Carbon production system and carbon production method

Abstract

To provide a carbon production system and a carbon production method that involve a reaction to synthesize methane from a feedstock comprising hydrogen and carbon dioxide and a reaction to form carbon from a methane-containing feedstock, both performed in the same reaction vessel, and conduct control over carbon dioxide levels, thereby achieving enhanced reactivity.SOLUTION: A carbon production system 1 comprises: a reaction vessel 10 that produces methane and water from a feedstock containing hydrogen and carbon dioxide; a hydrogen supply section 20 that supplies hydrogen to the reaction vessel 10; a carbon dioxide supply section 25 that supplies carbon dioxide to the reaction vessel 10; a circulation pathway 30 that connects the inlet and outlet of the reaction vessel 10 and returns the methane produced in the reaction vessel 10 back to the reaction vessel 10; and a water removal section 40 that is disposed in the circulation pathway 30 and removes at least part of the water from the gas containing methane and water produced in the reaction vessel. The carbon production system utilizes the contact between the gas inside the reaction vessel 10 and the catalyst to produce carbon, while controlling the carbon dioxide levels in the reaction vessel 10 to 5 vol.% or more and 30 vol.% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to carbon production systems and methods. [Background technology]

[0002] Carbon dioxide is seen as a problematic cause of global warming, and there has been a worldwide movement to curb carbon dioxide emissions. One method for reducing carbon dioxide emissions into the atmosphere and effectively utilizing carbon dioxide is to convert hydrogen and carbon dioxide into solid carbon.

[0003] Patent Document 1 discloses a carbon dioxide fixation system including a first reactor, a condenser, a second reactor, and a heat exchanger. The first reactor reacts hydrogen and carbon dioxide in the presence of a catalyst to generate a mixed gas containing methane and water vapor. The condenser condenses the moisture in the mixed gas generated in the first reactor. The second reactor produces carbon products such as carbon from methane gas. The heat exchanger exchanges heat between the mixed gas generated in the first reactor and methane gas supplied to the second reactor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-60137 A Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, the reaction in the first reactor is an exothermic reaction, and the reaction in the second reactor is an endothermic reaction. In Patent Document 1, the heat energy generated in the first reactor is recovered by exchanging heat between the mixed gas generated in the first reactor and the methane gas supplied to the second reactor, thereby improving the energy efficiency of the system. For this reason, carbon can be produced from carbon dioxide by carrying out, in the same reactor, a reaction for producing methane from a raw material containing hydrogen and carbon dioxide, and a reaction for producing carbon from the methane in the recycle gas by using the produced mixed gas as a recycle gas.

[0006] In such a process involving recirculated gas, since no exhaust gas is generated, it is necessary to continue supplying gas while maintaining the gas composition in the reactor within an appropriate range. In addition, in the chemical reaction formula for producing carbon from hydrogen and carbon dioxide, the molar ratio of hydrogen to carbon dioxide is 2, but there is an error when used industrially, and the accumulation of this error can cause the gas composition in the reactor to change over the long term. Therefore, the challenge was to build a system that measures the gas concentration in the reactor and controls it to the optimum gas concentration.

[0007] The present disclosure aims to provide a carbon production system and a carbon production method in which a reaction for producing methane from a raw material containing hydrogen and carbon dioxide, and a reaction for producing carbon from a raw material containing methane are carried out in the same reactor, and the reactivity is improved by controlling the carbon dioxide concentration. [Means for solving the problem]

[0008] The carbon production system according to the present disclosure includes a reactor that produces methane and water from a raw material containing hydrogen and carbon dioxide, a hydrogen supply unit that supplies hydrogen to the reactor, and a carbon dioxide supply unit that supplies carbon dioxide to the reactor. The carbon production system includes a circulation flow path that connects the inlet and outlet of the reactor and returns methane produced in the reactor to the reactor, and a water removal unit that is provided in the circulation flow path and removes at least a portion of water from a gas containing methane and water produced in the reactor. The carbon production system produces carbon by contacting the gas in the reactor with a catalyst. The carbon production system controls the concentration of carbon dioxide in the reactor to be 5% by volume or more and 30% by volume or less.

[0009] The carbon production method according to the present disclosure is a carbon production method for producing carbon in a reactor having an inlet and an outlet connected to a circulation flow path. The carbon production method includes a step of supplying hydrogen and carbon dioxide to the reactor. The carbon production method includes a step of producing methane and water in the reactor from a raw material containing hydrogen and carbon dioxide. The carbon production method includes a step of removing at least a portion of the water from a gas containing methane and water produced in the reactor in the circulation flow path. The carbon production method includes a step of supplying the gas from which at least a portion of the water has been removed to the reactor. The carbon production method includes a step of producing carbon in the reactor by contacting the gas in the reactor with a catalyst. The carbon production method includes a step of controlling a concentration of carbon dioxide in the reactor to be 5% by volume or more and 30% by volume or less.

[0010] The carbon production method may further include a step of measuring the concentration of gas in the reactor, and in the step of measuring the concentration of gas in the reactor, the gas to be measured may contain at least one type selected from the group consisting of carbon dioxide, hydrogen, carbon monoxide, and methane.

[0011] In the step of measuring the concentration of a gas in a reactor, the gas to be measured may contain carbon dioxide.

[0012] In the step of controlling the carbon dioxide concentration in the reactor to 5% by volume or more and 30% by volume or less, the carbon dioxide concentration may be controlled by adjusting the supply flow rate ratio of hydrogen to carbon dioxide. Effect of the Invention

[0013] According to the present disclosure, it is possible to provide a carbon production system and a carbon production method in which a reaction for producing methane from a raw material containing hydrogen and carbon dioxide, and a reaction for producing carbon from a raw material containing methane are carried out in the same reactor, and the carbon dioxide concentration is controlled to improve reactivity. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram illustrating a carbon production system according to some embodiments. [Diagram 2] 1 is a graph showing the relationship between carbon dioxide concentration and carbon production rate per unit weight of catalyst. [Diagram 3] FIG. 1 is a schematic diagram showing an experimental apparatus for measuring carbon dioxide concentration. [Figure 4] FIG. 1 is a schematic diagram showing a configuration of a reactor and its surroundings according to some embodiments. [Diagram 5] FIG. 1 is a schematic diagram illustrating a carbon production system according to some embodiments. [Figure 6] FIG. 1 is a schematic diagram illustrating a carbon production system according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, some exemplary embodiments will be described with reference to the drawings. Note that the dimensional ratios of the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios.

[0016] [First embodiment] First, a carbon production system 1 according to the first embodiment will be described with reference to Fig. 1. As shown in Fig. 1, the carbon production system 1 according to this embodiment includes a reactor 10, a hydrogen supply unit 20, a carbon dioxide supply unit 25, a circulation flow path 30, and a water removal unit 40. The circulation flow path 30 connects the inlet and outlet of the reactor 10.

[0017] The reactor 10 produces methane and water from a raw material containing hydrogen and carbon dioxide. The hydrogen supply unit 20 supplies hydrogen to the reactor 10. In FIG. 1, the hydrogen supply unit 20 supplies hydrogen to the reactor 10 via a circulation flow path 30, but the hydrogen may be directly supplied to the reactor 10. In addition, the carbon dioxide supply unit 25 supplies carbon dioxide to the reactor 10. As shown in FIG. 1, the carbon dioxide supply unit 25 may supply carbon dioxide to the reactor 10 via the circulation flow path 30, or may directly supply carbon dioxide to the reactor 10.

[0018] The circulation flow path 30 returns the methane produced in the reactor 10 to the reactor 10. The water removal section 40 is provided in the circulation flow path 30, and removes at least a portion of the water from the gas containing methane and water produced in the reactor 10. That is, the gas from which at least a portion of the water has been removed in the water removal section 40 (hereinafter, gas passing through the water removal section) contains the methane produced in the reactor 10, and is returned to the reactor 10 through the circulation flow path 30. Then, in the reactor 10, carbon is produced by contact of the gas in the reactor 10 with a catalyst.

[0019] In this manner, the reactor 10 produces methane and water from the feedstock containing hydrogen and carbon dioxide. This reaction is typically an exothermic reaction and is represented by the following reaction formula (1). 4H2+CO2→CH4+2H2O+165kJ (1)

[0020] The reactor 10 also produces carbon from a raw material containing methane. The raw material contains a gas that has passed through the water removal section and contains methane. This reaction is generally an endothermic reaction and is represented by the following reaction formula (2). CH4→C+2H2-75kJ (2)

[0021] Combining reaction equation (1) and reaction equation (2), we obtain the following reaction equation (3). 2H2+CO2→C+2H2O+90kJ (3)

[0022] As shown in the above reaction formulas (1) and (2), in the reactor 10, a reaction for producing methane from a raw material containing hydrogen and carbon dioxide, and a reaction for producing carbon from a raw material containing methane are carried out. As a result, as shown in the above reaction formula (3), carbon is produced from hydrogen and carbon dioxide in the reactor 10. In addition, by carrying out the reactions of the above reaction formulas (1) and (2) in the reactor 10, a part of the heat produced in the reaction shown in the above reaction formula (1) can be used for the reaction shown in the above reaction formula (2). Therefore, even without a complex heat exchange mechanism as in the case where the above two reactions are carried out in different reactors, thermal energy can be effectively used. Hereinafter, each component of the carbon production system 1 according to this embodiment will be described.

[0023] As described above, the reactor 10 produces methane and water from a raw material containing hydrogen and carbon dioxide. Note that, in the reactor 10, carbon monoxide may be produced from carbon dioxide, and methane may be produced from carbon monoxide. The reaction of producing methane from a raw material containing hydrogen and carbon dioxide is also called a methanation reaction, and can produce methane with high efficiency.

[0024] The raw material further contains gas passing through the water removal section that is supplied to the reactor 10 via the circulation flow path 30, and the gas passing through the water removal section contains methane produced in the reactor 10. Then, in the reactor 10, carbon is produced from the raw material containing methane.

[0025] The carbon produced in the reactor 10 may include at least one selected from the group consisting of graphite, carbon black, and carbon nanotubes. These carbon materials are used in various fields as useful functional materials.

[0026] The reactor 10 is not particularly limited, and may be a fluidized bed reactor, a kiln reactor, a fixed bed reactor, or a stirred reactor in which the mixture is forcibly stirred by an agitator or the like.

[0027] The catalyst produces carbon by contacting with the raw material. Carbon can be produced in the reactor 10 without using a catalyst, but the reaction temperature may be 1000°C or higher. The temperature in the reactor 10 is not particularly limited as long as carbon can be produced, but carbon can be produced at a low temperature, for example, 500°C to 800°C, by using an appropriate catalyst. The catalyst may be disposed in a flow path through which the raw material in the reactor 10 passes.

[0028] The catalyst may be a single type of catalyst or a mixture of multiple types of catalysts. That is, the catalyst may be a single type of catalyst that produces methane and water upon contact with hydrogen and carbon dioxide, and produces carbon upon contact with methane. The catalyst may also be a mixture of a catalyst that produces methane and water upon contact with hydrogen and carbon dioxide, and a catalyst that produces carbon upon contact with methane.

[0029] The catalyst may contain at least one selected from the group consisting of a metal, a supported catalyst in which a metal is supported on a carrier, and a carbon-based catalyst. The metal contained in the catalyst may contain at least one selected from the group consisting of nickel, iron, and cobalt. The carrier supporting the metal may contain at least one inorganic oxide of alumina and silica. The carbon-based catalyst may contain at least one of activated carbon and carbon black. Among these, it is preferable that the catalyst contains at least one of a supported catalyst in which nickel is supported on an alumina carrier, and a supported catalyst in which nickel is supported on silica. This is because these supported catalysts are inexpensive and have high reactivity at low temperatures.

[0030] From the viewpoint of the carbon production rate, the carbon production system 1 controls the carbon dioxide concentration in the reactor 10 to 5% by volume or more and 30% by volume or less. It is preferable to control the carbon dioxide concentration in the reactor 10 to 9% by volume or more and 25% by volume or less. By controlling the carbon dioxide concentration in the reactor 10 to be within such a range, the gas composition in the reactor 10 can be kept within an appropriate range, and the reactivity can be improved. The carbon dioxide concentration in the reactor 10 is measured by sampling a small amount of the gas passing through the water removal section, or is measured during the reaction. The method for measuring the carbon dioxide concentration is not particularly limited, but for example, gas chromatography and an NDIR sensor (non-dispersive infrared absorption type) can be used.

[0031] The carbon production system 1 may be equipped with a temperature measuring unit 11 that measures the temperature inside the reactor 10. By providing the carbon production system 1 with the temperature measuring unit 11, the reaction temperature can be grasped and the temperature inside the reactor 10 can be controlled.

[0032] The carbon production system 1 may include a concentration measurement unit (not shown) that measures the concentration of the gas in the reactor 10. By including the concentration measurement unit in the carbon production system 1, the concentration of the gas containing carbon dioxide can be grasped and the concentration of the gas in the reactor 10 can be controlled.

[0033] The reactor 10 may be configured so that the temperature of the catalyst arranged downstream of the reactor 10 is lower than the temperature of the catalyst arranged upstream of the reactor 10. This increases the moisture ratio in the gas flowing through the circulation flow path 30. Therefore, water is easily removed in the water removal section 40, and the methane concentration in the gas passing through the water removal section can be increased. In addition, by lowering the catalyst temperature downstream of the reactor 10, it is expected that the methanation reaction will be promoted. The carbon production system 1 may include a cooler that cools the catalyst arranged downstream of the reactor 10. The cooler may include a cooling pipe that contacts the catalyst arranged downstream of the reactor 10. In order to lower the catalyst temperature downstream of the reactor 10, at least a part of the raw material may be supplied to the catalyst downstream of the reactor 10. The raw material supplied to the catalyst downstream of the reactor 10 may include at least one selected from the group consisting of hydrogen, carbon dioxide, and the gas passing through the water removal section. The temperature of the catalyst arranged downstream of the reactor 10 is preferably adjusted to 200°C to 500°C.

[0034] The reaction temperature in the reactor 10 may be adjusted by cooling with a cooling pipe in contact with the catalyst housed in the reactor 10, and the flow rates and temperatures of the hydrogen, carbon dioxide and water removal section passing gas supplied to the reactor 10. The temperature in the reactor 10 may also be adjusted by the position at which the hydrogen, carbon dioxide and water removal section passing gas supplied to the reactor 10 are supplied to the reactor 10, by supplying a cooled catalyst to the reactor 10, etc.

[0035] The exhaust gas generated in the reactor 10 and containing methane is discharged from the reactor 10 through the outlet of the reactor 10. The exhaust gas discharged from the reactor 10 may contain not only methane but also unreacted hydrogen and carbon dioxide, by-product carbon monoxide and water, and impurities such as nitrogen and argon contained in the raw material. The gas discharged from the reactor 10 is supplied to the water removal section 40 via the circulation flow path 30.

[0036] The pressure in the reactor 10 is preferably near normal pressure. The pressure in the reactor 10 may be, for example, from −0.05 MPaG to 0.1 MPaG. The pressure in the reactor 10 can be controlled by the amount of raw material supplied by the hydrogen supply unit 20 or the carbon dioxide supply unit 25, and the amount of gas passing through the water removal unit supplied via the circulation flow path 30. The pressure in the reactor 10 can also be controlled by adjusting the amount of exhaust gas discharged from the reactor 10 or the temperature in the reactor 10.

[0037] The hydrogen supply unit 20 supplies hydrogen to the reactor 10. As described above, the hydrogen supply unit 20 may supply hydrogen to the reactor 10 via the circulation flow path 30, or the hydrogen supply unit 20 may supply hydrogen directly to the reactor 10. The hydrogen supply unit 20 may include a hydrogen flow path 22, a hydrogen source 23, and a hydrogen flow rate adjustment unit 24. The hydrogen flow path 22 is provided with the hydrogen source 23 and the hydrogen flow rate adjustment unit 24, and hydrogen may be supplied from the hydrogen source 23 to the reactor 10 via the hydrogen flow path 22.

[0038] The hydrogen source 23 may be, for example, a tank containing hydrogen. The hydrogen may be obtained by electrolyzing water using renewable energy such as solar, wind, and hydraulic power. By using such hydrogen, the carbon production system 1 as a whole can reduce carbon dioxide emissions. The hydrogen flow rate regulator 24 may include a regulator valve, and the amount of hydrogen supplied from the hydrogen source 23 to the reactor 10 may be adjusted by adjusting the opening of the regulator valve with instrument air.

[0039] The carbon dioxide supply unit 25 supplies carbon dioxide to the reactor 10. As described above, the carbon dioxide supply unit 25 may supply carbon dioxide to the reactor 10 via the circulation flow path 30, or the carbon dioxide supply unit 25 may directly supply carbon dioxide to the reactor 10. The carbon dioxide supply unit 25 may include a carbon dioxide flow path 26, a carbon dioxide source 27, and a carbon dioxide flow rate adjustment unit 28. The carbon dioxide flow path 26 may be provided with the carbon dioxide source 27 and the carbon dioxide flow rate adjustment unit 28, and carbon dioxide may be supplied from the carbon dioxide source 27 to the reactor 10 via the carbon dioxide flow path 26. In addition, carbon dioxide may be supplied from a supply port and an exhaust port of the catalyst, a shaft seal of the fan 43, or the like.

[0040] The carbon dioxide source 27 may include a carbon dioxide capture unit that captures carbon dioxide discharged from a carbon dioxide generation source such as a power plant or a factory. By using carbon dioxide captured from the carbon dioxide generation source as a raw material, the amount of carbon dioxide released into the atmosphere can be reduced. The carbon dioxide capture unit may capture carbon dioxide by, for example, a chemical absorption method, a pressure swing adsorption method, a temperature swing adsorption method, a membrane separation concentration method, or a combination of these. Note that the carbon dioxide source 27 is not limited to the above-mentioned form, and may be, for example, a tank containing carbon dioxide. The carbon dioxide flow rate adjustment unit 28 may include an adjustment valve, and the supply amount of carbon dioxide supplied to the reactor 10 from the carbon dioxide supply unit 25 may be adjusted by adjusting the opening degree of the adjustment valve with instrument air.

[0041] In the above embodiment, hydrogen and carbon dioxide are supplied to the reactor 10 by the hydrogen supply unit 20 and the carbon dioxide supply unit 25, respectively. However, a mixed raw material in which carbon dioxide and hydrogen are mixed may be stored in a tank, and the mixed raw material may be supplied from the tank to the reactor 10.

[0042] The ratio of the supply flow rate of hydrogen to carbon dioxide supplied by the hydrogen supply unit 20 and the carbon dioxide supply unit 25 can be set appropriately, and may be 1.8 or more, or 1.9 or more in molar ratio. The ratio of the supply flow rate of hydrogen to carbon dioxide may be less than 2.2, or may be less than 2.1 in molar ratio.

[0043] The circulation flow path 30 returns the methane produced in the reactor 10 to the reactor 10. Specifically, the circulation flow path 30 connects the exhaust port of the reactor 10 to the supply port of the reactor 10. The circulation flow path 30 is provided so that the methane discharged from the exhaust port of the reactor 10 is supplied to the supply port of the reactor 10. The circulation flow path 30 is provided with a water removal unit 40.

[0044] The water removal section 40 removes at least a portion of the water, and generates a gas passing through the water removal section, which contains methane produced in the reactor 10. When water is removed from the exhaust gas produced in the reactor 10 and containing methane, the equilibrium of the reaction shown in the above reaction formula (1) to reaction formula (3) shifts to the right. Therefore, the carbon yield is improved by removing the water in the water removal section 40. It is not necessary to completely remove the water in the water removal section 40, and it is sufficient to remove at least a portion of the water, and moisture may remain in the gas passing through the water removal section.

[0045] The water removal section 40 is not particularly limited as long as it can remove at least a part of the water. As shown in FIG. 1, the water removal section 40 may include a heat exchanger 41 and a gas-liquid separator 42. The heat exchanger 41 cools the exhaust gas to a dew point or lower to liquefy the water. The gas-liquid separator 42 separates the exhaust gas discharged from the reactor 10 into water liquefied by the heat exchanger 41 and gas passing through the water removal section containing methane. The gas-liquid separator 42 includes a cooling tank 42a, a water flow path 42b, a pump 42c, and a water cooler 42d. The water flow path 42b is connected to the cooling tank 42a. The pump 42c and the water cooler 42d are provided in the water flow path 42b. The water in the cooling tank 42a is circulated through the water flow path 42b by the pump 42c, and the water cooled by the water cooler 42d is supplied to the cooling tank 42a. The water removal section passing gas separated by the gas-liquid separator 42 is sent to the heat exchanger 41 by the fan 43 provided in the circulation flow path 30. In this embodiment, the fan 43 is provided downstream of the gas-liquid separator 42 and upstream of the reactor 10. Specifically, the fan 43 is provided upstream of the heat exchanger 41. The heat exchanger 41 exchanges heat of the exhaust gas supplied to the gas-liquid separator 42 with heat of the water removal section passing gas separated in the gas-liquid separator 42. The water removal section passing gas heated in the heat exchanger 41 is supplied to the reactor 10. Although the heat exchanger 41 is used to cool the exhaust gas, a cooler may be used instead of the heat exchanger 41. The cooler may be provided downstream of the reactor 10 and upstream of the gas-liquid separator 42 in the circulation flow path 30.

[0046] Moreover, the water removal section 40 may include an adsorbent that adsorbs moisture instead of or in addition to the gas-liquid separator 42. The adsorbent may include at least one inorganic substance selected from the group consisting of zeolite, silica, and alumina. The shape of the adsorbent is not particularly limited, and may be in the form of powder, particles, tablets, or lumps.

[0047] The carbon production system 1 may further include a cooler 32 that is provided downstream of the water removal section 40 and upstream of the reactor 10 in the circulation flow path 30 and cools the gas passing through the water removal section that is supplied to the reactor 10. By providing the cooler 32, the temperature of the gas supplied into the reactor 10 can be lowered, and the temperature inside the reactor 10 can be finely adjusted.

[0048] The carbon production system 1 may further include a heater 33 that is provided downstream of the water removal unit 40, the hydrogen supply unit 20, and the carbon dioxide supply unit 25 in the circulation flow path 30 and upstream of the reactor 10, and that heats the gas supplied to the reactor 10. By providing the heater 33, the temperature of the gas supplied to the reactor 10 can be increased, and the temperature inside the reactor 10 can be finely adjusted.

[0049] The gas passing through the water removal section 40 from which at least a portion of the water has been removed is supplied to the reactor 10 as part of the raw material. As described above, carbon is produced in the reactor 10 by contacting the raw material containing the gas in the reactor 10 with the catalyst. Since the produced carbon adheres to the catalyst, the carbon adhered to the catalyst can be recovered by recovering the catalyst from the reactor 10.

[0050] The carbon production system 1 may further include a gas flow rate adjustment unit 31 provided in the circulation flow path 30. The gas flow rate adjustment unit 31 may adjust the flow rate of the gas supplied to the reactor 10. The gas flow rate adjustment unit 31 may include an adjustment valve, and the flow rate of the gas supplied to the reactor 10 may be adjusted by adjusting the opening degree of the adjustment valve with instrument air. The higher the temperature in the reactor 10, the lower the proportion of moisture contained in the circulation flow path 30 tends to be, and the water is more difficult to remove in the water removal unit 40. Therefore, methane as a raw material is supplied to the reactor 10, and the amount of methane in the reactor 10 is adjusted and the temperature in the reactor 10 can be reduced. This improves the efficiency of water removal by the water removal unit 40, thereby improving the carbon yield.

[0051] The carbon production system 1 may include a control unit 50. The control unit 50 may control the temperature in the reactor 10 so that the temperature in the reactor 10 measured by the temperature measurement unit 11 is within a range of 500°C or more and 650°C or less. By controlling the temperature in the reactor 10 to be within the above range, the yield of carbon produced in the reactor 10 can be improved. The control unit 50 may control at least one selected from the group consisting of the hydrogen flow rate adjustment unit 24, the carbon dioxide flow rate adjustment unit 28, and the gas flow rate adjustment unit 31 based on the temperature in the reactor 10 measured by the temperature measurement unit 11. The control unit 50 may also control at least one selected from the group consisting of the hydrogen flow rate adjustment unit 24, the carbon dioxide flow rate adjustment unit 28, and the gas flow rate adjustment unit 31 based on the concentration of the gas (carbon dioxide) in the reactor 10 measured by the concentration measurement unit.

[0052] The control unit 50 may include a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU can read a program recorded in the ROM and execute instructions such as calculations and control according to the program. The program may be stored in advance in a recording medium other than the ROM, or may be supplied to the recording medium via a wide area communication network including the Internet. The RAM records information acquired from the temperature measurement unit 11 and the concentration measurement unit, etc., and the CPU can read the information recorded in the RAM and use it for processing such as calculations.

[0053] As described above, the carbon production system 1 according to the present embodiment includes the reactor 10, the hydrogen supply unit 20, the carbon dioxide supply unit 25, the circulation flow path 30, and the water removal unit 40. The reactor 10 produces methane and water from raw materials containing hydrogen and carbon dioxide. The hydrogen supply unit 20 supplies hydrogen to the reactor 10. The carbon dioxide supply unit 25 supplies carbon dioxide to the reactor 10. The circulation flow path 30 connects the inlet and outlet of the reactor 10, and returns methane produced in the reactor 10 to the reactor 10. The water removal unit 40 is provided in the circulation flow path 30, and removes at least a portion of water from the gas containing methane and water produced in the reactor 10. Carbon is produced by contacting the gas in the reactor 10 with a catalyst, and the concentration of carbon dioxide in the reactor 10 is controlled to be 5% by volume or more and 30% by volume or less.

[0054] Next, a description will be given of a carbon production method using the carbon production system 1. The carbon production method using the carbon production system 1 is a carbon production method in which carbon is produced in a reactor 10 having an inlet and an outlet connected to a circulation flow path 30.

[0055] The carbon production method using the carbon production system 1 includes the step of supplying hydrogen and carbon dioxide to the reactor 10. As described above, the hydrogen supply unit 20 supplies hydrogen to the reactor 10, and the carbon dioxide supply unit 25 supplies carbon dioxide to the reactor 10.

[0056] In the case of such a process involving recirculation, if impurities such as nitrogen and argon, which are components of air, remain in the reactor 10 and the circulation flow path 30 (hereinafter, referred to as "inside the system") when the system is started, the impurities will continue to remain in the system during the reaction, causing a decrease in the reaction rate. Furthermore, if oxygen remains in the system, it can cause problems such as catalyst deterioration. Therefore, before starting the carbon production system 1, the air in the system may be replaced with carbon dioxide. When replacing the air in the system with carbon dioxide, the concentration of carbon dioxide in the system is preferably 80% by volume or more, and more preferably 90% by volume or more.

[0057] The carbon production method using the carbon production system 1 includes a step of producing methane and water in a reactor from a raw material containing hydrogen and carbon dioxide. As described above, as represented by the above reaction formula (1), the reactor 10 produces methane and water from a raw material containing hydrogen and carbon dioxide.

[0058] The carbon production method using the carbon production system 1 includes a step of removing at least a portion of water from a gas containing methane and water produced in the reactor in the circulation flow path, and a step of supplying the gas from which at least a portion of the water has been removed to the reactor 10. As described above, the circulation flow path 30 returns the methane produced in the reactor 10 to the reactor 10. The water removal section 40 is provided in the circulation flow path 30, and removes at least a portion of water from the gas containing methane and water produced in the reactor 10. That is, the gas passing through the water removal section contains methane produced in the reactor 10, and is returned to the reactor 10 through the circulation flow path 30.

[0059] The carbon production method using the carbon production system 1 includes a step of producing carbon in the reactor 10 by contacting the gas supplied into the reactor 10 with a catalyst. As described above, the gas in the reactor 10 contains gas that has passed through the water removal section, which contains methane, and carbon is produced in the reactor 10 by contacting the gas in the reactor 10 with the catalyst, as represented by the above reaction formula (2).

[0060] The carbon production method using the carbon production system 1 includes a step of controlling the carbon dioxide concentration in the reactor 10 to 5% by volume or more and 30% by volume or less. As described above, by controlling the carbon dioxide concentration in the reactor 10 to such a range, the gas composition in the reactor 10 can be kept within an appropriate range, and reactivity can be improved. That is, this step controls a predetermined carbon dioxide concentration for maintaining a high carbon production rate. From the viewpoint of the carbon production rate, it is preferable to control the carbon dioxide concentration in the reactor 10 to 9% by volume or more and 25% by volume or less.

[0061] In the step of controlling the carbon dioxide concentration in the reactor 10 to 5% by volume or more and 30% by volume or less, the carbon dioxide concentration may be controlled by adjusting the supply flow rate ratio of hydrogen to carbon dioxide. When increasing the carbon dioxide concentration in the system, it is preferable to make the supply flow rate ratio of hydrogen to carbon dioxide smaller than 2. On the other hand, when decreasing the carbon dioxide concentration, it is preferable to make the supply flow rate ratio of hydrogen to carbon dioxide larger than 2. Then, when a predetermined carbon dioxide concentration is reached, it is preferable to return the supply flow rate ratio of hydrogen to carbon dioxide to 2.

[0062] The carbon production method using the carbon production system 1 may further include a step of measuring the concentration of the gas in the reactor 10. By measuring the concentration of the gas in the reactor 10, the concentration of carbon dioxide in the reactor 10 can be controlled as described above. The gas in the reactor 10 contains carbon monoxide and methane in addition to carbon dioxide and hydrogen. That is, the gas to be measured may contain at least one selected from the group consisting of carbon dioxide, hydrogen, carbon monoxide, and methane. Since the concentrations of the gas components in the reactor 10 are linked, if the concentration of at least one of carbon dioxide, hydrogen, carbon monoxide, and methane can be measured, a predetermined carbon dioxide concentration for maintaining a high carbon production rate can be controlled. The gas concentration in the reactor 10 can be measured in the same manner as the carbon dioxide concentration as described above.

[0063] In the step of measuring the concentration of the gas in the reactor 10, the gas to be measured may contain carbon dioxide. Since the concentration of carbon dioxide is relatively easy to measure, it is preferable to directly measure the concentration of carbon dioxide in the reactor 10 and control it to a predetermined concentration for maintaining a high carbon production rate.

[0064] Thus, the carbon production method using the carbon production system 1 includes a step of supplying hydrogen and carbon dioxide to the reactor 10, and a step of producing methane and water in the reactor 10 from a raw material containing hydrogen and carbon dioxide. The carbon production method using the carbon production system 1 also includes a step of removing at least a portion of the water from a gas containing methane and water produced in the reactor in a circulation flow path. The carbon production method using the carbon production system 1 also includes a step of supplying the gas from which at least a portion of the water has been removed to the reactor 10, and a step of producing carbon in the reactor 10 by contacting the gas in the reactor 10 with a catalyst. Furthermore, the carbon production method using the carbon production system 1 also includes a step of controlling the concentration of carbon dioxide in the reactor 10 to be 5% by volume or more and 30% by volume or less.

[0065] 2 is a graph showing the relationship between the carbon dioxide concentration and the carbon production rate per unit weight of the catalyst. Specifically, the experimental data in FIG. 2 was measured using an experimental apparatus 100 shown in FIG.

[0066] The experimental apparatus 100 used a fixed-bed reactor in which a magnetic dish 111 was placed in a quartz tube 110 (inner diameter 22 mm) and a catalyst 116 was placed on the magnetic dish 111. The quartz tube 110 corresponds to the reactor 10 in the carbon production system 1. The quartz tube 110 was heated from the outside by an electric furnace 112, and the test temperature (temperature inside the tubular electric furnace) was set to about 600°C. The catalyst 116 mainly contained a supported catalyst in which nickel was supported on silica. A predetermined amount of hydrogen and carbon dioxide was supplied to the quartz tube 110 to produce methane. Then, the outlet gas of the quartz tube 110 was cooled with cold water (chiller water) at 10°C, and moisture was condensed and removed. The gas after the moisture removal contained methane and was returned to the quartz tube 110 by a recirculation pump 113. Then, carbon was produced by contacting the gas in the quartz tube 110 with the catalyst. Meanwhile, a sampling port 120 was branched off just before the recirculation pump 113, and a small amount of gas was sampled to measure the carbon dioxide concentration by gas chromatography (GL Sciences, Agilent 990 Micro GC) at a frequency of about once every 3 minutes.

[0067] 2, when the carbon dioxide concentration exceeds 5 volume %, the carbon generation rate increases, the carbon generation rate is highest in the range of 9 volume % to 25 volume % and the carbon generation rate tends to decrease when the carbon dioxide concentration exceeds 25 volume %. In other words, from the viewpoint of the carbon generation rate, the carbon dioxide concentration in the reactor 10 is 5 volume % to 30 volume %, and preferably 9 volume % to 25 volume %.

[0068] As described above, the carbon production method according to this embodiment is a carbon production method in which carbon is produced in a reactor 10 having an inlet and an outlet connected to a circulation flow path. The method includes a step of supplying hydrogen and carbon dioxide to the reactor 10. The method includes a step of producing methane and water in the reactor 10 from a raw material containing hydrogen and carbon dioxide. The method includes a step of removing at least a portion of water from a gas containing methane and water produced in the reactor in the circulation flow path. The method includes a step of supplying the gas from which at least a portion of the water has been removed to the reactor 10. The method includes a step of producing carbon in the reactor 10 by contacting the gas in the reactor 10 with a catalyst. The method also includes a step of controlling the concentration of carbon dioxide in the reactor 10 to be 5% by volume or more and 30% by volume or less.

[0069] The carbon production method according to this embodiment can increase the carbon production rate and improve reactivity by including a step of controlling the carbon dioxide concentration in the reactor 10 to 5% by volume or more and 30% by volume or less. Therefore, it is possible to provide a carbon production system and a carbon production method in which a reaction for producing methane from a raw material containing hydrogen and carbon dioxide and a reaction for producing carbon from a raw material containing methane are carried out in the same reactor and the carbon dioxide concentration is controlled to improve reactivity.

[0070] [Second embodiment] Next, a carbon generation system 1 according to a second embodiment will be described with reference to Fig. 4. As shown in Fig. 4, the carbon generation system 1 according to this embodiment further includes a catalyst supplying unit 60 and a catalyst discharging unit 70 in addition to the carbon generation system 1 according to the above embodiment. The other parts are similar to those of the carbon generation system 1 according to the above embodiment, and therefore descriptions thereof will be omitted.

[0071] The catalyst supplying unit 60 supplies a catalyst to the reactor 10. The catalyst supplying unit 60 may include a first hopper 61, a second hopper 62, a first catalyst flow path 63, a first catalyst supply amount adjustment unit 64, a second catalyst flow path 65, and a second catalyst supply amount adjustment unit 66.

[0072] The first hopper 61 and the second hopper 62 are connected via a first catalyst passage 63. A first catalyst supply amount adjustment unit 64 is provided in the first catalyst passage 63. The first catalyst supply amount adjustment unit 64 adjusts the amount of catalyst supplied from the first hopper 61 to the second hopper 62.

[0073] The second hopper 62 and the reactor 10 are connected via a second catalyst passage 65. A second catalyst supply amount adjustment unit 66 is provided in the second catalyst passage 65. The second catalyst supply amount adjustment unit 66 adjusts the supply amount of catalyst supplied from the second hopper 62 to the reactor 10.

[0074] The carbon dioxide supplying unit 25 may supply carbon dioxide to the catalyst supplying unit 60. The carbon dioxide supplying unit 25 that supplies carbon dioxide to the reactor 10 and the carbon dioxide supplying unit 25 that supplies carbon dioxide to the catalyst supplying unit 60 may be the same or different. The catalyst supplying unit 60 may supply the catalyst to the reactor 10 in a state in which the catalyst is purged with the carbon dioxide supplied by the carbon dioxide supplying unit 25. Carbon dioxide is supplied from the carbon dioxide supplying unit 25 to the first hopper 61. The carbon dioxide supplied to the first hopper 61 is supplied to the reactor 10 via the first catalyst flow path 63, the second hopper 62, and the second catalyst flow path 65.

[0075] The reactor 10 includes a reaction vessel 12, an agitator shaft 13, an agitator blade 14, and a motor 15. The reaction vessel 12 contains the agitator shaft 13 and the agitator blade 14 attached to the agitator shaft 13. The agitator shaft 13 is connected to the motor 15. The reaction vessel 12 contains a catalyst 16, which forms a catalyst layer. The motor 15 rotates the agitator shaft 13, so that the catalyst 16 in the reaction vessel 12 is agitated by the agitator blade 14, and adhesion of the powdered catalyst 16 is suppressed. An outlet is provided at the bottom of the reactor 10, and the catalyst is discharged by a catalyst discharge unit 70.

[0076] The reactor 10 is connected to a circulation flow path 30, and gas passing through the water removal section containing methane is supplied via the circulation flow path 30. Hydrogen is also supplied to the reactor 10 from the hydrogen supply section 20 via the circulation flow path 30. Furthermore, carbon dioxide is supplied to the reactor 10 from the carbon dioxide supply section 25 via the catalyst supply section 60. Then, as described above, methane and carbon are produced in the reactor 10, and the methane is discharged from the reactor 10 and returned to the reactor 10 via the circulation flow path 30.

[0077] The catalyst discharge section 70 discharges the catalyst 16, on which carbon is generated and adhered due to contact with the raw material, from the reactor 10 without passing through the circulation flow path 30. The flow path of the catalyst 16 discharged by the circulation flow path 30 and the catalyst discharge section 70 is different. The catalyst discharge section 70 includes a cylinder 71, a screw 72, and a motor 73. The screw 72 is disposed within the cylinder 71. The motor 73 is connected to the screw 72. The screw 72 rotates in conjunction with the rotation of the motor 73. The catalyst 16 supplied from the reactor 10 to the catalyst discharge section 70 is pushed out from the discharge port of the catalyst discharge section 70 by the rotation of the screw 72.

[0078] Carbon dioxide may be supplied from the outlet of the catalyst discharger 70 that discharges the catalyst 16. This allows the catalyst 16 to be cooled, to which carbon has been attached and discharged from the catalyst discharger 70. Also, it is possible to suppress the intrusion of air into the reactor 10. The carbon production system 1 may further include a storage tank 74 that is connected to the catalyst discharger 70 and stores the catalyst 16 discharged from the catalyst discharger 70. Carbon dioxide may be supplied to the storage tank 74 from the carbon dioxide supply unit 25. The carbon dioxide supply unit 25 that supplies carbon dioxide to the reactor 10 and the carbon dioxide supply unit 25 that supplies carbon dioxide to the storage tank 74 may be the same or different. Also, carbon dioxide may be supplied from the storage tank 74 to the outlet of the catalyst discharger 70, or may be supplied directly to the outlet of the catalyst discharger 70 without passing through the storage tank 74.

[0079] Also, an example has been described in which the catalyst supplying unit 60 includes two hoppers, the first hopper 61 and the second hopper 62. However, the catalyst supplying unit 60 may include only one hopper, or may include three or more hoppers.

[0080] Also, an example has been described in which the reactor 10 is a stirred reactor including the stirring shaft 13, the stirring blade 14, and the motor 15. However, the catalyst 16 is supplied to the reactor 10 by the catalyst supply unit 60, and the catalyst 16 in the reactor 10 is discharged by the catalyst discharge unit 70. Therefore, the catalyst 16 in the reactor 10 is flowed by the catalyst supply unit 60 and the catalyst discharge unit 70. Therefore, the reactor 10 does not need to include the stirring shaft 13, the stirring blade 14, and the motor 15.

[0081] Also, an example has been described in which the catalyst discharging unit 70 is an extruder including the cylinder 71, the screw 72, and the motor 73. However, the catalyst discharging unit 70 only needs to be able to discharge the catalyst 16 from the reactor 10, and may be a flow rate control valve provided at the discharge port of the reactor 10, or the like.

[0082] As described above, the carbon production system 1 according to this embodiment includes a catalyst supplying section 60 that supplies the catalyst 16 to the reactor 10, and a catalyst discharging section 70 that discharges the catalyst 16, to which carbon is generated and attached by contact with the raw material, from the reactor 10 without passing through the circulation flow path 30. This allows the catalyst 16 to be continuously supplied to and discharged from the reactor 10. Therefore, carbon can be continuously produced in the reactor 10 without stopping the reaction in the reactor 10 to take out the carbon.

[0083] [Third embodiment] Next, a carbon generation system 1 according to a third embodiment will be described with reference to Fig. 5. As shown in Fig. 5, the carbon generation system 1 according to this embodiment further includes a catalyst supply unit 60 and a carbon recovery unit 80 in addition to the carbon generation system 1 according to the above embodiment. The other parts are similar to those of the carbon generation system 1 according to the above embodiment, and therefore descriptions thereof will be omitted.

[0084] The catalyst supplying section 60 supplies a catalyst to the reactor 10. As the catalyst supplying section 60, the one described in the second embodiment can be used.

[0085] The carbon recovery section 80 is provided downstream of the reactor 10 and upstream of the water removal section 40 in the circulation flow path 30. The carbon recovery section 80 recovers the catalyst discharged from the reactor 10, which has been produced and adhered to the catalyst by contact with the raw material. The carbon recovery section 80 only needs to be able to recover the catalyst from the exhaust gas discharged from the reactor 10. The carbon recovery section 80 may include a cyclone or a filter, and may recover the catalyst by using these.

[0086] Carbon dioxide may be supplied from the outlet of the carbon recovery unit 80 that discharges the catalyst. This allows the catalyst to which carbon discharged from the carbon recovery unit 80 is attached to be cooled. Also, it is possible to suppress the intrusion of air into the reactor 10. The carbon production system 1 may further include a storage tank that is connected to the carbon recovery unit 80 and stores the catalyst recovered by the carbon recovery unit 80, as in the embodiment shown in FIG. 5. Carbon dioxide may be supplied to the storage tank from the carbon dioxide supply unit 25. The carbon dioxide supply unit 25 that supplies carbon dioxide to the reactor 10 and the carbon dioxide supply unit 25 that supplies carbon dioxide to the storage tank may be the same or different. Also, carbon dioxide may be supplied from the storage tank to the outlet of the carbon recovery unit 80, but may be supplied directly to the outlet of the carbon recovery unit 80 without passing through the storage tank.

[0087] As described above, the carbon production system 1 according to this embodiment includes the catalyst supplying section 60 and the carbon recovery section 80. The catalyst supplying section 60 supplies the catalyst to the reactor 10. The carbon recovery section 80 is provided downstream of the reactor 10 and upstream of the water removing section 40 in the circulation flow path 30, and recovers the catalyst discharged from the reactor 10 and adhering to the catalyst when carbon is generated on the catalyst by contact with the raw material. This allows the catalyst to be continuously supplied to and discharged from the reactor 10. Therefore, carbon can be continuously produced in the reactor 10 without stopping the reaction in the reactor 10 to take out the carbon.

[0088] [Fourth embodiment] Next, the carbon generation system 1 according to the fourth embodiment will be described with reference to Fig. 6. As shown in Fig. 6, the carbon generation system 1 according to this embodiment includes a gas discharge section 90 that is provided in the circulation flow path 30 and discharges at least a portion of the water removal section passing gas from which at least a portion of the water has been removed in the water removal section 40. The other parts are similar to those of the carbon generation system 1 according to the above embodiment, and therefore description thereof will be omitted.

[0089] The carbon production system 1 according to the embodiment produces solid carbon and liquid water from hydrogen and carbon dioxide as shown in the above reaction formula (3). Therefore, in theory, the carbon production system 1 does not produce exhaust gas. Also, as described above, before the carbon production system 1 is started, the air in the system is replaced with carbon dioxide, so that in theory, no impurities are contained. However, in reality, the raw material contains small amounts of impurities such as nitrogen and argon. As the reaction proceeds, there is a risk that impurities will accumulate in the reactor 10 and the circulation flow path 30. Therefore, by exhausting the gas passing through the water removal section by the gas exhaust section 90, the risk of impurities accumulating can be reduced.

[0090] Since the temperature of the gas passing through the water removal section is low, the gas discharge section 90 is preferably provided downstream of the gas-liquid separator 42 and upstream of the heat exchanger 41 in the circulation flow path 30. Since the pressure of the gas passing through the water removal section is high, the gas discharge section 90 is preferably provided downstream of the fan 43 in the circulation flow path 30.

[0091] As described above, the carbon production system 1 according to this embodiment includes a gas discharge section 90 that is provided in the circulation flow path 30 and discharges at least a portion of the water removal section passing gas from which at least a portion of the water has been removed in the water removal section 40. This makes it possible to suppress the accumulation of impurities such as nitrogen and argon in the circulation flow path 30.

[0092] Although several embodiments have been described, the embodiments can be modified or modified based on the above disclosure. All components of the above embodiments and all features described in the claims may be individually extracted and combined as long as they are not mutually inconsistent.

[0093] This disclosure can contribute, for example, to Goal 13 of the United Nations-led Sustainable Development Goals (SDGs), "Take urgent action to combat climate change and its impacts." [Explanation of symbols]

[0094] 1 Carbon Generation System 10. Reactor 20 Hydrogen supply unit 25 Carbon dioxide supply unit 30 Circulation flow path 40 Water removal section

Claims

1. A reactor for producing methane and water from a feedstock comprising hydrogen and carbon dioxide; A hydrogen supply unit that supplies hydrogen to the reactor; A carbon dioxide supply unit that supplies carbon dioxide to the reactor; a circulation flow path that connects an inlet and an outlet of the reactor and returns methane produced in the reactor to the reactor; a water removal unit provided in the circulation flow path and removing at least a portion of the water from the gas containing the methane and the water produced in the reactor; Equipped with producing carbon by contacting the gas in the reactor with a catalyst; A carbon production system that controls the concentration of carbon dioxide in the reactor to be equal to or greater than 5% by volume and equal to or less than 30% by volume.

2. 1. A method for producing carbon in a reactor having an inlet and an outlet connected to a circulation flow path, comprising: supplying hydrogen and carbon dioxide to the reactor; producing methane and water from a feedstock containing the hydrogen and the carbon dioxide in the reactor; removing at least a portion of the water from the gas containing the methane and the water produced in the reactor in the circulation flow path; supplying the gas from which at least a portion of the water has been removed to the reactor; producing carbon in the reactor by contacting the gas in the reactor with a catalyst; A step of controlling the concentration of carbon dioxide in the reactor to 5% by volume or more and 30% by volume or less; 16. A method for producing carbon comprising:

3. measuring a concentration of gas in the reactor; 3. The carbon production method according to claim 2, wherein in the step of measuring the concentration of gas in the reactor, the gas to be measured contains at least one selected from the group consisting of carbon dioxide, hydrogen, carbon monoxide and methane.

4. 4. The carbon production method according to claim 3, wherein in the step of measuring the concentration of the gas in the reactor, the gas to be measured contains carbon dioxide.

5. 4. The carbon production method according to claim 2 or 3, wherein in the step of controlling the carbon dioxide concentration in the reactor to 5% by volume or more and 30% by volume or less, the carbon dioxide concentration is controlled by adjusting the supply flow rate ratio of hydrogen to carbon dioxide.

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