PREFERENTIAL SORPTION IN ION-EXCHANGE PERVAPORATION MEMBRANES - SORPTION OF WATER-ETHANOL MIXTURE BY SODIUM POLYETHYLENE SULFONATE

Sorption of water and ethanol from aqueous ethanol solutions by sulpho nated polyethylene membrane is studied both theoretically and experime ntally, particular attention being paid to the effect of ionogenic-gro up content (capacity) on the sorption and sorption selectivity. A theo retical model is proposed based on models of salting-out and swelling of ion-exchangers. Examination of the experimental results obtained us ing the isopiestic method reveals a satisfactory agreement with the mo del, i.e. with a modified BET equation for sorption of water and a mod ified Setschenow equation for salting-out. Based on the results of thi s study, the following conclusions may be drawn: sorption selectivity toward water increases as capacity increases; the per equivalent uptak e of water is determined primarily by water activity in the outside so lution and the presence of ethanol plays only a minor role; the osmoti c effect associated with deformation of the matrix has a negligible in fluence on selectivity. The model makes it possible to estimate sorpti on selectivity and may have applications in the calculation of pervapo ration membrane performance. The sorption of water by the polymer was found to be far more pressure-dependent than that expected from thermo dynamics, presumably due to the nonelastic behavior of the noncrosslin ked polyethylene matrix.