Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Patent
1997-07-30
1998-05-12
Ivy, C. Warren
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C07C 1726
Patent
active
057508100
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This application is a 371 of PCT/FR96/10070, Jan. 16, 1996.
The present invention relates to the simultaneous manufacture of difluoromethane (F32) and 1,1,1,2-tetrafluoroethane (F134a) by pyrolysis of chlorodifluoromethane in the presence of hydrogen, working at a temperature above 500.degree. C. in the absence of any catalyst or metal surface. Depending on the operating conditions chosen, this process also makes it possible predominantly to manufacture either F134a or F32.
BACKGROUND OF THE INVENTION
1,1,1,2-tetrafluoroethane (F134a) is already manufactured industrially to replace difluorodichloromethane (F12) in domestic refrigeration and motor vehicle air conditioning in particular. Two routes are currently used commercially. They involve processes which consist: ##STR1## or in fluorinating perchloroethylene and then in hydrogenolysing, depending on the case, 1,1-dichloro-1,2,2,2-tetrafluoroethane (F114a) or 1-chloro-1,2,2,2-tetrafluoroethane (F124). ##STR2##
These processes require new units which are particularly expensive in investment terms and the need to use very sophisticated catalysts whose lifetime and performance are not without effect on the cost of the commercial product.
Difluoromethane CH.sub.2 F.sub.2 (F32) is a potentially very advantageous compound since, in combination with pentafluoroethane (F125), it gives an azeotropic mixture which is an excellent replacement product for chlorodifluoromethane (F22) which is scheduled to be banned between 2005 and 2015 on account of its potential effect on weakening the stratospheric ozone layer.
Chlorodifluoromethane is used on a large scale as a refrigerating fluid for commercial refrigeration and for air conditioning in large buildings.
Four routes are selected for the commercial manufacture of F32:
1. Fluorination of methylene chloride CH.sub.2 Cl.sub.2 with HF in the liquid phase in the presence of an antimony-based catalyst.
2. Fluorination of methylene chloride CH.sub.2 Cl.sub.2 with HF in the gas phase on a chromium-based catalyst and at high temperature.
These two processes are not satisfactory since they involve the co-production of large amounts of highly toxic chlorofluoromethane (F31) (LC 50=2 ppm).
3. Hydrogenolysis of chlorodifluoromethane (F22) in the presence of a catalyst based on precious metal, at temperatures of between 200.degree. and 300.degree. C., or in the presence of metals such as aluminium, molybdenum, titanium, nickel, iron or cobalt at a temperature of between 300.degree. and 700.degree. C., as in patent application WO 91/05752.
Hydrogenolysis is entirely unselective and leads to considerable formation of methane along with smaller amounts of F31.
4. A novel process for the manufacture of F32 proposed more recently, which eliminates the co-production of F31 but is very cumbersome and relatively unselective, is based on the fluorination of formaldehyde with HF as described in patent application EP 518,506. F.fwdarw.CH.sub.2 F.sub.2 +CH.sub.2 O
This process requires two steps and co-produces water in the presence of hydrofluoric acid, which induces high risks of corrosion.
DESCRIPTION OF THE INVENTION
Chlorodifluoromethane (F22) is currently manufactured on a large scale for commercial refrigeration but also to serve as a starting material for the production of PTFE. When the use of F22 as a refrigerant liquid is banned, it will be useful to be able to continue exploiting this compound in other applications. The present invention provides a particularly advantageous means in this respect, since it has been found that chlorodifluoromethane (F22) can be converted selectively into F134a and F32 by continuously pyrolysing F22 at a temperature of above 500.degree. C. in the presence of hydrogen, but in the absence of metals in the reaction zone.
The amount of hydrogen used is such that the H.sub.2 /F.sub.22 molar ratio is between 2 and 50 and more particularly between 5 and 15.
The working pressure may range up to 100 bar, but the process is generally carried out at a pressure of between 0.1 and
Hub Serge
Lantz Andre
Schirmann Jean-Pierre
Dahlen Garth M.
Elf Atochem S.A.
Ivy C. Warren
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