WO2011136045A1

WO2011136045A1 - Method and apparatus for producing carbon monoxide

Info

Publication number: WO2011136045A1
Application number: PCT/JP2011/059383
Authority: WO
Inventors: 和也木下; 雄一妹尾; 陽介柴田; 明弘菅野; 勇八島
Original assignee: 三井金属鉱業株式会社
Priority date: 2010-04-26
Filing date: 2011-04-15
Publication date: 2011-11-03
Also published as: TW201141783A; JPWO2011136045A1

Abstract

Disclosed is a method for producing carbon monoxide, which is characterized in that a carbon dioxide gas and a metal oxide that has oxygen ion conductivity and reversible oxygen deficiency are brought into contact with each other, while being heated, so that carbon dioxide is reduced by a stoichiometric reaction, thereby generating carbon monoxide. The metal oxide is preferably composed of cerium oxide that has reversible oxygen deficiency. The metal oxide oxidized by the contact with the carbon dioxide gas is preferably regenerated by being brought into contact with a reducing gas.

Description

Carbon monoxide production method and production apparatus

The present invention relates to a method and apparatus for producing carbon monoxide using carbon dioxide as a raw material. Moreover, this invention relates to the conversion agent used for this manufacturing method.

Carbon dioxide is known as a greenhouse gas. The concentration of carbon dioxide in the atmosphere continues to rise, which is considered to contribute to global warming. Therefore, from the viewpoint of preventing global warming, a technique for recovering carbon dioxide released into the environment is very important.

As a technique for recovering carbon dioxide, for example, an oxygen deficient iron oxide is used to decompose carbon dioxide gas into carbon monoxide gas and oxygen gas, and the oxygen gas generated generates oxygen deficient iron oxide. A technique for returning to the original iron oxide and recovering only carbon monoxide gas has been proposed (see Patent Document 1).

The above-mentioned technique is a technique for producing carbon monoxide gas from carbon dioxide by a stoichiometric reaction with carbon dioxide using an iron oxide having oxidizing power, whereas catalytic catalytic reduction. A technique for generating carbon monoxide gas from carbon dioxide has also been proposed. For example, in Non-Patent Document 1, carbon monoxide gas or carbon is obtained by catalytic reduction of carbon dioxide using a metal oxide such as WO ₃ , Y ₂ O ₃ , ZnO or the like as a catalyst and hydrogen or methane as a reducing agent. It has been reported that it can be generated.

Apart from these techniques, Patent Document 2 proposes a method of separating carbon dioxide into carbon monoxide and oxygen using a solid reaction membrane having an oxygen ion conductor made of CeO ₂ and a catalyst. In this method, oxygen is separated from carbon dioxide by a catalyst supported on an oxygen ion conductor made of CeO ₂ , and this oxygen is diffused in the oxygen ion conductor by a potential generated due to a difference in oxygen concentration. .

Patent Document 3 describes that carbon monoxide is brought into contact with an oxygen ion conductive ceramic at a high temperature, and the ceramic is at least partially saturated with oxygen to generate carbon monoxide. Examples of the ceramic include CeO ₂ doped with CaO.

Japanese Patent Laid-Open No. 5-68853 JP 2001-322958 A US Pat. No. 6,464,955

According to the technique described in Patent Document 1, carbon monoxide gas is certainly generated from carbon dioxide gas. However, iron oxide has low oxygen ion conductivity, and if the surface is oxidized, the oxygen deficiency will come into contact with carbon dioxide gas even if oxygen deficiency exists inside the oxide. I can't. Therefore, in order to increase the conversion efficiency from carbon dioxide gas to carbon monoxide gas, it is necessary to use a large amount of iron oxide having oxygen deficiency, which is economically disadvantageous.

In the technique described in Non-Patent Document 1, it is necessary to introduce hydrogen and methane simultaneously with carbon dioxide. In addition to carbon monoxide and carbon as a product, unreacted carbon dioxide, hydrogen, methane, and the like are mixed. Therefore, it is economically disadvantageous in that it requires a separation step in the end, and when the product is carbon, the catalytic activity tends to decrease due to the precipitation on the catalyst. .

The technique described in Patent Document 2 is economically disadvantageous because a noble metal catalyst is used to decompose carbon dioxide into carbon monoxide and oxygen. Moreover, cerium oxide carrying a noble metal catalyst is only used as an ion pump for diffusing oxygen ions, and cerium oxide is not directly involved in the production of carbon monoxide from carbon dioxide.

In Patent Document 3, CeO ₂ doped with CaO, which is supposed to generate carbon monoxide from carbon dioxide, has only irreversible oxygen vacancies. CeO ₂ having only irreversible oxygen vacancies has a low ability to convert carbon dioxide to carbon monoxide.

Therefore, an object of the present invention is to provide a method for producing carbon monoxide from carbon dioxide that can eliminate the various disadvantages of the above-described conventional technology.

In the present invention, a metal oxide having oxygen ion conductivity and having a reversible oxygen deficiency is brought into contact with carbon dioxide gas under heating, and carbon dioxide is reduced by a stoichiometric reaction. A method for producing carbon monoxide, characterized in that is produced.

Further, the present invention provides a suitable apparatus for carrying out the manufacturing method as described above.
An outer tube, and an inner tube disposed in the outer tube,
The inner tube includes a metal oxide having oxygen ion conductivity and having a reversible oxygen deficiency,
Carbon dioxide gas is circulated between the outer tube and the inner tube, and a reducing gas is circulated in the inner tube, or a reducing property is provided between the outer tube and the inner tube. An apparatus for producing carbon monoxide configured to circulate gas and circulate carbon dioxide gas in the inner pipe is provided.

Furthermore, the present invention provides another suitable apparatus for carrying out the above manufacturing method.
Two or more batch type reactors, and a switching valve having an input unit connected to each of the carbon dioxide gas source and the reducing gas source and an output unit connected to each of the reactors, An apparatus for producing carbon monoxide capable of arranging a metal oxide having oxygen ion conductivity and having reversible oxygen vacancies,
Carbon dioxide gas or reducing gas is alternatively and simultaneously supplied to each reactor via the switching valve, and the type of gas supplied to each reactor can be switched by switching the switching valve. An apparatus for producing carbon monoxide configured as described above is provided.

Furthermore, the present invention provides another suitable apparatus for carrying out the above manufacturing method.
This is a carbon monoxide production apparatus in which plate-like bodies comprising a metal oxide having oxygen ion conductivity and having reversible oxygen vacancies and plate-like separators are alternately stacked. And
A plurality of ridges and ridges extending in one direction are alternately arranged on each surface of each separator,
Carbon dioxide gas is circulated through the concave portion located on the opposing surface of one separator and the plate-like body in the two separators facing each other across the plate-like body, and the other separator and the plate-like body The carbon monoxide manufacturing apparatus comprised so that a reducing gas may be distribute | circulated to the concave part located in the opposing surface of this.

According to the present invention, carbon monoxide can be efficiently generated using carbon dioxide as a raw material.

FIG. 1 is a schematic view showing an apparatus suitably used in the method for producing carbon monoxide of the present invention. FIG. 2 is a schematic view showing another apparatus suitably used in the method for producing carbon monoxide of the present invention. FIG. 3 is a schematic view showing still another apparatus suitably used in the method for producing carbon monoxide of the present invention. FIG. 4 is a schematic diagram showing the apparatus used in the example.

Hereinafter, the present invention will be described based on preferred embodiments thereof. In the present invention, carbon dioxide gas is heated with a specific metal oxide (hereinafter, this metal oxide is also referred to as “converter to carbon monoxide” or simply “converter”). Carbon monoxide gas is produced by contact. The reaction between the conversion agent and carbon dioxide gas is a stoichiometric reaction utilizing the reducing power of the conversion agent. That is, the conversion agent made of this metal oxide is not used as a catalyst, but as a reactant itself.

As the conversion agent comprising the specific metal oxide, one having oxygen ion conductivity and having reversible oxygen vacancies is used. Since this conversion agent has a reversible oxygen deficiency, the conversion agent acquires the reducibility of carbon dioxide. A reversible defect | deletion is produced | generated when oxygen is forcibly extracted from a metal oxide by the process under strong reducing conditions. A reversible defect is a defect in which oxygen can be taken into a deficient site. For example, when the metal oxide is cerium oxide, which will be described later, in cerium oxide having a reversible defect, an unbalanced state of charge due to lack of oxygen is reduced to a part of tetravalent cerium to trivalent. To compensate. Trivalent cerium is unstable and easily returns to tetravalent. Therefore, by incorporating oxygen into the deficient site, trivalent cerium returns to tetravalent, and the charge balance is always kept at zero. By incorporating oxygen into the deficient site, the deficiency disappears, but oxygen deficiency is generated again by treatment under strong reducing conditions. “Reversible oxygen deficiency” is used in this sense.

On the other hand, irreversible oxygen deficiency is also known. Irreversible oxygen deficiency is formed by doping a metal oxide with an element having a valence lower than that of the metal. Irreversible oxygen deficiency differs from reversible oxygen deficiency and is not a deficiency generated by treatment under strong reducing conditions. Irreversible oxygen vacancies include, for example, mixing a metal oxide with an oxide of a valence element lower than the valence of the metal, firing in the atmosphere, etc., and substituting solid solution with the low valence element. To obtain. When the inorganic oxide is, for example, cerium oxide, the valence of cerium in cerium oxide having irreversible oxygen deficiency is all tetravalent. Therefore, oxygen is not taken into the deficient site. For example, when 20 mol% of Ca is dissolved in CeO ₂ (Ce _0.8 Ca _0.2 O ₂ ), the average cation valence is 4 × 0.8 + 2 × 0.2 = 3.6. The number of oxygen atoms necessary to balance this valence is 3.6 ÷ 2 = 1.8. This number is less than the stoichiometric amount of two oxygen atoms, and oxygen vacancies are generated accordingly. However, this oxygen deficiency is not capable of absorbing oxygen. Thus, the irreversible oxygen deficiency is not caused by forced extraction of oxygen but is caused by charge compensation in the metal oxide.

The conversion agent comprising the metal oxide used in the present invention has oxygen ion conductivity as described above. The oxygen ion conductivity may be developed at a temperature at which the production method of the present invention is performed. Since this conversion agent has oxygen ion conductivity, almost all of the reversible oxygen vacancies present in this conversion agent can be effectively utilized for the reaction with carbon dioxide. The reason is as follows. That is, since the production method of the present invention is a reaction between a solid metal oxide and a gaseous carbon dioxide gas, the reaction mainly proceeds on the solid surface. And the oxygen deficiency which exists in the surface of a metal oxide couple | bonds with the oxygen in a carbon dioxide, The oxygen deficiency in this surface lose | disappears, and a carbon dioxide is converted into carbon monoxide. In this case, since the metal oxide has oxygen ion conductivity, oxygen associated with oxygen vacancies existing on the surface of the metal oxide is in the state of oxygen ions (O ²⁻ ). The oxygen vacancies disappear inside the metal oxide, and reversible oxygen vacancies are generated again on the surface of the metal oxide. By repeating this, almost all of the reversible oxygen vacancies present in the conversion agent can contribute to the reaction with carbon dioxide. On the other hand, for example, the iron oxide having oxygen vacancies described in Patent Document 1 described in the background section does not have oxygen ion conductivity, so that oxygen vacancies remain in the oxide. Even so, when all the oxygen vacancies present on the surface of the oxide disappear, the reactivity with carbon dioxide is greatly reduced.

The conversion agent comprising the metal oxide used in the present invention has oxygen ion conductivity and has the following advantages. That is, in this conversion agent, the reversible oxygen deficiency present in the converter can also contribute to the reaction with carbon dioxide, so that the reactivity with carbon dioxide can be achieved without excessively increasing the specific surface area of this conversion agent. Is hard to decline. Therefore, there is a degree of freedom that the reactant containing the conversion agent can be formed into a desired shape such as a granular shape, a pellet shape, a plate shape, or a cylindrical shape. On the other hand, a metal oxide that does not have oxygen ion conductivity, for example, an iron oxide having an oxygen vacancy described in Patent Document 1 described in the background section, has an oxygen vacancy existing therein. Since it hardly contributes to the reaction with carbon dioxide, it is necessary to increase the specific surface area of the oxide in order to effectively utilize the oxygen deficiency. In other words, it is indispensable to use it in the state of fine powder, resulting in low handleability and flexibility in designing the reactor.

As described above, the conversion agent comprising the metal oxide used in the production method of the present invention is essential to have oxygen ion conductivity and to have reversible oxygen vacancies. Examples of the metal oxide having fluorite include, for example, cerium oxide; metal oxide having a fluorite structure represented by stabilized zirconia (substantially a cubic fluorite type at a temperature used for reaction with carbon dioxide) And the oxide having the fluorite structure substituted with a metal element for improving oxygen ion conductivity and oxygen deficiency; bismuth oxide and bismuth oxide with oxygen ion conductivity and those obtained by substituting a metal element to enhance oxygen deficiency; formula ABO ₃ (a and B is a metal element) oxide and the a site and B site of the ABO ₃ has a perovskite structure represented by Those obtained by substituting a metal element to enhance oxygen ion conductivity, oxygen deficiency,; oxide and said A general formula A ₂ B ₂ O ₅ (A and B represents a metal element) having a brownmillerite type structure represented by ₂ B ₂ O ₅ A site and B site substituted with a metal element for improving oxygen ion conductivity and oxygen deficiency; general formula Ln ₁₀ Si ₆ O ₂₇ (Ln is La, Pr, Nd, Sm, Gd or A rare earth silicate represented by Dy); an oxide having a moznaite structure such as La ₂ Mo ₂ O ₉ ; a general formula Nd ₂ Ln ₂ O ₃ F ₆ (Ln is Y, Ce, Eu, Sm) Or a rare earth metal oxyfluoride represented by Gd). In particular, it is preferable to use cerium oxide from the viewpoints of high oxygen ion conductivity and reversible oxygen vacancies, and economical efficiency.

When cerium oxide is used as the conversion agent used in the production method of the present invention, as the cerium oxide, CeO _2-x (wherein Ce has a tetravalent and trivalent mixed valence, x is And a reversible oxygen deficiency and a fluorite-type crystal structure are preferably used. In this cerium oxide, cerium oxide having a fluorite structure (CeO ₂ ) is produced by firing a cerium-containing salt or a hydrate thereof in an oxidizing atmosphere such as air, and then the cerium oxide is strongly reduced. And reversible oxygen deficiency. Regarding the firing conditions, the temperature is preferably 500 to 1400 ° C., more preferably 600 to 1300 ° C., and the time is preferably 1 to 20 hours, more preferably 1 to 5 hours. In strong reduction, a hydrogen-containing atmosphere having a hydrogen concentration of not less than the lower explosion limit, preferably not less than 20% by volume, is used as the reducing atmosphere. Of course, the hydrogen concentration may be 100% by volume. The temperature is preferably 700 to 1100 ° C., more preferably 800 to 1050 ° C., and the time is preferably 1 to 3 hours, more preferably 1 to 2 hours. Details of such cerium oxide are described, for example, in WO2010 / 004963 relating to the earlier application of the present applicant.

Further, the cerium oxide is represented by CeO _2-x (wherein Ce has a trivalent and mixed valence of less than trivalent, and x represents a number of 0.5 to 0.7), and is reversible. Those having a typical oxygen deficiency and having a superlattice structure similar to fluorite are also preferably used. Fluorite-like is a state in which the oxygen vacancies that initially exist at random are changed into ordered oxygen vacancies as oxygen escapes from the crystals of fluorite-type structures such as ordinary cerium oxide. Strictly speaking, it means a state that cannot be called a fluorite structure. Examples thereof include a magnetoplumbite type structure represented by PbFe ₁₂ O ₁₉ and a structure such as YBa ₂ Cu ₃ O _6.9 exhibiting superconductivity. The superlattice is a crystal lattice whose periodic structure is longer than the basic unit lattice by superimposing a plurality of types of crystal lattices. It can be confirmed, for example, by X-ray structural analysis that cerium oxide has a superlattice structure similar to fluorite. Cerium oxide having such a structure can be obtained by using an oxygen-containing cerium salt or a hydrate thereof as a precursor and directly reducing it. The reduction treatment is performed in a strong reducing atmosphere in which the concentration of a reducing gas such as hydrogen gas, acetylene gas, or carbon monoxide gas is high and heat treatment is performed at a high temperature. The reducing gas concentration is preferably not less than the lower limit of explosion to 100% by volume, more preferably 20% to 100% by volume. The treatment temperature is preferably 500 ° C. or higher, more preferably 700 ° C. to 1200 ° C., and still more preferably 1000 ° C. to 1050 ° C. The strongly reducing atmosphere is generally atmospheric pressure, but pressure conditions may be used instead. During the reduction treatment, a reducing gas atmosphere is maintained throughout the reaction system, and the reaction system is not exposed to the oxygen-containing gas atmosphere. The details of such cerium oxide are described in, for example, WO2008 / 140004 related to the applicant's previous application.

By the way, in addition to the metal oxide having reversible oxygen deficiency used in the present invention, an OSC (oxygen storage and release capability) material is known as a metal oxide capable of absorbing oxygen. OSC materials are often used as promoters for automotive catalysts. The OSC material uses oxygen ion conductivity and valence change of cerium oxide, releases oxygen for oxidation reaction and absorbs oxygen for reduction reaction, so that the gas composition in exhaust gas Is used for the purpose of stably purifying exhaust gas with a three-way catalyst. Therefore, the OSC material is a co-catalyst for converting carbon monoxide in the exhaust gas to carbon dioxide, and is used in a reaction process opposite to the production method of the present invention that generates carbon monoxide from carbon dioxide. Is.

The reaction between the conversion agent and carbon dioxide gas used in the production method of the present invention is performed under heating. The heating temperature is set to, for example, 450 to 1000 ° C., particularly 450 to 800 ° C., particularly 500 to 750 ° C., to increase the conversion efficiency from carbon dioxide to carbon monoxide and to the action of carbon monoxide once generated. From the viewpoint of effectively preventing the conversion agent from being reduced and carbon dioxide from being regenerated. The reaction may be carried out batchwise or continuously. Since the reaction of this production method is a stoichiometric reaction, the amount of the conversion agent and carbon dioxide gas may be 1 equivalent or more, particularly 3 equivalents or more with respect to 1 equivalent of carbon dioxide. preferable. For example, when the conversion agent is cerium oxide represented by CeO _2-x (x is as defined above), x / 2 mol of CO ₂ is equivalent to x / 2 mol of CO _2. To react.

The conversion agent can be contacted with carbon dioxide gas in various forms. For example, in the case of a batch reactor, the powdered conversion agent can be allowed to stand (or filled) to carry out the reaction, and the conversion agent can be granulated, pelletized, massive, or plate-shaped. It is also possible to use a product formed into a shape such as a honeycomb shape, a Raschig ring shape, or a bell saddle shape by leaving (or filling). The reaction time of the carbon dioxide gas in the batch reactor is sufficient to convert carbon dioxide to carbon monoxide and prevent the generated carbon monoxide from reacting with the conversion agent and returning to carbon dioxide. From this point, it is preferable to set the time to 5 minutes to 3 hours, particularly 5 minutes to 1 hour. On the other hand, in the case of a continuous reaction apparatus, a reaction surface that converts carbon dioxide into carbon monoxide is separated from a regeneration surface that generates oxygen deficiency with a reducing gas by a dense membrane such as a cylinder, plate, or disk. Any structure can be used.

The carbon dioxide gas to be brought into contact with the conversion agent is ideal if it is 100% carbon dioxide gas because a separation step is not necessary later, but it may contain a small amount of other gases. However, when the other gas is an oxygen-containing gas such as oxygen gas or water vapor, the ratio to the total amount of the supplied gas is preferably as small as possible.

FIG. 1 schematically shows a carbon monoxide production apparatus suitably used in the production method of the present invention. The apparatus shown in the figure is of a continuous type and has a double tube structure. Specifically, the apparatus 10 shown in the figure includes an outer tube 11 and an inner tube 12 disposed in the outer tube 11. A heating device 13 such as a heater is disposed in the inner tube 12. The inner tube 12 contains the conversion agent. In this apparatus, carbon dioxide gas is circulated in the space between the outer tube 11 and the inner tube 12. While carbon dioxide gas circulates in this space, carbon dioxide gas reacts with the conversion agent contained in the inner tube 11 to generate carbon monoxide.

The apparatus 10 shown in FIG. 1 is configured to circulate reducing gas in the inner pipe 12 in addition to circulating carbon dioxide gas in the space between the outer pipe 11 and the inner pipe 12. (In FIG. 1, hydrogen, which is a typical example of reducing gas, is described.) As a result, oxygen is extracted from the conversion agent oxidized by contact with carbon dioxide gas, and lost oxygen vacancies are generated again. Thus, if the apparatus 10 shown in the figure is used, carbon monoxide is generated by bringing the conversion agent into contact with carbon dioxide gas, and then the conversion agent oxidized by contact with the carbon dioxide gas is reduced. The metal oxide can be regenerated by carrying out strong reduction by contacting with a reactive gas. The reason why such repeated regeneration treatment is possible is that the conversion agent has oxygen ion conductivity. As the reducing gas, for example, hydrogen gas or acetylene gas can be used. In particular, it is preferable to use a reducing gas containing hydrogen gas. The concentration of hydrogen gas in such a reducing gas is preferably not less than the lower limit of explosion to 100% by volume, more preferably 20% to 100% by volume. The treatment temperature is preferably 500 to 1200 ° C, more preferably 700 ° C to 1200 ° C, and still more preferably 1000 ° C to 1050 ° C. Strong reducing gas is generally at atmospheric pressure.

In the apparatus shown in FIG. 1, the heating device 13 is disposed inside the inner tube 12, but a heating device may be disposed around the outer tube 11 instead. However, in general, the temperature at which oxygen is forcibly extracted from the oxidized conversion agent 24 is higher than the temperature at which the reaction between the carbon dioxide gas and the conversion agent 24 occurs. It is advantageous to arrange 13 in terms of ease of forced extraction of oxygen.

In the apparatus shown in FIG. 1, the flow direction of carbon dioxide gas and the flow direction of reducing gas are the same direction, but instead, the flow direction of carbon dioxide gas and the flow direction of reducing gas are opposite directions. It may be. Further, as a modification of the apparatus shown in FIG. 1, a reducing gas can be circulated in the space between the outer tube 11 and the inner tube 12, and carbon dioxide gas can be circulated in the inner tube 12. . In this case, in order to efficiently regenerate the conversion agent contained in the inner tube 12, it is preferable to arrange a heating device around the outer tube 11.

The apparatus 20 shown in FIG. 2 includes two batch-

type reaction apparatuses

21 and 22. Furthermore, the device 20 includes a switching valve 23. The switching valve 23 has

input parts

23a and 23b respectively connected to a carbon dioxide gas source and a reducing gas source (in FIG. 2, hydrogen, which is a representative example of the reducing gas, is described). . Furthermore, the switching valve 23 has

output parts

23c and 23d connected to the

reaction devices

21 and 22, respectively. The conversion agent 24 can be arranged in each of the reaction apparatuses 21 and 22. A heating device 25 is disposed around each of the

reaction devices

21 and 22.

In the apparatus 20 shown in FIG. 2, carbon dioxide gas or reducing gas is alternatively and simultaneously supplied to each of the reaction apparatuses 21 and 22 via the switching valve 23. In addition to this, the type of gas supplied to each reactor can be switched by switching the switching valve 23.

When the apparatus shown in FIG. 2 is operated, first, the switching valve 23 is set to the position shown in FIG. 2, carbon dioxide gas is supplied to the second reaction apparatus 22, and reducing gas is supplied to the first reaction apparatus 21. To be supplied to. And each

reaction apparatus

21 and 22 is heated with the heating apparatus 25, and reducing gas and carbon dioxide gas are supplied to each

reaction apparatus

21 and 22. FIG. In this way, in the first reaction device 21, the conversion agent 24 placed inside is strongly reduced, oxygen is forcibly extracted, and a reversible oxygen deficiency is generated in the conversion agent 24. . On the other hand, in the second reactor 22, carbon monoxide is generated by the reaction of carbon dioxide and the conversion agent 24, and the number of oxygen vacancies in the conversion agent 24 gradually decreases. When the amount of carbon monoxide produced in the second reactor 22 decreases, the switching valve 23 is switched to supply carbon dioxide gas to the first reactor 21 and reducing gas to the second reactor 22. To be supplied. Since the conversion agent 24 that is stationary in the first reactor 21 is highly active that is not in contact with carbon dioxide gas, the amount of carbon monoxide produced is increased by bringing it into contact with carbon dioxide gas. Turn to. On the other hand, in the second reactor 22, the conversion agent 24 whose activity is reduced due to a decrease in the number of oxygen vacancies is strongly reduced, oxygen is forcibly extracted, and reversible oxygen vacancies are generated again in the conversion agent 24. .

In the apparatus 20 shown in FIG. 2, the heating temperatures of the first reaction apparatus 21 and the second reaction apparatus 22 may be set to the same or different temperatures. In general, the temperature at which oxygen is forcibly extracted from the oxidized conversion agent 24 is higher than the temperature at which the reaction between carbon dioxide gas and the conversion agent 24 occurs. Is preferably set higher than the heating temperature of the reactor that produces carbon monoxide.

In this manner, the carbon dioxide gas and the conversion agent 24 are alternately reacted in the first reaction device 21 and the second reaction device 22 to regenerate the conversion agent 24 and generate carbon monoxide. Semi-continuous operation is possible. In the apparatus 20 shown in FIG. 2, two batch reactors are used, but three or more reactors may be used instead.

The apparatus 30 shown in FIG. 3 has a structure in which plate-like bodies 31 including the conversion agent and plate-like separators 32 are alternately stacked. A plurality of convex portions 33 and concave portions 34 extending in one direction are alternately arranged on each surface of each separator 32. As a result, a space is formed between the plate-like body 31 and the pair of separators that are opposed to each other with the gas formed by the concave portions 34. Moreover, although not shown in figure, the apparatus 30 is equipped with the heating apparatus arrange | positioned around the stack structure.

When the apparatus 30 shown in FIG. 3 is operated, in the two separators 32a and 32b facing each other with the plate-like body 31 interposed therebetween while the stack structure is heated to a predetermined temperature by a heating device (not shown). Carbon dioxide gas is circulated through the concave portion 34a located on the opposing surface of one separator 32a and the plate-like body 31. While carbon dioxide gas flows through the recess 34a, the carbon dioxide gas reacts with the conversion agent contained in the plate 31 to generate carbon monoxide. In addition to this, the reducing gas is circulated through the concave portion 34b located on the opposing surface of the other separator 32b and the plate-like body 31 (in FIG. 3, a representative example of reducing gas). Some hydrogen is described.) As a result, oxygen is extracted from the conversion agent oxidized by contact with carbon dioxide gas, and lost oxygen vacancies are generated again. As described above, when the apparatus 30 is used, as in the apparatus 10 shown in FIG. 1 described above, the conversion agent is brought into contact with carbon dioxide gas to generate carbon monoxide, and then the carbon dioxide gas is used. The metal oxide can be regenerated by bringing the conversion agent oxidized by contact into contact with a reducing gas and performing strong reduction.

In each separator 32 of the device 30 shown in FIG. 3, the extending direction of the convex portion 33 and the concave portion 34 formed on one surface and the other surface is shifted by 90 degrees. However, the extending direction of the convex portion 33 and the concave strip portion 34 formed on each surface of the separator 32 is not limited to this. For example, the extending direction of the convex part 33 and the concave line part 34 formed on each surface of the separator 32 may intersect at an angle other than 90 degrees, or the same direction. When the extending direction of the convex part 33 and the concave line part 34 formed on each surface of the separator 32 is the same direction, the direction of the gas flowing through the concave line part 34 on one surface side of the separator 32 and the other The direction of the gas flowing through the groove 34 on the surface side may be the same direction or the opposite direction.

Note that, regarding the device shown in FIGS. 2 and 3, the description regarding the device shown in FIG.

Further, according to the present invention, a system for converting carbon dioxide into carbon monoxide using the conversion agent is also provided. In this system, carbon dioxide contained in exhaust gas generated from a smelter, ironworks or thermal power plant, which is a main source of carbon dioxide gas, is separated using a known method. The separated carbon dioxide is brought into contact with the conversion agent. At this time, if the waste heat generated from the smelter, ironworks or thermal power plant is contacted under heating, it is advantageous in that energy efficiency can be increased. Carbon monoxide is produced by the contact under heating. According to this system, not only carbon dioxide gas is prevented from being released into the atmosphere, but also the produced carbon monoxide can be effectively used as a raw material for C1 chemistry. Alternatively, the produced carbon monoxide can be fed back to, for example, a blast furnace at a steel mill and reused.

In smelters or steelworks, carbon dioxide gas is generated as exhaust gas, and hydrogen gas is also generated. Particularly in smelters, hydrogen gas is produced in large quantities. If this hydrogen gas is used for regeneration of the conversion agent oxidized by contact with carbon dioxide gas, the conversion agent having a reversible oxygen deficiency can be obtained without preparing a separate hydrogen gas. Therefore, energy efficiency is further increased, which is advantageous.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Example 1]
(1) Production of cerium oxide having reversible oxygen vacancies (a) Synthesis of cerium oxide without oxygen vacancies 100 g of cerium carbonate was allowed to stand in a heating furnace and baked by heating while circulating air. . Heating was started from room temperature, heated at a rate of temperature increase of 10 ° C./min, and after reaching 1000 ° C., this temperature was maintained for 1 hour. Then, it naturally left to cool. The air flow rate was 1000 SCCM. In this way, a porous body of cerium oxide having no oxygen defects was obtained. Measurement by XRD confirmed that this cerium oxide was represented by CeO ₂ and had a fluorite-type crystal structure. This cerium oxide was pulverized by a ball mill.
(B) Synthesis of cerium oxide having oxygen defects The cerium oxide (50 g) obtained in the previous section (a) is left in an atmosphere-controlled heating furnace, and is heated and reduced while flowing 100% hydrogen gas. went. Heating was started from room temperature, heated at a rate of temperature increase of 10 ° C./min, and after reaching 1000 ° C., this temperature was maintained for 1 hour. Then, it naturally left to cool. The circulation amount of hydrogen gas was 1000 SCCM. In this way, cerium oxide having reversible oxygen defects was obtained. As a result of measurement by XRD, it was confirmed that this cerium oxide has a fluorite-type crystal structure. As a result of elemental analysis, this cerium oxide was represented by Ce (IV, III) O _1.75 .

(2) Production of carbon monoxide gas from carbon dioxide gas A tubular furnace using the apparatus shown in FIG. 4 was installed in a glove box in a nitrogen gas atmosphere. In the tubular furnace, 8.5 g of cerium oxide powder having reversible oxygen vacancies obtained in the preceding item (1) is placed. First, the valve V5 was closed, all other valves were opened, and the inside of the tubular furnace was vacuumed. In this state, the valve V1 was closed and the tubular furnace was heated to 750 ° C. Next, after the valves V2 and V3 were closed, the suction in the tubular furnace was stopped. The valve V4 was closed and carbon dioxide gas (100%) was supplied into the tubular furnace. The supply was continued until the pressure in the tubular furnace reached atmospheric pressure. Then, the valve V1 was closed and left for 1 hour. At this time, the stoichiometric ratio of carbon dioxide gas to cerium oxide having reversible oxygen deficiency was set to 1: 1 (that is, 1 equivalent described above). Thereafter, the valve V2 was opened, and nitrogen gas was supplied into the tubular furnace until the gas recovery bag was slightly expanded. Next, the valve V2 was closed, and the gas recovery bag was heat sealed and separated from the tube. In this state, the temperature of the tubular furnace was lowered and cooled to room temperature. After completion of cooling, the valve V1 was opened and nitrogen gas was supplied into the tubular furnace. The supply was continued until the pressure in the tubular furnace reached atmospheric pressure. Finally, the valves V3 and V5 were opened, and carbon monoxide in the tubular furnace was extruded with nitrogen gas. The gas after reaction collected in the gas collection bag was qualitatively and quantitatively analyzed using gas chromatography. As a result, the conversion rate from carbon dioxide to carbon monoxide was 60%.

[Examples 2 to 9]
Carbon monoxide gas was produced from carbon dioxide gas in the same manner as in Example 1 except that the conditions shown in Table 1 below were adopted. The conversion rate at that time is shown in the same table. In the table, the results of Example 1 are also shown.

[Comparative Example 1]
This comparative example is an example in which cerium oxide having no oxygen defect is used instead of cerium oxide having reversible oxygen deficiency used in Example 1. The cerium oxide having no oxygen defects is the same as the cerium oxide having no oxygen defects, which is an intermediate produced in the course of the production process of cerium oxide having reversible oxygen vacancies in Example 1. Carbon monoxide gas was produced from carbon dioxide gas in the same manner as in Example 1 except that this cerium oxide having no oxygen defect was used and the conditions shown in Table 1 were adopted. The conversion rate at that time is shown in the same table.

[Comparative Example 2]
In this comparative example, cerium oxide having only irreversible oxygen vacancies was used instead of cerium oxide having reversible oxygen vacancies used in Example 1. As cerium oxide having only irreversible oxygen vacancies, calcium-doped cerium oxide produced by the following method was used. This calcium-doped cerium oxide corresponds to the substance described in column 5, lines 59 to 64 of Patent Document 3 described in the background art section. Using this calcium-doped cerium oxide, carbon monoxide gas was produced from carbon dioxide gas in the same manner as in Example 1 except that the conditions shown in Table 1 were adopted. The conversion rate at that time is shown in the same table.

[Synthesis of calcium-doped cerium oxide with only irreversible oxygen deficiency]
While stirring an aqueous solution in which ammonium hydrogen carbonate, ammonia, ammonium carbonate and oxalic acid were dissolved in water, a cerium nitrate aqueous solution and a calcium nitrate aqueous solution were added dropwise and reverse neutralized to form a precipitate. The dropping amount of the cerium nitrate aqueous solution and the calcium nitrate aqueous solution was adjusted so that the molar concentration of cerium and calcium was 0.2 with respect to cerium 0.8. The produced precipitate was washed twice with ion-exchanged water and filtered. Thereafter, the filtrate was calcined at 300 ° C. for 3 hours in the air, and then calcined at 1000 ° C. for 3 hours in the air to obtain calcium-doped cerium oxide. As a result of measurement by XRD, the lattice constant of this calcium-doped cerium oxide was 5.4158Å. Since the lattice constant of cerium oxide not doped with calcium is 5.4113 Å, it was confirmed that the obtained calcium-doped cerium oxide expanded in lattice and solid-dissolved calcium.

As is clear from Table 1, it is understood that high conversion can be obtained when carbon dioxide is converted into carbon monoxide using cerium oxide having reversible oxygen deficiency (Examples 1 to 9). On the other hand, when carbon dioxide is converted to carbon monoxide using cerium oxide having no oxygen deficiency (Comparative Example 1), it can be seen that the conversion rate is extremely low. It can be seen that also when cerium oxide having only irreversible oxygen deficiency is used (Comparative Example 2), the conversion rate is extremely low.

Claims

A metal oxide having oxygen ion conductivity and reversible oxygen deficiency is brought into contact with carbon dioxide gas under heating, and carbon monoxide is reduced by a stoichiometric reaction to generate carbon monoxide. A process for producing carbon monoxide characterized by the above.
The method according to claim 1, wherein the metal oxide is made of cerium oxide having reversible oxygen vacancies.
The metal oxide is represented by CeO 2-x (wherein Ce has a tetravalent and trivalent mixed valence, and x represents a positive number less than 0.5) and is reversible. 3. The production method according to claim 2, comprising cerium oxide having an oxygen deficiency and a fluorite-type crystal structure.
The metal oxide is represented by CeO 2-x (wherein Ce has trivalent and mixed valences less than trivalent, x represents a number of 0.5 to 0.7), The production method according to claim 2, comprising cerium oxide having a reversible oxygen deficiency and a superlattice structure similar to fluorite.
After contacting the metal oxide with carbon dioxide gas to produce carbon monoxide, the metal oxide oxidized by contact with the carbon dioxide gas is contacted with a reducing gas to regenerate the metal oxide. The manufacturing method according to any one of claims 1 to 4.
An outer tube, and an inner tube disposed in the outer tube,
The inner tube includes a metal oxide having oxygen ion conductivity and having a reversible oxygen deficiency,
Carbon dioxide gas is circulated between the outer tube and the inner tube, and a reducing gas is circulated in the inner tube, or a reducing property is provided between the outer tube and the inner tube. An apparatus for producing carbon monoxide configured to circulate gas and circulate carbon dioxide gas in the inner pipe.
Two or more batch type reactors, and a switching valve having an input unit connected to each of the carbon dioxide gas source and the reducing gas source and an output unit connected to each of the reactors, An apparatus for producing carbon monoxide capable of arranging a metal oxide having oxygen ion conductivity and having reversible oxygen vacancies,
Carbon dioxide gas or reducing gas is alternatively and simultaneously supplied to each reactor via the switching valve, and the type of gas supplied to each reactor can be switched by switching the switching valve. Carbon monoxide production equipment configured in
This is a carbon monoxide production apparatus in which plate-like bodies comprising a metal oxide having oxygen ion conductivity and having reversible oxygen vacancies and plate-like separators are alternately stacked. And
A plurality of ridges and ridges extending in one direction are alternately arranged on each surface of each separator,
Carbon dioxide gas is circulated through the concave portion located on the opposing surface of one separator and the plate-like body in the two separators facing each other across the plate-like body, and the other separator and the plate-like body An apparatus for producing carbon monoxide configured to allow a reducing gas to circulate through a concave portion located on the opposite surface.
Separating carbon dioxide contained in exhaust gas generated from smelters, steelworks or thermal power plants,
Contacting the separated carbon dioxide with a metal oxide having oxygen ion conductivity and reversible oxygen deficiency under heating using waste heat generated from a smelter, ironworks or thermal power plant A system for converting carbon dioxide to carbon monoxide, characterized in that carbon dioxide is reduced by a stoichiometric reaction to produce carbon monoxide.
10. The system according to claim 9, wherein the metal oxide oxidized by contact with carbon dioxide gas is brought into contact with hydrogen generated from a smelter or an ironworks to cause reversible oxygen deficiency in the metal oxide.
An agent for converting carbon dioxide to carbon monoxide, comprising a metal oxide having oxygen ion conductivity and reversible oxygen deficiency.