High-Performance Carbon Molecular Sieve Membranes Derived from a Cross-Linked Polyimide

We report a high-performance carbon molecular sieve (CMS) membrane derived from a novel three-dimensional cross-linked polyimide (CBPI) synthesized from self-made triamine (1,3,5-triple (2-trifluoromethyl-4-aminobenzyl) benzene [TFAPOB]), cyclopentanone bis-spirocyclobutane tetracarboxylic dianhydride (CpODA), and 4,4-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA). The unique cross-linked and fluorinated structure of CBPI endows the precursor with high thermal stability and enables the formation of an ultramicroporous, graphitized carbon framework with a tunable pore structure upon controlled pyrolysis. Optimized carbonization at 550 °C yields a CBPI-550 CMS membrane offering exceptional CO2 (3038.3 Barrer) and H2 (4325.8 Barrer) permeability, with CO2/CH4 and CO2/N2 selectivities reaching the 2019 Robeson upper bounds. At higher temperatures, H2/CH4 and H2/N2 selectivities exceed the 2015 bounds. Structural characterization (e.g., XRD, Raman, etc.) links this performance evolution to increased graphitization, reduced interlayer d-spacing, and narrowed pore-size distribution. Moreover, the membranes demonstrate promising stability and adaptability under varying operational conditions, highlighting their potential for practical CO2 capture and H2 purification.