Molecular simulation studies were made of methane and butane in silicalite at room temperature. Adsorption isotherms and diffusion coefficients were calculated for a range of pressures. At low pressures (<20bar), adsorption occurred predominantly at specific potential-energy minima in the silicalite channels while, at higher pressures, adsorption was determined by the total accessible channel volume. Diffusion was found to be strongly anisotropic, with the fastest diffusion being along the straight channels. The diffusivities of methane and butane at 300K were 1.34 x 10-4 and 1.7 x 10-5cm2/s, respectively. Good agreement was found with experimental results for orientationally averaged diffusion coefficients. At low pressures, diffusion was described well by a pseudo-Bosanquet formula which identified two independent contributions (collisions with walls, intermolecular collisions) to diffusional resistance. At short times, significant molecular force correlations arose due to the difficulty of methane molecules to pass each other in the channel intersections of the silicalite lattice.

Molecular Simulation of Methane and Butane in Silicalite. S.J.Goodbody, K.Watanabe, D.MacGowan, J.P.R.B.Walton, N.Quirke: Journal of the Chemical Society - Faraday Transactions, 1991, 87, 1951-8