Methods of producing 1,1,1,2,2-pentafluoroethane

Details Methods of producing 1,1,1,2,2-pentafluoroethane Methods of producing 1,1,1,2,2-pentafluoroethane

1995-09-05

1998-05-12

Siegel, Alan

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

Organic compounds

Halogen containing

570166, 570167, 570168, C07C 1708

Patent

active

057508097

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/JP94/00348 filed Mar. 3, 1994.
The present invention relates to methods of producing 1,1,1,2,2-pentafluoroethane.


INDUSTRIAL FIELDS WHERE THE INVENTION CAN BE UTILIZED

This invention relates to methods of producing 1,1,1,2,2-pentafluoroethane that is useful as a substitute for freons and is expected to serve as a refrigerant.


PRIOR ART

1,1,1,2,2-pentafluoroethane (HPC-125) is expected to be applied as a refrigerant and is also useful as a substitute for freons.
In recent years, under circumstances whereby freons are regulated, the reduction plan for HCFCs has been determined after that of CFCs. At present, HCFC-22 (CHClF.sub.2) that is a kind of HCFC, is widely used as a refrigerant. It is therefore useful to determine and produce a substitute for HCFC-22. As its possible substitutes, HFC-32 (CF.sub.2 H.sub.2), HFC-152a (CH.sub.3 CHF.sub.2), HFC-143a (CH.sub.3 CF.sub.3), HFC-134a (CF.sub.3 CH.sub.2 F), and HFC-125 are proposed. This invention relates to a method of producing HFC-125, one of the proposed substitutes.
As production methods of HFC-125, some reactions have been known: fluorination of perchloroethylene (Jap. Pat. Publication No. 17263/1964, U.S. Pat. No. 4,766,260); fluorination of HCFC-122 (Jap. Pat. Opening No. 172932/1990, Jap. Pat. Opening No. 29940/1992); fluorination of HCFC-123 (Jap. Pat. Opening No. 226927/1992, WO92/16482, EF513823); and reduction of CFC-115 (Jap. Pat. Opening No. 258632/1989). This invention relates to the reaction process of producing HFC-125 by fluorinating perchloroethylene.
As a method of producing HFC-125, it is reported that the fluorination reaction of a perhaloethylene as a starting material, especially perchloroethylene, is conducted at a temperature from 350.degree. to 380.degree. C. in the presence of a chromium-oxide catalyst (Jap. Pat. Publication No. 178237/1964). In Jap. Pat. Opening No. 178237/1990, reactions have been improved by changing catalysts. According to the improvement, the conversion of perchloroethylene has been raised, but the selectivity of HFC-125 still remains at a low level of about 15%. As shown in WO92/16479, the low selectivity is unchanged even if the catalyst is changed to one based on Zn.
Like this, in reactions using perchloroethylene as a raw material, the conversion of perchloroethylene has been improved. It cannot, however, be sufficiently confirmed at present whether technology to improve the selectivity of HFC-125 together with its conversion has been achieved.
Accordingly, a reaction starting from HCFC-123 (2,2dichloro-1,1,1-trifluoroethane) has been proposed. In Jap. Pat. Opening No. 226927/1992; it is shown that HCFC-124 (2chloro-1,1,1,2-tetrafluoroethane) and HFC-125 can be obtained selectively by using a chromium catalyst having an valence number of three or more. In WO92/16482, a reaction with a catalyst mainly comprised of Zn is explained, showing a result of the high selectivity of HCFC-124. In EP513823, a reaction with a chrom-manganese catalyst is attempted. In any case, these proposals are aimed at a high yield of HFC-125 by improving their catalysts.
When HFC-125 is produced, 1-chloro-1,1,,2,2-pentafluoroethane (CFC-115) is formed as an impurity, for example, in the process of producing HFC-125 by fluorinating perchloroethylene.
Inasmuch as CFC-115 is one of specified freons whose production must be discontinued in 1995, it is necessary to lower the content of CFC-115 as little as possible in the production of HFC-125. There exists a limit, however, in raising the purity of HFC-125 by rectification because HFC-125 and CFC-115 form an azeotrope-like composition.
The reaction itself of reducing CFC-115 to HFC-125 is already known. Jap. Pat. Opening No. 258632/1989 shows that this reaction is conducted by using a catalyst, in which a metal chosen from the platinum and iron groups or from rhenium is carried on active carbon or alumina. Jap. Pat. Opening No. 29941/1992 shows a method to control the formation of excessively reduced products. WO91/05752 shows a method of performin

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