Study of molecular mechanism and extraction performance evaluation for separation of phenolics from alkaline wastewater through synergistic extraction

Phenols were a kind of pollutant in coal chemical wastewater with high concentration and difficult to decompose and have a significant impact on the subsequent biochemical treatment of the wastewater. In addition, phenols were a kind of weak electrolytes that partially dissociation oxidation under weakly alkaline conditions, making recovery more difficult. In order to solve this problem, phenols were extracted from weak alkaline wastewater with a synergistic solvent. First, the interaction between solvents and phenols and the solvent effect of solvents were calculated by quantum chemistry and the synergistic extractant cyclohexanone/1-pentanol was determined to have significant advantages. Moreover, the synergistic extractant was further analyzed through independent gradient model based on Hirshfeld partition analysis, atoms in molecule topology analysis, electrostatic potential analysis. Results indicated that the synergistic extract can provide multiple hydrogen bond interactions with phenol due to the double action sites of the C=O group of ketone and the -OH group of alcohol. In addition, the efficacy of the extractant was validated by multistage extraction, indicating partial dissociation oxidation of hydroquinone to benzoquinone under weakly alkaline conditions, with removal rates of 99.5% and 99.2% for phenol and hydroquinone, respectively. In general, the synergistic extractant can effectively remove phenols.