Method for producing solid carbon

Abstract

A method for producing solid carbon is provided that can produce solid carbon from a gas containing CO2 in an environment of 500°C. A method for producing solid carbon includes mixing a gas containing CO2 with a gas containing H2 and CH4 to obtain a mixed gas that satisfies the following formulas (1) and (2), and contacting the mixed gas with a catalyst. H2 / (H2+CO2)>30% (1) CH4 / CO2≧30% (2) In the above equations (1) and (2), H2 is the hydrogen component concentration (volume %) in the mixed gas, CO2 is the carbon dioxide component concentration (volume %) in the mixed gas, and CH4 is the methane component concentration (volume %) in the mixed gas.

Description

[Technical Field]

[0001] The present invention relates to a method for producing solid carbon from a gas containing CO2. [Background technology]

[0002] Global warming is an urgent issue for industries that use combustion or reduction. Steelworks in particular generate large amounts of CO2, and technologies to reduce CO2 emissions, such as hydrogen reduction technology that can reduce direct CO2 emissions and CCUS (Carbon dioxide capture, utilization, and storage), are currently being developed.

[0003] As a technology for reducing CO2 emissions from blast furnaces, Patent Document 1 discloses a technology for producing solid carbon from blast furnace gas emitted from the blast furnace and reusing it in the blast furnace. According to Patent Document 1, solid carbon and water can be obtained by thermally decomposing methane gas into solid carbon and hydrogen, and then reacting the hydrogen with carbon dioxide separated from the blast furnace gas. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-165214 [Non-patent literature]

[0005] [Non-Patent Document 1] Yoshio Matsumoto and 1 other person, "On the Coke Oven Gas Separation Device," Hitachi Review, March 1962, pp. 40-43 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 mainly discloses the production of solid carbon according to the following formula (3).

[0007] CO2 + 2H2 → 2C + 2H2O (3)

[0008] However, according to the inventors' investigations, the reaction of the above formula (3) hardly proceeds at 500°C, and solid carbon could not be produced. Patent Document 1 also discloses that the reaction of the following formula (4) proceeds between CH4 that has not been pyrolyzed and CO2.

[0009] CO2 + CH4 → 2C + 2H2O (4)

[0010] However, Patent Document 1 does not disclose the amount of remaining CH4, nor does it disclose the amount of solid carbon produced by the reaction of the above formula (4). The present invention has been made in consideration of such conventional techniques, and its object is to provide a method for producing solid carbon that can produce solid carbon from a gas containing CO2 in an environment of 500°C. [Means for solving the problem]

[0011] The means for solving the above problems are as follows. [1] A method for producing solid carbon, comprising mixing a gas containing CO2 with a gas containing H2 and CH4 to obtain a mixed gas that satisfies the following formulas (1) and (2), and contacting the mixed gas with a catalyst. H2 / (H2+CO2)>30% (1) CH4 / CO2≧30% (2) In the above equations (1) and (2), H2 is the hydrogen component concentration (volume %) in the mixed gas, CO2 is the carbon dioxide component concentration (volume %) in the mixed gas, and CH4 is the methane component concentration (volume %) in the mixed gas. [2] The method for producing solid carbon according to [1], wherein the mixed gas and the catalyst are heated to 400°C or higher and 600°C or lower. [3] The method for producing solid carbon according to [1] or [2], wherein the catalyst is iron oxide. [4] The method for producing solid carbon according to any one of [1] to [3], wherein the gas containing H2 and CH4 is produced using coke oven gas generated from a coke oven. [5] The method for producing solid carbon according to any one of [1] to [4], wherein the gas containing CO2 is produced using blast furnace gas generated from a blast furnace. [Effects of the Invention]

[0012] By implementing the method for producing solid carbon according to the present invention, it becomes possible to produce solid carbon from a gas containing CO2 in an environment at 500°C. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional schematic diagram showing a blast furnace and its associated equipment. [Figure 2] FIG. 2 is a schematic diagram showing the reactor used in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be specifically described below through embodiments of the present invention. Hereinafter, the method for producing solid carbon according to this embodiment will be described using an example in which blast furnace gas is used as the gas containing CO2 and coke oven gas is used as the gas containing H2 and CH4, but the present invention is not limited to these embodiments. Fig. 1 is a cross-sectional schematic diagram showing a blast furnace 10 and its associated equipment. In Fig. 1, reference numeral 10 denotes a blast furnace, reference numeral 12 denotes a tuyere, reference numeral 14 denotes a dehydration device, and reference numeral 16 denotes a solid carbon production device.

[0015] In a blast furnace 10, raw ore and coke are alternately charged into the blast furnace from the top of the furnace. Sintered ore, lump ore, or pellets are used as raw ore. A plurality of tuyere openings 12 are provided in the lower part of the blast furnace 10. Blast gas and, as needed, various reducing agents (such as pulverized coal) are injected into the blast furnace 10 through the plurality of tuyere openings 12.

[0016] The blast gas, the reducing material injected into the tuyere, and the coke in the blast furnace are combusted in the raceway in front of the tuyere to produce gases containing carbon monoxide and hydrogen. The ore raw material charged into the blast furnace 10 is reduced by the gases containing carbon monoxide and hydrogen to produce pig iron. This reduction reaction of the ore raw material produces carbon dioxide. This carbon dioxide, along with the carbon monoxide and hydrogen that did not react with the ore raw material, is discharged from the top of the blast furnace 10 as blast furnace gas.

[0017] The top of the blast furnace is under high pressure of about 2.5 atmospheres. When the blast furnace gas discharged from the top of the blast furnace 10 returns to normal pressure, it expands and cools, causing the steam to condense. The condensed water produced by the condensation of the steam is removed by a dehydrator 14.

[0018] A portion of the blast furnace gas from which the condensed water has been removed is introduced into the solid carbon production device 16. In this embodiment, the blast furnace gas is an example of a gas containing CO2. The remainder of the blast furnace gas is transported to and stored in a gas holder. As the gas containing CO2, blast furnace gas whose component concentration has been adjusted using a gas separation device that separates specific components may also be used. In other words, as the gas containing CO2, gas produced using blast furnace gas generated from the blast furnace 10 may also be used. In this embodiment, the gas produced using blast furnace gas includes the blast furnace gas itself.

[0019] Coke oven gas is introduced into the solid carbon production apparatus 16. In this embodiment, the coke oven gas is an example of a gas containing H2 and CH4. As disclosed in Non-Patent Document 1, the coke oven gas generated from a coke oven contains about 50% by volume of H2 and about 30% by volume of CH4. For this reason, the coke oven gas is preferably used as a gas containing H2 and CH4.

[0020] As the gas containing H and CH, coke oven gas whose component concentrations have been adjusted using a gas separation device that separates specific components may be used. That is, as the gas containing H and CH, gas produced using coke oven gas generated in a coke oven may be used. In this embodiment, the gas produced using coke oven gas includes the coke oven gas itself.

[0021] In the solid carbon production apparatus 16, blast furnace gas and coke oven gas are mixed to produce a mixed gas. This mixed gas is brought into contact with a metal oxide catalyst, and the mixed gas and the metal oxide are heat-treated to produce solid carbon. The produced solid carbon precipitates on the surface of the metal oxide catalyst. The solid carbon is separated and recovered from the metal oxide catalyst by, for example, sieving. Oxides of transition metals such as iron, nickel, and cobalt can be used as the metal oxide catalyst. In this way, in the method for producing solid carbon according to this embodiment, solid carbon is produced using blast furnace gas, which is a gas containing CO2.

[0022] In the method for producing solid carbon according to this embodiment, the blast furnace gas and the coke oven gas are introduced into the solid carbon production apparatus 16 so that the mixed gas obtained by mixing the blast furnace gas and the coke oven gas satisfies the following formulas (1) and (2).

[0023] H2 / (H2+CO2)>30% (1) CH4 / CO2≧30% (2) In the above equations (1) and (2), H2 is the hydrogen component concentration (volume %) in the mixed gas, CO2 is the carbon dioxide component concentration (volume %) in the mixed gas, and CH4 is the methane component concentration (volume %) in the mixed gas.

[0024] By introducing blast furnace gas and coke oven gas into the solid carbon production device 16 so that the H2 concentration, CO2 concentration, and CH4 concentration of the mixed gas satisfy the above formulas (1) and (2), it becomes possible to produce solid carbon from the blast furnace gas and coke oven gas in an environment of 500°C. In particular, by including a predetermined amount of CH4 in the mixed gas, it becomes possible to produce solid carbon directly from CH4 according to the following formula (5), or to produce CO, which can easily produce solid carbon from CH4 according to the following formula (6).

[0025] CO2 + CH4 → 2C + 2H2O (5) CO2 + CH4 → 2CO + 2H2 (6)

[0026] In the presence of a transition metal such as iron, cobalt, or nickel, CO is oxidized to produce solid carbon when it comes into contact with the metal, as shown in formula (7) below. The oxide of the transition metal oxidized in formula (7) below is reduced with hydrogen, as shown in formula (8) below.

[0027] M + CO → MO + C (7) MO + H2 → M + H2O (8) M is a transition metal such as iron, cobalt, or nickel, and MO is an oxide of a transition metal such as iron, cobalt, or nickel.

[0028] To promote the production of solid carbon according to formula (7), it is preferable to keep the mixed gas and metal oxide at 400°C or higher and 600°C or lower. On the other hand, below 600°C, the reverse reaction of formula (6) above proceeds, resulting in a decrease in the CO required for formula (7) above. To address this issue, the CH4 / CO2 ratio is set to 30% or higher to suppress the reverse reaction of formula (6) above. This suppresses the decrease in CO and promotes the production of solid carbon according to formula (7) above.

[0029] On the other hand, if the CH4 / CO2 ratio is greater than 200%, the increase in CH4 increases the contact between CH4 and the catalyst, reducing the opportunity for CO2 to come into contact with the catalyst. This results in a decrease in the amount of solid carbon produced from CO2, which is undesirable. Furthermore, an increase in CH4 requires an increase in the equipment capacity, which increases the equipment cost, which is undesirable. Therefore, it is preferable that the CH4 / CO2 ratio be 200% or less.

[0030] Furthermore, by increasing H2 / (H2+CO2) to more than 30%, it is possible to promote the reduction of the catalyst according to the above formula (8). As a result, the production of solid carbon according to the above formula (7) and the reduction of the catalyst according to the above formula (8) are promoted, and the production of solid carbon from CO2 can be promoted. It is preferable that H2 / (H2+CO2) is 90% or less. By keeping H2 / (H2+CO2) 90% or less, it is possible to prevent excessive hydrogen from being contained in the mixed gas. This prevents hydrogen from interfering with the contact between CO2 and the catalyst, and it is possible to prevent a decrease in the amount of solid carbon produced from CO2.

[0031] It is preferable to use iron oxide as the metal oxide catalyst. As mentioned above, in order to recover solid carbon, it is necessary to separate the solid carbon from the metal oxide catalyst. However, if iron oxide is used as the metal oxide, the mixture of the solid carbon and the metal oxide catalyst can be used as is as a raw material for iron making without separating them. The mixture of solid carbon and iron oxide can be used, for example, as a raw material for sintering to produce sintered ore.

[0032] As described above, in the method for producing solid carbon according to this embodiment, blast furnace gas and coke oven gas are mixed to produce a mixed gas that satisfies the above formulas (1) and (2), and the mixed gas is brought into contact with a metal oxide. This makes it possible to produce solid carbon from blast furnace gas, which is a gas containing CO2, in an environment of 500°C.

[0033] Although the method for producing solid carbon according to this embodiment has been described using blast furnace gas and coke oven gas as an example, the present invention is not limited to this. The CO2-containing gas is not limited to a gas produced using blast furnace gas, and other CO2-containing gases may be used as long as they satisfy the above formulas (1) and (2). Furthermore, the H2- and CH4-containing gas is not limited to a gas produced using coke oven gas, and other H2- and CH4-containing gases may be used as long as they satisfy the above formulas (1) and (2).

[0034] However, it is preferable to use a gas produced using blast furnace gas as the CO2-containing gas, as this will enable the amount of CO2 emitted from the blast furnace to be reduced.It is also preferable to use a gas produced using coke oven gas as the H2- and CH4-containing gas.This makes it possible to produce solid carbon using coke gas, a by-product of steelworks, without having to separately procure gas containing H2 and CH4. [Example]

[0035] Next, an example will be described in which solid carbon was produced by carrying out the method for producing solid carbon according to this embodiment using a vertical reactor 20. FIG. 2 is a schematic cross-sectional view of the reactor 20 used in this example. The reactor 20 includes a cylindrical furnace core tube 22 with an inner diameter of 80 mm and a heater 24 surrounding the furnace core tube 22. The furnace core tube 22 is arranged so that its axial direction is vertical.

[0036] An alumina support 26, alumina balls 28, and iron ore pellets 30 were charged into the furnace core tube 22 from above, in this order, and a sedimentary layer of the alumina balls 28 was formed on the alumina support 26 inside the furnace core tube 22, and a sedimentary layer of the iron ore pellets 30 was formed on top of that. The temperature inside the furnace was controlled by adjusting the output of the heater 24. A thermocouple 32 was inserted into the sedimentary layer of the iron ore pellets 30, and the thermocouple 32 measured the temperature inside the furnace.

[0037] A mixed gas containing carbon monoxide, carbon dioxide, hydrogen, methane, and nitrogen with adjusted flow rates was introduced for 90 minutes from an inlet pipe 34 disposed below the furnace core tube 22 of the reaction furnace 20, causing soot-like solid carbon to precipitate on the surfaces of the iron ore pellets 30. After the mixed gas had been introduced for 90 minutes, the iron ore pellets 30 were removed, and the solid carbon was sieved and recovered using a sieve with 125 μm openings. The invention examples and comparative examples were evaluated based on the amount of recovered solid carbon.

[0038] In this example, the CO2-containing gas used was a gas containing only CO2 and a gas with a flow rate ratio of CO2 to CO of 1:1. Since the component concentration ratio of CO2 to CO in blast furnace gas is approximately 1:1, the gas with a flow rate ratio of CO2 to CO of 1:1 is a gas that simulates blast furnace gas.

[0039] First, the results of producing solid carbon using a gas containing only CO2 as the CO2-containing gas will be explained. The test conditions and the amount of recovered solid carbon are shown in Table 1 below.

[0040] [Table 1]

[0041] As shown in Table 1, in Comparative Example 1, in which a mixed gas containing only H2 and no CH4 was used, solid carbon could not be produced in an environment of 500° C. Similarly, in Comparative Example 2, in which a mixed gas containing only CH4 and no H2 was used, solid carbon could not be produced in an environment of 500° C.

[0042] Among Comparative Example 3 and Invention Examples 1 to 3, which used a mixed gas containing CH4 and H2, Comparative Example 3 is an example of producing solid carbon in which the mixed gas did not satisfy CH4 / CO2 ≧ 30%. In Comparative Example 3, solid carbon could not be produced in an environment at 500°C. On the other hand, Invention Examples 1 to 3 are examples of producing solid carbon in which the mixed gas satisfied H2 / (H2 + CO2) > 30% and CH4 / CO2 ≧ 30%. In Invention Examples 1 to 3, solid carbon could be produced even in an environment at 500°C. From these results, when a gas containing only CO2 is used as the CO2-containing gas, a gas containing H2 and CH4 is mixed so that the mixed gas satisfies H2 / (H2 + CO2) > 30% and CH4 / CO2 ≧ 30%. This confirmed that solid carbon can be produced using a gas containing only CO2 even in an environment at 500°C.

[0043] Next, the results of producing solid carbon using a gas containing CO and CO2 as the CO2-containing gas will be described. The test conditions and the amount of solid carbon recovered are shown in Table 2 below.

[0044] [Table 2]

[0045] As shown in Table 2, in Comparative Example 4, a sufficient amount of solid carbon was produced, but the reaction of formula (3) that produces solid carbon from CO2 and H2 hardly proceeded, so this solid carbon was not CO2 but 、 This is solid carbon produced mainly from CO. In order to evaluate the amount of solid carbon produced from CO, in the examples using a gas containing CO and CO, the amount of recovered solid carbon produced in Comparative Example 4 was used as the basis for evaluation of other comparative examples and examples of the invention.

[0046] Comparative Example 5 is an example of producing solid carbon in which the mixed gas does not satisfy CH4 / CO2 ≥ 30%. In Comparative Example 5, the CH4 / CO2 ratio was set to 20.0%, but the amount of recovered solid carbon was almost the same as in Comparative Example 4. From this result, in Comparative Example 5, as in Comparative Example 4, it was found that the amount of recovered solid carbon was almost the same as in Comparative Example 4, 、It was confirmed that solid carbon was produced mainly by CO.

[0047] Comparative Example 6 is a production example in which solid carbon was produced in a gas mixture that did not satisfy CH4 / CO2 ≥ 30%, and the heating temperature of the gas mixture and iron ore pellets as a catalyst was set to 600°C. It was confirmed that the amount of solid carbon produced by CO decreased when the heating temperature of the gas mixture and iron ore pellets reached 600°C.

[0048] Comparative Example 7 is a production example in which solid carbon was produced in a gas mixture that did not satisfy the CH / CO ratio of 30% or more, and the heating temperature of the gas mixture and iron ore pellets as a catalyst was set to 700°C. It was confirmed that the amount of solid carbon produced by CO further decreased when the heating temperature of the gas mixture and iron ore pellets was set to 700°C.

[0049] Comparative Example 8 is a production example in which solid carbon was produced in a case where the mixed gas did not satisfy the CH4 / CO2 ≥ 30% ratio and the heating temperature of the mixed gas and iron ore pellets as a catalyst was set to 300°C. It was confirmed that when the heating temperature of the mixed gas and iron ore pellets reached 300°C, the reaction rate slowed down and solid carbon could no longer be produced from CO.

[0050] Examples 4 and 5 are examples of producing solid carbon in which the mixed gas satisfies H2 / (H2 + CO2) > 30% and CH4 / CO2 ≥ 30%. The amount of solid carbon recovered in Examples 4 and 5 was greater than that in Comparative Example 4. These results confirmed that the solid carbon recovered in Examples 4 and 5 contains not only CO but also solid carbon produced from CO2 according to the above formula (5), or solid carbon produced from CO produced from CO2 according to the above formula (6). These results suggest that when a gas containing CO and CO2 is used as the CO2-containing gas, the gas containing H2 and CH4 is mixed so that the mixed gas satisfies H2 / (H2 + CO2) > 30% and CH4 / CO2 ≥ 30%. This confirmed that solid carbon can be produced from CO2 even in a 500°C environment.

[0051] Examples 5 to 9 of the present invention are examples of solid carbon production in which a mixed gas satisfying H2 / (H2+CO2)>30% and CH4 / CO2≧30% is used, and the heating temperature of the mixed gas and iron ore pellets as a catalyst is changed within the range of 300 to 700°C. The results of Examples 5 to 8 confirmed that when the heating temperature of the mixed gas and iron ore pellets is higher than 600°C, the amount of recovered solid carbon was greater than in the comparative example with the same heating temperature, but the amount of recovered solid carbon tended to decrease as the heating temperature increased.

[0052] The results of Inventive Examples 5, 6, and 9 show that when the heating temperature of the mixed gas and iron ore pellets was 300°C, the amount of solid carbon recovered was greater than in the comparative example at the same heating temperature, but the amount of solid carbon recovered was less. This result is thought to be due to the slower reaction rate compared to Inventive Example 4, where the heating temperature was 400°C, and therefore the amount of solid carbon recovered was also less. The results of Inventive Examples 5 to 9 confirmed that the heating temperature of the mixed gas and iron ore pellets in producing solid carbon is preferably 400°C or higher and 600°C or lower, and more preferably 400°C or higher and 500°C or lower.

[0053] In Examples 2 and 3 of Table 1 and Examples 5 to 9 of Table 2, the flow rate ratio of H2 to CH4 was adjusted to 5:3. Since the component concentration ratio of H2 to CH4 in coke oven gas is about 5:3, Examples 2 and 3 of Table 1 and Examples 5 to 8 of Table 2 simulate the production of solid carbon using coke oven gas as a gas containing H2 and CH4.

[0054] As described above, in the solid carbon production examples shown in Table 2, a gas simulating blast furnace gas is used as the CO2-containing gas. Therefore, Examples 5 to 9 in Table 2 show production examples in which solid carbon was produced from a gas simulating blast furnace gas and a gas simulating coke oven gas, and these results confirmed that solid carbon could be produced using blast furnace gas and coke oven gas. [Explanation of symbols]

[0055] 10 blast furnace 12 Tuyere 14 Dehydration equipment 16 Solid carbon production equipment 20 Reactor 22 Furnace tube 24 Heater 26 Alumina support 28 alumina balls 30 iron ore pellets 32 Thermocouple 34 Introductory tube

Claims

1. CO ２ A gas containing H ２ and CH ４ A method for producing solid carbon, comprising mixing a gas containing a substance with a gas to obtain a mixed gas satisfying the following equations (1) and (2), and contacting the mixed gas with a catalyst. H ２ / (H ２ +CO ２ )>30%・・・(1) CH ４ / CO ２ ≧30%・・・(2) In the above formulas (1) and (2), H ２ is the component concentration (volume %) of hydrogen in the mixed gas, CO ２ is the component concentration (volume %) of carbon dioxide in the mixed gas, CH ４ is the component concentration (volume %) of methane in the mixed gas.

2. A method for producing solid carbon according to claim 1, wherein the mixed gas and the catalyst are heated to a temperature of 400°C or higher and 600°C or lower.

3. The method for producing solid carbon according to claim 1 or claim 2, wherein the catalyst is iron oxide.

4. The aforementioned H ２ and CH ４ The method for producing solid carbon according to claim 1 or claim 2, wherein the gas containing is produced using coke oven gas generated from a coke oven.

5. The method for producing solid carbon according to claim 3, wherein the gas containing H2 and CH4 is produced using coke oven gas generated from a coke oven.

6. The aforementioned CO ２ The method for producing solid carbon according to claim 1 or claim 2, wherein the gas containing the solid carbon is produced using blast furnace gas generated from a blast furnace.

7. The method for producing solid carbon according to claim 3, wherein the gas containing CO2 is produced using blast furnace gas generated from a blast furnace.

8. The method for producing solid carbon according to claim 4, wherein the gas containing CO2 is produced using blast furnace gas generated from a blast furnace.

9. The method for producing solid carbon according to claim 5, wherein the gas containing CO2 is produced using blast furnace gas generated from a blast furnace.

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