Poly(ethylene oxide)-Based Copolymer-IL Composite Membranes for CO 2 Separation.

Poly(ethylene oxide) (PEO)-based copolymers are at the forefront of advanced membrane materials for selective CO 2 separation. In this work, free-standing composite membranes were prepared by blending imidazolium-based ionic liquids (ILs) having different structural characteristics with a PEO-based copolymer previously developed by our group, targeting CO 2 permeability improvement and effective CO 2 /gas separation. The effect of IL loading (30 and 40 wt%), alkyl chain length of the imidazolium cation (ethyl- and hexyl- chain) and the nature of the anion (TFSI - , C(CN) 3 - ) on physicochemical and gas transport properties were studied. Among all composite membranes, PEO-based copolymer with 40 wt% IL3-[HMIM][TFSI] containing the longer alkyl chain of the cation and TFSI - as the anion exhibited the highest CO 2 permeability of 46.1 Barrer and ideal CO 2 /H 2 and CO 2 /CH 4 selectivities of 5.6 and 39.0, respectively, at 30 °C. In addition, almost all composite membranes surpassed the upper bound limit for CO 2 /H 2 separation. The above membrane showed the highest water vapor permeability value of 50,000 Barrer under both wet and dry conditions and a corresponding H 2 O/CO 2 ideal selectivity value of 1080; values that are comparable with those reported for other highly water-selective PEO-based polymers. These results suggest the potential application of this membrane in hydrogen purification and dehydration of CO 2 gas streams.