Liquid-Liquid Equilibrium of Quaternary Systems: Experimental Data and NRTL Model Predictions for Water, Lactic Acid, 1-Octanol, and Salts

D. Laiadi, K. Athmani, C. Laiadi, E. Guettaf Temam, A. Merzougui and A. Hasseine

Abstract
This study investigates the liquid–liquid equilibrium (LLE) behavior of ternary and quaternary systems composed of water, lactic acid, 1-octanol, and salts (NaCl and KCl). Phase behaviour was predicted using the non-random two-liquid (NRTL) model. Accu rate thermodynamic modeling is essential for optimizing separation processes in the pharmaceuticals, food, and bio-based chemical industries. Experimental tie-line data were obtained at salt mass fractions from 0 to 15 % and validated with Othmer–Tobias and Hand correlations, which confirmed the high consistency of the data. The NRTL predictions were evaluated using the root mean square deviation (RMSD), yielding low values (0.1418 for 15 % NaCl, 0.1088 for 15 % KCl), demonstrating strong predictive reliability. The salting-out effect was quantified through binary interaction parameters, such as 20.4174 for water–1-octanol (15 % KCl) and 15.5637 for the same pair (15 % NaCl), indicating enhanced lactic acid partitioning into the organic phase. Overall, the results confirm the accuracy of the NRTL model in describing ionic interactions and phase separation, offering a reliable framework for efficient extraction and purification processes.

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Keywords
liquid-liquid equilibrium, NRTL model, lactic acid, 1-octanol, salting-out effects