Prediction of the Basicity of Aqueous Amine Solutions and the Species Distribution in the Amine−H2O−CO2 System Using the COSMO-RS Method

A conductor-like screening model for real solvents (COSMO-RS) was applied to the study of the amine−H2O−CO2 system. pK a values for 25 amines including a variety of alkanolamines and some cyclic or aromatic amines were calculated by the COSMO-RS method coupled with the density functional theory (DFT). The predictions of pK a values were compared using different DFT levels for geometry optimization and also with those based on another solvation model (SM5.4/A). The DFT-COSMO calculation at the BP/TZVP level has shown a relatively good correlation with experimental values for the 25 amines (R 2 ≅ 0.8) at a low computational cost. With this method, we have developed a calculation model to predict the equilibrium ratio between carbamate and bicarbonate anions in a CO2-loaded aqueous amine solution and have confirmed the validity of the prediction model by 13C NMR spectroscopy.