Hydrogenation catalyst and process

Details Hydrogenation catalyst and process Hydrogenation catalyst and process

1998-07-10

2000-12-12

Ambrose, Michael G.

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

Organic compounds

Halogen containing

502330, C07C 17354

Patent

active

061601888

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a hydrogenation catalyst and to a hydrogenation processes employing the catalyst. The term "hydrogenation" as used herein means all reactions of starting materials with hydrogen and includes hydrogenolysis reactions (replacement of halogen by hydrogen in saturated molecules) as well as hydrogenation reactions (addition of hydrogen across ethylenic double bonds). In a particular embodiment the invention relates to a catalyst and a process for the hydrogenation of halofluorocarbons and hydrohalofluorocarbons to produce hydrofluoroalkanes, for example hydrogenation of dichlorodifluoromethane and chlorodifluoromethane to produce difluoromethane, hydrogenation of chiloropentafluoroethane to produce pentafluoroethane and hydrogenation of dichlorotetrafluoroethane and chlorotetrafluoroethane to produce tetrafluoroethane especially 1,1,1,2-tetrafluoroethane.
Hydrofluorocarbons (HFCs) such as difluoromethane, also known as HFA 32, pentafluoroethane, also known as HFA 125 and 1,1,1,2-tetrafluoroethane, also known as HFA 134a are of interest as replacements for chlorofluorocarbons (CFCs) in the many applications in which CFCs have hitherto been used and in particular in refrigeration and air-conditioning applications. Hydrochlorofluorocarbons (HCFCs) are also of interest as at least transitional replacements for CFCs
Many processes have been proposed for the production of hydrofluorocarbons and hydrochlorofluorocarbons, including the catalysed gas phase hydrofluorination of halocarbons and hydrohalocarbons and the catalysed hydrogenation of halocarbons and hydrohalocarbons which contain fluorine. The catalysed hydrogenation of chlorofluorocarbons and hydrohalofluorocarbons by reaction with hydrogen in the presence of a hydrogenation catalyst is considered to be a potentially commercially attractive process. Hydrogenation of dichlorotetrafluoroethane and chlorotetrafluoroethane to 1,1,1,2-tetrafluoroethane is described, for example, in UK Patent No. 1,578,933; hydrogenation of chloropentafluoroethane to pentafluoroethane has been described, for example, in Japanese Laid-Open Patent Application No. J4-29941; hydrogenation of chlorodifluoromethane to difluoromethane is described, for example, in European Patent Publication No. 0 508 660.
Hydrogenation catalysts for use in the production of HFCs and usually comprising palladium carried on a support such as carbon or alumina are well known and much attention has been directed towards improving such catalysts to increase the activity of the catalyst and/or especially to increase the selectivity with which the desired HFA product is produced using the catlayst. Thus, catalysts for use in the hydrogenation of chlorofluorocarbons and hydrochlorofluorocarbons have been disclosed, inter alia, in International Patent Publications Nos. WO90/08748, WO92/12113 and WO94/11328, US Pat. No. 5,136,113, European Patent Application No. 0 347 830 and Japanese Kokai No. J4-179322.
The present invention is based on the improvement of palladium-based catalysts and in particular on improvement of the selectivity of such catalysts by incorporating an alkali metal such as potassium in the catalysts.
According to the present invention there is provided a catalyst which comprises palladium and an alkali metal carried on a support.
Any alkali metal may be used as a component of the catalyst although caesium or potassium is preferred, especially potassium.
The palladium and alkali metal components may be used in combination with other metals, for example other Group VIII metals such as nickel, Group IB metals such as silver and gold or other metals.
The metals are carried on a suitable support, for example alumina, fluorinated alumina, silica, silicon carbide or carbon but in particular alumina or carbon. We particularly prefer to employ a carbon having a high surface area for example greater than 200 m.sup.2 /gm. Activated carbon supports with low inorganic impurity levels are particularly suitable.
The loading of the metals on the support material may be dependent at lea

REFERENCES:
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patent: 4496666 (1985-01-01), Frederick et al.
patent: 5053377 (1991-10-01), Lerot et al.
patent: 5561096 (1996-10-01), Schoebrechts et al.

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