Method and apparatus for producing carbon monoxide-containing synthesis gas

Abstract

To provide a method that enables efficient conversion of carbon dioxide into carbon monoxide.SOLUTION: The present invention provides a method which comprises: a carbon dioxide application step in which carbon dioxide is applied to an ionic liquid; and a plasma irradiation step in which carbon dioxide is converted into carbon monoxide by irradiating the ionic liquid, to which carbon dioxide has been applied, with a plasma.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and an apparatus for producing a synthesis gas containing carbon monoxide. [Background technology]

[0002] According to a report by the U.S. Department of Energy's Energy Information Administration (EIA), global energy consumption is expected to increase by 28% between 2015 and 2040. As energy use increases, energy-related carbon dioxide (CO2) emissions are also expected to increase by 16% over the same period, with annual emissions rising from 33.9 billion tons in 2015 to 39.3 billion tons in 2040.

[0003] Conversion of carbon dioxide to produce sustainable carbonaceous fuels is the most promising option for tackling greenhouse gases in the short to medium term, and carbon dioxide is also expected to serve as a renewable, cheap, and abundant C1 chemical feedstock for producing valuable chemicals such as carbon monoxide (CO).

[0004] For example, one technique proposed for converting carbon dioxide to carbon monoxide is to irradiate carbon dioxide with plasma at specific heat equilibrium (see Patent Document 1). It is also known that by using such a plasma device under optimal conditions, the net conversion rate from carbon dioxide to carbon monoxide can reach nearly 4%, but there are problems in that further increasing the conversion rate requires high output and a long processing time. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-252987 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for efficiently converting carbon dioxide into carbon monoxide. [Means for solving the problem]

[0007] The present inventors discovered that carbon dioxide held (dissolved) in an ionic liquid can be efficiently converted into carbon monoxide by irradiating the carbon dioxide with plasma, and thus completed the present invention.

[0008] That is, the present invention is as follows. [1] a carbon dioxide addition step of adding carbon dioxide to an ionic liquid; a plasma irradiation step of irradiating the ionic liquid to which carbon dioxide has been added with plasma to convert the carbon dioxide into carbon monoxide; 1. A method for producing a synthesis gas containing carbon monoxide, comprising: [2] The method for producing a synthesis gas containing carbon monoxide according to [1] above, wherein the carbon dioxide is added to the ionic liquid in the carbon dioxide adding step by adding the carbon dioxide to the surface of the ionic liquid. [3] The method for producing a carbon monoxide-containing synthesis gas according to [2] above, wherein the carbon dioxide is added to the ionic liquid in the carbon dioxide addition step by adding the carbon dioxide to the ionic liquid that has been spread out in a plane. [4] The method for producing a synthesis gas containing carbon monoxide according to [1] above, wherein the carbon dioxide is added to the ionic liquid in the carbon dioxide addition step by adding the carbon dioxide to the ionic liquid. [5] The method for producing a synthesis gas containing carbon monoxide according to any one of [1] to [4] above, wherein the plasma irradiation in the plasma irradiation step is performed by irradiating the ionic liquid spread in a plane. [6] The method for producing a synthesis gas containing carbon monoxide according to any one of [1] to [5] above, further comprising, after the plasma irradiation step, an ionic liquid heating step of heating the ionic liquid to purify the ionic liquid. [7] The method for producing a synthesis gas containing carbon monoxide according to [6] above, wherein the ionic liquid purified in the ionic liquid heating step is reused as the ionic liquid in the carbon dioxide providing step. [8] The method for producing a carbon monoxide-containing synthesis gas according to any one of [1] to [7] above, wherein the ionic liquid is at least one selected from the group consisting of 1-butyl-3-methylimidazolium acetate ([BMIM]AC), 1-butyl-2,3-dimethylimidazolium chloride ([BDMIM]Cl), 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([BDMIM]BF4), 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac), 1-methyl-3-n-octylimidazolium chloride ([OMIM]Cl), and dimethylammonium N,N-dimethylcarbamate (DIMCARB).

[0009] [9] A carbon dioxide supplying means for supplying carbon dioxide to the ionic liquid; a plasma irradiation means for irradiating the ionic liquid to which carbon dioxide has been added with plasma; 1. An apparatus for producing a synthesis gas containing carbon monoxide, comprising:

[10] The apparatus for producing a carbon monoxide-containing synthesis gas according to [9] above, further comprising a heating means for heat-treating the ionic liquid after plasma irradiation. [Effects of the Invention]

[0010] According to the production method of the present invention, carbon dioxide can be efficiently converted into carbon monoxide, and a synthesis gas containing carbon monoxide can be efficiently produced. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram of a carbon monoxide synthesis gas production apparatus (continuous system) according to a first embodiment of the present invention. [Figure 2] FIG. 2 is an explanatory diagram of a carbon monoxide synthesis gas production apparatus (continuous system) according to a second embodiment of the present invention. [Figure 3]FIG. 1 is an explanatory diagram of an apparatus used in Example 1. [Figure 4] 1 is a photograph of the device used in Example 1. [Figure 5] FIG. 1 is a graph showing the concentration of carbon monoxide produced relative to the concentration of the ionic liquid when 1-butyl-2,3-dimethylimidazolium chloride ([BDMIM]Cl) is used as the ionic liquid. [Figure 6] FIG. 1 is a graph showing the concentration of carbon monoxide produced relative to the concentration of ionic liquid when N,N-dimethylammonium carbamate (DIMCARB) is used as the ionic liquid. [Figure 7] FIG. 1 is an explanatory diagram of the apparatus and procedure used in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0012] The method for producing a carbon monoxide-containing synthesis gas of the present invention is characterized by comprising a carbon dioxide addition step of adding carbon dioxide to an ionic liquid, and a plasma irradiation step of irradiating the ionic liquid to which carbon dioxide has been added with plasma to convert the carbon dioxide to carbon monoxide.

[0013] According to the production method of the present invention, carbon dioxide can be efficiently converted to carbon monoxide, and a carbon monoxide-containing synthesis gas can be efficiently produced. Furthermore, the production method of the present invention 1) can be carried out under atmospheric pressure using low-power plasma, 2) uses an inexpensive and reusable ionic liquid, and 3) can use carbon dioxide in the air or exhaust gas as a raw material gas, making it possible to inexpensively produce a carbon monoxide-containing synthesis gas.

[0014] The carbon monoxide-containing synthesis gas produced by the method of the present invention may be used as is, or the carbon monoxide may be separated before use.

[0015] Next, each step of the production method of the present invention will be described in detail. [Carbon dioxide addition process] The carbon dioxide addition step is a step of adding carbon dioxide to an ionic liquid. The method of adding carbon dioxide to an ionic liquid is not particularly limited as long as it is a method that can retain (dissolve) carbon dioxide in the ionic liquid, and examples thereof include a method of adding carbon dioxide to the surface of an ionic liquid and a method of adding carbon dioxide into the ionic liquid. Specifically, an example of a method of adding carbon dioxide to the surface of an ionic liquid is a method in which the ionic liquid is placed in a carbon dioxide atmosphere or under a carbon dioxide gas flow and brought into contact with the ionic liquid. Furthermore, an example of a method of adding carbon dioxide into the ionic liquid is a method in which carbon dioxide is bubbled through the ionic liquid. The temperature of the ionic liquid when carbon dioxide is added may be any temperature at which the ionic liquid is in liquid state, and is preferably from -40 to 100°C, and more preferably from 0 to 50°C, for example.

[0016] Carbon dioxide may be applied to the surface of the ionic liquid held at a predetermined height in a container, but it is preferable to apply carbon dioxide to the ionic liquid spread out in a flat plane, as this allows for more efficient application of carbon dioxide.

[0017] (ionic liquid) The ionic liquid used in the production method of the present invention is not particularly limited as long as it is a salt consisting of a cation and an anion and in a liquid state at room temperature, and is preferably a salt having a melting point of 25° C. or lower, more preferably a salt of 10° C. or lower, and even more preferably a salt of −20° C. or lower. One type of ionic liquid may be used alone, or two or more types may be used in combination.

[0018] Examples of cations constituting the ionic liquid include imidazolium ions represented by the following general formula (1), pyridinium ions represented by the general formula (2), ammonium ions represented by the general formula (3), pyrrolidinium ions represented by the general formula (4), phosphonium ions represented by the general formula (5), and sulfonium ions represented by the general formula (6). Among these, imidazolium ions represented by the general formula (1) and ammonium ions represented by the general formula (3) are preferred.

[0019] [ka]

[0020] In general formula (1), R 1 and R 2 are the same or different and represent an optionally substituted alkyl group or a hydrogen atom (provided that R 1 and R 2 is not simultaneously a hydrogen atom). The alkyl group is not particularly limited as long as the cation can form an ionic liquid. The alkyl group may be either branched or straight-chain, but is preferably straight-chain. Examples of the alkyl group include alkyl groups having 1 to 8 carbon atoms, preferably alkyl groups having 1 to 4 carbon atoms, and more specific examples include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, and octyl groups.

[0021] Specific examples include 1-butyl-3-methylimidazolium ion, 1-butyl-2,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium ion, and 1-methyl-3-n-octylimidazolium.

[0022] In general formula (2), R 3represents an alkyl group which may be substituted. The alkyl group is not particularly limited as long as the cation can form an ionic liquid. The alkyl group may be either branched or linear, but is preferably linear. Examples of the alkyl group include alkyl groups having 1 to 5 carbon atoms, preferably alkyl groups having 1 to 3 carbon atoms, and more specific examples include methyl, ethyl, propyl, butyl, and pentyl groups.

[0023] In general formula (3), R 4 ~R 7 are the same or different and represent an optionally substituted alkyl group or a hydrogen atom (provided that R 4 ~R 7 is not simultaneously a hydrogen atom). The alkyl group is not particularly limited as long as the cation can form an ionic liquid. The alkyl group may be either branched or straight-chain, but is preferably straight-chain. Examples of the alkyl group include alkyl groups having 1 to 5 carbon atoms, preferably alkyl groups having 1 to 3 carbon atoms, and more specific examples include methyl, ethyl, propyl, butyl, and pentyl groups.

[0024] A specific example is dimethylammonium ion.

[0025] In general formula (4), R 8 and R 9 are the same or different and represent an optionally substituted alkyl group or a hydrogen atom (provided that R 8 and R 9 is not simultaneously a hydrogen atom). The alkyl group is not particularly limited as long as the cation can form an ionic liquid. The alkyl group may be either branched or straight-chain, but is preferably straight-chain. Examples of the alkyl group include alkyl groups having 1 to 8 carbon atoms, preferably alkyl groups having 1 to 6 carbon atoms, and more specific examples include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, and octyl groups.

[0026] In general formula (5), R 10 ~R 13are the same or different and represent an optionally substituted alkyl group or a hydrogen atom (provided that R 10 ~R 13 is not simultaneously a hydrogen atom). The alkyl group is not particularly limited as long as the cation can form an ionic liquid. The alkyl group may be either branched or straight-chain, but is preferably straight-chain. Examples of the alkyl group include alkyl groups having 1 to 5 carbon atoms, preferably alkyl groups having 1 to 3 carbon atoms, and more specific examples include methyl, ethyl, propyl, butyl, and pentyl groups.

[0027] In general formula (6), R 14 ~R 16 are the same or different and represent an optionally substituted alkyl group or a hydrogen atom (provided that R 14 ~R 16 is not simultaneously a hydrogen atom). The alkyl group is not particularly limited as long as the radically polymerizable group-containing cation can form an ionic liquid. The alkyl group may be either branched or straight-chain, but is preferably straight-chain. Examples of the alkyl group include alkyl groups having 1 to 5 carbon atoms, preferably alkyl groups having 1 to 3 carbon atoms, and more specific examples include methyl, ethyl, propyl, butyl, and pentyl groups.

[0028] In the general formulas (1) to (6), examples of the substituent of the alkyl group include a hydroxyl group, a carbonyl group, a methoxy group, an amino group, a carboxyl group, an aryl group, and a radically polymerizable group. A radically polymerizable group can also be used instead of a hydrogen atom. The radically polymerizable group is not particularly limited as long as it is capable of addition polymerization by a radical and the radically polymerizable group-containing cation can form an ionic liquid. Specific examples of the radically polymerizable group include a vinyl group, an allyl group, an isopropenyl group, an acryloyl group, a methacryloyl group, and a maleoyl group, and preferred examples include a vinyl group, an allyl group, and an acryloyl group.

[0029] Examples of anions that constitute ionic liquids include organic carboxylate ions (for example, organic carboxylate ions having one carboxy group and 1 to 8 carbon atoms (preferably 2 to 4, more preferably 2 to 3)), dialkylcarbamate ions, halide ions, dialkylphosphate ions, and tetrafluoroborate ions (BF4 - ), BF3CF3 - , BF3C2F5 - , BF3C3F7 - , BF3C4F9 - , hexafluorophosphate ion (PF6 - ), bis(trifluoromethanesulfonyl)imidate ion ((CF3SO2)2N - ), perchlorate ion (ClO4 - ), tris(trifluoromethanesulfonyl)carbonate ion ((CF3SO2)3C - ), trifluoromethanesulfonate ion (CF3SO3 - ), dicyanamide ion ((CN)N - ), trifluoroacetate ion (CF3COO - ), and amino acid-derived ions.

[0030] Among these, organic carboxylate ions, dialkylcarbamate ions, halide ions, tetrafluoroborate ions (BF4 - ) are preferred, specifically acetate ion, dimethylcarbamate ion, chloride ion, tetrafluoroborate ion (BF4 - ) is preferred.

[0031] Specifically, preferred ionic liquids include 1-butyl-3-methylimidazolium acetate ([BMIM]AC), 1-butyl-2,3-dimethylimidazolium chloride ([BDMIM]Cl), 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([BDMIM]BF), 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac), 1-methyl-3-n-octylimidazolium chloride ([OMIM]Cl), and dimethylammonium N,N-dimethylcarbamate (DIMCARB).

[0032] Ionic liquids can be produced according to known methods (see, for example, Chem. Lett., 2000, p. 922, J. Phys. Chem. B, 103, 1999, p. 4164, etc.). In the present invention, ionic liquids produced according to known methods or commercially available products may be used.

[0033] The ionic liquid may be used as is, but is preferably dissolved in a solvent before use. Examples of the solvent include water and various organic solvents, with water being preferred. Examples of the organic solvent include alcohol, acetone, acetonitrile, benzene, and toluene. One solvent may be used alone, or two or more solvents may be used in combination. The concentration of the ionic liquid is, for example, preferably 1 to 100% by mass, more preferably 30 to 95% by mass, and even more preferably 50 to 90% by mass.

[0034] (carbon dioxide) The carbon dioxide used in the production method of the present invention is not particularly limited, and may be pure carbon dioxide gas or a mixed gas containing other components. Specific examples of the mixed gas include air and exhaust gases generated in facilities such as factories, waste treatment facilities, and thermal power plants.

[0035] [Plasma irradiation process] The plasma irradiation step is a step of converting carbon dioxide into carbon monoxide by irradiating the ionic liquid to which carbon dioxide has been added in the carbon dioxide addition step with plasma. In this step, carbon dioxide is efficiently converted into carbon monoxide due to the synergy between the ionic liquid and the plasma.

[0036] The plasma generator used in the plasma irradiation step of the present invention is not particularly limited, and any conventionally known plasma generator can be used.

[0037] The plasma discharge method is not particularly limited, and examples thereof include non-equilibrium plasma methods such as RF discharge, corona discharge, dielectric barrier discharge, and microwave discharge, and thermal equilibrium plasma methods such as arc discharge. Examples of plasma irradiation methods include remote plasma, direct plasma, and spot plasma.

[0038] The plasma gas (process gas) is not particularly limited, and examples thereof include air, nitrogen gas, halogen-containing gas, oxygen gas, and hydrogen gas, and a mixture of these gases may also be used. In the present invention, air plasma or nitrogen gas plasma (N2 plasma) is preferred. It is preferable to previously purge the space containing the ionic liquid with plasma gas before plasma irradiation. The flow rate of the plasma gas can be appropriately determined depending on the distance between the electrodes, the cross-sectional area and length of the gas flow surface in the discharge field, the frequency of the applied high frequency, the composition of the plasma gas, and the like.

[0039] The plasma irradiation in the plasma irradiation step of the present invention may be low-pressure plasma irradiation or atmospheric pressure plasma irradiation, and the pressure range is, for example, 0.001 to 1.0 × 10 8 Pa, 0.01 to 1 x 10 7 Pa is preferred, and 0.1 to 1 × 10 6 More preferably, Pa. The plasma irradiation time is, for example, 1 to 6000 seconds, preferably 10 to 1000 seconds, more preferably 20 to 500 seconds, and even more preferably 30 to 200 seconds.

[0040] The plasma irradiation of the ionic liquid may be localized, but preferably widespread. For example, by widely irradiating an ionic liquid in which carbon dioxide has been dissolved and spread in a flat plane with plasma, a large amount of carbon dioxide can be efficiently converted into carbon monoxide. The ionic liquid in which carbon dioxide has been dissolved and spread in a flat plane may be one to which carbon dioxide has been added in a flat state, or one to which carbon dioxide has been added and then spread in a flat state.

[0041] [Ionic liquid heating process] The production method of the present invention preferably further includes an ionic liquid heating step after the plasma irradiation step, in which the ionic liquid is heated to purify the ionic liquid. This step allows the various gases generated in the plasma irradiation step to be released from the ionic liquid, leaving a purified ionic liquid, which regenerates the carbon dioxide absorbency. This regenerated ionic liquid can be reused for the carbon dioxide addition of the present invention.

[0042] [Other processes] In addition to the above steps, the production method of the present invention may include other steps such as a step of purifying the ionic liquid and a step of purifying carbon dioxide.

[0043] [Estimated reaction of the present invention] The present inventors have found that when carbon dioxide dissolved in water is irradiated with plasma,

[0044] [ka]

[0045] On the other hand, by using an ionic liquid as in the present invention, the reaction proceeds as follows:

[0046] [ka]

[0047] It is speculated that the following reaction occurs, resulting in efficient conversion of carbon dioxide to carbon monoxide.

[0048] Specifically, when 1-butyl-3-methylimidazolium acetate ([BMIM]AC) is used as the ionic liquid, the following reaction is presumed to proceed.

[0049] [ka]

[0050] Furthermore, when N,N-dimethylammonium dimethylcarbamate (DIMCARB) is used as the ionic liquid, the following reaction is presumed to proceed.

[0051] [ka]

[0052] The above reaction is based on the speculation of the inventors and does not limit the scope of the present invention.

[0053] Next, the manufacturing apparatus of the present invention will be described. The apparatus for producing a carbon monoxide-containing synthesis gas of the present invention is characterized by comprising a carbon dioxide supplying means for supplying carbon dioxide to an ionic liquid, and a plasma irradiation means for irradiating the ionic liquid to which carbon dioxide has been added with plasma. The production apparatus of the present invention can be used to carry out the method for producing a carbon monoxide-containing synthesis gas of the present invention.

[0054] The carbon dioxide supplying means is not particularly limited as long as it can supply carbon dioxide to the ionic liquid, and examples include means for supplying carbon dioxide to the surface of the ionic liquid and means for supplying carbon dioxide into the ionic liquid.

[0055] A specific example of a means for providing carbon dioxide to the surface of an ionic liquid is a carbon dioxide supply device that circulates a gas containing carbon dioxide over the surface of the ionic liquid, and a specific example of a means for providing carbon dioxide into the ionic liquid is a bubbling device that bubbles a gas containing carbon dioxide into the ionic liquid.

[0056] As the plasma irradiation means, a conventionally known device can be used. Specific examples include devices capable of performing the plasma irradiation described in the manufacturing method of the present invention. For example, a device (remote type) can be used, which includes a pair of electrodes, a dielectric provided on at least one of the opposing surfaces of the pair of electrodes, and a high-frequency power source that applies a voltage between the pair of electrodes, and which introduces the discharge generated between the pair of electrodes into the ionic liquid using a process gas to irradiate the ionic liquid with plasma.

[0057] Furthermore, the apparatus for producing a carbon monoxide-containing synthesis gas of the present invention preferably includes a heating means for heat-treating the ionic liquid after plasma irradiation, thereby restoring the carbon dioxide absorption ability of the ionic liquid and enabling the ionic liquid to be reused.

[0058] The apparatus for producing a carbon monoxide-containing synthesis gas of the present invention may be a batch system in which carbon dioxide is added to an ionic liquid contained in a storage tank or the like and plasma is irradiated thereto, or a continuous system in which carbon dioxide is added to a circulating ionic liquid and plasma is irradiated thereto continuously, but a continuous system is preferred.

[0059] Specifically, an example of a batch processing apparatus is an ionic liquid storage tank equipped with a carbon dioxide supplying means and a plasma irradiation means. An example of a continuous processing apparatus is one equipped with a first tank equipped with a carbon dioxide supplying means and a second tank connected to the first tank equipped with a plasma irradiation means, in which a continuously supplied ionic liquid is circulated from the first tank to the second tank. An example of a continuous processing apparatus is one equipped with a plasma irradiation means having an electrode rod connected to a high-frequency power source inserted into a dielectric tube (e.g., a glass tube) surrounded by an electrode material, an ionic liquid supplying means for supplying ionic liquid along the inner wall of the dielectric tube, and a carbon dioxide supplying means for circulating carbon dioxide within the dielectric tube.

[0060] Hereinafter, one embodiment of the carbon monoxide synthesis gas production apparatus of the present invention will be specifically described with reference to the drawings, but the present invention is not limited to this embodiment.

[0061] Here, Fig. 1 is an explanatory diagram of a carbon monoxide synthesis gas production apparatus (continuous system) according to a first embodiment of the present invention, and Fig. 2 is an explanatory diagram of a carbon monoxide synthesis gas production apparatus (continuous system) according to a second embodiment of the present invention.

[0062] As shown in Figure 1, the carbon monoxide-containing synthesis gas production apparatus 1 according to the first embodiment of the present invention includes a first tank 3 equipped with a bubbling device 2 as a carbon dioxide supplying means, a second tank 4 connected to the first tank 3 and equipped with a plasma irradiation means for irradiating plasma onto the ionic liquid flowing in from the first tank 3, and a third tank 6 connected to the second tank 4 and equipped with a heat treatment means 5 for heat-treating the ionic liquid flowing in from the second tank 4. Furthermore, the third tank 6 is also connected to the first tank 3, and the ionic liquid heat-treated in the third tank 6 is sent to the first tank 3, allowing the ionic liquid to be circulated. The production apparatus 1 is capable of continuously producing carbon monoxide by circulating the ionic liquid.

[0063] The carbon monoxide-containing synthesis gas production apparatus 1 according to the first embodiment of the present invention performs continuous treatment by circulating the ionic liquid through the first tank 3, second tank 4, and third tank 6. However, the first tank 3, second tank 4, and third tank 6 can also be a batch-type apparatus in which the first tank 3, second tank 4, and third tank 6 are combined into a single tank equipped with a carbon dioxide supplying means, a plasma irradiation means, and a heat treatment means.

[0064] 2, a carbon monoxide-containing synthesis gas production apparatus 7 according to a second embodiment of the present invention includes a glass tube 8 as an upright dielectric tube, a metal sheet 9 as a sheet-like electrode covering the glass tube 8, and plasma irradiation means including a metal rod 11 as a rod-like electrode connected to a high-frequency power supply (high-voltage pulse power supply) 10 and inserted into the glass tube 8. The production apparatus 7 also includes an ionic liquid supply means for supplying an ionic liquid from above along the inner wall of the glass tube 8, and a carbon dioxide supply means for circulating carbon dioxide inside the glass tube 8 from above.

[0065] The carbon dioxide supplying means adds carbon dioxide to the ionic liquid supplied by the ionic liquid supplying means and flowing along the inner wall of the glass tube 8. The plasma irradiating means generates plasma discharge from the metal rod 11 toward the metal sheet 9, and irradiates the ionic liquid flowing along the inner wall of the glass tube 8 to which carbon dioxide has been added with plasma. This allows the production apparatus 7 to continuously produce carbon monoxide. [Example]

[0066] [Example 1] Using the device shown in Figure 3, a test was conducted to convert carbon dioxide to carbon monoxide.

[0067] In this test, carbon dioxide is introduced into a container containing an ionic liquid (IL) to attach carbon dioxide to the surface of the ionic liquid, and then plasma is irradiated onto the ionic liquid to synthesize carbon monoxide from the carbon dioxide.

[0068] Specifically, the test was carried out under the following conditions. <Condition> Ionic Liquids (ILs) (1) 1-Butyl-3-methylimidazolium chloride ([BMIM]Cl) (2) N,N-dimethylammonium carbamate (DIMCARB) ·IL concentration: 0-80wt% Gas: CO2 Gas flow rate: 300sccm ·Temperature: normal temperature Plasma generation power supply: PVM500 (Information Unlimited) Input power: 10~12W Applied frequency, applied voltage: 24-25kHz, 6-7kVpp Processing time: 4 minutes CO detector: Gastec gas detector tube (Tube No.: 1HH)

[0069] <Result 1: When [BMIM]Cl was used as the ionic liquid> The concentration of carbon monoxide produced versus the ionic liquid concentration is shown in Figure 5. As shown in Figure 5, the carbon monoxide concentration increased with an increase in the ionic liquid concentration, reaching approximately 30% at an ionic liquid concentration of 80 wt%. On the other hand, when only water was used without any ionic liquid (0 wt% ionic liquid), the carbon monoxide concentration was low at around 3%. Furthermore, when plasma irradiation was not performed (circle in Figure 5), no carbon monoxide was generated.

[0070] <Result 2: When DIMCARB was used as the ionic liquid> The concentration of carbon monoxide produced versus the ionic liquid concentration is shown in Figure 6. As shown in Figure 6, the carbon monoxide concentration increased, reaching approximately 30% at an ionic liquid concentration of 80 wt%. On the other hand, when only water was used without any ionic liquid (0 wt% ionic liquid), the carbon monoxide concentration was low at around 3%. Furthermore, when plasma irradiation was not performed (circle in Figure 6), no carbon monoxide was generated.

[0071] Since the introduction of carbon dioxide and the plasma irradiation were carried out at roughly the same time, it is thought that the conversion to carbon monoxide was promoted by the synergy between the plasma and the ionic liquid on the surface of the ionic liquid solution.

[0072] [Example 2] In this test, carbon dioxide gas was bubbled into a container containing a predetermined concentration of ionic liquid, and after leaving it for a certain period of time, the ionic liquid was irradiated with plasma to convert the carbon dioxide into carbon monoxide.

[0073] The test was carried out in accordance with the following steps 1) to 3), as shown in FIG. 1) Carbon dioxide gas was bubbled through the ionic liquid for 2 minutes (left panel of Figure 7). The flow rate of the carbon dioxide gas was 300 sccm, and the bottle was loosely capped during bubbling. 2) After bubbling, the mixture was stored for 24 hours to confirm its carbon dioxide retention capacity (center diagram in Figure 7). The storage temperature was 20°C. 3) After 24 hours of storage, the ionic liquid was irradiated with plasma (right diagram in FIG. 7). The discharge parameters were the same as in Example 1.

[0074] First, we used [BMIM]Cl as an ionic liquid and investigated its concentration dependence. Specifically, 4 wt%, 12 wt%, and 20 wt% [BMIM]Cl were used as the ionic liquid. Carbon dioxide gas was bubbled through the ionic liquid for 2 minutes, and then the liquid was stored for 24 hours. The carbon dioxide concentration in the ionic liquid after 24 hours was measured using a CGP-31 sensor (DKK-TOA Corporation). Furthermore, the ionic liquid stored for 24 hours was irradiated with air plasma for 1 minute, and the carbon monoxide concentration was measured. For comparison, water (0 wt% ionic liquid) was used. The results are shown in Table 1.

[0075] [Table 1]

[0076] As shown in Table 1, as the concentration of the ionic liquid increased, the carbon dioxide retention capacity increased and the amount of carbon monoxide conversion tended to increase. On the other hand, water had a low carbon dioxide retention capacity, and after 24 hours the carbon dioxide concentration in the liquid had decreased to about 1% of the initial concentration.

[0077] Next, similar tests were performed using different ionic liquids (ILs), such as [BMIM]Ac, [BDMIM]Cl, [BDMIM]BF4, [BMIM]Ac, [DIMCARB], and [OMIM]Cl, after storage for 4 or 10 days after CO2 addition. The results are shown in Table 2.

[0078] [Table 2]

[0079] As shown in Table 2, it was clear that the conversion to carbon monoxide was efficient regardless of the ionic liquid used.

[0080] [Example 3] In Example 2, plasma irradiation was carried out in an air atmosphere, but in this example, plasma irradiation was carried out in a nitrogen atmosphere.

[0081] Specifically, DIMCARB was used as the ionic liquid, and after bubbling with carbon dioxide for 2 minutes, the ionic liquid was stored for 4 days. The carbon dioxide concentration in the ionic liquid after 4 days was measured using a CGP-31 sensor (DKK-TOA Corporation). After purging with nitrogen for 4 minutes, the ionic liquid stored for 4 days was irradiated with N2 plasma for 1 minute, and the concentration of carbon monoxide generated was measured. For comparison, water (0 wt% ionic liquid) was used. The results are shown in Table 3.

[0082] [Table 3]

[0083] As shown in Table 3, the results obtained with nitrogen plasma were similar to those obtained with air plasma (Table 2). Therefore, it is believed that there is no effect of carbon dioxide in the air. [Industrial Applicability]

[0084] The present invention is industrially useful because it can produce carbon monoxide, a useful chemical raw material. [Explanation of symbols]

[0085] 1. Carbon monoxide-containing synthesis gas production apparatus (first embodiment) 2. Bubbling device 3 First tank 4 Second tank 5. Heat treatment method 6 Third tank 7. Apparatus for producing carbon monoxide-containing synthesis gas (second embodiment) 8 Glass tube (dielectric) 9 Metal sheet (sheet electrode) 10 High frequency power supply 11 Metal rod (rod-shaped electrode)

Claims

1. a carbon dioxide addition step of adding carbon dioxide to the ionic liquid; a plasma irradiation step of irradiating the ionic liquid to which carbon dioxide has been added with plasma to convert the carbon dioxide into carbon monoxide; 1. A method for producing a synthesis gas containing carbon monoxide, comprising:

2. 2. The method for producing a carbon monoxide-containing synthesis gas according to claim 1, wherein the carbon dioxide is added to the ionic liquid in the carbon dioxide adding step by adding the carbon dioxide to the surface of the ionic liquid.

3. 3. The method for producing a carbon monoxide-containing synthesis gas according to claim 2, wherein the carbon dioxide is added to the ionic liquid in the carbon dioxide adding step by spreading the ionic liquid in a plane.

4. 2. The method for producing a carbon monoxide-containing synthesis gas according to claim 1, wherein the carbon dioxide is added to the ionic liquid in the carbon dioxide adding step by adding the carbon dioxide to the ionic liquid.

5. 5. The method for producing a synthesis gas containing carbon monoxide according to claim 1, wherein the plasma irradiation in the plasma irradiation step is performed by irradiating the ionic liquid spread in a plane.

6. The method for producing a synthesis gas containing carbon monoxide according to any one of claims 1 to 5, further comprising, after the plasma irradiation step, an ionic liquid heating step of heating the ionic liquid to purify the ionic liquid.

7. 7. The method for producing a synthesis gas containing carbon monoxide according to claim 6, wherein the ionic liquid purified in the ionic liquid heating step is reused as the ionic liquid in the carbon dioxide providing step.

8. The ionic liquid may be 1-butyl-3-methylimidazolium acetate ([BMIM]AC), 1-butyl-2,3-dimethylimidazolium chloride ([BDMIM]Cl), or 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([BDMIM]BF ４ 8. The method for producing a carbon monoxide-containing synthesis gas according to any one of claims 1 to 7, wherein the catalyst is at least one selected from the group consisting of 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac), 1-methyl-3-n-octylimidazolium chloride ([OMIM]Cl), and N,N-dimethylammonium carbamate (DIMCARB).

9. a carbon dioxide supplying means for supplying carbon dioxide to the ionic liquid; a plasma irradiation means for irradiating the ionic liquid to which carbon dioxide has been added with plasma; 1. An apparatus for producing a synthesis gas containing carbon monoxide, comprising:

10. 10. The apparatus for producing a carbon monoxide-containing synthesis gas according to claim 9, further comprising a heating means for heat-treating the ionic liquid after plasma irradiation.

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