(376p) Synthesis and Techno-Economic Analysis of Novel Facilitated Transport Membrane for Post-Combustion Carbon Capture
Large-scale application of membrane in post-combustion carbon capture has been limited by the trade-off between CO2 permeance and CO2/N2 selectivity of most polymeric membrane materials. In order to overcome this limitation, research efforts on facilitated transport membrane (FTM) have been devised with the objectives of (1) developing carriers with high CO2 loading capacity and reactive diffusivity, and (2) designing membrane processes that can capitalize on the outstanding selectivities shown by FTM. In this presentation, novel FTM was synthesized in a composite membrane configuration with an 170 nm selective layer coated on a polyethersulfone nanoporous substrate. In the selective layer, polyvinylamine with amine-sites covalently bound to the polymer backbone was used as fixed-site carrier and an amino acid salt, synthesized by deprotonating sarcosine with 2-(1-piperazinyl)ethylamine, was blended as mobile carrier. The membrane demonstrated a CO2 permeance of 1500 GPU (1 GPU = 10-6 cm3 (STP)·cm-2·s-1·cmHg-1) and a CO2/N2 selectivity >140 at 67 °C with 1 atm feed and permeate pressures. Two membrane processes were designed for the FTM to decarbonizing coal derived flue gas with 90% CO2 recovery. In the first membrane process, i.e., air sweep process, the flue gas flowed to a vacuum membrane stage to produce a >95% pure CO2 permeate; the remaining CO2 was removed by an air-sweep membrane stage. The CO2-laden sweep air was fed to a power plant boiler as combustion air. In the second membrane process, i.e., retentate recycle process, the flue gas was passed to two membrane stages in an enriching cascade. A portion of the CO2-depleted retentate of the first membrane stage was recycled as its own sweep gas, while a vacuum was pulled for the second membrane stage. Both membrane processes yielded a capture cost <40/tonne CO2 in the 2007 dollars, which met the target set by the Department of Energy (DOE) for 2025. A common element in these two processes was a vacuum membrane stage with a permeate pressure as low as 0.3 atm. Under this testing condition, however, the elastic selective layer of the synthesized FTM sunk into the nanoporous substrate, which resulted in a drastically reduced CO2 permeance. To address this issue, multi-walled carbon nanotubes (MWNTs) wrapped by a copolymer poly(vinylpyrrolidone-co-vinyl acetate) were dispersed in the selective layer as reinforcement fillers. The gas permeation measurements showed that the incorporation of MWNTs strengthened the polymer matrix and the selective layer penetration was refrained by a 3 wt.% MWNTs loading. The presence of MWNTs also mitigated the polymer compaction if the feed gas was compressed. The reinforced membrane demonstrated stable separation performance for a feed pressure up to 4 atm with a vacuum of 0.3 atm pull on the permeate side.