A boundary-driven non-equilibrium simulation method was used to study gas permeation through microporous amorphous silica membranes. Two types of silica membranes were prepared: one by random atom-removal and the other by the usual pore-digging. The first was a dense membrane that served as a model for network pores formed by silica polymers, and the second had a penetrating cylindrical pore which simulated an interparticle pore. The permeation of He, H2 and Ne through network models with densities of 1.7 and 1.8g/cm3 increased with decreasing temperature, while activated permeation was observed for the denser models. Deviations of the permeation properties, from those predicted by the Knudsen model, became greater with increasing membrane density as a result of molecular sieving effects. The permeation of H2 through a cylindrical pore 0.6nm in diameter was greater than that for He at all temperatures, as predicted by the Knudsen model. The greater interaction of CO2 with the pore surface yielded a larger temperature-dependence curve for permeation, as compared to He and H2. The simulated properties of several gases were in agreement with experimental data on microporous silica membranes.

Molecular Dynamics Study of Gas Permeation Through Amorphous Silica Network and Inter-Particle Pores on Microporous Silica Membranes. Yoshioka, T., Tsuru, T., Asaeda, M.: Molecular Physics, 2004, 102[2], 191-202