The Effects of the Viscous Flow of a Gas and the Porous Structure of a Support on the Permeability of a Composite Membrane

The resistance model has been employed to derive an expression for the permeability of a composite membrane taking into account the viscous flow of a gas and the porous structure of a membrane support. Mathematical simulation has been used to show that, when the material of a selective layer does not penetrate into the pores of the skin layer of the support, the viscous flow of a gas in the support may noticeably affect the permeability and selectivity of the composite membrane, and the effect is enhanced with a decrease in the effective porosity and an increase in the permeability of the selective layer. It has been found that the influence of the porous structure of the support on the permeability of the composite membrane diminishes with a rise in the effective porosity of the support skin layer and the average pore size. The case in which selective layer material fills the pores of the support to the entire depth of the skin layer has been analyzed in detail. It has been shown that, in this case, the effect of the support on the membrane permeability is governed only by the porosity of the skin layer and the ratio between the thicknesses of the support skin layer and the selective layer.