FIELD OF THE INVENTION
The present invention relates to the process of preparing Trifluoroacetyl fluoride by catalytic vapor phase fluorination of trichloroacetyl chloride with anhydrous hydrogen fluoride using chromia - alumina impregnated with Zinc salt as the catalyst.
PRIOR ART
It is known that number of metal compounds exhibit catalytic effect in gas phase fluorination of perchloro compounds such as trichloroacetyl chloride, trichloroacetaldehyde and hexachloroacetone. The oxides, fluorides & oxyfluoride compounds of chromium as a catalyst for this purpose are described in number of patents.
US patent application S. No. 2748866 teaches the use of a catalyst, which is capable of performing halogen exchange in aliphatic compounds wherein, the halogenated carbonyl compounds are known for their deactivating action of such catalyst.
US patent number 2745886 addresses deactivation of chromia catalyst by treatment with oxygen at a temperature of 500 degree C. This treatment activates the catalyst for a short time only.
British Patent No. GB976316 describes vapor phase fluorination of trichloroacetyl chloride over chromia gel catalyst wherein chlorodifluoroacetyl fluoride is formed as a major product.
US Patent No. 3804778 an attempt is to complete perfluorination of perchlorinated compound by elevating the reactor temperature, wherein only limited product yield is obtained due to significant parasitic cracking of trichloroacetyl chloride leading to the formation of carbon monoxide and aliphatic chlorinated/ fluorinated hydrocarbon
US Patent No. 3787489 addresses the undesirable decomposition of perchloro compound

during the fluorination reaction by partitioning the reactor into three different zones maintained at different temperature, each zone is separated by intermediate layer of alumina. Packing the catalyst in such a manner & maintaining different temperature in each zone of the reactor is complicated and is uneconomical on commercial scale.
US patent No. 5672748 overcomes the problem by using Chromia - Magnesia catalyst for fluorination of trichloroacetyl chloride. It describes the use of a single catalyst bed maintained at constant temperature, eliminating decomposition products, and achieving 83-95% selectivity of trifluoroacetyl fluoride, and 3.4 -17% of undesirable chlorodifluoroacetyl fluoride. However, the productivity of the catalyst towards trifluoroacetyl fluoride is not good. Only when the reaction is carried out a very low feed rate per catalyst weight ratio, that is, at 34.5 gm/hr of trichloroacetyl chloride per kg of catalyst, 95.4% of trifluoroacetyl fluoride and 3.4% of chlorodifluoroacetyl fluoride is obtained at the outlet of the reactor. However, if it is increased to 61.9gm/hr of trichloroacetyl chloride per kg of catalyst, selectivity of trifluoroacetyl fluoride drops to 83%, and 17% of chlorodifluoroacetyl fluoride is formed as by product.
An article by Rao, J. M. et al [See J. M. Rao et al Journal of Fluorine Chemistry 95 (1999) 177-180] teaches a process for preparing a catalyst based on co-precipitated chromia-alumina doped with zinc and/or magnesium involving the steps of co-precipitating chromia and alumina, washing and drying, shaping and impregnation of zinc chloride. The article also explains the occurrence of dismutation reaction in catalytical vapor phase halogen exchange reaction, which was attributed to the presence of strong acid centres in the catalyst. PCT application no. WO 01/74483 also mentions coprecipitated catalyst promoted with zinc.
SUMMARY OF THE INVENTION
The present invention relates to the process for preparation of trifluroacetyl fluoride by reacting trichloroacetyl chloride and anhydrous hydrogen fluoride in vapor phase over a chromia - alumina impregnated with the zinc salt.

It is surprisingly found that when a chromia-alumina catalyst impregnated with zinc is used, higher selectivity of trifluoroacetyl fluoride is obtained at high feed rate per weight of catalyst, while minimizing generation of chlorodifluoroacetyl fluoride.
It is an object of the present invention to provide a method for preparation of perfluoro compound by the vapor phase reaction of perhalo compounds with anhydrous hydrogen fluoride using chromia alumina catalyst impregnated with zinc, wherein the outlet from the reactor contains at least 97% and normally 99% of desired perfluoro compound.
It is yet another object of the invention to provide a catalyst for preparation of trifluoroacetyl fluoride, which is capable of achieving complete fluorination of perchloro compound while limiting the decomposition reaction below 3%.
It is a special advantage of the present process that the catalysts used for the process is very active. Even after a prolonged period of use the activity of the catalysts does not decrease to a measurable degree. Thus with the above catalysts there is attained, either a higher degree of fluorination at the same temperature or the same degree of fluorination at a lower temperature. The application of lower temperatures is especially desirable for the reasons of reducing the decomposition product of the reaction.
The chromia alumina zinc catalyst of the invention represent fluorination catalysts having such a high activity. The use of this catalyst offers the advantage that higher degree of fluorination and that the reaction can be performed at lower temperatures. By this latter fact the corrosion of the apparatus is largely reduced and very low decomposition products are formed.
The catalyst as taught by Rao et.el. was calcined and further activated by treating sequentially with N.sub.2 at 400.degree. C. for 24 hours followed by fluorination in the temperature range 150.degree.to 400.degree.C. until HF content of the effluent is equal to the one entering the reactor. The time of treatment generally ranges from 24 to 48 hours.

The molar ration of hydrogen fluoride to trichloroacetyl chloride is generally between 5 moles to 15 moles for each moles of trichloroacetyl chloride. The temperature at which the reaction is carried out is between 240 to 350 degree C. The lower temperature of the reaction results in the extended life of the catalyst.
For the sake of simplicity, the process of the invention is carried out at an atmospheric pressure. It is likewise possible, to operate the reactor at a higher pressure up to 5-bar gauge, application of super atmospheric pressure increases the degree of fluorination.
The contact time for the fluorination of trichloroacetyl chloride using hydrogen fluoride and the co precipitated chromia alumina with zinc salt as catalyst is generally very short for example 3-20 seconds, preferably, in the range of 5-10 seconds. By using the catalyst of the invention, the quantity of catalyst used is less than half as compared with the catalyst taught in the prior art for producing the same quantity of product.
STATEMENT OF THE INVENTION
According to the present invention, a process for the preparation of Trifluoroacetyl fluoride from trichloroacetyl chloride comprises reacting trichloroacetyl chloride and anhydrous hydrogen fluoride in vapor phase using chromia - alumina catalyst impregnated with Zinc salt wherein the output from the reactor is at least 97% and normally 99% of desired perfluoro compound, thus limiting the decomposition reaction below 3%.
The molar ratio of trichloroacetyl chloride to anhydrous hydrogen fluoride ranges between 1:5 to 1:15.
In an embodiment of the present invention, the reaction of trichloroacetyl chloride and anhydrous hydrogen fluoride is carried out in a temperature range of 200 deg. C. to 400 deg. C. preferably at a temperature ranging from 240 deg. C to 350 deg. C.

In another embodiment of the present invention, the reactor can be operated optionally in at least three different temperature zones ranging from 200 deg C. to 350 deg. C. along the length of the catalyst.
In yet another embodiment of the present invention, the catalyst is first calcined and than activated by treating sequentially with N.sub.2 at a temperature ranging between 200-400 deg. C. for a period ranging between 24 hours to 28 hours followed by fluorination in the temperature range 150 deg. C. to 400 deg. C. enabling hydrogen fluoride content of the effluent equal to one entering the reactor.
In yet another embodiment of the present invention, the contact time for the fluorination is in the range of 3 seconds to 20 seconds preferably between 5 seconds to 10 seconds.
hi still another embodiment of the present invention, the lower fluorinated compounds are recycled back to the original feed stream.
A more complete appreciation of the invention and the attendant advantages thereof will be more clearly understood by reference to the following non -limiting examples which are for illustrative purposes, hence the same should not be construed to restrict the scope of the invention.
Example I
Fluorination of trichloroacetyl chloride
450 ml of the catalyst comprising corn-precipitated chromia alumina impregnated with zinc chloride (chemical composition - Cr: Al:Zn - 22:75:3), in the form of extrudes, was packed into an electrically heated Inconel tubular reactor provided with multiple temperature sensing points. The catalyst was calcined in a current of nitrogen at about 375-400 degree C. for 6 hours. The temperature of the catalyst bed was then lowered to

200 degree C. and was exposed anhydrous hydrogen fluoride diluted with N.sub.2 (1 mole of HF to 10 moles of nitrogen). Adjusting the flowrates of N.sub.2 and anhydrous hydrogen fluoride controls the highly exothermic reaction occurring and the temperature of the catalyst bed is not allowed to exceed 50 degree C. As the fluorination proceeds, N.sub.2 is withdrawn and pure hydrogen fluoride was passed while simultaneously raising the temperature to 400 degree C. The activation of the catalyst is completed when the moisture content in the exit stream of anhydrous hydrogen fluoride becomes less than 1%.
Then the temperature of the catalyst bed is brought to 250 degree C after which the fluorination of trichloroacetyl chloride with anhydrous hydrogen fluoride was carried out by co-feeding the reactants comprising a mixture of trichloroacetyl chloride 60 gm/hr and hydrogen fluoride 66 gm/hr in vapor from over the activated catalyst. The effluent stream from the catalyst was analyzed by gas chromatography, which gave the following results
Trifluoroacetyl fluoride 98.2%
Chlorodifluoroacetyl fluoride 1.6%
Monofluorodifluoroacetyl fluoride 0%
Difluoroacetyl fluoride 0.2%
Example 2
Employing the equipment and the procedure of the Example 1, for calcinations and activation of catalyst, a gas mixture of trichloroacetyl chloride 60 gm/hr and 90 gm/h of hydrogen fluoride in vapor form was passed over the activated catalyst maintained at a reactor temperature of 240 degree C. The analysis of the gas mixture from the reactor outlet showed the following composition:
Trifluoroacetyl fluoride 98.9 %
Chlorodifluoroacetyl fluoride 0.98%
Monofluorodichloroacetyl fluoride 0%

Difluoroacetyl fluoride 0.1%
Example 3
A mixture of 60 gm/hr of trichloroacetyl chloride and 76 gm/hr of hydrogen fluoride in vapor form was passed over catalyst of example I maintained at a reactor temperature of 310 degree C. The gas chromatographic analysis of the effluent gas from the reactor showed the following composition:
Trifluoroacetyl fluoride 99.25 %
Chlorodifluoroacetyl fluoride 0.55%
Monofluorodichloroacetyl fluoride 0%
Difluoroacetyl fluoride 0.2%
Example 4
Employing the equipment and procedure as detailed in example I, a mixture of 45 gm/hr of trichloroacetyl chloride and 57 gm /hr of anhydrous hydrogen fluoride were passed over heated catalyst maintained at a temperature of 310 degree C. The analysis of gas mixture at the exit of the reactor showed following composition:
Trifluoroacetyl fluoride 99.52 %
Chlorodifluoroacetyl fluoride 0.28%
Difluoroacetyl fluoride 0.2%
While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in are that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

We claim:
1. A process for the preparation of Trifiuoroacetyl fluoride from trichloroacetyl chloride
comprising reacting trichloroacetyl chloride and anhydrous hydrogen fluoride in vapor
phase using chromia - alumina catalyst impregnated with Zinc salt wherein the output
from the reactor is at least 97% and normally 99% of desired perfluoro compound, thus
limiting the decomposition reaction below 3%.
2. A process as claimed in claim 1, wherein the reaction of trichloroacetyl chloride and
anhydrous hydrogen fluoride is carried out in a temperature range of 200 deg. C. to 400
deg. C. preferably at a temperature ranging from 240 deg. C to 350 deg. C.
3. A process as claimed in claim 1, wherein the reactor is optionally operated in at least
three different temperature zones ranging from 200 deg C. to 350 deg. C. along the length
of the catalyst.
4. A process as claimed in claim 1 , wherein the fluorination catalyst is coprecipitated
chromia-alumina impregnated with zinc salt comprising weight % of the zinc compound
based on the weight of the catalyst ranging from 3-11%.
5. A process as claimed in claim 1, wherein the said catalyst is first calcined and than
activated by treating sequentially with N.sub.2 at a temperature ranging between 200-400
deg. C. for a period ranging between 24 hours to 48 hours followed by fluorination in the
temperature range 150 deg. C. to 400 deg. C. enabling hydrogen fluoride content of the
effluent equal to one entering the reactor.
6. A process as claimed in claim 1, wherein the molar ratio of tricholoroacetyl chloride to
anhydrous hydrogen fluoride ranges between 1:5 to 1:15.
7. A process as claimed in claim 1, wherein the reaction of trichloroacetyl chloride and
hydrogen fluoride is carried out at a pressure ranging from atmosphere pressure to 5 bar
gauge.
8. A process as claimed in claiml, wherein the contact time for the fluorination is in the
range of 3 seconds to 20 seconds preferably between 5 seconds to 10 seconds.
9. A process as claimed in claim 1, wherein the gaseous mixture produced in the reactor
comprises of 97-99 % of trifluoroacetyl fluoride, 0.5-3% of chlorodifluoroacetyl fluoride,
0-0.5% of fluorodichloroacetyl fluoride and 0.0.2% of difluoroacetyl fluoride.
10. A process as claimed in claiml, wherein the lower fluorinated compounds are
recycled back to the original feed stream.
1 1. A process for the preparation of Trifluoroacetyl fluoride from trichloroacetyl chloride comprising reacting trichloroacetyl chloride and anhydrous hydrogen fluoride in vapor phase using chromia - alumina catalyst impregnated with Zinc salt substantially as hereinbefore described with reference to the accompanying examples.