DESALINATION BY MEMBRANE DISTILLATION: FABRICATION OF HIGH PERFORMANCE MEMBRANES SINA BONYADI (B Eng (Chemical) (Hons.), Amirkabir University of Technology) A THESIS SUBMITED FOR THE DEGREE OF MASTER OF ENGINEERING DEPARTMENT OF CHEMICAL & BIOMOLECUALR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2008 Acknowledgement First of all, I would like to express my deepest heartfelt appreciation to my supervisor Prof TaiShung Chung Neal, in Dept of Chemical & Biomolecular Engineering of NUS, for his excellent guidance, enthusiastic encouragements and invaluable suggestions throughout my two year master study From him, I have learnt a great deal on both research knowledge and active work spirits I am especially grateful to Prof William B Krantz Isac mayor professor in Dept of Chemical & Biomolecular Engineering of NUS for his wise guidance regarding my first paper in the journal of membrane science Special thanks are also due to Mr NG Kim Po the workshop chief at NUS Chemical Engineering department for the fabrication of membrane distillation experimental set up I also want to take this opportunity to give my sincere thanks to all the colleagues in my research group for their kind assistance My association with them is a memorable part of my experience and study at NUS I gratefully acknowledge A*STAR for providing me an opportunity to pursue my Master degree and research scholarship i Table of Contents Acknowledgement……………………………………………………………………………… i Summary………………………………………………………………………………………… vi List of Tables…………………………………………………………………………………….viii List of Figures………………………… …………………………………………………… ix List of symbols………………………………………………………………………………… xii Chapter Background Review and Objectives 1.1 Introduction…………………………………………………………….……………… 1.2 Desalination Processes………………………………………………….……………… 1.3 Alternative desalination processes………………………………… .6 1.4 Introduction to membrane distillation as an alternative desalination approach…… .7 1.5 Membrane distillation configurations……………………………………………………8 1.6 Temperature polarization phenomenon…………………… 1.7 Wetting phenomenon………………………………………………………………… 1.8 Applications of membrane distillation……………………………………………… 10 1.9 Membrane distillation advantages and drawbacks………………………………… ….10 Chapter Literature Review 2.1 Overview on MD literature…………………………………………………………… 12 2.2 Literature review on membrane fabrication for MD…………………………………….13 2.3 Research objectives…………………………………………………………………… 17 Chapter Theory and model development 3.1 Mass transfer…………………………………………………………………………… 19 ii 3.2 Heat transfer…………………………………………………………………………… 22 3.3 Characteristics of a high performance MD membrane………………………………… 24 3.3.1 High membrane permeability…………………………………………………… 24 3.3.2 High membrane wetting resistance and long term stability…………………… 26 3.3.3 Suitable membrane geometry and dimensions……………………………………26 3.3.4 Hydrophilic layer porosity and thermal conductivity…………………………….27 Chapter Experimental 4.1 Materials……………………………………………………………………………… 28 4.2 Dope preparation……………………………………………………………………… 29 4.3 Fabrication of flat sheet membranes…………………………………… .30 4.4 Fiber spinning……………………………………………………………………………30 4.5 Morphology study of hollow fibers by SEM…………………………… .31 4.6 Contact angle measurements…………………………………………… 31 4.7 Porosity measurement……………………………………………………………………32 4.8 Pore-size distribution measurement…………………………………………………… 33 4.9 Gas permeation test………………………………………………………………………33 4.10 Polymer flow observation by a high magnification camera…………………………… 34 4.11 Video microscopy flow visualization…………………………………… 34 4.12 Module Fabrication……………………………………………………… 34 4.13 DCMD experiments…………………………………………………………………… 35 Chapter Fabrication of Dual Layer Hydrophilic-Hydrophobic Hollow Fibers 5.1 Effect of coagulant on the surface morphology of PVDF membranes………………… 37 5.2 First batch of fiber spinning…………………………………………………………… 39 5.2.1 Membrane morphology………………………………………………………… 40 iii 5.2.2 5.3 5.4 DCMD performance…………………………………………………………… 41 Second batch of hollow fiber spinning………………………………………………… 41 5.3.1 Hollow fibers morphology ……………………………………… 43 5.3.2 Pore-size distribution…………………………………………… .45 5.3.3 Gas permeation and porosity measurement tests………………… 45 5.3.4 Contact angle measurements…………………………………………………… 45 5.3.5 DCMD results…………………………………………………………………….46 Summary……………………………………………………………………………… 50 Chapter Investigation of Corrugation Phenomenon in the Inner Contour of Hollow Fibers during the Non-solvent Induced Phase-Separation Process 6.1 Introduction………………………………………………………………………………51 6.2 Experimental observations……………………………………………… .53 6.3 Discussion……………………………………………………………………………… 58 6.3.1 System description………………………………………………………………… 59 6.3.1.1 Phases I1, I2 or O1, O2…………………………………….……………………60 6.3.1.2 Phase I3 or O3…………………………………………………………………60 6.4 Possible instability mechanisms……………………………………………………… 61 6.4.1 Hypothesis (Mass transfer and hydrodynamic instability)……………………… 62 6.4.2 Hypothesis (Elastic and Buckling Instability)………………… 64 6.5 Effect of air-gap distance……………………………………………………………… 66 6.6 Effect of bore fluid composition…………………………………….………………… 68 6.7 Effect of external coagulant………………………………………….………………… 68 6.8 Effect of take-up speed……………………………………………… 68 6.9 Effect of dope concentration………………………………………… 69 6.10 Summary……………………………………………………………………………… 69 iv Chapter Conclusion………………………………………………………………………… 70 Bibliography…………………………………………………………………………………… 72 Appendix…………………………………………………………………………………………84 v Summary For the first time, co-extrusion was applied for the fabrication of dual layer hydrophilichydrophobic hollow fibers especially for the direct contact membrane distillation (DCMD) process The effect of different non-solvents on the morphology of the PVDF membranes was investigated and it was found that weak coagulants such as water/methanol (20/80 wt%) can induce a 3-dimensional porous structure on PVDF membranes with high surface and bulk porosities, big pore size, sharp pore size distribution, high surface contact angle and high permeability but rather weak mechanical properties Hydrophobic and hydrophilic clay particles were incorporated into the outer and inner layer dope solutions, respectively, in order to enhance mechanical properties and modify the surface tension properties in the membrane inner and outer layers Different membrane characterizations such as pore size distribution, gas permeation test, porosity and contact angle measurements were carried out as well Ultimately, the fabricated hollow fibers were tested for the DCMD process and flux as high as 55 kg/m2hr and energy efficiency of 83% at 90 °C was achieved in the test The obtained flux is much higher than most of the previous reports, indicating that the application of dual layer hydrophilic-hydrophobic hollow fibers may be a promising approach for MD In the second part of this research, by proposing a novel mechanism, we revealed one of the most controversial issues in the hollow fiber fabrication process regarding the instability leading to the deformed cross-section of fibers fabricated through nonsolvent induced phase separation We analyzed possible instability mechanisms based on our experimental observations and then postulated that the principal instability occurs in the external coagulation bath where the rigid precipitated polymer shell in the dope and bore fluid interface is buckled due to a generated pressure The pressure is postulated to be induced in the nascent fiber outer layer as a result of vi diffusion/convection, precipitation, densification and shrinkage In addition, the effect of some spinning conditions such as air-gap distance, bore fluid composition, take-up speed, external coagulant and dope concentration on the final shape of the fiber cross-section have been investigated The proposed mechanism was in good qualitative agreement with all our observations vii List of Tables Table.2.1 Summary of commercial membranes applied by some studies in the literature Table.4.1 Specifications of Cloisite particles Table.5.1 Total solubility parameter (δt) of water, methanol, NMP and PVDF Table.5.2 Spinning conditions applied for the first batch of spinning Table.5.3 DCMD operating conditions and the obtained flux for the fabricated fibers Table.5.4 Comparison of the maximum flux obtained in this study with the literature for DCMD processes with a hollow fiber configuration Table.6.1 Spinning conditions of hollow fiber membrane fabrication viii List of Figures Fig.1.1 Distribution of Earth’s water Fig.1.2 Fresh water resources Fig.1.3 Schematic presentation of a Multi-Stage Flash desalination plant Fig.1.4 Schematic diagram of world’s desalination plants capacity percentage by 1998 Fig.1.5 Typical Costs for a Reverse-Osmosis Desalination Plant Fig.1.6 Schematic diagram representing the separation mechanism involved in MD Fig.1.7 Schematic diagrams representing different configurations of the MD process Fig.1.8 Schematic diagram of temperature polarization phenomenon in DCMD Fig.2.1 Schematic diagram representing a typical melt spinning process Fig.2.2 A composite hydrophilic-hydrophobic membrane before the MD test (left) A composite hydrophilic-hydrophobic membrane during the MD test (right) Fig.2.3 Schematic picture of a dual layer hydrophilic-hydrophobic fiber Fig.3.1 Schematic DCMD process with dual layer hydrophilic-hydrophobic hollow fibers Fig.4.1 Chemical structure of PVDF polymer Fig.4.2 Chemical structure of PAN polymer Fig 4.3 Schematic representation of the fiber spinning line Fig.4.4 Schematic diagram showing the steps involved in fabrication of lab scale membrane modules Fig.4.5 Schematic experimental set-up applied for direct contact membrane distillation process Fig.5.1 SEM pictures from the top surface (facing the coagulant) of the PVDF flat sheet membranes for different coagulant compositions Fig.5.2 SEM pictures representing the structure of first spinning batch fibers Fig.5.3 Delamination phenomenon during the DCMD process using the first batch of fibers Fig.5.4 The spinning conditions applied in the second batch of spinning process Fig.5.5 Cross section morphology of fibers fabricated through the second batch of spinning ix Chapter Conclusion The following conclusions can be drawn out of this study: 1- Very different membrane morphologies can be formed in PVDF membranes by tailoring the strength of coagulation bath Highly porous membrane structure with three dimensional networks is formed in PVDF membranes using weak coagulants such as methanol/water mixtures Such membrane morphologies possess a very high gas permeability , leading to a high flux in membrane distillation process 2- PVDF surface tension and mechanical properties can be modified by blending the PVDF polymer with hydrophobic or hydrophilic clay particles The addition of hydrophobic particles to the hydrophobic layer further increases the contact angle of the functional hydrophobic layer by increasing the membrane surface roughness 3- The surface tension of PVDF polymer can be reduced significantly by blending the PVDF polymer with hydrophilic PAN as well as the hydrophilic lay particles 4- Co-extrusion looks to be an efficient approach to fabricate hydrophilic-hydrophobic hollow fiber membranes to be applied in MD process This process provides the freedom to easily tailor membrane properties such as porosity, pore size distribution and thickness 5- Delamination between the two hydrophilic and hydrophobic layers of the fibers can be prevented by carefully formulating the dope composition of the two layer in a way that the two layers are compatible with each other   70   6- High flux and high energy efficiency can be obtained using the dual layer hydrophilichydrophobic fibers 7- The non-uniform cross section of hollow fibers can be attributed to an instability occurring during the fabrication of hollow fibers It was postulated that the main instability happens in the coagulation bath where the pressure induced in the nascent fiber outer layer as a result of diffusion/convection, precipitation, densification and shrinkage will buckle the rigid elastic shell formed in the interface between the bore fluid and the dope solution It is also inferred that since it takes only a fraction of second for a nascent fiber traveling through the air gap region, the hydrodynamic instability may not have enough time to magnify its effects Therefore, it is postulated that the hydrodynamic instability may be the initial stage of causing instability and the elastic and buckling instability is the magnifying stage for the development of non-uniform cross section of hollow fibers 8- The proposed buckling mechanism can effectively explain all our experimental observations regarding the effect of different spinning parameters on the final shape of the hollow fibers 9- The proposed qualitative mechanism can be applied to quantitatively model the corrugation phenomenon in hollow fiber spinning by phase inversion process In summary, this thesis provides a contribution to tackle one of the major barriers against commercialization of membrane distillation process regarding the relatively low membrane flux in this process, by fabricating high flux PVDF composite membranes Furthermore, this study provides an explanation for the irregular cross section phenomenon in hollow fiber membranes fabricated through non-solvent induced phase inversion process   71   Bibliography [1] Global Environmental Outlook (GEO) 2000 [2] http://ga.water.usgs.gov/edu/watercyclefreshstorage.html [3] http://www.palomar.edu/oceanography/salty_ocean.htm [4] http://www.grida.no/climate/vital/37.htm [5] J H Van’t Hoff, “The role of osmotic pressure in the analogy between solutions and gases,” Z Phys Chem 1, (1887) 481–508 [6] F P Chinard and T Enns, “Osmotic pressure,” Science 124, (1956) 472–474 [7] K.S Spiegler, Y.M El-Sayed, The energetics of desalination processes, Desalination 134 (2001) 109 [8] Y.M El-Sayed, Designing desalination systems for higher productivity, Desalination 134 (2001) 129 [9] K S Spiegler, M A El-Sayed, A Desalination Primer Balaban Desalination Publications, Santa Maria Imbaro, Italy (1994) [10] R Trussell, State of the Science of Membrane Technologies, JWR&DTF Workshop, San Diego, (2005) [11] http://people.uwec.edu/piercech/desalination/MSF.htm [12] J E Miller, Review of Water Resources and Desalination Technologies, SAND 2003-0800, Sandia National Laboratories, (2003) [13] http://pls.atu.edu/biology/people/elovely/Water/new_page_1_files/image004.jpg   72   [14] G F Leitner, Desalination and Water Reuse Quarterly 5, (1995) 24 [15] http://www.pacinst.org/images/desal_typical_costs.gif [16] B.R Bodell, Silicone rubber vapor diffusion in saline water distillation, 691 United States Patent Serial No 285,032 (1963) [17] K W Lawson, D R Lloyd, Membrane distillation (Review), J Membr Sci 124 (1997) [18] M.S El-Bourawi, Z Ding, R Ma, M Khayet, A framework for better understanding membrane distillation separation process, J Membr Sci 285 (2006) [19] E Curcio, E Drioli, Membrane Distillation and Related Operations (A Review), Sep Pur Rev., 34: 35–86, 2005 [20] K W Lawson, D.R Lloyd, Membrane distillation II Direct contact membrane distillation, J Membr Sci 120 (1996) 123 [21] S.H Duan, A Ito, A Ohkawa, Removal of trichloroethylene from water by aeration, pervaporation and membrane distillation, J Chem Eng Jpn 34 (8) (2001) 1069–1073 [22] F.A Banat, J Simandl, Removal of benzene traces from contaminated water by vacuum membrane distillation, Chem Eng Sci 51 (8) (1996) 1257–1265 [23] S Nene, S Kaur, K Sumod, B Joshi, K.S.M.S Raghavarao, Membrane distillation for the concentration of raw cane-sugar syrup and membrane clarified sugarcane juice, Desalination 147 (2002) 157–160   73   [24] C Varming, M.L Andersen, L Poll, Influence of thermal treatment on black currant (Ribes nigrum L.) juice aroma, J Agric Food Chem 52 (25) (2004) 7628–7636 [25] N Qureshi, M.M Meagher, R.W Hutkins, Recovery of 2,3-butanediol by vacuum membrane distillation, Sep Sci Technol 29 (13) (1994) 1733–1748 [26] F A Banat, M Al-Shannag, Recovery of dilute acetone–butanol–ethanol (ABE) solvents from aqueous solutions via membrane distillation, Bioprocess Eng 23 (6) (2000) 643–649 [27] M Khayet, A Vel´azquez, J.I Mengual, Direct contact membrane distillation of humic acid solutions, J Membr Sci 240 (2004) 123–128 [28] M Khayet, J.I Mengual, Effect of salt concentration during the treatment of humic acid solutions by membrane distillation, Desalination 168 (2004) 373–381 [29] F Banat, S Al-Asheh, M Qtaishat, Treatment of waters colored with methylene blue dye by vacuum membrane distillation, Desalination 174 (2005) 87–96 [30] R W Schofield, A G Fane, C J D Fell, Gas and vapour transport through microporous membranes II Membrane distillation, J Membr Sci., 53 (1990) 173-185 [31] R W Schofield, A G Fane, C J D Fell, Heat and mass transfer in membrane distillation, Journal of Membrane Science, 33 (1987) 299-313 [32] S Kimura, S.I Nakao, S.I Shimatani, Transport phenomena in membrane distillation, J Membr Sci 33 (3) (1987) 285–298 [33] K Schnieder, T.J van Gassel, Membrane distillation, Chem Eng Technol 56 (1984) 514– 521   74   [34] K.W Lawson, D.R Lloyd, Membrane distillation I Module design and performance evaluation using vacuum membrane distillation, J Membr Sci 120 (1996) 111–121 [35] C Zhu, G.L Liu, C.S Cheung, C.W Leung, Z.C Zhu, Ultrasonic stimulation on enhancement of air gap membrane distillation, J Membr Sci 161 (1999) 85–93 [36] J Phattaranawik, R Jiraratananon, A.G Fane b, C Halim, Mass flux enhancement using spacer filled channels in direct contact membrane distillation, J Membr Sci 187 (2001) 193–201 [37] J Phattaranawik, R Jiraratananon, A G Fane, Heat transport and membrane distillation coefficients in direct contact membrane distillation, J Membr Sci 212 (2003) 177–193 [38] L Martinez-Diez, M.I Vazquez-Gonzalez, F.J Florido-Diaz, Study of membrane distillation using channel spacers, J Membr Sci 144 (1998) 45-46 [39] M M Teoh, S Bonyadi, T S Chung, Investigation of different hollow fiber module designs for flux enhancement in the membrane distillation process, J Membr Sci 311 (2008) 371-379 [40] A Burgoyne, M.M Vahdati, Direct contact membrane distillation, Sep 693 Sci Technol 35 (2000) 1257 [41] E Drioli, A Criscuoli, E Curcio,  Membrane Contactors: Fundamentals, Applications and Potentials, 11, Elsevier (Chapter 2) [42] M Khayet, C Y Feng, K C Kulbe, T Matsuura, Preparation and characterization of polyvinylidene fluoride hollow fiber membranes for ultrafiltration, Polymer 43 (2002) 3879-3890 [43] W.Z Langa, Z.L Xua,b, H Yanga, W Tong, Preparation and characterization of PVDFPFSA blend hollow fiber UF membrane, J Membr Sci 288 (2007) 123–131   75   [44] M Khayet, C.Y Feng, K.C Khulbe, T Matsuura, Study on the effect of a non-solvent additive on the morphology and performance of ultrafiltration hollow-fiber membranes, Desalination 148 (2002) 321-327 [45] M Khayet, The effects of air gap length on the internal and external morphology of hollow fiber membranes, Chemical Engineering Science 58 (2003) 3091 – 3104 [46] J Ren, R Wang, H Y Zhang, Z Li, D T Liang, J H Tay, Effect of PVDF dope rheology on the structure of hollow fiber membranes used for CO2 capture, J Membr Sci 281 (2006) 334–344 [47] J Ren, R Wang, H Y Zhang, Z Li, D T Liang, J H Tay Effect of PVDF dope rheology on the structure of hollow fiber membranes used for CO2 capture, J Membr Sci 281 (2006) 334–344 [48] S Atchariyawut, C Feng, R Wang, R Jiraratananon, D.T Liang, Effect of membrane structure on mass-transfer in the membrane gas–liquid contacting process using microporous PVDF hollow fibers, Journal of Membrane Science 285 (2006) 272–281 [49] K Li, J F Kong, Dongliang Wang, and W K Teo, Tailor-Made Asymmetric PVDF Hollow Fibers for Soluble Gas Removal, AIChE Journal (1999) Vol 45, No 1211 [50] D Wang, W.K Teo, K Li, Removal of H2S to ultra-low concentrations using an asymmetric hollow fibre membrane module, Sep Puri Tech 27 (2002) 33–40 [51] H Zhen, S M J Jang, W K Teo, K Li, Modified Silicone–PVDF Composite HollowFiber Membrane Preparation and Its Application in VOC Separation, Journal of Applied Polymer Science, Vol 99, 2497–2503 (2006)   76   [52] M Ortiz de Zfirate, L Pefia, J.I Mengual, Characterization of membrane distillation membranes prepared by phase inversion, Desalination 100 (1995) 139-148 [53] Tomaszewska, M., 1996 Preparation and properties of flat-sheet membranes from poly(vinylidene fluoride) for membrane distillation Desalination 104, [54] M Khayet, T Matsuura, Preparation and characterization of polyvinylidene fluoride membranes for membrane distillation, Ind Eng Chem Res 40 724 (2001) 5710 [55] (a) D.Y Cheng, S.J Wiersma, Composite membranes for a membrane distillation system, U.S Patents 4,316,772 (1982); (b) D.Y Cheng, S.J Wiersma, Composite membranes for a membrane distillation system, U.S Patents 4,419,242 (1983) [56] Y Wu, Y Kong, X Lin, W Liu, J Xu, Surface-modified hydrophilic membranes in membrane distillation, J Membr Sci 72 (1992) 189 [57] Y Kong, X Lin, Y.Wu, J Cheng, J Xu, Plasma polymerization of octaflu-orocyclobutane and hydrophobic microporous composite membranes for membrane distillation, J Appl Polym Sci 46 (1992) 191 [58] M Khayet, T Matsuura, Application of surface modifying macromolecules for the preparation of membranes for membrane distillation, Desalination 158 (2003) 51 [59] M Khayet, J I Mengual, T Matsuura, Porous hydrophobic/hydrophilic composite membranes application in desalination using direct contact membrane distillation, J Membr Sci 252 (2005) 101   77   [60] P Peng, A.G Fane, X Li, Desalination by membrane distillation adopting a hydrophilic membrane, Desalination 173 (2005) 45-54 [61] W Kasta, C R Hohenthanner, Mass transfer within the gas-phase of porous media, Int J Heat Mass Trans 43 (2000) 807-823 [62] J Phattaranawik, R Jiraratananon, and A G Fane, Effect of Pore Size Distribution and Air Flux on Mass Transport in Direct Contact Membrane Distillation J Membrane Sci., 215 (2003) 75–85 [63] M Gryta, M Tomaszewska, Heat transport in the membrane distillation process, J Membr Sci 144 (1998) 211 [64] B.A Li, K.K Sirkar, Novel Membrane and Device for Direct Contact, Membrane Distillation-Based Desalination Process, Ind Eng Chem Res 43 (2004) 5300 [65] J I Mengual, M Khayet, M P Godino, Heat and mass transfer in vacuum membrane distillation, Int J Heat Mass Tra 47 (2004) 865 [66] M Gryta, Influence of polypropylene membrane surface porosity on the performance of membrane distillation process, Journal of Membrane Science 287 (2007) 67–78 [67] Li Y, Chung TS, Exploration of highly sulfonated polyethersulfone (SPES) as a membrane material with the aid of dual-layer hollow fiber fabrication technology for protein separation, J Membr Sci 2008; 309:45-55 [68] Widjojo N, Zhang SD, Chung TS, Liu Y, Enhanced gas separation performance of dual-layer hollow fiber membranes via substructure resistance reduction using mixed matrix materials, J Membr Sci 2007; 306:147-158   78   [69] R W Schofield, P A Hogan, A G Fane, C J D Fell, Developments in membrane distillation, Desalination, 62 (1987) 728 [70] F Lagana, G Barbieri, E Drioli, Direct contact membrane distillation: modeling and concentration experiments, J Membr Sci 166 (2000) [71] L Mart´ınez, J.M Rodr´ıguez-Maroto, Membrane thickness reduction effects on direct contact membrane distillation performance, Journal of Membrane Science 312 (2008) 143–156 [72] Zhang, Q M., Bharti, V., Kavarnos, G., Schwartz, M (Ed.), (2002) "Poly (Vinylidene Fluoride) (PVDF) and its Copolymers", Encyclopedia of Smart Materials, Volumes 1-2, John Wiley & Sons, 807-825 [73] D W Chae, B C Kim, Effects of Zinc Oxide Nanoparticles on the Physical Properties of Polyacrylonitrile, Journal of Applied Polymer Science, Vol 99, 1854–1858 (2006) [74] L Palacio, P Pradanos, J.I Calvo, A Hernandez, Porosity measurements by a gas penetration method and other techniques applied to membrane characterization, Thin Solid Films 348 (1–2) (1999) 22–29 [75] D L Wang, W.K Teo, K Li, Preparation and characterization of high-flux polysulfone hollow fibre gas separation membranes, J Membr Sci 204 (2002) 247 [76] D.F Li, T.S Chung, R Wang, Y Liu, Fabrication of fluo768ropolyimide/polyethersulfone (PES) dual-layer asymmetric hollow fiber membranes for gas separation, J Membr Sci 198 (2002) 211 [77] D Li, R Wang, T.S Chung, Fabrication of lab-scale hollow fiber membrane modules with high packing density, Sep Pur Tech 40 (2004) 15–30   79   [78] O Olabisi, L.M Robeson, M.T Shaw, Polymer–Polymer Miscibility, Academic Press, New York, 1979 (Chapter 2) [79] T Yamaguchi, S Nakao, S Kimura, Design of pervaporation membrane of organic-liquid separation based on solubility control by plasma-graft filling polymerization technique, Ind Eng Chem Res 32 (1993) 848–853 [80] J.W van Dyk, H.L Frisch, D.T Wis, Solubility, solvency and solubility 782 parameters, Ind Eng Chem Prod Res Dev 24 (1985) 473 [81] A Bowino, G Capannelli, S Munari, A Turturro, Solubility parameters of poly(vinylidene fluoride), J Polym Sci B: Polym Phys 26 (1988) 785 [82] A.J Reuvers, C.A Smolders, Formation of membranes by means of immersion precipitation Part II, J Membr Sci 34 (1987) 67 [83] P Radovanovic, S.W Thiel, S.T Hwang, Formation of asymmetric polysulfone membranes by immersion precipitation Part II, J Membr Sci 65 (1992) 231 [84] F Hussain, M Hojjati, M Okamoto, R.E Gorga, Polymer–matrix nanocomposites, processing, manufacturing, and application: an overview, J Compos Mater 40 (2006) 1511 [85] M Gryta, M Tomaszewska, J Grzechulska, A.W Morawski, Membrane distillation of NaCl solution containing natural organic matter, J Membr Sci 181 (2001) 279 [86] L Song, B Li, K.K Sirkar, J.L Gilron, Direct contact membrane distillation-based desalination: novel membranes, devices, larger-scale studies and a model, Ind Eng Chem Res 46 (2007) 2307   80   [87] J Li, Z Xu, Z Liu, W Yuan, H Xiang, S Wang, Y Xu, Microporous polypropelene and polyethelene hollow fiber membranes Part Experimental studies on membrane distillation for desalination, Desalination 155 (2003) 153 [88] Y Fujii, S Kigoshi, H Iwatani, M Aoyama, Selectivity and characteristics of direct contact membrane distillation type experiment I Permeablity and selectivity through dried hydrophobic fine porous membranes, J Membr Sci 72 (1992) 53 [89] S A McKelvey, D T Clausi, W J Koros, A guide to establishing hollow fiber macroscopic properties for membrane applications, J Membr Sci 124 (1997) 223 [90] K Y Wang, T Matsuura, T S Chung, W F Guo, The effects of flow angle and shear rate within the spinneret on the separation performance of poly(ethersulfone) (PES) ultrafiltration hollow fiber membranes, J Membr Sci 240 (2004) 67 [91] H.A Tsai, C.Y Kuo, J.H Lin, D.M Wang, A Deratani, C Pochat-Bohatier, K.R Lee, J.Y Lai, Morphology control of polysulfone hollow fiber membranes via water vapor induced phase separation, J Membr Sci 278 (2006) 390 [92] Y Su , G G Lipscomb , H Balasubramanian , D R Lloyd, Observations of recirculation in the bore fluid during hollow fiber spinning, AICHE, 52 (2006), 2072 [93] R.G Larson, Instabilities in viscoelastic flows, Rheol Acta, 31 (1992) 213 [94] C J S Petrie, M M Denn, Instabilities in polymer processing, AICHE Journal, 22 (1976), 209 [95] G G Lipscomb, The melt hollow fiber spinning process: steady-state behavior, sensitivity and stability, polymers for advanced technologies, (1994) 745   81   [96] W Nijdam, J de Jong, C.J.M van Rijn, T Visser, L Versteeg, G Kapantaidakis, G.H Koops, M Wessling, High performance micro-engineered hollow fiber membranes by smart spinneret design, J Membr Sci., 256 (2005) 209 [97] N Widjojo, T.S Chung, The thickness and air-gap dependence of macrovoid evolution in phase-inversion asymmetric hollow fiber membranes, Ind Chem Eng Res 45 (2006) 7618 [98] Y E Santoso, T S Chung, K Y Wang, M Weber, The investigation of irregular inner-skin morphology of hollow fiber membranes at high speed spinning and the solutions to overcome it, J Membr Sci., 282 (2006), 383 [99] J P Van’t Hoff, Wet spinning of polyethersulfone gas separation membranes, Ph.D Thesis, Twente University, 1988 (Chapter 2) [100] C.C.Pereira, R.Nobrega, C.P.Borges, Spinning process variables and polymer solution effects in the die swell phenomenon during hollow fiber membrane formation, Brazil J Chem Eng 17 (2000), 599 [101] H Strathmann, K Kock, P Amar, R.W Baker, The formation mechanism of asymmetric membranes, Desalination, 16 (1975), 179 [102] P.S.T Machado, A.C Habert, C.P Borges, Membrane formation mechanism based on precipitation kinetics and membrane morphology: flat and hollow fiber polysulfone membranes, J Membr Sci., 155 (1999), 171 [103] F Bloom, D Coffin, Handbook of Thin Plate Buckling and Postbuckling, CHAPMAN & HALL/CRC, 2000 (Chapter 1) [104] L Yilmaz, A J McHugh, Analysis of Nonsolvent -Solvent -Polymer Phase Diagrams and Their Relevance to Membrane Formation Modeling, J App Poly Sci 31 (1986), 997   82   [105] L Yilmaz, A J McHugh, Modeling of asymmetric membrane formation II The effects of surface boundary conditions, J App Poly Sci 35 (1988), 1967 [106] S S Shojaie, W B Krantz, A R Greenberg, Membrane formation via the dry-cast process Part I Model development, J Membr Sci., 94 (1994), 255 [107] M Levy, Memoire sur un nouveau cas integrable du probleme de l’elastique et l’une de Ses applications J de Math (Liouville), Series 3, 10 (1884), [108] A G Greenhill, The elastic curve under uniform normal pressure, Math Ann, 52 (1899), 465 [109] I Tadjbakhsh, F Odeh, Equilibrium states of elastic rings, J Math Ann App., 18 (1967), 59   83   Appendix List of papers prepared and published during M Eng Study S Bonyadi, T.S Chung, Flux Enhancement in Membrane Distillation by Fabrication of Dual Layer Hydrophilic-Hydrophobic Hollow Fiber Membranes, Journal of Membrane Science, 306 (2007) 134–146 S Bonyadi, T.S Chung, W.B Krantz, Investigation of the Corrugation Phenomenon in the Inner Contour of Hollow Fibers during Non-solvent Induced Phase Separation Process, Journal of Membrane Science, 299 (2007) 200-210 M.M Teoh, S Bonyadi, T.S Chung, J.J Shieh, Investigation of different module designs for flux enhancement in the membrane distillation process, Journal of Membrane Science, 311 (2008) 371–379 S Bonyadi, T.S Chung, K.Y Wang, Fabrication of High Performance Dual Layer Hydrophilic-Hydrophobic Hollow Fibers for Membrane Distillation Process, a US Patent filed, March 2007 S Bonyadi, T.S Chung, W.B Krantz, Investigation of the Corrugation Phenomenon in the Inner Contour of Hollow Fibers during Non-solvent Induced Phase Separation AIChE Annual Meeting (2007) Salt Lake City, Utah   S Bonyadi, T.S Chung, Flux Enhancement in Membrane Distillation by Fabrication of Dual Layer Hydrophilic-Hydrophobic Hollow Fiber Membranes AIChE Annual Meeting (2007) Salt Lake City, Utah   84   ... spinning 29 4.3 Fabrication of flat sheet membranes In order to investigate the effect of different coagulants on the surface porosity and roughness of the PVDF membranes, PVDF flat sheet membranes. .. review on membrane fabrication for MD The membranes commonly applied in membrane distillation literature have been the commercially available membranes actually fabricated for other membrane applications... in MD process by fabrication of novel high performance membranes In this respect, we have devoted this chapter to review membrane distillation literature regarding membranes applied in this process