(371b) Modeling Separations in Mesoporous Membranes Using Lattice Based and Molecular Simulation Techniques

Mesoporous membranes provide an energy efficient alternative for processes where enrichment or separation of condensable vapor is required given its mixture with a light gas. With continuous progress in synthesis methods for these membranes, it is now possible to fine tune both geometry and surface chemistry of mesopores. However, a rational design requires rules to establish link between transport mechanisms and mesopore properties. Absence of such correlations is one of the obstacles to the wide-spread usage of mesoporous membranes. Determination of these design rules would require a thorough knowledge of various transport phenomenon present in the membrane process and how they cooperate to give rise to macroscopic quantities such as selectivity and permeance. Dynamic mean field theory (DMFT), a lattice-based density functional theory which is computationally efficient and sufficiently descriptive, was applied to these systems to understand the underlying nature of transport processes. We initially applied DMFT to permporometry, an experimental technique where light gas permeates through condensable vapor under small pressure gradients. We then investigated a separation process where condensable vapor is separated from its mixture with light gas under significant pressure gradient. During our studies, we found a nonequilibrium steady state with capillary condensation confined to the high pressure (feed side) of the pore. We investigated the effect of this state on separation efficiency and permeation using different pore geometries and surface chemistries. Based on the understanding that we gained through our model, we attempted design better pore structure incorporating effects of partial capillary condensation which would provide higher efficiency and yield in separation.