Solid carbon deposition method and solid carbon deposition system

Abstract

To provide a deposition method of solid-state carbon and a deposition system of solid-state carbon capable of improving a recovery rate of solid-state carbon deposited from a raw material gas in CO2 stabilization.SOLUTION: A deposition method of solid-state carbon includes a step for bringing a raw material gas containing carbon dioxide and hydrogen into contact with a catalyst for activating methanation reaction to form methane and water from the raw material gas, a step for heating while bringing the formed methane into contact with a catalyst for activating dry reforming reaction to convert the methane to carbon monoxide, and a step for bringing the carbon monoxide obtained by conversion into contact with a catalyst for activating Boudoir reaction to deposit solid-state carbon from the carbon monoxide. The raw material gas has a molar ratio of H2 / CO2 of 1.5 or more and 3.5 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Currently, there is an urgent need worldwide to reduce and fix carbon dioxide, which has a negative impact on the environment as a greenhouse gas. In response to this, various technologies are being researched and developed for practical use, including CO2 emission reduction technology, CO2 separation and capture technology, CO2 utilization technology, and CO2 fixation technology.

[0003] As a method for effectively utilizing carbon dioxide, for example, it is known that methane can be synthesized by a methanation reaction when a mixed gas of carbon dioxide and hydrogen is passed through in the presence of a catalyst heated to 250 to 500°C (see Patent Document 1). Also known is a technique for precipitating solid carbon by high-temperature pyrolysis of methane (see Patent Documents 2 to 5).

[0004] Patent Document 2 discloses a continuous carbon removal system in which a first reactor that causes a methanation reaction without using a catalyst and a second reactor that decomposes methane under temperature conditions of 1200°C or higher are connected in series.

[0005] Patent Document 3 discloses a method for fixating carbon dioxide, which includes a first reaction step in which carbon dioxide and hydrogen are reacted in the presence of a catalyst to produce a mixed gas containing methane and water, and a second reaction step in which the methane gas obtained in the first reaction step is used as a raw material to produce at least one carbon product selected from the group consisting of carbon, graphite, carbon nanotubes, and diamond.

[0006] In Patent Document 4, a methanation reactor that contacts a raw material gas containing carbon dioxide and hydrogen with a catalyst for activating the methanation reaction to produce methane and hydrogen from the raw material gas, and a methane pyrolysis reactor that decomposes methane into solid carbon and hydrogen by heating the methane produced in the methanation reactor are disclosed, including a carbon dioxide fixation system.

[0007] In Patent Document 5, a mixed gas with a carbon dioxide to methane ratio of 7:3 is passed through a pre-reactor filled with 30 wt% Ni / SiO2 catalyst and reacted at a reaction temperature of 550 °C for a certain period of time by a heating furnace to convert it into a mixed gas of carbon dioxide, methane, hydrogen, and carbon monoxide. Then, it is passed through a main reactor filled with 50 wt% Fe / SiO2 catalyst mainly composed of iron, and a technique is disclosed in which carbon dioxide is subjected to a catalytic reduction reaction with hydrogen at a low temperature of 400 °C by a heating furnace to deposit carbon.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, the above Patent Documents 2 to 4 do not disclose the composition ratio of the raw material gas supplied to the reactor where the methanation reaction occurs. Patent Document 5 discloses the composition ratio of the raw material gas, but only mentions that the ratio of carbon dioxide to methane is 7:3. Therefore, the composition ratio of the raw material gas has not been fully investigated, and there is still room for improvement.

[0010] The present invention has been made in view of the above circumstances, and aims to provide a solid carbon deposition method and a solid carbon deposition system that make it possible to improve the recovery rate of solid carbon deposited from a raw material gas in the fixation of CO2. [Means for solving the problem]

[0011] (1) In order to achieve the above object, the method for precipitating solid carbon of the present invention includes the steps of: bringing a feed gas containing carbon dioxide and hydrogen into contact with a catalyst that activates a methanation reaction to produce methane and water from the feed gas; heating the produced methane in contact with a catalyst that activates a dry reforming reaction to convert the methane into carbon monoxide; and bringing the converted carbon monoxide into contact with a catalyst that activates a Boudoir reaction to precipitate solid carbon from the carbon monoxide, wherein the feed gas has a H2 / CO2 molar ratio of 1.5 or more and 3.5 or less.

[0012] (2) In the method for depositing solid carbon of the present invention, the raw material gas has a molar ratio of H2 / CO2 of 2.1 or more and 3.2 or less.

[0013] (3) In the method for depositing solid carbon of the present invention, the raw material gas has a molar ratio of H2 / CO2 of 2.3 or more and 3.0 or less.

[0014] (4) The present invention also provides a solid carbon deposition system for depositing solid carbon from a feed gas containing carbon dioxide and hydrogen, comprising: a first reactor that brings the feed gas into contact with a catalyst that activates a methanation reaction to produce methane and water from the feed gas; a second reactor that heats the produced methane in contact with a catalyst that activates a dry reforming reaction to convert the methane to carbon monoxide; a third reactor that brings the converted carbon monoxide into contact with a catalyst that activates a Boudoir reaction to precipitate the solid carbon from the carbon monoxide; and a control unit that controls the feed gas to be supplied to the first reactor, wherein the control unit controls the H / CO molar ratio in the feed gas to be supplied to the first reactor to be within a range specified by a user. [Effects of the Invention]

[0015] According to the present invention, it is possible to improve the recovery rate of solid carbon precipitated from the feed gas in the fixation of CO2. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing the configuration of a solid carbon deposition device according to the present invention. [Figure 2] 1 is a schematic diagram showing the configuration of a solid carbon deposition system according to the present invention. [Figure 3] FIG. 1 is a schematic diagram showing a spiral catalyst. DETAILED DESCRIPTION OF THE INVENTION

[0017] [principle] The following reaction formulas are considered as reactions for precipitating solid carbon from carbon dioxide, methane, and carbon monoxide, respectively. CO2→C+O2ΔH=395kJ / mol…(Formula 1) CH4→C+2H2ΔH=75kJ / mol…(Formula 2) 2CO→C+CO2ΔH=-172kJ / mol…(Formula 3) CO+H2→C+2H2O ΔH=-131kJ / mol…(Formula 4) CO2+2H2→C+H2O ΔH=-90kJ / mol…(Formula 5)

[0018] As shown in Equation 1, the Gibbs free energy of the direct decomposition reaction of carbon dioxide is 395 kJ / mol, requiring a large amount of energy. In contrast, as shown in Equation 2, it is possible to precipitate solid carbon by thermally decomposing methane at high temperatures. In this case, carbon dioxide is converted to methane, which is then thermally decomposed. However, Equation 2 also requires a large amount of energy, as it is an endothermic reaction with a Gibbs free energy of 75 kJ / mol. In Equation 1 and Equation 2, providing external energy as thermal energy requires high temperatures of 1000°C or higher, resulting in significant costs.

[0019] In contrast, when solid carbon is deposited from carbon monoxide, the reaction rate is -172 kJ / mol in Equation 3 and -131 kJ / mol in Equation 4, which is an exothermic reaction. Therefore, there is no need to provide a large amount of energy to the reactor, making it possible to deposit solid carbon at low cost. Furthermore, since Equation 5 is an exothermic reaction of -90 kJ / mol, it is also possible to deposit solid carbon at low cost when depositing solid carbon from carbon dioxide and hydrogen.

[0020] Therefore, it is thought that carbon dioxide can be converted to solid carbon at low cost by converting it to carbon monoxide and then precipitating solid carbon, or by precipitating solid carbon from carbon dioxide and hydrogen.

[0021] Based on the above, in the present invention, solid carbon is precipitated from a raw material gas containing carbon dioxide and hydrogen according to the following reaction formula. First reaction: CO2 + 4H2 → CH4 + 2H2O ΔH = -165 kJ / mol… (Equation 6) Second reaction: CO2+CH4→2CO+2H2ΔH=248kJ / mol…(Equation 7) Third reaction: 2CO → C + CO2 ΔH = -172 kJ / mol (Equation 8)

[0022] As described above, in the present invention, first, a methanation reaction is carried out to convert carbon dioxide and hydrogen into methane, as shown in Equation 6. Next, a dry reforming reaction is carried out to convert carbon dioxide and methane into carbon monoxide, as shown in Equation 7. Then, solid carbon is precipitated from carbon monoxide by the Boudoir reaction, as shown in Equation 8. By combining the dry reforming reaction and the Boudoir reaction, the reaction can be carried out at a relatively low temperature, and the energy required to precipitate solid carbon from carbon dioxide can be kept low.

[0023] Next, a description will be given of the change in the raw material gas when the raw material gas consisting of carbon dioxide and hydrogen is reacted continuously from the first reaction to the third reaction.

[0024] In the first reaction, methane and water vapor are typically produced from 1 mol of carbon dioxide and 4 mol of hydrogen via a catalyst. Even if the H2 / CO2 molar ratio is the theoretical value of 4, not all of the carbon dioxide and hydrogen react to produce 1 mol of methane. That is, the feed gas containing carbon dioxide and hydrogen becomes a mixed gas consisting of the methane synthesized in the first reaction, unreacted carbon dioxide, hydrogen, and water vapor. The feed gas after the first reaction contains water vapor, but since the water vapor may reduce the methane conversion rate in the second reaction, it is preferable to remove the water vapor from the feed gas before proceeding to the second reaction.

[0025] In the second reaction, 2 mol of carbon monoxide and 2 mol of hydrogen are produced from 1 mol of methane and 1 mol of carbon dioxide synthesized in the first reaction via a catalyst. After the second reaction, the raw material gas becomes a mixed gas containing hydrogen, methane, carbon dioxide, and carbon monoxide.

[0026] In the third reaction, 2 moles of carbon monoxide are converted into 1 mole of solid carbon and 1 mole of carbon dioxide through a catalyst. The solid carbon is deposited on the surface of the catalyst, so the catalyst is also recovered to recover the deposited solid carbon. Note that various reaction systems compete in the third reaction. Therefore, the raw gas that has completed the third reaction is a mixed gas containing hydrogen, methane, carbon dioxide, carbon monoxide, and water vapor.

[0027] [Configuration of solid carbon deposition device] An embodiment of the present invention will be described below. Figure 1 shows a solid carbon deposition apparatus according to the present invention. The solid carbon deposition apparatus 1 is an apparatus for depositing solid carbon from process exhaust gases containing carbon dioxide. Process exhaust gases refer to exhaust gases containing carbon dioxide emitted from cement clinker burning processes, quicklime manufacturing processes, thermal power plants, waste incineration facilities, ceramic and other burning facilities, steel mills, and chemical plants.

[0028] 1, the solid carbon deposition apparatus 1 has three reactors in which different reactions occur, and the three reactors are connected in series. When the reactor to which the raw material gas is supplied is designated as the first reactor 10, the reactions proceed in the order of the first reactor 10, the second reactor 20, and the third reactor 30, and solid carbon is deposited in the third reactor 30.

[0029] In addition to the three reactors, the solid carbon deposition apparatus 1 is equipped with a hydrogen supply system 3, a hydrogen flow meter 4, a first gas mixer 5, a second gas mixer 6, a third gas mixer 7, a first gas separator 8, a second gas separator 9, water vapor removal systems 41 to 43 provided at the outlets of each reactor, and a flow meter 50. The solid carbon deposition apparatus 1 also preferably includes a system 61 for removing sulfur oxides, which cause catalyst deterioration, a carbon dioxide concentration system 62, and a system 70 for recycling the mixed gas discharged from the third reactor 30. Furthermore, since the absolute amount of the feed gas increases if nitrogen or oxygen is contained in the process exhaust gas, a system for removing nitrogen or oxygen from the process exhaust gas may be further provided upstream of the first reactor.

[0030] The gas mixers 5 to 7 mix multiple gases to prepare the mixed gas to be supplied to each reactor. Each of the gas mixers 5 to 7 is preferably equipped with a flow meter for measuring the flow rate of the mixed gas. The first gas mixer 5 prepares the raw material gas to be supplied to the first reactor 10, the second gas mixer 6 prepares the mixed gas to be supplied to the second reactor 20, and the third gas mixer 7 prepares the mixed gas to be supplied to the third reactor 30. The second gas mixer 6 and the third gas mixer 7 are not essential to the solid carbon deposition apparatus 1, but the mixed gas discharged from each reactor does not necessarily have a composition ratio suitable for the next reaction. Therefore, it is preferable to adjust the mixed gas discharged from each reactor by using the second gas mixer 6 and the third gas mixer 7 to partially remove or add other gases.

[0031] The first gas mixer 5 mixes hydrogen supplied from the hydrogen supply equipment 3 with a process exhaust gas containing carbon dioxide to generate a raw material gas to be supplied to the first reactor 10. At this time, the raw material gas is mixed so that the H2 / CO2 molar ratio is 1.5 or more and 3.5 or less, more preferably 2.1 or more and 3.2 or less, and even more preferably 2.3 or more and 3.0 or less. Since the H2 / CO2 molar ratio is 1.5 or more and 3.5 or less, solid carbon can be stably recovered from the raw material gas. In addition, it is preferable that sulfur oxides are removed from the process exhaust gas in a sulfur oxide removal equipment 61 and the carbon dioxide concentration is increased in a carbon dioxide concentration equipment 62 before the process exhaust gas is supplied to the first gas mixer 5. In addition, when equipment 70 for circulating and utilizing the mixed gas discharged from the third reactor 30 is provided, the mixed gas discharged from the third reactor 30 may be mixed with the raw material gas.

[0032] The first reactor 10 brings the raw material gas supplied from the first gas mixer 5 into contact with a catalyst that activates the methanation reaction, producing methane and water from the raw material gas as shown in Equation 6. The raw material gas is preferably supplied to the first reactor 10 so that the space velocity is 2000 to 8000 / h. The first reactor 10 includes a gas flow reaction tube filled with a catalyst that activates the methanation reaction, and a heating furnace that can heat the gas flow reaction tube to 300 to 550°C. Since the gas flow path is not clogged by solid products, for example, an atmospheric flow reactor, which is a fixed gas flow tube, is used for the first reactor 10.

[0033] The catalyst that activates the methanation reaction may be one capable of producing methane from carbon dioxide and hydrogen, such as Ni, Ru, Pt, or Rh. Furthermore, various oxides and aluminosilicates, such as CeO2, ZrO2, YO3, and Al2O3, can be used as the support. The catalyst may have any shape as long as it can achieve the desired space velocity, but a spiral shape is preferred because it requires a small catalyst volume. A spiral catalyst is produced by forming a metal plate, such as aluminum, into a spiral shape and applying a catalyst paste to it.

[0034] The second reactor 20 converts methane to carbon monoxide as shown in Equation 7 by heating the mixed gas containing methane supplied from the first reactor 10 in contact with a catalyst that promotes the dry reforming reaction. The mixed gas supplied to the second reactor 20 is preferably supplied so that the space velocity is 1300 to 5400 / h. The second reactor 20 includes a gas flow reaction tube filled with a catalyst that activates the dry reforming reaction, and a heating furnace that can heat the gas flow reaction tube to 700 to 800°C. Since there is little concern that the gas flow path in the reactor will be blocked by solid products, the second reactor 20 may be, for example, an atmospheric flow reactor that is a fixed gas flow side tube.

[0035] The catalyst that activates the dry reforming reaction may be one capable of producing carbon monoxide and hydrogen from carbon dioxide and methane, such as Ni or Rh. Furthermore, various oxides and aluminosilicates, such as CeO2, ZrO2, YO3, and Al2O3, can be used as the support, with γ-Al2O3 being preferred. The catalyst may have any shape as long as it can achieve the desired space velocity, but a spiral shape is preferred because it requires a small catalyst volume. A spiral catalyst is produced by forming a metal plate, such as stainless steel, into a spiral shape and applying a paste-like catalyst to it.

[0036] The third reactor 30 brings the carbon monoxide-containing mixed gas supplied from the second reactor 20 into contact with a catalyst that activates the Boudoir reaction, thereby precipitating solid carbon from the carbon monoxide, as shown in Equation 8. The mixed gas supplied to the third reactor 30 is preferably supplied so that the maximum space velocity is 680 / h. The third reactor 30 includes a gas flow reaction tube filled with a catalyst that activates the Boudoir reaction, and a heating furnace capable of heating the gas flow reaction tube to 400 to 500°C. The third reactor 30 is preferably capable of continuously discharging the catalyst on which solid carbon has been precipitated and continuously supplying new catalyst into the reactor, and is preferably, for example, a fluidized bed, a moving bed, or a rotary kiln.

[0037] The catalyst that activates the Boudoir reaction can be one capable of precipitating solid carbon from carbon monoxide, such as Ni or Fe, although iron-based catalysts are preferred for environmental reasons. Various oxides and aluminosilicates, such as CeO2, ZrO2, Y2O3, and Al2O3, can be used as supports. The catalyst can have any shape as long as it achieves the desired space velocity, but a spiral shape is preferred because it requires a smaller catalyst volume. A spiral catalyst is produced by forming a metal plate, such as stainless steel, into a spiral shape and applying a paste-like catalyst to it.

[0038] 1, water vapor removal equipment 41 to 43 is provided at the outlet of each reactor. The water vapor removal equipment 41 to 43 cools the gas discharged from the outlet of the corresponding reactor to concentrate the water vapor, and discharges it as industrial wastewater.

[0039] The methanation reaction in the first reactor 10 generates water vapor. However, if the mixed gas containing water vapor is transferred to the second reactor 20, the methane conversion rate may decrease. Therefore, it is preferable to provide a first water vapor removal system 41 at the outlet of the first reactor 10 to actively remove water vapor. On the other hand, the dry reforming reaction in the second reactor 20 does not generally generate water vapor. Therefore, a second water vapor removal system 42 may not be provided at the outlet of the second reactor 20. However, considering the competition between various reaction systems within the second reactor 20 and the possibility of water vapor generation when the catalyst type, temperature conditions, etc. are changed, it may be provided. Furthermore, although the solid carbon deposition reaction is dominant in the third reactor 30, it is possible that a reaction generating water vapor may occur in some cases. Therefore, it is preferable to provide a third water vapor removal system 43 at the outlet of the third reactor 30.

[0040] Furthermore, as described above, the solid carbon deposition apparatus 1 preferably includes equipment 70 capable of recycling the mixed gas discharged from the third reactor 30. Equipment 70 capable of recycling the mixed gas discharged from the third reactor 30 may be equipment that supplies the mixed gas discharged from the third reactor 30 to each reactor. Because the mixed gas discharged from the third reactor 30 contains carbon dioxide, the mixed gas can be used as a raw material for the feed gas without being discharged to the outside, thereby preventing the emission of carbon dioxide. The equipment 70 capable of recycling the mixed gas discharged from the third reactor 30 may be capable of recycling not only the third reactor 30, but also a portion of the mixed gas discharged from the first reactor 10 and the second reactor 20. In this case, it is preferable to use gas mixers 5 to 7 to adjust the composition ratio of the mixed gas before supplying it to each reactor, rather than directly supplying the discharged mixed gas to each reactor.

[0041] In order to adjust the composition ratio of the mixed gas, it is preferable to install sensors that measure the composition ratio of the gases supplied to the gas mixers 5 to 7, valves that can adjust the flow rate of each mixed gas, and the gas mixers 5 to 7. The sensors need only be capable of determining the component ratios of at least hydrogen, methane, carbon dioxide, and carbon monoxide, and it is preferable that valves that can adjust the flow rate of each mixed gas be installed not only at the outlet through which the process exhaust gas is discharged and at the hydrogen supply facility 3, but also when the mixed gas discharged from the first reactor 10 and the second reactor 20 and the mixed gas discharged from the third reactor 30 are recycled to each gas mixer.

[0042] Furthermore, in the solid carbon deposition apparatus 1, the reactions in the first reactor 10 and the third reactor 30 are exothermic reactions, whereas the reaction in the second reactor 20 is an endothermic reaction. Therefore, it is preferable to recover the sensible heat of the mixed gas discharged from the first reactor 10 and the third reactor 30 by a heat exchanger and use it as an energy source for the second reactor 20.

[0043] [Solid carbon deposition system] Next, the solid carbon deposition system will be described. Fig. 2 is a schematic diagram showing the configuration of the solid carbon deposition system. The solid carbon deposition system 500 controls the composition ratio of the mixed gas supplied to each reactor in the solid carbon deposition apparatus 1 to within a range specified by the user.

[0044] The solid carbon deposition system 500 includes a solid carbon deposition apparatus 1 and a gas composition ratio control device 100. The gas composition ratio control device includes a memory unit 110, an operation unit 120, and a control unit 130. The memory unit 110 records values ​​measured in the solid carbon deposition apparatus 1. The values ​​measured in the solid carbon deposition apparatus 1 include, for example, the composition ratios of the gases supplied to the gas mixers 5 to 7, such as the composition ratios of the mixed gas and process exhaust gas discharged from each reactor.

[0045] The operation unit 120 is a device that allows a user to input data arbitrarily, such as a keyboard, mouse, or touch panel. The user can input any range for the composition ratio of the mixed gas supplied to each reactor via the operation unit 120. The control unit 130 controls the composition ratio of the mixed gas so that it falls within the range specified by the user, based on the data recorded in the storage unit 110. Specifically, by recognizing the gas flow rate from each facility and controlling the valves of the gas supplied to the gas mixers 5 to 7, the control unit 130 controls the composition ratio of the mixed gas in the gas mixers 5 to 7 so that it falls within the range specified by the user.

[0046] In this embodiment, an example has been described in which the composition ratio of the mixed gas in all reactors is controllable, but it is sufficient that the molar ratio of H2 / CO2 in the raw material gas supplied to at least the first reactor 10 is controllable within a range specified by the user, and it is not necessary that the composition ratio of the mixed gas supplied to at least one of the second reactor 20 and the third reactor 30 is controllable.

[0047] [Solid carbon deposition method] Next, a method for depositing solid carbon will be described. First, the raw material gas to be supplied to the first reactor 10 is adjusted. The raw material gas is prepared by mixing hydrogen supplied from the hydrogen supply equipment 3 with process exhaust gas containing carbon dioxide, and is adjusted so that the H2 / CO2 molar ratio is 1.5 or more and 3.5 or less.

[0048] Next, the raw material gas is supplied to the first reactor 10 and circulated through the gas flow reaction tube of the first reactor 10. The gas flow reaction tube is filled with a catalyst heated to 300 to 500°C in a heating furnace, and the raw material gas comes into contact with the catalyst that activates the methanation reaction, producing methane from the raw material gas. After the raw material gas with a H2 / CO2 molar ratio of 2.57 is supplied to the first reactor and methanated, the mixed gas after the first reaction is completed and the water vapor is removed has a hydrogen concentration of 42 vol%, a methane concentration of 27 vol%, and a carbon dioxide concentration of 30 vol%, for example.

[0049] Next, the mixed gas discharged from the first reactor 10 is supplied to the second reactor 20, and the mixed gas is passed through the gas flow reaction tube of the second reactor 20. The gas flow reaction tube is filled with a catalyst heated to approximately 800°C in a heating furnace, and the mixed gas comes into contact with the catalyst that activates the dry reforming reaction, converting methane to carbon monoxide. After the second reaction and the water vapor has been removed, the mixed gas has, for example, a hydrogen concentration of 58% by volume, a methane concentration of 0.5% by volume, a carbon dioxide concentration of 11% by volume, and a carbon monoxide concentration of 30% by volume.

[0050] Next, the mixed gas discharged from the second reactor 20 is supplied to the third reactor 30, and the mixed gas is passed through the gas flow reaction tube of the third reactor 30. The gas flow reaction tube is filled with a catalyst heated to approximately 450°C by a heating furnace, and the mixed gas comes into contact with the catalyst that activates the Boudoir reaction, turning carbon monoxide into solid carbon, which deposits on the surface of the catalyst. The solid carbon can then be recovered by recovering the catalyst on which the solid carbon has deposited. The solid carbon deposited on the catalyst surface can be recovered, for example, in a volume of 8.7 cm. 3 The free space in the third reactor 30 is filled at a rate of 1 / hr. After the third reaction is completed and the water vapor is removed, the mixed gas has a hydrogen concentration of 62% by volume, a methane concentration of 0% by volume, a carbon dioxide concentration of 22% by volume, and a carbon monoxide concentration of 15% by volume, for example.

[0051] As described above, in the method for precipitating solid carbon according to the present invention, the raw material gas can be reacted continuously from the time it is supplied to the first reactor until solid carbon is precipitated in the third reactor. This makes the process more efficient than when each reaction is performed independently. Furthermore, since the H2 / CO2 molar ratio in the raw material gas is 1.5 or more and 3.5 or less, 20% or more of the carbon input as carbon dioxide can be recovered as solid carbon.

[0052] [Example] Example 1 The heating furnace that constitutes the first reactor is a temperature-controllable one-zone electric furnace (ceramics electric tubular furnace manufactured by Asahi Rika Seisakusho, effective length 300 mm), and the atmospheric pressure flow-type reaction tube is a quartz tube with an inner diameter of 8 mm and a length of 600 mm. Two catalysts with 10 wt% Ni / CeO2 coated on the surface of a spiral structure as shown in Figure 3 were installed at the position of the thermocouple used to control the temperature of the heating furnace inside the atmospheric pressure flow-type reaction tube as catalysts to activate the methanation reaction.

[0053] The catalyst that activates the methanation reaction is CeO2 (a reagent manufactured by Kanto Chemical Co., Ltd.), which is supported with 10 wt% Ni (Ni(NO3)2·6H2O: 98% Wako Pure Chemical Industries) by evaporation to dryness. After the support, it is fired in an air atmosphere at 500°C for 2 hours to separate the nitric acid component. After cooling the fired product, distilled water is added and it is ground in a mortar to produce a Ni / CeO2 paste.

[0054] Separately from the Ni / CeO2 paste, a spirally twisted aluminum plate (JIS A1100 H14, width 7 mm x length 50 mm, thickness 1.5 mm) was surface treated with a 0.8 mol NaOH aqueous solution and a 3.0 mol hydrochloric acid solution as shown in Figure 3. The spirally twisted aluminum plate was then repeatedly dried with cold air and immersed in water until a sufficient amount of Ni / CeO2 catalyst was supported on it to achieve the desired methanation.

[0055] The second reactor was prepared in the same manner as the first reactor, except that a catalyst for activating the dry reforming reaction was used instead of the catalyst for activating the methanation reaction. The catalyst for activating the dry reforming reaction was a commercially available γ-Al2O3 (C20 manufactured by Nippon Light Metal Co., Ltd.) support, which was coated with 10 wt% Ni (Ni(NO3)2·6H2O: 98% Wako Pure Chemical Industries) by evaporation to dryness. The Ni / γ-Al2O3 paste was applied to a spirally twisted stainless steel plate (SUS304, 7 mm wide x 50 mm long, 0.5 mm thick) as shown in Figure 3. The catalyst was prepared in the same manner as the catalyst for activating the methanation reaction.

[0056] The third reactor was prepared in the same manner as the first reactor, except that a 21 mm diameter, 600 mm long quartz tube was used as the atmospheric flow reactor. Instead of the methanation catalyst, eight Boudoir catalysts were placed inside the atmospheric flow reactor (two bundles of four in series). The Boudoir catalyst was magnetite (FeO reagent: 98% Wako Pure Chemical Industries, Ltd.), which was prepared as a paste by adding distilled water to the magnetite. The magnetite paste was applied to a spirally twisted stainless steel plate (SUS304, 7 mm wide x 50 mm long, 0.5 mm thick) as shown in Figure 3. The magnetite paste was then applied to a spirally twisted stainless steel plate (SUS304, 7 mm wide x 50 mm long, 0.5 mm thick). The magnetite paste was then applied to a spirally twisted stainless steel plate (SUS304, 7 mm wide x 50 mm long, 0.5 mm thick) as shown in Figure 3. ...

[0057] After preparing each reactor, the catalyst was reduced by maintaining the temperature at 500°C for 1 hour while flowing hydrogen at 200 ml / min. Next, the control temperature of the first reactor was set to 450°C, that of the second reactor to 800°C, and that of the third reactor to 450°C. After all reactors reached the designated temperatures, a standard hydrogen gas cylinder was used as hydrogen supply equipment 3, and a standard carbon dioxide gas cylinder was used instead of the process exhaust gas. The raw material gas was supplied to the first reactor via the mass flow controller and the first gas mixer.

[0058] The H2 / CO2 molar ratio in the raw material gas was set to 2.57, and solid carbon was collected for 4 hours. Specifically, the mass flow controllers were used to set the hydrogen flow rate to 180 ml / min, the carbon dioxide flow rate to 70 ml / min, and the total raw material gas flow rate to 250 ml / min, and the raw material gas was supplied to the first reactor.

[0059] At the outlet of each reactor, a water vapor removal device and a sampling hole were installed. 30 minutes after the indicated temperature of each reactor reached the set temperature, a sample was taken from the sampling hole using a syringe, and hydrogen, nitrogen, oxygen, methane, carbon monoxide, and carbon dioxide were quantitatively analyzed using a gas chromatograph GC-2014 (Shimadzu Corporation).

[0060] A wet gas meter was installed at the outlet of the third reactor to measure the gas flow rate. The mixed gas discharged from the third reactor was not recycled but discharged to an outdoor abatement facility. After the third reactor had cooled sufficiently, the catalyst was removed from the atmospheric flow-type reaction tube, the weight of the precipitated solid carbon was measured, and the recovery rate of the solid carbon was calculated using the following equation 9. Solid carbon recovery rate (%) = (molar amount of precipitated solid carbon) / (molar amount of carbon supplied to the solid carbon precipitater) × 100 (Equation 9)

[0061] Example 2 The same procedure as in Example 1 was carried out except that the flow rate of hydrogen was 190 ml / min, the flow rate of carbon dioxide was 60 ml / min, and the molar ratio of H2 / CO2 in the raw material gas was 3.17.

[0062] Example 3 The same procedure as in Example 1 was carried out except that the flow rate of hydrogen was 170 ml / min, the flow rate of carbon dioxide was 80 ml / min, and the molar ratio of H2 / CO2 in the raw material gas was 2.13.

[0063] Example 4 The same procedure as in Example 1 was carried out except that the flow rate of hydrogen was 160 ml / min, the flow rate of carbon dioxide was 90 ml / min, and the molar ratio of H2 / CO2 in the raw material gas was 1.78.

[0064] (Comparative Example 1) The same procedure as in Example 1 was carried out except that the flow rate of hydrogen was 200 ml / min, the flow rate of carbon dioxide was 50 ml / min, and the molar ratio of H2 / CO2 in the raw material gas was 4.00.

[0065] (Experimental results) The experimental results of Examples 1 to 4 and Comparative Example 1 are shown in Table 1 below. Table 1 shows the H2 / CO2 molar ratio in the raw material gas, the gas concentrations of hydrogen, methane, carbon dioxide, and carbon monoxide in the mixed gas sampled from the sampling hole provided at the outlet of the third reactor, and the solid carbon recovery rate. [Table 1]

[0066] In Examples 1 to 4, the solid carbon recovery rate was as high as 20% or more. In contrast, in Comparative Example 1, where the H2 / CO2 molar ratio in the raw material gas was 3.5 or more, the solid carbon recovery rate was 10.3%, which was 20% or less. Therefore, by setting the H2 / CO2 molar ratio in the raw material gas to 3.5 or less, the solid carbon recovery rate can be improved.

[0067] Furthermore, in all of Examples 1 to 4, the solid carbon recovery rate was 20% or more, but since the gas concentrations of carbon dioxide and carbon monoxide in the mixed gas discharged from the third reactor increase as the H2 / CO2 molar ratio in the raw material gas decreases, it is preferable that the H2 / CO2 molar ratio in the raw material gas is 1.5 or more. [Explanation of symbols]

[0068] 1. Solid carbon deposition device 3 Hydrogen supply equipment 4 Hydrogen flow meter 5. First gas mixer 6 Second gas mixer 7. Third gas mixer 8. First Gas Separator 9 Second gas separator 10 First reactor 20 Second reactor 30 Third reactor 41 First Water Vapor Removal Facility 42 Second water vapor removal facility 43 Third Water Vapor Removal Facility 50 flow meter 61 Sulfur oxide removal equipment 62 Carbon dioxide concentration equipment 70 Equipment for recycling mixed gases 100 Gas composition ratio control device 110 Storage section 120 Operation section 130 Control Unit 500 Solid Carbon Deposition System

Claims

1. a 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; converting the produced methane to carbon monoxide by heating the methane in contact with a catalyst that activates a dry reforming reaction; contacting the converted carbon monoxide with a catalyst that activates the Boudoir reaction to precipitate solid carbon from the carbon monoxide; The source gas is H ２ / CO ２ The method for depositing solid carbon is characterized in that the molar ratio of

2. A solid carbon deposition system for depositing solid carbon from a feed gas containing carbon dioxide and hydrogen, comprising: a first reactor in which the raw material gas is brought into contact with a catalyst that activates a methanation reaction to produce methane and water from the raw material gas; a second reactor in which the methane produced is heated in contact with a catalyst that activates a dry reforming reaction, thereby converting the methane into carbon monoxide; a third reactor in which the converted carbon monoxide is contacted with a catalyst that activates a Boudoir reaction to separate the solid carbon from the carbon monoxide; a control unit that controls the raw material gas supplied to the first reactor, The control unit is configured to adjust H in the raw material gas supplied to the first reactor. ２ / CO ２ A solid carbon deposition system characterized by controlling the molar ratio of

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