Note: Descriptions are shown in the official language in which they were submitted.
1~37~3
A PROCESS FOR THE PREPARATIO~ OF
FISCXER-TROPSCX CATALYSTS
The invention relates to a process for the preparation
of Fischer-Tropsch catalysts.
The preparation of hydrocarbons from a mixture of
carbon monoxide and hydrogen by contacting this mixture
at elevated temperature and pressure with a catalyst is
referred to in the literature as the hydrocarbon synthesis
according to Fischer-Tropsch. Catalysts which are often used
for this purpose contain one or more metals from the iron
group together with one or more promoters and sometimes a
carrier material. The preparation of the Fischer-Tropsch
catalysts can, in principle, be carried out in three ways,
viz. by precipitation, by melting or by impregnation. The
preparation of the catalysts by precipitation briefly
consists in an aqueous solution of a salt of a metal from
the iron group, to which, if desired, a salt of a promoter
and a carrier material may have been added, being rendered
alkaline, resulting in the precipitation of the catalyst.
One or more promoters and a carrier material may be added
to this precipitate. The preparation of the catalysts by
melting is effected, for instance, for iron catalysts
by fusing iron oxide with one or more promoter oxides.
Both the precipitation route and the melting route are not
very attractive procedures for the preparation of the
Fischer-Tropsch catalysts, since their reproducibility is
small. The nrecipitation route has the additional dis-
advantage that it takes up a great deal of time, whilst the
melting route requires much energy. ~loreover, the catalytic
properties of the catalysts prepared by melting and by
' `~
1~3'7~3
precipitation, particularly the activit;y and stability,
are often unsatisfactory. A much more attractive procedure
for the preparation of the Fischer-TroE)sch catalysts is
the impregnation route. It is easy to carry out, gives well
reproducible results and, as a rule leads to catalysts
with high activity and stability. The impregnation route
briefly consists in a porous carrier being impregnated
with one or more aqueous solution~ of salts of one or more
metals from the iron group and of one ;r more promoters,
followed by drying caIcining and reducing of the composite.
Many elements, ~uch as alkali metals, alkaline-earth metals,
metals from Group VI B, Ti, Zr, Th, V, Mn and Cu, are
eligible promoters for the catalysts prepared by impregnation.
A3 the carrier materials for the catalysts prepared by
impregnation, amorphous as well as crystalline materials
may be used. Suitable carriers are, inter alia, silica,
alumina, zirconia, thoria, boria and combinations thereof,
such as silica-alumina and silica-magnesia and further
zeolites, such as mordenite, faujasite and zeolite-omega.
The Applicant has carried out an extensive investigation
concerning the preparation of hydrocarbons from H2/C0
mixtures with an H2/C0 molar ratio smaller than 1.0, using
Fischer-Tropsch catalysts prepared by impregnation. In the
above-mentioned conversion the behaviour of these catalysts
25 was found to be greatly dependent on the following factors:
1) the nature of the metal from the iron group and the
load used,
2) the nature of the promoter and the load used,
3) the nature of the carrier, and
4) the temperature treatment used
Catalysts prepared by impregnation were found to have a
very high activity and a very high stability for the
conversion of H2/C0 mixtures with an H2/C0 molar ratio
smaller than 1.0, if they contain 30-75 pbw iron and
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5-40 pbw magnesium per 100 pbw alumina and have been calcined at a temperature of
from 700 to 1200C. These are novel catalysts.
The present patent application therefore relates to a process for
the preparation of novel catalysts, in which catalysts containing 30-75 pbw iron
and 5-40 pbw magnesium per lO0 pbw alumina are prepared by impregnating an
alumina carrier with one or more aqueous solutions of salts of iron and of
magnesium, followed by drying the composite, calcining it at a temperature of
from 700 to 1200C and reducing it. The patent application further relates to
the use of these catalysts for the preparation of hydrocarbons from an H2/C0
mixture with an H2/CO molar ratio smaller than 1.0 as the starting material.
The hydrocarbons are prepared by contacting the H2/C0 mixture at elevated
temperature and pressure with a novel catalyst as hereinbefore described.
When for the above-mentioned application use is made of catalysts
prepared according to the invention, preferred catalysts are those containing
40-60 pbw iron and 7.5-30 pbw magnesium per 100 pbw alumina. Further,
preferance is given to catalysts which contain, in addition to iron and
magnesium, a reduction promoter and a selectivity promoter. A suitable reduction
promoter is copper. Suitable selectivity promoters are the alkali metals, in
particular potassium. In addition to iron and magnesium it is preferred in the
catalyst preparation according to the invention to incorporate 0.5-5 pbw copper
and 1-5 pbw potassium per 100 pbw alumina into the catalyst by impregnation.
In the preparation of the catalysts the metal salts can be
deposited on the carrier in one or more steps. Between the impregnation steps
the material is dried and, optionally, calcined. Impregnation in more than one
step may be necessary for the preparation of catalysts with a high meta] load.
The metal salts may be deposited on the
, - 3 -
~143~3
carrier separately or together from one solution. An
attractive method of depositing the metal salts on the
carrier i9 the dry impreenation technique, according to
which a carrier is contacted with an aqueous solution of
the salts concerned, which aqueous solution has a volume
which is substantially the same as the pore volume of the
carrier. Sorption of the aqueous solution by the carrier
can be facilitated by heating the mixture. If this method
is chosen for the preparation of catalysts with a high
metal load, it may be neeessary to earry out more than
one dry impregnation and to dry the material between the
separate impregnation steps and, optionally, to ealeine
it. The requirement of using a ca~eination temperature
of 700-1200 C only applies to the ealeination immediately
preceding the reduetion. If more calcinations are carried
out in the eatalyst preparation, e.g. between several
impregnation steps, these ealeinationq may, if desired,
be carried out at a lower temperature. The ealcination
immediately preceding the reduction i9 preferably carried
20 out at a temperature of 750-850 C. The eatalyst preparation
is finished with a reduction. This reduetion is earried
out at elevated temperature with a hydrogenous ga~, e.gt
a mixture of hydrogen and nitrogen. The reduetion i9
preferably earried out at a temperature of 250-350 C.
The eatalysts prepared aeeording to the invention
are pre-eminently suitable for the preparation of hydro-
earbons from an H2/C0 mixture with an H2/CO molar ratio
smaller than 1Ø Sueh H2/C0 mixtures ean very suitably
be prepared by steam gasifieation of a carbon-containing
material. Examples of such materials are brcwn coal,
anthracite, eoke, erude mineral oil and fractions thereof
and oils produced from tar sand and bituminous shale.
The steam gasification is preferably carried out at a
temperature of from 900 to 1500C and a pressure of from
~143713
--5--
10 to 50 bar.
The preparation of hydrocarbons from an H2~C0 mixture
with an H2/C0 molar ratio smaller than 1.0, using a
Fischer-Tropsch catalyst according to the invention is
preferably carried out at a temperature of from 200 to
350C and in particular of from 250 to 350C, a pressure
of from 10 to 70 bar and in particular of from 20 to
50 bar and a space velocity of from 500 to 5000 and in
particular of from 500 to 2500 Nl gas/l catalyst/h. The
hydrocarbon preparation according to the invention can
very suitably be carried out by contacting the feed in
upward or downward direction through a vertically mounted
reactor in which a fixed or a moving bed of the catalyst
concerned is present.
The invention will now be explained with reference
to the following example.
Example
Eleven catalysts (A-H and 1-3) were prepared and
tested for the hydrocarbon synthesis aceording to Fischer-
Tropsch. The preparation of the catalysts was effectedby impregnating an alumina or silica earrier with aqueous
solutions containing one or more of the following salts:
iron nitrate, magnesium nitrate, copper nitrate and
potassium nitrate. In all impregnations the dry impregnation
technique was used. The reduction of the catalysts was
carried out at atmospheric pressure with an H2/N2 mixture
in a volume ratio of 3:1 at a superficial gas rate of 1.6 m/s.
Further details about the preparation of the individual
catalysts are given below.
Catalyst A
This eatalyst was prepared by impregnating an alumina
carrier first with a solution of Mg(N03)2, followed by
drying at 120 C and caleining for two hours at 400 C, and
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-6-
then impregnating with a solution of Fe(N03)3, Cu(N03)2
and KN03, followed by drying at 120 C, calcining for two
hours at 400C and reduction at 280C.
Catalyst B
The preparation of this catalyst was performed in
substantially the same way as the preparation of catalyst
A, the difference beine that after the second calcination
at 400C another calcination was carried out at 800C.
Catalyst C
The preparation of this catalyst wa~ performed in
sub~tantially the same way a~ the preparation of catalyst
A, the differences being that in the second impregnation a
; solution was used with higher concentration~ of Fe, Cu and
K and that the ~econd calcination was carried out for
16 hours at 650 C.
Catalyst D
This catalyst was prepared by impregnating an alumina
carrier with a solution of Mg(N03)2-, Fe(N03)3, Cu(N03)2
and KN03, followed by drying at 120 C, calcining for two
hours at 400 C and reduction at 280 C.
Catalyst E
The preparation of this catalyst was performed in
substantially the qame way as the preparation of catalyst D,
the differences being that a solution with higher concentrations
of Fe, Cu and K and not containing Mg was used, and that the
calcination was carried out for fourteen hour3 at 800C.
Catalyst F
The preparation of this catalyst was performed in
substantially the same way as the preparation of catalyst D,
the difference~ being that silica was used as the carrier,
that a solution was used with higher concentrations of
Fe, Cu and K3 and that the calcination was carried out
for fourteen hours at 800 C.
7~3
~: C _ yst G
The preparation of thi~ catalyst was performed in
substantially the same way as tbe preparation of cata-
lyst D, the differences being that a so:Lution with higher
concentrations of Mg, Fe, Cu and K was used, and that the
calcination was carried out for fourteen hours at 800C.
_talyst H
The preparation of this catalyst was performed in
substantially the same way a~ the preparation of cata-
lyst A, the difference being that the reduction wascarried out at 400 C.
CataLyst 1
The preparation of this catalyst was performed in
substantially the same way as the preparation of catalyst A,
the differences being that in the second impregnation
a solution with higher concentrations of Fe, Cu and K
was used, that the second calcination was carried out
for sixteen hours at 300C, and that the reduction was
carried out at 325C.
Catalyst 2
The preparation of this catalyst was performed in
substantially the same way as the preparation of cata-
lyst A, the differences being that in the first impregnation
a solution with a higher concentration of Mg was used,
that in the second impregnation a solution with higher
concentrations of Fe, Cu and K was used, that the second
calcination was carried out for sixteen hours at 800C,
and that the reduction was carried out at 300C.
Catalyst 3
The preparation of this catalyst was performed in
substantially the same way as the preparation of cata-
lyst A, the differences being that calcination after the
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--8--
first impregnation step was omitted, that in the second
impregn2tion a solution with higher concentrations of Fe,
Cu and K was used, that the calcination after the second
impregnation was carried out for sixteen hours at 800 C,
and that the reduction was carried out at 325C.
The composition of the catalysts is shown in Table A.
Table A
Cat. No. Composition expressed in pbw
Fe Mg Cu 2 3 SiO2
.
A 25 20 1.25 2 100 ---
B 25 20 1.25 2 100 ---
C 50 20 2.5 4 100 ---
D 25 20 1.25 2 100 ---
E 50 -- 2.5 4 100 -__
F 50 20 2.5 4 --- 100
G 50 50 2.5 4 100 ---
H 25 20 1.25 2 100 ---
1 50 20 2.5 4 100 ---
2 50 `10 2.5 4 100 ---
3 60 20 3 4 100 ___
_
- The teating of the catalysta A-H and 2 and 3 for the
hydrocarbon aynthesis according to Fiacher-Tropsch from
aynthesis gas with an H2/C0 molar ratio of 0.5 as the
starting material was performed in a 250-ml reactor which
contained a catalyst bed with a volume of 50 ml. The expe-
rimenta were carried out at a temperature of 280 C, a
preasure of 30 bar and a space velocity of 1000 Nl.l 1.h
The results of these experimenta are shown in Table B.
~L14~7~3
.
g
Table B
Exp. No. Cat. No. conversion of the ~ynthesis gas, %
After 25 hAfter 500 h
_
1 A 75
2 B 28
3 C 87 37
4 D 64
E 71
6 F 74
7 G 69
8 H 76
9 2 91 89
3 92 89
Catalyst l was tested for 3150 h for the hydrocarbon
~ynthesis accordine to Fischer-Tropsch from a synthesis gas
with an H2/C0 molar ratio of 0.6 as the starting material.
The experiment (exp. 11) was carried out in substantially
the same way as the experiments 1-10, the difference being
that the experiment was continued over a longer period,
during which temperature and space velocity were varied.
The results of experiment 11 and the reaction conditions
used are shown in Table C.
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-10
Table C
Conditions during the experiment Result __ __
Period in Temp., Space velocity At run Conversion of
run hours C Nl.l .h 1 hourthe synthesis gas,
-- -- -- .. . . .
0- 25 280 1000 25 93
25- 500 280 1000 500 90
500- 900 280 1000 900- 85
900-1350 270 500 1350 80
1350-1850 280 500 1a50 80
1850-2300 295 500 2300 85
2300-2800 305 500 2800 81
2800-3150 305 350 3150 80
_ _ . _ _ _
Of the experiments mentioned in Tables B and C only
experiments 9-11 were carried out with catalysts prepared
according to the invention. In these experiments the
catalysts showed both a very high activity and a very high
stability. The experiments 1-8 were carried out with catalysts
which are outside the scope of the invention. They have
been included in the patent application for comparison.
The iron content of the catalyst~ A, D and H was
too low and the temperature at which these catalysts had
been calcined was too low. The results of experiments
1, 4 and 8 show that these catalysts had a low activity.
The catalysts ~, E, F and G contained too little
iron, no magnesium, no alumina and too much magnesium
respectively. The results of experiments 2, 5, 6 and 7
show that these catalysts had a low activity.
The temperature at which catalyst C had been calcined
was too low. The result3 of experiment 3 show that this
catalyst indeed had a high activity, but a very low stability.
