Hydrogen production apparatus and hydrogen production method

Abstract

The present invention addresses the problem of providing a hydrogen production apparatus and a hydrogen production method which, in the production of hydrogen by electrolysis of water, allow the use of salt water as a feedstock while suppressing generation of chlorine.　In order to solve the above-described problem, the present invention provides: a hydrogen production apparatus for producing hydrogen by electrolysis of salt water, the hydrogen production apparatus being provided with an electrolysis unit in which a cation exchanger is disposed between electrodes, wherein an electrolyte solution that does not contain chloride ions is introduced to the anode side of the electrolysis unit, and salt water is introduced to the cathode side of the electrolysis unit; and a hydrogen production method.　According to the present invention, electrolysis can be performed while maintaining a state in which chloride ions that cause chlorine gas generation do not exist on the anode side. Consequently, in the production of hydrogen by electrolysis of water, salt water can be used as the feedstock for the production of hydrogen while suppressing the generation of chlorine, and, when the hydrogen production apparatus is increased in scale, the cost and the environmental load can be reduced.

Description

Hydrogen production device and hydrogen production method

[0001] The present invention relates to a hydrogen production device and a hydrogen production method, and more particularly to a hydrogen production device and a hydrogen production method that use water containing chloride ions (chlorine) as a raw material and are capable of suppressing chlorine generation.

[0002] Carbon dioxide is believed to have a major impact on environmental problems such as global warming, and reducing its emissions into the environment is an issue that must be addressed immediately. To address this issue, research is being conducted into technologies to reduce carbon dioxide emissions themselves, as well as technologies to capture and fix emitted carbon dioxide.

[0003] In recent years, research into technologies for energy sources that do not generate or emit carbon dioxide has been progressing from the perspective of reducing carbon dioxide emissions into the atmosphere. One such energy source is hydrogen. Hydrogen has the advantage of not emitting carbon dioxide when used as an energy source, such as in the generation of electricity by reacting with oxygen or in heat recovery by combustion. This has led to its potential as a next-generation energy source. While hydrogen has the advantage of being able to be produced from a variety of resources, the currently mainstream method of producing hydrogen, steam reforming using fossil fuels, poses the problem of emitting carbon monoxide and carbon dioxide when producing hydrogen. Therefore, there is a need for technologies that do not emit carbon dioxide when producing hydrogen.

[0004] For example, Patent Document 1 describes a hydrogen production device that includes a solar power generation unit equipped with a solar power generation module that generates electricity using sunlight, an electrolysis module that electrolyzes water (pure water) using the electricity obtained by the solar power generation unit, and heating means that heats the water to be supplied to the electrolysis module.

[0005] Japanese Patent Application Laid-Open No. 2020-196927

[0006] As described in Patent Document 1, hydrogen production by water electrolysis does not generate carbon dioxide during the process, and hydrogen produced by water electrolysis is also known as green hydrogen and has attracted attention. Furthermore, as described in Patent Document 1, it is known that hydrogen production without carbon dioxide emissions is possible by using renewable energy, such as solar power, as the energy required for water electrolysis and water heating. Here, Patent Document 1 describes pure water as the target for electrolysis. In order to utilize hydrogen as a next-generation energy source in the future, hydrogen production equipment will need to be scaled up. However, the hydrogen production described in Patent Document 1 requires the use of large amounts of pure water. On the other hand, from the perspective of effective use of water resources, consuming large amounts of pure water as a raw material for hydrogen production is undesirable. Furthermore, adding chemicals as electrolytes to pure water to improve the efficiency of hydrogen production is also undesirable because it increases costs when scaled up. Therefore, in order to establish hydrogen production by water electrolysis (green hydrogen production) as an environmentally friendly and sustainable technology, a technology that reduces the amount of pure water used is required.

[0007] One technique for producing hydrogen by water electrolysis while reducing the amount of pure water used is to use water that is not suitable for drinking (water containing a certain amount of electrolytes) as a raw material instead of pure water. More specifically, hydrogen can be produced by electrolyzing seawater. Approximately 70% of the Earth's surface is covered by ocean, making seawater a more abundant water resource than pure water or freshwater. Therefore, hydrogen production using seawater is expected to be an environmentally sustainable technology. However, electrolysis of water containing chloride ions (chlorine), such as seawater (hereinafter referred to as "saltwater"), produces chlorine gas. This chlorine gas poses a significant environmental burden and cannot be directly released into the atmosphere. It must be recovered and detoxified, which poses a significant cost increase when hydrogen production is scaled up.

[0008] Therefore, an object of the present invention is to provide a hydrogen production device and a hydrogen production method that can use salt water as a raw material and suppress the generation of chlorine in hydrogen production by water electrolysis.

[0009] As a result of extensive research into the above-mentioned problems, the present inventors discovered that, in an electrolysis unit that electrolyzes brine, by introducing an electrolyte solution that does not contain chloride ions into the anode side and introducing brine into the cathode side, it is possible to suppress the generation of chlorine and use brine as a raw material for hydrogen production, and thus completed the present invention. That is, the present invention relates to the following hydrogen production device and hydrogen production method.

[0010] The hydrogen production device of the present invention, which solves the above-mentioned problems, is a hydrogen production device that produces hydrogen by brine electrolysis, and is characterized by including an electrolysis unit with a cation exchanger disposed between electrodes, and introducing a chloride ion-free electrolyte into the anode side of the electrolysis unit, and introducing brine into the cathode side of the electrolysis unit. In the hydrogen production device of the present invention, brine is introduced into the cathode side of the electrolysis unit with a cation exchanger disposed between the electrodes, while introducing a chloride ion-free electrolyte into the anode side. By introducing brine into the cathode side of the electrolysis unit with a cation exchanger disposed between the electrodes, and introducing a chloride ion-free electrolyte into the anode side, the cation exchanger inhibits the migration of chloride ions from the cathode side to the anode side during electrolysis, enabling electrolysis to be performed while maintaining the absence of chloride ions, which cause chlorine gas generation, on the anode side. In other words, during electrolysis, hydrogen is generated on the cathode side, while chlorine gas generation on the anode side is inhibited. This enables the use of brine as a raw material for hydrogen production while inhibiting chlorine generation, and also enables cost reduction and environmental impact reduction when implementing large-scale hydrogen production devices.

[0011] Furthermore, one embodiment of the hydrogen production device of the present invention is characterized in that moisture is supplied from brine via an FO membrane to the electrolyte on the anode side of the electrolysis unit. On the anode side of the electrolysis unit in the hydrogen production device of the present invention, instead of chlorine production by chloride ions, an oxygen production reaction occurs due to water decomposition. Therefore, as electrolysis progresses, the amount of water (moisture) on the anode side decreases. Therefore, to continuously produce hydrogen, it is necessary to supply water (moisture) to the anode side. This feature allows the moisture that permeates brine when it comes into contact with the FO membrane to be used as moisture supplied to the anode side, thereby further increasing the proportion of brine used in the hydrogen production device. This further reduces the amount of pure water used in hydrogen production by water electrolysis, enabling both the effective use of water resources and the effective production of green hydrogen.

[0012] The present invention also provides a hydrogen production method for solving the above problems, which is a hydrogen production method for producing hydrogen by brine electrolysis. The method includes the steps of: using an electrolysis unit having a cation exchanger disposed between electrodes; introducing a chloride ion-free electrolyte solution to the anode side of the electrolysis unit; introducing brine to the cathode side of the electrolysis unit; and performing electrolysis with suppressed chlorine generation. The hydrogen production method of the present invention introduces brine to the cathode side of the electrolysis unit having a cation exchanger disposed between the electrodes; and introducing a chloride ion-free electrolyte solution to the anode side. During electrolysis, the cation exchanger inhibits the migration of chloride ions from the cathode side to the anode side, enabling electrolysis to be performed while maintaining the absence of chloride ions, which could cause chlorine gas generation, on the anode side. In other words, electrolysis can be performed while generating hydrogen on the cathode side and suppressing chlorine gas generation on the anode side. This allows for the use of brine as a raw material for hydrogen production while suppressing chlorine generation in water electrolysis. This also enables cost reduction and reduced environmental impact when implementing large-scale hydrogen production equipment.

[0013] According to the present invention, it is possible to provide a hydrogen production device and a hydrogen production method that can use salt water as a raw material and suppress the generation of chlorine in hydrogen production by water electrolysis.

[0014] FIG. 1 is a schematic explanatory diagram of a hydrogen production apparatus according to a first embodiment of the present invention. FIG. 2 is a schematic explanatory diagram showing the steps relating to hydrogen production and recovery in the hydrogen production apparatus according to the first embodiment of the present invention. FIG. 3 is a schematic explanatory diagram of a hydrogen production apparatus according to a third embodiment of the present invention. FIG. 4 is a schematic explanatory diagram showing the steps relating to hydrogen production and recovery, and carbon dioxide fixation in the hydrogen production apparatus according to the third embodiment of the present invention.

[0015] Hereinafter, embodiments of the hydrogen production apparatus and method according to the present invention will be described in detail with reference to the drawings. Note that the hydrogen production apparatus and method described in the embodiments are merely examples for the purpose of explaining the hydrogen production apparatus and method according to the present invention, and are not limited thereto.

[0016] The hydrogen production apparatus and method of the present invention relate to hydrogen production by water electrolysis, and more specifically, to hydrogen production involving brine electrolysis using brine as a raw material for hydrogen production. Here, brine in the present invention refers to an aqueous solution containing chloride ions (chlorine). Furthermore, brine in the present invention also functions as an electrolyte. In particular, it is preferable to use brine that is abundant and easily obtained as a water resource, specifically seawater. Other examples of brine in the present invention include river water and lake water containing chloride ions, as well as industrial wastewater and factory wastewater containing chloride ions. The following description will be given primarily of a case where seawater is used as brine, but the present invention is not limited thereto.

[0017] [First embodiment] (Hydrogen production device) Figure 1 is a schematic explanatory diagram showing the structure of a hydrogen production device in a first embodiment of the present invention. As shown in Figure 1, the hydrogen production device 10A in this embodiment has an electrolysis unit 20 that electrolyzes salt water (hereinafter referred to as "seawater"). The electrolysis unit 20 also includes a seawater inlet (line L1) for introducing seawater, an electrolyte inlet (line L2) for introducing an electrolyte that does not contain chloride ions (hereinafter simply referred to as "electrolyte E"), a hydrogen recovery unit (line L3) for recovering hydrogen, and an oxygen recovery unit (line L4) for recovering oxygen.

[0018] The electrolysis unit 20 in this embodiment electrolyzes seawater to generate hydrogen and recover the generated hydrogen. The source of seawater introduced into the electrolysis unit 20 (hereinafter referred to as the "seawater source") is not particularly limited. For example, the natural environment (ocean) may be used as the seawater source, and seawater may be introduced directly from the ocean into the electrolysis unit 20. Alternatively, artificially temporarily stored seawater, such as seawater used for ocean carbon dioxide storage or as ballast water for ships, may be used as the seawater source. Note that the cost of procuring seawater as a raw material is primarily the cost of transporting the seawater. For example, by installing the hydrogen production device 10A of the present invention on land near the sea or on the sea (including on ships, etc.), it becomes possible to use seawater with minimal transportation costs.

[0019] As shown in Fig. 1, the electrolysis unit 20 in this embodiment includes a pair of electrodes (electrodes 22a, 22b) and a cation exchanger 23 provided in a treatment tank 21. As shown in Fig. 1, two spaces (spaces 24a, 24b) are formed within the treatment tank 21 via the cation exchanger 23.

[0020] The treatment tank 21 may be made of any material or have any shape as long as it is capable of stably storing seawater and electrolyte. For example, the treatment tank 21 may be made of any material or have any shape that is used in structures known as electrolytic cells or electrodialysis cells.

[0021] The electrodes 22a and 22b are provided in the spaces 24a and 24b, respectively, and are connected by wires. The electrodes 22a and 22b may be provided on or near the surface of the cation exchanger 23, and the electrodes 22a and 22b and the cation exchanger 23 may be treated as an integrated unit. The electrodes 22a and 22b may function as either an anode or a cathode, and the material and shape of the electrodes 22a and 22b are not particularly limited. In this embodiment, the following description will be given assuming that the electrode 22a functions as the anode and the electrode 22b functions as the cathode. Examples of materials for the electrodes 22a and 22b include carbon and metals (stainless steel, platinum, copper, etc.) that are widely used as electrode materials in the field of electrochemistry. Examples of shapes for the electrodes 22a and 22b include a flat, rod-like, and mesh-like shape. When the electrodes 22a and 22b are provided on or near the surface of the cation exchanger 23, it is preferable that the electrodes 22a and 22b have a shape that minimizes the inhibition of mass transfer to the cation exchanger 23. Examples of such shapes include a mesh shape and a thin rod shape such as a wire. Another example of the electrodes 22a, 22b is an electrode pattern formed directly on the surface of the cation exchanger 23 by a technique such as plating. In this case, the shape of the electrode pattern is not particularly limited, but it is preferable that the shape be such that it can suppress the inhibition of mass transfer to the cation exchanger 23.

[0022] Furthermore, when connecting the electrodes 22a and 22b with a conductor, it is preferable to provide a DC power supply to supply electrical energy between the electrodes. In this case, the power supply means for the DC power supply connected to the pair of electrodes is not particularly limited, but it is preferable to use a power supply facility that uses renewable energy such as solar, wind, or wave power, or surplus power from other facilities. This makes it possible to reduce the energy used in hydrogen production (hydrogen generation and recovery). In particular, adopting a power supply means that uses renewable energy that does not emit carbon dioxide during power generation also has the effect of promoting the reduction of carbon dioxide emissions.

[0023] The cation exchanger 23 is a membrane that partitions the treatment tank 21 and is capable of selectively allowing cations to pass from a space 24a (hereinafter also referred to as the "anode side") in which the anode (electrode 22a) is disposed to a space 24b (hereinafter also referred to as the "cathode side") in which the cathode (electrode 22b) is disposed. The cation exchanger 23 in this embodiment is a membrane that prevents chloride ions on the cathode side from migrating to the anode side and also prevents hydrogen ions (H ＋ ) to the cathode side. This suppresses the generation of chlorine gas on the anode side, and allows hydrogen ions generated on the anode side to migrate to the cathode side, thereby increasing the reaction efficiency of the reaction involving hydrogen production on the cathode side. In this embodiment, the cation exchanger 23 may be any membrane that has the function of restricting the migration of anions and at least allowing hydrogen ions to pass through, and the specific components and structure are not particularly limited. For example, a membrane that has been treated to selectively allow monovalent cations to pass through (a so-called monovalent ion selective membrane) or a known cation exchange membrane that allows the migration of divalent or higher cations in addition to monovalent cations can be used.

[0024] The treatment tank 21 is connected to a line L1 as a seawater inlet that introduces seawater from a seawater source to the cathode side (space 24b) of the electrolysis unit 20, and a line L2 as an electrolyte inlet that introduces electrolyte E to the anode side (space 24a) of the electrolysis unit 20.

[0025] The line L1 that introduces seawater to the cathode side of the electrolysis unit 20 is not particularly limited as long as it is connected to the space 24b and has a material and structure that allows stable transport of seawater. It is preferable that the line L1 be provided with a means for preventing contaminants and organisms in the seawater from entering the treatment tank 21. For example, a filter or net for capturing contaminants and organisms in the seawater may be provided on the line L1.

[0026] Furthermore, the line L2 for introducing the electrolytic solution E to the anode side of the electrolysis unit 20 is not particularly limited as long as it is connected to the space 24a and has a material and structure capable of stably transporting the electrolytic solution E. The electrolytic solution E may be any solution that does not contain chloride ions and is electrically conductive. For example, the electrolytic solution E in this embodiment may be prepared by dissolving an electrolyte (excluding substances containing chloride ions) in pure water. Specific examples of the electrolytic solution E include aqueous solutions of strong acids (excluding hydrochloric acid) or strong bases, in terms of ease of procurement, cost, and the degree of ionization. In particular, it is preferable to use an aqueous solution of a hydroxide (strong base), such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution, as the electrolytic solution E in this embodiment. As a result, only the reaction related to water electrolysis proceeds on the anode side, as described below. This improves the reaction efficiency related to water electrolysis throughout the electrolysis unit 20, thereby enabling high efficiency in hydrogen production.

[0027] As will be described later, in the hydrogen production device 10A of this embodiment, hydrogen is produced on the cathode side and oxygen is produced on the anode side by performing electrolysis in the electrolysis unit 20. Therefore, the treatment tank 21 is provided with a line L3 as a hydrogen recovery unit that recovers the gas (hydrogen) produced on the cathode side, and a line L4 as an oxygen recovery unit that recovers the gas (oxygen) produced on the anode side.

[0028] As will be described later, the hydrogen recovered by the hydrogen recovery unit (line L3) in this embodiment is produced without emitting carbon dioxide, and is known as green hydrogen, a substance that is attracting attention as a next-generation energy source. Therefore, it is preferable to provide a means for removing gases other than hydrogen (such as water vapor) on line L3. This allows for the recovery of highly pure hydrogen, enabling the recovered hydrogen to be used more effectively as an energy source. Furthermore, line L3 may be connected to equipment for storing hydrogen or equipment for controlling the amount of hydrogen supplied. This allows the generated and recovered hydrogen to be used as an energy source as appropriate.

[0029] On the other hand, the oxygen recovered by the oxygen recovery section (line L4) in this embodiment may be utilized by connecting line L4 to equipment for recovering and utilizing high-purity oxygen, as in the case of hydrogen, or may be discharged directly to the outside of the system.

[0030] Furthermore, the treatment tank 21 may be provided with respective discharge lines (not shown) for discharging the solutions on the cathode side and the anode side after electrolysis.

[0031] (Hydrogen Production Method) In this embodiment, the hydrogen production method by saltwater electrolysis involves electrolyzing saltwater (seawater) using a treatment tank 21 partitioned by a cation exchanger 23, thereby generating and recovering hydrogen. The steps involved in generating and recovering hydrogen in the electrolysis unit 20 will be described below with reference to FIG. 2 . FIG. 2 is a schematic diagram illustrating the steps of generating and recovering hydrogen in the electrolysis unit 20 of the hydrogen production device 10A of this embodiment. The configuration inside the treatment tank 21 in FIG. 2 is the same as the configuration shown in FIG. 1 . Note that FIG. 2 mainly illustrates the movement of ions and molecules involved in the generation and recovery of hydrogen, and some ions and molecules are not shown.

[0032] As shown in Figure 2, seawater is first introduced into the cathode side (space 24b) of treatment tank 21 via line L1, and electrolyte E is introduced into the anode side (space 24a) of treatment tank 21 via line L2. Then, a voltage is applied between electrodes 22a and 22b from a DC power supply. At this time, the reaction at electrode 22a in space 24a (anode side reaction) is expressed by the following formula 1:

[0033] 2, the hydrogen ions generated by the reaction of formula 1 move to the cathode side (space 24b) through the cation exchanger 23. As described above, the oxygen generated by the reaction of formula 1 may be recovered and utilized via line L4, or may be discharged directly to the outside of the system.

[0034] When the hydrogen production device 10A of this embodiment is used, an electrolyte solution (electrolyte solution E) that does not contain chloride ions is used on the anode side, and the migration of chloride ions from the cathode side to the anode side is suppressed by the cation exchanger 23. Therefore, unlike normal saltwater (seawater) electrolysis, the reaction of chloride ions to chlorine gas does not proceed.

[0035] On the other hand, the reaction at the electrode 22b in the space 24b (the reaction on the cathode side) is expressed by the following formula 2.

[0036] Furthermore, the hydrogen ions that have moved from the space 24a to the space 24b undergo a reaction at the electrode 22b to produce hydrogen (Equation 3).

[0037] As shown in Equations 1 to 3, hydrogen can be generated from saltwater (seawater) by the electrolysis unit 20. The generated hydrogen is recovered via line L3 and utilized as an energy source. Furthermore, as shown in Equations 1 to 3, the hydrogen production device 10A and hydrogen production method of this embodiment do not produce carbon dioxide in the processes related to hydrogen generation and recovery, making it possible to suppress carbon dioxide emissions in addition to hydrogen production.

[0038] 1 and 2, the electrolysis unit 20 in the hydrogen production device 10A may be provided with various additional means for efficiently generating and recovering hydrogen. Examples of such means include means for suppressing the formation of precipitates on the surfaces of the electrodes 22a and 22b, and means for suppressing a decrease in the ion permeation efficiency of the cation exchanger 23.

[0039] As described above, in the hydrogen production device 10A of this embodiment and the hydrogen production method using this device 10A, saltwater is introduced to the cathode side of an electrolysis unit having a cation exchanger disposed between the electrodes, while an electrolyte solution containing no chloride ions is introduced to the anode side. During electrolysis, the cation exchanger inhibits the migration of chloride ions from the cathode side to the anode side, enabling electrolysis to be performed while maintaining the absence of chloride ions, which would otherwise cause chlorine gas generation, on the anode side. That is, during electrolysis, hydrogen is generated on the cathode side, while chlorine gas generation on the anode side is inhibited. This enables the use of saltwater as a raw material for hydrogen production while inhibiting chlorine generation, and also enables cost reduction and reduced environmental impact when the hydrogen production device is scaled up.

[0040] [Second Embodiment] The hydrogen production device 10B according to the second embodiment is provided with a means for supplying moisture to the electrolytic solution E introduced into the anode side (space 24a) of the electrolysis unit 20 according to the first embodiment. More specifically, moisture from salt water is supplied to the electrolytic solution E on the anode side via the FO membrane 25.

[0041] FIG. 3 is a schematic diagram showing a hydrogen production device 10B according to a second embodiment of the present invention. As shown in FIG. 3, the hydrogen production device 10B of this embodiment further includes an FO membrane 25 in the treatment tank 21 shown in the first embodiment, and forms a space 24c outside the space 24a. It also includes a saltwater supply unit (line L5) that supplies saltwater (seawater) to the space 24c, a circulation discharge unit (line L6) that discharges and circulates the seawater introduced into the space 24b, and a circulation discharge unit (line L7) that discharges and circulates the seawater supplied to the space 24c. Note that the description of the same components as those in the first embodiment will be omitted.

[0042] As described above, on the anode side of the electrolysis unit 20, the water decomposition reaction based on Equation 1 progresses, and as electrolysis progresses, the water (moisture) on the anode side decreases. Therefore, in order to continuously produce hydrogen, it is necessary to supply water (moisture) to the anode side. Here, from the viewpoint of effective use of water resources, it is preferable to use a water resource other than pure water as the water to be supplied to the anode side. In this case, it is particularly preferable to use saltwater as the water resource used, and the same saltwater (seawater, etc.) as that introduced to the cathode side can be used. In addition, it is preferable to be able to supply water according to the amount of moisture consumed on the anode side.

[0043] The FO membrane 25 used in the hydrogen production device 10B of this embodiment is also called a forward osmosis membrane and is a type of semipermeable membrane that allows water molecules to pass through but not molecules or ions above a certain size. Therefore, by using this FO membrane 25, it is possible to allow only water to pass from saltwater (seawater). Furthermore, the FO membrane 25 allows only water (moisture) to pass from a solution with low osmotic pressure to a solution with high osmotic pressure. Therefore, by utilizing the ability to allow water to pass through depending on the osmotic pressure difference between the solutions facing each other via the FO membrane 25, it is possible to supply water from saltwater (seawater) depending on the amount of water consumed on the anode side. The specific material of the FO membrane 25 in this embodiment is not particularly limited, and known materials can be used.

[0044] The hydrogen production device 10B in this embodiment may be any device capable of supplying moisture from saltwater to the electrolyte solution E via the FO membrane 25. For example, as shown in FIG. 3 , the FO membrane 25 is used to partition the treatment tank 21 into a space 24a and a space 24c, and saltwater (seawater) is supplied to the space 24c via a line L5. This allows the saltwater (seawater) in the space 24c to face the electrolyte solution E in the space 24a via the FO membrane 25. To ensure moisture supply from the space 24c to the space 24a via the FO membrane 25, a means for lowering the electrolyte concentration of the saltwater supplied to the space 24c below the electrolyte concentration of the electrolyte solution E in the space 24a may be provided. For example, a means for adding an electrolyte (excluding substances containing chloride ions) to the electrolyte solution E or a means for diluting the saltwater supplied to the space 24c may be provided.

[0045] Furthermore, the water decomposition reaction based on Equation 2 also progresses on the cathode side of the electrolysis unit 20, and the water (moisture) on the cathode side decreases as electrolysis proceeds. Therefore, the hydrogen production device 10B in this embodiment is preferably provided with a circulating supply unit (lines L1 and L6) for circulating and supplying salt water (seawater) to be introduced to the cathode side of the treatment tank 21, as shown in Fig. 3. This makes it possible to continue electrolysis (hydrogen production) without causing a decrease in moisture on the cathode side.

[0046] Furthermore, when saltwater (seawater) is supplied to the space 24c, the amount of water in the saltwater in the space 24c decreases by supplying water to the electrolyte E on the anode side. Therefore, the hydrogen production device 10B in this embodiment is preferably provided with a circulating supply unit (lines L5 and L7) for circulating the saltwater (seawater) to be supplied to the space 24c, as shown in Fig. 3. This allows for a stable supply of water to the electrolyte E on the anode side.

[0047] The method of producing hydrogen by brine electrolysis in the hydrogen production device 10B of this embodiment is similar to the hydrogen production in the first embodiment described above, in that brine (seawater) is electrolyzed to generate and recover hydrogen, and in addition includes a step of supplying moisture from the brine to the electrolyte solution E on the anode side via the FO membrane 25.

[0048] The steps involved in the generation and recovery of hydrogen in the hydrogen production device 10B of this embodiment will be described below with reference to Fig. 4. Fig. 4 is a schematic diagram illustrating the steps of generating and recovering hydrogen in the electrolysis unit 20 of the hydrogen production device 10B of this embodiment. The configuration inside the treatment tank 21 in Fig. 4 is the same as the configuration shown in Fig. 3. Note that Fig. 4 mainly illustrates the components involved in the generation and recovery of hydrogen (during electrolysis), with some components not shown. Fig. 4 also mainly illustrates the movement of ions and molecules involved in the generation and recovery of hydrogen, with some ions and molecules not shown.

[0049] As in the first embodiment, seawater is introduced into the cathode side (space 24b) of treatment tank 21 via line L1, and electrolytic solution E is introduced into the anode side (space 24a) of treatment tank 21 via line L2. A voltage is then applied between electrodes 22a and 22b by a DC power supply. At this time, the seawater introduced into the cathode side is discharged via line L6 and then circulated and supplied again to space 24b via line L1.

[0050] Furthermore, salt water (seawater) is supplied to the space 24c of the treatment tank 21 via line L5. The timing of supplying salt water to the space 24c is not particularly limited, and may be before, during, or after the application of voltage. The salt water supplied to the space 24c is then discharged via line L7 and circulated back to the space 24c via line L5.

[0051] By applying a voltage, a reaction (anode side reaction) proceeds at the electrode 22a in the space 24a according to formula 1. Here, the hydrogen ions generated according to formula 1 move to the cathode side (space 24b) through the cation exchanger 23 as shown in FIG. 4. Furthermore, according to formula 1, water (H ２ O) will be consumed.

[0052] Water (H ２ When the electrolyte E and the saltwater in the space 24c are consumed, an osmotic pressure difference occurs between the electrolyte E and the saltwater in the space 24c, and water (H ２ O) passes through the space 24a and is supplied to the electrolytic solution E. As a result, in the space 24a, only water (H ２ O) is supplied via the FO membrane 25 in the amount consumed. At this time, the electrolyte itself in the electrolytic solution E is not consumed, and the absolute amount does not change. Therefore, it is not necessary to supply chemicals (electrolytes) or pure water to the anode side (space 24 a) other than the water supply via the FO membrane 25.

[0053] It should be noted that, unlike ordinary saltwater (seawater) electrolysis, the reaction of chloride ions to chlorine gas does not proceed on the anode side when the hydrogen production device 10B of this embodiment is used. Furthermore, the oxygen generated by Equation 1 may be recovered and utilized via line L4, as described above, or may be discharged directly to the outside of the system.

[0054] Meanwhile, the reaction (cathode reaction) at the electrode 22b in the space 24b proceeds based on Equations 2 and 3, generating hydrogen. As described above, the generated hydrogen is recovered via line L3 and utilized as an energy source.

[0055] As described above, the hydrogen production device 10B and hydrogen production method of this embodiment allow the moisture that permeates saltwater when it comes into contact with the FO membrane to be used as moisture to be supplied to the electrolyte on the anode side, which decreases with electrolysis, and thus makes it possible to further increase the proportion of saltwater used in hydrogen production. This makes it possible to further reduce the amount of pure water used in hydrogen production by water electrolysis, making it possible to effectively utilize water resources and produce green hydrogen at the same time.

[0056] [Third embodiment] The hydrogen production device 10C according to the third embodiment has a configuration that enables carbon dioxide fixation treatment in addition to hydrogen production with reduced carbon dioxide emissions. More specifically, carbon dioxide fixation is performed using the solution (seawater) on the cathode side after electrolysis in the electrolysis unit 20. The electrolysis unit 20 in this embodiment may be any of the electrolysis units 20 in the first and second embodiments described above. The electrolysis unit 20 in this embodiment will be described as having the same configuration as the electrolysis unit 20 in the second embodiment, and descriptions of components that are the same as those in the second embodiment will be omitted.

[0057] 5 is a schematic diagram showing a hydrogen production device 10C according to a third embodiment of the present invention. As shown in Fig. 5, the hydrogen production device 10C according to this embodiment includes a carbon dioxide supply unit (line L8) that supplies carbon dioxide to the electrolysis unit 20 in order to perform a carbon dioxide fixation process using the solution that has been subjected to electrolysis in the electrolysis unit 20.

[0058] The supply source (or generation source) of carbon dioxide supplied via the carbon dioxide supply unit (line L8) is not particularly limited. Specific examples of carbon dioxide supply sources include gases containing carbon dioxide emitted from various facilities (power generation facilities, factories, ordinary households, etc.) and transportation means in connection with daily life and industrial activities, as well as naturally occurring gases containing carbon dioxide such as the atmosphere and volcanic gases.

[0059] The carbon dioxide supply unit (line L8) may be provided with a means for adjusting the amount of carbon dioxide supplied or a means for more effectively dissolving carbon dioxide in the saltwater on the cathode side. Specific examples include providing a flow control valve or a pressure mechanism on line L8, or providing a structure at the end of line L8 for blowing carbon dioxide into the saltwater on the cathode side.

[0060] The method of producing hydrogen by brine electrolysis in the hydrogen production device 10C of this embodiment is similar to the hydrogen production in the first and second embodiments described above, in that brine (seawater) is electrolyzed to generate and recover hydrogen, and additionally includes a step of using the solution after electrolysis for fixation of carbon dioxide.

[0061] The steps of hydrogen production and recovery and carbon dioxide immobilization in the hydrogen production device 10C of this embodiment will be described below with reference to FIG. 6 . FIG. 6 is a schematic diagram illustrating the steps of hydrogen production and recovery and carbon dioxide immobilization in the electrolysis unit 20 of the hydrogen production device 10C of this embodiment. The configuration inside the treatment tank 21 in FIG. 6 is the same as the configuration shown in FIG. 5 . Note that FIG. 6 mainly illustrates the components involved in hydrogen production and recovery (during electrolysis) and carbon dioxide immobilization, with some components not shown. Also, FIG. 6 mainly illustrates the movement of ions and molecules involved in hydrogen production and recovery and carbon dioxide immobilization, with some ions and molecules not shown.

[0062] First, the reaction involved in the fixation of carbon dioxide will be described. Generally, when carbon dioxide is dissolved in water, a chemical equilibrium equation such as the following equation 4 holds true.

[0063] The carbonate ion (CO ３ ２－ ) reacts with divalent metal ions (calcium ions) to form carbonate as shown in Equation 5. This progresses the fixation process of carbon dioxide.

[0064] In addition, although Formula 5 shows calcium ions as divalent metal ions, the carbon dioxide fixation treatment of this embodiment is not limited to this. For example, divalent ions of Group 2 elements other than Ca (Mg ２＋ etc.), and divalent ions of transition metals (Fe ２＋ , Co ２＋ , Ni ２＋ Examples include using a divalent metal ion source such as a saltwater source (e.g., a saltwater source containing divalent metal ions) that is introduced into the cathode. It is particularly preferable to use divalent metal ions that are already contained in the saltwater introduced into the cathode. For example, when the saltwater introduced into the cathode is seawater, it contains a certain amount of Ca and Mg in ionic form, and therefore can be used as a divalent metal ion source that can supply a stable amount of divalent metal ions. Carbonates of Group 2 elements have low solubility in water and are harmless, so the generated carbonates do not need to be further treated. Furthermore, the generated carbonates are easy to recover, and have the advantage that the recovered carbonates can be used as a resource for various purposes.

[0065] It can be seen from Equations 4 and 5 that the efficiency of the carbon dioxide fixation process can be improved by progressing the chemical equilibrium reaction in the direction of producing carbonate ions. In other words, by progressing the chemical equilibrium in Equation 4 to the right and increasing the amount of carbonate ions in Equation 5, the efficiency of the carbon dioxide fixation process can be improved.

[0066] Meanwhile, in the process of generating and recovering hydrogen in the hydrogen production device 10C of this embodiment, brine electrolysis is performed using the electrolysis unit 20 of this embodiment, as in the second embodiment. At this time, as described above, hydroxide ions are generated on the cathode side (space 24b) based on Equation 2, and hydrogen is released as gas from the cathode side via line L3, thereby alkalizing the brine (seawater) on the cathode side.

[0067] Here, by supplying carbon dioxide to the cathode side via line L8, the chemical equilibrium of equation 4 is promoted in the direction of producing carbonate ions on the cathode side, and as a result, the calcium carbonate production reaction based on equation 5 is promoted, calcium carbonate precipitates on the cathode side (space 24b), and the carbon dioxide fixation process progresses.

[0068] As described above, the hydrogen production device 10C of this embodiment can effectively promote the fixation process of carbon dioxide in addition to hydrogen production.

[0069] The above-described embodiments are merely examples of the hydrogen production device and the hydrogen production method according to the present invention. The hydrogen production device and the hydrogen production method according to the present invention are not limited to the above-described embodiments, and the hydrogen production device and the hydrogen production method according to the above-described embodiments may be modified within the scope of the gist of the claims.

[0070] The hydrogen production device and method of the present invention can be suitably used as a technology for producing hydrogen using salt water. In particular, the hydrogen production device and method of the present invention can be suitably used as a technology for producing green hydrogen.

[0071] 10A, 10B, 10C hydrogen production device, 20 electrolysis unit, 21 treatment tank, 22a, 22b electrodes, 23 cation exchanger, 24a, 24b, 24c space, 25 FO membrane, L1 to L7 lines, E chloride ion-free electrolyte

Claims

1. A hydrogen production device that produces hydrogen by salt water electrolysis, comprising an electrolysis section having a cation exchanger disposed between electrodes, an electrolyte solution that does not contain chloride ions being introduced to the anode side of the electrolysis section, and salt water being introduced to the cathode side of the electrolysis section.

2. The hydrogen production device according to claim 1, wherein moisture is supplied from salt water via an FO membrane to the electrolytic solution on the anode side of the electrolysis section.

3. A hydrogen production method for producing hydrogen by salt water electrolysis, comprising the steps of: using an electrolysis unit having a cation exchanger disposed between electrodes; introducing an electrolyte solution not containing chloride ions to the anode side of the electrolysis unit; introducing salt water to the cathode side of the electrolysis unit; and performing electrolysis while suppressing the generation of chlorine.

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