Achieving global carbon neutrality by 2050 requires technologies capable of capturing CO 2 at atmospheric concentrations. Membrane‐based direct air capture (DAC) offers an energy‐efficient route, and facilitated transport membranes (FTMs) using ionic liquids (ILs) are promising owing to their structural diversity with tunable reactivity. This study examines the influence of diamine‐functionalized IL carrier structure and process conditions on CO 2 separation in DAC‐relevant environments. FTMs are prepared by impregnating a porous polymer support with blended ILs composed of 1‐ethyl‐3‐methylimidazolium acetate (C 2 mimAcO) and various diamine‐functionalized ILs. The relationship between CO 2 solubility and CO 2 permeability of the FTMs shows an optimum solubility range that affords high CO 2 permeability. When CO 2 solubility is excessive, CO 2 permeability becomes relatively low. Suppressing the solubility through molecular modification by introducing hydroxyethyl groups or adjusting the diamine spacer effectively shifts the solubility value into a suitable range that enables higher CO 2 permeability. Further decrease in the solubility results in low permeability. The effects of both temperature and humidity on the separation performance are also assessed, and optimal temperature conditions and mixing ratios are identified for superior CO 2 permeability. These findings clarify the chemical structure–performance relationships and inform the design of efficient FTMs for DAC applications.
Kanasaki et al. (Fri,) studied this question.