SWELLING AND THICKNESS EFFECTS ON THE SEPARATION OF STYRENE AND ETHYLBENZENE BASED ON FACILITATED TRANSPORT THROUGH IONOMER MEMBRANES

The substitution of silver ion for sodium ion in hydrated ionomer membranes causes the transmembrane fluxes for styrene (STY) and ethylbenzene (EBZ) to increase by 2-3 orders of magnitude. These flux increases result from the reversible interaction of STY and EBZ with silver ion in the membrane (facilitated transport). Separation factors of STY/EBZ for thick membranes (approximately 25 and 175-mu-m thick) have been previously reported to range from 8 to 36. Treatment of the 175-mu-m membranes with glycerine at elevated temperatures causes a permanent expansion of the membrane structure (swelling), which increases diffusion coefficients by 1 order of magnitude. The heat-treated membranes have higher water contents resulting in lower silver ion concentrations and diminished STY/EBZ separation factors. Cast ionomer membranes of approximately 2.5 and 5-mu-m in thickness display permeate fluxes that are 2-100 times greater than those observed for the non-heat-treated commercial membranes while STY/EBZ separation factors are maintained near 10.