Gas permeation through the micropores of a vitreous silica membrane were studied. Virtual membranes were prepared via melt-quench methods using the modified Born-Mayer-Huggins pair potential and Stillinger-Weber three-body interactions. The particle-generating non-equilibrium molecular dynamics technique was used to simulate gas permeation phenomena, where permeating molecules were modelled as Lennard-Jones particles. This simulation method accommodated a change in the number of particles in a unit cell and hence an accurate simulation of the steady-state permeation process could be achieved. The dependence of permeation upon temperature and pressure was considered. For cylindrical pores, about 5Å in diameter, the calculated temperature dependences of the permeation of He-like Lennard-Jones particles were similar to those predicted by the normal Knudsen permeation mechanism. For CO2 permeation, a temperature dependence greater than for He and a significant deviation from Knudsen was observed. In the relatively high-temperature region (400 to 800K), the simulated permeation of CO2 was almost independent of the up-stream pressure while, below 300K, a pressure dependence of the permeation was observed. The results indicated that gas-like permeation occurred in the higher-temperature region, where the permeation flux was proportional to the pressure-drop across the pore. However, at lower temperatures, the transport of molecules - as some sort of adsorption phase - could predominate in such a small pore. A simple gas permeation model, considering the effect of the pore-wall potential field and Langmuir-type adsorption within a micropore, explained well the permeation properties.

Molecular Dynamics Studies on Gas Permeation Properties through Microporous Silica Membranes. Yoshioka, T., Tsuru, T., Asaeda, M.: Separation and Purification Technology, 2001, 25[1-3], 441-9. See also: Journal of Membrane Science, 2007, 293[1-2], 81-93