Hydrocarbon Production Systems

Abstract

This hydrocarbon production system (100), by which hydrogen and carbon monoxide required for hydrocarbon synthesis are secured using water and carbon dioxide as raw materials and hydrocarbon containing high-calorie gas can be efficiently produced, is obtained. The hydrocarbon production system comprises: an electrolytic reaction unit (10) which converts water and carbon dioxide into hydrogen and carbon monoxide through an electrolytic reaction; a catalytic reaction unit (30) which converts a product produced in the electrolytic reaction unit (10) into hydrocarbon through a catalytic reaction; and branch paths (41) and (51) which branch some of outlet components of the catalytic reaction unit (30).

Description

[Technical Field]

[0001] The present invention relates to a hydrocarbon production system for producing hydrocarbons from at least water and carbon dioxide. [Background technology]

[0002] An example of this type of hydrocarbon production system is disclosed in Patent Document 1. 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 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, the technology disclosed in Patent Document 1 provides a hydrocarbon synthesis section downstream of an electrolysis reaction section, and synthesizes (produces) hydrocarbons using water and carbon dioxide as starting materials.

[0003] In this prior art, 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). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2016-522166 Summary of the Invention [Problem to be solved by the invention]

[0005] However, although heterogeneous catalysts are used to synthesize hydrocarbons, it is difficult to select such catalysts, and a technology for stably synthesizing hydrocarbons has not yet been established. Furthermore, the inventors have found that in the production of hydrocarbons, hydrogen and carbon monoxide are obtained from the starting materials water and carbon dioxide, but various components (water, carbon dioxide, hydrogen) remain in the hydrocarbon-containing gas obtained in this manner. However, there is no disclosure regarding what to do with these types of components during the hydrocarbon production process.

[0006] In view of this situation, a main object of the present invention is to provide a hydrocarbon production system that can efficiently produce hydrocarbons by using water and carbon dioxide as raw materials and securing the hydrogen and carbon monoxide necessary for hydrocarbon synthesis. [Means for solving the problem]

[0007] The first characteristic configuration of the present invention is as follows: The system is characterized by comprising an electrolytic reaction section that converts water into hydrogen through an electrolytic reaction, or converts water and carbon dioxide into hydrogen and carbon monoxide through an electrolytic reaction, a catalytic reaction section that converts the product produced in the electrolytic reaction section into hydrocarbons through a catalytic reaction, and a branch path that branches off a portion of the outlet component of the catalytic reaction section.

[0008] The hydrocarbon production system having this configuration comprises an electrolytic reaction section and a catalytic reaction section, and in the former reaction section, at least hydrogen, or hydrogen and carbon monoxide, required for hydrocarbon synthesis, are obtained from water or water and carbon dioxide. Here, when only hydrogen is obtained in the electrolytic reaction section, one or more of carbon monoxide and carbon dioxide may be supplied before the catalytic reaction section. Then, in the catalytic reaction section, hydrocarbons are obtained from the supplied hydrogen and one or more of carbon monoxide and carbon dioxide.

[0009] In this system configuration, the reaction in the catalytic reaction section synthesizes hydrocarbons from hydrogen and one or more of carbon monoxide and carbon dioxide, so water, carbon dioxide, or unreacted hydrogen are released from the catalytic reaction section along with the hydrocarbons. Therefore, by providing a branch path that branches off a portion of the outlet component of the catalytic reaction section, useful hydrocarbons contained in the gas produced in the catalytic reaction section can be extracted. Furthermore, for example, the calorific value per unit volume, which is an important characteristic for high-calorie gas, can be adjusted.

[0010] The second characteristic configuration of the present invention is: The catalytic reaction section converts the product produced in the electrolytic reaction section into a high-calorie gas containing at least lower saturated hydrocarbons through a catalytic reaction.

[0011] As mentioned above, the catalytic reaction section functions as a hydrocarbon synthesis reaction section. When the hydrocarbons produced in this section become gases containing at least low saturated hydrocarbons, the gases have a calorific value of, for example, 39 MJ / Nm 3 It can be a high-calorie gas with a calorie content of more than 10 ... As a result, by using the hydrocarbon production system according to the present invention, it is possible to construct a relatively simple and stable system for producing very useful high-calorie gases.

[0012] The third characteristic configuration of the present invention is The present invention is characterized in that a carbon dioxide separation section is provided for separating carbon dioxide from the outlet component of the catalytic reaction section, and the separated carbon dioxide is discharged from the branch path.

[0013] As will be described later, when hydrocarbon synthesis is carried out by a catalytic reaction, carbon dioxide may remain along with the production of hydrocarbons. However, by separating and discharging this carbon dioxide from the gas obtained from the catalytic reaction section, the concentration of the hydrocarbon component side can be increased and the discharged carbon dioxide can be utilized.

[0014] A fourth characteristic configuration of the present invention is as follows: The present invention is characterized in that a hydrogen separation section is provided for separating hydrogen from the outlet component of the catalytic reaction section, and the separated hydrogen is discharged from the branch passage.

[0015] In the reaction in the catalytic reaction section, unreacted hydrogen may remain, but by separating and discharging this hydrogen from the gas obtained from the catalytic reaction section, the concentration of the hydrocarbon component side can be increased and the discharged hydrogen can be utilized.

[0016] A fifth characteristic configuration of the present invention is The present invention is characterized in that a water separation section is provided for separating water from at least one of the outlet component and the inlet component of the catalytic reaction section, and the separated water is discharged from the branch path.

[0017] Although the reaction in the catalytic reaction section is basically a reaction between hydrogen and carbon monoxide, the presence of oxygen results in the production of water, and by separating and discharging this water from the gas obtained from the catalytic reaction section, the concentration of the hydrocarbon component side can be increased and the discharged water can be utilized. Furthermore, although unreacted water may remain in the reaction in the electrolysis reaction section, separating this water before the catalytic reaction section makes it easier for the catalytic reaction in the catalytic reaction section to proceed, so it is also preferable to separate and discharge the water before the catalytic reaction section.

[0018] A sixth characteristic configuration of the present invention is The branching path becomes a recycling line.

[0019] As explained above, the hydrocarbon production system according to the present invention uses water and carbon dioxide as its starting materials. If a branch path is provided in the system and this branch path is used as a recycle line, for example, one or more of the recycle gases (water, carbon dioxide, and hydrogen) can be usefully utilized by returning from this line to the main route where hydrocarbon synthesis is carried out.

[0020] Here, water can be recycled upstream of the electrolysis reactor. Carbon dioxide can be recycled to the electrolysis reactor or, if a reverse water-gas shift reactor is provided, to the reverse water-gas shift reactor. Hydrogen can be recycled and used upstream of the catalytic reactor, which serves as the hydrocarbon synthesis unit.

[0021] A seventh characteristic configuration of the present invention is The present invention is characterized in that it comprises a heavy hydrocarbon separation section for separating heavy hydrocarbons from the outlet components of the catalytic reaction section.

[0022] By providing a heavy hydrocarbon separation section, heavy hydrocarbons, which are useful hydrocarbon components, can be separated and utilized.

[0023] An eighth characteristic feature of the present invention is that the catalytic reaction section is provided in a plurality of stages.

[0024] According to this characteristic configuration, the catalytic reaction units are arranged in multiple stages, which increases the amount of hydrocarbons synthesized and makes it possible to obtain the desired high-calorie gas. For example, by changing the reaction conditions, such as the reaction temperature, of each catalytic reaction unit, it is possible to cause an appropriate reaction in each stage.

[0025] A ninth characteristic feature of the present invention is that the reactor includes a reverse water gas shift reactor.

[0026] The hydrocarbon production system according to the present invention comprises an electrolytic reaction section and a catalytic reaction section, in which at least hydrogen is produced in the electrolytic reaction section and this hydrogen is used for hydrocarbon synthesis, while the catalytic reaction section requires hydrogen and one or more of carbon monoxide and carbon dioxide.

[0027] As explained above, although it is possible to separately supply carbon monoxide and carbon dioxide to the catalytic reaction section, hydrocarbon synthesis can be performed effectively by generating carbon monoxide from carbon dioxide in the reverse water gas shift reaction section and supplying the carbon monoxide to the catalytic reaction section.

[0028] Furthermore, when co-electrolysis is performed in the electrolysis reaction section, in which both water and carbon dioxide are electrolyzed, the electrolysis reaction may be biased toward water, and carbon monoxide may not be produced sufficiently. However, by causing a reverse water-gas shift reaction between the hydrogen produced in the electrolysis reaction section and the unreacted carbon dioxide in the electrolysis reaction section, the carbon monoxide concentration is increased and the carbon monoxide is supplied to the catalytic reaction section, thereby enabling good hydrocarbon synthesis.

[0029] The tenth characteristic configuration of the present invention is The electrolysis reaction section has an electrolysis cell in which at least an electrode layer, an electrolyte layer, and a counter electrode layer are formed on a support.

[0030] According to this characteristic configuration, the electrolytic cell used in the electrolytic reaction unit includes, for example, a thin-film electrode layer, an electrolyte layer, and a counter electrode layer on a thin but sufficiently strong, robust support. This allows for an effective electrolytic reaction while reducing the amount of material used to form these layers of the electrolytic cell. As a result, a compact, high-performance electrolytic cell unit with excellent strength and reliability can be constructed. Metals and ceramics can be selected as materials for forming this type of support.

[0031] An eleventh characteristic feature of the present invention is that the support is made of metal.

[0032] By using metal as the support, material costs can be reduced by ensuring strength with inexpensive metal materials, and it is easier to process than ceramics. [Brief explanation of the drawings]

[0033] [Figure 1] Diagram showing the configuration of a hydrocarbon production system [Figure 2] Schematic diagram showing the configuration of the electrolytic reaction section [Figure 3] A diagram showing the configuration of a system that integrates an electrolysis reactor and a reverse water gas shift reactor. [Figure 4] Schematic diagram of an electrolysis cell unit equipped with an electrolysis reactor and a reverse water-gas shift reactor [Figure 5]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. [Figure 6] Configuration diagram of a system equipped with a heat exchanger between the electrolysis reactor and the reverse water gas shift reactor. [Figure 7] Diagram showing another configuration of a hydrocarbon production system in which CO2 is introduced into a reverse water gas shift reactor. [Figure 8] FIG. 1 is a diagram showing another configuration of a hydrocarbon production system equipped with a hydrogen separation unit. [Figure 9] FIG. 10 is a diagram showing yet another configuration of a hydrocarbon production system including a water separation section before a hydrocarbon synthesis reaction section. [Figure 10] 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. [Figure 11] An explanatory diagram showing the preparation state of the catalyst [Figure 12] An explanatory diagram showing the catalyst coating and calcination state and pre-reduction treatment [Figure 13] 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. [Figure 14] FIG. 1 shows another configuration of a hydrocarbon production system. [Figure 15] FIG. 1 shows yet another configuration of a hydrocarbon production system. DETAILED DESCRIPTION OF THE INVENTION

[0034] An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of one embodiment of a hydrocarbon production system 100 proposed by the present inventors.

[0035] As shown in the figure, this hydrocarbon production system 100 is configured to include, in order, an electrolysis 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).

[0036] The electrolytic reaction section 10 is a section that electrolyzes at least a portion of the inflowing gas, the first catalytic reaction section 20 is a reverse water-gas shift reaction section that performs a reverse water-gas shift reaction on at least a portion of the inflowing gas, and the second catalytic reaction section 30 is configured to function as a hydrocarbon synthesis reaction section that synthesizes at least a portion of the inflowing gas into hydrocarbons. The hydrocarbons synthesized here are primarily 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 the catalyst used in the second catalytic reaction section 30, it is possible to synthesize heavier hydrocarbons with a carbon number greater than the lower saturated hydrocarbons, unsaturated hydrocarbons, oxygenated hydrocarbons, and the like. Therefore, in this specification, hydrocarbons are a concept that includes all of these, and are also collectively referred to as hydrocarbons.

[0037] The heavy hydrocarbon separation unit 35, water separation unit 40, and carbon dioxide separation unit 50 are units that remove at least a portion of predetermined components (in the order listed, CnHm, HO, and CO2) from the gas flowing therethrough. The components removed and recovered by the water separation unit 40 and 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 FIG. 1, and are reused. The return lines 41 and 51 are indicated by HO and CO2, respectively, that are returned via these return lines. These return lines 41 and 51 are branch lines in each unit 40, 50. As a result, this hydrocarbon production system 100 is established as a carbon-closed system that does not substantially release CO2 outside the system.

[0038] In the figure, the gases flowing into each part are shown before each part, and the gases released from each part are shown after each part.

[0039] In the electrolysis reaction section 10, H2O and CO2 as starting materials are introduced and electrolyzed inside, with H2O being decomposed into H2 and O2, and part of the CO2 being decomposed into CO and O2 and released.

[0040] The reaction is described as follows: 2H2O→2H2+O2 (formula 1) 2CO2→2CO+O2 (formula 2) These formulas 1 and 2 are also shown in the box representing the electrolytic reaction section 10 in FIG.

[0041] In the first catalytic reaction section 20 (reverse water-gas shift reaction section), H2 and CO2 are introduced and a reverse water-gas shift reaction occurs therein, whereby CO2 is converted into CO and H2 is converted into H2O, which are then released.

[0042] The reaction is written as the following equilibrium reaction, but the reverse water gas shift reaction is a reaction in which the reaction described in Equation 3 below proceeds to the right (CO2 and H2 react to produce CO and HO). CO2+H2⇔CO+H2O (Formula 3) This formula 3 is also shown in the box representing the first catalytic reaction section 20 (reverse water gas shift reaction section) in Figure 1. The reverse water gas shift catalyst cat1 used in the reaction is also shown schematically in this box.

[0043] In the second catalytic reaction section 30 (hydrocarbon synthesis reaction section), H2 and CO are flowed in, and hydrocarbons are synthesized by a catalytic reaction. For example, the reaction in which CH4 is synthesized from CO and H2 is expressed as the following equilibrium reaction, but the reaction in which CH4 is synthesized 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 HO). CO+3H2⇔CH4+H2O (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, olefinic hydrocarbons, etc. can be synthesized from CO and H2.

[0044] As will be described later, the inventors have shown an example of a catalyst that uses ruthenium as its catalytically active component as the hydrocarbon synthesis catalyst cat2 to be placed in the second catalytic reaction section 30, but heavy hydrocarbons are also synthesized with a catalyst that contains iron, cobalt, or the like as its catalytically active component, and these types of heavy hydrocarbons condense as the temperature decreases and can be separated from the carrier gas. Therefore, the above-mentioned heavy hydrocarbon separation section 35 separates the hydrocarbon components separated in this manner.

[0045] The H2O 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).

[0046] The CO2 produced in the carbon dioxide separation section 50 is separated and returned to the upstream side of the electrolysis reaction section 10 via a carbon dioxide return path 51 (carbon dioxide recycle line).

[0047] As a result, in this hydrocarbon production system 100, hydrocarbons are ultimately synthesized and can be supplied to the outside.

[0048] The above is an overview of the hydrocarbon production system 100, and the configuration and role of each part will be explained below. [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 H2O and CO2.

[0049] FIG. 2 shows a schematic cross-sectional configuration of this electrolytic reaction section 10. The figure shows an electrolysis cell unit U in which a plurality of units are stacked to form an electrolysis stack (not shown), and this electrolysis cell unit U includes an electrolysis cell 1, which 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 electrolysis cell 1, and the counter electrode layer 3 serves as the anode. Incidentally, this electrolysis cell unit U is supported by a metal support 4. Note that, here, an example is shown in which a solid oxide electrolysis cell is used as the electrolysis cell 1.

[0050] 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.

[0051] 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 a high temperature 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 film formation processes that can be used in a low-temperature range can provide an electrolyte layer 1a that is dense and has high airtightness and gas barrier properties without firing at a high temperature above 1100°C, for example. This can suppress damage to the metal support 4 and interdiffusion of elements between the metal support 4 and the electrode layer 2, thereby realizing an electrolysis cell unit U with excellent performance and durability. In particular, low-temperature firing methods and spray coating methods are preferred because they allow for low-cost elements to be realized. Furthermore, spray coating is more preferable because it is easy to obtain a dense electrolyte layer 1a that is airtight and has high gas barrier properties in a low temperature range.

[0052] Furthermore, the electrolyte layer 1a is densely structured to prevent gas leakage 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. When the electrolyte layer 1a is a uniform layer, the density is preferably 95% or more, and more preferably 98% or more. When the electrolyte layer 1a is structured in a multi-layer structure, it is preferable that at least a portion of the layers contains a layer (a dense electrolyte layer) with a density of 98% or more, and more preferably a layer (a dense electrolyte layer) with a density of 99% or more. 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 when the electrolyte layer 1a is structured in a multi-layer structure.

[0053] 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 the electrode layer 2 is a thin layer, its thickness can be, for example, about 1 μm to 100 μm, preferably 5 μm to 50 μm. Such a thickness makes it possible to reduce the amount of expensive electrode layer material used, thereby cutting costs, while ensuring sufficient electrode performance. The entire area where the holes (through holes) 4a are provided is covered with 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.

[0054] The electrode layer 2 can be made of a composite material such as NiO-GDC, Ni-GDC, NiO-YSZ, Ni-YSZ, CuO-CeO, or Cu-CeO. In these examples, GDC, YSZ, or CeO can be referred to as 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 at a low temperature without firing at a high temperature above 1100°C), a spray coating method (e.g., thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, or cold spray), a PVD method (e.g., sputtering or pulsed laser deposition), or a CVD method. These processes, which can be used at low temperatures, can produce a good electrode layer 2 without firing at a high temperature above 1100°C. This is preferable because it prevents damage to the metal support 4 and suppresses interdiffusion of elements between the metal support 4 and the electrode layer 2, thereby realizing an electrochemical element with excellent durability. Furthermore, the use of a low-temperature firing method is even more preferable because it facilitates handling of the raw materials.

[0055] The counter electrode layer 3 can be formed as a thin layer on the surface of the electrolyte layer 1a opposite to the electrode layer 2. When the counter electrode layer 3 is a thin layer, its thickness can be, for example, about 1 μm to 100 μm, preferably 5 μm to 50 μm. This thickness reduces the amount of expensive counter electrode layer material used, thereby reducing costs, while 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 thereof. It is particularly preferred 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.

[0056] The electrolyte layer 1a, the electrode layer 2, and the counter electrode layer 3 are formed as thin films as will be described later, which the inventors call "thin layer formation."

[0057] 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 number of holes 4a are formed in the metal support 4, penetrating the front and back surfaces. Gases (H2O and CO2) supplied via the electrode layer side gas supply channel 5a are electrolyzed and supplied to the electrode layer 2 via the many holes 4a. Furthermore, the generated gases (H2, CO2) flow out from the holes 4a.

[0058] On the other hand, a supply channel forming member 6 for forming a counter electrode layer side gas supply channel 6a is also provided on the counter electrode layer 3 side. As shown in the figure, this supply channel 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 channel 6a.

[0059] 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 cylindrical shape, are also possible. The metal support 4 may have sufficient strength 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.

[0060] The metal support 4 has, for example, a plurality of holes 4a formed through 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 to the front surface of the metal support 4. 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 FIG. 2).

[0061] By using a ferritic stainless steel material (an example of an Fe-Cr alloy) as the base material of 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 the electrolyte layer 1a. This makes the electrolysis cell unit U less susceptible to damage even when subjected to repeated temperature cycles of low and high temperatures. This is preferable because it allows for an electrolysis cell unit U with excellent long-term durability.

[0062] The supply channel forming members 5 and 6 of the electrolysis cell unit U can be made of the same material as the metal support 4, and the thickness thereof can also be made approximately the same.

[0063] The metal support 4 and both supply path forming members 5 and 6 are electrically conductive, but are configured to be airtight, so that they function as separators that separate the supply paths 5a and 6a.

[0064] 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 1a. In this embodiment, as shown in the figure, the electrode layer 2 side is negative and the counter electrode layer 3 side is positive. Depending on the configuration of the 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, HO and CO, from an 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 HO may be supplied as either water or water vapor, or both. Therefore, in the present invention, an electrolysis cell device is constructed including at least an electrolysis cell unit U, an electrolysis raw material supply unit that supplies water and / or water vapor and carbon dioxide to the electrolysis cell unit U, and a power supply unit that supplies power.

[0065] In FIG. 2, the gases supplied (HO, CO) and released (HO, H, CO, O, CO) 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 (HO, CO) 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 (HO, H, CO, O, CO) 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 g, such as air, can be flowed into the electrolytic cell unit U to smoothly discharge O produced during the electrolytic reaction.

[0066] 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.

[0067] [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 CO to CO using supplied H, and converts H to H O. That is, in the electrolysis reaction unit 10, which supplies H O and CO and performs electrolysis, CO that remains without being decomposed is converted to CO.

[0068] The reaction here is as shown in formula 3, but this reaction is an endothermic reaction and an equilibrium reaction depending on the reaction temperature conditions. As a result, as explained above, a catalyst that can cause the reaction shown in formula 3 at as high a temperature as possible (for example, 600°C to 800°C) is preferred.

[0069] 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 carrying out an impregnation process in which a carrier (metal oxide) is immersed in a solution containing catalytically active components (metal components), removed, dried, and heated. This process is called calcination. The preparation and use of this catalyst will be described with reference to Figures 11 and 12.

[0070] The preparation method described here is similar for various combinations of catalytically active components and supports, except for the starting materials. Figure 11 shows examples of the reverse water-gas shift catalyst cat1 and 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 support is labeled cb1. Meanwhile, for the hydrocarbon synthesis catalyst cat2, its catalytically active component is labeled ca2, and its support is labeled cb2.

[0071] As shown in Figure 11, 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, stirred, and impregnated in the impregnation-supporting process (a). The resulting mixture is then evaporated to dryness, dried, and then crushed and molded in the drying-crushing-molding process (b). The resulting molded body is then calcined in air in the calcination process (c), yielding the target product (Cat1 and Cat2). This type of catalyst is therefore also known as an impregnated-supported catalyst.

[0072] In this case, the catalyst can be applied to the area where it is to be used and then calcined, as shown in the example of reverse water gas shift catalyst cat1 in Figure 12. Figure 12(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. Figure 12(b) shows the pre-reduction process in which H2 is passed through the reverse water gas shift catalyst cat1 before use.

[0073] When the calcination process 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 12(b) shows the state in which reduction pretreatment is performed by flowing a reducing gas (typically H2) over the surface of the catalyst.

[0074] (Catalyst used) The inventors selected a catalyst that satisfies the following requirements as the reverse water gas shift catalyst cat1 used in the first catalytic reaction section 20.

[0075] This catalyst is constructed by supporting at least one or both of nickel and iron as catalytically active components Ca1 on a support Cb1 primarily composed of a ceria-based metal oxide or a zirconia-based metal oxide. Here, the ratio of support Cb1 to the entire catalyst is preferably 55% by weight or more, more preferably 60% by weight or more, and even more preferably 65% ​​by weight or more, in order to enhance the strength of the catalyst Cat1. The upper limit of this ratio can be set to, for example, 99.5% by weight, but if it exceeds this ratio, the catalytically active component Ca1 cannot be sufficiently supported, and it may become difficult to obtain the effect of the reverse water gas shift catalyst Cat1.

[0076] 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.

[0077] In addition, since the reverse water gas shift reaction can be smoothly promoted, the amount of the catalytically active component Ca1 supported is preferably 0.5 wt% or more, more preferably 1 wt% or more, and even more preferably 5 wt% or more. Moreover, even if the amount of the catalytically active component Ca1 supported is too large, 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 the catalyst cost. Therefore, the amount of the catalytically active component Ca1 supported is preferably 35 wt% or less, more preferably 30 wt% or less, and even more preferably 25 wt% or less.

[0078] Furthermore, it is also preferable to add either or both of nickel and iron to the catalytically active component ca1 and to 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 either or both of nickel and iron as the main catalytically active component ca1 supported on the catalytically active component ca1.

[0079] The following describes test results of examples in which the catalytically active component ca1 and the carrier cb1 of the reverse water gas shift catalyst cat1 used in the first catalytic reaction section 20 are changed in various ways. As the catalytically active component ca1, Ni and Fe were examined and compared with Pt (platinum). The carrier cb1 was selected from ZrO2 (zirconia), YSZ (yttria-stabilized zirconia), GDC (gadolinium-doped ceria), and CeO2 (ceria), and Al2O3 (alumina) was also investigated.

[0080] The following explanation will introduce Test Example 1 and Test Example 2. The difference between the two tests is that in the calcination of the reverse water gas shift catalyst cat1, the calcination temperature in Test Example 1 was set to 450°C, while the calcination temperature in Test Example 2 was set to a higher temperature of 600°C to 1000°C.

[0081] (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. The supports used were ZrO2 (zirconia), YSZ (yttria-stabilized zirconia), GDC (gadolinium-doped ceria), and CeO2 (ceria), and Al2O3 (alumina) was also investigated.

[0082] (Catalyst preparation) To prepare the reverse water gas shift catalyst cat1, an aqueous solution is prepared by dissolving 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, iron ammonium sulfate, iron acetate, iron oxalate, iron citrate, etc.) in a measured amount, depending on the desired catalyst composition. To support copper as an additional catalytically active component ca1, a water-soluble copper compound (copper nitrate, copper chloride, copper sulfate, copper ammonium sulfate, copper acetate, copper oxalate, copper citrate, etc.) is similarly dissolved in a measured amount. A predetermined amount of support 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 process is referred to as the "impregnation process" in this invention, and the resulting product is the "impregnated support." 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.

[0083] The temperatures for the evaporation to dryness, drying, and calcination in the preparation of the catalyst can be within a commonly used temperature range, but in Test Example 1, the temperatures for the catalysts in the following examples were 80°C, 80°C, and 450°C, respectively.

[0084] Table 1 shows Examples 1 to 19 of the reverse water gas shift catalyst cat1 of the present invention. The horizontal axis represents the type of carrier cb1, the amount of metal supported 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 at 350° C. in a hydrogen atmosphere for 1 hour.

[0085] [Table 1]

[0086] (Catalytic activity test) The catalytic activity test was carried out using a 50% H2-50% CO2 mixed gas (a mixed gas containing H2 and CO2 in a 1:1 (volume ratio)) as the reaction gas, with a GHSV (Gas Hourly Space Velocity) of 10,000 / h and the reaction temperature varied 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.

[0087] The CO2 conversion rate (%) was calculated according to the following formula based on the gas analysis results at the catalyst layer outlet. [CH4 concentration] + [CO concentration] / ([CH4 concentration] + [CO concentration] + [CO2 concentration])

[0088] 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).

[0089] [Table 2]

[0090] (Test Example 2) The test results of Examples (20-29) 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. The carriers used in the examples are CeO2 (ceria) and ZrO2 (zirconia), and Al2O3 (alumina) is also being considered.

[0091] (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.

[0092] Table 3 shows the catalysts prepared in Examples (20 to 29).

[0093] [Table 3]

[0094] (Catalytic activity test) The catalytic activity test was carried out using a mixed gas containing H2 and CO2 in a 1:1 (volume ratio) ratio as the reaction gas, with a GHSV of 10,000 / h and the reaction temperature varied 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.

[0095] [Table 4]

[0096] For reference, the equilibrium values ​​(calculated values) of the CO2 conversion rate under these experimental conditions are shown in Table 4.

[0097] Iron-zirconia catalyst and iron-alumina catalyst The 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, the 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, despite slight differences in metal loading, the iron-zirconia catalyst exhibits superior reverse water-gas shift reaction activity compared with the iron-alumina catalyst. Furthermore, the iron-zirconia catalyst exhibits very high catalytic activity not only at 450°C but also at higher calcination temperatures of 600°C, 800°C, and 1000°C, achieving CO2 conversion close to equilibrium at all calcination temperatures.

[0098] Nickel-ceria catalyst The test results for calcination temperatures of 450°C, 600°C, 800°C, and 1000°C are shown in Examples 4, 20, 24, and 28, respectively. As can be seen from these results, the nickel-ceria catalyst has very high catalytic activity not only at a calcination temperature of 450°C, but also at higher calcination temperatures of 600°C, 800°C, and 1000°C, and the CO2 conversion rate reaches close to the equilibrium value at all calcination temperatures.

[0099] Nickel-alumina catalyst The test results 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.

[0100] Nickel-copper-ceria catalyst Test results for calcination temperatures of 450°C, 600°C, and 800°C are shown in Examples 6, 21, and 25, respectively. These results show that the nickel-copper-ceria catalyst tends to have a slightly lower CO2 conversion rate when the calcination temperature is increased to 600°C or 800°C, but is still superior to the iron-alumina catalyst, which has the same calcination temperature conditions as mentioned above. Furthermore, the nickel-copper-ceria catalyst, which has a calcination temperature of 450°C, achieves a CO2 conversion rate close to the equilibrium value.

[0101] Usefulness as a reverse water gas shift catalyst As shown above, iron-zirconia and nickel-ceria catalysts exhibit extremely high reverse water-gas shift catalytic activity even when the calcination temperature is varied between 450°C and 1000°C. Therefore, they are useful because they can easily ensure high performance and durability even when used in combination with solid oxide electrolysis cells operated in the high-temperature range of, for example, around 600°C to 800°C.

[0102] From the above results, as previously shown, the reverse water gas shift catalyst cat1 used in this first catalytic reaction section 20 can be a catalyst composed of a carrier cb1 mainly composed of ceria-based metal oxide or zirconia-based metal oxide, and at least one or both of nickel and iron supported as catalytically active components ca1.

[0103] Furthermore, the ceria-based metal oxide as the carrier cb1 may be ceria doped with at least one of gadolinium, samarium, and yttrium.

[0104] The zirconia-based metal oxide as the carrier cb1 may be zirconia stabilized with at least one of yttria and scandia.

[0105] Furthermore, it is also preferred to add either or both of nickel and iron to the catalytically active component ca1 and support copper as a further catalytically active component ca1.

[0106] Furthermore, by using the reverse water gas shift catalyst cat1 in the first catalytic reaction section 20 (reverse water gas shift reaction section), the reverse water gas shift reaction can be carried out at a CO2 conversion rate (%) equal to or higher than that of a highly active but very expensive Pt catalyst at around 600 to 1000°C. The test in this example was conducted under a very high GHSV condition of 10,000 / h. Therefore, it is possible to perform the reverse water-gas shift reaction at a higher CO conversion rate (%) by reducing the GHSV to less than 10,000 / h, i.e., by increasing the amount of catalyst used relative to the amount of gas to be treated.

[0107] [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. The reaction in the electrolytic reactor 10 can be exothermic depending on the reaction conditions, while the reaction in the reverse water gas shift reactor 20 is endothermic. Therefore, integrating these two reactors 10 and 20 can improve the thermal efficiency of the system. Figure 3 shows the configuration of the combined and integrated reactors 10 and 20, with the two reactors enclosed to indicate their integration. The reactions in this integrated reactor are shown in the same box. Essentially, the reactions represented by Equations 1, 2, and 3 are carried out. When combining and integrating the electrolytic reactor 10 and the reverse water gas shift reactor 20, it is preferable to surround them with a heat-insulating material, as this allows for efficient heat transfer between the electrolytic reactor 10 and the reverse water gas shift reactor 20. Furthermore, a heat-transfer material may be used to connect the electrolytic reactor 10 and the reverse water gas shift reactor 20 to transfer heat generated in the electrolytic reactor 10 to the reverse water gas shift reactor 20.

[0108] [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 electrolysis cell unit U that serves as the electrolysis reactor 10. This is because, when a solid oxide electrolysis cell that operates at around 600 to 800°C is used as the electrolysis cell 1, the reverse water gas shift catalyst cat1 of the present invention, which exhibits high activity at around 600 to 800°C, can be used in the electrolysis reactor 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.

[0109] An electrolysis cell unit U equipped with such a reverse water gas shift reactor 20 is shown in Figure 4. Figure 4 is a diagram illustrating the electrolysis cell unit U shown in cross section in Figure 2, including the direction of gas advection.

[0110] As shown in the figure, the cross sections of the electrolysis cell units U are basically the same. That is, this electrolysis cell unit U also includes an electrolysis cell 1 in which an electrode layer 2 and a counter electrode layer 3 are formed with an electrolyte layer 1a sandwiched therebetween, a metal support 4 that functions as a support for the electrolysis cell 1 and also functions as a separator, and supply channel-forming members 5 and 6, and is configured to form an electrode layer-side gas supply channel 5a and a counter electrode layer-side gas supply channel 6a. More specifically, as can be seen from the figure, when viewed in the gas advection direction, the metal support 4 has a hole 4a formed in a portion corresponding to the electrolysis 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.

[0111] In this example, however, the reverse water gas shift catalyst cat1 described above is applied to the inner surfaces of the electrode layer-side gas supply channels 5a (the inner surfaces of the supply channel-forming member 5 on the supply channel side, 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.

[0112] As a result, the electrode layer side gas supply path 5a of the electrolysis cell unit U serves as an exhaust path for exhausting at least H2 generated in the electrode layer 2, and the electrolysis reaction section 10 and the reverse water gas shift reaction section 20 are integrally provided in the electrolysis cell unit U.

[0113] In this configuration, the metal support 4 functions as a separator that separates H generated in the electrode layer 2 from O generated in the counter electrode layer 3, and at least a portion of the separator on the H discharge path side serves as a reverse water-gas shift reactor 20. 2 and 4, a large number of electrolysis cell units U are stacked and electrically connected to form a so-called electrolysis cell module (not shown). Naturally, useful gases are generated across multiple layers.

[0114] Based on the concept of combining the electrolytic reaction unit 10 and the reverse water gas shift reaction unit 20 (using the electrode layer side gas supply channel 5a of the electrolytic reaction unit 10 as the reverse water gas shift reaction unit 20), the inventors conducted an experiment by storing a granular reverse water gas shift catalyst cat1 in the electrode layer side gas supply channel 5a. FIG. 5 shows a cross section of the electrolysis cell unit U used in this experiment.

[0115] 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 fabricated as the metal support 4 by laser machining a 0.3 mm-thick ferritic stainless steel metal plate with multiple through-holes (which became the holes 4a). An electrode layer 2 and an intermediate layer 2a were laminated in this order on the metal substrate, and an electrolyte layer 1a was laminated on the intermediate layer 2a of the metal substrate so as to cover the intermediate layer 2a. Furthermore, a reaction prevention layer 7 and a counter electrode layer 3 were laminated in this order on the electrolyte layer 1a to fabricate 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, 10 μm, 5 μm, 5 μm, and 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 reaction prevention layer 7 are preferably formed by a low-temperature firing method (e.g., a wet method using a firing process in a low-temperature range that does not involve firing at a high temperature 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 the 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 therefore preferable because it allows for the realization of an electrolysis 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.

[0116] For the electrolysis cell unit U obtained as described above, we investigated whether performance improvement could be achieved by installing a granular reverse water gas shift catalyst cat1 in the electrode layer side gas supply path 5a (which also serves as an exhaust path for the gas electrolyzed in the electrolysis reaction section 10).

[0117] Results without reverse water gas shift catalyst cat1 An electrolysis reaction was carried out while supplying a 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. The experimental results are shown as Comparative Examples A1 and A2.

[0118] [Table 5]

[0119] Results when reverse water gas shift catalyst cat1 is installed A granular catalyst obtained by supporting approximately 10% Ni on an 8YSZ carrier similar to that used in Example 2 was used as the reverse water gas shift catalyst cat1. An electrolysis reaction was carried out while supplying a gas containing HO and CO to the electrolytic cell unit U, and the ratio of H to CO in the gas at the outlet 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.

[0120] [Table 6]

[0121] The above comparative experiments demonstrated that the 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 the discharge path for the electrolyzed gas, was able to increase the composition ratio of CO to H produced by electrolysis.

[0122] Comparing an electrolysis cell unit U that does not include the 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 electrolysis cell unit U that does include the catalyst cat1, the hydrogen / carbon monoxide ([H2 / CO]) ratio at the outlet is approximately 10 or more and approximately 5. This is because combining the reactions in the electrolysis reactor 10 and the reverse water gas shift reactor 20 ensures an amount of CO advantageous for synthesizing various hydrocarbons, which is preferable. In addition, adopting the CO methanation reaction rather than the CO2 methanation reaction can improve the thermal efficiency of the hydrocarbon production system 100, and combining the reactions in the electrolysis reactor 10 and the reverse water gas shift reactor 20 ensures an amount of CO. This is because methanation of 1 mole of CO2 produces 2 moles of HO, whereas methanation of 1 mole of CO only produces 1 mole of HO. Therefore, the hydrocarbon production system 100 that employs the CO methanation reaction can reduce the loss of latent heat and sensible heat equivalent to 1 mole of HO throughout the 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 (electrolysis 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).

[0123] [A heat exchanger is installed between the electrolysis reactor and the reverse water gas shift reactor] In the explanations so far, 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 together. However, it is also possible to use a configuration in which the two sections 10 and 20 are separate sections and a heat exchanger 11 is provided between the two sections 10 and 20 to enable heat transfer between the two sections. This configuration is shown in Figure 6, which corresponds to Figure 1. The hollow double lines indicate heat transfer between the two sections. With this configuration, the temperature of each section 10 and 20 can be appropriately controlled.

[0124] The inventors call the system consisting of the electrolysis reactor 10 and the reverse water gas shift reactor 20 described above an "electrolysis reactor system."

[0125] [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.

[0126] (Example of hydrocarbon synthesis catalyst) As activity tests of the catalyst (hydrocarbon synthesis catalyst cat2) used in this second catalytic reaction section 30, the inventors conducted the following evaluation tests 1, 2, 3, 4, and 5. Here, evaluation tests 1 to 4 are tests to determine whether a gas having a desired number of calories or more (referred to as a high-calorie gas) can be produced, and evaluation test 5 is a confirmation test of heavy hydrocarbons that are obtained simultaneously during production.

[0127] As an example of hydrocarbon synthesis catalyst cat2, catalysts were prepared by changing the support and catalytically active components in various ways. As catalytically active components ca2, Ru, Ru with added Mo, V, Fe, Co, etc., and Ni were examined. As supports cb2, ZrO2, Al2O3, SiO2, MgO, and TiO2 were examined.

[0128] (Catalyst preparation) The hydrocarbon synthesis catalyst cat2 is also prepared by the method described in FIGS. That is, an aqueous solution is prepared by dissolving a measured amount of a water-soluble ruthenium compound (such as ruthenium nitrate, ruthenium chloride, ruthenium sulfate, ruthenium ammonium sulfate, ruthenium acetate, ruthenium oxalate, or ruthenium citrate) according to the desired catalyst composition. Furthermore, when supporting molybdenum, vanadium, iron, or cobalt as an additional catalytically active component, the water-soluble metal compounds are similarly measured and dissolved in the aqueous solution. Using this aqueous solution, for example, a predetermined amount of support particles (ZrO2, Al2O3, SiO2, MgO, or TiO2) are added to the aqueous solution, impregnated with the catalytically active component, and the catalyst is then 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 supporting both ruthenium and a catalytically active component other than ruthenium, they were prepared using a sequential loading method (a two-stage loading method in which a catalytically active component other than ruthenium is first loaded on a support, and then ruthenium is loaded). Evaluation test 5 is described separately.

[0129] (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.

[0130] The following two indicators were used to organize the test results.

[0131] 1. Estimated hydrocarbon conversion rate for CO2 removal = [number of carbon atoms in hydrocarbons in outlet gas] / [number of carbon atoms in outlet gas - number of carbon atoms in 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.

[0132] 2.C1-C4 calorific value (MJ / Nm 3 )=Σ(Nn×HN) / Σ Nn Nn [mol]: Number of moles of Cn hydrocarbons in the catalytic reaction gas (n = 1 to 4) HN [MJ / m 3 (N)]: Calorific 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 produced in addition to methane.

[0133] Regarding evaluation test 1, Tables 7 and 8 shown below show Examples B1 to B3 of the hydrocarbon synthesis catalyst cat2 of the present invention.

[0134] [Table 7]

[0135] [Table 8]

[0136] As shown in Tables 7 and 8, it was confirmed that hydrocarbons can be synthesized from a mixed gas of CO, CO2, H2, and H2O using, as the hydrocarbon synthesis catalyst cat2, 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 can be seen that the hydrocarbon production system 100 described above produces a C1-C4 calorific value of 39 MJ / Nm 3 It was confirmed that the above high calorie gases could be produced.

[0137] (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. Note that 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.

[0138] The following two indicators were used to organize the test results.

[0139] 1. Hydrocarbon conversion rate = [number of hydrocarbon carbons in the outlet gas] / [number of carbons in the 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.

[0140] 2. Estimated hydrocarbon conversion rate for CO2 removal = [number of carbon atoms in hydrocarbons in outlet gas] / [number of carbon atoms in outlet gas - number of carbon atoms in 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.

[0141] 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.

[0142] [Table 9]

[0143] [Table 10]

[0144] (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 the activity of the hydrocarbon synthesis catalyst cat2 was tested 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 support was used. Note that the reactant gas in this case is an example of a 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 the gas obtained by the co-electrolysis reaction of water and carbon dioxide, is introduced into the hydrocarbon synthesis reaction section 30 to perform the hydrocarbon synthesis reaction.

[0145] The results of Evaluation Test 3 are shown in Table 11.

[0146] [Table 11]

[0147] As shown in Table 11, it was confirmed that hydrocarbons can be synthesized from a mixed gas containing H2 and CO using a catalyst in which ruthenium and iron or cobalt are supported on a titania carrier as the hydrocarbon synthesis catalyst cat2.

[0148] The hydrocarbon production system 100 described above produces a C1-C4 calorific value of 39 MJ / Nm 3 It was confirmed that the above high calorie gases could be produced.

[0149] (Evaluation Test 4) In evaluation test 4, a mixed gas containing 0.5% CO, 20.0% CO2, and 79.5% H2 was used as the reaction gas, and the activity of the hydrocarbon synthesis catalyst cat2 was tested at a GHSV of 5000 / h (dry basis) and a reaction temperature between about 260°C and about 290°C. The reaction gas in this case corresponds to the mixed gas obtained by separating and removing moisture from the reaction gas used in evaluation test 2.

[0150] The test results for Evaluation Test 4 are shown in Table 12.

[0151] [Table 12]

[0152] From the above results, comparing the test results of Evaluation Test 2 and Evaluation Test 4, it was found that by separating water upstream of the second catalytic reaction section 30 (hydrocarbon synthesis reaction section), the hydrocarbon conversion rate in the hydrocarbon synthesis reaction section 30 can be improved even at a lower reaction temperature, and the activity of the catalyst can be improved. Therefore, the configuration of a hydrocarbon production system 100 shown in Fig. 9, which will be described later in another embodiment, is also effective.

[0153] (Evaluation Test 5) Catalyst preparation In this evaluation test 5, the hydrocarbon synthesis catalyst cat2 was also prepared by the method described with reference to FIGS. Catalyst cat2 had ruthenium and iron as catalytically active components and titania as the support. A ruthenium chloride aqueous solution was used in the ruthenium component loading process, and an iron nitrate aqueous solution was used in the iron component loading process. As previously mentioned, aqueous solutions of other compounds containing ruthenium or iron can also be used.

[0154] The specific preparation method is as follows. A titania carrier serving as a metal oxide carrier was impregnated with an iron-containing aqueous solution of a predetermined concentration to support iron on the titania carrier. This iron-supported titania was then impregnated with a ruthenium chloride aqueous solution of a predetermined concentration. A wet reduction treatment was then performed using an aqueous hydrazine solution to obtain iron-ruthenium-supported titania as hydrocarbon synthesis catalyst cat2.

[0155] The amounts of iron and ruthenium supported in the hydrocarbon synthesis catalyst cat2 can be set as desired by adjusting the concentrations of the aqueous solutions and the impregnation conditions. In evaluation test 5, a spherical titania support having a diameter of 2 to 4 mm was used as the hydrocarbon synthesis catalyst cat2, and iron-ruthenium supported titania (2 wt.%Ru / 2 wt.%Fe / TiO2) was used, with an iron content (supported amount) of 2 wt.% and a ruthenium content (supported amount) of 2 wt.%.

[0156] Reduction pretreatment In the test, a pre-reduction treatment shown in FIG. 12(b) was carried out. Specifically, nitrogen gas containing 10% hydrogen was flowed as a hydrogen-containing gas into the catalyst storage section which serves as the hydrocarbon synthesis reaction section 30, while the temperature of the catalyst section was maintained at 350°C, and hydrogen treatment (pre-reduction treatment) of the catalyst before use was carried out for 1 hour. Here, by using a mixed gas of hydrogen and nitrogen as the hydrogen-containing gas used in the reduction pretreatment, the amount of hydrogen consumed can be reduced. Therefore, in this reduction pretreatment, it is preferable to use a mixed gas of hydrogen and nitrogen with a hydrogen concentration of 20% by volume or less, for example. In this embodiment, the reduction pretreatment of the hydrocarbon synthesis catalyst cat2 is performed using a hydrogen-containing gas containing 10% by volume of hydrogen and the remainder being nitrogen gas.

[0157] Test conditions In evaluation test 5, a mixed gas containing H2 and CO in a volume ratio of 3:1 (H2 / CO = 3) was used as the reaction gas, and the hydrocarbon synthesis catalyst cat2 was tested under the condition of GHSV = 2000 / h. The reaction pressure in this test was 0.6 MPa.

[0158] Heavy hydrocarbon confirmation test 1 Using the hydrocarbon synthesis catalyst cat2 (2 wt.% Ru / 2 wt.% Fe / TiO2) that had undergone the above-mentioned reduction pretreatment, a hydrocarbon synthesis test was carried out at a reaction temperature of 275°C for approximately 80 hours. As a result, gas analysis using a gas chromatograph confirmed that methane (CH4) was the main component, and C2 to C6 hydrocarbons such as ethane, propane, and butane were continuously produced at the outlet of the catalytic reaction section. On the other hand, when the waxy deposit obtained in the air-cooled section (corresponding to the heavy hydrocarbon separation section 35) located below the catalytic reaction section was analyzed, it was identified as straight-chain higher aliphatic hydrocarbons (average chain length: C26) by IR and C13 NMR analysis. Furthermore, when the precipitates on the hydrocarbon synthesis catalyst cat2 were solvent extracted and analyzed by MS, peaks were obtained every 14 mass units between 268 and 604 (with the maximum intensity at 352). These results indicated that higher hydrocarbons of C19 to C43 (C25 being the most abundant) were precipitated on the hydrocarbon synthesis catalyst cat2.

[0159] Heavy hydrocarbon confirmation test 2 Similar to the above test, hydrocarbon synthesis catalyst cat2 (2 wt.% Ru / 2 wt.% Fe / TiO2) was used, and reduction pretreatment was performed at 550°C. A hydrocarbon synthesis test was then conducted at a reaction temperature of 325°C for approximately 270 hours. Gas analysis using a gas chromatograph confirmed that methane (CH4) was the main component, along with C2-C6 hydrocarbons such as ethane, propane, and butane, and that this was being continuously produced at the outlet of the catalytic reaction section. Meanwhile, a waxy deposit (straight-chain higher aliphatic hydrocarbons (average chain length: C18)) was observed in the air-cooled area below the catalytic reaction section (corresponding to the heavy hydrocarbon separation section 35). Furthermore, higher hydrocarbons ranging from C19 to C60 (C29 being the most abundant) were found to be deposited on the hydrocarbon synthesis catalyst cat2.

[0160] Hydrocarbon production with alternative hydrocarbon synthesis catalysts Furthermore, a different hydrocarbon synthesis catalyst (2 wt.% Ru / 2 wt.% Co / TiO2) from the above-mentioned hydrocarbon synthesis catalyst (2 wt.% Ru / 2 wt.% Fe / TiO2) was used. It underwent a reduction pretreatment at 450°C, and a hydrocarbon synthesis test was conducted at temperatures ranging from 250°C to 270°C for approximately 380 hours. Gas analysis using a gas chromatograph confirmed that methane (CH4) was the main component, along with hydrocarbons such as ethane, propane, and butane, continuously produced at the outlet of the catalytic reaction section. Meanwhile, a waxy deposit (straight-chain higher aliphatic hydrocarbons (average chain length: C27)) was observed in the air-cooled area below the catalytic reaction section (corresponding to the heavy hydrocarbon separation section 35). Furthermore, higher hydrocarbons ranging from C23 to C60 (C37 being the most abundant) were found to deposit on the hydrocarbon synthesis catalyst (2 wt.% Ru / 2 wt.% Co / TiO2).

[0161] Evaluation test 5 confirmed that the use of the hydrocarbon synthesis catalyst cat2 according to the present invention made it possible to produce not only lower saturated hydrocarbons but also heavy hydrocarbons.

[0162] From the above results, as previously shown, a catalyst in which at least ruthenium is supported on a metal oxide carrier 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 that at least one of molybdenum, vanadium, iron, and cobalt is supported as the catalytically active component ca2.

[0163] It has been 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 preferably 0.1% by weight or more and 5% by weight or less, and that it is preferable that the metal oxide carrier cb2 further supports, in addition to ruthenium, at least one of molybdenum, vanadium, iron, and cobalt as a catalytically active component ca2.

[0164] 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.

[0165] Furthermore, among such hydrocarbon synthesis catalysts cat2, the highly active catalysts had carbon monoxide adsorption amounts of 0.4 ml / g or more.

[0166] [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 described 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.

[0167] [Water separation section] The water separation section 40 is provided with a condenser, which adjusts the temperature and pressure of the inflowing gas containing H2O to a predetermined level, condenses the gas, and extracts the water to the outside.

[0168] [Carbon dioxide separation section] For example, a PSA is provided in this section 50, which separates CO2 from the incoming CO2-containing gas by adsorbing it onto an adsorbent under a predetermined temperature and pressure, and then desorbs the separated CO2 from the adsorbent, thereby effectively separating CO2. The separated CO2 can be returned to the front of the electrolysis reaction section 10 via the carbon dioxide return path 51 and reused. It 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.

[0169] [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.

[0170] (2) In the above embodiment, no particular mention was made of H in the gas obtained from the hydrocarbon synthesis reaction section 30. However, a hydrogen separation section (shown as H separation section in the figure) 60 that separates H using a hydrogen separation membrane or the like may be provided to separate H for separate use. This configuration is shown in FIG. 8. In this example, the H separated in the hydrogen separation section 60 may be returned to a location before the reverse water gas shift reaction section 20 and used for the reverse water gas shift reaction. In this case, hydrogen is also separated from the hydrogen separation section 60 into a branch path.

[0171] (3) In the above embodiment, the water separation section 40 is provided downstream of the hydrocarbon synthesis reaction section 30. However, as shown in Fig. 9, the water separation section 40 may be provided between the reverse water gas shift reaction section 20 and the hydrocarbon synthesis reaction section 30. The main function of this water separation section 40 is to facilitate the hydrocarbon synthesis reaction.

[0172] (4) In the above embodiment, both HO and CO are supplied to the electrolysis reaction unit 10 for the electrolysis reaction. However, as shown in Fig. 10, a system may be used in which only HO is supplied to the electrolysis reaction unit 10 for the electrolysis reaction. In this case, carbon consumed in the hydrocarbon synthesis is input to the reverse water gas shift reaction unit 20 as carbon dioxide.

[0173] (5) In the above embodiment, an example was shown in which a solid oxide electrolysis cell was used as the electrolysis cell 1 in the electrolysis reaction section 10. However, the electrolysis cell 1 may also be an alkaline electrolysis cell or a polymer membrane electrolysis cell.

[0174] (6) 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. 13. In this figure, 30a denotes 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 this metal support a functions as a separator that separates the produced hydrocarbons from oxygen.

[0175] (7) In the above embodiment, the hydrocarbon production system 100 is configured to include the reverse water-gas shift reactor 20. However, as shown in FIG. 14, instead of using the reverse water-gas shift reactor 20, water can be electrolyzed in the electrolysis reactor 10, and at least one selected from carbon monoxide and carbon dioxide can be introduced upstream of the hydrocarbon synthesis reactor 30 to obtain a high-calorie gas. In this way, when the hydrocarbon production system (which will be a high-calorie gas production system) according to the present invention is constructed with the electrolysis reaction section 10 and the hydrocarbon synthesis reaction section 30, the hydrocarbon synthesis reaction section may be configured in multiple stages. Fig. 15 shows an example in which the hydrocarbon synthesis reaction section 30 is configured in two stages (30a, 30b). In this way, different hydrocarbon synthesis catalysts cat2 can be arranged in different hydrocarbon synthesis reaction sections 30, and they can be operated in different temperature ranges.

[0176] (8) 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, chemical raw materials can also be synthesized from hydrogen, carbon monoxide, etc. introduced into the hydrocarbon synthesis reaction section 30. [Explanation of symbols]

[0177] 1 electrolysis cell 1a Electrolyte layer 2 electrode layer 3. Counter electrode layer 4 Metal support (support / separator) 4a hole 5. Supply path forming member (separator) 6. Supply path forming member (separator) 10 Electrolytic reaction section 20 First catalytic reaction section (reverse water gas shift reaction section) 20a Coating layer 30 Second catalytic reaction section (hydrocarbon synthesis reaction section) 40 Water separation section 50 Carbon dioxide separation section 60 Hydrogen separation section U Electrolysis Cell Unit Cat 1 reverse water gas shift catalyst ca1 Catalytically active component (metal component) cb1 Carrier (metal oxide) Cat2 hydrocarbon synthesis catalyst ca2 Catalytic active component (metal component) cb2 carrier (metal oxide)

Claims

1. A hydrocarbon production system for producing hydrocarbons from at least water and carbon dioxide, comprising: an electrolytic reaction section to which at least water and carbon dioxide are introduced and to which an outlet gas contains carbon dioxide and hydrogen; a catalytic reaction section including, in this order, a reverse water gas shift reaction section as a first catalytic reaction section; and a hydrocarbon synthesis reaction section as a second catalytic reaction section, the reverse water gas shift reaction section receiving the outlet gas of the electrolytic reaction section and comprising a branch passage for branching off a part of the outlet component of the catalytic reaction section; and a carbon dioxide separation section for separating carbon dioxide from the outlet component of the hydrocarbon synthesis reaction section, the separated carbon dioxide being discharged from the branch passage, and the branch passage serving as a recycle line upstream of the reverse water gas shift reaction section; the electrolysis reaction unit includes an electrolysis cell on one surface of a support, the electrolysis cell having an electrode layer and a counter electrode layer sandwiching an electrolyte layer therebetween; a gas flow path is formed along the other surface of the support to penetrate the electrolysis reaction unit and has a plurality of through-holes extending between the one surface and the other surface of the support; the gas flow path forms an electrode layer-side gas supply path for supplying water and carbon dioxide to the electrode layer and also serves as an exhaust path for discharging hydrogen generated in the electrode layer; and the gas discharged via the exhaust path is received as the outlet gas in the reverse water gas shift reaction unit provided on the support.

2. 1. A hydrocarbon production system for producing hydrocarbons from at least water and carbon dioxide, comprising: a catalytic reaction section including, in the stated order, an electrolytic reaction section to which at least water and carbon dioxide are introduced and to which an outlet gas contains carbon dioxide and hydrogen; a reverse water gas shift reaction section as a first catalytic reaction section; and a hydrocarbon synthesis reaction section as a second catalytic reaction section, the reverse water gas shift reaction section receiving the outlet gas of the electrolytic reaction section and comprising a branch passage for branching off a part of the outlet component of the catalytic reaction section; and a hydrogen separation section for separating hydrogen from the outlet component of the hydrocarbon synthesis reaction section, the separated hydrogen being discharged from the branch passage, and the branch passage serving as a recycle line to the upstream side of the reverse water gas shift reaction section.

3. 3. The hydrocarbon production system according to claim 1, wherein the catalytic reaction section converts the product produced in the electrolytic reaction section into a high-calorie gas containing at least lower saturated hydrocarbons through a catalytic reaction.

4. 4. The hydrocarbon production system according to claim 1, further comprising a heavy hydrocarbon separation section for separating heavy hydrocarbons from the outlet components of the catalytic reaction section.

5. 3. The hydrocarbon production system according to claim 2, wherein the electrolysis reaction section comprises an electrolysis cell in which at least an electrode layer, an electrolyte layer, and a counter electrode layer are formed on a support.

6. 3. The hydrocarbon production system according to claim 2, wherein the electrolysis reaction unit comprises an electrolytic cell on one surface of a support, the electrolytic cell including an electrode layer and a counter electrode layer sandwiching an electrolyte layer, a gas flow path penetrating along the other surface of the support and having a plurality of through-holes extending between the one surface and the other surface of the support, the gas flow path forming an electrode layer-side gas supply path for supplying water and carbon dioxide to the electrode layer and also serving as an exhaust path for discharging hydrogen generated in the electrode layer, and the gas discharged via the exhaust path is received as the outlet gas in the reverse water gas shift reaction unit provided on the support.

7. 7. The hydrocarbon production system of claim 1, 5 or 6, wherein the support is a metal.

8. The hydrocarbon production system according to any one of claims 1 to 7, wherein the reverse water gas shift reaction section contains a reverse water gas shift catalyst, the reverse water gas shift catalyst comprising a carrier mainly composed of a zirconia-based metal oxide, and either or both of nickel and iron supported as catalytically active components.

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