Hydrogen production method and hydrogen production apparatus

Abstract

To provide a method and an apparatus that efficiently produce hydrogen at a low temperature while suppressing corrosion of a reaction vessel.SOLUTION: A method for producing hydrogen comprises a sodium generating step in which sodium oxide is reacted with a metal containing at least one of nickel, iron, molybdenum, tungsten and aluminum to produce an oxide containing the metal and sodium and sodium, a reduction step in which the oxide produced in the sodium producing step is reacted with water to produce sodium hydroxide, and a hydrogen producing step in which sodium produced in the sodium producing step and sodium hydroxide produced in the reduction step are reacted to produce hydrogen.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a hydrogen production method and a hydrogen production apparatus.

Background Art

[0002] Hydrogen has attracted attention as an energy source that does not generate greenhouse gases such as carbon dioxide (CO₂) when used. Electrolysis of water is well known as a method for producing hydrogen. However, such an electrochemical method can hardly achieve economies of scale, and electrolyzers used for electrolysis are generally expensive.

[0003] Accordingly, techniques for producing hydrogen using thermochemical methods have been proposed. However, conventional thermochemical methods generally require controlling the reaction temperature to 900°C or higher. Maintaining such a temperature (e.g., storing heat to maintain the temperature) is difficult, which has been an obstacle to stable hydrogen production.

[0004] To improve this point, for example, Patent Document 1 discloses a hydrogen production apparatus that produces hydrogen by thermochemically decomposing water, the apparatus comprising: a reaction vessel for causing a chemical reaction of an active material; a sodium supply unit that supplies sodium to the reaction vessel; a water supply unit that supplies water to the reaction vessel; and a heating unit that heats the reaction vessel. The document describes that the apparatus carries out: a first reaction of generating sodium oxide and hydrogen by reacting sodium hydroxide in the reaction vessel with sodium supplied from the sodium supply unit; a second reaction of generating sodium peroxide and sodium from sodium oxide in the reaction vessel; and a third reaction of generating sodium hydroxide and oxygen by reacting sodium peroxide in the reaction vessel with water supplied from the water supply unit.

[0005] Furthermore, Patent Document 2 describes a hydrogen production method comprising: a first hydrogen generation step of reacting an alkali metal with an alkali metal hydroxide to generate alkali metal oxide and hydrogen molecules; a reduction step of decomposing the alkali metal oxide produced in the first hydrogen generation step to generate alkali metal and oxygen molecules; and a second hydrogen generation step of reacting the alkali metal produced in the reduction step with water to generate alkali metal hydroxide and hydrogen molecules, wherein the steps are performed in the order of the first hydrogen generation step, the reduction step, and the second hydrogen generation step. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2014-166931 [Patent Document 2] Japanese Patent Publication No. 2015-134709 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] By utilizing oxidation-reduction cycles such as those described in Patent Documents 1 and 2, it becomes possible to produce hydrogen even at temperatures of around 500°C, and it also becomes possible to produce hydrogen using, for example, solar heat or waste heat.

[0008] However, hydrogen production methods involving oxidation-reduction reactions as described above often require the use of highly corrosion-resistant reaction vessels (e.g., nickel alloy vessels), and corrosion of the reaction vessels could occur even at temperatures of around 500°C.

[0009] This invention was made in view of the above background, and its purpose is to provide a hydrogen production method and a hydrogen production apparatus that can efficiently produce hydrogen at low temperatures while suppressing corrosion of the reaction vessel. [Means for solving the problem]

[0010] One aspect of the present invention for achieving the aforementioned objectives is a hydrogen production method comprising: a sodium production step of reacting sodium oxide with a metal containing at least one of nickel, iron, molybdenum, tungsten, or aluminum to produce an oxide containing the metal and sodium, and sodium; a reduction step of reacting the oxide produced in the sodium production step with water to produce sodium hydroxide; and a hydrogen production step of reacting the sodium produced in the sodium production step with the sodium hydroxide produced in the reduction step to produce hydrogen.

[0011] In this way, by actively introducing elements that form stable ternary oxides with sodium, such as nickel, iron, molybdenum, tungsten, and aluminum, to Na2O, thermodynamically stable oxides containing the above metals and sodium can be produced. Hydrogen can then be generated by reacting the NaOH produced by hydrolysis of these oxides with the Na produced together with the oxides. Since this reaction proceeds at a lower temperature than the reaction temperature of conventional thermodynamic hydrogen reactions (e.g., 500°C), corrosion of the reaction vessel caused by the reaction of Na2O with the metal of the reaction vessel can be prevented. Thus, according to the hydrogen production method of the present invention, hydrogen can be efficiently produced at low temperatures while suppressing corrosion of the reaction vessel.

[0012] Furthermore, another aspect of the present invention for achieving the aforementioned objectives is that in the reduction step, the oxide produced in the sodium production step is reacted with water to produce the metal and sodium hydroxide, and in the hydrogen production step, the sodium produced in the sodium production step is reacted with the sodium hydroxide produced in the reduction step to produce hydrogen and sodium oxide.

[0013] Thus, the metal and Na2O consumed in the sodium production process are regenerated in the reduction and hydrogen production processes, respectively, establishing a redox cycle (Na-redox cycle) consisting of the sodium production, reduction, and hydrogen production processes. This allows for the efficient production of hydrogen.

[0014] Another aspect of the present invention for achieving the aforementioned objectives is to set the reaction temperature to 200°C or higher in the sodium production step.

[0015] This allows the reaction to proceed more rapidly, ensuring the more reliable production of the oxide and Na.

[0016] Another aspect of the present invention for achieving the aforementioned objectives is to set the reaction temperature to 300°C or lower in the sodium production step.

[0017] In other words, the reaction can proceed at a much lower temperature compared to conventional thermochemical hydrogen production methods. This also allows for more reliable prevention of corrosion of the reaction vessel.

[0018] Another aspect of the present invention for achieving the aforementioned objectives is to set the reaction temperature to 350°C or lower in the hydrogen production step.

[0019] This makes it possible to produce hydrogen at temperatures of 100°C or higher compared to conventional thermochemical hydrogen production methods.

[0020] Another aspect of the present invention for achieving the aforementioned objectives is to carry out each of the reactions in the sodium generation step, the reduction step, and the hydrogen generation step in a reaction vessel made of a material containing a nickel alloy.

[0021] This makes it possible to more reliably suppress corrosion of the reaction vessel.

[0022] Furthermore, in another aspect of the present invention for achieving the above object, in the sodium production step, sodium oxide and nickel are reacted to produce sodium nickel oxide and sodium; in the reduction step, the sodium nickel oxide produced in the sodium production step is reacted with water to produce sodium hydroxide; and in the hydrogen production step, the sodium produced in the sodium production step and the sodium hydroxide produced in the reduction step are reacted to produce hydrogen.

[0023] As described above, by actively introducing Ni to Na₂O, thermodynamically stable Na₂NiO₂ is produced, and hydrogen can be generated by reacting NaOH produced by hydrolyzing this Na₂NiO₂ with Na produced together with Na₂NiO₂. Since such a reaction proceeds at a temperature lower than the reaction temperature of a conventional thermodynamic hydrogen reaction (e.g., 500°C), corrosion of the reaction vessel caused by the reaction of Na₂O with the metal of the reaction vessel can be prevented.

[0024] Furthermore, in another aspect of the present invention for achieving the above object, in the reduction step, the sodium nickel oxide produced in the sodium production step is reacted with water to produce nickel and sodium hydroxide; and in the hydrogen production step, the sodium produced in the sodium production step and the sodium hydroxide produced in the reduction step are reacted to produce hydrogen and sodium oxide.

[0025] As described above, since Ni and Na₂O consumed in the sodium production step are respectively reproduced in the reduction step and the hydrogen production step, an oxidation-reduction cycle (Na-redox cycle) consisting of the sodium production step, the reduction step, and the hydrogen production step is established. Thereby, hydrogen can be produced efficiently.

[0026] Another aspect of the present invention for achieving the above object is a hydrogen production apparatus, which comprises a reaction vessel made of a material containing a nickel alloy, wherein the reaction vessel causes the respective reactions of: a sodium generation step of reacting sodium oxide with a metal containing at least one of nickel, iron, molybdenum, tungsten, or aluminum to generate oxides of said metal and sodium and sodium; a reduction step of reacting the oxide generated in said sodium generation step with water to generate sodium hydroxide; and a hydrogen generation step of reacting the sodium generated in said sodium generation step and the sodium hydroxide generated in said reduction step to generate hydrogen.

[0027] Thereby, hydrogen can be efficiently produced at low temperatures while effectively suppressing corrosion of the reaction vessel by the nickel alloy.

[0028] Another aspect of the present invention for achieving the above object is a hydrogen production apparatus, comprising: a temperature control device that heats the reaction vessel; a water supply unit that supplies water to the reaction vessel; an oxygen discharge unit that discharges the generated oxygen from the reaction vessel; a sodium storage unit that stores the generated sodium and introduces the stored sodium into the reaction vessel; and a hydrogen recovery unit that recovers the generated hydrogen.

[0029] With such an apparatus configuration, a redox cycle reaction consisting of a sodium generation step, a reduction step, and a hydrogen generation step can be realized.

Effects of the Invention

[0030] According to the present invention, hydrogen can be efficiently produced at low temperatures while suppressing corrosion of the reaction vessel.

Brief Description of Drawings

[0031] [Figure 1] It is a diagram showing an example of the steps of the hydrogen production method according to the present embodiment. [Figure 2] It is a diagram showing an example of the configuration of the hydrogen production apparatus according to the present embodiment. [Figure 3]These are the XRD diffraction charts of the deposits at 250°C and 300°C in Experiment 1. [Figure 4] These are XRD diffraction charts of the heated portion of the pellet at 250°C and 300°C in Experiment 1. [Figure 5] This is the XRD diffraction chart of the product in Experiment 2-1. [Figure 6] This is the chromatogram from the gas chromatograph in Experiment 2-2. [Figure 7] This is the XRD diffraction chart from Experiment 2-2. [Figure 8] This is the XRD diffraction chart (details) from Experiment 2-2. [Figure 9] This is the XRD diffraction chart of the mixed sample in Experiment 3-1. [Figure 10] This is the chromatogram resulting from the first gas chromatograph measurement in Experiment 3-2. [Figure 11] This is the chromatogram resulting from the second gas chromatograph measurement in Experiment 3-2. [Figure 12] This is the XRD diffraction chart from Experiment 3-2. [Modes for carrying out the invention]

[0032] The hydrogen production method according to one embodiment of the present invention will be described below with reference to the drawings.

[0033] The inventors conducted various reaction experiments using the sodium redox reaction cycle described in Patent Documents 1 and 2 (hereinafter referred to as the Na-redox cycle). As a result, it was found that in these Na-redox cycles, the generation of sodium is important for the reaction to proceed (hydrogen generation). On the other hand, when experiments were conducted using reaction vessels made of various metal alloys in addition to highly corrosion-resistant nickel alloys, or when the reactants did not come into direct contact with the reaction vessel, corrosion of the reaction vessel was particularly observed when a nickel alloy was used. From this, the inventors hypothesized that the generated sodium reacts easily with the nickel in the reaction vessel, making the reaction vessel prone to corrosion.

[0034] Therefore, the inventors conceived of actively introducing nickel into the Na-redox cycle to suppress corrosion of the nickel reaction vessel.

[0035] Furthermore, due to the characteristics of the Na-redox cycle reaction described later, similar effects can be expected not only for nickel, but also for other metals that form stable ternary oxides with sodium, such as iron, molybdenum, tungsten, or aluminum. In this embodiment, the case where the above metal is nickel will be described.

[0036] Figure 1 shows an example of the steps of the hydrogen production method according to this embodiment. As shown in the figure, first, a sodium production step is carried out in which sodium oxide (Na2O) and nickel (Ni) are reacted in a reaction vessel made of nickel alloy to produce an oxide (sodium nickel oxide (Na2NiO2)) and sodium (Na) (s1). The reaction in the sodium production step is represented by the following formula (1).

[0037] 2Na₂O + Ni → Na₂NiO₂ + 2Na (1)

[0038] Thus, in the hydrogen production method of this embodiment, nickel, which is also the material of the reaction vessel (the same applies to elements other than nickel, such as iron, molybdenum, tungsten, or aluminum, which form stable ternary oxides with sodium, similar to nickel), is actively introduced into the reaction system.

[0039] In the sodium production step, it is preferable to set the reaction temperature to 200°C or higher. This allows equation (1) to proceed more reliably and generate sodium. The sodium produced by equation (1) is an important product for promoting the reactions in the reduction step and hydrogen production step described later.

[0040] Furthermore, in the sodium production process, it is preferable to set the reaction temperature to 300°C or lower. Even at temperatures below 300°C, the reaction in equation (1) proceeds, and hydrogen can be produced as described later. In other words, hydrogen can be produced at a lower temperature than the reaction temperature (500°C) required for hydrogen production by conventional thermochemical methods. Moreover, at such temperatures, corrosion of the reaction vessel can be suppressed even when a nickel alloy is used for the reaction vessel.

[0041] Furthermore, the reason why equation (1) proceeds even at low temperatures below 300°C is thought to be because the Na2NiO2 produced in equation (1) is thermodynamically stable.

[0042] Next, a reduction step is carried out in the reaction vessel described above, in which the oxide (sodium nickel oxide (Na2NiO2)) produced in the sodium production step is reacted with water (hydrolysis) to produce the above metal and sodium hydroxide (NaOH) (s2). Specifically, the Na2NiO2 produced in the sodium production step is reacted with water (H2O) to produce Ni and NaOH. Oxygen is generated during this process. The reaction in this reduction step is represented by the following equation (2).

[0043] Na2NiO2+H2O→Ni+2NaOH+1 / 2O2(2)

[0044] The reaction in the reduction step can and preferably proceed at room temperature. Furthermore, it is preferable to discharge the generated oxygen outside the reaction vessel.

[0045] In addition, along with the reaction in equation (2), the unreacted Na2O in equation (1) may also react with water (hydrolysis) to produce NaOH. This reaction is represented by the following equation (2').

[0046] Na2O + H2O → 2NaOH (2')

[0047] Next, a hydrogen production step is carried out in which the Na produced in the sodium production step and the NaOH produced in the reduction step are reacted to produce hydrogen (H2) (s3). The reaction in the hydrogen production step is represented by the following equation (3).

[0048] 2Na+2NaOH+Ni →2Na2O+Ni+H2(3)

[0049] In the hydrogen generation process, the reaction temperature is preferably set to 350°C or lower, and more preferably to 300°C or lower. Although Ni is present on both sides of equation (3), it does not substantially contribute to the reaction.

[0050] The three processes described above, i.e., the Na-redox cycle, can be represented overall by the following equation (4).

[0051] H2O → H2 + 1 / 2O2 (4)

[0052] In this way, hydrogen can be efficiently produced through the thermochemical reaction of the Na-redox cycle.

[0053] <Device configuration> The hydrogen production described above can be achieved, for example, by the following equipment configuration.

[0054] Figure 2 shows an example of the configuration of a hydrogen production apparatus according to this embodiment. This hydrogen production apparatus 10 comprises a reaction vessel 20 for containing active material, a temperature control device 30 for controlling the temperature of the reaction vessel 20, a water supply unit 40 (e.g., composed of pipes, valves, pumps, etc.) for supplying water to the reaction vessel 20, a sodium storage unit 50 for temporarily storing substances generated in the reaction vessel 20, an oxygen discharge unit 60 (e.g., composed of pipes, valves, pumps, etc.) for discharging oxygen generated in the reaction vessel 20, and a hydrogen recovery unit 70 (e.g., composed of pipes, valves, pumps, etc.) for recovering hydrogen generated in the reaction vessel 20. Note that the oxygen discharge unit 60 and the hydrogen recovery unit 70 may be the same.

[0055] For example, in the sodium production process, a mixed powder of Na2O and Ni is placed in the reaction vessel 20, and then heated to the predetermined temperature using the temperature control device 30. As a result, Na2NiO2 is produced in the reaction vessel 20, while the generated gaseous Na is stored in the sodium storage unit 50.

[0056] Next, the temperature inside the reaction vessel 20 is lowered to room temperature by the temperature control device 30 or by leaving it for a predetermined time. Then, as a reduction step, H2O is introduced into the reaction vessel 20 by the water supply unit 40 and reacted with Na2NiO2. As a result, NaOH is produced in the reaction vessel 20, and the generated O2 is discharged through the oxygen discharge unit 60. In addition, NaOH is also produced when unreacted Na2O reacts with H2O in the sodium production step.

[0057] In the hydrogen generation process, the temperature inside the reaction vessel 20 is controlled to a predetermined temperature by the temperature control device 30, and Na stored in the sodium storage unit 50 is introduced into the NaOH inside the reaction vessel 20. This generates hydrogen, which is then recovered by the hydrogen recovery unit 70.

[0058] Furthermore, within the reaction vessel 20, Na2O is produced by the hydrogen generation step, and Ni produced in the reduction step is also present. Therefore, in this state, the sodium generation step can be carried out again, and a series of Na-redox cycles are established.

[0059] <Experiment> The inventors conducted the following reaction experiments to confirm that each of the above reactions (1) to (3) actually proceeds.

[0060] (Experiment 1: Sodium production process) (Experimental method) First, Na2O and Ni powder were mixed in a 1:1 molar ratio using a hand mill, and the mixture was pressurized at 30 MPa for 5 minutes to produce pellets (samples). The prepared pellets were then placed in a nickel alloy reaction vessel, and the vessel was positioned so that the pellets were at the focal point of a pre-prepared point-focusing heating device. Subsequently, the pellets were heated while vacuuming was performed using a rotary pump.

[0061] In this heating method, the power supply voltage of the point focusing heater was increased at a rate of 2V / min to 10V, and then, above 10V, it was increased at a rate of 0.8 V / min while observing the sample and the water cooling section. The relationship between the voltage and temperature of the point focusing heater was 250°C at 13.2V and 300°C at 16.8V.

[0062] When deposits (condensed gases presumably formed from the sample) were observed in the water-cooled section, the voltage increase was stopped, and the system was left for about 20 minutes. After this period, the power supply voltage was reduced to 0V.

[0063] During heating, samples of the attached material and the heated portion of the pellet were taken at 250°C and 300°C, and analyzed by XRD (X-ray diffraction).

[0064] (Experimental results) Visual observation: On the surface of the water-cooled section, deposits with a metallic luster were observed in the temperature range of 200°C to 250°C. However, the metallic luster disappeared above 300°C.

[0065] XRD: Figure 3 shows the XRD diffraction charts of the deposits at 250°C and 300°C in Experiment 1. As shown in the figure, a Na peak was observed at 250°C, suggesting that Na was produced by reaction (1). On the other hand, at 300°C, the Na2O peak became clearer than the Na peak. However, this is presumed to be because the produced Na was oxidized.

[0066] Figure 4 shows the XRD diffraction charts of the heated portion of the pellet at 250°C and 300°C in Experiment 1. As shown in the figure, at 250°C, in addition to the Ni peak, a Na2NiO2 peak was observed. On the other hand, at 300°C, a Na2NiO2 peak was also observed, but no Ni peak was observed. The absence of a Ni peak is consistent with the observation of peaks for each oxide, Na2O, Na2O2, and Na2NiO2, suggesting that all the Ni was consumed in the reaction and oxygen was produced.

[0067] The results above confirm that the reaction represented by equation (1) proceeds in the range of 200°C to 300°C, producing Na and Na2NiO2. In other words, the reaction (1) does not require high temperatures (above 500°C) as in conventional thermochemical hydrogen production, and as a result, corrosion of the reaction vessel can be reduced.

[0068] (Experiment 2: Reduction Process) (Experimental method) (Experiment 2-1) First, the pellet sample (containing Na2NiO2) obtained in Experiment 1 was ground in a hand mill for several minutes. At this time, the ground sample and BN (boron nitride) were mixed in a hand mill in a molar ratio of 1:1. Next, the resulting mixture was sealed in a vial with Parafilm inside a Glove Box (GB). Then, it was removed from the GB, and water was added dropwise through the septum at the top of the vial. All of the above was carried out under room temperature conditions. After the reaction was completed by adding water, the sample was heated at 80°C while being pumped with a scroll pump to dehydrate and dry it. After dehydration, it was powdered in a hand mill inside the GB, and then measured by XRD.

[0069] (Experiment 2-2) The pellet sample (containing Na2NiO2) obtained in Experiment 1 was ground in a hand mill for several minutes. Under room temperature conditions, 300 mg of the ground pellet sample was sealed in a SUS reaction vessel, and then 2 cm of water was passed through the septum of the reaction vessel for 10 minutes. 3 The substance was added dropwise. During this process, a temperature increase from room temperature to 62.3°C was observed. After the reaction, the gas generated in the container was analyzed by gas chromatography (GC). In addition, the sample after the reaction was measured by XRD.

[0070] (Experimental results) Figure 5 shows the XRD diffraction chart of the product from Experiment 2-1. Ni and NaOH peaks were observed in the product chart.

[0071] Figure 6 shows the chromatogram from the gas chromatograph in Experiment 2-2. As shown in the figure, a prominent peak for O2 was observed.

[0072] Figures 7 and 8 show the XRD diffraction charts from Experiment 2-2. As shown in these figures, the peaks for the Na2O and Na2NiO2 phases disappeared. However, for NaOH, the peak for the NaOH hydrate was also observed due to the large amount of H2O added.

[0073] Based on the above, it was confirmed that reactions (2) or (2') proceed at room temperature, producing NaOH and Ni from Na2NiO2, as well as generating O2.

[0074] (Experiment 3: Hydrogen Production Process) (Experimental method) (Experiment 3-1) First, a sample was prepared by mixing NaOH powder and Ni powder in a molar ratio of 1:1 using a hand mill for several minutes. Then, metallic Na was placed on a BN boat, and the prepared mixed sample was placed on top of it. The sample area was heated to 350°C using a point-focusing heating device and held for 20 hours. After that, the mixed sample was analyzed by XRD. (Experiment 3-2) 1. First, NaOH powder and Ni powder were mixed in a hand mill for 3 minutes to prepare the sample. 2. Metallic sodium was placed in a BN boat, and the NaOH and Ni powders were placed on top of it. The mixing ratio (molar ratio) of this mixed sample was Na:NaOH:Ni = 2:2:1. 3. The mixed sample was sealed in a glass tube, and the space was evacuated using a dry pump for 10 minutes. 4. This apparatus was made into a closed system, and the mixed sample was heated to 300°C. 5. After heating at 300°C for 4 hours, the first component analysis of the mixed sample was performed using gas chromatography. 6. After the first component analysis, the sample was heated for another 16 hours, and a second component analysis of the mixed sample was performed using gas chromatography. 7. Furthermore, the mixed sample was analyzed by XRD.

[0075] (Experimental results) (Experiment 3-1) Figure 9 shows the XRD diffraction chart of the mixed sample from Experiment 3-1. As shown in the figure, clear peaks for Ni and Na2O were observed. On the other hand, no peaks for Na and NaOH were observed.

[0076] (Experiment 3-2) Figure 10 shows the chromatogram obtained from the first gas chromatograph measurement in Experiment 3-2. As is clear when compared with the blank sample, a hydrogen peak was observed.

[0077] Figure 11 shows the chromatogram from the second gas chromatograph measurement in Experiment 3-2. Compared to the first measurement (4hs vac), the hydrogen peak intensity was clearly increased in the second measurement (20hs vac), confirming that more hydrogen was produced.

[0078] Figure 12 shows the XRD diffraction chart from Experiment 3-2. As shown in the figure, the observation of diffraction peaks belonging to Ni suggests that no side reactions (side reactions by Ni) occurred.

[0079] Based on the above experimental results, it was confirmed that even when the reaction temperature is 350°C or lower, more preferably 300°C or lower, the reaction shown in reaction (3) proceeds reliably, and Na2O is produced from Na and NaOH, along with the generation of hydrogen.

[0080] As described above, the hydrogen production method of this embodiment includes a sodium production step in which sodium oxide is reacted with a metal containing at least one of nickel, iron, molybdenum, tungsten, or aluminum to produce an oxide containing the metal and sodium, and sodium; a reduction step in which the oxide produced in the sodium production step is reacted with water to produce sodium hydroxide; and a final step in which the sodium produced in the sodium production step and the sodium hydroxide produced in the reduction step are reacted to produce hydrogen.

[0081] In this way, by actively introducing elements that form stable ternary oxides with sodium, such as nickel, iron, molybdenum, tungsten, and aluminum, to Na2O, a thermodynamically stable oxide can be produced. Hydrogen can then be generated by reacting the NaOH produced by hydrolysis of this oxide with the Na produced along with the oxide. Since this reaction proceeds at a lower temperature than the reaction temperature of conventional thermodynamic hydrogen reactions (e.g., 500°C), corrosion of the reaction vessel caused by the reaction of Na2O with the metal of the reaction vessel can be prevented. Thus, according to the hydrogen production method of this embodiment, hydrogen can be efficiently produced at low temperatures while suppressing corrosion of the reaction vessel.

[0082] Furthermore, in the reduction step of the hydrogen production method of this embodiment, the oxide produced in the sodium production step is reacted with water to produce a metal and sodium hydroxide, and in the hydrogen production step, the sodium produced in the sodium production step and the sodium hydroxide produced in the reduction step are reacted to produce hydrogen and sodium oxide.

[0083] Thus, the metal and Na2O consumed in the sodium production process are regenerated in the reduction and hydrogen production processes, respectively, establishing a redox cycle (Na-redox cycle) consisting of the sodium production, reduction, and hydrogen production processes. This allows for the efficient production of hydrogen.

[0084] Furthermore, in the sodium production step of the hydrogen production method of this embodiment, the reaction temperature is set to 200°C or higher. This allows the reaction to proceed more rapidly, and the oxide and Na can be produced more reliably.

[0085] Furthermore, in the hydrogen production method of this embodiment, the reaction temperature in the sodium production step is set to 300°C or lower.

[0086] In other words, the reaction can proceed at a much lower temperature compared to conventional thermochemical hydrogen production methods. This also allows for more reliable prevention of corrosion of the reaction vessel.

[0087] Furthermore, in the hydrogen production method of this embodiment, the reaction temperature is set to 350°C or lower in the hydrogen production process.

[0088] This makes it possible to produce hydrogen at temperatures of 100°C or higher compared to conventional thermochemical hydrogen production methods.

[0089] Furthermore, in the hydrogen production method of this embodiment, each reaction in the sodium generation step, reduction step, and hydrogen generation step is carried out in a reaction vessel made of a material containing a nickel alloy.

[0090] This makes it possible to more reliably suppress corrosion of the reaction vessel.

[0091] Furthermore, in the hydrogen production method of this embodiment, in the sodium production step, sodium oxide and nickel are reacted to produce sodium nickel oxide and sodium; in the reduction step, the sodium nickel oxide produced in the sodium production step is reacted with water to produce sodium hydroxide; and in the hydrogen production step, the sodium produced in the sodium production step and the sodium hydroxide produced in the reduction step are reacted to produce hydrogen.

[0092] In this way, by actively introducing Ni to Na2O, thermodynamically stable Na2NiO2 can be produced. Hydrogen can then be generated by reacting the NaOH produced by hydrolysis of this Na2NiO2 with the Na produced along with Na2NiO2. Since this reaction proceeds at a lower temperature than the reaction temperature of conventional thermodynamic hydrogen reactions (e.g., 500°C), corrosion of the reaction vessel caused by the reaction of Na2O with the metal of the reaction vessel can be prevented.

[0093] Furthermore, in the reduction step of the hydrogen production method of this embodiment, nickel and sodium hydroxide are produced by reacting the sodium oxide produced in the sodium production step with water, and in the hydrogen production step, hydrogen and sodium oxide are produced by reacting the sodium produced in the sodium production step with the sodium hydroxide produced in the reduction step.

[0094] Thus, since the Ni and Na2O consumed in the sodium generation process are regenerated in the reduction and hydrogen generation processes, respectively, a redox cycle (Na-redox cycle) consisting of the sodium generation, reduction, and hydrogen generation processes is established. This allows for the efficient production of hydrogen.

[0095] Furthermore, the hydrogen production apparatus of this embodiment includes a reaction vessel made of a nickel alloy material that carries out each of the following reactions: a sodium production step in which sodium oxide is reacted with a metal containing at least one of nickel, iron, molybdenum, tungsten, or aluminum to produce an oxide of the metal and sodium, and sodium; a reduction step in which the oxide produced in the sodium production step is reacted with water to produce sodium hydroxide; and a hydrogen production step in which the sodium produced in the sodium production step and the sodium hydroxide produced in the reduction step are reacted to produce hydrogen.

[0096] This allows for efficient hydrogen production at low temperatures while effectively suppressing corrosion of the reaction vessel using a nickel alloy.

[0097] Furthermore, the hydrogen production apparatus of this embodiment includes a temperature control device for heating the reaction vessel, a water supply unit for supplying water to the reaction vessel, an oxygen discharge unit for discharging the generated oxygen from the reaction vessel, a sodium storage unit for storing the generated sodium and introducing the stored sodium into the reaction vessel, and a hydrogen recovery unit for recovering the generated hydrogen.

[0098] This apparatus configuration makes it possible to realize an oxidation-reduction cycle reaction consisting of a sodium generation step, a reduction step, and a hydrogen generation step.

[0099] The above description of embodiments is for the purpose of facilitating understanding of the present invention and does not limit it. The present invention can be modified and improved without departing from its spirit, and equivalents thereof are included. [Explanation of Symbols]

[0100] 10 Hydrogen production equipment, 20 Reaction vessel, 30 Temperature control device, 40 Water supply unit, 50 Sodium storage unit, 60 Oxygen discharge unit, 70 Hydrogen recovery unit

Claims

1. A sodium production step involves reacting sodium oxide with a metal containing at least one of nickel, iron, molybdenum, tungsten, or aluminum to produce an oxide containing the metal and sodium, and sodium. A reduction step in which the oxide produced in the sodium production step is reacted with water to produce sodium hydroxide, A hydrogen generation step in which the sodium produced in the sodium production step and the sodium hydroxide produced in the reduction step are reacted to produce hydrogen. A method for producing hydrogen.

2. In the reduction step, the oxide produced in the sodium production step is reacted with water to produce the metal and sodium hydroxide. In the hydrogen generation step, the sodium produced in the sodium generation step and the sodium hydroxide produced in the reduction step are reacted to produce hydrogen and sodium oxide. The hydrogen production method according to claim 1.

3. The hydrogen production method according to claim 1, wherein the reaction temperature in the sodium production step is set to 200°C or higher.

4. The hydrogen production method according to claim 1, wherein the reaction temperature in the sodium production step is set to 300°C or lower.

5. The hydrogen production method according to claim 1, wherein the reaction temperature in the hydrogen production step is set to 350°C or lower.

6. The hydrogen production method according to claim 1, wherein each of the reactions in the sodium production step, the reduction step, and the hydrogen production step is carried out in a reaction vessel made of a material containing a nickel alloy.

7. In the sodium production step, sodium oxide and nickel are reacted to produce nickel sodium oxide and sodium. In the reduction step, the sodium nickel oxide produced in the sodium production step is reacted with water to produce sodium hydroxide. In the hydrogen generation step, the sodium produced in the sodium generation step and the sodium hydroxide produced in the reduction step are reacted to produce hydrogen. The hydrogen production method according to claim 1.

8. In the reduction step, the sodium nickel oxide produced in the sodium production step is reacted with water to produce nickel and sodium hydroxide. In the hydrogen generation step, the sodium produced in the sodium generation step and the sodium hydroxide produced in the reduction step are reacted to produce hydrogen and sodium oxide. The hydrogen production method according to claim 7.

9. A hydrogen production apparatus comprising a reaction vessel made of a nickel alloy material, which carries out the following reactions: a sodium production step in which sodium oxide is reacted with a metal containing at least one of nickel, iron, molybdenum, tungsten, or aluminum to produce an oxide of the metal and sodium and sodium; a reduction step in which the oxide produced in the sodium production step is reacted with water to produce sodium hydroxide; and a hydrogen production step in which the sodium produced in the sodium production step and the sodium hydroxide produced in the reduction step are reacted to produce hydrogen.

10. The hydrogen production apparatus according to claim 9, comprising: a temperature control device for heating the reaction vessel; a water supply unit for supplying water to the reaction vessel; an oxygen discharge unit for discharging the generated oxygen from the reaction vessel; a sodium storage unit for storing the generated sodium and introducing the stored sodium into the reaction vessel; and a hydrogen recovery unit for recovering the generated hydrogen.

Images