Efficiency And Mechanism Of CuFe₂O₄ And CuFe₂O₄/TNTs Catalytic Oxidation In Shale Gas Produced Water Condensate Treatment

With the advent of the shale gas revolution,shale gas has become one of the most strategic energy sources and a research frontier and competition field in the world.Since a large amount of high-concentration and refractory shale gas produced water condensate is produced during the mining process,and it can cause serious threat to the environment and water safety.Therefore,solving the problem of water pollution caused by condensate is important for the sustainable development of the shale gas industry and environmental protection.Among the many water treatment technologies,advanced oxidation technology based on ozone-catalyzed oxidation to produce hydroxyl radicals?HO·?is one of the most effective mothods for treating organic wastewater.In recent years,spinel catalyzed ozone oxidation technology has received extensive attention.With the advantages of stable crystal structure,safety,high efficiency,easy separation and recovery,this technology has become a research hotspot of water treatment technology.However,due to the high production cost and the lack of experience in actual sewage treatment,the technology has been greatly restricted in its promotion and development.Therefore,the development of high-efficiency,low-cost spinel catalysts,and studying its application in ozone catalytic oxidation condensate treatment by ozone catalytic oxidation,has important scientific and practical significance.Four low-cost and high-efficiency spinel catalysts of CoFe₂O₄,CuFe₂O₄,NiFe₂O₄ and ZnFe₂O₄ were prepared by self-combustion method in this paper,and the calcination temperature is reduced and the preparation costs is saved.Four catalysts were characterized by modern techniques such as SEM,BET,XRD,VSM and XPS,and the results show that the four catalysts are all spinel structures with loose porous structure,and the average pore diameter is between 6 nm and 14 nm,and show good ferromagnetism.The catalytic performance of four spinels is evaluated and screened by studying the efflux efficiency of shale gas produced in ozone catalytic oxidation systems.The results show that the four catalytic systems can greatly improve the processing efficiency,and the metal elution amount is low,with good cycle and recyclability.Under a low catalyst dosage(0.15 g?L^-1)and low ozone dosage(1.0 mg?L^-1?min^-1)condition,the catalytic oxidation systems can elevate the biodegradability?B/C ratio?of the condensate from less than 0.1 to above 0.3,increase the assimible organic carbon?AOC?concentration by 5 times,AOC/TOC ratio can be increased to 8%,biological toxicity is significant declined.The treatment efficiency of the four catalytic oxidation systems for the condensate is CuFe₂O₄> NiFe₂O₄> CoFe₂O₄> ZnFe₂O₄.In the experiments of treating high concentration condensate sewage,it is found that,since the surface pore size of CuFe₂O₄ is larger and the surface pores are not easily blocked,so the diffusion efficiency in the pore is less affected by the high concentration organic matter.The mechanism model of the influence of pore size distribution on catalytic efficiency is proposed.In this paper,through the investigation of the condensate treatment efficiency,the CuFe₂O₄ catalyst with excellent performance was screened out.The catalyst loaded with titanium nanotubes?TNTs?is prepared by hydrothermal method.The catalyst thus prepared is named CuFe₂O₄/TNTs.The characterization results show that,since the crystal form of CuFe₂O₄ is bound to the surface of TNTs,so CuFe₂O₄ crystal particles have smaller particle size,and this structural feature will reduce the influence of the internal diffusion process on its catalytic efficiency,and improve its chemical stability,mechanical stability and recycling performance.In addition,CuFe₂O₄/TNTs also show a significant advantage in catalytic performance.The catalytic oxidation experiments show that CuFe₂O₄/TNTs/O₃ system can effectively improve the mineralization ability of organic matter,and the dissolution of metallic elements is only one third of the CuFe₂O₄/O₃ system.CuFe₂O₄/TNTs is less prone to agglomeration when the catalyst dosage is high.When the dosage of ozone reaches 5 mg?L^-1·min^-1,the TOC removal rate of condensate in CuFe₂O₄/TNTs/O₃ system can reach 87%,and the CODCr removal rate can reach 93%,which is about 20% higher than the CuFe₂O₄/O₃ system.This paper studies in depth the catalytic mechanism of spinel catalytic system.It is cleared that both CuFe₂O₄/O₃ and CuFe₂O₄/TNTs/O₃ catalytic systems follow the hydroxyl radical path and the first-order reaction kinetics model.Through kinetics analysis,it is found that the ozone decomposition rate is in linear relationship with the apparent rate constant.CuFe₂O₄/TNTs/O₃ system has a higher ozone utilization rate,and the apparent reaction rate can be more than 1.4 times that of CuFe₂O₄/O₃ system.A quantitative method for the determination of HO· yield in heterogeneous catalytic systems by tert-butanol and methanol complete capture is established.The results show that the yield of HO· in CuFe₂O₄/TNTs/O₃ system is 10^-18% higher than that of CuFe₂O₄/O₃ system.It is found that the adsorption had a lower effect on the methanol complete capture method,because the higher formaldehyde yield.Through the phosphate substitution experiment and the catalyst raw material ratio optimization experiment,the important role of surface hydroxyl groups of CuFe₂O₄/TNTs in the catalytic process is clarified.After oxidation reduction potential analysis and element valence analysis,it reveals that there is not only the valence transition of the A-site element Cu?II?-Cu?III?in the spinel catalyst,but also a valence transition process ofFe?II?-Fe?III?,and it plays an important role in the catalytic process.Furthermore,the synergistic effect of titanium nanotubes?TNTs?promotes the electron transfer process is clarified.The catalytic mechanism model of CuFe₂O₄/TNTs/O₃ system is proposed.It is found that the catalytic system has a higher oxidation efficiency for organic matter with faster diffusion in the pores.Through the Weber-Morris model and the Scatchard model analysis,it is clear that the in-diffusion process is an important rate-limiting step in the kinetics,and the relationship between in-diffusion and binding affinity is confirmed.The quadratic of the in-diffusion rate constant has a positive linear correlation with the number of high affinity points.Through thermodynamic analysis and elemental valence analysis,it is found that the binding affinity is significantly affected by the spatial configuration of chemical groups in the pore,and the mechanism model of the spatial configuration influence on binding affinity is proposed.