Aqueous MAPA, DEEA, and Their Blend as CO2 Absorbents: Interrelationship between NMR Speciation, pH, and Heat of Absorption Data

On the basis of speciation by nuclear magnetic resonance (NMR) spectroscopy, heat of absorption, and pH data, the reactions occurring in aqueous MAPA (3-(methylamino)propylamine), DEEA (2-(diethylamino)ethanol), and their blend at various carbon dioxide (CO2) loadings were identified and discussed. At increasing CO2 loading, the basicity of the solutions decreased. In the MAPA solvent, this led to the hydrolysis of the carbamate species, which corresponded to a drop in the heat of absorption. In the blend, due to the activity of DEEA, such a drop in both pH and heat of absorption was not noticeable. In the presence of MAPA, in the early loadings DEEA had not yet an influence on the (bi)carbonate formation but mainly on the MAPA activity. However, as soon as the trend for (bi)carbonate formation went as in DEEA singly, the released heat steadily decreased. Both in single and in blended MAPA, the carbamate hydrolyses started at similar pH values, i.e., about 9.8-9.5.