Compositions – Vaporization – or expansion – refrigeration or heat or energy...
Reexamination Certificate
2000-11-27
2003-04-01
Hardee, John (Department: 1751)
Compositions
Vaporization, or expansion, refrigeration or heat or energy...
C570S134000, C570S136000
Reexamination Certificate
active
06540933
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the synthesis of hexafluoropropene from 2,3-dichloro-1,1,1,2,3,3-hexafluoropropane and the azeotrope of the latter compound with HF.
BACKGROUND
Commercial methods for the preparation of hexafluoropropene (CF
3
CF═CF
2
or HFP), a fluoromonomer, typically involve temperatures greater than 600° C. The high reaction temperatures lead to the formation of perfluoroisobutylene, an extremely toxic compound which is costly to remove and destroy (e.g., see European Patent Application No. 002,098). Processes for the manufacture of HFP at lower temperatures based on the use of acyclic three-carbon hydrocarbons or partially halogenated three-carbon hydrocarbons are disclosed in U.S. Pat. Nos. 5,043,491, 5,057,634 and 5,068,472.
There is a need for alternative methods of manufacturing hexafluoropropene.
2,3-Dichloro-1,1,1,2,3,3-hexafluoropropane (i.e., CClF
2
CClFCF
3
or CFC-216ba) is a known compound. For example, it can be prepared as described in J. Kvicala et al., J. Fluorine Chem., 43 (1989) 155-175. C
3
Cl
3
F
5
containing 90% of CF
3
CClFCCl
2
F (CFC-215bb) is reacted with a fluorination mixture containing HF (90 vol. %) and Cl
2
(10 vol. %) in the vapor phase in the presence of a ferric chloride on charcoal catalyst at 390° C. to obtain a C
3
Cl
2
F
6
product which contained 85% CClF
2
CClFCF
3
and 15% CF
3
CCl
2
CF
3
. The product was collected in an aqueous sodium hydroxide trap. A similar preparation is disclosed in German Patent Application No. DE 1,237,084. CFC-215bb is reacted in the vapor phase at 115° C. with an HF/Cl
2
mixture using an SbCl
5
supported on carbon catalyst which was treated with HF prior to use. The product gas mixture was washed with water and aqueous NaOH.
SUMMARY OF THE INVENTION
This invention provides a process for the manufacture of CF
3
CF═CF
2
. The process comprises contacting 2,3-dichloro-1,1,1,2,3,3-hexafluoropropane with at least 0.1 mole of hydrogen in a reaction vessel of titanium, nickel or iron or their alloys, which is either empty or packed with particles or formed shapes of titanium, nickel or iron or their alloys, at a temperature within the range of from about 350° C. to about 600° C. and for a time sufficient to produce hexafluoropropene.
Also provided are compositions which comprise hydrogen fluoride in combination with an effective amount of CClF
2
CClFCF
3
to form an azeotrope or azeotrope-like composition with hydrogen fluoride, said composition containing from about 8.7 to 33.6 mole percent CClF
2
CClFCF
3
.
DETAILED DESCRIPTION
CFC-216ba or its azeotrope with HF (see below) can be dechlorinated with hydrogen to afford hexafluoropropylene.
The reaction of CFC-216ba with hydrogen is done in a reaction vessel of titanium, nickel or iron or their alloys. A reaction vessel of these materials (e.g., a metal tube) optionally packed with the metal in suitable form may also be used. When reference is made to alloys, it is meant a nickel alloy containing from 1 to 99.9% (by weight) nickel, an iron alloy containing from 0.2 to 99.9% (by weight) iron and a titanium alloy containing 72 to 99.8% (by weight) titanium.
Most preferred for the practice of this invention is an empty reaction vessel made of nickel or alloys of nickel such as those containing 40% to 80% nickel, e.g., Inconel® 600 nickel alloy, Hastelloy® C617 nickel alloy or Hastelloy® C276 nickel alloy.
When used for packing the metal or alloys may be particles or formed shapes such as, perforated plates, saddles, rings, wire, screen, chips, pipe, shot, gauze and wool.
The reaction temperature can be between from about 350° C. to about 600° C. Preferably the reaction temperature is at least about 450° C.
The amount of hydrogen contained in the gas stream contacted with CFC-216ba should be at least 0.1 mole per mole of CFC-216ba. In general, the amount of hydrogen is between from about 0.2 to 60 moles per mole of CFC-216ba and more preferably is between from about of 0.4 to 10 moles per mole of CFC-216ba. The higher the ratio of H
2
:CFC-216ba, the more CHF
2
CHFCF
3
is formed. The hydrogen can be diluted with an inert gas, e.g., nitrogen, helium or argon.
Although substantial conversions can be achieved in a once-through system, recycle of unreacted CFC-216ba can be employed in a conventional manner.
In addition to the preparations described above, CFC-216ba may also be prepared by contacting CFC-215bb in the vapor phase (e.g., at 115° C.) with a mixture of HF and Cl
2
in the presence of a catalyst (e.g., an SbCl
5
supported on carbon catalyst which is treated with HF prior to use). The reaction product effluent comprises CFC-215bb, CFC-216ba, HF and HCl before scrubbing with water. As noted above, it has now been found that CFC-216ba forms an azeotrope with HF. A portion of the CFC-216ba produced can be used as an azeotropic composition of CFC-216ba with HF and reacted to form CFC-217ba (see below); with another portion of the CFC-216ba being used for HFP production.
The present invention further provides compositions which consist essentially of hydrogen fluoride and an effective amount of CClF
2
CClFCF
3
to form an azeotropic combination with hydrogen fluoride. By effective amount is meant an amount which, when combined with HF, results in the formation of an azeotrope or azeotrope-like mixture. As recognized in the art, an azeotrope or an azeotrope-like composition is an admixture of two or more different components which, when in liquid form under given pressure, will boil at a substantially constant temperature, which temperature may be higher or lower than the boiling temperatures of the individual components, and which will provide a vapor composition essentially identical to the liquid composition undergoing boiling.
An azeotrope is a liquid mixture that exhibits a maximum or minimum boiling point relative to the boiling points of surrounding mixture compositions. An azeotrope is homogeneous if only one liquid phase is present. An azeotrope is heterogeneous if more than one liquid phase is present. Regardless, a characteristic of minimum boiling azeotropes is that the bulk liquid composition is then identical to the vapor composition in equilibrium therewith, and distillation of the azeotropic mixture is ineffective as a separation technique. For the purpose of this discussion, azeotrope-like composition means a composition which behaves like an azeotrope (i.e., has constant-boiling characteristics or a tendency not to fractionate upon boiling or evaporation). Thus, the composition of the vapor formed during boiling or evaporation of such compositions is the same as or substantially the same as the original liquid composition. Hence, during boiling or evaporation, the liquid composition, if it changes at all, changes only to a minimal or negligible extent. This is to be contrasted with non-azeotrope-like compositions in which during boiling or evaporation, the liquid composition changes to a substantial degree.
Accordingly, the essential features of an azeotrope or an azeotrope-like composition are that at a given pressure, the boiling point of the liquid composition is fixed and that the composition of the vapor above the boiling composition is essentially that of the boiling liquid composition (i.e., no fractionation of the components of the liquid composition takes place). It is also recognized in the art that both the boiling point and the weight percentages of each component of the azeotropic composition may change when the azeotrope or azeotrope-like liquid composition is subjected to boiling at different pressures. Thus an azeotrope or an azeotrope-like composition may be defined in terms of the unique relationship that exists among components or in terms of the compositional ranges of the components or in terms of exact weight percentages of each component of the composition characterized by a fixed boiling point at a specified pressure. It is also recognized in the art that various azeotropic compositions (including their boiling points at particular pressures) may be calculated (see, e.g
Rao V. N. Mallikarjuna
Sievert Allen Capron
E. I. du Pont de Nemours and Company
Hardee John
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