Note: Descriptions are shown in the official language in which they were submitted.
1~87213
This invention relates to a process for the production
of l,l-difluoroethylene in which acetylene is used as starting
material and in which no intermediate products are isolated.
It is known that l,l-difluoroethylene is produced in
three stages. In a first stage, l,l-difluoroethane is obtained by
the hydrofluorination of acetylene. The purified l,l-difluoro-`
ethane is then chlorinated. l,l-Difluoro-l-chloroethane is isolat-
ed from the chlorination products and, in a third stage, hydrogen
chloride is thermally libera-ted from the l,l-difluoro-chloroethane
thus isolated to form l,l-difluoroethylene.
It is already known that acetylene can be hydrofluorinat-
ed in the presence of a catalyst consisting of a pelletised mix-
ture of aluminium fluoride and bismuth flurinde. At most 97% of
the acetylene can be reacted by means of this catalyst. The reac-
tion products contain from 70 to 72 % by weight of l,l-difluoro-
ethane and from 25 to 27 % by weight of vinyl fluorine. Before
any product present in it can be further processed, a mixture such
as this has to be worked up by distillation before the l,l-difluoro-
ethane which it contains is used for further reactions.
Another catalyst which has already been proposed for the
hydrofluorination of acetylene into l,l-difluoroethane is a cata-
lyst containing aluminium fluorine which is produced by impregant-
ing r- or ~ -aluminium oxide with a bismuth and manganese salt so-
lution, predrying the aluminium oxide impregnated with the salts
at temperatures of up to 100C and then heating it at temperatures
between 150 and 250C first in a nitrogen atmosphere and then in
air with increasing concentrations of hydrogen fluoride up to a
100 % hydrogen fluoridc atmosphcre, The production of a catalyst
such as this is described, for example, in DT-OS No. 2,000,200.
The reaction product obtained by hydrofluorination with a catalyst
such as this may contain up to 2 % of acetylene and at most about
; 4.5 % of vinyl fluoride. Accordingly, both secondary products have
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hitherto always been separated oEf before further processing of the
difluoroethane.
The further processing of a purified l,l-difluoroethane
into l,l-difluoroethylene by a one-stage process is already describ-
ed in Applicant's Canadian application No. 279,856 of June 3, 1977.
In the process described in that application, l,l-difluoroethane is
photochlorinated to form l,l-difluoro-l-chloroethane and immediate-
ly afterwards the reaction products obtained are heated to tempera-
tures of from 550 to 750C without isolating the l,l-difluoro-l-
chloroethane.
Further development of this process has now shown thatan impure reaction product from the catalytic hydrofluorination of
acetylene which contains up to 3 % by volume of acetylene and at
most 8.0 % by volume of vinyl fluoride may be used as starting
product for this process.
Despite the presence of impurities, namely actylene and
vinyl fluoride, in the starting product, yields of l,l-difluoro-
ethylene amounting to more than 90 %, based on the acetylene used,
are obtained where this process is applied. Accordingly, the se-
condary products present,particularly the unreacted acetylene, havehardly an~ effect upon the reaction as a whole. This is surpris-
ing insofar as it was not known that gas mixtures containing ace-
tylene could be photochlorinated without difficulty.
Another advantage of the process according to the in-
vention over knwon processes in which the intermediate products are
isolated is that plant costs can be considerably reduced. Thus,
there is no need in the process according to the invention for the
distillation apparatus and storage and transport containers which,
in conventional processes, have to be used in a large-scale indus-
trial plant.
In the first stage of the process, acet~ulene is hydro-
fluorinated in the presence of a hydrofluorination catalyst. One
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catalyst which has proved to be particularly suitable is a catalyst
produced by impregnating Y- or ~ -aluminium oxide with a solution of
bismuth salts, optionally together with manganese saLts, followed
by heating to temperatures of from 150 to 250C, first in a nitro-
gen atmosphere and then, after complete drying, with a mixture of
air and increasing concentrations of hydrogen fluoride up to a
100 % hydrogen fluoride atmosphere.
When the aluminium oxide is only impregnated with a bis-
muth salt solution, the final catalyst contains from 0.1 to 20 %
by weight of bismuth, from 35 to 66 % by weight of fluorine, from
24 to 42 % by weight of aluminium, the rest consisting primarily
of oxygen. When a manganese salt solution is additionally used for
impregnation, the final catalyst additionally contains from 0.1 to
10 % of manganese, whilst its aluminium content decreases to be-
tween 20 and 38 % by weight and its fluorine content to between 32
and 60 % by weight.
The catalyst is produced advantageously as follows:
~ - or ~ -aluminium oxide, which has preferably been
heated in vacuo (below 1 Torr) for about 1 hour at 80C, is im-
pregnated with an aqueous solution of a bismuth and a manganesesalt. Suitable bismuth salts are water-soluble or acid-soluble
bismuth salts, of which the solution is optionally stabilised by
a complex former. In the case of substantially insoluble bismuth
and also manganese salts, these complex formers enable a homogeneous
solution of these salts to be obtained. Suitable complex formers
are, for example, hydroxyl-group-containing organic compounds from
thc yroup comprising suyar alcohols, such as for example marlnitol,
~ SOl bi~ol or ribi~ol, or hydroxy acids, such as ror exarllple ~ar~aric
! acid, lactic acid, or the sugar acids. Other suitable complex for-
mers are amines and nitriles such as, for example, ethylene diamine,
nitrilotriacetic acid or succinodinitrile.
A homogeneous solution can also be obtained by adjusting
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a suitable acid pH-value.
Suitable bismuth salts are water-soluble or acid-soluble
bismuth salts, of which the solution is optionally stabilised by
the above-mentioned complex former.
It is prefereed to used the bismuth or bismuthoxy salts
of nitric acid, sulphuric acid, hydrochloric acid or perchloric
acid.
The concentration of the bismuth salt solution is not
critical to the process and is selected according to the required
bismuth content of the catalyst.
The manganese compound used is preferably the salt with
the same anion as the bismuth salt used. However, it is also pos-
sible to use any other water-soluble or acid-soluble manganese salt,
providing it does not form an insoluble deposit with the bismuth
salt used under the conditions specified.
It is preferred to use the manganese(II) and bismuth or
bismuthosy salts of nitric acid, sulphuric acid, hydrochloric acid
or perchloric acid.
The concentration of the manganese salt solution is also
not critical to the process and is selected according to the requir-
ed metal content of t~ catalyst.
The aluminium oxide impregnated with the bismuth or
bismuth/manganese salt solution is then dried at temperatures of
up to 100C and subsequently heated in a nitrogen atmosphere to be-
tween 150 and 250C. After complete drying of the catalyst, the
nitrogen is replaced by air and increasing concentrations of hydro-
gen fluoride. The exothermic reaction which then begins is also
carricd out at tomperatures of from 150 to 250~C. Towards the end
of the exothermic reaction, the reaction mixture is heated in a
100 % hydrogen fluoride atmosphere until the exothermic reaction has
abated.
To carry out the hydrofluorination reaction, acetylene
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is mixed with the above-mentioned excess of hydrogen fluoride and
the resulting mixture is preheated to the necessary reaction tempe-
rature. The preheated mixture is passed over the catalyst which is
kept at a constant temperature of from 150 to 350C. The catalyst
may be arranged both in the form of a fixed bed and also in the
form of a fluidised bed.
After passage over the catalyst, the gas mixture is
washed in known manner, partially dried and then directly subjected
to photochlorination without separating off the impurities. How-
ever, it is also possible temporarily to store this gas mixture in
a gasometer and then directly to subject it to photochlorination.
Where this process is applied, yields of from 96 to 98 %
of the required l,l-difluoroethane are obtained, the conversion of
acetylene being almost complete. This high conversion of acetylene
is also obtained with a residence time of only from 5 to 30 seconds.
The preferred residence time is from 5 to 45 seconds.
The preferred temperature range is from 200 to 280C.
The higher the temperature selected, the shorter the residence time
can be for substantially the same conversions and yields.
In c~ntrast to other processes, hydrofluorination of
the acetylene does not have to be carried out with an excess of
hydrofluoric acid over the stoichiometrically necessary quantity
of 2 moles of HF per mole of acetylene. It takes place substantial-
ly quantitatively even with a stoichiometric ratio between the
reactants. It is advisable to use an approximately 5 % excess of
hydrofluoric acid. In principle, it is also possible to use an
excess of hydro~luoric acid of up to 50 %.
However, the difluoroethane may also be produced by
hydrofluorinating acetylene in the presence of another catalyst,
~, 30 resulting in the formation of a gas mixture which contains no more
than 3 % by volume and preferably no more than 2 % by volume of
acetylene. The vinyl fluoride content of the mix-ture may amount `
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1~87Z13
to 8 % by volume, although it preferably amounts to 7 % by volume.
In these cases, too, the gas mixture formed during the hydrofluori-
nation reaction may be directly subjected to the chlorination reac-
tion without separating off the acetylene or other reaction pro-
ducts. In order to obtain particularly high conversions and yields,
it is advisable to arrange one behind the other two identical reac-
tors filled with the same catalyst, the second reactor having a
temperature approximately 20 to 50C lower than the first reactor.
In this way, the gas mixture issuing from the first reactor after
almost complete conversion - afterpassing through the second reac-
tor by far the predominant secondary product, vinyl fluoride, is
also largely converted into difluoroethane by reaction ~ith the
¦ excess hydrogen fluride present.
The gas mixture which may be used for photochlorination
in accordance with Canadian application No. 279,856 may contain
the most important secondary products, acetylene and vinyl fluride,
~ formed during the catalytic hydrofluorination of acetylene in
5: quantities of up to 3 % by volume and 8 % by volume (vinyl fluoride).
The preferred upper limit to the vinyl fluoride content is 7 % by
volume. Other secondary products which are formed in the catalytic
hydrofluorination of acetylene may also be present in srnall quanti-
ties in the gas mixture to be chlorinated.
~ The chlorination of the mixture of l,l-difluoroethane,
i~ acetylene and vinyl fluoride is carried out in known manner. It is
~; preferably carried out in the presence of light. The wavelength
of the light rays may lie both in the visible region and also in
the W region. The preferred region is from 500 to 600 nm.
The molar ratio between the hydrofluorination product
and chlorine during the chlorination reaction should be 1:1. A
~` slight excess of chlorine is possible. If possible, however, the
molar ratio in question should not exceed 1:1.2.
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The chlorination reaction is carried out at ternperatures
of from 0 to 150C. The preferred temperature range is from 20 to
70C. The residence time in the chlorination reactor, which prefer-
ably consists of glass, should as far as possible am~unt to between
20 and 100 seconds, based on a temperature of 0C and an empty
reactor.
Immediately after chlorinakion, the chlorination products
are subjected to dehydrochlorination by pyrolysis. They consists
predominantly of l,l-difluoro-l-chloroethane and hydrogen chloride,
together with small quantities of more highly chlorinated fluoro-
chloroethanes and unreacted difluoroethane. The proportion of
higher boiling secondary products generally amounts to between 2
and 4 % by volume.
Dehydrochlorination takes place at temperatures of from
500 to 750C. The effect of the reaction products formed during
chlorination of the l,l-difluoroethane (primarily the hydrogen
chloride liberated) is that pyrolysis of the l,l-difluoro-l-chloro-
ethane gives the required l,l-difluoroethylene in a yield of almost
100 %. These high yields are obtained in particular when the de-
hydrochlorination reactor is filled with a material of hifh thermal
conductivity such as, for example, metal chips which are not affect-
ed under the reaction conditions, for example nickel chips. The
preferred pyrolysis temperature is in the range from 650 to 720C.
The residence time in the pyrolysis reactor should
amount to between 1 and 150 seconds, based on an empty reactor and
' a temperature of 0C. The preferred range is from 2.5 to 90 seconds.
The reactor must consist of a material which is not
affected under the reaction conditions. Nickel reactors in the ;~
form of tube reactors are particularly suitable.
In general, the dehydrochlorination step is carried out
under atmospheric pressure or under the pressure which is sponta-
, neously adjusted during the reaction. This pressure is generally
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no higher than about 1.1 atmosphere. In principle, however, it is
also possible to work under higher pressures.
The process according to the invention is preferably
carried out continuously. To this end, the hydrof~orinabon reac-
tor, the chlorination reactor and the dehydrochlorinatDn reactor
are arranged immediately one behind the other in than order. A
washing stage using water is best provided between the hydrofluo-
rination reactor and the chlorination reactor in order to reMove
excess hydrogen fluoride. After leaving the last reactor, the reac-
tion products are washed wi-th water and/or dilute alkali hydroxyde
solution and subsequently dried. The gas mixture obtained then
mainly contains as impurities more highly chlorinated products which
can readily be separated off from the l,l-difluoroethylene in known
manner. The yields. of l,l-difluoroethylene then amount to more
than 90 %, based on the acetylene used.
The invention will now be illustrated with reference to
the following non-restrictive examples.
EXAMPLE 1
To produce the catalyst, 700 g of r-aluminium oxide in
the form of 3 mm diameter pellets are evacuated for 1 hour at 80C
to ~1 Torr in a glass tube provided with a heating jacket. After
cooling ln vacuo to room temperature, a solution of 160 g of
Bi(No3)3.5H2o, 65 g of Mn(N03)2.4H20 and 80 ml of 14 n nitric acid
in 900 ml of water is run into the tube. After the impregnation
batch has been aired, it is left standing for 1 hour at 80C. The
aqueous phase is then run off and the catalyst mass is predried in
the vacuun of a water jet pump.
~; For hydrofluorination, the catalyst is introduced into
a double-jacketed Ni-tube 150 cm long and 5 cm in diameter of which
the temperature can be regulated by means of an oil circuit. The
catalyst is thoroughly dried with nitrogen at 200C and subsequent-
ly activated with a mixture of air and increasing concentrations of
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hydrogen fluoride. The temperature is kept below 250C by varying
the concentration of HF. After a 100 % HF stream has been reached,
the treatmentis continued for 1 hour, followed by drying with air
for 1 hour. The bismuth content of the catalyst then amounts to
approximately 5 %, the manganese content to approximately 3 % and
the fluoride content to approximately 50 %.
A gaseous mixture of 12.6 moles/h of hydrogen fluoride
and 6 moles/h of acetylene (molar ratio 2.1:1) is passed over the
catalyst, activated as described above, in a nickel reactor with
a heatable volume when empty of 1.8 litres at a temperature of
230 to 240C.
After passing through a water wash, the reaction mixture
is mixed with 6.6 moles/h of chlorine and subjected to the gas
phase reaction at around 30C in a 3.6 litre glass reactor in the
presence of light from a 250 watt halogen metal vapour lamp of the
OSRAM- ower- tar HGJ type.
The mixture issuing from the chlorination reactor is
directly introduced into a nickel reactor heated to around 690C
(heated volume 0.75 litre). The reaction product leaving the reac-
tor is washed with water and dilute sodium hydroxide solution andd ed.
A mixture of organic compounds having the following
composition, as determined by gas chromatography, is obtained:
CF2=CH291.9 %
2-CH30.5 %
CF2Cl-CH30.2 %
CF~-CHCl1.4 %
higher boiling
fractions 6.0 %.
30 Accordingly, for a 100 % conversion of the acetylene
used, the three stage reaction produced a total yield of 91.9 %.
The structure of the test installation enables samples
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freed from hydrogen halides and chlorine by washing with water to
be taken after each reactor in order to be able to follow the in-
dividual reaction stages. In this way, it was possible to determi-
ne the following stage results by gas-chromatographic analyses:
a) ~Ivdrofluorination (Staye 1):
CHF2-CII3 97.4 %
CHF=CH~ 2.5 %
CH-CH 0.1 %
corresponding to a 99.9 % conversion, yield 97.5 %
b) Chlorination (Stage 2):
CF2C1-CH3 94.1 %
CH 2 H3 2.3 %
higher boiling
fractions 3.6 %
which, taking into account the above-indicated composi-
tion of the starting mixture subjected to chlorination,
corresponds to a yield of 98.9 % for a 97.6 % conver-
sion.
c) Thermal cleavaqe (S-tage 3):
The above-mentioned result which is identical with the
overall result so far as the composition of the product
is concerned corresponds to a yield of 97.9 % for a
99.8 % conversion, again -taking into account the compo-
sition of the starting mixture defined in b).
EXAMPLE 2
The test on which this Example is based was carried out
in the apparatus described in Example 1. In order to obtain as
complete as possible a conversion of acetylene into difluoroethane,
the above mentioned hydrofluorination reactor was fol.lowed for
hydrofluorination (stage 1) by a second reactor filled with the
same catalyst of which the temperature was kept at around 200C,
i.e. approximately 30 to 40C lower than in reactor 1.
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Under otherwise the same conditions, the following over-
all result was obtained:
2 2 %
CHF2 CH3 1,8 %
CF2Cl-CH3 0.2 %
CF2=CHCl 1.1 %
hlgher boiling
fractions 3.3 %
The overall reaction produced a 93.7 % yield of l,l-di-
fluoroethylene for a 100 % conversion of the acetylene used.
A breakdown according to Example 1 produced -the follow-
ing stage results:
a) Hydrofluorination:
CHF2-CH3 99 0 %
CHF=CH2 0~5 %
, CH-CH 0.5 % ~:
99.5 % conversion, 99.5 % yield. -;
b) Chlorination:
CF2Cl-CH3 95.8 %
CHF2-CEI3 2.0 % ~:
higher boiling
fractions 2.2 %
98.0 % conversion, 98.8 % yield.
c) Cleavaqe:
For the composition as determined by gas chromatography,
' see above (under "overall result"), ~-
99.8 % conversion, 98.0 % yield.
~:. EX~MI'LF, 3
.~ In order to demonstrate the effectiveness of the overall
~1 reaction, a test was selected in which the hydrofluorination cata-
s, . .
lyst showed distinctly reduced activity through prolonged use and
was ready for regeneration. The test was carried out with the same
apparatus and in the same way as in Example 1, i..e. using only one
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hydrofluorination reactor in order deliberately to have a relatively
high proportion of CHF=CH2 in the crude product of sub-reaction 1,
Overal result:
CF2 CH2 . %
CHF2-CI-I31.1 %
CF2Cl-CII30.1 %
CF2=CHC12.1 %
higher boiling
fractions6.8 %
overall conversion 100 %; overall yield 90.0 %.
The breakdown into component reaction steps produced
the following results: -
a) Hydrofluorination:
CHF2-CH3 94.9 %
CI~F=CH2 4.2 %
CH-CH 1.0 %
conversion 99.0 % yield 95.8 %
b) Chlorination:
CF2C1-CH3 92.2 %
2 3 2.4 %
higher boiling
fractions 5.4 %
conversion 97.5 %, yie].d 99.6 %.
c) Cleava~e: :
For product composition see above, .-
converslon 99.9 %: yield 97.7 %.
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