Abstract
Non-equilibrium molecular dynamics simulations of condensable vapor permeation and separation of condensable and non-condensable gas mixtures through a sub-nano scale pore were conducted on a virtual amorphous silica membrane which was prepared by the melt-quench procedures. Concerning the permeation properties of ethane-like LJ particle through a pore of 8 Å in diameter, a surface diffusion-like temperature dependency was observed at relatively high temperature region (400-800 K), while around room temperatures, the permeance decreased with decreasing temperature. The permeances of non-condensable nitrogen-like particle, which has smaller affinity with the pore surface than ethane, was smaller than those of ethane and the Knudsen or surface diffusion-like temperature dependency curve could be seen. In simulations of separation for ethane/nitrogen binary mixtures at 260 K, a temperature below the critical temperature (TC) of actual ethane, the concentration dependency of ethane permeance showed an almost flat curve in low concentration (partial pressure) region, and at a higher specific concentration, the permeance largely decreased. The permeances of nitrogen were smaller at any partial pressure conditions compared with those observed in single nitrogen gas permeation simulations. Especially at a large partial pressure of ethane, the permeance of nitrogen became very small. This fact indicates a condensable component that has larger interaction with the pore surface could obstruct the transport of a non-condensable one to decrease its permeance. Above mentioned results suggest that the micropore filling of condensable gases could occur in a micropore at temperatures below TC and at sufficiently high pressures, and this phenomenon would play an important role in determining the separation performance of these gases through a micropore.
