Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A PROCESS FOR THE PREPARATION 0~ A CATALYST
The present invention relates to a process for
the preparation of a catalyst to carry out the water
gas shift reaction according to the equation:
CO ~ H20 ~ ~ 3 C2 + H2
The catalyst contains the following components:
1) alumina and 2) at least one transition metal. It
is already known to prepare catalysts of this type by
impregnating alumina carriers with solutions of salts
of transition metals.
The catalysts thus prepared have the disadvantage
that they are affected by sulphur, that is to say by
the H2S often contained in mixtures of CO, H20 and
C2 obtained, for example, by the gasification of coal
- or heavy residues of crude oil. Likewise, they do not
exhibit a satisfactory activity at low temperature,
which would have been favourable from the point of
view of thermodynamic equilibrium. Moreover, said
preparation method is somewhat cumbersome, especially
if large quantities of catalyst have to be prepared~
and it is never known exactly how much metal will be
deposited from a solu'ion of a certain concentration,
nor whether the metals will be distributed in a
homogeneous manner in the alumina.
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It has now been found that it is possible to avoid
said disadvantages by melting a thermally decomposable
aluminium compound, dissolving in the melt the metal or metals,
in elemental form or as compound(s), decomposing the aluminium
compound by heating and subsequently cooling the mixture and
shaping it into a form which is suitable for catalysis.
The invention therefore relates to a process for the
preparation of a catalyst for carrying out the water gas shift
reaction, which catalyst contains 1) alumina and 2) at least
one transition metal, characterized in that a thermaLly
decomposable aluminium compound is melted, the metal or metals
is/are dissolved in the melt in elemental form or as compound~s),
the aluminium compound is decomposed by heating and the
mixture is cooled and is shaped into a form which is suitable
for catalysis.
In general the catalysts thus prepared no longer have
said disadvantages, but they also possess a larger number o~
active sites ~metal sites) which are moreover better distribu~ed.
The resistance to sulphur as well as the mechanical resistance
are excellent. If desired, the mechanical resistance can be
improved by the addition of binders, for example cement.
It is not known exactly in what state the metals
are distributed in the catalysts, as atoms or irons,
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complex or not, but this does not affect the in
vention. Reference is usually made to oxides or
sulphides, but especially in the presence of re-
active components of the water gas shift reaction,
more complex compounds are possible.
The aluminium compound is preferably melted
at a temperature of 75-800C for 5-120 minutes,
optionally in an oxidizing atmosphere, at a pres-
sure of 0.2-20 bars. Decisive factors are -the
melting temperature as well as the decomposition
temperature. For example, when using aluminium
nitrate (melting point 73.5C, decomposition point
150C), the compound is heated at 80-90C for
10-20 minutes.
Subsequently the transition metal or metals
is/are dissolved and the solution is further heated
at 250-800C, preferably at 450-550QC for 1-4 hours,
to decompose the aluminium compound and the other
dissolved compounds as far as they are decomposa~le.
Preferably, at least one alkali metal or one
alkali metal compound is also dissolved, since they
are effective as activators, that is to say that the
activators themselves are not catalysts, but when
added to a catalyst they improve the activity of
the catalyst. The alkali ~.etal is almost in~ariably
dissolved as a compound, especially as oxide or salt,
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optionally thermally decomposable. Preferred are the
compounds which melt at the temperature of the molten
aluminium compound, in view of their optimum homo-
geneous distribution.
It is possible to use, for example~ acetatesg
formates, oxalates~ carbonates, nitrates, nitrites,
which decompose into oxides, of which carbonates and
nitrates are preferred. It is also possible to use
other salts, such as halides or sulphides, or salts
or oxides mixed with transition metals, for example
permanganate, molybdate, dichromate, tungstenate~
manganate, (meta-)aluminate, oxaloferrate, ruthenate,
which offer the additional advantage of simultaneously
introducing an alkali metal and a transition metal,
or aluminium. But the quantity is not already correct
in advance in all cases. It is essentially also pos-
sible to use acid or basic double salts. When using
double salts, it is also possible to introduce at the
same time transition metals, for example by means of
iridium or potassium osmyloxalate. Of the alkali
metals (Li, Na, K~ Rb, Cs) potassium gives the best
results.
Prefer~ed is 0.01-12% of aikali metal, calculated
as metal based on the weight of the finished catalyst.
Special preference is given to quantities of 0.1-1.0%
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and 9-11%. The effect of a catalyst containing about
2-8% is about one fifth lower, but still not lower
than the effect of a catalyst without alkali metal.
As regards the aluminium compound, use has to
be made of a thermally decomposable compound, the
decomposition product being alumina.
Suitable are therefore bromate, bromide, per~
chlorate, tristearate, etc. but particularly
nitrate, in view of its low melting temperature
(73.5 C). The general observations made for the
alkali metal compounds are also applicable here.
The transition metals can be added in elemental
form, as powder, ~ilings, filaments, wool, granules~
etc., or as a compound. A suitable compound is for
example ammonium paramolybdate ((NH4)6Mo7024.4H20,
decomposition point 190C), if desired dissolved in
concentrated ammonia. It i~ already known that the
water gas shift reaction can be carried out with
metals of group VI B of the Periodic System (Cr, Mo,
W) and of the iron group (Fe, Co, Ni). Of said metals
iron (Fe203.H20) and especially iron provided with
an activating quantity of chromium (Cr203) is satis~
factory, provided the feed gas does not contain
sulphur.
In the presence of sulphur the catalysts are
subject to crumbling. This will not occur if use is
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made of a catalyst prepared according to the in-
vention, preferably containing molybdenum with cobalt
or nickel in oxidic or sulphuric form and which also
contains an almost negligible quantity of alkali
metal. Instead of molybdenum use can also be made of
tungsten or chromium.
A quantity of 1-15% (based on the weight of the
finished catalyst) of transition metal, in particular
1-3% of Co or 5-10% of Ni and 4-15% of Mo, is usually
applied.
After decomposition of the alumînium compound
and of the other dissolved compounds as far as they
are decomposable, the mixture is further heated to
dry and precalcine the material. Finally, the mixture
is left to cool or subjected to a cooling treatment.
As usual in the preparation of catalysts, the
catalyst obtained can be calcined. The catalyst is
preferably activated by calcination at 450-550C for
1-3 hours. A stony catalyst is obtained, which is
pulverized. By pulverizing and sieving the catalyst,
catalytic particles are obtained which have a size
of preferably 0.2-0.6 mm ~for industrial installations
a size of 1.5-10 mm is preferred).
By subsequent treatments the particles can be
shaped into a form which is suitable for catalysis,
but they can often be used as such. The catalyst can
~econverted into tablets, extrudates, rings, granules
or other bodies.
EXAMPLE I
Catalysts were prepared by impregnation and
according to the invention (by dissolving metallic
Ni, Co and Mo in molten Al(N03)3) to demonstrate the
technical ef~ect. Originally the components were
mainly in oxidic form.
A reactor was charged with 4 ml of catalyst
particles (size 0.2-0.6 mm) and the particles ~ere
contacted with a gas mixture comprising 45% by
volume of CO, 5% by volume of C02, 49.6% by volume
of H2 and 0.4% by volume of H2S. Water or steam was
injected with the gas and the composition of the gas
analyzed before and after the reaction by gas
chromatography. The degree of CO conversion was
thus calculated as a percentage (volume, weight or
molar). The following conditions were applied:
pressure 30 bar
space velocity 3,300 Nl/l.h
molar quantity (dry gas/stea~ 1.35
temperature 220C
pretreatment none
duration 20 hours
After 20 hours the quantity of converted CO
was measured.
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A. 2.5 CoO/9 MoO3/88.5 A1203, or containing 2.0%
by wt of Co and 6.o% by wt of Mo.
preparation calcination surface conversion
(C) m2/g (%)
5 impregnation
( commercial
product) - 279 29
molten nitrate 600 326 30
B. 4 CoO/12 MoO3/84 Al203, or containing 3.2%
by wt of Co and 8.0% by wt of Mo.
impregnation 650 229 19
molten nitrate 500 449 38
" " 650 284 26
C. 10 NiO/20 MoO3/70 Al203, or containing 7.7%
by wt of Ni and 13.3% by wt of Mo.
impregnation 650 170 26
molten nitrate 500 463 68
" " 650 226 46
It is clear that the catalysts prepared ac-
cording ~ the invention are more effective.
EXAMPLE II
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To compare the resistance to sulphur the
catalysts of the type used in Example I A. were
exposed to different sulphur concentrations, each
test being carried out in five consecutive steps
corresponding with dif.ferent H2S concentrations:
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% by volume of H2S 0 0.4 1 3 0
duration of the
step (hours) 24 24 24 24 8
The (H2 + H2S) concentration was maintained at
50% by volume. The other conditions were identical
to those of Example I, except the volume of the
catalytic bed, which was now 8.5 ml.
preparatlon surface conversion (%)
(m2/~) in the 5 steps
A. molten nitrate 420 0-10-18-30-23
B. " " 302 0-9-16-26-22
C
+ 8.3% by wt of K ex KN03 213 o-7-28-30-64
D. molten nitrate,
+ 8.3% by wt of K ex K2C03 237 1-23-33-38-76
It is clear that all the Co-Mo-A1203 catalysts
must be sulphurized in order to convert the C0.
After having been tested in sulphuric form, the
catalysts A and B were less effective when the H2S
content was reduced. But the addition of potassium
(+ 10% of K20 based on the weight of the catalyst
without K) and the subsequent sulphurization were
very favourable: the effectiveness improved when
the H S content was reduced
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EXAMPLE III
To determine the best source of alkali metal,
catalysts of the type used in Example I C. were
prepared according to the invention by adding 10% by
weight of K20, i.e. containing 7.1% by weight of
Ni, 12.1% by weight of Mo and 8.3% by weight of K,
based on the weight of the finished catalyst.
Al(N03)3 was melted (80C), and metallic Ni and a
potassium compound and subsequently the ammonium
paramolybdate were dissolved in the melt with con-
tinuous stirring. This gelatinous mixture was dried
at 200C until the ammonium nitrate had sublimed
completely and subsequently the mixture was calcined
at 500C for 2 hours. After cooling the stony
catalyst obtained was pulverized and sieved. The
test was identical to Example I except that the
cakalyst was preheated:
1) the temperature was increased under N2 to 220C
in 1 hour;
2) the dry charge was injected at 220C and 30 bar
for 30 minutes;
3) the test was started with the injection of
water vapour at 220C.
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catalyst source of K Co conversion
( % )
Ni-Mo-Al203 - 67
Ni-Mo-Al2o3-K 3 93
,. K2S04 57
~ KCl 77
" KMnO4 76
" K2MoO4 71
K2Cr207 68
2C3 87
" KQH 80
It is clear that with the exception of the
sulphate all the potassium compounds improve the
activity of the basic catalyst. The nitrate and
carbonate are most favourable.
5 EXAMPLE IV
To determine the maximum potassium content ex KN0
several catalysts having different potassium con-
centrations in the same basic composition
(10 NiO/20 MoO3/70 A1203) were prepared according to
Example III. The conditions of the test were identical
to those of Example III. The weight of the added
pokassium was calculated in K20 and was based on the
weight of the basic catalyst.
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containin~ K20 (~) conversion of C0 (~)
0 67
0.1 83
1.0 72
2.0 72
5.0 65
10.0 93
It is therefore favourable that the catalyst -~
contains either a minimum quantity (0.1%) or a
considerable quantity ~10%) of potassium.
