Post-combustion carbon dioxide capture via 6FDA/BPDA-DAM hollow fiber membranes at sub-ambient temperatures

Post-combustion carbon dioxide capture has the greatest near-term potential compared to other technological pathways to mitigate CO2 emissions. The hybrid membrane and cryogenic distillation process developed at American AirLiquide allows sub-ambient temperature (−50 °C to −20 °C) CO2 capture to be cost effective. In previous work, Matrimid® hollow fiber membranes with so-called “nodular” selective layers were successfully formed and showed a combination of high selectivity and high permeance at temperatures below −20 °C. Despite good performance, considering the low CO2 concentration and large volume of flue gas to be treated, the permeance of the “nodular” Matrimid® fibers still required improvement. In this work, a new membrane material with higher fractional free volume than Matrimid®, 6FDA/BPDA-DAM (1:1), was investigated for sub-ambient temperature (SAT) CO2 capture. Defect free 6FDA/BPDA-DAM hollow fiber membranes were successfully formed; however, the bare fibers lost selectivity at temperatures below 0 °C, possibly due to the development of minor defects in the thin selective layer. This problem was corrected by post-treatment with polydimethyl siloxane (PDMS). The PDMS post-treated 6FDA/BPDA-DAM hollow fiber membranes displayed much higher permeance than the Matrimid® fibers with a high selectivity. The high selectivity is presumably due to additional polymer backbone rigidity at SAT conditions combined with possible local chain orientation; and the high permeance is believed to be a result of hindered packing of the polymer backbone.