Hydrocarbon production system, production method thereof, and operation method thereof

Abstract

Provided is a hydrocarbon production system (100) as a hydrogen production system for synthesizing a hydrocarbon using water and carbon dioxide as raw materials, the hydrocarbon production system (100) making it possible to secure hydrogen and carbon monoxide which are needed for the synthesis of a hydrocarbon and to produce a hydrocarbon.　The hydrocarbon production system (100) for producing a hydrocarbon from at least water and carbon dioxide is equipped with at least an electrolytic reaction unit (10), a reverse water gas shift reaction unit (20) and a hydrocarbon synthesis reaction unit (30).

Description

Hydrocarbon production system, its production method and operation method

[0001] The present invention relates to a hydrocarbon production system for producing hydrocarbons from at least water and carbon dioxide, and to a production method and an operation method of this hydrocarbon production system.

[0002] This type of hydrocarbon production system is disclosed in Patent Document 1 or 2. 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 the synthesis gas obtained in the electrolytic single cells is converted into a desired combustible gas by heterogeneous catalytic action. Therefore, the technology disclosed in Patent Document 1 includes a hydrocarbon synthesis section downstream of the electrolytic reaction section, and synthesizes (produces) hydrocarbons using water and carbon dioxide as starting materials.

[0003] On the other hand, the technology disclosed in Patent Document 2 relates to a power-to-gas unit that produces useful gas (specifically, methane) from electricity, and specifically discloses a technology in which a methanation reaction catalyst material is included in the cathode of a stack of basic solid oxide electrolysis (SOEC) cells. In the technology disclosed in Patent Document 2, the basic electrolysis cells also serve as the electrolysis reaction unit, and the methanation reaction catalyst material provided in the cathode constitutes the hydrocarbon synthesis unit.

[0004] In these prior art technologies, the electrolysis reaction section performs so-called "co-electrolysis," in which water and carbon dioxide are electrolyzed together. A heterogeneous catalyst is used for the synthesis of hydrocarbons (so-called methanation).

[0005] JP 2016-522166 A JP 2019-112717 A

[0006] However, the inventors have found that the following problems exist with co-electrolysis in the electrolysis reaction section and hydrocarbon synthesis in the hydrocarbon synthesis section. 1. Problems with co-electrolysis Because the electrolysis voltage of water is around 1.23 V and the electrolysis voltage of carbon dioxide is around 1.33 V, the electrolysis reaction of carbon dioxide is more difficult to occur than the electrolysis reaction of water. As a result, even if an attempt is made to cause a co-electrolysis reaction, the electrolysis reaction of carbon dioxide is difficult to occur, and it is not possible to ensure a sufficient concentration of carbon monoxide required for hydrocarbon synthesis.

[0007] 2. Problems in hydrocarbon synthesis It is said that heterogeneous catalysts are used for hydrocarbon synthesis, but selecting this type of catalyst is difficult, and technology for stable hydrocarbon synthesis has not yet been established.

[0008] In view of this situation, a main object of the present invention is to provide a hydrocarbon production system that synthesizes hydrocarbons using water and carbon dioxide as raw materials, and that can produce hydrocarbons while securing the hydrogen and carbon monoxide necessary for hydrocarbon synthesis.

[0009] A first characteristic feature of the present invention is a hydrocarbon production system for producing hydrocarbons from at least water and carbon dioxide, which comprises at least an electrolysis reaction section, a reverse water gas shift reaction section, and a hydrocarbon synthesis reaction section.

[0010] This hydrocarbon production system includes an electrolysis reaction unit, a reverse water-gas shift reaction unit, and a hydrocarbon synthesis reaction unit. In this configuration, the spatial positional relationship between the units is not important, but at least with regard to gases advecting between these units, it is sufficient that gas decomposed in the electrolysis reaction unit is advected to the reverse water-gas shift reaction unit, and hydrogen and carbon monoxide obtained through reactions in this unit are advected to the hydrocarbon synthesis reaction unit, where hydrocarbons are synthesized.

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

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

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

[0014] A second characteristic feature of the present invention is that the electrolysis reaction of water is carried out in the electrolysis reaction section.

[0015] According to this characteristic configuration, the hydrogen required in the hydrocarbon synthesis reaction section can be obtained by electrolysis of one or more of water and steam.

[0016] A third characteristic feature of the present invention is that a co-electrolytic reaction of water and carbon dioxide takes place in the electrolytic reaction section.

[0017] According to this characteristic configuration, hydrogen and a certain amount of carbon monoxide can be obtained by decomposing both water and carbon dioxide in the electrolytic reaction unit. As described above, co-electrolysis mainly contributes to the provision of hydrogen, but in the hydrocarbon production system according to the present invention, by providing a reverse water-gas shift reactor downstream of the electrolytic reaction unit, carbon monoxide that tends to be insufficient can be supplemented by this reverse water-gas shift reactor. Furthermore, when co-electrolysis is performed in the electrolytic reaction unit, the gas flowing in from the electrolytic reaction unit contains water, hydrogen, carbon dioxide, and carbon monoxide, and therefore can undergo the reverse water-gas shift reaction almost directly.

[0018] A fourth characteristic feature of the present invention is that the reverse water gas shift reactor has a reverse water gas shift catalyst in which an active metal is supported on a metal oxide support.

[0019] According to this characteristic feature, a catalyst in which an active metal is supported on a metal oxide support (in the present invention, this catalyst is referred to as a reverse water gas shift catalyst) can be used to cause the reverse water gas shift reaction. Such a catalyst in which an active metal is supported on a metal oxide support can be easily produced by, for example, immersing the metal oxide support in a solution in which the active metal is dissolved. Therefore, this is preferable because the concentration of the metal oxide support and the active metal in the catalyst can be well controlled.

[0020] Here, to obtain this type of catalyst (reverse water gas shift catalyst), it is preferable to produce it through a calcination step in which it is calcined at a temperature of 450°C or higher. A calcination temperature of 600°C or higher, or 800°C or higher, is even more preferable. This catalyst must be used at high temperatures because it can advance the equilibrium reaction toward the reverse water gas shift reaction targeted by the present invention at high temperatures, and it also needs to be resistant to high temperatures. For example, the catalyst can be used stably even when combined with a solid oxide electrolysis cell used at relatively high temperatures (e.g., 600°C to 800°C). Furthermore, since the cost of the calcination step becomes too high if the calcination temperature is too high, the upper limit is about 1200°C.

[0021] Furthermore, it is preferable to use the catalyst after a reduction pretreatment. As described above, the catalyst obtained through the calcination process has at least a part of the catalytically active components in an oxidized state, and the catalyst may not be able to fully exhibit its activity. Therefore, by performing a reduction pretreatment, the catalytically active components in an oxidized state are reduced, allowing the catalyst to fully exhibit its activity.

[0022] Therefore, in the hydrocarbon production system described above, it is preferable to operate the system after subjecting the reverse water gas shift reactor to a reduction pretreatment. This is the sixteenth characteristic feature of the present invention.

[0023] Furthermore, by applying the catalyst (reverse water gas shift catalyst) obtained in this manner to the surface of, for example, a metal support, the reverse water gas shift reaction can be caused in gases advecting in contact with the applied surface.

[0024] As described in a fourteenth characteristic configuration of the present invention, the hydrocarbon production system having this configuration can be produced by disposing an impregnated support obtained through an impregnation step of impregnating a metal oxide support with an active metal in at least the reverse water gas shift reaction section.

[0025] A fifth characteristic feature of the present invention is that the reverse water gas shift catalyst is a reverse water gas shift catalyst having at least one of nickel and iron, or both, supported as active metals on a metal oxide support mainly composed of a ceria-based metal oxide or a zirconia-based metal oxide.

[0026] According to this characteristic configuration, by supporting either or both of nickel and iron as catalytically active components (active metals) on a carrier mainly composed of ceria-based metal oxide or zirconia-based metal oxide, a catalyst with high activity at relatively high temperatures is obtained, as will be explained later with reference to Tables 1, 2, 3, and 4. The performance of the catalyst with this configuration exhibited activity comparable to that of platinum, an expensive noble metal, as a catalytically active component.

[0027] When either or both of nickel and iron are used as catalytically active components, the cost per unit weight can be reduced to 1 / 1000 or less compared to platinum, and this is preferable because it allows for a reduction in cost or, when the same cost is required, a significantly increased amount of catalyst to be used.

[0028] Furthermore, by using a ceria-based metal oxide or a zirconia-based metal oxide as the support, it is possible to ensure resistance in high temperature ranges.

[0029] In the present invention, a reverse water-gas shift reactor is provided downstream of the electrolytic reaction unit (the side where the gas generated in the electrolytic reaction unit flows). By using a ceria-based metal oxide or a zirconia-based metal oxide as the support for the reverse water-gas shift catalyst, the thermal expansion coefficient of the catalyst can be made close to that of the material constituting the electrolytic reaction unit, and reactions can be effectively generated in both units in approximately the same high-temperature range.

[0030] To obtain this reverse water gas shift catalyst, a support mainly composed of a ceria-based metal oxide or a zirconia-based metal oxide is added to a solution containing either or both of nickel and iron, and an impregnation / support step is at least carried out to impregnate and support at least either or both of nickel and iron onto the support, thereby producing the reverse water gas shift catalyst.

[0031] A sixth characteristic feature of the present invention is that the ceria-based metal oxide is ceria doped with at least one of gadolinium, samarium, and yttrium.

[0032] According to this characteristic feature, the activity as a catalyst can be improved by performing a doping treatment as described below.

[0033] A seventh characteristic feature of the present invention is that the zirconia-based metal oxide is zirconia stabilized with at least one of yttria and scandia.

[0034] According to this characteristic feature, the activity can be improved by using a stabilized zirconia catalyst, as will be described later.

[0035] An eighth characteristic feature of the present invention is that the reverse water gas shift catalyst described above supports copper as the active metal.

[0036] According to this characteristic feature, the activity as a reverse water gas shift catalyst can be improved.

[0037] Furthermore, in the method for producing a hydrocarbon production system, the step of forming the reverse water gas shift reactor preferably includes at least a calcination step of calcining at a temperature of 450° C. or higher. This is a seventeenth characteristic configuration of the present invention.

[0038] As will be described later, the reverse water gas shift catalyst is housed in the reverse water gas shift reactor, and it is preferable to perform a calcination treatment during the manufacturing process of the reverse water gas shift catalyst to enhance its stability under high-temperature operating conditions. The calcination treatment can be performed during the formation of the reverse water gas shift reactor.

[0039] A ninth characteristic feature of the present invention is that the hydrocarbon synthesis reaction section has a hydrocarbon synthesis catalyst in which an active metal is supported on a metal oxide support.

[0040] According to this characteristic feature, a hydrocarbon synthesis reaction can be caused by using a catalyst in which an active metal is supported on a metal oxide support (in the present invention, this catalyst is referred to as a hydrocarbon synthesis catalyst). Such a catalyst in which an active metal is supported on a metal oxide support can be easily produced by, for example, immersing the metal oxide support in a solution in which the active metal is dissolved. This is preferable because it allows for good control of the metal oxide support concentration and the active metal concentration in the catalyst.

[0041] Furthermore, by applying the catalyst (hydrocarbon synthesis catalyst) thus obtained to the surface of, for example, a metal support, a hydrocarbon synthesis reverse hydrolysis reaction can be caused in gas flowing in contact with the applied surface.

[0042] Therefore, as described in the fourteenth characteristic configuration of the present invention, a hydrocarbon production system can also be produced by disposing an impregnated support obtained through an impregnation step of impregnating an active metal onto a metal oxide support in both the reverse water gas shift reaction section and the hydrocarbon synthesis reaction section.

[0043] A tenth characteristic feature of the present invention is that the active metal is ruthenium.

[0044] According to this characteristic configuration, hydrocarbons can be synthesized with high activity, as will be shown later.

[0045] An eleventh characteristic configuration of the present invention is that 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.

[0046] 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.

[0047] A twelfth characteristic feature of the present invention is that the support is made of metal.

[0048] 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.

[0049] A fifteenth characteristic feature of the present invention is that the hydrocarbon synthesis reaction section is supported by a support, and the support is made of metal.

[0050] According to this characteristic configuration, the hydrocarbon synthesis reaction can be effectively caused while reducing the amount of catalyst required for hydrocarbon synthesis, and a hydrocarbon synthesis unit with excellent heat resistance and durability can be obtained.

[0051] Furthermore, by using a metal as the support, the strength and heat resistance of the hydrocarbon synthesis section used at high temperatures can be ensured, and stable performance can be achieved.

[0052] Diagram showing the configuration of a hydrocarbon production system Schematic diagram showing the configuration of the electrolysis reaction section Diagram showing the configuration of a system integrating an electrolysis reaction section and a reverse water gas shift reaction section Schematic diagram of an electrolysis cell unit equipped with an electrolysis reaction section and a reverse water gas shift reaction section Cross-sectional view of an electrolysis cell unit used in a comparative experiment in which the electrode layer side gas supply channel was used as the reverse water gas shift reaction section Diagram of a system equipped with a heat exchanger between the electrolysis reaction section and the reverse water gas shift reaction section ２Fig. 1 shows another configuration of a hydrocarbon production system in which water is introduced into a reverse water gas shift reactor Fig. 2 shows another configuration of a hydrocarbon production system equipped with a hydrogen separation unit Fig. 3 shows yet another configuration of a hydrocarbon production system equipped with a water separation unit before a hydrocarbon synthesis reactor Fig. 4 shows yet another configuration of a hydrocarbon production system in which only water is introduced into an electrolysis reactor Explanatory diagram showing the preparation state of a catalyst Explanatory diagram showing the application and calcination state of a catalyst and reduction pretreatment Schematic diagram of an electrolysis cell unit equipped with an electrolysis reactor, a reverse water gas shift reactor, and a hydrocarbon synthesis reactor

[0053] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. Fig. 1 shows the configuration of one embodiment of a hydrocarbon production system 100 proposed by the present inventors.

[0054] As shown in the figure, this hydrocarbon production system 100 includes 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 (H ２ O separation section) and carbon dioxide separation section 50 (CO ２ The separator is configured to include a separator (shown in the figure) in order.

[0055] The electrolytic reaction unit 10 is a unit that electrolyzes at least a part of the inflowing gas, the first catalytic reaction unit 20 is a reverse water-gas shift reaction unit that performs a reverse water-gas shift reaction on at least a part of the inflowing gas, and the second catalytic reaction unit 30 is configured to function as a hydrocarbon synthesis reaction unit that synthesizes at least a part of the inflowing gas into hydrocarbons. ４ (hydrocarbons with one carbon atom), but also includes 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 larger carbon number than the lower saturated hydrocarbons, hydrocarbons that are not saturated, or oxygen-containing hydrocarbons. Therefore, in this specification, hydrocarbons are a concept that includes all of these, and are also collectively referred to as hydrocarbons.

[0056] The heavy hydrocarbon separation unit 35, the water separation unit 40, and the carbon dioxide separation unit 50 extract predetermined components (Cn, Hm, H ２ O and CO２ The components removed and recovered by the water separation unit 40 and the carbon dioxide separation unit 50 are returned to a predetermined part of the system via a water return line 41 and a carbon dioxide return line 51, as shown in FIG. 1, and are reused. ２ O and CO ２ As a result, the hydrocarbon production system 100 is substantially CO ２ This creates a carbon-closed system that does not release any carbon dioxide outside the system.

[0057] 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.

[0058] In the electrolysis reaction section 10, H ２ O and CO ２ is introduced and electrolyzed inside, ２ O is H ２ and O ２ and some CO ２ CO and O ２ are broken down and released.

[0059] The reaction is described as follows: ２ O → 2H ２ +O ２ (Formula 1) 2CO ２ →2CO+O ２ (Equation 2) These equations 1 and 2 are also shown in the box representing the electrolytic reaction section 10 in FIG.

[0060] In the first catalytic reaction section 20 (reverse water gas shift reaction section), H ２ and CO ２ is introduced, the reverse water gas shift reaction occurs inside, and CO ２ CO, H ２ Is H ２ It becomes O and is released.

[0061] The reaction is described as the following equilibrium reaction. The reverse water gas shift reaction is a reaction in which the reaction described in Equation 3 below proceeds to the right (CO ２ and H ２reacts to form CO and H ２ The reaction proceeds in the direction of producing CO. ２ +H ２ ⇔CO + H ２ O (Equation 3) Equation 3 is also shown in the box representing the first catalytic reaction section 20 (reverse water gas shift reaction section) in Fig. 1. The reverse water gas shift catalyst cat1 used in the reaction is also shown schematically in this box.

[0062] In the second catalytic reaction section 30 (hydrocarbon synthesis reaction section), H ２ and CO are introduced and hydrocarbons are synthesized through a catalytic reaction. ２ From CH ４ The reaction by which CO and H are synthesized is described as the following equilibrium reaction. ２ From CH ４ The reaction in which CO is synthesized is the reaction in which the reaction described in the following formula 4 proceeds to the right (CO and H ２ reacts to CH ４ and H ２ The reaction proceeds in the direction of producing O. ２ ⇔CH ４ +H ２ O (Equation 4) This equation 4 is also shown in the box showing 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 in this box. Furthermore, the equilibrium reaction of (Equation 3) also occurs in this section. Depending on the type of catalyst used in the second catalytic reaction section 30, it is possible to proceed with the FT (Fischer-Tropsch) synthesis reaction, etc., so that the equilibrium reaction of CO and H ２ From this, various hydrocarbons can be synthesized, including ethane, propane, butane, pentane, hexane, paraffins, and olefinic hydrocarbons.

[0063] 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 catalysts that contain iron, cobalt, or the like as their catalytically active components, and these types of heavy hydrocarbons condense as the temperature drops 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.

[0064] H generated in the water separation section 40 ２ O is separated and returned to the upstream side of the electrolysis reaction section 10 via a water return line 41 (water recycle line).

[0065] CO generated in the carbon dioxide separation section 50 ２ is separated and returned to the upstream side of the electrolysis reaction section 10 via a carbon dioxide return line 51 (carbon dioxide recycle line).

[0066] As a result, in this hydrocarbon production system 100, hydrocarbons are ultimately synthesized and can be supplied to the outside.

[0067] The above is an overview of the hydrocarbon production system 100. The configuration and role of each part will be described below. [Electrolytic Reaction Part] As described above, the electrolytic reaction part 10 consumes the power supplied in accordance with the above formulas 1 and 2 to convert the inflowing H ２ O and CO ２ Disassemble.

[0068] Figure 2 shows a schematic cross-sectional configuration of this electrolysis 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 includes an electrode layer 2 on one surface of an electrolyte layer 1a and a counter electrode layer 3 on the other surface. The electrode layer 2 serves as the cathode in the electrolysis cell 1, and the counter electrode layer 3 serves as the anode. Incidentally, this electrolysis cell unit U is supported by a metal support 4. Note that, here, a case where a solid oxide electrolysis cell is used as the electrolysis cell 1 is illustrated as an example.

[0069] The electrolyte layer 1a can be formed as a thin film having 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.

[0070] The electrolyte layer 1a is preferably formed by a low-temperature firing method (e.g., a wet method using firing in a low-temperature range without firing in a high-temperature range exceeding 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 using firing in a high-temperature range exceeding 1100°C, for example. This can suppress damage to the metal support 4 and also suppress 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.

[0071] Furthermore, the electrolyte layer 1a is densely configured 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, its density is preferably 95% or more, and even more preferably 98% or more. When the electrolyte layer 1a is configured in a multi-layer structure, it is preferable that at least a portion of the layers include a layer (dense electrolyte layer) having a density of 98% or more, and even more preferably a layer (dense electrolyte layer) having a density of 99% or more. When such a dense electrolyte layer is included as part of the electrolyte layer 1a, it is easy to form an electrolyte layer 1a that is dense and has high airtightness and gas barrier properties, even when the electrolyte layer 1a is configured in a multi-layer structure.

[0072] The electrode layer 2 can be provided as a thin layer on the front surface of the metal support 4 in an area larger than the area where the holes 4a are provided. When a thin layer is provided, its thickness can be, for example, 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 reducing 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.

[0073] The constituent material of this electrode layer 2 is, for example, NiO-GDC, Ni-GDC, NiO-YSZ, Ni-YSZ, CuO-CeO ２ , Cu—CeO ２ Examples of such composites include GDC, YSZ, CeO ２can be called the aggregate of the composite material. The electrode layer 2 is preferably formed by a low-temperature firing method (e.g., a wet method using firing in a low-temperature range without firing in a high-temperature range 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 processes that can be used in a low-temperature range can provide a good electrode layer 2 without firing in a high-temperature range above 1100°C, for example. 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, using a low-temperature firing method is even more preferable because it facilitates handling of raw materials.

[0074] The counter electrode layer 3 can be formed as a thin layer on the surface of the electrolyte layer 1a opposite the electrode layer 2. When a thin layer is formed, its thickness can be, for example, approximately 1 μm to 100 μm, preferably 5 μm to 50 μm. This thickness reduces the amount of expensive counter electrode layer material used, thereby 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 preferable that the counter electrode layer 3 contain a perovskite-type oxide containing two or more elements selected from the group consisting of La, Sr, Sm, Mn, Co, and Fe. The electrolyte layer 1a, electrode layer 2, and counter electrode layer 3 are formed as thin films, as described below, which the inventors refer to as being formed in a thin layer.

[0075] As described above, the electrolysis cell unit U is of a metal support type, and includes a metal support 4 as a support for the electrode layer 2. A supply channel forming member 5 that forms a U-shaped electrode layer side gas supply channel 5a is provided on the opposite side of the metal support 4 from the electrode layer 2. Furthermore, a large number of holes 4a are provided in the metal support 4 so as to penetrate from the front to the back. A gas (H２ O and CO ２ ) is electrolyzed and supplied to the electrode layer 2 through the numerous holes 4a. ２ , CO) flows out from this hole 4a.

[0076] On the other hand, a supply channel forming member 6 for forming a counter electrode layer side gas supply channel 6 a 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 6 a.

[0077] 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 only needs to have sufficient strength to form the electrolytic cell unit U as a support, and can 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 can also be made of, for example, ceramics.

[0078] 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 ).

[0079] By using a ferritic stainless steel material (an example of an Fe—Cr alloy) as the material for 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. Therefore, the electrolysis cell unit U is 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 to be realized.

[0080] The supply path forming members 5 and 6 of the electrolysis cell unit U can be made of the same material as the metal support 4, and the thickness thereof can also be made approximately the same.

[0081] The metal support 4 and the 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.

[0082] In the electrolysis operation of the electrolysis cell unit U having the above configuration, DC power is supplied from a power supply unit (shown as a battery in FIG. 2 ) between a pair of electrode layers 2 and 3 disposed on either side of the electrolyte layer 1 a. In this embodiment, as shown in the figure, the electrode layer 2 side is negative and the counter electrode layer 3 side is positive. Depending on the configuration of the electrolysis cell unit U, the electrode layer 2 side may be positive and the counter electrode layer 3 side may be negative. Then, H 2 , a gas to be electrolyzed, is supplied to the electrode layer 2. ２ O and CO ２ is supplied from the electrolysis raw material supply section (the upstream portion of the electrolysis reaction section 10 in FIG. 1 ) and a carrier gas g2 is supplied to the counter electrode layer side, whereby the reactions shown in Equations 1 and 2 are caused to occur in the electrolysis cell 1, and the decomposed gas can be extracted. ２ The supply of O may be either water or water vapor, or both. Therefore, in the present invention, an electrolytic cell apparatus is constructed including at least an electrolytic cell unit U, an electrolysis raw material supply unit that supplies water and / or water vapor and carbon dioxide to the electrolytic cell unit U, and a power supply unit that supplies electric power.

[0083] Gas (H２ O, CO ２ ) and released gas (H ２ O, H ２ , CO, O ２ , CO ２ 2, the electrode layer side gas supply channel 5a and the counter electrode layer side gas supply channel 6a are shown above and below the electrolysis cell unit U 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 paper surface of FIG. 2. For example, the supply side gas (H ２ O, CO ２ ) from the front side of the paper, and the gas (H ２ O, H ２ , CO, O ２ , CO ２ ) can be recovered from the back side of the paper (see FIG. 4 described later). ２ In order to facilitate the discharge of the oxidizing gas, a carrier gas g2 such as air may be passed through the electrolysis cell unit U.

[0084] The electrolytic reaction section 10 ２ O and CO ２ When electrolysis is carried out by supplying H ２ O is CO ２ Since the electrolysis voltage is lower than that of H, it is easily electrolyzed. ２ O and CO ２ When the electrolysis reaction is carried out by supplying the hydrogen to the electrolysis reaction unit 10, the concentration of H is higher than that of CO at the outlet of the electrolysis reaction unit 10. ２ The concentration tends to be higher, and unreacted CO ２ is likely to remain.

[0085] [First catalytic reaction section (reverse water gas shift reaction section)] As described above, the first catalytic reaction section 20 (reverse water gas shift reaction section) causes a reverse water gas shift reaction to convert the supplied H ２ Using CO ２ is converted to CO and H ２ H ２ O. That is, H ２ O and CO ２ In the electrolysis reaction section 10, CO is supplied and electrolyzed.２ is converted to CO.

[0086] 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 preferable.

[0087] In describing catalysts herein, a component having catalytic activity may be referred to as a "catalytically active component," and a support supporting the catalytically active component may be referred to as a "support." As described below, the inventors have investigated various combinations of catalytically active components and supports, and have found that a specific combination is suitable. This type of catalyst can be produced by carrying out an impregnation process in which a support (metal oxide support) is immersed in a solution containing the catalytically active component (active metal), removed, dried, and heated. This process easily yields a support-supported catalyst (impregnated support) in which the catalytically active component is distributed on the support surface. This heat treatment is referred to as a calcination process. The preparation and use of the catalyst will be described with reference to Figures 11 and 12.

[0088] The preparation method described here is similar for various combinations of catalytically active components and carriers, except for the different starting materials. Figure 11 shows examples of a reverse water gas shift catalyst cat1 and a hydrocarbon synthesis catalyst cat2 according to the present invention. In the figure, the catalytically active component of the reverse water gas shift catalyst cat1 is labeled ca1, and its carrier is labeled cb1. Meanwhile, for the hydrocarbon synthesis catalyst cat2, its catalytically active component is labeled ca2, and its carrier is labeled cb2.

[0089] 11, in catalyst preparation, an aqueous solution of a compound containing metal components (metal catalysts) that become catalytically active components ca1 and ca2 is obtained, and carriers cb1 and cb2 are added to the aqueous solution and stirred and impregnated in an impregnation-supporting step (a). This is followed by evaporation to dryness, drying, and then a drying / crushing / shaping step (b) of pulverizing and shaping the resulting shaped body, and a calcination step (c) of calcining the resulting shaped body in air to obtain the target product (cat1, cat2). Therefore, this type of catalyst is also called an impregnated-supported catalyst.

[0090] In this case, as shown in Fig. 12 using the reverse water gas shift catalyst cat1 as an example, the catalyst can be applied to the area where it is to be used and then calcined. Fig. 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 thereon to form a coating layer 20a, followed by calcination. Fig. 12(b) 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 thereon to form a coating layer 20a, followed by calcination. ２ This shows a pre-reduction treatment step in which the above-mentioned

[0091] When the calcination treatment is performed in air, the supported catalytic active components ca1 and ca2 are partially or entirely 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 surface of the catalyst being exposed to a reducing gas (typically H ２ ) is circulated and undergoes reduction pretreatment.

[0092] (Catalyst Used) As the reverse water gas shift catalyst cat1 to be used in the first catalytic reaction section 20, the inventors selected a catalyst that satisfies the following requirements.

[0093] The 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 the support cb1 to the entire catalyst is preferably 55 wt. % or more, more preferably 60 wt. % or more, and even more preferably 65 wt. % or more, because this increases the strength of the catalyst cat1. The upper limit of this ratio can be, for example, 99.5 wt. However, if the ratio exceeds this limit, the catalytically active components ca1 may not be sufficiently supported, making it difficult to achieve the desired effect as a reverse water gas shift catalyst cat1.

[0094] Furthermore, the ceria-based metal oxide may be ceria doped with at least one of gadolinium, samarium, and yttrium, and the zirconia-based metal oxide may be zirconia stabilized with at least one of yttria and scandia.

[0095] In addition, since the reverse water gas shift reaction can be smoothly progressed, 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 increased too much, it becomes difficult to support the catalytically active component ca1 in a highly dispersed manner, making it difficult to obtain a significant improvement in catalytic activity and increasing the catalyst cost, so 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.

[0096] 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.

[0097] The following describes the 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 were changed in various ways. As the catalytically active component ca1, Ni and Fe were examined and compared with Pt (platinum). The carrier cb1 was ZrO ２ (zirconia), YSZ (yttria-stabilized zirconia), GDC (gadolinium-doped ceria), CeO ２ (ceria) as an example, and Al ２ O ３ (alumina) was also considered.

[0098] In the following explanation, Test Example 1 and Test Example 2 will be introduced. The difference between the two tests is that in the calcination of the reverse water gas shift catalyst cat. 1, 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.

[0099] (Test Example 1) The following describes the test results of Examples (1 to 19) in which the carrier was changed in various ways as the catalyst used in the first catalytic reaction section 20. As catalytically active components, Ni and Fe were investigated and compared with Pt (platinum). The carrier was ZrO ２ (zirconia), YSZ (yttria-stabilized zirconia), GDC (gadolinium-doped ceria), CeO ２ (ceria) as an example, and Al ２ O ３ (alumina) was also considered.

[0100] (Catalyst Preparation) When preparing the reverse water gas shift catalyst cat1, an aqueous solution is prepared by dissolving a measured amount of either or both of a water-soluble nickel compound (nickel nitrate, nickel chloride, nickel sulfate, nickel ammonium sulfate, nickel acetate, nickel oxalate, nickel citrate, etc.) and a water-soluble iron compound (iron nitrate, iron chloride, iron sulfate, iron ammonium sulfate, iron acetate, iron oxalate, iron citrate, etc.) according to the composition of the target catalyst. Furthermore, when supporting copper as a further catalytically active component ca1, an aqueous solution is prepared by dissolving a measured amount of a water-soluble copper compound (copper nitrate, copper chloride, copper sulfate, copper ammonium sulfate, copper acetate, copper oxalate, copper citrate, etc.) in the same manner. A predetermined amount of carrier powder (ceria, zirconia, GDC, YSZ, Al ２ O ３ ) is added, stirred, and impregnated, then evaporated to dryness and dried, and then crushed, molded, and calcined in air. This impregnation is the "impregnation-supporting step" referred to in the present 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. Furthermore, a Pt-based catalyst was prepared using tetraammineplatinum hydroxide.

[0101] The temperatures for the evaporation to dryness, drying, and calcination in the preparation of the catalyst can be within a commonly used temperature range. In Test Example 1, the temperatures for the catalysts in the following examples were 80°C, 80°C, and 450°C, respectively.

[0102] 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 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.

[0103]

[0104] (Catalytic Activity Test) The catalytic activity test was carried out at 50% H ２ -50% CO ２ Mixture of gases (H ２ and CO ２ The reaction was carried out using a mixed gas containing 1:1 (volume ratio) of 1H2O and 1H2O as the reaction gas, with a GHSV (Gas Hourly Space Velocity) of 10,000 / h and varying the reaction temperature from 600°C to 800°C in 50°C increments. Before the catalytic activity test, the catalyst was pre-treated at 600°C for reduction while passing hydrogen gas through the catalyst layer. The test results showed that CO ２ The CO concentration (%) and CH4 concentration (%) at the outlet of the reaction section are shown in Table 2 together with the conversion rate (%).

[0105] In addition, CO ２ The conversion rate (%) was calculated according to the following formula based on the results of gas analysis at the outlet of the catalyst layer. ４ Concentration] + [CO concentration] / ([CH ４ Concentration] + [CO concentration] + [CO ２ concentration〕)

[0106] As mentioned above, the reverse water gas shift catalyst cat1 used in the first catalytic reaction section 20 (reverse water gas shift reaction section) is a catalyst that can convert CO ２ A high percent conversion is desirable.

[0107]

[0108] (Test Example 2) The test results of Examples (20 to 29) of Test Example 2 will be explained below. In this example, Ni and Fe were investigated as catalytically active components, and the addition of Cu was also investigated. The carrier was CeO ２ (ceria), ZrO ２ (zirconia) as an example, and Al ２ O ３ (alumina) was also considered.

[0109] (Catalyst Preparation) The reverse water gas shift catalyst cat 1 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.

[0110] Table 3 shows the catalysts prepared for each of the Examples (20-29).

[0111]

[0112] (Catalytic Activity Test) The catalytic activity test was carried out using H ２ and CO ２ A mixed gas containing 1:1 (volume ratio) of CO was used as the reaction gas, and the reaction temperature was changed from 600°C to 800°C in 50°C increments under the condition of GHSV of 10,000 / h. Before the catalytic activity test, the catalyst was pre-treated at 600°C for reduction while passing hydrogen gas through the catalyst layer. ２ Along with the conversion rate (%), the CO concentration (%) at the outlet of the reaction section, CH ４ The concentrations (%) are shown in Table 4.

[0113]

[0114] For reference, the CO ２ The equilibrium values ​​(calculated values) of the conversion rates are shown in Table 4.

[0115] Iron-Zirconia Catalyst and Iron-Alumina Catalyst For the iron-zirconia catalyst, test results for calcination temperatures of 450°C, 600°C, 800°C, and 1000°C are shown in Examples 8, 22, 26, and 29, respectively. Meanwhile, for the iron-alumina catalyst, test results for calcination temperatures of 450°C, 600°C, and 800°C are shown in Examples 14, 23, and 27, respectively. As can be seen from these results, although the metal loadings are slightly different, the iron-zirconia catalyst has superior activity in the reverse water gas shift reaction compared to the iron-alumina catalyst. Furthermore, the iron-zirconia catalyst exhibits 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. At any calcination temperature, CO ２ The conversion rate reaches near the equilibrium value.

[0116] The test results for nickel-ceria catalysts at 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. ２ The conversion rate reaches near the equilibrium value.

[0117] The test results for the nickel-alumina catalyst when the calcination temperature was set to 450°C are shown in Example 7. The results show that the nickel-alumina catalyst has a higher CO2 content than the nickel-ceria catalyst mentioned above. ２ The conversion rate was low.

[0118] The test results for nickel-copper-ceria catalysts at calcination temperatures of 450°C, 600°C, and 800°C are shown in Examples 6, 21, and 25, respectively. These results show that with nickel-copper-ceria catalysts, when the calcination temperature is increased to 600°C or 800°C, a slight increase in CO ２Although the conversion rate tends to decrease, it is superior to the iron-alumina catalyst under the same calcination temperature conditions as mentioned above. ２ The conversion rate reaches near the equilibrium value.

[0119] Usefulness as a reverse water gas shift catalyst As described above, iron-zirconia-based catalysts and nickel-ceria-based catalysts exhibit extremely high reverse water gas shift catalytic activity even when the calcination temperature is changed to various temperatures, such as 450°C to 1000°C. Therefore, even when used in combination with a solid oxide electrolysis cell operated in a high temperature range, for example, around 600°C to 800°C, high performance and durability can be easily ensured, making them useful.

[0120] 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.

[0121] Furthermore, the ceria-based metal oxide as the carrier cb1 may be ceria doped with at least one of gadolinium, samarium, and yttrium.

[0122] The zirconia-based metal oxide as the carrier cb1 may be zirconia stabilized with at least one of yttria and scandia.

[0123] 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.

[0124] By using the reverse water gas shift catalyst cat1 in the first catalytic reaction section 20 (reverse water gas shift reaction section), CO reduction is equivalent to or better than that of a highly active but very expensive Pt catalyst at around 600 to 1000°C. ２The test in this example was conducted under a very high GHSV condition of 10,000 / h, so it is possible to achieve a higher CO 2 conversion rate by increasing the amount of catalyst used relative to the amount of gas to be treated under conditions where the GHSV is lower than 10,000 / h. ２ It is also possible to carry out the reverse water gas shift reaction at a conversion rate (%).

[0125] [Combination of Electrolytic Reaction Unit and Reverse Water Gas Shift Reaction Unit] In the above explanation, the electrolytic reaction unit 10 and the reverse water gas shift reaction unit 20 are individually arranged in the order shown along the gas advection direction according to the system configuration shown in FIG. 1 . The reaction in the electrolytic reaction unit 10 may be exothermic depending on the reaction conditions, while the reaction in the reverse water gas shift reaction unit 20 is endothermic. Therefore, integrating these two reaction units 10 and 20 can improve the thermal efficiency of the system. FIG. 3 shows a configuration in which these two reaction units 10 and 20 are combined and integrated, with the integration indicated by a box around both units. The reactions when integrated in this manner are also shown in the same box. Essentially, the reactions represented by Equations 1, 2, and 3 shown above are carried out. When combining and integrating the electrolytic reaction unit 10 and the reverse water gas shift reaction unit 20, it is preferable to surround them with a heat-insulating material to efficiently exchange heat between the electrolytic reaction unit 10 and the reverse water gas shift reaction unit 20. In addition, in order to transfer the heat generated in the electrolytic reaction unit 10 to the reverse water gas shift reaction unit 20, the electrolytic reaction unit 10 and the reverse water gas shift reaction unit 20 may be connected using a heat conductive member.

[0126] [Electrolytic cell unit including both an electrolytic 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 reaction section 20 in the electrolytic cell unit U that serves as the electrolytic reaction section 10. This is because, when a solid oxide electrolytic cell that operates at around 600 to 800°C is used as the electrolytic cell 1, the reverse water gas shift catalyst cat1 of the present application, which exhibits high activity at around 600 to 800°C, can be used in the electrolytic reaction section 10 and the reverse water gas shift reaction section 20 in approximately the same temperature range. In this case, it is also sufficient that the gas that has passed through the electrolytic reaction section 10 is guided to the reverse water gas shift reaction section 20 to cause the reverse water gas shift reaction.

[0127] An electrolytic cell unit U equipped with such a reverse water gas shift reactor 20 is shown in Figure 4. Figure 4 is a diagram illustrating the electrolytic cell unit U shown in cross section in Figure 2, including the direction of gas advection.

[0128] As shown in the figure, the cross section of the electrolytic cell unit U is basically the same. That is, this electrolytic cell unit U also includes an electrolytic cell 1 in which an electrode layer 2 and a counter electrode layer 3 are formed with an electrolyte layer 1a sandwiched therebetween, a metal support 4 that functions as a support for the electrolytic cell 1 and also functions as a separator, and supply channel forming members 5 and 6, 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 position corresponding to the electrolytic cell 1, but no hole is formed downstream of the electrode layer 2. Therefore, the metal support 4 serves as a separator that effectively separates the gas supplied to and released from the electrode layer 2 from the gas supplied to and released from the counter electrode layer 3.

[0129] 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 channels 5a extend beyond the electrolysis reaction section 10, and the coating layer 20a is also provided on this extension side.

[0130] As a result, the electrode layer side gas supply passage 5 a of the electrolysis cell unit U receives at least H 2 generated in the electrode layer 2 . ２ The electrolysis cell unit U is configured to integrally include the electrolysis reaction section 10 and the reverse water gas shift reaction section 20 .

[0131] In this configuration, the metal support 4 is used to separate H2 generated in the electrode layer 2 and O2 generated in the counter electrode layer 3. ２ The separator is configured to function as a separator for separating the ２ At least a portion of the discharge channel side of the electrolytic cell unit U serves as a reverse water gas shift reactor 20. By stacking the electrolytic cell units U configured in this manner in the left-right direction in Figures 2 and 4, a large number of stacked electrolytic cell units U can be electrically connected to form a so-called electrolytic cell module (not shown). Naturally, useful gases produced can be obtained across multiple layers.

[0132] Based on the concept of combining the electrolysis reaction unit 10 and the reverse water gas shift reaction unit 20 (the electrode layer side gas supply channel 5a of the electrolysis reaction unit 10 is used as the reverse water gas shift reaction unit 20), the inventors carried out an experiment in which a granular reverse water gas shift catalyst cat1 was placed 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.

[0133] A detailed description will be given below with reference to FIG. 5 . This figure shows a cross-sectional view of the electrolytic cell unit U. Here, a metal-supported solid oxide electrolytic cell was used as the electrolytic cell 1. A metal substrate was prepared as the metal support 4 by laser machining a 0.3 mm-thick ferritic stainless steel metal plate. 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 prepare the electrolytic cell 1. The electrode layer 2 was formed using a mixture of NiO powder and GDC powder, the intermediate layer 2a was formed using GDC powder, the electrolyte layer 1a was formed using 8YSZ (8 mol% yttria-stabilized zirconia) powder, the reaction prevention layer 7 was formed using GDC powder, and the counter electrode layer 3 was formed using a mixture of GDC powder and LSCF powder. The thicknesses of the electrode layer 2, intermediate layer 2a, electrolyte layer 1a, reaction prevention layer 7, and counter electrode layer 3 were approximately 25 μm, approximately 10 μm, approximately 5 μm, approximately 5 μm, and approximately 20 μm, respectively. The performance and durability of the electrolysis cell 1 can be improved by providing the intermediate layer 2a between the electrode layer 2 and the electrolyte layer 1a, or by providing the reaction prevention layer 7 between the electrolyte layer 1a and the counter electrode layer 3. The intermediate layer 2a and the reaction prevention layer 7 are preferably formed by a low-temperature firing method (e.g., a wet method using a firing treatment in a low-temperature range that does not involve firing 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 a low temperature range make it possible to obtain a good intermediate layer 2a and a good reaction-preventing layer 7 without using firing at a high temperature range higher than, for example, 1100°C. This is therefore preferable because it allows for the realization of an electrolytic cell 1 with excellent performance and durability without damaging the metal support 4. Furthermore, the use of a low-temperature firing method is even more preferable because it facilitates the handling of raw materials.

[0134] 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).

[0135] Results when reverse water gas shift catalyst cat1 was not installed. ２ O and CO ２ The electrolysis reaction is carried out while supplying a gas containing H ２ The ratio of CO to CO was measured using a gas chromatograph. The results are shown in Table 5 below. The experimental results are described as Comparative Examples A1 and A2.

[0136] Results when reverse water gas shift catalyst cat. 1 was installed. As the reverse water gas shift catalyst cat. 1, a granular catalyst obtained by supporting approximately 10% Ni on an 8YSZ carrier similar to that in Example 2 was installed. ２ O and CO ２ The electrolysis reaction is carried out while supplying a gas containing H ２ The ratio of CO to CO was measured using a gas chromatograph. The results are shown in Table 6. This experimental result is referred to as Example A1.

[0137]

[0138] From the above comparative experiments, it was confirmed that the electrolytic cell 1 was formed in a thin layer on the metal support 4, and CO was produced by the reverse water gas shift reaction. ２ and the above H ２ In the electrolysis cell unit U, a reverse water gas shift reactor 20 that generates CO using H generated by electrolysis is provided in the electrode layer side gas supply path 5a, which serves as an exhaust path for electrolyzed gas. ２ It was possible to increase the composition ratio of CO to CO.

[0139] When comparing an electrolysis cell unit U that does not include a reverse water gas shift catalyst cat1 in the electrode layer side gas supply channel 5a (which serves as an outlet channel for electrolyzed gas), and an electrolysis cell unit U that does include a reverse water gas shift catalyst cat1, the hydrogen / carbon monoxide ([H ２The CO [CO / CO] ratio is about 10 or more to about 5, and by combining the reaction in the electrolysis reactor 10 and the reaction in the reverse water gas shift reactor 20, an amount of CO advantageous for synthesizing various hydrocarbons can be secured, which is preferable. ２ Since the thermal efficiency of the hydrocarbon production system 100 can be improved by adopting the CO methanation reaction rather than the CO methanation reaction, it is preferable to combine the reaction in the electrolysis reactor 10 and the reaction in the reverse water gas shift reactor 20, since the amount of CO can be secured. ２ When methanating, 2 moles of H ２ When 1 mole of CO is methanated, 1 mole of H is produced. ２ Therefore, the hydrocarbon production system 100 employing the CO methanation reaction can produce 1 mole of H ２ This is because the loss of latent heat and sensible heat of O can be suppressed. ２ O and CO ２ The ratio of hydrogen to carbon monoxide ([H ２ / CO] ratio is set to a value suitable for the second catalytic reaction section 30 (hydrocarbon synthesis reaction section) in the subsequent stage (for example, the equivalent ratio of H ２ / CO=3, etc.

[0140] [Installing a Heat Exchanger Between the Electrolysis Reaction Unit and the Reverse Water Gas Shift Reaction Unit] The above explanation has mainly focused on an example in which the electrolysis reaction unit 10 and the first catalytic reaction unit (reverse water gas shift reaction unit) 20 are integrated together. However, the two units 10 and 20 may be separate units, and a heat exchanger 11 may be installed between the two units 10 and 20 to allow heat transfer between the two units. This configuration is shown in Figure 6, corresponding to Figure 1. The hollow double lines indicate heat transfer between the two units. With this configuration, the temperature of each unit 10 and 20 can be appropriately controlled.

[0141] 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."

[0142] [Second catalytic reaction section (hydrocarbon synthesis reaction section)] In this second catalytic reaction section 30 (hydrocarbon synthesis reaction section), at least H ２ and CO are introduced into the reactor, and a catalytic reaction is carried out to produce hydrocarbons (methane and various hydrocarbons with two or more carbon atoms).

[0143] (Examples of Hydrocarbon Synthesis Catalyst) As activity tests of the catalyst (hydrocarbon synthesis catalyst cat2) used in the second catalytic reaction section 30, the inventors conducted evaluation tests 1, 2, and 3 shown below.

[0144] As an example of hydrocarbon synthesis catalyst cat2, catalysts were prepared by changing the carrier and catalytically active component in various ways. As catalytically active component ca2, Ru, Ru with Mo, V, Fe, Co, etc., and Ni were investigated. As carrier cb2, ZrO ２ , Al ２ O ３ , SiO ２ , MgO, TiO ２ We considered the following.

[0145] (Catalyst Preparation) The hydrocarbon synthesis catalyst cat2 is also prepared by the method described with reference to Figures 11 and 12. That is, an aqueous solution is prepared by dissolving a measured amount of a water-soluble ruthenium compound (ruthenium nitrate, ruthenium chloride, ruthenium sulfate, ruthenium ammonium sulfate, ruthenium acetate, ruthenium oxalate, ruthenium citrate, etc.) according to the composition of the target catalyst. When supporting molybdenum, vanadium, iron, or cobalt as an additional catalytically active component, an aqueous solution is prepared by similarly measuring and dissolving these water-soluble metal compounds. Using this aqueous solution, a predetermined amount of carrier particles (ZrO ２ , Al ２ O ３ , SiO ２ , MgO, TiO ２) is impregnated with a catalytically active component, and then subjected to necessary treatment steps such as drying, calcination, and reduction to obtain hydrocarbon synthesis catalyst cat 2. The catalysts in the following examples were prepared using an aqueous ruthenium chloride solution, an aqueous ammonium molybdate solution, an aqueous vanadyl oxalate solution, an aqueous iron nitrate solution, and an aqueous cobalt nitrate solution, respectively, and when both ruthenium and a catalytically active component other than ruthenium were supported, they were prepared using a sequential support method (a two-stage support method in which a catalytically active component other than ruthenium is first supported on a support, and then ruthenium is supported).

[0146] (Evaluation Test 1) In evaluation test 1, CO was 12.4% and CO ２ 24.8%, H ２ 37.2%, H ２ Contains 12.4% O and the remainder N ２ The activity test of the hydrocarbon synthesis catalyst cat2 was carried out using a mixed gas of the above as the reaction gas, with a GHSV of 4000 / h (wet basis) and reaction temperatures between 275°C and 360°C. The reaction gas in this case was CO, CO after the co-electrolysis reaction of water and carbon dioxide in the electrolysis reaction unit 10 under conditions where the electrolysis reaction rate of carbon dioxide was low, and the reverse water-gas shift reaction of carbon dioxide in the reverse water-gas shift reaction unit 20 installed in the subsequent stage. ２ , H ２ , H ２ This is an example of a model in which a mixed gas of O is introduced into the hydrocarbon synthesis reaction section 30 to carry out a hydrocarbon synthesis reaction.

[0147] The following two indicators were used to organize the test results.

[0148] 1. CO ２ Expected removal hydrocarbon conversion rate = [carbon number of hydrocarbons in outlet gas] / [carbon number in outlet gas - outlet CO ２ This index is calculated by dividing the CO ２ It is an index showing the conversion rate to hydrocarbons when excluding the above, and it is preferable that this index is high.

[0149] 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 section 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.

[0150] Regarding evaluation test 1, Tables 7 and 8 shown below show Examples B1 to B3 of the hydrocarbon synthesis catalyst cat 2 of the present invention.

[0151]

[0152]

[0153] As shown in Tables 7 and 8, CO, CO ２ , H ２ , H ２ It was confirmed that hydrocarbons can be synthesized from a mixed gas of 0 using 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, as the hydrocarbon synthesis catalyst cat2. From the above results, it was confirmed that the hydrocarbon production system 100 can synthesize hydrocarbons with a C1-C4 calorific value of 39 MJ / Nm ３ It was confirmed that the above high calorie gases could be produced.

[0154] (Evaluation Test 2) In evaluation test 2, CO was added at 0.45% and CO ２ 18.0%, H ２ 71.55%, H ２An activity test of the hydrocarbon synthesis catalyst cat 2 was carried out using a mixed gas containing 10.0% O as the reaction gas, with a GHSV of 5000 / h (DRY basis) and a reaction temperature between about 230° C. and about 330° C. The reaction 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.

[0155] The following two indicators were used to organize the test results.

[0156] 1. Hydrocarbon conversion rate = [carbon number of hydrocarbons in outlet gas] / [carbon number in outlet gas] This index is the ratio of CO ２ This is an index showing the proportion of carbon atoms that have been converted into hydrocarbons without being converted into olefins, and it is preferable that this index is high.

[0157] 2 CO ２ Expected removal hydrocarbon conversion rate = [carbon number of hydrocarbons in outlet gas] / [carbon number in outlet gas - outlet CO ２ This index is the number of carbon atoms in the CO ２ It is an index showing the conversion rate to hydrocarbons when excluding the above, and it is preferable that this index is also high.

[0158] 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.

[0159]

[0160]

[0161] (Evaluation Test 3) In Evaluation Test 3, H ２ and CO in a volume ratio of 3:1 (H ２An activity test of the hydrocarbon synthesis catalyst cat 2 was carried out using a ruthenium-containing catalyst (CO = 3) as the reaction gas, setting the GHSV to 2000 / h, and at reaction temperatures between 235°C and approximately 330°C. In this activity test, a catalyst (Examples B17 and B18) in which iron or cobalt in addition to ruthenium was supported on a titania carrier was used. Note that the reaction gas in this case is an example of an assumed model in which a hydrocarbon synthesis reaction is carried out by introducing into the hydrocarbon synthesis reaction section 30 a mixed gas in which carbon monoxide is added 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 necessary from a gas obtained by a co-electrolysis reaction of water and carbon dioxide.

[0162] The results of Evaluation Test 3 are shown in Table 11.

[0163]

[0164] As shown in Table 11, H ２ It was confirmed that hydrocarbons can be synthesized from a mixed gas containing ruthenium and CO using a catalyst comprising ruthenium and iron or cobalt supported on a titania carrier as the hydrocarbon synthesis catalyst cat2.

[0165] 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.

[0166] From the above results, as previously shown, a catalyst in which at least ruthenium is supported as the catalytically active component ca2 on a metal oxide support cb2 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.

[0167] 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 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.

[0168] 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.

[0169] Furthermore, among such hydrocarbon synthesis catalysts cat. 2, the highly active catalysts had carbon monoxide adsorption amounts of 0.4 ml / g or more.

[0170] [Heavy Hydrocarbon Separation Section] The gas reaching this heavy hydrocarbon separation section 35 is cooled, so that the heavy hydrocarbons contained in the gas released from the hydrocarbon synthesis reaction section 30 are condensed, and the heavy hydrocarbons can be taken out. For example, in the case of the 2 wt. % Ru / 2 wt. % Fe / TiO ２ In the hydrocarbon synthesis reaction section 30 using a catalyst, H ２ and CO in a volume ratio of 3:1 (H ２ When a sulphur dioxide gas (CO2 / CO=3) was introduced and the reaction was carried out at 275°C, straight-chain higher aliphatic hydrocarbons with an average chain length of 26 carbon atoms were extracted from the heavy hydrocarbon separation section 35, and 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 from the heavy hydrocarbon separation section 35.

[0171] [Water Separation Section] The water separation section 40 is provided with a condenser. ２ The O-containing gas is adjusted to a predetermined temperature and pressure, and the condensed water is taken out.

[0172] [Carbon dioxide separation section] For example, a PSA is arranged in this section 50, and the inflowing CO ２ CO is adsorbed onto an adsorbent at a predetermined temperature and pressure from a gas containing CO ２ and the separated CO ２ By desorbing from the adsorbent, CO ２ Separated CO ２ can be reused by returning it to the front of the electrolytic reaction unit 10 via the carbon dioxide return path 51. It is also possible to use a PSA or the like to form the carbon dioxide separation unit and the water separation unit into the same separation unit.

[0173] [Other Embodiments] (1) In the above embodiment, the CO separated in the carbon dioxide separation unit 50 ２ is returned before the electrolysis reaction section 10, but in the hydrocarbon production system 100 according to the present invention, CO ２ The conversion of CO into CO is mainly carried out in the reverse water gas shift reactor 20. ２ The return destination may be before the reverse water gas shift reactor 20. This configuration is shown in FIG.

[0174] (2) In the above embodiment, H in the gas obtained from the hydrocarbon synthesis reaction section 30 ２ Regarding this, although there was no particular mention of it, it is possible to use a hydrogen separation membrane or the like to separate H ２ The hydrogen separation section (H in the figure) separates ２ A separation section (60) is provided to ２ This configuration is shown in FIG. 8. In this example, the H separated in the hydrogen separation section 60 ２ The return destination may be before the reverse water gas shift reactor 20 and used for the reverse water gas shift reaction.

[0175] (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.

[0176] (4) In the above embodiment, H ２ O and CO ２ 10, an example in which both H and H are supplied to the electrolysis reaction section 10 is shown. ２ A system may be used in which only O is supplied for the electrolysis reaction. In this case, the carbon consumed in the hydrocarbon synthesis is input to the reverse water gas shift reactor 20 as carbon dioxide.

[0177] (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, an alkaline electrolysis cell, a polymer membrane electrolysis cell, or the like may also be used as the electrolysis cell 1.

[0178] (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 these reaction sections 10 and 20. An example of this structure is shown in FIG. 13. In this figure, 30a indicates a coating layer of the hydrocarbon synthesis catalyst cat2. In this structure, the reaction sections 10, 20, and 30 can also be formed on a metal support 4, and this metal support 4 functions as a separator for separating the produced hydrocarbons from oxygen.

[0179] (7) In the above embodiment, an example was shown in which hydrocarbons such as methane were synthesized in the hydrocarbon synthesis reaction section 30. However, depending on how the hydrocarbon synthesis catalyst used in the hydrocarbon synthesis reaction section 30 is selected, it is also possible to synthesize chemical raw materials from hydrogen, carbon monoxide, etc. introduced into the hydrocarbon synthesis reaction section 30.

[0180] REFERENCE SIGNS LIST 1 Electrolysis cell 1a Electrolyte layer 2 Electrode layer 3 Counter electrode layer 4 Metal support (support / separator) 4a Hole 5 Supply channel forming member (separator) 6 Supply channel forming member (separator) 10 Electrolysis reaction section 20 First catalytic reaction section (reverse water gas shift reaction section) 20a Coating layer 30 Second catalytic reaction section (hydrocarbon synthesis reaction section) 40 Water separation section 50 Carbon dioxide separation section 60 Hydrogen separation section U Electrolysis cell unit Cat 1 reverse water gas shift catalyst ca1 Catalytically active component (active metal) cb1 Support (metal oxide support) Cat 2 Hydrocarbon synthesis catalyst ca2 Catalytically active component (active metal) cb2 Support (metal oxide support)

Claims

1. A hydrocarbon production system for producing hydrocarbons from at least water and carbon dioxide, the hydrocarbon production system having at least an electrolysis reaction section, a reverse water gas shift reaction section, and a hydrocarbon synthesis reaction section.

2. The hydrocarbon production system according to claim 1, wherein an electrolysis reaction of water is carried out in the electrolysis reaction section.

3. The hydrocarbon production system according to claim 1, wherein a co-electrolysis reaction of water and carbon dioxide is carried out in the electrolysis reaction section.

4. The hydrocarbon production system according to any one of claims 1 to 3, wherein the reverse water gas shift reaction section has a reverse water gas shift catalyst in which an active metal is supported on a metal oxide carrier.

5. The hydrocarbon production system according to claim 4, wherein the reverse water gas shift catalyst is a reverse water gas shift catalyst in which at least one of nickel and iron is supported as the active metal on a carrier mainly composed of a ceria-based metal oxide or a zirconia-based metal oxide.

6. The hydrocarbon production system according to claim 5, wherein the ceria-based metal oxide is ceria doped with at least one of gadolinium, samarium, and yttrium.

7. The hydrocarbon production system according to claim 5, wherein the zirconia-based metal oxide is zirconia stabilized with at least one of yttria and scandia.

8. The hydrocarbon production system according to any one of claims 4 to 7, wherein copper is supported as the active metal.

9. The hydrocarbon production system according to any one of claims 1 to 8, wherein the hydrocarbon synthesis reaction section has a hydrocarbon synthesis catalyst in which an active metal is supported on a metal oxide carrier.

10. The hydrocarbon production system according to claim 9, wherein the active metal is ruthenium.

11. The hydrocarbon production system according to any one of claims 1 to 10, wherein the electrolysis reaction section has an electrolytic cell in which at least an electrode layer, an electrolyte layer, and a counter electrode layer are formed on a support.

12. The hydrocarbon production system according to claim 11, wherein the support is a metal.

13. The hydrocarbon production system according to claim 12, wherein the hydrocarbon synthesis reaction section is supported by a support, and the support is a metal.

14. A method for manufacturing a hydrocarbon production system according to any one of claims 1 to 13, the method comprising disposing an impregnated support obtained through an impregnation and support step of impregnating and supporting an active metal on a metal oxide support in the reverse water gas shift reaction section and the hydrocarbon synthesis reaction section.

15. A method for manufacturing a hydrocarbon production system according to any one of claims 1 to 13, the method comprising disposing an impregnated support obtained through an impregnation and support step of impregnating and supporting an active metal on at least a part of a support to form the reverse water gas shift reaction section.

16. A method for manufacturing a hydrocarbon production system according to any one of claims 1 to 13, the method comprising at least a firing step of firing at a temperature of 450 °C or higher in a step of forming the reverse water gas shift reaction section.

17. A method for operating a hydrocarbon production system according to any one of claims 1 to 13, the method comprising operating the hydrocarbon production system after performing a pre-reduction treatment on the reverse water gas shift reaction section.

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