Highly efficient separation of phenol with tetraethylammonium chloride-based deep eutectic solvents: Experiments and theoretical calculations

To gain more insight into the mechanism of the separation of phenols by deep eutectic solvents (DESs), four DESs: tetraethylammonium chloride (TEAC)-ethylene glycol (EG), TEAC-diethylene glycol (DEG), TEAC-triethylene glycol (TEG) and TEAC-tetraethylene glycol (TTEG) were prepared for the extraction of phenols from model oil. Experimental parameter optimization results indicated that four DESs were effective in extracting phenols, and TEAC-EG had the highest extraction efficiency (EE), with EE up to 98.95%. Subsequently, the formation mechanism of DESs and the extraction mechanism were revealed at the molecular/atomic level by quantum calculations using density functional theory (DFT). The most stable configurations, hydrogen bonding lengths, and interaction energies of DESs and corresponding systems have been calculated, and the weak interactions in the systems were visualized and further analyzed. The results showed that DESs formation were mainly due to a combined effect of hydrogen bonding and van der Waals (vdW) forces. Besides, hydrogen bonding and vdW forces between DESs and phenol were the main forces acting to extract phenol, and the hydrogen bonding within DESs was weakened when DESs interacted with phenol.