CO2 absorption in blended amine solvent: Speciation, equilibrium solubility and excessive property

Mixing different amines is a common method to develop better solvents for CO2 capture. As the mixing provides more adjustability on the solvent properties, it introduces complex interaction between dissimilar amine molecules who may perform diverse role in the reactions. Here we studied CO2 absorption in monoethanolamine (MEA), methyldiethanolamine (MDEA) and their mixtures thereof. The speciation profiles along with CO2 loading were provided via NMR to reveal the competition/coordination of MEA and MDEA in participating the key reactions that drove CO2 absorption (i.e. carbamate formation and amine protonation). Furthermore, the CO2 loading of the solvents were measured under equilibrium for various temperature, CO2 partial pressure. The excessive CO2 loading was firstly introduced to analyze the loading data regarding the solvent composition. Accordingly, an excessive property model was applied for data correlation. The calculated CO2 loading agreed well with experimental data with average absolution relative deviation of 1.7%.