Theoretical Study of Differential Enthalpy of Absorption of CO₂ with MEA and MDEA as a Function of Temperature

Temperature dependent correlations for enthalpy of deprotonation, carbamate formation, and heat of absorption of the overall reaction between aqueous MEA and MDEA and gaseous CO₂ are calculated on the basis of computational chemistry based ln K values input to the Gibbs–Helmholtz equation. Temperature dependency of reaction equilibrium constants for deprotonation and carbamate formation reactions is calculated with the SM8T continuum solvation model coupled with density functional theoretical calculations at the B3LYP/6-311++G(d,p) level of theory. Calculated reaction equilibrium constants and enthalpies of individual reactions and overall heat of absorption are compared against experimental data in the temperature range 273.15–373 K. Temperature dependent correlations for different reaction equilibrium constants and enthalpies of reactions are given. These correlated results can be used in thermodynamic models such as UNIQUAC and NRTL for better understanding of post-combustion CO₂ capture solvent chemistry.