Ammonia synthesis system

Abstract

To provide an ammonia synthesis system capable of improving the utilization efficiency of a raw material gas.SOLUTION: The synthesis system includes an electrochemical cell that generates hydrogen by electrolysis of water vapor contained in a raw material gas, a separation device that separates a product obtained by a chemical reaction between the hydrogen generated by the electrochemical cell and nitrogen contained in the raw material gas from an unreacted substance, a detection device that detects an amount of the unreacted substance separated by the separation device, a reintroduction unit that mixes the unreacted substance with the raw material gas, and a control device that adjusts at least one of an amount of the water vapor and an amount of the nitrogen in the raw material gas supplemented with the unreacted substance based on the amount of the unreacted substance.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ammonia synthesis system that synthesizes ammonia as a product. [Background technology]

[0002] A prior art technique for synthesizing ammonia by a chemical reaction between nitrogen in a raw material gas and hydrogen generated by electrolysis of water is disclosed in Patent Document 1. Patent Document 2 and Non-Patent Document 1 disclose prior art techniques for synthesizing ammonia using an electrochemical cell containing a proton-conductive electrolyte. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-164736 [Patent Document 2] Chinese Utility Model No. 217148587 [Non-patent literature]

[0004] [Non-Patent Document 1] ACS Energy Lett. 2021, 6, 2, 313-319 Summary of the Invention [Problem to be solved by the invention]

[0005] In the prior art, there is a demand for an improvement in the ratio of the amount of product to the amount of raw gas (utilization efficiency).

[0006] The present invention has been made to meet this demand, and has as its object to provide a synthesis system that can improve the utilization efficiency of raw material gases. [Means for solving the problem]

[0007] A first aspect for achieving this object is a synthesis system for synthesizing ammonia as a product, comprising: an electrochemical cell that generates hydrogen by electrolysis of water vapor contained in a raw material gas; a separation device that separates the product and unreacted matter obtained by a chemical reaction between the hydrogen generated by the electrochemical cell and the nitrogen contained in the raw material gas; a detection device that detects the amount of unreacted matter separated by the separation device; a re-injection unit that mixes the unreacted matter with the raw material gas; and a control device that adjusts at least one of the amount of water vapor and the amount of nitrogen in the raw material gas to replenish the unreacted matter based on the amount of unreacted matter.

[0008] In a second aspect of the present invention, in the first aspect, the control device adjusts the amount of nitrogen in the source gas so as to decrease it.

[0009] In a third aspect, in the first or second aspect, a plasma generating device for exciting nitrogen contained in the source gas is further provided. [Effects of the Invention]

[0010] According to the present invention, the amount of at least one of water vapor and nitrogen in the source gas that replenishes the unreacted substances is adjusted by the adjusting device based on the amount of unreacted substances detected by the detecting device, thereby improving the utilization efficiency of the source gas. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram of an ammonia synthesis system according to a first embodiment. [Figure 2] FIG. 1 is a schematic cross-sectional view of a plasma generating device and an electrochemical cell. [Figure 3] FIG. 10 is a schematic cross-sectional view of a plasma generator and an electrochemical cell of a synthesis system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a block diagram of an ammonia synthesis system 10 according to a first embodiment. The synthesis system 10 includes an electrochemical cell 20 that generates hydrogen by electrolyzing water vapor contained in a raw material gas. In this embodiment, the synthesis system 10 also includes a plasma generator 11 (see Fig. 2).

[0013] 2 is a schematic cross-sectional view of a plasma generator 11 and an electrochemical cell 20. The plasma generator 11 is a device that generates reactive plasma, so-called atmospheric pressure plasma, in a high-density medium at atmospheric pressure or higher. The plasma generator 11 includes an electrode member 11a including an electrode 12, and a power supply 17 that applies a voltage to the electrode 12. The electrode member 11a includes a dielectric 16 arranged on the electrode 12. In this embodiment, the electrode member 11a includes a cylindrical electrode 12 with a bottom, and a cylindrical dielectric 16 arranged on the outer periphery of the electrode 12.

[0014] The electrode member 11a is hollow and cylindrical, with at least one end 12a open and a first space 13 provided inside, and has holes 14 that connect to the first space 13. The holes 14 are connected through the electrode 12 and the dielectric 16. A plurality of holes 14 are scattered between the end 12a and the other end 12b of the electrode member 11a. The size of the holes 14 is smaller than the inner diameter D of the electrode 12 (the diameter of the first space 13). The holes 14 may be formed in the electrode member 11a using a tool such as a drill or laser processing. Alternatively, the electrode 12 and the dielectric 16 may be made of a material such as a mesh or fiber, and the holes 14 may be formed between the fibers or openings in the mesh.

[0015] In this embodiment, the electrode member 11a includes a restricting portion 15 whose end 12b is closed. The restricting portion 15 closes the first space 13 inside the electrode member 11a and restricts the flow of the source gas near the end 12b, which flows from the end 12a toward the end 12b of the electrode member 11a. The source gas contains nitrogen and water (water vapor).

[0016] Examples of the material of electrode 12 include metal and carbon. When electrode 12 is made of a metal, electrode 12 contains one or more elements selected from Groups 4 to 14 of the periodic table based on the IUPAC 1990 Recommendations. Examples of elements include Al, Ti, Cr, Fe, Ni, Co, Cu, Zn, Ru, Ag, Pd, Pt, and Au.

[0017] The dielectric 16 prevents arc discharge caused by a large current flowing locally between the electrode 12 and the cathode 22 (described later). Because electric charge accumulates in the dielectric 16, when the direction of the voltage changes after the initial discharge, a discharge can be generated at a lower voltage than the initial discharge. Therefore, plasma can be generated with a small input energy. Examples of the dielectric 16 include a membrane, film, or cylinder made of a material selected from glass, ceramics, synthetic resin, etc. The dielectric 16 may be provided inside the hole 14 of the electrode 12 as long as it does not block the hole 14.

[0018] The power supply 17 is a device that applies an AC voltage between the electrode 12 and the cathode 22 (described later). The AC voltage may be, for example, a sine wave, a triangular wave, a sawtooth wave, or a pulse wave of about 50 Hz to 100 MHz.

[0019] The electrochemical cell 20 is a device that generates hydrogen and oxygen by electrolysis of water (water vapor). The electrochemical cell 20 is disposed outside the electrode member 11a and is heated to the operating temperature of the electrochemical cell 20 (approximately 400°C to 900°C) by a heater (not shown). Because the electrochemical cell 20 is disposed outside the electrode member 11a, the electrochemical cell 20 can be easily heated by the heater.

[0020] The electrochemical cell 20 includes a cylindrical electrolyte 21, a cathode 22 disposed inside the electrolyte 21, and an anode 23 disposed outside the electrolyte 21. The electrochemical cell 20 is a so-called cylindrical vertical stripe cell. The positive electrode of a power supply 24 (DC power supply) is connected to the anode 23, and the negative electrode of the power supply 24 is connected to the cathode 22. The cathode 22 is grounded and also serves as the earth electrode of the plasma generator 11, which is connected to the earth.

[0021] The electrolyte 21 is made of a solid oxide that exhibits oxide ion conductivity under the operating conditions of the electrochemical cell 20. Examples of the solid oxide include stabilized zirconia and ceria-based solid solutions. Examples of the solid oxide include a solid solution of alumina with one or more selected from stabilized zirconia and ceria-based solid solutions. Examples of stabilizers for stabilized zirconia include CaO, MgO, YO, ScO, and YbO. Examples of elements that dissolve in ceria in ceria-based solid solutions include Gd, Sm, and Y.

[0022] The cathode 22 includes a current collector connected to a power source 24, and a reduction reaction occurs on the cathode 22. The cathode 22 is exemplified by a cermet containing a metal catalyst having electronic conductivity and an oxide having oxide ion conductivity. Examples of the metal catalyst include Cr, Fe, Co, Cu, Ru, Pd, Ag, Pt, Au, and Ni. The oxide is a solid electrolyte, and examples thereof include stabilized zirconia and ceria-based solid solutions. Examples of stabilizers for stabilized zirconia include CaO, MgO, YO, ScO, and YbO. Examples of elements dissolved in ceria in ceria-based solid solutions include Gd, Sm, and Y. Ceria-based solid solutions have electronic conductivity and oxygen ion conductivity.

[0023] The anode 23 includes a current collector connected to a power source 24, and the oxidation reaction occurs on the anode 23. The material of the anode 23 is a perovskite oxide, La 1-X Sr X MnO 3-δ ,La 1-X Sr X CoO 3-δ ,La 1-X Sr X Co 1-Y Fe Y O 3-δ ,Pr 1-X Sr X MnO 3-δ Examples of the material for the anode 23 include a composite material of one or more oxides selected from these perovskite oxides and a material that can form the electrolyte 21.

[0024] A cylindrical second space 25 is provided between the dielectric 16 of the plasma generator 11 and the cathode 22 of the electrochemical cell 20. Holes 14 provided in the electrode member 11a of the plasma generator 11 connect the first space 13 and the second space 25. The size of the largest hole among the holes 14 is 1 / 6 or less of the inner diameter D of the electrode 12.

[0025] When the overlapping portion between the electrode member 11a and the electrochemical cell 20 (the portion where the second space 25 is provided) is divided into two equal parts in the longitudinal direction (the vertical direction in FIG. 2 ), and the electrode member 11a, the first space 13, and the second space 25 are partitioned into an upstream portion 26 close to the end 12a of the electrode member 11a and a downstream portion 27 close to the end 12b of the electrode member 11a, the number of holes 14 per unit area of ​​the electrode member 11a is greater in the downstream portion 27 than in the upstream portion 26. In addition, the total area of ​​the holes 14 provided in the downstream portion 27 is greater than the total area of ​​the holes 14 provided in the upstream portion 26.

[0026] The synthesis system 10 synthesizes ammonia as a product of a chemical reaction represented by the chemical reaction equation 2N2 + 6H2O → 4NH3 + 3O2. The electrochemical cell 20 is heated to an operating temperature of approximately 400°C to 900°C. A plurality of holes 14 are formed in the electrode member 11a. The size of the holes 14 is smaller than the inner diameter D of the electrode 12. Therefore, when a raw material gas containing nitrogen and water (water vapor) is supplied from the end 12a of the electrode member 11a, the raw material gas passes through the holes 14 and moves little by little from the first space 13 to the second space 25 while flowing toward the end 12b of the electrode member 11a. The water vapor contained in the raw material gas is reduced at the cathode 22, generating hydrogen and oxygen ions.

[0027] When an AC voltage is applied between the electrode 12 and the cathode 22 of the plasma generator 11, and the voltage reaches a discharge initiation voltage, the gas in the second space 25 undergoes dielectric breakdown, generating a dielectric barrier discharge in the second space 25. The nitrogen contained in the source gas is converted into active nitrogen molecules or atomic nitrogen by the dielectric barrier discharge, resulting in the cleavage of nitrogen-nitrogen triple bonds. Highly reactive active species, such as active nitrogen molecules and atomic nitrogen, are present in the plasma in the second space 25. Because the cathode 22 is located in the second space 25, atomic hydrogen generated on the surface of the cathode 22 is more likely to react with active nitrogen molecules or atomic nitrogen before becoming hydrogen molecules. This improves the reactivity of hydrogen. As a result, selectivity to ammonia is improved.

[0028] If the source gas were to be excessively consumed in the upstream section 26, a reaction synthesizing ammonia would occur locally in the upstream section 26, destabilizing the flow rate of the source gas reaching the downstream section 27 and destabilizing the amount of ammonia produced. According to this embodiment, the source gas flows through the first space 13 and reaches the entire second space 25 via the holes 14 in the electrode member 11a, and the reaction between activated nitrogen and hydrogen generated at the cathode 22 occurs in both the upstream section 26 and the downstream section 27. This increases the amount of ammonia produced, enabling stable ammonia production. Furthermore, this prevents localized reactions, reducing partial wear of the cathode 22. This contributes to a longer life for the electrochemical cell 20.

[0029] The oxygen ions generated at the cathode 22 pass through the electrolyte 21 to reach the anode 23 and are oxidized at the anode 23, generating oxygen at the anode 23. The oxygen generated at the anode 23 is supplied to, for example, a combustor (not shown). The combustor supplied with oxygen can reduce the amount of nitrogen involved in combustion, thereby significantly improving efficiency and further reducing the generation of NOx.

[0030] In the synthesis system 10, the electrochemical cell 20 has a high operating temperature of approximately 400°C to 900°C, resulting in a very low activation overvoltage, enabling highly efficient hydrogen production relative to the amount of power input. Furthermore, heat from a waste heat source such as a combustor can be used to raise the operating temperature of the electrochemical cell 20 and to produce steam. This allows less power to be input to the electrochemical cell 20 to obtain the same amount of hydrogen compared to the power input for water electrolysis in prior art. This therefore reduces the power consumption rate for ammonia synthesis.

[0031] Since the electrochemical cell 20 includes an oxide-ion conductive electrolyte 21, the transport number of ionic conduction in the electrolyte 21 can be increased, thereby improving the faradaic efficiency of the synthesis system 10.

[0032] The size of the largest hole among holes 14 is 1 / 6 or less of the inner diameter D of electrode 12, which prevents a large amount of source gas from leaking from the large holes into second space 25. This reduces the variation in concentration of the source gas supplied to second space 25 through holes 14, allowing for more stable production of ammonia.

[0033] Since the raw material gas flows from end 12a to end 12b of first space 13, the ammonia concentration in downstream portion 27 of second space 25 becomes higher than the ammonia concentration in upstream portion 26. Therefore, in order to allow the chemical reaction that produces ammonia from nitrogen and hydrogen to proceed in downstream portion 27, it is advantageous for the amount of raw material gas supplied to second space 25 in downstream portion 27 to be greater than the amount of raw material gas supplied to second space 25 in upstream portion 26.

[0034] In the synthesis system 10, the number of holes 14 per unit area of ​​the electrode member 11a is greater in the downstream portion 27 of the electrode member 11a than in the upstream portion 26 thereof, and therefore, compared to the reverse relationship, the amount of source gas supplied to the downstream portion 27 of the second space 25 can be made greater than the amount of source gas supplied to the upstream portion 26 of the second space 25. Since the chemical reaction that produces ammonia can also proceed in the downstream portion 27, the amount of ammonia produced can be increased.

[0035] In synthesis system 10, the sum of the areas of holes 14 provided in downstream portion 27 of electrode member 11a is larger than the sum of the areas of holes 14 provided in upstream portion 26 of electrode member 11a, and therefore, compared to the reverse relationship, the amount of source gas supplied to downstream portion 27 of second space 25 can be made larger than the amount of source gas supplied to upstream portion 26 of second space 25. Since the chemical reaction that produces ammonia can also proceed in downstream portion 27, the amount of ammonia produced can be increased.

[0036] In synthesis system 10, because electrode member 11a is provided with restrictor 15, the flow rate of the raw material gas in downstream section 27 of first space 13 can be made smaller than the flow rate of the raw material gas in upstream section 26. Because the average flow velocity of the raw material gas in downstream section 27 in first space 13 is smaller than the average flow velocity of the raw material gas in upstream section 26, the partial pressure of the raw material gas in downstream section 27 becomes higher than the partial pressure of the raw material gas in upstream section 26. Because the chemical reaction that produces ammonia can also proceed in downstream section 27, the amount of ammonia produced can be increased.

[0037] Returning to FIG. 1 , the synthesis system 10 includes a nitrogen gas generator 28 that generates nitrogen and a water vapor generator 29 that generates water vapor. The nitrogen gas generator 28 is exemplified by a velocity dispersion type gas separation device that separates and concentrates nitrogen from air by pressure swing adsorption (PSA) using the difference in diffusion rates between nitrogen and oxygen. The nitrogen gas generator 28 is exemplified by one that includes a compressor (not shown) that compresses air and sends it to an adsorption tower (not shown). The water vapor generator 29 is exemplified by a device that generates water vapor by a heating method, an evaporation method, an ultrasonic method, or the like.

[0038] The control device 48 includes a central processing unit (CPU), non-volatile memory (ROM), and volatile memory (RAM) (none of which are shown). The control device 48 controls the nitrogen gas generator 28 and the water vapor generator 29, thereby controlling the amounts of nitrogen and water vapor. The nitrogen generated by the nitrogen gas generator 28 and the water vapor generated by the water vapor generator 29 travel through pipes 30 and 31, respectively. Nitrogen and water vapor are components of the source gas.

[0039] A regulator 32 for regulating the flow rate of the gas is connected downstream of the pipes 30, 31. The regulator 32 includes mass flow controllers (hereinafter referred to as "MFC") 33, 34. The MFC 33 measures the mass flow rate of nitrogen and controls it to a flow rate set by a control device 48. The MFC 34 measures the mass flow rate of water vapor and controls it to a flow rate set by the control device 48. The pipes 30, 31 downstream of the MFCs 33, 34 are connected to a plasma generator 11 and an electrochemical cell 20.

[0040] A pressure gauge 35 connected to the pipe 31 between the steam generator 29 and the MFC 34 measures the pressure of the gas in the pipe 31. A moisture meter 36 connected to the pipe 31 measures the concentration of water vapor in the gas. A flow meter 37 measures the volumetric flow rate of the gas in the pipe 31. The pressure gauge 35, moisture meter 36, and flow meter 37 input their measurement results to a control device 48. The control device 48 detects the flow rate of hydrogen flowing through the pipe 31 based on the inputs from the pressure gauge 35, moisture meter 36, and flow meter 37.

[0041] When a raw material gas containing nitrogen and water vapor is supplied to the electrochemical cell 20 and the plasma generator 11 (see FIG. 2), a chemical reaction occurs, resulting in the discharge of a product gas. The product gas consists of a product (ammonia) and impurities. The impurities include unreacted substances (nitrogen and hydrogen) and water vapor. The synthesis system 10 separates the product from the impurities by an equilibrium separation operation such as distillation, adsorption, or extraction, or by membrane separation. The synthesis system 10 in this embodiment includes a first cooler 38 and a first separator 39 that cool the product gas to separate the water, and a second cooler 40 and a second separator 41 that cool the product gas to separate the product from the unreacted substances.

[0042] The first cooler 38 and the first separator 39 are exemplified by devices that condense water in the produced gas by heat exchange with cold water at 0°C at atmospheric pressure. The water separated from the produced gas in the first separator 39 is returned to the steam generator 29. The second cooler 40 and the second separator 41 are exemplified by devices that cool the produced gas to about -33°C at atmospheric pressure to liquefy ammonia (the product) and separate the product from unreacted substances. The unreacted substances separated from the product in the second separator 41 move through a pipe 42.

[0043] A detection device 43 disposed in the pipe 42 detects the amount of unreacted substances in the pipe 42. The detection device 43 includes a pressure gauge 44 and a hydrogen concentration meter 45. The pressure gauge 44 measures the pressure of the unreacted substances in the pipe 42. The hydrogen concentration meter 45 measures the hydrogen concentration in the pipe 42. A flow meter 46 connected to the pipe 42 measures the volumetric flow rate of the unreacted substances. The pressure gauge 44, the hydrogen concentration meter 45, and the flow meter 46 input the measurement results to a control device 48.

[0044] Since the unreacted matter in the pipe 42 is a mixed gas of nitrogen and hydrogen, the partial pressure of hydrogen and the partial pressure of nitrogen can be determined from the pressure of the unreacted matter measured by the pressure gauge 44 and the concentration of hydrogen in the unreacted matter. While the synthesis system 10 is operating, the control device 48 repeatedly detects the volumetric flow rates of hydrogen and nitrogen flowing through the pipe 42 based on inputs from the pressure gauge 44, the hydrogen concentration meter 45, and the flow meter 46. The pipe 42 is connected to the plasma generator 11 (see FIG. 2) and the electrochemical cell 20.

[0045] In the synthesis system 10, the temperature of the gas containing water vapor flowing through the flowmeter 37 is made equal to the temperature of the gas (unreacted substance) flowing through the flowmeter 46, so that the control device 48 obtains the ratio of the volumetric flow rate of the water vapor (source gas), the volumetric flow rate of the hydrogen (unreacted substance), and the volumetric flow rate of the nitrogen (unreacted substance). The control device 48 controls the nitrogen gas generator 28 to control the volumetric flow rate of the nitrogen (source gas).

[0046] The control device 48 adjusts the ratio of nitrogen and hydrogen supplied to the plasma generator 11 (see FIG. 2) and the electrochemical cell 20 so that the chemical reaction represented by the chemical reaction equation N2 + 3H2 → 2NH3 proceeds with minimal unreacted matter contained in the generated gas. The control device 48 controls the water vapor generator 29 according to the amount of hydrogen (unreacted matter) returned through the pipe 42 to adjust the amount of water vapor (source gas). The control device 48 controls the nitrogen gas generator 28 according to the amount of nitrogen (unreacted matter) returned through the pipe 42 to adjust the amount of nitrogen (source gas). This improves the ratio (utilization efficiency) of the amount of product relative to the amount of source gas. The control device 48 controls the flow rate of the source gas using the adjustment device 32 so that the ratio of nitrogen and hydrogen supplied to the electrochemical cell 20 and the plasma generator 11 (the ratio (element conversion ratio) between the number of nitrogen atoms contained in the nitrogen-containing substance and the number of hydrogen atoms contained in the hydrogen-containing substance) is stoichiometric.

[0047] The control device 48 controls the nitrogen gas generator 28 to reduce the amount of nitrogen in the raw material gas by supplementing the raw material gas with unreacted materials. Because the amount of nitrogen gas generated by the nitrogen gas generator 28 can be reduced, the operating rate of the nitrogen gas generator 28 can be reduced, thereby reducing the energy input to the nitrogen gas generator 28. This makes it possible to improve the ratio of the energy of the product to the energy input to the synthesis system 10 (energy efficiency).

[0048] A second embodiment will be described with reference to Fig. 3. In the first embodiment, a synthesis system 10 having an electrochemical cell 20 including an oxide-ion conductive electrolyte 21 will be described. In contrast, in the second embodiment, a synthesis system 10 having an electrochemical cell 52 including a proton-conductive electrolyte 53 will be described. The synthesis system 10 in the second embodiment includes a plasma generator 50. In the second embodiment, parts that are the same as those described in the first embodiment will be assigned the same reference numerals as in the first embodiment, and descriptions thereof will be omitted.

[0049] FIG. 3 is a schematic cross-sectional view of a plasma generator 50 and an electrochemical cell 52 of a synthesis system 10 according to the second embodiment. The plasma generator 50 includes a cylindrical electrode member 50a having a hole 14 formed therein. The electrode member 50a includes a cylindrical electrode 12 and a cylindrical dielectric 16 disposed on the outer periphery of the electrode 12. The hole 14 is formed in an upstream portion 26 near the end 12a of the electrode member 50a and a downstream portion 27 near the end 12b of the electrode member 50a, which are formed by dividing the overlapping portion between the electrode member 50a and the electrochemical cell 52 (the portion where the second space 56 is provided) into two equal parts in the longitudinal direction (the vertical direction in FIG. 3). No hole 14 is formed in any portion of the electrode member 50a other than the upstream portion 26 and the downstream portion 27. This is to prevent waste of the raw material gas.

[0050] A restricting unit 51 that makes the flow rate of the raw material gas in the downstream section 27 less than the flow rate of the raw material gas in the upstream section 26 is connected to the end section 12b of the electrode member 50a. In this embodiment, the restricting unit 51 is a valve whose opening degree can be adjusted, and as the opening degree becomes smaller, the flow rate of the raw material gas in the restricting unit 51 decreases, and when the restricting unit 51 is completely closed, the flow of the raw material gas in the restricting unit 51 stops.

[0051] The electrochemical cell 52 includes a cylindrical electrolyte 53 disposed on the outside of the electrode member 50a, a cathode 54 disposed on the inner periphery of the electrolyte 53, and an anode 55 disposed on the outer periphery of the electrolyte 53. The electrochemical cell 52 is a so-called cylindrical vertical stripe cell. The cathode 54 also serves as a ground electrode for the plasma generator 50.

[0052] The material of the electrolyte 53 may be a substance that exhibits proton conductivity under the operating conditions of the electrochemical cell 52. Examples of the substance that exhibits proton conductivity include perovskite-type oxides (ceramics) such as BaZrO3 in which the B site is substituted with trivalent metal ions such as Y or In.

[0053] The cathode 54 may be made of a cermet containing an electron-conducting metal catalyst and a proton-conducting oxide. Examples of the metal catalyst include Cr, Fe, Co, Cu, Ru, Pd, Ag, Pt, Au, and Ni. Examples of the oxide include perovskite-type oxides such as BaZrO3 in which the B site is substituted with a trivalent metal ion such as Y or In.

[0054] The anode 55 is made of perovskite oxide, La 1-X Sr X MnO 3-δ ,La 1-X Sr X CoO 3-δ ,La 1-X Sr X Co 1-Y Fe Y O 3-δ ,Pr 1-X Sr X MnO 3-δ Examples of the material for the anode 55 include a composite material of one or more oxides selected from these perovskite oxides and a material that can form the electrolyte 53.

[0055] A cylindrical second space 56 is provided between the cathode 54 and the dielectric 16. A cylindrical third space 58 is provided between the anode 55 and an outer cylinder 57 arranged outside the anode 55. The outer cylinder 57 can be made of stainless steel or the like. Water (water vapor) is supplied to the third space 58 from the upstream section 26. The water vapor is carried to the anode 55 by an inert gas such as nitrogen or argon, or air. At the anode 55, hydrogen is converted from the water into protons (H + ) and are separated.

[0056] The protons generated at the anode 55 pass through the electrolyte 53 to reach the cathode 54 and are reduced at the cathode 54, generating hydrogen at the cathode 54. While flowing through the first space 13, the raw material gas passes through the holes 14 of the electrode member 50a and spreads throughout the second space 56.

[0057] Because the cathode 54 also serves as the ground electrode of the plasma generator 50, nitrogen ions, activated nitrogen molecules, atomic nitrogen, and the like in the plasma are more likely to reach the surface of the cathode 54. This increases the probability that atomic hydrogen generated on the surface of the cathode 54 will react with activated nitrogen molecules, atomic nitrogen, or nitrogen ions before becoming molecular hydrogen. This improves the reactivity of hydrogen with nitrogen. The reaction between activated nitrogen and hydrogen generated on the cathode 54 occurs in both the upstream section 26 and the downstream section 27, increasing the amount of ammonia produced and ensuring stable ammonia production. Furthermore, because localized reactions can be prevented, partial wear of the cathode 54 can be reduced. This is expected to extend the life of the electrochemical cell 52.

[0058] Since the operating temperature of the electrochemical cell 52 including the proton-conductive electrolyte 53 is lower than the operating temperature of the electrochemical cell 20 in the first embodiment, the temperature of the second space 56 can be lower than in the first embodiment. As a result, the equilibrium concentration reached in the second space 56 in the reaction of synthesizing ammonia from nitrogen and hydrogen can be increased. Therefore, the synthesis system including the electrochemical cell 52 is advantageous for obtaining ammonia with a high concentration.

[0059] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0060] In the embodiment, the synthesis system 10 including the plasma generators 11, 50 that utilize dielectric barrier discharge has been described, but the present invention is not limited to this. Naturally, other plasmas can be used. Examples of other plasmas include corona discharge, surface discharge, atmospheric pressure glow discharge, and microwave discharge. Naturally, it is possible to combine multiple plasmas.

[0061] In the embodiment, the electrode members 11a, 50a are described, each having a hole 14 penetrating both the cylindrical electrode 12 and the cylindrical dielectric 16. However, this is not necessarily limited to this. Other examples of the electrode members 11a, 50a include electrodes 12 arranged in vertical or horizontal stripes on the inner surface of a cylindrical dielectric 16 having holes 14. The electrodes 12 arranged at intervals in a horizontal or vertical stripe pattern are electrically connected to each other. In this case, the source gas flows between the first space 13 and the second space 25, 56 through the gaps between the electrodes 12 arranged in a stripe pattern and through the holes 14, thereby achieving the same effects as those of the present embodiment.

[0062] In the second embodiment, the proton-conductive electrolyte 53 includes a perovskite oxide such as BaZrO3, but is not necessarily limited to this. It is of course possible to use a perfluorocarbon or hydrocarbon polymer electrolyte as the electrolyte 53. Examples of perfluorocarbon proton conductors include Nafion (registered trademark) and Aquivion (registered trademark), in which a sulfo group is linked to a perfluoroalkyl polymer. To improve the properties of the proton conductor, a polymer and inorganic particles may be combined.

[0063] Examples of hydrocarbon-based proton conductors include polymers in which sulfo groups or phosphate groups are linked to aromatic hydrocarbon-based engineering plastics. Examples of hydrocarbon-based proton conductors include polymers (SPEEK) in which sulfo groups are introduced into the main chain of polyether ether ketone. To improve the properties of proton conductors, hetero elements such as fluorine, sulfur, nitrogen, and phosphorus, or units containing these elements, may be introduced.

[0064] When a polymer electrolyte is used for the electrolyte 53, the anode 55 and the cathode 54 can be made of porous carbon carrying a catalyst such as Pt or Pt—Ru. The operating temperature of the electrochemical cell 52 containing a polymer electrolyte for the electrolyte 53 is 120° C. or less, and therefore the temperature of the second space 56 can be lowered accordingly.

[0065] Although not described in the embodiment, the temperature of the second spaces 25, 56 is set appropriately within a range from room temperature to 500° C. The pressure of the second spaces 25, 56 is set appropriately within a range from 101 kPa to 1000 kPa.

[0066] Although not described in the embodiment, it is possible to place a catalyst in the second spaces 25 and 56. There are no particular limitations on the catalyst as long as it is present in the second spaces 25 and 56. For example, the catalyst can be attached to the surface of the dielectric 16 that contacts the second spaces 25 and 56. Examples of the shape of the catalyst attached to the dielectric 16 include a mesh, plate, and film. The catalyst contains one or more elements selected from Groups 4 to 14 of the Periodic Table based on the IUPAC 1990 Recommendations. Examples of elements include Al, Ti, Cr, Fe, Ni, Co, Cu, Zn, Ru, Ag, Pd, Pt, and Au.

[0067] A catalyst may be filled in the second spaces 25, 56. When the catalyst is filled in the second spaces 25, 56, an example of the catalyst is one in which a three-dimensional network structure skeleton made of a porous body made of an oxide such as alumina or zirconia supports the catalyst.

[0068] In the embodiment, the synthesis system 10 is described as including the plasma generators 11, 50, but this is not necessarily limited to this. If ammonia can be synthesized by providing a catalyst in the second spaces 25, 56 or by adjusting the temperature and pressure, it is naturally possible to omit the plasma generators 11, 50. Even when the plasma generators 11, 50 are omitted, by providing holes 14 in the member separating the first space 13 and the second spaces 25, 56, the raw material gas can flow through the holes 14 into the second spaces 25, 56, thereby synthesizing ammonia.

[0069] In the embodiments, restricting units 15, 51 have been described as those that close end 12b of electrode 12 and those that connect a valve to end 12b of electrode 12, but the present invention is not limited to this. Restricting units 15, 51 may be configured to make the flow rate of the source gas in downstream section 27 smaller than the flow rate of the source gas in upstream section 26, and therefore may be configured, for example, to close the end of dielectric 16, to make the cross-sectional area of ​​downstream section 27 of first space 13 smaller than the cross-sectional area of ​​upstream section 26, or to connect a tube having a cross-sectional area smaller than the cross-sectional area of ​​first space 13 to end 12b of electrode 12.

[0070] In the embodiment described above, the spacing between the holes 14 in the downstream section 27 is narrower than the spacing between the holes 14 in the upstream section 26. However, this is not necessarily limited to this. It is of course possible to make the spacing between the holes 14 in the downstream section 27 equal to the spacing between the holes 14 in the upstream section 26 and to make the area of ​​each of the holes 14 in the downstream section 27 greater than the area of ​​each of the holes 14 in the upstream section 26. This is because, in this case, the amount of source gas supplied to the downstream section 27 of the second space 25, 56 can be made greater than the amount of source gas supplied to the upstream section 26 of the second space 25, 56. It is also of course possible to make the spacing between the holes 14 in the downstream section 27 equal to the spacing between the holes 14 in the upstream section 26 and to make the area of ​​the holes 14 in the downstream section 27 equal to the area of ​​the holes 14 in the upstream section 26, or to make the number of holes 14 in the downstream section 27 equal to the number of holes 14 in the upstream section 26. This is because, in this case, the flow rate of the source gas reaching the downstream section 27 can be secured.

[0071] In the embodiment, the case where unreacted hydrogen is supplied to the plasma generator 11 and the electrochemical cell 20 has been described, but the present invention is not necessarily limited to this. It is of course possible to arrange a hydrogen separator such as a hydrogen separation membrane in the pipe 42 upstream of the pressure gauge 44 and extract hydrogen outside the synthesis system 10.

[0072] In the first embodiment, a case has been described in which a mixed gas of nitrogen and water vapor is supplied from end 12a to first space 13, and no gas is supplied from end 12a to second space 25, but this is not necessarily limited to this. It is of course possible to supply nitrogen to first space 13 and water vapor to second space 25, or to supply nitrogen to first space 13 and a mixed gas of nitrogen and water vapor to second space 25. It is also of course possible to supply water vapor to first space 13 and a mixed gas of nitrogen and water vapor to second space 25, or to supply a mixed gas of nitrogen and water vapor to first space 13 and second space 25. Unreacted materials can be supplied to first space 13 or second space 25.

[0073] In the second embodiment, a case has been described in which nitrogen is supplied from the end 12a to the first space 13 and gas is not supplied from the end 12a to the second space 56, but this is not necessarily limited to this. It is of course possible to supply nitrogen from the end 12a to the first space 13 and the second space 56. Unreacted materials can be supplied to the first space 13 or the second space 56. [Explanation of symbols]

[0074] 10 Synthesis System 11,50 Plasma generator 20,52 Electrochemical Cell 41 Second Separator (Separator) 42 Tube (refill section) 43 Detection Device 48 Control Device

Claims

1. 1. A synthesis system for synthesizing ammonia as a product, comprising: an electrochemical cell that generates hydrogen by electrolysis of water vapor contained in the raw material gas; a separation device that separates the product obtained by a chemical reaction between the hydrogen generated by the electrochemical cell and the nitrogen contained in the raw material gas from an unreacted substance; a detection device that detects the amount of the unreacted substance separated by the separation device; a re-injection section for mixing the unreacted material with the raw material gas; a control device that adjusts at least one of the amount of water vapor and the amount of nitrogen in the raw material gas that replenishes the unreacted substances based on the amount of the unreacted substances.

2. 2. The synthesis system according to claim 1, wherein the control device adjusts the amount of nitrogen in the source gas to decrease.

3. The synthesis system according to claim 1 or 2, further comprising a plasma generator for exciting nitrogen contained in the raw material gas.

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