Oxygen-containing hydrocarbon production system, production method and operation method thereof

Abstract

To provide, as an oxygen-containing hydrocarbon production system for synthesizing oxygen-containing hydrocarbons using water and carbon dioxide as raw materials, an oxygen-containing hydrocarbon production system capable of producing oxygen-containing hydrocarbons by securing hydrogen and carbon monoxide necessary for the synthesis of oxygen-containing hydrocarbons.SOLUTION: Provided is an oxygen-containing hydrocarbon production system 100 for producing oxygen-containing hydrocarbons from at least water and carbon dioxide and having at least an electrolysis reaction part 10, a reverse water gas shift reaction part 20 and an oxygen-containing hydrocarbon synthesis reaction part 40.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a system for producing oxygen-containing hydrocarbons, such as methanol, from at least water and carbon dioxide, and to a production method and an operation method of the oxygen-containing hydrocarbon production system. [Background technology]

[0002] This type of oxygen-containing hydrocarbon production system is disclosed in Patent Documents 1 and 2. The system disclosed in Patent Document 1 includes a synthesis gas generator equipped with a solid oxide electrolysis device that performs electrical reduction of water vapor and carbon dioxide, and a fuel synthesizer that uses the synthesis gas generated in the synthesis gas generator to synthesize fuels such as methanol, and is equipped with a mechanism that branches off from a supply path for supplying synthesis gas from the synthesis gas generator to the fuel synthesizer, and circulates a portion of the generated synthesis gas to an inlet of the synthesis gas generator at a desired flow rate and ratio.

[0003] On the other hand, Patent Document 2 discloses a system including a steam electrolysis device that produces hydrogen by electrolyzing water vapor at high temperature, a carbon dioxide electrolysis device that produces carbon monoxide by electrolyzing carbon dioxide at high temperature, and a methanol synthesis device that synthesizes methanol using the hydrogen and carbon monoxide produced by the electrolysis device and the carbon monoxide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-152219 A [Patent Document 2] JP 2017-178810 A Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 discloses an electrolysis reaction section that performs so-called co-electrolysis, in which water vapor and carbon dioxide are both electrolyzed to obtain hydrogen and carbon monoxide (CO), but because the composition of the synthesis gas (mixed gas of hydrogen and CO) obtained from the electrolysis reaction section is unlikely to be suitable for, for example, methanol synthesis, the outlet gas of the electrolysis reaction section is circulated to the inlet of the electrolysis reaction section. However, there is no description of the specific conditions under which the outlet gas of the electrolysis reaction section should be circulated to the inlet of the electrolysis reaction section.

[0006] In Patent Document 2, an electrolysis reaction unit that electrolyzes water vapor to obtain hydrogen and an electrolysis reaction unit that electrolyzes carbon dioxide to obtain carbon monoxide (CO) are separately provided, and the hydrogen and CO obtained from each reaction unit are mixed to synthesize methanol.

[0007] As described above, when attempting to obtain a mixed gas of hydrogen and CO through an electrolytic reaction, which is necessary for producing oxygen-containing hydrocarbons such as methanol, it is difficult to adjust the ratio of hydrogen and CO. This necessitates measures such as dividing the electrolytic reaction section into two or configuring the electrolytic reaction gas to circulate, resulting in issues such as higher system costs and a larger system size.

[0008] In view of this situation, a main object of the present invention is to provide a compact, highly efficient, and low-cost oxygen-containing hydrocarbon production system that synthesizes oxygen-containing hydrocarbons using water and carbon dioxide as raw materials, which is capable of producing oxygen-containing hydrocarbons by securing the hydrogen and carbon monoxide necessary for the synthesis of oxygen-containing hydrocarbons in a simple manner. [Means for solving the problem]

[0009] The first characteristic configuration of the present invention is as follows: The oxygen-containing hydrocarbon production system produces oxygen-containing hydrocarbons from at least water and carbon dioxide, and comprises at least an electrolysis reaction section, a reverse water gas shift reaction section, and an oxygen-containing hydrocarbon synthesis reaction section.

[0010] This oxygen-containing hydrocarbon production system includes an electrolysis reaction section, a reverse water gas shift reaction section, and an oxygen-containing hydrocarbon synthesis reaction section. In this configuration, the spatial positional relationship between each section is not important, but at least with regard to the gas transport between these sections, it is sufficient that the gas decomposed in the electrolysis reaction section is transported to the reverse water gas shift reaction section, and the hydrogen and carbon monoxide obtained through the reaction in this section are transported to the oxygen-containing hydrocarbon synthesis reaction section, where oxygen-containing hydrocarbons such as methanol and dimethyl ether (DME) are synthesized.

[0011] That is, the electrolysis reaction section decomposes the gas supplied to this section to obtain at least hydrogen. The reverse water gas shift reaction section produces carbon monoxide from carbon dioxide, and this reaction produces the carbon monoxide required for the synthesis of oxygen-containing hydrocarbons in the oxygen-containing hydrocarbon synthesis reaction section. As a result, oxygen-containing hydrocarbons can be efficiently produced in the oxygen-containing hydrocarbon synthesis reaction section by using the carbon monoxide produced in the reverse water gas shift reaction section in addition to the hydrogen produced in the electrolysis reaction section.

[0012] Therefore, even if carbon monoxide is not produced well in the electrolytic reaction section, a sufficient amount of carbon monoxide can be secured by providing the reverse water gas shift reaction section.

[0013] In addition, the electrolysis reaction section is a high-temperature reaction, but the efficiency of the system can be improved by combining the reverse water gas shift reaction section, which is an endothermic reaction, with the electrolysis reaction section.

[0014] A second characteristic feature of the present invention is that the oxygen-containing hydrocarbon is methanol.

[0015] According to this characteristic configuration, methanol, which is useful as a chemical raw material, etc., can be obtained with high system efficiency from at least water and carbon dioxide using a system having at least an electrolysis reaction section, a reverse water gas shift reaction section, and an oxygen-containing hydrocarbon synthesis reaction section.

[0016] A third characteristic feature of the present invention is that an electrolysis reaction of water takes place in the electrolysis reaction section.

[0017] According to this characteristic configuration, hydrogen required in the oxygen-containing hydrocarbon synthesis reaction section can be obtained by electrolysis of at least one of water and water vapor.

[0018] A fourth characteristic configuration of the present invention is that a co-electrolytic reaction of water and carbon dioxide takes place in the electrolytic reaction section.

[0019] According to this characteristic configuration, hydrogen and a certain amount of carbon monoxide can be obtained by decomposing both water and carbon dioxide in the electrolytic reaction section. As described above, co-electrolysis mainly contributes to the supply of hydrogen, but in the oxygen-containing hydrocarbon production system according to the present invention, by providing a reverse water gas shift reaction section downstream of the electrolytic reaction section, carbon monoxide that tends to be insufficient can be supplemented by this reverse water gas shift reaction section. Furthermore, when co-electrolysis is performed in the electrolytic reaction section, the gas flowing in from the electrolytic reaction section contains water, hydrogen, carbon dioxide, and carbon monoxide, and therefore the reverse water gas shift reaction can be caused almost directly.

[0020] The fifth characteristic configuration of the present invention is as follows: The reverse water gas shift reaction section has a reverse water gas shift catalyst containing at least a metal oxide and an active metal component.

[0021] According to this characteristic feature, a catalyst containing at least a metal oxide and an active metal component can be used as a reverse water gas shift catalyst to cause a reverse water gas shift reaction. For example, an impregnated product obtained by impregnating a metal oxide as a carrier with an active metal component can be disposed in the reverse water gas shift reaction section as the reverse water gas shift catalyst. This is the twelfth characteristic feature of the present invention. A catalyst in which an active metal component is supported on a metal oxide support can be easily produced by, for example, immersing the metal oxide support in a solution in which the active metal component is dissolved, and is therefore preferable because the concentrations of the metal oxide support and the active metal component in the catalyst can be well controlled.

[0022] Here, in order to obtain this type of catalyst (reverse water gas shift catalyst), it is preferable to manufacture it through a calcination process in which the catalyst is calcined at a temperature of 450°C or higher. It is more preferable to set the temperature at 600°C or higher, or 800°C or higher. This is because this catalyst can advance its equilibrium reaction to the reverse water gas shift reaction side, which is the object of the present invention, in a high temperature range, so it is necessary to use it at a high temperature side and also requires high temperature resistance. For example, even when combined with a solid oxide electrolysis cell used in a relatively high temperature range (for example, 600°C to 800°C), the catalyst can be used stably. In addition, if the calcination temperature is too high, the cost of the calcination process becomes too high, so the upper limit is about 1200°C.

[0023] In addition, it is preferable to use the product after carrying out a reduction pretreatment. The catalyst obtained through the calcination step as described above has at least a part of the catalytically active components in an oxidized state, and may not be able to fully exhibit its activity. Therefore, the reduction pretreatment is performed to reduce the catalytically active components in an oxidized state, thereby enabling the catalyst to fully exhibit its activity.

[0024] Therefore, as for the operating method of the oxygen-containing hydrocarbon production system described above, it is preferable to operate the system after subjecting the reverse water gas shift reactor to a reduction pretreatment. This is the fourteenth characteristic configuration of the present invention.

[0025] Furthermore, by applying the catalyst (reverse water gas shift catalyst) obtained in this manner to the surface of a metal support, for example, it is possible to cause a reverse water gas shift reaction in gas flowing in contact with the applied surface.

[0026] The sixth characteristic configuration of the present invention is The reverse water gas shift catalyst is a reverse water gas shift catalyst containing at least one of nickel and iron as the active metal component.

[0027] According to this characteristic configuration, by containing either or both of nickel and iron as active metal components, the catalyst becomes highly active at relatively high temperatures, as will be described later with reference to Tables 1, 2, 3, and 4. The catalyst performance of this composition was comparable to that of platinum, an expensive precious metal, as a catalytically active component.

[0028] When either or both of nickel and iron are used as the catalytically active components, the cost per unit weight can be reduced to 1 / 1000 or less compared to platinum, and this is preferable because it allows the cost to be reduced or, when the same cost is required, the amount of catalyst used can be increased significantly.

[0029] It is preferable to use a ceria-based metal oxide or a zirconia-based metal oxide as the support, since this makes it easier to ensure resistance in high temperature ranges.

[0030] In the present invention, a reverse water gas shift reaction section is provided downstream of the electrolytic reaction section (the side to which the gas generated in the electrolytic reaction section flows). By using a ceria-based metal oxide or a zirconia-based metal oxide as the support for the reverse water gas shift catalyst, the thermal expansion coefficient can be made close to that of the material constituting the electrolytic reaction section, so that reactions can be smoothly generated in both sections in approximately the same high temperature range.

[0031] For example, in order to obtain this reverse water gas shift catalyst, a support mainly composed of a ceria-based metal oxide or a zirconia-based metal oxide is added to a solution containing either or both of nickel and iron, and an impregnation / support process is at least carried out to impregnate and support at least either or both of nickel and iron on the support, thereby producing the reverse water gas shift catalyst.

[0032] The seventh characteristic configuration of the present invention is The oxygen-containing hydrocarbon synthesis reaction section has an oxygen-containing hydrocarbon synthesis catalyst containing at least a metal oxide and an active metal component.

[0033] According to this characteristic configuration, a catalyst containing at least a metal oxide and an active metal component can be used as an oxygen-containing hydrocarbon synthesis catalyst to cause an oxygen-containing hydrocarbon synthesis reaction. For example, a catalyst obtained by forming a precipitate containing a desired metal component by a coprecipitation method can be placed in the oxygen-containing hydrocarbon synthesis reaction section as the oxygen-containing hydrocarbon synthesis catalyst. This is the thirteenth characteristic configuration of the present invention. In such a catalyst, since a precipitate can be obtained using a plurality of solutions containing different kinds and concentrations of metal components as metal oxides and active metal components, a precipitate with a desired metal content can be easily produced. Therefore, it is preferable that the concentrations of the metal oxides and active metal components in the catalyst can be well controlled.

[0034] Here, in order to obtain this type of catalyst (oxygen-containing hydrocarbon synthesis catalyst), it is preferable to produce it through a calcination step in which the precipitate is calcined.

[0035] In addition, it is preferable to use the product after carrying out a reduction pretreatment. The catalyst obtained through the calcination step as described above has at least a part of the catalytically active components in an oxidized state, and may not be able to fully exhibit its activity. Therefore, the reduction pretreatment is performed to reduce the catalytically active components in an oxidized state, thereby enabling the catalyst to fully exhibit its activity.

[0036] Therefore, as for the operating method of the oxygen-containing hydrocarbon production system explained so far, it is preferable to operate the system after carrying out a reduction pretreatment in the oxygen-containing hydrocarbon synthesis reaction section. This is the fifteenth characteristic configuration of the present invention.

[0037] Furthermore, the catalyst (oxygen-containing hydrocarbon synthesis catalyst) obtained in this manner can be applied to the surface of a metal support, for example, to cause a synthesis reaction of oxygen-containing hydrocarbons in a gas flowing in contact with the applied surface.

[0038] The eighth characteristic configuration of the present invention is as follows: The active metal component contains at least copper.

[0039] According to this characteristic feature, as will be described later, oxygen-containing hydrocarbons can be synthesized with high activity.

[0040] The ninth characteristic configuration of the present invention is The electrolytic reaction section has an electrolytic cell in which at least an electrode layer, an electrolyte layer and a counter electrode layer are formed on a support.

[0041] According to this characteristic configuration, the electrolytic cell used in the electrolytic reaction section is provided with, for example, a thin-film electrode layer, an electrolyte layer, and a counter electrode layer on a sturdy support that is thin but has sufficient strength, thereby making it possible to effectively cause an electrolytic reaction while reducing the amount of material used to constitute these layers that make up the electrolytic cell. As a result, it is possible to configure an electrolytic cell unit that is compact, has high performance, and is strong and reliable. Metals and ceramics can be selected as materials for this type of support.

[0042] The tenth characteristic configuration of the present invention is as follows: The support is made of a metal.

[0043] By using metal as the support, material costs can be reduced by ensuring strength using inexpensive metal materials, and it is easier to process than ceramics.

[0044] The eleventh characteristic configuration of the present invention is The reverse water gas shift reactor is incorporated inside the electrolysis reactor.

[0045] According to this characteristic configuration, the reaction heat required for the reverse water gas shift reaction, which is an endothermic reaction, can be generated by utilizing the exhaust heat of the electrolysis reaction section, so that a highly efficient system for producing oxygen-containing hydrocarbons can be obtained and the system can also be made compact. [Brief description of the drawings]

[0046] [Figure 1] FIG. 1 shows the configuration of an oxygen-containing hydrocarbon production system. [Diagram 2] Schematic diagram showing the configuration of the electrolytic reaction section [Diagram 3] FIG. 1 shows the configuration of a system that integrates an electrolysis reactor and a reverse water gas shift reactor. [Figure 4] Schematic diagram of an electrolysis cell unit equipped with an electrolysis reactor and a reverse water gas shift reactor. [Diagram 5] Cross-sectional view of the electrolysis cell unit used in a comparison experiment in which the electrode layer side gas supply channel was used as a reverse water-gas shift reactor. [Figure 6] A diagram showing the configuration of a system equipped with a heat exchanger between the electrolysis reactor and the reverse water gas shift reactor. [Figure 7] A diagram showing another configuration of a system for producing oxygen-containing hydrocarbons in which CO2 is introduced into a reverse water gas shift reaction section. [Figure 8] FIG. 1 is a diagram showing another configuration of an oxygen-containing hydrocarbon production system equipped with a hydrogen separation unit. [Figure 9] FIG. 13 is a diagram showing yet another configuration of the oxygen-containing hydrocarbon production system in which only water is introduced into the electrolysis reaction section. [Figure 10] An explanatory diagram showing the preparation state of the catalyst [Figure 11] An explanatory diagram showing the catalyst coating and calcination state and pre-reduction treatment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of one embodiment of a system 100 for producing oxygen-containing hydrocarbons proposed by the present inventors.

[0048] As shown in the figure, this oxygen-containing hydrocarbon production system 100 is configured to include, in order, an electrolytic reaction section 10, a first catalytic reaction section 20, a water separation section 30 (illustrated as an H2O separation section), a second catalytic reaction section 40, and a carbon dioxide separation section 50 (illustrated as a CO2 separation section).

[0049] The electrolytic reaction section 10 is a section for electrolyzing at least a part of the inflowing gas, the first catalytic reaction section 20 is a reverse water-gas shift reaction section for performing a reverse water-gas shift reaction on at least a part of the inflowing gas, and the second catalytic reaction section 40 is configured to function as an oxygen-containing hydrocarbon synthesis reaction section for synthesizing at least a part of the inflowing gas into oxygen-containing hydrocarbons. The oxygen-containing hydrocarbons synthesized here are mainly methanol, but dimethyl ether (DME) and the like can also be synthesized by including a dehydration process.

[0050] The water separation unit 30 and the carbon dioxide separation unit 50 are units that remove at least a portion of predetermined components (H2O, CO2, in that order) from the gas flowing inside. The components removed and recovered by the water separation unit 30 and the carbon dioxide separation unit 50 are returned to predetermined parts of the system via the water return path 31 and the carbon dioxide return path 51, as shown in Fig. 1, and are reused. The H2O and CO2 returned via these return paths 31, 51 are shown above each other. As a result, the oxygen-containing hydrocarbon production system 100 is established as a carbon-closed system in which CO2 is not substantially released outside the system.

[0051] In the figure, the gases flowing into each part are shown before each part, and the gases discharged from each part are shown after each part.

[0052] In the electrolysis reaction section 10, H2O and CO2 as starting materials are flowed in and electrolyzed therein, whereby H2O is decomposed into H2 and O2, and a part of CO2 is decomposed into CO and O2 and released.

[0053] The reaction is described as follows: 2H2O→2H2+O2 (formula 1) 2CO2→2CO+O2 (formula 2) These formulas 1 and 2 are also shown in the box representing the electrolytic reaction section 10 in FIG.

[0054] In the first catalytic reaction section 20 (reverse water-gas shift reaction section), H2 and CO2 are introduced and a reverse water-gas shift reaction occurs therein, whereby CO2 becomes CO and H2 becomes H2O, which are then released.

[0055] The reaction is written as the following equilibrium reaction, but the reverse water gas shift reaction is a reaction in which the reaction described in equation 3 below proceeds to the right (in the direction in which CO2 and H2 react to produce CO and HO). CO2+H2⇔CO+H2O (Formula 3) This formula 3 is also shown in the box representing the first catalytic reaction section 20 (reverse water gas shift reaction section) in Fig. 1. The reverse water gas shift catalyst cat1 used in the reaction is also shown diagrammatically in this box.

[0056] The H2O produced in the water separation section 30 is separated and returned to the upstream side of the electrolysis reaction section 10 via a water return line 31 (water recycle line).

[0057] In the second catalytic reaction section 40 (oxygen-containing hydrocarbon synthesis reaction section), at least H2 and CO are flowed in, and oxygen-containing hydrocarbons are synthesized by catalytic reaction. For example, the reaction in which methanol (CH3OH) is synthesized from CO and H2 is described as the following equilibrium reaction, but the reaction in which methanol (CH3OH) is synthesized from CO and H2 is a reaction in which the reaction described in the following formula 4 proceeds to the right (a reaction in which CO and H2 react to produce CH3OH). CO+2H2⇔CH3OH (Formula 4) This formula 4 is also shown in the box representing the second catalytic reaction section 40 (oxygen-containing hydrocarbon synthesis reaction section) in FIG. In addition, the equilibrium reaction of (Equation 3) may also occur at this site.

[0058] The CO2 produced in the carbon dioxide separation section 50 is separated and returned to the upstream side of the electrolysis reaction section 10 via a carbon dioxide return path 51 (carbon dioxide recycle line).

[0059] As a result, in the oxygen-containing hydrocarbon production system 100, oxygen-containing hydrocarbons are finally synthesized and can be supplied to the outside.

[0060] The above is an overview of the oxygen-containing hydrocarbon production system 100. The configuration and role of each part will be described below. [Electrolytic reaction section] As described above, the electrolytic reaction section 10 consumes the power supplied in accordance with the above formulas 1 and 2 to decompose the inflowing H2O and CO2.

[0061] FIG. 2 shows a schematic cross-sectional configuration of the electrolytic reaction section 10. As shown in FIG. The figure shows an electrolysis cell unit U in which a plurality of units are stacked to form an electrolysis stack (not shown), and this electrolysis cell unit U includes an electrolysis cell 1, which includes an electrode layer 2 on one surface of an electrolyte layer 1a and a counter electrode layer 3 on the other surface. The electrode layer 2 serves as the cathode in the electrolysis cell 1, and the counter electrode layer 3 serves as the anode. Incidentally, this electrolysis cell unit U is supported by a metal support 4. Note that here, an example is shown in which a solid oxide electrolysis cell is used as the electrolysis cell 1.

[0062] The electrolyte layer 1a can be formed in a thin film state with a thickness of 10 μm or less. The constituent material thereof can be YSZ (yttria-stabilized zirconia), SSZ (scandia-stabilized zirconia), GDC (gadolinium-doped ceria), YDC (yttrium-doped ceria), SDC (samarium-doped ceria), LSGM (strontium-magnesium-doped lanthanum gallate), etc. In particular, zirconia-based ceramics are preferably used.

[0063] The electrolyte layer 1a is preferably formed by a low-temperature firing method (for example, a wet method using firing in a low-temperature range without firing in a high-temperature range exceeding 1100°C), a spray coating method (such as a thermal spray method, an aerosol deposition method, an aerosol gas deposition method, a powder jet deposition method, a particle jet deposition method, or a cold spray method), a PVD method (such as a sputtering method or a pulse laser deposition method), or a CVD method. By using these film formation processes that can be used in a low-temperature range, it is possible to obtain an electrolyte layer 1a that is dense and has high airtightness and gas barrier properties without firing in a high-temperature range exceeding 1100°C. Therefore, damage to the metal support 4 can be suppressed, and the interdiffusion of elements between the metal support 4 and the electrode layer 2 can be suppressed, thereby realizing an electrolysis cell unit U with excellent performance and durability. In particular, it is preferable to use a low-temperature firing method or a spray coating method, since it is possible to realize a low-cost element. Furthermore, the use of a spray coating method is more preferable because it makes it easy to obtain an electrolyte layer 1a that is dense and has high airtightness and gas barrier properties in a low temperature range.

[0064] In addition, the electrolyte layer 1a is densely constructed in order to block gas leakage and to exhibit high ion conductivity. The density of the electrolyte layer 1a is preferably 90% or more, more preferably 95% or more, and even more preferably 98% or more. When the electrolyte layer 1a is a uniform layer, the density is preferably 95% or more, and more preferably 98% or more. When the electrolyte layer 1a is constructed in a multi-layered form, it is preferable that at least a part of the electrolyte layer 1a includes a layer (dense electrolyte layer) having a density of 98% or more, and more preferably includes a layer (dense electrolyte layer) having a density of 99% or more. When such a dense electrolyte layer is included in a part of the electrolyte layer 1a, it is easy to form an electrolyte layer 1a that is dense, airtight, and has high gas barrier properties, even when the electrolyte layer 1a is constructed in a multi-layered form.

[0065] The electrode layer 2 can be provided in a thin layer state on a region on the front side of the metal support 4 that is larger than the region where the holes 4a are provided. When the electrode layer 2 is provided as a thin layer, the thickness can be, for example, about 1 μm to 100 μm, preferably 5 μm to 50 μm. With such a thickness, it is possible to ensure sufficient electrode performance while reducing the amount of expensive electrode layer material used to reduce costs. The entire region where the holes (through holes) 4a are provided is covered with the electrode layer 2. That is, the holes 4a are formed inside the region of the metal support 4 where the electrode layer 2 is formed. In other words, all the holes 4a are provided facing the electrode layer 2.

[0066] The material constituting the electrode layer 2 may be a composite material such as NiO-GDC, Ni-GDC, NiO-YSZ, Ni-YSZ, CuO-CeO2, or Cu-CeO2. In these examples, GDC, YSZ, and CeO2 may be called aggregates of the composite material. The electrode layer 2 is preferably formed by a low-temperature firing method (e.g., a wet method using firing in a low-temperature range without firing in a high-temperature range higher than 1100°C), a spray coating method (such as a thermal spray method, an aerosol deposition method, an aerosol gas deposition method, a powder jet deposition method, a particle jet deposition method, or a cold spray method), a PVD method (such as a sputtering method or a pulsed laser deposition method), or a CVD method. By using these processes that can be used in a low-temperature range, a good electrode layer 2 can be obtained without firing in a high-temperature range higher than 1100°C. This is preferable because it is possible to realize an electrochemical element having excellent durability without damaging the metal support 4 and suppressing interdiffusion of elements between the metal support 4 and the electrode layer 2. Furthermore, the use of a low-temperature firing method is even more preferable because it facilitates handling of the raw materials.

[0067] The counter electrode layer 3 can be formed in a thin layer state on the surface of the electrolyte layer 1a opposite to the electrode layer 2. When the counter electrode layer 3 is a thin layer, the thickness can be, for example, about 1 μm to 100 μm, preferably 5 μm to 50 μm. With such a thickness, it is possible to reduce the amount of expensive counter electrode layer material used to reduce costs while ensuring sufficient electrode performance. As the material for the counter electrode layer 3, for example, composite oxides such as LSCF and LSM, ceria-based oxides, and mixtures thereof can be used. In particular, it is preferable that the counter electrode layer 3 contains a perovskite-type oxide containing two or more elements selected from the group consisting of La, Sr, Sm, Mn, Co, and Fe. The electrolyte layer 1a, the electrode layer 2 and the counter electrode layer 3 are formed as thin films as described below, and the inventors call this being formed in a thin layer shape.

[0068] As described above, the electrolysis cell unit U is of a metal support type, and includes a metal support 4 as a support for the electrode layer 2, and a supply path forming member 5 that forms a U-shaped electrode layer side gas supply path 5a on the opposite side of the electrode layer 2 across the metal support 4. Furthermore, a large number of holes 4a are provided in the metal support 4, penetrating the front and back surfaces. Gases (H2O and CO2) supplied via the electrode layer side gas supply path 5a are subjected to electrolysis, and are supplied to the electrode layer 2 via the large number of holes 4a. Furthermore, the generated gases (H2, CO) flow out from the holes 4a.

[0069] On the other hand, a supply path forming member 6 for forming a counter electrode layer side gas supply path 6a is also provided on the counter electrode layer 3 side. As shown in the figure, this supply path forming member 6 is provided with many grooves on the counter electrode layer 3 side, and is configured to supply a carrier gas g2 (e.g., air, etc.) to this counter electrode layer side gas supply path 6a.

[0070] The metal support 4 supports the electrode layer 2, the electrolyte layer 1a, and the counter electrode layer 3, and serves as a support that maintains the strength of the electrolysis cell 1 and the entire electrolysis cell unit U. In this example, a plate-shaped metal support 4 is used as the metal support, but other shapes, such as a box shape or a cylindrical shape, are also possible. The metal support 4 may have a sufficient strength as a support to form the electrolysis cell unit U, and may have a thickness of, for example, about 0.1 mm to 2 mm, preferably about 0.1 mm to 1 mm, and more preferably about 0.1 mm to 0.5 mm. In this embodiment, the support is made of metal, but it may also be made of, for example, ceramics.

[0071] The metal support 4 has, for example, a plurality of holes 4a provided penetrating the front and back surfaces of the metal plate. For example, the holes 4a can be provided in the metal support 4 by mechanical, chemical, or optical drilling. The holes 4a have the function of allowing gas to pass from the back surface to the front surface of the metal support 4. The holes 4a may be provided at an angle to the gas advection direction (the front-to-back direction of the paper in FIG. 2).

[0072] By using ferritic stainless steel (an example of an Fe-Cr alloy) as the base material of the metal support 4, it is possible to bring the thermal expansion coefficient closer to that of YSZ (yttria-stabilized zirconia) or GDC (gadolinium-doped ceria, also known as CGO), which are used as materials for the electrode layer 2 and the electrolyte layer 1a. Therefore, the electrolysis cell unit U is less susceptible to damage even when temperature cycles of low and high temperatures are repeated. This is preferable because it allows for the realization of an electrolysis cell unit U with excellent long-term durability.

[0073] The supply path forming members 5 and 6 of the electrolysis cell unit U can be made of the same material as the metal support 4, and the thickness thereof can also be made approximately the same.

[0074] The metal support 4 and both supply path forming members 5 and 6 are electrically conductive, but are configured to be airtight, so that they function as separators that separate the supply paths 5a and 6a.

[0075] In the electrolysis operation, the electrolysis cell unit U having the above configuration supplies DC power from a power supply unit (shown as a battery in FIG. 2) between a pair of electrode layers 2 and 3 disposed on either side of the electrolyte layer 1a. In this embodiment, as shown in the figure, the electrode layer 2 side is negative and the counter electrode layer 3 side is positive. Depending on the configuration of the electrolysis cell unit U, the electrode layer 2 side may be positive and the counter electrode layer 3 side may be negative. Then, H2O and CO2, which are gases to be electrolyzed, are supplied to the electrode layer 2 from an electrolysis raw material supply unit (an upstream portion of the electrolysis reaction unit 10 in FIG. 1), and a carrier gas g2 is supplied to the counter electrode layer side, thereby causing the reactions shown in formulas 1 and 2 in the electrolysis cell 1 and allowing the decomposed gas to be extracted. Here, the supply of H2O may be either water or water vapor, or both. Therefore, in the present invention, an electrolysis cell device is constructed including at least an electrolysis cell unit U, an electrolysis raw material supply unit that supplies water and / or water vapor and carbon dioxide to the electrolysis cell unit U, and a power supply unit that supplies power.

[0076] In Fig. 2, the gases supplied (H2O, CO2) and the gases discharged (H2O, H2, CO, O2, CO2) in the electrolysis reaction are shown above and below the electrolysis cell unit U, but this is for ease of understanding. In reality, the electrode layer side gas supply path 5a and the counter electrode layer side gas supply path 6a are formed to extend in the front-to-back direction of the paper surface of Fig. 2. For example, the supply side gases (H2O, CO2) shown above the electrolysis cell unit U in Fig. 2 can be recovered from the front side of the paper surface, and the discharge side gases (H2O, H2, CO, O2, CO2) shown below the electrolysis cell 1 can be recovered from the back side of the paper surface (see Fig. 4 described later). In addition, in order to smoothly discharge O2 generated in the electrolysis reaction, a carrier gas g2 such as air can be flowed into the electrolysis cell unit U.

[0077] When H2O and CO2 are supplied to the electrolytic reaction unit 10 and electrolyzed, H2O has a lower electrolytic voltage than CO2 and is more easily electrolyzed. Therefore, if equal amounts of H2O and CO2 are supplied to the electrolytic reaction unit 10 to carry out an electrolytic reaction, the H2 concentration is likely to be higher than the CO concentration at the outlet of the electrolytic reaction unit 10, and unreacted CO2 is likely to remain.

[0078] [First catalytic reaction section (reverse water gas shift reaction section)] As described above, the first catalytic reaction unit 20 (reverse water gas shift reaction unit) causes a reverse water gas shift reaction, converts CO2 to CO using the supplied H2, and converts H2 to H2O. That is, in the electrolysis reaction unit 10 which supplies H2O and CO2 and electrolyzes them, the CO2 remaining without being decomposed is converted to CO.

[0079] The reaction here is as shown in formula 3, but this reaction is an endothermic reaction and an equilibrium reaction depending on the reaction temperature conditions. As a result, as explained above, it is preferable to use a catalyst that can cause the reaction shown in formula 3 at as high a temperature as possible (for example, 600°C to 800°C).

[0080] In describing catalysts in this specification, a component having catalytic activity may be referred to as a "catalytically active component", and a support that supports the catalytically active component may be referred to as a "support". As described below, the inventors have investigated various combinations of catalytically active components and supports, and found that certain combinations are preferable. This type of catalyst can be easily produced by carrying out an impregnation process in which a carrier (metal oxide) is immersed in a solution containing catalytically active components (active metal components), and then removed and dried / heat-treated, to obtain a carrier-supported catalyst (impregnated support) in which the catalytically active components are distributed on the carrier surface. This heat treatment is called a calcination process. The preparation and use of the catalyst will be described with reference to Figures 10 and 11.

[0081] The preparation method described here is similar for various combinations of catalytically active components and carriers, but only differs in the starting materials. Figure 10 shows an example of a reverse water gas shift catalyst cat1 according to the present invention. In the figure, the catalytically active component of the reverse water gas shift catalyst cat1 is denoted as ca1, and its carrier is denoted as cb1.

[0082] As shown in Figure 10, in the catalyst preparation, an aqueous solution of a compound containing a metal component that will be the catalytically active component CA1 is obtained, and the carrier CB1 is put into the aqueous solution, and the impregnation support process (a) is carried out by stirring and impregnating the carrier CB1, followed by evaporation to dryness, drying, and then the drying, crushing, and molding process (b) of crushing and molding the carrier CB1, and then the firing process (c) of firing the resulting molded body in air to obtain the target product (CAT1). Therefore, this form of catalyst is also called an impregnated support catalyst.

[0083] In this case, the catalyst can be applied to the area where it is to be used and then fired, as shown in the example of reverse water gas shift catalyst cat1 in Fig. 11. Fig. 11(a) shows a coating and firing process in which the reverse water gas shift catalyst cat1 is applied to a metal support 4 having holes 4a therein to form a coating layer 20a, and then fired. Fig. 11(b) shows a pre-reduction treatment process in which H2 is passed through the reverse water gas shift catalyst cat1 to perform pre-reduction treatment before use.

[0084] When the calcination process is performed in air, the supported catalytic active component ca1 is partially or entirely oxidized. Before using the catalyst, a so-called reduction pretreatment can be performed to reduce the oxidized catalytic active component and sufficiently increase its activity. Figure 11(b) shows the state in which a reducing gas (typically H2) is circulated over the surface of the catalyst to perform the reduction pretreatment.

[0085] (Catalyst used) As the reverse water gas shift catalyst cat1 to be used in the first catalytic reaction section 20, the inventors selected a catalyst that satisfies the following requirements.

[0086] A catalyst comprising a carrier cb1 mainly composed of a ceria-based metal oxide or a zirconia-based metal oxide, and at least one of nickel and iron as a catalytically active component ca1. Here, the ratio of the carrier cb1 to the entire catalyst is preferably 55% by weight or more, more preferably 60% by weight or more, and even more preferably 65% ​​by weight or more, in order to increase the strength of the catalyst cat1. The upper limit of this ratio can be, for example, 99.5% by weight, but if it is more than this, the catalytically active component ca1 cannot be sufficiently supported, and it may be difficult to obtain the effect of the reverse water gas shift catalyst cat1.

[0087] Furthermore, the ceria-based metal oxide may be ceria doped with at least one of gadolinium, samarium, and yttrium. The zirconia-based metal oxide may be zirconia stabilized with at least one of yttria and scandia.

[0088] In addition, since the reverse water gas shift reaction can be smoothly carried out, the amount of the catalytically active component ca1 is preferably 0.5% by weight or more, more preferably 1% by weight or more, and even more preferably 5% by weight or more. Also, even if the amount of the catalytically active component ca1 is increased too much, it becomes difficult to support the catalytically active component ca1 in a highly dispersed manner, making it difficult to obtain a significant improvement in catalytic activity, and the catalyst cost also increases, so the amount of the catalytically active component ca1 is preferably 35% by weight or less, more preferably 30% by weight or less, and even more preferably 25% by weight or less.

[0089] Furthermore, it is also preferable to add either or both of nickel and iron to the catalytically active component ca1 and support copper as the further catalytically active component ca1. In this configuration, the amount of copper supported is equal to or less than the amount of either or both of nickel and iron as the main catalytically active component ca1 supported by the catalytically active component ca1.

[0090] The following describes test results of examples in which the catalytically active component ca1 and the carrier cb1 of the reverse water gas shift catalyst cat1 used in the first catalytic reaction section 20 are changed in various ways. As the catalytically active component ca1, Ni and Fe were examined and compared with Pt (platinum). As the support cb1, ZrO2 (zirconia), YSZ (yttria stabilized zirconia), GDC (gadolinium doped ceria), and CeO2 (ceria) were used as examples, and Al2O3 (alumina) was also investigated.

[0091] In the following explanation, Test Example 1 and Test Example 2 will be introduced. The difference between the two tests is that in the calcination of the reverse water gas shift catalyst cat1, the calcination temperature in Test Example 1 was set to 450°C, while the calcination temperature in Test Example 2 was set to a higher temperature of 600°C to 1000°C.

[0092] (Test Example 1) The test results of Examples (1 to 19) in which the carrier used as the catalyst in the first catalytic reaction section 20 was changed in various ways will be described. As catalytically active components, Ni and Fe were examined and compared with Pt (platinum). The supports used were ZrO2 (zirconia), YSZ (yttria stabilized zirconia), GDC (gadolinium doped ceria), and CeO2 (ceria), with Al2O3 (alumina) also being investigated.

[0093] (Catalyst preparation) In preparing the reverse water gas shift catalyst cat1, either or both of water-soluble nickel compounds (nickel nitrate, nickel chloride, nickel sulfate, nickel ammonium sulfate, nickel acetate, nickel oxalate, nickel citrate, etc.) and water-soluble iron compounds (iron nitrate, iron chloride, iron sulfate, ammonium iron sulfate, iron acetate, iron oxalate, iron citrate, etc.) are measured and dissolved in an aqueous solution according to the composition of the target catalyst. When supporting copper as a further catalytically active component ca1, a water-soluble copper compound (copper nitrate, copper chloride, copper sulfate, copper ammonium sulfate, copper acetate, copper oxalate, copper citrate, etc.) is similarly measured and dissolved in an aqueous solution. A predetermined amount of carrier powder (ceria, zirconia, GDC, YSZ, Al2O3) is added to the aqueous solution, stirred, impregnated, evaporated to dryness, dried, then crushed, molded, and fired in air. This impregnation is the "impregnation-supporting step" referred to in the present invention, and the result is the "impregnated support". In the following examples, the catalysts were prepared using nickel nitrate hexahydrate, iron nitrate nonahydrate, and copper nitrate trihydrate, respectively, and the catalyst using Pt was prepared using tetraammineplatinum hydroxide.

[0094] In the preparation of the above catalyst, the temperatures for the evaporation to dryness, drying, and calcination can be within the commonly used temperature range. In Test Example 1, the temperatures for the catalysts in the following examples were 80°C, 80°C, and 450°C, respectively.

[0095] Table 1 shows Examples 1 to 19 of the reverse water gas shift catalyst cat1 of the present invention. The horizontal axis indicates the type of carrier cb1, the amount of metal supported as a catalytically active component (weight %; indicated as wt.% in the table), the amount of CO adsorption (ml / g), and the BET surface area (m 2 / g). The CO adsorption amount was measured after the catalyst was subjected to a reduction pretreatment in a hydrogen atmosphere at 350° C. for 1 hour.

[0096] [Table 1]

[0097] (Catalytic activity test) The catalytic activity test was performed using a mixed gas of 50% H2-50% CO2 (a mixed gas containing H2 and CO2 in a 1:1 (volume ratio)) as the reaction gas, with a GHSV (Gas Hourly Space Velocity) of 10,000 / h and the reaction temperature changed in 50°C increments from 600°C to 800°C. Before the catalytic activity test, the catalyst was subjected to a reduction pretreatment at 600° C. while passing hydrogen gas through the catalyst layer. As test results, the CO2 conversion rate (%), CO concentration (%) and CH4 concentration (%) at the reaction section outlet are shown in Table 2.

[0098] The CO2 conversion rate (%) was calculated according to the following formula based on the gas analysis results at the catalyst layer outlet. [CH4 concentration] + [CO concentration] / ([CH4 concentration] + [CO concentration] + [CO2 concentration])

[0099] As described above, it is desirable for the reverse water gas shift catalyst cat1 used in the first catalytic reaction section 20 (reverse water gas shift reaction section) to have a high CO2 conversion rate (%) on the high temperature side (for example, around 600 to 800°C).

[0100] [Table 2]

[0101] (Test Example 2) The test results of Examples (20 to 29) of Test Example 2 will be described below. As catalytically active components, Ni and Fe were examined, and the addition of Cu was also examined. The supports used in the examples were CeO2 (ceria) and ZrO2 (zirconia), and Al2O3 (alumina) was also investigated.

[0102] (Catalyst preparation) The reverse water gas shift catalyst cat1 used in Test Example 2 was prepared in the same manner as in Test Example 1, except that the calcination temperature was changed to 600°C, 800°C, and 1000°C.

[0103] Table 3 shows the catalysts prepared in Examples (20 to 29).

[0104] [Table 3]

[0105] (Catalytic activity test) The catalytic activity test was performed using a mixed gas containing H2 and CO2 in a 1:1 (volume ratio) ratio as the reaction gas, with a GHSV of 10,000 / h and the reaction temperature changed from 600°C to 800°C in 50°C increments. Before the catalytic activity test, the catalyst was subjected to a reduction pretreatment at 600° C. while passing hydrogen gas through the catalyst layer. As test results, the CO2 conversion rate (%), CO concentration (%) and CH4 concentration (%) at the reaction section outlet are shown in Table 4.

[0106] [Table 4]

[0107] For reference, the equilibrium values ​​(calculated values) of the CO2 conversion rate under these experimental conditions are shown in Table 4.

[0108] Iron-zirconia catalyst and iron-alumina catalyst The test results of the iron-zirconia catalyst when the calcination temperatures were 450°C, 600°C, 800°C, and 1000°C are shown in Examples 8, 22, 26, and 29, respectively. On the other hand, the test results of the iron-alumina catalyst when the calcination temperatures were 450°C, 600°C, and 800°C are shown in Examples 14, 23, and 27, respectively. As can be seen from these results, although the metal loadings are slightly different, the iron-zirconia catalyst has a higher activity in the reverse water gas shift reaction than the iron-alumina catalyst. In addition, the iron-zirconia catalyst has a very high catalytic activity not only when the calcination temperature was 450°C, but also when the calcination temperature was increased to 600°C, 800°C, and 1000°C, and the CO2 conversion rate reached near the equilibrium value at any calcination temperature.

[0109] Nickel-ceria catalyst The test results for calcination temperatures of 450°C, 600°C, 800°C, and 1000°C are shown in Examples 4, 20, 24, and 28, respectively. As can be seen from these results, the nickel-ceria catalyst has extremely high catalytic activity not only at a calcination temperature of 450°C, but also at higher calcination temperatures of 600°C, 800°C, and 1000°C, and the CO2 conversion rate reaches close to the equilibrium value at any calcination temperature.

[0110] Nickel-alumina catalyst The test results when the calcination temperature was 450°C are shown in Example 7. The results showed that the nickel-alumina catalyst had a lower CO2 conversion rate than the nickel-ceria catalyst mentioned above.

[0111] Nickel-copper-ceria catalyst The test results for calcination temperatures of 450°C, 600°C, and 800°C are shown in Examples 6, 21, and 25, respectively. These results show that the nickel-copper-ceria catalyst tends to have a slightly lower CO2 conversion rate when the calcination temperature is high, such as 600°C or 800°C, but is superior to the iron-alumina catalyst with the same calcination temperature conditions mentioned above. In addition, with the nickel-copper-ceria catalyst with a calcination temperature of 450°C, the CO2 conversion rate reaches close to the equilibrium value.

[0112] Usefulness as a reverse water-gas shift catalyst As described above, iron-zirconia catalysts and nickel-ceria catalysts exhibit extremely high reverse water-gas shift catalytic activity even when the calcination temperature is changed to various values, such as 450°C to 1000°C. Therefore, even when used in combination with a solid oxide electrolysis cell operated at high temperatures, for example, around 600°C to 800°C, they are useful because they can easily ensure high performance and durability.

[0113] From the above results, as described above, the reverse water gas shift catalyst cat1 used in the first catalytic reaction section 20 can be a catalyst composed of a carrier cb1 mainly composed of a ceria-based metal oxide or a zirconia-based metal oxide, and at least one or both of nickel and iron supported as catalytically active components ca1.

[0114] Furthermore, the ceria-based metal oxide as the carrier cb1 may be ceria doped with at least one of gadolinium, samarium, and yttrium.

[0115] Furthermore, the zirconia-based metal oxide as the carrier cb1 can be zirconia stabilized with at least one of yttria and scandia.

[0116] Furthermore, it is also preferred to add either or both of nickel and iron to the catalytically active component ca1 and support copper as a further catalytically active component ca1.

[0117] By using the reverse water gas shift catalyst cat1 in the first catalytic reaction section 20 (reverse water gas shift reaction section), the reverse water gas shift reaction can be carried out at a CO2 conversion rate (%) equal to or higher than that of a Pt catalyst, which is highly active but very expensive, at around 600 to 1000°C. It should be noted that the test in this embodiment was performed under very high GHSV conditions of 10,000 / h. It is therefore possible to perform the reverse water gas shift reaction with a higher CO2 conversion rate (%) under conditions where the GHSV is lower than 10,000 / h, i.e., by increasing the amount of catalyst used relative to the amount of gas to be treated.

[0118] [Combination of electrolysis reactor and reverse water gas shift reactor] In the above description, the electrolysis reaction unit 10 and the reverse water gas shift reaction unit 20 are individually provided in the illustrated order along the gas advection direction in accordance with the system configuration shown in FIG. The reaction in the electrolytic reaction section 10 may be an exothermic reaction depending on the reaction conditions, and the reaction in the reverse water gas shift reaction section 20 may be an endothermic reaction. Therefore, by integrating these two reaction sections 10 and 20, the thermal efficiency of the system can be improved. FIG. 3 shows the configuration in which these two reaction sections 10 and 20 are combined and integrated, and both parts are enclosed to show that they are integrated. The reaction in the case where they are integrated in this way is also shown in the same box. Basically, the above-mentioned formulas 1, 2, and 3 are carried out. When the electrolytic reaction section 10 and the reverse water gas shift reaction section 20 are combined and integrated, it is preferable to surround them with a heat insulating member, since this allows efficient exchange of heat between the electrolytic reaction section 10 and the reverse water gas shift reaction section 20. In addition, the electrolytic reaction section 10 and the reverse water gas shift reaction section 20 may be connected using a heat conductive member in order to transfer heat generated in the electrolytic reaction section 10 to the reverse water gas shift reaction section 20.

[0119] [Electrolysis cell unit equipped with both electrolysis reaction section and reverse water gas shift reaction section] Based on the above concept, it is preferable to provide a reverse water gas shift reactor 20 in the electrolysis cell unit U serving as the electrolysis reaction section 10. This is because, when a solid oxide electrolysis cell operating at about 600 to 800°C is used as the electrolysis cell 1, the reverse water gas shift catalyst cat1 of the present application, which exhibits high activity at about 600 to 800°C, can use the electrolysis reaction section 10 and the reverse water gas shift reactor 20 in approximately the same temperature range. In this case as well, it is only necessary that the gas that has passed through the electrolytic reaction section 10 is guided to the reverse water gas shift reaction section 20 and the reverse water gas shift reaction occurs.

[0120] An electrolysis cell unit U equipped with such a reverse water gas shift reactor 20 is shown in Fig. 4. Fig. 4 is a drawing of the electrolysis cell unit U shown in cross section in Fig. 2, including the gas advection direction.

[0121] As shown in the figure, the cross sections of the electrolysis cell units U are basically the same. That is, the electrolysis cell unit U also includes an electrolysis cell 1 in which an electrode layer 2 and a counter electrode layer 3 are formed with an electrolyte layer 1a sandwiched therebetween, a metal support 4 that functions as a support for the electrolysis cell 1 and also functions as a separator, and supply channel forming members 5 and 6, and is configured to form an electrode layer side gas supply channel 5a and a counter electrode layer side gas supply channel 6a. More specifically, as is clear from the figure, when the metal support 4 is viewed in the gas advection direction, a hole 4a is provided at a position corresponding to the electrolysis cell 1, but no hole is provided downstream of the electrode layer 2. Therefore, the metal support 4 serves as a separator that effectively separates the gas supplied to the electrode layer 2 and released from the electrode layer 2 from the gas supplied to the counter electrode layer 3 and released from the counter electrode layer 3.

[0122] In this example, however, the reverse water gas shift catalyst cat1 described above is applied to the inner surface of the electrode layer side gas supply channel 5a (the inner surface on the supply channel side of the supply channel forming member 5, the surface of the metal support 4 opposite to the surface on which the electrode layer 2 is formed, and the surfaces of the plurality of holes 4a). This coating layer 20a is indicated by a thick solid line. This configuration is an example in which the reverse water gas shift reactor 20 is incorporated inside the electrolysis reactor 10. Furthermore, the electrode layer side gas supply passage 5a is extended beyond the electrolytic reaction section 10, and the coating layer 20a is also provided on this extension side.

[0123] As a result, the electrode layer side gas supply path 5a of the electrolysis cell unit U serves as an exhaust path for exhausting at least H2 generated in the electrode layer 2, and the electrolysis reaction section 10 and the reverse water gas shift reaction section 20 are integrally provided in the electrolysis cell unit U.

[0124] In this configuration, the metal support 4 acts as a separator to separate H generated in the electrode layer 2 and O generated in the counter electrode layer 3, and at least a portion of the separator on the H discharge path side serves as a reverse water-gas shift reaction section 20. 2 and 4, a large number of electrolysis cell units U are stacked and electrically connected to form a so-called electrolysis cell module (not shown). Naturally, useful gases can be generated across multiple layers.

[0125] Based on the concept of combining the electrolytic reaction unit 10 and the reverse water gas shift reaction unit 20 (the electrode layer side gas supply passage 5a of the electrolytic reaction unit 10 serves as the reverse water gas shift reaction unit 20), the inventors conducted an experiment by storing a granular reverse water gas shift catalyst cat1 in the electrode layer side gas supply passage 5a. FIG. 5 shows a cross section of the electrolysis cell unit U used in this experiment.

[0126] A specific description will be given below with reference to Fig. 5, which shows a cross-sectional view of the electrolysis cell unit U. Here, a metal-supported solid oxide electrolysis cell was used as the electrolysis cell 1. A metal substrate was prepared by providing a plurality of through holes (holes 4a) in a ferritic stainless steel metal plate having a thickness of 0.3 mm by laser processing as the metal support 4. An electrode layer 2 and an intermediate layer 2a were laminated in order on the metal substrate, and an electrolyte layer 1a was laminated on the intermediate layer 2a of the metal substrate so as to cover the intermediate layer 2a. Furthermore, a reaction prevention layer 7 and a counter electrode layer 3 were laminated in order on the electrolyte layer 1a to prepare the electrolysis cell 1. Note that a mixture of NiO powder and GDC powder was used as the material for forming the electrode layer 2, GDC powder was used as the material for forming the intermediate layer 2a, 8YSZ (8 mol% yttria-stabilized zirconia) powder was used as the material for forming the electrolyte layer 1a, GDC powder was used as the material for forming the reaction prevention layer 7, and a mixture of GDC powder and LSCF powder was used as the material for forming the counter electrode layer 3. The thicknesses of the electrode layer 2, intermediate layer 2a, electrolyte layer 1a, reaction prevention layer 7, and counter electrode layer 3 were about 25 μm, about 10 μm, about 5 μm, about 5 μm, and about 20 μm, respectively. The performance and durability of the electrolytic cell 1 can be improved by providing the intermediate layer 2a between the electrode layer 2 and the electrolyte layer 1a, or by providing the reaction prevention layer 7 between the electrolyte layer 1a and the counter electrode layer 3. The intermediate layer 2a and the reaction prevention layer 7 are preferably formed by a low-temperature firing method (for example, a wet method using a firing process in a low-temperature range that does not include a firing process in a high-temperature range higher than 1100° C.), a spray coating method (such as a thermal spray method, an aerosol deposition method, an aerosol gas deposition method, a powder jet deposition method, a particle jet deposition method, or a cold spray method), a PVD method (such as a sputtering method or a pulsed laser deposition method), or a CVD method. These processes that can be used in the low temperature range make it possible to obtain a good intermediate layer 2a and reaction prevention layer 7 without using firing in a high temperature range, for example, higher than 1100° C. This is preferable because it allows the electrolysis cell 1 to be realized with excellent performance and durability without damaging the metal support 4. Furthermore, the use of a low-temperature firing method is even more preferable because it allows the raw materials to be easily handled.

[0127] For the electrolysis cell unit U obtained as described above, we investigated the performance improvement when a granular reverse water gas shift catalyst cat1 was placed in the electrode layer side gas supply passage 5a (which also serves as an exhaust passage for the gas electrolyzed in the electrolysis reaction section 10).

[0128] Results without reverse water gas shift catalyst cat1 An electrolysis reaction was carried out while supplying a gas containing H2O and CO2 to the electrolysis cell unit U, and the ratio of H2 to CO in the outlet gas of the electrolysis cell unit U was measured using a gas chromatograph. The results are shown in Table 5 below. These experimental results are described as Comparative Examples A1 and A2. [Table 5]

[0129] Results when reverse water gas shift catalyst cat1 is installed A granular catalyst obtained by supporting approximately 10% Ni on the same 8YSZ carrier as in Example 2 was placed as the reverse water gas shift catalyst cat1, and an electrolysis reaction was carried out while supplying a gas containing H2O and CO2 to the electrolysis cell unit U, and the ratio of H2 to CO in the outlet gas of the electrolysis cell unit U was measured using a gas chromatograph. The results are shown in Table 6. This experimental result is described as Example A1.

[0130] [Table 6]

[0131] From the above comparative experiments, it was found that in the electrolytic cell unit U in which the electrolytic cell 1 was formed in a thin layer on the metal support 4 and the reverse water-gas shift reaction section 20, which produces CO using CO and the H by the reverse water-gas shift reaction, was provided in the electrode layer side gas supply path 5a, which serves as a discharge path for the electrolyzed gas, the composition ratio of CO to H produced by electrolysis could be increased.

[0132] Comparing an electrolysis cell unit U that does not include a reverse water gas shift catalyst cat1 in the electrode layer side gas supply path 5a (which serves as an exhaust path for electrolyzed gas) with an electrolysis cell unit U that does include the catalyst, the hydrogen / carbon monoxide ([H2 / CO]) ratio at the outlet becomes approximately 5 from approximately 10 or more, and this is preferable because combining the reaction in the electrolysis reaction section 10 with the reaction in the reverse water gas shift reaction section 20 can ensure an amount of CO that is advantageous for synthesizing oxygen-containing hydrocarbons such as methanol. By appropriately adjusting the ratio of H2O and CO2 introduced into the electrolytic reaction unit 10, the reaction conditions of the electrolytic reaction unit 10 (electrolytic voltage, reaction temperature, etc.), and the reaction conditions of the reverse water gas shift reaction unit 20 (amount of catalyst used, GHSV, reaction temperature, etc.), the hydrogen / carbon monoxide ([H2 / CO]) ratio at the outlet of the reverse water gas shift reaction unit 20 can be adjusted to a value suitable for the downstream second catalytic reaction unit 40 (oxygen-containing hydrocarbon synthesis reaction unit) (for example, H2 / CO=2, which is the equivalent ratio in the reaction of synthesizing methanol from CO and H2).

[0133] [A heat exchanger is installed between the electrolysis reactor and the reverse water gas shift reactor] In the above explanation, the electrolysis reaction section 10 and the first catalytic reaction section (reverse water gas shift reaction section) 20 are mainly integrated together, but it is also possible to adopt a configuration in which the two sections 10, 20 are separate sections and a heat exchanger 11 is provided between the two sections 10, 20 to allow heat transfer between the two sections. This configuration is shown in FIG. 6 corresponding to FIG. 1. The hollow double lines indicate heat transfer between the two sections. With this configuration, the temperature of each section 10, 20 can be appropriately controlled.

[0134] The inventors call the system consisting of the electrolysis reaction section 10 and the reverse water gas shift reaction section 20 described above an "electrolysis reaction system."

[0135] [Second catalytic reaction section (oxygen-containing hydrocarbon synthesis reaction section)] At least H2 and CO are flowed into this second catalytic reaction section 40 (oxygen-containing hydrocarbon synthesis reaction section), and oxygen-containing hydrocarbons such as methanol are produced by catalytic reaction.

[0136] (Examples of oxygen-containing hydrocarbon synthesis catalysts) As the catalyst (oxygen-containing hydrocarbon synthesis catalyst) used in this second catalytic reaction section 40, a precious metal catalyst can be used, but since the cost is high, for example, a copper-zinc catalyst is preferably used. Below, a copper-zinc-aluminum methanol synthesis catalyst is shown as an example of the oxygen-containing hydrocarbon synthesis catalyst in this embodiment.

[0137] (Catalyst preparation) A copper-zinc-aluminum based methanol synthesis catalyst (a methanol synthesis catalyst mainly composed of oxides of copper, zinc, and aluminum) can be prepared, for example, by a coprecipitation process in which a precipitate is formed by the coprecipitation method described below. A mixed solution of an aqueous solution containing a copper compound (e.g., copper nitrate, copper acetate, etc.) and a zinc compound (e.g., zinc nitrate, zinc acetate, etc.) and an aluminum compound (e.g., aluminum nitrate, aluminum hydroxide, etc.) is added dropwise to an aqueous solution of an alkaline substance (e.g., sodium carbonate, potassium carbonate, etc.) kept at about 60°C while stirring to generate a precipitate. In this case, the order of adding the mixed solution for generating the precipitate may be reversed, and the copper, zinc, and aluminum compounds may be added to the alkaline substance solution. Alternatively, aluminum hydroxide may be added to the alkaline substance solution, and an aqueous solution containing a copper compound and a zinc compound may be mixed therewith to generate a precipitate. It is preferable to use aluminum hydroxide as the aluminum source, since it is easy to obtain a catalyst having excellent heat resistance and durability.

[0138] The resulting precipitate is then thoroughly washed with water, filtered, and dried. The resulting precipitate is then calcined at a temperature in the range of, for example, 200 to 650°C to obtain a mixed oxide of copper oxide-zinc oxide-aluminum oxide. The resulting mixed oxide is molded into a shape such as a tablet or extrusion product after adding an auxiliary (e.g., graphite, etc.) as necessary. In order to achieve both heat resistance and performance of the catalyst, the calcination temperature range is preferably 300°C or higher as the lower limit, more preferably 350°C or higher, and more preferably 600°C or lower, and more preferably 550°C or lower as the upper limit.

[0139] The compounding ratio of copper oxide, zinc oxide and aluminum oxide in the mixed oxide is preferably copper:zinc:aluminum=1:0.3-10:0.05-2, more preferably about 1:0.6-3:0.3-1, in terms of the atomic ratio of metal atoms.

[0140] (Mixed oxide preparation test) Aluminum hydroxide was added to an aqueous solution of sodium carbonate and kept at 60°C, while a mixed aqueous solution containing copper nitrate and zinc nitrate was gradually added dropwise while stirring to generate a precipitate. The precipitate was then thoroughly washed, filtered, and dried. It was then calcined at a temperature of 550°C for 3 hours to obtain a mixed oxide containing copper oxide, zinc oxide, and aluminum oxide in a molar ratio of 1:1:0.2.

[0141] (Pre-reduction treatment) Next, the mixed oxide obtained through the above-mentioned steps is subjected to hydrogen reduction as necessary and then used in a catalytic reaction (reduction pretreatment). In hydrogen reduction, since copper has a low melting point, the particle size increases and the surface area is easily reduced by heat, and the pore structure changes slightly due to excessive heat, resulting in a large change in the properties as a methanol synthesis catalyst. Therefore, in the hydrogen reduction pretreatment of the mixed oxide, it is preferable to proceed with hydrogen reduction of copper oxide to copper, which is an exothermic reaction, under mild conditions. For example, a method of reducing pretreatment while maintaining a temperature of about 150 to 300°C in the presence of hydrogen gas diluted with a gas that does not participate in the reaction (e.g., nitrogen gas, argon gas, etc.) so that the hydrogen content is 6% by volume or less, more preferably about 0.5 to 4% by volume is suitable. In particular, an inert gas such as nitrogen gas can be preferably used as the gas that does not participate in the reaction.

[0142] The copper-zinc-aluminum methanol synthesis catalyst obtained by the above method has a dense structure consisting of an aggregate of fine particles, in which very small copper particles are uniformly dispersed on the surface of zinc oxide particles and are in a highly active state due to chemical interaction with zinc oxide. Meanwhile, aluminum oxide is distributed throughout, preventing sintering of copper particles and zinc oxide particles due to heat and maintaining a highly active state. Therefore, when using these methanol synthesis catalysts, it is possible to maintain high catalytic activity for a long time even in a relatively high temperature range, for example, above 300°C.

[0143] [Water separation section] A condenser is provided in this water separation section 30, which adjusts the temperature and pressure of the inflowing H2O-containing gas to a predetermined level, condenses the gas, and removes the water to the outside. Note that it is preferable to place the water separation section 30 in the upstream stage of the second catalytic reaction section 40 to reduce the amount of water in the gas introduced into the second catalytic reaction section 40, since this makes it easier for the catalytic reaction for synthesizing oxygen-containing hydrocarbons in the second catalytic reaction section 40 to proceed.

[0144] [Carbon dioxide separation section] For example, a PSA is provided in this section 50, which separates CO2 from the incoming CO2-containing gas by adsorbing it onto an adsorbent under a predetermined temperature and pressure, and then desorbs the separated CO2 from the adsorbent, thereby separating the CO2 satisfactorily. The separated CO2 can be returned to the front of the electrolysis reaction section 10 via the carbon dioxide return path 51 and reused. It should be noted that the carbon dioxide separation section and the water separation section may be integrated into one separation section by using PSA or the like.

[0145] [Another embodiment] (1) In the above embodiment, the CO2 separated in the carbon dioxide separation section 50 is returned to the area before the electrolysis section 10. However, in the oxygen-containing hydrocarbon production system 100 according to the present invention, the conversion of CO2 to CO is mainly performed in the reverse water gas shift reaction section 20, so that the CO2 may be returned to the area before the reverse water gas shift reaction section 20. This configuration is shown in FIG.

[0146] (2) In the above embodiment, no particular mention was made regarding H2 in the gas obtained from the oxygen-containing hydrocarbon synthesis reaction section 40. However, a hydrogen separation section (shown as H2 separation section in the figure) 60 that separates H2 using a hydrogen separation membrane or the like may be provided to separate H2 for separate use. This configuration is shown in Fig. 8. In this example, the H2 separated in the hydrogen separation section 60 may be returned to the upstream of the reverse water gas shift reaction section 20 and used for the reverse water gas shift reaction.

[0147] (3) In the above embodiment, an example was shown in which both H2O and CO2 were supplied to the electrolytic reaction unit 10 for the electrolytic reaction. However, as shown in FIG. 9, a system may be used in which only H2O is supplied to the electrolytic reaction unit 10 for the electrolytic reaction.

[0148] (4) In the above embodiment, an example was shown in which a solid oxide electrolysis cell was used as the electrolysis cell 1 in the electrolysis reaction section 10. However, the electrolysis cell 1 may also be an alkaline electrolysis cell or a polymer membrane electrolysis cell.

[0149] (5) In the above embodiment, an example of synthesizing methanol in the oxygen-containing hydrocarbon synthesis reaction section 40 has been shown, but depending on the method of selecting the oxygen-containing hydrocarbon synthesis catalyst used in the oxygen-containing hydrocarbon synthesis reaction section 40 and the combination of the dehydration step and the dehydrogenation step, etc., it is also possible to synthesize alcohols other than methanol such as ethanol, ethers such as dimethyl ether (DME), aldehydes such as formaldehyde, and carboxylic acids such as formic acid and methyl formate from hydrogen and carbon monoxide introduced into the oxygen-containing hydrocarbon synthesis reaction section 40. Note that, in the case where formaldehyde is synthesized from hydrogen and carbon monoxide via methanol in the oxygen-containing hydrocarbon synthesis reaction section 40 equipped with a dehydrogenation step using oxygen, the oxygen generated in the electrolysis reaction section 10 can be used in the dehydrogenation step using oxygen, so that a highly efficient, compact, and low-cost oxygen-containing hydrocarbon production system can be constructed.

[0150] (6) In the above embodiment, a copper-zinc-aluminum type (copper oxide-zinc oxide-aluminum oxide type) catalyst is shown as an example of an oxygen-containing hydrocarbon synthesis catalyst. However, a copper-zinc-zirconium type (copper oxide-zinc oxide-zirconium oxide type) catalyst or a copper-zinc-chromium type (copper oxide-zinc oxide-chromium oxide type) catalyst can also be used as an oxygen-containing hydrocarbon synthesis catalyst.

[0151] (7) In the above embodiment, a highly efficient oxygen-containing hydrocarbons production system can be constructed by using the reaction heat generated in the oxygen-containing hydrocarbons synthesis reaction section 40 to vaporize the HO introduced into the electrolysis reaction section 10. In this case, a mechanism (e.g., a heat exchanger) for exchanging heat between the reaction fluid of the oxygen-containing hydrocarbons synthesis reaction section 40 and the HO introduced into the electrolysis reaction section 10 can be provided to construct such a highly efficient oxygen-containing hydrocarbons production system. [Explanation of symbols]

[0152] 1 Electrolysis cell 1a Electrolyte layer 2 electrode layer 3 Counter electrode layer 4 Metal support (support / separator) 4a hole 5 Supply path forming member (separator) 6 Supply path forming member (separator) 10 Electrolytic reaction section 20 First catalytic reaction section (reverse water gas shift reaction section) 20a Coating layer 30 Water separation section 40 Second catalytic reaction section (oxygen-containing hydrocarbon synthesis reaction section) 50 Carbon dioxide separation section 60 Hydrogen separation section U Electrolysis cell unit Cat1 Reverse water gas shift catalyst ca1 Catalyst active component (active metal) cb1 Carrier (metal oxide carrier)

Claims

1. An oxygen-containing hydrocarbon production system for producing oxygen-containing hydrocarbons from at least water and carbon dioxide, comprising at least an electrolysis reaction section, a reverse water gas shift reaction section, and an oxygen-containing hydrocarbon synthesis reaction section, The system for producing oxygen-containing hydrocarbons, wherein the reverse water gas shift reaction section is incorporated inside the electrolysis reaction section.

2. 2. The system for producing oxygen-containing hydrocarbons according to claim 1, wherein the oxygen-containing hydrocarbons are methanol.

3. 3. The system for producing oxygen-containing hydrocarbons according to claim 1 or 2, wherein an electrolysis reaction of water is carried out in the electrolysis reaction section.

4. 3. The system for producing oxygen-containing hydrocarbons according to claim 1 or 2, wherein a co-electrolytic reaction of water and carbon dioxide is carried out in the electrolytic reaction section.

5. 5. The system for producing oxygen-containing hydrocarbons according to claim 1, wherein the reverse water gas shift reaction section has a reverse water gas shift catalyst containing at least a metal oxide and an active metal component.

6. 6. The system for producing oxygen-containing hydrocarbons according to claim 5, wherein the active metal component contains at least one of nickel and iron.

7. 7. The system for producing oxygen-containing hydrocarbons according to claim 1, wherein the oxygen-containing hydrocarbon synthesis reaction section has an oxygen-containing hydrocarbon synthesis catalyst containing at least a metal oxide and an active metal component.

8. 8. The system for producing oxygen-containing hydrocarbons according to claim 7, wherein the active metal component contains at least copper.

9. 9. The system for producing oxygen-containing hydrocarbons according to claim 1, wherein the electrolytic reaction section has an electrolytic cell in which at least an electrode layer, an electrolyte layer, and a counter electrode layer are formed on a support.

10. 10. The system for producing oxygen-containing hydrocarbons according to claim 9, wherein the support is a metal.

11. A method for producing an oxygen-containing hydrocarbon production system according to any one of claims 1 to 10, comprising the steps of: impregnating and supporting an active metal component on a metal oxide support; and disposing an impregnated support obtained through an impregnation step in which an active metal component is impregnated and supported on a metal oxide support in the reverse water gas shift reaction section.

12. A manufacturing method for an oxygen-containing hydrocarbon production system according to any one of claims 1 to 10, comprising placing a precipitate obtained through a coprecipitation step of forming a precipitate by a coprecipitation method in the oxygen-containing hydrocarbon synthesis reaction section.

13. A method for operating the oxygen-containing hydrocarbon production system according to any one of claims 1 to 10, which is operated after performing a reduction pretreatment on the reverse water gas shift reaction section.

14. A method for operating an oxygen-containing hydrocarbon production system according to any one of claims 1 to 10, which is operated after performing a reduction pretreatment in the oxygen-containing hydrocarbon synthesis reaction section.

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