Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
1994-09-27
2001-04-17
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
Reexamination Certificate
active
06218587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the catalytic hydrogenolysis of fluorohalocarbons or fluorohalohydrocarbons and more particularly to carbon supported Group VII or Group VIII metal catalysts and their use in the hydrogenolysis of fluorohalocarbons or fluorohalohydrocarbons.
2. Background
A number of chlorinated fluorocarbons are considered to be detrimental toward the Earth's ozone layer. There is a world-wide effort to develop materials that can serve as effective replacements. For example, 1,1,1,2-tetrafluoroethane (HFC-134a), a fluorohydrocarbon containing no chlorine, is being considered as a replacement for dichlorodifluoromethane (CFC-12) in refrigeration systems because of its zero ozone depletion potential. There is thus a need for manufacturing processes that provide fluorocarbons that contain less chlorine.
One method of reducing the chlorine content of halogen substituted hydrocarbons containing chlorine as well as fluorine is reacting organic starting materials containing chlorine and fluorine with hydrogen at elevated temperature in the presence of a hydrogenation catalyst. (e.g. supported Group VII or Group VIII metal catalysts). British Patent Specification 1,578,933 discloses, for example, that HFC-134a can be prepared by the hydrogenolysis of 2,2-dichloro-1,1,1,2-tetrafluoroethane (CFC-114a) or 1,1,1,2-tetrafluorochloroethane (HCFC-124) over palladium on carbon or palladium on alumina hydrogenation catalysts. There remains a continued interest in providing improved hydrogenolysis processes for the manufacture of HFC-134a as well as other fluorohydrocarbons and fluorohalohydrocarbons.
Techniques for enhancing the activity of Group VIII metal hydrogenolysis catalysts have been disclosed. The catalyst improvements described in Eur. Pat. Appln. 347,830 and Jap. Pat. Appln. 1-128,942 are achieved by the addition of other elements, such as Group IB, lanthanum, lanthanide elements, and rhenium to the Group VIII metal catalysts. The additives are said to prevent sintering and also increase the activity and the mechanical strength of the catalysts.
Palladium catalysts are considered generally to be resistant to catalyst poisons (Augustine, “Catalytic Hydrogenation” Marcel Dekker, inc., N.Y., 1965, page 38); although Rylander “Catalytic Hydrogenation over Platinum Metals,” Academic Press, New York, 1967, p. 19, reveals that all types of metal cations may cause drastic inhibition of platinum metal catalysts. However, there is no way of generalizing what the effect of any particular cation will be. Furthermore ions such as Na
+
, K
+
, and Ca
2+
have been reported to be nontoxic to platinum (J. T. Richardson, “Principles of Catalyst Development,” Plenum Press, New York, 1989, p. 206) and in view of the above are considered to be non-toxic toward palladium.
U.S. Pat. No. 2,942,036 claims a process for hydrogenating 1,2,2-trichloropentafluoropropane over a palladium supported on activated carbon catalyst. The carbon support may be treated prior to depositing palladium on it with aqueous HF. The purpose of this treatment is to remove any silica from the carbon.
Various processes using catalysts containing acid-washed carbon have been studied. A. A. Goleva et al., Russ. J. Phys. Chem., 44
2
, 290-1 (1970) disclose the dehydrochlorination of 1,1,2,2-tetrachlorethane to trichloroethylene and HCl using activated charcoal as the catalyst. Activated charcoal treated with hydrochloric acid proved to be more active than an untreated specimen for the production of the olefin, trichloroethylene. M. Biswas et al, J. Macromol. Sci., Chem., A20(8), 861-76 (1983) disclose that the activity of carbon black catalysts for the polymerization of N-vinylcarbazole can be enhanced by treatment with protonic acids such as HNO
3
, H
2
SO
4
and HClO
4
. Chem. Abst. 80 (25): 145470q and Chem. Abst. 80 (25): 145469w disclose an increase in yields of unsaturated glycol diesters when the active carbon catalyst support was treated with HNO
3
compared with untreated carbon.
SUMMARY OF THE INVENTION
This invention provides a process for the catalytic hydrogenolysis of fluorohalocarbons and fluorohalohydrocarbons using a catalyst of at least one metal selected from the group consisting of rhenium, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum supported on carbon, which is characterized by said catalyst containing less than about 200 parts per million (ppm) phosphorus and less than about 200 ppm sulfur based on the total weight of the catalyst. Suitable hydrogenolysis catalysts may be prepared by treating a carbon support with acid, washing said support with deionized water, drying said support, and depositing a catalyst precursor (e.g. palladium chloride) on said support. Preferred catalysts for hydrogenolysis contain less than about 100 ppm potassium.
The process of this invention is considered particularly useful for the conversion of 2,2-dichloro-1,1,1,2-tetrafluoroethane (CFC-114a) to 2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124) and 1,1,1,2-tetrafluoroethane (HFC-134a), and HCFC-124 to HFC-134a.
DETAILS OF THE INVENTION
This invention provides a process for the catalytic hydrogenolysis of fluorohalocarbons and fluorohalohydrocarbons using a low phosphorus, low sulfur carbon supported catalyst containing at least one metal selected from the group consisting of rhenium, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum. In accordance with this invention, the catalyst used for hydrogenolysis contains less than about 200 ppm phosphorus and less than about 200 ppm sulfur (based on the total catalyst weight).
The fluorohalocarbons and/or fluorohalohydrocarbons used in the hydrogenolysis reactions of this invention are preferably those wherein halo is chloro or bromo. Included are fluorohalocarbons consisting of carbon, fluorine and chlorine and/or bromine; and fluorohalohydrocarbons, consisting of carbon, fluorine, hydrogen, and chlorine and/or bromine. Hydrogenolysis of chlorofluorocarbons (i.e. CFCs) and hydrochlorofluorocarbons, (i.e. HCFCs) is thus provided by this invention. Suitable fluorohalocarbons and fluorhalohydrocarbons may contain 1 to 6 carbon atoms, and include the cyclic as well as acyclic compounds represented by the empirical formula C
n
H
m
F
p
X
q
, wherein each X is independently selected from Cl and Br, and is preferably Cl, and wherein n is an integer from 1 to 6, m is an integer from 0 to 12, p is an integer from 1 to 13, and q is an integer from 1 to 13, provided that m+p+q equals 2n+2 when the compound is saturated and acyclic, equals 2n when the compound is saturated and cyclic or is olefinic and acyclic, and equals 2n−2 when the compound is olefinic and cyclic. The hydrogenolysis process produces predominantly saturated products.
Preferred applications include hydrogenolysis of compounds containing 1 to 3 carbon atoms. Examples of acyclic compounds which undergo hydrogenolysis include 1,1,1,2-tetrachloro-2,2-difluoroethane (CFC-112a), which may be hydrogenolyzed to 1,1-difluoroethane (HFC-152a); 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) which may be hydrogenolyzed to 1,1-dichloro-1,2,2-trifluoroethane (HCFC-123a); 1,1,1-trichloro-2,2,2-trifluoroethane (CFC-113a) which may be hydrogenolyzed to 2,2,-dichloro-1,1,1,-trifluoroethane (HCFC-123); 1,2-dichloro-1,1,2,2-tetrafluoroethane (CFC-114) which may be hydrogenolyzed to 1-chloro-1,1,2,2-tetrafluoroethane (HCFC-124a) and 1,1,2,2,-tetrafluoroethane (HFC-134); 2,2-dichloro-1,1,1,2-tetrafluoroethane (CFC-114a), which may be hydrogenolyzed to 2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124) and 1,1,1,2-tetrafluoroethane (HFC-134a); and HCFC-124 itself which may be hydrogenolyzed to HFC-134a. Examples of cyclic compounds include 4,5-dichloro-1,1,2,2,3,3-hexafluorocyclopentane which may be hydrogenolyzed to 1,1,2,2,3,3-hexafluorocyclopentane.
In a preferred embodiment the fluorohalocarbons and/or fluorhalohydrocarbons are represented by the above empirical formula where n is 1 to 3, m is 0
E. I. Du Pont de Nemours and Company
Siegel Alan
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