Method and system for producing urea

Abstract

The present invention relates to a method for producing urea. According to the method, urea is synthesized from ammonia and carbon dioxide, with the carbon dioxide for urea synthesis being at least to some degree, in particular completely being obtained from the surrounding air by direct air capture (DAC).

Description

[0001] DESCRIPTION

[0002] Process and plant for the production of urea

[0003] The present invention relates to a process for producing urea, in which urea is synthesized from ammonia and carbon dioxide, wherein the carbon dioxide for the urea synthesis is obtained at least partially, in particular completely, directly from ambient air by means of direct air capture (DAC). Furthermore, the invention relates to a plant for producing urea, comprising a urea synthesis device for synthesizing urea from ammonia and carbon dioxide, wherein the plant has a device for producing ammonia, which is connected to the urea synthesis device, wherein the plant further comprises an electrolysis device for generating hydrogen for the N2 / H2 mixture.

[0004] Urea, also known as urea in English, plays an important role in many chemical and biological processes. Chemically, urea is the diamide of carbonic acid. Its chemical formula is CH4N2O or CO(NH2)2. Among other things, urea serves as a nitrogen fertilizer and an important starting material in the chemical industry. Urea is also used in pharmaceuticals.

[0005] The large-scale production of urea usually takes place from ammonia (NH3) and carbon dioxide (CO2). In a first step, ammonium carbamate (NH4COO)NH4 is usually produced from ammonia and carbon dioxide. This is an exothermic reaction that takes place at a high pressure of, for example, 150 bar. In a further step, the ammonium carbamate reacts in an endothermic reaction to form urea and water. The ammonia required for the production of urea can, for example, be produced or provided starting from a nitrogen / hydrogen mixture. The Haber-Bosch process, for example, can be used for this. Nitrogen is mixed with hydrogen and converted to ammonia under a high pressure of, for example, 100-300 bar and at temperatures of 250-550 °C.The hydrogen (H2) required for this is usually obtained from natural gas through steam reforming or autothermal reforming. This produces carbon dioxide, which is separated and used directly to produce urea.

[0006] This approach has proven to be fundamentally successful. However, such a process requires the availability of natural gas as a fossil fuel.

[0007] It is also possible and particularly desirable to use green hydrogen, produced by electrolysis of water, for urea production. Electricity from renewable energy sources is preferred for this purpose. This approach is also fundamentally suitable for producing hydrogen in larger quantities. However, unlike the use of natural gas, it does not produce carbon dioxide, which is essential for urea production.

[0008] DE 102022 210 053 A1 discloses a process for producing urea. In this process, urea is synthesized from ammonia and carbon dioxide, whereby the carbon dioxide for urea synthesis can be obtained from ambient air using direct air capture (DAC). Another process for producing urea is known from WO 2020 / 212926 A1. A direct air capture process is disclosed in US Pat. No. 11,612,853 B1.

[0009] The object of the present invention is therefore to provide an alternative process and an alternative plant for the production of urea, which are particularly suitable for producing urea from non-fossil raw materials.

[0010] This object is achieved by a method having the features of claim 1. Correspondingly, the object is achieved by a system having the features of claim 14.

[0011] The invention is therefore based on the fundamental idea of ​​extracting the carbon dioxide required for urea production not from a fossil source such as natural gas, but directly from the ambient air. The invention takes advantage of the fact that carbon dioxide is present in the ambient air and is therefore available virtually everywhere. This eliminates the need to supply and / or burn fossil fuels, with all the associated difficulties such as logistics or supply reliability.

[0012] Direct air capture (DAC) processes are particularly characterized by the ability to capture carbon dioxide directly from the ambient air. Direct air capture (DAC) preferably involves three steps. In a first step, the ambient air is directed onto a sorbent, e.g., using fans. The carbon dioxide from the ambient air can then be bound by adsorbing or absorbing substances. Finally, the carbon dioxide can be separated from the sorbent again by applying thermal or electrical energy. This makes the sorbent available for another cycle.

[0013] Specifically, adsorption and calcination can occur at high temperatures. Carbon dioxide can be absorbed with potassium hydroxide as an aqueous solution. Calcination can precipitate the potassium carbonate resulting from the absorption into calcium carbonate, which can be decomposed into carbon dioxide and calcium oxide.

[0014] Direct air capture (DAC), which involves adsorption and subsequent resorption, is also conceivable. In this process, the carbon dioxide is first bound to a sorbent via organic-chemical adsorption, which is then regenerated by low-temperature heat, for example, in the range of approximately 100 °C, and / or moisture. Regeneration under vacuum is also possible. The sorbent can, for example, be porous granules on whose surface amine compounds are deposited.

[0015] In a further embodiment, the direct air capture (DAC) may comprise absorption with alkali and / or alkaline earth hydroxides and / or carbonization and / or organic-inorganic hybrid absorption, and / or take place using metal-organic frameworks, and / or comprise membrane deposition, in particular using semipermeable membranes.

[0016] In a conventional manner, the ammonia can be produced from an N2 / H2 mixture, also referred to as forming gas. Before the ammonia is produced, the N2 / H2 mixture can be compressed. For example, pressures in the range of at least 100 bar, in particular at least 150 bar, and / or at most 300 bar, in particular at most 250 bar, can be achieved.

[0017] Specifically, the ammonia can be produced using the Haber-Bosch process. The ammonia can be produced at a pressure of at least 100 bar, in particular at least 150 bar, and / or at most 300 bar, in particular at most 250 bar, and / or at a temperature of at least 250 °C, in particular at least 300 °C, and / or at most 550 °C, in particular at most 520 °C.

[0018] Correspondingly, the plant according to the invention can comprise a device for producing ammonia, in particular according to the Haber-Bosch process, which is connected to the urea synthesis device. The device for producing ammonia can be preceded by a compression device in which an N2 / H2 mixture can be compressed, in particular to a pressure of at least 100 bar, in particular of at least 150 bar, and / or of at most 300 bar, in particular of at most 250 bar.

[0019] The Haber-Bosch process is a widely used industrial process for the synthesis of ammonia. The process involves the synthesis of ammonia from nitrogen and hydrogen. A catalyst containing iron is preferred.

[0020] In a further embodiment of the process according to the invention, any hydrogen and / or nitrogen still present after the production of ammonia prior to urea synthesis can be separated from the ammonia and returned to the N2 / H2 mixture. Accordingly, in the plant according to the invention, a hydrogen / nitrogen separation device can be arranged between the device for producing ammonia and the urea synthesis device, which separates any hydrogen and / or nitrogen still present after the production of ammonia from the ammonia. The hydrogen / nitrogen separation device can be an ammonia (NH3) condensation unit. The hydrogen / nitrogen separation device and the compression device can be connected to one another via a return line in order to feed the hydrogen separated in the hydrogen / nitrogen separation device to the compression device.This can reduce losses of hydrogen, which has to be produced at great expense, and / or losses of nitrogen.

[0021] The reaction heat generated during ammonia production can be used to generate steam. Furthermore, the reaction heat generated during ammonia production and / or the steam produced therefrom can be used for direct air capture (DAC). This embodiment of the process according to the invention takes advantage of the fact that ammonia synthesis, in particular according to the Haber-Bosch process, is a substantially exothermic reaction that generates heat. This heat can be used efficiently, for example, to generate steam, which can be used in other process steps or in other systems. For example, the generated steam can be fed to an electrolysis device.For this purpose, the system according to the invention can have steam generating means, which in particular comprise a heat exchanger, so that the reaction heat generated during the production of ammonia can be used to generate steam, wherein the steam generating means are connected in particular via appropriate lines to an electrolysis device and / or to the direct air capture (DAC) device in order to supply water vapor to this. The hydrogen for the N2 / H2 mixture can be produced by electrolysis, in particular by high-temperature electrolysis, of water obtained from the ambient air. The electrolysis can take place in an electrolysis device, in particular in a solid oxide cell, preferably in a reversible solid oxide cell. The use of a polymer electrolyte fuel cell is also possible. Alkaline electrolysis or electrolysis via an anion exchange membrane is also conceivable.

[0022] According to the invention, the water and carbon dioxide can be extracted together using direct air capture (DAC). The carbon dioxide can then be separated from the water before being fed into the urea synthesis process. This design is based on the idea of ​​not only extracting the carbon dioxide required for urea synthesis from the ambient air, but also simultaneously extracting the required water from the ambient air. Hydrogen can then be extracted from the water through electrolysis, which, together with nitrogen, produces an N2 / H2 mixture. This mixture can then be used to produce ammonia.

[0023] Correspondingly, the system according to the invention can further comprise an electrolysis device for generating hydrogen for the N2 / H2 mixture. The electrolysis device can be designed to be reversible. The electrolysis device is preferably designed as a solid oxide cell, in particular as a reversible solid oxide cell, or comprises such a cell. It is also possible for the electrolysis device to be designed as a polymer electrolyte fuel cell or to comprise such a cell. An electrolysis device that is designed to be reversible, for example as a reversible solid oxide cell, can be operated in an electrolysis mode or in a fuel cell mode. In principle, it is also possible to operate solid oxide electrolyzer cells (SOEC) in fuel cell mode. In electrolysis mode, the electrolysis device, in particular the solid oxide cell, can generate hydrogen from water by electrolysis.In fuel cell operation, the electrolysis device, in particular the solid oxide cell, can be operated with hydrogen or ammonia to generate electricity. A reversible electrolysis device, in particular a reversible solid oxide cell, which can be operated in both modes, makes it possible to generate electricity if, for example, a power supply from renewable energy sources is interrupted for a certain period of time. In this way, the urea synthesis device and / or the device for producing ammonia can continue to operate even if no external power supply is available. The system can also be equipped with a battery storage system to ensure continued operation during a brief power interruption, particularly at low loads.

[0024] In a solid oxide cell, particularly a reversible solid oxide cell, an electrolyte in the solid state is provided. Specifically, the solid electrolyte can be designed as a thin membrane capable of transporting oxygen ions with low energy. Solid oxide cells typically operate at high temperatures, particularly in the range of 600 to 1000°C. Anode and / or cathode materials for solid oxide cells can be nickel, nickel oxide, silver, platinum, yttrium-stabilized zirconium dioxide (YSZ), BSCF, YSZ / LSM, LSC, samarium-doped cerium (SDC), and the like, or mixtures thereof. Possible electrolyte materials include, among others: YSZ, SDC, BZCY, BCGO, BCNO.

[0025] During electrolysis operation, nitrogen, preferably obtained from the ambient air by air separation, can be supplied to the electrolysis device, in particular the reversible solid oxide cell, particularly on the anode side. This can dilute the anode side of the reversible solid oxide cell. During fuel cell operation, oxygen, preferably obtained from the ambient air by air separation, can be supplied to the electrolysis device, in particular the reversible solid oxide cell. This can improve the efficiency of the solid oxide cell.

[0026] Steam can be supplied to the electrolysis device, especially to the reversible solid oxide cell, particularly on the cathode side. For this purpose, the electrolysis device can be connected to a steam system. The steam can be generated, for example, using the reaction heat generated during ammonia production. By supplying steam, a certain temperature level can be reached in the solid oxide cell, thereby improving its efficiency. Furthermore, the steam can also be used as a dilution medium.

[0027] The electrolysis device and the compression device can be connected to each other to supply the hydrogen obtained during electrolysis to the compression device. Preferably, a compressor for compressing the hydrogen is arranged between the electrolysis device and the compression device. This allows the hydrogen to reach a certain pressure level even before mixing with nitrogen.

[0028] The electrolysis device can be connected to the direct air capture (DAC) device, so that water extracted from the ambient air is used for electrolysis. In a further embodiment, a separation device can be arranged between the DAC device and the electrolysis device, in which the carbon dioxide extracted from the ambient air and water are separated from one another. The separation device is connected to the urea synthesis device via a supply line in order to supply carbon dioxide to the urea synthesis device, and the separation device is connected to the electrolysis device via a water line in order to supply the water extracted from the ambient air to the urea synthesis device. Thus, the DAC device can extract both carbon dioxide and water from the air.This can then be separated in a further step, so that the carbon dioxide can be fed to the urea synthesis unit, and the water to the electrolysis unit. The carbon dioxide and water extracted from the air can be further purified to remove contaminants previously present in the air. Appropriate cleaning agents can be provided for this purpose.

[0029] In a further embodiment of the process according to the invention, the nitrogen for the N2 / H2 mixture can be obtained from the ambient air by air separation. At the same time, oxygen can be obtained from the ambient air, which is fed to the reversible solid oxide cell, particularly during fuel cell operation. Correspondingly, the system according to the invention can comprise an air separation device for extracting nitrogen from the ambient air. The air separation device is preferably connected to the compression device in order to supply it with nitrogen to generate the N2 / H2 mixture.

[0030] Preferably, hydrogen and / or nitrogen and / or carbon dioxide, in particular liquefied carbon dioxide, and / or ammonia, in particular liquefied ammonia, and / or oxygen are temporarily stored in a respective tank. Correspondingly, the system according to the invention can have a hydrogen tank and / or a nitrogen tank and / or a carbon dioxide tank, in particular for liquefied carbon dioxide, and / or an ammonia tank, in particular for liquefied ammonia, and / or an oxygen tank and / or an electricity storage unit and / or a heat storage unit. This embodiment is based on the consideration of providing appropriate storage units or storage containers in order to ensure the most continuous operation of the system possible, even if individual substances are temporarily unavailable.The system may also contain another fuel cell, which can generate electricity temporarily or permanently and can in particular be fed with hydrogen from a hydrogen tank.

[0031] For further details of the invention, reference is made to the dependent claims and the following description of an embodiment with reference to the drawing. The drawing shows:

[0032] Figure 1 shows a system according to the invention in a schematic representation.

[0033] Figure 1 shows a plant 1 for producing urea according to the present invention. The plant 1 comprises a direct air capture (DAC) device 2, which is designed to extract carbon dioxide and water from the ambient air. The DAC device 2 has an outlet 3 for the air depleted of carbon dioxide and water.

[0034] Downstream of the DAC device 2 is a separation device 4, in which carbon dioxide and water obtained from the ambient air are separated from one another. The separation device 4 is connected to an electrolysis device 6 via a water line 5, so that the water obtained from the ambient air can be fed to it. The electrolysis device 6 is designed as a reversible solid oxide cell, which can be operated in an electrolysis mode or in a fuel cell mode. In electrolysis mode, the solid oxide cell generates hydrogen through the electrolysis of water. Downstream of the electrolysis device 6 is a compressor 7 for compressing the hydrogen. This brings the hydrogen to a certain pressure level. The system 1 further comprises a compression device 8, into which a nitrogen line 9 from an air separation device 10 and a hydrogen line 11 from the compressor 7 open.The compression device 8 is designed to compress the resulting N2 / H2 mixture to a pressure of 150 to 300 bar.

[0035] Plant 1 further comprises a facility for producing ammonia 12 according to the Haber-Bosch process. The compression facility 8 is connected downstream of the ammonia production facility 12. A hydrogen / nitrogen separation facility 13 is connected downstream of the ammonia production facility 12 to separate the hydrogen and / or nitrogen still present after the ammonia production from the ammonia. The hydrogen / nitrogen separation facility 13 and the compression facility 8 are connected to each other via a return line 14 to supply the hydrogen separated in the hydrogen / nitrogen separation facility 13 to the compression facility 8.

[0036] Plant 1 further comprises a urea synthesis unit 15 for synthesizing urea from ammonia and carbon dioxide. This unit is connected downstream of the hydrogen / nitrogen separation unit 13. Furthermore, a supply line 16 leading from the separation unit 4 flows into the urea synthesis unit 15 to supply the carbon dioxide obtained from the ambient air to the urea synthesis unit 15.

[0037] The urea synthesis device 15 can contain means for processing the urea produced in order to increase its purity. The reaction heat generated during the production of ammonia is used in corresponding steam generating means 17 to produce steam, which is fed to the electrolysis device 6 and / or the DAC device 2 via corresponding steam lines 18, 19. For this purpose, the steam generating means 17, which comprise, for example, a heat exchanger, are provided with a water inlet 20. Preferably, the water inlet 20 is connected to the DAC device 2 so that the water obtained there from the ambient air can be used for steam generation. At the same time, the reaction heat generated in the electrolysis device 6 is also used to generate steam in the steam generating means 17. The flow of the reaction heat is shown schematically by arrows 21, 22.

[0038] Urea is thus produced in the urea synthesis device 15. For this purpose, carbon dioxide, which is extracted from the ambient air by the DAC device 2 and subsequently separated from the water in the separation device 4, and ammonia are supplied as starting materials. Ammonia is produced from hydrogen, which is produced in the electrolysis device 6 from the water extracted from the ambient air, and nitrogen, which is also extracted from the ambient air by the air separation device 10. This makes it possible to completely eliminate the need for fossil fuels. All essential components can be extracted from the ambient air using renewable energy sources to generate electricity. At the same time, the solid oxide cell is suitable not only for the electrolysis of water, but also, in practice, for generating electricity when no electricity from renewable energies is available.This ensures high operational reliability. The process according to the invention is also characterized by high efficiency, since the reaction heat generated during ammonia production is utilized for subsequent process steps. REFERENCE NUMBER LIST.

[0039] 1 system

[0040] 2 Direct Air Capture (DAC) setup

[0041] 3 Outlet

[0042] 4 Separation device

[0043] 5 water pipe

[0044] 6 Electrolysis device

[0045] 7 Compressor

[0046] 8 Compaction device

[0047] 9 Nitrogen line

[0048] 10 Air separation unit

[0049] 11 Hydrogen pipeline

[0050] 12 Ammonia production facility

[0051] 13 Hydrogen / nitrogen separation facility

[0052] 14 Return line

[0053] 15 Urea synthesis facility

[0054] 16 Supply line

[0055] 17 Steam generating agents

[0056] 18 Steam line

[0057] 19 Steam line

[0058] 20 Water inlet

[0059] 21 Heat of reaction

[0060] 22 Heat of reaction

Claims

CLAIMS 1. A process for the production of urea, in which urea is synthesized from ammonia and carbon dioxide, the carbon dioxide for the urea synthesis being obtained at least partially, in particular completely, directly from ambient air by means of direct air capture (DAC), characterized in that the ammonia is produced from an N2 / H2 mixture, the hydrogen for the N2 / H2 mixture being produced by electrolysis, in particular by high-temperature electrolysis, of water which is obtained from the ambient air, the water and the carbon dioxide being obtained together by means of DAC and the carbon dioxide then being separated from the water before it is fed to the urea synthesis.

2. The method according to claim 1, characterized in that the direct air capture (DAC) comprises absorption with alkali and / or alkaline earth hydroxides and / or carbonization and / or organic-inorganic hybrid absorption, and / or takes place using metal-organic frameworks, and / or comprises membrane separation, in particular using semipermeable membranes.

3. Process according to claim 1 or 2, characterized in that the N2 / H2 mixture is compressed before the production of the ammonia.

4. Process according to one of the preceding claims, characterized in that the ammonia is produced by means of the Haber-Bosch process.

5. The process according to claim 4, characterized in that the production of the ammonia takes place at a pressure of at least 100 bar, in particular of at least 150 bar, and / or of at most 300 bar, in particular of at most 200 bar, and / or at a temperature of at least 250 °C, in particular of at least 300 °C, and / or of at most 550 °C, in particular of at most 520 °C.

6. Process according to one of the preceding claims, characterized in that after the production of ammonia prior to the urea synthesis, any hydrogen still present is separated and returned to the N2 / H2 mixture.

7. A process according to any one of claims 3 to 6, characterized in that the heat of reaction generated during the production of ammonia is used to generate steam.

8. The method according to any one of claims 3 to 7, characterized in that the reaction heat generated during the production of the ammonia and / or the water vapor produced therefrom is used for direct air capture (DAC), and / or that the water vapor produced with the reaction heat from the production of the ammonia is fed to an electrolysis device, in particular a solid oxide cell, preferably a reversible solid oxide cell.

9. Method according to one of the preceding claims, characterized in that the electrolysis takes place in a particularly reversible solid oxide cell (rSOC), which can be operated as required in an electrolysis mode or in a fuel cell mode, wherein the solid oxide cell in the electrolysis mode produces hydrogen by electrolysis of water. and can be operated in fuel cell mode with hydrogen or ammonia to generate electricity.

10. The method according to claim 9, characterized in that in electrolysis operation of the solid oxide cell, nitrogen is supplied, in particular on the anode side, which is preferably obtained from the ambient air by air separation in order to dilute the anode side of the solid oxide cell, and / or that in fuel cell operation of the reversible solid oxide cell, oxygen is supplied, which is in particular obtained from the ambient air by air separation.

11. The method according to claim 9 or 10, characterized in that steam is supplied to the solid oxide cell.

12. Method according to one of the preceding claims, characterized in that hydrogen and / or nitrogen and / or carbon dioxide, in particular liquefied carbon dioxide, and / or ammonia, in particular liquefied ammonia, and / or oxygen are temporarily stored in a respective tank.

13. A process according to any one of the preceding claims, characterized in that the nitrogen for the H2 / N2 mixture is obtained from the ambient air by air separation.

14. Plant (1) for producing urea, in particular according to a method according to one of the preceding claims, comprising a urea synthesis device (15) for synthesizing urea from ammonia and carbon dioxide, wherein the plant (1) has a direct air capture (DAO) device (2) which is designed to extract carbon dioxide from the ambient air and is connected to the urea synthesis device (15). is connected in order to supply carbon dioxide thereto, wherein the plant (1) has a device for producing ammonia (12) which is connected to the urea synthesis device (15), wherein the plant further comprises an electrolysis device (6) for generating hydrogen for the N2 / H2 mixture, characterized in that the electrolysis device (6) is connected to the DAC device (2) so that water obtained from the ambient air is used for the electrolysis, wherein a separation device (4) is arranged between the DAC device (2) and the electrolysis device (6), in which separation device carbon dioxide and water obtained from the ambient air are separated from one another, wherein the separation device (4) is connected to the urea synthesis device (15) in order to supply carbon dioxide thereto, and the separation device (4) is connected to the electrolysis device (6) in order to supply the water obtained from the ambient air thereto.

15. Plant (1) according to claim 14, characterized in that the device for producing ammonia (12) is designed according to the Haber-Bosch process.

16. Plant (1) according to claim 15, characterized in that the device for producing ammonia (12) is preceded by a compression device (8) in which an N2 / H2 mixture can be compressed in particular to a pressure of at least 150 bar and / or at most 300 bar.

17. Plant (1) according to claim 14 or 15, characterized in that a hydrogen separation device (13) is arranged between the device for producing ammonia (12) and the urea synthesis device (15), which separates any hydrogen still present from the ammonia after the production of ammonia.

18. Plant (1) according to claim 16 and claim 17, characterized in that the hydrogen separation device (13) and compression device (8) are connected to one another via a return line (14) in order to supply the hydrogen separated in the hydrogen separation device (13) to the compression device (8).

19. Plant (1) according to one of claims 14 to 18, characterized in that it is designed as a particularly reversible solid oxide cell which can be operated in an electrolysis mode or in a fuel cell mode, wherein the solid oxide cell in electrolysis mode can generate hydrogen by electrolysis of water and the solid oxide cell in fuel cell mode can be operated with hydrogen or ammonia to generate electricity.

20. Plant (1) according to claim 21, characterized in that the electrolysis device (6) and the compression device (8) are connected, wherein in particular between the electrolysis device (6) and the compression device (8) a compressor (7) for compressing the hydrogen is arranged.

21. Plant (1) according to one of claims 14 to 20, characterized in that the plant (1) comprises an air separation device (10) for obtaining nitrogen from the ambient air, the air separation device (10) being connected to the compression device (8) in order to supply nitrogen to the latter for producing the IXh / Fh mixture.

22. Plant (1) according to one of claims 14 to 21, characterized in that the plant (1) has steam generating means (17), which in particular comprise a heat exchanger, so that the steam generated during the production reaction heat arising from the production of ammonia can be used to generate steam, wherein the steam generating means (17) are connected in particular via corresponding lines to the electrolysis device (6) and / or to the DAC device (2) in order to supply this water steam.

23. Plant (1) according to one of claims 147 to 22, characterized in that it has a hydrogen tank and / or a nitrogen tank and / or a carbon dioxide tank, in particular for liquefied carbon dioxide, and / or an ammonia tank, in particular for liquefied ammonia, and / or an oxygen tank and / or an electricity storage device and / or a heat storage device.

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