Thermodynamic Modeling of Aqueous Amine-Electrolyte Solvents for CO₂ Absorption

The coupling process of carbon capture and utilization technology (CCU) that is gaining a lot of interest is called integrated CO₂ capture–conversion (ICCC) where it is a part of the technological advancement aligning to one of the Sustainable Development Goals (SDGs) domains, which is SDG 13 (climate action). It electrochemically transforms CO₂ extracted from the post-combustion emissions into valuable products using amine-electrolyte solution, eliminating the need for an energy-intensive sorbent regeneration step. Extensive work on the chemical equilibria of the solvent combination is crucial to reveal the effect of salt addition towards the absorption mechanism. In this work, the chemical equilibria of the amine-electrolyte solvent systems are modeled using the Deshmukh–Mather model. The binary interaction parameters used in the modeling are fitted using experimental data, and the fitted model showed the average absolute deviation less than 10% for all the amine-electrolyte solvent systems, which showed better results than the extended Debye–Hückel model. The modeled speciation was compared using the protonated amine, bicarbonate, and carbamate concentration as a function of the solution pH. The concentration of carbamate showed a peak at a pH approximately equal to the protonation constant of the amines. The carbamate produced in the potassium chloride-containing solutions was approximately following the stoichiometry of the reaction. Moreover, potassium bicarbonate can be treated as the reactive electrolyte for higher production of carbamate during the absorption process. Overall, this article emphasizes the speciation modeling that can be used as the foundation for other possible blends of absorbents.