Methane gas conversion method and methane gas conversion equipment

Abstract

To provide a methane gas conversion method and methane gas conversion equipment, each efficiently converting methane gas into organic matter.SOLUTION: The methane gas conversion method is provided in which fluid formed by mixing an ozone-containing fluid with methane gas-containing fluid, is irradiated with light having a wavelength of 200 nm to 411 nm, inclusive, thereby converting the methane gas into organic matter. The methane gas conversion equipment comprises: a reaction vessel which includes a first supply port supplying the ozone-containing fluid and a second supply port supplying the methane gas-containing fluid; and a light source for irradiating the inside of the reaction vessel with light having a wavelength of 200 nm to 411 nm, inclusive.SELECTED DRAWING: Figure 2A

Description

[Technical field]

[0001] The present invention relates to a method and an apparatus for converting methane gas. [Background technology]

[0002] Methane gas is released into the atmosphere from sewage, livestock waste, food waste, etc. Methane gas is known as a greenhouse gas that causes global warming. The global warming potential of methane gas is said to be 25 times that of carbon dioxide, so it is not desirable to release methane gas directly into the atmosphere. Therefore, the recovery of methane gas released into the atmosphere has been considered. Methane gas can be decomposed by using the recovered methane gas to operate an engine or extracting thermal energy in a boiler. However, methane gas is a gas at room temperature and pressure, and transporting it in a gaseous state to the combustion site is inefficient and difficult to store.

[0003] There is a known method of converting the captured methane gas to produce organic matter. If the captured methane gas is used as a raw material to produce organic matter, not only will the amount of methane gas released be reduced, but the carbon contained in the methane gas will also be fixed, further contributing to curbing global warming. Furthermore, the cost of converting the methane gas can be recovered by selling the organic matter produced. Furthermore, converting methane gas into organic matter is also advantageous in terms of the efficiency of transporting methane gas and the ease of storing it.

[0004] Patent Document 1 describes a method in which light is applied to an environment in which hydrocarbons such as methane and chlorine dioxide are present to generate chlorine radicals, which are then bonded to the hydrocarbons to generate organic substances such as methanol. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6080281 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology described in Patent Document 1 requires chlorine dioxide. To prepare chlorine dioxide, it is necessary to prepare raw materials for chlorine dioxide, such as NaClO2 and HCl, and chemically react them. Then, energy is required for distillation and evaporation to separate methanol and formic acid from the generated salt NaCl and the aqueous solution containing HCl. In other words, monetary and energy costs are incurred to prepare chlorine dioxide and separate the product. Regarding energy costs, it is not desirable from the viewpoint of carbon neutrality to input a large amount of energy for the conversion of methane gas, which is a greenhouse gas. Furthermore, there is a problem that chlorine-based materials such as chlorine dioxide are prone to corrode equipment such as reaction vessels.

[0007] Therefore, a method for converting methane gas without using chlorine-based materials such as chlorine dioxide is provided. [Means for solving the problem]

[0008] The methane gas conversion method of the present invention is characterized in that a mixed fluid, in which an ozone-containing fluid and a methane-containing fluid are mixed, is irradiated with light having a wavelength of 200 nm or more and 411 nm or less, to convert the methane gas into organic matter. As will be described in detail later, by irradiating the mixed fluid with light having a wavelength of 200 nm or more and 411 nm or less, a large amount of atomic oxygen, particularly O( 1 D) and produces a large amount of an intermediate called methoxy in the methane gas conversion process. The presence of methoxy triggers a cycle reaction that leads to the production of organic substances, methanol or formic acid. This allows large amounts of methane gas to be converted into industrially useful organic substances, such as methanol or formic acid, without using chlorine-based materials.

[0009] In this specification, the organic matter obtained by converting methane gas is methanol and formic acid. However, the "organic matter" obtained by converting methane gas may be an organic matter other than methanol and formic acid. In this specification, the "organic matter" is a compound containing carbon, excluding carbon monoxide, carbon dioxide, and methane. The "organic matter" may be, for example, an alcohol other than methanol, a carboxylic acid other than formic acid, or an ester obtained by dehydration condensation of an alcohol and a carboxylic acid. Methane gas may be converted into a compound containing carbon other than methanol or formic acid (e.g., methyl formate) after producing methanol or formic acid as an intermediate in the conversion process.

[0010] The ozone-containing fluid may be generated by passing ozone gas through an ozone-permeable membrane immersed in a polar solvent or a non-polar solvent. This generates a liquid in which ozone is dissolved as bubbles with a diameter of less than 1 mm (including microbubbles or nano-sized ultrafine bubbles). When the bubbles are less than 1000 μm, a state in which ozone is dissolved in the liquid at a high concentration for a long period of time (a state in which ozone is not discharged from the liquid) can be maintained. The methane gas-containing fluid may be a fluid (gas) containing only methane gas, or may contain gases or liquids other than methane gas.

[0011] The mixed fluid may be heated in addition to the light irradiation, whereby the chemical reaction is promoted.

[0012] The mixed fluid may be contacted with a catalyst, which aids in exceeding the activation energy required to cause a chemical reaction, particularly a cyclic reaction, and thus accelerates the chemical reaction.

[0013] The ozone-containing fluid may be ozone water.

[0014] The light may be irradiated onto a liquid layer formed in the mixed fluid without passing through a gas layer formed in the mixed fluid, and since a chemical reaction caused by the light occurs in the liquid layer and is less likely to occur in the gas layer, the risk of explosion can be reduced.

[0015] The mixed fluid may be stirred during or before the light irradiation, which can promote the chemical reaction.

[0016] The present invention provides a methane gas conversion device for converting methane gas into organic matter, comprising: a reaction vessel including a first supply port for supplying a fluid containing ozone and a second supply port for supplying the fluid containing methane gas; and a light source that irradiates the inside of the reaction vessel with light having a wavelength of 200 nm or more and 411 nm or less.

[0017] The reaction vessel may be provided with a stirrer. The mixed fluid is in the reaction vessel, and the stirrer stirs the mixed fluid. Stirring can promote a chemical reaction.

[0018] The bottom of the reaction vessel may be inclined with respect to the horizontal plane so that the stirrer is disposed across the liquid layer and the gas layer, thereby allowing the methane gas contained in the gas layer to dissolve in the liquid layer.

[0019] The light source may be disposed so that the light is irradiated onto a liquid layer formed in the mixed fluid without passing through a gas layer formed in the reaction vessel in the mixed fluid, and since a chemical reaction caused by the light occurs in the liquid layer and is less likely to occur in the gas layer, the risk of explosion can be reduced. Effect of the Invention

[0020] This makes it possible to convert methane gas into organic matter without using chlorine-based materials such as chlorine dioxide. Because no chlorine-based materials are used, no energy is required to separate the organic matter obtained by converting methane gas from the chlorine-based materials. Furthermore, there are no problems with the generation of chlorine gas, equipment corrosion due to chlorine-based materials, and waste liquid treatment of chlorine-based materials. In particular, the distillation tank for separating organic matter from chlorine-based solutions is large, and the costs of introducing and maintaining the equipment are high. If the distillation layer is no longer necessary, this will greatly contribute to reducing the space and costs.

[0021] Converting methane gas into organic matter is expected to be a technology that contributes to global warming countermeasures by suppressing the release of methane gas into the atmosphere. In addition, converting methane gas into organic matter such as methanol and formic acid and then transporting or storing it is also expected to contribute to global warming countermeasures by contributing to improving the efficiency of methane gas transportation and the storage properties of methane gas. Converting methane gas to produce methanol and formic acid will contribute to Goal 13 of the United Nations-led Sustainable Development Goals (SDGs), "Take urgent action to mitigate climate change and its impacts." [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing an overview of a methane gas conversion process. [Figure 2A] FIG. 1 illustrates a first embodiment of a methane gas conversion apparatus. [Figure 2B] 2B is a cross-sectional view taken along line 2B-2B in FIG. 2A. [Diagram 3] FIG. 2 illustrates a second embodiment of a methane gas conversion apparatus. [Figure 4] FIG. 13 illustrates a third embodiment of a methane gas conversion apparatus. [Diagram 5] FIG. 13 illustrates a fourth embodiment of a methane gas conversion apparatus. [Figure 6] FIG. 1 is a diagram showing an experimental setup for a methane gas conversion experiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The following description will be given with reference to the drawings as appropriate. Note that the drawings are all schematic illustrations, and the dimensional ratios in the drawings do not necessarily match the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily match.

[0024] <Methane gas conversion process> First, the methane gas conversion process will be described. FIG. 1 is a diagram showing an overall view of the methane gas conversion process. With reference to FIG. 1, the process of decomposing methane to produce methanol (CH3OH) and formic acid (HCOOH) will be described. In FIG. 1, CH4 and O3 enclosed in squares represent methane and ozone input into the reaction field. Methane gas and ozone input into the reaction field are mainly decomposed according to the methane gas conversion process shown in FIG. 1. Underlined CH3OH and HCOOH represent methanol and formic acid to be produced. Each major chemical reaction in the methane gas conversion process is given a symbol combining R and a number. Each major intermediate generated in the methane gas conversion process is given a symbol combining P and a number. In this specification, an intermediate refers to a substance that exists temporarily during the methane gas conversion process. The overall view of the methane gas conversion process will be described while explaining each chemical reaction and each intermediate.

[0025] [Photodecomposition of ozone] The mixed fluid in the reaction field includes a fluid containing ozone and a fluid containing methane gas. Ozone may be present in a state dissolved (dispersed) in the liquid. Such a liquid may be water or a non-polar solvent. Examples of non-polar solvents include hexane, cyclohexane, n-decane, n-octane, n-nonane, octane, isooctane, perfluorohexane, tetradecafluorohexane, perfluoroheptane, perfluorooctane, octadecafluorooctane, perfluorononane, eicosafluorononane, and perfluorodecalin. In the following, the case where the fluid is water, that is, the case where the "fluid containing ozone" is ozone water, will be described. However, the type of fluid to contain ozone is not particularly limited. In addition, even when ozone water is used as the "fluid containing ozone", the ozone water may contain other materials (e.g., additives). In the "methane gas conversion process" section, the "fluid containing methane gas" is treated as being composed of only methane gas.

[0026] Chemical reaction R1 represents the decomposition reaction of ozone by light L1 having a wavelength of 200 nm or more and 411 nm or less. When light L1 is irradiated to ozone water and the energy hν of light L1 is given to ozone molecules, atomic oxygen O( 1 D) or O( 3 P) is taken out. O( 1 D) is atomic oxygen in an active state, O( 3 P) is atomic oxygen in the ground state. Chemical reaction R1 is expressed by formula (1) or formula (2). In Figure 1, there are two chemical reactions R1 in which ozone is irradiated with light L1 to produce O. The "O" that appears in both chemical reactions R1 is O( 1 D) and O( 3 In other words, the "O" in Figure 1 is a concept that includes both O( 1 D) and O( 3 P) may include at least one of the following: O3+hν → O( 1 D) + O2 (1) O3+hν → O(3 P) + O2 (2)

[0027] When light with a wavelength of 200 nm or more and 411 nm or less is used, the reaction of formula (1) is particularly likely to occur, and a large amount of O( 1 D). When light with a wavelength of more than 411 nm and less than 1180 nm is used, the reaction in formula (1) does not occur, and the reaction in formula (2) occurs. Details will be described later, but O( 3 P) is O( 1 D) is less reactive than O( 1 It is preferable to generate D). For this purpose, in this embodiment, light having a wavelength of 200 nm or more and 411 nm or less is used.

[0028] [Methyl (CH3) production] A chemical reaction R2 occurs in which atomic oxygen generated by light L1 combines with methane. Chemical reaction R2 is shown in formulas (3) and (4). CH3 generated in formulas (3) and (4) is methyl as intermediate P1. The chemical reaction of formula (3) proceeds even if the temperature of the reaction field is room temperature. In contrast, the chemical reaction of formula (4) does not proceed easily unless the temperature of the reaction field is approximately 300°C or higher. Therefore, in this embodiment, light with a wavelength of 200 nm or more and 411 nm or less is used so that the reaction proceeds even at room temperature. O( 1 D) + CH4 → CH3 + OH (3) O( 3 P) + CH4 → CH3 + OH (4)

[0029] The OH (hydroxyl radical) generated in formulas (3) and (4) (especially formula (3)) undergoes chemical reaction R3 in which it combines with CH4. Chemical reaction R3 is shown in formula (5). Formula (5) also generates methyl as an intermediate P1. OH+CH4 → CH3+H2O (5)

[0030] The places where OH is generated are not limited to formulas (3) and (4) (chemical reaction R2). Although not shown in Figure 1, when light L1 containing wavelengths of 200 nm or more and 411 nm or less is used, a large amount of O( 1 D), but O( 1 D) reacts with water (HO) to generate a large amount of OH. This is shown in equation (6). The large amount of OH generated promotes chemical reaction R3 (equation (5)). O( 1 D) + H2O → 2OH (6)

[0031] In this way, a large amount of intermediate P1 (methyl) is produced by chemical reaction R2 and chemical reaction R3. However, all O( 1 D) does not lead to the reaction of equation (3). O( 1 D) is inactivated and O( 3 P) and O( 3 P) combine with each other to produce oxygen molecules, or O( 1 D) often combines with oxygen molecules to produce ozone again. Also, as shown in chemical reaction R4, O( 1 D) can also combine with methane to produce methanol directly. Chemical reaction R4 is shown in equation (7). O( 1 D) + CH4 → CH3OH (7)

[0032] Chemical reaction R4 is a favorable reaction that converts methane directly into methanol with a small chemical reaction process. However, it is a minor chemical reaction, and the amount of methanol directly produced by chemical reaction R4 is small. The major chemical reactions that convert methane into methanol or formic acid are various chemical reactions R5 to R9 starting from methoxy, as described below.

[0033] [Methoxy (CH3O) generation and cycle reaction] Methoxy (CH3O) is produced by chemical reaction R5 from intermediate P1 (CH3) and atomic oxygen obtained by irradiating ozone with light L1. Chemical reaction R5 is shown in formula (8). In formula (8), O( 1 D), but O( 3 P), a reaction similar to that shown in equation (8) occurs. CH3+O( 1 D) → CH3O (8)

[0034] The intermediate P2, methoxy, undergoes chemical reaction R6 in which it combines with methane. Chemical reaction R6 is shown in equation (9). CH3O+CH4→ CH3OH+CH3...(9)

[0035] As shown in formula (9), chemical reaction R6 produces methyl and the target product, methanol. Methyl combines with atomic oxygen in chemical reaction R5 to produce methoxy again. Thus, a cyclic reaction (Loop A) occurs in which chemical reactions R5 and R6 are repeated. A large amount of methane is decomposed by Loop A to produce a large amount of methanol.

[0036] [Formic acid produced by reaction of methoxy with oxygen molecules] The intermediate P2, methoxy, can undergo chemical reaction R7, in which it combines with an oxygen molecule. Chemical reaction R7 is shown in equation (10). CH3O+O2 → HCHO+HO2 (10)

[0037] The formaldehyde (HCHO) obtained by formula (10) is a stable substance and exists for a relatively long time. However, an oxidation reaction in which it gradually bonds with oxygen atoms contained in oxygen molecules in the reaction vessel progresses, and as this progresses, formic acid is obtained. Because ozone is used, atomic oxygen and oxygen molecules that have not contributed to the reaction up to this point are utilized in chemical reaction R7, making it highly efficient. In Figure 1, the notation "[O]" stands for "oxygen atoms contained in oxygen molecules." The hydroperoxide (HO2) obtained by formula (10) is used as an oxidizing agent in other chemical reactions, and as a result, it is converted into water.

[0038] [Formic acid production starting from CH2(OH)] The intermediate P2, methoxy, can be converted to intermediate P3 (CH2(OH)). Intermediate P3 (CH2(OH)) undergoes chemical reaction R8, combining with an oxygen molecule to produce intermediate P4 (CH2(OH)OO). Chemical reaction R8 is shown in equation (11). CH2(OH)+O2→ CH2(OH)OO ···(11)

[0039] The intermediate P4 (CH2(OH)OO) undergoes chemical reaction R9, combining with methane. Chemical reaction R9 is shown in equation (12). CH2(OH)OO+CH4→ CH2(OH)+CH3OOH ···(12)

[0040] Methyl hydroperoxide (CH3OOH) produced by chemical reaction R9 is converted into formaldehyde and water. As mentioned above, formaldehyde gradually combines with oxygen atoms contained in the oxygen molecules in the reaction vessel in an oxidation reaction to produce formic acid.

[0041] Intermediate P3 (CH2(OH)) produced by chemical reaction R9 undergoes chemical reaction R8 again to obtain intermediate P4 (CH2(OH)OO). Thus, a cyclic reaction (Loop B) occurs in which chemical reactions R8 and R9 are repeated. A large amount of formic acid is produced from intermediate P3 (CH2(OH)), which is converted from methoxy (intermediate P2) by Loop B.

[0042] Not all intermediates P4 reach the cycle reaction shown in Loop B. As shown in Figure 1, intermediates P4 may combine with each other to produce formic acid, formaldehyde, water, and oxygen molecules. As described above, formaldehyde gradually combines with oxygen atoms contained in oxygen molecules in the reaction vessel through an oxidation reaction to produce formic acid, which is the target product.

[0043] [Direct production of methanol and formic acid starting from methyl] The chemical reaction R10 in which intermediate P1 (methyl) combines with an oxygen molecule produces intermediate P5 (methyl peroxide (CH3O2)). Chemical reaction R10 is shown in formula (13). M represents a third unit. CH3+O2+M→ CH3O2+M ···(13)

[0044] Chemical reaction R11, in which two molecules of intermediate P5 (CH3O2) combine, produces methanol, formaldehyde, and oxygen. Chemical reaction R11 is shown in equation (14). 2CH3O2→ CH3OH+HCHO+O2···(14)

[0045] As mentioned above, formaldehyde gradually combines with oxygen atoms contained in oxygen molecules in the reaction vessel to produce formic acid through an oxidation reaction. In this way, methanol and formic acid can be produced directly from the intermediate P1, methyl, without going through methoxy. In addition, methoxy can be produced from two methyl peroxide (CH3O2) molecules through chemical reaction R12. Chemical reaction R12 is shown in equation (15). 2CH3O2 → 2CH3O+O2 (15)

[0046] As mentioned above, the methoxy obtained by formula (15) is a starting material for producing methanol and formic acid through various reaction pathways. From this point of view, the chemical reaction R10 constituting the methoxy production route can also be said to be an important chemical reaction. However, the amount of methoxy produced through chemical reaction R10 and chemical reaction R12 is smaller than the amount of methoxy produced through chemical reaction R5. This is because the chemical reaction R10, which does not involve atomic oxygen, is unlikely to occur, and the concentration of methyl peroxide (CH3O2) is low. When the concentration of methyl peroxide is low, the probability that two methyl peroxide molecules (CH3O2) will come into contact with each other in the liquid is low. As a result, the chemical reaction R12 is unlikely to occur. Similarly, the chemical reaction R11 is also unlikely to occur. In other words, the direct production of methanol and formic acid starting from methyl (intermediate P1) (chemical reaction R10-chemical reaction R11) and the production of methoxy via chemical reaction R10-chemical reaction R12 cannot be expected because the chemical reaction R10 is the rate-determining step. In contrast, a large amount of methoxy is produced through chemical reaction R5, which combines with atomic oxygen from intermediate P1 (methyl). In addition, the above-mentioned cycle reaction accelerates the chemical reaction. As a result, a large amount of methanol and formic acid is produced. This is the reason why atomic oxygen, especially O( 1 D) is evidence of its importance.

[0047] [Summary of methane gas conversion process] In the methane gas conversion process, atomic oxygen generated by irradiating light L1 on ozone is involved in chemical reactions at various points, oxidizing methane gas and converting it into organic matter. In particular, methoxy, which is obtained as a result of the oxidative decomposition of methane gas, is the starting point for two cycle reactions (Loop A and Loop B). The two cycle reactions produce large amounts of methanol (CH3OH) and formic acid (HCOOH).

[0048] First Embodiment [Outline of methane gas conversion equipment] 2A is a diagram showing a first embodiment of a methane gas conversion apparatus. The methane gas conversion apparatus includes a reaction vessel 10, a light source 4 that irradiates the inside of the reaction vessel 10 with light L1, a stirrer 5, and a power source 6 for the stirrer 5.

[0049] The reaction vessel 10 has a first supply port 11 for supplying a fluid containing ozone, and a second supply port 21 for supplying a fluid containing methane gas. The first supply port 11 is connected to a supply source 12 of the fluid containing ozone via a pump Pa.

[0050] There is a liquid layer S1 in the reaction vessel 10. The liquid layer S1 is mainly composed of ozone water as a fluid containing ozone. The supply source 12 is a generator in which ozone water is stored, or in which ozone water is generated, or is a gaseous ozone supply source. Ozone water or gaseous ozone is supplied from a first supply port 11. The gaseous ozone is bubbled through the liquid layer in the reaction vessel while being stirred with a stirrer, whereby the ozone can be dissolved in the liquid layer. Details of the ozone water will be described later.

[0051] The pump Pa feeds a predetermined amount of ozone water or gaseous ozone from the supply source 12 into the liquid layer S1 in the reaction vessel 10. The pump Pa is controlled by a control unit (not shown). The second supply port 21 is connected to a methane gas supply source 22 via a pump Pb. Methane gas is stored in the supply source 22. Such methane gas is, for example, gas recovered from sewage, livestock waste, or food waste. The pump Pb feeds a predetermined amount of methane gas from the supply source 22 into the liquid layer S1 of the reaction vessel 10. The pump Pb is controlled by a control unit (not shown). The methane gas fed into the liquid layer S1 is dissolved in the liquid layer S1 by bubbling and stirring by the stirrer. The methane gas that is not completely dissolved in the liquid layer S1 constitutes a gas layer S2.

[0052] In this embodiment, the main component of the liquid layer S1 is ozone water. The main component of the gas layer S2 is methane gas. However, since the contents of the reaction vessel 10 are stirred by a stirrer described later, bubbles 25 of methane gas are contained in the liquid layer S1. In addition, droplets of ozone water, oxygen molecules, and ozone molecules may be contained in the gas layer S2.

[0053] The internal space of the reaction vessel 10 has a cylindrical shape. The volume of the internal space is not particularly limited, but is, for example, 1 liter (0.001 m 3 ) or more, and 1000 liters (1 m 3 ) or less.

[0054] [Ozone water] Details of ozone water will be explained. Ozone water is water (H2O) in which O3 molecules are dissolved. Ozone water also includes substances other than O3 molecules. For example, ozone water also includes O2 molecules (oxygen molecules). Ozone is an unstable substance, and changes into O2 molecules (oxygen molecules) by itself over time, exposure to light, or heat. Ozone water may be a liquid in which ozone exists as bubbles with a diameter of less than 1000 μm. Ozone water in which ozone is dissolved in the form of bubbles with a diameter of less than 1000 μm can maintain ozone in water for a long period of time. The bubbles may be microbubbles (bubbles with a diameter of 1 μm or more and less than 100 μm) or nano-sized ultrafine bubbles (bubbles with a diameter of less than 1 μm).

[0055] There are various methods for generating ozone water, such as a method of passing ozone gas through an ozone-permeable membrane immersed in a polar or non-polar solvent, or a method of placing electrodes in water to sandwich an electrolyte membrane and applying a voltage between the two electrodes to cause electrolysis. By using a method of passing ozone through an ozone-permeable membrane, it is possible to generate a large amount of highly concentrated ozone water in which ozone dissolves as ultrafine nano-sized bubbles that are finer than microbubbles.

[0056] [light source] In this embodiment, a light source 4 that generates light L1 is located outside the reaction vessel 10. The reaction vessel 10 includes a light guide section 3. The light L1 from the light source 4 is guided through the light guide section 3 into the reaction vessel 10. The light L1 passes through a liquid layer S1 of the ozone water and is irradiated toward the interface between the granular methane gas and the ozone. The light L1 activates the ozone dissolved in the ozone water, converting it into atomic oxygen (O( 1 D) or O( 3 As described above, atomic oxygen near the grain boundary surface generated by light L1 combines with methane molecules at the grain boundary surface, causing a chemical reaction shown in chemical reaction R2 or chemical reaction R4. As described above, atomic oxygen combines with intermediate P1 (methyl) generated by chemical reaction R2 to generate intermediate P2 (methoxy). These reactions mainly occur around bubbles 25 of methane gas present in liquid layer S1, but also occur near the interface between the liquid layer and the gas layer.

[0057] The light L1 is light having a wavelength of 200 nm or more and 411 nm or less. As described above, the light having a wavelength of 200 nm or more and 411 nm or less converts a large amount of O( 1 D), and the large amount of OH obtained by the reaction of (3) and (6) promotes the reaction of (5). As a result, the methane gas conversion process is accelerated by the above-mentioned cycle reactions (Loop A and Loop B). Equations (1), (3), (5), and (6) are shown below. O3+hν → O( 1 D) + O2 (1) O( 1 D) + CH4 → CH3 + OH (3) OH+CH4 → CH3+H2O (5) O( 1 D) + H2O → 2OH (6)

[0058] As the light source 4 that emits light having a wavelength of 200 nm or more and 411 nm or less, it is preferable to use a solid-state light source such as an LED or LD.

[0059] The light source 4 may be constantly lit, or may be intermittently lit by repeatedly turning on (ON) and off (OFF) to irradiate light intermittently. Regarding the interval between turning on and off the light source 4, for example, the light may be turned on and off repeatedly at a fixed interval. The light-on time may be 5 to 60 seconds, or 10 to 20 seconds. The light-off time may be 5 to 60 seconds, or 10 to 20 seconds. The light-on time and the light-off time may be the same. By intermittent lighting, the overall reaction rate of the chemical reaction can be controlled.

[0060] [Reaction vessel] It is preferable to use a material that transmits light having a wavelength of 200 nm or more and 411 nm or less well for the light guiding part 3 of the reaction vessel 10. A light diffusing element such as a lens may be disposed at the tip of the light guiding part 3 to diffuse the light L1.

[0061] The light guide 3 may be a rod-like long part in one direction or an optical fiber, which may be inserted deep into the reaction vessel 10. This can suppress the attenuation of light in the liquid and allow the light L1 to reach every corner of the reaction vessel 10. It is particularly preferable to use quartz glass for the light guide 3. When the light guide 3 is made of optical fiber, it has the advantage that it is more resistant to mechanical distortion than general glass and is less likely to be damaged even if the weight of the liquid is applied to the optical fiber. As a modified example, a reaction vessel 10 in which the light source 4 is embedded in the wall may be used without using the light guide 3.

[0062] Since methane gas is flammable, there is a risk of explosion if the methane gas is present in the gas layer S2 at a concentration equal to or higher than the lower explosion limit. When methane gas is present in high concentration in the gas layer S2 inside the reaction vessel 10, the passage of light L1 through the gas layer S2 increases the risk of explosion.

[0063] As shown in Fig. 1, in this embodiment, light L1 is irradiated toward the liquid layer S1 without passing through the gas layer S2. Although the liquid layer S1 also contains bubbles 25 of methane gas, the risk of explosion of the methane gas bubbles 25 is low, so that the risk of explosion is low when irradiating the liquid layer S1. The emission direction and diffusion angle of light L1 may be adjusted by the light guide unit 3 so that the light L1 is not irradiated toward the gas layer S2. When the gas layer S2 does not exist or when the concentration of methane gas in the gas layer S2 is low, the light L1 may be directed toward the gas layer S2.

[0064] The number of light guiding units 3 may be one or more. The number of light guiding units 3 may be set depending on the size of the reaction vessel 10, etc. When a plurality of light guiding units 3 are arranged on the side surface of the reaction vessel 10, the light guiding units 3 may be arranged so as to have equal angles or unequal angles with respect to the central axis of the reaction vessel 10. In order to reduce the risk of an explosion of methane gas in the gas layer S2, the emission direction and light diffusion angle of each light guiding unit 3 may be adjusted individually.

[0065] As shown in FIG. 2A, the reaction vessel 10 is provided with a reflective film 7 so as to contact the inner wall of the reaction vessel 10. The reflective film 7 reflects the light L1 from the light source 4. By preventing the light from leaking out, photons are utilized without being wasted, and the photoreaction efficiency can be improved. In order to reduce the risk of an explosion of methane gas in the gas layer S2, the reflective film 7 may be provided away from the upper part of the reaction vessel 10 which is likely to come into contact with the gas layer S2.

[0066] The reflective film 7 is preferably made of a material that is highly corrosion-resistant to the liquid in the reaction vessel 10. If a material with high corrosion resistance is not used, a light-transmitting material with high corrosion resistance may be provided on the surface of the reflective film 7. For example, the reflective film 7 in this embodiment is formed by depositing an aluminum-based material, but the surface on which the aluminum-based material is deposited may be protected by glass. If the inner wall of the reaction vessel 10 itself reflects the light L1, the reflective film 7 does not need to be formed. Thus, it is preferable that the inner wall of the reaction vessel 10 has a reflective surface that reflects the light L1, but the reflective surface is not a required configuration.

[0067] In this embodiment, the liquid layer S1 is mainly composed of one liquid layer, which is ozone water. However, the liquid layer S1 may be composed of multiple liquid layers. For example, the liquid layer S1 may be composed of a first liquid layer mainly composed of ozone water and a second liquid layer composed of a non-polar solvent in which methane is easily dissolved. In this case, when the liquid layer is left to stand in the reaction vessel, the two liquid layers do not dissolve in each other, and are separated in the direction of gravity due to the difference in specific gravity between the two liquid layers. In the case of separation, particularly when the liquid layer located at the top is a light-absorbing solution, light is less likely to reach the gas layer S2, so that even if light L1 is irradiated upward in the reaction vessel 10, the risk of explosion is less likely to increase. If the light L1 irradiated upward is also reflected by the reflective film 7, the utilization efficiency of the light L1 is further improved, and the reaction efficiency is further increased.

[0068] Both the liquid layer S1 and the gas layer S2 may contain other substances. The internal pressure of the reaction vessel 10 may be increased using pumps (Pa, Pb). Increasing the internal pressure of the reaction vessel 10 further promotes the chemical reaction. The fluid containing methane gas in the gas layer S2 may be collected and sent back to the liquid layer S1 for bubbling.

[0069] [Stir bar] FIG. 2B is a cross-sectional view taken along the line 2B-2B in FIG. 2A. As shown in FIG. 2A and FIG. 2B, in this embodiment, an electromagnetic coil is used as the power source 6, and a magnetic material is used as the stirrer 5. The stirrer 5 is disposed inside the reaction vessel 10, particularly near the bottom of the reaction vessel 10. The stirrer 5, which is not in physical contact with the power source 6, is rotated using multiple electromagnetic coils. As the stirrer 5 rotates, the interface BS flows, and bubbles of methane gas are generated in the liquid layer S1, promoting the conversion reaction of methane gas. In this embodiment, the stirrer 5 and the power source 6 are a non-contact type power transmission system that is not physically connected, but a contact type power transmission system in which the stirrer 5 and the power source 6 are physically connected, as shown in the second embodiment and thereafter, may be adopted.

[0070] The stirrer 5 may be rotated continuously or intermittently. When the stirrer 5 is rotated intermittently, irradiation with light L1 and stirring with the stirrer 5 may be performed alternately, or a period during which irradiation with light L1 and stirring with the stirrer 5 are performed simultaneously may be included.

[0071] The light source 4 may be constantly turned on to continuously irradiate the light L1, while the stirrer 5 is intermittently rotated and stopped. The interval between repeated rotation and stopping of the stirrer 5 may be set to 5 to 60 seconds, preferably 10 to 20 seconds. The stop time of the stirrer 5 may be set to 5 to 60 seconds, preferably 10 to 20 seconds. The rotation time and the stop time may be set to the same time, and repeated.

[0072] The contents of the reaction vessel 10 may be stirred by a method other than using the stirrer 5. For example, the reaction vessel 10 may be moved continuously. "Continuously moving" the reaction vessel 10 includes, for example, rotating, rocking, and vibrating the reaction vessel 10. Note that relocating the installation location of the reaction vessel 10 does not fall under "continuously moving". The methane gas conversion device may have a power source for continuously moving the reaction vessel 10. If there is a protruding piece protruding from the inner wall of the reaction vessel 10 toward the inside, it is easier to stir the contents when the reaction vessel 10 is moved continuously. In addition, instead of vibrating the reaction vessel 10, the contents of the reaction vessel 10 may be stirred by introducing or discharging the contents (liquid containing ozone and methane gas) of the reaction vessel 10, or vibrating the contents themselves. In addition, stirring may be performed by bubbling methane gas into the liquid layer S1. Therefore, the stirrer 5 and its power source 6 are not essential components.

[0073] Second Embodiment A second embodiment of a methane gas conversion apparatus will be described with reference to Fig. 3. The second embodiment will be described with a focus on features that are different from the previously described embodiments, and features that are common to the previously described embodiments will not be described in principle. The same applies to the third and subsequent embodiments.

[0074] The second embodiment will be described with reference to FIG. 3. The reaction vessel 60 is arranged with a vertically long cylindrical shape tilted. The bottom surface 61 of the cylindrical reaction vessel 60 is tilted with respect to the horizontal plane. Inside the reaction vessel 60, there is a liquid layer S1 filled mainly with ozone water, and a gas layer S2 containing mainly methane gas. By tilting the vertically long reaction vessel 60, the area of ​​the interface BS between the liquid layer S1 and the gas layer S2 increases, and the stirrer 5 is rotated therein, so that methane is easily dissolved in the liquid layer S1.

[0075] In the first embodiment (see FIG. 1), the second supply port 21 is designed to be located in the liquid layer S1 so that methane can be bubbled into the liquid layer S1, but in the case where methane can be dissolved in the liquid layer S1 without bubbling as in the present embodiment, the second supply port 21 may be designed to be located in the gas layer S2. Of course, even in the present embodiment in which the reaction vessel 60 is tilted, the position of the second supply port 21 may be adjusted so that methane gas can be directly drawn into the liquid layer S1. The fluid in the gas layer S2 may be collected and sent again to the liquid layer S1 for bubbling.

[0076] In this embodiment, the light source 4 is disposed near the side wall of the reaction vessel 60. In this embodiment, the reaction vessel 60 is disposed at an angle, so that the light source 4 is located below the reaction vessel 60.

[0077] In this embodiment, the stirrer 5 is physically connected to the power source 6 arranged outside the reaction vessel 30 by a rod 35 that transmits rotation. The extension direction of the rod 35 coincides with the axial direction of the rotation axis x1 of the stirrer 5. The angle t1 between the axial direction of the rotation axis x1 and any direction including the horizontal plane h1 is preferably 45 degrees or less, more preferably 35 degrees or less. This makes it easy for the stirrer 5 to be located across the liquid layer S1 and the gas layer S2. This allows the stirrer 5 to be rotated using the power source 6, so that the components in the mixed fluid are mixed together more and the contact area of ​​each component increases. As can be seen in FIG. 3, many bubbles 25 of methane gas appear in the liquid layer S1, and many droplets 26 of ozone water appear in the gas layer S2. The increase in the bubbles 25 and droplets 26 leads to an increase in the contact area between the ozone water and the methane gas, promoting the chemical reaction.

[0078] Note that arranging the stirrer 5 across the liquid layer S1 and the gas layer S2 is one method for increasing the contact area, and is not a requirement when tilting the reaction vessel 60. Even when tilting the reaction vessel 60 so that the stirrer 5 is present in the liquid layer S1, the contact area is expected to increase, and the conversion of methane gas is promoted.

[0079] <Third embodiment> The third embodiment will be described with reference to Fig. 4. In the reaction vessel 70, the light source 4 is surrounded by a heat transfer unit 31. The heat transfer unit 31 is fitted into the opening of the reaction vessel 70 and is in direct contact with the liquid layer S1. This allows the heat generated by the light source 4 to be directly transferred to the liquid layer S1. In the above-mentioned methane gas conversion process, as the temperature of the mixed fluid increases, it becomes easier to secure the activation energy required to cause a reaction (particularly a cycle reaction), and the reactivity becomes higher.

[0080] Furthermore, in the reaction vessel 70 of this embodiment, the power source 6 is surrounded by the heat transfer unit 32. The heat transfer unit 32 is fitted into the opening of the reaction vessel 70 and is in direct contact with the liquid layer S1. This allows the heat generated by the power source 6 to be directly transferred to the liquid layer S1.

[0081] The heat transfer units (31, 32) may incorporate, for example, a heat pipe, and may be made of a material with high thermal conductivity. In addition to utilizing waste heat from the light source 4 and the power source 6, heat from outside the methane gas conversion device may be introduced. A heater for heating the mixed fluid may be disposed in the reaction vessel 70. Furthermore, at least one of the ozone-containing liquid and the methane gas may be heated in advance and supplied into the reaction vessel 70. In order to assist in the activation energy of the cycle reaction, the temperature rise range is preferably set to 10° C. or more and 80° C. or less, and more preferably set to 30° C. or more and 60° C. or less.

[0082] <Fourth embodiment> The fourth embodiment will be described with reference to FIG. 5. A catalyst 9 (hatched granules in S1 of FIG. 5) is placed inside the reaction vessel 60. The catalyst 9 assists in exceeding the activation energy required to cause a reaction (particularly a cycle reaction). The catalyst 9 may be in powder form. The average particle size of the catalyst 9 may be, for example, 10 μm or more and 1 mm or less. Examples of the catalyst 9 include SnO2 particles, TiO2 particles, or ZrO2 particles. The catalyst 9 is selected according to the wavelength of the light L1 used. Furthermore, platinum, which is resistant to oxidation, may be used as a co-catalyst. Specifically, a co-catalyst in which platinum is supported on a TiO2 catalyst may be used. Furthermore, silver nanoparticles, which are resistant to oxidation, may be used as the catalyst 9. Silver nanoparticles have the property of being easily adsorbed to the interface BS, and have the effect of promoting the interface reaction in particular. While there was a restriction on the use of the catalyst 9 in a chlorine-based solution as in the past, various catalysts 9 can be used without significant restrictions in a liquid containing ozone.

[0083] A number of embodiments and their modifications have been described above. The above-described embodiments and their modifications are merely examples of the present invention, and the present invention is not limited to the above-described embodiments and their modifications. Various modifications or improvements can be made to the above-described embodiments and their modifications, or the above-described embodiments or the above-described modifications can be combined, without departing from the spirit of the present invention. EXAMPLES

[0084] In order to confirm whether the above-mentioned methane gas conversion method and methane gas conversion device are effective, the following experiment was carried out. The scale of the experiment was relatively small, as shown in the experimental conditions below, but it is theoretically assumed that the experimental results will have the same tendency regardless of the scale of the experiment.

[0085] [Experimental content] The experimental apparatus is shown in Figure 6. The experimental apparatus includes a methane gas supply source 22 (gas cylinder), a flow rate controller 27, a reaction vessel 80, a light source 4, and a collection vessel 85. The reaction vessel 80 has a liquid layer S1 and a gas layer S2. The reaction vessel 80 is a synthetic quartz glass beaker. The reaction vessel 80 is sealed using a silicone rubber plug 81, and has a maximum capacity of approximately 50 cm3. 3 The liquid layer is 15 cm 3 The first liquid layer S11 is ozone water (O3 content: 1.5 ppm) and the second liquid layer S12 is 15 cm 3 and a second liquid layer S12 of perfluorohexane (hereinafter referred to as "PFH"). PFH is a non-polar solvent that easily dissolves methane gas. In the above-mentioned embodiment, PFH may be introduced as the second liquid layer, as in the experimental apparatus.

[0086] A glass tube for supplying methane gas is inserted into the reaction vessel 80. The liquid layers (S11, S12) are bubbled while the amount of methane gas introduced from the supply source 22 is adjusted by the flow rate controller 27. The light source 4 is disposed below the reaction vessel 80 and irradiates light from the bottom of the reaction vessel 80. The light source 4 is a 250 W U-shaped constant pressure mercury lamp (dominant wavelength showing maximum intensity: 253.7 nm, irradiation energy: 61 J / cm 2 ) are used. In this experimental configuration, no stirrer is used because the liquid layers (S11, S12) are stirred by the bubbling of methane gas. Chemical reactions caused by light irradiation can occur not only between the bubbled methane gas and the first liquid layer S11, but also between the second liquid layer S12 and the first liquid layer S11, and between the gas layer S2 and the first liquid layer S11.

[0087] A pipe 87 for collecting a sample is inserted into the reaction vessel 80. The pipe 87 is connected to a collection vessel 85. The collection vessel 85 has a pure water 86 to be stored and an exhaust line for a gas G1. Gas G1 such as methane gas, ozone, and PFH is exhausted from the exhaust line. On the other hand, the pure water 86 traps formic acid and methanol that are generated and evaporated in the reaction vessel 80.

[0088] In the experimental apparatus described above, methane gas was pumped at 500 cm 3 / min for 60 minutes, while keeping the light source 4 on. After 60 minutes had elapsed, the amounts of methanol and formic acid contained in the reaction vessel 80 and the collection vessel 85 were measured. The amount of formic acid was measured by electrophoresis. The amount of methanol was measured by GCMS (gas chromatography mass spectrometry).

[0089] [Experimental Results] Table 1 shows the measurement results for formic acid and methanol at 1 L (1000 cm 3 The content is shown as the mass content per unit mass of the container. Table 1 shows the total amount in the container calculated based on the content and the amount of liquid in the container.

[0090] [Table 1]

[0091] [Discussion of experimental results] 15cm containing 1.5ppm O3 3 The mass of O3 contained in the ozone water is 22.5μg. The total amount of formic acid and methanol produced, which are the products, calculated from Table 1, is 29.2μg. This indicates that the reaction efficiency is about 130% (≒29.2 / 22.5×100). This reaction efficiency value is considered to be high from the viewpoint of energy balance with carbon neutrality in mind, and also from the economic viewpoint. This experiment was carried out in an environment where the reaction vessel 80 was at approximately atmospheric pressure and at approximately room temperature.

[0092] The reason why the product could be obtained with high reaction efficiency even when the reaction vessel 80 was in the range of room temperature and pressure is believed to be that light having a wavelength of 200 nm or more and 411 nm or less was used. 3 In the case of P), 300°C or higher is required to generate intermediate P1, but it is possible to convert a large amount of O( 1 D), which is thought to have promoted the methane gas conversion process even at room temperature and pressure. [Explanation of symbols]

[0093] 3: Light guide section 4:Light source 5: Stirring bar 6: (Stirrer) power source 7: Reflective film 9: Catalyst 10, 30, 60, 70, 80: Reaction vessel 11:First supply port 12: Ozone source 21:Second supply port 22: Methane gas source 25: Bubble 26: Splash 27:Flow control meter 31, 32: Heat transfer section 61: Bottom surface (of reaction vessel) 81: (Reaction vessel) stopper 85: Liquid collection container 86: Pure water 87: tube BS: Interface L1: light S1:Liquid layer S11: First liquid layer S12: Second liquid layer S2: air layer Pa, Pb: Pump

Claims

1. A method for converting methane gas, comprising: irradiating a mixed fluid, which is a mixture of a fluid containing ozone and a fluid containing methane gas, with light having a wavelength of 200 nm or more and 411 nm or less, thereby converting the methane gas into organic matter.

2. 2. The method for converting methane gas according to claim 1, wherein the ozone-containing fluid is generated by passing ozone gas through an ozone-permeable membrane immersed in a polar solvent or a non-polar solvent.

3. 3. The method for converting methane gas according to claim 1, wherein the mixed fluid is heated while the light is irradiated.

4. 3. The method for converting methane gas according to claim 1, further comprising contacting the mixed fluid with a catalyst.

5. 3. The method for converting methane gas according to claim 1, wherein the fluid containing ozone is ozone water.

6. 3. The method for converting methane gas according to claim 1, wherein the light is irradiated onto a liquid layer formed in the mixed fluid without passing through a gas layer formed in the mixed fluid.

7. 3. The method for converting methane gas according to claim 1, wherein the mixed fluid is stirred during or before the light irradiation.

8. A methane gas conversion device for converting methane gas into organic matter, a reaction vessel including a first supply port for supplying a fluid containing ozone and a second supply port for supplying the fluid containing methane gas; A methane gas conversion apparatus comprising: a light source that irradiates the inside of the reaction vessel with light having a wavelength of 200 nm or more and 411 nm or less.

9. 9. The methane gas conversion apparatus according to claim 8, further comprising a stirrer in the reaction vessel.

10. 10. The methane gas conversion apparatus according to claim 9, wherein the bottom of the reaction vessel is inclined with respect to a horizontal plane so that the stirrer is disposed across the liquid layer and the gas layer.

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