ROLE OF ION-EXCHANGE MEMBRANE MORPHOLOGY AND SORPTION PROPERTIES IN FACILITATED TRANSPORT DI-OLEFIN MONO-OLEFIN SEPARATIONS/

Our research using silver-exchanged Neosepta(R) membranes has shown th at these membranes, Like Nafion(R) [P.M. Thoen, R.D. Noble, C.A. Coval , Unexpectedly large selectivities for olefin separations utilizing si lver ion in ion-exchange membranes, J. Phys. Chem. 98 (1994) 1262], sh ow high selectivities in certain important olefin separations. However , differences in absorption and transport properties between these two types of membranes have been observed, which we believe are caused by the morphological differences between these two membranes. Small angl e X-ray scattering (SAXS) analyses confirmed that, Like Nafion(R), Neo septa(R) membranes have hydrophilic sulfonate regions on the size scal e of Il nm in diameter interspersed with hydrophobic polymer regions. Also, di-olefin/mono-olefm separation studies show that, Like Nafion(R ), Neosepta(R) membranes have a high transport selectivity for di-olef ins over mono-olefins. For instance, Neosepta(R) CM-1 membranes separa te 1,5-hexadiene from 1-hexene with a separation factor of about 70. H owever, less competitive suppression of the 1-hexene flux by 1,5-hexad iene is seen in the Neosepta(R) membranes than in the Nafion(R) membra nes. The following work correlates the morphological characteristics o f Nafion(R) and Neosepta(R) membranes to transport through these membr anes in order to gain a better understanding of facilitated olefin tra nsport within silver(I)-based systems. (C) 1998 Elsevier Science B.V.