Synergistic tuning of microstructure and morphology in carbon molecular sieve hollow fibers for propylene/propane separation

Asymmetric carbon molecular sieve (CMS) hollow fiber membranes with tunable micro- and macro-structural morphologies for energy efficient propylene-propane separation are reported here. A sub-glass transition temperature (sub-Tg) thermal oxidative crosslinking strategy enables simultaneous optimization of the intrinsic molecular sieving properties while also reducing the thickness of the CMS “skin” derived from the 6FDA:BPDA/DAM polyimide precursors. Such synergistic tuning of CMS microstructure and macroscopic morphology of CMS hollow fibers enables significantly increased propylene permeance (reaching 186.5 GPU) while maintaining an appealing propylene/propane selectivity of 13.3 for 50/50 propylene/propane mixed gas feeds. Our findings reveal a more refined and versatile tool than available with previous O2-doping pretreatments. The advanced approach here should be broadly useful to other polyimide precursors and diverse gas pairs.