Equilibrium molecular dynamics and mean first passage time analysis of the separation of exhaust gases at high temperatures by silica nanoporous membranes

摘要

An investigation of mechanisms associated with the high selectivity of a gas mixture at high temperatures by silica nanoporous membranes has been conducted in the framework of equilibrium classical molecular dynamic simulations and formalism of fractional diffusion equation on a sample of a gas mixture of exhaust gases. The important feature is the quite realistic modeling of the silica nanoporous membranes based on the use of an analytic bond order potential and the conception of dangling bonds. The last two were successfully employed to model the realistic silica chemical vapor deposition process (Burlakov et al 2001 Phys. Rev. Lett. 86 3052). The dependence of the selective properties on temperature, density (voidage volume) and morphology has been investigated. The selectivity at a low temperature (673 K) is found to be more efficient than at a high temperature (873 K). When only Lennard-Jones interaction between a gas and a solid is included the selectivity is found to be changed at the low temperature (673 K) from 1.2 : 1 for a density of 50% to 1.03 : 1 for a density of 80%. Including an additional electrostatic interaction increases the selectivity from 1.79 : 1 for a density of 50% to 2.26 : 1 for a density of 80%. At the high temperature (873 K) when only Lennard-Jones potential is included the selectivity is found to be changed from 1.21 : 1 for a density of 50% to 1.13 : 1 for a density of 80%. With an additional electrostatic force the selectivity is found to be the same for all densities at around 1.43 : 1. The conclusion is that the most efficient conditions for the selective membrane are a temperature of 673K and a high density. Under these conditions the mean first passage times for species O-2 and N-2 are almost the same and much less than for species CO2. The methodology developed is general. This paper is based on the author's PhD thesis.