Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a process for the ma-
nufacture of ethanol by reacting carbon monoxide with hydro-
gen on a cobalt catalyst, modified by gold andJor silver
and/or rhenium.
Processes for the manufacture of alcohols from synthesis
gas are already known.
It is known, for example, that the use of rhodium cata-
lysts together with certain promotors in the synthesis gas
reaction favour the formation of oxygen-containing compounds
(DE-AS 25 03 204). The disadvantage is the relatively high
price of rhodium. It is also known to use cheaper cobalt ca-
talysts (Fischer Tropsch) in the synthesis gas reaction. He-
reby, however, a variety of products is formed, preferably
hydrocarbons, but only small amounts of oxygenated compounds.
The modification of cobalt catalysts by copper, chro-
mium, zinc, alkali earth metals, alkali metals, aluminium,
rare earths or iron provide a series of products from metha-
nol to butanol, but the proportion of ethanol is only about
30 ~ by weight (DE-PS 857 799, DE-PS 5L14 665, FR-PS 660 678,
FR-PS 1 074 0l~5, F~-PS 2 7Ll8 0g7). Besides this, these cata-
lysts are very sensitive, concerning the manufacture, the
initiation and the continuous operation. Therefore, in most
cases they are not long-lived. Thus, the task was to produce
ethanol from synthesis gas with high selectivity on resis-
tant and long-lived catalysts.
Now it has been found that the selectivity of ethanol
is considerably increased on cobalt catalysts by the addi-
tion gold and/or silver and/or rhenium as promotors.
Subject of the invention is, therefore, a process for
the manufacture of ethanol fro~ carbon monoxide and hydrogen
on cobalt catalysts, which comprises using a catalyst contain-
ing, besides cobalt as metal or compound, at least one of
the elements gold, silver and rhenium as metal or compound.
Besides cobalt, the catalyst preferab]y contains gold, but
even more preferably the combination gold/silver. The result
that the selectivity of the synthesis gas reaction to etha-
nol is increased to such a considerable degree by the addi-
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tion of the abovementioned elements - with, at the same time,
a good space-time yield - is extremely surprising and could
not be foreseen, because gold and silver are known as cata-
lyst poisons in hydrogenations, whilst hydrogenations with
rhenium, ln general, yield hydrocarbons.
Besides ethanol which is formed according to the inven
tion in high selectivity, there are formed small amounts of
methanol, propanol and butanol and some acetaldehyde as by-
products.
The catalysts for the process according to the inven-
tion are preferably obtained by impregnating a catalyst car-
rier with a solution of cobalt, gold and/or silver andJor
rhenium salts and by subsequent drying, the salts being ap-
plied together or one after the other. Suitable salts are
all soluble cobalt, gold, silver and rhenium salts, such as
the chlorides, bromides, nitrates, acetates, propionates,
lactates, citrates of cobalt, the chlorides, acetates, pro-
pionates of gold, as well as aurates (such as barium aceto-
aurate or barium propionoaurate), furthermore the acetate,
propionate, butyrate, lactate and nitrate of silver, as well
as rhenium heptoxide, perrhenates and rhenates.
The salts mentioned are dissolved in suitable solvents.
Suitable solvents are, for example, water, aqueous
carboxylic acids and anhydrous carboxylic acids, especially
water and acetic acid.
Suitable supports are the common carrier materials with
different specific surfaces and pore volumes. Carriers with
a specific surface of from 50 - 1000 m2/g and a pore volu-
~le of more than 0.3 ml/g are preferably used.
Suitable products are, for example, silicic acid, natu-
ral or synthetic silicat.es of elements of the II. up to the
VIII. group of the periodical system (for example the sili-
cates of magnesium, aluminium or manganese, furthermore alu-
minium oxide, thorium oxide and spinels.
It is also possible, however, to produce suitable cata-
lysts by precipitation of cobalt oxide together with gold
and/or silver and/or rhenium or by subsequent impregnation
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of cobalt oxide with salts of gold and/or rhenium.
Preferably the catalyst is reduced prior to its use with
a suitable reduction agent, such as hydrogen, carbon monoxide
or methanol and this is expediently being done in the synthe-
sis gas reactor itself. In general, the temperature duringthe reduction is lower than 400C, preferably between 200
and 300C. In many cases it is advisable not to carry out
the reduction with the undiluted reducing gases, but with an
additional portion of inert gases, such as nitrogen, carbon
dioxide and noble gases.
The concentration of cobalt in the catalysts may vary
within a very wide range; the cobalt compounds without car-
riers, for example cobalt oxide, can be used as well as sup-
ported catalysts with a minimum of 1 % by weight of cobalt.
The concentration of the promotors depends on the con-
centration of the cobalt, per mole of cobalt from 0.001 to
0.5 mole, preferabiy from 0.02 to 0.2 mole of eaoh promotor
being used.
For carrying out the process acording to the invention
gas mixtures, which totally or predominantly consist of
carbon monoxide and hydrogen and which optionally may also
contain other components such as nitrogen, argon, carbon
dioxide or methane, are passed over the catalyst. The ratio
by volume of carbon monoxide to hydrogen may vary within a
great range. Preferred ratios are from 5 : 1 and 1 : 5,
especially from 3 : 1 to 1 : 3. The reaction temperaure in
general is between 1~5 and 375C, preferably between 200
and 350C.
The reaction pressure lies between 1 and 30~ bar, pre-
ferably between 20 and 200 bar.
For carrying out the reaction, the gaseous phase is
preferred. The usual solid bed reactors may be used. Fur-
thermore, there are suitable reactors with moved catalysts
bed or fluidized bed reactors.
The reaction of the synthesis gas can also be performed
in the presenc~ of the solid and finely divided catalyst
suspended in inert solvents and/or reaction products.
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An especially preferred embodiment of the invention
consist in carrying out the reaction in a cycle gas appara-
tus in the gaseous phase, in which, after the separation of
the condensable reaction products, the non-reacted gas
mixture is recycled into the reactor.
This embodiment is especially economical and by dilu-
tion of the fresh gas with the rest gas poorer in hydro-
gen which is recycled, it allows higher reaction temperatu-
res and thus higher space-time yields without~ change of se-
lectivity. Suitable cycle gas apparatus are those with in-
terior or exterior gas circulation.
The following examples illustrate the invention.
E X A M P L E S
A) General test description
The apparatus consists of a heated reaction tube of
20 cm length and 14 mm inner diameter of corrosion resis~
tent steel and a centrally installed shell for measuring
the temperature with a thermocouple.
This reactor is in a heating bath of Wood's metal in
which the synthesis gas is also preheated. The tempera~
ture in the reactor as well as the temperature of the me-
tal bath may be followed on a recorder. In the case of an
overheating of the catalyst, N2 is passed through.
The reduction of the catalyst freshly filled into
the reactor, is carried out with a mixture of H2/N2 in
a ratio of 1 : 4 at atmospheric pressure and at 300C.
The synthesis gas mixture ~CO : H2 ~ 1 : 1) is
taken from a compressed gas cylinder, the amount being
measured by the fall of pressure with a sensitive gas
manometer.
Pressure adjustment and pressure maintenance are
provided by a pressure controller. Prior for the pressure
controller the condensable proportions of the reaction
mixture are condensed in a separator and passed to the
GC-analysis.
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According to thls method the catalysts described below
are examined. The following table shows the tes-t conditions
as well as the space~time-yields of oxygenated C2 products
per liter of catalyst and hour as well as the selectivities
to ethanol.
Description of the catalyst
The following percentages are given by weight.
E mple 1
40 g of a commercial silica gel carrier with a specific
surface of 400 m2~g, a pore volume of 1.2 ml/g and an appa-
rent density of 0.4 g/ml are soaked ~ith a solution of 16.3 g
of cobalt acetate, 3.5 g of barium acetoaurate and 0.5 g sil-
ver acetate in a mixture of 35 ml of water and 5 ml of acetic
acid and dried at 60C under 250 mbar. The catalyst con-
tains 8.4 % Co, 2.8 % Au, 0.7 % AG and 1 % Ba in the form of
the acetates.
Example 2
35 g of the carriers mentioned in Example 1 are soaked
with a solition of 16.3 g cobalt acetate, 1.7 g of barium
acetoaurate and 2.0 g of rhenium heptoxide in 43 ml of a 7%
acetic acid and dried at 110C under atmospheric pressure.
The finished catalyst contains 9.4 % Co, 1.5 % Au, 3.7 g Re
t and 0.6 % Ba.
Example 3
35 g of the carrier mentioned in Example 1 are soaked
with a solution of 16.3 g cobalt acetate and 2 g rheniumhept-
oxide in 43 ml of 7% acetic acid and dried at 80 in a ni-
trogen flow. The finished catalyst contains 9.5 % Co and
3.8 % Re.
Example 4
,~
40 g of` a commercial silicic acid carrier (250 m'/g
surface, o.8 ml/g pore volume, 0.7 ml/g apparent density)
are soaked with a solution of 16.3 g cobalt acetate and 1.9 g
gold acetate in 40 ml of 12.5 % acetic acid in two stages,
after each soaking the product is dried until it has reached
a constant weight. The finished catalyst contains 8.3 ~ Co
and 2 % Au.
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Test results
The following table shows the test results:
Ex. Pres- tempe- space space-tlme-yield (g/l.h)
sure rature velo-
(bar) (C) city metha- etha- propa- buta- acet- selec-
(Nl/ nol nol nol nol alde- tivity
l.h) hyde * to
etha-
nol
_
100 280 1200 7.2 16.5 4.5 0 0.05 60
2 80 ~75 6000 9.9 33 9.9 1.6 o 6Z
3 100 260 8050 8.5 27.5 6.7 0.7 0 65
4 150 280 7000 14.6 19.7 5.6 1.3 1.0 52
comp.100 280 6500 0.5 0.04 0.030.01 0.03 7~**
ex .
**
* Definition of the seleCtivitY: Mol CO totally reacted
** Comparative example with cobalt alone; catalyst manufactured
in other respects as in Example 1.
*** The other reaction products consist of saturated and unsatu-
rated hydrocarbons.
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