(293a) New Facilitated Transport Membrane and Process for CO2 Capture from Flue Gas

Application of membrane for CO₂ capture from flue gas has been limited by the trade-off between CO₂ permeance and CO₂/N₂ selectivity for most polymeric membrane materials. To overcome this limitation, we have studied the facilitated transport membrane (FTM) possessing both high permeance and selectivity and designed a membrane process that can capitalize on high-selectivity offered by FTM. We have elucidated the carrier saturation phenomenon, characteristic of FTMs, using a new FTM containing the aminoacid salt of 2-(1-piperazinyl)ethylamine sarcosinate as mobile carrier and polyvinylamine as fixed-site carrier. The membrane was used to fabricate 1.4-m² spiral-wound modules, which exhibited a CO₂ permeance of 1450 GPU and a CO₂/N₂ selectivity of 185 at 67°C with actual coal-derived flue gas at the National Carbon Capture Center (NCCC) in Wilsonville, AL, USA. Furthermore, a significant increase in CO₂ permeance has been achieved upon the bulk removal of CO₂ for the range of CO₂ partial pressures relevant to carbon capture from coal flue gas. For instance, the CO₂ permeance increased from 1464 to 1918 GPU when the CO₂ partial pressure reduced from 74.1 to 3.9 kPa at 67°C. Such a carrier saturation phenomenon has been modeled and incorporated into a novel 2-stage membrane process featuring partial retentate recycle. As the bulk CO₂ removal reduces the CO₂ partial pressure gradually in the membrane module, this feature mitigates the carrier saturation and results in an uprising CO₂ permeance upon the CO₂ removal. In addition, an integrated skid of the 2-stage membrane process was tested at the NCCC with an actual natural gas flue gas, demonstrating 90 – 99% CO₂ capture degrees, all with ≥95% purity (on dry basis), during the parametric testing and at steady state for 500 h cumulatively with 91.0% CO₂ capture and >95% CO₂ purity.