Process for preparing chlorofluorocarbons via an in situ generated activated aluminum trihalide catalyst

Abstract: A process of isomerizing a chlorofluorocarbon of the formula: CClFYCClFX wherein X and Y are independently selected from chlorine and fluorine provided that X is not -Cl when Y is -F to the compound of the formula: CCl₂YCF₂X The process comprises contacting the chloroflurocarbon with an activated aluminum trihalide catalyst. The catalyst is prepared by contacting the chlorofluorocarbon with anhydrous aluminum trichloride in the presence of a metal. The metal is selected from the group consisting of stainless steel, chromium, manganese, molybdenum, tungsten and combinations thereof.

Description: This invention relates to activated aluminum trihalide catalysts and the process of isomerizing chlorofluorocarbons in the presence of such in situ produced catalysts. The use of the activated catalyst in the isomerization process renders a product mixture having negligible non-isomerized material. Chlorofluorocarbons have been widely used in industry as refrigerants and aerosols. When released into the atmosphere, the accumulation of such chlorofluorocarbons can eventually cause depletion of the ozone layer. Many countries have barred the use of CCl₂F₂ and CCl₃F due to their ability to reach the stratosphere. The industry has focused on the use of perfluorocarbons, tetrafluoroethanes and chlorofluorohydrocarbons in recent years since these compounds are believed not to significantly contribute to ozone depletion. Of particular interest to the refrigerant industry is 1,1,1, 2-tetrafluoroethane. Such compounds can be derived from the intermediates 1,1-difluorotetrachloroethane, 1,1,1-trifluorotrichloroethane and 1,2,2,2-tetrafluorodichloroethane. These intermediates are, in turn, the isomers of the more readily obtainable chlorofluoroethanes 1,2-difluoro-1,1,2,2-tetrachloroethane, 1,1,2-trifluoro-1,2,2-trichloroethane and 1,1,2,2-tetrafluoro-1,2,-dichloroethane, respectively. The isomerization of such chlorofluoroethanes by treatment with aluminum trihalide is well documented in the art. For example, Okuhara in J. Org. Chem ., Vol.43, No.14, pages 2745-2749 (1978) reports the use of aluminum trihalide and an inert solvent for isomerizing 1,1,2-trichloro-1,2,2-trifluoroethane. Unfortunately, the prior art methods render a high amount of starting material in the final reaction mixture. This is evidenced in, for example, German Patent No. 1,668,346 which discloses an isomerization method for the production of 1,1,1-trifluorotrichloroethane. This process involves the preactivation of an aluminum chloride catalyst with 1,1,2-trifluorotrichloroethane at 30° to 60°C, subsequent cooling and then addition of new starting material. The amount of starting material in the final reaction mixture is from about 2% to 10%. As the boiling point of starting material and the desired isomerized product are roughly the same, conventional distillation techniques can not be employed to separate the compounds. US-A-3398202 discloses a process for increasing the proportion of symmetric dichlorotetrafluoroethane by passing a mixture of symmetric and asymmetric dichlorotetrafluoroethane over a catalyst maintained between 50 and 500°C. Alternative methods for obtaining the isomerized product with negligible amounts of non-isomerized starting material are therefore needed. We have now developed a process for isomerizing the chlorofluorocarbons 1,2-difluoro-1,1,2,2-tetrachloroethane, 1,1,2-trifluoro-1,2,2-trichloroethane and 1,1,2,2-tetrafluoro-1,2-dichloroethane in the presence of an activated aluminum trichloride catalyst which gives a reaction product in which the amount of non-isomerized chlorofluorocarbon starting material is generally negligible. According to a first aspect of the present invention, there is provided a process for isomerizing chlorofluorocarbons, which comprises: (i) contacting a chlorofluorocarbon of the formula: CClFYCClFX (I) wherein X and Y are independently selected from -Cl and -F, provided that X is not -Cl when Y is -F, with anhydrous aluminum trichloride, the weight ratio of chlorofluorocarbon (I) to aluminum trichloride being from 16:1 to 80:1, in the presence of a metal for a time and at a temperature sufficient for the chlorofluorocarbon (I) to isomerize to a compound of the formula CCl₂YCF₂X (II); (ii) separating at least the majority of the organic phase from the activated catalyst; and (iii) isolating the chlorofluorocarbon of formula (II) from the separated organic phase. The chlorofluorocarbon of formula I is preferably CCl₂FCClF₂ or CClF₂CClF₂. The contacting of the chlorofluorocarbon (I) with the anhydrous aluminum trichloride and metal leads to the generation of an activated aluminum trihalide and the high yields of isomerized product obtained by the process are attributed to this in situ generated activated catalyst. The weight ratio of the chlorofluorocarbon (I) to aluminum trichloride is preferably 30:1. The metal used in the process may be either an elemental metal or a metal powder. The metal is preferably stainless steel, chromium, manganese, molybdenum, or tungsten or a combination of two or more thereof. When a metal powder is used, its particle size is preferably from -200 to -300. A combination of metals having a weight ratio of from 1:3 to 3:1 is preferably employed; the combination preferably comprises chromium and manganese. The aluminum trichloride : metal weight ratio is preferably from 200 : 1 to 2000 : 1 and most preferably about 600 : 1. Where the reaction is conducted in a stainless steel, instead of a glass, vessel the requisite metal may be leached into the reaction vessel. In such instances, it may be desired to add an additional metal in order to ensure the desired AlCl₃ : metal weight ratio. The introduction of the chlorofluorocarbon of formula (I), anhydrous aluminum trichloride and metal to the reaction vessel generates in situ an aluminum trihalide catalyst to which the high yields of the desired isomer in the product mixture is attributed. Experimental data on the conversion of 1, 1, 2, 2 -tetrafluorodichloroethane to 1,2,2,2-tetrafluorodichloroethane indicates halogen exchange between the chlorofluorocarbon and AlCl₃. The presence of CF₃CCl₃ and the absence of the disproportionation product CF₃CF₂Cl in the product mixture supports the following reaction: 3CClF₂CClF₂ + AlCl₃ → 3CCl₃CF₃ + AlF₃ The isomerization process of this invention is conducted at a temperature above the melting point of the desired isomerized product. The reaction is generally allowed to proceed until the amount of reactant of formula (I) in the reaction mixture is less than 45,000 ppm. Where the 1,2-difluoro and 1,1,2-trifluoro intermediates are the compounds being isomerized, the isomerization may generally be permitted to proceed until less than 10,000 ppm of the non-isomerized compound constitutes the product mixture. Following isomerization, the reaction vessel is cooled to a temperature slightly above the melting point of the desired isomerized product. The activated aluminum trihalide is allowed to settle to the bottom of the reaction vessel. Upon settling, the organic media is decanted allowing for recovery of the catalyst. A thin layer of organic media, generally between about 10 to about 20 weight percent, is permitted to remain with the catalyst. This thin layer of organic media and catalyst, hereinafter collectively referred to as the "catalytic heel", prevents water vapor from contaminating the catalyst and further facilitates the removal of spent catalyst from the reactor as a fine slurry. By not siphoning off all of the available crude product produced in a given batch, loss of finely divided catalyst is kept to a minimum. Normally 10 to 20 weight percent of the product mixture is allowed to remain as a slurry with the catalyst to form the catalytic heel. When the difluoro and trifluoro intermediates are isomerized, the reaction temperature ranges generally between about 36° to about 52°C. When the intermediate is the difluoro intermediate, i.e. X and Y of formula (I) are both -Cl, the reaction temperature is preferably between about 44° and 50°C. When the intermediate is the trifluoro intermediate, i.e., X and Y of formula (I) are chlorine and fluorine, respectively, the reaction temperature is preferably from about 45°C to about 51°C. The difluoro and trifluoro intermediates preferably are generally allowed to isomerize until the amount of non-isomerized reactant of formula (I) is minimal, usually less than about 10,000 ppm. The reaction vessel is cooled to about 2° to about 5°C above its melting point, wherein the catalyst derivative settles to the bottom of the reactive vessel. Cooling of the reaction vessel is preferably from about 17° to about 30°C when the trifluoro intermediate is isomerized and about 42° to about 44°C when the difluoro intermediate is isomerized. When the tetrafluoro intermediate (wherein X and Y of formula (I) are both -F) is isomerized, the reaction temperature is generally between about 120° and about 130°C, i.e., about 15° to 25°C below the critical temperature of the reactant of formula (I). The organic media is decanted after the reaction vessel is cooled to a temperature between about -20°C and about -10°C. The isomerization normally proceeds at atmospheric pressure. However, since the autocatalytic reaction between anhydrous aluminum trihalide and certain chlorofluorocarbons, such as CCl₂FCClF₂, can be violent, especially at high temperatures under adiabatic conditions, the activation process may be performed in a suitable high pressure vessel. Separation of the trace amount of (non-isomeric) by-products from the organic phase then proceeds by techniques well known to those skilled in the art, such as distillation. The non-isomerized reactant of formula (I) after being separated from the organic phase may be re-introduced to fresh anhydrous aluminum trichloride and metal and isomerization repeated under the conditions recited herein. The catalytic heel comprising the in situ generated activated aluminum trihalide catalyst may further be used to isomerize a fresh sample of 1,2-difluoro-, 1,1,2,2-tetrachloroethane or 1,1,2-trifluoro-1,2,2-trichloroethane. The catalytic heel generated in a reaction vessel containing either the di-, tri- or tetrafluorochlorocarbon of formula (I) may serve as the activated aluminum trihalide catalyst in the isomerization of this (second) fresh sample of di- and trifluorochlorocarbon. It is not necessary that the activated aluminum trihalide catalyst employed in the second isomerization reaction be generated in a product mixture comprising the chlorofluorocarbon sought to be isomerized. For example, if the desired isomerized product is that obtained from the process: wherein X is either -Cl or -F, the activated aluminum trihalide catalyst may be generated from either the di-, tri-, or tetrafluorointermediate. In other words, a catalytic heel obtained from the isomerization of the 1,2-diiluoro or 1,1,2,2-tetrafluoro, as well as that obtained from the 1,1,2 trifluoro, intermediate may be used as the activated aluminum trihalide catalyst for the isomerization of the 1,1,2-trifluoro intermediate. similarly, the catalytic heel obtained from the isomerization of the 1,1,2-trifluoro or 1,1,2,2-tetrafluoro, as well as the 1,2-difluoro, intermediate can be used as the activated aluminum trihalide catalyst for the isomerization or a 1,2,-difluoro intermediate. Such isomerizations employing catalytic heel as activated aluminum trihalide catalyst are generally terminated when the amount of chlorofluorocarbon of formula (IV) in the reaction vessel is less than about 15,000 ppm. Preferably, the catalyst is terminated when the non-isomerized product, such as that of formula (IV) wherein X is -F, is less than 400 ppm. Such conversion normally requires from about 2 hours to about 24 hours, most often 8 hours. The activated trihalide catalyst may be reused until the catalyst no longer effectively renders an isomerized product mixture containing less than 450 ppm non-isomerized chlorofluorocarbon. The process is repeated by adding approximately an equivalent weight amount of fresh chlorofluorocarbon (to that weight amount of product mixture removed) to the catalytic heel. Following the removal of the resulting catalytic heel from each isomerization, the organic phase of each isomerization can be pooled together. The separation of desired isomers, by such conventional techniques as distillation, from the organic phases can then be collectively performed. In general, the weight ratio of chlorofluorocarbon to activated aluminum trihalide catalyst is greater than 16:1. Since the life span of the catalyst decreases as this ratio increases, commercial practicality dictates this ratio to be probably not greater than 80:1. The activated aluminum trihalide derivative may further be used to isomerize that portion of the non-isomerized reactant of formula (I) separated from the desired isomer of the product mixture. Example 1 To a 5.0 l glass flask equipped with motor stirrer, thermometer, heating mantle, and reflux condenser with drying tube, was charged 120 g of anhydrous aluminum chloride powder and 6.0 g of PROPACK (a square 0.41 cm (0.16 inch) 316 stainless steel protruded packing). To the flask was added 3,900 g of CCl₂FCClF₂ and vigorous agitation was applied. The mixture was heated to 49°-50°C (reflux) for 8 hours. Gas chromatography analysis indicated 3,846 ppm CCl₂FCClF₂. The mixture was allowed to stand for 2 hours to allow settling of the catalyst. Crude isomerized CCl₃CF₃ product was then carefully siphoned off (2,750 g) leaving the active catalyst heel in the bottom of the flask (with a liquid level up to the agitator blades). Example 2 The heating mantle was removed from the 5.0 l flask (example 1), and an adjustable ice bath and addition funnel were added. Over a period of 40 min., 2,750 g of fresh CCl₂FCClF₂ was added to the agitated mixture. Reaction temperature was maintained at 22° to 28°C. Upon completion of the addition, the mixture was stirred at 20°C for 3.5 hours after which gas chromatography analysis indicated only 366 ppm CCl₂PCClP₂ remaining. Agitation was stopped for 2 hours to allow settling of the catalyst bed. The CCl₃CF₃ product was siphoned off (2,750 g) and the process repeated (see Table 1). Example 3 A 5.0 l flask fitted with motor stirrer, thermometer, heating mantle, and reflux condenser with drying tube, was charged with 96.1 g of anhydrous aluminum trichloride powder, 0.1198 g chromium powder (-200 mesh), 0.0409 g of manganese powder (-325 mesh), and 3,044.5 g of CCl₂FCClF₂. With vigorous agitation, the flask was brought to reflux for 6 hours (48°C). The mixture was then allowed to agitate for 15 hours at 23°-26°C. At this time the amount of non-isomerized CCl₂FCClF₂ had been reduced to 18,400 ppm (IR analysis). The mixture was then brought back to reflux for 7 hours, and then cooled to 27°C. After allowing the catalyst to stand for 16 hours, the amount of non-isomerized CCl₂FCClF₂ had dropped to 4,551 ppm (g.c. analysis). The crude product (2127 g) was carefully decanted to avoid disturbing the active catalyst heel. Example 4 The 5.0 l flask (example 3) was fitted with an adjustable ice bath and addition funnel. To the flask was added 2,505 g of fresh CCl₂FCClF₂ and agitation begun. Temperature was maintained between 20° and 32°C. After 7 hours reaction, crude product was found to contain 367 ppm CCl₂FCClF₂. The catalyst was permitted to settle for 2 hours and 2,100 g of crude CCl₃CF₃ product carefully decanted. The process was repeated for a total of 19 cycles (see Table 2). Example 5 To a 2.0 l Parr bomb equipped with glass liner and tempered water heating coil was charged 1,000 g of CCl₂FCClF₂, 33.3 g of anhydrous aluminum trichloride, 0.04 g of powdered chromium, and 0.01 g of powdered manganese. With vigorous agitation, the mixture was heated from 20° to 50°C in 42 minutes and pressure was slowly increased. An exotherm then developed which elevated the temperature to 90°C within 10 minutes and increased pressure to 0.31 MPa gauge (45 psig). The mixture was allowed to cool and catalyst allowed to settle. The catalytic heel was collected from the mixture. Example 6 An insulated beaker with stirrer was charged with 43.5 g of previously prepared catalyst heel (example 5). To the beaker was added 20.2 g of CCl₂FCClF₂ and agitation begun. Within 14 minutes, the temperature was allowed to climb from 19°C until it reached a maximum of 35°C. After 22 minutes stirring, the mixture was sampled and found to contain 92.25% converted CCl₃CF₃ (g.c. analysis). Example 7 A 5.0 l flask fitted with a motor stirrer, heating mantle, thermometer, and reflux condenser with drying tube was charged with 120.5 g of anhydrous aluminum trichloride, 0.061 g of powdered manganese (-325 mesh), and 4,008 g of CCl₂FCClF₂. With vigorous agitation, the mixture was heated to reflux for 5 hours (49°C). Heating was then discontinued and the mixture stirred an additional 13 hours at 28° to 22°C. Gas chromatography analysis indicated approximately 660 ppm of CCl₂FCClF₂ in the product mixture. After allowing the catalyst to settle for 2 hours, the crude isomerized product was siphoned off (3100 g), leaving the catalyst in the bottom of the flask. Example 8 The 5.0 l flask (example 7) was fitted with an adjustable ice bath and addition funnel. Within 20 minutes, 3100 g of fresh CCl₂FCClF₂ was charged (vigorous agitation). After 2.5 hours stirring at 18° to 34°C, the amount of CCl₂FCClF₂ in the reaction mixture was approximately 446 ppm. After standing an additional 15 hours, the concentration was 410 ppm. The crude product was then siphoned off (3100 g) and the process repeated with the resulting catalytic heel and fresh CCl₂FCClF₂ (See Table 3). Example 9 A 2.0 l 4-neck flask fitted with motor stirrer, thermometer, and reflux condenser with drying tube was charged with 23.5 g of the resulting catalyst heel prepared as in Example 3. To the flask was added 256.5 g of CCl₂FCCl₂F and agitation begun. During the first 1.5 hours of stirring the temperature increased from 28° to 34°C. Since the solid product was starting to precipitate, the flask temperature was adjusted to 42°C and the mixture was then stirred for 2.5 hours. The IR spectrum of the reaction mixture was consistent with nearly total conversion to CCl₃CClF₂. Example 10 A pyrex glass liner from a 2.0 l Parr bomb reactor was charged with 50.0 g of anhydrous aluminum trichloride, 0.065 g chromium and 0.023 g of manganese powder. The pyrex liner was chilled on dry ice and quickly charged with 900 g. of pure CClF₂CClF₂. The liner was inserted into the reactor which was immediately sealed. With vigorous agitation, the reactor temperature was brought to approximately 120°C (1.91 MPa gauge [277 psig]) within 30 minutes. For an additional hour, the temperature was maintained between 120 and 130°C (2.09 MPa gauge [to 303 psig]). The mixture vas gradually cooled to -10°C and agitation shut off. The reactor was disassembled to allow direct sampling of the liquid phase. The catalytic heel was separated from the product mixture. Gas chromatographic analysis indicated the product mixture had a composition of 0.719% CF₃CF₂Cl, 72.67% C₂Cl₂F₄, , 26-6% CCl₃CF₃ (including a trace of CCl₂FCClF₂), 0,006% CCl₃CClF₂ and 0.006% CCl₃CCl₂F. A gas chromatographic isomer resolution technique determined the ratio of CCl₂FCF₃/CClF₂CClF₂ to be 9.64:1. Example 11 The pyrex liner of the 2.0 l Parr bomb was charged with 100.0 g of anhydrous AlCl₃, 0.130 g of chromium, and 0.050 g. of manganese powder. After chilling on dry ice, the liner was charged with 900 g. of pure CClF₂CClF₂, placed inside the steel reactor and sealed. With the agitator on, heat was applied to raise the temperature to 127°C in 30 minutes. Thereafter, the temperature was maintained at 127 to 142°C (1.61 MPa gauge [to 233 psig]) for 6 hours. The mixture was gradually cooled to -10°C and agitation shut off. The catalytic heel was separated from the product mixture. Gas chromatographic and FTIR analysis of the liquid phase was consistent with 1.00% CF₃CF₂Cl, 51.98% C₂Cl₂F₄, 46-71% CCl₃CF₃ (2054 ppm CClF₂Cl₂F), 0.24% CCl₃CClF₂, 0.002% CCl₃CCl₂F and 0.005% C₂Cl₆- The ratio of CCl₂FCF₃/CF₂ClCF₂Cl was determined to be 32.56:1 Example 12 The pyrex liner of a 2 0 l Parr bomb was charged with 50.0 g. of anhydrous aluminum trichloride, chilled on dry ice and charged with 900 g. of pure CClF₂CClF₂. After sealing the reactor, agitation was begun and contents were brought to 100°C within one hour. Over the next 30 minutes, the temperature was increased to 120°C. For 3.5 hours thereafter, the temperature was maintained between 120 and 135°C (1.85-2.25 MPa gauge [268-326 psig]). The reactor was gradually cooled to -10°C and agitation shut off to permit sampling of the liquid phase. The catalytic heel was separated from the product mixture. Gas chromatographic analysis indicated only 4.12% of starting material was converted to CCl₃CF₃. FTIR analysis indicated no formation of CF₃CFCl₂. No other products were detected. Example 13 A 3.0 g sample of the catalytic heel from example 10 was treated in a 10 ml test tube with 9.4 g of CCl₂FCClF₂and vigorously agitated. Within 4 minutes, the temperature climbed from 22 to 42°C. The resulting catalytic heel was separated from the product mixture. Gas chromatographic analysis one hour after initial mixing indicated only 320 ppm CCl₂FCClF₂ (major product = CCl₃CF₃). Example 14 The Parr bomb reaction mixture (from example 11) was chilled to -10°C and approximately 800 g of crude product was siphoned off, leaving the catalytic heel intact. A charge of 900 g. of pure CClF₂CClF₂ was quickly added and the Parr bomb resealed. After approximately 4 hours heating to 131°C (1.57 MPa gauge [229 psig]) FTIR analysis indicated no observable isomerization to CF₃CFCl₂. The invention has been described with reference to its preferred embodiments. Those of ordinary skill in the art may, upon reading this disclosure, appreciate changes or modifications which do not depart from the scope and spirit of the invention as described above or claimed hereafter.

Claims: A process for isomerizing chlorofluorocarbons, which comprises: (i) contacting a chlorofluorocarbon of the formula: CClFYCClFX (I) wherein X and Y are independently selected from -Cl and -F, provided that X is not -Cl when Y is -F, with anhydrous aluminum trichloride, the weight ratio of chlorofluorocarbon (I) to aluminum trichloride being from 16:1 to 80:1, in the presence of a metal for a time and at a temperature sufficient for the chlorofluorocarbon (I) to isomerize to a compound of the formula CCl₂YCF₂X (II); (ii) separating at least the majority of the organic phase from the activated catalyst; and (iii) isolating the chlorofluorocarbon of formula (II) from the separated organic phase. A process according to claim 1, wherein the chlorofluorocarbon (I) is contacted with the anhydrous aluminum trichloride at a temperature of from: 22° to 52°C when X is -Cl or -F and Y is -Cl; or 120° to 142°C when X is -F and Y is -F. A process according to claim 1 or 2, wherein the metal is stainless steel, chromium, manganese, molybdenum or tungsten or a combination of two of more thereof. A process according to any of claims 1 to 3, wherein the weight ratio of aluminum trichloride to metal in step (i) is from 200 : 1 to 2000 : 1. A process according to any of claims 1 to 4, which further comprises, subsequent to step (ii), (1) contacting a chlorofluorocarbon of the formula: CCl₂FCClFX (III) wherein X is -Cl or -F, with the catalytic heel of step (ii), the weight ratio of chlorofluorocarbon (III) to catalytic heel being from 16:1 to 80:1, for a time and at a temperature sufficient for the chlorofluorocarbon (III) to isomerize to a compound of the formula: CCl₃CF₂X (IV) wherein X has the above-stated meaning; (2) separating the organic phase from the resulting catalytic heel of step (1); and (3) isolating the chlorofluorocarbon of formula (IV) from the separated organic phase. A process according to claim 5, wherein the chlorofluorocarbon (III) is contacted with the catalytic heel for a time sufficient for the chlorofluorocarbon (III) to be present in an amount less than 15000 ppm in the product mixture of step (1). A process according to claim 5 or 6, further comprising, subsequent to step (2), successively adding the resulting catalytic heel to a second chlorofluorocarbon of formula (III) and then repeating steps (1) and (2). A process according to claim 7, wherein the organic phases separated in repetitive steps (2) are pooled together after completion of each step (2).

Inventors: ZAWALSKI ROBERT C, ZAWALSKI, ROBERT C.
Applicants: DIXIE CHEMICAL CO, DIXIE CHEMICAL COMPANY
Application year: 1990
Main classification: C07C17
IPC codes: C07C19, B01J27, C07C17, B01J37