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

The use of hydrophobic deep eutectic solvents (DESs)\nin extraction\nprocesses has gained much attention in recent years. Herein, a low-viscosity\nhydrophobic DES from dodecanoic and octanoic fatty acids, in a molar\nratio of 1:3, was used for separating phenol from salty aqueous solutions.\nThe influence of NaCl, Na<sub>2</sub>SO<sub>4</sub>, and MgSO<sub>4</sub> salts on the consistent liquid–liquid equilibrium\n(LLE) of the system was investigated at 298.2 K and the ambient pressure\nof 81.5 kPa. The results indicate an amazing improvement in the extraction\ncriteria owing to the salting-out effect. Under a salt mass fraction\nof 0.02 and a typical phenol mass fraction of 0.0035, the separation\nfactor was raised to 72.3, 207.7, and 501.7% higher values, compared\nwith the salt-free case with each of the salts, respectively. Consistent\nwith the Hofmeister series, the effectiveness of the salts appeared\nin the order of MgSO<sub>4</sub> > Na<sub>2</sub>SO<sub>4</sub> >\nNaCl. To evaluate the experimental data, the Eisen–Joffe correlation\nwas used. The well-known NRTL and UNIQUAC thermodynamic models accompanied\nby a specific group contribution approach were also employed for reproducing\ntie-line data. Both the models demonstrated good agreement with the\nexperimental data, giving very low root-mean-square deviations within\n0.0020–0.0063 and 0.0058–0.0074, respectively.