US EPA

8714542 

Journal Article 

Two component permeation through thin zeolite MFI membranes 

Keizer, K; Burggraaf, AJ; Vroon, ZAEP; Verweij, H 

1998 

Yes 

Journal of Membrane Science
ISSN: 0376-7388 

147 

2 

159-172 

English 

10.1016/S0376-7388(98)00133-1 

Two component permeation measurements have been performed by the Wicke-Kallenbach method on a thin (3 μm) zeolite MFI (Silicalite-1) membrane with molecules of different kinetic diameters, d(k). The membrane was supported by a flat porous α-Al2O3 substrate. The results obtained could be classified in six regimes based on differences in: Occupation degrees, θ, on the external surface. Occupation degrees, θ, in the zeolite pores. Mobilities in the zeolite pores. High separation factors are obtained for mixtures of 'weakly/strongly adsorbing' gases and for mixtures of 'small/large' gases. Separation by size-exclusion is demonstrated for 8 kPa n-C6H14/16 kPa 2,2-dimethylbutane (α > 600, T = 298-473 K) and 0.31 kPa p-xylene/0.26 kPa o-xylene (α > 200, T = 400 K). At low θ (high temperature, low pressures) the permeation of both components in a mixture equals the single-gas permeation of 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 with kinetic diameter d(k) < 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 permeation decreases with increasing d(k) of the molecules. Two component permeation measurements have been performed by the Wicke-Kallenbach method on a thin (3 μm) zeolite MFI (Silicalite-1) membrane with molecules of different kinetic diameters, dk. The membrane was supported by a flat porous α-Al2O3 substrate. The results obtained could be classified in six regimes based on differences in: Occupation degrees, θ, on the external surface. Occupation degrees, θ, in the zeolite pores. Mobilities in the zeolite pores. High separation factors are obtained for mixtures of `weakly/strongly adsorbing' gases and for mixtures of `small/large' gases. Separation by size-exclusion is demonstrated for 8 kPa n-C6H14/16 kPa 2,2-dimethylbutane (α>600, T = 298-473 K) and 0.31 kPa p-xylene/0.26 kPa o-xylene (α>200, T = 400 K). At low θ (high temperature, low pressures) the permeation of both components in a mixture equals the single-gas permeation of these components. At high θ (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 with kinetic diameter dk<0.45 nm ranges from 1×10-8 to 15×10-8 mol m-2 s-1 Pa-1 in the temperature range 298-473 K. The permeation decreases with increasing dk of the molecules. 

Ceramic membranes; Diffusion; Gas separations; Microporous and porous membranes