Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Patent
1997-05-22
1998-11-24
Siegel, Alan
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C07C 1908
Patent
active
058410082
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
Halogenated hydrocarbons containing fluorine together with chlorine or bromine have been widely used as refrigerants, propellants, cleaning agents and the like because of their desirable properties such as chemical stability and physiological inactivity. In recent years there have been concerns over the impact of chlorine-containing and bromine-containing materials on the atmosphere and the environment, and wide-ranging restrictions have been put on their production and use. Accordingly, there is currently interest in producing halogenated hydrocarbons of reduced bromine and chlorine content. Hydrogenolysis is a known method for achieving this. For example, U.K. Patent Specification No. 1,578,933 discloses a process for the hydrogenolysis of halogenated ethanes such as C.sub.2 Cl.sub.2 F.sub.4 and C.sub.2 HClF.sub.4 to produce C.sub.2 H.sub.2 F.sub.4 using conventional hydrogenation catalysts (e.g., palladium supported on alumina or carbon). The reaction is suitably carried out at a temperature not greater than 450.degree. C. (and preferably much lower). PCT Patent Publication No. 91/05752 discloses a process for the hydrogenolysis of various halogenated hydrocarbons containing fluorine (including C.sub.2 Cl.sub.2 F.sub.4 and/or C.sub.2 HClF.sub.4) at temperatures up to 700.degree. C. The reaction may be carried out in various selected reaction vessels, which may be empty or, in some embodiments, packed with selected materials.
Hydrogenolysis (whether using a conventional hydrogenation catalyst or not) is normally an exothermic reaction. The hydrogenolysis reactor may be operated isothermally or adiabatically. Numerous methods have been used to control the reactor temperature and remove heat from packed-bed catalytic hydrogenolyis reactors. For example, part of the product may be separated and mixed with the reactor feed; an inert gas may be added to the reactor feed; and/or an excess of one reactant may be used. Typically, for hydrogenolyis reactions using packed-bed reactors which are run under adiabatic conditions, high ratios of hydrogen to organic starting material are used and control the reaction temperature (the excess hydrogen acting to absorb the exothermic heat of reaction). In many cases, the use of a large excess of hydrogen as the only control of temperature rise for an adiabatic reaction can reduce the efficiency of the hydrogenolysis reaction as measured by space time yield (i.e., "STY"). Space time yield is defined as the quantity of product formed per unit time per unit reactor volume.
SUMMARY OF THE INVENTION
The present invention provides a process for producing a saturated hydrofluorocarbon (cyclic or acyclic) of the formula C.sub.n H.sub.a F.sub.b, wherein n is an integer from 1 to 6, a is an integer from 1 to 7 and b is an integer from 2 to 13, by reacting at least one saturated starting material having the same carbon structure as said saturated hydrofluorocarbon and the formula C.sub.n H.sub.c X.sub.d F.sub.b, wherein c is an integer from 0 to 3, d is an integer from 1 to 4, (n and b are as defined above) and each X is independently selected from Cl and Br, with hydrogen in a reaction vessel at a temperature of from about 350.degree. to 700.degree. C. and a pressure of from about 101 kPa to about 7000 kPa for a time sufficient to produce said saturated hydrofluorocarbon. The process is characterized by feeding to the reaction vessel (e.g., a tube) said at least one starting material and, for each mole of total carbon-chlorine and carbon-bromine bonds in said starting material, (a) at least 0.5 moles of hydrogen and (b) at least about 2.5/J moles of a saturated heat carrier compound which has a molar heat capacity greater than the heat capacity of hydrogen and has the formula C.sub.m H.sub.z F.sub.y (where J is the ratio of the molar heat capacity of the heat carrier compound to the molar heat capacity of hydrogen at the reaction temperature) wherein m is an integer from 1 to 4, z is an integer from 0 to 8 and y is an integer from 0 to 10; and reacting said starting m
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Gelblum Peter Gideon
Keane Thomas R.
Leib Tiberiu M.
Manogue William H.
E. I. Du Pont de Nemours and Company
Siegel Alan
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