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

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.