Hyperaging Tuning of a Carbon Molecular-Sieve Hollow Fiber Membrane with Extraordinary Gas-Separation Performance and Stability

This study reports 6FDA:BPDA-DAM polyimide-derived hollow fiber carbon molecular-sieve (CMS) membranes for hydrogen and ethylene separation. Since H₂/C₂H₄ selectivity is the lowest among H₂/(C₁-C₃) hydrocarbons, an optimized CMS fiber for this gas pair is useful for removing hydrogen from all-cracked gas mixtures. A process we term hyperaging provides highly selective CMS fiber membranes by tuning CMS ultramicropores to favor H₂ over larger molecules to give a H₂/C₂H₄ selectivity of over 250. Hyperaging conditions and a hyperaging mechanism are discussed in terms of an expedited physical aging process, which is largely controlled by the hyperaging temperature. For the specific CMS material considered here, a hyperaging temperature beyond 90 °C but less than 250 °C works best. Hyperaging also stabilizes CMS materials against physical aging and stabilizes the performance of H₂ separation over extended periods. This work opens a door in the development of CMS materials for the separation of small molecules from large molecules.