Interaction of trichloromethane and tetrachloromethane with nitrogen trifluoride

Article abstract of DOI:10.1134/S1070427211030153

Interaction of nitrogen trifluoride with trichloromethane and tetrachloromethane at temperatures in the range from 20 to 200°C and pressures of up to 6.0 MPa in the gas and liquid phases was studied.

Full text of DOI:10.1134/S1070427211030153

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 3, pp. 420–426. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © D.A. Mukhortov, D.S. Pashkevich, I.A. Blinov, M.P. Kambur, P.S. Kambur, V.B. Petrov, E.S. Kurapova, 2011, published in Zhurnal
Prikladnoi Khimii, 2011, Vol. 84, No. 3, pp. 428–434.
ORGANIC SYNTHESIS AND INDUSTRIAL
ORGANIC CHEMISTRY
Interaction of Trichloromethane and Tetrachloromethane
with Nitrogen Trifluoride
D. A. Mukhortov, D. S. Pashkevich, I. A. Blinov, M. P. Kambur, P. S. Kambur,
V. B. Petrov, and E. S. Kurapova
Applied Chemistry Russian Scientific Center, Federal State Unitary Enterprise, St. Petersburg, Russia
Received September 3, 2010
Abstract—Interaction of nitrogen trifluoride with trichloromethane and tetrachloromethane at temperatures in
the range from 20 to 200°C and pressures of up to 6.0 MPa in the gas and liquid phases was studied.
DOI: 10.1134/S1070427211030153
One of the most important problems in the tech-
interaction between nitrogen trifluoride and absorbents
can serve mechanisms described in the literature for
reactions between other fluorinating agents and
chloromethanes and the fluorinating properties of NF3.
nique for synthesis of nitrogen trifluoride NF by
3
fluorination of a melt of acid ammonium bifluoride
salts with fluorine is purification of the target product
to remove trifluoromethane CF . A method based on
the different solubilities of these gases in a number of
4
There are various processes of interaction between
trichloromethane and a fluorinating agent: fluorination
with hydrogen fluoride in the liquid phase at 60–100°C
and a pressure of 3.1 MPa [3, 4], gas-phase catalytic
method [4], and fluorination of trichloromethane with
antimony trifluoride in the presence of antimony
pentafluoride at 100°C and a pressure of 5.89 MPa [5].
In these processes, the reaction occurs with successive
substitution of chlorine atoms with fluorine, with
predominant formation of dichlorofluoromethane
fluids has been suggested for separation of NF and
3
CF by absorption. It has been shown that tetrachloro-
4
methane and trichloromethane are absorbents satis-
fying a number of technological and economical
requirements [1].
To develop an industrial technology for purification
of nitrogen trifluoride to remove tetrafluoromethane by
the above method, it is necessary to evaluate the
reactivity of the suggested absorbents toward NF3,
which is a fluorinating agent under certain conditions
CHCl F. Tetrafluoromethane has been found as a main
2
product only upon interaction of fluorine diluted with
nitrogen with trichloromethane and tetrachloromethane
in the combustion mode [6].
[
2]. A study of this kind is necessary for solution of
problems related to, first, provision of a safe operation
of equipment, second, to determination of gaseous
impurities that appear in nitrogen trifluoride upon its
contact with the absorbent, and, third, to estimation of
the service life of the absorbent.
According to [6], many processes of interaction
between tetrachloromethane and fluorinating agents
are similar to processes involving trichloromethane.
The reaction of fluorination of tetrachloromethane with
higher fluorides of variable-valence metals and, in
particular, with cobalt trifluoride yields compounds
appearing in Eq. (1) [7, 8]:
No data on the nature of interaction between
nitrogen trifluoride (NTF) and chloromethanes could
be found in the literature, and, therefore, the goal of
our study was to experimentally examine the inter-
action of trichloromethane and tetrachloromethane
with nitrogen trifluoride under various conditions.
4CCl + 12CoF → CCl F + 2CClF + CF
4
4
3
2
2
3
+ 12CoF + 6Cl .
2
2
(1)
At low temperatures (up to 300°C), nitrogen
trifluoride behaves in reactions as a passive oxidizing
agents [2]. In contrast to other nitrogen fluorides, this
Interaction of chlorocarbons with fluorinating
agents. As an analog in development of a model of
4
20

INTERACTION OF TRICHLOROMETHANE AND TETRACHLOROMETHANE
421
compound does not react with an aqueous solution of
potassium iodide at room temperature. At low tem-
necessary to perform experimental studies for both the
processes. It follows from the technological parameters
of the absorption purification of nitrogen trifluoride
and from its physicochemical properties that the
peratures, only a single fluorine atom is reactive in the
·
2
nitrogen trifluoride molecule, and NF radical is trans-
formed into tetrafluorohydrazine upon dimerization.
temperature and pressure at which NF
methanes can interact will not exceed 200°C and
MPa. To these values was limited the range of our
3
and chloro-
Depending on the number of fluorine atoms
abstracted from the nitrogen trifluoride molecule (one,
two, or three), the possible reaction products are,
respectively, tetrafluorohydrazine N F , difluorodi-
6
experimental study.
2
4
Interaction of trichloromethane and nitrogen
trifluoride in the liquid phase. The interaction of
nitrogen trifluoride and trichloromethane was studied
on an experimental installation by the method
described in [1] in the isobaric-isothermal mode. The
reaction duration was up to 96 h. Several samples were
taken from the gas and liquid phases. After the liquid
phase was sampled, gas was desorbed from the
absorbent and the gas and absorbent were analyzed.
azines N F , and nitrogen. Because difluorodiazines
2
2
decompose at above 70°C into nitrogen and fluorine,
the remaining reaction products are tetrafluorohyd-
razine and nitrogen [2]. The most important reaction
with nitrogen trifluoride is its conversion into tetra-
fluorohydrazine:
NF
3
+ M → N
2
F
4
+ MF
n
.
(2)
A number of substances: carbon, mercury, copper,
iron, nitrogen oxide, and sodium chloride have been
suggested as fluorine acceptors M [9, 10].
A gas-chromatographic analysis procedure that can
most fully determine the content of chlorofluoro-
methanes was reported in [1]. The retention time of
trichloromethane was not specified, but we found by
making test analyses that this component can be
detected by this method and determined the relative
retention time.
Thus, we can conclude that the main process in
fluorination of chloromethanes is the successive
substitution of chlorine atoms with fluorines. A
hydrogen atom is commonly the last to be substituted
or is substituted under very severe conditions, at
temperatures higher than 500°C or with a strong
fluorinating agent (fluorine, chlorine trifluoride). In the
process, dimerization of radicals is possible.
Table 1 lists relative retention times of the com-
ponents and their minimum determinable concentra-
tions in conformity with GOST (State Standard)
1
9212–87 [11] and those experimentally measured
In fluorination at temperatures below 300°C,
nitrogen trifluoride commonly donates a fluorine atom,
with tetrafluorohydrazine formed. Thus, the main pro-
ducts formed in fluorination of trichloromethane and
tetrachloromethane with nitrogen trifluoride will
probably be tetrafluorohydrazine, chlorine, and di-
with a Kristall-2000M chromatograph.
The liquid phase was analyzed in accordance with
GOST 20015–88 [12], the presence of tetrafluoro-
hydrazine in a sample was determined and its con-
centration was measured by the method described in
[13].
chlorofluoromethane CHCl F for the first of the ab-
2
sorbents, and trichlorofluoromethane CCl F for the
In conformity with GOST 20015–88 [12],
3
second. In addition, also possible is formation of
smaller amounts of chlorodifluoromethane CHClF2,
difluorodichloromethane CCl F , and other chloro-
fluoromethanes. Deeper fluorination to give tetra-
fluoromethane, nitrogen, and chlorine is only possible
at higher temperatures.
trichloromethane is delivered to consumers with addi-
tion of a stabilizer whose role was played by ethanol in
an amount of up to 1 wt %. Trichloromethane manu-
factured by Khimprom Volgograd Open Joint-Stock
Company, with addition of 0.5 wt % ethanol, was used
in our experiments.
2
2
In the technological process for purification of
nitrogen trifluoride to remove tetrafluoromethane, an
The experiments were performed at temperatures of
20 to 150°C and pressures of 5.5–6.5 MPa. No special
treatment of the inner surface of the reaction vessel
was carried out. No impurities were detected at the
analysis procedure sensitivity in gas samples taken at
temperatures of up to 110°C taken both directly from
the reactor and from the liquid upon desorption of the
absorbent and NF will come in contact both in the
3
liquid phase, when the gas being purified is dissolved
in a fluid, and in the gas phase, in which there is
absorbent vapor. The rates of the gas- and liquid-phase
processes may substantially differ. Therefore, it is
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 3 2011

4
22
MUKHORTOV et al.
a smaller amount of the stabilizer (0.01 to 0.1 wt %)
into trichloromethane. Therefore, we prepared a
sample containing 0.05 wt % amylene. An experiment
was performed with this sample, and the results
obtained are presented in Fig. 1, straight line 4. It can
be seen that the rate of trichloromethane fluorination
with nitrogen trifluoride is almost the same with 0.5 wt %
ethanol or 0.05 wt % amylene used as a stabilizer.
The appearance of dichlorofluoromethane in the
products of interaction between nitrogen trifluoride
and trichloromethane is evidence in favor of the
following scheme of the fluorination process:
τ, h
Fig. 1. Amount X of dichlorofluoromethane formed in the
gas phase vs. the residence time τ of reagents in the inter-
action of trichloromethane stabilized with (1–3) ethanol
and (4) 0.05 wt % amylene with nitrogen trifluoride in the
liquid phase. Temperature (°C): (1) 111, (2) 135, (3) 152,
and (4) 149. Pressure (MPa): (1) 6.5, (2) 6.4, (3) 5.6, and
2CHCl
+ 2NF
→ 2CHCl
F + N
F
+ Cl
.
(3)
3
3
2
2
4
2
To determine whether tetrafluorohydrazine is
present in gas samples, we performed a mass-spectro-
metric analysis with a MI-1309 instrument. The
analysis revealed the presence of trace amounts of
N F in the samples.
(4) 5.3.
2
4
Because the suggested reaction scheme could not
gas. In gas samples taken at temperatures of 110 to
50°C, only an admixture of dichlorofluoromethane
be reliably confirmed by the results of the experiments
described above, we carried out more prolonged
experiments at higher temperatures. For this purpose,
we changed the experimental procedure by placing the
1
CHCl F was found. An analysis of the liquid phase did
2
not reveal any changes in the composition of
trichloromethane, compared with the starting sub-
stance. The parameters of the experiments and the
amount of dichlorofluoromethane in samples taken
from the gas phase of the reactor and from the gas
desorbed from the liquid are presented in Fig. 1.
reactor filled with trichloromethane and NF in an air
3
thermostat heated to the working temperature.
The experiment was performed under the following
conditions: temperature 165°C, pressure 5.6 MPa,
residence time 96 h, chloroform with 0.05 wt %
amylene. The following results were obtained: content
of dichlorofluoromethane in the gas phase of the
reactor, 0.233 vol %, and that in the gas upon the
Specialists from the manufacture plant suggested to
use amylene, a mixture of pentene isomers, as a
stabilizer for trichloromethane. The advantage pro-
vided by the replacement of ethanol with amylene is in
that the stabilizing effect is provided by introduction of
desorption state, 0.031 vol %. In addition, N F was
2 4
Table 1. Relative retention time of chloromethanes and fluorochloromethanes and their minimum determinable concentrations
Minimum determinable c, vol %
Reagents and fluorination products of tri- and
tetrachloromethanes with nitrogen trifluoride
Relative retention
time
by the method from [11]
experiment
a
Air (NTF)
0.59
0.69
1.65
2.50
4.42
8.00
0.015
0.007
0.019
0.095
0.034
0.013
n.f
a
Trifluorochloromethane
Difluorochloromethane
Fluorotrichloromethane
Fluorodichloromethane
Carbon tetrachloride
Chloroform
n.f
a
n.f
0.002
0.002
a
n.f
b
10.82
–
0.003
a
b
n.f., substances not found in a sample; the same for Tables 2–4. Absent in the procedure from [11].
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 3 2011

INTERACTION OF TRICHLOROMETHANE AND TETRACHLOROMETHANE
PG
423
CV1
Blow out
Vacuum
3
Sampling
CV3 CV4
Evacuation
Fig. 2. Schematic of a laboratory installation for studies of the interaction between chloroform and nitrogen trifluoride in the gas
phase. (1) Cylinder with NTF, (2) vessel for preparation of a gas mixture of NTF and chloroform, (3) gas-phase reactor,
(
PG) pressure gages, and (CV) control valves.
found in the gas phase in an amount of 0.06–0.08 vol %.
No other impurities were found in the liquid phase.
phase, we modified the laboratory installation and the
experimental procedure. The modified laboratory
installation is shown schematically in Fig. 2. The
reactor for gas-phase fluorination had the form of a
To determine the fluid composition from the last
experiment with a higher precision, we performed a
chromato-mass-spectrometric analysis of a sample on a
Hewlett–Packard GC5890-MSD 5972A instrument. It
was found that amylene is entirely absent in
chloroform after its reaction with nitrogen fluoride and
there appear products formed in chlorination of
amylene: dichloropentane, 1-chloro-2-methylbutene,
tube with an inner diameter of 12 mm, length of
3
7
00 mm, and volume of 66 cm . The reactor was made
of 12Kh18N10T stainless steel. Because nitrogen
fluoride reacts with metals to give tetrafluorohydrazine
[2], the reactor walls were preliminarily passivated
with fluorine.
2
-chloro-2,3-dimethylbutane, etc. In addition, the
The study was performed in the following way.
Nitrogen trifluoride was bubbled through a vessel
filled with liquid trichloromethane and thereby was
saturated with a trichloromethane vapor. The mixture
was delivered into the reactor for gas-phase
fluorination. The pressure in the vessel was chosen so
that the equilibrium concentration of the trichloro-
methane vapor was 4–6 vol % at a given temperature.
sample contained trace amounts of hexachloroethane
and fluorotrichloromethane. When determining
molecular chlorine, we found that its concentration in
the liquid phase is 0.013 wt %.
Thus, our experiments demonstrated that chloro-
form and nitrogen trifluoride interact in the liquid
phase by scheme (3). The resulting chlorine enters into
the reaction with the stabilizer, amylene, to give
organochlorine compounds. No other impurities were
found in chloroform.
The mixture of NF and the absorbent vapor was
3
passed through the reactor at a prescribed temperature
under atmospheric pressure. Samples for a gas-chro-
matographic analysis were taken at the reactor outlet.
Interaction of trichloromethane and nitrogen
trifluoride in the gas phase. To study the fluorination
of trichloromethane with nitrogen trifluoride in the gas
To determine the effect of the stabilizer vapor on
the gas-phase fluorination of trichloromethane, we
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 3 2011

4
24
MUKHORTOV et al.
Table 2. Variation of the impurity formation rates with tem-
perature in the gas-phase fluorination of trichloromethane
with nitrogen trifluoride
Table 3. Effect of temperature on the impurity formation
rate in the gas-phase fluorination of trichloromethane with
nitrogen trifluoride in reactor B, unpassivated and with
apparatus walls passivated with fluorine
–1
Formation rate, vol % h
–1
Formation rate, vol % h
CHCl
composition
3
CHCl
composition
3
Т, °С
Т, °С
CНCl Cl CCl
2
F
C
2
Н
2
4
4
CНCl
2
F
2
C Н
Cl
2 4
CCl
4
Unpassivated reactor
1
1
1
27
53
69
0.008
0.023
0.041
–
–
–
1
1
1
1
1
47
64
29
71
32
0.105
0.047
0.337
0.024
0.439
0.038
0.006
0.013
n.f.
–
Unstabilized
0.880
0.046
0.807
0.059
Unstabilized
0.006
0.061
0.003
0.006
0.018
–
Stabilized
with 0.5 wt %
ethanol
1
1
80
38
0.128
0.005
0.009
n.f.
Stabilized
with 0.05 wt %
amylene
Stabilized
with 1 wt %
ethanol
1
58
0.011
0.012
–
1
53
0.255
Passivated reactor
0.064
0.006
1
1
70
83
0.037
0.095
0.015
0.032
–
–
1
1
33
65
0.005
0.002
0.009
n.f.
Unstabilized
0.034
0.003
1
49
0.009
0.012
–
1
52
Stabilized
with 0.5 wt %
ethanol
0.010
0.039
0.008
0.013
_
1
1
1
61 Stabilized with
0.021
0.069
0.166
0.089
0.096
0.090
0.003
0.005
0.004
176
142
0.008
0
.05 wt %
72
87
0.006
0.011
0.002
0.003
n.f.
n.f.
amylene
Stabilized
with 0.05 wt %
amylene
1
55
performed experiments both with an unstabilized
substance and with that stabilized with 1 wt % ethanol
or 0.05 wt % amylene. The experiment parameters and
rates of impurity formation under prescribed
conditions are listed in Table 2.
increase in the rate of impurity formation, compared
with the liquid-phase fluorination of trichloromethane,
in which the process occurs only by scheme (3). The
presence of an insignificant amount of difluorochloro-
methane in samples is in good agreement with the
hypothesis of a successive substitution of chlorine
atoms with fluorines. The experimental results in Table 2
demonstrate that the gas-phase fluorination of
trichloromethane is not affected by the absence or
presence of a stabilizer and its type. A probable reason
is that the stabilizer concentration in the gas phase is
very low.
It can be seen in Table 2 that reaction products
contain noticeable amounts of tetrachloroethane whose
appearance is impossible if trichloromethane is
fluorinated by the scheme described by Eq. (3). Based
on the results obtained, we suggested the following
chain fluorination mechanism including the stage of
heterogeneous chain initiation at active centers of the
reactor wall:
To confirm the suggested fluorination mechanism
of trichloromethane, we studied the influence exerted
by the geometric characteristics of the apparatus (its
surface area-to-volume ratio) and by a preliminary
treatment of the apparatus surface with fluorine
*
*
2
*
CHCl
3
+ M → CHCl
+ Cl + M,
F + N
Cl
(4)
(5)
(6)
(7)
*
2
2
CHCl
+ 2NF
3
→ 2CHCl
2
2
F
4
,
*
2
*
2
CHCl
+ CHCl
→ C
2
H
2
4
,
(
passivation). For this purpose, we performed a series
*
*
2
Cl + Cl → Cl .
of experiments in a reactor with the following
geometric parameters: inner diameter 20 mm; length
It is the occurrence of a heterogeneous chain
initiation that leads to a nearly an order-of-magnitude
3
160 mm; volume 50 cm ; and ratio between the surface
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 3 2011

INTERACTION OF TRICHLOROMETHANE AND TETRACHLOROMETHANE
425
2
3
area of the apparatus to its volume, 1.0 cm /cm
(
Table 4. Effect of temperature on the impurity formation
rate in the gas-phase fluorination of tetrachloromethane with
nitrogen trifluoride
2
3
5.7 cm /cm in the preceding series of experiments).
The first reactor is denoted in the text by symbol A,
and the second, B.
–1
Formation rate, vol % h
Т, °С
Table 3 lists the results of experiments on trichloro-
methane fluorination in an unpassivated reactor B and
upon passivation of the apparatus with fluorine.
3
CCl F
2 6
C Cl
1
1
27
48
0.002
0.008
0.056
0.155
0.958
n.f.
n.f.
Comparison of the experimental results in
Tables 2–4 suggests that the rate of impurity formation
in fluorination of trichloromethane in the gas phase is
the most strongly affected by processes occurring at
the apparatus surface. In the case of the unpassivated
reactor surface, the maximum impurity formation ate is
observed. For example, dichlorofluoromethane, the
main product of chloroform fluorination, is formed in
an unpassivated reactor at the same temperature in an
amount exceeding by nearly an order of magnitude that
in the reactor preliminarily treated with fluorine.
Moreover, a decrease in the specific surface area of the
apparatus also leads to a lower rate of the fluorination
reaction. All this confirms the validity of the above-
suggested mechanism of trichloromethane fluorination
by nitrogen trifluoride in the gas phase, which includes
the heterogeneous stage of chain initiation.
164
0.009
0.023
0.096
1
1
82
97
It can be seen that the gas-phase fluorination of
tetrachloromethane with trifluoride nitrogen occurs by
a similar mechanism, with the formation rates of the
main impurities, trichlorofluoromethane for tetrafluoro-
methane and dichlorofluoromethane for trichloro-
methane, nearly coincide under similar conditions in
the temperature range 120–180°C.
CONCLUSIONS
(
1) A study of the interaction of nitrogen trifluoride
with tetrachloromethane and trichloromethane demon-
strated that, at temperatures below 110°C and pres-
sures of up to 6 MPa, the reaction rate is such that
fluorination products can be found neither in the gas
phase, nor in the liquid phase at contact duration on the
order of 100 h.
To determine how pressure affects the rate of
impurity formation in the gas-phase process, we
carried out experiments by the above-described proce-
dure at pressures of 1.2 and 3.7 MPa. The results ob-
tained demonstrate that raising the pressure to 3.7 MPa
has no significant effect on the fluorination of tri-
chloromethane in the gas phase.
(
2) At temperatures higher than 110°C, the main
products formed in fluorination of trichloromethane
and tetrachloromethane are, respectively, fluorodi-
chloromethane and fluorotrichloromethane, with tetra-
fluorohydrazine and molecular chlorine formed as by-
products.
Interaction of tetrachloromethane with nitrogen
trifluoride in the gas phase. It was shown in the
experiments with trichloromethane that the rate of
impurity formation in the liquid phase is substantially
lower than that in the gas phase, Therefore, we
experimentally studied only the gas-phase fluorination
of tetrachloromethane by nitrogen trifluoride. The
experiments were carried out on the same installation
and by the same procedure as those in the case of
trichloromethane under atmospheric pressure in reactor
B. Because trichlorofluoromethane, dichlorofluoro-
methane, tetrafluorohydrazine, and chlorine must be
formed as products in fluorination of tetrachloro-
methane, the methods described above can be used for
analysis of these substances [11, 13]. We used
tetrachloromethane of pure grade (GOST 20288–74
(
3) The rate of trichloromethane fluorination in an
apparatus passivated with fluorine is an order of
magnitude lower that in an unpassivated equipment,
which is accounted for by the occurrence of the
reaction by the radical mechanism with heterogeneous
chain initiation on the metallic surface of the reactor.
(4) When industrially manufactured stabilizer-
containing chloroform interacts with nitrogen tri-
fluoride in the liquid phase, the process of a chemical
transformation of the stabilizer occurs in the first
place. Therefore, it can be recommended to use in the
industry trichloromethane stabilized with amylene,
whose amount can be minimized to 0.01 wt %.
[14]. Table 4 lists the results of experiments on tetra-
chloromethane fluorination in the gas phase.
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26
MUKHORTOV et al.
7. Ruff, O. and Keim, R., Anorg. Allgem. Chem., 1931,
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