Coordination enhancement of hydrogen and helium recovery in polybenzimidazole-based carbon molecular sieve membranes

Tailoring the microporous architecture of the precursors facilitates the gas separation performance in carbon molecular sieve (CMS) membranes. Herein, we report a facile strategy to tune the gas separation performance of CMS membranes through coordination between rare earth and imidazoles in the hierarchical triptycene-based polybenzimidazole (TPBI) precursor. By optimizing the pyrolysis condition and rare earth doping level, the resulting CMS membranes exhibited unprecedented H 2 and He permeabilities and high gas selectivities, and the TPBI-Yb 0.67 @700 CMS membrane exhibited a 3-fold increase in H 2 permeability and a 2-fold increase in H 2 /CO 2 selectivity compared to the TPBI-CMS@700 CMS membrane. It was demonstrated by the solution/diffusion coefficients and microporosity analysis that the enhancement of gas separation performance originated from the more pronounced hierarchically slit-like micropore structure, as well as the boosted diffusion and sorption selectivities. The TPBI-Yb 0.67 @700 membrane displayed a H 2 permeability of 8648 Barrer and a mixed-gas H 2 /CO 2 selectivity of 14.5 at 150 °C, far exceeding the experimental CMS upper bound.