Hydrogen-generating composition, method for producing same, and method for generating hydrogen

Abstract

The invention relates to a hydrogen generating composition, a method for producing the same, and a method for generating hydrogen. Provided is a means capable of generating hydrogen gas at a high yield and a high production amount. One embodiment of the present invention relates to a hydrogen-generating composition containing magnesium hydride in the form of a powder and citric acid in the form of a powder, the mass ratio of citric acid to magnesium hydride being in the range of 2.5-3.5, and the hydrogen-generating composition being in the form of a press-molded product. Another aspect of the present invention relates to a method for producing a hydrogen gas generating composition and a method for generating hydrogen gas.

Description

Technical Field

[0001] This invention relates to hydrogen-generating compositions and methods for manufacturing the same, as well as methods for generating hydrogen. Background Technology

[0002] The demand for hydrogen is increasing as it is used as a fuel gas in fuel cells. Methods for supplying and / or storing hydrogen include storing it in high-pressure cylinders, storing liquid hydrogen in cylinders, storing it in hydrogen storage alloys, and modifying gases such as natural gas or methanol to obtain hydrogen.

[0003] In addition to the methods described above, there are also known methods for generating hydrogen by hydrolyzing metal hydrides. For example, Patent Document 1 describes a method for generating hydrogen, in which hydrogen is generated by hydrolyzing granular material obtained by pressurizing magnesium hydride.

[0004] Patent document 2 discloses a method for generating hydrogen, wherein hydrogen is generated by supplying water to a mixture of a solid hydride and a solid acid.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2012-236725

[0008] Patent Document 2: Japanese Patent Application Publication No. 2006-298670 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] In existing methods for hydrolyzing metal hydrides to generate hydrogen, it is known that adding acid to inhibit the formation of a passive state of metal hydroxide on the surface of the metal hydride can increase the yield of generated hydrogen (e.g., Patent Document 2). On the other hand, if the amount of acid added increases while the amount of metal hydroxide decreases relatively, the amount of hydrogen generated will decrease. However, the optimal mixing ratio of metal hydride and acid for generating hydrogen with high yield and high production volume is not yet known.

[0011] Therefore, the object of the present invention is to provide a means for generating hydrogen with high yield and high production volume.

[0012] Methods for solving problems

[0013] The inventors have conducted various studies on methods for solving the above-mentioned problems. The inventors discovered that by separately using magnesium hydride in powder form as a metal hydride and citric acid in powder form as an acid, mixing them in a prescribed mass ratio and preparing them into a press-molded form, a composition capable of generating hydrogen gas in high yield and high production quantity can be obtained. Based on the above insights, the inventors completed the present invention.

[0014] That is, the present invention includes the following methods and implementation methods.

[0015] (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 hydrogen generating composition is in the form of a pressure-molded article.

[0016] (Embodiment 2) The hydrogen generating composition according to Embodiment 1, wherein the magnesium hydride has a particle size in the range of 60 to 120 μm.

[0017] (Embodiment 3) A method for generating hydrogen, wherein hydrogen is generated by contacting the hydrogen generating composition described in Embodiment 1 or 2 with water.

[0018] (Embodiment 4) The method for manufacturing the hydrogen generating composition described in Embodiment 1 or 2 includes: a mixing step of mixing magnesium hydride in powder form and citric acid in powder form; and a molding step of pressing the mixture obtained in the mixing step.

[0019] (Embodiment 5) The method according to Embodiment 4 further includes a magnesium hydride preparation step of preparing magnesium hydride in the form of powder with a particle size in the range of 60 to 120 μm.

[0020] Invention Effects

[0021] This invention provides a means for generating hydrogen with high yield and high production volume. Attached Figure Description

[0022] Figure 1 The figure shows the hydrogen yield in hydrogen generation using the hydrogen generating compositions of Examples 1-4 and Comparative Examples 1-9. In the figure, the horizontal axis represents the mass ratio of citric acid to MgH2 in the hydrogen generating composition, and the vertical axis represents the hydrogen yield (%). Hollow circles (○) represent the results of Examples 1-3, × represents the results of Example 4, black circles (●) represent the results of Comparative Examples 1-3, hollow triangles (△) represent the results of Comparative Examples 4-6, and hollow quadrilaterals (□) represent the results of Comparative Examples 7-9.

[0023] Figure 2The figure shows the amount of hydrogen generated in hydrogen generation using the hydrogen generating compositions of Examples 1-4 and Comparative Examples 1-9. In the figure, the horizontal axis represents the mass ratio of citric acid to MgH2 in the hydrogen generating composition, and the vertical axis represents the amount of hydrogen generated (L). Hollow circles (○) represent the results of Examples 1-3, × represents the results of Example 4, black circles (●) represent the results of Comparative Examples 1-3, hollow triangles (△) represent the results of Comparative Examples 4-6, and hollow quadrilaterals (□) represent the results of Comparative Examples 7-9. Detailed Implementation

[0024] The preferred embodiments of the present invention will now be described in detail.

[0025] <1: Hydrogen-generating composition>

[0026] One aspect of the present invention relates to a hydrogen-generating composition. This hydrogen-generating composition contains magnesium hydride (hereinafter also referred to as "MgH2") and citric acid (hereinafter also referred to as "C(OH)(CH2COOH)2COOH"). By contacting this hydrogen-generating composition with water, magnesium hydride is hydrolyzed to generate hydrogen. At this time, it is presumed that the following hydrogen-generating reaction occurs. In this reaction, it is presumed that the citric acid contained in the hydrogen-generating composition inhibits the formation of inactive magnesium hydroxide, which can be generated through the hydrolysis of magnesium hydride. That is, theoretically, 1 mol of magnesium hydride can generate 2 mol of hydrogen.

[0027] 3MgH2+2C(OH)(CH2COOH)2COOH+6H2O→Mg 2+ 3[C(OH)(CH2COO - )2COO - ]2+6H2O+6H2

[0028] In the hydrogen-generating composition of this method, both magnesium hydride and citric acid are in powder form. The particle size of the magnesium hydride powder is preferably in the range of 60–120 μm, more preferably in the range of 80–120 μm, further preferably in the range of 80–110 μm, and particularly preferably in the range of 101–110 μm. The particle size of the citric acid powder is preferably in the range of 60–120 μm, more preferably in the range of 80–120 μm, further preferably in the range of 80–110 μm, and particularly preferably in the range of 101–110 μm. When the particle size of magnesium hydride is smaller than the above-mentioned lower limit, the time required to micronize the magnesium hydride may become longer in the method for manufacturing the hydrogen-generating composition described below. Furthermore, when the particle sizes of magnesium hydride and citric acid, especially magnesium hydride, exceed the above-mentioned upper limit, the yield and / or amount of hydrogen generated may decrease. Therefore, by containing magnesium hydride and citric acid in the form of powder with the above-mentioned particle size, especially magnesium hydride, the hydrogen generating composition of this method can generate hydrogen in high yield and high production volume.

[0029] In various embodiments of the present invention, the particle size of magnesium hydride and citric acid contained in the hydrogen-generating composition can be determined, for example, by breaking up a pressurized molded part of the hydrogen-generating composition and measuring the particle size of the resulting powder using a particle size distribution measuring device.

[0030] In the hydrogen-generating composition of this method, 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. When the mass ratio is less than the lower limit mentioned above, the yield and amount of hydrogen produced may decrease. Furthermore, when the mass ratio exceeds the upper limit mentioned above, the content of magnesium hydride decreases relatively, and therefore the amount of hydrogen produced may decrease. Therefore, by containing magnesium hydride and citric acid in the mass ratios within the above ranges, the hydrogen-generating composition of this method can generate hydrogen with high yield and high amount produced.

[0031] In various embodiments of the present invention, the presence and content of magnesium hydride and citric acid contained in the hydrogen-generating composition can be determined, for example, by analysis using X-ray diffraction (XRD), mass spectrometry (MS), or nuclear magnetic resonance spectroscopy (NMR).

[0032] The hydrogen-generating composition of this method is in the form of a pressurized article. The shape of the pressurized article is not particularly limited; examples include cylindrical, spherical, and plate-shaped articles. The maximum length of the pressurized article is typically in the range of 1 to 100 mm. By having a pressurized article form, compared with prior art compositions in powder form, the hydrogen-generating composition of this method can generate hydrogen with high yield and high production quantity.

[0033] In various embodiments of the present invention, the morphology and shape of the hydrogen-generating composition can be determined, for example, by observing the hydrogen-generating composition using a microscope.

[0034] In various embodiments of the present invention, the amount of hydrogen generated can be determined, for example, by adding water to the hydrogen generating composition, capturing the generated hydrogen, and measuring its volume.

[0035] In various embodiments of the present invention, the yield of hydrogen can be calculated, for example, based on the following formula. In the following formula, a is the molar volume (L / mol), which is a constant of 22.4 under standard conditions. b is the number of moles of hydrogen generated from 1 mol of MgH2, which is a constant of 2. The number of moles of MgH2 used can be calculated based on the mass of the hydrogen-generating composition used, the mass ratio of MgH2 to citric acid in the hydrogen-generating composition, and the molecular weight of MgH2 (26.32).

[0036] Hydrogen yield (%) = Hydrogen production (L) / (Number of moles of MgH2 used) × a × b × 100

[0037] <2: Method for manufacturing hydrogen-generating compositions>

[0038] Another aspect of the present invention relates to a method for manufacturing a hydrogen-generating composition. This method includes a mixing step and a molding step. The method may, as desired, include a magnesium hydride preparation step and a citric acid preparation step. Each step is described in detail below.

[0039] [2-1: Magnesium hydride preparation process]

[0040] This process includes preparing magnesium hydride in powder form.

[0041] The magnesium hydride powder prepared in this process preferably has the particle size described above.

[0042] In this process, magnesium hydride with a specified particle size can be prepared, for example, by pulverizing magnesium hydride. Examples of pulverizing methods for magnesium hydride include ball mills, bead mills, jet mills, and ultrasonic homogenizers. Specific conditions (e.g., stirring speed, stirring time, rotation speed, etc.) of the methods described above are not particularly limited and can be appropriately set within any range. The pulverized magnesium hydride can be size-separated using an automatic sieving machine or the like with one or more sieves, as desired. 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.

[0043] [2-2: Citric Acid Preparation Process]

[0044] This process includes preparing citric acid in powder form.

[0045] The citric acid in powder form prepared in this process preferably has the particle size described above.

[0046] In this process, citric acid in powder form with a specified particle size can be prepared, for example, by pulverizing citric acid. The pulverization of citric acid and the separation of the pulverized citric acid according to the desired size can be carried out in the same manner as the magnesium hydride preparation process.

[0047] [2-3: Mixing Process]

[0048] This process involves mixing magnesium hydride in powder form and citric acid in powder form.

[0049] In this process, the mixing of magnesium hydride in powder form and citric acid in powder form can be achieved using methods such as ball mills, bead mills, jet mills, and ultrasonic homogenizers. The specific conditions of the methods described above (e.g., stirring speed, stirring time, and rotation speed) are not particularly limited and can be appropriately set within any range.

[0050] [2-4: Molding process]

[0051] This process includes pressing and molding the mixture obtained in the mixing process.

[0052] In this process, the pressure molding of the mixture can be carried out, for example, by feeding the mixture into a mold of a predetermined shape and applying a load to the mold. The shape of the mold used can be appropriately selected based on the shape of the hydrogen-generating 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.

[0053] As explained above, one aspect of the hydrogen-generating composition of the present invention is in the form of a pressurized molded product, thereby enabling the generation of hydrogen with high yield and high production volume even when the particle size of magnesium hydride and citric acid in powder form, particularly magnesium hydride, is 60 μm or larger. Therefore, in the magnesium hydride preparation step, it is not necessary to micronize the magnesium hydride in powder form to a particle size of less than 60 μm. Therefore, by carrying out this process under the conditions illustrated above, the hydrogen-generating composition of one aspect of the present invention can be manufactured in a shorter time compared to compositions of the prior art.

[0054] <3: Methods for generating hydrogen>

[0055] Another aspect of the present invention relates to a method for generating hydrogen. This method includes a hydrogen generation step of contacting a hydrogen-generating composition of one aspect of the present invention with water to generate hydrogen.

[0056] In the hydrogen generation process, there are no particular limitations on the conditions under which the hydrogen generating composition comes into contact with water. This process can be carried out, for example, by adding water dropwise to the hydrogen generating composition, immersing the hydrogen generating composition in water, or allowing water to flow through a flow path containing the hydrogen generating composition.

[0057] The water used in the hydrogen generation process can be pure water, or any one of an aqueous solution or aqueous dispersion containing one or more other components.

[0058] As detailed above, hydrogen production composition according to one aspect of the present invention can generate hydrogen in high yield and high quantity. Therefore, hydrogen production composition according to one aspect of the present invention can provide a fuel gas supply means for fuel cells.

[0059] Example

[0060] The present invention will now be described in more detail using examples. However, the scope of the present invention is not limited to these examples.

[0061] [I: Materials]

[0062] Magnesium hydride (MgH2) is "magnesium hydride powder" manufactured by Biocoke Corporation. Citric acid [C(OH)(CH2COOH)2COOH] is "citric acid (anhydrous)" manufactured by NACALAI TESQUE.

[0063] [II: Preparation of the Hydrogen-Generating Composition]

[0064] (Citrate preparation process)

[0065] Citric acid was pulverized using a ball mill for 60 minutes. The resulting citric acid powder was then sieved using an automatic sieve equipped with a 106 μm mesh to obtain citric acid in powder form with a particle size of approximately 106 μm.

[0066] (Magnesium hydride preparation process)

[0067] Magnesium hydride was pulverized using a ball mill for 20 minutes (Examples 1-4 and Comparative Examples 1-6) or 60 minutes (Comparative Examples 7-9). The obtained magnesium hydride powder was sieved using an automatic sieve equipped with a sieve with a mesh size of 106 μm (Examples 1-4 and Comparative Examples 1-6) or 53 μm (Comparative Examples 7-9) to obtain magnesium hydride in a powder form with a particle size of approximately 106 μm (Examples 1-4 and Comparative Examples 1-6) or in a particulate form with a particle size of approximately 53 μm (Comparative Examples 7-9).

[0068] (Mixed process)

[0069] The powdered or particulate magnesium hydride and powdered citric acid obtained in the citric acid preparation process and the magnesium hydride preparation process are placed in a container at a specified mixing ratio and mixed until they become visually uniform.

[0070] (Molding process)

[0071] Regarding Examples 1-4 and Comparative Examples 1-3, the mixture (17.5 g) obtained in the mixing process was placed into a cylindrical mold (inner diameter: 10 mm, height: 10 mm). The mixture was pressurized by applying a load of 0.8 kN to the mold to obtain a hydrogen-generating composition in the form of a pressurized cylindrical article (diameter: 10 mm, height: 50 mm).

[0072] Regarding Comparative Examples 4 to 9, the mixture obtained in the mixing process was not subjected to pressure molding to obtain hydrogen-generating compositions in powder form (Comparative Examples 4 to 6) or in the form of a mixture of particles and powder (Comparative Examples 7 to 9).

[0073] [III: Hydrogen Generation]

[0074] Water was added dropwise to the hydrogen-generating compositions of Examples 1-4 and Comparative Examples 1-9 at a rate of 2 mL / min for 15 minutes. The generated hydrogen gas was collected, and the integral value of the hydrogen generation amount (L) was measured. The hydrogen yield (%) was calculated based on the following formula. In the following formula, a is the molar volume (L / mol), which is a constant of 22.4 under standard conditions. b is the number of moles of hydrogen gas generated from 1 mol of MgH2, which is a constant of 2. The number of moles of MgH2 used can be calculated based on the mass of the hydrogen-generating composition used, the mass ratio of MgH2 to citric acid in the hydrogen-generating composition, and the molecular weight of MgH2 (26.32).

[0075] Hydrogen yield (%) = Hydrogen production (L) / (Number of moles of MgH2 used) × a × b × 100

[0076] The results of hydrogen generation using the hydrogen generating compositions of Examples 1-4 and Comparative Examples 1-9 are shown in Table 1. Additionally, the hydrogen yield in hydrogen generation using the hydrogen generating compositions of Examples 1-4 and Comparative Examples 1-9 is shown in Table 1. Figure 1 In the figure, the horizontal axis represents the mass ratio of citric acid to MgH2 in the hydrogen-generating composition, and the vertical axis represents the hydrogen yield (%). The amount of hydrogen generated in hydrogen generation using the hydrogen-generating compositions of Examples 1-4 and Comparative Examples 1-9 is shown in the figure. Figure 2 In the figure, the horizontal axis represents the mass ratio of citric acid to MgH2 in the hydrogen-generating composition, and the vertical axis represents the amount of hydrogen generated (L). Figure 1 and 2 In the examples, the hollow circle (○) represents the results of Examples 1 to 3, the × represents the results of Example 4, the black circle (●) represents the results of Comparative Examples 1 to 3, the hollow triangle (△) represents the results of Comparative Examples 4 to 6, and the hollow quadrilateral (□) represents the results of Comparative Examples 7 to 9.

[0077] [Table 1]

[0078]

[0079]

[0080]

[0081]

[0082] As shown in Table 1 and Figure 1 and 2As shown, hydrogen generation reactions were carried out using the hydrogen generation compositions of Examples 1-4, where the mass ratio of citric acid to MgH2 was in the range of 2.5 to 3.5, resulting in high yields and high production amounts of hydrogen. In contrast, hydrogen generation reactions were carried out using the hydrogen generation compositions of Comparative Examples 1-3, where the mass ratio of citric acid to MgH2 was outside the aforementioned range, resulting in low hydrogen production. Furthermore, hydrogen generation reactions were carried out using the hydrogen generation compositions of Comparative Examples 4-6, which were in powder form, resulting in both low hydrogen yield and low hydrogen production amount. When hydrogen generation reactions were carried out using the hydrogen generation compositions of Comparative Examples 7-9, both hydrogen yield and hydrogen production amount were approximately the same as those of the hydrogen generation compositions of Examples 1-4. However, the hydrogen generation compositions of Comparative Examples 7-9 were in the form of a mixture of microparticles and powder, therefore, compared to the hydrogen generation compositions of Examples 1-4, the manufacturing of these hydrogen generation compositions, particularly the pulverization process in the magnesium hydride preparation step, required a longer time.

[0083] It should be noted that the present invention is not limited to the above embodiments and may include various modifications. For example, the above embodiments are examples described in detail for the purpose of easily understanding the present invention and are not necessarily limited to examples having all the described configurations. In addition, regarding a part of the configuration of each embodiment, other configurations may be added, deleted, and / or replaced.

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 hydrogen-generating composition is in the form of a pressure-molded article.

2. The hydrogen-generating composition according to claim 1, wherein, Magnesium hydride has a particle size ranging from 60 to 120 μm.

3. A method for generating hydrogen, wherein, Hydrogen gas is generated by contacting the hydrogen-generating composition of claim 1 with water.

4. A method for manufacturing the hydrogen-generating composition according to claim 1, comprising: A mixing process that combines magnesium hydride in powder form and citric acid in powder form. A molding process that involves pressing the mixture obtained in the mixing process into shape.

5. The method according to claim 4, further comprising: Magnesium hydride preparation process for preparing magnesium hydride in powder form with a particle size in the range of 60 to 120 μm.

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