Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
1995-06-02
2004-07-13
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
Reexamination Certificate
active
06762333
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to halogen-substituted hydrocarbons containing fluorine, and more particularly, to a process for reducing the fluorine content of hydrofluorocarbons and hydrohalofluorocarbons.
BACKGROUND
Hydrofluorocarbons (i.e., compounds containing only the elements carbon, fluorine, and hydrogen) and hydrohalofluorocarbons (i.e., compounds containing only the elements carbon, fluorine, hydrogen and chlorine and/or bromine) are widely used as refrigerants, aerosol propellants, blowing agents, cleaning agents, fire extinguishants and chemical intermediates. Commercially, many of such compounds are prepared by the reactions of hydrogen fluoride with olefins or saturated compounds containing chlorine. Some compounds (e.g., various hydrofluorocarbons) can be prepared by the hydrogenolysis of an appropriate chlorine and/or bromine-containing precursor. These processes can also produce halogenated hydrocarbons having a lesser commercial value and/or not having the desired properties. Furthermore, the supply/demand situation for any particular product can vary and there may be an oversupply of a particular hydrofluorocarbon or hydrohalofluorocarbon. For environment al reasons, it may not be advantageous to dispose of surplus or by-products by such methods as incineration, but rather to further react these materials to increase the yields of useful products. A reduction of the fluorine content of various hydrofluorocarbons and hydrochlorofluorocarbons can improve their value as commercial products and/or as precursors for producing other useful products.
SUMMARY OF THE INVENTION
This invention provides a method for reducing the fluorine content of an acyclic saturated compound of the formula C
n
F
a
X
b
H
c
wherein each X is independently selected from the group consisting of Cl and Br, and wherein n is 1 to 6, a is 1 to 13, b is 0 to 12, c is 1 to 9, and a+b+c equals 2n+2. The method comprises the step of reacting the acyclic saturated compound with HCl in the vapor phase at an elevated temperature in the presence of a catalyst, the mole ratio of HCl to the acyclic saturated compound being at least about 1:1.
DETAILED DESCRIPTION
The present invention provides a process for reducing the fluorine content of an acyclic saturated compound of the formula C
n
F
a
X
b
H
c
wherein each X is independently selected from Cl and Br, and wherein n is 1 to 6, a is 1 to 13, b is 0 to 12, c is 1 to 9, and a+b+c equals 2n+2, by reacting the acyclic saturated compound with HCl in the vapor phase in the presence of a catalyst. Of particular note are embodiments of the invention where n is 1, embodiments of the invention where n is 2, and embodiments of the invention where n is 3. Where n is 2 or more, the reaction products having reduced fluorine content may include saturated and/or olefinic compounds. For example, CH
3
CF
3
may be reacted to produce saturated compounds (e.g., CH
3
CClF
2
and CH
3
CCl
2
F) and unsaturated compounds (e.g., CH
2
═CF
2
, CH
2
═CClF and CH
2
═CCl
2
).
Included in this invention is the reaction of an acyclic saturated compound of the formula C
n
F
a
X
b
H
c
wherein n is at least 2, c is at least 2 and the mole ratio of HCl to the compound is at least about 5:1 to produce a hydrogen-containing olefinic product. Also included is the reaction of an acyclic saturated compound of the formula C
n
F
a
X
b
H
c
wherein n is 2, c is 1 and the mole ratio of HCl to the compound is at least about 5:1 to produce a perhalogenated olefinic product. For example, CF
3
CF
2
H may be reacted with HCl (preferably in a molar ratio of HCl:CF
3
CF
2
H of at least about 6:1) in the presence of a catalyst (e.g., an aluminum fluoride catalyst) to produce CCl
2
═CCl
2
as the major halogenated hydrocarbon reaction product. Also included is the reaction of an acyclic saturated compound of the formula C
n
F
a
X
b
H
c
where n is at least 2 (e.g., n is 2 or n is 3) and the mole ratio of HCl to the compound is about 5:1 or less (e.g., from 2:1 to 5:1) at an elevated temperature less than about 350° C. (e.g., 250° C. to 325° C.) to produce compounds of reduced fluorine content which are primarily (i.e., more than 50 mole percent) saturated compounds. Other embodiments involve the reaction of an acyclic saturated compound of the formula CF
a
X
b
H
c
wherein b is 0 to 2.
The invention includes reactions of HCl with mixtures of compounds of the formula C
n
F
a
X
b
H
c
with each other and/or with other organic compounds such as ethers (e.g., dimethylether), alcohols (e.g., methanol) and hydrocarbons (e.g., propane and/or cyclohexane). In some embodiments, the mixtures are azeotropic. Examples of acyclic saturated compounds which may be reacted with HCl in accordance with this invention include CH
2
FCF
3
, CHF
3
, CHF
2
CF
3
, CH
3
CF
3
, CH
3
CHF
2
, CHCl
2
F, CHClF
2
, CHCl
2
CF
3
, CHClFCF
3
, CH
2
ClCF
3
, CH
3
CF
2
Cl, CHBrF
2
and CF
3
CHBrF.
Chlorine may be present in some process embodiments, either as an initial reactant or as an in-situ formed product. Of note are reactions wherein Cl
2
is present during the reaction and a perhalogenated product is produced.
Suitable catalysts which can be used for reducing the fluorine content of the starting materials by reaction with HCl include vapor phase fluorination catalysts. Catalysts which may be used in accordance with this invention include metals (including elemental metals, metal oxides and/or other metal salts); alumina; fluorided alumina; aluminum fluoride; metals on alumina; metals on aluminum fluoride; magnesium fluoride on aluminum fluoride; metals on fluorided alumina; alumina on carbon; aluminum fluoride on carbon; fluorided alumina on carbon; metals on carbon; chromium catalysts (e.g., Cr
2
O
3
by itself or with other metals such as Mg and/or Zn); mixtures of metals, aluminum fluoride, and graphite; and chromium-magnesium optionally on graphite. Suitable metals for use as catalysts (optionally on alumina, aluminum fluoride, fluorided alumina or carbon) 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, gadolonium, terbium, dysprosium, holmiun, eribum, thulium, ytterbium or lutetium). Preferably, when used with 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 are well known in the art (see e.g., U.S. Pat. No. 5,036,036). Chromium supported on alumina can be prepared as described in U.S. Pat. No. 3,541,165. Chromium supported on carbon can be prepared as described in U.S. Pat. No. 3,632,834. Catalysts comprising chromium and magnesium may be prepared as described in Canadian Patent No. 2,025,145. Other metals and magnesium optionally on graphite can be prepared in a similar manner to the latter patent. Preferred catalysts include catalysts comprising aluminum fluoride and catalysts comprising chromium oxide.
Weak catalysts for this reaction such as silicon carbide may also be used.
The reaction of the acyclic saturated compound of the formula C
n
F
a
X
b
H
c
with HCl in the presence of the catalysts of the instant invention is suitably conducted at a temperature within the range of from about 250° C. to 450° C., preferably from about 300° C. to 400° C., and most preferably from about 325° C. to about 375° C. The contact time is typically from about 1 to about 120 seconds, preferably from about 5 to about 60 seconds.
The amount of HCl should be at least a stoichiometric amount. Generally,
Manzer Leo Ernest
Rao V. N. Mallikarjuna
Swearingen Steven Henry
Barts Samuel
E. I. du Pont de Nemours and Company
Price Elvis O.
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