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

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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 CO 2, N 2, and CH 4 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 CO 2 /N 2 and CO 2 /CH 4 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 CO 2 /N 2 separation than CO 2 /CH 4 . Poly(RTIL)−RTIL composites are highly tunable materials with excellent promise as gas separation membranes.