Effect of Anion on Gas Separation Performance of Polymer-Room-Temperature Ionic Liquid Composite Membranes

Composite gas separation membranes were fabricated by photopolymerization of a room-temperature ionic liquid (RTIL) monomer in the presence of 20 mol % of nonpolymerizable RTILs with various anions. The solid, composite membranes contained polymer-bound cations, "free" cations, and "free" anions. The composite materials exhibit no phase separation between these components. The permeabilities of CO2, N-2, and CH4 in these poly(RTIL)-RTIL composites were observed to increase by 2-5 times relative to those in the neat poly(RTIL) without a "free" RTIL component. These largely increased permeabilities resulted in CO2/N-2 and CO2/CH4 ideal separation selectivities that were only slightly diminished relative to the poly(RTIL) without a "free" RTIL. When viewed on "Robeson plots", poly(RTIL)-RTIL composites are shown to be more favorable for CO2/N-2 separation than CO2/CH4. Poly(RTIL)-RTIL composites are highly tunable materials with excellent promise as gas separation membranes.