneous Membranes 224 10.2.3 Bipolar Membrane 224 10.2.4 Permselectivity 225 10.3 Energy Requirement, Current Utilization, Efficiency 225 10.4 Concentration Polarization and Limiting Current Density 228 10.5 Other Operating Parameters 230 10.6 Batch and Continuous Electrodialysis 230 10.7 Electrodialysis Reversal (EDR) 232 10.8 Electrodeionization (EDI) 232 10.8.1 Working Principle 233 10.8.2 Advantages and Disadvantages of EDI 234 10.9 Applications of Electrodialysis 235 Short Questions 237 Problems 238 11 Introduction to Liquid Membrane 11.1 Benefits of Liquid Membranes 239 11.2 Types of Liquid Membranes 240 11.2.1 Bulk Liquid Membranes 240 11.2.2 Emulsion Liquid Membranes (ELM) 241 11.2.3 Thin Sheet Supported Liquid Membranes 11.2.4 Hollow Fibre Supported Liquid Membranes 11.2.5 Polymer Inclusion Membrane 245 11.3 Mechanism of Mass Transfer in Liquid Membranes 11.3.1 Simple Permeation Mechanism 246 11.3.2 Facilitated Transport Mechanism 247 11.4 Applications 248 Short Questions 251 239-251 243 244 246 12 Facilitated Transport 252-264 12.1 Mechanism of Facilitated Transport 253 12.2 Coupled Transport 255 12.2.1 Carrier Agent 257 12.2.2 Competitive Facilitated Transport with Two Permeants and One Carrier 257
Contents IX 12.3 Active and Passive Transport 261 12.3.1 Symport and Antiport 261 12.4 Some Potential Applications of Facilitated Transport 263 Short Questions and Problems 263 13 Other Membrane Processes 265-285 13.1 Membrane Contactor 265 13.1.1 Advantages and Disadvantages 266 13.1.2 Principle of Operation 266 13.1.3 Applications 268 13.2 Membrane Distillation 268 13.2.1 Mechanism 270 13.3 Membrane Reactors 271 13.4 Membrane Bioreactors 275 13.4.1 Membrane Recycle Bioreactor 276 13.4.2 Plug Flow Bioreactor 277 13.5 Charge Mosaic Membranes 277 13.5.1 Piezodialysis 279 13.6 Perstraction 279 13.6.1 Flux and Separation 13.7 Membrane Chromatography 280 in Perstraction 280 13.8 PEM Hydrogen Fuel Cell 281 13.9 Integration of Membrane and Non-membrane Processes 283 Short. Questions 284 14 Biomedical Applications of Membranes 286-295 14.1 Blood Oxygenator 286 14.2 Controlled Drug Delivery 287 14.2.1 Controlled Release Mechanisms 289 14.2.2 Polymers Used in Controlled Release 290 14.2.3 Application of Controlled Release 291 14.3 Plasmapheresis 292 14.4 Membranes in Bioartificial Organs 293 Short Questions 295 Appendix 297-306 References and Further Reading Index 307-317 319-322