Electrolyte production device, electrolyte production method, and fluorine gas production method

Abstract

There is provided a device for producing an electrolyte for producing a fluorine gas having a low vapor pressure of hydrogen fluoride. An electrolyte production device (1) includes an anode (3) having a nickel electrode (31) and a carbon electrode (32); a cathode having a metal electrode (4); and an electrolyte production tank (2) in which a liquid to be treated (8), containing potassium fluoride and hydrogen fluoride, is capable of being accommodated and the liquid to be treated (8) is subjected to an electrolytic treatment using the anode (3) and the cathode (4), in which the electrolyte production device (1) has a structure with which a direct current is capable of being applied for energization through both the nickel electrode (31) and the carbon electrode (32).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a production device and a production method for an electrolyte for producing a fluorine gas, and a fluorine gas production method.BACKGROUND ART

[0002] The fluorine gas (F2) can be synthesized by an electrolytic method using an electrolyte consisting of molten salt containing hydrogen fluoride (HF). In the electrolytic synthesis of the fluorine gas, the fluorine gas is obtained from the anode, and the hydrogen gas (H2) is obtained from the cathode, respectively. However, these obtained gases include a hydrogen fluoride gas as an impurity. This is because the hydrogen fluoride in the electrolyte is in the form of a gas and is mixed. Since the hydrogen fluoride gas contained in the electrolytically synthesized gas is expensive in terms of the recovery equipment, the hydrogen fluoride gas is usually removed and discarded. As a result, the loss of the hydrogen fluoride contained in the gas obtained by the electrolytic method has occurred during production.

[0003] The concentration of the hydrogen fluoride gas contained as an impurity is determined by the vapor pressure of the hydrogen fluoride in the electrolyte. NPL 1 discloses a relational formula that makes it possible to calculate a vapor pressure of hydrogen fluoride in an electrolyte from a concentration of the hydrogen fluoride and a temperature in the electrolyte. As a result, when the vapor pressure of the hydrogen fluoride in the electrolyte can be reduced, the concentration of the hydrogen fluoride gas contained in the gas obtained by the electrolytic method is also reduced.CITATION LISTPatent LiteraturePTL 1: JP 5772102 B2Non Patent LiteratureNPL 1: A. T. Kuhn, “Industrial Electrochemical Processes”, Elsevier Science Ltd, 1971, P. 7-10SUMMARY OF INVENTIONTechnical ProblemRegarding the synthesis of the fluorine gas by an electrolytic method, there is an electrode for electrolytic synthesis (PTL 1) or the like. However, a method of further reducing the vapor pressure of the hydrogen fluoride gas to be lower than a vapor pressure calculated from the above-described relational formula is not disclosed.

[0007] An object of the present disclosure is to provide a production device and a production method for an electrolyte for producing a fluorine gas having a low vapor pressure of a hydrogen fluoride gas, and a fluorine gas production method.Solution to Problem

[0008] To achieve the above object, one aspect of the present disclosure is as the following [1] to [9].

[0009] [1] An electrolyte production device including:

[0010] an anode having a nickel electrode and a carbon electrode;

[0011] a cathode having a metal electrode; and

[0012] an electrolyte production tank in which a liquid to be treated, containing potassium fluoride and hydrogen fluoride, is capable of being accommodated, and the liquid to be treated is subjected to an electrolytic treatment using the anode and the cathode,

[0013] in which the electrolyte production device has a structure with which a direct current is capable of being applied for energization through both the nickel electrode and the carbon electrode.

[0014] [2] An method for producing an electrolyte for producing a fluorine gas by using the electrolyte production device according to [1], including:

[0015] energizing in which the nickel electrode, the carbon electrode, and the metal electrode are immersed in the liquid to be treated, which is accommodated in the electrolyte production tank, and a current of 0.02 A or more and 0.2 A or less per 1 L of the liquid to be treated is allowed to flow through the nickel electrode,

[0016] in which in the energizing, a current is allowed to flow through the nickel electrode until an energization quantity, which is a product of a current allowed to flow through an electrode and an energizing time, reaches 40 Ahr or more per 1 L of the liquid to be treated.

[0017] [3] The electrolyte production method according to [2], in which a current density of the current allowed to flow through the nickel electrode in the energizing is 0.01 A / cm2 or more and 0.1 A / cm2 or less.

[0018] [4] The electrolyte production method according to [2] or [3], in which a ratio (Ac / Ani) of a total surface area (Ac) of a portion of the carbon electrode in contact with the liquid to be treated to a total surface area (Ani) of a portion of the nickel electrode in contact with the liquid to be treated is 5 or more and 30 or less.

[0019] [5] The electrolyte production method according to any one of [2] to [4], in which an energization quantity through the carbon electrode in the energizing is 5 times or more and 20 times or less with respect to an energization quantity through the nickel electrode.

[0020] [6] The electrolyte production method according to any one of [2] to [5], further including:

[0021] supplying hydrogen fluoride to the liquid to be treated so that, during the energizing, a concentration of the hydrogen fluoride contained in the liquid to be treated is 39% by mass or more and 42% by mass or less.

[0022] [7] The electrolyte production method according to any one of [2] to [6], in which a temperature of the liquid to be treated in the energizing is 80° C. or more and 100° C. or less.

[0023] [8] A fluorine gas production method including:

[0024] electrolyzing the electrolyte for producing a fluorine gas produced by the electrolyte production method according to any one of [2] to [7], in an electrolytic cell to generate a fluorine gas.

[0025] [9] The fluorine gas production method according to [8], in which the electrolytic cell is an electrolytic cell for producing a fluorine gas.Advantageous Effects of Invention

[0026] According to the present disclosure, it is possible to provide a production device and a production method for an electrolyte for producing a fluorine gas having a low vapor pressure of a hydrogen fluoride gas, and a fluorine gas production method.BRIEF DESCRIPTION OF DRAWINGS

[0027] FIG. 1 is a schematic view of a production device for an electrolyte for producing a fluorine gas in one embodiment according to the present disclosure;

[0028] FIG. 2 is a schematic view of a production device for an electrolyte for producing a fluorine gas according to another embodiment of the present disclosure;

[0029] FIG. 3 is a graph showing a correlation between a temperature of an electrolyte for producing a fluorine gas and a concentration of a hydrogen fluoride gas in a gas phase part in another embodiment of the present disclosure;

[0030] FIG. 4 is a graph showing a correlation between a temperature of an electrolyte for producing a fluorine gas and a concentration of a hydrogen fluoride gas in a gas phase part in another embodiment of the present disclosure;

[0031] FIG. 5 is a graph showing a correlation between a concentration of hydrogen fluoride in an electrolyte for producing a fluorine gas and a concentration of a hydrogen fluoride gas in a gas phase part in another embodiment of the present disclosure; and

[0032] FIG. 6 is a schematic view of a production device for an electrolyte for producing a fluorine gas according to another embodiment of the present disclosure.DESCRIPTION OF EMBODIMENTS

[0033] Embodiments of the present disclosure will now be described. The embodiments are merely examples of the present disclosure, and the present disclosure is not limited to the embodiments. Various modifications or improvements can be made in the embodiments, and such modifications and improvements can be encompassed by the present disclosure.

[0034] An electrolyte production device according to the present embodiment includes an anode having a nickel electrode and a carbon electrode; a cathode having a metal electrode; and an electrolyte production tank in which a liquid to be treated, containing potassium fluoride and hydrogen fluoride, is capable of being accommodated and the liquid to be treated is subjected to an electrolytic treatment using the anode and the cathode, where the electrolyte production device has a structure with which a direct current is capable of being applied for energization through both the nickel electrode and the carbon electrode.

[0035] In addition, a method for producing an electrolyte for producing a fluorine gas by using the electrolyte production device according to the present embodiment includes energizing in which the nickel electrode, the carbon electrode, and the metal electrode are immersed in the liquid to be treated, which is accommodated in the electrolyte production tank, and a current of 0.02 A or more and 0.2 A or less per 1 L of the liquid to be treated is allowed to flow through the nickel electrode, where in the energizing, a current can be allowed to flow through the nickel electrode until an energization quantity, which is a product of a current allowed to flow through an electrode and an energizing time, reaches 40 Ahr or more per 1 L of the liquid to be treated.

[0036] According to the electrolyte production device and the production method in the above-described embodiment, the vapor pressure of the hydrogen fluoride in the produced electrolyte for producing a fluorine gas can be reduced as compared with a conventional electrolyte.

[0037] Therefore, by using the electrolyte for producing a fluorine gas produced by the production device and the production method according to the present embodiment, the amount of hydrogen fluoride generated from the electrolyte during the electrolytic synthesis is reduced, which not only makes it possible to reduce the load on the system for removing the hydrogen fluoride gas from the fluorine gas or hydrogen gas synthesized by the electrolytic synthesis of the fluorine gas but also makes it possible to reduce the loss of the hydrogen fluoride, which is a raw material of the electrolyte.

[0038] Although the mechanism by which the vapor pressure of hydrogen fluoride is easily reduced in the electrolyte for producing a fluorine gas obtained by the electrolyte production device and the electrolyte production method according to the present embodiment as compared with the conventional electrolyte is not clear, it is considered as follows.

[0039] By allowing a direct current to flow through both anodes of the nickel electrode and the carbon electrode, nickel in the electrode can be dissolved at a slower rate than when only the nickel electrode is used. Since the concentration of the dissolved nickel is low, the deposition of the nickel in the liquid to be treated is suppressed, and the nickel is diffused as nickel fluoride ions. The diffused nickel fluoride ions are further oxidized by the fluorine gas generated in the vicinity of the carbon electrode. However, since the concentration of the nickel fluoride ion is low, for example, a high-order nickel fluoride ion such as a tetravalent nickel fluoride ion is slowly formed. Further, the solubility of a part of the formed high-order nickel fluoride ions reaches the saturation solubility and then is deposited in the liquid to be treated, however, the rate of the deposition is slow, and thus the high-order nickel fluoride ion becomes a solid of a fine nickel compound. It is presumed that both the high-order nickel fluoride ion and solid of the fine nickel compound, which are formed in this manner, strongly interact with the hydrogen fluoride in the liquid to be treated.

[0040] From the above, it is considered that by containing the above-described high-order nickel fluoride ion and a nickel compound formed from the high-order nickel fluoride ion, it is possible to produce an electrolyte for producing a fluorine gas, in which the vapor pressure of the hydrogen fluoride gas is reduced.

[0041] Hereinafter, the production device and the production method for an electrolyte for producing a fluorine gas in the present embodiment will be described in more detail with reference to FIG. 1.

[0042] An electrolyte production device 1 in the present embodiment includes an electrolyte production tank 2, an anode 3 having a nickel electrode 31 and a carbon electrode 32, and a cathode 4 having a metal electrode. The form of the electrolyte production tank is not particularly limited, and the same form as the form of a general electrolytic cell for producing a fluorine gas can be adopted. The material of the electrolyte production tank 2 may be any corrosion-resistant material, such as nickel, iron, or a nickel copper alloy (Monel) can be used, for example.

[0043] As the carbon electrode 32, a carbonaceous electrode formed of a carbon material such as conductive diamond, diamond-like carbon, amorphous carbon, graphite, or glassy carbon can be used. For example, when a conductive diamond electrode is used, the anodic effect is less likely to occur, and thus it is possible to stably produce an electrolyte for producing a fluorine gas.

[0044] The cathode 4 may be made of any metal, such as nickel, copper, or iron can be used, for example. The nickel electrode 31 and the carbon electrode 32 may be supplied with a direct current in parallel from one rectifier 5, or may be supplied with a current from each of two rectifiers (not illustrated). In addition, the electrolyte production device 1 may have a structure with which a direct current is capable of being simultaneously applied for energization through both the nickel electrode 31 and the carbon electrode 32. The timing of the start and the timing of the end of the energization with the direct current to the nickel electrode 31 and the carbon electrode 32 may be different from each other or may be the same.

[0045] Power supply terminals of the anode 3 and the cathode 4 are attached to a lid 6 provided in the electrolyte production tank 2, so that the power supply terminals are electrically insulated. The lid 6 has an airtight structure so that gas does not leak from the inside of the electrolyte production tank 2, and the lid 6 includes a diaphragm 7 on a surface on the inner side of the electrolyte production tank 2. When the liquid to be treated 8 is accommodated in the electrolyte production tank 2, the lower end of the diaphragm 7 is immersed in the liquid to be treated 8. As a result, the diaphragm 7 partitions the gas phase part of the electrolyte production tank 2 into an anode chamber in which the anode 3 is disposed and a cathode chamber in which the cathode 4 is disposed. The material of the diaphragm 7 may be any corrosion-resistant material, such as nickel copper alloy (Monel) or nickel can be used.

[0046] The fluorine gas generated from the anode 3 and the hydrogen gas generated from the cathode 4 in association with the production of the electrolyte can be extracted to the outside of the electrolyte production tank 2 by providing a fluorine gas outlet and a hydrogen gas outlet (not illustrated) on the lid 6, respectively.

[0047] The current allowed to flow through the nickel electrode 31 may be 0.02 A or more and 0.2 A or less or may be 0.06 A or more and 0.15 A or less per 1 L of the liquid to be treated 8, and the current can be allowed to flow until the energization quantity reaches 40 Ahr or more and 60 Ahr or less per 1 L of the liquid to be treated 8.

[0048] When the current allowed to flow through the nickel electrode 31 is 0.02 A / L or more, the amount of nickel dissolved per hour is not excessively decreased, and thus the time required for producing the electrolyte is less likely to be prolonged. When the current is 0.2 A / L or less, nickel dissolved from the nickel electrode 31 is less likely to be deposited, and thus the loss of the nickel electrode 31 is reduced.

[0049] In addition, when the energization quantity through the nickel electrode 31 is in the above-described range, it is easy to improve the effect of reducing the vapor pressure of the hydrogen fluoride in the liquid to be treated.

[0050] Although the treatment time can be determined from the current and the energization quantity per 1 L of the liquid to be treated 8, from the viewpoint of production, it is preferable to adjust the current allowed to flow through the nickel electrode 31 so that the treatment time is in a range of 200 hours to 600 hours.

[0051] When a current is allowed to flow through the nickel electrode 31, it is preferable that the current to be allowed to flow through is gradually increased from a low current. In this case, an aspect in which the current is increased is not particularly limited, and for example, the current value may be continuously increased, or the current value may be increased stepwise.

[0052] The current density of the current allowed to flow through the nickel electrode 31 in the energizing may be 0.01 A / cm2 or more and 0.1 A / cm2 or less, or may be 0.015 A / cm2 or more and 0.05 A / cm2 or less. When the current density is 0.01 A / cm2 or more, the rate of the dissolution of nickel from the nickel electrode 31 is easy to be higher than the rate of the reaction between the dissolved nickel and the fluorine gas generated from the carbon electrode 32. Therefore, the nickel concentration in the liquid to be treated 8 is less likely to decrease, and the time required for producing the electrolyte is less likely to be prolonged. In addition, when the current density is 0.1 A / cm2 or less, the nickel dissolved from the nickel electrode 31 is less likely to be deposited, and thus the loss of the nickel electrode 31 is reduced.

[0053] In addition, when an amorphous carbon electrode is used as the carbon electrode 32, the current density is preferably less than 0.1 A / cm2 since the anodic effect is less likely to occur.

[0054] A ratio (Ac / Ani) of a total surface area (Ac) of a portion of the carbon electrode 32 in contact with the liquid to be treated to a total surface area (Ani) of a portion of the nickel electrode 31 in contact with the liquid to be treated may be 5 or more and 30 or less. When Ac / Ani is 5 or more, the amount of reaction between the nickel dissolved from the nickel electrode 31 and the fluorine gas generated from the carbon electrode 32 increases, and thus the rate of reaction with the fluorine gas is higher than the rate of dissolution from the nickel electrode 31. As a result, a nickel compound formed from a high-order nickel fluoride ion is easily deposited, and thus the vapor pressure of the hydrogen fluoride in the electrolyte is easily reduced. In addition, when Ac / Ani is 30 or less, the loss of the hydrogen fluoride, which is a raw material of the liquid to be treated 8, is reduced.

[0055] The energization quantity through the carbon electrode 32 in the energizing may be 5 times or more and 20 times or less with respect to an energization quantity through the nickel electrode 31. When the energization quantity is 5 times or more, as a result, a nickel compound formed from a high-order nickel fluoride ion is easily deposited, and thus the vapor pressure of the hydrogen fluoride in the electrolyte is easily reduced. In addition, when the energization quantity is 20 times or less, the fluorine gas is not excessively formed, and thus the loss of the hydrogen fluoride, which is a raw material of the liquid to be treated 8, is reduced.

[0056] The shape of the nickel electrode 31 is not particularly limited, but it is preferably a plate shape. This is because, when a plate-shaped nickel electrode is used, the decrease in the total surface area of the portion of the electrode in contact with the liquid to be treated 8 is relatively small even when the nickel is dissolved, and thus the current density is less likely to increase, which facilitates the control. In addition, the shape of the carbon electrode 32 is also preferably a plate shape.

[0057] The liquid to be treated 8 is a liquid that contains potassium fluoride (KF) and hydrogen fluoride, and undergoes an electrolytic treatment using the above-described anode 3 and cathode 4. Additives such as cesium fluoride (CsF) and lithium fluoride (LiF) may be added to the liquid to be treated 8. Since the hydrogen fluoride in the liquid to be treated is consumed by electrolysis during the energizing, it is preferable that hydrogen fluoride is continuously or intermittently supplied to the liquid to be treated 8. In this case, the hydrogen fluoride can be supplied to the electrolyte production tank so that the concentration of the hydrogen fluoride in the liquid to be treated 8 is 39% by mass or more and 42% by mass or less. When the concentration of the hydrogen fluoride in the liquid to be treated 8 is 39% by mass or more, the melting point of the liquid to be treated is less likely to be high. When the concentration of the hydrogen fluoride in the liquid to be treated 8 is 42% by mass or less, the vapor pressure of the hydrogen fluoride is less likely to be high, and thus it is easy to suppress the loss of the hydrogen fluoride in the liquid to be treated 8.

[0058] The temperature of the liquid to be treated 8 in the energizing may be 80° C. or more and 100° C. or less. When the temperature is 80° C. or more, the solubility of the nickel fluoride ion is less likely to decrease, and thus the nickel dissolved from the nickel electrode 31 is less likely to be deposited in the liquid to be treated 8. When the temperature is 100° C. or less, the vapor pressure of the hydrogen fluoride of the liquid to be treated is less likely to be increased, and the hydrogen fluoride in the liquid to be treated 8 is less likely to be evaporated, and thus the loss thereof is easily suppressed.

[0059] In another aspect, the fluorine gas production method according to the present disclosure may include electrolyzing the electrolyte for producing a fluorine gas produced by the above-described electrolyte production method, in an electrolytic cell to generate a fluorine gas. The electrolytic cell is not particularly limited as long as the electrolytic cell is an electrolytic cell which can generate a fluorine gas, and the electrolytic cell may be an electrolytic cell for producing a fluorine gas. When the electrolyte production device 1 according to the present disclosure is used as an electrolytic cell, a fluorine gas can be generated by stopping the power supply to the nickel electrode 31 and supplying power only to the carbon electrode 32.EXAMPLES

[0060] Hereinafter, the present disclosure will be described in more detail based on examples, however, the present disclosure is not limited to these examples.Example 1

[0061] An electrolyte production device 1 having the same configuration as the configuration of FIG. 2 was prepared. The figure on the left side of FIG. 2 is a cross-sectional view illustrating a configuration of the electrolyte production device 1 when the electrolyte production device 1 is cut along a plane penetrating the nickel electrode 31 and a power supply terminal connected to the nickel electrode 31, where the plane is a plane which is parallel to a plate surface of the plate-shaped nickel electrode 31. In addition, the figure on the right side of FIG. 2 is a cross-sectional view illustrating a configuration of the electrolyte production device 1 when the electrolyte production device 1 is cut along a plane penetrating the nickel electrode 31 and a power supply terminal connected to the nickel electrode 31, where the plane is a plane which is perpendicular to the plate surface of the plate-shaped nickel electrode 31 and is parallel to the vertical direction. The electrolyte production device 1 has an electrolyte production tank 2. The inner dimensions of the electrolyte production tank 2 are 75 cm in width×75 cm in length×45 cm in depth. The electrolyte production tank 2 includes a lid 6. The lid 6 includes a diaphragm 7 obtained by welding. Further, the lid 6 includes a fluorine gas outlet 62 and a hydrogen gas outlet 63 for respectively purging the fluorine gas and the hydrogen gas from the anode chamber and the cathode chamber described below. The electrolyte production tank 2 and the lid 6 were made of carbon steel, and the diaphragm 7 was made of Monel. In addition, a sheet made of polytetrafluoroethylene (PTFE) having a thickness of 3 mm was laid over the entire surface of the inner bottom surface of the electrolyte production tank 2 (not illustrated), and moreover, the space between the electrolyte production tank 2 and the lid 6 was insulated by a packing 64 made of polytetrafluoroethylene.

[0062] Two anode chambers and one cathode chamber are provided in the inside of the electrolyte production tank 2, the anodes 3 are disposed in the anode chambers, and the cathode 4 is disposed in the cathode chamber. In addition, the anode chamber and the cathode chamber are partitioned by the diaphragm 7. The anode 3 was formed of a total of six sheets, that is, one sheet of the nickel electrode 31 and five sheets of the carbon electrode 32 which was Grade ABR manufactured by SGL Carbon AG. The dimensions of the electrode plate of the nickel electrode 31 are 20 cm in width×35 cm in length×1 cm in thickness, and the dimensions of the electrode plate of the carbon electrode 32 are 20 cm in width×35 cm in length×5 cm in thickness. Three sheets of the anodes 3 were installed in one anode chamber. As the cathode 4, an electrode made of carbon steel was installed. The power supply terminal of each electrode was fixed to the lid 6, and the fixed portion was made to have an airtight and insulated structure with an insulating airtight material 61.

[0063] In addition, the cathode 4 was installed in the electrolyte production tank 2 so that the distance between the anode 3 and the cathode 4 was 4 cm. Further, a thermocouple for measuring the temperature of the liquid to be treated 8 which is to be accommodated, a liquid level measuring device, a pipe for supplying hydrogen fluoride, and a jacket for heating and cooling the liquid to be treated 8 (none of which are illustrated) were installed in the electrolyte production tank 2.

[0064] 200 L of KF·2HF was accommodated in such an electrolyte production tank 2 as described above, as the liquid to be treated 8. Then, the anode 3 and the cathode 4 were immersed in the liquid to be treated. The liquid to be treated 8 was immersed in the anode 3 from the lower end of the anode 3 to a height of 25 cm. In this case, the total surface area of the portion of the one surface of the anode 3 in contact with the liquid to be treated 8, more specifically, the total surface area of the one surface of the anode 3 that contributes to the electrolysis is 20 cm in length×25 cm in width=500 cm2. Since a current is allowed to flow on both surfaces of the electrode, the total surface area contributing to the electrode per one sheet of the anode 3 is 1000 cm2. The total surface area of the portions per one sheet of the anode 3 in contact with the liquid to be treated is the same as the total surface area of the portion per one sheet of the nickel electrode 31 and the total surface area of the portion per one sheet of the carbon electrode 32. Therefore, the energization quantity through the carbon electrode 32 in which the number of sheets of electrodes is 5 is 5 times the energization quantity through the nickel electrode 31 in which the number of sheets of electrodes is 1.

[0065] The temperature of the liquid to be treated 8 was set to 85° C., and a current was applied for energization through the liquid to be treated 8 as follows, thereby obtaining an electrolyte for producing a fluorine gas in Example 1. In addition, during the energization, hydrogen fluoride was intermittently supplied to the liquid to be treated 8.

[0066] First, a current of 90 A was allowed to flow through the anode 3 at a current density of 0.015 A / cm2 for 25 hours until the current efficiency of the fluorine gas generation was 85% or more. Next, after the current was increased to 120 A (current density: 0.02 A / cm2) and then the energization was carried out for 120 hours, the liquid to be treated 8 was sampled. As a result of measuring the nickel concentration of the liquid to be treated by inductively coupled plasma (ICP) emission spectrometry, the nickel concentration of the liquid to be treated was 262 ppm by mass. Thereafter, while increasing the current to 180 A (current density: 0.03 A / cm2), the energization was further carried out for 210 hours, thereby obtaining an electrolyte for producing a fluorine gas in Example 1. When a current was allowed to flow through the anode 3, both the nickel electrode 31 and the carbon electrode 32 were simultaneously energized.

[0067] The energization quantity applied to the nickel electrode 31 was 9075 Ahr, which was 45.4 Ahr per 1 L of the liquid to be treated 8.

[0068] The obtained electrolyte for producing a fluorine gas was sampled, and the nickel concentrations in the electrolyte before and after filtration were measured by the inductively coupled plasma atomic emission spectrometry. As a result, the nickel concentration after filtration was 303 ppm by mass, and the nickel concentration before filtration was 1090 ppm by mass. In addition, the concentration of the hydrogen fluoride in the obtained electrolyte for producing a fluorine gas was 41.2% by mass.

[0069] Next, the concentration of the hydrogen fluoride gas in the gas phase part of the electrolyte production tank 2 when the temperature of the electrolyte for producing a fluorine gas in the electrolyte production tank 2 was changed was determined. Specifically, first, a mixed gas of the gas in the anode chamber and the nitrogen gas was extracted to the outside by supplying the nitrogen gas for purging to the anode chamber. Subsequently, the concentration of the hydrogen fluoride gas in the extracted mixed gas was quantitatively measured using a Fourier transform infrared spectrophotometer (FT-IR). Then, the concentration of the hydrogen fluoride gas in the gas phase part was calculated from the concentration of the hydrogen fluoride in the obtained mixed gas. The results are shown in Table 1.TABLE 1Temperature of electrolyte (°C)81.181.983.083.990.596.097.0100.0Concentration of HF gas in gas phase part (% by volume)2.672.822.532.863.054.673.494.27Comparative Example 1

[0070] An electrolyte of Comparative Example 1 was obtained in the same manner as in Example 1, except that all the anodes 3 were carbon electrodes. The obtained electrolyte was sampled, and the nickel concentration in the electrolyte was measured by the inductively coupled plasma atomic emission spectrometry. As a result, the nickel concentration was 10 ppm by mass or less. It is considered that the measured nickel component is a nickel component dissolved from the Monel used for the diaphragm 7. In addition, the concentration of the hydrogen fluoride in the electrolyte was 41.2% by mass.

[0071] Next, in the same manner as in Example 1, the temperature of the electrolyte for producing a fluorine gas in the electrolyte production tank was changed, and the concentration of the hydrogen fluoride gas in the gas phase part of the electrolyte production tank was determined. The obtained results are shown in Table 2.

[0072] Each of the literature values in Table 2 indicates the concentration of the hydrogen fluoride gas in the gas phase part at each temperature, which is calculated according to the following Formula (1) described in NPL 1. In Formula (1), T indicates the temperature of the electrolyte, C indicates the concentration of the hydrogen fluoride in the electrolyte, and P indicates the vapor pressure of hydrogen fluoride when the temperature of the electrolyte is T.Log⁢ (P⁢ mm⁢ Hg)=2.0733-4244⁢ (1 / T)+0.2975 C+47.97 (C / T)-0.003785C2(1)

[0073] Further, the results of Example 1 and Comparative Example 1 are shown in the graph of FIG. 3.TABLE 2Temperature of electrolyte (°C)86.286.988.989.181.785.286.997.0Concentration of HF gas in gas phase part (% by volume)4.854.925.475.364.004.724.927.42Literature value (% by volume)5.145.295.735.774.274.935.297.85

[0074] As shown in Table 2, it has been found that the concentration of the hydrogen fluoride gas in the gas phase part in Comparative Example 1 indicates a value close to the literature value. The concentration of the hydrogen fluoride gas in the gas phase part is determined by the vapor pressure of the hydrogen fluoride in the electrolyte. As a result, the concentration of the hydrogen fluoride gas in the gas phase part is a value corresponding to the vapor pressure of the hydrogen fluoride in the electrolyte. As a result, it is considered that the vapor pressure of the hydrogen fluoride in the electrolyte in Comparative Example 1 is equivalent to the vapor pressure of the hydrogen fluoride in the conventional electrolyte.

[0075] In addition, as shown in the graph of FIG. 3, it has been found that the concentration of the hydrogen fluoride in the gas phase part in Example 1 is low as compared with the concentration of the hydrogen fluoride in the gas phase part in Comparative Example 1. This indicates that the vapor pressure of the hydrogen fluoride in the electrolyte for producing a fluorine gas in Example 1 is reduced as compared with the literature value. When electrolytically synthesizing a fluorine gas using such an electrolyte for producing a fluorine gas, it is possible to reduce the loss of hydrogen fluoride as compared with the conventional electrolyte.Example 2

[0076] The electrolyte for producing a fluorine gas, which had been obtained in Example 1, was accommodated in another electrolytic cell for producing a fluorine gas, and electrolytic synthesis of a fluorine gas was carried out. As the electrolytic cell, an electrolytic cell having the same structure as the structure in Example 1 was used except that all the anodes 3 were carbon electrodes.

[0077] The temperature of the electrolyte for producing a fluorine gas was set to 85° C., and a current of 600 A was applied for energization through the anode at a current density of 0.1 A / cm2 for 500 hours. The current efficiency of the fluorine gas generation was more than 85%.

[0078] After the end of the energization, the electrolyte was sampled from the electrolytic cell, and the nickel concentrations in the electrolyte after and before filtration were measured by the inductively coupled plasma atomic emission spectrometry. As a result, the nickel concentration after filtration was 310 ppm by mass, and the nickel concentration before filtration was 1200 ppm by mass. In addition, the concentration of the hydrogen fluoride in the electrolyte was 41.0% by mass.

[0079] In addition, in the same manner as in Example 1, the concentration of the hydrogen fluoride gas in the gas phase part of the electrolytic cell when the temperature of the electrolyte for producing a fluorine gas was changed was determined. The obtained results are shown in Table 3. In addition, the results of Example 1 and Example 2 are shown in the graph of FIG. 4.TABLE 3Temperature82.083.586.093.094.097.099.6of electrolyte(°C)Concentration2.792.802.843.103.393.724.24of HF gas ingas phase part(% by volume)

[0080] As shown in Table 3 and FIG. 4, even when the obtained electrolyte for producing a fluorine gas was accommodated in another electrolytic cell for producing a fluorine gas different from the electrolyte production tank used for producing an electrolyte, and then electrolytic synthesis of a fluorine gas was carried out, the concentration of the hydrogen fluoride gas in the gas phase part exhibited the same tendency as in Example 1. From this, it has been found that in the electrolyte produced by the electrolyte production method according to the present disclosure, the vapor pressure of the hydrogen fluoride is reduced as compared with the vapor pressure of hydrogen fluoride, which is calculated from the literature value even when electrolytic synthesis is carried out using a conventional electrolytic cell for producing a fluorine gas.Example 3

[0081] An electrolyte for producing a fluorine gas was produced in the same manner as in Example 1, and then the temperature of the electrolyte in the electrolyte production tank 2 was set to 83° C. A current of 250 A was applied for energization through the carbon electrode 32 other than the nickel electrode 31 to change the liquid level of the electrolyte for producing a fluorine gas in the electrolyte production tank 2, thereby changing the concentration of the hydrogen fluoride in the electrolyte.

[0082] The electrolyte was sampled when the liquid level of the electrolyte was changed, and the concentration of the hydrogen fluoride in the electrolyte was measured by the inductively coupled plasma atomic emission spectrometry. The electrolyte used for the measurement was sampled after temporarily stopping the energization. In addition, the concentration of the hydrogen fluoride gas in the gas phase part was determined using a Fourier transform infrared spectrophotometer in the same manner as in Example 1. The obtained results are shown in Table 4.

[0083] In Table 4, the literature values calculated from Formula (1) are also shown in the same manner as in Table 2. Further, FIG. 5 shows the results of Table 4 as a graph.TABLE 4Concentration of HF gas in39.139.540.941.042.0electrolyte (% by mass)Concentration of HF gas in1.702.072.862.533.53gas phase part (% by volume)Literature value (% by volume)2.432.754.154.275.60

[0084] When comparing Example 3 with the literature value, it was found that the concentration of the hydrogen fluoride gas in the gas phase part of Example 3 is low even when the concentration of the hydrogen fluoride in the electrolyte has been changed. From this, it has been found that in the electrolyte produced by the electrolyte production method according to the present disclosure, even when the concentration of the hydrogen fluoride in the electrolyte has changed, the vapor pressure of the hydrogen fluoride is reduced as compared with the vapor pressure of hydrogen fluoride, which is calculated from the literature value.Comparative Example 2

[0085] An electrolyte production device 1 having the same configuration as the configuration of FIG. 6 was prepared. The electrolyte production device 1 has an electrolyte production tank 2. The electrolyte production tank 2 includes a lid 6, and the lid 6 includes a diaphragm 7 obtained by welding. The electrolyte production tank 2, the lid 6, and the diaphragm 7 were all made of polytetrafluoroethylene.

[0086] The anode chamber and the cathode chamber are provided in the inside of the electrolyte production tank 2, the anode 3 is disposed in the anode chamber, and the cathode 4 is disposed in the cathode chamber. The anode chamber and the cathode chamber are partitioned by the diaphragm 7. Nickel electrodes were installed as both the anode 3 and the cathode 4. The power supply terminal of each electrode was fixed to the lid 6, and the fixed portion was made to have an airtight and insulated structure with an insulating airtight material (not illustrated).

[0087] In addition, the total surface area of the portions of the anode 3 and the cathode 4, which were in contact with the liquid to be treated 8, was set to 6 cm2. Further, the outside of the electrolyte production tank 2 was configured to be capable of being heated with an electric heater (not illustrated).

[0088] 725 g (370 mL) of KF·2HF was accommodated as the liquid to be treated 8, in the inside of such an electrolyte production tank 2 as described above. The temperature of the liquid to be treated 8 was set to 85° C., and a current of 600 mA was allowed to flow through the anode 3 at a current density of 0.1 A / cm2. The energization was carried out until the energization quantity through the anode 3 was 16 Ahr, and the energization quantity per 1 L of the liquid to be treated 8 was 43 Ahr, thereby obtaining an electrolyte of Comparative Example 2.

[0089] As a result of determining the nickel concentration in the electrolyte from the mass change of the nickel electrode of the anode 3 before and after the energization, the nickel concentration reached 2715 ppm by mass with respect to the electrolyte.

[0090] The electrolyte after the end of the energization was cloudy, but the cloudiness disappeared immediately after the electrolyte was allowed to stand. As a result of measuring the nickel concentration in the supernatant of the electrolyte by the inductively coupled plasma atomic emission spectrometry, the nickel concentration was 160 ppm by mass. After stirring the electrolyte after the energization, the electrolyte was sampled, and as a result of measuring the nickel concentration of the liquid to be treated by the inductively coupled plasma atomic emission spectrometry, the nickel concentration was 1720 ppm by mass.

[0091] Since the nickel concentration obtained by the inductively coupled plasma atomic emission spectrometry is lower than the nickel concentration obtained from the mass change, in the electrolyte production method of Comparative Example 2, it is considered that the particles of the nickel compound deposited in the electrolyte become large and easily precipitated, and thus a difference is seen in the obtained nickel concentration.

[0092] The concentration of the hydrogen fluoride in the electrolyte after the end of the energization was 39.5% by mass.

[0093] In addition, the electrolyte after the end of the energization was set to 85° C., and the concentration of the hydrogen fluoride gas in the gas phase part of the electrolyte production tank 2 was measured with a Fourier transform infrared spectrophotometer. As a result of the measurement, the concentration of the hydrogen fluoride gas in the gas phase part was 3.24% by volume.

[0094] From the results of Comparative Example 2, it was found that since the concentration of the hydrogen fluoride gas in the gas phase part according to Formula (1) is 3.02% by volume, the vapor pressure of hydrogen fluoride has not been reduced from the literature value in the electrolyte according to the method of Comparative Example 2.Example 4

[0095] An electrolyte for producing a fluorine gas was prepared in the same manner as in Example 1, except that the dimensions of the nickel electrode 31 were changed to 6.7 cm in width×35 cm in length×5 cm in thickness.

[0096] Since the total surface area (Ani) of the portion of the nickel electrode in contact with the liquid to be treated 8 was 335 cm2, and the total surface area (Ac) of the portion of the carbon electrode in contact with the liquid to be treated 8 was 5000 cm2, Ac / Ani was 5000 / 335=15.

[0097] The electrolysis temperature was set to 85° C., and a current was applied for energization through the liquid to be treated 8 as follows, thereby obtaining an electrolyte for producing a fluorine gas in Example 4. In addition, during the energization, hydrogen fluoride was intermittently supplied to the liquid to be treated 8.

[0098] A current of 90 A was applied for energization through the anode 3 at a current density of 0.017 A / cm2 for 25 hours until the current efficiency of the fluorine gas generation was 85% or more. Next, after the current was increased to 120 A (current density: 0.022 A / cm2) and then the energization was carried out for 240 hours, the liquid to be treated 8 was sampled. As a result of measuring the nickel concentration of the liquid to be treated 8 by the inductively coupled plasma atomic emission spectrometry, the nickel concentration was 318 ppm by mass. Thereafter, the current was gradually increased to 360 A (current density: 0.067 A / cm2), and the energization was further carried out for 360 hours to obtain an electrolyte for producing a fluorine gas. When a current was allowed to flow through the anode 3, both the nickel electrode 31 and the carbon electrode 32 were simultaneously energized.

[0099] The energization quantity through the nickel electrode 31 until the end of the energization was 9183 Ahr, which was 45.9 Ahr per 1 L of the liquid to be treated 8. The ratio of the total surface area (Ac) of the portion of the carbon electrode 32 in contact with the liquid to be treated 8 to the total surface area (Ani) of the portion of the nickel electrode 31 in contact with the liquid to be treated 8 is 15. As a result, the energization quantity through the carbon electrode 32 was 15 times the energization quantity through the nickel electrode 31.

[0100] The electrolyte was sampled from the electrolyte production tank 2, and the electrolyte after filtration and the electrolyte before filtration were subjected to the inductively coupled plasma atomic emission spectrometry. As a result, the nickel concentration of the electrolyte after the filtration was 347 ppm by mass, and the nickel concentration of the electrolyte before the filtration was 987 ppm by mass. In addition, the concentration of the hydrogen fluoride in the electrolyte was 41.2% by mass.

[0101] Next, while changing the temperature of the obtained electrolyte for producing a fluorine gas and in the same manner as in Example 1, the concentration of the hydrogen fluoride gas in the gas phase part when the temperature of the electrolyte for producing a fluorine gas was changed was determined. Table 5 shows the obtained concentration of the hydrogen fluoride gas for each temperature in the gas phase part and the literature values.TABLE 5Temperature of electrolyte (° C.)83.086.096.0Concentration of HF gas in gas phase part2.072.533.28(% by volume)Literature value (% by volume)4.515.107.56

[0102] From the results of Example 4, it was found that the concentration of the hydrogen fluoride gas in the gas phase part was lower than the literature value at any temperature. From this, it was found that, when producing an electrolyte for producing a fluorine gas, even when the ratio of the total surface area of the portion of the carbon electrode in contact with the liquid to be treated to the total surface area of the portion of the nickel electrode in contact with the liquid to be treated is increased, it is possible to produce an electrolyte in which the vapor pressure of the hydrogen fluoride is reduced as compared with the vapor pressure of hydrogen fluoride, which is calculated from the literature value.

[0103] In addition, the following points were found from Examples 1 to 4 and Comparative Examples 1 and 2.

[0104] (1) It was found from Examples 1 to 4 that by the electrolyte production device and the electrolyte production method according to the present disclosure, it is possible to produce an electrolyte in which the vapor pressure of the hydrogen fluoride in the electrolyte is reduced as compared with the conventional electrolyte for producing a fluorine gas. In addition, the nickel concentration dissolved in the electrolyte in Examples 1 to 4 was in a range of 100 ppm by mass to 350 ppm by mass.

[0105] (2) From the results of Examples 1 and 4, it was found that as the energizing proceeds, the transparency of the liquid to be treated is lost, and a floating substance which is less likely to be precipitated is generated. In addition, it was found that this floating substance contains nickel.

[0106] (3) From the results of Comparative Examples 1 and 2, it was found that in the electrolyte in which the anode was produced as only a carbon electrode or only a nickel electrode, the vapor pressure of hydrogen fluoride is the same as the vapor pressure of hydrogen fluoride in the conventional electrolyte.

[0107] (4) From the results of Comparative Example 2, it was found that a floating substance which is less likely to be precipitated is not generated in the electrolyte produced using only the nickel electrode.REFERENCE SIGNS LIST1: electrolyte production device

[0109] 2: electrolyte production tank

[0110] 3: anode

[0111] 31: nickel electrode

[0112] 32: carbon electrode

[0113] 4: cathode

[0114] 5: rectifier

[0115] 6: lid

[0116] 7: diaphragm

[0117] 8: liquid to be treated

Claims

1. An electrolyte production device comprising:an anode having a nickel electrode and a carbon electrode;a cathode having a metal electrode; andan electrolyte production tank in which a liquid to be treated, containing potassium fluoride and hydrogen fluoride, is capable of being accommodated, and the liquid to be treated is subjected to an electrolytic treatment using the anode and the cathode,wherein the electrolyte production device has a structure with which a direct current is capable of being applied for energization through both the nickel electrode and the carbon electrode.

2. A method for producing an electrolyte for producing a fluorine gas by using the electrolyte production device according to claim 1, comprising:energizing in which the nickel electrode, the carbon electrode, and the metal electrode are immersed in the liquid to be treated, which is accommodated in the electrolyte production tank, and a current of 0.02 A or more and 0.2 A or less per 1 L of the liquid to be treated is allowed to flow through the nickel electrode,wherein in the energizing, a current is allowed to flow through the nickel electrode until an energization quantity, which is a product of a current allowed to flow through an electrode and an energizing time, reaches 40 Ahr or more per 1 L of the liquid to be treated.

3. The electrolyte production method according to claim 2, wherein a current density of the current allowed to flow through the nickel electrode in the energizing is 0.01 A / cm2 or more and 0.1 A / cm2 or less.

4. The electrolyte production method according to claim 2, wherein a ratio (Ac / Ani) of a total surface area (Ac) of a portion of the carbon electrode in contact with the liquid to be treated to a total surface area (Ani) of a portion of the nickel electrode in contact with the liquid to be treated is 5 or more and 30 or less.

5. The electrolyte production method according to claim 2, wherein an energization quantity through the carbon electrode in the energizing is 5 times or more and 20 times or less with respect to an energization quantity through the nickel electrode.

6. The electrolyte production method according to claim 2, further comprising:supplying hydrogen fluoride to the liquid to be treated so that, during the energizing, a concentration of the hydrogen fluoride contained in the liquid to be treated is 39% by mass or more and 42% by mass or less.

7. The electrolyte production method according to claim 2, wherein a temperature of the liquid to be treated in the energizing is 80° C. or more and 100° C. or less.

8. A fluorine gas production method comprising:electrolyzing the electrolyte for producing a fluorine gas produced by the electrolyte production method according to claim 2, in an electrolytic cell to generate a fluorine gas.

9. The fluorine gas production method according to claim 8, wherein the electrolytic cell is an electrolytic cell for producing a fluorine gas.

10. The electrolyte production method according to claim 3, wherein a ratio (Ac / Ani) of a total surface area (Ac) of a portion of the carbon electrode in contact with the liquid to be treated to a total surface area (Ani) of a portion of the nickel electrode in contact with the liquid to be treated is 5 or more and 30 or less.

11. The electrolyte production method according to claim 3, wherein an energization quantity through the carbon electrode in the energizing is 5 times or more and 20 times or less with respect to an energization quantity through the nickel electrode.

12. The electrolyte production method according to claim 3, further comprising:supplying hydrogen fluoride to the liquid to be treated so that, during the energizing, a concentration of the hydrogen fluoride contained in the liquid to be treated is 39% by mass or more and 42% by mass or less.

13. The electrolyte production method according to claim 3, wherein a temperature of the liquid to be treated in the energizing is 80° C. or more and 100° C. or less.

14. A fluorine gas production method comprising:electrolyzing the electrolyte for producing a fluorine gas produced by the electrolyte production method according to claim 3, in an electrolytic cell to generate a fluorine gas.

15. The fluorine gas production method according to claim 14, wherein the electrolytic cell is an electrolytic cell for producing a fluorine gas.

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