Gas reaction method and gas reaction device

Abstract

To provide a gas reaction method and a gas reaction device capable of reducing the energy required for the reaction of source gas.SOLUTION: A gas reaction method according to an embodiment of the present invention comprises changing source gas into plasma and bringing the source gas in the plasma state into contact with a catalyst to induce a chemical reaction of the source gas in the plasma state.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas reaction method and a gas reaction device. [Background technology]

[0002] Technologies for producing desired reaction products by chemically reacting raw material gases are being continuously developed. A representative example is a technique for thermally decomposing the raw material gas. One such technique has been proposed (Patent Document 1), in which a hydrocarbon gas is blown into molten metal heated to 900°C to 1200°C to decompose the hydrocarbon gas into carbon and hydrogen. In this technique, heat is supplied to the hydrocarbon gas by heat transfer from the molten metal, and therefore a furnace is required that can accommodate a sufficient amount of molten metal relative to the amount of hydrocarbon gas supplied and maintain the molten metal at the above temperature. This results in problems of increased equipment and maintenance costs. To avoid such problems, methods for decomposing a source gas using non-thermal plasma have been investigated in recent years. For example, a method has been proposed in which a source gas containing methane is supplied between multiple electrodes to which a voltage is applied, a gliding arc plasma is generated, and hydrogen is produced from methane (Non-Patent Document 1). However, this method has the problem that the energy required for the methane reaction cannot be sufficiently reduced. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 154732 [Non-patent literature]

[0004] [Non-Patent Document 1] Journal of Renewable and Sustainable Energy,4,021202,p.1-8(2012) Summary of the Invention [Problem to be solved by the invention]

[0005] A primary object of the present invention is to provide a gas reaction method and a gas reaction apparatus that can reduce the energy required for the reaction of raw material gases. [Means for solving the problem]

[0006] A gas reaction method according to an embodiment of the present invention includes the steps of: converting a raw material gas into plasma; and bringing the raw material gas in the plasma state into contact with a catalyst to induce a chemical reaction of the raw material gas in the plasma state. In one embodiment, the source gas includes a hydrocarbon gas. In one embodiment, the hydrocarbon gas is methane gas. In one embodiment, the source gas in a plasma state is decomposed in the chemical reaction. In one embodiment, hydrogen and carbon are produced from the source gas in a plasma state in the chemical reaction. In one embodiment, the catalyst is present in a liquid. In one embodiment, the liquid is a molten metal or a molten salt. In one embodiment, the catalyst is in a liquid state. In one embodiment, the catalyst is a molten metal or a molten salt. In one embodiment, the raw material gas in a plasma state is sprayed onto the catalyst. A gas reaction apparatus according to another aspect of the present invention is capable of carrying out the above-described gas reaction method. The gas reaction apparatus includes a plasma generating unit that converts a raw material gas into plasma, and a catalyst holding unit having a catalyst that can come into contact with the raw material gas in a plasma state supplied from the plasma generating unit. The catalyst holding unit may also be in a state where a liquid containing the catalyst is dispersed in a space. In one embodiment, the plasma generating unit is a plasma torch. [Effects of the Invention]

[0007] According to the embodiment of the present invention, it is possible to reduce the energy required for the reaction of the source gas. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of a gas reaction device according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments. A. Gas reaction method A gas reaction method according to an embodiment of the present invention includes a step of converting a raw material gas into plasma (plasma conversion step); and a step of inducing a chemical reaction of the raw material gas in the plasma state by contacting the raw material gas in the plasma state with a catalyst (reaction induction step). According to this method, the plasma conversion step and the reaction induction step can be carried out separately, thereby preventing reaction products resulting from the chemical reaction of the raw material gas from being present in the reaction field of the plasma conversion step. Therefore, in the plasma conversion step, supply of energy to anything other than the raw material gas (e.g., reaction products) can be prevented. As a result, energy can be efficiently supplied to the raw material gas, and the raw material gas can be converted into plasma with excellent energy efficiency. Then, the raw material gas in the plasma state is contacted with a catalyst to induce a chemical reaction, thereby efficiently producing the desired reaction product.

[0010] The raw material gas typically contains a hydrocarbon gas. Typical examples of hydrocarbon gas include methane gas and ethane gas. The hydrocarbon gas is preferably methane gas. The raw material gas may also contain trace components (e.g., carbon dioxide gas) that do not react in the reaction induction step. The raw material gas particularly preferably consists essentially of hydrocarbon gas alone. More specifically, the content of hydrocarbon gas in the raw material gas is, for example, 95% by volume or more, preferably 99% by volume or more, and typically 100% by volume or less.

[0011] In one embodiment, in the plasma generation step, the raw material gas is excited into a plasma state by a plasma generation means. The plasma generation means may be a DC plasma torch, an inductively coupled plasma torch, a multilayer AC arc, a microwave plasma torch, or the like, and may be appropriately selected depending on the type of raw material gas. The plasma generation means is preferably a plasma torch (a DC plasma torch, an inductively coupled plasma torch, or a microwave plasma torch), and more preferably an inductively coupled plasma torch.

[0012] In one embodiment, in the chemical reaction (reaction inducing step), a source gas in a plasma state is decomposed. More specifically, the source gas in a plasma state is decomposed to produce hydrogen and carbon. In this case, the gas reaction method is a hydrogen production method in which hydrogen is produced by decomposing a source gas into hydrogen and carbon. According to this hydrogen production method, CO2-free hydrogen can be produced with reduced energy. CO2-free hydrogen is hydrogen that is substantially not mixed with carbon dioxide (CO2). Furthermore, the carbon produced together with the hydrogen can be used for various purposes.

[0013] A catalyst that can come into contact with a raw material gas in a plasma state can be appropriately selected depending on the chemical reaction to be induced. The catalyst typically contains a metal element (hereinafter referred to as an active metal element) as an active component. Examples of the active metal element include Ni, Fe, and Co. The active metal elements can be used alone or in combination. Of the active metal elements, Ni is preferred. In one embodiment, the catalyst is in a liquid state (molten state). When the catalyst is in a liquid state, even if a solid reaction product is produced in the reaction inducing step, the reaction product can be prevented from adhering to the catalyst, and a decrease in catalytic activity can be suppressed. The liquid catalyst is, for example, a molten metal or a molten salt. The molten metal catalyst is composed of the active metal element. The molten salt catalyst contains a cation and a counter anion of the active metal element. Among such liquid catalysts, a molten metal is preferred.

[0014] In one embodiment, the catalyst is present in a liquid. This makes it possible to more stably prevent the reaction products from adhering to the catalyst. More specifically, the catalyst is dissolved and / or dispersed in the liquid. In other words, the liquid is a medium (solvent or dispersion medium) that dilutes the catalyst. It is advantageous for separating the decomposition products if the specific gravity of the liquid is heavier than the substances produced by decomposition of the feed gas. Such a liquid can be appropriately selected depending on the application. The liquid typically contains a metal element other than the above-mentioned active metal element (hereinafter referred to as a mediate metal element). Examples of the mediate metal element include Sn, Bi, and Ga. The mediate metal elements can be used alone or in combination. Of the mediate metal elements, Sn is preferred. The liquid is, for example, a molten metal or a molten salt. The molten metal as a liquid is composed of the above-mentioned mediator metal element. The molten salt as a liquid contains the cation and counter anion of the above-mentioned mediator metal element. Of these liquids, the molten metal is preferred. When the catalyst is present in the liquid, the catalyst content is, for example, 0.1 mass % or more, for example, 20 mass % or less, and preferably 5 mass % or less, based on the total of the catalyst and the liquid. If the catalyst content is within the above range, a chemical reaction of the raw material gas in a plasma state can be stably induced.

[0015] In one embodiment, in the reaction induction step, the plasma-state raw material gas is sprayed onto the catalyst. Therefore, stable contact between the plasma-state raw material gas and the catalyst can be achieved. Particularly when the catalyst is present in a liquid, the plasma-state raw material gas is sprayed onto the surface of the molten metal containing the catalyst and the liquid. Therefore, even if the amount of molten metal is reduced, sufficient contact between the plasma-state raw material gas and the catalyst can be achieved, allowing the plasma-state raw material gas to react stably. Furthermore, even if a solid reaction product is generated by the reaction, the solid reaction product can be removed from the surface of the molten metal by continuously spraying the plasma-state raw material gas. As a result, the surface of the molten metal can be constantly cleaned up, and a decrease in catalytic activity can be more stably suppressed.

[0016] The temperature of the catalyst in the reaction inducing step is, for example, 800°C or less, preferably 600°C or less. Even if the temperature of the catalyst in the reaction inducing step is below the upper limit, the raw material gas is converted into plasma before contacting with the catalyst, so that the chemical reaction can be stably induced. Therefore, the desired reaction product can be produced while suppressing operating costs. The lower limit of the catalyst temperature in the reaction inducing step is typically 400°C or more. Furthermore, even when the catalyst is present in a liquid, the temperature range of the catalyst is the same as above. That is, in the reaction inducing step, the temperature of the molten metal containing the catalyst and the liquid is adjusted to the above range. If the temperature of the molten metal is equal to or lower than the above upper limit, the vapor pressure of the molten metal can be reduced, and the escape of the molten metal can be suppressed. In particular, when the catalyst is molten metal of Ni and the liquid is molten metal of Sn, the molten metal containing Ni and Sn is preferably adjusted to 400°C or higher and 600°C or lower. This allows the molten metal containing Ni and Sn to be stably maintained in a liquid state (molten state).

[0017] B. Gas Reactor The gas reaction method described above can be carried out, for example, by the gas reaction apparatus shown in the drawings. Figure 1 is a schematic diagram of the gas reaction apparatus according to one embodiment of the present invention. The illustrated gas reaction apparatus 10 includes a plasma generating unit 1 and a catalyst holding unit having the above-described catalyst. The plasma generating unit 1 can convert the above-described raw material gas into plasma. An appropriate device can be selected as the plasma generating unit 1 depending on the application. The plasma generating unit 1 is preferably an inductively coupled plasma torch 1a. When the plasma generating unit is an inductively coupled plasma torch, the raw material gas can be stably excited into a plasma state. In the illustrated example, the catalyst holding unit is a catalytic bath 2. The catalytic bath 2 typically includes a molten metal containing the above-described catalyst and liquid, and a storage tank for storing the molten metal. The storage tank is provided with a heater (not shown), which can adjust the temperature of the molten metal within the above-described range. The liquid surface of the molten metal in the catalytic bath 2 and the outlet of the plasma torch 1a face each other at a predetermined distance.

[0018] The illustrated gas reactor 10 further comprises a chamber 3, a supply line 6 and a discharge line 7. The chamber 3 contains the catalytic bath 2. The chamber 3 supports the plasma torch 1a such that the discharge port of the plasma torch 1a is located within the chamber 3. The supply line 6 is a pipe through which the raw material gas supplied to the plasma generating unit 1 (plasma torch 1a) can pass. The downstream end of the supply line 6 in the direction in which the raw material gas passes is connected to the plasma generating unit 1 (plasma torch 1a). Although not shown, the upstream end of the supply line 6 is connected to a storage facility for the raw material gas. The discharge line 7 is a pipe through which the desired product gas generated by the chemical reaction of the raw material gas can pass. The upstream end of the discharge line 7 in the direction of the product gas passage is connected to the chamber 3. Although not shown, the downstream end of the discharge line 7 is connected to a storage facility for the product gas. A filter 4 can be provided in the discharge line 7. The filter 4 allows the gas to pass through while preventing dust particles accompanying the gas from passing through.

[0019] The gas reactor 10 may further comprise a separator 5 and a return line 8 . The separator 5 is provided in the discharge line 7. In the illustrated example, the separator 5 is located downstream of the filter 4 in the direction in which the product gas passes through the discharge line 7. The separator 5 is capable of separating the product gas from the feed gas that may be mixed into the product gas. When the product gas is hydrogen gas and the feed gas is methane gas, the separator 5 is typically a pressure swing adsorption (PSA) device or a hydrogen separation membrane. The return line 8 is a pipe through which the raw material gas separated in the separator 5 can pass. The upstream end of the return line 8 in the direction in which the raw material gas passes is connected to the separator 5. The downstream end of the return line 8 is connected to the supply line 6. Therefore, the raw material gas mixed into the production gas can be returned to the plasma generating unit (plasma torch), thereby improving the yield.

[0020] Next, an overview of the operation of the gas reaction apparatus 10 will be described for the case where the raw material gas is methane gas and the desired product gas is hydrogen gas. In the gas reaction device 10, methane gas is supplied from a methane gas storage facility to the plasma torch 1a via a supply line 6. The methane gas supplied to the plasma torch 1a is excited into a plasma state by energy, and then sprayed by the plasma torch 1a toward the surface of the molten metal in the catalytic bath 2. The methane gas in the plasma state then comes into contact with the catalyst on the surface of the molten metal and is decomposed into hydrogen and carbon as shown in the following formula (1). CH4 → 2H2 + C (1) The produced carbon is in a solid state and is mechanically discharged from the chamber 3 by a solid carbon discharger (not shown). The hydrogen is in a gaseous state and is discharged from the chamber 3 through a discharge line 7, and entrained dust is removed by a filter 4. The hydrogen gas passing through the discharge line 7 may be mixed with methane gas, which is the raw material gas. The methane gas mixed with the hydrogen is separated from the hydrogen gas by a separator 5 and returned to the supply line 6 via a return line 8. The hydrogen gas that has passed through the separator 5 is sent to a storage facility (not shown). As a result, CO2-free hydrogen gas can be smoothly produced from methane gas with excellent energy efficiency. [Industrial Applicability]

[0021] The gas reaction method and gas reaction apparatus according to the embodiments of the present invention can be used in a wide range of fields to produce desired reaction products from raw material gases, and can be particularly suitably used for hydrogen production, that is, producing hydrogen from methane gas. [Explanation of symbols]

[0022] 1. Plasma generation unit 1a Plasma torch 2. Catalyst bath 3 chambers

Claims

1. a step of converting a raw material gas into plasma; bringing the raw material gas in a plasma state into contact with a catalyst to induce a chemical reaction of the raw material gas in the plasma state; the catalyst is present in a liquid; a gas reaction method in which the raw material gas in a plasma state is sprayed onto a surface of a molten metal containing the catalyst and the liquid to induce the chemical reaction, and the generated solid reaction product is removed from the surface of the molten metal.

2. 2. The gas reaction method according to claim 1, wherein the source gas includes a hydrocarbon gas.

3. 3. The gas reaction method according to claim 2, wherein the hydrocarbon gas is methane gas.

4. 4. The gas reaction method according to claim 1, wherein the source gas in the plasma state is decomposed in the chemical reaction.

5. 5. The gas reaction method according to claim 1, wherein hydrogen and carbon are produced from the source gas in the plasma state in the chemical reaction.

6. 6. A gas reaction method according to claim 1, wherein the liquid is a molten metal or a molten salt.

7. 7. The gas reaction method according to claim 1, wherein the catalyst is in a liquid state.

8. 8. The gas reaction method according to claim 7, wherein the catalyst is a molten metal or a molten salt.

9. A gas reaction apparatus capable of carrying out the gas reaction method according to any one of claims 1 to 8, a plasma generating unit that generates plasma from a raw material gas; a catalyst holding unit having a catalyst capable of coming into contact with the raw material gas in a plasma state supplied from the plasma generating unit, the catalyst is present in a liquid; The catalyst holding unit includes a molten metal containing the catalyst and the liquid.

10. 10. The gas reaction apparatus according to claim 9, wherein said plasma generating unit is a plasma torch.

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