A facilitated transport ion-gel membrane for propylene/propane separation using silver ion as a carrier

Facilitated transport membranes are effective for gas separations but they have some disadvantages, such as leakage of the carrier solution under pressure and volatilization of solvents from the membrane. In this study, a novel gas separation membrane, a facilitated transport ion-gel membrane, with high permselectivity, high stability and high pressure tolerance was fabricated using a gelled ionic liquid with a selective-transport carrier for the target gas. Imidazolium type-ionic liquids, silver salts, and low molecular weight gelators were used to fabricate the ion-gel membrane. Gas absorption isotherms of the ion-gels were measured and studied using a theoretical model considering both physical and chemical absorption. It was found during absorption tests that some gelators deactivated the function of silver ions as a propylene carrier. In addition, gas permeation through ion-gel membranes was analyzed by applying an absorption model that accounted for the decrease in diffusivity caused by gelation of the ionic liquid. Theoretical analysis indicated that the fabricated ion-gel membranes transported propylene via a facilitated transport mechanism and thus facilitated transport ion-gel membranes were successfully fabricated. This is the first report describing the fabrication of facilitated transport ion-gel membranes.