Title of Invention

"A PROCESS FOR PREPARATION OF 1,1,1,2-TETRAFLUOROETHANE"

Abstract

This invention relates to a process for the preparation of 1,1,12-tetrafluoroethane (HFC-13a) using a novel catalyst. HFC-134a which is used as a replacement for some chlorofluorocarbons in refrigeration and air-conditioning industry. The process steps are, contacting in the gas phase a feed consisting of 2-chloro-l, 1,1-trifluoroethane and HF with a co-precipitated chromia-alumina catalyst impregnated with a zinc compound at a temperature of 275 - 400°C optionally under pressure and recovering 1,1,1,2-tetrafluoroethane in a conventional manner from the product stream.

Full Text

This invention relates to a process for the preparation of 1,1,1,2-tetrafiuoroethane. Particularly it relates to the preparation of HFC-134 a using a novel catalyst.HFC-134a which is used as replacement for some chlorofluorocarbons in refrigeration and air conditioning industry. It is known in the art that the catalytic vapor phase fluorination of haloalkanes with hydrogen fluoride results in the formation of fluorine rich haloalkanes. Aluminium fluoride is one of the catalysts known in the art for the halogen exchange. However a suitable catalyst is required for the fluorination of 2-chloro-1, 1,1,-trifluoroethane (HCFC-133a) to give HFC-134a. A US Patent 2,885,427 (1959) has found CrF3.3H2O as a suitable catalyst for the fluorination of haloalkanes and haloalkenes. CrF3.3H2O is only a precatalyst , which is oxygenated at 600°C to obtain an active catalyst whose empirical formula was found to be CrO3F2. The reaction of trichloroethylene with HF in vapor phase at 350°C using the above catalyst gave HCFC-133a as the major component and HFC-134a as a minor component. It is known in the art that the ease of replacement of chlorine bound to a carbon, by fluorine follows the order trihalide (-CX3)> dihalide (-CHX2) > primary halide (-CH2X) where X = CI. However the replacement of the primary halide present in HCFC-133a requires an efficient catalyst and relatively higher temperature to get good conversions and high selectivity, which are important for commercial preparation. An UK Patent GB 2,030,981 A (1979) reported the fluorination of HCFC-133a at 400°C using CrF3.3H2O as precatalyst. The catalyst was activated by treatment first with air and then with a mixture of HF and air. After activation and during the initial period of fluorination, HCFC-133a and HF were passed in a mole ratio of 1:6 over the catalyst to obtain 31% conversion and 98% selectivity for HFC-134a. Subsequently the reaction was continued by introducing additionally air during which time both conversion and selectivity started falling gradually. The discovery of oxygenated CrF3.3H2O as a precatalyst lead to the development of several new catalysts based on the oxides of chromium, nickel, cobalt, aluminium etc., The US patents 4,129,603 and 4,158,675 claim a highest conversion of 18.2% in the fluorir»fon using^^*^ HF: HCFC-133a in mole ratio 3:1. at a reaction temperature in the range 339°-355° C and atmospheric pressure. The selectivity for HFC-134a was 91%. There have been further modifications in the preparation of the precatalyst based on chromium hydroxide. The European Patent 0514932 (1992) described the preparation of Cr(OH)3 from Cr(NO3)3 with different surface areas in the range 48-180 m 2/g and used graphite as an additive. TNs catalyst gave a maximum conversion of 20.3% with a selectivity of 95.7% for HFC-134a using HF:HCFC-133a in mole ratio 4.6:1. at a reaction temperature of 330° G and a space velocity of 2250/h. The EP 0546883 (19j32Jjej>orted the jfeparation of chromia with or without Ni compound using sol gel technique. The addition of nickel compound has improved the life of the catalyst. The patents 0486333 Ai (1991) and EP 0554165 Al (1993) reported a catalyst containing chromia/nickel salt impregnated on partially fluorinated alumina or AIF3. The fluorination of HCFC-133a was carried out under pressure and in the presence of oxygen, to give HFC-134a with a maximum conversion of 21% and 99% selectivity. The EP 0641598 A2( 1994) discloses a process for the fluorination catalyst by firing Cr (III) hydroxide in hydrogen atmosphere. The catalyst obtained was crystalline Cr2O3. Using a mote ratio of HF: 133a 8:1 a conversion of 19.8% HCFC-133a and 99.3% selectivity for HFC-134a was obtained. The US patent 4792643 (1988) report the preparation of different catalysts by impregnation of CrO3, TiCU. CrCI3, CoCb and NiCb on porous activated alumina. These catalysts were used to obtain directly HFC-134a by fluorination of TCE. The selectivity for HFC-134a was very low. The US patent 5155082 (1992) disclosed a catalyst prepared by blending Al (OH)3 and chromium oxide in the presence of a solvent. The fluorination of HCFC-133a was reported to give 18% conversion with 94% selectivity for HFC-134 a. The EP 0328127 Al (1989) reports the use of a catalyst obtained by impregnation of compounds of Co, Mn, Ni, pd, Ag and Ru on alumina or AIOF as a precatalyst for the fluorination of HCFC-133a. The catalyst obtained from CoCl/Al2O3 gave conversion of 33.5% with selectivity 93.7% for HFC-134a in the fluorination of HCFC-133a using HF containing ppm levels of oxygen. The above catalyst has been further modified in Indian Patent 172054 (1989) by using additives selected from compounds of metals having atomic number 58-71. At temperature above 350°C and using HF: HCFC-133a in mole ratio in the range 10:1 to 20:1, conversions in the range 30-40% were obtained. At higher temperatures the conversions were higher but the selectivity dropped to 82.9%. The patents WO 92/16480 (1992) and WO 92/16481 (1992) disclosed a new catalyst prepared by impregnation of zinc compound on Al2O3 and optionally containing one or more other metals selected from this group with atomic number 57-71. This catalyst gave very high selectivity for HFC-13a. The use of compounds of zinc and/or magnesium as promoters on chromium based catalyst impregnated on alumina or AIF3 was reported in the EP 0502605 Al (1992) for the fluorination using HF: HCFC-133a in mole ratio 3.5:1 at reaction temperature of 330°C and contact time 2s. The main object of the present invention is to provide a process of preparation of HFC-134a by fluorination of HCFC-133a using a novel catalyst. Another object of the invention is to reduce the relative percentage of strong acid sites in the catalyst in order to achieve high selectivity. Yet another objective is to provide enough crushing strength to the catalyst for use under pressure. Accordingly the present invention relates to a process for the preparation of 1,1,1,2-tetrafluoroethane which comprises; contacting in the gas phase a feed consisting of 2-chloro-l,l,l-trifluoroethane and hydrogen fluoride, characterized in that with a co-precipitated chromia-alumina catalyst impregnated with a zinc compound at a temperature of 275 - 400°C optionally under pressure, and recovering 1,1,1,2-tetrafluoroethane in a conventional manner from the product stream. The co-precipitated chromia-alumina catalyst may contain choromium: aluminum in the atomic ratio of 1:1 to 1:14. The amount of zinc compound used for impregnation of co-precipitated chromia-alumina catalyst may range from 2-12% by weight. The mole ratio of anhydrous hydrogen fluoride and 2-chloro-l,l,l-trifluoroethane may be in the range of 4:1 to 15:1. The ratio of the catalyst to feed (W/F) may be in the range of 80 to 150 g.h./mole. The contacting may be carried out in the pressure range of 150-210 psig. DETAILS OF THE INVENTION A commercial process for HFC-134a uses HCFC-133a and anhydrous hydrogen fluoride as raw materials. The process can be carried out both at atmospheric pressure and under pressure. The process under pressure has the advantage of directly feeding the product stream into distillation columns operating under pressure for the separation of the desired product and byproducts and to recover and recycle the unreacted starting materials and intermediates. The factors that influence the conversions and selectivity are given below: 1. The precatalyst and its activation with HF. 2. Mole ratio of HF:HCFC-133a 3. Reaction temperature 4. The ratio of weight of the catalyst to the number moles per hour in the feed expressed as w/F g.h/mole. 5. Pressure. The catalyticaliy activity in the halogen exchange has been attributed to the Lewis acid sites.In the case of chromia based catalyst the activity was attributed to the number of reversibly oxidizable sites in the precatalyst.In the alumina-based catalyst the formation of Q>- AIF3 during activation is critical to the catafytcal activity. The catalyst based on chromia atone was found quite efficient in fiuorinalion at atmospheric pressures. Under pressure this catalyst exhibited a fall in the conversions and selectivity. Also volatile compounds are generated that condense at the reactor exit causing blockage, a serious draw back for commercial operation. The use of graphite to increase the strengtfi of the catalyst resulted in a loss in adivity. This invention takes advantage of the catalytical activity of both chromia and alumina and reports the preparation of a co-precipitated catalyst starting from salts of Cr3* and Al (NO3) 3 The relative atomic ratios of Cr: Al can be in the range 1:1 to 1:14 preferably in the range 1:3 to 1:10 and most preferably in tie range 1:3 to 1:5. The co-precipitation is done by using a "base selected from NaOH, KOH and NH4OH, preferably with NH4OH. The precipitation is carried out at various dilutions using the base of strength 1 to 6 molar, preferably 4-6 molar. The quantity of water used to dissolve the combined quantity of chromium (III) salt and aluminium nitrate are in foe weight ratio 38:1 to 4:1 preferably 19:1 to 4:1 and most preferably 10:1 to 4:1. The precipitation of metal trihydroxides are completed by adjusting the final pH in the range of 7-8 and filtered, washed with water and dried to constant weight at a temperature in the range 70-150 deg.C, preferably in the range 70-120 deg.C. The dried catalyst is powdered and shaped into tablets or extrudes and calcined in nitrogen atmosphere at a temperature in the range 350-400 deg.C, preferably in the range 380-400 deg.C for 24 to 48 hours. The calcined catalyst was activated by treating sequentially with N2 at 400 deg.C for 24 hours followed by fluorination in the temperature range 150-400 deg.C till the exit stream of HF contains less than 1 % of moisture. The process also economises on the use of the Cr compound as raw material for the preparation of the catalyst thus minimising the cost and problems related to effluent disposal of the spent catalyst It was found that the performance of the co-precipitated Cr2O3/Al2O3 catalyst can be further improved by reducing the total acidity by impregnation or deposition with a compound of zinc The addition of zinc compound results in suppressing the formation of 2-chtoro-l,1,l,2-tetrafluoroethane (HCFC-124), pentafluoroethane (HFC-125) and 1,1,1-trifluoroethane (HFC-143a) in the fluorination of HCFC-133a. The addition of a zinc compound on Cr2O3/Al2O3 reduced the percentage of strong acid centers relative to the weak and medium acid centers as revealed by TPD of ammonia. The quantity of zinc compound taken is to give a zinc content of 2 - 12%, preferably in the range 3-7% by weight of co-precipitated Cr2O3/Al2O3 catalyst. In the fluorination of HCFC-133a to HFC-134a the mole ratio of HF: HCFC-133a should be in the range 4:1 to 15:1, preferably in the range 6:1 to 10:1. The degree of conversion and selectivity depends on the residence time, which determines the W/F value. It was found that the preferred W/F value is in the range 80-150, most preferably in the range 100 -150. Pressure was found to have an effect in the fluorination of HCFC-133a to HFC-134a. Under the same set of conditions of temperature, mole ratio ard W/F toe conversions were higher, at atmospheric pressure compared to the reaction under pressure. It was found advantageous to carry out the fluorination under pressure keeping in view the separation of different components in the product mixture. The required pressure was found to be in the range 70-210 psig. It was found that the fluorination of HCFC-133a can be carried out in the temperature range 275 ° -400 ° C and preferably in the range of 300 ° - 375 °C to obtain good conversions and selectivity to the desired product. The preparation of the precatalyst, its activation and use in the fluorination of HCFC-133a to give HFC-134a is illustrated in the examples given below: Examples Catalyst Preparations: All chemicals used are of commercial grade. Deminerafised water was used throughout Catalyst A: Cr2O3/Al2O3 341 g Cr (NO3)3 9H2O and 1440 g Al (NO3) 39H2O were dissolved in 8600 g water at room temperature. The solution is kept under stiming and 10% ammonia solution is added at a uniform rate of 1300gAi till the pH attains 7.5. The slurry obtained is charged into an autoclave and heated at 90 °C for 2h and cooled to 50 °C. The resulting slurry was filtered and washed with water. The cake obtained was divided into two portions in weight ratio 3:1. The major portion was dried for 2h at 70 °C and then at 120° C till constant weight. The dried cake was powdered to a particle size >125 mesh. The second portion was partially dried at 70° c and mixed with powder and extruded into 2.5 mm dia pellets using standard procedures. The extrudes were calcinated at 400 °C for 24 h in N2 atmosphere to get 262 g of co-precipitated catalyst designated as catalyst - A. The catalyst is x-ray amorphous. Catalyst B: ZnCb/C^Oa/AbOa 100 g of extrudes of catalyst A was suspended for 1 h in a solution obtained by dissolving 15.4 g ZnCb in 89.0 g water. The mixture was filtered by gravity and the solids were dried at 120 ° C to constant weight to give 110 g of the impregnated catalyst ZnCI2/Cr2O3/Al2O3. X-ray revealed the amorphous nature of the catalyst. The zinc content in the catalyst was found tobe4.3wt%. Catalyst C: ZnCl2/Cr2O3/Al2O3 157.35 g Cr (NO3) 39H2O and 532.7 g Al (NO3) 39H2O were dissolved in 25.75 Kg water A 1 7 % of ammonia solution was added at a uniform rate over a period of 18.25 h to the above solution, kept under stirring till the precipitation is complete and the final pH reaches 7.5. The slurry is filtered, washed with water and dried at 120 °C till constant weight to obtain 116.7 g of the catalyst 50 g of the above catalyst was powdered and mixed with a solution of 4.17 g of ZnCb in 55 g of water. The mixture is hanged on a rotavapor and water is removed by slow vaporisation to dryness The solid obtained is shaped into 3 mm tablets and calcined at 400 °C in N2 atmosphere for 24 h to obtain 40.5 g of catalyst C. X-ray showed the amorphous nature of the catalyst. Catalyst D: ZnCI2/Cr2O3/Al2O3 157.35 g Kr ((NO3) 39H2O and 532.7 g Al (NO3) 39H2O were dissolved in 12.89 kg water. Ammonia solution (5%) was added at a uniform rate over a period of 18.25 h to the above solution, kept under stirring till the precipitation is complete and the final pH attains 7.5. The slurry is filtered, washed with water and dried at 120 °C till constant weight to obtain 128.7 g of the base catalyst. The above catalyst 50 g was powdered and mixed with a solution of 4.5 g of ZnCI2 in 45 g of water. The subsequent workup was done as in the case of catalyst C to obtain 39.5 g of catalyst D. X-ray showed the amorphous nature of the catalyst. Catalyst E: ZnCI2/Cr2O3/Al2O3 A mixture of 157.35 g Cr (NO3)3.9H2O and 532.7 g Al (NO3)39H2O was dissolved in 6.45 Kg of water. The precipitation was done by adding 1.7-% ammonia solution at a constant rate over a period of 19.25 h to the above solution with constant stirring till the pH of the slurry attalns-7.5. The slurry was filtered, washed with water and dried at 120° C till constant weight to obtain 116.7 g of the catalyst 50 g of the above catalyst was powdered and mixed with a solution of 4.5 g of ZnCb in 45 g of water. The water was removed as described in the case of catalyst C. The dried catalyst was calcined at 400° C for 24 h and shaped into tablets of 3 mm size to obtain 38.6 g of the catalyst E. X-ray revealed amorphous nature. Catalyst F: ZnCI2/Cr2O3/Al2O3 157.35 g of Cr (NO3) 39H2O and 532.7 g of AI'(NO3) 39H2O were dissolved in 6.4 Kg of water The precipitation was done by the addition of 1.7% ammonia solution over a period of 12 min with constant stirring till the precipitation is completed and the final pH of slurry attained 7.5. The slurry was filtered, washed and dried at 120° C till constant weight to obtain 136.5 g of the base catalyst. 50 g of the above catalyst was powdered and mixed with a solution of 4.16 g ZnCI2 in 45 g of water. The water was removed as described in the case of catalyst C. The dried catalyst was calcined at 400° C for 24 h and shaped into tablets of the size 3 mm to obtain 40.5 g of the catalyst F. The X-ray showed amorphous nature. Catalyst G: ZnCl2/Cr2O3/Al2O3 A solution of Cr(NO3)3.9H2O (157.35 g) and AKNO3)3.9H2O (532.7 g) in 19.32 Kg. water was prepared to which 1.7% ammonia solution was added with constant stirring over a period of 18 h till the pH reaches 7.5. The slurry was filtered, washed and dried at 120° C till constant weight to obtain 149.4 g of the catalyst. 50 g of the above catalyst was powdered and mixed with a solution of 4.5 g of ZnCI2 in 45 g of water. The water was removed on rotavapor as described in the case of catalyst C and the solid was calcined at 400° C for 24 h and shaped into tablets of 3 mm size to obtain 36 g of the catalyst G The X-ray showed amorphous nature. Catalyst H: ZnCl2/Cr2O3/Al2O3 58.41 g of Cr(NO3)3.9H2O and 197.9 g of AI(NO3)3.9H2O were dissolved in 1600 ml of H2O A 3.75 % solution of ammonia was added at a uniform rate over a period of 7 h under stirring till the pH reaches 7.5. The slurry was filtered, washed with water and the wet cake obtained was transferred into an autoclave and mixed with 500 g of water. The mixture was stirred in a closed system for 6 h at 90° C. After completion of the thermal treatment the slurry was cooled to 35° C and filtered, washed with water and dried at 120°C till constant weight to obtain 59.5 g Cr2O3/Al2O3 catalyst: The above (25 g) catalyst was powdered and mixed with a solution of 1.0 g of zinc chloride in 17 g of water. The water was removed on rotavapor and dried to obtain 27 g of the catalyst The catalyst was shaped into tablets of 3 mm size and calcined at 400 °C for 24 h to get 18.67 g of catalyst H Catalyst I: Cr2O3/Al2O3 Following the procedure described for catalyst A the co-precipitated catalyst is prepared starting with 95 g of Cr(NO3)3.9H2O and 603 g AI(NO3)3.9H2O dissolved in 3.4 Kg. water and 10% ammonia solution to obtain 103 g of calcined catalyst-l. Catalyst J: ZnCh/Cr2O3/Al2O3 92 g of catalyst - A was suspended in a solution of 16.35 g zinc chloride in 100 g of water and the mixture was slowly vaporised to dryness on a rotevapor under vacuum. The product obtained was dried to constant weight at 120° C to obtain 110 g of catalyst - d. Catalyst K: ZnCl2/Cr2O3/Al2O3 92 g of catalyst A was suspended in a solution of 24.65 g of zinc chloride in 100 g of water and the mixture was slowly vaporised to dryness on rotavapor under vacuum. The product obtained was dried to constant weight at 120° C to obtain 119 g of catalyst - K. Bulk Chromia Catalyst: Cr2O3 The procedure described in Inorganic synthesis (1946) Vol. Il.pp 190-191, was followed to reduce CrO3 with ethanol to obtain CrOOH, which was filtered, washed with water, dried at 120° C till constant weight. The product was powdered, shaped into 3 mm tablets and calcinated at 400 °C for 24 h in nitrogen atmosphere. General method of fluorination: The experimental set up consists of separate feed ines for HF and HCFC-133a, vaporiser and a 90 cm long 1" id. inconel tubular reactor, pressure relief trap, alkali scrubber, drier, condenser and a receiver cooled in dry ice acetone mixture. A sample of the product stream is drawn periodically from a sampling valve between the drier and condenser. The temperatures in different zones are maintained by electrically heated block furnaces and PID controllers. The catalyst is loaded into the tubular reactor and pretreated with nitrogen at 400c C for 24 h. The temperature is then lowered to 150° C and a slow stream of HF is introduced along with nitrogen. After the initial exothermicity nitrogen is slowly withdrawn while raising the temperature of the catalyst bed to 375 ° C. The fluorination is continued until the moisture content in the exit HF is below 1%. The bed temperature of the catalyst is then brought and maintained at the reaction temperature and HCFC-133a is introduced into the system along with HF The feed quantity of HF and HCFC-133a were adjusted to give the desired molar ratios and W/F. The product stream is scrubbed with aq. KOH solution and then condensed in a trap cooled in dry .ice acetone. The composition of the product sfream is determined by GC after reaching steady state and is based on the peak areas. The fluorination experiments were carried out both at atmospheric pressure and under pressure as indicated in the examples given below: Example -1 Fluorination of HCFC-133a to HFC-134a at atmospheric pressure (Table Removed) Example - 2 Fluorination of HCFC-133a toHFC-134a under pressure (Table Removed) Example - 3 Fluorination of HCFC-133a to HFC-134a under pressure (Table Removed) Example - 4 Fluorination of HCFC-133a at atmospheric pressure (Table Removed) Example - 5 Fluorination of HCFC-133a at atmospheric pressure (Table Removed) The advantage of the co-precipitated chromia-alumina catalyst impregnated with zinc lies in the economisation of relatively costly chromium salt as compared to bulk chromia. The co-precipitated catalyst exhibits longer life and higher crushing strength as compared to an impregnated chromia-alumina catalyst used in fluorination reactions. The impregnation of the co-precipitated chromia-alumina catalyst with zinc reduces the relative percentage of strong acid sites which are responsible for the formation of side products like HFC-125, HFC-143a and HCFC-1122 thus increasing selectivity for HFC-134a. We Claim: 1. A process for the preparation of 1,1,1 ,2-tetrafluoroethane which comprises; contacting in the gas phase a feed consisting of 2-chioro- 1,1,1 -trifluoroethane and hydrogen fluoride, characterized in that with a co-precipitated chromia-alumina catalyst impregnated with a zinc compound at a temperature of 275 - 4000C optionally under pressure, and recovering 1.1,1 ,2-tetrafluoroethane in a conventional manner from the product stream. 2. A process as claimed in Claim-I where in the co-precipitated chromialumina catalyst contains chromium: aluminum in the atomic ratios of 1:1 to 1:14. 3. A process as claimed in Claims I and 2 where in the amount of zinc in the coprecipitated chromia-alumina catalyst is in the range of 2 12% weight. 4. A process as claimed in claims 1 to 3 wherein the mole ratio of anhydrous hydrogen fluoride and 2-chloro- 1,1,1 -trifluoroethane are in the range of 4:1 to 15:1. 5. A process as claimed in Claims 1 to 4 wherein the ratio of catalyst to feed ranges from 80 -150 gram-hour/mole. 6. A process as claimed in Claims I to 5 wherein the contacting is carried out in the pressure range of 1 to 15 kg. 7. A process for the preparation of 1,1,1 ,2-tetrafluoroethane substantially as here in described with reference to examples.

Documents:

62-del-1999-abstract.pdf

62-del-1999-claims.pdf

62-del-1999-complete specification (granted).pdf

62-del-1999-correspondence-others.pdf

62-del-1999-correspondence-po.pdf

62-del-1999-description (complete).pdf

62-del-1999-form-1.pdf

62-del-1999-form-19.pdf

62-del-1999-form-2.pdf