Organic Ionic Plastic Crystal-Based Composite Membranes for Light Gas Separation: The Impact of Varying Ion Type and Casting Method.

The promise of organic ionic plastic crystals (OIPCs) for development of a novel type of gas separation membrane with competitive gas selectivity for CO2 /N2 was recently demonstrated. This work aimed to design more selective membranes by investigating a different type of OIPC and a new membrane preparation method. Two different OIPCs were solvent-cast or co-cast with poly(vinylidene difluoride) (PVDF), and their gas transport properties were compared. The first OIPC, methyl(diethyl)isobutylphosphonium hexafluorophosphate ([P122i4 ][PF6 ]), was previously studied using the co-cast method, and this was used as a benchmark. The second, N-methyl-N-ethylpyrrolidinium bis(fluorosulfonyl)imide ([C2 mpyr][FSI]), was investigated for the first time for gas separation applications, achieving high selectivities (α CO 2 / N 2 >40). The thermophysical properties of the composites indicated that the co-casting method is a good way to fabricate solid, mechanically stable and durable membranes. Additionally, the enhanced molecular interactions indicated in OIPC/PVDF co-cast composites point to a new approach for synthesis of other highly selective OIPC-based membranes.