2-COMPONENT PERMEATION THROUGH THIN ZEOLITE MFI MEMBRANES

Two component permeation measurements have been performed by the Wicke -Kallenbach method on a thin (3 mu m) zeolite MFI (Silicalite-1) membr ane with molecules of different kinetic diameters, d(k). The membrane was supported by a flat porous alpha-Al2O3 substrate. The results obta ined could be classified in six regimes based on differences in: Occup ation degrees, theta, on the external surface. Occupation degrees, the ta in the zeolite pores. Mobilities in the zeolite pores. High separat ion factors are obtained for mixtures of ''weakly/strongly adsorbing'' gases and for mixtures of ''small/large'' gases. Separation by size-e xclusion is demonstrated for 8 kPa n-C6H14/16 kPa 2,2-dimethylbutane ( alpha>600, T=298-473 K) and 0.31 kPa p-xylene/0.26 kPa o-xylene (alpha >200, T=400 K). At low a thigh temperature, low pressures) the permeat ion of both components in a mixture equals the single-gas permeation o f these components. At high a (low temperature and high pressure) the permeation of both components in mixtures is different from single-gas permeation values. The single-gas permeance of ''small'' molecules wi th kinetic diameter dk <0.45 nm ranges from 1 x 10(-8) to 15 x 10(-8) mol m(-2) s(-1) Pa-1 in the temperature range 298-473 K. The permeatio n decreases with increasing dk of the molecules. (C) 1998 Elsevier Sci ence B.V. All rights reserved.