Hydrogen gas production method

Abstract

This invention provides a hydrogen gas production technology that prevents the solidification of transition metal oxides. [Solution] A method for producing hydrogen gas, comprising the steps of: filling a container with a powder or granular material consisting mainly of particles with a particle diameter of 0.03 mm or more and 4.0 mm or less, having a particle size distribution in which the volume ratio of particles with a particle diameter of less than 0.03 mm is 10% or less and the volume ratio of particles with a particle diameter of more than 4.0 mm is 10% or less, and containing particles that include a transition metal oxide; introducing an inert gas into the container to form a fluidized bed of the powder or granular material; heating the container to set the temperature of the fluidized bed within the range of 400°C or more and 700°C or less; and while maintaining the temperature of the fluidized bed within the range, introducing water vapor into the container to generate hydrogen gas through a reaction between the transition metal oxide and the water vapor.

Description

Technical Field

[0001] The present invention relates to a method for producing hydrogen gas.

Background Art

[0002] Most of the energy supplied to various industrial fields is derived from fossil fuels, and reduction of carbon dioxide emissions is required from the perspective of global warming. For this reason, hydrogen gas has attracted attention as an energy source in recent years, and the utilization of hydrogen gas has been promoted. Accordingly, hydrogen gas that can be supplied at low cost is in demand.

[0003] Patent Document 1 reports a method for producing hydrogen gas by introducing water at 200°C to 600°C into iron oxide, nickel oxide, cobalt oxide and manganese oxide. Patent Document 2 reports a method for producing hydrogen gas by forming a fluidized bed by suspending a catalyst in a particulate form, and introducing fuel gas (hydrocarbon) and steam. In Patent Document 2, when Fe is used as the catalyst, hydrogen gas is generated through a reduction reaction caused by the reaction between FeO and the fuel gas, and hydrogen gas is also produced by the reaction of carbon dioxide generated by the reduction reaction with the fuel gas and steam. Patent Document 3 reports a method for producing hydrogen gas by bringing water, steam or a gas containing steam, and metallic iron particles into contact with each other. In Patent Document 3, an ionic liquid is used to prevent coalescence of the metallic iron particles.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of Invention

Problem to be Solved by the Invention

[0005] However, in the production of hydrogen gas by reacting transition metal oxides with water vapor, there is a problem in that the transition metal oxide particles, especially in the particle size range of 4.0 mm or less, solidify, reducing the reaction efficiency. Patent Document 1 does not disclose any technology to prevent the solidification of iron oxide and the like by introducing water. Patent Document 2 also uses a fluidized bed for particle movement to introduce catalyst particles into the particle tube, but does not disclose any technology to prevent particle solidification. Patent Document 3 targets metallic iron particles with an average particle size range of 1 nm to 200 nm, and does not disclose any technology for metallic iron particles with larger particle sizes or technology to prevent the solidification of iron oxide and the like.

[0006] In view of the above problems, the present invention aims to provide a method for producing hydrogen gas by reacting a transition metal oxide with water vapor, which can suppress the solidification of the transition metal oxide. [Means for solving the problem]

[0007] The inventors of the present invention have diligently studied to solve the above problems and have found that the solidification of transition metal oxides can be prevented by the following method: A granular material consisting of particles containing transition metal oxides is filled into a container, and an inert gas is introduced into the container to form a fluidized bed of the granular material. The container is heated to bring the temperature of the fluidized bed within the range of 400°C to 700°C, and water vapor is introduced into the container to generate hydrogen gas through the reaction of the transition metal oxides with the water vapor.

[0008] In other words, the gist of the present invention is as follows:

[0009] [1] A process of filling a container with a powder or granular material consisting mainly of particles with a particle diameter of 0.03 mm or more and 4.0 mm or less, having a particle size distribution in which the volume ratio of particles with a particle diameter of less than 0.03 mm is 10% or less and the volume ratio of particles with a particle diameter of more than 4.0 mm is 10% or less, and which contains particles including an oxide of a transition metal, The process involves introducing an inert gas into the container to form a fluidized bed of the powder and granules, A step of heating the container to bring the temperature of the fluidized bed within a range of 400°C to 700°C, The process involves maintaining the temperature of the fluidized bed within the range, introducing water vapor into the container, and generating hydrogen gas through the reaction between the transition metal oxide and the water vapor. A method for producing hydrogen gas, comprising:

[0010] [2] The method for producing hydrogen gas according to [1] above, wherein the oxide of the transition metal includes iron(II) oxide.

[0011] [3] The method for producing hydrogen gas according to [2] above, wherein the granular material comprises one or more selected from the group consisting of scale, dust, and sludge, which are by-products of the steelmaking process.

[0012] [4] A method for producing hydrogen gas according to any one of the above [1] to [3], wherein the temperature of the water vapor introduced into the container is 100°C or higher and less than or equal to the temperature of the fluidized bed.

[0013] [5] A method for producing hydrogen gas according to any one of the above [1] to [4], wherein the introduction of the inert gas into the container and the introduction of the water vapor are started simultaneously. [Effects of the Invention]

[0014] According to the present invention, a method for producing hydrogen gas by reacting a transition metal oxide with water vapor can be provided that can suppress the solidification of the transition metal oxide. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram of the test apparatus 100 used in the embodiment of the present invention. [Figure 2] This is a photograph of the powder material recovered after testing in Example 3 of the embodiments of the present invention. [Figure 3]This is a photograph of the granular material recovered after the test in Comparative Example 3 of the examples of the present invention. [Mode for Carrying Out the Invention]

[0016] Hereinafter, a method for producing hydrogen gas according to one embodiment of the present invention will be described. The embodiment described below is a specific example embodying the present invention, and is not intended to limit the configuration of the present invention by this specific example.

[0017] [Granular material composed of particles containing transition metal oxide] The granular material used in the present embodiment is composed of particles containing a transition metal oxide, is mainly composed of particles with a particle diameter of 0.03 mm or more and 4.0 mm or less, and has a particle size distribution in which the volume ratio of particles with a particle diameter of less than 0.03 mm is 10% or less, and the volume ratio of particles with a particle diameter of more than 4.0 mm is 10% or less. In the particle size distribution of the granular material, the volume ratio of particles with a particle diameter of less than 0.03 mm is preferably 5% or less, and the volume ratio of particles with a particle diameter of more than 4.0 mm is preferably 5% or less. In the granular material, when the volume ratio of particles with a particle diameter of less than 0.03 mm exceeds 10%, caking occurs due to the introduction of water vapor even when a fluidized bed described later is formed. On the other hand, the lower limit of the volume ratio of particles with a particle diameter of less than 0.03 mm is not particularly limited, and the volume ratio may be 0%. Further, in the granular material, when the volume ratio of particles with a particle diameter of more than 4.0 mm exceeds 10%, the caking which is the problem of the present invention is less likely to occur. On the other hand, the lower limit of the volume ratio of particles with a particle diameter of more than 4.0 mm is not particularly limited, and the volume ratio may be 0%. From the above, the granular material is mainly composed of particles with a particle diameter of 0.03 mm or more and 4.0 mm or less, and the volume ratio thereof is preferably 90% or more, and may be 100%. The particle diameter of the granular material can be measured using a sieve.

[0018] In a preferred embodiment, the transition metal oxide comprises iron(II) oxide. Within the temperature range of the fluidized bed, the absolute value of the Gibbs free energy change in the oxidation reaction of iron(II) oxide is greater than the absolute value of the Gibbs free energy change in the oxidation reaction of hydrogen. Inside the fluidized bed, a further oxidation reaction of iron(II) oxide and generation of hydrogen gas by a reduction reaction of water vapor occur simultaneously. Both the oxidation reaction of iron(II) oxide and the oxidation reaction of hydrogen are exothermic reactions, and the Gibbs free energy change ΔG in these reactions is a negative value in each case. If the absolute value of the Gibbs free energy change in the oxidation reaction of the transition metal oxide is greater than the absolute value of the Gibbs free energy change for water generation in the reaction by oxidation of hydrogen, the total change amount of the Gibbs free energy in the above series of oxidation-reduction reactions becomes a negative value. Thereby, the generation of hydrogen gas can be allowed to proceed spontaneously under constant temperature and pressure.

[0019] In a more preferred embodiment, the powdery or granular material composed of particles containing the transition metal oxide comprises one or more selected from the group consisting of scale, dust, and sludge which are by-products of an ironmaking process. In the present embodiment, it is necessary to replace the powdery or granular material with new one at the point when the oxidation of the powdery or granular material has progressed. By utilizing these by-products for the powdery or granular material to be replaced, the raw material cost required for the production of hydrogen gas can be reduced.

[0020] Further, in the present embodiment, a powdery or granular material composed of particles containing a transition metal oxide is used. However, from the viewpoint of using particles having a Gibbs free energy in an oxidation reaction whose absolute value is larger than the Gibbs free energy change in the oxidation reaction of hydrogen, the particles containing the transition metal oxide may further contain an unoxidized transition metal. The transition metal in this case may be, for example, Fe, Mn, or Ti.

[0021] (Method for producing hydrogen gas) A hydrogen gas production method according to one embodiment of the present invention comprises the steps of: filling a container with a granular material consisting of particles containing a transition metal oxide having the aforementioned particle size distribution; introducing an inert gas into the container to form a fluidized bed of the granular material; heating the container to set the temperature of the fluidized bed within the range of 400°C to 700°C; and while maintaining the temperature of the fluidized bed within the above range, introducing water vapor into the container to generate hydrogen gas by a reaction between the transition metal oxide and water vapor (oxidation reaction of the transition metal). In this embodiment, a hydrogen gas production apparatus can be used that includes a container for forming a fluidized bed of granular material, a device for introducing an inert gas into the container, a device for introducing water vapor into the container, a device for heating the fluidized bed, and a device for recovering hydrogen gas and inert gas.

[0022] In the hydrogen gas production method according to this embodiment, first, a granular material consisting of particles containing a transition metal oxide is filled into a container. Next, an inert gas is introduced into the container to form a fluidized bed of the granular material. The granular material is blown upward by the inert gas introduced into the container, and then descends due to its own weight. A fluidized bed of granular material is formed as the granular material, mixed with the inert gas, flows while repeatedly rising and falling within the container. N2 or the like can be used as the inert gas. The presence or absence of a fluidized bed can be determined by visually inspecting the inside of the container.

[0023] The flow rate of the inert gas introduced is adjusted according to the particle size of the powder. Preferably, the flow rate of the inert gas is 40 × y (mL / min) to 275 × y (mL / min), where y (g) is the weight of the transition metal oxide particles with a particle size of 0.03 mm to 4.0 mm. By setting the flow rate of the inert gas within the above range, the solidification of the transition metal oxide can be effectively suppressed. Furthermore, preferably, the temperature of the introduced inert gas is between room temperature (15°C) and 700°C.

[0024] Next, the container is heated to bring the temperature of the fluidized bed to a range of 400°C to 700°C. In this specification, "temperature of the fluidized bed" refers to the temperature measured at the location where the fluidized bed is formed. The temperature of the fluidized bed can be measured, for example, by installing a temperature sensor such that its temperature-sensing element is located at the location where the fluidized bed is formed. The temperature of the fluidized bed is maintained within the above range while the reaction for generating hydrogen gas (oxidation reaction of transition metals), which will be described later, is taking place. If the temperature of the fluidized bed is below 400°C, the reaction between iron oxide and water vapor is not promoted, and a sufficient amount of hydrogen gas is not produced. Therefore, the temperature of the fluidized bed should be 400°C or higher, preferably 500°C or higher. On the other hand, if the temperature of the fluidized bed exceeds 700°C, the absolute value of the change in Gibbs free energy in the oxidation reaction of hydrogen is smaller than the absolute value of the change in Gibbs free energy in the oxidation reaction of transition metal oxides, so a sufficient amount of hydrogen gas is not produced by the reduction of water vapor. Therefore, the temperature of the fluidized bed should be 700°C or lower, preferably 650°C or higher.

[0025] Next, while maintaining the temperature of the fluidized bed within the above range, water vapor is introduced into the container to generate hydrogen gas through the reaction of the transition metal oxide with the water vapor. Introducing liquid water into the container would inhibit the formation of the fluidized bed, so water vapor is introduced into the container instead.

[0026] The temperature of the water vapor introduced into the container is preferably 100°C or higher and below the temperature of the fluidized bed. By introducing water vapor within the above temperature range, hydrogen gas can be suitably obtained. Furthermore, the amount of water vapor introduced, in terms of water volume, is preferably greater than 0 mL / min and less than or equal to 0.1 × y (mL / min), where y (g) is the weight of the powder. By setting the amount of water vapor introduced within the above range, hydrogen gas can be suitably obtained.

[0027] The introduction of water vapor into the container may be started simultaneously with the introduction of the inert gas. Since the hydrogen gas production reaction proceeds after the temperature of the fluidized bed reaches the above range, hydrogen gas production can be carried out rapidly.

[0028] Next, hydrogen gas generated by the reaction between the transition metal oxide and water vapor (oxidation reaction of the transition metal) is recovered. The recovery method is not particularly limited, but a drain trap or the like can be used.

[0029] For processes and conditions not described in this specification, conventional methods may be used. [Examples]

[0030] The operation and effects of the present invention will be described below using examples. However, the present invention is not limited to the following examples.

[0031] Figure 1 shows a schematic diagram of the test apparatus 100 used. The test apparatus 100 comprises a tubular furnace 10, a device for blowing gas into the lower part of the tubular furnace 10, and a device for recovering gas from the upper part of the tubular furnace 10. A φ10 mm quartz tube 12 was placed inside the tubular furnace 10, quartz wool 16 was packed inside the quartz tube 12, and powder material was placed on top of it. Inert gas and water vapor were introduced into the quartz tube 12 from the lower part of the tubular furnace 10 by a pump 20. A ribbon heater 22 was wound around a steel pipe connected from the pump 20 to the tubular furnace 10, and the ribbon heater 22 heated the inert gas and water, turning the water vapor before it was introduced into the quartz tube. A heat retention device 18 was installed at the top of the tubular furnace 10, and the generated gas was sent to a drain trap 30 through the heat retention device 18. The drain trap 30 was cooled by an ice bath 32, which condensed and removed any remaining water vapor in the gas. The gas from which the water vapor has been removed is recovered in the gas bag 34. The temperature at the location where the fluidized bed 14 is formed inside the tubular furnace 10 is measured with a thermometer 40 and recorded as the temperature of the fluidized bed. The tubular furnace 10 is also equipped with a window (not shown) that allows observation of the inside, so the presence or absence of fluidized bed formation can be confirmed visually.

[0032] For each example, 2g of scale (iron oxide) generated during the steelmaking process was used as the granular material. Two types of granular material were prepared, with particle sizes ranging from 0.03mm to 0.25mm and 0.25mm to 4.0mm (100% by volume). XRD analysis of the granular materials confirmed that both iron oxides contained FeO and Fe3O4.

[0033] N2 was used as the inert gas. The N2 flow rate was adjusted according to the particle size of the iron oxide. Steam was supplied at a rate of 0.167 mL / min (in terms of water volume) after heating to 200°C. The steam was introduced after the container was heated. Tables 1 and 2 show the particle size of the powder used in each example, the flow rate of the inert gas, whether or not a fluidized bed was formed, whether or not solidification of the powder occurred, the temperature of the fluidized bed, and the amount of hydrogen gas generated. Even when a fluidized bed was not formed due to insufficient flow rate of the inert gas, the temperature inside the quartz tube 12 at the same position as when a fluidized bed was formed was measured with a thermometer 40.

[0034] [Table 1]

[0035] [Table 2]

[0036] As shown in Tables 1 and 2, in Comparative Examples 1 and 4, where the fluidized bed temperature was 350°C, although the formation of the fluidized bed suppressed the solidification of iron oxide, the reaction between iron oxide and water vapor did not proceed due to insufficient temperature, resulting in zero hydrogen gas production. Similarly, in Comparative Examples 2 and 5, where the fluidized bed temperature was 750°C, although the formation of the fluidized bed suppressed the solidification of iron oxide, the temperature was too high for the water vapor to be reduced by the iron oxide, resulting in zero hydrogen gas production.

[0037] As shown in Table 1, when comparing Invention Example 2 and Comparative Example 3, both set at a temperature of 575°C, Invention Example 2, which successfully suppressed the solidification of iron oxide by forming a fluidized bed, produced a higher amount of hydrogen gas than Comparative Example 3, where the fluidized bed could not be formed due to insufficient inert gas flow rate, thus preventing the solidification of iron oxide. Similar results were confirmed when comparing Invention Example 5 and Comparative Example 6 in Table 2. From the above, it is clear that the hydrogen gas production method of the present invention can prevent the solidification of iron oxide and efficiently produce hydrogen gas.

[0038] Figures 2 and 3 show photographs of the powder and granular materials recovered after testing in Invention Example 3 and Comparative Example 3, respectively. In Invention Example 3, where a fluidized bed was formed, no solidification was observed, whereas in Comparative Example 3, solidification of transition metal oxides was confirmed. [Industrial applicability]

[0039] According to the present invention, a method for producing hydrogen gas by reacting a transition metal oxide with water vapor can be provided that can suppress the solidification of the transition metal oxide. [Explanation of symbols]

[0040] 100 devices 10 tube furnace 12 Quartz tube 14 Fluidized bed 16 Quartz wool 18 Heat retention device 20 pumps 22 Ribbon Heater 30 Drain traps 32 Ice bath 34 Gasback 40 thermometer

Claims

1. A process of filling a container with a powder or granular material consisting mainly of particles with a particle diameter of 0.03 mm or more and 4.0 mm or less, having a particle size distribution in which the volume ratio of particles with a particle diameter of less than 0.03 mm is 10% or less, and the volume ratio of particles with a particle diameter of more than 4.0 mm is 10% or less, and which also contains particles containing a transition metal oxide, and The process involves introducing an inert gas into the container to form a fluidized bed of the powder and granules, A step of heating the container to bring the temperature of the fluidized bed within a range of 400°C to 700°C, The process involves maintaining the temperature of the fluidized bed within the range, introducing water vapor into the container, and generating hydrogen gas through the reaction between the transition metal oxide and the water vapor. A method for producing hydrogen gas, comprising:

2. The method for producing hydrogen gas according to claim 1, wherein the oxide of the transition metal includes iron(II) oxide.

3. The method for producing hydrogen gas according to claim 2, wherein the granular material comprises one or more selected from the group consisting of scale, dust, and sludge, which are by-products of the steelmaking process.

4. A method for producing hydrogen gas according to any one of claims 1 to 3, wherein the temperature of the water vapor introduced into the container is 100°C or higher and less than or equal to the temperature of the fluidized bed.

5. A method for producing hydrogen gas according to any one of claims 1 to 3, wherein the introduction of the inert gas into the container and the introduction of the water vapor are started simultaneously.

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