Geometric Restriction of Gas Permeance in Ultrathin Film Composite Membranes Evaluated Using an Integrated Experimental and Modeling Approach

Abstract

Gas permeation through ultrathin film composite (uTFC) membranes can be restricted by the pore size and porosity of the porous supports, resulting in a reduction in permeance. Although this geometric restriction has been demonstrated using empirical and computational models, a systematic experimental validation of the models is still lacking. This study addresses the gap by preparing a series of uTFC membranes comprising glassy perfluoropolymers (such as Teflon AF1600 and Hyflon AD80) as selective layers on top of a commercial poly­(ether sulfone) (PES) microporous support and investigating the effects of the surface morphology and selective layer thickness on the gas permeance. The geometric restriction resulting from the porous support becomes more severe as the selective layer becomes thinner. For example, the PES support decreased the gas permeance of a 100-nm-thick Hyflon AD80 film by as much as 42%. The experimental data agreed well with the modeling results, which convincingly confirms that porous supports with high porosity and small pores are needed to prepare high-flux uTFC membranes. This study also provides a nonintrusive method for determining the pore size and porosity of support surfaces, despite their great nonuniformity.

Effect of Support on Gas Transport Properties of PTMSP/UFFK and PTMSP/MFFK-1 Composite Membranes

“…In the study, we determined the permeabilities of individual gases through the supports. These results were analyzed using the "dusty gas" model [1,11,12], in which the gas flux through unit surface of a porous support is described by the following expression 10 µm 1 0 µm and are the structural parameters of the porous substrate, R is the gas constant, T is the temperature, M and are respectively the molecular weight and viscosity of the gas, and and and are the differential and average pressure of the gas on the support.…”

“…In [1,2], to assess the influence of supports on the permeance of composite membranes, it was proposed to additionally use the parameter which characterizes the deviation of the permeance of the composite membrane from that of a polymer coating the support layer. Obviously, such an approach allows one to only qualitatively judge the degree of influence of the support on the permeance of the composite membrane and does not take into account possible changes in the porous structure of the support and, as a consequence, its permeability due to the possible penetration of the polymer that forms the selective layer on the surface of the support skin layer.…”

“…Assuming that the gas flow through the composite membrane is one-dimensional and the polymer layer is free of defects, the basic equation for gas transport through the composite membrane in the resistance model has the form (1) where are the gas permeabilities through the composite membrane, the polymer layer, and the support, respectively.…”

Lithium chloride (LiCl)-modified polyethersulfone (PES) substrate surface pore architectures on thin poly(dimethylsiloxane) (PDMS) dense layer formation and the composite membrane's performance in gas separation

“…4 Based on the literature evaluation of the inuence of porous substrate's surface pore architectures on the composite membrane formation and performance, minimal lateral diffusion can be achieved by substrates with high surface porosity and pore density but low surface pore sizes. 4,8,13 On the other hand, similar characteristics can increase the effect of pore penetration by capillary action and surface wetting, depending on the chemistry of the coating solution and its underlying substrate. 7,14 Together with the increased gas ow resistance of smaller pore-sized membranes, 15 choosing substrates for composite membrane gas separation with optimum surface morphologies can become complicated.…”

“…16 Nevertheless, membrane fabrication methodology for waterbased application has rarely studied the gas permeability of these membranes, [17][18][19] while composite membrane gas research that uses commercial samples does not provide an insight into the fabrication methodology of these substrates in terms of materials and modications involved, which can make it a good substrate. 13 Hence, the inuence of pore forming agents, usually used as hydrophilic additives for porous membrane formation in water-based application, is relatively unknown when used as porous substrates for composite membrane gas separation. D. Wu et al (2018) tried to elucidate this idea by blending PES with hydrophilic additives to manipulate its interfacial properties and surface morphology.…”