Method for preparing formamide by synergistically treating ammonia-nitrogen wastewater and waste PET plastic

Abstract

This invention provides a method for preparing formamide by synergistically treating ammonia nitrogen wastewater and waste PET plastic, belonging to the field of solid waste and wastewater synergistic treatment technology. The method includes the following steps: adding magnesium and phosphate salts to ammonia nitrogen wastewater, adjusting the pH to alkaline for reaction, and obtaining magnesium ammonium phosphate precipitate; heating and decomposing the magnesium ammonium phosphate precipitate, absorbing the ammonia gas generated in the reaction with water to obtain ammonia water; mixing waste PET plastic with an alkaline solution and carrying out a hydrothermal reaction, followed by acidification of the resulting reaction solution, solid-liquid separation, and obtaining a hydrolysate containing ethylene glycol; mixing the ammonia water, the ethylene glycol-containing hydrolysate, and H2SO4 to obtain an electrolyte, using nickel foam loaded with metal / metal oxide as the working electrode, and carrying out an electrolytic reaction to obtain formamide. This invention synergistically utilizes the treatment of ammonia nitrogen wastewater and waste PET plastic, preparing formamide under mild conditions, simultaneously achieving efficient treatment of ammonia nitrogen wastewater and upgraded utilization of waste PET plastic.

Description

Technical Field

[0001] This invention relates to the field of co-treatment technology of solid waste and wastewater, and in particular to a method for co-treating ammonia nitrogen wastewater and waste PET plastic to prepare formamide. Background Technology

[0002] Nitrogen is widely distributed in natural ecosystems, forming a rich variety of compounds. Various forms of nitrogen maintain a dynamic balance under the action of microorganisms, and their interconversion constitutes the global microbial nitrogen cycle. However, with rapid social development, large amounts of ammonia nitrogen wastewater are discharged, mainly including domestic sewage, chemical wastewater, metallurgical wastewater, and agricultural wastewater. If ammonia nitrogen wastewater is discharged directly into the natural environment without proper treatment, it will cause eutrophication of water bodies, leading to the proliferation of algae and plankton, which in turn causes other aquatic organisms to die from oxygen depletion, severely disrupting the balance and stability of the ecosystem. Furthermore, the nitrates and nitrites in the wastewater can easily form carcinogens in the human body, seriously threatening human health.

[0003] Ammonia nitrogen wastewater has a complex composition and is difficult to treat, therefore, research on ammonia nitrogen removal technology is of great significance. Currently, ammonia nitrogen wastewater treatment technologies are mainly divided into physicochemical methods and biological methods. Among them, chemical precipitation for ammonia nitrogen removal has advantages such as high efficiency, simple operation, and minimal temperature dependence, and is widely used. The main principle is to add magnesium and phosphorus sources to the wastewater, causing them to react with ammonia to form insoluble salt precipitates, thereby achieving effective removal of ammonia nitrogen.

[0004] The widespread use of plastics and inadequate treatment methods have led to their continuous accumulation in nature. Faced with the increasingly severe plastic pollution crisis, developing sustainable plastic recycling strategies is imperative. Compared to the harsh conditions such as high temperature and high pressure required for traditional plastic degradation, current electrocatalytic technology can convert waste PET plastics into high-purity monomers terephthalic acid (PTA) and ethylene glycol (EG) under milder conditions, further generating high-value-added products such as formic acid and glycolic acid. However, the value of existing products is limited, and more economically viable high-value products remain to be developed.

[0005] Formamide (HCONH2), an important class of amide compounds, is a widely used and valuable chemical raw material with key applications in organic synthesis, pharmaceutical production, and pesticide preparation. However, current industrial production of formamide primarily relies on high-temperature, high-pressure amination processes, resulting in enormous energy consumption and significant greenhouse gas emissions, contradicting the requirements of green chemical engineering. Electrocatalysis, as an emerging green synthesis strategy, offers a highly promising alternative for the green synthesis of formamide. Summary of the Invention

[0006] Based on the above, this invention proposes a method for the synergistic treatment of ammonia nitrogen wastewater and waste PET plastic to prepare formamide, aiming to achieve resource utilization of solid waste and green synthesis of high-value chemicals. This invention first treats ammonia nitrogen wastewater through chemical precipitation, then depolymerizes waste PET plastic through alkaline hydrolysis, and finally achieves CN-CN coupling through electrocatalysis to complete the high-value conversion of ammonia nitrogen wastewater and waste PET plastic into formamide.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for co-treating ammonia nitrogen wastewater and waste PET plastic to prepare formamide includes the following steps: Magnesium salts and phosphate salts were added to the ammonia nitrogen wastewater, and the pH was adjusted to alkaline to carry out the reaction, resulting in magnesium ammonium phosphate precipitate. The magnesium ammonium phosphate precipitate is decomposed by heating, and the ammonia gas produced in the reaction is absorbed by water to obtain ammonia water; Waste PET plastic is mixed with an alkaline solution and subjected to a hydrothermal reaction. The resulting reaction solution is then acidified, and solid-liquid separation is performed to obtain a hydrolysate containing ethylene glycol. An electrolyte is prepared by mixing ammonia water, ethylene glycol-containing hydrolysate, and H2SO4. Electrolysis is carried out using nickel foam loaded with metal / metal oxide as the working electrode to obtain formamide. In the nickel foam loaded with metal / metal oxide, the metal is at least one of Pd, Pt, Mn and Co, and the metal oxide is WO3.

[0008] The present invention discloses the following technical effects: (1) This invention recovers ammonia-rich water from ammonia nitrogen wastewater through chemical precipitation. Waste PET plastic is subjected to alkaline hydrolysis to obtain a hydrolysate containing ethylene glycol. The ammonia and the ethylene glycol-containing hydrolysate are incorporated into an electrochemical synthesis system, and formamide is prepared by CN-C coupling reaction of ammonia and ethylene glycol through electrocatalysis. This invention synergistically utilizes the treatment of ammonia nitrogen wastewater and waste PET plastic, making full use of the treatment liquid generated during the waste treatment process to prepare formamide under mild conditions, thus simultaneously achieving efficient treatment of ammonia nitrogen wastewater and upgraded utilization of waste PET plastic.

[0009] (2) This invention innovatively proposes a new method for electrocatalytic synthesis of formamide, realizing the efficient preparation of formamide under short process; this invention selects specific metal oxides for the preparation of working electrodes to achieve efficient catalytic synthesis; in addition, compared with the traditional formamide synthesis process, it can be carried out under mild conditions of room temperature and pressure, which greatly reduces energy consumption and equipment requirements, while effectively reducing carbon emissions, and has good economic benefits and industrial application prospects. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is a process flow diagram of the present invention for the synergistic treatment of ammonia nitrogen wastewater and waste PET plastic to prepare formamide; Figure 2 This is a SEM image of the Pd / WO3-loaded nickel foam in Example 1 of the present invention; Figure 3 Linear sweep voltammetry (LSV) curve testing of the electrolytic system in Example 1 of this invention; Figure 4 The electrolysis reaction products in Example 1 of this invention 1 H NMR; Figure 5 The XRD pattern of Pd / WO3 used in Embodiment 1 of the present invention; Figure 6 The XRD pattern of WO3 used in Comparative Example 1 of this invention; Figure 7 The LSV curves of the electrolysis systems of Example 1 and Comparative Example 1 in the presence of 1M EG and NH3 were tested. Detailed Implementation

[0012] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0013] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0014] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0015] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0016] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0017] This invention first adds magnesium and phosphate salts to ammonia nitrogen wastewater, filters to obtain magnesium ammonium phosphate precipitate, heats and decomposes it to obtain ammonia gas, and then dries the ammonia gas and passes it into cold water to obtain ammonia water. Waste PET plastic is mixed with an alkaline solution and subjected to a hydrothermal reaction, which hydrolyzes the PET to obtain a PET hydrolysate containing ethylene glycol. The obtained ammonia water is mixed with the ethylene glycol-containing PET hydrolysate to form an electrolyte, and the ethylene glycol and ammonia in the PET hydrolysate are converted to formamide via CN coupling through electrocatalysis. While synthesizing high-value products, the invention fully utilizes the treatment liquid from the waste treatment process, simultaneously achieving efficient treatment of ammonia nitrogen wastewater and upgraded utilization of waste PET plastic.

[0018] Specifically, the method for preparing formamide by synergistic treatment of ammonia nitrogen wastewater and waste PET plastic according to the present invention includes the following steps: Magnesium salts and phosphate salts were added to the ammonia nitrogen wastewater, and the pH was adjusted to alkaline to carry out the reaction, resulting in magnesium ammonium phosphate precipitate. The magnesium ammonium phosphate precipitate is decomposed by heating, and the ammonia gas produced in the reaction is absorbed by water to obtain ammonia water; Waste PET plastic is mixed with an alkaline solution and subjected to a hydrothermal reaction. The resulting reaction solution is then acidified, and solid-liquid separation is performed to obtain a hydrolysate containing ethylene glycol. An electrolyte is prepared by mixing ammonia water, ethylene glycol-containing hydrolysate, and H2SO4. Electrolysis is carried out using nickel foam loaded with metal / metal oxide as the working electrode to obtain formamide. In the nickel foam loaded with metal / metal oxide, the metal is at least one of Pd, Pt, Mn and Co, and the metal oxide is WO3.

[0019] In this invention, the ammonia nitrogen wastewater contains NH4. + .

[0020] In a preferred embodiment of the present invention, the magnesium salt is MgCl2 or MgSO4, and the phosphate salt is K2HPO4, KH2PO4, or K3PO4; the pH is 8.5-9.5, and the reagent used to adjust the pH to alkaline is potassium hydroxide. The present invention ensures complete precipitation by adjusting the pH to 8.5-9.5, allowing NH4+ to... + It is converted into magnesium ammonium phosphate.

[0021] In a preferred embodiment of the present invention, the heating temperature for decomposing the magnesium ammonium phosphate precipitate is 80-100°C, and the heating time is 1-2 h. By heating the magnesium ammonium phosphate precipitate, it can be decomposed into MgHPO4, NH3, and H2O, wherein MgHPO4 can be used as a magnesium and phosphorus source for ammonia production from wastewater.

[0022] Increasing the pyrolysis temperature is beneficial for releasing ammonia; however, excessively high temperatures can also lead to further dehydration of magnesium hydrogen phosphate to form magnesium pyrophosphate (Mg2P2O7). This product has a stable structure and poor water solubility, reducing the recycling rate of magnesium and phosphorus sources. Simultaneously, high temperatures also result in higher equipment energy consumption, exacerbate equipment corrosion, and pose greater safety risks.

[0023] In this invention, when the ammonia gas produced by the reaction is absorbed by water, the concentration of the prepared ammonia water can be controlled by controlling the ammonia gas introduction rate and the introduction time.

[0024] In a preferred embodiment of the present invention, the alkaline solution is a 2-6 mol / L KOH solution; the mass-to-volume ratio of waste PET plastic to alkaline solution is 1 g: 20-30 mL.

[0025] In a preferred embodiment of the present invention, the waste PET plastic is selected from at least one of waste PET granules, waste PET fibers, waste PET films, and waste PET bottles. Before subjecting the waste PET plastic to a hydrothermal reaction, the method further includes mechanically crushing the waste PET plastic to form uniform waste PET powder, followed by washing and drying.

[0026] In a preferred embodiment of the present invention, the temperature of the hydrothermal reaction is 60-90 °C and the time is 8-16 h.

[0027] In a preferred embodiment of the present invention, the reaction solution obtained by acidification is prepared by acidifying the reaction to a pH of 2-3; the reagent used for acidification of the reaction solution is dilute sulfuric acid. After acidification of the reaction solution, the precipitated TPA is separated to obtain a hydrolysate containing ethylene glycol.

[0028] In a preferred embodiment of the present invention, the electrolyte contains 1-5 mol / L of NH3, 1-3 mol / L of ethylene glycol, and 0.25 mol / L of H2SO4.

[0029] In a preferred embodiment of the present invention, the method for preparing the metal / metal oxide-supported nickel foam includes the following steps: Na2WO4 was dispersed in water, and then acetic acid, metal salt solution and nickel foam were added in sequence, followed by a hydrothermal reaction. After the hydrothermal reaction is completed, the product is washed and dried to obtain nickel foam loaded with metal / metal oxide. The mass ratio of Na2WO4 to the metal salt is 0.494:(0.01-0.05) (preferably 0.494:0.013, 0.494:0.015, 0.494:0.017, or 0.494:0.041); the hydrothermal reaction is carried out at a temperature of 180-200 °C for 4-5 hours.

[0030] In a preferred embodiment of the present invention, the conditions for the electrolysis reaction are set as follows: constant voltage conditions, and the voltage relative to the reference electrode Ag / AgCl is 1.35-1.45 V, at room temperature.

[0031] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0032] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0033] In this embodiment, the relevant formulas are as follows: Yield = number of moles of formamide produced in the reaction / (time * working electrode reaction area (1 cm * 1 cm)). Faraday efficiency = Amount of formamide produced / (Amount of charge on reaction / (n × 96485 C mol)) –1 ))×100%, where n refers to the number of electrons transferred during the reaction process, and n = 3 when the product is formamide.

[0034] Example 1 S1. Add 2.45g MgCl2 and 4.48g K2HPO4 to 300 mL of ammonia nitrogen wastewater, filter to obtain 5.59g magnesium ammonium phosphate precipitate, then heat the magnesium ammonium phosphate precipitate at 100 ℃ for 1 h, dry the ammonia gas produced by the reaction and pass it into cold water to obtain ammonia water.

[0035] S2. Mix 1 g of waste PET plastic with 30 mL of 6 mol / L KOH solution and transfer it to a hydrothermal reactor with a polytetrafluoroethylene liner. React at 90 °C for 10 h. After the reaction is complete, add dilute sulfuric acid to the resulting reaction solution to acidify it to pH=3. Then, separate the solid and liquid phases to obtain TPA precipitate and a hydrolysate containing ethylene glycol.

[0036] S3. The obtained ammonia water, ethylene glycol-containing hydrolysate, and sulfuric acid are mixed to obtain an electrolyte, wherein the concentration of sulfuric acid in the electrolyte is 0.25 M, the concentration of NH3 is 1 M, and the concentration of ethylene glycol is 1 M; the electrolysis reaction adopts a three-electrode system, consisting of a working electrode, a counter electrode, and a reference electrode, wherein the working electrode is nickel foam loaded with Pd / WO3, the reference electrode is Ag / AgCl, and the counter electrode is a platinum sheet electrode. The electrolysis reaction is carried out at room temperature, the electrolysis voltage is 1.40 V vs. Ag / AgCl, and the reaction time is 120 min.

[0037] Analysis of the solution after the electrolysis reaction revealed a formamide yield of 148.1 μmol / cm³. -2 h -1 (The formamide obtained from the reaction) 1 H NMR image as shown Figure 4 As shown in the figure, the Faraday efficiency is 48.5%.

[0038] The preparation steps of Pd / WO3-loaded nickel foam are as follows: Dissolve 0.494 g Na₂WO₄·2H₂O in 20 mL of deionized water while stirring continuously. Add 2 mL of acetic acid dropwise, then add 0.017 g PdCl₂ to the solution. 2， Stir continuously for 30 min until a homogeneous and stable mixed solution is formed. Then, 1 cm * 1 cm nickel foam is ultrasonically cleaned sequentially in acetone, ethanol, and deionized water for 15 min each. The cleaned nickel foam and the solution are then transferred to an autoclave and reacted at 180 °C for 5 h. After the reaction, the nickel foam is washed three times alternately with ethanol and water to remove unreacted chemicals and impurities from the surface. The nickel foam is then placed in an oven and dried at 60 °C for 2 h to obtain Pd / WO3-loaded nickel foam.

[0039] Figure 2 The SEM image of the prepared Pd / WO3-loaded nickel foam shows that the loaded Pd / WO3 has a uniform nanosheet structure.

[0040] Example 2 S1. Add 2.45 g MgCl2 and 3.5 g KH2PO4 to 300 mL of ammonia nitrogen wastewater, filter to obtain 5.48 g magnesium ammonium phosphate precipitate, then heat the magnesium ammonium phosphate precipitate at 80 ℃ for 2 h, dry the ammonia gas produced by the reaction and pass it into cold water to obtain ammonia water.

[0041] S2. Mix 1 g of waste PET plastic with 30 mL of 4 mol / L KOH solution and transfer it to a hydrothermal reactor with a polytetrafluoroethylene liner. React at 80 °C for 16 h. After the reaction is complete, add dilute sulfuric acid to the resulting reaction solution to acidify it to pH=3. Then, separate the solid and liquid phases to obtain TPA precipitate and a hydrolysate containing ethylene glycol.

[0042] S3. The obtained ammonia water, ethylene glycol-containing hydrolysate, and sulfuric acid were mixed to obtain an electrolyte, wherein the concentration of sulfuric acid in the electrolyte was 0.25 M, the concentration of NH3 was 1 M, and the concentration of ethylene glycol was 2 M; the electrolysis reaction adopted a three-electrode system, consisting of a working electrode, a counter electrode, and a reference electrode, wherein the working electrode was nickel foam loaded with Pt / WO3, the reference electrode was Ag / AgCl, and the counter electrode was a platinum sheet electrode. The electrolysis reaction was carried out at room temperature, the electrolysis voltage was 1.39 V vs. Ag / AgCl, and the reaction time was 120 min.

[0043] Analysis of the solution after the electrolysis reaction revealed a formamide yield of 145.4 μmol / cm³. -2 h -1 The Faraday efficiency is 47.2%.

[0044] The preparation steps of Pt / WO3-loaded nickel foam are as follows: Dissolve 0.494 g Na₂WO₄·2H₂O in 20 mL of deionized water while stirring continuously. Add 2 mL of acetic acid dropwise, then add 0.041 g H₂PtCl₂ to the solution. 4， Stir continuously for 30 min until a homogeneous and stable mixed solution is formed. Then, 1 cm * 1 cm nickel foam is ultrasonically cleaned sequentially in acetone, ethanol, and deionized water for 15 min each. The cleaned nickel foam and the solution are then transferred to an autoclave, and the reaction is carried out at 180 ℃ for 5 h. After the reaction, the nickel foam is washed three times alternately with ethanol and water to remove unreacted chemicals and impurities from the surface. The nickel foam is then placed in an oven and dried at 60 ℃ for 2 h to obtain Pt / WO3-loaded nickel foam.

[0045] Example 3 S1. Add 3.1 g MgSO4 and 4.48 g K2HPO4 to 300 mL of ammonia nitrogen wastewater, filter to obtain 5.53 g magnesium ammonium phosphate precipitate, then heat the magnesium ammonium phosphate precipitate at 90 ℃ for 1 h, dry the ammonia gas produced by the reaction and pass it into cold water to obtain ammonia water.

[0046] S2. Mix 1 g of waste PET plastic with 30 mL of 4 mol / L KOH solution and transfer it to a hydrothermal reactor with a polytetrafluoroethylene liner. React at 80 ℃ for 14 h. After the reaction is completed, add dilute sulfuric acid to the resulting reaction solution to acidify it to pH=3. Then, separate the solid and liquid phases to obtain TPA precipitate and a hydrolysate containing ethylene glycol.

[0047] S3. The obtained ammonia water, ethylene glycol-containing hydrolysate, and sulfuric acid were mixed to obtain an electrolyte, wherein the concentration of sulfuric acid in the electrolyte was 0.25 M, the concentration of NH3 was 1 M, and the concentration of ethylene glycol was 3 M; the electrolysis reaction adopted a three-electrode system, consisting of a working electrode, a counter electrode, and a reference electrode, wherein the working electrode was nickel foam loaded with Mn / WO3, the reference electrode was Ag / AgCl, and the counter electrode was a platinum sheet electrode. The electrolysis reaction was carried out at room temperature, the electrolysis voltage was 1.41 V vs. Ag / AgCl, and the reaction time was 120 min.

[0048] Analysis of the solution after the electrolysis reaction revealed a formamide yield of 138.6 μmol / cm³. -2 h -1 The Faraday efficiency is 43.5%.

[0049] The preparation steps of Mn / WO3-loaded nickel foam are as follows: Dissolve 0.494 g Na₂WO₄·2H₂O in 20 mL of deionized water while stirring continuously. Add 2 mL of acetic acid dropwise, then add 0.015 g MnSO₄ to the solution. 4， Stir continuously for 30 min until a homogeneous and stable mixed solution is formed. Then, 1 cm * 1 cm nickel foam is ultrasonically cleaned sequentially in acetone, ethanol, and deionized water for 15 min each. The cleaned nickel foam and the solution are then transferred to an autoclave, and the reaction is carried out at 180 ℃ for 5 h. After the reaction, the nickel foam is washed three times alternately with ethanol and water to remove unreacted chemicals and impurities from the surface. The nickel foam is then placed in an oven and dried at 60 ℃ for 2 h to obtain Mn / WO3-loaded nickel foam.

[0050] Example 4 S1. Add 3.1 g MgSO4 and 3.5 g KH2PO4 to 300 mL of ammonia nitrogen wastewater, filter to obtain 5.37 g magnesium ammonium phosphate precipitate, then heat the magnesium ammonium phosphate precipitate at 80 ℃ for 2 h, dry the ammonia gas produced by the reaction and pass it into cold water to obtain ammonia water.

[0051] S2. Mix 1 g of waste PET plastic with 30 mL of 5 mol / L KOH solution and transfer it to a hydrothermal reactor with a polytetrafluoroethylene liner. React at 90 °C for 12 h. After the reaction is complete, add dilute sulfuric acid to the resulting reaction solution to acidify it to pH=3. Then, separate the solid and liquid phases to obtain TPA precipitate and a hydrolysate containing ethylene glycol.

[0052] S3. The obtained ammonia water, ethylene glycol-containing hydrolysate, and sulfuric acid were mixed to obtain an electrolyte, wherein the concentration of sulfuric acid in the electrolyte was 0.25 M, the concentration of NH3 was 5 M, and the concentration of ethylene glycol was 1 M; the electrolysis reaction adopted a three-electrode system, consisting of a working electrode, a counter electrode, and a reference electrode, wherein the working electrode was nickel foam loaded with Co / WO3, the reference electrode was Ag / AgCl, and the counter electrode was a platinum sheet electrode. The electrolysis reaction was carried out at room temperature, the electrolysis voltage was 1.43 V vs. Ag / AgCl, and the reaction time was 120 min.

[0053] Analysis of the solution after the electrolysis reaction revealed a formamide yield of 139.2 μmol / cm³. -2 h -1 The Faraday efficiency is 41.3.

[0054] The preparation steps of Co / WO3-loaded nickel foam are as follows: Dissolve 0.494 g Na₂WO₄·2H₂O in 20 mL of deionized water while stirring continuously. Add 2 mL of acetic acid dropwise, then add 0.013 g CoCl₂ to the solution. 2， Stir continuously for 30 min until a homogeneous and stable mixed solution is formed. Then, 1 cm * 1 cm nickel foam is ultrasonically cleaned sequentially in acetone, ethanol, and deionized water for 15 min each. The cleaned nickel foam and the solution are then transferred to an autoclave, and the reaction is carried out at 180 ℃ for 5 h. After the reaction, the nickel foam is washed three times alternately with ethanol and water to remove unreacted chemicals and impurities from the surface. The nickel foam is then placed in an oven and dried at 60 ℃ for 2 h to obtain Co / WO3-loaded nickel foam.

[0055] Comparative Example 1 Similar to Example 1, except that the Pd / WO3-loaded nickel foam is replaced with WO3-loaded nickel foam; the preparation steps of the WO3-loaded nickel foam are as follows: 1) Disperse 20 mM Na₂WO₄ in 20 mL of deionized water while continuously stirring. Add 2 mL of acetic acid dropwise, then transfer 1 cm x 1 cm nickel foam and the solution together into an autoclave. React at 180 °C for 5 h. After the reaction, wash the nickel foam three times alternately with ethanol and water to remove unreacted chemicals and impurities from the surface. Place the nickel foam in an oven and dry at 60 °C for 2 h to obtain WO₃-loaded nickel foam. Figure 6 The XRD pattern of the catalyst confirms its successful synthesis.

[0056] Analysis of the solution after the electrolysis reaction revealed a formamide yield of 71.1 μmol / cm³. -2 h -1 The selectivity rate was 33.7%.

[0057] Depend on Figure 3 It can be seen that the onset potential and current density of the reaction are optimal in the presence of only NH3. When both NH3 and EG are present, the onset potential shifts significantly negatively compared to when only EG is present, and the current density increases significantly, indicating that there is a synergistic effect between CH3OH and NH3, which makes the oxidation reaction easier to occur, promotes the CN coupling reaction, and improves the electrochemical oxidation performance.

[0058] Depend on Figure 7 It can be seen that Pd / WO3 has a higher current response than WO3, indicating higher formamide catalytic activity.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for the preparation of formamide by synergistically treating ammonia-nitrogen wastewater with waste PET plastics, characterized in that, The method comprises the following steps: adding magnesium salt and phosphorus salt into ammonia-nitrogen wastewater, adjusting pH to alkaline to react, and obtaining magnesium ammonium phosphate precipitate; heating and decomposing the magnesium ammonium phosphate precipitate, absorbing ammonia gas generated in the reaction with water, and obtaining ammonia water; mixing waste PET plastic with alkaline solution, and then performing hydrothermal reaction, acidifying the obtained reaction solution, and performing solid-liquid separation to obtain hydrolysis solution containing ethylene glycol; mixing the ammonia water, the hydrolysis solution containing ethylene glycol and H2SO4 to obtain electrolyte, using foam nickel loaded with metal / metal oxide as working electrode, and performing electrolysis reaction to obtain formamide; in the foam nickel loaded with metal / metal oxide, the metal is at least one of Pd, Pt, Mn and Co, and the metal oxide is WO3.

2. The method of claim 1, wherein, The magnesium salt is MgCl2 or MgSO4, the phosphorus salt is K2HPO4, KH2PO4 or K3PO4, the pH is 8.5-9.5, and the reagent used for adjusting the pH to alkaline is potassium hydroxide.

3. The method of claim 1, wherein, The heating temperature for heating and decomposing the magnesium ammonium phosphate precipitate is 80-100 ℃, and the heating time is 1-2 h.

4. The method of claim 1, wherein, The alkaline solution is 2-6 mol / L KOH solution, and the mass-volume ratio of waste PET plastic to alkaline solution is 1 g:20-30 mL.

5. The method of claim 1, wherein, The temperature of the hydrothermal reaction is 60-90 ℃, and the time is 8-16 h.

6. The method of claim 1, wherein, The obtained reaction solution is acidified to pH 2-3, and the reagent used for acidifying the obtained reaction solution is dilute sulfuric acid.

7. The method of claim 1, wherein, In the electrolyte, the concentration of NH3 is 1-5 mol / L, the concentration of ethylene glycol is 1-3 mol / L, and the concentration of H2SO4 is 0.25 mol / L.

8. The method of claim 1, wherein, The preparation method of the foam nickel loaded with metal / metal oxide comprises the following steps: dispersing Na2WO4 in water, and then sequentially adding acetic acid, metal salt and foam nickel, and performing hydrothermal reaction; after the hydrothermal reaction is completed, the obtained product is cleaned and dried to obtain the foam nickel loaded with metal / metal oxide.

9. The method of claim 8, wherein, The mass ratio of the Na2WO4 to the metal salt is 0.494:(0.01-0.05), the temperature of the hydrothermal reaction is 180-200 ℃, and the time is 4-5 h.

10. The method of claim 1, wherein, The condition of the electrolysis reaction is set as: constant voltage condition, and the voltage relative to the reference electrode Ag / AgCl is 1.35-1.45 V, and the room temperature.

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