PROCESS FOR PREPARING HYDROGEN CONTAINING FLUOROETHYLENES AND CHLOROFLUOROETHYLENES FROM CHLOROFLUOROETHANES

Abstract: A process for preparing fluoroethylenes and chlorofluoroethy­ lenes starting from chlorofluoroethanes and hydrogen, carried out in gas phase at a temperature ranging from 150 to 600°C, in the presence of a hydrogenation catalyst, wherein the chlorofluoroetha­ nes have at least one chlorine atom on each carbon atom, and the catalyst is selected preferably from palladium, nickel, chromium, cobalt, platinum, copper and mixtures thereof, and it is utilised either as such or on inert materials.

Description: This invention relates to a process for preparing hydrogen-containing fluoroethylenes and chlorofluoroethylenes by hydrogenolysis of certain chlorofluoroethanes. Fluoroethylenes and chlorofluoroethylenes are halogenated olefins well known in literature and they are advantageously utilized as intermediates in the preparation of fluoroplastomers, fluoroelastomers and as comonomers in the preparation of fluorinated copolymers. Fluorine-containing olefins are generally prepared by dehydrohalogenation or dehalogenation of the corresponding haloalkanes in the liquid phase, according to well known procedures. For example, 1-chloro-1,2-difluoroethylene and 1,2-dichloro-difluoroethylene are prepared by reduction, with zinc in an alcohol solution, of 1,2-difluoro-1,1,2-trichloroethane and 1,2-difluoro-tetrachloroethane, respectively (J. Chem. Soc. London 1957, pages 2800-06). The high addition of zinc necessary to the reaction and its difficult removal render these processes little attractive from an industrial viewpoint. The preparation of 1,2-difluoroethylene using 1,2-difluoro-tetrachloroethane as a starting material is described in literature. Said reaction occurs in two steps, the former comprising the obtainment of 1,2-difluoro-1,2-dichloroethane through reduction by means of LiAlH₄ or through UV-radiation in the presence of 2-propanol, while the latter consists in the dehalogenation of the abovesaid intermediate in the presence of Mg (Collection Czechloslov. Chem. Commun. Vol. 39, (1974) pages 2801-07). EP-A-53 657 describes a 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 platinum-group metal supported on an alkali magnesium fluoride. US-A-2,704,775 is directed to the preparation of chlorotrifluoroethylene by heating a mixture of 1,1,2-trichloro-1,2,2-trifluoroethane and hydrogen in the presence of a nickel catalyst. US-A-2,864,873 relates to a process for preparing 1,1,2-trifluoro-2-chloroethylene by reacting a mixture of hydrogen and 1,1,2-trifluoro-1,2,2-trichloroethane in the vapor phase under heating and in the presence of a catalyst comprising copper metal and an oxide of chromium. US-A-3,505,417 describes the dehalogenation of fluorohalocarbons having from 2 to 8 carbon atoms by contacting them, in the presence of hydrogen, with a catalytic composition consisting essentially of aluminium fluoride and from 0.05 to 30 weight percent of at least one of CuO, Cr₂O₃, RhCl₃, CoO and Pt. US-A-3,636,173 also deals with the dehalogenation of fluorohalocarbons with hydrogen. In this case the catalyst to be employed is a nickel or chromium phosphate supported on certain forms of fluorinated alumina. Finally, JP-A-60-185,734 (Chem. Abstr. 104, 109005x) describes the preparation of chlorotrifluoroethylene by dechlorination of 1,1,2-trichloro-1,2,2-trifluoroethane with hydrogen in the presence of active carbon from coconut shell. It has now surprisingly been found that hydrogen-containing fluoroethylenes and chlorofluoroethylenes are preparable in a single step by reaction, in the gas phase, of certain chlorofluoroethanes with hydrogen, in the presence of certain hydrogenation catalysts. Thus, the object of the present invention is a continuous process for preparing fluoroethylenes and chlorofluoroethylenes containing one or more hydrogen atoms, which process comprises reacting hydrogen in a single step with a chlorofluoroethane selected from 1,2-difluorotetrachloroethane, 1,1-difluorotetrachloroethane and mixtures thereof, in the gas phase at a temperature of from 200°C to 400°C, with a molar ratio of hydrogen to said chlorofluoroethane of from 2 to 5 and in the presence of a hydrogenation metal catalyst selected from palladium and nickel. The process of the present invention is an improvement as compared with those of the art because of its profitability, easy operability on a commercial scale and because it permits to prepare hydrogen-containing fluoroethylenes and chlorofluoroethylenes in a single step. Said process permits to obtain a very high conversion of the reagents. The hydrogenation catalysts employed according to the present invention can be utilized either as such or, preferably, on inert materials such as, e.g., carbon, aluminium oxide, barium sulphate at a concentration ranging from 0.1 to 10% by weight. The hydrogenation is carried out in tubular reactors made of materials such as, for example, nickel, Inconel, stainless steel. The present process can be carried out either at atmospheric pressure or at a higher pressure. The contact time of the reagents with the catalyst generally ranges from 5 to 60 seconds, preferably from 10 to 20 seconds. Hydrogen can be fed either in the pure state or diluted with an inert gas such as for example nitrogen, helium, argon. The specific molar ratio between hydrogen and chlorofluoroethanes is selected as a function of the product to be obtained; the higher said molar ratio is, the more the product mixture gets rich in hydrogenated fluoroethylenes. Furthermore, when high hydrogen/chlorofluoroethane molar ratios are employed, it is possible also to obtain the saturated products resulting from the addition of hydrogen to the fluoro-olefins and chlorofluoro-olefins produced, such as for example CFHCl-CFHCl and CH₂F-CH₂F. When leaving the reactor, the vapours are washed with a water solution containing 5-20% by weight of alkali hydroxide, then they are dried over CaCl₂ and cooled until complete condensation. For a better understanding of the present invention, the following illustrative examples are given, which, however, are not to be construed as a limitation of the invention. In the examples, the percentages are by weight, unless otherwise specified. EXAMPLES 1-10 Into a cylindrical reactor made of steel AISI 316, having an inside diameter of 12 mm and a useful volume of 125 ml, containing 100 ml of activated carbon granules with a palladium content of 0.5% by weight, there was introduced, at atmospheric pressure, a mixture, preheated to 105°C, of hydrogen and difluorotetrachloroethane. The difluorotetrachloroethane consisted of a mixture containing 88% by weight of 1,2-difluorotetrachloroethane and 12% by weight of 1,1-difluorotetrachloroethane. Contact time, reaction temperature and H₂/C₂Cl₄F₂ molar ratio are indicated in Table 1. When leaving the reactor, the vapours were washed with a 10% NaOH solution, dried and condensed in a trap maintained at -78°C by means of dry ice. According to gas-chromatographic analysis, the reaction mixture was composed of: difluoroethylene (C₂H₂F₂) chlorodifluoroethylene (C₂HClF₂) dichlorodifluoroethylene (C₂Cl₂F₂). The percentages by weight of the products are reported in Table 1. The balance to 100 consisted of low boiling by-products. Generally, the unreacted starting product was present only in small amounts. EXAMPLE 11 (comparative test) The reaction was carried out according to the modalities of Examples 1-10, with a H₂/reagents molar ratio equal to 5.0, a contact time of 20 seconds and a temperature of 120°C. The following results (% by weight) were obtained: C₂H₂F₂ 10 C₂Cl₂F₂ 10 The balance to hundred consisted of traces of by-products and of unreacted chlorofluoroethane (78%). EXAMPLE 12 Into a cylindrical reactor made of steel AISI 316, having an inside diameter of 12 mm and a useful volume of 125 ml, containing 100 ml of activated carbon granules, with a palladium content of 0.5% by weight, thermoregulated at 320°C, there were introduced, at atmospheric pressure, 0.37 moles/h of a mixture, preheated to 105°C, composed of hydrogen and of 1,1-difluorotetrachloroethane in the following molar ratio: H₂/C₂Cl₄F₂ = 2.5. The vapours leaving the reactor were washed with a NaOH solution at 10%, dried and condensed in a trap maintained at -78°C by means of dry ice. On gas-chromatographic analysis, the reaction mixture exhibited the following composition: (% by weight) CF₂ = CCl₂ 15.2 CF₂ = CHCl 22.3 CF₂ = CH₂ 37.8 CH₃ ― CHF₂ 9.2 EXAMPLE 13 Into the same reactor and under the same conditions as in Example 12 there were introduced, at atmospheric pressure, 0.37 moles/h of a mixture, preheated to 105°C, of hydrogen and of 1,2-difluorotetrachloroethane in a molar ratio H₂/C₂Cl₄F₂ = 2.5. The vapours leaving the reactor were washed with a 10% NaOH solution, dried and condensed in a trap maintained at -78°C by means of dry ice. On gas-chromatographic analysis, the reaction mixture exhibited the following composition (% by weight): CClF = CClF 9.8 CHF = CHF 53.2 CClF = CHF 8.4 CH₂F = CH₂F 8.6 The balance to hundred consisted of low-boiling by-products. EXAMPLE 14 (comparative test) Into the same reactor and under the same conditions as in Example 12 there was introduced, at atmospheric pressure, a mixture of hydrogen and of 1,1,2-trifluorotrichloroethane in the molar ratio: H₂/C₂Cl₃F₃ = 2.4, said mixture having been preheated to 105°C. The contact time was of 17 seconds. The vapours leaving the reactor were washed with a 10% NaOH solution, dried and condensed in a trap maintained at -78°C by means of dry ice. The reaction mixture, subjected to gas-chromatographic analysis, exhibited the following composition: (% by weight) CF₂ = CHF 30 CF₂ = CClF 8 CF₂H - CH₂F 35 EXAMPLES 15-17 Under the same conditions as in Example 12, but using as catalyst Ni on carbon, there was introduced into the usual reactor, at atmospheric pressure, a mixture, preheated to 105°C, composed of hydrogen and of difluorotetrachloroethane (88% by weight of 1,2-difluorotetrachloroethane and 12% by weight of 1,1-difluorotetrachloroethane). The contact time was of 20 seconds. Three tests were carried out, using different H₂/difluorotetrachloroethane molar ratios. The vapours leaving the reactor were treated in like manner as in Example 12. The gas-chromatographic analysis revealed that the reaction products were present in the % by weight reported in Table 2. The balance to hundred consisted of low-boiling by-products. EXAMPLE 18 (comparative test) A test was carried out in the same reactor and under the same operative conditions of Examples 15-17, but using Cr on carbon as catalyst. The gas-chromatographic analysis revealed that in the product mixture the olefin C₂Cl₂F₂ was present at 64% by weight. Example T °C Molar ratio Contact time (sec) C₂H₂F₂ C₂HClF₂ C₂Cl₂F₂ C₂H₄F₂ 1 220 2.5 22 51 5.2 10 8,1 2 220 3.6 20 41 3.5 10 24 3 220 1.3 20 13 20 47 2 4 320 2.5 21 55.5 6.5 13.3 6.5 5 320 4.2 20 41 5.0 5.0 25 6 320 1.7 20 11 30 40.0 4.0 7 220 5.0 20 29 2.0 3 43 8 400 2.5 20 61 5.0 2.2 12.3 9 320 3.0 20 51 7 7 11 10 150 2.5 20 15 10 32 3.5 Example Molar ratio C₂H₂F₂ C₂HClF₂ C₂Cl₂F₂ C₂H₂Cl₂F₂ 15 5.0 80 - - 7 16 2.5 45 37 - 1.5 17 1.3 5 24 62 1.2

Claims: A continuous process for preparing fluoroethylenes and chlorofluoroethylenes containing one or more hydrogen atoms, which process comprises reacting hydrogen in a single step with a chlorofluoroethane selected from 1,2-difluorotetrachloroethane, 1,1-difluorotetrachloroethane and mixtures thereof, in the gas phase at a temperature of from 200°C to 400°C, with a molar ratio of hydrogen to said chlorofluoroethane of from 2 to 5 and in the presence of a hydrogenation metal catalyst selected from palladium and nickel. The process according to claim 1, wherein the hydrogenation catalyst is supported on active carbon.

Inventors: GERVASUTTI, CLAUDIO
Applicants: AUSIMONT S.P.A.
Application year: 1987
Main classification: C07C21
IPC codes: C07C17, C07C67, C07C21, B01J23, C07B61