A comparative simulation study of the adsorption of nitrogen and methane in siliceous heulandite and chabazite

Grand canonical Monte Carlo simulation has been used to study adsorption of single components and mixtures of nitrogen and methane in purely siliceous models of chabazite and heulandite. The adsorbate framework interactions were modelled with both the Kiselev and the PN potentials. The latter predict rather narrower pores than the former, and this has significant effects on the predictions of the two models. In heulandite the differences can be related to the accessibility of 8-ring pores to nitrogen, since these form a large proportion of the pore space. In chabazite the differences are less notable since the framework contains wide cavities. Isotherms, heats of adsorption and selectivity from mixtures are discussed. Selectivity is found to be reversed between the two models. It may be concluded that the presence of cations in a silica-alumina framework is essential for viable selectivity, and that access through the narrow pores of the framework is a crucial factor. (C) 2001 Elsevier Science BN. All rights reserved.