PREPARATION OF CHLOROTRIFLUOROETHYLENE AND TRIFLUOROETHYLENE

Abstract: 1,1,2-trichloro-1,2,2-trifluoroethane is dechlorinated with hydrogen to produce chlorotrifluoroethylene and tri­ fluoroethylene. Chlorotrifluoroethylene may be further de­ chlorinated to trifluoroethylene. Trifluoroethylene may then be hydrofluorinated with or without the use of catalyst to produce tetrafluoroethane and, particularly, assymmetrical tetrafluoroethane. Tetrafluoroethane produced by this pro­ cess can be purified for refrigeration and other applications more easily than tetrafluoroethane produced by other pro­ cesses since impurities which form azeotropes with tetra­ fluoroethane are minimized. A catalyst for the low tempera­ ture dechlorination of trichlorotrifluoroethane and of chloro­ trifluoroethylene is a platinum-group metal such as palladium on an alkali magnesium fluoride support. Catalysts for the high temperature dechlorination of trichlorotrifluoroethane are alkali magnesium fluorides alone or coated with iron, copper or nickel. These catalyst can be reactivated with oxygen or air at elevated temperatures. The products chlorotrifluoroethylene and trifluoroethylene are useful as monomers while tetrafluoroethane is useful as a refrigerant.

Description: DESCRIPTION PREPARATION OF CHLOROTRI FLUOROETHYLENE AND TRI FLUOROETHYLENE BACKGROUND OF THE INVENTION Tetrafluoroethane, and particularly asymmetrical tetrafluoroethane, has been suggested for refrigeration and other applications where chlorofluorocarbons and other fluorocarbons are now used. German published patent application DOS 2,822,471 describes the production of tetrafluoroethane by hydrogenation of chlorofluoroethanes such as symmetrical and asymmetrical dichlorotetrafluoroethane. U.S. Patent 4,129,603 discloses the manufacture of asymlaetrical tetrafluoroethane by reacting 1,1,1trifluoro-2-chloroethane with hydrogen fluoride in the presence of a chromium oxide catalyst and removing certain unsaturated impurities by contactiny the crude product with aqueous permanganate salts. It has been found that both of these methods for producing tetrafluoroethane have in the crude products materials such as asymlaetrical dichlorotetrafluoroethane (fluorocarbon 114a) and asymmetrical trifluoroethane (fluorocarbon 143a). Both of these materials are now believed to form azeotropes with tetrafluoroethane and especially asymmetrical tetrafluoroethane. Under these conditions, it is difficult to separate tetrafluoroethane from such impurities by standard distillation techniques. The production of chlorotrifluoroethylene (fluorocarbon 1113) and trifluoroethylene (fluorocarbon 1123) from trichlorotrifluoroethane is described, for example, in U.S. Patent 2,802,887 to Miller et al. (August 13, 1957) and U.S. Patent 3,564,064 to Nakagawa (February 16, 1971). Both of these patents employ a palladium or platinum on an activated carbon or alumina catalyst. Similar processes limited to production of chlorotrifluoroethylene from trichlorotrifluoroethane, (fluorocarbon 113) but with other catalysts, are known from references such as U.S. Patents 2,704,775 to Clark (March 22, 1955) and 2,697,124 to Mantell (December 14, 1954). Chlorotrifluoroethylene is useful as a inonomer in fluoropolymers, while trifluoroethylene can be hydrofluorinated to tetrafluoroethane. Tetrafluoroethane produced from trifluoroethylene is easier to purify by distillation than tetrafluoroethane produced by other techniques. BRIEF DESCRIPTION OF '±HE MENTION The present invention includes an improved process for producing chlorotrifluoroethylene or trifluoroethylene by the dechlorination in the vapor phase of l,l,2-trichloro-l,2,2-trifluoroethane or chlorotrifluoroethylene with hydrogen in the presence of a supported platinum-group metal catalyst, wherein the improvement cos,lpr-ises: : a) reacting a feed of 1,1,2-trichloro-1,2,2- trifluoroethane, chlorotrifluoroethylene or mixtures thereof with hydrogen at a reaction teinperature of about 175 to about 3000C in the presence of a platinum-group metal supported on an alkali magnesium fluoride support as the catalyst, b) contacting the catalyst with an oxygen-containing gas at a reactivation temperature between about 400 and about 6000C to reactivate the catalyst, and c) reacting the feed with hydrogen in the presence of the reactivated catalyst at the reaction temperature. The present invention also includes an improved process for producing chlorotrifluoroethylene by the catalytic dechlorination in the vapor phase of 1,1,2-trichloro-1,2,2-trifluoroethane with hydrogen, wherein the improvement comprises conducting the reaction at a temperature of between about 400 and about 6000C in the presence a catalyst selected from the group consisting of alkali magnesium fluorides and alkali magnesium fluorides coated with at least one of iron, copper and nickel and periodically reactivating the catalyst by contacting the catalyst with an oxygen-containing gas at a reactivation temperature between about 4000C and about 6000C. DETAILED DESCRIPTION OF THE INVENTION The present invention relates particularly to a vapor phase dechlorination reaction in the presence of a catalyst. The catalyst for the lower-temperature reactor is a supported platinum-group metal, i.e. ruthenium, rhodium, palladium, osmium, iridium or platinum and is preferably palladium. Under the reducing conditions of the reaction, the metal is partly or even predominantly at a zero valence state, but may include salts or oxides with the platinum-group metal at a positive valence state. The support is an alkali magnesium fluoride such as sodium or potassium magnesium fluoride. It may be formed by precipitating magnesium and alkali metals with fluoride from aqueous solutions of water-soluble alkali metal and magnesium salts such as the chlorides. The precipitation is designed to form a mixed salt wherein the alkali metal and magnesium are in substantially equimolar amounts as described in Zeitschrift fur Anorganische and Allgemeine Chemie, bond 355-280-1967. The support may contain some chloride in place of fluoride, derived either from the aqueous solution used to make support or by halogen replacement with HC1 under deciilorination reaction conditions. Tlie support may also contain other cations or alteration in the proportion of cations without significant loss of activity. Catalyst particles for the low-te.nperature reaction may be conveniently prepared by drying, grinding and screening the precipitated alkali magnesium fluoride and then coating the resultant particles with a palladium-metal salt such as PdCl2. The coated particles may then be dried and the palladium metal at least partly reduced to a zero valence state with hydrogen, conveniently at the reaction temperature. For the higher temperature reaction, the alkali magnesium fluoride may be used uncoated or coated with at least one of iron, copper or nickel. The preferred catalysts are the uncoated particles and those coated with nickel. Sodium magnesium fluoride is preferred, with potassium magnesium fluoride also being satisfactory. If the particles are to be used as such, one should directly activate the screened particles. If copper, iron or nickel are to be coated on, they should be coated on as a water soluble salt, then dried, and then optionally activated with hydrogen alone before introducing fluorocarbon 113. During the dechlorination reaction various deposits build up on the catalyst which gradually reduce its activity. This build-up, apparently in the form of polymeric material and of coke, also occurs with other supports for palladium such as activated carbon. Unlike the palladium-on-activated carbon supports of the prior art, however, the present catalysts can be reactivated by exposure at elevated temperatures, such as about 4000C to about 6000 C, preferably about 500-5500C, to an oxygencontaining gas such as air. It is preferred to contact the reactivated catalyst with hydrogen only at the reaction teinperature before resuming the feed of chlorofluorocarbon. The feed may be 1,1,2-trichloro-1,2,2-tri- fluoroethane (fluorocarbon 113) used to produce chlorotrifluoroethylene (fluorocarbon 1113) or trifluoroethylene (fluorocarbon 1123) based on reaction with two or three molecules of hydrogen with each laolecule of fluorocarbon 113. Alternatively, the feed may be fluorocarbon 1113 (which is commercially available) used to produce fluorocarbon 1123 by reaction of one molecule of hydrogen with each molecule of fluorocarbon 1113. In the high temperature reaction, only the feed of fluorocarbon 113 to produce fluorocarbon 1113 is feasible. It is preferred that mixtures of fluorocarbons 113 and 1113 be fed in the low temperature reaction to produce fluorocarbon 1123. It has been found that tne dechlorination of fluorocarbon 113 to fluorocarbon 1123 is enhanced by the presence of fluorocarbon 1113 (the intermediate) in the feed. This can be accomplished by recycling fluorocarbon 1113 from the effluent of the reaction and using fluorocarbon 113 as the feed since, with hydrogen being provided at less than large excesses, some of the fluorocarbon 113 will be dechlorinated only to fluorocarbon 1113. By contrast, Canadian Patent 655,897 claims to minimize the production of fluorocarbon 1113 when dechlorinating fluorocarbon 113 to fluorocarbon 1123. Fluorocarbon 1113 is acceptable or even desirable in the effluent if it is to be recycled. By contrast, 1,1,2-trifluoroethane (fluorocarbon 143) which may be formed by the addition of a fourth mole of hydrogen to fluorocarbon 1123 is considered an undesired by-product that can be reclaimed only by chlorinating the entire distance back to fluorocarbon 113. If fluorocarbons 133 and 123a are formed during the reaction, they can be recycled. The level of palladium-group metal does not appear especially critical, with the range of not more than 2.5% of total weight of catalyst (preferably 0.5 2.0%) stated for palladium-on-activated carbon in Canadian Patent 655,897 being satisfactory. Similar levels of other metals are used in the higher te.npera- ture catalyst. Contact times are also not critical, with a range of 1 to 10 seconds being satisfactory. The reaction temperature when using a platinum group metal coated catalyst is about l75-3000C, preferably about 200-250 C. The ratio of hydrogen to chlorofluorocarbon fed may vary from as little as 0.1 to 1 to as much as 2 to 1 or even higher. In general more hydrogen should be fed as the proportion of fluorocarbon 113 in the feed increases since fluorocarbon 113 has three chlorines to remove rather than one. When fluorocarbon 1113 is the sole feed, the above ratio should not exceed 1 to 1. The hydrogen level is too high when fluorocarbon 143 can be detected in significant quantities in the effluent. When fluorocarbon 1123 is produced by the present process, it may be hydrofluorinated to produce assymmetrical tetrafluoroethane. A catalytic vapor phase process is described in Belgian Patent 870,530 of Imperial Chemicals Industries, Ltd. (March 15, 1979). The reaction temperature for uncoated, iron coated, nickel coated or copper coated catalysts is about 400 to 6000C, preferably about 4750C to about 5500C. The feed ratio is preferably below about 1:1 hydrogen: fluorocarbon 113 since higher levels of hydrogen increase the deactivation rate of the catalyst and thus requires more frequent reactivation. Example 1 - Preparation of NaMgF3 and NaMgF3 Supported Catalysts 317 g (7.55 mol) sodium fluoride (NaF) was dissoved in 7 L of distilled water in a 12 L glass flask. The mixture was heated to 90-950C. 487.3 g (3.00 mol) of magnesium chloride (MgC12.6H2O) was separately dissolved in 1 L of distilled water and this solution added to the sodium fluoride solution dropwise over a period of about 1.5 h with mechanical agitation. Agitation and temperature (90-950C) were maintained for 1 h more. The mixture was allowed to cool and settle overnight. The clear liquid (aqueous Nail) was siphoned off and the precipitate vacuum filtered through #4 Batman paper. While the cake was still wet it was washed with 10-100 mL portions of water and then filtered semidry. The cake was dried overnight at 1600C in a vacuum oven. When used "neat" (without impregnating a metal) this dried cake was calcined at 5500C in a muffled furnace for 16 hours, broken into chunks and screened for particles between American standard mesh 8 (about 2.0 mm) and American Standard mesh 20 (about 0.71 mm). For the coated catalyst, the filter cake was calcined at 5500C in a muffled furnace for 16 hours, broken into chunks and screened for particles between American Standard mesh 8 (2.0 mm diameter) and American Standard mesh 20 (0.71 mm diameter). Palladium was then added as an aqueous PdC12 solution (with HC1 as required to completely dissolve the PdC12). The wet coated catalyst was dried in a steam bath until free flowing. The resultant granules were then dried overnight at 1600C in a vacuum oven. The dried catalyst was then placed in the reactor tube (described below) and treated with hydrogen for about 2 hours at 2000C to convert the PdC12 to elemental palladium. Example 2 Dechlorination of Fluorocarzon 113 With NaMgF3 Supported Catalysts A 1 inch by 30 inch (2.54 by 7b.2 cm) stainless steel pipe reactor lined with a 3/4 inch (1.91 cm) inside diameter Coors 998 pure fused alumina liner was fitted with a 1/4 inch (0.64 cm) outside diameter Coors alumina thermowell running its entire length from the gas feed at the bottom to the product exit at the top for gases flowing between the thermowell and the liner. The reactor was placed in a vertically mounted 24 inch, three zone, electrically heated tube furnace. The effluent line was fitted with for on-line gas chromatography analysis and acid detersllination in water by caustic titration. 152 g (170 mL) of 0.5% Pd on NaMgF3 prepared as described in Example 1 was charged to the reactor and reduced with hydrogen as indicated in Example 1. Hydrogen and chlorotrifluoroethylene (fluorocarbon 1113) were then passed into the reactor at an equimolar ratio with flow rates adjusted to give contact time varying from 2 seconds (463 g/h of fluorocarbon 1113) to 5 seconds (161 g/h of fluorocarbon 1113). During the first 22 hours of operation the furnace was kept at 2000C except for a 5.5 h period as indicated in Table 1. The contact times, % molar conversion of fluorocarbon 1113, % molar yield of product fluorocarbon 1123 (based on 1113 converted) and % molar yield of by-product fluoro carbon 143 (based on 1113 converted) are summarized in Table 1. Each line represents two or more readings over the indicated period with percent conversion and percent yields rounded off to the nearest whole percent. TABLE 1 H2:113 Time Contact mole % 1113 % 1123 % 143 From Start Time ratio Conversion Yield Yield 1-2.5 2.75 1 83-84 73-84 15-24 5-9 2 1 34-68 89-90 9 10-11 5 1 62-67 83-84 14 12 3/4-15 3/4 2 1 30-31 89-90 9-10 16.5-19 5 1 54-55 86-88 10-11 20-22 2 1 24-32 91 7-8 23.5-25 5 1 41-47 84-88 8-10 25.5-29 3 0.5 22-30 90-91 7-8 30-33 5 0.5 26-45 87-90 8-9 34-37 3 1 33-40 89-91 8-10 39-40.5 5 1 48-52 86-87 11-12 43-44 3 1 31-32 87-88 9-11 46-50* 3 0.5 14-19 93 5-6 51-59 5 1 28-32 84-88 9-12 *Furnace at 2500C. The catalyst was then regenerated by heatiny the furnace to 5500C, passing air through the reactor for about 3 h, reducing the furnace temperature to 4000C and flowing hydrogen through the reactor for 7 h as the furnace temperature was gradually lowered to 2000C. The catalytic dechlorination of fluorcarbon 1113 was then resumed as indicated in Table 2. The molar feed ratios of H2 to fluorocarbon 1113 was varied between 1:1 and 0.5:1, the contact time was varied between 3 and 5 seconds, the furnace temperature was varied between 1500C and 2000 C. TABLE 2 H2 Time Con- 1113 % 1113 From tact Mole Conver- t 1123 % 143 Start Time Temperature Ratio sion Yield Yield 60.5 h 5 s 200 1 78 83 15 61.5-64 5 150 1 64-65 82-83 15-16 66-72.5 3 150 0.5 26-32 89-91 8-9 74-81 3 150 0.5 19-27 90-91 7-8 82.5-92 5 200* 1 29-53 86-90 8-12 116-119 - Activity check with fluorocarbon 113 - low conversion; regeneration at 5500C with air 120-125 5 200 1 48-65 83-85 13-15 Catalyst used for unrelated fluorocarbon studies; regeneration at 550 C; catalyst then idle for 1 week 136-140 5 200 1 66-82 79-85 14-20 *Furnace cooled down for a few hours causing temporary temperature drop in reactor. Example 3 Dechlorination of Fluorocarbon 113 with NaMgF3 Supported Catalyst Using the catalyst of Example 2 after 92 hours and the reaction of Example 2, fluorocarbon 113 and hydrogen were passed over the catalyst at molar ratios of 2:1, 1.3:1 and 1:1, at furnace temperatures of 2000C, 30UOC and 5000C and at contact times of 3, 4.2 and 5 seconds. The results, as indicated in Table 3, are of enhanced, but still low conversions of fluorocarbon 113 after reactivation. Table 3 H2: 113 Time Con- Tem- 113 Con- % % % from tact pera- Mole ver- 1123 1113 143 133 123a Start Time ture Ratio sion Yield Yield Yield Yield Yield 93 5 200 2:1 5 46 29 - 28 94 5 200 2:1 6 33 47 - 23 95 5 200 2:1 8 42 29 - 24 96 5 ' 300 2:1 14 49 39 - 11 Regenerated at 5500C with air 97 4.2 200 1.3:1 22 40 11 30 19 98 4.2 200 1.3:1 13 29 9 37 25 100 5 200 2:1 9 41 11 37 33 107 3 500 1:1 40 6 85 - 3 108 3 500 1:1 15 - 95 - 1 110 3 500 1:1 15 - 82 - 4 14 Example 4 Using the catalyst and reactor of Example 2, fluorocarbon 113, fluorocarbon 1113 and hydrogen were passed over the catalyst at a molar ratio of 1:1:2 with a 2000C furnace telaperature and a 5 second contact time. The results are displayed in Table 4 with the % 1113 conversion based on the net decrease in 1113 observed. Yields are- based on fluorocarbons 1113 and 113 converted. Table 4 Time % 113 % 1113 from Conver- Conver- % 1123 % 143 % 133 % 123a Start sion sion Yield Yield Yield Yield 127 13 44 82 16 4 0.7 128 13 37 81 14 4 1.6 129 12 35 81 1 4 0.8 130 30 28 81 14 3 0.7 131 30 24 81 14 3 0.6 Exalnples 5-7 Similar reactions with the sodium magnesium fluoride alone as catalyst or nickel on sodium magnesium fluoride were effective to convert fluorocarbon 113 to fluorocarbon 1113 at elevated temperatures above 400QC so long as hydrogen levels were kept low as described below. Whenever sufficient hydrogen was provided to produce fluorocaroon 1123, the high temperature apparently caused decomposition of fluorocarbon 1123, apparently to a polymer. Similar reactions with palladium on carbon produce fluorocarbons 1113 and 1123 as described in the prior art but, eventually, the catalyst is deactivated by carbonaceous or polymer deposits. Unlike the catalysts used in the present invention, carbon-based catalysts cannot be regenerated with air. EXAMPLE 5 DECHLORINATION OF FbUOROCARBON 113 WITH UNCOATED NaMgF3 3 Using freshly activated sodium magnesium fluoride catalyst prepared as in Example 1 but without coating and the reactor arrangement described in Example 2, fluorocarbon 113 was reacted with hydrogen at 500 C. Conversions and yield data are shown in Table 5. Simiiar results are obtained with uncoated potassium magnesium fluoride. These results show lower fluorocarbon 113 conversions versus similar runs when copper, iron or nickel coated NaMgF3 was used. No deactivation of the uncoated NaMgF3 was observed at 5000C during the first 108 hours of reaction. After 108 hours, variable studies at 5350C showed initial higher activity but catalyst activity decline in about 20 hours. Regeneration with oxygen at 5500C to maintain the higher activity at 5350C was required. Periodic catalyst activity checks were made at 5000C by repeating a standard run. After 330 hours, the catalyst activity was equal to that observed at 108 hours. The standard run data are shown in Table 5. TABLE 5 H2 i13 Time Con- Tem- 113 Con- % % % From tact pera- Moleo ver- 1123 1113 133 123a Start Time ture OC Ratio sion Yield Yield Yield Yield 88h 3 s 500 0.5 21.3 7.12 83.90 5.66 3.56 108 3 500 0.5 25.5 8.06 84.52 3.49 3.92 130 3 500 0.25 9.9 5.18 89.83 2.54 2.44 Variable Study - 2 Regeneration 5500C 218 3 500 0.5 26.5 7.79 82.18 3.72 6.31 Variable Study - 2 Regeneration 5500C 330 3 500 0.5 25.1 6.00 84.46 2.84 6.70 EXAMPLE 6 DECHLOKINATION OF FLUOROCARBON 113 W H NICKEL ON NaMgF3 NaMgF3 catalyst was prepared as in Example 1, but NiC12 was applied instead of PdC12. The concentration of nickel on the catalyst was 8.3%. Results are summarized in Table 6. The catalyst was more active but required more frequent regeneration. Catalyst regeneration by burning off a carbon deposit was required about every 36 hours. No loss in catalyst activity was observed after regeneration. TABLE 6 H2: Mole %113 Mole Mole Time Con- 113 Con- % % Mole Mole From tact Temp Mole ver- 1123 1113 % 133 % 123a Start Time OC Ratio sion Yield Yield Yield Yield 0-18h 3.04s 400 1.0 15.2 5.50 87.25 2.44 4.82 52-68 3.09 400 1.0 16.2 3.30 88.21 4.72 4.95 154-172 3.18 400 1.0 14.8 3.89 87.92 3.47 4.72 70-86 3.06 425 1.0 13.7 7.10 86.83 2.26 3.80 100-120 3.06 450 1.0 21.7 4.68 89.37 2.03 3.92 134-144 3.10 450 0.99 19.7 4.38 89.21 2.44 3.98 36-50 3.10 500 0.99 71.4 5.68 78.13 3.55 10.20 264-284 3.09 500 1.0 49.6 9.96 78.79 3.68 7.57 EXAMPLE 7 DECHLORINATION OF FLUOROCARBON 113 WITH COPPER ON NaMgF3 A NaMgF3 catalyst was prepared as in Example 1, but Curl2 was applied instead of PdC12. The concentration of copper on the catalyst was 6.3%. Results are summarized in Table 7. TABLE 7 H2: % 113 Mole Mole Mole Con- 113 Con- % % % Mole % tact Temp Mole ver- 1123 1113 133 123a Time bC Ratio sion Yield Yield Yield Yield 3.24 s 450 0.99 12.9 1.5 92.4 2.2 3.9 6.34 450 0.99 18.8 5.7 86.5 2.5 5.3 6.19 475 0.99 35.6 6.4 85.2 2.4 S.0 3.26 475 0.20 16.9 0 96.0 0.4 3.6 3.23 475 0.97 23.8 6.2 87.0 2.2 4.6 3.39 500 0.20 20.1 0 93.6 0 6.4 3.27 500 0.97 38.9 6.5 86.2 2.4 4.8

Claims: We claim: 1. An improved process for producing chlorotrifluoroethylene or trifluoroethylene by the dechlorination in the vapor phase of 1,1,2-trichloro- 1,2,2-trifluoroethane or chlorotrifluoroethylene with hydrogen in the presence of a supported platinum-group metal catalyst, wherein the improvement comprises: : a) reacting a feed of 1,1,2-trichloro-1,2,2- trifluoroethane, chlorotrifluoroethylene or mixtures thereof with hydrogen at a reaction temperature of about 175 to about 3000C in the presence of a platinum-group metal supported on an alkali magnesium fluoride support as the catalyst, b) contacting the catalyst with an oxygencontaining gas at a reactivation temperature between about 400 and about 6000C to reactivate the catalyst, and c) reacting the feed with hydrogen in the presence of the reactivated catalyst at the reaction temperature. 2. The process of claim 1 wherein the feed is a mixture of 1,1,2-trichloro-1,2,2-trifluoroethane and chlorotrifluoroethylene, with trifluoroethylene being recovered as product. 3. The process of claim 1 wherein the reaction temperature is between about 2000C and about 2500C. 4. The process of claim 1 wherein the catalyst is palladium. 5. An improved process for producing chlorotrifluoroethylene by the catalytic dechlorination in the vapor phase of l,l,l-trichloro-1,2,2-trifluoroethane feed with hydrogen, wherein the improvement comprises: a) conducting the reaction at a temperature of between about 4000C and about 6000C in the presence of a catalyst selected from the group consisting of alkali magnesium fluorides and alkali magnesium fluorides coated with at least one of iron, copper and nickel, and b) periodically reactivating the catalyst by contacting the catalyst within an oxygen containing gas at a reactivation temperature between about 4009C and about 6000C. 6. The process of claim 5 wherein the catalyst is an alkali magnesium fluoride. 7. The process of claim 6 wherein the catalyst is sodium magnesium fluoride coated with nickel. 8. The process ot claim 7 wherein the reaction temperature is between about 4750C and about 5500C.

Inventors: CUNNINGHAM, WILLIAM JOSEPH, PISKORZ, RONALD FABIAN, SMITH, ADDISON MILES
Applicants: ALLIED CORPORATION
Application year: 1981
Main classification: C07C21
IPC codes: B01J27, C07C17, C07C67, B01J23, C07B61, C07C21