A study of trichloroethylene hydrofluorination using a kinetic model

Article abstract of DOI:10.1023/A:1020310629164

The kinetic features of catalytic hydrofluorination of trichloroethylene and 2-chloro-1,1,1-trifluoroethane on chromium fluoride/magnesium fluoride catalyst were studied. The effect of pressure and addition of various components of the reaction mixture at the reactor inlet was studied using the developed model.

Full text of DOI:10.1023/A:1020310629164

Russian Journal of Applied Chemistry, Vol. 75, No. 5, 2002, pp. 771 776. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 5,
002, pp. 789 794.
Original Russian Text Copyright
2
2002 by Dmitriev, Trukshin, Smykalov.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
A Study of Trichloroethylene Hydrofluorination
1
Using a Kinetic Model
A. V. Dmitriev, I. G. Trukshin, and P. Yu. Smykalov
Prikladnaya Khimiya Russian Scientific Center, St. Petersburg, Russia
Received January 17, 2002
Abstract The kinetic features of catalytic hydrofluorination of trichloroethylene and 2-chloro-1,1,1-trifluo-
roethane on chromium fluoride/magnesium fluoride catalyst were studied. The effect of pressure and addition
of various components of the reaction mixture at the reactor inlet was studied using the developed model.
The procedure of production of 1,1,1,2-tetrafluoro-
ethane by gas-phase catalytic hydrofluorination of
trichloroethylene is well known in the world practice
and is commercially used by various companies.
There are many patents related to this procedure of
tetrafluoroethane production [1 3] and to the catalyst
production [4, 5]. In gas-phase fluorination processes,
chromium(III) compounds in the form of fluorides and
oxofluorides are mainly used.
fed into the reactor through nickel capillaries. The
flow rate of these reagents was set using the calibrat-
ing plot of the flow rate vs. the pressure in the service
vessels, which, in turn, was produced by their tempera-
ture control. Trichloroethylene was fed into the reactor
with a dosing pump. The flows of the initial reagents
were mixed and fed into a coil-type evaporator
equipped with electrical heating, and then into the
reactor. After washing with water, neutralization,
and drying, the reaction mixture was collected in
a glass condenser cooled with a mixture of dry ice and
CCl /CHCl .
At the same time, there are no published data on
the kinetics and mechanism of hydrofluorination of
trichloroethylene, which are necessary to design the
reaction unit.
4
3
The reaction mixture was analyzed on a Tsvet-
00M chromatograph equipped with a heat conductiv-
5
The goal of this work was to study experimentally
this process on the chromium fluoride/magnesium
fluoride catalyst and, based on the developed kinetic
model, to study the effect of pressure and addition of
various components of the reaction mixture (hydrogen
chloride, 1,1-difluoroethylene, 1,1,1-trifluoroethane,
and pentafluoroethane) at the reactor inlet.
ity detector. The 2-m chromatographic column was
packed with ASK silica gel impregnated with liquid
paraffin (10%).
The products were identified by gas chromatogra-
phy mass spectrometry on a Hewlett Packard device
equipped with an Al O /KCl capillary column (l =
2
3
5
0 m).
To determine the kinetic parameters, the experi-
EXPERIMENTAL
ments were performed in the reactor with a fluidized
bed of the chromium fluoride/magnesium fluoride
catalyst.2
The study was carried out on a continuous installa-
tion consisting of a nickel reactor with electrical heat-
ing, units for dosing the initial reagents, and a system
for collection and analysis of the synthesis products.
The initial 2-chloro-1,1,1-trifluoroethane and tri-
chloroethylene were purified by fractional distillation.
3
The total capacity of the reactor was 1000 cm ; the
When developing the kinetic model, the following
assumptions were made: the process is kinetically
controlled; the catalyst activity is constant in time;
inner diameter was 36 mm. The reactor temperature
was monitored by a multizone thermocouple. Hydro-
gen fluoride and 2-chloro-1,1,1-trifluoroethane were
2
This catalyst (chromium fluoride applied to magnesium fluor-
1
Reported at the Third International Conference Chemistry,
Technology, and Application of Fluorine Compounds,
St. Petersburg, June 6 9, 2001.
ide) is produced by the pilot plant of the Prikladnaya Khimiya
Russian Scientific Center and is used in various hydrofluori-
nation processes.
1
070-4272/02/7505-0771$27.00 2002 MAIK Nauka/Interperiodica

772
DMITRIEV et al.
the catalyst can operate as a fluorine transfer agent;
thermal decomposition of synthesis products is insig-
nificant [6]; in the course of synthesis, products of
asymmetric structure are mainly formed; only one
chlorine-containing organic compounds.
With these assumptions, the process scheme can be
presented as a series of successive stages considering
the processes related to production of 2-chloro-1,1,1-
trifluoroethane from trichloroethylene and subsequent
fluorination to 1,1,1,2-tetrafluoroethane:
fluorine atom in CrF participates in exchange with
3
chlorine atom; and the reaction of CrF with HCl is
3
significantly faster than the reaction of CrF with
3
CFClCClH
CF CClH
2
CCl CClH
CFCl2 CClH2
CF Cl CClH2
CF3 CClH2
CF3 CFH2
2
2
CF3 CF H
CF3 CFClH
CF3 CCl H CF3 CH3
2
2
CF CClH2 + =Cr F
CF CFH + =Cr Cl
CF Cl CClH2 + =Cr Cl
CFCl CClH2 + =Cr F
2
3
3
2
2
{
k /k },
(1)
{k /k 12},
(12)
1
1
12
CFCl CClH2 + =Cr Cl
CCl CClH2 + =Cr F
=
Cr Cl + HF
=Cr F + HCl
{k /k }, (2)
2
3
2
2
{
k /k 13},
(13)
1
3
=
Cr F + 2CF CClH
[=Cr F 2CF CClH ]
3 2
3
2
CCl CClH2 + =Cr F
[CCl CClH2 =Cr F]
{
k /k },
(3)
3
3
3
3
{
k /k 14},
(14)
1
4
[
=Cr F 2CF CClH ] CF CH + CF CCl H + =Cr F
3
2
3
3
3
2
[
CCl CClH2 =Cr F]
3
CCl =CClH + HCl + =Cr F
2
{
k /k },
(4)
(5)
(6)
(7)
4
4
{k /k 15},
(15)
1
5
CF CCl H + =Cr F
CF CFClH + =Cr Cl
3
3
2
CCl =CClH + HF + =Cr F
[CCl =CClH HF =Cr F]
2
2
{k /k },
5 5
{k /k 16},
(16)
1
6
CF CFClH + =Cr F
CF CF H + =Cr Cl
3 2
3
[
CCl =CClH HF =Cr F]
2
CFCl CClH2 + =Cr F
2
{k /k },
6 6
{k /k 17},
(17)
1
7
CF CClH2 + =Cr Cl
CF Cl CClH + =Cr F
2 2
3
CFCl CClH2 + =Cr F
[CFCl CClH2 =Cr F]
2
2
{k /k },
7 7
{k /k 18},
(18)
1
8
CF Cl CClH2 + =Cr F
[=Cr F CF Cl CClH ]
2 2
2
[
CFCl CClH2 =Cr F]
CFCl=CClH + HCl + =Cr F
2
{
k /k },
(8)
8
8
{
k /k 19},
(19)
1
9
[
=Cr F CF Cl CClH ]
CF =CClH + HCl + =Cr F
2
2
2
CFCl=CClH + HF + =Cr F
[CFCl=CClH HF =Cr F]
(20)
{k /k },
(9)
9
9
{
k /k 20},
2
0
CF =CClH + HF + =Cr F
[CF =CClH HF =Cr F]
2
2
[
CFCl=CClH HF =Cr F]
k /k 21}.
CF Cl CClH + =Cr F
2
2
{
k /k 10},
(10)
1
0
{
(21)
2
1
[
CF =CClH HF =Cr F]
CF CClH + =Cr F
2
3
2
Based on the developed scheme of this catalytic
process, using the methods of pathways for com-
{
k /k 11},
(11)
1
1
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 5 2002

A STUDY OF TRICHLOROETHYLENE HYDROFLUORINATION
773
plicated reactions [7], we derived a kinetic model
considering the stages of formation of 2-chloro-1,1,1-
trifluoroethane and 1,1,1,2-tetrafluoroethane. In so
doing, each reaction was considered as a multistage
process [8]. The developed model describes variation
of the concentrations of HF, HCl, CF CClH , CF
Table 1. Rate constants and activation energies of the
process stages
Rate
constant
E,
Rate
E,
lnki
lnki
kcal mol 1 constant
kcal mol
1
3
2
3
3
2
k
k1
k 1
k5
k 5
k6
k 6
k7
k 7
43
50
k
kn
k
k
k 9
k50
k 12
k12
k18
0
0
8.5
CFH , CF CH , CF CCl H, CF CFClH, CF
2
3
2
3
3
2
3
2
11.7
15.6
30.5
36.9
11
22.7
43.5
20.5
17
18.3
12.2
33.7
32.3
15
20
50
20
20
CF H, CF Cl CClH , C HCl , CF =CClH, CFCl
2
2
2
3
5
35
20
45
77.6
2.1
34.9
49.6
38.8
CClH , and CFCl=CClH:
t
3
2
26.2
23.7
29.5
82.8
0.8
38.7
58.7
46.7
dc1
=
k 7c8 k c c
k c + k c c + k c c
10 2 10
7 1 11
1 1
1 3 11
d
2
2
k c
2k c + 2k c + 2k c c ,
3 1 n 1 t 4 11
5
0 1
k8
k10
k16
k 19
k20
dc3
=
k c
k c c ,
1 3 11
1
1
12.2
33.8
10
29.9
d
dc4
2
2
=
k c
k c
k c c ,
t 4 11
3
1
n 1
c11 = c + (c 01 c ) + 2(c0 c ) + (c0 c6) + 2(c c )
0
0
d
11
1
5
5
6
8
8
+ 3(c0 c ) + (c0 c ) + 3(c0 c ) + 2(c0 c ),
dc5
9
9
10
10
12
12
13
13
2
2
=
k c
k c
k c c
k c + k c c ,
5 5 5 6 11
3
1
n 1
t 4 11
d
where c is the concentration of CF CClH (Freon
1
3
2
1
33a), c is that of HF, c is that of CF CFH
dc6
2 3 3 2
(Freon 134a), c is that of CF CH (Freon 143a),
c is that of CF CCl H (Freon 123a), c is that of
CF CFClH (Freon 124a), c is that of CF CF H
(Freon 125), c is that of CF Cl CClH (Freon 132a),
c is that of C HCl (trichloroethylene), c is that
of CF =CClH (1,1-difluorochloroethylene), c is that
of HCl, c is that of CFCl CClH (Freon 131),
=
k c
k c c
k c + k c c ,
6 6 6 7 11
5
5
5 6 11
4 3 3
d
5
3
2
6
dc7
3
7
3
2
=
k c
k c c ,
6
6
6 7 11
8 2 2
d
9
2
3
10
11
2
dc8
=
k 1 c c
k c c
k c + k c c
0.5k c
8 8
12
2
2
2 2 12
12 8 11
7 8
7 1 11
d
c13 is that of CFCl=CClH (1-fluoro-1,2-dichloroethyl-
ene); and k are the kinetic constants:
+
0.5k c c + k c c ,
i
9
10 11
20 2 13
k14 k13 k12
k 14 k14 k 15
k 3 k3
dc9
=
k c c + k c c + k c c ,
k = 2
, k =
, k =
,
1
6 2 9
8 11
9 11
n
d
k 13 k 14
k 15 k 13
k 3 + k4
dc10
k 3 k 4
k 1 k10
=
0.5k8c8
0.5k c c
k c c + k c ,
kt =
, k50
=
,
9 10 11
10 2 10
50 1
d
k 3 + k4
k10 + k11
dc12
k = k [=Cr F]; [=Cr F]
const.
i
i
=
k c c
k
c c + k c c
0.5k c
18 12
1
6 2 9
12 2 12
12 8 11
d
The constants were determined by regression analy-
sis. The functional to be minimized was the weighted
sum of squared deviations of the experimental and cal-
culated concentrations. As a procedure of numerical
integration, we used the LSODA method designated
for solving rigid systems of differential equations [9].
The functional was minimized by the Gauss Newton
method.
+
0.5k 1 c c ,
9 11 13
dc13
=
0.5k c
0.5k c c
k c c ,
20 2 13
1
8 12
19 11 13
d
c = c0 3(c1 c ) 4(c3 c ) 3(c4 c ) 3(c5 c )
0
0
0
0
2
2
1
3
4
5
0
0
0
0
4
(c6 c ) 5(c7 c ) 2(c8 c ) 2(c10 c )
6 7 8 10
The kinetic constants obtained are listed in Table 1.
The developed kinetic model is adequate in the
0
0
(
c12
c )
(c13
c ),
13
12
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 5 2002

774
DMITRIEV et al.
Table 2. Hydrofluorination of 2-chloro-1,1,1-trifluoroethane and trichloroethylene. Residence time 10 s
Concentration at reactor inlet, M
Concentration at reactor outlet,
M
initial reactants
component added
2
-Chloro-1,1,1-trifluoroethane*
0
0
3
4
c = 0.003733, c = 0.01493
c = 0.75 10 , c = 0.3 10 ,
3 4
1
2
5
5
c = 0.53 10 , c = 0.75 10
7
10
0
0
0
4
4
c = 0.47 10 4
c4 = 0.63 10 4
c = 0.003733, c = 0.01493 CF CH :
c = 0.3 10
1
2
3
3
4
4
0
c = 0.6 10
4
0
0
0
5
c = 0.63 10 5
c7 = 0.82 10 5
c10 = 0.75 10 5
c = 0.003733, c = 0.01493 CF CF H: c = 0.53 10
1
2
3
2
7
7
0
5
c = 1.6 10
7
c = 0.003733, c = 0.01493 CF = CClH: c = 0.1 10 4
0
0
0
1
2
2
10
0
= 0.8 10 4
= 0.7 10 5
= 0.7 10 4
= 0.7 10 3
c10 = 0.1 10 4
c10 = 0.7 10 5
c10 = 0.7 10 5
c10 = 0.7 10 5
c
c
c
c
1
0
0
0
0
c = 0.003733, c = 0.01493 HCl:
1
2
11
0
1
0
1
1
1
c3 = 0.5 10 3
Trichloroethylene**
0
0
c = 0.35 10 , c = 0.45 10 13,
9
c = 0.01991, c = 0.005856
2
9
4
7
c10 = 0.3 10 4
c4 = 0.45 10 5
c = 0.87 10 5
0
0
0
5
c = 0.01991, c = 0.005856 CF CH :
c = 1 10
2
0
9
0
3
3
4
0
5
c = 0.01991, c = 0.005856 CF CF H: c = 1 10
2
0
9
0
3
2
7
0
7
c = 0.01991, c = 0.005856 CF = CClH: c = 0.3 10 4
c10 = 0.42 10 4
2
9
2
10
*
Molar ratio HF : CF CClH = 4 : 1, 380 C
3 2
*
* Molar ratio HF : C HCl = 3.4 : 1, 200 C.
2 3
following intervals of the process parameters: tem-
perature 175 420 C; molar ratio of reactants
of the process parameters on the main reaction
stages. The influence of pressure was studied under
the following conditions: molar ratio of reactants
HF : C HCl = 3.4 : 1, 200 C (first stage); HF : Fre-
HF : C H ClF = (2 18) : 1 and HF : C HCl = (3.4
2
2
3
2
3
1
3.6) : 1.
2
3
on 133a = 4 : 1, 380 C (second stage); and contact
time = 10 s. The course of the process was analyzed
at a pressure of 1, 3, 6, and 10 atm. The results of
evaluation (Figs. 1, 2) show the following.
Using this kinetic model, we studied the influence
3
7
,
, %; c1 10 , c
10 , M
2
(1) In the stage of trichloroethylene hydrofluorina-
tion with hydrogen fluoride to Freon 133a, conversion
of trichloroethylene increases (to 95 97%) with in-
creasing pressure to 6 atm, the selectivity with respect
to Freon 133a increases up to a pressure of 3 atm and
then becomes practically constant (approximately
9
0%); the concentration of Freon 134a increases up to
p, atm
a pressure of approximately 6 atm and then increases
insignificantly, but the yield of by-products increases.
Thus, increase of the pressure above 6 atm is not
appropriate.
Fig. 1. Hydrofluorination of trichloroethylene: (1) conver-
sion of trichloroethylene , (2) concentration of 2-chloro-
,1,1-trifluoroethane c 10 , (3) selectivity with respect to
-chloro-1,1,1-trifluoroethane , and (4) concentration of
3
1
2
1
1
7
,1,1,2-tetrafluoroethane c 10 ; (p) pressure.
(2) In the stage of hydrofluorination of Freon 133a
2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 5 2002

A STUDY OF TRICHLOROETHYLENE HYDROFLUORINATION
Table 3. Hydrofluorination of 2-chloro-1,1,1-trifluoroethane*
775
Mixture composition, %
at reactor inlet (without HF) at reactor outlet (without HF and HCl)
CF CClH 97.02, others 2.98 CF CClH2 71.45, CF CFH2 23.24,
Run
no.
Component
added
1
2
3
4
5
6
7
8
3
2
3
3
CF CF H 2.38, CF CH 1.86, others 1.08
3
2
3
3
CF CF H
CF CClH 92.79, CF CFH2 0.46,
CF CClH2 69.98, CF CFH2 22.29,
CF CF H 5.06, CF CH 1.82, others 0.85
3 2 3 3
3
2
3
2
3
3 3
CF CF H 3.88, others 2.87
3
2
CF CF H
CF CClH 85.79, CF CFH2 0.24,
CF CClH2 64.89, CF CFH2 23.99,
3
2
3
2
3
3 3
CF CF H 12.43, CF CH 0.04, others 1.5 CF CF H 7.82, CF CH 2.11, others 1.19
3
2
3
3
3
2
3
3
CF CClH 99.69, CF CH3 0.12,
others 0.19
CF CClH2 62.96, CF CH3 3.56,
CF CFH 30.48, CF CF H 2.08, others 0.92
3 2 3 2
3
2
3
3 3
CF CH3
CF CClH 99.0, CF CH3 0.68,
others 0.32
CF CClH2 64.23, CF CH3 3.58,
CF CFH 28.98, CF CF H 2.44, others 0.77
3 2 3 2
3
3
2
3
3 3
CF CH3
CF CClH 92.49, CF CH3 7.14,
others 0.37
CF CClH2 60.58, CF CH3 8.48,
CF CFH 27.08, CF CF H 2.73, others 1.13
3 2 3 2
3
3
2
3
3 3
CF CClH
100
CF CClH2 82.39, CF CFH2 16.93,
3
2
3 3
CF =CClH 0.15, others 1.13
2
Mixture of
CF CClH 71.45, CF CFH2 25.41,
CF CClH2 56.66, CF CFH2 41.12,
3
2
3
3 3
CF CFH2 and
CF = CClH 1.56, others 1.58
CF =CClH 0.10, others 2.12
2
3
2
CF = CClH
2
*
Reactor with fixed catalyst bed, V = 0.25 l (run nos. 1 3) and with fluidized catalyst bed, V = 0.4 l (run nos. 4 8); molar ratio
HF : CF CClH = 8.3 : 1 (run nos. 1 3), 10 : 1 (run nos. 4 6), 19.6 : 1 (run nos. 7 and 8); temperature 400 (run nos. 1 3), 420
3
2
(
run nos. 4 6), and 380 C (run nos. 7 and 8); residence time 4.8 (run nos. 1 3), 6.1 (run nos. 4 6), and 4.3 s (run nos. 7 and 8;
with addition of a mixture of CF CFH and CF =CClH, 3 s).
3
2
2
with hydrogen fluoride, an increase in the pressure
results in decreased conversion of Freon 133a; in this
case, the conversion is decreased to the greatest extent
in the pressure range from 1 to 3 atm (from 22.3 to
CONCLUSIONS
(1) Study of the process of 1,1,1,2-tetrafluoro-
ethane production using the developed kinetic model
describing the process in the temperature range 175
420 C at a molar ratio of reagents HF : C H ClF =
15.8%). At a higher pressure, the conversion becomes
practically constant (14.6 14.9%). Thus, elevated
pressure has a detrimental effect on this stage.
2
2
3
(2 18) : 1, HF : C HCl = (3.4 13.6) : 1 showed that
2
3
an increase in pressure to 6 atm has a positive effect
on the conversion and selectivity in hydrofluorination
Calculated data on the effect of adding various
components of the reaction mixture at the reactor inlet
are listed in Table 2.
, , %
Our results show that addition of 2-chloro-1,1-di-
fluoroethylene decreases the degree of its formation in
the course of synthesis, i.e., in the process a mixture
of Freon 134a and 2-chloro-1,1-difluoroethylene can
be supplied to the reactor inlet for subsequent re-
covery. In a similar manner, addition of Freons 125
and 143a into the initial mixture decreases the degree
of their formation in the course of synthesis. How-
ever, the presence of hydrogen chloride in the initial
mixture in the stage of formation of Freon 134a from
Freon 133a decreases the yield of Freon 134a. The
results of the experiments confirmed the validity of
evaluation of the influence of the process parameters
p, atm
Fig. 2. Hydrofluorination of 2-chloro-1,1,1-trifluoroethane:
1) conversion of 2-chloro-1,1,1-trifluoroethane
2) selectivity with respect to 1,1,1,2-tetrafluoroethane
(
(
and
;
(Table 3).
(p) pressure.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 5 2002

7
76
DMITRIEV et al.
4. US Patent 51555082.
of trichloroethylene. However, in hydrofluorinaton of
-chloro-1,1,1-trifluoroethane, an increase in pressure
to 3 atm adversely affects the process.
2
5
6
. WO Patent 9810862.
. Dmitriev, A.V., Trukshin, I.G., and Vishnyakov, V.M.,
Abstracts of Papers, 3-ya Mezhdunarodnaya konferen-
tsiya Khimiya, tekhnologiya i primenenie ftorsoedine-
nii (Third Int. Conf. Chemistry, Technology, and
Application of Fluorine Compounds ), St. Petersburg:
Teza, 2001.
(
2) A partial return of by-products (pentafluoro-
ethane, 1,1,1-trifluoroethane, and 2-chloro-1,1-di-
fluoroethylene) to synthesis decreases their formation
in the synthesis.
(
3) Owing to reversibility of 2-chloro-1,1,1-triflu-
7
8
. Bezdenezhnykh, A.A., Inzhenernye metody sostavle-
niya uravnenii skorostei reaktsii i rascheta kinetiche-
skikh konstant (Engineering Approach to Setting up of
Equations for the Reaction Rates and Evaluating Kinet-
ic Constants), Leningrad: Khimiya, 1973.
oroethane hydrofluorination, the presence of hydrogen
chloride in the initial reaction mixture adversely af-
fects the process of 1,1,1,2-tetrafluoroethane produc-
tion. Removal of hydrogen chloride from the reaction
area is favorable for increasing the yield of the target
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. Trukshin, I.G., Smykalov, P.Yu., Goncharov, E.P.,
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RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 5 2002