Exploring Phase Behavior and Thermodynamic Modeling of Ternary System Water + Lactic Acid + Propylene Carbonate at Different Temperatures

This study presents experimental measurements of tie-line and solubility points for the ternary mixtures (water + lactic acid + propylene carbonate) at temperatures of 298.2 and 308.2 K and 101.7 kPa. HPLC measurements were employed to determine the mass fractions of solvent and water layers. The cloud point method was utilized to verify the Type-1 liquid-liquid equilibrium (LLE) behavior of the studied system. To ascertain the reliability of the tie-line points, Othmer-Tobias and Hand plots were analyzed. The thermodynamic correlation of tie-line data was achieved using the NRTL model, and the resulting binary interaction parameters were rigorously validated. Excellent agreement was observed between experimental and correlated data, with a root-mean-square deviation (rmsd) of only 0.3%. The study further explored activity coefficients calculated via the NRTL equation, revealing significant negative deviations for lactic acid and positive deviations for water and propylene carbonate from Raul's law. Extraction quality of propylene carbonate was investigated through the figuring of distribution coefficients and separation factors across the non-miscible region. Interestingly, separation factors increased from 1.07 to 1.11 when lactic acid mass fraction in aqueous layer increased from 0.036 to 0.105. However, distribution coefficients increased from 0.12 to 0.18 in the same investigated area.