(285c) Small Pore Zeolites as Materials for Gas Separation Membranes

Despite their small size, the pores of most zeolites are not small enough to give strong size selectivity for membrane-based separations of hydrogen/methane or methane/carbon dioxide mixtures. We will describe atomically-detailed simulations of two strategies for achieving high membrane selectivities for separations of these mixtures. First, we have examined methane and carbon dioxide adsorption and transport inside zeolite DDR, where the small pores separating adjacent zeolite cages significantly hinder diffusion of methane. We have used molecular dynamics simulations to probe both single component and mixture transport in DDR in order to predict the performance of DDR as a membrane under practical operating conditions. Second, we have developed simulation methods to examine zeolite membranes in which deposition of amorphous silica around the zeolite pore mouth has been used to create a size-selective barrier layer. These simulations give insight into the physical conditions that must be controlled in experimental applications of this concept.