PRODUCTION OF FLUORINATED ETHANES USING ELEMENTAL FLUORINE
1273
the presence of argon diluent and at a fluorine excess,
the conversion of the initial compound was almost
quantitative and the selectivity of HFE formation was
about 97%. The yield of fluoromethanes was low. It
should be noted that the temperature of the reactor
wall was 200 250 C. We failed to generate a thermal
wave of gas-phase fluorination at the temperature of
the reactor wall of 10 C.
Our calculations show that 1,1-DFE conversion in
a series of three wave reactors with recycling of in-
termediate fluorination products can reach 90% [11].
EXPERIMENTAL
In the bench experiments were used the following
chemicals: commercial 1,1,1,2-TFE (ICI company,
UK); PFE, HFE, and 1,1-DFE produced by Priklad-
naya Khimiya Russian Research Center on a pilot in-
stallation for enthylene fluorination with cobalt tri-
fluoride; commercial hydrogen fluoride (Khimprom
Joint-Stock Company); and commercial argon (Len-
tekhgaz plant).
To simulate the operation of a sequence of two
series-connected wave reactors, we studied the syn-
thesis of PFE from 1,1,1,2-TFE by fluorination of
a PFE (32 vol %)-1,1,1,2-TFE (68 vol %) mixture in
the wave mode (Fig. 1b).
The content of PFE formed under these conditions
is maximal (43 vol %) at the fluorine concentration
of 27 vol %. The HFE content is 6 vol % and fluoro-
methanes are virtually absent.
To determine the kinetic parameters of 1,1,1,2-TFE
fluorination under the steady-state thermal conditions,
a mixture of 1,1,1,2-TFE and fluorine was passed
through a 2-mm copper tube thermostat in which the
temperature was maintained in the range from 105 to
148 C. The reaction time was controlled by varying
the flow rate of the initial mixture and the tube length.
The fluorine concentration in the initial mixture was
4 10 vol %, which provided fluorination under the
isothermal conditions. Gas samples were taken at the
tube outlet, neutralized, and analyzed chromatograph-
ically. The reactor scheme and experimental procedure
were described in detail in [7].
The ratio of the rate constants of fluorination of
1,1,1,2-TFE and PFE was estimated from the data
presented in Fig. 1 b. At the fluorine concentration
of 25 vol % (adiabatic temperature in the reaction
zone 1000 K) the rate constant of 1,1,1,2-TFE fluori-
nation is higher than that of PFE by a factor of 1.5.
In this calculation, we assumed that 1,1,1,2-TFE is
converted only into PFE, and PFE only into HFE. The
activation energy of PFE fluorination was estimated
1
to be 53 kJ mol . We assumed that the activation
1
Fluorination of 1,1,1,2-TFE was performed in a
25-mm steel ampule 150 mm long under the condi-
tions of thermal explosion. An ampule was purged
energy of 1,1,1,2-TFE fluorination is 50 kJ mol [7].
The activation energy of high-temperature fluori-
nation of 1,1-DFE, estimated from the data presented
mixture so as to provide ten-
with a 1,1,1,2-TFE F2
1
in Table 2, is 44 kJ mol . In this calculation, we
fold gas exchange. Then the inlet and outlet valves
were closed and the ampule was immersed in a heat-
transfer agent heated to 100 C. The thermal explosion
was monitored with the aid of a 200 m Chromel
Copel thermocouple fixed inside the ampule without
protective covers. The gaseous samples for chromato-
graphic analysis were taken with a medical syringe.
assumed that 1,1-DFE is converted only into 1,1,1-
TFE, 1,1,2-TFE, 1,1,1,2-TFE, and 1,1,2,2-TFE, and
1,1,1,2-TFE, only into PFE and HFE [11].
Based on the experimental data on wave-mode
fluorination of 1,1,1,2-TFE, PFE, and their mixtures,
we proposed a kinetic model of this process. Forma-
tion of both the substitution products and fluorometh-
anes is taken into account in this model. We suggested
that the ratio of the activation energies of hydrogen
substitution and degradative fluorination is equal to
the ratio of the energies of the C H and C C bonds
[14, 15].
The bench experiments on wave-mode fluorination
of fluoroethanes were performed as follows. A fluoro-
ethane-fluorine mixture was fed in a reactor, which
was, unless otherwise noted, a steel tube 300 mm long
and 10 mm in diameter. An electric heater initiating
the wave process was fixed on the reactor surface in
the vicinity of the outlet. A thermal wave rose from
the heated region counter to the flow and was stabi-
lized in the region of reverse flows at the reactor in-
let. The reactor surface in this region was cooled with
water to 10 C. Three Chromel Copel thermocouples
200 m in diameter were fixed without protective
covers inside the reactors. The thermocouple junctions
Parameters of 1,1-DFE fluorination to a mixture of
PFE and HFE in the ratio 3 : 1 in two-step and three-
step wave reactors were calculated by this model, re-
fined using the experimental data on 1,1-DFE fluori-
nation. The fluorine concentration in each step was
23 vol %. Intermediate tetra- and trifluoroethanes
were recycled.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 8 2002