| The exploitation of oil and gas resources promotes the continuous progress of society,and the demand for oil and gas resources in the world is in full swing.As one of the most effective methods to improve oil and gas production,hydraulic fracturing has been widely used in the development of oil and gas resources in recent decades.However,due to the presence of a large number of organic pollutants,the fracturing fluid with high COD,high viscosity,stable physical and chemical properties has brought new problems,and its emissions are prone to serious environmental pollution.As a new green environmental protection technology,photocatalytic has great potential in the treatment of fracturing backflow fluid in oil field.In this paper,the bismuth-rich photocatalyst Bi24O31X10(X=Cl,Br)was studied,and the silver-bismuth halide based composite photocatalyst Ag/AgX/Bi24O31X10(X=Cl,Br,I)was prepared.The degradation effect and mechanism of the filtrated fracturing fluid and hydroxypropyl guanidine gum were evaluated.The main research contents and results are as follows:(1)A series composite photocatalysts of Ag/AgX/Bi24O31X10(X=Cl,Br,I)were synthesiz-ed by molecular precursor calcination and light reduction precipitation.The preparation parameters such as calcination time,calcination temperature,chlorine-bromine ratio,photo-reduction time,type of silver halide and mass fraction of silver halide were optimized by degradation of Rhodamine B,and three kinds of composite photocatalysts were optimized.The photocatalysts were 8-Ag/AgI/Bi24O31Cl10,4-Ag/AgBr/Bi24O31Br10,15-Ag/AgI/Bi24O31Cl5Br5,respectively.The structure and properties of the photocatalysts were characterized and their cyclic stability was evaluated preliminarily.(2)The optimized composite photocatalyst was used to degrade the organic pollutant hydroxypropyl guanidine gum in fracturing effluents.The effects of photocatalysts dosage,hydroxypropyl guanidine gum concentration,pH,light intensity(xenon lamp current),temperature and light source(incident light wavelength)on the degradation of hydroxypropyl guanidine gum were studied.The results showed that the degradation rate of hydroxypropyl guanidine gum was greatly improved by the composite photocatalyst after step-by-step optimi-zation of degradation conditions.The results of cyclic experiment showed that the composite photocatalyst still had the ability to degrade hydroxypropyl guanidine gum after 4 times of repeated degradation.The degradation effect of the composite photocatalyst on the fracturing efflux was tested by using the optimized degradation conditions and COD as the evaluation standard.(3)The active species produced during the degradation of hydroxypropyl guanidine gum by composite photocatalyst were investigated by capture experiment,and the mechanism of degradation of hydroxypropyl guanidine gum by each composite photocatalyst was analyzed by combining the active species and the energy band structure.The results show that the three composite photocatalysts are Z-scheme heterojunction composite structure with silver Ag0 as electron transfer intermediate.The enhanced photogenerated carrier separation,the enhancement of visible light absorption by the SP1 effect of silver Ag0,and the generation of oxygen-containing active species make the photodegradation activity of the composite photocatalyst significantly higher than that of the monomer photocatalyst.In this paper,the photocatalytic oxidation technique was used to evaluate the properties of fracturing liquid and hydroxypropyl guanidine gum,and the degradation rate of hydroxypropyl guanidine gum in the solution reached 78.08%and 89.72%under visible light,respectively.At last,the degradation mechanism of photocatalyst is deeply studied,which provides a new method and theoretical support for environmental protection treatment of hydroxypropyl guanidine gum in fracturing backflow solution. |
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