Iron-based powder and hydrogen production agent for hydrogen production

Abstract

To provide an iron-based powder allowed to produce hydrogen with greater efficiency.SOLUTION: An iron-based powder for producing hydrogen comprises, internally of a particle, pores communicating with an external thereof, to have a metallic-iron content of 60 mass% or higher and 100 mass% or lower, in which out of the pores a pore having a diameter of 3 nm-500 μm has a bulk per unit mass of equal to or greater than 0.05 cm3 / g.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to iron-based powder for hydrogen production. [Background technology]

[0002] In recent years, the development of highly efficient and simple methods for producing hydrogen for industrial use has been explored.

[0003] For example, Patent Document 1 discloses a method for producing hydrogen by grinding and mixing inorganic substances such as silicon and aluminum with a solvent using a planetary ball mill.

[0004] Patent document 2 discloses a method for producing hydrogen by imparting residual stress to silicon powder in advance and then reacting it with water. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-47789 [Patent Document 2] Japanese Patent Publication No. 2021-134107 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The method proposed in Patent Document 1 above is a method for producing hydrogen using a mechanochemical reaction. However, this method requires the application of mechanical energy to the metal material using a planetary ball mill, which complicates the apparatus.

[0007] Even in the method proposed in Patent Document 2 mentioned above, it is necessary to pre-treat the silicon powder using a planetary ball mill in order to impart residual stress to the silicon powder, which complicates the process and equipment.

[0008] Therefore, as a method for producing hydrogen more simply, a method using iron-based powder is known. This method utilizes the corrosion reaction of iron to generate hydrogen by the reaction of iron and water, enabling hydrogen production without the need for pretreatment or complex devices. However, the hydrogen generation efficiency still cannot be said to be sufficient, and further improvement in efficiency has been demanded.

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide an iron-based powder capable of generating hydrogen with higher efficiency.

Means for Solving the Problems

[0010] In order to solve the above problems, the present invention focuses on the metallic iron content and the pore volume per unit mass of the iron-based powder, and by setting the respective condition ranges, it has been found that it is possible to provide an iron-based powder that realizes highly efficient hydrogen generation. The present invention is based on the above findings, and the main configuration is as follows.

[0011] [1] An iron-based powder for hydrogen production having pores connecting to the outside inside the particles, wherein the metallic iron content is 60% by mass or more and 100% by mass or less, and the volume per unit mass of the pores having a diameter of 3 nm to 500 μm among the pores is 0.05 cm 3 / g or more, an iron-based powder for hydrogen production.

[0012] [2] The median diameter D of the particle size calculated from the volume-based particle size distribution 50 is 1.00 μm or more and 500.00 μm or less, and the average diameter of the pores having a diameter of 3 nm to 500 μm among the pores is 0.10 μm or more and 100.00 μm or less, the iron-based powder for hydrogen production according to [1] above.

[0013] [3] A hydrogen production agent using the iron-based powder for hydrogen production according to [1] or [2] above.

Effects of the Invention

[0014] According to the present invention, it is possible to provide an iron-based powder that can generate hydrogen with higher efficiency.

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be specifically described. In the following description, unless otherwise specified, “%” refers to “mass %”. Further, the “iron-based powder” refers to a powder containing 50% or more of Fe.

[0016] [Iron-based powder] The iron-based powder according to the present invention has pores connecting the inside and the outside of the particles. By reacting such an iron-based powder having pores with water, the corrosion reaction of iron proceeds, and as a result, hydrogen is generated. The mechanism will be described below.

[0017] First, there are two types of iron corrosion reactions: oxygen-consuming corrosion represented by the following formula (1) and hydrogen-generating corrosion represented by the following formula (2). (1) Fe→Fe 2+ +2e - H2O+1 / 2O2+2e - →2OH - (2) Fe→Fe 2+ +2e - 2H + +2e - →H2

[0018] In a general neutral-condition corrosion environment, the oxygen-consuming corrosion of the above (1) proceeds. In this case, the hydroxide ions generated by the reduction of oxygen and the iron ions generated by the oxidation of iron react to generate iron hydroxide, that is, rust, and hydrogen is not generated.

[0019] ​​​​​Therefore, in order to produce hydrogen, it is necessary to induce the hydrogen-generating corrosion described in (2) above in the iron-based powder.

[0021] Here, crevice corrosion is a typical case in which hydrogen-generating corrosion described in (2) above occurs in general steel products. When a steel product has a gap and moisture is present in that gap, oxygen-consuming corrosion described in (1) above initially progresses inside the gap, and dissolved oxygen is consumed. On the other hand, the outside of the gap is in contact with the atmosphere, so the dissolved oxygen concentration remains high. As a result, an oxygen concentration difference is formed between the inside and outside of the gap.

[0022] Furthermore, within the gap, iron ions generated by corrosion undergo hydrolysis, and hydrogen ions accumulate.

[0023] Thus, inside the gap, the oxygen concentration decreases and the hydrogen ion concentration increases, resulting in the hydrogen-generating corrosion described in (2) above replacing the oxygen-consuming corrosion described in (1) above.

[0024] It is believed that hydrogen generation through this mechanism also occurs in the pores of iron-based powder. That is, when moisture enters the pores, an oxygen concentration difference is formed between the outside and inside of the pores. Furthermore, inside the pores, iron ions are generated by the oxygen-consuming corrosion described in (1) above, and hydrogen ions accumulate through their hydrolysis. As a result, hydrogen-generating corrosion occurs in the pore areas. In other words, the presence of pores inside the iron-based powder that connect to the outside allows the hydrogen generation reaction to proceed.

[0025] [Metallic iron content] The iron-based powder according to the present invention has a metallic iron content of 60% to 100%, preferably 70% to 100%. If the metallic iron content is less than 60%, the elution of iron ions is insufficient, so the corrosion reaction does not proceed sufficiently, and hydrogen cannot be efficiently generated.

[0026] The metallic iron content mentioned above shall be measured in accordance with the "Method for Determining Metallic Iron" specified in JIS A 5011-2.

[0027] In the present invention, the component composition of the iron-based powder is not particularly limited, and as long as the content of metallic iron, which is a component involved in hydrogen generation, satisfies the above conditions, the remainder can be of any composition. In one embodiment of the present invention, an iron-based powder having a component composition consisting of Fe, O, and unavoidable impurities can be used.

[0028] [Pore volume per unit mass] When iron-based powder has pores inside the particles that connect to the outside, these pores can have a wide range of sizes depending on the manufacturing conditions. However, our research has shown that when the diameter of the pores is less than 3 nm or greater than 500 μm, the contribution of the pores to hydrogen generation is significantly reduced. This is thought to be due to the following reasons. First, when the diameter is less than 3 nm, it is difficult for water to penetrate into the pores, making it difficult for the hydrogen generation reaction to occur. On the other hand, when the diameter is greater than 500 μm, a sufficient difference in dissolved oxygen concentration is not formed between the inside and outside of the pores, which also makes it difficult for the hydrogen generation reaction to occur.

[0029] Therefore, in order to increase the hydrogen generation efficiency, it is necessary to increase the amount of pores that contribute to the hydrogen generation reaction, i.e., pores with a diameter of 3 nm to 500 μm. For this reason, in the present invention, the volume of pores with a diameter of 3 nm to 500 μm per unit mass of iron-based powder (hereinafter sometimes referred to as "pore volume") is set to 0.05 cm³. 3 / g or more, preferably 0.08cm 3 The minimum amount should be / g or more.

[0030] [Average pore diameter] In the iron-based powder of the present invention, the average diameter of pores in the range of 3 nm to 500 μm (hereinafter sometimes referred to as "average pore diameter") is preferably 0.10 μm or more and 100.00 μm or less. When the average pore diameter is 0.10 μm or more, water can easily enter the pores, thus increasing the hydrogen generation efficiency. Furthermore, when the average pore diameter is 100.00 μm or less, the difference in dissolved oxygen concentration in the water within the pores becomes larger, further increasing the hydrogen generation efficiency.

[0031] The pore volume and average pore diameter are measured by the mercury intrusion method. Specifically, the pore distribution of the iron-based powder is first measured by the mercury intrusion method using a pore distribution analyzer (Shimadzu Corporation - Micromerics Autopore V9620). For the measurement, approximately 1 g of the sample is placed in a 5 cc powder cell and measured under the following conditions: initial pressure of 7 kPa, mercury contact angle of 130°, and mercury surface tension of 485 dynes / cm. Then, the volume per unit mass and average diameter of pores in the pore size range of 3 nm to 500 μm are calculated from the measurement results.

[0032] [Median particle size D calculated from volume-based particle size distribution] 50 ] The iron-based powder according to the present invention has a median particle size D calculated from the volume-based particle size distribution. 50 It is preferable that the particle size is 1.00 μm or larger, and more preferably 1.50 μm or larger. 50 If the particle size is less than 1.00 μm, the particles become excessively fine, resulting in the generation of a large amount of agglomerated powder. This makes it difficult for the particles inside the agglomerated powder to come into contact with moisture, making it harder for moisture to be trapped in the pores of the internal particles, and thus slightly reducing the efficiency of the hydrogen generation reaction.

[0033] Meanwhile, D 50 It is preferably 500.00 μm or less, and more preferably 300.00 μm or less. 50 By setting the particle size to 500.00 μm or less, moisture penetrates into the interior of the particle, allowing the entire particle to contribute to hydrogen generation, thus increasing the efficiency of hydrogen generation.

[0034] [D 10 and D 90] D of the iron-based powder according to the present invention 10 It is preferable that it is 0.50 μm or larger. 10 By setting the particle size to 0.50 μm or larger, aggregate powder generation becomes less likely, and moisture is more easily captured by each particle in the iron-based powder. Furthermore, the D of the iron-based powder according to the present invention 90 It is preferable that it is 800.00 μm or less. 90 By setting the particle size to 800.00 μm or less, moisture can penetrate into the interior of each particle, thus increasing the efficiency of hydrogen generation.

[0035] Note D 50 , D 10 and D 90 This is measured by laser diffraction / scattering. Specifically, first, the volume-based particle size distribution of the iron-based powder is measured using a laser diffraction / scattering particle size distribution analyzer (LA-950V2, manufactured by Horiba, Ltd.). This measurement is performed after the iron-based powder is placed in ethanol as a solvent and dispersed by ultrasonic vibration for 1 minute. From the obtained volume-based particle size distribution, the median value D is calculated. 50 , Value D at 10% cumulative from the fine granule side 10 And the value D at 90% cumulatively from the fine granule side. 90 Calculate.

[0036] [Method for producing powder] Next, a method for producing the iron-based powder according to one embodiment of the present invention will be described. Note that the following description is merely an example of a manufacturing method, and the present invention is not limited to the following description.

[0037] The iron-based powder according to the present invention can be manufactured by any method. For example, the iron-based powder can be manufactured by atomization, oxide reduction, or pulverization. The atomization method involves blowing water or gas onto molten metal to pulverize it and then cooling and solidifying it; either water atomization or gas atomization can be used. The oxide reduction method is, for example, a method of roughly reducing iron oxide generated from the surface of steel plates during hot rolling of steel materials or iron ore powder mined from mines. The pulverization method is a method of pulverizing small metal pieces using a pulverizer. Furthermore, the iron-based powder according to the present invention may be manufactured by performing a finish reduction on the powder manufactured by the atomization method or oxide reduction method. Performing the finish reduction can increase the metallic iron content. However, when the iron-based powder is manufactured by the pulverization method, the metallic iron content is sufficiently high, so the finish reduction step is usually not required.

[0038] Furthermore, the particle size of the iron-based powder produced by the above-described method may be adjusted. Here, the powder produced by the atomization method, oxide reduction method, and pulverization method, as well as the powder after the final reduction, are referred to as the powder before particle size adjustment. The powder before particle size adjustment may be used as is as the iron-based powder according to the present invention, or it may be classified, crushed, or mixed to produce the iron-based powder according to the present invention.

[0039] The specific manufacturing conditions are described below. In the following description, rough reduction and finish reduction may be collectively referred to as reduction or the reduction process.

[0040] It is preferable to perform the reduction step in order to increase the metallic iron content of the iron-based powder according to the present invention. It is preferable to use a powder with a high total iron content as the raw material for the reduction step.

[0041] For example, a tunnel furnace can be used for the rough reduction process, and a belt furnace can be used for the final reduction process. As the reducing agent, for example, a carbon substance such as coke can be used for the rough reduction process, and hydrogen can be used for the final reduction process.

[0042] The reduction temperature in the reduction step shall be 800°C or higher. This shall result in a volume per unit mass of pores with a diameter of 3 nm to 500 μm in the iron-based powder according to the present invention being 0.05 cm³. 3 It can be 1g or more.

[0043] The reduction time in the reduction step is preferably 1 hour or more. This makes it possible to make the average diameter of the pores in the iron-based powder according to the present invention, with a diameter of 3 nm to 500 μm, 0.10 μm or more.

[0044] Next, the conditions for classification etc. will be explained. D of the iron-based powder according to the present invention 50 To make the particle size 1.00 μm or larger, the powder before particle size adjustment may be sieved to remove fine particles. Alternatively, the powder before particle size adjustment may be classified by sieving to obtain two or more powders with different particle sizes, and these powders may be mixed in an appropriate ratio.

[0045] Meanwhile, D 50 To make the particle size 500.00 μm or less, the crushing conditions of the powder before particle size adjustment may be adjusted, or the powder before particle size adjustment may be sieved to remove coarse particles. Alternatively, two or more powders with different particle sizes may be obtained by classifying the powder before particle size adjustment by sieving, and these powders may be mixed in an appropriate ratio.

[0046] Furthermore, in order to make the average diameter of the pores in the iron-based powder according to the present invention, which have a diameter of 3 nm to 500 μm, 100.00 μm or less, the powder before particle size adjustment may be impact-milled with a hammer mill or classified by sieving.

[0047] [Hydrogen production agent] The hydrogen production agent according to the present invention is made using the iron-based powder described above. The hydrogen production agent may be made using the iron-based powder itself, or it may be made using the iron-based powder and one or more other materials.

[0048] [Method of using iron-based powder and hydrogen production agent] Next, a method of using the iron-based powder and hydrogen production agent in one embodiment of the present invention will be described. Note that the following description is merely an example of a method of use, and the present invention is not limited to the following description.

[0049] The method of using the iron-based powder or hydrogen-producing agent according to the present invention is not particularly limited. For example, hydrogen can be generated by reacting the iron-based powder or hydrogen-producing agent according to the present invention with water. Any water can be used as the water, but distilled water is preferred.

[0050] Furthermore, additives may be added to the above-mentioned moisture. Examples of additives include sodium chloride, calcium chloride, potassium chloride, and magnesium chloride, and one or more of these can be used. A passive film composed of iron oxide is formed on the surface of the iron-based powder. However, by using the above-mentioned additives, the passive film is destroyed by chloride ions, and a phenomenon of oxidation (pitting corrosion) occurs inside the iron-based powder. As a result, corrosion progresses, and the hydrogen generation efficiency can be further improved. In addition, an acid can be used as the above-mentioned additive. This lowers the pH of the solution, promotes hydrogen generation type corrosion that occurs under low pH conditions, and further improves the hydrogen generation efficiency. For example, citric acid can be used as the above-mentioned acid. [Examples]

[0051] Next, the present invention will be described in more detail based on the following examples. However, the present invention is not limited by the following examples, and can be modified as appropriate within the scope that is consistent with the spirit of the invention, and all of these modifications fall within the technical scope of the present invention.

[0052] First, powders were prepared by atomization or oxide reduction. The particle size of these powders was adjusted by reduction and classification at 600-790°C to obtain iron-based powders of Comparative Examples 1-13. Furthermore, the particle size of these powders was adjusted by reduction and classification at 800-1300°C to obtain iron-based powders of Invention Examples 14-34. The iron-based powders of Comparative Examples 1-13 and Invention Examples 14-34 all have a component composition consisting of Fe, O, and unavoidable impurities. For these iron-based powders, the metallic iron content, pore volume, average pore diameter, and D were determined using the methods described above. 50 , D 10 and D 90 They sought it.

[0053] The hydrogen generation efficiency of the above iron-based powder was evaluated by the following method.

[0054] 1.0 g of each iron-based powder, 3.0 g of distilled water, and 0.9 g of sodium chloride were placed in a 150 mL glass beaker, and the glass beaker was sealed with a rubber stopper under atmospheric pressure. The glass beaker itself was then kept warm at 60°C and stirred at a rotation speed of 1800 rpm. A shaking incubator (manufactured by AS ONE Corporation) was used for warming and stirring. 480 minutes after the start of stirring, a hole was made in the rubber stopper, and 1 mL of gas from the glass beaker was collected using a syringe. The hydrogen concentration in the gas was measured using a gas chromatograph (manufactured by GL Sciences Co., Ltd.).

[0055] Table 1 shows the manufacturing methods and evaluation results for each iron-based powder. The higher the hydrogen concentration, the more hydrogen is generated in the same amount of time, indicating good hydrogen generation efficiency for iron-based powders. When using iron-based powders that meet the conditions of the present invention, a high hydrogen concentration of 10% by volume or more was observed, and hydrogen generation proceeded more efficiently than with iron-based powders that did not meet the conditions of the present invention.

[0056] Furthermore, the average pore size is 0.10 to 100.00 μm and D 50 Examples 26-34 of the invention, which use iron-based powder with a particle size of 1-500 μm, show a hydrogen concentration of 17% by volume or more, indicating a higher hydrogen generation efficiency compared to other examples of the invention.

[0057] Comparing Invention Example 26 and Invention Example 27, the iron-based powder D 10 Inventive Example 27, where the particle size is 0.50 μm or larger, the hydrogen concentration is higher and the hydrogen generation efficiency is superior.

[0058] Comparing Invention Example 28 and Invention Example 29, the iron-based powder D 90 Inventive Example 29, where the particle size is 800.00 μm or less, the hydrogen concentration is high and the hydrogen generation efficiency is superior.

[0059] Comparing Invention Example 27 and Invention Example 30, the iron-based powder D 50 Inventive Example 30, where the particle size is 1.5 to 300 μm, the hydrogen concentration is high and the hydrogen generation efficiency is superior.

[0060] Comparing Invention Example 30 and Invention Example 31, Invention Example 31, in which the metallic iron content of the iron-based powder is 70% to 100%, has a higher hydrogen concentration and superior hydrogen generation efficiency.

[0061] Comparing Invention Example 30 and Invention Example 32, the volume per unit mass of pores with a diameter of 3 nm to 500 μm in the iron-based powder is 0.08 cm³. 3 Invention example 30, with a hydrogen concentration of 1 / g or more, has a higher hydrogen concentration and superior hydrogen generation efficiency.

[0062] [Table 1]

Claims

1. An iron-based powder for hydrogen production having pores inside the particles that connect to the outside, The metallic iron content is 60% by mass or more and 100% by mass or less. Of the aforementioned pores, those with a diameter of 3 nm to 500 μm have a volume of 0.05 cm³ per unit mass. ３ / g or more, Iron-based powder for hydrogen production, wherein the average diameter of the pores with a diameter of 3 nm to 500 μm is 17.58 μm or more and 110.25 μm or less.

2. Median particle size D calculated from volume-based particle size distribution ５０ The particle size is between 1.00 μm and 500.00 μm. The iron-based powder for hydrogen production according to claim 1, wherein the average diameter of the pores with a diameter of 3 nm to 500 μm is 17.58 μm or more and 100.00 μm or less.

3. A hydrogen production agent comprising the iron-based powder for hydrogen production described in claim 1 or 2.

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