Method for removing aromatic compounds in wastewater by electro-catalytic oxidation to produce maleic acid

Abstract

The application discloses a method for removing aromatic compounds in wastewater by electro-catalytic oxidation to prepare maleic acid, and belongs to the technical field of electro-catalytic oxidation and wastewater resourceization. The method comprises the following steps: constructing an electro-catalytic oxidation reaction device, wherein the device comprises an anode pool, a cathode pool, an anode arranged in the anode pool and a cathode arranged in the cathode pool; adding inert inorganic salt electrolyte, peroxide and target wastewater containing aromatic pollutants into the anode pool in sequence; and connecting a power supply, so that active species are generated in situ on the surface of the anode by anodic oxidation under the conditions of a set reaction temperature, a current density and a reaction time, wherein the active species comprise hydrogen trioxide. The application can improve the preparation yield of maleic acid while treating wastewater, and solves the problems of high reagent consumption and energy consumption and low selectivity of maleic acid which is a high value-added product when treating wastewater containing aromatic pollutants.

Description

Technical Field

[0001] This invention relates to the interdisciplinary field of electrocatalytic oxidation and wastewater resource utilization, specifically a method for producing maleic acid by removing aromatic compounds from wastewater through electrocatalytic oxidation. Background Technology

[0002] Wastewater from the pharmaceutical and chemical industries is generally characterized by high chemical oxygen demand (COD), low biodegradability (BOD5 / COD<0.2), and strong biological inhibition. 60%-85% of the organic matter in the wastewater is aromatic compounds. If it enters the wastewater biological treatment unit directly, it will lead to the poisoning and inactivation of activated sludge. Although Fenton technology and electrochemical advanced oxidation technology, which use hydroxyl radicals (·OH) as active species, can achieve pollutant mineralization (COD removal rate >80%), they face the following drawbacks: (1) High COD wastewater will significantly increase the reagent consumption of the Fenton system and the energy consumption of the electrochemical advanced oxidation process; (2) Carbon resources are dissipated in the form of CO2, and the directional conversion of carbon into chemicals cannot be achieved. Therefore, it is urgent to develop new water treatment technologies to achieve the directional resource utilization of high-carbon wastewater.

[0003] Existing chemical oxidation technologies can convert aromatic compounds into high-value-added products such as maleic acid and terephthalic acid. However, the reaction conditions for converting aromatic compounds into maleic acid are harsh, requiring not only noble metal catalysts (such as Pt / V2O5) but also maintaining high temperature (200-400°C) and high pressure conditions. On the other hand, although electrocatalytic oxidation technology can achieve the catalytic oxidation of pollutants under normal temperature and pressure conditions, the generated ·OH is prone to non-selective reactions and can only generate low-value-added small molecule acids such as acetic acid and oxalic acid, and cannot obtain maleic acid with high yield. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing maleic acid by electrocatalytic oxidation of aromatic compounds in wastewater. By establishing a reaction process based on hydrogen trioxide electrocatalytic oxidation, it is possible not only to treat wastewater containing aromatic compounds, but also to improve the yield of maleic acid while treating the wastewater. This solves the problems of high reagent and energy consumption and low selectivity of maleic acid, a high-value-added product, in the current treatment of wastewater containing aromatic pollutants.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for producing maleic acid by electrocatalytic oxidation of aromatic compounds in wastewater includes the following steps: An electrocatalytic oxidation reactor is constructed, wherein the reactor comprises an anode cell, a cathode cell, an anode placed in the anode cell, and a cathode placed in the cathode cell; An inert inorganic salt electrolyte, a peroxide, and target wastewater containing aromatic pollutants are sequentially added to the anode tank, and a background electrolyte is added to the cathode tank. The aromatic pollutants have a benzene ring structure, and the concentration ratio of aromatic pollutants to peroxide is 1:1 to 1:5000. When the power is turned on, under the set reaction temperature, current density and reaction time conditions, the peroxide is anoly oxidized in situ to generate active species on the anode surface, wherein the active species include hydrogen trioxide (HOOOH). Maleic acid is generated by electrophilic addition-directed cleavage of the benzene ring structure based on the hydrogen trioxide; After the reaction is complete, an organic phase containing maleic acid and an aqueous phase are extracted and separated from the aqueous phase using an organic solvent. The aqueous phase is then recycled back into the anode tank as a solvent. The organic solvent in the organic phase is removed by vacuum distillation to obtain the maleic acid product.

[0006] As a further aspect of the present invention, the electrolyte also includes a background electrolyte, which is a 50 mM potassium dihydrogen phosphate solution.

[0007] As a further aspect of the present invention: the aromatic pollutant is any one or more combinations of phenolic compounds, benzoic acid compounds, aniline compounds, nitrobenzene compounds, halogenated aromatic compounds, aromatic sulfonic acid compounds, aromatic pharmaceutical intermediates, or dye intermediates containing aromatic rings.

[0008] As a further aspect of the present invention: the aromatic pollutant contains a benzene ring structure, or contains a fused ring aromatic structure, or a heterocyclic aromatic structure.

[0009] As a further aspect of the present invention: the inert inorganic salt electrolyte includes any one or more combinations of sulfates, phosphates, nitrates, perchlorates, or carbonates; The concentration of the inert inorganic salt electrolyte is 0.01M to 1M, or 0.05M to 0.5M.

[0010] As a further aspect of the present invention: the peroxide is a peroxide compound that can be converted into hydrogen trioxide by anodic oxidation, including any one or more combinations of hydrogen peroxide, persulfate, monopersulfate, peracetic acid, percarbonate or organic peroxide.

[0011] As a further aspect of the present invention, the initial concentration ratio of the aromatic pollutant to the peroxide can also be 1:10 to 1:500.

[0012] As a further aspect of the present invention: the anode is an electrode material with electrocatalytic activity, including any one of platinum electrode, gold electrode, palladium electrode, ruthenium-iridium mixed oxide electrode, RuO2 / Ti electrode, IrO2 / Ti electrode, RuIr / Ti electrode, boron-doped diamond electrode or lead dioxide electrode; The cathode is any one of a platinum electrode, a titanium electrode, a stainless steel electrode, or a carbon electrode.

[0013] As a further aspect of the present invention: the reaction temperature is set to 5°C to 60°C, and the current density is 0.5 mA / cm². 2 Up to 50 mA / cm 2 The reaction time is 10 to 120 minutes.

[0014] As a further aspect of the present invention: the reaction temperature can also be set to 20°C to 40°C, and the current density can also be 1 mA / cm². 2 Up to 20mA / cm 2 .

[0015] As a further aspect of the present invention: after adding the electrolyte and before adding the peroxide, a pH buffer is added to the anode to maintain the pH value of the reactants in the anode pool between 2 and 7; the pH buffer includes any one of phosphate, acetate or citrate.

[0016] As a further aspect of the present invention: the organic solvent used for extracting maleic acid is ethyl acetate or diethyl ether; the extraction operation is repeated 1 to 5 times, and the organic phases are combined.

[0017] As a further aspect of the present invention: the temperature of vacuum distillation is 30°C to 50°C, and the vacuum degree is 0.01MPa to 0.08MPa.

[0018] As a further aspect of the present invention, the method further includes a post-treatment step for the anode pool solution after the reaction: before extracting maleic acid, a small amount of insoluble precipitate generated in the anode pool is removed by filtration or centrifugation; before the aqueous phase after extraction and separation is added back to the reaction device for recycling, the consumed electrolyte and peroxide precursor are replenished to the initial concentration.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention constructs an electrocatalytic oxidation reaction device to electrocatalytically oxidize aromatic pollutants to produce maleic acid within a given temperature and current density range. Maleic acid is extracted from the aqueous phase, and the aqueous solvent is recycled back into the reaction device. The organic phase is decomposed by vacuum distillation to remove the solvent, thus obtaining maleic acid. This invention can improve the yield of maleic acid while treating wastewater, and solves the problems of high reagent and energy consumption and low selectivity of maleic acid, a high-value-added product, in the current treatment of wastewater containing aromatic pollutants.

[0020] 2. This invention utilizes the active species of hydrogen trioxide generated at the anode to directionally cleave the benzene ring structural units of pollutants. By carrying out the degradation reaction in an electrocatalytic oxidation reactor, it can effectively complete the degradation of benzoic acid and the generation of maleic acid. This not only avoids the substitution pre-activation process required for traditional free radical cleavage of benzene rings, but also effectively prepares maleic acid and degrades benzoic acid. It features pure products, low energy consumption, and simple process, and is suitable for the resource utilization of high-carbon wastewater from pharmaceutical and chemical industries.

[0021] 3. Unlike traditional advanced oxidative degradation of aromatic pollutants, which requires the generation of more toxic intermediate products through substitution and pre-activation, this invention can directly and directionally cleave aromatic pollutants, significantly reducing the accumulation of more toxic intermediate products. By electrocatalytically oxidizing and directionally cleaving aromatic compounds and selectively generating high-value-added maleic acid, it can achieve resource recovery while rendering pollutants harmless. Attached Figure Description

[0022] Figure 1 This is a graph showing the ion source intensity of maleic acid produced by benzoic acid degradation in Example 2 of the present invention and the ion source intensity of maleic acid produced by benzoic acid degradation in the UV / H2O2 system. Figure 2 This is a graph showing the changes in phenol degradation rate and maleic acid yield with reaction time in Example 1; Figure 3 This is a graph showing the changes in benzoic acid degradation rate and maleic acid yield with reaction time in Example 2 of the present invention; Figure 4 This is a graph showing the changes in nitrobenzene degradation rate and maleic acid yield with reaction time in Example 3 of the present invention; Figure 5 This is a graph showing the changes in nitrobenzene degradation rate and maleic acid yield with reaction time in Example 4 of the present invention; Figure 6 This is a diagram illustrating the method steps of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1:

[0025] Please see Figure 4 This embodiment provides a method for producing maleic acid by electrocatalytic oxidation of aromatic compounds in wastewater, comprising the following steps: S1: Construct an electrocatalytic oxidation reaction device, wherein the device includes an anode pool, a cathode pool, an anode placed in the anode pool, and a cathode placed in the cathode pool.

[0026] The electrocatalytic oxidation experiment was conducted in a 100 mL H-type electrochemical cell using a two-electrode system. The anode and cathode were both platinum sheet electrodes, with a working area of ​​4 cm² for each electrode. 2 The two-electrode system is placed in parallel in the experimental setup, with an electrode spacing of 8 cm. S2: Inert inorganic salt electrolyte, peroxide and target wastewater including aromatic pollutants are added sequentially to the anode tank, and background electrolyte is added to the cathode tank.

[0027] S3: When the power is turned on, under the set reaction temperature, current density and reaction time conditions, the peroxide is anolyte generated in situ on the anode surface to generate active species through anodic oxidation. The active species is hydrogen trioxide.

[0028] S4: Maleic acid is generated by the electrophilic addition-directed cleavage reaction of hydrogen trioxide on the benzene ring structure.

[0029] S5: After the reaction is completed, an organic solvent is used to extract and separate the maleic acid-containing organic phase and aqueous phase from the aqueous phase. The aqueous phase is then added back to the anode tank as a solvent for recycling. The organic solvent in the organic phase is removed by vacuum distillation to obtain the maleic acid product.

[0030] Specifically, a phenol solution with an initial concentration of 1 mM was added to the anode tank as simulated wastewater, along with a 30 mM persulfate solution. Simultaneously, a 50 mM potassium dihydrogen phosphate solution was added to the cathode tank as a background electrolyte. The anode tank stirring speed was set to 300 rpm, and a DC power supply at 7.5 mA / cm² was used. 2The degradation reaction was initiated with a constant current density, and 1 mL of sample was taken every 10 min for a total degradation time of 50 min at a reaction temperature of 25°C. Immediately after sample removal, 100 μL of methanol was added to quench the reaction. After filtration through a 0.22 μm filter membrane, the phenol concentration was determined by high performance liquid chromatography (HPLC), and the maleic acid concentration was determined by ultra-high performance liquid chromatography-high resolution mass spectrometry (LC-MS).

[0031] The results are as follows Figure 2 As shown, after 50 min of degradation, the removal rate of phenol was 91.2%, and the yield of maleic acid was 41.3%.

[0032] Example 2:

[0033] This embodiment provides a method for producing maleic acid by electrocatalytic oxidation of aromatic compounds in wastewater, comprising the following steps: S1: Construct an electrocatalytic oxidation reaction device, wherein the device includes an anode pool, a cathode pool, an anode placed in the anode pool, and a cathode placed in the cathode pool.

[0034] The electrocatalytic oxidation experiment was conducted in a 100 mL H-type electrochemical cell using a two-electrode system consisting of an anode and a cathode. The anode was a RuO2 / Ti electrode, and the cathode was a platinum electrode made of platinum sheet. The working area of ​​both electrodes was 4 cm². 2 The two-electrode system is placed in parallel in the experimental setup, with an electrode spacing of 8 cm.

[0035] S2: Inert inorganic salt electrolyte, peroxide and target wastewater including aromatic pollutants are added sequentially to the anode tank, and background electrolyte is added to the cathode tank.

[0036] S3: When the power is turned on, under the set reaction temperature, current density and reaction time conditions, the peroxide is anolyte generated in situ on the anode surface to generate active species through anodic oxidation. The active species is hydrogen trioxide.

[0037] S4: Maleic acid is generated by the electrophilic addition-directed cleavage reaction of hydrogen trioxide on the benzene ring structure.

[0038] S5: After the reaction is completed, an organic solvent is used to extract and separate the maleic acid-containing organic phase and aqueous phase from the aqueous phase. The aqueous phase is then added back to the anode tank as a solvent for recycling. The organic solvent in the organic phase is removed by vacuum distillation to obtain the maleic acid product.

[0039] Specifically, a 1 mM benzoic acid solution was added to the anode tank as simulated target wastewater. A 10 mM potassium dihydrogen phosphate aqueous solution was added to the anode tank as a pH buffer to adjust the pH to 5.0 ± 0.2. A 30 mM persulfate solution was added to the anode tank, while a 50 mM potassium dihydrogen phosphate solution was added to the cathode tank as a background electrolyte. The anode tank stirring speed was set to 300 rpm, and a DC power supply of 7.5 mA / cm² was used. 2 The degradation reaction was initiated with a constant current density, and 1 mL of sample was taken every 10 min for a total degradation time of 50 min at a reaction temperature of 25°C. Immediately after sample removal, 100 μL of methanol was added to quench the reaction. After filtration through a 0.22 μm filter, the benzoic acid concentration was determined by high performance liquid chromatography (HPLC), and the maleic acid concentration was determined by ultra-high performance liquid chromatography-high resolution mass spectrometry (LC-MS).

[0040] like Figure 3 As shown, after 50 minutes of degradation, the degradation rate of benzoic acid was 92.7%, and the yield of maleic acid was 51.5%. This embodiment demonstrates that by carrying out the degradation reaction in an electrocatalytic oxidation reactor, the degradation of benzoic acid and the generation of maleic acid can be effectively achieved.

[0041] like Figure 1 As shown, the experimental results indicate that the method disclosed in this invention can efficiently remove aromatic pollutants from wastewater and significantly increase the yield of maleic acid, thereby achieving efficient degradation of pollutants in pharmaceutical wastewater and carbon resource utilization.

[0042] In this embodiment, the method further includes a post-treatment step for the anode pool solution after the reaction: before extracting maleic acid, a small amount of insoluble precipitate generated in the anode pool is removed by filtration or centrifugation; before the aqueous phase after extraction and separation is added back to the reaction device for recycling, the consumed electrolyte and peroxide precursor are replenished to the initial concentration.

[0043] Example 3:

[0044] This embodiment provides a method for producing maleic acid by electrocatalytic oxidation of aromatic compounds in wastewater, comprising the following steps: S1: Construct an electrocatalytic oxidation reaction device, wherein the device includes an anode pool, a cathode pool, an anode placed in the anode pool, and a cathode placed in the cathode pool.

[0045] The electrocatalytic oxidation experiment was conducted in a 100 mL H-type electrochemical cell using a two-electrode system consisting of an anode and a cathode. The anode was an IrO2 / Ti electrode, and the cathode was a platinum electrode made of a platinum sheet. The working area of ​​both electrodes was 4 cm². 2 The two-electrode system is placed in parallel in the experimental setup, with an electrode spacing of 8 cm.

[0046] S2: Inert inorganic salt electrolyte, peroxide and target wastewater including aromatic pollutants are added sequentially to the anode tank, and background electrolyte is added to the cathode tank.

[0047] S3: When the power is turned on, under the set reaction temperature, current density and reaction time conditions, the peroxide is anolyte generated in situ on the anode surface to generate active species through anodic oxidation. The active species is hydrogen trioxide.

[0048] S4: Maleic acid is generated by the electrophilic addition-directed cleavage reaction of hydrogen trioxide on the benzene ring structure.

[0049] S5: After the reaction is completed, an organic solvent is used to extract and separate the maleic acid-containing organic phase and aqueous phase from the aqueous phase. The aqueous phase is then added back to the anode tank as a solvent for recycling. The organic solvent in the organic phase is removed by vacuum distillation to obtain the maleic acid product.

[0050] Specifically, a 1 mM nitrobenzene solution was added to the anode tank as simulated target wastewater. A 100 mM potassium dihydrogen phosphate aqueous solution was added to the anode tank as a pH buffer to adjust the pH to 5.0 ± 0.2. A 30 mM persulfate solution was added to the anode tank, while a 50 mM potassium dihydrogen phosphate solution was added to the cathode tank as a background electrolyte. The anode tank stirring speed was set to 300 rpm, and a DC power supply of 7.5 mA / cm² was used. 2 The degradation reaction was initiated with a constant current density, and 1 mL of sample was taken every 10 min for a total degradation time of 50 min at a reaction temperature of 25°C. Immediately after sample removal, 100 μL of methanol was added to quench the reaction. After filtration through a 0.22 μm filter, the concentration of nitrobenzene was determined by high performance liquid chromatography (HPLC), and the concentration of maleic acid was determined by ultra-high performance liquid chromatography-high resolution mass spectrometry (LC-MS).

[0051] like Figure 4 As shown, after 50 min of degradation, the degradation rate of nitrobenzene was 70.7%, and the yield of maleic acid was 30.5%. In this embodiment, the degradation reaction was carried out in an electrocatalytic oxidation reactor, which effectively completed the degradation of nitrobenzene and the generation of maleic acid.

[0052] Example 4:

[0053] This embodiment provides a method for producing maleic acid by electrocatalytic oxidation of aromatic compounds in wastewater, comprising the following steps: S1: Construct an electrocatalytic oxidation reaction device, wherein the device includes an anode pool, a cathode pool, an anode placed in the anode pool, and a cathode placed in the cathode pool.

[0054] The electrocatalytic oxidation experiment was conducted in a 100 mL H-type electrochemical cell using a two-electrode system consisting of an anode and a cathode. The anode was an IrO2 / Ti electrode, and the cathode was a platinum electrode made of a platinum sheet. The working area of ​​both electrodes was 4 cm². 2 The two-electrode system is placed in parallel in the experimental setup, with an electrode spacing of 8 cm.

[0055] S2: Inert inorganic salt electrolyte, peroxide and target wastewater including aromatic pollutants are added sequentially to the anode tank, and background electrolyte is added to the cathode tank.

[0056] S3: When the power is turned on, under the set reaction temperature, current density and reaction time conditions, the peroxide is anolyte generated in situ on the anode surface to generate active species through anodic oxidation. The active species is hydrogen trioxide.

[0057] S4: Maleic acid is generated by the electrophilic addition-directed cleavage reaction of hydrogen trioxide on the benzene ring structure.

[0058] S5: After the reaction is completed, an organic solvent is used to extract and separate the maleic acid-containing organic phase and aqueous phase from the aqueous phase. The aqueous phase is then added back to the anode tank as a solvent for recycling. The organic solvent in the organic phase is removed by vacuum distillation to obtain the maleic acid product.

[0059] Specifically, a 1 mM nitrobenzene solution was added to the anode tank as simulated target wastewater. A 100 mM potassium dihydrogen phosphate aqueous solution was added to the anode tank as a pH buffer to adjust the pH to 5.0 ± 0.2. A 30 mM persulfate solution was added to the anode tank, while a 50 mM sodium sulfate solution was added to the cathode tank as a background electrolyte. The anode tank stirring speed was set to 300 rpm, and a DC power supply of 7.5 mA / cm² was used. 2 The degradation reaction was initiated with a constant current density, and 1 mL of sample was taken every 10 min for a total degradation time of 50 min at a reaction temperature of 25°C. Immediately after sample removal, 100 μL of methanol was added to quench the reaction. After filtration through a 0.22 μm filter, the concentration of nitrobenzene was determined by high performance liquid chromatography (HPLC), and the concentration of maleic acid was determined by ultra-high performance liquid chromatography-high resolution mass spectrometry (LC-MS).

[0060] like Figure 5 As shown, after 50 minutes of degradation, the degradation rate of nitrobenzene was 75.7%, and the yield of maleic acid was 25.5%. In this embodiment, the degradation reaction was carried out in an electrocatalytic oxidation reactor, which effectively completed the degradation of nitrobenzene and the generation of maleic acid.

[0061] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for producing maleic acid by electrocatalytic oxidation of aromatic compounds in wastewater, characterized in that, Includes the following steps: An electrocatalytic oxidation reactor is constructed, wherein the reactor comprises an anode cell, a cathode cell, an anode placed in the anode cell, and a cathode placed in the cathode cell; An inert inorganic salt electrolyte, a peroxide, and target wastewater containing aromatic pollutants are sequentially added to the anode tank, and a background electrolyte is added to the cathode tank. The aromatic pollutants have a benzene ring structure, and the concentration ratio of the aromatic pollutants to the peroxide is 1:1 to 1:5000. When the power is turned on, under the set reaction temperature, current density and reaction time conditions, the peroxide is anoly oxidized in situ to generate active species on the anode surface, wherein the active species include hydrogen trioxide. Maleic acid is generated by electrophilic addition-directed cleavage of the benzene ring structure based on the hydrogen trioxide; After the reaction is complete, an organic phase containing maleic acid and an aqueous phase are extracted and separated from the aqueous phase using an organic solvent. The aqueous phase is then recycled back into the anode tank as a solvent. The organic solvent in the organic phase is removed by vacuum distillation to obtain the maleic acid product.

2. The method for producing maleic acid from wastewater by electrocatalytic oxidation according to claim 1, characterized in that, The aromatic pollutants are organic pollutants containing benzene rings, fused ring aromatic structures, or heterocyclic aromatic structures.

3. The method for producing maleic acid from wastewater by electrocatalytic oxidation according to claim 2, characterized in that, Inert inorganic salt electrolytes include any one or more combinations of sulfates, phosphates, nitrates, perchlorates, or carbonates; the concentration of inert inorganic salt electrolytes is from 0.01M to 1M.

4. The method for producing maleic acid by electrocatalytic oxidation of aromatic compounds in wastewater according to claim 3, characterized in that, The peroxide is a peroxide compound that can be converted into hydrogen trioxide by anodic oxidation, including any one of monopersulfate, hydrogen peroxide, perdisulfate, and peracetic acid. The background electrolyte includes potassium dihydrogen phosphate solution.

5. The method for producing maleic acid by electrocatalytic oxidation of aromatic compounds in wastewater according to claim 4, characterized in that, The anode is an electrode material with electrocatalytic activity, and the anode is any one of RuO2 / Ti electrode, platinum electrode, IrO2 / Ti electrode and RuIr / Ti electrode; The cathode is any one of a platinum electrode, a titanium electrode, a stainless steel electrode, or a carbon electrode.

6. The method for producing maleic acid from wastewater by electrocatalytic oxidation according to claim 5, characterized in that, The reaction temperature was set to 5℃ to 60℃, and the current density was 0.5mA / cm². 2 Up to 50 mA / cm 2 The reaction time is 10 to 120 minutes.

7. The method for producing maleic acid by electrocatalytic oxidation of aromatic compounds in wastewater according to claim 6, characterized in that, After the electrolyte is added and before the peroxide is added, a pH buffer is added to the anode to maintain the pH of the reactants in the anode cell between 2 and 7; the pH buffer includes any one of phosphate, acetate or citrate.

8. The method for producing maleic acid by electrocatalytic oxidation of aromatic compounds in wastewater according to claim 7, characterized in that, The organic solvent used for extracting maleic acid is ethyl acetate or diethyl ether; the extraction operation is repeated 1 to 5 times, and the organic phases are combined.

9. The method for producing maleic acid by electrocatalytic oxidation of aromatic compounds in wastewater according to claim 8, characterized in that, The temperature for vacuum distillation is 30℃ to 50℃, and the vacuum degree is 0.01MPa to 0.08MPa.

10. The method for producing maleic acid from wastewater by electrocatalytic oxidation according to claim 9, characterized in that, The method also includes a post-treatment step for the anode pool solution after the reaction: before extracting maleic acid, a small amount of insoluble precipitate generated in the anode pool is removed by filtration or centrifugation; before the aqueous phase after extraction and separation is added back to the reaction device for recycling, the consumed electrolyte and peroxide precursor are replenished to the initial concentration.

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