Electro-catalysis equipment and method for treating phthalic acid ester in shale gas flowback fluid

Abstract

The invention discloses electro-catalysis equipment and method for treating phthalic acid ester in shale gas flow-back fluid, and belongs to the field of shale gas flow-back fluid treatment. An iron monatomic modified graphite electrode is adopted as a cathode of the electro-catalysis equipment, a ruthenium iridium oxide loaded titanium substrate electrode is adopted as an anode, and the anode and the cathode are connected to a constant-voltage and constant-current power supply through an electric lead. Compared with an unmodified graphite felt electrode, the iron monatomic modified graphite electrode prepared by the preparation method disclosed by the invention is used as a cathode of electro-catalysis equipment, can efficiently degrade phthalic acid ester in shale gas flowback fluid, and meanwhile, reduces generation of halogenated organic products and biotoxicity of effluent.

Description

Technical Field

[0001] The invention belongs to the field of shale gas flowback fluid treatment, and specifically relates to an electrocatalytic device and method for treating phthalates in shale gas flowback fluid. Background Art

[0002] With the continuous expansion of energy demand and the continuous advancement of energy extraction technology, the global recoverable oil and gas reserves are declining year by year. Shale gas, as a clean and efficient unconventional energy source, has received widespread attention. my country's demand for oil and gas resources, especially natural gas, is growing rapidly, and the exploration and development of shale gas is of great significance. However, during the hydraulic fracturing and extraction of shale gas, a large amount of return water with complex components will be produced. These return waters contain a large amount of inorganic salts, heavy metals and organic pollutants, such as polycyclic aromatic hydrocarbons, benzene series, phthalate esters (PAEs), etc. Phthalates are difficult to decompose in the natural environment by conventional means due to their stable chemical structure and strong resistance to degradation. They are typical refractory organic pollutants. If people are exposed to an environment containing such pollutants for a long time, directly or indirectly contacting organic pollutants in return water, they may cause endocrine system damage, induce acute toxicity, and even increase the risk of cancer. Therefore, it is particularly important to develop a clean and efficient treatment technology for such pollutants.

[0003] Traditional biological methods are inefficient in treating high-salinity shale gas flowback water. Although the advanced oxidation processes (AOPs) in the chemical method have the advantages of fast reaction rate and strong oxidation ability, they often produce highly toxic and difficult to degrade halogenated intermediates when treating high-salinity organic wastewater, which limits its scope of application.

[0004] As a new type of environmentally friendly technology, the electrochemical advanced oxidation process (EAOP) has been used to treat high-salt organic wastewater and has shown many outstanding advantages. The process has strong oxidation ability, does not require external agents, is easy to instrument and can be automatically controlled, and has a good treatment effect on difficult-to-degrade organic pollutants. In the electrochemical advanced oxidation process, the oxygen reduction reaction at the cathode can promote oxygen to produce strong oxidizing substances, thereby improving the oxidation performance. Commonly used graphite felt as a cathode material has the advantages of few side reactions in the oxygen reduction reaction, good conductivity, and facilitating gas diffusion, which is conducive to the transfer of oxygen to the electrode surface. However, traditional graphite cathodes also have some disadvantages, such as the lack of reactive active sites on the surface of graphite felt, resulting in poor catalytic activity.

[0005] Therefore, it is urgent to develop an electrocatalytic oxidation technology to improve the indirect oxidation effect of the cathode, so as to achieve efficient and green removal of phthalate organic pollutants in shale gas flowback fluid. Summary of the invention

[0006] The purpose of the present invention is to solve the deficiencies of the prior art and to provide an electrocatalytic device and method for treating phthalates in shale gas flowback fluid.

[0007] The specific technical solutions adopted by the present invention are as follows:

[0008] In a first aspect, the present invention provides an electrocatalytic device for treating phthalates in shale gas return fluid, wherein the cathode of the electrocatalytic device adopts a graphite electrode modified with a single iron atom, and the anode is a ruthenium iridium oxide-loaded titanium substrate electrode, and the anode and the cathode are connected to a constant voltage and constant current power supply through a conductive wire.

[0009] Preferably, the preparation method of the graphite electrode modified with a single iron atom is as follows: S1: pretreating a graphite felt substrate with a deposition liquid; S2: placing the pretreated graphite felt substrate in a deposition liquid for electrodeposition to obtain an electrodeposited substrate; S3: freeze-drying the obtained electrodeposited substrate and then performing a pyrolysis treatment to finally obtain a graphite electrode modified with a single iron atom;

[0010] The ruthenium iridium oxide-loaded titanium substrate electrode Ti / (Ru 0.7 Ir 0.3 ) 2 The molar ratio of ruthenium to iridium atoms is 7:3.

[0011] Preferably, the pretreatment process uses a magnetic stirrer to stir at a speed of 800-1000 r / min for 8-10 hours.

[0012] Preferably, the deposition solution comprises: 0.1-0.5 mol / L polyaniline, 0.5 mol / L H 2 SO 4 , the total iron ion concentration is 0.05-0.15 mmol / L; the total iron ion concentration is the sum of divalent iron ions and trivalent iron ions, wherein the molar ratio of trivalent iron ions to divalent iron ions is 2:1.

[0013] Furthermore, the electrodeposition process is specifically as follows: the graphite felt substrate is used as the working electrode, the platinum wire is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode, and a constant current is passed for electrodeposition, the deposition current is 1A, the deposition voltage is a constant voltage of 0.8V, and the deposition time is 15 to 60s.

[0014] Preferably, the freeze-drying process of the electrodeposited substrate is as follows: firstly put it into a -80°C refrigerator for freezing for 0.5 to 1 hour, and then put it into a freeze dryer for freeze drying for 8 hours.

[0015] Preferably, the pyrolysis treatment adopts a tubular furnace, the pyrolysis atmosphere is nitrogen, the pyrolysis temperature is 300-500°C, the pyrolysis time is 4h, and the heating rate is 5°C / min.

[0016] In a second aspect, the present invention provides a method for treating phthalates in shale gas return fluid using the electrocatalytic device described in the first aspect, wherein shale gas return fluid containing phthalates is added to the electrolytic cell of the electrocatalytic device, the current density between the anode and the cathode is controlled to be constant, and an electrocatalytic reaction is performed to degrade the phthalates in the shale gas return water.

[0017] Preferably, the current density is 66 mA / cm 2 .

[0018] As a preferred method, Cl in shale gas flowback fluid - The concentration is 0.2-0.4 mol / L; the phthalate is diethyl phthalate.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention prepares a graphite electrode modified with single iron atoms (GF@Fe SACs-PANIc). Compared with the unmodified graphite felt electrode, the surface of the electrode is doped with single iron atoms to improve the catalytic activity and has a stronger pollutant detoxification ability. Using it as the cathode of the electrocatalytic device can efficiently degrade phthalates in shale gas return fluid. Experimental verification shows that the removal rate of phthalates can reach more than 99.7% after 5 hours of electrocatalytic reaction. While effectively reducing the generation of organic halogenated intermediates, the biological toxicity of the treated effluent is also significantly reduced.

[0021] (2) The method for treating phthalates in shale gas flowback fluid using the electrocatalytic device provided by the present invention has a simple reaction process, convenient operation, and low requirements for equipment; in addition, the method has mild reaction conditions, can be carried out at room temperature and pressure, does not generate energy consumption such as heating, cooling, and pressurization, and can reduce operating costs. This technology can be widely used in the fields of environmental pollution control and environmental remediation, and has a good market prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a scanning transmission electron microscopy image (HAADF) of the iron single atom modified graphite electrode (GF@Fe SACs-PANIc) prepared in Example 1.

[0023] Figure 2This is a spherical aberration high-resolution scanning transmission electron microscopy image (AC-HAADF-STEM) of the iron single atom modified graphite electrode (GF@Fe SACs-PANIc) prepared in Example 1.

[0024] Figure 3 The extended X-ray absorption fine structure image (EXAFs) of the iron single atom modified graphite electrode (GF@Fe SACs-PANIc) prepared in Example 1.

[0025] Figure 4 This is a comparison chart of the degradation of PAEs of the iron single atom modified graphite electrode prepared under different pyrolysis temperature conditions in Example 2 and the unmodified graphite felt electrode in Comparative Example 1.

[0026] Figure 5 This is a comparison chart of the degradation of PAEs of the graphite electrode modified with single iron atoms prepared under different deposition time conditions in Example 3 and the unmodified graphite felt electrode in Comparative Example 1.

[0027] Figure 6 This is a comparison chart of the degradation of PAEs of the iron single atom modified graphite electrode prepared at different iron ion concentrations in Example 4 and the unmodified graphite felt electrode in Comparative Example 1.

[0028] Figure 7 This is a comparison chart of the linear sweep voltammetry test (LSV) of the graphite electrode modified with single iron atoms under different pyrolysis temperature conditions in Example 5 and the unmodified graphite felt electrode in Comparative Example 2.

[0029] Figure 8 This is a comparison chart of the degradation of PAEs at different chloride ion concentrations in Example 6.

[0030] Fig. 9 This is a comparison chart of the water toxicity test after the three groups of electrocatalytic reactions in Example 7.

[0031] Fig.10 This is a comparison chart of the concentrations of organic halogenated intermediates in the effluent water after the three groups of electrocatalytic reactions in Example 7.

[0032] Fig.11 This is a comparison chart of the COD concentration test of the graphite electrode modified with single iron atoms and the unmodified graphite felt electrode before and after the degradation of actual return water in Example 8.

[0033] Fig.12 This is a comparison chart of the TOC concentration test of the graphite electrode modified with single iron atoms and the unmodified graphite felt electrode before and after degradation of actual return water in Example 8.

[0034] Fig.13 This is a comparison chart of the biological toxicity tests of the graphite electrode modified with single iron atoms and the unmodified graphite felt electrode before and after degradation of actual return water in Example 8. DETAILED DESCRIPTION

[0035] The present invention is further described and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0036] Example 1

[0037] This example prepares a graphite electrode modified with a single iron atom, and the specific method is as follows:

[0038] (1) Preparation of deposition solution

[0039] In a 250 mL volumetric flask, add 0.3 mol / L polyaniline (PANI), 0.5 mol / L H 2 SO 4 、0.1mol / LFeCl 3 6H 2 O and 0.05 mol / LFeSO 4 7H 2 O, dilute to the mark with ultrapure water and mix well.

[0040] (2) Pretreatment of graphite felt substrate

[0041] A graphite felt with a size of 5 cm×3 cm was selected as the substrate material. The graphite felt substrate was immersed in the deposition liquid and stirred at 900 r / min for 8 h using a magnetic stirrer to complete the pretreatment.

[0042] (3) Electrodeposition

[0043] During electrodeposition, a three-electrode working system was used, with a graphite felt substrate (GF) as the working electrode, a platinum wire as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode placed in the deposition solution, and a constant current of 1 A was passed for electrodeposition. The deposition time was 30 s to obtain an electrodeposited substrate.

[0044] (4) Freezing

[0045] The electrodeposited substrate was first frozen at -80°C for 1 hour and then freeze-dried in a freeze dryer for 8 hours.

[0046] (5) Pyrolysis

[0047] The freeze-dried electrodeposited substrate was placed in a tubular furnace for pyrolysis treatment. Nitrogen was purged during the pyrolysis process. The temperature was increased to 400°C at a heating rate of 5°C / min and maintained for 4 h. Finally, an iron single atom modified graphite electrode (GF@Fe SACs-PANIc) was prepared.

[0048] Figure 1This is a scanning transmission electron microscopy image (HAADF) of the iron single atom modified graphite electrode (GF@Fe SACs-PANIc) prepared in this example. Figure 1 It can be seen that the Fe element is distributed in a uniform dispersion state in the material, and it is speculated that Fe may exist on the electrode surface in the form of an atomic state. The modified graphite electrode was analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES). The specific operation was to grind 0.0168g of the modified electrode into powder with a mixed solution of concentrated nitric acid and hydrogen peroxide (4:1), digest it in a digester for 6 hours, and dilute it ten times before testing. It was calculated that the mass fraction of Fe in the modified graphite electrode material was 0.29334wt%. Therefore, there is a certain form of Fe element in the electrode, and the conclusions on its distribution state and existence form have been preliminarily verified by image observation and elemental analysis technology respectively.

[0049] Figure 2 This is a spherical aberration high-resolution scanning transmission electron microscopy (AC-HAADF-STEM) image of the iron single atom modified graphite electrode (GF@Fe SACs-PANIc) prepared in this example. Figure 2 It can be seen that the Fe element is evenly distributed, and no clusters or tiny nanoparticles are observed. It can be inferred that Fe exists on the electrode surface in the form of atoms.

[0050] Figure 3 The extended X-ray absorption fine structure images (EXAFs) of the iron single atom modified graphite electrode (GF@Fe SACs-PANIc) prepared in this example. Figure 3 It can be seen that there is only one major peak in the EXAFs spectrum, which can be attributed to the Fe-N bond. The second peak at can be interpreted as the peak of the Fe-Fe bond. This verifies that the modified electrode material is a single-atom material.

[0051] Example 2

[0052] This example uses a graphite electrode modified with a single iron atom prepared at different pyrolysis temperatures as the cathode of an electrocatalytic device for degrading diethyl phthalate phthalate, as follows:

[0053] (1) Preparation of graphite electrodes modified with single iron atoms

[0054] The specific preparation method is as in Example 1, and the pyrolysis temperature is adjusted to 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, and 900°C to prepare graphite electrodes modified with single iron atoms at different pyrolysis temperatures.

[0055] (2) Preparation of a ruthenium-iridium oxide-loaded titanium substrate electrode with a ruthenium-iridium atomic molar ratio of 7:3

[0056] ① Pretreatment of titanium substrate: sandblast the titanium substrate of 1.5mm×50mm×70mm, then ultrasonically wash it with deionized water for 15min, place it in 500mL of 50mg / L sodium hydroxide solution, and react it in a water bath at 80℃ for 60min. Rinse it with deionized water, place it in 500mL of 10% oxalic acid solution, heat it to boiling and keep it for 120min. Rinse it with deionized water again, place it in 1% oxalic acid solution for future use.

[0057] ②Prepare ruthenium-iridium coating solution: weigh 0.06931 g of RuCl 3 and 0.07376 g chloroiridic acid (H 2 IrCl 6 ·xH 2 O), dissolved in 4 mL of anhydrous methanol, and then added with 1 mL of 6% concentrated hydrochloric acid, and ultrasonicated for 20 minutes.

[0058] ③ Ruthenium-iridium coating liquid is doped on the titanium substrate: 200 μL of ruthenium-iridium coating liquid is taken and evenly applied on the surface of the pretreated titanium substrate with an area of ​​5 cm×7 cm using a coating rod. It is placed under an infrared lamp until the surface solvent is completely evaporated, and then placed in a muffle furnace, thermally oxidized at 500°C for 10 minutes, and cooled to room temperature. Repeat the coating and thermal oxidation 10 times, and the last thermal oxidation time is 60 minutes. Finally, a ruthenium-iridium oxide-loaded titanium substrate electrode with a ruthenium-iridium atomic molar ratio of 7:3 is obtained, and the electrode is recorded as Ti / (Ru 0.7 Ir 0.3 ) 2 .

[0059] (3) Degradation experiment

[0060] A two-electrode working system is used, with the anode having an effective area of ​​15 cm 2 Ruthenium iridium oxide supported titanium substrate (Ti / (Ru 0.7 Ir 0.3 ) 2 ) electrode, and the cathode respectively used graphite electrodes modified with single iron atoms of the same size and different pyrolysis temperatures prepared in step (1), and the distance between the two electrodes was fixed at 2 cm. The anode and cathode were connected to a constant current power supply through a conductive wire, and the current intensity was controlled to be 1A. During the reaction, the effective reaction area of ​​the electrode exposed to the electrolyte was 5 cm×3 cm. In order to ensure the accuracy of the data, the electrode was immersed in the solution to be degraded for 8 hours to remove the influence of adsorption on its test effect. The entire electrocatalytic reaction was carried out on a magnetic stirrer (600 rpm). For each electrocatalytic reaction, 250 mL of simulated shale gas return fluid was added to the electrolytic cell, in which diethyl phthalate (PAEs) was 1 mg / L, Cl - It is 0.2mol / L and pH is 7.

[0061] After the electrocatalytic reaction is started, samples are taken in sequence according to the set time gradient. Use a pipette to take 1 mL of sample in a centrifuge tube, immediately add 1 mL of n-hexane, and oscillate in a vortex oscillator for 5 minutes for extraction. Take the upper organic phase after separation and add an appropriate amount of anhydrous sodium sulfate to remove water. Use a 2.5 mL disposable syringe to extract the upper organic phase through a 0.22 μm membrane. The sample is qualitatively and quantitatively analyzed by gas chromatography-mass spectrometry (GC-MS). The instrument test parameters refer to the "Gas Chromatography-Mass Spectrometry for the Determination of Six Phthalate Esters in Soil and Sediment" (HJ 1184-2021) promulgated by the Ministry of Ecology and Environment of China.

[0062] Comparative Example 1

[0063] This comparative example uses a two-electrode working system, and an unmodified graphite felt electrode with an effective area of ​​5 cm × 3 cm is used as the cathode of the electrocatalytic device, and an effective area of ​​15 cm 2 Ruthenium iridium oxide supported titanium substrate (Ti / (Ru 0.7 Ir 0.3 ) 2 ) electrode was used as the anode, and the distance between the two electrodes was fixed at 2 cm. The anode and cathode were connected to a constant current power supply through a conductive wire, and the current intensity was controlled to be 1A. In order to ensure the accuracy of the data, the electrode was immersed in the solution to be degraded for 8 hours to remove the influence of adsorption on its test effect. The entire electrocatalytic reaction was carried out on a magnetic stirrer (600 rpm), and 250 mL of simulated shale gas return fluid was added to the electrolytic cell, in which diethyl phthalate (PAEs) was 1 mg / L, Cl - It is 0.2mol / L and pH is 7.

[0064] Figure 4 The degradation comparison diagram of PAEs of the graphite electrode modified with single iron atoms prepared under different pyrolysis temperature conditions in Example 2 and the unmodified graphite felt electrode in Comparative Example 1 is shown. Figure 4 It can be seen that compared with the unmodified graphite felt electrode, the graphite electrode modified with single iron atoms has a better electrocatalytic effect, among which the graphite electrode modified with single iron atoms prepared at 400°C is far superior to the graphite electrodes modified with single iron atoms prepared under other pyrolysis temperature conditions. The electrode has a greatly improved degradation effect on PAEs, and the removal rate of PAEs is increased by up to 15 times compared with other electrodes.

[0065] Example 3

[0066] In this example, the graphite electrode modified with single iron atoms prepared at different electrodeposition times was used as the cathode of the electrocatalytic device to degrade diethyl phthalate, as follows:

[0067] (1) Preparation of graphite electrodes modified with single iron atoms

[0068] The specific preparation method is as in Example 1, and the electrodeposition time is adjusted to 15s, 30s, 60s, 120s, and 240s, respectively, to prepare a graphite electrode modified with single iron atoms under the electrodeposition time.

[0069] (2) Degradation experiment

[0070] A two-electrode working system is used, with the anode having an effective area of ​​15 cm 2 Ruthenium iridium oxide supported titanium substrate (Ti / (Ru 0.7 Ir 0.3 ) 2 ) electrode, and the cathode are graphite electrodes modified with single iron atoms prepared in step (1) of the same size and different electrodeposition times, and the distance between the two electrodes is fixed at 2 cm. The other conditions are the same as those in Example 2.

[0071] Figure 5 The degradation comparison diagram of PAEs of the graphite electrode modified with single iron atoms prepared under different deposition time conditions in Example 3 and the unmodified graphite felt electrode in Comparative Example 1 is shown. Figure 4 It can be seen that compared with the unmodified graphite felt electrode, the graphite electrode modified with single iron atoms has a better electrocatalytic effect. Among them, the graphite electrode modified with single iron atoms prepared at a deposition time of 30s is far superior to other electrodes, and the degradation effect of PAEs is greatly improved. If the deposition time is too short, the electrode surface is not enough to be doped with sufficient single iron atom active sites, and if the deposition time is too long, the electrode surface will be doped with nanocluster particles, and the effect is not as good as that of Fe single atoms.

[0072] Example 4

[0073] This example uses a graphite electrode modified with single iron atoms prepared at different iron ion concentrations as the cathode of an electrocatalytic device for degrading diethyl phthalate, as follows:

[0074] (1) Preparation of graphite electrodes modified with single iron atoms

[0075] The specific preparation method is as in Example 1, adjusting the total iron ions (including Fe 2+ and Fe 3+ , where Fe 3+ and Fe 2+ The molar ratio is 2:1) and the concentrations are 0.05mmol / L, 0.1mmol / L, 0.15mmol / L, 0.3mmol / L, and 0.45mmol / L, respectively, to prepare iron single atom modified graphite electrodes at different iron ion concentrations.

[0076] (2) Degradation experiment

[0077] A two-electrode working system is used, with the anode having an effective area of ​​15 cm 2 Ruthenium iridium oxide supported titanium substrate (Ti / (Ru 0.7 Ir 0.3 ) 2 ) electrode, and the cathode are respectively prepared in step (1) with the same size and different iron ion concentrations and the graphite electrode modified with iron single atom, and the distance between the two electrodes is fixed at 2 cm. The other conditions are the same as those in Example 2.

[0078] Figure 6 The degradation comparison diagram of PAEs of the graphite electrode modified with single iron atoms prepared under different iron ion concentrations in Example 4 and the unmodified graphite felt electrode in Comparative Example 1 is shown. The electrode prepared under lower iron ion concentration conditions (0.05-0.15 mmol / L) has better performance than the graphite electrode modified with single iron atoms prepared under high iron ion concentration conditions (0.3-0.45 mmol / L). This may be because excessive Fe atom doping may form too many inactive impurity clusters or aggregations inside the carbon material. These clusters will occupy the original pore space, reduce active sites, affect the charge transfer efficiency between it and the reactants, and ultimately affect the catalytic activity.

[0079] Example 5

[0080] In this example, a graphite electrode modified with single iron atoms prepared at different pyrolysis temperatures was used as the cathode of the electrocatalytic device, and a linear sweep voltammetry (LSV) test was performed, as follows:

[0081] (1) Preparation of graphite electrodes modified with single iron atoms

[0082] The specific preparation method is the same as in Example 1, and the pyrolysis temperature is adjusted to 300° C., 400° C., and 600° C. to prepare graphite electrodes modified with single iron atoms at different pyrolysis temperatures.

[0083] (2) LSV test

[0084] A three-electrode working system was used, with the anode having an effective area of ​​15 cm 2 Ruthenium iridium oxide supported titanium substrate (Ti / (Ru 0.7 Ir 0.3 ) 2 ) electrode, the cathode is a graphite electrode modified with iron single atom prepared at different pyrolysis temperatures and of the same size prepared in step (1), and the reference electrode is an Ag / AgCl electrode. The concentration of diethyl phthalate (PAEs) in the solution is 1 mg / L, and Cl - The concentration is 0.2mol / L and the pH is 7.

[0085] Comparative Example 2

[0086] This comparative example uses a three-electrode working system, with the anode having an effective area of ​​15 cm 2 Ruthenium iridium oxide supported titanium substrate (Ti / (Ru 0.7 Ir 0.3 ) 2 ) electrode, the cathode is an unmodified graphite felt electrode, and the reference electrode is an Ag / AgCl electrode. The concentration of diethyl phthalate (PAEs) in the solution is 1 mg / L, Cl - The concentration is 0.2mol / L and the pH is 7.

[0087] Figure 7 This is a comparison chart of the linear sweep voltammetry (LSV) test of the graphite electrode modified with single iron atoms under different pyrolysis temperature conditions in Example 5 and the unmodified graphite felt electrode in Comparative Example 2. Figure 7 It can be seen that at 400°C, the chlorine evolution potential reaches the lowest value. Since the chlorine evolution potential refers to the electrode potential required for the chlorine evolution reaction to occur under certain conditions, the lower its value, the smaller the energy barrier that needs to be overcome for the chlorine evolution reaction, which is more conducive to the occurrence of the chlorine evolution reaction. The smooth progress of the chlorine evolution reaction can produce chlorine species with strong oxidizing properties, thereby promoting the degradation of pollutants. Therefore, the modified graphite electrode at 400°C is more likely to promote the degradation of pollutants than the graphite electrode modified with single iron atoms and the unmodified graphite felt electrode at other pyrolysis temperatures.

[0088] Example 6

[0089] In this example, the iron single atom modified graphite electrode prepared in Example 1 was used to electrocatalytically degrade diethyl phthalate in simulated shale gas flowback fluids containing different chloride ion concentrations, and the NaCl concentrations in the simulated shale gas flowback fluids were 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.8 mol / L, and 1 mol / L, respectively. The degradation experiment was the same as in Example 2.

[0090] Figure 8 This is a comparison chart of the effects of different chloride ion concentrations on the degradation of diethyl phthalate (PAEs). Figure 8 It can be seen that Cl - When the concentration is 0.2-0.4 mol / L, the degradation effect of the graphite electrode modified with single iron atoms is good. - When the concentration increased to 1 mol / L, the PAEs degradation effect gradually became worse, which shows that too low chloride ion concentration is not conducive to the production of active substances, while too high chloride ion concentration will produce side reactions, which may react with the generated active substances, and may also affect the existence form and activity of the active substances, thereby affecting the degradation effect.

[0091] Example 7

[0092] This example conducts a toxicity test on the effluent after the electrocatalytic reaction in Example 2 and Comparative Example 1, as follows:

[0093] The iron single atom modified graphite electrode prepared in Example 2 (pyrolysis temperature is 400°C and 600°C) or the unmodified graphite felt electrode in Comparative Example 1 is used as the cathode. The PAEs degradation test is first carried out according to the experimental method of Example 2, and the raw water and the effluent of the electrocatalytic reaction for 1 min, 5 min, 10 min, 20 min, 30 min, 1 h, 3 h, and 5 h are respectively taken for toxicity test.

[0094] Toxicity test method: Vibrio fischeri was used as the test organism, and the luminescent bacteria toxicity instrument was used to conduct the luminescent bacteria toxicity test of the sample. The specific steps are as follows:

[0095] (1) Sterilization: Pipette tips (1 ml, 100 μL), test tubes (lyophilized powder vials), centrifuge tubes (5 mL) and other consumables are sterilized by high-temperature steam sterilization at 121.3°C for 30 minutes;

[0096] (2) Preparation of diluent and buffer solution: Weigh 2.00 g and 22.00 g of NaCl respectively into a beaker, add ultrapure water to dissolve, and transfer to a 100 mL volumetric flask. Shake to volume and then prepare the diluent (2% NaCl solution) and buffer solution (22% NaCl solution).

[0097] (3) Luminescent bacteria resuscitation: Take 1 mL of the resuscitation solution in a freeze-dried powder vial, wait for 15 minutes, then take 1 mL of the bacterial solution and dilute it to 40 mL to prepare the luminescent bacteria working solution.

[0098] (4) Luminescent bacteria toxicity test: After turning on the instrument, let the Delta Tox II analyzer self-check for 5 minutes and set the analysis mode to B-Tox. Take 1 mL of water sample into test tube A and add 100 μL of buffer; start another test tube B and add 100 μL of luminescent bacteria solution. Put test tube B on the sample table, take it out after the instrument reads, and immediately transfer 900 μL of solution from test tube A to test tube B. After reacting for 5 minutes, put it back on the sample table for testing and record the inhibition degree of luminescent bacteria.

[0099] Fig. 9The following is a comparison chart of the toxicity test of the effluent after the three groups of electrocatalytic reactions. Within 1 minute of the initial reaction, the inhibition rate of luminescent bacteria in all systems remained at 100%. As the electrocatalytic oxidation reaction proceeded, the inhibition rate of luminescent bacteria in the effluent by the unmodified graphite felt electrode system remained unchanged, and the inhibition rate of luminescence in the effluent by the modified iron single atom-modified graphite electrode system gradually decreased. This shows that the unmodified graphite felt electrode is difficult to catalytically degrade PAEs, and a large number of toxic halogenated intermediates may be generated. Compared with the unmodified graphite felt electrode, the modified electrode can effectively degrade PAEs, reducing the toxicity of the effluent after treatment.

[0100] (5) Test for organic halogenated intermediates: The organic halogenated intermediates in the effluent after electrocatalytic treatment of an iron single atom-modified graphite electrode and an unmodified graphite felt electrode with pyrolysis temperatures of 400°C and 600°C, respectively, were tested. The test method referred to the standard "Microcoulometric Method for the Determination of Adsorbable Organic Halogen (AOX) in Water Quality" (HJ 1214-2021).

[0101] Fig.10 The figure is a comparison chart of the concentration of organic halogenated intermediates in the effluent after three groups of electrocatalytic reactions. At 60 minutes of electrocatalytic reaction, the concentration of halogenated intermediates in the effluent of the graphite electrodes modified by single iron atoms at two pyrolysis temperatures was lower than that of the unmodified graphite felt electrode, and the concentration of halogenated intermediates in the graphite electrode modified by single iron atoms at 400°C was the lowest. As the electrocatalytic reaction proceeds, at 180 minutes, the concentration of halogenated intermediates in the effluent after the unmodified graphite felt electrode treatment only decreased by 0.4 mg / L compared with 60 minutes, while the concentration of halogenated intermediates in the effluent after the graphite electrode modified by single iron atoms was significantly reduced. The modified graphite felt electrodes at 400°C and 600°C reduced the concentration of halogenated intermediates by 2.5 mg / L and 1.88 mg / L, respectively, which explains the reduction in the acute toxicity of the effluent organisms after treatment. Therefore, compared with the unmodified graphite felt electrode, the graphite electrode modified by single iron atoms prepared by the present invention can effectively reduce the generation of organic halogenated intermediates.

[0102] Example 8

[0103] In this embodiment, a graphite electrode modified with a single iron atom and an unmodified graphite felt electrode are used to electrocatalyze actual shale gas return water, as follows:

[0104] Flowback water was obtained from a shale gas well field in Nanchuan District, Chongqing. A two-electrode system was used, and the iron single atom-modified graphite electrode prepared in Example 1 and the unmodified graphite felt electrode were selected as the cathode of the electrocatalytic device, with an effective area of ​​15 cm 2 Ruthenium iridium oxide supported titanium substrate (Ti / (Ru 0.7 Ir 0.3 ) 2) electrode as the anode, and the other conditions were the same as in Example 2. The above actual shale gas return water was subjected to electrocatalytic treatment for 300 minutes, and the COD (test method reference HJ 924-2017) and TOC (test method reference HJ 501-2009) before and after the reaction were tested. According to the toxicity test method of Example 7, the biological toxicity of the return water before and after the electrocatalytic treatment of the above two groups was tested.

[0105] like Fig.11 and Fig.12 Compared with the unmodified graphite felt electrode, the modified graphite electrode modified with single iron atoms has better removal effect on COD and TOC in actual return water. After 300 minutes of electrocatalytic treatment, the COD removal rate increased from 27% to 53%, and the TOC removal rate increased from 45% to 57%.

[0106] like Fig.13 The modified graphite electrode modified with single iron atoms reduces the acute biological toxicity in the return water by 53%, while the unmodified graphite felt electrode reduces the biological toxicity by only 9%. Therefore, the graphite electrode modified with single iron atoms prepared by the present invention can effectively degrade organic pollutants including diethyl phthalate in actual return water as the cathode of the electrocatalytic device, and can effectively reduce the biological toxicity of actual return water, and has better degradation effect and biological toxicity reduction effect on organic pollutants in return water than the unmodified graphite felt electrode.

[0107] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. An electrocatalytic device for treating phthalates in shale gas flowback fluid, characterized in that: The cathode of the electrocatalytic device adopts a graphite electrode modified with a single iron atom, and the anode is a ruthenium iridium oxide-loaded titanium substrate electrode. The anode and the cathode are connected to a constant voltage and current power supply through a conductive wire.

2. The electrocatalytic device for treating phthalates in shale gas flowback fluid according to claim 1, characterized in that: The preparation method of the graphite electrode modified with a single iron atom is as follows: S1: pretreating a graphite felt substrate with a deposition liquid; S2: placing the pretreated graphite felt substrate in a deposition liquid for electrodeposition to obtain an electrodeposited substrate; S3: freeze-drying the obtained electrodeposited substrate and then performing a pyrolysis treatment to finally obtain a graphite electrode modified with a single iron atom; The ruthenium iridium oxide-loaded titanium substrate electrode Ti / (Ru 0.7 Ir 0.3 )The molar ratio of ruthenium to iridium atoms in O2 is 7:

3.

3. The electrocatalytic device for treating phthalates in shale gas flowback fluid according to claim 2, characterized in that: The pretreatment process uses a magnetic stirrer to stir at a speed of 800-1000 r / min for 8-10 hours.

4. The electrocatalytic device for treating phthalates in shale gas flowback fluid according to claim 2, characterized in that: The deposition solution comprises: 0.1-0.5 mol / L polyaniline, 0.5 mol / L H2SO4, and a total iron ion concentration of 0.05-0.15 mmol / L; the total iron ion concentration is the sum of divalent iron ions and trivalent iron ions, wherein the molar ratio of trivalent iron ions to divalent iron ions is 2:

1.

5. The electrocatalytic device for treating phthalates in shale gas flowback fluid according to claim 4, characterized in that: The electrodeposition process is specifically as follows: the graphite felt substrate is used as the working electrode, the platinum wire is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode, and a constant current is passed for electrodeposition, the deposition current is 1A, the deposition voltage is a constant voltage of 0.8V, and the deposition time is 15 to 60s.

6. The electrocatalytic device for treating phthalates in shale gas flowback fluid according to claim 2, characterized in that: The freeze-drying process of the electrodeposited substrate is as follows: firstly put it into a -80°C refrigerator for freezing for 0.5 to 1 hour, and then put it into a freeze dryer for freeze drying for 8 hours.

7. The electrocatalytic device for treating phthalates in shale gas flowback fluid according to claim 2, characterized in that: The pyrolysis treatment adopts a tubular furnace, the pyrolysis atmosphere is nitrogen, the pyrolysis temperature is 300-500° C., the pyrolysis time is 4 hours, and the heating rate is 5° C. / min.

8. A method for treating phthalates in shale gas flowback fluid using the electrocatalytic device according to any one of claims 1 to 7, characterized in that: Shale gas return fluid containing phthalates is added to the electrolytic cell of the electrocatalytic device, and the current density between the anode and the cathode is controlled to be constant, so as to perform an electrocatalytic reaction to degrade the phthalates in the shale gas return fluid.

9. The method for treating phthalates in shale gas flowback fluid according to claim 8, characterized in that: The current density is 66 mA / cm 2 .

10. The method for treating phthalates in shale gas flowback fluid according to claim 8, characterized in that: Cl in shale gas flowback fluid - The concentration is 0.2-0.4 mol / L; the phthalate is diethyl phthalate.

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