Abstract:
The invention relates to the manufacture of chlorofluoroethanes of formula CF 3  --CHF x  Cl 2-x , where x is equal to 0 or 1, by the catalytic hydrogenation of a perhaloethane of formula: CF 3  --CF x  Cl 3-x . The use of a ruthenium-based catalyst deposited on a support enables the selectivity to be improved.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the manufacture of chlorofluoroethanes of formula: 
     
         CF.sub.3 -CHF.sub.x Cl.sub.2--x                            (I) 
    
     where x is equal to 0 or 1, by the catalytic hydrogenation of a perhaloethane of formula: 
     
         CF.sub.3 CF.sub.x Cl.sub.3--x                              (II) 
    
     BACKGROUND OF THE INVENTION 
     The two starting materials, included in formula (II), are 1,1,1-trichloro-2,2,2-trifluoroethane (CF 3  CCl 13 ) and 1,1-dichloro-1,2,2,2-tetrafluoroethane (CF 3  CFCl 2 ), in which the substitution of a chlorine atom by a hydrogen atom leads, respectively, to 1,1-dichloro-2,2,2-trifluoroethane (CF 3  CHCl 2 ) and to 1-chloro-1,2,2,2-tetrafluoroethane (CF 3  CHFCl). 
     The catalytic hydrogenation of the compounds (II) has already been described, but the selectivities for the product corresponding to the removal of a single chlorine atom are low. Thus, the hydrogenolysis of 1,1-dichloro-1,2,2,2-tetrafluoroethane at 280° C. on a catalyst containing 5% of a palladium on charcoal (British Patent No. 1,578,933) yields a product containing 70% of 1,1,1,2-tetrafluoroethane. Similar results are obtained by C. GERVASUTTI, et al., Fluorine Chemistry, 1, 1-20 (1981) on a catalyst containing 0.5% of palladium on charcoal. At 170° C., the hydrogenolysis of 1,1-dichloro-1,2,2,2-tetrafluoroethane leads to 76% of 1,1,1,2-tetrafluoroethane. To solve the problem of the removal of a single chlorine atom, it is necessary to resort, according to Japanese patent application No. 106,051/82 (publication JP 222038/83) to a chemical reduction with the zinc/ethanol system. Under the conditions described, the selectivity of the hydrogenolysis of 1,1,1-trichloro-2,2,2-trifluoroethane to 1,1-dichloro-2,2,2-trifluoroethane reaches 90%. However, this process has the drawback of using costly metallic zinc, and of yielding zinc chloride as a by-product which must be destroyed. 
     The preceding references are hereby incorporated by reference. 
     DETAILED DESCRIPTION OF THE INVENTION 
     It has now been found that the catalytic removal of a single chlorine atom is accomplished very selectively if a ruthenium-based catalyst is used. 
     The subject of the present invention is a process for preparing chlorofluoroethanes of formula (I) by the catalytic hydrogenation of a perhaloethane of formula (II), characterized in that a ruthenium-based catalyst deposited on a support is used. 
     In the catalyst used according to the invention, the ruthenium content can range from 0.1 to 10% by weight, but is preferably between 0.2 and 8%. 
     The nature of the support can be highly diverse. It is chosen, for example, from aluminas, aluminum fluoride and active charcoals. Charcoals having a specific surface area of between 200 and 1500 m 2/  g (preferably between 600 and 1200 m 2/  g), a high porosity (0.3 to 0.7 cm 3/  g) and a particle size compatible with a fixed-bed catalysis (1 to 10 mm) are preferred supports. These products are marketed in extruded or bead form by many companies. 
     The catalyst according to the invention may be prepared by impregnation of the support with an aqueous or organic solution of a ruthenium derivative, evaporation of the water or solvent and heat treatment to a temperature ranging from 200° to 600° C. (preferably 300° to 450° C.) and under a stream of hydrogen (preferably under a pressure of 1 to 5 bars) to liberate the ruthenium. The nature of the ruthenium derivative used is unimportant. It can be, for example, a chloride, a nitrate, a chlororuthenic acid, an ammonium salt, or an acetylacetonate. 
     The catalyst according to the invention can also be chosen from commercially available products. For example, those from the ENGELHARD Company which proposes catalysts containing from 0.5 to 5% of ruthenium on aluminas or extruded charcoals can be used. 
     The catalytic hydrogenation according to the invention may be performed at a temperature ranging from 50° to 250° C., with a mole ratio hydrogen/perhaloethane (II) ranging from 0.5 to 4, under a pressure of 1 to 20 bars (preferably 1 to 5 bars) and an hourly flow rate of 1 to 20 moles of perhaloethane (II) per liter of catalyst. 
    
    
     EXAMPLES 
     The examples which follow illustrate the invention without limiting it. In Examples 2 to 4, the results are expressed as the overall degree of conversion (DC O ) and the selectivity (S) for a reaction product: ##EQU1## The analysis at admission to and emergence from the reactor being performed by on-line gas chromatography. 
     EXAMPLE 1 - Preparation of the catalysts 
     A rotary evaporator is charged with 50 ml (23 g) of an active charcoal having a porosity of 0.6 cm 3  /g and a specific surface area of 950 m 2  /g in extruded form 1.8 mm in diameter. After outgassing for 3 hours at 100° C. under reduced pressure (1 kPa), 70 ml of an aqueous solution of hydrated ruthenium trichloride RuCl 3 .xH 2  O containing 1.5 g of ruthenium are introduced. The water is then evaporated off under reduced pressure (1 kPa). The residue is dried at 100° C. The latter is then treated at 400° C. for 2 hours under a stream of hydrogen (10 Nl/h). A catalyst containing 6% of ruthenium (catalyst A) is thereby obtained. 
     By working in the same manner but with an aqueous solution containing 0.12 g of ruthenium, a catalyst containing 0.5% of ruthenium (catalyst B) is obtained. 
     EXAMPLE 2 
     50 ml of the catalyst A described in Example 1 are introduced into an electrically heated Inconel tube 45 cm long and 2.72 cm in internal diameter. A mixture of hydrogen and 1,1-dichloro-1,2,2,2-tetrafluoroethane is then passed through the tube at the mole ratios, flow rates and temperatures shown in the following table. The last part of which collates the results obtained. 
     
                                           TABLE 1__________________________________________________________________________       TEST NO.       1    2     3    4     5__________________________________________________________________________Working Conditions:Temperature (°C.)       150  200   200  200   200Mole ratio H.sub.2 /C.sub.2 F.sub.4 Cl.sub.2        4    4     1    1      0.5Flow rate C.sub.2 F.sub.4 Cl.sub.2          0.07               0.07                     0.18                          0.08                                0.10(mole/hour)Results% DC.sub.O of C.sub.2 F.sub.4 Cl.sub.2       43   91    40   56    33% S for CF.sub.3 CHFCl       49   82    84   87    88% S for CF.sub.3 CH.sub.3       50   16    14   11    11__________________________________________________________________________ 
    
     In most cases, the selectivity of the hydrogenolysis of a single C-Cl bond is greater than 80%. 
     By way of comparison, test nos. 1 and 2 were repeated, but with the catalyst A according to the invention replaced by a catalyst containing 5% of palladium prepared in the same manner and on the same support as in Example 1 with PdCl 2  instead of RuC 3 . The results, collated in Table 2 below, show that, with this palladium catalyst, selectivity of the reaction is decidedly biased towards the abstraction of two chlorine atoms. 
     
                       TABLE 2______________________________________           COMPARATIVE TEST NO.           6        7______________________________________Working Conditions:Temperature (°C.)             150        200Mole ratio H.sub.2 /C.sub.2 F.sub.4 Cl.sub.2             4          4Flow rate C.sub.2 F.sub.4 Cl.sub.2 (mole/hour)               0.07       0.07Results% DC.sub.O of C.sub.2 F.sub.4 Cl.sub.2             100        100% S for CF.sub.3 CHFCl             4          3% S for CF.sub.3 CH.sub.3             1            1.2% S for CF.sub.3 CH.sub.2 F              94.5      95______________________________________ 
    
     EXAMPLE 3 
     50 ml of a fresh charge of catalyst A, on which various tests of hydrogenation of 1,1,1-trichloro-2,2,2-trifluoroethane (CF 3  -CCl 3 ) are performed successively, are introduced into the same apparatus as in Example 2. 
     The working conditions for the tests and the results obtained are collated in Table 3 below. Besides the expected product, 1,1-dichloro-2,2,2-trifluoroethane (CF 3  CHCl 2 ), 1,1,1-trifluoroethane (CF 3  CH 3 ) is mainly found as a by-product and, in some cases, C 4  olefinic condensation products. 
     
                                           TABLE 3__________________________________________________________________________WORKING CONDITIONS           C.sub.2 F.sub.3 Cl.sub.3                 RESULTS    Mole   Flow  % DC.sub.O                       % S   % STest    Temp Ratio  Rate  of    for   forNo. °C.    H.sub.2 /C.sub.2 F.sub.3 Cl.sub.3           (moles/h)                 C.sub.2 F.sub.3 Cl.sub.3                       CF.sub.3 CHCl.sub.2                             CF.sub.3 CH.sub.3__________________________________________________________________________11   50  0.83   0.12  10    100   --12  100  0.83   0.12    28.5                       94    413  110  0.83   0.12    42.5                       89    314  150  1      0.10  70    77    315  170  0.90   0.14  74    79    4.516  200  0.83   0.12  68    59    3.517  115  0.56   0.19  59    63    1.618  100  0.91   0.14  64    79    2.119  100  1.6     0.096                 80    80    320  100  3       0.093                 55    80    4.221  150  3       0.093                 87    53    8.322  100  3       0.058                 59    92    6.3__________________________________________________________________________ 
    
     EXAMPLE 4 
     In the same apparatus as in Example 2, and with a charge of 50 ml of catalyst, various tests of hydrogenolysis of 1,1,1-trichloro-2,2,2-trifluoroethane were performed using the following catalysts B, C and D: 
     B: catalyst containing 0.5% of Ru on charcoal, described in the last paragraph of Example 1, 
     C: catalyst containing 1% of palladium on charcoal, prepared as in Example 1, but with PdCl 2  instead of RuCl 3 , 
     D: catalyst containing 5% of platinum on charcoal, prepared as in Example 1, but with PtCl 6  H 2  instead of RuCl 3 . 
     The working conditions and the results of these tests are collated in Table 4 below: 
     
                                           TABLE 4__________________________________________________________________________      TEST NO.      According to      the invention                Comparative      31   32   33   34   35   36__________________________________________________________________________Working Conditions:Catalyst   B    B    C    D    D    DTemperature (°C.)      200  150  150  80   100  125Mole ratio   0.5              2.5                  0.5                       1.4                            1.4                                  1.8H.sub.2 /C.sub.2 F.sub.3 Cl.sub.3Flow rate C.sub.2 F.sub.3 Cl.sub.3         0.12              0.6                   0.11                        0.10                             0.10                                  0.10(mole/hour)Results% DC.sub.O of C.sub.2 F.sub.3 Cl.sub.3      21    6   18   92     93.5                               100% S for CF.sub.3 CHCl.sub.2      80   100  28   64   64    27% S for CF.sub.3 CH.sub.3       0    0   72   32   34    48*__________________________________________________________________________ *S for CF.sub.3 CHCl.sub.2 = 20% 
    
     Although the invention has been described in conjunction with specific embodiments, it is evident that many alternatives and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, the invention is intended to embrace all of the alternatives and variations that fall within the spirit and scope of the appended claims.