PERVAPORATION OF WATER ETHANOL MIXTURES THROUGH A POLY(ACRYLIC ACID) GRAFTED POLYETHYLENE MEMBRANE - INFLUENCE OF TEMPERATURE AND NATURE OF COUNTER-IONS

Both the permeability and the selectivity to water of poly (acrylic acid) grafted polyethylene films increase when the counter-ion is changed from Li+ to Na+ or K+. The acid membrane behaves in a singular manner: high permeability at low water contents, slight selectivity to water for ethanol-rich mixtures, reversal in selectivity at 60 wt.% of water (at 60°C) and slight selectivity to ethanol in water-rich mixtures. Both partial water and ethanol fluxes increase with pervaporation temperature, according to an Arrhenius-like relationship, but with different activation energies. The activation energy for ethanol permeation is always higher than that for water permeation, but both of them decrease with increasing water content and when the counter-ion is changed from Li+ to Na+ or K+. As a consequence, selectivity to water is strongly reduced by an increase in pervaporation temperature, especially for the K+ membrane. Most of the results can be interpreted on the basis of the extent of ionization of the carboxylate groups, and the effects of swelling on the activation energy. © 1990.