Study On Catalytic Methods And Mechanism Of Degradation Of Benzene By Fenton And Electro-Fenton Systems

Benzene is one of the representative pollutant of VOCs,because of its great harm to human body and wide variety of sources,by the WHO as I cancer-causing pollutants.The existing treatment methods of benzene mainly include absorption method,adsorption method and biodegradation method,but the related methods have the problems of low degradation efficiency,slow degradation rate and secondary pollution respectively.It is imperative to develop efficient and economical benzene treatment technology without secondary pollution.Fenton advanced oxidation technology has been widely used in the field of environmental governance in recent years because of its advantages of strong oxidation,high efficiency,clean and mild reaction conditions.However,there are few reports on the degradation of benzene by this technique.The internal reaction of Fenton system is complex and a variety of oxidizing substances coexist.The degradation mechanism and characteristics of Fenton system for benzene are still unclear.To clarify the mechanism of degradation of benzene by Fenton technology,on this basis,promoting methods are proposed,which can greatly improve the treatment effect of benzene,reduce the cost of system operation,and lay the foundation for the development of clean and efficient advanced oxidation technology of benzene.In this paper,experimental methods were used to compare the oxidation capacity of different oxidizing active substances to benzene in Fenton system,the degradation characteristics of benzene in Fenton system are defined,and the reaction mechanism of degradation of benzene in Fenton system was revealed.The Fenton reaction path is controlled by additives,which improve the utilization rate of oxidized substances and the degradation ability of benzene in the system.The effect of floating cathode Electro-Fenton system with Fenton derivative technology on benzene is discussed,and the influence of different factors of the system on benzene degradation is explored.The reaction behavior of two main reactants,H₂O₂ and Fe²⁺,has been clarified,which provides theoretical guidance for the subsequent related research.This paper explored the reaction mechanism of benzene degradation in Fenton system,analyzed the influence of temperature and other key factors on the degradation of benzene system,and obtained the best reaction conditions.The results show that the degradation of benzene by oxidizing substances in Fenton system is in the order from strong to weak is·OH>HO₂·>H₂O₂>O₂^-·,the most active substance is·OH radical.It is found that the main products of benzene oxidation degradation are phenol and diphenol,and the final products are CO₂ and H₂O.Through single factor experiment verification,the best reaction conditions for degradation of benzene by Fenton system are obtained as T=30℃,C_H2O2=7 mmol·L^-1,C_H2O2:C_Fe2+=1,p H=3.In order to improve the yield of active substance·OH,additives were added into the Fenton system to regulated the existing reaction path,promoted the generation of·OH and reduced the amount of Fe²⁺.In this paper,the appropriate additives ware firstly selected,and then the factors affecting the degradation of benzene by improved Fenton system and the adding methods of the additives are analyzed.Finally,the mechanism of the additives in the improved Fenton system was discussed.Studies have shown that ascorbic acid promotes the formation of·OH significantly and is environmentally friendly,so it is suitable to be used as an additive in Fenton system.The optimal reaction conditions and additive addition methods of the improve Fenton system are C_H2O2=10mmol·L^-1,C_H2O2:C_Fe2+=3,C_VC:C_Fe2+=2,secondary addition（1:0.25）,p H=2 and 20℃.The main promotion mechanism of the additive is to generate Fe²⁺by reducing Fe³⁺,which not only blocks the formation of low oxidizing substances HO₂·and O₂^-·,but also strengthens the formation reaction of·OH.Compared with the traditional Fenton system,the oxidation performance of the improve system is significantly enhanced.At the same time,this method can effectively solve the problems of high cost and iron sludge deposition caused by the large amount of Fe²⁺in the traditional system.Based on the research of Fenton,the characteristics and mechanism of degradation of benzene by Electro-Fenton system,a new derivative technology,were studied in this paper.In this paper,the floating cathode was introduced into Electro-Fenton system to solve the error of benzene volatilization caused by aeration in the system.Firstly,the placement form of the floating cathode was explored in this paper.On this basis,the influencing factors of the degradation of benzene by Electro-Fenton system were analyzed to obtain the optimal reaction conditions.Furthermore,the mechanism of the degradation of benzene by Electro-Fenton system was explored to reveal the effect of the Cathode and anode on H₂O₂,and the conversion path of iron in the system was clarified.The results show that the bottom immersion is more conducive to promote the degradation of benzene by the floating cathode Electro-Fenton system.The optimal reaction conditions for the degradation of benzene by the system are C_Na2SO4=50 mmol·L^-1,C_Fe2+=0.30 mmol·L^-1,p H=2,I=0.2 A,T=20℃.Through mechanism verification,it is found that the cathode can not only produce H₂O₂but also consume H₂O₂,and the rate is directly related to the current,while the anode is the main place of ineffective consumption of H₂O₂.In addition to electroreduction,Fe³⁺can also be reduced to Fe²⁺by reacting with H₂O₂ to generate HO₂·.This mechanism provides a theoretical basis for further research on the reaction characteristics of anode and cathode in Electro-Fenton system,analysis of the source pathway of Fe²⁺,and control of the reaction region.