Liquid–Liquid Equilibrium Study of the Ternary Systems (Water + Lactic Acid + Trioctylamine or Butyronitrile) at T = 293.2 K and Ambient Pressure

In this work, liquid–liquid equilibrium (LLE) data were experimentally determined for ternary systems comprising water, lactic acid, and either trioctylamine (TOA) or butyronitrile (BN). TOA exhibited a substantially greater capacity for lactic acid extraction than BN, as indicated by its higher distribution coefficients and separation factors. The nonrandom two-liquid (NRTL) model was used to correlate the experimental tie-line data, and the associated binary interaction parameters were estimated by regression. The predictive performance of the NRTL model for the investigated systems was assessed quantitatively by calculating the root-mean-square deviation (rmsd) and thermodynamically using a graphical user interface (GUI)-based computational tool. Based on the rmsd values, the NRTL model provided an excellent correlation for the BN-containing system, with an rmsd of 0.41%, whereas its performance for the TOA-containing system was less satisfactory, with an rmsd of 1.97%. The GUI-based thermodynamic analysis indicated that the NRTL model was unable to adequately represent the phase behavior of the TOA-containing system. This limitation may be attributed to specific interactions, potentially including acid–base association or partial chemical reaction between lactic acid and TOA, which are not fully accounted for by the conventional NRTL formulation.