Influence of Solvents and Salts on CO₂ Solubility and the Impact on an Esterification Reaction

Abstract

The influence of solvents and salts on the CO 2 solubility and the impact on esterification reaction kinetics and equilibrium are of particular interest, e.g., for the esterification of acetic acid with ethanol under the influence of CO 2 , N-methyl-2pyrrolidone (NMP), or electrolytes. In this work, the equation of state (EOS) electrolyte Perturbed-Chain Statistical Associating Fluid Theory (ePC-SAFT advanced) was first applied to predict the CO 2 solubility in solvent mixtures containing NMP and water with additional electrolytes (NaCl, CsCl). New experimental data on the CO 2 solubility in electrolyte solutions were measured by two different static synthetic methods, and the ePC-SAFT predictions matched well with the experimental data. As a result, NMP increased the CO 2 solubility, compared to water as the only solvent, while electrolytes caused a salting-out effect on the CO 2 solubility in all investigated systems. Further, the kinetics and equilibria of the esterification reaction were studied in the presence of CO 2 , NMP, and electrolytes. New data were measured by using a high-pressure autoclave with in situ ATR-FTIR spectroscopy, which enabled real-time monitoring of the kinetic profiles. Therein, CO 2 and NMP showed a negative effect on the kinetics. However, the additional CO 2 in the reaction mixture positively influenced the equilibrium, while NMP had a negative influence. Finally, ePC-SAFT advanced was applied to predict the influence of CO 2 and NMP on both kinetics and equilibrium of ethanol esterification using a thermodynamic activity-based kinetic approach. Therein, the experimental findings were successfully predicted by the model without fitting any model parameter to the experimental data. Ultimately, this approach reduces the experimental effort toward screening most suitable reaction conditions for chemical reactions and screening the influence of other compounds on kinetics and equilibria.