Carbon Molecular Sieve Membranes Derived from Spirobifluorene-Based Microporous Polyimides for Gas Separation

Carbon molecular sieve membranes (CMSMs) have attracted growing attention in gas separation, attributed to their excellent thermal stability and chemical resistance. The structural characteristics of polymeric precursors significantly influence the pore size, pore shape, and so on, which govern gas separation performance. Herein, CMSMs with favorable gas separation performance are developed by using spirobifluorene-based polyimide precursors. The bulky rigid spirobifluorene groups effectively suppress most pore collapse during pyrolysis, endowing CMSMs with a high gas permeability. Simultaneously, most micropores (7-9 Å) shrink into ultramicropores (3-7 Å), narrowing the pore size distribution. As a result, the as-prepared CMSM shows favorable pure gas separation performance with H₂, He, and CO₂ permeabilities of 5002.9, 2017.2, and 1900.2 Barrer and corresponding α (H₂/CH₄), α (He/CH₄), and α (CO₂/CH₄) up to 1916.8, 772.9, and 728.0, respectively. Furthermore, the structural characteristics of the precursors not only influence the plate packing of CMSMs but also modulate the graphitization degree, affecting their storage stability.