Adsorption and diffusion of a Lennard-Jones vapor in microporous silica

The properties of a dilute Lennard-Jones vapor in contact with an adsorbing microporous medium are investigated using grand canonical ensemble Monte Carlo and molecular dynamics techniques. The bulk structure of the microporous system is modeled as an assembly of randomly distributed interconnected solid spheres, and vapor/surface interactions are treated in two ways: (i) using a smooth continuous interaction potential and (ii) using a molecular model for the surface structure of the solid. The microporous solid representation employed in these simulations is chosen to conform in realistic manner with the bulk and surface properties of silica gel. The results obtained from the simulations include equilibrium partition coefficients, diffusivities, and related microscopic properties. By comparing these results with available experimental data it is shown that the properties of simple nonpolar gases in microporous silica may be predicted with reasonable accuracy. This is particularly true when the molecular structure of the silica surface is taken into consideration.