Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2000-07-13
2002-06-18
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
Reexamination Certificate
active
06407297
ABSTRACT:
The present invention relates to a process for the preparation of fluorine-containing organic compounds by reacting a haloalkene with hydrogen fluoride, particularly to a process for the preparation of hydrofluorocarbons from fluoroalkenes, more particularly to a process for the preparation of 1,1,1,2,3,3,3-heptafluoropropane from hexafluoropropene, azeotropes or azeotrope-like mixtures of a hydrofluorocarbonthydrogen fluoride, particularly azeotropes or azeotrope-like mixtures of 1,1,1,2,3,3,3-heptafluoropropane/hydrogen fluoride and azeotropes or azeotrope-like mixtures of a haloalkene/hydrogen fluoride, particularly azeotropes or azeotrope-like mixtures of hexafluoropropene/hydrogen fluoride.
Hydrofluorocarbons are widely used as replacements for chlorofluorocarbon compounds in a variety of applications. Such applications include use in medical applications, for example as an aerosol propellant, use as a fire suppressant, use in refrigeration applications and in other applications. 1,1,1,2,3,3,3-heptafluoropropane, which is known in the art as Hydrofluorocarbon 227ea and will hereinafter be referred to as “HFC 227ea” for convenience, has zero ozone depletion potential and is particularly beneficial in medical applications in the light of its combination of properties including low toxicity, non-flammability, solvent properties and boiling point.
It is known to produce hydrofluorocarbons by the hydrofluorination of a fluoroalkene to the corresponding hydrofluoroalkane, optionally in the presence of a catalyst, in the liquid phase or vapour phase. Hydrogen fluoride is known for use as a hydrofluorination agent in such hydrofluorination processes.
A variety of materials may be employed as catalysts in such hydrofluorination processes.
For example, in the vapour phase reaction of fluoroalkenes with hydrogen fluoride for the preparation of hydrofluorocarbons, eg HFC 227ea from hexafluoropropene, DE 2712732 and GB 902590 disclose the use of a chromium oxyfluoride catalyst and an activated carbon catalyst respectively.
For example, in the liquid phase reaction of fluoroalkenes with hydrogen fluoride for the preparation of hydrofluorocarbons, eg HFC 227ea from hexafluoropropene, WO 97/11042 and WO 96/0243 disclose the use of catalysts comprising an organic amine complexed with hydrogen fluoride and certain antimony catalysts respectively.
The disclosures in the aforementioned patent specifications are incorporated herein by way of reference.
A stoichiometric excess of hydrogen fluoride to fluoroalkene is normally employed in the aforementioned processes and the degree of conversion of fluoroalkene to hydrofluorocarbon is dependent on inter alia the catalyst employed, if any, and the conditions in the reactor, etc.
The product from such reactions typically comprises the desired fluorine-containing organic compound, organic by-products and hydrogen fluoride. For example, where the haloalkene is hexafluoropropene, which will hereinafter be referred to as “HFP” for convenience, the product stream leaving the reactor in which HFP is reacted with hydrogen fluoride typically contains HFC 227ea, HFP, hydrogen fluoride and azeotropes thereof.
It is normal practice to recover as much as possible of the hydrogen fluoride from the product stream from such hydrofluorination reactions for re-use. This may be partially achieved by distillation. However, the presence in the product stream of an azeotrope or azeotrope-like mixture of HFC 227ea/hydrogen fluoride and an azeotrope or azeotrope-like mixture of HFP/hydrogen fluoride limits the extent to which hydrogen fluoride can be separated from the fluoro-organic compounds by simple distillation.
It is known that the stream comprising the hydrofluorocarbonriydrogen fluoride azeotrope, eg HFC 227ea/hydrogen fluoride azeotrope, and the halo alkene/hydrogen fluoride azeotrope, eg HFP/hydrogen fluoride azeotrope, after recovery of a portion of the hydrogen fluoride by distillation, can be water-washed to allow recovery of both a mixture of organic compounds essentially free of hydrogen fluoride and aqueous hydrogen fluoride. However, such a treatment is wasteful of hydrogen fluoride since it is normal practice for aqueous hydrogen fluoride generated in this way to be neutralised with caustic solution and/or lime and ultimately disposed of.
Alternatively, the product stream from the reaction of a haloalkene with hydrogen fluoride, after recovery of a portion of the hydrogen fluoride by distillation, may be treated with a solution of alkali metal dissolved in anhydrous hydrogen fluoride as described in our patent specification WO 97/13179. However, although such a process recovers hydrogen fluoride for re-use within the process, it has the disadvantage of requiring additional equipment.
Furthermore, it is known that in the preparation of fluorine-containing organic compounds by the reaction of a haloalkene with hydrogen fluoride the haloalkene/hydrogen fluoride azeotrope can be separated from the fluorine-containing compound/hydrogen fluoride azeotrope by fractional distillation and hydrogen fluoride can be removed from the fluorine-containing organic compound/hydrogen fluoride azeotrope by treatment with water. However, treatment of the fluorine-containing organic compound/hydrogen fluoride azeotrope with water to remove hydrogen fluoride therefrom involves the use of expensive equipment and is wasteful of hydrogen fluoride.
It will be appreciated that whereas aqueous scrubbing is an effective way of removing hydrogen fluoride from the organic compound(s) after reacting hydrogen fluoride with a haloatkene aqueous scrubbing tends to be expensive in terms of hydrogen fluoride loss from the process. Preferably as much as possible, more preferably essentially all, of the hydrogen fluoride is separated from the product stream before aqueous scrubbing and particularly more preferably aqueous scrubbing is avoided.
Where in the preparation of a fluorine-containing organic compound by the reaction of a haloalkene with hydrogen fluoride the haloalkene/hydrogen fluoride azeotrope is more volatile, ie has a lower boiling point, than the fluorine-containing organic compound/hydrogen fluoride azeotrope produced in the reaction we have now found that by (a) charging the reaction product to a distillation column, (b) introducing the haloalkene into the distillation column and (c) distilling the resulting mixture both the fluorine-containing organic compound substantially free of hydrogen fluoride and the haloalkene/hydrogen fluoride azeotrope can be separated.
The separated haloalkene/hydrogen fluoride azeotrope can be recycled to the reaction vessel, can be used in another reaction or preferably at least a portion thereof is separated into a haloalkene-rich liquid phase and a hydrogen fluoride-rich liquid phase as is hereinafter more fully described.
According to the first aspect of the present invention there is provided a process for the preparation of a fluorine-containing organic compound by reacting a haloalkene with hydrogen fluoride wherein both the fluorine-containing organic compound and the haloalkene separately form azeotropes with hydrogen fluoride and wherein the haloalkene/hydrogen fluoride azeotrope is more volatile than the fluorine-containing organic compound/hydrogen fluoride azeotrope characterised by the Steps of:
A. charging the haloalkene and the mixture comprising the fluorine-containing organic compound/hydrogen fluoride azeotrope, or azeotrope-like mixture, and optionally the haloalkene/hydrogen fluoride azeotrope, or azeotrope-like mixture, and/or hydrogen fluoride arising from the reaction of the haloalkene with hydrogen fluoride to a distillation column
B. recovering the haloalkene/hydrogen fluoride azeotrope, or azeotrope-like mixture, and the fluorine-containing organic compound from the distillation column separately; and
C. optionally separating at least a portion of the haloalkene/hydrogen fluoride azeotrope, or azeotrope-like mixture, recovered from Step B into a haloalkene-rich liquid phase and a hydrogen fluoride-rich liquid phase.
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Ineos Fluor Holdings Limited
Siegel Alan
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