JP2924660B2 - Purification method of tetrafluoromethane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying tetrafluoromethane (hereinafter abbreviated as FC-14). FC
-14 is used for dry etching in a semiconductor manufacturing process, and therefore, a high-purity product is required.

[0002]

2. Description of the Related Art Various methods have been known for producing FC-14. For example, a method of reacting dichlorodifluoromethane with hydrogen fluoride in the presence of a catalyst, a method of reacting monochlorotrifluoromethane with hydrogen fluoride in the presence of a catalyst, a method of reacting trifluoromethane with fluorine, or a method of reacting tetrafluoroethylene FC-1
And thermal decomposition into carbon. However, when FC-14 is produced by these methods, trifluoromethane used as a by-product of the reaction or trifluoromethane used as a raw material forms an azeotrope-like mixture with FC-14, which is a target substance. Extremely difficult. Therefore, it is extremely difficult to produce high-purity FC-14 containing almost no trifluoromethane by a known method, and it has been desired to develop an industrially advantageous purification method.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a purification method capable of obtaining high-purity FC-14 containing almost no trifluoromethane.

[0004]

The present invention provides a high-purity FC-
In the process of producing No. 14, trifluoromethane (hereinafter referred to as HFC)
HFC-23 in FC-14 containing
The present invention relates to a method for selectively adsorbing and removing only those compounds.
In the present invention, zeolite can be used as the adsorbent. In particular, zeolite having a pore size of 3.5 to 11% is effective for this purpose because it selectively adsorbs HFC-23. Further, a carbonaceous adsorbent (molecular sieving carbon) of the same type as activated carbon is also effective.

According to calculations, the molecular diameters of HFC-23 and FC-14 are about 3.7 ° and about 3.9 °, respectively, and it is considered that the difference between the molecular diameters is small. Therefore, it is presumed that it is difficult to selectively adsorb HFC-23 in FC-14 only by the difference in molecular diameter. In response to this problem, the present inventors have studied various purification methods including selective adsorption. Selective adsorption requires an appropriate balance between the polarity and pore size of the adsorbent and the dipole moment and molecular size of the adsorbate.

In the case of the present invention, zeolite as an adsorbent generally easily adsorbs polar substances, and when considering the dipole moment of the adsorbate, FC-14 is zero, whereas HFC-23 is zero. Has a polarity of 1.66 Debye. In consideration of these, the earnestly studied about the reduction of the HFC-23 content, such as changing the type of the adsorbent and the adsorption treatment conditions. As a result, in particular, using a zeolite having a pore diameter of 3.5 mm or more, for example, about 4.2 mm,
By performing the adsorption operation at room temperature, the content of HFC-23 can be reduced from FC-14 containing about 12,000 ppm of HFC-23, and the content of HFC-23 can be reduced depending on the type of zeolite. FC-14 of 10ppm or less
It turned out to get.

On the other hand, the pore diameter is not more than 3.5.degree.
In zeolite having a pore size of about 2 mm, the content was hardly reduced. A similar experiment was conducted on a carbonaceous adsorbent (molecular sieving carbon) having a pore diameter of about 4 °.
A decrease in the content of FC-23 was observed. As a method of the adsorption treatment, any of a method of contacting in a gas phase and a method of contacting in a liquid phase is possible, but it is more preferable to adsorb in a liquid phase. A known method such as a batch system or a continuous system can be used as a method for bringing into contact with the liquid phase. However, industrially, two adsorption towers are provided as a fixed bed, and this is switched when saturation adsorption is reached. Further, the processing temperature and pressure are not particularly limited because they are determined depending on the processing method.

[0008]

Examples of the present invention will be described below. Example 1 A commercially available stainless steel cylinder having a capacity of 100 ml was filled with 10 ml of each of three types of commercially available zeolites (manufactured by Union Showa Co., Ltd.). After vacuum drying, the cylinder was cooled while containing 12,000 ppm of HFC-23 while cooling. 1
Each 4 g was filled with 40 g, and after about 20 hours with occasional stirring at room temperature, the liquid phase was analyzed by gas chromatography. Table 1 shows the results.

[0009]

[Table 1] Zeolite No. 1 Molecular sieves 4A (pore size 3.5
Å) 2. Molecular sieves 5A (pore size 4.2
Å) 3. Molecular sieves 13X (pore size 10
Å)

As is clear from Table 1, FC-14 containing HFC-23 has a pore size of 3.5 to 1 using adsorbent.
By using 1% zeolite and contacting,
Reduce the content of HFC-23, the content is 10pp
m or less.

Example 2 In the same manner as in Example 1, 10 ml of each of two commercially available carbonaceous adsorbents (manufactured by Takeda Pharmaceutical Co., Ltd.) was filled, and after drying under vacuum, 12,000 ppm of HFC-23 was added while cooling.
Each 40 g of the FC-14 contained was filled, and after about 20 hours with occasional stirring at room temperature, the liquid phase was analyzed by gas chromatography. Table 2 shows the results.

[0012]

[Table 2] Carbonaceous adsorbent No.1. 1. Molecular sieving carbon 4A (average pore diameter 4 mm) Molecular sieving carbon 5A (average pore size 5Å)

As is apparent from Table 2, when the carbonaceous adsorbent (molecular sieving carbon) is used as the adsorbent, the effect of reducing the HFC-23 content is also recognized.

Comparative Example In the same manner as in Example 1, 10 ml of each of two types of commercially available zeolites (manufactured by Union Showa Co., Ltd.) was filled, dried under vacuum, and cooled, followed by cooling while containing FC-12 containing 12,000 ppm of HFC-23. Was charged in each case, and after about 20 hours with occasional stirring at room temperature, the liquid phase was analyzed by gas chromatography. Table 3 shows the results.

[0015]

[Table 3] Zeolite No. 1 1. Molecular sieves 3A (pore size 3 mm) Molecular sieves HX-9 (pore size 3.2
Å)

As is apparent from Table 3, the pore size is 3.5 mm.
No decrease in the content of HFC-23 was observed in the zeolite of less than.

[0017]

According to the present invention, the removal of HFC-23 in FC-14, which has been very difficult in the past, is carried out by using a zeolite having an average pore diameter of 3.5 to 11 ° as an adsorbent. Can greatly reduce the content of HFC-23, and depending on the type of zeolite, H
The content of FC-23 becomes 10 ppm or less.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-72437 (JP, A) JP-A-52-62207 (JP, A) US Patent 3026359 (US, A) WO 93/17988 (WO, A1) (58) Fields investigated (Int. Cl. ⁶ , DB name) C07C 19/08 C07C 17/389 CA (STN) CAOLD (STN) REGISTRY (STN)

Claims (1)

(57) [Claims] 1. A sorbent and liquid is to pore size tetrafluoromethane zeolite or carbonaceous adsorbent containing trifluoromethane no 3.5Å as impurities 11Å
A method for purifying tetrafluoromethane, characterized in that trifluoromethane is reduced by contact in a phase .