Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2000-03-13
2001-08-14
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
Reexamination Certificate
active
06274782
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for purifying hexafluoroethane (hereinafter referred to as “FC-116” or “CF
3
CF
3
”) and, more particularly, to a method for purifying FC-116 containing, as impurities, hydrofluorocarbons including two carbon atoms in a molecule (hereinafter referred to as “HFCs”), thereby reducing the impurities of HFCs.
2. Related Background Art
FC-116 is used, for example, for dry etching of semiconductor and, therefore, high-purity FC-116 is demanded.
Various methods have been proposed heretofore as to methods for producing this FC-116.
Specific examples of the methods well known include (1) electrolytic fluorination using ethane and/or ethylene as a raw material, (2) thermal decomposition for thermally decomposing tetrafluoroethylene or the like, (3) methods for fluorinating acetylene, ethylene, and/or ethane by use of metal fluoride, (4) methods for fluorinating dichlorotetrafluoroethane or chloropentafluoroethane or the like by use of hydrogen fluoride, (5) direct fluorination for letting fluorine gas react with ethane or a hydrofluorocarbon, and so on.
However, when FC-116 is produced by these methods, FC-116 as an objective product forms an azeotropic mixture or an azeotrope-like mixture with intermediates or by-products produced in reactions to FC-116 or with the hydrofluorocarbon used as a raw material. Therefore, the problem is that separation of FC-116 is extremely difficult.
For solving this problem, an example proposed is a purification method of FC-116 for treating FC-116 containing the impurities of chlorotrifluoromethane (CClF
3
) and/or trifluoromethane (CHF
3
) including one carbon atom with an adsorbent such as active carbon or a zeolite (U.S. Pat. No. 5,523,499).
There existed, however, no easy, economical, industrially advantageous method for purifying FC-116 containing the impurities of HFCs including two carbon atoms in a molecule and thereby producing high-purity FC-116 little containing the HFCs.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a purification method of FC-116 capable of readily, economically, and industrially advantageously obtaining high-purity FC-116 little containing the impurities of HFCs by making FC-116 containing the HFCs including two carbon atoms in a molecule contact an adsorbent to adsorptively remove the HFCs.
The inventors conducted extensive and intensive studies in order to solve the above problem and came to find that when, in a process for producing high-purity FC-116, FC-116 containing the HFCs was made to contact a zeolite having a specific mean micropore size and a specific silicon/aluminum ratio (Si/Al), or an adsorbent comprising the above-described zeolite and a carbonaceous adsorbent (molecular sieving carbon) having a specific mean micropore size, the HFCs were able to be selectively adsorptively removed and high-purity FC-116 little containing the HFCs could be obtained, thereby accomplishing the present invention.
Specifically, the present invention provides a purification method for purifying hexafluoroethane (FC-116), comprising a step of making hexafluoroethane (FC-116) containing impurities of hydrofluorocarbons (HFCs) including two carbon atoms in a molecule contact a zeolite having a mean micropore size in a range of 3.5 Å to 11 Å and a silicon/aluminum ratio of not more than 1.5 or an adsorbent comprising the above-described zeolite and a carbonaceous adsorbent having a mean micropore size in a range of 3.5 Å to 11 Å, thereby reducing the hydrofluorocarbons (HFCs).
In the purification method of the present invention, the hydrofluorocarbons (HFCs) are preferably at least one compound selected from the group consisting of fluoroethane, 1,1-difluoroethane, 1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane, and pentafluoroethane. Further, FC-116 may include at least one fluorine-containing unsaturated compound selected from a group consist of tetrafluoroethylene, trifluoroethylene, 1,1-difluoroethylene, 1,2-difluoroethylene and monofluoroethylene as the HFCs.
In the purification method of the present invention, the hexafluoroethane (FC-116) containing the impurities of the hydrofluorocarbons (HFCs) including two carbon atoms in a molecule is preferably hexafluoroethane (FC-116) produced by a direct fluorination method for letting fluorine gas react with a hydrofluorocarbon including two carbon atoms in a molecule.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
When the method for producing FC-116 is, for example, a direct fluorination method for letting fluorine gas (F
2
) react with fluoroethane (hereinafter referred to as C
2
H
5
F or as CH
2
FCH
3
or “HFC-161”) which is a hydrofluorocarbon including two carbon atoms in a molecule, reactions represented by formula (1) to formula (5) below, take place in addition to the principal reaction represented by formula (6) below.
C
2
H
5
F+F
2
→C
2
H
4
F
2
+HF formula (1)
C
2
H
4
F
2
+F
2
→C
2
H
3
F
3
+HF formula (2)
C
2
H
3
F
3
+F
2
→C
2
H
2
F
4
+HF formula (3)
C
2
H
2
F
4
+F
2
→C
2
HF
5
+HF formula (4)
C
2
HF
5
+F
2
→C
2
F
6
+HF formula (5)
C
2
H
5
F+5F
2
→C
2
F
6
+5HF formula (6)
In addition to FC-116 as an objective product, HFCs including two carbon atoms in a molecule, such as difluoroethane (C
2
H
4
F
2
) trifluoroethane (C
2
H
3
F
3
), tetrafluoroethane (C
2
H
2
F
4
), pentafluoroethane (C
2
HF
5
, which will be referred to hereinafter as “HFC-125” or “CF
3
CHF
2
”), are produced as intermediates to FC-116.
In ordinary cases, 1,1-difluoroethane (hereinafter referred to as “HFC-152a” or “CHF
2
CH
3
”) is produced in a greater amount among the difluoroethanes, 1,1,1-trifluoroethane (hereinafter referred to as “HFC-143a” or “CF
3
CH
3
”) is produced in a greater amount among the trifluoroethanes, and 1,1,1,2-tetrafluoroethane (hereinafter referred to as “HFC-134a” or “CF
3
CH
2
F”) is produced in a greater amount among the tetrafluoroethanes.
Below listed are boiling points of FC-116 as an objective product and the HFCs as intermediates under the atmospheric pressure.
HFC-152a (CHF
2
CH
3
)−24.2° C.
HFC-134a (CF
3
CH
2
F)−26.5° C.
HFC-161 (CH
2
FCH
3
)−37.1° C.
HFC-143a (CF
3
CH
3
)−47.4° C.
HFC-125 (CF
3
CHF
2
)−48.6° C.
FC-116 (CF
3
CF
3
)−78.1° C.
FC-116 and HFC-134a form an azeotrope-like mixture and FC-116 and HFC-125 form another azeotrope-like mixture. HFC-143a, HFC-161, and HFC-152a are materials very hard to separate from FC-116 by distillation. Therefore, the normal distillation operation involves countermeasures of increasing the number of steps of distillation column or increasing the number of distillation columns in order to minimize these impurities, but such countermeasures are uneconomical. rn addition, it is extremely difficult to produce high-purity FC-116 little containing the HFCS.
For selectively adsorptively removing the HFCs in FC-116, a zeolite having a mean micropore size in the range of 3.5 Å to 11 Å and the silicon/aluminum ratio of not more than 1.5 is axed am the adsorbent in the present invention.
The zeolite may be used singly, or two or more kinds of the zeolite may be used in combination at any ratio.
Further, for selectively adsorptively removing the HFCs (including the fluorine-containing unsaturated compounds) in FC-116, an adsorbent comprising the above-described zeolite and a carbonaceous adsorbent having a mean micropore size in the range of 3.5 Å to 11 Å can be used.
The mixing ratio of the zeolite to the carbonaceous adsorbent is preferably not less than 1.0 by weight.
Specific examples of the HFCs that can be removed by these adsorbents are at least one compound selected from HFC-161, HFC-152a, HFC-143a, 1,1,2,2-tetrafluoroethane (hereinafter referred to as “HFC-134” or “CHF
2
CHF
2
”), HFC-134a, HFC-125, and so on. Among these, the HFCs that can be remov
Arai Tatsuharu
Nakajo Tetsuo
Ohi Toshio
Ohno Hiromoto
Showa Denko K.K.
Siegel Alan
Sughrue Mion Zinn Macpeak & Seas, PLLC
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