Influence of polybenzimidazole main chain structure on H2/CO2 separation at elevated temperatures

Abstract Four polybenzimidazole (PBI) derivatives were prepared to study the effects of main chain chemistry and structure on H 2 /CO 2 perm-selectivity of cast films. These structural variations were designed to exhibit high localized mobility at elevated temperatures, contain rigid and bent configurations that frustrated close chain packing, or possess bulky side groups. The modified PBIs exhibited high molecular weights, slightly lower thermal stabilities, and higher organo-solubilities compared with commercial m-PBI. Dilute polymer solutions ( 2 permeability (up to 997.2 barrer) compared with m-PBI (76.81 barrer) at 250 °C and 50 psia. However, lower H 2 /CO 2 selectivities (5–7 (modified PBIs) versus 23 (m-PBI)) were also measured and reflected the general trade-off between gas permeability and selectivity. When tested at 250 °C, PBI-based materials exhibited gas separation performance higher than the Robeson upper bound prediction and are promising materials for high temperature H 2 separation from syngas.