High-Performance Carbon Molecular Sieve Membrane Derived from a Crown Ether-Containing Co-Polyimide Precursor for Gas Separation

A carbon molecular sieve (CMS) membrane was prepared via a co-polyimide precursor containing a crown ether segment. Two elements ensured that the CMS membrane achieved both high permeability and selectivity: (1) preferential decomposition of the crown ether segment at relative low temperature and (2) the transformation of a pore structure from a micropore (>7 Å) to an ultra-micropore (<7 Å) at a higher-temperature pyrolysis. A BET analysis showed the CMS membrane formed a micropore below 500 °C. Then, the micropore structure gradually transformed to an ultra-micropore when the heat-treatment temperature raised to 500 and 650 °C, followed by formation of a single-distribution ultra-micropore pyrolyzed at 800 °C. The performance of membranes treated at 650 and 800 °C surpassed the 2015 upper bound for H₂ separation and the 2019 upper bound for CO₂ separation. Furthermore, the membrane treated at 650 °C exhibited remarkable mixed-gas separation performance and possessed a CO₂ permeability of 7266.4 ± 22.85 to 7496.3 ± 22.34 barrer and a CO₂/N₂ (20/80, vol%) and CO₂/CH₄ (10/90, vol%) selectivity of ∼60.