Gas-phase fluorination of fluoroethanes with elemental fluorine

Article abstract of DOI:10.1023/A:1013023102787

Scientific basis for industrial gas-phase fluorination of fluoroethanes with elemental fluorine allowing production of higher-fluorinated fluoroethanes from lower-fluorinated compounds is developed. 2001 MAIK "Nauka/Interperiodica".

Full text of DOI:10.1023/A:1013023102787

Russian Journal of Applied Chemistry, Vol. 74, No. 7, 2001, pp. 1151 1155. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 7,
001, pp. 1120 1124.
Original Russian Text Copyright
2
2001 by Pashkevich, Mukhortov, Alekseev, Asovich, Rozhdestvenskaya.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Gas-Phase Fluorination of Fluoroethanes
with Elemental Fluorine
D. S. Pashkevich, D. A. Mukhortov, Yu. I. Alekseev,
V. S. Asovich, and O. V. Rozhdestvenskaya
Prikladnaya Khimiya Russian Scientific Center, St. Petersburg, Russia
Received May 22, 2000; in final form, February 2001
Abstract Scientific basis for industrial gas-phase fluorination of fluoroethanes with elemental fluorine
allowing production of higher-fluorinated fluoroethanes from lower-fluorinated compounds is developed.
Fluorine is extremely reactive and its reactions are
highly exothermic. Therefore, at present preparation
of fluorinated organic compounds using fluorine has
almost no industrial application.
the corresponding industrial procedures still are not
developed.
The kinetics of 1,1,1,2-TFE fluorination was
studied in [6]; it was found that industrial synthesis in
the steady-state thermal mode is unsuitable. As shown
in [7], industrial fluorination of fluoroethanes should
be carried out in the nonstationary thermal mode
(wave or combustion modes). In this case fluoro-
methanes are not formed in noticeable amounts at the
initial concentration of fluorine lower than 30 vol %.
Fluorine is commercially available, and its utili-
zation for production of valuable fluorinated prod-
ucts is rather urgent. These products include a series
of fluoroethanes, e.g., 1,1-difluoroethane (DFE,
R152a), 1,1,2-trifluoroethane (R143a), 1,1,1,2-tetra-
fluoroethane (TFE, R134a), pentafluoroethane (PFE,
R125), and hexafluoroethane (HFE, R116), which are
widely used as refrigerants, propellants, fire ex-
tinguishers, reagents for plasmochemical production
of superlarge integrated circuits, gas dielectrics, etc.
Development of the industrial process for fluorina-
tion of fluoroethanes requires understanding of the
principles of scaling the reactor for gas-phase fluorina-
tion operating in the wave mode.
[1]. The world’s consumption of these compounds
reaches tens thousands tons per year.
One of the features of combustion is that the reac-
tion profile in a laminar torch comprises tenth frac-
tions of millimeter. In tunnel jets conversion of com-
pounds in the turbulent torch reaches 80% within the
length of five diameters of the crater [8]. Such a struc-
ture of the turbulent torch suggests that, if the thermal
radiation of the gas is negligible, the main conversion
of compounds proceeds at temperature fairly close to
adiabatic. In this case the composition of the products
of 1,1,1,2-TFE gas-phase fluorination in the mode of a
steady-state self-propagating wave should be indepen-
dent of the diameter of the reaction unit and of the gas
flow mode (without taking into account thermal de-
composition of fluoroethanes outside the fluorination
The modern industrial process for production of
fluoroethanes is based on catalytic fluorination of
fluorochloroethanes and ethylenes with hydrogen
fluoride. The initial chlorinated materials used in this
case are ozone-dangerous, and, in accordance with the
Montreal Protocol, their production should be ter-
minated. Moreover, this process yields significant
amounts of hydrogen chloride (by-product) and re-
quires periodical replacement and utilization of the
spent chromium manganese fluoride catalyst. Thus,
development of alternative procedures for synthesis of
fluoroethanes is urgent. One of such procedures can
be synthesis of higher-fluorinated ethanes by gas-
phase fluorination of lower-fluorinated compounds zone). To verify this assumption, we performed a
with elemental fluorine.
series of tests with reactors of various diameters.
The first data on the gas-phase fluorination are
given in [2 5]. In particular, the gas-phase fluorina-
tion of ethane with fluorine was studied and the pos-
sibility of preparing HFE was confirmed. However,
The tests we carried out using changeable tubes
with an internal diameter of 10, 4, 3, and 2 mm at
flow rates of the cold reaction mixture providing con-
stant velocities of the gas flow. To eliminate the
1
070-4272/01/7407-1151$25.00 2001 MAIK Nauka/Interperiodica

1152
PASHKEVICH et al.
Table 1. Experimental parameters and the composition of the reaction products after fluorination of 1,1,1,2-TFE
in the mode of self-propagating thermal wave using reactors of various diameters
Experimental parameters
Product composition
d, mm
um, m s 1
Re
, W m 2 K 1
C H F
C2HF5
C F
2 6
FM*
2
2 4
1
0
4
3
2
1.0
1.5
1.4
1.2
572
368
140
147
25.6
64.1
85.6
62.4
64.1
64.1
63.8
31.0
30.1
30.0
30.2
5.5
4.9
5.1
5.2
1.1
0.9
0.8
0.8
128.2
*
FM is total content of fluoromethanes in the reaction products.
breakthrough of the reaction front up with a gas flow
into a mixer, the internal diameter of the latter was
this process. To explain this feature, we studied the
effect of the formed hydrogen fluoride on the reaction
rate [6].
0
.8 mm. The parameters of these tests (reactor diam-
eter d, gas velocity u , Re number, and convection
m
As-produced fluorine always contains hydrogen
fluoride [1]. Special treatment is required to remove
HF, which increases the cost of its production. Thus,
investigation of the effect of small amounts of hydro-
gen fluoride in the initial mixture on the composition
of the reaction products in the mode of self-propagat-
ing thermal wave is urgent.
coefficient of the heat exchange from the reaction
zone to the reactor wall ) and the composition of the
reaction products are listed in Table 1; the fluorine
concentration was 30 vol %.
The composition of products formed in the wave
process is independent of the convection coefficient of
the heat exchange in the 25 130 W m 2
K
1
range,
The procedure and experimental setup used were
described previously in [7]. Fluorine was mixed with
which confirms our assumption that there is no heat
exchange in the reaction zone of fluorine and 1,1,1,2-
TFE and allows extrapolation of these results to larger
reactors at a constant initial concentration of fluorine.
5
10% of hydrogen fluoride, the fluorine concentra-
tion was 11 47 vol %, and the flow rate of the cold
3
1
reaction mixture was 50 75 cm s .
Thus, the fluorine concentration is a unique param-
eter affecting the composition of the products of the
wave synthesis, which simplifies design and operation
of the reactor.
As in the case of pure fluorine [7], we observed the
dependences typical for the wave modes. The com-
position of the reaction products as influenced by
the fluorine concentration is shown in Fig. 1. Com-
parison of these results with those determined for pure
fluorine [7] shows that the composition of the reaction
products obtained in the wave mode of PFE synthesis
is almost independent of the concentration of hydro-
gen fluoride (5 10 vol %) in the reaction mixture in
the entire range of fluorine concentrations.
The kinetic study of the gas-phase fluorination of
,1,1,2-TFE revealed the autocatalytic character of
1
,
vol %
This fact allows utilization in the wave synthesis
mode of the electrolysis gas of fluorine production
without additional treatment.
The disadvantage of the wave mode is the require-
ment to perform the reaction at the substoichiometric
concentration of one of the components. In the gas-
phase fluorination of fluoroethanes the maximum
permissible concentration of fluorine is about
C , vol %
F
2
3
0 vol %. At higher concentrations and thus at higher
Fig. 1. Composition of the products of 1,1,1,2-TFE fluo-
rination in the wave mode as influenced by fluorine con-
adiabatic temperature of the wave process the degrada-
tion of fluoroethanes becomes pronounced, and sig-
nificant amounts of fluoromethanes appear in the
reaction products.
centration C in the presence of 5 10 vol % of hydrogen
F
2
fluoride: (1) 1,1,1,2-TFE, (2) PFE, (3) HFE, and (4) total
content of fluoromethanes; the same for Fig. 2.
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GAS-PHASE FLUORINATION OF FLUOROETHANES
1153
Table 2. Composition of the fluorination products of the mixture of 1,1-DFE (14 vol %) and HFE (85 vol %) in the wave
mode as influenced by the fluorine concentration CF2 (vol %)
Product composition, vol %
C ,
vol %
F
2
CHF CH CHF CH F CF CH CHF CHF2 CF CH F C2HF5
C F
2 6
CF4
CHF3 CH2F2
2
3
2
2
3
3
2
3
2
15.4
18.8
19.4
22.1
23.0
23.6
24.3
28.6
31.7
6.7
4.6
4.8
4.4
4.1
4.1
3.3
2.9
2.1
3.2
3.2
1.3
1.0
1.3
1.8
1.7
2.0
1.3
1.3
1.3
1.0
0.20
0.71
1.08
1.11
1.48
1.21
1.08
1.32
1.34
83.8
85.8
83.1
83.3
82.6
85.5
86.7
86.0
86.4
0.47
0.41
0.36
0.44
0.36
0.41
0.41
0.47
0.72
0.15
0.08
0.12
0.13
0.17
0.31
0.36
0.69
1.42
2.8
3.7
3.4
3.5
2.2
2.1
2.0
1.4
3.0
3.3
3.3
3.1
2.4
2.0
1.7
1.3
1.2
1.2
1.6
2.0
1.2
1.1
1.2
0.8
0.64
0.78
1.37
1.46
2.17
2.88
Table 3. Experimental parameters and composition of the products in fluorination of 1,1,1,2-TFE to HFE using dilution
with argon
Initial mixture, vol %
Composition of the reaction gas, vol %
Ar
F2
C H F
C H F
C2HF5
C F
CF4
CHF3
0.4
CH F
2 2
2
2 4
2
2 4
2 6
8
4.4
8.1
0.7
0.6
13.9
10.1
7.4
1.72
1.80
1.85
2.79
1.1
0.9
6.0
97.6
97.3
88.0
76.6
0.9
1.3
3.2
2.8
8
9
9
0.5
3.9
3.8
6.6
14.6
2.1
Tetrafluoromethane (TFM) boils at 128 C, which
causes the loss of the desired product during distilla-
tion. According to the calculations of the distilla-
tion column, the content of TFM should not exceed
tial 1,1-DFE (14 vol % concentration) contained
0.35% CHF and 0.49% CF CH . The conversion of
3
3
3
1,1-DFE reached 80%, and the selectivity with respect
to trifluoroethanes was 50%. However, at the concen-
tration of fluorine >20 vol % the content of TFM
became significant. This is probably due to the fact
that at such fluorine concentrations HFE is not ab-
solutely inert to fluorine under the wave synthesis
conditions.
0
.5 vol %.
At fluorine concentrations lower than 30 vol %
distillation of the reaction products becomes simpler,
but the conversion of the initial material is relatively
low. The following ways to increase conversion are
used. (1) A certain fraction of the material to be
fluorinated can be replaced by HFE, which does not
participate in the reaction at a fluorine concentration
We studied preparation of HFE from 1,1,1,2-TFE
using dilution with argon. The process parameters and
the reaction product composition are given in Table 3.
With excess fluorine, the dilution with argon provides
almost complete conversion of the initial material, and
the selectivity with respect to HFE reaches 97%. The
degradation of fluoroethanes under such conditions is
insignificant. It should be noted that the reaction was
carried out at a temperature of the reaction wall of
200 250 C. At a temperature of the reaction wall of
<
30 vol %, or by another inert compound. (2) Fluori-
nation can be performed using several series-con-
nected wave reactors with intermediate cooling of the
reaction mixture. (3) The reaction mixture can be
recycled, with recovery of the unchanged material
from the products of the wave process and its addition
to the initial reaction mixture.
1
0 C the gas flow blew off the thermal wave from
To illustrate the first way, we studied the wave
fluorination of 1,1-DFE to prepare trifluoroethanes
the reactor.
(
Table 2); HFE was used as inert diluent, which in-
A series of tests with a mixture containing 32 vol %
PFE and 68 vol % 1,1,1,2-TFE was carried out to
creases the conversion of the initial material. The ini-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 7 2001

1154
PASHKEVICH et al.
experimental data (Table 2 in [7]), also assuming that
the activation energy of 1,1,1,2-TFE fluorination E =
,
vol %
1
5
0 kJ mol . In the course of calculations we assumed
that fluorination of 1,1-DFE yields 1,1,1-TFE, 1,1,2-
TFE, 1,1,1,2-TFE, and 1,1,2,2-TFE, whereas in the
case of 1,1,1,2-TFE only PFE and HFE are obtained.
Based on the experimental data on fluorination of
1
,1,1,2-TFE, PFE, and their mixtures in the wave
mode, the kinetic model of the process was con-
structed, which involves two main fluorination reac-
tions: hydrogen substitution and cleavage of the C C
bond with formation of fluoromethanes. Based on
published data on the bond energies in the correspond-
ing molecules [9, 10], we determined the ratio of the
activation energies of these reactions. The ratio of
the rate constants was refined using experimental data.
The composition of the reaction mixture at the inlet
and outlet of the single-stage wave reactor with re-
cycling of incompletely fluorinated products and HFE
was simulated by the PC treatment of the system of
the corresponding equations. The data on the com-
position of the inlet, outlet, and recycling reaction
mixtures at fluorine concentration in the inlet flow of
C , vol %
F
2
Fig. 2. Composition
of the fluorination products of the
mixture of PFE (32 vol %) and 1,1,1,2-TFE (68 vol %) in
the wave mode as influenced by the fluorine concentration
C
.
F
2
simulate two-step conversion of 1,1,1,2-TFE into
pentafluoroethane. The results are shown in Fig. 2.
In the course of fluorination the content of PFE in
the reaction products passes a maximum (43 vol %)
corresponding to the fluorine concentration of
2
7 vol %. In this case the content of HFE is 6 vol %,
25 vol % are listed in Table 4 for the reactor with
and fluoromethanes are almost absent. The results
given in Fig. 2 allow estimation of the ratio of the
fluorination rate constants of 1,1,1,2-TFE and PFE.
Assuming that fluorination of 1,1,1,2-TFE and PFE
yields only PFE and HFE, respectively, we obtained
that at a fluorine concentration of 25 vol % (1000 K
adiabatic temperature in the reaction zone) the rate
constant of 1,1,1,2-TFE fluorination is 1.5 times
greater.
a capacity of 100 tons per year.
This PC program was improved using the experi-
mental data on fluorination of 1,1-DFE, and fluorina-
tion of 1,1-DFE to prepare PFE and HFE using two-
and three-stage wave reactors at fluorine concentration
of 23 vol % was simulated. The results are shown
in Table 5. The intermediate incompletely fluorinated
products are recycled. The flow compositions are
given for the capacities with respect to PFE and HFE
of 954 and 250 tons per year, respectively.
The activation energy of PFE fluorination of
3 kJ mol 1 was evaluated from the data given in
5
Fig. 2; the activation energy of 1,1,1,2-TFE fluorina-
As seen from Table 5, in the case of three-stage
wave reactor and recycling of incompletely fluorinated
products the 1,1-DFE conversion reaches 90%.
tion was taken as 50 kJ mol 1 [6].
The activation energy of high-temperature fluorina-
1
tion of 1,1-DFE of 44 kJ mol was calculated from
CONCLUSIONS
Table 4. Simulated data on the composition of the inlet,
outlet, and recycling gas flows in conversion of 1,1,1,2-TFE
into HFE on a single-stage wave reactor with recycling of
incompletely fluorinated products
(
1) The gas-phase fluorination of fluoroethanes
with fluorine in the mode of self-propagating thermal
wave was studied.
Composition of the gas mixture, kg h 1
(2) The principles for scaling of the wave gas-
phase reactor were developed.
Flow
C H F
C2HF
C F
CF4
HF
2
2 4
5
2 6
(3) In the wave mode the composition of the fluo-
rination products of fluoroethanes is not noticeably
influenced by the presence of hydrogen fluoride.
Inlet
Outlet
Recycling
11.91
0.83
0.83
3.59
3.59
3.59
31.88 0.14 0.40
46.84 0.21 4.43
31.88 0.14 0.36
(4) Based on experimental and theoretical data, the
ways to improve conversion of the initial raw material
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GAS-PHASE FLUORINATION OF FLUOROETHANES
1155
Table 5. Simulated data on the composition of the inlet and outlet gas flows in conversion of 1,1,1,2-TFE into PFE and
HFE on single-, two-, and three-stage wave reactors
Composition of the gas mixture, kg h 1
Flow
CHF CH CHF CH F CF CH CHF CHF CF CH F C2HF5
C F
2 6
FM
HF
2
3
2
2
3
3
2
2
3
2
First stage inlet
90.0
48.6
11.5
26.3
7.6
300.1
303.3
First stage outlet,
second stage intlet
10.6
38.9
91.1
2.7
27.5
56.8
84.0
Second stage outlet,
third stage intlet
19.4
9.0
25.7
11.5
9.0
303.0
302.5
16.6
31.6
0.9
1.6
Third stage outlet
7.7
120.4
and selectivity with respect to the desired product are
proposed, which involve dilution of the initial gas
mixture with an inert compound, recycling of incom-
pletely fluorinated products, and utilization of two-
and three-stage wave reactors.
Bigelow, L.A., J. Am. Chem. Soc., 1961, vol. 83,
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6
7
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9
. Pashkevich, D.S., Muhortov, D.A., Podpalkina, E.A.,
and Baranov, V.G., J. Fluorine Chem., 1999, no. 6,
pp. 3 5.
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