US20220154353A1 - Method for producing fluorine gas and device for producing fluorine gas - Google Patents

Method for producing fluorine gas and device for producing fluorine gas Download PDF

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US20220154353A1
US20220154353A1 US17/595,958 US202017595958A US2022154353A1 US 20220154353 A1 US20220154353 A1 US 20220154353A1 US 202017595958 A US202017595958 A US 202017595958A US 2022154353 A1 US2022154353 A1 US 2022154353A1
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electrolytic cell
flow path
fluorine gas
fluid
mist
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Shinya OGURO
Yohsuke FUKUCHI
Hiroshi Kobayashi
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Resonac Corp
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Showa Denko KK
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/24—Halogens or compounds thereof
    • C25B1/245—Fluorine; Compounds thereof
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/042—Electrodes formed of a single material
    • C25B11/043—Carbon, e.g. diamond or graphene
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/02—Process control or regulation
    • C25B15/023—Measuring, analysing or testing during electrolytic production
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/02—Process control or regulation
    • C25B15/023—Measuring, analysing or testing during electrolytic production
    • C25B15/025—Measuring, analysing or testing during electrolytic production of electrolyte parameters
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/02—Process control or regulation
    • C25B15/023—Measuring, analysing or testing during electrolytic production
    • C25B15/025—Measuring, analysing or testing during electrolytic production of electrolyte parameters
    • C25B15/029—Concentration
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/60—Constructional parts of cells

Definitions

  • the present invention relates to a method for producing fluorine gas and a device for producing fluorine gas.
  • Fluorine gas can be synthesized (electrolytically synthesized) by electrolyzing an electrolyte containing hydrogen fluoride and a metal fluoride. Electrolyzing an electrolyte generates mist (for example, a mist of the electrolyte) together with fluorine gas, and thus the fluorine gas sent from an electrolytic cell is accompanied with mist.
  • mist for example, a mist of the electrolyte
  • the mist accompanying fluorine gas becomes fine particles, which may clog pipes and valves used to send fluorine gas. This may force a production operation of fluorine gas to discontinue or stop and has interfered with continuous operation to produce fluorine gas by the electrolytic method.
  • PTL 1 discloses technology of heating fluorine gas accompanied with mist or a pipe through which the gas passes, to a temperature equal to or higher than the melting point of an electrolyte.
  • PTL 2 discloses a gas production device including a gas diffusion unit as a space to roughly collect mist and a filler storage unit storing a filler for adsorbing mist.
  • the present invention is intended to provide a method for producing fluorine gas and a device for producing fluorine gas capable of suppressing clogging of pipes and valves with mist.
  • aspects of the present invention are the following [1] to [5].
  • a method for producing fluorine gas the fluorine gas being produced by electrolyzing an electrolyte containing hydrogen fluoride and a metal fluoride, the method including
  • electrolyzing the electrolyte in an electrolytic cell including an anode chamber having an anode and a cathode chamber having a cathode in an inside of the electrolytic cell,
  • the flow path in which the fluid flows is switched in accordance with the water concentration measured in the measuring a water concentration, such that the fluid is sent to a first flow path that sends the fluid from the inside of the electrolytic cell to a first outside when the water concentration measured in the measuring a water concentration is not more than a predetermined reference value, or the fluid is sent to a second flow path that sends the fluid from the inside of the electrolytic cell to a second outside when the water concentration is more than the predetermined reference value, and
  • the predetermined reference value is a numerical value of 0.01% by volume or more and 0.09% by volume or less.
  • the metal fluoride is a fluoride of at least one metal selected from the group consisting of potassium, cesium, rubidium, and lithium.
  • a device for producing fluorine gas the fluorine gas being produced by electrolysis of an electrolyte containing hydrogen fluoride and a metal fluoride, the device including
  • an electrolytic cell including an anode chamber having an anode and a cathode chamber having a cathode in an inside of the electrolytic cell, storing the electrolyte, and configured to perform the electrolysis,
  • a water concentration measurement unit configured to measure a water concentration in a fluid generated in the cathode chamber during the electrolysis
  • a flow path configured to send a fluid generated in the inside of the electrolytic cell during the electrolysis of the electrolyte, from the inside to an outside of the electrolytic cell.
  • the flow path includes a first flow path configured to send the fluid from the inside of the electrolytic cell to a first outside and a second flow path configured to send the fluid from the inside of the electrolytic cell to a second outside and includes a flow path switching unit configured to switch the flow path in which the fluid flows, to the first flow path or the second flow path in accordance with the water concentration measured by the water concentration measurement unit,
  • the flow path switching unit is configured to send the fluid from the inside of the electrolytic cell to the first flow path when the water concentration measured by the water concentration measurement unit is not more than a predetermined reference value, or to send the fluid from the inside of the electrolytic cell to the second flow path when the water concentration is more than the predetermined reference value, and
  • the predetermined reference value is a numerical value of 0.01% by volume or more and 0.09% by volume or less.
  • clogging of pipes and valves with mist can be suppressed when an electrolyte containing hydrogen fluoride and a metal fluoride is electrolyzed to produce fluorine gas.
  • FIG. 1 is a view schematically illustrating an example light scattering detector used as an average particle size measurement unit in a device for producing fluorine gas pertaining to an embodiment of the present invention
  • FIG. 2 is a schematic view illustrating an example device for producing fluorine gas pertaining to an embodiment of the present invention
  • FIG. 3 is a view schematically illustrating an example mist remover used as a mist removal unit in the device for producing fluorine gas in FIG. 2 ;
  • FIG. 4 is a schematic view illustrating a first alternative embodiment of the device for producing fluorine gas in FIG. 2 ;
  • FIG. 5 is a schematic view illustrating a second alternative embodiment of the device for producing fluorine gas in FIG. 2 ;
  • FIG. 6 is a schematic view illustrating a third alternative embodiment of the device for producing fluorine gas in FIG. 2 ;
  • FIG. 7 is a schematic view illustrating a fourth alternative embodiment of the device for producing fluorine gas in FIG. 2 ;
  • FIG. 8 is a schematic view illustrating a fifth alternative embodiment of the device for producing fluorine gas in FIG. 2 ;
  • FIG. 9 is a schematic view illustrating a sixth alternative embodiment of the device for producing fluorine gas in FIG. 2 ;
  • FIG. 10 is a schematic view illustrating a seventh alternative embodiment of the device for producing fluorine gas in FIG. 2 ;
  • FIG. 11 is a schematic view illustrating an eighth alternative embodiment of the device for producing fluorine gas in FIG. 2 ;
  • FIG. 12 is a schematic view illustrating a ninth alternative embodiment of the device for producing fluorine gas in FIG. 2 ;
  • FIG. 13 is a schematic view illustrating a tenth alternative embodiment of the device for producing fluorine gas in FIG. 2 ;
  • FIG. 14 is a graph illustrating a particle size distribution of a mist contained in a fluid generated on the anode in Reference Example 1;
  • FIG. 15 is a graph illustrating a relation between average particle size of a mist and amount of the mist generated on the anode in Reference Example 1;
  • FIG. 16 is a graph illustrating a relation between average particle size of a mist and water concentration in a cathode gas in Reference Example 1.
  • a mist is liquid microparticles or solid microparticles generated together with fluorine gas in an electrolytic cell by electrolysis of an electrolyte.
  • a mist is microparticles of an electrolyte, solid microparticles formed by phase change of microparticles of an electrolyte, and solid microparticles generated by reaction of fluorine gas with members included in an electrolytic cell (for example, metals included in an electrolytic cell, gaskets for an electrolytic cell, and a carbon electrode).
  • the inventors of the present invention measured the average particle size of a mist contained in a fluid generated in an electrolytic cell during electrolysis of an electrolyte and have found that the average particle size of the mist changes with time. As a result of intensive studies, the inventors of the present invention have also found a relation between average particle size of a mist and water concentration in a fluid generated in a cathode chamber of an electrolytic cell during electrolysis (hereinafter also called “water concentration in a cathode gas”) and have further found a relation between average particle size of a mist and likelihood of clogging of pipes and valves that send a fluid.
  • the inventors of the present invention have found that the clogging of pipes and valves can be suppressed by improving a flow path for sending a fluid generated in an electrolytic cell in accordance with the water concentration in a cathode gas, and the frequency of discontinuance or stop of an operation for producing fluorine gas can be reduced and have completed the present invention. Embodiments of the present invention will now be described.
  • a method for producing fluorine gas in an embodiment is a method for producing fluorine gas by electrolyzing an electrolyte containing hydrogen fluoride and a metal fluoride.
  • the method includes electrolyzing the electrolyte in an electrolytic cell including an anode chamber having an anode and a cathode chamber having a cathode in the inside of the electrolytic cell, measuring the water concentration in a fluid generated in the cathode chamber in the electrolyzing, and sending a fluid generated in the inside of the electrolytic cell in the electrolyzing the electrolyte, from the inside to the outside of the electrolytic cell through a flow path.
  • the flow path in which the fluid flows is switched in accordance with the water concentration measured in the measuring the water concentration.
  • the fluid is sent to a first flow path that sends the fluid from the inside of the electrolytic cell to a first outside when the water concentration measured in the measuring the water concentration is not more than a predetermined reference value, or the fluid is sent to a second flow path that sends the fluid from the inside of the electrolytic cell to a second outside when the water concentration is more than the predetermined reference value.
  • the predetermined reference value is a numerical value of 0.01% by volume or more and 0.09% by volume or less.
  • a device for producing fluorine gas in an embodiment is a device for producing fluorine gas by electrolysis of an electrolyte containing hydrogen fluoride and a metal fluoride.
  • the device includes an electrolytic cell including an anode chamber having an anode and a cathode chamber having a cathode in the inside of the electrolytic cell, storing the electrolyte, and configured to perform the electrolysis, a water concentration measurement unit configured to measure the water concentration in a fluid generated in the cathode chamber during the electrolysis, and a flow path configured to send a fluid generated in the inside of the electrolytic cell during the electrolysis of the electrolyte, from the inside to the outside of the electrolytic cell.
  • the flow path includes a first flow path configured to send the fluid from the inside of the electrolytic cell to a first outside and a second flow path configured to send the fluid from the inside of the electrolytic cell to a second outside.
  • the flow path also includes a flow path switching unit configured to switch the flow path in which the fluid flows, to the first flow path or the second flow path in accordance with the water concentration measured by the water concentration measurement unit.
  • the flow path switching unit is configured to send the fluid from the inside of the electrolytic cell to the first flow path when the water concentration measured by the water concentration measurement unit is not more than a predetermined reference value, or to send the fluid from the inside of the electrolytic cell to the second flow path when the water concentration is more than the predetermined reference value.
  • the predetermined reference value is a numerical value of 0.01% by volume or more and 0.09% by volume or less.
  • the flow path in which the fluid flows is switched to the first flow path or the second flow path in accordance with the water concentration in a cathode gas.
  • the flow path is switched to the first flow path or the second flow path in accordance with the average particle size of a mist, and thus the mist is unlikely to cause clogging of the flow paths.
  • the method for producing fluorine gas and the device for producing fluorine gas of the embodiments can suppress the clogging of pipes and valves with mist when an electrolyte containing hydrogen fluoride and a metal fluoride is electrolyzed to produce fluorine gas. This can reduce the frequency of discontinuance or stop of an operation for producing fluorine gas and facilitates continuous operation. As a result, fluorine gas can be economically produced.
  • the measurement of the water concentration in a cathode gas may be performed continuously, periodically at regular intervals (for example, at intervals of one second), or irregularly at any time during electrolysis.
  • the first flow path differs from the second flow path, but the first outside and the second outside may be different sections or the same section.
  • the first flow path is a flow path through which a fluid is sent from the inside of the electrolytic cell through a mist removal unit for removing a mist from the fluid to a fluorine gas selection unit for selectively collecting fluorine gas from the fluid.
  • the second flow path is a flow path through which a fluid is sent from the inside of the electrolytic cell to the fluorine gas selection unit but not through the mist removal unit.
  • a fluid is sent to the mist removal unit on the first flow path when the water concentration in the cathode gas is not more than a predetermined reference value, and a fluid is not sent to the mist removal unit when the water concentration is more than the predetermined reference value.
  • the fluorine gas selection unit corresponds to the first outside and the second outside, and the first outside and the second outside are the same section, but the first outside and the second outside may be different sections.
  • the second flow path has a clogging suppression mechanism that suppresses the clogging of the second flow path with mist.
  • the clogging suppression mechanism may be any mechanism that can suppress the clogging of the second flow path with mist, and examples include the following mechanisms.
  • examples include a pipe having a large diameter, an inclined pipe, a rotary screw, and an airflow generator, and these members may be used in combination.
  • the second flow path at least partially includes a pipe having a larger diameter than the first flow path
  • the clogging of the second flow path with mist can be suppressed.
  • the second flow path at least partially includes a pipe that is inclined relative to the horizontal direction and extends downward from the upstream side to the downstream side, the clogging of the second flow path with mist can be suppressed.
  • the clogging of the second flow path with mist can be suppressed.
  • the second flow path has an airflow generator for sending airflow to increase the flow rate of a fluid flowing in the second flow path, the clogging of the second flow path with mist can be suppressed.
  • Another mist removal unit different from the mist removal unit on the first flow path may be provided on the second flow path as the clogging suppression mechanism.
  • the first flow path is unlikely to be clogged with mist because the mist removal unit removes a mist from the fluid, and the second flow path is unlikely to be clogged with mist because the clogging suppression mechanism is provided.
  • the method for producing fluorine gas and the device for producing fluorine gas of the embodiments can suppress the clogging of pipes and valves with mist when an electrolyte containing hydrogen fluoride and a metal fluoride is electrolyzed to produce fluorine gas.
  • the electrolytic cell may be any cell that can electrolyze an electrolyte containing hydrogen fluoride and a metal fluoride to generate fluorine gas.
  • the inside of the electrolytic cell is sectioned by a partition member such as a partition wall into an anode chamber having an anode and a cathode chamber having a cathode, and this structure prevents the fluorine gas generated on the anode from mixing with the hydrogen gas generated on the cathode.
  • a partition member such as a partition wall into an anode chamber having an anode and a cathode chamber having a cathode, and this structure prevents the fluorine gas generated on the anode from mixing with the hydrogen gas generated on the cathode.
  • anode for example, a carbonaceous electrode formed from a carbon material such as diamond, diamond-like carbon, amorphous carbon, graphite, glassy carbon, and indefinite carbon can be used.
  • a metal electrode formed from a metal such as nickel and Monel (trademark) can also be used in addition to the carbon material.
  • a metal electrode formed from a metal such as iron, copper, nickel, and Monel (trademark) can be used.
  • the electrolyte contains hydrogen fluoride and a metal fluoride.
  • the metal fluoride may be any type and is preferably a fluoride of at least one metal selected from the group consisting of potassium, cesium, rubidium, and lithium. When containing cesium or rubidium, the electrolyte has a larger specific gravity and thus suppresses the amount of a mist generated during electrolysis.
  • a mixed molten salt of hydrogen fluoride (HF) and potassium fluoride (KF) can be used as the electrolyte.
  • a typical electrolyte is KF.2HF where the ratio of hydrogen fluoride to potassium fluoride is 2:1, and the mixed molten salt has a melting point of about 72° C.
  • the electrolyte has corrosivity, and thus a portion to come into contact with the electrolyte, such as the inner face of the electrolytic cell, is preferably formed from a metal such as iron, nickel, and Monel (trademark).
  • a direct current is applied to the anode and the cathode. Accordingly, a gas containing fluorine gas is generated on the anode, whereas a gas containing hydrogen gas is generated on the cathode.
  • the hydrogen fluoride in the electrolyte has a vapor pressure, and thus gases generated on the anode and the cathode are accompanied with hydrogen fluoride.
  • a gas generated by the electrolysis also contains a mist of the electrolyte.
  • the gas phase in the electrolytic cell contains a gas generated by electrolysis, hydrogen fluoride, and a mist of the electrolyte.
  • the substance sent from the inside to the outside of the electrolytic cell contains a gas generated by electrolysis, hydrogen fluoride, and a mist of the electrolyte and is called a “fluid” in the present invention.
  • a pipe for continuously or intermittently feeding and resupplying hydrogen fluoride into the electrolytic cell may be connected to the electrolytic cell.
  • Hydrogen fluoride may be fed to either the cathode chamber or the anode chamber of the electrolytic cell.
  • a mist is generated during electrolysis of an electrolyte mainly due to the following reason.
  • the temperature of an electrolyte during electrolysis is adjusted, for example, at 80 to 100° C.
  • KF.2HF has a melting point of 71.7° C., and thus the electrolyte is in the liquid state when the temperature is adjusted as above. Bubbles of the gas generated on both the electrodes in the electrolytic cell rise in the electrolyte and burst on the surface of the electrolyte. On the bursting, the electrolyte is partially discharged into the gas phase.
  • the gas phase has a temperature lower than the melting point of the electrolyte, and thus the discharged electrolyte changes in phase into such a state as microscopic particles.
  • the fine particles are supposedly a mixture of potassium fluoride and hydrogen fluoride, KF.nHF.
  • the fine particles float on a separately generated gas and become a mist, forming a fluid generated in the electrolytic cell.
  • Such a mist has tackiness and the like and thus is difficult to efficiently remove by conventional countermeasures such as installation of filters.
  • a carbonaceous electrode as the anode may be reacted with fluorine gas generated by electrolysis to generate impalpable particles of an organic compound as a mist in a small amount.
  • an electric current supply portion to the carbonaceous electrode has a contact resistance in many cases and may have a temperature higher than the temperature of the electrolyte due to Joule heat.
  • the carbon included in the carbonaceous electrode may be reacted with fluorine gas to generate a soot-like organic compound, CFx, as a mist.
  • the electrolytic cell preferably has a structure in which bubbles generated on the anode or the cathode used in the electrolysis can vertically rise in the electrolyte to reach the surface of the electrolyte.
  • a plurality of bubbles are likely to gather to form large bubbles. The resulting large bubbles reach the surface of the electrolyte and burst, and the amount of a mist is likely to increase.
  • an electrolytic cell has a structure in which bubbles can vertically rise in an electrolyte to reach the surface of the electrolyte, small bubbles reach the surface of the electrolyte and burst, and thus the amount of a mist is likely to decrease.
  • the device for producing fluorine gas of the embodiment may have an average particle size measurement unit for measuring the average particle size of a mist contained in a fluid.
  • the average particle size measurement unit may include a light scattering detector for measuring the average particle size by light scattering.
  • the light scattering detector can measure the average particle size of a mist in a fluid flowing in a flow path while the device for producing fluorine gas is continuously operated and thus is preferred as the average particle size measurement unit.
  • the light scattering detector in FIG. 1 is a light scattering detector usable as the average particle size measurement unit in the device for producing fluorine gas of the embodiment (for example, the devices for producing fluorine gas in FIG. 2 and FIGS. 4 to 13 described later).
  • the light scattering detector measures the average particle size of a mist contained in a fluid generated in the electrolytic cell when an electrolyte containing hydrogen fluoride and a metal fluoride is electrolyzed in the electrolytic cell of the device for producing fluorine gas to produce fluorine gas.
  • the light scattering detector may be connected to the device for producing fluorine gas, and the average particle size of a mist may be measured while a fluid is sent from the inside of the electrolytic cell to the light scattering detector.
  • the light scattering detector may not be connected to the device for producing fluorine gas and may measure the average particle size of a mist while a fluid is sampled from the inside of the electrolytic cell and is introduced to the light scattering detector.
  • the light scattering detector in FIG. 1 includes a sample chamber 1 for receiving a fluid F, a light source 2 for applying light for light scattering measurement L to the fluid F in the sample chamber 1 , a scattered light detection unit 3 for detecting scattered light S generated when the light for light scattering measurement L is scattered by a mist M in the fluid F, a transparent window 4 A that is placed in the sample chamber 1 and is in contact with the fluid F and through which the light for light scattering measurement L passes, and a transparent window 4 B that is placed in the sample chamber 1 and is in contact with the fluid F and through which the scattered light S passes.
  • the transparent windows 4 A, 4 B are formed from at least one selected from the group consisting of diamond, calcium fluoride (CaF 2 ), potassium fluoride (KF), silver fluoride (AgF), barium fluoride (BaF 2 ), and potassium bromide (KBr).
  • the light for light scattering measurement L (for example, a laser beam) emitted from the light source 2 passes through a converging lens 6 and the transparent window 4 A of the sample chamber 1 , enters the sample chamber 1 , and is applied to the fluid F received in the sample chamber 1 .
  • the fluid F contains a light reflective substance such as a mist M
  • the light for light scattering measurement L is reflected and scattered.
  • the scattered light S generated when the light for light scattering measurement L is scattered by the mist M partially passes through the transparent window 4 B of the sample chamber 1 , is retrieved from the sample chamber 1 to the outside, and enters the scattered light detection unit 3 through a condensing lens 7 and a throttle 8 .
  • the average particle size of the mist M can be determined.
  • the average particle size determined by the detector is a number average particle size.
  • an aerosol spectrometer for example, Welas (registered trademark) digital 2000 manufactured by PALAS can be used.
  • the transparent windows 4 A, 4 B are in contact with the fluid F.
  • the fluid F contains highly reactive fluorine gas, and thus the transparent windows 4 A, 4 B are required to be formed from a material that is unlikely to be corroded by fluorine gas.
  • the material for forming the transparent windows 4 A, 4 B is, for example, at least one selected from the group consisting of diamond, calcium fluoride, potassium fluoride, silver fluoride, barium fluoride, and potassium bromide.
  • a glass such as quartz having a surface coated with a film formed of such a material as above can also be used as the transparent windows 4 A, 4 B.
  • the portion to come into contact with the fluid F is coated with a film formed of such a material as above, and thus the deterioration by contact with the fluid F can be suppressed while the cost is reduced.
  • Each transparent window 4 A, 4 B may be a laminate in which a face to come into contact with the fluid F is formed of such a material as above, and the other portions are formed of a common glass such as quartz.
  • the members of the light scattering detector except the transparent windows 4 A, 4 B may be made from any material having corrosion resistance against fluorine gas, and, for example, a metal material such as Monel (trademark) that is a copper-nickel alloy, hastelloy (trademark), and stainless steel is preferably used.
  • a metal material such as Monel (trademark) that is a copper-nickel alloy, hastelloy (trademark), and stainless steel is preferably used.
  • the inventors of the present invention measured the average particle size of a mist generated during production of fluorine gas by electrolysis of an electrolyte, by using the light scattering detector. An example of the result will be described. After the anode of a device for producing fluorine gas is exchanged for a new anode or an electrolytic cell is filled with a fresh electrolyte, electrolysis is started, and the average particle size of a mist in a fluid generated on the anode was measured for a certain period of time from just after the start of electrolysis. As a result, the mist had an average particle size of 0.5 to 2.0 ⁇ m. After a sufficient time period of continuous electrolysis, the electrolysis is becoming stable. During the stable electrolysis, the mist in the fluid had an average particle size of about 0.2 ⁇ m.
  • a mist having a relatively large particle size is generated from just after the start of electrolysis to the stable electrolysis. If the fluid containing a mist having a large size just after the start of electrolysis flows in pipes and valves, the mist is likely to adsorb onto the inner face of the pipes and valves, causing clogging of the pipes and valves.
  • the generated mist has a relatively small particle size. Such a small mist is unlikely to settle or deposit in a fluid and thus can flow stably in pipes and valves.
  • a fluid consisting of a mist and a gas generated on an electrode has a relatively low possibility of causing clogging of pipes and valves.
  • the time from the start of electrolysis to the stable electrolysis is typically 25 hours or more and 200 hours or less. From the start of electrolysis to the stable electrolysis, an electric energy of about 40 kAh or more is required to be applied for 1,000 L of an electrolyte.
  • the inventors of the present invention have found a close relation between the average particle size of a mist and the water concentration in a cathode gas.
  • the water concentration in a cathode gas is typically large at the start of electrolysis and is more than 0.05% by volume.
  • the mist has an average particle size of more than 0.4 ⁇ m.
  • the cathode gas has a lower water concentration, and when the water concentration reaches 0.05% by volume or less, the mist has an average particle size of 0.4 ⁇ m or less.
  • the average particle size of a mist has a relation to the water concentration in a cathode gas.
  • the water concentration in a cathode gas can be measured during electrolysis in place of the average particle size of a mist, and the measurement result can be used to switch a flow path.
  • the flow path in which a fluid generated by the electrolysis flows can be appropriately switched at the certain timing in accordance with the measurement result.
  • the device for producing fluorine gas of the embodiment has a first flow path and a second flow path, and a flow path switching unit (for example, a switching valve) may be used to select, from the two flow paths, a flow path used to convey a fluid.
  • a flow path switching unit for example, a switching valve
  • the device for producing fluorine gas of the embodiment may have two flow paths and a transfer and replacement mechanism for transferring and replacing an electrolytic cell. From the two flow paths, a flow path used to convey a fluid may be selected, and an electrolytic cell maybe transferred near the flow path and be connected to the flow path. This can switch the flow path.
  • the device has the first flow path and the second flow path as described above. Hence, even while one flow path is blocked and cleaned, the other flow path can be opened, and the device for producing fluorine gas can be continuously operated.
  • a mist having a relatively large average particle size is generated from the start of electrolysis to the stable electrolysis, and thus a fluid can be sent to the second flow path having a clogging suppression mechanism.
  • a mist having a relatively small average particle size is generated, and thus the flow path can be switched such that the fluid is sent to the first flow path having a mist removal unit.
  • Such switching the flow path is performed in accordance with the measured water concentration in a cathode gas, and the flow path is switched on the basis of a predetermined reference value.
  • the appropriate reference value of the average particle size of a mist generated on an anode varies with devices and is, for example, 0.1 ⁇ m or more and 1.0 ⁇ m or less, preferably 0.2 ⁇ m or more and 0.8 ⁇ m or less, and more preferably 0.4 ⁇ m.
  • the appropriate reference value of the water concentration in a cathode gas is accordingly 0.01% by volume or more and 0.09% by volume or less, preferably 0.03% by volume or more and 0.07% by volume or less, and more preferably 0.05% by volume.
  • the fluid can be sent to the second flow path, and when the water concentration is not more than the reference value, the fluid can be sent to the first flow path.
  • the water concentration in the cathode gas may be measured by any method, including infrared spectroscopy and Fourier transformation infrared spectroscopy.
  • the water concentration in the fluid generated in the anode chamber of the electrolytic cell can be measured but is changed by the reaction of fluorine gas with water, and thus the water concentration in the cathode gas (hydrogen gas) is preferably measured.
  • a certain amount of the cathode gas is introduced into a cell of an infrared spectrometer, and the absorption intensity at a wavelength specific to water is used to quantitatively determine the water concentration. For example, by introducing a cathode gas into a cell while the gas flow rate is controlled with amass flow meter, a certain amount of the cathode gas can be introduced into the cell.
  • the fluid (mainly containing hydrogen gas) generated on the cathode for example, contains 20 to 50 ⁇ g of fine particles (calculated assuming that a mist has a specific gravity of 1.0 g/mL) per unit volume (1 liter), and the fine particles have an average particle size of about 0.1 ⁇ m with a distribution of ⁇ 0.05 ⁇ m.
  • the mist contained in the fluid generated on the cathode has a smaller average particle size than the mist contained in the fluid generated on the anode and thus is unlikely to cause clogging of pipes and valves as compared with the mist contained in the fluid generated on the anode.
  • the mist contained in the fluid generated on the cathode can be removed from the fluid by using an appropriate removal method.
  • the device for producing fluorine gas in FIG. 2 is an example including two electrolytic cells, but a single electrolytic cell may be included, or three or more, for example, 10 to 15 electrolytic cells may be included.
  • the device for producing fluorine gas illustrated in FIG. 2 includes electrolytic cells 11 , 11 in which an electrolyte 10 is stored and electrolysis is performed, an anode 13 placed in each electrolytic cell 11 and immersed in the electrolyte 10 , and a cathode 15 placed in each electrolytic cell 11 , immersed in the electrolyte 10 , and facing the anode 13 .
  • each electrolytic cell 11 is sectioned into an anode chamber 22 and a cathode chamber 24 by a partition wall 17 extending from a ceiling face in the electrolytic cell 11 downward in the vertical direction and having a lower end immersed in the electrolyte 10 .
  • the anode 13 is placed, and in the cathode chamber 24 , the cathode 15 is placed.
  • the space above the surface of the electrolyte 10 is separated by the partition wall 17 into a space in the anode chamber 22 and a space in the cathode chamber 24 , and a portion of the electrolyte 10 above the lower end of the partition wall 17 is separated by the partition wall 17 , but a portion of the electrolyte 10 below the lower end of the partition wall 17 is not directly separated by the partition wall 17 but continues.
  • the device for producing fluorine gas illustrated in FIG. 2 includes a water concentration measurement unit 39 that measures the water concentration in a fluid generated in the cathode chamber 24 of each electrolytic cell 11 during electrolysis of the electrolyte 10 , a first average particle size measurement unit 31 that measures the average particle size of a mist contained in a fluid generated in each electrolytic cell 11 during electrolysis of the electrolyte 10 , a first mist removal unit 32 that removes a mist from a fluid, a fluorine gas selection unit (not illustrated) that selectively collects fluorine gas from a fluid, and a flow path configured to send a fluid from the inside of each electrolytic cell 11 to the fluorine gas selection unit.
  • a water concentration measurement unit 39 that measures the water concentration in a fluid generated in the cathode chamber 24 of each electrolytic cell 11 during electrolysis of the electrolyte 10
  • a first average particle size measurement unit 31 that measures the average particle size of a mist contained in a fluid generated in each electrolytic cell 11 during
  • the flow path includes a first flow path that sends a fluid from the inside of each electrolytic cell 11 through the first mist removal unit 32 to the fluorine gas selection unit and a second flow path that sends a fluid from the inside of each electrolytic cell 11 to the fluorine gas selection unit but not through the first mist removal unit 32 .
  • the flow path also includes a flow path switching unit configured to switch the flow path in which the fluid flows, to the first flow path or the second flow path in accordance with the water concentration in a cathode gas measured by the water concentration measurement unit 39 . In other words, at an intermediate point of the flow path extending from the electrolytic cell 11 , the flow path switching unit is provided, and the flow path switching unit can alter the flow path in which a fluid flows.
  • the flow path switching unit sends a fluid from the inside of each electrolytic cell 11 to the first flow path when the water concentration in a cathode gas measured by the water concentration measurement unit 39 is not more than a predetermined reference value or sends a fluid from the inside of each electrolytic cell 11 to the second flow path when the water concentration is more than the predetermined reference value.
  • the second flow path has a clogging suppression mechanism that suppresses the clogging of the second flow path with mist.
  • the electrolytic cell 11 when the water concentration in a cathode gas is not more than a reference value, the electrolytic cell 11 is connected to a fluorine gas selection unit, and the fluid is sent to the first flow path with the first mist removal unit 32 .
  • the electrolytic cell 11 is connected to a fluorine gas selection unit, and the fluid is sent to the second flow path with the clogging suppression mechanism.
  • FT-IR Fourier transformation infrared spectrometer
  • a mist remover capable of removing a mist having an average particle size of 0.4 ⁇ m or less from a fluid is used.
  • the type of mist remover, or the system of removing a mist is not specifically limited, but a mist has a small average particle size, and thus, for example, an electric dust collector, a venturi scrubber, or a filter can be used as the mist remover.
  • the mist remover illustrated in FIG. 3 is preferably used.
  • the mist remover illustrated in FIG. 3 is a scrubber type mist remover using a liquid hydrogen fluoride as a circulating liquid.
  • the mist remover illustrated in FIG. 3 can efficiently remove a mist having an average particle size of 0.4 ⁇ m or less from a fluid.
  • the mist remover uses a liquid hydrogen fluoride as a circulating liquid.
  • the circulating liquid is preferably cooled in order to reduce the concentration of hydrogen fluoride in a fluorine gas, and thus the concentration of hydrogen fluoride in a fluorine gas can be controlled by adjusting the cooling temperature.
  • the main component of the anode gas is fluorine gas, and accessory components are mist, hydrogen fluoride, carbon tetrafluoride, oxygen gas, and water.
  • the fourth pipe 44 is connected to the first mist removal unit 32 , and the anode gas is sent through the fourth pipe 44 to the first mist removal unit 32 .
  • the first mist removal unit 32 removes mist and hydrogen fluoride in the anode gas from the anode gas.
  • the anode gas from which the mist and hydrogen fluoride have been removed is sent from the first mist removal unit 32 through a sixth pipe 46 connected to the first mist removal unit 32 to a fluorine gas selection unit (not illustrated).
  • the fluorine gas selection unit then selectively collects fluorine gas from the anode gas.
  • the first mist removal unit 32 is connected to an eighth pipe 48 , and a liquid hydrogen fluoride as the circulating liquid is supplied through the eighth pipe 48 to the first mist removal unit 32 .
  • the first mist removal unit 32 is further connected to a ninth pipe 49 .
  • the ninth pipe 49 is connected through third pipes 43 to the electrolytic cells 11 , 11 , and a circulating liquid (liquid hydrogen fluoride) containing a mist and having used to remove a mist in the first mist removal unit 32 is returned from the first mist removal unit 32 to the electrolytic cells 11 , 11 .
  • the cathode chamber 24 in each electrolytic cell 11 is substantially the same as the anode chamber 22 .
  • a second pipe 42 that sends a fluid generated in the cathode chamber 24 in each electrolytic cell 11 (hereinafter also called “cathode gas”) to the outside connects the electrolytic cell 11 to a fifth pipe 45 , and the cathode gases sent from the two electrolytic cells 11 , 11 are sent through the second pipes 42 to the fifth pipe 45 and are mixed.
  • the main component of the cathode gas is hydrogen gas, and accessory components are mist, hydrogen fluoride, and water.
  • the cathode gas contains a fine mist and 5 to 10% by volume of hydrogen fluoride, and thus it is unfavorable to directly discharge the cathode gas to the atmosphere.
  • the fifth pipe 45 is connected to a second mist removal unit 33 , and the cathode gas is sent through the fifth pipe 45 to the second mist removal unit 33 .
  • the second mist removal unit 33 removes mist and hydrogen fluoride in the cathode gas from the cathode gas.
  • the cathode gas from which the mist and hydrogen fluoride have been removed is discharged from the second mist removal unit 33 through a seventh pipe 47 connected to the second mist removal unit 33 to the atmosphere.
  • the type of second mist removal unit 33 or the system of removing a mist is not specifically limited, and a scrubber type mist remover using an aqueous alkali solution as the circulating liquid can be used.
  • the pipe diameters and the installation directions (i.e., a pipe extending direction, for example, the vertical direction, the horizontal direction) of the first pipe 41 , the second pipe 42 , the fourth pipe 44 , and the fifth pipe 45 are not specifically limited.
  • the first pipe 41 and the second pipe 42 are preferably installed so as to extend from the electrolytic cell 11 in the vertical direction and preferably have a pipe diameter such that fluids flowing in the first pipe 41 and the second pipe 42 have a flow rate of 30 cm/sec or less in a normal state. In such conditions, even when a mist contained in a fluid falls under its own weight, the mist settles in the electrolytic cell 11 , and thus the clogging in the first pipe 41 and the second pipe 42 with fine particles is unlikely to be caused.
  • the fourth pipe 44 and the fifth pipe 45 are preferably installed so as to extend in the horizontal direction and preferably have a pipe diameter such that fluids flowing in the fourth pipe 44 and the fifth pipe 45 have a flow rate about 1 ton times more than that in the first pipe 41 and the second pipe 42 .
  • a second bypass pipe 52 for sending the anode gas to the outside of the electrolytic cell 11 is further provided separately from the first pipe 41 .
  • the second bypass pipe 52 connects each electrolytic cell 11 to a first bypass pipe 51 , and the anode gases sent from the two electrolytic cells 11 , 11 are sent through the second bypass pipes 52 to the first bypass pipe 51 and are mixed.
  • the anode gas is sent to a fluorine gas selection unit (not illustrated).
  • the fluorine gas selection unit selectively collects fluorine gas from the anode gas.
  • the fluorine gas selection unit connected to the first bypass pipe 51 may be the same as or different from the fluorine gas selection unit connected to the sixth pipe 46 .
  • the pipe diameter and the installation direction of the second bypass pipe 52 are not specifically limited, and the second bypass pipe 52 is preferably installed so as to extend from the electrolytic cell 11 in the vertical direction and preferably has a pipe diameter such that a fluid flowing in the second bypass pipe 52 has a flow rate of 30 cm/sec or less in a normal state.
  • the first bypass pipe 51 is installed so as to extend in the horizontal direction.
  • the first bypass pipe 51 has a larger pipe diameter than the fourth pipe 44 , and the pipe diameter of the first bypass pipe 51 is such a size as to be unlikely to cause clogging of the first bypass pipe 51 with depositing fine particles.
  • the first bypass pipe 51 has a larger pipe diameter than the fourth pipe 44 , and this functions as the clogging suppression mechanism.
  • the pipe diameter of the first bypass pipe 51 is preferably more than 1.0 time and not more than 3.2 times that of the fourth pipe 44 and more preferably not less than 1.05 times and not more than 1.5 times.
  • the first bypass pipe 51 preferably has a flow path cross-sectional area not more than 10 times that of the fourth pipe 44 .
  • the first pipes 41 and the fourth pipe 44 constitute the above first flow path
  • the first bypass pipe 51 and the second bypass pipes 52 constitute the above second flow path.
  • the first bypass pipe 51 included in the second flow path has the clogging suppression mechanism.
  • Each first pipe 41 has a first pipe valve 61 .
  • Each second bypass pipe 52 has a bypass valve 62 .
  • the device for producing fluorine gas includes the water concentration measurement unit 39 , and the water concentration in the cathode gas generated in the cathode chamber 24 during electrolysis can be measured.
  • the water concentration measurement unit 39 is provided at an intermediate point of the fifth pipe 45 and at the downstream side of the junctions to the second pipes 42 .
  • a first average particle size measurement unit 31 is provided between the electrolytic cells 11 and the first mist removal unit 32 , specifically, at an intermediate point of the fourth pipe 44 and at the downstream side of the junctions to the first pipes 41 .
  • the first average particle size measurement unit 31 measures the average particle size of a mist contained in the anode gas flowing in the fourth pipe 44 .
  • a second average particle size measurement unit 34 is also provided, and the second average particle size measurement unit 34 measures the average particle size of a mist contained in the anode gas flowing in the first bypass pipe 51 .
  • the device for producing fluorine gas illustrated in FIG. 2 may not include the first average particle size measurement unit 31 or the second average particle size measurement unit 34 .
  • the water concentration in a cathode gas is measured by the water concentration measurement unit 39 .
  • the bypass valve 62 is switched to an open state to send the anode gas from the electrolytic cell 11 to the first bypass pipe 51
  • the first pipe valve 61 is switched to a closed state not to send the anode gas to the fourth pipe 44 and the first mist removal unit 32 .
  • the anode gas is sent to the second flow path.
  • the first pipe valve 61 is switched to an open state to send the anode gas to the fourth pipe 44 and the first mist removal unit 32 , and the bypass valve 62 is switched to a closed state not to send the anode gas from the electrolytic cell 11 to the first bypass pipe 51 .
  • the anode gas is sent to the first flow path.
  • the first pipe valve 61 and the bypass valve 62 constitute the above flow path switching unit.
  • a plurality of pipes with filters may be prepared, and electrolysis may be performed while the pipes are appropriately switched to exchange the filters.
  • a time period when frequent exchange of filters is needed and a time period when frequent exchange of filters is not needed can be determined by measuring the water concentration in a cathode gas.
  • a first alternative embodiment will be described with reference to FIG. 4 .
  • the second bypass pipes 52 connect the electrolytic cells 11 to the first bypass pipe 51 .
  • second bypass pipes 52 connect first pipes 41 to a first bypass pipe 51 .
  • the device for producing fluorine gas in the first alternative embodiment has substantially the same constitution as the device for producing fluorine gas in FIG. 2 except the above structure, and thus similar structures are not described.
  • a device for producing fluorine gas in the second alternative embodiment illustrated in FIG. 5 includes a single electrolytic cell 11 .
  • a first average particle size measurement unit 31 is not provided on a fourth pipe 44 but on a first pipe 41 and is provided at the upstream side of a first pipe valve 61 .
  • the device includes no second bypass pipe 52 , and a first bypass pipe 51 is directly connected to an electrolytic cell 11 but not through a second bypass pipe 52 .
  • the first bypass pipe 51 has a larger diameter than the fourth pipe 44 and thus functions as the clogging suppression mechanism.
  • a mist pool space is further provided, for example, at the downstream end of the first bypass pipe 51 , and this can further improve the clogging suppression effect.
  • the mist pool space include a space formed from the downstream end portion of the first bypass pipe 51 and having a larger pipe diameter than the center portion in the installation direction (for example, a pipe diameter not less than 4 times that at the center portion in the installation direction) and a space formed from the downstream end portion of the first bypass pipe 51 and having a container shape.
  • the mist pool space can suppress clogging of the first bypass pipe 51 . This is aimed at a clogging suppression effect by a large flow path cross-sectional area and a clogging suppression effect using mist free fall by a reduction in linear velocity of a flowing gas.
  • a bypass valve 62 is provided on a third bypass pipe 53 that connects the first bypass pipe 51 to a fluorine gas selection unit (not illustrated).
  • the device for producing fluorine gas in the second alternative embodiment has substantially the same constitution as the device for producing fluorine gas in FIG. 2 except the above structure, and thus similar structures are not described.
  • a third alternative embodiment will be described with reference to FIG. 6 .
  • a device for producing fluorine gas in the third alternative embodiment a first average particle size measurement unit 31 is provided on an electrolytic cell 11 , and the average particle size of a mist is measured by introducing the anode gas in the electrolytic cell 11 directly into the first average particle size measurement unit 31 .
  • the device for producing fluorine gas in the third alternative embodiment has no second average particle size measurement unit 34 .
  • the device for producing fluorine gas in the third alternative embodiment has substantially the same constitution as the device for producing fluorine gas in the second alternative embodiment except the above structure, and thus similar structures are not described.
  • a fourth alternative embodiment will be described with reference to FIG. 7 .
  • a device for producing fluorine gas in the fourth alternative embodiment differs from that in the second alternative embodiment illustrated in FIG. 5 in the clogging suppression mechanism.
  • the first bypass pipe 51 is provided so as to extend in the horizontal direction.
  • a first bypass pipe 51 is inclined relative to the horizontal direction and extends downward from the upstream side to the downstream side. This inclination prevents fine particles from depositing in the first bypass pipe 51 . As the inclination is larger, the effect of suppressing fine particle deposition is larger.
  • the inclination angle of the first bypass pipe 51 is preferably 30 degrees or more and more preferably 40 degrees or more and 60 degrees or less where the depression angle from the horizontal plane is less than 90 degrees.
  • the device for producing fluorine gas in the fourth alternative embodiment has substantially the same constitution as the device for producing fluorine gas in the second alternative embodiment except the above structure, and thus similar structures are not described.
  • a fifth alternative embodiment will be described with reference to FIG. 8 .
  • a device for producing fluorine gas in the fifth alternative embodiment differs from that in the third alternative embodiment illustrated in FIG. 6 in the clogging suppression mechanism.
  • the first bypass pipe 51 is provided so as to extend in the horizontal direction.
  • a first bypass pipe 51 is inclined relative to the horizontal direction and extends downward from the upstream side to the downstream side. This inclination prevents fine particles from depositing in the first bypass pipe 51 .
  • the inclination angle of the first bypass pipe 51 is preferably substantially the same as in the fourth alternative embodiment.
  • the device for producing fluorine gas in the fifth alternative embodiment has substantially the same constitution as the device for producing fluorine gas in the third alternative embodiment except the above structure, and thus similar structures are not described.
  • a sixth alternative embodiment will be described with reference to FIG. 9 .
  • a device for producing fluorine gas in the sixth alternative embodiment differs from that in the second alternative embodiment illustrated in FIG. 5 in the structure of an electrolytic cell 11 .
  • the electrolytic cell 11 has one anode 13 and two cathodes 15 , 15 and is sectioned into one anode chamber 22 and one cathode chamber 24 by a cylindrical partition wall 17 surrounding the one anode 13 .
  • the anode chamber 22 is formed to extend above the top face of the electrolytic cell 11 , and a first bypass pipe 51 is connected to the top section of the anode chamber 22 of the electrolytic cell 11 .
  • the device for producing fluorine gas in the sixth alternative embodiment has substantially the same constitution as the device for producing fluorine gas in the second alternative embodiment except the above structure, and thus similar structures are not described.
  • a seventh alternative embodiment will be described with reference to FIG. 10 .
  • a device for producing fluorine gas in the seventh alternative embodiment differs from that in the sixth alternative embodiment illustrated in FIG. 9 in the structure of a first bypass pipe 51 .
  • a first bypass pipe 51 is inclined relative to the horizontal direction and extends downward from the upstream side to the downstream side as with the fourth alternative embodiment and the fifth alternative embodiment.
  • the inclination angle of the first bypass pipe 51 is preferably substantially the same as in the fourth alternative embodiment.
  • the device for producing fluorine gas in the seventh alternative embodiment has substantially the same constitution as the device for producing fluorine gas in the sixth alternative embodiment except the above structure, and thus similar structures are not described.
  • a device for producing fluorine gas in the eighth alternative embodiment differs from that in the second alternative embodiment illustrated in FIG. 5 in the clogging suppression mechanism.
  • a rotary screw 71 constituting the clogging suppression mechanism is provided in a first bypass pipe 51 .
  • the rotary screw 71 has a rotating shaft that is parallel to the longitudinal direction of the first bypass pipe 51 .
  • the rotary screw 71 is rotated by a motor 72 , and accordingly a mist deposited in the first bypass pipe 51 can be sent to the upstream side or the downstream side. This structure prevents fine particles from depositing in the first bypass pipe 51 .
  • the device for producing fluorine gas in the eighth alternative embodiment has substantially the same constitution as the device for producing fluorine gas in the second alternative embodiment except the above structure, and thus similar structures are not described.
  • a ninth alternative embodiment will be described with reference to FIG. 12 .
  • a device for producing fluorine gas in the ninth alternative embodiment differs from that in the second alternative embodiment illustrated in FIG. 5 in the clogging suppression mechanism.
  • an airflow generator 73 constituting the clogging suppression mechanism is provided on a first bypass pipe 51 .
  • the airflow generator 73 sends an airflow (for example, a nitrogen gas stream) from the upstream side toward the downstream side in the first bypass pipe 51 and increases the flow rate of an anode gas flowing in the first bypass pipe 51 . This structure prevents fine particles from depositing in the first bypass pipe 51 .
  • the flow rate of an anode gas flowing in the first bypass pipe 51 is preferably 1 m/sec or more and 10 m/sec or less.
  • the flow rate can be increased to more than 10 m/sec, but in such a case, the pipe resistance in the first bypass pipe 51 increases the pressure loss, and the pressure in an anode chamber 22 of an electrolytic cell 11 increases.
  • the pressure in the anode chamber 22 and the pressure in a cathode chamber 24 are preferably substantially the same.
  • the device for producing fluorine gas in the ninth alternative embodiment has substantially the same constitution as the device for producing fluorine gas in the second alternative embodiment except the above structure, and thus similar structures are not described.
  • a tenth alternative embodiment will be described with reference to FIG. 13 .
  • a first average particle size measurement unit 31 is provided on an electrolytic cell 11 , and the average particle size of a mist is measured by introducing the anode gas in the electrolytic cell 11 directly into the first average particle size measurement unit 31 .
  • the device for producing fluorine gas in the tenth alternative embodiment has no second average particle size measurement unit 34 .
  • the device for producing fluorine gas in the tenth alternative embodiment has substantially the same constitution as the device for producing fluorine gas in the ninth alternative embodiment illustrated in FIG. 12 except the above structure, and thus similar structures are not described.
  • An electrolyte was electrolyzed to produce fluorine gas.
  • a mixed molten salt (560 L) of 434 kg of hydrogen fluoride and 630 kg of potassium fluoride was used.
  • the anode 16 amorphous carbon electrodes manufactured by SGL Carbon (30 cm in width, 45 cm in length, and 7 cm in thickness) were placed in an electrolytic cell.
  • the cathode punching plates formed from Monel (trademark) were placed in the electrolytic cell.
  • One anode faced two cathodes, and portions of one anode facing the cathodes had a total area of 1,736 cm 2 .
  • the electrolysis temperature was controlled at 85 to 95° C.
  • the temperature of the electrolyte was set at 85° C., and a direct current of 1,000 A was applied at a current density of 0.036 A/cm 2 to start electrolysis.
  • the electrolyte had a water concentration of 1.0% by mass. The water concentration was measured by Karl Fischer analysis method.
  • Electrolysis was started in the above conditions, and small explosive sound was observed near the anodes in the anode chamber for 10 hours after the start of electrolysis (until the accumulated electric energy reached 10 kAh).
  • the explosive sound is supposed to be caused by reaction of fluorine gas generated and water in the electrolyte.
  • the fluid generated in the cathode chamber at this stage was collected when sent out from the cathode chamber of the electrolytic cell to the outside, and the water concentration in the fluid was measured to be 0.1% by volume.
  • the fluid generated on the anodes at this stage was collected when sent out from the anode chamber of the electrolytic cell to the outside, and the mist contained in the fluid was analyzed.
  • 1 L of the fluid generated on the anodes contained 5.0 to 9.0 mg of fine particles (calculated assuming that the mist has a specific gravity of 1.0 g/mL, hereinafter the same is applied), and the fine particles had an average particle size of 1.0 to 2.0 ⁇ m.
  • the fine particles were observed under an optical microscope, and particles having a hollow spherical shape were mainly observed.
  • the current efficiency of fluorine gas production was 0 to 15%.
  • the electrolysis was continued until the accumulated electric energy reached 30 kAh, and the frequency of explosive sound in the anode chamber was reduced.
  • the electrolyte had a water concentration of 0.7% by mass.
  • the fluid generated in the cathode chamber at this stage was collected when sent out from the cathode chamber of the electrolytic cell to the outside, and the water concentration in the fluid was measured to be 0.07% by volume.
  • the fluid generated on the anodes at this stage was collected when sent out from the anode chamber of the electrolytic cell to the outside, and the mist contained in the fluid was analyzed.
  • step (1) The step of electrolysis from the start of electrolysis to this stage is regarded as “step (1)”.
  • the electrolyte was continuously electrolyzed. Accordingly, hydrogen fluoride was consumed, and the level of the electrolyte was reduced. Hence, hydrogen fluoride was appropriately resupplied from a hydrogen fluoride tank into the electrolytic cell.
  • the hydrogen fluoride to be resupplied had a water concentration of 500 ppm by mass or less.
  • step (2) The step of electrolysis from the end of the step (1) to this stage is regarded as “step (2)”.
  • the current was increased to 3,500 A to increase the current density to 0.126 A/cm 2 , and the electrolyte was continuously electrolyzed.
  • the fluid generated on the anodes at this stage was collected when sent out from the anode chamber of the electrolytic cell to the outside, and the mist contained in the fluid was analyzed.
  • 1 L of the fluid generated on the anodes contained 0.03 to 0.06 mg of fine particles, and the fine particles had an average particle size of about 0.2 ⁇ m (0.15 to 0.25 ⁇ m) with a particle size distribution of about 0.1 to 0.5 ⁇ m.
  • FIG. 14 illustrates the measurement result of particle size distribution of the fine particles.
  • the current efficiency of fluorine gas production was 94%.
  • the step of electrolysis from the end of the step (2) to this stage is regarded as “stable step”.
  • Table 1 illustrates electric current, electrolysis time, electric energy, the water concentration in an electrolyte, the mass of a mist contained in 1 L of a fluid generated on the anodes (“anode gas” in Table 1), the average particle size of a mist, current efficiency, the amount of a fluid (containing fluorine gas, oxygen gas, and a mist) generated on the anodes, the amount of a mist generated on the anodes, the intensity of explosive sound, and the water concentration in a fluid formed on the cathodes (the water concentration in a cathode gas” in Table 1).
  • FIG. 15 A graph representing the relation between average particle size of a mist and amount of the mist generated on the anodes is illustrated in FIG. 15 .
  • the graph in FIG. 15 reveals that the average particle size of a mist has a relation to the amount of the mist generated on the anodes. As the amount of a mist generated increases, the clogging of pipes and valves is more frequently caused. When a mist having an average particle size of more than 0.4 ⁇ m is generated, the amount of a mist generated increases, and the mist is settled by gravity.
  • the relation represented by the graph in FIG. 15 therefore illustrates a relation between the average particle size of a mist and likelihood of clogging of pipes and valves.
  • FIG. 16 A graph representing the relation between average particle size of a mist and water concentration in a cathode gas is illustrated in FIG. 16 . As the average particle size of a mist increases, the clogging of pipes and valves is more frequently caused. The relation represented by the graph in FIG. 16 therefore illustrates a relation between the water concentration in a cathode gas and likelihood of clogging of pipes and valves.
  • Electrolysis was performed in the same manner as in Reference Example 1 using the device for producing fluorine gas illustrated in FIG. 2 .
  • the fluid generated on the anodes was allowed to flow through the second bypass pipes, the bypass valves, and the first bypass pipe.
  • the electrolysis was once stopped, and the inside of the device for producing fluorine gas was inspected. As a result, a mist deposited in the first bypass pipe, but the first bypass pipe had a large pipe diameter, and thus the pipe was not clogged.
  • the electrolysis reached the step (2) where the mist had an average particle size of 0.4 ⁇ m or less (the water concentration of the fluid generated in the cathode chamber, or the water concentration in the cathode gas was about 0.02% by volume, which was not more than the reference value, 0.05% by volume), and thus the fluid generated on the anodes was allowed to flow through the first pipes, the first pipe valves, the fourth pipe, and the first mist removal unit. Neither mist deposition nor clogging was caused in the first pipes, the first pipe valves, or the fourth pipe, but the fluid generated on the anodes was fed to the first mist removal unit, and the mist was removed by the first mist removal unit.
  • the first mist removal unit was a scrubber type mist remover that sprayed liquid hydrogen fluoride to remove microparticles such as a mist and had a mist removal rate of 98% or more.
  • Electrolysis was performed in the same manner as in Example 1 except that the fluid generated on the anodes in the electrolysis in the step (1) was allowed to flow through the first pipes, the first pipe valves, the fourth pipe, and the first mist removal unit.
  • the insides of the first pipes, the first pipe valves, and the fourth pipe were inspected.
  • the first pipes were not clogged because the pipes extended in the vertical direction. Deposition of a small amount of fine particles was observed in the first pipe valves, and the inlet portions to the downstream pipe of the first pipe valves, or to the fourth pipe, were clogged with fine particles. Deposition of fine particles was also observed in the fourth pipe, but the deposition was such a small amount as not to clog the pipe.

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US17/595,958 2019-12-27 2020-12-17 Method for producing fluorine gas and device for producing fluorine gas Pending US20220154353A1 (en)

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