Preferential sorption versus preferential permeability in pervaporation

Abstract

SummaryTransport of liquids by pervaporation takes place by a solution-diffusion mechanism. In order to investigate the "solution part" of this transport model, preferential sorption has been compared with preferential permeability. Sorption equilibria and pervaporation experiments for the systems water-ethanol-cellulose acetate, water-ethanol-polyacrylonitrile and water-ethanol-polysulfone have been investigated. Theoretical values of preferential sorption have been derived from Flory-Huggins thermodynamics, extended with concentration dependent interaction parameters. These calculated sorption values show a reasonable agreement with experimental values. The large difference in molar volumes between water and ethanol determines the preferential sorption of water in these systems to a great extent, and this effect increases with decreasing swelling value. Comparison of preferential sorption experiments with pervaporation experiments indicates that, apart from the effect of differences m diffusivity for the permeating components, preferential sorption contributes to a major extent to selective transport

A rationale for the preparation of asymmetric pervaporation membranes

“…The interaction parameters are taken from Altena and SmoldersB and Mulder et a1. 32 The g,, parameters for both water/acetone and water/ DMSO as a function of the volume fraction of water are given in Figure 6. If the g,, parameter is large (i.e., a high value for the excess free energy of mixing and a low mutual affinity), the binodal demixing gap is shifted to higher nonsolvent concentrations while for low g,, values (i.e., low or negative values for the free energy of mixing) the binodal is shifted to lower nonsolvent content.…”

Segmented network structures for the separation of water/ethanol mixtures by pervaporation

“…Attempts have been made to describe this complex e †ect in a quantitative way. 27,28 Considering the degrees to which di †erent membranes swell in water, in ethanol and in the solvent mixture with 20% of water ( Table 2), it can be concluded that the presence of polyDXL plays a predominant role in the coupling e †ect. Indeed, only for membranes which contain polyDXL segments, is a maximum in the swelling curve detected at an intermediate composition of water and ethanol.…”

Permeation of methanol/methyl-t-butyl ether mixtures through poly(ethylene-co-vinyl acetate) films

“…The solubility in the polymer depends on different factors: the molar volume of the penetrant, the affinity with the polymer and the mutual interactions between the penetrants [18].…”