JP7367809B2 - Carbon and hydrogen production methods, carbon materials, reducing agents, carbon dioxide decomposition methods - Google Patents

Description

The present invention relates to a method for producing carbon and hydrogen using carbon dioxide and water, a carbon material, a reducing agent, and a method for decomposing carbon dioxide.

For example, large amounts of carbon dioxide (CO ₂ ) are emitted in steel plants, thermal power plants, cement factories, garbage incineration facilities, and the like. Therefore, from the perspective of preventing global warming, it has become important to recover carbon dioxide without releasing it into the atmosphere.
On the other hand, with the increasing demand for hydrogen from fuel cell vehicles (FCVs) and hydrogen power generation, there is a need for hydrogen that can be supplied in large quantities at low cost.

Conventionally, chemical absorption methods, physical absorption methods, membrane separation methods, and the like are known as techniques for separating and recovering carbon dioxide. In addition, techniques for decomposing the recovered carbon dioxide include semiconductor photocatalytic method, photochemical reduction method using metal colloid catalysts, metal complexes, catalysts, etc., electrochemical reduction method, chemical fixation conversion reaction, etc. Decomposition methods using reactions, transfer reactions, dehydration reactions, addition reactions, etc. are known. However, all of these carbon dioxide decomposition methods have problems in that they are not practical in terms of reaction efficiency, cost, energy consumption, etc.

For this reason, for example, in Patent Document 1, carbon dioxide is reduced using magnetite with vacancies that are oxygen defect sites in the lattice, that is, oxygen-deficient iron oxide, and carbon is produced, and methane and methanol are produced from the carbon. A method for obtaining the information is disclosed. In the invention of Patent Document 1, carbon dioxide is decomposed (reduction reaction) by oxygen-deficient iron oxide, and the oxidized iron oxide is reduced with hydrogen to return it to oxygen-deficient iron oxide, thereby continuously decomposing carbon dioxide (reduction reaction). It is said that a closed system that can decompose carbon dioxide efficiently and efficiently can be realized.

On the other hand, as a method for producing high-purity hydrogen, for example, in Patent Document 2, iron chloride and water are reacted at 410°C or higher to generate magnetite, hydrogen chloride, and hydrogen, and the generated hydrogen is passed through a separation membrane. Disclosed is a method for using and recovering the material. In the invention of Patent Document 2, it is said that hydrogen, which is a clean energy fuel, can be obtained by thermochemical decomposition technology by effectively utilizing process waste heat discharged from various plants and using water as a raw material.

Japanese Patent Application Publication No. 5-184912 Japanese Patent Application Publication No. 2001-233601

However, under the reaction conditions disclosed in Patent Document 1, the degree of oxygen deficiency of the oxygen-deficient iron oxide is small (when the oxygen-deficient iron oxide is represented by Fe ₃ O _4-δ , δ is at most 0.16 degree), and its ability to decompose carbon dioxide was low, so there was a problem that it was not possible to decompose carbon dioxide efficiently. In addition, when carbon dioxide is continuously decomposed using the method of Patent Document 1, it is necessary to supply hydrogen from outside to reduce magnetite to oxygen-deficient iron oxide, and there is also the problem that the cost associated with hydrogen supply is high. there were.
Furthermore, since Patent Document 1 uses expensive nano-sized magnetite, the cost of decomposing carbon dioxide is high. Furthermore, since the carbon produced is not nanocarbon with high added value (>1 μm), there is a problem that the economic efficiency of the carbon dioxide decomposition plant is low.

In Patent Document 2, there are many substances involved in the hydrogen production reaction (there are also magnesium compounds in addition to magnetite, which is an iron compound), and the reaction mechanism is complicated. Furthermore, since the temperature required for the reaction is high (approximately 1000° C.), there is a problem that energy consumption is large and manufacturing costs are high.
Furthermore, Patent Document 2 focuses only on the effective use of exhaust heat emitted from various plants that consume large amounts of energy, and also focuses on the effective use of carbon dioxide that is emitted along with the exhaust heat from many of these plants. is required.

This invention was made in view of the above-mentioned circumstances, and it is possible to efficiently generate carbon and hydrogen from carbon dioxide and water, and to repeatedly generate and use the reducing agent used in the reaction. The present invention aims to provide a method for producing carbon and hydrogen, a carbon material obtained thereby, a reducing agent, and a method for decomposing carbon dioxide.

In order to solve the above problems, the present invention proposes the following means.
(1) The method for producing carbon and hydrogen according to Aspect 1 of the present invention includes a carbon dioxide decomposition step of reacting carbon dioxide with a reducing agent to produce magnetite with carbon attached to the surface, and the carbon dioxide decomposition step. A carbon separation step in which the magnetite with carbon attached to the surface obtained in step 1 is reacted with hydrochloric acid or hydrogen chloride gas to produce carbon and iron chloride, and iron chloride obtained in the carbon separation step. An iron chloride reduction step in which iron chloride (III) contained in , a hydrogen production step of producing magnetite, hydrogen, and hydrogen chloride gas; and a reduction of reacting the magnetite and hydrogen obtained in the hydrogen production step with each other to produce the reducing agent used in the carbon dioxide decomposition step. the reducing agent is represented by Fe ₃ O _4-δ (where δ is 1 or more and less than 4) obtained by reducing magnetite while maintaining the crystal structure of magnetite. Oxygen-deficient iron oxide, or oxygen-deficient iron (δ = 4) obtained by completely reducing magnetite, or oxygen-deficient iron oxide obtained by reducing hematite or used body warmers, or hematite or used It is characterized by being completely oxygen-deficient iron obtained by completely reducing used body warmer.
(2) The method for producing carbon and hydrogen according to Aspect 2 of the present invention includes a carbon dioxide decomposition step of reacting carbon dioxide with a reducing agent to produce magnetite with carbon attached to the surface, and the carbon dioxide decomposition step. A carbon separation step in which the magnetite with carbon attached to the surface obtained in step 1 is reacted with hydrochloric acid or hydrogen chloride gas to produce carbon and iron chloride, and iron chloride obtained in the carbon separation step. and water to produce magnetite, hydrogen, and hydrogen chloride gas; and the carbon dioxide decomposition step, in which the magnetite and hydrogen obtained in the hydrogen production step are reacted with each other. and a reducing agent regeneration step of generating the reducing agent to be used, wherein the reducing agent is Fe ₃ O _4-δ obtained by reducing magnetite while maintaining the crystal structure of magnetite (where δ is 1 Oxygen-deficient iron oxide represented by (above and less than 4), or oxygen-completely deficient iron (δ = 4) obtained by completely reducing magnetite, or oxygen-deficient iron obtained by reducing hematite or used body warmers. It is oxygen-completely defective iron obtained by completely reducing iron oxide, hematite, and used hand warmers, and is characterized by additionally adding magnetite, which does not have carbon adhesion, in the carbon separation process.
(3) The method for producing carbon and hydrogen according to Aspect 3 of the present invention includes a carbon dioxide decomposition step of reacting carbon dioxide with a reducing agent to produce magnetite with carbon attached to the surface, and the carbon dioxide decomposition step. A carbon separation step in which the magnetite with carbon attached to the surface obtained in step 1 is reacted with hydrochloric acid or hydrogen chloride gas to produce carbon and iron chloride, and iron chloride obtained in the carbon separation step. An iron chloride reduction step in which iron chloride (III) contained in , a hydrogen production step of producing magnetite, hydrogen, and hydrogen chloride gas; and a reduction of reacting the magnetite and hydrogen obtained in the hydrogen production step with each other to produce the reducing agent used in the carbon dioxide decomposition step. the reducing agent is represented by Fe ₃ O _4-δ (where δ is 1 or more and less than 4) obtained by reducing magnetite while maintaining the crystal structure of magnetite. Oxygen-deficient iron oxide, or oxygen-deficient iron (δ = 4) obtained by completely reducing magnetite, or oxygen-deficient iron oxide obtained by reducing hematite or used body warmers, or hematite or used It is oxygen-completely deficient iron obtained by completely reducing used body warmer, and is characterized by additionally adding magnetite, which does not have carbon adhesion, in the carbon separation process.

According to the present invention, by reducing carbon dioxide using oxygen-deficient iron oxide or oxygen-completely deficient iron, which maintains the crystal structure of magnetite and has many atomic vacancies due to the detachment of oxygen atoms, as a reducing agent, Carbon can be efficiently produced from carbon dioxide at low cost.

Furthermore, by reacting iron chloride obtained in the carbon separation step with water, water can be decomposed efficiently at low cost to produce highly pure hydrogen. In such hydrogen production, the amount of hydrogen produced can be easily increased simply by increasing the amount of magnetite or iron chloride circulated.

(4) Aspect 4 of the present invention is that in the method for producing carbon and hydrogen according to any one of Aspects 1 to 3 , the carbon dioxide decomposition step may be performed at a reaction temperature of 300°C or more and 450°C or less. good.

(5) Aspect 5 of the present invention is that in the method for producing carbon and hydrogen according to any one of Aspects 1 to 4 , the carbon dioxide decomposition step may be performed at a reaction pressure of 0.01 MPa or more and 5 MPa or less. good.

(6) Aspect 6 of the present invention is the method for producing carbon and hydrogen according to any one of aspects 1 to 5 , in which the carbon separation step may have a reaction temperature in a range of 10° C. or more and 300° C. or less.

(7) Aspect 7 of the present invention is the method for producing carbon and hydrogen according to any one of Aspects 1 to 6 , in which the reaction temperature in the hydrogen production step may be set in a range of 10°C or more and 800°C or less.

(8) Aspect 8 of the present invention is that in the method for producing carbon and hydrogen according to any one of Aspects 1 to 7 , in the reducing agent regeneration step, the reaction temperature may be set in a range of 300°C or more and 450°C or less. .

(9) Aspect 9 of the present invention is that in the method for producing carbon and hydrogen according to any one of Aspects 1 to 8 , the concentration of hydrogen used in the reducing agent regeneration step is in a range of 5% by volume or more and 100% by volume or less. It's okay.

(10) Aspect 10 of the present invention is the method for producing carbon and hydrogen according to any one of Aspects 1 to 9 , wherein in the reducing agent regeneration step, the magnetite has a specific surface area of 0.1 m ² /g by the BET method. It may be in the range of 10 m ² /g or less.

(11) Aspect 11 of the present invention is that in the method for producing carbon and hydrogen according to any one of aspects 1 to 10, in the reducing agent regeneration step, the magnetite has an average particle diameter (volume cumulative average diameter (50% diameter ) may be in the range of 1 μm or more and 1000 μm or less.

(12) Aspect 12 of the present invention is that in the method for producing carbon and hydrogen according to any one of Aspects 1 to 11 , in the reducing agent regeneration step, the magnetite has a bulk density of 0.3 g/cm ³ or more, and 3 g /cm ³ or less.

According to the present invention, a method for producing carbon and hydrogen that can efficiently produce carbon and hydrogen from carbon dioxide and water, and can repeatedly produce and use a reducing agent used in the reaction, and a method for producing carbon and hydrogen, which can be obtained thereby. It becomes possible to provide a carbon dioxide decomposition method that can decompose carbon dioxide with high reaction efficiency using a carbon material, a reducing agent, and a reducing agent with high reducing ability.

FIG. 2 is a schematic diagram showing the crystal structure of a 1/4 unit lattice of magnetite. 1 is a flowchart showing a method for producing carbon and hydrogen according to an embodiment of the present invention. 3 is a graph showing the results of Example 1. 3 is a graph showing the results of Example 2. 3 is a graph showing the results of Example 3. 3 is a graph showing the results of Example 4. 3 is a graph showing the results of Example 5. 7 is a graph showing the results of Example 6. 7 is a graph showing the measurement results of the degree of oxygen deficiency δ in Example 7. 7 is a graph showing the measurement results of the oxygen defect consumption rate in Example 7. 12 is a graph showing the measurement results of the degree of oxygen deficiency δ in Example 8. 12 is a graph showing the measurement results of the oxygen defect consumption rate in Example 8. 7 is a graph showing the results using nanoparticle magnetite of Example 9. 12 is a graph showing the results using fine particle magnetite of Example 9. 12 is a graph showing the results using powdered magnetite of Example 9. 3 is an XRD analysis result of a sample after hydrogen reduction in Example 10. 3 is an XRD analysis result of a sample after carbon dioxide decomposition in Example 10. 3 is an XRD analysis result of a sample after hydrogen reduction in Example 11. 3 is an XRD analysis result of a sample after carbon dioxide decomposition in Example 11. Figure 2 is an SEM photograph of the product after reacting the reducing agent with carbon dioxide.

Hereinafter, a method for producing carbon and hydrogen, a carbon material, a reducing agent, and a method for decomposing carbon dioxide according to an embodiment of the present invention will be described with reference to the drawings. It should be noted that the embodiments shown below are specifically explained in order to better understand the gist of the invention, and unless otherwise specified, the embodiments are not intended to limit the invention. Furthermore, in order to make the features of the present invention easier to understand, the drawings used in the following explanation may show important parts enlarged for convenience, and the dimensional ratio of each component may be the same as the actual one. Not necessarily.

First, the reducing agent used in the carbon and hydrogen production method of this embodiment will be explained.
The reducing agent is a material that reduces carbon dioxide and decomposes it into carbon and oxygen by reacting with carbon dioxide in the carbon dioxide decomposition step S1 described below. The reducing agent used in this embodiment is an oxygen-deficient iron oxide of magnetite (triiron tetroxide) represented by Fe ₃ O _4-δ (where δ is 1 or more and less than 4), hematite, and used body warmers (mainly The component used is oxygen-deficient iron oxide (iron hydroxide) or oxygen-completely deficient iron.

FIG. 1 is a schematic diagram showing the crystal structure of a quarter unit cell of magnetite.
Crystallographically, magnetite has a spinel-type crystal lattice structure, in which oxygen ions (O ^2- ) are arranged in a cubic close-packed arrangement, and +trivalent iron (Fe ⁺³ ) is present in the gaps (Asite, Bsite). , +2-valent iron (Fe ²⁺ ) are arranged at a ratio of 2:1. Magnetite is represented by the general formula Fe ₃ O ₄ .

The reducing agent used in this embodiment is an oxygen-deficient iron oxidation agent obtained by removing oxygen ions at arbitrary positions shown in FIG. 1 while maintaining the crystal structure of magnetite, that is, the spinel crystal lattice structure. (1≦δ<4), or oxygen-completely defective iron (δ=4) obtained by completely reducing magnetite, or oxygen-deficient iron oxide obtained by reducing hematite or used hand warmers, Or it is oxygen-completely deficient iron obtained by completely reducing hematite or used hand warmers. Such a reducing agent is generated in a reducing agent regeneration step S4, which will be described later.

Oxygen-deficient iron oxide obtained by reducing magnetite is represented by Fe ₃ O _4-δ , and δ is in the range of 1 or more and less than 4 depending on the ratio of oxygen ions (O ^2- ) released from magnetite. be made into Moreover, magnetite in which all oxygen ions are removed (ie, δ=4) becomes the above-mentioned oxygen completely defective iron.

δ is defined as the degree of oxygen vacancy, which is the ratio of oxygen vacancies to magnetite in the oxygen-deficient iron oxide while maintaining the crystal structure of magnetite, that is, the spinel crystal lattice structure. The degree of oxygen deficiency δ is determined by measuring the difference between the mass of magnetite before it reacts with hydrogen and the mass after the reaction in the reducing agent regeneration step S4, and the amount of decrease in mass (difference) is determined by the amount of oxygen released from magnetite ( Since the location of this released oxygen in the lattice is the same as that of an atomic vacancy (that is, a defect), the degree of oxygen deficiency δ (δ = 1 to 4) can be calculated from the amount of mass decrease.

Then, the sites where oxygen ions are removed from magnetite become atomic vacancies while maintaining the spinel crystal lattice structure, and more cations are trapped in the crystal lattice by the amount of removed cations, resulting in an expanded lattice spacing. The atomic vacancies caused by such oxygen elimination cause a deoxygenation reaction (reduction reaction) of carbon dioxide as a reducing agent.

The reducing agent (oxygen-deficient iron oxide, oxygen-completely deficient iron) of this embodiment only needs to have an average particle diameter larger than 1 μm, preferably 1 μm or more and less than 20 μm, and more than 50 μm and less than 200 μm. It is also preferable.

According to experimental results, when the average particle size of the reducing agent is smaller than 1 μm, the rate of carbon monoxide production increases when carbon dioxide is decomposed, and the carbon recovery rate decreases. By using a reducing agent with an average particle diameter of 1 μm or more, a high carbon recovery rate can be maintained, and at the same time, the agglomeration of the reducing agent particles is reduced, so problems such as sticking to the reactor wall can be avoided. Application to industrial reactors such as rotary kilns becomes possible.

Furthermore, by setting the average particle size of the reducing agent to less than 20 μm, a high reaction rate can be maintained. In addition, when the average particle diameter of the reducing agent is more than 50 μm and less than 200 μm, particle scattering is reduced and fluidization performance is improved, making it possible to apply it to industrial reactors such as fluidized beds. In this case, compared to a rotary kiln type reactor, solid-gas contact and heat transfer properties are better, equipment costs are lower, and the size of the reactor can be made more compact.

FIG. 2 is a flowchart showing step-by-step a method for producing carbon and hydrogen, including a method for decomposing carbon dioxide, according to an embodiment of the present invention.
The method for producing carbon and hydrogen according to the present embodiment includes a carbon dioxide decomposition step S1 for producing magnetite with carbon attached to its surface, a carbon separation step S2 for producing carbon and iron chloride, and a carbon dioxide decomposition step S2 for producing magnetite with carbon attached to its surface. , a hydrogen production step S3 for producing hydrogen chloride gas, and a reducing agent regeneration step S4 for producing a reducing agent. Further, the carbon dioxide decomposition method of this embodiment includes a carbon dioxide decomposition step S1. In each of these steps, carbon and hydrogen are produced from carbon dioxide and water supplied from the outside by recycling magnetite and a reducing agent obtained by reducing magnetite.

(Carbon dioxide decomposition step S1)
The carbon dioxide decomposition step S1 uses a reaction device (carbon dioxide decomposition furnace) such as a rotary kiln or a bubbling fluidized bed, for example, to convert gaseous dioxide while stirring a powdery reducing agent with an average particle size of about 1 μm to 500 μm. Carbon dioxide is decomposed (reduced) by contacting it with carbon. Then, magnetite with carbon attached to its surface is produced.

A circulating fluidized bed can be used as the reaction device used in the carbon dioxide decomposition step S1, but compared to a bubble fluidized bed, the height of the entire reactor is higher, the equipment cost is higher, and the design of the particle recirculation loop is and the operation is complicated, the residence time of particles is short (residence time in the reactor is on the order of seconds), the particle size of the reducing agent that can be used is limited, particle abrasion is accelerated, and it is difficult to maintain a high gas flow rate. There are disadvantages such as the high energy cost required to circulate the powder.

Sources of carbon dioxide used in this carbon dioxide decomposition step S1 include, for example, facilities that emit a large amount of carbon dioxide, such as steel plants, thermal power plants, cement factories, garbage incineration facilities, biogas generation facilities, and natural gas wells. Carbon dioxide emitted from sources such as carbon dioxide may be used. Further, the reducing agent is supplied from the reducing agent regeneration step S4, which will be described later.

The reaction temperature in the carbon dioxide decomposition step S1 may be in the range of 300°C or higher and 450°C or lower, preferably 350°C or higher and 400°C or lower.
In this way, by controlling the reaction temperature to a temperature range of 300° C. or higher and 450° C. or lower, the reducing agent can maintain the spinel crystal lattice structure. If the reaction temperature is high, such as 500° C. or higher, there is a concern that the reducing agent may not be able to maintain the spinel crystal lattice structure due to repeated use of magnetite. In addition, there is a concern that energy consumption during reaction will increase.

In the carbon dioxide decomposition step S1, in order to raise the temperature to such a reaction temperature range, heat (exhaust heat) generated from the operation of carbon dioxide supply sources such as steel plants, thermal power plants, cement factories, and garbage incineration facilities is used. It is also preferable to effectively utilize renewable energy and the thermal energy of a high-temperature gas reactor, which is a nuclear reactor capable of extracting high-temperature heat, as a heat source.

The reaction pressure in the carbon dioxide decomposition step S1 may be in the range of 0.01 MPa or more and 5 MPa or less, preferably 0.1 MPa or more and 1 MPa or less.
If the reaction pressure is 0.01 MPa or higher, the reaction rate required for a practical process can be obtained, and if the reaction pressure is 0.1 MPa or higher, it is possible to directly respond to actual exhaust gas with a low carbon dioxide concentration. Become. Further, if the reaction pressure is 5 MPa or less, the manufacturing cost of the device can be suppressed.

In the carbon dioxide decomposition step S1, by increasing the reaction temperature and reaction pressure, the decomposition rate of carbon dioxide can be increased and the processing efficiency of carbon dioxide can be increased. On the other hand, if the reaction temperature is too high, the spinel structure of the reducing agent may be destroyed.

In the decomposition of carbon dioxide in the carbon dioxide decomposition step S1, the following two-stage reactions of formulas (1) and (2) and one-stage reaction of formula (3) occur.
CO ₂ → CO (intermediate product) + O ² -...(1)
CO→C+O ² -...(2)
CO ₂ →C+2O ² -...(3)
The oxygen generated in the above formulas (1), (2), and (3) can be converted into oxygen-deficient iron oxide (formula (4)) or oxygen-completely deficient iron (formula (4)) in the following formulas (4) and (5). It is inserted into the atomic vacancy of formula (5)).
Fe ₃ O _4-δ + δO ^2- → Fe ₃ O ₄ (however, δ=1 or more and less than 4)...(4)
3Fe+4O ^2- →Fe ₃ O ₄ ...(5)

In addition, in the carbon dioxide decomposition method of this embodiment, only the above equation (1) can be performed in the carbon dioxide decomposition step S1. The obtained carbon monoxide (CO) can be used as a raw material for obtaining hydrocarbons such as methane and methanol and useful chemical products such as various resins by hydrogenation.

In the above-mentioned reaction in the carbon dioxide decomposition step S1, when all the carbon dioxide is reacted up to formula (2) or according to formula (3), no gas is generated as a final product. That is, it is considered that all the oxygen in carbon dioxide is taken into oxygen-deficient iron oxide or oxygen-completely deficient iron. Taking this into consideration, the reaction between carbon dioxide and oxygen-deficient iron oxide is expressed by equation (6), and the reaction between carbon dioxide and oxygen-completely defective iron is expressed by equation (7).
2Fe ₃ O _4-δ + δCO ₂ → 2Fe ₃ O ₄・δC (carbon-adhered magnetite. However, δ = 1 or more and less than 4)... (6)
3Fe+2CO ₂ →Fe ₃ O _4.2C (carbon-attached magnetite)...(7)

The reason why oxygen-deficient iron oxide and oxygen-completely deficient iron used as reducing agents in the carbon dioxide decomposition step S1 can decompose carbon dioxide to carbon is due to the metastable crystal structure of these reducing agents formed in a non-equilibrium state. This is because it has a certain spinel-type crystal lattice structure and gradually reacts with oxygen even at room temperature, and attempts to convert oxygen ions into more stable Fe ₃ O ₄ . That is, it is thought that this occurs because an unstable spinel-type crystal lattice structure having atomic vacancies in the lattice attempts to change to a more stable spinel-type crystal lattice structure without atomic vacancies.

In the process of stabilizing oxygen-deficient iron oxides and oxygen-completely deficient iron (making them magnetite), when oxygen ions are incorporated into the crystal, the crystal tries to maintain electrical neutrality, so electrons are transferred to the crystal surface. try to release it from In oxygen-deficient iron oxide and oxygen-completely deficient iron, +2-valent Fe (Fe ²⁺ ) exists as an atom that can emit electrons, but due to the instability of the crystals of oxygen-deficient iron oxide and oxygen-completely deficient iron, This is thought to be due to a reduction potential different from normal.

In the carbon dioxide decomposition step S1, in order to maximize the carbon dioxide decomposition ability of the oxygen-deficient iron oxide or oxygen-completely deficient iron used as a reducing agent, the oxygen concentration in the reaction environment should be kept at 5% by volume or less. is preferred.

If the oxygen concentration in the reaction environment in the carbon dioxide decomposition step S1 is higher than 5% by volume, this reduction occurs before the oxygen constituting carbon dioxide is incorporated into the reducing agent (oxygen-deficient iron oxide or oxygen-completely deficient iron). There is a concern that oxygen in the reaction atmosphere may be taken into the oxygen-deficient sites of the reducing agent, reducing the carbon dioxide decomposition ability of the reducing agent.

Carbon produced by decomposition of carbon dioxide in the carbon dioxide decomposition step S1 is produced as nano-sized carbon with a particle size of 1 μm or less. In the carbon dioxide decomposition step S1, under the same temperature conditions, the reaction rate of formula (1) described above is slower than the reaction rate of formula (2), but by increasing the reaction rate of formula (1), formula (2) The reaction proceeds quickly, producing fine nano-sized carbon particles. The reaction rates of formulas (1) and (2) can be increased by increasing the degree of oxygen vacancy δ and by increasing the reaction temperature and reaction pressure.

Such nano-sized carbon is generated so as to adhere to or cover the surface of magnetite produced by oxidation of oxygen-deficient iron oxide or oxygen-completely deficient iron. The magnetite with carbon attached to its surface is sent to the next carbon separation step S2.

On the other hand, in this embodiment, the reducing agent becomes magnetite (Fe ₃ O ₄ ) due to the decomposition of carbon dioxide in the carbon dioxide decomposition step S1, and hematite (Fe ₂ O ₃ ) is not generated.
In this embodiment, carbon is produced in a state in which it is relatively firmly attached to the surface of magnetite.

(Carbon separation step S2)
The carbon separation step S2 includes a magnetite chlorination reaction (conversion of magnetite to iron(III) chloride (FeCl ₃ ) and iron(II) chloride (FeCl ₂ )) and a carbon recovery operation.
The chlorination reaction of magnetite includes a wet chlorination method using hydrochloric acid dissolution and a dry chlorination method using hydrogen chloride gas.

(Wet chlorination)
When the chlorination reaction of magnetite is carried out by wet chlorination, the magnetite obtained in the carbon dioxide decomposition step S1 with carbon attached to its surface is reacted with hydrochloric acid (aqueous solution of hydrogen chloride), thereby dissolving the magnetite in the hydrochloric acid. , to separate carbon insoluble in hydrochloric acid from magnetite. Magnetite dissolved in hydrochloric acid generates iron chloride (iron(III) chloride and iron(II) chloride) and water by reaction with hydrogen chloride.

Magnetite dissolved in hydrochloric acid and carbon may be separated by, for example, solid-liquid separation such as filtration. Further, the produced iron chloride (a mixture of iron (III) chloride and iron (II) chloride) is sent to the next hydrogen production step S3. In the case of such wet chlorination, all the iron oxide produced is dissolved and carbon can be separated.

Hydrochloric acid used in the carbon separation step S2 (wet chlorination) may have a hydrogen chloride concentration in the range of, for example, 5% by mass to 37% by mass.
If the hydrogen chloride concentration of hydrochloric acid is less than 5% by mass, there is a concern that the reaction will be slow. Further, concentrated hydrochloric acid exceeding 37% by mass is difficult to handle because hydrogen chloride evaporates quickly.
The reaction temperature in the carbon separation step S2 (wet chlorination) may be in the range of 10°C or higher and 150°C or lower, preferably 50°C or higher and 100°C or lower.
If the temperature is less than 10°C, the reaction rate is slow and cooling equipment is required. If the temperature exceeds 150°C, a large amount of energy is consumed and the solution evaporates, resulting in poor efficiency.
In the carbon separation step S2 (wet chlorination), it is also preferable to effectively utilize, for example, the same heat source as in the carbon dioxide decomposition step S1 in order to raise the temperature to such a reaction temperature range.

The chlorination reaction of magnetite in the carbon separation step S2 (wet chlorination) is expressed by the following formulas (8) to (9).
2Fe ₃ O ₄・δC+16HCl→4FeCl ₃ +2FeCl ₂ +8H ₂ O+δC (wet chlorination: 10 to 150°C) (however, δ = 1 to 4)...(8)
2Fe ₃ O ₄ +16HCl → 4FeCl ₃ +2FeCl ₂ +8H ₂ O (wet chlorination: 10°C to 150°C) (9)

(dry chlorination)
When the chlorination reaction of magnetite is carried out by dry chlorination, the magnetite obtained in the carbon dioxide decomposition step S1 with carbon attached to its surface or the magnetite obtained in the hydrogen production step S3 is reacted with hydrogen chloride gas. It produces iron chloride (iron(III) chloride and iron(II) chloride) and water.

The hydrogen chloride gas used in the carbon separation step S2 (dry chlorination) may have a hydrogen chloride concentration in the range of, for example, 50% by mass to 100% by mass.
If the concentration of hydrogen chloride is less than 50% by mass, there is a concern that the reaction will be slow.
The reaction temperature in the carbon separation step S2 (dry chlorination) may be in the range of 50°C or higher and 300°C or lower, preferably 80°C or higher and 200°C or lower.
If it is less than 50°C, the reaction rate is slow, and if it exceeds 300°C, it consumes a lot of energy and becomes inefficient, and at the same time, since the chlorination reaction is an exothermic reaction, high temperatures are disadvantageous to the progress of the reaction.
In the carbon separation step S2 (dry chlorination), in order to raise the temperature to such a reaction temperature range, it is also preferable to effectively utilize, for example, the same heat source as in the carbon dioxide decomposition step S1.

The chlorination reaction of magnetite in the carbon separation step S2 (dry chlorination) is expressed by the following formulas (8) to (9).
2Fe ₃ O ₄・δC+16HCl→4FeCl ₃ +2FeCl ₂ +8H ₂ O+δC (dry chlorination: 50 to 300°C) (however, δ = 1 to 4)...(8)
2Fe ₃ O ₄ +16HCl → 4FeCl ₃ +2FeCl ₂ +8H ₂ O (dry chlorination: 50°C to 300°C) (9)

In order to reduce energy consumption, it is preferable to use such dry chlorination with hydrogen chloride gas for magnetite to which no carbon is attached (magnetite obtained in the hydrogen production step S3 and circulated simply for hydrogen production). In the case of dry chlorination, carbon can be separated as an insoluble component by converting carbon-attached magnetite to iron chloride with hydrogen chloride gas and then dissolving the product in water.

The carbon (carbon material) separated from magnetite in the carbon separation step S2 is nano-sized carbon with a particle size of 1 μm or less, and carbon with a particle size exceeding 1 μm is hardly produced. These nano-sized carbon powders are highly pure carbon with a purity of, for example, 99% or higher, and can be used as carbon black, activated carbon, additives for rubber reinforcement, battery materials, toners, colorants, conductive materials, catalysts, adsorbents, etc. It can be used directly as a functional carbon material, as a reducing agent, or as a substitute for coke in steelmaking. Furthermore, it can be used as a raw material for producing carbon materials such as artificial graphite, carbon fiber, and carbon nanotubes.

(Hydrogen production process S3)
Hydrogen production step S3 involves a reduction reaction of iron(III) chloride obtained in carbon separation step S2 (from iron(III) chloride to iron(II) chloride) using a solid-gas reactor such as a rotary kiln or a fluidized bed. operations such as concentration, drying, and granulation of an iron(II) chloride solution; and a reaction of producing magnetite, hydrogen, and hydrogen chloride by reacting iron(II) chloride with water. Contains. The magnetite produced in this hydrogen production step S3 is sent to the next reducing agent regeneration step S4. Further, hydrogen chloride can be used as a raw material for producing hydrochloric acid used in the carbon separation step S2.
Operations such as concentration, drying, and granulation of the iron(II) chloride solution are carried out using devices such as a membrane separator, evaporator, crystallizer, and spray dryer. ) After being made into particles, it may be sent to hydrogen and magnetite production reactions.

Reduction of iron (III) chloride includes, for example, a thermal reduction method in which iron (III) chloride is thermally decomposed at a high temperature, and a reduction method in which a reducing agent (CuCl, Fe, etc.) is added at a low temperature.

(thermal reduction method)
Details of the reduction reaction of iron(III) chloride by the thermal reduction method in the hydrogen production step S3 are shown in the following equations (10) to (11).
4FeCl ₃ →4FeCl ₂ +2Cl ₂ (reduction of iron(III) chloride: 300°C to 600°C)...(10)
2Cl ₂ + 2H ₂ O → 4HCl + O ₂ (reverse Deacon reaction: 400°C to 800°C) (11)
Note that the reverse Deacon reaction of formula (11) does not necessarily have to be performed.

(Reduction method using CuCl)
Details of the reduction reaction of iron(III) chloride in the hydrogen production step S3 by the reduction method using CuCl are shown in the following equations (12) to (14).
4FeCl ₃ +4CuCl→4FeCl ₂ +4CuCl ₂ (reduction of iron(III) chloride: 10°C to 100°C)...(12)
4CuCl ₂ → 4CuCl+2Cl ₂ (Reduction of CuCl ₂ : 300°C to 600°C) (13)
2Cl ₂ + 2H ₂ O → 4HCl + O ₂ (reverse Deacon reaction: 400°C to 800°C) (14)
Note that the reverse Deacon reaction of formula (14) does not necessarily have to be performed.

(Reduction method using Fe)
The details of the reduction reaction of iron(III) chloride in the hydrogen production process S3 by the reduction method using Fe are shown in the following equation (15).
4FeCl ₃ +2Fe→6FeCl ₂ (reduction of iron(III) chloride: 10°C to 100°C)...(15)

(Reaction between iron(II) chloride produced by each reduction method and water: Hydrogen, magnetite production reaction)
The reaction temperature in the hydrogen and magnetite production reaction in which iron (II) chloride produced in the reduction reaction of iron (III) chloride is reacted with water by each of the above-mentioned reduction methods is 300°C or more and 800°C or less, preferably It may be within the range of 400°C or higher and 600°C or lower. In the hydrogen production step S3, it is also preferable to effectively utilize the same heat source as in the carbon dioxide decomposition step S1, for example, in order to raise the temperature to such a reaction temperature range.

In the reaction between iron(II) chloride and water in the hydrogen production process S3, a reaction expressed by the following formula (16) occurs.
_3FeCl2 + _4H2O → _Fe3O4 + _6HCl + _H2 ...(16)
The hydrogen obtained by such a reaction is highly pure hydrogen, for example, with a purity of 99% or more, and can be used as a hydrogen station for fuel cell vehicles (FCV), hydrogen power generation, and various industrial hydrogen sources.

A portion of the hydrogen generated in the hydrogen production step S3 is also used in the next reducing agent regeneration step S4, but in order to increase the amount of hydrogen extracted to the outside, magnetite (magnetite without carbon adhesion) is used in the carbon separation step S2. ), or by additionally adding iron chloride (FeCl ₂ ) in the hydrogen production process S3, it is possible to generate more hydrogen than is required in the reducing agent regeneration process S4, resulting in high purity hydrogen. It can be used as a low-cost hydrogen source.

However, if the magnetite generated in the hydrogen production step S3 from the additionally input iron compound (magnetite, iron chloride) is supplied to the reducing agent regeneration step S4, magnetite becomes excessive and the process load of the reducing agent regeneration step S4 increases. Therefore, it is preferable to extract the amount derived from the additionally introduced iron compound from the magnetite produced in the hydrogen production process S3 and input it into the carbon separation process S2 in a state without carbon adhesion. That is, by supplying only the amount of magnetite required for the carbon dioxide decomposition step S1 to the reducing agent regeneration step S4, and circulating the remainder through the carbon separation step S2 and the hydrogen production step S3, the carbon dioxide decomposition step S1 and the reducing agent regeneration step are performed. The amount of hydrogen produced in the hydrogen production step S3 can be increased without affecting the step S4.
For example, in this embodiment, 25% by mass of the magnetite produced in the hydrogen production step S3 is supplied to the reducing agent regeneration step S4, and the remaining 75% by mass is supplied to the carbon separation step S2.

(Reducing agent regeneration step S4)
In the reducing agent regeneration step S4, the hydrogen produced in the hydrogen production step S3 is reacted with magnetite to remove oxygen ions contained in the magnetite (deoxygenation (reduction) reaction) and change the crystal structure of the magnetite, i.e. Oxygen-deficient iron oxide (Fe ₃ O _4-δ (however, δ is 1 or more and less than 4)) in which oxygen atoms in magnetite have vacancies at any position while maintaining a spinel-type crystal lattice structure, or Generates oxygen-completely defective iron.

Note that the magnetite introduced in the reducing agent regeneration step S4 is the magnetite obtained in the hydrogen production step S3, but the magnetite reduced during the initial stage of each step and during the implementation of each step is supplemented with pure magnetite. It is not limited to magnetite, and may contain other substances.

As a raw material for magnetite (magnetite material) in the case of introducing magnetite from the outside, for example, iron sand, which is a natural mineral, or iron sand contained in iron ore used in iron works, etc. can be used. By using these iron sands as magnetite, magnetite can be easily obtained at low cost.
Further, as the magnetite material, hematite (hematite: Fe ₂ O ₃ ), used iron oxidation type hand warmer (main component is iron hydroxide), etc. can also be used.

The magnetite of this embodiment has a specific surface area measured by the BET method of 0.1 m ² /g or more and 10 m ² /g or less, preferably 0.3 m ² /g or more and 8 m ² /g or less, more preferably The range is 1 m ² /g or more and 6 m ² /g or less.

If the specific surface area of magnetite is 0.1 m ² /g or more, the contact area between solid and gas necessary for solid-gas reaction can be secured, and the reaction rate required for a practical process can be obtained. In addition, if the specific surface area of magnetite is 10 m ² /g or less, a fast reaction rate can be ensured, and the rate of carbon monoxide generated when carbon dioxide is decomposed will be low, improving the carbon recovery rate. can.

Note that the reducing agent obtained by reducing magnetite in the reducing agent regeneration step S4 of the present embodiment has a larger specific surface area than the magnetite before reduction. The specific surface area of the reducing agent is 0.1 m ² /g or more and 30 m ² /g or less, preferably 0.3 m ² /g or more and 25 m ² /g or less, more preferably 1 m ² /g or more and 18 m ² /g. It is as follows. Further, the specific surface area of the reducing agent is 1 time or more and 3 times or less, preferably 1 time or more and 2.5 times or less, and more preferably 1 time or more and 2.0 times or less than the specific surface area of magnetite.

Moreover, the magnetite of this embodiment has an average particle diameter in the range of 1 μm or more and 1000 μm or less, preferably in the range of 1 μm or more and less than 20 μm, or in the range of more than 50 μm and 200 μm or less.

If the average particle diameter of magnetite is 1 μm or more, the rate of carbon monoxide generated when carbon dioxide is decomposed becomes low, and the carbon recovery rate can be improved. Furthermore, by making the average particle size larger than 1 μm, particle agglomeration and scattering properties are reduced, and fluidity and handling properties are improved, which reduces problems such as sticking to the reactor wall and clinker formation. Trouble can be avoided and it can be applied to industrial reactors such as rotary kilns and fluidized beds.
Moreover, if the average particle diameter of magnetite is 1000 μm or less, the contact area between the solid and gas necessary for the solid-gas reaction can be secured, and the reaction rate required for a practical process can be obtained.

In addition, the magnetite of this embodiment has a bulk density of 0.3 g/cm ³ or more and 3 g/cm ³ or less, preferably 0.4 g/cm ³ or more and 2 g/cm ³ or less, and more preferably 0. The range is .5 g/cm ³ or more and 1 g/cm ³ or less.

If the bulk density of magnetite is 0.3 g/ ^cm3 or more, particle agglomeration and scattering properties will be low, and fluidity will be improved, making it possible to apply it to industrial reactors such as rotary kilns and fluidized beds. Become. Further, if the bulk density of magnetite is 3 g/cm ³ or less, the porosity between and within the particles can be ensured, the reaction gas can easily diffuse into the particles, and the reaction rate required for a practical process can be obtained.

In the reducing agent regeneration step S4, for example, using a solid-gas reactor such as a rotary kiln or a fluidized bed, powdered magnetite is stirred and brought into contact with the hydrogen produced in the hydrogen production step S3, thereby forming magnetite. Oxygen atoms are released and react with hydrogen to produce water (steam). In addition, magnetite from which oxygen atoms have been removed is oxygen-deficient iron oxide, which maintains the crystal structure of magnetite, that is, a spinel crystal lattice structure, and has vacancies at the positions of the removed oxygen atoms, or oxygen-completely defective iron. becomes.

In the reducing agent regeneration step S4, when the magnetite material contains hematite, hematite is reduced to magnetite, and further reduced to oxygen-deficient iron oxide or oxygen-completely defective iron.

The reaction temperature in the reducing agent regeneration step S4 may be in the range of 300°C or higher and 450°C or lower, preferably 350°C or higher and 400°C or lower.
When the reaction temperature is 300° C. or higher, a reaction rate required for a practical process can be obtained. Further, if the reaction temperature is 450° C. or lower, the crystal structure of the reducing agent is not destroyed during the reaction, high reactivity can be maintained, and the reducing agent can be used repeatedly. Moreover, the energy consumption during reaction can be suppressed.
In the reducing agent regeneration step S4, in order to raise the temperature to such a reaction temperature range, it is also preferable to effectively utilize, for example, the same heat source as in the carbon dioxide decomposition step S1.

The reaction pressure in the reducing agent regeneration step S4 may be in the range of 0.1 MPa or more and 5 MPa or less, preferably 0.1 MPa or more and 1 MPa or less.
When the reaction pressure is 0.1 MPa or more, a reaction rate necessary for a practical process can be obtained, and the size of the reaction apparatus can be made compact. Further, if the reaction pressure is 5 MPa or less, the manufacturing cost of the device can be suppressed.

The concentration of the hydrogen gas used in the reducing agent regeneration step S4 may be in a range of 5% by volume or more and 100% by volume or less, preferably 10% by volume or more and 90% by volume or less. Even if the concentration of hydrogen gas is, for example, about 90% by volume, there is substantially no significant difference in reducing ability from hydrogen gas having a concentration of 100% by volume. Therefore, by using hydrogen gas with a concentration of about 90 volume %, which is lower in cost than hydrogen gas with a concentration of 100 volume %, a reducing agent can be produced from magnetite at a low cost.

In the reduction of magnetite with hydrogen in the reducing agent regeneration step S4, a reducing agent is generated as shown in the following equations (17) and (18).
Fe ₃ O ₄ +δH ₂ →Fe ₃ O _4−δ +δH ₂ O (however, δ=1 or more and less than 4)...(17)
_Fe3O4 + _4H2 →3Fe _{+ 4H2O} ...(18)

Here, in order to maintain the activity of the obtained reducing agent, it is preferable to prevent oxidation due to mixing of air into the reducing agent, etc. from the reducing agent regeneration step S4 to the carbon dioxide decomposition step S1. For example, when transferring the reducing agent from the reducing agent regeneration step S4 to the carbon dioxide decomposition step S1, if the structure is such that the reducing agent can be transferred while being in a sealed state to prevent air from entering, the reducing agent may be transferred in the reducing agent regeneration step S4. The obtained reducing agent can be supplied to the carbon dioxide decomposition step S1 without being oxidized.

In addition, in order to increase the production efficiency of carbon produced in the carbon separation step S2, the carbon dioxide decomposition step S1 and the reducing agent regeneration step S4 are repeated two or more times, and the carbon-attached magnetite produced in the carbon dioxide decomposition step S1 is It is also possible to perform the carbon separation step S2 and the hydrogen production step S3 after increasing the carbon concentration. Thereby, nano-sized carbon can be produced at lower cost.

According to the carbon material and hydrogen production method of the present embodiment as described above, the crystal structure of magnetite is maintained and oxygen-deficient iron oxide (Fe ₃ O _4-δ (However, δ = 1 or more and less than 4)) or oxygen-completely deficient iron (δ = 4), which is obtained by completely reducing magnetite, is used as a reducing agent to reduce carbon dioxide at low cost. Carbon materials can be efficiently produced from carbon dioxide.

Furthermore, by reacting the iron chloride obtained in the carbon separation step S2 with water, water can be decomposed efficiently at low cost to produce highly pure hydrogen. In such hydrogen production, the amount of hydrogen produced can be easily increased simply by increasing the amount of magnetite circulated. - Can be widely used in recycling (CCU) technology, hydrogen sources for hydrogen fuel cells, hydrogen sources for hydrogen power generation, etc.

Then, by supplying the magnetite produced in the hydrogen production process S3 to the reducing agent regeneration process and regenerating the reducing agent using the hydrogen produced in the hydrogen production process, only carbon dioxide and water are supplied from the outside. , it is possible to construct a closed system that decomposes carbon dioxide to produce carbon materials and also decomposes water to produce hydrogen.

Hydrogen and oxygen generated during each of these steps are generated in different steps, and do not come into contact with each other within one step. For example, hydrogen is generated in the hydrogen production step S3, and oxygen is generated in the carbon separation step S2, and these do not coexist in the same reaction tank or the like. Thereby, there is no fear that oxygen and hydrogen will come into contact with each other and cause an explosive reaction, and the reactions in each step can be carried out stably.

The magnetite used in these carbon materials and hydrogen production methods is recycled while changing its material form, such as being reduced during the treatment process and becoming a reducing agent, so there is no need to supply magnetite from outside except for loss. , carbon and hydrogen can be produced at low cost.

In addition, in the carbon separation step S2, nano-sized carbon materials with a particle size of 1 μm or less are obtained by dissolving magnetite with carbon attached to its surface in hydrochloric acid (aqueous solution of hydrogen chloride) and separating carbon that is insoluble in hydrochloric acid. Obtainable.

In addition, in the carbon dioxide decomposition process S1, carbon separation process S2, hydrogen production process S3, and reducing agent regeneration process S4, for example, heat generated due to the operation of steel plants, thermal power plants, cement factories, garbage incineration facilities, etc. By effectively using waste heat) as a heat source during reactions, the amount of waste heat released into the atmosphere can be suppressed, contributing to the prevention of global warming. In addition, by effectively utilizing electricity and heat storage derived from renewable energy, as well as thermal energy from high-temperature gas reactors, which are nuclear reactors that can extract high-temperature heat, it is possible to suppress _CO2 emissions and realize a carbon-neutral and decarbonized society. Contribute to

Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. This embodiment and its modifications are included within the scope and gist of the invention as well as within the scope of the invention described in the claims and its equivalents.

For example, in the embodiments described above, the general composition of magnetite is Fe ₃ O ₄ , but such magnetite may also be iron sand containing other substances, such as titanium (Ti). These other materials, such as titanium, may contribute to the reduction of carbon dioxide as a catalyst.

Below, the effects of the present invention were verified.
First, Table 1 summarizes the properties of each magnetite material used in Examples 1 to 11 below.

(Example 1)
An experiment was conducted to investigate the relationship between the reaction temperature and the degree of oxygen deficiency δ in the reducing agent regeneration process.
Using a fixed bed reactor as a reaction device, 1 g of magnetite (particle size distribution is 50 to 100 nm) was reacted with hydrogen to reduce the magnetite while maintaining the crystal structure of the magnetite, thereby producing a reducing agent.

The reaction time was 1 hour, the hydrogen flow rate was 1.0 L/min, the hydrogen concentration was 100% by volume, and the reaction temperatures were set at 280°C, 300°C, 320°C, 350°C, 360°C, and 370°C, respectively, and magnetite was reduced with hydrogen. (deoxygenation reaction) to obtain samples (reducing agents) at each reaction temperature. Then, the degree of oxygen deficiency δ of the reducing agent was calculated from the reducing agent (oxygen-deficient iron oxide, oxygen-completely deficient iron) obtained at each reaction temperature.
The results of Example 1 are shown graphically in FIG. Note that the point in FIG. 3 where the degree of oxygen deficiency δ exceeds 4 is due to a measurement error, and δ is substantially 4.

According to the results shown in FIG. 3, by setting the reaction temperature in the range of 350°C to 360°C under the above-mentioned reaction conditions, the degree of oxygen vacancy δ can be maximized, and δ = 4, that is, the magnetite crystal It was confirmed that oxygen-completely defective iron was obtained in which all oxygen ions were removed while maintaining the structure.

(Example 2)
An experiment was conducted to investigate the relationship between the reaction time and the degree of oxygen deficiency δ in the reducing agent regeneration process.
Using a fixed bed reactor as a reaction device, 1 g of magnetite (particle size distribution is 50 to 100 nm) was reacted with hydrogen to reduce the magnetite while maintaining the crystal structure of the magnetite, thereby producing a reducing agent.

Assuming that the reaction temperature is 280°C, 310°C, 330°C, and 350°C, the hydrogen flow rate is 1.0 L/min, and the hydrogen concentration is 100% by volume, the reaction time (reduction time) is 30 minutes, 60 minutes, and 180 minutes at each of the above-mentioned reaction temperatures. Samples (reducing agents) were obtained at each reaction temperature and reaction time by reducing magnetite with hydrogen (deoxygenation reaction). Then, the degree of oxygen deficiency δ of the reducing agent was calculated from each of the obtained reducing agents (oxygen-deficient iron oxide, oxygen-completely defective iron).
The results of Example 2 are shown graphically in FIG. Note that the point in FIG. 4 where the degree of oxygen deficiency δ exceeds 4 is due to a measurement error, and δ is substantially 4.

According to the results shown in Figure 4, if the reaction temperature is in the range of 330°C to 350°C under the above reaction conditions, the degree of oxygen deficiency δ can be maximized by making the reaction time (reduction time) exceed 60 minutes. It was confirmed that δ=4, that is, completely oxygen-deficient iron in which all oxygen ions were removed while maintaining the magnetite crystal structure was obtained. In addition, if the temperature is in the range of 330°C to 350°C, oxygen-deficient iron oxide that maintains the crystal structure of magnetite with δ = 2 to 2.8 can be obtained even if the reaction time (reduction time) is about 30 minutes. It was confirmed that

(Example 3)
An experiment was conducted to investigate the relationship between hydrogen flow rate and oxygen defect degree δ in the reducing agent regeneration process.
Using a fixed bed reactor as a reaction device, 1 g of magnetite (particle size distribution is 50 to 100 nm) was reacted with hydrogen to reduce the magnetite while maintaining the crystal structure of the magnetite, thereby producing a reducing agent.

The reaction temperature was 330°C, the hydrogen concentration was 100% by volume, and the reaction time was 60 minutes, and the hydrogen flow rate was 0.1 L/min, 0.25 L/min, 0.5 L/min, 0.75 L/min, and 1.0 L/min. Samples (reducing agents) were obtained at each hydrogen flow rate by reducing magnetite with hydrogen (deoxygenation reaction). Then, the degree of oxygen deficiency δ of the reducing agent was calculated from each of the obtained reducing agents (oxygen-deficient iron oxide, oxygen-completely defective iron).
The results of Example 3 are shown graphically in FIG. Note that the point in FIG. 5 where the degree of oxygen deficiency δ exceeds 4 is due to a measurement error, and δ is substantially 4.

According to the results shown in FIG. 5, if the hydrogen flow rate is 0.75 L/min or more under the above reaction conditions, the oxygen defect degree δ can be increased to the maximum, and δ = 4, that is, the crystal structure of magnetite is It was confirmed that oxygen-completely defective iron was obtained in which all oxygen ions were removed while maintaining the oxygen content. Furthermore, it was confirmed that even if the hydrogen flow rate was about 0.5 L/min, an oxygen-deficient iron oxide that maintained a magnetite crystal structure with δ exceeding 3.5 could be obtained.

(Example 4)
An experiment was conducted to investigate the relationship between hydrogen concentration and oxygen defect degree δ in the reducing agent regeneration process.
Using a fixed bed reactor as a reaction device, 1 g of magnetite (particle size distribution is 50 to 100 nm) was reacted with hydrogen to reduce the magnetite while maintaining the crystal structure of the magnetite, thereby producing a reducing agent.

At a reaction temperature of 330°C, a hydrogen flow rate of 1.0 L/min, and a reaction time of 60 minutes, the hydrogen concentrations were set to 50 vol%, 75 vol%, 90 vol%, and 100 vol%, respectively, and magnetite was reduced (deoxidized) with hydrogen. Samples (reducing agents) were obtained at each hydrogen concentration. Then, the degree of oxygen deficiency δ of the reducing agent was calculated from each of the obtained reducing agents (oxygen-deficient iron oxide, oxygen-completely defective iron).
The results of Example 4 are shown graphically in FIG. Note that the point in FIG. 6 where the degree of oxygen deficiency δ exceeds 4 is due to a measurement error, and δ is substantially 4.

According to the results shown in Figure 6, when the hydrogen concentration is 90% by volume or more under the above reaction conditions, the degree of oxygen vacancy δ can be increased to the maximum, and δ = 4, that is, the crystal structure of magnetite is maintained. It was confirmed that oxygen-completely defective iron, in which all oxygen ions were removed, was obtained. Even if the concentration of hydrogen gas is around 90% by volume, there is virtually no difference in reducing ability from hydrogen gas with a concentration of 100% by volume, and the concentration of hydrogen gas with a concentration of 90% is lower in cost than hydrogen gas with a concentration of 100% by volume. % of hydrogen gas, it is possible to produce a reducing agent with the maximum oxygen defect degree δ at low cost. Furthermore, it was confirmed that even if the concentration of hydrogen gas was about 75% by volume, an oxygen-deficient iron oxide that maintained the crystal structure of magnetite with δ exceeding 3.5 could be obtained.

(Example 5)
An experiment was conducted to investigate the relationship between reaction temperature and oxygen defect consumption rate in the carbon dioxide decomposition process.
Oxygen defect consumption rate is the rate at which oxygen ions in carbon dioxide are taken into atomic vacancies in the lattice of the reducing agent's spinel crystal lattice structure when carbon dioxide reacts with a certain amount of reducing agent. In the range of 0 to 100%, the closer this value is to 100%, the higher the carbon dioxide decomposition (reduction) ability of the reducing agent.

A fixed bed reactor was used as the reaction device, and a reducing agent with an oxygen defect degree δ of approximately 4 (oxygen completely defective iron, particle size distribution 50 to 100 nm) was used to conduct carbon dioxide at a reaction temperature of 315°C to 390°C. Reacted with carbon to produce carbon. Then, the oxygen defect consumption rate was calculated based on the difference between the mass of the reducing agent before the reaction, the oxygen defect degree δ, and the mass of the oxidized reducing agent (magnetite) after the reaction, the oxygen defect degree δ.
The results of Example 5 are shown graphically in FIG.

According to the results shown in FIG. 7, when the reaction temperature is 360° C. or higher under the above-mentioned reaction conditions, the oxygen defect consumption rate is 40% or higher. In particular, when the reaction temperature is 370°C or higher, the oxygen defect consumption rate is 50% or more, and oxygen ions in carbon dioxide account for 50% or more of the total number of vacancies in the lattice of the spinel crystal lattice structure of the reducing agent. can be taken in. Therefore, it was confirmed that by setting the reaction temperature in the carbon dioxide decomposition step to 360° C. or higher, carbon dioxide can be decomposed (reduced) using a reducing agent efficiently to generate carbon.

(Example 6)
An experiment was conducted to investigate the relationship between the type of magnetite material, the oxygen vacancy consumption rate in the carbon dioxide decomposition process, and the oxygen vacancy degree δ in the reducing agent regeneration process.

As magnetite materials, 1 g and 0.5 g of nanoparticle magnetite with an average particle size of about 800 nm, 0.5 g of fine particle magnetite with an average particle size of about 1.1 μm, 1 g of iron sand from Japan, and 1 g of iron sand from New Zealand were prepared. Using each magnetite material, using a fixed bed reactor as a reaction device, each magnetite material was reduced to produce reducing agents, and the degree of oxygen deficiency δ of these reducing agents was calculated.

Further, the specific surface area of the reducing agent that reduced particulate magnetite was measured and found to be 9.36 m ² /g. It can be seen that the specific surface area has increased approximately 1.77 times from 5.28 m ² /g before reduction.

Next, using each reducing agent, a fixed bed reactor is used as a reaction device, and carbon dioxide is reacted at a reaction temperature of 360°C, and the mass of the reducing agent before the reaction, the degree of oxygen deficiency δ, and the The oxygen defect consumption rate was calculated based on the difference between the mass of the oxidized reducing agent and the oxygen defect degree δ.
The results of Example 6 are shown graphically in FIG.

According to the results shown in Figure 8, most of the reducing agents produced by reduction with hydrogen using nanoparticle magnetite and fine particle magnetite have an oxygen defect degree δ of 4, and almost all the oxygen in magnetite is released and atoms It was confirmed that oxygen-completely defective iron with vacancies was obtained. On the other hand, it was found that New Zealand iron sand had an oxygen deficiency degree δ of less than 1 after hydrogen reduction, and its ability to decompose (reduce) carbon dioxide as a reducing agent was low.

Furthermore, the oxygen defect consumption rate of these reducing agents was approximately 60% to 80% for the reducing agent prepared using fine particle magnetite, and it was confirmed that the reducing agent had particularly excellent carbon dioxide decomposition ability.
From these results, it was found that it is particularly preferable to use fine particle magnetite having an average particle diameter of about 1.1 μm as the magnetite material.

(Example 7)
Experiments were conducted to investigate the particle size of the magnetite material, the degree of oxygen vacancies δ in the reducing agent regeneration process, and the oxygen vacancy consumption rate in the carbon dioxide decomposition process.
Magnetite materials include nanoparticle magnetite with an average particle size of about 800 nm, fine particle magnetite with an average particle size of about 1.1 μm, powder magnetite with an average particle size of about 40 μm, and large particle size powder magnetite with an average particle size of about 70 μm. prepared. Then, each magnetite material was reduced at a reaction temperature of 330° C. to produce a reducing agent, and the degree of oxygen deficiency δ of these reducing agents was calculated. Note that the conditions other than the reaction temperature were the same as in Example 6.

Next, using each reducing agent, carbon dioxide was reacted at a reaction temperature of 380° C., and the oxygen defect consumption rate was calculated. Note that the conditions other than the reaction temperature were the same as in Example 6.
The measurement results of the oxygen defect degree δ of Example 7 are shown in FIG. 9, and the measurement results of the oxygen defect consumption rate are shown in FIG. 10, respectively.

According to the results shown in FIG. 9, there is almost no difference in the reducing agent obtained by reduction with hydrogen depending on the particle size of the raw material magnetite. On the other hand, according to the results shown in FIG. 10, reducing agents made from fine particle magnetite are particularly excellent in oxygen defect consumption rate after reacting these reducing agents with carbon dioxide. Therefore, it has been found that it is preferable to generate the reducing agent using fine particle magnetite as a raw material.

(Example 8)
An experiment was conducted to investigate the relationship between the raw material of the reducing agent, the oxygen defect degree δ in the reducing agent regeneration process, and the oxygen defect consumption rate in the carbon dioxide decomposition process.
Magnetite materials include nanoparticle magnetite with an average particle size of about 800 nm, fine particle magnetite with an average particle size of about 1 μm, powder magnetite with an average particle size of about 40 μm, iron sand from Japan, iron sand from New Zealand, copper slag, iron powder. prepared. Then, under the same conditions as in Example 6, the oxygen deficiency degree δ of these reducing agents was calculated. Note that since the iron powder is in a completely reduced state, δ = 4 for convenience.

Next, using each reducing agent, carbon dioxide was reacted under the same conditions as in Example 6, and the oxygen defect consumption rate was calculated.
The measurement results of the oxygen defect degree δ of Example 8 are shown in FIG. 11, and the measurement results of the oxygen defect consumption rate are shown in FIG. 12, respectively.

According to the results shown in FIG. 11, all of the reducing agents obtained by hydrogen reduction using magnetite as a raw material are excellent with a value of 3.5 or more. On the other hand, the oxygen defect degree δ of copper slag is approximately 0.

On the other hand, according to the results shown in FIG. 12, reducing agents made from fine particle magnetite are particularly excellent in oxygen defect consumption rate after reacting these reducing agents with carbon dioxide. In addition, it was found that copper slag and iron powder had an oxygen defect consumption rate of almost 0%, and had no ability to decompose (reduce) carbon dioxide. The difference in oxygen defect consumption rate between domestic iron sand and NZ iron sand is thought to be caused by the catalytic effect of the trace amount of titanium contained in domestic iron sand.

(Example 9)
An experiment was conducted to examine whether the reducing agent deteriorates and the amount of carbon produced when the reducing agent regeneration process and carbon dioxide decomposition process are repeated for each particle size of the magnetite material.
A reducing agent was produced under the same magnetite material and reaction conditions as in Example 7, and its mass was measured (reducing agent regeneration step).

Next, carbon dioxide was decomposed using each reducing agent at a reaction temperature of 380° C., and the mass of the reducing agent + product (carbon) after the reaction was measured. Note that the carbon separation step was not performed after the carbon dioxide decomposition step, and the generated carbon was left as it was. The reducing agent regeneration step and carbon dioxide decomposition step using each reducing agent were repeated three times, and the mass of the sample was measured at each step.
In Example 9, the results using nanoparticle magnetite are shown in FIG. 13, the results using fine particle magnetite are shown in FIG. 14, and the results using powder magnetite are shown in FIG. 15, respectively.

According to the results shown in Figures 13 to 15, no matter which particle size of magnetite is used as the raw material for the reducing agent, the combustion-infrared absorption method is It was confirmed that the measured mass of carbon increased almost linearly, that there was no deterioration of the reducing agent, and that the reducing agent could be used repeatedly to perform the reducing agent regeneration process and carbon dioxide decomposition process multiple times. Ta. In addition, especially when fine particle magnetite or powder magnetite is used as the raw material for the reducing agent, the amount of increase in carbon mass is greater than when nano particle magnetite is used, and the increase is due to carbon accumulation. Taking this into consideration, it was confirmed that it is preferable to use fine particle magnetite or powder magnetite as the raw material for the reducing agent.

On the other hand, when nanoparticle magnetite is used as a raw material for the reducing agent, the mass of carbon is almost halved when the reducing agent regeneration process is performed after the carbon dioxide decomposition process, and the generated carbon is gasified and removed from the system. It is thought that it was done. On the other hand, with fine particle magnetite and powder magnetite, no loss due to such reaction of generated carbon is observed. For this reason, nanoparticle magnetite has a high reaction activity and a large surface area, so the generated and attached carbon easily reacts with oxygen in the reducing agent or hydrogen in the reducing agent regeneration process, and carbon loss occurs with repeated use. It was found that this is easy to occur. It has been confirmed that it is preferable to use fine particle magnetite or powdered magnetite as a raw material for the reducing agent, also from the viewpoint of loss due to carbon gasification.

(Example 10)
An experiment was conducted to examine the carbon dioxide decomposition performance when hematite (Fe ₂ O ₃ ) was used as the magnetite material.
Powdered α-Fe ₂ O ₃ (average particle size 1 μm, purity 99.9% by mass (manufactured by Kojundo Kagaku Kenkyujo)) was used as a sample, and the temperature was heated to 110°C under an argon gas flow as a pretreatment. After warming, the chamber was held for 10 minutes, and then air was drawn into the chamber to create a vacuum state, and the chamber was held for another 10 minutes.

Using the pretreated sample obtained in this way, a fixed bed reactor was used as the reaction device, and the sample was heated under the conditions of a reaction temperature of 330°C, a reaction time of 1 hour, a hydrogen flow rate of 1.0 L/min, and a hydrogen concentration of 100% by volume. was reduced to produce a reducing agent and its mass was measured.
Table 2 shows the mass changes of the sample before and after pretreatment, and after hydrogen reduction. For reference, the mass change when magnetite is used as a raw material is described.
Further, the XRD analysis results of the sample after hydrogen reduction are shown in FIG. 16, and the XRD analysis results of the sample after carbon dioxide decomposition are shown in FIG.

According to the results shown in Table 2, it is considered that hematite has been completely reduced to the state of oxygen-completely deficient iron, based on the weight change due to hydrogen reduction.

Moreover, according to the XRD analysis results, the product is mostly Fe, and these XRD analysis results also indicate that the hematite is completely reduced to the state of oxygen-completely deficient iron.

Next, using the obtained hematite-derived reducing agent, carbon dioxide is decomposed at a reaction temperature of 370°C until there is no pressure change, and using the pressure and temperature inside the reactor, gas is generated according to the ideal gas equation of state. The change in the amount of material in the phase was calculated, and the mass of the product (carbon) was measured by combustion-infrared absorption method (carbon dioxide decomposition process).
Table 3 shows the changes in the amount of substances in the gas phase after decomposition of carbon dioxide, the mass of the product (carbon), and the changes in the amount of substances in the gas phase per mole of iron in the reducing agent. For reference, the case where magnetite is used as a raw material is also described.

According to the results shown in Table 3, it was confirmed that carbon dioxide can be decomposed using a reducing agent obtained by reducing hematite with hydrogen. Furthermore, from the fact that the color tone of the reducing agent derived from hematite after decomposing carbon dioxide was black, and from the XRD analysis results, even if the reducing agent derived from hematite, after decomposing carbon dioxide, only magnetite was oxidized. It is thought that it will not change (will not return to hematite).

(Example 11)
An experiment was conducted to examine the carbon dioxide decomposition performance using powder containing iron hydroxide extracted from used body warmers as a raw material for producing a reducing agent.
As a used hand warmer, "Poka Poka Kazoku Regular 10 pieces (PKN-10R)" manufactured by Iris Ohyama Co., Ltd. was used, and as a pretreatment, the temperature was raised to 110 °C under an argon gas flow state, and then held for 10 minutes. Then, a vacuum was applied and maintained for an additional 10 minutes.

The pretreated used hand warmers (powder) thus obtained were processed using a fixed bed reactor as a reaction device at a reaction temperature of 330°C, a reaction time of 1 hour, a hydrogen flow rate of 1.0 L/min, and a hydrogen concentration of 100% by volume. The product was reduced under the following conditions to produce a reducing agent and its mass was measured.
Table 4 shows the mass changes of the samples before and after pretreatment, and before and after hydrogen reduction.
For reference, the mass change when hematite is used as a raw material is described.
Further, the XRD analysis results of the sample after hydrogen reduction are shown in FIG. 18, and the XRD analysis results of the sample after carbon dioxide decomposition are shown in FIG.

The color tone of the reducing agent derived from the used body warmer after hydrogen reduction was black, the same as the reducing agent derived from magnetite and hematite, so it is thought that the used body warmer has been reduced to the state of completely oxygen-deficient iron. .
Further, according to the XRD analysis results, the product is mostly Fe, and from these XRD analysis results, it is considered that the iron hydroxide in the used body warmer has been reduced to the state of oxygen-completely deficient iron.

Next, using the obtained reducing agent derived from the used hand warmer, carbon dioxide was decomposed at a reaction temperature of 370° C. until there was no pressure change, and the mass was measured. The mass change of the sample before and after carbon dioxide decomposition is shown in Table 4 above.

According to the results shown in Table 4, it was confirmed that carbon dioxide can be decomposed using a reducing agent obtained by reducing used body warmers with hydrogen. In addition, the color tone of the reducing agent after decomposing carbon dioxide was black, and the XRD analysis results showed that even if the reducing agent was derived from used body warmers, it would only oxidize to magnetite after decomposing carbon dioxide. (It does not return to iron hydroxide).

(Example 12)
We observed the appearance of magnetite with carbon attached to its surface, which was produced by reacting carbon dioxide with a reducing agent during the carbon dioxide decomposition process. An electron microscope (SEM) was used for observation.
FIG. 20 shows a SEM photograph of magnetite with carbon attached to its surface.
In the SEM photograph shown in Figure 20, the white part of the amorphous product shows the oxidized reducing agent (magnetite), and the black part shows the nano-sized carbon particles.By reducing carbon dioxide with the reducing agent, It was confirmed that magnetite with carbon attached to the surface was produced.

(Example 13)
In the hydrogen production process, hydrogen and magnetite were actually produced, and the conversion rate (reaction conversion rate) due to the reaction between iron chloride and water was investigated.
In the experiment, water vapor was passed through a reaction tube filled with iron(II) chloride to carry out the reaction shown in the following formula (19).
_3FeCl2 + _4H2O → _Fe3O4 + _6HCl + _H2 ...(19)
Table 5 shows the conditions for implementing Examples 1 to 4 of the present invention. Table 6 shows the reaction conversion rates of the reactions shown in formula (19), which were carried out under the conditions shown in Table 5.

According to the results of Example 13 shown in Table 6, the reaction conversion rate was 90% or more under all conditions, making it possible to efficiently produce magnetite and hydrogen by reacting iron(II) chloride and steam. It was confirmed that this was the case.

INDUSTRIAL APPLICATION This invention can produce|generate a carbon material and hydrogen efficiently at low cost using carbon dioxide and water. For example, by applying it to plants that emit a lot of carbon dioxide and waste heat, such as steel plants, thermal power plants, cement manufacturing plants, and garbage incineration facilities, it can reduce carbon dioxide emissions, effectively use hydrogen, and Concomitantly, high value-added carbon materials such as nano-sized carbon can be produced. Therefore, it has industrial applicability.

S1...Carbon dioxide decomposition process S2...Carbon separation process S3...Hydrogen production process S4...Reducing agent regeneration process

Claims (12)

a carbon dioxide decomposition step in which carbon dioxide and a reducing agent are reacted to produce magnetite with carbon attached to the surface;
a carbon separation step of reacting the magnetite obtained in the carbon dioxide decomposition step with carbon attached to its surface and hydrochloric acid or hydrogen chloride gas to generate carbon and iron chloride;
an iron chloride reduction step of reducing iron chloride (III) contained in the iron chloride obtained in the carbon separation step to iron chloride (II);
a hydrogen production step in which iron (II) chloride obtained in the carbon separation step and the iron chloride reduction step is reacted with water to produce magnetite, hydrogen, and hydrogen chloride gas;
a reducing agent regeneration step in which the magnetite and hydrogen obtained in the hydrogen production step are reacted with each other to generate the reducing agent used in the carbon dioxide decomposition step,
The reducing agent is an oxygen-deficient iron oxide represented by Fe ₃ O _4-δ (where δ is 1 or more and less than 4) obtained by reducing magnetite while maintaining its crystal structure, or magnetite. Oxygen-deficient iron (δ = 4) obtained by complete reduction, or oxygen-deficient iron oxide obtained by reducing hematite and used hand warmers, or by completely reducing hematite and used hand warmers. A method for producing carbon and hydrogen, characterized in that the obtained oxygen-completely defective iron is obtained. a carbon dioxide decomposition step in which carbon dioxide and a reducing agent are reacted to produce magnetite with carbon attached to the surface;
a carbon separation step of reacting the magnetite obtained in the carbon dioxide decomposition step with carbon attached to its surface and hydrochloric acid or hydrogen chloride gas to generate carbon and iron chloride;
a hydrogen production step of reacting iron chloride obtained in the carbon separation step with water to produce magnetite, hydrogen, and hydrogen chloride gas;
a reducing agent regeneration step in which the magnetite and hydrogen obtained in the hydrogen production step are reacted with each other to generate the reducing agent used in the carbon dioxide decomposition step,
The reducing agent is an oxygen-deficient iron oxide represented by Fe ₃ O _4-δ (where δ is 1 or more and less than 4) obtained by reducing magnetite while maintaining its crystal structure, or magnetite. Oxygen-deficient iron (δ = 4) obtained by complete reduction, or oxygen-deficient iron oxide obtained by reducing hematite and used hand warmers, or by completely reducing hematite and used hand warmers. The resulting oxygen-completely defective iron ,
A method for producing carbon and hydrogen, characterized in that , in the carbon separation step, magnetite to which carbon does not adhere is additionally added . a carbon dioxide decomposition step in which carbon dioxide and a reducing agent are reacted to produce magnetite with carbon attached to the surface;
a carbon separation step of reacting the magnetite obtained in the carbon dioxide decomposition step with carbon attached to its surface and hydrochloric acid or hydrogen chloride gas to generate carbon and iron chloride;
an iron chloride reduction step of reducing iron chloride (III) contained in the iron chloride obtained in the carbon separation step to iron chloride (II);
a hydrogen production step in which iron (II) chloride obtained in the carbon separation step and the iron chloride reduction step is reacted with water to produce magnetite, hydrogen, and hydrogen chloride gas;
a reducing agent regeneration step in which the magnetite and hydrogen obtained in the hydrogen production step are reacted with each other to generate the reducing agent used in the carbon dioxide decomposition step,
The reducing agent is an oxygen-deficient iron oxide represented by Fe ₃ O _4-δ (where δ is 1 or more and less than 4) obtained by reducing magnetite while maintaining its crystal structure, or magnetite. Oxygen-deficient iron (δ = 4) obtained by complete reduction, or oxygen-deficient iron oxide obtained by reducing hematite and used hand warmers, or by completely reducing hematite and used hand warmers. The resulting oxygen-completely defective iron ,
A method for producing carbon and hydrogen, characterized in that , in the carbon separation step, magnetite to which carbon does not adhere is additionally added . The method for producing carbon and hydrogen according to any one of claims 1 to 3, wherein the carbon dioxide decomposition step is performed at a reaction temperature of 300°C or higher and 450°C or lower. The method for producing carbon and hydrogen according to any one of claims 1 to 3, wherein in the carbon dioxide decomposition step, the reaction pressure is set in a range of 0.01 MPa or more and 5 MPa or less. The method for producing carbon and hydrogen according to any one of claims 1 to 3, characterized in that in the carbon separation step, the reaction temperature is set in a range of 10°C or higher and 300°C or lower. The method for producing carbon and hydrogen according to any one of claims 1 to 3, wherein in the hydrogen production step, the reaction temperature is set in a range of 10°C or higher and 800°C or lower. The method for producing carbon and hydrogen according to any one of claims 1 to 3, wherein the reducing agent regeneration step sets the reaction temperature to a range of 300°C or higher and 450°C or lower. The method for producing carbon and hydrogen according to any one of claims 1 to 3, wherein the concentration of hydrogen used in the reducing agent regeneration step is in a range of 5% by volume or more and 100% by volume or less. . In the reducing agent regeneration step, the magnetite has a specific surface area of 0.1 m ² /g or more and 10 m ² /g or less according to the BET method. The method for producing carbon and hydrogen as described in Section . The method for producing carbon and hydrogen according to any one of claims 1 to 3, wherein in the reducing agent regeneration step, the magnetite has an average particle size in a range of 1 μm or more and 1000 μm or less. . According to any one of claims 1 to 3, in the reducing agent regeneration step, the magnetite has a bulk density in a range of 0.3 g/cm ³ or more and 3 g/cm ³ or less. carbon and hydrogen production method.

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