Microporous pentiptycene-based polybenzimidazole membranes for high temperature H2/CO2 separation

Separating H2 from syngas at elevated temperatures (100-250 degrees C) have attracted significant attention in recent years as a means to reduce energy consumption and capital costs in precombustion carbon capture processes, such as those following steam reforming of natural gas or coal gasification. Polybenzimidazole (PBI), particularly m-PBI, has been reported as a leading membrane material for high-temperature H2/CO2 separation. However, m-PBI exhibits extremely low H2 permeability, even at high temperatures, which limits its productivity in H2/CO2 separation applications. To address this limitation, this work introduces a new pentiptycene-based polybenzimidazole (PPBI) featuring significantly enhanced H2 permeability and attractive high-temperature H2/CO2 separation performance, which stems from the unique configurational free volume elements introduced by pentiptycene moieties. Further tuning of the free volume architecture of PPBI films is achieved via acid doping with phosphoric acid (PA) or trans-aconitic acid (TaA), which introduces crosslinking among PPBI chains. Under mixed-gas environment (50/50 mol% H2/CO2) at 180 degrees C, the acid-doped PPBI films exhibit a-230 % increase in H2/CO2 selectivity compared to pristine PPBI film while maintaining high H2 permeability that is nearly 500 % of m-PBI. These properties approach the predicted upper bound for membrane operating at 180 degrees C, highlighting its great potential for high-temperature H2/CO2 separation.