Production of pentafluoroethane

Details Production of pentafluoroethane Production of pentafluoroethane

1996-06-14

1999-04-27

Rotman, Alan L.

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

Organic compounds

Halogen containing

570165, 570168, 570169, C07C 1908, C07C 1720, C07C 17093, B01J 2706

Patent

active

058980881

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a process for the production of pentafluoroethane.
Pentafluoroethane (HFA 125) has been proposed as a component of non ozone-depleting refrigerant blends, for example as a component of blends together with other hydrofluoroalkanes such as difluoromethane HFA 32, 1,1,1-trifluoroethane HFA 143a, and/or 1,1,1,2-tetrafluoroethane HFA 134a, which are suitable replacements for various chlorofluorocarbons and hydrochlorofluorocarbons and in particular the refrigerant blend R502 and chlorodifluoromethane HCFC 22 in the many applications in which chlorofluorocarbons and hydrochlorofluorocarbons are employed, and in particular in low-temperature refrigeration.
Recently, many processes have been proposed for the production of pentafluoroethane, amongst which may be mentioned the hydrogenation of chloropentafluoroethane CFC 115 and the hydrofluorination of perchloroethylene.
The hydrogenation of chloropentafluoroethane is typically effected under conditions which provide incomplete conversion of chloropentafluoroethane and which therefore result in the production of pentafluoroethane contaminated with chloropentafluoroethane. Chloropentafluoroethane and pentafluoroethane have very similar boiling points, -38.degree. C. and -48.degree. C. respectively, and also form a minimum boiling azeotrope, and are difficult to separate by conventional techniques such as distillation with the result that the pentafluoroethane produced may have an unacceptably low purity due to the presence of significant amounts of CFC 115, for example an amount of CFC 115 which may be as much as 5 wt %.
The hydrofluorination of perchloroethylene has a serious productivity restriction due to the large number of halogen exchange reactions which are required in order to yield pentafluoroethane. Moreover, the catalysts which are typically employed in the hydrofluorination of perchloroethylene become seriously coked and consequently deactivated by the sequential halogen exchange reactions which occur.
Furthermore, in addition to the sequential halogen exchange reactions through tetrachlorofluoroethane HCFC 121, trichlorodifluoroethane HCFC 122, dichlorotrifluoroethane HCFC 123 and chlorotetrafluoroethane HCFC 124 which lead to the production of pentafluoroethane, the sequential reactions through pentachlorofluoroethane CFC 111, tetrachlorodifluoroethane CFC 112, trichlorotrifluoroethanes (CFCs 113 and 113a) and dichlorotetrafluoroethanes (CFCs 114 and 114a) which lead to the production of chloropentafluoroethane may, under certain conditions and with certain catalysts, leading to contamination of pentafluoroethane with significant amounts of chloropentafluoroethane.
Recently much attention has focused on achieving a satisfactory separation of chloropentafluoroethane from pentafluoroethane. Thus, for example a variety of processes for the purification of pentafluoroethane have been disclosed in U.S. Pat. No. 5,087,329, WO94/22793, WO93/23355, JP6-92879, WO94/20441, WO94/19301 and EP 0 612 709, all of which focus on the removal of chloropentafluoroethane from pentafluoroethane.
In contrast, we have now devised a process for the production of pentafluoroethane in which the production of chloropentafluoroethane may be substantially reduced or even eliminated, thus reducing or even completely overcoming the problem of separation of chloropentafluoroethane from pentafluoroethane.
According to the present invention there is provided a process for the production of pentafluoroethane which comprises the steps (i) producing a composition comprising a compound of formula C.sub.2 HCl.sub.x F.sub.y in which x=1, 2 or 3 and y=2, 3 or 4 provided that x+y is 5, contaminated with a compound of formula C.sub.2 Cl.sub.x+1 F.sub.y in which x and y have the meanings above, (ii) separating the compound of formula C.sub.2 HCl.sub.x F.sub.y from the compound of formula C.sub.2 Cl.sub.x+1 F.sub.y and (iii) contacting the compound of formula C.sub.2 HCl.sub.x F.sub.y with hydrogen fluoride in the presence of a fluorination catalyst whereby to produce p

REFERENCES:
patent: 5155082 (1992-10-01), Tung et al.
patent: 5494876 (1996-02-01), Tsuji et al.
patent: 5494877 (1996-02-01), Tsuji et al.

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