Method and device for synthesizing percarbamide through electrochemical in-situ extraction of urea in urine

Abstract

The invention belongs to the technical field of percarbamide preparation, and particularly relates to a method and a device for synthesizing percarbamide through electrochemical in-situ extraction of urea in urine. Comprising the following steps: by taking a carbon-based catalyst as a working electrode, a metal active material as an anode and concentrated urine as an electrolyte solution, continuously introducing oxygen into the electrolyte solution, carrying out electrochemical in-situ extraction synthesis under constant voltage, and combining urea molecules with an oxidation intermediate adsorbed on the surface of the carbon-based catalyst, so as to obtain a urea compound; the percarbamide is generated through protonation, and urea in the urine is converted into the percarbamide. On the basis of an electrochemical technology, urea in urine is converted into percarbamide in situ, the conversion process is based on ingenious combination of an electrochemical oxygen reduction reaction and a urea conversion reaction, efficient combination of urea and * OOH is achieved, high-purity solid percarbamide is generated, efficient separation and conversion of urea are achieved under the condition of low energy consumption, and the method is suitable for industrial production. The complex operation of the traditional process is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of percarbamide preparation, and specifically relates to a method and a device for synthesizing percarbamide by electrochemical in-situ extraction of urea in urine. Background Art

[0002] Urine, as one of the main components of wastewater, is rich in urea and other nitrogen sources and is known as "liquid gold", but its potential value has not yet been fully developed. The current centralized wastewater treatment method is energy-intensive and costly, and even after treatment, a large amount of residual nitrogen substances will remain, which will burden the environment.

[0003] like Figure 1 As shown, the existing urine treatment technology requires five to six complex steps to separate solid urea from urine, and the obtained urea often contains a large amount of impurities. Therefore, there are many deficiencies in the efficient separation of urea from a complex urine system. Urine contains a large amount of salts and organic substances. The traditional existing separation methods require multiple steps of physical or chemical operations, which are not only time-consuming and labor-intensive, but also difficult to achieve efficient urea extraction. At the same time, centralized sewage treatment plants consume a lot of energy and rely on high-temperature treatment or chemical oxidation to decompose urea. These processes will generate by-products, such as greenhouse gases such as nitrogen oxides, which pollute the environment. Traditional urea oxidation and recovery processes also generate harmful gases, which increases the complexity of the treatment process and requires expensive and complex equipment, which is not suitable for large-scale or decentralized applications. In addition, the existing technology lacks an effective resource recycling system, and the treated waste liquid is usually discharged directly, resulting in a waste of resources, and fails to achieve the reuse of urea and support the development of a circular economy.

[0004] Therefore, existing urine extraction processes mostly rely on chemical or physical separation methods when separating urea from other salts and impurities. The steps are complicated, time-consuming, costly, and inefficient, making large-scale urine resource utilization challenging and hindering its promotion in decentralized application scenarios. Summary of the invention

[0005] To solve the above problems, the present invention provides a method and device for synthesizing percarbonate by electrochemical in-situ extraction of urea from urine. The method is based on electrochemical technology, and converts urea in urine into percarbonate in situ. This conversion process is based on the ingenious combination of electrochemical oxygen reduction reaction and urea conversion reaction, and realizes the efficient combination of urea and *OOH to generate high-purity solid percarbonate, and realizes efficient separation and conversion of urea under low energy consumption conditions, avoiding the complex operation of traditional processes. It reduces energy consumption, reduces the emission of greenhouse gases and other harmful byproducts, realizes efficient recovery and reuse of urea, and supports the development of circular economy.

[0006] The present invention solves the above technical problems through the following technical solutions.

[0007] One of the purposes of the present invention is to provide a method for electrochemical in-situ extraction of urea from urine to synthesize percarbamide, comprising the following steps: Using a carbon-based catalyst as the working electrode, a metal active material as the anode, and concentrated urine as the electrolyte solution, oxygen is continuously introduced into the electrolyte solution, and electrochemical in situ extraction synthesis is carried out under a constant voltage. During the electrochemical in situ extraction synthesis process, urea molecules combine with the oxidative intermediates adsorbed on the surface of the carbon-based catalyst, and percarbamide is generated through protonation, thereby converting the urea in the urine into percarbamide.

[0008] Furthermore, the preparation method of the electrolyte solution comprises the following steps: Citric acid is added to the urine to adjust the pH to 3.5-4.5, and then the urine is concentrated to form concentrated urine, wherein the mass concentration of urea in the concentrated urine is 15 wt.%-50 wt.%.

[0009] Furthermore, the carbon-based catalyst is a modified graphite carbon catalyst or a graphite carbon catalyst.

[0010] Furthermore, the preparation method of the modified graphite carbon catalyst comprises the following steps: Methane and oxygen are input into the preheating zone of the burner for mixing to form a premixed gas.

[0011] The premixed gas is transported to the reaction zone of the burner and burned. Then, sp³ hybrid defect sites are introduced into the graphite carbon layer by methane combustion to obtain a modified graphite carbon catalyst.

[0012] During the formation of the premixed gas and the combustion process, the H / O ratio of methane and oxygen in the premixed gas and the combustion temperature are controlled by adjusting the equivalent ratio Φ, and the equivalent ratio Φ is 0.6 to 1.4.

[0013] Furthermore, the potential of the constant voltage is 0.2V to 0.5V.

[0014] Furthermore, the temperature of the electrochemical in-situ extraction synthesis is 1°C to 30°C.

[0015] Further, the flow rate of oxygen is ≥100 SCCM.

[0016] Furthermore, the electrochemical in-situ extraction synthesis adopts a three-electrode system, the reference electrode is Ag / AgCl, the metal active material is a platinum sheet, and after the electrochemical in-situ extraction synthesis, it is filtered and dried to obtain solid percarbamide.

[0017] The second object of the present invention is to provide a device for in-situ extraction of urea from urine to synthesize percarbamide, which is used to implement the above-mentioned electrochemical in-situ extraction method of urea from urine to synthesize percarbamide, comprising: A collection and purification unit, used for collecting, concentrating and purifying to obtain concentrated urine; A concentration detection detection unit for monitoring the concentration of concentrated urine; The electrochemical reaction device unit is used to extract concentrated urine in situ at the anode under the action of a catalyst under power supply conditions and synthesize percarbonate amide by inputting air at the cathode; the electrochemical reaction device unit is provided with a temperature controller and an oxygen input device; The separation unit is used to separate and collect the percarbonate, and transport the separated unreacted urine to the collection and purification unit for recycling.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a method for synthesizing percarbamide by electrochemical in-situ extraction of urea from urine. The method is based on electrochemical technology and converts urea in urine into percarbamide in-situ. The conversion process is based on the combination of electrochemical oxygen reduction reaction and urea conversion reaction, thereby achieving highly selective extraction of urea and high value-added conversion. The reaction mechanism is a full reaction: CN 2 H 4 O+O 2 +2H + +2e - CN 2 H 6 O 3 , the specific reaction process is as follows: O 2 →*OOH ; *OOH+urea→*OOH⋅urea ; *OOH⋅urea+urea+H + +e-→percarbamide ; It achieves efficient separation and conversion of urea under low energy consumption conditions, avoids the complex operations of traditional processes, reduces the emission of greenhouse gases and other harmful by-products, and realizes efficient recovery and reuse of urea. It has wide applicability and is not only suitable for human urine treatment, but also for animal urine and synthetic urine treatment. It shows great flexibility and directly generates percarbonate after urea extraction, which not only avoids nitrogen loss, but also can be used in agriculture as a slow-release fertilizer and oxygen supply product to improve crop yield and growth efficiency.

[0019] (2) The present invention also provides a device for implementing the method of in-situ extraction of urea from urine to synthesize percarbonate. A closed-loop circulation system from urine treatment to resource recovery is constructed through a collection and purification unit, a concentration detection unit, an electrochemical reaction device unit and a separation unit, which realizes the efficient recovery and reuse of urea, supports the development of a circular economy, is suitable for decentralized applications in cities and rural areas, and can also be seamlessly connected with existing sewage treatment facilities to meet the urine treatment needs in different scenarios, providing a new solution for future resource utilization. It can also be seamlessly integrated with the existing sewage treatment system, greatly improving the overall efficiency and economic value of the system. Compared with traditional methods, this technology realizes efficient separation and high-purity conversion of urea, providing a sustainable solution for urban sewage management and rural agricultural development. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a flow chart for comparing the processes of the existing urine treatment technology with the method of the present invention for synthesizing percarbonate by electrochemical in-situ extraction of urea from urine.

[0021] Figure 2 The present invention is a structural diagram of a device for implementing a method for in-situ extraction of urea from urine to synthesize percarbonate.

[0022] Figure 3 The phase diagram and in-situ test conditions of the precipitation process of the synthesized percarbamide of the present invention are as follows: Figure 3 a in the figure is the phase diagram of the percarbamide precipitation process, and b is the in-situ test conditions.

[0023] Figure 4 The ternary phase diagram of the electrochemical in-situ extraction of urea from urine to synthesize percarbamide prepared in Examples 1 to 9 of the present invention is as follows: Figure 4 a is the precipitation curve in the urea-hydrogen peroxide-water three-phase system, b is the precipitation curve under temperature control, c is the locally enlarged phase diagram of a, and d is the precipitation curve in the real urine environment.

[0024] Figure 5 The performance diagram of the electrochemical in-situ extraction of urea from urine to synthesize percarbonate at different potentials of the present invention is shown in FIG. Figure 5 a is the current-potential curve, and b is the Faraday efficiency diagram.

[0025] Figure 6 The X-ray diffraction pattern and infrared spectrum of the electrochemical in-situ extraction of urea from urine to synthesize percarbamide in Example 1 of the present invention are shown in FIG. Figure 6 a is the X-ray diffraction spectrum and b is the infrared spectrum.

[0026] Figure 7 This is a scanning electron microscope image of the electrochemical in-situ extraction of urea from urine to synthesize percarbamide in Example 1 of the present invention. Figure 7 a, b and c are scanning electron micrographs of urea at different scales, and d, e and f are scanning electron micrographs of the corresponding synthesized percarbamide of urea in a, b and c at different scales.

[0027] Figure 8 This is a growth diagram of the percarbamide of the present invention used in the cultivation of peanut seedlings. Figure 8 Figure a is a photo of peanut seedling cultivation, b is a schematic diagram of the effect of percarbamide on plant roots, and c is a quantitative comparison result of crop growth.

[0028] Fig. 9 This is a flow chart of the present invention for detecting the residual urea recovery from the unreacted urine after separation by the separation unit. Fig. 9 In the figure, a is the reaction of urea with concentrated nitric acid to form urinary nitrate precipitate; b is the solid mixture of urea and potassium nitrate obtained after evaporating water; c is the solid potassium nitrate obtained by dissolving urea in hot alcohol and filtering; d is the alcohol solution formed after urea is dissolved; e is the evaporation of alcohol, cooling and crystallization of urea; f is the solid urea obtained after filtration.

[0029] Fig.10 This is a performance diagram of the present invention for detecting urea in unreacted urine after separation by the separation unit. Fig.10 a is an XRD analysis diagram, b is a schematic diagram of the steps for separating urea from waste liquid, and c is a purity cycle step diagram. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0032] like Figure 1 As shown, the existing urine processing technology specifically includes the following steps: first, the urine is concentrated by filtration to remove large particle impurities and further reduce the water content; second, urea is precipitated together with other dissolved substances to form a solid mixture containing salts and inorganic impurities; next, hot ethanol is used to dissolve the urea and form a suspension at the same time, so that some insoluble impurities can be separated, but this step cannot completely remove all impurities; thirdly, the low-solubility components are removed by filtration to obtain an ethanol solution containing urea and some soluble impurities. However, during the recrystallization process of urea, since the solubility of some impurities is close to or is encapsulated in the urea crystals, the final urea still contains a certain amount of impurities and the purity is limited. This method has problems such as residual impurities, complex process, and limited purity, which makes large-scale urine resource utilization challenging and difficult to meet high-demand applications, hindering its promotion in decentralized application scenarios.

[0033] Based on the above problems, the present invention provides a strategy for in-situ extraction of urea from urine based on electrochemical technology, such as Figure 1 As shown in the figure, through the optimized electrochemical reaction path, the efficient separation and conversion of urea is achieved to generate high value-added percarbamide. This innovative solution solves the problems of high energy consumption, low efficiency and difficult by-product treatment in the existing technology. The details are as follows:

[0034] A method for synthesizing percarbamide by electrochemical in-situ extraction of urea from urine comprises the following steps: Using a carbon-based catalyst as the working electrode, a metal active material as the anode, and concentrated urine as the electrolyte solution, oxygen is continuously introduced into the electrolyte solution, and electrochemical in situ extraction synthesis is carried out under a constant voltage. During the electrochemical in situ extraction synthesis process, urea molecules combine with the oxidative intermediates adsorbed on the surface of the carbon-based catalyst, and percarbamide is generated through protonation, thereby converting the urea in the urine into percarbamide.

[0035] The present invention provides a method for synthesizing percarbamide by electrochemical in-situ extraction of urea from urine. The method is based on electrochemical technology, converts urea in urine into percarbamide in-situ, and efficiently converts urea into percarbamide through a two-electron redox reaction (2e-ORR). The hydrogen bonding of urea and the reaction characteristics of its oxidation intermediates (such as H2O2 or *OOH) are fully utilized at the molecular level, thereby achieving highly selective extraction and high value-added conversion of urea. The reaction mechanism is a full reaction: CN 2 H 4 O+O 2 +2H + +2e - CN 2 H 6 O 3 , the specific reaction process is as follows:

[0036] O 2 →*OOH *OOH+urea → *OOH⋅urea *OOH⋅urea+urea+H + +e-→percarbamide This conversion process is based on the ingenious combination of electrochemical oxygen reduction reaction and urea conversion reaction, which realizes the efficient combination of urea and *OOH, generates high-purity solid percarbamide, and realizes efficient separation and conversion of urea under low energy consumption conditions, avoiding the complex operation of traditional processes. It reduces energy consumption, greenhouse gas and other harmful by-product emissions, and realizes efficient recovery and reuse of urea. It has a wide range of applicability, not only suitable for human urine treatment, but also for animal urine and synthetic urine treatment, showing great flexibility.

[0037] The invention directly generates percarbamide after urea extraction, which not only avoids nitrogen loss, but also can be used in agriculture as a slow-release fertilizer and oxygen supply product to improve crop yield and growth efficiency.

[0038] In a specific embodiment, the method for preparing the electrolyte solution comprises the following steps: Citric acid is added to the urine to adjust the pH to 3.5-4.5, and then the urine is concentrated to form concentrated urine. The mass concentration of urea in the concentrated urine is 15 wt.%-50 wt.%.

[0039] In the present invention, citric acid is added to adjust the pH, inhibit the enzymatic decomposition of urea, and prevent it from decomposing into ammonia and carbon dioxide. The process is operated at a low temperature close to 0°C to avoid chemical changes in organic and inorganic components. The concentrated urine can also be freeze-dried to form a solid substance, and then prepared as a suspension in low-temperature water close to 0°C. Finally, the insoluble by-products are removed by low-temperature filtration to obtain a clear urine concentrate, thereby ensuring that there is no interference from impurities in the subsequent reaction process.

[0040] In a specific embodiment, the carbon-based catalyst is a modified graphite carbon catalyst or a graphite carbon catalyst. The carbon-based catalyst used in the present invention is used as a working electrode. During the electrochemical in-situ extraction and synthesis process, the carbon-based catalyst adsorbs O2 and provides electron transfer, promotes the combination of oxygen and electrons to form its oxidation intermediates (such as H2O2 or *OOH), and utilizes the hydrogen bonding of urea and the reaction characteristics of its oxidation intermediates, thereby achieving highly selective extraction and high value-added conversion of urea. And through modification, carbon-based materials can not only improve catalytic activity, but also show performance comparable to or even exceeding that of precious metal catalysts in certain electrocatalytic reactions.

[0041] In a specific embodiment, the preparation method of the modified graphite carbon catalyst comprises the following steps: S1. Methane and oxygen are input into the preheating zone of the burner for mixing to form a premixed gas.

[0042] S2. The premixed gas is transported to the reaction zone of the burner, and after combustion, sp³ hybridized defect sites are introduced into the graphite carbon layer by using methane combustion to obtain a modified graphite carbon catalyst; during the formation of the premixed gas and the combustion process, the H / O ratio of methane and oxygen in the premixed gas and the combustion temperature are controlled by adjusting the equivalent ratio Φ, and the equivalent ratio Φ is 0.6 to 1.4.

[0043] The present invention accurately controls the relationship between the H / O ratio, combustion temperature and propagation speed by adjusting the single variable of the equivalent ratio Φ, ensures the efficient conduct of the hydrogenation process, and realizes the precise control of defect generation to ensure that the reducibility and heat supply of the combustion process reach the best balance. In the combustion process, methane combustion is used as an energy source and a free radical generation pathway to achieve efficient modification of the surface and edge of the carbon material. The laminar premixed methane combustion technology ensures the controllability and stability of the combustion process, shortens the modification process from several hours to several seconds, greatly improves production efficiency, realizes efficient modification of carbon materials under mild conditions, and realizes the preparation of efficient catalysts in a short time, and greatly improves its catalytic performance. In a specific embodiment, the preparation method of modified graphite carbon catalyst includes the following steps: S1, controlling the equivalent ratio Φ to 1.0, inputting methane and oxygen into the preheating zone of the burner for mixing to form a premixed gas. S2. The premixed gas is transported to the reaction zone of the burner. After combustion, the combustion temperature is controlled between 950°C and 1000°C to ensure that the material is heated gently and avoid excessive defect generation, thereby obtaining a defective graphite carbon catalyst, named AGC.

[0044] In a specific embodiment, the potential of the constant voltage is 0.2 V to 0.5 V. In the present invention, at this potential, the carbon-based catalyst can provide an efficient O2 reduction path, while inhibiting the four-electron oxygen reduction reaction (4e-ORR), stabilizing the *OOH species, inhibiting the complete dissociation of the OO bond, and promoting the reaction to tend to the two-electron oxygen reduction reaction (2e-ORR), thereby maximizing the synthesis of percarbamide.

[0045] In a specific embodiment, the temperature of the electrochemical in-situ extraction synthesis is 1°C to 30°C. In the present invention, the temperature of the electrochemical in-situ extraction synthesis is to optimize the urea oxidation and two-electron oxygen reduction reaction (2e-ORR), and to improve the selectivity and purity of the product. First, low temperature can inhibit the hydrolysis of urea and prevent it from decomposing into ammonia and carbon dioxide at high temperature, thereby maintaining the stability of urea and increasing the effective concentration of the reactants. Secondly, the low temperature environment can ensure the life of *OOH, thereby improving the selectivity of 2e-ORR and making full use of urea in the urea oxidation reaction (UOR). In addition, the oxidation reaction of urea with H2O2 can reduce the generation of by-products (such as carbamate or uric acid) at low temperature, improve the synthetic selectivity of percarbamide, and at the same time, low temperature can also optimize the crystallization process of percarbamide, reduce impurity co-precipitation, and improve the purity of the product. On the other hand, low temperature operation also helps to reduce electrode corrosion and side reaction rates, improve the stability of the catalyst, and ensure the long-term controllability of the electrochemical reaction.

[0046] In a specific embodiment, the flow rate of oxygen is ≥100 SCCM. In the present invention, the continuous introduction of oxygen into the electrolyte solution is mainly to ensure CN 2 H 4 O+O 2 +2H + +2e - CN 2 H 6 O 3 For the reaction, the oxygen flow rate only needs to be slightly higher than the 1:1 ratio with urea. Air can also be introduced, but the oxygen flow rate in the air must be greater than or equal to 100 SCCM.

[0047] In a specific embodiment, the electrochemical in situ extraction synthesis adopts a three-electrode system, the reference electrode is Ag / AgCl, the metal active material is a platinum sheet, and after the electrochemical in situ extraction synthesis, the solid percarbamide is obtained after filtration and drying.

[0048] In addition, the present invention also provides a device for in-situ extraction of urea-synthesized percarbamide from urine, which is used to implement the above-mentioned electrochemical in-situ extraction method of urea-synthesized percarbamide from urine, such as Figure 2 As shown, including: The collection and purification unit 1 is used for collecting, concentrating and purifying to obtain concentrated urine; the collection and purification unit 1 can collect urine from various sources, such as urban and rural areas. The urine can be human urine, animal urine and synthetic urine. After being stabilized by the collection and purification unit 1, impurities are removed through the concentration and filtration process to generate high-concentration urine. Clean water and solid by-products are generated during the purification process to reduce interference factors in subsequent reactions. The concentrated urine is transported to the concentration control module set in the collection and purification unit to accurately adjust the urea concentration according to the reaction requirements to ensure the efficiency and selectivity of the electrochemical reaction.

[0049] The concentration detection unit 2 is used to monitor the concentration of concentrated urine; the concentration detection unit 2 continuously monitors the urea concentration of the concentrated urine, and when the set threshold is reached, the concentrated urine is transported to the electrochemical reaction device unit 3.

[0050] The electrochemical reaction device unit 3 is used to decompose the concentrated urine at the anode under the action of the catalyst under the condition of power supply and synthesize the percarbamide by inputting air at the cathode; the electrochemical reaction device unit 3 is provided with a temperature controller 4 and an oxygen input device 5; urea is converted into precipitated solid percarbamide through an in-situ electrochemical reaction; The separation unit 6 is used to separate and collect percarbonate, and transport the separated unreacted urine to the collection and purification unit 1 for recycling. The precipitated solid percarbonate is separated and collected by the separation unit 6 to ensure the separation efficiency of high-purity percarbonate. The residual urine containing low-concentration urea continues to enter the collection and purification unit for further concentration and filtration until the urine is completely converted into percarbonate, pure water and solid by-products.

[0051] The present invention provides a device for implementing the method of synthesizing percarbonate by in-situ extraction of urea from urine. A closed-loop circulation system from urine treatment to resource recovery is constructed through a collection and purification unit, a concentration detection unit, an electrochemical reaction device unit and a separation unit, which realizes the efficient recovery and reuse of urea, supports the development of circular economy, is suitable for decentralized applications in cities and rural areas, and can also be seamlessly connected with existing sewage treatment facilities to meet the urine treatment needs in different scenarios, providing a new solution for future resource utilization. It can also be seamlessly integrated with the existing sewage treatment system, greatly improving the overall efficiency and economic value of the system. Compared with traditional methods, this technology realizes efficient separation and high-purity conversion of urea, providing a sustainable solution for urban sewage management and rural agricultural development.

[0052] The invention is further described below through specific examples.

[0053] Example 1 A method for synthesizing percarbamide by electrochemical in-situ extraction of urea from urine comprises the following steps: S1. Preparation of electrolyte solution: collecting urine from people of different genders aged 5 to 70 years old, adding citric acid to the urine to adjust the pH to 3.5-4.5, and then concentrating the urine to form concentrated urine, wherein the mass concentration of urea in the concentrated urine is 36 wt%.

[0054] S2. Using modified graphite carbon catalyst as working electrode, platinum sheet as anode, Ag / AgCl as reference electrode, and a three-electrode system, concentrated urine was used as electrolyte solution, and oxygen was continuously introduced into the electrolyte solution at a flow rate of 100 SCCM. Electrochemical in situ extraction and synthesis were carried out at a constant voltage of 0.5 V. The temperature of electrochemical in situ extraction and synthesis was 1°C to convert urea in urine into percarbamide.

[0055] Example 2 A method for synthesizing percarbamide by electrochemical in-situ extraction of urea from urine comprises the following steps: S1. Preparation of electrolyte solution: collecting urine from people of different genders aged 5 to 70 years old, adding citric acid to the urine to adjust the pH to 3.5-4.5, and then concentrating the urine to form concentrated urine, wherein the mass concentration of urea in the concentrated urine is 15 wt%.

[0056] S2. Using modified graphite carbon catalyst as working electrode, platinum sheet as anode, Ag / AgCl as reference electrode, and a three-electrode system, concentrated urine was used as electrolyte solution, and oxygen was continuously introduced into the electrolyte solution at a flow rate of 100 SCCM. Electrochemical in situ extraction and synthesis were carried out at a constant voltage of 0.5 V. The temperature of electrochemical in situ extraction and synthesis was 1°C to convert urea in urine into percarbamide.

[0057] Example 3 A method for synthesizing percarbamide by electrochemical in-situ extraction of urea from urine comprises the following steps: S1. Preparation of electrolyte solution: collecting urine from people of different genders aged 5 to 70 years old, adding citric acid to the urine to adjust the pH to 3.5-4.5, and then concentrating the urine to form concentrated urine, wherein the mass concentration of urea in the concentrated urine is 38 wt%.

[0058] S2. Using modified graphite carbon catalyst as working electrode, platinum sheet as anode, Ag / AgCl as reference electrode, and a three-electrode system, concentrated urine was used as electrolyte solution, and oxygen was continuously introduced into the electrolyte solution at a flow rate of 100 SCCM. Electrochemical in situ extraction and synthesis were carried out at a constant voltage of 0.5 V. The temperature of electrochemical in situ extraction and synthesis was 1°C to convert urea in urine into percarbamide.

[0059] Example 4 A method for synthesizing percarbamide by electrochemical in-situ extraction of urea from urine comprises the following steps: S1. Preparation of electrolyte solution: collecting urine from people of different genders aged 5 to 70 years old, adding citric acid to the urine to adjust the pH to 3.5-4.5, and then concentrating the urine to form concentrated urine, wherein the mass concentration of urea in the concentrated urine is 36 wt%.

[0060] S2. Using modified graphite carbon catalyst as working electrode, platinum sheet as anode, Ag / AgCl as reference electrode, and a three-electrode system, concentrated urine was used as electrolyte solution, and oxygen was continuously introduced into the electrolyte solution at a flow rate of 100 SCCM. Electrochemical in situ extraction synthesis was carried out at a constant voltage of 0.2 V. The temperature of electrochemical in situ extraction synthesis was 1°C, and urea in urine was converted into percarbamide.

[0061] Example 5 A method for synthesizing percarbamide by electrochemical in-situ extraction of urea from urine comprises the following steps: S1. Preparation of electrolyte solution: collecting urine from people of different genders aged 5 to 70 years old, adding citric acid to the urine to adjust the pH to 3.5-4.5, and then concentrating the urine to form concentrated urine, wherein the mass concentration of urea in the concentrated urine is 36 wt%.

[0062] S2. Using modified graphite carbon catalyst as working electrode, platinum sheet as anode, Ag / AgCl as reference electrode, and a three-electrode system, concentrated urine was used as electrolyte solution, and oxygen was continuously introduced into the electrolyte solution at a flow rate of 100 SCCM. Electrochemical in situ extraction synthesis was carried out at a constant voltage of 0.3 V and the temperature of electrochemical in situ extraction synthesis was 1°C to convert urea in urine into percarbamide.

[0063] Example 6 A method for synthesizing percarbamide by electrochemical in-situ extraction of urea from urine comprises the following steps: S1. Preparation of electrolyte solution: collecting urine from people of different genders aged 5 to 70 years old, adding citric acid to the urine to adjust the pH to 3.5-4.5, and then concentrating the urine to form concentrated urine, wherein the mass concentration of urea in the concentrated urine is 36 wt%.

[0064] S2. Using modified graphite carbon catalyst as working electrode, platinum sheet as anode, Ag / AgCl as reference electrode, and a three-electrode system, concentrated urine was used as electrolyte solution, and oxygen was continuously introduced into the electrolyte solution at a flow rate of 100 SCCM. Electrochemical in situ extraction synthesis was carried out at a constant voltage of 0.4 V. The temperature of electrochemical in situ extraction synthesis was 1°C, and urea in urine was converted into percarbamide.

[0065] Example 7 A method for synthesizing percarbamide by electrochemical in-situ extraction of urea from urine comprises the following steps: S1. Preparation of electrolyte solution: collecting urine from people of different genders aged 5 to 70 years old, adding citric acid to the urine to adjust the pH to 3.5-4.5, and then concentrating the urine to form concentrated urine, wherein the mass concentration of urea in the concentrated urine is 36 wt%.

[0066] S2. Using modified graphite carbon catalyst as working electrode, platinum sheet as anode, Ag / AgCl as reference electrode, and a three-electrode system, concentrated urine was used as electrolyte solution, and oxygen was continuously introduced into the electrolyte solution at a flow rate of 100 SCCM. Electrochemical in situ extraction and synthesis were carried out at a constant voltage of 0.5 V. The temperature of electrochemical in situ extraction and synthesis was 15°C to convert urea in urine into percarbamide.

[0067] Example 8 A method for synthesizing percarbamide by electrochemical in-situ extraction of urea from urine comprises the following steps: S1. Preparation of electrolyte solution: collecting urine from people of different genders aged 5 to 70 years old, adding citric acid to the urine to adjust the pH to 3.5-4.5, and then concentrating the urine to form concentrated urine, wherein the mass concentration of urea in the concentrated urine is 36 wt%.

[0068] S2. Using modified graphite carbon catalyst as working electrode, platinum sheet as anode, Ag / AgCl as reference electrode, and a three-electrode system, concentrated urine was used as electrolyte solution, and oxygen was continuously introduced into the electrolyte solution at a flow rate of 100 SCCM. Electrochemical in situ extraction synthesis was carried out at a constant voltage of 0.5 V. The temperature of electrochemical in situ extraction synthesis was 30°C, and urea in urine was converted into percarbamide.

[0069] Example 9 A method for synthesizing percarbamide by electrochemical in-situ extraction of urea from urine comprises the following steps: S1. Preparation of electrolyte solution: collecting urine from people of different genders aged 5 to 70 years old, adding citric acid to the urine to adjust the pH to 3.5-4.5, and then concentrating the urine to form concentrated urine, wherein the mass concentration of urea in the concentrated urine is 36 wt%.

[0070] S2. Using graphite carbon catalyst (PGC) as the working electrode, platinum sheet as the anode, Ag / AgCl as the reference electrode, a three-electrode system was adopted, concentrated urine was used as the electrolyte solution, and oxygen was continuously introduced into the electrolyte solution at a flow rate of 100 SCCM. Electrochemical in situ extraction and synthesis were carried out at a constant voltage of 0.5 V. The temperature of the electrochemical in situ extraction and synthesis was 1°C to convert urea in urine into percarbamide.

[0071] The performance of electrochemical in-situ extraction of urea from urine to synthesize percarbonate prepared in Examples 1 to 9 was tested, and the results are shown below.

[0072] Figure 3 The phase diagram and in-situ test conditions of the precipitation process of the synthesized percarbamide of the present invention are as follows: Figure 3 a in the figure is the phase diagram of the percarbamide precipitation process, and b is the in-situ test conditions. Figure 3 As shown in a in the figure, region A in the phase diagram represents the coexistence region of unprecipitated low-concentration percarbonate, H2O2 and urea in the liquid phase; region B is the precipitation region of urea; region C is the precipitation region of percarbonate; and region D is the co-precipitation region of percarbonate and urea. It can be observed that under the same conditions, when the urea concentration is lower than 12wt% to 15wt%, the required amount of hydrogen peroxide increases significantly, and when the urea concentration exceeds 38wt%, it will cause the precipitation of urea itself, thereby reducing the purity of the final product, and the precipitation of percarbonate is easier than urea, and only a lower concentration of urea is required. This advantage makes the method of the present invention have significant advantages in product purity compared to traditional urea extraction processes; such as Figure 3As shown in b, the marks "E1" and "E2" represent the urease hydrolysis inhibition zone, "F" represents the urease hydrolysis zone, "G" represents the urea chemical hydrolysis zone, and "H" represents the ice formation zone. The white line and symbols in the figure correspond to the left y-axis (temperature), while the magenta points correspond to the right y-axis (the defined "difficulty coefficient" of percarbamide precipitation, the higher the value, the more difficult the precipitation). The figure combines the consideration of multiple factors, including urease activity, H2O2 stability, urea chemical hydrolysis, the possibility of impurity co-precipitation, catalytic performance, required stable dosage, and freezing point. The final analysis shows that the conditions represented by the light purple points are most suitable for the operation of this system. The figure shows in detail the precipitation process and optimization conditions of percarbamide. In the phase diagram, the precipitation of percarbamide is easier to occur than urea, and only a lower urea concentration is required to achieve it, which provides an important advantage for the method of the present invention in product purity. The optimized test condition diagram shows how to balance factors such as urea hydrolysis, H2O2 stability and impurity co-precipitation under different temperatures and reaction conditions to ensure that the system achieves optimal performance. The conditions represented by the light purple dots finally determined can effectively improve the precipitation efficiency of percarbonate amide while avoiding the influence of adverse factors.

[0073] Figure 4 The ternary phase diagram of the electrochemical in-situ extraction of urea from urine to synthesize percarbamide prepared in Examples 1 to 9 of the present invention is as follows: Figure 4 a is the precipitation curve in the urea-hydrogen peroxide-water three-phase system, b is the precipitation curve under temperature control, c is the local enlarged phase diagram of a, and d is the precipitation curve in the real urine environment. Figure 4 As shown in a in the figure, the derivative of the precipitation boundary curve has an obvious inflection point near the urea concentration of 12wt% to 15wt%, indicating that below this concentration, the reaction of urea and hydrogen peroxide is limited, and a higher concentration of H2O2 is required to drive the formation of percarbamide; and when the urea concentration exceeds 38wt%, the urea itself begins to be supersaturated and precipitate, thereby reducing the purity of the final product. Based on this analysis, the optimal concentration range of urea is determined to be 15wt% to 38wt% to balance the utilization of H2O2, ensure the efficient precipitation of percarbamide, and avoid the formation of by-products; Figure 4 As shown in b, the precipitation behavior of urea at 1°C, 15°C and 30°C is shown. It is found that the precipitation is most stable at 1°C, and the urea conversion rate is the highest, which is suitable for low-temperature electrochemical systems; the precipitation zone is significantly reduced at 30°C, indicating that the high temperature environment may accelerate the hydrolysis of urea or change the precipitation kinetics, which is not conducive to the formation of efficient products; and 15°C, as an intermediate temperature, shows a certain degree of precipitation optimization effect, but the effect is still weaker than 1°C; Figure 4As shown in Figure c, the local enlarged phase diagram further refines the precipitation area near the electrode, emphasizing the effect of urea concentration gradient on the electrochemical precipitation process. Due to the limited diffusion of urea, its local concentration near the electrode is high, which may cause supersaturated precipitation to occur early, while the area far from the electrode may be restricted due to the limited diffusion of H2O2, resulting in hindered reaction kinetics. This figure helps to reveal the differences in urea precipitation behavior in different electrolytic cell areas and provides a basis for optimizing electrode structure and fluid dynamics; Figure 4 As shown in d, by introducing the actual components in urine, the effects of other components in urine (such as inorganic salts, uric acid, etc.) on the precipitation behavior of urea were investigated. The results show that compared with the urea solution prepared in the laboratory, there is a certain deviation in the precipitation behavior in the real urine system, which may be due to the consumption or complexation of other impurities in urine on H2O2 affecting the precipitation kinetics of the urea-hydrogen peroxide reaction. Therefore, the applicability of the ternary phase diagram in the real urine system was verified, and the conditions for urea concentration and electrolytic synthesis were further optimized.

[0074] Electrochemical tests were performed at different urea concentrations (18%, 36%, and 44% wt), and the formation of percarbamide precipitation was monitored. The results showed that a urea concentration of 6 M (36 wt%) was most conducive to improving the reaction efficiency. Under this condition, the average yield of percarbamide reached 527.3 μmol / h, and the purity of the precipitated product was as high as 98.6%. In addition, local accumulation of hydrogen peroxide (H2O2) was observed, and the reaction utilization of H2O2 was optimized by controlling the urea concentration, ensuring that the precipitation rate remained stable, allowing the electrochemical synthesis process to continue for 200 hours until the urea concentration dropped below the threshold.

[0075] From a mechanistic point of view, the effect of urea concentration on the electrochemical process is mainly reflected in the control of H2O2 generation kinetics and precipitation rate. In the process of H2O2 generation, a higher urea concentration helps to increase the local concentration of H2O2, thereby promoting the two-electron oxygen reduction reaction (2e-ORR) and increasing the reaction rate. However, when the urea concentration is too high, H2O2 may self-decompose, resulting in a decrease in reaction efficiency. In addition, the local concentration of urea determines the nucleation rate and growth mechanism of percarbamide. The appropriate urea concentration (6M) can uniformly form percarbamide precipitation on the electrode surface and in the solution, while when the urea concentration is too high, it may cause uneven precipitation, affecting the purity of the final product. Therefore, in the electrochemical synthesis process, the optimization of urea concentration is crucial to ensure high-purity and high-yield percarbamide.

[0076] Figure 5 The performance diagram of the electrochemical in-situ extraction of urea from urine to synthesize percarbonate at different potentials of the present invention is shown in FIG. Figure 5a is the current density-potential curve, and b is the Faraday efficiency graph. Figure 5 As shown in Figure 2, the optimal potential range for the two-electron oxygen reduction reaction (2e-ORR) is 0.3 V to 0.5 V (vs. RHE), especially under the conditions of AGC (modified graphitic carbon) catalyst, this potential range can provide an efficient O2 source path while inhibiting the four-electron oxygen reduction reaction (4e-ORR) and maximizing the H2O2 yield. Figure 5 As shown in a, in the range of 0.3 V to 0.6 V, the reduction current of AGC increases significantly, indicating that it can effectively catalyze O2 reduction at this potential, while PGC (unmodified graphite carbon) has almost no significant current response in the same potential range, indicating that its 2e-ORR activity is low; Figure 5 As shown in b, the effect of potential on H2O2 selectivity is further verified. Between 0.2 V and 0.5 V, the FE of the AGC system is maintained above 90%, indicating that the oxygen reduction reaction in this potential range almost completely follows the 2e-ORR mechanism, while the FE of the PGC system is only 60% to 70%, indicating that some electrons enter the 4e-ORR pathway, resulting in a decrease in H2O2 selectivity. Mechanistically, the sp³ hybridization defects in AGC can effectively adsorb O2 and stabilize *OOH species, inhibit the complete dissociation of the OO bond, and promote the reaction to 2e-ORR, thereby maximizing the synthesis of percarbamide. 0.3 V to 0.5 V (vs. RHE) should be selected as the optimal potential range for 2e-ORR to ensure the highly selective generation of H2O2 and promote the oxidation conversion of urea.

[0077] Figure 6 The X-ray diffraction pattern and infrared spectrum of the electrochemical in-situ extraction of urea from urine to synthesize percarbamide in Example 1 of the present invention are shown in FIG. Figure 6 a is the X-ray diffraction spectrum, and b is the infrared spectrum. Figure 6 As shown in a in the figure, a continuous cycle scanning technique was used to record the different stages of precipitation formation (Stage I to Stage V). In the initial stage (Stage I), no obvious diffraction peaks were detected in the liquid phase, and only a broad curved peak (18° to 36°) was observed. This was due to the X-rays penetrating the liquid and reaching the substrate. As the reaction proceeded, (111) and (200) diffraction peaks were observed in Stage II, indicating that crystal nucleation had begun. In Stage III and Stage IV, the intensity of the diffraction peaks gradually increased, indicating that the crystals continued to grow and entered a stable state in Stage V, completing the precipitation process. This indicates that the growth direction of percarbamide is mainly along the

[100] direction, while the

[010] direction also has a certain contribution. This change in growth mode may be related to the nucleation and growth mechanism under the interaction between hydrated hydroperoxide (H2O2) and urea. Figure 6 As shown in b, Fourier transform infrared spectroscopy (FTIR) monitoring is used to analyze the changes in functional groups during the precipitation process. The results show that from the liquid phase to the completely dry state (0 min to 40 min), the solid percarbamide retains the characteristic peaks of urea and H2O2 (such as NH, C=O, CN and HOOH). During the precipitation process (10 min to 30 min), the spectrum did not change significantly, while when completely dried (40 min), the OH vibration peak was significantly weakened, indicating that water was removed and H2O2 was successfully solidified into the crystal; FTIR analysis did not find the formation of new chemical bonds between urea and H2O2, indicating that they are mainly bound to each other through hydrogen bonds rather than chemical reactions. This result is consistent with the XRD crystallinity change, further confirming that the nucleation and growth process of percarbamide mainly involves physical interactions rather than chemical bond reorganization.

[0078] Figure 7 This is a scanning electron microscope image of the electrochemical in-situ extraction of urea from urine to synthesize percarbamide in Example 1 of the present invention. Figure 7 a, b and c in the figure are scanning electron micrographs of urea at different scales, and d, e and f are scanning electron micrographs of the corresponding synthetic percarbamide of urea in a, b and c at different scales. Figure 7 As shown, the corresponding morphological structures of percarbonate synthesized by electrochemical in situ extraction of urea from urine at different scales are demonstrated.

[0079] The percarbamide prepared in Example 1 is used for cultivating peanut seedlings, which specifically comprises the following steps: Coconut bran was used as the culture matrix with the same lighting conditions and a cultivation period of 12 days. Three groups of experiments were set up, namely pure deionized water, deionized water with a nitrogen concentration of 0.2 wt% urea, and deionized water containing 0.2 wt% percarbonate. Pure deionized water, deionized water with a nitrogen concentration of 0.2 wt% urea, and deionized water containing 0.2wt% percarbonate were applied once every three days, and irrigation was carried out once a day.

[0080] Figure 8 This is a growth diagram of the percarbamide of the present invention used in the cultivation of peanut seedlings. Figure 8 Figure a is a photo of peanut seedling cultivation, b is a schematic diagram of the effect of percarbamide on plant roots, and c is a quantitative comparison result of crop growth. Figure 8 As shown in a, the growth of peanut seedlings in different treatment groups is shown: pure water group (upper left), water + urea group (upper right) and water + percarbamide group (below). Figure 8As shown in Figure b, it shows the triple effects of percarbamide on plant roots: first, it provides oxygen to plants and enhances their respiration; second, it serves as a source of nitrogen fertilizer to promote plant growth; third, it regulates pH, locks in ammonium nitrogen, prevents nitrogen loss during urea conversion, and improves the nitrogen absorption efficiency of the roots. Figure 8 As shown in Figure c, a quantitative comparison of crop growth height is shown. The y-axis represents the rough height measurement of each crop, showing the growth of peanut seedlings under different treatment conditions and the role of percarbamide in agricultural applications. The results show that the percarbamide group showed the best growth effect among all crops, especially in promoting root growth. In contrast, the urea group also had good growth, but because urea needs to be converted into ammonium nitrogen by urease in the soil, its hydrolysis process consumes hydrogen and increases the soil pH, resulting in ammonia volatilization loss. The crops in the water group (no fertilizer) grew the worst, with obvious wilting. The superiority of the percarbamide group lies in its slow release of oxygen, which can improve the redox environment of the roots and promote healthy root growth. At the same time, its moderate acidity helps to regulate soil pH and reduce ammonia volatilization. Therefore, percarbamide is not only used as a nitrogen fertilizer, but also can improve soil fertilizer efficiency and crop growth rate. It can be seen that percarbamide promotes plant respiration by providing oxygen, improves crop nutrition as a nitrogen fertilizer, and regulates pH to stabilize ammonium nitrogen, thereby improving the efficiency of plant nitrogen absorption. Quantitative comparison of crop heights further proves that the application of percarbamide can significantly promote crop growth and provide an effective solution for agricultural development.

[0081] A device for in-situ extraction of urea from urine to synthesize percarbamide, used to implement the above-mentioned electrochemical in-situ extraction method of urea from urine to synthesize percarbamide, such as Figure 2 As shown, including: The collection and purification unit 1 collects urine from residential areas and office buildings, or animal urine and wastewater from livestock farms, or urine discharged from toilets in schools and public institutions. After being stabilized by the collection and purification unit 1, impurities are removed through concentration and filtration processes to generate high-concentration urine. Clean water and solid by-products are generated during the purification process to reduce interference factors in subsequent reactions. The concentrated urine is transported to the concentration control module 1 set in the collection and purification unit to accurately adjust the urea concentration according to the reaction requirements to ensure the efficiency and selectivity of the electrochemical reaction; the concentration detection unit 2 continuously monitors the urea concentration of the concentrated urine. When the set threshold is reached, the concentrated urine is transported to the electrochemical reaction device unit; the electrochemical reaction device unit is powered on at the catalytic converter under 3 conditions. Under the action of the agent, the concentrated urine is decomposed at the anode and synthesized into percarbonate by inputting air at the cathode; the temperature controller 4 monitors the temperature of the electrochemical reaction device unit in real time, and the oxygen input device 5 inputs air into the electrochemical reaction device unit, and converts urea into precipitated solid percarbonate through in-situ electrochemical reaction; the separation unit 6 separates and collects the percarbonate, and transports the separated unreacted urine to the collection and purification unit for recycling. The precipitated solid percarbonate is separated and collected by the separation unit 6 to ensure the separation efficiency of high-purity percarbonate, and the residual urine containing low-concentration urea continues to enter the collection and purification unit, and is further concentrated and filtered until the urine is completely converted into percarbonate, pure water and solid by-products. The solid by-products can be pure water, potassium nitrate, etc. Potassium nitrate can be used as a fertilizer on the farm, and pure water is used for livestock drinking and crop irrigation. The generated percarbonate can be used as a high-value agricultural fertilizer, and the pure water can be used for irrigation or reuse, achieving a balance between environmental protection and economic benefits. Through the recycling of the device, nitrogen pollution is effectively reduced and the demand for external water resources is reduced. At the same time, the thermostat 6 can operate in conjunction with solar and wind energy, reducing operating costs.

[0082] Fig. 9 The present invention is a flow chart for detecting the residual urea recovery of the unreacted urine after separation by the separation unit, as shown in FIG. Fig. 9As shown in the figure, the process includes the following steps: a. urea reacts with concentrated nitric acid to form urine nitrate precipitate; b. evaporating water to obtain a solid mixture of urea and potassium nitrate; c. dissolving urea in hot alcohol and filtering to obtain solid potassium nitrate; d. alcohol solution formed after urea is dissolved; e. evaporating alcohol, cooling and crystallizing urea; f. filtering to obtain solid urea. The process describes the specific steps for recovering residual urea. First, urea reacts with concentrated nitric acid to form urine nitrate precipitate, and then a mixture of urea and potassium nitrate is obtained by evaporating water. Next, urea is dissolved in hot alcohol and potassium nitrate is filtered out. The dissolved alcohol solution is evaporated and cooled to cause urea crystals to precipitate, and finally high-purity solid urea is obtained by filtration. This process shows how to achieve efficient recovery and purification of residual urea through precise chemical treatment and separation steps, thereby improving product purity and recovery efficiency.

[0083] Fig.10 This is a diagram of the detection of urea in unreacted urine after separation by the separation unit of the present invention. Fig.10 a is the XRD analysis diagram, b is the schematic diagram of the steps of separating urea from waste liquid, and c is the purity cycle step diagram. Fig.10 As shown, in Fig.10 It can be observed from the XRD analysis of (a) that both the recovered urea and the filtered KNO3 contain impurities mixed with each other. Fig.10 (b) shows a schematic diagram of the steps for separating urea from waste liquid. Fig.10 (c) shows a series of cyclic steps starting from the initial recovery of urea to obtain higher purity. XRD analysis shows that the purity of urea after recrystallization is significantly improved. This process shows the process of urea recovery and purification through XRD analysis and cyclic treatment. Both the initially recovered urea and the by-product KNO3 contain impurities mixed with each other. Through a series of rigorous separation and cyclic recrystallization steps, the purity of the final urea is significantly improved and verified in XRD analysis. This process shows how to achieve higher quality urea extraction by optimizing the recovery and purification steps, improving the efficiency of the device and the value of the product.

[0084] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0085] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for electrochemical in-situ extraction of urea from urine to synthesize percarbamide, characterized in that: The following steps are involved: Using a carbon-based catalyst as the working electrode, a metal active material as the anode, and concentrated urine as the electrolyte solution, oxygen is continuously introduced into the electrolyte solution, and electrochemical in situ extraction synthesis is carried out under a constant voltage. During the electrochemical in situ extraction synthesis process, urea molecules combine with the oxidative intermediates adsorbed on the surface of the carbon-based catalyst, and percarbamide is generated through protonation, thereby converting the urea in the urine into percarbamide.

2. The method for electrochemical in-situ extraction of urea from urine to synthesize percarbonate according to claim 1, characterized in that: The method for preparing an electrolyte solution comprises the following steps: Citric acid is added to the urine to adjust the pH to 3.5-4.5, and then the urine is concentrated to form concentrated urine, wherein the mass concentration of urea in the concentrated urine is 15 wt.%-50 wt.%.

3. The method for electrochemical in-situ extraction of urea from urine to synthesize percarbonate according to claim 1, characterized in that: The carbon-based catalyst is a modified graphite carbon catalyst or a graphite carbon catalyst.

4. The method for electrochemical in-situ extraction of urea from urine to synthesize percarbonate according to claim 3, characterized in that: The preparation method of the modified graphite carbon catalyst comprises the following steps: Inputting methane and oxygen into the preheating zone of the burner for mixing to form a premixed gas; The premixed gas is transported to the reaction zone of the burner, and after combustion, sp³ hybrid defect sites are introduced into the graphite carbon layer by methane combustion to obtain a modified graphite carbon catalyst; During the formation of the premixed gas and the combustion process, the H / O ratio of methane and oxygen in the premixed gas and the combustion temperature are controlled by adjusting the equivalent ratio Φ, and the equivalent ratio Φ is 0.6 to 1.

4.

5. The method for electrochemical in-situ extraction of urea from urine to synthesize percarbonate according to claim 1, characterized in that: The potential of the constant voltage is 0.2V to 0.5V.

6. The method for electrochemical in-situ extraction of urea from urine to synthesize percarbamide according to claim 1, characterized in that: The temperature of the electrochemical in-situ extraction synthesis is 1°C to 30°C.

7. The method for electrochemical in-situ extraction of urea from urine to synthesize percarbonate according to claim 1, characterized in that: The flow rate of oxygen is ≥100 SCCM.

8. The method for electrochemical in-situ extraction of urea from urine to synthesize percarbonate according to claim 1, characterized in that: The electrochemical in-situ extraction synthesis adopts a three-electrode system, the reference electrode is Ag / AgCl, the metal active material is a platinum sheet, and after the electrochemical in-situ extraction synthesis, the solid percarbamide is obtained after filtering and drying.

9. A device for in-situ extraction of urea from urine to synthesize percarbamide, characterized in that: The method for implementing the electrochemical in-situ extraction of urea from urine to synthesize percarbamide according to any one of claims 1 to 8 comprises: A collection and purification unit (1) is used for collecting, concentrating and purifying to obtain concentrated urine; A concentration detection unit (2) for monitoring the concentration of concentrated urine; The electrochemical reaction device unit (3) is used to synthesize percarbonate amide by inputting air into the concentrated urine cathode at the anode under the action of a catalyst under the condition of power supply; the electrochemical reaction device unit is provided with a temperature controller (4) and an oxygen input device (5); The separation unit (6) is used to separate and collect the percarbonate, and to transport the separated unreacted urine to the collection and purification unit (1) for recycling.

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