Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Patent
1996-12-19
1998-04-28
Rotman, Alan L.
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
570165, C07C 1720, C07C 1908
Patent
active
057446598
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This application is a 35 USC 371 National Stage Filing of PCT/JP95/01122, published as WO/95/35271 on Dec. 28, 1995.
The present invention relates to a process for the preparation of difluoromethane comprising fluorinating dichloromethane with hydrogen fluoride in a liquid phase in the presence of a catalyst.
PRIOR ART
Difluoromethane (hereinafter referred to as "R32") attracts attention as a substitute refrigerant for chlorodifluoromethane which is used as a refrigerant for air conditioners.
It is known that R32 is prepared by reacting dichloromethane (hereinafter referred to as "R30") with hydrogen fluoride (HF) in a gas or liquid phase in the presence of a catalyst.
U.S. Pat. Nos. 2,749,374 and 2,749,375 disclose a process for the preparation of R32 comprising reacting R30 and HF in a liquid phase at a temperature between 110 and 175.degree. C. in the presence of an antimony chlorofluoride catalyst (SbCl.sub.x F.sub.y in which x +y=3,y/(x+y)=0.8 and Sb(V)>5%). However, this process produces a large amount of by-products of R40 series such as monochlorometane (hereinafter referred to as "R40") and fluoromethane (hereinafter referred to as "R41") which are undesirable impurities in addition to R30 and decrease the yield of R32. It is very important for the reaction system not to corrode the materials of reaction apparatuses in the production of R32, but HF and halogenated antimony are known to corrode such the materials. Neither of the above U.S. Pat. Nos. describe that the materials of reaction apparatuses had the corrosion resistance when the reaction was performed under the above conditions.
U.S. Pat. No. 4,138,355 discloses the addition of an equimolar amount of antimony trihalide to antimony pentahalide to prevent the corrosion of a reactor caused by a mixture of halogen-containing organic compounds with HF and antimony pentahalide. However, the composition of the catalyst may vary with the progress of the reaction since the amount of antimony trihalide increases due to the degradation of the catalyst.
JP-A-59-231030 discloses a process for the preparation of R32 comprising reacting R30 and HF in a gas phase at a temperature of 200.degree. C. in the presence of aluminum fluoride or chromium fluoride as a catalyst. This process is not economically advantageous since the reaction temperature is as high as 200.degree. C. and the gas phase reaction requires more complicated apparatuses than the liquid phase reaction.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above problems associated with the prior art and to provide a process for preparing R32 economically and safely.
Accordingly, the present invention provides a process for the preparation of R32 comprising reacting R30 and HF in a liquid phase in the presence of a fluorination catalyst, wherein the reaction pressure is between 1 and 10 kg/cm.sup.2 ab., and the reaction temperature is between 50.degree. and 150.degree. C., provided that the selected reaction temperature is higher than a temperature at which HF is not liquefied under the selected reaction pressure.
DETAILED DESCRIPTION OF THE INVENTION
Examples of the fluorination catalyst used in the process of present invention are antimony chlorofluorides, titanium chlorofluorides, tin chlorofluorides, and the like. A preferable catalyst is an antimony chlorofluoride of the general formula: formula in which y is a number of between 1 and 4 is preferable. When y is less than 1 (one), the conversion of R30 is low and the yield of R32 per unit weight of the catalyst decreases. Therefore, a large amount of the catalyst should be used. Nevertheless, the antimony catalyst of the general formula in which the index y is between 0.5 and 1 may be used. When the index y is larger than 4, the process is less economical since a large amount of HF should be recycled. The index y is preferably between 2 and 3.
The antimony chlorofluoride is a chlorofluoride of pentavalent antimony prepared in situ by partial fluorination of antimony pentachloride
REFERENCES:
patent: 2005711 (1935-06-01), Daudt et al.
patent: 2749374 (1956-06-01), Ruh et al.
patent: 2749375 (1956-06-01), Ruh et al.
patent: 4138355 (1979-02-01), Ferstandig
patent: 5208395 (1993-05-01), Elsheikh
patent: 5495057 (1996-02-01), Nam et al.
Shibanuma Takashi
Tsuda Takehide
Yamada Yasufu
Daikin Industries Ltd.
Rotman Alan L.
Smith Lyman H.
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