Thermodynamics of aqueous potassium carbonate, piperazine, and carbon dioxide

A rigorous thermodynamic model was developed, based on the electrolyte nonrandom two-liquid (ENRTL) theory, to describe the equilibrium behavior of the solvent. Modeling work established that the carbamate stability of piperazine and piperazine carbamate resembles primary amines and gives approximately equal values for the heats of reaction, ΔHrxn (18.3 and 16.5 kJ/mol). The pKa of piperazine carbamate is twice that of piperazine, but the ΔHrxn values are equivalent (∼−45 kJ/mol). Overall, the heat of CO2 absorption is lowered by the formation of significant quantities of HCO3− in the mixed solvent and strongly depends on the relative concentrations of K+ and PZ, ranging from −40 to −75 kJ/mol.