Study On The Treatment Of Pure Terephthalic Acid Production Wastewater Based On Persulfate Advanced Oxidation Process And Its Mechanism

The petrochemical industry involves a long industrial chain,complex process,and a wide variety of raw materials and products.The wastewater generated in the production process usually has the characteristics of large discharge,complex composition and a large amount of toxic substances.As the largest dicarboxylic acid in the petrochemical industry,purified terephthalic acid has a very high demand for water in the production process.After the oxidation,washing and refining stages of the process are completed,a large amount of high COD wastewater is produced.The existing processing technology has the disadvantages of large area occupied,high cost and poor treatment effect.Therefore,a new method of high efficiency,greenness and energy-saving is urgently needed for the treatment of the wastewater.Based on the advanced oxidation technology of sodium persulfate,this paper selects the typical organic terephthalic acid in wastewater,investigates the reaction conditions and the influence of coexisting substances on the oxidative degradation process,and based on this,the actual wastewater treatment process is preliminary.In this paper,first,the effects of reaction conditions on the degradation of terephthalic acid were investigated.The four factors of temperature,pollutant concentration,oxidant concentration and initial p H were explored.Considering energy consumption and cost,the suitable degradation conditions of TA were at 80°C,initial TA concentration of 100 mg/L,initial sodium persulfate concentration of 1 g/L,p H=12,reaction time of 3 h and the degradation ratio of TA can reach up to 97.40%.The mechanism of sulfate free generation can be preliminarily obtained by studying the hydrolysis process of sodium persulfate.The degradation process of organic matter and the hydrolysis process of sodium persulfate were consistent with pseudo first-order kinetics and the two processes had a corresponding relation.It can be seen from the free radical characterization and free radical scavenging tests that there were two groups of sulfate radicals and hydroxyl radicals in the reaction and the sulfate radicals played a major in oxidation.At the same time,the main degradation pathway of TA was a decarboxylation process.Then,the effects of coexisting-ions(Mn²⁺and Co²⁺)and coexisting-organic（acetic acid）substances in the actual production wastewater in the degradation process of TA were studied.Mn²⁺and Co²⁺showed opposite effects.Mn²⁺showed significant inhibition on the degradation process,and Co²⁺showed a slight improvement effect on the degradation process.The addition of acetic acid directly competes with the contaminants for oxidants,showing inhibition of the degradation process.By characterizing the solid after reaction and the substituting Mn O₂ for Mn²⁺,the reason for the inhibition of Mn²⁺was given that Mn²⁺was directly oxidized by Na₂S₂O₈ to Mn O₂ with no activation property.Finally,the actual PTA production wastewater was selected,and the experimental results of the previous simulated wastewater were used as the basis.Preliminary study on the process of advanced oxidation treatment of PTA production wastewater by sodium persulfate was explored.After the acid precipitation pretreatment of the wastewater,the oxidation reaction in an alkaline environment was beneficial to the removal of COD.At 80°C,the initial concentration of sodium persulfate was 30 g/L,the initial acid precipitation p H was 1,and the secondary adjustment p H value was12 and reaction time of 3 h,the removal ratio of COD in the actual PTA production wastewater was 96.55%.The research results provide a theoretical reference and technical guidance for the treatment of PTA production wastewater.