A high-flux polyimide hollow fiber membrane to minimize footprint and energy penalty for CO2 recovery from flue gas

Using a process-guided approach, a new 6FDA-based polyimide — 6FDA–DAM:DABA(4:1) — has been developed in the form of hollow fiber membranes for CO2 recovery from post-combustion flue gas streams. Dense film studies on this polymer reveal a CO2 permeability of 224 Barrers at 40 °C at a CO2 feed pressure of 10 psia. The dense films exhibit an ideal CO2/N2 permselectivity of 20 at 40 °C, which permits their use in a two-step counter-flow/sweep membrane process. Dry-jet, wet-quench, non-solvent-induced phase inversion spinning was used to create defect-free hollow fibers from 6FDA–DAM:DABA(4:1). Membranes with defect-free skin layers, approximately 415 nm thick, were obtained with a pure CO2 permeance of 520 GPU at 30 °C and an ideal CO2/N2 permselectivity of 24. Mixed gas permeation and wet gas permeation are presented for the fibers. The CO2 permeance in the fibers was reduced by approximately a factor of 2 in feeds with 80% humidity. As a proof-of-concept path forward to increase CO2 flux, we incorporated microporous ZIF-8 fillers into 6FDA–DAM:DABA(4:1) dense films. Our 6FDA–DAM:DABA(4:1)/ZIF-8 dense film composites (20 wt% ZIF-8) had a CO2 permeability of 550 Barrers and a CO2/N2 selectivity of 19 at 35 °C. Good adhesion between the ZIF and the 6FDA–DAM:DABA(4:1) matrix was observed. CO2 capture costs of $27/ton of CO2 using the current, “non-optimized” membrane are estimated using a custom counterflow membrane model. Hollow fiber membrane modules were estimated to have order-of-magnitude reductions in system footprint relative to spiral-wound modules, thereby making them attractive in current space-constrained coal-fired power stations.