Precarbonization Structural Regulation in CMS Membranes via Volatile Small Molecules for Enhanced Gas Separation

Abstract

Carbon molecular sieve (CMS) membranes hold substantial promise for energy-efficient gas separation. A novel membrane formation regulation strategy was developed by introducing ammonium acetate (AA) into a 6FDA-TMPD polyimide (PI) precursor to tailor precursor chain packing and carbon microstructure evolution in CMS membranes. During membrane formation and thermal treatment, the volatilization and removal of AA loosened PI chain packing (d-spacing from 5.66 to 5.87 Å) and optimized free-volume distribution, which further promoted favorable carbon layer stacking, as well as abundant micropore and ultramicropore formation. By optimizing AA content and carbonization temperature, the optimal CMS membrane with 10 wt % AA at 550 °C (PI-10AA-550) delivered significantly enhanced gas permeabilities (H2 = 11580.1 ± 363.4 Barrer, CO2 = 7065.6 ± 103.7 Barrer) and selectivities (H2/CH4 = 102.9 ± 4.1, CO2/CH4 = 62.8 ± 2.1), surpassing the state-of-the-art upper bounds. Moreover, the membrane showed excellent anti-aging property and long-term stability over 28 days of operation, demonstrating considerable potential for efficient H2 and CO2 separation.