Salting-out Effects in Extraction of Phenol from Aqueous Solutions Using a Hydrophobic Deep Eutectic Solvent Based on Dodecanoic and Octanoic Acids: Experimental Study and Comparison

The use of hydrophobic deep eutectic solvents (DESs) in extraction processes has gained much attention in recent years. Herein, a low-viscosity hydrophobic DES from dodecanoic and octanoic fatty acids, in a molar ratio of 1:3, was used for separating phenol from salty aqueous solutions. The influence of NaCl, Na₂SO₄, and MgSO₄ salts on the consistent liquid–liquid equilibrium (LLE) of the system was investigated at 298.2 K and the ambient pressure of 81.5 kPa. The results indicate an amazing improvement in the extraction criteria owing to the salting-out effect. Under a salt mass fraction of 0.02 and a typical phenol mass fraction of 0.0035, the separation factor was raised to 72.3, 207.7, and 501.7% higher values, compared with the salt-free case with each of the salts, respectively. Consistent with the Hofmeister series, the effectiveness of the salts appeared in the order of MgSO₄ > Na₂SO₄ > NaCl. To evaluate the experimental data, the Eisen–Joffe correlation was used. The well-known NRTL and UNIQUAC thermodynamic models accompanied by a specific group contribution approach were also employed for reproducing tie-line data. Both the models demonstrated good agreement with the experimental data, giving very low root-mean-square deviations within 0.0020–0.0063 and 0.0058–0.0074, respectively.