Computer Simulations of Diffusion in Monolayers Physisorbed in Model Pores

Abstract

AbstractTwo types of model pore have been considered as sorbents of methane at 300 K: the first is a straight cylinder with atomically rough walls characteristic of an amorphous solid. Three cylinder radii plus the reference flat surface were taken for study. The second is a parallel-walled slit pore made up of graphite basal planes that had been modified by the insertion of sulfide atoms. Here, two values of sulfur loading were taken together with the reference pure graphite pore. Two values of the wall spacing were assumed for each sulfur loading. Thermodynamic and structural properties are presented elsewhere; here, the dependence of diffusion constants as a function of the monolayer density is presented for methane in the various model pores. It is shown that these diffusivities depend primarily on the methane-methane collisions in the monolayer films. There is a slight dependence upon the nature of the solid surface which is interpreted in terms of the hindrances produced by soft obstacles to molecular motion parallel to the surfaces.