Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a process for the manufac-
lure of ethanol by reaction of carbon monoxide with hydra-
gun on a supported rhodium catalyst.
It is known from German Auslegeschriften DE-AS 2,503,233
and 2,628,463 that the gas phase reaction of synthesis gas
in the presence of catalysts containing metallic rhodium
yield substantially mixtures of oxygen-containing compounds
having two carbon atoms in the molecule, such as acetic
acid, ethanol and acetaldehyde.
It is further known from DE-AS 2,503,204 that the so-
lectivity of ethanol can be increased by the addition of
iron salts. The addition of iron salts strongly reduces,
however, the activity of the rhodium catalyst. According
to Table 1 of DE-AS 2,503,204 the space-time yields with
iron containing rhodium catalysts are about 4 times lower
than that of an iron-free rhodium catalyst used for Compaq
risen. With regard to the economy of a process such a de-
crease in the yield with regard to the formation of oxygen-
containing C2-compounds is extremely unsatisfactory.
From US-Patent 4,096,164 it is known that the select
tivity with respect to the formation of alcohols can be
generally increased by adding molybdenum or tungsten to
rhodium-containing catalysts. But these two cocatalysts
do not lead to a substantially increased formation of
ethanol in the first place larger amounts of methanol
propanol and buttonhole are formed.
It is, therefore, the aim of the present invention to
improve the ethanol selectivity of rhodium catalysts that
29 is to say to reduce the formation of other compounds such
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as methanol, propanol and buttonhole without diminishing at
the same time the space-time-yield of ethanol.
It has now been found that the ethanol selectivity and
simultaneously the space-time-yield of ethanol can be sub-
staunchly improved by using rhodium catalysts additional-
lye containing, applied onto a carrier, at least one of the
elements zirconium, hafnium, lanthanum, platinum, cry-
mum and mercury.
The present invention thus provides a process for the
manufacture ox ethanol by reaction of carbon monoxide with
hydrogen in the presence of a supported rhodium catalysts,
which comprises using as cocatalyst at least one of the
elements zirconium, hafnium, lanthanum, platinum, chromium
and mercury.
The finding that the composition of the reaction pro-
duct can be shifted by the use of the aforesaid elements in
savor of ethanol with simultaneous increase ox the space-
time yield is surprising and could not have be foreseen.
Besides ethanol, which is formed with a high select-
viny in the process of the invention, smaller amounts of other oxygen containing C2-compounds are formed, such as
acetaldehyde and acetic acid and other products which can
be wormed from these compounds in a secondary reaction 9 for
example by esterification, acetalization or condensation.
Compounds of the latter type are inter alias ethyl acetate
and the deathly acutely of acetaldehyde. The proportion of
other oxygen-containing compounds having three or more car-
bun atoms in the molecule is very low and generally it is
; 29 below 5 mow %, calculated on reacted carbon monoxide. The
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total selectivity for oxygen-containing C2-compounds9 in-
eluding the products converted into ethyl acetate and act-
alluded deathly acutely, is up to 81 %, calculated on the
reacted carbon monoxide The remainder of the carbon monk
oxide is converted into the aforesaid products having 3 anymore carbon atoms and in addition essentially into methane
and other gaseous hydrocarbons and a small proportion of
carbon dioxide.
To synthesize the catalyst to be used in the process
of the present invention, salts or complex compounds of
rhodium can be used, for example chlorides, bromides and
iodizes as well as double salts of rhodium with alkali me-
tat halides, for example dipotassium-trichlororhodate.
There are also suitable complex compounds containing, be-
sides rhodium and halogen, complex-~orming ligands, such
as trialkyl-phosphines, triaryl-phosphines, ethylene dip
amine, pardon, carbon monoxide, olefins or water. Come
pounds of this type are, for example, tristriphenylphos-
phine-rhodium~I~chloride9 -bromide or iodide, tristri
2Q phenylphosphine-rhodium-III-chloride, dichloro-bisethyle-
ne-diamine-rhodium-I-chloride, trisethylenediamine-rho-
dummy chloride, bis-tri-o-tolyl phosphine-rhodium~
chloride, carbollyl-bistriphenylphosphine-rhodium-I-bromide
or dlcesiumcarbonyl-pentachlororhodate-III. In addition,
compounds of rhodium can be used in which it is bound by
ion or complex bonds to a carrier, such as zealots and
ion exchangers which have been exchanged with rhodium
halides.
29 As cocatalyst in the process ox the invention where is
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used at least one of the elements zirconium, hafnium, fan-
thanum, platinum, chromium and mercury applied onto the
carrier in the form of their salts or complex compounds.
Zirconium, hafnium, lanthanum, chromium or mercury are pro-
S erred and more preferably hafnium, chromium or mercury aroused. The elements can be used in the form of simple in-
organic or organic salts for example the chlorides, brow
modes, nitrates, formats, acetates, preferably, however,
the chlorides. The oxides, hydroxides or carbonates can
also be used, provided that they are converted into the
aforesaid salts by a treatment with mineral acids or garb-
oxylic acids. Especially suitable complex compounds are
chloro-complexes of rhodium of the formula Mm/~hCl6 on in
which M denotes the element of the cocatalyst, in the case
of chromium, for example, the complex Creakily 7-2 H20 ?
which can be obtained by reacting chromium chloride with
rhodium chloride at 100C in acetic acid.
Complexes of the aforesaid type can be applied onto
the carrier by impregnation. Because of the poor ~olubili-
try of some complexes it is often advantageous to impregnate the carrier with a solution of rhodium-III-chloride and one
or several chlorides of the elements named as cocatalysts
in acetic cold and subsequently to heat the treated carrier
to a temperature of 100C, whereupon the complexes form in
the pores. Alternatively, the element acting as cocatalyst
can be applied to the carrier first or it can be incorpo-
rated into a skeleton substance, for example a carrier ma
tonal containing a silicate or aluminum oxide, for example
29 silicic acid, al~ninum oxide or aluminum silicate. A fur-
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then advantageous method consists in binding the cations of
the elements acting as cocatalysts by means of ion exchange
to a cation exchanger which can also be used as carrier for
the rhodium and which is stable under the reaction condo-
lions, for example natural or synthetic aluminum silicates known as molecular sieves. Suitable catalysts can also be
obtained when the carrier is impregnated in the reverse or-
don of succession, i.e. first with a rhodium compound and
then with the respective cocatalyst. The catalyst effi-
Chinese with an unchanged high selectivity for ethanol canoe further improved by adding other promoters, especially
magnesium.
Suitable catalyst carriers are the usual carrier ma-
trials having different specific surfaces. Carriers have
in a specific surface in the range of from 50 to 1,000 mug are preferred. Suitable materials are, for example 9 Six
licic acid, natural or synthetic silicates-of elements of
groups It to VIII ox the Periodic Table (that is, for ox
ample, the silicates of magnesium, calcium, aluminum, man-
I Gaines), furthermore aluminum dioxide, thorium dioxide,zeolites and spinets. Silicic acid and silicates are pro-
furred.
For the manufacture of the catalysts the carrier ma-
twirl is impregnated with the active components either
simultaneously or successively. When rhodium-III-salts
are used, a subsequent treatment with a suitable reducing
agent such as hydrogen, carbon monoxide or methanol proved
advantageous. This reduction can be carried out in a so-
29 pirate apparatus or in the reactor itself In general, the
.
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temperatures applied in the reduction are below 300C, pro-
drably in the range of from 100 to 275C. In many cases
it is expedient to carry out the reduction not with the us-
diluted reducing gases but with a gas mixture additionally
5 containing an inert gas, for example nitrogen, carbon dip
oxide or a noble gas.
It is likewise possible to produce the carrier material
in the presence of the active components, for example by
concomitant precipitation of the active components with
silicates.
The concentration of rhodium and cocatalyst in the cay
talysts can vary within wide limits. In general, a gala-
lust contains 0.1 to 20 by weight of rhodium and Q.1 to
25 % by weight of cocatalyst, preferably 1.0 to 10 % by
weight of rhodium and 0.1 to 20 % by weight of cocatalyst.
lo carry out the process of thy invention a gas mix-
lure wholly or substantially consisting of carbon monoxide
and hydrogen and possibly containing other components such
as nitrogen, argon, carbon dioxide, or methane is passed
over the catalyst. The molar proportion of carbon monoxide
to hydrogen can be varied in wide limits Molar proportions
ox from 5:1 to 1:5 and especially 3:1 to 1:3 are preferred.
In general, the reaction temperatures are in the range of
prom 175C to 375C, preferably 200C to 350C and the no-
action pressure ranges from 1 to 300 bar, preferably 20 to
200 bar.
Temperature and pressure should be adjusted to one an-
other in such a manner that a high selectivity for the ox-
29 gen-containing compounds is ensured while the exothermal
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formation of methane which is favored by elevated tempera-
lures is kept low. Hence, high pressures and low temperate-
ryes will be preferred. The conversiorl of carbon monoxide
should not exceed 50 g, in general, since a higher conversion
may readily lead to the formation ox an increased amount of
byproducts consisting not only of methane carbon dioxide and
gaseous hydrocarbons but also of liquid hydrocarbons of
higher molecular weight and oxygen-containing products.
The process is preferably carried out in the gaseous
phase. Conventional fixed bed reactors can be used in
which, for a satisfactory dissipation of hefty the gala-
lust is used in thin layers. Reactors with moved catalyst
bed or fluidized bed reactors can also be used.
Alternatively, the reaction of synthesis gas can be
carried out in the presence of a suspension of the solid
and finely dispersed catalyst in inert media and/or react
lion products.
According to an especially preferred embodiment of
the invention, the reaction is carried out in the gaseous
phase in an apparatus with gas circulation from which, aft
ton separation ox the condensable reaction products, the
unrequited gas mixture is recycled into the reactor.
This mode of operation is particularly economic. Due
to the fact that the fresh gas is diluted with the recycled
residual gas having a lower hydrogen content, higher react
lion temperatures can be used so that higher space-time-
yields are obtained with an unchanged selectivity. As apt
pyrites with gas circulation those with internal or ox-
29 vernal gas cycle can be used.
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.
The following examples illustrate the invention, but
they are not intended to limit it thereto
E X A M P L E S
_
A) General description of the test
The apparatus used consists of a heated reaction
tube, having a length of 1 meter and an inner diameter
of 16 millimeters and made of corrosion-resistant steel,
with coccal fitted housing for a thermometer having
an outer diameter of 6 mm, a following condenser a no-
sever for the condensate and a compressor for recycling
part of the non condensed gas to the reactor (cycle gas).
In each test the reactor is charged with 100 ml of the
catalysts defined below. After flushing of the appear-
tusk with nitrogen, first a pressure of 100 bar is ad-
jutted with a synthesis gas consisting of 49 % by vow
fume of CO, 49 % by volume of Ho, 1 % by volume of COY,
1 % by volume of No and minor amounts of other combo-
newts and the reactor is heated to 275C. During heat-
in and during the course of the test 450 normal liters
of synthesis gas having the aforesaid composition are
added to the cycle gas over the suction side of the come
presser and the mixture is passed over the catalyst.
The gas mixture leaving the reactor is cooled to about
~5C in the condenser cooled with brine and the con-
dented fractions are collected in the receiver. Aster
the addition of fresh synthesis gas, the non condensed
residual gas is returned to the reactor via the compress
son. To maintain the pressure and to remove by-products
29 part of the residual gas is branched off as exhaust gas
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-
via a pressure keeping valve. All catalysts defined be-
low are tested by this method. In the table are India
acted the duration of the tests, the space-time~yields
of oxygen-containing C2-compounds per liter of catalyst
and hour as well as the selectivities for ethanol, act-
~ldehyde and acetic acid (in mow % of CO calculated on
reacted CO). Minor amounts of ethyl acetate and act-
alluded deathly acutely formed are calculated as acetic
acid, ethanol and acetaldehyde.
B) Preparation of the catalyst
Each time 40 g of silicic acid having a BET surface
of 270 mug a pore volume of 1.27 ml/g and an apparent
density of 0.4 kg/l are impregnated with a solution of
5.2 g of RhC13 ' x HO (38.0 % by weight of Rho in 50 ml
ox water and dried for 1.5 hours at 80C, for 1.5 hours
at 110C and for 1.5 hours at 150C.
This catalyst is used for the comparative Example.
For Examples 1 to 7 the catalyst obtained is further
impregnated with an aqueous or alcoholic solution of the
hollowing chlorides, each time in 50 ml of solvent, and
dried for 2 hours at 80C and then for 2 hours at 150C.
Example no. _ cocatalyst _ amount in g
1 Or Clue 3.4
2 La Clue 4.8
3 Pi Clue 4~9
4 Or C13 6 H20 5.2
Hi C14 4.7
6 Hug Clue 7.9
29 7 Or Clue + My Clue H20 3.4 -I 3
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Next, the catalysts for Example 1 to 7 obtained are
heated for 5 hours to 100C in a glass flask with reflex
condenser together with 50 ml of acetic acid and then
dried for 1.5 hours at 110C, for 3 hours at 150C and
finally for 1 hour at 300C under nitrogen.
The catalysts for examples 1 to 7 are then reduced
in a flow tube made of glass my passing over 30 Nl/hr
of hydrogen. for 3 hours at 225 to 275C under atmosphe-
fig pressure.
C) Test results
The results obtained are summarized in the follow-
in table. The indicated values are average values ox-
twined with reaction times of 100 hours each.
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-
T a b l e
Reaction conditions: apparatus with gas circulation, 100 bar, 275C,
feed gas 400 Nl/hr with KIWI ratio of 1:1, catalyst volume 0.1 l,
duration of test 100 hours (Awoke acetic acid, Ash acetaldehyde,
Etch ethanol)
Example catalyst space time-yield selectivity (mow % CO)
No. in g/l ho
C -O Etch QcOH Ash Etch ~C2-0
Comparative Rho 52 31 17~2 6~4 24; 48~0
example
1 Rh/Zr 390 343 I 1 1 ox 70~ 1 76~0
2 Rh/La 380 318 7-0 4~0 67~5 78~5
3 Rapt 350 320 3 2 2.4 75~0 80~6
4 Rh/Cr 390 351 5~4 3~5 68~1 77~0
Rh/Hf 360 311 6~4 2~2 66~4 75~U
6 Rh~Hg 375 340 4~0 2~5 74~5 81~0
7 Rh/Zr/Mg 475 420 4~8 2.8 69~9 77~5
The space~time~yield (STY) is given in gram per liter of catalyst and
hour; in the first column the STY of oxygen-containing C2-compounds,
I acetic acid, aoetaldehyde and ethanol is given ( ~C2-0) and in
the second column the STY ox ethanol alone (Etch)
mow % calculated on reacted carbon monoxide
