Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2000-04-05
2001-07-31
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S169000
Reexamination Certificate
active
06268541
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for the preparation of 1,1,1,2,2-pentafluoroethane (HFC-125).
BACKGROUND ART
1,1,1,2,2-pentafluoroethane (HFC-125), which is a useful hydrofluorocarbon compound for its zero ozone depleting potential, is used in various applications such as foaming agent, propellant, refrigerant and the like.
Known processes for preparing HFC-125 include a process comprising fluorinating 2-chrolo-1,1,1,2-tetrafluoroethane (HCFC-124) with hydrogen fluoride (HF) in the gas phase. According to this process, in addition to the desired HFC-125, HC1 is produced as a by-product which reacts with HCFC-124 (reverse reaction) to produce 2,2-dichloro-1,1,1-trifluoroethan (HCFC-123). Further, the process produces impurities including chrolofluoroethanes (CFCs) such as 1,2,2-trichrolo-1,1,2-trifluoroethane (CFC-113), 2,2,2-trichrolo-1,1,1-trifluoroethane (CFC-113a), 1,2-dichrolo-1,1,2,2-tetrafluoroethane (CFC-114), 2,2-dichrolo-1,1,1,2-tetrafluoroethane (CFC-114a), 2-chrolo-1,1,1,2,2-pentafluoroethane (CFC-115), etc.; 2-chrolo-1,1,1-trifluoroethane (HCFC-133a), 1,1,1,2-tetrafluoroethane (HFC-134a) and the like.
The unreacted HCFC-124 and HCFC-123 formed in the reverse reaction can be converted into the desired HFC-125 by fluorination and, therefore, they can be recycled to the process and economically reused as starting materials. On the contrary, the CFCs, HCFC-133a and HFC-134a can not be fluorinated to form HFC-125 and, therefore, the ratios of these components in the reaction product need to be minimized to improve the yield of HFC-125. Especially, CFC-115 is difficult to be separated from HFC-125 because it has a boiling point close to that of HFC-125, which leads to a degraded purity of the desired HFC-125. Therefore, production of CFC-115 should be kept as low as possible. Further, CFC-113a and CFC114a have close boiling points to those of HCFC-123 and HCFC-124, which necessitates a fractionator having a large number of trays in order to separate them completely. If HCFC-123 and HCFC-124 are recycled to the process as starting materials without being purified by a fractionator, CFC-113a and CFC-114a are unavoidably contained in the starting materials. These CFCs are fluorinated in the process to eventually give CFC-115, thereby further degrading the purity of CFC-125.
As described above, the separation of CFC-115 from CFC-125 is difficult, and the separation necessitates additional apparatuses for extractive distillation and the like, which leads to increased costs of equipment and production. Besides, the ban on CFCs has been agreed by international conventions and, therefore, the production should be decreased. Thus, there is a demand for a process for the production of HFC-125 by fluorinating HCFC-124 wherein the formation of CFCs is suppressed as low as possible.
Among the known processes for the preparation of HFC-125 using HCFC-124 as a starting material with reduced production of CFCs, U.S. Pat. No. 5,475,167 discloses a process which uses as catalyst Cr
2
O
3
having a high surface area or Cr
2
O
3
pretreated with CO, H
2
or H
2
O. However, the process requires maintaining the production ratio of HFC-125 at a level of 50% or higher. According to the Examples in this U.S. patent, it is necessary to conduct the reaction at a high temperature of 350° C. or higher with relatively long contact time of 6.8 (g·s/cc) for achieving the above production ratio. Further, it is observed from the Examples of the above patent that the production of CFCs is not suppressed satisfactorily. Specifically, though the production of CFCs is lowest in the case where a high surface area Cr
2
O
3
catalyst is used, the production ratio of CFCs (ratio of CFCs relative to HFC-125 produced) therein is about 3000 ppm. In other cases, the production ratios are 5000 ppm or larger.
U.S. Pat. No. 5,334,787 discloses a process for preparing HFC-125 by reacting in the gas phase HCFC-123 or HCFC-124 used as a starting material with HF in the presence of a Cr
2
O
3
catalyst. However, it is necessary also in this process to maintain the production ratio of HFC-125 at 50% or higher for inhibiting the production of CFCs, which results in the relatively long contact time of 10-100 seconds. The production of the CFCs is not satisfactorily suppressed also by the process.
Furthermore, U.S. Pat. No. 5,399,549 discloses a process for preparing HFC-125 by reacting in the gas phase HCFC-123 or HCFC-124 used as a starting material with HF in the presence of a Cr
2
O
3
catalyst. However, also in this process, the production of CFCs is not satisfactorily suppressed.
DISCLOSURE OF INVENTION
A primary object of the present invention is to provide a process for the preparation of HFC-125 by fluorinating in the gas phase a halogenated hydrocarbon feedstock containing HCFC-124, wherein the production of CFCs is minimized.
In view of the deffects of the above known processes, the present inventors conducted an extensive research to produce HFC-125 with very low contents of CFCs by the fluorination of HCFC-124 containing feedstock with HF in the gas phase. As a result, the inventors found that when the fluorination is conducted in the presence of a fluorinated chromium oxide catalyst obtained by fluorinating chromium oxide represented by the formula: CrOm (1.5<m<3) with HF, in a specific range of mixing ratios of the halogenated hydrocarbon to HF and in a specific range of reaction temperatures, the desired HFC-125 with greatly reduced CFCs contents can be obtained. Moreover, the inventors found that the ratio of CFCs to HFC-125 can be reduced by decreasing the yield of the desired HFC-125, and that the HFC-125 with a remarkably reduced content of CFCs can be produced especially when maintaining the yield of HFC-125 at less than 50%. The invention was accomplished based on these new findings.
The present invention provides the following process for the production of HFC-125.
(1) A process for the preparation of 1,1,1,2,2-pentafluoroethane by fluorinating in the gas phase a halogenated hydrocarbon feedstock containing 2-chloro-1,1,1,2-tetrafluoroethane with hydrogen fluoride, the process being characterized in that:
(i) a fluorinated chromium oxide obtained by fluorinating a chromium oxide represented by the formula: CrOm (1.5<m<3) is used as a catalyst,
(ii) the mixing ratio (by mole) of hydrogen fluoride to halogenated hydrocarbon feedstock ranges from 1.5 to 10, and
(iii) the fluorination is conducted at a temperature of 250 to 350° C.
(2) A process according to item (1), wherein the halogenated hydrocarbon feedstock is 2-chloro-1,1,1,2tetrafluoroethane or a mixture of 2-chloro-1,1,1,2-tetrafluoroethane and 2,2-dichloro-1,1,1-trifluoroethane containing at least 50 mole % of 2-chloro-1,1,1,2-tetrafluoroethane.
(3) A process according to the item (1) or (2), wherein the yield of 1,1,1,2,2-pentafluoroethane is controlled at a level lower than 50%.
(4) A process according to any one of the items (1) to (3), wherein the fluorinated chromium oxide has a specific surface area of 25-130 m
2
/g.
(5) A process according to any one of the items (1) to (4), wherein 2-chloro-1,1,1,2-tetrafluoroethane, 2,2-dichloro-1,1,1-trifluoroethane and hydrogen fluoride in the reaction mixture are recycled to the process as feedstock.
In the invention, it is necessary to use, as a fluorination catalyst, a catalyst obtained by fluorinating with hydrogen fluoride (HF) a chromium oxide represented by the formula: CrOm (1.5<m<3). By using such a specific catalyst, the amount of CFCs contained in the reaction products can be reduced. The catalyst can be prepared by the process disclosed in Japanese Unexamined Patent Publication No. 146680/1993. The process for the preparation of the catalyst employed in the present invention is illustrated briefly in the following.
The chromium oxide is represented by the formula: CrOm, wherein m is in the range of 1.5<m<3, preferably 2<m<2.75, more preferably 2<m<2.3.
One of the examples for the preparation process of the chromium oxide is descr
Kanemura Takashi
Kono Satoru
Shibanuma Takashi
Takahashi Kazuhiro
Yoshimura Toshikazu
Daikin Industries Ltd.
Larson & Taylor PLC
Siegel Alan
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