Enhancement of molecular sieving and plasticization resistance of polybenzimidazole membranes through chemical crosslinking for helium recovery from multi-component natural gas

Polybenzimidazole membranes with excellent size-sieving and plasticization resistance have attracted extensive attention for helium recovery from natural gas. Herein, we present a novel approach to fabricating polybenzimidazole membranes with exceptional gas selectivities and enhanced plasticization resistance. The strategy involves in-situ crosslinking of triptycene-containing polybenzimidazole membranes using 1,3,5-benzenetricarbonyl trichloride as the crosslinking agent. The crosslinking process tightens the polymer chains, resulting in reduced inter-segmental distance and fractional free volume, which significantly boosts the He/CH₄ and He/N₂ selectivities compared to non-crosslinked triptycene-containing polybenzimidazole membranes. The TPBI@CL₂₄ membrane exhibits a high mixed-gas He/CH₄ selectivity of 465 under a ternary 0.3:49.4:50.3 He/CO₂/CH₄ (v/v/v) mixture at 100 PSIA and 35 °C. Moreover, the microporosity is feasibly tailored by controlling the crosslinking degree. Notably, the TPBI@CL_x membranes demonstrate remarkable plasticization resistance under high-pressure three-component mixed-gas feed. The TPBI@CL₂₄ membrane experiences only a 9 % decrease in the mixed-gas He/CH₄ selectivity when the feed pressure increases from 100 to 500 PSIA at 35 °C, rendering the TPBI@CL_x membranes with versatile separation performance applicable for industrial He recovery from natural gas.