A 13C NMR Investigation of CO2 Absorption and Desorption in Aqueous 2,2 -Iminodiethanol and N-Methyl-2,2 -iminodiethanol

The carbon dioxide capture and release from aqueous 2,2-iminodiethanol (DEA) and N-methyl-2,2- iminodiethanol (MDEA) have been investigated by means of 13C NMR spectroscopy. We have designed two experimental procedures using a gas mixture containing 12% (v/v) CO2 in N2 or air and 0.667M aqueous solutions of DEA and MDEA. To understand the CO2-amine reaction equilibria, separate experiments of CO2 absorption (at 293, 313 and 333 K) and desorption (at boiling temperature, room pressure) were carried out. The 13C NMR analysis has allowed us to establish: (1) the percentage of CO2 stored in solution as HCO3-, CO3 2- and DEA carbamate; (2) the formation of DEA carbamate as a function of absorption temperature and time; (3) the slower decomposition of DEA carbamate than that of bicarbonate. In the experiments planned to test the reuse of the regenerated amines, the absorbent solution was continuously circulated in a closed cycle while it was absorbing CO2 in the absorber (set at 293 K) and simultaneously regenerating amine in the desorber (set at 388 K). After the equilibrium has been reached (13 h), the CO2 absorption efficiency is comprised between 84.0% (DEA) and 82.6% (MDEA) and the average amine regeneration efficiency ranges between 69.6% (DEA) and 78.2% (MDEA). Additionally, MDEA is more stable towards thermal degradation than DEA.