Method for producing carbon and hydrogen, carbon material, reducing agent, method for decomposing carbon dioxide

Abstract

Carbon and hydrogen are efficiently generated from carbon dioxide and water, and a reducing agent is repeatedly generated and used. The process includes: a carbon dioxide decomposition step of generating magnetite having carbon attached to a surface; a carbon separation step of generating carbon and iron chloride; a hydrogen production step of generating magnetite, hydrogen, and hydrogen chloride gas; and a reducing agent regeneration step of generating the reducing agent used in the carbon dioxide decomposition step, the reducing agent being an Fe3O4-based material obtained by reducing magnetite while maintaining a crystal structure of the magnetite. 4‑δ (where δ is 1 or more and less than 4) or an oxygen completely-deficient iron (δ = 4) obtained by completely reducing magnetite, an oxygen-deficient iron oxide obtained by reducing hematite or a used hot pack, or an oxygen completely-deficient iron obtained by completely reducing hematite or a used hot pack.

Description

Technical Field

[0001] This invention relates to a method for producing carbon and hydrogen using carbon dioxide and water, carbon materials, reducing agents, and a method for decomposing carbon dioxide.

[0002] This application claims priority based on Japanese Patent Application No. 2021-107907 filed on June 29, 2021 and Japanese Patent Application No. 2022-103360 filed on June 28, 2022, the contents of which are incorporated herein by reference. Background Technology

[0003] For example, large amounts of carbon dioxide (CO2) are emitted from iron smelters, thermal power plants, cement plants, and waste incineration facilities. Therefore, from the perspective of preventing the global greenhouse effect, it is important to recycle carbon dioxide instead of releasing it into the atmosphere.

[0004] On the other hand, with the increasing demand for hydrogen from fuel cell vehicles (FCVs) or hydrogen power generation, there is a need for hydrogen that can be supplied in large quantities at low cost.

[0005] Previously, technologies for separating and recovering carbon dioxide included chemical absorption, physical absorption, and membrane separation. Furthermore, technologies for decomposing the recovered carbon dioxide included semiconductor photocatalysis, photochemical reduction using colloidal metal catalysts or metal complex catalysts, electrochemical reduction, and decomposition methods using chemical conversion reactions (e.g., reactions with bases, transfer reactions, dehydration reactions, addition reactions, etc.). However, these carbon dioxide decomposition methods are impractical in terms of reaction efficiency, cost, and energy consumption.

[0006] Therefore, for example, Patent Document 1 discloses a method in which magnetite, i.e., oxygen-deficient iron oxide, which has vacancies as oxygen-deficient sites in its crystal lattice, is used to reduce carbon dioxide to produce carbon, and methane or methanol is obtained from the carbon. In this invention of Patent Document 1, by using oxygen-deficient iron oxide to decompose carbon dioxide (reduction reaction) and using hydrogen to reduce the iron oxide produced by oxidation back to oxygen-deficient iron oxide, a closed system that can continuously and efficiently decompose carbon dioxide can be realized.

[0007] On the other hand, as a method for producing high-purity hydrogen, for example, Patent Document 2 discloses a method in which ferric chloride is reacted with water at a temperature above 410°C to produce magnetite, hydrogen chloride, and hydrogen, and a separation membrane is used to recover the generated hydrogen. In this invention of Patent Document 2, process waste heat discharged from various factories can be effectively utilized, and hydrogen as a clean energy fuel can be obtained using water as a raw material through thermochemical decomposition technology.

[0008] Patent Document 1: Japanese Patent Application Publication No. 5-184912

[0009] Patent Document 2: Japanese Patent Application Publication No. 2001-233601

[0010] However, under the reaction conditions disclosed in Patent Document 1, there is a problem as follows: the oxygen vacancy degree of oxygen-deficient iron oxide is relatively small (in the reaction of Fe3O4). 4-δ In the case of oxygen-deficient iron oxides (where δ is at most around 0.16), the decomposition capacity for carbon dioxide is low, thus making it impossible to effectively decompose carbon dioxide. Furthermore, when continuously decomposing carbon dioxide using the method in Patent Document 1, hydrogen needs to be supplied externally to reduce magnetite to oxygen-deficient iron oxides, and there is also the problem of high cost for supplying hydrogen.

[0011] Furthermore, in Patent Document 1, the cost of carbon dioxide decomposition is high due to the use of expensive nano-sized magnetite. Also, since the generated carbon is not high-value-added nano-carbon (>1μm), the economic viability of the carbon dioxide decomposition plant is low.

[0012] In Patent Document 2, a large number of substances participate in the hydrogen production reaction (magnesium compounds in addition to magnetite, an iron compound), resulting in a complex reaction mechanism. Furthermore, due to the high temperature required for the reaction (around 1000°C), there are issues of high energy consumption and increased manufacturing costs.

[0013] Furthermore, while Patent Document 2 focuses on the effective utilization of waste heat emitted from various energy-intensive factories, it also requires the effective utilization of carbon dioxide emitted along with waste heat from most of these factories. Summary of the Invention

[0014] The present invention was made in view of the foregoing circumstances, and its object is to provide a method for producing carbon and hydrogen that can be efficiently generated from carbon dioxide and water and repeatedly generated and utilized by the reducing agent used in the reaction, the carbon material obtained thereby, the reducing agent, and the decomposition method of carbon dioxide.

[0015] To address the above problems, the present invention proposes the following method.

[0016] That is, the method for producing carbon and hydrogen of the present invention is characterized by comprising: a carbon dioxide decomposition step, wherein carbon dioxide is reacted with a reducing agent to generate magnetite with carbon adhering to its surface; a carbon separation step, wherein the magnetite with carbon adhering to its surface obtained in the carbon dioxide decomposition step is reacted with hydrochloric acid (an aqueous solution of hydrogen chloride) or hydrogen chloride gas to generate carbon and ferric chloride; a hydrogen production step, wherein the ferric chloride obtained in the carbon separation step is reacted with water to generate magnetite, hydrogen, and hydrogen chloride gas; and a reducing agent regeneration step, wherein the magnetite and hydrogen obtained in the hydrogen production step react with each other to generate the reducing agent used in the carbon dioxide decomposition step, wherein the reducing agent is obtained by reducing magnetite while maintaining the crystal structure of magnetite, and is composed of Fe3O4. 4-δ (where δ is 1 or more and less than 4) represents oxygen-deficient iron oxide, oxygen-completely deficient iron obtained by completely reducing magnetite (δ = 4), oxygen-deficient iron oxide obtained by reducing hematite or used hand warmers (Kairo), or oxygen-completely deficient iron obtained by completely reducing hematite or used hand warmers.

[0017] According to the present invention, carbon can be produced efficiently from carbon dioxide at low cost by using an oxygen-deficient iron oxide or an oxygen-completely-deficient iron oxide that maintains the crystal structure of magnetite and has a large number of atomic vacancies caused by the loss of oxygen atoms as a reducing agent to reduce carbon dioxide.

[0018] Furthermore, by reacting ferric chloride obtained in the carbon separation process with water, high-purity hydrogen can be produced by efficiently decomposing water at low cost. In this hydrogen production, the amount of hydrogen generated can be easily increased simply by increasing the recycling rate of magnetite or ferric chloride.

[0019] Furthermore, in this invention, the reaction temperature can be set within the range of 300°C or higher and 450°C or lower during the carbon dioxide decomposition process.

[0020] Furthermore, in this invention, the reaction pressure can be set within a range of 0.01 MPa or higher and 5 MPa or lower during the carbon dioxide decomposition process.

[0021] Furthermore, in this invention, the reaction temperature can be set within the range of 10°C or higher and 300°C or lower in the carbon separation process.

[0022] Furthermore, in this invention, the reaction temperature can be set within the range of 10°C or higher and 800°C or lower in the hydrogen production process.

[0023] Furthermore, in this invention, the reaction temperature can be set in the range of 300°C or higher and 450°C or lower during the reducing agent regeneration process.

[0024] Furthermore, in this invention, the concentration of hydrogen used in the reducing agent regeneration process can be in the range of 5% by volume or more and 100% by volume or less.

[0025] Furthermore, in this invention, during the reducing agent regeneration process, the specific surface area of ​​the magnetite based on the BET method can be as small as 0.1 m². 2 / g or more and 10m 2 Within the range of / g and below.

[0026] Furthermore, in the present invention, during the reducing agent regeneration process, the average particle size (cumulative average diameter (50% diameter) of the magnetite, hereinafter the same) can be in the range of 1 μm or more and 1000 μm or less.

[0027] Furthermore, in this invention, during the reducing agent regeneration process, the bulk density of the magnetite can be 0.3 g / cm³. 3 Above and 3g / cm 3 Within the following range.

[0028] Furthermore, in this invention, the carbon can be nanoscale carbon with a particle size of less than 1 μm.

[0029] The carbon material of the present invention is characterized in that it is manufactured by the carbon and hydrogen manufacturing methods described above.

[0030] The reducing agent of the present invention is characterized in that the reducing agent is a reducing agent generated in the reducing agent regeneration step of the carbon and hydrogen manufacturing methods described above.

[0031] The carbon dioxide decomposition method of the present invention is characterized in that a reducing agent is reacted with carbon dioxide to decompose the carbon dioxide, wherein the reducing agent is obtained by reducing magnetite while maintaining the crystal structure of magnetite, and is composed of Fe3O4. 4-δ (where δ is greater than 1 and less than 4) represents oxygen-deficient iron oxide or oxygen-completely deficient iron obtained by completely reducing magnetite (δ = 4).

[0032] According to the present invention, a method for producing carbon and hydrogen that can be efficiently generated from carbon dioxide and water and repeatedly generated and utilized by the reducing agent used in the reaction, a carbon material obtained thereby, a reducing agent, and a method for decomposing carbon dioxide that can decompose carbon dioxide with high reaction efficiency using a reducing agent with high reducing power are provided. Attached Figure Description

[0033] Figure 1 This is a schematic diagram representing the crystal structure of a quarter-unit lattice of magnetite.

[0034] Figure 2 This is a flowchart illustrating a method for manufacturing carbon and hydrogen according to one embodiment of the present invention.

[0035] Figure 3 This is a graph representing the results of Example 1.

[0036] Figure 4 This is a graph representing the results of Example 2.

[0037] Figure 5 This is a graph showing the results of Example 3.

[0038] Figure 6 This is a graph representing the results of Example 4.

[0039] Figure 7 This is a graph representing the results of Example 5.

[0040] Figure 8 This is a graph representing the results of Example 6.

[0041] Figure 9 This is a graph showing the measurement results of oxygen vacancy degree δ in Example 7.

[0042] Figure 10 This is a graph showing the results of the oxygen vacancy consumption rate measurement in Example 7.

[0043] Figure 11 This is a graph showing the measurement results of oxygen vacancy degree δ in Example 8.

[0044] Figure 12 This is a graph showing the results of the oxygen vacancy consumption rate measurement in Example 8.

[0045] Figure 13 The graph shows the results of using the nanoparticle magnetite from Example 9.

[0046] Figure 14 This is a graph showing the results of using the particulate magnetite from Example 9.

[0047] Figure 15 This is a graph showing the results of using the powdered magnetite from Example 9.

[0048] Figure 16 The results are XRD analysis of the hydrogen-reduced sample from Example 10.

[0049] Figure 17 The results are XRD analysis results of the sample after carbon dioxide decomposition in Example 10.

[0050] Figure 18 The results are XRD analysis results of the hydrogen-reduced sample from Example 11.

[0051] Figure 19 The results are XRD analysis results of the sample after carbon dioxide decomposition in Example 11.

[0052] Figure 20 This is an SEM image of the product after the reducing agent reacts with carbon dioxide. Detailed Implementation

[0053] 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 accompanying drawings. Furthermore, the embodiments shown below are detailed descriptions provided to better understand the gist of the invention and do not limit the invention unless otherwise specified. Also, in the accompanying drawings used in the following description, for ease of understanding of the features of the invention, parts that are considered key components are sometimes shown enlarged, and the dimensional ratios of each component may not be the same as actual dimensions.

[0054] First, the reducing agent used in the carbon and hydrogen manufacturing method of this embodiment will be explained.

[0055] The reducing agent is a material that, in the carbon dioxide decomposition step S1 described later, reacts with carbon dioxide to reduce it into carbon and oxygen. In this embodiment, the reducing agent used is Fe3O4. 4-δ (where δ is greater than 1 and less than 4) refers to oxygen-deficient iron oxides of magnetite (Fe3O4), hematite, or oxygen-deficient iron oxides or oxygen-completely-deficient iron oxides of used hand warmers (the main component of which is iron hydroxide).

[0056] Figure 1 This is a schematic diagram representing the crystal structure of a quarter-unit lattice of magnetite.

[0057] Magnetite has a spinel-type crystal structure, which allows oxygen ions (O2) to pass through it. 2- The configuration is a cubic close-packed structure, with +3 valence iron (Fe3+) arranged in a 2:1 ratio in the gaps (site A, site B). 3+ Iron with a +2 valence (Fe) 2+ Magnetite is represented by the general formula Fe3O4.

[0058] The reducing agent used in this embodiment is one that maintains the crystal structure of this magnetite, namely the spinel-type lattice structure, by making... Figure 1The oxygen-deficient iron oxides obtained by the removal of oxygen ions at any position shown (1≤δ<4), the oxygen-completely-deficient iron obtained by the complete reduction of magnetite (δ=4), the oxygen-deficient iron oxides obtained by the reduction of hematite or used hand warmers, or the oxygen-completely-deficient iron obtained by the complete reduction of hematite or used hand warmers. This reducing agent is generated in the reducing agent regeneration process S4 described later.

[0059] The oxygen-deficient iron oxide obtained by reducing magnetite is produced by Fe3O 4-δ This indicates that, based on the oxygen ions (O) detached from magnetite... 2- The proportion of oxygen ions removed from magnetite is set to a range of 1 or higher and less than 4. Furthermore, the substance obtained by completely removing oxygen ions from magnetite (i.e., δ = 4) is the aforementioned oxygen-deficient iron.

[0060] δ represents the oxygen vacancy degree, which is the ratio of oxygen-deficient iron oxides to oxygen vacancies in magnetite, maintaining its spinel-type crystal structure. This oxygen vacancy degree δ is measured by the difference between the mass of magnetite before and after the reaction with hydrogen in the reducing agent regeneration step S4. Since the decrease in mass (difference) is equal to the amount of oxygen lost from magnetite (which is positioned as atomic vacancies in the crystal lattice), the oxygen vacancy degree δ (δ = 1–4) can be calculated from this decrease in mass.

[0061] Furthermore, the sites where oxygen ions detach from magnetite become atomic vacancies while maintaining the spinel-type crystal lattice structure. Only the detached cations are largely encapsulated within the lattice, resulting in an expanded lattice spacing. These atomic vacancies caused by oxygen detachment act as reducing agents, producing carbon dioxide through a deoxygenation reaction (reduction reaction).

[0062] The average particle size of the reducing agent (oxygen-deficient iron oxide, oxygen-completely-deficient iron) in this embodiment is greater than 1 μm, preferably 1 μm or more and less than 20 μm, and also preferably greater than 50 μm and less than 200 μm.

[0063] When the average particle size of the reducing agent is less than 1 μm, experimental results show that the proportion of carbon monoxide generated during the decomposition of carbon dioxide increases, resulting in a lower carbon recovery rate. By using a reducing agent with an average particle size of 1 μm or more, a higher carbon recovery rate can be maintained, while the agglomeration of the reducing agent particles is reduced, thus avoiding problems such as adhesion to the reactor wall. This allows it to be applied in industrial reaction devices such as rotary kilns.

[0064] Furthermore, by setting the average particle size of the reducing agent to less than 20 μm, a high reaction rate can be maintained. Moreover, when the average particle size of the reducing agent is set to greater than 50 μm but less than 200 μm, particle dispersion is reduced, and fluidization performance becomes excellent, thus enabling its application in industrial reaction devices such as fluidized bed reactors. In this case, compared to rotary kiln reactors, solid-gas contact and heat transfer are superior, equipment costs are lower, and the reactor size can be made more compact.

[0065] Figure 2 This is a flowchart illustrating, in stages, a method for producing carbon and hydrogen, including the carbon dioxide decomposition method according to an embodiment of the present invention.

[0066] The carbon and hydrogen production method of this embodiment includes: a carbon dioxide decomposition step S1 to generate magnetite with carbon adhering to its surface; a carbon separation step S2 to generate carbon and ferric chloride; a hydrogen production step S3 to generate magnetite, hydrogen, and hydrogen chloride gas; and a reducing agent regeneration step S4 to generate a reducing agent. Furthermore, the carbon dioxide decomposition method of this embodiment includes a carbon dioxide decomposition step S1. In each of these steps, magnetite and the reducing agent used to reduce it are recycled, and carbon and hydrogen are produced from carbon dioxide and water supplied from an external source.

[0067] (Carbon dioxide decomposition process S1)

[0068] In the carbon dioxide decomposition process S1, a reaction apparatus (carbon dioxide decomposition furnace) such as a rotary kiln and a bubble flow layer is used. While stirring a powdered reducing agent with an average particle size of about 1 μm to 500 μm, the agent is brought into contact with gaseous carbon dioxide, thereby decomposing (reducing) the carbon dioxide. In addition, magnetite with carbon adhering to its surface is generated.

[0069] As a reaction device used in the carbon dioxide decomposition process S1, a circulating flow layer can also be used. However, compared with a bubble flow layer, it has disadvantages such as higher overall reactor height, higher equipment cost, more complex design and operation of particle recirculation loop, shorter particle residence time (the residence time in the reaction device is on the order of seconds), limited particle size of the reducing agent that can be used, increased particle wear, and higher energy cost required to maintain high gas flow rate or circulate powder.

[0070] The carbon dioxide used in the carbon dioxide decomposition process S1 can be supplied from facilities that emit large amounts of carbon dioxide (e.g., iron smelters, thermal power plants, cement plants, waste incineration facilities, biogas generation facilities, natural gas wells, etc.). The reducing agent is supplied from the reducing agent regeneration process S4, which will be described later.

[0071] The reaction temperature in the carbon dioxide decomposition process S1 only needs to be above 300°C and below 450°C, preferably above 350°C and below 400°C.

[0072] Thus, by setting the reaction temperature within a range of 300°C to 450°C, the reducing agent can maintain a spinel-type crystal structure. However, if the reaction temperature is, for example, above 500°C, there are concerns that the reducing agent may be unable to maintain a spinel-type crystal structure due to repeated use of magnetite. Furthermore, there are concerns about increased energy consumption during the reaction.

[0073] In the carbon dioxide decomposition process S1, in order to raise the temperature to this reaction temperature range, it is preferable to effectively utilize the heat (waste heat) generated by the operation of the ironworks, thermal power plant, cement plant, waste incineration facility, etc., which serve as carbon dioxide supply sources, the heat energy of the nuclear furnace, i.e., the heat energy of the high-temperature gas furnace, as well as the heat energy of the furnace that outputs high temperature.

[0074] The reaction pressure in the carbon dioxide decomposition process S1 only needs to be above 0.01 MPa and below 5 MPa, preferably above 0.1 MPa and below 1 MPa.

[0075] If the reaction pressure is 0.01 MPa or higher, the reaction rate required for practical processes can be obtained. Furthermore, if the reaction pressure is 0.1 MPa or higher, it can directly handle actual exhaust gases with low carbon dioxide concentrations. Moreover, if the reaction pressure is below 5 MPa, the manufacturing cost of the equipment can be controlled.

[0076] In the carbon dioxide decomposition process S1, increasing the reaction temperature and pressure can increase the decomposition rate of carbon dioxide, thereby improving the carbon dioxide treatment efficiency. On the other hand, if the reaction temperature is too high, the spinel structure of the reducing agent may be destroyed.

[0077] In the carbon dioxide decomposition process S1, the decomposition of carbon dioxide produces the following two stages (1) and (2) and one stage (3).

[0078] CO2→CO (intermediate product)+O 2- (1)

[0079] CO→C+O 2- (2)

[0080] CO2→C+2O 2- (3)

[0081] Moreover, the oxygen generated in the above formulas (1), (2), and (3) is inserted into the atomic vacancies of oxygen-deficient iron oxide (formula (4)) and oxygen-completely-deficient iron (formula (5)) through the following formulas (4) and (5).

[0082] Fe3O 4-δ +δO 2- →Fe3O4 (where δ = 1 or more and less than 4) (4)

[0083] 3Fe + 4O 2- →Fe3O4 (5)

[0084] Furthermore, in the carbon dioxide decomposition method of this embodiment, in the carbon dioxide decomposition step S1, only the above formula (1) can be performed. The obtained carbon monoxide (CO) can be used as a raw material for obtaining useful chemical products such as methane, methanol and other hydrocarbons and various resins by adding hydrogen.

[0085] In the above reaction in the carbon dioxide decomposition process S1, if all carbon dioxide is reacted to formula (2) or formula (3), no gas is generated as the final product. That is, it is assumed that all the oxygen in the carbon dioxide enters the oxygen-deficient iron oxide or the oxygen-completely-deficient iron. Taking this into consideration, the reaction of carbon dioxide with oxygen-deficient iron oxide is represented by formula (6), and the reaction of carbon dioxide with oxygen-completely-deficient iron is represented by formula (7).

[0086] 2Fe3O 4-δ +δCO2→2Fe3O4·δC (Magnetite with attached carbon. Where δ=1 or more and less than 4) (6)

[0087] 3Fe + 2CO2 → Fe3O4·2C (magnetite with attached carbon) (7)

[0088] In the carbon dioxide decomposition process S1, the oxygen-deficient iron oxide and oxygen-completely-deficient iron oxide used as reducing agents can decompose carbon dioxide into carbon. This is because these reducing agents have a metastable crystal structure, namely a spinel-type lattice structure, formed under non-equilibrium conditions. At room temperature, they also react slowly with oxygen to absorb oxygen ions, attempting to transform into the more stable Fe3O4. That is, it is believed that they are produced by attempting to transform the unstable spinel-type lattice structure with atomic vacancies in the crystal lattice into a more stable spinel-type lattice structure without atomic vacancies.

[0089] In the stabilization (magnetization) process of oxygen-deficient iron oxides and oxygen-completely deficient iron, if oxygen ions enter the crystal, the crystal attempts to release electrons from the crystal surface to maintain electroneutrality. It is believed that in oxygen-deficient iron oxides and oxygen-completely deficient iron, the +2 valence Fe (Fe²⁺)... 2+It exists as an atom capable of releasing electrons, but due to the instability of oxygen-deficient iron oxides and oxygen-completely-deficient iron crystals, it produces a reduction potential that is different from the usual one.

[0090] In the carbon dioxide decomposition step S1, in order to maximize the decomposition capacity of carbon dioxide caused by oxygen-deficient iron oxide and oxygen-completely-deficient iron used as reducing agents, it is preferable to keep the oxygen concentration in the reaction environment below 5% by volume.

[0091] If the oxygen concentration in the reaction environment of the carbon dioxide decomposition process S1 is higher than 5% by volume, there is a concern that before the oxygen constituting carbon dioxide enters the reducing agent (oxygen-deficient iron oxide or oxygen-completely-deficient iron), the oxygen in the reaction atmosphere enters the oxygen-deficient sites of the reducing agent, thereby reducing the carbon dioxide decomposition capacity of the reducing agent.

[0092] In the carbon dioxide decomposition process S1, the carbon produced by the decomposition of carbon dioxide is generated as nano-sized carbon with a particle size of less than 1 μm. In the carbon dioxide decomposition process S1, under the same temperature conditions, the reaction rate of the above formula (1) is slower than that of formula (2). However, by increasing the reaction rate of formula (1), the reaction of formula (2) proceeds rapidly, and fine nano-sized carbon particles can be generated. Regarding the reaction rates of formula (1) and formula (2), they can be increased by increasing the oxygen vacancy degree δ and increasing the reaction temperature and reaction pressure.

[0093] These nanoscale carbons are generated by attaching to or covering the surface of magnetite produced by the oxidation of oxygen-deficient iron oxides and fully oxygen-deficient iron oxides. The magnetite with carbon attached to its surface is then sent to the next carbon separation process, S2.

[0094] On the other hand, in this embodiment, during the carbon dioxide decomposition process S1, the reducing agent becomes magnetite (Fe3O4) through the decomposition of carbon dioxide, and hematite (Fe2O3) is not produced.

[0095] In this embodiment, carbon is produced in a state where it is relatively firmly attached to the surface of magnetite.

[0096] (Carbon separation process S2)

[0097] The carbon separation process S2 consists of the chlorination reaction of magnetite (conversion from magnetite to ferric chloride (III)(FeCl3) and ferric chloride (II)(FeCl2)) and carbon recovery operations.

[0098] The chlorination reaction of magnetite includes wet chlorination based on hydrochloric acid dissolution and dry chlorination based on hydrogen chloride gas.

[0099] (Wet chlorination)

[0100] In the case of chlorination of magnetite by wet chlorination, the magnetite with carbon adhering to its surface, obtained in the carbon dioxide decomposition step S1, is dissolved in hydrochloric acid (an aqueous solution of hydrogen chloride) by reacting it with the hydrochloric acid, and the carbon insoluble in the hydrochloric acid is separated from the magnetite. The magnetite dissolved in the hydrochloric acid reacts with hydrogen chloride to produce ferric chloride (ferric chloride (III) and ferric chloride (II)) and water.

[0101] Regarding the separation of magnetite dissolved in hydrochloric acid from carbon, it can be carried out, for example, by solid-liquid separation such as filtration. Furthermore, the resulting ferric chloride (a mixture of ferric chloride (III) and ferric chloride (II)) is sent to the next hydrogen production process S3. In this wet chlorination process, all the generated ferric oxide is dissolved, thus enabling the separation of carbon.

[0102] In the carbon separation process S2 (wet chlorination), the hydrochloric acid used only needs to be hydrochloric acid with a hydrogen chloride concentration in the range of, for example, 5% to 37% by mass.

[0103] If the concentration of hydrogen chloride in hydrochloric acid is less than 5% by mass, there is a concern that the reaction will slow down. Furthermore, concentrated hydrochloric acid with a concentration greater than 37% by mass is difficult to handle due to the rapid volatilization of hydrogen chloride.

[0104] The reaction temperature in the carbon separation process S2 (wet chlorination) only needs to be above 10°C and below 150°C, preferably above 50°C and below 100°C.

[0105] If the temperature is below 10°C, the reaction rate is slow and cooling equipment is required. If the temperature is above 150°C, more energy is consumed, and the solution will evaporate, resulting in poor efficiency.

[0106] In the carbon separation process S2 (wet chlorination), in order to raise the temperature to this reaction temperature range, it is preferable to utilize the same heat source as in the carbon dioxide decomposition process S1.

[0107] The chlorination reaction of magnetite in carbon separation process S2 (wet chlorination) is represented by the following formulas (8) to (9).

[0108] 2Fe3O4·δC + 16HCl → 4FeCl3 + 2FeCl2 + 8H2O + δC (Wet chlorination: 10–150℃) (where δ = 1–4) (8)

[0109] 2Fe3O4 + 16HCl → 4FeCl3 + 2FeCl2 + 8H2O (Wet chlorination: 10℃~150℃) (9)

[0110] (Dry chlorination)

[0111] In the case of chlorination of magnetite by dry chlorination, ferric chloride (ferric chloride (III) and ferric chloride (II)) and water are generated by reacting magnetite with carbon attached to its surface obtained in the carbon dioxide decomposition step S1 or magnetite obtained in the hydrogen production step S3 with hydrogen chloride gas.

[0112] In the carbon separation process S2 (dry chlorination), the hydrogen chloride gas used only needs to be in the range of hydrogen chloride concentration, for example, 50% to 100% by mass.

[0113] If the concentration of hydrogen chloride is less than 50% by mass, there is a concern that the reaction may slow down.

[0114] The reaction temperature in the carbon separation process S2 (dry chlorination) only needs to be above 50°C and below 300°C, preferably above 80°C and below 200°C.

[0115] If the temperature is below 50°C, the reaction rate is slow. If the temperature is above 300°C, more energy is consumed and the efficiency decreases. In addition, since the chlorination reaction is an exothermic reaction, it is not conducive to the reaction under high temperature conditions.

[0116] In the carbon separation process S2 (dry chlorination), in order to raise the temperature to this reaction temperature range, it is preferable to utilize the same heat source as in the carbon dioxide decomposition process S1.

[0117] The chlorination reaction of magnetite in carbon separation process S2 (dry chlorination) is represented by the following formulas (8) to (9).

[0118] 2Fe3O4·δC + 16HCl → 4FeCl3 + 2FeCl2 + 8H2O + δC (dry chlorination: 50–300℃) (where δ = 1–4) (8)

[0119] 2Fe3O4 + 16HCl → 4FeCl3 + 2FeCl2 + 8H2O (Dry chlorination: 50℃~300℃) (9)

[0120] To reduce energy consumption, magnetite without attached carbon (magnetite obtained in hydrogen production step S3 that is recycled solely for hydrogen production) is preferably subjected to dry chlorination using hydrogen chloride gas. In the case of dry chlorination, after converting the carbon-attached magnetite to ferric chloride using hydrogen chloride gas, the product is dissolved in water, thereby allowing the separation of carbon as an insoluble component.

[0121] The carbon (carbon material) separated from magnetite in carbon separation process S2 is nanoscale carbon with a particle size of less than 1 μm, and almost no carbon particles larger than 1 μm are generated. This nanoscale carbon powder is high-purity carbon with a purity of, for example, 99% or higher. It can be directly used as carbon black or activated carbon in functional carbon materials such as rubber reinforcing additives, battery materials, toners, colorants, conductive materials, catalysts, and adsorbents, or as a reducing agent to replace coke used in ironmaking. Furthermore, it can be used as a raw material for manufacturing carbon materials such as artificial graphite, carbon fiber, and carbon nanotubes.

[0122] (Hydrogen manufacturing process S3)

[0123] The hydrogen production process S3 includes: a reduction reaction of ferric chloride (III) obtained in the carbon separation process S2 (reduction of ferric chloride (III) to ferric chloride (II)) using a solid-gas reaction apparatus such as a rotary kiln and a flow bed; operations such as concentration, drying, and granulation of the ferric chloride (II) solution; and a reaction to generate magnetite, hydrogen, and hydrogen chloride by reacting ferric chloride (II) with water. The magnetite produced in this hydrogen production process S3 is sent to the next reducing agent regeneration process S4. Furthermore, the hydrogen chloride can be used as a raw material for the production of hydrochloric acid used in the carbon separation process S2.

[0124] In addition, in the concentration, drying, and granulation of ferric chloride (II) solution, membrane separation devices, evaporation devices, crystallization devices, spray dryers and other devices are sometimes used to produce ferric chloride (II) particles with a specified particle size, which are then sent to the hydrogen and magnetite manufacturing reaction.

[0125] The reduction methods of ferric chloride (III) include, for example, thermal reduction by thermal decomposition of ferric chloride (III) at high temperature; and reduction by adding a reducing agent (CuCl, Fe, etc.) at low temperature.

[0126] (Thermal reduction method)

[0127] The details of the reduction reaction of ferric chloride (III) carried out by thermal reduction in hydrogen production process S3 are shown in the following formulas (10) to (11).

[0128] 4FeCl3→4FeCl2+2Cl2 (Reduction of ferric chloride (III): 300℃~600℃)……(10)

[0129] 2Cl2 + 2H2O → 4HCl + O2 (Anti-Deacon reaction: 400℃~800℃)……(11)

[0130] Alternatively, the anti-Deacon reaction of equation (11) may not necessarily occur.

[0131] (Reduction method using CuCl)

[0132] The details of the reduction reaction of ferric chloride (III) carried out in hydrogen production process S3 by using CuCl reduction are shown in the following formulas (12) to (14).

[0133] 4FeCl3 + 4CuCl → 4FeCl2 + 4CuCl2 (Reduction of ferric chloride (III): 10℃~100℃) (12)

[0134] 4CuCl2→4CuCl+2Cl2 (Reduction of CuCl2: 300℃~600℃) (13)

[0135] 2Cl₂ + 2H₂O → 4HCl + O₂ (Anti-Deacon reaction: 400℃~800℃) (14)

[0136] Alternatively, the anti-Deacon reaction of equation (14) may not necessarily occur.

[0137] (Using the reduction method of Fe)

[0138] The details of the reduction reaction of ferric chloride (III) carried out in hydrogen production process S3 by means of Fe reduction are shown in the following formula (15).

[0139] 4FeCl3 + 2Fe → 6FeCl2 (Reduction of ferric chloride (III): 10℃~100℃) (15)

[0140] (The reaction of ferric chloride (II) produced in various reduction processes with water: hydrogen, magnetite manufacturing reaction)

[0141] By employing the aforementioned reduction methods, the reaction temperature in the hydrogen production reaction, where ferric chloride (II) produced in the reduction reaction of ferric chloride (III) reacts with water, only needs to be within the range of 300°C to 800°C, preferably 400°C to 600°C. In the hydrogen production step S3, to raise the temperature to this reaction temperature range, it is also preferable to effectively utilize the same heat source as in the carbon dioxide decomposition step S1.

[0142] In the reaction of ferric chloride (II) with water in hydrogen production process S3, the following reaction (16) is produced.

[0143] 3FeCl2+4H2O→Fe3O4+6HCl+H2 (16)

[0144] The hydrogen obtained through this reaction is, for example, high-purity hydrogen with a purity of over 99%, which can be used as hydrogen stations for fuel cell vehicles (FCVs), hydrogen power generation, and hydrogen sources for various industries.

[0145] In addition, some of the hydrogen produced in the hydrogen production process S3 will also be used in the next reducing agent regeneration process S4. However, in order to increase the amount of hydrogen output to the outside, magnetite (magnetite without attached carbon) is added in the carbon separation process S2 or ferric chloride (FeCl2) is added in the hydrogen production process S3. This allows more hydrogen to be generated than the hydrogen required in the reducing agent regeneration process S4, and it can be used as a high-purity and low-cost hydrogen source.

[0146] However, if the magnetite produced in the hydrogen production step S3 is supplied to the reducing agent regeneration step S4 from the additional iron compounds (magnetite, ferric chloride), the process load of the reducing agent regeneration step S4 will increase due to the excess magnetite. Therefore, it is preferable to extract the amount of iron compounds derived from the additional iron compounds from the magnetite produced in the hydrogen production step S3 and feed it into the carbon separation step S2 in a carbon-free state. 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 remainder is recycled in the carbon separation step S2 and the hydrogen production step S3, thereby increasing the amount of hydrogen produced in the hydrogen production step S3 without affecting the carbon dioxide decomposition step S1 and the reducing agent regeneration step S4.

[0147] For example, in this embodiment, 25% by mass of the magnetite produced in the hydrogen production process S3 is supplied to the reducing agent regeneration process S4, and the remaining 75% by mass is supplied to the carbon separation process S2.

[0148] (Reducing agent regeneration process S4)

[0149] In the reducing agent regeneration step S4, the hydrogen generated in the hydrogen production step S3 is reacted with magnetite to remove oxygen ions contained in the magnetite (deoxidation (reduction) reaction), and oxygen-deficient iron oxide (Fe3O4) with vacant oxygen atoms is generated while maintaining the crystal structure of magnetite, i.e., spinel-type crystal structure. 4-δ (where δ is greater than 1 and less than 4) or oxygen is completely absent iron.

[0150] In addition, the magnetite introduced into the reducing agent regeneration process S4 is the magnetite obtained in the hydrogen production process S3. However, the replenishment of magnetite that is reduced in the initial stage of each process and during the implementation of each process is not limited to pure magnetite, but may also include other substances.

[0151] As a raw material for importing magnetite from external sources (magnetite material), iron sand, which is a natural mineral, or iron ore contained in iron ore used in iron smelters, can be used. By using these iron sands as magnetite, magnetite can be easily obtained in a cheap manner.

[0152] Furthermore, as a magnetite material, hematite (Fe2O3) and heat packs (mainly composed of iron hydroxide) that have been used through iron oxidation can also be used.

[0153] The specific surface area of ​​the magnetite in this embodiment, based on the BET method, is 0.1 m². 2 / g or more and 10m 2 Within the range of / g or less, preferably within 0.3m 2 / g or more and 8m 2 In the range of / g or less, more preferably in the range of 1m 2 / g or more and 6m 2 Within the range of / g and below.

[0154] If the specific surface area of ​​magnetite is 0.1 m² 2 A specific surface area of ​​10 m² or higher ensures the necessary contact area between the solid and gas for the solid-gas reaction, allowing for the reaction rate required for practical processes. Furthermore, if the specific surface area of ​​magnetite is 10 m² / g... 2 A concentration below / g ensures a rapid reaction rate and reduces the proportion of carbon monoxide generated during carbon dioxide decomposition, thus improving carbon recovery.

[0155] Furthermore, the specific surface area of ​​the reducing agent obtained by reducing magnetite through the reducing agent regeneration step S4 of this embodiment is greater than the specific surface area of ​​the magnetite before reduction. The specific surface area of ​​the reducing agent is 0.1 m². 2 / g or more and 30m 2 / g or less, preferably 0.3m 2 / g or more and 25m 2 / g or less, preferably 1m 2 / g or more and 18m 2 / g or less. Furthermore, the specific surface area of ​​the reducing agent is more than 1 and less than 3 times that of the specific surface area of ​​magnetite, preferably more than 1 and less than 2.5 times, and more preferably more than 1 and less than 2.0 times.

[0156] Furthermore, the average particle size of the magnetite in this embodiment is 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 greater than 50 μm and less than 200 μm.

[0157] If the average particle size of magnetite is greater than 1 μm, the proportion of carbon monoxide generated during the decomposition of carbon dioxide decreases, thereby improving carbon recovery. Moreover, by setting the average particle size to be greater than 1 μm, the agglomeration and dispersion of particles decrease, resulting in better flowability and operability. This avoids problems such as adhesion to the reactor wall or the formation of molten material, making it suitable for use in industrial reaction equipment such as rotary kilns and flow beds.

[0158] Furthermore, if the average particle size of magnetite is below 1000 μm, the contact area between the solid and gas required for the solid-gas reaction can be ensured, and the reaction rate required for practical processes can be obtained.

[0159] Furthermore, the bulk density of the magnetite in this embodiment is 0.3 g / cm³. 3 Above and 3g / cm 3 Within the following range, preferably 0.4 g / cm³ 3 Above and 2g / cm 3 Within the following range, more preferably within 0.5 g / cm³ 3 Above and 1g / cm 3 Within the following range.

[0160] If the bulk density of magnetite is 0.3 g / cm³ 3 The above results in lower particle aggregation and dispersion, and improved fluidity, making it suitable for use in industrial reaction equipment such as rotary kilns and flow beds. Furthermore, if the bulk density of magnetite is 3 g / cm³... 3 The following ensures the porosity between and within particles, allowing reactant gases to easily diffuse into the particles and achieve the reaction rate required for practical processes.

[0161] In the reducing agent regeneration step S4, a solid-gas reaction apparatus, such as a rotary kiln and a flow layer, is used to stir powdered magnetite while bringing it into contact with hydrogen generated in the hydrogen production step S3. This causes oxygen atoms in the magnetite to detach and react with the hydrogen to produce water (water vapor). Furthermore, the magnetite with detached oxygen atoms retains its crystal structure, i.e., a spinel-type lattice structure, and forms oxygen-deficient iron oxide or oxygen-completely-deficient iron at the vacant oxygen atom positions.

[0162] In the reducing agent regeneration process S4, if the magnetite material contains hematite, the hematite is reduced to magnetite, and further reduced to oxygen-deficient iron oxide or oxygen-completely-deficient iron.

[0163] The reaction temperature of the reducing agent regeneration process S4 only needs to be within the range of 300°C to 450°C, preferably 350°C to 400°C.

[0164] If the reaction temperature is above 300℃, the reaction rate required for practical processes can be obtained. Furthermore, if the reaction temperature is below 450℃, the crystal structure of the reducing agent is not destroyed during the reaction, maintaining high reactivity and allowing for repeated use of the reducing agent. Additionally, the energy consumption during the reaction can be controlled.

[0165] In the reducing agent regeneration step S4, in order to raise the temperature to this reaction temperature range, it is preferable to utilize the same heat source as in the carbon dioxide decomposition step S1.

[0166] The reaction pressure of the reducing agent regeneration process S4 only needs to be between 0.1 MPa and 5 MPa, preferably between 0.1 MPa and 1 MPa.

[0167] If the reaction pressure is 0.1 MPa or higher, the reaction rate required for practical processes can be obtained, allowing for a compact reaction apparatus. Furthermore, if the reaction pressure is 5 MPa or lower, the manufacturing cost of the apparatus can be controlled.

[0168] In the reducing agent regeneration step S4, the concentration of hydrogen used only needs to 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 is, for example, around 90% by volume, there is not much difference in reducing power compared to hydrogen with a concentration of 100% by volume. Therefore, if hydrogen with a concentration of around 90% by volume, which is cheaper than hydrogen with a concentration of 100% by volume, is used, the reducing agent can be generated from magnetite at a low cost.

[0169] In the reduction of magnetite using hydrogen in the reducing agent regeneration process S4, the reducing agent is generated as shown in formulas (17) and (18) below.

[0170] Fe3O4 + δH2 → Fe3O 4-δ +δH2O (where δ = 1 or more and less than 4) (17)

[0171] Fe3O4 + 4H2 → 3Fe + 4H2O (18)

[0172] In order to maintain the activity of the obtained reducing agent, it is preferable to prevent oxidation caused by the introduction of the reducing agent by air during the period from the reducing agent regeneration step S4 to the carbon dioxide decomposition step S1. For example, if the structure is designed to prevent the introduction of air while transferring the reducing agent from the reducing agent regeneration step S4 to the carbon dioxide decomposition step S1, then the reducing agent obtained in the reducing agent regeneration step S4 can be supplied to the carbon dioxide decomposition step S1 without oxidation.

[0173] Furthermore, to improve the carbon generation efficiency in the carbon separation process S2, the carbon dioxide decomposition process S1 and the reducing agent regeneration process S4 can be repeated more than twice. After increasing the carbon concentration of the carbon-attached magnetite generated in the carbon dioxide decomposition process S1, the carbon separation process S2 and the hydrogen production process S3 can be performed. As a result, nanoscale carbon can be manufactured at a lower cost.

[0174] According to the carbon material and hydrogen manufacturing method of this embodiment described above, oxygen-deficient iron oxide (Fe3O4) that maintains the crystal structure of magnetite and has a large number of atomic vacancies caused by the loss of oxygen atoms is produced. 4-δ (where δ = 1 or more and less than 4) or oxygen-deficient iron (δ = 4) obtained by completely reducing magnetite can be used as a reducing agent to reduce carbon dioxide, enabling the efficient production of carbon materials from carbon dioxide at low cost.

[0175] Furthermore, by reacting ferric chloride obtained in the carbon separation process S2 with water, high-purity hydrogen can be produced by efficiently decomposing water at low cost. In this hydrogen production, the amount of hydrogen generated can be easily increased simply by increasing the amount of magnetite recycled. For example, it can be widely used in hydrogen reduction ironmaking processes in next-generation iron smelters, hydrogen refining processes in oil refineries, carbon dioxide recovery and reuse (CCU) technology, hydrogen sources for hydrogen fuel cells, and hydrogen sources for hydrogen power generation.

[0176] Furthermore, the magnetite generated in the hydrogen production process S3 is supplied to the reducing agent regeneration process, and the hydrogen generated in the hydrogen production process S3 is used to regenerate the reducing agent. Thus, by supplying only carbon dioxide and water from the outside, a closed system can be constructed that decomposes carbon dioxide to produce carbon materials and decomposes water to produce hydrogen.

[0177] In this process, the hydrogen and oxygen produced in each step are generated in different steps and do not come into contact with each other in a single step. For example, hydrogen is generated in the hydrogen production step S3, and oxygen is generated in the carbon separation step S2. They do not mix in the same reaction tank or the like. Therefore, there is no need to worry about explosive reactions caused by oxygen and hydrogen coming into contact, and the reactions in each step can proceed stably.

[0178] In this method of manufacturing carbon materials and hydrogen, the magnetite used is reduced during the processing to become a reducing agent, etc., and is recycled while changing its material form. Therefore, even if no magnetite is supplied from the outside except for the loss, carbon and hydrogen can be manufactured at low cost.

[0179] Furthermore, in the carbon separation process S2, by dissolving the magnetite with carbon attached to its surface with hydrochloric acid (an aqueous solution of hydrogen chloride) to separate the carbon that is insoluble in hydrochloric acid, it is possible to obtain carbon materials with a particle size of less than 1 μm.

[0180] Furthermore, in the carbon dioxide decomposition process S1, carbon separation process S2, hydrogen production process S3, and reducing agent regeneration process S4, for example, by effectively using the heat (waste heat) generated during the operation of iron smelters, thermal power plants, cement plants, waste incineration facilities, etc., as a heat source during the reaction, the amount of waste heat released into the atmosphere can be suppressed, which helps to prevent the greenhouse effect. Moreover, by effectively utilizing the electrical energy derived from renewable energy and the thermal energy of nuclear furnaces (i.e., high-temperature gas furnaces) that store and output high-temperature heat, CO2 production can be suppressed, contributing to the realization of carbon neutrality and a decarbonized society.

[0181] The embodiments of the present invention have been described above, but these embodiments are provided as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included within the scope or spirit of the invention, and are included within the scope of the invention as described in the claims and its equivalents.

[0182] For example, in the above embodiments, the usual composition of magnetite is set as Fe3O4, but this magnetite can be iron sand containing other substances (such as titanium (Ti)). These other substances (such as titanium) may act as catalysts to facilitate the reduction of carbon dioxide.

[0183] Example

[0184] The following demonstrates the effectiveness of the present invention.

[0185] First, the properties of the various magnetite materials used in Examples 1 to 11 are summarized in Table 1.

[0186] [Table 1]

[0187]

[0188] (Example 1)

[0189] An experiment was conducted to investigate the relationship between the reaction temperature and the oxygen vacancy degree δ in the regeneration process of the reducing agent.

[0190] A fixed-bed reactor was used as the reaction device to react 1g of magnetite (particle size distribution of 50-100nm) with hydrogen. A reducing agent was generated by reducing the magnetite while maintaining its crystal structure.

[0191] The reaction time was set to 1 hour, the hydrogen flow rate to 1.0 L / min, and the hydrogen concentration to 100% by volume. The reaction temperatures were set to 280℃, 300℃, 320℃, 350℃, 360℃, and 370℃, respectively. Magnetite was reduced (deoxidized) with hydrogen to obtain samples (reducing agents) at each reaction temperature. Furthermore, the oxygen deficiency degree δ of the reducing agent was calculated based on the reducing agents (oxygen-deficient iron oxide and oxygen-completely-deficient iron) obtained under each reaction temperature condition.

[0192] The results of Example 1 are presented in graphical form. Figure 3 In addition, Figure 3 Points with an oxygen deficiency degree δ greater than 4 represent measurement errors; in reality, δ = 4.

[0193] according to Figure 3 The results show that the following can be confirmed: by setting the reaction temperature in the range of 350℃~360℃ under the above reaction conditions, the oxygen vacancy degree δ can be increased to the maximum, and oxygen-deficient iron with δ=4 can be obtained, which means that all oxygen ions have been removed while maintaining the crystal structure of magnetite.

[0194] (Example 2)

[0195] An experiment was conducted to investigate the relationship between reaction time and oxygen vacancy δ in the regeneration process of the reducing agent.

[0196] A fixed-bed reactor was used as the reaction device to react 1g of magnetite (particle size distribution of 50-100nm) with hydrogen. A reducing agent was generated by reducing the magnetite while maintaining its crystal structure.

[0197] The reaction temperatures were set to 280℃, 310℃, 330℃, and 350℃, the hydrogen flow rate was set to 1.0 L / min, and the hydrogen concentration was set to 100% by volume. The reaction times (reduction times) under each of the above reaction temperature conditions were set to 30 minutes, 60 minutes, and 180 minutes, respectively. Magnetite was then reduced (deoxidized) with hydrogen, thereby obtaining samples (reducing agents) at each reaction temperature and reaction time. Furthermore, the oxygen deficiency degree δ of the reducing agent was calculated based on the obtained reducing agents (oxygen-deficient iron oxide and oxygen-completely-deficient iron).

[0198] The results of Example 2 are presented in graphical form. Figure 4 In addition, Figure 4 Points with an oxygen deficiency degree δ greater than 4 represent measurement errors; in reality, δ = 4.

[0199] according to Figure 4The results show that if the reaction temperature is within the range of 330℃ to 350℃ under the above reaction conditions, then as long as the reaction time (reduction time) is greater than 60 minutes, the oxygen vacancy degree δ can be increased to the maximum, resulting in oxygen-deficient iron with δ = 4, meaning all oxygen ions have detached while maintaining the crystal structure of magnetite. Furthermore, it can be confirmed that even with a reaction time (reduction time) of approximately 30 minutes within the range of 330℃ to 350℃, oxygen-deficient iron oxides with δ = 2 to 2.8 that maintain the crystal structure of magnetite can be obtained.

[0200] (Example 3)

[0201] An experiment was conducted to investigate the relationship between hydrogen flow rate and oxygen vacancy degree δ in the reducing agent regeneration process.

[0202] A fixed-bed reactor was used as the reaction device to react 1g of magnetite (particle size distribution of 50-100nm) with hydrogen. A reducing agent was generated by reducing the magnetite while maintaining its crystal structure.

[0203] The reaction temperature was set to 330℃, the hydrogen concentration to 100% by volume, the reaction time to 60 minutes, and the hydrogen flow rate to 0.1 L / min, 0.25 L / min, 0.5 L / min, 0.75 L / min, and 1.0 L / min, respectively. Magnetite was then reduced (deoxidized) with hydrogen to obtain samples (reducing agents) at each hydrogen flow rate. Furthermore, the oxygen deficiency degree δ of the reducing agent was calculated based on the obtained reducing agents (oxygen-deficient iron oxide and oxygen-completely-deficient iron).

[0204] The results of Example 3 are presented in graphical form. Figure 5 In addition, Figure 5 Points with an oxygen deficiency degree δ greater than 4 represent measurement errors; in reality, δ = 4.

[0205] according to Figure 5 The results show that, under the above reaction conditions, a hydrogen flow rate of 0.75 L / min or higher can maximize the oxygen vacancy degree δ, resulting in oxygen-deficient iron with a δ of 4, meaning all oxygen ions have detached while maintaining the crystal structure of magnetite. Furthermore, it can be confirmed that even with a hydrogen flow rate of approximately 0.5 L / min, oxygen-deficient iron oxides maintaining the crystal structure of magnetite with a δ greater than 3.5 can be obtained.

[0206] (Example 4)

[0207] An experiment was conducted to investigate the relationship between hydrogen concentration and oxygen vacancy degree δ in the regeneration process of the reducing agent.

[0208] A fixed-bed reactor was used as the reaction device to react 1g of magnetite (particle size distribution of 50-100nm) with hydrogen. A reducing agent was generated by reducing the magnetite while maintaining its crystal structure.

[0209] The reaction temperature was set to 330℃, the hydrogen flow rate to 1.0 L / min, and the reaction time to 60 minutes. Hydrogen concentrations were set to 50 vol%, 75 vol%, 90 vol%, and 100 vol, respectively. Magnetite was then reduced (deoxidized) with hydrogen to obtain samples (reducing agents) at various hydrogen concentrations. Furthermore, the oxygen deficiency degree δ of the reducing agent was calculated based on the obtained reducing agents (oxygen-deficient iron oxide and oxygen-completely-deficient iron).

[0210] The results of Example 4 are presented in graphical form. Figure 6 In addition, Figure 6 Points with an oxygen deficiency degree δ greater than 4 represent measurement errors; in reality, δ = 4.

[0211] according to Figure 6 The results show that, under the above reaction conditions, a hydrogen concentration of 90% by volume or higher can maximize the oxygen vacancy degree δ, resulting in oxygen-deficient iron with a δ of 4, meaning all oxygen ions have detached while maintaining the crystal structure of magnetite. Even with a hydrogen concentration of approximately 90% by volume, the reducing power is virtually indistinguishable from that of 100% by volume hydrogen. Therefore, using hydrogen at a concentration of approximately 90% by volume, which is less expensive than 100% by volume hydrogen, allows for the low-cost generation of a reducing agent that maximizes the oxygen vacancy degree δ. Furthermore, it can be confirmed that even with a hydrogen concentration of approximately 75% by volume, an oxygen-deficient iron oxide with a δ greater than 3.5, maintaining the crystal structure of magnetite, can be obtained.

[0212] (Example 5)

[0213] An experiment was conducted to investigate the relationship between reaction temperature and oxygen vacancy consumption rate in the carbon dioxide decomposition process.

[0214] Oxygen vacancy consumption rate is the proportion of oxygen ions from carbon dioxide entering atomic vacancies in the spinel-type crystal lattice of the reducing agent when carbon dioxide reacts with a certain amount of reducing agent. It is in the range of 0 to 100%. The closer the value is to 100%, the higher the carbon dioxide decomposition (reduction) ability of the reducing agent.

[0215] A fixed-bed reactor was used as the reaction apparatus. A reducing agent with an oxygen deficiency degree δ of approximately 4 (oxygen-deficient iron, particle size distribution of 50–100 nm) was used to react with carbon dioxide within a reaction temperature range of 315°C–390°C to generate carbon. Furthermore, the oxygen deficiency consumption rate was calculated based on the difference between the mass of the reducing agent before the reaction, the oxygen deficiency degree δ, the mass of the oxidized reducing agent (magnetite) after the reaction, and the oxygen deficiency degree δ.

[0216] The results of Example 5 are presented in graphical form. Figure 7 middle.

[0217] according to Figure 7 The results show that if the reaction temperature is above 360°C under the above reaction conditions, the oxygen vacancy consumption rate is above 40%. In particular, when the reaction temperature is above 370°C, the oxygen vacancy consumption rate is above 50%, meaning that more than 50% of the total number of atomic vacancies in the spinel-type crystal lattice of the reducing agent can be utilized to decompose (reduce) carbon dioxide and generate carbon. Therefore, it has been confirmed that by setting the reaction temperature in the carbon dioxide decomposition process to above 360°C, the reducing agent can be effectively used to decompose (reduce) carbon dioxide to generate carbon.

[0218] (Example 6)

[0219] An experiment was conducted to investigate the relationship between the type of magnetite material and the oxygen deficiency consumption rate in the carbon dioxide decomposition process and the oxygen deficiency degree δ in the reducing agent regeneration process.

[0220] As magnetite materials, 1g and 0.5g of nanoparticle magnetite with an average particle size of approximately 800nm, 0.5g of microparticle magnetite with an average particle size of approximately 1.1μm, 1g of iron sand from Japan, and 1g of iron sand from New Zealand were prepared. Furthermore, using each magnetite material, a fixed-bed reactor was used as the reaction apparatus. The magnetite materials were reduced to generate reducing agents under the conditions of a reaction temperature of 350℃, a reaction time of 1 hour, a hydrogen flow rate of 1.0L / min, and a hydrogen concentration of 100% by volume. The oxygen vacancy degree δ of these reducing agents was calculated.

[0221] Furthermore, the specific surface area of ​​the reducing agent derived from the reduction of particulate magnetite was determined to be 9.36 m². 2 / g. It can be seen that the specific surface area increased from 5.28m² before reduction. 2 / g increased to approximately 1.77 times.

[0222] Next, using various reducing agents, a fixed-bed reactor was used as the reaction device to allow carbon dioxide to react at a reaction temperature of 360°C. The oxygen deficiency consumption rate was calculated based on the difference between the mass of the reducing agent and the oxygen deficiency degree δ before the reaction and the mass of the oxidized reducing agent and the oxygen deficiency degree δ after the reaction.

[0223] The results of Example 6 are presented in graphical form. Figure 8 middle.

[0224] according to Figure 8 The results show that the oxygen vacancy degree δ of most of the reducing agents generated by reducing magnetite with hydrogen using nanoparticle magnetite and particulate magnetite is 4, which allows for the almost complete loss of oxygen in the magnetite, resulting in oxygen-deficient iron with atomic vacancies. On the other hand, it is known that the oxygen vacancy degree δ of iron sand from New Zealand after hydrogen reduction is less than 1, and its ability to decompose (reduce) carbon dioxide as a reducing agent is low.

[0225] Furthermore, it can be confirmed that the oxygen deficiency consumption rate of these reducing agents is about 60% to 80% for those made from microparticle magnetite, and their carbon dioxide decomposition ability is particularly excellent.

[0226] Based on these results, it is evident that microparticle magnetite with an average particle size of approximately 1.1 μm is particularly preferred as the magnetite material.

[0227] (Example 7)

[0228] An experiment was conducted to investigate the relationship between the particle size of magnetite material and the oxygen deficiency degree δ in the reducing agent regeneration process and the oxygen deficiency consumption rate in the carbon dioxide decomposition process.

[0229] As magnetite materials, nanoparticle magnetite with an average particle size of approximately 800 nm, microparticle magnetite with an average particle size of approximately 1.1 μm, powdered magnetite with an average particle size of approximately 40 μm, and large-particle powdered magnetite with an average particle size of approximately 70 μm were prepared. Furthermore, each magnetite material was reduced at a reaction temperature of 330°C to generate a reducing agent, and the oxygen vacancy degree δ of these reducing agents was calculated. All conditions except for the reaction temperature were the same as in Example 6.

[0230] Next, carbon dioxide was reacted using various reducing agents at a reaction temperature of 380°C, and the oxygen vacancy consumption rate was calculated. All other conditions except for the reaction temperature were the same as in Example 6.

[0231] The results of the oxygen vacancy δ measurement in Example 7 are shown below. Figure 9 The results of the oxygen deficiency consumption rate determination are presented in [the document / reference]. Figure 10 middle.

[0232] according to Figure 9 The results show that the reducing agent obtained by utilizing hydrogen reduction has almost no difference due to the particle size of the magnetite in the raw material. On the other hand, according to Figure 10The results show that the reducing agent using particulate magnetite as a raw material has a particularly superior oxygen vacancy consumption rate after reacting these reducing agents with carbon dioxide. Therefore, it is preferable to use particulate magnetite as a raw material to generate the reducing agent.

[0233] (Example 8)

[0234] An experiment was conducted to investigate the relationship between the raw materials of the reducing agent, the oxygen deficiency degree δ in the reducing agent regeneration process, and the oxygen deficiency consumption rate in the carbon dioxide decomposition process.

[0235] As magnetite materials, nanoparticle magnetite with an average particle size of about 800 nm, microparticle magnetite with an average particle size of about 1 μm, powdered magnetite with an average particle size of about 40 μm, iron sand from Japan, iron sand from New Zealand, copper slag, and iron powder were prepared. Furthermore, the oxygen vacancy degree δ of these reducing agents was calculated under the same conditions as in Example 6. Additionally, since the iron powder was in a completely reduced state, it was set to δ = 4 for convenience.

[0236] Next, carbon dioxide was reacted using each reducing agent under the same conditions as in Example 6, and the oxygen vacancy consumption rate was calculated.

[0237] The results of the oxygen vacancy δ measurement in Example 8 are shown below. Figure 11 The results of the oxygen deficiency consumption rate determination are presented in [the document / reference]. Figure 12 middle.

[0238] according to Figure 11 The results show that, regarding the oxygen deficiency δ of the reducing agent obtained by reducing with hydrogen, the reducing agent using magnetite as raw material has an excellent value of 3.5 or higher. On the other hand, the oxygen deficiency δ of copper slag is almost 0.

[0239] On the other hand, according to Figure 12 The results show that the reducing agent using particulate magnetite as a raw material exhibits particularly excellent oxygen vacancy consumption rate after reacting these reducing agents with carbon dioxide. Furthermore, it is known that the oxygen vacancy consumption rate of copper slag and iron powder is almost 0%, indicating no decomposition (reduction) ability of carbon dioxide. Additionally, the difference in oxygen vacancy consumption rate between Japanese and New Zealand iron sand is believed to be due to the catalytic effect caused by trace amounts of titanium contained in the Japanese iron sand.

[0240] (Example 9)

[0241] Based on the particle size of magnetite materials, experiments were conducted to investigate the presence or absence of reducing agent degradation and the amount of carbon generated during repeated reducing agent regeneration and carbon dioxide decomposition processes.

[0242] The reducing agent was generated under the same magnetite material and reaction conditions as in Example 7, and its quality was determined (reducing agent regeneration process).

[0243] Next, carbon dioxide was decomposed using various reducing agents at a reaction temperature of 380°C, and the mass of the reducing agent + product (carbon) after the reaction was measured. Furthermore, no carbon separation step was performed after the carbon dioxide decomposition step, and the generated carbon remained in its original state. This reducing agent regeneration step and carbon dioxide decomposition step were repeated three times, and the mass of the sample was measured in each step.

[0244] In Example 9, the results using nanoparticle magnetite are shown. Figure 13 The results using microparticle magnetite will be presented in the following table. Figure 14 The results using powdered magnetite will be presented in the following table. Figure 15 middle.

[0245] according to Figures 13-15 The results confirmed that even when magnetite of arbitrary particle size is used as the raw material for the reducing agent, the mass of carbon, as measured by combustion-infrared absorption, increases almost linearly with each repeated regeneration and carbon dioxide decomposition process, without any degradation of the reducing agent. This allows for repeated regeneration and carbon dioxide decomposition processes using the reducing agent. Furthermore, it was confirmed that when particulate or powdered magnetite is used as the raw material for the reducing agent, the increase in carbon mass is greater compared to the use of nanoparticle magnetite. Considering that this increase is due to carbon accumulation, the use of particulate or powdered magnetite as the raw material for the reducing agent is preferred.

[0246] On the other hand, it is believed that when using nanoparticle magnetite as a raw material for a reducing agent, the carbon mass is reduced by almost half during the reducing agent regeneration process after the carbon dioxide decomposition process, as the generated carbon is vaporized and removed from the system. However, no loss due to the reaction of this generated carbon has been observed in microparticle magnetite or powdered magnetite. Therefore, it can be concluded that due to the high reactivity and large surface area of ​​nanoparticle magnetite, the generated and attached carbon easily reacts with oxygen in the reducing agent or hydrogen in the reducing agent regeneration process, leading to carbon loss during repeated use. Based on the consideration of this carbon vaporization loss, it is also preferable to use microparticle magnetite or powdered magnetite as a raw material for a reducing agent.

[0247] (Example 10)

[0248] An experiment was conducted to investigate the carbon dioxide decomposition performance when hematite (Fe2O3) was used as the magnetite material.

[0249] As a sample, powdered α-Fe2O3 (average particle size 1 μm, purity 99.9% by mass (manufactured by Kojundo Chemical Laboratory Co., Ltd.)) was used as a pretreatment. After heating to 110°C under argon flow, it was held for 10 minutes, then aspirated to create a vacuum state, and held for another 10 minutes.

[0250] Using the pretreated sample obtained in this way, a fixed-bed reactor was used as the reaction device to reduce the sample to generate a reducing agent under the conditions of reaction temperature 330°C, reaction time 1 hour, hydrogen flow rate 1.0 L / min, and hydrogen concentration 100% by volume, and the mass was determined.

[0251] The mass changes of the samples before and after pretreatment, as well as after hydrogen reduction, are shown in Table 2. Additionally, the mass changes when magnetite was used in the raw material are recorded for reference.

[0252] Furthermore, the XRD analysis results of the hydrogen-reduced sample are shown in... Figure 16 The XRD analysis results of the sample after carbon dioxide decomposition are shown in the figure. Figure 17 middle.

[0253] [Table 2]

[0254] Reducing agent raw materials Before pretreatment (g) After pretreatment (g) After hydrogen reduction (g) Hematite 1.000 0.996 0.697 magnetite 1.001 0.995 0.705

[0255] Based on the results shown in Table 2, it is believed that, according to the mass change caused by hydrogen reduction, hematite is completely reduced to a state of oxygen-deficient iron.

[0256] Furthermore, based on the XRD analysis results, the product is considered to be almost entirely Fe. According to this XRD analysis result, hematite is also completely reduced to a state of oxygen-deficient iron.

[0257] Next, using the reducing agent obtained from hematite, carbon dioxide was decomposed at a reaction temperature of 370°C until the pressure change disappeared. Using the pressure and temperature inside the reactor, the change in the amount of substance in the gas phase was calculated according to the ideal gas law, and the mass of the product (carbon) was determined using the combustion-infrared absorption method (carbon dioxide decomposition process).

[0258] Table 3 shows the changes in the amount of substance in the gaseous phase after carbon dioxide decomposition, the amount of carbon generated, the amount of substance of Fe, and the change in the amount of substance in the gaseous phase per mole of iron in the reducing agent. Additionally, the use of magnetite in the raw materials is also documented for reference.

[0259] [Table 3]

[0260]

[0261] Based on 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, based on the black hue of the reducing agent derived from hematite after carbon dioxide decomposition and the XRD analysis results, it was concluded that even if the reducing agent is derived from hematite, it only oxidizes to magnetite after carbon dioxide decomposition (it does not revert to hematite).

[0262] (Example 11)

[0263] As a raw material for generating a reducing agent, an experiment was conducted to investigate the decomposition performance of carbon dioxide using powder containing ferric hydroxide extracted from a used hand warmer.

[0264] As a pretreatment, IRIS OHYAMAInc.'s "Hot Baby Family Standard Pack of 10 (PKN-10R)" was used. The temperature was raised to 110°C under argon flow and held for 10 minutes. Then, the gas was drawn in to create a vacuum state, which was held for another 10 minutes.

[0265] Using a fixed-bed reactor as the reaction apparatus, the pretreated used hand warmers (powder) obtained in this way were reduced to generate a reducing agent under the conditions of reaction temperature 330℃, reaction time 1 hour, hydrogen flow rate 1.0 L / min, and hydrogen concentration 100% by volume, and the mass was determined.

[0266] The mass changes of the samples before and after pretreatment, and before and after hydrogen reduction, are shown in Table 4.

[0267] In addition, the quality changes when hematite was used as a raw material are recorded for reference.

[0268] Furthermore, the XRD analysis results of the hydrogen-reduced sample are shown in... Figure 18 The XRD analysis results of the sample after carbon dioxide decomposition are shown in the figure. Figure 19 middle.

[0269] [Table 4]

[0270]

[0271] It is believed that because the reducing agent derived from used hand warmers after hydrogen reduction is black, just like the reducing agent derived from magnetite or hematite, the used hand warmers are reduced to a state where oxygen is completely absent and iron is absent.

[0272] Furthermore, based on the XRD analysis results, the product is considered to be almost entirely Fe. According to this XRD analysis result, the ferric hydroxide in the used hand warmer was also reduced to a state of complete oxygen deficiency iron.

[0273] Next, the carbon dioxide was decomposed at a reaction temperature of 370°C using the reducing agent obtained from used hand warmers until the pressure change disappeared, and the mass was measured. The mass changes of the samples before and after carbon dioxide decomposition are shown in Table 4 above.

[0274] Based on the results shown in Table 4, it was confirmed that carbon dioxide can be decomposed using a reducing agent obtained by reducing a used hand warmer with hydrogen. Furthermore, based on the black hue of the reducing agent after carbon dioxide decomposition and the XRD analysis results, it was determined that even if the reducing agent originated from a used hand warmer, it only oxidizes to magnetite after carbon dioxide decomposition (does not revert to ferric hydroxide).

[0275] (Example 12)

[0276] Magnetite with carbon adhering to its surface, produced by reacting carbon dioxide with a reducing agent during a carbon dioxide decomposition process, was observed. Observations were performed using a electron microscope (SEM).

[0277] exist Figure 20 The image shows a SEM photograph of magnetite with carbon adhering to its surface.

[0278] The following can be confirmed: In Figure 20 In the SEM image shown, the white parts of the irregularly shaped product represent the oxidized reducing agent (magnetite), and the black parts represent nano-sized carbon particles. Magnetite with carbon adhering to its surface is generated by reducing carbon dioxide with a reducing agent.

[0279] (Example 13)

[0280] In the hydrogen production process, hydrogen and magnetite were actually produced, and the conversion rate of the reaction between ferric chloride and water (reaction conversion rate) was investigated.

[0281] Regarding the experiment, water vapor was passed through a reaction tube filled with ferric chloride (II) and the reaction shown in the following formula (19) was carried out.

[0282] 3FeCl2+4H2O→Fe3O4+6HCl+H2 (19)

[0283] The implementation conditions of Examples 1 to 4 of the present invention are shown in Table 5. Furthermore, the reaction conversion rates of the reactions represented by Equation (19) carried out under the conditions in Table 5 are shown in Table 6.

[0284] [Table 5]

[0285]

[0286] [Table 6]

[0287] Reaction conversion rate (%) Example 1 of the present invention 91.5 Example 2 of the present invention 100 Example 3 of the present invention 100 Example 4 of the present invention 100

[0288] Based on the results of Example 13 shown in Table 6, it can be confirmed that the reaction conversion rate is above 90% under any conditions, and magnetite and hydrogen can be effectively produced by reacting ferric chloride (II) with water vapor.

[0289] Industrial availability

[0290] This invention enables the efficient and low-cost generation of carbon materials and hydrogen using carbon dioxide and water. For example, by applying it to factories that emit large amounts of carbon dioxide and waste heat, such as iron smelters, thermal power plants, cement plants, and waste incineration facilities, it can reduce carbon dioxide emissions, efficiently utilize hydrogen, and consequently produce high-value-added carbon materials such as nanoscale carbon. Therefore, it has industrial applicability.

[0291] Symbol Explanation

[0292] S1 Carbon dioxide decomposition process

[0293] S2 Carbon Separation Process

[0294] S3 Hydrogen Production Process

[0295] S4 Reducing Agent Regeneration Process

Claims

1. A method for producing carbon and hydrogen, characterized in that, include: The carbon dioxide decomposition process involves reacting carbon dioxide with a reducing agent to produce magnetite with carbon adhering to its surface. The carbon separation process involves reacting magnetite with carbon adhering to its surface, obtained in the carbon dioxide decomposition process, with hydrochloric acid or hydrogen chloride gas to produce carbon and ferric chloride. The hydrogen production process involves reacting ferric chloride obtained in the carbon separation process with water to produce magnetite, hydrogen, and hydrogen chloride gas; and The reducing agent regeneration process involves reacting magnetite and hydrogen obtained in the hydrogen production process to generate the reducing agent used in the carbon dioxide decomposition process. The reducing agent is obtained by reducing magnetite while maintaining its crystal structure, and is composed of Fe3O4. 4-δ The oxygen-deficient iron oxides, oxygen-completely deficient iron obtained by completely reducing magnetite, oxygen-deficient iron oxides obtained by reducing hematite or used hand warmers, or oxygen-completely deficient iron obtained by completely reducing hematite or used hand warmers, wherein in the oxygen-deficient iron oxides, δ is 1 or more and less than 4, and in the oxygen-completely deficient iron, δ = 4.

2. The method for producing carbon and hydrogen according to claim 1, characterized in that, In the carbon dioxide decomposition process, the reaction temperature is set in the range of above 300°C and below 450°C.

3. The method for producing carbon and hydrogen according to claim 1 or 2, characterized in that, In the carbon dioxide decomposition process, the reaction pressure is set within the range of 0.01 MPa or higher and 5 MPa or lower.

4. The method for producing carbon and hydrogen according to claim 1 or 2, characterized in that, In the carbon separation process, the reaction temperature is set within the range of 10°C or higher and 300°C or lower.

5. The method for producing carbon and hydrogen according to claim 1 or 2, characterized in that, In the hydrogen production process, the reaction temperature is set within the range of 10°C or higher and 800°C or lower.

6. The method for producing carbon and hydrogen according to claim 1 or 2, characterized in that, In the reducing agent regeneration process, the reaction temperature is set in the range of 300°C or higher and 450°C or lower.

7. The method for producing carbon and hydrogen according to claim 1 or 2, characterized in that, The concentration of hydrogen used in the reducing agent regeneration process is in the range of 5% by volume or more and 100% by volume or less.

8. The method for producing carbon and hydrogen according to claim 1 or 2, characterized in that, In the reducing agent regeneration process, the specific surface area of ​​the magnetite based on the BET method is 0.1 m². 2 / g or more and 10m 2 Within the range of / g and below.

9. The method for producing carbon and hydrogen according to claim 1 or 2, characterized in that, In the reducing agent regeneration process, the average particle size of the magnetite is in the range of 1 μm or more and 1000 μm or less.

10. The method for producing carbon and hydrogen according to claim 1 or 2, characterized in that, In the reducing agent regeneration process, the bulk density of the magnetite is 0.3 g / cm³. 3 Above and 3g / cm 3 Within the following range.

11. The method for producing carbon and hydrogen according to claim 1 or 2, characterized in that, The carbon is nanoscale carbon with a particle size of less than 1 μm.

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