Although chlorofluorocarbons (CFCs), like trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) and chloropentafluoroethane (CFC-115) have a variety of industrial and household applications including refrigerant, solvent and blowing agent applications, they may be deleterious to the earth's protective ozone layer. Because of the potential destruction of atmospheric ozone by CFCs, there is a great need to develop substitutes for these compounds which function in substantially the same way as the CFCs but are low or zero ozone depleting. Several such replacement materials include 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123), 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124), pentafluoroethane (HFC-125) and 1,1,1,2-tetrafluoroethane (HFC-134a). Because the demand for these and others low or zero ozone depleting materials will increase dramatically in the future, commercially viable processes for the preparation of these materials are needed.
Several methods for the production of hydrochlorofluorocarbons and hydrofluorocarbons are reported in the prior art. These methods, however, are not without their shortcomings. Many of these known processes utilize catalysts which are not very selective and, as a result, produce the desired hydrochlorofluorocarbons or hydrofluorocarbon along with a host of other by-products thus reducing the yield of the desired product. Some of these catalysts are hindered by their very short life span which makes them impractical for commercial production. The operating conditions described in the art also make many of the known processes for the production of hydrochlorofluorocarbons and hydrofluorocarbons impractical for commercial production. Among the prior art processes, the following are typical. Except where otherwise indicated, the term "combined 120's" as used herein shall refer to the combined selectivities of chlorofluorocarbons and/or hydrochlorofluorocarbons and/or hydrofluorocarbons produced in a given hydrofluorination reaction.
U.S. pat. No. 3,755,477 to Imperial Chemical Industries Ltd. describes a process for producing fluorinated aliphatic hydrocarbons which comprises fluorinating a halogenated hydrocarbon, including tetrachloroethylene, by reaction in the gas phase with HF in the presence of a steam-treated and calcined chromium oxide catalyst prepared by a multi-step process. The process of the invention as exemplified by Example 23 reports a selectivity for combined 120's of only 70% while producing a substantial amount of the less desired chloropentafluoroethane.
U.S. Pat. No. 3,258,500 to DuPont describes a process for the catalytic vapor phase reaction of HF with halohydrocarbons, including tetrachloroethylene, employing a catalyst that consists essentially of a heat-activated anhydrous chromium (III) oxide which may be supported on alumina. The reference also discloses that catalysts, in the form of activated chromium (III) oxide admixed with aluminum oxide may be used in the process of the invention. The catalyst is prepared by co-precipitation. Like the above-described process, this process exhibits a selectivity for combined 120's of only 73.7%. The remaining almost 26% was unaccounted for (and presumably was waste). See Example 17.
GB 1,000,485 to Scipioni et al., describes a process for the preparation of organic fluorinated compounds by fluorination of halo-olefins in the gaseous phase. The catalyst consists essentially of partially fluorinated alumina impregnated with one or more polyvalent metal halides. The polyvalent metal may be chromium, cobalt, nickel or manganese. The total content of polyvalent metal halide, expressed as oxide, is not more than 15% by weight of the partially fluorinated (70-80%) alumina. Example 4 (Table 4) shows that reaction of tetrachloroethylene with HF over said catalyst yields dichlorotrifluoroethane as the major product. The patent also provides that if fluorination of the catalyst is excessive, the activity of the catalyst is impaired.
U.S. Pat. No. 4,843,181 to DuPont describes a gas-phase process for the manufacture of 1,1,1-trifluorodichloroethane and/or 1,1,1,2-tetrafluoroethane by contacting a suitable tetrahaloethylene, including tetrachloroethylene, and/or pentahaloethane with HF in the presence of Cr.sub.2 O.sub.3 prepared by pyrolysis of (NH.sub.4).sub.2 Cr.sub.2 O.sub.7. In order to obtain the desired product in high yield, this process requires a long contact time (i.e., 90 seconds) between the catalyst and reactants making the process impractical for commercial operation.
U.S. Pat. No. 4,967,023 to Ausimont discloses a process for preparing 1,1,1-trifluoro-2,2-dichloroethane by hydrofluorination, in the gas phase, of perchloroethylene in the presence of a catalyst comprising chromium oxide supported on AlF3 in the gamma and/or beta form. This process suffers from low conversion of the reactants resulting in low productivity of 1,1,1-trifluoro-2,2-dichloroethane.
Kokai Patent Publication No. 178237 Published Jul. 11, 1990, discloses a method of making 1,1,2-trichloro-2,2-difluoroethane, 1,1-dichloro-2,2,2-trifluoroethane, 1-chloro-1,2,2,2-tetrafluoroethane and pentafluoroethane by fluorinating perchloroethylene in the gas phase with HF in the presence of a fluorination catalyst which consists of an oxide containing Cr and at least one element selected from the group of Al, Mg, Ca, Ba, Sr, Fe, Ni, Co and Mn. The catalyst is prepared by co-precipitation.
It is a particular object of the invention to provide a catalyst which is useful in the production of chlorofluorocarbons, hydrochlorofluorocarbons and hydrofluorocarbons.
It is another object of the invention to provide a catalyst with a high productivity.
It is another object of the invention to provide a catalyst which is highly active.
It is another object of the invention to provide a catalyst which has a long life.
Still another object of the invention is to provide a catalyst which can be easily regenerated.
Other objects and advantages of the invention will become apparant from the following description.