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 that these membranes, Like Nafion(R) [P.M. Thoen, R.D. Noble, C.A. Coval, Unexpectedly large selectivities for olefin separations utilizing silver ion in ion-exchange membranes, J. Phys. Chem. 98 (1994) 1262], show 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 angle X-ray scattering (SAXS) analyses confirmed that, Like Nafion(R), Neosepta(R) membranes have hydrophilic sulfonate regions on the size scale 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-olefins over mono-olefins. For instance, Neosepta(R) CM-1 membranes separate 1,5-hexadiene from 1-hexene with a separation factor of about 70. However, less competitive suppression of the 1-hexene flux by 1,5-hexadiene is seen in the Neosepta(R) membranes than in the Nafion(R) membranes. The following work correlates the morphological characteristics of Nafion(R) and Neosepta(R) membranes to transport through these membranes in order to gain a better understanding of facilitated olefin transport within silver(I)-based systems. (C) 1998 Elsevier Science B.V.