Process for the production of fluorine containing olefins

Details Process for the production of fluorine containing olefins Process for the production of fluorine containing olefins

1997-02-04

1999-01-05

Siegel, Alan

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

Organic compounds

Halogen containing

570158, C07C 1725

Patent

active

058565930

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/GB95/01799 filed Jul. 31, 1995.
The present invention relates to a process for the production of a fluorine containing olefin and more particularly to a process for the production of trifluoroethylene.
According to the present invention there is provided a process for the production of a fluorine containing olefin which process comprises passing a gaseous feed comprising a saturated hydrohalocarbon reactant having a fluorine substituent and one or more further halogen substituents through a heated reaction zone in which there is contained a Lewis acid catalyst.
In the process of the present invention, a gaseous feed comprising a saturated hydrohalocarbon reactant having a fluorine substituent and one or more further halogen substituents is passed through a heated reaction zone where it is subjected to a dehydrohalogenation reaction in the presence of a Lewis acid catalyst so as to yield the desired fluorine containing olefin.
The process of the present invention may be used to prepare a variety of fluorine containing olefins, but is particularly concerned with the production of fluorine containing ethylenes and more specifically with the production of trifluoroethylene. Fluorine containing ethylenes are prepared by subjecting a hydrohaloethane starting material containing a fluorine substituent and one or more further halogen substituents to the process of the present invention. The one or more further halogen substituents contained in the hydrohaloethane may be fluorine, chlorine, bromine and/or iodine atoms, but will preferably be fluorine and/or chlorine atoms and more preferably will be exclusively fluorine atoms. When the process of the present invention is being used to prepare trifluoroethylene, the hydrohaloethane starting material is preferably one of 1,1,1,2-tetrafluoroethane (hereinafter R-134a) and 1,1,2,2-tetrafluoroethane (hereinafter R-134), and more preferably is R-134a.
The heated reaction zone may be provided by any suitably configured reactor vessel. Conveniently, the heated reaction zone is provided by a heated tube reactor. The reactor vessel should, of course, be made of a thermally conductive material which is stable, i.e. will not decompose or melt, at the elevated temperatures and under the chemical environment prevailing during operation of the process. Thus, the reactor vessel may, for example, be made of carbon, graphite or a conductive metal or metal alloy such as nickel and its alloys. It has been found that reactor vessels made of nickel are particularly efficacious in the process of the present invention.
Suitable Lewis acid catalysts for the present process include chromia (Cr.sub.2 O.sub.3) and materials comprising chromia which has been doped with a metal, possibly in the form of a metal compound. Suitable metals for doping the chromia include nickel, cobalt, zinc, iron and copper, especially zinc.
Other suitable catalysts are the fluorine containing Lewis acids such as aluminium fluoride (AlF.sub.3) and materials comprising a fluorine containing Lewis acid which has been doped with a metal, possibly in the form of a metal compound. Suitable metals for doping the fluorine containing Lewis acid include nickel, cobalt, zinc, iron and copper, especially iron.
Preferred catalysts are those comprising a fluorine containing Lewis acid and catalysts comprising aluminium fluoride are especially preferred. The catalyst may be compressed into pellets and used in a fixed bed or, alternatively, it may be used in particulate form in a fluidised bed. Mixtures of two or more different catalysts may also be used in the process of the present invention. The catalyst will tend to lose its activity after a time, but spent catalyst may be regenerated by heating it in air at a temperature in the range of from 500.degree. to 1000.degree. C., more preferably in the range of from 600.degree. to 1000.degree. C.
The process of the present invention is carried out at elevated temperature in a heated reaction zone. Reaction temperatures in the range of from 350.degre

REFERENCES:
patent: 2599631 (1952-12-01), Harmon
patent: 2774799 (1956-12-01), Mantell et al.
patent: 3432562 (1969-03-01), Gardner
patent: 3636172 (1972-01-01), Gardner

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