Method for removing hydrogen fluoride

Abstract

To provide a method for removing hydrogen fluoride which hardly causes deterioration of a hydrogen fluoride remover and hardly causes necessity of replacement of the hydrogen fluoride remover.SOLUTION: A method for removing hydrogen fluoride includes: a sorption step of circulating crude fluorine gas which is fluorine gas containing hydrogen fluoride, in a hydrogen fluoride gas removing tower filled with a hydrogen fluoride remover having a sintered body of sodium fluoride, and making the hydrogen fluoride remover sorb the hydrogen fluoride in the crude fluorine gas; and a desorption step of desorbing hydrogen fluoride from a hydrogen fluoride remover having sorbed the hydrogen fluoride in the sorption step and reproducing the hydrogen fluoride remover, and recycling the hydrogen fluoride remover in the sorption step. Volume density of a sintered body of the sodium fluoride is more than 1.60 g / mL and 2.5 g / mL or less. The sorption step makes 1 vol.% or more and 100 vol.% or less of the total amount of the hydrogen fluoride remover filled into the hydrogen fluoride removing tower sorb the hydrogen fluoride up to a maximum hydrogen fluoride sorption amount of the hydrogen fluoride remover.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for removing hydrogen fluoride. [Background technology]

[0002] When KF·2HF molten salt electrolyte is electrolyzed, fluorine gas (F2) is generated from the anode. Because KF·2HF molten salt electrolyte has the vapor pressure of hydrogen fluoride (HF), the fluorine gas generated from the anode is mixed with hydrogen fluoride at a concentration of 4 to 10% by volume. As a method for removing hydrogen fluoride from crude fluorine gas, which is fluorine gas containing hydrogen fluoride, there is known a method in which hydrogen fluoride is adsorbed onto pellets of sodium fluoride (NaF), which is a hydrogen fluoride remover (see, for example, Patent Document 1). In order to continuously perform a process of removing hydrogen fluoride from a crude fluorine gas by supplying the crude fluorine gas to a hydrogen fluoride removal tower filled with a hydrogen fluoride removal agent, it is necessary to use a plurality of hydrogen fluoride removal towers. For example, when two hydrogen fluoride removal towers are used, one hydrogen fluoride removal tower performs a hydrogen fluoride removal process of removing hydrogen fluoride from the crude fluorine gas, while the other hydrogen fluoride removal tower performs a hydrogen fluoride desorption process of desorbing hydrogen fluoride from the hydrogen fluoride removal agent that has adsorbed hydrogen fluoride, thereby regenerating the hydrogen fluoride removal agent. Then, by alternately switching between the hydrogen fluoride removal towers that perform the hydrogen fluoride removal process, the hydrogen fluoride removal process and the hydrogen fluoride desorption process can be performed in parallel in both hydrogen fluoride removal towers, thereby continuously performing a process of removing hydrogen fluoride from a crude fluorine gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-215588 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the hydrogen fluoride removal process and the hydrogen fluoride desorption process (i.e., the regeneration process) are repeatedly performed alternately, there is a problem that the hydrogen fluoride removal agent in the hydrogen fluoride removal tower may crack or powder, or the hydrogen fluoride removal agents may fuse together. If the hydrogen fluoride removal agent in the hydrogen fluoride removal tower cracks or powders, or if the hydrogen fluoride removal agent melts and adheres to itself, the gas flow path in the hydrogen fluoride removal tower may become blocked or uneven flow may occur, so it was necessary to replace the hydrogen fluoride removal agent with a new one after one or several regeneration treatments.

[0005] Since the replacement work of the hydrogen fluoride removing agent is troublesome, if the replacement work of the hydrogen fluoride removing agent needs to be carried out frequently, there is a risk that the process of removing hydrogen fluoride from the crude fluorine gas cannot be carried out simply. Furthermore, since sodium fluoride pellets are not inexpensive, if the replacement work of the hydrogen fluoride removing agent needs to be carried out frequently, there is a risk that the process of removing hydrogen fluoride from the crude fluorine gas will become uneconomical. In this specification, cracking, powdering, or fusion of the hydrogen fluoride removing agent will also be referred to as "deterioration." An object of the present disclosure is to provide a method for removing hydrogen fluoride in which deterioration of the hydrogen fluoride remover is unlikely to occur and the need to replace the hydrogen fluoride remover is unlikely to occur. [Means for solving the problem]

[0006] In order to solve the above problems, one aspect of the present disclosure is as follows [1] to [8]. [1] A method for removing hydrogen fluoride from a crude fluorine gas containing hydrogen fluoride by using a hydrogen fluoride removing agent having a sintered body of sodium fluoride, comprising: a sorption step of passing the crude fluorine gas through a hydrogen fluoride removal tower filled with the hydrogen fluoride removing agent, and sorbing the hydrogen fluoride in the crude fluorine gas onto the hydrogen fluoride removing agent; a desorption step of desorbing the hydrogen fluoride from the hydrogen fluoride removing agent that has sorbed the hydrogen fluoride in the sorption step to regenerate the hydrogen fluoride removing agent so that it can be reused in the sorption step; Equipped with The volume density of the sintered body of sodium fluoride is more than 1.60 g / mL and not more than 2.5 g / mL, In the sorption step, the hydrogen fluoride is sorbed into the hydrogen fluoride removal agent in an amount of 1% by volume or more and 100% by volume or less of the total amount of the hydrogen fluoride removal agent filled in the hydrogen fluoride removal tower, up to the maximum hydrogen fluoride sorption amount of the hydrogen fluoride removal agent.

[0007] [2] The method for removing hydrogen fluoride according to [1], wherein the sorption step and the desorption step constitute one cycle, and the cycle is repeated 10 or more times. [3] The method for removing hydrogen fluoride according to [1] or [2], wherein the sintered body of sodium fluoride is obtained by sintering a molded body of sodium fluoride at a temperature of 700°C or higher and 900°C or lower.

[0008] [4] The method for removing hydrogen fluoride according to [3], wherein the sodium fluoride molded body is obtained by molding sodium hydrogen fluoride and firing it at a temperature of 400°C or higher and 650°C or lower. [5] The method for removing hydrogen fluoride according to [4], wherein the volume density of the sodium fluoride molded body is 1.4 g / mL or more and 1.7 g / mL or less. [6] The method for removing hydrogen fluoride according to any one of [1] to [5], wherein the sorption step is a step of contacting the hydrogen fluoride removing agent with the crude fluorine gas at a temperature of 50°C or higher and 150°C or lower.

[0009] [7] The method for removing hydrogen fluoride according to any one of [1] to [6], wherein the desorption step is a step of heating the hydrogen fluoride removing agent to a temperature of 150°C or higher and 300°C or lower under a flow of an inert gas. [8] The method for removing hydrogen fluoride according to any one of [1] to [7], wherein the maximum hydrogen fluoride sorption amount of the hydrogen fluoride removing agent is 5% by mass or more and 27% by mass or less. [Effects of the Invention]

[0010] According to the present disclosure, it is possible to provide a method for removing hydrogen fluoride in which the hydrogen fluoride remover is less likely to deteriorate and the need to replace the hydrogen fluoride remover is less likely to occur. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a graph showing the relationship between sintering temperature and volume density of a sintered body. [Figure 2] 1 is a graph showing the relationship between the sintering temperature and the rate of decrease in diameter before and after sintering. [Figure 3] 1 is a graph showing the relationship between the sintering temperature and the rate of decrease in length before and after sintering. [Figure 4] 1 is a graph showing the relationship between sintering temperature and maximum hydrogen fluoride sorption amount. [Figure 5] 1 is a graph showing the relationship between the number of repetitions of the sorption treatment and the regeneration treatment and the pressure loss. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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.

[0013] Conventionally, when hydrogen fluoride is removed from crude fluorine gas, which is fluorine gas containing hydrogen fluoride, using a hydrogen fluoride removal agent made of sodium fluoride, if the hydrogen fluoride sorption treatment (i.e., hydrogen fluoride removal treatment) and the hydrogen fluoride desorption treatment (i.e., hydrogen fluoride removal agent regeneration treatment) are repeatedly performed alternately, there has been a problem that, as mentioned above, the hydrogen fluoride removal agent may crack or powder, or the hydrogen fluoride removal agents may fuse together.

[0014] If the hydrogen fluoride removal agent cracks or powders, or if the hydrogen fluoride removal agent melts and adheres to itself, the gas flow path in the hydrogen fluoride removal tower filled with the hydrogen fluoride removal agent may become blocked or uneven flow may occur, so it was necessary to replace the hydrogen fluoride removal agent with a new one after one or several regeneration treatments.

[0015] As a result of extensive research, the present inventors believe that the cause of the deterioration of the hydrogen fluoride remover is as follows. The adsorption of hydrogen fluoride onto sodium fluoride is not adsorption onto the surface of a solid, but can be said to be the formation of a composition between sodium fluoride and hydrogen fluoride. For example, after hydrogen fluoride is adsorbed (condensed) onto the surface of a hydrogen fluoride remover, the adsorbed hydrogen fluoride is absorbed and diffused into the interior of the sodium fluoride crystals, resulting in a phenomenon that can be said to be the formation of a composition. Hereinafter, this phenomenon of adsorption and absorption will be referred to as "sorption."

[0016] When the amount of hydrogen fluoride sorbed increases, the rate at which hydrogen fluoride diffuses into the sodium fluoride crystals slows, and the amount of hydrogen fluoride condensing on the surface of the hydrogen fluoride removing agent increases, so the hydrogen fluoride concentration of the sodium fluoride-hydrogen fluoride composition formed on the surface of the hydrogen fluoride removing agent increases and the melting point decreases.This is thought to be why the phenomenon of contacting hydrogen fluoride removing agents fusing together occurs.

[0017] Furthermore, sodium fluoride swells when it sorbs hydrogen fluoride, and shrinks when it desorbs hydrogen fluoride. Therefore, it is thought that repeated swelling and shrinkage causes cracking and further progresses to pulverization. The greater the amount of hydrogen fluoride sorbed, the greater the degree of swelling and shrinkage, and therefore the greater the amount of hydrogen fluoride sorbed, the worse the degree of cracking and pulverization. Therefore, if the hydrogen fluoride removal agent is used repeatedly and sorption and desorption are repeated, the hydrogen fluoride removal agent will repeatedly swell and shrink, causing cracking and pulverization.

[0018] A hydrogen fluoride removal agent with a large sorption capacity of hydrogen fluoride (i.e., the maximum amount of hydrogen fluoride that can be sorbed) is prone to cracking and powdering due to its large degree of swelling and shrinkage. In this specification, the sorption capacity of hydrogen fluoride is sometimes referred to as the "maximum hydrogen fluoride sorption capacity." This maximum hydrogen fluoride sorption capacity can be calculated using the following formula, using the mass of the hydrogen fluoride removal agent that has sorbed hydrogen fluoride up to the maximum sorption capacity and the mass of hydrogen fluoride sorbed by the hydrogen fluoride removal agent at that time. Maximum hydrogen fluoride sorption amount (mass%) = (mass of hydrogen fluoride sorbed by the hydrogen fluoride removal agent) / (mass of the hydrogen fluoride removal agent with hydrogen fluoride sorbed) × 100

[0019] The maximum hydrogen fluoride sorption capacity of conventional hydrogen fluoride removal agents made of sodium fluoride is 32% by mass, which has the advantage of being able to sorb a large amount of hydrogen fluoride in a single sorption, but the disadvantage is that the degree of swelling and shrinkage increases, making the agent more susceptible to cracking and pulverization. Therefore, when hydrogen fluoride is sorbed up to the maximum hydrogen fluoride sorption capacity and then desorbed, cracking and pulverization are more likely to occur, and the lifespan of the hydrogen fluoride removal agent is shorter, so it has been necessary to frequently replace the hydrogen fluoride removal agent in the hydrogen fluoride removal tower with a new one.

[0020] As a result of extensive research, the present inventors have found that if a hydrogen fluoride removing agent with a small maximum hydrogen fluoride sorption amount is used, the hydrogen fluoride removing agent is less likely to deteriorate and the need for replacement of the hydrogen fluoride removing agent is less likely to occur. This is explained in detail below. When the flow of crude fluorine gas begins through a hydrogen fluoride removal tower filled with a hydrogen fluoride removal agent made of sodium fluoride, the hydrogen fluoride removal agent arranged near the inlet (gas inlet) of the hydrogen fluoride removal tower preferentially sorbs hydrogen fluoride. Therefore, as the flow of crude fluorine gas continues, the hydrogen fluoride removal agent arranged near the inlet of the hydrogen fluoride removal tower sorbs hydrogen fluoride up to the maximum hydrogen fluoride sorption amount, while the hydrogen fluoride removal agents arranged in other parts of the hydrogen fluoride removal tower do not sorb hydrogen fluoride up to the maximum hydrogen fluoride sorption amount.

[0021] To give one example, a few volume percent of the total amount of hydrogen fluoride removal agent packed in the hydrogen fluoride removal tower will sorb hydrogen fluoride up to the maximum hydrogen fluoride sorption amount, and the remaining hydrogen fluoride removal agent will sorb an amount of hydrogen fluoride less than the maximum hydrogen fluoride sorption amount.

[0022] As the flow of crude fluorine gas continues, the proportion of hydrogen fluoride removal agent that has sorbed hydrogen fluoride up to the maximum hydrogen fluoride sorption amount increases. For example, several tens of volume percent of the total amount of hydrogen fluoride removal agent filled in the hydrogen fluoride removal tower will sorb hydrogen fluoride up to the maximum hydrogen fluoride sorption amount.

[0023] If the flow of crude fluorine gas is further continued, the hydrogen fluoride removing agent disposed near the outlet (gas outlet) of the hydrogen fluoride removal tower sorbs hydrogen fluoride up to the maximum hydrogen fluoride sorption amount, and the entire amount of hydrogen fluoride removing agent filled in the hydrogen fluoride removal tower, i.e., 100% by volume, sorbs hydrogen fluoride up to the maximum hydrogen fluoride sorption amount. Once this state is reached, no further sorption of hydrogen fluoride into the hydrogen fluoride removing agent occurs even if the flow of crude fluorine gas is continued.

[0024] Therefore, although it is possible for the entire amount of hydrogen fluoride removal agent packed in the hydrogen fluoride removal tower to be in a state in which it sorbs hydrogen fluoride up to the maximum hydrogen fluoride sorption amount, it is not possible for the entire amount of hydrogen fluoride removal agent packed in the hydrogen fluoride removal tower to be in a state in which it sorbs hydrogen fluoride in an amount of hydrogen fluoride less than the maximum hydrogen fluoride sorption amount, except for a short period after the start of the flow of crude fluorine gas.

[0025] The maximum hydrogen fluoride sorption capacity of a conventional hydrogen fluoride removal agent made of sodium fluoride is 32 mass%. Therefore, when hydrogen fluoride is removed from crude fluorine gas using a conventional hydrogen fluoride removal agent made of sodium fluoride, the total amount of hydrogen fluoride removal agent filled in the hydrogen fluoride removal tower sorbs up to 32 mass% of hydrogen fluoride. Therefore, when hydrogen fluoride removal treatment and hydrogen fluoride desorption treatment are repeatedly performed alternately, the degree of swelling and shrinkage that occurs in the hydrogen fluoride removal agent is large, and the hydrogen fluoride removal agent is likely to deteriorate. Therefore, it is difficult to repeatedly perform hydrogen fluoride removal treatment and hydrogen fluoride desorption treatment alternately multiple times on the hydrogen fluoride removal agent, and deterioration may occur even after performing only one hydrogen fluoride removal treatment and one hydrogen fluoride desorption treatment. Therefore, the hydrogen fluoride removal agent had to be replaced frequently. The hydrogen fluoride removal method according to this embodiment uses a hydrogen fluoride removal agent with a small maximum hydrogen fluoride sorption amount, so the hydrogen fluoride removal agent is less likely to deteriorate and is less likely to need to be replaced.

[0026] Specifically, when the maximum hydrogen fluoride sorption capacity of the hydrogen fluoride removal agent is small, the phenomenon of fusion between contacting hydrogen fluoride removal agents is unlikely to occur. Furthermore, when the maximum hydrogen fluoride sorption capacity of the hydrogen fluoride removal agent is small, even when the hydrogen fluoride removal treatment and the hydrogen fluoride desorption treatment are alternately and repeatedly performed, the degree of swelling and shrinkage that occurs in the hydrogen fluoride removal agent made of sodium fluoride is small. Therefore, even when the hydrogen fluoride removal treatment and the hydrogen fluoride desorption treatment are alternately and repeatedly performed, deterioration (cracking, powdering) of the hydrogen fluoride removal agent is unlikely to occur. Because deterioration of the hydrogen fluoride removal agent is unlikely to occur, the hydrogen fluoride removal treatment (sorption step) and the hydrogen fluoride desorption treatment (desorption step) constitute one cycle, and this cycle can be repeated multiple times for the hydrogen fluoride removal agent.

[0027] That is, the method for removing hydrogen fluoride according to this embodiment is a method for removing hydrogen fluoride from a crude fluorine gas, which is a fluorine gas containing hydrogen fluoride, by using a hydrogen fluoride removing agent having a sintered body of sodium fluoride, and comprises: a sorption step of flowing the crude fluorine gas through a hydrogen fluoride removal tower filled with a hydrogen fluoride removing agent, and sorbing the hydrogen fluoride in the crude fluorine gas onto the hydrogen fluoride removing agent; and a desorption step of desorbing hydrogen fluoride from the hydrogen fluoride removing agent that has sorbed hydrogen fluoride in the sorption step, thereby regenerating the hydrogen fluoride removing agent and making it reusable for the sorption step, wherein the volume density of the sintered body of sodium fluoride is more than 1.60 g / mL and not more than 2.5 g / mL, In the sorption step, the hydrogen fluoride is sorbed into 1% by volume or more and 100% by volume or less of the total amount of the hydrogen fluoride removal agent filled in the hydrogen fluoride removal tower, up to the maximum hydrogen fluoride sorption amount of the hydrogen fluoride removal agent.

[0028] According to the hydrogen fluoride removal method of this embodiment, a hydrogen fluoride removing agent with a small maximum hydrogen fluoride sorption capacity is used, and therefore, even if the entire amount of hydrogen fluoride removing agent filled in the hydrogen fluoride removal tower sorbs hydrogen fluoride up to the maximum hydrogen fluoride sorption capacity, the degree of swelling and shrinkage of the hydrogen fluoride removing agent when the hydrogen fluoride removal treatment and the hydrogen fluoride desorption treatment are repeatedly performed alternately is small. Therefore, even if the hydrogen fluoride removal treatment and the hydrogen fluoride desorption treatment are repeatedly performed alternately, the hydrogen fluoride removing agent is unlikely to deteriorate, and the need to replace the hydrogen fluoride removing agent is unlikely to arise.

[0029] For example, according to the method for removing hydrogen fluoride according to this embodiment, a cycle consisting of a sorption step and a desorption step can be repeated 10 or more times. The number of times the cycle is repeated can be 10 or more, or can be 200 or more. The number of times the cycle is repeated can be 500 or less, or can be 300 or less.

[0030] In the hydrogen fluoride removal method according to this embodiment, hydrogen fluoride is sorbed up to the maximum hydrogen fluoride sorption capacity of the hydrogen fluoride removing agent in an amount of 1% by volume or more and 100% by volume or less of the total amount of hydrogen fluoride removing agent packed in the hydrogen fluoride removal tower, and the lower limit of the numerical range of the proportion of hydrogen fluoride removing agent that sorbs hydrogen fluoride up to the maximum hydrogen fluoride sorption capacity of the hydrogen fluoride removing agent may be 10% by volume or more or 30% by volume or more, and the upper limit of the numerical range may be 99% by volume or less or 70% by volume or less.

[0031] If the proportion of the hydrogen fluoride removing agent that sorbs hydrogen fluoride up to the maximum hydrogen fluoride sorption amount of the hydrogen fluoride removing agent is 10% by volume or more, a large amount of hydrogen fluoride can be sorbed by the hydrogen fluoride removing agent. Therefore, the proportion of the hydrogen fluoride removing agent that sorbs hydrogen fluoride up to the maximum hydrogen fluoride sorption amount of the hydrogen fluoride removing agent is preferably close to 100% by volume, and more preferably 100% by volume.

[0032] However, if the proportion of the hydrogen fluoride removal agent that sorbs hydrogen fluoride up to its maximum hydrogen fluoride sorption capacity is close to 100% by volume, there is a risk that unsorbed hydrogen fluoride will pass through the hydrogen fluoride removal tower and be discharged, so it is preferable to connect multiple hydrogen fluoride removal towers in series and sorb the hydrogen fluoride that has passed through the hydrogen fluoride removal tower in the subsequent hydrogen fluoride removal tower. In this case, the amount of hydrogen fluoride supplied to the subsequent hydrogen fluoride removal tower is small, so the specifications of the hydrogen fluoride removal agent filled in the subsequent hydrogen fluoride removal tower and the size of the hydrogen fluoride removal tower may be the same as or different from those of the previous hydrogen fluoride removal tower.

[0033] The diameter of the hydrogen fluoride removal tower and the height (layer height) of the packed bed of the hydrogen fluoride removing agent packed in the hydrogen fluoride removal tower are not particularly limited. In the case of a conventional hydrogen fluoride removing agent made of sodium fluoride, the heat generated when hydrogen fluoride is sorbed is large, so increasing the tower diameter makes it difficult to remove the heat, and there is a drawback in that the internal temperature of the hydrogen fluoride removing agent becomes uneven. However, the hydrogen fluoride removing agent according to this embodiment has a small maximum hydrogen fluoride sorption amount, and therefore generates little heat when hydrogen fluoride is sorbed, so there is no problem even if the tower diameter is increased.

[0034] However, when the hydrogen fluoride removal tower is heated for the desorption treatment, if the tower diameter is too large, it may take time or cost to bring the entire amount of the hydrogen fluoride removing agent to the desired temperature. Therefore, although the tower diameter of the hydrogen fluoride removal tower varies depending on the amount of hydrogen fluoride to be removed from the crude fluorine gas and the cycle time for switching between the sorption step and the desorption step, it is preferable that the tower diameter be 100 cm or less and the bed height be 300 cm or less.

[0035] In the hydrogen fluoride removal method according to this embodiment, the sorption step may be a step of contacting the hydrogen fluoride removing agent with the crude fluorine gas at a temperature of 50°C or higher and 150°C or lower. If the temperature (sorption temperature) at which the hydrogen fluoride removing agent is contacted with the crude fluorine gas is 50°C or higher, fusion of the sodium fluoride sintered body is unlikely to occur. Furthermore, if the sorption temperature is 150°C or lower, desorption of hydrogen fluoride from the sodium fluoride sintered body is unlikely to occur. The sorption temperature is preferably 50°C or higher and 150°C or lower, but the lower limit of the above-mentioned numerical range of the sorption temperature is more preferably 60°C or higher, and the upper limit of the above-mentioned numerical range of the sorption temperature is more preferably 100°C or lower.

[0036] Furthermore, in the hydrogen fluoride removal method according to this embodiment, the desorption step may be a step of heating the hydrogen fluoride remover to a temperature of 150°C or higher and 300°C or lower under a flow of inert gas. To achieve sufficient desorption economically, the temperature at which hydrogen fluoride is desorbed from the hydrogen fluoride remover (desorption temperature) is preferably 150°C or higher and 300°C or lower, but the lower limit of the aforementioned numerical range of the desorption temperature is more preferably 190°C or higher, and even more preferably 200°C or higher. The upper limit of the aforementioned numerical range of the desorption temperature is more preferably 250°C or lower, and even more preferably 230°C or lower. The type of inert gas used in the desorption step is not particularly limited as long as it does not react with sodium fluoride, and air, nitrogen gas, helium, argon, etc. can be used.

[0037] Furthermore, in the method for removing hydrogen fluoride according to this embodiment, there are no particular limitations on the concentration of hydrogen fluoride in the crude fluorine gas. The concentration of hydrogen fluoride in the crude fluorine gas may be, for example, several thousand ppm by volume or a few % by volume. Specific examples include 2% by volume or more and 10% by volume or less, and 20% by volume or more and 30% by volume or less. When the concentration of hydrogen fluoride in the crude fluorine gas is 20% by volume or more, the concentration of hydrogen fluoride in the crude fluorine gas may be reduced by a condensation operation or the like before removing hydrogen fluoride by the method for removing hydrogen fluoride according to this embodiment.

[0038] Furthermore, in the method for removing hydrogen fluoride according to the present embodiment, when the crude fluorine gas is brought into contact with the hydrogen fluoride removing agent to sorb hydrogen fluoride, the linear velocity of the flowing crude fluorine gas is not particularly limited, but in order to prevent a large pressure loss and an increase in the amount of unsorbed hydrogen fluoride, a linear velocity of 0.1 m / sec or less is preferred.

[0039] Since the maximum amount of hydrogen fluoride sorption in the hydrogen fluoride removal agent can be freely controlled by the sintering temperature of the sodium fluoride sintered body, various sorption modes can be adopted in the hydrogen fluoride removal method according to this embodiment. Generally, when sorption and desorption of hydrogen fluoride to the hydrogen fluoride removal agent are repeated, multiple hydrogen fluoride removal towers are arranged in parallel with the gas flow, and the hydrogen fluoride removal treatment and hydrogen fluoride desorption treatment (i.e., regeneration treatment of the hydrogen fluoride removal agent) are continuously performed by switching between the hydrogen fluoride removal tower that performs the sorption step and the hydrogen fluoride removal tower that performs the desorption step.

[0040] The smaller the maximum hydrogen fluoride sorption amount of the hydrogen fluoride remover, the higher its resistance to repeated use (the hydrogen fluoride remover is less likely to deteriorate), and so it can be used repeatedly many times.However, since the amount of hydrogen fluoride sorbed in one sorption process is small, the frequency of the above-mentioned switching operation will increase.

[0041] Furthermore, the larger the maximum hydrogen fluoride sorption capacity, the narrower the breakthrough zone of the hydrogen fluoride removing agent, and therefore the lower the hydrogen fluoride concentration of the gas that has passed through the hydrogen fluoride removal tower. In other words, the smaller the maximum hydrogen fluoride sorption capacity, the wider the breakthrough zone of the hydrogen fluoride removing agent, and therefore the higher the hydrogen fluoride concentration of the gas that has passed through the hydrogen fluoride removal tower. Therefore, multiple hydrogen fluoride removal towers (e.g., two towers) may be connected in series, and the upstream hydrogen fluoride removal tower (e.g., the first tower) may be filled with a hydrogen fluoride removing agent with a small maximum hydrogen fluoride sorption capacity, and the downstream hydrogen fluoride removal tower (e.g., the second tower) may be filled with a hydrogen fluoride removing agent with a large maximum hydrogen fluoride sorption capacity.

[0042] In this way, since the high hydrogen fluoride concentration in the crude fluorine gas has been reduced to a certain extent in the upstream hydrogen fluoride removal tower, it becomes easy to reduce the hydrogen fluoride concentration in the crude fluorine gas to a desired concentration in the downstream hydrogen fluoride removal tower. Since the hydrogen fluoride removing agent packed in the upstream hydrogen fluoride removal tower is less susceptible to deterioration (highly resistant to repeated use), and the hydrogen fluoride removing agent packed in the downstream hydrogen fluoride removal tower sorbs a smaller amount of hydrogen fluoride, both the upstream hydrogen fluoride removal tower and the downstream hydrogen fluoride removal tower can be repeatedly used more frequently.

[0043] The hydrogen fluoride removal tower may be filled with a hydrogen fluoride removing agent having a small variation in volume density, or may be filled with a hydrogen fluoride removing agent having a large variation in volume density. Alternatively, a hydrogen fluoride removing agent having a large volume density may be disposed near the inlet (gas inlet) of the hydrogen fluoride removal tower, a hydrogen fluoride removing agent having a small volume density may be disposed near the outlet (gas outlet) of the hydrogen fluoride removal tower, and a hydrogen fluoride removing agent having a medium volume density may be disposed in the intermediate portion between the inlet and outlet of the hydrogen fluoride removal tower. That is, a hydrogen fluoride removing agent having a smaller volume density than the hydrogen fluoride removing agent disposed near the inlet of the hydrogen fluoride removal tower but a larger volume density than the hydrogen fluoride removing agent disposed near the outlet may be disposed in the intermediate portion between the inlet and outlet of the hydrogen fluoride removal tower. In this case, the hydrogen fluoride removing agent may be disposed in the intermediate portion between the inlet and the outlet of the hydrogen fluoride removing tower so that the volume density of the hydrogen fluoride removing agent gradually decreases from the inlet toward the outlet of the hydrogen fluoride removing tower.

[0044] Since the crude fluorine gas supplied near the inlet of the hydrogen fluoride removal tower has a high hydrogen fluoride concentration and the closer it is to the outlet, the lower the hydrogen fluoride concentration of the crude fluorine gas, the more easily the hydrogen fluoride removal tower is charged with a hydrogen fluoride removal agent having a different volume density. This is similar to the above-mentioned embodiment in which a plurality of hydrogen fluoride removal towers filled with hydrogen fluoride removal agents having different volume densities are connected in series.

[0045] Next, the hydrogen fluoride remover used in the hydrogen fluoride removal method according to this embodiment will be described. The hydrogen fluoride remover according to this embodiment has a sintered body of sodium fluoride (for example, consists of a sintered body of sodium fluoride) and has a volume density of more than 1.60 g / mL and 2.5 g / mL or less. By using the hydrogen fluoride remover according to this embodiment, it is possible to remove hydrogen fluoride from a crude fluorine gas, which is a fluorine gas containing hydrogen fluoride, to perform purification, thereby producing a purified fluorine gas having a reduced concentration of hydrogen fluoride.

[0046] The hydrogen fluoride remover used in the hydrogen fluoride removal method according to this embodiment has a lower maximum hydrogen fluoride sorption capacity than conventional hydrogen fluoride removers made of sodium fluoride. The maximum hydrogen fluoride sorption capacity of the hydrogen fluoride remover is preferably 5% by mass or more and 27% by mass or less (e.g., 16% by mass), but the lower limit of the numerical range of the maximum hydrogen fluoride sorption capacity of the hydrogen fluoride remover may be 10% by mass or more, or 15% by mass or more. The upper limit of the numerical range may be 25% by mass or less, or 23% by mass or less. The hydrogen fluoride removing agent according to this embodiment has a small sorbable amount of hydrogen fluoride, and therefore is less likely to fuse together when in contact with the hydrogen fluoride removing agent.

[0047] Furthermore, although it is difficult to sorb large amounts of hydrogen fluoride compared to conventional hydrogen fluoride removers made of sodium fluoride, the degree of swelling and shrinkage that occurs in the hydrogen fluoride remover is small when hydrogen fluoride removal treatment and hydrogen fluoride desorption treatment are alternately repeated. Therefore, as mentioned above, the hydrogen fluoride remover is less likely to deteriorate, and it is possible to alternately repeat the hydrogen fluoride removal treatment and hydrogen fluoride desorption treatment (i.e., the above cycle) for the hydrogen fluoride remover, for example, 200 times or more. Therefore, the need to replace the hydrogen fluoride remover is less likely to occur. The shape of the hydrogen fluoride remover according to this embodiment is not particularly limited, and may be, for example, cylindrical, spherical, oval, or plate-shaped.

[0048] The method for removing hydrogen fluoride according to the present embodiment is a method for removing hydrogen fluoride from a crude fluorine gas, which is a fluorine gas containing hydrogen fluoride, but can also be applied to the case of removing hydrogen fluoride from a crude gas that is another type of gas containing hydrogen fluoride. Examples of other gases include gases of fluorine-containing compounds, and specific examples include chlorine monofluoride (ClF), chlorine trifluoride (ClF3), chlorine pentafluoride (ClF5), bromine trifluoride (BrF3), bromine pentafluoride (BrF5), bromine heptafluoride (BrF7), iodine trifluoride (IF3), iodine pentafluoride (IF5), iodine heptafluoride (IF7), uranium hexafluoride (UF6), tungsten hexafluoride (WF6), molybdenum hexafluoride (MoF6), xenon hexafluoride (XeF6), silicon tetrafluoride (SiF4), nitrogen trifluoride (NF3), and sulfur tetrafluoride (SF4).

[0049] The hydrogen fluoride remover used in the hydrogen fluoride removal method according to this embodiment may be manufactured as follows: That is, the sodium fluoride sintered body contained in the hydrogen fluoride remover according to this embodiment may be obtained by sintering a sodium fluoride molded body at a temperature of 700°C or higher and 900°C or lower.

[0050] When the sintering temperature is as high as described above, the specific surface area of ​​the sintered body of sodium fluoride is small, the volume density is high, and the maximum hydrogen fluoride sorption amount is low. Therefore, the hydrogen fluoride remover according to this embodiment is resistant to deterioration, and it is possible to alternately repeat the hydrogen fluoride removal process and the hydrogen fluoride desorption process, for example, 200 times or more. Furthermore, because the sintering temperature is high, strength such as crushing strength is high. Therefore, the hydrogen fluoride remover according to this embodiment is resistant to cracking and powdering.

[0051] When producing the hydrogen fluoride remover according to this embodiment, a sintered body may be formed by sintering a sodium fluoride compact at a temperature of 700°C or higher and 900°C or lower, or a sintered body may be formed by sintering a sodium fluoride compact at a temperature of 700°C or higher and 850°C or lower. The hydrogen fluoride remover according to this embodiment can be produced by molding sodium fluoride powder or granules into a molded body of sodium fluoride and sintering this molded body of sodium fluoride to produce a sintered body of sodium fluoride, but it can also be produced using sodium hydrogen fluoride (NaF HF) as a raw material.

[0052] That is, in the hydrogen fluoride remover according to this embodiment, the sodium fluoride molded body may be obtained by molding sodium hydrogen fluoride and firing it at a temperature of 400°C or higher and 650°C or lower. When sodium hydrogen fluoride is used as a raw material, no binder is required during molding, and it is easy to obtain a sintered body with a large specific surface area.

[0053] The temperature at which the sodium hydrogen fluoride molded body is fired (firing temperature) is preferably 400° C. or higher and 650° C. or lower, and more preferably 400° C. or higher and 600° C. or lower. Firing at this temperature makes it possible to obtain a molded body with high strength. Furthermore, the dimensions of the obtained molded body are less likely to vary.

[0054] The length of time (calcination time) for calcining the sodium hydrogen fluoride molded body is not particularly limited, but is preferably 2 hours or more, more preferably 4 hours or more. Since the volume density of the obtained molded body varies slightly depending on the length of the calcination time, the calcination time may be adjusted according to the desired volume density. The atmosphere during firing is not particularly limited, but for example, at least one gas selected from air, nitrogen gas (N2), helium (He), and argon (Ar) can be used.

[0055] Whether the raw material for the sodium fluoride compact is sodium fluoride or sodium hydrogen fluoride, in order to produce a high-strength sintered body of sodium fluoride, it is preferable to increase the tableting pressure when tableting the powder or granules. When a molded body of sodium hydrogen fluoride is fired, hydrogen fluoride is released from the sodium hydrogen fluoride to form sodium fluoride. The release of hydrogen fluoride forms voids within the molded body, and the contact areas between sodium fluoride particles crystallize, increasing the specific surface area of ​​the molded body and providing the molded body with structural strength. Therefore, a sintered body of sodium fluoride with a large specific surface area and high strength can be produced.

[0056] When the raw material for the sodium fluoride compact is sodium fluoride, the voids do not increase by firing, but merely promotes crystallization at the contact points between sodium fluoride particles, so in order to form voids in the compact, it is preferable to form voids during tableting by lowering the tableting pressure. Thus, when the raw material for the sodium fluoride compact is sodium fluoride, if the tableting pressure is lowered, the strength of the sodium fluoride sintered body will be lower than when the raw material is sodium hydrogen fluoride.

[0057] On the other hand, if the tableting pressure is increased to increase the strength of the compact, the strength of the sodium fluoride compact increases, but the voids within the compact decrease. Therefore, if the tableting pressure is increased when the raw material for the sodium fluoride compact is sodium fluoride, the specific surface area of ​​the sodium fluoride sintered body decreases compared to when the raw material is sodium hydrogen fluoride. For these reasons, it is preferable to use sodium hydrogen fluoride as the raw material for the sodium fluoride compact.

[0058] When a compact of sodium hydrogen fluoride is produced by tableting, the volume density of the resulting compact of sodium hydrogen fluoride is not particularly limited, but a higher volume density is preferable. The volume density of the compact of sodium hydrogen fluoride is, for example, preferably 2.2 g / mL or more and 2.5 g / mL or less, and more preferably 2.29 g / mL or more and 2.44 g / mL or less.

[0059] The volume density of a molded body is the value obtained by dividing the mass of the molded body by the geometric volume. The method for measuring the geometric volume of a molded body is not particularly limited. For example, in the case where the molded body is cylindrical, the diameter and length of the cylindrical molded body can be measured using a caliper or the like, and the geometric volume can be calculated from the measured values. The diameter of the cylindrical molded body may be, for example, the average value of the values ​​measured at three positions: the upper, middle, and lower sections.

[0060] The volume density of the sodium fluoride compact to be sintered is not particularly limited, but is preferably 1.4 g / mL or more and 1.7 g / mL or less. Furthermore, the lower limit of the above-mentioned numerical range for the volume density of the sodium fluoride compact to be sintered is more preferably 1.5 g / mL or more, and even more preferably 1.55 g / mL or more. The upper limit of the above-mentioned numerical range for the volume density of the sodium fluoride compact to be sintered is more preferably 1.7 g / mL or less, and even more preferably 1.65 g / mL or less.

[0061] That is, when a molded body of sodium hydrogen fluoride is fired to produce a molded body of sodium fluoride, the volume density of the resulting molded body of sodium fluoride is preferably within the above-mentioned range. The porosity of a molded body of sodium fluoride having the above-mentioned volume density is 40% or more and 47% or less. Then, by sintering a molded body of sodium fluoride having the above-mentioned volume density, a sintered body with high strength can be obtained. Furthermore, the dimensions of the obtained sintered body are less likely to vary.

[0062] The crushing strength of the sodium fluoride compact to be sintered is 5N / mm 2 More than 15N / mm 2It is preferable that the crushing strength is equal to or less than 0.05. If the crushing strength of the sodium fluoride compact is within the above-mentioned numerical range, the strength and porosity of the sodium fluoride sintered body are likely to be high. The crushing strength measurement in the present disclosure was carried out using a force tester. The tester used was an MCT-2150 manufactured by A&D Co., Ltd. When measuring the crushing strength, a head larger than the cross-sectional area of ​​the sample (e.g., sodium fluoride compact, sodium fluoride sintered body) was used, and the head was lowered at a speed of 10 mm / min to compress the sample, and the strength when the sample was crushed was determined.

[0063] Since hydrogen fluoride is generated when sodium hydrogen fluoride is fired, it is preferable that the materials of the equipment and tools used for firing the sodium hydrogen fluoride molded body are resistant to corrosion by hydrogen fluoride. Examples of materials resistant to corrosion by hydrogen fluoride include nickel and Hastelloy (trademark).

[0064] Next, the sintering of the sodium fluoride molded body will be described. The sodium fluoride sintered body may be obtained by sintering the sodium fluoride molded body at a temperature of 700°C or higher and 900°C or lower. Sintering at the above sintering temperature makes it easy to obtain a sintered body that has high strength and a suitable maximum hydrogen fluoride sorption amount. The atmosphere during sintering is not particularly limited, but for example, at least one gas selected from air, nitrogen gas (N2), helium (He), and argon (Ar) can be used.

[0065] The volume density of the sintered body of sodium fluoride obtained by sintering is more than 1.60 g / mL and not more than 2.5 g / mL, but is preferably 1.65 g / mL or more and not more than 2.5 g / mL. Sintered bodies of sodium fluoride having a volume density within the above range have high strength and are suitable for the maximum hydrogen fluoride sorption amount. In addition, sintered bodies of sodium fluoride having a volume density within the above range have a tensile strength of 18 N / mm 2 This is 1.9 times or more the crushing strength of the sodium fluoride compact before sintering.

[0066] The length of time (sintering time) for sintering the sodium fluoride compact is not particularly limited, but is preferably 2 hours or more, more preferably 6 hours or more. The degree of progress of sintering varies depending on the sintering temperature and sintering time, and the volume density achieved is determined by the sintering temperature. Therefore, the sintering temperature and sintering time can be adjusted so as to obtain a sintered body exhibiting the desired volume density.

[0067] The sodium fluoride sintered body obtained in this manner can be used as a hydrogen fluoride remover, but the maximum hydrogen fluoride sorption amount may decrease due to the sorption and desorption of hydrogen fluoride. As a result of extensive research, the present inventors have found that by subjecting the sodium fluoride sintered body obtained as described above to the hydrogen fluoride treatment described below, a hydrogen fluoride remover can be obtained that is resistant to a decrease in the maximum hydrogen fluoride sorption amount even when the sorption and desorption of hydrogen fluoride are repeatedly performed.

[0068] That is, the hydrogen fluoride treatment is a process in which hydrogen fluoride is sorbed onto a sintered body of sodium fluoride and then desorbed. A specific example of the hydrogen fluoride treatment is shown below. A cylindrical treatment tower made of a metal such as nickel is filled with a sintered body of sodium fluoride and maintained at a temperature between room temperature and 150°C. Hydrogen fluoride diluted with at least one diluent gas selected from fluorine gas, nitrogen gas, oxygen gas, helium, and argon is then circulated through the cylindrical treatment tower to sorb hydrogen fluoride onto the sintered body of sodium fluoride. Next, the sintered body of sodium fluoride with sorbed hydrogen fluoride is maintained at a temperature between 180°C and 300°C in an inert gas atmosphere to desorb hydrogen fluoride from the sintered body of sodium fluoride.

[0069] The concentration of hydrogen fluoride in hydrogen fluoride diluted with a dilution gas is not particularly limited, but may be, for example, 1% by volume or more and 10% by volume or less. The amount of hydrogen fluoride to be sorbed into the sodium fluoride sintered body in the hydrogen fluoride treatment is not particularly limited, but if the sodium fluoride sintered body is allowed to sorb hydrogen fluoride up to its maximum sorption amount, the maximum sorption amount of hydrogen fluoride is less likely to decrease when hydrogen fluoride is subsequently sorbed and desorbed.

[0070] The type of inert gas used for desorption in the hydrogen fluoride treatment is not particularly limited, but at least one selected from nitrogen gas, oxygen gas, helium, and argon can be used. The desorption temperature in the hydrogen fluoride treatment is preferably 180°C or higher and 300°C or lower, and more preferably 200°C or higher and 250°C or lower. The maximum hydrogen fluoride sorption amount of the sodium fluoride sintered body that has been subjected to the hydrogen fluoride treatment is, for example, 5% by mass or more and 27% by mass or less. [Example]

[0071] The present disclosure will be described in more detail below with reference to examples and comparative examples. Example 1 Sodium hydrogen fluoride (NaF HF) manufactured by Morita Chemical Industry Co., Ltd. was pulverized using a powder mill (dry pulverizer) to obtain sodium hydrogen fluoride granules. The obtained granules were filled into a cylindrical mold with an inner diameter of 6 mm and pressed at 150 N / mm using a tablet press. 2 The compact was compressed at a pressure of 1000 kJ / cm2 to obtain a compact of sodium hydrogen fluoride. The obtained compact was cylindrical in shape and had a length of 6 mm. The volume density of this sodium hydrogen fluoride compact was measured and found to be 2.29 g / mL. A large number of compacts were produced by this tableting method, and a total of 200 g of sodium hydrogen fluoride compacts were obtained.

[0072] 35 mL of the sodium hydrogen fluoride compact obtained as described above was packed into a nickel tube with an inner diameter of 30 mm, and while nitrogen gas was circulated through the nickel tube at a gas flow rate of 200 mL / min under standard conditions, the outside of the nickel tube was heated to 500°C with an electric heater. The sodium hydrogen fluoride compact was fired by heating at 500°C for 4 hours, and then cooled to room temperature to obtain a sodium fluoride compact.

[0073] The cooled compact was removed from the nickel tube, and it was confirmed that the compact had no cracks or powdering. The sodium fluoride compact obtained as described above was cylindrical, with a diameter of 6 mm and a length of 6 mm. This firing process was carried out on a large number of sodium hydrogen fluoride compacts, and a total of 175 mL of sodium fluoride compacts was prepared. The volume density of the compacts was measured, and the minimum value was 1.55 g / mL, the maximum value was 1.65 g / mL, and the average value was 1.60 g / mL. The crushing strength was 9±3 N / mm 2 It was.

[0074] 35 mL of the sodium fluoride compact was placed in a nickel crucible and heated for 2 hours at temperatures of 700°C, 750°C, 800°C, 825°C, 850°C, or 900°C using a small electric furnace (mini-BSI) manufactured by Nitto Kagaku Co., Ltd., followed by cooling to room temperature to obtain a sintered sodium fluoride compact. The sintering was carried out in an air atmosphere. The heating rate from room temperature to the sintering temperature was 0.6°C / sec, and the cooling time from the sintering temperature to room temperature was 5 hours.

[0075] The diameter (average value of the diameters at three locations: top, middle, and bottom) and length of all sintered compacts obtained at each sintering temperature were measured to determine the geometric volume of each sintered compact, and the mass of each sintered compact was also measured. This allowed the volume density of each sintered compact to be calculated. The results are shown in Table 1, which also shows the sintering temperature and the average volume density of the sintered compacts. Figure 1 is a graph showing the relationship between the sintering temperature and the average volume density of the sintered compacts. The dimensions of the sodium fluoride compact obtained by the above firing process were compared with the dimensions of the sodium fluoride sintered body obtained by the above sintering process. That is, the reduction rates of the diameter, length, and volume before and after sintering were calculated. The results are shown in Table 2 and Figures 2 and 3.

[0076] [Table 1]

[0077] [Table 2]

[0078] As can be seen from the results shown in Table 2, the dimensions were reduced by sintering, and the sintered body of sodium fluoride was smaller than the compacted body of sodium fluoride. When the compacted and sintered bodies of sodium fluoride are cylindrical, the shrinkage in the diameter direction is proportional to the sintering temperature, so the volume density of the sintered body of sodium fluoride can be predicted from the rate of reduction in diameter.

[0079] That is, since the values ​​on the vertical axis of the graph in Fig. 2 correspond to the dimensions, the approximation line shown in the graph in Fig. 2 is used to read the firing temperature (value on the horizontal axis) at which the diameter reduction rate becomes a predetermined value. Next, the approximation line shown in the graph in Fig. 1 is used to read the volume density at which the firing temperature becomes the same value as the firing temperature read using Fig. 2. This read volume density is then the volume density when the diameter reduction rate becomes the predetermined value.

[0080] Next, the maximum hydrogen fluoride sorption capacity of the sodium fluoride sintered body was determined. The maximum hydrogen fluoride sorption capacity is the maximum amount of hydrogen fluoride that can be sorbed. 30 mL of sodium fluoride sintered body was filled into a nickel tube with an inner diameter of 30 mm, and the total mass of the nickel tube filled with the sodium fluoride sintered body was measured. The nickel tube was then heated to 80°C, and nitrogen gas and hydrogen fluoride gas were passed through it. The nitrogen gas flow rate was 180 mL / min under standard conditions, and the hydrogen fluoride gas flow rate was 20 mL / min under standard conditions. The gas exiting the nickel tube was then analyzed using a Fourier transform infrared spectrophotometer (FT-IR) to measure the hydrogen fluoride concentration in the exit gas.

[0081] After 25 hours of gas flow, the hydrogen fluoride concentration in the outlet gas reached 10% by volume. In other words, the sodium fluoride sintered body was no longer sorbing hydrogen fluoride. The flow of nitrogen gas and hydrogen fluoride gas was stopped, the nickel tube was cooled, and the total mass of the nickel tube filled with the sodium fluoride sintered body was measured. By comparing the total mass before and after the flow of hydrogen fluoride gas, the mass of hydrogen fluoride sorbed in the sodium fluoride sintered body was determined, and this value was used to calculate the maximum hydrogen fluoride sorption capacity of the sodium fluoride sintered body. Table 1 shows the maximum hydrogen fluoride sorption capacity of sodium fluoride sintered bodies sintered at each temperature. The relationship between sintering temperature and maximum hydrogen fluoride sorption capacity is shown in the graph in Figure 4.

[0082] Next, the nickel tube was heated to 200°C and nitrogen gas was passed through to carry out a hydrogen fluoride desorption treatment (i.e., regeneration treatment). The flow rate of nitrogen gas was 400 mL / min under standard conditions. The outlet gas coming out of the outlet of the nickel tube was analyzed using a Fourier transform infrared spectrophotometer to measure the hydrogen fluoride concentration in the outlet gas. The hydrogen fluoride desorption treatment was carried out until the hydrogen fluoride concentration in the outlet gas reached 100 ppm by volume. When the hydrogen fluoride concentration in the outlet gas reached 100 ppm by volume, the flow of nitrogen gas was stopped and the nickel tube was cooled. The maximum hydrogen fluoride sorption amount of the sintered sodium fluoride body regenerated as described above was determined in exactly the same manner as above. The results are shown in the graph in Figure 4.

[0083] Example 2 In Example 1, the maximum hydrogen fluoride sorption amount of the sintered body of sodium fluoride that had been subjected to a single regeneration treatment was shown, while in Example 2, the sintered body of sodium fluoride of Example 1 that had been subjected to a single regeneration treatment was used to evaluate the hydrogen fluoride sorption capacity (degree of deterioration in hydrogen fluoride sorption capacity) of the sintered body of sodium fluoride that had been subjected to two or more regeneration treatments.

[0084] [Operation 1] In the same manner as in Example 1, hydrogen fluoride was sorbed onto the regenerated sintered body of sodium fluoride up to the maximum hydrogen fluoride sorption amount. [Operation 2] The sintered body of sodium fluoride to which hydrogen fluoride had been sorbed in operation 1 was subjected to a regeneration treatment in the same manner as in Example 1. When the hydrogen fluoride concentration in the gas at the outlet of the nickel tube became 100 ppm by volume or less, the flow rate of nitrogen gas was increased to 2000 mL / min under standard conditions, and the pressure difference (pressure loss) between the inlet and outlet of the nickel tube was measured using water column manometers attached to the piping at the inlet and outlet of the nickel tube.

[0085] The above-mentioned operations 1 and 2 were repeated for sintered bodies of sodium fluoride sintered at temperatures of 700°C, 750°C, or 800°C, and the number of repetitions and pressure loss were evaluated. The results are shown in Table 3 and the graph in Figure 5.

[0086] [Table 3]

[0087] In Comparative Example 1 described later, the pressure loss was 70 mmH2O when the number of repetitions was 5, but by using the graph in FIG. 5, the number of repetitions at which the pressure loss becomes 70 mmH2O can be determined. When the sintering temperature was 700°C (the amount of sodium fluoride sintered body filled was 28.2 g), the number of repetitions was about 75 times, when it was 750°C (the amount of sodium fluoride sintered body filled was 31.2 g), it was about 250 times, and when it was 800°C (the amount of sodium fluoride sintered body filled was 34.2 g), it was about 380 times.

[0088] When the sintering temperature was 700°C, the total amount of hydrogen fluoride that could be sorbed during 75 regeneration cycles was 596 g (0.22 × 28.2 / (1 − 0.22) × 75). Similarly, when the sintering temperature was 750°C, the total amount of hydrogen fluoride that could be sorbed during 250 regeneration cycles was 1485 g (0.16 × 31.2 / (1 − 0.16) × 250). When the sintering temperature was 800°C, the total amount of hydrogen fluoride that could be sorbed during 380 regeneration cycles was 1941 g (0.13 × 34.2 / (1 − 0.13) × 380).

[0089] The maximum amount of hydrogen fluoride sorbed per gram of sodium fluoride sintered body was calculated by dividing the total amount of hydrogen fluoride that could be sorbed by the packed amount of the sodium fluoride sintered body, and the results were 21.1 g / g-NaF when the sintering temperature was 700° C., 47.6 g / g-NaF when the sintering temperature was 750° C., and 56.7 g / g-NaF when the sintering temperature was 800° C. These values ​​are 9 to 24 times the value (2.35 g / g-NaF) calculated from the total amount of hydrogen fluoride that could be sorbed during five regeneration treatments in Comparative Example 1.

[0090] Sodium fluoride sintered bodies sintered at temperatures of 750°C and 800°C were subjected to regeneration treatment 300 times, and the sintered bodies were taken out and evaluated. 9-15% by mass were fused, 5-10% by mass were cracked, and 2-4% by mass were powdered material that could pass through a 20 mesh sieve. The remaining sintered bodies were in good condition, and the crushing strength was 20 N / mm. 2 That was all.

[0091] As described above, the sintered body after 300 regeneration treatments did not collapse or deteriorate, unlike Comparative Example 1. Furthermore, since no pressure loss occurs under the conditions for sorbing hydrogen fluoride (i.e., no blockage of the gas flow path due to fusion of the sodium fluoride sintered body occurs), it can be seen that the regeneration treatment can be further repeated and the body can be used to remove hydrogen fluoride. Therefore, it can be said that the number of times the sodium fluoride sintered body of Example 1 can be repeatedly used while being regenerated is greater than the result shown in Table 3.

[0092] Example 3 300 mL of a sodium hydrogen fluoride compact was prepared in the same manner as in Example 1. Then, the sodium hydrogen fluoride compact was fired in the same manner as in Example 1, except that the heating time was 6 hours, to obtain a sodium fluoride compact. The cooled compact was removed from the nickel tube, and it was confirmed that the compact was not cracked or pulverized. The volume density of the compact was measured and found to be 1.55 g / mL.

[0093] 300 mL of the sodium fluoride compact obtained as described above was placed in a nickel crucible, and sintered by heating at 740°C for 3 hours using a small electric furnace mini-BSI manufactured by Nitto Kagaku Co., Ltd., followed by cooling to room temperature, to obtain a sintered body of sodium fluoride. The sintering was carried out in an air atmosphere.

[0094] The volume density of the obtained sintered body was determined in the same manner as in Example 1, and was found to vary within the range of 1.7 g / mL to 1.9 g / mL. It is believed that the temperature distribution in the electric furnace affects the sintering results. Therefore, sodium fluoride sintered bodies having a volume density of 1.75 g / mL or more and 1.85 g / mL or less were selected, and the average volume density of the selected sodium fluoride sintered bodies was adjusted to 1.8 g / mL.

[0095] 300 mL (312 g) of this selected sodium fluoride sintered body was packed into a nickel tube with an inner diameter of 30 mm, forming a packed layer of sodium fluoride sintered body inside the nickel tube. The height of this packed layer (layer height) was 30 cm. The detailed method of packing is as follows: 300 mL of sodium fluoride sintered body was divided into six equal parts to prepare six sintered body groups of 50 mL each, and the mass of each sintered body group was measured.

[0096] The six groups of sintered compacts were then packed into the nickel tube one after the other. The height of the packed bed consisting of one group of sintered compacts was 5 cm. However, a nickel mesh was placed between two adjacent groups of sintered compacts. This nickel mesh was a circular sheet mesh with a diameter of 30 mm woven with wires of 0.5 mm thickness. By placing the mesh between the two adjacent groups, it was possible to remove the sodium fluoride sintered compacts from the nickel tube by dividing the 300 mL of sodium fluoride sintered compacts into six equal portions.

[0097] Next, the nickel tube filled with the sodium fluoride sintered body was heated to 80°C, and nitrogen gas and hydrogen fluoride gas were passed through it to sorb hydrogen fluoride into the sodium fluoride sintered body. The nitrogen gas flow rate was 320 mL / min under standard conditions, and the hydrogen fluoride gas flow rate was 80 mL / min under standard conditions. The outlet gas from the nickel tube was analyzed using a Fourier transform infrared spectrophotometer to measure the hydrogen fluoride concentration in the outlet gas. The nitrogen gas and hydrogen fluoride gas flow were continued for 63 hours until the hydrogen fluoride concentration in the outlet gas reached 20% by volume, at which point the flow of nitrogen gas and hydrogen fluoride gas was stopped. The maximum hydrogen fluoride sorption capacity of the sodium fluoride sintered body was calculated from the Fourier transform infrared spectrophotometer analysis value to be 25% by mass.

[0098] Furthermore, the nickel tube filled with the sodium fluoride sintered body was heated to 220°C, and nitrogen gas was passed through it to desorb hydrogen fluoride. The flow rate of nitrogen gas was 400 mL / min under standard conditions. The hydrogen fluoride desorption process was continued until the hydrogen fluoride concentration in the outlet gas reached 100 ppm by volume.

[0099] Next, hydrogen fluoride was sorbed onto the sodium fluoride sintered body that had been regenerated as described above. Specifically, a nickel tube filled with the sodium fluoride sintered body was heated to 80°C, and fluorine gas and hydrogen fluoride gas were passed through it to sorb hydrogen fluoride onto the sodium fluoride sintered body. The flow rate of fluorine gas was 360 mL / min under standard conditions, and the flow rate of hydrogen fluoride gas was 40 mL / min under standard conditions. The outlet gas from the outlet of the nickel tube was analyzed using a Fourier transform infrared spectrophotometer to measure the hydrogen fluoride concentration in the outlet gas. The flow of fluorine gas and hydrogen fluoride gas continued for 18.4 hours until the hydrogen fluoride concentration in the outlet gas reached 0.4% by volume, after which the flow of fluorine gas and hydrogen fluoride gas was stopped.

[0100] The sodium fluoride sintered body with hydrogen fluoride sorbed was removed from the nickel tube, and its mass was measured to determine the amount of hydrogen fluoride sorbed (mass percentage) in the sodium fluoride sintered body. The maximum hydrogen fluoride sorption amount in the sodium fluoride sintered body with this volume density was 16 mass%.

[0101] Six groups of sintered compacts were packed into the nickel tube, and the sintered compacts arranged from the gas inlet side were named Group 1, Group 2, Group 3, Group 4, Group 5, and Group 6. The sorption amount of hydrogen fluoride for Groups 1, 2, and 3 (i.e., layer heights of 0 to 15 cm) was 16 mass %. The sorption amount of hydrogen fluoride for Group 4 (i.e., layer heights of 15 to 20 cm) was 11 mass %, the sorption amount of hydrogen fluoride for Group 5 (i.e., layer heights of 20 to 25 cm) was 5.5 mass %, and the sorption amount of hydrogen fluoride for Group 6 (i.e., layer heights of 25 to 30 cm) was 0.5 mass %. From this result, it can be seen that about 50% by volume of the sodium fluoride sintered bodies out of all the sodium fluoride sintered bodies packed in the nickel tube sorbed the maximum amount of hydrogen fluoride.

[0102] Example 4 Sodium fluoride pellets manufactured by Morita Chemical Industry Co., Ltd. were prepared. The pellets were cylindrical bodies with a diameter of 6 mm and a length of 6 mm. The dimensions and mass of each pellet were measured to calculate the volume density, which was found to be a minimum of 1.55 g / mL, a maximum of 1.65 g / mL, and an average of 1.60 g / mL. The crushing strength was 9±3 N / mm 2 It was.

[0103] 35 mL of this sodium fluoride pellet was placed in a nickel crucible and sintered by heating at 825°C for 2 hours using a small electric furnace (mini-BSI) manufactured by Nitto Kagaku Co., Ltd., followed by cooling to room temperature. Sintering was performed in an air atmosphere. The heating rate from room temperature to the sintering temperature was 0.6°C / sec, and the cooling time from the sintering temperature to room temperature was 5 hours.

[0104] The average volume density of the sintered body of sodium fluoride obtained as described above was 2.10 g / mL. The maximum hydrogen fluoride sorption amount of the sintered body of sodium fluoride was measured in the same manner as in Example 1 and was found to be 16.2% by mass. Furthermore, the maximum hydrogen fluoride sorption amount of the sintered body of sodium fluoride that had been subjected to the regeneration treatment was measured in the same manner as in Example 1 and was found to be 9.8% by mass.

[0105] (Comparative Example 1) A molded body of sodium fluoride was produced in the same manner as in Example 1. The obtained molded body of sodium fluoride was taken out of the nickel tube and the crushing strength was measured, which was 9±3 N / mm 2 It was.

[0106] The sodium fluoride compacts were again packed into the same nickel tube, and the total mass of the nickel tube filled with the sodium fluoride compacts was measured. Then, the nickel tube was heated to 80°C, and fluorine gas and hydrogen fluoride gas were passed through it to sorb the hydrogen fluoride into the sodium fluoride compacts. The flow rate of the fluorine gas was 180 mL / min under standard conditions, and the flow rate of the hydrogen fluoride gas was 20 mL / min under standard conditions.

[0107] The gas coming out of the outlet of the nickel tube was analyzed with a Fourier transform infrared spectrophotometer to measure the hydrogen fluoride concentration in the gas. After 25 hours of flow, the hydrogen fluoride concentration in the gas reached 10% by volume. In other words, the sodium fluoride compacts no longer adsorbed hydrogen fluoride.

[0108] The flow of fluorine gas and hydrogen fluoride gas was stopped, the nickel tube was cooled, and the total mass of the nickel tube filled with the sodium fluoride molded bodies was measured. By comparing the total mass before and after the flow of hydrogen fluoride gas, the mass of hydrogen fluoride sorbed in the sodium fluoride molded bodies was determined, and from this value the maximum hydrogen fluoride sorption amount of the sodium fluoride molded bodies was calculated. As a result, the maximum hydrogen fluoride sorption amount of the sodium fluoride molded bodies was found to be 32 mass%. The hydrogen fluoride sorption amount can also be calculated from the hydrogen fluoride concentration in the outlet gas obtained by analysis with a Fourier transform infrared spectrophotometer, and this value was also 32 mass%.

[0109] Next, the nickel tube was heated to 200°C and nitrogen gas was passed through to desorb hydrogen fluoride. The flow rate of nitrogen gas was 400 mL / min under standard conditions. The outlet gas coming out of the outlet of the nickel tube was analyzed using a Fourier transform infrared spectrophotometer to measure the hydrogen fluoride concentration in the outlet gas. The hydrogen fluoride desorption process was continued until hydrogen fluoride was no longer detected in the outlet gas. Once hydrogen fluoride was no longer detected in the outlet gas, the flow of nitrogen gas was stopped and the nickel tube was cooled.

[0110] Next, the nickel tube was again heated to 80°C, and fluorine gas and hydrogen fluoride gas were passed through it to sorb hydrogen fluoride into the sodium fluoride compact (second sorption treatment). The flow rate of fluorine gas was 180 mL / min under standard conditions, and the flow rate of hydrogen fluoride gas was 20 mL / min under standard conditions. After 25 hours of flowing fluorine gas and hydrogen fluoride gas, the maximum amount of hydrogen fluoride sorption was calculated by measuring the mass, and was found to be 31 mass%, similar to the first hydrogen fluoride sorption.

[0111] The nickel tube was then heated to 200°C, and nitrogen gas was passed through it to desorb hydrogen fluoride (the second desorption treatment). The nitrogen gas flow rate was 400 mL / min under standard conditions. This sorption and desorption treatment was repeated alternately, for a total of five treatments.

[0112] After the fifth desorption, the nitrogen gas flow rate was set to 400 mL / min under standard conditions, and the pressure difference (pressure loss) between the inlet and outlet of the nickel tube was measured using water column manometers attached to the inlet and outlet piping. As no pressure loss was detected, the nitrogen gas flow rate was increased to 2000 mL / min under standard conditions, and the pressure loss was measured. The pressure loss in the packed bed was found to be 70 mmH2O.

[0113] Furthermore, after the fifth desorption, the sodium fluoride compacts were removed from the nickel tube and visually inspected. Significant deformation and deterioration were observed in the compacts. None of the compacts retained their appearance from before the first sorption treatment, and cracks were observed in 48% of the compacts. 25% of the compacts had cracked or broken into small pieces. Furthermore, fusion between compacts was confirmed in 27% of the compacts. An attempt was made to measure the crushing strength of a molded sodium fluoride body that still retained its shape, but the molded body was too brittle to measure the crushing strength (i.e., the crushing strength was lower than the lower limit of measurement).

[0114] The mass of the sodium fluoride compacts initially filled into the nickel tube without sorbing hydrogen fluoride was 32.4 g (35 mL). Since the maximum hydrogen fluoride sorption amount was 32 mass%, the amount of hydrogen fluoride sorbed was 15.2 g (0.32 × 32.4 / (1 - 0.32)). If the limit for repeated use of sodium fluoride compacts is five times, the amount of hydrogen fluoride that can be removed by these compacts is 76.0 g (5 times × 15.2 g). The amount of hydrogen fluoride that can be removed by these compacts before deterioration is 2.35 g / g-NaF (76.0 g / 32.4 g) per unit mass.

[0115] (Comparative Example 2) A compact of sodium fluoride was produced in the same manner as in Example 1, and a cylindrical compact with a diameter of 6 mm and a length of 6 mm was obtained. The volume density of this compact of sodium fluoride was 1.6 g / mL. Furthermore, the compact of sodium fluoride was free of cracks and powdering.

[0116] 35 mL (32.4 g) of the sodium fluoride compact obtained as described above was placed in a nickel crucible and sintered by heating at 950°C for 2 hours using a small electric furnace (mini-BSI) manufactured by Nitto Kagaku Co., Ltd., followed by cooling to room temperature. The sintering was carried out in an air atmosphere. The volume density of the obtained sintered body was determined in the same manner as in Example 1, and the average volume density was 2.61 g / mL.

[0117] Next, the sodium fluoride sintered body was filled into a nickel tube with an inner diameter of 30 mm, and the total mass of the nickel tube filled with the sodium fluoride sintered body was measured.The nickel tube was then heated to 80°C, and nitrogen gas and hydrogen fluoride gas were passed through it.The flow rate of nitrogen gas was 180 mL / min under standard conditions, and the flow rate of hydrogen fluoride gas was 20 mL / min under standard conditions.The outlet gas coming out of the outlet of the nickel tube was then analyzed with a Fourier transform infrared spectrophotometer, and the hydrogen fluoride concentration in the outlet gas was measured.

[0118] After 1 minute of gas flow, the hydrogen fluoride concentration in the outlet gas reached 10% by volume. In other words, the sodium fluoride sintered body was no longer sorbing hydrogen fluoride. This result showed that the sodium fluoride sintered body of Comparative Example 2 hardly sorbed any hydrogen fluoride.

[0119] (Comparative Example 3) A compact of sodium fluoride was produced in the same manner as in Example 1, and a cylindrical compact with a diameter of 6 mm and a length of 6 mm was obtained. The volume density of this compact of sodium fluoride was 1.6 g / mL. Furthermore, the compact of sodium fluoride was free of cracks and powdering.

[0120] 35 mL (32.4 g) of the sodium fluoride compact obtained as described above was placed in a nickel crucible and sintered by heating at 650°C for 2 hours using a small electric furnace (mini-BSI) manufactured by Nitto Kagaku Co., Ltd., followed by cooling to room temperature. Sintering was performed in an air atmosphere. The volume density of the obtained sintered body was determined in the same manner as in Example 1, and the average volume density was 1.6 g / mL, indicating that sintering had not progressed sufficiently.

[0121] Next, the sodium fluoride sintered body was filled into a nickel tube with an inner diameter of 30 mm, and the total mass of the nickel tube filled with the sodium fluoride sintered body was measured.The nickel tube was then heated to 80°C, and fluorine gas and hydrogen fluoride gas were passed through it. The flow rate of fluorine gas was 180 mL / min under standard conditions, and the flow rate of hydrogen fluoride gas was 20 mL / min under standard conditions.The outlet gas coming out of the outlet of the nickel tube was then analyzed with a Fourier transform infrared spectrophotometer, and the hydrogen fluoride concentration in the outlet gas was measured.

[0122] After 25 hours of flow, the hydrogen fluoride concentration in the outlet gas reached 10% by volume. In other words, the sodium fluoride molded body was no longer sorbing hydrogen fluoride. The flow of fluorine gas and hydrogen fluoride gas was stopped, the nickel tube was cooled, and the total mass of the nickel tube filled with the sodium fluoride sintered body was measured. The maximum hydrogen fluoride sorption capacity of the sodium fluoride sintered body was determined by comparing the total mass before and after the flow of hydrogen fluoride gas. As a result, the maximum hydrogen fluoride sorption capacity of the sodium fluoride sintered body was 32% by mass, which was not significantly different from the maximum hydrogen fluoride sorption capacity of the sodium fluoride sintered body in Comparative Example 1.

[0123] (Comparative Examples 4 to 7) Sodium fluoride pellets manufactured by Morita Chemical Industry Co., Ltd. were prepared. The pellets were cylindrical bodies with a diameter of 6 mm and a length of 6 mm. The dimensions and mass of each pellet were measured to calculate the volume density, which was found to be a minimum of 1.55 g / mL, a maximum of 1.65 g / mL, and an average of 1.60 g / mL. The crushing strength was 9±3 N / mm 2 It was.

[0124] 100 g of these sodium fluoride pellets were packed into a nickel tube with an inner diameter of 37 mm, and the maximum hydrogen fluoride sorption amount was measured in the same manner as in Example 1. However, the conditions for sorbing hydrogen fluoride onto the sodium fluoride pellets were variously changed, and the maximum hydrogen fluoride sorption amount was measured. That is, nitrogen gas and hydrogen fluoride were passed through the nickel tube, but the hydrogen fluoride concentration of the passing gas, the flow rate of hydrogen fluoride, the temperature during sorption (sorption temperature), and the time for which the sorption treatment was performed (sorption time) were variously changed, as shown in Table 4. The results are shown in Table 4. As can be seen from the results shown in Table 4, even when the conditions for sorbing hydrogen fluoride onto sodium fluoride pellets were changed in various ways, the maximum amount of hydrogen fluoride sorption hardly changed.

[0125] [Table 4]

Claims

1. A method for removing hydrogen fluoride from a crude fluorine gas containing hydrogen fluoride, using a hydrogen fluoride removing agent having a sintered body of sodium fluoride, comprising: a sorption step of passing the crude fluorine gas through a hydrogen fluoride removal tower filled with the hydrogen fluoride removing agent, and sorbing the hydrogen fluoride in the crude fluorine gas onto the hydrogen fluoride removing agent; a desorption step of desorbing the hydrogen fluoride from the hydrogen fluoride removing agent that has sorbed the hydrogen fluoride in the sorption step to regenerate the hydrogen fluoride removing agent so that it can be reused in the sorption step; Equipped with The volume density of the sintered body of sodium fluoride is more than 1.60 g / mL and not more than 2.5 g / mL, In the sorption step, the hydrogen fluoride is sorbed into the hydrogen fluoride removal agent in an amount of 1% by volume or more and 100% by volume or less of the total amount of the hydrogen fluoride removal agent filled in the hydrogen fluoride removal tower, up to a maximum hydrogen fluoride sorption amount of the hydrogen fluoride removal agent.

2. 2. The method for removing hydrogen fluoride according to claim 1, wherein the sorption step and the desorption step constitute one cycle, and the cycle is repeated 10 or more times.

3. 3. The method for removing hydrogen fluoride according to claim 1, wherein the sintered body of sodium fluoride is obtained by sintering a molded body of sodium fluoride at a temperature of 700°C or higher and 900°C or lower.

4. 4. The method for removing hydrogen fluoride according to claim 3, wherein the sodium fluoride molded body is obtained by molding sodium hydrogen fluoride and firing it at a temperature of 400°C or higher and 650°C or lower.

5. 5. The method for removing hydrogen fluoride according to claim 4, wherein the volume density of the sodium fluoride molded body is 1.4 g / mL or more and 1.7 g / mL or less.

6. 3. The method for removing hydrogen fluoride according to claim 1, wherein the sorption step is a step of contacting the hydrogen fluoride removing agent with the crude fluorine gas at a temperature of 50°C or higher and 150°C or lower.

7. 3. The method for removing hydrogen fluoride according to claim 1, wherein the desorption step is a step of heating the hydrogen fluoride removing agent to a temperature of 150° C. or higher and 300° C. or lower under a flow of an inert gas.

8. 3. The method for removing hydrogen fluoride according to claim 1, wherein the maximum hydrogen fluoride sorption amount of the hydrogen fluoride removing agent is 5% by mass or more and 27% by mass or less.

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