Polybenzimidazole based random copolymers containing hexafluoroisopropylidene functional groups for gas separations at elevated temperatures

• Synthesized PBI copolymers containing hexafluoroisopropylidene diphenyl and phenylene groups.
• Reported H2 perm-selectivity character of PBI-based copolymer membranes.
• Demonstrated ability to control H2 permeability and H2/CO2 selectivity by varying copolymer ratio.

Polybenzimidazoles (PBIs) are attractive membrane materials for H2/CO2 separation at hydrocarbon fuel derived synthesis gas operating conditions due to their exceptional physicochemical stability and promising permselectivity character. PBI molecular structure modification is a viable approach to disrupt chain packing altering the free-volume architecture which results in improved gas transport characteristics. This work is focused on the synthesis and characterization of novel PBI random copolymers for application as elevated temperature H2/CO2 membranes. The co-polymerization route is expected to result in tailorable permeability and selectivity by combining the high H2 permeability aspect of the highly disrupted loosely packed hexafluoroisopropylidene diphenyl group containing PBI segments (6F-PBI) with the highly selective tightly packed phenylene group containing PBI segments (m-PBI). 6F/m-PBI copolymers with varying 6F-PBI and m-PBI ratios having high inherent viscosity were synthesized. The structure and ratio of the 6F- and m-PBI fractions were confirmed using FTIR and NMR spectroscopic techniques. The measured gas transport properties of copolymer thin films cast in controlled environment were measured as a function of the operating conditions. The H2 permeability increased while H2/CO2 selectivity decreased as the 6F-PBI copolymer fraction was increased.

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