1,1,1,2,3,3,3-heptafluoropropane manufacturing process

Details 1,1,1,2,3,3,3-heptafluoropropane manufacturing process 1,1,1,2,3,3,3-heptafluoropropane manufacturing process

1999-04-01

2001-08-28

Siegel, Alan (Department: 1621)

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

Organic compounds

Halogen containing

C570S169000

Reexamination Certificate

active

06281395

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a synthesis of 1,1,1,2,3,3,3-heptafluoropropane by contacting HF and hexafluoropropylene in the presence of a catalyst.
BACKGROUND
1,1,1,2,3,3,3-Heptafluoropropane (i.e., CF
3
CHFCF
3
or HFC-227ea) is useful as a fire extinguishant, refrigerant, blowing agent and propellant. It can be prepared by the addition of hydrogen fluoride to hexafluoropropylene. British Patent Specification No. 902,590 claims a process for the manufacture of HFC-227ea by contacting in the vapor phase an equimolar mixture of HF and hexafluoropropylene in the presence of activated carbon at temperatures between 250° C. and 450° C. The reaction temperatures cited in the two examples of this publication were 392 to 402° C. and 300 to 306° C. Various problems are reported associated with operating at such high reaction temperatures including operating safety, corrosion of the construction materials involved and in particular, production of toxic products, especially perfluoroisobutylene (PFIB). U.S. Pat. No. 5,399,795 discloses the manufacture of HFC-227ea by the reaction of HF and hexafluoropropene in the presence of a weakly basic ion exchange resin. U.S. Pat. No. 5,689,019 discloses the same reaction in the presence of an antimony catalyst. Both of these patents suggest that reaction temperatures of less than 120° C. are necessary in order to suppress the formation of PFIB. PFIB removal is addressed in U.S. Pat. No. 5,705,719.
There is a need for a high yield HFC-227ea manufacturing process which does not co-produce even small quantities of PFIB.
SUMMARY OF THE INVENTION
A process is provided for the manufacture of 1,1,1,2,3,3,3-heptafluoropropane containing less than 0.01 ppm (CF
3
)
2
C═CF
2
. The process comprises (a) contacting hexafluoropropene in the vapor phase at a temperature of less than about 260° C. with hydrogen fluoride in the presence of a fluorination catalyst selected from the group consisting of (i) an activated carbon treated to contain from about 0.1 to about 10 weight % added alkali or alkaline earth metals, (ii) three dimensional matrix porous carbonaceous materials, (iii) supported metal catalysts comprising trivalent chromium and (iv) unsupported chrome oxide (Cr
2
O
3
) prepared by the pyrolysis of (NH
4
)
2
Cr
2
O
7
, to produce a product containing less than 10 parts perfluoroisobutylene per million parts of 1,1,2,3,3,3-heptafluoropropane; and (b) treating the product of (a) as necessary to remove excess perfluoroisobutylene.
DETAILS OF THE INVENTION
This invention provides a process for the preparation of 1,1,1,2,3,3,3-heptafluoropropane (i.e., CF
3
CHFCF
3
or HFC-227ea) by contacting hexafluoropropylene (i.e., CF
2
═CFCF
3
, or HFP) with anhydrous HF in the presence of selected catalysts. The catalysts used herein are selected to facilitate producing only low levels (i.e., 10 ppm, or less, based on the HFC-227ea produced) of PFIB. This in turn reduces the cost of any further treatment to obtain the desired product having less than 0.01 ppm PFIB (i.e., less than 0.01 parts by weight PFIB per million parts HFC-227ea) in the final product.
Among the suitable catalysts of this invention is treated activated carbon. It is noted that carbon may have alkali and/or alkaline earth metal associated with its inherent ash content. However, in accordance with this invention, added alkali or alkaline earth metal is desirable. Indeed, preferably, a low ash content carbon is used. Preferably, the low ash content carbon is treated with an alkali or akaline earth metal compound selected from lithium, sodium, potassium, rubidium cesium, magnesium, calcium, strontium and/or barium. Potassium is particularly preferred. In accordance with one embodiment of this invention, the carbon used for HFC-227ea preparation contains less than about 0.1 weight percent ash. The low ash content carbon is prepared as described in U.S. Pat. No. 5,136,113 which is incorporated herein by reference. Typically, the low ash content carbon is treated so as to have a total content of from about 0.1 to 10 weight percent of added alkali or alkaline earth metals. The treatment is done using soluble of the metals by procedures well known to those skilled in the art.
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 suitable vapor phase fluorination catalysts include certain catalysts comprising trivalent chromium. Examples include supported CrX
3
, where each X is independently Cl or F. In addition to a catalytically effective amount of trivalent chromium such fluorination catalysts can include other components to increase catalyst activity and/or life such as one or more divalent metal cations (e.g., zinc, magnesium and/or cobalt). The trivalent chromium catalyst may be supported, for example on alumina, aluminum fluoride, fluorided alumina, magnesium fluoride or carbon. Suitable unsupported Cr
2
O
3
may be prepared by the pyrolysis of (NH
4
)
2
Cr
2
O
7
as described in U.S. Pat. No. 5,036,036.
The physical shape of the catalyst is not critical and may, for example, include pellets, powders or granules.
The catalytic hydrofluorination of CF
3
CF═CF
2
to CF
3
CHFCF
3
is suitably conducted at a temperature in the range of from about 175° C. to about 260° C., provided that when a carbon is used as the fluorination catalyst, the reaction temperature is less than about 230° C., and preferably from about 200° C. to about 230° C. The contact time is typically from about 1 to about 300 seconds, preferably from about 10 to about 60 seconds. The mole ratio of HF:HFP is typically in the range of 1:1 to 30: 1, and is preferably from 2: 1 to 5:1.
The HFP starting material can be produced by conventional means. However, of particular note is HFP produced (along with HFC-227ea itself) by hydrodechlorination of 2-chloro-1,1,1,2,3,3,3-heptafluoropropane (i.e., CF
3
CClFCF
3
or CFC-217ba). Further information on production of HFP/CFC-227ea mixtures using CFC-217ba is provided in U.S. patent application No. 60/080,708, the priority document for U.S. patent application Ser. No. 09/283,450 which issued as U.S. Pat. No. 6,018,083.
The reaction pressure can be subatmospheric, atmospheric or superatmospheric.
The process of this invention can be carried out readily in the vapor using well known chemical engineering practice.
Traces of PFIB can be removed by treatment with a solution of hydrogen fluoride and/or hydrogen chloride in methanol at a temperature and pressure at which the methanol solution is liquid. Further details about the PFIB removal treatment can be found in European Patent Application No. 0 002 098 and U.S. Pat. No. 5,705,719. Thus, when necessary in (b), excess PFIB can be removed by sorption or reaction with methanol.
Without further elaboration, it is believed that one skilled in the art can, using the description herein, utilize the present invention to its fullest extent. The following specific embodiments are to be construed as illustrative, and not as constraining the remainder of the disclosure in any way whatsoever.


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