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Investigation of gas permeation properties of film forming polymeric ionic liquids (PILs) based on polybenzimidazoles

Rupesh S. Bhavsar, Santosh C. Kumbharkar, Ulhas K. Kharul
Journal of membrane science 2014 v.470 pp. 494-503
anions, artificial membranes, carbon dioxide, cations, gases, hydrogen, ionic liquids, methane, permeability, sorption
Polymeric ionic liquids (PILs) are emerging as new generation membrane materials for CO2 separation. Gas permeation properties of a recently developed PIL family based on three structurally different polybenzimidazoles (PBIs) possessing excellent film forming characteristics are reported. Effects of cationic backbone and anions on gas permeation properties of PILs using pure gases (He, H2, N2, CH4 and CO2) were examined at 20atm upstream pressure and correlated with their physical properties. In comparison to the parent PBIs, PILs exhibited generally higher CO2 permeability, without largely affecting CO2 based selectivity. Some of these PILs exhibiting high PCO2/PCH4 selectivity and PH2/PCO2 approaching ~1 indicated dominance of CO2 sorption over diffusion. The CO2 sorption specificity of these PILs was distinctly observed based on their improved SCO2/SN2, SCO2/SCH4 and SCO2/SH2 selectivity than their parent PBIs. A large variation in permeation properties of PILs based on a common polycation but different anions indicated that anions play a crucial role on governing gas permeation properties of these PILs.