Mechanism Analysis And Process Optimization Of Synergistic Extraction For Dephenolization

Coal chemical industry plays an important role in China’s energy supply.With the development of coal chemical industry,the treatment of coal chemical wastewater has become the most important issue in the development of coal chemical industry.The treatment of coal chemical wastewater is of great significance to the sustainable development of the industry.Phenolic is one of the main pollution of coal chemical wastewater.It has the characteristics of high concentration and difficult to decompose,which has great influence on the subsequent biochemical treatment system,Therefore,the treatment of phenols is particularly urgent.In addition,coal chemical wastewater is weakly alkaline,while phenolic is a kind of weak electrolytes that partially dissolve and oxidize under weakly alkaline conditions,making recovery more difficult.The treatment of phenolic in coal chemical wastewater has become the bottleneck of the sustainable and healthy development of coal chemical industry.In order to remove phenolic from wastewater efficiently,the optimal extraction agent was determined by extraction selection,solvation effect analysis and molecular mechanism analysis,the process flow of extraction dephenol was set up,the simulation and optimization of the process were carried out to verify the feasibility of the extractant.Firstly,for the dissociation and oxidation of phenol and hydroquinone in water,the interaction of single-solvent extraction of methyl isobutyl ketone(MIBK),methyl propyl ketone(MPK),mesityl oxide(MO),cyclohexane(CYC),and synergetic extractant of mesityl oxide/1-pentanol(MO/1-PA),cyclohexanone/1-pentanol(CYC/1-PA),and water with phenols in molecular,ionic and oxidizing states were optimized by quantum chemistry,and the optimal configuration was calculated.The results showed a strong hydrogen bond between the extractant and phenolic,with a strong interaction between CYC/1-PA synergistic phenols.The solvent free energy and solvent constant of phenol and hydroquinone in MIBK,MPK,MO,CYC,1-PA and aqueous solvents were calculated.In addition,synergistic extraction mechanisms were analyzed by independent gradient model based on Hirshfeld partition(IGMH),atoms in molecules(AIM),and electrostatic potential(ESP).The results show that the polar area of the synergistic extractant is larger than that of the single extractor and can provide strong static power.In addition,the oxidation state of phenol and hydroquinone can be determined by preparing phenolic water samples with different p H and observing the color change of the samples with different p H conditions.And the samples with different p H were analyzed by HPLC.The results showed that phenol was stable under real industrial p H conditions,and the content of phenol remained largely unchanged.The partial oxidation of hydroquinone to benzoquinone resulted in a conversion rate of 16.6%.The representative extractant of CYC,CYC/1-PA and MO/1-PA were selected based on molecular simulation to carry out four-stage extraction and dephenolization experiments.The results showed that the synergistic extractant of CYC/1-PA was still effective under weak alkaline conditions,with 98.90%and 97.77%removal rates for phenol and hydroquinone.The removal rates of phenol and hydroquinone by synergistic extractant of MO/1-PA were 98.79%and 96.25%.The single solvent extraction of CYC showed poor removal of phenol and hydroquinone,with 94.20%and 92.86%,respectively.Finally,CYC/1-PA synergistic extraction processes were simulated and optimized using Aspen Plus software.The amount of extractant used in the extraction column was optimized,and the solvent ratio of CYC/1-PA synergistic extractant was 6:4,and the ratio of extractant to wastewater is 1:13.The column parameters of solvent recovery tower and Extractive residual phase stripping tower were optimized with minimum TAC as the target.The number of plates in the solvent recovery tower was determined to be 28,the feed was in the 4th plate,the number of plates in the stripper was 14,the feed was in the 1st plate,and the TAC cost was 14.09×10~5$/year.Under this condition,the removal rate of phenol reached 99.98%,and the removal rate of hydroquinone was 96.94%.