Influence of adsorption on the diffusion selectivity for mixture permeation across mesoporous membranes

Abstract

Molecular dynamics (MD) simulations were carried out to determine the self-diffusivities, D 1,self, and D 2,self for a variety of binary mixtures: methane (C1)–ethane (C2), C1–propane (C3), C1–n-butane (nC4), C1–n-hexane (nC6), C2–nC4, C2–nC6, Ar–C1, Ar–C2, Ar–C3, Ar–nC4, Ar–nC6, and Ar - Kr in a cylindrical silica mesopores. The diffusion selectivity, defined by ( D 1,self/ D 2,self) was found to be significantly different from the Knudsen selectivity, M 2 / M 1 , where M i is the molar mass of species i. For mixtures in which component 2 is more strongly adsorbed than component 1, ( D 1 , self / D 2 , self ) / M 2 / M 1 has values in the range 1.5–4; the departures from the Knudsen selectivity increased with increasing differences in adsorption strengths of the constituent species.