JPH10510206A - Hydrogenation catalyst and hydrogenation method - Google Patents

Abstract

  (57) [Summary] A hydrogenation catalyst comprising palladium and platinum in a weight ratio of 2: 1 to 500: 1 supported on a support such as carbon and having improved activity and selectivity, and a hydrogenation catalyst such as chlorodifluoromethane or dichlorodifluoromethane. A) a process for producing a hydrofluorocarbon, such as difluoromethane, comprising contacting a halofluorocarbon with hydrogen, preferably in the gas phase, at an elevated temperature in the presence of said catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION Hydrogenation catalysts and hydrogenation processes The present invention relates to catalysts, in particular to hydrogenolysis (replacement of halogen by hydrogen in saturated molecules) catalysts and hydrogenation (ethylenic dihydrogenation). (Addition of hydrogen to heavy bonds) (hereinafter collectively referred to as "hydrogenation") and hydrogenation processes using the above catalysts, especially halofluorocarbons and hydrohalofluorocarbons for producing hydrofluoroalkanes. Hydrogenation, for example hydrogenation of dichlorodifluoromethane and chlorodifluoromethane to produce difluoromethane, hydrogenation of chloropentafluoroethane to produce pentafluoroethane and tetrafluoroethane, especially 1,1,1 Dichlorotetrafluoroethane and chlorotetrafluoroethane for the production of 1,2-tetrafluoroethane Hydrogenation of the emissions related to. In recent years, there has been increasing international interest in the fact that chlorofluorocarbons, which are used in large quantities worldwide, can destroy the Earth's protective ozone layer, limiting and completely abolishing their production and use today Especially international consent has been obtained. Chlorofluorocarbons have been used, for example, as refrigerants, as foam blowing agents, as cleaning solvents, and as propellants in aerosol sprays for a number of virtually unlimited applications. Accordingly, a great deal of effort has been made to find suitable alternatives to chlorofluorocarbons that perform satisfactorily in many applications where chlorofluorocarbons are used, but do not exhibit the destructive effects described above on the ozone layer. Has been made. One method of searching for a suitable alternative focuses on fluorocarbons that do not contain chlorine but contain hydrogen. Hydrofluorocarbons such as difluoromethane, also known as HFA 32, pentafluoroethane, also known as HFA 125, and 1,1,1,2-tetrafluoroethane, also known as HFA134a, Of particular interest are alternatives in cooling, air conditioning and other applications. Hydrofluorocarbons and hydrochlorofluorocarbons, including catalysed gas-phase hydrofluorination of halocarbons or hydrohalocarbons and catalytic hydrogenation of halocarbons or hydrohalocarbons containing fluorine Numerous methods have been proposed for the production of Catalytic hydrogenation of chlorofluorocarbons and hydrohalofluorocarbons by reacting with hydrogen in the presence of a hydrogenation catalyst is considered to be a potentially commercially viable process. The production of 1,1,1,2-tetrafluoroethane by hydrogenation of dichlorotetrafluoroethane and chlorotetrafluoroethane is described, for example, in GB 1,578,933, and is described by pentane by hydrogenation of chloropentafluoroethane. The production of fluoroethane is described, for example, in JP-A-4-29941, and the production of difluoromethane by hydrogenation of chlorodifluoromethane is described in European Patent Application 0 508 660. Much attention has been directed to improving the catalyst used in the hydrogenation process, for example, to increase the activity of the catalyst and / or increase the selectivity to obtain the desired HFA product. For example, improved catalysts for use in the hydrogenation of chlorofluorocarbons and hydrochlorofluorocarbons are described, inter alia, in International Patent Applications WO 90/08748, WO 92/12113, WO 94/11328, US Pat. No. 5,136,113. And European Patent Application No. 0 347 830 and Japanese Patent Publication No. J4-179322. The present invention is based on the discovery that the activity, particularly the selectivity, of a palladium catalyst is improved by incorporating a controlled amount of platinum into the catalyst. The present invention provides a hydrogenation catalyst comprising palladium and platinum in a weight ratio of 2: 1 to 500: 1 supported on a support. The palladium and platinum components can be used alone or in combination with other metals, such as Group VIII metals such as nickel, Group IB metals such as Ag and Au, and even other group metals. The metal is supported on a suitable support, for example alumina, fluorinated alumina, silica, silicon carbide or carbon, especially alumina or carbon. It is particularly preferred to use a carbon support having a high surface area of carbon, for example, 200 m ² / g or more. Activated carbon supports with a low content of organic impurities are particularly suitable. The amount of metal on the support material may depend, at least in part, on the particular metal catalyst / support combination used and the difficulty of the hydrogenation reaction. However, the total weight percent of palladium and platinum relative to the support is typically from about 0.1 to about 40% by weight, preferably from about 0.5 to about 20% by weight, more preferably from about 2.0 to about 20% by weight. Especially about 5 to about 15% by weight. Although the proportions of palladium and platinum present can vary over a wide range, catalysts having at least twice as much palladium as platinum are preferred. It is particularly preferred to use palladium and platinum in a weight ratio of about 2: 1 to about 500: 1, more preferably about 3: 1 to about 100: 1. Preferred catalysts are, especially when supported on activated carbon, about 0.5 to 20% by weight, in particular about 5 to 15% by weight of palladium and about 0.05 to 5% by weight, in particular about 0.1 to 4% by weight of platinum. It contains. Overall, the amount of platinum is usually from about 0.01% to about 10% by weight of the catalyst. Numerous methods for producing metal-supported catalysts are known to those skilled in the art, for example, as described in the prior art references mentioned above, and the method of the present invention involves the precious metal-supported catalysts prepared by such methods. Available. A typical method consists of impregnating a support with an aqueous solution of a soluble salt of a metal, for example a halide, and then drying the catalyst. The improved catalysts of the present invention are particularly useful for hydrogenolysis or hydrogenation of halofluorocarbons or hydrohalofluorocarbons at elevated temperatures with hydrogen, and thus, according to a second aspect of the present invention, a halofluorocarbon Alternatively, there is provided a process for producing a hydrofluorocarbon, which comprises contacting a hydrohalofluorocarbon with hydrogen at an elevated temperature in the presence of the improved hydrogenation catalyst of the present invention. The halofluorocarbons and hydrohalofluorocarbons used as starting materials usually contain at least one chlorine or bromine and will therefore generally be chlorofluorocarbons or hydrochlorofluorocarbons. The chlorofluorocarbon or hydrochlorofluorocarbon will typically contain 1, 2 or 3 carbon atoms, but they may contain more than 3, for example up to 6 carbon atoms. (Hydro) halofluorocarbons can be unsaturated or saturated, cyclic or acyclic and linear or branched, while (hydro) halofluorocarbons are usually linear saturated acyclic compounds, i.e., linear ( It would be a hydro) halofluoroalkane. Particularly useful hydrogenation reactions that can use the hydrogenation catalysts of the present invention include (a) haloethanes having 4 fluorine atoms, especially chloroethanes such as 1,1-dichlorotetrafluoroethane, 1,2- Hydrogenation of dichlorotetrafluoroethane and chlorotetrafluoroethane to give chlorotetrafluoroethane and / or tetrafluoroethane, in particular 1,1,1,2-tetrafluoroethane, and (b) the formula CF ₂ XY ( Wherein X and Y are each Cl, Br or H, provided that both X and Y are not H) to obtain difluoromethane. The conditions for carrying out these hydrogenation reactions are described, for example, in GB 1,578,933 and EP 0 508 660, the descriptions of which are incorporated herein by reference. Have been. An important feature of successful hydrogenation catalysts is that they exhibit high hydrocracking activity for carbon-chlorine and / or carbon-bromine bonds, but exhibit low hydrocracking activity for carbon-fluorine bonds, thus The purpose is to prevent product loss due to removal of fluorine atoms. The catalyst according to the invention is used with particular advantage in the production of difluoromethane, in which case the catalyst according to the invention improves the selectivity for the production of difluoromethane by reducing the degree of overreaction It has a remarkable effect. According to a preferred embodiment of the second aspect of the present invention, there is provided a compound of the formula XYCF ₂ , wherein X and Y are each H, Cl or Br, wherein at least one of X and Y is an atom other than hydrogen. A) contacting the compound with hydrogen at an elevated temperature in the presence of the hydrogenation catalyst of the present invention. The method, as mixed or separate fluids may be conveniently carried out by feeding a feed stream comprising the formula XYCF ₂ and hydrogen in a container containing a hydrogenation catalyst. The starting compounds of the formula XYCF ₂ are dichlorodifluoromethane, dibromodifluoromethane, chlorobromodifluoromethane, chlorodifluoromethane and bromodifluoromethane. Mixtures of these compounds may also be used. Typically, the compound of formula XYCF ₂ is chlorinated difluoromethane, with chlorodifluoromethane being the preferred starting compound. The ratio of hydrogen and the starting compound of formula XYCF ₂ can vary widely. Usually, at least a stoichiometric amount of hydrogen is used to displace chlorine and / or bromine, and much more than the stoichiometric amount of hydrogen, for example, 4 moles or more per mole of the starting compound. The above hydrogen may be used. When each of X and Y is chlorine or bromine, it is preferable to use at least 2 moles (stoichiometric amount) of hydrogen per mole of the starting compound. When starting compounds of formula XYCF ₂ is chlorodifluoromethane is chlorodifluoromethane per mole, it is preferable to use 1 to 2 moles of hydrogen. Atmospheric pressure or superatmospheric pressure, for example up to about 60 barg, may be used. It has been found that operating the process of the present invention under superatmospheric pressure substantially increases the selectivity of the process to difluoromethane. It is preferred to carry out the process of the invention under a pressure of from about 2 bar to about 60 bar, more preferably from about 2 bar to about 30 bar, especially from 5 bar to 30 bar. The reaction is suitably carried out in the gas phase at a temperature of at least about 150 ° C and up to about 500 ° C, usually from about 225 ° C to about 400 ° C, preferably from about 240 ° C to about 360 ° C. Will be The most preferred temperature depends on the temperature at which the operation is performed; under atmospheric pressure, it is preferred that the operation be performed at about 220 ° C. to about 320 ° C., but at a pressure of about 7.5 barg, about 260 ° C. to about 380 ° C. It is preferred to use temperature. When the reaction is carried out in the gas phase, the contact time is usually 1 to 60 seconds, particularly 5 to 30 seconds. In the process according to a preferred embodiment of the second aspect of the invention, unreacted hydrogen and other starting materials may be recycled together with the organic by-products. The present invention is illustrated by the following examples, but the present invention is not limited by these examples. A. Samples were ground carbon support having an approximate surface area of the preparation 800sq.m / g of catalyst (Norrit Co.), manufactured 1.0-1.2Mm, particles with a particle size of 50cm ³ -60cm ³ sieved The ground carbon was then washed with distilled water and the water was flushed through a No. 4 sinter funnel. The washed carbon was then transferred to a Buchner flask. Next, the target weight of palladium chloride or mixed metal chloride was dissolved in a minimum volume of concentrated concentrated hydrochloric acid, and the solution was added to the carbon particles in the Buchner flask. An additional 200 cm ³ of distilled water was added to the Buchner flask and the slurry was evaporated to dryness on a rotary evaporator using an oil bath temperature of 120 ° C. The catalyst was completed by heating the obtained granules in a vacuum oven at 150 ° C. for about 16 hours. Separately, the catalyst was prepared on a large scale. For large scale catalyst preparation, a 300 cm ³ carbon support was used and the particle size was increased to 3 mm. B. Testing of the catalyst in the hydrocracking process 50 cm ³ of the 1.1 mm or 3 mm catalyst to be tested were charged to a 1.25 cm Inconel reactor and heated to 300 ° C. in a nitrogen flow of 300 cm ³ / min. After drying the catalyst for 2 hours, the nitrogen stream was replaced with a mixed reactant gas stream. In the following examples for comparison, the flow rate of the mixed reactant stream was 180 cm ³ / min, and the molar ratio of hydrogen: HCFC 22 was 2: 1. The reactor effluent gas was passed through a water scrubber to remove acid products and analyzed by conventional gas chromatography analysis. Catalyst performance was measured for reactor temperatures between 300-380 ° C. Example 1 Eight catalysts were prepared (small and large scale as shown in the table), tested, and analyzed for% conversion of chlorodifluoromethane and% selectivity to difluoromethane. , 2 and 3. The platinum-promoted palladium hydrogenation catalyst ^* was found to have the highest reaction selectivity, showing significant advantages over other palladium catalysts containing Cu, Ni, Ru or Rh. Example 2 Two catalysts were prepared for a series of comparative studies. Catalyst "A" contains 10% by weight Pd metal on carbon catalyst, and catalyst "B" contains 10% by weight Pd catalyst and 1.8% by weight Pt catalyst on the same Norrit carbon support. I was Each of these catalysts was prepared by dissolving the metal chloride in a minimum volume of hydrochloric acid, and then impregnating 1-1.2 mm carbon granules with the resulting solution. The slurry was stirred and evaporated to dryness. Then, the catalyst was degassed under a nitrogen flow at 120 ° C. for 16 hours to obtain a completed catalyst. 50 cm ³ of catalyst "A" was then charged to a 1/2 inch Inconel reactor and heated to 300 ° C. for 2 hours in a 300 ml / min stream of nitrogen before testing. The test raw material mixture was a 2: 1 feed molar ratio of hydrogen: CFC 115, which was fed to the conditioned catalyst at a flow rate of 180 ml / min. The catalyst was stabilized under these feed conditions for about 2 hours and then cooled to about 200 ° C. under the reaction conditions. The conversion of CFC 115 and the selectivity to HFC 125 were measured and are shown in Table 4. At the measured temperatures of 199 ° C., 213 ° C. and 236 ° C., the conversion of CFC 115 was found to increase from about 66% to 84% and finally to 97%; Examples A1, A2 and See A3. Initial reaction selectivity was 99.77%, but was found to decrease to 99.59% as feed conversion increased. The above catalyst test procedure was repeated using the Pt promoted catalyst "B". The results are shown in Table 4, Examples B1, B2 and B3. Pt-promoted catalysts may be more active (operating at lower temperatures for a given feed conversion) and more selective (forming lower levels of by-products) compared to the base palladium catalyst. Admitted. Example 3 The test described in Example 2 was repeated using two catalysts "A" and "B", but using a mixture of 114 and 114a instead of 115. The results are shown in Table 5. With catalyst "A", a conversion of 114 of 81.6-88.7% at 114-204 ° C was achieved compared to 173 ° C for the platinum promoted catalyst. Although the conversion of 114a was 100% for both catalysts, the level of perhydrocracking products was reduced for the Pt-containing catalyst. Thus, the platinum promoted catalyst was more active and more selective than the base palladium catalyst.

────────────────────────────────────────────────── ─── Continuation of front page    (81) Designated countries EP (AT, BE, CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, M C, NL, PT, SE), CA, CN, JP, KR, M X, US (72) Inventor Goodyear, Gray             United Kingdom Merseyside El 63 0             Pikiyu, Wirral, Bromborough, Sa             Merville Crows 49 (72) Inventors Matsukashii, Jillon, Charles             UK               2D, Wollington, Penke             Su, Grand Drive 63

Claims (1)

[Claims] 1. A hydrogenation catalyst comprising palladium and platinum in a weight ratio of 2: 1 to 500: 1 supported on a support. 2. The catalyst according to claim 1, wherein the support is carbon. 3. 3. The catalyst according to claim 1, wherein the total amount of palladium and platinum is from 0.1% to 40% based on the support. 4. The catalyst according to any one of claims 1 to 3, wherein the weight ratio of palladium to platinum is 3: 1 to 100: 1. 5. 5. The catalyst according to claim 1, wherein the support is carbon and contains 0.5 to 20% by weight of palladium and 0.05 to 5% by weight of platinum. 6. The catalyst according to any one of claims 1 to 5, wherein the amount of platinum is 0.01 to 10% by weight of the catalyst. 7. A method for producing a hydrofluorocarbon, comprising bringing a halofluorocarbon or a hydrohalofluorocarbon into contact with hydrogen at an elevated temperature in the presence of the catalyst according to any one of claims 1 to 6. 8. A process for producing difluoromethane wherein the halofluorocarbon or hydrohalofluorocarbon has the formula CF ₂ XY, wherein X and Y are H, Cl or Br, wherein both X and Y are not H. The method according to claim 7. 9. 9. A method according to claim 7 or claim 8 wherein the halofluorocarbon or hydrohalofluorocarbon is in the gas phase and the elevated temperature is between 150C and 500C. 10. The method according to any of claims 7 to 9, wherein the stoichiometric excess of hydrogen is present.