High CO2 separation performance of amino acid ionic liquid-based double network ion gel membranes in low CO2 concentration gas mixtures under humid conditions

This work focused on separating low concentrations of CO2 (500–1000 ppm) from humid mixtures of CO2/N2 using an amino acid ionic liquid (AAIL)-based ion gel membrane. The effects of relative humidity (RH), CO2 partial pressure, and temperature on the CO2 separation performance were investigated. At 303 K, RH 70%, and a CO2 partial pressure of 0.1 kPa, the ion gel membrane showed high CO2 permeability (around 52,000 barrer) and CO2/N2 selectivity (8100), both of which were considerably higher than those observed using a conventional facilitated transport membrane (FTM). Changes in RH were found to slightly affect the CO2 permeation properties of the ion gel membrane, while the CO2 separation performance of the conventional FTM was strongly dependent on RH, decreasing sharply at RH <50%. Enhanced CO2 permeability of the ion gel membrane was observed with decreasing CO2 partial pressure, indicating a facilitated transport mechanism. Moreover, increasing the temperature at a constant RH was found to enhance CO2 permeability, while CO2/N2 selectivity remained constant. The outstanding and stable performance of the AAIL-based ion gel membrane demonstrated its potential for CO2 separation from gas mixtures containing low concentrations of CO2 across a wide RH range around room temperature.