Single and binary surface diffusion permeation through zeolite membranes using new Maxwell-Stefan factors for Dubinin-type isotherms and occupancy-dependent kinetics

The development of accurate mass transfer models is essential to describe and, most importantly, to predict the dynamic behavior of separation and reaction processes. In this work, the Maxwell-Stefan (MS) thermodynamic factors for Dubinin-Astakhov (DA) and Dubinin-Radushkevich (DR) isotherms are derived for the first time, with the objective to model the permeation of pure and mixed gases through zeolite membranes, which implies reliable kinetic and equilibrium data/equations. The new MS expressions are validated using equilibrium and permeation data for (methane, ethane)/silicalite-1 systems according to the following procedure: (i) the best modeling approaches for single DA and DR isotherms are determined; (ii) the binary DA and DR isotherms are then predicted from pure gas data; (iii) the influence of surface loading on the diffusivity of permeating species is carefully assessed; (iv) the diffusion parameters of each gas are obtained from unary permeation data; (v) the MS counter-sorption diffusivities are then predicted using the Vignes correlation; finally (vi) the separation of methane/ethane mixtures in the silicalite-1 membrane is totally predicted using the new MS thermodynamic factors combined with the binary isotherms. The results achieved for the permeation of pure methane, pure ethane, and methane/ethane mixtures reveal that the new MS factors are able to correlate data of single gases and accurately predict binary permeation through silicalite-1 membrane, particularly if DA is selected. The calculated root mean square deviations are only 8.75×10-3 mol m−2 s−1 in the first case and 1.55×10-3 mol m−2 s−1 for prediction.