Hydrogen generation composition and method for producing the same, and method for generating hydrogen

Abstract

To provide means capable of generating hydrogen with high yield and high generation amount.SOLUTION: One aspect of the present invention relates to a hydrogen generation composition comprising magnesium hydride in a powder form and citric acid in a powder form, wherein a mass ratio of citric acid to magnesium hydride is in a range of 2.5 to 3.5, and which is in a form of a pressure-molded product. Another aspect of the present invention relates to a method for producing a hydrogen generation composition and a method for generating hydrogen.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a hydrogen generating composition, a method for producing the same, and a method for generating hydrogen. [Background technology]

[0002] Demand for hydrogen as a fuel gas for fuel cells is increasing. Known methods for supplying and / or storing hydrogen include storing hydrogen gas in high-pressure cylinders, storing liquid hydrogen in cylinders, storing hydrogen in hydrogen storage alloys, and obtaining hydrogen by reforming gases such as natural gas or methanol.

[0003] In addition to the above-mentioned methods, methods for generating hydrogen by hydrolyzing metal hydrides are also known. For example, Patent Document 1 describes a method for generating hydrogen by hydrolyzing granules obtained by pressure molding magnesium hydride.

[0004] Patent Document 2 describes a method for generating hydrogen by supplying water to a solid mixture of a solid hydride and a solid acidic substance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-236725 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-298670 Summary of the Invention [Problem to be solved by the invention]

[0006] In conventional methods for producing hydrogen by hydrolyzing metal hydrides, it is known that the addition of an acid can improve the yield of hydrogen produced by preventing the formation of passivated metal hydroxides on the surface of the metal hydride (e.g., Patent Document 2). On the other hand, if the amount of acid added increases and the amount of metal hydroxide decreases relatively, the amount of hydrogen produced may decrease. However, the optimal mixing ratio of metal hydride and acid that can produce hydrogen in high yield and in high production amount has not been known.

[0007] Therefore, an object of the present invention is to provide a means for producing hydrogen in high yield and high production amount. [Means for solving the problem]

[0008] The present inventors have investigated various means for solving the above problems. They have found that by using powdered magnesium hydride as the metal hydride and powdered citric acid as the acid, mixing them in a predetermined mass ratio and forming them into a pressure-molded product, a composition capable of generating hydrogen in high yield and in high production amount can be obtained. Based on this finding, the present inventors have completed the present invention.

[0009] That is, the present invention includes the following aspects and embodiments. (Embodiment 1) A hydrogen generating composition comprising magnesium hydride in powder form and citric acid in powder form, wherein the mass ratio of citric acid to magnesium hydride is in the range of 2.5 to 3.5, and the composition is in the form of a pressure-molded product. (Embodiment 2) The hydrogen generating composition of embodiment 1, wherein the magnesium hydride has a particle size in the range of 60 to 120 μm. (Embodiment 3) A method for generating hydrogen, comprising contacting the hydrogen generation composition according to embodiment 1 or 2 with water to generate hydrogen. (Embodiment 4) A mixing step of mixing magnesium hydride in powder form and citric acid in powder form; a molding step of pressurizing and molding the mixture obtained in the mixing step; 3. A method for producing the hydrogen generation composition according to embodiment 1 or 2, comprising: (Embodiment 5) A magnesium hydride preparation step, comprising: preparing magnesium hydride in the form of a powder having a particle size in the range of 60 to 120 μm; 5. The method of embodiment 4, further comprising: [Effects of the Invention]

[0010] The present invention makes it possible to provide a means for producing hydrogen in high yield and in high production amount. [Brief explanation of the drawings]

[0011] [Figure 1] The figure shows the hydrogen yield in hydrogen generation using the hydrogen generation compositions of Examples 1 to 4 and Comparative Examples 1 to 9. In the figure, the horizontal axis represents the mass ratio of citric acid to MgH in the hydrogen generation composition, and the vertical axis represents the hydrogen yield (%). Open circles (○) represent the results of Examples 1 to 3, × represents the results of Example 4, filled circles (●) represent the results of Comparative Examples 1 to 3, open triangles (△) represent the results of Comparative Examples 4 to 6, and open squares (□) represent the results of Comparative Examples 7 to 9. [Figure 2] The figure shows the amount of hydrogen produced during hydrogen generation using the hydrogen generation compositions of Examples 1 to 4 and Comparative Examples 1 to 9. In the figure, the horizontal axis represents the mass ratio of citric acid to MgH in the hydrogen generation composition, and the vertical axis represents the amount of hydrogen produced (L). Open circles (○) represent the results of Examples 1 to 3, × represents the result of Example 4, filled circles (●) represent the results of Comparative Examples 1 to 3, open triangles (△) represent the results of Comparative Examples 4 to 6, and open squares (□) represent the results of Comparative Examples 7 to 9. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the present invention will now be described in detail.

[0013] <1: Hydrogen generating composition> One aspect of the present invention relates to a hydrogen generation composition. The hydrogen generation composition of this aspect contains magnesium hydride (hereinafter also referred to as "MgH") and citric acid (hereinafter also referred to as "C(OH)(CHCOOH)COOH"). When the hydrogen generation composition of this aspect is brought into contact with water, the magnesium hydride is hydrolyzed to generate hydrogen. At this time, the following hydrogen generation reaction is presumed to proceed. In this reaction, the citric acid contained in the hydrogen generation composition is presumed to suppress the formation of passive magnesium hydroxide that can be generated by hydrolysis of magnesium hydride. In other words, theoretically, 2 mol of hydrogen can be generated from 1 mol of magnesium hydride. 3MgH2+ 2C(OH)(CH2COOH)2COOH + 6H2O→Mg 2+ 3[C(OH)(CH2COO - )2COO - ]2+6H2O + 6H2

[0014] In the hydrogen generation composition of this embodiment, both magnesium hydride and citric acid are in the form of powder. The particle size of the powdered magnesium hydride is preferably in the range of 60 to 120 μm, more preferably in the range of 80 to 120 μm, even more preferably in the range of 80 to 110 μm, and particularly preferably in the range of 101 to 110 μm. The particle size of the powdered citric acid is preferably in the range of 60 to 120 μm, more preferably in the range of 80 to 120 μm, even more preferably in the range of 80 to 110 μm, and particularly preferably in the range of 101 to 110 μm. If the particle size of the magnesium hydride is below the lower limit, it may take a long time to microparticulate the magnesium hydride in the method for producing the hydrogen generation composition described below. Furthermore, if the particle size of the magnesium hydride and citric acid, especially magnesium hydride, exceeds the upper limit, the yield and / or amount of hydrogen produced may decrease. Therefore, by including magnesium hydride and citric acid in the form of powder having the above particle size, particularly magnesium hydride, the hydrogen generating composition of this embodiment can generate hydrogen in a high yield and in a high production amount.

[0015] In each aspect of the present invention, the particle size of the magnesium hydride and citric acid contained in the hydrogen generation composition can be determined, for example, by destroying a press-molded product of the hydrogen generation composition and measuring the particle size of the resulting powder using a particle size distribution measuring device.

[0016] In the hydrogen generation composition of this embodiment, the mass ratio of citric acid to magnesium hydride is in the range of 2.5 to 3.5, preferably in the range of 2.5 to 3, and more preferably about 3. If the mass ratio is below the lower limit, the yield and amount of hydrogen produced may decrease. On the other hand, if the mass ratio exceeds the upper limit, the magnesium hydride content may decrease relatively, which may decrease the amount of hydrogen produced. Therefore, by containing magnesium hydride and citric acid at a mass ratio within the above range, the hydrogen generation composition of this embodiment can produce hydrogen at a high yield and in a high amount.

[0017] In each embodiment of the present invention, the presence and content of magnesium hydride and citric acid contained in the hydrogen generation composition can be determined by analysis using, for example, X-ray diffraction (XRD), mass spectrometry (MS), nuclear magnetic resonance spectroscopy (NMR), or the like.

[0018] The hydrogen generation composition of this embodiment is in the form of a pressure-molded product. The shape of the pressure-molded product is not particularly limited, and examples thereof include a cylindrical shape, a spherical shape, and a plate shape. The maximum length of the pressure-molded product is usually in the range of 1 to 100 mm. By having the pressure-molded shape, the hydrogen generation composition of this embodiment can generate hydrogen at a higher yield and in a higher production amount than conventional compositions in the form of powder.

[0019] In each aspect of the present invention, the form and shape of the hydrogen generation composition can be determined, for example, by observing the hydrogen generation composition using a microscope.

[0020] In each embodiment of the present invention, the amount of hydrogen produced can be determined, for example, by adding water dropwise to the hydrogen generating composition, collecting the produced hydrogen, and measuring its volume.

[0021] In each aspect of the present invention, the hydrogen yield can be calculated, for example, based on the following formula: In the formula, a is the molar volume (L / mol) and is a constant of 22.4 under standard conditions. b is the number of moles of hydrogen produced from 1 mol of MgH2 and is a constant of 2. The number of moles of MgH2 used can be calculated from the mass of the hydrogen generation composition used, the mass ratio of MgH2 to citric acid in the hydrogen generation composition, and the molecular weight of MgH2 (26.32). Hydrogen yield (%) = Amount of hydrogen produced (L) / (Number of moles of MgH2 used) × a × b × 100

[0022] <2: Method for producing hydrogen generating composition> Another aspect of the present invention relates to a method for producing a hydrogen generation composition. The method of this aspect includes a mixing step and a molding step. The method of this aspect may also include a magnesium hydride preparation step and a citric acid preparation step, as desired. Each step will be described in detail below.

[0023] [2-1: Magnesium hydride preparation process] The process involves providing magnesium hydride in powder form.

[0024] The magnesium hydride in powder form prepared in this step preferably has the particle size described above.

[0025] In this step, magnesium hydride in the form of a powder having a predetermined particle size can be prepared, for example, by pulverizing magnesium hydride. Examples of means for pulverizing magnesium hydride include a ball mill, a bead mill, a jet mill, and an ultrasonic homogenizer. The specific conditions (e.g., stirring speed, stirring time, and rotation speed) of the above-exemplified means are not particularly limited and can be appropriately set within any range. If desired, the pulverized magnesium hydride may be separated by size using an automatic sieving machine or the like having one or more sieves. In this case, the mesh size of the sieve used can be appropriately selected based on the particle size described above. The mesh size of the sieve is preferably 120 μm, more preferably 110 μm, and even more preferably 106 μm.

[0026] [2-2: Citric acid preparation process] The process involves providing citric acid in powder form.

[0027] The powdered citric acid prepared in this step preferably has the particle size described above.

[0028] In this step, citric acid in the form of a powder having a predetermined particle size can be prepared, for example, by pulverizing citric acid. The pulverization of citric acid and, if desired, size separation of the pulverized citric acid can be carried out in the same manner as in the magnesium hydride preparation step.

[0029] [2-3: Mixing process] The process involves mixing magnesium hydride in powder form and citric acid in powder form.

[0030] In this step, powdered magnesium hydride and powdered citric acid can be mixed using means such as a ball mill, a bead mill, a jet mill, an ultrasonic homogenizer, etc. The specific conditions for the means exemplified above (e.g., stirring speed, stirring time, rotation speed, etc.) are not particularly limited and can be set appropriately within any range.

[0031] [2-4: Molding process] This step involves pressure molding the mixture obtained in the mixing step.

[0032] In this step, the mixture can be pressure-molded by, for example, pouring the mixture into a mold of a predetermined shape and applying a load to the mold. The shape of the mold to be used can be appropriately selected based on the shape of the hydrogen generation composition described above. The pressure-molding load is typically in the range of 0.1 to 1 kN, for example, in the range of 0.1 to 0.8 kN.

[0033] As explained above, the hydrogen generation composition of one embodiment of the present invention is in the form of a pressure-molded product, and therefore can generate hydrogen in high yield and in high production amount even when the magnesium hydride and citric acid are in powder form, particularly when the particle size of the magnesium hydride is 60 μm or more. Therefore, in the magnesium hydride preparation step, it is not necessary to microparticulate the powdered magnesium hydride to a particle size of less than 60 μm. Therefore, by performing this step under the conditions exemplified above, the hydrogen generation composition of one embodiment of the present invention can be produced in a shorter time than compositions of the prior art.

[0034] <3: Hydrogen generation method> Yet another aspect of the present invention relates to a method for producing hydrogen, which method includes a hydrogen production step of producing hydrogen by contacting the hydrogen generation composition of one aspect of the present invention with water.

[0035] In the hydrogen generation step, the conditions for contacting the hydrogen generation composition with water are not particularly limited. This step can be carried out by, for example, dropping water onto the hydrogen generation composition, immersing the hydrogen generation composition in water, or flowing water through a flow path in which the hydrogen generation composition is disposed.

[0036] The water used in the hydrogen generation step may be either pure water or an aqueous solution or dispersion containing one or more other components.

[0037] As described above in detail, the hydrogen generation composition of one embodiment of the present invention can be used to generate hydrogen in high yield and in high production amount. Therefore, the hydrogen generation composition of one embodiment of the present invention can provide a fuel gas supply means for a fuel cell. [Example]

[0038] The present invention will be described in more detail below using examples, although the technical scope of the present invention is not limited to these examples.

[0039] [I: Material] Magnesium hydride (MgH2) was used as "Magnesium hydride powder" manufactured by Biocoke Giken Co., Ltd. Citric acid [C(OH)(CH2COOH)2COOH] was used as "Citric acid (anhydrous)" manufactured by Nacalai Tesque, Inc.

[0040] [II: Production of hydrogen generating composition] (Citric acid preparation process) Citric acid was ground for 60 minutes using a ball mill, and the resulting citric acid powder was sieved using an automatic sieving machine equipped with a sieve with 106 μm openings to obtain citric acid in the form of a powder having a particle size of approximately 106 μm.

[0041] (Magnesium hydride preparation process) Magnesium hydride was pulverized using a ball mill for 20 minutes (Examples 1 to 4 and Comparative Examples 1 to 6) or 60 minutes (Comparative Examples 7 to 9). The obtained magnesium hydride powder was sieved using an automatic sieving machine equipped with a sieve with an opening of 106 μm (Examples 1 to 4 and Comparative Examples 1 to 6) or 53 μm (Comparative Examples 7 to 9), to obtain magnesium hydride in the form of a powder having a particle size of about 106 μm (Examples 1 to 4 and Comparative Examples 1 to 6) or in the form of fine particles having a particle size of about 53 μm (Comparative Examples 7 to 9).

[0042] (Mixing process) Magnesium hydride in the form of powder or fine particles obtained in the citric acid preparation step and magnesium hydride preparation step, and citric acid in the form of powder were placed in a container at a predetermined mixing ratio and mixed until the mixture was visually uniform.

[0043] (molding process) For Examples 1 to 4 and Comparative Examples 1 to 3, the mixture (17.5 g) obtained in the mixing step was placed in a cylindrical mold (inner diameter: 10 mm, height: 10 mm). A load of 0.8 kN was applied to the mold to pressure-mold the mixture, yielding a hydrogen generation composition in the form of a cylindrical pressure-mold (diameter: 10 mm, height: 50 mm).

[0044] For Comparative Examples 4 to 9, the mixture obtained in the mixing step was not pressure-molded, and a hydrogen generating composition was obtained in the form of a powder (Comparative Examples 4 to 6) or a mixture of fine particles and powder (Comparative Examples 7 to 9).

[0045] [III: Hydrogen generation]

[0046] Water was added dropwise to the hydrogen generation compositions of Examples 1 to 4 and Comparative Examples 1 to 9 at a rate of 2 mL / min for 15 minutes. The generated hydrogen was collected, and the integrated value (L) of the amount of hydrogen generated was measured. The hydrogen yield (%) was calculated using the following formula. In the formula, a is the molar volume (L / mol) and is a constant of 22.4 under standard conditions. b is the number of moles of hydrogen generated from 1 mol of MgH2 and is a constant of 2. The number of moles of MgH2 used can be calculated from the mass of the hydrogen generation composition used, the mass ratio of MgH2 to citric acid in the hydrogen generation composition, and the molecular weight of MgH2 (26.32). Hydrogen yield (%) = Amount of hydrogen produced (L) / (Number of moles of MgH2 used) × a × b × 100

[0047] Table 1 shows the results of hydrogen generation using the hydrogen generation compositions of Examples 1 to 4 and Comparative Examples 1 to 9. Figure 1 shows the hydrogen yield during hydrogen generation using the hydrogen generation compositions of Examples 1 to 4 and Comparative Examples 1 to 9. In the figure, the horizontal axis represents the mass ratio of citric acid to MgH in the hydrogen generation composition, and the vertical axis represents the hydrogen yield (%). Figure 2 shows the amount of hydrogen generated during hydrogen generation using the hydrogen generation compositions of Examples 1 to 4 and Comparative Examples 1 to 9. In the figure, the horizontal axis represents the mass ratio of citric acid to MgH in the hydrogen generation composition, and the vertical axis represents the amount of hydrogen generated (L). In Figures 1 and 2, open circles (○) represent the results of Examples 1 to 3, × represents the results of Example 4, filled circles (●) represent the results of Comparative Examples 1 to 3, open triangles (△) represent the results of Comparative Examples 4 to 6, and open squares (□) represent the results of Comparative Examples 7 to 9.

[0048] [Table 1] TIFF2025176442000002.tif79158TIFF2025176442000003.tif79158TIFF2025176442000004.tif79158

[0049] As shown in Table 1 and FIGS. 1 and 2, hydrogen was generated at a high yield and in a high amount by performing a hydrogen generation reaction using the hydrogen generation compositions of Examples 1 to 4, in which the mass ratio of citric acid to MgH2 was in the range of 2.5 to 3.5. In contrast, when the hydrogen generation reaction was performed using the hydrogen generation compositions of Comparative Examples 1 to 3, in which the mass ratio of citric acid to MgH2 was outside the above range, the amount of hydrogen produced was low. Furthermore, when the hydrogen generation reaction was performed using the hydrogen generation compositions of Comparative Examples 4 to 6, which were in powder form, both the hydrogen yield and the amount of hydrogen produced were low. When the hydrogen generation reaction was performed using the hydrogen generation compositions of Comparative Examples 7 to 9, both the hydrogen yield and the amount of hydrogen produced were almost equivalent to those of the hydrogen generation compositions of Examples 1 to 4. However, because the hydrogen generation compositions of Comparative Examples 7 to 9 were in the form of a mixture of fine particles and powder, the production of these hydrogen generation compositions, particularly the milling process in the magnesium hydride preparation step, required longer time than the hydrogen generation compositions of Examples 1 to 4.

[0050] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to add, delete, and / or replace part of the configuration of each embodiment with other configurations.

Claims

1. A hydrogen generating composition comprising magnesium hydride in powder form and citric acid in powder form, wherein the mass ratio of citric acid to magnesium hydride is in the range of 2.5 to 3.5, and the composition is in the form of a pressed molded product.

2. 10. The hydrogen generating composition of claim 1, wherein the magnesium hydride has a particle size in the range of 60 to 120 μm.

3. A method for generating hydrogen, comprising contacting the hydrogen generating composition according to claim 1 with water to generate hydrogen.

4. a mixing step of mixing magnesium hydride in powder form and citric acid in powder form; a molding step of pressurizing and molding the mixture obtained in the mixing step; The method for producing the hydrogen generation composition of claim 1, comprising:

5. providing magnesium hydride in the form of a powder having a particle size in the range of 60 to 120 μm; 5. The method of claim 4, further comprising:

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