Method for producing hydrocarbon, and method for producing metal carbonate and hydrogen

Abstract

A method for producing a hydrocarbon according to the present invention comprises: a step for making a metal and carbon dioxide react in water to produce a carbonate of the metal and hydrogen; and a step for making the hydrogen and carbon dioxide react in the water containing the carbonate of the metal to produce a hydrocarbon. The metal is at least one selected from the group consisting of iron, magnesium, zinc, and manganese.

Description

Method for producing hydrocarbons, and methods for producing metal carbonates and hydrogen

[0001] The present invention relates to a method for producing hydrocarbons, and to a method for producing metal carbonates and hydrogen.

[0002] Methanation is a process in which carbon dioxide (CO ) is produced by the Sabatier reaction shown in Equation 1 below. ２ ) and hydrogen (H ２ ) to methane (CH ４ Methanation is also attracting attention from the perspective of effective utilization of carbon dioxide. (Equation 1) CO ２ + 4H ２ → CH ４ + 2H ２ O

[0003] Normally, even when a catalyst such as nickel is used, the reaction system must be heated to a temperature exceeding 300°C and a pressure exceeding 1 atmosphere in order to proceed with the reaction and synthesize methane. As a technology to solve this problem, photomethanation, which promotes the reaction by irradiating light, has been proposed (see, for example, Non-Patent Document 1). It has been reported that photomethanation can proceed with the reaction and synthesize methane without high temperature and pressure (for example, at room temperature and atmospheric pressure).

[0004] On the other hand, there is known a technique called submerged photosynthesis of crystallites (SPsC), which uses water and light to synthesize nanocrystals. For example, Non-Patent Document 2 discloses that zinc oxide nanocrystals can be synthesized by irradiating water in which a plasma-treated zinc plate is immersed with ultraviolet light.

[0005] Thampi, K., Kiwi, J. & Gratzel, M., "Methanation and photo-methanation of carbon dioxide at room temperature and atmospheric pressure", Nature, 327, 506-508.Melbert Jeem, Muhammad Rafiq Mirza bin Julaihi, Junya Ishioka, Shigeo Yatsu, Kazumasa Okamoto, Tamaki Shibayama, Tomio Iwasaki, Takahiko Kato & Seiichi Watanabe, "A pathway of nanocrystallite fabrication by photo-assisted growth in pure water", Scientific Reports, 5, 11429.

[0006] Conventional methanation and photomethanation technologies require the supply of hydrogen to the reaction system.

[0007] An object of the present invention is to provide a method for producing hydrocarbons that can produce hydrocarbons without supplying hydrogen, a method for producing metal carbonates and hydrogen that can be used in the hydrocarbon production method, and a method for producing hydrocarbons using the metal carbonates.

[0008] The present invention relates to the following methods for producing hydrocarbons, and methods for producing metal carbonates and hydrogen. [1] A method for producing hydrocarbons, comprising the steps of reacting a metal with carbon dioxide in water to produce a carbonate of the metal and hydrogen, and reacting the hydrogen with carbon dioxide in the water containing the carbonate of the metal to produce hydrocarbons, wherein the metal is at least one selected from the group consisting of iron, magnesium, zinc, and manganese. [2] The method for producing hydrocarbons according to [1], which is carried out in a sealed container. [3] The method for producing hydrocarbons according to [1] or [2], which is carried out while irradiating the water with light. [4] The method for producing hydrocarbons according to [3], wherein the light is ultraviolet light or visible light. [5] When the light is ultraviolet light, the irradiance of the ultraviolet light is 5 mW / cm. ２ or more, and when the light is visible light, the irradiance of the visible light is 50 mW / cm ２[4] A method for producing hydrocarbons according to any one of [1] to [5], which is carried out at a temperature of 300°C or less. [7] A method for producing hydrocarbons according to any one of [1] to [6], which is carried out under a pressure of 4 atmospheres or less. [8] A method for producing hydrocarbons according to any one of [1] to [7], wherein the metal is iron or magnesium. [9] A method for producing hydrocarbons according to [8], wherein the metal is iron.

[10] A method for producing hydrocarbons according to any one of [1] to [9], wherein the metal before reacting with carbon dioxide is in the form of particles having an average particle size of 100 nm to 30 μm.

[11] A method for producing hydrocarbons according to any one of [1] to

[10] , wherein the metal carbonate is in the form of particles having a plurality of protrusions.

[12] A method for producing hydrocarbons according to any one of [1] to

[11] , wherein the hydrocarbon is at least one selected from methane, ethane, propane, butane, ethylene, propylene, butene, and butadiene.

[13] A method for producing hydrocarbons according to

[12] , wherein the hydrocarbon is methane.

[14] A method for producing hydrocarbons, comprising a step of reacting hydrogen and carbon dioxide in water containing a metal carbonate to produce hydrocarbons, wherein the metal is at least one selected from the group consisting of iron, magnesium, zinc, and manganese.

[15] A method for producing metal carbonate and hydrogen, comprising a step of reacting a metal with carbon dioxide in water while irradiating it with light in a sealed container to produce particles of the metal carbonate having a plurality of protrusions and hydrogen, wherein the metal is at least one selected from the group consisting of iron, magnesium, zinc, and manganese, and the metal carbonate particles have an average particle size of 1 μm or less.

[0009] According to the present invention, it is possible to provide a method for producing hydrocarbons that can produce hydrocarbons without supplying hydrogen, a method for producing metal carbonates and hydrogen that can be used in the hydrocarbon production method, and a method for producing hydrocarbons using the metal carbonates.

[0010] FIG. 1 is a flowchart of a hydrocarbon production method according to one embodiment of the present invention. FIGS. 2A and 2B are metal potential-pH diagrams. FIGS. 3A and 3B are cross-sectional schematic diagrams showing an example of a hydrocarbon production apparatus for carrying out the hydrocarbon production method according to the present invention. FIG. 4 is an SEM image of iron powder used in the examples. FIG. 5A is a TEM image of a precipitate after 3 hours of reaction with ultraviolet light irradiation. FIG. 5B is a TEM image of a precipitate after 24 hours of reaction with ultraviolet light irradiation. FIG. 5C is a TEM image of a precipitate after 24 hours of reaction without light irradiation. FIG. 6A is an XRD pattern obtained from a precipitate after 3 hours of reaction in a sealed state. FIG. 6B is an XRD pattern obtained from a precipitate after 24 hours of reaction in an open state. FIG. 7 is an XRD pattern obtained from a precipitate after 24 hours of reaction in a sealed state. FIG. 8A is a TEM image of iron carbonate particles after 3 hours of reaction with visible light irradiation. Figure 8B is a TEM image of iron carbonate particles after 6 hours of reaction with visible light irradiation. Figure 8C is a TEM image of iron carbonate particles after 3 hours of reaction with UV light irradiation. Figure 8D is a TEM image of iron carbonate particles after 6 hours of reaction with UV light irradiation. Figure 9 is a STEM-EDS mapping image of O, Fe, and C of the iron carbonate particles shown in Figure 8B. Figure 10A is an SEM image of iron carbonate particles after 4 hours of reaction with UV light irradiation. Figure 10B is an SEM image of iron carbonate particles after 18 hours of reaction with UV light irradiation. Figure 10C is an SEM image of iron carbonate particles after 24 hours of reaction with UV light irradiation. Figure 10D is an SEM image of iron carbonate particles after 4 hours of reaction without light irradiation. Figure 10E is an SEM image of iron carbonate particles after 18 hours of reaction without light irradiation. Figure 10F is an SEM image of iron carbonate particles after 24 hours of reaction without light irradiation. Figure 11A is a graph showing the relationship between reaction time and the amount of hydrogen and methane produced. Figure 11B is a graph showing the relationship between reaction time and the amount of methane produced. Figure 12 is a graph showing the relationship between the amount of iron powder and the amount of hydrogen and methane produced. Figure 13 is a graph showing the results of gas chromatography when magnesium powder was used.FIG. 14 is a graph showing the results of gas chromatography when iron powder and magnesium powder were used.

[0011] The present inventors have found that the above-mentioned problems can be solved by combining the reaction shown in the following formula 2, which produces iron carbonate and hydrogen by underwater crystal photosynthesis, with the reaction shown in the following formula 3, which produces methane by photomethanation. In formulas 2 and 3, "hv" means that light is irradiated, and "cat." means that a catalyst is present. (Formula 2) Fe + CO ２ + H ２ O + hv → FeCO ３ ↓ + H ２ ↑ (Formula 3) CO ２ + 4H ２ +hv +cat. →CH ４ ↑ + 2H ２ O

[0012] Specifically, iron carbonate (FeCO) produced by the reaction of Equation 2 ３ ) is used as a catalyst (cat.) in the reaction of Equation 3, and hydrogen (H ２ By using 4Fe + 5CO as a raw material in the reaction of Equation 3, methane can be produced from carbon dioxide and water without supplying hydrogen from an external source. More precisely, iron carbonate and methane can be produced from iron, carbon dioxide, and water, as shown in Equation 4 below. (Equation 4) 4Fe + 5CO ２ + 2H ２ O (+ hv) → 4FeCO ３ + CH ４

[0013] According to experiments conducted by the present inventors, it has been confirmed that the above reaction proceeds even without light irradiation (see Example 1). Therefore, from the viewpoint of promoting the reaction, it is preferable to irradiate with light, but irradiation is not necessarily required.

[0014] Furthermore, the metal used as the raw material for the catalyst does not have to be iron. As will be explained later, methane can also be produced by using magnesium (Mg), zinc (Zn), manganese (Mn), etc. instead of iron (Fe). Two or more types of metals used as the raw material for the catalyst may be used in combination. For example, the metals used as the raw material for the catalyst may be a combination of iron and magnesium.

[0015] The method for producing hydrocarbons according to the present invention will now be described in more detail.

[0016] Fig. 1 is a flowchart of a hydrocarbon production method according to one embodiment of the present invention. As shown in Fig. 1, the hydrocarbon production method according to the present invention includes a first step (aqueous crystal photosynthesis step; S110) of reacting a metal with carbon dioxide in water to produce metal carbonate and hydrogen, and a second step (photomethanation step; S120) of reacting hydrogen with carbon dioxide in water containing metal carbonate to produce hydrocarbons. Note that although the terms "aqueous crystal photosynthesis" and "photomethanation" are used in this flowchart, as mentioned above, light irradiation is preferable from the viewpoint of promoting the reaction, but is not necessarily required.

[0017] If it is desired to produce only metal carbonate and / or hydrogen, only the first step (aqueous crystal photosynthesis step; S110) may be performed without performing the second step (S120). Also, if metal carbonate and hydrogen have already been prepared, only the second step (photomethanation step; S120) may be performed without performing the first step (S110). Each step will be described below.

[0018] In the first step (underwater crystal photosynthesis step; S110), metal (M) and carbon dioxide (CO) are reacted in water as shown in the following formula 5. ２ ) to produce metal carbonate (MCO ３ ) and hydrogen (H ２) is produced. From the viewpoint of promoting the reaction, it is preferable to irradiate with light, but irradiation is not necessarily required. By dissolving carbon dioxide in water, the water becomes acidic. This makes it easier for metals to dissolve and for hydrogen to be produced. Note that substances other than the above metals and carbon dioxide may be dissolved or dispersed in the water. (Equation 5) M + CO ２ + H ２ O → MCO ３ ↓ + H ２ ↑

[0019] The type of metal is not particularly limited as long as it can function as a catalyst that can promote the production of hydrogen and hydrocarbons in its original state or in the form of a carbonate. For example, as shown in FIG. 2A, in the potential-pH diagram of a metal (M), M and M ２＋ The metals where the boundary line A is located below the dashed line b are preferred. In the region below the dashed line b, hydrogen is generated. Therefore, in the colored region in FIG. 2A, M ２＋ and hydrogen (H ２ On the other hand, as shown in FIG. 2B, both M and M ２＋ Metals whose boundary line A is located above the dashed line b are not preferred.

[0020] Examples of metals that can be used in the present invention include iron (Fe), magnesium (Mg), zinc (Zn), and manganese (Mn). These metals may be used alone or in combination of two or more. These metals may be used in a simple state or in an alloy state. These metals may also contain other elements. Iron is preferred from the standpoint of availability and price. For example, the iron may be scrap iron.

[0021] Table 1 shows the reactions that can occur for the four metals, the enthalpy change ΔH (25°C), and the Gibbs energy change ΔG (25°C). Table 1 shows that when any of these four metals is used, the reaction of formula 5 (the reaction in the first step) and the subsequent reaction of formula 8 (the reaction in the second step) proceed even at room temperature.

[0022]

[0023] The shape of the metal before reacting with carbon dioxide is not particularly limited, but a shape with a large specific surface area is preferred. For example, the metal is preferably in the form of particles, more preferably particles with an average particle size of 100 nm to 500 μm, and particularly preferably particles with an average particle size of 100 nm to 30 μm. The shape of the particles is not particularly limited, and may be, for example, approximately spherical, flake-like, a shape with multiple protrusions, or an irregular shape.

[0024] Here, in this specification, the average particle size of particles is preferably measured by the following measurement method. First, particles are photographed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) to obtain an image. 100 particles are selected from the large number of particles present in the obtained image. For each particle, the maximum length and minimum length are measured, and the average value of these is taken as the particle size of the particle. The average value of the particle sizes of the 100 particles is taken as the average particle size of the particles.

[0025] The numerical value of the average particle size varies slightly depending on the measurement method. For example, when a particle size distribution analyzer is used, the value may vary depending on the measurement principle, and when image analysis is used, the value may vary depending on the image processing method. However, the range of the average particle size of the metal particles (and metal carbonate particles, described later) specified in this specification takes such variations into consideration, and regardless of the method used to measure the average particle size, the desired effect can be stably achieved as long as it falls within the range specified in this specification.

[0026] The amount of metal in water (e.g., the amount of metal particles dispersed in water) is not particularly limited as long as it can promote the reaction, but is preferably in the range of 0.01 to 0.1 mol / L. For example, when the metal is iron, the amount of iron in water may be about 0.03 mol / L.

[0027] The concentration of carbon dioxide in water is not particularly limited as long as the metal can be converted into a metal ion. ２＋For example, when the metal is iron, it is preferable to supply carbon dioxide so that the pH of the water (aqueous solution) is 5 or less.

[0028] In the first step, it is preferable to supply water, metal, and carbon dioxide into a sealed container and react them in the sealed container. By reacting them in a sealed container under a low oxygen partial pressure, a carbonate of the metal (e.g., iron carbonate, FeCO ３ ) can be efficiently produced (Equation 6). On the other hand, if the reaction is carried out in an open system with a high oxygen partial pressure, the metal reacts with oxygen, and metal hydroxides (e.g., goethite, α-FeOOH) are more likely to be produced (Equation 7). These metal hydroxides can be used, for example, as electrode materials for lithium-ion batteries. (Equation 6) M + CO ２ + H ２ O → MCO ３ + H ２ (Formula 7) 4M ２＋ + 6H ２ O + O ２ → 4MOOH + 8H ＋

[0029] The shape of the metal carbonate produced in the first step is not particularly limited, but may be, for example, a particle having multiple protrusions. The particle does not have to be composed solely of metal carbonate; for example, it may be a particle having a metal particle as a core, with numerous carbonate microcrystals attached around the core. When these carbonate microcrystals grow approximately radially from the core, they appear as protrusions. In particular, when the reaction is carried out under light irradiation, the metal carbonate microcrystals tend to grow approximately radially from the core by underwater crystal photosynthesis (see Non-Patent Document 2), and the metal carbonate tends to become particles with multiple protrusions. On the other hand, when the reaction is carried out without light irradiation, the metal carbonate microcrystals tend to aggregate around the core, and the metal carbonate tends to become aggregate-like particles with few distinct protrusions.

[0030] In the first step, it is preferable to carry out the reaction while irradiating the water with light. By carrying out the reaction while irradiating light, the reaction can be promoted (see Examples). The type of light is not particularly limited as long as it can promote the reaction. For example, the light is ultraviolet light with a wavelength of 200 to 380 nm, or visible light with a wavelength of 380 to 780 nm. The irradiance of the light is not particularly limited as long as it can promote the reaction. Here, the irradiance means the irradiance at the part of the water interface that is closest to the light source. When irradiating ultraviolet light, the irradiance of the ultraviolet light is, for example, 5 mW / cm ２ When irradiating with visible light, the irradiance of the visible light is, for example, 50 mW / cm ２ The upper limit of the irradiance is not particularly limited.

[0031] In the first step, it is preferable to carry out the reaction while stirring water, etc. By carrying out the reaction while stirring water, etc., the reaction can be promoted. The stirring method and stirring speed are not particularly limited. The stirring speed may be, for example, about 50 to 500 rpm.

[0032] In the first step, unlike conventional methanation and photomethanation, the reaction proceeds even at room temperature (25°C) and 1 atmosphere. Therefore, the reaction may be carried out at a temperature of 300°C or lower, or at a pressure of 4 atmospheres or lower.

[0033] In the second step (photomethanation step; S120), metal carbonate (MCO ３ ) in water containing hydrogen (H ２ ) and carbon dioxide (CO ２ ) to form a hydrocarbon (e.g., CH ４ ) is produced. Metal carbonate is thought to function as a catalyst. From the viewpoint of promoting the reaction, it is preferable to irradiate with light, but it is not necessarily required. When irradiated with light, it is thought that metal carbonate functions as a photocatalyst. (Equation 8) CO ２ + 4H ２ + cat. (MCO ３ ) → CH ４ ↑ + 2H２ O

[0034] Usually, once the first step has progressed to a certain extent and metal carbonate and hydrogen have been produced, the second step begins naturally. After that, the first and second steps proceed in parallel in the same vessel.

[0035] The second step primarily produces methane, but other hydrocarbons may also be produced. Examples of hydrocarbons produced in the second step include methane, ethane, propane, butane, ethylene, propylene, butene, and butadiene.

[0036] In the second step, too, it is preferable to carry out the reaction in a sealed container. By carrying out the reaction in a sealed container under conditions of low oxygen partial pressure, hydrocarbons can be produced efficiently. From the viewpoint of productivity, it is preferable to carry out the reaction in the second step by continuing to use the same sealed container used in the first step.

[0037] In the second step, too, it is preferable to carry out the reaction while irradiating the water with light. By carrying out the reaction while irradiating light, the reaction can be promoted (see Examples). The type of light is not particularly limited as long as it can promote the reaction. For example, the light is ultraviolet light with a wavelength of 200 to 380 nm, or visible light with a wavelength of 380 to 780 nm. The irradiance of the light is not particularly limited as long as it can promote the reaction. As mentioned above, the irradiance means the irradiance at the part of the water interface that is closest to the light source. When irradiating ultraviolet light, the irradiance of the ultraviolet light is, for example, 5 mW / cm ２ When irradiating with visible light, the irradiance of the visible light is, for example, 50 mW / cm ２ The upper limit of the irradiance is not particularly limited.

[0038] In the second step, too, it is preferable to carry out the reaction while stirring the water, etc. By carrying out the reaction while stirring the water, etc., the reaction can be promoted. The stirring method and stirring speed are not particularly limited. The stirring speed may be, for example, about 50 to 500 rpm.

[0039] In the second step, unlike conventional methanation and photomethanation, the reaction proceeds even at room temperature (25°C) and 1 atmosphere. Therefore, the reaction may be carried out at a temperature of 300°C or lower, or at a pressure of 4 atmospheres or lower.

[0040] By carrying out the above-mentioned first step (underwater crystal photosynthesis step) and second step (photomethanation step), hydrocarbons can be produced from carbon dioxide and water without supplying hydrogen from an external source. In addition, metal carbonates (e.g., iron carbonate) produced together with hydrocarbons can be used as photocatalysts, materials for batteries, and materials for capacitors.

[0041] As described above, the hydrocarbon production method according to the present invention can produce hydrocarbons from carbon dioxide and water without supplying hydrogen from an external source. Furthermore, because iron (Fe) is used as the catalyst (raw material), which is more readily and inexpensively available than nickel (Ni) or ruthenium (Ru), which have been used as catalysts in (photo)methanation up to now, hydrocarbons can be produced more easily and inexpensively than with conventional (photo)methanation.

[0042] 3A and 3B are cross-sectional schematic views showing examples of hydrocarbon production apparatuses for carrying out the hydrocarbon production method according to the present invention.

[0043] In the example shown in FIGS. 3A and 3B, the hydrocarbon production apparatus 100 has a reaction vessel 110, a light source 120, and an agitator blade 130. At least a portion of the reaction vessel 110 is made of a material that transmits light from the light source 120. The reaction vessel 110 is also provided with a carbon dioxide supply port 112 and a hydrocarbon recovery port 114. As shown in FIG. 3B, a hydrocarbon separation membrane 140 may be installed in the hydrocarbon recovery port 114. In the example shown in FIG. 3A, hydrogen (H ２ ) and hydrocarbons (e.g., methane (CH ４ )) is recovered from the hydrocarbon recovery port 114, whereas in the example shown in FIG. ４ )) will be collected.

[0044] For example, hydrocarbons can be produced using the hydrocarbon production apparatus 100 by the following procedure. First, water 150 and metal particles 160 (e.g., iron powder) are supplied into the reaction vessel 110. Next, carbon dioxide (CO ) is supplied into the reaction vessel 110 through the carbon dioxide supply port 112. ２ ) is supplied to the reaction vessel 110, and the first and second steps are carried out. At this time, it is preferable to irradiate the reaction vessel 110 with light 122 from the light source 120, and to stir the water 150 in the reaction vessel 110 with the stirring blades 130. The stirring speed is not particularly limited, but is, for example, about 50 to 500 rpm. In the first step, metal carbonate particles 170 (for example, iron carbonate (FeCO ３ The metal carbonate particles 170 can function as a photocatalyst, and in the second step, hydrocarbons (e.g., methane (CH ４ )) and the resulting hydrocarbons (e.g., methane (CH ４ )) is recovered from the hydrocarbon recovery port 114.

[0045] The present invention will be described in more detail by the following examples, but the present invention is not limited to these examples.

[0046] Example 1 330 mL of water with carbon dioxide dissolved therein (carbonated water, pH: 3.7 to 4.5) and 0.5 g of iron powder (Kojundo Chemical Laboratory Co., Ltd., average particle size 3 to 5 μm) were placed in a light-transmitting airtight container (a 500 mL plastic bottle) and sealed. Figure 4 shows a scanning electron microscope (SEM) image of the iron powder.

[0047] The reaction was allowed to proceed for a predetermined time (3 to 48 hours) under a room temperature (25°C) environment, with or without irradiation of ultraviolet light (wavelength 365±10 nm) or visible light (wavelength 400 to 600 nm) on the water and iron powder in the container from outside the container, while stirring the water and iron powder in the container at 50 to 200 rpm. The ultraviolet light source used was a UVP lamp (B-100AP) manufactured by UVP Corporation. The visible light source used was a spot light source (LIGHTNINGCURE LC8, L9566) manufactured by Hamamatsu Photonics. The ultraviolet irradiance was 10 mW / cm. ２ or 100 mW / cm ２The irradiance of visible light was 80 mW / cm ２ , 100 mW / cm ２ or 160 mW / cm ２ The experiment was carried out multiple times with different stirring speeds. The gas generated in the vessel was collected and analyzed by gas chromatography, and the precipitate in the vessel was also collected and analyzed.

[0048] Figure 5A is a transmission electron microscope (TEM) image of the precipitate (iron carbonate particles) after 3 hours of reaction with ultraviolet (UV) light at room temperature. Figure 5B is a TEM image of the precipitate (iron carbonate particles) after 24 hours of reaction with ultraviolet light at room temperature. Figure 5C is a TEM image of the precipitate (iron carbonate particles) after 24 hours of reaction at room temperature without light (dark). These images show that iron carbonate grew from the surface of the iron particles, forming iron carbonate particles with multiple protrusions. It also shows that light (UV) irradiation promoted the growth of iron carbonate crystals (protrusions).

[0049] Fig. 6A is an XRD pattern obtained from the precipitate after reacting in a sealed state for 3 hours. Fig. 6B is an XRD pattern obtained from the precipitate after reacting in an open state for 24 hours for comparison. Fig. 7 is an XRD pattern obtained from the precipitate after reacting in a sealed state for 24 hours. In these graphs, "UV" indicates irradiation with ultraviolet light, and "Dark" indicates no irradiation with light. Figs. 6A and 7 show that when reacted in a sealed state, iron carbonate (FeCO ３ On the other hand, it can be seen from FIG. 6B that goethite (α-FeOOH) was produced when the reaction was carried out in an open state.

[0050] Figure 8A is a TEM image of iron carbonate particles after 3 hours of reaction with visible light (VIS) irradiation. Figure 8B is a TEM image of iron carbonate particles after 6 hours of reaction with visible light irradiation. Figure 8C is a TEM image of iron carbonate particles after 3 hours of reaction with ultraviolet (UV) irradiation. Figure 8D is a TEM image of iron carbonate particles after 6 hours of reaction with UV irradiation. Figure 9 is a STEM-EDS mapping image of O, Fe, and C of the iron carbonate particles shown in Figure 8B. These images show that iron carbonate grew from the surface of the iron particles over time, forming iron carbonate particles with multiple protrusions. It also shows that iron carbonate protrusions formed more densely when UV was irradiated than when visible light was irradiated.

[0051] Figure 10A is an SEM image of iron carbonate particles after 4 hours of reaction with ultraviolet (UV) light irradiation. Figure 10B is an SEM image of iron carbonate particles after 18 hours of reaction with ultraviolet light irradiation. Figure 10C is an SEM image of iron carbonate particles after 24 hours of reaction with ultraviolet light irradiation. Figure 10D is an SEM image of iron carbonate particles after 4 hours of reaction without light irradiation (dark). Figure 10E is an SEM image of iron carbonate particles after 18 hours of reaction without light irradiation. Figure 10F is an SEM image of iron carbonate particles after 24 hours of reaction without light irradiation. These images show that light (ultraviolet) irradiation promoted the growth of iron carbonate crystals (protrusions).

[0052] FIG. 11A is a graph showing the relationship between reaction time and the amounts of hydrogen and methane produced. ２ Dark) indicates the amount of hydrogen produced when no light is irradiated (scale on the vertical axis on the left), and the solid line with triangles (H ２ VIS) indicates the amount of hydrogen generated when irradiated with visible light (scale on the left vertical axis), and the dashed line with a circle (CH ４ The solid line (CH ４VIS) shows the amount of methane produced when irradiated with visible light (the scale on the vertical axis on the right). This graph shows that hydrogen and methane were produced even without light irradiation. It also shows that irradiation with visible light promoted the production of hydrogen and methane.

[0053] FIG. 11B is a graph showing the relationship between reaction time and the amount of methane produced. At each time, the white bar on the right (CH ４ The hatched bar in the center (CH ４ VIS) indicates the amount of methane produced when irradiated with visible light, and the black bar on the left (CH ４ The graph shows the amount of methane produced when exposed to ultraviolet light (UV). This graph shows that methane was produced even without light irradiation. It also shows that methane production was promoted by irradiating the plant with visible light or ultraviolet light.

[0054] FIG. 12 is a graph showing the relationship between the amount of iron powder and the amount of hydrogen and methane produced in 330 mL of water (carbonated water) with carbon dioxide dissolved therein. In this experiment only, the amount of iron powder was changed from 0.5 g to 0.1 g or 1.0 g and the reaction was carried out. ２ VIS) indicates the amount of hydrogen generated when irradiated with visible light (scale on the left vertical axis), and a circle (CH ４ VIS) shows the amount of methane produced when irradiated with visible light (scale on the vertical axis on the right). From this graph, it can be seen that a certain amount of iron powder is required for methane production.

[0055] Table 2 shows the relationship between light irradiance and the amount of methane produced. In this experiment, the reaction was carried out for 24 hours. This table shows that, for both visible light and ultraviolet light, increasing the irradiance increases the amount of methane produced.

[0056]

[0057] Table 3 shows the relationship between the amount of methane produced and whether or not the water was degassed with nitrogen. In this experiment, the reaction was carried out for 24 hours. This table shows that the production of methane was suppressed by degassing with nitrogen. This suggests that oxygen is involved in the production of methane.

[0058]

[0059] Table 4 shows the relationship between the temperature of water during the reaction and the amount of methane produced. In this experiment, the reaction was carried out for 3 hours. A hyphen indicates that the amount of methane produced was below the detection limit. This table shows that methane can be produced in a short time if the temperature is increased.

[0060]

[0061] Table 5 shows the relationship between the average particle size of iron powder and the amount of hydrogen and methane produced when no light is irradiated. Table 6 shows the relationship between the average particle size of iron powder and the amount of hydrogen and methane produced when irradiated with visible light. Table 7 shows the relationship between the average particle size of iron powder and the amount of hydrogen and methane produced when irradiated with ultraviolet light. In these experiments, the reaction was carried out for 24 hours. A hyphen indicates that the amount of methane produced was below the detection limit. These tables suggest that the smaller the particle size of the iron powder, the greater the amount of methane produced.

[0062]

[0063]

[0064]

[0065] Example 2 330 mL of water with dissolved carbon dioxide (carbonated water, pH: 3.7-4.5) and 0.5 g of magnesium powder (Kanto Chemical Co., Inc., average particle size 150-500 μm) were placed in a light-transmitting sealed container (a 500 mL plastic bottle) and sealed. Under a room temperature (25°C) environment, the water and magnesium powder in the container were irradiated with ultraviolet light (wavelength 365±10 nm) from outside the container, and the water and magnesium powder in the container were stirred at 0-200 rpm, allowing the reaction to proceed for 24 hours. A UVP lamp (B-100AP) from UVP Corporation was used as the ultraviolet light source. The ultraviolet irradiance was 100 mW / cm. ２ The experiment was carried out multiple times with different stirring speeds. The gas generated in the vessel was collected and analyzed by gas chromatography.

[0066] Figure 13 is a graph showing the results of gas chromatography, which shows that even when magnesium powder was used, methane was produced, although in small amounts.

[0067] Example 3: 330 mL of water (carbonated water, pH: 3.7-4.5) with dissolved carbon dioxide, iron powder (Kojundo Chemical Laboratory Co., Ltd., average particle size 3-5 μm), and magnesium powder (Kanto Chemical Co., Ltd., average particle size 212-600 μm) were placed in a light-transmitting sealed container (a 500 mL plastic bottle) and sealed. The amount of iron powder was 5.00 mmol. The amount of magnesium powder was 1.00 mmol, 2.00 mmol, 3.00 mmol, 4.00 mmol, or 5.00 mmol. For comparison, an experiment was also conducted in which only 0.500 g (8.95 mmol) of iron powder was added without magnesium powder. At room temperature (25°C), the reaction was allowed to proceed for 24 hours while irradiating the water, iron powder, and magnesium powder inside the container with ultraviolet light (wavelength 365±10 nm) from outside the container. A UVP lamp (B-100AP) from UVP Corporation was used as the ultraviolet light source. The ultraviolet irradiance is 10 mW / cm ２ The gas generated in the vessel was collected and analyzed by gas chromatography.

[0068] FIG. 14 is a graph showing the results of gas chromatography. This graph shows the amount of gas (hydrogen or methane) produced per 1.00 mmol of metal (iron powder and magnesium powder) placed in a sealed container. Under each condition, the black bars on the left (H ２ ) indicates the amount of hydrogen produced, and the white bar on the right (CH ４ ) indicates the amount of methane produced. The result on the far right shows the result when no magnesium powder was used and only 0.500 g (8.95 mmol) of iron powder was used. This graph shows that methane was also produced when iron and magnesium were used in combination. It also shows that the most hydrogen and methane were produced when 5.00 mmol of iron and 2.00 mmol of magnesium were combined.

[0069] This application claims priority from Japanese Patent Application No. 2024-005312, filed January 17, 2024. The entire contents of the specification and drawings of said application are incorporated herein by reference.

[0070] The hydrocarbon production method according to the present invention can produce methane, which is useful as a fuel, a chemical raw material, etc., without preparing hydrogen and using inexpensive water, carbon dioxide, and iron. The hydrocarbon production method according to the present invention is useful from the viewpoints of being able to produce methane without preparing hydrogen, being able to effectively use carbon dioxide, being able to reuse iron, and being able to use an inexpensive catalyst.

[0071] REFERENCE SIGNS LIST 100 Hydrocarbon production apparatus 110 Reaction tank 112 Carbon dioxide supply port 114 Hydrocarbon recovery port 120 Light source 122 Light 130 Stirring blade 140 Hydrocarbon separation membrane 150 Water 160 Metal particles 170 Metal carbonate particles

Claims

1. A step of reacting a metal with carbon dioxide in water to produce a carbonate and hydrogen of the metal; a step of reacting hydrogen with carbon dioxide in the water containing the carbonate of the metal to produce a hydrocarbon; and the method for producing a hydrocarbon, wherein the metal is at least one selected from the group consisting of iron, magnesium, zinc, and manganese.

2. The method for producing a hydrocarbon according to claim 1, which is carried out in a sealed container.

3. The method for producing a hydrocarbon according to claim 1, which is carried out while irradiating light on the water.

4. The method for producing a hydrocarbon according to claim 3, wherein the light is ultraviolet light or visible light.

5. When the light is ultraviolet light, the irradiance of the ultraviolet light is 5 mW / cm ２ or more, and when the light is visible light, the irradiance of the visible light is 50 mW / cm ２ or more. The method for producing a hydrocarbon according to claim 4.

6. The method for producing a hydrocarbon according to claim 1, which is carried out at a temperature of 300 °C or lower.

7. The method for producing a hydrocarbon according to claim 1, which is carried out under a pressure of 4 atmospheres or lower.

8. The method for producing a hydrocarbon according to claim 1, wherein the metal is iron or magnesium.

9. The method for producing a hydrocarbon according to claim 8, wherein the metal is iron.

10. The method for producing a hydrocarbon according to claim 1, wherein the metal before reacting with carbon dioxide is particles having an average particle size of 100 nm to 30 μm.

11. The method for producing a hydrocarbon according to claim 1, wherein the carbonate of the metal is particles having a plurality of protrusions.

12. The method for producing a hydrocarbon according to claim 1, wherein the hydrocarbon is at least one selected from the group consisting of methane, ethane, propane, butane, ethylene, propylene, butene, and butadiene.

13. The method for producing a hydrocarbon according to claim 12, wherein the hydrocarbon is methane.

14. A method for producing a hydrocarbon, comprising a step of reacting hydrogen with carbon dioxide in water containing a carbonate of a metal to produce a hydrocarbon, wherein the metal is at least one selected from the group consisting of iron, magnesium, zinc, and manganese.

15. A method for producing a carbonate and hydrogen of a metal, comprising a step of reacting a metal with carbon dioxide in water while irradiating light in a sealed container to produce particles of the carbonate of the metal having a plurality of protrusions and hydrogen, wherein the metal is at least one selected from the group consisting of iron, magnesium, zinc, and manganese, and the average particle size of the particles of the carbonate of the metal is 1 μm or less.

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