Poly(ethylene oxide)-Based Copolymer-IL Composite Membranes for CO2 Separation

Poly(ethylene oxide) (PEO)-based copolymers are at the forefront of advanced membrane materials for selective CO2 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 CO2 permeability improvement and effective CO2/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 CO2 permeability of 46.1 Barrer and ideal CO2/H-2 and CO2/CH4 selectivities of 5.6 and 39.0, respectively, at 30 degrees C. In addition, almost all composite membranes surpassed the upper bound limit for CO2/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 H2O/CO2 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 CO2 gas streams.

Automated summary

This study prepared free-standing composite membranes by blending imidazolium-based ionic liquids (ILs) with a previously developed PEO-based copolymer, aiming to improve CO2 permeability and CO2/gas separation. The effect of IL loading, alkyl chain length, and anion nature on physicochemical and gas transport properties were investigated. The PEO-based copolymer with 40 wt% IL3-[HMIM][TFSI] exhibited the highest CO2 permeability and CO2/H2 and CO2/CH4 selectivities. The membrane also showed high water vapor permeability and H2O/CO2 ideal selectivity, suggesting potential applications in hydrogen purification and CO2 gas stream dehydration.