Direct Air Capture of CO(2) Using a Liquid Amine–Solid Carbamic Acid Phase-Separation System Using Diamines Bearing an Aminocyclohexyl Group

[Image: see text] The phase separation between a liquid amine and the solid carbamic acid exhibited >99% CO(2) removal efficiency under a 400 ppm CO(2) flow system using diamines bearing an aminocyclohexyl group. Among them, isophorone diamine [IPDA; 3-(aminomethyl)-3,5,5-trimethylcyclohexylamine] exhibited the highest CO(2) removal efficiency. IPDA reacted with CO(2) in a CO(2)/IPDA molar ratio of ≥1 even in H(2)O as a solvent. The captured CO(2) was completely desorbed at 333 K because the dissolved carbamate ion releases CO(2) at low temperatures. The reusability of IPDA under CO(2) adsorption-and-desorption cycles without degradation, the >99% efficiency kept for 100 h under direct air capture conditions, and the high CO(2) capture rate (201 mmol/h for 1 mol of amine) suggest that the phase separation system using IPDA is robust and durable for practical use.