Treatment And Recycling Of Wastewater From The Condensation Section In The 2,4-D Pesticide Production Process

As one of phenoxycarboxylic acids,2,4-dichlorophenoxyacetic acid?2,4-D?is a highly selective herbicide.Wastewater from the production of it often contains high concentration of phenoxyacetic acid,phenol and by-product glycolic acid,accompanied by a large amount of inorganic salt.According to the properties of 2,4-D production wastewater from Tianyu Chemical co.LTD in Jiangxi,the pesticide wastewater was pretreated by the way of complex extraction with suitable extractant.First,phenoxyacetic acid and phenol in wastewater were recycled as raw materials to realize the resource application of wastewater.Then,glycolic acid left was further separated by precipitation.Afterwards,advanced treatment was applied to reduce COD based on the demands of relevant enterprises.In this paper,on the basis of the characteristics of the wastewater,the factors on extraction efficiency were investigated including the selection of the extraction agent,the concentration of complexing agent,pH,oil/water ratio,NaOH concentration,regeneration performance of extractant and so on.At the same time,the possible mechanism was discussed based on the thermal effects of the extraction process,complex extraction equilibrium experiment and reaction extraction equilibrium model of phenoxyacetic acid.Meanwhile,glycolic acid left in wastewater was further recovered by calcium salt precipitation.Then,a novel Bi₂MoO₆/Bi₂Ti₂O₇ heterojunction photocatalyst prepared by a solvothermal route was applied in the photodegradation of glycolic acid.The mechanism of photocatalytic reaction was also discussed.Oxidation,adsorption and adsorption-oxidation were used for advanced treatment of pesticide wastewater.The results are shown as follows:1.The wastewater from pesticide 2,4-D production was pretreated by complex extraction with C110 extractant.The COD removal rate can reach 68.8%and COD was 16000 mg·L^-1 under the optimum conditions.NaOH solution with a mass fraction of 20%was used as the stripping agent to recycle phenoxyacetic acid,phenol and extraction agent.The extraction of phenoxyacetic acid was exothermic reaction.Three types of extracts?1:1?,?1:2?,?2:1?were formed in the system;2.Calcium salt precipitation was used to separate the remaining glycolic acid.When the CaO dosage was 0.04 kg·L^-1 and the initial pH was about 1.5,separation efficiency of glycolic acid can reach 96.1%and COD was 3000 mg·L^-1;3.The Bi₂MoO₆/Bi₂Ti₂O₇ nanocomposite was prepared by a solvothermal route.The physico-chemical characterizations were conducted by SEM,TEM,XRD,XPS,UV-vis DRS and PL analysis.The Bi₂MoO₆/Bi₂Ti₂O₇?2:1?photocatalyst exhibits highest photocatalytic performance.The glycolic acid(30 mg·L^-1)degradation efficiency can reach 99.9%at pH 4 after 150 min irradiation under visible light.MT2 photocatalyst was used to treat the wastewater and COD was 1500 mg·L^-1;4.Fenton oxidation and adsorption-oxidation were adopted for advanced treatment of wastewater.The COD was 525 mg·L^-1 and 450 mg·L^-1,respectively.The total COD removal rate can reach more than 98%,meeting the technical requirements for wastewater treatment of enterprises.