OBTENTION INDUSTRIELLE DE COMPOSES HALOGENES

MANUFACTURE OF HALOGENATED COMPOUNDS

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
1,1,1,2-tetrafluoroethane is manufactured by
bringing trifluoroethylene into reaction with hydrogen
fluoride in the vapour phase at elevated temperature
in the presence of a chromium oxide or basic chromium
fluoride hydrofluorination catalyst.

Revendications

The embodiments of the invention in which an
exclusive property or privilege is claimed are defined
as follows:
1. A process for the manufacture of 1,1,1,2-
tetrafluoroethane which comprises bringing trifluoro-
ethylene into reaction with hydrogen fluoride in the
vapour phase at elevated temperature in the presence
of a chromium oxide or basic chromium fluoride hydro-
fluorination catalyst.
2. A process as claimed in Claim 1 in which the
hydrofluorination catalyst is chromium oxide.
3. A process as claimed in Claim 2 in which the
chromium oxide catalyst is one obtained by treating a
chromium hydroxide paste in an atmosphere comprising
from 10 to 100 percent by weight of steam at a
temperature in the range from 50°C to 180°C for at least
one hour and then calcining the product.
4. A process as claimed in Claim 1, 2 or 3
in which there is employed 1 to 2 moles hydrogen
fluoride per mole of trifluoroethylene.
5. A process as claimed in Claim 1, 2 or 3 in
which there is employed 1.4 moles to 1,8 moles hydrogen
fluoride per mole of trifluoroethylene.
6. A process as claimed in Claim 1, 2 or 3
in which the reaction temperature is in the range 200°C
to 500°C.

7. A process as claimed in Claim 1, 2 or 3 in
which the reaction temperature is in the range 300°C to
410°C.

Description

4 5
1. MD 29795
This invention relates to a process for the
manufacture of 1,1,1,2-tetrafluoroethane.
According to the present invention there is
provided a process for the manufacture of 1,1,1,2-
tetrafluoroethane which comprises bringing intoreaction in the vapour phase at eleva~ed
temperature trifluoroethylene with hydrogen fluoride
in the presence of a hydrofluorination catalyst.
The catalyst may be supported or unsupported.
One very suitable catalyst is chromium oxide. The
chromium o~ide catalyst may be activated by heating in
an atmosphere such as nitrogen or air. Again the
catalyst may comprise a basic chromium fluoride
in which chromium is associated with oxygen and
fluorine atoms. A particularly preferred catalyst
is a chromium;oxide obtained by treating a chromium
hydroxide paste with steam and calcined, suitably
in air,as is more~ fully described and claimed in
our UK Patent Specification 1 307 224. The catalyst
of said UK Patent Specification may be given a pre-
fluorination treatment~by passing hydrogen fluoride
over the catalyst at 250C to 450C for at least
30 minutes~ The catalysts may be compressed into~
pellets and used in a fixed bed. Alternatively the
catalyst of appropriate particle size may be used
~: .
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11~7~l~5
2. MD 2g795
in a fluidised bed. In use the chromium oxide
catalyst takes up variable amounts of fluorine and
can be present in the form Oe complex mixtures of
oxides oxyfluorides, hydroxy fluorides and fluorides
of chromium.
Suitably 1 to 2 moles of hydrogen ~luoride is
employed per mole of trifluoroethylene. Greater
molar ratios of hydrogen fluoride to trifluoro-
ethylene can be employed but too great a molar
ratio is undesired as this makes the process less
economic. It is preferred to employ a molar ratio
of hydrogen fluoride to tri1uoroethylene in the
range 1.4:1 to 1.8:1, for example 1.6:1.
Reaction temperatures are suitably in the range
200C to 500C, preferably 300C to 410C.
Contact times are in the range 1 to 15 seconds.
Atmospheric or superatmospheric pressures may be
employed.
In the present process particularly when operating
under preferred process conditions very high
conversions of trifluoroethylene to hydrofluorinated
product and highly selective yields to 1,1,1,2-
tetrafluoroethane are obtained. Conversions of up
to 100% of fluorinated organic compounds with
yields of greater than 9S% to 1,1,1,2-tetrafluoroethane
can in fact be obtained in the present procesq.
The desired 1,1,1,2-tetrafluoroethane can be
recovered using conventional techniques, for example,
by washing the exit gases with water and aqueous
sodium hydro;xide solution, drying and collecting
the desired product by condensation.

3. MD 29795
The trifluoroethylene starting material can be
obtained by various methods. Thus it may b0
obtained by the reaction of hydrogen with trifluoro-
chloroethylene in the vapour phase in the presence
of a hydrogenation catalyst such as platinum or
palladium. Another useful method is provided
by bringing hydrogen into reaction with 1,1,2-
trichloro 1,2,2-trifluoroethane in the presence of
a hydrogenation catalyst such as palladium.
The ollowing Examples illustrate the invention.
EXAMPLE 1
Into a tubular nickel reactor 90 cms long and
2.5 cms internal diameter were placed 170 grams
of a chromium oxide catalyst. The latter had been
prepared by steam treatment of a chromium hydroxide
paste at 95C for 18 hours and subsequently was
calcined at 340C for 11 hours as described in our
UK Patent Specification No 1307224. The catalyst was
then pretreated with hydrogen fluoride at 350C for
4 hours. The tubular reactor was heated by an
electric furnace.
~ Iydrogen fluoride and trifluoroethylene in two
different molar ratios were passed through the tube,
the catalyst bed being maintained at 350C. The
flow rates of organic material and hydrogen fluoride
were 185 cc/min and 130 cc/min, respectively, for Run
1, 370 cc/min and 260 cc/min, respectively for Run 2,
440 cc/min and 286 cc/min, respectively, through
half the catalytic bed length for Run 3.
The % v/v of organic materials in the exit gas
was determined by gas/liquid chromatography.
The reaction conditions and composition of the
product were as shown in Table I.

111',,'~.~5
4. MD 29795
TABLE I
Product Contact time ~ secs )
14 L7 ~3 .
Molar Ratio of HF: CF2=CFH
1.43:1 1.43:1 l.5~:~
...
CF3CH2F 97 . 8 97 . 5 97 . 5
:~ , _ .
CF4 1.0 0. 2 0.04
~,: . ~ . ._
C2F6 _ _ 0 . 04
~ .
2H2 0. 2 0. 3 0.04
~ ., __ .. __
C2F5H ~ 1 . 0 1 . 1 1 . 5
20 _
'~ U2 _ _ I o,j I ~.8
:'
~ .
:: .

5. MD 29795
EXAMPLE 2
The apparatus and procedure were broadly similar
to those of Example l. However the internal diameter
of the reactor was larger (.3.8 cms) and the reactor was
5 constructed of 'Monel' ('Monel' is a Trade Mark).
The amount of catalyst was 1 kg. The flow rates of
hydrogen fluoride and trifluoroethylene were 200 g hr l
and 125 1 hr l (gas) tri1uoroethylene, respectively.
The molar ratio o~ HF:CF2=CFH was 1.9:1. The contact
time was 4 seconds.
The exit gas was washed with water and aqueous
- alkaline hydroxide solution, passed through a catchpot
to collect water droplets, dried; the product was
collected by condensation and was distilled.
The conversion to CF3CH2F was > 95%. The product
contained only 0.5% of fluorinated methanes and
fluorinated ethane.
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