Apparatus and method for producing carbon monoxide

Abstract

To provide an apparatus for producing carbon monoxide from carbon dioxide using microwave plasma, wherein a microwave waveguide to a reaction chamber has no isolator and impedance matching device, and a production method using the same.SOLUTION: An apparatus for producing carbon monoxide comprises a reaction chamber 1 that includes: a dielectric cylindrical container 4 for generating microwave plasma along an inner wall surface; a conductive cylindrical chamber 5 provided outside the dielectric cylindrical container so as not to contact the cylindrical container; a cylindrical waveguide region 6 that is a region between the dielectric cylindrical container and the conductive cylindrical chamber and contains one or more kinds of dielectrics; a supply port 7 for supplying carbon dioxide gas into the dielectric cylindrical container; and a microwave introduction port 8 provided on the side of the cylindrical waveguide region containing the dielectric. The waveguide 3 has no isolator and impedance matching device. A method for producing carbon monoxide uses the apparatus for producing carbon monoxide.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a carbon monoxide production apparatus and a method for producing carbon monoxide. [Background technology]

[0002] 2. Description of the Related Art In recent years, from the viewpoint of global warming issues and the like, technology for producing carbon monoxide and methanol from carbon dioxide has been attracting attention. As a technique for producing carbon monoxide from carbon dioxide, a method of producing carbon monoxide from carbon dioxide using microwave plasma is known.

[0003] Claim 1 of Patent Document 1 describes a "gas conversion system using microwave plasma, the gas conversion system having a microwave waveguide for propagating microwaves, a gas flow tube passing through the microwave waveguide and configured to propagate microwaves through the gas flow tube, a first temperature control means for controlling a temperature of the microwave waveguide, a temperature sensor disposed near the gas flow tube and configured to measure a temperature of the microwave waveguide, a plasma generator positioned near the gas flow tube and configured to generate plasma in the gas flow tube so that the plasma converts gas flowing in the gas flow tube during operation, and a plasma detector disposed near the gas flow tube and configured to monitor the plasma." Paragraph

[0011] of Patent Document 1 also describes that the gas conversion system can be used to convert carbon dioxide into carbon monoxide and oxygen.

[0004] Claim 1 of Patent Document 2 describes a method for decomposing carbon dioxide using microwave non-equilibrium plasma, characterized in that microwaves are irradiated into a reduced pressure system, and simple carbon dioxide is introduced at the position where the microwaves are irradiated, thereby ionizing the introduced carbon dioxide to obtain carbon monoxide. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2014-520663 [Patent Document 2] JP 2015-155356 A Summary of the Invention [Problem to be solved by the invention]

[0006] Generally, when generating microwave plasma in a reaction vessel, microwaves generated by a microwave oscillator are guided to a microwave inlet of the reaction vessel via a waveguide, and the microwaves are irradiated into the reaction vessel from the microwave inlet of the reaction vessel. However, if the microwave energy is not sufficiently consumed in the reaction vessel, the generated reflected wave may travel through the waveguide and reach the microwave oscillator, possibly causing a breakdown in the microwave oscillator. For this reason, the waveguide is usually provided with a device for dealing with reflected waves, such as an isolator that absorbs reflected waves or an impedance matching device that suppresses reflected waves, thereby preventing the reflected waves from reaching the microwave oscillator. For example, paragraphs

[0008] to

[0009] of Patent Document 1 describe a circuit breaker 15 having a dummy load 16 and a circulator 18 as a device for preventing reflected waves, and paragraph

[0019] of Patent Document 2 describes an isolator 7 and a stub tuner 9.

[0007] However, providing these devices for dealing with reflected waves is not preferable from the viewpoint of miniaturization and simplification of the reaction apparatus. Also, from the viewpoint of energy efficiency, it is preferable to stably generate microwave plasma without using these devices for dealing with reflected waves.

[0008] The present invention has been made under these circumstances, and has an object to provide a carbon monoxide production apparatus which has a reaction chamber, a microwave oscillator, and a waveguide, and which produces carbon monoxide from carbon dioxide by utilizing microwave plasma, wherein the waveguide does not have an isolator or an impedance matching device, and a method for producing carbon monoxide using this carbon monoxide production apparatus. [Means for solving the problem]

[0009] In order to solve the above problems, the present inventors have conducted extensive research into a carbon monoxide producing apparatus that produces carbon monoxide from carbon dioxide by utilizing microwave plasma. As a result, the inventors discovered that by providing a cylindrical waveguide region containing a dielectric on the outside of a cylindrical dielectric container and irradiating microwaves to this cylindrical waveguide region containing a dielectric, microwave plasma can be efficiently generated along the inner wall surface of the cylindrical dielectric container, and further that microwave plasma can be stably generated without adversely affecting the microwave oscillator even without providing an isolator and an impedance matching device in the waveguide, thereby completing the present invention.

[0010] Thus, according to the present invention, there are provided the following carbon monoxide production apparatuses (1) to (10) and carbon monoxide production methods (11) to (14). [1] A carbon monoxide production apparatus having a reaction chamber, a microwave oscillator that generates microwaves, and a waveguide that guides the microwaves generated by the microwave oscillator to the reaction chamber, wherein the reaction chamber comprises a dielectric cylindrical container that generates microwave plasma along an inner wall surface, a conductive cylindrical chamber that is provided outside the dielectric cylindrical container without contacting the dielectric cylindrical container, and a cylindrical waveguide region that includes one or more dielectrics, which is a region between the dielectric cylindrical container and the conductive cylindrical chamber, a carbon dioxide gas supply port that supplies carbon dioxide gas into the dielectric cylindrical container, and a microwave inlet port that is provided to the side of the cylindrical waveguide region that includes the dielectric, and the waveguide does not include an isolator or an impedance matching device. [2] The carbon monoxide generating apparatus according to [1], wherein the dielectric material constituting the dielectric cylindrical container has a relative dielectric constant of 3.0 to 10.0. [3] The carbon monoxide generating apparatus according to [1] or [2], wherein the inner diameter of the cylindrical dielectric container is 12 to 300 mm. [4] The carbon monoxide generating apparatus according to any one of [1] to [3], wherein the wall thickness of the cylindrical dielectric container is 2 to 100 mm. [5] The carbon monoxide generating apparatus according to any one of [1] to [4], wherein at least one of the dielectrics included in the dielectric-containing cylindrical waveguide region has a relative dielectric constant different from a relative dielectric constant of a dielectric constituting the dielectric cylindrical container. [6] The carbon monoxide generating apparatus according to any one of [1] to [5], wherein at least one of the dielectrics contained in the cylindrical waveguide region containing the dielectric has a relative dielectric constant higher than a relative dielectric constant of a dielectric constituting the cylindrical container made of the dielectric. [7] The carbon monoxide generating apparatus according to any one of [1] to [6], wherein at least one of the dielectrics contained in the dielectric-containing cylindrical waveguide region has a relative dielectric constant of 1.5 or more. [8] The carbon monoxide generating apparatus according to any one of [1] to [7], wherein the shortest distance between the dielectric cylindrical container and the conductive cylindrical chamber is 2 to 200 mm. [9] The carbon monoxide generating apparatus according to any one of [1] to [8], wherein a is the number of the dielectric cylindrical containers, b is the number of the conductive cylindrical chambers, and c is the number of the microwave inlets, and a≧2, b=1, and a≧c.

[10] The carbon monoxide producing apparatus according to any one of [1] to [9], comprising a plurality of the dielectric cylindrical containers and a gas accumulation chamber located downstream of the plurality of dielectric cylindrical containers.

[11] A method for producing carbon monoxide using the carbon monoxide production apparatus according to any one of [1] to

[10] above, comprising the step of irradiating a dielectric cylindrical container with microwaves from a microwave inlet while supplying carbon dioxide gas into the dielectric cylindrical container to generate microwave plasma in the dielectric cylindrical container.

[12] The method for producing carbon monoxide according to

[11] , wherein the step of generating microwave plasma is carried out in the presence of a reduction catalyst that reduces carbon dioxide to carbon monoxide.

[13] A method for producing carbon monoxide described in

[11] or

[12] , wherein the step of generating microwave plasma is carried out while supplying hydrogen gas into a cylindrical dielectric container.

[14] The method for producing carbon monoxide according to any one of

[11] to

[13] , further comprising a step of separating carbon monoxide from the gas after the reaction. Effect of the Invention

[0011] According to the present invention, there is provided a carbon monoxide production apparatus having a reaction chamber, a microwave oscillator, and a waveguide, and for producing carbon monoxide from carbon dioxide using microwave plasma, wherein the waveguide does not have an isolator or an impedance matching device, and a method for producing carbon monoxide using this carbon monoxide production apparatus. [Brief description of the drawings]

[0012] [Figure 1] 1(a) is a schematic cross-sectional view showing an example of a carbon monoxide producing apparatus of the present invention, and (b) is a cross-sectional view taken along the line AA in FIG. [Diagram 2] Fig. 2(a) is a schematic cross-sectional view showing another example of the carbon monoxide producing apparatus of the present invention, and Fig. 2(b) is a cross-sectional view taken along line BB of Fig. 2(a). [Diagram 3] 3(a) is a schematic cross-sectional view showing another example of the carbon monoxide producing apparatus of the present invention, (b) is a cross-sectional view taken along CC in FIG. 3(a), and (c) is a cross-sectional view taken along DD in FIG. 3(a). [Figure 4] 4(a) is a schematic cross-sectional view showing another example of the carbon monoxide producing apparatus of the present invention, (b) is a cross-sectional view taken along line EE of FIG. 4(a), and (c) is a cross-sectional view taken along line FF of FIG. 4(a). [Diagram 5] FIG. 1 is a diagram showing a model used in Reference Examples 1 to 14. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will be described in detail below, divided into 1) a carbon monoxide production apparatus and 2) a carbon monoxide production method.

[0014] 1) Carbon monoxide production equipment The carbon monoxide production apparatus of the present invention comprises a reaction chamber, a microwave oscillator that generates microwaves, and a waveguide that guides the microwaves generated by the microwave oscillator to the reaction chamber. The reaction chamber comprises a dielectric cylindrical container that generates microwave plasma along an inner wall surface, a conductive cylindrical chamber that is provided outside the dielectric cylindrical container without contacting the dielectric cylindrical container, a cylindrical waveguide region that is a region between the dielectric cylindrical container and the conductive cylindrical chamber and includes one or more dielectrics, a carbon dioxide gas supply port that supplies carbon dioxide gas into the dielectric cylindrical container, and a microwave inlet port that is provided on the side of the cylindrical waveguide region that includes the dielectric. The waveguide does not include an isolator and an impedance matching device.

[0015] In this specification, a dielectric material refers to a material whose relative dielectric constant is equal to or greater than that of air, that is, a material whose relative dielectric constant is 1 or greater. In this specification, a conductor is defined as a material having an electrical resistivity of 10 3This refers to materials with a resistivity of Ω·m or less.

[0016] The carbon monoxide producing apparatus of the present invention will be described below with reference to FIG. Fig. 1 is a diagram showing an example of an embodiment of a carbon monoxide producing apparatus of the present invention, Fig. 1(a) is a schematic cross-sectional view of a carbon monoxide producing apparatus 100, and Fig. 1(b) is a view of the AA cross section of Fig. 1(a) seen from above.

[0017] The carbon monoxide production apparatus 100 has a reaction chamber 1, a microwave oscillator 2 that generates microwaves, and a waveguide 3 that guides the microwaves generated by the microwave oscillator 2 to the reaction chamber 1. The reaction chamber 1 has a dielectric cylindrical container 4 that generates microwave plasma along the inner wall surface, a conductive cylindrical chamber 5 that is provided outside the dielectric cylindrical container 4 without contacting the dielectric cylindrical container 4, a cylindrical waveguide region 6 that is a region between the dielectric cylindrical container 4 and the conductive cylindrical chamber 5 and contains one or more types of dielectrics, a carbon dioxide gas supply port 7 that supplies carbon dioxide gas into the dielectric cylindrical container 4, and a microwave inlet 8 provided on the side of the cylindrical waveguide region 6 containing a dielectric. Furthermore, the reaction chamber 1 of the carbon monoxide production apparatus 100 has a product gas outlet 9, which is an optional component of the carbon monoxide production apparatus of the present invention. The product gas outlet 9 can be used to take out the gas produced after the reaction to the outside of the reaction chamber 1. An exhaust pump (not shown) is usually connected to the downstream of the product gas outlet 9. This exhaust pump keeps the inside of the dielectric cylindrical container 4 at a reduced pressure. The upstream and downstream ends of the reaction chamber 1 are closed by a pressure-resistant material so that at least the inside of the dielectric cylindrical container 4 is kept at a reduced pressure. The waveguide 3 does not have an isolator or an impedance matching device, which makes it possible to achieve a compact and simplified carbon monoxide producing device.

[0018] The dielectric cylindrical container 4 constituting the reaction chamber 1 is maintained at a reduced pressure inside, and when microwaves are irradiated while carbon dioxide gas is being supplied, microwave plasma is generated along the inner wall surface.

[0019] The cylindrical container 4 made of a dielectric material is preferably one having excellent corrosion resistance against plasma. The relative dielectric constant of the dielectric material constituting the dielectric cylindrical container 4 is preferably 3.0 to 10.0, and more preferably 3.0 to 5.0. Examples of the dielectric material constituting the dielectric cylindrical container 4 include quartz (relative dielectric constant: 3.9), alumina (relative dielectric constant: 9.0), boron nitride (relative dielectric constant: 4), and aluminum nitride (relative dielectric constant: 8.5). Among these, quartz is preferable as the dielectric material constituting the dielectric cylindrical container 4 because it is capable of generating plasma efficiently.

[0020] Microwave plasma is generated in a cylindrical shape along the inner wall surface of the dielectric cylindrical container 4. Therefore, when focusing on a certain cross section inside the dielectric cylindrical container 4, there may be a region in the center of the dielectric cylindrical container 4 where microwave plasma is not generated, such as a doughnut-shaped (annular) hollow portion. Carbon dioxide molecules in the region where microwave plasma is not generated are not converted into carbon monoxide molecules, so the efficiency of carbon monoxide generation decreases as the proportion of such regions increases. Therefore, it is preferable to allow microwave energy to reach the center of the dielectric cylindrical container 4 so that microwave plasma is generated not only near the inner wall surface of the dielectric cylindrical container 4 but also near the center of the dielectric cylindrical container 4.

[0021] On the other hand, if the dielectric cylindrical container 4 is extremely thin, an amount of microwave energy far exceeding the amount required to generate microwave plasma throughout the entire interior of the dielectric cylindrical container 4 will be supplied to the reaction chamber 1, making the use of such a dielectric cylindrical container 4 undesirable from the standpoint of energy efficiency.

[0022] As described above, from the viewpoint of carbon monoxide production efficiency and energy efficiency, the inner diameter of the dielectric cylindrical container 4 is preferably 0.10 to 2.4 times the wavelength of the microwaves, more preferably 0.15 to 1.6 times, and even more preferably 0.20 to 1.0 times.

[0023] As shown in the examples (Reference Examples 1 to 7), for example, when the microwave frequency is 2.4 GHz, the microwave wavelength is 125 mm, so that the inner diameter of the dielectric cylindrical container 4 is preferably 12 to 300 mm, more preferably 19 to 200 mm, and even more preferably 25 to 125 mm.

[0024] In a similar manner, a preferable length of the dielectric cylindrical container 4 (the vertical length in FIG. 1(a)) can be derived. In other words, when looking at the vertical cross section of the dielectric cylindrical container 4, the point at the same height as the microwave inlet 8 is the point where the amount of microwave plasma generated is maximum, and the amount of microwave plasma generated decreases as you move away from this point vertically. Use of a cylindrical dielectric vessel 4 having spaces above and below where microwave plasma is hardly generated is not preferable from the viewpoint of miniaturization of the carbon monoxide production apparatus 100. In addition, the generated carbon monoxide molecules have more chances to collide with radicals or activated molecules, which may cause them to turn into other molecules, resulting in a decrease in the efficiency of carbon monoxide production.

[0025] On the other hand, if the dielectric cylindrical container 4 is extremely short, an amount of microwave energy far exceeding the amount required to generate microwave plasma throughout the entire interior of the dielectric cylindrical container 4 will be supplied to the reaction chamber 1, and therefore using such a dielectric cylindrical container 4 is not preferable from the standpoint of energy efficiency.

[0026] As described above, from the viewpoint of carbon monoxide production efficiency and energy efficiency, the length of the dielectric cylindrical container 4 is preferably 0.20 to 5.0 times the wavelength of the microwaves, more preferably 0.30 to 4.0 times, and even more preferably 0.50 to 3.0 times.

[0027] As shown in the examples (Reference Examples 8 to 14), for example, when the microwave frequency is 2.4 GHz, the microwave wavelength is 125 mm, so the length of the dielectric cylindrical container 4 is preferably 25 to 625 mm, more preferably 37 to 500 mm, and even more preferably 62 to 375 mm.

[0028] The wall thickness of the dielectric cylindrical container 4 is preferably 2 to 100 mm, and more preferably 2 to 50 mm.

[0029] The conductive cylindrical chamber 5 constituting the reaction chamber 1 is provided outside the dielectric cylindrical container 4 without contacting the dielectric cylindrical container 4. By providing the conductive cylindrical chamber 5, microwaves can be confined within the conductive cylindrical chamber 5. This makes it possible to generate microwave plasma safely and efficiently.

[0030] As long as it can confine microwaves, there is no particular limitation on the material of the conductive cylindrical chamber 5. Examples of the material of the conductive cylindrical chamber 5 include stainless steel, copper, nickel, and aluminum.

[0031] The cylindrical waveguide region 6 containing a dielectric material constituting the reaction chamber 1 is a region between the cylindrical dielectric container 4 and the cylindrical conductive chamber 5. Since this region contains one or more types of dielectric material, microwaves introduced from the microwave inlet 8 are diffused cylindrically along the cylindrical waveguide region 6 containing a dielectric material. For this reason, in the carbon monoxide production apparatus 100, microwave plasma is generated cylindrically along the inner wall surface of the cylindrical dielectric container 4 as described above.

[0032] Examples of the dielectric material contained in the cylindrical waveguide region 6 containing the dielectric material include mica (6 to 8), acrylic resin (2.7 to 4.5), urethane (6.5 to 7.1), glass (3.7 to 10.0), glass-epoxy laminate (4.5 to 5.2), trifluoroethylene resin (2.4 to 2.5), silicone resin (3.5 to 5), silicone rubber (3.0 to 3.5), styrene-butadiene rubber (3.0 to 7.0), quartz glass (3.5 to 4.0), styrene resin (2.3 to 3.4), tetrafluoroethylene resin (2.0), nylon (3.5 to 5.0), neoprene (6.0 to 9.0), paraffin (1.9 to 2.5), fluorine resin (4.0 to 8.0), unsaturated polyester resin (2.8 to 5.2), polyamide (2.5 to 2.6), polyester resin (2.8 ~8.1), polyethylene (2.3 to 2.4), polybutylene (2.2 to 2.3), polypropylene (2.0 to 2.3), phenolic resin (3.0 to 12.0), polyacetal resin (3.6 to 3.7), polyurethane (5.0 to 5.3), polyethylene terephthalate (2.9 to 3.0), polycarbonate (2.9 to 3.0), polystyrene (2.4 to 2.6), polystyrene (2.0 to 2.6), polyvinyl alcohol (2.0), polybutylene resin (2.25), polypropylene resin (2.2 to 2.6), polymethyl acrylate (4.0), melamine resin (4.7 to 10.2), methacrylic resin (2.2 to 3.2), wood (2.0 to 6.0), petrolatum (2.2 to 2.9), air (1.0), etc. The numerical value in parentheses after each dielectric material indicates the relative dielectric constant.

[0033] The dielectric-containing cylindrical waveguide region 6 may contain one type of dielectric material or two or more types of dielectric material. At least one of the dielectrics contained in the dielectric-containing cylindrical waveguide region 6 preferably has a relative dielectric constant different from the relative dielectric constant of the dielectric constituting the dielectric cylindrical container 4. Furthermore, it is preferable that at least one of the dielectrics contained in the dielectric-containing cylindrical waveguide region 6 has a relative dielectric constant higher than the relative dielectric constant of the dielectric that constitutes the dielectric cylindrical container 4. At least one of the dielectrics contained in the dielectric-containing cylindrical waveguide region 6 has a relative dielectric constant higher than the relative dielectric constant of the dielectric material constituting the dielectric cylindrical container 4, so that microwave energy can be utilized more efficiently for plasma generation. For the same reason, the relative dielectric constant of at least one of the dielectrics contained in the dielectric-containing cylindrical waveguide region 6 is preferably 1.5 or more, more preferably 3.0 or more, and even more preferably 5.0 or more.

[0034] The thickness of the cylindrical waveguide region 6 containing a dielectric (the distance between the outer wall of the dielectric cylindrical container 4 and the inner wall of the conductive cylindrical chamber 5) is preferably 2 to 200 mm, more preferably 2 to 100 mm.

[0035] The carbon dioxide gas supply port 7 constituting the reaction chamber 1 is used to supply carbon dioxide gas into the cylindrical container 4 made of a dielectric material. The carbon monoxide generating apparatus of the present invention may have a gas supply port other than the carbon dioxide gas supply port. Also, a mixed gas containing carbon dioxide gas and another gas may be supplied into the cylindrical container made of a dielectric material from the carbon dioxide gas supply port.

[0036] The microwave inlet 8 constituting the reaction chamber 1 is provided on the side of the cylindrical waveguide region 6 containing a dielectric material. When the carbon monoxide production apparatus 100 is used, microwaves are irradiated from the microwave inlet 8 . Since the carbon monoxide production apparatus 100 has the cylindrical waveguide region 6 containing a dielectric as described above, microwaves propagate through the cylindrical waveguide region 6 containing a dielectric, and microwave plasma is generated along the inner wall surface of the cylindrical container 4 made of a dielectric.

[0037] The microwave oscillator 2 is a device that generates microwaves. The microwave oscillator 2 excites and oscillates a predetermined high-frequency electromagnetic wave by a high voltage of a microwave power source (not shown). As the microwave oscillator 2, a known one can be appropriately used.

[0038] The waveguide 3 guides the microwaves generated by the microwave oscillator 2 to the reaction chamber 1. The waveguide 3 may be a rectangular waveguide.

[0039] The waveguide 3 does not have an isolator or an impedance matcher. Generally, in a microwave plasma generating device, in order to prevent the generated reflected wave from traveling through the waveguide to reach the microwave oscillator and causing damage to the microwave oscillator, the waveguide is provided with an isolator that absorbs the reflected wave and an impedance matching device that suppresses the reflected wave. In particular, since the impedance of the plasma generating section differs significantly before and after the operation of the microwave plasma generating device (when plasma is generated from a non-plasma generated state) and while the microwave plasma generating device is operating (when the plasma generation state is maintained), it is necessary to continuously suppress reflected waves by adjusting the impedance matching device installed in the waveguide.

[0040] On the other hand, in the carbon monoxide production apparatus 100, microwaves generate microwave plasma in the dielectric cylindrical vessel 4 while diffusing in the cylindrical waveguide region 6 containing the dielectric, so that the influence of the impedance fluctuation of the plasma generating section on the microwave oscillator is smaller than that when microwaves are directly irradiated into the reaction vessel from the microwave inlet.

[0041] Furthermore, when the carbon monoxide production apparatus 100 is used, since a substantially uniform microwave plasma can be generated in the dielectric cylindrical container 4, the microwave energy can be used more efficiently for plasma generation than when microwave plasma is generated locally in the reaction container. Therefore, the microwave energy is sufficiently consumed and reflected waves are suppressed.

[0042] In this way, since the carbon monoxide manufacturing apparatus 100 has the cylindrical waveguide region 6 including a dielectric, reflected waves that may damage the microwave oscillator 2 are unlikely to be generated during operation of the carbon monoxide manufacturing apparatus 100. For this reason, in the carbon monoxide manufacturing apparatus 100, a waveguide 3 that guides the microwave generated by the microwave oscillator 2 to the reaction chamber 1 can be used that does not have an isolator or an impedance matching device.

[0043] 2 to 4 are diagrams showing other examples of the embodiment of the carbon monoxide producing apparatus of the present invention. In the following, each carbon monoxide producing apparatus will be described, but the description of matters common to other carbon monoxide producing apparatuses may be omitted.

[0044] FIG. 2(a) is a schematic cross-sectional view of a carbon monoxide production apparatus 200, and FIG. 2(b) is a view of the BB cross section of FIG. 2(a) seen from above.

[0045] The carbon monoxide production apparatus 200 has a reaction chamber 10, a microwave oscillator 11, and a waveguide 12. The reaction chamber 10 has a cylindrical container 13 made of a dielectric material, a cylindrical chamber 14 made of a conductor, a cylindrical waveguide region 15 containing one or more types of dielectric material, a carbon dioxide gas supply port 16, and a microwave inlet port 17. The carbon monoxide production apparatus 200 has a gas accumulation chamber 18 and an exhaust pump 19 downstream of the reaction chamber 10. The reaction chamber 10 and the gas accumulation chamber 18 are separated by a partition wall 20. The material of the partition 20 may be the same as that of the cylindrical chamber 14 made of a conductive material.

[0046] The carbon monoxide producing apparatus of the present invention may be entirely enclosed in a cylindrical chamber made of a conductive material, like carbon monoxide producing apparatus 200.

[0047] Fig. 3(a) is a schematic cross-sectional view of a carbon monoxide production apparatus 300. Fig. 3(b) is a view of the CC cross section of Fig. 3(a) seen from above, and Fig. 3(c) is a view of the DD cross section of Fig. 3(a) seen from above.

[0048] The carbon monoxide producing apparatus 300 has a reaction chamber and a gas accumulation chamber, and is entirely covered with a cylindrical chamber made of a conductive material, like the carbon monoxide producing apparatus 200. However, as described below, the carbon monoxide producing apparatus 300 differs from the carbon monoxide producing apparatus 200 in that two cylindrical containers made of a dielectric material are housed in the cylindrical chamber made of a conductive material.

[0049] The carbon monoxide production apparatus 300 has a reaction chamber 21, a microwave oscillator 22, and a waveguide 23. The reaction chamber 21 has cylindrical containers 24 and 25 made of a dielectric material, a cylindrical chamber 26 made of a conductor, a cylindrical waveguide region 27 containing one or more types of dielectric material, carbon dioxide gas supply ports 28 and 29, and a microwave inlet 30. The carbon monoxide production apparatus 300 has a gas accumulation chamber 31 and an exhaust pump 32 downstream of the reaction chamber 21. The reaction chamber 21 and the gas accumulation chamber 31 are separated by a partition wall 33.

[0050] In the carbon monoxide production apparatus 300, the shortest distance between the dielectric cylindrical containers 24, 25 and the conductive cylindrical chamber 26 (the thinnest part of the dielectric-containing cylindrical waveguide region 27) is preferably 2 to 200 mm, more preferably 2 to 100 mm.

[0051] Like carbon monoxide production apparatus 300, the carbon monoxide production apparatus of the present invention is not limited to one having one dielectric cylindrical container, one conductive cylindrical chamber, and one microwave inlet. For example, when the number of dielectric cylindrical containers is represented by a, the number of conductive cylindrical chambers is represented by b, and the number of microwave inlets is represented by c, the carbon monoxide production apparatus 300 has an a of 2, a b of 1, and c of 1. Thus, an example of the carbon monoxide producing apparatus of the present invention is one in which a ≧ 2, b = 1, and a ≧ c. In such a carbon monoxide producing apparatus, the surface area of ​​the inner wall surface of the cylindrical dielectric vessel can be increased, so that microwave energy can be used more efficiently to generate plasma.

[0052] When the value of b (the number of cylindrical chambers made of a conductive material) is 1, the value of a (the number of cylindrical containers made of a dielectric material) is preferably 2-10, and more preferably 2-5.

[0053] In a carbon monoxide production apparatus having multiple dielectric cylindrical containers, such as carbon monoxide production apparatus 300, a gas accumulation chamber is provided downstream of the multiple dielectric cylindrical containers, thereby making it possible to efficiently separate carbon monoxide from the generated gas.

[0054] Fig. 4(a) is a schematic cross-sectional view of a carbon monoxide production apparatus 400. Fig. 4(b) is a diagram showing the EE cross section of Fig. 4(a) as viewed from above, and Fig. 4(c) is a diagram showing the FF cross section of Fig. 4(a) as viewed from above.

[0055] The carbon monoxide producing apparatus 400 has two cylindrical dielectric containers, similar to the carbon monoxide producing apparatus 300. However, as described below, the carbon monoxide producing apparatus 400 differs from the carbon monoxide producing apparatus 300 in that the cylindrical dielectric containers each constitute a different reaction chamber.

[0056] The carbon monoxide production apparatus 400 has reaction chambers 34, 35, microwave oscillators 36, 37, and waveguides 38, 39. The reaction chambers 34, 35 each have cylindrical containers 40, 41 made of a dielectric material, cylindrical chambers 42, 43 made of a conductive material, cylindrical waveguide regions 44, 45 containing one or more types of dielectric material, carbon dioxide gas supply ports 46, 47, and microwave inlets 48, 49. The carbon monoxide production apparatus 400 has a gas accumulation chamber 50 and an exhaust pump 51 downstream of the reaction chambers 34 and 35. The gas accumulation chamber 50 is the internal space of a gas accumulation container 52. Examples of materials for the gas accumulation container 52 include the same materials as those for the cylindrical chambers 42 and 43 made of a conductive material.

[0057] 2) Carbon monoxide production method The carbon monoxide production method of the present invention is a method for producing carbon monoxide using the carbon monoxide production apparatus of the present invention, and includes a step of irradiating microwaves from a microwave inlet while supplying carbon dioxide gas into a cylindrical dielectric container, thereby generating microwave plasma in the cylindrical dielectric container.

[0058] Carbon dioxide gas is supplied into the cylindrical dielectric container through a carbon dioxide gas supply port. The supply amount of carbon dioxide gas is usually 0.1 to 100,000 sccm, preferably 1 to 10,000 sccm, and more preferably 10 to 1,000 sccm.

[0059] In the method for producing carbon monoxide of the present invention, a gas component other than carbon dioxide gas may be supplied into the cylindrical dielectric vessel. Gas components other than carbon dioxide gas may be supplied into the dielectric cylindrical container from a gas supply port separate from the carbon dioxide gas supply port, or may be mixed with carbon dioxide gas and supplied into the dielectric cylindrical container from the carbon dioxide gas supply port.

[0060] An example of the gas component other than carbon dioxide gas is hydrogen gas. When hydrogen gas is supplied into a cylindrical dielectric container, the amount of hydrogen gas supplied is usually 0.001 to 2 times, preferably 0.01 to 1 times, and more preferably 0.1 to 0.6 times the amount of carbon dioxide gas on a volume basis. When the supply amount of hydrogen gas is within the above range, the efficiency of carbon monoxide production is improved.

[0061] In the method for producing carbon monoxide of the present invention, the inside of the cylindrical dielectric vessel is usually kept under reduced pressure. The pressure inside the dielectric cylindrical container is usually 0.01 to 1,000 Pa, preferably 0.1 to 200 Pa, and more preferably 1 to 50 Pa.

[0062] The exhaust capacity of the exhaust pump required to maintain the above reduced pressure is usually 0.1 to 100,000 m 3 / h, preferably 1 to 10,000 m 3 / h, more preferably 100 to 1,000 m 3 / h.

[0063] The microwave used generally has a frequency of 2.4 to 2.5 GHz, and an irradiation output of generally 50 to 3,000 W, preferably 100 to 2,000 W, and more preferably 200 to 1,000 W.

[0064] The step of generating microwave plasma may be performed in the presence of a reduction catalyst that reduces carbon dioxide to carbon monoxide. By generating microwave plasma in the presence of a reduction catalyst, the efficiency of carbon monoxide production may be improved.

[0065] The reduction catalyst may contain one or more metal elements from the fourth period or later of the periodic table. Metal elements in the fourth or higher period of the periodic table include titanium, vanadium, chromium, iron, cobalt, nickel, copper, zinc, gallium, zirconium, molybdenum, ruthenium, palladium, tantalum, tungsten, platinum, gold, and gadolinium.

[0066] The shape of the reduction catalyst is not particularly limited. The shape of the reduction catalyst may be, for example, particulate, fibrous, plate, or foil.

[0067] The method for producing carbon monoxide of the present invention may further include a step of separating carbon monoxide from the gas after the reaction. Carbon monoxide can be separated from the gas after the reaction, for example, by adsorbing the carbon monoxide onto a porous material. EXAMPLES

[0068] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples in any way.

[0069] Example 1 A quartz tube (dielectric constant: 3.9) with an inner diameter of 194 mm, an outer diameter of 200 mm, and an axial length of 158 mm, a two-layer tube with an outer diameter of 226 mm obtained by wrapping mica with a thickness of 3 mm around a quartz tube with an inner diameter of 214 mm, an outer diameter of 220 mm, and an axial length of 158 mm, and a stainless steel cylindrical chamber (with an opening for a microwave inlet in part) with an inner diameter of 236 mm and an axial length of 158 mm were concentrically arranged, and the upper and lower parts were covered with stainless steel plates. Next, a gas supply port for supplying gas into the innermost quartz tube and a gas exhaust port for exhausting gas from the innermost quartz tube were provided to manufacture a reaction chamber. A waveguide (not having an isolator or an impedance matching device) and a microwave oscillator were connected to this reaction chamber to obtain a carbon monoxide production device.

[0070] With the pressure in the reaction chamber of the carbon monoxide production equipment at 12 Pa, CO2 was supplied into the reaction chamber at a flow rate of 5 SCCM, and the components of the exhaust gas were examined with a mass spectrometer. Before microwaves were applied to the reaction chamber, the CO / CO2 value in the exhaust gas was 0, but when 500 W of microwaves were applied to the reaction chamber, the CO / CO2 value in the exhaust gas became 7.1.

[0071] [Examples 2 to 8] Carbon monoxide was produced by applying microwaves to the reaction chamber in the same manner as in Example 1, except that the amounts of CO2 and H2 supplied to the reaction chamber were changed to those shown in Table 1. The CO / CO2 value in the exhaust gas is shown in Table 1.

[0072] [Table 1]

[0073] Comparative Example 1 A model of a microwave plasma generator was created in which a cylindrical vessel made of quartz (dielectric constant: 3.9) with an inner diameter of 80 mm, an outer diameter of 100 mm, and an axial length of 100 mm was concentrically arranged with a cylindrical stainless steel chamber with an inner diameter of 100 mm, an outer diameter of 200 mm, and an axial length of 100 mm, and the upper and lower parts were covered with stainless steel plates. Using this model, the maximum plasma intensity in the cylindrical quartz vessel was calculated by OpenFDTD (EEM Corporation).

[0074] Example 9 A model of a microwave plasma generator was created by concentrically arranging a cylindrical container made of quartz (dielectric constant: 3.9) with an inner diameter of 80 mm, an outer diameter of 100 mm, and an axial length of 100 mm, and a cylindrical stainless steel chamber with an inner diameter of 180 mm, an outer diameter of 200 mm, and an axial length of 100 mm, and covering the upper and lower parts with stainless steel plates. Using this model, the maximum plasma intensity in the cylindrical quartz container was determined by the same method as in Comparative Example 1. The difference from the maximum plasma intensity in Comparative Example 1 is shown in Table 2.

[0075] [Examples 10 to 16] In the model produced in Example 9, the dielectrics shown in Table 2 were placed in each region between the quartz cylindrical vessel and the stainless steel cylindrical chamber (region 1: 100-120 mm from the center, region 2: 120-140 mm from the center, region 3: 140-160 mm from the center, region 4: 160-180 mm from the center) to produce models of the microwave plasma generators of Examples 10-16. Using these models, the maximum plasma intensity in the quartz cylindrical vessel was determined by the same method as in Comparative Example 1. The difference from the maximum plasma intensity in Comparative Example 1 is shown in Table 2.

[0076] [Table 2]

[0077] [Reference Examples 1 to 7, Reference Examples 8 to 14] In the carbon monoxide production apparatus of the present invention, microwave plasma is generated along the inner wall surface of a cylindrical dielectric vessel. Therefore, depending on the inner diameter and length of the dielectric cylindrical container, there is a risk that spaces will be created where microwave plasma is not generated sufficiently, or that more energy than necessary will be supplied to the dielectric cylindrical container. For this reason, we investigated the shape of the quartz tube suitable for use with 2.4 GHz microwaves. Reference Examples 1 to 7 show the effect of differences in the inner diameter of the quartz tube on the carbon monoxide generation efficiency and energy efficiency, and Reference Examples 8 to 14 show the effect of differences in the length of the quartz tube on the carbon monoxide generation efficiency and energy efficiency.

[0078] Reference Examples 1 to 7 were examined using the model shown in Fig. 6(a). Fig. 6(a) is a cross-sectional view of a quartz tube 54 having an inner diameter D (53 in Fig. 6(a)). Microwave plasma is generated in a region 57 (hereinafter referred to as the "effective electric field region") within a certain distance 56 (hereinafter referred to as the "effective thickness") from an inner wall 55 of the quartz tube 54 toward the center. The effective thickness is empirically calculated from plasma observations by multiplying the microwave wavelength by 0.2. Since the wavelength of a 2.4 GHz microwave is 125 mm, the effective thickness in this study is 25 mm.

[0079] Next, the effective electric field area ratio was calculated by "(cross-sectional area of ​​effective electric field area) / (cross-sectional area inside the quartz tube)". The effective electric field area ratio represents the proportion of the area where microwave plasma is sufficiently generated and used for reaction when focusing on the cross section inside the quartz tube. Note that when the cross-sectional area of ​​the effective electric field area exceeds the cross-sectional area inside the quartz tube, the effective electric field area ratio was set to 1. The results are shown in Table 3.

[0080] Next, the ineffective ratio 1 was calculated by "{(diameter of the circle whose radius is the effective thickness value) - (inner diameter of the quartz tube)} / (diameter of the circle whose radius is the effective thickness value)". The ineffective ratio 1 is an index showing whether the inherent plasma generating ability of microwave energy is being fully exerted when focusing on the cross section of the quartz tube. That is, a cylindrical reaction tube whose cross-sectional radius is equal to the effective thickness is an ideal reaction tube capable of generating microwave plasma in all regions within its cross-sectional area without wastefully using microwave energy. Therefore, by comparing this ideal reaction tube with the quartz tube to be used, it can be determined whether the quartz tube can fully exert the plasma generating ability inherent to microwave energy. When the inner diameter of the quartz tube is equal to the diameter of the circle whose radius is the effective thickness value, the quartz tube is an ideal reaction tube and the value of the ineffective fraction 1 is 0. On the other hand, when the value of the ineffective ratio 1 is large, it indicates a state in which microwave energy is being used wastefully, and the energy efficiency is poor. In addition, when the inner diameter of the quartz tube exceeds the diameter of the circle whose radius corresponds to the effective thickness value, the ineffective ratio 1 is set to 0. The results are shown in Table 3.

[0081] [Table 3]

[0082] Reference Examples 8 to 14 were examined using the model shown in Fig. 6(b). Fig. 6(b) is a vertical cross-sectional view of a quartz tube 54 having a length L (58 in Fig. 6(b)). Microwave plasma is generated in an area 61 within a certain distance 60 in the vertical direction (hereinafter, this distance will be referred to as the "effective length") centered on the height 59 of the microwave inlet. The effective length is empirically calculated from plasma observations as (wavelength of microwave) / 2. Since the wavelength of 2.4 GHz microwave is 125 mm, the effective thickness in this study is 62.5 mm.

[0083] Next, the effective intensity ratio was calculated by dividing the effective length by the length of the quartz tube. The effective intensity ratio indicates the proportion of the area in the vertical cross section of the quartz tube where microwave plasma is sufficiently generated and used for reaction. When the effective length exceeds the length of the quartz tube, the effective intensity ratio was set to 1. The results are shown in Table 4.

[0084] Next, the ineffective ratio 2 was calculated by "{(effective length) - (length of quartz tube)} / (effective length)". The ineffective ratio 2 is an index showing whether the inherent plasma generating ability of microwave energy is being fully exerted when focusing on the vertical cross section of the quartz tube. That is, a reaction tube whose length is equal to the effective length is an ideal reaction tube that can generate microwave plasma in all regions within its longitudinal cross section without wasteful use of microwave energy. Therefore, by comparing this ideal reaction tube with the quartz tube being used, it can be determined whether the quartz tube can fully utilize the plasma generating ability inherent to microwave energy. When the length of the quartz tube is equal to the effective length, the quartz tube is an ideal reaction tube and the value of the ineffective fraction 2 is 0. On the other hand, when the value of the ineffective ratio 2 is large, it indicates a state in which microwave energy is being used wastefully, and the energy efficiency is poor. When the length of the quartz tube exceeded the effective length, the ineffective ratio 2 was set to 0. The results are shown in Table 4.

[0085] [Table 4]

[0086] The results of Reference Examples 1 to 14 show the influence of the size of the cylindrical dielectric container and the like on the carbon monoxide generation efficiency and energy efficiency. This result can also be used to fully consume the energy of the irradiated microwaves and efficiently suppress reflected waves. [Explanation of symbols]

[0087] 1, 10, 21, 34, 35... Reaction chamber 2, 11, 22, 36, 37... Microwave oscillator 3, 12, 23, 38, 39... Waveguide 4, 13, 24, 25, 40, 41: Cylindrical container made of dielectric material 5, 14, 26, 42, 43: Cylindrical chamber made of conductive material 6, 15, 27, 44, 45... Cylindrical waveguide region containing dielectric 7, 16, 28, 29, 46, 47 Carbon dioxide gas supply port 8, 17, 30, 48, 49...Microwave inlet 9. Produced gas outlet 18, 31, 50 Gas accumulation chamber 19, 32, 51... Exhaust pump 20, 33...bulkhead 52 Gas accumulation container 53...Inner diameter D of quartz tube 54...Quartz tube 55...Inner wall of quartz tube 56 Effective thickness 57 Effective electric field area 58...Length of quartz tube L 59...Height of microwave inlet 60... Effective length 61...Area defined by the height and effective length of the microwave inlet 100, 200, 300, 400... Carbon monoxide production equipment

Claims

1. A reaction chamber; A microwave oscillator that generates microwaves; a waveguide for guiding the microwave generated by the microwave oscillator to the reaction chamber; A carbon monoxide producing apparatus comprising: The reaction chamber includes a cylindrical dielectric vessel in which microwave plasma is generated along an inner wall surface thereof, a conductive cylindrical chamber provided outside the dielectric cylindrical container in a state not in contact with the dielectric cylindrical container; a cylindrical waveguide region between the dielectric cylindrical container and the conductive cylindrical chamber, the cylindrical waveguide region including one or more dielectric materials; a carbon dioxide gas supply port for supplying carbon dioxide gas into the cylindrical dielectric container; a microwave introduction port provided on a side of a cylindrical waveguide region including the dielectric material, The carbon monoxide producing apparatus, wherein the waveguide does not include an isolator and an impedance matching device.

2. 2. The carbon monoxide manufacturing apparatus according to claim 1, wherein the dielectric material constituting the dielectric cylindrical container has a relative dielectric constant of 3.0 to 10.

0.

3. 2. The carbon monoxide generating apparatus according to claim 1, wherein the inner diameter of the cylindrical dielectric container is 12 to 300 mm.

4. 2. The carbon monoxide generating apparatus according to claim 1, wherein the wall thickness of the cylindrical dielectric container is 2 to 100 mm.

5. 2. The carbon monoxide generating apparatus according to claim 1, wherein at least one type of dielectric contained in the cylindrical waveguide region containing the dielectric has a relative dielectric constant different from a relative dielectric constant of the dielectric constituting the dielectric cylindrical container.

6. 2. The carbon monoxide generating apparatus according to claim 1, wherein at least one of the dielectrics contained in the cylindrical waveguide region containing the dielectric has a relative dielectric constant higher than a relative dielectric constant of the dielectric constituting the dielectric cylindrical container.

7. 2. The carbon monoxide generating apparatus according to claim 1, wherein at least one of the dielectrics contained in the dielectric-containing cylindrical waveguide region has a relative dielectric constant of 1.5 or more.

8. 2. The carbon monoxide generating apparatus according to claim 1, wherein the shortest distance between the dielectric cylindrical container and the conductive cylindrical chamber is 2 to 200 mm.

9. 2. The carbon monoxide production apparatus according to claim 1, wherein a ≧ 2, b = 1, and a ≧ c are satisfied, where a is the number of the dielectric cylindrical containers, b is the number of the conductive cylindrical chambers, and c is the number of the microwave inlets.

10. 2. The carbon monoxide producing apparatus according to claim 1, further comprising a gas accumulation chamber located downstream of the dielectric cylindrical containers.

11. A method for producing carbon monoxide using the carbon monoxide production apparatus according to claim 1, comprising: A method for producing carbon monoxide, comprising the steps of supplying carbon dioxide gas into a cylindrical dielectric container while irradiating the container with microwaves from a microwave inlet to generate microwave plasma in the cylindrical dielectric container.

12. The method for producing carbon monoxide according to claim 11, wherein the step of generating microwave plasma is carried out in the presence of a reduction catalyst that reduces carbon dioxide to carbon monoxide.

13. The method for producing carbon monoxide according to claim 11, wherein the step of generating microwave plasma is performed while supplying hydrogen gas into a cylindrical dielectric container.

14. The method for producing carbon monoxide according to claim 11, further comprising a step of separating carbon monoxide from the gas after the reaction.

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