Electrolytic solution production device, electrolytic solution production method, and fluorine gas production method

Abstract

Provided is a device that produces an electrolyte solution for producing a fluorine gas with a low vapour pressure of hydrogen fluoride. An electrolytic solution production device (1) includes: a positive electrode (3) including a nickel electrode (31) and a carbon electrode (32); a negative electrode (4) including a metal electrode; and an electrolytic solution production tank (2) in which a liquid to be treated (8) containing potassium fluoride and hydrogen fluoride can be stored and the liquid to be treated (8) is electrolysed using the positive electrode (3) and the negative electrode (4). The electrolytic solution production device (1) has a structure whereby direct current can be passed through both the nickel electrode (31) and the carbon electrode (32).

Description

Electrolyte solution manufacturing apparatus, electrolyte solution manufacturing method, and fluorine gas manufacturing method

[0001] The present disclosure relates to an apparatus and method for producing an electrolyte solution for producing fluorine gas, and a method for producing fluorine gas.

[0002] Fluorine gas (F ２ Fluorine gas can be synthesized by electrolysis using an electrolyte made of a molten salt containing hydrogen fluoride (HF). In the electrolytic synthesis of fluorine gas, fluorine gas flows from the anode and hydrogen gas (H ２ ) are obtained, respectively. However, these obtained gases contain hydrogen fluoride gas as an impurity. This is because the hydrogen fluoride in the electrolyte becomes gaseous and becomes mixed in. The hydrogen fluoride gas contained in the electrolytically synthesized gas is usually removed and discarded because recovery equipment is expensive. Therefore, the hydrogen fluoride contained in the gas obtained by electrolysis is lost during production.

[0003] The concentration of hydrogen fluoride gas contained as an impurity is determined by the hydrogen fluoride vapor pressure of the electrolyte. Non-Patent Document 1 discloses a relational expression that allows the hydrogen fluoride vapor pressure of the electrolyte to be calculated from the hydrogen fluoride concentration and temperature in the electrolyte. Therefore, if the hydrogen fluoride vapor pressure of the electrolyte can be reduced, the concentration of hydrogen fluoride gas contained in the gas obtained by electrolysis will also be reduced.

[0004] Patent No. 5772102

[0005] AT Kuhn, “Industrial Electrochemical Processes”, Elsevier Science Ltd, 1971, P.7-10

[0006] Regarding the synthesis of fluorine gas by electrolysis, there is an electrode for electrolysis (Patent Document 1), etc. However, there is no disclosure of a method for further reducing the vapor pressure of hydrogen fluoride gas below that calculated from the above relational expression.

[0007] An object of the present disclosure is to provide an apparatus and method for producing an electrolyte solution for producing fluorine gas, which produces hydrogen fluoride gas with a low vapor pressure, and a method for producing fluorine gas.

[0008] In order to solve the above problems, one aspect of the present disclosure is as follows: [1] to [9]. [1] An electrolytic solution manufacturing apparatus comprising: an anode having a nickel electrode and a carbon electrode, a cathode having a metal electrode, and an electrolytic solution production tank capable of containing a liquid to be treated containing potassium fluoride and hydrogen fluoride and in which the liquid to be treated is electrolyzed using the anode and the cathode, the electrolytic solution manufacturing apparatus having a structure capable of passing a direct current to both the nickel electrode and the carbon electrode. [2] A method for producing an electrolytic solution for fluorine gas production using the electrolytic solution manufacturing apparatus described in [1], the method comprising: a current passing step of immersing the nickel electrode, the carbon electrode, and the metal electrode in the liquid to be treated contained in the electrolytic solution production tank, and passing a current of 0.02 A or more and 0.2 A or less per liter of the liquid to be treated to the nickel electrode, wherein in the current passing step, the current is passed to the nickel electrode until the amount of current passed, which is the product of the current passed through the electrode and the current passing time, reaches 40 Ahr or more per liter of the liquid to be treated. [3] The current density of the current flowing through the nickel electrode in the current application step is 0.01 A / cm ２ 0.1A / cm or more ２[4] The method for producing an electrolyte solution according to [2], wherein the ratio (Ac / Ani) of the total surface area (Ac) of the portions of the carbon electrodes in contact with the liquid to be treated to the total surface area (Ani) of the portions of the nickel electrodes in contact with the liquid to be treated is 5 or more and 30 or less. [5] The method for producing an electrolyte solution according to any one of [2] to [4], wherein the amount of current passing through the carbon electrodes in the current passing step is 5 to 20 times the amount of current passing through the nickel electrodes. [6] The method for producing an electrolyte solution according to any one of [2] to [5], comprising supplying hydrogen fluoride to the liquid to be treated during the current passing step so that the concentration of hydrogen fluoride contained in the liquid to be treated is 39% by mass to 42% by mass. [7] The method for producing an electrolyte solution according to any one of [2] to [6], wherein the temperature of the liquid to be treated in the current passing step is 80°C to 100°C. [8] A method for producing fluorine gas, comprising an electrolysis step of electrolyzing the electrolyte solution for producing fluorine gas, produced by the method for producing an electrolyte solution according to any one of [2] to [7], in an electrolytic cell to generate fluorine gas. [9] The method for producing fluorine gas according to [8], wherein the electrolytic cell is an electrolytic cell for producing fluorine gas.

[0009] According to the present disclosure, it is possible to provide an apparatus and a method for producing an electrolyte solution for producing fluorine gas, which produces hydrogen fluoride gas with a low vapor pressure, and a method for producing fluorine gas.

[0010] Fig. 1 is a schematic diagram of an apparatus for producing an electrolyte solution for producing fluorine gas in one embodiment of the present disclosure. Fig. 2 is a schematic diagram of an apparatus for producing an electrolyte solution for producing fluorine gas in another embodiment of the present disclosure. Fig. 3 is a graph showing the correlation between the temperature of an electrolyte solution for producing fluorine gas and the hydrogen fluoride gas concentration in the gas phase in another embodiment of the present disclosure. Fig. 4 is a graph showing the correlation between the temperature of an electrolyte solution for producing fluorine gas and the hydrogen fluoride gas concentration in the gas phase in another embodiment of the present disclosure. Fig. 5 is a graph showing the correlation between the hydrogen fluoride concentration in an electrolyte solution for producing fluorine gas and the hydrogen fluoride gas concentration in the gas phase in another embodiment of the present disclosure. Fig. 6 is a schematic diagram of an apparatus for producing an electrolyte solution for producing fluorine gas in another embodiment of the present disclosure.

[0011] An embodiment of the present disclosure will be described below. Note that this embodiment shows an example of the present disclosure, and the present disclosure is not limited to this embodiment. Furthermore, various modifications or improvements can be made to this embodiment, and such modifications or improvements may also be included in the present disclosure.

[0012] The electrolyte solution manufacturing apparatus according to this embodiment includes an anode having a nickel electrode and a carbon electrode, a cathode having a metal electrode, and an electrolyte solution manufacturing tank capable of accommodating a liquid to be treated containing potassium fluoride and hydrogen fluoride and in which the liquid to be treated is electrolyzed using the anode and the cathode, and has a structure capable of passing a direct current through both the nickel electrode and the carbon electrode.

[0013] Furthermore, a method for producing an electrolyte solution for fluorine gas production using the electrolyte solution production apparatus according to this embodiment includes a current-passing step of immersing the nickel electrode, the carbon electrode, and the metal electrode in the liquid to be treated contained in the electrolyte solution production tank and passing a current of 0.02 A or more and 0.2 A or less per liter of the liquid to be treated to the nickel electrode, and in the current-passing step, a current can be passed through the nickel electrode until the amount of current passed through the electrode, which is the product of the current passed through the electrode and the current-passing time, reaches 40 Ahr or more per liter of the liquid to be treated.

[0014] According to the electrolytic solution manufacturing apparatus and manufacturing method of the above embodiment, the vapor pressure of hydrogen fluoride in the electrolytic solution for producing fluorine gas that is manufactured can be made lower than that of conventional electrolytic solutions.

[0015] Therefore, when the electrolyte solution for producing fluorine gas produced by the production apparatus and production method of the present embodiment is used, the amount of hydrogen fluoride generated from the electrolyte solution during electrolytic synthesis is reduced, which not only reduces the load on the system that removes hydrogen fluoride gas from fluorine gas and hydrogen gas synthesized in the electrolytic synthesis of fluorine gas, but also reduces loss of hydrogen fluoride, which is a raw material for the electrolyte solution.

[0016] The mechanism by which the hydrogen fluoride vapor pressure of the electrolyte for fluorine gas production produced by the electrolyte production apparatus and electrolyte production method according to this embodiment is more easily reduced than that of conventional electrolytes is not clear, but it is thought to be as follows. By applying a direct current to both the nickel electrode and the carbon electrode anode, nickel in the electrodes can be dissolved at a slower rate than when only a nickel electrode is used. Because the concentration of the dissolved nickel is low, its precipitation into the treated solution is suppressed and it diffuses as nickel fluoride ions. The diffused nickel fluoride ions are further oxidized by fluorine gas generated near the carbon electrode. However, because the concentration of nickel fluoride ions is low, higher nickel fluoride ions, such as tetravalent nickel fluoride ions, are slowly formed. Furthermore, some of the formed higher nickel fluoride ions reach saturation solubility and precipitate in the treated solution, but because the rate of deposition is slow, they become fine nickel compound solids. It is presumed that both the higher nickel fluoride ions and the fine nickel compound solids thus formed have a strong interaction with hydrogen fluoride in the treated solution. From the above, it is considered that by containing the above-mentioned higher order nickel fluoride ions and nickel compounds formed from higher order nickel fluoride ions, it is possible to produce an electrolyte solution for producing fluorine gas in which the vapor pressure of hydrogen fluoride gas is reduced.

[0017] The apparatus and method for producing an electrolyte solution for producing fluorine gas according to this embodiment will be described in more detail below with reference to FIG. 1 as an example.

[0018] The electrolyte solution production apparatus 1 in this embodiment includes an electrolyte solution 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 shape of the electrolyte solution production tank is not particularly limited and can be the same as that of a general electrolytic tank for producing fluorine gas. The material of the electrolyte solution production tank 2 may be any corrosion-resistant material, and for example, nickel, iron, and nickel-copper alloy (Monel) can be used.

[0019] A carbonaceous electrode made of a carbon material such as conductive diamond, diamond-like carbon, amorphous carbon, graphite, or glassy carbon can be used as the carbon electrode 32. For example, a conductive diamond electrode is less likely to cause the anode effect, and therefore an electrolyte for producing fluorine gas can be stably produced.

[0020] The cathode 4 may be made of any metal, such as nickel, copper, or iron. The nickel electrode 31 and the carbon electrode 32 may be supplied with direct current in parallel from a single rectifier 5, or may be supplied with current from two rectifiers (not shown). The electrolytic solution manufacturing apparatus 1 may also have a structure that allows direct current to be passed through both the nickel electrode 31 and the carbon electrode 32 simultaneously. The timings at which the direct current begins and ends to be passed through the nickel electrode 31 and the carbon electrode 32 may be different from each other, or may be simultaneous.

[0021] The power supply terminals of the anode 3 and the cathode 4 are attached to a lid 6 provided on the electrolytic solution production tank 2 so as to be electrically insulated. The lid 6 has an airtight structure to prevent gas from leaking from the inside of the electrolytic solution production tank 2, and is provided with a partition wall 7 on the surface facing the inside of the electrolytic solution production tank 2. When the liquid to be treated 8 is placed in the electrolytic solution production tank 2, the lower end of the partition wall 7 is immersed in the liquid to be treated 8. Therefore, the partition wall 7 divides the gas phase of the electrolytic solution production tank 2 into an anode chamber in which the anode 3 is placed and a cathode chamber in which the cathode 4 is placed. The material of the partition wall 7 may be any corrosion-resistant material, and nickel-copper alloy (Monel), nickel, etc. may be used.

[0022] Fluorine gas generated from the anode 3 and hydrogen gas generated from the cathode 4 during 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 shown) in the lid 6.

[0023] The current passed through the nickel electrode 31 may be 0.02 A or more and 0.2 A or less per liter of the liquid 8 to be treated, or 0.06 A or more and 0.15 A or less, and the current can be passed until the amount of current passed reaches 40 Ahr or more and 60 Ahr or less per liter of the liquid 8 to be treated. If the current passed through the nickel electrode 31 is 0.02 A / L or more, the amount of nickel dissolved per hour does not become too small, so the time required to produce the electrolyte is not likely to be long. If the current is 0.2 A / L or less, the dissolved nickel is less likely to precipitate from the nickel electrode 31, so loss of the nickel electrode 31 is reduced. Furthermore, if the amount of current passed through the nickel electrode 31 is within the above range, the effect of reducing the hydrogen fluoride vapor pressure of the liquid to be treated is easily improved.

[0024] The treatment time can be calculated from the current and current flow per liter of the liquid 8 to be treated, but from a manufacturing standpoint, it is preferable to adjust the current flowing through the nickel electrode 31 so that the treatment time is between 200 and 600 hours.

[0025] When a current is applied to the nickel electrode 31, it is preferable to gradually increase the current from a low current. In this case, the manner in which the current is increased is not particularly limited, but for example, the current value may be increased continuously or in a stepwise manner.

[0026] The current density of the current flowing through the nickel electrode 31 in the current application step is 0.01 A / cm ２ 0.1A / cm or more ２ may be less than or equal to 0.015 A / cm ２ 0.05A / cm or more ２ The current density may be 0.01 A / cm or less. ２ If the current density is 0.1 A / cm or more, the rate at which nickel dissolves from the nickel electrode 31 is likely to be higher than the rate at which the dissolved nickel reacts with the fluorine gas generated from the carbon electrode 32. Therefore, the nickel concentration in the treated liquid 8 is unlikely to decrease, and the time required to produce the electrolyte solution is unlikely to be long. ２If the current density is less than 0.1 A / cm, the dissolved nickel is less likely to deposit from the nickel electrode 31, resulting in less loss of the nickel electrode 31. Furthermore, when an amorphous carbon electrode is used as the carbon electrode 32, the anode effect is less likely to occur, so the current density should be less than 0.1 A / cm. ２ It is preferable to make it smaller.

[0027] The ratio (Ac / Ani) of the total surface area (Ac) of the carbon electrode 32 in contact with the liquid to the total surface area (Ani) of the nickel electrode 31 in contact with the liquid to be treated may be 5 or more and 30 or less. If Ac / Ani is 5 or more, the amount of nickel dissolved from the nickel electrode 31 reacts with the fluorine gas generated from the carbon electrode 32 in a large amount, so that the reaction rate with the fluorine gas is faster than the dissolution rate from the nickel electrode 31. As a result, nickel compounds formed from higher-order nickel fluoride ions are more likely to precipitate, which makes it easier to reduce the hydrogen fluoride vapor pressure of the electrolyte. Furthermore, if Ac / Ani is 30 or less, loss of hydrogen fluoride, which is a raw material for the liquid to be treated 8, is reduced.

[0028] The amount of current flowing through the carbon electrode 32 in the current application step may be 5 to 20 times the amount of current flowing through the nickel electrode 31. If the amount of current flowing is 5 times or more, nickel compounds formed from higher-order nickel fluoride ions are likely to precipitate, which makes it easier to reduce the hydrogen fluoride vapor pressure of the electrolytic solution. If the amount of current flowing is 20 times or less, fluorine gas is not excessively formed, which reduces the loss of hydrogen fluoride, which is a raw material for the liquid to be treated 8.

[0029] Although there are no particular limitations on the shape of the nickel electrode 31, a plate shape is preferable. This is because, when a plate-shaped nickel electrode is used, the reduction in the total surface area of ​​the electrode in contact with the liquid to be treated 8 is relatively small even as the dissolution of nickel progresses, making it difficult for the current density to increase and easier to control. Furthermore, a plate shape is also preferable for the carbon electrode 32.

[0030] The liquid to be treated 8 contains potassium fluoride (KF) and hydrogen fluoride and is subjected to electrolysis using the 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. Because hydrogen fluoride in the liquid to be treated is consumed by electrolysis during the current application step, it is preferable to continuously or intermittently supply hydrogen fluoride to the liquid to be treated 8. In this case, hydrogen fluoride can be supplied to the electrolyte production tank so that the hydrogen fluoride concentration in the liquid to be treated 8 is 39% by mass or more and 42% by mass or less. If the hydrogen fluoride concentration in the liquid to be treated 8 is 39% by mass or more, the melting point of the liquid to be treated is unlikely to increase. If the hydrogen fluoride concentration in the liquid to be treated 8 is 42% by mass or less, the vapor pressure of hydrogen fluoride is unlikely to increase, making it easier to suppress loss of hydrogen fluoride in the liquid to be treated 8.

[0031] The temperature of the liquid to be treated 8 in the current application step may be 80° C. or higher and 100° C. or lower. If the temperature is 80° C. or higher, the solubility of nickel fluoride ions is less likely to decrease, and therefore nickel dissolved from the nickel electrode 31 is less likely to precipitate in the liquid to be treated 8. If the temperature is 100° C. or lower, the vapor pressure of hydrogen fluoride in the liquid to be treated is less likely to increase, and hydrogen fluoride in the liquid to be treated 8 is less likely to evaporate, making it easier to suppress loss.

[0032] In another aspect, the method for producing fluorine gas according to the present disclosure may include an electrolysis step in which the electrolyte solution for producing fluorine gas, produced by the above-mentioned method for producing an electrolyte solution, is electrolyzed in an electrolytic cell to generate fluorine gas. The electrolytic cell is not particularly limited as long as it is an electrolytic cell that can generate fluorine gas, and may be an electrolytic cell for producing fluorine gas. When the electrolytic solution producing apparatus 1 according to the present disclosure is used as an electrolytic cell, fluorine gas can be generated by stopping the supply of power to the nickel electrode 31 and supplying power only to the carbon electrode 32.

[0033] The present disclosure will be explained in more detail below based on examples, but the present disclosure is not limited to these examples in any way.

[0034] Example 1 An electrolyte solution manufacturing apparatus 1 having a configuration similar to that shown in FIG. 2 was prepared. The left side of FIG. 2 is a cross-sectional view showing the configuration of the electrolyte solution manufacturing apparatus 1 when cut along a plane that penetrates the nickel electrode 31 and the power supply terminal connected to the nickel electrode 31 and is parallel to the plate surface of the plate-shaped nickel electrode 31. The right side of FIG. 2 is a cross-sectional view showing the configuration of the electrolyte solution manufacturing apparatus 1 when cut along a plane that penetrates the nickel electrode 31 and the power supply terminal connected to the nickel electrode 31, is perpendicular to the plate surface of the plate-shaped nickel electrode 31, and is parallel to the vertical direction. The electrolyte solution manufacturing apparatus 1 has an electrolyte solution manufacturing tank 2. The internal dimensions of the electrolyte solution manufacturing tank 2 are 75 cm wide x 75 cm long x 45 cm deep. The electrolyte solution manufacturing tank 2 is equipped with a lid 6. The lid 6 is equipped with a partition wall 7 by welding. The lid 6 further includes a fluorine gas outlet 62 and a hydrogen gas outlet 63 for purging fluorine gas and hydrogen gas from the anode chamber and cathode chamber, respectively, as described below. The electrolyte production tank 2 and lid 6 were made of carbon steel, and the partition wall 7 was made of Monel. A 3 mm-thick polytetrafluoroethylene (PTFE) sheet (not shown) was laid across the entire interior bottom surface of the electrolyte production tank 2, and a polytetrafluoroethylene gasket 64 was used to insulate the electrolyte production tank 2 from the lid 6. The electrolyte production tank 2 contained two anode chambers and one cathode chamber. The anode chamber contained an anode 3, and the cathode chamber contained a cathode 4. The anode and cathode chambers were separated by a partition wall 7. The anode 3 consisted of one nickel electrode 31 and five carbon electrodes 32 (ABR grade, manufactured by SGL)—a total of six electrodes. The nickel electrode 31 had dimensions of 20 cm wide x 35 cm long x 1 cm thick, and the carbon electrode 32 had dimensions of 20 cm wide x 35 cm long x 5 cm thick. Three anodes 3 were installed per anode chamber. A carbon steel electrode was installed as the cathode 4. The power supply terminal of each electrode was fixed to the lid 6, and the fixed portion was made airtight and insulated by an insulating airtight material 61. The cathode 4 was installed in the electrolytic solution production tank 2 so that the distance between the anode 3 and the cathode 4 was 4 cm. Furthermore, the electrolytic solution production tank 2 was equipped with a thermocouple for measuring the temperature of the liquid to be treated 8 contained therein, a liquid level measuring device, piping for supplying hydrogen fluoride, and a jacket for heating and cooling the liquid to be treated 8 (all of which are not shown).200 L of KF·2HF was placed in the above-described electrolytic solution production tank 2 as the liquid to be treated 8. The anode 3 and cathode 4 were then immersed in the liquid to be treated. The liquid to be treated 8 was immersed in the anode 3 to a height of 25 cm from the bottom end of the anode 3. At this time, the total surface area of ​​the portion of one side of the anode 3 in contact with the liquid to be treated 8, i.e., the total surface area of ​​one side of the anode 3 contributing to electrolysis, was 20 cm wide x 25 cm long = 500 cm. ２ Since current flows through both sides of the electrode, the total surface area contributed to the electrode per anode 3 is 1000 cm ２ The total surface area of ​​the portion of each anode 3 that comes into contact with the liquid to be treated is the same for the nickel electrode 31 and the carbon electrode 32. Therefore, the amount of current passing through the five carbon electrodes 32 is five times that of the one nickel electrode 31.

[0035] The temperature of the liquid 8 to be treated was set to 85°C, and a current was passed through the liquid 8 to be treated as follows, to obtain the electrolyte solution for producing fluorine gas of Example 1. During the current passage, hydrogen fluoride was intermittently supplied to the liquid 8 to be treated. First, a current density of 0.015 A / cm was applied to the anode 3 until the current efficiency of fluorine gas generation reached 85% or more. ２ A current of 90 A was passed for 25 hours. Then, the current was increased to 120 A (current density 0.02 A / cm ２ ), and the current was passed for 120 hours, after which the liquid to be treated 8 was sampled. The nickel concentration in this liquid to be treated was measured by inductively coupled plasma (ICP) atomic emission spectrometry, and was found to be 262 mass ppm. Thereafter, the current was increased to 180 A (current density 0.03 A / cm ２) and electricity was passed through for a further 210 hours, thereby obtaining an electrolyte solution for producing fluorine gas of Example 1. When a current was passed through the anode 3, electricity was passed through both the nickel electrode 31 and the carbon electrode 32 simultaneously. The amount of electricity passed through the nickel electrode 31 was 9075 Ahr, which was 45.4 Ahr per liter of the liquid 8 to be treated. The obtained electrolyte solution for producing fluorine gas was sampled, and the nickel concentrations in the electrolyte solution before and after filtration were measured by inductively coupled plasma atomic emission spectrometry. The nickel concentration after filtration was 303 ppm by mass, and the nickel concentration before filtration was 1090 ppm by mass. The hydrogen fluoride concentration in the obtained electrolyte solution for producing fluorine gas was 41.2% by mass.

[0036] Next, the hydrogen fluoride gas concentration in the gas phase of the electrolytic solution production tank 2 was determined when the temperature of the electrolytic solution for producing fluorine gas in the electrolytic solution production tank 2 was changed. Specifically, first, nitrogen gas for purging was supplied to the anode chamber, and a mixed gas of the gas in the anode chamber and nitrogen gas was extracted to the outside. Next, the concentration of hydrogen fluoride gas in the extracted mixed gas was quantitatively measured using a Fourier transform infrared spectrophotometer (FT-IR). Then, the hydrogen fluoride gas concentration in the gas phase was calculated from the hydrogen fluoride concentration in the obtained mixed gas. The results are shown in Table 1.

[0037]

[0038] [Comparative Example 1] An electrolyte solution of Comparative Example 1 was obtained in the same manner as in Example 1, except that all anodes 3 were carbon electrodes. A sample of the obtained electrolyte solution was taken, and the nickel concentration in the electrolyte solution was measured by inductively coupled plasma atomic emission spectrometry. The nickel content was 10 ppm by mass or less. The measured nickel content is considered to be the dissolved nickel content of the Monel used for the partition walls 7. The hydrogen fluoride concentration in the electrolyte solution was 41.2% by mass.

[0039] Next, in the same manner as in Example 1, the temperature of the electrolyte solution for producing fluorine gas in the electrolyte solution production tank was changed, and the hydrogen fluoride gas concentration in the gas phase of the electrolyte solution production tank was determined. The results obtained are shown in Table 2. The literature values ​​in Table 2 indicate the hydrogen fluoride gas concentration in the gas phase at each temperature, calculated using the following formula (1) described in Non-Patent Document 1. In formula (1), T indicates the temperature of the electrolyte solution, C indicates the hydrogen fluoride concentration in the electrolyte solution, and P indicates the hydrogen fluoride vapor pressure when the temperature of the electrolyte solution is T. Log(PmmHg)=2.0733-4244(1 / T)+0.2975C+47.94(C / T)-0.003785C ２ (1) Furthermore, the results of Example 1 and Comparative Example 1 are shown in the graph of FIG.

[0040]

[0041] As shown in Table 2, it was found that the hydrogen fluoride gas concentration in the gas phase in Comparative Example 1 was close to the literature value. The hydrogen fluoride gas concentration in the gas phase is determined by the hydrogen fluoride vapor pressure of the electrolyte. Therefore, the hydrogen fluoride gas concentration in the gas phase is a value equivalent to the hydrogen fluoride vapor pressure of the electrolyte. Therefore, it is considered that the hydrogen fluoride vapor pressure of the electrolyte in Comparative Example 1 is equivalent to that of a conventional electrolyte. Furthermore, as shown in the graph in FIG. 3, it was found that the hydrogen fluoride gas concentration in the gas phase in Example 1 was lower than that of Comparative Example 1. This indicates that the hydrogen fluoride vapor pressure of the electrolyte for producing fluorine gas in Example 1 was reduced compared to the literature value. When fluorine gas is electrolytically synthesized using such an electrolyte for producing fluorine gas, it is possible to reduce hydrogen fluoride loss compared to conventional electrolytes.

[0042] [Example 2] The electrolytic solution for producing fluorine gas obtained in Example 1 was placed in another electrolytic cell for producing fluorine gas, and electrolytic synthesis of fluorine gas was carried out. The electrolytic cell used had the same structure as in Example 1, except that all of the anodes 3 were carbon electrodes.

[0043] The electrolyte for producing fluorine gas was heated to 85°C, and a current density of 0.1 A / cm was applied to the anode. ２A current of 600 A was passed through the electrolytic cell for 500 hours. The current efficiency for fluorine gas generation exceeded 85%. After the end of the current passing, the electrolytic solution was sampled from the electrolytic cell, and the nickel concentrations in the electrolytic solution before and after filtration were measured by inductively coupled plasma atomic emission spectroscopy. The nickel concentration after filtration was 310 ppm by mass, and the nickel concentration before filtration was 1,200 ppm by mass. The hydrogen fluoride concentration in the electrolytic solution was 41.0% by mass.

[0044] The hydrogen fluoride gas concentration in the gas phase of the electrolytic cell was determined when the temperature of the electrolytic solution for producing fluorine gas was changed in the same manner as in Example 1. The results obtained are shown in Table 3. The results of Examples 1 and 2 are shown in the graph of Figure 4.

[0045]

[0046] 4 , even when the obtained electrolyte solution for producing fluorine gas was placed in an electrolytic cell for producing fluorine gas that was different from the electrolyte solution production cell used to produce the electrolyte solution and electrolytic synthesis of fluorine gas was carried out, the hydrogen fluoride gas concentration in the gas phase tended to be similar to that in Example 1. This shows that the electrolyte solution produced by the electrolyte solution production method according to the present disclosure has a hydrogen fluoride vapor pressure that is lower than the hydrogen fluoride vapor pressure calculated from literature values, even when electrolytic synthesis is carried out using a conventional electrolytic cell for producing fluorine gas.

[0047] Example 3 After producing an electrolyte solution for fluorine gas production in the same manner as in Example 1, the temperature of the electrolyte solution in the electrolyte solution production tank 2 was set to 83°C. A current of 250 A was passed through the carbon electrodes 32 other than the nickel electrodes 31 to change the liquid level of the electrolyte solution for fluorine gas production in the electrolyte solution production tank 2, thereby changing the hydrogen fluoride concentration in the electrolyte solution. The electrolyte solution was sampled when the liquid level of the electrolyte solution was changed, and the hydrogen fluoride concentration in the electrolyte solution was measured using inductively coupled plasma atomic emission spectroscopy. The electrolyte solution used for measurement was sampled after temporarily stopping the current flow. Furthermore, the hydrogen fluoride gas concentration in the gas phase was determined using a Fourier transform infrared spectrophotometer in the same manner as in Example 1. The obtained results are shown in Table 4. Table 4 also lists literature values ​​calculated from equation (1), as in Table 2. Furthermore, FIG. 5 graphically illustrates the results of Table 4.

[0048]

[0049] A comparison of Example 3 with the literature value revealed that even when the hydrogen fluoride concentration in the electrolyte solution changed, the hydrogen fluoride gas concentration in the gas phase was lower in both cases in Example 3. This shows that the electrolyte solution produced by the electrolyte solution production method according to the present disclosure has a hydrogen fluoride vapor pressure that is lower than the hydrogen fluoride vapor pressure calculated from the literature value, even when the hydrogen fluoride concentration in the electrolyte solution changes.

[0050] Comparative Example 2 An electrolytic solution production apparatus 1 having the same configuration as in FIG. 6 was prepared. The electrolytic solution production apparatus 1 had an electrolytic solution production tank 2. The electrolytic solution production tank 2 was equipped with a lid 6, and the lid 6 was equipped with a partition wall 7 by welding. The electrolytic solution production tank 2, lid 6, and partition wall 7 were all made of polytetrafluoroethylene. An anode chamber and a cathode chamber were provided inside the electrolytic solution production tank 2, with an anode 3 disposed in the anode chamber and a cathode 4 disposed in the cathode chamber. The anode chamber and the cathode chamber were then separated by the partition wall 7. Nickel electrodes were installed as the anode 3 and the cathode 4. The power supply terminals of each electrode were fixed to the lid 6, and the fixed parts were made airtight and insulated by an insulating airtight material (not shown). The total surface area of ​​the parts of the anode 3 and cathode 4 that came into contact with the liquid to be treated 8 was set to 6 cm. ２Furthermore, the outside of the electrolyte solution production tank 2 was configured to be able to be heated by an electric heater (not shown).

[0051] 725 g (370 mL) of KF·2HF was placed inside the electrolytic solution production tank 2 as described above as the liquid to be treated 8. The temperature of the liquid to be treated 8 was set to 85° C., and a current density of 0.1 A / cm was applied to the anode 3. ２ A current of 600 mA was passed through the anode 3 until the current flow rate reached 16 Ahr and the current flow rate per liter of the solution 8 to be treated reached 43 Ahr, thereby obtaining an electrolyte solution of Comparative Example 2. The nickel concentration in the electrolyte solution was determined from the mass change before and after current flow through the nickel electrode of the anode 3, resulting in a value of 2715 ppm by mass relative to the electrolyte solution. The electrolyte solution was cloudy after current flow was terminated, but the cloudiness disappeared immediately upon standing. The nickel concentration of the supernatant of this electrolyte solution was measured by inductively coupled plasma atomic emission spectroscopy, resulting in a value of 160 ppm by mass. The electrolyte solution after current flow was stirred and then sampled, and the nickel concentration was measured by inductively coupled plasma atomic emission spectroscopy, resulting in a value of 1720 ppm by mass. Since the nickel concentration measured by inductively coupled plasma atomic emission spectroscopy was lower than the nickel concentration obtained from the mass change, it is believed that the difference in the obtained nickel concentration was due to the larger particles of the nickel compound precipitated in the electrolyte solution and becoming more susceptible to settling in the electrolyte solution produced by the method of producing the electrolyte solution of Comparative Example 2. After the current was applied, the concentration of hydrogen fluoride in the electrolyte was 39.5% by mass.

[0052] After the current was turned off, the electrolyte solution was cooled to 85° C., and the hydrogen fluoride gas concentration in the gas phase of the electrolyte solution production tank 2 was measured using a Fourier transform infrared spectrophotometer. As a result of the measurement, the hydrogen fluoride gas concentration in the gas phase was 3.24% by volume.

[0053] From the results of Comparative Example 2, it was found that the hydrogen fluoride gas concentration in the gas phase according to formula (1) was 3.02% by volume, and therefore the hydrogen fluoride vapor pressure in the electrolytic solution prepared by the method of Comparative Example 2 was not reduced below the literature value.

[0054] [Example 4] An electrolyte solution for producing 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 wide x 35 cm long x 5 cm thick. The total surface area (Ani) of the nickel electrode in contact with the liquid to be treated 8 was 335 cm ２ The total surface area (Ac) of the carbon electrode in contact with the liquid to be treated 8 is 5000 cm ２ Therefore, Ac / Ani is 5000 / 335=15.

[0055] The electrolysis temperature was set to 85°C, and a current was passed through the liquid 8 to be treated as follows, to obtain an electrolytic solution for producing fluorine gas of Example 4. During the current passing, hydrogen fluoride was intermittently supplied to the liquid 8 to be treated. A current density of 0.017 A / cm was applied to the anode 3. ２ A current of 90 A was passed for 25 hours until the current efficiency of fluorine gas generation reached 85% or more. Then, the current was increased to 120 A (current density 0.022 A / cm ２ ), and after energizing for a further 240 hours, the liquid to be treated 8 was sampled. The nickel concentration in the liquid to be treated 8 was measured by inductively coupled plasma atomic emission spectrometry, and was found to be 318 mass ppm. Thereafter, the current was increased to 360 A (current density 0.067 A / cm ２ ), and continued for a further 360 hours to obtain an electrolyte solution for fluorine gas production. When current was passed through the anode 3, both the nickel electrode 31 and the carbon electrode 32 were simultaneously passed through. The current flow through the nickel electrode 31 until the current flow was terminated was 9,183 Ahr, which was 45.9 Ahr per L of the liquid 8 to be treated. The ratio of the total surface area (Ac) of the carbon electrode 32 in contact with the liquid 8 to the total surface area (Ani) of the nickel electrode 31 in contact with the liquid 8 to the total surface area (Ani) of the nickel electrode 31 was 15. Therefore, the current flow through the carbon electrode 32 was 15 times that of the nickel electrode 32. The electrolyte solution was sampled from the electrolyte solution production tank 2, and the filtered and unfiltered electrolyte solutions were subjected to inductively coupled plasma atomic emission spectroscopy. The nickel concentration in the filtered electrolyte solution was 347 ppm by mass, and the nickel concentration in the unfiltered electrolyte solution was 987 ppm by mass. The concentration of hydrogen fluoride in the electrolyte was 41.2 mass %.

[0056] Next, the hydrogen fluoride gas concentration in the gas phase was determined while changing the temperature of the obtained electrolytic solution for producing fluorine gas, and also while changing the temperature of the electrolytic solution for producing fluorine gas, in the same manner as in Example 1. The obtained hydrogen fluoride gas concentration in the gas phase for each temperature and the literature value are shown in Table 5.

[0057]

[0058] The results of Example 4 show that the hydrogen fluoride gas concentration in the gas phase was lower than the literature value at all temperatures. This shows that, even if the ratio of the total surface area of ​​the nickel electrodes in contact with the liquid to be treated to the total surface area of ​​the carbon electrodes in contact with the liquid to be treated is increased when producing an electrolyte solution for producing fluorine gas, it is possible to produce an electrolyte solution having a hydrogen fluoride vapor pressure lower than the hydrogen fluoride vapor pressure calculated from the literature value.

[0059] Furthermore, the following was found from Examples 1 to 4 and Comparative Examples 1 and 2. (1) Examples 1 to 4 demonstrated that the electrolytic solution manufacturing apparatus and electrolytic solution manufacturing method disclosed herein can manufacture electrolytic solutions with reduced hydrogen fluoride vapor pressure compared to conventional electrolytic solutions for fluorine gas production. Furthermore, the nickel concentration dissolved in the electrolytic solutions in Examples 1 to 4 ranged from 100 ppm by weight to 350 ppm by weight. (2) The results of Examples 1 and 4 demonstrated that as the current application process progressed, the transparency of the treated solution was lost and suspended matter that was difficult to settle was generated. Furthermore, it was found that this suspended matter contained nickel. (3) The results of Comparative Examples 1 and 2 demonstrated that electrolytic solutions manufactured using only a carbon electrode or only a nickel electrode as the anode had the same hydrogen fluoride vapor pressure as conventional electrolytic solutions. (4) The results of Comparative Example 2 demonstrated that electrolytic solutions manufactured using only a nickel electrode did not produce suspended matter that was difficult to settle.

[0060] REFERENCE SIGNS LIST 1 Electrolyte production device 2 Electrolyte production tank 3 Anode 31 Nickel electrode 32 Carbon electrode 4 Cathode 5 Rectifier 6 Lid 7 Partition wall 8 Liquid to be treated

Claims

1. An electrolytic solution manufacturing apparatus comprising: an anode having a nickel electrode and a carbon electrode; a cathode having a metal electrode; and an electrolytic solution manufacturing tank capable of containing a liquid to be treated containing potassium fluoride and hydrogen fluoride, wherein electrolysis of the liquid to be treated is performed using the anode and the cathode, and having a structure capable of passing a direct current through both the nickel electrode and the carbon electrode.

2. A method for manufacturing an electrolytic solution for producing fluorine gas using the electrolytic solution manufacturing apparatus according to claim 1, the method including: immersing the nickel electrode, the carbon electrode, and the metal electrode in the liquid to be treated contained in the electrolytic solution manufacturing tank; and a energization step of flowing a current of 0.02 A or more and 0.2 A or less per 1 L of the liquid to be treated through the nickel electrode, wherein in the energization step, a current is flowed through the nickel electrode until an energization amount, which is a product of the current flowing through the electrode and the energization time, becomes 40 Ahr or more per 1 L of the liquid to be treated.

3. The current density of the current flowing through the nickel electrode in the energization step is 0.01 A / cm ２ or more and 0.1 A / cm ２ or less. The method for producing an electrolytic solution according to claim 2.

4. The electrolytic solution manufacturing method according to claim 2 or 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.

5. The electrolytic solution manufacturing method according to claim 2 or claim 3, wherein an energization amount of the carbon electrode in the energization step is 5 times or more and 20 times or less an energization amount of the nickel electrode.

6. The electrolytic solution manufacturing method according to claim 2 or claim 3, including supplying hydrogen fluoride to the liquid to be treated so that a concentration of hydrogen fluoride contained in the liquid to be treated becomes 39% by mass or more and 42% by mass or less during the energization step.

7. The electrolytic solution manufacturing method according to claim 2 or claim 3, wherein a temperature of the liquid to be treated in the energization step is 80° C. or more and 100° C. or less.

8. A method for manufacturing fluorine gas including an electrolysis step of electrolyzing the electrolytic solution for producing fluorine gas manufactured by the electrolytic solution manufacturing method according to claim 2 or claim 3 in an electrolytic cell to generate fluorine gas.

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

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