The pressure-driven gas permeation of gases in porous silica models was simulated by using a dual control volume grand canonical molecular dynamics technique. This technique permitted spatial variation of the chemical potential and hence an accurate simulation of this steady-state process. The molecular-sieving nature of microporous zeolites and amorphous silica made using sol-gel methods were compared. One mesoporous and one microporous membrane model were tested with Lennard-Jones gases corresponding to He, H2, Ar and CH4. The mesoporous membrane model clearly indicated a Knudsen diffusion mechanism, while the microporous model, having a hard-sphere cut-off pore diameter of ~3.4Å, demonstrated molecular sieving of CH4 (σ = 3.8Å), but anomalous behavior for Ar (σ = 3.4Å).

Massively Parallel Molecular Dynamics Simulation of Gas Permeation Across Porous Silica Membranes. Pohl, P.I., Heffelfinger, G.S.: Journal of Membrane Science, 1999, 155[1], 1-7