System for producing urea by co-reduction of carbon dioxide and nitrate through photoelectrocatalysis

Abstract

The invention relates to a photoelectrochemical system for synthesizing urea through co-reduction of carbon dioxide (CO2) and nitrate ions (NO3 <->). The system comprises a solar power supply system, a photoelectrocatalysis (PEC) reaction system, a raw material pretreatment system and a product recovery system. The PEC reaction system is communicated with the raw material pretreatment system and the product recovery system in series; and an integrated coupling reaction system is formed. According to the system, solar energy is used as a main energy source, and a co-reduction reaction of CO2 and NO3 <-> is realized through a novel PEC flow cell device, so that urea is directly synthesized. The reaction liquid is conveyed to a product recovery system through a pipeline, and a high-purity urea product is obtained through evaporative crystallization; unreacted CO2 and NO3 <-> can be circulated to the raw material pretreatment system through the reflux device and are further utilized. The method provided by the invention realizes efficient and green synthesis of urea, optimizes the whole process, reduces energy consumption and system complexity, has good economical efficiency and environmental friendliness, and is suitable for the fields of agricultural fertilizers, waste gas and wastewater resourceful treatment and the like.

Description

Technical Field

[0001] The present invention relates to the field of photoelectrochemistry, and in particular to a method for reacting carbon dioxide (CO2) with nitrate (NO3 - )Photoelectrocatalytic system for co-reduction synthesis of urea. Background Art

[0002] Photoelectrocatalysis (PEC) technology is an emerging green sustainable technology that can use solar energy to drive chemical reactions and convert CO2 and NO3 into - Reducing it to high-value-added chemicals avoids dependence on traditional fossil fuels and fundamentally reduces the consumption of fossil energy and related greenhouse gas emissions in the production process.

[0003] Compared to traditional industrial urea synthesis processes (such as the Bosch-Meiser process, which operates at reaction conditions of 150-250 bar and 150-200°C), this method eliminates the need for high-temperature and high-pressure operations, resulting in higher energy efficiency and lower carbon emissions. Urea is currently a major global nitrogen-containing chemical product, with an annual production exceeding 60 million tons, and is widely used in agriculture, chemical industry, and other fields. However, traditional urea production methods are not only energy-intensive but also rely on the synthesis of ammonia, which accounts for approximately 80% of global ammonia production, resulting in significant energy consumption and carbon emissions.

[0004] There is no complete PEC system for the co-reduction of CO2 and NO3- to synthesize urea in the existing technology. Therefore, the development of an efficient, stable, and green photoelectrochemical reaction system for the co-reduction of CO2 and NO3- to directly synthesize urea has important practical significance and broad application prospects. Summary of the Invention

[0005] In order to solve the problems of high energy consumption, complex process and waste of resources in the existing technology, the present invention provides a solar-driven photoelectrocatalytic CO2 and NO3 - A reaction system for co-reduction production of urea.

[0006] In the first aspect, the embodiment of the present application provides a method for CO2 and NO3 - A photoelectrochemical system for co-reduction and urea production comprises: a solar power supply system, a PEC reaction system, a raw material pretreatment system, and a product recovery system, wherein the PEC reaction system is coupled in series with the raw material pretreatment system and the product recovery system; the solar power supply system provides energy for the system;

[0007] The raw material pretreatment system is connected to the PEC reaction system via a pipeline, and is used to transport the treated raw materials to the PEC reaction system; the PEC reaction system is used to efficiently output a solution containing the target product and is connected to the product recovery system via a pipeline; the product recovery system evaporates and crystallizes the solution containing the target product to obtain a high-purity urea product.

[0008] In conjunction with the first aspect of the present application, in an optional embodiment, a PEC reaction system includes: an illumination unit, a voltage application unit, and ten or more catalytic reaction units; the illumination unit provides visible light for the reaction, causing the catalyst to generate photogenerated carriers to drive the reaction and reduce reaction energy consumption; the voltage application unit provides a low bias voltage for the reaction, promoting the transfer of photogenerated electrons and holes to drive the reaction; the catalytic reaction unit performs a catalytic reaction to generate a target product;

[0009] The catalytic reaction unit is a flow-type PEC reaction electrolytic cell, comprising a reference electrode, a counter electrode, a working electrode, an anode reactor assembly, a cathode reactor assembly and a flow channel separator assembly;

[0010] The working electrode is a Pt sheet; the reference electrode is an Ag / AgCl electrode; the working electrode is a catalyst electrode for urea synthesis;

[0011] The reference electrode is fixed in the reserved hole of the anode reactor assembly; the counter electrode is fixed at the center position of the side of the anode reactor assembly; the working electrode is fixed at the center position of the side of the cathode reactor assembly; four or more rubber pads or latex pads must be provided between the cathode reactor assembly, the anode reactor assembly and the flow channel partition assembly to maintain the sealing of the flow-type PEC reaction electrolytic cell; the anode reactor assembly, the cathode reactor assembly and the flow channel partition assembly are fixed by bolts and nuts;

[0012] The cathode chamber and anode chamber of the flow-type PEC reaction electrolytic cell exist independently; the cathode chamber and the anode chamber are separated by an anion exchange membrane; in addition, the cathode chamber is equipped with a CO2 input channel and an output channel; the cathode chamber is also equipped with an electrolyte input channel and an output channel; in addition, the anode chamber is equipped with an electrolyte input channel;

[0013] The cathode reactor assembly is equipped with a light-transmitting quartz window, an inorganic glass window or a transparent plastic (acrylic, polystyrene, polycarbonate, acrylonitrile-butadiene-styrene copolymer, transparent nylon) window to ensure continuous illumination of the working electrode.

[0014] In conjunction with the first aspect of the present application, in an optional embodiment, the raw material pretreatment system includes: an exhaust gas pretreatment unit, a wastewater pretreatment unit, a gas storage tank and a liquid storage tank; the CO2 and NO3 obtained by the exhaust gas pretreatment unit and the wastewater pretreatment unit - The solutions are transported to the gas storage tank and the liquid storage tank respectively;

[0015] The exhaust gas pretreatment unit is connected to the first air pump through a gas pipeline. The first air pump transports the industrial flue gas to the exhaust gas treatment unit for desulfurization, denitrification and dehydration to further increase the CO2 concentration. The exhaust gas pretreatment unit transports the treated CO2 gas to the gas storage tank through the first gas pipeline. A first gas valve is provided on the first gas pipeline.

[0016] The gas tank is equipped with a pressure detection device to monitor the pressure changes of CO2 in the tank in real time. In addition, the gas tank is connected to the PEC reaction system via a second gas pipeline. The second gas pipeline is provided with a first gas pump and a first gas flow controller. The gas pump provides sufficient CO2 to the PEC reaction system. The first gas flow controller can adjust the CO2 feed rate.

[0017] The wastewater pretreatment unit is connected to the first water pump through a liquid pipeline; the first water pump transports the industrial wastewater to the wastewater treatment unit for filtration and precipitation to further reduce the impact of impurities on the reaction device; the wastewater pretreatment unit transfers the treated NO3 - The liquid is transported to the liquid storage tank; a first liquid valve is provided on the first liquid pipeline;

[0018] The liquid storage tank is equipped with a temperature detection device and a concentration detection device to monitor the temperature and NO3 in the tank in real time. - concentration changes; in addition, the liquid storage tank is connected to the PEC reaction system via a second gas-liquid pipeline; the second liquid pipeline is provided with a second water pump and a first liquid flow controller; the second water pump provides sufficient NO3 inside the PEC reaction system - The first liquid flow controller can adjust NO3 - Feed rate;

[0019] In conjunction with the first aspect of the present application, in an optional embodiment, the product recovery system includes: a urea separation unit, a CO2 recovery unit and a waste liquid circulation unit;

[0020] The urea separation unit obtains urea products by evaporation and crystallization; the CO2 recovery unit and the waste liquid circulation unit recover unreacted CO2 and NO3 - It is circulated to the raw material pretreatment system through the return pipeline for reuse.

[0021] In conjunction with the first aspect of the present application, in an optional embodiment, the urea separation unit includes: an evaporator, a crystallizer, a centrifuge, and a dryer; the PEC reaction system transports the reaction liquid to the evaporator through a second liquid pipeline; a second liquid valve is provided on the second liquid pipeline;

[0022] The evaporator evaporates the solvent (water) at high temperature to obtain a concentrated liquid; the evaporator is connected to the crystallizer via a third liquid pipeline; the concentrated liquid is transported to the crystallizer via the third liquid pipeline; a third liquid valve is provided on the third liquid pipeline;

[0023] The crystallizer obtains mother liquor after crystallization at a fixed temperature. The mother liquor passes through the centrifugal separator to separate urea crystals (wet) from the mother liquor; the centrifugal separator is connected to the dryer through a conveyor belt; the dryer further dries the urea crystals (wet) to obtain urea powder for canning and storage.

[0024] In combination with the first aspect of the present application, in an optional embodiment, the CO2 recovery unit includes: a compression device and a drying device; the unreacted CO2 gas is circulated to the gas storage tank through a third gas pipeline; the compression device and the drying device are both on the third gas pipeline; in addition, a third gas valve is provided on the third gas pipeline.

[0025] In conjunction with the first aspect of the present application, in an optional embodiment, the waste liquid circulation unit includes: a waste liquid tank; the waste liquid tank and the centrifuge are connected through a fifth liquid pipeline to transfer the waste liquid containing NO3 - The waste liquid is transported to the waste liquid tank; the waste liquid tank is connected to the wastewater pretreatment unit through a sixth liquid pipeline, and the NO3-containing - The waste liquid is circulated to the wastewater pretreatment unit; the fifth liquid pipeline and the sixth liquid pipeline are respectively provided with a fifth liquid valve and a sixth liquid valve.

[0026] In combination with the first aspect of the present application, in an optional embodiment, the solar power function system includes: a solar power panel and a distribution box; the solar power panel is composed of multiple small solar panel units connected in parallel or in series; the distribution box is connected to the solar power panel through a high-voltage wire to distribute and protect the power supply line; the distribution box transmits electrical energy to electrical appliances through the high-voltage wire.

[0027] CO2 and NO3 provided in the examples of this application - Photoelectrochemical device system for co-reduction of urea, facing CO2 in industrial waste gas and NO3 in wastewater - The ingenious design uses solar panels as a source of electricity to convert CO2 in exhaust gas and NO3 in wastewater into- In the raw material pretreatment system, high-purity CO2 and high-concentration NO3 are obtained respectively - , a co-reduction reaction is carried out in a new PEC flow cell device to directly synthesize urea, and then high-purity urea and NH3 are obtained through the product recovery system, and the unreduced CO2 and NO3 - Recycling to the raw material pretreatment system reduces energy consumption, systematically optimizes the treatment process, reduces the complexity of the system, and greatly reduces costs.

[0028] For the raw material pretreatment system, an automatic control device is added to adjust the concentration of CO2 and NO3 - Accurately adjust the flow rate and other conditions of the gas flow controller and liquid flow controller to increase the concentration of CO2 and NO3 - The reaction efficiency is improved without affecting the normal operation of the PEC reaction system, thus ensuring the stability of the entire system operation.

[0029] The electrolyte containing urea is treated by setting up a product recovery system, collecting the products obtained by the urea separation unit, and the CO2 and NO3 obtained by the CO2 recovery unit and the waste liquid circulation unit - Recycling;

[0030] CO2 and NO3 - The recycling to the raw material pretreatment system realizes the rational allocation of resources, improves energy utilization, greatly reduces the energy consumption of the PEC urea synthesis system, and improves energy efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 PEC CO2 and NO3 for an embodiment - Schematic diagram of the system for co-reduction production of urea;

[0032] Figure 2 Schematic diagram of the cathode-A plate structure of the reaction unit in this embodiment;

[0033] Figure 3 Schematic diagram of the flow channel partition plate-B plate structure of the reaction unit in this embodiment;

[0034] Figure 4 Schematic diagram of the flow channel partition plate-C plate structure of the reaction unit in this embodiment;

[0035] Figure 5 Schematic diagram of the anode-D plate structure of the reaction unit in this embodiment;

[0036] Figure 6 Schematic diagram of the PEC reaction unit flow cell device in this embodiment. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0038] The present application embodiment provides a method for - Photoelectrochemical device system for co-reduction of urea, reference Figure 1 , including: solar power supply system, PEC reaction system, raw material pretreatment system and product recovery system. The PEC reaction system is coupled in series with the raw material pretreatment system and product recovery system, and the solar power supply system provides energy for the system.

[0039] CO2 and NO3 provided in the examples of this application - Photoelectrochemical device system for co-reduction of urea, facing CO2 in industrial waste gas and NO3 in wastewater - The ingenious design uses solar panels as a source of electricity to convert CO2 in exhaust gas and NO3 in wastewater into - In the raw material pretreatment system, high-purity CO2 and high-concentration NO3 are obtained respectively - , a co-reduction reaction is carried out in a new PEC flow cell device to directly synthesize urea, and then high-purity urea and NH3 are obtained through the product recovery system, and the unreduced CO2 and NO3 - Recycling to the raw material pretreatment system reduces energy consumption, systematically optimizes the treatment process, reduces the complexity of the system, and greatly reduces costs.

[0040] In the possible implementation of this application, raw material pretreatment is an essential process in chemical production. - Industrial waste gas and industrial waste water are treated with waste gas pretreatment unit and waste water pretreatment unit for CO2 and NO3 - The raw materials undergo standardized processing. In a possible embodiment of the present application, an air pump ① transports the industrial waste gas to a waste gas treatment device 3 via a first gas pipeline 6. The waste gas treatment device 3 is used to desulfurize, denitrify, and dehydrate the industrial waste gas to produce high-purity CO2 gas. The treated CO2 gas is transported via gas pipeline 6 to a gas storage tank 8. A first gas valve ① is provided on gas pipeline 6.

[0041] In the above embodiment, gas tank 8 was modified to include a pressure detection device for real-time monitoring of the CO2 gas pressure within, thereby adjusting the processing power of exhaust gas pretreatment device 3. When the pressure within gas tank 8 reaches a certain value, the CO2 gas is transported to PEC reaction unit 30 via second gas pipeline 15 and third gas pipeline 10 by air pump ④. A gas flow controller ② is provided on third gas pipeline 10 to adjust the flow rate of CO2 delivered to PEC reaction unit 30. Optionally, gas flow controller ② automatically adjusts the air volume and air speed of the air pump after comparing the treated CO2 concentration with an optimal range.

[0042] In a possible embodiment of the present application, the water pump ② transports the industrial wastewater to the wastewater treatment device 4 through the liquid pipeline 5, which is used to filter and precipitate the industrial wastewater, remove impurities of different sizes, and obtain pure, high-concentration NO3 - Solution to avoid damage to the subsequent reaction system. - The solution is transported to the liquid storage tank 7 through the liquid pipeline 5. The liquid pipeline 5 is provided with a first liquid valve ②.

[0043] In the above embodiment, the liquid storage tank 7 is modified to add a temperature detection device and a concentration detection device, which are used to detect the NO3 - The temperature and concentration of the solution are detected in real time in order to adjust the processing power of the wastewater treatment pre-device 4. When the concentration in the storage tank 7 reaches a certain value, the NO3 - The solution is transported to the PEC reaction unit 30 through the liquid pipeline 9. A liquid flow controller ① is provided on the liquid pipeline 9 to regulate the NO3 transported to the PEC reaction unit 30. - Flow rate of the solution. Optionally, the liquid flow controller ① will process the treated NO3 - After comparing the solution concentration with the optimal value range, the power and water output of the water pump and other conditions are automatically adjusted.

[0044] The PEC reaction unit 30 includes at least 16 flow-type PEC reactors connected in series, a group of illumination units 20, and a voltage application unit 18. In a possible embodiment of the present application, the illumination unit 20 provides visible light to the flow-type PEC reactor, causing the catalyst to generate photogenerated carriers to drive the reaction and reduce the reaction energy consumption; the voltage application unit 18 provides a low bias voltage for the reaction, promoting the transfer of photogenerated electrons and holes to drive the reaction; the flow-type PEC reactor performs a catalytic reaction to produce urea. Photoelectrocatalysis of CO2 and NO3 - The principle of co-reduction to produce urea is that the photocathode material stimulates photogenerated electrons and holes under light, and the photogenerated electrons reduce CO2 to key carbon-containing intermediates and NO3 -Co-reduction to a key nitrogen-containing intermediate; photogenerated holes reduce H2O molecules to protons H + , used for the hydrogenation step of the reaction process; carbon-containing intermediates and nitrogen-containing intermediates undergo a CN coupling process at the active site of the catalyst, and urea molecules are formed after a multi-step proton-coupled electron transfer process.

[0045] refer to Figures 2 to 5 , respectively, are the dimensions of the flow-type PEC reactor including the cathode reaction-A plate, the flow channel separator-B plate, the flow channel separator-C plate and the anode reactor-D plate. The standard unit in the embodiment is centimeters.

[0046] In a possible implementation of the present application, for the cathode reaction-A plate, its size is designed to be a rectangular parallelepiped of 30cm×30cm×7.5cm. In addition, a window for light transmission is designed, with a size of 8cm×8cm, and the light window material is quartz; the size of the cathode reaction chamber is 6cm×6cm×4cm, and the diameter of the reserved cylindrical gas and liquid flow channels is 1cm.

[0047] In a possible embodiment of the present application, the flow channel partition-B plate is designed to be a rectangular parallelepiped of 30cm×30cm×5cm; the size of the reaction chamber is 6cm×6cm×5cm, and the diameter of the reserved cylindrical gas, liquid flow channel and reference electrode channel is 1cm.

[0048] In a possible embodiment of the present application, the flow channel partition-C plate is designed to be a rectangular parallelepiped of 30cm×30cm×5cm; the size of the reaction chamber is 6cm×6cm×5cm, and the diameter of the reserved cylindrical gas, liquid flow channel and reference electrode channel is 1cm.

[0049] In a possible embodiment of the present application, the anode reactor-D plate is designed to be a cuboid of 30 cm×30 cm×7.5 cm in size.

[0050] Four or more rubber pads are provided between the cathode reaction-A plate, the flow channel partition-B plate, the flow channel partition-C plate and the anode reactor-D plate to maintain the sealing of the flow-type PEC reaction electrolytic cell; the cathode reaction-A plate, the flow channel partition-B plate, the flow channel partition-C plate and the anode reactor-D plate are fixed by bolts and nuts.

[0051] In a possible embodiment of this application, the product recovery system is a key component of this embodiment. In this possible embodiment, the evaporator 23 is connected to the PEC reaction unit 30 via a third liquid line 19. It evaporates the solvent in the reaction liquid under high temperature conditions to produce a high-concentration urea concentrate. A second liquid valve ④ is provided on the third liquid line 19.

[0052] In a possible embodiment of the present application, the crystallizer 25 is connected to the evaporator 23 via the fourth liquid pipeline 24. Under low temperature conditions, the solution is crystallized by utilizing a temperature difference to obtain a mother liquor containing urea crystals. A third liquid valve ⑤ is provided on the fourth liquid pipeline 24.

[0053] In a possible embodiment of the present application, the centrifuges 1 to 6 are connected to the crystallizer 25 via the fifth liquid pipeline 17 to separate urea from the mother liquor under different rotation speed conditions to obtain a urea solid product.

[0054] In the above embodiment, the design is focused on centrifugal separators, and the centrifugal separators 1 to 6 include at least three high-speed centrifuges and three low-speed centrifuges.

[0055] In a possible embodiment of the present application, the centrifugal separator is connected to the dryer 27 via a first conveyor belt 26 to remove moisture from the urea crystals at high temperature to obtain a urea powder product.

[0056] In the above embodiment, a powder filling device is provided for the storage of urea powder.

[0057] In a possible embodiment of the present application, the centrifuge is connected to the recovery tank 29 via the sixth liquid pipeline 21 for storing NH3 separated from the centrifuge. In addition, the centrifuge is connected to the waste liquid tank 28 via the seventh liquid pipeline 22 for storing NO3 separated from the centrifuge. - The sixth liquid pipeline 21 and the seventh liquid pipeline 22 are respectively provided with a fourth liquid valve ⑧ and a fifth liquid valve ⑦.

[0058] In the above embodiment, the waste liquid tank 28 is connected to the waste water treatment device 4 via the eighth liquid pipeline 16. The water pump ⑤ transports the waste liquid in the waste liquid tank 28 to the waste water treatment device 4. The eighth liquid pipeline 16 is provided with a sixth liquid valve ⑥.

[0059] In a possible implementation manner of the present application, the compression device 31 is connected to the PEC reaction unit 30 via the fourth gas pipeline 11 to compress and recover the CO2 produced for the reaction.

[0060] In the above embodiment, the compression device 31 is connected to the dryer 13 via the fifth gas line 12 to remove water molecules carried by unreacted CO2 gas. The dryer 13 is connected to the second gas line 15 to circulate the CO2 to the gas storage tank 8, thereby improving CO2 utilization and reducing costs. A second gas valve ③ is provided on the fifth gas line 12.

[0061] In a possible implementation of the present application, the solar power supply system includes at least two solar panels and two distribution boxes: solar panel ①, solar panel ②, distribution box ① and distribution box ②, which provide electrical energy for each electrical device in the system without the need for additional energy input.

[0062] CO2 and NO3 in the examples of this application - The working process of the photoelectrochemical device system for co-reduction of urea is as follows:

[0063] When pump ① is working, it will transport the industrial waste gas to the waste gas pretreatment device 3, the first gas valve ① is in the open state, and the treated gas is transferred to the gas storage tank 8 through the first gas pipeline 6; when pump ② is working, it will transport the industrial waste water to the waste water pretreatment device 4, the first liquid valve ② is in the open state, and the treated liquid is transferred to the liquid storage tank 7 through the first liquid pipeline 5; when pump ④ is working, it will transport CO2 gas to the flow controller ②, set the relevant parameters of the flow controller ②, and further transport the CO2 gas to the PEC reaction unit; when pump ③ is working, it will transport NO3 - The solution is transported to the flow controller ①, and the relevant parameters of the flow controller ① are set to further transfer NO3 - The solution is transported to the PEC reaction unit.

[0064] Raw material pretreatment system converts CO2 and NO3 - After the solution is transported to the PEC reaction unit 20 , the illumination unit 20 and the voltage application unit 18 are turned on and their parameters are adjusted to ensure that the PEC reaction is under optimal conditions.

[0065] Optionally, the photocathode catalyst includes but is not limited to Cu2O, ZnO, TiO2, etc.

[0066] The second liquid valve ④ and the third liquid valve ⑤ are in the open state, and the reaction liquid is transported to the evaporator 23 via the third liquid pipeline 19. In operation, the evaporator 23 removes the solvent from the reaction liquid, producing a concentrated liquid by controlling the evaporation time and temperature. The concentrated liquid is transported to the crystallizer 25 via the third liquid pipeline 24, where a mother liquor containing urea crystals is produced by controlling the crystallization time and temperature. The mother liquor is transported to the centrifuge via the fifth liquid pipeline 17, which separates the urea crystals from the mother liquor during operation. The urea crystals are connected to the dryer 27 via the first conveyor belt 26, which completely removes moisture from the urea crystals during operation, producing urea powder. The urea powder is then canned and stored.

[0067] When the fourth liquid valve ⑧ is in the open stage, the mother liquor is transported to the centrifuge through the fifth liquid pipeline 17. When the centrifuge is working, NH3 is separated from the mother liquor and transported to the recovery tank 29 through the sixth liquid pipeline 21.

[0068] Water pump ⑤, sixth liquid valve ⑥, and fifth liquid valve ⑧ are in the open state. Waste liquid separated by the centrifuge is transported to waste liquid tank 28 via seventh liquid pipeline 22. Wastewater in waste liquid tank 28 is transported by water pump ⑤ through eighth liquid pipeline 16 to wastewater pretreatment device 4 for recycling.

[0069] The second gas valve ③, dryer 13, and compression device 31 are in the open stage. The untreated CO2 in the PEC reaction unit is transported to the compression device 31 through the fourth gas pipeline 11. The compression device 31 compresses the gas to a fixed pressure in the working state and transports it to the dryer 13 through the fifth gas pipeline 12. When the dryer 13 is working, it removes the water molecules carried by the compressed gas.

[0070] In an embodiment of the present application, the compression device 31 is connected to the PEC reaction unit 30 via a fourth gas pipeline 11 to compress and recover unreacted CO 2 .

[0071] In the above embodiment, the compression device 31 is connected to the dryer 13 through the fifth gas pipeline 12 to remove water molecules carried by the unreacted CO2 gas; the dried compressed gas is transported to the gas storage tank 8 through the second gas pipeline 15 for recycling.

[0072] In addition, solar panels ①, solar panels ②, distribution box ① and distribution box ② are in working condition, absorbing solar energy, converting it into electrical energy, storing it and transmitting it to various electrical appliances.

[0073] The embodiment of the present application is used to recover CO2 and NO3 from industrial flue gas and industrial wastewater - , and co-reduction to produce urea under the conditions of photoelectrocatalytic technology, achieving the environmental goal of reducing pollution and carbon emissions and improving resource utilization. This application designs a new type of flow-type PEC reactor, which is transported by the raw material pretreatment system to CO2 and NO3 - , providing carbon and nitrogen source support, and the solar power supply system delivers energy and provides power support, without the need for additional energy input, the system is streamlined, the cost is low, and it can replace industrial urea synthesis technology to achieve a systematic, green, and efficient urea synthesis process. The embodiment of the present application solves the problems of the existing technology of over-reliance on liquid ammonia as a raw material for urea synthesis and high energy consumption, by recycling CO2 and NO3 in industrial waste gas and industrial wastewater. - , improve resource utilization, reduce system energy consumption and increase economic value.

Claims

1. A method for photoelectrocatalytic conversion of carbon dioxide (CO2) and nitrate ions (NO3 - ) A system for co-reduction synthesis of urea, characterized in that include: A solar power supply system, a photoelectrocatalytic (PEC) reaction system, a raw material pretreatment system, and a product recovery system; the PEC reaction system is coupled in series with the raw material pretreatment system and the product recovery system; the solar power supply system provides energy input for the entire system; The raw material pretreatment system is connected to the PEC reaction system via a pipeline for transporting the pretreated raw materials to the PEC reaction system; the PEC reaction system is used to achieve a synergistic reduction reaction of CO2 and NO3- to generate a reaction liquid containing urea, which is transported to the product recovery system via a pipeline; the product recovery system is used to evaporate and crystallize the post-reaction solution to obtain a high-purity urea product.

2. The system according to claim 1, wherein: The PEC reaction system includes: an illumination unit, a voltage application unit and ten or more catalytic reaction units; the illumination unit provides light for the reaction, excites the catalyst to generate photogenerated carriers to drive the reaction; the voltage application unit is used to provide a low bias voltage to promote the separation and transfer of photogenerated electrons and holes in the catalyst to drive the reaction; the catalytic reaction unit is used to realize the co-reduction catalytic reaction of CO2 and NO3- to generate urea product.

3. The system according to claim 2, wherein: The catalytic reaction unit is a flow-type PEC reaction electrolytic cell, which includes a reference electrode, a counter electrode, a working electrode, an anode reactor component, a cathode reactor component and a flow channel separator component.

4. The system according to claim 1, wherein: The raw material pretreatment system includes: a waste gas pretreatment unit, a wastewater pretreatment unit, a gas storage tank and a liquid storage tank; the waste gas pretreatment unit is used to treat waste gas from a CO2 source, and the resulting CO2 gas is stored in the gas storage tank; the wastewater pretreatment unit is used to treat wastewater containing NO3-, and the resulting liquid is stored in the liquid storage tank.

5. The system according to claim 4, wherein: The waste gas pretreatment unit is connected to the first air pump through a gas pipeline. The first air pump transports the industrial flue gas to the waste gas pretreatment unit. The waste pretreatment unit desulfurizes, denitrifies and dehydrates the flue gas in sequence to enrich CO2; the treated CO2 gas is transported to the gas storage tank through the first gas management; a first gas valve is provided on the first gas pipeline.

6. The system according to claim 4, wherein: The wastewater pretreatment unit is connected to the first water pump; the first water pump transports the industrial wastewater to the wastewater pretreatment unit through a liquid pipeline, and the wastewater pretreatment unit filters and precipitates the wastewater to remove impurities; the treated wastewater contains NO3 - The liquid is transported to the liquid storage tank through a first liquid pipeline; a first liquid valve is provided on the first liquid pipeline.

7. The system according to claim 1, wherein: The product recovery system includes: a urea separation unit, a CO2 recovery unit and a waste liquid circulation unit; The urea separation unit is used to recover urea products by evaporation and crystallization; the CO2 recovery unit and the waste liquid circulation unit recover unreacted CO2 and NO3 - It is circulated to the raw material pretreatment system through the return pipeline for reuse.

8. The system according to claim 7, wherein: The urea separation unit includes: an evaporator, a crystallizer, a centrifugal separator and a dryer; the PEC reaction system transports the reaction liquid to the evaporator through a second liquid pipeline; and a second liquid valve is provided on the second liquid pipeline.

9. The system according to claim 7, wherein: The waste liquid circulation unit includes a waste liquid tank; the waste liquid tank is connected to the centrifuge through a fifth liquid pipeline, and the waste liquid tank is connected to the centrifuge through a fifth liquid pipeline. - The waste liquid is transported to the waste liquid tank; the waste liquid tank is connected to the wastewater pretreatment unit through a sixth liquid pipeline, and the liquid pump contains NO3 - The waste liquid is recycled for raw material pretreatment; the fifth liquid pipeline and the sixth liquid pipeline are respectively provided with a fifth liquid valve and a sixth liquid valve.

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