JPH0680592A - Method for purifying chlorofluoroalkane - Google Patents

Abstract

PURPOSE:To obtain a highly pure chlorofluoroalkane by decomposing chlorofluoro alkenes contained in the chlorofluoroalkane in a slight amount. CONSTITUTION:The chlorofluoro alkane containing chlorofluoro alkenes is brought into contact with an active carbon catalyst at a temperature of 80-300 deg.C in the presence of oxygen in gas phase to decompose the chlorofluoroalkenes.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method suitable for obtaining a highly pure salt-fluorinated alkane by decomposing a salt-fluorinated alken contained in a small amount in the salt-fluorinated alkane.

[0002]

BACKGROUND OF THE INVENTION Chlorofluorinated alkenes are chlorofluorocarbons such as trichlorofluoromethane or dichlorofluoromethane, which are believed to be alternatives to dichlorofluoromethane, such as 2,2-dichloro-1,1,1-trifluoro. It is formed as a by-product in the production process of ethane or 1,1,1,2-tetrafluoroethane. Since some of these by-products are potentially toxic and corrosive, their presence in relatively small amounts is undesirable and necessitates the removal of chlorofluorinated alkenes from chlorofluorinated alkanes. However, since the boiling point of the chlorofluoroalkane is very close to that of the chlorofluoroalkane to be the product, it cannot be easily removed to a sufficiently low level by a conventional fractional distillation method.

Conventionally, in order to remove the chlorofluoroalkene in the chlorofluoroalkane, a method of contacting with an aqueous solution of an alkali metal permanganate salt is used as an oxidative decomposition method (JP-A-2-28).
2338, U.S. Pat. No. 4,129,603), but not only the large amount of alkali metal permanganate is required, but also waste liquid treatment becomes a problem. As an adsorption method, a method of adsorbing and removing with activated carbon (Japanese Patent Laid-Open No. 2-268124) is also shown, but it is not only easily affected by the concentration of the chlorofluorinated alkene to be removed, but also a large amount relative to the amount removed. Activated carbon is required or frequent regeneration of activated carbon bed is required. Further, as a hydrogenation method, a method of reacting with hydrogen in the presence of a platinum group catalyst is disclosed (JP-A-2-273634).
A large number of by-products are generated due to hydrogenation, and the cost of the catalyst used is expensive.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for purifying a chlorofluorinated alkane containing a chlorofluorinated alkene, which is free from the drawbacks of the above-mentioned conventional methods.

[0005]

The method for purifying a salt-fluorinated alkane according to the present invention is a salt-fluorinated alkane containing a salt-fluorinated alkene in a gas phase in the presence of oxygen at 80 ° C. to 300 ° C.
Is characterized in that the chlorofluoroalkene salt is decomposed by contacting it with an activated carbon catalyst at a temperature in the range of.

The fluorinated alkanes to which the present invention is applied have 2 to 6 carbon atoms, and a typical example thereof is 2,2-dichloro-1,
1,1-trifluoroethane (hereinafter referred to as HCFC-123),
1,1,1,2-Tetrafluoroethane (hereinafter referred to as HFC-134a), 1-chloro-1,2,2,2-tetrafluoroethane and the like can be mentioned.

As a typical example of the salt-fluorinated alkenes contained in these salt-fluorinated alkanes, 1,1-dichloro-2,2-
Difluoroethylene (hereinafter referred to as CFC-1112a), 1-chloro-1,2,2-trifluoroethylene (hereinafter referred to as CFC-1113), 2-chloroperfluorobutene-2 (hereinafter referred to as CFC-13)
17mx), 1-chloro-2,2-difluoroethylene, 2-
Chloro-1,1,1,4,4,4-hexafluorobutene-2,1,1,2-
Examples include trifluoroethylene.

Activated carbon as a catalyst has a specific surface area of 1000
Activated carbon for the gas phase, which has a m ² / g or more and is excellent in the adsorptive power of CFCs and which is used for the recovery of catalyst, catalyst carrier or solvent, is preferable, for example, commercially available Nippon Carbon Co., Ltd. “Columbia JXN”. Or "Columbia MBV", Taihei Chemical Co., Ltd. "Yashikor LL" and Kuraray Chemical Co. "G.
C "etc. are mentioned.

With respect to the reaction temperature, if the reaction temperature is 80 ° C. or lower, a sufficiently high decomposition activity cannot be obtained.
A range of ° C is used. The contact time of the salt-fluorinated alkane containing the salt-fluorinated alken used for the reaction (hereinafter referred to as sample gas) with the catalyst is the reaction temperature, the concentration of the salt-fluorinated alken in the sample gas, the ratio of the sample gas and oxygen, Depending on the catalyst used, it may be appropriately determined, but a sufficiently high decomposition activity cannot be obtained with a contact time of 0.3 seconds or less, while a salt fluoride excluding the chlorofluorinated alkenes with a contact time of 10 seconds or more. Since it takes too long to obtain the modified alkane, the range of 0.3 to 10 seconds is preferable.

The amount of oxygen to be coexisted may be appropriately determined depending on the reaction temperature, the contact time between the sample gas and the catalyst, the concentration of the chlorofluorinated alkene in the sample gas, and the catalyst used. If the amount of oxygen is too small relative to the amount of alkene halide, the fluorinated alkene salt cannot be decomposed sufficiently, so that the fluorinated alkene: oxygen volume ratio is 1: 1.
The above is required. That is, the amount of chlorofluorinated alkenes contained as impurities in the chlorofluoroalkane is 1%.
In this case, the amount of oxygen used may be a sample gas: oxygen volume ratio of 1: 0.01 or more. The maximum value of the oxygen amount is not particularly limited, but for economic reasons, the range of sample gas: oxygen volume ratio of 1:10 or less is preferable. The oxygen used can be pure oxygen or a mixture of oxygen and other inert gases such as air.

CO ₂ CO and the like are detected as the main decomposition products from the chlorinated alkene after the reaction.

Hereinafter, the present invention will be described in more detail with reference to Examples.

[0013]

[Example 1] Using a fixed bed gas phase flow reactor, 1.0 g of "Columbia JXN" (specific surface area: about 1200 m ^{2 /} g) manufactured by Nippon Carbon Co., Ltd. as activated carbon was surrounded by an electric furnace and made of a quartz reaction tube ( The inner diameter was 10 mm and the length was 300 mm. HCF containing 3000ppm of CFC-1112a as a sample
C-123 was gasified and introduced through a vaporizer. Sample supply rate is 120 ml / min, coexisting oxygen supply rate is 2
The reaction was carried out at 0 ml / min by passing through the catalyst layer at a reaction temperature of 120 ° C., and then the product was analyzed by gas chromatography. The content of CFC-1112a in the product 5 hours after the start of the test was 2 ppm or less, which was the same after 15 hours. In addition, the weight of the activated carbon after the reaction was measured and no change in the weight of the activated carbon was observed before and after the reaction.
It was confirmed that C-1112a was not adsorbed and removed by activated carbon.

[0014]

[Example 2] "GC" manufactured by Kuraray Chemical Co. as activated carbon
Example 1 except that (specific surface area of about 1000 m ² / g) was used
The reaction was performed in the same manner as in. In the product 5 hours after the start of the test
The content of CFC-1112a was 2 ppm or less, which was the same after 15 hours.

[0015]

[Example 3] "Yashikor L" manufactured by Taihei Chemical Co., Inc.
The reaction was carried out in the same manner as in Example 1 except that L ″ (specific surface area: about 1200 m ² / g) was used. The content of CFC-1112a in the product 5 hours after the start of the test was 2 ppm or less, and the reaction time was 15 hours. It was the same afterwards.

[0016]

Example 4 The reaction was performed in the same manner as in Example 1 except that the reaction temperature was changed to 180 ° C. The content of CFC-1112a in the product 5 hours after the start of the test was 2 ppm or less, which was the same after 15 hours.

[0017]

Fifth Embodiment Sample supply rate is 70 ml / min (gas),
Example 1 except that the oxygen supply rate was changed to 70 ml / min
The reaction was performed in the same manner as in. In the product 5 hours after the start of the test
The content of CFC-1112a was 2 ppm or less, which was the same after 15 hours.

[0018]

Example 6 As a sample, 30 ppm of CFC-1317mx was contained.
As a result of the same reaction as in Example 1 except that HCFC-123 was used, the content of CFC-1317mx after 5 hours was 1 ppm or less. In addition, no change in weight was observed before the reaction with activated carbon and after 5 hours.

[0019]

Example 7 HCFC-123 containing 3% of CFC-1113 as a sample
As a result of carrying out the reaction in the same manner as in Example 1 except that
The content of CFC-1113 after 5 hours was 0.9%. In addition, no change in weight was observed before the reaction with activated carbon and after 5 hours.

[0020]

Comparative Example 1 The reaction was carried out in the same manner as in Example 1 except that activated carbon was not placed in the reaction tube. The content of CFC-1112a in the product after 5 hours from the start of the test was 3000 ppm, the same after 15 hours, and CFC-1112a was not decomposed at all.

[0021]

Comparative Example 2 The reaction was performed in the same manner as in Example 1 except that oxygen was not supplied. CFC-1112 in the product 5 hours after the start of the test
Content of a is 2900ppm, 3000p after 15 hours
At pm, CFC-1112a was neither decomposed nor adsorbed.

[0022]

Comparative Example 3 The reaction was performed in the same manner as in Example 1 except that hydrogen was supplied instead of oxygen. The content of CFC-1112a in the product after 5 hours from the start of the test was 3000 ppm, the same after 15 hours, and CFC-1112a was not removed at all.

[0023]

Comparative Example 4 Example 2 except that the reaction temperature was changed to 70 ° C.
The reaction was performed in the same manner as in. In the product 5 hours after the start of the test
Content of CFC-1112a is 450ppm, 12 after 15 hours
At 00 ppm, the decomposition rate of CFC-1112a was low.

The results of Examples 1 to 5 and Comparative Examples 1 to 4 are summarized below. Content of CFC-1112a After 5 hours After 15 hours Example 1 <2 ppm <2 ppm Example 2 <2 ppm <2 ppm Example 3 <2 ppm <2 ppm Example 4 <2 ppm <2 ppm Example 5 <2 ppm <2 ppm Comparative Example 1 3000ppm 3000ppm Comparative Example 2 2900ppm 3000ppm Comparative Example 3 3000ppm 3000ppm Comparative Example 4 450ppm 1200ppm

[0025]

The fluorinated alkenes in the fluorinated alkanes can be removed by a simple operation, and there is no problem of waste liquid treatment or by-product treatment.

Claims (1)

[Claims] 1. A fluorinated alkane containing a fluorinated alkene is contacted with an activated carbon catalyst at a temperature in the range of 80 ° C. to 300 ° C. in the gas phase in the presence of oxygen to decompose the fluorinated alkene. A method for purifying a chlorofluoroalkane.