Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2001-07-17
2003-02-18
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
Reexamination Certificate
active
06521803
ABSTRACT:
The present invention relates to a process for the separation of a mixture comprising a hydrofluoroalkane and hydrogen fluoride, as well as to processes for the preparation of a hydrofluoroalkane and to azeotropic compositions.
Hydrofluoroalkanes can be prepared by reaction of an appropriate chlorinated precursor with hydrogen fluoride, as disclosed, for example, in Patent Applications EP-A1-0,699,649 and WO-A1-97/15540 (on behalf of Solvay) and in Patent Application WO-A1-97/05089. In such a process, at the outlet of the reactor, the mixture of reaction products comprises, in addition to the desired hydrofluoroalkane, hydrogen chloride originating from the removal of the chlorine atom or atoms from the starting chlorinated precursor, hydrogen fluoride, chlorofluorinated intermediates, generally unconverted chlorinated precursor, possibly inert diluents, and various byproducts in small amounts. Given that the operation is usually carried out with an excess of hydrogen fluoride with respect to the chlorinated precursor, unconverted hydrogen fluoride is generally present in the mixture of reaction products. Whereas the majority of the constituents of the mixture of reaction products can be easily and completely separated by distillation, complete separation between the hydrofluoroalkane and the hydrogen fluoride is generally very difficult to achieve by distillation, this being because these compounds often form azeotropic mixtures.
Patent Application WO-A1-97/05089 discloses a process for the purification of hydro-(chloro)fluoroalkanes (in particular 1,1,1,3,3-pentafluoropropane or HFC-245fa) from azeotropic mixtures with hydrogen fluoride by an azeotropic distillation technique comprising two successive stages of distillation at different temperatures and at different pressures.
However, this azeotropic distillation technique exhibits the disadvantages of requiring a large difference in temperature or in pressure between the two columns, so as to have available a sufficient separation potential (difference in composition between the low pressure/temperature azeotrope and the high pressure/temperature azeotrope), and of producing a high recycling flow rate between the two columns.
Patent Application WO-A1-97/13719 discloses a process for the separation and recovery of hydrogen fluoride from its (azeotropic) mixtures with, inter alia, hydrofluoroalkanes comprising from 1 to 6 carbon atoms (in particular HFC-245fa). The mixture is brought into contact with an alkali metal fluoride (in particular, potassium fluoride or caesium fluoride) solution and the organic phase is separated from the phase comprising the hydrogen fluoride and the alkali metal fluoride.
Through this known process, contamination of the organic phase by the potassium fluoride or caesium fluoride and the risk of decomposition of the hydrofluoroalkanes which this contamination might bring about may be feared. Moreover, these alkali metal fluorides, and more particularly caesium fluoride, are very expensive.
An object of the present invention is to provide a process for the separation of a mixture comprising at least one hydrofluoroalkane, preferably comprising from 3 to 6 carbon atoms, and hydrogen fluoride which does not exhibit the disadvantages of the abovementioned processes.
The invention consequently relates to a process for the separation of a mixture comprising at least one hydrofluoroalkane and hydrogen fluoride, hereinafter known as hydrofluoroalkane/hydrogen fluoride mixture, according to which the hydrofluoroalkane/hydrogen fluoride mixture is reacted with at least one organic compound capable of reacting with hydrogen fluoride.
The reaction of the hydrofluoroalkane/hydrogen fluoride mixture with at least one organic compound capable of reacting with hydrogen fluoride makes it possible to consume at least a portion of the hydrogen fluoride. The separation process according to the invention thus provides a mixture of reaction products which is depleted in hydrogen fluoride. This is of advantage in the context of a hydrofluoroalkane synthesis, it being possible for the said mixture to be used in particular as extraction solvent. The mixture of reaction products obtained is also highly suitable as starting material when it is subjected to at least one subsequent stage of treatment intended to recover the hydrofluoroalkane. Hydrofluoroalkane essentially devoid of hydrogen fluoride can thus be obtained.
A specific advantage arises when the hydrofluoroalkane is capable of forming an azeotrope or pseudoazeotrope with hydrogen fluoride because it is possible to “break” such an azeotrope, that is to say that the separation process according to the invention is capable of providing a mixture in which the hydrofluoroalkane and the hydrogen fluoride are present in proportions different from those for which they form an azeotrope or a pseudoazeotrope.
The term “hydrofluoroalkane” is understood to denote the hydrocarbonaceous compounds corresponding to the general formula C
a
H
(2a+2)−b
F
b
in which a=1 to 6 and b=1 to 2a+1. The hydrofluoroalkanes which comprise from 3 to 6 carbon atoms are preferred. The hydrofluoroalkanes which comprise from 3 to 4 carbon atoms are particularly preferred.
Mention may be made, as examples of hydrofluoroalkanes which can be separated from mixtures with hydrogen fluoride by the separation process according to the invention, of 1,1,1,3,3-pentafluoropropane (HFC-245fa), 1,1,2,2,3-pentafluoropropane (HFC-245ca), 1,1,1,2,3-pentafluoropropane (HFC-245eb), 1,1,1,3,3,3-hexafluoropropane (HFC-236fa), 1,1,1,2,3,3-hexafluoropropane (HFC-236ea), 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), 1,1,1,3,3-pentafluoro-2-methylpropane (HFC-365mps), 1,1,1,3,3-pentafluorobutane (HFC-365mfc), 1,1,1,4,4,4-hexafluorobutane (HFC-356mff) and 1,1,1,2,3,4,4,5,5,5-decafluoropentane (HFC-43-10mee). Among these compounds, 1,1,1,3,3-pentafluoropropane (HFC-245fa) and 1,1,1,3,3-pentafluorobutane (HFC-365mfc) are particularly preferred. 1,1,1,3,3-Pentafluorobutane (HFC-365mfc) is very particularly preferred.
The organic compounds used in the separation process according to the invention are capable of reacting with hydrogen fluoride. Organic compound examples are, inter alia, linear or branched alkanes comprising from 1 to 10 carbon atoms which are preferably chlorinated and/or brominated and optionally substituted, and optionally substituted alkenes comprising from 2 to 10 carbon atoms. A chlorinated or chlorofluorinated organic compound is often employed. Halogenated olefins, such as chlorinated, fluorinated or chlorofluorinated olefins, such as, for example, vinyl chloride, vinylidene chloride, trichloroethylene, perchloroethylene, vinylidene fluoride and chlorotrifluoroethylene or fluoropropenes, such as, for example, hexafluoropropene, are well suited, for example.
The organic compound is preferably a chlorinated or chlorofluorinated precursor of the hydrofluoroalkane.
The term “chlorinated or chlorofluorinated precursor of the hydrofluoroalkane” is understood to denote hydrochloroalkanes and hydrochlorofluoroalkanes, that is to say, respectively, chlorinated and chlorofluorinated hydrocarbonaceous compounds comprising at least one chlorine atom and at least one hydrogen atom, the same number of carbon atoms as the desired hydrofluoroalkane and at least one fluorine atom less than the desired hydrofluoroalkane. The desired hydrofluoroalkane can be obtained, starting from at least one chlorinated or chlorofluorinated precursor of the hydrofluoroalkane, by a reaction of this precursor with hydrogen fluoride.
Mention may be made, as examples of chlorinated or chlorofluorinated precursors of hydrofluoroalkanes which can be used in the separation process according to the invention, of hydrochloroalkanes, such as 1,1,1,3,3-pentachloropropane (HCC-240fa), 1,1,2,2,3-pentachloropropane (HCC-240aa), 1,1,1,2,3-pentachloropropane (HCC-240db), 1,1,1,3,3,3-hexachloropropane (HCC-230fa), 1,1,1,2,3,3-hexachloropropane (HCC-230da), 1,1,1,2,3,3,3-heptachloropropane (HCC-220da), 1,1,1,3,3-pentachlo
Lambert Alain
Wilmet Vincent
Connolly Bove & Lodge & Hutz LLP
Siegel Alan
Solvay ( Societe Anonyme)
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