Note: Descriptions are shown in the official language in which they were submitted.
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"PREPARING A CATALYST CONTAINING A
GROUP VIII METAL AND A NON-ACIDIC PROMOTER
DISPERSED ON A SUPPORT VIA SIMULTANEOUS IMPREGNATION"
BACKGROUND OF THE INVENTION
Catalyst containing Group VIII metals plus modifiers such as alkali metals,
tin,
germanium, lead, indium, gallium, etc. are well known in the art. For example,
US-A-
4914075 discloses a dehydrogenation catalyst comprising a Group VIII metal
component, an
alkali or alkaline earth metal component and a component selected from tin,
germanium, lead,
indium, gallium, thallium or mixtures thereof. This catalyst is prepared by
impregnating the
support with the desired components. It is also known that chelating ligands
can be used to
impregnate metals onto a support. For example, US-A-4719196 discloses
preparing a catalyst
using a solution containing ethylene diaminetetraacetic acid (EDTA), a noble
metal and
ammonia.
A process for preparing catalysts has now been found which involves the use of
a
chelating ligand to simultaneously impregnate a Group VIII metal and a non-
acidic promoter
metal. The process involves preparing a solution containing a chelating ligand
such as EDTA
and a promoter metal. This solution is heated and then mixed with a solution
containing a
Group VIII metal compound and the resultant mixed solution aged. This aged
solution is now
used to impregnate a refractory oxide support such as O-alumina, followed by
calcination and
reduction to provide the desired catalyst having both the promoter metal and
the Group VIII
metal dispersed on the support.
SUMMARY
This invention relates to a process for preparing a catalyst via simultaneous
impregnation. The catalyst comprises a Group VIII metal and a non-acidic
modifier metal
dispersed on a solid refractory oxide support. Accordingly, one embodiment of
the invention
comprises a process of: a) mixing a first and a second aqueous solution to
give a mixed
solution, the first solution containing a chelating agent and at least one
promoter metal salt,
said first solution having been heated to a temperature from 80°C to
its boiling point, the
second solution containing at least one Group VIII metal compound; b) ageing
the mixed
solution for a time of 5 minutes to 4 hours at a temperature of 40 to
100°C; c) impregnating
said aged mixed solution onto a solid refractory oxide support to give an
impregnated solid
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CA 02166522 2003-03-20
support; d) calcining the impregnated solid support at a temperatwe of 300 to
850°C for a
time of 10 minutes to 8 hows to give a calcined catalyst; and e) reducing the
calcined
catalyst at a temperatwe of 300 to 850°C for a time of 30 minutes to 8
hours, thereby
providing said catalyst.
In another embodiment the catalyst from the process described above is treated
with
a stream of hydrogen chloride/chlorine at a temperatwe of 300 to 850°C
for a time of 30
minutes to 8 bows.
In a further embodiment, aluminum chloride may also be deposited on said
catalyst.
DETAILED DESCRIPTION
The catalyst prepared by the instant invention comprises a solid refractory
oxide
support having dispersed thereon at least one Group VIII metal and a non-
acidic promoter
metal. The support can be any of a number of well known supports in the art
including
aluminas, silica/alumina, silica, titanic, zirconia, and zeolites. The
aluminas which can be used
as support include gamma alumina, theta alumina, delta alumina, and alpha
alumina with
gamma and theta alumina being preferred. Included among the aluminas are
aluminas which
contain modif ers such as tin, zirconium, titanium and phosphate. The zeolites
which can be
used include: faujasites, zeolite beta, L-zeolite, ZSM-5, ZSM-8, ZSM-11, ZSM-
12 and
ZSM-35. The supports can be formed in any desired shape such as spheres,
pills, cakes,
extrudates, powders, granules, etc. and they may be utilized in any particular
size. A preferred
shape is spherical with a preferred particle size of about 1.59 millimeters in
diameter, though
particles as small as 0.79 millimeters and smaller also may be utilized.
One way of preparing a spherical alumina support is by the well known oil drop
method which is described in US-A-2620314° The oii drop
method comprises forming an aluminum hydrosol by any of the techniques taught
in the art
and preferably by reacting aluminum metal with hydrochloric acid; combining
the hydrosol
with a suitable gelling agent; and dropping the resultant mixtwe into an oil
bath maintained
at elevated temperatwes. The droplets of the mixture remain in the oil bath
until they set and
form hydrogel spheres. The spheres are then continuously withdrawn from the
oil bath and
typically subjected to specific ageing and drying treatments in oil and
ammoniacal solutions
to further improve their physical characteristics. The resulting aged and
gelled spheres are
then washed and dried at a relatively low temperature of 80 to 260°C
and then calcined at a
2
TEr_~iiperature of 455 to 705°C for a period of 1 to 20 hours. This
treatment effects conversion
of the hydrogel to the corresponding crystalline gamma alumina. If theta
alumina is desired
then the hydrogel spheres are calcined at a temperature of 950 to
1100°C.
The Group VIII metal or metals are dispersed onto the desired support as
follows.
First, an aqueous solution of a chelating ligand and at least one non-acidic
promoter salt is
prepared. The chelating ligands which can be used in the process of this
invention include
amino acids which upon decomposing do not leave detrimental components on the
support,
e.g., sulfur. Specific examples of these amino acids include
ethylenediaminetetraacetic acid,
nitrilotriacetic acid, N-methylaminodiacetic acid, iminodiacetic acid,
glycine, alanine,
sarcosine, a-aminoisobutyric acid, N,N-dimethylglycine, a, (3-
diaminopropionate, aspartate,
glutamate, histidine, and methionine.
Another necessary component of this first solution is a salt of a non-acidic
metal
promoter. The metal promoter is selected from the group consisting of alkali
and alkaline
earth metals. Examples of the salts of these promoter metals which can be used
include
potassium hydroxide, lithium hydroxide, sodium hydroxide, cesium hydroxide,
magnesium
hydroxide, etc. The resultant solution is heated to a temperature from about
80°C to its
boiling point and preferably from 90 to 102°C. The ratio of chelating
ligand to the metal salt
will vary from 1 to 8 and preferably from 1.5 to 4.
This first solution is now mixed with a second aqueous solution containing at
least one
Group VIII metal compound. Of the Group VIII metals which can be dispersed on
the desired
support, preferred metals are rhodium, palladium, platinum, nickel, cobalt and
iron, with
rhodium, palladium and platinum more preferred and platinum being most
preferred.
Illustrative of the Group VIII metal compounds which can be used in the
process of this
invention are chloroplatinic acid, palladic acid, tetraamine platinum
chloride, tetraamine
palladium chloride, bromoplatinic acid, rhodium chloride, ruthenium chloride,
gallium nitrate,
nickel chloride, nickel nitrate, cobalt nitrate, iron nitrate and iron
chloride.
Mixing of the first and second solutions results in the formation of a complex
between
the Group VIII metal and the chelating ligand. The metal promoter may also be
part of the
complex. In order to form the complex, the ratio of chelating ligand to Group
VIII metal
varies from 0.5 to 30 and preferably from 5 to 13. The ratio depends on the
concentration of
promoter metal and Group VIII metal, with higher ratios desirable for higher
concentrations
of metals. The concentration of the Group VIII metal and promoter metal can
vary
considerably, but is usually chosen to give a concentration on the support in
terms of weight
3
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percent of the support (as the metal) from 0.2 to 1 wt.% and from 0.5 to 3
wt.%, respectively.
The first solution described above may also contain a basic compound selected
from
the group consisting of ammonium hydroxide and quaternary ammonium compounds
having
the formula NR,RZR3R41X- where R,, R2, R3, R4 are each methyl, ethyl, propyl,
butyl or
t-butyl and X is hydroxide. The purpose of adding one or more of these basic
compounds is
to adjust the pH of the solution in order to vary the distribution of the
metals. That is, in
some cases it may be desirable to have a uniform distribution of the metals
whereas in other
cases a greater concentration on the surface may be desirable. Further, the
distribution of the
Group VIII metal may be different from the distribution of the promoter metal.
Without wishing to be bound by any one theory, it appears that there is a
relationship
between the isoelectric point (IEP) of the support and the pH of the
impregnating solution.
Thus, if the IEP is high, say 8, and the pH is low (1-2), then strong bonding
or chemisorption
may result in surface impregnation of the metal. By increasing the pH to 6-9,
a substantially
uniform distribution will be obtained. Similarly if both the IEP and pH are
low then uniform
distribution of the metals will result.
After obtaining the mixed solution, it is aged for a time of 5 minutes to 4
hours at a
temperature of 40 to 100°C. The aged mixed solution is now used to
deposit the metals onto
the support by means well known in the art. Examples of said means include
spray
impregnation and evaporative impregnation. Spray impregnation involves taking
a small
volume of the mixed solution and spraying it over the support while the
support is moving.
When the spraying is over, the wetted support can be transferred to other
apparatus for drying
or finishing steps.
One particular method of evaporative impregnation involves the use of a steam
jacketed
rotary dryer. In this method the support is immersed in the impregnating
solution which has
been placed in the dryer and the support is tumbled by the rotating motion of
the dryer.
Evaporation of the solution in contact with the tumbling support is expedited
by applying
steam to the dryer jacket. The impregnated support is then dried at a
temperature of 60 to
about 300°C and then calcined at a temperature of 300 to 850°C
for a time of 30 minutes to
8 hours to give the calcined catalyst. Finally, the calcined catalyst is
reduced by heating the
catalyst under a reducing atmosphere, preferably dry hydrogen, at a
temperature of 300 to
850°C for a time of 30 minutes to 8 hours. This ensures that the Group
VIII metal is in the
metallic or zerovalent state.
An optional step in the process of this invention involves oxychlorination of
the
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CA 02166522 2005-11-16
calcined catalyst described above prior to the reduction step. If such a step
is desired, the
calcined catalyst is placed in a reactor and a gaseous stream containing
chloride or chlorine
is flowed over the catalyst at a flow rate of 2 to 40 lb/hr, at a temperature
of 300 to 850°C
for a time of 10 minutes to 6 hours. The gaseous stream can be a hydrogen
chloride%hlorine
stream, a water/HCl stream, a waterlCl2 stream or a chlorine stream. The
purpose of this step
is to provide optimum dispersion of the Group VIII metal and provide a certain
amount of
chloride on the final catalyst.
In addition to the catalytic components described above, other components may
be
added to the catalyst. For example, a second modifier metal selected from the
group
consisting of tin, germanium, lead, indium, gallium, thallium, and mixtures
thereof may be
added to the catalyst. This second modifier metal either can be added to the
support during
the preparation of the support, for example, by adding a solution of the metal
compound to
the hydrosol or it may be impregnated onto the support either before or after
the impregnation
with the Group VIII metal and the non-acidic promoter. Impregnation onto the
support is
carried out in a manner similar to that described above with a suitable
impregnation solution
for the second modifier metal.
If the catalyst is to be used for alkylation, then the catalyst will also
contain a metal
halide having Friedel-Crafts activity. Alkylation here refers to alkylation of
C2-C6 olefins
with alkanes in the 4-6 carbon range. This type of alkylation is usually
referred to as motor
fuel alkylation. This metal halide is deposited onto the catalyst after the
catalyst has been
calcined, optionally oxychlorinated and reduced. Among the metals which have
Friedel-Crafts
activity are included aluminum, zirconium, tin, tantalum, titanium, gallium,
antimony, and
mixtures thereof. Preferred metals are aluminum, gallium, boron and mixtures
thereof.
Suitable halides are the fluorides, chlorides, and bromides. Representative of
such metal
halides include aluminum chloride, aluminum bromide, ferric chloride, ferric
bromide,
zirconium chloride, zirconium bromide, boron trifluoride, titanium
tetrachloride, gallium
chloride, tin tetrachloride, antimony fluoride, tantalum chloride, tantalum
fluoride, and so
forth. Of these metal halides the aluminum halides are .preferred, especially
aluminum
chloride. Except for boron trifluoride, the chlorides are generally the
preferable halides.
These metal halides are reacted with bound hydroxyls of the support.
Therefore, for
this type of alkylation catalyst it is necessary that the support have bound
hydroxyls. The
reaction between the metal halides and the bound surface hydroxyl groups of
the support is
readily accomplished by, for example, sublimation or distillation of the metal
halide onto the
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CA 02166522 2003-03-20
surface of the particles of the support. The reaction is attended by the
elimination of between
0.5 to 2.0 moles of hydrogen halide per mole of metal halide adsorbed thereon.
The reaction
temperature will depend upon such variables as the reactivity of the metal
halides and its
sublimation temperature or boiling point, where the metal halide is reacted in
the gas phase,
as well as on the nature of the support. For example, using aluminum chloride
and alumina
as shown in the examples, reaction readily occurs within the range between 190
to 600°C.
The amount of metal halide which is reacted with the bound surface hydroxyl
groups
of the support is generally given in terms of the weight percent of the
Friedel-Crafts metal on
the composite. This amount will vary with the support used, the relative
number of bound
surface hydroxyls of the support (which may be related to the particular oxide
phase utilized),
the specific Friedel-Crafts metal halide employed, as well as the particular
procedure used to
effect reaction between the Friedel-Crafts type metal halide and the bound
surface hydroxyl.
As a rough rule of thumb for aluminum chloride on alumina, as an example, the
amount of
aluminum chloride reacted expressed as weight percent aluminum in the final
composite ranges
from 0.1 up to 2.5%, with the level being a function primarily of the number
of bound
surface hydroxyl groups on the support.
The various catalysts prepared by the process of this invention are useful for
a number
of hydrocarbon conversion processes. For example, catalysts containing a Group
VIII metal,
especially platinum, and a first modifier metal, especially potassium, and a
second modifier
metal, especially tin, find uses as a dehydrogenation catalyst.
Dehydrogenation of
hydrocarbons involves contacting the catalyst with a dehydrogenatable
hydrocarbon in a
dehydrogenation zone maintained at dehydrogenation conditions. This contacting
may be
accomplished using a fixed catalyst bed system, a moving catalyst bed system,
a fluidized bed
system, or in a batch type system, with a fixed bed system being preferred.
The hydrocarbons
which can be dehydrogenated include dehydrogenatable hydrocarbons having from
2 to 30 or
more carbon atoms including para~ns, alkyl aromatics, naphthenes, and olefins.
Especially
preferred dehydrogenatable hydrocarbons are the C2-C6 paraffins and primarily
propane and
butanes.
Dehydrogenation conditions include a temperature from 400 to 900°C, a
pressure from
1 to 1013 kPa (0.01 to 10 atmospheres absolute) and a liquid hourly space
velocity (LHSV)
from 0.1 to 100 hr's. Other conditions and general considerations for carrying
out a
dehydrogenation process are well known in the art and are set forth, for
example, in US-A
4914075 .
6
With the addition of a metal halide function, the catalyst of this invention
can also be
used for motor fuel alkylation. Motor fuel alkylation is carried out by taking
a feedstock
mixture of alkanes and alkenes and reacting it with the desired catalyst at
alkylation
conditions. Alkylation conditions include a temperature as low as -10°C
and as high as 100°C
depending upon the particular feedstock used and the nature of the catalyst.
Temperatures
between 10 to 50°C are preferred. The reaction is carried out under a
pressure sufficient to
maintain the reactant in a liquid phase. The alkylation reaction zone normally
uses a bed of
the desired catalyst with the liquid phase reactant mixture being flowed
through it at a LHSV
of 0.1 to 5.0 hr-' .
EXAMPLE 1
A solution was prepared by combining in a flask 262.5 g of deionized water,
22.3 g
of a potassium hydroxide solution (39.5% KOH) and 11.6 g of EDTA. This
solution was
heated to boiling and then transferred to a rotary evaporator which was
controlled at 70°C.
To the evaporator there was added a second solution containing 79.1 g of
deionized water and
86 g of a solution containing chloroplatinic acid (2.92% Pt). The mixed
solution was aged
in the evaporator for 45 minutes.
To the aged solution there were added 283.5 g of gamma alumina spheres which
contained 0.3 weight percent tin and were prepared as described in US-A-
4914075 (Example
1). The temperature was raised to 100°C and the support rolled for 5
hours.
Next the impregnated support was heated to a temperature of 565°C in
dry air. When
the temperature was reached, an air stream containing HCl and C12 was flowed
through the
catalyst for 6 hours.
Finally, the catalyst was reduced by flowing pure hydrogen over the catalyst
at a
temperature of 562°C for 2-1/2 hours.
Analysis of the catalyst showed it to contain 0.75 wt.% Pt and 2.2 wt.% K. The
platinum was evenly distributed throughout the support while the potassium had
a slight
gradient from the surface toward the interior (higher at the surface). This
catalyst was
identified as catalyst A.
7
,, ,
EXAMPLE 2
A solution was prepared by combining in a flask 276.7 g of deionized water,
8.1 g of
a potassium hydroxide solution (39.5% KOH) and 4.2 g of EDTA. This solution
was heated
to boiling and then transferred to a rotary evaporator which was controlled at
70°C. To the
evaporator there was added a second solution containing 102.7 g of deionized
water and 62.4 g
of a solution containing chloroplatinic acid (2.92% Pt). The mixed solution
was aged in the
evaporator for 45 minutes.
To the aged solution there were added 310.5 g of theta alumina spheres which
contained 0.3 weight percent tin and were prepared by first preparing gamma
alumina spheres
(plus Sn) as described in US-A-4914075 (Example 1) and then calcining the
support to a
temperature of 565°C for 2 hours. The temperature was raised to
100°C and the support rolled
for 5 hours.
Next the impregnated support was heated to a temperature of 565°C in
dry air. When
the temperature was reached, an air stream containing HCl and C12 was flowed
through the
I S catalyst for 6 hours.
Finally, the catalyst was reduced by flowing pure hydrogen over the catalyst
at a
temperature of 562°C for 2-1/2 hours.
Analysis of the catalyst showed it to contain 0.60 wt.% Pt and 0.73 wt.% K.
This
catalyst was identified as catalyst B. The catalyst was found to have the
platinum evenly
distributed, while the potassium was concentrated on the surface.
EXAMPLE 3
A solution was prepared by combining in a flask 276.8 g of deionized water,
7.9 g of
a potassium hydroxide solution (39.5% KOH), 4.17 g of EDTA, and 4.0 g of
tetramethylammonium hydroxide. This solution was heated to boiling and then
transferred to
a rotary evaporator which was controlled at 70°C. To the evaporator
there was added a second
solution containing 102.34 g of deionized water and 62.8 g of a solution
containing
chloroplatinic acid (2.92% Pt). The mixed solution was aged in the evaporator
for 45 minutes.
To the aged solution there were added 310.5 g of theta alumina spheres which
contained 0.3 weight percent tin and were prepared by first preparing gamma
alumina spheres
(plus Sn) as described in US-A-4914075 (Example 1 ) and then calcining the
support to a
temperature of 1037°C for about 2 hours. The temperature was raised to
100°C and the
8
,,
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support rolled for 5 hours.
Next the impregnated support was heated to a temperature of 565°C in
dry air. When
the temperature was reached, an air stream containing HCl and C12 was flowed
through the
catalyst for 6 hours.
Finally, the catalyst was reduced by flowing pure hydrogen over the catalyst
at a
temperature of 562°C for 2-1/2 hours.
Analysis of the catalyst showed it to contain 0.6 wt.% Pt and 0.7 wt.% K. Both
the
platinum and potassium were evenly distributed throughout the support. This
catalyst was
identified as catalyst C.
EXAMPLE 4
Catalysts A, B and C were tested for dehydrogenation activity as follows. In a
vertical
reactor there were placed 20 cc of the catalyst which was heated to about
532°C. Through the
reactor there was flowed a feedstream consisting of isobutane and hydrogen at
a Hz/HC ratio
of 1.0 mol/mol and at a LHSV of 20 hr-'. Conversion is measured versus time on
stream.
The results for each catalyst from this test are presented in the Table below.
Table
Catalyst Conversion Selectivity
Initial Final Initial Final
A 36 31 92 92
B 41 3 5 92.5 94
. C 41 35 95 95
The data indicate that catalyst C with both the platinum and potassium evenly
distributed has
the best conversion and selectivity.
9
