JPH0999216A - Harmful gas purifying agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a purifying agent capable of efficiently removing fluorine- contg. gases such as tungsten hexafluoride, hydrogen fluoride, fluorine, boron trifluoride and silicon tetrafluoride contained in waste gas discharged from a semiconductor producing process. SOLUTION: Strontium hydroxide as a base is molded with an org. binder as a molding agent and hydroxide of an alkaline earth metal other than strontium as a molding aid to obtain the objective purifying agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toxic gas purifying agent, and more specifically, it is mainly used in semiconductor manufacturing processes such as hydrogen fluoride, fluorine, tungsten hexafluoride, silicon tetrafluoride, and boron trifluoride. The present invention relates to a purifying agent used for purifying harmful gases discharged after being used, particularly fluorine-based gas containing fluorine atoms.

In recent years, with the development of the semiconductor industry and the oproelectronics industry, the types and amounts of fluorine-based gases such as hydrogen fluoride, fluorine, tungsten hexafluoride, silicon tetrafluoride and boron trifluoride have increased. These fluorine-based gases are indispensable substances as film growth of crystalline silicon, amorphous silicon or silicon oxide films, or as etching gas in the manufacturing industry of silicon semiconductors and compound semiconductors. Further, these fluorine-based gases are used as they are in the semiconductor manufacturing process or after being used in a state diluted with helium, argon, nitrogen, hydrogen, etc., and then as they are or further diluted with a gas such as nitrogen or air. The gas concentration is not constant because the gas is discharged in. Since all of these fluorine-based gases are highly toxic and adversely affect the human body and the environment, harmful gases containing these fluorine-based gases are purified before being released into the atmosphere after being used in semiconductor manufacturing processes. There is a need to.

[0003]

2. Description of the Related Art Conventionally, a scrubber, a spray tower, a rotary fine bubble generator, etc. have been used as a means for removing halogen-containing gas including fluorine-containing gas.
Wet method of absorbing and decomposing these gases by contacting them with an aqueous alkali solution such as sodium hydroxide (JP-A-61-20).
No. 4022, JP-A No. 62-125827, etc.) and adsorbents such as magnesium, sodium, potassium oxides and carbonates (JP-A No. 63-232844).
Japanese Patent Laid-Open No. 60-68051), or a dry method in which a solid substance such as a purifying agent containing soda lime as an active ingredient is filled in a filling cylinder and these harmful gases are caused to flow to purify. ing.

[0004]

However, the wet method generally has a problem in that post-treatment is difficult, and not only the apparatus is complicated and large, but also a large amount of equipment and maintenance are required. . On the other hand, as the dry method, an adsorbent such as an oxide of magnesium, sodium, potassium, or a carbonate is used, but there is a disadvantage that the removal capacity per unit volume of the adsorbent is small. Further, a purifying agent in which activated carbon is impregnated with a zinc compound and an alkali metal compound is also known, but its removal capacity is not always sufficient,
When the concentration of fluorine-based gas is high or the amount of treated gas is large, not only there is the problem that the treatment cannot be completed, but the purification agent using activated carbon causes a fire when treating highly reactive gases such as fluorine. There is also the risk of.

Further, although soda lime has a somewhat larger treatment amount than the above-mentioned purifying agents, there is a problem that when the purifying agent is dried or when the concentration of fluorine-based gas is low, the removal ability is significantly lowered. There is a point. Therefore, the harmful gas has a low concentration, and is excellent in removing performance against various fluorine-based gases discharged from the semiconductor manufacturing process, such as a dry state, and there is no risk of fire during purification, Moreover, the advent of a cleaning agent that can be removed with high efficiency has been desired.

[0006]

Means for Solving the Problems As a result of intensive studies to solve these problems, the inventors of the present invention have used strontium hydroxide as a main component and an organic binder as a molding agent and By using a hydroxide of an alkaline earth metal other than strontium as an auxiliary agent as a cleaning agent, it has a large cleaning capacity for the removal of fluorine-based gas, and the removal capacity also decreases in the dry state. The present invention has been completed by finding that there is no fire, and there is no fear of fire and that it has excellent safety. That is, the present invention is mainly composed of strontium hydroxide,
Molding using an organic binder as a molding agent and an alkaline earth metal hydroxide other than strontium hydroxide as a molding aid, and contacting with a gas containing a harmful fluorine gas to remove the fluorine gas It is a toxic gas purifier characterized by the following.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The purifying agent of the present invention is applied to purifying harmful gases including fluorine-containing gas such as exhaust gas discharged from a semiconductor process. As the harmful gas to be purified, nitrogen, argon, helium, air and the like are fluorine-based gas, for example, hydrogen fluoride, fluorine, boron trifluoride, tungsten hexafluoride or silicon tetrafluoride. It is a gas containing at least one kind of gas.

In the present invention, strontium hydroxide is used as the main component of the cleaning agent. Strontium hydroxide [Sr (OH) ₂ ] can be produced, for example, by reacting strontium chloride with caustic soda, but since it is commercially available in the form of octahydrate or the like with a purity of 98% or more, Usually, these commercial products can be used. When strontium hydroxide is octahydrate, it may be used as it is, but since stable monohydrate can be obtained relatively easily when heated to about 80 ° C., a form corresponding to this monohydrate is obtained. May be used, or an anhydride containing no water of crystallization may be used.

Although strontium hydroxide is molded into a purifying agent, polyvinyl alcohol, as a molding agent, is used for the purpose of enhancing moldability and molding strength during molding.
Polyethylene glycol, polypropylene glycol,
Organic binders such as methyl cellulose and carboxymethyl cellulose may be used alone or in combination. The amount of molding agent added is determined by the amount of strontium hydroxide water of crystallization, molding conditions, etc.
Usually, 0.1 to 40 parts by weight, preferably 0.5 to 2 parts by weight, relative to 100 parts by weight of strontium hydroxide in terms of anhydride.
0 parts by weight.

Further, in order to further improve the moldability, a hydroxide of an alkaline earth metal other than strontium is added as a molding aid. A hydroxide of an alkaline earth metal other than strontium is advantageous because it can improve the formability without deteriorating the purification ability of strontium hydroxide and has a purification ability itself. Furthermore, depending on the harmful gas species to be removed such as fluorine and hydrogen fluoride, the alkaline earth metal hydroxides other than strontium hydroxide added as a molding aid show a synergistic effect with strontium hydroxide, which is extremely convenient. is there. As those alkaline earth metals, magnesium hydroxide [Mg
(OH) ₂ ], calcium hydroxide [Ca (OH) ₂ ],
Barium hydroxide [Ba (OH) ₂ ] and the like, and commercially available products thereof can be usually used.

These hydroxides of alkaline earth metals other than strontium may be used alone or in combination of two or more. Regarding the mixing ratio of hydroxides of alkaline earth metals other than strontium to strontium hydroxide, if the ratio of hydroxides of alkaline earth metals other than strontium is too high, the purification capacity will decrease, and it will also be too low. In this case, since the purifying ability is deteriorated and the moldability is deteriorated, the molar ratio (Sr: M) of strontium hydroxide and the total amount of hydroxides of alkaline earth metals other than strontium (hereinafter abbreviated as M) is usually Is about 1: 0.05 to 1, preferably about 1: 0.1 to 0.5.

The purifying ability of the purifying agent of the present invention for the fluorine-containing gas is less affected by the amount of water in the purifying agent, and it is possible to purify even a small amount of water in the purifying agent. However, an appropriate amount of water may be contained in the purifying agent for the purpose of further enhancing the purifying ability. The water content in that case is usually 30% by weight or less, preferably 15% by weight or less, as the water content after the molding and preparation, including the water constituting the hydrate of strontium hydroxide. It

There are various methods for preparing the purifying agent. For example, a mixture of strontium hydroxide and other alkaline earth metal hydroxide preliminarily mixed in a predetermined ratio and an organic binder are used. The resulting slurry or cake is extruded and molded, and the pellets obtained by cutting into an appropriate length are dried in a drier to a specified water content and used as a purifying agent. There is a method, or a method in which the slurry or cake as described above is dried and then crushed and tablet-molded, or a method in which the slurry or cake is granulated using a granulator or the like. In addition, strontium hydroxide, an organic binder, a hydroxide of an alkaline earth metal other than strontium is uniformly mixed at a predetermined ratio, and any method capable of molding is applied to the method for preparing the purifying agent of the present invention. be able to. Of these, it is generally preferable to extrude into pellets in terms of moldability, ease of selection of shape and size.

The size and shape of the molded product are not particularly limited, but typical examples include spherical, cylindrical, cylindrical and granular forms. If the size is spherical, the diameter is 0.
5 to 10 mm, pellets, tablets and the like having a cylindrical shape have a diameter of 0.5 to 10 mm and a height of about 2 to 20 mm. It is about 8 to 6 mm. The packing density when the molded body is packed in the purifying cylinder is usually 0.4 to 2.
It is about 0 g / ml.

The purifying agent of the present invention can be used not only as a fixed bed but also as a moving bed or a fluidized bed, but it is usually used as a fixed bed. The purifying agent is filled in the purifying cylinder, and the harmful gas containing the fluorine-based gas is caused to flow into the purifying cylinder and brought into contact with the purifying agent to remove the fluorine-based gas as a harmful component. The concentration of the fluorine-based gas contained in the harmful gas to which the purifying agent of the present invention is applied is not particularly limited, but is generally purified from a high concentration of tens of thousands ppm to a low concentration of several ppm emitted during semiconductor manufacturing. Is possible.

The purifying cylinder is designed according to the concentration of fluorine-based gas, the amount of harmful gas to be purified, the allowable pressure loss, and the like. The filling length of the purifying agent in the purifying cylinder varies depending on the flow rate of the gas, the concentration of the harmful gas and the like and cannot be specified unconditionally, but in practice, it is usually about 50 to 1500 mm. The inner diameter of the purifying cylinder is designed so that the empty cylinder reference linear velocity (LV) of the gas flowing in the cylinder is about 0.1 to 150 cm / sec. Generally, these conditions are determined by the pressure loss of the packed bed, the gas contact efficiency, the concentration of the fluorine-based gas, and the like.

The contact temperature is usually 0 to 90 ° C., preferably operating at a temperature around room temperature (0 to 40 ° C.), and heating or cooling is not particularly required. After the contact is initiated, the reaction heat may cause a slight temperature rise depending on the type and concentration of the fluorine-based gas, but there is no danger of ignition because no combustible material such as activated carbon is used. There is no particular limitation on the pressure at the time of contact, and it is usually performed at normal pressure, but 0.5 to 2 k
It is also possible to operate under reduced pressure or increased pressure such as g / cm ² abs. Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0018]

【Example】

Example 1 Strontium hydroxide _{[Sr (OH) 2 · 8H} 2 O]
Dry strontium hydroxide 130 by drying 248 g (purity 99%) in a dryer at 80 ° C. for 18 hours.
g was obtained. This had a weight corresponding to monohydrate. To 130 g of this dried strontium hydroxide was mixed 35 g of calcium hydroxide (Kanto Kagaku Co., Ltd., first-grade reagent) (molar ratio, Sr: Ca = 1: 0.5), and polyvinyl alcohol (abbreviated as PVA) was added thereto. , Shin-Etsu Chemical Co., Ltd.
(Manufactured by PA-05), a solution prepared by dissolving 8 g of PA-05) in 48 g of water was added and stirred. The obtained cake is extruded through a 1.6 mmφ nozzle plate, and the obtained molded product is cut to a length of 3 to
Approximately 24 mm at 100 ° C in a dryer with pellets of about 5 mm
After drying for 160 hours, 160 g of Purifying Agent A was obtained.
The packing density of this cleaning agent A was 0.60 g / ml.
The water content of the purifying agent A was measured by a dry moisture meter (CZA1000, manufactured by Chino Co., Ltd.) and found to be 0.9% by weight.

Next, 125.6 ml of this purifying agent A was put into a purifying cylinder made of quartz glass having an inner diameter of 40 mm and a length of 200 mm.
(Filling length 100 mm), filled with nitrogen containing 1000 ppm of tungsten hexafluoride gas at 20 ° C. under normal pressure, 2260 ml / min (empty cylinder reference linear velocity LV = 3 c
(m / sec), the time until breakthrough was measured, and the amount of tungsten hexafluoride gas removed per liter of the cleaning agent was determined from this. The breakthrough of the tungsten hexafluoride gas was detected by sampling a part of the purification cylinder outlet gas and using a detector for fluoride (TG-3700 manufactured by Bionics Instruments Co., Ltd.). In addition,
Lower limit of detection of tungsten hexafluoride gas is 0.6 ppm
It is. The cleaning agent composition is shown in Table 1, and the cleaning test result is shown in Table 2.

Examples 2 to 6 Strontium hydroxide [Sr (OH) ₂ .8H ₂ O] 2
35 g of calcium hydroxide was mixed with 47 g, and a solution prepared by dissolving 8 g of polyvinyl alcohol in 48 g of water was added thereto and stirred. From the obtained cake, 158 g of purifying agent B was obtained in the same manner as in Example 1. The packing density of this cleaning agent B was 0.57 g / ml. The water content was 1.2% by weight.

The purification agent B was subjected to a purification test for tungsten hexafluoride, silicon tetrafluoride, boron trifluoride, fluorine and hydrogen fluoride in the same manner as in Example 1. The supply concentration of each fluorine-based gas is 1000 p
It was done in pm. In the breakthrough detection, a part of the purification cylinder outlet gas was sampled and measured using a fluoride detector (manufactured by Bionics Instruments Co., Ltd.) below. The lower detection limit of each fluorine-based gas is as follows: Fluorine-based gas detector Lower detection limit (ppm) Tungsten hexafluoride TG-3700 0.6 Silicon tetrafluoride TG-3700 0.6 Boron bromide TG-3700 0.6 Fluorine TG-1400 0.2 Hydrogen fluoride TG-700 0.6 The cleaning agent composition is shown in Table 1, and the cleaning test result is shown in Table 2.

Example 7 Strontium hydroxide [Sr (OH) ₂ .8H ₂ O] 2
A solution of 8 g of methyl cellulose (abbreviated as MC, manufactured by Kanto Chemical Co., Inc.) in 48 g of water was added to 47 g of calcium hydroxide, and the mixture was stirred. 160 g of the purifying agent C was obtained from the obtained cake in the same manner as in Example 1. The packing density of this purifying agent C is 0.58 g / ml
Met. The water content was 1.0% by weight. With respect to this purifying agent C, a purifying test of nitrogen containing 1000 ppm of tungsten hexafluoride was conducted in the same manner as in Example 1. The cleaning agent composition is shown in Table 1, and the cleaning test result is shown in Table 2.

Example 8 Purification agent D (135 g) was obtained in the same manner as in Example 2 except that the amount of calcium hydroxide added was changed to 7 g. The packing density of this cleaning agent D was 0.55 g / ml. Also,
The water content was 1.2% by weight. About this purifying agent D, in the same manner as in Example 1, 1 part of tungsten hexafluoride was added.
A purification test of nitrogen containing 000 ppm was conducted. The cleaning agent composition is shown in Table 1, and the cleaning test result is shown in Table 2.

Example 9 Instead of calcium hydroxide, magnesium hydroxide [Mg
(OH) ₂ ] (Kanto Chemical Co., Inc., reagent grade 1) 54 g was used in the same manner as in Example 2 to obtain 181 g of the purifying agent E. The packing density of this purifying agent E is 0.65 g / m
It was l. The water content was 1.2% by weight. With respect to this purifying agent E, a purifying test of nitrogen containing 1000 ppm of tungsten hexafluoride was conducted in the same manner as in Example 1. The cleaning agent composition is shown in Table 1, and the cleaning test result is shown in Table 2.

Example 10 Instead of calcium hydroxide, barium hydroxide [Ba (O
_{H) 2 · 8H 2 O]} ( Kanto Chemical Co., Ltd., first grade reagent) 8
209 g in the same manner as in Example 2 except that 0 g was used.
Purifying agent F was obtained. The packing density of this purifying agent F is 0.68
It was g / ml. The water content was 1.3% by weight. This purifying agent F was subjected to a purifying test for nitrogen containing 1000 ppm of tungsten hexafluoride in the same manner as in Example 1. The cleaning agent composition is shown in Table 1, and the cleaning test result is shown in Table 2.

Example 11 Strontium hydroxide [Sr (OH) ₂ .8H ₂ O] 2
To 47 g, 35 g of calcium hydroxide and 54 g of magnesium hydroxide were mixed, and 8 g of polyvinyl alcohol was mixed with 4 g of this.
A solution dissolved in 8 g of water was added and stirred. The obtained cake was treated in the same manner as in Example 1 to obtain 215 g of a purifying agent G. The packing density of this cleaning agent G was 0.64 g / ml. The water content was 0.9% by weight. With respect to this purifying agent G, a purifying test of nitrogen containing 1000 ppm of tungsten hexafluoride was conducted in the same manner as in Example 1. The cleaning agent composition is shown in Table 1, and the cleaning test result is shown in Table 2.

Comparative Example 1 Soda lime (Soda Lime No. 2, manufactured by Wako Pure Chemical Industries, Ltd.) having a particle size of 3.5 to 5.5 mm was subjected to 100 in a nitrogen stream.
It was dried for 24 hours in a drying pot at ℃. The packing density of this dried soda lime was 0.78 g / ml, and the water content was 1.0% by weight. Using this dried soda lime, in the same manner as in Example 1, tungsten hexafluoride 1
A purification test of nitrogen containing 000 ppm was conducted. The results are shown in Table 3.

Comparative Example 2 Coconut husk activated carbon having a particle size of 5 to 8 mesh (BET method surface area: 1200 m ² / g) was impregnated with an aqueous sodium hydroxide solution, and then dried in a drier at 100 ° C. for 24 hours in a nitrogen stream to obtain water. A purifying agent I supporting 10% by weight of sodium oxide was obtained. The packing density of this cleaning agent I was 0.63 g / ml, and the water content was 0.5% by weight. Using this purifying agent I, tungsten hexafluoride was added to 1 in the same manner as in Example 1.
A purification test of nitrogen containing 000 ppm was conducted. The results are shown in Table 3.

[0029]

[Table 1] Table 1 Examples Molding aid Molar ratio Molding agent Water content M ₁ or M ₂ Sr: M ₁ + M ₂ (wt%) 1 Ca (OH) ₂ 1: 0.5 PVA 0.9 2-6 Ca (OH) ₂ 1: 0.5 PVA 1.2 7 Ca (OH) ₂ 1.0.5 MC 1.0 8 Ca (OH) ₂ 1: 0.1 PVA 1.2 9 Mg (OH) ₂ 1 : 0.5 PVA 1.2 10 Ba (OH) ₂ 1: 0.5 PVA 1.3 11 Ca (OH) ₂ + Mg (OH) ₂ 1: 0.5 +0.5 PVA 0.9

[0030]

[Table 2] Table 2 Examples Fluorine-based gas type Time to remove fluorine-based gas until breakthrough (min) (L / L purification agent) 1 Tungsten hexafluoride 2223 40 2 Tungsten hexafluoride 2278 41 3 Hydrogen hydride 11392 205 4 Fluorine 6113 110 5 Silicon tetrafluoride 3223 58 6 Boron trifluoride 4334 78 7 Tungsten hexafluoride 2167 39 8 Tungsten hexafluoride 2501 45 9 Tungsten hexafluoride 2056 37 10 Tungsten hexafluoride 2056 37 11 Tungsten hexafluoride 2167 39

[0031]

[Table 3] Table 3 Comparative example Fluorine-based gas type Time to remove fluorine-based gas Removal amount (min) (L / L purifying agent) 1 Tungsten hexafluoride 406 7.3 2 Tungsten hexafluoride 311 5 .6

Example 12 Strontium hydroxide [Sr (OH) ₂ .8H ₂ O] 2
To 66 g, 74 g of calcium hydroxide was mixed, to which a solution of 8 g of polyvinyl alcohol in 48 g of water was added and stirred. The obtained cake is extruded into pellets having a diameter of 1.6 mmφ and a length of 3 to 5 mm,
After drying in a dryer at 100 ° C. for 24 hours, 202 g of purifying agent J was obtained. The packing density of this cleaning agent J was 0.6 g / ml. The water content was 0.9% by weight. For this purifying agent J, hydrogen fluoride was added to 1 in the same manner as in Example 1.
A purification test was performed on nitrogen containing 000 ppm.
The cleaning agent composition is shown in Table 4, and the cleaning test result is shown in Table 5.

Example 13 160 g of Purifying Agent K was obtained in the same manner as in Example 12 except that the amount of calcium hydroxide added was changed to 37 g. The packing density of this cleaning agent K was 0.5 g / ml. The water content was 0.9% by weight. About this purification agent K
A method for purifying nitrogen containing 1000 ppm of hydrogen fluoride was conducted in the same manner as in Example 1. The cleaning agent composition is shown in Table 4,
The purification test results are shown in Table 5.

Example 14 Strontium hydroxide [Sr (OH) ₂ .8H ₂ O] 2
66 g was mixed with 14 g of calcium hydroxide, and a solution prepared by dissolving 6 g of polyvinyl alcohol in 36 g of water was added thereto and stirred. The obtained cake is extruded into pellets having a diameter of 1.6 mmφ and a length of 3 to 5 mm,
It dried at 100 degreeC in the dryer for 24 hours, and obtained 135 g of purifying agents L. The packing density of this purifying agent L is 0.57 g / ml
Met. The water content was 1.2% by weight. This purifying agent L was subjected to a purifying test for nitrogen containing 1000 ppm of hydrogen fluoride in the same manner as in Example 1. The cleaning agent composition is shown in Table 4, and the cleaning test result is shown in Table 5.

Example 15 Strontium hydroxide [Sr (OH) ₂ .8H ₂ O] 2
Calcium hydroxide (3.5 g) was mixed with 66 g, and a solution prepared by dissolving 4 g of polyvinyl alcohol in 24 g of water was added and stirred. Extrude the obtained cake,
Pellets having a diameter of 1.6 mmφ and a length of 3 to 5 mm were prepared, and dried in a dryer at 100 ° C. for 24 hours to obtain 120 g of the purifying agent M. The packing density of this purifying agent M is 0.58 g
/ Ml. The water content was 1.0% by weight.
This purifying agent M was subjected to a purifying test for nitrogen containing 1000 ppm of hydrogen fluoride in the same manner as in Example 1. The cleaning agent composition is shown in Table 4, and the cleaning test result is shown in Table 5.

Examples 16 to 19 Purifying agents J to M prepared in Examples 12 to 15 were subjected to a purifying experiment of nitrogen containing 1000 ppm of fluorine in the same manner as in Example 1. The cleaning agent composition is shown in Table 4, and the cleaning test result is shown in Table 5.

Comparative Example 3 Strontium hydroxide [Sr (OH) ₂ .8H ₂ O] 2
To 66 g, 111 g of calcium hydroxide was mixed, to which a solution of 10 g of polyvinyl alcohol in 48 g of water was added and stirred. The obtained cake was extruded to form pellets having a diameter of 1.6 mmφ and a length of about 3 to 5 mm, and dried in a dryer at 100 ° C. for 24 hours to obtain 235 g of a purifying agent N. The packing density of this purifying agent N is 0.55 g
/ Ml. The water content was 1.2% by weight.
With this purifying agent N, a hydrogen fluoride purification test was conducted in the same manner as in Example 1. The cleaning agent composition is shown in Table 6, and the cleaning test result is shown in Table 7.

Comparative Example 4 Strontium hydroxide [Sr (OH) ₂ .8H ₂ O] 2
A solution prepared by dissolving 8 g of polyvinyl alcohol in 48 g of water was added to 66 g and the mixture was stirred. The obtained cake is extruded to form pellets having a diameter of 1.6 mmφ and a length of 3 to 5 mm, and dried in a dryer at 100 ° C. for 24 hours.
0 g of purifier O was obtained. The packing density of this purifying agent O is 0.
It was 48 g / ml. The water content was 1.2% by weight. In the preparation of this purifying agent O, the shape retention during extrusion was poor, and part of the powder was pulverized during the drying process. With respect to this purifying agent O, a hydrogen fluoride purification test was conducted in the same manner as in Example 1. Table 6 shows the composition of the cleaning agent
Table 7 shows the purification test results.

Comparative Examples 5 to 6 With respect to the cleaning agents N to O prepared in Comparative Examples 3 to 4, a fluorine cleaning experiment was conducted in the same manner as in Example 1. The cleaning agent composition is shown in Table 6, and the cleaning test result is shown in Table 7.

[0040]

[Table 4] Table 4 Examples Molding aid Molar ratio Molding agent Moisture content M ₁ Sr: M ₁ (wt%) 12,16 Ca (OH) ₂ 1: 1 PVA 0.9 13,17 Ca (OH) ₂ 1: 0.5 PVA 0.9 14,18 Ca ( OH) 2 1: 0.18 PVA 1.2 15,19 Ca (OH) 2 1: 0.05 PVA 1.0

[0041]

[Table 5] Table 5 Examples Types of fluorine-based gas Time of fluorine-based gas until breakthrough Removal amount (min) (L / L purifying agent) 12 Hydrogen fluoride 8058 145 13 Hydrogen fluoride 11392 205 205 14 Hydrogen fluoride 11115 200 15 Hydrogen fluoride 8614 155 16 Fluorine 5557 100 17 Fluorine 6113 110 18 Fluorine 6115 110 19 Fluorine 5003 90

[0042]

Table 6 Comparative Examples Molding Aid Molar Ratio Molding Agent Moisture Content M ₁ Sr: M ₁ (wt%) 3,5 Ca (OH) ₂ 1: 1.5 PVA 0.9 4,6 ─── ─ 1: 0 PVA 0.9

[0043]

[Table 7] Table 7 Comparative Examples Type of Fluorine-based gas Time of Fluorine-based gas until breakthrough Removal amount (min) (L / L purification agent) 3 Hydrogen fluoride 4168 75 4 Hydrogen fluoride 2668 48 5 Fluorine 1945 35 6 Fluorine 1339 24

[0044]

Industrial Applicability The harmful gas purifying agent of the present invention has a large ability to remove fluorine-based gas, and efficiently uses fluorine-based gas such as tungsten hexafluoride, hydrogen fluoride, fluorine, and silicon tetrafluoride. Since it can be safely removed, an excellent effect can be obtained in purification of harmful gas containing fluorine-based gas discharged from the semiconductor manufacturing process or the like.

Claims (5)

[Claims] 1. A strontium hydroxide as a main component, an organic binder as a molding agent, and an alkaline earth metal hydroxide other than strontium hydroxide as a molding aid are molded to remove harmful fluorine gas. A toxic gas purifying agent, which is characterized in that it is brought into contact with a gas containing the fluorinated gas to remove the fluorinated gas. 2. The organic binder is polyvinyl alcohol,
Polyethylene glycol, polypropylene glycol,
The cleaning agent according to claim 1, which is at least one selected from methyl cellulose and carboxymethyl cellulose. 3. The purifying agent according to claim 1, wherein the alkaline earth metal hydroxide other than strontium hydroxide used as a molding aid is at least one selected from magnesium hydroxide, calcium hydroxide and barium hydroxide. . 4. The ratio of the total amount of alkaline earth metal hydroxides other than strontium hydroxide used as a molding aid to strontium hydroxide in a molar ratio of 1: 0.05-1.
The purifying agent according to claim 1, which is 5. The purifying agent according to claim 1, wherein the fluorine-based gas is at least one of hydrogen fluoride, fluorine, tungsten hexafluoride, silicon tetrafluoride, and boron trifluoride.