Preparation Of Sb-droped SnO₂ Electrode On Ti Substrate And Its Application To Treatment Of High Concentration Refractory Wastewater In Oil And Gas Field

The treatment of high-concentration refractory wastewater generated during the exploitation of oil and gas fields has always been a problem in the industry.In recent years,electrocatalytic oxidation technology(ECOP)has become one of the research hotspots in the treatment of this type of wastewater as an advanced oxidation technology without additive.In ECOP,the efficient anode material represented by Sb-doped SnO₂ electrodes can produce strong oxidized hydroxyl radical,which can completely oxidize and decompose organic pollutants.However,the low electrode life limits the application and development of Sb-doped SnO₂ electrodes.This paper optimized and modifies the substrate microscopic changes and the pulse electrodeposition process,and investigated the treatment effect of two typical oil and gas fields with high concentration of refractory wastewater(drilling waste fluid and oil field fracturing wastewater).In this paper,the preparation conditions of TiO₂ nanotube array of Sb-doped SnO₂electrode were optimized firstly.The experimental results showed that the TiO₂nanotube modified Sb-doped SnO₂ electrode(TiO₂-NTs/SnO₂-Sb)obtained by oxidation voltage between 30?50 V,oxidation time 1 h,heat treatment temperature450?,and reduction time 40 min has a well effect.The nanotube has a pore size of70-130 nm,and the surface of the coating has a rough spherical convex shape.The oxygen evolution potential was increased from 1.9 V to 2.03 V,which can generate more hydroxyl radicals.The degradation rate of phenol in 3 h was increased from 60.57%to 76.4%,and the COD removal rate of phenol was increased from 54.86%to 73.23%.And the electrode working life increased from 503 to 1554.25 h.In the experiment,the pulse electrodeposition process was utilized to prepare Sb-doped SnO₂ electrode Ti/SnO₂-Sb(PED).The experimental results showed that Ti/SnO₂-Sb(PED)was best when the pulse frequency was 50 Hz,the current was 62.5m A·cm^-2,and the duty ratio was 10%.The minimum SnO₂ grain size on the surface of the catalytic layer was 20.31 nm.The degradation rate of phenol in 3 h and the removal rate of COD were 83.4%and 77.8%,respectively.However,the electrode prepared by pulse condition also has obvious problems.The working life of Ti/SnO₂-Sb(PED)and TiO₂-NTs/SnO₂-Sb(PED)electrodes was 39 h and 469.5 h respectively,which was much shorter than the life of Sb-doped SnO₂ electrode prepared by the direct-current type.The treatment effect of the modified Sb-doped SnO₂ electrode on actual drilling waste fluid and oilfield fracturing flowback fluid was investigated.The results showed that,TiO₂-NTs/SnO₂-Sb electrode treatment of drilling wastewater could achieve good decolorization effect,treatment for after 24 h the COD was reduced from 7912.5 mg·L^-1 to 1468 mg·L^-1.And the“poisoning effect”of the anode during the treatment process could be avoided.Oilfield fracturing flowback fluid could be greatly reduced after chemical softening and coagulation pretreatment reduce water hardness and prevent cathode scaling during electrochemical treatment.The TiO₂-NTs/SnO₂-Sb electrode has a TOC removal rate of 40.1%at 40 m A·cm^-2 and p H 9.0 for 12 h.The proportion of small molecules increased after wastewater treatment,and the removal effect of aromatic organic compounds in organics was obvious.And some alcohol hydroxyl bond,ether bond,carboxy bond and other functional groups were generated.the particle size of the particulate matter in oilfield fracturing flowback fluid was reduced,the size of the nanometer particle size was increased,and the organic matter on the surface of the particle was decomposed,resulting in particles destabilization reunion,particle size distribution mainly concentrated at 1000 nm.