Production of difluoromethane

Details Production of difluoromethane Production of difluoromethane

1995-09-06

1998-06-09

Siegel, Alan

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

Organic compounds

Halogen containing

570168, 570169, C07C 1708

Patent

active

057637040

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/GB94/00498 filed Mar. 14, 1994.


This invention relates to a process for the production of difluoromethane.

In recent years there has been increasing international concern that chlorofluorocarbons, which are used on a large scale around the world, may be damaging the earth's protective ozone layer and there is now in place international legislation to ensure that their manufacture and use is completely phased out. Chlorofluorocarbons are used, for example, as refrigerants, as foam blowing agents, as cleaning solvents and as propellants for aerosol sprays in which the variety of applications is virtually unlimited. Consequently, much effort is being devoted to finding suitable replacements for chlorofluorocarbons which will perform satisfactorily in the many applications in which chlorofluorocarbons are used but which will not have the aforementioned damaging effect on the ozone layer. One approach in the search for suitable replacements has centred on fluorocarbons which do not contain chlorine but which contain hydrogen. The hydrofluorocarbon difluoromethane, also known as HFA 32, is of interest as one such replacement, in particular in a blend thereof with other hydrofluoroalkanes, for example HFA 134a and HFA 125, as a replacement for R-22 and R-502 in refrigeration, air-conditioning and other applications.
Processes have been proposed for the production of difluoromethane. Thus, in U.S. Pat. No. 2,744,148, there is described a process for the production of difluoromethane comprising contacting dichloromethane with hydrogen fluoride in the presence of a fluorination catalyst which comprises nickel, chromium, cobalt, copper or palladium carried on aluminium fluoride. Many other catalysts have been proposed for use in the hydrofluorination of dichloromethane, for example, chromium fluoride on alumina in U.S. Pat. No. 4,147733; aluminium fluoride, chromium fluoride, mixtures thereof, aluminium fluoride on active carbon or ferric chloride on active carbon in EP 128510; chromium oxyfluoride in U.S. Pat. No. 2,745,886 and chromia in GB 1,307,224.
However, a serious problem with the production of difluoromethane by the hydrofluorination of dichloromethane is that a substantial amount of a highly toxic by-product, monochloromonofluoromethane, HCFC 31, is produced as an intermediate. HCFC 31 has an Occupational Exposure Limit of 10 parts per billion, and may be produced in substantial quantities, indeed as much as 20% or more of the product from the hydrofluorination of dichloromethane.
We have now found that with certain fluorination l catalysts the selectivity to difluoromethane may be substantially increased and thus the yield of HCFC 31 produced may be substantially decreased.
According to the present invention there is provided a process for the production of difluoromethane comprising contacting dichloromethane with hydrogen fluoride in the presence of a fluorination catalyst comprising zinc or a compound of zinc and a metal oxide, fluoride or oxyfluoride.
We prefer to employ a catalyst as described in EP 0502605 or PCT/GB93/00244, the disclosures of which are incorporated herein by reference.
Thus the metal of the metal oxide, fluoride or oxyfluoride, the amount of zinc, the catalyst preparation method, the catalyst prefluorination treatment, the form of the catalyst, the catalyst regeneration treatment, and the presence of other metals or compounds thereof in the catalyst may be as described in EP 0502605 or PCT/GB93/00244, and especially as described in EP 0502605. These preferred catalyst preparations, forms and compositions are disclosed in this document as they are described in EP 0502605 and PCT/GB93/00244.
The conditions of temperature, pressure and amount of starting materials under which the process is carried out may be as previously proposed for the hydrofluorination of dichloromethane. Thus, the temperature may be in the range from about 100.degree. C. to about 500.degree. C., preferably from about 200.degree. C. to about 400.degree. C., although use of the c

Affiliated with

Also associated with

Rating

Production of difluoromethane does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Production of difluoromethane, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Production of difluoromethane will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2201504