Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PREPARATIO~ OF CATALYST MIXTURES
The invention relates to a process for the preparation
of a catalyst mixture suitable for the conversion of a mix-
ture of carbon monoxide and hydrogen into an aromatic hydro-
carbon mixture.
Mixtures of carbon monoxide and hydrogen can be conver-
ted into an aromatic hydrocarbon mixture by using a mixture
of two catalysts, one of which is a zinc-containing compo-
sition which, in addition to zinc, comprises one or more of
the metals chromium, copper and aluminium and which compo-
sition has been prepared by the calcination of one or more
precipitates obtained by adding a basic reacting substance
to one or more aqueous solutions comprising salts of the
metals involved, and the other a crystalline metal silicate
having a special structure. The said crystalline metal sili-
cates are characterized in that, after one hour's calcina-
tion in air at 500C, they have the following properties:
a) thermally stable up to a temperature of at least 600C,
b) an X-ray powder dif~raction pattern in which the strongest
lines are the four lines mentioned in Table A.
Table A
d(A) Relative Intensity
11.1 + 0.2 S
10.0 + 0.2 S
3.84 = 0.07 VS
3.72 + o.o6 vs
in which the letters used have the following meanings:
VS = very strong 9 S = strong, and
c) in the formula which represents the composi'cion of the
silicate, expressed in moles of the oxides, and which,
in additlon to SiO2, includes one or more oxides of a
trivalent metal A chosen from the group formed by aluminium,
iron, gallium, rhodium, chromium and scandium, the SiO2/A2O3
molar ratio is higher than 10.
In the present patent application a crystalline sili-
cate having a thermal stability of tC should be taken tobe a silicate whose X-ray powder diffraction pattern remains
substantially unchanged upon heating to a temperature of tC.
The above-mentioned catalyst mixtures have till now
been used in the form of a coarse mixture obtained by mecha-
nically mixing particles of the zinc-containing composition
and the crystalline silicate, each having an average par-
ticle size in the range of from 0.1 to 0.5 mm. Although the
above-mentioned catalyst mixtures show quite an acceptable
performance when used for converting a H2/CO mixture into
an aromatic hydrocarbon mixture, there still is a desire to
enhance this performance, particularly where the Cs~ select
ivity and aromatics production are concerned.
On the presumption that the above-mentioned proper-
ties of the catalyst mixture might possibly be improved
b~ bringing about a more intimate contact between the two
components of the mixture9 a number of experiments were
carried out using catalysts based on a fine mixture, which
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catalysts had been obtained by grinding each individual
original mixture component having an average particle size
in the range of from 0.1 to 0.5 mm to an average particle
size of less than 5 micron, mixing the resulting powders
mechanically, and pressing and grinding the mixture into
particles of an average particle size in the range of from
0.1 to 0.5 mm. The results of these experiments were most
unsatisfactory. Although an improvement was seen in the
Cs~selectivity, this was accompanied with a very sharp
decrease in activity as well as a decrease in C3~ selec-
tivity and aromatics production.
Although from the above mentioned results one could
not but conclude that the chosen manner of bringing about
a more intimate contact between the mixture components will
not lead to the achievement of the object in view (enhance-
ment of the catalytic properties of th`e mixture~, an attempt
was nevertheless made at attaining a more intimate contact
between the components in a different wa~y. The method of
preparing the mixture chosen for the purpose was spray-
drying. Spray-drying is a method which for many years past
has been in use on a commercial scale for preparing small
spherical particles starting from a solid material or
mixture of solid materials. The method comprises atomising
a dispersion in water of the substance to be spray-dried
through a nozzle or from a rotating disc into a hot gas.
This method is particularly suitable for effecting a very
intimate contact between various substances.
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In the preparation of the present catalyst mixtures
by spray-drying the starting material was an aqueous disper-
sion which in addition to the crystalline silicate, comprised
a zinc-containing precipitate prepared in the same manner
as the precipitate mentioned hereinbefore which had been
calcined to form one of the two catalyst components. The
small spherical particles obtained during spray-drying were
pressed and the pressed material was ground to an average
particle size in the range of from 0.1 to 0.5 mm to yield a
catalyst having excellent properties for the conversion of
a H2/C0 mixture into an aromatic hydrocarbon mixture.
In comparison with the coarse mixture obtained by mechanical
mixing described hereinbefore, the mixture prepared by spray
drying showed both a much higher Cs~ selectivity and a
much higher aromatics production. In view of the previous
disappointing results concerning intimate contact between
the catalyst components, obtained in the experiments with
the catalysts prepared starting from the fine mixture, the
result now obtained is considered to be surprising. The pre-
paration of the present catalyst mixtures by spray-drying
is novel.
The present patent application therefore relates to
a process for the preparation of a catalyst mixture in
which a crystalline metal silicate having the properties
mentioned under a)-c) is dispersed in water together with
one or more precipitates in which zinc and one or more
metals chosen from chromium, aluminium and copper are
present, and which precipitates have been obtained by ad-
ding a basic reacting substance to one or more aqueoussolutions of salts of the metals involved, and in which
from the dispersion thus obtained the desired catalyst
mixture is prepared by spray-drying~ In view of their
form, size and strength, the catalyst particles prepared
according to the invention are very suitable for use in
a fluidized state.
Although in the process according to the invention
crystalline silicates comprising more than one metal A
may be used, preference is given to silicates in which
only one metal A is present and in particular to silicates
comprising aluminium, iron or gallium as metal A. The
crystalline silicates should have an SiO2/A203 molar ratio
higher than 10. Preferably silicates are used having an
Si02/A203 molar ratio lower than 1000 and in particular
in the range of from 20 to 500. The crystalline silicates
are defined, among other things, by the X-ray powder dif-
fraction pattern. Its strongest lines should be the four
lines given in Table A. The complete X~ray powder diffrac-
tion pattern of a typical example of a silicate that maybe used in the process according to the invention is given
in Table B.
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Table B
d(~) Rel. int. d(~)Rel. int.
11.1 57 3.84 (D) 100
10.0 (D) 31 3.70 (D) 70
8.93 1 3.63 16
7.99 1 3.47
7.42 2 3.43 5
6.68 7 3.34 2
6.35 11 3.30 5
5.97 17 3.25
5.70 7 3.05
5.56 10 2.98 11
5.35 2 2.96 3
4.98 (D) 6 2.86 2
4.60 4 2.73 2
4.35 5 2.60 2
4.25 7 2.48 3
4.07 2 2.40 2
4.00 4
(D) = doublet
The crystalline silicates may be prepared starting from
an aqueous mixture comprising the following compounds: one
or more silicon compounds, one or more compounds in which
a mono-valent organic cation (R) is present or from which
-
s~
- such a cation is formed during the preparation of the sili-
cate, one or more compounds in which a trivalent metal A is
present and, if desired, one or more compounds of an alkali
metal (M). The preparation is carried out by maintaining
the mixture at an elevated temperature until the silicate
has formed and subsequently separating the silicate crystals
from the mother liquor, and washing, drying and calcining
the crystals. In the aqueous mixture from which the sili-
cates are prepared the various compounds should be present
in the following ratios, expressed in moles of the oxides:
M20 : SiO2 < 0.35,
R20 : SiO2 = 0.01-0.5,
SiO2 ~ A203 > 10, and
H20 : SiO2 = 5-65.
When in the preparation of the crystalline silicates
the starting mixture is an aqueous mixture comprising one
or more alkali metal compounds, crystalline silicates may
be obtained which comprise alkali metal. Subject to the
concentration of the alkali metal compounds in the aqueous
mixture, the crystalline silicates obtained may comprise
more than 1% w alkali metal. Since the presence of alkali
metal in the crystalline silicates has an unfavourable
influence on their catalytic properties, the usual proce-
dure when crystalline silicates have a relatively high
alkali metal content, is to reduce this content before
using such silicates as catalysts. Reduction of the alkali
metal content to about 200 ppmw is sufficient to this end.
,
, .,
-- 8 --
It has been found that further reduction of the alkali
metal content will have virtually no more effect on the
catalytic properties of the silicate. The reduction of the
alkali metal content of crystalline silicates may very
suitably be carried out by treating the silicates once
or several times with a solution of an ammonium compound.
In this treatment alkali metal ions are exchanges for NH
ions, and the silicate is converted into the NH4+ form.
The NH41 form of the silicate is converted into the
H-~ form by calcination.
In the preparation of ~he catalyst mixtures according
to the invention one or more precipitates are used in
which zinc is present together with one or more of the me-
tals chromium, aluminium and copper and which precipitates
have been obtained by adding a basic reacting substance
to one or more aqueous solutions of salts of the metals
involved. Examples of metal combinations eligible for intro-
duction, ~ia the precipitates, into the catalyst mixtures
to be prepared by spray-drying are zinc-chromium, zinc-
chromium-copper and zinc-aluminium-copper. Preference is
given to the use of precipitates which, in addition to
zinc, comprise chromium, in particular precipitates in
which the atomic percentage of zinc, calculated on the sum
of zinc and copper, it is at least 60% and in particular
of from 60-80%. The metal-containing precipitates which,
in the process according to the invention, are dispersed
in water together with the crystalline silicate, may be
S~
- 9
prepared by precipitation of the indiviclual metals, or by
co-precipitation of the desired metal combination. Thus,
for the preparation of a catalyst mixture in which the
metal combination zinc-chromium is to be incorporated via
the precipitates, preclpitates may be formed starting from an
aqueous solution of a zinc salt and an aqueous solution of a
chromium salt, by adding a basic reacting substance to each of
these solutions, and the two precipitates may be dispersed in
water either individually or a~ter previous mixing, together
with the crystalline silicate. In the process according to the
invention preference is given to the use of a co-precipitate
obtained by adding a basic reacting substance to an aqueous
solution comprising all the metals involved. Such a co precipit-
ation is preferably carried out in a blending unit with a
continuous supply of an aqueous solution comprising the metal
salts involved and an aqueous solution of the basic reacting
substance in a stoichiometric quantity, calculated on the
metals, and with a continuous discharge of the co-precipi-
tate formed. It is advisable to allow the metal precipitates to
age in the mother liquor for some time and subseauently to wash
them thoroughly with water before dispersing them, together with
the crystalline silicate, in water. Suitable basic reacting sub-
stances that may be used in the preparation of the metal
precipitates are ammonium hydroxide, sodium carbonate and
alkali metal hydroxides. The basic reacting substances are
preferably used in the form of an aqueous solution.
As regards the ratios between the quantities of metal-
t~
-- 10 --
containing precipitate and crystalline silicate present
in the dispersion from which the catalyst mixture is pre-
pared by spray-drying, these are preferably chosen such
that a catalyst mixture is obtained which per pbw of sili-
5 cate comprises 2.5-12.5 pbw, and more in particular 4-8 pbw,
of metal oxides originating in the precipitake. Conditions
suitable f`or carrying out the conversion of a H2/CO mix-
ture into an aromatic hydrocarbon mixture using a catalyst
mixture prepared according to the invention are: a tempe-
10 rature of from 200-500C and in particular of from 300-450C,
a pressure of` from 1-150 bar and in particular of from 5-100
bar and a space velocity of from 50-5000 and in particular of
from 300-3000 Nl gas/l catalyst/hour. Pre~erably the feed used
is a H2/C0 mixture having a H2/C0 molar ratio in the range
15 of from 0.25 to 1Ø Such H2/C0 mixtures may very suitably be
prepared by steam gasification of a carbonaceous material, such
as coal, at a temperature of from 900-1500C and a pressure of
from 10-50 bar.
The conversion of a H2/C0 mixture into an aromatic
20 hydrocarbon mixture described hereinbefore may very suit-
ably be used as the first step in a two-step process for
the conversion of H2/C0 mixtures into hydrocarbon mix-
tures. In that case carbon monoxide and hydrogen present
in the reaction product from the first step are contacted
25 in a second step - together with other components of this
reaction product, if desired - with a catalyst comprising
one or more metal components having catalytic activity
5~
~or the conversion of a H2/C0 mixture into paraffinic
hydrocarbons, which metal components have been chosen from
the group formed by cobalt, nickel and ruthenium, care being
taken that the feed for the second step has a H2/CO molar
ratio of from 1.75-2.25.
The conversion of a H2/C0 mixture into an aromatic
hydrocarbon mixture described hereinbefore may further be
used very suitably as the first step of a three-step pro-
cess for the preparation, inter alia, of middle distillates
from a H2/C0 mixture. In that case carbon monoxide and
hydrogen present in the reaction product from the first
step, are contacted in a second step ~ together with other
components of this reaction product, if desired - with a
cobalt catalyst comprising zirconium, titanium or chromium
as promoter~ care being taken that the feed for the second
step has a H2/C0 molar ratio of from 1.75-2.25. At least
that part of the reaction product ~rom the second step whose
initial boiling point lies above the final boiling point of
the heaviest middle distillate desired as end product is
subjected in a third step to a catalytic hydrotreatment.
The invention is now illustrated with the aid of the
following Example.
Example
Catalyst preparation.
Preparation of a Zn/Cr precipitate.
Zn(N03)2.6 aq and Cr(N03)3O9 aq were dissolved in water
in such quantities that a Zn/Cr solution was obtained com-
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- 12 -
prising 1.15 g ion Zn ~ Cr per litre and having a Zn/Zn ~ Cr
atomic ratio of 0.67. This solution, together with a stoi-
chiometric quantity of a 10% aqueous NH3 solution, was
pumped with stirring through a blending unit which was kept
at a temperature of 20C. The volume of the blending unit
was 350 ml. The ratio of the feed rates was chosen such as
to ensure a value for the pH, measured at the outlet of the
blending unit, of between 7 and 8. The pumping rates were
chosen such as to allow a throughput of 100 1 per hour. The
Zn/Cr precipitate obtained was collected and left to age
for one hour with stirring at 20C. The solid material was
filtered off and washed with water until the wash water
was free from N03- ions. The N03~-free Zn/Cr precipitate thus
obtained was divided into two portions A and B.
Catalyst 1
.
This catalyst was prepared by drying the above-mentioned
portion A of the Zn/Cr precipitate for 16 hours at 120C,
grinding the dried material to an average particle size
of 0.4 mm and calcining the ground material for one hour
in air at 400C.
Catalyst 2
A crystalline aluminium silicate was prepared as follows.
A mixture of NaOH, (C3H7)4NOH, amorphous silica and
NaA102 in water, having the molar composition
3Na2- 4-5 [(C3H7)4N]20. 25 SiO2. 0.04 Al203. 450 H20,
was heated for 24 hours with stirring in an autoclave at
150C under autogenous pressure. After cooling of the re-
action mixture the silicate formed was filtered off, washedwith water until the pH of the wash water was about 8, and
dried at 120C. After one hour's calcination in air at 500C
the silicate had the following properties:
a) thermally stable up to a temperature of at least 900C,
b) an X-ray powder diffraction pattern substantially
corresponding with that given in Table B, and
c) an SiO2/Al203 molar ratio of 225.
The silicate was boiled with a 1.0 molar NH4N03
solution, washed with water, boiled again with a 1.0 molar
NH4N03 solution and washed with water and dried at
120C. Catalyst 2 was prepared by pressing and grinding
the dried material to an average particle size of 0.4 mm
and calcining the ground material for one hour in air at
500C.
Catalyst 3
-
Catalyst 3 was prepared starting from a crystalline
aluminium silicate, which after one hour's calcination in
air at 500C, had the following properties:
a) thermally stable up to a temperature of at least 8000C,
b) an X-ray powder diffraction pattern substantially
corresponding with that given in Table B, and
c) an SiO2/Al203 molar ratio of 290.
The silicate was boiled with a 1.0 molar NH4N03 solu-
: 25 tion and washed with water. The silicate thus obtained was
divided into two portions C and D.
Catalyst 3 was prepared by drying the above-mentioned
portion C of the silicate at 120C, pressing and grinding
.
.
r~
the dried material to an average particle size of 0.4 mm and
calcining the ground material for one hour in air at 500C.
Catalyst mixture I
This catalyst mixture was prepared by mixing catalyst 1
and catalyst 2 in a weight ratio of 1001.
Catalyst mixture II
This catalyst mixture was prepared by milling each of
catalysts 1 and 2 individually in a ball mill to an average
particle size o~ less than 5 micron, mixing the milled ca-
talysts 1 and 2 very intimately in the weight ratio of 10:1,and finally pressing and grinding the mixture to an average
particle size of 0.4 mm.
Catalyst mixture III
This catalyst mixture was prepared by mixing catalyst 1
and catalyst 3 in a weight ratio of 5:1.
Catalyst mixture IV
This catalyst mixture was prepared by milling each of
catalysts 1 and 3 individually in a ball mill to an average
particle size of less than 5 micron, mixing the milled cata-
lysts 1 and 3 very intimately in the weight ratio of 5:1 andfinally pressing and grinding the mixture to an average par-
ticle size of 0.4 mm.
Portion D of the crystalline silicate was dried for
16 hours at 120C and then calcined in air for one hour
at 500C. The material thus obtained was dispersed in water
using a turbostirrer to give a concentration of 200 g per
litre. So much of portion B of the Zn/Cr precipitation was
- 15 -
stirred into the dispersion thus obtained that the weight
ratio of ZnO + Cr2O3 to silicate in the dispersion was
5:1O Finally so much water was stirred into the dispersion
that the solids content thereof was 15% w. Settling of the
dispersion was prevented by continuous st.irring. The dis-
persion thus obtained was spray-dried in air in a counter-
current operation using compressed air. The inlet tempe-
rature of the air was 300C, the outlet temperature of
the air was 120C. The pressure used was 0.4 bar. The
powder obtained, which consisted substantially of sphe-
rical particles having an average particle size of 50
micron and a bulk density of 1.33 g~ml, was divided into
two ~ortions E and F. Catalyst mixture V was prepared
from portion E by pressing, grinding to an a~erage par
ticle size of 0.4 mm and calcination in air for one hour
at 400C. Catalyst mixture VI was prepared from portion
F, by calcination in air for one hour at 400C.
Catalyst mixtures I-VI were tested for the prepara-
tion of an aromatic hydrocarbon mixture from a H2/C0
mixture. Catalyst mixtures I V were tested in a 50-ml
reactor containing a fixed catalyst bed of 7.5 ml volume.
In five experiments a H2/CO mixture having a H2/CO molar
ratio of 0.5 was passed over each of catalyst mixtures I-V
at a temperature of 375C, a pressure of 60 bar and a space
velocity of 850 Nl.kg-1.h-1. The results of the experiments,
averaged over the first 100 hours~ are given in Table C.
- 16 -
Table C
Experiment No. 1 2 3 4 5
Catalyst mixture No. I II III IV V
Conversion of syn-
thesis gas, %v 60 41 60 45 55
C3~ selectivity, cal-
culated on C1 T ~ %W93 89 93 88 93
Cs~ seleckivity, cal-
culated on C1~, %w 73 79 63 72 81
Composition of
Cs+ product, %w
paraffins 25 17 30 2l 6
naphthenes 16 30 10 22 9
aromatics ~ 52 60 57 85
Catalyst mixture VI was tested in a vertically arranged
fluid-bed reactor, 175 cm in height and of 500 ml volume,
containing 314 ml catalyst. The depth of the catalyst bed
in the settled condition was 100 cm. A H2/C0 mixture having
a H2/C0 molar ratio of 0.5 was contacted with catalyst
mixture VI at a temperature of 380C, a pressure of 60 bar
and a superficial gas rate of 1.3 cm/s (corresponding with
a space velocity of about 850 Nl.kg-1.h-1). The results
of this experiment (Experiment 6), averaged over the first
50 hours, are given in Table D.
~ ~ ~ 5
- 17 -
Table D
Experiment No. 6
Catalyst mixture No~ VI
Conversion of synthesis gas, % v 55
C3+ selectivity, calculated on C1+, % w 94
Cs+ selectivity, calculated on C1~, % w 82
Composition of Cs+ product, % w
:
paraffins 10
naphtenes 15
aromatics 75
Research octane number (RON-O) of the
Cs+ fraction g9
As regards the results mentioned in Table C, the
following may be observed:
a) Of catalyst mixtures I-V only catalyst mixture V was
prepared according to the invention. The other cata-
lyst mixtures fall outside the scope of the invention.
They have been included in the patent application for
comparison.
b) Of Experiments 1-5 only Experiment 5 was carried out
using a catalyst mixture prepared according to the
invention.
c) Comparison of the results of Experiment 1 (using
a 10:1 coarse catalyst mixture) with those of Experi-
ment 2 (using a 10:1 fine catalyst mixture) clearly
shows the unfavourable effect of the intimate mixing
upon activity, C3+ selectivity and aromatics pro-
duction.
d) A similar effect may be seen upon comparison of the
results of Experiment 3 (using a 5:1 coarse catalyst
mixture) with those of Experiment 4 (using a 5:1 fine
catalyst mixture).
e) Comparison o~ the results of Experiment 3 (using
a 5:1 coarse catalyst mixture) with those of Experi-
ment 5 (using a 5:1 catalyst mixture prepared by spray-
drying) clearly shows the highly favourable influence
of the preparation through spray-drying on C5+ selec
tivity and aromatics production.
As regards the results mentioned in Table D the follow-
ing may be ob~erved. Fluid-bed Experiment 6, carried out using
a catalyst mixture prepared according to the invention yielded
a very attractive Cs+ product having a high aromatics
content and a high octane number.
