Method for producing carbon, system for producing carbon, and method for treating carbon dioxide

Abstract

Provided is a technique capable of treating carbon dioxide. This method for producing carbon includes: a Boudouard step for causing a Boudouard reaction between carbon and carbon dioxide; a carburization step for carburizing a metal with carbon monoxide and carbon dioxide generated by the Boudouard step; and a precipitation step for precipitating carbon on the surface of the metal by lowering the temperature below that of the carburization step after the carburization step.

Description

Methods for producing carbon, carbon production systems, and methods for treating carbon dioxide

[0001] This disclosure relates to a method for producing carbon. This application is based on Japanese Patent Application No. 2025-016490, filed on 4 February 2025, the contents of which are incorporated herein by reference.

[0002] In recent years, efforts have been made to achieve carbon neutrality. For example, in order to recycle carbon dioxide contained in exhaust gases and other substances resulting from the use of fossil fuels, efforts are being made to convert it into synthetic fuels mainly composed of hydrocarbons using the FT (Fisher-Tropsch) synthesis process, which uses carbon dioxide and hydrogen as raw materials (for example, Patent Document 1). In addition, for example, carbon dioxide contained in exhaust gases and other substances can be stored deep underground through carbon dioxide capture and storage (CCS) (for example, Non-Patent Document 1).

[0003] Japanese Patent Publication No. 2024-124190

[0004] Shigeo Murai and Yuichi Fujioka, "Challenges in Separation, Capture, and Storage of Carbon Dioxide," Journal of the Institute of Electrical Engineers of Japan, 2007, 127, 4, pp. 242-245.

[0005] In a fuel synthesis reaction as shown in Patent Document 1, CO ２ Because a large amount of free hydrogen is needed, its stable production and transportation are problematic. Also, in CCS as shown in Non-Patent Document 1, CO ２ There is a problem in that the costs required for the separation, recovery, and transportation of carbon dioxide are high. For this reason, other technologies that can process carbon dioxide are needed.

[0006] This disclosure can be implemented in the following forms:

[0007] (1) According to one embodiment of the present disclosure, a method for producing carbon is provided. This method for producing carbon includes a boudoir step of reacting carbon with carbon dioxide in a boudoir reaction, a carburizing step of carburizing a metal with carbon monoxide and carbon dioxide produced in the boudoir step, and a precipitation step of depositing carbon on the surface of the metal after the carburizing step by lowering the temperature compared to the carburizing step. According to this embodiment of the method for producing carbon, carbon dioxide can be processed.

[0008] (2) The carbon production method described in (1) above further includes a thermal decomposition step in which hydrogen and carbon are produced by thermal decomposition of a gas containing methane, and the carbon produced by the thermal decomposition step may be used in the boudoir step. With this form of carbon production method, since the boudoir reaction is carried out using carbon produced by the thermal decomposition of a gas containing methane, low-grade carbon can be effectively utilized.

[0009] (3) In the method for producing carbon described in (1) or (2) above, the method further includes a thermal decomposition step in which hydrogen and carbon are produced by thermal decomposition of a gas containing methane, and the hydrogen produced by the thermal decomposition step may be used in the precipitation step. According to this form of carbon production method, the precipitation of carbon in the precipitation step can be promoted by utilizing a portion of the turquoise hydrogen produced by the thermal decomposition of a gas containing methane.

[0010] (4) In the carbon production method described in any one of the above items (1) to (3), the thermal energy generated in the precipitation step may be used in the boudoir step. This form of carbon production method can increase thermal efficiency.

[0011] (5) In the method for producing carbon described in any one of the above items (1) to (4), the Boudoir step may be carried out at a temperature of 800°C or higher and 930°C or lower. This form of carbon production method can improve the efficiency of the Boudoir reaction.

[0012] (6) In the carbon production method described in any one of the above items (1) to (5), the carburizing step may be carried out at a temperature of 900°C or higher and 950°C or lower. This form of carbon production method can improve the efficiency of carburizing.

[0013] (7) In the method for producing carbon described in any one of the above items (1) to (6), the precipitation step may be carried out at a temperature of 25°C or higher and 500°C or lower. This form of carbon production method can improve the efficiency of precipitation.

[0014] (8) Another embodiment of the present disclosure provides a carbon production system, comprising: a first furnace for a boudoir reaction of carbon and carbon dioxide; and a second furnace for carburizing a metal with carbon monoxide and carbon dioxide recovered from the first furnace, and then depositing carbon on the surface of the metal by lowering the temperature below that of the carburizing period. This embodiment of the carbon production system allows for the processing of carbon dioxide.

[0015] (9) In the carbon production system described in (8) above, in the first furnace, a thermal decomposition reaction is carried out to thermally decompose a gas containing methane before the Boudoir reaction, and the carbon produced by the thermal decomposition reaction may be used in the Boudoir reaction. In this form of carbon production system, the furnace for the thermal decomposition reaction to thermally decompose a gas containing methane and the furnace for the Boudoir reaction can be carried out using the first furnace.

[0016] (10) In the carbon production system described in (8) or (9) above, a third furnace for thermally decomposing a gas containing methane may be further provided, and the carbon recovered from the third furnace may be supplied to the first furnace. With this form of carbon production system, since the carbon produced by the thermal decomposition of a gas containing methane is used for the boudoir reaction, low-grade carbon can be effectively utilized.

[0017] (11) In the carbon production system described in any one of the above paragraphs (8) to (10), the second furnace includes a pair of furnaces in which carburizing of the metal and carbon deposition are performed alternately. This form of carbon production system makes it possible to suppress a decrease in thermal efficiency.

[0018] (12) Another embodiment of the present disclosure provides a method for treating carbon dioxide. This method for treating carbon dioxide includes a boudoir step of reacting carbon and carbon dioxide in a boudoir reaction, a carburizing step of carburizing a metal with carbon monoxide and carbon dioxide produced in the boudoir step, and a precipitation step of depositing carbon on the surface of the metal after the carburizing step by lowering the temperature compared to the carburizing step. This embodiment of the method for treating carbon dioxide allows for the treatment of carbon dioxide.

[0019] Furthermore, this disclosure can be implemented in various forms, for example, in the form of a carbon production apparatus, a carbon dioxide treatment apparatus, and the like.

[0020] This is a process diagram showing a method for producing carbon. This is an explanatory diagram showing an example of the general reaction in a carbon production method. This is a block diagram showing the general configuration of a carbon production system. This is an explanatory diagram for explaining the configuration of a first furnace. This is an explanatory diagram for explaining the configuration of a second furnace. This is a process diagram showing a method for producing carbon in a second embodiment. This is an explanatory diagram for explaining the configuration of a first furnace in the system of the second embodiment. This is a block diagram showing the general configuration of another example of a carbon production system. This is a process diagram showing a method for treating carbon dioxide.

[0021] A. Method for producing carbon and production system (1) First embodiment Figure 1 is a process diagram showing a method for producing carbon as one embodiment of the present disclosure. Figure 2 is an explanatory diagram showing an example of a schematic reaction in the method for producing carbon. In Figure 2, "Q" represents the heat of reaction, "C(p)" represents low-grade carbon, and "C(f)" represents high-grade carbon. In the method for producing carbon in the present disclosure, carbon dioxide is treated and high-grade carbon is produced by performing a boudoir reaction, carburizing a metal, and precipitation of carbon. As shown in Figure 1, the method for producing carbon in this embodiment includes a thermal decomposition step (P110), a boudoir step (P120), a carburizing step (P130), and a precipitation step (P140).

[0022] In the pyrolysis process (P110), as shown in Figure 2, hydrogen and carbon are produced by thermally decomposing a gas containing methane. In the pyrolysis process (P110), so-called methane pyrolysis, that is, the reaction shown in the following chemical equation (1), mainly proceeds.

[0023] CH ４ →2αH ２ +αC+(1-α)CH ４ ... (1)

[0024] The methane-containing gas is not particularly limited, but examples include methane gas, natural gas, and biomethane. The natural gas is not particularly limited and may be conventional natural gas, or unconventional natural gas such as shale gas, tight gas, coalbed methane, or methane hydrate. The methane-containing gas is thermally decomposed by heating in a gas reactor. The temperature in the thermal decomposition step (P110) can be set according to the type of catalyst provided in the gas reactor, but from the viewpoint of improving the efficiency of the thermal decomposition reaction, it is preferably carried out at 600°C to 800°C, and more preferably at 650°C to 700°C. The catalyst is not particularly limited as long as it promotes the thermal decomposition reaction, but for example, it is formed by multiple metal catalyst plates. The metal catalyst plates are not particularly limited as long as they promote the thermal decomposition reaction, but for example, they are formed by electroplated Ni plates. The catalyst is preferably formed so that its surface area is relatively large, for example, by arranging it to radially surround the heater in the gas reactor or by forming it to have a fin-like external shape. The carbon produced by the thermal decomposition reaction is relatively low-grade carbon and may include, for example, fine particles derived from catalysts such as Ni. More specifically, the carbon produced by the thermal decomposition reaction may be particulate carbon, fibrous carbon, or mixtures thereof. The hydrogen produced by the thermal decomposition reaction is CO ２ It's free turquoise hydrogen.

[0025] In the Boudoir step (P120), carbon and carbon dioxide are subjected to a Boudoir reaction, as shown in Figure 2. In the Boudoir step (P120), for example, the reaction shown in the following chemical equation (2) proceeds.

[0026] 0.425C+0.575CO ２ →0.85CO+0.15CO ２ ... (2)

[0027] In this embodiment, the boudoir process (P120) uses carbon produced by the pyrolysis process (P110). Therefore, from the viewpoint of efficiency, the boudoir process (P120) is preferably carried out in the gas reactor where the pyrolysis process (P110) was performed. More specifically, it is preferable that the boudoir process (P120) is performed in the gas reactor where the pyrolysis process (P110) was performed, by switching the gas supplied to the gas reactor while carbon produced by the pyrolysis reaction is still present.

[0028] The carbon dioxide used in the Boudoir process (P120) is not particularly limited and may be of any origin, such as carbon dioxide produced by steam reforming and shift reactions of methane, carbon dioxide produced by combustion reactions, or carbon dioxide recovered from the atmosphere. The Boudoir reaction occurs when the carbon dioxide supplied to the gas reactor and the carbon produced by the pyrolysis reaction are heated in the gas reactor. The temperature in the Boudoir process (P120) is not particularly limited, but from the viewpoint of improving the efficiency of the Boudoir reaction, it is preferably carried out at 800°C to 930°C, and more preferably at 830°C to 920°C. The Boudoir reaction produces carbon monoxide and carbon dioxide from carbon and carbon dioxide. In the following description, the mixed gas of carbon monoxide and carbon dioxide produced by the Boudoir reaction is also called the "carburizing gas". The proportion of carbon monoxide in the carburizing gas is not limited as long as the carbon potential is relatively high, but it is preferable that it contains 75% or more by volume of carbon monoxide, more preferably 80% or more by volume, even more preferably 85% or more by volume, and even more preferably 90% or more by volume. As an example of a carburizing gas, for example, as shown in the chemical reaction equation (2) above, it may contain about 85% by volume of carbon monoxide and about 15% by volume of carbon dioxide. Note that the higher the temperature in the boudoir process (P120), the more carbon monoxide can be produced, and thus the higher the carbon potential of the carburizing gas can be.

[0029] In the carburizing process (P130), carburization of the metal is performed using carbon monoxide and carbon dioxide generated in the Boudouard process (P120). In other words, in the carburizing process (P130), carburization of the metal is performed using the carburizing gas generated in the Boudouard process (P120). The carburizing process (P130) may be performed in the gas reactor in which the Boudouard process (P120) is performed, but from the viewpoint of system efficiency improvement, it is preferably performed in a furnace different from the gas reactor in which the Boudouard process (P120) is performed. In the carburizing process (P130), the reaction shown in the following chemical reaction formula (3) proceeds. In the following chemical reaction formula (3) and the chemical reaction formula (4) described later, "M" represents the metal used for carburization, and "M(C)" represents the carburized metal.

[0030] 2CO + 2CO ２ + M → M(C) + 3CO ２ ...(3)

[0031] The metal used for carburization is not particularly limited as long as it can be carburized. For example, Ni, Fe, etc. may be mentioned. From the viewpoint of the ability to absorb carbon, Ni is preferable, and from the economic viewpoint, Fe is preferable. The metal used for carburization is preferably formed so that its surface area is relatively large, such as in a plate shape surrounding the heater in the furnace radially, a fin shape, or a granular shape with a diameter of about several millimeters. The temperature in the carburizing process (P130) is not particularly limited, but from the viewpoint of improving the efficiency of carburization, it is preferably performed at 900 °C or higher and 950 °C or lower.

[0032] In the precipitation process (P140), carbon is precipitated on the surface of the metal by lowering the temperature compared to the carburizing process (P130). In the precipitation process (P140), the reaction shown in the following chemical reaction formula (4) proceeds.

[0033] M(C) → M + C...(4)

[0034] The precipitation step (P140) is preferably carried out in the furnace in which the carburizing step (P130) has been performed from the viewpoint of efficiency. More specifically, in the furnace in which the carburizing step (P130) has been performed, it is preferable that the precipitation step (P140) is executed by lowering the temperature in the furnace while the carburized metal is present. The temperature in the precipitation step (P140) is not particularly limited as long as it is lower than that in the carburizing step (P130), but from the viewpoint of lowering the temperature of carbon and safely recovering it, it may be about normal temperature (25°C). The temperature in the precipitation step (P140) is preferably carried out at 20°C or higher and lower than 900°C, and more preferably at 25°C or higher and 500°C or lower, from the viewpoints of improving the precipitation efficiency of carbon and lowering the temperature of the recovered carbon. The carbon precipitated by the precipitation step (P140) is discharged from the furnace and recovered. The recovery of the precipitated carbon is preferably carried out in a state where an inert gas such as nitrogen gas is purged into the furnace. The precipitated carbon is relatively high-grade carbon, and more specifically, for example, high-purity carbon having a fine structure such as carbon nanofibers can be mentioned.

[0035] In the precipitation step (P140), the supply of hydrogen can further promote the precipitation of carbon. Therefore, the precipitation step (P140) is preferably executed by lowering the temperature in a state where hydrogen is supplied, compared to the carburizing step (P130). When hydrogen is supplied in the precipitation step (P140), the reaction shown in the following chemical reaction formula (5) proceeds.

[0036] 2H ２ + CO ２ → 2H ２ O + C...(5)

[0037] The reaction shown in the above chemical equation (5) produces, for example, high-purity particulate carbon (carbon black). Here, as described above, the carbon production method of this embodiment includes a thermal decomposition step (P110), in which hydrogen is produced. For this reason, from the viewpoint of system efficiency, it is more preferable that a portion of the hydrogen produced by the thermal decomposition step (P110) is used in the precipitation step (P140). This allows CO to be introduced from outside the system to promote carbon deposition. ２ The supply of free hydrogen can be omitted. Furthermore, the supply of hydrogen in the deposition process (P140) may be omitted. Also, the deposition process (P140) is an endothermic reaction. Therefore, from the viewpoint of increasing the thermal efficiency of the system, it is preferable that the thermal energy generated in the deposition process (P140) is used in the boudoir process (P120).

[0038] The carbon production method of this embodiment described above can process carbon dioxide. More specifically, it can process carbon dioxide and produce high-quality carbon. As a result, the CO2 required for the conventional recycling of carbon dioxide can be reduced. ２ This allows for a reduction in the supply of free hydrogen. Furthermore, compared to synthetic fuels, which are one of the conventional methods of carbon dioxide recycling, it eliminates the loop between carbon dioxide capture and recycling. As a result, it enables longer-term carbon dioxide sequestration and helps to suppress the increasing costs of carbon dioxide recycling.

[0039] Furthermore, as described above, the carbon production method of this embodiment includes a thermal decomposition step (P110) before the boudoir step (P120). Therefore, equipment for methane thermal decomposition can be used to produce carbon as a raw material for the boudoir step (P120). Also, by methane thermal decomposition, CO ２Turquoise hydrogen, which is free hydrogen, can be produced as a by-product. Also, in the Boudouard process (P120), when carbon dioxide recovered from the combustion gas of fossil fuels is used, zero emissions can be achieved from the perspective of LCA (Life Cycle Assessment). Furthermore, in the Boudouard process (P120), when carbon dioxide recovered from the atmosphere or carbon dioxide recovered from the combustion gas of biomass fuel is used, negative emissions can be achieved from the perspective of LCA.

[0040] An example of a system for realizing the carbon production method of the present embodiment will be described below.

[0041] FIG. 3 is a block diagram showing a schematic configuration of a carbon production system 100. The carbon production system 100 (hereinafter also referred to as "system 100") in the present embodiment includes a first furnace 10 and a second furnace 20.

[0042] The first furnace 10 is formed by a gas reactor. In the present embodiment, in the first furnace 10, a so-called methane pyrolysis reaction and a Boudouard reaction are performed in this order. In other words, the system 100 of the present embodiment uses the first furnace 10 to serve as both a furnace for performing a pyrolysis reaction and a furnace for performing a Boudouard reaction.

[0043] FIG. 4 is an explanatory diagram for explaining the configuration of the first furnace 10. The first furnace 10 has, for example, a substantially cylindrical external shape. The first furnace 10 includes a first gas introduction part 11, a first gas discharge part 12, a second gas introduction part 13, a second gas discharge part 14, a first heater 15, and a catalyst 16. The first heater 15 is provided inside the first furnace 10 and heats the inside of the furnace. The first heater 15 has, for example, a substantially columnar external shape. The catalyst 16 is provided to promote methane pyrolysis. The catalyst 16 is formed, for example, by a plurality of metal catalyst plates that radially surround the first heater 15 inside the furnace.

[0044] The first gas inlet 11 and the first gas outlet 12 are used when carrying out a thermal decomposition reaction. The first gas inlet 11 supplies a gas containing methane into the first furnace 10. The gas containing methane supplied into the first furnace 10 is heated in the furnace and thermally decomposed into hydrogen and carbon. The first gas outlet 12 discharges a mixed gas of hydrogen produced by the thermal decomposition reaction and gas containing unreacted methane to the outside of the first furnace 10. The mixed gas discharged to the outside of the first furnace 10 may be supplied to a separator (not shown) to separate the gases, and the hydrogen that passes through this separator may be recovered as a product.

[0045] The second gas inlet 13 and the second gas outlet 14 are used when carrying out the Boudoir reaction. The second gas inlet 13 supplies carbon dioxide into the first furnace 10. The carbon dioxide supplied into the first furnace 10 and the carbon produced by the thermal decomposition reaction are heated inside the furnace, causing the Boudoir reaction to occur. This Boudoir reaction produces, for example, about 85 volume percent carbon monoxide and about 15 volume percent carbon dioxide from the carbon and carbon dioxide. The second gas outlet 14 discharges the carburizing gas containing the carbon monoxide and carbon dioxide produced by the Boudoir reaction to the outside of the first furnace 10.

[0046] In the second furnace 20 shown in Figure 3, carburizing of the metal and carbon deposition are performed in that order. In other words, in this embodiment, the system 100 uses the second furnace 20 to serve as both a furnace for carburizing and a furnace for carbon deposition. In this embodiment, the second furnace 20 also includes a pair of furnaces 28 and 29. The pair of furnaces 28 and 29 have the same configuration. In the pair of furnaces 28 and 29, carburizing and carbon deposition are performed alternately. That is, when carburizing is performed in one of the furnaces 28, carbon deposition is performed in the other furnace 29, and when carbon deposition is performed in one of the furnaces 28, carburizing is performed in the other furnace 29. Although carbon deposition is performed at a relatively low temperature, the fact that the second furnace 20 is configured to include a pair of furnaces 28 and 29 helps to suppress a decrease in the thermal efficiency of the system 100. The second furnace 20 may be formed by a single furnace instead of the pair of furnaces 28 and 29.

[0047] Figure 5 is an explanatory diagram illustrating the configuration of the second furnace 20. In Figure 5, only one of the pair of furnaces 28 and 29, furnace 28, is shown as representative of the configuration of the second furnace 20. The second furnace 20 has, for example, a substantially cylindrical external shape. The second furnace 20 comprises a third gas inlet 21, a third gas outlet 22, a fourth gas inlet 23, a fourth gas outlet 24, a second heater 25, a metal 26, and a carbon outlet 27. The second heater 25 is provided inside the second furnace 20 and heats the inside of the furnace. The second heater 25 has, for example, a substantially cylindrical external shape. The metal 26 is provided for carburizing and carbon deposition, absorbing carbon and depositing carbon on its surface. The metal 26 is formed, for example, by a plurality of metal catalyst plates that radially surround the second heater 25 inside the furnace. The carbon emission unit 27 is located vertically downward in the second furnace 20. The carbon emission unit 27 is equipped with a valve (not shown) for adjusting the amount and timing of carbon emission to the outside of the second furnace 20.

[0048] The third gas inlet 21 and the third gas outlet 22 are used during carburizing. The third gas inlet 21 supplies a carburizing gas containing carbon monoxide and carbon dioxide produced by the Boudoir reaction in the first furnace 10 into the second furnace 20. From the viewpoint of thermal efficiency, it is preferable that the carburizing gas be supplied from the first furnace 10 to the second furnace 20 at a relatively high temperature. The carburizing gas supplied into the second furnace 20 causes carburizing of the metal 26 to proceed. The third gas outlet 22 discharges the gas, whose carbon potential has decreased due to carburizing, to the outside of the second furnace 20.

[0049] After sufficient carburizing has occurred, the internal temperature of the second furnace 20 is reduced by lowering the heating temperature of the second heater 25 or by stopping heating by the second heater 25. A cooling mechanism (not shown) may be used to further accelerate the reduction in internal temperature of the second furnace 20. As the internal temperature of the second furnace 20 decreases below the temperature during carburizing, carbon precipitates on the surface of the metal 26. To further promote carbon precipitation, the second furnace 20 may be provided with a hydrogen supply unit (not shown) for supplying hydrogen. Furthermore, from the viewpoint of improving the efficiency of the system 100, hydrogen discharged from the first gas discharge unit 12 may be supplied to the second furnace 20 via this supply unit.

[0050] The fourth gas inlet 23 and the fourth gas outlet 24 are used to recover the precipitated carbon. The fourth gas inlet 23 supplies an inert gas such as nitrogen gas into the second furnace 20, and the fourth gas outlet 24 discharges the inert gas to the outside of the second furnace 20. The precipitated carbon is discharged to the outside of the second furnace 20 from the carbon outlet 27 and recovered.

[0051] The system 100 preferably further comprises a heat recovery mechanism (not shown). The heat recovery mechanism recovers thermal energy from the second furnace 20 and supplies it to the first furnace 10. The heat recovery mechanism may include, for example, a heat pump. In an embodiment in which the system 100 comprises a heat recovery mechanism, the thermal energy generated when carbon precipitates in the second furnace 20 can be recovered and used for the boudoir reaction in the first furnace 10, thereby increasing the thermal efficiency of the system 100.

[0052] (2) Figure 6 of the second embodiment is a process diagram showing the method for producing carbon in the second embodiment. Compared with the method for producing carbon in the first embodiment, the method for producing carbon in the second embodiment omits the thermal decomposition step (P110). Other than this, it is the same as the first embodiment, so a detailed explanation is omitted.

[0053] The carbon production method in the second embodiment includes a boudoir step (P120), a carburizing step (P130), and a precipitation step (P140). In the boudoir step (P120), the boudoir reaction proceeds by supplying and heating carbon and carbon dioxide, respectively. The carbon used in the boudoir step (P120) is not particularly limited, but examples include carbon produced by methane pyrolysis carried out outside the system, carbon obtained by reducing carbon dioxide or carbon monoxide, and unused coke.

[0054] The carbon production method in the second embodiment may be implemented using a carbon production system 100 (system 100) as in the first embodiment. In the system 100 shown in Figure 3, the methane pyrolysis reaction that was performed in the first furnace 10 is omitted, and the first furnace 10 may have the following configuration, for example.

[0055] Figure 7 is an explanatory diagram illustrating the configuration of the first furnace 10a in the system 100 of the second embodiment. Compared to the first furnace 10 in the system 100 of the first embodiment, the first furnace 10a may omit the first gas inlet 11, the first gas outlet 12, and the catalyst 16. In addition, the first furnace 10a is provided with a carbon supply unit 17a compared to the first furnace 10. The carbon supply unit 17a supplies solid carbon from the outside into the first furnace 10a. In the first furnace 10a, it is preferable to have carbon supplied to the inside of the first furnace 10a in advance via the carbon supply unit 17a, and then supply carbon dioxide from the second gas inlet 13.

[0056] Figure 8 is a block diagram illustrating the schematic configuration of another example of a carbon production system. This carbon production system 100b (hereinafter also referred to as "system 100b") further comprises a third furnace 30b for thermally decomposing a methane-containing gas, compared to system 100 of the second embodiment. Thus, system 100b comprises a third furnace 30b for thermally decomposing a methane-containing gas, a first furnace 10a for a boudoir reaction between carbon and carbon dioxide, and a second furnace 20 for carburizing a metal 26 with carbon monoxide and carbon dioxide recovered from the first furnace 10a, and then depositing carbon on the surface of the metal 26 by lowering the temperature from that during carburizing.

[0057] The third furnace 30b may omit the second gas inlet 13 and the second gas outlet 14 compared to the first furnace 10 in the system 100 of the first embodiment. The third furnace 30b is also provided with a carbon outlet (not shown) compared to the first furnace 10. This carbon outlet discharges carbon from the inside to the outside of the third furnace 30b. In system 100b, the carbon discharged and recovered from the third furnace 30b is supplied to the first furnace 10a. Even in this configuration of system 100b, since the boudoir reaction is carried out using carbon produced by the thermal decomposition of methane-containing gas, low-grade carbon can be effectively utilized.

[0058] The carbon production methods and carbon production systems 100 and 100b of the present disclosure described above produce carbon by processing carbon dioxide. Therefore, according to other embodiments of the present disclosure, a method for processing carbon dioxide is provided as shown below.

[0059] B. Method for Treating Carbon Dioxide Figure 9 is a process diagram showing a method for treating carbon dioxide as another embodiment of the present disclosure. The method for treating carbon dioxide includes a boudoir step (P120), a carburizing step (P130), and a precipitation step (P140). In the boudoir step (P120), carbon and carbon dioxide are subjected to a boudoir reaction as described above. In the carburizing step (P130), the metal is carburized using carbon monoxide and carbon dioxide produced in the boudoir step (P120). In the precipitation step (P140), which is performed after the carburizing step (P130), carbon is deposited on the surface of the metal by lowering the temperature compared to the carburizing step (P130).

[0060] The carbon dioxide treatment method of this disclosure can be used to treat carbon dioxide. The carbon dioxide treatment method may include the above-described pyrolysis step (P110) before the boudoir step (P120).

[0061] This disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from its spirit. For example, the technical features in each embodiment corresponding to the technical features in each form described in the summary of the invention can be replaced or combined as appropriate in order to solve some or all of the above-described problems, or to achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate.

[0062] 10, 10a...First furnace, 11...First gas inlet, 12...First gas outlet, 13...Second gas inlet, 14...Second gas outlet, 15...First heater, 16...Catalyst, 17a...Carbon supply unit, 20...Second furnace, 21...Third gas inlet, 22...Third gas outlet, 23...Fourth gas inlet, 24...Fourth gas outlet, 25...Second heater, 26...Metal, 27...Carbon outlet, 28...One of a pair of furnaces, 29...The other of a pair of furnaces, 30b...Third furnace, 100, 100b...System (Carbon production system)

Claims

1. A method for producing carbon, comprising: a boudoir step of reacting carbon and carbon dioxide in a boudoir reaction; a carburizing step of carburizing a metal with carbon monoxide and carbon dioxide produced by the boudoir step; and a precipitation step of depositing carbon on the surface of the metal by lowering the temperature after the carburizing step compared to the carburizing step.

2. A method for producing carbon according to claim 1, further comprising a thermal decomposition step of producing hydrogen and carbon by thermal decomposition of a gas containing methane, wherein the carbon produced by the thermal decomposition step is used in the boudoir step.

3. A method for producing carbon according to claim 1, further comprising a thermal decomposition step of generating hydrogen and carbon by thermal decomposing a gas containing methane, wherein the hydrogen produced by the thermal decomposition step is used in the precipitation step.

4. A method for producing carbon according to claim 1 or claim 2, wherein the boudoir step uses the thermal energy generated in the precipitation step.

5. A method for producing carbon according to claim 1 or claim 2, wherein the boudoir step is performed at a temperature of 800°C or higher and 930°C or lower.

6. A method for producing carbon according to claim 1 or claim 2, wherein the carburizing step is performed at a temperature of 900°C or higher and 950°C or lower.

7. A method for producing carbon according to claim 1 or claim 2, wherein the precipitation step is performed at a temperature of 25°C or higher and 500°C or lower.

8. A carbon production system comprising: a first furnace for a boudoir reaction between carbon and carbon dioxide; and a second furnace for carburizing a metal with carbon monoxide and carbon dioxide recovered from the first furnace, and then depositing carbon on the surface of the metal by lowering the temperature below that of the carburizing process.

9. A carbon production system according to claim 8, wherein, in the first furnace, a thermal decomposition reaction is carried out to thermally decompose a gas containing methane before the boudoir reaction, and the carbon produced by the thermal decomposition reaction is used in the boudoir reaction.

10. A carbon production system according to claim 8, further comprising a third furnace for thermally decomposing a gas containing methane, wherein carbon recovered from the third furnace is supplied to the first furnace.

11. A carbon production system according to claim 8 or claim 9, wherein the second furnace comprises a pair of furnaces, in which carburizing of the metal and precipitation of carbon are alternately performed in each of the pair of furnaces.

12. A method for treating carbon dioxide, comprising: a boudoir step of reacting carbon and carbon dioxide in a boudoir reaction; a carburizing step of carburizing a metal with carbon monoxide and carbon dioxide produced by the boudoir step; and a precipitation step of depositing carbon on the surface of the metal by lowering the temperature after the carburizing step compared to the carburizing step.

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