Computational Comparison of the Reactions of Substituted Amines with CO2

Substituted amines are a popular choice as molecules to selectively react with and separate CO2 from gas mixtures. Such separations are of particular interest, for example, for CO2 separations for carbon capture and sequestration. It is desirable to tune amine CO2 reaction energies to suit a particular separation. Herein, we use DFT-B3LYP simulations to characterize the products and energetics of reactions of CO2 with a range of substituted amines, considering both 1:1 and 2:1 amine/CO2 reaction stoichiometries. The results show that by adjusting both the nature and the placement of functional groups, it is possible to tune reaction energies over a substantial range. Decomposition of the 2:1 reaction into separate carbamate and ammonium formation steps shows that the Bronsted basicity and Lewis basicity towards CO2 are largely uncorrelated and provide an independent means of tuning the overall reaction energies.