Laminate, gas decomposition device, method for decomposing oxygen compound gas, and method for producing methanol

Abstract

Provided is a laminate capable of electrolyzing an oxygen compound gas represented by CO2 with high conversion efficiency and suppressing deterioration in electrolytic performance. In this laminate having a structure in which an electrolyte layer is sandwiched between an anode catalyst layer and a cathode catalyst layer, a perovskite oxide and CuFe2O4 are contained in the cathode catalyst layer, and the content of CuFe2O4 in the cathode catalyst layer is at least 10 mass%.

Description

Laminate, gas decomposition device, method for decomposing oxygen compound gas, and method for producing methanol

[0001] The present invention relates to a laminate, a gas decomposition device, a method for decomposing oxygen compound gases, and a method for producing methanol.

[0002] Due to the effects of global warming, oxygen compound gases, especially carbon dioxide (CO ２ ) emissions must be reduced urgently. ２ One of the methods to reduce CO emissions is CCS (carbon capture and storage). ２ Carbon dioxide capture and storage (geological) technology) is being considered. ２ There are many concerns about the safety of long-term storage of CO and the selection of appropriate sites. ２ However, this does not provide a fundamental solution to reducing CO2 emissions.

[0003] CO ２ Another method to reduce CO2 emissions is ２ Among them, CO ２ Electrolysis technology (hereinafter referred to as electrolysis technology) has been 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] Also, CO ２ Carbon monoxide (CO) generated by the electrolysis of CO can be used, for example, as energy in steel mills or as a raw material for chemical products such as methanol. In particular, the blast furnace process is used in the production of steel in steel mills. In this blast furnace process, iron ore is reduced by coal. Therefore, CO ２ In addition to CO, hydrogen (H ２ ) is also used as a raw material. Therefore, oxygen compound gas, especially CO ２ , and even CO ２ In addition to water vapor (H ２Therefore, it is very important to establish electrolysis technology for gases containing HCl.

[0005] As such an electrolysis technique, for example, Patent Document 1 discloses a CO ２ a voltage generator for applying a voltage between the electrodes; and a voltage generator for detecting CO in the gas. ２ CO concentration adjustment ２ Concentration adjusting means, CO ２ A cracking device is disclosed.

[0006] Furthermore, Patent Documents 2 and 3 disclose electrochemical cells equipped with an electrode containing Ni as a catalytic component of the cathode catalyst layer (fuel electrode), for example, an electrode containing nickel oxide as a main component, or an electrode containing Ni-containing cermet and a solid oxide.

[0007] Japanese Patent Publication No. 2006-205153 Japanese Patent No. 5910539 Japanese Patent No. 5637652

[0008] Here, in the technology of Patent Document 1, CO ２ By applying a high voltage of 10 kV or more to exhaust gas containing CO ２ However, the concentration of CO actually produced is between several hundred ppm and several thousand ppm. ２ The conversion efficiency from CO to CO is extremely low. In addition, a large area of ​​land is required to prepare an environment for using high voltage, and installation locations are limited. Furthermore, CO ２ In order to reduce the metal used in the cathode, it becomes necessary to replace it as it deteriorates, which increases costs.

[0009] Furthermore, when an electrode containing Ni is used as a catalytic component of the cathode catalyst layer (fuel electrode) as in the techniques of Patent Documents 2 and 3, Ni is reoxidized, which increases overvoltage and leads to deterioration of electrolysis performance.

[0010] The present invention has been developed in view of the above-mentioned circumstances, ２The present invention aims to provide a laminate that can electrolyze oxygen compound gases, such as those represented by the following, with high conversion efficiency and that can suppress deterioration of electrolysis performance. The present invention also aims to provide a gas decomposition device having the laminate, and a method for decomposing oxygen compound gases using the laminate. A further object of the present invention is to provide a method for producing methanol, in which methanol is synthesized using a by-product gas generated in the method for decomposing oxygen compound gases.

[0011] The oxygen compound gas is a gas containing an oxygen compound. The oxygen compound is a gaseous compound containing an oxygen atom as a part thereof. Examples of such oxygen compounds include CO ２ and H ２ Examples of such gases include O, NOx, and SOx. Hereinafter, the conversion efficiency of oxygen compound gases by electrolysis will also be referred to as "electrolysis efficiency." The degradation suppression property of electrolysis performance will also be referred to as "resistance to degradation of electrolysis performance." Furthermore, in this disclosure, any numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, respectively.

[0012] The inventors have conducted extensive research to achieve the above object, and as a result have found that the above object can be achieved by satisfying the following points in a laminate having a structure in which an electrolyte layer is sandwiched between an anode catalyst layer and a cathode catalyst layer: - The cathode catalyst layer contains a perovskite-type oxide and CuFe ２ O ４ CuFe in the cathode catalyst layer ２ O ４ The content of is 10 mass % or more.

[0013] The present invention has been completed based on the above findings and further investigations. That is, the gist and configuration of the present invention are as follows.

[0014] 1. A laminate comprising an electrolyte layer, an anode catalyst layer, and a cathode catalyst layer, wherein the laminate has a structure in which the electrolyte layer is sandwiched between the anode catalyst layer and the cathode catalyst layer, and the cathode catalyst layer is made of a perovskite-type oxide and CuFe２ O ４ and the CuFe in the cathode catalyst layer ２ O ４ The laminate has a content of 10% by mass or more.

[0015] 2. The content of the perovskite oxide in the cathode catalyst layer is 40 to 60 mass %, and the CuFe ２ O ４ 2. The laminate according to 1, wherein the content of

[0016] 3. The perovskite oxide is La α Sr β Fe γ Mn δ O ３ 3. The laminate according to 1 or 2 above, wherein α, β, γ and δ are each 0 to 1, α+β is 1, and γ+δ is 1.

[0017] 4. The laminate according to any one of 1 to 3 above, wherein the content of Ni oxide in the cathode catalyst layer is 0.5 mass % or less.

[0018] 5. The laminate according to any one of 1 to 4 above, wherein the electrolyte layer and the anode catalyst layer contain a perovskite-type oxide.

[0019] 6. A gas decomposition device comprising: a raw material gas supply unit that supplies an oxygen compound gas as a raw material gas; an electrolysis unit that generates oxygen and a by-product gas by electrolysis from the oxygen compound gas supplied from the raw material gas supply unit; an oxygen recovery unit that recovers the oxygen; and a by-product gas recovery unit that recovers the by-product gas, wherein the electrolysis unit has the laminate described in any one of 1 to 5 above.

[0020] 7. The gas decomposition apparatus according to 6 above, wherein the raw material gas supply section has a preheating device.

[0021] 8. A method for decomposing an oxygen compound gas, comprising: a supply step of supplying an oxygen compound gas as a raw material gas to the laminate described in any one of 1 to 5 above; an electrolysis step of applying a voltage to the laminate to generate oxygen and a by-product gas from the oxygen compound gas by electrolysis; an oxygen recovery step of recovering the oxygen; and a by-product gas recovery step of recovering the by-product gas.

[0022] 9. The oxygen compound gas is CO ２ 9. The method for decomposing an oxygen compound gas according to 8 above, wherein the by-product gas contains CO.

[0023] 10. The oxygen compound gas is CO ２ and H ２ and the by-product gas contains CO and H ２ 9. The method for decomposing oxygen compound gases according to 8 above, comprising:

[0024] 11. The method for decomposing an oxygen compound gas according to any one of 8 to 10 above, wherein the supply temperature of the oxygen compound gas is 100°C or higher and 800°C or lower.

[0025] 12. The method for decomposing oxygen compound gases according to any one of 8 to 11 above, wherein the voltage applied in the electrolysis step is 0.6 V or more and 2.0 V or less.

[0026] 13. A method for producing methanol, comprising synthesizing methanol using a by-product gas generated in the method for decomposing an oxygen compound gas according to any one of 8 to 12 above.

[0027] According to the present invention, a laminate for electrolysis can be obtained that can achieve both high electrolysis efficiency and excellent resistance to deterioration of electrolysis performance. Furthermore, the laminate of the present invention can achieve high electrolysis efficiency even when the applied voltage is relatively low, particularly 2 V or less, thereby suppressing the generation of Joule heat and being extremely advantageous from the viewpoint of effective energy utilization.

[0028] 1 is a schematic diagram showing an example of a stack according to one embodiment of the present invention; 2 is a schematic diagram showing an example of a gas decomposition device according to one embodiment of the present invention; 3 is a diagram showing the relationship between the minimum current density and the voltage applied to the stack for each mass ratio of LSFM to CFO in the cathode catalyst layer; and 4 is a diagram showing the relationship between the mass ratio of LSFM to CFO in the cathode catalyst layer and the minimum current density and the production volume ratio.

[0029] The present invention will be described based on the following embodiments: First, a laminate according to one embodiment of the present invention will be described.

[0030] [1] Stack As shown in Figure 1, a stack according to one embodiment of the present invention includes an electrolyte layer, an anode catalyst layer, and a cathode catalyst layer. The stack 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 stack can also be described as a stack in which an anode catalyst layer is stacked on one side of the electrolyte layer and a cathode catalyst layer is stacked on the side of the electrolyte layer opposite the side on which the anode catalyst layer is stacked. In Figure 1, reference numeral 1 denotes the stack, 11 denotes the anode catalyst layer, 12 denotes the electrolyte layer, 13 denotes the cathode catalyst layer, and 3 denotes a power source.

[0031] First, a stack according to one embodiment of the present invention was used to measure CO ２ CO and O ２ The principle of electrolysis will be explained below.

[0032] (CO ２ Principle of electrolysis) As shown in Figure 1, when a voltage is applied between the anode catalyst layer and the cathode catalyst layer of the laminate, CO ２ An oxygen compound gas containing CO is supplied to the laminate, particularly to the cathode catalyst layer, so that the CO contained in the oxygen compound gas is brought into contact with the laminate, particularly to the cathode catalyst layer. ２ CO and O ２ During this process, the following reactions occur in the cathode catalyst layer and the anode catalyst layer: Cathode catalyst layer: CO ２ +2e － →CO+O ２－ (1) Anode catalyst layer 2O ２－ →O ２ +4e－ (2)

[0033] That is, in the cathode catalyst layer, CO ２ The O generated in the cathode catalyst layer is converted to CO by the anode catalyst layer. ２－ diffuses through the electrolyte layer and reaches the anode catalyst layer, where the reaction of formula (2) above occurs. ２－ An electron is removed from O ２ occurs.

[0034] In addition, H ２ When O is electrolyzed, the following reactions occur in the cathode catalyst layer and the anode catalyst layer: Cathode catalyst layer: H ２ O + 2e － →H ２ +O ２－ (3) Anode catalyst layer 2O ２－ →O ２ +4e － (4)

[0035] Next, the electrolyte layer, anode catalyst layer, and cathode catalyst layer that constitute the laminate according to one embodiment of the present invention will be described.

[0036] (Electrolyte Layer) The electrolyte layer is formed by transferring oxygen from the cathode side to the anode side when a voltage is applied between the anode catalyst layer and the cathode catalyst layer. ２－In a laminate according to one embodiment of the present invention, the material of the electrolyte layer is not particularly limited, and common materials for electrolysis, such as spinel oxides and perovskite oxides, can be used. In particular, the electrolyte layer 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 may contain either a spinel oxide or a perovskite oxide alone. Alternatively, the electrolyte layer may contain both a spinel oxide and a perovskite oxide. When a spinel oxide and a perovskite oxide are simultaneously contained, 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. Note that the electrolyte layer may contain a remaining substance other than the spinel oxide and the perovskite oxide in a total amount of 10% by mass or less. Examples of the remaining substance include oxides other than the spinel oxide and the perovskite oxide, unavoidable impurities, and the like.

[0037] (Anode Catalyst Layer) The anode catalyst layer is formed on one side of the electrolyte layer, functions as an anode, and promotes the reactions shown in the above formulas (2) and (4). In the laminate according to one embodiment of the present invention, the anode catalyst layer is formed of a catalyst generally used for electrolysis, i.e., a catalyst that converts oxygen ions (O ２－ A highly active substance that quickly recombines hydrogen atoms (Cu) 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 ｎ CoO ３Here, 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 because this minimizes electrical resistance. The anode catalyst layer may contain a total of 10% by mass or less of residual substances other than perovskite oxides. Examples of residual substances include oxides other than perovskite oxides and unavoidable impurities. However, it is preferable that the content of Ni oxide is 0.5% by mass or less.

[0038] (Cathode catalyst layer) The cathode catalyst layer is formed on the electrolyte layer, on the opposite side of the anode catalyst layer. The cathode catalyst layer functions as a cathode and promotes the reactions shown in the above formulas (1) and (3). As described above, it is extremely important that the cathode catalyst layer of the laminate according to one embodiment of the present invention simultaneously satisfy the following requirements: - The cathode catalyst layer contains a perovskite-type oxide and CuFe ２ O ４ CuFe in the cathode catalyst layer ２ O ４ The content of is 10 mass % or more.

[0039] That is, as shown in FIG. 4, which plots data obtained from an example described later, the cathode catalyst layer contains a perovskite-type oxide and a spinel-type oxide, CuFe ２ O ４ and are simultaneously contained, and at that time, CuFe ２ O ４ By setting the content of CuFe to 10 mass % or more, it is possible to achieve both high electrolysis efficiency and excellent resistance to deterioration of electrolysis performance. The methods for evaluating the electrolysis efficiency and resistance to deterioration of electrolysis performance are as described in the examples below. ２ O ４ The content of CuFe is preferably 20 mass % or more, more preferably 30 mass % or more, and further preferably 40 mass % or more. ２ O ４ The content is preferably 95% by mass or less, more preferably 85% by mass or less, even more preferably 70% by mass or less, and still more preferably 60% by mass or less.

[0040] The content of the perovskite oxide is preferably 5% by mass or more, more preferably 15% by mass or more, even more preferably 30% by mass or more, and still more preferably 40% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and still more preferably 60% by mass or less.

[0041] In particular, the content of the perovskite oxide is 40 to 60 mass % and CuFe ２ O ４ By making the content of 40 to 60 mass %, it is possible to obtain a perovskite-type oxide alone and CuFe ２ O ４ This is extremely advantageous since it provides a higher electrolysis efficiency than when the cathode catalyst layer is formed alone.

[0042] The cathode catalyst layer contains perovskite oxide and CuFe ２ O ４ The remaining substances may be contained in an amount of 10 mass % or less in total. Examples of the remaining substances include CuFe ２ O ４ Examples of the oxides include spinel oxides other than those mentioned above, oxides other than perovskite and spinel oxides, and unavoidable impurities.

[0043] The perovskite oxide and CuFe contained in the cathode catalyst layer ２ O ４ Of the remaining substances other than the above, the content of Ni oxide is preferably 0.5 mass % or less. By reducing the content of Ni oxide in the cathode catalyst layer, it is possible to more effectively prevent the deterioration of electrolysis performance due to overvoltage. ２ and H ２ The generation of methane in the electrolysis of O can also be suppressed, and when methanol is synthesized using the by-product gas of the electrolysis, it becomes possible to produce methanol more efficiently. That is, in the electrolysis, a methanation reaction may occur as a side reaction of the electrolysis. In particular, in the cathode catalyst layer, ２When a component that improves the surface reaction activity by dissociating and adsorbing Ni is present, the methanation reaction becomes prominent. Here, if Ni oxide is contained in the cathode catalyst layer, a portion of the Ni oxide may be reduced to metallic Ni during the electrolysis process, thereby accelerating the methanation reaction. In the synthesis of methanol, a lower methane content in the feed gas enables more efficient methanol production. In other words, when methanol is synthesized using the by-product gas of the electrolysis, a lower Ni oxide content in the cathode catalyst layer is advantageous. Therefore, the Ni oxide content in the cathode catalyst layer is preferably 0.5% by mass or less, more preferably 0.1% by mass or less. The Ni oxide content in the cathode catalyst layer may be 0% by mass. Methanol synthesis may be performed, for example, by the Fischer-Tropsch reaction.

[0044] The content of unavoidable impurities in the cathode catalyst layer is preferably 1.0 mass% or less, more preferably 0.5 mass% or less, and even more preferably 0.1 mass% or less. The content of unavoidable impurities may be 0 mass% (the same applies to the content of unavoidable impurities in the electrolyte layer and the anode catalyst layer).

[0045] The perovskite oxide used in the cathode catalyst layer is not particularly limited, but may be La α Sr β Fe γ Mn δ O ３ Here, α, β, γ, and δ are 0 to 1, α+β is 1, and γ+δ is 1. It is more preferable that α is 0.5 to 1, and γ is 0.05 to 0.3.

[0046] 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 a mixture of perovskite-type oxide and a spinel-type oxide, CuFe ２ O ４ This makes it possible to more advantageously improve the electrolysis efficiency.

[0047] The electrolyte layer, anode catalyst layer, and cathode catalyst layer can be formed by, for example, 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.

[0048] A laminate according to one embodiment of the present invention can be formed, for example, by applying a metal oxide for the anode catalyst layer to one surface of a plate-shaped electrolyte layer and a metal oxide for the cathode catalyst layer to the other surface of the electrolyte layer, followed by firing. Alternatively, the laminate can be formed by processing the electrolyte layer into a cylindrical shape, applying a metal oxide for the cathode catalyst layer to the inner surface of the cylindrical electrolyte layer and a metal oxide for the anode catalyst layer to the outer surface of the cylindrical electrolyte layer, followed by firing.

[0049] Furthermore, the thickness ratio of the electrolyte layer, anode catalyst layer, and cathode catalyst layer is preferably 1:1, with the cathode catalyst layer being 0.5 to 5:10 to 50. If the electrolyte layer is too thin relative to the anode catalyst layer or the cathode catalyst layer, it may not be able to withstand thermal stress and may crack. On the other hand, if the electrolyte layer is too thick, Joule heat increases due to increased electrical resistance, which may reduce electrolysis efficiency.

[0050] Other than the above, there are no particular limitations, and a general configuration of a laminate for electrolysis can be appropriately adopted.

[0051] [2] Gas Decomposition Apparatus Next, a gas decomposition apparatus according to one embodiment of the present invention will be described.

[0052] As shown in Fig. 2, a gas decomposition apparatus according to one embodiment of the present invention comprises: a raw material gas supply unit that supplies an oxygen compound gas as a raw material gas; an electrolysis unit that generates oxygen and a by-product gas by electrolysis from the oxygen compound gas supplied from the raw material gas supply unit; an oxygen recovery unit that recovers the oxygen; and a by-product gas recovery unit that recovers the by-product gas, wherein the electrolysis unit has the laminate described in [1] above. In Fig. 2, reference numeral 1 denotes the laminate, 11 denotes an anode catalyst layer, 12 denotes an electrolyte layer, 13 denotes a cathode catalyst layer, 2 denotes a gas decomposition apparatus, 21 denotes the 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.

[0053] (Feedstock Gas Supply Unit) The feedstock gas supply unit supplies an oxygen compound gas serving as a feedstock gas to the electrolysis unit, preferably so that the oxygen compound gas comes into contact with the cathode catalyst layer of the stack. The feedstock gas supply unit is configured, for example, by a gas flow path adjacent to the cathode catalyst layer of the stack of the electrolysis unit described below. The gas flow path 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 path may also be configured by piping, ducts, or the like. Furthermore, the feedstock gas supply unit may have a device for pressure-feeding the feedstock gas. Examples of such devices include a fan and a blower. The feedstock gas supply unit may also include a device for preheating the feedstock gas or a CO ２ The feed gas preheating device and the oxygen compound separator / recovery device may be disposed, for example, in the gas flow passage. From the viewpoint of suppressing a decrease in the temperature of the feed gas, it is preferable to dispose the feed gas preheating device 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 feed gas preheating device include a burner and a heat exchanger that utilizes exhaust heat.

[0054] The heat source of the heat exchanger can be, for example, exhaust heat from a steelworks. Examples of the exhaust heat from a steelworks include sensible heat from slag, sensible heat from coke oven gas (COG), and sensible heat from sintered ore. Low-temperature exhaust heat of about 200°C can also be used, so that heating furnace gas and hot stove exhaust gas can be used directly as the heat source for the heat exchanger. In addition, when CO is added to the raw material gas, ２ When the catalyst contains CO and O, electrolysis produces CO and O at high temperature. ２ These may be used as the heat source for the heat exchanger.

[0055] The oxygen compound gas used as the raw material gas is CO ２ Preferably, the mixture contains CO ２ and H ２ It is more preferable that the oxygen compound gas contains both CO and O. ２ and H ２ When both Ar and N are contained, deterioration of the surface of the cathode catalyst layer is suppressed, contributing to a longer life of the equipment. The ratio of these gases may be set to any ratio depending on the source of the raw material gas, etc. In addition, the oxygen compound gas serving as the raw material gas may contain a remaining gas other than the oxygen compound. Examples of the remaining gas include Ar and N. ２ For example, blast furnace gas, a by-product of the steelmaking process, and combustion exhaust gas from hot stoves and heating furnaces contain CO ２ Since the blast furnace gas contains 10% by volume or more of CO, it is suitable as a raw material gas. ２ Gas obtained by treating it to increase its concentration can also be used. ２ A contained gas may also be used.

[0056] (Electrolysis Unit) The electrolysis unit has the laminate described in the above [1]. As shown in FIG. 2, an oxygen compound gas, for example, CO ２ and H ２ When O is brought into contact with the cathode catalyst layer of the laminate described in [1] above, it is electrolyzed according to the above formulas (1) to (4) to generate oxygen and by-product gases.

[0057] Here, the electrolysis unit is configured to apply a voltage to the stack of [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, it must be converted to a DC power source using a converter or the like before current flows through the stack. The electrolysis unit may also have a casing (housing) for housing the stack, various measuring instruments such as a voltmeter, and a heater for the stack. The casing may also have a gas flow (inlet) path for bringing the raw material gas into contact with the cathode catalyst layer of the stack, and a gas flow (recovery) path for recovering by-product gas and oxygen generated by electrolysis.

[0058] (Oxygen Recovery Section and By-Product Gas Recovery Section) The oxygen recovery section and the by-product gas recovery section recover the oxygen and the by-product gas generated in the electrolysis section, respectively. The oxygen recovery section and the by-product gas recovery section 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 section. 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, etc. Furthermore, the oxygen recovery section and the by-product gas recovery section may each have a device for pumping or sucking 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 section may be supplied, for example, to equipment or storage units that use the oxygen and the by-product gas, via the oxygen recovery section and the by-product gas recovery section, respectively.

[0059] (Others) In addition, the gas decomposition device according to one embodiment of the present invention may have a sweep gas supply unit that supplies a sweep gas to the anode catalyst layer of the stack of the electrolysis unit. The sweep gas supply unit is configured, for example, by a gas flow passage adjacent to the anode catalyst layer of the stack of the electrolysis unit. The gas flow passage is defined, for example, by a casing that houses the stack. The gas flow passage may also be configured by piping, ducts, etc. Furthermore, the sweep gas supply unit may have a device that pressurizes or sucks the sweep gas. Examples of such devices include a fan and a blower. By supplying a sweep gas to the anode catalyst layer, O on the surface of the anode catalyst layer is reduced. ２ Partial pressure (hereinafter, O ２ This can lower the surface partial pressure, ２ The production rate of increases. This is expected to improve the reaction efficiency. For example, by supplying air as a sweep gas, oxygen-enriched air can be produced, which can be used for combustion as it is. The sweep gas is not particularly limited, and N ２ Inert gases such as O and Ar may also be used. ２ By absorbing the O ２ The surface partial pressure can also be reduced.

[0060] Other than the above, there are no particular limitations, and a general configuration of a gas decomposition device using electrolysis can be appropriately adopted.

[0061] [3] Method for Decomposing Oxygen Compound Gas Next, a method for decomposing an oxygen compound gas according to one embodiment of the present invention will be described.

[0062] A method for decomposing an oxygen compound gas according to one embodiment of the present invention includes: a supply step of supplying an oxygen compound gas, which is a raw material gas, to the laminate of the above [1]; an electrolysis step of applying a voltage to the laminate of the above [1] to generate oxygen and a by-product gas from the oxygen compound gas by electrolysis; an oxygen recovery step of recovering the oxygen; and a by-product gas recovery step of recovering the by-product gas.

[0063] (Supply Step) In the supply step, an oxygen compound gas as a raw material gas is supplied to the laminate of the above [1]. 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 laminate of the above [1]. The oxygen compound gas as a raw material gas can be supplied, for example, via a gas flow passage such as a pipe or duct connected to a raw material gas supply source.

[0064] In addition, the supply temperature of the raw material gas to the stack of [1] 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 of [1] 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 (upstream of the stack) in the casing that houses the stack or immediately before the casing.

[0065] Furthermore, the source gas may be preheated in order to control the supply temperature of the source gas, as exemplified in the above [2].

[0066] Furthermore, as described in the above [2], the oxygen compound gas used as the raw material gas preferably has a high concentration. ２ The concentration of is not particularly limited, but is preferably 10% by volume or more in terms of electrolysis efficiency.

[0067] The gas delivered from the source gas source (hereinafter also referred to as the delivery gas) may be directly supplied as the source gas to the laminate of the above [1]. ２ or the like may be separated and recovered in advance, and the separated and recovered gas (hereinafter also referred to as separated and recovered gas) may be supplied to the laminate of the above [1] as a raw material gas. ２ The method for separating and recovering CO is not particularly limited. For example, ２ a method for liquefying or solidifying CO in a basic aqueous solution of caustic soda and an amine, ２After absorbing CO into activated carbon and zeolite, separation and recovery are performed by heating or reducing pressure. ２ and then separating and recovering the CO by heating or reducing pressure. ２ The CO in the separated and recovered gas is ２ The concentration is not particularly limited, but is preferably 80% by volume or more, which is advantageous because it allows the gas decomposition device, particularly the stack used during electrolysis, and the equipment associated with this stack to be made smaller.

[0068] Additionally, if desired, the feed gas may be pre-cleaned of harmful components such as sulfur and NOx.

[0069] (Electrolysis Step) In the electrolysis step, a voltage is applied to the laminate of the above [1], 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.

[0070] 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] 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 is more than 2.0 V, the CO ２ But solid carbon (C) and O ２ This makes it difficult to generate CO. Furthermore, Joule heat accumulates in the laminate, which may cause decomposition of the laminate itself.

[0071] It is also preferable to control the temperature of the laminate during electrolysis to 100° C. or higher and 900° C. or lower. That is, it is preferable to control the temperature of the laminate during electrolysis to 100° C. or higher and 900° C. or lower, taking into consideration Joule heat due to electrical resistance.

[0072] 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.

[0073] (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.

[0074] (Others) The method for decomposing oxygen compound gas 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 can be supplied, for example, through a gas flow channel adjacent to the anode catalyst layer of the electrolysis unit. The sweep gas is as described in [2] above.

[0075] 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 described in [2] above.

[0076] The conditions other than those mentioned above are not particularly limited, and may be those according to conventional methods.

[0077] [4] Method for Producing Methanol Next, a method for producing methanol according to one embodiment of the present invention will be described.

[0078] In a method for producing methanol according to one embodiment of the present invention, methanol is synthesized using a by-product gas generated in the method for decomposing an oxygen compound gas described above in [3].

[0079] The method for synthesizing methanol is not particularly limited and may be a conventional method. For example, the Fischer-Tropsch reaction may be used. As an example, the by-product gas generated in the electrolysis step of the oxygen compound gas decomposition method described in [3] above is compressed (pressurized) using a compressor. The pressure of the by-product gas after compression is preferably, for example, 1 MPa or more and 10 MPa or less. Next, the by-product gas is brought into contact with a methanol synthesis catalyst, for example, a catalyst using Cu—Zn oxide, to synthesize methanol. The temperature of the catalyst is preferably adjusted to, for example, 200° C. or more and 300° C. or less.

[0080] Example 1 A laminate was produced in the following manner.

[0081] <Electrolyte Layer> The electrolyte layer is ０．９ Sr ０．１ Ga ０．８ Mg ０．２ O ３ First, a perovskite oxide having a molar ratio of La to give a predetermined composition was used. ２ O ３ , SrCO ３ , Ga ２ O ３ and MgO were mixed in an alumina mortar for 30 minutes. 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 then mixed in a mortar for 30 minutes. The powder was then uniaxially pressed 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 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] <Material for forming anode catalyst layer> Ba ０．６ La ０．４ CoO ３First, a predetermined amount of Ba(NO ３ ) ２ , La(NO ３ ) ３ ・6H ２ O and Co(NO ３ ) ２ ・6H ２ O was 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 a material for forming an anode catalyst layer.

[0083] <Material for forming cathode catalyst layer> The cathode catalyst layer is ０．６ Sr ０．４ Fe ０．９ Mn ０．１ O ３ A perovskite oxide (hereinafter also referred to as LSFM) having the composition of CuFe ２ O ４ (hereinafter also referred to as CFO) were mixed at various mass ratios shown in Table 1. Here, LSFM and CFO at predetermined mass ratios were mixed in a mortar for 30 minutes to obtain materials 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 side of the electrolyte layer by screen printing, and a cathode catalyst layer was formed on the other side. Specifically, first, ethyl cellulose and the powdered anode catalyst layer forming material were mixed in an agate mortar so that the ratio was 8:100 (by mass). Similarly, ethyl cellulose and the powdered cathode catalyst layer forming material were mixed so that the ratio was 8:100 (by mass). Next, these mixtures were thoroughly mixed to an appropriate viscosity while adding an appropriate amount of 3-hydroxy-2,2,4-trimethylpentyl dropwise, and the mixture was stirred for a predetermined time and then degassed. The resulting paste was applied to the electrolyte layer by screen printing. Here, the 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. At the same time, a platinum wire (0.1 mm diameter) was attached to the end of the anode catalyst layer using platinum paste (reference electrode). In this way, a laminate for electrolysis was obtained.

[0085] Using the laminate thus obtained, a gas decomposition device as shown in Figure 2 was fabricated. The laminate 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 a glass packing. This ensured a flow path for the raw material gas to the laminate, as well as flow paths for oxygen and by-product gases. Next, various voltages were applied between the anode catalyst layer and the cathode catalyst layer by a power source, and an oxygen compound gas (30% by volume CO ) serving as the raw material gas was supplied from the raw material gas supply unit. ２ / 30% by volume H ２ O / 40% by volume Ar) was supplied to the cathode catalyst layer at a flow rate of 100 ml / min converted to standard conditions (0°C, 1 atm). Air was supplied as a sweep gas to the anode catalyst layer from the sweep gas supply unit at a flow rate of 100 ml / min converted to standard conditions (0°C, 1 atm). Electrolysis was carried out at 800°C in both cases, and CO２ The by-product gases such as CO generated by the reduction of ２ The electrolysis time (total supply time of the raw material gas) was 8 hours in all cases.

[0086] Then, the electrolysis efficiency and the resistance to deterioration of the electrolysis performance were evaluated in the following manner.

[0087] Evaluation of electrolysis efficiency The electrolysis efficiency is determined by the current density during electrolysis and the ratio of CO and H ２ The evaluation was based on the volume ratio of the generated current to the generated current. That is, the current density is an index of the electrolysis efficiency, and the higher the current density, the higher the electrolysis efficiency. Here, the evaluation was performed using the minimum current density when the voltage applied to the laminate was 1.6 V. Note that, since the current density becomes negative during electrolysis, it can be said that the more negative (smaller) the current density, the better the electrolysis efficiency. In addition, generally, CO ２ and H ２ Compare O to H ２ O is easier to electrolyze, and CO ２ Therefore, CO and H in the by-product gas are difficult to electrolyze. ２ The volume ratio of CO produced to H ２ (hereinafter also referred to as the volume ratio) ２ and H ２ The volume ratio of O (CO ２ Volume of ÷ H ２ The closer the ratio is to the volume of CO and H in the by-product gas, the better the electrolysis efficiency. ２ The volume ratio of the produced methyl methacrylate to the produced methyl methacrylate was determined by gas chromatography analysis.

[0088] From the above viewpoints, the electrolysis efficiency was evaluated according to the following criteria. The evaluation results are also shown in Table 1. For reference, FIG. 3 plots the relationship between the minimum current density and the voltage applied to the stack for Nos. 1 to 5 and 7. FIG. 4 plots the relationship between the mass ratio of LSFM to CFO in the cathode catalyst layer and the minimum current density and the generation volume ratio. Note that FIG. 4 shows data when the voltage applied to the stack was 1.6 V. A (pass, particularly excellent): Minimum current density was -1.10 A / cm ２ or less and the generated volume ratio is the reference volume ratio -0.80 or more B (pass, excellent): The minimum current density is -0.45 A / cm ２ or less and the generated volume ratio is the reference volume ratio -0.85 or more (excluding A) F (Fail): The minimum current density is -0.45 A / cm ２ and / or the generated volume ratio is less than the reference volume ratio - 0.85

[0089] - Deterioration Resistance of Electrolytic Performance The deterioration resistance of electrolytic performance was evaluated based on the degree of catalyst decomposition on the surfaces of the anode catalyst layer and the cathode catalyst layer of the laminate. Specifically, powder X-ray diffraction measurements were performed on the surfaces of the anode catalyst layer and the cathode catalyst layer before and after the above electrolysis. The sampling width was 2θ = 10 to 80°. The deterioration resistance of electrolytic performance was evaluated according to the following criteria: A (pass, excellent): No new peaks (peaks other than those confirmed in the spectrum obtained by powder X-ray diffraction measurement before electrolysis, hereinafter simply referred to as new peaks) were observed in the spectrum obtained by powder X-ray diffraction measurement after electrolysis in both the anode catalyst layer and the cathode catalyst layer. F (fail): A new peak was observed in at least one of the anode catalyst layer and the cathode catalyst layer.

[0090]

[0091] As shown in Table 1, the cathode catalyst layer contains LSFM, which is a perovskite-type oxide, and CuFe. ２ O ４ and CuFe in the cathode catalyst layer. ２ O ４In all of the invention examples in which the content of CuFe was 10 mass % or more, high electrolysis efficiency and excellent resistance to deterioration of electrolysis performance were achieved. ２ O ４ Inventive Examples Nos. 2 to 4, in which the content of the perovskite oxide was 40 to 60 mass %, and the content of the perovskite oxide was 40 to 60 mass %, all exhibited particularly excellent electrolysis efficiency.

[0092] On the other hand, in the comparative examples, at least one of the electrolysis efficiency and the resistance to deterioration of electrolysis performance was not sufficient.

[0093] In addition, various perovskite-type oxides and CuFe ２ O ４ Using CuFe ２ O ４ Even when the content was changed in various ways within a range of 10 mass % or more, similarly to the above-mentioned invention examples, high electrolysis efficiency and excellent resistance to deterioration of electrolysis performance could be achieved at the same time.

[0094] Example 2 An oxygen compound gas (50% by volume CO ) serving as a raw material gas was supplied from a raw material gas supply unit to a gas decomposition device using the No. 4 laminate of Example 1 (hereinafter also simply referred to as the No. 4 laminate) and a laminate (hereinafter also referred to as the Ni-YSZ laminate) having the same configuration as the No. 4 laminate except that Ni-YSZ (Ni content: over 10% by mass) was used for the cathode catalyst layer. ２ / 50% by volume H ２ O) was supplied to the cathode catalyst layer at a flow rate of 13,440 L / min converted to standard conditions (0°C, 1 atm). Air was supplied as a sweep gas to the anode catalyst layer from the sweep gas supply unit at a flow rate of 13,440 L / min converted to standard conditions (0°C, 1 atm). Electrolysis was carried out at 700°C in both cases, and CO ２ The by-product gases such as CO generated by the reduction of ２was recovered from the oxygen gas recovery section. The voltage applied to the laminate was 1.4 V in all cases, and the electrolysis time (total supply time of the raw material gas) was 8 hours in all cases. The amount of each component in the by-product gas produced per unit time was then measured. Furthermore, the by-product gases generated by the electrolysis were each recovered, dehumidified, and compressed, and then methanol was synthesized using the by-product gases, and the amount of methanol produced per unit time was measured. The measurement results are shown in Table 2. The pressure of the by-product gases after compression was 5 MPa in all cases.

[0095]

[0096] As shown in Table 2, when the Ni-YSZ laminate was used, methane was detected in the by-product gas, whereas when the No. 4 laminate was used, methane was not detected in the by-product gas, and the total amount of carbon monoxide and hydrogen produced (CO + H ２ ) was increased. When the laminate No. 4 was used, the amount of methanol produced was significantly increased compared to when the Ni-YSZ laminate was used.

[0097] REFERENCE SIGNS LIST 1 laminate 11 anode catalyst layer 12 electrolyte layer 13 cathode catalyst layer 2 gas decomposition device 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 source

Claims

1. A laminate comprising an electrolyte layer, an anode catalyst layer, and a cathode catalyst layer, wherein the laminate has a structure in which the electrolyte layer is sandwiched between the anode catalyst layer and the cathode catalyst layer, and the cathode catalyst layer is made of a perovskite-type oxide and CuFe ２ O ４ and the CuFe in the cathode catalyst layer ２ O ４ The laminate has a content of 10% by mass or more.

2. The content of the perovskite oxide in the cathode catalyst layer is 40 to 60 mass %, and the CuFe ２ O ４ The laminate according to claim 1, wherein the content of 3. The perovskite oxide is La α Sr β Fe γ Mn δ O ３ 3. The laminate according to claim 1, wherein α, β, γ, and δ are each 0 to 1, α+β is 1, and γ+δ is 1.

4. The laminate according to any one of claims 1 to 3, wherein the content of Ni oxide in the cathode catalyst layer is 0.5 mass % or less.

5. The laminate according to any one of claims 1 to 4, wherein the electrolyte layer and the anode catalyst layer contain a perovskite-type oxide.

6. A gas decomposition device comprising: a raw material gas supply unit that supplies an oxygen compound gas as a raw material gas; an electrolysis unit that generates oxygen and a by-product gas by electrolysis from the oxygen compound gas supplied from the raw material gas supply unit; an oxygen recovery unit that recovers the oxygen; and a by-product gas recovery unit that recovers the by-product gas, wherein the electrolysis unit has the laminate according to any one of claims 1 to 5.

7. The gas decomposition apparatus according to claim 6, wherein the raw material gas supply section has a preheating device.

8. A method for decomposing an oxygen compound gas, comprising: a supply step of supplying an oxygen compound gas, which is a raw material gas, to the laminate according to any one of claims 1 to 5; an electrolysis step of applying a voltage to the laminate to generate oxygen and a by-product gas from the oxygen compound gas by electrolysis; an oxygen recovery step of recovering the oxygen; and a by-product gas recovery step of recovering the by-product gas.

9. The oxygen compound gas is CO ２ and the by-product gas contains CO.

10. The oxygen compound gas is CO ２ and H ２ and the by-product gas contains CO and H ２ The method for decomposing oxygen compound gases according to claim 8, comprising:

11. The method for decomposing oxygen compound gases according to any one of claims 8 to 10, wherein the supply temperature of the oxygen compound gases is 100°C or higher and 800°C or lower.

12. The method for decomposing oxygen compound gases according to any one of claims 8 to 11, wherein the voltage applied in the electrolysis step is 0.6 V or more and 2.0 V or less.

13. A method for producing methanol, which comprises synthesizing methanol using a by-product gas generated in the method for decomposing an oxygen compound gas according to any one of claims 8 to 12.

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