System and method for producing synthesis gas by electrolytic urea-carbon dioxide reduction

Abstract

The present invention discloses a system and method for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction, wherein the system includes a urea electrolysis unit, a carbon dioxide electrolyzer, a carbon dioxide storage tank and a separator; the urea electrolysis unit includes a urea electrolyzer, and the urea electrolyzer includes a first anode chamber and a first cathode chamber; the inlet of the first anode chamber is connected to the outlet of the anolyte storage tank, and the outlet of the first anode chamber is connected to the inlet of the anode gas-liquid separator and the inlet of the anolyte storage tank in sequence; the inlet of the first cathode chamber is connected to the outlet of the cathode electrolyte storage tank, and the outlet of the first cathode chamber is connected to the inlet of the cathode gas-liquid separator and the inlet of the cathode electrolyte storage tank in sequence. The system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction of the present invention can improve the efficiency of electrolytic hydrogen production reaction, reduce the overall cost of the process, and achieve zero-carbon hydrogen production; at the same time, it can effectively avoid the risk of hydrogen-oxygen mixed explosion.

Description

Technical Field

[0001] The invention belongs to the technical field of electrolytic hydrogen production and carbon dioxide utilization, and in particular relates to a system and method for preparing synthesis gas by electrolytic urea-carbon dioxide reduction. Background Art

[0002] At present, hydrogen production by water electrolysis is the only technical approach that can achieve industrial green hydrogen production, which is of great significance to the realization of the dual carbon goals. In order to improve the cost competitiveness of green hydrogen produced by water electrolysis, it is necessary to further reduce the power consumption of water electrolysis. As an electrolyte additive, urea can reduce the theoretical energy consumption of hydrogen production by electrolysis in principle (only 1 / 5 of direct water electrolysis), and urea can be obtained from industrial waste or human and animal urine. While obtaining hydrogen, it has the additional effect of wastewater purification, which is a good way to reduce the cost of hydrogen production. However, the electrolytic hydrogen production system with urea as the electrolyte will also produce carbon dioxide, which is easily converted into carbonate in an alkaline environment, leading to problems such as diaphragm blockage, increased alkali consumption, and decreased hydrogen quality. In addition, the existing technology produces hydrogen and oxygen in a co-electrolyzer, and the mixture of hydrogen and oxygen is prone to explosion.

[0003] Therefore, it is necessary to solve the problem of carbon dioxide produced in the process of urea electrolysis to produce hydrogen, avoid direct emission of carbon dioxide and pollution of hydrogen, as well as consumption of alkaline ions by carbon dioxide and blockage by carbonates. At the same time, it is also necessary to solve the problem of explosiveness of hydrogen and oxygen mixture. Summary of the invention

[0004] In view of this, an object of the present invention is to provide a system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction. Since a urea electrolyzer and a carbon dioxide electrolyzer are provided, hydrogen can be produced by urea electrolysis in the urea electrolyzer, and at the same time, carbon dioxide produced by urea oxidation is introduced into the carbon dioxide electrolyzer, and the carbon dioxide is continuously converted into carbon monoxide and oxygen by the carbon dioxide electrolyzer, so that the carbon dioxide produced by urea electrolysis is timely separated from the urea electrolysis anode chamber system during the reaction, thereby avoiding the consumption of hydroxyl ions in the alkaline system by carbon dioxide, reducing the fouling of the electrolysis diaphragm, improving the efficiency of the electrolysis hydrogen production reaction, reducing the overall cost of the process, and realizing zero-carbon hydrogen production; at the same time, the energy consumption of hydrogen produced by urea electrolysis is lower than that of water electrolysis, and since oxygen production and hydrogen production are separated in two different electrolyzers, the risk of hydrogen and oxygen mixed explosion can be effectively avoided.

[0005] The second object of the present invention is to provide a method for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction.

[0006] To achieve the above-mentioned object, the first embodiment of the present invention provides a system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction, comprising a urea electrolysis unit, a carbon dioxide electrolysis cell, a carbon dioxide storage tank and a separator;

[0007] The urea electrolysis unit comprises a urea electrolysis cell, and the urea electrolysis cell comprises a first anode chamber and a first cathode chamber; the inlet of the first anode chamber is connected to the outlet of the anode electrolyte storage tank, and the outlet of the first anode chamber is connected to the inlet of the anode gas-liquid separator and the inlet of the anode electrolyte storage tank in sequence; the inlet of the first cathode chamber is connected to the outlet of the cathode electrolyte storage tank, and the outlet of the first cathode chamber is connected to the inlet of the cathode gas-liquid separator and the inlet of the cathode electrolyte storage tank in sequence;

[0008] The carbon dioxide electrolysis cell is a solid oxide electrolysis cell; the inlet of the carbon dioxide electrolysis cell is connected to the outlet of the carbon dioxide storage tank;

[0009] The inlet of the carbon dioxide storage tank is connected to the carbon dioxide outlet of the separator and the external carbon dioxide;

[0010] The inlet of the separator is connected to the gas outlet of the anode gas-liquid separator; the nitrogen outlet of the separator is connected to a nitrogen storage tank or a nitrogen pipeline.

[0011] The system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction in the embodiment of the present invention is provided with a urea electrolyzer and a carbon dioxide electrolyzer, so that hydrogen can be produced by urea electrolysis in the urea electrolyzer, and carbon dioxide produced by urea oxidation is introduced into the carbon dioxide electrolyzer, and the carbon dioxide is continuously converted into carbon monoxide and oxygen by the carbon dioxide electrolyzer, so that the carbon dioxide produced by urea electrolysis is promptly separated from the urea electrolysis anode chamber system during the reaction, thereby avoiding the consumption of hydroxyl ions in the alkaline system by carbon dioxide, reducing the fouling of the electrolysis diaphragm, improving the efficiency of the electrolysis hydrogen production reaction, reducing the overall cost of the process, and realizing zero-carbon hydrogen production; at the same time, since oxygen production and hydrogen production are separated in two different electrolyzers, the risk of hydrogen and oxygen mixed explosion can be effectively avoided.

[0012] In addition, the system for preparing synthesis gas by electrolysis of urea and reduction of carbon dioxide according to the above embodiment of the present invention may also have the following additional technical features:

[0013] In some embodiments of the present invention, the system for producing synthesis gas by electrolysis of urea-carbon dioxide reduction further includes an alkali solution storage tank and a urea storage tank; the outlet of the alkali solution storage tank is connected to the inlet of the cathode electrolyte storage tank and the inlet of the anode electrolyte storage tank; the outlet of the urea storage tank is connected to the inlet of the anode electrolyte storage tank; the gas outlet of the cathode gas-liquid separator is connected to a hydrogen storage tank or a hydrogen pipeline; the electrolyte in the cathode electrolyte storage tank is an alkaline aqueous solution, and the electrolyte in the anode electrolyte storage tank is an alkaline urea solution.

[0014] In some embodiments of the present invention, the urea electrolyzer also includes a first outer shell; a first anode, a first diaphragm and a first cathode are sequentially arranged in the first outer shell, and a distance is left between the first anode, the first diaphragm and the first cathode; the first anode, the first diaphragm and the inner wall of the first outer shell are sealed to form the first anode chamber, and the first cathode, the diaphragm and the inner wall of the first outer shell are sealed to form the first cathode chamber.

[0015] In some embodiments of the present invention, the first anode and the first cathode are both conductive substrates with an active catalytic layer on the surface; the conductive substrate is a metal plate or a porous plate; the material of the active catalytic layer is one or an alloy of more than two of Pt, Ru, Rh, Ir, Ni, Co, Fe, Zn, and Ti.

[0016] In some embodiments of the present invention, the thickness of the conductive substrate is 100-500 micrometers; the thickness of the active catalytic layer is 5-100 nanometers; and the porous plate is foamed metal or carbon material.

[0017] In some embodiments of the present invention, the first membrane is a porous membrane or a membrane having OH - Conductive anion exchange membrane; the porous membrane is a Zirfon membrane; the anion exchange membrane is a polyarylether membrane, polyethylene membrane, polystyrene membrane, polytetrafluoroethylene membrane or polyphenyl membrane modified with cationic groups; the cationic groups are polyalkylammonium salts, imidazole salts, pyridinium salts or piperidine salts.

[0018] In some embodiments of the present invention, the carbon dioxide electrolyzer includes a second outer shell, in which a second anode, a second diaphragm and a second cathode are arranged in sequence in close contact with each other; the second anode, the second diaphragm and the inner wall of the second outer shell are sealed to form a second anode chamber, and the second cathode, the second diaphragm and the inner wall of the second outer shell are sealed to form a second cathode chamber; the gas inlet of the second cathode chamber is connected to the outlet of the carbon dioxide storage tank.

[0019] In some embodiments of the present invention, the second anode is a perovskite oxide composite electrode; the second diaphragm is a solid oxide ceramic membrane; the second cathode is a yttria-stabilized zirconia material loaded with an active metal layer; the material of the active metal layer is one or an alloy of more than two of Cu, Pb, Hg, Tl, In, Sn, Cd, and Bi.

[0020] In some embodiments of the present invention, the system for producing synthesis gas by electrolysis of urea-carbon dioxide reduction also includes a CO2 / CO separator; the inlet of the CO2 / CO separator is connected to the gas outlet of the second cathode chamber, the CO outlet of the CO2 / CO separator is connected to a CO storage tank or a CO pipeline, and the CO2 outlet of the CO2 / CO separator is connected to the gas inlet of the second cathode chamber; the gas inlet of the second anode chamber is connected to an external water vapor pipeline, and the gas outlet of the second anode chamber is connected to an O2 dryer; the outlet of the O2 dryer is connected to an oxygen storage tank or an oxygen pipeline.

[0021] To achieve the above object, the second embodiment of the present invention provides a method for producing synthesis gas by electrolysis of urea-carbon dioxide reduction, comprising:

[0022] Electrolyzing an alkaline aqueous solution in a first cathode chamber of a urea electrolyzer to generate hydrogen;

[0023] Electrolyzing an alkaline urea solution in a first anode chamber of a urea electrolyzer to convert urea into nitrogen, water and carbon dioxide, and then introducing the carbon dioxide into a carbon dioxide electrolyzer;

[0024] Carbon dioxide is electrolyzed in a carbon dioxide electrolyzer to produce carbon monoxide and oxygen.

[0025] The beneficial effects of the method for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction in the embodiment of the present invention and the system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction in the embodiment of the present invention are basically the same, and will not be repeated here.

[0026] In some embodiments of the present invention, the operating temperatures of the second cathode chamber and the second anode chamber of the carbon dioxide electrolyzer are both 650-1000° C., and the operating pressures are both 0.2-0.6 MPa.

[0027] In some embodiments of the present invention, the carbon dioxide in the carbon dioxide electrolyzer also includes exogenous carbon dioxide.

[0028] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0030] Figure 1 It is a simple structural schematic diagram of a system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction according to one embodiment of the present invention (that is, a simple flow chart of a method for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction according to one embodiment of the present invention).

[0031] Figure 2 It is a simple structural schematic diagram of a system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction according to another embodiment of the present invention (that is, a simple flow chart of a method for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction according to another embodiment of the present invention).

[0032] Figure 3 It is a simple structural schematic diagram of a system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction according to another embodiment of the present invention (that is, a simple flow chart of a method for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction according to another embodiment of the present invention).

[0033] Reference numerals:

[0034] 1-urea electrolyzer; 11-first anode; 12-first diaphragm; 13-first cathode; 14-first shell; 15-anode gas-liquid separator; 16-cathode gas-liquid separator; 17-anode electrolyte storage tank; 18-cathode electrolyte storage tank; 2-carbon dioxide electrolyzer; 21-second anode; 22-second diaphragm; 23-second cathode; 24-second shell; 3-alkali solution storage tank; 4-urea storage tank; 5-carbon dioxide storage tank; 6-separator; 7-CO2 / CO separator; 8-O2 dryer; 9-exogenous carbon dioxide. DETAILED DESCRIPTION

[0035] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0036] Unless otherwise specified, the raw materials and equipment involved in the embodiments of the present invention are all commercially available raw materials and equipment; the methods involved in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0037] The following describes a system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction and a method for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction according to an embodiment of the present invention in conjunction with the accompanying drawings.

[0038] Figure 1 It is a simple structural schematic diagram of a system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction according to one embodiment of the present invention (that is, a simple flow chart of a method for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction according to one embodiment of the present invention).

[0039] like Figure 1As shown, the system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction according to the embodiment of the present invention comprises a urea electrolysis unit, a carbon dioxide electrolysis cell 2, a carbon dioxide storage tank 5 and a separator 6; the urea electrolysis unit comprises a urea electrolysis cell 1, and the urea electrolysis cell 1 comprises a first anode chamber and a first cathode chamber; the inlet of the first anode chamber is connected to the outlet of the anode electrolyte storage tank 17, and the outlet of the first anode chamber is connected to the inlet of the anode gas-liquid separator 15 and the inlet of the anode electrolyte storage tank 17 in sequence; the inlet of the first cathode chamber is connected to the outlet of the cathode electrolyte storage tank 18 The outlet of the first cathode chamber is connected to the inlet of the cathode gas-liquid separator 16 and the inlet of the cathode electrolyte storage tank 18 in sequence; the carbon dioxide electrolyzer 2 is a solid oxide electrolyzer; the inlet of the carbon dioxide electrolyzer 2 is connected to the outlet of the carbon dioxide storage tank 5; the inlet of the carbon dioxide storage tank 5 is connected to the carbon dioxide outlet of the separator 6 and the exogenous carbon dioxide 9; the inlet of the separator 6 is connected to the gas outlet of the anode gas-liquid separator 15; the nitrogen outlet of the separator 6 is connected to a nitrogen storage tank or a nitrogen pipeline for collecting or utilizing the nitrogen generated by urea oxidation.

[0040] It is understandable that the anolyte storage tank 17 and the cathode electrolyte storage tank 18 provide electrolyte for the first anode chamber and the first cathode chamber of the urea electrolyzer 1, respectively. If it is required that the electrolytes in the first cathode chamber and the second anode chamber are in their respective circulation states, a circulation pump can be installed on the connecting pipeline between the first anode chamber and the anolyte storage tank 17, and a circulation pump can be installed on the connecting pipeline between the first cathode chamber and the cathode electrolyte storage tank. For example, a circulation pump is installed on the connecting pipeline between the liquid outlet of the cathode gas-liquid separator 16 and the inlet of the cathode electrolyte storage tank 18, on the connecting pipeline between the outlet of the cathode electrolyte storage tank 18 and the inlet of the first cathode chamber, on the connecting pipeline between the liquid outlet of the anode gas-liquid separator 15 and the inlet of the anolyte storage tank 17, and on the connecting pipeline between the outlet of the anolyte storage tank 17 and the inlet of the first anode chamber. Here, the exogenous carbon dioxide 9 can be understood as a carbon dioxide pipeline or carbon dioxide source from outside the system for producing synthesis gas by electrolysis of urea-carbon dioxide reduction in an embodiment of the present invention, such as carbon capture from thermal power plants, chemical plants, steelmaking and other industries.

[0041] The system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction in the embodiment of the present invention is provided with a urea electrolyzer and a carbon dioxide electrolyzer, so that hydrogen can be produced by urea electrolysis in the urea electrolyzer, and carbon dioxide produced by urea oxidation is introduced into the carbon dioxide electrolyzer, and the carbon dioxide is continuously converted into carbon monoxide and oxygen by the carbon dioxide electrolyzer, so that the carbon dioxide produced by urea electrolysis is promptly separated from the urea electrolysis anode chamber system during the reaction, thereby avoiding the consumption of hydroxyl ions in the alkaline system by carbon dioxide, reducing the fouling of the electrolysis diaphragm, improving the efficiency of the electrolysis hydrogen production reaction, reducing the overall cost of the process, and realizing zero-carbon hydrogen production; at the same time, the energy consumption of hydrogen produced by urea electrolysis is lower than that of water electrolysis, and since oxygen production and hydrogen production are separated in two different electrolyzers, the risk of hydrogen and oxygen mixed explosion can be effectively avoided.

[0042] Optionally, in some embodiments of the present invention, the electrolyte in the cathode electrolyte storage tank 18 is an alkaline aqueous solution, preferably 20-30% by mass of potassium hydroxide, more preferably 25% by mass of potassium hydroxide; the electrolyte in the anode electrolyte storage tank 17 is an alkaline urea solution, preferably a mixed solution of potassium hydroxide, urea and water, the contents of potassium hydroxide and urea in the mixed solution are 20-30wt% and 1-10wt%, preferably, the contents of potassium hydroxide and urea in the mixed solution are 25wt% and 5wt%, respectively. The cathode electrolyte storage tank 18 is regularly replenished with water to maintain a certain alkaline concentration of the electrolyte in the first cathode chamber.

[0043] Optionally, in some embodiments of the present invention, Figure 2 As shown, the system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction also includes an alkali liquid storage tank 3 and a urea storage tank 4 in order to facilitate the preparation of alkaline aqueous solution and alkaline urea solution. Among them, the alkali liquid storage tank is used to store potassium hydroxide, and the urea storage tank is used to store urea; the outlet of the alkali liquid storage tank 3 is connected to the inlet of the cathode electrolyte storage tank 18 and the inlet of the anode electrolyte storage tank 17; the outlet of the urea storage tank 4 is connected to the inlet of the anode electrolyte storage tank 17, and the inlet of the urea storage tank 4 is continuously replenished with urea (industrial urea products or urea-containing wastewater after simple filtration) to maintain a certain urea concentration in the anode electrolyte storage tank 17. It should be noted that the source of urea can come from livestock and human urine in addition to industrial urea products or urea-containing wastewater after simple filtration, so as to realize waste into treasure.

[0044] Optionally, in order to collect hydrogen or utilize the gas outlet of the cathode gas-liquid separator 16 of the urea electrolyzer is connected to a hydrogen storage tank or a hydrogen pipeline (not shown in the figure), which can be used to collect hydrogen or utilize hydrogen.

[0045] Optional, such as Figure 1 and Figure 2As shown, the urea electrolyzer 1 also includes a first shell 14; a first anode 11, a first diaphragm 12 and a first cathode 13 are sequentially arranged in the first shell 14, and a distance is left between the first anode 11, the first diaphragm 12 and the first cathode 13; the first anode 11, the first diaphragm 12 and the first cathode 13 are sealed to form a first anode chamber, and the first cathode 13, the diaphragm 12 and the inner wall of the first shell 14 are sealed to form a first cathode chamber.

[0046] It should be noted that, optionally, in some embodiments of the present invention, the first anode 11 and the first cathode 13 may be in close contact with the inner wall of the first housing 14 adjacent thereto (eg, Figure 1 and Figure 2 In other embodiments of the present invention, a gap may be left between the first anode 11 and the first cathode 13 and the inner wall of the first housing 14 adjacent thereto.

[0047] Optionally, the first anode 11, the first diaphragm 12 and the first cathode 13 can be welded to the inner wall of the first housing 14 or sealed and connected to the inner wall of the housing by means of a sealing ring and bolts, etc., as long as the first cathode chamber and the first anode chamber are both closed chambers. The first cathode chamber undergoes a hydrogen evolution reaction, and the first anode chamber undergoes a urea oxidation reaction. Specifically, a urea oxidation reaction occurs at the first anode of the urea electrolyzer 1:

[0048] CO(NH2)2+6OH - →N2+5H2O+CO2+6e - ;

[0049] At the first cathode of the urea electrolyzer 1, a hydrogen evolution reaction of water occurs:

[0050] 6H2O+6e - →3H2+6OH - .

[0051] It should be noted that the shape of the first shell is not limited, and can be a rectangular parallelepiped, a cube, a cylinder, etc.; the material of the first shell is also not limited, and can be a metal material such as stainless steel, or a corrosion-resistant plastic material such as polytetrafluoroethylene. The first anode 11, the first diaphragm 12 and the first cathode 13 can be arranged in parallel with each other, or they can be arranged at different angles to each other, as long as the first anode 11, the first diaphragm 12 and the first shell can form a first anode chamber, and the first diaphragm 12 and the first cathode and the first shell can form a first cathode chamber. Preferably, in order to facilitate processing and installation, the first shell is a rectangular parallelepiped or a cube, and the first anode 11, the first diaphragm 12 and the first cathode 13 are arranged in parallel, and are all arranged perpendicular to the top and bottom of the first shell.

[0052] Optionally, the first anode 11 and the first cathode 13 are both conductive substrates with active catalytic layers on their surfaces. In some embodiments of the present invention, the conductive substrate can be a metal plate, such as a copper plate, a stainless steel plate, etc.; in other embodiments of the present invention, the conductive substrate can be a porous plate such as a foam metal or a carbon material, wherein the foam metal can be foamed nickel, foamed copper, foamed iron-nickel alloy, foamed nickel-molybdenum alloy, etc., and the carbon material can be graphite, activated carbon, etc. Optionally, the material of the active catalytic layer is an alloy of one or more of Pt, Ru, Rh, Ir, Ni, Co, Fe, Zn, and Ti. Optionally, in some embodiments of the present invention, the thickness of the conductive substrate of the first anode 11 and the first cathode 13 is 100-500 microns, and the thickness of the active catalytic layer is 5-100 nanometers.

[0053] It should be noted that, in some embodiments of the present invention, the preparation method of a conductive substrate having an active catalytic layer loaded on its surface is: the material of the active catalytic layer is formed on the conductive substrate by methods such as electrodeposition and impregnation. The specific formation method and process conditions are conventional techniques in the field and are not the focus of the embodiments of the present invention.

[0054] Optionally, in some embodiments of the present invention, the first diaphragm 12 may be a porous diaphragm, such as a commercial Zirfon membrane (polysulfone loaded with 85 wt % ZrO2 nanoparticles), etc.; in other embodiments of the present invention, the first diaphragm 12 may be a porous diaphragm having OH - Conductive anion exchange membrane. Preferably, the anion exchange membrane can be selected from polyarylether membrane, polyethylene membrane, polystyrene membrane, polytetrafluoroethylene membrane or polyphenyl membrane modified with cationic groups, wherein the cationic groups can be selected from polyalkylammonium salts, imidazole salts, pyridinium salts or piperidinium salts, for example, the polyalkylammonium salts can be selected from trialkyl quaternary ammonium salts, trimethyl quaternary ammonium salts, etc.

[0055] In some embodiments of the present invention, having OH - The preparation method of the conductive anion exchange membrane is: monomer polymerization (direct polymerization of monomers modified with cationic groups and structural groups. For example: quaternary ammonium poly (N-methyl-piperidinyl-co-p-terphenyl) (QAPPT) -

[0056] 1) Under the catalysis of trifluoromethanesulfonic acid and trifluoroacetic acid, p-terphenyl reacts with N-methyl-4-piperidone to form a linear polymer. 2) The piperidine group of the polymer is converted into a quaternary ammonium salt: react with CH3I at 70°C in a NMP / DMSO mixed solvent. 3) With OH -The final formation of QAPPT: treated with KOH solution for a period of time. ) or post-modification (directly modifying the polymer membrane with cationic groups. For example, using polytetrafluoroethylene membrane as the base material, modifying chloromethylstyrene on it through grafting reaction, and then using trimethylamine solution and KOH solution for quaternization and alkalization reaction).

[0057] Optional, such as Figure 1 As shown, the carbon dioxide electrolyzer 2 includes a second outer shell 24, in which a second anode 21, a second diaphragm 22 and a second cathode 23 are arranged in sequence in close contact with each other; the second anode 21, the second diaphragm 22 and the inner wall of the second outer shell 24 are sealed to form a second anode chamber, and the second cathode 23, the second diaphragm 22 and the inner wall of the second outer shell 24 are sealed to form a second cathode chamber; the gas inlet of the second cathode chamber is connected to the outlet of the carbon dioxide storage tank 5.

[0058] It should be noted that, in some embodiments of the present invention, the second anode 21 and the second cathode 23 are both in close contact with the inner wall of the second housing adjacent thereto (e.g. Figure 1 and Figure 2 As shown), in other embodiments of the present invention, the second anode 21 and the second cathode 23 are spaced apart from the inner wall of the second housing adjacent thereto. The shape of the second housing is not limited, but for the convenience of processing, a rectangular parallelepiped or a cube shape is preferred. Optionally, the second anode 21, the second diaphragm 22 and the second cathode 23 can be welded to the inner wall of the second housing or sealed and connected to the inner wall of the second housing by a sealing ring and bolts, etc., as long as the second anode chamber and the second cathode chamber are both closed chambers.

[0059] Optionally, in some embodiments of the present invention, the operating temperature range of the carbon dioxide electrolyzer 2 is 650-1000°C.

[0060] The overall reaction occurring in the carbon dioxide electrolyzer 2 is:

[0061] CO2→CO+1 / 2O2;

[0062] in:

[0063] The second cathode reaction is: CO2+2e - →CO+O 2- ;

[0064] The second anode reaction is: 2- →1 / 2O2+2e - ;

[0065] The produced CO can be used as an intermediate product and applied to industrial synthesis gas, organic production raw materials, etc.

[0066] Optionally, the carbon dioxide electrolyzer 2 is a fully solid-state electrolyzer. The second anode 21 is a perovskite oxide composite electrode, preferably La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O3 electrode; the thickness of the second anode is 10-200 microns, and the porosity is 30-40%. The second diaphragm 22 is a solid oxide ceramic membrane, preferably a yttria-stabilized zirconia material; the thickness of the second diaphragm is 10-200 microns, and the porosity is 50-70%. The second cathode 23 is a yttria-stabilized zirconia material loaded with an active metal layer, and the porosity is 30-40%; preferably, the material of the active metal layer is one or more alloys of Cu, Pb, Hg, Tl, In, Sn, Cd, and Bi; the thickness of the yttria-stabilized zirconia material in the second cathode 23 is 20-200 microns; the thickness of the active metal layer is 1-10 microns.

[0067] It should be noted that, in some embodiments of the present invention, the preparation method of the yttria-stabilized zirconia material loaded with an active metal layer is: the material of the active metal layer is formed on the yttria-stabilized zirconia material by electrodeposition, impregnation, etc. The specific formation method and process conditions are conventional technologies in the field and are not the focus of the embodiments of the present invention.

[0068] Optionally, in some embodiments of the present invention, Figure 3 As shown, in order to separate the carbon dioxide and carbon monoxide produced by the carbon dioxide electrolyzer 2, the system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction also includes a CO2 / CO separator 7; the inlet of the CO2 / CO separator 7 is connected to the gas outlet of the second cathode chamber; the CO outlet of the CO2 / CO separator 7 is connected to the CO storage tank or the CO pipeline for collecting or utilizing carbon monoxide. The CO2 outlet of the CO2 / CO separator 7 is connected to the gas inlet of the second cathode chamber, and the separated carbon dioxide can be reused to achieve zero carbon emissions. The gas inlet of the second anode chamber is connected to the external water vapor pipeline, and the gas outlet of the second anode chamber is connected to the O2 dryer 8 to dry the generated oxygen; the outlet of the O2 dryer 8 is connected to the oxygen storage tank or the oxygen pipeline for collecting or utilizing oxygen. It should be noted that during the entire process of electrolyzing carbon dioxide in the carbon dioxide electrolyzer, the operating temperature of the second cathode chamber is 650-1000°C, the operating pressure is 0.2-0.6MPa, and the CO purity at the gas outlet of the second cathode chamber is above 99%; the operating temperature of the second anode chamber is 650-1000°C, and the operating pressure is 0.2-0.6MPa. The purity of O2 at the gas outlet is above 99%. The gas inlet of the second anode chamber is connected to an external water vapor pipeline, and water vapor is only required to be used to activate oxygen ions for 1-2h at the initial stage of the reaction.

[0069] It should be noted that the inlet and outlet of the first anode chamber in the urea electrolyzer are both arranged on the first shell corresponding to the first anode chamber, such as the top of the first shell; the inlet and outlet of the first cathode chamber in the urea electrolyzer are both arranged on the first shell corresponding to the first anode chamber, such as the top of the first shell. The inlet and outlet of the second cathode chamber in the carbon dioxide electrolyzer are both arranged on the second shell corresponding to the second cathode chamber, such as the inlet of the second cathode chamber is arranged on the left side of the second shell, and the outlet of the second cathode chamber is arranged on the right side of the second shell; the inlet and outlet of the second oxygen chamber in the carbon dioxide electrolyzer are both arranged on the second shell corresponding to the second anode chamber, such as the inlet and outlet of the second anode chamber are arranged on the right side of the second shell, or the inlet of the second anode chamber is arranged on the left side of the second shell, and the outlet of the second anode chamber is arranged on the right side of the second shell. It can be understood that the second anode chamber of the carbon dioxide electrolyzer is the part where the second anode and the second diaphragm are located on the second anode side, and the second cathode chamber is the part where the second cathode and the second diaphragm are located on the second cathode side.

[0070] Optionally, in some embodiments of the present invention, the anode gas-liquid separator 15 and the cathode gas-liquid separator 16 both use gravity separators, the separator 6 and the CO2 / CO separator both use membrane separators, and the O2 dryer uses a molecular sieve absorption tower.

[0071] It should also be noted that in the embodiments of the present invention, unless otherwise specified, two components in a communication relationship are connected by pipelines. In some embodiments of the present invention, valves can be installed on the connecting pipelines of the inlet and outlet of each component in a communication relationship as needed. These are all relatively conventional operations in the field and are not the focus of the present invention.

[0072] Optionally, as a preferred embodiment of the present invention, the working temperature of the urea electrolyzer 1 is room temperature, the working pressure is 0.3MPa, and the urea decomposition efficiency is above 95%. Wherein: the electrolyte alkaline aqueous solution of the first cathode chamber is a 25wt% potassium hydroxide solution, and the electrolyte alkaline urea solution of the first anode chamber is a mixed solution of water, potassium hydroxide and urea, the mass fraction of potassium hydroxide in the mixed solution is 25%, and the mass fraction of urea is 5%. The first cathode 11 is a stainless steel plate with nickel loaded on the surface; the thickness of the stainless steel plate is 500 microns, and the thickness of the nickel loading layer is 10 nanometers. The first diaphragm 12 is a commercial Zirfon membrane (polysulfone loaded with 85wt% ZrO2 nanoparticles). The first anode 3 is a carbon paper with a Ni-Zn alloy loaded on the surface, the thickness of the carbon paper is 200 microns, and the thickness of the Ni-Zn alloy loading layer is 10 nanometers. The carbon dioxide electrolyzer 2 is a solid oxide electrolyzer, and its operating temperature range is 700-850°C, more preferably 800°C. The second diaphragm 22 is made of yttria-stabilized zirconium oxide material, the thickness of the second diaphragm 22 is 30 microns, and the porosity is 60%; the second anode 21 is La0.6 Sr 0.4 Co 0.2 Fe 0.8 O3, the thickness of the second anode 21 is 30 microns and the porosity is 30%; the second cathode is a yttria-stabilized zirconia material loaded with active metal Cu, the thickness of the yttria-stabilized zirconia material is 100 microns, and the thickness of the active metal Cu loading layer is 2 microns. The operating temperature of the second cathode chamber is 700-850°C, more preferably 800°C, the operating pressure is 0.3MPa, and the CO purity of the gas outlet is above 99%. The operating temperature of the second anode chamber is 700-850°C, more preferably 800°C, and the operating pressure is 0.3MPa. The purity of O2 at the gas outlet is above 99%.

[0073] The working principle of the system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction in the embodiment of the present invention (i.e., the method for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction) is as follows:

[0074] Electrolyzing an alkaline aqueous solution in a first cathode chamber of a urea electrolyzer 1 to generate hydrogen;

[0075] Electrolyzing an alkaline urea solution in a first anode chamber of a urea electrolyzer 1 to convert urea into nitrogen, water and carbon dioxide, and then introducing the carbon dioxide into a carbon dioxide electrolyzer;

[0076] Carbon dioxide is electrolyzed in the carbon dioxide electrolyzer 2 to generate carbon monoxide and oxygen.

[0077] More specifically, the working principle of the system for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction in the embodiment of the present invention (i.e., the method for preparing synthesis gas by electrolysis of urea-carbon dioxide reduction) is:

[0078] When in use, the first anode of the urea electrolyzer 1 is connected to the positive electrode of the external power supply, the first cathode is connected to the negative electrode of the external power supply, the second anode of the carbon dioxide electrolyzer 2 is connected to the positive electrode of the external power supply, and the second cathode is connected to the negative electrode of the external power supply. Figure 1-3As shown, the alkali solution in the alkali solution storage tank 3 is introduced into the cathode electrolyte storage tank 18 to prepare an alkaline aqueous solution. The alkaline aqueous solution in the cathode electrolyte storage tank 18 enters the first cathode chamber, and the first cathode chamber electrolyzes water to produce hydrogen. The electrolytic product enters the cathode gas-liquid separator 16 for gas-liquid separation. The separated hydrogen enters the hydrogen storage tank for collection or enters the hydrogen pipeline for utilization, and the liquid enters the cathode electrolyte storage tank 18. Urea is added to the urea storage tank 4, and then the urea in the urea storage tank 4 and the alkali solution in the alkali solution storage tank 3 are introduced into the anode electrolyte storage tank 17 for mixing to obtain an alkaline urea solution. The alkaline urea solution in the anode electrolyte storage tank 17 enters the first anode chamber, and the first anode chamber electrolyzes the alkaline urea solution, and the urea is converted into nitrogen, water and carbon dioxide. The electrolyzed product enters the anode gas-liquid separator 15 for gas-liquid separation, wherein the liquid enters the anode electrolyte storage tank 17, and the mixed gas of carbon dioxide and nitrogen enters the separator 6. After separation by the separator 6, the nitrogen enters the nitrogen storage tank for collection or enters the nitrogen pipeline for use, and the carbon dioxide enters the carbon dioxide storage tank for storage for standby use. The carbon dioxide from the urea electrolyzer in the carbon dioxide storage tank enters the second cathode chamber of the carbon dioxide electrolyzer 2. Under the working conditions of 650-1000°C and 0.2-0.6MPa, the carbon dioxide is converted into carbon monoxide and oxygen ions. After the carbon monoxide and the unreacted carbon dioxide are separated by the CO2 / CO separator 7, the carbon monoxide enters the carbon monoxide storage tank for collection or enters the carbon monoxide pipeline for utilization, and the carbon dioxide enters the second cathode chamber for reuse. At the same time, the oxygen ions enter the second anode chamber through the second diaphragm 22. In the second anode chamber, the oxygen ions are activated by exogenous water vapor and converted into oxygen under the working conditions of 650-1000°C and 0.2-0.6MPa. After being dried, the oxygen enters the oxygen storage tank for collection or enters the oxygen pipeline for utilization.

[0079] It should be noted that, during the entire working process described above, the carbon dioxide entering the carbon dioxide storage tank 5 and used for electrolysis in the carbon dioxide electrolyzer 2 may also include exogenous carbon dioxide 9, such as carbon capture from thermal power plants, chemical plants, steelmaking and other industries. This can produce a comprehensive effect: it increases the carbon dioxide content in the second cathode chamber, thereby improving the reaction efficiency; and it also produces additional carbon emission reduction effects.

[0080] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0081] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0082] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0083] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0084] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0085] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A system for producing synthesis gas by electrolysis of urea and reduction of carbon dioxide, characterized in that: It comprises a urea electrolysis unit, a carbon dioxide electrolysis cell (2), a carbon dioxide storage tank (5) and a separator (6); The urea electrolysis unit comprises a urea electrolysis cell (1), wherein the urea electrolysis cell (1) comprises a first anode chamber and a first cathode chamber; the inlet of the first anode chamber is connected to the outlet of the anolyte storage tank (17), and the outlet of the first anode chamber is connected to the inlet of the anolyte gas-liquid separator (15) and the inlet of the anolyte storage tank (17) in sequence; the inlet of the first cathode chamber is connected to the outlet of the catholyte storage tank (18), and the outlet of the first cathode chamber is connected to the inlet of the catholyte storage tank (18) in sequence; the electrolyte in the catholyte storage tank (18) is an alkaline aqueous solution, and the electrolyte in the anolyte storage tank (17) is an alkaline urea solution; The urea electrolyzer (1) further comprises a first housing (14); a first anode (11), a first diaphragm (12) and a first cathode (13) are sequentially arranged in the first housing (14); the first diaphragm (12) is a porous diaphragm or has OH - An anion exchange membrane with conductive function; the porous diaphragm is a Zirfon membrane; the anion exchange membrane is a polyarylether membrane, a polyethylene membrane, a polystyrene membrane, a polytetrafluoroethylene membrane or a polyphenyl membrane modified with a cationic group; the cationic group is a polyalkylammonium salt, an imidazole salt, a pyridinium salt or a piperidinium salt; the first anode (11) and the first cathode (13) are both conductive substrates with an active catalytic layer on the surface; the conductive substrate is a porous plate; the porous plate is a carbon material; the material of the active catalytic layer is one or an alloy of two or more of Pt, Ru, Rh, Ir, Ni, Co, Fe, Zn and Ti; The carbon dioxide electrolyzer (2) is a solid oxide electrolyzer; the carbon dioxide electrolyzer (2) comprises a second outer shell (24), wherein a second anode (21), a second diaphragm (22) and a second cathode (23) are sequentially arranged in close contact with each other in the second outer shell (24); the second anode (21), the second diaphragm (22) and the inner wall of the second outer shell (24) are sealed to form a second anode chamber, and the second cathode (23), the second diaphragm (22) and the inner wall of the second outer shell (24) are sealed to form a second cathode chamber; the gas inlet of the second cathode chamber is connected to the outlet of the carbon dioxide storage tank (5); The inlet of the carbon dioxide storage tank (5) is connected to the carbon dioxide outlet of the separator (6) and the external carbon dioxide (9); The inlet of the separator (6) is connected to the gas outlet of the anode gas-liquid separator (15); and the nitrogen outlet of the separator (6) is connected to a nitrogen storage tank or a nitrogen pipeline.

2. The system for preparing synthesis gas by electrolysis of urea and reduction of carbon dioxide according to claim 1, characterized in that: It also comprises an alkali liquid storage tank (3) and a urea storage tank (4); the outlet of the alkali liquid storage tank (3) is connected to the inlet of the cathode electrolyte storage tank (18) and the inlet of the anode electrolyte storage tank (17); the outlet of the urea storage tank (4) is connected to the inlet of the anode electrolyte storage tank (17); and the gas outlet of the cathode gas-liquid separator (16) is connected to a hydrogen storage tank or a hydrogen pipeline.

3. The system for preparing synthesis gas by electrolysis of urea and reduction of carbon dioxide according to claim 1, characterized in that: A spacing is left between the first anode (11), the first diaphragm (12) and the first cathode (13) adjacent to each other; the first anode (11), the first diaphragm (12) and the inner wall of the first outer shell (14) are sealed to form the first anode chamber, and the first cathode (13), the diaphragm (12) and the inner wall of the first outer shell (14) are sealed to form the first cathode chamber.

4. The system for preparing synthesis gas by electrolysis of urea and reduction of carbon dioxide according to claim 3, characterized in that: The thickness of the conductive substrate is 100-500 micrometers; the thickness of the active catalytic layer is 5-100 nanometers.

5. The system for preparing synthesis gas by electrolysis of urea and reduction of carbon dioxide according to claim 1, characterized in that: The second anode (21) is a perovskite oxide composite electrode; the second diaphragm (22) is a solid oxide ceramic membrane; the second cathode (23) is a yttria-stabilized zirconia material loaded with an active metal layer; the material of the active metal layer is one or an alloy of two or more of Cu, Pb, Hg, Tl, In, Sn, Cd, and Bi.

6. The system for preparing synthesis gas by electrolysis of urea and reduction of carbon dioxide according to claim 5, characterized in that: It also includes a CO2 / CO separator (7); the inlet of the CO2 / CO separator (7) is connected to the gas outlet of the second cathode chamber, the CO outlet of the CO2 / CO separator (7) is connected to a CO storage tank or a CO pipeline, and the CO2 outlet of the CO2 / CO separator (7) is connected to the gas inlet of the second cathode chamber; the gas inlet of the second anode chamber is connected to an external water vapor pipeline, and the gas outlet of the second anode chamber is connected to an O2 dryer (8); the outlet of the O2 dryer (8) is connected to an oxygen storage tank or an oxygen pipeline.

7. A method for producing synthesis gas by electrolyzing urea-carbon dioxide reduction using the system according to any one of claims 1 to 6, characterized in that: include Electrolyzing an alkaline aqueous solution in a first cathode chamber of a urea electrolysis cell (1) to generate hydrogen; Electrolyzing an alkaline urea solution in a first anode chamber of a urea electrolyzer (1) to convert urea into nitrogen, water and carbon dioxide, and then introducing the carbon dioxide into a carbon dioxide electrolyzer; Carbon dioxide is electrolyzed in the carbon dioxide electrolyzer (2) to generate carbon monoxide and oxygen.

8. The method according to claim 7, characterized in that The operating temperatures of the second cathode chamber and the second anode chamber of the carbon dioxide electrolyzer (2) are both 650-1000° C., and the operating pressures are both 0.2-0.6 MPa; the carbon dioxide in the carbon dioxide electrolyzer (2) also includes exogenous carbon dioxide.

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