Molecular simulations of hydrogen and methane permeation through pore mouth modified zeolite membranes

Membrane-based separations are an attractive means to separate hydrogen from gas mixtures in order to use hydrogen in energy-related applications. Zeolite membranes are robust materials that are well suited to be used in harsh conditions, but they are not typically selective for hydrogen. Several studies have shown that highly selective separations of hydrogen are possible using zeolite membranes whose pore mouths have been chemically modified. An important challenge for materials of this kind is to develop methods by which hydrogen selectivity can be retained without significantly reducing the hydrogen flux possible with an unmodified zeolite membrane. Motivated by this, the effect of the pore mouth modification of silicalite was examined using atomic-scale simulations. We developed methods to mimic the chemical vapour deposition of Si and O atoms near the surface of a silicalite crystal, and examined the flux of CH4 and H2 through the resulting materials. Under some degrees of surface modification, the CH4 flux was reduced much more than the H2 flux. This observation indicates that careful control of surface modifying layers may be a useful means of tailoring the performance of zeolite membranes for H2 separations.