(699b) Vapor Phase Infiltration to Fine-Tune Micropores of Carbon Molecular Sieve Membranes to Improve Molecular Size-Sieving Ability

Carbon molecular sieve (CMS) membranes, derived from the pyrolysis of polymer precursors, possess multi-modal pore structures and thus excellent gas separation properties. However, precisely tailoring micropores of CMS membranes to push the performance to a higher level remains a formidable challenge, despite significant progress in engineering precursor architectures and optimizing pyrolysis conditions. In this study, we present a novel and facile approach of fine-tuning CMS micropores at an atomic level through vapor phase infiltration (VPI), illustrated by polybenzimidazole (PBI)-derived CMS membranes for H₂/CO₂ separation and 6FDA-DAM-derived CMS membranes for C₃H₆/C₃H₈ separation. During the VPI process, CMS was exposed to a trimethylaluminum (TMA) vapor, allowing it to infiltrate the micropores and react with water vapor to generate AlO_x molecules on the pore surface. By controlling the TMA exposure time and cycle number, micropores were precisely tuned at the atomic level to exhibit strong size-sieving ability even on those CMS membranes carbonized at low temperatures (500 – 600 °C). For instance, a PBI CMS membrane carbonized at 550 °C exhibits a remarkable increase in H₂/CO₂ selectivity from 10 to 61 at 100 °C with just one VPI cycle. Importantly, this sample demonstrates stable and outstanding H₂/CO₂ separation performance under simulated practical conditions, surpassing the upper bounds and outperforming most CMS materials. Moreover, 6 VPI cycles for 6FDA-DAM derived CMS increase C₃H₆/C₃H₈ selectivity from 16 to 67 at 35 °C though C₃H₆ permeability decreased from 570 to 80 Barrer. The successful fine-tuning of micropores achieved in this study underscores the versatility of the VPI process in engineering porous membranes.