Separation of Phenolic\nCompounds in Coal Tar by Using\nDeep Eutectic Solvent Extraction with Choline-Urea: Based on Phase\nEquilibrium Experiments and Molecular Mechanism Investigation

The objective of this study was to assess the environmental\ncompatibility\nand efficacy of deep eutectic solvents (DESs) prepared from choline\nchloride and urea as a means of extracting phenolic compounds from\ncoal tar. This method was developed with the objective of addressing\nthe limitations and environmental concerns associated with conventional\nextraction techniques. Initial predictions of extraction efficiency\nwere made using Hansen dissolution parameters (HSPs) and thermodynamic\nconsiderations, with subsequent confirmation obtained through liquid–liquid\nphase equilibrium experiments. The application of quantum chemistry\nand visualization techniques demonstrated that hydrogen bonding represents\nthe primary interaction between DESs and phenolic compounds. Furthermore,\nit was observed that the extraction efficiency of phenol, <i>m</i>-toluene, <i>p</i>-toluene, and <i>o</i>-toluene decreased in a sequential manner. The results emphasize\nthe significance of hydrogen bonding in the extraction process and\nprovide practical and theoretical guidance for the utilization of\nDESs in the sustainable and efficient extraction of phenolic compounds.