Modeling permeation of binary mixtures through zeolite membranes

Abstract

The separation of ethane/methane and propane/methane mixtures with a silicalite‐1 membrane was investigated as a function of composition, total hydrocarbon pressure (up to 425 kPa), and temperature (273–373 K). The selectivity of the membrane is highly dependent on these operating conditions. The generalized Maxwell–Stefan equations were used to predict the fluxes and the associated selectivities. These model predictions, based on separately determined single‐component adsorption and diffusion parameters, were in excellent agreement with the experimental data. Using the empirical Vignes relation for the prediction of the binary Maxwell–Stefan surface diffusivity, there were no fitting parameters involved in the model prediction. The importance of incorporation of adsorbate–adsorbate interactions in the model is clearly shown, both for transient and steady‐state mixture permeation. Theoretical analysis showed that for mixtures of a fast, weakly adsorbing component and a slow, strongly adsorbing component the maximum selectivity obtained with microporous membrane separation is always a factor of 2 lower than the one obtained under equilibrium adsorption conditions.