Hydrogen production method

Abstract

To provide a hydrogen production method which can achieve improved hydrogen production efficiency.SOLUTION: A hydrogen production method includes milling and mixing a material to be milled and a solvent with a milling device having a container storing a milling medium to produce hydrogen by a mechanochemical reaction. The solvent includes water. The material to be milled is an inorganic oxide which is oxidized by the mechanochemical reaction, resulting in the substance which serves as an oxidant for an inorganic substance constituting at least one of the milling medium and the container.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The technology disclosed herein belongs to the technical field related to a method for producing hydrogen. [Background technology]

[0002] In recent years, there has been a worldwide demand for the promotion of the use of natural energy. One such proposal is to use hydrogen as an energy source. For example, hydrogen is used as fuel in fuel cells for automobiles. Hydrogen itself can also be used as a gaseous fuel. Because the exhaust gases from these automobiles do not contain carbon dioxide, hydrogen energy has attracted attention as an energy source that can curb global warming and environmental pollution.

[0003] A method for producing hydrogen has been known in the past, in which fossil fuels such as natural gas are steam reformed, but this method generates carbon dioxide during the hydrogen production process.

[0004] Therefore, for example, a manufacturing method such as that described in Patent Document 1 has been proposed in which an inorganic substance such as silicon (Si) or aluminum (Al) is ground and mixed with a solvent using a planetary ball mill having a container containing a grinding medium, and hydrogen is produced by a mechanochemical reaction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-47789 A Summary of the Invention [Problem to be solved by the invention]

[0006] Generally, an oxide film is formed on the surface of an inorganic material, particularly on the surface of a metal, by reaction with oxygen in the air. Since part of the inorganic material becomes the oxide film, the actual amount of the inorganic material alone is smaller than the theoretical amount. In particular, when the inorganic material is in powder form, the surface area is large, and the proportion of the oxide film also increases accordingly. If the proportion of the oxide film increases, the hydrogen production efficiency relative to the amount of material to be crushed decreases. On the other hand, in order to efficiently proceed with the mechanochemical reaction, it is preferable for the surface area of ​​the material to be crushed to be large.

[0007] As described in Patent Document 1, when inorganic substances are used, the above-mentioned trade-off relationship occurs, and therefore there is room for improvement in order to increase the efficiency of hydrogen production.

[0008] The technology disclosed herein has been made in consideration of the above points, and has an object to provide a hydrogen production method capable of improving the efficiency of hydrogen production. [Means for solving the problem]

[0009] In order to solve the above problems, a first aspect of the technology disclosed herein is directed to a hydrogen production method in which a grinding device having a container containing grinding media is used to grind and mix materials to be ground with a solvent to produce hydrogen by a mechanochemical reaction, the solvent containing water, and the materials to be ground are inorganic oxides that, after being oxidized by the mechanochemical reaction, act as an oxidizing agent for the inorganic material constituting at least one of the grinding media and the container.

[0010] That is, when a mechanochemical reaction proceeds between the inorganic oxide and water, the inorganic oxide is oxidized to generate an oxide with a higher oxidation number. At this time, the water is reduced to generate hydrogen. If the generated oxide (the oxide with a higher oxidation number) becomes an oxidizing agent for the inorganic substance constituting at least one of the grinding medium and the container, the inorganic substance is oxidized by a mechanochemical reaction. On the other hand, the oxidized inorganic oxide is reduced to generate the original inorganic oxide. After that, when the reduced inorganic oxide is oxidized by the mechanochemical reaction, hydrogen is generated again. This process is repeated to continue producing hydrogen.

[0011] In addition, since the material to be crushed is an inorganic oxide, even if it is exposed to air, the surface is unlikely to turn into another oxide film. Therefore, even if the material is made into a powder and the surface area is increased, the proportion of inorganic oxide itself can be increased.

[0012] Therefore, the efficiency of hydrogen production can be improved.

[0013] In a second aspect of the technology disclosed herein, in the first aspect, the material to be crushed is chromium oxide (Cr 2 O 3 ), iron(III) oxide (Fe 2 O 3 ), or nickel(II) oxide (NiO).

[0014] For example, chromium oxide (Cr 2 O 3 ) is oxidized by mechanochemical reaction as follows: Cr 2 O 3 + 5H 2 O → 2CrO 4 2- + 4H + + 3H 2 This chromate ion (CrO 4 2- ) has an oxidation number of 6 and acts as a strong oxidizing agent, oxidizing the inorganic materials that make up the grinding media and container. This results in CrO 42- It is reduced to Cr 2 O 3 This process is repeated to continue producing hydrogen. Therefore, with the above-described configuration, it is possible to further improve the efficiency of hydrogen production.

[0015] In a third aspect of the technique disclosed herein, in the second aspect, at least one of the grinding medium and the container is made of stainless steel.

[0016] That is, stainless steel contains iron as an inorganic substance. Since iron is easily oxidized, it is relatively easily oxidized by the oxidizing agent generated by the oxidation of the crushed material. As a result, the crushed material easily returns to its original inorganic oxide, and the hydrogen production efficiency can be further improved.

[0017] In a fourth aspect of the technology disclosed herein, in any one of the first to third aspects, the grinding device is a planetary ball mill using balls as grinding media, and the rotation speed of the planetary ball mill is 200 rpm to 700 rpm.

[0018] The inventors of the present application have conducted extensive research and found that when the rotation speed of a planetary ball mill is set to 200 rpm or more, supercritical water is generated locally when the grinding media collide with the container wall or when the grinding media collide with each other. When supercritical water is generated, the oxidation of inorganic oxides is promoted, making it easier to produce hydrogen. This can further improve the efficiency of hydrogen production.

[0019] A fifth aspect of the technology disclosed herein relates to a method for producing hydrogen by a mechanochemical reaction, in which a grinding device having a container containing grinding media is used to grind and mix materials to be ground, a solvent, and a reaction promoter, and hydrogen is produced by a mechanochemical reaction, in which the solvent contains water, and the materials to be ground are oxidized by the mechanochemical reaction, and the oxidized material is an inorganic oxide that serves as an oxidizing agent for the inorganic substance that constitutes the reaction promoter.

[0020] According to this configuration, even if the grinding medium and the container are made of materials that are difficult to oxidize, the reaction accelerator is oxidized, thereby reducing the grinding, thereby improving the efficiency of hydrogen production.

[0021] In a sixth aspect of the technology disclosed herein, in the fifth aspect, the material to be crushed is chromium oxide (Cr 2 O 3 ).

[0022] As described above, by using these inorganic oxides as the grinding material, the efficiency of hydrogen production can be further improved.

[0023] A seventh aspect of the technique disclosed herein is the sixth aspect, wherein the reaction accelerator is iron particles.

[0024] As described above, iron is easily oxidized, and is therefore relatively easily oxidized by the oxidizing agent produced by the oxidation of the crushed material. This produces the original inorganic oxide, which can further improve the efficiency of hydrogen production.

[0025] In an eighth aspect of the present disclosure, in any one of the fifth to seventh aspects, the grinding medium and the container are made of zirconia (ZrO 2 ).

[0026] According to this configuration, since the zirconia is already oxidized, it is difficult for the oxidizing reaction to occur even if the crushed material is oxidized to become an oxidizing agent, which makes it possible to extend the life of the container and stably produce hydrogen for a long period of time. Effect of the Invention

[0027] As described above, according to the technique disclosed herein, it is possible to improve the efficiency of hydrogen production. [Brief description of the drawings]

[0028] [Figure 1]FIG. 1 is a cross-sectional view showing the configuration of a planetary ball mill used in the hydrogen production method according to the first embodiment. [Diagram 2] FIG. 2 is a diagram for explaining the movement of the material and the grinding media inside the container of the planetary ball mill apparatus of FIG. [Diagram 3] FIG. 3 is a schematic diagram illustrating the process of producing hydrogen. [Figure 4] FIG. 4 is a diagram for explaining the movement of the material and the grinding media inside the container of the planetary ball mill apparatus in the second embodiment. [Diagram 5] FIG. 5 shows the results of gas chromatography of the gas generated when the material to be crushed was chromium oxide. [Figure 6] FIG. 6 shows the results of gas chromatography of the gas generated when the material to be crushed was chromium. [Figure 7] FIG. 7 is a graph showing the amount of hydrogen produced when the material to be crushed is chromium oxide and when the material to be crushed is chromium. [Figure 8] FIG. 8 is a graph showing the relationship between the materials of the grinding media and container of the planetary ball mill and the amount of hydrogen produced. [Figure 9] FIG. 9 is a graph showing the relationship with the amount of hydrogen produced when no crushed material is fed. [Figure 10] FIG. 10 is a graph showing the relationship between the rotation speed of the planetary ball mill and the amount of hydrogen produced. [Figure 11] FIG. 11 is a graph showing the relationship between the atmosphere in the container and the amount of hydrogen produced when the material to be crushed is chromium oxide. [Figure 12] FIG. 12 is a graph showing the relationship between the atmosphere in the container and the amount of hydrogen produced when the material to be crushed is titanium. [Figure 13] FIG. 13 is a graph showing the relationship between the presence or absence of a reaction accelerator and the amount of hydrogen produced. [Figure 14] FIG. 14 is a graph showing the amount of hydrogen produced when the materials to be crushed are iron oxide (III), iron oxide (II,III), iron oxide (II), and iron. [Figure 15] FIG. 15 is a graph showing the amount of hydrogen produced when the material to be crushed is nickel (II) oxide and when it is nickel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. Note that the following embodiments are merely illustrative and should not be interpreted as limiting the scope of the present invention. The scope of the present invention is defined by the claims, and all modifications and changes within the scope of the claims are within the scope of the present invention.

[0030] (Embodiment 1) FIG. 1 is a cross-sectional view showing the configuration of a planetary ball mill device 1 as a pulverizing device used in the hydrogen production method according to the first embodiment.

[0031] The first embodiment is a method for producing hydrogen at room temperature by a mechanochemical reaction in which inorganic oxides as the material 3 and water as the solvent 4 are pulverized and mixed using a planetary ball mill 1, and mechanical energy is applied by friction, impact, or the like to increase the activity of the material 3 and the solvent 4. As an apparatus for carrying out this mechanochemical reaction, any apparatus can be used, not limited to the planetary ball mill 1, as long as it is an apparatus equipped with a reaction vessel 5 and containing a grinding medium 2 for applying mechanical energy in the vessel 5. From the viewpoint of stirring efficiency and energy application efficiency, the planetary ball mill 1 having a vessel 5 containing the grinding medium 2 is preferable. As an apparatus, in addition to the planetary ball mill, a ball mill, a bead mill, a rod mill, a jet mill, a SAG mill, a ROM mill, a rotary stone mill, and the like are selected.

[0032] The planetary ball mill apparatus 1 is composed of a rotating shaft 11 that is driven to rotate around its central axis, a table 6 that rotates integrally with the rotating shaft 11, two containers 5 (mill pots) rotatably supported on the table 6 via a casing 13, and a plurality of grinding media 2 (balls) housed in each of the two containers 5. The table 6 functions as a rotatable support member while rotatably supporting the two containers 5.

[0033] The container 5 is a cylindrical body with a top lid attached, which is inserted into the casing 13 from above and fixed thereto. The container 5 is configured so that the top lid is opened and the grinding media 2 and materials (particularly inorganic oxides and water) are put in. The container 5 is preferably made of a material that contains an inorganic substance that is easily oxidized, for example, stainless steel (SUS). The size of the container 5 is not particularly limited, and may be, for example, 40 cm 3 A container having a volume of 0.1 to 1.0 can be used.

[0034] The grinding media 2 may be substantially spherical. The size of the grinding media 2 is not particularly limited, and grinding media 2 having diameters of, for example, 1.6 mm, 5 mm, and 10 mm may be used, and grinding media 2 of various sizes may be combined. In addition, the material of the grinding media 2 is preferably one containing an inorganic substance that is easily oxidized, for example, stainless steel (SUS). The grinding media 2 may be a combination of grinding media 2 made of various materials.

[0035] In addition, as long as at least one of the materials of the container 5 and the grinding media 2 contains an inorganic substance that is easily oxidized, the material of the container 5 and the material of the grinding media 2 may be different. For example, the material of the container 5 may be stainless steel (SUS), and the material of the grinding media 2 may be tungsten carbide (WC).

[0036] The planetary ball mill apparatus 1 is a ball mill apparatus capable of adjusting the rotation speed of the rotating shaft 11 and the rotation speed of the container 5. Each of the rotation speeds is set to a value at which hydrogen is efficiently produced.

[0037] In the present embodiment, the material 3 to be crushed is an inorganic oxide that is oxidized by a mechanochemical reaction and the oxidized material serves as an oxidizing agent for the inorganic material constituting at least one of the grinding medium 2 and the container 5. More specifically, the material 3 to be crushed is chromium oxide (Cr 2 O 3 ), iron(III) oxide (Fe 2 O 3 ), and nickel oxide (NiO).

[0038] Next, chromium oxide (Cr 2 O 3 The following description will be given of a case where hydrogen is produced using Cr 2 , and using stainless steel (SUS) as the grinding medium 2 and the container 5. In the following description, "chromium oxide" is defined as Cr 2 O 3 "Stainless Steel" means SUS.

[0039] First, as shown in Fig. 2, chromium oxide powder and water are charged into each container 5 containing the grinding media 2. Next, the container 5 is inserted into and fixed in the casing 13 provided on the table 6 shown in Fig. 1.

[0040] Next, the planetary ball mill apparatus 1 is driven. As a result, a gear (not shown) attached to the rotating shaft 11 meshes with a gear (not shown) attached to each casing 13, causing each container 5 to revolve around the rotating shaft 11 while each container 5 itself rotates around a rotating shaft (not shown) separate from the rotating shaft 11.

[0041] 3 is a schematic diagram showing a hydrogen production mechanism when chromium oxide is used as the material 3 to be crushed. The reaction shown in FIG.

[0042] As shown in FIG. 3, when the grinding media 2 and the container 5 or the grinding media 2 collide with each other in the planetary ball mill apparatus 1, a mechanochemical reaction proceeds, and chromium oxide is oxidized and hydrogen is generated as described below. Cr 2 O3 + 5H 2 O → 2CrO 4 2- + 4H + + 3H 2 In particular, the water becomes in a high-temperature and high-pressure state due to the collision between the grinding media 2 and the container 5, or between the grinding media 2 and each other, and supercritical water is generated locally. This supercritical water and chromium oxide undergo an oxidation-reduction reaction to produce chromate ions (CrO 4 2- In addition, by pulverizing the chromium oxide, the size of the chromium oxide is reduced and the surface area of ​​the chromium oxide is increased, so that a mechanochemical reaction can proceed with respect to the chromium oxide in the container 5.

[0043] When the grinding media 2 and the container 5, or the grinding media 2 collide with each other, parts of the grinding media 2 and the container 5 are scraped off. As a result, inorganic substances that make up stainless steel, such as iron, chromium, and nickel, are present in the water.

[0044] When iron is present in water, a mechanochemical redox reaction occurs between chromate ions and iron, as shown in Figure 3. In particular, chromate ions have an oxidation number of 6 and function as a strong oxidizing agent, so the reaction proceeds as follows: 8CrO 4 2- +9Fe+16H + → 4Cr 2 O 3 + 3Fe 3 O 4 + 8H 2 O In other words, the oxidized chromium oxide is reduced by oxidizing iron, producing the original chromium oxide.

[0045] As shown in Figure 3, when chromium oxide is generated by the redox reaction, the generated chromium oxide is re-oxidized by the mechanochemical reaction, and hydrogen is generated again. This process is repeated, and hydrogen continues to be generated.

[0046] Therefore, in this embodiment 1, in the method for producing hydrogen by a mechanochemical reaction by grinding and mixing the material 3 and the solvent 4 using a planetary ball mill 1, the solvent 4 contains water, and the material 3 is an inorganic oxide that is oxidized by a mechanochemical reaction and the oxidized material becomes an oxidizing agent for the inorganic material constituting at least one of the grinding medium 2 and the container 5. Since the material 3 is an inorganic oxide, even if it is exposed to air, the surface is unlikely to become another oxide film. Therefore, even if the surface area is increased by making it into a powder, the proportion of the inorganic oxide itself can be made high. In addition, after being oxidized by a redox reaction with water, the original inorganic oxide is generated by a redox reaction with the inorganic material constituting at least one of the grinding medium 2 and the container 5, so that hydrogen can be continuously produced. In addition, when the amount of water is low, hydrogen can be produced again by adding water. Therefore, the efficiency of hydrogen production can be improved.

[0047] (Embodiment 2) Hereinafter, a detailed description will be given of the embodiment 2. In the following description, the same reference numerals will be used to designate the same parts as those in the embodiment 1, and detailed description thereof will be omitted.

[0048] The second embodiment differs from the first embodiment in that, in addition to the material 3 and water, iron is also used as a reaction accelerator. 2 ) in that the second embodiment differs from the first embodiment.

[0049] Specifically, in the second embodiment, as shown in Fig. 4, the material to be crushed 3, iron particles 200, and water are charged into a container 5, and are pulverized and mixed by a planetary ball mill device 1. The material to be crushed 3 is an inorganic oxide similar to that in the first embodiment.

[0050] Since the material of the grinding medium 2 and the material of the container 5 are zirconia, even if the material 3 to be crushed is oxidized, it does not undergo an oxidation-reduction reaction with the inorganic substances constituting the grinding medium 2 and the container 5. Instead, the oxide of the material 3 to be crushed undergoes an oxidation-reduction reaction with the iron particles 200. The original inorganic oxide is generated by the oxidation-reduction reaction of the oxide of the material 3 to be crushed with the iron particles 200. This makes it possible to produce hydrogen again from the inorganic oxide.

[0051] Therefore, according to this embodiment 2, by using an inorganic oxide as the material to be crushed 3, which is oxidized by a mechanochemical reaction and the oxidized material becomes an oxidizing agent for the inorganic substance constituting the reaction promoter, the hydrogen production efficiency can be improved.

[0052] (Other embodiments) The technology disclosed herein is not limited to the above-described embodiment, and may be substituted without departing from the spirit and scope of the claims.

[0053] For example, in the above-described first and second embodiments, water is used as the solvent. However, the solvent is not limited to this, and water (H 2 O), and may be, for example, seawater or an alkaline solution. EXAMPLES

[0054] The present invention will be described below based on examples. Note that the present invention is not limited to these examples, and these examples can be modified or changed based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

[0055] In the following explanation, "chromium oxide" means Cr 2 O 3 means that "chromate ion" is CrO 4 2- "Iron(III) oxide" means Fe 2 O 3 "Iron(II,III) oxide" means Fe 3 O 4"iron(II) oxide" means FeO, and "ferrate ion" means FeO 4 2- "Nickel(II) oxide" means NiO, "Nickel(III) oxide" means Ni 2 O 3 "Nickel oxyhydroxide" means NiO(OH), and "stainless steel" means SUS.

[0056] Example 1 A planetary ball mill (manufactured by Fritsch, Germany, product name: Premium Line P-7) was used to grind and mix chromium oxide and water to produce hydrogen. More specifically, 2 mmol of chromium oxide was charged as the grinding material and 560 mmol of water was charged as the solvent into a container (made of stainless steel) containing a grinding medium made of stainless steel. The planetary ball mill was then rotated at a rotation speed of 400 rpm for 600 minutes to grind and mix chromium oxide and water, thereby generating hydrogen. The atmosphere inside the container was argon.

[0057] Comparative Example 1 Hydrogen was produced under the same conditions as in Example 1, except that the powder contained 2 mmol of chromium.

[0058] Qualitative analysis by gas chromatography The container was connected to a sampling bag and a vacuum pump, and the connection line was evacuated to move the gas in the container to the sampling bag. The container was then connected to a cylinder filled with argon gas, and the container was filled with argon gas until the internal pressure of the sampling bag reached 1 atm.

[0059] The gas in the sampling bag was then collected using a syringe, and a qualitative analysis of the gas was performed using a gas chromatograph mass spectrometer (manufactured by Shimadzu Corporation).

[0060] 5 and 6, it can be seen that a very strong hydrogen peak (retention time: 1 minute) can be confirmed in both Example 1 and Comparative Example 1. It can also be seen that there are no significant peaks other than hydrogen. From the above, it was confirmed that hydrogen was generated in both Example 1 and Comparative Example 1.

[0061] Next, the results of calculating the amount of hydrogen produced in Example 1 and Comparative Example 1 are shown in FIG.

[0062] As shown in Figure 7, when the material is chromium oxide, the amount of hydrogen produced is significantly greater than when the material is chromium. Specifically, at 600 minutes of milling time, the amount of hydrogen produced was about five times as much. In particular, although theoretically 6 mmol of hydrogen is produced from 2 mmol of chromium oxide, more than 6 mmol of hydrogen was produced.

[0063] In addition, when the material is chromium oxide, the amount of hydrogen produced increases almost linearly with respect to the milling time, whereas when the material is chromium, hydrogen production becomes difficult (the hydrogen production rate decreases) when the milling time exceeds 200 minutes. As described above, when the material is chromium oxide, hydrogen continues to be produced by repeating oxidation-reduction between the inorganic material constituting the grinding medium and the container and chromium oxide. On the other hand, when the material is chromium, hydrogen production becomes difficult when most of the input chromium is oxidized. In fact, theoretically, 3 mmol of hydrogen is produced from 2 mmol of chromium, but referring to FIG. 7, it can be seen that the amount of hydrogen produced converges to around 3 mmol. Therefore, the amount of hydrogen produced when the material is chromium oxide is significantly different from that when the material is chromium.

[0064] The difference in hydrogen production rate is considered to be due to the difference in local temperature when the grinding media 2 and the container 5, or when the grinding media 2 collide with each other. In fact, when the local temperature is calculated for chromium and chromium oxide, it is about 400°C when the material is chromium, and about 1000°C when the material is chromium oxide. When the local temperature is difficult to increase, the mechanochemical reaction is difficult to proceed, and hydrogen is difficult to produce. As a result, the hydrogen production rate is slower when the material is chromium than when the material is chromium oxide.

[0065] It is considered that when the material to be crushed is chromium, chromium oxide is produced in the process of producing hydrogen. However, as shown in FIG. 5, the results are different when the material to be crushed is chromium and when the material to be crushed is chromium oxide. This result is considered to be due to the fact that chromium spreads along the wall of the crushing medium or container to form a film during the process of crushing and mixing chromium. Since the chromium that has become this film itself acts as a shock absorber, even if the surface area of ​​the film becomes chromium oxide through a mechanochemical reaction, the central part of the film does not become chromium oxide and remains as chromium. It is considered that the remaining chromium acts as a shock absorber, making it difficult for the oxidation reaction from chromium oxide to chromate ions and the reduction reaction from chromate ions to chromium oxide to proceed.

[0066] Comparative Example 2 Hydrogen was produced under the same conditions as in Example 1, except that the grinding media and the container were made of tungsten carbide (WC).

[0067] Comparative Example 3 The grinding media and container are made of zirconia (ZrO 2 Hydrogen was produced under the same conditions as in Example 1, except that

[0068] Comparative Example 4 Hydrogen was produced under the same conditions as in Example 1, except that no crushed material was added.

[0069] Comparative Example 5 Hydrogen was produced under the same conditions as in Comparative Example 2, except that no crushed material was added.

[0070] Comparative Example 6 Hydrogen was produced under the same conditions as in Comparative Example 3, except that no crushed material was added.

[0071] <Relationship between the materials of grinding media and container and the amount of hydrogen produced> 8 shows the results of calculating the amounts of hydrogen produced in Example 1, Comparative Example 2, and Comparative Example 3. FIG. 9 shows the results of calculating the amounts of hydrogen produced in Comparative Examples 4-6.

[0072] As shown in Figure 8, when the grinding media and container are stainless steel, the amount of hydrogen produced is significantly greater than when the grinding media and container are tungsten carbide or zirconia. As shown in Figure 9, when no material is added, almost no hydrogen is produced, regardless of the material of the grinding media, etc. From this, it can be said that the reason why the amount of hydrogen produced is greater when the grinding media, etc. are stainless steel is not because the grinding media or container themselves are raw materials and hydrogen is generated, but because of the combination of the material of the grinding media, etc.

[0073] As mentioned above, stainless steel contains iron. Since iron is particularly easily oxidized, when the grinding medium, etc. is made of stainless steel, chromate ions are easily reduced. On the other hand, inorganic substances constituting tungsten carbide and zirconia are not easily oxidized. In particular, since zirconia is already oxidized, it is basically not further oxidized. For this reason, it is considered that the amount of hydrogen produced is significantly higher when the grinding material is chromium oxide and the grinding medium, etc. is stainless steel. Furthermore, when the grinding medium, etc. is tungsten carbide, the amount of hydrogen produced is greater than when the grinding medium, etc. is zirconia. This is because tungsten is not as easily oxidized as iron, but is more easily oxidized than zirconia.

[0074] Example 2 Hydrogen was produced under the same conditions as in Example 1, except that the rotation speed of the planetary ball mill was set to 100 rpm.

[0075] Example 3 Hydrogen was produced under the same conditions as in Example 1, except that the rotation speed of the planetary ball mill was set to 200 rpm.

[0076] Example 4 Hydrogen was produced under the same conditions as in Example 1, except that the rotation speed of the planetary ball mill was set to 500 rpm.

[0077] Example 5 Hydrogen was produced under the same conditions as in Example 1, except that the rotation speed of the planetary ball mill was set to 600 rpm.

[0078] Example 6 Hydrogen was produced under the same conditions as in Example 1, except that the rotation speed of the planetary ball mill was set to 700 rpm.

[0079] <Relationship between rotation speed and hydrogen production amount> FIG. 10 shows the amount of hydrogen produced in Examples 1 to 6. As shown in FIG. 10, it can be seen that the higher the rotation speed, the higher the hydrogen production rate. In particular, it can be seen that hydrogen is produced efficiently when the rotation speed is 200 rpm or more. This is because when the rotation speed is 200 rpm or more, when the container and the grinding media or the grinding media collide with each other, the water becomes in a high temperature and high pressure state, and supercritical water is generated locally. It is considered that the hydrogen production rate will increase even if the rotation speed is further increased from 700 rpm, but considering the damage to the device itself, it is preferable to set the upper limit of the rotation speed to about 700 rpm. Therefore, hydrogen can be produced efficiently by setting the rotation speed of the planetary ball mill to 200 rpm to 700 rpm.

[0080] Example 7 Hydrogen was produced under the same conditions as in Example 1, except that the atmosphere inside the vessel was air.

[0081] Comparative Example 7 Hydrogen was produced under the same conditions as in Example 1, except that the crushed material contained 2 mmol of titanium.

[0082] Comparative Example 8 Hydrogen was produced under the same conditions as in Comparative Example 7, except that the atmosphere inside the container was air.

[0083] <Relationship between the atmosphere in the container and the amount of hydrogen produced> 11 shows the amount of hydrogen produced in Examples 1 and 7. FIG. 12 shows the amount of hydrogen produced in Comparative Examples 7 and 8.

[0084] As shown in Fig. 11, when the material to be ground was chromium oxide, the amount of hydrogen produced was slightly greater in the argon atmosphere, but similar trends were observed whether the atmosphere in the container was air or argon. At 600 minutes of milling time, the difference in the amount of hydrogen produced between the air atmosphere and the argon atmosphere was about 6%.

[0085] As shown in Figure 12, when the material to be crushed is titanium, the same tendency is observed up to about 100 minutes of milling time, whether the atmosphere in the container is air or argon. In the case of an air atmosphere, the production rate decreases once the milling time exceeds 100 minutes. In the case of an argon atmosphere, the production rate decreases once the milling time exceeds 200 minutes. The difference in the amount of hydrogen produced at 600 minutes of milling time was about 21%.

[0086] From this result, it can be seen that when the material is chromium oxide, the hydrogen production efficiency is hardly affected by the atmosphere in the vessel. This is because, while the surface of a metal material such as titanium is oxidized in air, and the amount of metal actually used for hydrogen production becomes less than the theoretical amount, inorganic oxides such as chromium oxide are not oxidized in air.

[0087] Therefore, it can be said that the use of inorganic oxides as the particles to be crushed can stabilize the efficiency of hydrogen production more than the use of metals as the particles to be crushed.

[0088] Example 8 A planetary ball mill (manufactured by Fritsch, Germany, product name: Premium Line P-7) was used to grind and mix chromium oxide and water to produce hydrogen. More specifically, 1 mmol of chromium oxide was charged as a grinding material into a container (made of zirconia) containing grinding media made of zirconia, and 560 mmol of water was charged as a solvent, and iron particles were also charged as a reaction accelerator. The planetary ball mill was then rotated at a rotation speed of 400 rpm for 600 minutes to grind and mix chromium oxide, water, and iron to produce hydrogen. The atmosphere in the container was argon.

[0089] Comparative Example 9 Hydrogen was produced under the same conditions as in Example 8, except that the crushed material was iron particles only.

[0090] <Hydrogen production using oxide grinding media and vessels> FIG. 13 shows the amount of hydrogen produced in Example 8 and the combined amount of hydrogen produced in Comparative Examples 3 and 9.

[0091] As shown in FIG. 13, the amount of hydrogen produced when chromium oxide and iron particles are added is greater than the total amount of hydrogen produced when only chromium oxide and only iron particles are added. This does not mean that the amount of hydrogen produced is increased by the amount of hydrogen produced by the reaction between water and iron particles, but that a synergistic effect is achieved by adding both chromium oxide and iron particles to a common container. Specifically, this means that the iron particles as a reaction promoter reduce chlorine ions through a mechanochemical reaction to produce chromium oxide. Therefore, even if the container itself is an oxide, the hydrogen production efficiency can be improved by adding iron particles as a reaction promoter. This allows the grinding medium and the container to be maintained in a constant state, which is advantageous when hydrogen is produced for a long period of time.

[0092] In Example 8, unlike the case where the grinding media is stainless steel, the hydrogen production rate decreases when the milling time exceeds 100 minutes. This is because the amount of iron that can reduce chromate ions is smaller than when the grinding media is stainless steel. Therefore, when hydrogen is to be produced for a long period of time, it is necessary to replenish iron particles in addition to water.

[0093] Example 9 Hydrogen was produced under the same conditions as in Example 1, except that the ground material was changed to 2 mmol of iron (III) oxide.

[0094] Example 10 Hydrogen was produced under the same conditions as in Example 1, except that the ground material was 2 mmol of nickel (II) oxide.

[0095] Comparative Example 10 Hydrogen was produced under the same conditions as in Example 1, except that the ground material was changed to 2 mmol of iron oxide (II, III).

[0096] Comparative Example 11 Hydrogen was produced under the same conditions as in Example 1, except that the ground material was changed to 2 mmol of iron (II) oxide.

[0097] Comparative Example 12 Hydrogen was produced under the same conditions as in Example 1, except that the crushed material was changed to 2 mmol of iron.

[0098] Comparative Example 13 Hydrogen was produced under the same conditions as in Example 1, except that the crushed material was changed to 2 mmol of nickel.

[0099] <Production of hydrogen using other inorganic oxides> 14 shows the amount of hydrogen produced in Example 9 and Comparative Examples 10 to 12. FIG 15 shows the amount of hydrogen produced in Example 10 and Comparative Example 12.

[0100] As shown in Figure 14, when the material to be crushed is iron oxide (III), the amount of hydrogen produced is greater than when the material is iron oxide (II, III), iron oxide (II), or elemental iron. This is thought to be because, as when the material to be crushed is chromium oxide, the product produced by the oxidation of iron oxide (III) through a mechanochemical reaction oxidizes the iron constituting the grinding medium, etc., and the original iron oxide (III) is produced again.

[0101] Specifically, when iron oxide (III) and water are pulverized and mixed in a planetary ball mill, the iron oxide (III) is oxidized to generate ferric oxide ions and hydrogen, as shown below. Fe 2 O 3 + 5H 2 O → 2FeO 4 2- + 4H + + 3H 2 Ferrate ions have an oxidation number of 6 and function as a strong oxidizing agent. Since iron, which is a constituent material of the grinding media, is present in the water, a mechanochemical reaction occurs between the ferrate ions and iron, causing an oxidation-reduction reaction. The reaction proceeds as follows: 8FeO 4 2- +9Fe+16H + → 4Fe 2 O 3 +3Fe 3 O 4 +8H 2 O In other words, when iron(III) oxide is oxidized, the oxide (ferrate ion) is reduced by oxidizing iron, producing the original iron(III) oxide.

[0102] When iron oxide (III) is generated by the oxidation-reduction reaction, the generated iron oxide (III) is re-oxidized by the mechanochemical reaction, and hydrogen is generated again. This process is repeated, and hydrogen continues to be generated. Therefore, even when the material is iron oxide (III), the hydrogen production efficiency can be improved.

[0103] As shown in Fig. 15, when the material to be crushed is nickel alone, almost no hydrogen is produced, whereas when the material to be crushed is nickel oxide (II), hydrogen is produced. This is thought to be because, as in the case when the material to be crushed is chromium oxide, the product produced by the oxidation of nickel oxide (II) through a mechanochemical reaction oxidizes the iron constituting the grinding medium, etc., and the original nickel oxide (II) is produced again.

[0104] Specifically, when nickel oxide (II) and water are pulverized and mixed in a planetary ball mill, nickel oxide (II) is oxidized to produce nickel oxide (III) and nickel oxyhydroxide, and hydrogen is produced, as shown below. 2NiO + H 2 O → Ni 2 O 3 + H 2 2NiO + 2H 2 O → 2NiO(OH) + H 2 On the other hand, since iron constituting the grinding medium is present in the water, a mechanochemical reaction occurs in which nickel oxide (III) and nickel oxyhydroxide react with iron to produce a redox reaction. The reaction proceeds as follows: 4Ni 2 O 3 + 3Fe → 8NiO + Fe 3 O 4 8NiO(OH) + 3Fe → 8NiO + Fe 3 O 4 + 4H 2 O In other words, nickel(II) oxide is oxidized to oxides (nickel(III) oxide and nickel oxyhydroxide), which are then reduced by oxidizing iron to produce the original nickel(II) oxide.

[0105] When nickel oxide (II) is generated by the oxidation-reduction reaction, the generated nickel oxide (II) is re-oxidized by the mechanochemical reaction, and hydrogen is generated again. This process is repeated, so that hydrogen continues to be generated. Therefore, even when the material is nickel oxide (II), the hydrogen production efficiency can be improved. [Industrial Applicability]

[0106] The technology disclosed herein is useful as a hydrogen production method in which a grinding device having a container containing grinding media is used to grind and mix materials to be ground and a solvent to produce hydrogen through a mechanochemical reaction. [Explanation of symbols]

[0107] 1. Planetary ball mill (grinding device) 2 Grinding media 3 Crushed material 4. Solvent 5 containers 200 iron particles

Claims

1. A method for producing hydrogen by pulverizing and mixing a material to be pulverized and a solvent using a pulverizing device having a container containing pulverizing media, and producing hydrogen by a mechanochemical reaction, comprising: The solvent comprises water; A method for producing hydrogen, wherein the material to be crushed is an inorganic oxide that, after being oxidized by the mechanochemical reaction, serves as an oxidizing agent for the inorganic material constituting at least one of the grinding medium and the container.

2. The method for producing hydrogen according to claim 1, The material to be ground is chromium oxide (Cr ２ O ３ ), iron(III) oxide (Fe ２ O ３ ), or nickel (II) oxide (NiO).

3. The method for producing hydrogen according to claim 2, 2. A method for producing hydrogen, wherein at least one of the grinding medium and the container is made of stainless steel.

4. In the method for producing hydrogen according to any one of claims 1 to 3, The grinding device is a planetary ball mill using balls as grinding media, A method for producing hydrogen, wherein the rotation speed of the planetary ball mill is 200 rpm to 700 rpm.

5. A method for producing hydrogen by a mechanochemical reaction by pulverizing and mixing a material to be pulverized, a solvent, and a reaction accelerator using a pulverizing device having a container containing pulverizing media, comprising: The solvent comprises water; A method for producing hydrogen, characterized in that the crushed material is oxidized by the mechanochemical reaction, and the oxidized material is an inorganic oxide that serves as an oxidizing agent for the inorganic substance that constitutes the reaction accelerator.

6. The method for producing hydrogen according to claim 5, The material to be ground is chromium oxide (Cr ２ O ３ ) A method for producing hydrogen,

7. The method for producing hydrogen according to claim 6, The method for producing hydrogen, wherein the reaction accelerator is iron particles.

8. The method for producing hydrogen according to claim 7, The grinding medium and the container are made of zirconia (ZrO ２ ) A method for producing hydrogen.

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