Title of Invention

"A PROCESS FOR PREPARATION OF TRIFLUOROACETYL FLUORIDE"

Abstract

The present invention relates to a novel process of preparation of trifluoroacetyl fluoride by the reaction of trichloroacetyl chloride and anhydrous hydrofluoric acid by vapor phase reaction on a chromia- alumina catalyst impregnated with Zinc salt. Higher selectivity of trifluoroacetyl fluoride is obtained at high feed rate per weight of catalyst, while minimizing generation of chlorodifluoroacetyl fluoride. The process is performed at a temperature which decreases the risk of corrosion of the apparatus.

Full Text

FIELD OF INVENTION: The present invention relates to the process for preparation of trifluroacetyl fluoride by the reaction of trichloroacetyl chloride and anhydrous hydrofluoric acid by vapor phase reaction on a chromia-alumina catalyst impregnated with Zinc salt. BACKGROUND OF INVENTION: It is well 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. Although the catalyst of US 248866 is capable of performing halogen exchange in aliphatic compounds, the halogenated carbonyl compounds are known for their deactivating action of such catalyst. U S 2745886 relates to deactivation of chromia catalyst by treatment with oxygen at a temperature of 500 degree C. However such a measure is effective for short time only. GB 976316 describes vapor phase fluorination of trichloroacetyl chloride over chromia gel catalyst wherein chlorodifluoroacetyl fluoride is formed as a major product. US 3804778 attempt to complete perfluorination of perchlorinated compound by elevating the reactor temperature, 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 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 as it increases the reactor size. US 5672748 overcome this 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 trifluoacetyl fluoride is not good. Only when the reaction is carried out at very low feed rate per catalyst weight ratio, that is, at 34.5 gm/hr of trichloroacetyl chloride per kg of catalyst, 95.4% trifluoroacetyl fluoride and 3.4% chlorodifluoroacetyl fluoride is obtained at the outlet of the reactor. However, if it is increased to 61.9 gm/hr of trichloroacetyl chloride per kg of catalyst, selectivity of trifluoroacetyl fluoride drops to 83% and 17% of chlorodifluoroacetyl fluoride is formed as byproduct. It is surprisingly found that when a known 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. OBJECTIVES: An objective 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 preferably 99% of desired perfluoro compound. Another objective of the invention is 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%. Yet another objective of the present invention is to provide a catalyst with higher selectivity of the product and lesser formation of side products. 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. The catalyst of the present invention i.e. coprecipitated chromia alumina catalyst impregnated with zinc salt has unexpectedly high activity. The use of these catalysts 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 formed are reduced. Vapor phase fluorination is done over the calcined catalyst in a moisture free reactor. The temperature of the catalyst bed is brought down 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/h and HF 66 gm/h in vapor form over the activated catalyst. STATEMENT OF INVENTION: According to the present invention there is provided a process for preparation of trifluoroacetyl fluoride which comprises contacting trichloroacetyl chloride and anhydrous hydrogen fluoride with a catalyst, in vapor phase, wherein said catalyst is chromia-alumina catalyst impregnated with zinc catalyst. DETAILED DESCRIPTION OF THE INVENTION: It is a special advantage of the present process that the catalyst used for the process is very active. Even after a prolonged period of use the activity of the catalyst 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. It is surprising that the catalyst of the present invention i.e. coprecipitated chromia alumina catalyst impregnated with zinc salt has unexpectedly high activity. The use of these catalysts 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 formed are reduced. Journal of Fluorine Chemistry 95 (1999) 177-180, teaches a process for preparing the catalyst of present invention 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 catalyst of the present invention has been prepared following the above procedure. The coprecipitated chromia-alumina catalyst is impregnated with zinc salt preferably zinc chloride. Zinc chloride based on the weight of the catalyst ranges from 3-11%. The catalyst is calcined in inert atmosphere in presence of nitrogen and further activated by treating with N2 at 100 to 400 degree C. until the reactor is free of moisture, followed by fluorination in the temperature range 150 degree to 400 degree C, preferably 240 to 350 degree C for 10 to 24 hrs. until HF content of the effluent is equal to the one entering the reactor. The temperature of the catalyst bed is brought to 200 to 400 degree C which the fluorination of trichloroacetyl chloride with anhydrous hydrogen fluoride was carried out by co-feeding the reactants comprising a mixture of trichloroacetyl chloride HF in vapor form over the activated catalyst. The molar ratio of hydrogen fluoride to trichloroacetyl chloride is generally between 5 moles to 15 moles for each mole of trichloroacetyl chloride, i.e. the molar ratio of trichloroacetyl chloride to anhydrous hydrogen fluoride is in the range of 1:5 to 1:15. The reaction can be carried out in a reactor having single chamber operated at a constant temperature or more than one chamber. For reactors having more than one chamber, the process can be carried out at different temperature in different chambers of the reactor between 200 to 400 degree C. Reactors having three chambers, the temperature of every chamber may or may not be same, lying within the range of fluorination conditions. For the sake of simplicity, the process of the invention is carried out at atmospheric pressure. It is likewise possible, to operate at higher or lower pressures; the application of super atmospheric pressure often increases the degree of fluorination. The preferred pressure range for the reaction is 1 to 5 atm. pressure. The contact time for the fluorination of trichloroacetyl chloride using anhydrous hydrogen fluoride and the co-precipitated chromia alumina with zinc salt as catalyst is generally very short i.e. 3-20 seconds, preferably, in the range of 5-10 seconds. The by products so obtained are lower fluorinated components which can be recycled back to the original feed stream. The by-products of the fluorination reaction i.e. the lower fluorinated components produced in process are again contacted with anhydrous hydrogen fluoride in presence of said catalyst. The by-products formed are Chlorodifluoroacetyl fluoride, Monofluorodifluoroacetyl fluoride, Difluoroacetyl fluoride. The process has higher selectivity and conversion rate for the desired product trifluoroacetyl fluoride. The yield of greater than 99 % of trifluoroacetyl fluoride can be achieved by this process. Having described the basic concept of the invention, references now made to the following examples, which are provided by the way of illustration and not of limitation, of the practice of the invention in the preparation of the catalyst and their use in fluorination of trichloroacetyl chloride. The process of the present invention has better yield and higher selectivity for the desired product. (Table Removed) Example 1: 450 ml of the catalyst comprising co-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 at the rate of a rise in temperature of 20-degree C/ hour. The temperature of the catalyst bed was then lowered to 200 degree C and was exposed to anhydrous hydrogen fluoride diluted with N2 (lmole of HF to 4 moles of nitrogen). Adjusting the flowrates of N2 and anhydrous hydrogen fluoride controls the highly exothermic reaction occurring and the temperature of the catalyst bed is not allowed to exceed 400 degree C. As the fluorination proceeds, N2 is withdrawn and pure hydrogen fluoride was passed while simultaneously raising the temperature to 380 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 240 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/h and HF 66 gm/h in vapor form over the activated catalyst. The effluent stream from the catalyst bed 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/h and 76 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 gas mixture from the reactor outlet showed the following composition: - Trifluoroacetyl fluoride: 98.8 % Chlorodifluoroacetyl fluoride: 0.98 % Monofluorodichloroacetyl fluoride: 0 % Difluorocaetyl fluoride: 0.2 % Example 3 A mixture of 60 gm/h of trichloroacetyl chloride and 76 gm/h of hydrogen fluoride in vapor form was passed over catalyst of example 1 maintained at a reactor temperature of 310 C°. The gas chromatographic analysis of the effluent gas from the reactor showed the following composition: - Trifluroacetyl 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 1, a mixture of 45 gm/hr of trichloroacetyl chloride and 57gm/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%. We Claim: 1. A process for preparation of trifluoroacetyl fluoride comprises contacting trichloroacetyl chloride and anhydrous hydrogen fluoride with a catalyst, in vapor phase, wherein said catalyst is chromia-alumina catalyst impregnated with zinc salt, where the reaction is carried out at a temperature in the range of 200 degree C to 400 degree C. 2. A process as claimed in claim 1, wherein the catalyst is co precipitated chromia-alumina impregnated with zinc chloride. 3. A process as claimed in claim 2, wherein the weight % of the zinc chloride based on the weight of the catalyst ranges from 3-11%. 4. The process as claimed in any of the preceding claim, wherein prior to use the coprecipitated chromia-alumina catalyst impregnated with zinc chloride is calcined in presence of N2 at a temperature range of 100 to 400 degrees C. 5. A process as claimed in any of the preceding claims, wherein the reaction is carried out at a temperature in the range of 240 degree C to 350 degree C. 6. A process as claimed in claim 1, wherein the reaction is carried out in a single chamber reactor operated at a single temperature. 7. A process as claimed in claim 1, wherein the reaction is carried out in a reactor with more than one chamber, each chamber of the reactor being operated at a same temperature lying between 200 degree C to 400 degree C. 8. A process as claimed in claim 1, wherein the reaction is carried out in a reactor with more than one chamber, each chamber of the reactor being operated at different temperature lying between 200 degree C to 400 degree C. 9. The process as claimed in claim 1, wherein in the reaction of trichloroacetyl chloride and anhydrous hydrogen fluoride is carried out at a pressure of 1- 5 bar. 10. A process as claimed in claim 1, wherein the molar ratio of trichloroacetyl chloride to anhydrous hydrogen fluoride is in the range of 1:5 to 1:15. 11. A process as claimed in claim 1, wherein the contact time for the fluorination of trichloroacetyl chloride and anhydrous hydrogen fluoride with said catalyst is in the range 3 to 20 seconds. 12. A process as claimed in claim 1, wherein the contact time for the fluorination of trichloroacetyl chloride and anhydrous hydrogen fluoride with said catalyst is 5 to 10 seconds. 13. A process as claimed in claim 1, wherein lower fluorinated components chlorodifluoroacetyl fluoride, Monofluorodifluoroacetyl fluoride, Difluoroacetyl fluoride produced in process of claim 1 are again contacted with anhydrous hydrogen fluoride in presence of said catalyst.

Documents:

1665-del-2008-abstract.pdf

1665-del-2008-Claims-(07-06-2013).pdf

1665-del-2008-claims.pdf

1665-del-2008-Correspondence-Others-(07-06-2013).pdf

1665-del-2008-correspondence-others.pdf

1665-del-2008-description (complete).pdf

1665-del-2008-form-1.pdf

1665-del-2008-form-2.pdf

1665-del-2008-form-3.pdf

1665-del-2008-form-5.pdf