(428d) Nano-Confined Ionic Liquid Membranes Operated Under Water Vapor Sweep Mode for Greatly Boosting CO2 Capture Efficiency from Natural Gas Flue Gas

Membrane separation has attracted significant attention for CO₂ capture from flue gas because of its potentially lower energy consumption. Among all the membranes, facilitated transport membrane (FTM) is one of the promising candidates for highly efficiently separating low-concentration CO₂ from other inert gases, especially with the aid of water vapor. However, the loss of active species incorporated within FTM is always an issue. Amino acid ionic liquids (AAILs) may serve as an ideal active species for CO₂ transport due to their negligible vapor pressure, excellent thermal stability, and amino functional group in cation that can reversibly react with CO₂. To apply ionic liquid into membrane, we designed and fabricated a nano-confined structure utilizing a single-walled carbon nanotube and nitrogen-doped graphene oxide quantum dot (SWCNT/N-GOQD) to fix AAIL. The nano-confined space, modified by trapped N-GOQDs in SWCNT mesh, ensures excellent mechanical stability of infiltrated AAIL. To maximize the facilitated transport capability of AAIL, water vapor was used to sweep the permeate side of membrane. In this case, the introduction of water vapor also balanced the water partial pressure on both sides of NCIL membrane and further stabilized NCIL membrane. The influence of water sweeping rate, relative humidity, feed flow rate, and permeate pressure on AAIL membrane separation performance was evaluated. Rationally designed AAIL membranes with regulated confinement effect exhibited excellent CO₂ separation performance with CO₂ permeance >2,000 GPU and CO₂/N₂ selectivity >1,500 for simulated natural gas flue gas separation. Separation performance of a 75-cm² AAIL membrane with stage cut was also evaluated, demonstrating one-step enrichment of CO₂ from 4% to 95% (dry-base purity) with as high as 90-97% CO₂ capture rate for over 50 hours. We expect this “nano-confined” platform might provide new opportunities for developing membranes with high selectivity for highly efficient CO₂ capture from flue gas.