Electrochemical system and method for producing carbonyl compound

Abstract

To provide an electrochemical system capable of increasing a percentage content of a target carbonyl compound in an electrolytic solution.SOLUTION: An electrochemical system 20 comprises; an electrochemical cell 10 including a cathode 11 and an anode 12, wherein a reduction reaction for reducing carbon dioxide to carbon monoxide occurs on a cathode side, and an oxidation reaction occurs on an anode side; a carbon dioxide supply passage 31 for supplying carbon dioxide to the cathode side of the electrochemical cell 10; a circulation path 45 for circulating an electrolytic solution 13Y containing an alcohol-based compound from a region on the anode side of the electrochemical cell 10 to an outside of the region and then back to the region on the anode side; and a carbon monoxide supply passage 28 for supplying a gas G containing carbon monoxide generated on the cathode side to the electrolytic solution in the circulation path 45, thereby generating a carbonyl compound from the carbon monoxide and the alcohol-based compound in the electrolytic solution.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrochemical system for producing a carbonyl compound using carbon dioxide as a raw material, and a method for producing a carbonyl compound. [Background technology]

[0002] Carbon dioxide reduction devices, which generate valuable resources by electrically reducing carbon dioxide, have attracted attention as a method for reducing carbon dioxide emissions and storing natural energy, and research and development is being conducted on them. Carbon dioxide reduction is known to be performed using an electrochemical cell, in which case carbon dioxide is generally reduced on the cathode side. There are also many known methods for oxidizing organic compounds using the anode of an electrochemical cell to obtain new valuable resources.

[0003] In recent years, in order to more efficiently produce valuable resources from carbon dioxide, methods for producing valuable resources from carbon dioxide using both a cathode and an anode have been studied. For example, Patent Document 1 discloses an electrochemical cell including a cathode chamber in which a cathode is provided, an anode chamber in which an anode is provided and which contains a reaction substrate (raw material) such as an alcohol-based compound, an ion transport membrane separating the cathode chamber from the anode chamber, and a connecting path connecting the cathode chamber to the anode chamber. In the electrochemical cell of Patent Document 1, carbon dioxide is reduced to carbon monoxide at the first electrode, and the generated carbon monoxide is discharged into the anode chamber via the connecting path, where valuable resources such as carbonate compounds are produced from the carbon monoxide and a reaction substrate such as methanol.

[0004] Patent Document 2 also discloses an electrochemical system including an electrochemical cell and a reactor separate from the electrochemical cell. The electrochemical system of Patent Document 2 discloses that a carbonate compound produced in an anode chamber is supplied to a reactor, where the carbonate compound is subjected to a dealcoholization reaction to produce a first product, and the released alcohol compound is supplied to the anode side of the electrochemical cell for reuse. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2022 / 025138 [Patent Document 2] International Publication No. 2020 / 067577 Summary of the Invention [Problem to be solved by the invention]

[0006] In electrochemical reactions, the product generated from carbon monoxide is generally in a liquid state, and in practical applications, a process for separating it from the electrolyte is required. Therefore, in order to perform the separation process efficiently, it is necessary to increase the product content in the electrolyte.

[0007] Therefore, an object of the present invention is to increase the content of the carbonyl compound, which is the product, in the electrolyte in a system for producing a carbonyl compound such as an organic carbonate from carbon monoxide by utilizing an electrochemical reaction. [Means for solving the problem]

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

[14] . [1] An electrochemical system for electrochemically synthesizing carbonyl compounds from carbon dioxide, comprising: an electrochemical cell including a cathode and an anode, in which a reduction reaction of reducing carbon dioxide to carbon monoxide occurs on the cathode side and an oxidation reaction occurs on the anode side; a carbon dioxide supply channel for supplying carbon dioxide to the cathode side of the electrochemical cell; a circulation path for circulating an electrolyte solution containing an alcohol-based compound from the anode side region of the electrochemical cell to the outside of the region and then back to the anode side region; a carbon monoxide supply path for supplying a gas containing carbon monoxide generated on the cathode side to the electrolytic solution in the circulation path, and for generating a carbonyl compound from the carbon monoxide and the alcohol-based compound in the electrolytic solution; An electrochemical system comprising: [2] a discharge path for discharging the electrolyte solution containing the carbonyl compound from the circulation path; The electrochemical system according to [1] above, further comprising a switching mechanism capable of switching between discharging the electrolytic solution from the discharge path and circulating the electrolytic solution in the circulation path. [3] A raw material supply path is provided for supplying at least the alcohol-based compound to the circulation path, The electrochemical system according to [2] above, wherein at least the alcohol-based compound is supplied from the raw material supply channel to the circulation channel while the electrolytic solution is discharged from the discharge channel. [4] A purification device is provided which separates and purifies carbonyl compounds from the electrolytic solution, The electrochemical system according to the above [2] or [3], wherein the electrolytic solution discharged from the discharge channel is supplied to the refining device. [5] The electrochemical system according to the above [3] or [4], wherein the alcohol-based compound separated from the electrolytic solution by the purification device is supplied from the raw material supply channel to the circulation path. [6] The carbon dioxide supply channel supplies carbon dioxide contained in an electrolytic solution to the cathode side of the electrochemical cell; The electrochemical system according to any one of the above [1] to [5], further comprising a first gas-liquid separator that separates the electrolytic solution discharged from the cathode side of the electrochemical cell into gas and liquid. [7] A reactor is provided in the circulation path, The electrochemical system according to any one of the above [1] to [6], wherein the reactor contains a carbonyl compound synthesis catalyst that generates a carbonyl compound from the carbon monoxide and the alcohol-based compound. [8] The electrochemical system according to the above [7], wherein the reactor brings the gas containing carbon monoxide into countercurrent contact with the electrolyte solution containing the alcohol-based compound. [9] The circulation path includes a tank in which an electrolyte solution containing the carbonyl compound is stored, The electrochemical system according to any one of the above [1] to [8], wherein the electrolytic solution containing the carbonyl compound is discharged from the tank.

[10] A flow rate adjusting mechanism is provided in the carbon monoxide supply passage, The electrochemical system according to any one of the above [1] to [9], wherein the flow rate control mechanism adjusts the flow rate of the carbon monoxide-containing gas, thereby adjusting the amount of carbon dioxide supplied to the cathode side of the electrochemical cell.

[11] A synthesis system comprising a plurality of synthesis units each including the electrochemical cell, the carbon dioxide supply channel, the circulation channel, the carbon monoxide supply channel, and the discharge channel; each discharge path of the plurality of synthesis units is connected to the purification device, and the electrolyte of the plurality of synthesis units can be supplied to the purification device; The electrochemical system according to any one of the above [2] to

[10] , wherein the switching mechanism supplies the electrolyte of at least one of the electrochemical cells from the discharge path to the refining device, and circulates the electrolyte in at least another of the electrochemical cells.

[12] A plurality of synthesis units each including the electrochemical cell, the carbon dioxide supply channel, the circulation channel, the carbon monoxide supply channel, and the discharge channel; and the electrochemical system comprises a tank;

[12] The electrochemical system according to any one of the above [2] to

[11] , wherein each discharge path of the plurality of synthesis units is connected to the tank, the electrolytic solution of the plurality of synthesis units can be supplied to the tank, and the electrolytic solution can further be supplied from the tank to the purification device.

[13] A discharge path for discharging the electrolytic solution containing the carbonyl compound from the circulation path; a raw material supply path for supplying at least the alcohol-based compound to the circulation path; The electrochemical system according to any one of the above [1] to

[12] , wherein the alcohol-based compound is supplied from the raw material supply unit while the electrolyte solution is discharged from the discharge channel.

[14] A method for producing a carbonyl compound, in which a carbonyl compound is electrochemically synthesized from carbon dioxide using an electrochemical system including an electrochemical cell, comprising: supplying carbon dioxide to a cathode side of the electrochemical cell; reducing carbon dioxide to carbon monoxide at the cathode; causing an oxidation reaction on the anode side of the electrochemical cell; circulating an electrolyte solution containing an alcohol-based compound from an anode-side region of the electrochemical cell to the outside of the electrochemical cell and then back to the anode-side region; supplying the carbon monoxide generated on the cathode side to the electrolytic solution in the circulation path, and generating a carbonyl compound from the carbon monoxide and the alcohol-based compound in the electrolytic solution; A method for producing a carbonyl compound comprising: [Effects of the Invention]

[0009] INDUSTRIAL APPLICABILITY In the present invention, in a system for producing a carbonyl compound such as an organic carbonate from carbon dioxide by utilizing an electrochemical reaction, the content of the target carbonyl compound in the electrolyte can be increased. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing an electrochemical system according to a first embodiment. [Figure 2] FIG. 4 is a schematic diagram showing an electrochemical system according to a second embodiment. [Figure 3] FIG. 10 is a schematic diagram showing an electrochemical system according to a third embodiment. [Figure 4] FIG. 10 is a schematic diagram showing an electrochemical system according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The electrochemical system and the method for producing a carbonyl compound using the electrochemical system of the present invention will be described below with reference to the drawings. In the following description, elements having the same configurations will be designated by the same reference numerals.

[0012] First Embodiment The electrochemical system 20 according to the first embodiment of the present invention is a system (also referred to as an electrochemical reaction device) for electrochemically synthesizing a carbonyl compound. The carbonyl compound generated in the electrochemical system 20 is an organic carbonate, an organic oxalate, or both.

[0013] The electrochemical system 20 includes an electrochemical cell 10 and a reactor 43. The electrochemical cell 10 includes a cathode 11 and an anode 12. The cathode 11 and the anode 12 are disposed inside the electrochemical cell 10. The electrochemical cell 10 includes a separator 25 disposed between the anode 12 and the cathode 11 inside the electrochemical cell 10. The separator 25 divides the interior of the electrochemical cell 10 into an area on the cathode 11 side (cathode chamber 10X) and an area on the anode 12 side (anode chamber 10Y). The anode 12 and the cathode 11 are disposed in contact with the separator 25. The anode 12, the separator 25, and the cathode 11 are stacked in this order to form a laminate. The laminate may be a membrane-electrode assembly in which the anode 12 and the cathode 11 are joined together via, for example, an ion exchange membrane. However, the cathode 11 and the anode 12 are not limited to the above configuration, and may be disposed in positions away from the separator 25 in the cathode chamber 10X and the anode chamber 10Y, as long as they are in contact with the electrolytic solutions 13X and 13Y, respectively, which will be described later.

[0014] In this embodiment, the cathode chamber 10X contains a first catalyst that reduces carbon dioxide to carbon monoxide. The first catalyst may be contained in the cathode 11. A voltage is applied between the anode 12 and the cathode 11 by a power supply 19, which causes a reduction reaction in the cathode chamber 10 to reduce carbon dioxide to carbon monoxide. In addition, an oxidation reaction, which will be described later, occurs in the anode chamber 10Y. The electrochemical cell 10 is provided with first and second supply ports 16X and 16Y as supply ports to the electrochemical cell 10, and first and second discharge ports 17X and 17Y as discharge ports. The first supply port 16X and the first discharge port 17X are provided in the cathode chamber 10X. The second supply port 16Y and the second discharge port 17Y are provided in the anode chamber 10Y.

[0015] The electrochemical system 20 further includes a mixer 34, a first gas-liquid separator 30, and a carbon dioxide supply channel 31. In this embodiment, at least the cathode chamber 10X is filled with the electrolytic solution 13X. The mixer 34 and the gas-liquid separator 30 also contain the electrolytic solution 13X. On the cathode side, the electrolytic solution 13X is sent sequentially through the cathode chamber 10X, the first gas-liquid separator 30, and the mixer 34, and is returned from the mixer 34 to the cathode chamber 10X. That is, on the cathode side, a circulation path (hereinafter sometimes referred to as the "first circulation path") 35 including the cathode chamber 10X is formed, and the electrolytic solution 13X is circulated through the first circulation path 35 so as to be discharged to the outside of the cathode chamber 10X and then returned to the cathode chamber 10X. The outlet 17X of the cathode chamber 10X and the first gas-liquid separator 30, and the first gas-liquid separator 30 and the mixer 34 are connected via connection paths 32A and 32B, respectively, and a first circulation path 35 is formed by the connection paths 32A and 32B and the carbon dioxide supply path 31 (the second supply path 31B described later).

[0016] The carbon dioxide supply path 31 is a supply path that supplies carbon dioxide from a carbon dioxide supply source (not shown) to the cathode chamber 10X. The carbon dioxide supply path 31 is made up of a first supply path 31A that connects the carbon dioxide supply source to the mixer 34, and a second supply path 31B that connects the mixer 34 to the first supply port 16X of the cathode chamber 10X. Carbon dioxide supplied from a carbon dioxide supply source is supplied to mixer 34 via first supply path 31A and mixed with electrolytic solution 13X in mixer 34. Electrolytic solution 13X containing carbon dioxide obtained by mixing is supplied to cathode chamber 10X via second supply path 31B. Mixer 34 is not particularly limited, and may be composed of a tank or may have a stirring device such as a stirring blade. The connection paths, supply paths, and discharge paths described below are not particularly limited, but may be configured by piping or the like.

[0017] Carbon dioxide may be supplied alone from a carbon dioxide supply source, or may be supplied together with other gases, such as an inert gas such as argon or nitrogen, or oxygen gas. The carbon dioxide supply source is not particularly limited, and may be a gas cylinder or the like. Carbon dioxide may also be obtained from exhaust gas emitted from any of the following facilities: a power plant, a steel mill, a cement factory, and a waste incineration plant, and any of these facilities may serve as the carbon dioxide supply source. These facilities generate large amounts of exhaust gas, which generally contains a large amount of carbon dioxide. Therefore, the exhaust gas generated in each of these facilities may be supplied to the electrochemical cell 20.

[0018] Carbon dioxide-containing electrolytic solution 13X is supplied to cathode chamber 10X, where the carbon dioxide is reduced to carbon monoxide. Carbon dioxide is supplied in a state where at least a portion of it is dissolved in electrolytic solution 13X, and a reduction reaction occurs in the liquid phase in cathode chamber 10X. The electrochemical reaction that occurs in cathode 11 is typically as shown in formula (A) below. CO2+2H + +2e - →CO+H2O (A)

[0019] The carbon monoxide produced in the cathode chamber 10X is supplied together with the electrolytic solution 13X to the first gas-liquid separator 30. In the first gas-liquid separator 30, the electrolytic solution 13X is separated into gas and liquid, and the carbon monoxide-containing gas G is separated from the electrolytic solution X and supplied to an anode-side circulation path (hereinafter, sometimes referred to as a "second circulation path") 45, which will be described later, via a carbon monoxide supply path 28. The carbon monoxide supply path 28 is a connection path that connects the first circulation path 35 on the cathode side with the second circulation path 45 on the anode side. The carbon monoxide supply path 28 supplies gas G containing carbon monoxide to the electrolytic solution 13Y in the second circulation path 45, causing a reaction in the electrolytic solution 13Y that produces a carbonyl compound, which will be described later. The gas G supplied to the second circulation path 45 on the anode side may consist of carbon monoxide alone, but typically also contains unreacted carbon dioxide and impurities other than carbon monoxide and carbon dioxide. Examples of impurities include hydrogen gas by-produced in the cathode chamber 10X and gas components contained in the gas when it was supplied from the carbon dioxide supply source.

[0020] The first gas-liquid separator 30 and the second gas-liquid separator 40 (described later) are not particularly limited as long as they can separate gas and liquid. For example, they may be devices that separate gas and liquid by extracting gas from the top of a container and extracting liquid from the bottom of a container. The first gas-liquid separator 30 may also separate two gaseous components at room temperature and normal pressure by changing the temperature, pressure, or both to convert one into a liquid and then separating the components. For example, the temperature of a carbon dioxide / carbon monoxide mixed gas may be lowered to liquefy carbon dioxide for separation. This increases the carbon monoxide concentration in the carbon dioxide and carbon dioxide mixed gas, thereby improving the reaction yield in the reactor 43. Two liquid components at room temperature and normal pressure can also be separated in the gas-liquid separator 30. For example, the temperature of a water / alcohol-based compound may be increased to gasify and separate the alcohol-based compound. This is effective when water is contained as an impurity, and the alcohol-based compound as the electrolyte may be supplied to the anode side together with carbon monoxide. Alternatively, the alcohol-based compound may be circulated on the cathode side without being supplied to the anode side. Similarly, the second gas-liquid separator 40 may be used to separate two components that are gaseous at room temperature and normal pressure or two components that are liquid at room temperature and normal pressure, as appropriate. The first gas-liquid separator 30 and the second gas-liquid separator 40 may be of the same type, or may be of different types. The electrolytic solution 13X separated from the gas G in the first gas-liquid separator 30 is returned to the mixer 34. Note that the first gas-liquid separator 30 does not need to completely separate the gas from the electrolytic solution 13X, and the electrolytic solution 13X separated in the gas-liquid separator 30 and returned to the mixer 34 may contain carbon dioxide or carbon monoxide. The same applies to the second gas-liquid separator 40 described below.

[0021] The electrolytic solution 13X may be circulated through the first circulation path 35 by a pump such as, but not limited to, a diaphragm pump, a syringe pump, or a peristaltic pump in the order of the mixer 34, the cathode chamber 10X, and the gas-liquid separator 30. However, the electrolytic solution 13X may be caused to flow by known means other than a pump, and may be circulated by forming convection using, for example, gravity. The electrolytic solution 13Y on the anode side, which will be described later, may also be circulated through the second circulation path 45 by a pump or by means other than a pump.

[0022] In this embodiment, the region upstream of the carbon monoxide supply channel 28 (i.e., the first circulation path 35, the inside of the cathode chamber 10X, the inside of the mixer 34, the inside of the gas-liquid separator 30, etc.) may be adjusted to a pressurized state, for example, to a pressure of 0.2 MPa or more and 2 MPa or less, preferably 0.4 MPa or more and less than 1 MPa, and more preferably 0.6 MPa or more and 0.9 MPa or less. Note that in this specification, pressure is absolute pressure. When the pressure in the upstream region of the carbon monoxide supply channel 28 becomes high as described above, gases such as carbon dioxide and carbon monoxide are more likely to dissolve in the electrolytic solution 13X. As a result, the amount of carbon dioxide dissolved in the electrolytic solution 13X increases, which makes it easier to improve the efficiency of reducing carbon dioxide to carbon monoxide in the cathode chamber 10X.

[0023] The carbon monoxide supply channel 28 may be provided with a control valve (flow rate adjustment mechanism) 51 that adjusts the flow rate of gas G in the carbon monoxide supply channel 28. The control valve 51 may adjust the flow rate of gas G in the carbon monoxide supply channel 28 in accordance with the flow rate of gas in the carbon dioxide supply channel 31 (first supply channel 31A). In this way, by adjusting the flow rate of gas G in the carbon monoxide supply channel 28, the amount of carbon dioxide supplied from the carbon dioxide supply channel 31 to the cathode chamber 10X can be adjusted. Specifically, if the flow rate of carbon dioxide in the carbon dioxide supply channel 31 is smaller than the set value, the flow rate of gas G in the carbon monoxide supply channel 28 can be increased, thereby increasing the amount of carbon dioxide supplied to the cathode chamber 10X. On the other hand, if the flow rate of carbon dioxide in the carbon dioxide supply channel 31 is larger than the set value, the flow rate of gas G in the carbon monoxide supply channel 28 can be decreased, thereby decreasing the amount of carbon dioxide supplied to the cathode chamber 10X. The control valve 51 is connected to a control unit (not shown) and may be controlled by the control unit according to the flow rate of carbon dioxide in the carbon dioxide supply channel 31, or may be adjusted manually. The control unit can be a known control device, and may be a personal computer or the like, or may be configured by a known control circuit or the like. Furthermore, the control valves 52 and 53 and the on-off valves 62, 63 and 64, which will be described later, may also be connected to the control unit and controlled by the control unit, or may be adjusted manually.

[0024] The above-mentioned set values ​​may be appropriately set so as to optimize the efficiency of carbon monoxide production at the cathode 11 and the efficiency of carbonyl compounds production at the anode side. In this embodiment, the flow rate is adjusted by the control valve 51, and the production efficiency is optimized, thereby enabling more efficient production of carbonyl compounds. Furthermore, in this embodiment, the control valve 51 is provided in the carbon monoxide supply passage 28, which makes it easier to increase the pressure in the upstream region thereof (i.e., the first circulation passage 35, the inside of the cathode chamber 10X, etc.). This increases the amount of carbon dioxide dissolved in the electrolytic solution 13X on the cathode side, making it easier to further improve the efficiency of reducing carbon dioxide to carbon monoxide in the cathode chamber 10X.

[0025] The electrochemical system 20 further includes a second gas-liquid separator 40, a reaction chamber 43, and a tank 44. In the electrochemical system 20, the anode chamber 10Y and the reaction chamber 43 are filled with an electrolytic solution 13Y. In the reaction chamber 43, the electrolytic solution 13Y serves as a reaction liquid for producing a carbonyl compound.

[0026] In the electrochemical system 20, the pressure in the region downstream of the carbon monoxide supply channel 28 (i.e., the second circulation path 45, the anode chamber 10Y, the reactor 43, the second gas-liquid separator 40, and the inside of the tank 44) may be lower than the pressure in the region upstream of the carbon monoxide supply channel 28. The pressure in the region downstream of the connection part 28 is not particularly limited, but may be atmospheric pressure or a slight increase in pressure, and is not particularly limited, but may be, for example, about 0.1 MPa to 0.5 MPa, or 0.15 MPa to 0.3 MPa. Lowering the pressure in the region downstream of the connection part 28 facilitates improving workability. In addition, gas is less likely to dissolve in the electrolytic solution 13Y, facilitating gas-liquid separation in the second gas-liquid separator 40, and facilitating the discharge of gas from the gas discharge channel 48, which will be described later. The operating temperature of the electrochemical system 20 is not particularly limited, but is preferably around room temperature. Therefore, the temperatures inside the anode chamber 10Y, the cathode chamber 10X, the reactor 43, etc. are not particularly limited, but are preferably around room temperature, for example, about 0 to 60°C, and preferably about 10 to 40°C.

[0027] On the anode side, the electrolytic solution 13Y is sent in this order through the anode chamber 10Y, the second gas-liquid separator 40, the reactor 43, and the tank 44, and is returned from the tank 44 to the anode chamber 10Y again. That is, on the anode side, a second circulation path 45 including the anode chamber 10Y is formed, and the electrolytic solution 13Y is circulated through the second circulation path 45 so as to be discharged to the outside of the anode chamber 10Y and then returned to the anode chamber 10Y. The outlet 17Y of the anode chamber 10Y and the second gas-liquid separator 40, the second gas-liquid separator 40 and the reaction chamber 43, the reaction chamber 43 and the tank 44, and the tank 44 and the anode chamber 10Y are connected via connection paths 29A, 29B, 29C, and 29D, respectively, and a second circulation path 45 is formed by these connection paths 29A to 29D.

[0028] The electrolyte solution 13Y contains a reaction substrate and a redox species. The electrolyte solution 13Y may also contain a solvent in addition to the reaction substrate and the redox species. At the anode 12, the redox species formed by the electrolyte are converted from reduced species to oxidized species (e.g., a redox mediator). When the electrolyte (redox species) is a brominated salt, the reaction occurring at the anode 12 is as shown in the following formula (B), producing bromine as an oxidized species. 2Br - → Br2+2e - (B)

[0029] The oxidant produced at the anode 12 may be a liquid, and is supplied together with the electrolytic solution 13Y to the reactor 43 via the second gas-liquid separator 40. On the other hand, the carbon monoxide-containing gas G supplied from the cathode side is supplied to a tank 44 constituting a second circulation path 45, and is supplied from the tank 44 to the reactor 43.

[0030] The tank 44 is not particularly limited as long as it can store a certain amount or more of the electrolytic solution 13Y. The tank 44 is a reaction chamber downstream tank provided downstream of the reactor 43. The tank 44 is typically provided with outlets at the top and bottom, and the gas G supplied from the cathode side is preferably discharged from the outlet at the top and supplied to the reactor 43. On the other hand, as will be described later, the electrolytic solution 13Y supplied from the reactor 43 to the tank 44 is preferably discharged from the bottom of the tank 44 and supplied to the anode chamber 10Y. In other words, the tank 44 is supplied with both the liquid (electrolytic solution 13Y) and the gas (gas G), but the liquid (electrolytic solution 13Y) and the gas (gas G) are discharged from separate outlets, and therefore the tank 44 preferably functions as a gas-liquid separator. Tank 44 is provided with a supply port connected to carbon monoxide supply channel 28. The height position of this supply port is not particularly limited, but may be, for example, between the upper and lower outlets. Furthermore, tank 44 is provided at its upper part with a supply port that is connected to reactor 43 via connection channel 29C and through which electrolytic solution 13Y is supplied from reactor 43. The upper supply port may be common to the upper outlet described above, or may be provided separately.

[0031] The reactor 43 is a countercurrent contact reactor having an electrolytic solution supply port and a gas outlet at the top and an electrolytic solution outlet and a gas supply port at the bottom. The electrolytic solution supply port and the gas outlet may be a common port or may be provided separately. Similarly, the electrolytic solution outlet and the gas supply port may be a common port or may be provided separately.

[0032] The reactor 43 contains a carbonyl compound synthesis catalyst (second catalyst) that produces a carbonyl compound from carbon monoxide and an alcohol-based compound. In the reactor 43, the electrolytic solution 13Y supplied from the top flows downward due to gravity, while the gas G supplied from the bottom of the reactor 43 rises within the reactor 43 due to the difference in specific gravity between the gas G and the electrolytic solution 13Y, resulting in countercurrent contact between the gas G and the electrolytic solution 13Y within the reactor 43. The countercurrent contact between the gas G and the electrolytic solution 13Y in the presence of the second catalyst produces a carbonyl compound from carbon monoxide, an oxidant (redox species), and an alcohol-based compound. As described above, the carbonyl compound is at least one of an organic carbonate and an organic oxalate, with organic carbonate being preferred.

[0033] Although not particularly limited, an example of a reaction in which the reaction substrate is methanol and the electrolyte (redox species) is a bromide salt is shown in the following formula (C). When the reaction substrate is methanol and the redox species is a bromide salt, carbon monoxide and methanol react in reactor 43 to produce dimethyl carbonate (DMC). Bromine is also reduced to bromide ions, producing, for example, hydrogen bromide. CO+Br2+CH3OH → DMC+2HBr (C)

[0034] The carbonyl compounds produced in the reactor 43 are discharged from the bottom of the reactor 43 together with the electrolytic solution 13Y, sent to the tank 44, temporarily stored in the tank 44, and then returned to the anode chamber 10Y together with the electrolytic solution 13Y. In this way, the electrolytic solution 13Y is circulated through the second circulation path 45, while the carbonyl compounds are produced.

[0035] Meanwhile, gas G, which has been in countercurrent contact with the electrolytic solution 13Y in the reactor 43, is discharged from the top of the reactor 43 to the second gas-liquid separator 40. The second gas-liquid separator 40 is supplied with the electrolytic solution 13Y from the anode chamber 10Y and the gas G from the reactor 43, and the gas G and the electrolytic solution 13Y are mixed in the second gas-liquid separator 40. The mixture is separated into gas and liquid in the second gas-liquid separator 40, and the separated gas is discharged to the outside of the electrochemical system 20 through the gas discharge channel 48. The gas discharged to the outside typically contains unreacted carbon monoxide and carbon dioxide, but may also contain hydrogen and other gases in addition to carbon monoxide and carbon dioxide. The separated liquid (electrolytic solution 13Y) is supplied to the reactor 43 as described above.

[0036] In this embodiment, a raw material supply path 42 is provided which is connected to the supply port 16Y of the anode chamber 10Y. The raw material supply path 42 is a supply path for supplying raw materials (alcohol-based compounds), solvents, redox species, etc. contained in the electrolytic solution. The raw material supply path 42 is provided with an open / close valve 64 and a control valve 53, which adjust whether or not the raw material is supplied from the raw material supply path 42 to the anode chamber 10Y (i.e., the second circulation path 45) and the amount of raw material supplied.

[0037] Furthermore, connection path 29D connecting tank 44 and anode chamber 10Y branches off to provide discharge path 27. Opening and closing valves 62 and 63 are provided in discharge path 27 and connection path 29D, respectively. Furthermore, discharge path 27 may be further provided with control valve 52. By providing control valve 52, the flow rate of electrolytic solution 13Y discharged from discharge path 27 can be adjusted.

[0038] In this embodiment, as described above, carbonyl compounds are generated by circulating the electrolytic solution 13Y through the second circulation path 45. The electrolytic solution 13Y containing the generated carbonyl compounds is discharged from the second circulation path 45 via the discharge path 27. In this embodiment, the circulation of the electrolytic solution 13Y through the second circulation path 45 and the discharge of the electrolytic solution 13Y from the discharge path 27 are switched by open / close valves 62 and 63 (collectively referred to as a "switching mechanism"). That is, by opening the on-off valve 63 and closing the on-off valve 62, the circulation of the electrolytic solution 13Y in the second circulation path 45 continues, and the production of carbonyl compounds also continues. On the other hand, by closing the on-off valve 63 and opening the on-off valve 62, the circulation of the electrolytic solution 13Y can be stopped, and the electrolytic solution 13Y can be discharged from the discharge path 27. Here, the electrolytic solution 13Y discharged from the discharge channel 27 is not particularly limited as long as it contains a carbonyl compound, but typically contains unreacted alcohol-based compounds, by-products, redox species, and the like.

[0039] Furthermore, the amount of electrolytic solution 13Y discharged from discharge path 27 is not particularly limited, but may be an amount determined by the capacities of tank 44, reaction chamber 43, second gas-liquid separator 40, and the piping therebetween; for example, an amount of electrolytic solution 13Y approximately equal to the capacity of tank 44 may be discharged. Since the electrolytic solution 13Y stored in tank 44 has been reacted in reactor 43, it is often in a state where conversion to carbonyl compounds has progressed relatively far. Therefore, by discharging a certain amount of electrolytic solution 13Y stored in tank 44 from discharge path 27, it is possible to discharge electrolytic solution 13Y having a relatively high content of carbonyl compounds.

[0040] Furthermore, in this embodiment, the on-off valve 64 of the raw material supply path 42 may be closed while the on-off valve 63 is opened and the discharge valve 62 is closed, and while the electrolytic solution 13Y is circulating in the second circulation path 45. In other words, while the electrolytic solution 13Y is circulating in the second circulation path 45, raw materials such as alcohol-based compounds do not need to be supplied from the raw material supply path 42. Meanwhile, while the on-off valve 63 is closed and the discharge valve 62 is open, and the electrolytic solution 13Y is discharged from the discharge channel 27, the on-off valve 64 of the raw material supply channel 42 is opened, and the raw material is supplied from the raw material supply channel 42 to the second circulation path 45 (i.e., the anode chamber 10Y). Here, the supplied raw material only needs to contain at least an alcohol-based compound, but redox species are also discharged from the discharge channel 27 together with the carbonyl compound, and if a solvent is used, the solvent is also discharged. Therefore, the supplied raw material preferably contains redox species in addition to the alcohol-based compound, and may also contain a solvent as appropriate.

[0041] In this embodiment, the electrolytic solution containing the carbonyl compound discharged from the discharge channel 27 may be supplied to the purification device 50. The purification device 50 is a device that separates and purifies the carbonyl compound (target product) from the electrolytic solution. The electrolytic solution 13X discharged from the discharge channel 27 usually contains, in addition to the carbonyl compound, unreacted alcohol compounds, by-products, redox species (e.g., oxidized forms of redox species), solvents, and the like. However, by separating and purifying the carbonyl compound from these, a carbonyl compound with a higher purity can be obtained. In the electrochemical system 20, the units other than the purification device 50 (i.e., the units that produce carbonyl compounds from carbon dioxide and raw materials and discharge the produced carbonyl compounds from the discharge path 27) may be referred to as synthesis units 54.

[0042] The purification apparatus 50 is not particularly limited as long as it is an apparatus capable of separating the carbonyl compound from other substances, but is preferably a distillation apparatus. Use of a distillation apparatus facilitates obtaining a highly pure carbonyl compound. Furthermore, as described below, a bromide salt is preferred as the redox species. In this case, bromine is often contained as an impurity. However, use of a distillation apparatus makes it possible to easily separate the carbonyl compound from bromine and the alcohol compound serving as the reaction substrate. The distillation apparatus is not particularly limited, and a known distillation column or the like may be used. However, when bromine is contained as an impurity, a highly corrosion-resistant glass distillation column or the like may be used. Furthermore, the raw material alcohol-based compound may be separated from other substances such as carbonyl compounds in the purification apparatus 50. For example, if the purification apparatus 50 is a distillation apparatus, the product carbonyl compound and the raw material alcohol-based compound may be fractionally distilled to obtain a purified carbonyl compound and a purified alcohol-based compound, respectively.

[0043] The alcohol-based compound separated in the purification device 50 may be reused in the electrochemical system 10, and may be supplied to the second circulation path 45 via the raw material supply path 42, for example. The means for supplying the alcohol-based compound from the purification device 50 to the raw material supply path 42 is not particularly limited, and may be a connection path (not shown) connecting the raw material supply path 42 and the purification device 50, or the alcohol-based compound once extracted from the purification device 50 may be transported by known means and then supplied from the raw material supply path 42.

[0044] As described above, in this embodiment, by circulating the electrolytic solution 13Y through the second circulation path 45 including the anode chamber 10Y, the content of carbonyl compounds in the electrolytic solution 13Y can be made relatively high. This can therefore improve, for example, the energy efficiency in the subsequent purification process. Furthermore, in this embodiment, the electrolytic solution 13Y is circulated for a certain period of time, and when the amount of carbonyl compounds produced reaches a certain level, the switching mechanism switches from circulation to discharge, so that the electrolytic solution 13Y with a relatively high content of carbonyl compounds can be easily discharged from the second circulation path 45.

[0045] Furthermore, in this embodiment, while the electrolytic solution 13Y is being discharged from the second circulation path 45, a raw material containing an alcohol-based compound is supplied to the second circulation path 45 (anode chamber 10Y) from the raw material supply path 42. Therefore, even while the electrolytic solution 13Y is being discharged, the anode chamber 10Y continues to be filled with the electrolytic solution 13Y, and the operation of the electrochemical cell 10 (i.e., application of voltage to the power source 19) can be continued, facilitating continuous operation. The circulation of the electrolytic solution 13Y and the discharge of the electrolytic solution 13Y may be repeated alternately, which allows continuous operation over a long period of time.

[0046] Each component used in the electrochemical system will now be described in detail. [Cathode] (First catalyst) As described above, the cathode 11 preferably contains the first catalyst. The first catalyst may be supported on the electrode substrate that constitutes the cathode 11. The first catalyst is a reduction catalyst capable of reducing carbon dioxide to a reduced product such as carbon monoxide. The first catalyst is not particularly limited as long as it is a catalyst capable of reducing carbon dioxide to a reduced product such as carbon monoxide, but may contain, for example, a metal element. The metal element may be the metal itself or a metal compound. The metal element in the above metal is not particularly limited, but examples thereof 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. As the metal compound, inorganic metal compounds and organic metal compounds of these metals can be used, and specific examples thereof include metal halides, metal oxides, metal hydroxides, metal nitrates, metal sulfates, metal acetates, metal phosphates, metal carbonyls, and metal acetylacetonates.

[0047] The metal element used in the first catalyst is preferably a metal element of Groups 7 to 12. Specific preferred examples include Mn, Fe, Ni, Ru, Co, Rh, Cu, Zn, Ag, Au, Pd, Ir, Pt, and Os. The use of these metal elements facilitates increasing the efficiency of carbon dioxide conversion to carbon monoxide, and enhances catalytic activity. The metals used in the metal derivative may be used alone or in combination of two or more.

[0048] The first catalyst may contain a carbon compound in addition to the metal or metal compound. The carbon compound is preferably a conductive carbon compound. More specifically, examples of the carbon compound include mesoporous carbon, activated carbon, carbon black such as ketjen black and acetylene black, graphite, carbon fiber, graphene, and carbon nanotubes. Of these, carbon black is preferred, and conductive carbon black is even more preferred. The carbon compound is preferably a metal compound. When the first catalyst contains a carbon compound, the metal or metal compound may be supported on the carbon compound. The carbon compound may be mixed with a complex containing the metal element and heat-treated to form a catalyst powder. The first catalyst in which the metal or metal compound is supported on the carbon compound may be further supported on an electrode substrate.

[0049] The first catalyst may also be a catalyst containing a nitrogen element and a metal element (nitrogen-containing metal catalyst). Here, the nitrogen element used in the nitrogen-containing metal catalyst may be derived from a nitrogen-containing compound such as a pyridine derivative, an imidazole derivative, a pyrazole derivative, or a triazole derivative. Specific examples of the metal element used in the nitrogen-containing metal catalyst are as described above, and the preferred metal elements are also as described above. The use of a nitrogen-containing metal catalyst increases the efficiency of carbon monoxide production, thereby increasing the selectivity of the synthesized carbonyl compound.

[0050] The nitrogen-containing metal catalyst is preferably a catalyst obtained by heat-treating a mixture containing a metal derivative and a nitrogen-containing compound, and more preferably a catalyst obtained by heat-treating a first catalyst raw material mixture containing a metal derivative, a nitrogen-containing compound, and a carbon compound. The heat treatment is typically calcination. The nitrogen-containing metal catalyst is preferably produced by heat-treating the first catalyst raw material mixture, so that metal-nitrogen element bonds derived from the metal derivative and the nitrogen-containing compound are formed in the catalyst. Furthermore, the carbon compound functions as a support in the catalyst, and components derived from the metal derivative and the nitrogen-containing compound are supported on the carbon compound. The nitrogen-containing metal catalyst having the above configuration efficiently reduces carbon dioxide to carbon monoxide, resulting in high conversion efficiency. The metal element in the metal derivative is as described above. The metal derivative preferably contains a metal ion. The metal derivative may be used in the form of, for example, a metal salt. Examples of the metal salt include metal nitrates, metal sulfates, metal chlorides, metal bromides, metal iodides, and metal acetates. Among these, metal nitrates are preferred.

[0051] In addition to the above, the first catalyst may be a carbon compound containing at least one of a heteroatom such as nitrogen, 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.

[0052] The first catalyst may be supported on the electrode substrate together with a catalyst additive or the like. The catalyst additive also functions as a binder when supporting the catalyst on the electrode substrate. It also functions as an ion conductor, improving the efficiency of the electrochemical reaction. The catalyst additive may be, for example, in the form of a powder or particles. Examples of the catalyst additive include cation-conductive compounds, anion-conductive compounds, and fluorine compounds other than cation-conductive compounds and anion-conductive compounds.

[0053] The method for supporting the first catalyst on the electrode substrate is not particularly limited, but examples thereof include a method in which a diluted solution prepared by diluting the first catalyst and components other than the catalyst, such as a catalyst additive that is added as needed, with a dilution solvent is applied to the electrode substrate using various coating devices or by spray coating, and then dried; and a method in which the electrode substrate is immersed in the diluted solution and then dried.

[0054] (electrode base material) The electrode substrate is not particularly limited, but examples thereof include a carbon substrate, a metal substrate, and a metal oxide substrate, and preferably has electrical conductivity. The substrate may also be porous. The substrate is a substrate that constitutes an electrode, and may be, for example, in the form of a sheet or plate. Of the above, carbon substrates are preferred, and porous carbon is more preferred. Specific examples of porous carbon include 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 "TORAYCA" (registered trademark) carbon paper manufactured by Toray Industries, Inc., "AvCarb 1071HCB" manufactured by New Metal and Chemicals, and the BC series manufactured by SGL. The metal substrate may be a metal mesh, and metals used may include gold, silver, platinum, nickel, titanium, chromium, etc. The metal oxide used in the metal oxide substrate may include indium oxide, tin oxide, tin-doped indium oxide, fluorine-doped tin oxide, etc.

[0055] [anode] The anode 12 may be made of, for example, an electrode substrate. Details of the electrode substrate are as described above, and a carbon substrate is preferred, and porous carbon is more preferred. In the anode chamber 10Y, the anode 12 oxidizes the redox species as described above to generate an oxidant (e.g., a redox mediator such as a halogen) that is an active intermediate species. In the anode chamber 10Y, the anode 12 is preferably disposed in a position where it contacts the electrolyte solution 13 filled in the anode chamber 10Y. Note that the electrochemical cell 10 (e.g., the anode chamber 11) may be provided with a reference electrode or the like.

[0056] Here, it is preferable that the anode 12 does not contain a catalyst. To incorporate a catalyst into the anode 12, a process is required in which a catalyst-containing coating solution is applied to an electrode substrate or the electrode substrate is immersed in a catalyst-containing immersion solution, thereby supporting the catalyst on the electrode. However, if the anode does not contain a catalyst, these processes are unnecessary. Therefore, a carbonyl compound can be synthesized with a simple configuration. Furthermore, the anode 12 can generate an oxidant even if it does not contain a catalyst.

[0057] The catalyst not contained in the anode 12 is a carbonyl compound synthesis catalyst such as the second catalyst that promotes an electrochemical reaction that synthesizes an organic carbonate, an organic oxalate, or both from carbon monoxide. Therefore, it is preferable that the anode 12 not support a carbonyl compound synthesis catalyst such as the first catalyst. However, for example, as in a fourth embodiment described later, when the anode 12 comes into contact with an electrolytic solution (catalyst-containing electrolytic solution) containing a catalyst (second catalyst), the catalyst contained in the catalyst-containing electrolytic solution may adhere to the anode 12. However, in this specification, such an embodiment in which the catalyst contained in the catalyst-containing electrolytic solution adheres to the anode 12 is not included in the embodiment in which "the anode (electrode) contains a catalyst."

[0058] [Second catalyst] In this embodiment, a second catalyst may be contained inside the reactor 43. The second catalyst contains at least one metal element selected from the group consisting of elements of Groups 8 to 11 as a catalytically active species. By using an element of Groups 8 to 11 as the second catalyst, it becomes easier to synthesize a carbonyl compound from carbon monoxide with high selectivity. Specific examples of Group 8 to Group 11 elements used in the 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, Cu, and Ir being more preferred, Pd and Cu being even more preferred, and Pd being even more preferred. The use of any of the above elements facilitates the synthesis of an organic carbonate, an organic oxalate, or both from carbon monoxide with high selectivity. Furthermore, among the above, the use of Pd facilitates the production of an organic carbonate with high selectivity.

[0059] The metal element used in the catalyst may be used alone or in combination of two or more. When two or more types are used in combination, two or more metal elements selected from Groups 8 to 11 may be used in combination, or a metal element of Groups 8 to 11 may be used in combination with a metal element other than Groups 8 to 11. As the metal element other than Groups 8 to 11, a metal element of Period 4 may be preferably used, but a metal element other than Period 4 may also be used.

[0060] (metal salts) The metal element constituting the second catalyst may be contained in the electrolytic solution in the form of a metal ion, or in a form other than a metal ion. In one embodiment, the catalyst is a metal salt, and is preferably blended into the electrolytic solution as a metal salt. The metal salt may be any salt of the metal element, but is preferably a palladium salt or a copper salt. Examples of metal salts 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. Specific examples of metal nitrates include cobalt nitrate (Co(NO3)2), nickel nitrate (Ni(NO3)2), copper nitrate (Cu(NO3)2), rhodium nitrate (Rh(NO3)3), palladium nitrate (Pd(NO3)2), silver nitrate (AgNO3), iridium nitrate (Ir(NO3)4), platinum nitrate (Pt(NO3)4), gold nitrate (AuNO3), ruthenium nitrate (Ru(NO3)3), iron nitrate (Fe(NO3)3), manganese nitrate (Mn(NO3)2), zinc nitrate (Zn(NO3)2), chromium nitrate (Cr(NO3)3), and tin nitrate (Sn(NO3)4). Specific examples of metal chlorides include PdCl2, RuCl3, IrCl3, PtCl4, AuCl3, and CuCl2. HAuCl4 and the like may also be used. Of the above metal salts, PdCl2, HAuCl4, Ir(III)Cl3, and CuCl2 are preferred, PdCl2 and CuCl2 are more preferred, and PdCl2 is even more preferred. The metal salts may be used alone or in combination of two or more.

[0061] In the present invention, a metal salt is blended into the electrolytic solution as the catalyst, and the electrolytic solution preferably contains one or more ions selected from nitrate ions, sulfate ions, chloride ions, bromide ions, iodide ions, and hydroxide ions, more preferably chloride ions or nitrate ions, and even more preferably chloride ions. The metal salt may also be a hydrate. The second catalyst may consist solely of a metal salt, or may be appropriately supported on a support described below.

[0062] (Active particle containing catalyst) In one embodiment, the second catalyst is preferably a catalyst containing active particles having the above-mentioned metal element (hereinafter also referred to as "active particle-containing catalyst"). In this case, it is more preferable that the active particle-containing catalyst further contains a support, and the active particles are supported on the support. The support used in the active particle-containing catalyst is not particularly limited, but from the viewpoint of synthesizing a carbonyl compound from carbon monoxide with high selectivity, examples include carbon compounds and metal compounds, and among these, carbon compounds are preferred. Therefore, in one embodiment, the catalyst contained in the electrolytic solution is preferably a catalyst having active particles containing a metal element and a carbon compound supporting the active particles.

[0063] The active particle-containing catalyst can be produced by mixing a metal precursor with a support and heat treating the mixture, as described below. The metal precursor is converted into active particles by heat treatment, and the active particles are supported on the support. The active particles in the active particle-containing catalyst have catalytic activity to promote the reaction when carbon monoxide is electrochemically synthesized into an organic carbonate, an organic oxalate, or both. The active particles containing a metal element are not particularly limited, but may be composed of a metal oxide, a metal itself, or both a metal oxide and a metal. The active particles may also be in the form of a metal salt. The active particles may be metal ions with anions derived from a metal salt of a metal precursor (described below) as counter anions. The active particles may also be an appropriate combination of these. The counter anions are not particularly limited, but include chloride ions, nitrate ions, sulfate ions, iodide ions, bromide ions, etc., with chloride ions being preferred. The metal elements used in the active particles are as described above.

[0064] In the active particle-containing catalyst, the active particles are preferably in the form of fine particles, and the fine particle active particles are preferably supported on a support. The active particles are not particularly limited, but are preferably nano-order particles, and preferably have an average particle diameter of 100 nm or less, more preferably 1 nm to 40 nm. The active particles have the above particle diameter, and by forming them into a nanostructure, the active area increases, making it easier to improve various performances of the catalyst. Note that the particle diameter refers to the area-equivalent circle diameter, which is calculated by determining the area of ​​each particle in image observation using TEM-EDX or the like, and then calculating the diameter from the area of ​​each particle when it is assumed to be a circle.

[0065] The carbon compound constituting the support is preferably porous carbon. The porous carbon is not particularly limited as long as it can support active particles, but a conductive carbon compound is preferred. The use of a conductive carbon compound increases the electrical conductivity of the electrode, making it easier to improve reaction efficiency, etc. More specifically, examples of porous carbon include mesoporous carbon, activated carbon, carbon black such as ketjen black and acetylene black, carbon nanotubes, graphite, and graphene. The porous carbon is preferably particulate. The porous carbon is preferably carbon black, and conductive carbon black is more preferably conductive carbon black. The carbon compound is preferably particulate. The BET specific surface area of ​​the porous carbon is the same as that of the porous carbon described above for the first catalyst.

[0066] The metal element in the metal compound constituting the support also includes metal elements known as metalloids, such as silicon. Examples of the metal element in the metal compound constituting the support include metal elements of groups 1 to 6 and metal elements of groups 13 to 14, and specific examples include silicon, zirconium, magnesium, titanium, cerium, niobium, tungsten, and aluminum. Examples of the metal compound include metal oxides, metal nitrides, metal borides, and metals, with metal oxides being preferred.

[0067] Specific examples of metal compounds constituting the support include silica, magnesia, titanium oxide, zirconia, alumina, cerium oxide, niobium oxide, silica alumina, silica magnesia, tungstate zirconia, zeolite, sulfated zirconia, and titanosilicate. Among these, alumina, silica, magnesia, titanium oxide, zirconia, cerium oxide, niobium oxide, silica-alumina, silica-magnesia, tungstate zirconia, and zeolite are preferred, with alumina, silica-alumina, and silica-magnesia being particularly preferred. The alumina is not particularly limited, and examples include α-alumina, β-alumina, and γ-alumina, with γ-alumina being preferred. Furthermore, zeolites that can be used include, but are not limited to, mordenite (MOR), FAU (Y), BEA (beta), and MFI (ZSM-5). The carrier may be used alone or in combination of two or more kinds.

[0068] The metal compound is preferably porous so that it can adequately support the active particles. The BET specific surface area of ​​the metal compound is, for example, 10 m 2 / g or more 1000m 2 / g or less, but preferably 20m 2 / g or more 500m 2 / g or less, more preferably 40m 2 / g or more 200m 2 The metal compound is not particularly limited, but may be, for example, in the form of powder or particles.

[0069] (Method for producing second catalyst) Next, a method for producing the second catalyst will be described. The second catalyst described above can be obtained by mixing a metal precursor and a support, and heat-treating the mixture containing the metal precursor and the support (hereinafter referred to as the "second catalyst raw material mixture").

[0070] The metal precursor is a compound that becomes the above-mentioned active particles by heat treatment. Therefore, the metal precursor is preferably a precursor containing a metal element selected from the above-mentioned Groups 8 to 11 elements, and the preferred metal elements are also as described above. The metal elements used in the metal precursor may be used alone or in combination of two or more. When two or more kinds are used in combination, it is preferable to use two or more kinds of precursors having a metal element selected from the above-mentioned Groups 8 to 11 elements in combination, or to use a precursor having a metal element selected from Groups 8 to 11 elements in combination with a precursor having a metal element other than Groups 8 to 11 (for example, a metal element of the fourth periodic element). When two or more metal precursors are used in combination, the second catalyst may be obtained by mixing two or more metal precursors with a metal compound and heat-treating the mixture; therefore, the catalyst raw material mixture may contain two or more metal precursors.

[0071] The metal precursor preferably contains a metal ion. The metal precursor may be used in the form of, for example, a metal salt. Examples of the metal salt 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 nitrates are more preferred from the viewpoint of forming suitable active particles. Specific examples of metal nitrates and metal chlorides used in the metal precursor are the same as those of the metal salts used as the catalyst, and therefore, a detailed description thereof will be omitted. The metal salts may be hydrates. The metal salts may be used singly or in combination of two or more. The support used as a raw material in this production method is as described above.

[0072] The content of the metal derived from the metal precursor in the second catalyst raw mixture is preferably 0.1% by mass or more and 70% by mass or less, and more preferably 2% by mass or more and 50% by mass or less, relative to the total amount of the catalyst raw mixture. The content of the support in the catalyst raw material mixture is not particularly limited, but is, for example, 10% by mass or more and 95% by mass or less, preferably 20% by mass or more and 85% by mass or less, and more preferably 30% by mass or more and 80% by mass or less, based on the total amount of the catalyst raw material mixture.

[0073] The temperature for heat-treating the second catalyst raw material mixture is preferably 150°C or higher and 1000°C or lower. By setting the heat-treatment temperature within this range, active particles can be appropriately formed from the metal precursor while suppressing the generation of unnecessary by-products. It also becomes possible to appropriately support the active particles on the support. Furthermore, migration of the active particles can be prevented, reducing the particle size of the active particles, and making it easier to increase the surface area of ​​the second catalyst. From the above viewpoints, the heat treatment temperature is preferably 180°C or higher and 1000°C or lower, and more preferably 190°C or higher and 500°C or lower. The heat treatment time is not particularly limited, but is, for example, from 0.25 hours to 10 hours, preferably from 0.5 hours to 8 hours, and more preferably from 1 hour to 5 hours. The heat treatment may be carried out in air, in an inert gas atmosphere such as argon or nitrogen gas, or in a reducing gas atmosphere such as hydrogen. In addition, reduction treatment may be carried out appropriately after the heat treatment, and examples of reduction treatment include a method of carrying out reduction treatment with a reducing gas such as hydrogen or carbon monoxide, and a method of carrying out wet reduction treatment using a reducing compound such as NaBH4. By carrying out reduction treatment, the proportion of zero-valent metal elements (i.e., metal itself) in the active catalyst tends to increase, and catalytic activity tends to be improved.

[0074] The second catalyst raw material mixture to be heat-treated is preferably in a powder or particulate form. If the second catalyst mixture is in a powder or particulate form, the catalyst obtained by the heat treatment can also be in a powder or particulate form. The second catalyst raw material mixture can be obtained, for example, by preparing a diluted solution of the second catalyst raw material mixture and drying the diluted solution. In the diluted solution of the catalyst raw material mixture, each component (metal precursor and support) is preferably dispersed or dissolved in a dilution solvent. By dispersing or dissolving each component in the dilution solvent, a second catalyst raw material mixture in which each component is homogeneously mixed can be obtained.

[0075] The dilution solvent used to dilute the second catalyst raw material mixture can be water or an organic solvent, with water being preferred. Alternatively, a mixed solvent of an organic solvent and water may be used as the dilution solvent. The dilution solvent may also contain an acid component such as hydrochloric acid, nitric acid, sulfuric acid, acetic acid, citric acid, or lauric acid, or a base component such as ammonia. The concentration of the diluted solution of the catalyst raw material mixture is not particularly limited, but the amount of metal precursor is, for example, 0.01 to 25 g / L, preferably 0.1 to 5 g / L.

[0076] In the reactor 43, the content of the second catalyst in the electrolytic solution 13Y is not particularly limited, but may be, for example, about 0.02 to 200 g / L, and preferably about 0.1 to 100 g / L. The content here refers to the amount of the second catalyst per 1 L of the electrolytic solution contained in the anode chamber 10Y or the reaction chamber 21.

[0077] The second catalyst may be dissolved, dispersed, or packed in a layer in the electrolytic solution 13Y in the reactor 43. For example, when the second catalyst is a metal salt, the second catalyst may be dissolved or dispersed in the electrolytic solution 13Y. When the second catalyst is an active particle-containing catalyst, the second catalyst may be dispersed in the reactor 43, or may be packed in a layer. When the second catalyst is packed in layers, it may be packed on a support such as a tray or mesh, but no support may be provided. Furthermore, when the second catalyst is dispersed inside the reactor 43, it may be dispersed by the flow of the electrolytic solution 13Y, but it may also be dispersed by a dispersion means other than the flow of the electrolytic solution 13Y. For example, it may be dispersed by bubbling with the gas G or bubbling with a gas other than the gas G, or a stirring device such as a stirring blade may be provided inside the reactor 43 to stir the second catalyst.

[0078] In addition, when the second catalyst is dissolved or dispersed in the electrolytic solution 13Y inside the reactor 43, a filter may be provided at the outlet of the reactor 43 to prevent the second catalyst from flowing out of the reactor 43. The filter may be any filter that does not allow the second catalyst to pass through, and may be, for example, a membrane filter, a mesh filter, or the like, when the second catalyst is dispersed in the electrolytic solution 13Y. On the other hand, when the second catalyst is dissolved in the electrolytic solution 13Y, a chemical adsorption filter, a physical adsorption filter, or the like may be used.

[0079] [Electrolyte on the anode side] In this embodiment, as described above, the anode chamber 10Y and the reactor 43 are filled with the electrolytic solution 13Y, and the electrolytic solution 13Y is circulated through the second circulation path 45. The electrolytic solution 13Y may contain a redox species. The redox species may be an electrolyte in the electrolytic solution 13Y. The redox species may be dissolved in a reaction substrate or a mixture of the reaction substrate and a solvent, which will be described later.

[0080] (redox species) The redox species can be, for example, one whose molecular or ionic size is smaller than that of the reaction substrate, such as an alcohol-based compound described below, and which has redox activity. Specific examples of electrolytes that can serve as redox species include halide salts, organic redox, and complex redox. Among these, halide salts are preferred from the viewpoint of improving faradaic efficiency and productivity. In this embodiment, the electrolytic solution contains a redox species as an electrolyte, and thus a redox mediator (an oxidant such as a halogen) is generated at the anode 12. In the reactor 43, the redox mediator enables efficient production of a carbonyl compound from carbon monoxide and a reaction substrate in the presence of a second catalyst.

[0081] Examples of halide salts include metal halide salts. Specific examples of metal halide salts include lithium halide salts such as lithium chloride, lithium bromide, and lithium iodide, sodium halide salts such as sodium chloride, sodium bromide, and sodium iodide, potassium halide salts such as potassium chloride, potassium bromide, and potassium iodide, and cesium halide salts such as cesium chloride, cesium bromide, and cesium iodide. Examples of halide salts also include ammonium halide salts such as ammonium chloride, ammonium bromide, and ammonium iodide.

[0082] Examples of organic redox compounds include TEMPO-based radical compounds such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MeO-TEMPO), and azaadamantane-N-oxyl (AZADO). Examples of complex redox include palladium complexes such as palladium acetylacetonate (Pd(OAc)2) and tetrakis(triphenylphosphine)palladium (Pd(PPh3)4 complex), and cobalt complexes such as tris(2,2'-bipyridine)cobalt (Co(bpy)3 complex) and tris[1,3-bis(4-pyridyl)propane)]cobalt (Co(bpp)3 complex).

[0083] Of the above, metal halide salts are preferred as the redox species from the viewpoint of increasing the selectivity for carbonyl compounds, and among these, metal chloride salts and metal bromide salts are more preferred, with metal bromide salts being even more preferred. Therefore, the electrolyte contains, as redox ions, halogen ions such as chloride ions and bromide ions, and it is particularly preferable that the electrolyte contains bromide ions. Preferred specific examples of metal chloride salts include lithium chloride, potassium chloride, and sodium chloride, and among these, sodium chloride is preferred from the viewpoint of easy availability. Preferred specific examples of metal bromide salts include lithium bromide, potassium bromide, and sodium bromide. Among these, lithium chloride and lithium bromide are preferred, and lithium bromide is particularly preferred, from the viewpoint of increasing the selectivity of carbonyl compounds. The redox species may be used alone or in combination of two or more.

[0084] The concentration of the redox species in the electrolytic solution 13Y is not particularly limited and may be adjusted to a level at which the synthesis of an oxygen-containing organic substance such as a carbonyl compound proceeds appropriately. A specific concentration of the redox species is, for example, 0.001 M or more and 5.0 M or less, preferably 0.01 M or more and 1.0 M or less, and more preferably 0.05 M or more and 0.5 M or less.

[0085] (reaction substrate) The reaction substrate is a compound that serves as a raw material for the carbonyl compound. An alcohol-based compound can be used as the reaction substrate. By using an alcohol-based compound as the reaction substrate, an organic carbonate, an organic oxalate, or both can be easily produced from carbon monoxide in the presence of an oxidant of a redox species and a first catalyst.

[0086] (alcohol-based compounds) The alcohol-based compound is a reaction substrate that reacts with carbon monoxide in the electrochemical system (in this embodiment, the reactor 43) to produce an organic carbonate, an organic oxalate, or both. The alcohol-based compound may be solid, liquid, or gaseous in the environment where the electrochemical reaction occurs in the electrochemical system, but is preferably a liquid. A liquid alcohol-based compound can be easily filled into the reactor 43, the anode chamber 10Y, etc., without using a solvent, which will be described later. An alcohol-based compound is a compound having at least one hydroxyl group, and more specifically, a compound represented by the following general formula (1): In this specification, the term "alcohol-based compound" is a concept that also includes aromatic hydroxy compounds in which a hydroxyl group is directly bonded to an aromatic ring such as a benzene ring, as typified by phenol, as will be described later.

[0087] ROH (1) (R represents an organic group having 1 to 15 carbon atoms.) The organic group having 1 to 15 carbon atoms represented by R in the above general formula (1) includes a hydrocarbon group having 1 to 15 carbon atoms. Examples of the hydrocarbon group include an alkyl group having 1 to 15 carbon atoms, an alkenyl group having 2 to 15 carbon atoms, and an aryl group 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 alkenyl groups having 2 to 15 carbon atoms 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. The term "various isomers" means various isomers including n-, sec-, tert-, and iso-. The alkyl or alkenyl group may be linear, branched, or cyclic. Examples of the aryl group having 6 to 15 carbon atoms include a phenyl group, a naphthyl group, etc. The hydrocarbon group may have a substituent, and in that case, the number of carbon atoms including the substituent is 1 to 15.

[0088] Furthermore, the organic group having 1 to 15 carbon atoms in the general formula (1) may contain a heteroatom such as a nitrogen atom, an oxygen atom, a sulfur atom, a phosphorus atom or a halogen atom. Among these, an oxygen atom is preferred. When an oxygen atom is present, the oxygen atom is preferably either a hydroxyl group or an oxygen atom of an ether bond. Therefore, R is preferably a hydrocarbon group having at least one of a hydroxyl group and an ether bond. Furthermore, it is preferable that R has one hydroxyl group. That is, the alcohol-based compound may have two hydroxyl groups. More specifically, the alcohol-based compound having two hydroxyl groups is preferably a group represented by the following formula (1-1). HO-R 11 -OH (1-1) In addition, in formula (1-1), R 11 is a divalent saturated hydrocarbon group having 2 to 15 carbon atoms, while R 11 The number of carbon atoms is preferably 2 to 4, and more preferably 2 to 3.

[0089] As the compound represented by the general formula (1), among the above, 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. 11 Those having 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. The alkyl group preferably has 1 to 3 carbon atoms, more preferably 1 or 2 carbon atoms, and most preferably 1 carbon atom. Specifically, from the viewpoints of reactivity and production efficiency, methanol, ethanol, phenol, 1-propanol, ethylene glycol, propylene glycol, etc. are preferred, and among these, methanol is more preferred. The alcohol-based compounds may be used alone or in combination of two or more.

[0090] When an alcohol-based compound is used as a reaction substrate, a reaction (also referred to as a first reaction) in which an organic carbonate is produced from carbon monoxide and the alcohol-based compound generally occurs in the electrochemical system 20. However, a reaction (also referred to as a second reaction) in which an organic oxalate is produced from carbon monoxide and the alcohol-based compound may also occur, and both the first and second reactions occur, but it is preferable that at least the first reaction occurs.

[0091] The first reaction is a carbonylation reaction that produces an organic carbonate, and specifically, the organic carbonate ((RO)2CO) is produced by the reaction shown in formula (i) below. CO+2ROH→(RO)2CO+2H + +2e - (i) In (i), R is the same as above, but preferably R is 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, more preferably an alkyl group or an aryl group, and even more preferably an alkyl group. The alkyl group more preferably has 1 to 3 carbon atoms, even more preferably has 1 or 2 carbon atoms, and most preferably has 1 carbon atom. However, as mentioned above, two or more alcohol compounds may be used in combination, and in this case, the two Rs in one molecule of (RO)2CO may be different from each other.

[0092] When ROH is represented by the general formula (1-1), an organic carbonate is produced by the reaction shown in the following formula (ii). [ka] In addition, in formula (ii), R 11 is the same as above, but R 11 The number of carbon atoms is preferably 2 to 4, more preferably 2 to 3, and even more preferably 2.

[0093] 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, and among these, dimethyl carbonate is more preferred.

[0094] The second reaction is a reaction in which carbon monoxide and an alcohol compound produce an organic oxalate represented by the following formula (2): Specifically, the organic oxalate represented by formula (2) may be synthesized by the reaction represented by formula (iii) below. [ka] (In formula (2), R is the same as above. However, two R in one molecule may be the same or different.) [ka] (In formula (iii), R is the same as above.)

[0095] When ROH is represented by the general formula (1-1), an organic oxalate represented by the following formula (2-1) is produced by the reaction represented by the following formula (iv). [ka] (In formula (2-1), R 11 is the same as above.) [ka] (In addition, in formula (iv), R 11 is the same as above.)

[0096] 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.

[0097] (solvent) When the above-mentioned reaction substrate is a solid or gas, or when it is necessary to improve the solubility of the redox species, the electrolytic solution 13Y may further contain a solvent. In this case, the reaction substrate may be filled into the reactor 43 or the anode chamber 10Y as a mixed solution with the solvent. Of course, even when the reaction substrate is a liquid, it may be filled as a mixed solution with the solvent. The solvent can be appropriately selected from solvents commonly used in electrochemical reactions, and examples thereof 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, sulfolane solvents, pyrrolidones, etc. These solvents may be used alone or in combination of two or more.

[0098] As described above, the electrolytic solution 13Y may contain redox species as an electrolyte, but may also contain electrolytes other than redox species in addition to the redox species. Examples of electrolytes other than redox species include perchlorates such as sodium perchlorate (NaClO), zinc perchlorate, barium perchlorate, lithium perchlorate, and ammonium perchlorate, as well as sodium sulfate, potassium sulfate, and ammonium sulfate. These electrolytes other than redox species may be used alone or in combination of two or more.

[0099] [Electrolyte on the cathode side] In this embodiment, the cathode-side electrolyte 13X may be any electrolyte that can be used in a reduction reaction, and at least one of the compounds exemplified as the solvent or reaction substrate in the anode-side electrolyte 13Y may be used as the electrolyte 13X. A preferred example of the electrolyte 13X is an alcohol-based compound. The detailed description of the alcohol-based compound is as above, and the preferred compounds are also the same. Therefore, the electrolyte 13X on the cathode side is preferably methanol, ethanol, phenol, 1-propanol, ethylene glycol, propylene glycol, etc., and among these, methanol is more preferable. Furthermore, the cathode-side electrolytic solution 13X may contain an electrolyte as appropriate, and as the electrolyte, compounds exemplified as redox species or compounds exemplified as electrolytes other than redox species can be used as appropriate.

[0100] [Isolation membrane] The separator 25 preferably separates the carbon monoxide generated in the first catalyst (cathode 11) from the oxidant generated in the anode 12. The separator 25 may be any membrane that is permeable to ions but not permeable to the electrolyte 13, carbon monoxide, or oxidant, and specifically, is preferably an ion exchange membrane. As the ion exchange membrane, a solid membrane is used, and examples include a cation exchange membrane that is permeable to cations such as protons, and an anion exchange membrane that is permeable to anions such as hydroxide ions, but a cation exchange membrane is preferred from the viewpoints of ion conductivity and cost.

[0101] Examples of cation exchange membranes include those having at least one of a sulfonyl group, a carboxyl group, a phosphate group, and a silicic acid group as a functional 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 commercially available products include "Nafion" (a trademark of DuPont). Polycarboxylic acids such as polyacrylic acid are examples of membranes having carboxyl groups as functional groups. Heteropolyacids such as silicotungstic acid and phosphotungstic acid can also be used as membranes having phosphoric acid or silicic acid functional groups. Furthermore, phosphate glasses such as SiO2-P2O5 and ceramics such as perovskite oxides can also be used as cation exchange membranes.

[0102] Examples of anion exchange membranes include resins containing quaternary ammonium salts, such as poly(styrylmethyltrimethylammonium chloride), polyethers, 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, such as 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).

[0103] <Second embodiment> Next, an electrochemical system according to a second embodiment of the present invention will be described. In the electrochemical system according to the first embodiment, one refinement device 50 is provided for one electrochemical cell 10, but in an electrochemical system 20A according to this embodiment, one refinement device 50 is provided for a plurality of electrochemical cells 10. 2 , the electrochemical system 20A includes a plurality of synthesis units 54, each including one electrochemical cell 10, and the discharge path 27 of each synthesis unit 54 is connected to one purification device 50. Therefore, in this embodiment, the electrolytic solution 13Y containing the carbonyl compound obtained in the plurality of synthesis units 54 can be supplied to one purification device 50. The number of synthesis units 54 (ie, electrochemical cells 10) provided in the electrochemical system 20A is not particularly limited as long as it is two or more, but is preferably about 2 to 100, and more preferably about 5 to 50.

[0104] In this embodiment, the switching mechanism may be used to switch the electrolytic solution 13Y discharged from at least one, preferably one, of the plurality of synthesis units 54 (electrochemical cells 10) so that the electrolytic solution 13Y is supplied to the purification device 50 through the discharge path 27. During this supply, at least one, preferably all, of the remaining synthesis units 54 (electrochemical cells 10) may circulate the electrolytic solution 13Y through the second circulation path 45 (see FIG. 1) on the anode side, thereby producing carbonyl compounds.

[0105] Here, when the supply of the electrolyte solution 13Y from at least one synthesis unit 54 is completed, it is preferable to switch to supplying the electrolyte solution 13Y discharged from at least one other synthesis unit 54, preferably another synthesis unit 54, to the purification device 50. While the electrolyte solution 13Y is being supplied from this other synthesis unit 54, it is preferable that the electrolyte solution 13Y is circulated in the second circulation path 45 (see FIG. 1) on the anode side in at least one other synthesis unit 54, preferably all other remaining synthesis units 54 (electrochemical cells 10), and carbonyl compounds are produced.

[0106] By repeating the above steps, the electrolytic solution 13Y containing the carbonyl compound is continuously supplied to the purification apparatus 50 from each synthesis unit 54, facilitating continuous operation of the purification apparatus 50. Therefore, a highly pure carbonyl compound can be obtained with higher production efficiency.

[0107] <Third embodiment> Next, an electrochemical system according to a third embodiment of the present invention will be described. As in the second embodiment, the electrochemical system 20B according to this embodiment includes a plurality of synthesis units 54, each including one electrochemical cell 10, and one purification device 50. However, in the third embodiment, the electrochemical system 20B further includes a tank (hereinafter, sometimes referred to as a "second tank") 55. In the present embodiment, the discharge path 27 of each synthesis unit 54 is connected to the second tank 55. Therefore, in the present embodiment, the electrolytic solution 13Y containing the carbonyl compound obtained in the plurality of synthesis units 54 can be supplied to the second tank 55. The second tank 55 is connected to the purification device 50, and the electrolytic solution 13Y can be further supplied from the second tank 55 to the purification device 50.

[0108] In this embodiment, each synthesis unit 54 also switches appropriately between discharging the electrolyte solution 13Y from the discharge path 27 and circulating the electrolyte solution 13Y in the second circulation path 45 (see FIG. 1 ), and in each synthesis unit 54, the electrolyte solution 13Y discharged from the discharge path 27 is supplied to the second tank 55, and the electrolyte solution 13Y is stored in the second tank 55. The stored electrolyte solution 13Y is sequentially supplied to the refinement device 50, thereby enabling the refinement device 50 to operate continuously. Here, the timing of discharging the electrolytic solution 13Y from the discharge path 27 is not particularly limited, and the electrolytic solution 13Y may be supplied to the second tank 55 from a plurality of synthesis units 54 at the same time, or a period during which the electrolytic solution 13Y is not supplied may continue for a long period of time as long as the electrolytic solution 13Y is stored in the second tank 55. In the present embodiment, the presence of the second tank 55 allows the refinery device 50 to operate continuously without adjusting the timing at which the electrolytic solution 13Y is discharged from each synthesis unit 54 to the refinery device 50.

[0109] <Fourth embodiment> Next, an electrochemical system according to a fourth embodiment will be described. In each of the above embodiments, a reactor 43 is provided and carbonyl compounds are synthesized in the reactor 43. However, in an electrochemical system 20C according to this embodiment, the reactor 43 is omitted and carbonyl compounds are synthesized in the anode chamber 10Y.

[0110] The following describes the fourth embodiment and the differences from the first embodiment. In this embodiment, since the carbonyl compound is synthesized in the anode chamber 10Y, the second catalyst may be contained in the electrolytic solution 13Y in the anode chamber 10Y. As in the first embodiment, the second catalyst may be dissolved in the electrolytic solution 13Y in the anode chamber 10Y, may be dispersed in the electrolytic solution 13Y, or may be filled in the form of a layer.

[0111] Similarly to the first embodiment, the electrochemical system 20C includes a first gas-liquid separator 30 and a mixer 34, and a first circulation path 35 is formed on the cathode side. The carbon monoxide-containing gas G generated in the cathode chamber 10X is supplied to a second circulation path 45X on the anode side via a carbon monoxide supply path 28.

[0112] The second circulation path 45X on the anode side is the same as that of the first embodiment except that the reactor 43 is not provided, and the same electrolytic solution 13Y as in the first embodiment is circulated through the anode chamber 10Y, the second gas-liquid separator 40, and the tank 44, in that order. The anode chamber 10Y and the second gas-liquid separator 40, the second gas-liquid separator 40 and the tank 44, and the tank 44 and the anode chamber 10Y are connected via connection paths 29A, 29E, and 29D, respectively, and the second circulation path 45X is formed by the connection paths 29A, 29E, and 29D. However, in this embodiment, the tank 44 may be omitted as appropriate.

[0113] In this embodiment, the carbon monoxide supply passage 28 is connected to the supply port 13Y of the anode chamber 10Y. Therefore, the carbon monoxide-containing gas G supplied from the carbon monoxide supply passage 28 is supplied to the anode chamber 10Y. In the anode chamber 10Y, as in the first embodiment, the redox species is converted from a reduced species to an oxidant (e.g., a redox mediator). Also, in the anode chamber 10Y, a carbonyl compound is produced from carbon monoxide and a reaction substrate by the redox mediator in the presence of a second catalyst. That is, in this embodiment, an oxidant of the redox species is produced in the anode chamber 10Y, and a carbonyl compound is also produced using the oxidant.

[0114] The carbonyl compounds produced in the anode chamber 10Y are discharged from the outlet 17Y together with the electrolytic solution 13Y containing the gas G, and are supplied to the second gas-liquid separator 40. In the second gas-liquid separator 40, the gas and liquid are separated, and the gas G is discharged via a gas discharge path 48, while the liquid (electrolytic solution 13Y) is supplied to a tank 44 and returned to the anode 13Y via the tank 44. In this way, the carbonyl compounds are produced while the electrolytic solution 13Y circulates through the second circulation path 45X. Furthermore, the produced electrolytic solution 13Y containing the carbonyl compound is stored in the tank 44 as described above, and the stored electrolytic solution 13Y is discharged from the second circulation path 45 via the discharge path 27. In the present embodiment as well, the circulation of the electrolytic solution 13Y in the second circulation path 45 and the discharge of the electrolytic solution 13Y from the discharge path 27 are switched by the open / close valves 62 and 63 (switching mechanism).

[0115] Also in this embodiment, while the electrolytic solution 13Y is circulated in the second circulation path 45X, raw materials such as alcohol-based compounds are not supplied from the raw material supply path 42, while the electrolytic solution 13Y is discharged from the discharge path 27, raw materials are supplied from the raw material supply path 42 to the second circulation path 45X (i.e., the anode chamber 10Y).

[0116] Therefore, in this embodiment, too, by circulating the electrolytic solution 13Y through the second circulation path 45X including the anode chamber 10Y, the content of carbonyl compounds in the electrolytic solution 13Y can be made relatively high. This can improve, for example, the energy efficiency in the subsequent purification process. Furthermore, in this embodiment, circulation is performed for a certain period of time, and when the amount of carbonyl compounds produced reaches a certain level or more, the switching mechanism switches from circulation to discharge, so that the electrolytic solution 13Y with a relatively high content of carbonyl compounds can be easily discharged from the second circulation path 45X.

[0117] Furthermore, in this embodiment as well, while the electrolytic solution 13Y is being discharged from the second circulation path 45X, a raw material containing at least an alcohol-based compound is supplied to the circulation path 45X (anode chamber 10Y) from the raw material supply path 42. Therefore, even while the electrolytic solution 13Y is being discharged, the anode chamber 10Y continues to be filled with the electrolytic solution 13Y, and the operation of the electrochemical cell 10 (i.e., application of a voltage to the power source 19) can be continued, facilitating continuous operation. The circulation of the electrolytic solution 13Y and the discharge of the electrolytic solution 13Y may be repeated alternately, which allows continuous operation over a long period of time.

[0118] <Other embodiments> In the fourth embodiment described above, the second catalyst is contained inside the anode chamber 10Y and not contained in the anode 12 itself. However, if the second catalyst is, for example, an active particle-containing catalyst, it may be contained in the anode 12. The second catalyst may be supported, for example, on an electrode substrate constituting the anode 12. The method for supporting the catalyst on the electrode substrate may be the same as that described for the first catalyst.

[0119] Furthermore, in the first embodiment, the second catalyst is contained inside the reactor 43, but the second catalyst may be contained in both the reactor 43 and the anode chamber 10Y. When the second catalyst is contained in the anode chamber 10Y, as described above, the second catalyst may be dissolved or dispersed in the electrolytic solution 13Y without being contained in the anode 12, or the anode chamber 10Y may be filled with the second catalyst, or the second catalyst may be contained in the anode 12.

[0120] In addition, in each of the above embodiments, the circulation of the electrolytic solution 13X in the second circulation path 45 (or 45X) and the discharge of the electrolytic solution 13Y from the discharge path 27 are alternately performed, and while the electrolytic solution 13Y is being discharged from the discharge path 27, a raw material containing an alcohol-based compound is supplied from the raw material supply path 42. However, the circulation of the electrolytic solution 13Y in the second circulation path 45 (or 45X) and the discharge of the electrolytic solution 13Y from the discharge path 27 do not have to be performed alternately, but the raw material may be supplied from the raw material supply path 42 while the electrolytic solution 13Y is circulated in the second circulation path 45 (or 45X) and the electrolytic solution 13Y is discharged from the discharge path 27. In this case, all of the on-off valves 62, 63, and 64 are opened, and the opening degrees of the control valves 52 and 53 are set relatively small. As a result, the raw material is supplied little by little from the raw material supply path 42, and the electrolytic solution 13Y is circulated through the second circulation path 45 (or 45X), while a small amount of the electrolytic solution 13Y is discharged from the discharge path 27. Therefore, since a small amount of the electrolyte solution 13Y is replaced while being circulated, it is possible to discharge the electrolyte solution 13Y with a relatively high content of carbonyl compounds, thereby improving the energy efficiency in the subsequent purification step.

[0121] In the above embodiments, the circulation path 35 is also formed on the cathode side, and the electrolytic solution 13X is circulated on the cathode side as well. However, it is not necessary to circulate the electrolytic solution 13X on the cathode side. For example, the first gas-liquid separator 30 and the mixer 34 may be omitted. In this case, for example, carbon dioxide may be supplied in a gas phase to the cathode chamber 10X, and carbon monoxide may be produced in the cathode chamber 10X by a gas-phase reaction. The carbon monoxide-containing gas G produced in the cathode chamber 10X may then be supplied directly to the second circulation path 45 (or 45X) via the carbon monoxide supply path 28.

[0122] Furthermore, although the above-described embodiments show an embodiment in which the second gas-liquid separator 40 and the tank 44 are provided, these may also be omitted as appropriate. For example, if the second gas-liquid separator 40 is omitted, the gas discharged from the reactor 43 may be directly discharged from the gas discharge path 48. Furthermore, even if the tank 44 is not provided, the electrolytic solution 13Y discharged from the reactor 43 may be directly discharged from the discharge path 27 or supplied to the anode chamber 10Y. Furthermore, the control valves 51, 52, and 53 and the on-off valves 62, 63, and 64 may also be omitted as appropriate or replaced with valves having different mechanisms as appropriate. [Explanation of symbols]

[0123] 10 Electrochemical Cell 10X cathode chamber 10Y anode chamber 11 Cathode 12 anodes 13X, 13Y electrolyte 19 Power supply 20, 20A~20C Electrochemical System 25 Separation membrane 27 Exhaust channel 28 Carbon monoxide supply line 30, 40 First and second gas-liquid separators 31 Carbon dioxide supply route 34 Mixer 35 First Circulation Route 42 Raw material supply route 43 Reaction Chamber 45 Second Circulation Route 50 Purification equipment 51, 52, 53 Control valve 54 Synthesis Unit 55 Tank 62, 63, 64 Opening and closing valves

Claims

1. An electrochemical system for electrochemically synthesizing a carbonyl compound from carbon dioxide, comprising: an electrochemical cell including a cathode and an anode, in which a reduction reaction of reducing carbon dioxide to carbon monoxide occurs on the cathode side and an oxidation reaction occurs on the anode side; a carbon dioxide supply channel for supplying carbon dioxide to the cathode side of the electrochemical cell; a circulation path for circulating an electrolyte solution containing an alcohol-based compound from the anode side region of the electrochemical cell to the outside of the region and then back to the anode side region; a carbon monoxide supply path for supplying a gas containing carbon monoxide generated on the cathode side to the electrolytic solution in the circulation path, and for generating a carbonyl compound from the carbon monoxide and the alcohol-based compound in the electrolytic solution; An electrochemical system comprising:

2. a discharge path for discharging the electrolytic solution containing the carbonyl compound from the circulation path; The electrochemical system according to claim 1 , further comprising a switching mechanism capable of switching between discharging the electrolytic solution from the discharge path and circulating the electrolytic solution in the circulation path.

3. a raw material supply path for supplying at least the alcohol-based compound to the circulation path; The electrochemical system according to claim 2 , wherein at least the alcohol-based compound is supplied from the raw material supply channel to the circulation channel while the electrolytic solution is discharged from the discharge channel.

4. a purification device that separates and purifies carbonyl compounds from the electrolytic solution, The electrochemical system according to claim 2 or 3, wherein the electrolytic solution discharged from the discharge path is supplied to the refinery device.

5. 5. The electrochemical system according to claim 4, wherein the alcohol-based compound separated from the electrolytic solution by the refiner is supplied from the raw material supply channel to the circulation path.

6. the carbon dioxide supply channel supplies carbon dioxide contained in an electrolytic solution to the cathode side of the electrochemical cell; 3. The electrochemical system according to claim 1, further comprising a first gas-liquid separator that separates the electrolytic solution discharged from the cathode side of the electrochemical cell into gas and liquid.

7. A reactor is provided in the circulation path, 2. The electrochemical system according to claim 1, wherein the reactor contains a carbonyl compound synthesis catalyst that produces a carbonyl compound from the carbon monoxide and the alcohol-based compound.

8. 8. The electrochemical system according to claim 7, wherein the reactor brings the gas containing carbon monoxide into countercurrent contact with the electrolyte solution containing the alcohol-based compound.

9. the circulation path includes a tank in which an electrolytic solution containing the carbonyl compound is stored, 3. The electrochemical system according to claim 1, wherein the electrolytic solution containing the carbonyl compound is discharged from the tank.

10. a flow rate adjusting mechanism is provided in the carbon monoxide supply passage; 3. The electrochemical system according to claim 1, wherein the flow rate adjusting mechanism adjusts the flow rate of the carbon monoxide-containing gas, thereby adjusting the amount of carbon dioxide supplied to the cathode side of the electrochemical cell.

11. a plurality of synthesis units each including the electrochemical cell, the carbon dioxide supply channel, the circulation channel, the carbon monoxide supply channel, and the discharge channel; each discharge path of the plurality of synthesis units is connected to the purification device, and the electrolyte of the plurality of synthesis units can be supplied to the purification device; 3. The electrochemical system of claim 2, wherein the switching mechanism supplies the electrolyte of at least one of the electrochemical cells from the outlet to the purification device and circulates the electrolyte in at least one other of the electrochemical cells.

12. a plurality of synthesis units each including the electrochemical cell, the carbon dioxide supply channel, the circulation channel, the carbon monoxide supply channel, and the discharge channel; and the electrochemical system comprises a tank; 3. The electrochemical system according to claim 2, wherein each of the discharge paths of the synthesis units is connected to the tank, and the electrolyte of the synthesis units can be supplied to the tank, and the electrolyte can be further supplied from the tank to the purification device.

13. a discharge path for discharging the electrolytic solution containing the carbonyl compound from the circulation path; a raw material supply path for supplying at least the alcohol-based compound to the circulation path; The electrochemical system according to claim 1 , wherein the alcohol-based compound is supplied from the raw material supply unit while the electrolytic solution is discharged from the discharge channel.

14. A method for producing a carbonyl compound, in which a carbonyl compound is electrochemically synthesized from carbon dioxide using an electrochemical system including an electrochemical cell, comprising: supplying carbon dioxide to a cathode side of the electrochemical cell; reducing carbon dioxide to carbon monoxide at the cathode; causing an oxidation reaction on the anode side of the electrochemical cell; circulating an electrolyte solution containing an alcohol-based compound from an anode-side region of the electrochemical cell to the outside of the electrochemical cell and then back to the anode-side region; supplying the carbon monoxide generated on the cathode side to the electrolytic solution in the circulation path, and generating a carbonyl compound from the carbon monoxide and the alcohol-based compound in the electrolytic solution; A method for producing a carbonyl compound comprising:

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