Ultra-selective membrane composed of charge-stabilized fixed carrier and amino acid-based ionic liquid mobile carrier for highly efficient carbon capture

Membrane technology has been extensively studied for CO₂ capture applications, especially for flue gas sources. In the past decades, facilitated transport membranes (FTMs) have made breakthroughs overcoming the permeance-selectivity trade-off upper bound restricting traditional CO₂ separation membranes, but are still facing challenges towards practical applications, including limited performance, such as insufficient CO₂/N₂ selectivity to achieve 95 % CO₂ dry-base purity by one step separation, and long-term stability. Herein, we designed and fabricated a novel FTM structure containing an ionic liquid (1-ethyl-3-methylimidazolium aminoacetate, [Emim][Gly]) as mobile CO₂-carrier and a polymeric amine (polyethyleneimine, PEI) as fixed CO₂-carrier. The fixed carrier is confined within a carbon nanotube (CNT) framework of 230 nm thickness via electrostatic forces adjusted by a polyelectrolyte (polystyrene sulfonate, PSS), while the mobile carrier diffuses freely within the CNT framework. After optimization of the membrane recipe and spray-coating fabrication procedure, following our previous work, the resulting CNT-PSS-PEI ∼ IL membranes demonstrated an ultra-high CO₂/N₂ selectivity up to 1,000 with CO₂ permeance up to 2,400 GPU (Gas Permeation Unit, 1 GPU = 3.348 × 10⁻¹⁰ mol·s⁻¹·m⁻²·Pa⁻¹) under vacuum operation condition. Furthermore, one 100-cm² flat sheet membrane sample was prepared and exhibited one-stage CO₂ enrichment from 15 % to 95 % purity (dry-base) for the first time amongst all reported CO₂ separation membranes. The membrane retained a stable performance over 50-h operation period under vacuum condition. The extraordinary CO₂ separation performance illustrates the great potential of the CNT-PSS-PEI ∼ IL membranes for flue gas carbon capture application.