Organic Hydride Producing System, Control Device for Organic Hydride Producing System, and Control Method for Organic Hydride Producing System

This application is a Divisional of U.S. application Ser. No. 18/254,295 filed May 24, 2023, which is the U.S. National Stage of International Patent Application No. PCT/JP2021/044349, filed on Dec. 2, 2021, and claims the benefit of priority from the prior Japanese Patent Application No. 2020-201822, filed on Dec. 4, 2020, the entire content of each of which is incorporated herein by reference.

The present invention relates to an organic hydride producing system, a control device for an organic hydride producing system, and a control method for an organic hydride producing system.

In recent years, in order to suppress the carbon dioxide emission amount in the energy generation process, it is expected to use renewable energy obtained by solar power, wind power, hydraulic power, geothermal power generation, and the like. As an example, a system for generating hydrogen by performing water electrolysis using power derived from renewable energy has been devised. In addition, an organic hydride system has attracted attention as an energy carrier for large-scale transportation and storage of hydrogen derived from renewable energy.

Regarding a technique for producing an organic hydride, there has been conventionally known an organic hydride producing system including an electrolytic bath including an oxidation electrode for generating protons from water and a reduction electrode for hydrogenating an organic compound (substance to be hydrogenated) having an unsaturated bond (see, for example, Patent Literature 1). In this organic hydride producing system, a current flows between the oxidation electrode and the reduction electrode while water is supplied to the oxidation electrode, and a substance to be hydrogenated is supplied to the reduction electrode, so that hydrogen is added to the substance to be hydrogenated to obtain an organic hydride.

As a result of intensive studies on the above-described technique for producing an organic hydride, the present inventors have recognized that in the conventional technique, the Faraday efficiency may decrease when the production speed of the organic hydride is increased.

The present invention has been made in view of such circumstances, and one object of the present invention is to provide a technique for improving a production speed of an organic hydride while suppressing a decrease in Faraday efficiency of an organic hydride producing system.

One aspect of the present invention is an organic hydride producing system. This organic hydride producing system includes: an electrolytic bath having a cathode chamber for accommodating a cathode electrode for hydrogenating a substance to be hydrogenated in a catholyte with a proton to generate an organic hydride; a catholyte supply device capable of supplying any catholyte selected from a plurality of the catholytes having different concentrations of substances to be hydrogenated to the cathode chamber; and a control device structured to control the catholyte supply device so as to supply a catholyte to the cathode chamber, the catholyte having a specific concentration of a substance to be hydrogenated determined according to a magnitude of a current flowing in the electrolytic bath.

Another aspect of the present invention is a control device of an organic hydride producing system including an electrolytic bath and a catholyte supply device. The electrolytic bath has a cathode chamber for accommodating a cathode electrode for hydrogenating a substance to be hydrogenated in a catholyte with a proton to generate an organic hydride. The catholyte supply device is capable of supplying any catholyte selected from a plurality of the catholytes having different concentrations of substances to be hydrogenated to the cathode chamber. The control device controls the catholyte supply device so as to supply the catholyte to the cathode chamber, the catholyte having a specific concentration of a substance to be hydrogenated determined according to a magnitude of a current flowing in the electrolytic bath.

Another aspect of the present invention is a method for controlling an organic hydride producing system including an electrolytic bath having a cathode chamber for accommodating a cathode electrode for hydrogenating a substance to be hydrogenated in a catholyte with a proton to generate an organic hydride. This control method includes supplying the catholyte to the cathode chamber, the catholyte having a specific concentration of a substance to be hydrogenated determined according to a magnitude of a current flowing in the electrolytic bath.

Any combinations of the above components and conversion of the expressions of the present disclosure among methods, devices, systems, and the like are also effective as aspects of the present disclosure.

Hereinafter, the present invention will be described based on preferred embodiments with reference to the drawings. The embodiments are illustrative rather than limiting the invention, and not all features described in the embodiments and combinations thereof are necessarily essential to the invention. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and redundant description will be omitted as appropriate.

In addition, the scale and shape of each part shown in each drawing are set for convenience in order to facilitate the description, and are not to be limitedly interpreted unless otherwise specified. Furthermore, when the terms “first”, “second”, and the like are used in the present specification or claims, the terms do not represent any order or importance, but are used to distinguish one configuration from another configuration. In addition, in each drawing, some of members that are not important for describing the embodiments are omitted.

is a schematic diagram of an organic hydride producing systemaccording to a first embodiment. The organic hydride producing systemmainly includes an electrolytic bath, a power supply, an anolyte supply device, a catholyte supply device, and a control device.

The electrolytic bathgenerates an organic hydride by hydrogenating substance to be hydrogenated, which is a dehydrogenated product of an organic hydride, by an electrochemical reduction reaction. The electrolytic bathincludes an anode electrode, a cathode electrode, an anode chamber, a cathode chamber, and a membrane.

The anode electrode(anode) oxidizes water in an anolyte to generate protons. The anode electrodehas, as an anode catalyst, a metal such as iridium (Ir), ruthenium (Ru), or platinum (Pt), or a metal oxide thereof. The anode catalyst may be dispersively supported or coated on a base material having electron conductivity. The base material is made of a material containing a metal as a main component, such as titanium (Ti) or stainless steel (SUS). Examples of the form of the base material include a sheet of a woven fabric or a nonwoven fabric, a mesh, a porous sintered body, a foamed molded body (foam), and an expanded metal. The anode catalyst may also be applied directly to the membrane.

The cathode electrode(cathode) hydrogenates a substance to be hydrogenated in a catholyte with protons to generate an organic hydride. The cathode electrodeof the present embodiment includes a catalyst layerand a diffusion layer. The catalyst layeris disposed closer to the membranethan the diffusion layer. The catalyst layerof the present embodiment is in contact with the main surface of the membrane. The catalyst layercontains, for example, platinum or ruthenium as a cathode catalyst for hydrogenating the substance to be hydrogenated. Preferably, the catalyst layercontains a porous catalyst support that supports a cathode catalyst. The catalyst support is made of an electron conductive material such as porous carbon, a porous metal, or a porous metal oxide. For example, the catalyst layeris formed by directly applying the cathode catalyst to the membrane.

The cathode catalyst is coated with an ionomer (cation exchange ionomer). For example, the catalyst support in a state of supporting the cathode catalyst is coated with an ionomer. Examples of the ionomer include perfluorosulfonic acid polymers such as Nafion (registered trademark) and Flemion (registered trademark). It is preferable that the cathode catalyst is partially coated with the ionomer. As a result, three elements (substances to be hydrogenated, protons, and electrons) necessary for an electrochemical reaction in the catalyst layercan be efficiently supplied to the reaction field.

The diffusion layeruniformly diffuses a substance to be hydrogenated in a liquid state supplied from the outside into the catalyst layer. An organic hydride generated in the catalyst layeris discharged to the outside of the catalyst layervia the diffusion layer. The diffusion layerof the present embodiment is in contact with a main surface of the catalyst layeron a side opposite to the membrane. The diffusion layeris made of a conductive material such as carbon or metal. The diffusion layeris a porous body such as a sintered body of fibers or particles or a foamed molded body. Specific examples of the material constituting the diffusion layerinclude a carbon woven fabric (carbon cloth), a carbon nonwoven fabric, and carbon paper.

The anode electrodeis accommodated in the anode chamber. The anode chamberis defined by, for example, the membrane, an end plate, and a spacer. The end plateis a plate material made of metal such as stainless steel or titanium, for example, and is installed on the anode electrodeon the side opposite to the membrane. The end plateas an example has a groove-shaped flow path on a main surface facing the anode electrodeside. The anolyte supplied to the anode chamberis supplied to the anode electrodethrough the flow path, and is discharged from the anode chamberthrough the flow path. The spaceris a frame-shaped sealing material disposed between the membraneand the end plate. A space excluding the anode electrodein the anode chamberconstitutes a flow path of the anolyte.

The end plateis provided with a first anode openingand a second anode openingthat communicate the inside and the outside of the anode chamber. The first anode openingis disposed below the second anode opening. In the present embodiment, the first anode openingis provided on a bottom surface of the anode chamber, and the second anode openingis provided on a top surface of the anode chamber. The first anode openingand the second anode openingmay or may not overlap when viewed from the vertical direction.

The cathode electrodeis accommodated in the cathode chamber. The cathode chamberis defined by, for example, the membrane, an end plate, and a spacer. The end plateis a plate material made of metal such as stainless steel or titanium, for example, and is installed on the cathode electrodeon the side opposite to the membrane. The end plateas an example has a groove-shaped flow path on a main surface facing the cathode electrodeside. The catholyte supplied to the cathode chamberis supplied to the cathode electrodethrough the flow path, and is discharged from the cathode chamberthrough the flow path. The spaceris a frame-shaped sealing material disposed between the membraneand the end plate. A space excluding the cathode electrodein the cathode chamberconstitutes a flow path of the catholyte.

The end plateis provided with a first cathode openingand a second cathode openingthat communicate the inside and the outside of the cathode chamber. The first cathode openingis disposed below the second cathode opening. In the present embodiment, the first cathode openingis provided on a bottom surface of the cathode chamber, and the second cathode openingis provided on a top surface of the cathode chamber. The first cathode openingand the second cathode openingmay or may not overlap when viewed from the vertical direction.

The anode chamberand the cathode chamberare partitioned by the membrane. The membraneis sandwiched between the anode electrodeand the cathode electrode. The membraneof the present embodiment is composed of a solid polymer electrolyte membrane having proton conductivity, and transfers protons from the anode chamberside to the cathode chamberside. The solid polymer electrolyte membrane is not particularly limited as long as it is a material through which protons conduct, and examples thereof include a fluorine-based ion exchange membrane having a sulfonate group.

The anolyte is supplied to the anode chamberby the anolyte supply device. The anolyte contains water for supply to the anode electrode. Examples of the anolyte include an aqueous sulfuric acid solution, an aqueous nitric acid solution, an aqueous hydrochloric acid solution, pure water, and ion-exchanged water.

The catholyte is supplied to the cathode chamberby the catholyte supply device. The catholyte contains an organic hydride raw material (substance to be hydrogenated) to be supplied to the cathode electrode. As an example, the catholyte does not contain an organic hydride before the operation of the organic hydride producing systemis started, and the organic hydride generated by electrolysis after the operation is started is mixed in, so that the catholyte becomes a liquid mixture of the substance to be hydrogenated and the organic hydride. The substance to be hydrogenated and the organic hydride are preferably liquid at 20° C. and 1 atm.

The substance to be hydrogenated and the organic hydride used in the present embodiment are not particularly limited as long as they are organic compounds capable of adding/desorbing hydrogen by reversibly causing a hydrogenation reaction/dehydrogenation reaction. For the substance to be hydrogenated and the organic hydride, for example, an acetone-isopropanol type, a benzoquinone-hydroquinone type, an aromatic hydrocarbon type, and the like can be widely used. Among these, an aromatic hydrocarbon type is preferable from the viewpoint of transportability during energy transport or the like.

The aromatic hydrocarbon compound used as the substance to be hydrogenated is a compound containing at least one aromatic ring. Examples of the aromatic hydrocarbon compound include benzene, alkylbenzenes, naphthalene, alkylnaphthalenes, anthracene, and diphenylethane. Alkylbenzenes include a compound in which 1 to 4 hydrogen atoms in the aromatic ring are substituted with a linear alkyl group or a branched alkyl group having 1 to 6 carbon atoms. Examples of such a compound include toluene, xylene, mesitylene, ethylbenzene, and diethylbenzene. Alkylnaphthalenes include a compound in which 1 to 4 hydrogen atoms in the aromatic ring are substituted with a linear alkyl group or a branched alkyl group having 1 to 6 carbon atoms. Examples of such a compound include methylnaphthalene. These compounds may be used alone or in combination.

The substance to be hydrogenated is preferably at least one of toluene and benzene. A nitrogen-containing heterocyclic aromatic compound such as pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole, or N-alkyldibenzopyrrole can also be used as the substance to be hydrogenated. The organic hydride is obtained by hydrogenating the above-mentioned substance to be hydrogenated, and examples thereof include cyclohexane, methylcyclohexane, dimethylcyclohexane, and piperidine.

Although only one electrolytic bathis shown in, the organic hydride producing systemmay include a plurality of electrolytic baths. In this case, the respective electrolytic bathsare arranged in the same direction so that, for example, the anode chamberand the cathode chamberare arranged in the same direction, and are stacked with an energizing plate interposed between the adjacent electrolytic baths. Thus, the respective electrolytic bathsare electrically connected in series. The energizing plate is made of a conductive material such as metal. The respective electrolytic bathsmay be connected in parallel, or may be arranged in a combination of series connection and parallel connection.

In the electrolytic bath, a reaction that occurs when toluene (TL) is used as an example of the substance to be hydrogenated is as follows. The organic hydride obtained in a case where toluene is used as the substance to be hydrogenated is methylcyclohexane (MCH).

That is, the electrode reaction in the anode electrodeand the electrode reaction in the cathode electrodeproceed in parallel. Protons generated by electrolysis of water in the anode electrodeare supplied to the cathode electrodevia the membrane. The electrons generated by electrolysis of water are supplied to the cathode electrodevia the end plate, an external circuit, and the end plate. The protons and electrons supplied to the cathode electrodeare used for hydrogenation of toluene in the cathode electrode. As a result, methylcyclohexane is generated.

Therefore, according to the organic hydride producing systemaccording to the present embodiment, the electrolysis of water and the hydrogenation reaction of the substance to be hydrogenated can be performed in one step. Therefore, it is possible to enhance the production efficiency of the organic hydride as compared with a conventional technique in which the organic hydride is produced by a two-stage process of a process of producing hydrogen by water electrolysis or the like and a process of chemically hydrogenating the substance to be hydrogenated in a reactor such as a plant. In addition, since a reactor for performing chemical hydrogenation, a high-pressure vessel for storing hydrogen produced by water electrolysis, or the like is unnecessary, a significant reduction in facility cost can be achieved.

In the cathode electrode, the following hydrogen gas generation reaction may occur as a side reaction together with the hydrogenation reaction of the substance to be hydrogenated as the main reaction. As the supply amount of the substance to be hydrogenated to the catalyst layerbecomes insufficient, this side reaction is likely to occur.

The power supplyis a DC power supply that supplies power to the electrolytic bath. When power is supplied from the power supplyto the electrolytic bath, a predetermined electrolysis voltage is applied between the anode electrodeand the cathode electrodeof the electrolytic bath, and an electrolysis current flows. The power supplyreceives power supply from a power supply deviceand supplies the power to the electrolytic bath. The power supply devicecan be constituted by a power generation apparatus that generates power using renewable energy, for example, a wind power generation apparatus, a solar power generation apparatus, or the like. Note that the power supply deviceis not limited to a power generation apparatus using renewable energy, and may be a system power supply, a power storage apparatus storing power from the renewable energy power generation apparatus or the system power supply, or the like. In addition, a combination of two or more of them may be used.

The anolyte supply devicesupplies the anolyte to the anode chamber. The anolyte supply deviceincludes an anolyte tank, a first anode pipe, a second anode pipe, and an anode pump. The anode pumpcan be constituted by a known pump such as a gear pump or a cylinder pump. The anolyte supply devicemay be caused to flow through the anolyte using a liquid feeding device other than the pump.

The anolyte tankstores the anolyte to be supplied to the anode chamber. The anolyte tankis connected to the anode chamberby the first anode pipe. The first anode pipehas one end connected to the anolyte tankand the other end connected to the first anode opening. The anode pumpis provided in the middle of the first anode pipe. The anolyte tankis also connected to the anode chamberby the second anode pipe. The second anode pipehas one end connected to the second anode openingand the other end connected to the anolyte tank.

The anolyte in the anolyte tankflows into the anode chamberfrom the first anode openingvia the first anode pipeby driving of the anode pump. The anolyte is supplied to the anode chamberand subjected to an electrode reaction in the anode electrode. The anolyte in the anode chamberis returned to the anolyte tankvia the second anode pipe. In the anode electrode, oxygen gas is generated by the electrode reaction. Therefore, oxygen gas is mixed into the anolyte discharged from the anode chamber. The anolyte tankalso functions as a gas-liquid separator, separates oxygen gas in the anolyte from the anolyte, and discharges the oxygen gas to the outside of the system. A gas-liquid separation tank may be provided in the middle of the second anode pipe.

The catholyte supply devicesupplies the catholyte to the cathode chamber. The catholyte supply devicecan supply any catholyte selected from a plurality of catholytes having different concentrations of substances to be hydrogenated to the cathode chamber. The catholyte supply deviceof the present embodiment includes a plurality of storages, a first cathode pipe, a second cathode pipe, a cathode pump, and a first on-off valveto a tenth on-off valve. The cathode pumpcan be constituted by a known pump such as a gear pump or a cylinder pump. The catholyte supply devicemay be caused to flow through the catholyte using a liquid feeding device other than the pump. The first on-off valveto the tenth on-off valvecan be constituted by a known valve such as an electromagnetic valve or an air drive valve. The number of catholytes selected is not limited to one. If a plurality of the catholytes is selected, they may be mixed in line by a line blending method and supplied to the cathode chamber.

The plurality of storagesindividually (by concentration) store a plurality of catholytes having different concentrations of substances to be hydrogenated. The catholyte supply deviceof the present embodiment includes, as the plurality of storages, an ultra-high concentration storage, a high concentration storage, a medium concentration storage, a low concentration storage, and an ultra-low concentration storage. The concentration of a substance to be hydrogenated in the catholyte stored in each of the storagesis the highest in the ultra-high concentration storage, the second highest in the high concentration storage, the third highest in the medium concentration storage, the fourth highest in the low concentration storage, and the lowest in the ultra-low concentration storage. The concentration of a substance to be hydrogenated in each catholyte is calculated by a ratio between the substance to be hydrogenated and an organic hydride which is a hydrogenated product of a substance to be hydrogenated in the catholyte. In the present embodiment, the case where the number of the plurality of storagesis five has been exemplified, but the present invention is not limited thereto. The plurality of storagesmay be two or more, or three or more. The upper limit number of the plurality of storagesis not particularly limited, but may be, for example, six or less, five or less, or four or less.

For example, in a preparation stage before the operation of the organic hydride producing systemis started, the catholyte whose concentration of a substance to be hydrogenated is adjusted in advance is stored in the ultra-high concentration storageto the ultra-low concentration storage. As an example, the ultra-high concentration storagestores a catholyte having a concentration of a substance to be hydrogenated of 100 mol %. The ultra-low concentration storagestores a catholyte having a concentration of a substance to be hydrogenated of 5 mol %. The high concentration storage, the medium concentration storage, and the low concentration storagestore catholytes having concentrations of substances to be hydrogenated of 75 mol %, 50 mol %, and 25 mol %, respectively. The concentration of a substance to be hydrogenated of 5 mol % is an example of a target concentration to be finally reached when the catholyte is electrolyzed in the electrolytic bath, but this numerical value may vary to any value from the viewpoint of energy efficiency of the present system. The concentration of a substance to be hydrogenated in the catholyte stored in the ultra-low concentration storagemay be 0 mol %. The concentration of a substance to be hydrogenated of each catholyte can be appropriately set based on experiments or simulations.

In the present embodiment, the storagesare constituted by tanks independent from each other. However, the present invention is not limited thereto, and for example, one tank may be partitioned into a plurality of mutually independent spaces, and each space may constitute the storage.

The plurality of storagesare connected to the cathode chamberby the first cathode pipe. One end of the first cathode pipeis branched into a plurality of parts and connected to each storage, and the other end is connected to the first cathode opening. One end of the first cathode pipeof the present embodiment is branched into five of a first branch pipeto a fifth branch pipe. The first branch pipeto the fifth branch pipeare disposed in this order, and the first branch pipeis disposed closest to the first cathode opening. The first branch pipeis connected to the ultra-high concentration storage, the second branch pipeis connected to the high concentration storage, the third branch pipeis connected to the medium concentration storage, the fourth branch pipeis connected to the low concentration storage, and the fifth branch pipeis connected to the ultra-low concentration storage. The arrangement order of the ultra-high concentration storageto the ultra-low concentration storageis not particularly limited.

The cathode pumpis provided in a region on the first cathode openingside of the first branch pipein the middle of the first cathode pipe. The first on-off valveis provided in the middle of the first branch pipe. The second on-off valveis provided in the middle of the second branch pipe. The third on-off valveis provided in the middle of the third branch pipe. The fourth on-off valveis provided in the middle of the fourth branch pipe. The fifth on-off valveis provided in the middle of the fifth branch pipe

The plurality of storagesare also connected to the cathode chamberby the second cathode pipe. One end of the second cathode pipeis connected to the second cathode opening, and the other end is branched into a plurality of parts and connected to each storage. The other end of the second cathode pipeof the present embodiment is branched into five of a sixth branch pipeto a tenth branch pipe. The sixth branch pipeis connected to the ultra-high concentration storage, the seventh branch pipeis connected to the high concentration storage, the eighth branch pipeis connected to the medium concentration storage, the ninth branch pipeis connected to the low concentration storage, and the tenth branch pipeis connected to the ultra-low concentration storage

The sixth on-off valveis provided in the middle of the sixth branch pipe. The seventh on-off valveis provided in the middle of the seventh branch pipe. The eighth on-off valveis provided in the middle of the eighth branch pipe. The ninth on-off valveis provided in the middle of the ninth branch pipe. The tenth on-off valveis provided in the middle of the tenth branch pipe

The catholyte in each storageflows into the cathode chamberfrom the first cathode openingvia the first cathode pipeby driving of the cathode pump. Which storagesupplies the catholyte to the cathode chambercan be switched according to the open/close states of the first on-off valveto the fifth on-off valve. The catholyte is supplied to the cathode chamberand subjected to an electrode reaction in the cathode electrode. The catholyte in the cathode chamberis returned to each storagevia the second cathode pipe. Which storagethe catholyte is returned to can be switched according to the open/close states of the sixth on-off valveto the tenth on-off valve.

As described above, in the cathode electrode, hydrogen gas may be generated by a side reaction. When a side reaction occurs, hydrogen gas is mixed in the catholyte discharged from the cathode chamber. Each storagealso functions as a gas-liquid separator, separates hydrogen gas in the catholyte from the catholyte, and discharges the hydrogen gas to the outside of the system. A gas-liquid separation tank may be provided in the middle of the second cathode pipe. When the protons travel from the anode chamberside to the cathode chamberside through the membrane, they travel together with water molecules. Therefore, water is mixed in the catholyte discharged from the cathode chamber. To deal with this mixed water, an oil water separation tank may be provided in the middle of the second cathode pipeto separate water in the catholyte from the catholyte.