Catalytic manufacture of pentafluoropropenes

Details Catalytic manufacture of pentafluoropropenes Catalytic manufacture of pentafluoropropenes

1999-07-26

2002-04-09

Siegel, Alan (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Halogen containing

C570S157000, C570S158000

Reexamination Certificate

active

06369284

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to processes for the production of pentafluoropropenes, and more particularly, to a catalytic process for the dehydrofluorination of hexafluoropropanes to pentafluoropropenes.
BACKGROUND
Hydrofluoropropenes are useful as materials for the preparation of fluoroplastics, fluoroelastomers and as monomers in the preparation of fluoropolymers.
European Patent Application EP 726 243 discloses a process for the manufacture of 1,2,3,3,3-pentafluoropropene (HFC-1225ye) by the dehydrofluorination of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea). The dehydrofluorination is done in the vapor phase in the presence of a trivalent chromium oxide or partly fluorinated trivalent chromium oxide catalyst.
U.S. Pat. No. 5,396,000 discloses that HFC-236ea can be dehydrofluorinated to HFC-1225ye in the vapor phase in the presence of a catalyst selected from the group consisting of aluminum fluoride, fluorided alumina, metal supported on aluminum fluoride, metal supported on fluorided alumina, and mixtures thereof.
SUMMARY OF THE INVENTION
A process is provided for the manufacture of a pentafluoropropene of the formula CFX═CYCF
3
where X is selected from H and F and where Y is F when X is H and Y is H when X is F. The process comprises contacting a hexafluoropropane of the formula CF
2
XCHYCF
3
at a temperature of from about 200° C. to 500° C. with a catalyst, optionally in the presence of an inert gas. The catalyst is selected form the group consisting of (1) catalysts of (a) at least one compound selected from the oxides, fluorides and oxyfluorides of magnesium, zinc and mixtures of magnesium and zinc, and optionally (b) at least one compound selected from the oxides, fluorides and oxyfluorides of aluminum, provided that the atomic ratio of aluminum to the total of magnesium and zinc in said catalyst is about 1:4, or less (e.g., 1:9), (2) lanthanum fluoride, (3) fluorided lanthanum oxide, (4) activated carbon, and (5) three-dimensional matrix carbonaceous materials.
DETAILED DISCUSSION
This invention provides a process for producing cis- and trans-1,2,3,3,3-pentafluoropropene (i.e., CF
3
CF═CHF or 1225ye) from 1,1,1,2,3,3-hexafluoropropane (i.e., CF
3
CHFCHF
2
, or HFC-236ea). A process is also provided for producing 1,1,3,3,3-pentafluoropropene (i.e., CF
3
CH═CF
2
or 1225zc) from 1,1,1,3,3,3-hexafluoropropane (i.e., CF
3
CH
2
CF
3
, or HFC-236fa). HFC-236ea and HFC-236fa can be prepared by known art methods. For example, CF
3
CH
2
CF
3
can be prepared by contacting a mixture of hydrogen fluoride and 1,1,1,3,3,3-hexachloropropane (i.e., CCl
3
CH
2
CCl
3
) in the vapor phase in the presence of a trivalent chromium catalyst as disclosed in U.S. Pat. No. 5,414,165 and CF
3
CHFCHF
2
can be prepared by hydrogenation of hexafluoropropene (i.e., CF
3
CF═CF
2
) in the the presence of a Pd/C catalyst.
In accordance with this invention, CF
3
CHFCHF
2
is dehydrofluorinated to CF
3
CF═CHF and CF
3
CH
2
CF
3
is dehydrofluorinated to CF
3
CH═CF
2
over a selected catalyst.
Suitable fluorided lanthanum oxide compositions can be prepared in any manner analogous to those known to the art for the preparation of fluorided alumina. For example, the catalyst composition can be prepared by fluorination of lanthanum oxide.
Suitable catalyst compositions can also be prepared by precipitation of lanthanum as the hydroxide which is thereafter dried and calcined to form an oxide, a technique well known to the art. The resulting oxide can then be pretreated as described herein.
The catalyst composition can be fluorinated to the desired fluorine content by treating with a fluorine-containing compound at elevated temperatures, e.g., at about 200° C. to about 450° C. The pretreatment with a vaporizable fluorine-containing compound such as HF, SF
4
, CCl
3
F, CCl
2
F
2
, CHF
3
, CHCIF
2
or CCl
2
FCCIF
2
can be done in any convenient manner including in the reactor which is to be used for carrying out the dehydrofluorination reaction. By vaporizable fluorine-containing compound is meant a fluorine-containing compound which, when passed over the catalyst at the indicated conditions, will fluorinate the catalyst to the desired degree.
A suitable catalyst may be prepared, for example, as follows:
La
2
O
3
is dried until essentially all moisture is removed, e.g., for about 18 hours at about 400° C. The dried catalyst is then transferred to the reactor to be used. The temperature is then gradually increased to about 400° C. while maintaining a flow of N
2
through the reactor to remove any remaining traces of moisture from the catalyst and the reactor. The temperature is then lowered to about 200° C. and the vaporizable fluorine-containing compound is passed through the reactor. If necessary, nitrogen or other inert gases can be used as diluents. The N
2
or other inert diluents can be gradually reduced until only the vaporizable fluorine-containing compound is being passed through the reactor. At this point the temperature can be increased to about 450° C. and held at that temperature to convert the La
2
O
3
to a fluorine content corresponding to at least 80% LaF
3
by weight, e.g., for 15 to 300 minutes, depending on the flow of the fluorine containing compound and the catalyst volume.
Another suitable procedure for the catalyst preparation is to add ammonium hydroxide to a solution of La(NO
3
)
3
.6H
2
O. The ammonium hydroxide is added to the nitrate solution to a pH of about 9.0 to 9.5. At the end of the addition, the solution is filtered, the solid obtained is washed with water, and slowly heated to about 400° C., where it is calcined. The calcined product is then treated with a suitable vaporizable fluorine-containing compound as described above.
Carbon from any of the following sources are useful for the process of this invention; wood, peat, coal, coconut shells, bones, lignite, petroleum-based residues and sugar. Commercially available carbons which may be used in this invention include those sold under the following trademarks: Barneby & Sutcliffe™, Darco™, Nucharm, Columbia JXN™, Columbia LCK™, Calgon PCB, Calgon BPL™, Westvaco™, Norit™ and Barnaby Cheny NB™. The carbon support can be in the form of powder, granules, or pellets, or the like.
Carbons include acid-washed carbons (e.g., carbons which have been treated with hydrochloric acid or hydrochloric acid followed by hydrofluoric acid). Acid treatment is typically sufficient to provide carbons which contain less than 1000 ppm of ash. Suitable acid treatment of carbons is described in U.S. Pat. No. 5,136,113. The carbons of this invention also include three dimensional matrix porous carbonaceous materials. Examples are those described in U.S. Pat. No. 4,978,649, which is hereby incorporated by reference herein in its entirety. Of note are three dimensional matrix carbonaceous materials which are obtained by introducing gaseous or vaporous carbon-containing compounds (e.g., hydrocarbons) into a mass of granules of a carbonaceous material (e.g., carbon black); decomposing the carbon-containing compounds to deposit carbon on the surface of the granules; and treating the resulting material with an activator gas comprising steam to provide a porous carbonaceous material. A carbon-carbon composite material is thus formed.
Other preferred catalysts include catalysts consisting essentially of magnesium fluoride, and catalysts consisting essentially of magnesium fluoride and at least one compound selected from the oxides, fluorides and oxyfluorides of aluminum.
A suitable catalyst may be prepared, for example, as follows:
Magnesium oxide is dried until essentially all water is removed, e.g., for about 18 hours at about 100° C. The dried material is then transferred to the reactor to be used. The temperature is then gradually increased to about 400° C. while maintaining a flow of nitrogen through the reactor to remove any remaining traces of moisture from the magnesium oxide and the reactor. The temperature is then lowered to about 200° C. and a fluoriding agent such as HF or other vaporizable fluo

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