JPH09183743A - Method for producing lower perfluoroalkane - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a method for producing a lower perfluoroalkane which can be reacted at a relatively low temperature and can be produced at low cost and easily. A method for producing a lower perfluoroalkane, in which a perfluoroalkene, particularly tetrafluoroethylene, alone or in the presence of an activated carbon catalyst, is thermally decomposed by reacting with carbon dioxide.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a lower perfluoroalkane (that is, tetrafluoromethane, hexafluoroethane, octafluoropropane, etc.) that can be used as an etching agent for semiconductors, a refrigerant, and a foaming agent. is there.

[0002]

2. Description of the Related Art The following (1) to (6) are known as methods for producing lower perfluoroalkanes. (1) A method of fluorinating carbon or hydrocarbon with fluorine gas. (2) A method of reacting polytetrafluoroethylene with fluorine (Japanese Patent Application Laid-Open No. 1-180839). (3) Method for fluorinating chlorofluoroalkane or hydrofluoroalkane with fluorine gas (Patent Publication 4-
81971 and JP-A-1-180838). (4) A method of fluorinating carbon halide with hydrogen fluoride. (5) A method of fluorinating a perfluoroalkene with fluorine (Japanese Patent Laid-Open No. 2-131438). (6) A method of decarbonizing perfluoroalkene with carbon dioxide (Japanese Patent Publication No. 58-42849).

However, in the above reaction (1),
Fluorine gas, which is highly reactive, is used, but the reaction is extremely violent and there is a danger of explosion. The above reaction (2) requires a special reaction apparatus because fluorine is allowed to act at high temperature while mixing solid polytetrafluoroethylene and a large amount of metal fluoride.

Further, in the above methods (3) and (4), trace amounts of impurities (eg, chlorotrifluoromethane, chloropentafluoroethane, etc.) are liable to be mixed, and separation is difficult. It is required that the gas for semiconductor etching does not contain chlorine at all, and it is not satisfactory to supply a product that meets such a requirement.

Further, in the above method (5), since the boiling points of the products hexafluoroethane and tetrafluoroethylene are close to each other, it is necessary to completely consume the raw materials. For this purpose, expensive fluorine gas is used. Is not economically preferable because it must be used excessively.

Further, the above reaction (6) is represented by the reaction formula of C ₂ F ₄ + CO ₂ → CF ₄ + 2CO 3C ₂ F ₄ + 2CO ₂ → 2C ₂ F ₆ + 4CO, but an inexpensive raw material is used. However, in addition to the production of impurities such as COF ₂ (carbonyl fluoride), a reaction temperature of more than 900 ° C is required, and expensive materials such as platinum are required for the reactor material. It is difficult to use.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a lower perfluoroalkane which can be reacted at a relatively low temperature and can be produced at low cost and easily.

[0008]

Means for Solving the Problems As a result of extensive studies on the above-mentioned method (6) for decarbonizing perfluoroalkene, particularly tetrafluoroethylene, the present inventor has found that by using a specific catalyst, The inventors of the present invention have found that lower perfluoroalkanes can be obtained at low temperatures and have reached the present invention.

That is, the present invention is carried out in the presence of an activated carbon catalyst,
A perfluoroalkene, especially tetrafluoroethylene, alone or by reacting with carbon dioxide for thermal decomposition,
The present invention relates to a method for producing a lower perfluoroalkane.

According to the production method of the present invention, perfluoroalkene is reacted alone or with carbon dioxide in the presence of an activated carbon catalyst, which is a specific catalyst.
Thermal decomposition at 0 ℃, especially 600 ℃ ~ 800 ℃ becomes possible,
An expensive material such as platinum is not required for the material of the reactor used, which makes it industrially feasible.

[0011]

Therefore, the reaction temperature applicable in the production method of the present invention is in the range of 500 ° C to 900 ° C.
It is preferably in the range of 600 ° C to 800 ° C.

The lower perfluoroalkane obtained by the production method of the present invention is a perfluoroalkane having 1 to 6 carbon atoms such as tetrafluoromethane, hexafluoroethane and octafluoropropane, although it varies depending on the raw materials used. .

In the production method of the present invention, if the gas used for the reaction is, for example, tetrafluoroethylene alone, tetrafluoromethane is produced by the reaction represented by C ₂ F ₄ → CF ₄ + C.

In such a reaction, carbon produced in the reaction tube may be clogged to cause clogging, or an explosion due to a disproportionation reaction may occur. However, it is possible to operate under conditions that suppress these. desirable. Then, as an effective method for avoiding such clogging and disproportionation reaction, it is preferable to coexist with carbon dioxide gas.

That is, in this case, the reaction proceeds according to the following equation, and the accumulation of carbon can be minimized. C ₂ F ₄ + CO ₂ → CF ₄ + 2CO 3C ₂ F ₄ + 2CO ₂ → 2C ₂ F ₆ + 4CO

Here, the mixing ratio of perfluoroalkene such as tetrafluoroethylene / carbon dioxide is (1
/ 3) to 4 is preferable, and (1/2) to (3/2) is more preferable.

Although the composition of the raw material gas has almost no influence on the composition of the product, it is economically disadvantageous to use carbon dioxide gas in an amount of 3 times or more, particularly 2 times or more, of tetrafluoroethylene. Other than that, there is no particular problem. Further, when tetrafluoroethylene is used in an amount four times or more that of carbon dioxide, it is desirable to dilute it with an inert gas such as nitrogen to prevent explosion due to disproportionation.

The activated carbon used in the production method of the present invention may be in the form of granules (crushed coal, granulated coal) or powder, but granules of 40 mesh or less are easy to use, and 4-10
A mesh grade is particularly suitable. The raw material for the activated carbon may be coconut husk, coal, wood, or the like, and is not particularly limited.

The contact time between the activated carbon catalyst and the raw material gas is 0.1
You can select from a wide range of seconds to 10 minutes, but 1
A range of up to 60 seconds is preferred. This contact time depends on the reaction temperature and can be short when the reaction is carried out at a high temperature and long when the reaction is carried out at a low temperature. If the contact time is too short, the conversion rate of the perfluoroolefin as the raw material tends to decrease, and if the contact time is too long, it is economically disadvantageous.

[0020]

According to the production method of the present invention, perfluoroalkene is reacted alone or with carbon dioxide in the presence of an active carbon catalyst which is a specific catalyst.
Thermal decomposition at ~ 900 ℃, especially 600 ℃ ~ 800 ℃ is possible, and expensive material such as platinum is not required for the material of the reactor used, and it can be industrially implemented. Thus, a lower perfluoroalkane (that is, tetrafluoromethane, hexafluoroethane, octafluoropropane, etc.) that can be used as an etching agent for semiconductors, a refrigerant, and a foaming agent can be obtained with high selectivity.

[0021]

Embodiments of the present invention will be described below.

Examples 1 to 4 Activated carbon (Kuraray Chemical Co., 4G, Kuraray Chemical Co., Ltd.) was placed in the center of a Hastelloy C reaction tube having an inner diameter of 3 cm and a length of 95 cm.
G, 4-6 mesh granules) 200 ml. The reaction temperature was measured by mounting a Ni sheath tube having an outer diameter of 3 mm inside the reaction tube.

The reactor was heated by an electric tubular furnace,
Tetrafluoroethylene (TFE) and carbon dioxide, or tetrafluoroethylene alone was supplied, and the produced gas was analyzed by gas chromatography. Table 1 below shows the composition of the product gas obtained by reacting at various raw material composition ratios, reaction temperatures, and contact times.

[0024]

From these results, it can be seen that the thermal decomposition of the raw material gas sufficiently proceeded even at 900 ° C. or lower, particularly 800 ° C. or lower, and the desired lower perfluoroalkane was obtained with high selectivity.

Examples 5 to 8 : The composition of the raw material gas was kept constant at TFE / CO ₂ = 0.5, the reaction temperature and the contact time were variously changed, and the other examples were
The composition of the produced gas obtained by reacting in the same manner as in No. 4 is shown in Table 2 below.

[0027]

From these results, it can be seen that the thermal decomposition of the raw material gas sufficiently proceeded even at 900 ° C. or lower, particularly 800 ° C. or lower, and the desired lower perfluoroalkane was obtained with high selectivity. It can also be seen that the composition of the raw material gas has almost no effect on the composition of the produced fluorine compound.

Example 9 Activated carbon (Kuraray Chemical Co., Ltd., Kuraray Coal 4G, manufactured by Kuraray Chemical Co., Ltd.) was placed in the center of a Hastelloy C reaction tube having an inner diameter of 3 cm and a length of 95 cm.
G, 4-6 mesh granules) 200 ml. The reaction temperature was measured by mounting a Ni sheath tube having an outer diameter of 3 mm inside the reaction tube. The reactor was heated by an electric tube furnace, fed with hexafluoropropene (HFP) and carbon dioxide, and the produced gas was analyzed by gas chromatography. The composition of each gas was as shown in Table 3 below.

[0030]

From these results, it can be seen that the target product can be effectively obtained even if the source gas is changed.

Example 10 Activated carbon (Fuji Activated Carbon BCW, 8-32 manufactured by Daisan Kogyo Co., Ltd.) was placed at the center of a Hastelloy C reaction tube having an inner diameter of 3 cm and a length of 95 cm.
(Granularity of mesh) 200 ml was filled. The reaction temperature was measured by mounting a Ni sheath tube having an outer diameter of 3 mm inside the reaction tube. The reactor was heated by an electric tube furnace, fed with tetrafluoroethylene and carbon dioxide, and the produced gas was analyzed by gas chromatography. When the gas flow rate and contact time were changed variously, the composition of the produced gas was as shown in Table 4 below.
It was as follows.

[0033]

From these results, it can be seen that the target product can be effectively obtained by reacting the activated carbon catalyst with appropriate particle size and contact time.

Comparative Example 1 Based on the method disclosed in Japanese Patent Publication No. 58-42849.
TFE and CO ₂ mixed gas was supplied to a platinum reaction tube with a length of 300 mm, an outer diameter of 10 mm, and an inner diameter of 9.4 mm, which was installed in an electric tubular furnace (high temperature type) IRH manufactured by Ishizuka Denki Seisakusho.
Was reacted with CO ₂ .

The pressure in the reaction tube is approximately atmospheric pressure, and the retention time of the mixed gas in the reaction tube is set in advance at 23 ° C. and 1 atmosphere for about 1 minute. The reaction temperature was measured by a platinum-platinum rhodium thermocouple attached to the outer surface of the reaction tube.

The obtained product was collected in a Tedra-Pak and analyzed for its composition by gas chromatography.
The compositions of the raw material (mixed) gas and the produced (product) gas, and the reaction conditions are shown in Table 5 below.

[0038]

From these results, according to the method of Comparative Example 1, CO
Impurities such as F ₂ (carbonyl fluoride) are generated, a reaction temperature of over 900 ° C is required, and expensive materials such as platinum are required for the reactor material, which is difficult to use industrially. It turns out that

Claims (6)

[Claims] 1. A process for producing a lower perfluoroalkane, which comprises subjecting a perfluoroalkene to heat decomposition in the presence of an activated carbon catalyst either alone or by reacting with carbon dioxide. 2. The production method according to claim 1, wherein tetrafluoroethylene is used as the perfluoroalkene. 3. A perfluoroalkene at 500 ° C. to 900 ° C.
The manufacturing method according to claim 1, wherein the decomposition is carried out at the temperature of. 4. A perfluoroalkene at 600 ° C. to 800 ° C.
The manufacturing method according to claim 3, wherein the decomposition is carried out by heating at the temperature of. 5. The production method according to claim 1, wherein the mixing ratio of perfluoroalkene / carbon dioxide is (1/3) to 4 in molar ratio. 6. The contact time between the activated carbon catalyst and the raw material gas is 1
The manufacturing method according to claim 1, wherein the time is -60 seconds.