Evidence for parallel pathways in the facilitated transport of alkenes through Ag+-exchanged nafion films

Facilitated transmembrane fluxes for feed solutions containing 1,5-hexadiene, l-hexene, and n-hexane are reported for hydrated Ag+-Nafion membranes that vary in thickness between 8 and 155 mu m. Fluxes for n-hexane are virtually undetectable. Analysis of the fluxes for 1,5-hexadiene and l-hexene suggests that two transport pathways are operating in parallel. The fluxes associated with one pathway are inversely proportional to membrane thickness and lead to a limiting diene/monoene separation factor of 47. The fluxes associated with the second pathway are independent of membrane thickness and lead to a limiting separation factor of 100. The differences in the selecivity for the two pathways result 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 from membranes as a function of time are determined and are used to infer properties associated with the two pathways.