Phase Equilibrium Behavior in Mixtures Containing Tributyl Citrate, Citric Acid, Butan-1-ol, and Water

Abstract

This work focused on the development of the phase equilibria models required to describe the behavior of mixtures involved in the synthesis of tributyl citrate (TBC) via esterification of citric acid (CA) and butan-1-ol (BuOH). Vapor–liquid equilibrium (VLE) for the mixture TBC–BuOH, liquid–liquid equilibrium (LLE) for the ternary mixture TBC–H2O–BuOH, and solubility data for the mixture CA–BuOH–TBC were measured at different temperatures. The thermodynamic consistency was verified with the Wisniak test for VLE data, and the LLE data exhibited linear behavior in an Othmer and Tobias plot. Anhydrous citric acid was characterized by differential scanning calorimetry exhibiting a melting point of 424.9 K, an enthalpy of fusion of 59.2 kJ/mol, an average heat capacity of 255.48 J/mol·K in the evaluated temperature range (320–375 K), and a change of heat capacity from solid to liquid of 236 J/mol·K. Together with reported equilibrium data from the open literature, and the evaluated physicochemical properties, the measured equilibrium data were regressed with the UNIQUAC equation to fit the binary interaction parameters of the components in the mixture. The obtained model agrees well with the whole set of experimental data and can be used for further process design.