High-performance carbon molecular sieving membrane derived from a novel hydroxyl-containing polyetherimide precursor for CO2 separations

Carbon molecular sieve (CMS) membrane with high CO2 separation performance were fabricated by pyrolysis of a novel hydroxyl-containing polyetherimide (BAHPPF-6FDA type HPEI) precursor. The thermal reactive ortho-OH group in HPEI resulted in the structural conversion when thermal treated at 450 °C, which simultaneously improved the chain rigidity and FFV of the precursor membrane. The structural evolution from HPEI precursor to intermediate polymer till CMS membrane was detected via TGA-MS, Py-GC/MS, FT-IR and WAXD. The pore structure, CO2 separation performance and aging behavior of CMS membranes were characterized and analyzed by physisorption and gas permeation measurements. Results indicated that the structural properties of the intermediate TR-polymers, which depend on the thermal treatment protocol, have an obvious influence on the CMS membrane performance. Increased thermal soak time of HPEI at 450 °C leads to the increased chain rigidity and FFV, resulting in a more open pore structure and higher CO2 permeability of derived CMS membranes. In addition, the prolonged soak time at 450 °C or increased pyrolysis temperature would result in the shrinkage of pore structure in CMS membranes and the enhanced molecular sieving performance. The high permeation CMS membrane prepared at the optimal thermal treatment protocol shows good performance stability under the mixed gas (50:50 mixture of CO2/N2 or CO2/CH4) feeds. The relative high CO2 permeability of about 10000 Barrer and CO2/N2 (or CH4) selectivity over 30 were obtained after 60 days aging under vacuum, which exhibits a good potential for CO2 separation application.