EVIDENCE FOR PARALLEL PATHWAYS IN THE FACILITATED TRANSPORT OF ALKENES THROUGH AG-EXCHANGED NAFION FILMS()

Facilitated transmembrane fluxes for feed solutions containing 1,5-hex adiene, l-hexene, and n-hexane are reported for hydrated Ag+-Nafion me mbranes that vary in thickness between 8 and 155 mu m. Fluxes for n-he xane are virtually undetectable. Analysis of the fluxes for 1,5-hexadi ene and l-hexene suggests that two transport pathways are operating in parallel. The fluxes associated with one pathway are inversely propor tional to membrane thickness and lead to a limiting diene/monoene sepa ration factor of 47. The fluxes associated with the second pathway are independent of membrane thickness and lead to a limiting separation f actor of 100. The differences in the selecivity for the two pathways r esult in separation factors for the 8-155 mu m membranes ranging from 50 to 70. Concentrations of solutes in the membranes under equilibrium and transport conditions and the rate of 1,5-hexadiene extraction fro m membranes as a function of time are determined and are used to infer properties associated with the two pathways.