Postcombustion CO₂ capture solvent characterization employing the explicit solvation shell model and continuum solvation models

A study on the explicit and implicit solvation models for calculation of solvation free energy of ions and pKa of amino acids presented recently [Gupta, M.; J. Chem. Theory. Comput. 2013, 9, 5021−5031] is extended for the study of amines and alkanolamines. Solvation free energies and pKa’s of a data set of 25 amines and alkanolamines are calculated using the explicit solvation shell (ESS) model given by da Silva et al. [ J. Phys. Chem. A 2009, 113, 6404] and continuum solvation models (polarized continuum solvation model (PCM), SM8T, and DivCon). An extensive overview involving the gas-phase basicity and proton affinity, calculated using density functional methods (B3LYP/6-311++G(d,p)) and composite methods (G3MP2B3, G3MP2, CBS-QB3, G4MP2) and compared with corresponding experimental results for amines and alkanolamines, is also included in the present work. This data set was selected based on the components’ potential as solvents for postcombustion CO₂ capture (PCC) processes. Results of gaseous-phase thermochemistry and pKa obtained from different models employed in this work are analyzed against experimental results for obtaining error estimates involved in each theoretical model. The ESS model for the calculation of the solvation free energy of ions combined with composite methods for gaseous-phase thermochemistry is found to give reasonable accuracy for pKa calculations of amines and alkanolamines and thereby constitutes a method for validation of pKa for new potential PCC solvents.