Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR THE PREPARATION OF CATALYST MICROSPHERES
The present invention relates to a process for the preparation of catalyst
compositions with a particle diameter in the range 20-2000 microns.
Within the specification, the term catalyst compositions also encompasses
catalyst additives and adsorbents.
For several catalytic applications, such as fluidized bed processes, small
catalyst particles are required. Such particles are generally produced by
spray-
drying a mixture of the catalyst ingredients. For instance, fluid catalytic
cracking
(FCC) catalysts are generally prepared by spray-drying an aqueous slurry of
zeolite, clay, and silica and/or alumina.
Spray-drying involves pumping a slurry containing the catalyst ingredients
through a nozzle (a high-pressure nozzle or a rotating wheel with nozzle) into
a
chamber heated with hot air. During this process, high shear is placed on the
slurry, thereby creating small droplets that quickly dry in the heated
chamber.
Depending on the type of nozzle used, the particle size distribution of the
resulting catalyst particles depends on either the nozzle pressure or the
rotating
speed of the wheel, but generally lies in the range of 30-90 microns.
Unfortunately, only slurries with a low solids content (i.e. below about 45
wt%
solids) and, consequently, a high liquid content can be spray-dried. Slurries
with
a higher solids content either are too viscous to be pumped through the nozzle
or will not give suitable droplets upon spraying.
Due to this low solids limitation, large volumes of liquid are required, which
have
to be evaporated during the drying step. This is energy inefficient.
This problem is solved by the process according to the present invention,
which
involves the following steps:
a) agitating at least two dry catalyst ingredients,
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b) spraying a liquid binding agent on the catalyst ingredients while
continuing
the agitation,
c) isolating formed catalyst particles with the desired particle diameter and
comprising the catalyst ingredients, and
d) optionally calcining the isolated catalyst particles.
This process requires less liquid than spray-drying. Hence, less liquid has to
be
evaporated in the drying step, making this process more energy efficient than
spray-drying.
The process according to the invention requires at least two individual
catalyst
ingredients to form a catalyst particle. It is not a process that involves
only
surface coating of existing catalyst particles as in US 5,286,370 and US
5,001,096.
Suitable agitation techniques involve fluidization and high-shear mixing.
Fluidization is performed by fluidizing the catalyst ingredients in a stream
of gas,
generally air. A nozzle is present above the so formed fluidized bed. Through
this nozzle, the liquid binding agent is sprayed on the catalyst ingredients.
A
suitable apparatus for performing this process is a fluidized bed granulator.
The gas velocity influences the size of the catalyst particles obtained. This
gas
velocity preferably ranges from 1-10 times the minimum fluidization velocity
and
most preferably from 1-5 times the minimum fluidization velocity, with the
minimum fluidization velocity being defined as the minimum gas velocity
required for holding up the catalyst ingredients. It will be clear that this
minimum
velocity depends on the particle size of the catalyst ingredients: the larger
the
particles, the higher the required minimum gas velocity. Catalyst ingredients
for
the preparation of FCC catalyst particles generally have a particle size up to
about 10 microns.
The temperature of the gas preferably ranges from 20° to
700°C, more
preferably from 50° to 200°C, and most preferably from
80° to 120°C.
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High-shear mixing is performed in a high-shear mixer. A nozzle is present in
the
mixer, above the catalyst ingredients. Through this nozzle, the liquid binding
agent is sprayed on the catalyst ingredients.
The preferred shear rate ranges from 250 to 5000 s ~, more preferably from 250
to 2500 s ~, and most preferably from 500 to 1000 s ~.
The temperature during high shear mixing preferably is below
100°C, more
preferably below 50°C, and most preferably ambient.
Catalyst ingredients which can be used in the process according to the
invention include solid acids, alumina, iron (hydr)oxide, (meta)kaolin,
bentonite,
(calcined) anionic clays, saponite, sepiolite, smectite, montmorillonite, and
mixtures thereof.
Suitable solid acids include zeolites such as zeolite beta, MCM-22, MCM-36,
mordenite, faujasite zeolites such as X-zeolites and Y-zeolites (including H-Y
zeolites, RE-Y zeolites, and USY-zeolites), pentasil-type zeolites such as ZSM
5, non-zeolitic solid acids such as silica-alumina, sulphated oxides such as
sulphated oxides of zirconium, titanium, or tin, sulphated mixed oxides of
zirconium, molybdenum, tungsten, etc., and chlorinated aluminium oxides.
Suitable aluminas include boehmite, pseudoboehmite, transition aluminas such
as alpha-, delta-, gamma-, eta-, theta-, and chi-alumina, aluminium trihydrate
such as gibbsite or bauxite ore concentrate (BOC), and flash-calcined
aluminium trihydrate.
Examples of suitable anionic clays (also called hydrotalcite-like materials or
layered double hydroxides) are Mg AI anionic clays, Fe AI anionic clays, Zn AI
anionic clays, Fe-Fe anionic clays, etc.
The catalyst ingredients used have to be dry before starting the process
according to the invention. The term "dry" in this context means that not more
than 90% of the pore volume of these ingredients is filled with water.
Most of the aluminas used for FCC applications are made via precipitation
processes. These processes usually involve the sequential steps of
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precipitation, crystallization, and dewatering. A suitable dewatering
technique to
obtain alumina sufficiently dry to be used in the process according to the
invention uses a high-pressure filter.
Zeolites are usually prepared via crystallization, washing/dewatering, ion-
s exchange with NH4 and rare earth metals (RE), drying, calcination, and
milling.
Suitable liquid binding agents include water, acidic aqueous solutions, or
aqueous silicon andlor aluminium-containing solutions or suspensions. The
term "liquid binding agent" refers to liquids, solutions, or suspensions that
assist
in binding of the catalyst ingredients to form the catalyst particles. The
liquid
binding agent can initiate this binding either during step b) or later, for
instance
during an additional calcination step. Whether or not binding takes place
during
step b) depends on the liquid binding agent and the catalyst ingredients used.
The desired liquid binding agent depends on the desired binder. For example:
If anionic clay is the desired binder, water can be used as the liquid binding
agent and a calcined anionic clay as one of the catalyst ingredients. Said
water
will rehydrate the calcined anionic clay to form a binder anionic clay.
If alumina is the desired binder, acidified water can be used as liquid
binding
agent and a peptizable alumina such as pseudoboehmite as one of the catalyst
ingredients. Alternatively, aluminium chlorohydrol (ACH) or aluminium
nitrohydrol (ANH)-containing suspensions can be used as liquid binding agent,
with formation of alumina binder, irrespective of the types of catalyst
ingredients
used. Consequently, if one of the catalyst ingredients is an alumina and ACH
or
ANH is used as liquid binding agent, the resulting catalyst will comprise two
types of alumina. Another option to obtain a catalyst particle with an alumina
binder is to use water as the liquid binding agent and flash-calcined
aluminium
trihydrate as one of the catalyst ingredients. Although the latter combination
does not result in binding of the particles during step b), binding does take
place
during an additional calcination step (step d).
If silica is the desired binder, a solution or suspension containing a silicon
compound can be used as liquid binding agent, irrespective of the types of
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catalyst ingredients used. Examples of suitable silicon compounds are silica
sol,
sodium (meta) silicate, and precipitated silica.
More than one liquid binding agent can be used, which can be sprayed on the
5 catalyst ingredients sequentially. For instance, a silicon-containing
solution or
sol, or an aluminium chlorohydrol or pitrohydrof-containing sol can be used as
a
first liquid binding agent, while acidified water can be used as a second
liquid
binding agent.
Depending on the extent of dryness of the catalyst ingredients, it may be
preferred to spray some water on the catalyst ingredients before spraying the
liquid binding agent. The required amount of water is such that about 90% of
the pores of the catalyst ingredients can be filled with water.
The liquid binding agent is preferably sprayed on the catalyst ingredients at
a
rate of 1-1.5 times the required amount divided by the residence time. This
residence time generally ranges from about 1 to 30 minutes.
The droplet size preferably is between 1 and 20 p,m.
Agitation is continued until the right particle size is obtained. In the case
of
fluidized bed granulation, the gas velocity is selected in such a way that it
can
only hold up particles smaller than the desired size. Hence, once the
particles
have the desired size, they fall down.
The particles obtained by the process according to the invention range in size
from about 20 to about 2000 microns, preferably 20-600 microns, more
preferably 20-200 microns, and most preferably 30-100 microns. For fluid
catalytic cracking (FCC) applications a particle size between 30 and 100
microns is preferred.
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If desired, the resulting particles are dried andlor calcined. If the applied
liquid
binding agent does not result in binding during agitation step b), a
calcination
step d) may be required to initiate this binding.
Drying involves heating of the formed particles at a temperature preferably in
the range 100-200°C. Calcination is preferably conducted at 300°-
1200°C, more
preferably 300°-800°C, and most preferably 300°-
600°C for 15 minutes to 24
hours, preferably 1-12 hours, and most preferably 2-6 hours.
The particles obtained by the process according to the invention can be used
for various purposes, e.g. as a catalyst, adsorbent, etc. Suitable catalytic
applications include Gas to Liquid processes (e.g. Fischer-Tropsch), E-bed and
H-oil processes, reforming, isomerization, alkylation, and auto exhaust
catalysis.
EXAMPLES
Example 1
This Example describes the preparation of FCC catalyst particles with the
following composition (on dry base): 15 wt% alumina, 20 wt% USY, 4 wt%
silica, 61 wt% kaolin.
A fluidized bed granulator was filled with about 200 g of a mixture of dry
pseudoboehmite, dry kaolin, and dry zeolite. The mixture was fluidized and
afterwards 35 g of silicasol were sprayed on top of the fluidized bed at a
rate of
4.8 g/min. Simultaneously, the inlet temperature of the gas was set to
70°C.
Next, 10% nitric acid solution was sprayed on top of the fluidized bed through
the same nozzle at a rate of 4.8 g/min. After addition of 100 g of the nitric
acid
solution, liquid addition was stopped and the gas inlet temperature was set to
135°C to dry the material.
The resulting FCC particles had a mean diameter (d50) of 76 microns. SEM
analysis showed that the particles had a uniform distribution of ingredients.
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Example 2
This Example describes the preparation of FCC catalyst particles with the
following composition (on dry base): 15 wt% pseudoboehmite, 20 wt% USY, 10
wt% alumina originating from aluminium chlorohydrol (ACH), 55 wt% kaolin.
A fluidized bed granulator was filled with about . 200 g of a mixture of dry
pseudoboehmite, dry kaolin, and dry zeolite. The mixture was fluidized and
afterwards 90 g of an aluminium chlorohydol suspension were sprayed on top of
the fluidized bed at a rate of 4.8 g/min. Simultaneously, the inlet
temperature of
the gas was set to 70°C. Next, a 10% nitric acid solution was sprayed
on top of
the fluidized bed through the same nozzle at a rate of 4.8 g/min. After
addition
of 100 g of the nitric acid solution, the liquid addition was stopped and the
gas
inlet temperature was set to 135°C to dry the material.
The resulting FCC particles had a mean diameter (d50) of 78 microns. SEM
analysis showed that the particles had a uniform distribution of ingredients.
Example 3
This Example describes the preparation of FCC catalyst particles with the
following composition (on dry base): 25 wt% pseudoboehmite, 25 wt% USY, 35
wt% kaolin, and 15 wt% Mg-AI anionic clay.
A Mg-AI anionic clay was first calcined and then rehydrated in aquesous
suspension at hydrothermal conditions, i.e. 130°C and autogeneous
pressure.
A fluidized bed granulator was filled with about 200 g of a mixture of dry
pseudoboehmite, kaolin, the anionic clay, and zeolite. The mixture was
fluidized
and afterwards 10% nitric acid solution was sprayed on top of the fluidized
bed
through the same nozzle at a rate of 4.8 g/min. Simultaneously, the inlet
temperature of the gas was set to 70°C. After addition of 100 g of the
nitric acid
solution, liquid addition was stopped and the gas inlet temperature was set to
135°C to dry the material.
The resulting FCC particles have a mean diameter (d50) of 75 microns. SEM
analysis showed that the particles had a uniform distribution of ingredients.
