Low-Temperature Desorption of CO from Carbamic Acid for CO Condensation by Direct Air Capture.

The high temperature requirement for the desorption of absorbed CO is one of the issues for the widespread use of direct air capture (DAC), which is a promising technology to reduce atmospheric CO concentration. This work realized a liquid diamine absorbent-solid carbamic acid (CA) phase-change DAC system with CO desorption at a low temperature by using a MeOH solvent. The CA of isophoronediamine [3-(aminomethyl)-3,5,5-trimethylcyclohexylamine, CA-IPDA] readily desorbed CO in MeOH at 50 °C, while IPDA showed the capacity to absorb low-concentration CO from air with an IPDA/CO ratio of 1:1. The CA-IPDA desorbed more than half of the absorbed CO at 60 °C without any gas flow, proving that this system can condense low-concentration CO in air to pure CO with low energy requirements. The low-temperature desorption of CO from CA-IPDA was owing to the high solubility of CA-IPDA in MeOH and the easy CO transfer between carbamic acid and MeOH to form methyl carbonate ions. This solubility control in the liquid-solid phase-change system opens up the low-energy DAC systems.