Method for removing hydrogen fluoride

Abstract

A method for removing hydrogen fluoride is provided by which, even when a gas to be treated has a high hydrogen fluoride concentration, hydrogen fluoride can be removed from the gas using sodium fluoride until the hydrogen fluoride concentration becomes low. The method for removing hydrogen fluoride comprises: a first adsorption step in which a gas to be treated is introduced into a first adsorption treatment part provided with sodium fluoride and is brought into contact with the sodium fluoride, and the hydrogen fluoride contained in the gas is adsorbed onto the sodium fluoride to thereby obtain a first adsorption-treated gas; and a second adsorption step in which the first adsorption-treated gas is introduced into a second adsorption treatment part provided with sodium fluoride and is brought into contact with the sodium fluoride, and the hydrogen fluoride contained in the first adsorption-treated gas is adsorbed onto the sodium fluoride to thereby obtain a second adsorption-treated gas. The sodium fluoride of the first adsorption treatment part in the first adsorption step has a higher temperature than the sodium fluoride of the second adsorption treatment part in the second adsorption step.

Description

How to remove hydrogen fluoride

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

[0002] Fluorine-containing compound gases such as fluorine gas, interhalogen compounds (e.g., chlorine monofluoride, chlorine trifluoride), tungsten hexafluoride, silicon tetrafluoride, nitrogen trifluoride, and sulfur tetrafluoride are useful as gases used in the production of semiconductors, but often contain hydrogen fluoride as an impurity. Patent Documents 1 and 2 disclose techniques for purifying fluorine-containing compound gases by removing hydrogen fluoride from the gases by adsorbing the hydrogen fluoride onto sodium fluoride.

[0003] Japanese Patent Publication No. 6792158 Japanese Patent Publication No. 4843635

[0004] However, sodium fluoride has a smaller hydrogen fluoride adsorption capacity than activated carbon, a common adsorbent, and therefore has the problem of early breakthrough. Therefore, when the hydrogen fluoride concentration in the gas to be treated from which hydrogen fluoride removal is performed is high, it is necessary to frequently replace the sodium fluoride adsorbent. Therefore, it is not easy to remove hydrogen fluoride from a gas to be treated that has a high hydrogen fluoride concentration using sodium fluoride until the hydrogen fluoride concentration becomes low. An object of the present disclosure is to provide a hydrogen fluoride removal method that can remove hydrogen fluoride from a gas to be treated using sodium fluoride until the hydrogen fluoride concentration becomes low, even if the gas to be treated has a high hydrogen fluoride concentration.

[0005] In order to solve the above problems, one aspect of the present disclosure is as follows: [1] to

[11] . [1] A method for removing hydrogen fluoride from a gas to be treated that contains hydrogen fluoride, comprising: a first adsorption step of introducing the gas to be treated into a first adsorption treatment unit comprising sodium fluoride, bringing the gas to be treated into contact with the sodium fluoride in the first adsorption treatment unit, and causing the hydrogen fluoride in the gas to be treated to be adsorbed by the sodium fluoride in the first adsorption treatment unit, thereby obtaining a first adsorption-treated gas, which is the gas to be treated, with a reduced hydrogen fluoride concentration; and a second adsorption step of introducing the first adsorption-treated gas into a second adsorption treatment unit comprising sodium fluoride, bringing the first adsorption-treated gas into contact with the sodium fluoride in the second adsorption treatment unit, and causing the hydrogen fluoride in the first adsorption-treated gas to be adsorbed by the sodium fluoride in the second adsorption treatment unit, thereby obtaining a second adsorption-treated gas, which is the first adsorption-treated gas with a reduced hydrogen fluoride concentration. a temperature of the sodium fluoride in the first adsorption treatment unit when the gas to be treated is brought into contact with the sodium fluoride in the first adsorption treatment unit in the first adsorption step is higher than a temperature of the sodium fluoride in the second adsorption treatment unit when the gas that has been subjected to the first adsorption treatment is brought into contact with the sodium fluoride in the second adsorption treatment unit in the second adsorption step; a ratio of the mass of the hydrogen fluoride in the gas to be treated introduced into the first adsorption treatment unit per unit time to the mass of the sodium fluoride in the first adsorption treatment unit before adsorption is 0.05 HF-mg / NaF-g / h or more and 70 HF-mg / NaF-g / h or less; and a ratio of the mass of the hydrogen fluoride in the gas that has been subjected to the first adsorption treatment per unit time to the mass of the sodium fluoride in the second adsorption treatment unit before adsorption is 0.001 HF-mg / NaF-g / h or more and 5 HF-mg / NaF-g / h or less in the second adsorption step.

[0006] [2] The method for removing hydrogen fluoride according to [1], further comprising: a desorption step of heating at least one of the sodium fluoride of the first adsorption treatment unit used in the first adsorption step and the sodium fluoride of the second adsorption treatment unit used in the second adsorption step under a heat treatment atmosphere gas, and desorbing hydrogen fluoride from both the sodium fluoride of the first adsorption treatment unit and the sodium fluoride of the second adsorption treatment unit at a rate of 10 mg or less per 1 g of sodium fluoride before adsorption and 10 mg or less per minute; and an exchange step of exchanging at least one of the sodium fluoride of the first adsorption treatment unit used in the first adsorption step and the sodium fluoride of the second adsorption treatment unit used in the second adsorption step with sodium fluoride from which hydrogen fluoride has been desorbed in the desorption step.

[0007] [3] The method for removing hydrogen fluoride according to [1] or [2], wherein the temperature of the sodium fluoride in the first adsorption treatment unit when contacting the gas to be treated in the first adsorption step is 50° C. or higher and 120° C. or lower. [4] The method for removing hydrogen fluoride according to any one of [1] to [3], wherein the temperature of the sodium fluoride in the second adsorption treatment unit when contacting the gas that has been subjected to the first adsorption treatment in the second adsorption step is −10° C. or higher and lower than 50° C.

[0008] [5] The method for removing hydrogen fluoride according to any one of [1] to [4], wherein in the first adsorption step, the ratio of the mass of the hydrogen fluoride in the gas to be treated introduced into the first adsorption treatment unit to the mass of sodium fluoride in the first adsorption treatment unit before adsorption is 10 HF-mg / NaF-g or more and 100 HF-mg / NaF-g or less.

[0009] [6] The method for removing hydrogen fluoride according to any one of [1] to [5], wherein in the second adsorption step, a ratio of the mass of the hydrogen fluoride in the gas that has undergone first adsorption treatment and that is introduced into the second adsorption treatment unit to the mass of sodium fluoride in the second adsorption treatment unit before adsorption is 100 HF-mg / NaF-g or less. [7] The method for removing hydrogen fluoride according to [2], wherein a heating temperature in the desorption step is 150°C or higher and 240°C or lower.

[0010] [8] The method for removing hydrogen fluoride according to [2] or [7], wherein the heat treatment atmospheric gas is at least one of nitrogen gas, helium, argon, oxygen gas, and air. [9] The method for removing hydrogen fluoride according to any one of [1] to [8], wherein the hydrogen fluoride concentration in the second adsorption-treated gas discharged from the second adsorption treatment unit is 0.01 ppm by volume or more and 250 ppm by volume or less.

[0011]

[10] The method for removing hydrogen fluoride according to any one of [1] to [9], wherein the gas to be treated contains hydrogen fluoride and at least one of fluorine gas, chlorine monofluoride, chlorine trifluoride, chlorine pentafluoride, bromine trifluoride, bromine pentafluoride, bromine heptafluoride, iodine trifluoride, iodine pentafluoride, iodine heptafluoride, tungsten hexafluoride, silicon tetrafluoride, nitrogen trifluoride, and sulfur tetrafluoride.

[11] The method for removing hydrogen fluoride according to any one of [1] to

[10] , wherein the sodium fluoride in the first adsorption treatment unit and the sodium fluoride in the second adsorption treatment unit are formed by tableting sodium fluoride powder.

[0012] According to the present disclosure, even if the gas to be treated has a high concentration of hydrogen fluoride, it is possible to remove hydrogen fluoride from the gas to be treated until the concentration of hydrogen fluoride becomes low by using sodium fluoride.

[0013] 1 is a graph showing an example of the transition of hydrogen fluoride concentration in the outlet gas of a sodium fluoride packed tower. 2 is a schematic diagram showing an example of a hydrogen fluoride removal device for explaining an embodiment of a hydrogen fluoride removal method according to the present disclosure. 3 is a schematic diagram showing an example of a desorption device for performing a desorption step.

[0014] 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.

[0015] Sodium fluoride (NaF) pellets, which have conventionally been used as an adsorbent for hydrogen fluoride (HF), are produced by tableting and heat-molding sodium fluoride powder (aggregates of sodium fluoride crystals). These pellets are molded under high tableting pressure and fired at high temperatures to reduce brittleness. Therefore, the specific surface area of ​​sodium fluoride pellets is small, resulting in a low hydrogen fluoride adsorption capacity. The present inventors conducted extensive research to solve the above-mentioned problems with sodium fluoride pellets, and by analyzing the interaction between sodium fluoride pellets and hydrogen fluoride, they arrived at the present disclosure. The details and results of the inventors' research are described below.

[0016] Fluorine gas containing 10% by volume of hydrogen fluoride was passed through a sodium fluoride-packed tower packed with sodium fluoride pellets, and the hydrogen fluoride concentration of the outlet gas discharged from the outlet of the sodium fluoride-packed tower was analyzed. A representative example of a curve plotting the change in hydrogen fluoride concentration of the outlet gas is shown in Figure 1. Details will be given later, but the behavior of hydrogen fluoride removal by sodium fluoride pellets will be explained with reference to Figure 1.

[0017] For a while after the fluorine gas containing hydrogen fluoride began to flow through the sodium fluoride-packed tower, the hydrogen fluoride concentration in the outlet gas was below the detection limit of the detection device, or even if it was detected, it was only a trace amount. Hereinafter, this region will be referred to as "Region I." When the fluorine gas containing hydrogen fluoride was further supplied to the sodium fluoride-packed tower, hydrogen fluoride began to be detected in the outlet gas, and the hydrogen fluoride concentration increased. This point corresponds to the first breakthrough point (the point at which a rapid increase in hydrogen fluoride is first observed in the time-dependent change in the breakthrough curve).

[0018] Although the hydrogen fluoride concentration of the outlet gas after the first breakthrough point increased, it was still much lower than the hydrogen fluoride concentration of the fluorine gas supplied to the sodium fluoride-packed column. The inventors have found that thereafter, a certain period of time continues during which the hydrogen fluoride concentration of the outlet gas does not increase. Hereinafter, this region will be referred to as "Region II" (see FIG. 1).

[0019] In adsorption using a general adsorbent (e.g., activated carbon), the breakthrough point occurs when the hydrogen fluoride concentration at the first breakthrough point begins to increase, and after the breakthrough, the hydrogen fluoride concentration continues to increase linearly until it reaches the hydrogen fluoride concentration of the fluorine gas supplied to the sodium fluoride-packed column. However, the present inventors have found that there is a region after the first breakthrough point where the increase in hydrogen fluoride concentration shows a gradual plateau curve.

[0020] When the supply of fluorine gas was continued after Region II, a second breakthrough point appeared (the point at which the hydrogen fluoride concentration in the outlet gas began to increase further in the time-dependent change in the breakthrough curve), and the hydrogen fluoride concentration in the outlet gas then continued to increase, reaching a value close to the hydrogen fluoride concentration in the fluorine gas supplied to the sodium fluoride-packed tower. Hereinafter, this region will be referred to as "Region III" (see Figure 1). Differences in the specific surface area, average pore size, and pore size distribution of the sodium fluoride pellets result in differences in the duration of Region I and Region II.

[0021] Although the mechanism is not clear, it is speculated that hydrogen fluoride is bound to the surface of the sodium fluoride crystals and that almost all of the hydrogen fluoride is fixed on the surface of the sodium fluoride crystals in Region I. Similarly, although the mechanism is not clear, it is speculated that hydrogen fluoride bound to the surface diffuses into the interior of the sodium fluoride crystals in Region II, forming a salt compound of hydrogen fluoride and sodium fluoride.

[0022] The method for removing hydrogen fluoride according to this embodiment is a method for removing hydrogen fluoride from a gas to be treated that contains hydrogen fluoride, and includes a first adsorption step of introducing the gas to be treated into a first adsorption treatment unit containing sodium fluoride, contacting the gas to be treated with the sodium fluoride in the first adsorption treatment unit, and causing the hydrogen fluoride in the gas to be treated to be adsorbed by the sodium fluoride in the first adsorption treatment unit to obtain a first adsorption-treated gas, which is a gas to be treated with a reduced hydrogen fluoride concentration, and a second adsorption step of introducing the first adsorption-treated gas into a second adsorption treatment unit containing sodium fluoride, contacting the first adsorption-treated gas with the sodium fluoride in the second adsorption treatment unit, and causing the hydrogen fluoride in the first adsorption-treated gas to be adsorbed by the sodium fluoride in the second adsorption treatment unit to obtain a second adsorption-treated gas, which is a first adsorption-treated gas with a reduced hydrogen fluoride concentration. The temperature of the sodium fluoride in the first adsorption treatment unit when contacting the gas to be treated in the first adsorption step is higher than the temperature of the sodium fluoride in the second adsorption treatment unit when contacting the first adsorption-treated gas in the second adsorption step.

[0023] In the first adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the gas to be treated introduced into the first adsorption treatment unit to the mass of sodium fluoride in the first adsorption treatment unit before adsorption is from 0.05 to 70 HF-mg / NaF-g / h. In the second adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the gas that has been first adsorbed and introduced into the second adsorption treatment unit to the mass of sodium fluoride in the second adsorption treatment unit before adsorption is from 0.001 to 5 HF-mg / NaF-g / h.

[0024] The first adsorption step will be described. As will be described in detail in Comparative Examples 1, 2, and 3 below, the amount of hydrogen fluoride that can be removed in Region I from fluorine gas containing 10% by volume of hydrogen fluoride at 30°C is 0.3% by mass of the mass of the sodium fluoride charged, and if the temperature during adsorption is increased, the amount of hydrogen fluoride that can be removed further decreases. With this amount of adsorption, the method of removing hydrogen fluoride using sodium fluoride cannot be used industrially.

[0025] Methods for increasing the amount of hydrogen fluoride adsorption include increasing the amount of sodium fluoride used and lowering the temperature of the sodium fluoride-packed tower. However, the present inventors have discovered a new method that does not use the above methods. That is, a method in which multiple sodium fluoride-packed towers are used, the temperature of sodium fluoride in the first sodium fluoride-packed tower is increased, and adsorption is performed in the first sodium fluoride-packed tower up to just before the second breakthrough point, and then the temperature of sodium fluoride in the second sodium fluoride-packed tower is lowered than that of the first tower. This method makes it possible to reduce the hydrogen fluoride concentration in the gas to be treated to 0.01 ppm by volume or more and 250 ppm by volume or less without drastically increasing the amount of sodium fluoride used. That is, the hydrogen fluoride concentration in the second adsorption-treated gas discharged from the second adsorption treatment unit can be reduced to 0.01 ppm by volume or more and 250 ppm by volume or less.

[0026] When sodium fluoride absorbs a large amount of hydrogen fluoride, the sodium fluoride pellets or granules may be bonded or pulverized. As a result of studies by the present inventors, it was found that bonding and pulverization can be suppressed by terminating the contact of hydrogen fluoride with sodium fluoride before the second breakthrough point is reached. In contrast, in region III after the second breakthrough point, bonding of sodium fluoride pellets or granules is likely to occur.

[0027] The type of gas to be treated from which hydrogen fluoride can be removed by the hydrogen fluoride removal method according to this embodiment is not particularly limited as long as it contains hydrogen fluoride and does not react with sodium fluoride, but it can be a gas of a fluorine-containing compound containing hydrogen fluoride. Examples of fluorine-containing compounds include fluorine gas (F), interhalogen compounds, tungsten hexafluoride (WF), silicon tetrafluoride (SiF), nitrogen trifluoride (NF), and sulfur tetrafluoride (SF). Examples of interhalogen compounds include chlorine monofluoride (ClF), chlorine trifluoride (ClF), chlorine pentafluoride (ClF), bromine trifluoride (BrF), bromine pentafluoride (BrF), bromine heptafluoride (BrF), iodine trifluoride (IF), iodine pentafluoride (IF), and iodine heptafluoride (IF).

[0028] That is, the gas to be treated may be a gas containing hydrogen fluoride and at least one of fluorine gas, chlorine monofluoride, chlorine trifluoride, chlorine pentafluoride, bromine trifluoride, bromine pentafluoride, bromine heptafluoride, iodine trifluoride, iodine pentafluoride, iodine heptafluoride, tungsten hexafluoride, silicon tetrafluoride, nitrogen trifluoride, and sulfur tetrafluoride. The hydrogen fluoride concentration in the gas to be treated is not particularly limited, but is preferably 20% by volume or less, and more preferably 3% by volume or more and 10% by volume or less.

[0029] The form of sodium fluoride used in the first adsorption treatment unit and the second adsorption treatment unit in the method for removing hydrogen fluoride according to this embodiment is not particularly limited, and examples thereof include granules, powder, and lumps. The shape of the sodium fluoride granules is not particularly limited, and examples thereof include columnar, spherical, oval-spherical, and plate-like shapes, with cylindrical pellets being preferred. The size of the sodium fluoride granules is not particularly limited, and cylindrical pellets may have a diameter of 2 mm to 10 mm and a height of 2 mm to 10 mm.

[0030] The sodium fluoride pellets may be commercially available products (for example, manufactured by Morita Chemical Co., Ltd.), or may be obtained by tableting sodium fluoride powder, forming it into tablets, and then firing it. That is, the sodium fluoride in the first adsorption treatment section and the sodium fluoride in the second adsorption treatment section may be obtained by tableting sodium fluoride powder.

[0031] The apparent density of one sodium fluoride granule (the mass of one sodium fluoride granule divided by the geometric volume) is not particularly limited, but is preferably 1.8 mL / g or more and 2.3 mL / g or less. If it is 1.8 mL / g or more and 2.3 mL / g or less, the crushing strength is high and powdering is difficult to occur, and in addition, there is no need to mold under high tableting pressure, so the productivity of the sodium fluoride granules is excellent.

[0032] The shape of the container of the first adsorption treatment unit used in the first adsorption step, i.e., the first-stage sodium fluoride packed tower, is not particularly limited, but may be a cylindrical container, for example, when filled with sodium fluoride granules. The diameter of the cylindrical container is not particularly limited, but is preferably large enough to accommodate 10 or more sodium fluoride granules in a cross section of the cylindrical container cut along a plane along the diameter of the cylinder, more preferably 20 or more, and even more preferably 40 or more. The height (length) of the cylindrical container is not particularly limited, but may be approximately the same as the diameter of the container, or may be several to several tens of times the diameter of the container.

[0033] The material forming the sodium fluoride packed tower is preferably one that is corrosion-resistant to the gas to be passed through (e.g., a fluorine-containing compound gas) and hydrogen fluoride, and specific examples include metals such as nickel (Ni), Hastelloy (trade name), Monel (trade name), stainless steel, copper (Cu), and mild steel.

[0034] The temperature of the sodium fluoride in the first adsorption treatment unit when contacting the gas to be treated in the first adsorption step is preferably 50°C or higher and 120°C or lower, with the lower limit more preferably 60°C or higher and the upper limit more preferably 100°C or lower. If the temperature is 50°C or higher, the amount of hydrogen fluoride adsorbed on the surface of the sodium fluoride is likely to be an appropriate amount, making it less likely that the contact areas between the sodium fluoride particles will melt and adhere to each other. Furthermore, if the temperature is 120°C or lower, a large amount of hydrogen fluoride is likely to be adsorbed before the second breakthrough point.

[0035] In the first adsorption step, the ratio of the mass of hydrogen fluoride in the gas to be treated introduced into the first adsorption treatment unit to the mass of sodium fluoride in the first adsorption treatment unit before adsorption is preferably 10 HF-mg / NaF-g or more and 100 HF-mg / NaF-g or less, with the lower limit being more preferably 20 HF-mg / NaF-g or more, and even more preferably 30 HF-mg / NaF-g or more, and the upper limit being more preferably 90 HF-mg / NaF-g or less, and even more preferably 80 HF-mg / NaF-g or less. If the ratio is 10 HF-mg / NaF-g or more and 100 HF-mg / NaF-g or less, not only does the hydrogen fluoride adsorption capacity increase, but also the phenomenon of melting and adhesion at contact points between sodium fluorides is less likely to occur.

[0036] Furthermore, in the first adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the gas to be treated introduced into the first adsorption treatment unit to the mass of sodium fluoride in the first adsorption treatment unit before adsorption is from 0.05 to 70 HF-mg / NaF-g / h, preferably from 0.05 to 60 HF-mg / NaF-g / h, and more preferably from 0.05 to 50 HF-mg / NaF-g / h. If the ratio is from 0.05 to 70 HF-mg / NaF-g / h, the amount of hydrogen fluoride absorbed by the second breakthrough point tends to be appropriate.

[0037] Furthermore, in the first adsorption step, the space velocity (hereinafter sometimes referred to as "SV") of the gas to be treated supplied to the first adsorption treatment unit is not particularly limited, but is preferably 10 ( / h) or more and 500 ( / h) or less, and more preferably 15 ( / h) or more and 300 ( / h) or less. If the SV is 10 ( / h) or more and 500 ( / h) or less, the amount of hydrogen fluoride absorbed up to the second breakthrough point tends to be appropriate. Furthermore, the pressure in the first adsorption step is not particularly limited, but it is preferable to carry out the step at a pressure close to atmospheric pressure. At atmospheric pressure, the SV of the gas to be treated supplied to the first adsorption treatment unit tends to be an appropriate value.

[0038] Furthermore, in the first adsorption step, the amount of hydrogen fluoride adsorbed onto sodium fluoride up to the second breakthrough point is preferably 2% by mass or more and 15% by mass or less, and more preferably 4% by mass or more and 11% by mass or less, of the mass of sodium fluoride in the first adsorption treatment unit before adsorption. If the amount is 2% by mass or more and 15% by mass or less, the hydrogen fluoride adsorption capacity increases, and the phenomenon of melting and adhesion at contact points between sodium fluoride particles is less likely to occur.

[0039] Next, the second adsorption step will be described. In the second adsorption step, hydrogen fluoride is adsorbed up to the first breakthrough point, and the hydrogen fluoride adsorption capacity is affected by the hydrogen fluoride concentration in the inlet gas of the sodium fluoride-packed tower in the second adsorption step (the gas to be treated, which is the gas that has been subjected to the first adsorption treatment and is supplied to the second adsorption treatment section).

[0040] With a general adsorbent, if we ignore deterioration of the adsorbent, etc., a fixed amount of adsorbate is adsorbed to a fixed number of adsorption sites, and therefore the amount of adsorbate that can be adsorbed is generally constant. In contrast, the present inventors have found that in the adsorption (absorption) of hydrogen fluoride onto sodium fluoride, the amount of hydrogen fluoride that can be adsorbed up to the first breakthrough point varies greatly depending on the hydrogen fluoride concentration in the gas phase.

[0041] As described in Example 6 below, the lower the hydrogen fluoride concentration in the gas to be treated supplied to the sodium fluoride-packed tower, the greater the amount of hydrogen fluoride adsorbed up to the first breakthrough point. This phenomenon is presumed to occur due to the balance between the rate at which hydrogen fluoride is adsorbed onto the surface of sodium fluoride (adsorption amount) and the rate at which hydrogen fluoride diffuses into the interior of the sodium fluoride crystals (diffusion amount).

[0042] The sodium fluoride used in the second adsorption treatment unit of the hydrogen fluoride removal method according to this embodiment is the same as the sodium fluoride used in the first adsorption treatment unit, and therefore a description thereof will be omitted.Furthermore, the second adsorption treatment unit used in the second adsorption step, i.e., the second-stage sodium fluoride-packed tower, is the same as the first adsorption treatment unit, i.e., the first-stage sodium fluoride-packed tower, and therefore a description thereof will be omitted.

[0043] The temperature of the sodium fluoride in the second adsorption treatment unit when contacting the first adsorption-treated gas in the second adsorption step is preferably −10° C. or higher and lower than 50° C., with the lower limit more preferably being 10° C. or higher and the upper limit more preferably being 30° C. or lower. If the temperature is −10° C. or higher, the amount of hydrogen fluoride adsorbed on the surface of the sodium fluoride tends to be appropriate, making it less likely that the contact points between the sodium fluoride particles will melt and adhere to each other. Furthermore, if the temperature is lower than 50° C., a larger amount of hydrogen fluoride will be adsorbed before the first breakthrough point.

[0044] In the second adsorption step, the ratio of the mass of hydrogen fluoride in the gas after the first adsorption treatment introduced into the second adsorption treatment unit to the mass of sodium fluoride in the second adsorption treatment unit before adsorption is preferably 100 HF-mg / NaF-g or less, more preferably 80 HF-mg / NaF-g or less, and even more preferably 50 HF-mg / NaF-g or less. If the ratio is 100 HF-mg / NaF-g or less, the phenomenon of melting and adhering at contact points between sodium fluorides is unlikely to occur.

[0045] In the second adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the first adsorption-treated gas introduced into the second adsorption treatment unit to the mass of sodium fluoride in the second adsorption treatment unit before adsorption is from 0.001 to 5 HF-mg / NaF-g / h, preferably from 0.001 to 4 HF-mg / NaF-g / h, and more preferably from 0.001 to 3 HF-mg / NaF-g / h. If the ratio is from 0.001 to 5 HF-mg / NaF-g / h, the amount of hydrogen fluoride absorbed up to the first breakthrough point tends to be appropriate.

[0046] Furthermore, in the second adsorption step, the space velocity of the first adsorption-treated gas supplied to the second adsorption treatment unit is not particularly limited, but is preferably 10 ( / h) or more and 500 ( / h) or less, and more preferably 15 ( / h) or more and 300 ( / h) or less. If the SV is 10 ( / h) or more and 500 ( / h) or less, the amount of hydrogen fluoride absorbed up to the first breakthrough point tends to be appropriate. Furthermore, the pressure in the second adsorption step is not particularly limited, but it is preferable to carry out the step at a pressure close to atmospheric pressure. At atmospheric pressure, the SV of the first adsorption-treated gas supplied to the second adsorption treatment unit tends to be an appropriate value.

[0047] Furthermore, in the second adsorption step, the amount of hydrogen fluoride adsorbed onto sodium fluoride up to the first breakthrough point is preferably 8% by mass or less, and more preferably 5% by mass or less, of the mass of sodium fluoride in the second adsorption treatment section before adsorption. If it is 8% by mass or less, the phenomenon of melting and adhesion at contact points between sodium fluoride particles is unlikely to occur.

[0048] Furthermore, the first breakthrough point in the second adsorption step can be detected by measuring the hydrogen fluoride that could not be adsorbed by sodium fluoride in the second adsorption treatment unit using a Fourier transform infrared spectrophotometer or the like. -1 The hydrogen fluoride concentration can be calculated from the peak.

[0049] By using two adsorption treatment units to perform the first adsorption step and then the second adsorption step, the following effects can be obtained, as will be seen from Example 6 and Comparative Example 2 described below. That is, in Comparative Example 2, the amount of hydrogen fluoride that can be adsorbed up to the first breakthrough point is 0.21 mass% of the mass of sodium fluoride. Even if the amount of sodium fluoride used is doubled (68 mL), 0.21 mass% can be removed, and the amount of hydrogen fluoride removed is 0.19 g / 68 mL-NaF.

[0050] In contrast, in Example 6, the amount of hydrogen fluoride that can be adsorbed in the first adsorption step up to the second breakthrough point is 5.9 mass% of the mass of sodium fluoride (2.6 g in terms of the mass of hydrogen fluoride), and by performing the second adsorption step using the same amount of sodium fluoride as in the first adsorption step, it is possible to make the hydrogen fluoride concentration in the outlet gas of the sodium fluoride-packed tower undetectable.

[0051] The amount of hydrogen fluoride removed in the second adsorption step is small and therefore can be ignored. The amount of hydrogen fluoride removed in the first and second adsorption steps is 2.6 g / 68 mL-NaF. Therefore, it can be seen that the amount of hydrogen fluoride removed is 15 times (2.6 / 0.17) greater than the amount of hydrogen fluoride removed up to the first breakthrough point.

[0052] The method for removing hydrogen fluoride according to this embodiment may further include a desorption step of heating at least one of the sodium fluoride in the first adsorption treatment unit used in the first adsorption step and the sodium fluoride in the second adsorption treatment unit used in the second adsorption step under a heat treatment atmosphere gas to desorb hydrogen fluoride from both the sodium fluoride in the first adsorption treatment unit and the sodium fluoride in the second adsorption treatment unit at a rate of 10 mg or less per gram of sodium fluoride before adsorption and 10 mg or less per minute, and an exchange step of exchanging at least one of the sodium fluoride in the first adsorption treatment unit used in the first adsorption step and the sodium fluoride in the second adsorption treatment unit used in the second adsorption step with the sodium fluoride from which hydrogen fluoride has been desorbed in the desorption step.

[0053] The sodium fluoride used in the first adsorption step or the second adsorption step can be reused in the first adsorption step or the second adsorption step after a regeneration treatment (desorption step) for dehydrofluorination. In order to continuously remove hydrogen fluoride from the gas to be treated, a spare sodium fluoride-packed tower may be installed so that the sodium fluoride-packed tower used in the first adsorption step and the sodium fluoride-packed tower used in the second adsorption step can be switched.

[0054] The sodium fluoride-packed towers used in each step may be installed in parallel. That is, two or more sodium fluoride-packed towers may be used in the first adsorption step, and two or more sodium fluoride-packed towers may be used in the second adsorption step. Alternatively, three sodium fluoride-packed towers may be used as a set, and one sodium fluoride-packed tower may be used in both the first adsorption step and the second adsorption step, and these may be operated in series.

[0055] The sodium fluoride-packed tower used in the first adsorption step or the second adsorption step may be replaced with a sodium fluoride-packed tower regenerated in the desorption step. This replacement operation is called the exchange step. The desorption step may be carried out in the sodium fluoride-packed tower used in the first adsorption step or the second adsorption step, or may be carried out in a separate location (e.g., a heat treatment device) after sodium fluoride is extracted from the sodium fluoride-packed tower.

[0056] The heat treatment in the desorption step can be carried out by heating sodium fluoride under a heat treatment atmospheric gas. When the desorption step is carried out in a sodium fluoride-packed tower, sodium fluoride may be heated while the heat treatment atmospheric gas is circulated through the sodium fluoride-packed tower. The type of the heat treatment atmospheric gas is not particularly limited, but may be at least one of nitrogen gas, helium, argon, oxygen gas, and air.

[0057] The heating temperature in the desorption step may be 150° C. or higher and 240° C. or lower, but is preferably 160° C. or higher and 220° C. or lower, and more preferably 180° C. or higher and 200° C. or lower. If the heating temperature is 150° C. or higher and 240° C. or lower, powdering of the sodium fluoride granules is unlikely to occur, and in addition, hydrogen fluoride can be desorbed in a short time, resulting in low energy costs.

[0058] The rate of temperature rise when raising the temperature to the above heating temperature in the desorption step is not particularly limited, but the temperature is preferably raised so that the desorption rate at which hydrogen fluoride adsorbed to sodium fluoride becomes gaseous hydrogen fluoride and is desorbed from sodium fluoride (or the vaporization rate of hydrogen fluoride) is 10 mg / min or less, and more preferably 3 mg / min or less, per 1 g of sodium fluoride adsorbing hydrogen fluoride.

[0059] In the desorption step, the extent to which hydrogen fluoride is desorbed from sodium fluoride is not particularly limited, but the desorption step is preferably carried out until the proportion of hydrogen fluoride in sodium fluoride becomes 0.1 mass % or less, more preferably 0.01 mass % or less, and even more preferably 0.001 mass % or less. However, it is most preferable to carry out the desorption of hydrogen fluoride until hydrogen fluoride no longer desorbs from sodium fluoride.

[0060] The end time of desorption of hydrogen fluoride can be detected as follows: The outlet gas discharged from the sodium fluoride packed tower is analyzed by a Fourier transform infrared spectrophotometer, and the absorption wavelength of hydrogen fluoride, 4038 cm -1 When the peak can no longer be detected, the desorption step is completed.

[0061] When the concentration of hydrogen fluoride in the outlet gas discharged from the sodium fluoride packed tower becomes equal to or less than a predetermined amount, the heating of the sodium fluoride packed tower is controlled to cool the temperature of the sodium fluoride to the adsorption temperature. The sodium fluoride cooled to the adsorption temperature can be reused as an adsorbent for hydrogen fluoride.

[0062] In the desorption step, the space velocity of the heat treatment atmosphere gas supplied to the sodium fluoride-packed tower is not particularly limited, but is preferably 200 ( / h) or more and 1000 ( / h) or less, and more preferably 500 ( / h) or more and 900 ( / h) or less. If the SV is 200 ( / h) or more and 1000 ( / h) or less, the desorption step can be completed in a short time, and the amount of heat treatment atmosphere gas used is small, making it economical. Furthermore, the pressure in the desorption step is not particularly limited, but it is preferably carried out at a pressure close to atmospheric pressure. At atmospheric pressure, the SV of the heat treatment atmosphere gas supplied to the sodium fluoride-packed tower is likely to be a suitable value.

[0063] According to the method for removing hydrogen fluoride of this embodiment, even if the gas to be treated has a high hydrogen fluoride concentration, it is possible to remove hydrogen fluoride from the gas to be treated using sodium fluoride until the hydrogen fluoride concentration becomes low. Furthermore, according to the method for removing hydrogen fluoride of this embodiment, it is possible to efficiently, stably, and continuously remove hydrogen fluoride from the gas to be treated. Furthermore, by using the method for removing hydrogen fluoride of this embodiment, it is possible to remove hydrogen fluoride, which is an impurity, from a gas of a fluorine-containing compound, and therefore it is possible to obtain a high-purity fluorine-containing compound that is useful as a gas used in the production of semiconductors.

[0064] The present disclosure will be described in more detail below with reference to examples and comparative examples. Example 1 A test was conducted to remove hydrogen fluoride from a hydrogen fluoride-containing gas to be treated using the hydrogen fluoride removal apparatus shown in Figure 2 and the desorption apparatus shown in Figure 3. First, the hydrogen fluoride removal apparatus shown in Figure 2 and the desorption apparatus shown in Figure 3 will be described.

[0065] The hydrogen fluoride removal apparatus shown in Fig. 2 is an apparatus that performs a first adsorption step and a second adsorption step. The desorption apparatus shown in Fig. 3 is an apparatus that performs a desorption step. More specifically, the hydrogen fluoride removal apparatus includes a hydrogen fluoride gas supply unit 1 that supplies hydrogen fluoride gas, a dilution gas supply unit 2 that supplies fluorine gas as a dilution gas for diluting the hydrogen fluoride gas, a hydrogen fluoride gas flow rate control device 3 that controls the flow rate of the hydrogen fluoride gas, a dilution gas flow rate control device 4 that controls the flow rate of the dilution gas, a cylindrical sodium fluoride-packed tower 5 packed with sodium fluoride granules (not shown), a temperature control unit 6 that controls the temperature of the sodium fluoride granules in the sodium fluoride-packed tower 5, a temperature measurement unit 7 that measures the temperature of the sodium fluoride granules in the sodium fluoride-packed tower 5, and an analysis unit that holds an outlet gas for analyzing the outlet gas that has passed through the sodium fluoride-packed tower 5 and been discharged from the exhaust port of the sodium fluoride-packed tower 5. the outlet gas in the analysis section 8; a Fourier transform infrared spectrophotometer 9 for performing infrared spectroscopic analysis of the outlet gas in the analysis section 8; a cylindrical sodium fluoride-packed tower 10 packed with sodium fluoride granules (not shown) for adsorbing hydrogen fluoride in the outlet gas that has passed through the analysis section 8 and been discharged from the exhaust port of the analysis section 8; a temperature control section 11 for controlling the temperature of the sodium fluoride granules in the sodium fluoride-packed tower 10; a temperature measurement section 12 for measuring the temperature of the sodium fluoride granules in the sodium fluoride-packed tower 10; an analysis section 13 for holding the outlet gas that has passed through the sodium fluoride-packed tower 10 and been discharged from the exhaust port of the sodium fluoride-packed tower 10 in order to analyze it; and a Fourier transform infrared spectrophotometer 14 for performing infrared spectroscopic analysis of the outlet gas in the analysis section 13.

[0066] The above-mentioned components of the hydrogen fluoride removal apparatus are connected to each other by piping, as shown in Figure 2. The hydrogen fluoride gas delivered from the hydrogen fluoride gas supply unit 1 and the fluorine gas delivered from the dilution gas supply unit 2 are mixed in the piping after their flow rates are controlled by the hydrogen fluoride gas flow rate control device 3 and the dilution gas flow rate control device 4, respectively.

[0067] A hydrogen fluoride-containing gas (gas to be treated), which is a mixed gas of hydrogen fluoride gas and fluorine gas, is sent through a pipe to the sodium fluoride-packed tower 5 and comes into contact with the sodium fluoride granules, whereby the hydrogen fluoride in the hydrogen fluoride-containing gas is adsorbed by the sodium fluoride granules. At this time, the temperature of the sodium fluoride granules in the sodium fluoride-packed tower 5 is measured by a temperature measuring unit 7 and controlled by a temperature control unit 6.

[0068] The outlet gas leaving the sodium fluoride packed tower 5 is sent via piping to an analysis unit 8, where it is subjected to infrared spectroscopic analysis by a Fourier transform infrared spectrophotometer 9, and the concentration of hydrogen fluoride is measured. The outlet gas leaving the analysis unit 8 is sent via piping to a sodium fluoride packed tower 10, where it comes into contact with sodium fluoride granules, and the hydrogen fluoride in the outlet gas of the sodium fluoride packed tower 5 is adsorbed by the sodium fluoride granules. At this time, the temperature of the sodium fluoride granules in the sodium fluoride packed tower 10 is measured by a temperature measurement unit 12 and controlled by a temperature control unit 11.

[0069] The outlet gas leaving the sodium fluoride packed tower 10 is sent via piping to an analysis section 13, where it is subjected to infrared spectroscopic analysis by a Fourier transform infrared spectrophotometer 14, and the concentration of hydrogen fluoride is measured. The outlet gas that has been subjected to infrared spectroscopic analysis is then discharged from the analysis section 13 to the outside of the hydrogen fluoride removal apparatus via piping.

[0070] The desorption apparatus also includes a heat treatment atmospheric gas supply unit 15 that supplies nitrogen gas as the heat treatment atmospheric gas, a heat treatment atmospheric gas flow rate control device 16 that controls the flow rate of the heat treatment atmospheric gas, a cylindrical sodium fluoride-packed tower 17 that is packed with sodium fluoride granules (not shown) that have been subjected to the first adsorption step or the second adsorption step and have adsorbed hydrogen fluoride, a temperature control unit 18 that controls the temperature of the sodium fluoride granules in the sodium fluoride-packed tower 17, a temperature measurement unit 19 that measures the temperature of the sodium fluoride granules in the sodium fluoride-packed tower 17, an analysis unit 20 that holds an outlet gas that has passed through the sodium fluoride-packed tower 17 and been discharged from an exhaust port of the sodium fluoride-packed tower 17 in order to analyze it, and a Fourier transform infrared spectrophotometer 21 that performs infrared spectroscopic analysis of the outlet gas in the analysis unit 20.

[0071] The above-mentioned components of the desorption apparatus are connected to each other by piping, as shown in Fig. 3. The heat treatment atmospheric gas sent from the heat treatment atmospheric gas supply unit 15 is sent through the piping to the sodium fluoride packed tower 17, and the sodium fluoride granules in the sodium fluoride packed tower 17 are heated in the heat treatment atmospheric gas. At this time, the temperature of the sodium fluoride granules in the sodium fluoride packed tower 17 is measured by a temperature measuring unit 19 and controlled by a temperature control unit 18.

[0072] The outlet gas leaving the sodium fluoride packed tower 17 is sent via piping to an analysis section 20, where it is subjected to infrared spectroscopic analysis by a Fourier transform infrared spectrophotometer 21, and the concentration of hydrogen fluoride is measured. The outlet gas that has been subjected to infrared spectroscopic analysis is then exhausted from the analysis section 20 to the outside of the desorption device via piping.

[0073] Next, the sodium fluoride granules will be described. The sodium fluoride granules are sodium fluoride pellets manufactured by Morita Chemical Co., Ltd., and have a cylindrical shape with a diameter of 3 mm and a height of 3 mm. The apparent density of one sodium fluoride pellet is 2.1 g / mL, and the packed bulk density is 1.3 g / mL. The specific surface area of ​​the sodium fluoride pellets was measured by mercury porosimetry and found to be 0.175 m2 Furthermore, the average pore diameter of the pores formed on the surface of the sodium fluoride pellets was measured by mercury intrusion porosimetry and was found to be 1.73 μm.

[0074] Next, the sodium fluoride packed tower 5, sodium fluoride packed tower 10, and sodium fluoride packed tower 17, which are filled with sodium fluoride pellets, will be described. The sodium fluoride packed tower 5 used in the first adsorption step, the sodium fluoride packed tower 10 used in the second adsorption step, and the sodium fluoride packed tower 17 used in the desorption step are all cylindrical members made of nickel and having an inner diameter of 38 mm, an outer diameter of 40 mm, and a length of 300 mm. The sodium fluoride packed tower 5, sodium fluoride packed tower 10, and sodium fluoride packed tower 17 are installed so that the longitudinal direction of the cylindrical members is along the vertical direction.

[0075] The sodium fluoride packed tower 5, the sodium fluoride packed tower 10, and the sodium fluoride packed tower 17 are filled with 44.2 g (volume 34 mL) of sodium fluoride pellets, but a nickel mesh is installed at the bottom of the cylindrical member, and by placing the sodium fluoride pellets on the nickel mesh, the sodium fluoride pellets are prevented from falling out of the cylindrical member.

[0076] Next, treatments (first and second adsorption steps) were carried out to adsorb hydrogen fluoride in a hydrogen fluoride-containing gas onto sodium fluoride pellets using the hydrogen fluoride removal apparatus shown in Figure 2. The temperature of the sodium fluoride pellets in sodium fluoride-packed tower 5 was adjusted to 60°C by temperature control unit 6. The temperature of the sodium fluoride pellets in sodium fluoride-packed tower 10 was adjusted to 20°C by temperature control unit 11.

[0077] Then, the hydrogen fluoride gas whose flow rate was adjusted by the hydrogen fluoride gas flow rate control device 3 and the fluorine gas whose flow rate was adjusted by the dilution gas flow rate control device 4 were mixed to prepare a hydrogen fluoride-containing gas, and this hydrogen fluoride-containing gas was supplied to the sodium fluoride-packed tower 5 via a pipe.

[0078] The hydrogen fluoride concentration of the hydrogen fluoride-containing gas supplied to the sodium fluoride-packed tower 5 was 10% by volume, and the SV of the hydrogen fluoride-containing gas was 265 / h. The ratio of the mass of hydrogen fluoride per unit time in the hydrogen fluoride-containing gas (gas to be treated) introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 18.2 HF-mg / NaF-g / h.

[0079] The entire amount of gas at the outlet of the sodium fluoride-packed tower 5 was sent to the analysis section 8 and analyzed by a Fourier transform infrared spectrophotometer 9. The change in the hydrogen fluoride concentration was tracked, and a peak (4038 cm) attributable to hydrogen fluoride appeared a few minutes after the start of the supply of the hydrogen fluoride-containing gas. -1 absorption wavelength) was detected.

[0080] The supply of hydrogen fluoride-containing gas to sodium fluoride-packed tower 5 was continued, and when the ratio of the mass of hydrogen fluoride in the hydrogen fluoride-containing gas introduced into sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption reached 58.34 HF-mg / NaF-g, the supply of hydrogen fluoride-containing gas was stopped. During the period from when the supply of hydrogen fluoride-containing gas to sodium fluoride-packed tower 5 was stopped until the supply was stopped, the hydrogen fluoride concentration in the outlet gas of sodium fluoride-packed tower 5 changed over time, rising to 270 ppm by volume after hydrogen fluoride was detected and then remaining at a substantially constant concentration.

[0081] The outlet gas leaving the analysis section 8 is supplied via piping to a sodium fluoride-packed tower 10. The hydrogen fluoride concentration of the outlet gas of the sodium fluoride-packed tower 5 supplied to the sodium fluoride-packed tower 10 is 270 ppm by volume, and the SV of the outlet gas of the sodium fluoride-packed tower 5 is 238 / h. The ratio of the mass of hydrogen fluoride per unit time in the outlet gas of the sodium fluoride-packed tower 5 introduced into the sodium fluoride-packed tower 10 to the mass of the sodium fluoride granules before adsorption is 0.04 HF-mg / NaF-g / h.

[0082] The supply of the outlet gas of the sodium fluoride packed tower 5 from the analysis section 8 to the sodium fluoride packed tower 10 was stopped when the ratio of the mass of hydrogen fluoride in the outlet gas of the sodium fluoride packed tower 5 introduced into the sodium fluoride packed tower 10 to the mass of the sodium fluoride granules before adsorption reached 0.14 HF-mg / NaF-g.

[0083] The entire amount of the outlet gas from the sodium fluoride packed tower 10 was sent to the analysis unit 13 and analyzed by a Fourier transform infrared spectrophotometer 14. The transition of the hydrogen fluoride concentration was tracked, and it was found that a peak (4038 cm) derived from hydrogen fluoride appeared from the start of supplying the outlet gas from the sodium fluoride packed tower 5 to the end of supplying it. -1 The hydrogen fluoride concentration in the outlet gas of the sodium fluoride packed tower 10 was not more than the lower detection limit of 0.1 ppm by volume.

[0084] As described above, hydrogen fluoride was removed from the hydrogen fluoride-containing gas using the hydrogen fluoride removal apparatus to obtain fluorine gas of Example 1. The hydrogen fluoride concentration in the fluorine gas obtained in Example 1 was 0.1 ppm by volume or less, which was about 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described below.

[0085] After the inside of the sodium fluoride packed tower 5 and the sodium fluoride packed tower 10 was thoroughly purged with nitrogen gas, sodium fluoride pellets were taken out of the sodium fluoride packed tower 5 and the sodium fluoride packed tower 10 and visually observed. As a result, there was no change in the appearance of the sodium fluoride pellets compared to before contact with hydrogen fluoride gas. In other words, there was no powdering of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets. The conditions for the first adsorption step and the second adsorption step are shown in Table 1, and the results are shown in Table 2.

[0086]

[0087]

[0088] Example 2 Hydrogen fluoride was removed in exactly the same manner as in Example 1, except that in the first adsorption step, the ratio of the mass of hydrogen fluoride in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 15.27 HF-mg / NaF-g, and in the second adsorption step, the ratio of the mass of hydrogen fluoride in the outlet gas of the sodium fluoride-packed tower 5 introduced into the sodium fluoride-packed tower 10 to the mass of the sodium fluoride granules before adsorption was 0.04 HF-mg / NaF-g.

[0089] The hydrogen fluoride concentration in the fluorine gas obtained in Example 2 was 0.1 ppm by volume or less, which was about 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described below. Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, there was no change in the appearance of the sodium fluoride pellets compared to before contact with hydrogen fluoride gas. That is, there was no pulverization of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0090] Example 3 Hydrogen fluoride was removed in exactly the same manner as in Example 1, except that the adsorption temperature in the second adsorption step was 40° C. The hydrogen fluoride concentration in the fluorine gas obtained in Example 3 was 0.1 ppm by volume or less, which was about 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described below.

[0091] Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, there was no change in the appearance of the sodium fluoride pellets compared to before contact with hydrogen fluoride gas. That is, there was no pulverization of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0092] Example 4 Hydrogen fluoride was removed in the same manner as in Example 1, except for the following differences in the first adsorption step and the second adsorption step: That is, in the first adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 1.2 HF-mg / NaF-g / h, the ratio of the mass of hydrogen fluoride in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 65.12 HF-mg / NaF-g, and the SV of the hydrogen fluoride-containing gas was 17.6 / h, which were different from Example 1.

[0093] In addition, in the second adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the outlet gas of the sodium fluoride-packed tower 5 introduced into the sodium fluoride-packed tower 10 to the mass of the sodium fluoride granules before adsorption is 0.003 HF-mg / NaF-g / h, the ratio of the mass of hydrogen fluoride in the outlet gas of the sodium fluoride-packed tower 5 introduced into the sodium fluoride-packed tower 10 to the mass of the sodium fluoride granules before adsorption is 0.16 HF-mg / NaF-g, and the SV of the outlet gas of the sodium fluoride-packed tower 5 is 15.9 / h, which are different from those in Example 1.

[0094] The hydrogen fluoride concentration in the fluorine gas obtained in Example 4 was 0.1 ppm by volume or less, which was about 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described below. Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, there was no change in the appearance of the sodium fluoride pellets compared to before contact with hydrogen fluoride gas. That is, there was no pulverization of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0095] Example 5 In the first adsorption step and the second adsorption step, hydrogen fluoride was removed in exactly the same manner as in Example 1, except for the following differences: In the first adsorption step, the adsorption temperature was 100°C, and the ratio of the mass of hydrogen fluoride in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 48.6 HF-mg / NaF-g, which were different from Example 1.

[0096] In addition, in the second adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the outlet gas of sodium fluoride packed tower 5 introduced into sodium fluoride packed tower 10 to the mass of sodium fluoride granules before adsorption is 0.57 HF-mg / NaF-g / h, the ratio of the mass of hydrogen fluoride in the outlet gas of sodium fluoride packed tower 5 introduced into sodium fluoride packed tower 10 to the mass of sodium fluoride granules before adsorption is 1.49 HF-mg / NaF-g, and the SV of the outlet gas of sodium fluoride packed tower 5 is 239 / h, which are different from Example 1.

[0097] The hydrogen fluoride concentration in the fluorine gas obtained in Example 5 was 0.1 ppm by volume or less, which was about 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described below. Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, there was no change in the appearance of the sodium fluoride pellets compared to before contact with hydrogen fluoride gas. That is, there was no pulverization of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0098] Example 6 Hydrogen fluoride was removed in the same manner as in Example 1, except for the following differences in the first adsorption step and the second adsorption step: That is, in the first adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 9.1 HF-mg / NaF-g / h, the ratio of the mass of hydrogen fluoride in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 61.89 HF-mg / NaF-g, and the hydrogen fluoride concentration of the hydrogen fluoride-containing gas supplied to the sodium fluoride-packed tower 5 was 5% by volume, which were different from Example 1.

[0099] The second adsorption step differs from Example 1 in that the adsorption temperature is -5°C, the ratio of the mass of hydrogen fluoride per unit time in the outlet gas of sodium fluoride packed tower 5 introduced into sodium fluoride packed tower 10 to the mass of sodium fluoride granules before adsorption is 0.05 HF-mg / NaF-g / h, the ratio of the mass of hydrogen fluoride in the outlet gas of sodium fluoride packed tower 5 introduced into sodium fluoride packed tower 10 to the mass of sodium fluoride granules before adsorption is 0.32 HF-mg / NaF-g, and the SV of the outlet gas of sodium fluoride packed tower 5 is 252 / h.

[0100] The hydrogen fluoride concentration in the fluorine gas obtained in Example 6 was 0.1 ppm by volume or less, which was about 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described below. Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, there was no change in the appearance of the sodium fluoride pellets compared to before contact with hydrogen fluoride gas. That is, there was no pulverization of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0101] Example 7 Hydrogen fluoride was removed in the same manner as in Example 1, except for the following differences in the first adsorption step and the second adsorption step: That is, in the first adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 60.6 HF-mg / NaF-g / h, the ratio of the mass of hydrogen fluoride in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 50.48 HF-mg / NaF-g, and the SV of the hydrogen fluoride-containing gas supplied to the sodium fluoride-packed tower 5 was 490 / h, which were different from Example 1.

[0102] In addition, in the second adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the outlet gas of sodium fluoride packed tower 5 introduced into sodium fluoride packed tower 10 to the mass of sodium fluoride granules before adsorption is 0.07 HF-mg / NaF-g / h, the ratio of the mass of hydrogen fluoride in the outlet gas of sodium fluoride packed tower 5 introduced into sodium fluoride packed tower 10 to the mass of sodium fluoride granules before adsorption is 0.06 HF-mg / NaF-g, and the SV of the outlet gas of sodium fluoride packed tower 5 is 402 / h, which are different from those in Example 1.

[0103] The hydrogen fluoride concentration in the fluorine gas obtained in Example 7 was 0.1 ppm by volume or less, which was about 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described below. Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, there was no change in the appearance of the sodium fluoride pellets compared to before contact with hydrogen fluoride gas. That is, there was no pulverization of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0104] Example 8 Hydrogen fluoride was removed in the same manner as in Example 1, except for the following differences in the first adsorption step and the second adsorption step: that is, the adsorption temperature was 115°C, the ratio of the mass of hydrogen fluoride per unit time in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 33.9 HF-mg / NaF-g / h, the ratio of the mass of hydrogen fluoride in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 44.18 HF-mg / NaF-g, and the SV of the hydrogen fluoride-containing gas supplied to the sodium fluoride-packed tower 5 was 494 / h.

[0105] In addition, in the second adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the outlet gas of sodium fluoride packed tower 5 introduced into sodium fluoride packed tower 10 to the mass of sodium fluoride granules before adsorption is 4.02 HF-mg / NaF-g / h, the ratio of the mass of hydrogen fluoride in the outlet gas of sodium fluoride packed tower 5 introduced into sodium fluoride packed tower 10 to the mass of sodium fluoride granules before adsorption is 4.68 HF-mg / NaF-g, the hydrogen fluoride concentration of the outlet gas of sodium fluoride packed tower 5 is 13,000 ppm by volume, and the SV of the outlet gas of sodium fluoride packed tower 5 is 451 / h, which are different from Example 1.

[0106] The hydrogen fluoride concentration in the fluorine gas obtained in Example 8 was 0.1 ppm by volume or less, which was about 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described below. Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, there was no change in the appearance of the sodium fluoride pellets compared to before contact with hydrogen fluoride gas. That is, there was no pulverization of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0107] Example 9 The first and second adsorption steps were carried out in exactly the same manner as in Example 1 to remove hydrogen fluoride from the hydrogen fluoride-containing gas, and then the desorption step was carried out to desorb hydrogen fluoride from the sodium fluoride pellets. That is, after the first and second adsorption steps were completed, the sodium fluoride pellets in the sodium fluoride-packed towers 5 and 10 were heated by the temperature control unit 18 while a heat treatment atmosphere gas was supplied from the heat treatment atmosphere gas supply unit 15 to the sodium fluoride-packed towers 5 and 10, thereby carrying out the desorption step. The heat treatment atmosphere gas was nitrogen gas, and the flow rate was adjusted to 450 NmL / min by the heat treatment atmosphere gas flow control unit 16. The temperature of the sodium fluoride pellets during the desorption step (desorption temperature) was 200°C. The conditions for the desorption step are shown in Table 1, and the results are shown in Table 2.

[0108] The desorption step may be carried out by transferring sodium fluoride pellets from the sodium fluoride-packed tower 5 and the sodium fluoride-packed tower 10 after the first adsorption step and the second adsorption step have been completed to another sodium fluoride-packed tower 17 (sodium fluoride-packed tower 17 for the desorption step). Therefore, in Fig. 3, for the sake of convenience of explanation, the sodium fluoride-packed tower for the desorption step is denoted by the reference numeral 17, but in Example 9, the sodium fluoride-packed tower 5 and the sodium fluoride-packed tower 10 for the first adsorption step and the second adsorption step were used as the sodium fluoride-packed tower 17 for the desorption step, as they were, to carry out the desorption step.

[0109] As in the case of the sodium fluoride packed tower 17, with regard to the temperature control unit 18, the temperature measurement unit 19, the analysis unit 20, and the Fourier transform infrared spectrophotometer 21 in FIG. 3 , in Example 9, the temperature control units 6 and 11, the temperature measurement units 7 and 12, the analysis units 8 and 13, and the Fourier transform infrared spectrophotometers 9 and 14 used in the first adsorption step and the second adsorption step were used as they were in the desorption step.

[0110] During the desorption step, the outlet gas from sodium fluoride-packed tower 5 was sent to analysis unit 8 and analyzed by Fourier transform infrared spectrophotometer 9, and the hydrogen fluoride concentration was measured, finding a maximum of 8.7% by volume. Since the flow rate of the heat treatment atmospheric gas was 450 NmL / min, hydrogen fluoride was desorbed at a rate of approximately 39 NmL / min, which corresponds to a mass rate of 35 mg / min.

[0111] Since the mass of the sodium fluoride pellets was 44.2 g, the desorption rate of hydrogen fluoride was 0.79 mg / min per 1 g of sodium fluoride pellets. In sodium fluoride-packed tower 10, hydrogen fluoride was desorbed under the same conditions as in sodium fluoride-packed tower 5. After the first adsorption step, second adsorption step, and desorption step were each carried out once in this manner, the temperature of the sodium fluoride pellets was brought to the adsorption temperature, and the same hydrogen fluoride adsorption operation as in the first adsorption step and second adsorption step was carried out again to obtain fluorine gas.

[0112] The hydrogen fluoride concentration in the fluorine gas thus obtained was 0.1 ppm by volume or less, which was about 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described below. Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, there was no change in the appearance of the sodium fluoride pellets compared to before contact with hydrogen fluoride gas. That is, there was no pulverization of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0113] (Example 10) Except that the desorption temperature in the sodium fluoride-packed tower 5 and the sodium fluoride-packed tower 10 in the desorption step was 150°C, the first adsorption step, the second adsorption step, and the desorption step were each carried out once in exactly the same manner as in Example 9, and then the hydrogen fluoride adsorption operation was carried out again in exactly the same manner as in Example 9. The hydrogen fluoride concentration in the fluorine gas thus obtained was 0.1 ppm by volume or less, which was about 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described later.

[0114] Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, it was found that the sodium fluoride pellets in the sodium fluoride packed tower 5 were pulverized, cracked, and bonded together. More specifically, the sodium fluoride pellets arranged in the vicinity of the inlet for the hydrogen fluoride-containing gas inside the sodium fluoride packed tower 5 (within a range of about 1 / 3 of the length of the sodium fluoride packed tower 5 in the central axis direction) were pulverized, cracked, and bonded together. In the sodium fluoride packed tower 5 in parts other than the vicinity of the inlet, no bonding between the sodium fluoride pellets occurred.

[0115] The appearance of the sodium fluoride pellets in the sodium fluoride packed tower 10 did not change compared to before contact with hydrogen fluoride gas. That is, there was no powdering of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0116] (Example 11) Except that the desorption temperature in the sodium fluoride-packed tower 5 and the sodium fluoride-packed tower 10 in the desorption step was 230°C, the first adsorption step, the second adsorption step, and the desorption step were each carried out once in exactly the same manner as in Example 9, and then the hydrogen fluoride adsorption operation was carried out again in exactly the same manner as in Example 9. The hydrogen fluoride concentration in the fluorine gas thus obtained was 0.1 ppm by volume or less, which was about 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described below.

[0117] Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, it was found that the sodium fluoride pellets in the sodium fluoride packed tower 5 were pulverized, cracked, and bonded together. More specifically, the sodium fluoride pellets arranged in the vicinity of the inlet for the hydrogen fluoride-containing gas inside the sodium fluoride packed tower 5 (within a range of about 1 / 3 of the length of the sodium fluoride packed tower 5 in the central axis direction) were pulverized, cracked, and bonded together. In the sodium fluoride packed tower 5 in parts other than the vicinity of the inlet, no bonding between the sodium fluoride pellets occurred.

[0118] The appearance of the sodium fluoride pellets in the sodium fluoride packed tower 10 did not change compared to before contact with hydrogen fluoride gas. That is, there was no powdering of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0119] In Example 9, the first adsorption step, the second adsorption step, and the desorption step were each carried out once, and then the hydrogen fluoride adsorption operation was carried out again to obtain fluorine gas, but in Example 12, 40 cycles were repeated, with one cycle consisting of one cycle of the first adsorption step, the second adsorption step, and the desorption step, and then the hydrogen fluoride adsorption operation was carried out again to obtain fluorine gas. Except for the fact that 40 cycles were repeated, the process was exactly the same as Example 9. The hydrogen fluoride concentration in the fluorine gas obtained in this manner was 0.1 ppm by volume or less, which was about 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described below.

[0120] Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, it was found that the sodium fluoride pellets in the sodium fluoride packed tower 5 were pulverized, cracked, and bonded together. More specifically, the sodium fluoride pellets arranged in the vicinity of the inlet for the hydrogen fluoride-containing gas inside the sodium fluoride packed tower 5 (within a range of about 1 / 3 of the length of the sodium fluoride packed tower 5 in the central axis direction) were pulverized, cracked, and bonded together. In the sodium fluoride packed tower 5 in parts other than the vicinity of the inlet, no bonding between the sodium fluoride pellets occurred.

[0121] The appearance of the sodium fluoride pellets in the sodium fluoride packed tower 10 did not change compared to before contact with hydrogen fluoride gas. That is, there was no powdering of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0122] (Example 13) The specific surface area of ​​the sodium fluoride pellets used was 1.5 m 2 / g, the same desorption step as in Example 9 was performed only on the sodium fluoride pellets in the sodium fluoride packed tower 5, and the desorption step was not performed on the sodium fluoride pellets in the sodium fluoride packed tower 10, the first adsorption step and the desorption step were repeatedly performed 60 times on the sodium fluoride pellets in the sodium fluoride packed tower 5, and the ratio of the mass of hydrogen fluoride in the outlet gas of the sodium fluoride packed tower 5 introduced into the sodium fluoride packed tower 10 to the mass of the sodium fluoride granules before adsorption in the second adsorption step was 89.37 HF-mg / NaF-g, and then the hydrogen fluoride adsorption operation was carried out again in the same manner as in Example 9.

[0123] The hydrogen fluoride concentration in the fluorine gas obtained in this manner was 0.1 volume ppm or less, which was about 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described below. Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, the sodium fluoride pellets in the sodium fluoride-packed tower 5 were found to have pulverized, cracked, and bonded together. More specifically, the sodium fluoride pellets arranged in the vicinity of the inlet for the hydrogen fluoride-containing gas inside the sodium fluoride-packed tower 5 (within a range of about 1 / 3 of the length in the central axis direction of the sodium fluoride-packed tower 5) were found to have pulverized, cracked, and bonded together. In the sodium fluoride-packed tower 5 in any portion other than the vicinity of the inlet, the sodium fluoride pellets were not bonded together.

[0124] The appearance of the sodium fluoride pellets in the sodium fluoride packed tower 10 did not change compared to before contact with hydrogen fluoride gas. That is, there was no powdering of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0125] Example 14 Except for using chlorine trifluoride instead of fluorine gas as the diluent gas for diluting hydrogen fluoride gas, hydrogen fluoride was removed in exactly the same manner as in Example 1. The hydrogen fluoride concentration in the chlorine trifluoride thus obtained was 0.1 ppm by volume or less, which was approximately 1 / 2700 or less of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described below.

[0126] Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, there was no change in the appearance of the sodium fluoride pellets compared to before contact with hydrogen fluoride gas. That is, there was no pulverization of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0127] Example 15 The first adsorption step, the second adsorption step, and the desorption step were each carried out 40 times in exactly the same manner as in Example 12, except that in the desorption step, the desorption temperature in the sodium fluoride-packed tower 5 and the sodium fluoride-packed tower 10 was 250°C and the flow rate of the heat treatment atmospheric gas to the sodium fluoride-packed tower 5 was 1000 NmL / min. Thereafter, the hydrogen fluoride adsorption operation was again carried out in exactly the same manner as in Example 9.

[0128] The hydrogen fluoride concentration in the fluorine gas thus obtained was not more than 0.1 ppm by volume, which was not more than about 1 / 2700 of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1 described later. However, when the first adsorption step, the second adsorption step, and the desorption step had been repeatedly performed 30 times, the pressure inside the sodium fluoride-packed tower 5 began to increase rapidly, and the outlet gas no longer flowed out of the sodium fluoride-packed tower 5.

[0129] Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, it was found that the sodium fluoride pellets in the sodium fluoride packed tower 5 had pulverized and cracked. It is believed that if the desorption rate of hydrogen fluoride is fast, the hydrogen fluoride adsorbed on the pellet surface will suddenly vaporize, making the pulverization and cracking more likely to occur. As a result, it is believed that clogging occurred, causing the gas flow path to become blocked.

[0130] Comparative Example 1 Except for the fact that the second adsorption step was not carried out and that hydrogen fluoride was removed only in the first adsorption step, hydrogen fluoride was removed in exactly the same manner as in Example 1. The hydrogen fluoride concentration in the fluorine gas thus obtained was 270 ppm by volume.

[0131] Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, there was no change in the appearance of the sodium fluoride pellets compared to before contact with hydrogen fluoride gas. That is, there was no pulverization of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0132] Comparative Example 2 Hydrogen fluoride was removed in exactly the same manner as in Comparative Example 1, except that the adsorption temperature was 80° C. The hydrogen fluoride concentration in the fluorine gas thus obtained was 1500 ppm by volume.

[0133] Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, there was no change in the appearance of the sodium fluoride pellets compared to before contact with hydrogen fluoride gas. That is, there was no pulverization of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0134] Comparative Example 3 Hydrogen fluoride was removed in exactly the same manner as in Comparative Example 1, except that the adsorption temperature was 100° C. The hydrogen fluoride concentration in the fluorine gas thus obtained was 3,500 ppm by volume.

[0135] Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, there was no change in the appearance of the sodium fluoride pellets compared to before contact with hydrogen fluoride gas. That is, there was no pulverization of the sodium fluoride pellets, no cracking of the sodium fluoride pellets, and no bonding between the sodium fluoride pellets.

[0136] Comparative Example 4 Hydrogen fluoride was removed in the same manner as in Example 1, except for the following differences in the first adsorption step and the second adsorption step: That is, in the first adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 0.03 HF-mg / NaF-g / h, the ratio of the mass of hydrogen fluoride in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 58.97 HF-mg / NaF-g, the hydrogen fluoride concentration of the hydrogen fluoride-containing gas supplied to the sodium fluoride-packed tower 5 was 2% by volume, and the SV of the hydrogen fluoride-containing gas supplied to the sodium fluoride-packed tower 5 was 2 / h.

[0137] In addition, in the second adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the outlet gas of the sodium fluoride-packed tower 5 introduced into the sodium fluoride-packed tower 10 to the mass of the sodium fluoride granules before adsorption is 0.0004 HF-mg / NaF-g / h, the ratio of the mass of hydrogen fluoride in the outlet gas of the sodium fluoride-packed tower 5 introduced into the sodium fluoride-packed tower 10 to the mass of the sodium fluoride granules before adsorption is 0.77 HF-mg / NaF-g, and the SV of the outlet gas of the sodium fluoride-packed tower 5 is 2 / h, which are different from those in Example 1.

[0138] The hydrogen fluoride concentration in the fluorine gas thus obtained was not more than 0.1 ppm by volume, which was not more than about 1 / 2700 of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1. However, when the amount of hydrogen fluoride adsorbed on the sodium fluoride pellets in the sodium fluoride-packed tower 5 reached approximately 5.5 mass % of the mass of sodium fluoride, the pressure inside the sodium fluoride-packed tower 5 began to increase rapidly, and the outlet gas no longer flowed out from the sodium fluoride-packed tower 5.

[0139] Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, it was found that the sodium fluoride pellets in the sodium fluoride packed tower 5 were pulverized and the pellets were bonded together. More specifically, the sodium fluoride pellets arranged in the vicinity of the inlet for the hydrogen fluoride-containing gas inside the sodium fluoride packed tower 5 (within a range of about 1 / 3 of the length in the central axis direction of the sodium fluoride packed tower 5) were pulverized and the pellets were bonded together. In the sodium fluoride packed tower 5 in the portions other than the vicinity of the inlet, the sodium fluoride pellets were not bonded together.

[0140] When the flow rate of the hydrogen fluoride-containing gas is low, the supply rate of the hydrogen fluoride also becomes low, which is thought to make it easier for hydrogen fluoride to be adsorbed onto the sodium fluoride pellets arranged in the part of the sodium fluoride-packed tower 5 nearest the inlet for the hydrogen fluoride-containing gas. As a result, the sodium fluoride pellets arranged in the part nearest the inlet for the hydrogen fluoride-containing gas adsorb a large amount of hydrogen fluoride, which is thought to cause pulverization and bonding, resulting in clogging and blocking of the gas flow path.

[0141] Comparative Example 5 Hydrogen fluoride was removed in the same manner as in Example 1, except for the following differences in the first adsorption step and the second adsorption step: That is, in the first adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 90.9 HF-mg / NaF-g / h, the ratio of the mass of hydrogen fluoride in the hydrogen fluoride-containing gas introduced into the sodium fluoride-packed tower 5 to the mass of the sodium fluoride granules before adsorption was 58.25 HF-mg / NaF-g, the hydrogen fluoride concentration of the hydrogen fluoride-containing gas supplied to the sodium fluoride-packed tower 5 was 25% by volume, and the SV of the hydrogen fluoride-containing gas supplied to the sodium fluoride-packed tower 5 was 529 / h.

[0142] In addition, in the second adsorption step, the ratio of the mass of hydrogen fluoride per unit time in the outlet gas of sodium fluoride packed tower 5 introduced into sodium fluoride packed tower 10 to the mass of sodium fluoride granules before adsorption is 0.07 HF-mg / NaF-g / h, the ratio of the mass of hydrogen fluoride in the outlet gas of sodium fluoride packed tower 5 introduced into sodium fluoride packed tower 10 to the mass of sodium fluoride granules before adsorption is 0.05 HF-mg / NaF-g, and the SV of the outlet gas of sodium fluoride packed tower 5 is 397 / h, which are different from those in Example 1.

[0143] The hydrogen fluoride concentration in the fluorine gas thus obtained was not more than 0.1 ppm by volume, which was not more than about 1 / 2700 of the hydrogen fluoride concentration in the fluorine gas obtained in Comparative Example 1. However, when the amount of hydrogen fluoride adsorbed on the sodium fluoride pellets in the sodium fluoride-packed tower 5 reached approximately 5.5 mass % of the mass of sodium fluoride, the pressure inside the sodium fluoride-packed tower 5 began to increase rapidly, and the outlet gas no longer flowed out from the sodium fluoride-packed tower 5.

[0144] Furthermore, when the sodium fluoride pellets were observed in the same manner as in Example 1, it was found that the sodium fluoride pellets in the sodium fluoride packed tower 5 were bonded together. More specifically, the sodium fluoride pellets arranged in the vicinity of the inlet for the hydrogen fluoride-containing gas inside the sodium fluoride packed tower 5 (within a range of about ⅓ of the length of the sodium fluoride packed tower 5 in the central axis direction) were bonded together. In the sodium fluoride packed tower 5 in parts other than the vicinity of the inlet, the sodium fluoride pellets were not bonded together.

[0145] When the flow rate of the hydrogen fluoride-containing gas is low, the supply rate of the hydrogen fluoride also becomes low, which is thought to make it easier for hydrogen fluoride to be adsorbed onto the sodium fluoride pellets arranged in the part of the sodium fluoride-packed tower 5 nearest the inlet for the hydrogen fluoride-containing gas. As a result, the sodium fluoride pellets arranged in the part nearest the inlet for the hydrogen fluoride-containing gas adsorb a large amount of hydrogen fluoride, which is thought to cause pulverization and bonding, resulting in clogging and blocking of the gas flow path.

[0146] 1... Hydrogen fluoride gas supply section 2... Dilution gas supply section 5... Sodium fluoride packed tower 10... Sodium fluoride packed tower 15... Heat treatment atmosphere gas supply section 17... Sodium fluoride packed tower

Claims

1. A method for removing hydrogen fluoride from a gas to be treated that contains hydrogen fluoride, comprising: a first adsorption step of introducing the gas to be treated into a first adsorption treatment section comprising sodium fluoride, bringing the gas to be treated into contact with the sodium fluoride in the first adsorption treatment section, and causing the hydrogen fluoride in the gas to be treated to be adsorbed by the sodium fluoride in the first adsorption treatment section, thereby obtaining a first adsorption-treated gas, which is the gas to be treated with a reduced hydrogen fluoride concentration; and a second adsorption step of introducing the first adsorption-treated gas into a second adsorption treatment section comprising sodium fluoride, bringing the first adsorption-treated gas into contact with the sodium fluoride in the second adsorption treatment section, and causing the hydrogen fluoride in the first adsorption-treated gas to be adsorbed by the sodium fluoride in the second adsorption treatment section, thereby obtaining a second adsorption-treated gas, which is the first adsorption-treated gas with a reduced hydrogen fluoride concentration, a temperature of the sodium fluoride in the first adsorption treatment unit when the gas to be treated is contacted in the first adsorption step is higher than a temperature of the sodium fluoride in the second adsorption treatment unit when the first adsorption-treated gas is contacted in the second adsorption step; in the first adsorption step, a ratio of the mass of the hydrogen fluoride per unit time in the gas to be treated introduced into the first adsorption treatment unit to the mass of the sodium fluoride in the first adsorption treatment unit before adsorption is 0.05 HF-mg / NaF-g / h or more and 70 HF-mg / NaF-g / h or less; and in the second adsorption step, a ratio of the mass of the hydrogen fluoride per unit time in the first adsorption-treated gas introduced into the second adsorption treatment unit to the mass of the sodium fluoride in the second adsorption treatment unit before adsorption is 0.001 HF-mg / NaF-g / h or more and 5 HF-mg / NaF-g / h or less.

2. A method for removing hydrogen fluoride as set forth in claim 1, further comprising: a desorption step of heating at least one of the sodium fluoride of the first adsorption processing unit used in the first adsorption step and the sodium fluoride of the second adsorption processing unit used in the second adsorption step under a heat treatment atmosphere gas, and desorbing hydrogen fluoride from both the sodium fluoride of the first adsorption processing unit and the sodium fluoride of the second adsorption processing unit at a rate of 10 mg or less per gram of sodium fluoride before adsorption and 10 mg or less per minute; and an exchange step of exchanging at least one of the sodium fluoride of the first adsorption processing unit used in the first adsorption step and the sodium fluoride of the second adsorption processing unit used in the second adsorption step with sodium fluoride from which hydrogen fluoride has been desorbed in the desorption step.

3. A method for removing hydrogen fluoride as described in claim 1 or 2, wherein the temperature of the sodium fluoride in the first adsorption treatment unit when contacting the gas to be treated in the first adsorption step is 50°C or higher and 120°C or lower.

4. A method for removing hydrogen fluoride according to claim 1 or 2, wherein the temperature of the sodium fluoride in the second adsorption treatment unit when contacting the first adsorption-treated gas in the second adsorption step is -10°C or higher and lower than 50°C.

5. A method for removing hydrogen fluoride as described in claim 1 or 2, wherein in the first adsorption step, the ratio of the mass of hydrogen fluoride in the gas to be treated introduced into the first adsorption treatment unit to the mass of sodium fluoride in the first adsorption treatment unit before adsorption is 10 HF-mg / NaF-g or more and 100 HF-mg / NaF-g or less.

6. A method for removing hydrogen fluoride as described in claim 1 or claim 2, wherein in the second adsorption step, the ratio of the mass of hydrogen fluoride in the first adsorption treated gas introduced into the second adsorption treatment unit to the mass of sodium fluoride in the second adsorption treatment unit before adsorption is 100 HF-mg / NaF-g or less.

7. A method for removing hydrogen fluoride according to claim 2, wherein the heating temperature in the desorption step is 150°C or higher and 240°C or lower.

8. The method for removing hydrogen fluoride according to claim 2 or claim 7, wherein the heat treatment atmospheric gas is at least one of nitrogen gas, helium, argon, oxygen gas, and air.

9. A method for removing hydrogen fluoride according to claim 1 or 2, wherein the hydrogen fluoride concentration in the second adsorption treated gas discharged from the second adsorption treatment unit is 0.01 ppm by volume or more and 250 ppm by volume or less.

10. A method for removing hydrogen fluoride as set forth in claim 1 or 2, wherein the gas to be treated contains hydrogen fluoride and at least one of fluorine gas, chlorine monofluoride, chlorine trifluoride, chlorine pentafluoride, bromine trifluoride, bromine pentafluoride, bromine heptafluoride, iodine trifluoride, iodine pentafluoride, iodine heptafluoride, tungsten hexafluoride, silicon tetrafluoride, nitrogen trifluoride, and sulfur tetrafluoride.

11. A method for removing hydrogen fluoride as described in claim 1 or claim 2, wherein the sodium fluoride in the first adsorption treatment unit and the sodium fluoride in the second adsorption treatment unit are formed by compressing sodium fluoride powder into tablets.

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