Carbon Dioxide Absorption Characteristics of Aqueous Alkanolamine Using Nuclear Magnetic Resonance Spectroscopy

In this study, the species generated during carbon dioxide (CO2) absorption by primary, secondary, or tertiary aqueous alkanolamines were studied by H-1 and C-13 nuclear magnetic resonance (NMR). Using a vapor-liquid equilibrium apparatus, the CO2 loading capacities and relative absorption rates of aqueous monoethanolamine (MEA), diethanolamine (DEA), or triethanolamine (TEA) were estimated. After reaching an absorption equilibrium, NMR spectroscopy was used to characterize the structural changes during absorption and to examine the species distribution. Mechanisms of CO2 absorption in each absorbent were elucidated based on the NMR measurements. In addition, vapor-liquid equilibrium experimental results revealed CO2 absorption rates in the order of MEA > DEA > TEA. Carbamates in MEA and DEA were found to be hydrolyzed to bicarbonate at CO2 loading levels and exceeded 0.5 mole. The tertiary amine, TEA, was found to absorb CO2 to form bicarbonate, and the absorption capacity was higher than that of the primary or secondary amines.