Adsorption and Diffusion of Methane and Nitrogen in Barium Exchanged ETS-4

Single component equilibrium and uptake of methane and nitrogen in barium exchanged ETS-4, Ba-ETS-4, have been measured in a constant volume apparatus over a wide range of temperatures and pressures followed by binary measurements in a differential adsorption bed at some selected conditions. Similar binary data in two strontium exchanged samples have also been included for which unary data were earlier reported from our laboratory.(12) Adsorbent particles used in these measurements were obtained by pressure-binding very fine crystals of Ba-ETS-4 synthesized in this laboratory, thus giving rise to a bidispersed pore structure with the controlling resistance to diffusion in the micropores. The effect of dehydration temperature on equilibrium and kinetics of aforementioned gases in Ba-ETS-4 has also been investigated. The uncoupled kinetic selectivity of nitrogen over methane in Ba-ETS-4 measured in this study far exceeds the selectivity reported for methane−nitrogen separation in other adsorbents in the literature. Kinetic selectivity including the coupling of equilibrium isotherm and uptake has also been calculated from binary measurements and is found to be equally encouraging. The impact of isotherm models on the concentration dependence of micropore diffusivity has been analyzed on the basis of chemical potential gradient as the driving force for diffusion. Binary equilibrium and kinetic models based on parameters independently established from unary experiments have been proposed that are able to explain the transport mechanism and capture the essential features of measured binary data.