This book addresses principles and practical applications of membrane distillation and osmotic distillation, separation technologies which are gaining increasing attention due to their advantages over conventional concentration processes.

Preface xi Acknowledgments xiii About the Authors xv Nomenclature xvii 1 General Introduction 1 1.1 Overview of Distillation Processes 1 1.2 Membrane Distillation (MD) 5 1.2.1 Historical Perspective 5 1.2.2 MD Process 7 1.3 Osmotic Distillation (OD) 11 1.3.1 Historical Perspective 11 1.3.2 OD Process 12 1.4 MD and OD as Alternatives to Established Stripping Processes 14 1.4.1 Nonvolatile Solutes Retention 15 1.4.2 Minimization of Heat Damage to Feed Components 15 1.4.3 Organic Volatiles Retention 18 1.4.4 Production of Highly Concentrated Solutions 19 1.4.5 Utilization of Waste Heat or Heat from Natural Sources 20 1.5 Established Stripping Processes 20 1.5.1 Multistage Flash Distillation (MSF) 20 1.5.2 Multiple-Effect Distillation (MED) 22 1.5.3 Vapor Compression Distillation (VCD) 25 1.5.4 Freeze Concentration (FC) 26 1.5.5 Reverse Osmosis (RO) 28 1.5.6 Electrodialysis (ED) 31 1.6 Other Membrane Processes 32 1.6.1 Microfiltration (MF) 33 1.6.2 Ultrafiltration (UF) 34 1.6.3 Nanofiltration (NF) 36 1.7 Concluding Remarks 38 2 Theoretical Aspects of Membrane Distillation 39 2.1 Introduction 39 2.2 MD Theory 40 2.2.1 Preliminary Considerations 40 2.2.2 Overall Approach to Theoretical Treatment 45 2.2.3 Overall Driving Force, Δpb 46 2.2.4 Overall Mass Transfer Coefficient, K 50 2.2.5 Vapor Pressure Polarization Coefficient, ;;v 60 2.3 MD Membrane Requirements 68 2.4 Effect of Operating Conditions on MD Performance 71 2.4.1 Feed Temperature 71 2.4.2 Strip Temperature 72 2.4.3 Feed Solutes Concentration 72 2.4.4 Feed Velocity 73 2.4.5 Strip Velocity 75 2.4.6 Membrane Type 76 2.4.7 Summary of Conditions Affecting MD Performance 77 2.5 MD Process Economics 79 2.6 Concluding Remarks 82 3 Theoretical Aspects of Osmotic Distillation 85 3.1 Introduction 85 3.2 OD Theory 87 3.2.1 Preliminary Considerations 87 3.2.2 Overall Approach to Theoretical Treatment 90 3.2.3 Overall Driving Force, Δpb 92 3.2.4 Overall Mass Transfer Coefficient, K 96 3.2.5 Vapor Pressure Polarization Coefficient, ;;v 97 3.3 OD Membrane Requirements 97 3.4 Effect of Operating Conditions on OD Performance 98 3.4.1 Osmotic Agent Concentration 99 3.4.2 Feed Solutes Concentration 99 3.4.3 Feed Velocity 100 3.4.4 Strip Velocity 100 3.4.5 Feed and Strip Temperature 101 3.4.6 Membrane Type 101 3.4.7 Summary of Conditions Affecting OD Performance 103 3.5 OD Process Economics 103 3.6 Concluding Remarks 105 4 Properties of Macroporous Hydrophobic Membranes 107 4.1 Introduction 107 4.2 Theoretical Aspects of Membrane Hydrophobicity 108 4.3 Membrane Types 111 4.3.1 Polypropylene (PP) 113 4.3.2 Polytetrafluoroethylene (PTFE) 115 4.3.3 Polyvinylidene Fluoride (PVDF) 118 4.3.4 Tailored PVDF-Based Membranes 118 4.3.5 Polyazole Membranes 119 4.3.6 Nanofibrous PVDF–PTFE Membranes 121 4.3.7 Surface-Modified Hydrophilic Membranes 122 4.3.8 Inorganic Membranes 122 4.4 Fouling of Hydrophobic Membranes 123 4.4.1 Inorganic Fouling or Scaling 126 4.4.2 Organic Fouling 127 4.4.3 Biological Fouling 129 4.4.4 Clean-in-Place (CIP) Operating Conditions 129 4.5 Protection Against Membrane Wet-Out 130 4.6 Hydrophobicity Restoration 132 4.7 Membrane Module Requirements 132 4.7.1 Plate-and-Frame Modules 133 4.7.2 Spiral Wound Modules 134 4.7.3 Hollow-Fiber Modules 135 4.8 Concluding Remarks 137 5 Membrane Distillation Applications 139 5.1 Introduction 139 5.1.1 Water Recovery 140 5.1.2 Electrical Energy Consumption 141 5.1.3 Thermal Energy Consumption 141 5.2 Desalination 142 5.2.1 Water Pretreatment 143 5.2.2 Brine Disposal 145 5.2.3 Applications 145 5.3 Industrial Wastewater Treatment 147 5.3.1 Radioactive Waste Treatment 150 5.3.2 Concentration of Nonvolatile Acids 153 5.3.3 Volatile Acid Recovery from Industrial Effluents 153 5.3.4 Salt Recovery by Membrane Distillation Crystallization (MDC) 154 5.3.5 Textile Industry Applications 155 5.4 Production of Liquid Food Concentrates 156 5.5 Miscellaneous Applications 161 5.5.1 Volatiles Recovery from Fruit Juice by VMD and SGMD 161 5.5.2 Dealcoholization of Fermented Beverages Using DCMD 162 5.5.3 Enhanced Ethanol Production Using DCMD 163 5.5.4 Production of Pharmaceutical Products 164 5.6 Concluding Remarks 165 6 Osmotic Distillation Applications 167 6.1 Introduction 167 6.2 Fruit and Vegetable Juice Applications 176 6.2.1 Orange Juice 176 6.2.2 Apple Juice 183 6.2.3 Kiwifruit Juice 187 6.2.4 Grape Juice 190 6.2.5 Melon Juice 193 6.2.6 Camu Camu Juice 196 6.2.7 Pomegranate Juice 198 6.2.8 Tomato Juice 200 6.2.9 Passion Fruit Juice 203 6.2.10 Pineapple Juice 206 6.2.11 Cornelian Cherry, Blackthorn, and Common Whitebeam Juice 207 6.2.12 Sour Cherry Juice 207 6.2.13 Cranberry Juice 208 6.3 Other Applications 209 6.3.1 Recovery and Concentration of Polyphenols from Olive Mill Wastewater 209 6.3.2 Recovery of Flavonoids from Orange Press Liquor 212 6.3.3 Echinacea Extract Concentration 213 6.3.4 Reconcentration of Spent Osmotic Dehydration Sucrose Solutions 215 6.3.5 Aroma Recovery from Artificial Solutions 216 6.4 Concluding Remarks 218 7 Future Prospects for Membrane Distillation and Osmotic Distillation 221 7.1 Introduction 221 7.2 Membrane Module Design 222 7.3 Membrane Protection Against Wet-Out 224 7.3.1 Reclamation of Water for Reuse During Long-Duration Human Space Missions 225 7.3.2 Production of Citrus Fruit Juice Concentrates 226 7.3.3 Whole Milk Concentration on the Farm 227 7.3.4 Concentration of Detergent-Containing Radioactive Waste Solutions 228 7.4 Utilization of Renewable Energy Sources 228 7.5 Membrane-Based Factory Processes of the Future: A Hypothetical Example 231 7.6 End Note 235 References 237 Index 261

Laboratory chemists use distillation to separate small quantities of individual compounds from each other while industrial operators use this process to effect large-scale separations involving complex materials such as liquid foods, beverages, seawater, petroleum products and factory waste streams. Membrane distillation and osmotic distillation are novel, closely related processes that offer several advantages over conventional distillation processes. This book addresses the principles and applications of membrane distillation and osmotic distillation, separation technologies that are gaining increasing attention for a wide range of industrial applications. Written by leading practitioners of these critical distillation methods, Understanding Membrane Distillation and Osmotic Distillation serves as a key resource for readers involved in chemical engineering, food processing, desalination, wastewater treatment or pollution control. Key benefits of this book include: Discussion of wide-ranging applications in the food, brewing, pharmaceuticals, desalination, wastewater treatment and pollution control industries. Consideration of theoretical and practical aspects, economics and the potential for integrated membrane processes to provide solutions to many separation problems. A complete package for researchers and plant operators.