Handbook ofMembraneSeparationsChemical, Pharmaceutical, Food,and Biotechnological ApplicationsPabby et al. / Handbook of Membrane Separations 9549_C000 Final Proof page i 21.5.2008 7:54pm Compositor Name: BManiPabby et al. /Handbook of Membrane Separations 9549_C000 Final Proof page ii 21.5.2008 7:54pm Compositor Name: BManiHandbook ofMembraneSeparationsChemical, Pharmaceutical, Food,and Biotechnological ApplicationsEdited byAnil K. PabbySyed S. H. RizviAna Maria SastreCRC Press is an imprint of theTaylor & Francis Group, an informa businessBoca Raton London New YorkPabby et al. /Handbook of Membrane Separations 9549_C000 Final Proof page iii 21.5.2008 7:54pm Compositor Name: BManiCRC PressTaylor & Francis Group6000 Broken Sound Parkway NW, Suite 300Boca Raton, FL 33487-2742 2009 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa businessNo claim to original U.S. Government worksPrinted in the United States of America on acid-free paper10 9 8 7 6 5 4 3 2 1International Standard Book Number-13: 978-0-8493-9549-9 (Hardcover)This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint.Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers.For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged.Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation with-out intent to infringe.Library of Congress Cataloging-in-Publication DataHandbook of membrane separations : chemical, pharmaceutical, food, and biotechnological applications / editor(s), Anil Kumar Pabby, Syed S.H. Rizvi, and Ana Maria Sastre.p. ; cm.Includes bibliographical references.ISBN-13: 978-0-8493-9549-9 (hardcover : alk. paper)ISBN-10: 0-8493-9549-6 (hardcover : alk. paper)1. Membrane separation--Handbooks, manuals, etc. I. Pabby, Anil Kumar. II. Rizvi, S. S. H., 1948- III. Sastre, Ana Maria. [DNLM: 1. Membranes, Artificial. 2. Biotechnology--methods. 3. Ultrafiltration. TP 159.M4 H236 2008]TP248.25.M46H35 2008660.2842--dc222008009730Visit the Taylor & Francis Web site athttp://www.taylorandfrancis.comand the CRC Press Web site athttp://www.crcpress.comPabby et al. / Handbook of Membrane Separations 9549_C000 Final Proof page iv 21.5.2008 7:54pm Compositor Name: BManiContentsForeword..................................................................................................................................................................................... ixPreface......................................................................................................................................................................................... xiEditors ....................................................................................................................................................................................... xiiiContributors ............................................................................................................................................................................... xvSECTION I Membrane Applications in Chemical and PharmaceuticalIndustries and in Conservation of Natural ResourcesChapter 1 Membrane Applications in Chemical and Pharmaceutical Industries and in Conservationof Natural Resources: Introduction....................................................................................................................... 3Ana Maria Sastre, Anil Kumar Pabby, and Syed S.H. RizviChapter 2 Application of Membrane Contactors as Mass Transfer Devices........................................................................ 7A. Sengupta and R.A. PittmanChapter 3 Membrane Chromatography............................................................................................................................... 25M.E. Avramescu, Z. Borneman, and M. WesslingChapter 4 Membranes in Gas Separation............................................................................................................................ 65May-Britt HggChapter 5 Pervaporation: Theory, Practice, and Applications in the Chemical and Allied Industries............................. 107Vishwas G. Pangarkar and Sangita PalChapter 6 Current Status and Prospects for Ceramic Membrane Applications................................................................ 139Christian Guizard and Pierre AmblardChapter 7 Membrane Technologies and Supercritical Fluids: Recent Advances ............................................................. 181D. Paolucci-Jeanjean, G.M. Rios, and S. SarradeChapter 8 Techniques to Enhance Performance of Membrane Processes ........................................................................ 193A.G. Fane and S. ChangChapter 9 Separation and Removal of Hydrocarbons Using Polymer Membranes ......................................................... 233S.I. SemenovaChapter 10 Zeolite Membranes: Synthesis, Characterization, Important Applications, and Recent Advances ................. 269M. Arruebo, R. Mallada, and M.P. PinaPabby et al. /Handbook of Membrane Separations 9549_C000 Final Proof page v 21.5.2008 7:54pm Compositor Name: BManivChapter 11 Membrane Fouling: Recent Strategies and Methodologies for Its Minimization............................................ 325Mattheus F.A. Goosen, S.S. Sablani, and R. Roque-MalherbeChapter 12 Membrane Extraction in Preconcentration, Sampling, and Trace Analysis..................................................... 345Jan ke JnssonChapter 13 Hybrid Liquid Membrane Processes with Organic Water-Immiscible Carriers (OHLM):Application in Chemical and Biochemical Separations ................................................................................... 371Vladimir S. KislikChapter 14 Advancements in Membrane Processes for Pharmaceutical Applications....................................................... 409Ralf Kuriyel, Masatake Fushijima, and Gary W. JungChapter 15 Membranes in Drug Delivery........................................................................................................................... 427Mario GrassiChapter 16 Bio-Responsive Hydrogel Membranes............................................................................................................. 473John Hubble and Rongsheng ZhangSECTION II Membrane Applications in Biotechnology,Food Processing, Life Sciences, and Energy ConversionChapter 17 Membrane Applications in Biotechnology, Food Processing, Life Sciences, and EnergyConversion: Introduction.................................................................................................................................. 495Syed S.H. RizviChapter 18 Ultraltration-Based Protein Bioseparation...................................................................................................... 497Raja GhoshChapter 19 Membrane Distillation in Food Processing...................................................................................................... 513Sanjay Nene, Ganapathi Patil, and K.S.M.S. RaghavaraoChapter 20 Applications of Membrane Separation in the Brewing Industry ..................................................................... 553Carmen I. Moraru and Ernst Ulrich SchraderChapter 21 Developments of Bipolar Membrane Technology in Food and Bio-Industries............................................... 581Gerald Pourcelly and Laurent BazinetChapter 22 Applications of Membrane Technology in the Dairy Industry........................................................................ 635Philipina A. Marcelo and Syed S.H. RizviChapter 23 Microporous Membrane Blood Oxygenators................................................................................................... 671S.R. Wickramasinghe and B. HanPabby et al. / Handbook of Membrane Separations 9549_C000 Final Proof page vi 21.5.2008 7:54pm Compositor Name: BManiviChapter 24 Transporting and Separating Molecules Using Tailored Nanotube Membranes ............................................. 693Punit Kohli and Charles R. MartinChapter 25 Use of Emulsion Liquid Membrane Systems in Chemical and Biotechnological Separations ....................... 709Jilska M. Perera and Geoff W. StevensChapter 26 Membrane Electroporation and Emerging Biomedical Applications............................................................... 741K.P. MishraChapter 27 Proton-Conducting Membranes for Fuel Cells................................................................................................. 759Vineet Rao, K. Andreas Friedrich, and Ulrich StimmingSECTION III Membrane Applications in Industrial Waste Management(Including Nuclear), Environmental Engineering,and Future Trends in Membrane ScienceChapter 28 Membrane Applications in Industrial Waste Management (Including Nuclear), EnvironmentalEngineering, and Future Trends in Membrane Science: Introduction ............................................................. 823Ana Maria Sastre and Anil Kumar PabbyChapter 29 Treatment of Radioactive Efuents: Introduction, Fundamentals, and Scope of DifferentMembrane Processes ........................................................................................................................................ 827B.M. Misra and V. RamachandhranChapter 30 Radioactive Waste Processing: Advancement in Pressure-Driven Processesand Current World Scenario............................................................................................................................. 843Grazyna Zakrzewska-TrznadelChapter 31 Liquid Membrane-Based Separations of Actinides.......................................................................................... 883P.K. Mohapatra and V.K. ManchandaChapter 32 Reverse Osmosis-Based Treatment of Radioactive Liquid Wastes Generated in Hospital Facilityand in Steel Industry: Case Studies.................................................................................................................. 919M. Sancho, J.M. Arnal, G. Verd, and J. LoraChapter 33 Evaluation of Membrane-Based Processing of Radioactive Nuclear Plant Waste: Case Studies ................... 933Anil Kumar Pabby, S.K. Gupta, S.R. Sawant, N.S. Rathore, P. Janardan,R.D. Changrani, and P.K. DeyChapter 34 Application of Donnan Membrane Process for Recovery of Coagulants from WaterTreatment Residuals ......................................................................................................................................... 945Prakhar Prakash and Arup K. SenGuptaChapter 35 Utilization of Membrane Processes in Treating Various Efuents Generatedin Pulp and Paper Industry ............................................................................................................................... 981Mika Mnttri and Marianne NystrmPabby et al. / Handbook of Membrane Separations 9549_C000 Final Proof page vii 21.5.2008 7:54pm Compositor Name: BManiviiChapter 36 Membrane Bioreactors for Wastewater Treatment......................................................................................... 1007Eoin CaseyChapter 37 Membrane-Assisted Solvent Extraction for the Recovery of Metallic Pollutants: ProcessModeling and Optimization............................................................................................................................ 1023Inmaculada Ortiz and J. Angel IrabienChapter 38 Membrane Contactors for Gaseous Streams Treatments ............................................................................... 1041Alessandra Criscuoli and Enrico DrioliChapter 39 Strip Dispersion Technique: Application for Strategic and Precious Metal Separationand Treatment of Wastewater Streams........................................................................................................... 1057Anil Kumar Pabby, S.C. Roy, J.V. Sonawane, F.J. Alguacil, and Ana Maria SastreChapter 40 Electrically Enhanced Membrane Separations and Catalysis......................................................................... 1071V.M. Linkov, B.J. Bladergroen, and A.M. MalulekeChapter 41 Membrane Processes for Treatment of Industrial Tannery Efuents: A Case Study.................................... 1087A. Bdalo, E. Gmez, and A.M. HidalgoChapter 42 New Developments in Nanoltration Technology: A Case Study on Recoveryof Impurity-Free Sodium Thiocyanate for Acrylic Fiber Industry................................................................. 1101S. Sridhar and B. SmithaChapter 43 Future Progresses in Membrane Engineering................................................................................................. 1131Enrico Drioli and Enrica FontananovaIndex...................................................................................................................................................................................... 1147Pabby et al. /Handbook of Membrane Separations 9549_C000 Final Proof page viii 21.5.2008 7:54pm Compositor Name: BManiviiiForewordDuringthemiddleof thelast century, whenthe rst syntheticmembranewithtailor-madeseparationpropertiesbecameavailable, a multitude of technically and commercially interesting applications were identied. Today, 50 years later,membranesand membrane processes have indeed become valuable tools for the separation of molecular mixtures. They arethe key components in articial organs and in devices for the controlled release of active agents, or in energy conversion andstorage systems. Seawater and brackish water desalination using reverse osmosis and electrodialysis are energy efcient andhighly economic processes for large-scale production of potable water. Micro- and ultraltration are used for the production ofhigh-quality industrial water and for the treatment of industrial efuents. Blood detoxication by hemodialysis and hemoltra-tion improvesthe quality of life for more than 1.3 million people suffering from acute and chronic renal failure. Membraneprocesses have found a multitude of applications in chemical and pharmaceutical industries as well as in food processing andbiotechnology. They are used on a large scale in gas separation and as tools in analytical laboratories. Todays membrane-basedindustry is serving a rapidly growing multibillion euro market with a large number of products and processes. The developmentof membranes with improved properties will most likely increase the importance of membranes and membrane processes in agrowing number of applications for the sustainable growth of modern industrial societies.The term membrane refers not to a single item, but covers a large variety of structures and materials with very differentproperties. Thesameistrueformembraneprocesses, whichcanbeverydifferent inthewaytheyfunction. However, allmembranes and membrane processes have one feature in common, i.e., they can perform the separation of certain molecularmixtures effectively and economically at ambient temperature, and without any toxic or harmful reaction by-products.Intheearlydaysofmembranescienceand technology,researchwasmainlyconcentratedon elucidatingthemembranemass transport mechanism and on developing membrane structures with specic mass transport properties. The fundamentalsof most membrane processes andmembrane preparationprocedures are describedingreat detail ina large number ofpublicationsinvariousscienticjournalsandinseveral excellent textbooks. However, theapplicationofmembranesandmembrane processes is much less comprehensively covered in todays literature. Only a relatively small number of applicationsof membrane processes such as reverse osmosis, micro- and ultraltration, and gas separation and pervaporation are treated intextbooks and reference books. A large number of interesting membrane applications in the food and drug industry, in chemicaland electrochemical synthesis, and in articial organs are often not adequately treated in the membrane-related literature, butarepublishedinjournals specicfor certainindustries, whichareoutsideof theinterest of manymembranescientists.Furthermore,application-orientedmembranestudiesthatareoftencarriedoutinindustrialenterprisesaredescribed onlyaspatents,orarenotpublishedatall.Therefore, itisdifculttoobtaina reasonablycompleteoverviewoftheverylargeandheterogeneouseld of membrane applications without reading a number of very different journals and patents where most ofthe publications are not really membrane related.The aim of Handbook of Membrane Separations: Chemical, Pharmaceutical, Food, and Biotechnological Applications is toll the gap in the presently available membrane literature by providing a comprehensive discussion of membrane applications inthechemical, food, andpharmaceutical industries, inbiotechnology, andinthetreatment oftoxicindustrial efuents. Theapplications of membranes in different areas are described by scientists and engineers who not only are experts in membranescienceandtechnologybutalsohaveextensiveexperienceinthespeciceldofmembraneapplication. Thisbookisnotcompetitive, but rathercomplementarytoother textbooksandhandbooksonmembranescienceandtechnologypresentlyavailablein the market. It provides enough background information on the various membranecomponents and processes toevaluate their potential applications without a detailed treatment of the fundamental aspects of membrane mass transport theoriesand membrane structure development. The book should, therefore, be of great value to scientists and engineers who are notnecessarily membrane experts but are interested in using membrane processes in solving specic separation and mass transportproblems. It is equally suited for the newcomers in theeld of membrane science as for engineers and scientists, who do havebasic knowledge in membrane technology but are interested in obtaining more information on specic present and potential futuremembrane applications. It also provides an excellent base for courses and lectures in postgraduate education.Professor Heiner StrathmannUniversity of StuttgartGermanyPabby et al. / Handbook of Membrane Separations 9549_C000 Final Proof page ix 21.5.2008 7:54pm Compositor Name: BManiixPabby et al. /Handbook of Membrane Separations 9549_C000 Final Proof page x 21.5.2008 7:54pm Compositor Name: BManiPrefaceDuring the past two decades, membrane technology has grown into an accepted unit operation for a wide variety of separationsin industrial processes and environmental applications. Tighter environmental legislation calls for equipment that is able to dealwiththeremoval of componentsacrossawiderangeof concentrationlevelsandthat offersconsiderable exibilityandefciency. Membrane technologyrst became important during the 1960s and 1970s in water treatment and in processes suchas reverse osmosis, ultraltration, dialysis, electrodialysis, and microltration. During the 1980s, membrane technology beganto be applied on a large scale in theeld of gas purication. The successful introduction of membrane technology in theseeldswas mainly the result of the development of reliable and selective polymeric membranes.There are a number of reference publications in theeld of membrane technology, such as handbooks, monographs, andcompendiaof conferenceandworkshopproceedings. Therelativeabundanceof suchworks begs thequestions, Whyanother? andHowwill this onebedifferent? Thesequestions areprobablybest answeredbyconsideringwhat theHandbook of Membrane Separations: Chemical, Pharmaceutical, Food, and Biotechnological Applications has to offer. Thehandbookcoversthefull spectrumofmembranetechnologyanddiscussesitsadvancement andapplicationsinaseriesofchapters written by experts, prominent researchers, and professionals from all over the world.Thehandbookisdividedintothreemainsections:Therstsectiondealswithmembraneapplicationsinchemical andpharmaceutical industries, andinconservationof natural resources; thesecondsectioncovers membraneapplications inbiotechnology, food processing, life sciences, and energy conversion. Finally, the third section deals with membraneapplications in industrial waste management (including nuclear), environmental engineering, and future trends in membranescience. Each section is divided into chapters that deal with the subject matter in depth and focus on cutting-edge advancementsin theeld. Several authors were commissioned to write the chapters under the supervision of the editors, and each chapter waspeer-reviewedforcontent andstylebeforeit wasacceptedfor publication. Theaimwastomaintaintheperspectiveofapractical handbook rather than merely a collection of review chapters.The editors would like to acknowledge the contributions of a number of authors and institutions that have played a majorrole in drafting the handbook from conception to publication. The handbook would not have been possible without their input.These contributors are leading experts in theirelds and bring a great wealth of experience to this book. The editors would alsolike to acknowledge the efforts of the reviewers who devoted their valuable time to revising the chapters before the deadlinesand suggested improvements to maintain the high standard of the handbook. Finally, we would like to acknowledge the supportofour homeinstitutionsat everystage inthe handbooks conception: theBhabhaAtomic Research Centre, Mumbai, India;Cornell University, Ithaca, New York; and the Universitat Politcnica de Catalunya, Barcelona, Spain.Anil Kumar PabbySyed S.H. RizviAna Maria SastrePabby et al. / Handbook of Membrane Separations 9549_C000 Final Proof page xi 21.5.2008 7:54pm Compositor Name: BManixiPabby et al. / Handbook of Membrane Separations 9549_C000 Final Proof page xii 21.5.2008 7:54pm Compositor Name: BManiEditorsAnil Kumar Pabby is afliated with one of the pioneering research centers ofIndia, theBhabhaAtomicResearchCentre(Department of AtomicEnergy),Tarapur, Mumbai, Maharashtra. HereceivedhisPhDfromtheUniversityofMumbai and subsequently completed his postdoctoral research at the UniversitatPolitcnica de Catalunya, Barcelona, Spain. Dr. Pabbyhas more than 150publications to his credit including 4 book chapters and a patent on nondisper-sive membrane technology. He was invited to join the team of associate editorsat the Journal of Radioanalytical and Nuclear Chemistry during 20022005. Hehas also served as consultant to the International Atomic Energy Agency (IAEA)for developing a technical document on the application of membrane technolo-gies for liquidradioactive waste processing. Dr. Pabbyhas beena regularreviewerforseveralnationalandinternationaljournalsandalsoservesontheeditorial board of various journals. His research interest includes pressure-drivenmembrane processes, nondispersive membrane techniques, extraction chromato-graphy, solvent extraction, and macrocyclic crown compounds. In 2003,Dr.Pabbywaselected fellowoftheMaharashtra AcademyofSciences(FMASc)forhiscontributiontomembranescienceand technology. In 2005, he received the prestigious Tarun Datta Memorial Award (instituted by Indian Association for NuclearChemists and Allied Scientists) for his outstanding contribution to nuclear chemistry and radiochemistry.Syed S.H. Rizvi is an international professor of food process engineering and hasservedas director ofgraduate studiesat theCornellInstituteof Food Science,Cornell University, Ithaca, New York. He has a PhD from Ohio State University,an MEng (chemical engineering) from the University of Toronto, and a BTechfrom Panjab University, India. Dr. Rizvi teaches courses devoted to engineeringand processing aspects of food science and related biomaterials. His laboratory isengagedinresearchonexperimental andtheoretical aspectsof bioseparationprocesses using supercritical uids and membranes, high-pressure extrusion withsupercritical carbon dioxide, physical and engineering properties of biomaterials,and novel food processing technologies. An invention of Cornell researchers, andsubsequently patented, supercriticaluid extrusion offers several advantages overthe conventional high-shear cooking extrusion and is being used to investigate thedynamics of the process andthe mechanics of the microcellular extrudatesgenerated for both food and nonfood applications. A major long-term goal is todevelop new and improved unit operations for value-added processing of food and biomaterials. Derivative goals include newtechniques for measurement and control of processes and properties for industrial applications. Dr. Rizvi has published more than140 technical papers, coauthored=edited 6 books, served on the editorial board of several journals, and holds 7 patents.AnaMariaSastreisaprofessor of chemical engineeringat theUniversitatPolitcnica de Catalunya (Barcelona, Spain), where she has been teachingchemistry for more than 28 years. She received her PhD from the AutonomousUniversityof Barcelona in1982andhas beenworkingfor manyyears inthe eld of solvent extraction, solvent impregnated resins, and membranetechnology.Shewasavisitingfellowat theDepartment of InorganicChemistry, theRoyal Institute of Technology, Sweden, during19801981andcarriedoutpostdoctoral research from October 1986 to April 1987 at Laboratoire de ChimieMinerale, EcoleEuropeennedesHautesEtudesdesIndustriesChimiquesdeStrasbourg, France. Professor Sastre has more than 190 journal publications andmorethan80papersininternational conferences. Dr. Sastrealsoholdsfourpatent applications, guided11PhDand16master thesis students, andis aPabby et al. /Handbook of Membrane Separations 9549_C000 Final Proof page xiii 21.5.2008 7:54pm Compositor Name: BManixiiireviewer of many international journals. In 2003, she was awarded the Narcis Monturiol medal for scientic and technologicalmerits, given by the Generalitat de Catalunya for her outstanding contribution to science and technology.Professor Sastre was the head of the chemical engineering department from 1999 to 2005 and is presently vice rector (vicechancellor) for academic policy at the Universitat Politcnica de Catalunya.Pabby et al. /Handbook of Membrane Separations 9549_C000 Final Proof page xiv 21.5.2008 7:54pm Compositor Name: BManixivContributorsF.J. AlguacilCentro Nacional de Investigaciones MetalrgicasConsejo Superior de Investigaciones CienticasCiudad UniversitariaMadrid, SpainPierre AmblardTechno-MembranesParc Scientique AgropolisMontpellier, FranceJ.M. ArnalChemical and Nuclear Engineering DepartmentPolytechnic University of ValenciaValencia, SpainM. ArrueboDepartment of Chemical and EnvironmentalEngineeringUniversity of ZaragozaZaragoza, SpainM.E. AvramescuMembrane Technology GroupFaculty of Science and TechnologyUniversity of TwenteEnschede, the NetherlandsLaurent BazinetInstitute of Nutraceuticals and Functional FoodsDepartment of Food Sciences and NutritionLaval UniversityLaval, Qubec, CanadaB.J. BladergroenSouth African Institute for AdvancedMaterials ChemistryUniversity of the Western CapeBellville, South AfricaA. BdaloDepartamento de Ingeniera QumicaUniversidad de Murcia, Campus de EspinardoMurcia, SpainZ. BornemanMembrane Technology GroupFaculty of Science and TechnologyUniversity of TwenteEnschede, the NetherlandsEoin CaseySchool of Chemical and Bioprocess EngineeringUniversity College DublinDublin, IrelandS. ChangGlobal Product Development, UF=MBR TechnologyGE Water & Process TechnologiesOakville, Ontario, CanadaR.D. ChangraniNuclear Recycle GroupBhabha Atomic Research CentreTarapur, Mumbai, Maharashtra, IndiaAlessandra CriscuoliResearch Institute on Membrane TechnologyUniversity of CalabriaRende, Cosenza, ItalyP.K. DeyNuclear Recycle GroupBhabha Atomic Research CentreTarapur, Mumbai, Maharashtra, IndiaEnrico DrioliResearch Institute on Membrane TechnologyUniversity of CalabriaRende, Cosenza, ItalyandDepartment of Chemical Engineering and MaterialsUniversity of CalabriaRende, Cosenza, ItalyA.G. FaneUNESCO Centre for Membrane Science and TechnologyUniversity of New South WalesSydney, New South Wales, AustraliaandSingapore Membrane Technology CentreNanyang Technological UniversitySingaporeEnrica FontananovaResearch Institute on Membrane TechnologyUniversity of CalabriaRende, Cosenza, ItalyandDepartment of Chemical Engineering and MaterialsUniversity of CalabriaRende, Cosenza, ItalyPabby et al. /Handbook of Membrane Separations 9549_C000 Final Proof page xv 21.5.2008 7:54pm Compositor Name: BManixvK. Andreas FriedrichGerman Aerospace CenterElectrochemical Energy TechnologyStuttgart, GermanyMasatake FushijimaCrossow Technology, SLSPall CorporationPort Washington, New YorkRaja GhoshDepartment of Chemical EngineeringMcMaster UniversityHamilton, Ontario, CanadaE. GmezDepartamento de Ingeniera QumicaUniversidad de MurciaCampus de EspinardoMurcia, SpainMattheus F.A. GoosenOfce of ResearchAlfaisal UniversityRiyadh, Saudi ArabiaMario GrassiDepartment of Chemical, Environmental, and RawMaterials EngineeringUniversity of TriesteTrieste, ItalyChristian GuizardLaboratoire de Synthse et Fonctionnalisation desCramiquesSaint Gobain CREECavaillon, FranceS.K. GuptaNuclear Recycle GroupBhabha Atomic Research CentreTarapur, Mumbai, Maharashtra, IndiaMay-Britt HggDepartment of Chemical EngineeringNorwegian University of Science and TechnologyTrondheim, NorwayB. HanDepartment of Chemical and Biological EngineeringColorado State UniversityFort Collins, ColoradoA.M. HidalgoDepartamento de Ingeniera QumicaUniversidad de MurciaCampus de EspinardoMurcia, SpainJohn HubbleDepartment of Chemical EngineeringUniversity of BathBath, United KingdomJ. Angel IrabienDepartamento de Ingeniera Qumica y Qumica InorgnicaUniversidad de CantabriaSantander, SpainP. JanardanNuclear Recycle GroupBhabha Atomic Research CentreTarapur, Mumbai, Maharashtra, IndiaJan ke JnssonAnalytical ChemistryLund UniversityLund, SwedenGary W. JungMembrane Technology ConsultantDaytona Beach, FloridaVladimir S. KislikCasali Institute of Applied ChemistryThe Hebrew University of JerusalemJerusalem, IsraelPunit KohliDepartment of Chemistry and BiochemistrySouthern Illinois UniversityCarbondale, IllinoisRalf KuriyelBiopharm Applications R&DPall Life SciencesPall CorporationNorthborough, MassachusettsV.M. LinkovSouth African Institute for Advanced Materials ChemistryUniversity of the Western CapeBellville, South AfricaJ. LoraChemical and Nuclear Engineering DepartmentPolytechnic University of ValenciaValencia, SpainR. MalladaDepartment of Chemical and EnvironmentalEngineeringUniversity of ZaragozaZaragoza, SpainPabby et al. /Handbook of Membrane Separations 9549_C000 Final Proof page xvi 21.5.2008 7:54pm Compositor Name: BManixviA.M. MalulekeSouth African Institute for Advanced Materials ChemistryUniversity of the Western CapeBellville, South AfricaV.K. ManchandaRadiochemistry DivisionBhabha Atomic Research CentreTarapur, Mumbai, Maharashtra, IndiaMika MnttriLaboratory of Membrane Technology and TechnicalPolymer ChemistryLappeenranta University of TechnologyLappeenranta, FinlandPhilipina A. MarceloDepartment of Chemical EngineeringThe Research Center for the Natural SciencesUniversity of Santo TomasManila, PhilippinesCharles R. MartinDepartment of ChemistryCenter for Research at the Bio=Nano InterfaceUniversity of FloridaGainesville, FloridaK.P. MishraRadiation Biology and Health Sciences DivisionBhabha Atomic Research CenterTarapur, Mumbai, Maharashtra, IndiaB.M. MisraNuclear Desalination UnitDivision of Nuclear PowerNuclear Power TechnologyDevelopment SectionDepartment of Nuclear EnergyVienna, AustriaP.K. MohapatraRadiochemistry DivisionBhabha Atomic Research CentreTarapur, Mumbai, Maharashtra, IndiaCarmen I. MoraruDepartment of Food ScienceCornell UniversityIthaca, New YorkSanjay NeneBiochemical Engineering GroupChemical Engineering and Process Development DivisionNational Chemical LaboratoryPune, Maharashtra, IndiaMarianne NystrmLaboratory of Membrane Technology and TechnicalPolymer ChemistryLappeenranta University of TechnologyLappeenranta, FinlandInmaculada OrtizDepartamento de Ingeniera Qumica y QumicaInorgnicaUniversidad de CantabriaSantander, SpainAnil Kumar PabbyNuclear Recycle GroupBhabha Atomic Research CentreTarapur, Maharashtra, IndiaSangita PalDepartment of Chemical EngineeringInstitute of Chemical TechnologyMumbai UniversityMumbai, Maharashtra, IndiaVishwas G. PangarkarDepartment of Chemical EngineeringInstitute of Chemical TechnologyMumbai UniversityMumbai, Maharashtra, IndiaD. Paolucci-JeanjeanEuropean Membrane InstituteUniversit MontpellierMontpellier, FranceGanapathi PatilDepartment of Food EngineeringCentral Food Technological Research InstituteMysore, Karnataka, IndiaJilska M. PereraDepartment of Chemical and BiomolecularEngineeringUniversity of MelbourneParkville, Victoria, AustraliaM.P. PinaDepartment of Chemical and EnvironmentalEngineeringUniversity of ZaragozaZaragoza, SpainR.A. PittmanMembrana-CharlotteCelgardCharlotte, North CarolinaPabby et al. /Handbook of Membrane Separations 9549_C000 Final Proof page xvii 21.5.2008 7:54pm Compositor Name: BManixviiGerald PourcellyEuropean Membrane InstituteUniversit Montpellier 2Montpellier, FrancePrakhar PrakashChevron Energy Technology CompanyRichmond, CaliforniaK.S.M.S. RaghavaraoDepartment of Food EngineeringCentral Food Technological Research InstituteMysore, Karnataka, IndiaV. RamachandhranDesalination DivisionBhabha Atomic Research CentreTarapur, Mumbai, Maharashtra, IndiaVineet RaoDepartment of PhysicsTechnische Universitt MnchenGarching, GermanyN.S. RathoreNuclear Recycle GroupBhabha Atomic Research CentreMumbai, Maharashtra, IndiaG.M. RiosEuropean Membrane InstituteUniversit MontpellierMontpellier, FranceSyed S.H. RizviFood Process EngineeringInstitute of Food ScienceCornell UniversityIthaca, New YorkR. Roque-MalherbeSchool of Science and TechnologyUniversity of TuraboGurabo, Puerto RicoandInstitute of Chemicaland Biological TechnologyUniversity of TuraboGurabo, Puerto RicoS.C. RoyNuclear Recycle GroupBhabha Atomic Research CentreTarapur, Maharashtra, IndiaS.S. SablaniDepartment of Biological Systems EngineeringWashington State UniversityPullman, WashingtonM. SanchoChemical and Nuclear Engineering DepartmentPolytechnic University of ValenciaValencia, SpainS. SarradeWaste Management DivisionFrench Atomic Energy CommissionBagnols sur Ceze, FranceAna Maria SastreChemical Engineering DepartmentUniversitat Politcnica de CatalunyaBarcelona, SpainS.R. SawantNuclear Recycle GroupBhabha Atomic Research CentreTarapur, Maharashtra, IndiaErnst Ulrich SchraderBeverage Engineering Inc.Concord, Ontario, CanadaS.I. SemenovaVladimir State UniversityVladimir, RussiaA. SenguptaMembrana-CharlotteCelgardCharlotte, North CarolinaArup K. SenGuptaDepartment of Civil and EnvironmentalEngineeringFritz Engineering LaboratoryLehigh UniversityBethlehem, PennsylvaniaB. SmithaMembrane Separation GroupChemical Engineering DivisionIndian Institute of Chemical TechnologyHyderabad, Andhra Pradesh, IndiaJ.V. SonawaneNuclear Recycle GroupBhabha Atomic Research CentreTarapur, Maharashtra, IndiaPabby et al. / Handbook of Membrane Separations 9549_C000 Final Proof page xviii 21.5.2008 7:54pm Compositor Name: BManixviiiS. SridharMembrane Separation GroupChemical Engineering DivisionIndian Institute of Chemical TechnologyHyderabad, Andhra Pradesh, IndiaGeoff W. StevensDepartment of Chemical and Biomolecular EngineeringUniversity of MelbourneMelbourne, Victoria, AustraliaUlrich StimmingDepartment of PhysicsTechnische Universitt MnchenGarching, GermanyandZAE Bayern, Division 1Garching, GermanyG. VerdChemical and Nuclear Engineering DepartmentPolytechnic University of ValenciaValencia, SpainM. WesslingMembrane Technology GroupUniversity of TwenteEnschede, the NetherlandsS.R. WickramasingheDepartment of Chemical and Biological EngineeringColorado State UniversityFort Collins, ColoradoGrazyna Zakrzewska-TrznadelDepartment of Nuclear Methods in Process EngineeringInstitute of Nuclear Chemistry and TechnologyWarszawa, Dorodna, PolandRongsheng ZhangDepartment of Chemical EngineeringUniversity of BathBath, United KingdomPabby et al. /Handbook of Membrane Separations 9549_C000 Final Proof page xix 21.5.2008 7:54pm Compositor Name: BManixixPabby et al. /Handbook of Membrane Separations 9549_C000 Final Proof page xx 21.5.2008 7:54pm Compositor Name: BManiSection IMembrane Applications in Chemicaland Pharmaceutical Industriesand in Conservation of Natural ResourcesPabby et al. /Handbook of Membrane Separations 9549_C001 Final Proof page 1 13.5.2008 12:54pm Compositor Name: BManiPabby et al. /Handbook of Membrane Separations 9549_C001 Final Proof page 2 13.5.2008 12:54pm Compositor Name: BMani1Membrane Applications in Chemicaland Pharmaceutical Industriesand in Conservation of NaturalResources: IntroductionAna Maria Sastre, Anil Kumar Pabby, and Syed S.H. RizviCONTENTSReferences .................................................................................................................................................................................... 5Inthelast 40years, membraneshavedevelopedfromaresearchtopictoamatureindustrial separationtechnology. Thisincrease in the use of membrane technology is driven by spectacular advances in membrane development, the wider acceptanceofthetechnologyinpreferencetoconventionalseparationprocesses,increasedenvironmentalawarenessand,mostimport-antly, strict environmental regulationsandlegislation. Variousmembraneprocessesarecurrentlyappliedinthechemical(including petrochemicals), pharmaceutical, and food and beverage industries. Particularly, strong development and growth ofmembrane technology can be observed in the purication of wastewater and the production of drinking water.This statement summarizes the discussions at a conference on the Exploration of the potential of membrane technology forsustainable decentralized sanitation held in Italy (at Villa Serbelloni, Bellagio) on 2326 April 2003 [1].*Due to plummeting costs and dramatically improving performance, water-treatment applications based on membranes are blossoming.In particular, membrane bioreactors (MBRs) are today robust, simple to operate, and ever more affordable. They take up little space,need modest technical support, and can remove many contaminants in one step. These advantages make it practical, for therst time, toprotect public health and safely reuse water for non-potable uses. Membranes can also be a component of a multi-barrier approach tosupplement potablewater resources. Finally, decentralization, whichovercomes someof thesustainabilitylimits of centralizedsystems, becomes more feasible with membrane treatment. Because membrane processes make sanitation, reuse, and decentralizationpossible, water sustainability can become an achievable goal for the developed and developing worlds.Amembranecanessentiallybedenedasabarrierthat separatestwophasesandselectivelyrestrictsthetransport ofvarious chemicals. It can be homogenous or heterogeneous, symmetric or asymmetric in structure, solid or liquid, and can carryapositiveornegativecharge, orbeneutral orbipolar. Transport acrossamembranecantakeplacebyconvectionorbydiffusion of individual molecules, or it can be induced by an electriceld or concentration, pressure or temperature gradient.The membrane thickness can vary from as little as 100 mm to several millimeters.Amembraneseparationsystemseparatesaninuent streamintotwoefuent streamsknownasthepermeateandtheconcentrate. The permeate is the portion of the uid that has passed through the semipermeable membrane, whereasthe concentrate stream contains the constituents that have been rejected by the membrane.Thecorrectchoiceofmembraneshouldbedeterminedbythespecicobjective,suchastheremovalofparticulatesordissolved solids, the reduction of hardness for the production of ultra pure water or the removal of specic gases=chemicals.The end use may also dictate the selection of membranes in industries such as potable water, efuent treatment, desalination, orwater supply for electronic or pharmaceutical manufacturing.Membranetechnologycoversvariouschemical technologydisciplines, suchasmaterial scienceandtechnology, masstransport and process design. By manipulating material properties, membranes can be tailor-made for particular separation tasks* From Fane, A.G., Editorial, J. Membr. Sci., 233, 127, 2004. With permission.3Pabby et al. /Handbook of Membrane Separations 9549_C001 Final Proof page 3 13.5.2008 12:54pm Compositor Name: BManitobeperformedunderspecicseparationconditions. Membranesaremanufacturedas at sheets, capillaries, orintubularshapes and are applied in various module congurations. The following membrane modules are commonly used for industrialapplications: (a) the plate and frame module; (b) the spiral wound module; (c) the tubular membrane module; (d) the capillarymembrane module; and (e) the hollowber membrane module.Membrane separation processes have numerous industrial applications and provide the following advantages: They offerappreciableenergysavings; theyareenvironmentallybenign; thetechnologyis cleanandeasytooperate; theyreplaceconventional processes likeltration, distillation, and ion exchange; they produce high-quality products; and they offer greaterexibilityinsystemdesign. Pressure-drivenprocessessuchasultraltration, nanoltration, andmicroltrationarealreadyestablished and various applications have been commercialized in theelds of pharmaceutical and biotechnology. Recently,thedevelopment of ameansof characterizing, controlling, andpreventingmembranefoulinghasbeenprovedvital. Thedevelopment oftailoredmembranes, foulingprevention, andoptimizationofchemicalcleaningwill ensureahighlevel ofmembrane process performance. In the lastve years, the development of new techniques for membrane characterization andthe improvement of existing techniques have increased our knowledge of the mechanisms involved in membrane fouling. Moreadvancedtechniques, suchasenvironmental scanningelectronmicroscopy(ESEM), havebeenusedtostudymembranefouling during the microltration of high metal content solutions with aluminum oxide membranes [2]. This will provide notonly useful insight into the fouling mechanism but also a better understanding of the factors that affect membrane fouling.Thecombinationofmolecularseparationwithachemicalreaction,ormembranereactors,offersimportantnewoppor-tunitiesfor improving theproduction efciencyin biotechnology and in thechemicalindustry.Withregardto thefutureofbiotechnology and pharmaceutical processes, the availability of new high-temperature-resistant membrane contactors offers animportant tool for the design of alternate production systems appropriate for sustainable growth.Membrane technology has widespread applications in chemical and pharmaceutical industries and its use in various otherelds is increasing rapidly. It has established applications in areas such as hydrogen separation, the recovery of organic vaporsfromprocessgasstreams, andtheselectivetransport oforganicsolvents, andit iscreatingnewpossibilitiesfor catalyticconversion in membrane reactors. It provides a unique solution for industrial waste treatment and for the controlled productionof valuable chemicals. Since it deals with the smallest penetrants in the size spectrum, gas separation requires extremely precisediscrimination of size and shapeoften in the range of 0.20.3 between permeated and rejected species. Such demandstrulypushthestateoftheartinmaterialsscienceforthesespecicapplications. Inadditiontopolymericmedia, ceramic,carbon, zeolite, and metal membranes are attractive options as they provide both precise separation and robustness. Vision andcommitment are required to make the most of the large energy savings (and CO2 emission reductions) offered by membraneswhen compared with traditional, thermally driven separations and energy conversion. The use of membranes for extraction inanalytical chemistry has increased recently. The main aim is to selectively extract and enrich the compounds to be determined(analytes) fromsamplesof varyingchemical complexity. Incontrast tomanytechnical usesof membranes, inanalyticalapplications it is essential to recover the extracted analytes as efciently as possible so that they can be transferred to suitableanalytical instruments for thenal quantitative determination.Similarly, membrane contactors have proved to be efcient contacting devices, due to their high area per unit volume thatresults in high mass transfer rates. They are not only compact but also eliminate several of the problems faced in conventionalprocesses such as ion exchange, solvent extraction, and precipitation. Membrane contactor processes, in which phasecontactingisperformedorfacilitatedbythestructureandshapeof theporousmembrane, providenewdimensiontothegrowthof membrane science andtechnologyandalsosatisfythe requirements for process intensication. Inaddition,membranecontactorsrepresent asignicant stepforwardfromtheinitial successof bloodoxygenators. Their integrationwithother membrane systems, includingmembrane reactors, couldleadtothe redesignof membrane-basedintegratedproduction lines.Thisintroductorysectionoutlinesseveral establishedapplications of membranes inthechemical andpharmaceuticalindustries, reviews the membranes and membrane processes available in thiseld, and discusses the huge potential of thesetechnologies. Inaddition, otherimportant topicdealingwithconservationofnatural resources(zeolitemembranes)isalsopresented in this section. Each chapter has been written by a leading international expert with extensive industrial experience intheeld.Chapter 1(thecurrent chapter) presentsanoverviewof different membraneprocessesandadescriptionof all of thechapters presented in Section I. Chapter 2 explains the potential of hollowber contactors in theeld of chemical technologyandhowtheyhave changedindustrial preferences regardingcontactingdevices. This chapter gives anintroductiontomembranecontact technology, itsprinciplesofoperation, andthebenetsobtainedfromtheuseofmembranecontactors.Important applications, new product development requirements, and future directions are also discussed. Chapter 3 deals withmembranechromatography. Thischapter discussesthelatest developmentsinmembrane-basedstationaryphases(afnitymembranes and mixed matrix membrane adsorbers) and monolithic separation media (organic and inorganic). It also providesinformation on new types of chromatographic support, focusing on membrane materials, properties, and preparation. Finally, itconsiders possibleapplications of chromatographic membranes invarious process conditions. Chapter 4focuses ontheimportant aspects of membrane applicationingas separation. It deals withthe subject comprehensively, providingan4 Handbook of Membrane SeparationsPabby et al. /Handbook of Membrane Separations 9549_C001 Final Proof page 4 13.5.2008 12:54pm Compositor Name: BManiintroduction and discussing transport mechanisms, different membrane materials for gas separation, module design, current andpotentialapplications,and noveldevelopmentsinthiseld.Chapter5 presentsdevelopmentsinpervaporation(PV).It rstgives a brief introduction to the theory of pervaporation and then discusses sorption thermodynamics in polymers, the solutiondiffusion model, the criteria for membrane polymer selection, and important applications of PV in different cases of aqueousand organic separation. Chapter 6 focuses on advances in theeld of ceramic membranes, covering interesting applications inthis area. Chapter 7 describes important developments in theelds of supercriticaluids and membrane technology. Chapter 8presents the various methodologies or techniques for improving the membrane performance of microltration, ultraltration,nanoltration, and reverse osmosis. The aim is to present the techniques that attempt to minimize concentration polarization(andfouling)and allowthe membraneto perform closer to its intrinsiccapability.The methodsrangefromthecritical uxapproach to the suite of hydrodynamic techniques and other potential strategies. Chapter 9 records important developments intheeld of polymeric membranes for the separation and removal of hydrocarbons. It provides an introduction to the subject,discusses the background and physicochemical regularities of hydrocarbon permeation in membrane-based glassy and rubberypolymers,and lists some important applications.Chapter 10 describes some of the main characteristics of the use of zeolitemembranes in separation applications. Zeolite membranes separate molecules based on the differences in their adsorption anddiffusion properties. They are therefore suitable for separating gas and liquid phase mixtures by gas separation and pervapora-tion, respectively. This chapter reviews the basic mechanisms of gas separation and pervaporation through zeolite membranesand presents examples of industrial applications. Chapter 11 focuses on membrane fouling and the strategies used to reduce itrelative to pressure-driven processes. This chapter highlights recent strategies for minimizing membrane fouling. In particular,it discusses theliteratureonfoulingphenomenainreverseosmosis andultraltrationmembranesystems, theanalyticaltechniques employed to quantify fouling, preventive methods, and membrane cleaning strategies.Specic recommendationsarealsomadeonhowscientists, engineers, andtechnical staff canhelptoimprovetheperformanceofthesesystemsbyminimizingmembrane foulingphenomena. Chapter 12describes membrane extractionandits use inpreconcentration,sampling, andtraceanalysis. Chapter13presentsapplicationsofaqueoushybridliquidmembranes(AHLM)andorganichybrid liquid membranes (OHLM) in the separation of organic and metal species, respectively.Chapter 14 provides an introduction to membrane applications in the pharmaceutical industry, its current status, and futurepotential in this very important area. Chapter 15 is devoted to membrane applications in the drug deliveryeld with emphasison the mechanisms governing mass transport to modulate the release kinetics. Hydrogel membranes, as a derivative construct ofhydrogels, havebecomeincreasinglyattractivefor preciselycontrollingthedrugdeliveryrateviachemical sensingandtriggering. Their current status, challenges, and opportunities are highlighted in Chapter 16.REFERENCES1. Fane, A.G., Editorial, J. Membr. Sci., 233, 127128, 2004.2. Skerlos, S.J., Rajagopalan, N., DeVor, R.E., Kapoor, S.G., andAngspatt, V.D., Microltrationpolyoxyalkylenemetalworkinguidlubricant additives using aluminum oxide membranes, J. Man. Sci. Eng. Trans., 123, 692699, 2001.Membrane Applications in Chemical and Pharmaceutical Industries 5Pabby et al. /Handbook of Membrane Separations 9549_C001 Final Proof page 5 13.5.2008 12:54pm Compositor Name: BManiPabby et al. /Handbook of Membrane Separations 9549_C001 Final Proof page 6 13.5.2008 12:54pm Compositor Name: BMani2Application of Membrane Contactorsas Mass Transfer DevicesA. Sengupta and R.A. PittmanCONTENTS2.1 Introduction ...................................................................................................................................................................... 72.2 Scope of This Chapter...................................................................................................................................................... 72.3 Description of Membrane Contactor................................................................................................................................ 82.4 Principle of Operation...................................................................................................................................................... 82.5 Benets of Membrane Contactor Technology............................................................................................................... 102.6 Mass Transfer Process in Membrane Contactor ............................................................................................................ 102.7 Literature Review on Membrane Contactor Applications ............................................................................................. 122.8 Use of GasLiquid or LiquidGasLiquid Contact....................................................................................................... 122.9 Use of LiquidLiquid Contact ....................................................................................................................................... 132.10 Review of Membrane Contactor Design Options.......................................................................................................... 142.11 Commercial or Precommercial Installations of Large-Scale Membrane Contactors..................................................... 15References .................................................................................................................................................................................. 202.1 INTRODUCTIONMembrane contactors as a type of membrane device have been known for quite a few years now [12]. They involve a uniqueclass of membrane-based mass transfer and separation technologies, which have grown beyond academic curiosity and foundcommercial applicationsacrossvariousindustriesandmarkets. It hasbeenfoundtobeacost-effectivetechnologyandistherefore used to supplant or replace other technologies that might or might not be based on membranes. In some situations,membrane contacting has emerged as an enabling technology that islling some previously unmet commercial needs.Bythestandardofbusinesssize, membranecontactortechnologyiscurrentlyaminorplayercomparedtoothermuchbetter-known membrane separation technologies such as reverse osmosis (RO), membraneltration, membrane gas separation,diffusion dialysis, and electrodialysis. By its very nature, the membrane contactor does not function or compete with the othermembrane devices, andthe capabilityandfunctionalityof contactors are signicantlydifferent fromtheother devices.But membrane contactor technology seems to have the potential to be applicable over a much wider array of industries. Useof membrane contactor devices in various forms is growing continuously. In many applications the contactor is not even calleda contactor but is referred to by other names depending on the specic application it is deployed in. Examples include bloodoxygenator (theearliest useof membranecontactor), gas transfer membrane, membranedegasier, membranedeaerator,membrane distillation device, osmotic distillation device, membrane gas absorber, membrane extractor, and membranehumidier.2.2 SCOPE OF THIS CHAPTERConsidering the wide applications of membrane contactors and the evolving nature of this technology, it is difcult to coverevery aspect in a monograph. The intent of this article is torst explain the technology and the principles of operation, withsomeremarksonthemasstransfer processinmembranecontactors. Thisisfollowedbydescriptionof varioustypesofcontacting possibilitiesand reviewof a widesampling ofliterature on thetechnology todate. Design optionsof membraneThe authors references to the various patents mentioned in this article do not constitute a grant of a license to practice any of these technologies, nor do theyimply the authors acknowledgment of the validity of any of the referenced patents.7Pabby et al. /Handbook of Membrane Separations 9549_C002 Final Proof page 7 13.5.2008 12:55pm Compositor Name: BManicontactors are then reviewed. Finally, some current and emerging commercial applications at different stages of developmentare discussed in detail.2.3 DESCRIPTION OF MEMBRANE CONTACTORFrom outward appearance membrane contactors look similar to other membrane devices. However, functionally the membranesusedincontactorsareverydifferent. Theyaremostlynonselectiveandmicroporous. Membranecontactorscanbemadeoutof atsheet membranesandtherearesomecommercialapplications. Mostcommoncommercialmembranecontactorsare, however, madefromsmall-diametermicroporoushollowber(orcapillary)membraneswithnepores(illustratedinFigure 2.1) that span the hollowber wall from theber inside surface to theber outside surface. The contactor shown asan example in Figure 2.1 resembles a tube-in-shell conguration with inlet=outlet ports for the shell side and tube side. Themembrane is typically made up of hydrophobic materials such as Polypropylene, Polyethylene, PTFE, PFA, and PVDF.The membrane in a contactor acts as a passive barrier and as a means of bringing two immiscibleuid phases (such as gasand liquid, or an aqueous liquid and an organic liquid, etc.) in contact with each other without dispersion. The phase interface isimmobilized at the membrane pore surface, with the pore volume occupied by one of the twouid phases that are in contact.Since it enables the phases to come in direct contact, the membrane contactor functions as a continuous-contact mass transferdevice, such as a packed tower. However, there is no need to physically disperse one phase into the other, or to separate thephases after separation is completed. Several conventional chemical engineering separation processes that are based on massexchangebetweenphases(e.g., gasabsorption, gasstripping, liquidliquidextraction, etc.)canthereforebecarriedout inmembrane contactors.2.4 PRINCIPLE OF OPERATIONPrincipleof membranecontactor operationis basedonthenatural phenomenonof capillaryforce. Whenonesideof ahydrophobicmicroporousmembraneisbroughtincontactwithwateroranaqueousliquid,themembraneisnot wettedby the liquid, i.e., the liquid is prevented from entering the pores, due to surface tension effect. The interface between a liquidand a solid substrate can be characterized by the parameter contact angle (Figure 2.2). The wettability of a solid surface by aliquid surface decreases as the contact angle increases. A contact angle of less than 908 implies that the liquid will tend to wetthe substrate (hydrophilic), whereas if contact angle is greater than 908 the liquid will not tend to wet the surface (hydrophobic).Table 2.1 lists the contact angle values for few different materials in water at ambient temperature.If a dry microporous hydrophobic hollowber membrane with air-lled pores was surrounded by water there would not beany penetration by water into the pores until the water pressure exceeds a certain critical breakthrough pressure. The magnitudeLumen fluidoutletLumen fluidinletMicroporoushollow fibersShellfluidoutletShell fluidinletPottingPoresFIGURE 2.1 Microporous hollowber membrane in a membrane contactor.Pabby et al. /Handbook of Membrane Separations 9549_C002 Final Proof page 8 13.5.2008 12:55pm Compositor Name: BMani8 Handbook of Membrane Separationsof this critical breakthrough pressure differential (water pressure minus air pressure) DPC has been mathematically derived,and is expressed [3] by the following equation that is often referred to as the YoungLaplace equation:DPC 4lcos ud(2:1)wherel is the surface tension of wateru is the contact angle for the system airwatermembrane in degreesd is the effective diameter of the membrane pore, assuming pores are circular in shapeFor a hydrophobic porous material with contact angle greater than 908, theDPC is>0 and depends on the liquid surfacetension and the membrane pore size. As an example, considering waterairpolypropylene system, one can calculate that for adry membrane with a pore size of 0.03 mm (30 nm) the critical entry pressure of water is more than 300 psi (>20 bar).Since theliquidphase does not enter thepores, astable gasliquidphase interface canbe createdandmaintained(as illustrated in Figure 2.3) as long as the liquid phase pressure is higher than the gas phase pressure and the phase pressuredifferential DPisbetween0andDPC. Theporesremainair lledat thiscondition. Theliquidandthegasphasescouldbeowingatdifferent owratesoneithersideofthemembranewall, butthephaseinterfaceremainsstableallalongthemembrane. Thus, by proper control of pressures, the two immiscible phases come in constant contact without a need to disperseone into the other. This allows mass transfer or mass exchange between phases [45], such as gas absorption or gas stripping(desorption).Thesameprincipleof operationas describedaboveis applicablealsotoliquidliquidextractionwhereanaqueousliquidandanorganicliquidcontacteachotherinsidethecontactorforextractionofasoluteselectivelyfromonephasetoanother [68]. The critical breakthrough pressure for liquidliquid system could be calculated by Equation 2.1, except that theterm l would now be the interfacial tension between the two liquids. Further variation of membrane contacting technology iscalledgas membraneor gasgap membrane wheretwo different liquid phasesow on either side of the membrane, but themembrane pores remain gaslled [910]. In this situation two separate gasliquid contact interfaces are supported on each sideof a single membrane.LiquiddropletContactangle (q)VaporSolid surfaceFIGURE 2.2 Representation of contact angle.TABLE 2.1Contact Angle for Various Materials in Waterat Ambient TemperatureSubstrate Contact Angle (In degrees)Ordinary glass 20Platinum 40Anodized aluminum 60PMMA 74Nylon 79Polyethylene 96Polypropylene 108Teon 112Pabby et al. /Handbook of Membrane Separations 9549_C002 Final Proof page 9 13.5.2008 12:55pm Compositor Name: BManiApplication of Membrane Contactors as Mass Transfer Devices 92.5 BENEFITS OF MEMBRANE CONTACTOR TECHNOLOGYPrimary list of features and resulting benets for the technology are shown in Table 2.2.2.6 MASS TRANSFER PROCESS IN MEMBRANE CONTACTORIngasliquid,liquidliquid,orliquidgasliquidcontactorsthereisnoconvectiveowofanyphaseacrossthemembrane.Masstransfer occursonlybydiffusionacrosstheimmobilizedphaseinthepores. Thedirectionof masstransfer of anymolecular species depends on the concentration driving force maintained across the membrane for that species. The presence ofthe stationary phase in the membrane pore creates an extra diffusional mass transfer resistance. However, it can be shown that inmany cases the membrane resistance is negligible, and that in most cases the high active mass transfer area created inside amembrane contactor more than compensates for any additional mass transfer resistance [45].Mass transfer resistanceinacontinuous-contact separationdeviceis theinverseof themass transfer coefcient. Inmembranecontactors, thetotal resistancecouldbeexpressedas threeresistances inseries. Theseincludetheindividualresistances in eachowing phase and the membrane resistance (Figure 2.4). For a liquidgas contact system Equation 2.2 couldbe written for each diffusing species:1dOUTKTOTAL1dOUTkSHELL1HdAVGkM1HdINkTUBE(2:2)whereK is the overall coefcientsk is the individual mass transfer coefcientsGas flowPores on hollowfiber wallA single hollowfiber wallGas phase flowing insidehollow fiber,gas pressure PGASTwo required conditions for stable phase interface,1.PLIQUID > PGAS, and2.0 < (PLIQUIDPGAS) < PCLiquid water phase flowingaround hollow fibers;Liquid pressure PLIQUIDLiquid-gas phaseinterface at stable conditionFIGURE 2.3 Liquidgas interface in a membrane contactor.TABLE 2.2Benets of Membrane Contactor TechnologyFeatures BenetsHigh concentration of active phase contact area Prole or footprint of membrane contactor systems are small; t into existing building; no additionalstructure neededFlow rates of phases in contact can be controlledindependentlyNo physical limitations such asooding or loading; contact area constant irrespective of phaseow rates; process moreexibleModular in nature Easier to add system capacity incrementally; can often be retrotted into existing systems;easier scale-upMass transfer does not depend on gravity Contactor can be mounted vertically or horizontally; will also work in microgravity; able to processtwouid phases of same densitiesNo need to disperse or coalesce phases Eliminates extra steps; more efcient utilization of device volumeCan be operated with highuid outlet pressures Eliminates or reduces need for transfer pumps or booster pumps after contactorPabby et al. / Handbook of Membrane Separations 9549_C002 Final Proof page 10 13.5.2008 12:56pm Compositor Name: BMani10 Handbook of Membrane SeparationsEach term on right side of Equation 2.2 represents an individual resistance as depicted in Figure 2.4. Hollowber diametersare dOUT and dIN. The term H is the Henry coefcient (liquidgas equilibrium constant) for the species in question. In the caseof liquidliquid contact, the term H in Equation 2.2 should be replaced by mD, the equilibrium distribution coefcient betweentube side liquid and shell side liquid.The membrane transfer coefcient kM is a function of (1) the diffusion coefcient in the phase occupying membrane poresand (2) various membrane geometric parameters. Assuming pure Fickian diffusion in a symmetric microporous membrane, kMcan be shown as [5]kM 2DMtMdOUT dIN (2:3)whereD is diffusivity in the pore phaseM and tM are membrane porosity and tortuosity factors, functions of the membrane morphologyIn case of complex membrane morphology such as asymmetric or composite membranes, or when Fickian diffusion is notvalid, evaluating kM will be more complex. Individual mass transfer coefcients in Equation 2.2 depend on multiple factorssuch as temperature, pressure, ow rates, and diffusion coefcients and could often be estimated from empirical correlationsavailable in literature [1,2,6].The rate of mass transfer, R, for each species from shell side to tube side at any point inside the contactor is given asR KTOTAL A CSHELL CTUBE (2:4)whereA is the membrane transfer area based on outside diameter of the hollowberCSHELL and CTUBE are bulk concentrations of the species in shell side and tube side, respectivelyStrictly speaking Equations 2.2 and 2.4 are valid only locally within the contactor. The concentrations in each phase couldchangecontinuouslyinsidethecontactor. It isalsopossibleforoneofthemasstransfercoefcientstochangewithinthecontactor. In such cases rate of mass transfer will be varying continually within the contactor, and the average overall masstransfer will be obtained by integrating over the entire contactor.Total mass transfer resistanceMembraneresistanceOuter phase (shellside) resistanceCSHELLFor compositemembrane,multipleresistancespossibleCTUBEDIN/2DOUT/2Inner phase (tubeside) resistanceHollow fiber wall(membrane)FIGURE 2.4 Mass transfer resistances in membrane contactor.Pabby et al. / Handbook of Membrane Separations 9549_C002 Final Proof page 11 13.5.2008 12:56pm Compositor Name: BManiApplication of Membrane Contactors as Mass Transfer Devices 11Useful simplications are often made in Equation 2.2. We will use gasliquid contact as an example, and assume gas-lledhomogeneousmembraneofhighporosity, thinwall, andlowtortuosity. Sincediffusioningasphaseisgenerallyofthreeorders of magnitude faster than in liquid phase, one can show that kM and kG are quite high in this case compared to kL, and sothecontrollingresistancetomasstransferisintheliquidphase. ThismeansKTOTALisessentiallythesameaskL.IfkLisconstant within the contactor the total mass transfer rate in Equation 2.4 can be approximated for the entire contactor asR kL ATOTALDCLOG---MEAN(2:5)DCLOGMEAN is the log mean of the concentration differential (CSHELL CTUBE) from one end of the contactor to the other.2.7 LITERATURE REVIEW ON MEMBRANE CONTACTOR APPLICATIONSOver the years many research and development groups, both academic and industrial, have investigated membrane contactortechnology and suggested or developed a wide range of possible applications. There is quite a spectrum of patent and publishedliteratureonthis subject. Markets andindustries that benet fromthedevelopment of this technologyincludemedical,biotechnology, pharmaceutical, semiconductorand electronics,food and beverage, environmental, and other special processindustries that arending new uses. It is impossible to mention all the work done to date.2.8 USE OF GASLIQUID OR LIQUIDGASLIQUID CONTACTAsmentionedearlier, membranebloodoxygenatorsprobablywouldqualifyastheearliest formofmembranecontactors.Reference [11] is a good illustration of a hollowber device. However, most work on liquidgas membrane contactor over theyearshasfocusedmainlyontwocategories: (1)separation, purication, andtreatment ofwateroraqueousmediaand(2)absorption of gaseous species from air either for purication or for recovery, which will be discussed separately. Applicationsin multiple markets and industries have been investigated in each category.An early example of a patent on membrane contactor for gas transfer is in Ref. [12]. Harvesting of oxygen dissolved inwater and discharging of CO2 to the water is presented in Ref. [13]. A membrane device to separate gas bubbles from infusionuidssuchashuman-bodyuidsisclaimedinRef.[14].Ahollowbermembranedeviceforremovalofgasbubblesthatdissolve gasses fromuids delivered into a patient during medical procedures is disclosed in Ref. [15]. Membrane contactorshave also found application in dissolved gas control in bioreactors discussed in Refs. [1617].Application of membrane contactors for water degasication has been thoroughly investigated and reported in Refs. [1821].During the last few years this has been one of the most successful applications of membrane contactors on large commercialscale. Specically, oxygen removal and gas transfer from ultrapure water for semiconductor industry have been discussed inRefs.[2227]. DeaerationprocessforbeveragewaterisdiscussedinRef. [28].OxygenremovalfromboilerfeedwaterassubstituteforsteamdeaeratororoxygenscavengerispresentedinRef.[29]. Membranecontactorshavealsobeenusedtocarbonate water [30], to nitrogenate beer [31], to simultaneously nitrogenate and decarbonate beer, to control CO2 level in beer,and to control dissolved gas prole in beverages using mixed sweep gases of CO2 and N2 [3233].Removal ofdissolvedvolatileorganiccompounds(VOC)fromwaterinmembranecontactorshasbeenthesubject ofseveral investigations. VOC can be separated from water by applying a vacuum, the process is often termed vacuum membranedistillation[3436]. Alternately, aircanbeusedasasweepgastostripVOCsfromwateracrossthemembrane[37]. Airstrippingofwaterinpacked orspraycolumns isawidelyaccepted processforgroundwaterorprocess watertreatment.Ifmembrane contactors were used broadly for this purpose, the market potentials are certainly high. A variation of membrane airstripping process is discussed in Ref. [38] where the driving force for VOC stripping of water is established using methano-tropic bacteria. Total organic carbon (TOC) reduction from ultrapure water during membrane degassing has been reported inRef. [39]. Removal of tri-halo methane (THM) compounds, a chemical class of undesirable species, from ultrapure water hasbeen discussed in Ref. [40]. Use of microporous membranes in combination with RO to separate dissolved gases from water isdisclosed in Ref. [41]. Study on removal and recovery of volatile aroma compounds from water was presented in Ref. [42].Adding oxygen or other benecial gas species to water without forming gas bubbles is another application of membranecontactors. This subject has been discussed in Refs. [4346]. Membranes in module form and hollowbers in unconned formhavebeeninvestigated. UseofmembranecontactorsforsupplyingoxygentoabiolmisclaimedinRef. [47]. Asimilarprocess where gaseous hydrogen is added to aqueous liquid without bubble formation is disclosed in Ref. [48]. The purpose forsuch a process would be to use dissolved hydrogen to biologically or catalytically remove oxygen, nitrite, or nitrate from water.Membrane contactors are also used to add trace quantity of CO2 into ultrapure water to control water resistivity and preventformation of static electricity [49]. A more recent and signicant application of membrane contactors is the addition of gaseousozone to water for the purpose of disinfection and removal of organic contamination, such a process is disclosed in Ref. [50].Anumberofapplicationsofthepreviouslytermedgasmembranehavealsobeenstudiedovertheyearstoremoveorrecover volatile species from water or other aqueous media. The primary drivers for these investigations are the intriguing andPabby et al. / Handbook of Membrane Separations 9549_C002 Final Proof page 12 13.5.2008 12:56pm Compositor Name: BMani12 Handbook of Membrane Separationscreative possibilities of the gas membrane, which in effect combines two gasliquid contact processes (stripping andabsorption)withinasinglemicroporousmembrane. Someoftheearly-publishedstudiesincluderecoveryofbromine[51],cyanide[52], ammonia[5355], andethanol [56]. Applicationsofthistechnologyforcommercial purposesareinvariousstages of development [57].Membrane processes termedas osmotic distillationor membrane distillationcouldbe showntobe applications ofmembranecontactor technology also. Both of these processes are based on gas membranes. Osmotic distillation, sometimescalled osmotic evaporation, involves transfer of water vapor across a gas-lled membrane, the process is driven by a differenceinwatervaporpressuremaintainedacrossthemembrane[5859]byseparateaqueousliquids. Membranedistillationisaprocess where water vapor transfer is driven solely by a temperature difference across the gas-lled membrane [6061]. Waterevaporates from a hot aqueous phase and condenses on a cooler surface. This process may be useful in desalinating water orproducing pure water if a good natural source of warm water is available, such as in a geothermal process.As mentioned in Table 2.2, one unique feature of membrane contactors is the ability to operate without the aid of gravity.This, along with the advantage of smaller sizes for contactor systems, has led to the interest in possible use of this technologyinmicrogravityandconnedspaces suchas spacesuits, mannedspacecrafts, andspacestation. Primaryapplications are(1) separating gas and liquid phases in microgravity and (2) removal of unwanted gas species from liquids [6264].We now discuss the second category of applications that focus on treatment and conditioning of air or gas streams. Thisisdoneeither (1) bycapturing(absorbing) gaseousspeciesfromair or other gasesintowater or aqueousliquidsor (2)bycontrollingthepropertiesofairorgasphasebyothermeansofheatandmasstransferacrossmembraneinacontactor.Therstdetailedinvestigationofabsorptionofagasspecies(CO2)inaliquidusingamembranecontactorwasdiscussedindetail inRefs. [4,5]. Themasstransfer analysisintheseearlypapershasbeenmost inuential for understandingthetechnology.AbsorptionofvariousgasessuchasCO2, SO2, NH3, andcarbonmonoxideinwaterusingmembranecontactorswasstudied by many other research groups and reported in Refs. [6570]. Removal of CO2 as a greenhouse gas from air and bulkremoval of CO2fromair incontactorsusingconventional absorbentshavebeenreportedinRefs. [7173]. Thetopicofscrubbing CO2 from air for self-contained breathing systems using microporous membrane is discussed in Ref. [74]. CapturingCO2 from atmosphere using membrane contactors, as part of a hydrogen storage process, was suggested in Ref. [75]. Use ofmembrane contactors for recovery of VOCs from air was reported in Ref. [76]. A hollowber membrane bioreactor, for thepurpose of destroying toxic compounds from air, is shown in Ref. [77].Controlling temperature and humidity of process air or ambient air is another unique application of membrane contactors.Membranes are used to humidify or dehumidify air by bringing air in contact with water or a hygroscopic liquid. Mass transferin such processes is very fast since mass transfer resistance in the liquid phase is negligible. Heat transfer and mass transfer aredirectlyrelatedtotheseprocesses,sincelatentheatofevaporation(orcondensation)createstemperatureprolesinsidethecontactor. Some of the references in Literature are shown in Refs. [7879]. Application of such processes has been proposed forconditioning air in aircraft cabins [80], in buildings or vehicles [81], or in containers to store perishable goods [82].2.9 USE OF LIQUIDLIQUID CONTACTAhistoricalperspectiveonaqueousorganicextractionusingmembranecontactortechnologyisavailableinRefs.[1,6,83].Themechanismofphaseinterfaceimmobilizationwas rst exploredinRef. [84], whileapplicationofmembranesolventextractionfor acommercial process was rst exploredinRef. [85]. Twoaspects of liquidliquidcontact inmembranecontactorsthataredifferentfromtypicalgasliquidcontactare(1)themembraneusedcouldbehydrophobic, hydrophilic,or a composite of both and (2) the membrane masstransferresistance is not always negligible. Ensuring that the right uidoccupies the membrane pores vis--vis the afnity of the solute in the two phases can minimize membrane resistance. Theseaspects have been discussed in detail in Refs. [6,86,87].Membranecontactor applicationsintheliquidliquidextractioneldfall intwocategories: (1) removal of unwantedspecies from water and (2) removal and recovery of valuable species from water. Many investigations have been conductedover the year by academia as well as by industry. Below we are providing some samples from the wide range of applicationsreported in literature. The examples presented are divided roughly into three sections: (a) biotech and pharmaceutical products,(b) industrial chemicals and VOC, and (c) metals.Processes for productionof ethanol andacetonebutanolethanol mixture fromfermentationproducts inmembranecontactor devices were presented in Refs. [88,89]. Recovery of butanol from fermentation was reported in Ref. [90]. Use ofcompositemembraneinamembranereactor toseparateandrecover valuablebiotechnologyproducts was discussedinRefs. [91,92]. A case study on using membrane contactor modules to extract small molecular weight compounds of interesttopharmaceutical industrywasshowninRef. [93]. Extractionofproteinandseparationofracemicproteinmixtureswerediscussed in Refs. [94,95]. Extractions of ethanol and lactic acid by membrane solvent extraction are reported in Refs. [96,97].Amembrane-basedsolvent extractionandstrippingprocess was discussedinRef. [98] for recoveryof Phenylalanine.Extraction of aroma compounds from aqueous feed solutions into sunower oil was investigated in Ref. [99].Pabby et al. / Handbook of Membrane Separations 9549_C002 Final Proof page 13 13.5.2008 12:56pm Compositor Name: BManiApplication of Membrane Contactors as Mass Transfer Devices 13Extraction ofphenol fromaqueous solution using hollowber membrane contactor wasrst investigated in Ref. [100].However, the membrane used was not completely microporous. Instead, it was a dialysis-type membrane. A commercial plantto separate phenol from hydrocarbon fraction using microporous membrane contactors was reported in Ref. [101]. Soda lye wasusedtoreact withthephenoltransferredfromthefeedphasetocreateandmaintainthedrivingforceforseparation. Thisindustrial-scale application enabled the processing of hydrocarbon fraction to a full-value raw material for phenol and acetonesynthesis.Therst known commercial membrane-based liquidliquid extraction system involved extraction of by-products from awastewater stream using an aromatic solvent [102]. Before the membrane system was installed, the entire wastewater streamhad to be incinerated leading to high costs for the gasred incinerator per year. The membrane system lowered the contaminantconcentration to adequate levels before the biological wastewater treatment plant, and saved signicant operating cost.A process to separate naphthenes from parafns is claimed in Ref. [103]. It involves the use of a polar solvent for separationin a microporous membrane device. Use of membrane extraction to remove p-nitrophenol in wastewater from dye and pesticidesynthesis was investigated in Ref. [104]. Removal of nonvolatile pesticide components from water is presented in Ref. [105].Removal of several important organic pollutants such as phenol, chlorophenol, nitrobenzene, toluene, and acrylonitrile fromwastewater was investigated in Ref. [106].Removal ofVOCcontaminantsfromwaterwasdiscussedinRef. [107]. Thisparticularprocessusedsunoweroil toabsorbtheVOCcompoundstransferredfromwater acrossagas-lledmicroporousmembrane. However, toprevent anypossibilityofliquidbreakthrough, aplasma-polymerizeddi-siloxanecoatingwasappliedontheoilsideofthemembrane.Report [108] presents results from a pilot trial where organic pollutants such as chlorinated organic compounds and aromaticorganic compounds were removed from plant wastewaters.Various investigators have also explored removal or recovery of metals from aqueous process or waste streams. Liquidliquidextractionisparticularlyuseful for metal removal sincealternatetechnologiessuchasdistillationarenot feasible.A process to separate molybdenum from tungsten leachate using a microporous membrane was disclosed in Ref. [109]. Copperextraction in a membrane contactor using metal chelating agent was presented in Ref. [110]. Other applications suggested inliteratureincludeextractionofgoldfromaqueoussolutions[111], removal ofcopperfromedibleoil [112], separationofyttriumfromheavyrare-earthmetals [113], removal of copper andchromiumfromwastewater [114], andextractionsof mercury, copper, and nickel from water [115].2.10 REVIEW OF MEMBRANE CONTACTOR DESIGN OPTIONSAlthough membrane is the heart of the membrane contactor technology, appropriate internal design of the contactor device ormodule is critical for any commercial advancement of the technology. Internal design dictates how the two phasesow insidethe contactor and how the hydrodynamics in each phase is managed. As shown in Equation 2.2, the rate of mass transfer isdirectlydependent onthe mass transfer coefcients ineachof the phases, whichinturnis dependent onthe internalhydrodynamics. Asthedevicesbecomelarger toservelargecommercial-scaleprocesscapacities, dependenceoninternalowmanagement becomesmorecritical. Thedevicedesignisalsoimportant indevelopingtheprocessesfor large-scalemanufacturing of the contactors. In the following section, we are reviewing various design options investigated over the years.Designs of membrane contactors with hollowber membranes fall in one of the two categories: (1) the primaryuid beingtreatedows through the inside (lumen) of the hollowbers and (2) the primaryuid being treatedows on the outside (shell)ofthehollowbers. Anotherconsiderationistheowdirectionoftheuidineachphasewithrespect totheaxisofthemembrane and with respect to each other. In most membrane contactors of early commercial designs, the contactor housing wasof cylindrical shape with tube-in-shell conguration (as in tubular heat exchangers) where the primaryuidows on the lumenside from one end of theber to the other and the otheruidows on the shell side in parallel direction. This design is generallycalled the parallel-ow design and is illustrated schematically in Figure 2.5a. The contactors of such a design are relatively easyto manufacture. However, the main drawback of the parallel-ow design is the nonuniform spacing of hollowbers and theresulting poorow distribution orow channeling on the shell side, particularly as the contactor diameter increases.Asignicantimprovementoverthisparallel-owdesignis thetransverse-owdesignwheretheprimaryuidowsonoutside of the hollowber membrane at a transverse direction to theber axis, while the otheruidows on lumen side of thehollowbers.TherelativemeritsofthetwodesignswererstanalyzedcomprehensivelyinRef. [116]. Itdeterminedthattransverse owonshell side signicantlyimproves the mass transfer coefcient comparedtothe parallel-owdesign.However,itwasstilldifculttoensurethatthetransverseowonshellsideiscompletelyuniformalongtheberlength.Most investigations on membrane contactors continued to focus on parallel-ow design, since they are easier to fabricate onsmall scale. The effect of shell side hydrodynamics in parallel-ow contactors was investigated and reported in Ref. [117].Thetwinproblems of (1) ensuringtransverse owuniformlyalongthelengthof bers and(2) ensuringeven owdistributionon shellside weresolved largely by adoptingthe conceptof hollowbers in fabricarray formthat was woundaround a central hollow mandrel with porous wall. The shell sideuid could be introduced in the membrane contactor throughthe central distribution mandrel. It could thenow radially outward, in a direction transverse to hollowber axes. The centralPabby et al. / Handbook of Membrane Separations 9549_C002 Final Proof page 14 13.5.2008 12:56pm Compositor Name: BMani14 Handbook of Membrane Separationshollow mandrel ensures axial uniformow distribution whereas the hollowber array ensures constantber-to-ber distancesand uniform transverse-ow distribution. A further improvement was the use of one or multipleow-directing bafe inside theshell, justaspracticedincommercialheatexchangers, whichmadethecontactormoreefcientandfacilitatedcommercialproduction. Figure 2.5b schematically illustrates a transverse-ow contactor withow-directing bafe. Detail investigations ofthis design are shown in Refs. [118120], and both cylindrical and rectangular contactors are investigated in Ref. [118].AninterestingvariationofthecontactordesignwithbafeisdisclosedinRef. [121]foradegassingapplication. Thisshows a spiral-wound contactor similar to that shown in Ref. [120], but the bafe was placed on the gas side of the device andthe waterow was on lumen side. Since most of the mass transfer resistances in liquid degassing process are essentially in theliquid phase, it is not clear how such a design would improve the hydraulic efciency of the device.Inadditiontowhat wasdiscussedabove, therehavebeenmanyother contactor designsproposedover theyears. Amembranecontactor of rectangular designisdisclosedinRef. [122] madebylaminatinghollowber fabricsheets, andpreventingow channeling by specifying the densities of the hollowbers and the warpber of the fabric. A similar structureof membrane contactor apparatus is claimed in Ref. [123]. Reference [124] discloses a contactor with multiple frames of square,polygonal, or circular, where the longitudinal directions of thebers or tubes of adjacent frames are substantially perpendicularto each other. Stackable sub-modules with multiple frames of hollowber membranes in each sub-module were suggested inRef. [125]. A rectangular contactor was also suggested in Ref. [75]. A tubular hollowber membrane contactor of parallel-owdesign, with special spacers on shell side to reduceow channeling, was disclosed in Ref. [50]. A radial-ow transverse-owmembrane contactor without anyow-directing bafe was shown in Ref. [126]. In some applications, particularly in degassingprocessesusingdeepvacuum,ithasbeenshownthatpresenceof ow-directingbafesuchasclaimedinRef. [119]couldactually be detrimental to performance because of internal diffusion in the gas phase. A hollowber membrane contactor thatdoes not use a shell at all has been disclosed in Ref. [127].2.11 COMMERCIAL OR PRECOMMERCIAL INSTALLATIONS OF LARGE-SCALEMEMBRANE CONTACTORSApplications of membrane contactor technology in commercial processes are in various stages of development. Early successhascomemainlyinwater degassingor gasadditionapplications. Membranecontactor systemsof awiderangeof owcapacitiesarecurrentlyinoperationinvariouspartsoftheworld. Systemswithlargecapacitieswerepossibleonlyaftermembrane contactors of sufciently large size and cost competitiveness could be produced commercially on a routine basis.Currently, the largest known commercially produced membrane contactor module has an active contact area of about 220 m2[128].Commercialavailabilityofsuchproductshasgreatlyfacilitatedthelarge-scaleacceptanceofthistechnology.Afewexamples of various installed contactor systems are provided below.Potting Hollow fibersShell fluid outletShell fluidoutletShell fluidinlet(a) Parallel-flow design(b) Transverse-flow designLumen fluidinletLumen fluid outletPorous center tube Center plug BaffleLumen fluid inletHollow fiberShell fluid inletLumen fluidoutletFIGURE 2.5 Primary design options for membrane contactors.Pabby et al. / Handbook of Membrane Separations 9549_C002 Final Proof page 15 13.5.2008 12:56pm Compositor Name: BManiApplication of Membrane Contactors as Mass Transfer Devices 15Figure2.6schematicallyillustratessectionsofatypicalsemiconductorultrapurewater(UPW)productionprocessinasemiconductor plant. The water circuit consists of two main sections: (1) makeup (or central) system and (2) polishing loop,which provides water at the point of use. There are multiple locations in such a water process where membrane degassing couldbe needed as shown in thegure. Reverse osmosis is mostly used in makeup line as the primary purication means in suchprocesses. In the past, large and inexible vacuum towers were frequently used after RO to remove dissolved gases, such as O2,N2, and CO2. Membrane contactors are the norm today for replacement or supplement to vacuum towers in makeup l