Exploratory development of dual-layer carbon-zeolite nanocomposite hollow fiber membranes with high performance for oxygen enrichment and natural gas separation

A type of novel precursor, namely dual-layer polyethersulfone (PES)-zeolite beta/BTDA-TDI/MDI co-polyimide (P84) composite hollow fibers, was applied to fabricate the dual-layer carbon-zeolite nanocomposite hollow fiber membranes through pyrolysis in this work. After pyrolysis at 800 °C, these newly developed nanocomposite hollow fibers exhibit a significantly enhanced O₂/N₂ and CO₂/CH₄ selectivity of 11.3 and 152, respectively, in the pure gas measurement, and meanwhile, they also show a comparable CO₂/CH₄ selectivity of 140 in the mixed gas measurement. TGA curves indicate that the presence of zeolite beta may assist the formation of carbon-zeolite nanocomposite structure in the outer layer and both outer layer and inner layer inside the dual-layer hollow fibers may experience a delayed decomposition pattern during pyrolysis compared with their corresponding single-layer membranes. After pyrolysis at 800 °C, X-ray diffraction (XRD) patterns suggest that the monolayer graphite sheets have been formed in the outer-layer carbon matrix with a d-space of 3.73 Å, scanning electron microscope (SEM) images reveal a uniform and compact dispersion of zeolite particles in the outer-layer carbon matrix, and both XRD patterns and energy dispersion of X-ray (EDX) data demonstrate the integrity of zeolite beta by an analysis of the crystalline structure and elemental composition. These above-mentioned characterizations support a conjecture from various aspects that a combining effect of carbon molecular sieve (CMS) and zeolite materials results in a remarkable improvement of dual-layer hollow fiber membranes in the performance of oxygen enrichment and natural gas separation through the molecular sieving mechanism.