Low-Temperature Desorption of CO₂ from Carbamic Acid for CO₂ Condensation by Direct Air Capture

The high temperature requirement for the desorption of absorbed CO₂ is one of the issues for the widespread use of direct air capture (DAC), which is a promising technology to reduce atmospheric CO₂ concentration. This work realized a liquid diamine absorbent-solid carbamic acid (CA) phase-change DAC system with CO₂ desorption at a low temperature by using a MeOH solvent. The CA of isophoronediamine [3-(aminomethyl)-3,5,5-trimethylcyclohexylamine, CA-IPDA] readily desorbed CO₂ in MeOH at 50 °C, while IPDA showed the capacity to absorb low-concentration CO₂ from air with an IPDA/CO₂ ratio of 1:1. The CA-IPDA desorbed more than half of the absorbed CO₂ at 60 °C without any gas flow, proving that this system can condense low-concentration CO₂ in air to pure CO₂ with low energy requirements. The low-temperature desorption of CO₂ from CA-IPDA was owing to the high solubility of CA-IPDA in MeOH and the easy CO₂ 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.