Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
1999-12-10
2002-05-14
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S176000
Reexamination Certificate
active
06388147
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the manufacture of hydrofluorocarbons (i.e., HFCs) and azeotropic compositions thereof, and more particularly to the production of hexafluoropropanes and their azeotropic compositions with HF.
BACKGROUND
1,1,1,2,3,3-hexafluoropropane (i.e., CHF
2
CHFCF
3
or HFC-236ea) and 1,1,1,3,3,3-hexafluoropropane (i.e., CF
3
CH
2
CF
3
or HFC-236fa) are useful as refrigerants, fire extinguishants, heat transfer media, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, carrier fluids, buffing and abrasive agents, displacement drying agents and power cycle working fluids. In particular, HFC-236ea and HFC-236fa are highly effective as refrigerants for use in refrigeration equipment.
U.S. Pat. No. 5,171,901 discloses a process for the preparation of HFC-236fa by contacting a mixture of hexachloropropene and HF with a catalyst consisting of a mixture of CrCl
3
and MgF
2
at temperatures ranging from 350° C. to 500° C. The reaction temperatures and yields of HFC-236fa were as follows: 350° C., none detected; 400° C., 10%; 450° C., 55%; and 500° C., 64%. Other products formed in varying amounts were CF
3
CHClCF
3
, CF
3
CCl
2
CF
3
, CF
3
CCl═CF
2
, CF
3
CCl═CClF, and CF
3
CCl═CCl
2
. HFC-236ea has been prepared by the hydrogenation of hexafluoropropane. There is an interest in developing additional, efficient processes for the manufacture of HFC-236ea and HFC-236fa from various starting materials.
SUMMARY OF THE INVENTION
This invention provides a process for producing CF
3
CHFCHF
2
. This process comprises reacting CF
3
CF═CHF with HF at an elevated temperature over a catalyst selected from the group consisting of aluminum fluoride, fluorided alumina, metals supported on aluminum fluoride, metals supported on fluorided alumina and catalysts comprising trivalent chromium. Also provided is a process for enriching CF
3
CF═CHF from a starting mixture containing CF
3
CF═CHF and CF
3
CH═CF
2
. This process comprises reacting said starting mixture with HF at an elevated temperature over a catalyst consisting essentially of carbon, a catalyst consisting essentially of metal halides supported on carbon, a catalyst consisting essentially of Cr
2
O
3
, or mixtures thereof (provided that when Cr
2
O
3
is present the temperature is about 250° C. or less) to produce a product mixture containing CF
3
CH
2
CF
3
and unreacted CF
3
CF═CHF wherein the mole ratio of CF
3
CF═CHF to CF
3
CH═CF
2
is greater than the ratio thereof in the starting mixture. This invention provides for production of CF
3
CH
2
CF
3
(or both CF
3
CFHCHF
2
and CF
3
CH
2
CF
3
) by reacting a starting mixture containing both CF
3
CF═CHF and CF
3
CH═CF
2
with HF at an elevated temperature over a fluorination catalyst.
This invention further provides compositions which consist essentially of hydrogen fluoride in combination with an efective amount of a compound selected from the group consisting of CF
3
CHFCHF
2
and CF
3
CH
2
CF
3
to form an azeotrope or azeotrope-like composition with hydrogen fluoride, said composition containing from about 31 to 60 mole percent CF
3
CHFCHF
2
or from about 41 to 63 mole percent CF
3
CH
2
CF
3
.
DETAILED DESCRIPTION
The addition of hydrogen fluoride across the double bond of olefinic compounds normally follows Markovnikov's rule (i.e., hydrogen is added to the carbon atom of the double bond which has a hydrogen atom, and fluorine to the olefinic carbon atom which has a fluorine atom). U.S. Pat. No. 5,268,122 provides examples of Markovnikov addition to olefinic fluoro-carbon bonds. In accordance with this invention, HF adds across the double bond of CF
3
CF═CHF to produce CH
2
CHFCF
3
rather than the Markovnikov expected product, CH
2
FCF
2
CF
3
. Thus, this invention provides a process which involves reacting CF
3
CF═CHF with HF to add H at the olefinic carbon different from the olefinic carbon already containing a hydrogen such that CF
3
CFHCHF2 is produced.
CF
3
CF═CHF can be prepared according to R. N. Hazeldine et al., J. Chem. Soc. Perkin Trans.1, 1303-07 (1974). CF
3
CF═CHF may also be produced from CF
3
CF
2
CH
2
F (i.e., HFC-236cb) by dehydrofluorination (e.g., by reacting CF
3
CF
2
CH
2
F with KOH). Because of this unexpected chemistry, HFC-236cb can be converted to HFC-236ea by first dehydrofluorinating HFC-236cb to CF
3
CF═CHF and then reacting the CF
3
CF═CHF with HF to afford HFC-236ea. Accordingly, this invention provides a process for producing CF
3
CHFCHF
2
from its isomer CF
3
CF
2
CH
2
F by dehydrofluorinating CF
3
CF
2
CH
2
F to CF
3
CF═CHF, and reacting CF
3
CF═CHF with HF to provide CF
3
CHFCHF
2
.
Preferred catalysts for the reaction of CF
3
CF═CHF with HF include aluminum fluoride, fluorided alumina, metals supported on aluminum fluoride, metals supported on fluorided alumina and catalysts containing trivalent chromium. Suitable metals (including metal oxides, metal halides and/or other metal salts) for use on aluminum fluoride or fluorided alumina include (in addition to trivalent chromium) Group VIII metals (iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum), Group VIIB metals (manganese, rhenium), Group IIIB metals (scandium, yttrium, lanthanum), Group IB metals (copper, silver, gold), zinc and/or metals having an atomic number of 58 through 71 (cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, or lutetium). Preferably the total metal content of the catalyst will be from about 0.1 to 20 percent by weight; typically from about 0.1 to 10 percent by weight of the supported catalyst. It is understood that in catalyst preparation a metal compound may be supported on an alumina, and the resulting supported metal composition may then be fluorinated. Especially preferred for the reaction of CF
3
CF═CHF are chrome oxide catalysts prepared by the pyrolysis of ammonium dichromate (see U.S. Pat. No. 5,036,036 for preparative details).
Typically the temperature for the reaction of CF
3
CF═CHF is from about 275° C. to 450° C. Temperatures between 300° C. and 400° C. are generally preferred.
A process for production of CF
3
CH
2
CF
3
is also provided by this invention. CF
3
CH
2
CF
3
may be produced by reacting CF
3
CH═CF
2
in a starting mixture containing CF
3
CH═CF
2
and CF
3
CF═CHF with HF to add H at the olefinic carbon already containing a hydrogen. Fluorination catalysts are used for this reaction. Preferably, the mole ratio of CF
3
CH═CF
2
to CF
3
CF═CHF in the starting mixture is from 5:95 to 95:5.
Suitable catalysts which can be used for reacting CF
3
CH═CF
2
with HF to produce CF
3
CH
2
CF
3
include vapor phase fluorination catalysts. Catalysts which may be used in accordance with this invention include metals (including metal oxides, metal halides and/or other metal salts); fluorided alumina; aluminum fluoride; metals on aluminum fluoride; metals on fluorided alumina; metals on carbon; and chromium catalysts. Suitable metals for use in such catalysts include chromium, Group VIII metals (iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum), Group VIIB metals (manganese, rhenium), Group IIIB metals (scandium, yttrium, lanthanum), Group IB metals (copper, silver, gold), zinc and/or metals having an atomic number of 58 through 71 (cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, or lutetium). Preferably, when used on a support, the total metal content of the catalyst will be from about 0.1 to 20 percent by weight; typically from about 0.1 to 10 percent by weight.
Fluorided alumina and aluminum fluoride can be prepared as described in U.S. Pat. No. 4,902,838. Metals on aluminum fluoride and metals on fluorided alumina can be prepared by procedures described in U.S. Pat. No. 4,766,260. Catalysts comprising chromium
Rao Velliyur Nott Mallikarjuna
Walczak Francis John
E. I. du Pont de Nemours and Company
Witherspoon Sikarl A.
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