Two component permeation through thin zeolite MFI membranes


Keizer, K. and Burggraaf, A.J. and Vroon, Z.A.E.P. and Verweij, H. (1998) Two component permeation through thin zeolite MFI membranes. Journal of Membrane Science, 147 (2). pp. 159-172. ISSN 0376-7388

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Abstract: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 -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 (>600, T=298–473 K) and 0.31 kPa p-xylene/0.26 kPa o-xylene (>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.

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Copyright:© 1998 Elsevier Science
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