Process for the preparation of 1,1,1-trifluoro-2,2-dichloroethane

This specification discloses a process for the preparation of 1,1,1-trifluoro-2,2-dichloroethane in which chlorination of 1,1,1-trifluoro-2-chloroethane is carried out in the presence of activated carbon by feeding chlorine and hydrogen into a reactor simultaneously or sequentially, thereby enhancing the selectivity to 1,1,1-trifluoro-2,2-dichloroethane without lowering the conversion of 1,1,1-trifluoro-2-chloroethane.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for the preparation of 
1,1,1-trifluoro-2,2-dichloroethane (CF.sub.3 CHCl.sub.2). More 
particularly, the present invention relates to an improved process for the 
preparation of 1,1,1-trifluoro-2,2-dichloroethane in which chlorination of 
1,1,1-trifluoro-2-chloroethane (CF.sub.3 CH.sub.2 Cl) is carried out by 
feeding chlorine and hydrogen into a reactor simultaneously or 
sequentially in the presence of activated carbon, thereby enhancing the 
selectivity to 1,1,1-trifluoro-2,2-dichloroethane. 
2. Description of the Prior Art 
1,1,1-trifluoro-2,2-dichloroethane has similar physical properties to 
trifluorochloromethane (CF.sub.3 Cl, known commercially as "CFC-11"), but 
it hardly decomposes the ozone layer and shows little influence on the 
warning of the earth. For these reasons, 
1,1,1-trifluoro-2,2-dichloroethane is attractive commercially as a 
potential substitute for CFC-11. 
A number of processes for the preparation of 
1,1,1-trifluoro-2,2-dichloroethane have been suggested. For example, 
European Patent Publication No. 0 346 612 A, and Japanese Patent Kokai 
(Laid-Open) Publication No. 89-290638, disclose a process for the 
preparation of 1,1,1-trifluoro-2,2-dichloroethane which comprises 
chlorinating 1,1,1-trifluoro-2-chloroethane in the presence of a catalyst 
such as CuCl.sub.2, NiCl.sub.2, and FeCl.sub.2 carried on AlF.sub.3. U.S. 
Pat. No. 4,060,469 discloses a process for the preparation of 
1,1,1-trifluoro-2,2-dichloroethane which comprises photochlorinating 
1,1,1-trifluoro-2-chloroethane under a radiation of specific wavelength 
range. 
In general, a chlorination of 1,1,1-trifluoro-2-chloroethane is carried out 
stepwise in accordance with following reactions: 
EQU CF.sub.3 CH.sub.2 Cl+Cl.sub.2 .fwdarw.CF.sub.3 CHCl.sub.2 +HCl(1) 
EQU CF.sub.3 CHCl.sub.2 +Cl.sub.2 .fwdarw.CF.sub.3 CCl.sub.3 +HCl(2) 
In the above reactions, Sequence (1) is the reaction of interest, and 
Sequence (2) is an undesired side reaction. However, it has been reported 
that the rate of Sequence (2) is faster than that of Sequence (1). Due to 
these characteristics, an amount of unnecessary by-product, CF.sub.3 
CCl.sub.3, in addition to the desired chlorinated product, CF.sub.3 
CHCl.sub.2, has been inevitably produced in the prior art processes. The 
by-product, CF.sub.3 CCl.sub.3 needs additional processes and apparatus 
for its treatment. 
Attempts have been made to overcome the problems mentioned above by 
increasing the selectivity to CF.sub.3 CHCl.sub.2 as much as possible. A 
typical process is disclosed in U.S. Pat. No. 4,060,469 and Japanese 
Patent Kokai (Laid-Open) Publication No. 91-52831, in which chlorination 
is carried out at a low molar ratio of Cl.sub.2 to CF.sub.3 CH.sub.2 Cl so 
as to suppress production of CF.sub.3 CCl.sub.3. However, this process 
causes the problem that the conversion ratio of CF.sub.3 CH.sub.2 Cl is 
low, rendering the process economically ineffective. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide an improved 
process for the preparation of CF.sub.3 CHCl.sub.2 in which chlorination 
of CF.sub.3 CH.sub.2 Cl is carried out with increased selectivity to 
CF.sub.3 CHCl.sub.2. 
It is another object of the present invention to provide an economically 
efficient process for the preparation of CF.sub.3 CHCl.sub.2 in which the 
additional steps for treating CF.sub.3 CCl.sub.3 are made unnecessary by 
suppressing the formation of CF.sub.3 CCl.sub.3. 
Further objects of the present invention will become apparent through 
reading the remainder of the specification.

DETAILED DESCRIPTION OF THE INVENTION 
We, the inventors, have unexpectedly found that when chlorination of 
CF.sub.3 CH.sub.2 Cl is carried out by using chlorine together with 
hydrogen in the presence of activated carbon, the resulting CF.sub.3 
CCl.sub.3 by-product can be converted into CF.sub.3 CHCl.sub.2 by 
hydrogenation; thus, greatly enhancing the selectivity to CF.sub.3 
CHCl.sub.2. 
The present invention provides a process for the chlorination of CF.sub.3 
CH.sub.2 Cl. The process is characterized in that hydrogen is used for the 
chlorination of CF.sub.3 CH.sub.2 Cl using chlorine in the presence of 
activated carbon. The hydrogen used reacts with the CF.sub.3 CCl.sub.3 
formed by the chlorination to convert it into the desired product, 
CF.sub.3 CHCl.sub.2. 
The chlorination of CF.sub.3 CH.sub.2 Cl and the hydrogenation of CF.sub.3 
CCl.sub.3 may usually be conducted at a temperature ranging from 
250.degree. to 500.degree. C. However, at temperatures lower than 
350.degree. C., the reaction rate is lowered, making the overall process 
inefficient. However, if the reaction temperature exceeds 450.degree. C., 
many problems such as the risks of decomposition of the reaction products 
and deactivation of the catalyst may occur. For these reasons, it is 
preferred to carry out the reactions at the temperature ranging from 
350.degree. to 450.degree. C. 
The contact time between the reactants and the catalyst ranges from 1 to 90 
seconds, and preferably, from 15 to 45 seconds. The molar ratio of 
chlorine to CF.sub.3 CH.sub.2 Cl ranges from 0.5 to 10, and preferably, 
from 1 to 5. The molar ratio of hydrogen to CF.sub.3 CH.sub.2 Cl ranges 
from 0.25 to 5, and preferably, from 0.5 to 3. 
The hydrogen and chlorine gases are preferably simultaneously fed into a 
reaction vessel. Alternatively, chlorine and then, hydrogen may be fed 
into the reaction vessel. 
The chlorination may be carried out under atmospheric pressure. However, it 
is preferable to carry out the reaction at a pressure ranging from 8 to 10 
atms in order to increase the selectivity to CF.sub.3 CHCl.sub.2, and to 
ensure efficient separation of the by-product, HCl. A higher pressure may 
be employed to obtain a longer contact time between the reactants and the 
catalyst, which increases the conversion of CF.sub.3 CH.sub.2 Cl and the 
yield of CF.sub.3 CHCl.sub.2. 
Chlorination vessels are known in the art. Any known vessel made of 
anti-corrosive materials may be used in the present invention. The 
preferred vessels are those made of Inconel-600, Hastelloy-C, nickel, and 
the like. 
According to the present invention, since the by-product, CF.sub.3 
CCl.sub.3, is converted into CF.sub.3 CHCl.sub.2 by hydrogenation, the 
selectivity to CF.sub.3 CHCl.sub.2 can be greatly enhanced. Due to the 
fact that the hydrogenation is conducted in the same reaction vessel, the 
process of the present invention does not impose any restrictions on the 
process conditions, which are the major factors to decrease the 
productivity in the prior art techniques, for example, to maintain the 
conversion ratios of CF.sub.3 CH.sub.2 Cl at a low level, in order to 
increase the selectivity to CF.sub.3 CHCl.sub.2. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be illustrated in greater detail by way of the 
following examples. The examples are presented for illustration purposes 
only and should not be construed as limiting the invention which is 
properly delineated in the claims. 
EXAMPLE 1 
A cylindrical reaction vessel made using an Inconel-600 tube having a 
diameter of 2.54 cm and a length of 30 cm was used. Activated carbon, in 
the form of pellets of 3 mm in diameter and 5 mm in length (available from 
Kanto Chemical Co., Inc., Tokyo, Japan), was packed into the vessel. 
CF.sub.3 CH.sub.2 Cl, chlorine, and hydrogen were simultaneously fed into 
the vessel to produce CF.sub.3 CHCl.sub.2. The molar ratio of the fed 
CF.sub.3 CHCl.sub.2, chlorine, and hydrogen was maintained at 1:1:0.5. The 
reaction temperature was 450.degree. C., and the reaction time was 30 
seconds. The above reactants were introduced into the vessel after the 
vessel was preheated to 200.degree. C. A mass flow controller was used in 
order to ensure a quantitative supply of the reactants. The effluent from 
the reactor was washed in turn with an aqueous NaOH solution and water to 
remove Cl.sub.2 and HCl, dried with CaCl.sub.2, cooled at -20.degree. C., 
and collected. The product was subjected to gas chromatograph using the 
Krytox-143AC column. 
The composition ratio of the resulting product is shown in Table 1 below. 
COMATIVE EXAMPLE 1 
The same chlorination reaction as described in Example 1 was carried out by 
using the same reaction vessel under the same reaction conditions, except 
that only CF.sub.3 CH.sub.2 Cl and chlorine were fed into the reaction 
vessel in the absence of a catalyst. 
The composition ratio of the resulting product is shown in Table 1 below. 
TABLE 1 
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Component 
Example No. CF.sub.3 CH.sub.2 Cl 
CF.sub.3 CHCl.sub.2 
CF.sub.3 CCl.sub.3 
______________________________________ 
Example 1 39.8% 52.8% 7.4% 
Comparative Example 1 
37.0% 33.9% 29.1% 
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EXAMPLES 2-9 
The same chlorination reaction as in Example 1 was carried out in the same 
reaction vessel, but while varying the reaction conditions. The conversion 
of CF.sub.3 CH.sub.2 Cl and the selectivity to CF.sub.3 CHCl.sub.2 are 
defined as follows. 
##EQU1## 
The results are listed in Table 2 below. 
TABLE 2 
______________________________________ 
Example No. 
T.sup.1 R.sub.a .sup.2 
R.sub.b .sup.3 
T.sup.4 
C.sup.5 
S.sup.6 
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2 450 1.0 1.0 30 55.0 0.88 
3 450 2.0 0.5 30 71.2 0.65 
4 400 1.0 0.5 30 46.7 0.78 
5 350 1.0 0.5 30 42.8 0.76 
6 450 1.0 1.0 15 49.2 0.87 
7 450 1.0 1.0 60 66.2 0.86 
8 450 5.0 1.0 30 79.2 0.86 
9 450 1.0 3.0 30 59.2 0.92 
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Remarks: 
T.sup.1 =reaction temperature (.degree.C.) 
R.sub.a.sup.2 =molar ratio of Cl.sub.2 to CF.sub.3 CH.sub.2 Cl 
R.sub.b.sup.3 =molar ratio of H.sub.2 to CF.sub.3 CH.sub.2 Cl 
T.sup.4 =contact time (seconds) 
C.sup.5 =conversion of CF.sub.3 CH.sub.2 Cl (mole %) 
S.sup.6 =selectivity to CF.sub.3 CHCl.sub.2