Direct CO2 Air Capture with aqueous 2-(ethylamino)ethanol and 2-(2-aminoethoxy)ethanol: 13C NMR speciation of the absorbed solutions and study of the sorbent regeneration improved by a transition metal oxide catalyst

The removal of CO2 from the atmosphere (DAC technology) has been accomplished at room temperature and pressure with aqueous solutions of 2-(ethylamino)ethanol (EMEA) and 2-(2-aminoethoxy)ethanol (DGA). The absorption efficiency of the sorbents has been investigated in five cycling steps of absorption-desorption, and the speciation of the solutions has been studied by 13C NMR analysis. The CO2 capture efficiency of both fresh amines is about 88%, and that of the regenerated EMEA solutions decreases to about 79% once the equilibrium between amine regeneration (at 110 °C) and CO2-loaded amine has been reached. Instead, the efficiency of regenerated DGA progressively decreases to 69% at the end of the fifth cycle. 13C NMR analysis of the absorbed solutions of EMEA indicates that CO2 is captured as amine carbamate and bicarbonate (nearly 1:1 proportion), whereas DGA carbamate is the sole species of captured CO2. To improve the efficiency of regenerated DGA solutions, solid WO3 has been employed as desorption catalyst in five subsequent cycles of absorption and desorption. At equilibrium, the efficiency of CO2 capture increased to 85%, substantially greater than that of regenerated EMEA. The catalyst has been recovered unchanged at the end of each desorption step.