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

Abstract

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 H2 and He permeabilities and high gas selectivities, and the TPBI-Yb0.67@700 CMS membrane exhibited a 3-fold increase in H2 permeability and a 2-fold increase in H2/CO2 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-Yb0.67@700 membrane displayed a H2 permeability of 8648 Barrer and a mixed-gas H2/CO2 selectivity of 14.5 at 150 °C, far exceeding the experimental CMS upper bound.