Pervaporation of water-ethanol mixtures with polyacrylate-grafted polyethylene acid (PE-g-AA) membranes - Physico-chemical analysis of the transport mechanism

Polyacrylate-grafted polyethylene (PE-g-AA) membranes were studied in perva poration. The membrane performances are improved by an increase in the acry lic grafting ratio. The water and ethanol sorption and diffusion properties in the membrane loaded with different counter-ions, as well as the interac tions between the solvent and the membrane ion pairs, were measured. The re sults show that the ion pairs are preferentially solvated by water, and the water content in the liquid mixture at which the ion pair is dissociated i s much smaller for the potassium membrane than for the lithium membrane. Th e easier dissociation of the K carboxylate ion pair in the water-ethanol mi xture explains the increase in the permeability according to the sequence L i+ < Na+ < K+. The apparent contradiction between the sulfonate and the car boxylate membranes with regards to the alkaline cation sequence according t o which the permeability changes is explained by the difference in the ioni zation ability of the sulfonate and carboxylate ion pairs. (C) 2002 Elsevie r Science B.V. All rights reserved.