Study of gas transport mechanisms in mesoporous membranes using dynamic means field theory

Conference Dates

September 11-16, 2016


Mesoporous membranes provide a means for energy-efficient removal of condensable species from light gases, such as volatile organic compounds from air or carbon dioxide from flue gas. Recent breakthroughs in materials synthesis allow a reasonable degree of control over the geometry and surface chemistry of the mesopores within the membrane. However, there are no general design rules that link these mesopore properties to the mechanisms that determine permeation rates, such as preferential adsorption, surface flow, and capillary condensation. Toward developing such design rules, we have applied dynamic mean field theory (DMFT), a lattice-based density functional theory, to the problem of predicting permeation of a mixture of condensable and non-condensable species across a mesopore under a pressure gradient. We first modeled the classic pervaporation experiment in which the permeation of a light gas is measured in the presence of a vapor that may condense in the pore. Several interesting effects, such as the transport of the light gas on top of an adsorbed layer of vapor prior to full capillary condensation, were observed. We next studied the removal of a condensable vapor from a light gas in a simple slit pore under a significant pressure gradient, and discovered an interesting phenomenon involving capillary condensation localized near the high pressure (feed side) of the pore. Consequences of this phenomenon on selectivity and permeance with model parameters of experimental relevance were investigated. Finally, we also explored the effects of pore geometry (especially ink-bottle-like structures) and surface chemistry on the separation. Comparisons with experimental results from the literature, and computationally expensive dual control volume – grand canonical molecular dynamics (DCV-GCMD) atomistic simulations, are used to put the results in perspective.

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