Electrolysis device

Abstract

Provided is an electrolysis device capable of collecting lithium from seawater, brackish water, recycled effluent, and the like that contain lithium ions, and capable of generating a carbon compound from carbon dioxide.　The electrolysis device comprises a first electrode part, a second electrode part, a lithium ion exchanging part, a first electrolytic solution, a second electrolytic solution that contains lithium ions, and a first gas supply part capable of supplying a first carbon gas including carbon dioxide. The first electrode part includes a catalyst layer. The catalyst layer is in contact with the first electrolytic solution. The second electrode part faces the first electrode part with the lithium ion exchanging part therebetween and is in contact with the second electrolytic solution. The lithium ion exchanging part is provided so as to separate the first electrolytic solution from the second electrolytic solution, and selectively allows passage of lithium ions from the second electrolytic solution to the first electrolytic solution. The electrolytic device is configured to, by applying voltage between the first electrode part and the second electrode part while supplying the first carbon gas from the first gas supplying part to the first electrode part, reduce carbon dioxide in the first carbon gas and generate a carbon compound different from carbon dioxide.

Description

electrolyzer

[0001] The present invention relates to an electrolysis device capable of recovering lithium from seawater or the like and further reducing carbon dioxide.

[0002] In recent years, in order to reduce the amount of carbon dioxide emissions, which are greenhouse gases, efforts have been made to generate carbon compounds from emitted carbon dioxide and to turn carbon dioxide into a resource (for example, Patent Document 1).

[0003] For example, the electrochemical reaction device of Patent Document 1 includes an anode section, a cathode section, a separator that separates the anode section and the cathode section, and a power supply. By applying a voltage between the anode section and the cathode section from the power supply, it is possible to reduce carbon dioxide in the cathode section to produce carbon compounds and hydrogen, and to oxidize water and hydroxide ions in the anode section to produce oxygen and hydrogen ions.

[0004] Patent No. 6818920

[0005] However, in recent years, the demand for lithium has increased with the spread of lithium-ion secondary batteries, and it is predicted that there will be a lithium supply shortage in the future, leading to an increase in costs. Lithium has traditionally been extracted from mines, but it is also known to be found in large amounts in seawater. If lithium could be recovered from seawater, it would be possible to meet the future demand for lithium and reduce the cost of lithium.

[0006] If it were possible to recover lithium from seawater or the like while simultaneously producing carbon compounds from carbon dioxide as in Patent Document 1, it would be possible to contribute to reducing carbon dioxide emissions while also meeting future demand for lithium.

[0007] Therefore, an object of the present invention is to provide an electrolysis device that can recover lithium from seawater, brine, recycled wastewater, etc. that contain lithium ions, and can produce carbon compounds from carbon dioxide.

[0008] The inventors of the present invention have conceived a method of using a stock solution containing lithium ions as the electrolyte solution on the anode side, and a lithium ion conductive material that allows only lithium ions to move as the separator. By applying a voltage between the anode and cathode, carbon dioxide is reduced at the cathode to produce a carbon compound, while the potential difference between the anode and cathode is used to transfer only lithium ions from the stock solution on the anode side to the recovered solution on the cathode side, making it possible to recover lithium from the recovered solution while using the power used to produce the carbon compound efficiently.

[0009] One aspect of the present invention derived from the above idea is an electrolysis device comprising a first electrode unit, a second electrode unit, a lithium ion exchange unit, a first electrolytic solution, a second electrolytic solution containing lithium ions, and a first gas supply unit capable of supplying a first carbon dioxide gas containing carbon dioxide, wherein the first electrode unit includes a catalyst layer, and the catalyst layer is in contact with the first electrolytic solution, the second electrode unit faces the first electrode unit across the lithium ion exchange unit, and is in contact with the second electrolytic solution, the lithium ion exchange unit is provided to separate the first electrolytic solution from the second electrolytic solution, and selectively allows the lithium ions to pass from the second electrolytic solution to the first electrolytic solution, and when a voltage is applied between the first electrode unit and the second electrode unit while the first carbon dioxide gas is supplied from the first gas supply unit toward the first electrode unit, carbon dioxide in the first carbon dioxide gas is reduced to produce a carbon compound other than carbon dioxide.

[0010] The term "carbon compound" as used herein refers to a compound containing carbon, and includes not only organic compounds but also oxides such as carbon monoxide, carbonates, and carbides. The same applies hereinafter.

[0011] According to this aspect, lithium ions contained in the second electrolytic solution pass through the lithium ion exchange unit and move to the first electrolytic solution, where they are concentrated in the first electrolytic solution. Therefore, by adding a precipitant or the like, the lithium ions in the first electrolytic solution can be precipitated, and lithium can be recovered. According to this aspect, carbon dioxide in the first carbon dioxide gas can be reduced to produce a carbon compound, so that the carbon compound can be produced while consuming carbon dioxide.

[0012] In a preferred aspect, the first electrode unit has the catalyst layer stacked on a gas diffusion electrode, and the first gas supply unit supplies the first carbon dioxide gas to the gas diffusion electrode on the opposite side to the catalyst layer.

[0013] According to this aspect, since a gas diffusion electrode is used, hydrogen is less likely to be generated on the first electrode portion, and a larger amount of carbon compounds can be produced.

[0014] In a preferred aspect, the lithium ion exchange portion is a lithium ion conductive solid electrolyte.

[0015] According to this aspect, the lithium ion exchange portion is formed of a solid electrolyte, and therefore has higher durability than when a resin ion exchange membrane is used.

[0016] In a preferred aspect, the second electrolyte solution contains lithium chloride or lithium sulfate.

[0017] According to this aspect, the lithium ions are easily ionized in the second electrolyte solution and easily assume the lithium ion state.

[0018] In a preferred aspect, the second electrolyte is seawater.

[0019] According to this aspect, since seawater is used as the second electrolyte, lithium can be recovered at low cost. According to this aspect, since the second electrolyte contains chloride ions, chlorine can also be generated on the second electrode portion.

[0020] In a preferred aspect, the first electrolytic solution is an alkaline aqueous solution.

[0021] According to this aspect, the reduction reaction of carbon dioxide can be efficiently promoted.

[0022] In a more preferred aspect, the first electrolytic solution includes an aqueous solution of lithium hydroxide.

[0023] According to this aspect, impurities are less likely to be generated in the first electrolytic solution.

[0024] In a preferred aspect, a second gas supply unit is provided that supplies a second carbon dioxide gas containing carbon dioxide to the first electrolytic solution.

[0025] According to this aspect, by supplying the second carbon dioxide gas to the first electrolytic solution in a state in which lithium ions are highly concentrated, lithium can be recovered as a precipitate of lithium carbonate.

[0026] In a preferred aspect, the carbon compound is a C1 compound or a C2 compound.

[0027] Here, "C1 compounds" refers to carbon compounds with one carbon atom, such as methane, carbon monoxide, methanol, etc. Here, "C2 compounds" refers to carbon compounds with two carbon atoms, such as ethane, ethanol, ethylene, etc.

[0028] According to this aspect, it is easy to produce from carbon dioxide.

[0029] According to the electrolysis device of the present invention, lithium can be recovered from seawater or wastewater containing lithium ions, and carbon compounds can be produced from carbon dioxide.

[0030] 1 is a cross-sectional view conceptually showing an electrolysis device according to a first embodiment of the present invention; FIG. 2 is a cross-sectional view conceptually showing an electrolysis device according to a second embodiment of the present invention; FIG. 3 is a cross-sectional view conceptually showing an electrolysis device according to the first embodiment of the present invention; FIG. 4 is a cross-sectional view conceptually showing an electrolysis device according to a second embodiment of the present invention;

[0031] Hereinafter, embodiments of the present invention will be described in detail.

[0032] The electrolysis device 1 of the first embodiment of the present invention recovers lithium from an electrolyte solution 8 such as seawater or waste liquid containing lithium ions, and further produces a carbon compound other than carbon dioxide from a first carbon dioxide gas containing carbon dioxide.

[0033] As shown in FIG. 1 , the electrolysis device 1 includes an electrolytic cell 2, a first electrode unit 3, a second electrode unit 5, a lithium ion exchange unit 6, a first electrolytic solution 7, a second electrolytic solution 8, a first gas supply unit 10, a second gas supply unit 11, a first gas discharge unit 12, a second gas discharge unit 13, a third gas discharge unit 14, an electrolytic solution introduction unit 15, a first electrolytic solution discharge unit 16, a second electrolytic solution discharge unit 17, and a power supply unit 18. The interior of the electrolytic cell 2 is partitioned into three spaces 20 to 22 by the first electrode unit 3 and the lithium ion exchange unit 6.

[0034] The first electrode unit 3 is a cathode electrode that reduces a first carbon dioxide gas containing carbon dioxide, and is resistant to the first electrolytic solution 7. As shown in the enlarged view of FIG. 1 , the first electrode unit 3 has a catalyst layer 31 laminated on a gas diffusion electrode 30.

[0035] The gas diffusion electrode 30 is a porous substrate having electrical conductivity, and is capable of transmitting gas in the thickness direction. The catalyst layer 31 is composed of one or more catalysts, and is capable of reducing carbon dioxide to C1 compounds and / or C2 compounds (carbon compounds) depending on the type of catalyst. The catalyst layer 31 is made of Ni-N-C, Ag, Ag-S-C, etc., when carbon monoxide, which is a C1 compound, is produced. ３ N ４ / CNT, CoPc-CN / CNT, CoO ｘ When producing formate, which is a C1 compound, the catalyst layer 31 can be made of Sn, Bi, SnO, etc. ２ For the catalyst layer 31, Cu, Cu-MOF, Cu(ERD), Cu, etc. can be used when producing ethylene, a C2 compound. For the catalyst layer 31, Cu, etc. can be used when producing methanol, a C1 compound. ２ In the case of producing ethanol, which is a C2 compound, the catalyst layer 31 may be CuO / ZnO. ２ S / Cu-V, CuZn, etc. can be used.

[0036] The second electrode unit 5 is an opposing electrode paired with the first electrode unit 3, and is an anode electrode that oxidizes the second electrolytic solution 8. The second electrode unit 5 is an electrode that is resistant to the second electrolytic solution 8 and has corrosion resistance against chlorine, and a metal electrode such as a platinum electrode can be used for the second electrode unit 5.

[0037] The lithium ion exchange unit 6 is a cation exchange unit that has lithium ion conductivity and allows only the movement of lithium ions from the second electrolytic solution 8 to the first electrolytic solution 7. The lithium ion exchange unit 6 is not particularly limited as long as it has lithium ion conductivity. For example, a lithium ion conductive solid electrolyte such as LATP (lithium aluminum titanium phosphate) having a NASICON crystal structure or LLTO (lithium lanthanum titanate) having a perovskite crystal structure can be used as the lithium ion exchange unit 6. The lithium ion exchange unit 6 may be composed of a lithium ion conductive material made of a resin, such as a cation exchange membrane, but is preferably composed of a lithium ion conductive solid electrolyte from the viewpoint of durability. Furthermore, when a lithium ion conductive solid electrolyte is used as the lithium ion exchange unit 6, a buffer layer may be formed on the surface to promote the movement of lithium ions into and out of the lithium ion conductive solid electrolyte. The lithium ion exchange unit 6 may be a composite of a solid electrolyte and a polymer membrane or a metal organic framework. The lithium ion exchange section 6 may also contain an adsorbent that selectively adsorbs specific ions other than lithium ions.

[0038] The first electrolytic solution 7 does not substantially react with lithium ions and can maintain the lithium ions in an ionic state, and may be, for example, an alkaline aqueous solution such as a lithium hydroxide aqueous solution (LiOH) or a sodium hydroxide aqueous solution (NaOH), or an acidic aqueous solution such as hydrochloric acid (HCl). The first electrolytic solution 7 of this embodiment is preferably lithium hydroxide from the viewpoint of precipitating lithium carbonate A with the second carbon dioxide gas.

[0039] The second electrolytic solution 8 contains a lithium salt and is maintained as lithium ions in a liquid such as an aqueous solution, an organic solvent, or an ionic liquid. For example, seawater containing lithium ions, recycled wastewater such as wastewater from lithium ion secondary batteries, treated water from lithia ore, or brine unsuitable for lithium production can be used as the second electrolytic solution 8. Examples of lithium salts contained in the second electrolytic solution 8 include lithium chloride and lithium sulfate. The second electrolytic solution 8 of this embodiment uses seawater and contains lithium chloride as the lithium salt.

[0040] The first gas supply unit 10 is a part that supplies a first carbon dioxide gas containing carbon dioxide to the first space 20. The first carbon dioxide gas is a gas whose main component is carbon dioxide, and preferably carbon dioxide accounts for 80% or more of all components, and more preferably carbon dioxide accounts for 95% or more of all components. Here, the term "main component" refers to a component that accounts for more than 50% of the total. The same applies hereinafter.

[0041] The second gas supply unit 11 is a part that supplies a second carbon dioxide gas containing carbon dioxide to the second space 21, and is equipped with a cylindrical nozzle that extends vertically. The second carbon dioxide gas is a gas whose main component is carbon dioxide, and it is preferable that carbon dioxide account for 80% or more of all components, and more preferably 95% or more of all components.

[0042] The first gas exhaust unit 12 is a unit that exhausts gas from the first space 20 to an external storage tank (not shown), and is capable of exhausting gas (e.g., carbon dioxide, carbon compounds, etc.) in the first space 20 to the external storage tank. The second gas exhaust unit 13 is a unit that exhausts gas from the second space 21 to an external storage tank (not shown), and is capable of exhausting gas (e.g., carbon dioxide, carbon compounds, hydrogen, etc.) in the second space to the external storage tank. The third gas exhaust unit 14 is a unit that exhausts gas from the third space 22 to an external storage tank (not shown), and is capable of exhausting gas (e.g., chlorine, oxygen, etc.) in the third space to the external storage tank.

[0043] The electrolyte introduction section 15 is a section through which the second electrolyte 8 is introduced into the third space 22 from an external electrolyte supply source (not shown).

[0044] First electrolytic solution discharge unit 16 is a portion that discharges first electrolytic solution 7 from second space 21 to an external storage tank (not shown). When the liquid level of first electrolytic solution 7 reaches a predetermined height, first electrolytic solution discharge unit 16 is capable of discharging first electrolytic solution 7 to the external storage tank (not shown) so that the first electrolytic solution 7 does not exceed the predetermined height.

[0045] Second electrolytic solution discharge portion 17 is a portion that discharges second electrolytic solution 8 from third space 22 to an external storage tank (not shown). When the liquid level of second electrolytic solution 8 reaches a predetermined height, second electrolytic solution discharge portion 17 is capable of discharging second electrolytic solution 8 to the outside so that the second electrolytic solution 8 does not exceed the predetermined height.

[0046] The power supply unit 18 is a component that applies a predetermined voltage between the first electrode unit 3 and the second electrode unit 5. The power supply unit 18 may apply the voltage using commercial power, or may apply the voltage using renewable energy generated by a power supply unit such as a solar cell or a fuel cell.

[0047] The first space 20 is a space that constitutes a first gas flow path for the first carbon dioxide gas from the first gas supply unit 10 to the first gas discharge unit 12, and is a space that is partially separated between the first gas supply unit 10 and the first gas discharge unit 12 by the first electrode unit 3. The second space 21 is a space that is separated from the first space 20 by the first electrode unit 3, and is separated from the third space 22 by the lithium ion exchange unit 6. The third space 22 is a space that is separated from the second space 21 by the lithium ion exchange unit 6.

[0048] Next, the positional relationship of each part of the electrolysis device 1 of this embodiment will be described.

[0049] 1 , in the electrolysis device 1, the first electrode unit 3 faces the second electrode unit 5 with a lithium ion exchange unit 6 interposed therebetween. Specifically, in the electrolysis device 1, the electrode units 3, 5 stand upright from the bottom surface toward the top surface of the electrolytic cell 2, and the catalyst layer 31 side of the first electrode unit 3 faces the lithium ion exchange unit 6. That is, the gas diffusion electrode 30 side of the first electrode unit 3 is exposed to the first space 20, and the catalyst layer 31 side is exposed to the second space 21.

[0050] In the electrolysis device 1, the first gas supply unit 10 is provided below the first gas discharge unit 12 in the first space 20, and a first gas flow path is formed to guide the first carbon dioxide gas from the first gas supply unit 10 to the first gas discharge unit 12 via the first space 20. In addition, in the electrolysis device 1, the gas diffusion electrode 30 of the first electrode unit 3 is exposed midway through the first gas flow path.

[0051] In the electrolysis device 1, the second gas supply unit 11 extends from the top surface of the electrolytic cell 2 to near the bottom surface in the second space 21, the second gas discharge unit 13 is provided on the top surface of the electrolytic cell 2, and the first electrolytic solution discharge unit 16 is provided on a side surface of the electrolytic cell 2. That is, the electrolysis device 1 is formed with a second gas flow path that guides the second carbon dioxide gas from the second gas supply unit 11 to the second gas discharge unit 13 after turning back near the bottom surface, and when the second space 21 is filled with the first electrolytic solution 7 up to the height of the first electrolytic solution discharge unit 16, a portion of the first electrolytic solution 7 is discharged to the outside from the first electrolytic solution discharge unit 16. Furthermore, in the electrolysis device 1, the catalyst layer 31 of the first electrode unit 3 is exposed midway through the second gas flow path.

[0052] In the electrolysis device 1, a third gas discharge part 14 is provided on the ceiling of the electrolytic cell 2 in the third space 22, an electrolytic solution introduction part 15 is provided on the bottom surface of the electrolytic cell 2, and a second electrolytic solution discharge part 17 is provided on the side surface of the electrolytic cell 2. In the electrolysis device 1, when the second electrolytic solution 8 introduced from the electrolytic solution introduction part 15 fills the third space 22 up to the height of the second electrolytic solution discharge part 17, a portion of the second electrolytic solution 8 is discharged from the second electrolytic solution discharge part 17 to an external storage tank.

[0053] Next, an electrolysis method using the electrolysis device 1 of this embodiment will be described.

[0054] The electrolysis method of the electrolysis device 1 of this embodiment is composed of an electrolysis step and a deposition step. The electrolysis step may be performed simultaneously with the deposition step, or may be performed separately. In the following description, a case will be described in which the electrolysis step and the deposition step are performed separately and independently, and the deposition step is performed after the electrolysis step.

[0055] (Electrolysis Process) In the electrolysis process, a voltage is applied between the first electrode unit 3 and the second electrode unit 5 by the power supply unit 18, carbon dioxide in the first carbon dioxide gas is reduced on the first electrode unit 3 to generate carbon compounds, and chloride ions are oxidized on the second electrode unit 5 to generate chlorine gas. Specifically, the potential difference between the first electrode unit 3 and the second electrode unit 5 generated by the power supply unit 18 oxidizes chloride ions around the second electrolytic solution 8, and lithium ions in the second electrolytic solution 8 pass through the lithium ion exchange unit 6 and reach the first electrolytic solution 7, whereby the lithium ions are concentrated in the first electrolytic solution 7. Furthermore, on the first electrode unit 3, carbon dioxide is reduced at the three-layer interface between the carbon dioxide in the first carbon dioxide gas passing through the first gas flow path, the catalyst layer 31, and the first electrolytic solution 7, to generate carbon compounds. If the carbon compound produced on the first electrode unit 3 is water-soluble, it dissolves in the first electrolytic solution 7 and accumulates in the first electrolytic solution 7. If the carbon compound produced on the first electrode unit 3 is water-insoluble, it passes through the first gas flow path and is discharged from the first gas discharge unit 12 to an external storage tank, or passes through the second gas flow path and is discharged from the second gas discharge unit 13 to an external storage tank.

[0056] Here, in the electrolysis step, as the reaction proceeds, lithium ions in the second electrolytic solution 8 move to the first electrolytic solution 7, and the concentration of lithium ions in the first electrolytic solution 7 increases. When the concentration in the first electrolytic solution 7 reaches a certain concentration, the electrolysis step is stopped or terminated, and the process proceeds to the precipitation step.

[0057] (Deposition Step) In the deposition step, a second carbon dioxide gas is introduced into the first electrolytic solution 7 to react with the first electrolytic solution 7, thereby depositing lithium carbonate A. Specifically, in the deposition step, the second carbon dioxide gas is supplied from the second gas supply unit 11 to the first electrolytic solution 7 in which lithium ions have been concentrated by the electrolysis step. Then, as shown in the following reaction formula, lithium hydroxide (lithium ions and hydroxide ions) in the first electrolytic solution 7 reacts with carbon dioxide, and lithium carbonate A is deposited. CO ２ +2Li ＋ +2OH － →Li ２ CO ３ +H ２ When a sufficient amount of lithium carbonate A is produced, the precipitation step is stopped or completed, and the electrolysis step is started as needed.

[0058] The electrolysis step and deposition step are repeated as necessary to reduce the carbon dioxide in the first carbon dioxide gas to a carbon compound, and recover lithium as lithium carbonate A.

[0059] According to the electrolysis device 1 of the first embodiment, lithium ions contained in the second electrolytic solution 8 pass through the lithium ion exchange unit 6 and move to the first electrolytic solution 7, and the lithium ions in the first electrolytic solution 7 are concentrated, and therefore lithium can be recovered by precipitating the lithium ions in the first electrolytic solution 7 using a precipitant or the like. According to the electrolysis device 1 of the first embodiment, carbon dioxide in the first carbon dioxide gas can be reduced to produce carbon compounds, and therefore carbon compounds can be produced while consuming carbon dioxide.

[0060] According to the electrolysis device 1 of the first embodiment, since seawater is used as the second electrolytic solution 8, the environmental load is small and lithium can be recovered at low cost. Chlorine gas can also be produced.

[0061] According to the electrolysis device 1 of the first embodiment, the carbon dioxide in the second carbon dioxide gas functions as a precipitant that precipitates lithium ions in the first electrolytic solution 7, so that a larger amount of carbon dioxide can be consumed.

[0062] According to the electrolysis device 1 of this embodiment, the electrolysis device 1 is partitioned by the gas diffusion electrode 30 of the first electrode unit 3, so that the water-soluble carbon compounds dissolve in the first electrolytic solution 7, and the water-insoluble carbon compounds are discharged from the first gas discharge part 12. Therefore, the produced carbon compounds can be separated into water-soluble and water-insoluble carbon compounds.

[0063] Next, an electrolysis device 100 according to a second embodiment of the present invention will be described. Note that the same components as those in the electrolysis device 1 according to the first embodiment will be denoted by the same reference numerals and will not be described again.

[0064] As shown in FIG. 2 , the electrolysis device 100 includes an electrolysis section 102, a deposition section 103, a first path 105, and a second path 106, and the electrolysis section 102, the first path 105, the deposition section 103, and the second path 106 form a circular circulation flow path 107.

[0065] (Electrolysis unit 102) The electrolysis unit 102 includes an electrolytic cell 2, a first electrode unit 3, a second electrode unit 5, a lithium ion exchange unit 6, a first electrolytic solution 7, a second electrolytic solution 8, a first gas supply unit 10, a first gas exhaust unit 12, a second gas exhaust unit 13, a third gas exhaust unit 14, a first electrolytic solution introduction unit 110, a second electrolytic solution introduction unit 15, a first electrolytic solution exhaust unit 16, a second electrolytic solution exhaust unit 17, and a power supply unit 18.

[0066] The first electrolytic solution inlet 110 is provided on the bottom surface of the electrolytic cell 2 and is a portion through which the first electrolytic solution 7 is introduced from the second path 106 into the second space 21. The first electrolytic solution outlet 16 is a portion through which the first electrolytic solution 7 is discharged from the second space 21 to the first path 105.

[0067] (Deposition Unit 103) As shown in Fig. 2, the deposition unit 103 includes a deposition tank 120, a third electrolytic solution introduction unit 121, a second gas supply unit 122, and a third electrolytic solution discharge unit 123. The third electrolytic solution introduction unit 121 is a unit that introduces the first electrolytic solution 7 from the second space 21 into the deposition tank 120 via the first path 105. The second gas supply unit 122, like the second gas supply unit 11 of the first embodiment, is a unit that supplies a second carbon dioxide gas containing carbon dioxide to the deposition tank 120 and includes a cylindrical nozzle that extends vertically. The third electrolytic solution discharge unit 123 is a unit that discharges the first electrolytic solution 7 from inside the deposition tank 120 into the second path 106.

[0068] The first path 105 is a connecting pipe that connects the first electrolytic solution discharge part 16 of the electrolysis part 102 with the third electrolytic solution introduction part 121 of the deposition part 103, and is provided with an on-off valve 130 midway.

[0069] The second path 106 is a connecting pipe that connects the third electrolytic solution discharge part 123 of the deposition part 103 and the first electrolytic solution introduction part 110 of the electrolysis part 102, and is provided with an on-off valve 131 and a circulation pump 132 midway. The circulation pump 132 is capable of supplying the first electrolytic solution 7 downstream at a predetermined flow rate.

[0070] Next, an electrolysis method using the electrolysis device 100 of this embodiment will be described.

[0071] The electrolysis device 100 of the second embodiment is composed of an electrolysis process and a deposition process, similar to the electrolysis device 1 of the first embodiment, but differs from the electrolysis device 1 of the first embodiment in that the part that performs the electrolysis process and the part that performs the deposition process are different.

[0072] 3 , the on-off valves 130 and 131 are closed to stop the circulation of the first electrolytic solution 7 in the circulation flow path 107, and in this state, similar to the electrolysis process, a voltage is applied between the first electrode unit 3 and the second electrode unit 5 by the power supply unit 18 to generate a carbon compound on the first electrode unit 3 and generate chlorine gas on the second electrode unit 5. When the concentration in the first electrolytic solution 7 reaches a certain concentration, a precipitation process is carried out in parallel.

[0073] 4 , the on-off valves 130 and 131 are opened, and the circulation pump 132 is driven to introduce the first electrolytic solution 7 in the precipitation tank 120 from the first electrolytic solution inlet 110 into the second space 21 via the second path 106. The first electrolytic solution 7 introduced from the first electrolytic solution inlet 110 causes the first electrolytic solution 7 to overflow from the first electrolytic solution outlet 16, which is then introduced into the precipitation tank 120 from the third electrolytic solution inlet 121 via the first path 105. In this manner, the first electrolytic solution 7 in the precipitation tank 120 is replaced with the first electrolytic solution 7 containing a high concentration of lithium ions, and a second carbon dioxide gas is supplied to the first electrolytic solution 7 from the second gas supply unit 122. This causes the lithium hydroxide (lithium ions and hydroxide ions) in the first electrolytic solution 7 to react with carbon dioxide, resulting in the precipitation of lithium carbonate A. When a sufficient amount of lithium carbonate A is produced, the precipitation step is stopped or terminated.

[0074] According to the electrolysis device 100 of the second embodiment, the electrolytic cell 2 and the precipitation cell 120 are separately provided, and lithium is precipitated as lithium carbonate A in the precipitation cell 120 outside the electrolytic cell 2. Therefore, lithium can be recovered in the precipitation cell 120 without stopping the electrolysis process in the electrolysis unit 102.

[0075] According to the electrolysis device 100 of the second embodiment, lithium is recovered by circulating the first electrolytic solution 7 through the circulation flow path 107, so that lithium can be recovered at low cost.

[0076] In the above embodiment, carbon dioxide is used as the precipitant for precipitating lithium carbonate A, but the present invention is not limited to this. Other precipitants may also be used.

[0077] In the first embodiment described above, the electrolysis step and the deposition step are separate and independent steps, but the present invention is not limited to this. The electrolysis step and the deposition step may be performed simultaneously. That is, the second carbon dioxide gas may be supplied by the second gas supply unit 11 while electrolysis is being performed in the electrolysis step, thereby depositing lithium carbonate A.

[0078] In the second embodiment described above, the electrolysis step and the deposition step are performed in parallel, but the present invention is not limited to this. The electrolysis step and the deposition step may be performed separately.

[0079] In the second embodiment described above, the first electrolytic solution 7 is returned from the deposition unit 103 to the electrolysis unit 102 via the second path 106, but the present invention is not limited to this. The first electrolytic solution 7 after the deposition step may be directly discharged into an external storage tank. In this case, it is preferable to connect the second path 106 to an external electrolytic solution supply source and supply the first electrolytic solution 7 from the electrolytic solution supply source into the second space 21 of the electrolytic unit 102 via the first electrolytic solution introduction unit 110.

[0080] In the above-described embodiment, the second carbon dioxide gas containing carbon dioxide is supplied from the second gas supply unit 11, 122 to the second space 21 or the precipitation tank 120 to precipitate lithium as lithium carbonate A, but the present invention is not limited to this. A precipitant other than the second carbon dioxide gas may be added from the second gas supply unit 11, 122 to precipitate lithium as a lithium precipitate. In this case, the second gas supply unit 11, 122 functions as a precipitant supply unit that supplies a solid, liquid, or gaseous precipitant.

[0081] In the above-described embodiments, each component can be freely substituted or added between the respective embodiments as long as it falls within the technical scope of the present invention.

[0082] 1,100 Electrolysis device 3 First electrode section 5 Second electrode section 6 Lithium ion exchange section 7 First electrolytic solution 8 Second electrolytic solution 10 First gas supply section 11,122 Second gas supply section 30 Gas diffusion electrode 31 Catalyst layer

Claims

1. a first electrode unit, a second electrode unit, a lithium ion exchange unit, a first electrolytic solution, a second electrolytic solution containing lithium ions, and a first gas supply unit capable of supplying a first carbon dioxide gas containing carbon dioxide; the first electrode unit includes a catalyst layer, the catalyst layer being in contact with the first electrolytic solution; the second electrode unit faces the first electrode unit across the lithium ion exchange unit and is in contact with the second electrolytic solution, the lithium ion exchange unit is provided to separate the first electrolytic solution from the second electrolytic solution, and selectively allows the lithium ions to pass from the second electrolytic solution to the first electrolytic solution, the lithium ion exchange portion is a lithium ion conductive solid electrolyte, an electrolysis device that reduces carbon dioxide in the first carbon dioxide gas and produces a carbon compound other than carbon dioxide by applying a voltage between the first electrode unit and the second electrode unit while the first carbon dioxide gas is being supplied from the first gas supply unit toward the first electrode unit.

2. the first electrode portion has the catalyst layer laminated on a gas diffusion electrode, The electrolysis device according to claim 1 , wherein the first gas supply unit supplies the first carbon dioxide gas to a side of the gas diffusion electrode opposite to the catalyst layer.

3. The electrolysis device according to claim 1 or 2, wherein the second electrolytic solution contains lithium chloride or lithium sulfate.

4. The electrolysis device according to claim 1 or 2, wherein the second electrolytic solution is seawater.

5. The electrolysis device according to claim 1 or 2, wherein the first electrolytic solution is an alkaline aqueous solution.

6. The electrolysis device according to claim 5 , wherein the first electrolytic solution includes an aqueous solution of lithium hydroxide.

7. The electrolysis device according to claim 1 or 2, further comprising a second gas supply unit that supplies a second carbon dioxide gas containing carbon dioxide to the first electrolytic solution.

8. 3. The electrolysis device according to claim 1, wherein the carbon compound is a C1 compound or a C2 compound.