Unexpectedly Strong Size-Sieving Ability in Carbonized Polybenzimidazole for Membrane H2/CO2Separation

Polymers with high permeability and strong size-sieving ability are needed for H2/CO2separation at temperatures ranging from 100 to 300 °C to enable an energy-efficient precombustion CO2capture process. However, such polymers usually suffer from a permeability/selectivity tradeoff, that is, polymers with high permeability tend to exhibit a weak size-sieving ability and thus low selectivity. Herein, we demonstrate that carbonization of a suitable polymer precursor (i.e., polybenzimidazole or PBI) generates microcavities (leading to high H2permeability) and ultramicroporous channels (leading to strong size-sieving ability and thus high H2/CO2selectivity). Specifically, carbonization of PBI at 900 °C (CMS@900) doubles H2permeability and increases H2/CO2selectivity from 14 to 80 at 150 °C. When tested with simulated syngas-containing equimolar H2and CO2in the presence of water vapor for 120 h, CMS@900 exhibits stable H2permeability of ≈36 barrer and H2/CO2selectivity of ≈53 at 150 °C, above Robeson’s 2008 upper bound and demonstrating robustness against physical aging and CO2plasticization.