JP7798519B2 - Electrolytic cell unit, hydrocarbon production system, and method for operating electrolytic cell unit - Google Patents

Description

The present invention relates to an electrolytic cell unit equipped with an electrolytic cell comprising an electrode layer and a counter electrode layer sandwiching an electrolyte layer, a hydrocarbon production system using the same, and an operating method for the electrolytic cell unit.

Patent Documents 1 and 2 disclose a hydrocarbon production system including an electrolysis cell unit.
The system disclosed in Patent Document 1 includes a high-temperature electrolyte (HTE) reactor (corresponding to the electrolytic reaction section of the present invention) equipped with a stack of electrolytic single cells (corresponding to the single-cell electrolytic cell units of the present invention) that produce either hydrogen or a synthesis feed gas ("synthesis gas" representing a mixture of hydrogen and carbon monoxide) from water vapor and carbon dioxide, and converts the synthesis gas obtained in the electrolytic single cells into a desired combustible gas by heterogeneous catalytic action.
Therefore, in the technology disclosed in Patent Document 1, a hydrocarbon synthesis section is provided downstream of an electrolysis reaction section, and hydrocarbons are produced using water and carbon dioxide as starting materials.
Referring to FIG. 3 of Patent Document 1, this system is a large cylindrical device.

On the other hand, the technology disclosed in Patent Document 2 relates to a power-to-gas unit that produces useful gas (specifically, methane) from electricity, and specifically discloses a technology in which a methanation reaction catalyst material is included in the cathode of a stack of basic solid oxide electrolysis cells (SOEC).
In the technology disclosed in Patent Document 2, the electrolysis cell also serves as the electrolysis reaction section, and the methanation reaction catalyst material provided on the cathode constitutes the hydrocarbon synthesis section.

In these prior art technologies, the electrolysis reaction section performs so-called "co-electrolysis," in which water and carbon dioxide are electrolyzed together. A heterogeneous catalyst is used for the synthesis of hydrocarbons (so-called methanation).

Special table 2016-522166 publication Japanese Patent Application Laid-Open No. 2019-112717

However, the inventors have found that the co-electrolysis in the electrolysis reaction section has the following problems.
1. Problems with co-electrolysis The electrolysis voltage of water is around 1.23 V, while the electrolysis voltage of carbon dioxide is around 1.33 V, making the electrolysis reaction of carbon dioxide more difficult to occur than the electrolysis reaction of water. As a result, even if a co-electrolysis reaction is attempted, the electrolysis reaction of carbon dioxide is difficult to occur, and it is not possible to ensure a sufficient concentration of carbon monoxide useful for the synthesis of hydrocarbons.

2. With reference to the apparatus described in Patent Document 1, the apparatus is large and there is room for improvement in terms of efficiently synthesizing hydrocarbons without consuming significant energy.

In light of this situation, the primary objective of the present invention is to provide an electrolytic cell unit that can serve as a hydrogen source or a carbon monoxide source, for example, an electrolytic cell unit that can adequately secure the hydrogen and carbon monoxide necessary for the synthesis of hydrocarbons.

The first characteristic configuration of the present invention is:
an electrolysis cell unit including at least an electrolysis cell in which an electrode layer and a counter electrode layer are formed with an electrolyte layer sandwiched therebetween, and an exhaust path through which hydrogen generated in the electrode layer is exhausted;
a reverse water gas shift reaction unit that generates carbon monoxide using carbon dioxide and the hydrogen through the reverse water gas shift reaction is provided in at least a part of the exhaust passage,
The electrolytic cell is a solid oxide electrolytic cell.

The electrolytic cell unit includes an electrolytic cell, and when an electric current flows between the electrode layer and counter electrode layer of the electrolytic cell, hydrogen is produced from the hydrogen source gas through an electrolysis reaction (electrolysis reaction). The hydrogen produced is released into the exhaust channel, and by making at least a portion of this area a reverse water-gas shift reactor, carbon dioxide flowing through the exhaust channel and hydrogen produced in the electrode layer can be used to produce carbon monoxide.

In this electrolytic cell unit, the functional parts for the electrolytic reaction section and the reverse water gas shift reaction section are constructed as separate sections (the former is the electrolytic cell, the latter the exhaust channel). Therefore, by using optimal materials for each section and maintaining an appropriate temperature environment, carbon dioxide that cannot be sufficiently decomposed in the electrolytic reaction section can be converted into carbon monoxide in the reverse water gas shift reaction section. Furthermore, these electrolytic reactions and reverse water gas shift reactions can also be carried out within the electrolytic cell unit. As described below, both reactions require relatively high temperatures, so it is preferable to house them within the same unit.

Furthermore, because the electrolytic cell according to the present invention is configured as a solid oxide electrolytic cell, it can perform electrolysis highly efficiently despite its robust structure, and the heat generated by the reaction can be used in the reverse water gas shift reaction section.

Furthermore, the solid oxide electrolysis cell can be structured to be supported by a support. In this case, a thin-layer solid oxide electrolysis cell can be formed using an inexpensive support, thereby reducing the amount of expensive materials used in the electrode layers and electrolyte layers of the solid oxide electrolysis cell, thereby reducing the manufacturing cost of the solid oxide electrolysis cell. While ceramics or metal materials can be used for the support, using a metal as the support is preferable because it ensures strength with an inexpensive metal material, reduces material costs, and is more easily processable than ceramics, allowing for greater shape selectivity. Furthermore, when a metal support is used, sufficient strength can be ensured even at a thin thickness compared to when a ceramic support is used, allowing the support to be made thinner. As a result, it becomes easier to reduce the thickness, size, and weight of the electrolysis cell or electrolysis cell unit.

When a support is provided in this manner, multiple through-holes may be provided through the support, an electrode layer may be provided on one surface of the support, and an exhaust channel may be provided along the other surface, with a reverse water gas shift reactor being provided on at least a portion of the inner surface of the exhaust channel.

With this configuration, hydrogen can be generated by providing an electrode layer on one side of the support. The hydrogen generated in this manner is guided from the electrode layer to the exhaust channel via multiple through-holes, where it effectively undergoes a reaction in the reverse water gas shift reactor located in at least a portion of this area. When carbon dioxide is supplied, at least carbon monoxide can be generated.

A second characteristic feature of the present invention is that the electrolytic cell is flat.

Here, the term "flat" means that the member has a two-dimensional extent.
The electrolytic cell is configured with an electrode layer and a counter electrode layer sandwiching an electrolyte layer, and a predetermined electrolytic reaction can be generated by flowing a predetermined gas on at least one side of these electrode layers. For example, in the embodiment described below, the target gas for electrolysis (H ₂ O, CO ₂ , or both) is flowed on the electrode layer side. Meanwhile, the counter electrode layer side receives oxygen ions guided to this layer via the electrolyte layer and releases them as oxygen. The released oxygen is released to the outside by a carrier gas flowing on the oxygen-releasing side of the counter electrode layer.
Therefore, since this layer has a two-dimensionally expanding surface on both the electrode layer side and the counter electrode layer side, it is possible to provide a reaction field and efficiently supply and release a predetermined gas to the reaction field. Also, the introduction and discharge of gas into and from the electrode layer and the counter electrode layer can be achieved with a relatively simple structure.

The third characteristic configuration of the present invention is
The reverse water gas shift catalyst contained in the reverse water gas shift reactor is a catalyst containing at least one of platinum, nickel, and iron.

This characteristic configuration allows for highly active reverse water gas shift performance, as described below.

The fourth characteristic configuration of the present invention is
The reverse water gas shift catalyst contained in the reverse water gas shift reactor is a catalyst containing at least one of ceria, zirconia, and alumina.

This characteristic configuration not only achieves highly active reverse water gas shift performance, as described below, but also ensures catalytic activity and durability in the high-temperature environments required for the reverse water gas shift reaction. At least one of ceria, zirconia, and alumina plays a role in retaining catalytically active components in the reverse water gas shift catalyst, and such components can withstand use at high temperatures.

In addition, by selecting ceria or zirconia, the thermal expansion coefficient can be made closer to that of the materials used for the constituent materials and support of the electrolytic cell, making the electrolytic cell unit less susceptible to damage even when subjected to repeated temperature cycles of low and high temperatures, resulting in an electrolytic cell unit with excellent reliability and durability.

When obtaining a reverse water gas shift catalyst, it is preferable to at least include a calcination step in which the catalyst is calcined at a temperature of 450°C or higher.

When using a reverse water gas shift catalyst, the reaction temperature must be relatively high to cause the desired reverse water gas shift reaction. A catalyst obtained by calcining within this temperature range can be used stably. A temperature of 450°C or higher is preferable, but temperatures of 600°C or higher or 800°C or higher are even more preferable, as they enhance stability at high temperatures. In the present invention, the catalyst can be used stably because it is combined with a solid oxide electrolysis cell operated at relatively high temperatures (e.g., 600°C to 800°C). Furthermore, because the cost of the calcination process becomes too high if the calcination temperature is too high, the upper limit is approximately 1200°C.

When using a reverse water gas shift catalyst, it is preferable to subject the catalyst to a reduction pretreatment before use in the reaction.

The catalytically active components contained in reverse water gas shift catalysts are often at least partially converted into metal oxides during the calcination process, but by subjecting the catalyst to pre-reduction treatment (a reduction treatment carried out before use), the oxidized catalytically active components can be reduced, allowing the catalyst to exhibit good catalytic activity.

A fifth characteristic configuration of the present invention is
The reverse water gas shift reactor is of a flat plate type.

Here, the term "flat" means that the region has a two-dimensional extent.
In the present invention, the reverse water gas shift reactor is a site for supplying at least hydrogen and carbon dioxide, and by making this site a site having a two-dimensional expansion, the gas can be caused to flow in the direction of the expansion, thereby allowing the reaction to proceed efficiently, as in the case of the electrolytic cell described above.
Furthermore, when the electrolytic cell is of a flat plate type, for example, the shape of the two-dimensional structure can be matched to easily realize the connection.

Furthermore, as a flat valve type, stacks can be easily realized by stacking multiple reverse water gas shift reactors. Naturally, stacks can also be constructed by combining them with electrolytic cells.

A sixth characteristic feature of the present invention is a structure including an electrolysis cell stack having a plurality of the electrolysis cells.

The electrolytic cell unit of the present invention is configured to include an electrolytic cell, and the electrolytic cell may have a functional part capable of electrolyzing a supplied gas, regardless of the support structure of the electrolytic cell or the supply structure of the gas to be electrolyzed.
In other words, it is sufficient to adopt a configuration in which multiple electrolytic cells are assembled, supply the gas to be electrolyzed to the functional part that performs the electrolytic function in the electrolytic cell, and exhaust the gas generated by the electrolysis of the gas to an exhaust path.

Therefore, by constructing an electrolytic cell stack containing multiple electrolytic cells, the gas to be electrolyzed can be passed through the stack, an exhaust path can be provided, and electrolysis of the specified gas can be carried out in the stack state, with at least a portion of the exhaust path serving as a reverse water-gas shift reactor.

In this way, by using an electrolytic cell stack in which the number of electrolytic cells is appropriately adjusted, its performance (electroresolution) and capacity (the amount of _H2 when electrolyzing _H2O , or the amount _{of H2O} and CO when electrolyzing _CO2 ) can be easily adjusted.

A seventh characteristic configuration of the present invention is
A heat transfer section is provided between the electrolytic cell or the electrolytic cell stack and the reverse water gas shift reactor.

In the present invention, since the electrolytic cell is a solid oxide electrolytic cell, its temperature becomes high as described above, and therefore, heat generated by electrolysis from the electrolytic cell or electrolytic cell stack can be utilized in the reverse water gas shift reactor.
That is, as shown in the tenth characteristic configuration of the present invention,
The heat generated by the electrolytic cell can be used for the endotherm of the reverse water gas shift reaction occurring in the reverse water gas shift reaction section.

The electrolysis cell unit module according to an eighth characteristic configuration of the present invention is characterized by:
The electrolysis cell unit module is an assembly of a plurality of electrolysis cell units as described above.

The inventors refer to an electrolytic cell unit including a single electrolytic cell as described above as a "single-cell electrolytic cell unit," and an electrolytic cell unit including an electrolytic cell stack formed by assembling a plurality of electrolytic cells as an "assembled electrolytic cell unit." That is, when it is desired to increase the amount of gas produced, a plurality of "single-cell electrolytic cell units" each including a reverse water-gas shift reaction unit in at least a portion of the hydrogen discharge channel of a single electrolytic cell can be assembled into a modularized "electrolytic cell unit module." Alternatively, a plurality of "assembled electrolytic cell units" each including a reverse water-gas shift reaction unit in at least a portion of the hydrogen discharge channel of an electrolytic cell stack formed by assembling a plurality of electrolytic cells can be assembled into a modularized "electrolytic cell unit module." In this way, by modularizing the electrolytic cell unit and appropriately adjusting the number of electrolytic cells, the performance (electrolytic resolution) and capacity (the amount of _H2 when electrolyzing _H2O , or the amount of _H2 and CO when electrolyzing _H2O and _CO2 ) can be easily adjusted.

A ninth characteristic configuration of the hydrocarbon production system of the present invention is as follows:
The feature is that the electrolytic cell unit or electrolytic cell unit module described above is at least provided with a hydrocarbon synthesis reaction section.

This characteristic configuration allows hydrocarbons to be synthesized in the hydrocarbon synthesis reaction section by receiving at least hydrogen and carbon monoxide from the electrolytic cell unit or electrolytic cell unit module described above. Here, the electrolytic cell unit or electrolytic cell unit module according to the present invention includes at least a reverse water-gas shift reaction section, and therefore the heat generated by the electrolytic cell can be used to absorb the heat of the reverse water-gas shift reaction that occurs in the reverse water-gas shift reaction section, resulting in an efficient, high-performance hydrocarbon production system.

FIG. 1 is a diagram showing the configuration of a hydrocarbon production system employing an electrolytic cell unit according to the present invention. Schematic diagram showing the configuration of the electrolytic reaction section A diagram showing the configuration of a system that integrates an electrolysis reactor and a reverse water gas shift reactor. Schematic diagram of an electrolysis cell unit equipped with an electrolysis reactor and a reverse water-gas shift reactor Cross-sectional view of the electrolysis cell unit used in a comparative experiment in which the electrode layer side gas supply channel was used as a reverse water-gas shift reactor. FIG. 1 shows an electrolysis cell stack composed of a pair of single-cell electrolysis cell units. 7 is a cross-sectional view of the electrolysis cell stack shown in FIG. 6 in the flow path direction. FIG. 1 shows an example of the configuration of a module equipped with an electrolysis reaction unit and a reverse water gas shift reaction unit. FIG. 1 shows an example of the configuration of a module equipped with an electrolysis reaction unit and a reverse water gas shift reaction unit. Diagram of a hydrocarbon production system equipped with a heat exchanger between the electrolysis reactor and the reverse water gas shift reactor. FIG. 1 shows another configuration of a hydrocarbon production system in which CO ₂ is introduced into a reverse water gas shift reaction section. FIG. 12 is a diagram showing an example of a module configuration corresponding to the alternative configuration shown in FIG. 11 . FIG. 1 is a diagram showing another configuration of a hydrocarbon production system equipped with a hydrogen separation unit. FIG. 10 is a diagram showing yet another configuration of a hydrocarbon production system provided with a water separation section before a hydrocarbon synthesis reaction section. FIG. 10 is a diagram showing yet another configuration of a hydrocarbon production system in which only water is introduced into the electrolysis reaction section. An explanatory diagram showing the preparation state of the catalyst An explanatory diagram showing the catalyst coating and baking state and pre-reduction treatment Schematic diagram of an electrolysis cell unit equipped with an electrolysis reaction section, a reverse water-gas shift reaction section, and a hydrocarbon synthesis reaction section.

An embodiment of the present invention will be described with reference to the drawings.
1 shows the configuration of one embodiment of a hydrocarbon production system 100 proposed by the inventors. As will be described below, this system 100 is configured to include an electrolysis reaction section 10, and at least this electrolysis reaction section 10 is mainly composed of the electrolysis cell unit proposed by the inventors.

As shown in the figure, this hydrocarbon production system 100 is configured to include, in order, an electrolytic reaction section 10, a first catalytic reaction section 20, a second catalytic reaction section 30, a heavy hydrocarbon separation section 35 (illustrated as a CnHm separation section), a water separation section 40 (illustrated as an _H2O separation section), and a carbon dioxide separation section 50 (illustrated as a _CO2 separation section).

The electrolytic reaction unit 10 is a unit that electrolyzes at least a portion of the inflowing gas, the first catalytic reaction unit 20 is a reverse water-gas shift reaction unit that performs a reverse water-gas shift reaction on at least a portion of the inflowing gas, and the second catalytic reaction unit 30 is configured to function as a hydrocarbon synthesis reaction unit that synthesizes at least a portion of the inflowing gas into hydrocarbons. The hydrocarbons synthesized here are mainly _CH4 (a hydrocarbon with one carbon atom), but also include lower saturated hydrocarbons with two to four carbon atoms. Furthermore, as will be described later, by appropriately selecting a catalyst used in the second catalytic reaction unit 30, it is possible to synthesize heavier hydrocarbons with a carbon number greater than the lower saturated hydrocarbons, non-saturated hydrocarbons, oxygen-containing hydrocarbons, and the like.

The heavy hydrocarbon separation unit 35, the water separation unit 40, and the carbon dioxide separation unit 50 are units that remove at least a portion of predetermined components (CnHm, _H2O , and _CO2 , in that order) from the gas flowing therethrough. The components removed and recovered by the water separation unit 40 and the carbon dioxide separation unit 50 are returned to predetermined parts of the system via a water return line 41 and a carbon dioxide return line 51, as shown in Figure 1, and are reused. The _H2O and _CO2 returned via the return lines 41 and 51 are shown corresponding to the components.
As a result, this hydrocarbon production system 100 is established as a carbon-closed system that does not substantially release CO ₂ outside the system.

In the diagram, the gas flowing into each part is shown before each part, and the gas released from that part is shown after.

In the electrolysis reaction section 10, _H2O and _CO2 as starting materials are introduced and electrolyzed inside, whereby _H2O is decomposed into _H2 and _O2 , and some of the _CO2 is decomposed into CO and _O2 and released.

The reaction is described as follows:
2H ₂ O → 2H ₂ +O ₂ (Formula 1)
_2CO2 → 2CO + _O2 (Equation 2)
These formulas 1 and 2 are also shown in the box representing the electrolytic reaction section 10 in FIG.

In the first catalytic reaction unit 20 (reverse water-gas shift reaction unit), H ₂ and CO ₂ are introduced and a reverse water-gas shift reaction occurs therein, whereby CO ₂ is converted into CO and H ₂ is converted into H ₂ O, which are then released.

The reaction is described as the following equilibrium reaction, but the reverse water gas shift reaction is a reaction in which the reaction described in the following equation 3 proceeds to the right (a reaction in which CO ₂ and H ₂ react to produce CO and H ₂ O).
CO ₂ + H ₂ ⇔ CO + H ₂ O (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 schematically in this box.

In the second catalytic reaction section 30 (hydrocarbon synthesis reaction section), at least _H2 and CO are introduced, and hydrocarbons are synthesized by a catalytic reaction. For example, the reaction of synthesizing _CH4 from CO and _H2 is expressed as the following equilibrium reaction, but the reaction of synthesizing _CH4 from CO and _H2 is a reaction in which the reaction expressed in the following formula 4 proceeds to the right (a reaction in which CO and _H2 react to produce _CH4 and _H2O ).
CO+3H ₂ ⇔ CH ₄ +H ₂ O (Formula 4)
This formula 4 is also shown in the box representing the second catalytic reaction section 30 (hydrocarbon synthesis reaction section) in Fig. 1. The hydrocarbon synthesis catalyst cat2 used in the reaction is also shown schematically in this box.
Furthermore, the equilibrium reaction of (Equation 3) also occurs at this site.
Furthermore, depending on the type of catalyst used in the second catalytic reaction section 30, it is possible to proceed with a Fischer-Tropsch (FT) synthesis reaction or the like, and therefore various hydrocarbons such as ethane, propane, butane, pentane, hexane, paraffin, olefin-based hydrocarbons, etc. can be synthesized from CO and _H2 .

As described below, the inventors have shown an example of a catalyst that uses ruthenium as the catalytically active component of the hydrocarbon synthesis catalyst cat2 placed in the second catalytic reaction section 30. However, catalysts that contain iron, cobalt, or other catalytically active components also synthesize heavy hydrocarbons, and these types of heavy hydrocarbons condense as the temperature drops and can be separated from the carrier gas. Therefore, the aforementioned heavy hydrocarbon separation section 35 separates the hydrocarbon components separated in this manner.

The H ₂ O produced in the water separation section 40 is separated and returned to the upstream side of the electrolysis reaction section 10 via a water return line 41 (water recycle line).

The CO ₂ 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).

As a result, hydrocarbons are ultimately synthesized in this hydrocarbon production system 100 and can be supplied to the outside.

The above is an overview of the hydrocarbon production system 100. The configuration and role of each part will now be described.
[Electrolytic reaction section]
As previously described, the electrolytic reaction section 10 consumes the power supplied in accordance with the above formulas 1 and 2 to decompose the inflowing H ₂ O and CO ₂ .

FIG. 2 shows a schematic cross-sectional view of the electrolytic reaction section 10. As shown in FIG.
The figure shows an electrolytic cell unit U (single-cell electrolytic cell unit) that is used by stacking a plurality of electrolytic cell units. This electrolytic cell unit U includes an electrolytic cell 1, and the electrolytic cell 1 is configured to include 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 electrolytic cell 1, and the counter electrode layer 3 serves as the anode. Incidentally, this electrolytic cell unit U is supported by a metal support 4. Here, a solid oxide electrolytic cell is used as the electrolytic cell 1.

The electrolyte layer 1a can be formed as a thin film with a thickness of 10 μm or less. Its constituent materials include YSZ (yttria-stabilized zirconia), SSZ (scandia-stabilized zirconia), GDC (gadolinium-doped ceria), YDC (yttrium-doped ceria), SDC (samarium-doped ceria), and LSGM (strontium-magnesium-doped lanthanum gallate). Zirconia-based ceramics are particularly suitable.

This electrolyte layer 1a is preferably formed by a low-temperature firing method (e.g., a wet method using firing at a low temperature without firing at temperatures above 1100°C), a spray coating method (thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, cold spray, etc.), a PVD method (sputtering, pulsed laser deposition, etc.), a CVD method, etc. These low-temperature deposition processes can be used to obtain a dense electrolyte layer 1a with high airtightness and gas barrier properties without firing at temperatures above 1100°C, for example. This suppresses damage to the metal support 4 and interdiffusion of elements between the metal support 4 and the electrode layer 2, resulting in an electrolysis cell unit U with excellent performance and durability. Low-temperature firing methods and spray coating methods are particularly preferred, as they allow for low-cost devices to be produced. Furthermore, spray coating is even more preferable because it makes it easy to obtain a dense electrolyte layer 1a with high airtightness and gas barrier properties at low temperatures.

The electrolyte layer 1a is densely structured to prevent gas leaks and exhibit high ionic 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. If the electrolyte layer 1a is a uniform layer, its density is preferably 95% or more, and even more preferably 98% or more. If the electrolyte layer 1a is structured as multiple layers, it is preferable that at least a portion of these layers include a layer with a density of 98% or more (dense electrolyte layer), and even more preferably a layer with a density of 99% or more (dense electrolyte layer). If such a dense electrolyte layer is included as part of the electrolyte layer 1a, it is easier to form an electrolyte layer 1a that is dense and has high airtightness and gas barrier properties, even if the electrolyte layer 1a is structured as multiple layers.

The electrode layer 2 can be provided as a thin layer on the front surface of the metal support 4 in an area larger than the area where the holes 4a are provided. When a thin layer is provided, its thickness can be, for example, approximately 1 μm to 100 μm, and preferably 5 μm to 50 μm. This thickness reduces the amount of expensive electrode layer material used, cutting costs, while ensuring sufficient electrode performance. The entire area where the holes (through-holes) 4a are provided is covered by the electrode layer 2. In other words, the holes 4a are formed inside the area of the metal support 4 where the electrode layer 2 is formed. In other words, all of the holes 4a are provided facing the electrode layer 2.

The constituent material of this electrode layer 2 can be, for example, a composite material such as NiO-GDC, Ni-GDC, NiO-YSZ, Ni-YSZ, CuO-CeO ₂ , or Cu-CeO ₂ . In these examples, GDC, YSZ, and CeO ₂ can be called the aggregate of the composite material. The electrode layer 2 is preferably formed by a low-temperature firing method (e.g., a wet method using a firing process in a low-temperature range without firing at a high temperature range above 1100°C), a spray coating method (such as a thermal spraying method, aerosol deposition method, aerosol gas deposition method, powder jet deposition method, particle jet deposition method, or 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 a low-temperature range can produce a good electrode layer 2 without firing at a high temperature range above 1100°C, for example. Therefore, it 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, it is even more preferable to use a low-temperature firing method because it makes it easier to handle the raw materials.

The counter electrode layer 3 can be formed as a thin layer on the surface of the electrolyte layer 1a opposite the electrode layer 2. When a thin layer is used, its thickness can be, for example, approximately 1 μm to 100 μm, preferably 5 μm to 50 μm. This thickness reduces the amount of expensive counter electrode layer material used, thereby cutting costs, while still ensuring sufficient electrode performance. Examples of materials that can be used for the counter electrode layer 3 include composite oxides such as LSCF and LSM, ceria-based oxides, and mixtures of these. It is particularly preferable that the counter electrode layer 3 contain 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, electrode layer 2, and counter electrode layer 3 are formed as thin films, as described below, and the inventors refer to this as being formed in a thin layer.

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. A supply channel forming member 5 that forms a U-shaped electrode layer side gas supply channel 5a is provided on the opposite side of the metal support 4 from the electrode layer 2. Furthermore, a large number of holes 4a are formed in the metal support 4, penetrating the front and back surfaces. Gases (H ₂ O and CO ₂ ) supplied via the electrode layer side gas supply channel 5a are electrolyzed and supplied to the electrode layer 2 via the large number of holes 4a. Furthermore, the generated gases (H ₂ , CO) flow out from the holes 4a.

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

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 electrolytic cell 1 and the entire electrolytic 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 cylinder shape, are also possible. When the metal support 4 is plate-shaped in this way, the electrolytic cell unit U becomes a flat plate type, as can be easily understood from Figures 2 and 4 .
The metal support 4 may have 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.

The metal support 4 has, for example, a plurality of holes 4a that penetrate the front and back surfaces of the metal plate. For example, the holes 4a can be formed in the metal support 4 by mechanical, chemical, or optical drilling. The holes 4a function to allow gas to pass from the back surface of the metal support 4 to the front surface. The holes 4a may be formed at an angle to the gas advection direction (the direction from the front to the back of the paper in Figure 2).

By using ferritic stainless steel (an example of an Fe-Cr alloy) as the base material for the metal support 4, the thermal expansion coefficient can be made 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 electrolyte layer 1a. Therefore, the electrolysis cell unit U is less likely to be damaged even when subjected to repeated low- and high-temperature cycles. This is preferable because it allows for an electrolysis cell unit U with excellent long-term durability.

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

The metal support 4 and both supply path forming members 5 and 6 are conductive, but are constructed airtight, so they act as separators separating each supply path 5a and 6a.

During electrolysis, the electrolytic 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 that are disposed on either side of the electrolyte layer 1 a. 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 electrolytic cell unit U, the electrode layer 2 side may be positive and the counter electrode layer 3 side may be negative.
Then, by supplying the gases to be electrolyzed, H ₂ O and CO ₂ , from the electrolysis raw material supply unit (upstream of the electrolysis reaction unit 10 in FIG. 1 ) to the electrode layer 2 and supplying a carrier gas g2 to the counter electrode layer side, the reactions shown in Equations 1 and 2 occur in the electrolysis cell 1, and the decomposed gas can be extracted. Here, the H ₂ O may be supplied as either water or steam, 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 steam and carbon dioxide to the electrolysis cell unit U, and a power supply unit that supplies power.

In Fig. 2 , the gases supplied (H ₂ O, CO ₂ ) and the gases released (H ₂ O, H ₂ , CO, O ₂ , CO ₂ ) during the electrolysis reaction are depicted above and below the electrolytic cell unit U. However, this is for ease of understanding. In reality, the electrode layer side gas supply channel 5a and the counter electrode layer side gas supply channel 6a are formed to extend in the front-to-back direction of the page in Fig. 2 . For example, the supply side gases (H ₂ O, CO ₂ ) depicted above the electrolytic cell unit U in Fig. 2 can be recovered from the front side of the page, and the release side gases (H ₂ O, H ₂ , CO, O ₂ , CO ₂ ) depicted below the electrolytic cell 1 can be recovered from the back side of the page (see Fig. 4 described below). Note that a carrier gas g2 such as air can be flowed into the electrolytic cell unit U to smoothly discharge O ₂ produced during the electrolytic reaction.

When _H2O and _CO2 are supplied to the electrolysis reaction unit 10 and electrolyzed, _H2O has a lower electrolysis voltage than _CO2 and is therefore more easily electrolyzed. Therefore, if equal amounts of _H2O and _CO2 are supplied to the electrolysis reaction unit 10 to carry out an electrolysis reaction, the _H2 concentration is likely to be higher than the CO concentration at the outlet of the electrolysis reaction unit 10, and unreacted _CO2 is likely to remain.

[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 supplied _H2 , and converts _H2 to _H2 O. That is, in the electrolysis reaction unit 10, which supplies _H2 O and _CO2 and performs electrolysis, _CO2 that remains without being decomposed is converted into CO.

The reaction here is as shown in Equation 3, but this reaction is an endothermic reaction and an equilibrium reaction that depends 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 Equation 3 to occur at as high a temperature as possible (e.g., 600°C to 800°C).

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 will be described later, the inventors have investigated various combinations of catalytically active components and supports, and have found that certain combinations are preferable.
This type of catalyst can be easily produced by an impregnation process in which a carrier is immersed in a solution containing catalytically active components (metals), removed, dried, and heated. This process is called a calcination process. The preparation and use of this catalyst will be described with reference to Figures 16 and 17.

The preparation method described here is similar for various combinations of catalytically active components and carriers, except for the starting materials. Figure 16 shows examples of a reverse water gas shift catalyst cat1 and a hydrocarbon synthesis catalyst cat2 according to the present invention. In the figure, the catalytically active component of the reverse water gas shift catalyst cat1 is labeled ca1, and its carrier is labeled cb1. On the other hand, for the hydrocarbon synthesis catalyst cat2, its catalytically active component is labeled ca2, and its carrier is labeled cb2.

As shown in Figure 16, catalyst preparation involves preparing an aqueous solution of a compound containing metal components (metal catalysts) that will become catalytically active components ca1 and ca2. Then, carriers cb1 and cb2 are added to the aqueous solution and stirred and impregnated (impregnation support process (a)). This is followed by evaporation to dryness and drying, followed by a drying, crushing, and molding process (b) in which the carrier is crushed and molded. The resulting molded body is then calcined in air (calcination process (c)), yielding the desired product (cat1, cat2). Therefore, this form of catalyst is also known as an impregnated-supported catalyst.

In this case, the catalyst can be applied to the location where it is to be used and then calcined, as shown in the example of reverse water gas shift catalyst cat1 in Fig. 17. Fig. 17(a) shows the application and calcination process in which the reverse water gas shift catalyst cat1 is applied to a metal support 4 having holes 4a to form a coating layer 20a, followed by calcination. Fig. 17(b) shows the pre-reduction process in which _H2 is passed through the reverse water gas shift catalyst cat1 before use.

When the calcination treatment is performed in air, the supported catalytic active components ca1 and ca2 are partially or completely oxidized. Before using the catalyst, a so-called reduction pretreatment can be performed to reduce the oxidized catalytic active components and sufficiently increase their activity. Figure 17(b) shows the state in which a reducing gas (typically H ₂ ) is passed over the surface of the catalyst to perform the reduction pretreatment.

(Catalyst to be used)
The inventors selected a catalyst that satisfies the following requirements as the reverse water gas shift catalyst cat1 to be used in the first catalytic reaction section 20.

This catalyst is constructed by supporting at least one or both of platinum, nickel, and iron as catalytically active components ca1 on a support cb1 primarily composed of ceria-based metal oxide or zirconia-based metal oxide. Here, the proportion of support cb1 relative 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 proportion can be set to, for example, 99.5% by weight, but if it is higher than this, the catalytically active component ca1 may not be sufficiently supported, making it difficult to achieve the desired effect as a reverse water gas shift catalyst cat1.

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.

In order to ensure good progress of the reverse water gas shift reaction, the amount of catalytically active component CA1 supported is preferably 0.5% by weight or more, more preferably 1% by weight or more, and even more preferably 5% by weight or more. Furthermore, if the amount of catalytically active component CA1 supported is too high, it becomes difficult to support the catalytically active component CA1 with high dispersion, making it difficult to achieve a significant improvement in catalytic activity and increasing catalyst costs. Therefore, the amount of catalytically active component CA1 supported is preferably 35% by weight or less, more preferably 30% by weight or less, and even more preferably 25% by weight or less.

Furthermore, it is also preferable to add one or both of platinum, nickel, and iron to the catalytically active component ca1 and support copper as a further catalytically active component ca1. In this configuration, the amount of copper supported is equal to or less than the amount of one or both of nickel and iron, the main catalytically active components ca1, supported in the catalytically active component ca1.

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, Fe, and Pt (platinum) were also investigated.
As the carrier cb1, ZrO ₂ (zirconia), YSZ (yttria-stabilized zirconia), GDC (gadolinium-doped ceria), and CeO ₂ (ceria) were used as examples, and Al ₂ O ₃ (alumina) was also investigated.

The following explanation introduces Test Example 1 and Test Example 2. The difference between the two tests is that when calcining the reverse water gas shift catalyst cat. 1, Test Example 1 used a calcination temperature of 450°C, while Test Example 2 used a higher calcination temperature of 600°C to 1000°C.

(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, Fe, and Pt (platinum) were also investigated.
As the support, ZrO ₂ (zirconia), YSZ (yttria stabilized zirconia), GDC (gadolinium doped ceria), and CeO ₂ (ceria) were used as examples, and Al ₂ O ₃ (alumina) was also investigated.

(Catalyst preparation)
In preparing the reverse water gas shift catalyst cat1, an aqueous solution is prepared by dissolving a quantity of either or both of a water-soluble nickel compound (nickel nitrate, nickel chloride, nickel sulfate, nickel ammonium sulfate, nickel acetate, nickel oxalate, nickel citrate, etc.) and a water-soluble iron compound (iron nitrate, iron chloride, iron sulfate, ammonium iron sulfate, iron acetate, iron oxalate, iron citrate, etc.) according to the desired catalyst composition. When supporting copper as an additional catalytically active component ca1, an aqueous solution is prepared by dissolving a quantity of a water-soluble copper compound (copper nitrate, copper chloride, copper sulfate, copper ammonium sulfate, copper acetate, copper oxalate, copper citrate, _etc. ) in a similar manner. A predetermined amount of carrier powder (ceria, zirconia, GDC, YSZ, _Al2O3 ) is added to the aqueous solution, stirred, impregnated, evaporated to dryness, dried, crushed, molded, and calcined in air. This impregnation is referred to as the "impregnation supporting step" in the present invention, and the resultant product is the "impregnated supported material."
The catalysts in the following examples were prepared using nickel nitrate hexahydrate, iron nitrate nonahydrate, and copper nitrate trihydrate, respectively, and the Pt-based catalyst was prepared using tetraammineplatinum hydroxide.

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

Table 1 shows Examples 1 to 19 of the reverse water gas shift catalyst cat. 1 of the present invention.
The horizontal axis represents the type of carrier cb1, the amount of metal carried as a catalytically active component (weight %; expressed 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.

(Catalytic activity test)
The catalytic activity test was carried out using a 50% H ₂ -50% CO ₂ mixed gas (a mixed gas containing H ₂ and CO ₂ in a 1:1 (volume ratio)) as the reaction gas, under the condition of a GHSV (Gas Hourly Space Velocity) of 10,000/h, while changing the reaction temperature 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 outlet of the reaction section are shown in Table 2.

The _CO2 conversion rate (%) was calculated according to the following formula based on the results of gas analysis at the outlet of the catalyst layer.
[CH ₄ concentration] + [CO concentration] / ([CH ₄ concentration] + [CO concentration] + [CO ₂ concentration])

As mentioned above, it is desirable that the reverse water gas shift catalyst cat1 used in the first catalytic reaction section 20 (reverse water gas shift reaction section) has a high _CO2 conversion rate (%) at high temperatures (for example, around 600 to 800°C).

(Test Example 2)
The test results of Examples (20 to 29) of Test Example 2 will be explained below.
As catalytically active components, Ni and Fe were investigated, and the addition of Cu was also investigated.
As the carrier, CeO ₂ (ceria) and ZrO ₂ (zirconia) are used in the examples, and Al ₂ O ₃ (alumina) is also being investigated.

(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.

Table 3 shows the catalysts prepared for each of the examples (20-29).

(Catalytic activity test)
The catalytic activity test was carried out using a mixed gas containing H ₂ and CO ₂ in a 1:1 (volume ratio) ratio as the reaction gas, under the condition of GHSV of 10,000/h, while changing the reaction temperature 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 outlet of the reaction section are shown in Table 4.

For reference, the equilibrium values (calculated values) of the _CO2 conversion rate under these experimental conditions are shown in Table 4.

Iron-Zirconia Catalyst and Iron-Alumina Catalyst Test results for the iron-zirconia catalyst at calcination temperatures of 450°C, 600°C, 800°C, and 1000°C are shown in Examples 8, 22, 26, and 29, respectively. Meanwhile, test results for the iron-alumina catalyst at calcination temperatures of 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 exhibits superior reverse water-gas shift reaction activity compared to the iron-alumina catalyst. Furthermore, the iron-zirconia catalyst exhibits very high catalytic activity not only at calcination temperatures of 450°C, but also at higher calcination temperatures of 600°C, 800°C, and 1000°C, and the _CO2 conversion rate reaches near equilibrium at all calcination temperatures.

The test results for nickel-ceria catalysts where the calcination temperatures were 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 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 all of the calcination temperatures.

The test results for the nickel-alumina catalyst when the calcination temperature was set to 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.

The test results for nickel-copper-ceria catalysts at 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 increased to 600°C or 800°C, but is superior to the iron-alumina catalyst with the same calcination temperature conditions described above. Furthermore, the nickel-copper-ceria catalyst with a calcination temperature of 450°C achieves a _CO2 conversion rate close to the equilibrium value.

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

From the above results, as previously shown, it is possible to use a catalyst as the reverse water gas shift catalyst cat1 used in this first catalytic reaction section 20, which is constructed by supporting at least one or both of nickel and iron as catalytically active components ca1 on a carrier cb1 primarily composed of ceria-based metal oxide or zirconia-based metal oxide. Furthermore, platinum can also be used if the cost is acceptable.

Furthermore, the ceria-based metal oxide used as the carrier cb1 can be ceria doped with at least one of gadolinium, samarium, and yttrium.

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

Furthermore, it is also preferable 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.

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 performed at a _CO2 conversion rate (%) at or above that of a highly active but very expensive Pt catalyst at around 600 to 1000°C.
It should be noted that the test in this example was conducted under conditions of a very high GHSV of 10,000/h. Therefore, it is 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.

[Combination of electrolysis reactor and reverse water gas shift reactor]
In the above description, the electrolysis reactor 10 and the reverse water gas shift reactor 20 are individually provided in the order shown along the gas advection direction in accordance with the system configuration shown in FIG. 1 .
Depending on the reaction conditions, the reaction in the electrolytic reaction unit 10 may be exothermic, while the reaction in the reverse water gas shift reaction unit 20 is endothermic. Therefore, integrating these two reaction units 10 and 20 can improve the thermal efficiency of the system. Figure 3 shows a configuration in which these two reaction units 10 and 20 are combined and integrated, with both units enclosed to indicate their integration. The reactions in this integrated configuration are also shown in the same box. Essentially, the reactions represented by Equations 1, 2, and 3 above are carried out. When combining and integrating the electrolytic reaction unit 10 and the reverse water gas shift reaction unit 20, it is preferable to surround them with a heat-insulating member, as this allows for efficient heat transfer between the electrolytic reaction unit 10 and the reverse water gas shift reaction unit 20. Furthermore, a heat-transfer member may be used to connect the electrolytic reaction unit 10 and the reverse water gas shift reaction unit 20 to transfer heat generated in the electrolytic reaction unit 10 to the reverse water gas shift reaction unit 20.

[Electrolysis cell unit equipped with both an electrolysis reaction section and a 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 electrolytic cell unit U that serves as the electrolytic reaction unit 10. This is because, when a solid oxide electrolytic cell that operates at around 600 to 800°C is used as the electrolytic cell 1, the reverse water gas shift catalyst cat1 of the present application, which exhibits high activity at around 600 to 800°C, can be used in the electrolytic reaction unit 10 and the reverse water gas shift reactor 20 in approximately the same temperature range.
In this case, too, it is sufficient that the gas that has passed through the electrolysis reactor 10 is guided to the reverse water-gas shift reactor 20 and the reverse water-gas shift reaction occurs.

An electrolytic cell unit U equipped with such a reverse water gas shift reactor 20 is shown in Figure 4. Figure 4 is a diagram of the electrolytic cell unit U shown in cross section in Figure 2, including the direction of gas advection.

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

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.
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.

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

In this configuration, the metal support 4 functions as a separator that separates _H2 generated in the electrode layer 2 from _O2 generated in the counter electrode layer 3, and at least a portion of this separator on the _H2 exhaust channel side serves as the reverse water-gas shift reactor 20. Even in this configuration, the electrolysis cell unit U can be said to be flat-plate type, and the reverse water-gas shift reactor 20 can also be said to be flat-plate type.

By stacking electrolytic cell units U configured in this manner in the left-right direction in Figures 2 and 4, a large number of electrolytic cell units U can be stacked and electrically connected to form an electrolytic cell stack. Therefore, the electrolytic cell units U described so far can be called "single-cell electrolytic cell units," and because the electrolytic cell stacks can also be configured and used as units, they can be called "aggregate electrolytic cell units." Furthermore, a large number of single-cell electrolytic cell units or a large number of aggregate electrolytic cell stacks can be stacked to form a module. In these electrolytic cell unit modules, the useful gases produced can naturally be obtained across multiple layers.

Based on the concept of combining the electrolysis reaction unit 10 and the reverse water gas shift reaction unit 20 (the electrode layer side gas supply channel 5a of the electrolysis reaction unit 10 is 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 channel 5a.
FIG. 5 shows a cross section of the electrolysis cell unit U used in this experiment.

A specific description will be given below with reference to Figure 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 as the metal support 4 by forming a plurality of through-holes (which became the holes 4a) in a 0.3 mm-thick ferritic stainless steel metal plate by laser processing. An electrode layer 2 and an intermediate layer 2a were sequentially laminated 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 sequentially laminated on the electrolyte layer 1a to prepare the electrolysis cell 1. The electrode layer 2 was formed using a mixture of NiO powder and GDC powder, the intermediate layer 2a was formed using GDC powder, the electrolyte layer 1a was formed using 8YSZ (8 mol% yttria-stabilized zirconia) powder, the reaction prevention layer 7 was formed using GDC powder, and the counter electrode layer 3 was formed using a mixture of GDC powder and LSCF powder. The thicknesses of the electrode layer 2, intermediate layer 2a, electrolyte layer 1a, reaction prevention layer 7, and counter electrode layer 3 were approximately 25 μm, approximately 10 μm, approximately 5 μm, approximately 5 μm, and approximately 20 μm, respectively. The performance and durability of the electrolysis 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 (e.g., a wet method using a firing treatment in a low-temperature range that does not involve firing treatment in a high-temperature range higher than 1100°C), a spray coating method (such as a thermal spraying 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 a low temperature range make it possible to obtain a good intermediate layer 2a and a good reaction-preventing layer 7 without using firing at a high temperature range, for example, higher than 1100°C. This is preferable because it allows for the realization of an electrolytic cell 1 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 facilitates the handling of raw materials.

For the electrolysis cell unit U obtained as described above, we investigated the performance improvement achieved by installing a granular reverse water gas shift catalyst cat1 in the electrode layer side gas supply path 5a (which also serves as the discharge path for the gas electrolyzed in the electrolysis reaction section 10).

Results when no reverse water gas shift catalyst cat. 1 was installed Electrolysis reaction was carried out while supplying gas containing _H2O and _CO2 to the electrolytic cell unit U, and the ratio of _H2 to CO in the outlet gas of the electrolytic cell unit U was measured using a gas chromatograph. The results are shown in Table 5 below. These experimental results are shown as Comparative Examples A1 and A2.

Results when reverse water gas shift catalyst cat. 1 was installed. A granular catalyst obtained by supporting approximately 10% Ni on an 8YSZ carrier similar to that used in Example 2 was installed as reverse water gas shift catalyst cat. Electrolysis reaction was carried out while supplying gas containing _H2O and _CO2 to the electrolytic cell unit U, and the ratio of _H2 to CO in the outlet gas of the electrolytic cell unit U was measured using a gas chromatograph. The results are shown in Table 6. This experimental result is referred to as Example A1.

The above comparative experiments demonstrated that in an electrolytic cell unit U in which the electrolytic cell 1 was formed as a thin layer on the metal support 4 and the reverse water-gas shift reactor 20, which produced 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 served as an exhaust path for the electrolyzed gas, the composition ratio of CO to _H produced by electrolysis could be increased.

Comparing an electrolytic cell unit U that does not include a reverse water gas shift catalyst cat1 in the electrode layer side gas supply channel 5a (which serves as the discharge channel for electrolyzed gas) with an electrolytic cell unit U that does include one, the hydrogen/carbon monoxide ([ _H2 /CO]) ratio at the outlet is about 10 or more to about 5, and combining the reaction in the electrolysis reactor 10 with the reaction in the reverse water gas shift reactor 20 is preferable because it ensures an amount of CO that is advantageous for synthesizing various hydrocarbons. In addition, adopting a CO methanation reaction rather than a _CO2 methanation reaction can improve the thermal efficiency of the hydrocarbon production system 100, and therefore combining the reaction in the electrolysis reactor 10 with the reaction in the reverse water gas shift reactor 20 is preferable because it ensures an amount of CO. This is because when 1 mole of _CO2 is methanated, 2 moles of _H2O are produced, whereas when 1 mole of CO is methanated, only 1 mole of _H2O is produced, and therefore the hydrocarbon production system 100, which employs the CO methanation reaction, can reduce the loss of latent heat and sensible heat equivalent to 1 mole of _H2O in the entire system.
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 30 (hydrocarbon synthesis reaction unit) (for example, _H2 /CO = 3, which is the equivalent ratio for the CO methanation reaction).

[Electrolysis cell stack]
In the single-cell electrolysis cell unit U described up to this point, the supply flow path constituent members 5, 6 have been described as separate entities. However, as described above, when a large number of this type of electrolysis cell unit U are stacked to form an electrolysis cell stack ST, a single separator S can be sandwiched between them, with the electrode layer side gas supply path 5a on one side and the counter electrode layer side gas supply path 6a on the other side.

Figures 6 and 7 show an electrolysis cell stack ST equipped with this type of separator S and constructed by stacking a pair of single-cell electrolysis cell units U. This electrolysis cell stack ST can be modularized by appropriately selecting the number of layers. While Figure 6 is a perspective view, the cross section shown in this figure, like the cross section shown in Figure 5, is a cross section intersecting the gas flow direction (upward and to the right in Figure 6). As can be seen from this figure, an electrode layer-side gas supply channel L2 (5a in Figure 2) through which the gas to be electrolyzed flows is formed on the electrode layer 2 side of the separator S (located on the upper side in Figure 6), and a counter electrode layer-side gas supply channel L1 (6a in Figure 2) for removing gas released from the counter electrode layer 3 is formed on the counter electrode layer 3 side of the separator S (located on the lower side in Figure 6).

Figure 7 is a perspective view of an electrolysis cell stack ST composed of a pair of electrolysis cell units U, cut in the gas flow direction. Even with this configuration, the electrode layer side gas supply channel 5a and the counter electrode layer side gas supply channel 6a are separated by a separator S, so the gases flowing through the two channels do not mix. Also, in Figures 6 and 7, Z indicates the area in which the through holes 4a are formed in the metal support 4.

The above is a description of the basic configuration of the electrolysis cell stack ST according to the present invention.
Hereinafter, an example will be described in which a pair of separators Sa and Sb having different shapes are used as the separator S, and the electrolysis reaction unit 10 and the reverse water gas shift reaction unit 20 are constructed in a single housing B. Fig. 8 shows a cross section of this reactor 500, which is constructed with a power supply unit 8.

In this reactor 500, the single-cell electrolysis cell unit U is configured to include an electrode layer 2, an electrolyte layer 1a, and a counter electrode layer 3 on a metal support 4. Furthermore, a separator S is provided to separate the first gas flow path L1 and the second gas flow path L2. However, this separator S includes a first separator Sa with an upward convex central portion to form the first gas flow path L1 above the counter electrode layer 3, and a second separator Sb with a downward convex central portion to form the second gas flow path L2 below the metal support 4.

As can be seen from FIG. 8 , from the bottom side of the interior of the housing, there are a bottom support SX, a first separator Sa, a metal support 4 having an electrolysis cell 1 on top, and a first separator Sa provided above the metal support 4 so as to form a first gas flow path L1.
Furthermore, with regard to the upper single-cell electrolysis cell unit U, as shown above the broken line, a metal support 4 having an electrolysis cell 1 thereon and a second separator Sb are provided in contact with the counter electrode layer 3 located at the top of the electrolysis cell 1. As a result, a second gas flow path L2 is formed between the second separator Sb and the metal support 4 located above it. A bottom support SY is provided on the top surface inside the housing.
By stacking (assembling) the first gas flow path L1 and the second gas flow path L2 in this manner, the first gas flow path L1 and the second gas flow path L2 are separately constructed.

The first gas flow path L1 is provided in a region outside the housing, and forms a flow path connecting the housing inlet L1in and the housing outlet L1out via the housing internal space L1S, enabling gas to be supplied to the first gas flow path L1 provided between the electrolysis cell units U. On the other hand, the second gas flow path L2 is provided in a region toward the center of the housing, and connects the housing inlet L2in to the second gas flow path L2 via piping 10, and is further guided to the housing outlet L2out via a manifold m, enabling gas to be supplied to the second gas flow path L2.

As a result, the required reaction gas can be obtained by flowing the source gas through the first gas flow path L1 without causing mixing of the gases flowing through the first gas flow path L1 and the second gas flow path L2.

In this example, a reverse water gas shift catalyst cat1 is disposed in the second gas flow path L2 to form a reverse water gas shift reaction section 20. This configuration is substantially the same as the configuration described above with reference to Fig. 5, and the assembled electrolysis cell unit is configured as an electrolysis cell stack ST in which a plurality of single cells 1 are assembled.
Therefore, this configuration is an example in which the electrode layer side gas supply channel L2 (5a in FIG. 2) of the single-cell electrolysis cell unit U is provided with the reverse water gas shift catalyst cat1 to form a reverse water gas shift reaction section 20, and the electrode layer side gas supply channel L2 serves as a hydrogen discharge channel. An "electrolysis cell unit module M" can be constructed by assembling a plurality of such single-cell electrolysis cell units U.

9 has the same structure as the example shown in Fig. 8, but a reverse water gas shift catalyst cat1 is disposed at a predetermined separator connection portion connected to a manifold m provided in the reactor 500, and this portion serves as a reverse water gas shift reaction portion 20. In this example, a part of the manifold m serves as the reverse water gas shift reaction portion 20.
Therefore, this configuration is an example in which a reverse water gas shift catalyst cat1 is provided in the discharge channel (which serves as a hydrogen discharge channel) continuing from the electrode layer side gas supply channel L2 (5a in FIG. 2) of a single-cell electrolysis cell unit U, forming a reverse water gas shift reaction section 20. Furthermore, an "electrolysis cell unit module M" can also be constructed by assembling a plurality of such single-cell electrolysis cell units U.

Furthermore, in this configuration, the gases that join via the second gas flow path L2 and the manifold m and are guided to the housing outlet L2out sequentially undergo a reverse water gas shift reaction upon contact with the reverse water gas shift catalyst cat1 located downstream. Therefore, in this configuration, rather than providing a reverse water gas shift reactor 20 for each individual single-cell electrolysis cell unit U, the discharge path (which serves as a hydrogen discharge path) leading to the electrolysis cell stack ST (an aggregated electrolysis cell unit), which is an aggregate of single-cell electrolysis cell units U, essentially serves as the reverse water gas shift reactor 20. In this configuration, the number of reverse water gas shift reactors 20 may be a single unit on the most downstream side, or multiple units as shown in the same figure; the number is not critical. Furthermore, an "electrolysis cell unit module M" can also be constructed by assembling multiple aggregated electrolysis cell units each equipped with a reverse water gas shift reactor 20 in the hydrogen discharge path.

Here, as shown in Figure 8, a reverse water-gas shift reactor 20 may be provided within the single-cell electrolysis cell unit U, and a further reverse water-gas shift reactor 20 may be provided downstream of the single-cell electrolysis cell unit U.

[A heat exchanger is installed between the electrolysis reactor and the reverse water gas shift reactor]
In the above explanation, we have mainly described an example in which the electrolysis reaction section 10 and the first catalytic reaction section (reverse water gas shift reaction section) 20 are integrated. However, a heat exchange section 11 may be provided between the two sections 10, 20 to allow heat transfer between the two sections. For example, in the structure shown in FIG. 4 described above, the reverse water gas shift reaction section 20 extends downstream, but a separate heat exchange layer with high thermal conductivity may be provided between the two sections. This configuration is shown in FIG. 10, corresponding to FIG. 1. The hollow double lines indicate heat transfer between the two sections. With this configuration, the temperatures of the sections 10, 20 can be appropriately controlled.

The inventors refer to the system consisting of the electrolysis reaction unit 10 and reverse water gas shift reaction unit 20 described above as an "electrolysis reaction system."

[Second catalytic reaction section (hydrocarbon synthesis reaction section)]
At least _H2 and CO are introduced into this second catalytic reaction section 30 (hydrocarbon synthesis reaction section), and hydrocarbons (methane and various hydrocarbons with two or more carbon atoms) and the like are produced by catalytic reaction.

(Examples of hydrocarbon synthesis catalysts)
As activity tests of the catalyst (hydrocarbon synthesis catalyst cat2) used in the second catalytic reaction section 30, the inventors conducted evaluation tests 1, 2, and 3 shown below.

As an example of hydrocarbon synthesis catalyst cat2, catalysts were prepared by changing the carrier and catalytically active component in various ways. As catalytically active component ca2, Ru, Ru with Mo, V, Fe, Co, etc., and Ni were investigated. As carrier cb2, _ZrO2 , _Al2O3 , _SiO2 , _MgO , and _TiO2 were investigated.

(Catalyst preparation)
The hydrocarbon synthesis catalyst cat2 is also prepared by the method described with reference to FIGS.
That is, an aqueous solution is prepared by dissolving a measured amount of a water-soluble ruthenium compound (ruthenium nitrate, ruthenium chloride, ruthenium sulfate, ruthenium ammonium sulfate, ruthenium acetate, ruthenium oxalate, ruthenium citrate, etc.) according to the composition of the target catalyst. Furthermore, when supporting molybdenum, vanadium, iron, or cobalt as an additional catalytically active component, a similar amount of a water-soluble metal compound is similarly measured and dissolved in the aqueous solution. Using this aqueous solution, a predetermined amount of carrier particles ( _ZrO2 , _Al2O3 , _SiO2 , MgO, _TiO2 ) is impregnated with the catalytically active component, for example, and _the resulting catalyst is subjected to necessary treatments such as drying, calcination, and reduction to obtain the hydrocarbon synthesis catalyst cat2.
The catalysts in the following examples were prepared using an aqueous ruthenium chloride solution, an aqueous ammonium molybdate solution, an aqueous vanadyl oxalate solution, an aqueous iron nitrate solution, and an aqueous cobalt nitrate solution, respectively, and when both ruthenium and a catalytically active component other than ruthenium were supported, they were prepared using a sequential support method (a two-stage support method in which a catalytically active component other than ruthenium is first supported on a support, and then ruthenium is supported).

(Evaluation Test 1)
In evaluation test 1, a mixed gas containing 12.4% CO, 24.8% _CO2 , 37.2% _H2 , 12.4% _H2O , and the remainder _N2 was used as the reactant gas, and an activity test of the hydrocarbon synthesis catalyst cat2 was performed at a GHSV of 4000/h (wet basis) and a reaction temperature between 275° C. and 360° C. Note that the reactant gas in this case is an example of an assumed model in which a co-electrolysis reaction of water and carbon dioxide is carried out in the electrolysis reaction unit 10 under conditions where the electrolysis reaction rate of carbon dioxide is low, and then the reverse water-gas shift reaction of carbon dioxide is carried out in the reverse water-gas shift reaction unit 20 installed downstream, and the resulting mixed gas of CO, _CO2 , _H2 , and _H2O is introduced into the hydrocarbon synthesis reaction unit 30 to carry out the hydrocarbon synthesis reaction.

The following two indicators were used to organize the test results.

1. _CO2 removal assumed hydrocarbon conversion rate = [carbon number of hydrocarbons in outlet gas] / [carbon number in outlet gas - carbon number of outlet _CO2 ]
This index indicates the conversion rate to hydrocarbons when _CO2 is removed from the outlet gas of the hydrocarbon synthesis reaction section 30 obtained by the catalytic reaction, and it is preferable that this index is high.

2. C1-C4 calorific value (MJ/Nm ³ ) = Σ (Nn x HN) / Σ Nn
Nn [mol]: Number of moles of Cn hydrocarbons in the catalytic reaction gas (n = 1 to 4)
HN [MJ/ ^m3 (N)]: Heat value of Cn hydrocarbons in the catalytic reaction gas [H1 = 39.8, H2 = 69.7, H3 = 99.1, H4 = 128.5]
This index indicates the amount of C1 to C4 components contained in the outlet gas of the hydrocarbon synthesis reaction section 30 obtained by the catalytic reaction, and if this value exceeds 39.8, it can be confirmed that hydrocarbons such as ethane, propane, and butane are being produced in addition to methane.

For Evaluation Test 1, Tables 7 and 8 below show Examples B1 to B3 of the hydrocarbon synthesis catalyst cat. 2 of the present invention.

As shown in Tables 7 and 8, it was confirmed that hydrocarbons can be synthesized from a mixed gas of CO, CO ₂ , H ₂ , and H ₂ O using, as the hydrocarbon synthesis catalyst cat 2, a catalyst in which ruthenium is supported on an alumina carrier, or a catalyst in which molybdenum or vanadium is supported in addition to ruthenium.
From the above results, it was confirmed that the hydrocarbon production system 100 can produce high-calorie gas with a C1-C4 calorific value of 39 MJ/ ^Nm3 or more.

(Evaluation Test 2)
In evaluation test 2, a mixed gas containing 0.45% CO, 18.0% _CO2 , 71.55% _H2 , and 10.0% _H2O was used as the reactant gas, and an activity test of the hydrocarbon synthesis catalyst cat2 was carried out at a GHSV of 5000/h (DRY basis) and a reaction temperature between approximately 230° C. and approximately 330° C. The reactant gas in this case is an example of an assumed model in which a mixed gas obtained when a co-electrolysis reaction of water and carbon dioxide is carried out in the electrolysis reaction section 10 under conditions where the electrolysis reaction rate of carbon dioxide is low is introduced into the hydrocarbon synthesis reaction section 30 to carry out the hydrocarbon synthesis reaction.

The following two indicators were used to organize the test results.

1. Hydrocarbon conversion rate = [carbon number of hydrocarbons in outlet gas] / [carbon number in outlet gas]
This index indicates the proportion of carbon atoms that are converted into hydrocarbons without being converted into _CO2 out of the total carbon atoms that are introduced, and it is preferable that this index is high.

2. _CO2 removal assumed hydrocarbon conversion rate = [carbon number of hydrocarbons in outlet gas] / [carbon number in outlet gas - carbon number of outlet _CO2 ]
This index indicates the conversion rate to hydrocarbons when _CO2 is removed from the outlet gas of the hydrocarbon synthesis reaction section obtained by the catalytic reaction, and it is preferable that this index is also high.

For Evaluation Test 2, the catalysts used (Examples B4 to B16) are shown in Table 9, and the test results are shown in Table 10.

(Evaluation Test 3)
In evaluation test 3, a mixed gas containing _H2 and CO at a volume ratio of 3:1 ( _H2 /CO = 3) was used as the reactant gas, and an activity test of hydrocarbon synthesis catalyst cat2 was performed at a GHSV of 2000/h and a reaction temperature between 235°C and approximately 330°C. In this activity test, a catalyst (Examples B17 and B18) in which iron or cobalt in addition to ruthenium was supported on a titania carrier was used. Note that the reactant gas in this case is an example of an assumed model in which a mixed gas obtained by adding carbon monoxide to hydrogen obtained by electrolysis of water in the electrolysis reaction section 10, or a mixed gas of hydrogen and carbon monoxide obtained by separating water or carbon dioxide as needed from a gas obtained by a co-electrolysis reaction of water and carbon dioxide, is introduced into the hydrocarbon synthesis reaction section 30 to perform a hydrocarbon synthesis reaction.

The results of Evaluation Test 3 are shown in Table 11.

As shown in Table 11, it was confirmed that hydrocarbons can be synthesized from a mixed gas containing H ₂ and CO using a catalyst in which ruthenium and iron or cobalt are supported on a titania carrier as the hydrocarbon synthesis catalyst cat 2.

It was confirmed that the hydrocarbon production system 100 described above can produce high-calorie gas with a C1-C4 calorific value of 39 MJ/Nm ³ or more.

From the above results, as previously shown, a catalyst in which at least ruthenium is supported on a metal oxide support cb2 as the catalytically active component ca2 can be used in this second catalytic reaction section 30 (hydrocarbon synthesis reaction section). Furthermore, it is preferable to support at least one of molybdenum, vanadium, iron, and cobalt as the catalytically active component ca2.

It was also found that the hydrocarbon synthesis catalyst cat2 is preferably a catalyst in which at least ruthenium is supported on a metal oxide carrier cb2, with the amount of ruthenium supported being 0.1% by weight or more and 5% by weight or less, and that in addition to ruthenium, the metal oxide carrier cb2 preferably further supports at least one of molybdenum, vanadium, iron, and cobalt as a catalytically active component ca2.

Here, the amount of at least one of molybdenum, vanadium, iron, and cobalt supported can be 0.2% by weight or more and 6% by weight or less.

Furthermore, among these hydrocarbon synthesis catalysts cat. 2, the highly active catalysts had a carbon monoxide adsorption capacity of 0.4 ml/g or more.

[Heavy Hydrocarbon Separation Section]
The gas reaching the heavy hydrocarbon separation section 35 is cooled, thereby condensing the heavy hydrocarbons contained in the gas released from the hydrocarbon synthesis reaction section 30, and the heavy hydrocarbons can be extracted to the outside. For example, in the hydrocarbon synthesis reaction section 30 using the 2 wt. % Ru/2 wt. % Fe/ _TiO2 catalyst shown in Example B17 above, a mixed gas containing _H2 and CO at a volume ratio of 3:1 ( _H2 /CO=3) was introduced and the reaction was carried out at 275°C, and straight-chain higher aliphatic hydrocarbons with an average chain length of 26 carbon atoms were extracted in the heavy hydrocarbon separation section 35. When the reaction was carried out at 325°C, straight-chain higher aliphatic hydrocarbons with an average chain length of 18 carbon atoms were extracted in the heavy hydrocarbon separation section 35.

[Water separation section]
The water separation section 40 is provided with a condenser, which adjusts the temperature and pressure of the H ₂ O-containing gas that is introduced thereinto, condenses the gas, and extracts the condensed water to the outside.

[Carbon dioxide separation section]
For example, a PSA is provided in this section 50, which separates CO2 from the inflowing _CO2- containing gas by adsorbing _it onto an adsorbent at a predetermined temperature and pressure, and then desorbs the separated _CO2 from the adsorbent, thereby effectively separating _CO2 . The separated _CO2 can be reused by returning it to the front of the electrolysis reaction section 10 via the carbon dioxide return path 51.
It is also possible to use PSA or the like to form the carbon dioxide separation section and the water separation section into the same separation section.

[Another embodiment]
(1) In the above embodiment, the _CO2 separated in the carbon dioxide separation unit 50 is returned to the upstream side of the electrolysis unit 10. However, in the hydrocarbon production system 100 according to the present invention, the conversion of _CO2 to CO is mainly performed in the reverse water-gas shift reactor 20. Therefore, the _CO2 may be returned to the upstream side of the reverse water-gas shift reactor 20. This configuration is shown in FIG.

12 shows an example of adopting the configuration of the reactor 500 shown in Figures 8 and 9 based on the concept of causing heat transfer between the electrolytic reaction unit 10 and the reverse water gas shift reaction unit 20 and performing only water electrolysis in the electrolytic reaction unit 10. In this example, the inside of the housing B of the reactor 500 is divided into two, one of which is the electrolytic reaction unit 10 and the other is the reverse water gas shift reaction unit 20.
Carbon dioxide is then supplied to the hydrogen-containing gas released from the electrolysis reaction section 10, and the gas is introduced into the reverse water-gas shift reaction section 20 located at the bottom of the reactor 500, whereby a desired gas (e.g., a gas suitable for the synthesis of hydrocarbons) can be obtained.
In this manner, an electrolytic cell stack ST having a plurality of electrolytic cells 1 may be constructed, and the reverse water gas shift reactor 20 of the present invention may be provided in the exhaust passage of the electrolytic cell stack ST. Furthermore, a plurality of "collected electrolytic cell units" having this configuration may be assembled into a module to form an "electrolytic cell unit module M."

(2) In the above embodiment, no particular mention was made of _H2 in the gas obtained from the hydrocarbon synthesis reaction unit 30. However, a hydrogen separation unit (shown as _H2 separation unit 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 Figure 13. In this example, the _H2 separated in the hydrogen separation unit 60 may be returned to the upstream side of the reverse water-gas shift reaction unit 20 and used for the reverse water-gas shift reaction.

(3) In the above embodiment, the water separation unit 40 was provided downstream of the hydrocarbon synthesis reaction unit 30. However, as shown in FIG. 14, the water separation unit 40 may be provided between the reverse water gas shift reaction unit 20 and the hydrocarbon synthesis reaction unit 30. The main function of this water separation unit 40 is to facilitate the hydrocarbon synthesis reaction.

(4) In the above embodiment, an example was shown in which both H ₂ O and CO ₂ were supplied to the electrolysis reaction unit 10 for the electrolysis reaction, but as shown in Fig. 15, a system may be used in which only H ₂ O is supplied to the electrolysis reaction unit 10 for the electrolysis reaction. In this case, carbon consumed in hydrocarbon synthesis is input to the reverse water gas shift reaction unit 20 as carbon dioxide.

(5) In the above embodiment, the electrolytic reaction section 10 and the first catalytic reaction section 20 are integrated into one structure. However, it is also possible to integrate the second catalytic reaction section 30 in addition to the reaction sections 10 and 20. An example of this structure is shown in FIG. 18. In this figure, 30a indicates a coating layer of the hydrocarbon synthesis catalyst cat2.
In this configuration, each of the reaction sections 10, 20, and 30 can be constructed on a metal support 4 and a supply path forming member 5, and the metal support 4 acts as a separator to separate the produced hydrocarbons from oxygen.

(6) In the above embodiment, an example was shown in which hydrocarbons such as methane were synthesized in the hydrocarbon synthesis reaction section 30. However, depending on how the hydrocarbon synthesis catalyst used in the hydrocarbon synthesis reaction section 30 is selected, it is also possible to synthesize chemical raw materials from hydrogen, carbon monoxide, etc. introduced into the hydrocarbon synthesis reaction section 30.

1 Electrolytic cell 1a Electrolyte layer 2 Electrode layer 3 Counter electrode layer 4 Metal support (support/separator)
4a hole (through hole)
5. Supply path forming member (separator)
6 Supply path forming member (separator)
10 Electrolysis reaction section 20 First catalytic reaction section (reverse water gas shift reaction section)
20a Coating layer 30 Second catalytic reaction section (hydrocarbon synthesis reaction section)
40 Water separation section 50 Carbon dioxide separation section 60 Hydrogen separation section M Electrolysis cell module U Electrolysis cell unit (single cell type electrolysis cell unit)
S Separator ST Electrolysis cell stack (collected electrolysis cell unit)
Cat1 Reverse water gas shift catalyst Ca1 Catalytically active component Cb1 Carrier Cat2 Hydrocarbon synthesis catalyst Ca2 Catalytically active component Cb2 Carrier

Claims (11)

An electrolysis cell unit comprising at least an electrolysis cell stack having a plurality of electrolysis cells each including an electrode layer and a counter electrode layer sandwiching an electrolyte layer , and an exhaust path for exhausting hydrogen generated in the electrolysis cell stack,
a reverse water-gas shift reactor that generates carbon monoxide using carbon dioxide and the hydrogen by a reverse water-gas shift reaction is provided in at least a part of the exhaust passage, and the electrolysis cell stack is integrated with the reverse water-gas shift reactor;
the electrolysis cell is a solid oxide electrolysis cell;
the electrolysis cell is operated at a temperature of 600°C to 800°C, and the reverse water gas shift reactor is operated at a temperature of 600°C to 800°C;
The electrolytic cell unit includes the electrolytic cell stack and the reverse water gas shift reactor surrounded by a heat insulating member, and heat generated in the electrolytic cell stack is utilized in the reverse water gas shift reactor. An electrolysis cell unit comprising at least an electrolysis cell stack having a plurality of electrolysis cells each including an electrode layer and a counter electrode layer sandwiching an electrolyte layer, and an exhaust path for exhausting hydrogen generated in the electrolysis cell stack,
a reverse water-gas shift reactor that generates carbon monoxide using carbon dioxide and the hydrogen by a reverse water-gas shift reaction is provided in at least a part of the exhaust passage, and the electrolysis cell stack is integrated with the reverse water-gas shift reactor;
The electrolysis cell unit, wherein the electrolysis cell is a solid oxide electrolysis cell. 3. The electrolytic cell unit according to claim 1 , wherein the electrolytic cell is of a flat plate type. 4. The electrolysis cell unit according to claim 1 , wherein the reverse water gas shift catalyst contained in the reverse water gas shift reactor is a catalyst containing at least one of platinum, nickel, and iron. 5. The electrolysis cell unit according to claim 1 , wherein the reverse water gas shift catalyst contained in the reverse water gas shift reactor is a catalyst containing at least one of ceria, zirconia, and alumina. 6. The electrolysis cell unit according to claim 1 , wherein the reverse water gas shift reaction section is a flat plate type. 7. The electrolysis cell unit according to claim 1, further comprising a heat transfer section between the electrolysis cell stack and the reverse water gas shift reactor. 8. The electrolytic cell unit according to claim 1 , wherein the electrolytic cell has a metal support, and the support supports the reverse water gas shift reactor in the discharge channel . An electrolysis cell unit module comprising a plurality of electrolysis cell units according to any one of claims 1 to 8. A hydrocarbon production system comprising at least the electrolytic cell unit according to any one of claims 1 to 8 or the electrolytic cell unit module according to claim 9 and a hydrocarbon synthesis reaction section. 9. The method for operating an electrolytic cell unit according to claim 1, wherein heat generated by the electrolytic cell stack including the electrolytic cell operated at a temperature of 600°C to 800°C is used to absorb heat from the reverse water gas shift reaction occurring in the reverse water gas shift reaction unit, and the reverse water gas shift reaction unit is operated at a temperature of 600°C to 800°C.