A PROCESS FOR PREPARING 1,1,1-TRIFLUOROETHANE

Abstract: A process for producing 1,1,1-trifluoroethane by reacting 1,1,1-trichloroethane with hydrogen fluoride in the presence of a fluorination catalyst under conditions sufficient to produce 1,1,1-trifluoroethane but in the absence of a solvent. The 1,1,1-trifluoroethane is useful as a refrigerant, in air conditioners, heat pumps, and as a propellant or blowing agent.

Description: A PROCESS FOR PREPARING 1.1.1-TRIFLUOROETHANE BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a process for preparing 1 , 1 , 1-trifluoroethane in high yield and selectivity by the catalytic hydrofluorination of 1,1,1-trichloroethane (HCC-140a) in a liquid phase reaction. The hydrofluorination is preferably conducted with anhydrous hydrofluoric acid in the presence of an antimony fluorination catalyst and in the absence of a solvent. Description of the Prior Art 1,1,1-Trifluoroethane (hereinafter referred to as HFC- 143a) is useful as a refriger¬ ant, in air conditioners, heat pumps, and as a propellant or blowing agent. European patent application 0 448 997 describes the use of 1,1,1-trifluoroethane in a low temperature refrigerator. U.S. patent 4,091,043 shows that 1 ,1,1 trifluoroet- hane can be obtained by fluorinating 1 ,1 ,1-trichloroethane with hydrofluoric acid in the presence of a fluorination catalyst and a halogenated hydrocarbon solvent which meets certain criteria. The process of U.S. patent 4,091,043 is not satisfactory for the production of HFC- 143a since it requires the subsequent separation of the solvent from the product and other by-products are also produced. U.S. patents 4,078,007 and 4,138,355 show the fluorination of certain hydrohalocarbons with liquid hydrogen fluoride in the presence of a catalyst which is a mixture of antimony pentahalide and antimony trihalide. However the processes of these latter patents can take as long as forty five hours to run. U.S. patent 4,885,416 shows the fluorination of haloalkanes with antimony chlorofluoride, however, 1,1,1- trifluoroethane is only produced as a minor by-product constituent whose production is to be avoided. /05156 PCMJS95/10410 SUMMARY OF THE INVENTION The invention provides a process for producing 1,1,1-trifluoroethane which comprises reacting 1 , 1 , 1-trichloroethane with hydrogen fluoride in the presence of a fluorination catalyst under conditions sufficient to produce 1,1,1-trifluoroethane but in the absence of a solvent. Thereafter, the 1,1 , 1-trifluoroethane is then recovered. Other features and advantages of the invention will become apparent from a consideration of the detailed description of preferred embodiment. BRTFF DESCRIPTION OF THE DRAWING Figure 1 shows a schematic representation of one version of the process of the invention. Figure 2 shows a schematic representation of another embodiment of the process of the invention. TlFTAπ FD DESCRIPTION OF THE INVENTION The invention provides a process for producing 1,1,1-trifluoroethane which comprises reacting 1 ,1,1-trichloroethane with hydrogen fluoride in the presence of a fluorination catalyst under conditions sufficient to produce 1,1,1-trifluoroethane but in the absence of a solvent. 1,1,1-trichloroethane is commercially available from Vulcan Chemicals of Birmingham, Alabama. Alternatively it may be synthesized by methods well known in the art. Examples of fluorination catalysts suitable for the process of the invention include halides, oxides or oxyhalides of a Group ma, IVa, IVb, Va, Vb, Via, VIb or vm elements. Examples of these include SbCl5, TiCl SnCl4 and BF3. Preferably the fluorination catalyst is an antimony containing compound, more preferably a pentavalent antimony compound. The pentavalent antimony compounds can be (I) a halide; (II) a mixed halide of the formula SbCl x F v where x can range from 1 to 5 and y can range from 0 to 4 provided that x+y=5; or (HI) mixtures of halide catalysts. Examples of catalysts of group (I) include antimony pentachloride and antimony pentafluoride. Examples of catalysts of group (II) include SbCl3F2 and SbCl2F3. Examples of catalysts of group (HE) include a mixture of antimony pentachloride and antimony pentafluoride. The most preferred fluorination catalyst is antimony pentachloride because of its low cost and availability. The fluorination catalysts used in the invention preferably have a purity of at least about 97%. Although the amount of fluorination catalyst used may vary widely, the fluorination catalyst is preferably present in an amount of from about 5% to about 80% by weight of the reaction mass, more preferably from about 15% to about 50%. The reaction mass is defined as the mixture present in the reactor at any given time including reactants, reaction products and intermediates. These include HC-140a, HFC-143a, HF, HC1, catalyst, HCFC-142a and any other intermediates and by- products present. In the preferred embodiment, chlorine is metered into the reaction mixture in order to keep the fluorination catalyst active, i.e. in the pentavalent state. Most preferably chlorine is present in the form of chlorine gas. The chlorine component is preferably added in an amount of from about .005 pounds to about .025 pounds or more preferably from about .008 pounds to about .015 per pound of HCC-140a feed. Any water in the HF will react with and deactivate the fluorination catalyst. Therefore, substantially anhydrous HF is preferred. By "substantially anhydrous" we mean that the HF contains less than about 0.05% water and preferably contains less than about 0.02% water. However, one of ordinary skill in the art will appreciate that the presence of water in the catalyst can be compensated for by increasing the amount of catalyst used. HF suitable for use in the reaction may be purchased from AlliedSignal Inc. of Morristown, New Jersey. The hydrogen fluoride can be introduced in the liquid or gaseous state, however, gaseous HF is much preferred since it provides reaction heat, agitation and better dispersion of the HF reactant. Based on reaction stoichiometry, the required mole ratio of HF to 1,1,1- trichloroethane is from about 2.5: 1 to about 4:1, or preferably from about 3:1 to about 3.6:1 and most preferably from about 3: 1 to about 3.1:1. One of ordinary skill in the art can readily optimize the conditions of the reaction without undue experimentation to get the claimed results but generally the hydrogen fluoride is allowed to flow into the reactor to contact the fluorination catalyst for from about 40 to about 400 seconds, more preferably from about 60 to about 200 seconds. Temperature and pressure are not critical. The reaction is preferably conducted at a temperature of from about 15 °C to about 70 °C, or more preferably from about 20 °C to about 50 °C while the pressure is preferably from about 15 psig to about 300 psig, or more preferably from about 100 psig to about 150 psig. The reaction may be conducted in any reaction vessel but it should be constructed from materials which are resistant to the corrosive effects of hydrogen fluoride such as Hastelloy, Inconel and Monel. Fluorination of 1,1,1-trichloroethane is preferably carried out by feeding gaseous anhydrous hydrofluoric acid and liquid 1 ,1 , 1-trichloroethane together into a reactor with the antimony pentachloride catalyst. The gas emitted from the reactor then is directed into a suitable separator which is preferably a distillation column provided with a condenser. Selection of a suitable cooling temperature for the condenser can easily be determined by those skilled in the art. The resulting product vapors are then subjected to a conventional scrubber to remove HC1 and excess HF. The product vapors pass through coolers, dryers and then are liquified in product cylinders chilled in a dry ice bath. The under fluorinated by-products can then be recycled so that they react with fresh hydrogen fluoride. The process of the invention can be carried out in a batch, semi-continuous or fully continuous manner. The process of the invention does not require a mechanical agitator thus simplifying the reaction apparatus and procedures. The conversion of 1 ,1 , 1-trichloroethane to 1,1,1-trifluoroethane typically ranges from about 95% to about 99.9% . The conversion of hydrogen fluoride to 1,1,1-trifluoroethane typically ranges from about 93 % to about 98 % . It will be readily appreciated that the respective amounts of the components of the product mixture will vary depending upon reactive conditions and catalysts employed and may be varied by the skilled artisan. Figure 1 provides a schematic representation of one preferred process flow of the invention. Liquid antimony pentachloride catalyst, initially charged along stream 2, and liquid 1,1 ,1-trichloroethane feed stream 4 are mixed to form a reactor feed stream 6 which is fed into a reactor 12. Chlorine liquid feed stream 8 is metered into the reactor to keep the catalyst in the pentavalent state. The reaction proceeds as gaseous hydrofluoric acid is metered by feed stream 10 into reactor 12. The effluent from the reactor 12 is the product mixture stream 14 which enters a catalyst stripper which is a separation column 16 having a partial condenser. Scrubber 18 separates HC1 and excess HF via stream 20 from the product stream 22. The product stream 22 is then chilled, dried and liquified. Figure 2 presents a more detailed version of the process. HCC-140a and anhydrous hydrofluoric acid are continuously fed to a steam jacketed reactor containing liquid phase antimony pentachloride catalyst. Chlorine is fed periodically at low rates to maintain a trivalent antimony content of 5% or less. The HCC-140a is directed from a pressurized tank car through a surge pot and then pumped through a steam heated vaporizer into the bottom of the reactor. Fresh anhydrous HF is provided from elevated storage tanks. Liquid HF flows through a surge pot and is then pumped to a steam heated vaporizer into the bottom of the reactor. Recycled high boiling organics from the distillation system are returned to the reactor for further reaction. In another embodiment recycled high boiling organics from the distillation system are pumped into the bottom of the catalyst stripper and subsequently returned to the reactor for further reaction. The vapors from the reactor enter the bottom of the catalyst stripper column. These gases contain catalyst, HF, HC1, intermediate product l-chloro-1,1- difluoroethane (HCFC-142b) and product HFC- 143a. The catalyst and most of the high boiling HF and HCFC-142b are stripped out in the catalyst stripper and flow down the column into the reactor. Internal reflux for the catalyst stripper is provided by an integral brine cooled condenser and accumulator. From the catalyst stripper overhead, crude gas passes through a back pressure control system into the HCl absorption system. HCl gas is absorbed in a falling film absorption system to produce a concentrated waste acid by-product. Absorbed acid flows into a pump tank where a pump recirculates acid to the inlet of the falling film absorber for concentration of the acid. Excess acid flows from the circulating line to a bulk acid storage tank. From the absorber, product gas enters a tails tower. Fresh water is introduced at the top of the tails tower and flows counter-current to the product gas stream. The fresh water absorbs traces of HCl gas remaining in the product gas. Liquid exits the tails tower and flows to the falling film absorber inlet. From the tails tower, product gas passes through two caustic scrubbing towers in series to remove chlorine and any acid carryover from the HCl absorption system. Both caustic scrubbers have a circulating stream of 2 to 20% NaOH solution. The product gas leaving the demister section of the second caustic tower flows through a chilled water cooler to an alumina silicate molecular sieve dryer which removes the water vapor present. From the dryer, product gas passes to the low pressure compressor suction tank. Product gas from the suction tank is compressed. The compressed gas passes through a total condenser where condensed liquid flows to the crude holding tank and any low boilers formed in the reactor along with non- condensables are purged through a scavenger condenser. Under normal operating conditions very little non-condensable purge is required. Crude organic liquid is pumped from the crude holding tank to the middle of the product distillation column. Reflux is provided by an external condenser, reflux tank and reflux pump. Product is pumped from the reflux tank into a tank having a dedicated molecular sieve dryer. Crude organics, stripped of low boilers are pumped from the product distillation column and recycled back into the reactor for further fluorination into product. The process of the invention provides a method for obtaining HFC- 143a as the major product at high productivity, normally greater than 10 lbs/hr/ft*-*. As used herein, the term "major product" means the single product that is produced by the process of the invention in the greatest amount, preferably in an amount of at least about 95 % , preferably at least about 98%, and most preferably at least about 99% based on the total weight of halocarbons produced as determined by gas chromatography. The following non-limiting examples will serve to illustrate the invention. EXAMPLE 1 Liquid antimony pentachloride catalyst was separately prepared by chlorinating antimony trichloride at a temperature of approximately 80°C in a 15 inch diameter Inconel reactor of 60 gallon capacity. Liquid antimony pentachloride (SbCl5) catalyst and 1,1,1-trichloroethane (HCC-140a) were charged into the reactor to attain the desired catalyst concentration and reactor liquid level. Chlorine gas was metered into the reactor to keep the catalyst in the pentavalent state. The reaction proceeded readily as liquid hydrofluoric acid and 1,1,1-trichloroethane were metered into the reactor. Tempered water was admitted into the reactor jacket to maintain reactor temperature as the reactor liquid begins to cool from vaporization of low boiling product. Reaction product vapors entered the bottom of a 6 inch diameter, 12 foot height Inconel separation column packed with 5/8 inch rings. A 35 square foot heat exchanger was positioned overhead to the separations column functions as a partial condenser. Reactor pressure was controlled by a pressure control valve after the partial condenser. Reaction product vapors passed through a pressure control valve and were scrubbed with water in a 6 inch diameter packed column to remove HCl and excess HF. Chlorine in the product vapor was removed in a 6 inch diameter packed bed by circulating 25 % NaOH solution. Acid free product vapors were chilled to 35°F to partially condense water vapor. The product vapors passed through alumina dryers and then are liquified in product cylinders chilled in a dry ice bath. Anhydrous HF and 1,1,1-trichloroethane were metered in at the following rates and reactor conditions to produce the foUowing results. TABLE 1 1 Run time Press. Temp range Reactor Charge Feed Rates Product Composition wt% SbCl 5 HCC-140a HCC-140a HF 143a 142b 141b 140a Others hrs. psig °F lbs lbs lb/hr lb/hr 15 55-70 262 none 11.3 8.6 96.2 1.5 0.3 0.3 1.7 • This example shows the high level of production of HFC- 143a by the process of this invention. HCC-140a is 1,1,1-trichloroethane, HCFC-143a is 1-1-1- trifluoroethane. HCFC-142b is l-chloro-l,l-difluoroethane. HCFC-141b is 1,1- dichloro- 1 -fluoroethane. EXAMPLE 2 As a comparison, the procedure of Examples 1 was repeated except catalyst was not used. The foUowing results were noticed. TABLE 2 The effect of performing the reaction without catalyst is that very high temperatures and pressure are required to attain any conversion to HFC- 143a as shown Table 2. EXAMPLE 3 Liquid antimony pentachloride catalyst was charged to an Inconel reactor. Liquid 1,1,1-trichloroethane (HCC-140a) was charged to the reactor to attain the desired catalyst concentration. The reaction proceeded readUy at ambient temperature as liquid 1 , 1 , 1-trichloroethane and approximately stoichiometric amounts of anhydrous HF were fed into the reactor. Anhydrous HF was vaporized into the reactor after liquid metering to provide some reactor agitation and to provide heat to vaporize product HFC- 143a and by-product HCl from the reactor into the catalyst stripper. Tempered water or low pressure steam was admitted into the reactor jacket to maintain reactor temperature as the reactor liquid begins to cool from vaporization of low boiling products. Reaction product vapors entered the bottom of a packed or multi-tray distillation column operated to separate and return under fluorinated ethanes, HF and any catalyst transported from the reactor. Reactor pressure was controUed at a nominal 100 psig to provide sufficient pressure to condense and reflux HFC- 143a at the top of the catalyst stripper. The reactor was operated from 15-300 psig. During the reaction process chlorine was added at the rate of 0.01 pounds of chlorine per pound of HC-140a feed to the reactor to maintain the catalyst in a pentavalent state. Reaction product vapors passed from the catalyst stripper through a pressure control valve and were scrubbed in a co-current flow aqueous acid scrubber. The scrubbed gases then passed through a series of two packed bed circulating 10% NaOH caustic scrubbers to remove residual acidity. The neutralized crude gas was dried in alumina silicate molecular sieve drying beds then compressed to 150 psig and distilled to produce HFC- 143a overhead and recycle of underfluorinated ethanes back to the reactor from the bottom of the distillation column. The above process produced the foUowing results: TABLE 3 This Table shows various reaction conditions to obtain good HFC-143a productivity.

Claims: What is claimed is: 1. A process for producing 1,1,1-trifluoroethane which comprises reacting 1,1,1- trichloroethane with hydrogen fluoride in the presence of a fluorination catalyst under conditions sufficient to produce 1 , 1 , 1-trifluoroethane but in the absence of a solvent. 2. The process of claim 1 wherein the fluorination catalyst is a pentavalent antimony halide, a mixed pentavalent antimony halide or a mixture of pentavalent antimony halides. 3. The process of claim 2 wherein the fluorination catalyst is antimony pentachloride. 4. The process of claim 1 wherein the reaction is further conducted in the presence of chlorine in an amount sufficient to maintain the activity of the fluorination catalyst. 5. The process of claim 1 wherein the total yield of 1,1 ,1-trifluoroethane is at least about 95 % based on the total weight of halocarbons produced. 6. The process of claim 1 wherein the fluorination catalyst is antimony pentachloride, the reaction is conducted at a temperature of from about 15 °C to about 70 °C, at a pressure of from about 15 psig to about 300 psig, the mole ratio feed of hydrogen fluoride to 1 , 1 , 1-trichloroethane is from about 3: 1 to about 3.6:1, the amount of catalyst in the reaction mixture ranges from about 5 weight percent to about 80 weight percent based on the weight of 1 , 1 , 1- trichloroethane, 1,1,1-trifluoroethane, hydrogen fluoride, intermediates and by- products present in the reaction; wherein the reaction is conducted in the presence of chlorine gas in an amount sufficient to maintain the activity of the fluorination catalyst and wherein the total yield of 1,1,1-trifluoroethane ranges from about 95 weight percent or more based on the total weight of halocarbons produced. 7. The process of claim 6 wherein said 1 , 1 , 1-trifluoroethane is thereafter recovered.

Inventors: SWAIN CHARLES F, SWAIN, CHARLES, F.
Applicants: ALLIED SIGNAL INC, ALLIEDSIGNAL INC.
Application year: 1995
Main classification: C07C17
IPC codes: C07C17