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

Abstract

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.