Preferential Sorption versus Preferential Permeability in Pervaporation*
نویسندگان
چکیده
Transport 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
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