Electrochemical reaction system and electrochemical reaction

Abstract

This electrochemical reaction system 10, which is used in performing an electrochemical reaction, comprises: an electrochemical device 11 having a cathode chamber 16 that includes a cathode 13, a supply line 14 for supplying an electrolyte-containing catholyte, and a discharge line 15 for discharging the catholyte, and an anode chamber 26 that includes an anode 23, a supply line 24 for supplying an electrolyte-containing anolyte, and a discharge line 25 for discharging the anolyte; and an electrolytic solution mixing device 40 for mixing a liquid that contains the catholyte and the anolyte discharged from the electrochemical device 11.

Description

Electrochemical reaction system, and electrochemical reaction

[0001] The present invention relates to an electrochemical reaction system and an electrochemical reaction, for example, to an electrochemical reaction system and an electrochemical reaction capable of electrochemically synthesizing a carbonyl compound from carbon monoxide.

[0002] Electrochemical synthesis methods have recently gained attention because they allow for the direct use of electricity from renewable energy sources. Furthermore, in recent years, there has been research into producing organic substances through electrochemical reactions using carbon dioxide and carbon monoxide obtained by reducing carbon dioxide as raw materials, with the aim of mitigating global warming and replacing fossil fuels.

[0003] For example, conventionally, as shown in Patent Document 1, an electrochemical apparatus has been disclosed comprising a cathode chamber provided with a cathode, an anode chamber provided with an anode and containing a reaction substrate such as an alcohol-based compound, an ion transport membrane separating the cathode chamber and the anode chamber, and a connecting passage connecting the cathode chamber and the anode chamber. In such an electrochemical apparatus, carbon dioxide is reduced to carbon monoxide in the cathode, the generated carbon monoxide is discharged into the anode chamber via the connecting passage, and valuable substances such as carbonyl compounds are produced in the anode chamber from the carbon monoxide and the reaction substrate.

[0004] Various improvements have been made to electrochemical apparatuses for producing carbonyl compounds. For example, Patent Document 1 discloses that the electrolyte filling the anode chamber contains a redox species, a catalyst, and a reaction substrate such as methanol, which is a raw material for the carbonyl compound. Patent Document 1 shows that with the above configuration, carbonyl compounds can be synthesized electrochemically with high selectivity.

[0005] International Publication No. 2023 / 038091

[0006] In the industrial production of organic substances using electrochemical apparatus, it is desirable to reuse electrolytes such as redox species contained in the electrolyte solution. However, electrolyte solutions contain not only solvents but also many target products and by-products, and when reusing electrolytes, it is necessary to separate and recover the electrolytes from the electrolyte solution. Separating and recovering electrolytes from the electrolyte solution requires the removal of solvents, products, and by-products by distillation, etc., which requires a great deal of thermal energy and is difficult to implement industrially.

[0007] Therefore, the object of the present invention is to provide an electrochemical reaction system and an electrochemical reaction method that can easily recover electrolytes from an electrolyte solution.

[0008] The present invention provides the following [1] to

[14] : [1] An electrochemical reaction system for performing an electrochemical reaction, comprising: an electrochemical apparatus having a cathode chamber having a cathode, a supply line for supplying a cathode solution containing an electrolyte, and a discharge line for discharging the cathode solution; an anode chamber having an anode, a supply line for supplying an anode solution containing an electrolyte, and a discharge line for discharging the anode solution; and an electrolyte mixing apparatus for mixing the cathode solution and the anode solution discharged from the electrochemical apparatus. [2] The electrochemical reaction system according to [1], wherein the mixture obtained by mixing the cathode solution and the anode solution contains two or more different solvents. [3] The electrochemical reaction system according to [2], wherein the two or more different solvents are separated. [4] The electrochemical reaction system according to [3], wherein the two or more different solvents are separated by at least one of membrane separation, distillation, and liquid-liquid phase separation. [5] The electrochemical reaction system according to [4], wherein the two or more different solvents include two or more solvents that are capable of liquid-liquid phase separation and are liquid-liquid phase separated. [6] The electrochemical reaction system according to any one of [3] to [5], wherein the solvent is separated into at least a first solvent and a second solvent, and the electrolyte is contained in the first solvent at a higher concentration than in the second solvent. [7] The electrochemical reaction system according to [6], wherein the first solvent is separated and recovered. [8] The electrochemical reaction system according to any one of [1] to [7], wherein the cathode solution contains water and the anode solution contains an organic solvent. [9] The electrochemical reaction system according to [8], wherein the organic solvent contains a carbonyl compound.

[10] The electrochemical reaction system according to any one of [1] to [9], wherein a reaction product is further generated from the reduced product produced in the cathode and the reaction substrate contained in the anode solution in the presence of an oxide produced in the anode.

[11] The electrochemical reaction system according to

[10] , further comprising a reaction unit for generating the reaction product from the reduced product and the reaction substrate in the presence of the oxide.

[12] The electrochemical reaction system according to

[10] or

[11] , wherein the reaction substrate is an alcohol compound and the reaction product is a carbonyl compound.

[13] The electrochemical reaction system according to any one of [1] to

[12] above, wherein the cathode solution contains carbon dioxide and the reduced product produced in the cathode contains carbon monoxide.

[14] An electrochemical reaction method for performing an electrochemical reaction in an electrochemical reaction system comprising an electrochemical apparatus having a cathode chamber having a cathode and an anode chamber having an anode, and an electrolyte mixing device, comprising the steps of: supplying a cathode solution containing an electrolyte to the cathode chamber; producing a reduced product in the cathode; discharging the cathode solution from the cathode chamber; supplying an anode solution containing an electrolyte to the anode chamber; producing an oxide in the anode; discharging the anode solution from the anode chamber; and mixing the cathode solution and the anode solution discharged from the electrochemical apparatus in the electrolyte mixing device.

[0009] According to the present invention, it is possible to provide an electrochemical reaction system and an electrochemical reaction method that can easily recover electrolytes from an electrolyte solution.

[0010] This is a schematic diagram showing an electrochemical reaction system according to the first embodiment. This is a schematic diagram showing an electrochemical reaction system according to the second embodiment. This is a schematic diagram showing an electrochemical reaction system according to the third embodiment.

[0011] The electrochemical reaction system and the electrochemical reaction method using the electrochemical reaction system of the present invention will be described below with reference to the drawings. In the following description, corresponding components will be denoted by the same reference numerals.

[0012] <First Embodiment> Figure 1 shows an electrochemical reaction system 10 according to a first embodiment of the present invention. The electrochemical reaction system 10 is a system for performing an electrochemical reaction and comprises an electrochemical apparatus 11 for performing electrochemistry and an electrolyte mixing apparatus 40. The electrochemical reaction system 10 may further include a separation apparatus 42 connected to the electrolyte mixing apparatus 40.

[0013] The electrochemical apparatus 11 comprises an electrochemical cell 12 and a reaction section 41. The electrochemical cell 12 comprises a cathode chamber 16 having a cathode 13, a first supply line 14, and a first discharge line 15, and an anode chamber 26 having an anode 23, a second supply line 24, and a second discharge line 25. The cathode 13 and anode 23 are arranged inside the cathode chamber 16 and anode chamber 26, respectively, and are positioned to be immersed in the cathode solution and anode solution inside the cathode chamber 16 and anode chamber 26, respectively, although they do not have to be immersed as long as they are in contact with the cathode solution and anode solution, respectively. The electrochemical cell 12 further comprises an isolation membrane 31 located between the cathode 13 and the anode 23, and the isolation membrane 31 partitions the cathode chamber 16 and the anode chamber 26. The isolation membrane 31 should be permeable to ions but not to the substances to be reduced X1, reduced Y1, oxide X2, oxide Y2, solvent, reaction substrate, etc., as described later.

[0014] The first supply line 14 is connected to the cathode chamber 16 and supplies the cathode liquid containing the electrolyte to the cathode chamber 16. The first discharge line 15 is connected to the cathode chamber 16 and discharges the cathode liquid supplied to the cathode chamber 16 to the outside of the cathode chamber 16. In this specification, the solvent can be any substance that can dissolve the electrolyte, and may be a compound produced in the reaction section 41, anode 23, cathode 13, etc. The solvent in the cathode liquid may be an organic solvent, but is preferably water. The solvent in the cathode liquid may be water alone, or it may contain an organic solvent other than water that is miscible with water. Specifically, examples include alcohol compounds such as methanol, ethanol, phenol, 1-propanol, ethylene glycol, and propylene glycol.

[0015] The concentration of the electrolyte in the cathode solution is not particularly limited, but is often, for example, 0.001 to 10 M, preferably 0.1 to 3 M, and also preferably 0.3 to 5 M. The concentration of the electrolyte in the cathode solution referred to here means the concentration in the fourth discharge line 45, which will be described later.

[0016] In this embodiment, the cathode liquid further contains a reducible substance X1, and the reducible substance X1 is reduced at the cathode 13 to generate a reduced substance Y1. Then, the reduced substance Y1 generated in the cathode chamber 16 is discharged to the outside of the cathode chamber 16 from the first discharge line 15 together with the cathode liquid.

[0017] The cathode 13 only needs to be able to reduce the reducible substance X1 to the reduced substance Y1, but it is preferably to contain a reduction catalyst that promotes the reduction reaction. For example, when the reducible substance X1 is carbon dioxide, it contains a carbon dioxide reduction catalyst that reduces carbon dioxide to carbon monoxide. Also, a power source 18 is connected to the cathode 13 and the anode 23, and a voltage is applied between the cathode 13 and the anode 23 by the power source 18. When the voltage is applied, a reduction reaction occurs at the cathode 13 and an oxidation reaction occurs at the anode 23.

[0018] The cathode liquid is preferably filled inside the cathode chamber 16. Here, the cathode liquid may be filled in the cathode chamber 16 with a space inside (for example, the upper part of the cathode chamber 16), but it is preferable that the cathode chamber 16 is filled without a space inside (for example, the upper part of the cathode chamber 16).

[0019] In this embodiment, the electrochemical device 11 further includes a cathode-side storage unit 19. The cathode liquid is stored in the cathode-side storage unit 19. The configuration of the cathode-side storage unit 19 is not particularly limited as long as it can store the cathode liquid, but an appropriate stirring device or the like may be provided, and the stored cathode liquid may be mixed by the stirring device. The cathode-side storage unit 19 is connected to a reducible substance supply line 17, and the reducible substance X1 is supplied from a reducible substance supply source (not shown) to the cathode-side storage unit 19 through the reducible substance supply line 17. In the cathode-side storage unit 19, the reducible substance X1 is mixed into the cathode liquid. However, the reducible substance supply line 17 does not necessarily need to be connected to the cathode-side storage unit 19, and as long as the reducible substance X1 is supplied to the cathode side, it may be connected to other than the cathode-side storage unit 19, for example, it may be connected to the cathode chamber 16.

[0020] The reducible substance X1 may be anything that can be reduced at the cathode such as carbon dioxide, and it is preferable to be blown into the cathode liquid stored in the cathode-side storage unit 19 as a gas. Also, the cathode liquid (solvent and electrolyte) may be supplied from the cathode liquid supply line 37 to the cathode-side storage unit 19, or may be supplied from the reuse supply line 46 described later. The reducible substance X1 may be continuously supplied or intermittently supplied to the cathode-side storage unit 19. Further, the reducible substance X1 is preferably supplied to the cathode-side storage unit 19 as the reducible substance X1 alone, but may be supplied to the cathode-side storage unit 19 together with an inert gas such as helium as a carrier gas. The source of the reducible substance is not particularly limited, and may be a gas cylinder or the like. Also, when the reducible substance X1 is carbon dioxide, the carbon dioxide may be obtained from the exhaust gas discharged from any of the facilities of a power plant, a steel mill, a cement factory, and a waste incinerator, and any of these facilities may also be a carbon dioxide supply source.

[0021] The first supply line 14 connects the cathode chamber 16 and the cathode-side storage unit 19. Further, the first discharge line 15 also connects the cathode chamber 16 and the cathode-side storage unit 19. Thereby, the cathode liquid circulates between the cathode chamber 16 and the cathode-side storage unit 19. That is, the cathode liquid circulates through the circulation path so as to return to the cathode chamber 16 again after being once discharged to the outside from the cathode chamber 16. And the cathode liquid is flowed along the flow in a certain direction through the circulation path, while the reducible substance X1 is appropriately mixed in the cathode-side storage unit 19, and is reduced to the reduced substance Y1 at the cathode 13, and the reduction reaction at the cathode 13 is efficiently performed. In the present embodiment, the circulation path on the cathode side consists of the cathode chamber 16, the first discharge line 15, the cathode-side storage unit 19, and the first supply line 14.

[0022] The cathode-side storage section 19 is equipped with a third discharge line 35, which is preferably configured to selectively discharge reduced substances Y1 from the cathode liquid circulating in the circulation path. Here, the reduced substances Y1 are preferably gases such as carbon monoxide, which have lower solubility in the cathode liquid than the reduced substance X1 (such as carbon dioxide), as will be described later, thereby making it easier to discharge them from the third discharge line 35. Furthermore, the cathode-side storage section 19 is preferably configured with space at the top, and the third discharge line 35 is preferably connected to the location of this space, thereby making it easier to discharge the reduced substances Y1 from the third discharge line 35. However, the reduced substances Y1 discharged from the third discharge line 35 may contain reduced substances X1 such as carbon dioxide, by-products generated in the cathode 13, etc. (e.g., hydrogen) or water vapor.

[0023] A second supply line 24 is connected to the anode chamber 26 and supplies the anode solution containing the electrolyte to the anode chamber 26. A second discharge line 25 is also connected to the anode chamber 26 and discharges the anode solution supplied to the anode chamber 26 to the outside of the anode chamber 26. In this embodiment, the electrochemical apparatus 11 further includes an anode-side storage section 29. The configuration of the anode-side storage section 29 is not particularly limited as long as it can store the anode solution, but a stirring device may be provided as appropriate, and the stored anode solution may be mixed by the stirring device. The second supply line 24 connects the anode-side storage section 29 and the anode chamber 26, and the second discharge line 25 also connects the anode-side storage section 29 and the anode chamber 26. The electrochemical apparatus 11 further includes first and second connection lines 27 and 28, with the first connection lines 27 and 28 each connecting the anode-side storage section 29 and the reaction section 41. As a result, the anode liquid circulates through a circulation path between the anode chamber 26, the anode-side storage section 29, and the reaction section 41. That is, the anode liquid circulates between the anode chamber 26 and the anode-side storage section 29, and between the anode-side storage section 29 and the reaction section 41, flowing in a constant direction. Therefore, the reduction reaction to oxide Y2, described later, and the reaction in the reaction section 41 are carried out efficiently. In this embodiment, the circulation path on the anode side consists of the anode chamber 26, the second discharge line 25, the anode-side storage section 29, the first connection line 27, the reaction section 41, the second connection line 28, and the second supply line 24. The anode liquid is preferably supplied to the anode-side storage section 29 from the anode liquid supply line 47. The anode liquid is preferably stored in the anode-side storage section 29. The anode liquid supply line 47 is preferably supplied from the raw material storage section 59 where the anode liquid is stored. Typically, the raw material storage section 59 stores the reaction substrate and the oxide X2 (e.g., a halogenated salt), which will be described later, but other components that constitute the anode solution may also be stored there.

[0024] A purge line 49 is preferably connected to the anode-side storage section 29. In the circulation path on the anode side, gaseous components such as the reduced substance Y1 supplied from the cathode side are circulated along with the anode liquid. If the amount of gaseous components increases or the amount of impurities in the gaseous components increases, it is preferable to discharge the gaseous components through the purge line 49. It is preferable that the anode-side storage section 29 has space at the top, and that the purge line 49 be connected to the location of this space, thereby making it easier to discharge the gaseous components through the purge line 49.

[0025] In the cathode and anode circulation paths, the cathode fluid and anode fluid should be flowed in a constant direction by the pump 56. Similarly, in the anode fluid supply line 47, the fourth and fifth discharge lines 45 and 55 (described later), and the reuse supply line 46, the cathode fluid and anode fluid should be flowed in a constant direction by the pump 56. The pumps are not particularly limited, but examples include diaphragm pumps, syringe pumps, and peristaltic pumps. Furthermore, the flow of the cathode fluid and anode fluid may be formed by known means other than pumps, for example, by utilizing gravity.

[0026] The anode solution contains a solvent in which an electrolyte is dissolved. Here, the solvent may be a compound produced in the reaction section 41, anode, cathode, etc., as described later. The solvent in the cathode solution and the solvent in the anode solution may be different types of solvents, and it is preferable that the solvent in the cathode solution and the solvent in the anode solution are solvents that can separate into liquid phases from each other, as can be achieved in the electrolyte mixing device 40 as described later. The solvent in the anode solution is preferably an organic solvent. Being an organic solvent makes it easier to separate into liquid phases from the water that constitutes the solvent in the cathode solution. The anode solution further contains the oxidized substance X2. The oxidized substance X2 may constitute an electrolyte, for example, a redox species. Furthermore, in this embodiment, the anode solution further contains a reaction substrate. The reaction substrate is a raw material for producing the target product by reacting with the reduced product Y1 in the reaction section 41 in the presence of the oxidized substance X2, as described later. The reaction substrate may constitute a solvent in the anode solution.

[0027] The concentration of the electrolyte in the anode solution is not particularly limited, but is often, for example, 0.001 to 10 M, preferably 0.1 to 3 M, and also preferably 0.3 to 5 M. The concentration of the electrolyte in the anode solution referred to here means the concentration in the fifth discharge line 55, which will be described later.

[0028] The anode 23 is not particularly limited as long as it can oxidize the oxide X2 to oxide Y2, but it may or may not contain a catalyst. The oxide X2 contained in the anode solution is oxidized in the anode 23 to produce oxide Y2 such as a halogen. The oxide Y2 is supplied to the reaction unit 41 by being circulated in the anode-side circulation path described above. In addition, a third discharge line 35 is connected to the anode-side circulation path, thereby supplying a reducer Y1 such as carbon monoxide to the anode-side circulation path, and the reducer Y1 is supplied to the reaction unit 41 via the third discharge line 35. In the reaction unit 41, in the presence of oxide Y2, the reducer Y1 and the reaction substrate contained in the anode solution further produce a reaction product (target product). Specifically, the reaction unit 41 generally contains a catalyst (second catalyst), and the second catalyst oxidizes halogens (X ２ ) and other oxides Y2 are reduced to Y3 (for example, halogen ions X － While being reduced to ), the reduced product Y1, such as carbon monoxide, reacts with a reaction substrate such as an alcohol compound to obtain a target product such as a carbonyl compound. The target product such as a carbonyl compound may constitute the anode solution as an organic solvent, as will be described later, or it may constitute the second solvent described later. The temperature inside the anode chamber 26, cathode chamber 16, and reaction chamber (reaction section) 41 in the electrochemical reaction system 10 is not particularly limited, but is preferably around room temperature, for example, about 0 to 60°C, preferably about 10 to 40°C.

[0029] In the reaction section 41, an electrolyte, which is a by-product, is also generated from the reduced product Y3. The electrolyte, which is a by-product, is a component derived from a redox species, and is typically a hydrogen halide as shown in formulas (iv), (iv-1), (v), (v-1) described later, but may be other than a hydrogen halogen. The electrolyte, which is a by-product, generated in the reaction section 41 is dissolved in the anode solution and circulates together with the anode solution through the circulation pathway on the anode side. On the anode side, the anode solution circulates as described above, and the oxide Y2 and the target product are sequentially generated.

[0030] The electrolyte on the anode side may, for example, have a portion (e.g., metal ions) supplied to the cathode chamber via the isolation membrane 31. This makes it easier for the reaction that produces the target product to occur in the reaction section 41. Furthermore, in the cathode solution, it is preferable that a portion (e.g., metal ions) of the electrolyte supplied from the anode side also constitutes the electrolyte on the cathode side. On the other hand, it is preferable that the electrolyte contained in the cathode solution be one that can be used as an oxide X2 (redox species) on the anode side. If an electrolyte that can be used as an oxide X2 is used, the oxidation reaction of the oxide X2 (redox species) on the anode side can be carried out more efficiently by supplying redox species ions (e.g., halogen ions) from the cathode side to the anode side via the isolation membrane 31.

[0031] The electrochemical apparatus 11 also includes a fourth discharge line 45 and a fifth discharge line 55. In this embodiment, the fourth discharge line 45 is connected to the cathode-side circulation path, allowing the cathode liquid to be discharged from the cathode-side circulation path. The fourth discharge line 45 is also connected to the electrolyte mixer 40, and the cathode liquid discharged through the fourth discharge line 45 is supplied to the electrolyte mixer 40. In this embodiment, the fifth discharge line 55 is connected to the anode-side circulation path, allowing the anode liquid to be discharged through the fifth discharge line 55. The fifth discharge line 55 is also connected to the electrolyte mixer 40, and the anode liquid discharged through the fifth discharge line 55 is supplied to the electrolyte mixer 40. In other words, the fourth and fifth discharge lines 45 and 55 are lines that discharge the cathode liquid and anode liquid, respectively, from the electrochemical apparatus 11 to the electrolyte mixer 40. In this embodiment, the fourth discharge line 45 is connected to the cathode-side storage unit 19 and discharges cathode liquid from the cathode-side storage unit 19, but it may be connected to any position in the cathode-side circulation path. Also, the fifth discharge line 55 is connected to the second connection line 28 and discharges anode liquid from the second connection line 28, but it may be connected to any position in the anode-side circulation path.

[0032] Here, the anode solution discharged from the fifth discharge line 55 contains the target product. In this embodiment, when the concentration of the target product in the anode solution reaches a certain amount or more (for example, 50% by mass or more, preferably 60% by mass or more, more preferably 75% by mass or more), the anode solution is discharged from the fifth discharge line 55 and supplied to the electrolyte mixing device 40. Furthermore, after the supply is started, the anode solution should be supplied to the electrolyte mixing device 40 in an amount that can maintain the concentration of the target product at a certain amount or more. Also, when the supply of anode solution to the electrolyte mixing device 40 is started from the anode side (i.e., the anode circulation path), the anode solution should be supplied to the anode side as appropriate from the anode solution supply line 47 or the like. As a result, the discharge and supply of anode solution are carried out continuously on the anode side, enabling continuous operation.

[0033] Similarly, cathode fluid is discharged from the fourth discharge line 45 on the cathode side and supplied to the electrolyte mixer 40. The supply of cathode fluid to the electrolyte mixer 40 may start, for example, when the supply of anode fluid begins, but it may also start before the supply of anode fluid begins. When the supply of cathode fluid to the electrolyte mixer 40 begins, cathode fluid may be supplied to the cathode side from the cathode fluid supply line 37, or from the reuse supply line 46, which will be described later. This ensures that the amount of cathode fluid on the cathode side remains constant, enabling continuous operation on the cathode side as well.

[0034] The electrolyte mixing device 40 is a device capable of mixing the supplied anode solution and cathode solution. The electrolyte mixing device 40 may be a line mixer such as a static mixer, or it may be a device other than a line mixer, such as a mixing tank or a mixer settra.

[0035] In the electrolyte mixing device 40, the mixture obtained by mixing the anode solution and the cathode solution contains both the anode solution and the cathode solution. Furthermore, the anode solution contains at least one solvent, and the cathode solution also contains at least one solvent. The mixture contains all the solvents present in the anode solution and the cathode solution. As described above, the solvents in the anode solution and the solvents in the cathode solution are different from each other. Therefore, the solvent in the mixture contains two or more different solvents.

[0036] The anode solution and cathode solution supplied to the electrolyte mixing device 40 can be mixed as described above to control the electrolyte concentration. That is, electrolytes contained in the anode solution move to the solvent constituting the cathode solution, or vice versa, thereby changing the concentration in each solvent. The electrolyte, which has become more concentrated in the solvent than before mixing, becomes easier to recover from the mixture, so electrolytes such as redox species can be easily recovered from the electrolyte while suppressing energy consumption. Note that electrolyte recovery can be performed by separating the mixture as described later.

[0037] The electrolyte in the anode solution may contain a large amount of hydrogen halides, for example, and may exhibit acidity. The electrolyte in the cathode solution may contain a large amount of basic substances, such as metal hydroxides, and may exhibit alkalinity. Therefore, when the anode solution and cathode solution supplied to the electrolyte mixing device 40 are mixed as described above, a neutralization reaction may occur.

[0038] In this embodiment, the mixture obtained in the electrolyte mixing device 40 is supplied to the separation device 42, where two or more different solvents in the mixture are separated. For example, it is preferable that the mixture be separated into a first solvent S1 and a second solvent S2. The electrolyte is preferably contained in the first solvent S1 at a higher concentration than in the second solvent S2. By separating the mixture into at least the first and second solvents S1 and S2, and by making the electrolyte concentration in one of the solvents high, it becomes easier to recover the electrolyte dissolved in the solvent. The first solvent S1 and the second solvent S2 referred to here may consist of a single solvent, as long as they are separated, or they may consist of two or more solvents. Furthermore, as described above, in order to dissolve the electrolyte at a high concentration, it is preferable to use a solvent for the first solvent S1 that has a higher solubility for the electrolyte than the second solvent S2. Furthermore, if there are three or more solvents, at least one solvent may be allocated to be contained in both the first solvent S1 and the second solvent S2.

[0039] The concentration of the electrolyte in the first solvent S1 is preferably 0.001 to 10 M, more preferably 0.1 to 3 M, and also preferably 0.3 to 5 M. On the other hand, the concentration of the electrolyte in the second solvent S2 is only required to be lower than the concentration of the electrolyte in the first solvent S1. Specifically, the ratio of the concentration of the electrolyte in the second solvent S2 to the concentration of the electrolyte in the first solvent S2 (concentration ratio S2 / S1) is preferably 0.5 or less, more preferably 0.1 or less. However, it is preferable that the second solvent S2 does not contain an electrolyte, and therefore, the concentration ratio S2 / S1 is most preferably 0.

[0040] The method for separating the solvent is not particularly limited, but it is preferably at least one of membrane separation, distillation, and liquid-liquid phase separation, and among these, it is preferable that two or more different solvents are included and that liquid-liquid phase separation is performed. That is, the separation device 42 may be a separation membrane, a distillation device, or a liquid-liquid phase separation device, but it is preferably a liquid-liquid phase separation device. In Figure 1, the separation device 42 is shown as a liquid-liquid phase separation device. Also, in Figure 1, the separation device 42 and the electrolyte mixing device 40 are shown as separate devices, but they may be configured as a single device. That is, the electrolyte mixing device 40 may be a device that mixes the anode solution and the cathode solution and separates the solvent.

[0041] The solvent is separated into a first solvent S1 and a second solvent S2 by liquid-liquid phase separation as described above, and it is preferable that the electrolyte is contained in the first solvent S1 at a higher concentration than in the second solvent S2. A known method can be used for liquid-liquid phase separation. Specifically, a mixture obtained by mixing the anode solution and the cathode solution is allowed to stand, separating the liquid phase into two layers, and each liquid phase is extracted.

[0042] Membrane separation is particularly effective when water and an organic solvent are used as solvents, and it is best to use a reverse osmosis membrane or a limiting filtration membrane capable of separating water and organic solvents. Separation by distillation is best performed by removing at least one of two or more solvents from the mixture.

[0043] Here, as described above, it is preferable that the solvent in the cathode solution is water and the solvent in the anode solution is an organic solvent, and therefore, it is preferable that the solvents contained in the mixed solution are water and an organic solvent. With water and an organic solvent, two or more solvents can be easily separated by the liquid-liquid phase separation or membrane separation described above. Also, electrolytes usually have a higher solubility in water than organic solvents. For this reason, it is preferable that water constitutes the first solvent S1 containing the electrolyte in high concentration, and the organic solvent constitutes the second solvent S2. However, if the organic solvent includes a solvent that is soluble in both water and other organic solvents, such as the alcohol compounds described later, such a solvent may be distributed to both the first and second solvents.

[0044] The electrolyte contained in the separated and recovered solvent is preferably reused in part, and more preferably the solvent containing the electrolyte is reused. Specifically, the solvent containing the electrolyte (e.g., the first solvent S1), which has become more concentrated than before mixing and separation as described above, is preferably recovered and reused. Specifically, the solvent (preferably the solvent containing the electrolyte) is preferably returned to the electrochemical apparatus 11 via the reuse supply line 46. In the embodiment shown in Figure 1, the reuse supply line 46 connects the separation apparatus 42 and the cathode-side storage unit 19, and the solvent containing the electrolyte (e.g., the first solvent S1) is shown to be returned to the cathode chamber 16 side. However, depending on the type of solvent, the separated and recovered solvent may be returned to the anode chamber 26 side. Furthermore, the separated and recovered solvent may be returned to both the cathode chamber side and the anode chamber side. Specifically, the first solvent S1 may be returned to the cathode chamber side and the second solvent S2 may be returned to the anode side.

[0045] Next, a preferred embodiment of this model will be specifically described by example, in which the substance to be reduced X1 is carbon dioxide, the reduced product Y1 is carbon monoxide, the electrolytes contained in the anode solution and cathode solution are halogenated salts, the oxide X2 is a halogenated salt, the oxide Y2 is a halogen, and the target product is a carbonyl compound.

[0046] In one aspect of this embodiment, when the reducible substance X1 is carbon dioxide and the reducing substance Y1 is carbon monoxide, the cathode 13 preferably contains a carbon dioxide reduction catalyst (first catalyst). Typically, one of the reactions represented by the following formula (i) or formula (ii) occurs at the cathode. CO ２ + 2H ＋ + 2e － → CO + H ２ O (i) CO ２ + H ２ O + 2e － → CO + 2OH － (ii)

[0047] And the cathode liquid preferably has water as a solvent and a halide salt as an electrolyte. Examples of the halide salt include metal halide salts, and among them, alkali metal halide salts are preferable. Specifically, lithium halide salts such as lithium chloride and lithium bromide, sodium halide salts such as sodium chloride and sodium bromide, potassium halide salts such as potassium chloride and potassium bromide, cesium halide salts such as cesium chloride and cesium bromide, etc. can be mentioned. Also, ammonium halides such as ammonium chloride and ammonium bromide can be mentioned. The halide salt is preferably a metal halide salt, more preferably an alkali metal halide salt. Among them, lithium chloride, potassium chloride, sodium chloride, potassium chloride, cesium chloride, lithium bromide, potassium bromide, sodium bromide, potassium bromide, cesium bromide are even more preferable. From the viewpoint of increasing the selectivity of the target product, lithium chloride, lithium bromide, sodium chloride, sodium bromide, potassium chloride, potassium bromide are particularly preferable.

[0048] On the other hand, the anode liquid also contains a halide salt as an electrolyte. In the anode liquid, the halide salt is used as a redox species. That is, the halide salt is the oxidizable substance X2, and typically, the reaction represented by the following formula (iii) occurs at the anode 23. In the following formula (iii), X is a halogen atom. 2X － → X ２ + 2e － (iii)

[0049] Furthermore, the anode solution contains a reaction substrate in addition to the above-mentioned halogenated salt. The reaction substrate is a compound that serves as a raw material for producing a carbonyl compound (target product) by reacting with carbon monoxide. The reaction substrate is changed depending on the type of target product to be produced. The target product is not particularly limited as long as it is a carbonyl compound, and is at least one selected from organic carbonates and organic oxalates, and it is preferable that an alcohol-based compound is used as the reaction substrate.

[0050] (Alcohol-based compound) The alcohol-based compound is a reaction substrate that reacts with carbon monoxide in the reaction section 41 to produce an organic carbonate, an organic oxalate, or both. The alcohol-based compound may be a solid, liquid, or gas under the temperature conditions of the reaction carried out in the reaction section 41, but it is preferably a liquid. A liquid alcohol-based compound can be easily filled into the reaction section 41 by mixing it with the electrolyte as the anode solution without using the anode solution solvent described later. The reaction substrate also functions as a solvent that dissolves the electrolyte.

[0051] Alcohol compounds are compounds having at least one hydroxyl group, and more specifically, compounds represented by the following general formula (1). In this specification, "alcohol compounds" is a concept that also includes aromatic hydroxy compounds, such as phenol, in which the hydroxyl group is directly bonded to an aromatic ring such as a benzene ring, as will be described later. ROH (1) (R represents an organic group having 1 to 15 carbon atoms.) Examples of organic groups having 1 to 15 carbon atoms represented by R in the above general formula (1) include hydrocarbon groups having 1 to 15 carbon atoms. Examples of hydrocarbon groups include alkyl groups having 1 to 15 carbon atoms, alkenyl groups having 2 to 15 carbon atoms, and aryl groups having 6 to 15 carbon atoms. Examples of alkyl groups having 1 to 15 carbon atoms include methyl groups, ethyl groups, various propyl groups, various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various dodecyl groups, and various pentadecyl groups. Examples of C2-C15 alkenyl groups include vinyl groups, various propynyl groups, various butynyl groups, various pentynyl groups, various hexenyl groups, various heptenyl groups, various octenyl groups, various nonenyl groups, various decenyl groups, various dodecenyl groups, and various pentadecenyl groups. "Various" refers to various isomers including n-, sec-, tert-, and iso-. Furthermore, alkyl or alkenyl groups may be linear, branched, or cyclic. Examples of C6-C15 aryl groups include phenyl groups and naphthyl groups. The above-mentioned hydrocarbon groups may have substituents, in which case the total number of carbon atoms, including the substituents, is 1-15.

[0052] Furthermore, the organic group having 1 to 15 carbon atoms in general formula (1) may contain heteroatoms such as nitrogen atoms, oxygen atoms, sulfur atoms, phosphorus atoms, and halogen atoms. Among these, oxygen atoms are preferred. If an oxygen atom is present, it is preferable that the oxygen atom is either a hydroxyl group or an ether bond oxygen atom. Therefore, R is preferably a hydrocarbon group having at least one of a hydroxyl group and an ether bond. Also, it is preferable that there is one hydroxyl group in R. That is, the alcohol compound may have two hydroxyl groups. More specifically, the alcohol compound having two hydroxyl groups is preferably the group represented by the following formula (1-1): HO-R 11 -OH (1-1) Note that in equation (1-1), R 11 R is a divalent saturated hydrocarbon group having 2 to 15 carbon atoms, 11 The number of carbon atoms is preferably 2 to 4, more preferably 2 to 3.

[0053] Among the compounds represented by the above general formula (1), R is preferably an alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, or an aryl group having 6 to 8 carbon atoms. Also, the compound represented by the general formula (1-1), R 11 Compounds with 2 to 4 carbon atoms are also preferred. Among these, compounds in which R is an alkyl group or an aryl group are more preferred, and compounds in which R is an alkyl group are even more preferred. Furthermore, alkyl groups with 1 to 3 carbon atoms are more preferred, with 1 or 2 carbon atoms being even more preferred, and 1 carbon atom being the most preferred. Specifically, from the viewpoint of reactivity and production efficiency, methanol, ethanol, phenol, 1-propanol, ethylene glycol, propylene glycol, etc. are preferred, and among these, methanol is more preferred. Note that one alcohol compound may be used alone, or two or more may be used in combination.

[0054] When an alcohol-based compound is used as the reaction substrate, the reaction section 41 generally carries out a reaction in which an organic carbonate is produced from carbon monoxide and the alcohol-based compound (also called the first reaction). However, a reaction in which an organic oxalate is produced from carbon monoxide and the alcohol-based compound (also called the second reaction) may also carry out, or both the first and second reactions may carry out, but it is preferable that at least the first reaction is carried out.

[0055] The first reaction described above is a carbonylation reaction that produces an organic carbonate, for example, by the reaction shown in formula (iv) below, the organic carbonate ((RO) ２ CO) is generated. At this time, in the reaction section 41, oxide Y2 (halogen (X) ２ )) is reduced product Y3 (halogen ion X － After being reduced to ), the reaction of formula (iv) below takes place. However, when ROH is represented by general formula (1-1), for example, an organic carbonate is produced by the reaction shown in formula (iv-1) below. When synthesizing carbonyl compounds as shown in formulas (iv), (iv-1) below and formulas (v), (v-1) described later, hydrogen halides are produced in reaction section 41. The hydrogen halides are preferably hydrogen chloride and hydrogen bromide, but more preferably hydrogen bromide. CO + 2ROH + 2X － → (RO) ２ CO+2HX (iv)

[0056] (Note that in equations (iv) and (iv-1), X is a halogen atom. R, R １１ (This is the same as above.)

[0057] Specific preferred organic carbonates include one or more selected from dimethyl carbonate, diethyl carbonate, ethylene carbonate, dipropyl carbonate, propylene carbonate, diphenyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, with dimethyl carbonate being the most preferred among these.

[0058] The second reaction involves the reaction of carbon monoxide and an alcohol compound to produce an organic oxalate represented by formula (2) below. For example, the organic oxalate represented by formula (2) may be synthesized by the reaction shown in formula (v) below. In equation (2), R is the same as above. However, the two Rs in a single molecule may be the same or different.

[0059] In equation (v), X and R are the same as above.

[0060] Furthermore, when ROH is represented by general formula (1-1), the reaction shown in formula (v-1) below produces the organic oxalate shown in formula (2-1) below. (Note that in equation (2-1), R １１ (This is the same as above.) (Note that in equation (vi), X and R １１ (This is the same as above.)

[0061] Specific preferred organic oxalates include one or more selected from dimethyl oxalate, diethyl oxalate, ethylene oxalate, dipropyl oxalate, propylene oxalate, diphenyl oxalate, ethyl methyl oxalate, methyl propyl oxalate, and ethyl propyl oxalate. Among these, dimethyl oxalate is more preferred.

[0062] If the reaction substrate described above is a solid or a gas, or if it is necessary to improve the solubility of the electrolyte, the reaction substrate (i.e., the anode solution) may be diluted with a solvent other than the reaction substrate (hereinafter also referred to as "solvent for the anode solution"). In that case, the reaction substrate may be filled into the reaction section 41 as a mixture with the solvent for the anode solution. Of course, even if the reaction substrate is a liquid, it may be filled into the reaction section 41 as a mixture with the solvent for the anode solution.

[0063] Examples of solvents for the anode solution include nitrile solvents such as acetonitrile, carbonate solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, lactone solvents such as γ-butyrolactone, ether solvents such as 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran, phosphate ester solvents, phosphoric acids, sulforane solvents, and pyrrolidones. These solvents may be used individually or in combination of two or more. Among these, carbonate solvents are preferred. The solvent for the anode solution may be the same compound as the target product, or the above-mentioned carbonyl compounds may be used as appropriate for the anode solution.

[0064] In this embodiment, the target product produced in the reaction section 41 is preferably a liquid, and preferably a solvent capable of dissolving electrolytes. That is, before the electrochemical reaction in the anode chamber and the reaction in the reaction section 41 begin, the solvent of the anode solution is either the reaction substrate, a mixed solvent of the reaction substrate and the solvent for the anode solution, or the solvent for the anode solution. However, once the reaction in the reaction section 41 begins, the solvent of the anode solution may become a mixed solvent of the reaction substrate and the target product, a mixed solvent of the reaction substrate, the solvent for the anode solution and the target product, or a mixed solvent of the solvent for the anode solution and the target product.

[0065] Then, as described above, when the electrochemical reaction proceeds and the concentration of the target product in the anode solution reaches a certain amount or more, the anode solution is discharged from the anode side via the fifth discharge line 55, and the cathode solution is also discharged from the cathode side via the fourth discharge line 45, and the cathode solution and anode solution are mixed in the electrolyte mixing device 40.

[0066] Here, the anode solution discharged to the electrolyte mixing device 40 contains an electrolyte in addition to the target product as described above. The electrolyte may contain either the halogenated salt and hydrogen halide introduced as raw materials, but it is preferable that it contains at least hydrogen halide. The hydrogen halide may be formed by by-products in the reaction section 41 or by halogen ions that have moved from the cathode side to the anode side via the isolation membrane 31. The cathode solution discharged to the electrolyte mixing device 40 also contains an electrolyte as described above. The electrolyte in the cathode solution may contain either the halogenated salt introduced as raw materials or a basic substance such as a metal hydroxide, but it is preferable that it contains at least a basic substance. The basic substance such as a metal hydroxide in the cathode solution is formed by a portion of the electrolyte (cations such as metal ions) that have moved from the anode side to the cathode side via the isolation membrane 31, or by halogen ions from the cathode side moving to the anode side and the remaining cations such as metal ions forming the electrolyte. Then, the cathode solution and anode solution are mixed in the electrolyte mixing device 40, and when a mixture is obtained, a neutralization reaction occurs between the hydrogen halide and a basic substance such as a metal hydroxide, preferably generating a halogenated salt.

[0067] Furthermore, once a mixture is obtained, it is preferable to separate and recover the two or more solvents contained in the mixture. Specifically, the solvents are preferably separated into a first solvent S1 containing water and a second solvent S2 containing an organic solvent. In this case, the first solvent S1 contains a high concentration of halogenated salts, which are electrolytes, and therefore, it is preferable to separate, recover, and reuse the first solvent S1. The first solvent S1 is preferably supplied directly to the cathode side via a reuse supply line 46. Alternatively, a distillation apparatus or the like may be placed in the reuse supply line 46 to remove at least a portion of the solvent contained in the first solvent S1 and concentrate it to further increase the electrolyte concentration. Specifically, since the first solvent S1 may contain alcoholic compounds, it is preferable to remove the alcoholic compounds. By removing the alcoholic compounds, it is possible to prevent the supply of impurities to the cathode side. In addition, the distillation apparatus may remove some of the water, or it may remove both the alcoholic compounds and water. By removing some of the water, the concentration of the electrolyte on the cathode side and the amount of water in the cathode solution can be adjusted. Furthermore, the first solvent S1 does not need to be supplied to the reuse supply line 46, but can be supplied to a distillation apparatus (not shown) located elsewhere than the reuse supply line 46, where some or all of the solvent can be removed and concentrated, and the solvent containing the high concentration of electrolyte obtained from the removal of the solvent, or the electrolyte itself, can be recovered and reused as appropriate. In this case, the solvent containing the electrolyte and the electrolyte can be supplied to the cathode side as the electrolyte or cathode solution on the cathode side, or they can be supplied to the anode side as the electrolyte on the anode side, etc.

[0068] On the other hand, the second solvent S2 contains the carbonyl compound, which is the target product. Therefore, the second solvent S2 should be discharged from the electrochemical reaction system. The target product can then be obtained by purifying it as appropriate.

[0069] As described above, the electrochemical reaction system according to this embodiment can be applied to a system that generates carbon monoxide from carbon dioxide on the cathode side and synthesizes a carbonyl compound from the obtained carbon monoxide and reaction substrate, thereby efficiently recovering and reusing the electrolyte.

[0070] Next, the cathode, anode, isolation membrane, and reaction section used in the electrochemical reaction system according to this embodiment will be described in more detail. (Cathode) The cathode 13 may contain a reduction catalyst (first catalyst) as described above, but for example, if the substance to be reduced X1 is carbon dioxide, it contains a carbon dioxide reduction catalyst. The carbon dioxide reduction catalyst is not particularly limited as long as it is a catalyst that can reduce carbon dioxide to a reducer such as carbon monoxide, but for example, it may contain a metal element. The metal element may be the metal itself or a metal compound. The metallic elements in the above metals are not particularly limited, but include V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, Zn, Os, and Nd. The above metal compounds can be inorganic metal compounds and organometallic compounds of these metals, and specifically include metal halides, metal oxides, metal hydroxides, metal nitrates, metal sulfates, metal acetates, metal phosphates, metal carbonyls, and metal acetylacetonates.

[0071] The metal elements used in the carbon dioxide reduction catalyst are preferably from Group 7 to Group 12. Preferred specific examples include Mn, Fe, Ni, Ru, Co, Rh, Cu, Zn, Ag, Au, Pd, Ir, Pt, and Os, with Co, Fe, Ni, Au, and Ag being more preferred, and Co being particularly preferred. Using these metal elements makes it easier to increase the conversion efficiency from carbon dioxide to carbon monoxide and thus enhances catalytic activity. The metal used in the metal derivative may be used alone or in combination of two or more.

[0072] The carbon dioxide reduction catalyst may contain a carbon compound in addition to the above-mentioned metal or metal compound. A conductive carbon compound is preferred as the carbon compound. More specifically, examples of carbon compounds include mesoporous carbon, activated carbon, carbon black such as Ketjenblack and acetylene black, graphite, carbon fiber, graphene, and carbon nanotubes, among which carbon black is preferred, and conductive carbon black is even more preferred. Furthermore, the carbon compound is preferably porous carbon. When the carbon dioxide reduction catalyst contains a carbon compound, the metal or metal compound may be supported on the carbon compound. Alternatively, the carbon dioxide reduction catalyst may be prepared as a catalyst powder by mixing the carbon compound with a complex containing the above-mentioned metal element and heat-treating it. The carbon dioxide reduction catalyst, in which the metal or metal compound is supported on the carbon compound, may further be supported on an electrode substrate as described later.

[0073] The carbon dioxide reduction catalyst is preferably a catalyst containing a nitrogen element and a metal element (also called a "nitrogen-containing metal catalyst"). Here, the nitrogen element used in the nitrogen-containing metal catalyst is preferably derived from a nitrogen-containing compound described later. The nitrogen-containing metal catalyst is often a catalyst obtained by heat-treating a mixture containing a metal derivative and a nitrogen-containing compound (hereinafter referred to as the "carbon dioxide reduction catalyst raw material mixture"), and among these, it is preferable to be a catalyst obtained by heat-treating a carbon dioxide reduction catalyst raw material mixture containing a metal derivative, a nitrogen-containing compound, and a carbon compound. Specific examples of nitrogen-containing compounds include pyridine derivatives, imidazole derivatives, pyrazole derivatives, and triazole derivatives. These compounds may be used individually or in combination of two or more. The metal element in the metal derivative is as described above. The metal derivative preferably contains a metal ion. Furthermore, the metal derivative may be used, for example, in the form of a metal salt. Examples of metal salts include metal nitrates, metal sulfates, metal chlorides, metal bromides, metal iodides, and metal acetates, among which metal nitrates are preferred. The above heat treatment is typically calcination. The heat treatment is preferably carried out at a temperature of 150 to 550°C, more preferably 200 to 470°C. By performing the heat treatment at such a low temperature, ring structures derived from nitrogen-containing compounds, such as pyridine ring structures, imidazole ring structures, pyrazole ring structures, and triazole ring structures, can be retained in the nitrogen-containing metal catalyst. This allows for the formation of metal-nitrogen element bonds in the nitrogen-containing metal catalyst.

[0074] The carbon compound used in the nitrogen-containing metal catalyst is not particularly limited as long as it can support heat-treated products (e.g., calcined products) of nitrogen-containing compounds such as metal derivatives and pyridine derivatives, but conductive carbon compounds are preferred. Using a conductive carbon compound increases the electrical conductivity at the cathode, making it easier to increase the conversion efficiency to carbon monoxide. Specific examples of carbon compounds are as described above, with carbon black being preferred, and conductive carbon black, represented by Ketjenblack, being even more preferred. The nitrogen-containing metal catalyst is preferably in powder or particulate form. Being in powder or particulate form makes it easier to support on the electrode substrate described later. It also makes it easier to increase the contact area with carbon dioxide, thus improving the conversion efficiency to carbon monoxide.

[0075] In addition to the above, the carbon dioxide reduction catalyst may also be a carbon compound containing at least one heteroatom such as nitrogen, or a metal or a metal compound. Examples of such carbon compounds include nitrogen-containing graphite, nitrogen-containing carbon nanotubes, nitrogen-containing graphene, Ni and nitrogen-containing graphite, Ni and nitrogen-containing carbon nanotubes, Ni and nitrogen-containing graphene, Cu and nitrogen-containing graphite, Cu and nitrogen-containing carbon nanotubes, Cu and nitrogen-containing graphene, Co and nitrogen-containing graphite, Co and nitrogen-containing carbon nanotubes, and Co and nitrogen-containing graphene. The carbon dioxide reduction catalyst may be used alone or in combination of two or more types.

[0076] The cathode 13 may have an electrode substrate (current collector). The electrode substrate is not particularly limited as long as it is a current collector conventionally used in carbon dioxide reduction electrodes, and examples include carbon substrates, metal substrates, and metal oxide substrates, and it is preferable that it is conductive. The electrode substrate may also be a porous material. The substrate is a substrate that constitutes the electrode, and may be in the form of a sheet or plate, for example, or it may be laminated on the wall of the anode chamber 26 or the isolation membrane 31.

[0077] Examples of carbon substrates include porous carbon such as carbon nonwoven fabrics. The carbon nonwoven fabric is not particularly limited, and known carbon nonwoven fabrics can be used. For example, commercially available carbon nonwoven fabrics for fuel cells can be used, such as Toray Industries' "Torayca" (registered trademark) carbon paper, Toray060, New Metal & Chemicals' "AvCarb 1071HCB", and SGL's BC series. Carbon felt can also be used. Examples of metal substrates include metal meshes, and metals that can be used include gold, silver, platinum, nickel, titanium, and chromium. Examples of metal oxides used in metal oxide substrates include indium oxide, tin oxide, tin-doped indium oxide, and fluorine-doped tin oxide (FTO).

[0078] The carbon dioxide reduction catalyst is preferably supported on an electrode substrate. The method of supporting the carbon dioxide reduction catalyst on the electrode substrate is not particularly limited; it is preferable to attach the carbon dioxide reduction catalyst to the electrode substrate, and it is particularly preferable to attach the nitrogen-containing metal catalyst described above to the electrode substrate. Here, attachment means that the catalyst is physically fixed to the electrode substrate, and the atoms constituting the electrode substrate are not chemically bonded to the atoms constituting the catalyst. Therefore, even if the electrode substrate contains a carbon compound such as porous carbon, the carbon compound itself does not have the metal-nitrogen element bond described above. It also does not have a metal-carbon element bond. Here, the carbon element refers to the carbon element constituting the carbon compound such as porous carbon, and the metal is a metal element derived from a metal derivative. By attaching the nitrogen-containing metal catalyst to the electrode substrate without chemical bonding, the conversion efficiency to carbon monoxide can be easily improved, and its manufacture can also be facilitated. However, the atoms constituting the carbon dioxide reduction catalyst may be chemically bonded to the atoms constituting the electrode substrate. For example, if the electrode substrate contains a carbon compound such as porous carbon, the carbon compound itself may have the metal-nitrogen element bond or metal-carbon element bond described above.

[0079] Furthermore, the carbon dioxide reduction catalyst may be supported on the electrode substrate together with catalyst additives. The catalyst additive also functions as a binder when supporting the catalyst on the electrode substrate. In addition, it also functions as an ion conductor, improving the efficiency of the electrochemical reaction. Examples of catalyst additives include cationic conductive compounds, anionic conductive compounds, and fluorine compounds other than cationic conductive compounds and anionic conductive compounds. The method for supporting the carbon dioxide reduction catalyst on the electrode substrate is not particularly limited, but examples include applying a diluted solution, obtained by diluting the carbon dioxide reduction catalyst and other components such as catalyst additives added as needed, with a diluting solvent to the electrode substrate using various coating equipment or by spray coating and drying, or immersing the electrode substrate in the above diluted solution and drying.

[0080] (Anode) The anode 23 may have an electrode substrate (current collector). The electrode substrate is not particularly limited as long as it is a current collector conventionally used in the anode of an electrochemical cell, and examples include carbon substrates, metal substrates, and metal oxide substrates, and it is preferable that it is conductive. The electrode substrate may also be a porous material. The substrate is a substrate that constitutes the electrode, and may be, for example, in the form of a sheet or plate, or it may be laminated on the wall of the anode chamber. The carbon substrate, metal substrate and metal oxide substrate used as the electrode substrate for the first electrode are as described above. The anode 23 does not have to contain a catalyst as long as it can oxidize the oxide X2 to oxide Y2 as described above, but it may contain a catalyst (anode catalyst). As the anode catalyst, known catalysts used in anodes in hydrochloric acid electrolysis, chloroalkali electrolysis, etc. can be used, and specifically iridium oxide, ruthenium oxide, iridium-ruthenium oxide, platinum, etc. can be used.

[0081] (Isolation membrane) The isolation membrane 31 may be an ion exchange membrane or a porous membrane other than an ion exchange membrane. As an ion exchange membrane, a solid membrane is used, and examples include a cation exchange membrane that can permeate cations such as protons and an anion exchange membrane that can permeate anions such as hydroxide ions, but a cation exchange membrane is preferred. When the isolation membrane 31 is a cation exchange membrane, cations such as protons move from the anode chamber 26 to the cathode chamber 16, and the reaction of formula (i) described above can easily occur in the cathode chamber 16. Also, when the isolation membrane 31 is a cation exchange membrane, it allows cations such as metal ions that constitute the halide salt to permeate, so metal ions can be moved from the anode chamber 26 to the cathode chamber 16 along with protons. Therefore, halogens are more easily generated from the halide salt at the anode 23. In addition, cations such as metal ions that constitute the halide salt can be supplied to the cathode side, and cations such as metal ions on the anode side can be effectively utilized as electrolytes on the cathode side. Furthermore, if the isolation membrane 31 is an anion exchange membrane, anions such as hydroxide ions move from the cathode chamber 16 side to the anode chamber 26 side, and the reaction of formula (ii) described above can easily occur in the cathode chamber 16. In addition, since halogen ions also move from the cathode chamber 16 side to the anode chamber 26 side along with hydroxide ions, halogens are more easily generated in the anode 23, and the electrolyte on the cathode side can be effectively utilized on the anode side.

[0082] Examples of cation exchange membranes include those having at least one of the following functional groups: sulfonyl group, carboxyl group, phosphate group, and silicate group. Examples of cation exchange membranes having a sulfonyl group as a functional group include hydrocarbon resin-based polysulfonic acids such as polyethylene sulfonic acid and fullerene crosslinked polysulfonic acid, and fluororesin-based sulfonic acids such as perfluoroethylene sulfonic acid. Examples of perfluoroethylene sulfonic acid include copolymers of tetrafluoroethylene and perfluoro[2-(fluorosulfonylethoxy)propyl vinyl ether], and a commercially available product is "Nafion" (a trademark of DuPont). Examples of membranes having a carboxyl group as a functional group include polycarboxylic acids such as polyacrylic acid. Examples of membranes having a phosphate group or silicate group as a functional group include heteropoly acids such as tetratungstic acid and phosphotungstic acid. Furthermore, as a cation exchange membrane, SiO ２ -P ２ O ５ Ceramics such as phosphated glass and perovskite oxides can also be used.

[0083] Furthermore, examples of anion exchange membranes include resins and polyethers containing quaternary ammonium salts such as poly(styrylmethyltrimethylammonium chloride), and polymers containing imidazolium groups. Examples of resins containing ammonium salts include "FAA-3-50" from FuMA-Tech GmbH and "TM1 Durion Grade" from Orion. Examples of polymers containing imidazolium groups include styrene-based polymers containing imidazolium groups, specifically copolymers of styrene and 1-(p-vinylbenzyl)-3-methylimidazolium (PSMIM), copolymers of styrene and 1-(p-vinylbenzyl)-tetramethylimidazolium (PSTMIM), and copolymers of styrene and 1-(p-vinylbenzyl)-2,3-dimethylimidazolium (PSDMIM).

[0084] Furthermore, the isolation membrane 31 may be a porous membrane other than an ion exchange membrane, and it is preferable that it be a porous membrane that allows both anions and cations to pass through. By using such a porous membrane, cations constituting halide salts such as metal ions can be moved from the anode side to the cathode side, and halogen ions can be moved from the cathode side to the anode side. As a result, halogens are more easily generated at the anode, and the cations and anions of the electrolyte can be utilized more effectively. Examples of porous membranes that allow both anions and cations to pass through include polyolefin porous membranes such as polypropylene porous membranes, and fluorine resin membranes such as polyvinylidene fluoride porous membranes.

[0085] As described above, if cations such as metal ions constituting the halide salt on the anode side move to the cathode side, or if halogen ions on the cathode side move to the anode side, the cathode solution on the cathode side will contain a large amount of cations such as metal ions. It is desirable that basic substances such as hydroxides be formed by such cations. The type of basic substance such as hydroxide varies depending on the type of halide salt, but metal hydroxides are preferred, and alkali metal hydroxides are more preferred among them. Suitable specific examples include lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, and ammonia, but among these, lithium hydroxide, sodium hydroxide, and potassium hydroxide are even more preferred.

[0086] (Reaction Section) The reaction section 41 is composed of a reactor separate from the anode chamber 26 and the cathode chamber 16. That is, the reaction section 41 is a reaction system separate from the reaction system composed of the anode chamber 26 and the reaction system composed of the cathode chamber 16. A known reactor may be used for the reaction section 41. The reaction section 41 may contain the second catalyst inside the reaction section 41 as described above. The second catalyst may be dispersed or dissolved in the anode solution in the reaction section 41. Alternatively, the second catalyst may not be dispersed or dissolved in the reaction solution as long as it is in contact with the reaction solution in the reaction section 41, and may be in the form of a fixed bed in the reaction section 41. Furthermore, a stirring device for stirring the reaction solution may be attached to the reaction section 41. In addition, filters or the like may be provided at the connection ports to each line in the reaction section 41 as needed to prevent the second catalyst from flowing out of the reaction section 41.

[0087] The second catalyst used in the reaction section 41 is preferably one that promotes a chemical reaction to synthesize the target product, a carbonyl compound, from carbon monoxide and a reaction substrate in the presence of a redox species (oxide Y2), and may contain a metal element, and more preferably contains a metal element selected from Group 8 to Group 11 elements. Using Group 8 to Group 11 elements in the catalyst facilitates the electrochemical synthesis of carbonyl compounds, particularly organic carbonates, from carbon monoxide with high selectivity.

[0088] Specifically, the Group 8 to Group 11 elements used in the second catalyst include Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au. Among these, Co, Ni, Cu, Rh, Pd, Ag, Ir, Au, and Pt are preferred, with Pd, Au, Ag, and Ir being more preferred. Using the above elements facilitates the synthesis of organic carbonates, organic oxalates, or both from carbon monoxide with high selectivity. From this viewpoint, the metal elements contained in the catalyst are more preferably Au and Pd, and particularly preferably Pd.

[0089] The metal element used in the second catalyst may be used alone or in combination of two or more elements. When using two or more elements in combination, two or more metal elements selected from Group 8 to Group 11 may be used, or a metal element from Group 8 to Group 11 may be used in combination with a metal element other than those from Group 8 to Group 11. Preferably, the metal element other than those from Group 8 to Group 11 is a metal element from the fourth period, but other metal elements may also be used. Specifically, it is preferable to combine Au with at least one selected from Ti, Mn, Fe, Co, Ni, Cu, and Zn. It is also preferable to combine Pd with at least one selected from Ti, Co, Ni, Cr, Mn, Fe, Cu, Zn, Ru, Rh, Ag, Ir, Pt, Au, and Sn. Furthermore, it is also preferable to combine Ir with at least one selected from Au, Rh, and Ru. This combination allows for a high level of selectivity when synthesizing carbonyl compounds while minimizing the amount of precious metals used.

[0090] The second catalyst may be a catalyst containing active particles, a metal salt, or a combination of both. By using a catalyst containing active particles or a metal salt, carbonyl compounds, particularly organic carbonates, can be produced from carbon monoxide with high conversion efficiency. Among these, the use of a catalyst containing active particles is preferred.

[0091] 《Catalyst Containing Active Particles》 In a catalyst containing active particles, the active particles have catalytic activity that promotes the reaction when synthesizing carbonyl compounds from carbon monoxide. Active particles containing metal elements are not particularly limited as long as they contain metal elements, and may be composed of metal oxides, metal itself, or both metal oxides and metal. The metal elements used for the active particles are as described above.

[0092] In the second catalyst, the active particles are, for example, particulate matter and are not particularly limited, but are preferably nano-order particles, preferably with an average particle diameter of 100 nm or less, and more preferably between 1 nm and 40 nm. By having the above particle diameter and nanostructuring the active particles, the active area increases, making it easier to improve various properties of the catalyst. The particle diameter refers to the area-circle equivalent diameter, which is calculated by determining the area of ​​each particle in image observation using TEM-EDX, etc., and then assuming each particle is a circle.

[0093] Furthermore, it is preferable that the active particle-containing catalyst further contains a support, with the active particles supported on the support. While not particularly limited, the support used in the active particle-containing catalyst includes carbon, silica, aluminum oxide, and zirconium oxide. From the viewpoint of synthesizing carbonyl compounds from carbon monoxide with high selectivity, porous carbon, silica, and aluminum oxide are preferred. Therefore, it is preferable that the active particle-containing catalyst is a catalyst comprising active particles having a metal element and porous carbon, silica, or aluminum oxide supporting the active particles. The use of porous carbon, silica, or aluminum oxide as the support facilitates the appropriate diffusion of the reaction substrate into the catalyst, improving selectivity and reaction efficiency during the synthesis of carbonyl compounds. The support may be used alone or in combination of two or more types.

[0094] Catalysts containing active particles, such as porous carbon, can be manufactured by mixing a metal precursor with a support (e.g., porous carbon, silica, or aluminum oxide) and heat-treating it, as described later. The metal precursor becomes active particles through heat treatment, and these active particles are supported on the support. The porous carbon used in the catalyst containing active particles is not particularly limited, but it is preferably composed of a powder or particulate carbon compound, and therefore the catalyst containing active particles is also preferably in powder or particulate form. When the catalyst containing active particles is in powder or particulate form, it is easier to disperse it in the electrolyte, and the contact area with carbon monoxide tends to increase, making it easier to improve the selectivity and reaction efficiency when synthesizing organic substances such as carbonyl compounds.

[0095] The porous carbon used in the active particle-containing catalyst is not particularly limited as long as it can support the active particles, but conductive carbon compounds are preferred. Using conductive carbon compounds increases the electrical conductivity at the electrodes, making it easier to improve reaction efficiency. More specifically, porous carbons include mesoporous carbon, activated carbon, carbon black such as Ketjenblack and acetylene black, carbon nanotubes, graphite, and graphene, among which carbon black is preferred, and conductive carbon black is even more preferred.

[0096] The active particle-containing catalyst may further contain components derived from nitrogen-containing compounds. The presence of nitrogen-containing components in the active particle-containing catalyst makes it easier to improve the conversion efficiency and selectivity when synthesizing carbonyl compounds. The nitrogen-containing component contains a nitrogen element, which coordinates to the metal element constituting the active particle (for example, the metal element constituting a metal oxide), forming a metal-nitrogen bond via coordination bonding. The nitrogen-containing component is preferably supported on a carrier such as porous carbon, silica, or aluminum oxide. That is, the nitrogen-containing component coordinates to the metal element constituting the active particle and is preferably supported on a carrier such as porous carbon. The nitrogen-containing compound preferably has a nitrogen-containing aromatic ring structure in which nitrogen is contained in the aromatic ring. When the active particle-containing catalyst contains components derived from nitrogen-containing compounds, it can be obtained by heat-treating a mixture of the carrier, a metal precursor, and the nitrogen-containing compound, as described later. Therefore, the nitrogen-containing component is a component obtained by heat-treating the nitrogen-containing compound.

[0097] In the catalyst containing active particles, the nitrogen-containing aromatic ring structure composed of nitrogen-containing compounds remains in the catalyst as the heat treatment temperature is lowered as described later. Furthermore, it is preferable that the component derived from the nitrogen-containing compound in the catalyst containing active particles has a nitrogen-containing aromatic ring structure. In the nitrogen-containing metal catalyst, the component derived from the nitrogen-containing compound may form bonds, such as coordination bonds, with the metal element derived from the metal derivative. Specific examples of nitrogen-containing compounds include pyridine derivatives, imidazole derivatives, pyrazole derivatives, and triazole derivatives. These compounds may be used individually or in combination of two or more.

[0098] 《Method for Producing an Active Particle-Containing Catalyst》 Next, a method for producing an active particle-containing catalyst will be described. The active particle-containing catalyst described above may be obtained by heat-treating at least a metal precursor, but preferably by mixing a metal precursor with a support such as porous carbon, silica, or aluminum oxide, and then heat-treating the mixture containing the metal precursor and the support. The metal precursor, or the mixture containing the metal precursor and the support, which is the raw material for the active particle-containing catalyst, will also be referred to as the second catalyst raw material below. The heat treatment is typically calcination. Furthermore, if the active particle-containing catalyst contains components derived from a nitrogen-containing compound, the nitrogen-containing compound may be further mixed with the metal precursor and the support, and the second catalyst raw material may contain the metal precursor, the support, and the nitrogen-containing compound.

[0099] The metal precursor is a compound that becomes the active particles described above upon heat treatment. Therefore, the metal precursor is preferably a precursor containing a metal element selected from the Group 8 to Group 11 elements described above, and the preferred metal elements are as described above. The metal element used in the metal precursor may be used alone or in combination of two or more. The combinations of metal elements when two or more are used are as described above. When two or more metal precursors are used in combination, the catalyst containing active particles is preferably obtained by mixing two or more metal precursors, or by mixing two or more metal precursors with a support such as porous carbon, silica, or aluminum oxide, and then heat treating it. Therefore, it is preferable that the second catalyst raw material contains two or more metal precursors.

[0100] The metal precursor preferably contains metal ions. Furthermore, the metal precursor may be used, for example, in the form of a metal salt. Examples of metal salts include metal nitrates, metal sulfates, metal chlorides, metal bromides, metal iodides, and metal acetates, among which metal chlorides and metal nitrates are preferred. Specific examples of metal nitrates and metal chlorides used in the metal precursor are the same as those used as the second catalyst described later, and therefore their explanation is omitted. The metal salt may also be in the form of a hydrate.

[0101] The metal content derived from the metal precursor in the second catalyst raw material is preferably 0.01% by mass or more and 70% by mass or less, and more preferably 0.12% by mass or more and 50% by mass or less, relative to the total amount of the second catalyst raw material. By keeping it within this range, the metal is contained in the catalyst without aggregation, and an appropriate amount of catalytic active sites are formed. As a result, it becomes easier to increase the selectivity when synthesizing carbonyl compounds, and the reaction efficiency is also increased.

[0102] Furthermore, the amount of the support in the second catalyst raw material is not particularly limited, but is, for example, 10% by mass or more and 99.99% by mass or less, preferably 20% by mass or more and 99.9% by mass or less, and more preferably 30% by mass or more and 80% by mass or less, relative to the total amount of the second catalyst raw material. By keeping the amount of the support within the above range, the catalytic activity can be well maintained while appropriately supporting the active particles and components derived from the nitrogen-containing compound. When using a nitrogen-containing compound, the amount of the nitrogen-containing compound blended in the second catalyst raw material is preferably adjusted so that the molar ratio of the nitrogen-containing aromatic ring of the nitrogen-containing compound to the metal element derived from the metal precursor (nitrogen-containing aromatic ring / metal element) is 0.1 or more and 30 or less, and more preferably 1 or more and 20 or less.

[0103] The temperature at which the second catalyst raw material is heat-treated is preferably 150°C to 800°C, more preferably 180°C to 550°C, and even more preferably 200°C to 380°C. The heat treatment time is not particularly limited, but for example, it is 0.25 hours to 10 hours, preferably 0.5 hours to 8 hours, and more preferably 1 hour to 5 hours. The heat treatment may be carried out under an inert gas atmosphere such as argon or nitrogen gas, or under a reducing atmosphere such as hydrogen.

[0104] The second catalyst raw material to be heat-treated is preferably in powder, particulate, or pellet form. If the second catalyst raw material is in powder or particulate form, the catalyst obtained by heat treatment can also be in powder or particulate form. Furthermore, it is more preferable that the second catalyst raw material to be heat-treated consists of a metal precursor and a support, or a metal precursor, a support, and a nitrogen-containing compound. The second catalyst raw material can be obtained, for example, by preparing a diluted solution of the second catalyst raw material and drying the diluted solution. In the diluted solution of the second catalyst raw material, it is preferable that each component (metal precursor and support, or a metal precursor, a nitrogen-containing compound, and a support) is dispersed or dissolved in the diluent. By dispersing or dissolving each component in the diluent, a second catalyst raw material in which each component is homogeneously mixed can be obtained. Water and organic solvents can be used as the diluent solvent to dilute the second catalyst raw material, and water is preferred. Acidic components, basic components, etc. may also be appropriately added to the diluent solvent.

[0105] <Metal Salts> Examples of metal salts used as a second catalyst include metal nitrates, metal sulfates, metal chlorides, metal bromides, metal iodides, and metal acetates. Among these, metal chlorides and metal nitrates are preferred, and metal chlorides are more preferred. Specifically, examples of metal nitrates include cobalt nitrate (Co(NO3)2), nickel nitrate (Ni(NO3)2), copper nitrate (Cu(NO3)2), and rhodium nitrate (Rh(NO3)2). ３ ), palladium nitrate (Pd(NO3) ２ ), silver nitrate (AgNO) ３ ), iridium nitrate (Ir(NO3) ４ ), platinum nitrate (Pt(NO3)４ ), gold nitrate (AuNO3), ruthenium nitrate (Ru(NO3) ３ ), iron nitrate (Fe(NO) ３ ) ３ ), manganese nitrate (Mn(NO) ３ ) ２ ), zinc nitrate (Zn(NO) ３ ) ２ ), chromium nitrate (Cr(NO) ３ ) 　３ ), tin nitrate (Sn(NO ３ ) ４ Examples include ) and others. Furthermore, specific examples of metal chlorides include palladium chloride (PdCl). ２ ), ruthenium chloride (RuCl ３ ), iridium chloride (IrCl ３ ), platinum chloride (PtCl ４ ), gold chloride (AuCl ３ Examples include ) and tetrachloride auric acid (HAuCl). ４ ) and others may also be used. Among these, palladium chloride, tetrachloridoaurate, and iridium chloride are preferred, with palladium chloride being more preferred.

[0106] The metal salt used as the second catalyst may be supported on a support. The support is as described above, and is preferably porous carbon, silica, or aluminum oxide. The metal salt may be supported on the support by, for example, dispersing the support and the metal salt in a solvent and drying the resulting dispersion. The second catalyst may be used alone or in combination of two or more types.

[0107] <Second Embodiment> Next, a second embodiment of the present invention will be described. The electrochemical reaction system 60 according to the second embodiment is an electrochemical reaction system with a more practical configuration, and the differences between the second embodiment and the first embodiment will be described below. In the following description, a preferred embodiment will be specifically described as one in which the reduced substance X1 is carbon dioxide, the reduced product Y1 is carbon monoxide, the electrolytes contained in the anode solution and cathode solution are halogenated salts, the oxide X2 is a halogenated salt, the oxide Y2 is a halogen, and the target product is a carbonyl compound. However, the second embodiment may also be other embodiments, similar to the first embodiment. In addition, Figure 2 specifically shows an example in which the reduced substance X1 is carbon dioxide, the components supplied to the raw material storage unit 59 are methanol and sodium bromide, and the target product is DMC, but other components may also be used.

[0108] The electrochemical reaction system 60 according to the second embodiment may further include a second separation device 62 and a third separation device 63. The second separation device 62 may be provided in the middle of the fourth discharge line 45 to separate a portion of the cathode liquid flowing into the fourth discharge line 45. The third separation device 63 may be provided in the middle of the fifth discharge line 55 to separate a portion of the cathode liquid flowing into the fifth discharge line 55. This makes it possible to remove excess components contained in the cathode liquid and anode liquid, making it easier to perform continuous operation appropriately. Here, the second separation device 62 may be a distillation device. The third separation device 63 may also be a distillation device.

[0109] More specifically, it is preferable that the second separation device 62 removes a portion of the water contained in the cathode solution and supplies it to the electrolyte mixing device 40. In the reduction reaction of carbon dioxide to carbon monoxide, water may be produced as a byproduct, as shown in equation (i) above. In this case, removing the water in the second separation device 62 removes the excess water, preventing an excess of water in the electrochemical reaction system. Also, as described above, since the water is returned to the anode side via the reuse supply line 46, the water circulates between the electrochemical device 11 and the electrolyte mixing device 40. By removing the water in the second separation device 62, the water circulation can be carried out while maintaining a constant amount of water, making continuous operation possible indefinitely.

[0110] Furthermore, the third separation device 63 may remove a portion of the organic solvent contained in the anode solution and supply the anode solution from which a portion of the organic solvent has been removed to the electrolyte mixing device 40. The anode solution typically contains a reaction substrate, and the organic solvent to be removed may be the reaction substrate. By removing the reaction substrate, the content of the target product (carbonyl compound) in the second solvent extracted from the separation device 42, which will be described later, can be increased, so that the target product can be produced more industrially advantageously. Note that the reaction substrate to be removed may be all of the reaction substrate contained in the anode solution, or it may be only a portion of the reaction substrate. The removed reaction substrate may be supplied to the raw material storage unit 59 via the reuse line 64, so that the reaction substrate separated and recovered in the third separation device 63 is returned to the anode side again.

[0111] In this embodiment, the purge line 49 is branched into an discharge line 49A that is released into the atmosphere and outside the system 10, and a return line 49B that is returned to the cathode side. The gaseous components purged from the anode side can be released into the atmosphere or returned to the cathode side as appropriate. More specifically, carbon monoxide is supplied to the circulation path on the anode side from the third discharge line 35, and the carbon monoxide is converted into a carbonyl compound in the reaction section 41, but some of it is discharged from the purge line 49 without reacting. Therefore, by returning the discharged carbon monoxide to the reduced material supply line 17 (i.e., the cathode side) via the return line 49B, the carbon monoxide can be reused, and the reaction can proceed more efficiently. However, the return line 49B may be connected to a line other than the reduced material supply line 17, as long as it is connected to the circulation path on the cathode side.

[0112] Furthermore, the gaseous components discharged from the purge line 49 contain by-products such as hydrogen in addition to carbon monoxide. If the gaseous components discharged from the purge line 49 are returned to the cathode side as described above without being purged from the system 10, by-products will accumulate. Therefore, to prevent the accumulation of by-products, it is preferable to release a portion of the gaseous components discharged from the purge line 49 to the outside of the system 10 through the discharge line 49A. Note that whether the gaseous components flow to the return line 49B or the discharge line 49A can be adjusted as appropriate by, for example, by providing a valve. Alternatively, both the return line 49B and the discharge line 49A may be left open at a certain degree, and the gaseous components of the purge line 49 may flow to both the return line 49B and the discharge line 49A. It is also preferable to provide a compressor 49C in the middle of the return line 49B, and the gaseous components of the return line 49B should be compressed by the compressor 49C before being returned to the cathode side.

[0113] Furthermore, in this embodiment, a heat exchanger 68 is preferably provided in the third discharge line 35. The gas passing through the third discharge line 35 is preferably cooled by the heat exchanger 68, and the cooled gas, with water vapor contained as an impurity condensed, is preferably returned to the cathode-side storage section 19 (i.e., the cathode-side circulation path) via the return line 69. In addition, the condensed water contains carbon dioxide, and it is preferable that the carbon dioxide is also returned. This makes it possible to increase the purity of carbon monoxide in the gas supplied to the anode side and improve the reaction efficiency on the anode side.

[0114] As described above, in the second embodiment, by providing a second separation device 62, a third separation device 63, and a heat exchanger 68, and by branching the purge line 49, it becomes easier to operate continuously indefinitely and to produce the target product efficiently. It should be noted that it is not necessary to adopt all of the configurations used in the second embodiment, and some of the configurations may be adopted as needed.

[0115] <Third Embodiment> Figure 3 shows an electrochemical reaction system according to the third embodiment. The differences between the electrochemical reaction system 70 according to the third embodiment and the first embodiment will be explained below. In this embodiment, the second discharge line 25 is connected to the reaction section 41, not to the anode-side storage section 29. Also, the second connection line 28 is omitted, and the first connection line 27 connects the anode-side storage section 29 and the reaction section 41. Therefore, the circulation path on the anode side consists of the anode chamber 26, the second discharge line 25, the reaction section 41, and the anode-side storage section 29, and the anode liquid flows in this order and is returned to the anode chamber 26 for circulation. Also, the fifth discharge line 55 is connected to the anode-side storage section 29, and the anode liquid is discharged from the anode-side storage section 29, but in this embodiment as well, the fifth discharge line 55 may be connected to a place other than the anode-side storage section 29.

[0116] In this embodiment as well, on the anode side, the anode solution circulates between the anode chamber 26, the anode side storage section 29, and the reaction section 41, flowing in a constant direction. Therefore, the reduction reaction to oxide Y2 and the reaction in the reaction section 41 can be carried out efficiently. And, as in the first embodiment, the cathode solution and anode solution are mixed in the electrolyte mixing device 40 from the cathode side and the anode side, respectively, so the electrolyte can be recovered efficiently.

[0117] <Other Embodiments> The first to third embodiments described above are examples of embodiments of the present invention, and the present invention can be modified in various ways without departing from the spirit of the invention. For example, although a reaction section 41 was provided in each of the above embodiments, the reaction section 41 may be omitted. In that case, the second catalyst may be contained inside the anode chamber 26, and the reaction to obtain the target compound from the reaction substrate and the reduced product Y1 in the presence of oxide Y2 may be carried out inside the anode chamber 26. In such embodiments, the connection lines 27 and 28 may be omitted, while the second supply line 24 and the second discharge line 25 may be connected to the anode chamber 26 and the anode-side storage section 29, respectively, so that the anode liquid flows in the order of anode chamber 26, second discharge line 25, anode-side storage section 29, second supply line 24, and anode chamber 26, circulating on the anode side.

[0118] Furthermore, the cathode-side storage section 19 and the anode-side storage section 29 may be omitted as appropriate. For example, if the cathode-side storage section 19 is omitted, the first supply line 14 and the first discharge line 15 are directly connected, and the cathode fluid may circulate on the cathode side by flowing in the order of cathode chamber 16, first discharge line 15, first supply line 14, and cathode chamber 16. In this case, the reuse supply line 46, cathode fluid supply line 37, and the third and fourth discharge lines 35 and 45 may be connected to any of the cathode-side circulation paths, for example, they may be connected to the cathode chamber 16. Similarly, if the anode-side storage section 29 is omitted, the connection lines 27 and 28 are omitted, and the second supply line 24 and the second discharge line 25 connect to the reaction section 41 and the anode chamber 26, respectively, so that the anode liquid flows in the order of anode chamber 26, second discharge line 25, reaction section 41, second supply line 24, and anode chamber 26, circulating on the anode side. The anode liquid supply line 47 and the fifth discharge line 55 may be connected to any of the circulation paths, for example, they may be connected to the anode chamber 26.

[0119] Furthermore, on the anode side, the anode storage section 29 and the reaction section 41 may be omitted. In this case, the second supply line 24 and the second discharge line 25 are directly connected, and the anode liquid flows in the order of anode chamber 26, second discharge line 25, second supply line 24, and anode chamber 26, circulating on the anode side. The anode liquid supply line 47 and the fifth discharge line 55 may be connected to any of the circulation paths, for example, they may be connected to the anode chamber 26.

[0120] Furthermore, on the cathode side, the cathode liquid does not need to circulate through the circulation path, in which case the cathode side storage section 19, the first supply line 14, and the first discharge line 15 may be omitted. Then, the reuse supply line 46, the cathode liquid supply line 37, and the third and fourth discharge lines 35 and 45 may be connected to the cathode chamber 16. Similarly, on the anode side, the anode liquid does not need to circulate through the circulation path, in which case the anode side storage section 29, the reaction section 41, the second supply line 24, the second discharge line 25, and the connection lines 27 and 28 may be omitted. Then, the anode liquid supply line 47 and the fifth discharge line 55 may be connected to the anode chamber 26.

[0121] While continuous operation is not possible without circulating the cathode solution and anode solution through the circulation path, even without continuous operation, the electrolyte can be efficiently recovered in the same manner as in the embodiments described above by supplying the cathode solution and anode solution from the cathode chamber and anode chamber, respectively, to the electrolyte mixing device 40 and mixing them.

[0122] Furthermore, although the above embodiments specifically described the case where the oxide X2 is a halide salt, other types of oxide X2 can also be used, such as organic redox species like quinone derivatives and anthraquinone derivatives. Inorganic redox species other than halide salts may also be used. Furthermore, organic-inorganic composite redox species, such as metal complexes, may also be used. Moreover, substances other than carbon dioxide can be used as the reduced substance X1, such as water. In that case, hydrogen can be produced by reducing the water.

[0123] Furthermore, the above explanation assumes that the anode solution contains a reaction substrate, but the reaction substrate is not required. If there is no reaction substrate, the reaction between the substance to be reduced X1 and the reaction substrate will not occur. In this case, the substance to be reduced X1 will be reduced to the reducer Y1 on the cathode side, and the substance to be oxided X2 will be oxidized to the oxide Y2 on the anode side. However, the reducer Y1 does not need to be supplied to the anode side, and the reaction section 41 does not need to be provided.

[0124] The present invention will be described in more detail by reference to examples, but the present invention is not limited in any way by these examples.

[0125] (Example 1) [Cathode preparation] 38.0 mg of poly(4-vinylpyridine) (P4VP, weight-average molecular weight 60,000) was dispersed in 50 ml of ethanol to obtain a P4VP dispersion. 20 mM Co(II)(NO ３ ) ２ 1.8 ml of ethanol solution (6.5 mg, Co = 2 mg) and 54 mg of Ketjenbrak ("ECP600JD", manufactured by Lion Specialty Chemicals Co., Ltd.) were mixed in a P4VP dispersion and dried to obtain a powder (first catalyst raw material mixture). The cobalt content in the first catalyst raw material mixture was 2% by mass. The obtained powder was calcined at 300°C for 3 hours under an argon atmosphere to obtain the first catalyst (carbon dioxide reduction catalyst). 10 μl of a dispersion of 2 mg of the first catalyst and 30% by mass of catalyst additive (Nafion) was dispersed in isopropanol and coated onto carbon paper. This was heated and dried at 80°C for 1 hour to obtain a cathode.

[0126] [Preparation of the second catalyst] 140 mg of PdCl ２ Aldrich (manufactured by Aldrich) was dissolved in 50 ml of ammonia aqueous solution (26 wt%, manufactured by Wako). 20 g of alumina (aluminum oxide) was dispersed in the resulting solution as a metal compound, and the solvent was evaporated using an evaporator. The resulting solid was heat-treated at 200°C for 3 hours in an air atmosphere to form a second catalyst (Pd / Al ２ O ３ A catalyst was obtained.

[0127] [Fabrication of Electrochemical Apparatus] In this example, an electrochemical apparatus 11 modeled after the third embodiment was assembled. Specifically, a 10 ml electrochemical cell 12 was divided into a cathode chamber 16 and an anode chamber 26 by a porous membrane (polypropylene, "Cellguard", manufactured by Polypore) as an isolation membrane 31, and the cathode 13 prepared as described above was placed inside the cathode chamber 16. A carbon felt (manufactured by EC Frontier) was placed inside the anode chamber 26 as an anode 23. In addition, two storage bottles were prepared, one for the cathode side storage section 19 and the other for the anode side storage section 29, each containing 100 ml of cathode solution and 100 ml of anode solution, respectively. A magnetic stirrer was placed inside each storage bottle to stir the cathode solution and anode solution, respectively. The cathode solution was a 0.1 M NaBr aqueous solution, and the anode solution was a 0.1 M NaBr methanol solution. In addition, a glass column packed with 10 g of the second catalyst was prepared as reaction section 41.

[0128] In the electrochemical apparatus 11, as shown in Figure 3, the cathode-side storage section 19 and the cathode chamber 16 were connected by a first supply line 14 and a first discharge line 15. The anode chamber 26 and the anode-side storage section 29 were connected by a second supply line 24, the anode-side storage section 29 and the reaction section 41 were connected by a first connection line 27, and the reaction section 41 and the anode chamber 26 were connected by a second discharge line 25. The cathode-side storage section 19 and the second discharge line 25 were connected by a third discharge line 35. Furthermore, a reduced material supply line 17 was connected to the cathode-side storage section 19, and a purge line 49 was connected to the anode-side storage section 29. The fourth and fifth discharge lines 45 and 55 were omitted.

[0129] In the electrochemical apparatus 11 described above, carbon dioxide was supplied from the reduced material supply line 17 to the cathode-side storage section 19 at a rate of 100 sccm. A constant current of 1 A was also passed between the cathode 13 and the anode 23 from the power supply 18, and the electrolytic reaction was carried out continuously for 120 hours. The electrochemical apparatus 11 was placed in a room temperature environment for the experiment. The components of the cathode solution and anode solution obtained by the electrolytic reaction are shown in Table 1. The weight of each component of the cathode solution and anode solution was measured by electronic balance, gas chromatography, and ion chromatography. As shown in Table 1, the cathode solution and anode solution contained sodium hydroxide and hydrogen bromide as electrolytes, respectively.

[0130] [Mixing and Separation of Anode and Cathode Solutions] The anode and cathode solutions obtained as described above were thoroughly mixed using a separatory funnel at room temperature and allowed to stand for 30 minutes, after which they separated into an aqueous phase (first solvent S1) and an organic phase (second solvent S2). The components of the aqueous and organic phases are shown in Table 1. The weight of each component of the aqueous and organic phases was determined by weight measurement of NaBr after the solution dried. All components except NaBr were measured by gas chromatography and ion chromatography. As shown in Table 1, by mixing the anode and cathode solutions, the electrolyte was neutralized to NaBr, and all of it was recovered into the aqueous phase, resulting in efficient electrolyte recovery.

[0131]

[0132] (Example 2) In Example 2, assuming that the solvent constituting the cathode solution is water, the solvent constituting the anode solution is DMC, and the electrolyte is NaBr, the recovery rate of the electrolyte when the cathode solution and anode solution are mixed was determined. In addition, from No. 2 onwards, methanol was further added assuming that the reaction substrate would remain in the electrolyte. In No. 1, 100 ml of water, 100 ml of DMC, and 4.1 g of NaBr (electrolyte) were mixed at room temperature (25°C) with stirring at 300 rpm, and after mixing, the mixture was allowed to stand in a separatory funnel at room temperature for 5 minutes to separate the liquid phases. Then, only the aqueous phase was taken out and dried by vacuum drying using an evaporator, and the weight of the recovered electrolyte (NaBr) and its recovery rate were determined. No. In experiment 2, 95 ml of water, 5 ml of methanol, 100 ml of DMC, and 4.1 g of NaBr (electrolyte) were mixed at room temperature (25°C) with stirring at 300 rpm. After mixing, the mixture was allowed to stand in a separatory funnel at room temperature for 5 minutes to separate the liquid phases. The aqueous phase was then extracted and dried by vacuum drying using an evaporator. The weight of the recovered electrolyte (NaBr) and its recovery rate were determined. Experiments No. 3 to No. 10 were carried out in the same manner as in experiment No. 2, except that the amounts of water, methanol, DMC, electrolyte, and type of electrolyte were changed as shown in Table 2.

[0133] *H in Table 2 ２ The units in the columns for O, MeOH, and DMC are ml.

[0134] As shown in Table 2, the electrolyte could be recovered from the aqueous phase with a high recovery rate even when the electrolyte concentration and the amount of remaining reaction substrate (methanol) fluctuated. Therefore, it can be understood that the electrolyte can be efficiently recovered even when the amount of electrolyte added and the amount of remaining reaction substrate fluctuate, making stable continuous production possible.

[0135] 10, 60, 70 Electrochemical reaction system 11 Electrochemical apparatus 13 Cathode 14 First supply line 15 First discharge line 16 Cathode chamber 17 Reduced material supply line 18 Power supply 19 Cathode-side storage section 23 Anode 24 Second supply line 25 Second discharge line 26 Anode chamber 29 Anode-side storage section 35 Third discharge line 40 Electrolyte mixing device 41 Reaction section 42 Separation device 45 Fourth discharge line 49 Purge line 55 Fifth discharge line 56 Pump S1 First solvent S2 Second solvent X1 Reduced material Y1 Reduced material X2 Oxide Y2 Oxide

Claims

1. An electrochemical reaction system for performing an electrochemical reaction, comprising: an electrochemical apparatus having a cathode chamber having a cathode, a supply line for supplying a cathode solution containing an electrolyte, and a discharge line for discharging the cathode solution; an anode chamber having an anode, a supply line for supplying an anode solution containing an electrolyte, and a discharge line for discharging the anode solution; and an electrolyte mixing apparatus for mixing the cathode solution and the anode solution discharged from the electrochemical apparatus.

2. The electrochemical reaction system according to claim 1, wherein the mixture obtained by mixing the cathode solution and the anode solution contains two or more different solvents.

3. The electrochemical reaction system according to claim 2, wherein two or more different solvents are separated.

4. The electrochemical reaction system according to claim 3, wherein the two or more different solvents are separated by at least one of membrane separation, distillation, and liquid-liquid phase separation.

5. The electrochemical reaction system according to claim 4, wherein the two or more different solvents include two or more solvents capable of liquid-liquid phase separation, and liquid-liquid phase separation is performed.

6. The electrochemical reaction system according to any one of claims 3 to 5, wherein the solvent is separated into at least a first solvent and a second solvent, and the electrolyte is contained in the first solvent at a higher concentration than in the second solvent.

7. The electrochemical reaction system according to claim 6, wherein the first solvent is separated and recovered.

8. The electrochemical reaction system according to claim 1, wherein the cathode solution contains water and the anode solution contains an organic solvent.

9. The electrochemical reaction system according to claim 8, wherein the organic solvent comprises a carbonyl compound.

10. The electrochemical reaction system according to claim 1, wherein a reaction product is further generated from the reduced product produced at the cathode and the reaction substrate contained in the anode solution, in the presence of the oxide produced at the anode.

11. The electrochemical reaction system according to claim 10, further comprising a reaction section for generating the reaction product from the reduced product and the reaction substrate in the presence of the oxide.

12. The electrochemical reaction system according to claim 10 or 11, wherein the reaction substrate is an alcohol compound and the reaction product is a carbonyl compound.

13. The electrochemical reaction system according to claim 10 or 11, wherein the cathode liquid contains carbon dioxide and the reduced product produced in the cathode contains carbon monoxide.

14. An electrochemical reaction method for performing an electrochemical reaction in an electrochemical reaction system comprising an electrochemical apparatus having a cathode chamber having a cathode and an anode chamber having an anode, and an electrolyte mixing device, comprising the steps of: supplying a cathode solution containing an electrolyte to the cathode chamber; generating a reduced product in the cathode; discharging the cathode solution from the cathode chamber; supplying an anode solution containing an electrolyte to the anode chamber; generating an oxide in the anode; discharging the anode solution from the anode chamber; and mixing the cathode solution and the anode solution discharged from the electrochemical apparatus in the electrolyte mixing device.

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