Oil-phenol separation by tetraethylammonium chloride-based deep eutectic solvents: Microscopic contribution of basic sites

Deep eutectic solvents (DESs) represent a significant advancement in eco-friendly solvents, especially have changed the traditional methods for oil-phenol separation. Given the weak acidity of phenol, hydrogen bond donors (HBDs) with basic sites can enhance interactions between DES and phenol. This study offers a novel microscopic perspective by systematically comparing monoethanolamide (MEA) and ethylene glycol (EG) as HBDs in the synthesis of DESs with tetraethylammonium chloride (TEAC) as the hydrogen bond acceptor (HBA). The focus is on the critical role of HBD structure in optimizing DES performance, particularly examining how molecular interactions affect efficiency. Liquid-liquid extraction (LLE) experiments demonstrated that TEACMEA was significantly more efficient at extracting phenols from the model oils compared to TEAC-EG. Quantum chemical (QC) calculation molecular dynamics (MD) simulations detailed a comparison of the phenol interaction sites within the two systems, revealed that the interaction between Cl from TEAC and phenol dominated, followed by the stronger interactions between MEA and phenol compared to EG. Micromechanical analysis revealed that the amino group in the MEA structure significantly enhanced its interaction with phenol compared to EG, as evidenced by energy, interaction type, and atomic contact area. These findings, cross- validated with LLE experimental data, underscore the importance of basic sites in HBDs for effective extraction and separation, providing valuable guidance for the design and application of DESs.