Articles & Issues

Language: English

Conflict of Interest: In relation to this article, we declare that there is no conflict of interest.

Publication history: Received September 9, 2003
Accepted December 19, 2003

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/bync/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

All issues

High Gas Permeability in Open-Structure Membranes

Guangxiang Wu^{1 2} Catherine L. Bothe Almquist^{1 3} Sun-Tak Hwang^1†

¹Department of Chemical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221-0012, USA ²Dept. of Chemistry, Purdue University, West Lafayette,IN 47907, USA ³Paper Science and Engineering, Miami University, Oxford, OH 45056, USA

shwang@alpha.che.uc.edu

Korean Journal of Chemical Engineering, March 2004, 21(2), 442-453(12), 10.1007/BF02705434

Download PDF

Abstract

For most polymeric membranes, the gas permeability coefficient (P) is often interpreted as the product of diffusivity (D) and solubility (S) of a penetrant gas in the polymer (P=D S). The basic assumption is that molecular diffusion is primarily responsible for mass transport in the membrane permeation process. However, for some open structure membranes, such as poly(1-trimethylsilyl-1-propyne) [PTMSP] or poly(dimethylsiloxane) [PDMS], the high permeabilities of some gases yield much higher diffusivities when calculated from the above relationship (P=D S) than when calculated by using the direct kinetic measurement of diffusivity. It is hypothesized that this discrepancy is due to the convective transport of gas molecules through such open structured polymers. In most cases, the convective contribution to mass transport through membranes is negligible. However, for polymer membranes with high free volume, such as PTMSP, whose free volume fraction is 20 to 25%, the convective term may dominate the permeation flux. In this study, a non-equilibrium thermodynamic formalism is employed to properly treat the diffusion term and convective term that constitute the Nernst-Planck equation. The current analysis indicates that the total permeation flux, which consists of a diffusion term and a convective term, agrees well with the experimental data for several permeation systems: pure components propane and n-butane/PTMSP, pure gas hydrogen/PTMSP, and mixed gas hydrogen/PTMSP. Also, the permeation systems of a nonporous rubbery membrane, PDMS, and eight organophosphorus compounds were included in the study. It is recommended that the proposed model be validated by using other polymers with high free volumes and high permeabilities of gases and vapors, such as poly(1-trimethylgermyl-1-propyne) [PTMGeP] and poly(4-methyl-2-pentyne) [PMP].

Keywords

Permeation Flux Diffusion Flux Convective (Bulk) Flux Large Permeability Poly(1-trimethylsilyl-1-propyne) Poly(dimethylsiloxane)

References

Almquist CB, unpublished work (1995)
Almquist CB, Hwang ST, J. Membr. Sci., 153(1), 57 (1999)
Anuraag S, "Gas and Vapor Sorption and Permeation Properties of High Free Volume Glassy Polymers," Ph.D. Dissertation, North Carolina State University (1997)
Bae SY, Lee KH, Yi SC, Kim HT, Kim YH, Kumazawa H, Korean J. Chem. Eng., 15(2), 223 (1998)
Bae SY, Kim HT, Kumazawa H, Korean J. Chem. Eng., 11(3), 211 (1994)
Bae SY, Cho DH, Kim HT, Kumazawa H, Korean J. Chem. Eng., 11(2), 127 (1994)
Bae SY, Cho DH, Ko SW, Kim HT, Kumazawa H, Korean J. Chem. Eng., 10(1), 44 (1993)
Balik CM, Macromolecules, 29(8), 3025 (1996)
Berens AR, Hopfenberg HB, Polymer, 19, 489 (1978)
Bird RB, Stewart WE, Lightfoot EN, "Transport Phenomena," 2nd ed., Wiley, New York, 513 (2002)
Crank J, "The Mathematics of Diffusion," 2nd ed., Clarendon Press, Oxford, 44 (1975)
Crank J, Park GS, "Diffusion in Polymers," Academic Press, New York, 1 (1968)
DeGroot SR, "Thermodynamics of Irreversible Processes," Interscience Publishers, Inc., New York, 5, 54 (1952)
Dixon-Garrett SV, Nagai K, Freeman BD, J. Polym. Sci. B: Polym. Phys., 38(8), 1078 (2000)
Felder RM, J. Membr. Sci., 3, 15 (1978)
Felder RM, Huvard GS, "Methods of Experimental Physics," Vol. 16, Part C, Academic Press, New York, 315 (1980)
Frisch HL, J. Phys. Chem., 60, 1177 (1956)
Hwang ST, Kammermeyer K, "Membrane in Separations," Wiley, New York, 18 (1975)
Kamaruddin HD, Koros WJ, J. Membr. Sci., 135(2), 147 (1997)
Katchalsky A, Curran PF, "Non-equilibrium Thermodynamics in Biophysics," Harvard University Press, Cambridge, MA, 85 (1967)
Koros WJ, J. Polym. Sci. B: Polym. Phys., 18, 981 (1980)
Koros WJ, Paul DR, Rocha AA, J. Polym. Sci. B: Polym. Phys., 14, 687 (1976)
Langsam M, Savoca ACL, U.S. Patent, 4,759,776 (1988)
Merkel TC, Bondar V, Nagai K, Freeman BD, J. Polym. Sci. B: Polym. Phys., 38(2), 273 (2000)
Morisato A, Pinnau I, J. Membr. Sci., 121(2), 243 (1996)
Pinnau I, Casillas CG, Morisato A, Freeman BD, J. Polym. Sci. B: Polym. Phys., 34(15), 2613 (1996)
Pinnau I, Toy LG, J. Membr. Sci., 116(2), 199 (1996)
Stern SA, J. Membr. Sci., 94, 1 (1994)
Zimmerman CM, Singh A, Koros WJ, J. Polym. Sci. B: Polym. Phys., 36(10), 1747 (1998)