Study On Screening Of Synergistic Extraction Solvents And Optimization Control Of Dephenolization Process For Phenolic Wastewater

With the increasing importance of China’s energy security issues,clean production is the need of current social development.At present,the new chemical industry is inclined to produce clean energy.However,the large amount of phenolic wastewater produced during chemical industry has high impurity content,complex composition,high organic content and chemical oxygen demand in the wastewater,and poor biochemical performance.Substandard discharge of wastewater will damage the environment and endanger human health.Phenolic wastewater contains a large number of volatile monophenols and non-volatile polyphenols,which are difficult to degrade and recover.In this paper,the removal of phenols from coal chemical wastewater was studied,including extraction solvent selection,process simulation and dynamic control.In view of the low removal rate of polyphenols,a new extraction solvent was designed to reduce the content of polyphenols.Firstly,the interaction between single solvent and phenols was calculated by molecular simulation.The interaction energy of MIBK,MPK,MIPK,mesityl oxide,n-butanol,sec-butanol,n-pentanol and isoamyl alcohol with phenols were calculated by Gaussian software.The nature and mechanism of extraction were analyzed by configuration optimization,frequency analysis,AIM and NBO analysis,and new ketone extractant and auxiliary extractant were screened out.The results show that the maximum interaction energy of mesityl oxide with phenol and catechol is-45.86 k J·mol^-1,-35.96k J·mol^-1,followed by MPK,and the maximum interaction energy of n-pentanol with phenol is-29.67 k J·mol^-1.The results of extraction mechanism show that the extractant and phenol are mainly combined in the form of hydrogen bond,and the electrostatic interaction,hydrogen bond strength and stabilization energy are mesityl oxide>MPK>MIPK>MIBK.Then the interaction between synergistic extraction solvent and phenol was calculated and analyzed by molecular simulation.Gaussian software was used to calculate the interaction of MIBK,MPK,MIPK,mesityl oxide and n-pentanol with phenols and water,respectively.The NCI analysis was carried out,and the mechanism of synergistic extraction was studied.The results show that the interaction energy of mesityl oxide+n-pentanol with phenol and catechol are-46.13 k J·mol^-1and-43.13 k J·mol^-1,respectively,and the absolute values of the difference between the interaction energy of mesityl oxide+n-pentanol and water are-14.30 k J·mol^-1and-11.30 k J·mol^-1,respectively.The results of extraction mechanism analysis show that O of ketone molecule and-OH of phenol molecule,O of phenol and-OH of n-pentanol are combined in the form of hydrogen bond,and the hydrogen bond action comes from the second lone pair electron of O and O-H anti bondσorbital;the electrostatic action,hydrogen bond strength and stabilization energy of synergistic extraction solvent are higher than those of single extraction solvent.The simulation results predict that mesityl oxide+n-pentanol will ensure the removal rate of monophenol and improve the extraction effect of polyphenolsA dephenolization process using mesityl oxide and n-pentanol as synergistic extraction solvent was established.Aspen plus was used to simulate and optimize the whole process.The performance of the synergistic extraction solvent was verified according to the concentration of phenol in the dephenolization water and the amount of solvent.Taking TAC as the objective,the optimal parameters of the process were determined.The results of extraction column simulation show that the ratio of mesityl oxide to n-pentanol is 6:4,the mass ratio is 1:12.92,and the extraction stage is 4.Taking TAC as the target,the operation parameters of solvent recovery column and stripping column were optimized.After optimization,the minimum TAC reach 1953（1000$/year）.The simulation results show that the removal rates of phenol and catechol reach 99.95%and 97.97%respectively,and the total phenol concentration decrease from 6499 mg/L to56 mg/L.Under the same amount of extractant,the removal rate of catechol increased by16.71%compared with mesityl oxide single extractant,and 28.65%compared with n-pentanol single extractant.In addition,the amount of fresh extractant added is only 0.95kg/h,which has the advantage of less solvent.Finally,Aspen dynamics simulation was used to investigate the dynamic control effect under the disturbance of±10%feed flow and±5%composition.The results show that the basic control scheme can quickly restore the stable value of the process operation under the disturbance.The controller shows good anti-interference performance.The control scheme is effective,and the extraction dephenol process device can operate safely and smoothly.