Hollow fiber membrane design for membrane distillation (MD) and MD based hybrid processes

HOLLOW FIBRE MEMBRANE DESIGN FOR MEMBRANE DISTILLATION (MD) AND MD BASED HYBRID PROCESSES PENG WANG NATIONAL UNIVERSITY OF SINGAPORE i HOLLOW FIBRE MEMBRANE DESIGN FOR MEMBRANE DISTILLATION (MD) AND MD BASED HYBRID PROCESSES PENG WANG (B.Eng. (Hons.), NUS) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2013 ii DECLARATION I hereby declare that this thesis is my original work and it has been written by me in entirety. I have duly acknowledged all the sources of information, which have been used in the thesis. This thesis has also not been submitted for any degree in any university previously. Student: Wang Peng Signature: Date: 23, Sept, 2013 i ACKNOWLEDGEMENT First of all, I would like to express my appreciation to my supervisor Prof. Chung Tai-Shung who introduced me into the world of membrane research. His guidance, enthusiastic encouragement and invaluable support throughout my Ph.D study are invaluable. From him, I have learned and benefited greatly in not only research knowledge but also developed the enthusiasm of a qualified researcher. I would like to express my appreciation to all former and current members of our research group, especially, Dr. Qingchun Ge, Dr. Bee Ting Low, Dr. Jincai Su, Dr. Shipeng Sun，Dr. Panu Sukitpaneenit, Dr. May May Teoh, Dr. Dingyu Xing, Dr. Kaiyu Wang, Dr. Yan Wang, Dr. Natalia Widjojo, Ms Xiu Ping Chue, Miss Felinia Edwie, Mr. Feng Jiang Fu, Ms Xiu Zhu Fu, Ms Xue Li, Ms Huey Yi Lin, Mr. Yi Hui Sim, Mr. Yee Kang Ong, Ms Rui Chin Ong and Ms Pei Shan Zhong for their invaluable suggestions, discussion and sharing of technical expertise. All members in Prof. Chung‘s group are cheerful and helpful to me, which have made my study in NUS enjoyable and memorable. I would like to gratefully acknowledge the research scholarship offered by the National University of Singapore (NUS), which provided me a positive, conductive and professional atmosphere for conducting research study (Aug, 2009- Mar, 2011). I also wish to express my recognition to Agency for Science, Technology and Research (A*STAR) and through the funding the research through the project ‘Development of Hybrid Desalination Processes using Cold Energy from LNG Re-gasification’ (grant number: R-279-000-291-305). ii My sincere thanks are due to all staff members in the Department of Chemical and Biomolecular Engineering that have helped me in material purchasing, equipment set-up, characterization techniques and given me professional suggestions. Special appreciation goes to Mr. Kim Poi Ng for his help and expertise advice in fabrication of equipment setup, machinery and spinneret. I must express my appreciation to my parents, my beloved wife and other family members for their unconditional love and support, which makes my life and study meaningful. Special thanks are given to my mother and mother-in-law who taught me cooking. Brilliant ideas were inspired from the ingredients and cooking observations. I should express a special appreciation to my parents-in-law, who not only give me their daughter, but also a distinguished polymer physicist. iii TABLE OF CONTENT ACKNOWLEDGEMENT ii SUMMARY . xi NOMENCLATURE xiv LIST OF TABLES . xvi LIST OF FIGURES xvii CHAPTER 1: Introduction & Objectives . 1.1 Membrane distillation and its historical development 1.2 Current applications of MD 1.2.1Desalination 1.2.2Treatment of NF and RO brine . 1.2.3Concentration of nonvolatile aqueous solutions . 1.2.4 Recovery of volatile compounds from aqueous solutions . 1.2.5 Removal of boron and other water-borne contaminants 1.3 Four configurations of MD . 1.4 Key challenges on the development of MD membranes 1.5 Research objectives and thesis organization . 10 1.6 References . 14 CHAPTER 2: Background and Literature Review . 20 2.1 Membrane development for MD 21 2.1.1 Membrane materials . 21 2.1.2 Membrane configurations 25 2.1.3 Recent progress in MD membrane development . 26 iv 2.2 Membrane wetting 29 2.3 Heat and mass transfer in MD process . 30 2.4 References . 35 CHAPTER 3: Experimental 41 3.1 Design and engineering principles for polymeric MD membranes 42 3.1.1 Polymer 42 3.1.2 Inorganic additives . 42 3.1.3 Organic solvents . 42 3.2 Polymer dope preparation . 43 3.3 Hollow fiber membrane fabrications 43 3.4 Membrane characterization . 45 3.4.1 Scanning electron microscope (SEM) . 45 3.4.2 Energy dispersion of X-ray (EDX) 45 3.4.3 Contact angle measurements 45 3.4.4 Mechanical property measurements 46 3.4.5 Overall porosity measurements 46 3.4.6 LEP measurements . 46 3.4.7 DCMD desalination experiments . 48 3.5.8 VMD desalination experiments . 50 3.6 References . 54 CHAPTER 4: Morphological Design of Dual-Layer Hollow Fiber Membrane for DCMD . 55 4.1 Introduction . 56 v 4.2 Experimental . 59 4.3 Results and discussion 60 4.3.1Membrane characterizations . 60 4.3.2 DCMD performance 69 4.3.3 Modeling of mass transfer in DCMD 70 4.3.4 Energy efficiency . 76 4.3.5 Long-term desalination performance . 79 4.3.6 Comparison with other MD membranes 79 4.4 Conclusions . 80 4.5 References . 82 CHAPTER 5: Design of Lotus-root-like Multi-bore Hollow Fiber Membrane for DCMD . 87 5.1 Introduction . 88 5.2 Experimental . 90 5.2.1 Spinneret design and membrane fabrication 90 5.2.3 Continuous DCMD Experiment 92 5.3 Results and discussion 93 5.3.1Membrane characterizations . 93 5.3.1.1 Membrane morphology . 93 5.3.1.2 Effect of bore flowrate 97 5.3.1.3Effect of dope flowrate 98 5.3.1.4 Effect of take-up speed . 100 5.3.2Membrane characterization and mechanical properties 102 vi 5.3.3 DCMD performance 105 5.3.3.1 Effect of bore flowrate and dope flowrate 105 5.3.3.2 Effect of take-up speed . 108 5.3.3 Continuous DCMD experiment . 109 5.4 Conclusions . 111 5.5 References . 113 CHAPTER 6: Highly Asymmetric Multi-bore Hollow Fiber Membrane for VMD 118 6.1 Introduction . 119 6.2 Experimental . 122 6.2.1 Spinneret design and membrane fabrication 122 6.2.2 Membrane post-treatment 123 6.3. Results and discussion . 124 6.3.1General membrane characterizations 124 6.3.2 Comparison between multi-bore and single-bore geometries . 128 6.3.3 Effect of bore fluid composition 130 6.3.4 Effect of polymer concentration 133 6.3.5 Effect of pore forming agent 135 6.3.6 Effect of post treatment concentration . 137 6.3.7 Effect of pore forming agent combination . 140 6.3.8 Comparison of 6-bore and 7-bore geometries . 144 6.3.9 MD performance 145 6.3.9.1 Comparison with DCMD performance . 145 6.3.9.2 VMD performance with different feed modes 148 vii 6.3.7.3 VMD performance with different operational parameters 149 6.4 Conclusions . 150 6.5 References . 152 CHAPTER 7: A conceptual Demonstration of Freeze Desalination – Membrane Distillation Hybrid Process Utilizing LNG Cold Energy . 158 7.1 Introduction . 159 7.2 Background and theories . 164 7.3 Experimental . 165 7.3.1 Hollow fiber fabrication and module preparation 165 7.3.2 FD-MD set-up and experiments . 166 7.3.2.1 FD-MD experiments . 166 7.3.2.2 ICFD set-up and experiments . 167 7.3.2.3 DCMD set-up and experiments 168 7.3.3 Microscopic characterization of ice crystals 169 7.4 Results and discussion 169 7.4.1 ICFD experiments 169 7.4.1.1 Effect of nucleate seeds addition 169 7.4.1.2 Effect of FD operation duration 173 7.4.1.3 Effect of feed salinity 174 7.4.2 DCMD Experiments 175 7.4.2.1 Membrane properties 175 7.4.2.2 Effect of module length 176 7.4.2.3 Effect of packing density 179 viii (a) (b) (c) Figure 8. Effect of time on (a) water transfer rate, (b) acid orange concentration, (c) PAA-Na (1200) concentration. On the FO side: draw solution: 0.48 g·mL-1 PAANa (1200) with volume of 300 mL, flow rate 500 mL/min, 66 °C; feed solution: 50 213 ppm acid orange 8, 500 mL, flow rate 100 mL/min, 66 °C. Operation mode: PRO. On the MD side: feed solution: 0.48 g·mL-1 PAA-Na (1200) with volume of 300 mL, flow rate 500 mL/min, 66 °C; draw solution: DI water at 20 ± 0.5 °C, flow rate 200 mL/min. 8.4 Conclusions A polyelectrolyte-promoted FO-MD hybrid process has been conceptualized and successfully applied to the acid dye-contained wastewater treatment. The following remarks can be concluded from this study. 1) Polyelectrolyte is an effective draw solute in wastewater treatment. The high stability and negligible salt leakage of PAA-Na (1200) draw solute demonstrates its superiority over other newly developed draw solutes [25] and commonly used inorganic salt counterparts. Such characteristics not only lower the replenishment cost of PAA-Na (1200) but also ensure the product quality. Hence its application can be extended to membrane-based protein or pharmaceutical product enrichment where high product quality is required. 2) The sustainable FO-MD hybrid process is more efficient than the individual FO process in wastewater treatment. The incorporation of a MD process into a FO process provides a simple but efficient way to recover the draw solution diluted in the FO process. The stability and repeatability of the FO-MD processes illustrate the practicability of such hybrid system in wastewater treatment. This study may open the way for the applications of polyelectrolyte-promoted FO-MD processes in aforementioned areas. 214 8.5 References [1] F. Han, V.S.R. Kambala, M. Srinivasan, D. Rajarathnam, R. Naidu, Tailored titanium dioxide photocatalysts for the degradation of organic dyes in wastewater treatment: A review, Applied Catalysis A: General 359 (2009) 25–40. [2] A. Bhatnagar, M. Sillanpää, Utilization of agro-industrial and municipal waste materials as potential adsorbents for water treatment—A review, Chemical Engineering Journal 157 (2010) 277–296. [3] E.S.Z. El-Ashtoukhy, N.K. Amin, Removal of acid green dye 50 from wastewater by anodic oxidation and electrocoagulation—A comparative study, Journal of Hazardous Materials 179 (2010) 113–119. [4] N. Daneshvar, D. Salari, S. Aber, Chromium adsorption and Cr (VI) reduction to trivalent chromium in aqueous solutions by soya cake, Journal of Hazardous Materials 94 (2002) 49–61. [5] A.I. del Río, J. Fernández, J. Molina, J. Bonastre, F. Cases, Electrochemical treatment of a synthetic wastewater containing a sulphonatedazo dye. Determination of naphthalenesulphonic compounds produced as main by-products, Desalination 273 (2011) 428–435. [6] S.J. Allen, K.Y.H. Khader, M. Bino, Electrooxidation of dyestuffs in waste waters, Journal of Chemical Technology and Biotechnology 62 (1995) 111–117. [7] I.C. Escobar, A summary of challenges still facing desalination and water reuse. In: Escobar, I.C., Schäfer, A.I. (Eds.), Sustainable water for the future-water recycling versus Desalination. Elsevier, The Netherlands, 2010, pp. 389-397. 215 [8] B.X. Mi, B.J. Marinas, D.G. Cahill, RBS characterization of arsenic(III) partitioning from aqueous phase into the active layers of thin-film composite NF/RO membranes, Environmental Science & Technology 41 (2007) 3290-3295. [9] D. Nanda, K.L. Tung, W.S. Hung, C.H. Lo, Y.C. Jean, K.R. Lee, C.C. Hu, J.Y. Lai, Characterization of fouled nanofiltration membranes using positron annihilation spectroscopy, Journal of Membrane Science 382 (2011) 124-134. [10] M. Amini, M. Arami, N.M. Mahmoodi, A. Akbari, Dye removal from colored textile wastewater using acrylic grafted nano-membrane, Desalination 267 (2011) 107–113. [11] S. Bampernga, T. Suwannacharta, S. Atchariyawutb, R. Jiraratananon, Ozonation of dye wastewater by membrane contactor using PVDF and PTFE Membranes, Separation and Purification Technology 72 (2010) 186–193. [12] N. Othman, S.N. Zailani, N. Mili, Recovery of synthetic dye from simulated wastewater using emulsion liquid membrane process containing tri-dodecyl amine as a mobile carrier, Journal of Hazardous Materials 198 (2011) 103-112. [13] A.L. Ahmad, W.A. Harris, Syafie, O.B. Seng, Removal of dye from wastewater of textile industry using membrane technology, Jurnal Teknologi 36 (2002) 31–44. [14] C. Das, M. Rungta, G. Arya, S. DasGupta, S. De, Removal of dyes and their mixture from aqueous solution using liquid emulsion membrane, Journal of Hazardous Materials 159 (2008) 365–371. [15] K.Y. Wang, M.M. Teoh, A. Nugroho, T.S. Chung, Integrated forward osmosis– membrane distillation (FO-MD) hybrid system for the concentration of protein solutions, Chemical Engineering Science 66 (2011) 2421–2430. [16] Q. Ge, J. Su, G.L. Amy, T.S. Chung, Exploration of polyelectrolytes as draw solutes in forward osmosis processes, Water Research 46 (2012) 1318-1326. 216 [17] A.D. McNaught, A. Wilkinson, Compendium of chemical terminology, 2nd ed. (the "Gold Book"). Blackwell Scientific Publications, Oxford, 1997. [18] I. Gültekin, G. Tezcanli-Güyer, N.H. Ince, Sonochemical decay of C.I. Acid Orange 8: Effects of CCl4 and t-butyl alcohol, Sonochem. 16 (2009) 577–581. [19] J. Su, T.S. Chung, Sublayer structure and reflection coefficient and their effects on concentration polarization and membrane performance in FO processes, Journal of Membrane Scence 376 (2011) 214–224. [20] P. Wang, M.M. Teoh, T.S. Chung, Morphological architecture of dual-layer hollow fiber for membrane distillation with higher desalination performance, Water Research 45 (2011) 5489-5500. [21] R.W. Schofield, A.G. Fane, C.J.D. Fell, Heat and mass transfer in membrane distillation, Journal of Membrane Scence 33 (1987) 299-313. [22] K.Y. Wang, T.S. Chung, M. Gryta, Hydrophobic PVDF hollow fiber membranes with narrow pore size distribution and ultra-thin skin for the fresh water production through membrane distillation, Chemical Engineering Science 63 (2008) 2587-2594. [23] S. Bonyadi, T.S. Chung, R. Rajagopalan, A novel approach to fabricate macrovoidfree and highly permeable PVDF hollow fiber membranes for membrane distillation, AIChE Journal 55 (2009) 828-833. [24] K.Y. Wang, S.W. Foo, T.S. Chung, Mixed matrix PVDF hollow fiber membranes with nanoscale pores for desalination through direct contact membrane distillation, Industrial & Engineering Chemistry Research 48 (2009) 4474-4483. [25] Q. Ge, J. Su, T.S. Chung, G. Amy, Hydrophilic superparamagnetic nanoparticles: synthesis, characterization, and performance in forward osmosis processes, Industrial & Engineering Chemistry Research 50 (2011) 382-388. 217 CHAPTER 9: Conclusions and Recommendations 218 9.1 Conclusions The development of hollow fiber membranes with desirable morphology, permeation flux, energy efficiency and wetting resistance is of crucial importance and challenge. Therefore, in this study, a systematic investigation on the key factors involved in the fabrication of MD hollow fiber membranes is investigated. The MD performance and mass transport phenomena through membranes were explored. In order to enhance the MD performance, the dual-layer hollow fiber membranes have been further developed. Subsequently, the multi-bore hollow fibers are also developed with DCMD and VMD configurations. Since MD process can be integrated into the existing separation processes, the integrated FDMD process and FO-MD is demonstrated and investigated. Based on above studies, the following conclusions can be drawn. 9.1.1 Morphological design of dual-layer hollow fiber DCMD Design of micro-structure on the PVDF dual-layer hollow fiber membranes is an effective method to enhance the MD performance. We have designed a novel dual-layer hollow fiber with a fully finger-like inner-layer and a totally sponge-like outer-layer. The resultant dual-layer membranes show enhanced DCMD performance without scarifying the membrane wetting resistance. With the membranes with the designed micro-structure, a permeation flux of 98.6 kg m2 hr-1 has been attained. The LEP values of dual-layer fibers are 0.3 bar lower than the single-layer hollow fibers. This indicates the minimum sacrifice wetting resistance. The modeling of heat and mass transfer process is performed to verify the contribution of the proposed structure. It shows that the dual-layer fiber has a much smaller resistance for vapor transfer. 219 9.1.2 Design of lotus-root-like multi-bore hollow fiber membrane for DCMD We have studied the fabrication and performance of the multi-bore fiber (MBF) membranes with lotus root-like geometry for DCMD application. A 7-needle spinneret with uniformly distribute needles are fabricated for MBF membrane spinning. The mechanical properties of MBF membranes are much better than the single bore and rectangular MBF membranes. The DCMD performance of MBF membranes is slightly lower than the traditional single-bore hollow fiber owing to the compensation of effective vapor condensation area. This gap can be minimized by lowering the dope flowrate or increasing the take-up speed. The 300 h continuous DCMD experiment has shown superior long-term operation stability of MBF membranes. Finally, MBF membranes with regular packed bore geometry have been attained under different bore flowrate, dope flowrate and take-up speed. The relative size of center bore channel tends to decrease with reducing bore flowrate. Under take-up drum stretching, the lotus-root structure gradually becomes the wheel structure as the take-up speed increases. 9.1.3 Highly asymmetric multi-bore hollow fiber membrane for VMD MBF membranes with a different micro-structure (a tight contact surface pore and porous cross-section) have been tailor-made for VMD application. The newly fabricated MBF membrane is proven as a preferred configuration as compared with the SBF membrane due to the larger effective evaporation surface, higher mechanical strength and improved wetting resistance. Among four types of membrane post treatments, both (1) freeze dry and (2) a combination of IPA, hexane and then air dry methods are able to maintain pore 220 structure, minimize membrane shrinkage and ensure high VMD performance. MBF membrane at VMD configuration shows higher flux than the DCMD configuration. The MBF membrane exhibits a better VMD flux and thermal efficiency for the mode of feed at the lumen side due to a larger effective surface area and a reduced thermal loss to the surrounding. The VMD flux and thermal efficiency increase dramatically with increasing feed flowrate and/or decreasing vacuum pressure. 9.1.4 A conceptual demonstration of freeze desalination-membrane distillation hybrid desalination process utilizing LNG cold energy A hybrid freeze desalination-membrane distillation (FD-MD) process for desalination is designed and systematically explored which utilizes waste cold energy. The concept of hybrid FD-MD process utilizes the indirect-contact freeze desalination (ICFD) and direct contact membrane distillation (DCMD) configurations as an example. Drinkable clean water has been successfully produced by the hybrid process with a total water recovery of 71.6%. We have optimized the operation parameters in FD and MD processes separately. Then the hybrid FD-MD experiments have been performed at the selected FD and MD operation parameters. There is an accelerated increase of salt concentration in the retentate of MD, thus permeation flux of water shows a continuous decrease. 9.1.5 Investigation on forward osmosis-membrane distillation hybrid process A FO-MD hybrid process has been conceptualized and successfully applied to the acid dye-contained wastewater treatment. A novel polyelectrolyte solution is employed as the draw solution. Polyelectrolyte is found as an effective draw solute in wastewater treatment. 221 The sustainable FO-MD hybrid process is more efficient than the individual FO process in wastewater treatment. The incorporation of a MD process into a FO process provides a simple but efficient way to recover the draw solution diluted in the FO process. 9.2 Recommendations and future work Based on the experimental results obtained, discussions presented and conclusions drawn from this research, the following recommendations may provide further insight for future investigations related to the development of membrane materials with potentially high separation properties and the innovation of membrane fabrication technology.  Investigation of fabricated dual-layer hollow fiber membranes with other MD configurations, i.e., AGMD, SGMD.  Exploring the membrane separation performance with real seawater. A further investigation on the membrane performance and long-term stability under actual seawater is recommended to bring the know-how technology close to industrial practices.  Investigation of energy efficiency of FD-MD and FO-MD hybrid processes.  Investigation of other MD configurations in the hybrid FD-MD or FO-MD processes.  Exploring the use of dual-layer hollow fibers and MBF membranes for hybrid FD-MD and FO-MD processes. 222 Appendix 1: Derivation Of Apparent Diffusivity In A DCMD Process The mathematical modeling of heat and mass transfers using microporous hollow fiber configurations for DCMD processes is described in this section. Based on the enthalpies change of feed and permeate streams, the heat fluxes can be calculated as: QF m f C p, f (T f ,in  T f ,out ) (A1.1) QP m p C p, p (Tp ,out  Tp,in ) (A1.2) At steady state DCMD operation, the heat transfer of feed and permeate streams ( QF and QP ) as well as membrane matrix ( Qm ) should be the same. In this regards, the heat flux can be calculated as the average enthalpies change from both feed and permeates sides. Qss  Qaverage  (QF  QP ) / (A1.3) The steady state heat flux ( Qss ) can also be expressed as boundary-layer heat transfer using the convective heat transfer coefficients. Qss  Q f h f Ao (T f  T f ,m ) (A1.4) Qss  Qp h p Ai (Tp,m  Tp ) (A1.5) 223 In order to evaluate the heat transfer coefficient h f and h p , empirical or semi-empirical correlations are referred to the two correlations . Properties used in the correlations are estimated under the logarithm mean temperature between inlet and outlet temperatures of the feed and permeate flows, respectively. Nu f  Re f  Nu p  Re p  h f Do kf  Do  0.8 0.33  f 0.14  0.0271   Re f PR f ( ) L  w  (A1.6)  f v f Do C  & Pr f  p , f f f kf hp Di kp 0.8  4.36  0.036 Re p Prp 0.33 ( Di L)     0.0012 Prp Di L 0.8 (A1.7)  p v p Di C  & Prp  p , p p p kp With equations and correlations obtained, membrane surface temperatures for both feed and permeate streams can be further derived as following: Qss h f Ao (A1.8) Qss  Tp h p Ao (A1.9) T f ,m  T f  T p,m  By neglecting the mass transfer resistances at two boundary layers, the trans-membrane vapor pressure difference in DCMD can be written as: 224 Nw  Mww Dw a * Pf ,m  Pp*,m Ylm ro R g ln( ro ri )Tm    (A1.10) where Ylm is the logarithm mean fraction of air in membrane pores and can be estimated using the vapor pressures at both membrane surfaces. In addition, the water vapor pressure can be acquired by the Antoine equation). Ylm  (1  Pf*,m Ptot )  (1  Pp*,m Ptot ) ln(1  Pf*,m Ptot )  ln(1  Pp*,m Ptot ) log10 P*  8.07131  1730.63 233.42  T (A1.11) (A1.12) Eventually, the apparent diffusivity ( Da ) can be derived as an indication of transmembrane mass transfer coefficient by solving. Da  Dwa  (A1.13) 225 Appendix 2: Publications & Conference presentations Journal Papers: Wang Peng, Teoh May May, Chung Tai-Shung, Morphological architecture of dual-layer hollow fiber for direct contact membrane distillation with higher desalination performance, Water Research, 45 (2011) 5489-5500. Wang Peng, Chung Tai-Shung, Freeze desalination – membrane distillation (FD-MD) hybrid process: A new desalination technology utilizing cold energy from liquefied natural gas (LNG), Water Research, 46 (2012) 4037-4052. Wang Peng, Chung Tai-Shung, Design and fabrication of lotus-root like multi-bore hollow fiber membrane for membrane distillation, Journal of Membrane Science, 421-422 (2012) 361-374. Wang Peng, Chung Tai-Shung, A new-generation asymmetric multi-bore hollow fiber membrane for sustainable water production via vacuum membrane distillation, Environmental Science and Technology, 47 (2013) 6272-6278. Wang Peng, Chung Tai-Shung, Exploring the spinning and operational parameters of highly asymmetric multi-bore hollow fiber membrane for vacuum membrane distillation, submitted to AIChE journal. Wang Peng, Luo Lin, Chung Tai-Shung, Tri-bore Ultra-filtration Hollow Fiber Membranes with a Novel Triangle-Shape Outer Geometry, Journal of Membrane Science, in press. 226 Ge Qingchun, Wang Peng, Wan Chunfeng, Chung Tai-Shung, Polyelectrolyte- promoted forward osmosis-membrane distillation (FO-MD) hybrid process for dye wastewater treatment, Environmental Science and Technology, 46 (2012) 6236-6243. Han Gang, Wang Peng, Chung Tai-Shung, Thin-film composite pressure retarded osmosis hollow fiber membranes with high robustness and power density for renewable salinity-gradient energy generation, Environmental Science and Technology, 47 (2013) 8070-8077. Su Jincai, Ong Rui Chin, Wang Peng, Chung Tai-Shung, Advanced FO membranes from newly synthesized CAP polymer and their application for wastewater reclamation through integrated FO-MD hybrid system, AIChE journal, 59 (2012) 1245–1254. 227 Conference papers and presentations: P. Wang, T.S. Chung, A New Generation Multi-bore hollow fiber membrane for water production via vacuum membrane distillation, 7th international conference on materials for advanced technologies (ICMAT 2013), Singapore [Jun 2013] Wang Peng, Chung Tai-Shung, ‘Development of lotus-root-like multi-bore hollow fiber membrane for direct contact and vacuum membrane distillation’, North America Membrane Society Annual Conference 2013, Boise, United States [Jun, 2013] Wang Peng, Chung Tai-Shung, ‘Design of hollow fiber membrane for membrane distillation desalination technologies’, International Water Association, Busan, Korea [Jun, 2012] Wang Peng, Felinia Edwie, Chung Tai-Shung, ‘Development of membrane distillationbased hybrid desalination technologies with utilization of LNG cold energy’, Europe Desalination Society Annual conference, Barcelona, Spain [Apr, 2012] Wang Peng, Teoh May May, Chung Tai-Shung, ‘Morphological architecture of duallayer hollow fiber for direct contact membrane distillation’, Asia Pacific Chemistry and Chemical Engineering Congress, Singapore [Feb 2012] Wang Peng, Teoh May May, Chung Tai-Shung, ‘Morphological design and modeling of dual-layer hollow fiber for direct contact membrane distillation’ ’Membrane Science and Technology 2011, Singapore [Aug 2011] Wang Peng, Teoh May May, Chung Tai-Shung, ‘Morphological architecture of duallayer hollow fiber for direct contact membrane distillation with higher desalination performance’ North America Membrane Society Annual Meeting 2011, Las Vegas [Jun 2011] 228 [...]... micro-morphology and macro-geometry of the hollow fiber membranes are investigated and carefully designed for direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD) processes In addition, two MD based hybrid processes are also explored Firstly, the micro-morphology of the hollow fiber membrane is designed to achieve both high permeation flux and excellent wetting resistance during MD. .. Morphological design of dual-layer hollow fiber DCMD 219 9.1.2 Design of lotus-root-like multi-bore hollow fiber membrane for DCMD 220 9.1.3 Highly asymmetric multi-bore hollow fiber membrane for VMD 220 ix 9.1.4 A conceptual demonstration of freeze desalination -membrane distillation hybrid desalination process utilizing LNG cold energy 221 9.1.5 Investigation on forward osmosis -membrane distillation. .. dual-layer hollow fiber D1 68 Figure 4.5 DCMD Permeation fluxes obtained for PVDF hollow fibers 70 Figure 4.6 Temperature profile for PVDF hollow fiber D1: Tf and Tp are the average temperatures for feed and permeate sides; Tf,m and Tp,m are temperatures calculated for membrane surfaces facing the feed and permeate sides, respectively 71 Figure 4.7 Temperature profile for. .. Temperature profile for PVDF hollow fiber D1: Tf and Tp are the average temperatures for feed and permeate sides; Tf,m and Tp,m are temperatures calculated for membrane surfaces facing the feed and permeate sides, respectively 73 Figure 4.8 Calculated apparent Diffusivities (Da) for PVDF hollow fibers 75 Figure 4.9 Calculated energy efficiencies for PVDF hollow fibers 77 Figure 4.10... attained Overall, by combining FD and MD processes, the hybrid FD -MD experiment has been successfully demonstrated A high total water recovery of 71.9 % has been achieved And the quality of the water obtained meets the standard for drinkable water Lastly, the concept of polyelectrolyte-promoted forward osmosis membrane distillation (FOMD) hybrid system is also developed and applied to recycle the wastewater... rejection and feasibility of utilizing low-grade waste energy Compared with flat sheet membranes, hollow fiber membranes have relatively large specific surface areas But the main drawback of the hollow fiber module in MD application is its low flux caused by poor flow dynamics and the resultant severe temperature polarization effect Hence, the development of suitable hollow fiber membranes for MD process... FO -MD processes 196 8.3 Results and discussion 199 8.3.1 Effects of temperature and concentration on the relative viscosity of PAA-Na (1200) 199 8.3.2 FO processes using CA hollow fiber membranes 201 8.3.3 MD processes using PVDF hollow fiber membranes 206 8.4 Conclusions 214 8.5 References 215 CHAPTER 9: Conclusions and. .. SGMD Permeate sweep gas Blower Hollow fiber module feed Condenser Figure 1.4 Illustration of a SGMD configuration (c) Sweep gas membrane distillation (SGMD): A cold inert gas sweeps the permeate side of the membrane carrying the vapor molecules and condensation takes place outside the membrane module 8 VMD Permeate vacuum Vacuum pump Hollow fiber module feed Condenser Figure 1.5 Illustration of a VMD... conductivity values of three polymer materials used in MD membranes 21 Table 4.1 Spinning conditions of single- and dual-layer PVDF hollow fibers 60 Table 4.2 Characteristic properties of single- and dual-layer PVDF hollow fibres 67 Table 4.3 Comparison of DCMD performances for MD membranes 79 Table 5.1 Spinning conditions of MBF membranes: A) MBF-1 - MBF-6, B) MBF-7 - MBF12 ... MBF membrane is also tailored for the VMD application As compared with DCMD, a highly asymmetric membrane structure with tight liquid contact surface and fully porous cross-section is proposed and demonstrated to maximize the wetting resistance and VMD permeation flux With comparable VMD performances, the MBF shows a much higher mechanical strength and wetting resistance than a SBF Moreover, the MD . HOLLOW FIBRE MEMBRANE DESIGN FOR MEMBRANE DISTILLATION (MD) AND MD BASED HYBRID PROCESSES PENG WANG NATIONAL UNIVERSITY OF SINGAPORE ii HOLLOW FIBRE MEMBRANE. of dual-layer hollow fiber DCMD 219 9.1.2 Design of lotus-root-like multi-bore hollow fiber membrane for DCMD 220 9.1.3 Highly asymmetric multi-bore hollow fiber membrane for VMD 220 x 9.1.4. investigated and carefully designed for direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD) processes. In addition, two MD based hybrid processes are also explored.