Methods for producing carbon and hydrogen

Abstract

To efficiently produce carbon and hydrogen from carbon dioxide and water, and to repeatedly generate and utilize a reducer.SOLUTION: There is provided a method of producing carbon and hydrogen, comprising a carbon-dioxide decomposition step for producing magnetite with carbon deposited on the surface thereof, a carbon separation step for producing carbon and iron chloride, a hydrogen production step of producing magnetite, hydrogen and hydrogen chloride gas, and a reducer regeneration step of producing the reducer to be used in the carbon-dioxide decomposition step. The hydrogen production step includes an electrolytic reduction step of reducing trivalent iron chloride by electrolysis to produce divalent iron chloride, and a hydrolysis step of causing the divalent iron chloride obtained in the electrolytic reduction step to react with water to produce magnetite, hydrogen, and hydrogen chloride gas.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This invention relates to a method for producing carbon and hydrogen by using carbon dioxide and water to produce carbon and hydrogen.

Background Art

[0002] For example, in steel mills, thermal power plants, cement factories, waste incineration facilities, etc., a large amount of carbon dioxide (CO2) is being emitted. Therefore, from the perspective of preventing global warming, it has become important to recover carbon dioxide without releasing it into the atmosphere. On the other hand, with the increasing demand for hydrogen in fuel cell vehicles (FCVs) and hydrogen power generation, etc., hydrogen that can be supplied in large quantities at low cost is in demand.

[0003] Conventionally, as technologies for separating and recovering carbon dioxide, chemical absorption methods, physical absorption methods, membrane separation methods, etc. are known. Also, as technologies for decomposing the recovered carbon dioxide, semiconductor photocatalytic methods, photochemical reduction methods using metal colloidal catalysts, metal complexes, catalysts, etc., electrochemical reduction methods, chemical fixation conversion reactions, for example, decomposition methods using reactions with bases, transfer reactions, dehydration reactions, addition reactions, etc. are known. However, these carbon dioxide decomposition methods all have problems in that they are not practical in terms of reaction efficiency, cost, energy consumption, etc.

[0004] Therefore, for example, in Patent Document 1, a method is disclosed in which carbon dioxide is reduced using magnetite having pores which are oxygen defect sites in the lattice, that is, oxygen-deficient iron oxide, to generate carbon, and methane or methanol is obtained from the carbon. In the invention of Patent Document 1, it is said that a closed system capable of continuously and efficiently decomposing carbon dioxide can be realized by decomposing (reduction reaction) carbon dioxide with oxygen-deficient iron oxide and reducing the iron oxide generated by oxidation with hydrogen to return it to oxygen-deficient iron oxide again.

[0005] On the other hand, as a method for producing high-purity hydrogen, for example, in Patent Document 2, a method is disclosed in which iron chloride and water are reacted at 410°C or higher to produce magnetite, hydrogen chloride, and hydrogen, and the produced hydrogen is recovered using a separation membrane. In the invention of Patent Document 2, it is said that process waste heat discharged from various plants can be effectively utilized, and hydrogen, which is a clean energy fuel, can be obtained by thermochemical decomposition technology using water as a raw material.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, under the reaction conditions disclosed in Patent Document 1, the oxygen deficiency degree of oxygen-deficient iron oxide is small (when oxygen-deficient iron oxide is represented by Fe3O 4-δ δ is at most about 0.16), and the decomposition ability of carbon dioxide is low, so there is a problem that carbon dioxide cannot be efficiently decomposed. Also, when continuously decomposing carbon dioxide by the method of Patent Document 1, it is necessary to externally supply hydrogen for reducing magnetite to oxygen-deficient iron oxide, and there is also a problem that the cost related to hydrogen supply is high. Furthermore, in Patent Document 1, since expensive nano-sized magnetite is used, the decomposition cost of carbon dioxide is high. Also, 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.

[0008] Patent Document 2 describes a hydrogen production reaction involving many substances (magnesium compounds in addition to magnetite, an iron compound), and the reaction mechanism is complex. Furthermore, the high temperature required for the reaction (around 1000°C) results in high energy consumption and high manufacturing costs. Furthermore, Patent Document 2 focuses solely on the effective utilization of waste heat emitted from various energy-consuming plants, but there is a need to effectively utilize the carbon dioxide emitted along with the waste heat from many of these plants.

[0009] This invention has been made in view of the circumstances described above, and aims to provide a method for producing carbon and hydrogen that efficiently generates carbon and hydrogen from carbon dioxide and water, and that allows for the repeated production and use of the reducing agent used in the reaction. [Means for solving the problem]

[0010] To solve the above problems, the method for producing carbon and hydrogen according to one embodiment of the present invention proposes the following means. (1) A method for producing carbon and hydrogen according to embodiment 1 of the present invention comprises: a carbon dioxide decomposition step of reacting carbon dioxide with a reducing agent to produce magnetite with carbon attached to its surface; a carbon separation step of reacting the magnetite with carbon attached to its surface obtained in the carbon dioxide decomposition step 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; and a reducing agent regeneration step of reacting the magnetite and hydrogen obtained in the hydrogen production step with each other to produce the reducing agent used in the carbon dioxide decomposition step, wherein the hydrogen production step comprises an electrolytic reduction step of reducing trivalent iron chloride by electrolysis to produce divalent iron chloride, and a hydrolysis step of reacting the divalent iron chloride obtained in the electrolytic reduction step with water to produce magnetite, hydrogen and hydrogen chloride gas, wherein the reducing agent is Fe3O obtained by reducing magnetite while maintaining the crystal structure of magnetite. 4-δThe present invention is characterized by being an oxygen-deficient iron oxide represented by (where δ is 1 or more and less than 4), or oxygen-completely deficient iron (δ=4) obtained by completely reducing magnetite while maintaining the crystal structure of magnetite, or an oxygen-deficient iron oxide with a maintained crystal structure of magnetite obtained by reducing hematite or used hand warmers, or oxygen-completely deficient iron with a maintained crystal structure of magnetite obtained by completely reducing hematite or used hand warmers.

[0011] (2) Aspect 2 of the present invention is a method for producing carbon and hydrogen according to aspect 1, characterized in that the electrolytic reduction process is carried out using an electrolytic apparatus having a cathode cell containing a cathode solution containing trivalent iron chloride, an anode cell containing an anode solution containing an electrolyte, a partition wall formed between the cathode cell and the anode cell and permeable to ions, a cathode electrode provided in the cathode cell, and an anode electrode provided in the anode cell.

[0012] (3) Embodiment 3 of the present invention is characterized in that, in the method for producing carbon and hydrogen according to Embodiment 2, the pH of the cathode solution is kept at 0.5 or less.

[0013] (4) Embodiment 4 of the present invention is a method for producing carbon and hydrogen according to Embodiment 2 or 3, characterized in that the anode liquid contains dilute sulfuric acid.

[0014] (5) Embodiment 5 of the present invention is a method for producing carbon and hydrogen according to any one of embodiments 2 to 4, characterized in that the cathode solution contains an aqueous hydrochloric acid solution in which trivalent iron chloride is dissolved.

[0015] (6) Embodiment 6 of the present invention is a method for producing carbon and hydrogen according to any one of embodiments 2 to 5, characterized in that the cathode electrode is a carbon electrode or a platinum electrode.

[0016] (7) Embodiment 7 of the present invention is a method for producing carbon and hydrogen according to any one of embodiments 2 to 6, characterized in that the anode electrode is a carbon electrode or a platinum electrode.

[0017] (8) Embodiment 8 of the present invention is a method for producing carbon and hydrogen according to any one of embodiments 2 to 7, characterized in that the partition is a cation exchange membrane or a glass filter.

[0018] (9) Embodiment 9 of the present invention is a method for producing carbon and hydrogen according to any one of embodiments 2 to 8, characterized in that the cathode cell is provided in an inert gas atmosphere.

[0019] (10) Embodiment 10 of the present invention is a method for producing carbon and hydrogen according to any one of embodiments 2 to 9, characterized in that the carbon is nano-sized carbon with a particle diameter of 1 μm or less. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a method for producing carbon and hydrogen that efficiently generates carbon and hydrogen from carbon dioxide and water, and that allows for the repeated production and use of the reducing agent used in the reaction. [Brief explanation of the drawing]

[0021] [Figure 1] This is a schematic diagram showing the crystal structure of a quarter unit cell of magnetite. [Figure 2] This is a flowchart showing a method for producing carbon and hydrogen according to one embodiment of the present invention. [Figure 3] This is a schematic diagram showing an example of an electrolytic apparatus used in the electrolytic reduction process S3-1, which constitutes the hydrogen production process S3. [Figure 4] This is a potential-pH graph for the electrolytic reduction of iron(III) chloride. [Figure 5] This graph shows the results of the verification example. [Figure 6] This is an XRD peak pattern diagram showing the results of a verification example. [Modes for carrying out the invention]

[0022] The following describes a method for producing carbon and hydrogen according to one embodiment of the present invention, with reference to the drawings. The embodiments described below are provided specifically to better illustrate the spirit of the invention and do not limit the present invention unless otherwise specified. In addition, the drawings used in the following description may be enlarged for convenience to make the features of the present invention easier to understand, and the dimensional ratios of each component may not be the same as in reality.

[0023] First, we will describe the reducing agent used in the carbon and hydrogen production method of this embodiment. The reducing agent is a material that reacts with carbon dioxide in the carbon dioxide decomposition step S1 described later, thereby reducing carbon dioxide and decomposing it into carbon and oxygen. The reducing agent used in this embodiment is Fe3O 4-δ The oxygen-deficient iron oxides used are magnetite (triiron tetroxide) represented by (where δ is between 1 and 4), hematite or used hand warmers (whose main component is iron hydroxide), or fully oxygen-deficient iron.

[0024] Figure 1 is a schematic diagram showing the crystal structure of a quarter unit cell of magnetite. Magnetite has a spinel-type crystal lattice structure crystallographically, and contains oxygen ions (O 2- ) are arranged in a cubic close-packed configuration, and in the gaps (Asite, Bsite), +3 valent iron (Fe +3 ), +2 valent iron (Fe 2+ The elements are arranged in a 2:1 ratio. Magnetite is represented by the general formula Fe3O4.

[0025] The reducing agent used in this embodiment is an oxygen-depleted iron oxide (1≦δ<4) obtained by removing oxygen ions at arbitrary positions shown in Figure 1 while maintaining the crystal structure of magnetite, i.e., the spinel-type crystal lattice structure; or oxygen-completely depleted iron (δ=4) with a spinel-type crystal lattice structure obtained by completely reducing magnetite; or oxygen-depleted iron oxide with a spinel-type crystal lattice structure obtained by reducing hematite or used hand warmers; or oxygen-completely depleted iron with a spinel-type crystal lattice structure obtained by completely reducing hematite or used hand warmers. Such reducing agents are generated in the reducing agent regeneration process S4 described later.

[0026] The oxygen-depleted iron oxide obtained by reducing magnetite, which retains a spinel-type crystal lattice structure, is Fe3O 4-δ It is represented as (O) oxygen ions released from magnetite. 2- Depending on the rate of oxygen ion removal, δ is set to a range of 1 to less than 4. Furthermore, when all oxygen ions are removed from magnetite (i.e., δ=4), it becomes the oxygen-depleted iron described above.

[0027] δ is defined as the oxygen defect degree, and it is the ratio of oxygen defects to magnetite in an oxygen-defective iron oxide that maintains the crystal structure of magnetite, i.e., the spinel-type crystal lattice structure. This oxygen defect degree δ can be calculated by measuring the difference between the mass of magnetite before and after the reaction in the reducing agent regeneration process S4. Since the amount of mass decrease (difference) is equal to the amount of oxygen released from the magnetite (the position of this released oxygen in the lattice becomes an atomic vacancy, i.e., a defect), the oxygen defect degree δ (δ=1~4) can be calculated from this amount of mass decrease.

[0028] Then, the areas where oxygen ions have detached from magnetite become atomic vacancies while maintaining the spinel-type crystal lattice structure. As a result, more cations are trapped within the crystal lattice, and the spacing between lattices widens. These atomic vacancies resulting from oxygen detachment cause a deoxygenation (reduction) reaction with carbon dioxide, which acts as a reducing agent.

[0029] The reducing agent (oxygen-depleted iron oxide, oxygen-completely depleted iron) in this embodiment only needs to have an average particle size greater than, for example, 1 μm, preferably 1 μm or more and less than 20 μm, and also preferably greater than 50 μm and less than 200 μm.

[0030] Experimental results show that when the average particle size of the reducing agent is smaller than 1 μm, the proportion of carbon monoxide produced during the decomposition of carbon dioxide increases, potentially leading to a lower carbon recovery rate. By using a reducing agent with an average particle size of 1 μm or larger, a high carbon recovery rate can be maintained, and at the same time, the aggregation of reducing agent particles is reduced, thus avoiding problems such as adhesion to the reactor walls, making it applicable to industrial reactors such as rotary kilns.

[0031] Furthermore, by keeping the average particle size of the reducing agent below 20 μm, a high reaction rate can be maintained. Also, when the average particle size of the reducing agent exceeds 50 μm but is 200 μm or less, the scattering of particles decreases and the fluidization performance improves, making it possible to apply it to industrial reactors such as fluidized beds. In this case, compared to rotary kiln type reactors, solid-gas contact and heat transfer are better, equipment costs are lower, and the size of the reactor can be made more compact.

[0032] Figure 2 is a flowchart illustrating a step-by-step method for producing carbon and hydrogen according to one embodiment of the present invention. The carbon and hydrogen production method of this embodiment includes a carbon dioxide decomposition step S1 that produces magnetite with carbon attached to its surface, a carbon separation step S2 that produces carbon and iron chloride, a hydrogen production step S3 that produces magnetite, hydrogen, and hydrogen chloride gas, and a reducing agent regeneration step S4 that produces a reducing agent. In each of these steps, magnetite and the reducing agent obtained by reducing it are recycled and used to produce carbon and hydrogen from carbon dioxide and water supplied from an external source.

[0033] <Carbon dioxide decomposition process S1> In the carbon dioxide decomposition process S1, a reaction apparatus (carbon dioxide decomposition furnace) such as a rotary kiln or a fluidized bed is used to decompose (reduce) carbon dioxide by bringing a powdered reducing agent with an average particle size of approximately 1 μm to 500 μm into contact with gaseous carbon dioxide while stirring. This then produces magnetite with carbon attached to its surface.

[0034] While a circulating fluidized bed can be used as the reactor for the carbon dioxide decomposition process S1, it has several disadvantages compared to a bubble fluidized bed, including a higher overall reactor height, higher equipment costs, a more complex design and operation of the particle recirculation loop, shorter particle residence time (residence time in the reactor is on the order of seconds), limited particle size range for usable reducing agents, accelerated particle wear, and high energy costs required to maintain high gas flow rates and circulate powders.

[0035] For the carbon dioxide decomposition process S1, the carbon dioxide used as a source can be, for example, carbon dioxide emitted from facilities that emit large amounts of carbon dioxide, such as steel mills, thermal power plants, cement factories, waste incineration plants, biogas production facilities, and natural gas wells. The reducing agent is supplied from the reducing agent regeneration process S4, which will be described later.

[0036] The reaction temperature in 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 within a range of 300°C to 450°C, the reducing agent can maintain its spinel-type crystal lattice structure. If the reaction temperature is high, for example, above 500°C, there is a concern that repeated use of magnetite may cause the reducing agent to lose its spinel-type crystal lattice structure. Furthermore, there is a concern that the energy consumed during the reaction will increase.

[0037] In the carbon dioxide decomposition step S1, in order to raise the temperature to such a reaction temperature range, it is also preferable to effectively utilize the heat (waste heat) generated by the operation of a steel mill, a thermal power plant, a cement factory, a waste incineration facility, etc., which are carbon dioxide sources, renewable energy, and the thermal energy of a high-temperature gas furnace, which is a nuclear reactor capable of extracting high-temperature heat, as a heat source.

[0038] 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. Further, if it is 0.1 MPa or more, it is also possible to directly handle actual exhaust gas with a low carbon dioxide concentration. Also, if the reaction pressure is 5 MPa or less, the manufacturing cost of the device can be suppressed.

[0039] In the carbon dioxide decomposition step S1, by increasing the reaction temperature and reaction pressure, the decomposition rate of carbon dioxide increases, and the treatment efficiency of carbon dioxide can be improved. On the other hand, if the reaction temperature is too high, there is a risk that the spinel structure of the reducing agent will be destroyed.

[0040] For the decomposition of carbon dioxide in the carbon dioxide decomposition step S1, two-step reactions of the following formulas (1) and (2) and one-step reaction of formula (3) occur. CO2 + 2e - → CO (intermediate product) + O 2- ···(1) CO + 2e - → C + O 2- ···(2) CO2 + 2e - → C + 2O 2- ···(3) And the oxygen generated in the above formulas (1), (2), and (3) is inserted into the atomic vacancies of oxygen-deficient iron oxide (formula (4)) or oxygen-complete-deficient iron (formula (5)) by the following formulas (4) and (5). Fe3O 4-δ + δO 2- → Fe3O¬4 + 2δe - (However, δ = 1 or more and less than 4) ···(4)<e 3Fe + 4O 2- →Fe3O4+8e - ...(5)

[0041] The carbon monoxide (CO) obtained by the above formula (1) can be used as a raw material for obtaining useful chemical products such as hydrocarbons like methane and methanol, and various resins, by hydrogenation.

[0042] In the carbon dioxide decomposition step S1, if all carbon dioxide is reacted up to equation (2) or equation (3), no gas is produced as the final product. That is, it is thought that all the oxygen in the carbon dioxide is incorporated into the oxygen-depleted iron oxide or the oxygen-completely-depleted iron. Taking this into consideration, the reaction between carbon dioxide and oxygen-depleted iron oxide is represented by equation (6), and the reaction between carbon dioxide and oxygen-completely-depleted iron is represented by equation (7). 2Fe3O 4-δ +δCO2→2Fe3O4·δC (carbon-deposited magnetite, where δ = 1 or greater and less than 4)··(6) 3Fe + 2CO2 → Fe3O4·2C (carbon-deposited magnetite)···(7)

[0043] The reason why oxygen-depleted iron oxides and oxygen-depleted iron used as reducing agents in carbon dioxide decomposition step S1 can decompose carbon dioxide to carbon is that these reducing agents have a spinel-type crystal lattice structure, which is a metastable crystal structure formed in a non-equilibrium state. Even at room temperature, they gradually react with oxygen, taking in oxygen ions and attempting to change into the more stable Fe3O4. In other words, it is thought that this occurs because the unstable spinel-type crystal lattice structure, which has atomic vacancies in the lattice, attempts to change into a more stable spinel-type crystal lattice structure without atomic vacancies.

[0044] During the stabilization (magnetization) process of these oxygen-depleted iron oxides and fully oxygen-depleted iron, when oxygen ions are incorporated into the crystal, the crystal attempts to maintain electrical neutrality by releasing electrons from its surface. In oxygen-depleted iron oxides and fully oxygen-depleted iron, +2 valent Fe(Fe 2+Although it exists as an atom capable of releasing electrons, it is thought that the instability of oxygen-depleted iron oxide and oxygen-completely-depleted iron crystals generates an unusual reduction potential.

[0045] In the carbon dioxide decomposition step S1, it is preferable to maintain the oxygen concentration in the reaction environment at 5% by volume or less in order to maximize the carbon dioxide decomposition capacity of oxygen-depleted iron oxide or oxygen-completely-depleted iron used as a reducing agent.

[0046] If the oxygen concentration in the reaction environment during carbon dioxide decomposition step S1 is higher than 5% by volume, there is a concern that oxygen from the reaction atmosphere will be incorporated into the oxygen vacancy sites of the reducing agent (oxygen-depleted iron oxide or fully oxygen-depleted iron) before the oxygen constituting carbon dioxide can be incorporated into the reducing agent, thereby reducing the carbon dioxide decomposition capacity of the reducing agent.

[0047] In the carbon dioxide decomposition process S1, the carbon produced by the decomposition of carbon dioxide is generated as nano-sized carbon particles with a particle diameter of 1 μm or less. In the carbon dioxide decomposition process S1, under the same temperature conditions, the reaction rate of equation (1) described above is slower than the reaction rate of equation (2). However, by increasing the reaction rate of equation (1), the reaction of equation (2) proceeds more rapidly, and fine nano-sized carbon particles can be produced. The reaction rates of equations (1) and (2) can be increased by increasing the oxygen deficiency degree δ and by increasing the reaction temperature and reaction pressure.

[0048] These nano-sized carbon particles adhere to or cover the surface of magnetite, which is formed when oxygen-depleted iron oxide or fully oxygen-depleted iron is oxidized. The magnetite with carbon attached to its surface is then sent to the next carbon separation step S2.

[0049] On the other hand, in this embodiment, the reducing agent becomes magnetite (Fe3O4) through the decomposition of carbon dioxide in the carbon dioxide decomposition step S1. In this embodiment, carbon is generated in a state where it is relatively firmly attached to the surface of magnetite.

[0050] <Carbon separation process S2> The carbon separation process S2 consists of a chlorination reaction of magnetite (conversion of magnetite to iron(III) chloride (FeCl3) and iron(II) chloride (FeCl2)) and a carbon recovery operation. There are two methods for chlorinating magnetite: a wet chlorination method using hydrochloric acid and a dry chlorination method using hydrogen chloride gas.

[0051] (Wet Chloridation) When the chlorination reaction of magnetite is carried out by wet chlorination, the magnetite with carbon attached to its surface obtained in carbon dioxide decomposition step S1 is reacted with hydrochloric acid (an aqueous solution of hydrogen chloride). This dissolves the magnetite in hydrochloric acid and separates the carbon that is insoluble in hydrochloric acid from the magnetite. The magnetite dissolved in hydrochloric acid reacts with hydrogen chloride to produce iron chloride (iron(III) chloride and iron(II) chloride) and water.

[0052] The separation of magnetite dissolved in hydrochloric acid from carbon can be carried out by solid-liquid separation, such as filtration. The resulting iron chloride (a mixture of iron(III) and iron(II) chloride) is then sent to the next hydrogen production step S3. In this type of wet chlorination, all of the generated iron oxide is dissolved, allowing for the separation of carbon.

[0053] The hydrochloric acid used in carbon separation step S2 (wet chlorination) should have a hydrogen chloride concentration in the range of, for example, 5% to 37% by mass. There is a concern that the reaction will be slow if the hydrogen chloride concentration of hydrochloric acid is less than 5% by mass. Also, concentrated hydrochloric acid exceeding 37% by mass is difficult to handle because the hydrogen chloride volatilizes quickly. The reaction temperature in 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. Below 10°C, the reaction rate is slow and cooling equipment is required. Above 150°C, energy consumption is high and evaporation of the solution occurs, making it inefficient. In the carbon separation step S2 (wet chlorination), it is preferable to effectively utilize a heat source similar to that used in the carbon dioxide decomposition step S1, for example, in order to raise the temperature to this reaction temperature range.

[0054] The chlorination reaction of magnetite in carbon separation step S2 (wet chlorination) is represented by the following equations (8) to (9). 2Fe3O4·δC + 16HCl → 4FeCl3 + 2FeCl2 + 8H2O + δC (wet chlorination: 10~150℃) (where δ=1~4) ... (8) 2Fe3O4 + 16HCl → 4FeCl3 + 2FeCl2 + 8H2O (Wet chlorination: 10℃~150℃) ... (9)

[0055] (Dry Chloridation) When the chlorination reaction of magnetite is carried out by dry chlorination, the magnetite with carbon attached to its 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 to produce iron chloride (iron(III) chloride and iron(II) chloride) and water.

[0056] The hydrogen chloride gas used in carbon separation step S2 (dry chlorination) should have a hydrogen chloride concentration in the range of, for example, 50% to 100% by mass. There is a concern that the reaction will be slow if the hydrogen chloride concentration is less than 50% by mass. The reaction temperature in 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. Below 50°C, the reaction rate is slow, and above 300°C, energy consumption increases and efficiency decreases. Furthermore, because the chloride reaction is an exothermic reaction, high temperatures are detrimental to the reaction's progress. In the carbon separation step S2 (dry chlorination), it is preferable to effectively utilize a heat source similar to that used in the carbon dioxide decomposition step S1, for example, in order to raise the temperature to this reaction temperature range.

[0057] The chlorination reaction of magnetite in carbon separation step S2 (dry chlorination) is represented by the following equations (8) to (9). 2Fe3O4·δC + 16HCl → 4FeCl3 + 2FeCl2 + 8H2O + δC (Dry chloride: 50~300℃) (where δ=1~4) ... (8) 2Fe3O4 + 16HCl → 4FeCl3 + 2FeCl2 + 8H2O (Dry chloride: 50℃~300℃) ... (9)

[0058] To reduce energy consumption, it is preferable to use dry chlorination with hydrogen chloride gas for magnetite that does not have carbon attached (magnetite that is simply recycled for hydrogen production obtained in hydrogen production process S3). In the case of dry chlorination, carbon-attached magnetite is converted to iron chloride with hydrogen chloride gas, and then the carbon can be separated as an insoluble component by dissolving the product in water.

[0059] The carbon (carbon material) separated from magnetite in carbon separation step S2 is nano-sized carbon with a particle size of 1 μm or less, and hardly any particles larger than 1 μm are produced. This nano-sized carbon powder is high-purity carbon with a purity of, for example, 99% or more, and can be 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 directly as a reducing agent, such as a substitute for coke in steelmaking. It can also be used as a raw material for manufacturing carbon materials such as artificial graphite, carbon fiber, and carbon nanotubes.

[0060] <Hydrogen production process S3> The hydrogen production process S3 includes an electrolytic reduction process S3-1, which uses an electrolytic device to reduce the iron(III) chloride obtained in the carbon separation process S2 (reduction from iron(III) chloride to iron(II) chloride), and a hydrolysis process S3-2, which reacts the divalent iron chloride obtained in the electrolytic reduction process S3-1 with water to produce magnetite, hydrogen, and hydrogen chloride gas. The magnetite produced in this hydrogen production process S3 is sent to the next reducing agent regeneration process S4. Furthermore, hydrogen chloride can be used as a raw material for producing hydrochloric acid used in the carbon separation process S2. Furthermore, operations such as concentration, drying, and granulation of the iron(II) chloride solution may be performed using equipment such as membrane separators, evaporators, crystallizers, and spray dryers to produce iron(II) chloride particles of a predetermined particle size, which may then be sent to the hydrogen and magnetite production reactions.

[0061] (Electrolytic reduction process S3-1) Figure 3 is a schematic diagram showing an example of an electrolytic apparatus used in the electrolytic reduction process S3-1, which constitutes the hydrogen production process S3. The electrolytic apparatus 10 of this embodiment includes a cathode cell 11, an anode cell 12, and a partition wall 13 formed between the cathode cell 11 and the anode cell 12. The cathode cell 11 is provided with a cathode electrode (working electrode) 21 and a reference electrode 22, and the anode cell 12 is provided with an anode electrode (counter electrode) 23. Furthermore, a power supply device 14 is provided to apply a voltage between the cathode electrode 21 and the anode electrode 23.

[0062] The cathode cell 11 is a liquid cell formed from a dielectric material such as glass, and contains a cathode solution containing trivalent iron chloride. In this embodiment, it contains a hydrochloric acid solution (cathode solution) of iron chloride (a mixture of iron(III) chloride and iron(II) chloride) obtained in the preceding carbon separation step S2. The hydrochloric acid concentration of this iron chloride hydrochloric acid solution (cathode solution) is adjusted so that, for example, the pH is 0.5 or less.

[0063] The anode tank 12 is a liquid tank formed from a dielectric material such as glass, and contains an anolyte containing an electrolyte, which in this embodiment is a dilute sulfuric acid aqueous solution (anolyte). The sulfuric acid concentration of this dilute sulfuric acid aqueous solution (anolyte) should be in the range of, for example, 0.1 mol / L or more and 5.0 mol / L or less.

[0064] The partition wall 13 is a membrane-like member positioned between the openings formed in the cathode chamber 11 and the anode chamber 12, respectively. One side of the partition wall 13 is in contact with the cathode liquid, and the other side is in contact with the anode liquid. Such a partition wall 13 can be made of a material that allows hydrogen ions to pass through, for example, a cation exchange membrane or a glass filter can be used. In this embodiment, a Nafion® membrane (cation exchange membrane) is used.

[0065] The cathode electrode (working electrode) 21 placed in the cathode cell 11 is connected to the negative electrode of the power supply unit 14. This cathode electrode 21 can be made of a conductor, such as a carbon electrode or a platinum electrode. In this embodiment, a carbon rod was used as the cathode electrode 21. The reference electrode (reference electrode) 22 placed in the cathode cell 11 is used to measure the oxidation-reduction potential, and in this embodiment, a silver / silver chloride electrode (electrode potential +0.199 V (vs. SHE, 25℃)) was used.

[0066] The anode electrode (counter electrode) 23, placed in the anode bath 12, is connected to the positive electrode of the power supply unit 14. This anode electrode 23 can be made of a conductor, such as a carbon electrode or a platinum electrode. In this embodiment, a platinum wire was used as the anode electrode 23.

[0067] In the electrolytic reduction process S3-1, the iron(III) chloride obtained in the carbon separation process S2 is electrolytically reduced using the electrolytic apparatus 10 described above, and is reduced to iron(II) chloride as shown in equation (10) below. FeCl3+e - +H + →FeCl2+HCl ···(10) Specifically, for example, the cathode cell 11 of the electrolytic device 10 contains a hydrochloric acid solution (cathode solution) of iron chloride (a mixture of iron(III) chloride and iron(II) chloride) obtained in the carbon separation step S2. The hydrochloric acid concentration of this cathode solution is adjusted so that the pH is 0.5 or lower, for example, to 0.1.

[0068] Furthermore, a dilute sulfuric acid aqueous solution (anode solution) is contained in the anode cell 12 as the electrolyte. This anode solution should have a sulfuric acid concentration in the range of 0.1 mol / L or more and 5.0 mol / L or less; for example, a dilute sulfuric acid aqueous solution with a sulfuric acid concentration of 0.2 mol / L is sufficient. If the concentration is less than 0.1 mol / L, H supplied from the anode cell 12 during the electrolytic reduction of FeCl3 to FeCl2 will be affected. + There are concerns that this may be insufficient. On the other hand, if it is greater than 5.0 mol / L, the osmotic pressure between the cathode bath 11 and the anode bath 12 may become too high, potentially causing the partition wall 13 to break or liquid leakage.

[0069] The electrolytic device 10 may be placed in the air, but more preferably it is installed in a chamber whose interior is purged with an inert gas, such as argon gas or nitrogen gas.

[0070] Next, a voltage is applied between the cathode electrode 21 and the anode electrode 23 by the power supply unit 14 to perform electrolytic reduction of iron(III) chloride in the cathode cell 11, producing iron(II) chloride, which is divalent iron chloride. The electrolytic reduction of iron(III) chloride, based on the potential-pH graph shown in Figure 4, proceeds under conditions of pH 0.5 or lower, with the Fe(II) / Fe(III) redox reaction following the following equation (11), resulting in a redox potential of +0.70V (E) relative to the standard hydrogen electrode (SHE). 0 ) occurs. FeCl2 + +e - →Fe 2+ +2Y - E 0 =0.70V vs. SHE ···(11) Note that the potential-pH graph in Figure 4 was extracted from the thermodynamic database (NIST Critically Selected Stability Constants of Metal Complexes; NIST Standard Reference Database 46, version 8.0) for Fe 2+ Fe 3+ Cl - and H + This is based on various stability constants (total Fe concentration: 0.1M, total Cl - Concentration: 3 mol / L, Ionic strength: 3 mol / L, Temperature: 25°C).

[0071] The oxidation-reduction potential (E) of equation (11) 0 Since this falls within the potential window of water (the region between the two dashed lines in the graph of Figure 4), in constant potential electrolysis in the region from +0.7V to 0.0V relative to the standard hydrogen electrode (SHE), it is possible to allow equation (11) to proceed dominantly without electrolysis of water.

[0072] Furthermore, even in the case of constant current electrolysis, as long as the supply of Fe(III) from the cathode solution to the cathode electrode (working electrode) 21 is sufficient, it is possible to allow equation (11) to proceed dominantly without the electrolysis of water. On the other hand, if the pH of the cathode solution exceeds 0.5, the hydrolysis reaction of Fe(III) will proceed, making it impossible to retain Fe(III) in the cathode solution, so the pH of the cathode solution must be kept below 0.5.

[0073] When the electrolytic reduction reaction of Fe(III) shown in equation (11) above proceeds at the cathode electrode (working electrode) 21, some kind of oxidation reaction also needs to proceed at the anode electrode (counter electrode) 23 in the anode bath 12. In order to keep the reaction system clean, the electrolysis of water shown in equation (12) is the most suitable oxidation reaction.

[0074] H2O → 2H + +2e - +1 / 2O2(g)···(12) By combining equations (11) and (12) described above, the net reaction occurring in the cathode cell 11 is represented by equation (13).

[0075] 2FeCl2 + +H2O→2Fe 2+ +2H + +4M - +1 / 2O2(g)···(13) Then, as equation (13) progresses, H flows from the anode chamber 12 to the cathode chamber 11 via the partition wall 13. + It moves. These H + To facilitate the smooth movement of the ions, the anodic acid is preferably acidic. However, if a hydrochloric acid aqueous solution similar to that used for the cathode is used as the anodic acid, the Cl - Oxidation may lead to the generation of Cl2 (Equation (14)), and consequently, the generation of hypochlorous acid (Equation (15)). 2Cl - →Cl2+2e - ...(14) Cl2 + H2O = HCl + HClO ... (15)

[0076] The formation of by-products shown in equations (14) and (15) is undesirable for maintaining the cleanliness of the reaction system. Therefore, it is necessary to use an anolyte containing an acidic substance that is resistant to oxidation reactions at the anode electrode (counter electrode) 23. Since sulfuric acid is an acidic substance that serves this purpose, dilute sulfuric acid is used as the anolyte in this embodiment. However, since preventing contamination of the cathode with sulfuric acid or sulfate ions is also important for maintaining the cleanliness of the reaction system, a cation exchange membrane is used as a partition 13 between the cathode cell 11 and the anode cell 12.

[0077] Furthermore, iron(II) chloride can be recovered from the cathode solution after the reaction is complete by drying under reduced pressure. For example, iron(II) chloride can be recovered by drying the cathode solution under reduced pressure using a rotary evaporator.

[0078] Through the electrolytic reduction process S3-1 described above, the iron(III) chloride obtained in the carbon separation process S2 is converted to iron(II) chloride, and the following hydrolysis process S3-2 is carried out.

[0079] (Hydrolysis process S3-2: Hydrogen and magnetite production reaction) In the hydrolysis process S3-2, a hydrogen and magnetite production reaction is carried out by reacting the iron(II) chloride produced in the electrolytic reduction reaction of iron(III) chloride in the electrolytic reduction process S3-1 with water. The reaction temperature in this hydrogen and magnetite production reaction can be in the range of 300°C to 800°C, preferably 400°C to 600°C. In the hydrogen production process S3, it is preferable to effectively utilize a heat source similar to that used in the carbon dioxide decomposition process S1, for example, to raise the temperature to this reaction temperature range.

[0080] In the hydrogen production process S3, the reaction between iron(II) chloride and water occurs as shown in equation (16) below. 3FeCl2+4H2O→Fe3O4+6HCl+H2...(16) The hydrogen obtained through these reactions is, for example, high-purity hydrogen with a purity of 99% or more, and can be used as a hydrogen station for fuel cell vehicles (FCVs), hydrogen power generation, and a hydrogen source for various industries.

[0081] Furthermore, some of the hydrogen produced in the hydrogen production process S3 is also used in the subsequent reducing agent regeneration process S4. However, to increase the amount of hydrogen extracted externally, additional magnetite (magnetite without carbon deposits) can be added in the carbon separation process S2, or additional iron chloride (FeCl2) can be added in the hydrogen production process S3. This allows for the generation of more hydrogen than required in the reducing agent regeneration process S4, enabling its use as a high-purity, low-cost hydrogen source.

[0082] However, if the magnetite produced in the hydrogen production process S3 from the additionally added iron compounds (magnetite, iron chloride) is supplied to the reducing agent regeneration process S4, an excess of magnetite will occur, increasing the process load of the reducing agent regeneration process S4. Therefore, it is preferable to extract the amount derived from the additionally added iron compounds from the magnetite generated in the hydrogen production process S3 and supply it to the carbon separation process S2 in a state free of carbon deposits. In other words, by supplying only the amount of magnetite necessary for the carbon dioxide decomposition process S1 to the reducing agent regeneration process S4, and circulating the remainder between the carbon separation process S2 and the hydrogen production process S3, the amount of hydrogen produced in the hydrogen production process S3 can be increased without affecting the carbon dioxide decomposition process S1 and the reducing agent regeneration process S4. For example, in this embodiment, 25% by mass of the magnetite generated 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.

[0083] (Reducing agent regeneration process S4) In the reducing agent regeneration step S4, the hydrogen produced in the hydrogen production step S3 is reacted with magnetite to remove oxygen ions contained in the magnetite (deoxygenation (reduction) reaction), and while maintaining the crystal structure of the magnetite, i.e., the spinel-type crystal lattice structure, oxygen-depleted iron oxide (Fe3O) is formed in which any position of the oxygen atom in the magnetite becomes a vacancy. 4-δ (where δ is between 1 and 4), or it produces oxygen-defective iron.

[0084] Furthermore, the magnetite introduced in the reducing agent regeneration process S4 is the magnetite obtained in the hydrogen production process S3. However, the replenishment of magnetite lost during the initial stages of each process and during the execution of each process is not limited to pure magnetite; other substances may also be used.

[0085] When introducing magnetite from an external source, the raw material for magnetite (magnetite material) can be, for example, natural iron sand or iron sand contained in iron ore used in steel mills. By using this iron sand as magnetite, magnetite can be obtained cheaply and easily. Additionally, hematite (Fe2O3) and used hand warmers made using the iron oxidation method (whose main component is iron hydroxide) can also be used as magnetite materials.

[0086] The magnetite in this embodiment has a specific surface area of ​​0.1 m² as determined by the BET method. 2 / g or more, 10m 2 A range of less than or equal to / g, preferably 0.3m 2 / g or more, 8m 2 A range of less than or equal to / g, more preferably 1m 2 / g or more, 6m 2 It is within the range of / g or less.

[0087] The specific surface area of ​​magnetite is 0.1 m². 2 If the specific surface area of ​​magnetite is 10 m² or more, the contact area between the solid and gas necessary for a solid-gas reaction can be secured, and the reaction rate required for a practical process can be obtained. 2 If the amount is less than / g, a fast reaction rate can be ensured, and the proportion of carbon monoxide produced during the decomposition of carbon dioxide will be reduced, improving the carbon recovery rate.

[0088] Furthermore, the reducing agent obtained by reducing magnetite in the reducing agent regeneration step S4 of this embodiment has a larger specific surface area than the magnetite before reduction. The specific surface area of ​​the reducing agent is 0.1 m². 2 / g or more, 30m 2 Less than or equal to / g, preferably 0.3m 2 / g or more, 25m2 / g or less, more comfortably 1m 2 / g or more, 18m 2 The amount is less than or equal to / g. Furthermore, the specific surface area of ​​the reducing agent is 1 or more and 3 or less than the specific surface area of ​​magnetite, preferably 1 or more and 2.5 or less, and more preferably 1 or more and 2.0 or less.

[0089] Furthermore, the magnetite in this embodiment has an average particle diameter in the range of 1 μm or more and 1000 μm or less, preferably in the range of 1 μm or more and less than 20 μm, or in the range of more than 50 μm and 200 μm or less.

[0090] If the average particle size of magnetite is 1 μm or larger, the proportion of carbon monoxide produced during the decomposition of carbon dioxide will be reduced, improving the carbon recovery rate. Furthermore, by using an average particle size larger than 1 μm, the aggregation and scattering of particles will be reduced, improving fluidity and handling properties. This will prevent problems such as adhesion to reactor walls and clinker formation, making it possible to apply magnetite to industrial reactors such as rotary kilns and fluidized beds. Furthermore, if the average particle size of magnetite is 1000 μm or less, the contact area between the solid and gas necessary for the solid-gas reaction can be secured, and the reaction rate required for a practical process can be obtained.

[0091] Furthermore, the magnetite in this embodiment has a bulk density of 0.3 g / cm³. 3 More than 3g / cm 3 The following range, preferably 0.4 g / cm³ 3 More than 2g / cm 3 The following range, more preferably 0.5 g / cm³ 3 More than 1g / cm 3 The range is as follows:

[0092] The bulk density of magnetite is 0.3 g / cm³. 3 If the above conditions are met, the particle cohesiveness and scattering will be reduced, and the fluidity will be improved, making it possible to apply it to industrial reactors such as rotary kilns and fluidized beds. 3Under the following conditions, sufficient porosity can be ensured between and within particles, allowing the reactant gas to diffuse easily into the particles, and enabling the reaction rate required for a practical process to be obtained.

[0093] In the reducing agent regeneration process S4, for example, using a solid-gas reactor such as a rotary kiln or fluidized bed, powdered magnetite is stirred and brought into contact with the hydrogen produced in the hydrogen production process S3. This causes the oxygen atoms constituting the magnetite to detach and react with the hydrogen to produce water (water vapor). Furthermore, the magnetite from which the oxygen atoms have detached retains its crystal structure, i.e., the spinel-type crystal lattice structure, but the detached oxygen atoms become vacancies, resulting in oxygen-depleted iron oxide or oxygen-completely-depleted iron.

[0094] In the reducing agent regeneration process S4, if the magnetite material contains hematite, the hematite is reduced to magnetite, and then further reduced to oxygen-depleted iron oxide or oxygen-completely depleted iron.

[0095] 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, the reaction rate required for a practical process can be obtained. Furthermore, if the reaction temperature is 450°C or lower, 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, energy consumption during the reaction can be reduced. In the reducing agent regeneration step S4, it is preferable to effectively utilize a heat source similar to that used in the carbon dioxide decomposition step S1, for example, in order to raise the temperature to this reaction temperature range.

[0096] 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, the reaction rate required for a practical process can be obtained, and the size of the reactor can be made more compact. Furthermore, if the reaction pressure is 5 MPa or lower, the manufacturing cost of the apparatus can be reduced.

[0097] The concentration of hydrogen gas used in the reducing agent regeneration process S4 should 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, around 90% by volume, there is virtually no significant difference in reducing ability compared to hydrogen gas with a concentration of 100% by volume. Therefore, by using hydrogen gas with a concentration of around 90% by volume, which is less expensive than hydrogen gas with a concentration of 100% by volume, the reducing agent can be produced from magnetite at a low cost.

[0098] In the reduction of magnetite by hydrogen in the reducing agent regeneration process S4, the reducing agent is generated as shown in the following equations (17) and (18). Fe3O4 + δH2 → Fe3O 4-δ +δH2O (where δ = 1 or greater and less than 4) ... (17) Fe3O4+4H2→3Fe+4H2O···(18)

[0099] Here, in order to maintain the activity of the obtained reducing agent, it is preferable to prevent oxidation of the reducing agent due to air mixing, etc., between the reducing agent regeneration step S4 and the carbon dioxide decomposition step S1. For example, if the reducing agent can be transported from the reducing agent regeneration step S4 to the carbon dioxide decomposition step S1 in a sealed state to prevent air mixing, the reducing agent obtained in the reducing agent regeneration step S4 can be supplied to the carbon dioxide decomposition step S1 without oxidation.

[0100] Furthermore, in order to increase the efficiency of carbon production in the carbon separation process S2, the carbon dioxide decomposition process S1 and the reducing agent regeneration process S4 can be repeated two or more times to increase the carbon concentration of the carbon-attached magnetite produced in the carbon dioxide decomposition process S1 before proceeding with the carbon separation process S2 and the hydrogen production process S3. This makes it possible to produce nano-sized carbon at a lower cost.

[0101] According to the carbon material and hydrogen production method of this embodiment described above, the crystal structure of magnetite is maintained, and an oxygen-defective iron oxide (Fe3O) with many atomic vacancies due to the departure of oxygen atoms is produced. 4-δ By using oxygen-defective iron (δ=4), obtained by completely reducing magnetite (where δ=1 or greater and less than 4), as a reducing agent to reduce carbon dioxide, carbon materials can be produced efficiently from carbon dioxide at low cost.

[0102] Furthermore, by converting iron(III) chloride to iron(II) chloride through electrolytic reduction in the electrolytic reduction process S3-1, which constitutes the hydrogen production process S3, it is possible to increase the proportion of iron(II) chloride, which can easily produce hydrogen through reaction with water, using a simple and low-cost method that can be reacted at room temperature, without resorting to costly methods such as heating the mixture of iron(III) chloride and iron(II) chloride obtained in the carbon separation process S2 to high temperatures for reduction.

[0103] Then, by reacting the iron(II) chloride obtained in the electrolytic reduction process S3-1 with water, water can be efficiently and inexpensively decomposed to produce high-purity hydrogen. In this hydrogen production method, the amount of hydrogen produced can be easily increased simply by increasing the amount of magnetite circulated, and it can be widely used in applications such as hydrogen reduction steelmaking processes in next-generation steel mills, hydrogenation refining processes in oil refineries, carbon dioxide capture and reuse (CCU) technology, hydrogen sources for hydrogen fuel cells, and hydrogen sources for hydrogen power generation.

[0104] Then, by supplying the magnetite generated in the hydrogen production process S3 to the reducing agent regeneration process, and regenerating the reducing agent using the hydrogen generated in the hydrogen production process, it is possible to construct a closed system that uses only carbon dioxide and water as external supplies to decompose carbon dioxide to produce carbon materials and decompose water to produce hydrogen.

[0105] The hydrogen and oxygen generated during each of these processes are produced in different stages and do not come into contact with each other within a single process. For example, hydrogen is produced in the hydrogen production process S3, and oxygen is produced in the carbon separation process S2, and these do not coexist in the same reaction vessel or other container. As a result, there is no concern that oxygen and hydrogen may come into contact and react explosively, and the reactions in each process can be carried out stably.

[0106] The magnetite used in these carbon materials and hydrogen production methods is recycled while changing its material form, such as being reduced and becoming a reducing agent during the processing. Therefore, carbon and hydrogen can be produced at low cost without supplying magnetite from external sources other than what is lost.

[0107] Furthermore, in the carbon separation step S2, by dissolving the magnetite with carbon attached to its surface in hydrochloric acid (an aqueous solution of hydrogen chloride) and separating the carbon that is insoluble in hydrochloric acid, a nano-sized carbon material with a particle size of 1 μm or less can be obtained.

[0108] 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 utilizing heat (waste heat) generated as a result of the operation of steel mills, thermal power plants, cement factories, and waste incineration facilities 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 utilizing electricity and heat storage derived from renewable energy, as well as thermal energy from high-temperature gas reactors that can extract high-temperature heat, CO2 emissions can be suppressed, contributing to the realization of carbon neutrality and a decarbonized society.

[0109] Although embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0110] For example, in the embodiments described above, the general composition of magnetite is given as Fe3O4, but such magnetite may also be iron sand containing other substances, such as titanium (Ti). These other substances, such as titanium, may contribute to the reduction of carbon dioxide as a catalyst. [Examples]

[0111] The following describes the effects of the electrolytic reduction process S3-1 in the carbon and hydrogen production method of the present invention. For the verification, we prepared an electrolytic apparatus with the configuration shown in Figure 4. The conditions are as follows: (1) Temperature: 25℃. (2) Pressure: Atmospheric pressure (1 atmosphere). (3) Cathode solution: Fe in 60 mL of 2 mol / L aqueous hydrochloric acid solution under an argon atmosphere 3+ A solution of magnetite dissolved to a concentration of 20.7 mol / L was used. The pH was maintained at 0.4 or lower. (4) Anode liquid: A dilute sulfuric acid aqueous solution with a concentration of 1 mol / L was used. (5) Cathode electrode (working electrode): Carbon rod (φ6mm: effective electrode area 9.7cm²) 2 ) was used. (6) Anode electrode (counter electrode): A platinum wire was used. (7) Reference electrode: A silver / silver chloride electrode (Ag / AgCl, +0.199 V relative to SHE) was used. (8) Septum: Nafion® membrane was used. (9) Cathode chamber atmosphere: Argon gas atmosphere was used. (10) Potential applied to the cathode electrode: The range was set to +0.7V to 0.0V relative to the standard hydrogen electrode (SHE) (a range of +0.5V to -0.2V relative to the reference electrode).

[0112] Under the conditions described above, the current value and the change in electrical charge from 0 seconds to 54,000 seconds were measured. The results are shown in Figure 5. Since the amount of Fe(III) used in this verification example was 1.242 mmol, the theoretical amount of electrical charge required for the completion of the reaction in equation (1) above is 119.85 C. In contrast, the amount of electrical charge consumed by the end of electrolysis shown in Figure 5 was 119.66 C, so it can be considered that the electrolytic reduction reaction in equation (1) was 99.8% completed. When the cathode solution after the reaction was dried under reduced pressure using a rotary evaporator, 0.1833 g of pale green powder was obtained.

[0113] Next, this pale green powder was analyzed using an X-ray diffractometer (XRD). The results are shown in Figure 6. In Figure 6, the upper line represents the measurement results, and the lower line represents the literature value for FeCl2·2H2O. As shown in Figure 6, the peak pattern of the obtained pale green powder has peaks that are similar to the known peak pattern of FeCl2·2H2O. Therefore, it was confirmed that the electrolytic reduction reaction shown in equation (1) proceeds dominantly and quantitatively. [Industrial applicability]

[0114] This invention enables the low-cost and efficient production of carbon materials and hydrogen using carbon dioxide and water. For example, by applying it to plants that emit large amounts of carbon dioxide and waste heat, such as steel plants, thermal power plants, cement manufacturing plants, and waste incineration facilities, it is possible to reduce carbon dioxide emissions, effectively utilize hydrogen, and consequently produce high-value-added carbon materials such as nano-sized carbon. Therefore, it has industrial applicability. [Explanation of symbols]

[0115] S1...Carbon dioxide decomposition process S2…Carbon separation process S3…Hydrogen production process S3-1…Electrolytic reduction process S3-2…Hydrolysis process S4…Reducing agent regeneration process

Claims

1. A carbon dioxide decomposition process in which carbon dioxide is reacted with a reducing agent to produce magnetite with carbon attached to its surface, A carbon separation step is performed by reacting magnetite, which has carbon attached to its surface obtained in the carbon dioxide decomposition step, with hydrochloric acid or hydrogen chloride gas to produce carbon and iron chloride. A hydrogen production process in which iron chloride obtained in the carbon separation process is reacted with water to produce magnetite, hydrogen, and hydrogen chloride gas. The process includes a reducing agent regeneration step in which magnetite and hydrogen obtained in the hydrogen production step are reacted with each other to produce the reducing agent used in the carbon dioxide decomposition step, The hydrogen production process comprises an electrolytic reduction process to produce divalent iron chloride by electrolysis of trivalent iron chloride, and a hydrolysis process to produce magnetite, hydrogen, and hydrogen chloride gas by reacting the divalent iron chloride obtained in the electrolytic reduction process with water. The reducing agent is obtained by reducing magnetite while maintaining the crystal structure of magnetite. ３ O ４－δ A method for producing carbon and hydrogen, characterized by using an oxygen-deficient iron oxide represented by (where δ is 1 or more and less than 4), or oxygen-completely deficient iron (δ=4) obtained by completely reducing magnetite while maintaining the crystal structure of magnetite, or oxygen-deficient iron oxide with the crystal structure of magnetite obtained by reducing hematite or used hand warmers, or oxygen-completely deficient iron with the crystal structure of magnetite obtained by completely reducing hematite or used hand warmers.

2. The method for producing carbon and hydrogen according to claim 1, characterized in that the electrolytic reduction process is carried out using an electrolytic apparatus having a cathode cell containing a cathode solution containing trivalent iron chloride, an anode cell containing an anode solution containing an electrolyte, a partition wall formed between the cathode cell and the anode cell and allowing ions to pass through, a cathode electrode provided in the cathode cell, and an anode electrode provided in the anode cell.

3. The method for producing carbon and hydrogen according to claim 2, characterized in that the pH of the cathode solution is kept at 0.5 or less.

4. The method for producing carbon and hydrogen according to claim 2, characterized in that the anode liquid contains dilute sulfuric acid.

5. The method for producing carbon and hydrogen according to claim 2, characterized in that the cathode solution contains an aqueous hydrochloric acid solution in which trivalent iron chloride is dissolved.

6. The method for producing carbon and hydrogen according to claim 2, characterized in that the cathode electrode is a carbon electrode or a platinum electrode.

7. The method for producing carbon and hydrogen according to claim 2, characterized in that the anode electrode is a carbon electrode or a platinum electrode.

8. The method for producing carbon and hydrogen according to claim 2, characterized in that the partition wall is a cation exchange membrane or a glass filter.

9. The method for producing carbon and hydrogen according to claim 2, characterized in that the cathode cell is provided in an inert gas atmosphere.

10. The method for producing carbon and hydrogen according to claim 1 or 2, characterized in that the carbon is nano-sized carbon with a particle diameter of 1 μm or less.

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