MEMBRANE MATERIALS AND FABRICATIONS FOR GAS SEPARATION TIN PEI SHI NATIONAL UNIVERSITY OF SINGAPORE 2005 MEMBRANE MATERIALS AND FABRICATIONS FOR GAS SEPARATION TIN PEI SHI (B Eng (Chemical) (Hons.), University Technology Malaysia) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2005 ACKNOWLEGEMENTS I wish to take this opportunity to express my sincere appreciation to all the contributors whose cooperation and assistance were essential in helping me to gradually acquire sharper tools toward the completion of my PhD study reported herein: First of all, I especially wish to record my deepest appreciation and thanks to my immediate advisor, Professor Neal Chung Tai-Shung for his invaluable guidance, advice, patience, constructive comments and challenges that helped me actualize and sharpen my professional skills I am also indebted to my co-advisors, Dr Wang Rong and Dr Liu Ye for their keen efforts and consistent consultation throughout my candidature I would like to gratefully acknowledge the research scholarship offered to me by the National University of Singapore (NUS), which provided me a positive, conducive and professional atmosphere for researching Sincere thanks to Institute of Materials Research and Engineering (IMRE) for the characterization instrument I also wish to express my recognition to Agency for Science, Technology and Research (A*Star) and National Research Council Canada (NRC) for their financial support that enables this work to be successfully completed I would like to convey my gratitude to Dr Pramoda Kumari Pallathadka, Dr Dharmarajan Rajarathnam and Mr Lim Poh Chong for their various assistances in operating characterization instrument and equipment I may also like to thank Dr i Anita J Hill for her collaboration in conducting the PALS to characterize the carbon membranes, as well as Dr Liu Songlin for sharing his expertise in the mixed gas permeation tests My gratitude is extended to efforts of Mr Ng Kim Poi, who fabricated and contributed expert advice in equipment setup and machinery Of course, personal thanks go to all members of our research group, especially Dr Cao Chun and Mr Xiao Youchang for many good times, discussion and sharing of technical expertise Special thanks to Ms Chng Mei Lin for all her kindest cooperation and handy help during my days in the laboratory Also worth mentioning are my friends that have been kind and helpful to me, which have made my study in NUS enjoyable and memorable I must express my deepest love and hearties gratefulness to my family for their endless support, enduring patience and positive encouragement that brighten up every phase of my life I can never sufficiently thank or acknowledge them for their unwavering and unconditional love Last but not least, acknowledgements are due to all those who have assisted me in any way throughout the period of my PhD study, for both directly and indirectly continued assistance and support that I received ii TABLE OF CONTENTS Page ACKNOWLEDGEMENT…………………………………………………………… i TABLEOF CONTENTS…………………………………………………………… iii SUMMARY………………………………………………………………………… x NOMENCLATURE…………………………………………………………………xiii LIST OF TABLES………………………………………………………………… xix LIST OF FIGURES…………………………………………………………………xxii CHAPTER INTRODUCTION AND PERSPECTIVE OF GAS SEPARATION MEMBRANE…… ………………………………………………….1 1.1 Membrane-Based Gas Separations…………………………………………….4 1.1.1 Scientific Milestones………………………………………………… 1.1.2 Advantages of Membrane Gas Separation…………………………….9 1.2 Industrial Applications of Membrane Gas Separation……………………….10 1.3 Engineering Principles for Membrane Gas Separation………………………14 1.3.1 Membrane Materials Selection…………………………………… 15 1.3.1.1 Organic (Polymeric) Materials………………………….….17 1.3.1.2 Inorganic Materials…………………………………………19 1.3.1.3 Mixed Matrix Membranes………………………………….20 1.3.2 1.3.3 Membrane Characterization and Evaluation…………………………24 1.3.4 1.4 Membrane Fabrication and Modification…………………………….22 Membrane Modules and Design Considerations…………………… 25 Gas Transport Mechanisms of Membrane Separation……………………….29 1.4.1 Poiseuille Flow……………………………………………………….31 iii 1.4.2 1.4.3 Molecular Sieving……………………………………………………32 1.4.4 1.5 Knudsen Diffusion………………………………………………… 31 Solution-Diffusion……………………………………………………33 Research Objective and Organization of Dissertation……………………….34 CHAPTER POLYMERIC MEMBRANES FOR GAS SEPARATION………38 2.1 Principles of Membrane Gas Separation…………………………………… 38 2.2 Theory of Gas Transport in Nonporous Glassy Polymeric Membranes…… 44 2.2.1 Polymers Free Volume and Occupied Volume………………………44 2.2.2 Dual-Mode Sorption Model ……………………………………… 45 2.2.3 Dual-Mode Model for Permeation ………………………………… 48 2.2.4 Effect of Upstream Pressure on Gas Sorption and Permeation………50 2.2.5 Effect of Temperature on the Gas Transport Properties…………… 52 2.3 Membrane Materials for Gas Separation-Polyimides……………………… 54 2.4 Advanced Modification of Polymeric Membranes………………………… 58 CHAPTER CARBON MOLECULAR SIEVE MEMBRANES FOR GAS SEPARATION………………………………………………………63 3.1 Introduction…………………………………………………… 63 3.2 Fabrication of Carbon Molecular Sieve Membranes……………………… 64 3.2.1 Selection of Polymeric Precursors and Membranes Preparation…….65 3.2.2 Pyrolysis of Polymeric Precursors………………………………… 67 3.2.3 Modification of Carbon Membranes…………………………………73 3.2.3.1 Pretreatment……………………………………………… 73 3.2.3.2 Post-treatment…………………………………………… 76 iv 3.2.4 Configurations of Carbon Membranes……………………………….79 3.3 Microstructure of Carbon Membranes……………………………………….82 3.4 Mechanisms of Gas Transport in Carbon Membranes……………………….85 CHAPTER MATERIALS AND EXPERIMENTAL PROCEDURES……… 89 4.1 Materials…………………………………………………………………… 89 4.1.1 4.1.2 4.2 Polymers…………………………………………………………… 89 Molecular Sieves…………………………………………………… 91 Preparation of Polymeric Membranes……………………………………… 92 4.2.1 Polymeric Dense Film Formation……………………………………92 4.2.2 4.3 Chemical Cross-linking Modification……………………………… 92 Fabrication of Carbon Membranes………………………………………… 93 4.3.1 Polymeric Dense Film Formation….…………………………………93 4.3.2 Pretreatment………………………………………………………… 93 4.3.2.1 Chemical Cross-linking Modification…………………… 93 4.3.2.2 Nonsolvent Pretreatment………………………………… 94 4.3.3 4.4 Pyrolysis Process…………………………………………………… 94 Fabrication of Carbon-Zeolite Composite Membranes………………………96 4.4.1 4.4.2 4.5 Preparation of Polymer-zeolite Mixed Matrix Membranes (MMMs) 96 Pyrolysis Process…………………………………………………… 96 Characterization of Physical Properties…………………………………… 97 4.5.1 Measurement of Gel Content……………………………………… 97 4.5.2 Fourier Transform Infrared Spectrometer (FTIR)……………………98 4.5.3 Differential Scanning Calorimetry (DSC)……………………………98 4.5.4 Modulated Differential Scanning Calorimetry (MDSC)…………… 98 v 4.5.5 Dynamic Mechanical Analysis (DMA)………………………………99 4.5.6 Thermomechanical Analysis (TMA)…………………………………99 4.5.7 Elemental Analysis………………………………………………….100 4.5.8 Measurement of Density……………………………………………100 4.5.9 Thermogravimetric Analysis (TGA)……………………………… 101 4.5.10 TGA-FTIR………………………………………………………… 101 4.5.11 Wide-angle X-ray Diffraction (WAXD)……………………………102 4.5.12 Surface Area and Pore Size Analyzer………………………………102 4.5.13 Positron Annihilation Lifetime Spectroscopy (PALS)…………… 103 4.5.14 Scanning Electron Microscope (SEM)…………………………… 103 4.6 Characterization of Gas Transport Properties………………………………104 4.6.1 Constant Volume-Variable Pressure Method……………………….104 4.6.2 Pure Gas Permeation Tests………………………………………….106 4.6.3 Mixed Gas Permeation Tests……………………………………… 109 4.6.4 Pure Gas Sorption Tests…………………………………………….113 CHAPTER CHEMICAL CROSS-LINKING MODIFICATION OF POLYIMIDE MEMBRANES FOR GAS SEPARATION…… 115 5.1 Introduction……………………………………………………………… 115 5.2 Results and Discussion…………………………………………………… 118 5.2.1 Characterization of Cross-Linked Matrimid Membranes………… 118 5.2.2 Mechanisms of Chemical Cross-linking Reaction…………………… 121 5.2.3 Pure Gas Transport Properties of Matrimid®5218…………………125 5.2.4 Effect of Cross-Linking on Plasticization Phenomenon……………134 5.2.5 Permeation Transport of Mixed Gases…………………………… 136 vi 5.3 Conclusion………………………………………………………………… 139 CHAPTER SEPARATION OF CO2/CH4 THROUGH CARBON MOLECULAR SIEVE MEMBRANES DERIVED FROM POLYIMIDES…………………………………………………… 141 6.1 Introduction…………………………………………………… 141 6.2 Results and Discussion…………………………………………………… 144 6.2.1 Characterization of Carbon Membranes…………………………….144 6.2.2 CO2/CH4 Permeation Performance of P84-derived Carbon Membranes………………………………………………………….151 6.2.3 A Comparison of Gas Separation Performance between P84-derived CMSMs and Other Commercially Available Polyimides-derived CMSMs……………………………………… 153 6.2.4 6.3 Separation of CO2/CH4 Binary Mixture……………………………158 Conclusion………………………………………………………………….160 CHAPTER NOVEL APPROACHES TO FABRICATE CARBON MOLECULAR SIEVE MEMBRANES BASED ON CHEMICAL MODIFIED AND NONSOLVENT-TREATED POLYMIDES………………………………………………………162 7.1 Introduction…………………………………………………………………162 7.2 Pretreatment I: Chemical Cross-Linking Modification…………………… 166 7.2.1 Results and Discussion…………………………………………… 167 7.2.1.1 Characterization of Carbon Membranes………………… 167 7.2.1.2 Effects of Pyrolysis on Pure Gas Permeation Properties…173 vii 7.2.1.3 Effects of Cross-linking Degree on the Gas Permeation Properties of CMSMs Derived from Matrimid Precursor 176 7.2.1.4 Pure Gas Permeation Properties of CMSMs Based on the Methanol Pretreated Polyimides………………… 177 7.3 Pretreatment II: Nonsolvent Pretreatment………………………………… 181 7.3.1 Results and Discussion…………………………………………… 181 7.3.2.1 Thermal Behavior of Nonsolvent Treated Matrimid and P84 Precursors…………………………… 181 7.3.2.2 Characterization of Carbon Membranes………………… 182 7.3.2.3 Effects of Nonsolvent Pretreatment on the Pure Gas Permeation Properties of Resultant Carbon Membranes……………………………………….190 7.3.2.4 Selective Transport in Carbon Membranes……………….194 7.4 Conclusion………………………………………………………………… 199 CHAPTER CARBON-ZEOLITE COMPOSITE MEMBRANES FOR GAS SEPARATION……………………………………………….202 8.1 Introduction…………………………………………………………………202 8.2 Results and Discussion…………………………………………………… 206 8.2.1 Characterization of Polymer-Zeolite Mixed Matrix Membranes (MMMs)……………………………………………….206 8.2.2 Characterization of Carbon-Zeolite Composite Membranes……… 208 8.2.3 Pure Gas Permeation Properties of Carbon-Zeolite Composite Membranes…………………………………………… 211 8.3 Conclusion………………………………………………………………… 215 viii Wright, W.W Application of Thermal Methods to the Study of the Degradation of Polyimides In Developments in Polymer Degradation, Vol 3, ed by N Grassie, pp 1-26 London: Applied Science Publishers 1981 Wright, C T and D R Paul Feasibility of Thermal Crosslinking of Polyacrylate Gas Separation Membranes Using Benzocyclobutene-based Monomers, J Membr Sci., 129, pp 47-53 1997 Wroblewski, S.V Wied Ann Phys, 8, pp 29 1879 Yampolskii, Y.P., A.Y Alexandre and K.A Loza Data Base on Gas Permeation Properties of Polymers, Polym Mater Sci Eng., 86, pp 127 2002 Yoneyama, H and Y Nishihara Porous Hollow Carbon Fiber Film and Method of Manufacturing the Same EP Patent, 0,394,449 1990 Yoshiharu, T The Physical Chemistry of Membranes In Membrane Science and Technology, ed by O Yoshihito and N Tsutomu, pp 3-58 New York: Marcel Dekker 1992 Yoshino, M., S Nakamura, H Kita, K Okamoto, N Tanihara and Y Kusuki Olefin/Paraffin Separation Performance of Carbonized Membranes Derived from An Asymmetric Hollow Fiber Membrane of 6FDA/BRDA-DDBT Copolyimide, J Membr Sci., 215, pp 169-183 2003 264 Zimmerman, C.M., A Singh and W.J Koros Diffusion in Gas Separation Membrane Materials: A Comparison and Analysis of Experimental Characterization Techniques, J Polym Sci Polym Phys., 36, pp 1747-1755 1998 Zimmerman, C.M and W.J Koros Polypyrrolones for Gas Membrane Gas Separations II Activation Energies and Heats of Sorption, J Polym Sci Polym Phys., 37, pp 1251-1265 1999 Zhang, L.X., K.E Gilbert, R M Baldwin and J D Way Preparation and Testing of Carbon/Silicalite-1 Composite Membranes, Chem Eng Comm., 191, pp 665-681 2004a Zhang, X.F., W.Q Zhu, H.O Liu and T.H Wang Novel Tubular Composite CarbonZeolite Membranes, Materials Letters, 58, pp 2223-2226 2004b Zolandz, R.R and Fleming, G.K Gas Permeation Applications, In Membrane Handbook, ed by W.S.W Ho and K.K Sircar, pp 78-94, New York: Chapman & Hall 1992 Zsigmondy, R and W Bachmann Filter for Ultramicroscopic Particles, US Patent 1,421,341 1992 265 APPENDIX A DERIVATIONS OF THE AVERAGE DIFFUSION COEFFICIENT AND THE EFFECTIVE DIFFUSION COEFFICIENT BASED ON THE DEFINITION OF PERMEABILITY (Wang et al., 2002b) The permeability (Pi) of a membrane for a given gas is defined as the flux (Ji) normalized for the pressure difference across the membrane and membrane thickness (l) One can derive the following equation for the permeability without any assumption: Pi = Ji Ji = ∆pi l ( pi − pi1 )l (A.1) where pi2 and pi1 are the pressures at the upstream and downstream of the membrane, respectively The gas transposrt through the membrane obeys Fick’s law as J i = − Di (Ci ) ∂Ci ∂x (A.2) where Di (Ci ) is a local concentration-dependent diffusion coefficient of a penetrant at any arbitrary point between the membrane and ∂Ci is the local concentration ∂x gradient at the same point in the membrane By combining equations (A.1) and (A.2) and integrating over the membrane thickness with a negligible downstream pressure, pi , one can obrain the following equation: Pi = pi Ci ∫ D (C )dC i i i (A.3) 266 Equation (A.3) may be written as Pi = Ci ∫ Di (Ci )dCi Ci Ci pi (A.4) = Di avg Si Ci where Diavg is defined as ∫ Di (Ci )dCi C , the solubility coefficient Si is equal to i , as Ci pi the downstream pressure is negligible The differentiation of equation (A.3) with respect to the concentration at any arbitraty point within the membrane yields: dPi d ⎛ ⎞ = ⎜ ⎟ dCi dCi ⎝ pi ⎠ =− dpi pi 2 dCi dp = − i2 pi dCi =− C ⎞ d ⎛ i2 Di (Ci )dCi + ⎜ ∫ Di (Ci )dCi ⎟ ∫ ⎟ pi dCi ⎜ 0 ⎝ ⎠ Ci Ci ⎞ dC d ⎛ ∫ Di (Ci )dCi + pi dCi ⎜ ∫ Di (Ci )dCi ⎟ dCii2 ⎜ ⎟ ⎝ ⎠ dCi Pi pi + Di (Ci ) pi dCi Ci (A.6) Pi dpi Di (Ci ) dCi + pi dCi pi dCi The above equation can be arranged as Di (Ci ) = Pi dpi dCi Ci + pi ⎛ dP ⎞ = ⎜ Pi + pi i ⎟ dpi ⎠ ⎝ dpi dCi Ci ⎛ dpi ⎞ ⎟ Pi ⎜ ⎝ dCi ⎠ (A.7) Pi 267 APPENDIX B CALCULATIONS OF THE VOLUMES OF DOWNSTREAM COMPARTMENTS IN A GAS PERMEATION CELL The three volumes of the downstream compartments of the gas permeation cell, shown in Figure 4.3 (Chapter Three: Experimental and Experimental Procedures) can be measured using a ‘known volume vessel’ method as follows The volumes of vessels and 3, V2 and V3, respectively are measured by repeated liquid-filling The volume of vessel 1, V1 is used to test the gas permeability for helium with a ⎛ dp ⎞ dense membrane The change of the downstream pressure with time ⎜ ⎟ is ⎝ dt ⎠1 obtained at 3.5 atm, 35°C Under the same prevailing experimental conditions, the test is repeated using ⎛ dp ⎞ volumes for vessels and 2, (V1+V2) and ⎜ ⎟ is obtained ⎝ dt ⎠2 Under the same prevailing experimental conditions, the test is repeated using ⎛ dp ⎞ volumes for vessels and 3, (V1+V3) and ⎜ ⎟ is obtained ⎝ dt ⎠3 V1 and the volume of the valve (x) can be solved simultaneously from these relations: ( dp / dt )1 ( dp / dt )2 V1 + V2 + x V1 (B.1) ( dp / dt )1 V1 + V3 + x = V1 ( dp / dt )3 (B.2) = 268 APPENDIX C CALCULATIONS OF THE FRACTIONAL OF FREE VOLUME (FFV) The fractional of free volume (FFV) was calculated by following equation: ⎛ V −V ⎞ FFV = ⎜ s o ⎟ ⎝ Vs ⎠ (C.1) where Vs and Vo are the specific volume and the occupied volume, respectively Specifically, the observed specific volume, Vs is calculated from the measured density and the occupied volume, Vo is calculated from the correlation: Vo = 1.3Vw (C.2) where Vw is the Van der Waals volumes, which is estimated using Bondi’s group contribution method (Bondi, 1964) For the polymers, Vw can be estimated from group contribution method (n = number of groups) proposed by Park and Paul (Park and Paul, 1997): Vw = ∑ (Vw )n (C.3) n 269 C.1 CALCULATION OF THE FFV OF MATRIMID® 5218 POLYIMIDE Table C.1 Calculation of Van der Waal Volume of Matrimid® 5218 by Group Contribution MW (g/mol) Vw (cm3/mol) 2× 145.11 2×69.4 1×28.01 1×11.7 1×76.09 1×43.32 1× 75.08 1×40.80 C(CH3)2 1× 42.08 1×30.7 C 1×12.01 1×3.33 1×13.02 1×6.78 1×15.03 1×13.67 Group & Polymer O N O O C CH CH3 O N O H3C O CH3 O N O H3C n ∑M W = 551.54 ∑V w = 289.1 270 a) The occupied volume of Matrimid® 5218 Vo = 1.3Vw ⎛ 289.1 ⎞ = 1.3 ⎜ ⎟ ⎝ 551.54 ⎠ = 0.6814 cm3 /g b) The specific volume of Matrimid® 5218 Vs = ρ 1.22 = 0.8197 cm3 /g = c) The FFV of Matrimid® 5218 FFV = (Vs − V0 ) Vs 0.8197 - 0.6814 0.8197 = 0.1687 = 271 C.2 CALCULATION OF THE FFV OF P84 POLYIMIDE O O O CH3 H N N O O C n H 80 % 20 % Copolymer A Copolymer B Table C.2a Calculation of Van der Waal Volume of Copolymer A by Group Contribution MW (g/mol) Vw (cm3/mol) 2× 145.11 2×69.4 1×28.01 1×11.7 1×15.03 1×13.67 1×75.08 Group & Polymer 1×41.8 O N O O C CH3 O O O CH N O N ∑M W = 408.34 ∑V w = 205.97 O 272 Table C.2b Calculation of Van der Waal Volume of Copolymer B by Group Contribution MW (g/mol) Vw (cm3/mol) 2× 145.11 2×69.4 1×28.01 1×11.7 2×76.09 2×43.32 1×14.02 Group & Polymer 1×10.23 O N O O C CH O O O N O N CH2 ∑M W = 484.43 ∑V w = 247.37 O a) The Van der Waal Volume of P84 Vw = φ1Vw1 + φ2Vw ⎛ 205.97 ⎞ ⎛ 247.37 ⎞ = 0.8 ⎜ ⎟ + 0.2 ⎜ ⎟ ⎝ 408.34 ⎠ ⎝ 484.43 ⎠ = 0.5057 b) The occupied volume of P84 Vo = 1.3Vw = 1.3(0.5057) = 0.6574 cm3 /g 273 c) The specific volume of P84 Vs = ρ 1.3138 = 0.7611 cm3 /g = d) The FFV of P84 FFV = (Vs − V0 ) Vs 0.7611- 0.5057 0.7611 = 0.1364 = 274 APPENDIX D CALCULATIONS OF SOLUBILITY PARAMETER (δsp) (Matsuura, 1994) The solubility parameter is a parameter to express the nature and magnitude of the interaction force working between molecules When applied to the membrane, the solubility parameter can give a measure to the interaction force working between the molecules that constitute the membrane material, and also the interaction force between the latter molecule and the penetrant molecule They are intrinsic to the chemical structure Solubility parameter can be calculated by applying addition rules to the structural components of the repeat unit of molecule, by following equation (Van Krevelen, 1976): δ sp = ΣEcoh ΣVm i (D.1) Where Ecoh is structural component for the overall solubility parameter (cal/mol) and Vmi is molar volume (cm3/mol) 275 D.1 CALCULATION OF THE SOLUBILITY PARAMETER OF P84 O O O CH3 H N N O O 80 % C n H 20 % Copolymer A Copolymer B D.1.1 Copolymer A Structural Group Ecoh (cal/mol) Vm i (cm3/mol) CON 2×7050 2×(-7.7) CO 3×4150 3×10.8 3×7630 3×33.4 1×1125 1×33.5 ΣEcoh = 50565 ΣVm i = 150.7 CH3 O O O CH N N O O δ sp , A = ΣEcoh ΣVm i 50565 150.7 = 18.32 = 276 D.1.2 Copolymer B Structural Group Ecoh (cal/mol) Vm i (cm3/mol) CON 2×7050 2×(-7.7) CO 3×4150 3×10.8 2×7630 2×33.4 2×7630 2×52.4 1×1180 1×16.1 ΣEcoh = 58250 ΣVm i = 204.7 CH O O O N N O CH2 O δ sp , B = ΣEcoh ΣVm i 58250 204.7 = 16.87 = δ sp = 0.8δ sp , A + 0.2δ sp , B = 0.8(18.32) + 0.2(16.87) = 18.03 277 D.2 CALCULATION OF THE SOLUBILITY PARAMETER OF MATRIMID® 5218 POLYIMIDE Structural Group Ecoh (cal/mol) Vm i (cm3/mol) CON 2×7050 2×(-7.7) CO 3×4150 3×10.8 3×7630 3×33.4 1×7630 1×52.4 CH3 3×1125 3×33.5 CH 1×1180 1×16.1 2×350 2×(-19.2) ΣEcoh = 62325 ΣVm i = 247.8 C O H3C O CH3 O N N O O δ sp = H3C n ΣEcoh ΣVm i 62325 247.8 = 15.86 = 278 ... Membrane Gas Separation? ??………………………….9 1.2 Industrial Applications of Membrane Gas Separation? ??…………………….10 1.3 Engineering Principles for Membrane Gas Separation? ??……………………14 1.3.1 Membrane Materials. .. necessities for successful gas separation membranes and strategies for the design of membranes systems must be identified In general, the chemical engineering of membranes for gas separation can... applications of gas separation membranes are listed in Table 1.4 The major applications for gas separation membranes are discussed Table 1.4 Industrial Applications of Gas Separation Membranes (Spillman