Understanding Carbamate Formation Reaction Thermochemistry of Amino Acids as Solvents for Postcombustion CO2 Capture.

The carbamate stability constant for a data set of 10 amino acids, having potential for being postcombustion CO2 capture (PCC) solvents, has been calculated using various implicit and explicit solvation shell models. This work also includes an extensive study of gas-phase free energy and enthalpy for the amino acid carbamate formation reaction with the Hartree Fock method, density functional methods [B3LYP/6-311++G(d,p)], and composite methods (G3MP2B3, G3MP2, CBS-QB3, and G4MP2). Ideal PCC solvent properties require finding a profitable tradeoff between various thermodynamic and system optimization parameters. Benchmark gaseous-phase and solution-phase thermodynamic properties given in this work can help in making informed decisions when choosing promising PCC solvents. The temperature dependency of the carbamate stability constant of amino acids is predicted using PCM and SM8T implicit solvation models. PCC is a temperature swing absorption-desorption process, and the high-temperature sensitivity of the ln KcAmCOO- value is of vital importance in attaining cost-efficient processes.