Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to a process for
preparing trichloroethylene from tetrachloroethylene and
hydrogen at an elevated temperature in the presence of a
catalyst containing a copper compound and, optionally,
an alkali metal compound on a carrier.
In a conventional process, tetrachloroethylene
is reacted with hydrogen in the presence of copper salts
distributed on aluminum oxide. The addition to tetrachloro-
ethylene of alkali metal salts, e.g. potassium-,rubidium-
and cesium salts has also been previously disclosed. How-
ever, German Auslegeschrift 11 94 403 mentions that the
system aluminum oxide/copper salt produces only low yields
which cannot be reproduced. The activation with alkali
metal salts likewise results only in a modest improvement
at temperatures from 200 to 325C.
It is therefore the object of the present in-
vention to provide a process for preparing trichloroethy-
lene from tetrachloroethylene which permits one to obtain
good yields at low temperatures and high selectivity.
This object is fulfilled according to the pre-
sent invention when tetrachloroethylene is reacted at
temperatures between 150 and 250C in an amount of 0.5
to 5 mol per hour and per liter of catalyst mass over a
catalyst consisting of an activated carbon carrier with more
than 500m /g BET surface, 0.5 to 20% by weight of copper
in elementar~ or chemically bound form, 0.01 to 1% by weight
of one or more of the group consisting of palladium, ruthen-
ium or rhodium in elemental form or in the form of a chemical
compound, and with up to 20% by wei~ht of one or several of
the metals potassium,rubidium or cesium, in the form of a
~119Z03
chemical compound, and with hydro~en at a pressure of 1 to
100 bar.
These new catalysts exhibit a surprising improve-
ment over catalysts known and used up to now. It could in
no way be expected that with a changeover from aluminum ox-
ide to activated carbon with surfaces of more than 500 m2/g
and the addition of 0.01 to 1% by weight of one or several
metals of the group of palladium, ruthenium or rhodium in
elemental form or as a chemical compound, the selectivity,
the yield, and space-time output could be so drastically
improved.
The catalyst according to the invention consists
of activated carbon as a carrier material and it has a BET-
surface of more than 500 m2/g; materials with surfaces of
up to 1400 m2/g are commercially available. The activated car-
bon is generally used in grain sizes of between 2 and 10 mm
diameter. The catalyst is coated with finely dispersed
salts of one or several of the metals palladium, ruthenium
or rhodium, as well as copper and if desired, the salts of
alkali metals, e.g. potassium, rubidium or cesium. As salts,
one may use any ino-rganic or organic salts highly soluble in
water or acids, with the proviso:that for the preparation of,
e.g. 1 kg of catalyst, the necessary salt quantities should
be dissolved in 0.5-- 10 liters of water.
The catalyst carrier is coated with 0.5 to 20~ by
weight of copper in elemental or chemical compound form, 0.01%
to 1~ by weight of one of the metals palladium, ruthenium or
rhodiu~ in elemental or chemical compound form, as well as a
compound of potassium, rubidium or cesium of U2 to 20~. At
the start or during the reaction, there occurs a partial or
~1~9203
or complete reduction of the salts of copper, palladium,
ruthenium or rhodium with formation of the respective
metals.
The preparation of the catalyst is carried out,
for instance, by starting ith 160 g of activated carbon
grains (BET-surfaces 500 m ~g) of a commerical product,
soaking or sprinkling it with 140 ml of an aqueous so-
lution which contains 260 mg palladium chloride, and 43 g
copper chloride dihydrate and subsequently drying it in a
nitrogen current. If desired, this solution may also con-
tain the alkali metal salts desirable in certain cases, such
as the potassium, rubidium or cesium chlorides. The treat-
ment of the activated carbon may also occur separately in se-
~uence with the salt solutions.
The preparation of the novel catal~st is much
simpler than the one of the known catalyst, as described in
; the German Offenlegungsschrift 11 94 403. The cumbersome
and dangerous treatment there applied with hydrogen and oxy-
gen at 300C is completely omitted in the catalyst according
to the invention.
Preferably, catalysts with a copper content between
3 and 15~ by weight are used. The catalyst in final form has
a bulk weight of 200 to 600 ~liter.
The activity of the catalyst depends almost linearly
on the content of one or several of the metals Pd,Ru or Rh.
For instance, under otherwise comparable conditions, the in-
crease from 0.01% Pd to 0.1% Pd in the novel catalyst raises
the yield in the desired product 10-fold; with a content of
0.2% Pd the yield is doubled again. With further increase
in the amount of Pd the yield further increases, and a peak
~1192()3
yield is already obtained at 0.8% Pd.
In amounts of below 1% by weight of copper, the
volatility of the copper component can be diminished by the
presence of small amounts of alkali metal chloride.
For carrying out the process, the newly-developed
catalyst is introduced into a reaction tube by shaking.
Tetrachloroethylene, which is gaseous at the reaction tempera-
ture, is fed-in in quantities of 0.5-5 mol per hour and per
liter of catalyst mass, and reacted with the 0.1-1 fold equi-
molar quantity of hydrogen gas. The reaction sets-in notice-
ably at temperatures above 150C; at 180C in the initial
phase of the catalyst formation, 98-99~ by weight of the
theoretical conversion is already occurring, whereas with
the catalysts known in this field, only 95~ can be maximally
obtained. The space-time yields are considerably higher
than the values obtained by the known processes even at
temperatures 50C below those employed in these known pro-
cesses.
Reaction temperatures above 250C are in general
not necessary. It is a further advantage of the novel pro-
cess that, contrary to known processes, operations can be
carried out at elevated hydrogen pressure. It is desirable
to operate at pressures of 1-100 bar: for best results,
pressures of 1-10 bar and especially between 3 and 10 bar,
are frequently used. The hydrogen chloride obtained in the
pressure process can be used in other suitable processes,
e.g. oxychlorination, without being pre-compressed. The
separation of the reaction products is also much simpler.
If the catalyst is used over a longer period, a
decrease in activity may be compensated by raising the tempera-
ture. It is advantageous to start the reaction at low
--4--
1119203
!
temperature,e.g., 180C, and increase the temperature
~;lowly, as the activity of the catalyst drops. The stability
of the catalyst is good for more than one year.
The process according to the invention will be
more fully described in a number of examples, but it should
be understood that these are given by way of illustration
and not of limitation.
EXAMPLE 1
160 g of granular activated carbon (grain size 2- -
lOmm) of the brand EKT-IV, made by the firm LURGI,
2 ~:
having a surface of 1200 m /g were steeped with 14Q ml of ~;
an aqueous solution of 260 mg pd chloride and 43 g copper
chloride dihydrate. After having been dried in a nltrogen
current at 160C for one hour the catalyst is ready for
use.
EXAMPLE 2 (Comparison test, German Ausle~sschrift 11 94 403)
335 g of aluminum oxide with a BET-surface of
190 m2/g were steeped with a solution-of 32 g of copper chlo-
ride dihydrate and 150 gof potassium chloride in 450 ml water,
dried, and after-treated first for 30 minutes with oxygen at
290C and then, after an intermediate rinsing with nitrogen,
treated for 30 minutes with hydrogen.
EXA~lPLE 3 (Comparison Test)
An activated carbon carrier as used in Example 1
was coated with 0.1% by weight of Pd in the form of its
chloride.
EXAMPLE 4 (Comparison Test)
An activated carbon carrier as used in Example 1,
was coated with lQ~ by weight of copper as chloride. With
the same conditions as in Example 1, only a low conversion
111~;~03
of tetrachloro- to trichloroethylene was achieved.
EX~PLE 5
151 g of granular activated carbon as in Example 1,
was steeped with a solution of 42.2 g of copper chloride
(CuC12-2 H20) and 385 mg of sodium hexachlororhodinate
(Na3~ICl6 12 H20) in 130 ml of water. After drying for one
hour at 160C, the catalyst is ready for use.
EX~PLE 6
151 g of granular activated carbon as in Example 1,
was steeped with a solution of 42.2 g of copper chloride
(CuC12~2 H20) and 366 mg of Ruthenium trichloride
(RuC13 2 1~20) in 130 ml water. After drying for one hour
at 160, the catalyst is ready for use.
EX~IPLE 7
151 g of granular activated carbon as in Example 1,
was steeped with a solution of 42.2 g of copper chloride
(CuC12-HzO) and 175 mg of sodiumhexachlororhodinate
(Na3RhC16 12 H20) in 130 ml water. After drying for one
hour at 160C, the catalyst was ready for use.
EXAMPLE 8
151 g of granular activated carbon as in Example 1,
was steeped in a solution of 21.1 g of copper chloride and
260 mg of palladium chloride in 130 ml of water.
After drying for one hour at 160C, the catalyst
is ready for use.
From the examples, the superiority of the process
according to the invention with the use of the novel cata-
lysts is clearly noticeable. (See the compilation in the
Table below.)
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203
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~3 ~.~ o~3 ~n3 ~P~ w~ ,-3 ~
Z Z o Z o o ~ o
P) t~ Q ~ ~ Q ~D
~SO) Qu~ _ 1~ ,~
O ~ ~ c W 1- 1- ~ ~_ .~P I CO ~ ~ ~
~D ~.
; I I l ~
`' ~~q ~ ; ~ 3
~
lo I 1- I ~ol oc~ o I I w~ ~OOnO I
~ :1 n ~ ~y B-
I` I ~ ~ ~ol o~_l 1- 1 1 ~l IhO I ~ g~ -~ lo
~'~;
W ~ I_~ ~0 I ~ Ul O I ~W~n
ina~ a~ i~ I~wl~~
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K
203
TABLE FOOTNOTES:
. .
1. According to Example la, only 0.3 g cis-, 0.06 g trans-
dichloroethylene, 0.08 g vinylidene chloride, 0.023 g ethylene,
and 0.002 g ethane were formed.
2. There the work was done at 5 bar. Formed were: 1.18 g
cis-, 0.38 g trans-dichloroethylene, and 0.36 g vinylidene
chloride.
3. As by-products 0.3 g cis-dichloroethylene, 0.15 g vinyliden~
chloride, 0.79 g ethane and 0.74gethylene were formed.
4. As by-products 0.015 g vinylidene chloride, 0.17 g cis-
dichloroethylene, 0.023 g trans-dichloroethylene, 1.4 mg ethy-
lene, and 0.1 mg ethane.
5. There the hydrogen pressure during the operation was
10.5 bar. As by-products 0.17 g vinylidene chloride, 1.2 g
cis- and 0.24 g trans-dichloroethylene were formed.
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