Relationship between Sorbate Transport Inside and at the Margins of Zeolite Crystals

Abstract

In addition to sorbate diffusion inside pore networks of microporous crystals, the properties of transport of sorbate molecules near and through the margins of these crystals are of a significant interest for understanding diffusion properties of micropore-containing membranes and catalysts. Such interest is related to the fact that under typical conditions of applications of membranes and catalysts sorbate molecules pass multiple times through the external surface of microporous crystals. This review focuses on several selected aspects of molecular transport near and at the external crystal surface as well as on selected issues related to diffusion inside of microporous crystals far away from their boundaries. The cases of both normal, i.e., Fickian diffusion and single-file diffusion are discussed. The interplay between molecular transport inside microporous crystals and that inside mesopores surrounding the crystals in a membrane is also briefly considered at the end of the paper. The discussed results are obtained by computer simulations and by analytical treatment.

Keywords:

• Boundary effect
• Mass-transfer coefficient
• Membrane
• Permeability
• Zeolite

ACKNOWLEDGMENTS

This work was financially supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of SPP 1155. O. Saengsawang and T. Nanok are grateful to DFG SPP 1155 for post-doctoral positions.