Indian Patents. 234572:"A CHROMIUM-CONTAINING FLUORINATION CATALYST"

Title of Invention	"A CHROMIUM-CONTAINING FLUORINATION CATALYST"
Abstract	A chromium-containing fluorination catalyst which comprises an activity-promoting amount of zinc in the range of about 0.5% to about 25% by weight of catalyst.

Full Text	The present invention relates to a chromium-containing fluorination catalyst. This inventionVre^lateB to an. improved fluorination catalyst and to a process for the production of fluorinated hydrocarbons by the catalysed reaction of hydrocarbons or halogenated hydrocarbons with hydrogen fluoride. The invention relates to a promoted chromium-containing catalyst, in particular to a promoted chromia, halogenated chromia or chromium oxyhalide .catalyst and in a particular embodiment- j ' to -a process for the production of 1, 1, L, 2-tetrafluoroethane by the catalysed reaction of l-chloro-2, 2, 2-tetrafluoroethane with hydrogen fluoi-ide,_ 1 me production of fluorinated hydrocarbons, which may also contain halogen atoms other than fluorine, by the catalysed vapour-phase fluorination of hydrocarbons or halogenated hydrocarbons with hydrogen fluoride . is well known and numerous catalysts have been proposed for use in such a process. Catalysts containing and typically based on chromium, and in particular chromia, are frequently employed in the known processes. Thus, for example chromia or a halogenated chrornia may be used in the vapour-phase reaction of tnichloroethylene with hydrogen fluoride to produce l-chloro-2, 2, 2-trifluoroethane as described in GB Patent 1,307,224 and in the vapoui—phase reaction of i-chloro-2, 2,2-trifluoroethane with hydrogen fluoride to produce 1,1, 1, 2-tetrafluoroethane as described in GB Patent 1, 589,924. The same catalyst may be used for the fluorination of chlorodifluoroethylene to l-chloro-2, 2, 2-trifluoroethane, for example in a process for. the removal of chlorodifluoroethylene impurity from 1, 1, 1, 2-tetrafluoroethane as also described in GB Patent 1,589,924. It has now been found that the activity of chromium-containing catalysts is promoted by the incorporation of controlled amounts of zinc in the catalyst. According to the present invention "there is~provided a chromium-containing fiuorination ,' catalyst which comprises an activity-promoting amount of zinc or a compound of zinc. According to the invention also there is provided a process for the production of fluorinated hydrocarbons vhich comprises reacting a hydrocarbon or a halogenated hydrocarbon with hydrogen fluoride in the vapour phase in the presence of a fluorination catalyst as herein defined. This invention relates to a process for the production of fluorinated hydrocarbons which comprises reacting at least once a halogenated hydrocarbon with hydrogen flouride in the vapour phase in the presence of a. chromium-containing fluorination catalyst which comprises an activity-promoting amount of zinc in the range of about 5 to 6% by weight of the catalyst, the halogenated hydrocarbon comprising an alkene or alkane having from- 1 to 4 carbon atoms and at least one chlorine atom. The activity promoting amount of zinc or a compound of zinc may be present in or on the chromium-containing catalyst, that is the zinc or compound of zinc may be incorporated into the chromium-containing catalyst or it may be supported upon the surface of the catalyst, depending at least to some extent upon the particular method employed for preparing the improved .catalyst of the invention and the particular composition of the catalyst. I Preferably, the chromium-containing catalyst contains chromium in the form of chromia, halogenated chromia or chromium oxyfluoride. Alternatively the chromium-containing catalyst may contain chromium itself. Typically however, during operation of the catalyst in the fluorination process in which it is employed, or during a prefluorination treatment of the catalyst as hereinafter described, chromium in whatever form in the initial catalyst is converted to chromia, halogenated chromia or chromium oxyfluoride. Furthermore, the chromium-containing catalyst may also comprise metal oxides, halogenated metal oxides or metal oxyfluorides other than chromia, halogenated chromia or chromium 'oxyfluoride, which may be present in addition to, or instead of chromia, halogenated chromia or chromium oxyfluoride. The metal oxide may be, for example alumina, magnesia or zirconia, and in particular magnesia and alumina, which during operation of the catalyst may be converted at least in part to aluminium fluoride and magnesium fluoride respectively. Thus, the chromium-containing catalyst may also comprise metal fluorides, for example aluminium fluoride and magnesium fluoride. Thus, the chromium-containing catalyst may comprise an activity promoting amount of zinc or a compound of zinc in and/or on a mixed metal oxide support, for example chromia/magnesia or chromia/alumina or the chromium-containing catalyst may comprise an activity promoting amount of zinc or a compound of zinc in and/or on a metal oxide support which also comprises chromium, for example, zinc on chromium-containing alumina or magnesia. In the latter case the chromium may be converted to chromia, halogenated chromia or chromium oxyfluoride during operation of the process employing the catalyst. Further, the chromium-containing catalyst may comprise an activity-promoting amount of zinc in and/or on a mixed metal oxide/fluoride support, for example alumina/chromium fluoride or chrornia/magnesiurn fluoride; or an activity promoting amount of zinc on a metal fluoride, for example chromium fluoride, magnesium fluoride or aluminium fluoride, or mixed metal fiuori-de support, for example c-hromium fluoride/aluminium fluoride or chrorn^Lum fluoride/magnesium fluoride, providing that in all these cases, the catalyst comprises chromium in one form or another. Moreover, the chromium-containing catalyst may comprise an activated carbon support. The amount of zinc present in the catalyst is such as to result in promotion of the activity of the chromium-containing catalyst to which the zinc or compound of zinc is introduced. The amount is important since the introduction of too much zinc may result in a decrease rather than an increase in catalyst activity and it is only when zinc is present in the optimum amount that substantial activity promotion occurs. The amount of zinc depends, at least to some extent on the surface area of the catalyst which depends itself on the composition of the catalyst, and the method of preparation of the catalyst. Generally, the larger the working surface area of the catalyst, the greater is the preferred amount of zinc which is present in and/or on the catalyst. By way of example, in the case of zinc introduced by impregnation in a typical chromia-based catalyst having a working surface area of between 20 and 50 m2 /g, optimum activity promotion results when the amount of zinc is within the range of about 0. 5% by weight to about 6X by weight of the catalyst, preferably in the range from about IX by weight to about 5% by weight and especially in the range from about 254 by weight to about 4% by weight; less than 0.5% by weight of zinc may be insufficient to result in significant promotion of catalyst activity whilst more than about 6% by weight of zinc may result in a decrease in catalyst activity suggesting poisoning of the basic catalyst. However, by way of guidance, for catalysts having larger working surface areas, for example about 100 m2/gf the amount of zinc may be as high as 15% to 25% by weight, whereas for catalysts having smaller working area, i.e. less than 20 m2/g, for example about 5 m2-/g, the amount of zinc may be as low as 0.5X to IX by weight. Overall, the amount of zinc'may be in the range from about O.5% by weight to about 25X by weight, the preferred amount within this range depending upon the nature of the chromium-containing catalyst. It is to be understood that the amounts of zinc given above refer to the amount of zinc, whether present as elemental zinc or a compound of zinc, but that where the zinc is present as a compound of zinc, the amount refers only to the amount of zinc, and not to the amount of the compound of zinc. As previously described, the amount of zinc introduced to the catalyst to achieve significant activity promotion will depend upon the particular basic catalyst employed and upon the method used to prepare the improved catalyst. However, for any particular basic, catalyst and catalyst preparation method, the optimum amount of promoter is readily determined by simple routine experimentation. The zinc promoter may be introduced into and/or onto the catalyst in the form of a compound, for example a halide, oxyhalide, oxide or hydroxide depending at least to some extent upon the catalyst preparation technique employed. In the case where catalyst preparation as by impregnation of a chromia, halogenated chromia or chromium oxyhalide, the compound as preferably a water-soluble salt, for example a halide, nitrate or carbonate, and is employed as an aqueous solution or slurry. Alternatively, the hydroxides of the promoter and chromium may be co-precipitated and then converted to the oxides to prepare the catalyst, for example a catalyst comprising a mixed oxide of zinc and chromium.-Mixing and milling of an insoluble zinc compound with the basic catalyst provides a further method of preparing the catalyst. A method for making catalysts based on chromium oxyhalide comprises adding a compound of the promoter to hydrated chromium halide and calcining the mixture. Further methods for preparing the catalyst include, for example, reduction of a chromium (VI) compound, for example a chromate, dichromate, in particular ammonium dichromate, to chromium (III), by zinc metal, followed by co-precipitation, washing and calcining; or mixing as so-lids, a chromium (VI) compound and an oxidisable zinc compound, for example z'inc acetate or zinc oxalate, and heating the mixture to high temperature in order to effect reduction of the chromium (VI) compound to chromium (III) oxide and the zinc salt to zinc oxide. Any of the aforementioned methods, or other methods, may be employed for the preparation of the chromium-containing zinc promoted catalysts of the present invention.' As stated above, the amount of promoter introduced to the catalyst depends upon the catalyst preparation employed. It is believed that the 'working catalyst has a surface containing the promoter cations located in a chromium-containing, for example chromium oxide, oxyhalide, or halide lattice and it is the amount of such surface promoter which determines the activity of the catalyst. Thus the amount of the promoter which is required is generally lower for catalysts made by impregnation than for catalysts made by other methods and containing the promoter in non-surface locations. The fluorination catalyst will usually be subjected to a prefluorination treatment with hydrogen fluoride, and optionally an inert diluent, prior to use in the catalysis of fluorination reactions. A trypical pretreatrnent comprises heating the catalyst at 250°C to 450°C in contact with hydrogen fluoride, preferably a mixture of hydrogen fluoride and air. The working catalyst may consequently comprise at least in part zinc fluoride in and/or on a fluorinated chromium-containing catalyst, for example fluorinated cbromia or chromium oxyfluoride. The catalyst may be in the form of pellets or granules of appropriate size for use in a fixed bed or a fluidised bed. It may be regenerated or reactivated periodically by heating in air at a temperature of from about 300°C to about 5OG°C. Air may be used as a mixture with an inert gas such as nitrogen or with hydrogen fluoride which emerges hot from the catalyst treatment process and may be used directly in fluorination processes employing the reactivated catalyst. Th'e activity of the base (unpromoted) chrom4ium-containing catalyst, for example halog.enated chromia or chromium oxyhalide catalyst is enhanced by the introduction of zinc or a compound of zinc. Furthermore, and in particular, the selectivity of the reaction catalysed by the catalyst towards the production of 1, 1, 1,2-tetrafluoroethane from 1-chloro-2, 2, 2-trifluoroethane arid hydrogen fluoride is at least as high as that using the corresponding unpromoted ca'talysts, typically in excess of 85% If desired, the catalyst may contain one or more metals other than zinc, for example nickel or cobalt, or it may contain for example other divalent metals although we generally prefer that the catalyst does not comprise other metals such as nickel, cobalt of other divalent metals. A further feature of the invention resides in use of the promoted catalyst in fluorination processes comprising reaction of a hydrocarbon or halogenated hydrocarbon with hydrogen fluoride in the vapour-phase. Alkenes (unsaturated hydrocarbons) .or halogenated alkanes of 1-4C atoms, preferably containing at least one chlorine atom, may be fluorinated and examples of specific fluorinations which may be effected are the production of 1,1,1,2-tetrafluoroethane from 1-chloro-2, 2,2-trifluoroethane, the production of l-chloro-2,2,2-trifluoroethane from trichloroethylene and the conversion of l-chloro-J2, 2-dif luoroethylene to 1-chloro-2,2,2-trifluoroethane. Examples of other fluorination reactions in which the catalyst is useful are the reaction of perchloroethylene with hydrogen fluoride in vapour phase to produce dichlorotrifluoroethane (123), chlorotetrafluoroethane (124) and/or pentafluoroethane (125), and the reaction of perchloroethylene with chlorine and hydrogen fluoride in vapour phase to produce trichlorotrifluoroethane (1 A3 ), dichlorotetrafluoroethane (114/114a) and/or chloropentafluoroethane (115 ) . The fluorination conditions employed may be those known to be useable when employing chromium-containing catalysts, for example atmospheric or superatmospheric pressure, hydrogen fluoride and temperatures in the range of 180°C to about 50O°C depending upon the particular fluorination reaction being carried out. However, the increased activity of the promoted catalyst permits reactions to be carried out without loss of efficiency at somewhat lower temperatures than those required when using the unpromoted catalyst. For example whilst the efficient production at atmospheric pressure of 1, 1, lr2-tetrafluoroethane from 1-chloro-2,2,2-trifluoroethane requires a temperature of 3GO°C or above when using the unpromoted catalyst, a lower temperature of say 2SO°C is sufficient to achieve the same reaction efficiency using a zinc promoted catalyst. Alternatively, if the temperature is the same, say 300"C. a shorter contact time is required using the promoted catalyst. A preferred embodiment of the process of the invention resides in a process for the preparation of 1, 1, 1,2-tetrafluoroethane which comprises reacting 1-chloro-2,2,2-trifiuoroethane with hydrogen fluoride in the vapour phase in the presence of the promoted catalyst of the invention^ This process may. be carried out under atmospheric or super atmospheric pressure at a temperature of from about 250°C to 500°C. The process may be one stage of a two or three-stage process, for example it may be the second stage of a process for the production of 1,1,1,2-tetrafluoroethane from trichloroethylene, the first stage being the vapour-phase fluorination of trichloroethylene with hydrogen fluoride in the presence of a chromium-containing catalyst. The promoted catalyst of the invention may be used in the first stage as well as in the second stage of this two-stage process. Typical reaction conditions for the the first stage are atmospheric or superatmospheric pressure and a temperature in the range of about 180°C to about 3OO°C. The production of 1, 1,1,2-tetrafluoroethane from l-chloro-2, 2, 2-trifluoroethane results in a1 product stream containing the toxic impurity 1-chloro-2, 2, -difluoroethylene. This impurity can be removed by reacting it with hydrogen fluoride in the va'pour phase in the presence of a chromium containing catalyst at a temperature below about 270°C, for example 150°C to 270°C. The promoted catalyst of the invention may be employed in this reaction, thus providing a three-stage process for the preparation of 1, 1,1,2-tetrafluoroethane essentially free from l-chloro-2, 2-difluoroethylene from trichloroethylene using the promoted catalyst in each of the three reaction stages. A particularly preferred embodiment of the above-described two-stage process for preparing 1, 1,1,2-tetrafluoroethane from trichloroethylene comprises the steps of: (A) contacting a mixture of l-chloro-2,2,2-trifluoroethane and hydrogen fluoride with the promoted catalyst at 250-350°C in a first reaction zone whereby to form a product containing 1,1,1,2-tetrafluoroethane and hydrogen chloride together with unreacted starting materials, (B) passing the total product of step A together with trichloroethylene to a second reaction zone containing the o promoted catalyst at 18O-300 whereby to form a .product containing l-chloro-2,2,2-trifluoroethane, 1,1,1,2-tetrafluoroethane and hydrogen chloride; (C) treating the product of step B whereby to separate a mixture containing hydrogen chloride and 1,1,1,2-tetrafluoroethane from l-chloro-2,2,2-trifluoroethane, unreacted hydrogen fluoride and unreacted trichloroethylene; (D) feeding the l-chloro-2,2,2-trifluoroethane mixture obtained from step C together with additional hydrogen fluoride to said first reaction zone, and (E) recovering 1,1,1;2-tetrafluoroethane from the 1,1,1,2-tetrafluoroethane/hydrogen chloride mixture obtained from step C. At least the stoichiometric amount of hydrogen fluoride is usually employed in step A of the preferred embodiment. Typical amounts include from 1 to 10 moles, and preferably from 1 to 6 moles, of hydrogen fluoride per mole of l-chloro-2,2,2-trifluoroethane. Accordingly, the product of this reaction step will usually contain unreacted hydrogen, fluoride in addition to 1,1,1,2- tetrafluorqethane, hydrogen chloride and by-products. Preferred reaction temperatures for this stage of the process are in the range from 28O°C to 35Q°C with contact times of from 1 to 1OO and preferably from 5 to 3O seconds at 5 to 20 bars pressure. From 10 to 10O, preferably from 15 to 60, moles of hydrogen fluoride per mole of trichloroethylene. are typically employed in Step B. Again, the reaction product of this stage will normally contain unreacted hydrogen fluoride. Contact times of 1 to 1OO seconds, preferably 5 to 3O seconds may be used, typically at 18O-3OO°C'and 5 to 2O bars pressure. .The reaction and separation steps which make up the preferred embodiment of the method of the invention may be performed using conventional equipment and techniques. Thus, for example, recovery of 1,1,1,2- tetrafluoroethane in step E may be effected .by washing the gaseous mixture (containing tetrafluoroethane and hydrogen chloride) with water and aqueous sodium hydroxide solution and then drying and condensing the tetrafluoroethane. It is preferred that the process according to the invention, including preferred embodiments, is operated" continuously. In practice, however, catalyst deactivation, necessitating periodic catalyst' regeneration or reactivation may interrupt continuous operation of the process. The feeding of air to the catalyst during operation of the process may counter catalyst deactivation and reduce the frequency of process interruption for catalyst regeneration or reactivation. The present invention relates to 1 process for increasing the activity of a chromium-containing fluorination catalyst which process comprises introducing an activity-promoting zinc in an amount of zinc from 0.5 to 25 % by weight of the catalyst or a compound of zinc of the kind such as hereindescribed, to the catalyst by at least the step of co-precipitating a zinc compound and a chromium compound or at least the step of impregnating a chromium compound with a zinc compound. The present invention also relates to a chromium-containing fluorination catalyst which comprises an activity-promoting amount of zinc or a compound of zinc. Brief description of the accompanying drawings: The invention is illustrated but in no way limited by the following examples. EXAMPLES 1 TO 5 10g of chrornia in the form of granules of size 0.5-1.4mm, and having a surface area of 50m /g, was added to an aqueous solution of zinc chloride (0.2g) in distilled water (10ml> and stirred to ensure thorough wetting of the solid by the solution. The mixture was then dried by direct heating and the resultant solid sieved to give particles, of size O.. 5-1. 4mm, of a finished catalyst comprising O, 9% zinc w/w on chromia. The above procedure was repeated except that zinc chloride solutions of increasing concentration were employed in order to produce a range of finished catalysts with up to 6% w/w zinc in the finished catalyst. The fluorination activities of the zinc promoted chromias were measured using an atmospheric pressure microreactor. Catalysts (2g) were charged to the microreactor and were conditioned in a stream of HF at 300°C for 1 hour and then heated to 350°C and further conditioned in an air/HF (ratio 1:20) stream for approximately 15hrs. The microreactor was then fed with a l-chloro-2, 2, 2-trifluoroethane The results of the study are presented as '/-. yields of 1, 1, 1,2-tetrafluoroethane in Table 1 and demonstrate the beneficial effect of zinc addition to chromia on increasing the yield of 1,1,1,2-tetrafluoroethane . The activity of the zinc impregnated-chromia catalyst reached a maximum at a zinc content in the range of about 2 to about 5X w/w. (Table Removed) EXAMPLE 6 The catalyst prepared in example 3 was charged to a pressure reactor and prefluorinated with HF at 250°C for 24 hours, using a> pressure of 1O bar. The reactor was then fed with a 133a and HF feed using a molar feed ratio of 1:3.5. Using the above feeds at a pressure of 1O bar, a reaction temperature of 325°C and a contact time of 10 seconds enable a 134a yield of >157. to be achieved. The reaction selectivity was >99*/.. EXAMPLE 7 A 2% w/w zinc-on-chromia catalyst was prepared by impregnating chrornia (4.8g) with an aqueous solution of zinc chloride (0.21g) in distilled water (5ml). The catalyst was dried in a heated air stream at 12O°C and charged to an Inconel reactor. The catalyst was dried at 310°C in nitrogen for 1 hour and prefluorinated at 31O°C with hydrogen fluoride for 2 hours. Trichloroethylene and HF were then fed to the reactor-at 310°C using a trichloroethylene: HF molar ratio of 1:1O and a contact time of 1 second. The zinc on chromia catalyst converted 4O.9% of the trichloroethylene to 1-chloro-2,2,2-trifluoroethane. This compared with a trichloroethylene conversion of 26.7% achieved using the original unpromoted chromia. EXAMPLES 8 TO 10. Zinc, either as an aqueous solution of zinc nitrate or as an aqueous slurry of zinc carbonate (as indicated), was added to a slurry of chromium (III) hydroxide and the pH of the solution was adjusted to 7 using ammonium hydroxide. The resultant solids were filtered, washed, calcined at 3OO C in nitrogen for 5 3 hours and pelleted to a density of 2g/cms , and the above procedure was repeated, using zinc carbonate or zinc nitrate solutions of various concentrations, to produce a number of catalysts with up to 10% zinc by weight in the finished catalyst. The catalysts were tested at atmospheric pressure according to the procedure of examples 1 to 5. The results of the study are presented as 7. yields of 1, 1, 1, 2-tetrafluoroethane in Table 2 and demonstrate the beneficial effect of zinc addition to chromia on increasing the yield of 1, 1, 1, 2-tetrafluoroethane (134a). Table 2 (Table Removed) EXAMPLES 11 - 13. A number of catalysts were prepared according to the procedure of examples 8 to 10 except that chromium (III) nitrate was used instead of chromium (III) hydroxide. The catalysts were tested according to the procedure described for examples 1 to 5. The results of the study are presented as % yields of 1,1,1,2-tetrafluoroethane in Table 3 and demonstrate the beneficial effect of zinc addition to chrornia on increasing the yield of 1, 1, 1,2-tetrafluoroethane (134a ) . Table 3 (Table Removed) EX-AMPLE 14. lOg of the catalyst prepared in example 9 was charged to a pressure reactor and pre±luorinated with HF at 30O"C for 24 hours, using a pressure of 10 bar. The reactor was then fed with HF and a mixed organic feed comprising 0.5V. by weight t rich lor oethylene in 133a using a molar feed ratio of organics to hydrogen fluoride- of 1:3.5. Using the ahove feeds at a pressure of 10 bar and a contact time of 11 seconds, 134a yields of 127. were achieved at a temperature of 295°C. The reaction selectivity was greater than 99. 5V.. In comparison, lOg of the unpromoted chromia catalyst gave 134a yields of 12% at a temperature of 330 C when pr'ef luorinated and tested at pressure under identical conditions to those described for example 17. The reaction selectivity was 99.O%. EXAMPLES 15 TO 19. 4.3g of alumina (supplied by Harehaw Ltd), 2 having a surface area of 180m /g, in the form of granules of size 0.5-1.4mm was added to an aqueous solution of zinc chloride (0.21g) and chromium (III) chloride hexahydrate (0.51g) in distilled water (5ml) and stirred to ensure thorough wetting of the solid by the solution. The mixture was then dried by'direct heating and the resultant solid sieved to give particles, of size 0. 5 - 1.4mm, of a finished catalyst comprising 2'/,Cr/2%.Zn by weight on alumina. The above procedure-' was repeated with various concentrations of zinc chloride to produce a range of finished catalysts containing 2.7. by weight chromium and up to 8%. by weight'zinc. The catalysts were tested at atmospheric pressure according to the procedure described for examples 1 to 5. For the purposes of comparison, the activity of a catalyst comprising 2% by weight chromium on alumina, prepared from an aqueous solution of chromium (III) chloride was also measured. The results of the study are presented as '/. yields of 1, 1, 1, 2-tetrafluoroethane in Table 4 and demonstrate the beneficial effect of zinc addition to chromium-containing alumina on increasing the yield of 1, 1, 1, 2-tetrafluoroethane (134a ). Table 4 (Table Removed) EXAMPLES 20 to 22. 4.43g of aluminium fluoride, prepared by treating alumina with hydrogen fluoride for 24 hours at 300 Cf in the form of granules of size 0. 5 - 1.4mm, and having a surface area of 13m /g, was added to an aqueous solution of zinc chloride (O.O53g) and chromium (III) chloride hexahydrate (0.51g) in distilled water (5ml) and stirred to ensure thorough wetting of the solid by the solution. The mixture was then dried by direct heating and the resultant solid sieved to give particles, of size O. 5 - 1.4mm, of a finished catalyst compx-ising 2'/.Cr/O. 5%Zn by weight on A1F . The above procedure was repeated with various O concentrations of zinc chloride to produce a range of finished catalysts- containing 2% by weight chromium and up to 2% by weight zinc. The catalysts were tested at atmospheric pressure according to the procedure described for examples 1 to 5. For purposes of comparison the activity of two catalysts containing 2X and 2.4% by weight chromium on aluminium fluoride, and prepared from an aqueous solution of chromium (III) chloride, were also measured. The results of the study are presented as % yields of 1, 1,1,2-tetrafluoroethane in Table 5 and demonstrate the beneficial effect of zinc addition to chromium—'containing aluminium fluoride on increasing the y^ield of 1, 1, 1, 2- tetraf luoroethane Table 5 (Table Removed) EXAMPLE 23. Magnesium oxide tablets (supplied by. Merck S. Co), were ground to give granules of size O.5-1.4mm. 4.44g of the ground magnesium oxide was added to an aqueous solution of zinc chloride (0.053g) and chromium (III) chloride hexahydrate CO.513g) in distilled vater (5ml) and stirred to ensure thorough wetting of the solid by the solution. The mixture was dried by direct heating and the resultant solid sieved to give particles, of size 0. 5 - 1.4mm of a finished catalyst comprising 2%Cr/O.5XZn by weight on magnesia. The catalyst was tested at atmospheric pressure according to the procedure described for examples 1 to 5. For the purposes of comparison, catalysts containing 2% and 2..4Y. by weight chromium, prepared by impregnating magnesium oxade granules of size (J. 5 -i.4mrn with an aqueous solution of chromium (III) chloride were also tested. The' results of the study are presented as '/. yields of 1,1,1,2-tetrafluoroethane in Table 6 and demonstrate the beneficial effect of zinc addition to chromium-containing magnesium oxide on increasing the yield of 1,1,1, 2-tetrafluoroethane (134a). table 6(Table Removed) WE CLAIM: 1. A chromium-containing fluorination catalyst which comprises an activity-promoting amount of zinc in the range of from about 0.5% to about 25% by weight of the catalyst. 2. A catalyst as claimed in claim 1, wherein the chromium- containing catalyst comprises chromia, halogenated chromia or a chromium oxyhalide. 3. A catalyst as claimed in claim 2, wherein the activity-promoting amount of zinc is supported on the chromia, halogenated chromia or chromium oxyhalide. 4. A catalyst as claimed in claim 2, wherein the chromia, halogenated chromia or chromium oxyhalide is impregnated with the activity promoting amount of zinc. 5. A catalyst as claimed in claim 1, wherein it comprises a mixed oxide of zinc and chromium. 6. A catalyst as claimed in claim 1, comprising an activity- promoting amount of zinc produced by co-precipitating zinc hydroxide and chromium hydroxide and thereafter converting the hydroxides to zinc oxide and chromium oxide. 7. A catalyst as claimed in any one of the preceding claims, comprising an activity-promoting amount of zinc in the range of from about 0.5% to about 6% by weight of the catalyst. 8. A catalyst as claimed in any one of the preceding claims further comprising a metal oxide, halogenated metal oxide or metal oxyhalide of magnesium, aluminium or zirconium. 9. A chromium-containing fluorination catalyst substantially as herein described with reference to the foregoing examples.

Full Text

The present invention relates to a chromium-containing fluorination catalyst.
This inventionVre^lateB to an. improved fluorination catalyst and to a process for the production of fluorinated hydrocarbons by the catalysed reaction of hydrocarbons or halogenated hydrocarbons with hydrogen fluoride. The invention relates to a promoted chromium-containing catalyst, in particular to a promoted chromia, halogenated chromia or chromium
oxyhalide .catalyst and in a particular embodiment-
j ' to -a process for the production of
1, 1, L, 2-tetrafluoroethane by the catalysed reaction of l-chloro-2, 2, 2-tetrafluoroethane with hydrogen fluoi-ide,_
1 me production of fluorinated
hydrocarbons, which may also contain halogen atoms other than fluorine, by the catalysed vapour-phase fluorination of hydrocarbons or halogenated hydrocarbons with hydrogen fluoride . is well known and numerous catalysts have been proposed for use in such a process. Catalysts containing and typically based on chromium, and in particular chromia, are frequently employed in the known processes. Thus, for example chromia or a halogenated chrornia may be used in the
vapour-phase reaction of tnichloroethylene with
hydrogen fluoride to produce
l-chloro-2, 2, 2-trifluoroethane as described in GB
Patent 1,307,224 and in the vapoui—phase reaction
of i-chloro-2, 2,2-trifluoroethane with hydrogen
fluoride to produce 1,1, 1, 2-tetrafluoroethane as
described in GB Patent 1, 589,924. The same
catalyst may be used for the fluorination of
chlorodifluoroethylene to
l-chloro-2, 2, 2-trifluoroethane, for example in a
process for. the removal of chlorodifluoroethylene impurity from 1, 1, 1, 2-tetrafluoroethane as also described in GB Patent 1,589,924.
It has now been found that the activity of chromium-containing catalysts is promoted by the incorporation of controlled amounts of zinc in the catalyst.
According to the present invention "there is~provided a chromium-containing fiuorination
,'
catalyst which comprises an activity-promoting amount of zinc or a compound of zinc.
According to the invention also there is provided a process for the production of fluorinated hydrocarbons vhich comprises reacting a hydrocarbon or a halogenated hydrocarbon with hydrogen fluoride in the vapour phase in the presence of a fluorination catalyst as herein defined.
This invention relates to a process for the production of fluorinated hydrocarbons which comprises reacting at least once a halogenated hydrocarbon with hydrogen flouride in the vapour phase in the presence of a. chromium-containing fluorination catalyst which comprises an activity-promoting amount of zinc in the range of about 5 to 6% by weight of the catalyst, the halogenated hydrocarbon comprising an alkene or alkane having from- 1 to 4 carbon atoms and at least one chlorine atom.
The activity promoting amount of zinc or a compound of zinc may be present in or on the chromium-containing catalyst, that is the zinc or compound of zinc may be incorporated into the chromium-containing catalyst or it may be supported upon the surface of the catalyst, depending at least to some extent upon the particular method employed for preparing the improved .catalyst of the invention and the particular composition of the catalyst.
I
Preferably, the chromium-containing catalyst contains chromium in the form of chromia, halogenated chromia or chromium oxyfluoride. Alternatively the chromium-containing catalyst may contain chromium

itself. Typically however, during operation of the catalyst in the fluorination process in which it is employed, or during a prefluorination treatment of the catalyst as hereinafter described, chromium in whatever form in the initial catalyst is converted to chromia, halogenated chromia or chromium oxyfluoride. Furthermore, the chromium-containing catalyst may also comprise metal oxides, halogenated metal oxides or metal oxyfluorides other than chromia, halogenated chromia or chromium 'oxyfluoride, which may be present in addition to, or instead of chromia, halogenated chromia or chromium oxyfluoride. The metal oxide may be, for example alumina, magnesia or zirconia, and in particular magnesia and alumina, which during operation of the catalyst may be converted at least in part to aluminium fluoride and magnesium fluoride respectively. Thus, the chromium-containing catalyst may also comprise metal fluorides, for example aluminium fluoride and magnesium fluoride.
Thus, the chromium-containing catalyst may comprise an activity promoting amount of zinc or a compound of zinc in and/or on a mixed metal oxide support, for example chromia/magnesia or chromia/alumina or the chromium-containing catalyst may comprise an activity promoting amount of zinc or a compound of zinc in and/or on a metal oxide support which also comprises chromium, for example, zinc on chromium-containing alumina or magnesia. In the latter case the chromium may be converted to chromia,
halogenated chromia or chromium oxyfluoride during operation of the process employing the catalyst. Further, the chromium-containing catalyst may comprise an activity-promoting amount of zinc in and/or on a mixed metal oxide/fluoride support, for example alumina/chromium fluoride or chrornia/magnesiurn fluoride; or an activity promoting amount of zinc on a metal fluoride, for example chromium fluoride, magnesium fluoride or aluminium fluoride, or mixed metal fiuori-de support, for example c-hromium fluoride/aluminium fluoride or chrorn^Lum fluoride/magnesium fluoride, providing that in all these cases, the catalyst comprises chromium in one form or another.
Moreover, the chromium-containing catalyst may comprise an activated carbon support.
The amount of zinc present in the catalyst is such as to result in promotion of the activity of the chromium-containing catalyst to which the zinc or compound of zinc is introduced. The amount is important since the introduction of too much zinc may result in a decrease rather than an increase in catalyst activity and it is only when zinc is present in the optimum amount that substantial activity promotion occurs. The amount of zinc depends, at least to some extent on the surface area of the catalyst which depends itself on the composition of the catalyst, and the method of preparation of the catalyst. Generally, the larger the working surface area of the catalyst, the greater is the preferred amount of zinc which is present in and/or on the catalyst. By way of example, in the case of zinc
introduced by impregnation in a typical
chromia-based catalyst having a working surface
area of between 20 and 50 m2 /g, optimum activity
promotion results when the amount of zinc is within the range of about 0. 5% by weight to about 6X by weight of the catalyst, preferably in the range from about IX by weight to about 5% by weight and especially in the range from about 254 by weight to about 4% by weight; less than 0.5% by weight of zinc may be insufficient to result in significant promotion of catalyst activity whilst more than about 6% by weight of zinc may result in a decrease in catalyst activity suggesting poisoning of the basic catalyst. However, by way of guidance, for catalysts having larger working surface areas, for example about 100 m2/gf the amount of zinc may be as high as 15% to 25% by weight, whereas for catalysts
having smaller working area, i.e. less than 20
m2/g, for example about 5 m2-/g, the amount of
zinc may be as low as 0.5X to IX by weight. Overall, the amount of zinc'may be in the range from about O.5% by weight to about 25X by weight, the preferred amount within this range depending upon the nature of the chromium-containing catalyst. It is to be understood that the amounts of zinc given above refer to the amount of zinc, whether present as elemental zinc or a compound of zinc, but that where the zinc is present as a compound of zinc, the amount refers only to the amount of zinc, and not to the amount of the compound of zinc.
As previously described, the amount of zinc introduced to the catalyst to achieve significant activity promotion will depend upon
the particular basic catalyst employed and upon the method used to prepare the improved catalyst. However, for any particular basic, catalyst and catalyst preparation method, the optimum amount of promoter is readily determined by simple routine experimentation.
The zinc promoter may be introduced into and/or onto the catalyst in the form of a compound, for example a halide, oxyhalide, oxide or hydroxide depending at least to some extent upon the catalyst preparation technique employed. In the case where catalyst preparation as by
impregnation of a chromia, halogenated chromia or
chromium oxyhalide, the compound as preferably a
water-soluble salt, for example a halide, nitrate or carbonate, and is employed as an aqueous solution or slurry. Alternatively, the hydroxides of the promoter and chromium may be co-precipitated and then converted to the oxides to prepare the catalyst, for example a catalyst comprising a mixed oxide of zinc and chromium.-Mixing and milling of an insoluble zinc compound with the basic catalyst provides a further method of preparing the catalyst. A method for making catalysts based on chromium oxyhalide comprises adding a compound of the promoter to hydrated chromium halide and calcining the mixture.
Further methods for preparing the catalyst include, for example, reduction of a chromium (VI) compound, for example a chromate, dichromate, in particular ammonium dichromate, to chromium (III), by zinc metal, followed by co-precipitation, washing and calcining; or mixing as so-lids, a chromium (VI) compound and an oxidisable zinc compound, for example z'inc
acetate or zinc oxalate, and heating the mixture to high temperature in order to effect reduction of the chromium (VI) compound to chromium (III) oxide and the zinc salt to zinc oxide.
Any of the aforementioned methods, or other methods, may be employed for the preparation of the chromium-containing zinc promoted catalysts of the present invention.'
As stated above, the amount of promoter introduced to the catalyst depends upon the catalyst preparation employed. It is believed that the 'working catalyst has a surface containing the promoter cations located in a chromium-containing, for example chromium oxide, oxyhalide, or halide lattice and it is the amount of such surface promoter which determines the activity of the catalyst. Thus the amount of the promoter which is required is generally lower for catalysts made by impregnation than for catalysts made by other methods and containing the promoter in non-surface locations.
The fluorination catalyst will usually be subjected to a prefluorination treatment with hydrogen fluoride, and optionally an inert diluent, prior to use in the catalysis of fluorination reactions. A trypical pretreatrnent comprises heating the catalyst at 250°C to 450°C in contact with hydrogen fluoride, preferably a mixture of hydrogen fluoride and air. The working catalyst may consequently comprise at least in part zinc fluoride in and/or on a fluorinated chromium-containing catalyst, for example fluorinated cbromia or chromium oxyfluoride.
The catalyst may be in the form of pellets or granules of appropriate size for use in a fixed bed or a fluidised bed. It may be regenerated or reactivated periodically by heating in air at a temperature of from about 300°C to about 5OG°C. Air may be used as a mixture with an inert gas such as nitrogen or with hydrogen fluoride which emerges hot from the catalyst treatment process and may be used directly in fluorination processes employing the reactivated catalyst.
Th'e activity of the base (unpromoted) chrom4ium-containing catalyst, for example halog.enated chromia or chromium oxyhalide catalyst is enhanced by the introduction of zinc or a compound of zinc. Furthermore, and in particular, the selectivity of the reaction catalysed by the catalyst towards the production of 1, 1, 1,2-tetrafluoroethane from 1-chloro-2, 2, 2-trifluoroethane arid hydrogen fluoride is at least as high as that using the corresponding unpromoted ca'talysts, typically in excess of 85%
If desired, the catalyst may contain one or more metals other than zinc, for example nickel or cobalt, or it may contain for example other divalent metals although we generally prefer that the catalyst does not comprise other metals such as nickel, cobalt of other divalent metals.
A further feature of the invention resides in use of the promoted catalyst in fluorination processes comprising reaction of a hydrocarbon or
halogenated hydrocarbon with hydrogen fluoride in the vapour-phase.
Alkenes (unsaturated hydrocarbons) .or halogenated alkanes of 1-4C atoms, preferably containing at least one chlorine atom, may be fluorinated and examples of specific fluorinations which may be effected are the production of 1,1,1,2-tetrafluoroethane from 1-chloro-2, 2,2-trifluoroethane, the production of l-chloro-2,2,2-trifluoroethane from trichloroethylene and the conversion of l-chloro-J2, 2-dif luoroethylene to
1-chloro-2,2,2-trifluoroethane. Examples of other fluorination reactions in which the catalyst is
useful are the reaction of perchloroethylene with
hydrogen fluoride in vapour phase to produce
dichlorotrifluoroethane (123),
chlorotetrafluoroethane (124) and/or
pentafluoroethane (125), and the reaction of
perchloroethylene with chlorine and hydrogen
fluoride in vapour phase to produce
trichlorotrifluoroethane (1 A3 ),
dichlorotetrafluoroethane (114/114a) and/or
chloropentafluoroethane (115 ) .
The fluorination conditions employed may be those known to be useable when employing chromium-containing catalysts, for example atmospheric or superatmospheric pressure, hydrogen fluoride and temperatures in the range of 180°C to about 50O°C depending upon the particular fluorination reaction being carried out.
However, the increased activity of the promoted catalyst permits reactions to be carried out without loss of efficiency at somewhat lower temperatures than those required when using the unpromoted catalyst. For example whilst the efficient production at atmospheric pressure of 1, 1, lr2-tetrafluoroethane from 1-chloro-2,2,2-trifluoroethane requires a temperature of 3GO°C or above when using the unpromoted catalyst, a lower temperature of say 2SO°C is sufficient to achieve the same reaction efficiency using a zinc promoted catalyst.
Alternatively, if the temperature is the same,
say 300"C. a shorter contact time is required using the promoted catalyst.
A preferred embodiment of the process of the invention resides in a process for the preparation of 1, 1, 1,2-tetrafluoroethane which comprises reacting 1-chloro-2,2,2-trifiuoroethane with hydrogen fluoride in the vapour phase in the presence of the promoted catalyst of the invention^ This process may. be carried out under atmospheric or super atmospheric pressure at a temperature of from about 250°C to 500°C.
The process may be one stage of a two or three-stage process, for example it may be the second stage of a process for the production of 1,1,1,2-tetrafluoroethane from trichloroethylene, the first stage being the vapour-phase fluorination of trichloroethylene with hydrogen fluoride in the presence of a chromium-containing catalyst. The promoted catalyst of the invention may be used in the first stage as well as in the
second stage of this two-stage process. Typical reaction conditions for the the first stage are atmospheric or superatmospheric pressure and a temperature in the range of about 180°C to about 3OO°C.
The production of 1, 1,1,2-tetrafluoroethane from l-chloro-2, 2, 2-trifluoroethane results in a1 product stream containing the toxic impurity 1-chloro-2, 2, -difluoroethylene. This impurity can be removed by reacting it with hydrogen fluoride in the va'pour phase in the presence of a chromium containing catalyst at a temperature below about 270°C, for example 150°C to 270°C. The promoted catalyst of the invention may be employed in this reaction, thus providing a three-stage process for the preparation of 1, 1,1,2-tetrafluoroethane essentially free from l-chloro-2, 2-difluoroethylene from
trichloroethylene using the promoted catalyst in each of the three reaction stages.
A particularly preferred embodiment of the above-described two-stage process for preparing 1, 1,1,2-tetrafluoroethane from trichloroethylene comprises the steps of:
(A) contacting a mixture of
l-chloro-2,2,2-trifluoroethane and hydrogen fluoride with the promoted catalyst at 250-350°C in a first reaction zone whereby to form a product containing
1,1,1,2-tetrafluoroethane and hydrogen chloride together with unreacted
starting materials,
(B) passing the total product of step A
together with trichloroethylene to a
second reaction zone containing the
o promoted catalyst at 18O-300 whereby
to form a .product containing l-chloro-2,2,2-trifluoroethane, 1,1,1,2-tetrafluoroethane and hydrogen chloride;
(C) treating the product of step B whereby
to separate a mixture containing
hydrogen chloride and
1,1,1,2-tetrafluoroethane from l-chloro-2,2,2-trifluoroethane, unreacted hydrogen fluoride and unreacted trichloroethylene;
(D) feeding the
l-chloro-2,2,2-trifluoroethane mixture obtained from step C together with additional hydrogen fluoride to said first reaction zone, and
(E) recovering 1,1,1;2-tetrafluoroethane
from the
1,1,1,2-tetrafluoroethane/hydrogen chloride mixture obtained from step C. At least the stoichiometric amount of hydrogen fluoride is usually employed in step A of the preferred embodiment. Typical amounts include from 1 to 10 moles, and preferably from 1 to 6 moles, of hydrogen fluoride per mole of
l-chloro-2,2,2-trifluoroethane. Accordingly, the product of this reaction step will usually contain unreacted hydrogen, fluoride in addition to 1,1,1,2-
tetrafluorqethane, hydrogen chloride and by-products. Preferred reaction temperatures for this stage of the process are in the range from 28O°C to 35Q°C with contact times of from 1 to 1OO and preferably from 5 to 3O seconds at 5 to 20 bars pressure.
From 10 to 10O, preferably from 15 to 60, moles of hydrogen fluoride per mole of trichloroethylene. are typically employed in Step B. Again, the reaction product of this stage will normally contain unreacted hydrogen fluoride. Contact times of 1 to 1OO seconds, preferably 5 to 3O seconds may be used, typically at 18O-3OO°C'and 5 to 2O bars pressure.
.The reaction and separation steps which make up the preferred embodiment of the method of the invention may be performed using conventional equipment and techniques. Thus, for example, recovery of 1,1,1,2- tetrafluoroethane in step E may be effected .by washing the gaseous mixture (containing tetrafluoroethane and hydrogen chloride) with water and aqueous sodium hydroxide solution and then drying and condensing the tetrafluoroethane.
It is preferred that the process according to the invention, including preferred embodiments, is operated" continuously. In practice, however, catalyst deactivation, necessitating periodic catalyst' regeneration or reactivation may interrupt continuous operation of the process. The feeding of air to the catalyst during operation of the process may counter catalyst deactivation and reduce the frequency of process interruption for catalyst regeneration or reactivation.
The present invention relates to 1 process for increasing the activity of a chromium-containing fluorination catalyst which process comprises introducing an activity-promoting zinc in an amount of zinc from 0.5 to 25 % by weight of the catalyst or a compound of zinc of the kind such as hereindescribed, to the catalyst by at least the step of co-precipitating a zinc compound and a chromium compound or at least the step of impregnating a chromium compound with a zinc compound.
The present invention also relates to a chromium-containing fluorination catalyst which comprises an activity-promoting amount of zinc or a compound of zinc. Brief description of the accompanying drawings:
The invention is illustrated but in no way limited by the following examples.
EXAMPLES 1 TO 5
10g of chrornia in the form of granules of size 0.5-1.4mm, and having a surface area of 50m /g, was added to an aqueous solution of zinc chloride (0.2g) in distilled water (10ml> and stirred to ensure thorough wetting of the solid by the solution. The mixture was then dried by direct heating and the resultant solid sieved to give particles, of size O.. 5-1. 4mm, of a finished catalyst comprising O, 9% zinc w/w on chromia. The above procedure was repeated except that zinc chloride solutions of increasing concentration were employed in order to produce a range of finished catalysts with up to 6% w/w zinc in the finished catalyst. The fluorination activities of the zinc promoted chromias were measured using an atmospheric pressure microreactor. Catalysts (2g) were charged to the microreactor and were conditioned in a stream of HF at 300°C for 1 hour and then heated to 350°C and further conditioned in an air/HF (ratio 1:20) stream for approximately 15hrs.
The microreactor was then fed with a l-chloro-2, 2, 2-trifluoroethane The results of the study are presented as '/-. yields of 1, 1, 1,2-tetrafluoroethane in Table 1 and demonstrate the beneficial effect of zinc addition to chromia on increasing the yield of 1,1,1,2-tetrafluoroethane .
The activity of the zinc impregnated-chromia catalyst reached a maximum at a zinc content in the range of about 2 to about 5X w/w.
(Table Removed)
EXAMPLE 6
The catalyst prepared in example 3 was charged to a pressure reactor and prefluorinated with HF at 250°C for 24 hours, using a> pressure of 1O bar. The reactor was then fed with a 133a and HF feed using a molar feed ratio of 1:3.5. Using the above feeds at a pressure of 1O bar, a reaction temperature of 325°C and a contact time of 10 seconds enable a 134a yield of >157. to be achieved. The reaction selectivity was >99*/..
EXAMPLE 7
A 2% w/w zinc-on-chromia catalyst was prepared by impregnating chrornia (4.8g) with an aqueous solution of zinc chloride (0.21g) in distilled water
(5ml). The catalyst was dried in a heated air stream at 12O°C and charged to an Inconel reactor. The catalyst was dried at 310°C in nitrogen for 1 hour and prefluorinated at 31O°C with hydrogen fluoride for 2 hours. Trichloroethylene and HF were then fed to the reactor-at 310°C using a trichloroethylene: HF molar ratio of 1:1O and a contact time of 1 second. The zinc on chromia catalyst converted 4O.9% of the trichloroethylene to 1-chloro-2,2,2-trifluoroethane. This compared with a trichloroethylene conversion of 26.7% achieved using the original unpromoted chromia.
EXAMPLES 8 TO 10.
Zinc, either as an aqueous solution of zinc nitrate or as an aqueous slurry of zinc carbonate (as indicated), was added to a slurry of chromium (III) hydroxide and the pH of the solution was adjusted to 7 using ammonium hydroxide. The resultant solids were
filtered, washed, calcined at 3OO C in nitrogen for 5
3 hours and pelleted to a density of 2g/cms , and the
above procedure was repeated, using zinc carbonate or zinc nitrate solutions of various concentrations, to produce a number of catalysts with up to 10% zinc by weight in the finished catalyst. The catalysts were tested at atmospheric pressure according to the procedure of examples 1 to 5.
The results of the study are presented as 7. yields of 1, 1, 1, 2-tetrafluoroethane in Table 2 and demonstrate the beneficial effect of zinc addition to chromia on increasing the yield of 1, 1, 1, 2-tetrafluoroethane (134a).
Table 2
(Table Removed)
EXAMPLES 11 - 13.
A number of catalysts were prepared according to the procedure of examples 8 to 10 except that chromium (III) nitrate was used instead of chromium (III) hydroxide. The catalysts were tested according to the procedure described for examples 1 to 5.
The results of the study are presented as % yields of 1,1,1,2-tetrafluoroethane in Table 3 and demonstrate the beneficial effect of zinc addition to chrornia on increasing the yield of 1, 1, 1,2-tetrafluoroethane (134a ) .
Table 3
(Table Removed)
EX-AMPLE 14.
lOg of the catalyst prepared in example 9 was charged to a pressure reactor and pre±luorinated with HF at 30O"C for 24 hours, using a pressure of 10 bar. The reactor was then fed with HF and a mixed organic feed comprising 0.5V. by weight t rich lor oethylene in 133a using a molar feed ratio of organics to hydrogen fluoride- of 1:3.5. Using the ahove feeds at a pressure of 10 bar and a contact time of 11 seconds, 134a yields of 127. were achieved at a temperature of 295°C. The reaction selectivity was greater than 99. 5V..
In comparison, lOg of the unpromoted chromia catalyst gave 134a yields of 12% at a temperature of 330 C when pr'ef luorinated and tested at pressure under identical conditions to those described for example 17. The reaction selectivity was 99.O%.
EXAMPLES 15 TO 19.
4.3g of alumina (supplied by Harehaw Ltd),
2 having a surface area of 180m /g, in the form of
granules of size 0.5-1.4mm was added to an aqueous solution of zinc chloride (0.21g) and chromium (III) chloride hexahydrate (0.51g) in distilled water (5ml) and stirred to ensure thorough wetting of the solid by the solution. The mixture was then dried by'direct heating and the resultant solid sieved to give particles, of size 0. 5 - 1.4mm, of a finished catalyst comprising 2'/,Cr/2%.Zn by weight on alumina. The above procedure-' was repeated with various concentrations of zinc chloride to produce a range of finished catalysts containing 2.7. by weight chromium and up to 8%. by weight'zinc. The catalysts were tested at atmospheric pressure according to the procedure described for examples 1 to 5. For the purposes of comparison, the activity of a catalyst comprising 2% by weight chromium on alumina, prepared from an aqueous solution of chromium (III) chloride was also measured.
The results of the study are presented as '/. yields of 1, 1, 1, 2-tetrafluoroethane in Table 4 and demonstrate the beneficial effect of zinc addition to chromium-containing alumina on increasing the yield of 1, 1, 1, 2-tetrafluoroethane (134a ).
Table 4
(Table Removed)
EXAMPLES 20 to 22.
4.43g of aluminium fluoride, prepared by treating alumina with hydrogen fluoride for 24 hours at 300 Cf in the form of granules of size 0. 5 - 1.4mm, and having a surface area of 13m /g, was added to an aqueous solution of zinc chloride (O.O53g) and chromium (III) chloride hexahydrate (0.51g) in distilled water (5ml) and stirred to ensure thorough wetting of the solid by the solution. The mixture was then dried by direct heating and the resultant solid sieved to give particles, of size O. 5 - 1.4mm, of a finished catalyst compx-ising 2'/.Cr/O. 5%Zn by weight on A1F . The above procedure was repeated with various
O
concentrations of zinc chloride to produce a range of finished catalysts- containing 2% by weight chromium
and up to 2% by weight zinc. The catalysts were tested at atmospheric pressure according to the procedure described for examples 1 to 5.
For purposes of comparison the activity of two catalysts containing 2X and 2.4% by weight chromium on aluminium fluoride, and prepared from an aqueous solution of chromium (III) chloride, were also measured.
The results of the study are presented as % yields of 1, 1,1,2-tetrafluoroethane in Table 5 and demonstrate the beneficial effect of zinc addition to chromium—'containing aluminium fluoride on increasing the y^ield of 1, 1, 1, 2- tetraf luoroethane Table 5
(Table Removed)
EXAMPLE 23.
Magnesium oxide tablets (supplied by. Merck S. Co), were ground to give granules of size O.5-1.4mm. 4.44g of the ground magnesium oxide was added to an
aqueous solution of zinc chloride (0.053g) and chromium (III) chloride hexahydrate CO.513g) in distilled vater (5ml) and stirred to ensure thorough wetting of the solid by the solution. The mixture was dried by direct heating and the resultant solid sieved to give particles, of size 0. 5 - 1.4mm of a finished catalyst comprising 2%Cr/O.5XZn by weight on magnesia. The catalyst was tested at atmospheric pressure according to the procedure described for examples 1 to 5.
For the purposes of comparison, catalysts containing 2% and 2..4Y. by weight chromium, prepared by impregnating magnesium oxade granules of size (J. 5 -i.4mrn with an aqueous solution of chromium (III) chloride were also tested.
The' results of the study are presented as '/. yields of 1,1,1,2-tetrafluoroethane in Table 6 and demonstrate the beneficial effect of zinc addition to chromium-containing magnesium oxide on increasing the yield of 1,1,1, 2-tetrafluoroethane (134a). table 6(Table Removed)

WE CLAIM:
1. A chromium-containing fluorination catalyst which comprises
an activity-promoting amount of zinc in the range of from about
0.5% to about 25% by weight of the
catalyst.
2. A catalyst as claimed in claim 1, wherein the chromium-
containing catalyst comprises chromia, halogenated chromia or
a chromium oxyhalide.
3. A catalyst as claimed in claim 2, wherein the activity-promoting
amount of zinc is supported on the chromia, halogenated
chromia or chromium oxyhalide.
4. A catalyst as claimed in claim 2, wherein the chromia,
halogenated chromia or chromium oxyhalide is impregnated
with the activity promoting amount of zinc.
5. A catalyst as claimed in claim 1, wherein it comprises a mixed
oxide of zinc and chromium.
6. A catalyst as claimed in claim 1, comprising an activity-
promoting amount of zinc produced by co-precipitating zinc
hydroxide and chromium hydroxide and thereafter converting
the hydroxides to zinc oxide and chromium oxide.
7. A catalyst as claimed in any one of the preceding claims,
comprising an activity-promoting amount of zinc in the range of
from about 0.5% to about 6% by weight of the catalyst.
8. A catalyst as claimed in any one of the preceding claims further
comprising a metal oxide, halogenated metal oxide or metal
oxyhalide of magnesium, aluminium or zirconium.

9. A chromium-containing fluorination catalyst substantially as herein described with reference to the foregoing examples.

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Patent Number

234572

Indian Patent Application Number

514/DEL/2005

PG Journal Number

28/2009

Publication Date

10-Jul-2009

Grant Date

09-Jun-2009

Date of Filing

09-Mar-2005

Name of Patentee

INEOS FLUOR HOLDINGS LIMITED

Applicant Address

FIRST FLOOR OFFICES, QUEENS GATE, 15-17 QUEENS TERRACE, SOUTHAMPTON, HAMPSHIRE S014 3BP, UK

Inventors:

#	Inventor's Name	Inventor's Address
1	JOHN DAVID SCOTT	HEALTH, RUNCORN, CHESHIRE WA7 4QE, ENGLAND.
2	MICHAEL JOHN WATSON	HEALTH, RUNCORN, CHESHIRE WA7 4QE, ENGLAND.

PCT International Classification Number

B01J 23/85

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	9104775.3	1991-03-07	U.K.