Method and apparatus for producing carbon monoxide

Abstract

Disclosed are a method and an apparatus for producing carbon monoxide from carbon dioxide, wherein, in a reaction vessel having a pressure adjusted to 1.0-10.0 kPa, carbon dioxide is decomposed by converting a flowing gas containing carbon dioxide into plasma using microwave irradiation, and then the decomposed gas of carbon dioxide is brought into contact with a carbon material.

Description

Method for producing carbon monoxide and carbon monoxide production apparatus

[0001] The present invention relates to a method and an apparatus for producing carbon monoxide from carbon dioxide.

[0002] The 20th century brought about advanced economic development due to the progress of science and technology, but on the other hand, it has caused serious environmental problems such as global warming. Carbon dioxide (CO ２ ), which is a greenhouse gas, is a gas that is emitted in large quantities when producing energy, so global warming is one of the most difficult environmental problems to solve. According to the announcement of the Ministry of the Environment, the greenhouse gas emissions in Japan in fiscal year 2022 were 1.135 billion tons (CO ２ conversion), and a huge amount of CO ２ is being emitted.

[0003] In recent years, in order to reduce this CO ２ , technologies for separating and recovering CO ２ and storing it underground (CCS; Carbon dioxide Capture and Storage) and technologies for effectively using the separated and recovered CO ２ (CCU; Carbon dioxide Capture and Utilization) have been extensively studied.

[0004] Regarding CCS, it has made great progress, such as conducting demonstration tests for CO ２ separation and recovery and injecting CO ２ into the ground. There are also some technologies that have been partially commercialized, but the production of synthesis gas is still in the technology development stage of an innovative process. However, in CCS, considering the limited storage capacity of CO ２ underground, the possibility of the stored CO ２ leaking again, and the large energy consumption for injecting it into the ground, etc., the development of new technologies related to CCU is essential.

[0005] In the Carbon Recycling Roadmap announced by the Ministry of Economy, Trade and Industry, various organic compounds are directly produced from CO ２ and H ２ via CO.The goal is to produce them from a mixture of CO and H. Many of these organic compounds are produced from a mixture of CO and H. ２ Since it is possible to manufacture from CO using current technology, ２ If it is possible to convert CO with high efficiency, it will be possible to produce a variety of high-value-added organic compounds.

[0006] However, CO ２ It is a very stable chemical species, unlike elemental CO ２ Converting CO is not easy. ２ Plasma is considered effective for this conversion, and various studies are being conducted on it.

[0007] As a method for efficiently decomposing carbon dioxide into carbon monoxide, for example, as described in Patent Document 1, a method has been proposed in which microwaves are irradiated into a system with a reduced pressure of less than 1000 Pa, and a carbon dioxide carrier is introduced at the microwave irradiation position, thereby ionizing the introduced carbon dioxide to obtain carbon monoxide without using a catalyst or gasifying agent.

[0008] Furthermore, CO, as described in Patent Document 2 ２ A process gas containing CO and O is supplied to a plasma jet generator to generate CO and oxygen species, these oxygen species are introduced into a carbon reaction chamber containing carbon donor particles and combined with carbon to form CO, and CO and CO ２ A method has been proposed in which the generated gas containing the substance is extracted, and then this generated gas is recirculated to a plasma jet generator.

[0009] Japanese Patent No. 6334947, International Publication No. 2023 / 222708

[0010] However, the method described in Patent Document 1 requires reducing the pressure in the system into which carbon dioxide is introduced to less than 1000 Pa, or even less than 200 Pa depending on the microwave output, and the method described in Patent Document 2 requires recirculating the generated gas to a plasma jet generator. Therefore, there was a need for an easy and highly efficient method that could decompose carbon dioxide into carbon monoxide.

[0011] The object of the present invention is to provide a method for producing carbon monoxide and a carbon monoxide production apparatus that can easily and efficiently produce carbon monoxide from carbon dioxide.

[0012] As a result of diligent research to achieve the above objectives, the inventors discovered that carbon monoxide can be easily and efficiently produced from carbon dioxide by combining the plasma generation of a gas containing carbon dioxide by microwave irradiation with the contact of the resulting decomposition gas with a carbon material, thus completing the present invention.

[0013] In other words, the present invention is as follows: [1] A method for producing carbon monoxide from carbon dioxide, characterized in that, in a reaction vessel where the pressure is adjusted to 1.0 to 10.0 kPa, a flowing gas containing carbon dioxide is plasma-generated by microwave irradiation to decompose the carbon dioxide, and then the decomposed carbon dioxide gas is brought into contact with a carbon material.

[0014] [2] The method for producing carbon monoxide according to [1] above, characterized in that the carbon material is a biomass-derived material.

[0015] [3] The method for producing carbon monoxide according to [1] or [2], characterized in that the carbon material filling section of the reaction vessel is located within 100 mm downstream of the microwave irradiation section.

[0016] [4] The method for producing carbon monoxide according to any one of [1] to [3] above, characterized in that the reaction vessel comprises a large-diameter portion including a portion filled with the carbon material and a small-diameter portion having a smaller diameter than the large-diameter portion and not including a portion filled with the carbon material.

[0017] [5] The method for producing carbon monoxide according to [3] or [4], characterized in that the initial filling height of the carbon material in the carbon material filling section is 5.0 mm or more.

[0018] [6] A method for producing carbon monoxide according to any one of [1] to [5] above, characterized in that the reaction vessel has a carbon material filling section above the microwave irradiation section, and the carbon material is fluidized by the carbon dioxide decomposition gas blown up through the microwave irradiation section, thereby bringing the carbon dioxide decomposition gas into contact with the carbon material.

[0019] [7] A carbon monoxide production apparatus comprising: a reaction vessel having a section filled with carbon material; a gas introduction means for introducing a gas containing carbon dioxide into the reaction vessel; a microwave irradiation means for irradiating the upstream section of the carbon material in the reaction vessel with microwaves; and a pressure adjustment means for adjusting the pressure in the reaction vessel. [8] The carbon monoxide production apparatus according to [7], further comprising a carbon supply means for supplying the carbon material to the reaction vessel.

[0020] [9] The carbon monoxide production apparatus according to [7] or [8], characterized in that the reaction vessel comprises a large-diameter portion including a portion filled with the carbon material and a small-diameter portion having a smaller diameter than the large-diameter portion and not including a portion filled with the carbon material.

[0021]

[10] The carbon monoxide production apparatus according to [7] or [8], characterized in that the reaction vessel is a fluidized bed type, comprising a section filled with the carbon material above a microwave irradiation section irradiated by the microwave irradiation means, and the carbon material is fluidized by the decomposition gas of carbon dioxide blown up through the microwave irradiation section.

[0022] According to the carbon monoxide production method and carbon monoxide production apparatus of the present invention, carbon monoxide can be produced easily and efficiently from carbon dioxide.

[0023] This is an explanatory diagram of the carbon monoxide production apparatus of the present invention. This is an explanatory diagram of the reaction vessel of the same carbon monoxide production apparatus. This is an explanatory diagram of the vicinity of the reaction vessel of another carbon monoxide production apparatus of the present invention. This is an explanatory diagram of the same reaction vessel. This is a graph of the emission spectrum distribution of the decomposition gas generated in the reaction vessel. This is an explanatory diagram showing the positional relationship between the filling section of the reaction vessel filled with carbon material and the microwave irradiation means. This is a graph showing the composition of the generated gas when the proportion of carbon dioxide in the supply gas is changed. This is a graph showing the results of the carbon monoxide conversion rate when the proportion of carbon dioxide in the supply gas is changed. This is an explanatory diagram of the reaction vessel used in test conditions 2 and 3 of the example.

[0024] The present invention provides a method for producing carbon monoxide, which is carbon dioxide (hereinafter referred to as CO2). ２ This method produces carbon monoxide (hereinafter also referred to as CO) from carbon dioxide, and is characterized by the following: in a reaction vessel where the pressure is adjusted to 1.0 to 10.0 kPa, the flowing gas containing carbon dioxide is plasma-generated by microwave irradiation to decompose the carbon dioxide, and then the decomposed carbon dioxide gas is brought into contact with a carbon material.

[0025] CO ２ When microwaves are irradiated onto it to create a plasma, the following reaction occurs: CO ２ → CO + O ... (1)

[0026] CO2 in the reaction field ２ If there are no other O radicals besides those that have been turned into plasma, the generated O radicals will continue to react with other O radicals, resulting in the following reaction: O + O → O ２ ... (2)

[0027] However, CO ２ CO and O ２ In addition to the reaction that produces CO, the reaction process involves the active CO and O being converted into CO as shown in the following equation. ２ A reaction that regenerates CO also occurs: CO + O → CO ２ ... (3)

[0028] After the above reactions, the final gas species contained in the produced gas is CO ２ CO, O ２ This is the result.

[0029] Thus, in the manufacturing method of the present invention, CO is produced by microwave irradiation. ２ CO is generated by the plasma formation process, but in this process, the generated CO ２ To suppress regeneration, the reaction is carried out by adjusting the pressure within a predetermined range. Furthermore, in order to consume and react the O radicals generated by this plasma formation and increase the amount of CO produced, the carbon material is brought into contact with the plasma following microwave irradiation. ２ If the O radicals generated by plasma formation can be consumed by reacting them with a carbon material to produce CO, then CO ２ Not only does the CO generated from this material become more concentrated, but CO is also synthesized from carbon materials, resulting in the generation of even more CO, which is a raw material for organic compounds.

[0030] As a result, the carbon monoxide production method of the present invention can improve the conversion rate from carbon dioxide to carbon monoxide.

[0031] The present invention will be described in detail below. CO supplied to the reaction vessel ２ Gas containing CO (hereinafter simply referred to as CO) ２ (Also referred to as gas) For example, CO ２ It is sufficient if it contains 10% or more by volume, CO ２ From the viewpoint of processing large quantities, it is preferable that it contains 50% by volume or more, more preferably 80% by volume or more, even more preferably 90% by volume or more, particularly preferably 95% by volume or more, and 100% by volume (CO ２ It is most preferable that it does not contain any other gases.

[0032] CO ２ The lower the pressure, the easier it is for CO to be turned into plasma by microwave irradiation and decomposed (ionized) into CO and O. However, the higher the pressure, the more stable the decomposed CO becomes, and the CO and O react to form CO again. ２ This makes the regeneration reaction less likely to occur. Therefore, by microwave irradiation alone, CO2 can be effectively produced. ２ To improve the conversion rate, the pressure inside the reaction vessel should be set to 1.0 to 10.0 kPa. The pressure inside the reactor is more effective in CO２ To improve the conversion rate, the pressure is preferably set to 1.5 to 7.0 kPa, more preferably to 2.0 to 6.0 kPa, and even more preferably to 2.5 to 5.0 kPa.

[0033] The carbon material used in this invention is a carbide or semi-carbide, and examples include biomass-derived carbon material (biomass carbon), carbon material derived from fossil resources such as coal, etc. From the viewpoint of carbon neutrality, biomass-derived carbon material is particularly preferred. Examples of this biomass include coconut shells, cedar, cypress, and other woody materials. The carbon material can be used in various shapes such as plates, tubes, granules, and rods. Furthermore, porous activated carbon is preferred.

[0034] In the present invention, it is preferable that the carbon material filling section of the reaction vessel is located within 100 mm downstream of the microwave irradiation section. Since the CO and O decomposed by the plasma from microwave irradiation are in an active state, the CO shown in formula (3) above is formed. ２ A regeneration reaction also occurs. For this reason, the carbon material is positioned so that the O radical, which is the decomposition gas of carbon dioxide, can come into contact with the carbon material before the reaction of equation (3) proceeds. It is more preferable to position the carbon material within 80 mm downstream of the microwave irradiation area, even more preferable to position it within 60 mm downstream, and particularly preferable to position it within 50 mm downstream. Note that positioning the carbon material within 100 mm downstream of the microwave irradiation area means that the end of the carbon material on the microwave irradiation area side is located within 100 mm.

[0035] Here, the initial filling height (initial filling amount) of the carbon material in the carbon material filling section is preferably 5.0 mm or more, and more preferably 10.0 mm or more. In order to maintain a predetermined amount of carbon in the carbon material filling section, carbon material may be added continuously or intermittently during the reaction. Although the amount of carbon material decreases during the reaction, it is preferable to maintain a height of 1.0 mm or more of carbon material in the filling section, more preferably 5.0 mm or more, and even more preferably 7.0 mm or more. In the case of a fluidized bed system, this refers to the height in the non-fluidized state. Furthermore, the upper limit is preferably 40.0 mm or less, more preferably 20.0 mm or less, and even more preferably 17.0 mm or less. This effectively promotes the generation of CO by the reaction between the carbon material and O radicals, and further the reaction proceeds to generate CO ２ This effectively suppresses the progression of the resulting reaction.

[0036] An example of a carbon monoxide production apparatus of the present invention to which the above-described method for producing carbon monoxide can be applied is an apparatus that includes, as shown in Figure 1, a reaction vessel having a carbon material filling section, a gas introduction means for introducing a gas containing carbon dioxide into the reaction vessel, a microwave irradiation means for irradiating the upstream part of the carbon material filling section in the reaction vessel with microwaves, and a pressure adjustment means for adjusting the pressure inside the reaction vessel. Furthermore, it is preferable to have a carbon supply means for supplying carbon material to the reaction vessel.

[0037] The carbon monoxide production apparatus according to one embodiment of the present invention will be described below with reference to Figures 1 and 2. As shown in Figures 1 and 2, the reaction vessel is, for example, cylindrical, and CO is present on one side in the axial direction. ２A gas supply port containing the gas is formed, and an exhaust port for gases such as CO produced in the reaction vessel is formed on the other side in the axial direction, so that gas supply and exhaust can be carried out continuously. The reaction vessel may have a shape other than cylindrical, specifically a rectangular tube, and can be made of materials such as ceramics, quartz, alumina, or metal. In particular, it is preferable that at least the part to which microwaves are irradiated is made of a transparent material so that microwaves can be irradiated into the reaction vessel, and it is preferable that it be made of quartz.

[0038] The reaction vessel preferably comprises a large-diameter section (wide section) containing a carbon material filling section and a small-diameter section (narrow section) smaller in diameter than the large-diameter section and not containing a carbon material filling section. Here, the inner diameter of the large-diameter section (diagonal length in the case of a rectangular tube) is preferably about 20 to 10,000 mm, more preferably 100 to 8,000 mm, even more preferably 300 to 5,000 mm, and particularly preferably 500 to 3,000 mm. The inner diameter of the small-diameter section (diagonal length in the case of a rectangular tube) is preferably about 30 to 90% of the inner diameter of the large-diameter section, more preferably 40 to 85%, and even more preferably 50 to 80%. This reduces the pressure loss caused by filling the reaction vessel with carbon material.

[0039] The gas introduction means is, for example, a CO2 injection device connected via a hose to the gas supply port of the reaction vessel described above. ２ It is equipped with a cylinder containing CO2 and a mass flow controller (mass flow meter) attached to this cylinder. This mass flow controller is a mass flow meter (a flow meter that measures mass flow rate) that also has a flow control function. Note that CO2 can be used instead of a cylinder. ２ It is also possible to connect devices such as generators.

[0040] For example, a microwave irradiation means comprises a microwave generator, a waveguide that guides the microwaves emitted from the microwave generator to the reaction vessel, and a tuner (stub tuner) that focuses the microwaves on the plasma formation area inside the reaction vessel. The microwaves are then irradiated onto the reaction vessel via an irradiation tube that communicates with the waveguide.

[0041] The pressure regulating means includes, for example, a vacuum pump connected via piping to the downstream end of the reaction vessel and a pressure gauge attached to the piping, which adjusts the pressure inside the reaction vessel. The vacuum pump is connected to a gas meter for measuring the amount of gas drawn in and a gas chromatograph for measuring the composition of the gas drawn in.

[0042] Next, a carbon monoxide production apparatus according to another embodiment of the present invention will be described. As shown in Figures 3 and 4, the reaction vessel in the carbon monoxide production apparatus according to this embodiment is equipped with a carbon material filling section above the microwave irradiation section, which is irradiated by the microwave irradiation means. Furthermore, the carbon monoxide production apparatus is a fluidized bed type in which the carbon material is fluidized by the decomposition gas of carbon dioxide blown up after passing through the microwave irradiation section.

[0043] For example, a block of carbon material packed into a reaction vessel does not react as a whole, but rather reacts sequentially in cross-section from the side where the decomposition gas flows in, thus limiting the flow rate that can be processed. On the other hand, a fluidized bed system has excellent heat transfer properties, with the temperatures of the solid and fluid being almost equal throughout, as well as excellent stirring and mixing properties, resulting in a very large contact area between the solid and fluid. Therefore, by using a fluidized bed system for the reaction vessel, the O radicals generated by plasma generation can be efficiently brought into contact with the carbon material and reacted, further reducing CO2 levels. ２ This can improve the conversion rate from CO to CO.

[0044] Furthermore, as a mounting plate for carbon material, which is installed at an intermediate position in the gas flow direction of the reaction vessel, for example, as shown in Figure 4, a slit can be formed by arranging two semicircular plates opposite each other with a gap between them, and blowing the placed carbon material through the slit. Other examples of such mounting plates include quartz plates or quartz filters (porous materials) with numerous small holes, mesh materials, and perforated metal (punched wire mesh).

[0045] The carbon monoxide production method and carbon monoxide production apparatus of the present invention described above can be used to easily and efficiently produce carbon monoxide from carbon dioxide.

[0046] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0047] [Example 1] First, we will describe the test conducted using the carbon monoxide production apparatus shown in Figures 1 and 2.

[0048] (Test conditions) The plasma is placed in a cylindrical quartz reaction vessel under reduced pressure using a vacuum pump, and CO2 is added. ２ The gas was generated by circulating 100% of the gas and irradiating it with microwaves. The reaction vessel consisted of a 750 mm long quartz tube, which was formed by connecting a 34 mm inner diameter, 500 mm long quartz tube with a 50 mm inner diameter, 250 mm long quartz tube. The microwave output was 1000 W, and the pressure inside the reaction vessel (hereinafter also referred to simply as pressure) was 1 to 5 kPa. The composition of the generated gas was measured by gas chromatography.

[0049] (1) When only microwave irradiation is performed CO ２ Under the condition of a flow rate of 1 L / min, CO ２ A conversion test was conducted. Here, the evaluation index was the CO2 value based on O, calculated from the following formula (4). ２ The conversion rate was used. The generated gas composition and CO2 were also considered. ２ Table 1 shows the results of the conversion rate (based on O).

[0050] CO based on O standard ２ Conversion rate [%] = {(2O(O ２ )+O(CO)) / (2O(O ２ )+O(CO)+2O(CO ２ ))} × 100 ... (4)

[0051]

[0052] As shown in Table 1, at a pressure of 3 kPa inside the reaction vessel, the most CO ２ The conversion rate increased. Note that the generated gas contains trace amounts of N2. ２ It contained [a certain substance], but the amount was so small that it was ignored.

[0053] As can be seen from the emission spectrum distribution graph in Figure 5, the plasma produced by microwave irradiation under reduced pressure in the test becomes stronger at lower pressures, and therefore CO2 is stronger at lower pressures. ２ Although we expected the conversion rate to be high, the highest CO2 ２ The conversion rate was 3 kPa, indicating the existence of an optimal pressure.

[0054] A strong emission spectrum indicates an active state, and the activity decreases as the pressure increases. ２ CO is more easily ionized into CO and O by microwave plasma at lower pressures, but the ionized CO is more stable at higher pressures, and the CO and O react to form CO again. ２ The regeneration reaction that results in CO becomes less likely to occur. In other words, in this test, at a pressure of 3 kPa in the reaction vessel, ２ It is thought that the ionization of CO and the stabilization of the ionized CO occurred in a well-balanced manner.

[0055] (2) When the carbon material is brought into contact after microwave irradiation, the CO2 ２ Based on a pressure of 3 kPa, which yielded a high conversion rate, the flow rate was adjusted, and the test was conducted by placing a section filled with biomass-derived carbon material downstream of the position where the microwave plasma is formed. To reduce pressure loss within the reaction vessel, the carbon material was packed into a quartz tube with a large diameter of 50 mm. As shown in Figure 6, the reaction vessel was placed inside the microwave waveguide so that the upper end of the carbon material section was 30 mm downstream from the lower part of the microwave waveguide (microwave irradiation section). The generated gas flow rate and CO2 amounted to the results of this test. ２ The conversion rate results are shown in Table 2. Note that the generated gas contains trace amounts of CH4. ４ , N ２ It contained [a certain substance], but the amount was so small that it was ignored.

[0056]

[0057] In this test, the carbon reacted while red-hot, CO ２ It was shown that an optimal flow rate of 0.4–0.5 L / min and a pressure of 1.6–3 kPa in the reaction vessel are desirable. For example, CO ２When the flow rate is 0.5 L / min and the pressure in the reaction vessel is 3 kPa (the second row of Table 2), O ２ (O) is almost consumed, and the composition of the generated gas is O ２ : 1.58%, CO: 63.30%, CO ２ : 34.80%, CO conversion rate based on O ２ : 48.85% was obtained as a result.

[0058] Next, from the generation flow rate and gas composition of the generated gas in this test, the generation flow rates of O ２ , CO, and CO ２ were calculated. The results are shown in Table 3. Note that all the CO ２ contained in the generated gas is composed of all the supplied CO ２ , and it was assumed that the CO contained in the generated gas is composed of the supplied CO ２ and the carbon material. Regarding the conversion rate based on C described in this Table 3, it was calculated by the following formula.

[0059] - CO derived from biomass = CO ２ (L / min) + CO (L / min) - input amount of CO ２ (L / min) ・ CO ２ derived from CO = CO (L / min) - CO derived from biomass ・ Conversion rate based on C = (CO ２ derived from CO) / (CO ２ derived from CO + CO ２ (L / min)) × 100 ( ) indicates the conversion rate based on C calculated from CO and CO ２ in the generated gas. ・ Conversion rate based on C2 = (CO) / ((CO) + (CO ２ )) × 100

[0060]

[0061] The supplied CO ２ flow rate is 0.5 L / min, and the pressure in the reaction vessel is 3 kPa (the second row of Table 3). Consider the case. CO is generated at 0.52 L / min, which is about the same as the supplied CO ２ (0.5 L / min), and the breakdown is the supplied CO ２The origin was 0.22 L / min, and the carbon material origin was 0.30 L / min. From this, it was shown that CO ２ was decomposed into CO and O by microwave plasma, and a large amount of CO was generated by the reaction of this O radical and the carbon material.

[0062] Furthermore, when not including the carbon material origin (C conversion rate) and when including it (C conversion rate 2), under the same conditions as above (the second row of Table 3), when not including it, it was 43.03%, and when including it, it was 64.53%. By installing the filling part of the carbon material, not only CO in the generated gas but also CO ２ increased. Therefore, when not including the CO derived from the carbon material, the value was slightly lower, but the value calculated from all the generated CO and CO ２ was a very high value.

[0063] [Example 2] Next, a test conducted using the carbon monoxide production apparatus (reaction vessel) shown in FIGS. 3 and 4 will be described.

[0064] (Test condition 1) Plasma was generated by flowing 100% CO ２ gas from below into a quartz cylindrical reaction vessel depressurized by a vacuum pump and irradiating it with microwaves. A tube with an inner diameter of 34 mm or 50 mm and a total length of 1000 mm, with a dispersion plate (mounting plate) installed at a position 350 mm above the lower end (30 mm above the microwave irradiation part), was used for the reaction vessel, and the dispersion plate was filled with biomass carbon (coconut shell activated carbon) as the carbon material. The microwave output was 1000 W, the supply gas flow rate of CO ２ was 0.5 to 1.0 L / min, and the pressure inside the reaction vessel was 2 to 5 kPa. ２

[0065] The inner diameter of the reaction vessel used, the slit width formed in the dispersion plate, and the amount of biomass-derived carbon material packed were as follows: Test (a): inner diameter 34 mm, slit width 1 mm, packing amount 45 g; Test (b): inner diameter 34 mm, slit width 2 mm, packing amount 22.5 g; Test (c): inner diameter 50 mm, slit width 2 mm, packing amount 45 g; Test (d): inner diameter 34 mm, slit width 2 mm, packing amount 22.8 g. In Test (e), an inner diameter 50 mm reaction vessel was used, and a quartz filter (porous material) was used as the dispersion plate, with 13.04 g of carbon material packed inside.

[0066] Table 4 summarizes the composition of the generated gases in tests (a) to (e). It also shows the generated gas flow rates and CO2 levels in tests (a) to (e). ２ Table 5 summarizes the conversion rates. Note that the generated gas contains trace amounts of N2. ２ Although it contained [unspecified substance], it was ignored in this case because the amount was extremely small. The composition of the generated gas was measured by gas chromatography. Here, the amount of CO derived from biomass, CO ２ CO derived from ２ The calculation of the conversion rate based on quantity and CO was the same as described above, and the conversion rate based on generated CO was obtained from the following formula.

[0067] • Conversion rate based on generated CO = (CO (L / min)) / (input amount CO) ２ (L / min))×100

[0068]

[0069]

[0070] As shown in Tables 4 and 5, under all conditions, a tendency was observed for CO concentration and CO flow rate to increase at pressures of 4 kPa or 5 kPa. This is thought to be because the probability of contact between O radicals and carbon materials increased with increasing pressure.

[0071] In this test, the CO2 input flow rate was 1 L / min. ２ A maximum of 1.039 L / min of CO was obtained, resulting in a conversion rate of 103.9% based on the generated CO (bottom row of (e) in Table 5). The breakdown of CO is as follows: supplied CO ２The amount derived from carbon dioxide was 0.34 L / min, and the amount derived from carbon materials was 0.70 L / min. On the other hand, in the test using the carbon monoxide production apparatus shown in Figures 1 and 2 (Example 1), the input flow rate was 1 L / min of CO ２ A maximum of 0.68 L / min of CO was obtained (top row of Table 3), indicating that the amount of CO generated was greater in this experiment. This suggests that a large amount of CO was produced by the reaction of O radicals generated by the microwave plasma with the carbon material.

[0072] As shown in Table 5, under the same conditions as above (bottom row of (e) in Table 5), the conversion rate of carbon-based carbon when carbon-derived carbon is not included and when carbon-derived carbon is included was 34.2% when carbon-derived carbon is not included and 61.2% when carbon-derived carbon is included. By installing a carbon material filling section, not only CO in the generated gas, but also CO ２ Because it also increases, the value was slightly lower when carbon-derived CO was not included, but all generated CO, CO ２ The value calculated from this was extremely high.

[0073] (Test condition 2) Plasma is introduced into a cylindrical quartz reaction vessel, which has been depressurized by a vacuum pump, from below, with CO2. ２ 100% CO ２ The material was generated by circulating gas and irradiating it with microwaves. The reaction vessel was a tube with an inner diameter of 50 mm and a total length of 1000 mm, with a dispersion plate (mounting plate) having an aperture ratio of 1%, consisting of 25 small holes with a diameter of 1 mm arranged concentrically, located 350 mm above the bottom end (30 mm above the microwave irradiation section) (see Figure 9). Biomass carbon (coconut shell activated carbon), a carbon material, was filled onto the dispersion plate to an initial height of 10 to 35 mm. Microwave output was 1000 W, CO2 ２ The supply gas flow rate was set to 1.0 L / min, and the pressure inside the reaction vessel was set to 4 kPa. The product gas concentration, product gas flow rate, and CO conversion results from this test are shown in Table 6.

[0074]

[0075] As shown in Table 6, under test condition 2, the CO conversion rate was sufficiently high with an initial packing height of 10 mm for the carbon material. The packing height after the reaction was 4 mm, but since the conversion rate was sufficiently high, it is considered that a packing height of 1 mm or more during the reaction is sufficient. Furthermore, the CO conversion rate was highest at 1.10 when the initial packing height was 15 mm. The packing height after the reaction was 8 mm, and it is considered particularly preferable to maintain a packing height of 8 to 15 mm during the reaction. Also, when the initial height was 35 mm, the CO conversion rate tended to decrease, so it is considered preferable to maintain a packing height of 40 mm or less during the reaction.

[0076] (Test condition 3) In the above test condition 3, the initial filling height of the biomass carbon was set to 15 mm, and the CO in the supply gas was ２ The test was conducted by varying the concentration of the substance. The results of the generated gas concentration, generated gas flow rate, and CO conversion from this test are shown in Tables 7 and 8, and Figures 7 and 8.

[0077]

[0078]

[0079] As shown in Table 8 and Figure 8, the CO conversion rate is determined by the CO content of the supplied gas. ２ It was hardly affected by the proportion.

[0080] As described above, by combining the plasma generation of a gas containing carbon dioxide by microwave irradiation with the contact of the resulting decomposition gas with a carbon material, it becomes possible to easily and efficiently produce carbon monoxide from carbon dioxide.

[0081] This invention is industrially useful because it can produce carbon monoxide from carbon dioxide.

Claims

A method for producing carbon monoxide from carbon dioxide, A method for producing carbon monoxide, characterized by using a reaction vessel with a pressure adjusted to 1.0 to 10.0 kPa, where a flowing gas containing carbon dioxide is plasma-generated by microwave irradiation to decompose the carbon dioxide, and then contacting the decomposed carbon dioxide gas with a carbon material. 　 The method for producing carbon monoxide according to claim 1, characterized in that the carbon material is a biomass-derived material. 　 The method for producing carbon monoxide according to claim 1, characterized in that the carbon material filling section of the reaction vessel is located within 100 mm downstream of the microwave irradiation section. 　 The method for producing carbon monoxide according to claim 1, characterized in that the reaction vessel comprises a large-diameter portion including a portion filled with the carbon material and a small-diameter portion having a smaller diameter than the large-diameter portion and not including a portion filled with the carbon material. 　 The method for producing carbon monoxide according to claim 3, characterized in that the initial filling height of the carbon material in the carbon material filling section is 5.0 mm or more. 　 The reaction vessel includes a section filled with the carbon material above the microwave irradiation section, A method for producing carbon monoxide according to claim 1, characterized in that the carbon material is fluidized by the decomposition gas of carbon dioxide blown up after passing through the microwave irradiation section, thereby bringing the decomposition gas of carbon dioxide into contact with the carbon material. 　 A reaction vessel equipped with a carbon material filling section, A gas introduction means for introducing a gas containing carbon dioxide into the reaction vessel, A microwave irradiation means for irradiating the upstream portion of the carbon material filling section within the reaction vessel with microwaves, A pressure adjustment means for adjusting the pressure inside the reaction vessel, A carbon monoxide production apparatus characterized by having the following features. 　 The carbon monoxide production apparatus according to claim 7, further comprising a carbon supply means for supplying the carbon material to the reaction vessel. 　 The carbon monoxide production apparatus according to claim 7, characterized in that the reaction vessel comprises a large-diameter portion including a portion filled with the carbon material and a small-diameter portion having a smaller diameter than the large-diameter portion and not including a portion filled with the carbon material. 　 The reaction vessel is provided with a carbon material filling section above the microwave irradiation section that is irradiated by the microwave irradiation means, The carbon monoxide production apparatus according to claim 7, characterized in that it is a fluidized bed type in which the carbon material is fluidized by the decomposition gas of carbon dioxide blown up after passing through the microwave irradiation section.

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