Analysis of Solvation Effects in Lactic Acid Ester-Containing Systems at 288.2–308.2 K: Liquid–Liquid Equilibrium Experiments, Thermodynamic and Quantum Chemical Studies, and Interaction Mechanism Analysis

In the traditional lactic acid ester synthesis process, lactic acid and 4-methyl-2-pentanol (MIBC) under certain temperature and acidic conditions undergo an esterification reaction to produce 2-hydroxypropanoic acid-1,3-dimethylbutyl ester (DIHP) and water, forming a complex system containing lactic acid, MIBC, DIHP, and water. To investigate the mutual solubility of the substances in the system, the ternary liquid–liquid equilibrium (LLE) data for DIHP + lactic acid + water and water + MIBC + DIHP were determined at 288.2–308.2 K and 101.3 kPa in this paper. The measured experimental data were correlated with nonrandom two-liquid (NRTL) and universal quasi-chemical (UNIQUAC) models to obtain the binary interaction parameters between substances. In addition, parameter rationality was evaluated by using the GUI-MATLAB tool, and the conclusions indicated that these parameters were reliable. This will provide critical and reliable fundamental data points for constructing a more complete thermodynamic model that predicts the phase behavior of the quaternary system. Finally, this paper reveals the interaction mechanism between the substances at the microscopic level by combining the experimental results with quantum chemical calculations, which, in turn, reflect the solvation effects between the substances.