Speciation and gas-liquid equilibrium study of CO2 absorption in aqueous MEA-DEEA blends

The blending of primary amines, with fast reaction kinetic, together with tertiary amines, with a large loading capacity, is an increasingly popular approach to develop high-performance CO2 capture sorbents with low energy requirements for regeneration. In this study, we investigated the CO2 absorption performance of several aqueous solutions obtained by mixing ethanolamine (MEA) and diethylethanolamine (DEEA) and compared them with that of individual MEA and DEEA. CO2 loadings at equilibrium were measured experimentally under a wide range of operating conditions, at temperatures between 298 and 323 K, CO2 partial pressures in the range 5-60 kPa, and different amine mixing ratios. In addition, 13C NMR spectroscopy was employed to elucidate the reaction mechanisms and identify the species formed during CO2 capture. The results of the study reveal the intricate interplay of MEA and DEEA in CO2 capture, where MEA carbamate formation predominates in the early stages, gradually shifting to bicarbonate formation as the amine concentration decreases. Moreover, excess properties, which reflect non-ideal behaviors in amine blends, were introduced as a key parameter in the study. An excess property model, based on excess CO2 loading, was developed to accurately predict the CO2 equilibrium solubility without constant experimental measurement. As a result, good agreement was found between the experimental data and those calculated with the model (excess CO2 loading) under the same operating conditions, with a average relative deviation of 1.1%.