JP2023008879A - Method of producing carbon and hydrogen, carbon material, reducing agent, and method of decomposing carbon dioxide - Google Patents

Abstract

To efficiently generate carbon and hydrogen from carbon dioxide and water, and repeatedly generate a reducing agent for use.SOLUTION: A method of producing carbon and hydrogen includes: a carbon dioxide-decomposing process of generating magnetite attached with carbon on the surface; a carbon-separating process of generating carbon and iron chloride; a hydrogen-producing process of generating magnetite, hydrogen, and a hydrogen chloride gas; and a reducing agent-regenerating process of generating a reducing agent used for the carbon dioxide-decomposing process, where the reducing agent is an oxygen defect iron oxide represented by Fe3O4-δ (provided that δ is 1 or more and less than 4) obtained by reducing magnetite while maintaining a crystal structure of magnetite, or an oxygen complete defect iron (δ=4) obtained by completely reducing magnetite, or an oxygen defect iron oxide obtained by reducing hematite or a used body warmer, or an oxygen complete defect iron obtained by completely reducing hematite or a used body warmer.SELECTED DRAWING: Figure 2

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, steel plants, thermal power plants, cement plants, garbage incineration facilities, and the like emit a large amount of carbon dioxide (CO ₂ ). Therefore, from the viewpoint of preventing global warming, it is important to recover carbon dioxide without releasing it into the atmosphere.
On the other hand, with the increasing demand for hydrogen such as fuel cell vehicles (FCV) and hydrogen power generation, there is a demand for hydrogen that can be supplied in large quantities at low cost.

Conventionally, as techniques for separating and recovering carbon dioxide, a chemical absorption method, a physical absorption method, a membrane separation method, and the like are known. In addition, as techniques for decomposing the recovered carbon dioxide, the semiconductor photocatalyst method, metal colloid catalyst, metal complex, photochemical reduction method using a catalyst, electrochemical reduction method, chemical fixation conversion reaction, for example, Decomposition methods using reaction, rearrangement reaction, dehydration reaction, addition reaction, etc. are known. However, none of these methods for decomposing carbon dioxide is practical in terms of reaction efficiency, cost, energy consumption, and the like.

For this reason, for example, in Patent Document 1, carbon dioxide is reduced using magnetite having vacancies that are oxygen-deficient sites in the lattice, that is, oxygen-deficient iron oxide, and carbon is produced, and methane or methanol is produced from the carbon. A method for obtaining is disclosed. In the invention of Patent Document 1, carbon dioxide is decomposed (reduction reaction) by the oxygen-deficient iron oxide, and the iron oxide produced by oxidation is reduced with hydrogen to return to the oxygen-deficient iron oxide again. It is said that a closed system capable of effectively and efficiently decomposing carbon dioxide 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 produce magnetite, hydrogen chloride, and hydrogen, and the produced hydrogen is separated by a membrane. Disclosed is a method of recovery using According to the invention of Patent Document 2, process waste heat discharged from various plants can be effectively used, and hydrogen, which is a clean energy fuel, can be obtained by thermochemical decomposition technology using water as a raw material.

JP-A-5-184912 JP-A-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 0.16 at maximum. degree), and the ability to decompose carbon dioxide is low, so there is a problem that carbon dioxide cannot be decomposed efficiently. In addition, when continuously decomposing carbon dioxide by the method of Patent Document 1, it is necessary to supply hydrogen from the outside for reducing magnetite to oxygen-deficient iron oxide, and the cost of hydrogen supply is high. there were.
Furthermore, in Patent Document 1, since expensive nano-sized magnetite is used, the decomposition cost of carbon dioxide is high. In addition, since the produced carbon is not nano-carbon 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 (magnesium compounds are also included in addition to magnetite, which is an iron compound), and the reaction mechanism is complicated. In addition, since the temperature required for the reaction is high (approximately 1000° C.), there is a problem that the amount of energy consumed is large and the production cost is high.
In addition, Patent Document 2 focuses only on the effective utilization of exhaust heat discharged from various plants that consume a large amount of energy, and it is also possible to effectively utilize carbon dioxide discharged together with the exhaust heat from many of these plants. is required.

The present invention has been 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. It is an object of the present invention to provide a method for producing carbon and hydrogen, the resulting carbon material, 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) A 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 generate magnetite having carbon attached to the surface thereof, and the carbon dioxide decomposition step. A carbon separation step of reacting the magnetite having carbon attached to the surface obtained in , with hydrochloric acid (aqueous solution of hydrogen chloride) or hydrogen chloride gas to produce carbon and iron chloride, and the carbon separation step a hydrogen production step of reacting the iron chloride obtained in step with water to produce magnetite, hydrogen, and hydrogen chloride gas, and reacting the magnetite and hydrogen obtained in the hydrogen production step with each other, a reducing agent regeneration step of generating the reducing agent used in the carbon dioxide decomposition step, wherein the reducing agent is Fe ₃ O _4-δ obtained by reducing magnetite while maintaining its crystal structure (with the proviso that , δ is 1 or more and less than 4), or oxygen-completely deficient iron (δ = 4) obtained by completely reducing magnetite, or by reducing hematite or used Cairo Oxygen-deficient iron oxide obtained, or completely oxygen-deficient iron obtained by completely reducing hematite or used warmers.

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

Further, by reacting the iron chloride obtained in the carbon separation step with water, water can be efficiently decomposed at low cost to produce high-purity hydrogen. In such hydrogen production, the production amount of hydrogen can be easily increased simply by increasing the circulation amount of magnetite or iron chloride.

(2) According to aspect 2 of the present invention, in the method for producing carbon and hydrogen according to aspect 1, the reaction temperature in the carbon dioxide decomposition step may be in the range of 300° C. or higher and 450° C. or lower.

(3) Aspect 3 of the present invention is the method for producing carbon and hydrogen according to aspect 1 or 2, wherein the carbon dioxide decomposition step may have a reaction pressure in the range of 0.01 MPa or more and 5 MPa or less.

(4) Aspect 4 of the present invention is the method for producing carbon and hydrogen according to any one of aspects 1 to 3, wherein the reaction temperature in the carbon separation step is in the range of 10° C. or higher and 300° C. or lower.

(5) Aspect 5 of the present invention is the method for producing carbon and hydrogen according to any one of Aspects 1 to 4, wherein the reaction temperature in the hydrogen production step is in the range of 10° C. or higher and 800° C. or lower.

(6) Aspect 6 of the present invention is the method for producing carbon and hydrogen according to any one of Aspects 1 to 5, wherein the reducing agent regeneration step may set the reaction temperature to a range of 300° C. or higher and 450° C. or lower. .

(7) Aspect 7 of the present invention is the method for producing carbon and hydrogen according to any one of Aspects 1 to 6, wherein the concentration of hydrogen used in the reducing agent regeneration step is in the range of 5% by volume or more and 100% by volume or less. may

(8) Aspect 8 of the present invention is the method for producing carbon and hydrogen according to any one of Aspects 1 to 7, wherein in the reducing agent regeneration step, the magnetite has a specific surface area of 0.1 m ² /g by BET method. Above, it may be in the range of 10 m ² /g or less.

(9) A ninth aspect of the present invention is the method for producing carbon and hydrogen according to any one of Aspects 1 to 8, wherein in the reducing agent regeneration step, the magnetite has an average particle diameter (volume cumulative average diameter (50% diameter ) below) may be in the range of 1 μm or more and 1000 μm or less.

(10) A tenth aspect of the present invention is the method for producing carbon and hydrogen according to any one of the first to ninth aspects, wherein 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.

(11) Aspect 11 of the present invention is the method for producing carbon and hydrogen according to any one of aspects 1 to 10, wherein the carbon may be nano-sized carbon having a particle size of 1 μm or less.

(12) A carbon material according to aspect 12 of the present invention is produced by the method for producing carbon and hydrogen according to any one of aspects 1 to 11.

(13) A reducing agent according to aspect 13 of the present invention is produced in the reducing agent regeneration step in the method for producing carbon and hydrogen according to any one of aspects 1 to 11.

(14) The method for decomposing carbon dioxide according to aspect 14 of the present invention is 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. Decomposing carbon dioxide by reacting carbon dioxide with a reducing agent that is oxygen-deficient iron (δ = 4) obtained by completely reducing the oxygen-deficient iron oxide represented or magnetite. characterized by

INDUSTRIAL APPLICABILITY According to the present invention, a method for producing carbon and hydrogen that efficiently produces carbon and hydrogen from carbon dioxide and water and repeatedly produces and utilizes a reducing agent used in the reaction, is obtained by this method. It is possible to provide a method for decomposing carbon dioxide that can decompose carbon dioxide with high reaction efficiency using a carbon material, a reducing agent, and a reducing agent with high reducing ability.

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

Hereinafter, a method for producing carbon and hydrogen, a carbon material, a reducing agent, and a method for decomposing carbon dioxide according to one embodiment of the present invention will be described with reference to the drawings. It should be noted that the embodiments shown below are specifically described for better understanding of the gist of the invention, and do not limit the invention unless otherwise specified. In addition, in the drawings used in the following description, in order to make it easier to understand the features of the present invention, there are cases where the main parts are enlarged for convenience, and the dimensional ratio of each component is the same as the actual one. not necessarily.

First, the reducing agent used in the method for producing carbon and hydrogen according to the present embodiment will be described.
The reducing agent is a material that reacts with carbon dioxide to reduce carbon dioxide and decompose it into carbon and oxygen in the carbon dioxide decomposition step S1 described later. The reducing agent used in the present embodiment is 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 As a component, oxygen-deficient iron oxide of iron hydroxide) or completely oxygen-deficient iron is used.

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, oxygen ions (O ²⁻ ) are arranged in a cubic close-packed arrangement, and +3 valent iron (Fe ⁺³ ) is placed in the gaps (Asite, Bsite). , +2-valent iron (Fe ²⁺ ) are arranged at a ratio of 2:1. Magnetite is represented by Fe ₃ O ₄ as a general formula.

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

The 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 rate of desorption of oxygen ions (O ^2- ) detached from magnetite. be made. Further, the iron completely deficient in oxygen is obtained by removing all the oxygen ions from the magnetite (that is, δ=4).

δ is defined as the degree of oxygen deficiency, which is the ratio of oxygen defects to the magnetite in the oxygen-deficient iron oxide that maintains the magnetite crystal structure, that is, the spinel-type crystal lattice structure. Such an oxygen defect degree δ is obtained by measuring the difference between the mass of magnetite before reacting with hydrogen in the reducing agent regeneration step S4 and the mass after the reaction, and the amount of decrease in mass (difference) is the amount of oxygen released from magnetite ( Since the arrangement position of the released oxygen in the lattice is the same as the atomic vacancy, that is, defect), the degree of oxygen defect δ (δ=1 to 4) can be calculated from the amount of decrease in mass.

The sites where oxygen ions are detached from the magnetite become atomic vacancies while maintaining the spinel crystal lattice structure. Atomic vacancies resulting from such elimination of oxygen 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 the present embodiment may have an average particle size of more than 1 μm, preferably 1 μm or more and less than 20 μm, and more than 50 μm and less than 200 μm. is also preferred.

When the average particle size of the reducing agent is smaller than 1 μm, experimental results show that 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 size of 1 μm or more, a high carbon recovery rate can be maintained, and at the same time, the cohesion of the reducing agent particles is low, so troubles such as sticking to the wall surface of the reactor 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. Further, when the average particle size of the reducing agent is more than 50 μm and 200 μm or less, the scattering property of the particles is reduced and the fluidization performance is improved. In this case, as compared with a rotary kiln type reactor, solid-gas contact and heat transfer are good, the equipment cost is low, and the size of the reactor can be made compact.

FIG. 2 is a flow chart showing steps of a method for producing carbon and hydrogen, including a method for decomposing carbon dioxide according to one 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 the surface, a carbon separation step S2 for producing carbon and iron chloride, magnetite, and hydrogen. , hydrogen chloride gas, and a reducing agent regeneration step S4 for producing a reducing agent. Further, the method for decomposing carbon dioxide according to the present embodiment has a carbon dioxide decomposition step S1. In each of these steps, magnetite and a reducing agent that reduces magnetite are recycled to produce carbon and hydrogen from carbon dioxide and water supplied from the outside.

(Carbon dioxide decomposition step S1)
In the carbon dioxide decomposition step S1, a reaction apparatus (carbon dioxide decomposition furnace) such as a rotary kiln or a bubbling fluidized bed is used to, for example, stir a powdery reducing agent having an average particle size of about 1 μm to 500 μm and convert gaseous dioxide. Carbon dioxide is decomposed (reduced) by contact with carbon. Then, magnetite with carbon attached to the surface is generated.

A circulating fluidized bed can be used as the reactor used in the carbon dioxide decomposition step S1, but compared to the bubbling fluidized bed, the height of the entire reactor is high, the equipment cost is high, and the design of the particle recirculation loop and operation are complicated, the residence time of the 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, the abrasion of the particles is accelerated, the maintenance of a high gas flow rate and the There are demerits such as high energy cost required for powder circulation.

Examples of carbon dioxide supply sources used in this carbon dioxide decomposition step S1 include facilities that emit a large amount of carbon dioxide, such as ironworks, thermal power plants, cement plants, garbage incineration facilities, biogas generation facilities, and natural gas wells. Carbon dioxide discharged from such as may be used. Also, 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.
Thus, by setting the reaction temperature in the 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 as high as, for example, 500° C. or higher, there is a concern that the reducing agent will not be able to maintain the spinel crystal lattice structure due to repeated use of magnetite. In addition, there is a concern that the energy consumed during the reaction will increase.

In the carbon dioxide decomposition step S1, in order to raise the temperature to such a reaction temperature range, the heat (exhaust heat) generated due to the operation of the carbon dioxide supply source such as a steel mill, a thermal power plant, a cement factory, a garbage incineration facility, etc. , renewable energy, and thermal energy of a high-temperature gas-cooled reactor, which is a nuclear reactor capable of extracting high-temperature heat, are also preferably used effectively as heat sources.

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 more, the reaction rate required for a practical process can be obtained, and if it is 0.1 MPa or more, it is possible to directly respond to actual exhaust gas with low carbon dioxide concentration. Become. Moreover, if the reaction pressure is 5 MPa or less, the manufacturing cost of the apparatus can be suppressed.

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

Decomposition of carbon dioxide in the carbon dioxide decomposition step S1 involves the following two-step reaction of formulas (1) and (2) and one-step reaction of formula (3).
CO ₂ → CO (intermediate product) + O ^2- (1)
CO→C+O ²⁻ (2)
CO ₂ →C+2O ²⁻ (3)
Then, the oxygen generated by the above formulas (1), (2), and (3) is converted to oxygen-deficient iron oxide (formula (4)) and oxygen-completely deficient iron ( It is inserted into the atomic vacancies of formula (5)).
Fe ₃ O _4−δ +δO ²⁻ →Fe ₃ O ₄ (where δ is 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 the present embodiment, only the above formula (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 useful chemical products such as hydrocarbons such as methane and methanol and various resins by hydrogenation.

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

The oxygen-deficient iron oxide and the completely oxygen-deficient iron used as reducing agents in the carbon dioxide decomposition step S1 can decompose carbon dioxide into carbon because these reducing agents have a metastable crystal structure formed in a non-equilibrium state. This is because it has a certain spinel-type crystal lattice structure, and even at room temperature, it gradually reacts with oxygen, absorbs oxygen ions, and tries to change into more stable Fe ₃ O ₄ . That is, it is considered that the unstable spinel-type crystal lattice structure having atomic vacancies in the lattice tends to change to a more stable spinel-type crystal lattice structure having no atomic vacancies.

In the process of stabilizing oxygen-deficient iron oxide and oxygen-completely deficient iron (magnetitization), when oxygen ions are incorporated into the crystal, the crystal tries to maintain electrical neutrality, so electrons are transferred to the crystal surface. trying to release from In oxygen-deficient iron oxides and oxygen-completely deficient iron, +2-valent Fe (Fe ²⁺ ) exists as atoms that can emit electrons, but due to the instability of the crystals of oxygen-defective iron oxides and oxygen-completely deficient iron, It is considered that a reduction potential different from usual is generated.

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

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

The carbon produced by decomposition of carbon dioxide in the carbon dioxide decomposition step S1 is produced as nano-sized carbon having a particle diameter 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). reaction proceeds rapidly, and fine nano-sized carbon particles can be produced. The reaction rates of formulas (1) and (2) can be increased by increasing the degree of oxygen deficiency δ and by increasing the reaction temperature and reaction pressure.

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

On the other hand, in the present embodiment, the reducing agent becomes magnetite (Fe ₃ O ₄ ) by decomposing carbon dioxide in the carbon dioxide decomposition step S1, and hematite (Fe ₂ O ₃ ) is not generated.
In this embodiment, the carbon occurs relatively strongly attached to the surface of the magnetite.

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

(Wet chlorination)
When the chlorination reaction of magnetite is performed by wet chlorination, the magnetite having carbon attached to the surface obtained in the carbon dioxide decomposition step S1 is reacted with hydrochloric acid (aqueous solution of hydrogen chloride) to dissolve the magnetite in hydrochloric acid. , separates the carbon insoluble in hydrochloric acid from the magnetite. Magnetite dissolved in hydrochloric acid produces iron chlorides (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 solid-liquid separation such as filtration, for example. Also, the generated iron chloride (a mixture of iron(III) chloride and iron(II) chloride) is sent to the next hydrogen production step S3. In such wet salification, any iron oxide produced is dissolved and the carbon can be separated.

Hydrochloric acid used in the carbon separation step S2 (wet salting) 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. 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 a cooling facility is required. If the temperature exceeds 150°C, a large amount of energy is consumed and the solution is evaporated, resulting in poor efficiency.
In the carbon separation step S2 (wet chlorination), it is also preferable to effectively use, 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 represented by the following equations (8) to (9).
2Fe ₃ O ₄ ·δC+16HCl→4FeCl ₃ +2FeCl ₂ +8H ₂ O+δC (wet salting: 10 to 150° C.) (where δ=1 to 4) (8)
2Fe ₃ O ₄ +16HCl→4FeCl ₃ +2FeCl ₂ +8H ₂ O (wet salting: 10° C. to 150° C.) (9)

(Dry chlorination)
When the chlorination reaction of magnetite is performed by dry chlorination, the magnetite having carbon attached to the surface obtained in the carbon dioxide decomposition step S1 or the magnetite obtained in the hydrogen production step S3 is reacted with hydrogen chloride gas. It produces iron chlorides (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 concern that the reaction will slow down.
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 the reaction temperature is less than 50°C, the reaction rate is slow, and if it exceeds 300°C, the energy consumption is large and the efficiency is low.
In the carbon separation step S2 (dry chlorination), it is also preferable to effectively use, 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 (dry chlorination) is represented by the following equations (8) to (9).
2Fe ₃ O ₄ ·δC+16HCl→4FeCl ₃ +2FeCl ₂ +8H ₂ O+δC (dry chlorination: 50 to 300° C.) (where 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, magnetite to which carbon is not attached (magnetite obtained in the hydrogen production step S3 and circulated for the mere production of hydrogen) is preferably subjected to such dry chlorination with hydrogen chloride gas. In dry salification, carbon can be separated as an insoluble component by converting the carbon-adhered 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 particles with a particle size exceeding 1 μm are rarely produced. Such nano-sized carbon powder is high-purity carbon with a purity of 99% or more, for example, 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 directly used as a functional carbon material, or as a reducing agent, such as a coke substitute for iron manufacturing. It can also be used as a raw material for producing carbon materials such as artificial graphite, carbon fiber, and carbon nanotube.

(Hydrogen production step S3)
In the hydrogen production step S3, a solid-gas reactor such as a rotary kiln or a fluidized bed is used to perform a reduction reaction of iron (III) chloride obtained in the carbon separation step S2 (from iron (III) chloride to iron (II) chloride). reduction), operations such as concentration, drying, and granulation of iron (II) chloride solution, and reaction of iron (II) chloride with water to produce magnetite, hydrogen, and hydrogen chloride. contains. The magnetite produced in this hydrogen production step S3 is sent to the next reducing agent regeneration step S4. Moreover, 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 membrane separators, evaporators, crystallizers, and spray dryers. ) 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 by thermal decomposition of iron (III) chloride at high temperature and a reduction method by addition of a reducing agent (CuCl, Fe, etc.) at low temperature.

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

(Reaction of iron (II) chloride generated by each reduction method with water: reaction to produce hydrogen and magnetite)
According to each of the reduction methods described above, the reaction temperature in the reaction for producing hydrogen and magnetite in which iron (II) chloride produced in the reduction reaction of iron (III) chloride is reacted with water is 300° C. or higher and 800° C. or lower, preferably The temperature may be in the range of 400° C. or higher and 600° C. or lower. In the hydrogen production step S3, it is also preferable to effectively use, 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.

In the reaction of iron (II) chloride and water in the hydrogen production step S3, the reaction of the following formula (16) occurs.
3FeCl ₂ +4H ₂ O→Fe ₃ O ₄ +6HCl+H ₂ (16)
Hydrogen obtained by such a reaction is, for example, high-purity hydrogen with a purity of 99% or more, and can be used as hydrogen stations for fuel cell vehicles (FCV), hydrogen power generation, and various industrial hydrogen sources.

A part of the hydrogen generated in the hydrogen production step S3 is also used in the next reducing agent regeneration step S4. ), or additional iron chloride (FeCl ₂ ) in the hydrogen production step S3, so that more hydrogen than necessary can be generated in the reducing agent regeneration step S4, and high purity It can be used as a low-cost hydrogen source.

However, if the magnetite generated in the hydrogen production step S3 from the additionally charged iron compound (magnetite, iron chloride) is supplied to the reducing agent regeneration step S4, the magnetite becomes excessive and the process load of the reducing agent regeneration step S4 increases. For this reason, it is preferable to extract the amount derived from the additionally charged iron compound from the magnetite generated in the hydrogen production step S3, and charge it to the carbon separation step S2 in a state without carbon deposition. That is, only the amount of magnetite required for the carbon dioxide decomposition step S1 is supplied to the reducing agent regeneration step S4, and the rest is circulated through the carbon separation step S2 and the hydrogen production step S3, thereby obtaining the carbon dioxide decomposition step S1 and the reducing agent regeneration. 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 generated 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 desorb oxygen ions contained in the magnetite (deoxygenation (reduction) reaction), so that the crystal structure of magnetite, that is, Oxygen-deficient iron oxide (Fe ₃ O _4-δ (where δ is 1 or more and less than 4)) in which arbitrary positions of oxygen atoms of magnetite become vacancies while maintaining the spinel crystal lattice structure, or Produces oxygen-completely deficient iron.

As the magnetite introduced in the reducing agent regeneration step S4, the magnetite obtained in the hydrogen production step S3 is used. It is not limited to magnetite, and may contain other substances.

When magnetite is introduced from the outside, the magnetite raw material (magnetite material) can be, for example, iron sand, which is a natural mineral, or iron sand contained in iron ore used in ironworks or the like. By using these iron sands as magnetite, magnetite can be easily obtained at a low cost.
As the magnetite material, hematite (hematite: Fe ₂ O ₃ ), used warmers of the iron oxidation system (main component is iron hydroxide), and the like can also be used.

The magnetite of the present embodiment has a BET specific surface area 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 It is in the range of 1 m ² /g or more and 6 m ² /g or less.

If the magnetite has a specific surface area of 0.1 m ² /g or more, the solid-gas contact area necessary for the solid-gas reaction can be ensured, and the reaction rate necessary for a practical process can be obtained. In addition, when the specific surface area of magnetite is 10 m ² /g or less, a high reaction rate can be secured, and the rate of carbon monoxide generation when decomposing carbon dioxide is low, so that the carbon recovery rate can be improved. can.

The reducing agent obtained by reducing the 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 below. The specific surface area of the reducing agent is 1 to 3 times, preferably 1 to 2.5 times, more preferably 1 to 2.0 times the specific surface area of magnetite.

The magnetite of the present embodiment has an average particle size of 1 μm or more and 1000 μm or less, preferably 1 μm or more and less than 20 μm, or more than 50 μm and 200 μm or less.

When the magnetite has an average particle size of 1 μm or more, the rate of carbon monoxide formation when decomposing carbon dioxide is low, and the carbon recovery rate can be improved. Furthermore, by making the average particle size larger than 1 μm, the aggregation and scattering properties of the particles are reduced, and the fluidity and handling properties are improved. Troubles can be avoided, and application to industrial reactors such as rotary kilns and fluidized beds becomes possible.
Moreover, if the magnetite has an average particle size of 1000 μm or less, the contact area between the solid and the gas necessary for the solid-gas reaction can be secured, and the reaction rate necessary for a practical process can be obtained.

In addition, the magnetite of the present embodiment has a bulk density in the range 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, more preferably 0 .5 g/cm ³ or more and 1 g/cm ³ or less.

If the magnetite has a bulk density of 0.3 g/cm ³ or more, the cohesiveness and scattering of the particles will be low, and the fluidity will be improved, so it can be applied to industrial reactors such as rotary kilns and fluidized beds. Become. If the magnetite has a bulk density of 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, by using a solid-gas reactor such as a rotary kiln or a fluidized bed, the powdered magnetite is stirred and brought into contact with the hydrogen generated in the hydrogen production step S3 to form magnetite. Oxygen atoms are released and react with hydrogen to produce water (steam). In addition, the magnetite from which the oxygen atoms are detached is an oxygen-deficient iron oxide in which the positions of the detached oxygen atoms are vacancies while maintaining the magnetite crystal structure, that is, the spinel crystal lattice structure, or oxygen-completely deficient iron. becomes.

In the reducing agent regeneration step S4, when the magnetite material contains hematite, the hematite is reduced to magnetite and further reduced to oxygen-deficient iron oxide or completely oxygen-deficient 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.
If the reaction temperature is 300° C. or higher, a reaction rate required for a practical process can be obtained. Further, when the reaction temperature is 450° C. or lower, the crystal structure of the reducing agent is not broken during the reaction, and high reactivity can be maintained, and the reducing agent can be used repeatedly. In addition, energy consumption during the reaction can be suppressed.
In the reducing agent regeneration step S4, it is also preferable to effectively use, 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 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.
If the reaction pressure is 0.1 MPa or higher, a reaction rate required for a practical process can be obtained and the size of the reactor can be made compact. Moreover, if the reaction pressure is 5 MPa or less, the manufacturing cost of the apparatus can be suppressed.

The concentration of the hydrogen gas used in the reducing agent regeneration step S4 may be in the range of 5% by volume or more and 100% by volume or less, preferably in the range of 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 reduction ability from hydrogen gas with a concentration of 100% by volume. Therefore, if hydrogen gas with a concentration of about 90% by volume, which is lower in cost than hydrogen gas with a concentration of 100% by volume, is used, a reducing agent can be produced from magnetite at 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 formulas (17) and (18).
Fe ₃ O ₄ +δH ₂ →Fe ₃ O _4-δ +δH ₂ O (where δ=1 or more and less than 4) (17)
Fe ₃ O ₄ +4H ₂ →3Fe+4H ₂ O (18)

Here, in order to maintain the activity of the obtained reducing agent, it is preferable to prevent the reducing agent from being oxidized due to air mixing or the like during the period 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 toward the carbon dioxide decomposition step S1, if the reducing agent can be transferred while preventing air from being mixed in a sealed state, the reducing agent regeneration step S4 can be performed. 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-adhered magnetite produced in the carbon dioxide decomposition step S1 After increasing the carbon concentration of the carbon separation step S2 and the hydrogen production step S3 can also be performed. Thereby, nano-sized carbon can be produced at a 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 by reducing carbon dioxide using completely oxygen-deficient iron (δ = 4), which is obtained by completely reducing magnetite, as a reducing agent. can efficiently produce a carbon material from carbon dioxide.

Further, by reacting the iron chloride obtained in the carbon separation step S2 with water, water can be efficiently decomposed at low cost to produce high-purity hydrogen. In such hydrogen production, it is possible to easily increase the amount of hydrogen produced simply by increasing the amount of magnetite circulating. • It can be widely used in reuse (CCU) technology, hydrogen source for hydrogen fuel cells, hydrogen source for hydrogen power generation, etc.

Then, the magnetite produced in the hydrogen production step S3 is supplied to the reducing agent regeneration step, and the hydrogen produced in the hydrogen production step is used to regenerate the reducing agent, so that only carbon dioxide and water are supplied from the outside. , it is possible to build a closed system that decomposes carbon dioxide to produce carbon materials and decomposes water to produce hydrogen.

Hydrogen and oxygen generated during each of these processes are generated in different processes and do not come into contact with each other in one process. For example, hydrogen is produced in the hydrogen production step S3 and oxygen is produced in the carbon separation step S2, and they do not coexist in the same reactor or the like. As a result, there is no concern that oxygen and hydrogen will come into contact with each other and react explosively, and reactions in each step can be stably carried out.

The magnetite used in these carbon materials and hydrogen production methods is cyclically used while changing its material form, such as being reduced in the process of processing to become a reducing agent. , low-cost production of carbon and hydrogen.

Further, in the carbon separation step S2, by dissolving magnetite with carbon attached to the surface in hydrochloric acid (aqueous solution of hydrogen chloride) to separate carbon insoluble in hydrochloric acid, a nano-sized carbon material having a particle diameter of 1 μm or less is obtained. Obtainable.

In addition, in the carbon dioxide decomposition step S1, the carbon separation step S2, the hydrogen production step S3, and the reducing agent regeneration step S4, for example, the heat ( By effectively using the waste heat as a heat source during the reaction, the amount of waste heat released into the atmosphere can be suppressed, contributing to the prevention of global warming. In addition, by effectively using electricity and heat storage derived from renewable energy and thermal energy from high-temperature gas-cooled reactors, which are nuclear reactors that can extract high-temperature heat, _CO2 generation can be suppressed, and a carbon-neutral and decarbonized society can be realized. contribute to

Although embodiments of the invention have been described above, such embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. This embodiment and its modifications are included in the scope and spirit of the invention, as well as in the scope of the invention described in the claims and equivalents thereof.

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

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

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

A reaction time of 1 hour, a hydrogen flow rate of 1.0 L/min, a hydrogen concentration of 100% by volume, and reaction temperatures of 280° C., 300° C., 320° C., 350° C., 360° C., and 370° C. were set to reduce magnetite with hydrogen. (Deoxygenation reaction) to obtain samples (reducing agents) at respective reaction temperatures. 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. It should be noted that the point where the degree of oxygen deficiency δ exceeds 4 in FIG.

According to the results shown in FIG. 3, the degree of oxygen deficiency δ can be maximized by setting the reaction temperature in the range of 350° C. to 360° C. under the reaction conditions described above. It was confirmed that oxygen-perfectly deficient iron was obtained in which all oxygen ions were removed while maintaining the structure.

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

Reaction temperatures of 280° C., 310° C., 330° C., and 350° C., hydrogen flow rate of 1.0 L/min, hydrogen concentration of 100% by volume, and reaction times (reduction times) of 30 minutes, 60 minutes, and 180 minutes at the respective reaction temperatures described above. Minutes were set for each, and magnetite was reduced with hydrogen (deoxygenation reaction) to obtain samples (reducing agents) at each reaction temperature and reaction time. Then, the degree of oxygen deficiency δ of the reducing agent was calculated from each of the reducing agents (oxygen-deficient iron oxide and completely oxygen-deficient iron).
The results of Example 2 are shown graphically in FIG. In addition, the point where the degree of oxygen deficiency δ in FIG. 4 exceeds 4 is a measurement error, and δ=4 in practice.

According to the results shown in FIG. 4, if the reaction temperature is in the range of 330° C. to 350° C. under the reaction conditions described above, the oxygen deficiency degree δ can be maximized if the reaction time (reduction time) exceeds 60 minutes. and δ=4, that is, oxygen-perfectly deficient iron in which all oxygen ions are detached while maintaining the crystal structure of magnetite can be obtained. If the temperature is in the range of 330° C. to 350° C., an oxygen-deficient iron oxide maintaining 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 the hydrogen flow rate and the degree of oxygen deficiency δ in the reducing agent regeneration step.
A fixed bed reactor was used as a reactor, and 1 g of magnetite (particle size distribution: 50 to 100 nm) was reacted with hydrogen to reduce the magnetite while maintaining the magnetite crystal structure, thereby producing a reducing agent.

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

According to the results shown in FIG. 5, if the hydrogen flow rate is 0.75 L/min or more under the reaction conditions described above, the oxygen defect degree δ can be maximized, and δ=4, that is, the magnetite crystal structure It was confirmed that oxygen-perfectly deficient iron was obtained in which all oxygen ions were desorbed while maintaining. Moreover, it was confirmed that oxygen-deficient iron oxide maintaining the crystal structure of magnetite exceeding δ=3.5 can be obtained even when the flow rate of hydrogen is about 0.5 L/min.

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

The reaction temperature is 330° C., the hydrogen flow rate is 1.0 L/min, and the reaction time is 60 minutes. By reacting), samples (reducing agents) at respective hydrogen concentrations were obtained. Then, the degree of oxygen deficiency δ of the reducing agent was calculated from each of the reducing agents (oxygen-deficient iron oxide and completely oxygen-deficient iron).
The results of Example 4 are shown graphically in FIG. In addition, the point where the degree of oxygen deficiency δ exceeds 4 in FIG.

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

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

A fixed-bed reactor is used as a reaction apparatus, and a reducing agent (oxygen-completely-defective iron, particle size distribution is 50 to 100 nm) having an oxygen defect degree δ of approximately 4 is used, and the dioxide is reacted at a reaction temperature in the range of 315°C to 390°C. It 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 and the degree of oxygen deficiency δ before the reaction and the mass of the oxidized reducing agent (magnetite) after the reaction and the degree of oxygen deficiency δ.
The results of Example 5 are shown graphically in FIG.

According to the results shown in FIG. 7, if the reaction temperature is 360° C. or higher under the reaction conditions described above, 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 higher, and 50% or more of the total number of atomic vacancies in the lattice of the spinel crystal lattice structure of the reducing agent contains oxygen ions in carbon dioxide. 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, the reducing agent can be efficiently used to decompose (reduce) carbon dioxide to produce carbon.

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

As magnetite materials, 1 g and 0.5 g of nano-particle 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 Japanese iron sand, and 1 g of New Zealand iron sand were prepared. Then, using each magnetite material, using a fixed bed reactor as a reaction apparatus, each magnetite material under the conditions of a reaction temperature of 350 ° 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 generate reducing agents, and the degree of oxygen deficiency δ of these reducing agents was calculated.

Further, when the specific surface area of the reducing agent used to reduce the fine particle magnetite was measured, it was 9.36 m ² /g. It can be seen that the specific surface area has increased about 1.77 times from 5.28 m ² /g before reduction.

Next, using each reducing agent, using a fixed bed reactor as a reaction apparatus, carbon dioxide is reacted at a reaction temperature of 360 ° C., 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 degree of oxygen defect δ.
The results of Example 6 are shown graphically in FIG.

According to the results shown in FIG. 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 of the oxygen in the magnetite is detached and atoms It was confirmed that completely oxygen-defective iron with vacancies was obtained. On the other hand, it was found that the New Zealand iron sand had an oxygen deficiency degree δ of less than 1 after hydrogen reduction and a low ability to decompose (reduce) carbon dioxide as a reducing agent.

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

(Example 7)
An experiment was conducted to examine the particle size of the magnetite material, the oxygen defect degree δ in the reducing agent regeneration process, and the oxygen defect consumption rate in the carbon dioxide decomposition process.
As the magnetite material, nano-particle 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 powder magnetite with an average particle size of about 70 μm. prepared. Then, each magnetite material was reduced under conditions of a reaction temperature of 330° C. to generate reducing agents, and the degree of oxygen deficiency δ of these reducing agents was calculated. The conditions other than the reaction temperature are 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. The conditions other than the reaction temperature are the same as in Example 6.
FIG. 9 shows the measurement results of the degree of oxygen vacancy δ of Example 7, and FIG. 10 shows the measurement results of the oxygen vacancy consumption rate.

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

(Example 8)
An experiment was conducted to examine the relationship between the raw material of the reducing agent, the degree of oxygen deficiency δ in the reducing agent regeneration process, and the oxygen deficiency consumption rate in the carbon dioxide decomposition process.
Magnetite materials include nano-particle 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, and iron powder. prepared. Then, under the same conditions as in Example 6, the degree of oxygen deficiency δ of these reducing agents was calculated. 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.
FIG. 11 shows the measurement results of the degree of oxygen vacancy δ of Example 8, and FIG. 12 shows the measurement results of the oxygen vacancy consumption rate.

According to the results shown in FIG. 11, all of the reducing agents obtained by reduction with hydrogen, which use magnetite as a raw material, are excellent at 3.5 or more. On the other hand, the degree of oxygen deficiency δ of copper slag is almost zero.

On the other hand, according to the results shown in FIG. 12, the oxygen defect consumption rate after reacting these reducing agents with carbon dioxide is particularly excellent for the reducing agents made from fine particle magnetite. Moreover, 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 deficiency consumption rate between the domestically produced iron sand and the NZ iron sand is considered to be caused by the catalytic effect of a small amount of titanium contained in the domestically produced iron sand.

(Example 9)
An experiment was conducted to examine the presence or absence of deterioration of the reducing agent and the amount of carbon produced when the reducing agent regeneration process and the carbon dioxide decomposition process were repeatedly performed 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 the mass was measured (reducing agent regeneration step).

Next, using each reducing agent, carbon dioxide was decomposed at a reaction temperature of 380° C., and the mass of the reducing agent+product (carbon) after the reaction was measured. The carbon separation step was not performed after the carbon dioxide decomposition step, and the generated carbon was kept as it was. The reducing agent regeneration step and the carbon dioxide decomposition step using each reducing agent were repeated three times, and the mass of the sample was measured in 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.

According to the results shown in FIGS. 13 to 15, even when magnetite of any particle size was used as a raw material of the reducing agent, the combustion-infrared absorption method showed that the reducing agent regeneration step and the carbon dioxide decomposition step were repeatedly performed. It was confirmed that the measured carbon mass increased almost linearly, the reducing agent was not deteriorated, and the reducing agent regeneration step and the carbon dioxide decomposition step could be performed multiple times by repeatedly using the reducing agent. rice field. In particular, when fine particle magnetite or powder magnetite is used as a raw material for the reducing agent, the amount of increase in carbon mass is greater than when nanoparticle magnetite is used, and the increase is due to the accumulation of carbon. Taking this into account, it was confirmed that it is preferable to use fine particle magnetite or powder magnetite as the raw material of the reducing agent.

On the other hand, when nanoparticle magnetite is used as the raw material of the reducing agent, the mass of carbon is reduced by almost half when the reducing agent regeneration step is performed after the carbon dioxide decomposition step, and the generated carbon is gasified and removed outside the system. considered to have been On the other hand, fine particle magnetite and powder magnetite do not show any loss due to the reaction of the generated carbon. For these reasons, nanoparticle magnetite has 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 is reduced with repeated use. It was found to occur easily. From the viewpoint of such loss due to gasification of carbon, it was confirmed that it is preferable to use fine particle magnetite or powder magnetite as a raw material of the reducing agent.

(Example 10)
An experiment was conducted to examine the decomposition performance of carbon dioxide when hematite (Fe ₂ O ₃ ) was used as the magnetite material.
As a sample, powdered α-Fe ₂ O ₃ (average particle size 1 μm, purity 99.9% by mass (manufactured by Kojundo Chemical Laboratory)) was used, and as a pretreatment, it was heated to 110° C. in an argon gas flow state. After heating, it was held for 10 minutes, then vacuumed and held for another 10 minutes.

Using the pretreated sample thus obtained, a fixed bed reactor was used as the reaction apparatus, and the reaction temperature was 330° C., the reaction time was 1 hour, the hydrogen flow rate was 1.0 L/min, and the hydrogen concentration was 100% by volume. was reduced to produce a reducing agent and the mass was measured.
Table 2 shows the change in mass of the sample before pretreatment, after pretreatment, and after hydrogen reduction. For reference, the change in mass when magnetite is used as the raw material is described.
FIG. 16 shows the XRD analysis result of the sample after hydrogen reduction, and FIG. 17 shows the XRD analysis result of the sample after carbon dioxide decomposition.

According to the results shown in Table 2, from the weight change due to hydrogen reduction, hematite is considered to be completely reduced to the state of completely oxygen-deficient iron.

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

Next, using the obtained hematite-derived reducing agent, carbon dioxide is decomposed at a reaction temperature of 370° C. until the pressure change disappears. The change in the amount of substance in the phase was calculated, and the mass of the product (carbon) was measured by the combustion-infrared absorption method (carbon dioxide decomposition step).
Table 3 shows changes in the amount of gas phase substances after the decomposition of carbon dioxide, the mass of the product (carbon), and the change in the amount of gas phase substances 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 hydrogen reduction of hematite. It should be noted that the color tone of the hematite-derived reducing agent after decomposing carbon dioxide was black, and from the XRD analysis results, even with the hematite-derived reducing agent, after decomposing carbon dioxide, only magnetite was oxidized. (does not revert to hematite).

(Example 11)
As a raw material for producing a reducing agent, an experiment was conducted to examine the decomposition performance of carbon dioxide using powder containing iron hydroxide taken out from used body warmers.
As a used body warmer, Iris Ohyama Co., Ltd.'s "Pokapoka Kazoku Regular 10 pieces (PKN-10R)" was used, and as a pretreatment, the temperature was raised to 110 ° C. in an argon gas flow state, and then held for 10 minutes. , a vacuum was drawn and held for an additional 10 minutes.

The used body warmer (powder form) after pretreatment thus obtained was treated with a fixed bed reactor as a reaction apparatus 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. was reduced under the conditions of to generate a reducing agent, and the mass was measured.
Table 4 shows the change in mass of the sample before and after pretreatment, and before and after hydrogen reduction.
For reference, the change in mass when hematite is used as the raw material is described.
FIG. 18 shows the XRD analysis result of the sample after hydrogen reduction, and FIG. 19 shows the XRD analysis result of the sample after carbon dioxide decomposition.

Since the color tone of the reducing agent derived from the used body warmer after hydrogen reduction was black, like the reducing agents derived from magnetite and hematite, it is considered 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 as well, it is considered that the iron hydroxide in the used body warmer has been reduced to the state of completely oxygen-deficient iron.

Next, using the obtained used body warmer-derived reducing agent, carbon dioxide was decomposed at a reaction temperature of 370° C. until the pressure change disappeared, and the mass was measured. The change in mass 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 hydrogen reduction of used body warmers. In addition, from the fact that the color tone of the reducing agent after decomposing carbon dioxide was black and the results of XRD analysis, even the reducing agent derived from used body warmers is only oxidized to magnetite after decomposing carbon dioxide. (does not return to iron hydroxide).

(Example 12)
We observed the appearance of magnetite with carbon attached to the surface, which was produced by reacting carbon dioxide with a reducing agent in the carbon dioxide decomposition process. An electron microscope (SEM) was used for observation.
FIG. 20 shows an SEM photograph of magnetite with carbon attached to the surface.
In the SEM photograph shown in FIG. 20, the white part of the amorphous product is the oxidized reducing agent (magnetite), and the black part is the nano-sized carbon particles. 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, steam was passed through a reaction tube filled with iron (II) chloride, and the reaction represented by the following formula (19) was performed.
3FeCl ₂ +4H ₂ O→Fe ₃ O ₄ +6HCl+H ₂ (19)
Table 5 shows the implementation conditions of Examples 1 to 4 of the present invention. Table 6 shows the reaction conversion rate of the reaction represented by the formula (19) performed under the conditions shown in Table 5.

According to the results of Example 13 shown in Table 6, the reaction conversion rate is 90% or more under any condition, and magnetite and hydrogen can be efficiently produced by reacting iron (II) chloride and steam. It was confirmed that

INDUSTRIAL APPLICABILITY The present invention can efficiently produce carbon materials and hydrogen 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, waste incineration facilities, etc., it is possible to reduce carbon dioxide emissions, effectively use hydrogen, and Concomitantly, production of high value-added carbon materials such as nano-sized carbon can be performed. Therefore, it has industrial applicability.

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

Claims (14)

a carbon dioxide decomposition step of reacting carbon dioxide and a reducing agent to produce magnetite having carbon attached to the surface;
a carbon separation step of reacting the magnetite obtained in the carbon dioxide decomposition step with carbon attached to the surface thereof with hydrochloric acid or hydrogen chloride gas to produce carbon and iron chloride;
a hydrogen production step of reacting the iron chloride obtained in the carbon separation step with water to produce magnetite, hydrogen, and hydrogen chloride gas;
a reducing agent regeneration step of reacting the magnetite and hydrogen obtained in the hydrogen production step 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 the crystal structure of magnetite, or magnetite. Oxygen-completely deficient iron (δ=4) obtained by complete reduction, or oxygen-deficient iron oxide obtained by reducing hematite or used body warmers, or by completely reducing hematite or used body warmers A method for producing carbon and hydrogen, characterized in that the resulting oxygen-completely deficient iron is obtained. 2. The method for producing carbon and hydrogen according to claim 1, wherein the carbon dioxide decomposition step is carried out at a reaction temperature in the range of 300[deg.] C. or higher and 450[deg.] C. or lower. 3. The method for producing carbon and hydrogen according to claim 1, wherein the carbon dioxide decomposition step is performed at a reaction pressure in the range of 0.01 MPa or more and 5 MPa or less. 3. The method for producing carbon and hydrogen according to claim 1 or 2, wherein the reaction temperature in the carbon separation step is in the range of 10°C or higher and 300°C or lower. 3. The method for producing carbon and hydrogen according to claim 1 or 2, wherein the reaction temperature in the hydrogen production step is in the range of 10[deg.]C or higher and 800[deg.]C or lower. 3. The method for producing carbon and hydrogen according to claim 1, wherein the reducing agent regeneration step is carried out at a reaction temperature in the range of 300[deg.] C. or higher and 450[deg.] C. or lower. 3. The method for producing carbon and hydrogen according to claim 1, wherein the concentration of hydrogen used in the reducing agent regeneration step is in the range of 5% by volume or more and 100% by volume or less. 3. The carbon and hydrogen according to claim 1 or 2, wherein in the reducing agent regeneration step, the magnetite has a BET specific surface area of 0.1 m ² /g or more and 10 m ² /g or less. manufacturing method. 3. The method for producing carbon and hydrogen according to claim 1, wherein in the reducing agent regeneration step, the magnetite has an average particle size in the range of 1 [mu]m to 1000 [mu]m. 3. The method for producing carbon and hydrogen according to claim 1, wherein in the reducing agent regeneration step, the magnetite has a bulk density in the range of 0.3 g/cm ³ or more and 3 g/cm ³ or less. . 3. The method for producing carbon and hydrogen according to claim 1, wherein the carbon is nano-sized carbon having a particle size of 1 μm or less. A carbon material produced by the method for producing carbon and hydrogen according to claim 1 or 2. 3. A reducing agent produced in the reducing agent regeneration step in the method for producing carbon and hydrogen according to claim 1 or 2. 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 the crystal structure of magnetite, or completely reducing magnetite A method for decomposing carbon dioxide, which comprises reacting carbon dioxide with a reducing agent that is oxygen-perfectly deficient iron (δ=4) obtained by the above to decompose the carbon dioxide.

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