Synthesizer for ammonia

Abstract

To provide a synthesizer capable of increasing the synthesis efficiency of ammonia.SOLUTION: A synthesizer comprises a plasma production device which produces plasma in a reaction field supplied with a raw material gas including nitrogen, an electrochemical cell which decomposes steam to produce hydrogen in the reaction field, and a controller which operates the plasma production device after operating the electrochemical cell. The controller may operate the plasma production device when determining that the reaction field meets conditions. The controller may operate the plasma production device based upon an electric signal of a hydrogen sensor, a steam sensor, a timer device, or a measuring device.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a synthesis apparatus for synthesizing ammonia by reacting nitrogen with hydrogen. [Background technology]

[0002] A prior art technique for synthesizing ammonia by reacting nitrogen excited using a plasma generator with 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 plasma in combination with 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, a high ammonia synthesis efficiency is preferred.

[0006] The present invention has been made to meet this demand, and an object of the present invention is to provide a synthesis apparatus that can increase the efficiency of ammonia synthesis. [Means for solving the problem]

[0007] A first aspect for achieving this object is a synthesis apparatus for synthesizing ammonia by exciting a nitrogen-containing raw material gas, comprising a plasma generation device that generates plasma in a reaction field to which the raw material gas is supplied, an electrochemical cell that decomposes water vapor to generate hydrogen in the reaction field, and a control device that operates the plasma generation device after operating the electrochemical cell.

[0008] In a second aspect, in the first aspect, the control device operates the plasma generating device when it is determined that the reaction field satisfies the conditions.

[0009] In the third aspect, in the second aspect, a hydrogen sensor is provided to detect the concentration of hydrogen in the reaction field, and the control device determines that the reaction field satisfies the conditions when the concentration of hydrogen detected by the hydrogen sensor is equal to or greater than a threshold value.

[0010] In a fourth aspect, in the second or third aspect, a water vapor sensor is provided that detects the concentration of water vapor supplied to the electrochemical cell, and the control device determines that the reaction field satisfies the conditions when the concentration of water vapor detected by the water vapor sensor is below a threshold value.

[0011] In a fifth aspect, in any of the second to fourth aspects, a timing device is provided that measures the time that the electrochemical cell has been operating, and the control device determines that the reaction field has satisfied the condition when the time measured by the timing device or a value based on the time is equal to or greater than a threshold value.

[0012] In a sixth aspect, in any of the second to fifth aspects, a measuring device for an integrated current value, which is the integrated value of the current that flows when the electrochemical cell is operating, is provided, and the control device determines that the reaction field satisfies the conditions when the integrated current value measured by the measuring device or a value based on the integrated current value is equal to or greater than a threshold value.

[0013] In a seventh aspect, in any of the first to sixth aspects, the electrochemical cell comprises a cylindrical electrolyte, a cathode arranged inside the electrolyte, and an anode arranged outside the electrolyte; the plasma generator comprises a cylindrical electrode member including an electrode arranged inside the electrochemical cell at a distance from the cathode; a reaction field is provided between the electrode member and the cathode; a raw material gas is supplied to a space inside the electrode member; a plurality of holes connecting the space and the reaction field are provided in the electrode member; and the cathode also serves as an earth electrode of the plasma generator. [Effects of the Invention]

[0014] According to the present invention, the control device operates the electrochemical cell and then operates the plasma generator to generate plasma in the reaction field. Hydrogen and nitrogen present in the reaction field are activated by the plasma and react to synthesize ammonia, which increases the efficiency of ammonia synthesis compared to when water vapor and nitrogen react in the plasma. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic cross-sectional view of an ammonia synthesis apparatus according to a first embodiment. [Figure 2] FIG. 10 is a schematic cross-sectional view of an ammonia synthesis apparatus according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a schematic cross-sectional view of an ammonia synthesis apparatus 10 according to a first embodiment. The synthesis apparatus 10 includes a plasma generator 11, an electrochemical cell 20, and a control device 32.

[0017] 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.

[0018] The electrode member 11a is hollow and cylindrical, with at least one end 12a open and a space 13 provided inside, and has holes 14 that connect to the 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 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 fibers or openings in the mesh.

[0019] In this embodiment, the electrode member 11a includes a restricting portion 15 with a closed end 12b. The restricting portion 15 closes the 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).

[0020] 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.

[0021] 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 in the hole 14 of the electrode 12 as long as it does not block the hole 14.

[0022] Power supply 17 is a device that applies an AC voltage between electrode 12 and cathode 22 (described later). Examples of the AC voltage include a sine wave, triangular wave, sawtooth wave, and pulse voltage of approximately 50 Hz to 100 MHz. Switch 18 switches the electrical circuit of plasma generator 11 between on (conducting) and off (non-conducting).

[0023] 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.

[0024] 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. The switch 25 switches the electric circuit that applies a potential difference between the anode 23 and cathode 22 of the electrochemical cell 20 between on (conduction) and off (non-conduction).

[0025] 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.

[0026] The cathode 22 includes a current collector connected to a power source 24, and a reduction reaction occurs on the cathode 22 when a switch 25 is on. 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.

[0027] The anode 23 includes a current collector connected to a power source 24, and when a switch 25 is turned on, an 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.

[0028] A cylindrical reaction field 26 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 space 13 to the reaction field 26. The size of the largest hole among the holes 14 is 1 / 6 or less of the inner diameter D of the electrode 12.

[0029] When the overlapping portion between the electrode member 11a and the electrochemical cell 20 (the portion where the reaction field 26 is provided) is divided into two equal parts in the longitudinal direction (the vertical direction in FIG. 1) to partition the electrode member 11a, the space 13, and the reaction field 26 into an upstream portion 27 near the end 12a of the electrode member 11a and a downstream portion 28 near 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 28 than in the upstream portion 27. In addition, the total area of ​​the holes 14 provided in the downstream portion 28 is greater than the total area of ​​the holes 14 provided in the upstream portion 27.

[0030] The water vapor sensor 29 is a sensor that detects the concentration of water vapor in the reaction field 26, and the hydrogen sensor 30 is a sensor that detects the concentration of hydrogen in the reaction field 26. The water vapor sensor 29 and the hydrogen sensor 30 are arranged in the dielectric 16. The water vapor sensor 29 and the hydrogen sensor 30 are arranged in positions that allow them to detect the entire atmosphere of the reaction field 26. The number of water vapor sensors 29 may be one or more. Similarly, the number of hydrogen sensors 30 may be one or more.

[0031] The timing device 31 is a device that measures the time from when the switch 25 of the electrochemical cell 20 was turned on to the present. The switches 18 and 25, the water vapor sensor 29, the hydrogen sensor 30, and the timing device 31 are connected to the control device 32. The measuring device 33 is a device that measures the integrated current value, which is the integrated value of the current that flows when the electrochemical cell 20 is operating. The measuring device 33 is connected to the control device 32.

[0032] In the synthesis apparatus 10, the electrochemical cell 20 is heated to an operating temperature of approximately 400°C to 900°C. The electrode member 11a is provided with a plurality of holes 14, each smaller than the inner diameter D of the electrode 12. Therefore, when a source gas containing nitrogen and water (water vapor) is supplied from the end 12a of the electrode member 11a, the source gas passes through the holes 14 and gradually moves from the space 13 to the reaction field 26 while flowing toward the end 12b of the electrode member 11a. When the switch 25 is turned on, the water vapor contained in the source gas is reduced at the cathode 22, generating hydrogen and oxygen ions. The timer 31 measures the time since the switch 25 was turned on and inputs the result to the control device 32. The measuring device 33 measures the integrated current flowing through the electrochemical cell 20 and inputs the result to the control device 32.

[0033] When water vapor is reduced at cathode 22, the concentration of water vapor in reaction field 26 decreases and the concentration of hydrogen in reaction field 26 increases, so the concentration of water vapor detected by water vapor sensor 29 decreases and the concentration of hydrogen detected by hydrogen sensor 30 increases. The water vapor sensor 29 and hydrogen sensor 30 input their detection results to control device 32.

[0034] The control device 32 includes a CPU, a ROM, and a RAM (none of which are shown). The control device 32 determines whether the conditions for synthesizing ammonia in the reaction field 26 are satisfied based on one or more of the electrical signals input to the control device 32 from the water vapor sensor 29, the hydrogen sensor 30, the timing device 31, and the measurement device 33.

[0035] The control device 32 determines that the reaction field 26 satisfies the condition when, for example, the concentration of water vapor detected by the water vapor sensor 29 is equal to or less than a first threshold (a predetermined concentration). The control device 32 also determines that the reaction field 26 satisfies the condition when the concentration of hydrogen detected by the hydrogen sensor 30 is equal to or greater than a second threshold (a predetermined concentration). The control device 32 may also determine that the reaction field 26 satisfies the condition when the time measured by the timing device 31 or a value based on the time is equal to or greater than a third threshold (a predetermined time or value). The control device 32 may also determine that the reaction field 26 satisfies the condition when the integrated current value measured by the measuring device 33 or a value based on the integrated current value is equal to or greater than a fourth threshold (a predetermined current value or value). These thresholds are set based on the results of simulations and trial runs and are stored in the ROM.

[0036] When the control device 32 determines that the reaction field 26 satisfies the conditions, it turns on the switch 18. When the switch 18 is turned on, an AC voltage is applied between the electrode 12 and the cathode 22 of the plasma generator 11. When the voltage reaches a discharge start voltage, the gas in the reaction field 26 undergoes dielectric breakdown, a dielectric barrier discharge occurs in the reaction field 26, and plasma is generated in the reaction field 26. The hydrogen present in the reaction field 26 is activated by the plasma. Because hydrogen is more easily activated by plasma than water vapor, the concentration of activated hydrogen in the reaction field 26 can be increased by operating the electrochemical cell 20 and then operating the plasma generator 11.

[0037] The nitrogen contained in the source gas is converted by the plasma into activated nitrogen molecules, or into atomic nitrogen by breaking the nitrogen-nitrogen triple bond. Since highly reactive activated species such as activated nitrogen molecules and atomic nitrogen exist in the reaction field 26, the highly reactive nitrogen activated species react with activated hydrogen in the plasma to synthesize ammonia. Therefore, the ammonia synthesis efficiency can be improved compared to when water vapor and nitrogen react in the plasma.

[0038] Because the cathode 22 is located in the reaction field 26, atomic hydrogen generated on the surface of the cathode 22 is more likely to react with activated nitrogen molecules or atomic nitrogen before becoming molecular hydrogen. This improves the reactivity of hydrogen, resulting in improved selectivity to ammonia.

[0039] If the source gas were to be excessively consumed in the upstream section 27, a reaction synthesizing ammonia would occur locally in the upstream section 27, destabilizing the flow rate of the source gas reaching the downstream section 28 and destabilizing the amount of ammonia produced. According to this embodiment, the source gas passes through the holes 14 in the electrode member 11a and reaches the entire reaction field 26 while flowing through the space 13, and the reaction between activated nitrogen and hydrogen generated at the cathode 22 occurs in both the upstream section 27 and the downstream section 28. This increases the amount of ammonia produced, enabling stable ammonia production. Furthermore, this prevents localized reactions, reducing partial wear of the cathode 22. This, in turn, is expected to extend the life of the electrochemical cell 20.

[0040] 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.

[0041] In the synthesis apparatus 10, the operating temperature of the electrochemical cell 20 is high, at around 400°C to 900°C, so the activation overvoltage is very low, and hydrogen can be produced with high efficiency relative to the amount of power input. Furthermore, heat from a waste heat source such as a combustor can be used to bring the electrochemical cell 20 to its operating temperature 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.

[0042] 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 apparatus 10.

[0043] The size of the largest hole among holes 14 is ⅙ or less of the inner diameter D of electrode 12, which prevents a large amount of raw material gas from leaking from the large holes into reaction field 26. This reduces the variation in concentration of the raw material gas supplied to reaction field 26 through holes 14, allowing for more stable production of ammonia.

[0044] Because the raw material gas flows from end 12a to end 12b of space 13, the ammonia concentration in downstream portion 28 of reaction field 26 is higher than the ammonia concentration in upstream portion 27. Therefore, in order to cause the chemical reaction that produces ammonia from nitrogen and hydrogen to proceed in downstream portion 28, it is advantageous for the amount of raw material gas supplied to reaction field 26 in downstream portion 28 to be greater than the amount of raw material gas supplied to reaction field 26 in upstream portion 27.

[0045] In the synthesis apparatus 10, the number of holes 14 per unit area of ​​the electrode member 11a is greater in the downstream portion 28 of the electrode member 11a than in the upstream portion 27 thereof, and therefore, compared to the reverse case, the amount of raw material gas supplied to the downstream portion 28 of the reaction field 26 can be made greater than the amount of raw material gas supplied to the upstream portion 27 of the reaction field 26. Since the chemical reaction that produces ammonia can also proceed in the downstream portion 28, the amount of ammonia produced can be increased.

[0046] In the synthesis apparatus 10, the sum of the areas of the holes 14 provided in the downstream section 28 of the electrode member 11a is larger than the sum of the areas of the holes 14 provided in the upstream section 27 of the electrode member 11a, and therefore, compared to the case where the relationship is reversed, the amount of raw material gas supplied to the downstream section 28 of the reaction field 26 can be made larger than the amount of raw material gas supplied to the upstream section 27 of the reaction field 26. Since the chemical reaction that produces ammonia can also proceed in the downstream section 28, the amount of ammonia produced can be increased.

[0047] In the synthesis apparatus 10, the restricting section 15 is provided in the electrode member 11a, so the flow rate of the raw material gas in the downstream section 28 of the space 13 can be made smaller than the flow rate of the raw material gas in the upstream section 27. Because the average flow velocity of the raw material gas in the downstream section 28 in the space 13 is smaller than the average flow velocity of the raw material gas in the upstream section 27, the partial pressure of the raw material gas in the downstream section 28 becomes higher than the partial pressure of the raw material gas in the upstream section 27. Because the chemical reaction that produces ammonia can also proceed in the downstream section 28, the amount of ammonia produced can be increased.

[0048] The control device 32 may turn off the switch 18 to stop the operation of the plasma generator 11 when the concentration of water vapor detected by the water vapor sensor 29 is equal to or higher than a fifth threshold (a predetermined concentration). An example of the fifth threshold is a value equal to or higher than the first threshold. The control device 32 may also turn off the switch 18 to stop the operation of the plasma generator 11 when the concentration of hydrogen detected by the hydrogen sensor 30 is equal to or lower than a sixth threshold (a predetermined concentration). An example of the sixth threshold is a value equal to or lower than the second threshold. If the control device 32 operates in this manner, when the concentration of hydrogen in the reaction field 26 decreases or the concentration of water vapor increases, the plasma generator 11 stops operating until the reaction field 26 meets the conditions, thereby reducing the power consumption of the plasma generator 11.

[0049] A second embodiment will be described with reference to Fig. 2. In the first embodiment, a synthesis apparatus 10 including an oxide ion conductive electrolyte 21 was described. In contrast, in the second embodiment, a synthesis apparatus 40 including a proton conductive electrolyte 44 will be described. In the second embodiment, the same parts as those described in the first embodiment are designated by the same reference numerals as in the first embodiment, and description thereof will be omitted.

[0050] 2 is a schematic cross-sectional view of an ammonia synthesis apparatus 40 according to the second embodiment. The synthesis apparatus 40 includes a plasma generator 41 that generates atmospheric pressure plasma, an electrochemical cell 43 that generates hydrogen and oxygen by electrolysis of water (water vapor), and a control device 32.

[0051] The plasma generator 41 includes a cylindrical electrode member 41a having a hole 14 formed therein. The electrode member 41a includes a cylindrical electrode 12 and a cylindrical dielectric 16 arranged on the outer periphery of the electrode 12. The hole 14 is provided in an upstream portion 27 near the end 12a of the electrode member 41a and a downstream portion 28 near the end 12b of the electrode member 41a, which are formed by dividing the overlapping portion between the electrode member 41a and the electrochemical cell 43 (the portion where the reaction field 26 is provided) into two equal parts in the longitudinal direction (the vertical direction in FIG. 2). No hole 14 is provided in any portion of the electrode member 41a other than the upstream portion 27 and the downstream portion 28. This is to prevent waste of the source gas.

[0052] A restrictor 42 is connected to the end 12b of the electrode member 41a, which makes the flow rate of the source gas in the downstream section 28 less than the flow rate of the source gas in the upstream section 27. In this embodiment, the restrictor 42 is a valve whose opening can be adjusted, and as the opening becomes smaller, the flow rate of the source gas in the restrictor 42 decreases, and when the restrictor 42 is completely closed, the flow of the source gas in the restrictor 42 stops.

[0053] The electrochemical cell 43 includes a cylindrical electrolyte 44 disposed on the outside of the electrode member 41a, a cathode 45 disposed on the inner periphery of the electrolyte 44, and an anode 46 disposed on the outer periphery of the electrolyte 44. The electrochemical cell 43 is a so-called cylindrical vertical stripe cell. The cathode 45 also serves as a ground electrode for the plasma generator 41.

[0054] The material of the electrolyte 44 may be a substance that exhibits proton conductivity under the operating conditions of the electrochemical cell 43. 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.

[0055] The cathode 45 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.

[0056] The material of the anode 46 is the 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 46 include a composite material of one or more oxides selected from these perovskite oxides and a material that can form the electrolyte 44.

[0057] A cylindrical reaction field 26 is provided between the cathode 45 and the dielectric 16. A cylindrical water vapor supply space 48 is provided between the anode 46 and an outer cylinder 47 arranged outside the anode 46. The outer cylinder 47 can be made of stainless steel or the like. The water vapor sensor 29 detects the concentration of water vapor in the supply space 48 and inputs the detected result to the control device 32.

[0058] Water (water vapor) is supplied to the supply space 48 from the upstream portion 27. The water vapor is carried to the anode 46 by an inert gas such as nitrogen or argon, or air. When the switch 25 is turned on, hydrogen is converted from the water to protons (H + ) and are separated.

[0059] The protons generated at the anode 46 pass through the electrolyte 44 to reach the cathode 45 and are reduced at the cathode 45, generating hydrogen at the cathode 45. As the raw material gas flows through the space 13, it passes through the holes 14 in the electrode member 41a and spreads throughout the reaction field 26.

[0060] When the control device 32 determines that the conditions are met in the reaction field 26, it turns on the switch 18. When the switch 18 is turned on, plasma is generated in the reaction field 26. Highly reactive nitrogen active species react with activated hydrogen in the plasma, synthesizing ammonia. Therefore, the efficiency of ammonia synthesis can be improved compared to when water vapor and nitrogen react in the plasma.

[0061] Since the cathode 45 also serves as the earth electrode of the plasma generator 41, there is a high probability that nitrogen ions, active nitrogen molecules, atomic nitrogen, and the like in the plasma will reach the surface of the cathode 45. This increases the probability that atomic hydrogen generated on the surface of the cathode 45 will react with active nitrogen molecules, atomic nitrogen, or nitrogen ions before becoming hydrogen molecules. This improves the reactivity of hydrogen with nitrogen.

[0062] The reaction between activated nitrogen and hydrogen generated at the cathode 45 occurs in both the upstream section 27 and the downstream section 28, increasing the amount of ammonia produced, and thus enabling stable ammonia production. Furthermore, localized reactions can be prevented, reducing partial wear of the cathode 45. This can be expected to extend the life of the electrochemical cell 43.

[0063] The operating temperature of the electrochemical cell 43 containing the proton-conductive electrolyte 44 is lower than that of the electrochemical cell 20 in the first embodiment, so the temperature of the reaction field 26 can be lower than in the first embodiment. As a result, the equilibrium concentration reached in the reaction field 26 in the reaction of synthesizing ammonia from nitrogen and hydrogen can be increased. Therefore, the synthesis device 40 is advantageous for obtaining ammonia with a high concentration.

[0064] 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.

[0065] In the embodiments, synthesis apparatuses 10 and 40 that utilize dielectric barrier discharge have been described, but the present invention is not limited to this. It is naturally possible to utilize other plasmas. Examples of other plasmas include corona discharge, surface discharge, atmospheric pressure glow discharge, and microwave discharge. It is naturally possible to combine multiple plasmas.

[0066] In the embodiments, the synthesis apparatuses 10, 40 have been described using as an example a so-called coaxial double cylindrical structure in which a cylindrical electrochemical cell 20, 43 is coaxially arranged on the outside of a cylindrical electrode 12, but this is not necessarily limited to this. There are no restrictions on the arrangement of the electrodes and electrochemical cells. For example, it is of course possible to adopt a coaxial cylindrical structure in which a cylindrical electrochemical cell is arranged on the outside of a rod-shaped electrode.

[0067] In the embodiments, the synthesis apparatuses 10, 40 are described as having electrochemical cells 20, 43 of a so-called vertically striped cylindrical type, but the present invention is not necessarily limited to this. Of course, it is possible to adopt various electrochemical cells such as flat-plate type, horizontally striped cylindrical type, and metal-supported flat-plate type.

[0068] In the embodiments, the cathodes 22, 45 of the electrochemical cells 20, 43 also serve as the earth electrodes of the plasma generators 11, 41, but this is not necessarily limited to this. It is of course possible to provide an earth electrode for the plasma generator separately from the cathodes of the electrochemical cells. The arrangement of the electrode and earth electrode of the plasma generator is not limited to a coaxial cylindrical or coaxial double cylindrical arrangement, and a so-called parallel plate arrangement in which a plate-shaped electrode faces a plate-shaped earth electrode may also be employed.

[0069] In the embodiment, the case where the water vapor sensor 29, hydrogen sensor 30, timing device 31, and measuring device 33 are connected to the control device 32 has been described, but this is not necessarily limited to this. As long as any one of the water vapor sensor 29, hydrogen sensor 30, timing device 31, and measuring device 33 is connected to the control device 32, it is of course possible to omit the other sensors and devices.

[0070] In the embodiment, the electrode members 11a and 41a are described as having holes 14 penetrating both the cylindrical electrode 12 and the cylindrical dielectric 16, but the present invention is not necessarily limited to this. Other examples of the electrode members 11a and 41a 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 space 13 and the reaction field 26 through the gaps between the electrodes 12 arranged in a stripe pattern and the holes 14, thereby achieving the same effects as those of the present embodiment.

[0071] In the second embodiment, the proton-conductive electrolyte 44 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 for the electrolyte 44. 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.

[0072] 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.

[0073] When a polymer electrolyte is used for the electrolyte 44, the anode 46 and the cathode 45 can be made of porous carbon carrying a catalyst such as Pt or Pt—Ru. The operating temperature of the electrochemical cell 43 containing the polymer electrolyte in the electrolyte 44 is 120° C. or less, and therefore the temperature of the reaction field 26 can be lowered accordingly.

[0074] Although not described in the embodiment, the temperature of the reaction field 26 is set appropriately within a range from room temperature to 500° C. The pressure of the reaction field 26 is set appropriately within a range from 101 kPa to 1000 kPa.

[0075] Although not described in the embodiment, it is possible to place a catalyst in the reaction field 26. There are no particular limitations on the catalyst as long as it is present in the reaction field 26. For example, the catalyst can be attached to the surface of the dielectric 16 that contacts the reaction field 26. 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.

[0076] A catalyst may be packed into the reaction field 26. When the catalyst is packed into the reaction field 26, 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.

[0077] In the embodiments, restricting units 15, 42 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, 42 may be configured to reduce the flow rate of the source gas in downstream portion 28 compared to the flow rate of the source gas in upstream portion 27. For example, restricting units 15, 42 may be configured to close the end of dielectric 16, to make the cross-sectional area of ​​downstream portion 28 of space 13 smaller than the cross-sectional area of ​​upstream portion 27, or to connect a tube having a cross-sectional area smaller than the cross-sectional area of ​​space 13 to end 12b of electrode 12.

[0078] In the embodiment described above, the spacing between the holes 14 in the downstream section 28 is narrower than the spacing between the holes 14 in the upstream section 27. However, this is not necessarily limited to this. It is naturally possible to make the spacing between the holes 14 in the downstream section 28 equal to the spacing between the holes 14 in the upstream section 27 and to make the area of ​​each of the holes 14 in the downstream section 28 greater than the area of ​​each of the holes 14 in the upstream section 27. This is because, in this case, the amount of source gas supplied to the downstream section 28 of the reaction field 26 can be made greater than the amount of source gas supplied to the upstream section 27 of the reaction field 26. It is also naturally possible to make the spacing between the holes 14 in the downstream section 28 equal to the spacing between the holes 14 in the upstream section 27 and to make the area of ​​the holes 14 in the downstream section 28 equal to the area of ​​the holes 14 in the upstream section 27, or to make the number of holes 14 in the downstream section 28 equal to the number of holes 14 in the upstream section 27. This is because, in this case, the flow rate of the source gas reaching the downstream section 28 can be secured. [Explanation of symbols]

[0079] 10,40 Synthesizer 11,41 Plasma generator 11a, 41a Electrode member 12 electrodes 13 Space 14 holes 20,43 Electrochemical Cell 21,44 electrolytes 22,45 Cathode (earth electrode) 23,46 Anode 26 Reaction Field 29 Water vapor sensor 30 Hydrogen sensor 31 Timing device 32 Control device 33 Measuring equipment

Claims

1. A synthesis apparatus for synthesizing ammonia by exciting a nitrogen-containing raw material gas, comprising: a plasma generator that generates plasma in a reaction field to which the raw material gas is supplied; an electrochemical cell that decomposes water vapor to generate hydrogen in the reaction field; a control device that activates the electrochemical cell and then activates the plasma generator.

2. 2. The synthesis apparatus according to claim 1, wherein the control device operates the plasma generator when it is determined that the reaction field satisfies the conditions.

3. a hydrogen sensor for detecting the concentration of hydrogen in the reaction field; 3. The synthesis apparatus according to claim 2, wherein the control device determines that the reaction field satisfies the conditions when the concentration of hydrogen detected by the hydrogen sensor is equal to or greater than a threshold value.

4. a water vapor sensor that detects the concentration of water vapor supplied to the electrochemical cell; 3. The synthesis apparatus according to claim 2, wherein the control device determines that the reaction field satisfies the conditions when the concentration of water vapor detected by the water vapor sensor is equal to or lower than a threshold value.

5. a timer for measuring the time the electrochemical cell has been operating; The synthesis apparatus according to claim 2 , wherein the control device determines that the reaction field satisfies the condition when the time measured by the timer or a value based on the time is equal to or greater than a threshold value.

6. a measuring device for measuring an integrated current value, which is an integrated value of a current flowing during operation of the electrochemical cell; The synthesis apparatus according to claim 2 , wherein the control device determines that the reaction field satisfies the conditions when the integrated current value measured by the measurement device or a value based on the integrated current value is equal to or greater than a threshold value.

7. The electrochemical cell includes a cylindrical electrolyte, a cathode disposed inside the electrolyte, and an anode disposed outside the electrolyte; the plasma generator includes a cylindrical electrode member including an electrode disposed inside the electrochemical cell with a gap between the cathode and the electrode; the reaction field is provided between the electrode member and the cathode, The raw material gas is supplied to the space inside the electrode member, a plurality of holes connecting the space and the reaction field are provided in the electrode member; 7. The synthesis apparatus according to claim 1, wherein the cathode also serves as a ground electrode for the plasma generating device.

Images