Solid-state carbon production method

Abstract

To provide a solid-state carbon production method capable of producing at high yield, solid-state carbon from carbon dioxide.SOLUTION: A solid-state carbon production method comprises: a first step for bringing a raw material gas including carbon dioxide and hydrogen, into contact with a catalyst for activating a methanation reaction, for producing methane and water from the raw material gas; a second step for bringing the methane produced in the first step into contact with a catalyst for activating a dry-reforming reaction, for producing carbon monoxide from the methane; and a third step for bringing the carbon monoxide produced in the second step into contact with a catalyst for activating a Boudouard reaction, for producing solid-state carbon from the carbon monoxide. In the third step, the catalyst for activating Boudouard reaction and being carried on an inorganic porous body whose void is 56% or more and catalyst carrying amount per unit volume is 0.01 g or more, is used.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing solid carbon. [Background technology]

[0002] Currently, reducing carbon dioxide emissions, which have a negative impact on the environment as a greenhouse gas, is an urgent issue, and in addition to technologies that reduce carbon dioxide emissions themselves through fuel conversion and the use of new energy sources, there is a growing need for carbon dioxide separation and capture technologies and carbon dioxide fixation technologies.

[0003] As a carbon dioxide fixation technology, for example, a method for producing solid carbon has been proposed, in which methane is produced from carbon dioxide and hydrogen by a methanation reaction, carbon monoxide is then produced from the methane and carbon dioxide by a dry reforming reaction, and solid carbon is then produced from the carbon monoxide by a Boudoir reaction (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-66417 Summary of the Invention [Problem to be solved by the invention]

[0005] Carbon dioxide fixation technology is effective not only because it can reduce carbon dioxide emissions but also because it can convert them into useful chemicals. However, because the carbon dioxide fixation process consumes energy, there is a need for a process that can produce useful chemicals from carbon dioxide in high yields. An object of the present invention is to provide a method for producing solid carbon, which is capable of producing solid carbon from carbon dioxide in a high yield. [Means for solving the problem]

[0006] The present inventors have focused on catalysts that activate the Boudoir reaction, which produces solid carbon from carbon monoxide, and have found that by supporting a catalyst that activates the Boudoir reaction on an inorganic porous material having specific properties and using this to carry out the Boudoir reaction, solid carbon can be produced from carbon dioxide in high yield.

[0007] That is, the present invention provides the following [1] to [3]. [1] A first step of contacting a raw material gas containing carbon dioxide and hydrogen with a catalyst that activates a methanation reaction to produce methane and water from the raw material gas; a second step of contacting the methane produced in the first step with a catalyst that activates a dry reforming reaction to produce carbon monoxide from the methane; A third step of contacting the carbon monoxide produced in the second step with a catalyst that activates the Boudoir reaction to produce solid carbon from the carbon monoxide. Including, In the third step, a catalyst for activating the Boudoir reaction is used, the catalyst being supported on an inorganic porous material having a porosity of 56% or more and a catalyst support amount per unit volume of 0.01 g or more. Methods for producing solid carbon. [2] The method for producing solid carbon according to [1] above, wherein the inorganic porous body is a crushed product of a fired mixture of aluminosilicate and perlite and / or volcanic ash shirasu. [3] The method for producing solid carbon according to [1] or [2] above, wherein the catalyst for activating the Boudoir reaction contains metallic iron and / or iron oxide. [Effects of the Invention]

[0008] According to the present invention, solid carbon can be produced from carbon dioxide in high yield. DETAILED DESCRIPTION OF THE INVENTION

[0009] The method for producing solid carbon of the present invention comprises a first step, a second step, and a third step. The reactions in each step are represented by the following formulas (i) to (iii): A feed gas containing carbon dioxide and hydrogen is supplied to a first reactor having a catalyst for activating a methanation reaction (hereinafter also referred to as a "methanation reaction catalyst"); a product gas containing methane and carbon dioxide is discharged from the first reactor; this product gas is then supplied to a second reactor having a catalyst for activating a dry reforming reaction (hereinafter also referred to as a "dry reforming reaction catalyst"); a product gas containing carbon monoxide and hydrogen is discharged from the second reactor; this product gas is then supplied to a third reactor having a catalyst for activating a Boudoir reaction (hereinafter also referred to as a "Boudoir reaction catalyst"); solid carbon is precipitated. That is, the production method of the present invention converts carbon dioxide to carbon monoxide and then precipitates solid carbon. Each step is described below.

[0010] First step: CO2 + 4H2 → CH4 + 2H2O (i) Second step: CO2 + CH4 → 2CO + 2H2(ii) Third step: 2CO → C + CO2(iii)

[0011] (First step) This step is a step in which a feed gas containing carbon dioxide and hydrogen is brought into contact with a methanation reaction catalyst in a first reactor to produce methane and water. According to the stoichiometric relationship shown in equation (i) above, 1 mol of carbon dioxide and 4 mol of hydrogen produce 1 mol of methane and 2 mol of water vapor. However, even if the H2 / CO2 molar ratio in the feed gas is the theoretical value of 4, not all of the carbon dioxide and hydrogen react to produce 1 mol of methane. That is, the product gas discharged from the first step is a mixed gas consisting of methane and water vapor produced in the methanation reaction and unreacted carbon dioxide and hydrogen. Therefore, the inventors found that when the H2 / CO2 molar ratio in the feed gas was reduced below the theoretical value of 4, the conversion rate of carbon dioxide to methane decreased and the molar ratio of carbon dioxide to methane (CO2 / CH4) approached 1, which is suitable for the subsequent dry reforming reaction. Therefore, by reducing the amount of hydrogen in the feed gas and increasing the proportion of carbon dioxide in the product gas, the dry reforming reaction following the methanation reaction can proceed more efficiently and for a longer period of time. Therefore, in this step, it is preferable to keep the H2 / CO2 molar ratio in the feed gas low.

[0012] From the viewpoint of promoting the dry reforming reaction, the H2 / CO2 molar ratio in the raw material gas is preferably less than 4.0, more preferably 3.5 or less, even more preferably 3.2 or less, and even more preferably 3.0 or less. From the viewpoint of promoting the methanation reaction, the H2 / CO2 molar ratio in the raw material gas is preferably 1.5 or more, more preferably 1.8 or more, and even more preferably 2.0 or more.

[0013] The feed gas may be a mixture of carbon dioxide and hydrogen in a predetermined molar ratio and supplied to the first reactor, or carbon dioxide and hydrogen may be supplied to the first reactor via separate pipes so that the carbon dioxide and hydrogen in the feed gas have a predetermined molar ratio in the first reactor. In order to adjust the H2 / CO2 molar ratio in the feed gas, it is preferable to install valves and sensors capable of adjusting the flow rates of carbon dioxide and hydrogen.

[0014] The flow rate of the raw material gas can be selected appropriately, but from the viewpoint of promoting the methanation reaction, the total flow rate of carbon dioxide and hydrogen is preferably 0.02 to 1.00 m / sec, more preferably 0.05 to 0.50 m / sec. The space velocity (SV) of the raw gas is set to 500 to 50,000 h from the viewpoint of promoting the methanation reaction. -1 is preferable, and 2000 to 20,000 hours -1 is more preferred.

[0015] The carbon dioxide may be carbon dioxide filled in a commercially available cylinder, but is preferably carbon dioxide derived from atmospheric carbon dioxide or exhaust gas. Examples of exhaust gas include combustion exhaust gas and calcination exhaust gas. Examples of combustion exhaust gas include exhaust gas generated by the combustion of fuel in thermal power plants, boilers, etc., and exhaust gas generated by the incineration of garbage in waste disposal plants. Examples of calcination exhaust gas include cement kiln exhaust gas generated by the calcination of clinker raw materials in cement kilns, and biomass exhaust gas generated by methane fermentation of biomass. Since exhaust gas contains sulfur oxides, nitrogen oxides, etc. in addition to carbon dioxide, the exhaust gas may be treated with a desulfurization device or a denitrification device to remove sulfur oxides and nitrogen oxides. Examples of hydrogen include, but are not limited to, hydrogen stored in a commercially available cylinder and hydrogen obtained by electrolyzing water.

[0016] The first reactor is not particularly limited as long as it can pass the raw material gas and discharge the produced gas, but an example of such a reactor is a cylindrical body. The shape of the cylindrical body may be either cylindrical or rectangular. A gas inlet pipe for supplying the raw material gas is installed at one end of the first reactor, and a gas outlet pipe for discharging the produced gas is installed at the other end. The size of the first reaction tube can be appropriately selected depending on the production scale etc., and in the case of a cylindrical shape, the inner diameter is, for example, 0.005 to 10 m and the length is 0.5 to 10 m. The material of the first reaction tube is not particularly limited as long as it has high heat resistance, and examples thereof include metal, glass, and quartz.

[0017] The first reactor may be, for example, one equipped with a gas flow pipe filled with a methanation reaction catalyst and a heating furnace capable of heating the gas flow pipe to, for example, 300 to 550° C., and may be, for example, an atmospheric pressure flow reactor that is a fixed gas flow pipe. In this case, the raw material gas flowing through the gas flow pipe comes into contact with the methanation reaction catalyst filled in the gas flow pipe and heated by the heating furnace, thereby producing methane from the raw material gas.

[0018] The methanation reaction catalyst is not particularly limited as long as it can produce methane from carbon dioxide and hydrogen, and examples thereof include nickel (Ni), ruthenium (Ru), zirconium (Zr), platinum (Pt), and rhodium (Rh). Note that the catalyst can be used alone or in combination of two or more. The catalyst may also be supported on a carrier, and examples of the carrier include various metal oxides, aluminosilicates, and silica. Among these, metal oxides are preferred, and transition metal oxides are more preferred. Examples include CeO2, ZrO2, and Y2O3. The carrier may be used alone or in combination of two or more.

[0019] The catalyst supported on a carrier may be used by being coated on a metal plate from the viewpoint of ensuring the space velocity of the raw material gas. The shape of the metal plate is not particularly limited as long as it ensures the space velocity of the raw material gas and has a large surface area, and examples thereof include a spiral shape and a honeycomb shape. When the catalyst is coated on a spiral metal plate, for example, it can be produced by forming a metal plate member made of aluminum, stainless steel, or the like into a spiral shape and coating it with a paste-like catalyst.

[0020] The product gas discharged from the first step may be supplied directly to the second reactor used in the second step, but since the product gas contains water vapor, there is a risk that the conversion rate to methane may decrease. Therefore, it is preferable to provide a water vapor removal facility at the outlet of the first reactor and actively remove water vapor before supplying the product gas to the second reactor.

[0021] (Second step) This step is a step in which the methane produced in the first step is brought into contact with a dry reforming reaction catalyst in a second reactor to produce carbon monoxide from the methane. According to the stoichiometric relationship shown in the above formula (ii), 2 mol of carbon monoxide and 2 mol of hydrogen are produced from 1 mol of methane and 1 mol of carbon dioxide produced in the first step via a catalyst, but the product gas discharged from the second step is a mixed gas containing hydrogen, methane, carbon dioxide, and carbon monoxide.

[0022] The second reactor may include, for example, a gas flow pipe filled with a dry reforming reaction catalyst and a heating furnace capable of heating the gas flow pipe to, for example, 700 to 1000° C. The second reactor may be the same as the first reactor, and the specific configuration is as described above.

[0023] The total amount of the raw material gas can be set appropriately, for example, to 0.03 to 0.42 m / sec. The space velocity (SV) of the raw gas is 1000 to 20,000 h -1 is preferable, and 1300 to 15,000 hours -1 is more preferred.

[0024] The dry reforming reaction catalyst is not particularly limited as long as it can produce carbon monoxide and hydrogen from carbon dioxide and methane, and examples thereof include nickel (Ni) and rhodium (Rh). Note that the catalyst can be used alone or in combination of two or more types. The catalyst may be supported on a carrier, and examples of the carrier include various oxides and aluminosilicates such as CeO2, ZrO2, YO3, and Al2O3. The carrier may be a single type or a combination of two or more types. Among these, γ-Al2O3 is preferred from the viewpoint of promoting the dry reforming reaction.

[0025] The catalyst supported on a carrier may be used by being coated on a metal plate from the viewpoint of ensuring the space velocity of the raw material gas. The shape of the metal plate is not particularly limited as long as it ensures the space velocity of the raw material gas and has a large surface area, and examples thereof include a spiral shape and a honeycomb shape. When the catalyst is coated on a spiral metal plate, for example, it can be produced by forming a metal plate member such as stainless steel into a spiral shape and coating it with a paste-like catalyst.

[0026] The product gas discharged from the second step may be directly supplied to the third reactor used in the third step. Although water vapor is not basically generated in the dry reforming reaction, a water vapor removal facility may be provided at the outlet of the second reactor.

[0027] (Third step) This step is a step in which the carbon monoxide produced in the second step is brought into contact with a Boudoir reaction catalyst in a third reactor to produce solid carbon from the carbon monoxide, and is characterized by using a Boudoir reaction catalyst supported on an inorganic porous material having a porosity of 56% or more and a catalyst loading per unit volume of 0.01 g or more. According to the stoichiometric relationship shown in the above formula (iii), 2 mol of carbon monoxide is converted to 1 mol of solid carbon and 1 mol of carbon dioxide via the catalyst, and the product gas discharged from the third step is a mixed gas containing hydrogen, methane, carbon dioxide, carbon monoxide, and water vapor. Note that the solid carbon deposits on the surface of the catalyst, and therefore, the deposited solid carbon is recovered together with the catalyst.

[0028] The third reactor can include a gas flow pipe filled with a Boudoir reaction catalyst and a heating furnace capable of heating the gas flow pipe to, for example, 400 to 500° C. The third reactor can be the same as the first reactor, and its specific configuration is as described above.

[0029] The total amount of the raw material gas can be set appropriately, for example, to 0.05 to 0.15 m / sec. The space velocity (SV) of the raw gas is 500 to 2000 h -1 is preferable, 750 to 1500 hours -1 is more preferred.

[0030] The Boudouard reaction catalyst is not particularly limited as long as it can produce solid carbon from carbon monoxide, and examples thereof include Fe (metallic iron) and iron oxide. Examples of iron oxide include wustite (FeO), magnetite (Fe3O4), and hematite (Fe2O3). Note that one or more catalysts can be used in combination. Among them, from the viewpoint of improving the recovery rate of solid carbon, Fe (metallic iron) and iron oxide are preferred, iron oxide is more preferred, and magnetite is even more preferred. Note that, since solid carbon deposition by the Boudouard reaction occurs with cementite (Fe3C) as a nucleus, cementitized material may be used in advance.

[0031] The inorganic porous body supporting the Boudoir reaction catalyst has a controlled porosity and catalyst support amount per unit volume. The porosity of the inorganic porous body is 56% or more, and from the viewpoint of improving the recovery rate of solid carbon, it is preferably 56.5% or more, more preferably 57% or more. The upper limit of the porosity is not particularly limited, but from the viewpoint of ensuring strength, it is preferably 65% ​​or less, more preferably 60% or less. The amount of catalyst supported per unit volume of the inorganic porous material is 0.01 g or more, but from the viewpoint of improving the recovery rate of solid carbon, it is preferably 0.013 g or more, more preferably 0.015 g or more per unit volume. The upper limit of the catalyst supported amount is not particularly limited, but from the viewpoint of production costs, it is preferably 0.05 g or less, more preferably 0.10 g or less.

[0032] In this specification, "void ratio" is analyzed by the following method. That is, the "full volume ratio" of the inorganic porous body is calculated by the following formula (1), and then the void ratio of the inorganic porous body is calculated by the following formula (2). In this specification, "volume" means aerated bulk density, which is measured in accordance with the Japan Powder Process Industry and Engineering Association standard SAP 01-79-1979 "Method for measuring bulk density of granulated materials." In addition, the bone dry density is measured in accordance with JIS A 1100:2020.

[0033] Actual area ratio [%] = (volume weight) / (absolute dry density) × 100 (1) Porosity [%] = 100-actual area ratio [%] (2)

[0034] In this specification, the "amount of catalyst supported per unit volume" is measured by the following method. That is, the "apparent volume" of the inorganic porous material is calculated by the following formula (3), and then the amount of catalyst supported per unit volume is calculated by the following formula (4). Specifically, the method is as follows: 20 inorganic porous particles are collected and weighed. Next, 20 inorganic porous particles, 10 g of magnetite, and 40 cm of water are mixed. 3The mixture is stirred and mixed for 2 minutes to prepare a slurry, and the stirring is stopped immediately to precipitate the inorganic porous material carrying magnetite in the slurry. The slurry is then filtered to recover the precipitate, which is then dried at 110°C for 18 hours, and the mass of the dried product is measured. The amount of magnetite is then calculated by subtracting the mass of 20 inorganic porous particles from the mass of the dried product. The "apparent volume" is then calculated using the following formula (3). In the following formula (3), "capacity" is synonymous with "capacity" in the above formula (1). The amount of catalyst carried per unit volume is then calculated using the following formula (4).

[0035] Apparent volume [cm 3 ] = (mass of inorganic porous particles) / (volume of inorganic porous material) (3) Catalyst loading per unit volume [g / cm 3 ] = (mass of magnetite) / (apparent volume) (4)

[0036] An example of an inorganic porous material having such properties is a crushed sintered mixture of aluminosilicate and perlite and / or volcanic ash shirasu. Here, in this specification, "perlite" refers to igneous rock that has been heated and foamed. The perlite may be obsidian perlite or perlite. Commercially available partlite may be used, such as Taiheiyo Partlite (manufactured by Taiheiyo Cement Corporation).

[0037] From the viewpoint of improving the recovery rate of solid carbon, the mass ratio (A / B) of the aluminosilicate (A) to the total amount (B) of perlite and volcanic ash silt in the mixture is preferably 7 or more, more preferably 7.5 or more, even more preferably 8 or more, and is preferably 20 or less, more preferably 15 or less, even more preferably 10 or less.

[0038] The mixture can be fired, for example, in an electric furnace. The firing temperature is, for example, 950 to 1200°C, and preferably 1000 to 1150°C. The firing time is, for example, 0.1 to 2 hours, and preferably 0.2 to 1 hour. Note that firing can be carried out under atmospheric pressure, and there is no need to reduce the pressure.

[0039] The sintered product can be crushed using a crusher or a pulverizer. Examples of crushers include jaw crushers, impact crushers, hammer crushers, roll crushers, and rotary crushers. Examples of pulverizers include disc mills, Wonder Blenders, rod mills, ball mills, and roller mills. Crushing can be carried out until the particle size of the sintered product is, for example, about 3 to 5 mm. Excessive crushing tends to destroy closed pores, increase bulk density, and hinder gas flow. After crushing, the sintered product may be sieved to collect sintered products of a desired particle size. Sieving can be performed using a sieve separator, and any of a vibrating type, an in-plane moving type, a rotary type, and a stationary type can be used for the sieving.

[0040] In the third step, solid carbon is precipitated on the surface of the catalyst supported on the inorganic porous material by a Boudoir reaction from carbon monoxide. The solid carbon can then be recovered by recovering the catalyst on which the solid carbon has precipitated. Note that the gas discharged from the third step contains, for example, carbon dioxide, and may be circulated to the first step.

[0041] As described above, in the production method of the present invention, the steps from supplying the raw material gas to the first reactor to depositing solid carbon in the third reactor can be carried out continuously, and therefore solid carbon can be produced efficiently. Moreover, according to the present invention, solid carbon can be produced with a high yield of usually 25% or more, preferably 30% or more.

[0042] The present invention has been described in detail above based on its embodiments. However, the present invention is not limited to the above embodiments. Various modifications of the present invention are possible without departing from the spirit and scope of the present invention. For example, in the above embodiment, the third step of supplying a raw material gas into a batch-type fixed-bed reactor packed with a Boudoir reaction catalyst supported on an inorganic porous material was described. However, the present invention is not limited to this. Instead of a batch-type fixed-bed reactor, for example, a rotary continuous reactor such as a rotary kiln or a cylindrical fixed reactor equipped with a screw extruder or the like inside the reactor may be used. This allows the catalyst on which solid carbon is precipitated to be continuously discharged from the third reactor, thereby preventing clogging of the reactor with precipitated solid carbon and facilitating the flow of the raw material gas. Furthermore, it is possible to continuously supply new catalyst into the reactor, allowing the Boudoir reaction to proceed more efficiently and for a longer period of time. [Example]

[0043] The following examples will explain the present invention in more detail, but the present invention is not limited to the examples below.

[0044] 1. Analysis of porosity of inorganic porous materials The "full volume ratio" was calculated using the following formula (1), and then the void ratio was calculated using the following formula (2). The "volume" was measured in accordance with the Japan Powder Process Industry and Engineering Association standard SAP 01-79-1979 "Method for measuring bulk density of granulated materials." The bone dry density was measured in accordance with JIS A 1100:2020.

[0045] Actual area ratio [%] = (volume weight) / (absolute dry density) × 100 (1) Porosity [%] = 100-actual area ratio [%] (2)

[0046] 2. Analysis of catalyst loading per unit volume of inorganic porous material Twenty inorganic porous particles were collected and weighed. Twenty inorganic porous particles, 10 g of magnetite, and 40 cm of water were mixed. 3The mixture was stirred and mixed for 2 minutes to prepare a slurry, and the stirring was stopped immediately to precipitate the inorganic porous material carrying magnetite in the slurry. The slurry was then filtered to recover the precipitate, which was then dried at 110°C for 18 hours, and the mass of the dried product was measured. The amount of magnetite was then calculated by subtracting the mass of 20 inorganic porous particles from the mass of the dried product. The "apparent volume" was then calculated using the following formula (3). The amount of catalyst carried per unit volume was then calculated using the following formula (4).

[0047] Apparent volume [cm 3 ] = (mass of inorganic porous particles) / (volume of inorganic porous material) (3) Catalyst loading per unit volume [g / cm 3 ] = (mass of magnetite) / (apparent volume) (4)

[0048] 3. Calculation of solid carbon recovery rate The recovery rate of solid carbon was calculated by the following formula (5). Solid carbon recovery rate (%) = C / D × 100 (5) (In formula (5), C represents the number of moles of precipitated solid carbon, and D represents the number of moles of carbon dioxide supplied to the first reactor.)

[0049] The number of moles (C) of precipitated solid carbon was calculated by the following formula (6). Number of moles of precipitated solid carbon (C) = EF (6) (In formula (6), E represents the number of moles of carbon dioxide supplied to the first reactor, and F represents the total number of moles of carbon monoxide, carbon dioxide, and methane discharged from the third reactor.)

[0050] The number of moles (E) of carbon dioxide supplied to the first reactor was calculated by the following formula (7). moles of carbon dioxide fed to the first reactor (E) =(G × 1000) / 22.4(L / mol) (7) (In formula (7), G represents the amount of carbon dioxide (mL / min) supplied to the first reactor.)

[0051] Furthermore, the total number of moles (F) of carbon monoxide, carbon dioxide, and methane discharged from the third reactor was calculated by the following formula (8). Total moles of carbon monoxide, carbon dioxide, and methane discharged from the third reactor (F) =(H × 1000) × (J / 100) / 22.4 (L / mol) (8) (In equation (8), H represents the gas flow rate (mL / min) at the outlet of the third reactor, and J represents the total concentration (vol%) of carbon monoxide, carbon dioxide, and methane discharged from the third reactor.)

[0052] (1) Experimental equipment The experimental apparatus used in this example is outlined below: The experimental apparatus used consisted of a first reactor that produced methane and water from a feed gas containing carbon dioxide and hydrogen through a methanation reaction, a second reactor that produced hydrogen and carbon monoxide from the methane produced in the first reactor and unreacted carbon dioxide through a dry reforming reaction, and a third reactor that precipitated solid carbon from the hydrogen and carbon monoxide through a Boudoir reaction, all connected in series through gas flow paths. A temperature-controllable one-zone electric furnace (tubular electric furnace TMF-500N manufactured by AS ONE Corporation, effective length 300 mm) was used as the heating furnace for the first reactor, second reactor, and third reactor. A quartz tube with an inner diameter of 8 mm and a length of 600 mm was used as the atmospheric pressure flow-type reaction tube for the first reactor and second reactor, and a quartz tube with an inner diameter of 21 mm and a length of 600 mm was used as the atmospheric pressure flow-type reaction tube for the third reactor. Inside the quartz tubes of the first, second and third reactors, at the positions where the temperature control thermocouples of the heating furnaces were installed, two, two and eight catalysts, each with a spiral structure coated on its surface with 10 wt% Ni / CeO2, 10 wt% Ni / γ-Al2O3 and magnetite, were installed, respectively.

[0053] (2) Preparation of catalyst The methanation catalyst was prepared as follows. Specifically, 10 wt% Ni(NO3)2·6H2O (98% Ni, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was supported on CeO2 (reagent, manufactured by Kanto Chemical Co., Ltd.) by evaporation to dryness. After the support was loaded, it was calcined in air at 500°C for 2 hours to separate the nitric acid component. After cooling, the calcined product was mixed with distilled water and ground in a mortar to produce a Ni / CeO2 paste. This Ni / CeO2 paste was applied to the surface of a spirally twisted aluminum plate (JIS A1100 H14, 7 mm wide x 50 mm long, 1.5 mm thick). This paste was then repeatedly dried with cold air and immersed in water until a sufficient amount of Ni / CeO2 catalyst was supported to achieve the desired methanation reaction. The reforming catalyst was prepared as follows: Commercially available γ-Al2O3 (C20 manufactured by Nippon Light Metal Co., Ltd.) was used as a support, and 10 wt% Ni(NO3)2·6H2O (98% manufactured by Wako Pure Chemical Industries) was supported by evaporation to dryness. The Ni / γ-Al2O3 paste was then applied to a spirally twisted stainless steel plate (SUS304, width 7 mm x length 50 mm, thickness 0.5 mm). The Boudoir reaction catalyst was prepared as follows: Magnetite (FeO reagent: 98% manufactured by Wako Pure Chemical Industries, Ltd.) was used as a precursor, and distilled water was added to the magnetite to form a paste, which was then applied to the surface of a spirally twisted stainless steel plate (SUS304, width 7 mm × length 50 mm, thickness 1 mm).

[0054] (3) Production of solid carbon After preparing each reactor, the catalyst and catalyst precursor were reduced by holding the reactor at 500°C for 1 hour while flowing hydrogen at 200 mL / min. The temperatures of the first, second, and third reactors were then controlled to 300°C, 800°C, and 450°C, respectively, with hydrogen flowing. Once all reactors reached the designated temperatures, H2 and CO2 were supplied to the first reactor at designated flow rates from standard H2 and CO2 gas cylinders via mass flow controllers and gas mixers. Moisture removal traps and gas sampling holes were installed between the first and second reactors, between the second and third reactors, and at the gas outlet of the third reactor to condense and separate water vapor. A wet gas meter was installed at the outlet of the third reactor to measure the gas flow rate. The gas passing through the wet gas meter was routed to an outdoor abatement facility. If necessary, sampling was performed using a syringe through the gas sampling hole, and H, N, O, CH, CO, and CO were quantitatively analyzed using a gas chromatograph (Agilent 990 Micro GC, manufactured by Agilent). After the experiment was completed, the third reactor was sufficiently cooled, and the mass of solid carbon precipitated in the quartz tube was measured.

[0055] Comparative Example 1 For the inorganic porous body of the comparative example, a clay calcined product obtained by firing Gaime clay at 950°C for 10 minutes was used. The dried Gaime clay lumps were crushed to form disk-shaped molded bodies with an outer diameter of approximately 4 cm and a thickness of approximately 1 cm, which were then fired in an electric furnace in an air atmosphere at 950°C for 10 minutes. After cooling, the molded bodies were crushed to a size of approximately 5 mm. The density of the calcined body was 0.44 g / cm. 3 , specific gravity is 0.97g / cm 3The water absorption was 56%. A paste made by adding water to magnetite was applied to the surface of the calcined product and then dried to prepare a Boudoir reaction catalyst. 8.225 g of this catalyst was placed in the homogenizing zone of the third reactor. Prior to the production of solid carbon, the first, second, and third reactors were heated to a set temperature of 550°C for approximately 1 hour while hydrogen was flowing through them at a rate of 200 mL / min to reduce the catalysts placed inside. Next, while hydrogen was flowing through them, the temperatures of the first, second, and third reactors were set to 300°C, 800°C, and 450°C, respectively. After the temperatures of each reactor reached the predetermined temperatures, the supply of raw material gas consisting of hydrogen and carbon dioxide to the first reactor was initiated, and solid carbon was produced for 3 hours. Hydrogen was supplied to the first reactor at 200 mL / min and carbon dioxide at 86 mL / min via mass flow controllers so that the H2 / CO2 molar ratio of the feed gas supplied to the first reactor was approximately 2.3. After cooling, the deposited solid carbon and catalyst were removed from the third reactor, and the mass of the deposited solid carbon was calculated. The recovered amount of solid carbon was 0.853 g. The gas flow rate from the gas outlet of the third reactor was 140 mL / min. The concentrations of H2, CH4, CO2, and CO were 51.8 vol%, 3.8 vol%, 7.1 vol%, and 37.3 vol%, respectively, resulting in a solid carbon recovery rate of 22%. The results are shown in Table 1.

[0056] Example 1 The inorganic porous body used in the experimental example was a fired mixture of Gaime clay and perlite. The dried Gaime clay lumps were powdered, and Gaime clay and perlite (manufactured by Toho Perlite Co., Ltd.) were mixed in a mass ratio of 8:1. Water was added and the mixture was kneaded to form a mass, which was then dried and fired in an electric furnace in an air atmosphere at 1150°C for 1 hour. After cooling, it was crushed into particles of approximately 5 mm in size. The density of this porous body was 0.47 g / cm. 3As in the Comparative Example, a paste made by adding water to magnetite was applied to the surface of this porous body, and then dried to obtain a Boudoir reaction catalyst. 8.041 g of the porous body carrying magnetite was placed in the homogenizing zone of the third reactor, and solid carbon was collected for 3 hours as in Comparative Example 1. Hydrogen was supplied to the first reactor at 200 mL / min and carbon dioxide at 88 mL / min via mass flow controllers so that the H2 / CO2 molar ratio of the feed gas supplied to the first reactor was approximately 2.3. After cooling, the deposited solid carbon and catalyst were removed from the third reactor, and the mass of the deposited solid carbon was calculated. The recovered amount of solid carbon was 1.739 g. The gas flow rate from the gas outlet of the third reactor was 135 mL / min. The concentrations of H2, CH4, CO2, and CO were 54.3 vol%, 7.1 vol%, 18.1 vol%, and 20.5 vol%, respectively, resulting in a solid carbon recovery rate of 30%. The results are shown in Table 1.

[0057] [Table 1]

[0058] Table 1 shows that solid carbon can be produced from carbon dioxide in high yield by carrying out the Boudoir reaction using a Boudoir reaction catalyst supported on an inorganic porous material having specific properties.

Claims

1. a first step of contacting a feed gas containing carbon dioxide and hydrogen with a catalyst that activates a methanation reaction to produce methane and water from the feed gas; a second step of contacting the methane produced in the first step with a catalyst that activates a dry reforming reaction to produce carbon monoxide from the methane; a third step of contacting the carbon monoxide produced in the second step with a catalyst that activates the Boudoir reaction to produce solid carbon from the carbon monoxide; Including, In the third step, a catalyst for activating the Boudoir reaction is used, the catalyst being supported on an inorganic porous material having a porosity of 56% or more and a catalyst support amount per unit volume of 0.01 g or more. Methods for producing solid carbon.

2. 2. The method for producing solid carbon according to claim 1, wherein the inorganic porous material is a crushed product of a fired mixture of aluminosilicate and perlite and / or volcanic ash shirasu.

3. 3. The method for producing solid carbon according to claim 1, wherein the catalyst for activating the Boudoir reaction comprises metallic iron and / or iron oxide.

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