Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
1994-12-08
2001-09-18
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
Reexamination Certificate
active
06291729
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to catalytic hydrogenolysis of halofluorocarbons; and more particularly to the hydrogenolysis of said materials using palladium-containing catalysts.
BACKGROUND
Various processes for the catalytic hydrogenolysis of chlorofluorocarbons and hydrochlorofluorocarbons are known. For example, British Patent Specification 1,578,933 illustrates that mixtures of C
2
Cl
2
F
4
isomers can be subjected to hydrogenolysis over a particulate catalyst of palladium on charcoal (which was intimately mixed with glass helices to prevent clogging) or palladium on alumina, to mixtures of C
2
H
2
F
4
isomers. U.S. Pat. No. 2,942,036 discloses the reaction of 1,2,2-trichloropentafluoropropane with hydrogen in the presence of palladium on activated carbon catalyst to produce 1,2,2-trihydropentafluoropropane. The examples show that under the conditions of the experiments one of the products from this reaction is CF
3
CH═CF
2
. The carbon support may be treated with aqueous HF prior to depositing palladium on the support for the purpose of removing silica from the carbon. U.S. Pat. No. 5,171,901 discloses inter alia the catalytic hydrogenation of CF
3
CCl
2
CF
3
and/or CF
3
CHClCF
3
using suitable catalysts (e.g., palladium). Disclosed support materials include activated carbons, aluminas, silicas, barium sulfate, spinels, silicates and titanium dioxide. Preferred supports are activated carbons and lithium/aluminum spinels. Examples are provided wherein 2,2,-dichlorohexafluoropropane and 2-chloro-2-hydrohexafluoropropane are hydrogenated using palladium supported on globular lithium/aluminum spinel. Japanese Patent Application Publication Hei 1(1989)-319441 discloses a process where one chlorine atom is selectively replaced by hydrogen in 1,1,1-trichlorotrifluoroethane using a platinum catalyst. For comparison, a palladium on carbon catalyst is disclosed to produce 1,1,1-trifluoroethane as the major product under the conditions of the experiment.
SUMMARY OF THE INVENTION
The present invention provides a process for the hydrogenolysis of 2,2-dichlorohexafluoropropane (i.e., CFC-216aa or CF
3
CCl
2
CF
3
) to 2,2-dihydrohexafluoropropane (i.e., HFC-236fa or CF
3
CH
2
CF
3
) and 2-chloro-2-hydrohexafluoropropane (i.e., 226da or CF
3
CHClCF
3
). The process comprises reacting said starting material with hydrogen at an elevated temperature of about 300° C. or less in the presence of a catalyst containing a catalytically effective amount of palladium supported on a support selected from the group consisting of fluorinated alumina, aluminum fluoride and mixtures thereof.
DETAILED DESCRIPTION
The catalysts suitable for the process of this invention comprise palladium. The palladium is supported on fluorinated alumina, aluminum fluoride and/or a mixture thereof. Preferred catalysts consist essentially of palladium on an aluminum fluoride or fluorinated alumina support. The procedure for preparing such a catalyst is described in U.S. Pat. No. 4,873,381, the entire contents of which are hereby incorporated herein by reference.
The concentration of palladium on the fluorinated alumina and/or aluminum fluoride support is typically within the range of from 0.1 to 10% by weight of the catalyst. The support can be prepared by fluorination of alumina at elevated temperatures. It is preferred that the fluorine content of the support be sufficient to provide a fluorine to aluminum atomic ratio of at least 2.4. The aluminum fluoride or fluorinated alumina support utilized in the instant invention has the advantage of being regeneratable by conventional means, which carbon-based supports do not have. For example, CF
3
CCl
2
CF
3
can be reacted with hydrogen over a catalyst of this invention until the conversion rate of CFC-216aa decreased by at least about 20 percent compared to the conversion rate of CFC-216aa using fresh catalyst at the same conditions; and the catalyst can then be regenerated (e.g., by first treating with air or oxygen at elevated temperature, and then reducing with hydrogen).
The reaction temperature is typically within the range of from about 100° C. to about 300° C. A preferred range is from about 100° C. to 250° C. Generally, in order to provide substantial hydrogenolysis product yields, the amount of hydrogen used is at least about 0.5 mole per mole of the CFC-216aa starting material. To provide yields desired in many embodiments, at least stoichiometric amounts of hydrogen are used. A considerable excess of hydrogen can also be advantageously employed to provide the yields desired in many embodiments in addition to serving as a heat sink to reduce the overall temperature rise in the reactor. The three-carbon hydrogenolysis product from the hydrogenolysis of CFC-216aa contains at least 90% of the fluorine atoms contained in the CFC-216aa reacted and less than 5 mole percent of said product contains 5 fluorine substituents.
CFC-216aa utilized in this process can be made by conventional means which are well known to the art (see, e.g., U.S. Pat. No. 5,068,472).
The hydrogenolysis of 2,2-dichlorohexafluoropropane with hydrogen may be conducted in any suitable reactor, including fixed and fluidized bed reactors. The reaction vessel should be constructed from materials which are resistant to the corrosive effects of hydrogen halide.
Pressure is not critical. Atmospheric and superatmospheric pressures are the most convenient and are therefore preferred.
Unreacted 2-chloro-2-hydrohexafluoropropane may be recycled to the reactor to produce additional quantities of 2,2-dihydrohexafluoropropane or be used as an organic intermediate to produce 2-hydroheptafluoropropane.
HFC-236fa is useful as a refrigerant, fire extinguishant, heat transfer medium, gaseous dielectric, sterilant carrier, polymerization medium, particulate removal fluid, carrier fluid, buffing abrasive agent, displacement drying agent and power cycle working fluid. In particular, HFC-236fa is a highly effective refrigerant.
The present process has the advantage that the desirable products are obtained in extremely high selectivity.
REFERENCES:
patent: 2942036 (1960-06-01), Smith et al.
patent: 4319060 (1982-03-01), Cunningham et al.
patent: 4873381 (1989-10-01), Kellner et al.
patent: 4980324 (1990-12-01), Kellner et al.
patent: 5068472 (1991-11-01), Webster et al.
patent: 5171901 (1992-12-01), Gassen et al.
patent: 2 081 813 (1993-05-01), None
patent: 0 349 115 (1990-01-01), None
patent: 0 442 075 (1991-08-01), None
patent: 0 539 989 (1993-05-01), None
patent: 1 578 933 (1980-11-01), None
patent: 1-319441 (1989-12-01), None
patent: WO 90/08748 (1990-08-01), None
patent: WO 94/20440 (1994-09-01), None
Bitner, J.L. et al, , “Thermochemical and Photochemical studies on organic fluorine compounds”,Chemical Abstracts, 54:22311C. (1959).
Bitner, J.L. et al,U.S. Dept. of Comm. Off. Tech. Ser./Report 136732, , pp. 25-27 (1958).
E. I. Du Pont de Nemours and Company
Siegel Alan
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