Production of pentafluoroethane

Details Production of pentafluoroethane Production of pentafluoroethane

1996-09-19

1998-06-09

Siegel, Alan

Organic compounds -- part of the class 532-570 series

Organic compounds

Halogen containing

570167, 570166, 570169, C07C 1708

Patent

active

057637075

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/GB95/00766 filed on Apr.4, 1995.
This invention relates to a process for the production of pentafluoroethane.
According to the present invention there is provided a process for the production of pentafluoroethane which comprises contacting a hydrofluorochloroethane having the formula: with hydrogen fluoride in the vapor phase and in the presence of a fluorination catalyst which comprises zinc or a compound of zinc and chromia, chromium fluoride or chromium oxyfluoride.
We have found that use of this particular catalyst for the fluorination of the defined hydrochlorofluoroethanes provides for highly selective production of pentafluoroethane with minimal formation of chlorofluorocarbons, in particular chloropentafluoroethane.
Preferred compositions, methods of preparation, methods of regeneration and forms of the catalyst are described in our published European Application No 502, 605, the contents of which are incorporated herein by reference.
The temperature at which the process is effected may be in the range from about 200.degree. to about 450.degree. C., preferably from about 300.degree. C. to about 450.degree. C. and especially from about 350.degree. C. to about 450.degree. C. Atmospheric, subatmospheric or superatmospheric pressures mat be employed, although to aid throughput of vapours thorough the equipment we prefer top employ superatmospheric pressure, say a superatmospheric pressure up to about 30 barg, and particularly a pressure on the range from about 5 barg to about 20 barg.
The relative proportion of hydrogen fluoride to starting compound of formula (hereafter referred to as the starting compound), may vary within wide limits although we generally prefer to employ a stoichiometric molar excess of hydrogen fluoride. The molar ratio of hydrogen fluoride to starting compound will therefore usually be greater than about 2:1 and we prefer to employ a molar ratio of hydrogen fluoride to starting compound in the range from about 2:1 to about 20:1 and preferably in the range from about 5:1 to about 15;1, especially in the range from about 5:1 to about 10:1.
Preferably the feed to the process of the invention is substantially free of hydrogen chloride. Thus, the process of the invention is preferably effected with a feed to the process comprising less than 10 mole % hydrogen chloride, especially less than 5 mole % hydrogen chloride.
The starting composition for the process of the present invention may be a single compound of formula C.sub.2 H.sub.1 Cl.sub.1+x F.sub.1+y, for example chlorotetrafluoroethane, dichlorotrifluoroethane or trichlorodifluoroethane although usually the starting composition will comprise a composition of two or more and even a composition comprising all of the starting compounds of formula C.sub.2 H.sub.1 Cl.sub.1+x F.sub.1+y since the starting composition for the process of the present invention is conveniently produced itself by the vapour phase catalytic reaction of perchloroethylene with hydrogen fluoride to form a composition which usually comprises amounts of most or even all of the hydrochlorofluoroethanes of formula C.sub.2 H.sub.1 Cl.sub.1+x F.sub.1+y.
According to a preferred embodiment of the invention there is provided a process for the production of pentafluoroethane which comprises (i) contacting perchloroethylene with hydrogen fluoride in the vapour phase in the presence of a fluorination catalyst whereby to form a product stream comprising a hydrochlorofluoroethane of formula C.sub.2 H.sub.1 Cl.sub.1+x F.sub.1+y wherein x and y are each independently 0, 1, 2 or 3 provided that x+y is 3, and (ii) contacting the product stream from step (i) with hydrogen fluoride in the vapour phase and in the presence of a fluorination catalyst comprising zinc and/or nickel or a compound of zinc and/or nickel and chromia, chromium fluoride or chromium oxyfluoride whereby to produce pentafluoroethane.
The temperature at which step (i) is effected may be in the range from about 150.degree. C. to about 350.degree. C., preferably from about 180.degre

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