Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2002-04-29
2004-04-13
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S164000, C570S165000, C570S166000, C570S167000, C570S168000, C570S175000
Reexamination Certificate
active
06720464
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing octafluoropropane, an octafluoropropane product, and uses thereof.
BACKGROUND ART
Octafluoropropane is used, for example, as a dry-etching or cleaning gas in the process for producing a semiconductor device. With respect to the production methods thereof, the following methods are known:
(1) a method of performing a direct fluorination reaction between hexafluoropropene and fluorine gas (see, Japanese Examined Patent Publication No. 62-61572 (JP-B-62-61572)),
(2) a method of performing an electrolytic fluorination of hexafluoropropene in hydrogen fluoride (see, Japanese Examined Patent Publication No. 62-61115 (JP-B-62-61115)),
(3) a method of reacting hexafluoropropene with fluorine in the presence of a catalyst (see, Japanese Examined Patent Publication No. 1-45455 (JP-B-1-45455)), and
(4) a method of reacting hexafluoropropene with a high-order metal fluoride (see, Japanese Examined Patent Publication No. 62-54777 (JP-B-62-54777)).
However, in these methods, by-products such as tetrafluoromethane (CF
4
) and hexafluoroethane (C
2
F
6
) are produced due to cleavage, C
6
F
12
and C
6
F
14
are produced due to radical addition, and a 4-membered ring is produced due to cyclization addition, for example, and as a result, the yield of and selectivity for the objective octafluoropropane decrease. Furthermore, some compounds in these impurities are difficult to separate by distillation and, in turn, high-purity octafluoropropane can hardly be obtained. Particularly, in the case of using hexafluoropropene as the starting material, chloropentafluoroethane (CFC-115) contained as an impurity scarcely reacts with fluorine gas and mostly remains in the objective octafluoropropane and since this impurity compound can hardly be separated by distillation, due to the similar boiling points, production of high-purity octafluoropropane is difficult.
DISCLOSURE OF INVENTION
The present invention has been made under these circumstances and the object of the present invention is to provide a method for producing octafluoropropane of high purity which can be used in a process of producing a semiconductor device, to provide high-purity octafluoropropane and to the uses thereof.
As a result of extensive investigations to attain the above-described object, the present inventors have found that high-purity octafluoropropane can be produced by using a production process comprising (1) a step of reacting hexafluoropropene with hydrogen fluoride in a gas phase at a temperature of 150 to 450° C. in the presence of a fluorination catalyst to obtain 2H-heptafluoropropane and (2) a step of reacting 2H-heptafluoropropane obtained in the step (1) with fluorine gas in a gas phase at a temperature of 250 to 500° C. in the absence of a catalyst to obtain octafluoropropane. The present invention has been accomplished based on this finding.
More specifically, the present invention (I) is a process for producing octafluoropropane, comprising (1) a step of reacting hexafluoropropene with hydrogen fluoride in a gas phase at a temperature of 150 to 450° C. in the presence of a fluorination catalyst to obtain 2H-heptafluoropropane and (2) a step of reacting 2H-heptafluoropropane obtained in the step (1) with fluorine gas in a gas phase at a temperature of from 250 to 500° C. in the absence of a catalyst to obtain octafluoropropane. In a preferred embodiment of the present invention (I), the starting hexafluoropropene contains at least one compound selected from the group consisting of dichlorodifluoromethane, chlorodifluoromethane, chloropentafluoroethane, chlorotetrafluoroethane and chlorotrifluoroethylene; and in the step (1), the fluorination catalyst is a bulk catalyst mainly comprising an oxide of chromium and obtained by adding at least one member selected from the group consisting of indium, zinc and nickel, and the molar ratio of hydrogen fluoride/hexafluoropropene is in the range from 0.8 to 3:1.
In a preferred embodiment of the present invention (I), a step of removing impurities contained in 2H-heptafluoropropane is provided before the step (2); the impurities are at least one compound selected from the group consisting of tetrafluoromethane, trifluoromethane, chlorotrifluoromethane, hexafluoroethane and pentafluoroethane; the step of removing impurities is a distillation step; and the 2H-heptafluoropropane has a chlorine compound content of 0.01 vol % or less.
In a preferred embodiment of the present invention (I), the step (2) is performed in the presence of a diluting gas and the diluting gas is at least one gas selected from the group consisting of hydrogen fluoride, tetrafluoromethane, hexafluoroethane and octafluoropropane; and in the step (2), the molar ratio of fluorine gas/2H-heptafluoropropane is in the range from 0.9 to 1.5:1, and the 2H-heptafluoropropane concentration at the reactor inlet is 8 mol % or less.
In a preferred embodiment of the present invention (I), at least a part of the outlet gas of the step (2) is circulated and reused as a diluting gas in the step (2); a step of reacting at least a part of the outlet gas of the step (2) with at least one hydrofluorocarbon to remove unreacted fluorine gas contained in the outlet gas is provided; the hydrofluorocarbon is selected from the group consisting of trifluoromethane, tetrafluoroethane, pentafluoroethane and 2H-heptafluoropropane; hydrogen fluoride contained in the outlet gas of the step (2) is separated and the separated hydrogen fluoride is returned to the step (1) and/or the step (2); and at least a part of the octafluoropropane is separated from the gas after the separation of hydrogen fluoride, and the remaining gas is returned to the step (1) and/or the step (2).
The present invention (II) is an octafluoropropane product comprising octafluoropropane having a purity of 99.995 vol % or more. In a preferred embodiment, the total amount of compounds having a chlorine atom within the molecule and cyclic compounds is 50 volppm or less based on the octafluoropropane product.
The present invention (III) is an etching gas comprising the above-described octafluoropropane product. The present invention (IV) is a cleaning gas comprising the above-described octafluoropropane product.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is described in detail below.
The hexafluoropropene (CF
3
CF═CF
2
) for use in the present invention (I) may be obtained as a by-product, for example, in the process of producing tetrafluoroethylene (CF
2
═CF
2
) through thermal decomposition of chlorodifluoromethane (CHClF
2
), or obtained, as described in Japanese Unexamined Patent Publication No. 4-145033 (JP-A-4-145033), by a method of chlorofluorinating, optionally with dehalogenation, propane, propylene or a partially halogenated C3 acyclic hydrocarbon. However, in the hexafluoropropene obtained by these methods, compounds having a chlorine atom within the molecule are intermixed as impurities in many cases, such as dichlorodifluoromethane, chlorodifluoromethane, chloropentafluoroethane, chlorotetrafluoroethane and chlorotrifluoroethylene. The present invention provides a process of producing octafluoropropane starting from hexafluoropropene which may contain such impurities. Here, the boiling points of the intermediate 2H-heptafluoropropane, the objective octafluoropropane and the above-described impurities are shown in Table 1 below.
TABLE 1
Name of Compound
Structural Formula
Boiling Point
Chlorodifluoromethane
CHClF
2
−41° C.
Chloropentafluoroethane
CF
3
CClF
2
−39.3° C.
Octafluoropropane
CF
3
CF
2
CF
3
−36.7° C.
Dichlorodifluoromethane
CCl
2
F
2
−29.2° C.
Hexafluoropropene
CF
3
CF═CF
2
−29° C.
Chlorotrifluoroethylene
CF
2
═CClF
−27.9° C.
2H-Heptafluoropropane
CF
3
CHFCF
3
−15.2° C.
Chlorotetrafluoroethane
CF
3
CHClF
−12° C.
As is apparent from the boiling points shown in Table 1, the boiling points of the compounds having a chlorine atom within the molecule, whi
Ohi Toshio
Ohno Hiromoto
Price Elvis O.
Richter Johann
Showa Denko K.K.
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