Fluorine gas production method and fluorine gas production device

Abstract

Provided is a fluorine gas production method capable of suppressing the clogging of pipes and valves due to mist. A fluorine gas is produced by a method which comprises: an electrolysis step for electrolyzing an electrolytic solution in an electrolytic cell; a current efficiency measuring step for measuring the current efficiency of the fluorine gas generation in the electrolysis; and an air feeding step for delivering, from the inside of the electrolytic cell to the outside via a flow path, a fluid generated inside the electrolytic cell when the electrolytic solution is electrolyzed. In the air feeding step, the flow path through which the fluid flows is switched in accordance with the current efficiency measured in the current efficiency measuring step. When the current efficiency measured in the current efficiency measuring step is equal to or greater than a preset reference value, the fluid is delivered to a first flow path for delivering the fluid from the inside of the electrolytic cell to a first outside part, and when the current efficiency is smaller than the preset reference value, the fluid is delivered to a second flow path for delivering the fluid from the inside of the electrolytic cell to a second outside part. The preset reference value is a numerical value within the range of 50% or higher.

Description

[Technical Field]

[0001] The present invention relates to a method for producing fluorine gas and a fluorine gas production apparatus. [Background technology]

[0002] Fluorine gas can be synthesized (electrolytic synthesis) by electrolyzing an electrolyte containing hydrogen fluoride and a metal fluoride. Electrolysis of the electrolyte generates mist (e.g., electrolyte mist) along with fluorine gas, so the mist is entrained in the fluorine gas discharged from the electrolytic cell. The mist entrained in the fluorine gas turns into powder and may clog the piping and valves used to deliver the fluorine gas. This sometimes makes it necessary to interrupt or stop the operation of producing fluorine gas, which has been an obstacle to continuous operation in the production of fluorine gas by electrolysis. In order to prevent the mist from clogging pipes and valves, Patent Document 1 discloses a technique of heating the fluorine gas carrying the mist or the pipe through which the gas passes to a temperature equal to or higher than the melting point of the electrolyte. Patent Document 2 also discloses a gas generator having a gas diffusion section which is a space for roughly collecting the mist, and a filler housing section which houses a filler for absorbing the mist. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 5584904 [Patent Document 2] Japanese Patent Publication No. 5919824 Summary of the Invention [Problem to be solved by the invention]

[0004] However, there has been a demand for technology that can more effectively prevent mist from clogging pipes and valves. An object of the present invention is to provide a method and apparatus for producing fluorine gas that can prevent clogging of pipes and valves due to mist. [Means for solving the problem]

[0005] In order to solve the above problems, one aspect of the present invention is as follows [1] to [5]. [1] A method for producing fluorine gas, which comprises electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride to produce fluorine gas, an electrolysis step in which the electrolysis is carried out in an electrolytic cell; a current efficiency measurement step of measuring the current efficiency of fluorine gas production in the electrolysis; an air supplying step of supplying a fluid generated inside the electrolytic cell during electrolysis of the electrolytic solution from the inside to the outside of the electrolytic cell through a flow path; Equipped with In the gas supplying step, a flow path for passing the fluid is switched in accordance with the current efficiency measured in the current efficiency measuring step; if the current efficiency measured in the current efficiency measuring step is equal to or greater than a preset reference value, the fluid is sent to a first flow path for sending the fluid from inside the electrolytic cell to a first outside; and if the current efficiency measured in the current efficiency measuring step is smaller than the preset reference value, the fluid is sent to a second flow path for sending the fluid from inside the electrolytic cell to a second outside; A method for producing fluorine gas, wherein the preset reference value is a value within a range of 50% or more.

[0006] [2] The method for producing fluorine gas according to [1], wherein the metal fluoride is a fluoride of at least one metal selected from potassium, cesium, rubidium, and lithium. [3] The method for producing fluorine gas according to [1] or [2], wherein the anode used in the electrolysis is a carbonaceous electrode made of at least one carbon material selected from diamond, diamond-like carbon, amorphous carbon, graphite, and glassy carbon. [4] The method for producing fluorine gas according to any one of [1] to [3], wherein the electrolytic cell has a structure that allows bubbles generated at the anode or cathode used in the electrolysis to rise vertically in the electrolytic solution and reach the liquid surface of the electrolytic solution.

[0007] [5] A fluorine gas production apparatus that produces fluorine gas by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride, an electrolytic cell containing the electrolytic solution and in which the electrolysis is carried out; a current efficiency measuring unit for measuring the current efficiency of fluorine gas generation in the electrolysis; a flow path for transporting a fluid generated inside the electrolytic cell during electrolysis of the electrolytic solution from the inside to the outside of the electrolytic cell; Equipped with the flow path includes a first flow path for sending the fluid from the inside of the electrolytic cell to a first outside, and a second flow path for sending the fluid from the inside of the electrolytic cell to a second outside, and a flow path switching unit for switching the flow path for the fluid between the first flow path and the second flow path in accordance with the current efficiency measured by the current efficiency measuring unit, the flow path switching unit sends the fluid from inside the electrolytic cell to the first flow path when the current efficiency measured by the current efficiency measuring unit is equal to or greater than a preset reference value, and sends the fluid from inside the electrolytic cell to the second flow path when the current efficiency is smaller than the preset reference value, A fluorine gas manufacturing apparatus, wherein the preset reference value is a numerical value within a range of 50% or more. [Effects of the Invention]

[0008] According to the present invention, when fluorine gas is produced by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride, clogging of pipes and valves due to mist can be suppressed. [Brief explanation of the drawings]

[0009] [Figure 1]FIG. 2 is a schematic diagram illustrating an example of a light scattering detector used as an average particle diameter measuring section in the fluorine gas production device according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating an example of a fluorine gas production apparatus according to an embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram illustrating an example of a mist removing device used as a mist removing section in the fluorine gas manufacturing apparatus of FIG. 2. [Figure 4] FIG. 3 is a schematic diagram illustrating a first modified example of the fluorine gas production apparatus of FIG. [Figure 5] FIG. 3 is a schematic diagram illustrating a second modified example of the fluorine gas production apparatus of FIG. [Figure 6] FIG. 3 is a schematic diagram illustrating a third modified example of the fluorine gas production apparatus of FIG. [Figure 7] FIG. 3 is a schematic diagram illustrating a fourth modified example of the fluorine gas production apparatus of FIG. [Figure 8] FIG. 10 is a schematic diagram illustrating a fifth modified example of the fluorine gas production apparatus of FIG. [Figure 9] FIG. 3 is a schematic diagram illustrating a sixth modified example of the fluorine gas production apparatus of FIG. [Figure 10] FIG. 10 is a schematic diagram illustrating a seventh modified example of the fluorine gas production apparatus of FIG. [Figure 11] FIG. 10 is a schematic diagram illustrating an eighth modified example of the fluorine gas production apparatus of FIG. [Figure 12] FIG. 10 is a schematic diagram illustrating a ninth modified example of the fluorine gas production apparatus of FIG. [Figure 13] FIG. 13 is a schematic diagram illustrating a tenth modification of the fluorine gas production apparatus of FIG. [Figure 14] 1 is a graph showing the particle size distribution of mist contained in a fluid generated at an anode in Reference Example 1. [Figure 15] 1 is a graph showing the correlation between the average particle size of the mist and the amount of mist generated at the anode in Reference Example 1. [Figure 16] 1 is a graph showing the relationship between the average particle size of mist and current efficiency in Reference Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will be described below. Note that this embodiment is merely an example of the present invention, and the present invention is not limited to this embodiment. Furthermore, various modifications and improvements can be made to this embodiment, and such modifications and improvements can also be included in the present invention.

[0011] The present inventors have conducted extensive research into the mist that causes clogging of pipes and valves in the electrolytic synthesis of fluorine gas. In this invention, "mist" refers to liquid fine particles or solid fine particles that are generated together with fluorine gas in an electrolytic cell by electrolysis of an electrolyte. Specifically, it refers to fine particles of the electrolyte, solid fine particles that result from a phase change of the fine particles of the electrolyte, and solid fine particles that are generated by the reaction of fluorine gas with components that constitute the electrolytic cell (such as metals that form the electrolytic cell, packing for the electrolytic cell, and carbon electrodes).

[0012] The present inventors measured the average particle size of mist contained in the fluid generated inside the electrolytic cell during electrolysis of the electrolyte, and confirmed that the average particle size of the mist changed over time. Furthermore, as a result of extensive research, they found that there is a correlation between the average particle size of the mist and the current efficiency of fluorine gas production in electrolysis, and further found that there is a correlation between the average particle size of the mist and the likelihood of clogging of piping and valves for transporting the fluid. They then found that by devising a flow path for transporting the fluid generated inside the electrolytic cell in accordance with the current efficiency of fluorine gas production in electrolysis, clogging of piping and valves can be suppressed, and the frequency of interruptions and stoppages in the operation of producing fluorine gas can be reduced, leading to the completion of the present invention. One embodiment of the present invention will be described below.

[0013] The method for producing fluorine gas of the present embodiment is a method for producing fluorine gas by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride, and includes an electrolysis step of performing electrolysis in an electrolytic cell, a current efficiency measurement step of measuring the current efficiency for producing fluorine gas in the electrolysis, and an air supply step of supplying a fluid generated inside the electrolytic cell during electrolysis of the electrolyte from the inside to the outside of the electrolytic cell via a flow path.

[0014] In the gas supply step, the flow path for the fluid is switched depending on the current efficiency measured in the current efficiency measurement step. That is, if the current efficiency measured in the current efficiency measurement step is equal to or greater than a preset reference value, the fluid is sent to the first flow path that sends the fluid from inside the electrolytic cell to the first outside, and if it is less than the preset reference value, the fluid is sent to the second flow path that sends the fluid from inside the electrolytic cell to the second outside. The preset reference value is a numerical value within a range of 50% or more.

[0015] The fluorine gas production apparatus of this embodiment is a fluorine gas production apparatus that produces fluorine gas by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride, and is equipped with an electrolytic cell that contains the electrolyte solution and performs electrolysis, a current efficiency measurement unit that measures the current efficiency of fluorine gas production in the electrolysis, and a flow path that sends a fluid generated inside the electrolytic cell during electrolysis of the electrolyte solution from the inside to the outside of the electrolytic cell.

[0016] The flow paths include a first flow path for transporting fluid from the inside of the electrolytic cell to a first outside, and a second flow path for transporting fluid from the inside of the electrolytic cell to a second outside. The flow paths also include a flow path switching unit that switches the flow path for the fluid between the first flow path and the second flow path depending on the current efficiency measured by the current efficiency measuring unit. The flow path switching unit sends the fluid from inside the electrolytic cell to the first flow path when the current efficiency measured by the current efficiency measuring unit is equal to or greater than a preset reference value, and sends the fluid from inside the electrolytic cell to the second flow path when the current efficiency is less than the preset reference value. The preset reference value is a numerical value within a range of 50% or greater.

[0017] In the fluorine gas production method and fluorine gas production apparatus of this embodiment, the flow path for flowing the fluid is switched to the first flow path or the second flow path depending on the current efficiency of fluorine gas production in electrolysis. As a result, the flow path is switched to the first flow path or the second flow path depending on the average particle diameter of the mist, and clogging of the flow path by mist is unlikely to occur. Therefore, the fluorine gas production method and fluorine gas production apparatus of this embodiment can suppress clogging of piping and valves by mist when producing fluorine gas by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride. Therefore, the frequency of interruptions and stops in the operation for producing fluorine gas can be reduced, and continuous operation can be easily performed. Therefore, fluorine gas can be produced economically.

[0018] In the fluorine gas production method and fluorine gas production apparatus of this embodiment, the measurement of the current efficiency may be carried out continuously during electrolysis, may be carried out periodically at regular intervals, or may be carried out irregularly as needed. Furthermore, while the first flow path and the second flow path are separate flow paths, the first outside and the second outside may be located at different positions or may be located at the same position.

[0019] Here, an example of a fluorine gas production method and a fluorine gas production apparatus according to this embodiment is shown. The first flow path is a flow path that sends a fluid from the inside of the electrolytic cell to a fluorine gas sorting section that selects and extracts fluorine gas from the fluid, via a mist removal section that removes mist from the fluid. The second flow path is a flow path that sends a fluid from the inside of the electrolytic cell to the fluorine gas sorting section without passing through the mist removal section. That is, when the current efficiency is equal to or greater than a preset reference value, the fluid is sent to the mist removal section provided in the first flow path, and when it is less than the preset reference value, the fluid is not sent to the mist removal section. In this example, the fluorine gas sorting section corresponds to the first outside and the second outside, and the first outside and the second outside are located at the same place, but the first outside and the second outside may be located at different places.

[0020] The second flow path has a clogging prevention mechanism that prevents the second flow path from being blocked by mist. The clogging prevention mechanism is not particularly limited as long as it can prevent the second flow path from being blocked by mist, and examples thereof include the following: a large-diameter pipe, an inclined pipe, a rotating screw, and an airflow generating device, and these may be used in combination. Specifically, by configuring at least a portion of the second flow path with a pipe having a larger diameter than the first flow path, it is possible to prevent the second flow path from being blocked by mist. Also, by configuring at least a portion of the second flow path with a pipe that is inclined with respect to the horizontal direction and extends in a downward direction from the upstream side to the downstream side, it is possible to prevent the second flow path from being blocked by mist.

[0021] Furthermore, by installing a rotating screw inside the second flow path that sends mist accumulated inside the second flow path upstream or downstream, it is possible to suppress clogging of the second flow path by mist. Furthermore, by installing an airflow generating device in the second flow path that generates an airflow to increase the flow velocity of the fluid flowing through the second flow path, it is possible to suppress clogging of the second flow path by mist. Note that a mist removal unit separate from the mist removal unit provided in the first flow path may be provided in the second flow path as a clogging suppression mechanism.

[0022] The first flow path is less likely to be clogged by mist because mist is removed from the fluid by the mist removal unit, and the second flow path is less likely to be clogged by mist because a clogging suppression mechanism is provided. Therefore, the fluorine gas production method and fluorine gas production device of this embodiment can suppress clogging of pipes and valves by mist when producing fluorine gas by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride. Note that even if a mist removal unit or a clogging suppression mechanism is not provided, the effect of suppressing clogging of pipes and valves by mist can be achieved simply by switching the flow path through which the fluid flows to another flow path (the first flow path or the second flow path), but the above effect is more pronounced when a mist removal unit or a clogging suppression mechanism is provided.

[0023] The method for producing fluorine gas and the apparatus for producing fluorine gas according to this embodiment will be described in further detail below. [Electrolytic cell] There are no particular limitations on the type of electrolytic cell, and any electrolytic cell can be used as long as it can generate fluorine gas by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride. Usually, the interior of an electrolytic cell is divided by a partition member such as a partition wall into an anode chamber in which an anode is placed and a cathode chamber in which a cathode is placed, so that fluorine gas generated at the anode and hydrogen gas generated at the cathode do not mix.

[0024] The anode may be a carbonaceous electrode made of a carbon material such as diamond, diamond-like carbon, amorphous carbon, graphite, glassy carbon, or amorphous carbon. In addition to the carbon materials, the anode may also be a metal electrode made of a metal such as nickel or Monel (trademark). The cathode may be a metal electrode made of a metal such as iron, copper, nickel, or Monel (trademark).

[0025] The electrolytic solution contains hydrogen fluoride and a metal fluoride, and the type of the metal fluoride is not particularly limited, but is preferably a fluoride of at least one metal selected from potassium, cesium, rubidium, and lithium. When the electrolytic solution contains cesium or rubidium, the specific gravity of the electrolytic solution increases, thereby suppressing the amount of mist generated during electrolysis.

[0026] The electrolyte can be, for example, a mixed molten salt of hydrogen fluoride (HF) and potassium fluoride (KF). The molar ratio of hydrogen fluoride to potassium fluoride in the mixed molten salt of hydrogen fluoride and potassium fluoride can be, for example, hydrogen fluoride:potassium fluoride = 1.5 to 2.5:1. A typical electrolyte is KF·2HF, where the ratio of hydrogen fluoride to potassium fluoride is 2:1, and the melting point of this mixed molten salt is approximately 72°C. Because this electrolyte is corrosive, the parts that come into contact with the electrolyte, such as the inner surface of the electrolytic cell, are preferably made of a metal such as iron, nickel, or Monel (trademark).

[0027] During electrolysis of the electrolyte, a direct current is applied to the anode and the cathode, and a gas containing fluorine gas is generated at the anode, and a gas containing hydrogen gas is generated at the cathode. Furthermore, because hydrogen fluoride in the electrolyte has a vapor pressure, the gases generated at the anode and the cathode are each accompanied by hydrogen fluoride. Furthermore, in the production of fluorine gas by electrolysis of the electrolyte, the gas generated by electrolysis contains a mist of the electrolyte. Therefore, the gas phase of the electrolytic cell consists of the gas generated by electrolysis and a mist of hydrogen fluoride and the electrolyte. Therefore, what is sent from the inside of the electrolytic cell to the outside consists of the gas generated by electrolysis and a mist of hydrogen fluoride and the electrolyte, and in the present invention, this is referred to as a "fluid."

[0028] Since hydrogen fluoride in the electrolytic solution is consumed as the electrolysis proceeds, a pipe for continuously or intermittently supplying hydrogen fluoride to the electrolytic cell for replenishment may be connected to the electrolytic cell. The hydrogen fluoride may be supplied to the cathode chamber side or the anode chamber side of the electrolytic cell. The main reasons why mist is generated during electrolysis of electrolyte are as follows: The temperature of the electrolyte during electrolysis is adjusted to, for example, 80-100°C. The melting point of KF·2HF is 71.7°C, so the electrolyte is in a liquid state when adjusted to this temperature. Gas bubbles generated at both electrodes of the electrolytic cell rise in the electrolyte and burst at the liquid surface of the electrolyte. At this time, part of the electrolyte is released into the gas phase.

[0029] Because the temperature of the gas phase is lower than the melting point of the electrolyte, the released electrolyte changes phase to a very fine powder-like state. This powder is thought to be a mixture of potassium fluoride and hydrogen fluoride, KF·nHF. This powder becomes mist along with the flow of other gases generated, forming the fluid generated in the electrolytic cell. This mist is difficult to effectively remove by ordinary measures such as installing filters due to its stickiness.

[0030] Furthermore, although the amount generated is small, a reaction between the carbonaceous electrode serving as the anode and the fluorine gas generated by electrolysis can generate a fine powder of organic compounds as a mist. More specifically, contact resistance often occurs in the part supplying the current to the carbonaceous electrode, and the temperature can become higher than that of the electrolyte due to Joule heat. Therefore, a reaction between the carbon that forms the carbonaceous electrode and the fluorine gas can generate a soot-like organic compound CFx as a mist.

[0031] The electrolytic cell preferably has a structure that allows bubbles generated at the anode or cathode used in electrolysis to rise vertically in the electrolyte and reach the liquid surface of the electrolyte. If the structure makes it difficult for bubbles to rise vertically in the electrolyte, but rather to rise in a direction inclined relative to the vertical, multiple bubbles tend to aggregate and generate large bubbles. As a result, large bubbles tend to reach the liquid surface of the electrolyte and burst, which increases the amount of mist generated. If the structure allows bubbles to rise vertically in the electrolyte and reach the liquid surface of the electrolyte, small bubbles tend to reach the liquid surface of the electrolyte and burst, which reduces the amount of mist generated.

[0032] [Average particle diameter measuring section] The fluorine gas production apparatus of this embodiment may be equipped with an average particle diameter measuring unit that measures the average particle diameter of the mist contained in the fluid, and this average particle diameter measuring unit may be composed of a light scattering detector that measures the average particle diameter by a light scattering method. A light scattering detector is preferable as the average particle diameter measuring unit because it can measure the average particle diameter of the mist in the fluid flowing through the flow path while the fluorine gas production apparatus is continuously operating.

[0033] An example of a light scattering detector will be described with reference to Fig. 1. The light scattering detector in Fig. 1 is a light scattering detector that can be used as an average particle size measuring unit in a fluorine gas production apparatus of this embodiment (for example, the fluorine gas production apparatuses in Figs. 2 and 4 to 13 described below). That is, it is a light scattering detector that measures the average particle size of mist contained in a fluid generated inside an electrolytic cell of a fluorine gas production apparatus when fluorine gas is produced by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride inside the electrolytic cell. The light scattering detector may be connected to the fluorine gas production apparatus and the fluid may be sent from inside the electrolytic cell to the light scattering detector to measure the average particle diameter of the mist, or the light scattering detector may not be connected to the fluorine gas production apparatus and the fluid may be taken out from inside the electrolytic cell and introduced into the light scattering detector to measure the average particle diameter of the mist.

[0034] The light scattering detector in Figure 1 includes a sample chamber 1 that contains a fluid F, a light source 2 that irradiates the fluid F in the sample chamber 1 with light scattering measurement light L, a scattered light detection unit 3 that detects scattered light S generated when the light scattering measurement light L is scattered by mist M in the fluid F, a transparent window 4A that is installed in the sample chamber 1 and comes into contact with the fluid F to transmit the light scattering measurement light L, and a transparent window 4B that is installed in the sample chamber 1 and comes into contact with the fluid F to transmit the scattered light S. The transparent windows 4A and 4B are made of at least one material selected from diamond, calcium fluoride (CaF2), potassium fluoride (KF), silver fluoride (AgF), barium fluoride (BaF2), and potassium bromide (KBr).

[0035] Light scattering measurement light L (e.g., laser light) emitted from the light source 2 passes through the converging lens 6 and the transparent window 4A of the sample chamber 1, enters the sample chamber 1, and is irradiated onto the fluid F contained in the sample chamber 1. At this time, if a light-reflecting substance such as mist M is present in the fluid F, the light scattering measurement light L is reflected and scattered. A portion of the scattered light S generated when the light scattering measurement light L is scattered by the mist M passes through the transparent window 4B of the sample chamber 1, is extracted from the sample chamber 1, and enters the scattered light detection unit 3 via the converging lens 7 and aperture 8. At this time, the average particle diameter of the mist M can be determined from information obtained from the scattered light S. Note that the average particle diameter obtained here is the number-average particle diameter. For example, the scattered light detection unit 3 can be an aerosol spectrometer, Welas® Digital 2000, manufactured by PALAS.

[0036] The transparent windows 4A, 4B come into contact with the fluid F, which contains highly reactive fluorine gas, so the transparent windows 4A, 4B must be made of a material that is resistant to corrosion by fluorine gas. Examples of materials for forming the transparent windows 4A, 4B include at least one selected from the group consisting of diamond, calcium fluoride, potassium fluoride, silver fluoride, barium fluoride, and potassium bromide. If the transparent windows 4A, 4B are made of any of the above materials, deterioration due to contact with the fluid F can be suppressed.

[0037] Alternatively, a film made of the above-mentioned material may be coated on the surface of glass such as quartz, and used as the transparent windows 4A, 4B. Because the portions that come into contact with the fluid F are coated with a film made of the above-mentioned material, deterioration due to contact with the fluid F can be suppressed while keeping costs down. The transparent windows 4A, 4B may be a laminate in which the surfaces that come into contact with the fluid F are made of the above-mentioned material and the other portions are made of ordinary glass such as quartz. The material of the light scattering detector other than the transparent windows 4A and 4B is not particularly limited as long as it is a material that is corrosion-resistant to fluorine gas, but it is preferable to use a metal material such as Monel (trademark), which is a copper-nickel alloy, Hastelloy (trademark), stainless steel, etc.

[0038] [Average particle size of mist and current efficiency of fluorine gas production in electrolysis] The inventors used a light scattering detector to measure the average particle size of mist generated during the production of fluorine gas by electrolysis of an electrolyte. An example of the results will be described below. After replacing the anode of a fluorine gas production device with a new anode or filling the electrolytic cell with new electrolyte, electrolysis was initiated, and the average particle size of mist in the fluid generated at the anode was measured for a certain period of time immediately after the start of electrolysis. The resulting average particle size of the mist was 0.5 to 2.0 μm. After that, electrolysis continued for a sufficient period of time, and the electrolysis began to stabilize, and the average particle size of the mist in the fluid during this stable electrolysis was approximately 0.2 μm. In this way, mist with relatively large particle diameters is generated immediately after the start of electrolysis until stable electrolysis is achieved. When a fluid containing large mist generated immediately after the start of electrolysis flows through pipes or valves, the mist is likely to adhere to the inner surfaces of the pipes or valves, causing blockage of the pipes or valves.

[0039] In contrast, during stable electrolysis, the particle size of the mist generated is relatively small. Such small mist is less likely to settle or accumulate in the fluid, allowing it to flow steadily through pipes and valves. Therefore, during stable electrolysis, the fluid consisting of mist and gas generated at the electrodes is relatively unlikely to cause blockages in pipes or valves. The time from immediately after the start of electrolysis to stable electrolysis is usually between 25 and 200 hours. Furthermore, from immediately after the start of electrolysis to stable electrolysis, a current of approximately 40 kAh or more per 1,000 L of electrolyte is required.

[0040] The inventors also discovered that there is a close relationship between the average particle size of the mist and current efficiency. Typically, the current efficiency is small at the start of electrolysis, showing a value smaller than 60%. At this time, the average particle size of the mist is larger than 0.4 μm. Thereafter, as electrolysis continues, the current efficiency increases, and when it reaches 60% or more, the average particle size of the mist becomes 0.4 μm or less.

[0041] As described above, since there is a correlation between the average particle size of the mist and the current efficiency, it is possible to measure the current efficiency instead of the average particle size of the mist during electrolysis and use the measurement result for switching the flow path. In other words, if the current efficiency is measured at a predetermined timing during electrolysis, it is possible to appropriately switch the flow path for the fluid generated by electrolysis at the predetermined timing in accordance with the measurement result.

[0042] Current efficiency indicates the percentage of the electricity used in the electrochemical reaction of electrolysis that is utilized in the target reaction out of the electricity applied, and is calculated as the ratio (percentage) of the actual production amount of the target substance to the theoretical production amount of the target substance, calculated from the amount of electricity applied using Faraday's law. In this embodiment, the target substance in the electrochemical reaction of electrolysis is fluorine gas, so the current efficiency for fluorine gas production in electrolysis can be calculated by dividing the amount of fluorine gas actually produced by the theoretical amount of fluorine gas to be produced, which is calculated from the amount of current passed (current (A) × time (s) = coulomb).

[0043] The method for measuring the amount of fluorine gas actually produced is not particularly limited, but it can be measured, for example, by the following titration method. That is, the gas generated at the anode is passed through an aqueous potassium iodide solution for a certain period of time, and the fluorine gas in the anode gas is absorbed into the aqueous potassium iodide solution. Then, iodine is liberated from the aqueous potassium iodide solution, and by titrating this liberated iodine, the amount of fluorine gas actually produced (mol / min) can be measured. Then, the current efficiency can be calculated by substituting the amount of fluorine gas actually produced and the current value applied into the following formula. Current efficiency = {actual amount of fluorine gas produced (mol / min)} / {current value (A) × 60 (sec / min) / 96500 (A sec) / 2} × 100

[0044] When measuring the amount of fluorine gas actually produced, the entire amount of fluorine gas generated at the anode may be absorbed in the aqueous potassium iodide solution, or a portion may be separated and absorbed. When a portion is separated, nitrogen gas is supplied to the electrolytic cell at a known flow rate, and the mixture ratio of the mixed gas of fluorine gas and nitrogen gas discharged from the electrolytic cell is measured. This mixture ratio can be determined by passing the mixed gas through an aqueous potassium iodide solution, causing the fluorine gas in the mixed gas to be absorbed by the aqueous potassium iodide solution, thereby quantifying the amount of fluorine gas, and quantifying the amount of nitrogen gas not absorbed by the aqueous potassium iodide solution using a gas meter or the like.

[0045] Based on this finding, the present inventors have invented the above-mentioned method for producing fluorine gas and apparatus for producing fluorine gas, which have a structure capable of switching the flow path for a fluid according to the current efficiency. The apparatus for producing fluorine gas of this embodiment has a first flow path and a second flow path, and may be configured to select one of the two flow paths to be used for transporting the fluid using a flow path switching unit (for example, a switching valve).

[0046] Alternatively, the fluorine gas production apparatus of this embodiment may have two flow paths and a moving and replacing mechanism for moving and replacing the electrolytic cell, and may be configured to select one of the two flow paths to be used for transporting a fluid, and move and connect the electrolytic cell to the vicinity of that flow path, thereby switching the flow paths. As described above, since the first flow path and the second flow path are provided, even while one flow path is blocked for cleaning, the other flow path can be opened and the fluorine gas production apparatus can be operated continuously.

[0047] According to the study by the inventors, mist with a relatively large average particle size is generated immediately after the start of electrolysis until stable electrolysis is achieved, and at this time, the fluid may be sent to the second flow path having a clogging prevention mechanism. As time passes and stable electrolysis is achieved, mist with a relatively small average particle size is generated, and at this time, the flow path may be switched so that the fluid is sent to the first flow path having a mist removal unit.

[0048] The flow path is switched in accordance with the measured current efficiency, but the flow path is switched based on a preset reference value. The appropriate reference value for the average particle size of the mist generated at the anode varies depending on the device, but is, for example, 0.1 μm to 1.0 μm, preferably 0.2 μm to 0.8 μm, and more preferably 0.4 μm.

[0049] Therefore, in view of the correlation between the average particle size of the mist and the current efficiency, the lower limit of the appropriate standard value for the current efficiency is 50% or more, preferably 60% or more. The upper limit of the standard value is preferably 99% or less, more preferably 90% or less. The most appropriate standard value for the current efficiency is 60%. If the current efficiency is smaller than the standard value, the fluid can be sent to the second flow path, and if it is equal to or greater than the standard value, the fluid can be sent to the first flow path. The fluid (mainly hydrogen gas) generated at the cathode contains, for example, 20 to 50 μg of powder per unit volume (1 liter) (calculated assuming the specific gravity of the mist is 1.0 g / mL), and the average particle size of this powder is approximately 0.1 μm with a distribution of ±0.05 μm.

[0050] In the fluid generated at the cathode, no significant difference in particle size distribution of the generated powder was observed due to current efficiency. The mist contained in the fluid generated at the cathode has a smaller average particle size than the mist contained in the fluid generated at the anode, and is therefore less likely to cause blockage of pipes or valves than the mist contained in the fluid generated at the anode. Therefore, the mist contained in the fluid generated at the cathode can be removed from the fluid using an appropriate removal method.

[0051] An example of the fluorine gas production apparatus of this embodiment will be described in detail with reference to Fig. 2. The fluorine gas production apparatus of Fig. 2 is an example equipped with two electrolytic cells, but the number of electrolytic cells may be one, or three or more, for example, 10 to 15. The fluorine gas production apparatus shown in FIG. 2 includes electrolytic cells 11, 11 that contain electrolytic solution 10 and perform electrolysis, an anode 13 that is disposed inside electrolytic cell 11 and immersed in electrolytic solution 10, and a cathode 15 that is disposed inside electrolytic cell 11 and immersed in electrolytic solution 10 and opposed to anode 13.

[0052] The interior of the electrolytic cell 11 is divided into an anode chamber 22 and a cathode chamber 24 by a partition wall 17 that extends vertically downward from the ceiling surface of the interior of the electrolytic cell 11 and has its lower end immersed in the electrolytic solution 10. An anode 13 is disposed in the anode chamber 22, and a cathode 15 is disposed in the cathode chamber 24. However, the space above the liquid surface of the electrolytic solution 10 is separated by the partition wall 17 into the space within the anode chamber 22 and the space within the cathode chamber 24, and a portion of the electrolytic solution 10 above the lower end of the partition wall 17 is separated by the partition wall 17, but a portion of the electrolytic solution 10 below the lower end of the partition wall 17 is not directly separated by the partition wall 17 and is continuous.

[0053] The fluorine gas production apparatus shown in FIG. 2 also includes a current efficiency measuring unit 38 that measures the current efficiency of fluorine gas production in electrolysis, a first average particle size measuring unit 31 that measures the average particle size of mist contained in the fluid generated inside the electrolytic cell 11 during electrolysis of the electrolyte 10, a first mist removal unit 32 that removes the mist from the fluid, a fluorine gas selection unit (not shown) that selects and extracts fluorine gas from the fluid, and a flow path that sends the fluid from inside the electrolytic cell 11 to the fluorine gas selection unit.

[0054] Furthermore, this flow path has a first flow path that sends the fluid from the inside of the electrolytic cell 11 to the fluorine gas selector via the first mist removal section 32, and a second flow path that sends the fluid from the inside of the electrolytic cell 11 to the fluorine gas selector without passing through the first mist removal section 32. In addition, this flow path has a flow path switching section that switches the flow path for the fluid between the first flow path and the second flow path depending on the current efficiency measured by the current efficiency measuring section 38. In other words, the flow path switching section is provided midway along the flow path extending from the electrolytic cell 11, and the flow path for the fluid to flow can be changed by the flow path switching section.

[0055] This flow path switching unit sends the fluid from inside the electrolytic cell 11 to the first flow path when the current efficiency measured by the current efficiency measuring unit 38 is equal to or greater than a preset reference value, and sends the fluid from inside the electrolytic cell 11 to the second flow path when the current efficiency is less than the preset reference value. The second flow path has a clogging suppression mechanism that suppresses clogging of the second flow path by mist. That is, when the current efficiency is equal to or greater than the reference value, the fluid is sent to the first flow path which connects the electrolytic cell 11 and the fluorine gas sorting section and is provided with the first mist removal section 32, and when the current efficiency is smaller than the reference value, the fluid is sent to the second flow path which connects the electrolytic cell 11 and the fluorine gas sorting section and is provided with a clogging prevention mechanism.

[0056] The configuration of the current efficiency measuring unit 38 is not particularly limited, but the current efficiency measuring unit 38 has a configuration that allows it to determine the current efficiency by, for example, the above-mentioned titration method. That is, the current efficiency measuring unit 38 may have an inert gas supply unit (not shown) that supplies an inert gas such as nitrogen gas at a predetermined flow rate to the anode chamber 22 of the electrolytic cell 11, a titration unit (not shown) that takes a portion of a mixed gas containing fluorine gas and an inert gas discharged from the anode chamber 22 of the electrolytic cell 11, passes the portion through an aqueous potassium iodide solution for a certain period of time to absorb the fluorine gas in the mixed gas into the aqueous potassium iodide solution, and titrates the iodine liberated from the aqueous potassium iodide solution, and a calculation unit (not shown) that calculates the current efficiency of fluorine gas production in electrolysis based on the flow rate of the inert gas in the inert gas supply unit, the titration result by the titration unit (the amount of fluorine gas actually produced), and the current value in the electrolysis.

[0057] For example, a mist removal device capable of removing mist with an average particle diameter of 0.4 μm or less from the fluid is used as the first mist removal section 32. The type of mist removal device, i.e., the method for removing the mist, is not particularly limited, but because the average particle diameter of the mist is small, for example, an electrostatic precipitator, a venturi scrubber, or a filter can be used as the mist removal device.

[0058] Of the mist removal devices described above, it is preferable to use the mist removal device shown in Fig. 3. The mist removal device shown in Fig. 3 is a scrubber-type mist removal device that uses liquid hydrogen fluoride as a circulating liquid. The mist removal device shown in Fig. 3 can efficiently remove mist with an average particle size of 0.4 µm or less from a fluid. Furthermore, although liquid hydrogen fluoride is used as the circulating liquid, it is preferable to cool the circulating liquid in order to reduce the concentration of hydrogen fluoride in the fluorine gas, and therefore the concentration of hydrogen fluoride in the fluorine gas can be adjusted by controlling the cooling temperature.

[0059] The fluorine gas production apparatus shown in Fig. 2 will be described in further detail. A first pipe 41, which sends the fluid generated in the anode chamber 22 of the electrolytic cell 11 (hereinafter sometimes referred to as "anode gas") to the outside, connects the electrolytic cell 11 to a fourth pipe 44, and the anode gas sent out from the two electrolytic cells 11, 11 is sent to the fourth pipe 44 by the first pipe 41 and mixed there. The anode gas is mainly composed of fluorine gas, and its secondary components are mist, hydrogen fluoride, carbon tetrafluoride, oxygen gas, and water.

[0060] The fourth pipe 44 is connected to the first mist removal unit 32, and the anode gas is sent to the first mist removal unit 32 via the fourth pipe 44, so that the mist and hydrogen fluoride in the anode gas are removed from the anode gas by the first mist removal unit 32. The anode gas from which the mist and hydrogen fluoride have been removed is sent from the first mist removal unit 32 to a fluorine gas selection unit (not shown) via a sixth pipe 46 connected to the first mist removal unit 32. The fluorine gas is then separated from the anode gas and extracted by the fluorine gas selection unit.

[0061] An eighth pipe 48 is connected to the first mist removal unit 32, and liquid hydrogen fluoride, which is a circulating fluid, is supplied to the first mist removal unit 32 by the eighth pipe 48. Furthermore, a ninth pipe 49 is connected to the first mist removal unit 32. The ninth pipe 49 is connected to the electrolytic cells 11, 11 via the third pipe 43, and the circulating fluid (liquid hydrogen fluoride) that is used to remove mist in the first mist removal unit 32 and contains mist, is returned from the first mist removal unit 32 to the electrolytic cells 11, 11.

[0062] The cathode chamber 24 of the electrolytic cell 11 is similar to the anode chamber 22. That is, a second pipe 42, which sends the fluid generated in the cathode chamber 24 of the electrolytic cell 11 (hereinafter sometimes referred to as "cathode gas") to the outside, connects the electrolytic cell 11 to a fifth pipe 45, and the cathode gases sent out from the two electrolytic cells 11, 11 are sent to the fifth pipe 45 by the second pipe 42 and mixed there. The main component of the cathode gas is hydrogen gas, and the secondary components are mist, hydrogen fluoride, and water.

[0063] Because the cathode gas contains fine mist and 5 to 10 volume % hydrogen fluoride, it is not preferable to discharge the cathode gas directly into the atmosphere. Therefore, fifth pipe 45 is connected to second mist removal unit 33, and the cathode gas is sent to second mist removal unit 33 via fifth pipe 45. The mist and hydrogen fluoride in the cathode gas are removed from the cathode gas by second mist removal unit 33. The cathode gas from which the mist and hydrogen fluoride have been removed is discharged from second mist removal unit 33 into the atmosphere via seventh pipe 47 connected to second mist removal unit 33. The type of second mist removal unit 33, i.e., the method for removing the mist, is not particularly limited, but a scrubber-type mist removal device that uses an alkaline aqueous solution as a circulating fluid can be used.

[0064] The pipe diameters and installation directions (meaning the direction in which the pipes extend, for example, vertically or horizontally) of the first pipe 41, the second pipe 42, the fourth pipe 44, and the fifth pipe 45 are not particularly limited, but it is preferable that the first pipe 41 and the second pipe 42 are installed so as to extend vertically from the electrolytic cell 11, and that the pipe diameters are such that the flow velocity of the fluid flowing through the first pipe 41 and the second pipe 42 is 30 cm / sec or less under standard conditions. In this way, even if mist contained in the fluid falls under its own weight, the mist will settle inside the electrolytic cell 11, making it less likely that the inside of the first pipe 41 and the second pipe 42 will be clogged with powder. Furthermore, it is preferable that the fourth pipe 44 and the fifth pipe 45 are installed to extend horizontally, and that the pipe diameter is such that the flow velocity of the fluid flowing through the fourth pipe 44 and the fifth pipe 45 is approximately 1 to 10 times faster than that of the first pipe 41 and the second pipe 42.

[0065] Furthermore, a second bypass pipe 52 for sending anode gas to the outside of the electrolytic cell 11 is provided separately from the first pipe 41. That is, the second bypass pipe 52 connects the electrolytic cell 11 with the first bypass pipe 51, and the anode gases sent out from the two electrolytic cells 11, 11 are sent to the first bypass pipe 51 by the second bypass pipe 52 and mixed therewith. Furthermore, the anode gas is sent out to a fluorine gas sorting section (not shown) by the first bypass pipe 51. Then, fluorine gas is sorted from the anode gas and extracted by the fluorine gas sorting section. The fluorine gas sorting section connected to the first bypass pipe 51 and the fluorine gas sorting section connected to the sixth pipe 46 may be the same or different.

[0066] The pipe diameter and installation direction of the second bypass pipe 52 are not particularly limited, but it is preferable that the second bypass pipe 52 is installed so as to extend vertically from the electrolytic cell 11 and that the pipe diameter is such that the flow rate of the fluid flowing through the second bypass pipe 52 is 30 cm / sec or less under standard conditions.

[0067] The first bypass pipe 51 is installed so as to extend horizontally. The first bypass pipe 51 has a larger diameter than the fourth pipe 44, and the diameter of the first bypass pipe 51 is set to be large enough to prevent clogging of the first bypass pipe 51 due to accumulation of powder. The first bypass pipe 51 has a larger diameter than the fourth pipe 44, thereby forming a clogging prevention mechanism. The pipe diameter of the first bypass pipe 51 is preferably more than 1.0 times and not more than 3.2 times that of the fourth pipe 44, and more preferably 1.05 times or more and 1.5 times or less. In other words, the flow path cross-sectional area of the first bypass pipe 51 is preferably not more than 10 times that of the fourth pipe 44.

[0068] As can be seen from the above description, the first flow path is formed by the first pipe 41 and the fourth pipe 44, and the second flow path is formed by the first bypass pipe 51 and the second bypass pipe 52. A clogging suppression mechanism is provided in the first bypass pipe 51 that forms the second flow path.

[0069] Next, the flow path switching unit will be described. Each of the first pipes 41 is provided with a first pipe valve 61. By switching the first pipe valve 61 between an open state and a closed state, it is possible to control whether or not anode gas is sent from the electrolytic cell 11 to the first mist removal unit 32. Each of the second bypass pipes 52 is provided with a bypass valve 62. By switching the bypass valve 62 between an open state and a closed state, it is possible to control whether or not anode gas is sent from the electrolytic cell 11 to the first bypass pipe 51.

[0070] Furthermore, in the current efficiency measuring unit 38 of the fluorine gas production apparatus, the titration unit that separates the anode gas, passes it through an aqueous potassium iodide solution, and titrates the liberated iodine is installed in the middle of the fourth pipe 44, downstream of the joint with the first pipe 41. The inert gas supply unit is preferably installed near the electrolytic cell 11, and the installation location of the calculation unit is not particularly limited.

[0071] Furthermore, a first average particle diameter measuring unit 31 is installed between the electrolytic cell 11 and the first mist removal unit 32, more specifically, in the middle of the fourth pipe 44 and downstream of the joint with the first pipe 41. The first average particle diameter measuring unit 31 measures the average particle diameter of the mist contained in the anode gas flowing through the fourth pipe 44. Furthermore, by analyzing the fluorine gas and nitrogen gas contained in the anode gas after measuring the average particle diameter of the mist, the current efficiency in the production of fluorine gas can be measured.

[0072] A similar second average particle diameter measuring unit 34 is also installed in the middle of the first bypass pipe 51 and downstream of the joint with the second bypass pipe 52, and the second average particle diameter measuring unit 34 measures the average particle diameter of the mist contained in the anode gas flowing through the first bypass pipe 51. However, the fluorine gas production apparatus shown in FIG. 2 does not necessarily have to include the first average particle diameter measuring unit 31 and the second average particle diameter measuring unit 34.

[0073] The current efficiency of fluorine gas production in electrolysis is measured by the current efficiency measuring unit 38, and if the measurement result is smaller than a preset reference value, the bypass valve 62 is opened to send the anode gas from the electrolytic cell 11 to the first bypass pipe 51, and the first pipe valve 61 is closed to prevent the anode gas from being sent to the fourth pipe 44 and the first mist removal unit 32. In other words, the anode gas is sent to the second flow path.

[0074] On the other hand, if the measurement result is equal to or greater than the preset reference value, the first piping valve 61 is opened to send the anode gas to the fourth piping 44 and the first mist removal unit 32, and the bypass valve 62 is closed to prevent the anode gas from being sent from the electrolytic cell 11 to the first bypass piping 51. In other words, the anode gas is sent to the first flow path. As can be seen from the above description, the first piping valve 61 and the bypass valve 62 constitute the flow path switching unit.

[0075] As described above, by operating the fluorine gas production apparatus while switching the flow paths depending on the current efficiency of fluorine gas production in electrolysis, smooth continuous operation can be performed while preventing clogging of pipes and valves due to mist. Therefore, the fluorine gas production apparatus shown in Fig. 2 can produce fluorine gas economically.

[0076] For example, a plurality of pipes each equipped with a filter may be prepared as the mist removal unit, and electrolysis may be performed by switching between them as appropriate and replacing the filters. Furthermore, it is advisable to determine the period when the filter should be replaced frequently and the period when the filter does not need to be replaced frequently based on the measurement of current efficiency. Then, by appropriately adjusting the frequency of switching the pipes through which the fluid flows based on the above determination, the fluorine gas production apparatus can be operated efficiently and continuously.

[0077] Next, a modified example of the fluorine gas production apparatus shown in FIG. 2 will be described. [First Modified Example] The first modified example will be described with reference to Fig. 4. In the fluorine gas production apparatus shown in Fig. 2, the second bypass pipe 52 connects the electrolytic cell 11 and the first bypass pipe 51, whereas in the fluorine gas production apparatus of the first modified example shown in Fig. 4, the second bypass pipe 52 connects the first pipe 41 and the first bypass pipe 51. The configuration of the fluorine gas production apparatus of the first modified example is almost the same as the fluorine gas production apparatus of Fig. 2 except for the above points, so a description of the similar parts will be omitted.

[0078] [Second Modification] The second modified example will be described with reference to Fig. 5. The fluorine gas production apparatus of the second modified example shown in Fig. 5 is an example equipped with one electrolytic cell 11. The first average particle diameter measurement unit 31 is provided in the first pipe 41 instead of the fourth pipe 44, and is provided upstream of the first pipe valve 61. In addition, the second bypass pipe 52 is not provided, and the first bypass pipe 51 is connected directly to the electrolytic cell 11 without going through the second bypass pipe 52.

[0079] The first bypass pipe 51 has a larger diameter than the fourth pipe 44, and therefore functions as a clogging prevention mechanism. Furthermore, the effect of clogging prevention can be further enhanced by providing a space for mist accumulation at the downstream end of the first bypass pipe 51, for example. Examples of this space for mist accumulation include a space in which the downstream end of the first bypass pipe 51 has a larger pipe diameter (for example, four times or more the pipe diameter of the central portion in the installation direction) than the central portion in the installation direction, or a space in which the downstream end of the first bypass pipe 51 is formed into a container-like shape. The mist accumulation space can prevent clogging of the first bypass pipe 51. This is intended to achieve the effect of preventing clogging by using the large cross-sectional area of the flow path and the effect of preventing clogging by utilizing the gravitational fall of mist due to a decrease in the linear velocity of the gas flow. Furthermore, the bypass valve 62 is provided in a third bypass pipe 53 that connects the first bypass pipe 51 with a fluorine gas selection section (not shown). Except for the above points, the configuration of the fluorine gas production apparatus of the second modified example is almost the same as that of the fluorine gas production apparatus of Fig. 2, so a description of the similar parts will be omitted.

[0080] [Third Modification] The third modified example will be described with reference to Fig. 6. In the fluorine gas production apparatus of the third modified example, a first average particle diameter measuring unit 31 is provided in the electrolytic cell 11, and the anode gas inside the electrolytic cell 11 is directly introduced into the first average particle diameter measuring unit 31 to measure the average particle diameter of the mist. The fluorine gas production apparatus of the third modified example does not have the second average particle diameter measuring unit 34. Except for the above points, the configuration of the fluorine gas production apparatus of the third modified example is substantially the same as that of the fluorine gas production apparatus of the second modified example, and therefore a description of the similar parts will be omitted.

[0081] [Fourth Modification] The fourth modified example will be described with reference to Fig. 7. The fluorine gas production apparatus of the fourth modified example is an example in which the clogging suppression mechanism is different from that of the second modified example shown in Fig. 5. In the fluorine gas production apparatus of the second modified example, the first bypass pipe 51 is installed to extend along the horizontal direction, but in the fluorine gas production apparatus of the fourth modified example, the first bypass pipe 51 is inclined with respect to the horizontal direction and extends in a downward direction from the upstream side to the downstream side. This inclination suppresses the accumulation of powder inside the first bypass pipe 51. The greater the inclination, the greater the effect of suppressing the accumulation of powder.

[0082] The inclination angle of the first bypass pipe 51 is preferably 30 degrees or more, with the depression angle from the horizontal plane being less than 90 degrees, and more preferably 40 degrees or more and 60 degrees or less. If clogging of the first bypass pipe 51 is likely to occur, hammering the inclined first bypass pipe 51 will make it easier for deposits inside the first bypass pipe 51 to move, thereby preventing clogging. The configuration of the fluorine gas production apparatus of the fourth modified example is almost the same as that of the fluorine gas production apparatus of the second modified example except for the above points, so a description of the similar parts will be omitted.

[0083] [Fifth Modification] The fifth modified example will be described with reference to FIG. 8. The fluorine gas production apparatus of the fifth modified example is an example in which the clogging suppression mechanism is different from that of the third modified example shown in FIG. 6. In the fluorine gas production apparatus of the third modified example, the first bypass pipe 51 is installed to extend along the horizontal direction, but in the fluorine gas production apparatus of the fifth modified example, the first bypass pipe 51 is inclined with respect to the horizontal direction and extends in a direction descending from the upstream side to the downstream side. This inclination suppresses the accumulation of powder inside the first bypass pipe 51. The preferred inclination angle of the first bypass pipe 51 is the same as in the fourth modified example. The configuration of the fluorine gas production apparatus of the fifth modified example is substantially the same as that of the fluorine gas production apparatus of the third modified example except for the above points, so a description of the similar parts will be omitted.

[0084] [Sixth Modification] The sixth modified example will be described with reference to Fig. 9. The fluorine gas production apparatus of the sixth modified example is an example in which the structure of the electrolytic cell 11 is different from that of the second modified example shown in Fig. 5. The electrolytic cell 11 has one anode 13 and two cathodes 15, 15, and is partitioned into one anode chamber 22 and one cathode chamber 24 by a cylindrical partition wall 17 that surrounds the one anode 13. The anode chamber 22 is formed to extend above the upper surface of the electrolytic cell 11, and a first bypass pipe 51 is connected to the upper end portion of the anode chamber 22 of the electrolytic cell 11. The configuration of the fluorine gas production apparatus of the sixth modified example is substantially the same as that of the fluorine gas production apparatus of the second modified example except for the above points, so a description of the similar parts will be omitted.

[0085] [Seventh Modification] The seventh modified example will be described with reference to Fig. 10. The fluorine gas production apparatus of the seventh modified example is an example in which the structure of the first bypass pipe 51 is different from that of the sixth modified example shown in Fig. 9. That is, in the fluorine gas production apparatus of the seventh modified example, the first bypass pipe 51 is inclined with respect to the horizontal direction and extends in a direction descending from the upstream side to the downstream side, similar to the fourth and fifth modified examples. The preferred angle of inclination of the first bypass pipe 51 is the same as in the fourth modified example. The configuration of the fluorine gas production apparatus of the seventh modified example is almost the same as that of the fluorine gas production apparatus of the sixth modified example except for the above points, so a description of the similar parts will be omitted.

[0086] [Eighth Modification] The eighth modified example will be described with reference to Fig. 11. The fluorine gas production apparatus of the eighth modified example is an example in which the clogging suppression mechanism is different from that of the second modified example shown in Fig. 5. In the fluorine gas production apparatus of the eighth modified example, a rotary screw 71 constituting the clogging suppression mechanism is installed inside the first bypass pipe 51. The rotary screw 71 is installed with its rotation axis parallel to the longitudinal direction of the first bypass pipe 51. By rotating the rotary screw 71 with the motor 72, the mist accumulated inside the first bypass pipe 51 can be sent upstream or downstream. This prevents the powder from accumulating inside the first bypass pipe 51. The configuration of the fluorine gas production apparatus of the eighth modified example is almost the same as that of the fluorine gas production apparatus of the second modified example except for the above points, so a description of the similar parts will be omitted.

[0087] [Ninth Modification] A ninth modified example will be described with reference to Fig. 12. The fluorine gas production apparatus of the ninth modified example is an example in which the clogging suppression mechanism is different from that of the second modified example shown in Fig. 5. In the fluorine gas production apparatus of the ninth modified example, an airflow generator 73 constituting the clogging suppression mechanism is installed in the first bypass pipe 51. The airflow generator 73 sends an airflow (for example, an airflow of nitrogen gas) from the upstream side to the downstream side of the first bypass pipe 51, thereby increasing the flow rate of the anode gas flowing inside the first bypass pipe 51. This prevents powder from accumulating inside the first bypass pipe 51.

[0088] At this time, the flow velocity of the anode gas flowing through the first bypass pipe 51 is preferably 1 m / sec or more and 10 m / sec or less. The flow velocity can be made greater than 10 m / sec, but in that case, the pressure loss due to the piping resistance in the first bypass pipe 51 increases, and the pressure in the anode chamber 22 of the electrolytic cell 11 increases. It is preferable that the pressure in the anode chamber 22 and the pressure in the cathode chamber 24 are approximately the same, but if the difference between the pressure in the anode chamber 22 and the pressure in the cathode chamber 24 becomes too large, the anode gas will flow over the partition wall 17 into the cathode chamber 24, causing a reaction between fluorine gas and hydrogen gas, which may hinder the generation of fluorine gas. The configuration of the fluorine gas production apparatus of the ninth modified example is almost the same as that of the fluorine gas production apparatus of the second modified example except for the above points, so a description of the similar parts will be omitted.

[0089] [Tenth Modification] The tenth modified example will be described with reference to Fig. 13. In the fluorine gas production apparatus of the tenth modified example, a first average particle diameter measuring unit 31 is provided in the electrolytic cell 11, and the anode gas inside the electrolytic cell 11 is directly introduced into the first average particle diameter measuring unit 31 to measure the average particle diameter of the mist. The fluorine gas production apparatus of the tenth modified example does not have a second average particle diameter measuring unit 34. Except for the above points, the configuration of the fluorine gas production apparatus of the tenth modified example is substantially the same as that of the fluorine gas production apparatus of the ninth modified example shown in Fig. 12, so a description of the similar parts will be omitted. [Example]

[0090] The present invention will be described in more detail below with reference to examples and comparative examples. [Reference example 1] Fluorine gas was produced by electrolyzing the electrolyte. A mixed molten salt (560 L) of 434 kg of hydrogen fluoride and 630 kg of potassium fluoride was used as the electrolyte. Amorphous carbon electrodes (30 cm wide, 45 cm long, 7 cm thick) manufactured by SGL Carbon were used as anodes, and 16 anodes were installed in the electrolytic cell. Furthermore, punched plates manufactured by Monel (trademark) were used as cathodes, and were installed in the electrolytic cell. Two cathodes faced one anode, and the total area of the parts of one anode facing the cathode was 1736 cm. 2 is.

[0091] The electrolysis temperature was controlled at 85 to 95°C. First, the electrolyte temperature was set to 85°C, and the current density was set to 0.036 A / cm 2 A direct current of 1000 A was applied at 1000 V to start electrolysis. The water concentration in the electrolytic solution at this time was 1.0 mass %. The water concentration was measured by Karl Fischer analysis. Electrolysis was started under the above conditions, and from immediately after the start of electrolysis until the cumulative current flow reached 10 kAh, a small popping sound was observed near the anode in the anode chamber. This popping sound was thought to be caused by a reaction between the generated fluorine gas and the water in the electrolyte.

[0092] The fluid generated at the anode under these conditions was sampled when it was sent out from the anode chamber of the electrolytic cell, and the mist contained in the fluid was analyzed. The results showed that 5.0 to 9.0 mg of powder (calculated assuming the specific gravity of the mist was 1.0 g / mL; the same applies below) was contained per liter of fluid generated at the anode, and the average particle size of this powder was 1.0 to 2.0 μm. When this powder was observed under an optical microscope, it was mainly found to be shaped like a sphere with the inside hollowed out. Furthermore, the current efficiency of fluorine gas generation at this time was 0 to 15%.

[0093] Furthermore, when electrolysis was continued until the cumulative current flow reached 30 kAh, the frequency of popping sounds occurring inside the anode chamber decreased. The water concentration in the electrolyte at this time was 0.7% by mass. Furthermore, the fluid generated at the anode in this state was sampled when it was discharged from the anode chamber of the electrolytic cell to the outside, and the mist contained in the fluid was analyzed. As a result, 0.4 to 1.0 mg of mist was contained per liter of fluid generated at the anode, and the average particle diameter of this mist was 0.5 to 0.7 μm. Furthermore, the current efficiency of fluorine gas generation at this time was 15 to 55%. The electrolysis stage from the start of electrolysis to this point is referred to as "Stage (1)."

[0094] Furthermore, electrolysis of the electrolyte was continued following step (1). As a result, hydrogen fluoride was consumed and the level of the electrolyte decreased, so hydrogen fluoride was appropriately replenished from the hydrogen fluoride tank to the electrolytic cell. The water concentration in the replenished hydrogen fluoride was 500 mass ppm or less. Further, as electrolysis continued and the cumulative current flow exceeded 60 kAh, the average particle size of the mist contained in the fluid generated at the anode became 0.36 μm (i.e., 0.4 μm or less). At this point, no popping sounds were generated inside the anode chamber. The water concentration in the electrolyte at this time was 0.2 mass% (i.e., 0.3 mass% or less). Furthermore, the current efficiency of fluorine gas production at this time was 65%. The electrolysis stage from the end of stage (1) to this point is referred to as "stage (2)."

[0095] Furthermore, the current was increased to 3500A, and the current density was reduced to 0.126A / cm 2 The current was increased to 0.03-0.06 mg per liter of fluid generated at the anode, and electrolysis of the electrolyte was continued from stage (2). The fluid generated at the anode under this condition was sampled when it was discharged from the anode chamber of the electrolytic cell to the outside, and the mist contained in the fluid was analyzed. The results showed that 0.03-0.06 mg of powder was contained per liter of fluid generated at the anode. The average particle size of this powder was approximately 0.2 μm (0.15-0.25 μm), with a particle size distribution of approximately 0.1-0.5 μm. Figure 14 shows the measurement results of the particle size distribution of this powder. Furthermore, the current efficiency for fluorine gas production at this time was 94%. The electrolysis stage from the end of stage (2) to this point is referred to as the "stable stage."

[0096] The details of the electrolysis of Reference Example 1 carried out as described above are summarized in Table 1. Table 1 shows the current, elapsed time of electrolysis, amount of current applied, water concentration in the electrolyte, mass of mist contained in 1 L of fluid generated at the anode (referred to as "anode gas" in Table 1), average particle size of the mist, and current efficiency, as well as the amount of fluid generated at the anode (containing fluorine gas, oxygen gas, and mist), the amount of mist generated at the anode, the intensity of the popping sound, and the water concentration in the fluid generated at the cathode (referred to as "water concentration in cathode gas" in Table 1).

[0097] Furthermore, Figure 15 shows a graph showing the relationship between the average particle size of the mist and the amount of mist generated at the anode. The graph in Figure 15 shows that there is a correlation between the average particle size of the mist and the amount of mist generated at the anode. The greater the amount of mist generated, the more likely it is that piping and valves will become clogged. Furthermore, when mist with an average particle size larger than 0.4 μm is generated, the amount of mist generated increases and it will then settle due to the action of gravity. Therefore, it can be said that the relationship shown in the graph in Figure 15 shows a correlation between the average particle size of the mist and the likelihood of piping and valves becoming clogged. Furthermore, a graph showing the relationship between the average particle size of the mist and current efficiency is shown in Figure 16. Since the larger the average particle size of the mist, the more likely it is that pipes and valves will become clogged, the relationship shown in the graph in Figure 16 can be said to represent the correlation between current efficiency and the likelihood of pipes and valves becoming clogged.

[0098] [Table 1]

[0099] Example 1 Electrolysis similar to that in Reference Example 1 was carried out using the fluorine gas production apparatus shown in Figure 2. In the electrolysis in stage (1), the fluid generated at the anode was circulated through the second bypass pipe, the bypass valve, and the first bypass pipe. After the electrolysis in stage (1) was completed, the electrolysis was temporarily stopped, and the inside of the fluorine gas production apparatus was inspected. As a result, although mist had accumulated in the first bypass pipe, no blockage of the pipe occurred because the diameter of the pipe had been increased.

[0100] Because the electrolysis reached stage (2), where the average particle size of the mist was 0.4 μm or less (current efficiency was 65%, which is more than 60% of the standard value), the fluid generated at the anode was circulated through the first pipe, the first pipe valve, the fourth pipe, and the first mist removal unit. No mist accumulation or blockage occurred in the first pipe, the first pipe valve, or the fourth pipe, and the fluid generated at the anode was supplied to the first mist removal unit, where the mist was removed. The first mist removal unit is a scrubber-type removal unit that sprays liquid hydrogen fluoride to remove fine particles such as mist, and the mist removal rate was more than 98%.

[0101] Comparative Example 1 In the electrolysis of step (1), the fluid generated at the anode was circulated through the first pipe, the first pipe valve, the fourth pipe, and the first mist removal section, except that the electrolysis was carried out in the same manner as in Example 1. During electrolysis in stage (1), the pressure gauge attached to the anode and cathode sides of the electrolytic cell gradually increased, and the pressure reading on the anode gauge gradually increased until the pressure difference with the cathode side reached 90 mmH2O, at which point electrolysis was stopped. The reason for the stoppage is as follows: The vertical length (immersion depth) of the part of the partition wall inside the electrolytic cell that was immersed in the electrolyte was 5 cm, so when the pressure on the anode side became approximately 100 mmH2O higher than the pressure on the cathode side, the electrolyte level on the anode side became lower than the bottom of the partition wall. As a result, fluorine gas overflowed the partition wall and mixed with hydrogen gas on the cathode side, causing a rapid reaction between the fluorine gas and hydrogen gas, which was extremely dangerous. After purging the system with nitrogen gas, etc., the inside of the first pipe, the first pipe valve, and the fourth pipe were inspected, and it was found that the first pipe was not blocked because it is a vertical pipe. A small amount of powder had adhered to the first pipe valve, and the pipe downstream of the first pipe valve, i.e., the inlet to the fourth pipe, was blocked by powder. There was also powder accumulation in the fourth pipe, but the amount was not enough to block the pipe. [Explanation of symbols]

[0102] 1. Sample chamber 2...Light source 3. Scattered light detection unit 4A, 4B: Transparent window 10...electrolyte 11...Electrolytic cell 13...Anode 15...Cathode 22...Anode chamber 24 Cathode chamber 31...1st average particle size measuring section 32 First mist removal section 33 Second mist removal section 34...Second average particle size measuring section 38 Current efficiency measurement section 41···First piping 42...Second piping 43 Third piping 44···Fourth piping 45···5th piping 46···6th piping 47···7th piping 48···8th piping 49. No. 9 Pipe 51···First bypass piping 52 Second bypass piping 61 First piping valve 62 Bypass valve F...Fluid L...Light for light scattering measurement M...Mist S...scattered light

Claims

1. A method for producing fluorine gas, comprising electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride to produce fluorine gas, an electrolysis step in which the electrolysis is carried out in an electrolytic cell; a current efficiency measurement step of measuring the current efficiency of fluorine gas production in the electrolysis; an air supplying step of supplying a fluid generated inside the electrolytic cell during electrolysis of the electrolytic solution from the inside to the outside of the electrolytic cell through a flow path; Equipped with In the gas supplying step, a flow path for passing the fluid is switched in accordance with the current efficiency measured in the current efficiency measuring step; if the current efficiency measured in the current efficiency measuring step is equal to or greater than a preset reference value, the fluid is sent to a first flow path for sending the fluid from inside the electrolytic cell to a first outside; and if the current efficiency measured in the current efficiency measuring step is smaller than the preset reference value, the fluid is sent to a second flow path for sending the fluid from inside the electrolytic cell to a second outside; The preset reference value is a value within a range of 50% or more, The first flow path has a mist removal section that removes mist contained in the fluid from the fluid, and the second flow path has a clogging prevention mechanism that prevents the second flow path from being blocked by the mist.

2. 2. The method for producing fluorine gas according to claim 1, wherein the metal fluoride is a fluoride of at least one metal selected from the group consisting of potassium, cesium, rubidium, and lithium.

3. 3. The method for producing fluorine gas according to claim 1, wherein the anode used in the electrolysis is a carbonaceous electrode formed from at least one carbon material selected from the group consisting of diamond, diamond-like carbon, amorphous carbon, graphite, and glassy carbon.

4. 4. The method for producing fluorine gas according to claim 1, wherein the electrolytic cell has a structure that allows bubbles generated at the anode or cathode used in the electrolysis to rise vertically in the electrolytic solution and reach the liquid surface of the electrolytic solution.

5. A fluorine gas production apparatus for producing fluorine gas by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride, an electrolytic cell containing the electrolytic solution and in which the electrolysis is carried out; a current efficiency measuring unit for measuring the current efficiency of fluorine gas generation in the electrolysis; a flow path for transporting a fluid generated inside the electrolytic cell during electrolysis of the electrolytic solution from the inside to the outside of the electrolytic cell; Equipped with the flow path includes a first flow path for sending the fluid from the inside of the electrolytic cell to a first outside, and a second flow path for sending the fluid from the inside of the electrolytic cell to a second outside, and a flow path switching unit for switching the flow path for the fluid between the first flow path and the second flow path in accordance with the current efficiency measured by the current efficiency measuring unit, the flow path switching unit sends the fluid from inside the electrolytic cell to the first flow path when the current efficiency measured by the current efficiency measuring unit is equal to or greater than a predetermined reference value, and sends the fluid from inside the electrolytic cell to the second flow path when the current efficiency is smaller than the predetermined reference value, The preset reference value is a value within a range of 50% or more, The first flow path has a mist removal section that removes mist contained in the fluid from the fluid, and the second flow path has a clogging prevention mechanism that prevents the second flow path from being blocked by the mist.

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