Liquid–Liquid Equilibria for Pseudo-Ternary Systems of 1-Hydroxypropan-2-one + Water + Cyclic Terpene-Based Mixtures at 298.15 K

Herein, liquid–liquid equilibria (LLE) were investigated for pseudo-ternary systems comprising water + 1-hydroxypropan-2-one + cyclic terpene-based mixtures at 298.15 K and 0.1 MPa. Menthol/levulinic acid-, menthol/dodecanoic acid-, menthol/thymol-, thymol/decanoic acid-, thymol/10-undecenoic acid-, and menthol/decanoic acid-based mixtures were prepared in 1:2, 2:1, 1:1, 1:1, 1:1, and 1:1 molar ratios, respectively, which are type V deep eutectic solvents (DESs). The pseudo-ternary system separation factors were determined. When decanoic acid was used as a hydrogen bond donor, the menthol-based DES exhibited a higher separation factor than the thymol-based DES. Among the pseudo-ternary systems, menthol- and decanoic-acid-based DESs exhibited the highest separation factor. A non-random two-liquid (NRTL) model was used to regress the LLE data. The Gibbs-energy-of-mixing (GM/RT) surface was topologically analyzed to determine the tie line consistency. The experimentally measured and NRTL-modeled tie lines were tangential to the GM/RT surface curve, indicating that the minimum Gibbs free energy of mixing was satisfied at equilibrium points.