Development of High Performance Pyrolized Polyimide‐based Carbon Molecular Sieves for Enhanced Selectivity of Propylene/Propane Gas Separation

Abstract

Abstract The replacement or de‐bottlenecking of the highly energy‐intensive distillation unit operation process for propylene/propane separation has long posed a formidable challenge. Although membrane technology can potentially offer a more energy‐efficient alternative, existing materials lack the requisite mixed‐gas selectivity for industrial use. Achieving effective separation for propylene and propane with only 0.13Å difference in molecular size requires membranes with superb molecular sieving properties. Here, we report extremely selective carbon molecular sieve (CMS) materials fabricated by utilizing a triptycene‐based intrinsically microporous 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride‐2,6(7)‐diamino triptycene (6FDA‐DAT1) polyimide precursor and adjusting its microstructure through finely tuned high‐temperature pyrolysis. A freshly prepared isotropic CMS membrane pyrolyzed at 800 °C for 2 h displayed a mixed‐gas propylene permeability of 56 Barrer combined with a C 3 H 6 /C 3 H 8 selectivity of 66. Notably, after an extended period of continuous mixed‐gas testing and aging at 4 bar over 147 days, the CMS membrane exhibited a remarkable increase in mixed‐gas propylene/propane selectivity to 152—an unmatched value to date for a CMS material—because of selective tightening of the CMS microstructure by physical aging.