Method for decomposing oxygen compound gas and gas decomposition apparatus

Abstract

To provide a method for decomposing oxygen compound gas, capable of electrolyzing the oxygen compound gas with high conversion efficiency and suppressing degradation of electrolysis performance, even in the presence of a sulfur compound in the oxygen compound gas, without requiring desulfurization treatment.SOLUTION: In a laminate for electrolysis, a cathode catalyst layer is made of a perovskite-type oxide, or of the perovskite-type oxide and a spinel-type oxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for decomposing an oxygen compound gas and a gas decomposition apparatus. [Background technology]

[0002] Due to the effects of global warming worldwide, there is an urgent need to reduce emissions of oxygen compound gases, especially carbon dioxide (CO2). CCS (CO2 Capture and Storage, a technology for capturing and storing carbon dioxide underground) is being considered as one method for reducing CO2 emissions. However, there are many concerns about the safety of long-term CO2 storage and the selection of appropriate sites, and CCS has not yet become a fundamental solution for reducing CO2 emissions.

[0003] Another method being considered for reducing CO2 emissions is CO2 Capture and Utilization (CCU), a technology that effectively utilizes carbon dioxide. Among these, CO2 electrolysis technology (hereinafter also referred to as electrolysis technology) is attracting attention. In particular, the increase in renewable energy, primarily solar power generation, can result in surplus electricity. With a view to making effective use of such surplus electricity, there are high hopes for power storage using electrolysis technology.

[0004] Furthermore, carbon monoxide (CO) generated by the electrolysis of CO2 can be used, for example, as energy in steelworks or as a raw material for chemicals such as methanol. In particular, the blast furnace process is used in the production of steel at steelworks. In this blast furnace process, iron ore is reduced using coal, which inevitably generates CO2. Furthermore, steelworks and other facilities use hydrogen (H2) as a raw material in addition to CO2. Therefore, it is extremely important to establish electrolysis technology for oxygen compound gases, especially CO2, and gases containing water vapor (H2O) in addition to CO2.

[0005] As such electrolysis techniques, for example, Patent Documents 1 and 2 disclose a laminate (cell) for electrolysis that uses an electrode containing Ni (hereinafter also referred to as a Ni-containing electrode) in the cathode catalyst layer (fuel electrode). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5910539 [Patent Document 2] Patent No. 5637652 [Patent Document 3] Patent No. 5738983 Summary of the Invention [Problem to be solved by the invention]

[0007] Incidentally, oxygen compound gases, such as gases generated secondarily in blast furnaces during the steelmaking process (hereinafter also referred to as blast furnace gas), may contain high concentrations of sulfur compounds. Here, sulfur compounds are gaseous compounds containing sulfur atoms as part of their structure. Examples of such sulfur compounds include sulfur oxides (SO ), such as sulfur dioxide (SO ). x ) and hydrogen sulfide (H2S).

[0008] When oxygen compound gases containing such sulfur compounds are electrolyzed using the electrolysis laminates disclosed in Patent Documents 1 and 2, electrolysis performance is significantly reduced.

[0009] Therefore, in the electrolysis of oxygen compound gas containing sulfur compounds, it is necessary to carry out desulfurization treatment (hydrodesulfurization) as a pre-step of the electrolysis process, as disclosed in Patent Document 3, for example.

[0010] However, desulfurization treatment increases the process cost. Therefore, there is a need for a method for decomposing oxygen compound gases that can electrolyze oxygen compound gases containing sulfur compounds at high conversion efficiency without desulfurization treatment and that can prevent deterioration of electrolysis performance.

[0011] The present invention has been developed to meet the above-mentioned demand, and aims to provide a method for decomposing oxygen compound gas, which can electrolyze oxygen compound gas with high conversion efficiency without desulfurization treatment when the oxygen compound gas contains sulfur compounds, and which can suppress deterioration of electrolysis performance. Another object of the present invention is to provide a gas decomposition apparatus that can be suitably used in the above-mentioned method for decomposing oxygen compound gases.

[0012] The oxygen compound gas is a gas containing an oxygen compound. The oxygen compound is a gaseous compound containing oxygen atoms as a part of its structure. Examples of such oxygen compounds include CO2, HO, NOx, and SOx. Hereinafter, the conversion efficiency of oxygen compound gas by electrolysis will also be referred to as electrolysis efficiency. The characteristic of inhibiting degradation of electrolysis performance when sulfur compounds are contained in oxygen compound gas will also be referred to as sulfur degradation resistance of electrolysis performance. Furthermore, in this specification, any numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits, respectively. [Means for solving the problem]

[0013] The inventors have conducted extensive research to achieve the above object. As a result, they found that the above object can be achieved by using a perovskite-type oxide or a combination of a perovskite-type oxide and a spinel-type oxide for the cathode catalyst layer in a laminate structure in which an electrolyte layer is sandwiched between an anode catalyst layer and a cathode catalyst layer. The present invention was completed based on the above findings and further investigations.

[0014] That is, the gist and configuration of the present invention are as follows. 1. A method for decomposing an oxygen compound gas, comprising: The method for decomposing the oxygen compound gas comprises: a supply step of supplying an oxygen compound gas as a raw material gas to a laminate including an electrolyte layer, an anode catalyst layer, and a cathode catalyst layer; an electrolysis step of applying a voltage to the laminate to generate O and a by-product gas containing CO from the oxygen compound gas by electrolysis; an oxygen recovery step of recovering the O2; a by-product gas recovery step of recovering the by-product gas; With The oxygen compound gas contains CO2 and a sulfur compound, the laminate has a structure in which the electrolyte layer is sandwiched between the anode catalyst layer and the cathode catalyst layer, The cathode catalyst layer is Perovskite oxides, or Perovskite-type oxides and spinel-type oxides, A method for decomposing oxygen compound gas.

[0015] 2. The method for decomposing oxygen compound gases according to 1 above, wherein the content of the spinel-type oxide in the cathode catalyst layer is 10 mass % or more.

[0016] 3. The method for decomposing oxygen compound gases according to 1 above, wherein the content of the perovskite-type oxide in the cathode catalyst layer is 40 to 60 mass % and the content of the spinel-type oxide is 40 to 60 mass %.

[0017] 4. The perovskite oxide is La α Sr β Fe γ Mn δ O3, 4. The method for decomposing oxygen compound gases according to any one of 1 to 3 above, wherein the spinel-type oxide is CuFe2O4. Here, α, β, γ, and δ are 0 to 1, α+β is 1, and γ+δ is 1.

[0018] 5. The method for decomposing oxygen compound gases according to any one of 1 to 4 above, wherein the electrolyte layer and the anode catalyst layer contain perovskite-type oxides.

[0019] 6. The method for decomposing oxygen compound gas according to any one of 1 to 5 above, wherein the temperature at which the raw material gas is supplied is 100°C or higher and 800°C or lower.

[0020] 7. The method for decomposing oxygen compound gas according to any one of 1 to 6 above, wherein the voltage applied in the electrolysis step is 0.6 V or more and 2.0 V or less.

[0021] 8. A gas decomposition device comprising: The gas decomposition device includes: a raw material gas supply unit that supplies an oxygen compound gas as a raw material gas; an electrolysis unit that generates a by-product gas containing O and CO by electrolysis from the oxygen compound gas supplied from the raw material gas supply unit; an oxygen recovery unit that recovers the O2; a by-product gas recovery unit that recovers the by-product gas; With The oxygen compound gas contains CO2 and a sulfur compound, the electrolysis unit has a laminate including an electrolyte layer, an anode catalyst layer, and a cathode catalyst layer; the laminate has a structure in which the electrolyte layer is sandwiched between the anode catalyst layer and the cathode catalyst layer, The cathode catalyst layer is Perovskite oxides, or Perovskite-type oxides and spinel-type oxides, This is a gas decomposition device.

[0022] 9. The gas decomposition device according to 8 above, wherein the content of the spinel-type oxide in the cathode catalyst layer is 10 mass % or more.

[0023] 10. The gas decomposition apparatus according to 8 above, wherein the content of the perovskite-type oxide in the cathode catalyst layer is 40 to 60 mass %, and the content of the spinel-type oxide in the cathode catalyst layer is 40 to 60 mass %.

[0024] 11. The perovskite oxide is La α Sr β Fe γ Mn δ O3, 11. The gas decomposition apparatus according to any one of 8 to 10 above, wherein the spinel-type oxide is CuFe2O4. Here, α, β, γ, and δ are 0 to 1, α+β is 1, and γ+δ is 1.

[0025] 12. The gas decomposition device according to any one of 8 to 11 above, wherein the electrolyte layer and the anode catalyst layer contain a perovskite-type oxide.

[0026] 13. The gas decomposition apparatus according to any one of 8 to 12 above, wherein the raw material gas supply section has a desulfurization device.

[0027] 14. The gas decomposition apparatus according to any one of 8 to 13 above, wherein the raw material gas supply section has a preheating device. [Effects of the Invention]

[0028] According to the present invention, when an oxygen compound gas contains sulfur compounds, the oxygen compound gas can be electrolyzed at a high conversion efficiency without desulfurization, and deterioration of electrolysis performance can be suppressed. Furthermore, by applying the method for decomposing an oxygen compound gas of the present invention, particularly when the oxygen compound gas contains sulfur compounds, it is possible to suppress an increase in the process cost associated with the desulfurization treatment, and therefore the present invention is of great industrial value. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic diagram showing an example of a laminate used in a method for decomposing an oxygen compound gas according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating an example of a gas decomposition apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will be described based on the following embodiments.

[0031] [1] Method for decomposing oxygen compound gases Next, a method for decomposing an oxygen compound gas according to one embodiment of the present invention will be described. A method for decomposing an oxygen compound gas according to one embodiment of the present invention includes the steps of: a supply step of supplying an oxygen compound gas as a raw material gas to a laminate including an electrolyte layer, an anode catalyst layer, and a cathode catalyst layer; an electrolysis step of applying a voltage to the laminate to generate O and a by-product gas containing CO from the oxygen compound gas by electrolysis; an oxygen recovery step of recovering the O2; a by-product gas recovery step of recovering the by-product gas; With The oxygen compound gas contains CO2 and a sulfur compound, the laminate has a structure in which the electrolyte layer is sandwiched between the anode catalyst layer and the cathode catalyst layer, The cathode catalyst layer is Perovskite oxides, or Perovskite-type oxides and spinel-type oxides, is.

[0032] First, an oxygen compound gas and a laminate used in a method for decomposing an oxygen compound gas according to one embodiment of the present invention will be described.

[0033] [1-1] Oxygen compound gas The oxygen compound gas used as the raw material gas contains CO2 and sulfur compounds. In particular, the method for decomposing an oxygen compound gas according to one embodiment of the present invention is particularly advantageous when applied to an oxygen compound gas having a CO2 concentration of 10 to 100% by volume and a sulfur compound concentration of 1% by volume or less, preferably 100 ppm by volume or less. Furthermore, the oxygen compound gas preferably contains HO in addition to CO2 and sulfur compounds. When the oxygen compound gas contains both CO2 and HO, deterioration of the surface of the cathode catalyst layer is suppressed, contributing to a longer life of the equipment. The concentration of HO may be set at any concentration depending on the source of the raw material gas, etc. In addition, the oxygen compound gas used as the raw material gas may contain a remaining gas other than the oxygen compound and sulfur compound. The (total) concentration of the oxygen compounds in the oxygen compound gas is preferably 5 to 100% by volume, more preferably 10 to 100% by volume. Examples of the remaining gas include Ar and N2. Blast furnace gas, combustion exhaust gas from hot stoves and heating furnaces, and the like contain 10% or more by volume of CO2, and are therefore suitable as raw material gases. Also, gas obtained by subjecting blast furnace gas to a process to increase the CO2 concentration, for example, can be used. Furthermore, CO2-containing gases generated in other industrial fields can also be used.

[0034] [1-2] Laminate The laminate used in the method for decomposing oxygen compound gases according to one embodiment of the present invention includes an electrolyte layer, an anode catalyst layer, and a cathode catalyst layer, as shown in Fig. 1. The laminate has a structure in which the electrolyte layer is sandwiched between the anode catalyst layer and the cathode catalyst layer (a so-called sandwich structure). The laminate can also be said to be a laminate in which an anode catalyst layer is laminated on one side of the electrolyte layer, and a cathode catalyst layer is laminated on one side of the electrolyte layer opposite to the side on which the anode catalyst layer is laminated. In FIG. 1, reference numeral 1 denotes a laminate, 11 denotes an anode catalyst layer, 12 denotes an electrolyte layer, 13 denotes a cathode catalyst layer, and 3 denotes a power source.

[0035] First, the principle of electrolyzing CO2 into CO and O2 using the above laminate will be described.

[0036] (Principle of CO2 electrolysis) As shown in Figure 1, while a voltage is applied between the anode catalyst layer and the cathode catalyst layer of the laminate, an oxygen compound gas containing CO2 is supplied so that it comes into contact with the laminate, particularly the cathode catalyst layer. This causes the CO2 contained in the oxygen compound gas to be electrolyzed into CO and O2. During this process, the following reactions occur in the cathode catalyst layer and the anode catalyst layer, respectively. Cathode catalyst layer CO2+2e - →CO+O 2- (1) Anode catalyst layer 2O 2- →O2+4e - (2)

[0037] That is, in the cathode catalyst layer, CO2 receives electrons, and the reaction of the above formula (1) occurs. This generates CO. Meanwhile, in the anode catalyst layer, O2 generated in the cathode catalyst layer is converted to CO2. 2- The O diffuses through the electrolyte layer and reaches the anode catalyst layer, where the reaction shown in formula (2) occurs. 2- An electron is removed from the atom to produce O2.

[0038] When electrolyzing H2O, the following reactions occur in the cathode catalyst layer and the anode catalyst layer. Cathode catalyst layer H2O+2e - →H2+O 2- (3) Anode catalyst layer 2O 2- →O2+4e - (4)

[0039] Next, the electrolyte layer, the anode catalyst layer, and the cathode catalyst layer that constitute the above-mentioned laminate will be described.

[0040] (electrolyte layer) The electrolyte layer is formed by transferring O from the cathode side to the anode side while a voltage is applied between the anode catalyst layer and the cathode catalyst layer. 2-The electrolyte layer of the laminate is not particularly limited in material, and materials commonly used for electrolysis can be used. The electrolyte layer preferably contains, for example, a spinel oxide or a perovskite oxide. Among these, the electrolyte layer more preferably contains a perovskite oxide. Perovskite oxides have high ionic conductivity even at low temperatures. The perovskite oxide is not particularly limited, but a perovskite oxide containing two or more elements selected from La, Sr, Ga, Mg, Zr, and Y is preferred. This makes it possible to achieve high electrolysis efficiency even when a relatively low voltage is applied between the anode catalyst layer and the cathode catalyst layer. The electrolyte layer can contain a spinel oxide or a perovskite oxide alone, or both oxides can be contained simultaneously. When a spinel oxide or a perovskite oxide is contained simultaneously, the content of the spinel oxide in the electrolyte layer is preferably 30% by mass or less, and the content of the perovskite oxide is preferably 70% by mass or more. The electrolyte layer may contain a remaining substance other than the spinel oxide or perovskite oxide in a total amount of 10 mass % or less, such as oxides other than the spinel oxide or perovskite oxide, and unavoidable impurities.

[0041] (Anode catalyst layer) The anode catalyst layer is formed on one side of the electrolyte layer, and functions as an anode while promoting the reactions shown in the above formulas (2) and (4). In the above laminate, the anode catalyst layer is a catalyst that is generally used for electrolysis, i.e., a catalyst that converts oxygen ions (O 2- A highly active substance that quickly recombines cations of cations (C, C, and C) into oxygen molecules (O-) is used. In particular, the anode catalyst layer preferably contains a perovskite-type oxide. The perovskite-type oxide is not particularly limited, but a perovskite-type oxide containing one or more elements selected from Ba, La, and Co is preferred. As such a perovskite-type oxide, Ba, m La nExamples of suitable materials include CoO3. Here, m and n are 0 to 1, and m+n is 1. Preferably, m is 0.1 to 1. Furthermore, m is more preferably 0.5, as this minimizes electrical resistance. The anode catalyst layer may contain a total of 10% by mass or less of residual substances other than the perovskite oxide. Examples of the residual substances include oxides other than the perovskite oxide and unavoidable impurities. However, it is preferable that the content of Ni oxide is 0.5% by mass or less.

[0042] (Cathode catalyst layer) The cathode catalyst layer is formed on the electrolyte layer, on the opposite side to the anode catalyst layer. The cathode catalyst layer functions as a cathode and promotes the reactions represented by the above-mentioned formulas (1) and (3). As described above, in the method for decomposing oxygen compound gas according to one embodiment of the present invention, it is extremely important that the cathode catalyst layer be made of a perovskite oxide or a combination of a perovskite oxide and a spinel oxide. By forming the cathode catalyst layer from a perovskite oxide, particularly a combination of a perovskite oxide and a spinel oxide, it is possible to achieve both high electrolysis efficiency and excellent resistance to sulfur degradation of electrolysis performance, even when the oxygen compound gas contains sulfur compounds.

[0043] The inventors believe that the reason for the above is as follows. As described above, in the cathode catalyst layer, CO and HO contained in the oxygen compound gas are electrolyzed by the reactions shown in the above formulas (1) and (3), respectively. Here, when the cathode catalyst layer is formed using a Ni-containing electrode, such as a cermet of nickel and yttria-stabilized zirconia (hereinafter also referred to as Ni-YSZ) as disclosed in Patent Document 3, Ni contributes to the reaction shown in the above formula (1), and YSZ contributes to the reaction shown in the above formula (3). However, when the oxygen compound gas contains a sulfur compound, Ni is poisoned by the sulfur compound, making the reaction shown in the above formula (1) less likely to occur. On the other hand, when the cathode catalyst layer is formed using a perovskite oxide or a perovskite oxide and a spinel oxide, the perovskite oxide contributes to the reaction shown in the above formula (1), and the spinel oxide contributes to the reaction shown in the above formula (3). Both perovskite oxides and spinel oxides have high resistance to poisoning by sulfur compounds, and therefore, by forming the cathode catalyst layer from perovskite oxides, particularly perovskite oxides and spinel oxides, it becomes possible to achieve both high electrolysis efficiency and excellent resistance to sulfur degradation of electrolysis performance, even when the oxygen compound gas contains sulfur compounds.

[0044] The content of the perovskite oxide in the cathode catalyst layer is preferably 5% by mass or more, more preferably 15% by mass or more, even more preferably 30% by mass or more, and even more preferably 40% by mass or more. The content of the perovskite oxide may be 100% by mass. The content of the perovskite oxide is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0045] The content of the spinel-type oxide in the cathode catalyst layer may be 0% by mass. By setting the content of the spinel-type oxide to 10% by mass or more, higher electrolysis efficiency can be obtained. The methods for evaluating the electrolysis efficiency and the resistance to sulfur degradation of electrolysis performance are as described in the Examples below. The content of the spinel-type oxide is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. The content of the spinel-type oxide is preferably 95% by mass or less, more preferably 85% by mass or less, even more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0046] In particular, it is extremely advantageous to set the content of the perovskite-type oxide to 40 to 60 mass % and the content of the spinel-type oxide to 40 to 60 mass %, since this provides a particularly high electrolysis efficiency.

[0047] The perovskite oxide used in the cathode catalyst layer is not particularly limited, but may be La α Sr β Fe γ Mn δ O3 is preferred. Here, α, β, γ, and δ are 0 to 1, α+β is 1, and γ+δ is 1. It is more preferred that α is 0.5 to 1, and γ is 0.05 to 0.3.

[0048] The spinel oxide used in the cathode catalyst layer is not particularly limited, but is preferably CuFeO. By using CuFeO as the spinel oxide, excellent resistance to sulfur degradation of electrolysis performance and particularly high electrolysis efficiency can be obtained.

[0049] The perovskite oxide and spinel oxide of the cathode catalyst layer may contain unavoidable impurities. The content of the unavoidable impurities is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. The content of the unavoidable impurities may be 0% by mass. The same applies to the content of the unavoidable impurities in the electrolyte layer and the anode catalyst layer.

[0050] Furthermore, as a combination of the electrolyte layer, the anode catalyst layer, and the cathode catalyst layer, the electrolyte layer and the anode catalyst layer are made of perovskite-type oxides, and the cathode catalyst layer is made of perovskite-type oxides and spinel-type oxides. α Sr β Fe γ Mn δ It is preferable that the catalyst is composed of O3 and CuFe2O4, which provides excellent resistance to sulfur degradation of electrolysis performance and more advantageously improves electrolysis efficiency.

[0051] The electrolyte layer, anode catalyst layer, and cathode catalyst layer can be formed, for example, by mixing and firing oxides of the metals (elements) that make up each layer to obtain a predetermined composition. Alternatively, nitrates or chlorides of the metals that make up each layer may be used.

[0052] The laminate can be formed, for example, by applying a metal oxide or the like for the anode catalyst layer to one surface of a plate-shaped electrolyte layer and a metal oxide or the like for the cathode catalyst layer to the other surface of the electrolyte layer, followed by firing.The laminate can also be formed by processing the electrolyte layer into a cylindrical shape, applying a metal oxide or the like for the cathode catalyst layer to the inner surface of the cylindrical electrolyte layer and a metal oxide or the like for the anode catalyst layer to the outer surface of the cylindrical electrolyte layer, followed by firing.

[0053] Furthermore, the thickness ratio of the electrolyte layer, anode catalyst layer, and cathode catalyst layer is preferably 1:1 for the anode catalyst layer, 0.5 to 5 for the cathode catalyst layer, and 10 to 50 for the electrolyte layer. If the thickness of the electrolyte layer is too small compared to the thickness of the anode catalyst layer or the cathode catalyst layer, it may not be able to withstand the thermal stress and may crack. On the other hand, if the thickness of the electrolyte layer is too large, Joule heat may increase due to increased electrical resistance, which may reduce the electrolysis efficiency.

[0054] Other than the above, there are no particular limitations, and a general configuration of a laminate for electrolysis can be appropriately adopted.

[0055] [1-3] Steps Next, each step of the method for decomposing oxygen compound gas according to one embodiment of the present invention will be described.

[0056] (Supply step) In the supply step, an oxygen compound gas as a raw material gas is supplied to the stack of the above [1-2]. Preferably, the oxygen compound gas as a raw material gas is supplied so as to come into contact with the cathode catalyst layer of the stack of the above [1-2]. The oxygen compound gas as a raw material gas can be supplied, for example, through a gas flow passage such as a pipe or duct connected to a raw material gas supply source.

[0057] In addition, the supply temperature of the raw material gas to the stack in [1-2] above is preferably 100°C or higher and 800°C or lower. The higher the supply temperature of the raw material gas, the more the power required for electrolysis can be reduced. However, from the viewpoint of designing the gas decomposition apparatus, heat generation due to Joule heat from the stack in [1-2] above can also be considered. Therefore, the supply temperature of the raw material gas is preferably 400°C or lower. In addition, the supply temperature of the raw material gas is preferably 200°C or higher. The supply temperature of the raw material gas may be measured, for example, in the gas flow passage in the casing that houses the stack (upstream of the stack) or immediately before the casing.

[0058] Furthermore, the raw material gas may be preheated in order to control the supply temperature of the raw material gas, as exemplified in [2] below.

[0059] Furthermore, although the oxygen compound gas used as the raw material gas is as described in [1-1] above, a higher concentration of the oxygen compound is preferable. For example, the concentration of CO2 is not particularly limited, but is preferably 10% by volume or more from the viewpoint of electrolysis efficiency.

[0060] The gas delivered from the source gas source (hereinafter also referred to as the delivery gas) may be directly supplied to the stack of [1-2] as the source gas. Alternatively, for example, CO2 and other components may be separated and recovered from the delivery gas in advance, and the separated and recovered gas (hereinafter also referred to as the separated and recovered gas) may be supplied to the stack of [1-2] as the source gas. The method for separating and recovering CO2 is not particularly limited. Examples include a method of liquefying or solidifying CO2 by pressurization or cooling, a method of absorbing CO2 into a basic aqueous solution such as caustic soda or amine, and then separating and recovering it by heating or reducing pressure, a method of adsorbing CO2 onto activated carbon or zeolite, and then separating and recovering it by heating or reducing pressure, and a method of separating and recovering it using a CO2 separation membrane. The CO2 concentration in the separated and recovered gas is not particularly limited, but is preferably 80% by volume or higher. This is advantageous because it allows for the miniaturization of gas decomposition devices, particularly the stack used during electrolysis, and the associated equipment for the stack.

[0061] Furthermore, if necessary, for example, when the concentration of sulfur compounds in the oxygen compound gas serving as the raw material gas is particularly high due to the operating conditions of the equipment serving as the raw material gas source, some of the sulfur compounds may be removed from the oxygen compound gas simultaneously with the supply step or between the supply step and the electrolysis step described below. The method for removing the sulfur compounds is not particularly limited. Examples of methods for removing sulfur compounds include a wet method using amine, methanol, ammonia water, etc., and a dry method using Fe, Cu, Zn, etc.

[0062] Furthermore, if necessary, during the supply step or between the supply step and the electrolysis step described below, harmful components such as NOx may be removed from the oxygen compound gas that serves as the raw material gas.

[0063] (Electrolysis step) In the electrolysis step, a voltage is applied to the laminate of the above [1-2], and oxygen and by-product gases are generated by electrolysis from the oxygen compound gas, which is the raw material gas, in the cathode catalyst layer of the laminate.

[0064] The applied voltage in the electrolysis step (the voltage applied between the anode catalyst layer and the cathode catalyst layer of the laminate of [1-2] above) is preferably 0.6 V or more and 2.0 V or less. If the applied voltage is less than 0.6 V, the voltage will be lower than the theoretical electrolysis voltage, and the electrolysis reaction may not proceed sufficiently. If the applied voltage exceeds 2.0 V, CO2 will decompose into solid carbon (C) and O2, making it difficult to generate CO2. Furthermore, Joule heat will accumulate in the laminate, which may cause decomposition of the laminate itself.

[0065] It is also preferable to control the temperature of the laminate during electrolysis to between 100° C. and 900° C. That is, it is preferable to control the temperature of the laminate during electrolysis to between 100° C. and 900° C., taking into consideration Joule heat due to electrical resistance.

[0066] The temperature of the laminate can be controlled by, for example, heating the laminate body with a heater or a heat exchanger using exhaust heat as described above, or by controlling the supply temperature of the raw material gas as described above.

[0067] (Oxygen recovery step and by-product gas recovery step) In the oxygen recovery step and the by-product gas recovery step, the oxygen and by-product gas generated in the electrolysis step are recovered, respectively. The oxygen and by-product gas generated in the electrolysis step can be recovered, for example, via gas flow channels adjacent to the anode catalyst layer and the cathode catalyst layer of the laminate of the electrolysis unit, respectively. The recovered oxygen and by-product gas can be supplied, for example, to equipment or storage units that use the oxygen and by-product gas.

[0068] (others) The method for decomposing oxygen compound gases according to one embodiment of the present invention may further include a sweep gas supply step of supplying a sweep gas to the anode catalyst layer of the electrolysis unit. The sweep gas may be supplied, for example, through a gas flow passage adjacent to the anode catalyst layer of the electrolysis unit. The sweep gas is described in detail in [2] below.

[0069] Furthermore, the method for decomposing oxygen compound gases according to one embodiment of the present invention can be particularly suitably carried out using, for example, the gas decomposition apparatus [2] described below.

[0070] The conditions other than those mentioned above are not particularly limited, and may be those according to conventional methods.

[0071] [2] Gas decomposition equipment Next, a gas decomposition apparatus according to one embodiment of the present invention will be described. As shown in FIG. 2, a gas decomposition apparatus according to one embodiment of the present invention includes: a raw material gas supply unit that supplies an oxygen compound gas as a raw material gas; an electrolysis unit that generates a by-product gas containing O and CO by electrolysis from the oxygen compound gas supplied from the raw material gas supply unit; an oxygen recovery unit that recovers the O2; a by-product gas recovery unit that recovers the by-product gas; With The oxygen compound gas contains CO2 and a sulfur compound, The electrolysis unit has the laminated body described in [1-2] above. In FIG. 2, reference numeral 1 denotes a laminate, 11 denotes an anode catalyst layer, 12 denotes an electrolyte layer, 13 denotes a cathode catalyst layer, 2 denotes a gas decomposition device, 21 denotes an electrolysis unit, 22 denotes a raw material gas supply unit, 23 denotes a sweep gas supply unit, 24 denotes a by-product gas recovery unit, 25 denotes an oxygen recovery unit, and 3 denotes a power source.

[0072] (raw gas supply unit) The raw material gas supply unit supplies an oxygen compound gas serving as a raw material gas to the electrolysis unit, preferably so that the oxygen compound gas contacts the cathode catalyst layer of the stack. The raw material gas supply unit is configured, for example, by a gas flow passage adjacent to the cathode catalyst layer of the stack of the electrolysis unit described below. The gas flow passage is defined, for example, by a casing that houses the stack. Packing or a glass seal may be used to prevent gas leakage from the casing. The gas flow passage may also be configured by piping, ducts, or the like. The raw material gas supply unit may further include a device for pressure-feeding the raw material gas. Examples of such devices include a fan or a blower. The raw material gas supply unit may also optionally include a desulfurization device that removes some of the sulfur compounds contained in the oxygen compound gas serving as the raw material gas, a raw material gas preheater, or a separator / recoverer for oxygen compounds such as CO2. The desulfurization device, raw material gas preheater, and oxygen compound separator / recoverer may be disposed, for example, in the gas flow passage. The desulfurization device is not particularly limited as long as it can remove sulfur compounds from the oxygen compound gas. The method for removing sulfur compounds is as described above. From the viewpoint of suppressing a decrease in the temperature of the raw material gas, it is preferable to dispose a raw material gas preheater immediately before the electrolysis section, for example, in the gas flow passage defined by the casing that houses the stack, or in a position adjacent to this gas flow passage. Examples of the raw material gas preheater include a burner and a heat exchanger that utilizes exhaust heat.

[0073] The heat source for the heat exchanger can be, for example, waste heat from a steelworks. Examples of waste heat from a steelworks include sensible heat from slag, coke oven gas (COG), and sintered ore. Low-temperature waste heat of around 200°C can also be used, so heating furnace gas or hot stove exhaust gas can be used directly as the heat source for the heat exchanger. Furthermore, if the raw material gas contains CO2, high-temperature CO and O2 are produced by electrolysis, and these can also be used as the heat source for the heat exchanger.

[0074] The oxygen compound gas used as the raw material gas is as described in [1-1] above, but a higher concentration of the oxygen compound is preferable. For example, the concentration of CO2 is not particularly limited, but is preferably 10% by volume or more from the viewpoint of electrolysis efficiency.

[0075] (Electrolysis section) The electrolysis unit has the laminate described in [1-1] above. As shown in Fig. 2, an oxygen compound gas, such as CO2 or HO, supplied as a raw material gas from the raw material gas supply unit is brought into contact with the cathode catalyst layer of the laminate described in [1] above, whereby electrolysis is carried out according to the above formulas (1) to (4), generating oxygen and by-product gases.

[0076] Here, the electrolysis unit is configured to apply a voltage to the stack of [1-1] above. For example, the anode catalyst layer and cathode catalyst layer of the stack are connected to a power source via a cable. The power source may be a DC power source or an AC power source. However, in the case of an AC power source, the AC power source must be converted to DC power using a converter or the like before current flows through the stack. The electrolysis unit may also have a casing (housing) to house the stack, various measuring instruments such as a voltmeter, a heater for the stack, and the like. The casing may also have a gas distribution (inlet) path for bringing the raw material gas into contact with the cathode catalyst layer of the stack, and a gas distribution (recovery) path for recovering by-product gas and oxygen generated by electrolysis.

[0077] (Oxygen recovery section and by-product gas recovery section) The oxygen recovery unit and the by-product gas recovery unit recover the oxygen and the by-product gas generated in the electrolysis unit, respectively. The oxygen recovery unit and the by-product gas recovery unit are each configured, for example, by gas flow channels adjacent to the anode catalyst layer and the cathode catalyst layer of the stack of the electrolysis unit. The gas flow channels are defined, for example, by a casing that houses the stack. The gas flow channels may also be configured by piping, ducts, or the like. Furthermore, the oxygen recovery unit and the by-product gas recovery unit may each have a device that pressurizes or sucks the oxygen and the by-product gas. Examples of such devices include a fan and a blower. The oxygen and the by-product gas generated in the electrolysis unit may be supplied, for example, to equipment or storage units that use the oxygen and the by-product gas, via the oxygen recovery unit and the by-product gas recovery unit, respectively.

[0078] (others) Additionally, a gas decomposition apparatus according to one embodiment of the present invention may include a sweep gas supply unit that supplies a sweep gas to the anode catalyst layer of the stack in the electrolysis unit. The sweep gas supply unit may be configured, for example, as a gas flow passage adjacent to the anode catalyst layer of the stack in the electrolysis unit. The gas flow passage may be defined, for example, by a casing that houses the stack. The gas flow passage may also be configured as a pipe or duct. The sweep gas supply unit may also include a device for pumping or sucking the sweep gas. Examples of such devices include a fan or a blower. Supplying a sweep gas to the anode catalyst layer can reduce the O2 partial pressure on the surface of the anode catalyst layer (hereinafter also referred to as O2 surface partial pressure), thereby increasing the O2 production rate. This is expected to improve reaction efficiency. For example, supplying air as a sweep gas can produce oxygen-enriched air, which can be used directly for combustion. The sweep gas is not particularly limited and may be an inert gas such as N2 or Ar. Furthermore, by absorbing O2, the surface partial pressure of O2 on the anode catalyst layer can be reduced.

[0079] Other than the above, there are no particular limitations, and a general configuration of a gas decomposition device using electrolysis can be appropriately adopted. [Example]

[0080] A laminate for electrolysis was prepared as follows.

[0081] <Electrolyte layer> The electrolyte layer is made of La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 A perovskite-type oxide with a composition of O3 was used. First, La2O3, SrCO3, Ga2O3, and MgO were mixed in an alumina mortar for 30 minutes in the molar ratios required to obtain the desired composition. The mixture was then placed in an alumina crucible, heated from room temperature to 1000°C over 5 hours, and fired at 1000°C for 6 hours. It was then cooled to room temperature over 5 hours. The resulting powder was mixed in a mortar for 30 minutes. The powder was then uniaxially molded into a 20 mm diameter disk at 20 MPa for 20 minutes. The molded body was then vacuum-packed in a rubber bag and isostatically pressed at 300 MPa for 30 minutes to obtain a pellet. The resulting pellet was then heated from room temperature to 1000°C over 5 hours, further heated to 1500°C over 5 hours, and fired at 1500°C for 6 hours. It was then cooled to 1000°C over 5 hours, further cooled to room temperature over 5 hours, and sintered. In this way, an electrolyte layer with a thickness of 0.3 mm was obtained.

[0082] <Materials for forming the anode catalyst layer> The anode catalyst layer is made of Ba 0.6 La 0.4 A perovskite-type oxide with a composition of CoO3 was used. First, the specified amounts of Ba(NO3)2, La(NO3)3·6H2O, and Co(NO3)2·6H2O were dissolved in water and evaporated to dryness. This was then fired at 400°C in a draft to decompose the nitrates into oxides. The resulting powder was then mixed in a mortar for 30 minutes. This powder was then placed in an alumina crucible and fired at 1200°C for 6 hours. The fired powder was then mixed in the mortar for 30 minutes to obtain the material for forming the anode catalyst layer.

[0083] <Cathode catalyst layer forming materials> The cathode catalyst layer is made of La 0.6 Sr 0.4 Fe 0.9 Mn 0.1 A mixture of perovskite oxide having a composition of O3 (hereinafter also referred to as LSFM) and CuFe2O4 (hereinafter also referred to as CFO) was used. Here, LSFM and CFO were mixed in a mortar for 30 minutes to obtain a material for forming a cathode catalyst layer.

[0084] <Formation of anode catalyst layer and cathode catalyst layer (screen printing method)> Using the anode catalyst layer forming material and cathode catalyst layer forming material obtained as described above, an anode catalyst layer was formed on one surface of the electrolyte layer by screen printing, and a cathode catalyst layer was formed on the other surface. Specifically, ethyl cellulose and the powdered material for forming the anode catalyst layer were mixed in an agate mortar at a mass ratio of 8:100. Similarly, ethyl cellulose and the powdered material for forming the cathode catalyst layer were mixed at a mass ratio of 8:100. Next, these mixtures were thoroughly mixed until an appropriate viscosity was achieved while adding an appropriate amount of 3-hydroxy-2,2,4-trimethylpentyl dropwise. The mixture was stirred for a predetermined time and then degassed. The resulting paste was applied to the electrolyte layer by screen printing. Screen printing was performed using a 200-mesh stainless steel mesh. The applied area was 8 mm diameter and the thickness was 5 to 10 μm. The electrolyte layer was then placed on an alumina boat and baked at 1100°C for 30 minutes. Simultaneously, platinum wires (0.1 mm diameter) were attached to the ends of the anode catalyst layer using platinum paste (reference electrode). In this manner, a laminate for electrolysis (hereinafter also referred to as laminate 1) was obtained. The LSFM content in the cathode catalyst layer of the laminate 1 was 50 mass %, and the CFO content was 50 mass %.

[0085] For comparison, a laminate (hereinafter also referred to as laminate 2) was prepared separately, in which the cathode catalyst layer was made of Ni-YSZ as disclosed in Patent Document 3. The Ni content in the cathode catalyst layer of laminate 2 was 50 mass %, and the YSZ content was 50 mass %.

[0086] Using the thus obtained stacks 1 and 2, gas decomposition devices as shown in Figure 2 were fabricated. Each of stacks 1 and 2 was sandwiched between an alumina tube and a Pyrex (registered trademark) glass ring from above and below, heated from room temperature to 800°C over two hours, and held at 800°C for one hour. After that, the Pyrex glass ring was softened and sealed with glass packing. This ensured flow paths for the source gas to stacks 1 and 2, as well as for oxygen and by-product gases.

[0087] Next, electrolysis of oxygen compound gas was carried out under the following conditions 1 and 2. ·Condition 1 Using the gas decomposition apparatus described above, a voltage was applied between the anode catalyst layer and the cathode catalyst layer from a power source. The voltage applied to the stack was 1.4 V, near the thermal self-sustaining potential. An oxygen compound gas consisting of 30% CO2 by volume, 30% H2O by volume, and the remainder Ar was supplied to the cathode catalyst layer at a flow rate of 100 ml / min from the raw gas supply unit. Air was supplied as a sweep gas to the anode catalyst layer at a flow rate of 100 ml / min from the sweep gas supply unit. In the gas decomposition apparatus using stack 1, electrolysis was performed at a stack temperature of 800°C. In the gas decomposition apparatus using stack 2, electrolysis was performed at a stack temperature of 700°C (the recommended temperature for stack 2). By-product gases, such as CO and H2, generated by the reduction of CO2 and H2O, respectively, during the electrolysis of the oxygen compound gas were recovered from the by-product gas recovery unit, and O2 was recovered from the oxygen gas recovery unit. The electrolysis time (total supply time of the raw material gas) was 8 hours in all cases. ·Condition 2 Electrolysis of oxygen compound gas was carried out under the same conditions as Condition 1, except that the oxygen compound gas used was a gas of CO2: 30 vol % / H2O: 30 vol % / H2S: 100 vol ppm / balance: Ar.

[0088] Then, the electrolysis efficiency and the resistance to sulfur degradation of electrolysis performance were evaluated in the following manner.

[0089] -Evaluation of electrolysis efficiency The electrolysis efficiency was evaluated according to the following criteria, based on the minimum current density (hereinafter also referred to as minimum current density) at a voltage of 1.4 V applied to the laminate under condition 2, and the volume ratio of CO to H produced in the by-product gas under condition 2 (volume of CO produced ÷ volume of H produced, hereinafter also referred to as volume ratio) (the volume of CO produced ÷ volume of H produced; hereinafter also referred to as volume ratio) (the volume of CO produced ÷ volume of H produced) under condition 2 (the volume of CO produced ÷ volume of H produced; hereinafter also referred to as volume ratio) The evaluation results are also shown in Table 1. Pass (Excellent): Minimum current density under condition 2 is -0.20 A / cm 2 or less, and the generated volume ratio under condition 2 is 0.20 or more Fail: Minimum current density under condition 2 is -0.20A / cm 2and / or the volume ratio of the product under condition 2 is less than 0.20 Here, the current density is an index of electrolysis efficiency, and the greater the absolute value of the current density, the greater the electrolysis efficiency. Note that the current density is negative during electrolysis, so the more negative (smaller) the current density, the better the electrolysis efficiency. In general, when comparing CO2 and HO, HO is easier to electrolyze, while CO2 is more difficult to electrolyze. Therefore, the closer the volume ratio of CO2 to HO contained in the feed gas, the better the electrolysis efficiency. Note that the volume ratio of CO2 to HO was determined by gas chromatography analysis.

[0090] -Sulfur degradation resistance of electrolysis performance The resistance to sulfur deterioration of electrolysis performance was evaluated based on the rate of decrease in the production volume ratio defined by the following formula, according to the following criteria. The evaluation results are also shown in Table 1. [Decrease in volume ratio (%)] = ([Volume ratio generated under condition 1] - [Volume ratio generated under condition 2]) ÷ [Volume ratio generated under condition 1] × 100 Pass (Excellent): The reduction in the volume ratio of the product is less than 50% Fail: The reduction in the volume ratio of the generated product is 50% or more.

[0091] [Table 1]

[0092] As shown in Table 1, the invention example was able to achieve both high electrolysis efficiency and excellent resistance to sulfur degradation of electrolysis performance.

[0093] On the other hand, in the comparative example, both the electrolysis efficiency and the resistance to sulfur degradation of electrolysis performance were not sufficient. This is thought to be because the electrolysis of H2O occurred preferentially.

[0094] Furthermore, when various perovskite-type oxides and spinel-type oxides were used in the cathode catalyst layer and their contents were varied within the range of 40 to 60 mass%, it was possible to achieve both high electrolysis efficiency and excellent resistance to sulfur degradation of electrolysis performance, as in the above-mentioned invention examples. [Explanation of symbols]

[0095] 1. Laminate 11 Anode catalyst layer 12 Electrolyte layer 13 Cathode catalyst layer 2. Gas decomposition unit 21 Electrolysis section 22 Raw material gas supply section 23 Sweep gas supply section 24 By-product gas recovery section 25 Oxygen recovery section 3 Power supply

Claims

1. A method for decomposing an oxygen compound gas, comprising: The method for decomposing the oxygen compound gas comprises: a supply step of supplying an oxygen compound gas as a raw material gas to a laminate including an electrolyte layer, an anode catalyst layer, and a cathode catalyst layer; A voltage is applied to the laminate, and O is produced from the oxygen compound gas by electrolysis. ２ and a by-product gas containing CO; The above O ２ an oxygen recovery step of recovering the a by-product gas recovery step of recovering the by-product gas; With The oxygen compound gas is CO ２ and a sulfur compound, the laminate has a structure in which the electrolyte layer is sandwiched between the anode catalyst layer and the cathode catalyst layer, The cathode catalyst layer is Perovskite oxides, or Perovskite-type oxides and spinel-type oxides, A method for decomposing oxygen compound gas.

2. 2. The method for decomposing oxygen compound gases according to claim 1, wherein the content of the spinel-type oxide in the cathode catalyst layer is 10 mass % or more.

3. 2. The method for decomposing oxygen compound gases according to claim 1, wherein the content of the perovskite-type oxide in the cathode catalyst layer is 40 to 60 mass %, and the content of the spinel-type oxide in the cathode catalyst layer is 40 to 60 mass %.

4. The perovskite oxide is La α Sr β Fe γ Mn δ O ３ and The spinel-type oxide is CuFe ２ O ４ 2. The method for decomposing oxygen compound gases according to claim 1, wherein Here, α, β, γ, and δ are 0 to 1, α+β is 1, and γ+δ is 1.

5. The perovskite oxide is La α Sr β Fe γ Mn δ O ３ and The spinel-type oxide is CuFe ２ O ４ 3. The method for decomposing oxygen compound gases according to claim 2, wherein Here, α, β, γ, and δ are 0 to 1, α+β is 1, and γ+δ is 1.

6. The perovskite oxide is La α Sr β Fe γ Mn δ O ３ and The spinel-type oxide is CuFe ２ O ４ 4. The method for decomposing oxygen compound gases according to claim 3, wherein Here, α, β, γ, and δ are 0 to 1, α+β is 1, and γ+δ is 1.

7. 7. The method for decomposing oxygen compound gases according to claim 1, wherein the electrolyte layer and the anode catalyst layer contain perovskite-type oxides.

8. 7. The method for decomposing oxygen compound gases according to claim 1, wherein the temperature at which the raw material gas is supplied is 100° C. or higher and 800° C. or lower.

9. 7. The method for decomposing oxygen compound gases according to claim 1, wherein the voltage applied in the electrolysis step is 0.6 V or more and 2.0 V or less.

10. A gas decomposition apparatus comprising: The gas decomposition device includes: a raw material gas supply unit that supplies an oxygen compound gas as a raw material gas; The oxygen compound gas supplied from the raw material gas supply unit is electrolyzed to produce O ２ and a by-product gas containing CO; The above O ２ an oxygen recovery unit that recovers a by-product gas recovery unit that recovers the by-product gas; With The oxygen compound gas is CO ２ and a sulfur compound, the electrolysis unit has a laminate including an electrolyte layer, an anode catalyst layer, and a cathode catalyst layer; the laminate has a structure in which the electrolyte layer is sandwiched between the anode catalyst layer and the cathode catalyst layer, The cathode catalyst layer is Perovskite oxides, or Perovskite-type oxides and spinel-type oxides, This is a gas decomposition device.

11. 11. The gas decomposition apparatus according to claim 10, wherein the content of the spinel-type oxide in the cathode catalyst layer is 10 mass % or more.

12. 11. The gas decomposition apparatus according to claim 10, wherein the content of the perovskite-type oxide in the cathode catalyst layer is 40 to 60 mass %, and the content of the spinel-type oxide in the cathode catalyst layer is 40 to 60 mass %.

13. The perovskite oxide is La α Sr β Fe γ Mn δ O ３ and The spinel-type oxide is CuFe ２ O ４ The gas decomposition apparatus according to claim 10, Here, α, β, γ, and δ are 0 to 1, α+β is 1, and γ+δ is 1.

14. The perovskite oxide is La α Sr β Fe γ Mn δ O ３ and The spinel-type oxide is CuFe ２ O ４ The gas decomposition apparatus according to claim 11, Here, α, β, γ, and δ are 0 to 1, α+β is 1, and γ+δ is 1.

15. The perovskite oxide is La α Sr β Fe γ Mn δ O ３ and The spinel-type oxide is CuFe ２ O ４ The gas decomposition apparatus according to claim 12, wherein Here, α, β, γ, and δ are 0 to 1, α+β is 1, and γ+δ is 1.

16. 16. The gas decomposition device according to claim 10, wherein the electrolyte layer and the anode catalyst layer contain a perovskite-type oxide.

17. The gas decomposition apparatus according to any one of claims 10 to 15, wherein the raw material gas supply section has a desulfurization device.

18. 16. The gas decomposition apparatus according to claim 10, wherein the raw material gas supply section has a preheating device.

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