Direct Air Capture of CO2 Using a Liquid Amine-Solid Carbamic Acid Phase-Separation System Using Diamines Bearing an Aminocyclohexyl Group
S. Kikkawa, K. Amamoto, Y. Fujiki, J. Hirayama, G. Kato, H. Miura, T. Shishido, S. Yamazoe
ACS Environ. Au, in press.

The phase separation between a liquid amine and the solid carbamic acid exhibited >99% CO2 removal efficiency under a 400 ppm CO2 flow system using diamines bearing an aminocyclohexyl group. Among them, isophorone diamine [IPDA; 3-(aminomethyl)-3,5,5-trimethylcyclohexylamine] exhibited the highest CO2 removal efficiency. IPDA reacted with CO2 in a CO2/IPDA molar ratio of ≥1 even in H2O as a solvent. The captured CO2 was completely desorbed at 333 K because the dissolved carbamate ion releases CO2 at low temperatures. The reusability of IPDA under CO2 adsorption-and-desorption cycles without degradation, the >99% efficiency kept for 100 h under direct air capture conditions, and the high CO2 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.