Computational chemistry study of reactions, equilibrium and kinetics of chemical CO2 absorption

The chemical reactions involved in CO2 absorption in amine systems are studied. For each mechanism, available experimental data are considered and quantum mechanical calculations carried out. Base-catalyzed bicarbonate formation is found to be a likely mechanism for all amine bases, not only tertiary amines. Direct formation of bicarbonate species from carbamate species is found to be unlikely. The carbamate formation has been proposed to take place through a single-step termolecular reaction, or through a two step mechanism with a zwitterionic intermediate. Quantum mechanical calculations suggest that if there is such a zwitterionic intermediate, it is likely to be short-lived. Quantum mechanical calculations together with solvation models are shown to predict the base strength and carbamate stability of different amine solvents with a useful degree of accuracy. Solvent effects and electron donation and withdrawal through bonds are identified as important factors in determining the overall reactivity of different amine solvents. Results suggest a strong correlation between the carbamate stability and base strength of amine solvents and their reaction kinetics. (C) 2007 Elsevier Ltd. All rights reserved.