Method of producing hydrogen

Abstract

To provide a method of producing hydrogen capable of improving a production amount of hydrogen.SOLUTION: A method of producing hydrogen includes: pulverizing and mixing a material to be pulverized and a solvent using a planet ball mill device having a container housed with a pulverization medium to produce hydrogen by mechanochemical reaction. The solvent includes water, the material to be pulverized is at least one of a metal, or a metallic compound of the metal as a main constituent, a material of at least one of the container and the pulverization medium is a material capable of reducing an oxide and a hydroxide of a metal by mechanochemical reaction, and a speed of rotation of the planet ball mill device is 400 rpm or more.SELECTED DRAWING: Figure 10

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 a planetary ball mill having a container containing a grinding medium is used to grind and mix inorganic substances such as silicon (Si) and aluminum (Al) as grinding materials with a solvent, 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] In the hydrogen production method described in Patent Document 1, hydrogen is generated when an oxide or hydroxide mainly composed of the inorganic substance is produced by an oxidation-reduction reaction between the inorganic substance and a solvent. However, after the inorganic substance becomes an oxide or hydroxide, the reaction does not proceed, and the amount of hydrogen produced reaches a plateau unless new crushed material is added.

[0007] As a result of extensive research, the inventors of the present application have found that by appropriately combining the materials to be crushed and the crushing conditions, it is possible to continue producing hydrogen even after the inorganic substances have turned into oxides or hydroxides.

[0008] The technology disclosed herein has been made in view of the above points, and has an object to provide a hydrogen production method capable of increasing the amount of hydrogen produced. [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 planetary ball mill apparatus having a container containing grinding media is used to grind and mix materials to be ground with a solvent to produce hydrogen through a mechanochemical reaction, the solvent containing water, the materials to be ground are at least one of a metal or a metal compound mainly containing the metal, the material of at least one of the container and the grinding media is a material capable of reducing oxides and hydroxides of the metal through a mechanochemical reaction, and the rotation speed of the planetary ball mill apparatus is 400 rpm or more.

[0010] The inventors of the present application have conducted extensive research and found that when metal oxides and metal hydroxides are pulverized at a rotation speed of 400 rpm or more, the metal oxides and metal hydroxides are reduced by a mechanochemical reaction to produce the metals that are the main components of the metal oxides and metal hydroxides. Therefore, by pulverizing and mixing at least one of zinc and a zinc compound with a solvent containing water at a rotation speed of 400 rpm or more using a pulverization medium made of a material capable of reducing metal oxides and metal hydroxides by a mechanochemical reaction, hydrogen can be produced continuously as long as water does not run out. This allows the amount of hydrogen produced to be increased.

[0011] A second aspect of the present disclosure is the first aspect, wherein the amount of the material per 10 mL of the solvent is 0.3 mmol to 1.8 mmol.

[0012] The inventors of the present application have conducted extensive research and found that when the volume of the solvent is constant, the hydrogen production efficiency changes depending on the amount of the crushed material. In particular, when the crushed material is zinc or a zinc compound, the production efficiency is high when the amount of the crushed material charged into the vessel is 0.3 mmol to 1.8 mmol per 10 mL of the solvent. Therefore, the amount of hydrogen produced can be efficiently increased by the above method.

[0013] A third aspect of the present disclosure is the second aspect, wherein the rotation speed of the planetary ball mill is increased as the amount of the material to be ground per 10 mL of the solvent increases.

[0014] As a result of extensive research, the inventors of the present application have found that when the amount of material per 10 mL of the solvent is large, the hydrogen production efficiency is increased by increasing the rotation speed of the planetary ball mill. With the above-mentioned configuration, the amount of hydrogen produced can be increased more efficiently.

[0015] A fourth aspect of the present disclosure is any one of the first to third aspects, wherein the grinding medium is made of tungsten carbide.

[0016] The inventors of the present application have found through extensive research that when a metal oxide and a metal hydroxide are mixed and ground with a solvent using a grinding medium made of tungsten carbide, an oxidation-reduction reaction occurs between the metal oxide and the metal hydroxide and tungsten carbide, producing the metal that constitutes the main component of the metal oxide and the metal hydroxide and tungsten oxide. Therefore, by using a grinding medium made of tungsten carbide, the amount of hydrogen produced can be increased. Effect of the Invention

[0017] As described above, according to the technique disclosed herein, it is possible to increase the amount of hydrogen produced. [Brief description of the drawings]

[0018] [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 shows the results of gas chromatography of the generated gas. [Diagram 5] FIG. 5 is a graph showing the relationship between the grinding time and the amount of hydrogen produced. [Figure 6] FIG. 6 is an X-ray diffraction pattern of the material produced by ball milling. [Figure 7] FIG. 7 is a graph showing the relationship between the grinding time and the amount of hydrogen produced when the rotation speed of the planetary ball mill is 400 rpm. [Figure 8] FIG. 8 is a graph showing the relationship between the grinding time and the amount of hydrogen produced when the rotation speed of the planetary ball mill is 500 rpm. [Figure 9] FIG. 9 is a graph showing the relationship between the grinding time and the amount of hydrogen produced when the rotation speed of the planetary ball mill is 600 rpm. [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 amount of zinc oxide fed and the amount of hydrogen produced when the rotation speed of the planetary ball mill is 400 rpm. [Figure 12] FIG. 12 is a graph showing the relationship between the amount of zinc oxide fed and the hydrogen production efficiency when the rotation speed of the planetary ball mill is 400 rpm. [Figure 13] FIG. 13 is a graph showing the relationship between the amount of zinc oxide fed and the amount of hydrogen produced when the rotation speed of the planetary ball mill is 500 rpm. [Figure 14] FIG. 14 is a graph showing the relationship between the amount of zinc oxide fed and the hydrogen production efficiency when the rotation speed of the planetary ball mill is 500 rpm. [Figure 15] FIG. 15 is a graph showing the relationship between the amount of zinc input and the amount of hydrogen produced when the rotation speed of the planetary ball mill is 400 rpm. [Figure 16] FIG. 16 is a graph showing the relationship between the amount of zinc fed and the hydrogen production efficiency when the rotation speed of the planetary ball mill is 400 rpm. [Figure 17] FIG. 17 is a graph showing the relationship between the amount of zinc oxide fed and the hydrogen production efficiency when the rotation speed of the planetary ball mill is 700 rpm. [Figure 18] FIG. 18 is a schematic diagram of a collision model of two colliding grinding media. [Figure 19] FIG. 19 is a graph showing the relationship between the rotation speed and the local pressure of the planetary ball mill. [Figure 20] FIG. 20 is a graph showing the relationship between the rotation speed and the local temperature of the planetary ball mill. [Figure 21] FIG. 21 is a phase diagram of water. [Figure 22] FIG. 22 is a graph showing the relationship between the rotation speed of a planetary ball mill and the local temperature, and the critical temperature of water. [Diagram 23]FIG. 23 is a graph showing the relationship between the rotation speed of the planetary ball mill and the hydrogen production efficiency. [Figure 24] FIG. 24 is a graph showing the measurement results of the surface area of ​​the material to be crushed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] 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.

[0020] 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 this embodiment.

[0021] The first embodiment is a method for producing hydrogen at room temperature by using a planetary ball mill device 1 to pulverize and mix materials 3 made of metals and metal compounds mainly containing the metals with water as a solvent 4, and imparting mechanical energy by friction, impact, or the like to the materials 3 and the solvent 4 to increase activity of the materials 3 and the solvent 4 through a mechanochemical reaction. Examples of the metal compounds include oxides and hydroxides. The materials 3 may contain both metals and metal compounds.

[0022] 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.

[0023] 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 lid is opened and the grinding media 2, the material 3 to be crushed, and the solvent 4 are poured in. The material of the container 5 is preferably one containing an inorganic substance that is easily oxidized, for example, tungsten carbide (WC). The size of the container 5 is not particularly limited, and may be, for example, 40 cm. 3 ~100cm 3 A container having a volume of 0.1 to 1.0 can be used.

[0024] 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, tungsten carbide (WC). The grinding media 2 may be a combination of grinding media 2 of various materials.

[0025] 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).

[0026] The planetary ball mill 1 is a ball mill 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.

[0027] Next, a case where hydrogen is produced by using zinc as the material 3 to be crushed and using tungsten carbide (WC) as the grinding media 2 and the container 5 will be described.

[0028] First, as shown in Fig. 2, zinc powder and water are put 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.

[0029] 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. The rotation speed of the planetary ball mill apparatus 1 is 400 rpm or more.

[0030] 3 is a schematic diagram showing a hydrogen production mechanism when zinc is used as the material 3 to be crushed. The reaction shown in FIG.

[0031] As shown in FIG. 3, the planetary ball mill apparatus 1 causes the grinding media 2 and the container 5, or the grinding media 2 to collide with each other. The zinc is sandwiched between the grinding media 2 and the container 5 and between the grinding media 2, and mechanical energy is applied to the zinc, which is locally placed in a high-energy state. This causes a mechanochemical reaction between the zinc and water to proceed. As the mechanochemical reaction proceeds, Zn + H2O → ZnO + H2 Zn + 2H2O → Zn(OH)2+ H2 As shown above, zinc oxide and zinc hydroxide are produced, and water is reduced to produce hydrogen.

[0032] Here, when zinc is being ground and mixed with the solvent in the container 5, a mechanochemical reaction occurs between the tungsten carbide constituting the container 5 and the grinding medium 2 and the tungsten carbide scraped from the container 5 and the grinding medium 2, and the zinc oxide and zinc hydroxide.

[0033] As shown in Figure 3, a mechanochemical reaction between zinc oxide / zinc hydroxide and tungsten carbide causes an oxidation-reduction reaction between zinc oxide / zinc hydroxide and tungsten carbide. The reaction is as follows: 3ZnO + WC → 3Zn + WO3 + C 3Zn(OH)2+ 2WC → 3Zn + 2WO3+ 2C + 3H2 In other words, zinc oxide and zinc hydroxide oxidize tungsten carbide and are reduced to produce the original zinc. In addition to the original zinc, zinc oxide with oxygen deficiencies (hereinafter referred to as deficient zinc oxide) and zinc hydroxide with hydroxide ion deficiencies (hereinafter referred to as deficient zinc hydroxide) are also produced. Deficient zinc oxide is a type of zinc oxide that is formed by the reaction of ZnO x where x is a decimal. Zinc hydroxide is Zn(OH) y where y is a decimal. Deficient zinc oxide and deficient zinc hydroxide have an oxidation number between 0 and 2. When water is reduced by deficient zinc oxide or deficient zinc hydroxide, hydrogen is produced. In addition, tungsten oxide is not only WO3, but also tungsten oxide with oxygen deficiencies. Tungsten oxide with oxygen deficiencies is WO z where z is a decimal fraction.

[0034] As shown in Figure 3, when zinc is produced by an oxidation-reduction reaction, zinc oxide and zinc hydroxide are produced again from the produced zinc by a mechanochemical reaction between zinc and water, and hydrogen is produced again. This process is repeated, and hydrogen continues to be produced.

[0035] Therefore, in this embodiment, in the hydrogen production method, the material 3 and the solvent 4 are pulverized and mixed by using the planetary ball mill apparatus 1 having the container 5 in which the grinding medium 2 is accommodated, to produce hydrogen by a mechanochemical reaction. The solvent 4 contains water, the material 3 is at least one of a metal and a metal compound mainly made of the metal, the material of at least one of the container 5 and the grinding medium 2 is a material capable of reducing the metal compound by a mechanochemical reaction, and the rotation speed of the planetary ball mill apparatus 1 is 400 rpm or more. When ball milling is performed under the above-mentioned conditions, the metal compound generated by the oxidation-reduction reaction with water is oxidized and reduced with the inorganic substance constituting the grinding medium 2, so that the metal that is the main component of the metal compound is generated, and hydrogen can be continuously produced. When the water is low, hydrogen can be produced again by adding water. Therefore, the hydrogen production efficiency can be improved.

[0036] From the viewpoint of efficiently stirring the metals and metal compounds with the solvent 4 and efficiently pulverizing the metals and metal compounds, the amount of material 3 to be put into the container 5 is preferably 0.3 mmol to 1.8 mmol per 10 mL of the solvent.

[0037] From the viewpoint of efficiently grinding metals and metal compounds, it is preferable that the rotation speed of the planetary ball mill apparatus 1 is higher as the amount of material 3 to be ground relative to the solvent 4 increases.

[0038] (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.

[0039] For example, in the above-mentioned first and second embodiments, water is used as the solvent. However, the solvent is not limited to this and may be any solvent containing water (H2O), for example, seawater or an alkaline solution. Note that "seawater" refers to water containing 3% or more of salt, and in this case, it particularly refers to an aqueous solution containing 3% or more of NaCl. Also, examples of the alkaline solution include an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, and an aqueous ammonia solution. EXAMPLES

[0040] 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.

[0041] Example 1 Zinc and water were milled and mixed using a planetary ball mill (manufactured by Fritsch, Germany, product name: Premium Line P-7) to produce hydrogen. More specifically, 2 mmol of zinc was added as a milling material to a container (made of tungsten carbide) containing a milling medium made of tungsten carbide, and 10 mL of water was added as a solvent. In other words, the amount of zinc added to the container was 2 mmol per 10 mL of solvent. The mass of the milling medium was 100 g. The planetary ball mill was rotated at a rotation speed of 400 rpm for 600 minutes to mill and mix the zinc and water, thereby producing hydrogen. The atmosphere in the container was argon.

[0042] Example 2 Hydrogen was produced under the same conditions as in Example 1, except that the rotation speed of the planetary ball mill was changed to 500 rpm.

[0043] Example 3 Hydrogen was produced under the same conditions as in Example 1, except that the rotation speed of the planetary ball mill was changed to 600 rpm and the grinding time was changed to 300 minutes.

[0044] Example 4 Hydrogen was produced under the same conditions as in Example 1, except that the powder was changed to 2 mmol of zinc oxide.

[0045] Example 5 Hydrogen was produced under the same conditions as in Example 1, except that the powder was changed to 2 mmol of zinc hydroxide.

[0046] Example 6 Hydrogen was produced under the same conditions as in Example 2, except that the powder was changed to 2 mmol of zinc oxide.

[0047] Example 7 Hydrogen was produced under the same conditions as in Example 2, except that the ground material was changed to 2 mmol of zinc hydroxide.

[0048] Example 8 Hydrogen was produced under the same conditions as in Example 3, except that the powder was changed to 2 mmol of zinc oxide.

[0049] Example 9 Hydrogen was produced under the same conditions as in Example 3, except that the powder was changed to 2 mmol of zinc hydroxide.

[0050] Comparative Example 1 Hydrogen was produced under the same conditions as in Example 1, except that no crushed material was used.

[0051] Comparative Example 2 Hydrogen was produced under the same conditions as in Example 1, except that the rotation speed of the planetary ball mill was changed to 300 rpm.

[0052] Qualitative analysis by gas chromatography In order to collect the gas generated in the ball mill vessel, a qualitative analysis was performed using a gas chromatography device. First, the sampling bag was connected to a vacuum pump, and the sampling bag and the vacuum line were evacuated. Next, the evacuated sampling bag was removed from the vacuum line and connected to the ball mill vessel. Through this process, the gas in the ball mill vessel moved to the sampling bag. After the sampling bag expanded and it was confirmed that the intake of gas had been completed, the valve of the sampling bag was closed.

[0053] 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 analyzer (manufactured by Shimadzu Corporation).

[0054] As shown in Fig. 4, it can be seen that a very strong hydrogen peak (retention time: 1 minute) can be confirmed. It can also be seen that there are no significant peaks other than hydrogen. From the above, it was confirmed that hydrogen was produced by Example 1.

[0055] <Relationship between hydrogen production volume and rotation speed> Next, the results of calculating the amount of hydrogen produced in Example 1 and Comparative Example 1 are shown in FIG.

[0056] As shown in Figure 5, when zinc is used as the crushing material, the amount of hydrogen produced increases rapidly in the first 30 minutes, and then continues to increase gradually. On the other hand, when no crushing material is used, a small amount of hydrogen is produced. From this, it can be said that the main reason hydrogen is produced is the oxidation-reduction reaction of zinc.

[0057] In theory, 2 mmol of hydrogen is produced from 2 mmol of zinc, but more than 2 mmol of hydrogen was produced. Because the slope of the increase does not match the slope of the curve when no crushing material is used, it is believed that the hydrogen is produced because a reaction occurs in which hydrogen is obtained again from zinc oxide and zinc hydroxide.

[0058] Figure 6 shows the X-ray diffraction pattern of the residual material remaining in the container after being ground and mixed. The substances that make up the residual material were identified from the obtained X-ray diffraction pattern. The residual material was identified by overlaying the X-ray diffraction patterns of the substances assumed to be residual materials (e.g. zinc oxide) on the X-ray diffraction pattern of the residual material. As a result of the identification, it was found that the residual material contained tungsten oxide, tungsten carbide, and zinc oxide.

[0059] 7 to 9 show the amounts of hydrogen produced in Examples 1 to 9, respectively. It can be seen that when the material is zinc oxide and zinc hydroxide, the amount of hydrogen produced increases gradually. Normally, zinc oxide and zinc hydroxide are difficult to oxidize further, so it is considered that hydrogen is basically difficult to generate. The reason why hydrogen continues to be produced in spite of this is that zinc is produced by the oxidation-reduction reaction between zinc oxide and zinc hydroxide and tungsten carbide, as described above. As shown in FIGS. 7 to 9, when the slope when the material is zinc oxide and zinc hydroxide is compared with the slope after the inflection point when the material is zinc, it can be seen that the slopes are similar.

[0060] Taking these results together, the reason why hydrogen is produced in excess of the theoretical value is that, specifically, when zinc is used as the material to be crushed and mixed with water using a planetary ball device having a crushing medium of tungsten carbide, hydrogen is first produced by an oxidation-reduction reaction between zinc and water. At this time, a large amount of hydrogen is produced suddenly. Next, when most of the zinc has turned into zinc compounds such as zinc oxide and zinc hydroxide, in the process of crushing and mixing the zinc compounds with water, Zinc compound is sandwiched between the container and the grinding media Zinc compounds are sandwiched between the grinding media The tungsten carbide and zinc compound scraped off from the container and grinding media are sandwiched between the container or grinding media and the grinding media. Tungsten carbide chipped from the container and grinding media collides with zinc compounds. As a result, a mechanochemical reaction occurs between the zinc compound and tungsten carbide. When the zinc compound and tungsten carbide undergo a mechanochemical reaction, zinc, deficient zinc oxide, and deficient zinc hydroxide are generated by an oxidation-reduction reaction between the zinc compound and tungsten carbide. Then, the zinc compound and hydrogen are generated again by an oxidation-reduction reaction between these substances and water. This is repeated, and hydrogen continues to be generated. At this time, the amount of hydrogen produced becomes gentle. When the material is zinc, the slope of the amount of hydrogen produced is largely split into two because, after most of the zinc is oxidized, the zinc compound must be reduced to generate zinc, deficient zinc oxide, and deficient zinc hydroxide before hydrogen is generated again, and the production efficiency becomes relatively low.

[0061] FIG. 10 shows the amounts of hydrogen produced by Examples 1 to 3 and Comparative Example 2. As shown in FIG. 10, when the rotation speed of the planetary ball mill is 300 rpm, the amount of hydrogen produced reaches a plateau at around 1.8 mmol. This is believed to be because, when the rotation speed is 300 rpm, the mechanical energy and local temperature generated when the grinding media collide with each other or the grinding media and the container are low, and the zinc compound is not reduced. Therefore, in order to increase the amount of hydrogen produced, it is necessary to increase the rotation speed of the planetary ball mill to 400 rpm or more.

[0062] Example 10 Hydrogen was produced under the same conditions as in Example 1, except that the ground material was changed to zinc oxide and the amount of zinc oxide was 0.1 mmol.

[0063] Example 11 Hydrogen was produced under the same conditions as in Example 10, except that the amount of zinc oxide was changed to 0.2 mmol.

[0064] Example 12 Hydrogen was produced under the same conditions as in Example 10, except that the amount of zinc oxide was changed to 0.3 mmol.

[0065] (Example 13) Hydrogen was produced under the same conditions as in Example 10, except that the amount of zinc oxide was changed to 0.5 mmol.

[0066] Example 14 Hydrogen was produced under the same conditions as in Example 10, except that the amount of zinc oxide was changed to 1 mmol.

[0067] Example 15 Hydrogen was produced under the same conditions as in Example 10, except that the amount of zinc oxide was changed to 3 mmol.

[0068] (Example 16) Hydrogen was produced under the same conditions as in Example 10, except that the amount of zinc oxide was changed to 4 mmol.

[0069] (Example 17) Hydrogen was produced under the same conditions as in Example 10, except that the rotation speed of the planetary ball mill was changed to 500 rpm.

[0070] (Example 18) Hydrogen was produced under the same conditions as in Example 17, except that the amount of zinc oxide was changed to 0.2 mmol.

[0071] (Example 19) Hydrogen was produced under the same conditions as in Example 17, except that the amount of zinc oxide was changed to 0.3 mmol.

[0072] (Example 20) Hydrogen was produced under the same conditions as in Example 17, except that the amount of zinc oxide was changed to 0.5 mmol.

[0073] Example 21 Hydrogen was produced under the same conditions as in Example 17, except that the amount of zinc oxide was changed to 1 mmol.

[0074] Example 22 Hydrogen was produced under the same conditions as in Example 17, except that the amount of zinc oxide was changed to 3 mmol.

[0075] Example 23 Hydrogen was produced under the same conditions as in Example 17, except that the amount of zinc oxide was changed to 4 mmol.

[0076] <Relationship between the amount of hydrogen produced and the weight of crushed material> FIG. 11 shows the relationship between the amount of hydrogen produced and the amount of zinc oxide in Examples 4, 10 to 16. FIG. 12 shows the relationship between the efficiency of hydrogen production and the amount of zinc oxide in Examples 4, 10 to 16. FIG. 13 shows the relationship between the amount of hydrogen production and the amount of zinc oxide in Examples 6, 17 to 23. FIG. 14 shows the relationship between the efficiency of hydrogen production and the amount of zinc oxide in Examples 6, 17 to 23. The efficiency of hydrogen production corresponds to the cycle speed at which the entire zinc oxide is reduced and oxidized. The cycle speed is calculated by dividing the number of oxidation-reduction cycles that occurred in 600 minutes (10 hours) by the grinding time (here, 10 hours), with one cycle being when all zinc oxide is reduced to zinc and then all of the zinc is oxidized to zinc oxide. The number of cycles was calculated by dividing the total amount of hydrogen produced by the amount of zinc oxide input. In FIG. 11 and FIG. 13, the dashed straight lines indicate the amount of hydrogen produced when one cycle of the above-mentioned cycle occurs. The area above the dashed line indicates that the reaction has gone through more than one cycle, and the area below the dashed line indicates that the reaction has gone through less than one cycle.

[0077] As shown in FIG. 11, when the amount of zinc oxide is in the range of 0.3 mmol to 1.8 mmol, the amount of hydrogen produced is large, and one or more redox cycles occur. In particular, when the amount of zinc oxide is in the range of 0.3 mmol to 0.5 mmol, the amount of hydrogen produced is dramatically improved, and it is found to be maximum when the amount of zinc oxide is 0.3 mmol. As shown in FIG. 12, the hydrogen production efficiency is also high when the amount of zinc oxide is in the range of 0.2 mmol to 1.8 mmol. In particular, when the amount of zinc oxide is in the range of 0.2 mmol to 0.5 mmol, the hydrogen production efficiency is dramatically improved, and it is found to be maximum when the amount of zinc oxide is 0.2 mmol. It is generally considered that when the amount of zinc oxide is increased, the amount of hydrogen produced increases, and the number of redox cycles also increases. However, since zinc oxide is a soft material compared to tungsten carbide, when the amount of zinc oxide increases too much, it reduces the collision energy of tungsten carbide, and plays an increased role as a cushion that weakens the impact, so to speak. For this reason, it is believed that hydrogen is produced with high efficiency when the amount of zinc oxide is neither too little nor too much relative to the volume of the solvent, that is, when the amount of zinc oxide per 10 mL of solvent is in the range of 0.3 mmol to 1.8 mmol.

[0078] On the other hand, as shown in FIG. 13 and FIG. 14, when the rotation speed of the planetary ball mill is increased from 400 rpm to 500 rpm, the hydrogen production amount and production efficiency decrease when the amount of zinc oxide is 0.2 mmol, and when the amount of zinc oxide is 0.3 mmol or more, the hydrogen production amount and production efficiency improve. As described above, the mechanochemical reaction between zinc oxide, which is a zinc compound, and tungsten carbide is caused by various phenomena, but when zinc oxide is sandwiched between the container and the grinding medium or between the grinding mediums, a particularly high collision energy occurs, and the mechanochemical reaction proceeds efficiently. When the rotation speed is high, the collision energy is also high, so even if the amount of zinc oxide is large, it is sufficient to overcome the energy barrier, and it is considered that the reduction reaction of the zinc compound occurs. Therefore, it can be said that the more the amount of zinc oxide is, the more efficiently the reduction reaction of zinc oxide proceeds by increasing the rotation speed of the planetary ball mill device, and the more efficiently the hydrogen production amount and production efficiency can be improved.

[0079] (Example 24) Hydrogen was produced under the same conditions as in Example 1, except that the amount of zinc was changed to 0.2 mmol.

[0080] (Example 25) Hydrogen was produced under the same conditions as in Example 24, except that the amount of zinc was changed to 0.3 mmol.

[0081] (Example 26) Hydrogen was produced under the same conditions as in Example 24, except that the amount of zinc was changed to 0.5 mmol.

[0082] Example 27 Hydrogen was produced under the same conditions as in Example 24, except that the amount of zinc was changed to 1 mmol.

[0083] (Example 28) Hydrogen was produced under the same conditions as in Example 24, except that the amount of zinc was changed to 3 mmol.

[0084] (Example 29) Hydrogen was produced under the same conditions as in Example 24, except that the amount of zinc was changed to 4 mmol.

[0085] FIG. 15 shows the relationship between the amount of hydrogen produced in Examples 1, 24 to 29 and the weight of zinc. FIG. 16 shows the relationship between the efficiency of hydrogen production in Examples 1, 24 to 29 and the weight of zinc. The efficiency of hydrogen production corresponds to the cycle speed at which the entire zinc is reduced and oxidized. The cycle speed is calculated by dividing the number of cycles that occurred in 600 minutes (10 hours) by the grinding time (here, 10 hours), with one cycle being when all zinc becomes zinc compounds and all of the zinc compounds are reduced to zinc. The number of cycles was calculated by dividing the total substance amount of hydrogen produced by the substance amount of zinc input. As shown in FIG. 5, etc., when the crushed material is zinc, there is a turning point in the amount of hydrogen produced, but FIG. 15 and FIG. 16 are graphs based on the amount of hydrogen produced after the turning point. The actual amount of hydrogen produced is greater than the value shown in FIG. 15 because hydrogen produced in the range before the turning point is added. The actual efficiency of hydrogen production is also higher than the value shown in FIG. 16.

[0086] As shown in FIG. 15 and FIG. 16, even when the powder is zinc, the amount and efficiency of hydrogen production vary depending on the amount of zinc. Specifically, when the amount of zinc is in the range of 0.3 mmol to 2.0 mmol, the amount of hydrogen production is particularly high. On the other hand, when the amount of zinc is more than 2.0 mmol, the amount of hydrogen production is flat. Also, from the viewpoint of hydrogen production efficiency, when the amount of zinc is in the range of 0.3 mmol to 2.0 mmol, the amount of zinc is particularly high. This is because zinc is a soft material compared to tungsten carbide, and if the amount of zinc increases too much, the collision energy of tungsten carbide is reduced. Therefore, even when the powder is zinc, when the amount of zinc is not too small or too large relative to the volume of the solvent, that is, when the amount of zinc per 10 mL of solvent is in the range of 0.3 mmol to 2.0 mmol, hydrogen can be generated with high efficiency.

[0087] The graph in Fig. 17 shows the relationship between the amount of zinc oxide fed and the amount of hydrogen produced when the rotation speed of the planetary ball mill is set to a predetermined rotation speed (700 rpm in this example). As shown in this graph, when the rotation speed of the planetary ball mill is set to a predetermined rotation speed and the amount of material 3 fed into the container 5 is set to, for example, 2.0 mmol or less, or 1.8 mmol or less and 0.3 mmol or more per 10 mL of solvent, the efficiency of hydrogen production is dramatically improved. Specifically, when the amount of material 3 fed into the container 5 is set to 0.5 mmol, the maximum number of cycles is 1906 / hour.

[0088] The reason why the efficiency of hydrogen production could be improved so dramatically is that the water solvent is in a supercritical state and the amount of material 3 to be crushed is within the above range.

[0089] The process in which the solvent water becomes a supercritical state will be described with reference to Fig. 18 to Fig. 21. Fig. 18 focuses on two grinding media 2, 2 that collide with each other due to the rotation of the planetary ball mill apparatus 1, out of a large number of grinding media 2 made of tungsten carbide housed in a container 5, and shows a schematic collision model showing these two grinding media 2, 2 locally and instantaneously.

[0090] As shown in Fig. 18, when the planetary ball mill 1 rotates at, for example, 500 rpm, the time (contact time) during which the two crushing media 2, 2 that collide with each other are in contact with each other is extremely short, less than 20 ns (nanoseconds). Also, when the planetary ball mill 1 rotates at, for example, 500 rpm, the shape of the part where the crushing media 2, 2 made of tungsten carbide are in contact with each other can be approximated to a circle, and the diameter (D) of the circular contact surface is small, less than 100 nm. The diameter of the crushing media 2 in Fig. 18 is, for example, about 1.6 mm.

[0091] The pressure on the contact surface of the grinding media 2, 2 is called the local pressure. The local pressure can be calculated by the formula (1).

[0092] σ * =1,3ρ0.2 θ1 -0.8 W 0.4 … (1) Here, σ * is the local pressure, ρ is the density of the grinding medium 2, θ1 is the compliance coefficient of the grinding medium 2, and W is the relative velocity of the grinding medium 2. The compliance coefficient of the grinding medium 2 can be calculated from the Young's modulus, Poisson's ratio, etc. of the grinding medium 2.

[0093] The range of ρ is 9.49×10 -10 gm -3 More than 22.6 x 10 +6 gm -3 The range of θ1 is 3.25×10 -12 Pa -1 More than 2.18 x 10 -7 Pa -1 The compliance coefficient can be expressed as follows using Young's modulus E and Poisson's ratio ν:

[0094] θ1=4(1-ν 2 ) / E … (2) In this case, the Young's modulus can be in the range of 0.912 MPa or more and 1220 GPa or less, and the Poisson's ratio can be in the range of 0.1 or more and 0.5 or less.

[0095] Figure 19 shows the relationship between the rotation speed of the planetary ball mill and the local pressure. As shown in this graph, the higher the rotation speed of the planetary ball mill, the higher the local pressure, and the tendency is that the local pressure increases in proportion to the 1 / 2 power (0.5 power) of the rotation speed. When the rotation speed of the planetary ball mill is 500 rpm, for example, the local pressure reaches 22 GPa.

[0096] On the other hand, the temperature of the contact surface of the grinding media 2, 2 is called the local temperature. The local temperature can be calculated by the formula (3).

[0097] ΔT=ξ1<σ * >w t (c1λ1ρ1) -0.5 τ1 0.5 iErfc[0] … (3) Here, ΔT is the local temperature change (temperature increase from room temperature), ξ1 is the kinetic friction coefficient of the grinding medium 2, c1 is the specific heat of the grinding medium 2, λ1 is the thermal conductivity of the grinding medium 2, ρ1 is the density of the grinding medium 2, and τ1 is the contact time of the grinding media 2, 2.

[0098] The range of ξ1 can be 0.07 or more and 0.7 or less. The range of c1 is 0.1 Jg -1 K -1 Over 55.2Jg -1 K -1 The range of λ1 is 0.17 Jm -1 K -1 s -1 More than 2400Jm -1 K -1 s -1 It can be as follows:

[0099] w t is the grinding ball relative velocity (tangential to the impact) and is determined by equation (4).

[0100] w t =0.38ρ1 -0.5 ρ -0.5 θ1 -0.2 θ1W 0.6 … (4) Figure 20 shows the relationship between the rotation speed of the planetary ball mill and the local temperature. As shown in this graph, the higher the rotation speed of the planetary ball mill, the higher the local temperature, and the tendency is a linear function. When the rotation speed of the planetary ball mill is 500 rpm, for example, the local temperature reaches 846 K.

[0101] As described above, when the rotation speed of the planetary ball mill is, for example, 500 rpm, the local pressure is 22 GPa and the local temperature is 846 K. Figure 21 is a phase diagram of water. The critical point of water is 22.1 MPa in pressure and 647 K in temperature, and when water reaches the critical point, the specific volumes of the saturated vapor and saturated liquid are equal. When the rotation speed of the planetary ball mill is, for example, 500 rpm, the pressure of the water existing between the grinding media 2, 2 colliding with each other corresponds to the local pressure and is 22 GPa, and the temperature of the water existing between the grinding media 2, 2 corresponds to the local temperature and is 846 K. Therefore, the water existing between the grinding media 2, 2 is in a supercritical state beyond the critical point on the phase diagram of water. As shown in Figure 22, when the rotation speed of the planetary ball mill is lower than 300 rpm, the temperature of the water exceeds the critical point (T C = 647 K), so it does not become supercritical water, but when the rotation speed of the planetary ball mill exceeds 300 rpm, the temperature of the water reaches its critical point.

[0102] In this way, when water becomes supercritical, it shows a very strong oxidizing power, so that it becomes possible to significantly oxidize zinc. At this time, the oxygen constituting the water molecules is consumed by zinc to produce zinc oxide, while the hydrogen atoms constituting the water molecules are liberated as hydrogen molecules, and a large amount of hydrogen is produced. Furthermore, because of the high temperature, the oxidation-reduction reaction between zinc oxide and zinc hydroxide and tungsten carbide as shown in Figure 3 tends to occur continuously, and zinc is produced again. This re-produced zinc reacts with supercritical water, forming a cycle of producing hydrogen. Specifically, as shown in Figure 23, the higher the rotation speed of the planetary ball mill, the higher the hydrogen production efficiency, that is, the number of cycles per unit time of the oxidation-reduction reaction between zinc, zinc oxide, and zinc hydroxide and tungsten carbide, increases. This increase in the number of cycles per unit time contributes to improving the hydrogen production efficiency by increasing the rotation speed of the catalyst, as shown in Figure 17.

[0103] FIG. 24 is a graph showing the measurement results of the surface area of ​​the material 3 made of zinc oxide, which is a so-called BET plot. Based on the measurement results of the surface area of ​​the material 3, the number of atoms present on the surface of the material 3 can be estimated, and thus the number of zinc atoms present per unit surface area of ​​the material 3 can be obtained. Therefore, it is possible to calculate the number of atoms reduced from zinc oxide to zinc by the grinding medium. Furthermore, by setting the amount of zinc oxide charged into the vessel 5 to a low amount of 0.3 mmol to 1.8 mmol per 10 mL of solvent, the hydrogen production efficiency can be improved.

[0104] As described above, the efficiency of hydrogen production is dramatically improved by setting the rotation speed of the planetary ball mill to a predetermined high rotation speed to bring water into a supercritical state, and setting the amount of material 3 to be charged into the container 5 to a predetermined low amount. In other words, in the hydrogen production method according to this embodiment, the rotation speed of the planetary ball mill is set so that the solvent is in a supercritical state exhibiting strong oxidizing power. Also, in the hydrogen production method according to this embodiment, the amount of material 3 to be charged into the container 5 is set to a predetermined low amount.

[0105] As described above, the present disclosure includes a method for producing hydrogen in which a planetary ball mill device having a container containing a grinding medium is used to grind and mix a material to be ground with a solvent to produce hydrogen through a mechanochemical reaction. The solvent in the hydrogen production method contains water. Furthermore, the material to be ground in the hydrogen production method is at least one of a metal or a metal compound mainly containing the metal, and the material of at least one of the container and the grinding medium is a material capable of reducing metal oxides and hydroxides through a mechanochemical reaction. In this hydrogen production method, the rotation speed of the planetary ball mill is set to a rotation speed at which the solvent becomes supercritical.

[0106] The present disclosure may include a hydrogen production apparatus. The hydrogen production apparatus includes an apparatus capable of executing the above-mentioned production method. That is, the hydrogen production apparatus includes a planetary ball mill apparatus 1 and a control device (not shown) that controls the rotation of the planetary ball mill. The control device rotates the planetary ball mill so that the solvent in the container 5 is in a supercritical state.

[0107] In the above embodiment, the distance between the rotation axis and the revolution axis of the planetary ball mill apparatus 1 is 6.75 cm, and the inner diameter of the container 5 is 2.35 cm, but the distance between the rotation axis and the revolution axis and the radius of the container 5 are not fixed to a single value and may include a specified range.

[0108] When the distance between the rotation axis and revolution axis of the planetary ball mill 1 used in the above embodiment is, for example, 8 times larger (revolution radius 0.54 m) and the inner diameter of the container 5 is 8 times larger than that in the above embodiment, the local temperature reaches 7000 K when the revolution speed (rotation speed of the planetary ball mill 1) is 1100 rpm. Even under these conditions, the solvent in the container 5 can be made into a supercritical state.

[0109] Furthermore, if the distance between the rotation axis and the revolution axis of the planetary ball mill apparatus 1 used in the above embodiment is, for example, eight times larger, and the inner diameter of the container 5 is eight times larger than that in the above embodiment, the solvent in the container 5 can be made into a supercritical state even if the revolution speed is 50 rpm.

[0110] In other words, even under conditions where the distance between the rotation axis and revolution axis of the planetary ball mill apparatus 1 is 6.75 cm or more and 54 cm or less, the inner diameter of the container 5 is 2.35 cm or more and 18.8 cm or less, and the rotation speed of the planetary ball mill apparatus 1 is 50 rpm or more and 1100 rpm or less, the solvent in the container 5 can be brought into a supercritical state, thereby improving the efficiency of hydrogen production.

[0111] The shape of the material to be crushed is not particularly limited, and may be, for example, granular, sandy, columnar, or rod-like. The material to be crushed may be porous. The surface of the powder may be a mirror surface or may be an uneven surface.

[0112] The material to be crushed may be titanium, titanium dioxide, iron, manganese, chromium oxide (Cr2O3), iron (III) oxide (Fe2O3), nickel (II) oxide (NiO), etc. Even when these materials are used as the material to be crushed, the oxidation-reduction reaction with the container 5 and the balls proceeds continuously, and hydrogen is continuously generated until the water runs out.

[0113] In addition, if the distance between the rotation axis and the revolution axis of the planetary ball mill apparatus 1 used in the above embodiment is, for example, 8 times, and the inner diameter of the container 5 is 8 times that of the above embodiment, when the planetary ball mill apparatus 1 rotates at, for example, 1100 rpm, the time during which the two grinding media 2, 2 that collide with each other are in contact (contact time) is 50 ns or less, and the diameter (D) of the contact surface is 600 nm or less. The contact time when the solvent in the container 5 becomes a supercritical state is in the range of 5 ns or more and 50 ns or less, and the diameter (D) of the contact surface when the solvent in the container 5 becomes a supercritical state can be specified to be in the range of 10 nm or more and 600 nm or less. The control device controls the rotation of the planetary ball mill so as to obtain such contact time and diameter of the contact surface.

[0114] In the above embodiment, the gas generated in the ball mill container was quantitatively analyzed by the gas chromatography device, and the hydrogen purity was found to be 99.3% or more. Thus, the hydrogen production method and hydrogen production device according to the present invention can produce high-purity hydrogen with high efficiency.

[0115] The vertical axis of the graphs shown in Figures 12, 14, and 16 shows the number of detected hydrogen molecules divided by the number of zinc oxide molecules put into the container. Therefore, when all the zinc oxide has reacted and been consumed, the cycle number is 1. In other words, a cycle number of 1 or more means that the same zinc oxide continues to undergo an oxidation-reduction reaction multiple times to generate hydrogen.

[0116] On the other hand, Figure 17 uses a different calculation method from the methods shown in Figures 12, 14, and 16. Specifically, the "number of surface molecules" of zinc oxide involved in the reaction is calculated from the BET measurements in Figure 24. The number of generated hydrogen molecules is divided by this calculated "number of zinc oxide molecules exposed on the surface," and when this value is 1, all zinc oxide molecules on the surface have been consumed.

[0117] From the above, the difference in values ​​between the vertical axis of the graphs shown in Figures 12, 14, and 16 and the vertical axis of the graph shown in Figure 17 is due to the fact that the number of zinc oxide molecules exposed on the surface is smaller than those not exposed on the surface (zinc oxide molecules present on the inside). However, the difference in values ​​is also related to the fact that the rotation speed of the planetary ball mill is set so that the solvent is in a supercritical state. [Industrial Applicability]

[0118] The technology disclosed herein is useful as a hydrogen production method in which a planetary ball mill is used to pulverize and mix materials and a solvent to produce hydrogen through a mechanochemical reaction. [Explanation of symbols]

[0119] 1. Planetary ball mill (grinding device) 2 Grinding media 3 Crushed material 4. Solvent 5 containers

Claims

1. A method for producing hydrogen by using a planetary ball mill having a container containing a grinding medium to grind and mix a material to be ground and a solvent to produce hydrogen through a mechanochemical reaction, comprising: The solvent comprises water; The material to be crushed is at least one of a metal and a metal compound mainly containing the metal, At least one of the container and the grinding medium is made of a material capable of reducing the oxide and hydroxide of the metal by a mechanochemical reaction; A method for producing hydrogen, wherein the planetary ball mill apparatus has a rotation speed of 400 rpm or more.

2. The method for producing hydrogen according to claim 1, The powder is zinc or a zinc compound, A method for producing hydrogen, wherein the amount of the crushed material charged into the vessel is 0.3 mmol to 1.8 mmol per 10 mL of the solvent.

3. The method for producing hydrogen according to claim 2, A method for producing hydrogen, characterized in that the rotation speed of the planetary ball mill is increased as the amount of the ground material per 10 mL of the solvent increases.

4. The method for producing hydrogen according to any one of claims 1 to 3, A method for producing hydrogen, wherein the grinding medium is made of tungsten carbide.

5. A method for producing hydrogen by using a planetary ball mill having a container containing a grinding medium to grind and mix a material to be ground and a solvent to produce hydrogen through a mechanochemical reaction, comprising: The solvent comprises water; The material to be crushed is at least one of a metal and a metal compound mainly containing the metal, At least one of the container and the grinding medium is made of a material capable of reducing the oxide and hydroxide of the metal by a mechanochemical reaction; A method for producing hydrogen, comprising setting the rotation speed of the planetary ball mill apparatus so as to bring the solvent into a supercritical state.

Images