U.S. Pat. No. 2,999,855 discloses a process for the removal of unsaturated fluorocarbons and saturated fluorohydrocarbons from saturated perfluorocarbon product streams by treatment with aqueous potassium permanganate at 20.degree. to 95.degree. C. GB 1,031,409 discloses a process for the purification of 2,2,2-trifluoro-1-chloro-1-bromoethane (CF.sub.3 CHBrCl) to remove fluorinated halogen butenes by treatment with an alcoholic solution of an alkali metal hydroxide or alcoholate.
U.S. Pat. No. 3,004,075 discloses a process for purifying impure saturated perfluorocarbon of 2-6 carbon atoms in which the impurities consist essentially of unsaturated highly fluorinated compounds which may also contain chlorine or hydrogen, which comprises intimately contacting the impure saturated perfluorocarbon with at least one member of the group consisting of piperdine, pyrrolidine and pyridine and mixtures thereof, at a temperature from about 0.degree. to about 80.degree. C, and separating the purified saturated perfluorocarbon from the reaction mixture.
U.S. Pat. No. 3,218,363 discloses a method of purifying a saturated perhalocarbon in which the halogen substituents are selected from the group consisting of fluorine and chlorine, said perhalocarbon containing impurities selected from the group consisting of (1) hydrogen-containing compounds of structure R-H wherein R is selected from the group consisting of perfluorocarbons, perfluorochlorocarbons, polyfluorohydrocarbons and polyfluorochlorohydro-carbons; comprising subjecting such perhalocarbon to an energy source consisting essentially of non-radiant heat at a temperature in the range of from 350.degree. to 700.degree. C in the presence of O.sub.2 and an initiator selected from the group consisting of F.sub.2, Cl.sub.2, Br.sub.2 and interhalogen compounds, for a time sufficient to oxidize the major part of the impurities, to form products easily removable from said perhalocarbon, but insufficient to cause degradation of a significant amount of said perhalocarbon.
U.S. Pat. No. 3,381,041 discloses a process for purifying impure 1-9 carbon fluorinated alkanes consisting of carbon and fluorine, and fluorinated alkanes consisting of carbon, fluorine and at least one member of the group consisting of hydrogen, chlorine, bromine and iodine to remove halogenated alkenes, which comprises contacting an impure fluorinated compound, at about 0.degree. to 150.degree. C for about 10 seconds to 30 minutes, with a mixture of H.sub.2 SO.sub.4 of at least 50 percent by weight concentration, and at least one mercury material, in the order of from 0.1 to 20 percent by weight of the sulfuric acid content of said mixture.
U.S. Pat. No. 3,696,156 discloses a process for the purification of 2-6 carbon saturated fluoroperhalohydro-carbons, containing only fluorine or fluorine and chlorine, and contaminated with perfluoro- and perfluorochloro-olefins, by vapor phase contact at 180-250.degree. C. with alumina containing .gtoreq.0.1% by weight base selected from alkali(ne earth) metal (hydr)oxides.
U.S. Pat. No. 4,129,603 discloses a process for reducing the 1,1-difluoro-2-chloroethylene, CF.sub.2 .dbd.CHCl, by-product obtained from the reaction of 1,1,1-trihalo-2-chloroethane and HF to produce 1,1,1,2-tetrafluoroethane, CF.sub.3 CH.sub.2 F, by contacting the reaction products with a metal permanganate in a liquid medium.
U.S. Pat. No. 4,158,675 teaches the removal of 1,1difluoro-2-chloroethylene from the 1,1,1,2-tetrafluoroethane product stream produced as in U.S. Pat. No. '603 above by vapor phase hydrofluorination of a 1,1,1-trihalo-2-chloroethane, by passing the impure stream together with HF over a chromium oxide catalyst at lower temperatures (100-275.degree. C.) than the hydrofluorination temperatures (300-400.degree. C.) of the tetrafluoroethane production step.
East German Patent 160,718 discloses a process for the separation and purification of perfluorinated alkanes from mixtures containing perfluoroolefins and HF which comprises quantitative reaction of olefinic impurities to form water soluble products by their reaction with reactive nucleophiles in the presence of acid acceptors, or reaction with alkali salts of reactive nucleophiles, or reaction with aqueous alkali solutions. The perfluorinated alkanes form a distinct phase which is separated and then refined.
The olefinic impurities which are present as impurities in the manufacture of saturated fluorocarbons and fluorohydrocarbons are particularly undesirable as contaminants as they may be toxic and for most uses their concentrations in the saturated products must be lowered to as a low a level as is practically possible. This is particularly true because the fluorocarbons and fluorohydrocarbons can be widely used as solvents, cleaning agents, blowing agents, and refrigerants where toxicity must be substantially eliminated. Distillation and other conventional physical methods which may be used to lower the concentrations of olefinic impurities are generally ineffective when the boiling points are too close and are generally too costly. Therefore, various chemical treatments have been proposed, some of which are described above. None of these prior processes is entirely satisfactory from a commercial viewpoint. The aqueous alkaline metal permanganate treatments of the U.S. Pat. Nos. '855 and '603 , for example, require that the halocarbon products exiting the treatment medium be dried (separated from its entrained water) before further refining, which adds to the expense of the treatment. Moreover, where saturated halo-hydrocarbon products are being treated, the possibility exists that some of the valuable saturated material could be lost to the alkaline oxidative medium along with the unsaturated impurities. The high temperatures of the U.S. Pat. Nos. '156 and '675 are objectionable because of the increased cost of unsaturates removal. Further the U.S. Pat. No. '156 treatment appears limited to perhalocarbons since hydrogen-bearing halocarbons are possibly susceptible to dehydrohalogenation to form unsaturated products under the high temperature alkaline process of the disclosed process.
It is an object of this invention to provide a hydrogenation process for reducing the concentration of olefinic impurities in fluorocarbons and fluorohydrocarbons, in particular in such fluorocarbons and fluorohydrocarbons having 2 to 4 carbon atoms.
Another object is to provide a process as above that operates at relatively low temperatures.
Still another object is to provide a process as above that reduces the content of the olefinic impurity in the fluorocarbon and fluorohydrocarbon process streams without substantial yield loss of the hydrogen-bearing halocarbon components.
Yet another object is to provide a process as above where the hydrogenated olefinic impurity can be recovered by distillation and used as a separate product.
A further object is to provide a process for which no drying is required.
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