Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS FOR THE PREPARATION OF CATALYST COMPOSITIONS
COMPRISING ZEOLITE AND A NON-ZEOLITIC COMPONENT
The present invention relates to a process for the preparation of shaped
catalyst
compositions comprising a zeolite and a non-zeolitic component.
It is generally known to prepare such compositions by mixing zeolite and a non-
zeolitic component, followed by shaping this mixture to form particles.
WO 01/12570, on the other hand, discloses the preparation of shaped bodies
comprising zeolite and non-zeolitic compounds (boehmite and anionic clay) by
a) preparing a precursor mixture comprising an aluminium compound, a
magnesium source, and zeolite,
b) shaping the precursor mixture to obtain shaped bodies, and
c) aging to obtain shaped bodies containing anionic clay, zeolite, and
boehmite,
the boehmite being formed from an excess of aluminium compound during the
aging step.
The advantage of having zeolite present during the formation of the non-
zeolitic
component is that the zeolite and the non-zeolitic component are more
homogeneously dispersed within the resulting shaped body than when using the
generally known method referred to above.
However, shaping the precursor mixture before aging, i.e. before the formation
of
the final amount of non-zeolitic component, generally results in relatively
low yields
of the non-zeolitic compound. One reason for this low yield is the fact that
the
(crystallization) reaction to obtain the non-zeolitic compound generally
occurs via
the water phase. After shaping, the shaped bodies will contain individual
precursor
particles at fixed positions in the body and interaction of these particles
with water
is therefore limited. Further, the fixation of the precursor particles in a
shaped body
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will also limit their contact with other precursor particles, which has a
negative
effect on the formation of non-zeolitic components from two different
precursors.
It has now been found that shaped bodies comprising homogeneously dispersed
zeolite and non-zeolitic component can be prepared wherein the yield of non-
zeolitic component is significantly higher.
The process according to the present invention comprises the steps of
a) aging a precursor mixture comprising zeolite and one or more precursors of
the
non-zeolitic component to obtain a composition comprising zeolite and non-
zeolitic component, and
b) shaping the composition comprising zeolite and non-zeolitic component to
form
shaped bodies.
The final product is a shaped body comprising zeolite and non-zeolitic
component.
The zeolite acts as a spacer embedded within the non-zeolitic component,
thereby
creating porosity and accessibility in the shaped body. The zeolite is
surrounded by
and in close contact with the non-zeolitic component. In other words, the
zeolite is
coated with the non-zeolitic component.
Preferred zeolites to be used in the process according to the present
invention are
pentasil zeolites (e.g.ZSM-5, zeolite beta), faujasite zeolites (e.g. zeolite
X and Y),
zeolite A, mordenite, chabazite, chinoptalozite, erionite, MCM-type materials
(e.g.
MCM-41), VIP-5, ITQ-21, SAPOs, ALPOs, and/or aluminasilicates according to
pre-published US patent application No. US/0048737 Al. If desired, the
zeolites
may be ultrastabilized (e.g. USY), flash-calcined, treated with organo-
silicate,
organo-borate, or organo-titanate, and/or optionally exchanged with alkaline
earth
metals, transition metals, and/or rare-earth metals.
In a preferred embodiment, both a faujasite zeolite and a pentasil zeolite are
used.
The process according to the invention allows both zeolites to be in intimate
contact
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with the non-zeolitic component (i.e. the matrix), resulting in enhanced
production
of light olefins when the shaped bodies are used as FCC catalyst or additive.
The
process according to the invention allows the faujasite zeolite and the active
matrix
(the primary cracking ingredient) to be in intimate contact (e.g. in NNN
arrangement) or, even better, to be attached to the pentasil-type zeolite (the
secondary cracking ingredient). Such a structural arrangement of primary and
secondary ingredients results in enhancement of the light olefins' yields in
the FCC
process.
Within this specification, the term "non-zeolitic component" is used for
compounds
which the person skilled in the art of catalysis does not regard as having a
zeolitic
structure. Examples of such non-zeolitic components include boehmite, anionic
clays (e.g. hydrotalcites), cationic clays (e.g. smectites), and aluminium
phosphate
gels.
A preferred non-zeolitic compound is boehmite. The term "boehmite" refers to
alumina hydrates which exhibit X-ray diffraction (XRD) patterns close to that
of
aluminum oxide-hydroxide [AIO(OH)] (naturally occurring boehmite or diaspore),
although they may contain different amounts of water of hydration and have
different surface areas, pore volumes, and specific densities, and different
thermal
characteristics upon thermal treatment. The XRD patterns of different types of
boehmite exhibit the characteristic boehmite [AIO(OH)] peaks, although the
sharpness and the precise location of these peaks depend on the degree of
crystallinity, the crystal size, and the amount of imperfections.
Broadly, there are two categories of boehmite aluminas: quasi-crystalline
boehmites (also called pseudo-boehmites or gelatinous boehmites) and micro-
crystalline boehmites. Quasi-crystalline boehmites usually have higher surface
areas, larger pores and pore volumes, and lower specific densities than micro-
crystalline boehmites. They disperse easily in water or acids, have a smaller
crystal
size, and contain a larger number of water molecules of hydration. As a result
of
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their smaller crystal sizes and their higher crystal imperfection, quasi-
crystalline
boehmites show broader XRD peaks than micro-crystalline boehmites.
For the purpose of this specification we define quasi-crystalline boehmites as
having (020) peak widths at half-length of the maximum intensity of 1.50 or
greater
than 1.50 2-theta. Boehmites having a (020) peak width at half-length of the
maximum intensity smaller than 1.5 2-theta are considered micro-crystalline
boehmites. For copper radiation, the (020) reflection appears at about 14 2-
theta.
Some typical, commercially available quasi-crystalline boehmites are Condea
Pural , Catapal , and Versal products. A typical commercially available micro-
crystalline boehmite is Condea's P-200 .
The crystallinity of the boehmite obtained in the product resulting from the
process
of the invention depends on the pH and the temperature of the precursor
mixture
during aging. With a higher temperature and pH, the crystallinity of the
resulting
boehmite increases.
Suitable boehmite precursors to be added to the precursor mixture of step a)
of the
process according to the invention are the aluminium compounds listed below.
It is
also possible to use two or more of these aluminium compounds as boehmite
precursors.
Other types of non-zeolitic components are anionic clays and cationic clays.
Anionic clays have a crystal structure consisting of positively charged layers
built
up of specific combinations of divalent and trivalent metal hydroxides between
which there are anions and water molecules. Hydrotalcite is an example of a
naturally occurring anionic clay, in which the trivalent metal is aluminium,
the
divalent metal is magnesium, and the predominant anion is carbonate;
meixnerite
is an anionic clay wherein the trivalent metal is aluminium, the divalent
metal is
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magnesium, and the predominant anion is hydroxyl. Synonyms of the term
"anionic
clay" are hydrotalcite-like material and layered double hydroxide.
Cationic clays are layered structures with cations between the layers. The
layers of
cationic clays are built up of trivalent and tetravalent metals and,
optionally,
divalent metals. A preferred class of cationic clays are smectite-type
materials.
Smectite-type materials comprise divalent, trivalent, and tetravalent metals
in the
layers, e.g. Mg, Al, and Si.
So, in order to obtain anionic clay as the non-zeolitic component, at least
two
precursors of the non-zeolitic component are required: a divalent and a
trivalent
metal compound. The formation of a cationic clay as the non-zeoltic component
requires at least a trivalent and a tetravalent and, optionally, a divalent
metal
compound as precursors.
Suitable divalent metal compounds include compounds of magnesium, zinc,
nickel,
copper, iron, cobalt, manganese, calcium, barium, and combinations thereof.
Suitable zinc, nickel, copper, iron, cobalt, manganese, calcium, and barium
compounds are the respective oxides, hydroxides, carbonates, acetates,
formates,
nitrates, and chlorides.
Suitable magnesium compounds include magnesium oxides or hydroxides such as
MgO, Mg(OH)2, hydromagnesite, magnesium salts such as magnesium acetate,
magnesium formate, magnesium hydroxy acetate, magnesium carbonate,
magnesium hydroxy carbonate, magnesium bicarbonate, magnesium nitrate, and
magnesium chloride, and magnesium-containing clays such as dolomite, saponite,
and sepiolite.
Preferred divalent metal compounds are oxides and hydroxides, as these
materials
are relatively inexpensive. Moreover, these materials do not leave anions in
the
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product which either have to be washed out or will be emitted as
environmentally
harmful gases upon heating.
Suitable tetravalent metal compounds include silicon compounds, such as sodium
(meta)silicate or water glass, stabilized silica sols, silica gels,
polysilicic acid, tetra
ethylortho silicate, fumed silicas, precipitated silicas, and mixtures
thereof.
Suitable trivalent metal compounds include compounds of aluminium, gallium,
indium, iron, chromium, vanadium, cobalt, manganese, cerium, niobium,
lanthanum, and mixtures thereof.
Suitable gallium, indium, iron, chromium, vanadium, cobalt, cerium, niobium,
lanthanum, and manganese compounds are the respective oxides, hydroxides,
carbonates, nitrates, chlorides, chlorohydrates, and alkoxides.
Preferred trivalent metal compounds are oxides and hydroxides, as these
materials
are relativeiy inexpensive. Moreover, these materials do not leave anions in
the
product which either have to be washed out or will be emitted as
environmentally
harmful gases upon heating.
Suitable aluminium compounds include aluminium alkoxide, aluminium hydroxides
prepared by precipitation of soluble aluminium salts such as aluminium
sulphate,
aluminium nitrate, aluminium chloride, and sodium aluminate, (pseudo)boehmite,
thermally treated aluminium trihydrate such as flash calcined aluminium
trihydrate
(Alcoa Cp alumina), amorphous gel alumina, aluminium trihydrate such as
gibbsite, BOC, and bayerite, and mixtures thereof.
Preferred aluminium compounds are (thermally treated) aluminium trihydrate and
amorphous gel alumina, as these materials are relatively inexpensive.
Moreover,
these materials do not leave anions in the product which either have to be
washed
out or will be emitted as environmentally harmful gases upon heating.
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Some of these aluminium compounds can act as a seed for the formation of
boehmite. Especially when aluminium trihydrate is used as boehmite-precursor,
seeds are desired. Suitable seeds are the known seeds to make boehmite such as
commercially available boehmite (Catapal , Condea Versal , P-200 etc.),
amorphous seeds, milled boehmite seeds, boehmite prepared from sodium
aluminate solutions, and thermally treated aluminium trihydrate seeds, e.g. FC-
ATH seeds.
If the precursor mixture contains two or more precursors of the non-zeolitic
component, it is possible to obtain more than one non-zeolitic component. For
instance, if the precursors of the non-zeolitic component are an aluminium
compound and a divalent metal compound, either anionic clay is the sole non-
zeolitic compound formed, or a mixture of boehmite and anionic clay is formed;
the
outcome will depend on the aluminium-to-divalent metal ratio and the process
conditions.
The precursor mixture may contain additional components, metal additives,
phosphorus-containing compounds, boron-containing compounds, kaolin, acids,
bases, etc.
Suitable metal additives are compounds comprising rare earth metals (e.g. Ce,
La),
Group VI metals, Group VIII metals (Pd, Pt), alkaline earth metals (for
instance Ca,
Mg, and Ba), and/or transition metals (for example Rh, Nb, Co, Mn, Fe, Ti, Cr,
Zr,
Cu, Ni, Zn, Mo, W, V, Sn).
Examples of phosphorus-containing compounds are phosphoric acid, ammonium
phosphates, and sodium phosphates. Together with aluminium-containing
compounds, aluminium phosphates can be formed. With the above metal
additives, this can lead to the formation of doped aluminium phosphates such
as
La-doped aluminium phosphate, Ce-doped aluminium phosphate, Zn-doped
aluminium phosphate, or Mg-doped aluminium phosphate.
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These additives can be added to the precursor mixture separately, or they can
be
added by way of the precursors of the non-zeolitic compound doped with one or
more of these additives.
The precursor mixture is aged. The term "aging" refers to treatment of the
suspension at thermal or hydrothermal conditions for about 30 minutes to about
72
hours. In this context, "hydrothermal" means in the presence of water (or
steam) at
temperatures above about 100 C and pressures above atmospheric, e.g.
autogenous pressure. "Thermal" means at temperatures between about 15 C and
100 C and atmospheric pressure.
The preferred aging temperature ranges from 25 C to 375 C, preferably from 50
C
to 200 C, and most preferably from 100 C to 175 C. The aging time preferably
is at
least about 30 minutes, more preferably at least about 45 minutes, and even
more
preferably at least about 1 hour; the aging time preferably is not more than
about
72 hours, more preferably not more than about 24 hours, and even more
preferably
not more than about 6 hours.
Additionally, it is possible to mill the precursor mixture, or any of its
ingredients,
before addition to the precursor mixture. In this specification the term
"milling" is
defined as any method that results in reduction of the particle size. Such a
particle
size reduction can at the same time result in the formation of reactive
surfaces
and/or heating of the particles. Instruments that can be used for milling
include ball
mills, high-shear mixers, colloid mixers, and electrical transducers that can
introduce ultrasound waves into a slurry. Low-shear mixing, i.e. stirring that
is
performed essentially to keep the ingredients in suspension, is not regarded
as
"milling".
The process is preferably conducted in a continuous fashion. More preferably,
this
is done in an apparatus comprising two or more conversion vessels, like the
apparatus according to non-prepublished patent application No. PCT/EP
02/04938.
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For example, zeolite and an aluminium compound are mixed with water in a feed
preparation vessel, after which the mixture is continuously pumped through two
or
more conversion vessels, in which aging takes place.
Additional components can be added to the precursor mixture before or during
aging, i.e. in the preparation vessel or in one of the conversion vessels. For
example, zeolite and aluminium compound are aged in a first conversion vessel
to
form a composition comprising zeolite and boehmite, while in the second
conversion vessel a magnesium compound is added and the mixture is aged to
form a composition comprising zeolite, and boehmite and Mg-Al anionic ciay as
the
non-zeolitic components.
Another example concerns the variation of the micro-crystalline boehmite to
quasi-
crystalline boehmite ratio in the resulting product. The precursor mixture
comprising aluminium compound and zeolite is added to the first preparation
vessel. In this vessel, the pH and the temperature are such that mainly micro-
crystalline boehmite is formed. To the second conversion vessel, in which the
pH
and the temperature are more favourable for quasi-crystalline boehmite
formation,
an additional amount of aluminium compound is added. This additional amount of
aluminium compound will be converted to quasi-crystalline boehmite, resulting
in a
composition comprising zeolite, quasi-crystalline boehmite, and micro-
crystalline
boehmite.
Using the same principles, several compositions can be prepared, containing,
e.g.,
different types of boehmite, anionic clay, and/or smectite.
I
The mixture comprising zeolite and non-zeolitic component is shaped to form
shaped bodies, optionally with the help of binders and/or fillers. Suitable
shaping
methods include spray-drying, pelletizing, granulation, extrusion (optionally
combined with kneading), beading, or any other conventional shaping method
used
in the catalyst and absorbent fields or combinations thereof. The amount of
liquid
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present in the mixture to be shaped should be adapted to the specific shaping
step
to be conducted. It might be advisable to partially remove the liquid present
in the
mixture and/or to add an additional or another liquid, and/or to change the pH
of
the mixture to make the mixture gellable and thus suitable for shaping.
Additives
commonly used in the different shaping methods, e.g. extrusion additives, may
be
added to the mixture.
Additional process steps can be applied. For instance, it is possible to flash-
calcine
the mixture containing zeolite and non-zeolitic component before the shaping
step
is applied. This (flash-)calcined product can then be rehydrated either before
or
after the shaping step.
During rehydration it is possible to add one or more of the additional
components
outlined above as suitable to be added to the precursor mixture. For instance,
a
magnesium compound can be added before or during this rehydration step, which
may result in the formation of a composition comprising zeolite, boehmite, and
Mg-
Al anionic clay
The final product can be combined with other catalyst ingredients, such as
binders,
fillers (e.g. clay such as kaolin, titanium oxide, zirconia, silica, silica-
alumina,
bentonite, etcetera), zeolites other than those already present in the
composition,
etc. It is also possible to add additional metal additives - e.g. rare earth
metals,
transition metals, and/or noble metals - to the shaped body by impregnation or
ion-
exchange.
The resulting catalyst composition can suitably be used in FCC processes, in
hydroprocessing, Fischer Tropsch synthesis, alkylation processes,
hydrocracking,
alkylation, isomerization, etc.
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EXAMPLES
Example 1
An aqueous slurry containing 25 wt% solids is prepared by high-shear mixing of
gibbsite, MgO (Mg/Al mole ratio 0.5), and RE-Y. The amount of RE-Y is about 10
wt% (based on total solids content) of RE-Y. After mixing, the average
particle size
is about 3 microns.
One portion of this slurry is aged at 185 C for 2 hours. The aged portion is
spray-
dried.
X-ray diffraction (XRD) shows that the composition aged at 185 C contained Mg-
Al
anionic clay, RE-Y, and micro-crystalline boehmite.
Example 2
Example 1 is followed, except that instead of gibbsite, flash-calcined
gibbsite is
used.
The composition prepared by aging at 85 C contains Mg-Al anionic clay, RE-Y,
and quasi-crystalline boehmite, whereas the composition aged at 185 C contains
Mg-Al anionic clay, RE-Y, and micro-crystalline boehmite.
Example 3
Example 2 is followed, except that 4 wt% Zn(N03)2 (based on total solids
content)
is added to the slurry.
The composition prepared by aging at 85 C contains Zn-doped Mg-Al anionic
clay,
RE-Y, and Zn-doped quasi-crystalline boehmite, whereas the composition aged at
185 C contains Zn-doped Mg-Al anionic clay, RE-Y, and Zn-doped micro-
crystalline boehmite.
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Example 4
Example 3 is followed, except that instead of Zn(N03)2, 6 wt% of La(N03)3
(based
on total solids content) is added to the slurry.
The composition prepared by aging at 85 C contains La-doped anionic clay, RE-
Y,
La-doped quasi-crystalline boehmite, whereas the composition aged at 185 C
contains La-doped anionic clay, RE-Y, and La-doped micro-crystalline boehmite.
Example 5
Example 1 is followed, except that instead of gibbsite a 50/50 mixture of
gibbsite
and flash-calcined gibbsite is used, the Mg/Al mole ratio was 0.25, and 5 wt%
Ce(N03)3 (based on total solids content) is added to the slurry.
The composition prepared by aging at 85 C contains Ce-doped anionic clay, RE-
Y,
and Ce-doped quasi-crystalline boehmite, whereas the composition aged at 185 C
contains Ce-doped anionic clay, RE-Y, and Ce-doped micro-crystalline boehmite.
Example 6
An aqueous slurry containing 25 wt% solids is prepared by high-shear mixing of
flash-calcined gibbsite, MgO (Mg/Al mole ratio 0.25), 8 wt% RE-Y, 6 wt%
Ce(N03)3, and 15 wt% kaolin (all based on total solids content).
One portion of this slurry is aged at 85 C for 18 hours; another portion is
aged at
185 C for 2 hours. The aged portions are spray-dried.
X-ray diffraction (XRD) shows that the composition prepared by aging at 85 C
contains anionic clay, kaolin, RE-Y, and Ce-doped quasi-crystalline boehmite,
whereas the composition aged at 185 C contains hydrotalcite, kaolin, RE-Y, and
Ce-doped micro-crystalline boehmite.
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After preparation, the compositions are tested for cracking activity, sulphur
reduction in gasoline and diesel, and SOX/NOX removal of FCC regenerator
exhaust gases.
Example 7
Example 6 is followed, except that the spray-dried product is calcined at 550
C for
4 hours, followed by rehydration in an aqueous solution containing 4 wt% of
ammonium vanadate. The resulting product is filtered and dried.
Example 8
A slurry is prepared by high-shear mixing of flash-calcined gibbsite, MgO
(Mg/Al
mole ratio 0.25), 15 wt% of iron-exchanged ZSM-5, and 4 wt% vanadyl sulphate.
One portion of this slurry is aged at 85 C for 18 hours; another portion is
aged at
185 C for 2 hours. The aged portions are spray-dried. The total amount of
gibbsite
and MgO was such that the final dried product contains about 90 wt% gibbsite
and
MgO.
Example 9
An aqueous slurry with 28 wt% solids is prepared by mixing finely ground
gibbsite,
MgO (Mg/Al mole ratio 2.3), 8 wt% RE-USY. The slurry is homogenized in a
colloid
mill.
One portion of this slurry is aged at 85 C for 18 hours; another portion is
aged at
185 C for 2 hours. The aged portions are spray-dried.
Example 10
An aqueous slurry comprising 70 wt% of flash-calcined gibbsite (Alcoa CP-30)
and
about 30 wt% RE-USY (wt% based on total solids content) is prepared. The
slurry
is homogenized by high-shear mixing. The pH of the slurry is adjusted to about
5.
The slurry is aged at 165 C for one hour.
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XRD indicates the formation of a composition comprising quasi-crystalline
boehmite and RE-USY.
The composition is flash-calcined, slurried in water, and spray-dried to form
microspheres. The microspheres are slurried in a suspension comprising MgO
(Mg/Al ratio in suspension was 1) and aged at 85 C for 18 hours. During aging,
the
pH is adjusted to 9.5 using ammonium hydroxide.
The resulting product contains RE-USY, quasi-crystalline boehmite, and Mg-Al
anionic clay.
Example 11
Example 10 is followed, except that the spray-drying step is performed not
before
but after aging at 85 C.
The resulting product contains RE-USY, quasi-crystalline boehmite, and Mg-Al
anionic clay.
Example 12
Example 10 is followed, except that after aging at 165 C MgO is added to the
slurry. The resulting Mg/Al ratio is 1; the pH is adjusted to about 9.
The resulting slurry is aged at 165 C for another hour, followed by flash-
calcination, re-slurrying in water, and spray-drying.
The resulting product contained RE-USY, quasi-crystalline boehmite, and Mg-Al
anionic clay.
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Example 13
An aqueous slurry is prepared comprising 60 wt% fine-particle gibbsite and
about
40 wt% RE-Y (wt% based on total solids content). The slurry is milled in a
colloid
mill and flash-calcined. The flash-calcined product is re-slurried in water,
with the
pH set at about 5 using formic acid, and rehydrated at 165 C for one hour, and
the
slurry contains 25 wt% solids.
MgO is added to the slurry (Mg/Al was about 1), the pH is adjusted to 9.5, and
the
slurry is aged at 85 C for 18 hours. The final mixture is spray-dried.
XRD indicates the formation of a composition comprising RE-Y, anionic clay,
and
boehmite.
Example 14
An aqueous slurry is prepared comprising 60 wt% fine-particle gibbsite and
about
40 wt% RE-Y (wt% based on total solids content). The slurry is milled in a
colloid
mill and flash-calcined. The flash-calcined product is re-slurried in water,
with the
pH set at about 5 using nitric acid, and rehydrated at 165 C for one hour.
To the resulting slurry, 10 wt% of sodium-free silicasol is added. The mixture
is
homogenized and spray-dried. The product comprises RE-Y, boehmite, and silica.
Example 15
An aqueous slurry containing 70 wt% USY zeolite and 30 wt% ZSM-5 (all based on
total solids content) is high-shear mixed and flash-calcined. After flash-
calcination
the product is re-slurried and high-shear mixed in a suspension comprising 35
wt%
of flash-calcined gibbsite and 10 wt% of nickel nitrate.
The resulting mixture is aged at 165 C for one hour at a pH of 6. The slurry
is
dewatered and extruded to form pellets. The pellets are calcined and
impregnated
with 6 wt% of cobalt nitrate.
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Example 16
An aqueous slurry containing 70 wt% USY zeolite and 30 wt% ZSM-5 (all based on
total solids content) is high-shear mixed and finally flash-calcined. After
flash-
calcination the product is re-slurried and high-shear mixed in a suspension
comprising flash-calcined gibbsite, MgO (Mg/Al molar ratio 0.5), and 10 wt% of
nickel nitrate. The total amount of MgO and flash-calcined gibbsite is about
40 wt%
of the amount of the two zeolites.
The resulting mixture is aged at 165 C for one hour at a pH of 9.5. The slurry
is
dewatered and extruded to form pellets. The pellets are finally calcined and
impregnated with 6 wt% of cobalt nitrate.
Example 17
A slurry comprising thermally stabilized REY, ground gibbsite, and magnesium
oxide is prepared. This slurry has a solids content of 28 wt% and a Mg/Al
molar
ratio of 2.3. The slurry is milled in a colloid mill.
The slurry is aged at 85 C for 18 hours. Next the aged slurry is spray-dried
to form
microspheres. The microspheres are calcined and subsequently rehydratated in
an
aqueous slurry at 85 C for 8 hours.
The resulting composition comprises zeolite REY and Mg-Al anionic clay as the
non-zeolitic compound.
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