Study On The Process And Mechanism Of Degradation Of Nitro-phenol By Advanced Oxidation Process

Phenolic compounds are refractory organic compounds and exist in many different industries, especially in chemical industry. There are more and more phenolic pollutants being discharged into the water with the industrial and economic development. As low concentration p-nitrophenol(PNP) causes poisoning, more and more attention has been paid to the degradation of phenolic compounds in recent years. In all of the degradation methods,the most commonly used methods are ultrasonic electrochemical method and advanced oxidation method.In this paper, we carried out the following researches:(1) Further studies were carried out to explore the degradation effects of p-nitrophenol treated by pulsed ultrasound(US),pulsed electrochemical(EC) process, simultaneous ultrasound enhanced electrochemical(US-EC) process and dual-pulse ultrasound enhanced electrochemical(dual-pulse US-EC)process. Reaction mechanism and kinetics were analyzed under pulsed EC, US-EC and dual-pulse US-EC conditions. Energy consumption and total organic carbon(TOC) of PNP solution treated by dual-pulse US-EC process as well as the feasibility of the industrial operation of this process was explored. The results showed that the degradation efficiency of PNP using dual-pulse US-EC coupling process(with TEC = 100 ms, TUS = 50 ms) reached94.1% at 2 h, higher than 89.0% of US-EC process and 58.9% of pulsed EC process. The dual-pulse US-EC process was the optimum reaction condition and the reaction follows the first-order kinetic model. TOC of PNP solution at 2 h was found to be basically unchanged comparing to the initial TOC. And the results showed that it was difficult to implement in the industry according to the analysis of the economic effects of dual-pulse US-EC method.Potassium permanganate(KMnO4) was used to treat PNP solution for researching a kind of more economical and efficient water treatment method. The temperature, initial pH,optimum dosage of KMnO4, optimum concentration of PNP and TOC removal rate of PNP solution were discussed to establish the optimal degradation conditions. FTIR, BET and XRD were used to analysis the differences between the newly situ formed manganese dioxide(MnO2-1) in degrading process and MnO2-2 formed by KMnO4 and MnSO4·H2O. Reaction mechanism and intermediate products were analyzed by TOC, GC-MS and LC-MS. The studyshowed that the optimal conditions were: mole ratio of KMnO4 and PNP was 10:1(K-P = 10),T = 40 ℃, pH = 2, PNP initial concentration 200 mg/L. The degradation rate of PNP reached99% at 5 min and the effect of adsorption and oxidation of situ formed MnO2-1 could be ignored. The process conditions could be applied to both low concentration and high concentration PNP solution. Intermediate compounds were discovered in the solution, such as hydroquinone, benzoquinone, 2,4-dinitrophenol, 4-nitrocatechol, nitrobenzene, phenol, maleic acid, poly-dimer compounds and so on. TOC removal rate was 97.9% at 1 h and possible degradation pathways were proposed in this paper. Finally, an efficient and economical method for the treatment of organic compounds was established.