Experimental Study On Catalytic Wet Oxidation Treatment Of Fracturing Flowback Fluid

In this paper,on the basis of fracturing flowback fluids(FFFs)for the characteristic of large capacity,high stability,complicated composition,difficult treatment and high content of organic compounds,which were inefficiently treated by the traditional water treatment technology and non-catalytic wet air oxidation.Therefore,catalytic wet air oxidation(CWAO)of FFFs was tested in a batch reactor.The catalyst preparation mechanism of action and stability of the catalyst were mainly studied.The reaction kinetics of the CWAOwas analyzed.FFF was treated with traditional water treatment technology including sodium hypochlorite solution and Fenton reagent.The result showed that the COD removal was 42.6%and 60.3%,respectively,after treatment with sodium hypochlorite solution and Fenton reagent.The optimal operating conditions for non-catalytic wet air oxidation were determined to be 250? and PO2=2.5 MPa.These conditions enabled the most COD removal,approximately 86.1%,after 120 min of reaction.Intermediate formations(e.g.,acetic acid,formic acid,etc)make up a majority of the remaining COD(446.1 mg/L),and analysis showed an acetic acid concentration of 387.4 mg/L.The high activation energy of the intermediate product is the main reason for hindering the non-catalytic wet oxidation performance.These catalysts for CWAO were mainly composed of homogeneous catalysts,metal oxides and supported catalysts.The result showed that both the homogeneous catalysts and supported catalysts showed good catalytic oxidation performance.However,the supported catalysts can effectively avoid the problem of homogeneous catalyst diafiltration.Supports(activated carbon(AC),silica gel(SiO2),y-Al2O3 and TiO2)supported copper catalysts,all of which were prepared by impregnation and were tested in CWAO of FFFs.The results show that the best support was AC.The physical and chemical properties of monometallic and bimetallic supported catalysts were characterized by temperature pmrammed duction(TPR),X-ray diffraction(XRD),BET surface area,scanning electron microscopy(SEM+EDS)and high resolution transmission electron microscopy(HRTEM).These results revealed that the AC supported Cu-Cr had a better catalytic performance due to superior dispersion,lower reduction temperature,and superior pore structure.Using the optimal 5%Cu 1%Cr/AC catalyst(loading 10 g/L),about 97%chemical oxygen demand(COD)removal was achieved.Catalyst stability studies showed that the catalytic activity of fresh and reused catalyst was little changed and the loss rate of catalyst active component was low.The organic structures of FFF were characterized by gas chromatography-mass spectrometer(GC-MS)and fourier transform infrared spectrometer(FT-IR).FT-IR analysis of functional groups and GC-MS analysis of functional groups on the organic matter were basically the same.The structure of organics changed greatly before and after CWAO.The GC-MS analysis results showed that the majority of the organic compounds had been decomposed after CWAO.The decomposition products mainly include alkyl compounds and a small number of aromatics,which shows that the complex of aromatic organic has an open-loop and broken chain reaction,eventually degrading as simple alkane compounds.The reaction kinetic analysis of CWAO showed that the first stage reaction rate equation for CWAO can be established by using the two-stage first-order reaction kinetic model.