Granules based on pyrogenically prepared silicon dioxide, a
process for their preparation and their use
The invention relates to granules based on pyrogenically
prepared silicon dioxide, the process for their preparation
and their use as a catalyst support.
It is known to prepare pyrogenic silicas or silicon
dioxides from SiCl4 by means of high temperature or flame
hydrolysis (Ullmanns Enzyklopadie der technischen Chemie
[Ullmanns Encyclopaedia of Industrial Chemistry], 4th
edition, volume 21, page 464 (1982)).
Pyrogenic silicon dioxides are distinguished by an extreme
fine division, a high specific surface area (BET), a very
high purity, a spherical particle shape and the absence of
pores. On the basis of these properties, pyrogenically
prepared silicon dioxides are finding increasing interest
as supports for catalysts (Dr. Koth et al., Chem. Ing.
Techn. 52, 628 (1980)). For this use, the pyrogenically
prepared silicon dioxide is shaped by a mechanical route by
means of, for example, tablet-making machines.
It is also known to shape pyrogenically prepared silicon
dioxide to spray granules by means of spray drying,
US 5776240 describes granules based on pyrogenic silicon
dioxide which are obtainable by spray drying an aqueous
suspension of pyrogenic silicon dioxide. Granules which are
prepared in such a manner have the disadvantage that they
have tucks on the surface (amphore formation), inner hollow
spaces and deformations. Such effects are well-known in
spray drying (K. Masters, Spray Drying, 2nd ed., 1976, John
Wiley & Sons, New York, p. 329). These morphological
defects have an adverse effect in the use as a catalyst
support. In olefin polymerization, for example, the form of
the catalyst support is copied by the polymer grain due to
the replica effect. This likewise results in hollow spaces
and deformations in the polymer, which lower the bulk

density (and therefore the capacity of the polymerization
plant) or can have the effect of inclusion of monomers,
which has an adverse effect in further processing. When
used as a support for other fluidized bed catalysts, these
defects lead to increased abrasion and therefore increased
catalyst consumption.
There was therefore the object of developing improved spray
granules of pyrogenically prepared silicon dioxide which
can be employed as a catalyst support for olefin
polymerization or other catalytic fluidized bed processes.
These should be distinguished by a lower content of
particles with tucks and hollow spaces compared with the
prior art.
The invention provides granules based on pyrogenically
prepared silicon dioxide with the following physico-
chemical characteristic data:
Average particle diameter: 10 to 120 um
BET surface area: 40 to 400 m2/g
Pore volume: 0.5 to 2.5 ml/g
Pore distribution: content of pores of pore
diameter < 5 nm in the total pore volume of less than 5%,
remainder meso- and macropores
Tamped density: 220 to 1,000 g/1
Numerical content of particles in the particle size range
above the D10 value of the particle size distribution
weighted according to volume which have tucks or closed off
inner hollow spaces: < 35 %
The granules according to the invention can be prepared by
a procedure in which silicon dioxide prepared from a
volatile sil icon compound by means of flame hydrolysis is
dispersed in a liquid, preferably water, with one or more
organic or inorganic auxiliary substances, the dispersion
is spray dried and the granules obtained are optionally

heat-treated at a temperature of 150 to 1,100°C and/or
silanized.
Halogenosilanes, alkoxysilanes, silazanes and/or siloxanes
can be employed for the silanization.
The following substances can be employed in particular as
halogenosilanes:
Halogeno-organosilanes of the type X3Si (CnH2n+1) X = Cl, Br
n =1-20
Halogeno-organosilanes of the type X2(R')Si (CnH2n+1) X = Cl, Br
R' = alkyl
n =1-20
Halogeno-organosilanes of the type X(R' )2Si (CnH2n+i) X = Cl, Br
R' = alkyl
n =1-20
Halogeno-organosilanes of the type X3Si(CH2)m-R'
X = Cl, Br
m - 0,1 - 20
R' = alkyl, aryl (e.g. -C6H5)
-C4F9, -OCF2-CHF-CF3, -C6F13, -0-CF2-CHF2
-NH2, -N3, -SCN, -CH=CH2,
-OOC(CH3)C = CH2
-OCH2-CH(O)CH2
-NH-CO-N-CO-(CH2) 5
-NH-COO-CH3, -NH-COO-CH2-CH3, -NH-(CH2)3Si(OR)3
-Sx-(CH2)3Si(OR)3
Halogeno-organosilanes of the type (R)X2Si(CH2)m-R'
X = Cl, Br
R = alkyl
™ = 0,1 - 20
R' = alkyl, aryl (e.g. -C6H5)
-C4F9, -OCF2-CHF-CF3, ~C6F13, -0-CF2-CHF2
-NH2, -N3, -SCN, -CH=CH2,
-OOC(CH3)C = CH2

-OCH2-CH(O)CH2
-NH-CO-N-CO- (CH2) 5
-NH-COO-CH3, -NH-COO-CH2-CH3, -NH-(CH2)3Si(OR)3
-Sx-(CH2)3Si(OR)3
Halogeno-organosilanes of the type (R) 2X Si(CH2)m-R'
X = Cl, Br
R = alkyl
m = 0,1 - 20
R' = alkyl, aryl (e.g. -C6H5)
-C4F9/ -OCF2-CHF-CF3/ -C6F13, -0-CF2-CHF2
-NH2, -N3, -SCN, -CH=CH2,
-OOC(CH3)C = CH2
-OCH2-CH(O)CH2
-NH-CO-N-CO-(CH2) 5
-NH-COO-CH3, -NH-COO-CH2-CH3, -NH-(CH2)3Si(OR)3
-Sx-(CH2)3Si(OR)3
The following substances can be employed in particular as
alkoxysilanes:
Organosilanes of the type (RO)3Si (CnH2n+1) R = alkyl
n =1-20
Organosilanes of the type R'x(RO)ySi (CnH2n+i) R = alkyl
R» = alkyl
n =1-20
x+y = 3
x = 1,2
y - 1,2
Organosilanes of the type (RO)3Si(CH2)m-R'
R = alkyl
ai = 0,1 - 20
R' = alkyl, aryl (e.g. -C6H5)
-C4F9, -OCF2-CHF-CF3, -C6F13, -0-CF2-CHF2
-NH2, -N3/ -SCN, -CH=CH2,
-OOC(CH3)C = CH2
-OCH2-CH(O)CH2
-NH-CO-N-CO- (CH2)5

-NH-COO-CH3, -NH-COO-CH2-CH3, -NH-(CH2) 3Si (OR) 3
-Sx-(CH2)3Si(OR)3
Organosilanes of the type (R") x (RO) ySi (CH2)m-R'
R" = alkyl x+y = 2
x = 1,2
y = 1,2
R' = alkyl, aryl (e.g. -C6H5)
-C4F9, -OCF2-CHF-CF3, -C6F13, -0-CF2-CHF2
-NH2, -N3, -SCN, -CH=CH2,
-O0C(CH3)C = CH2
-OCH2-CH(O)CH2
-NH-CO-N-CO-(CH2)5
-NH-COO-CH3, -NH-COO-CH2-CH3, -NH-(CH2)3Si(OR)3
-Sx-(CH2)3Si(OR)3
The silane Si 108 [ (CH30) 3-Si-C8H17] trimethoxyoctylsilane
can preferably be employed as the silanizing agent.
The following substances can be employed in particular as
silazanes:
Silazanes of the type R'R2Si-N-SiR2R'
I
H
R = alkyl
R" = alkyl, vinyl
and, for example, hexamethyldisilazane.
The following substances can be employed in particular as
siloxanes:
Cyclic polysiloxanes of the type D 3, D 4, D 5
e.g. octamethylcyclotetrasiloxane = D 4


The pore structure of the granules according to the
invention has predominantly meso- and macropores. The
content of pores smaller than 5 nm is not more than 5%,
based on the total pore volume.
The granules can comprise as secondary constituents the
auxiliary substances, residues of the auxiliary substances
which have remained after the heat treatment and/or silane
components. The carbon content of the granules according to
the invention can be 0 to 15 wt.%.
The particle size distribution of the granules according to
the invention can be of a form such that they have a volume
content of at least 80% of particles larger than 5 um and
at least 80% of particles smaller than 120 urn.
The invention also provides a process for the preparation
of granules based on pyrogenically prepared silicon

dioxide, which is characterized in that pyrogenically
prepared silicon dioxide, preferably silicon dioxide
prepared from silicon tetrachloride by means of flame
hydrolysis, is dispersed in a liquid with an organic or
inorganic auxiliary substance, it being possible for the
components of the dispersion to be added in any desired
sequence, the dispersion is spray dried, the granules
obtained are optionally heat-treated at a temperature of
150 to 1,100°C, the granules are optionally silanized and
the granules are optionally subjected to a sifting or
sieving, it being possible for the last three process steps
mentioned to be carried out in any desired sequence.
The dispersion can have a concentration of silicon dioxide
of 5 to 40 wt.%. The dispersing can be carried out
continuously or discontinuously.
Water, ethanol, propanol, isopropanol, butanol, isobutanol,
ethyl acetate or a mixture of these substances can be
employed e.g. as the dispersing medium. Water is preferably
employed as the dispersing medium.
Suitable auxiliary substances for the spray drying are,
inter alia, organic auxiliary substances, such as polymers,
e.g. cellulose derivatives, polyethylene glycol, waxes,
polyolefins, polyacrylates or polyvinyl alcohols, or
organic acids, e.g. lactic or citric acid, or inorganic
auxiliary substances, such as water-glass, silica sols,
aluminium oxide sols or sols of other oxides or tetraethyl
orthosilicate. These auxiliary substances can be employed
individually or in combination and have the effect of a
more uniform shape of the spray particle and a reduced
number of particles which have tucks or closed off inner
hollow spaces.
In addition, further auxiliary substances which have the
effect of lowering the viscosity, and therefore allow a
higher degree of filling of the suspension, can optionally

be added. Substances which are suitable for this are, for
example, acids, such as formic acid, acetic acid, oxalic
acid, hydrochloric acid or nitric acid, bases, such as
ammonia, amines or alkali metal, alkylammonium or alkaline
earth metal hydroxides, or other substances which have the
effect of modifying the surface charge on the dispersed
particles.
The auxiliary substances are preferably employed in a low
dosage of 0.01 to 10 wt.%, based on the solids content of
the dispersion, in order to minimize contamination.
The spray drying can preferably be carried out at an intake
temperature of the drying gas of 180 to 700°C and an exit
temperature of 50 to 250°C. Disc atomizers or nozzle
atomizers can be employed here. Any desired gases can be
employed as the drying medium, preferably air or nitrogen.
The optional heat treatment of the granules can be carried
out either in a static bed, such as, for example, in
chamber ovens, or in an agitated bed, such as, for example,
rotary tubular ovens or fluidized bed dryers or calciners.
The optional silanization can be carried out with the same
halogenosilanes, alkoxysilanes, silazanes and/or siloxanes
as described above, it being possible for the silanizing
agent optionally to be dissolved in an organic solvent,
such as, for example, ethanol.
The silane Si 108 [(CH3O) 3-Si-C8H17] trimethoxyoctylsilane
can preferably be employed as the silanizing agent.
The silanization can be carried out by a procedure in which
the granules are sprayed with the silanizing agent at room
temperature and the mixture is then heat-treated at a
temperature of 105 to 400°C over a period of 1 to 6 h.
An alternative method of the silanization of the granules
can be carried out by a procedure in which the granules are

treated with the silanizing agent in vapour form and the
mixture is then heat-treated at a temperature of 50 to
800°C over a period of 0.5 to 6 h.
The heat treatment can optionally be carried out under an
inert gas, such as, for example, nitrogen.
The silanization can be carried out continuously or
batchwise in heatable mixers and dryers with spray devices.
Suitable devices can be, for example: plough share mixers
or plate, fluidized bed or flow-bed dryers.
A wind sifter is preferably employed in the optional
sifting, in order preferably to separate off fine
particles. Alternatively or in addition, sieving can be
employed to separate off coarse particles. The sifting can
be carried out at any desired point of the process after
the spray drying. Particle fractions which have been
separated off can optionally be recycled by admixing them
to the starting suspension.
By varying the starting substances, the conditions during
spraying, the heat treatment and the silanization, the
physico-chemical parameters of the granules, such as the
specific surface area, the particle size distribution, the
pore volume, the tamped density and the silanol group
concentration, pore distribution and pH, can be modified
within the stated limits.
The granules according to the invention can be employed as
a support for catalysts, in particular as a support for
catalysts for olefin polymerization, the preparation of
phthalic anhydride, the preparation of vinyl acetate, the
preparation of aniline or the Fischer-Tropsch synthesis.
They advantageously have a high purity, a high heat
stability, a content of micropores of < 5 nm in the total
pore volume of less than 5% and a numerical content of
particles with tucks or inner hollow spaces in the particle

size range above the D10 value of the particle size
distribution weighted according to volume of less than 35%.
The invention also provides the use of the granules as a
catalyst support.

Examples
Silicon dioxides with the following physico-chemical
characteristic data are employed as pyrogenically prepared
silicon dioxides:



To prepare the silicon dioxides, a volatile silicon
compound is injected into an oxyhydrogen gas flame of
hydrogen and air. Silicon tetrachloride is used in most
cases. This substance hydrolyses to silicon dioxide and
hydrochloric acid under the influence of the water formed
during the oxyhydrogen gas reaction. After leaving the
flame the silicon dioxide enters into a so-called
coagulation zone, in which the Aerosil primary particles
and primary aggregates agglomerate. The product present as
a type of aerosol in this stage is separated from the
gaseous concomitant substances in cyclones and then after-
treated with damp hot air.
The residual hydrochloric acid content can be lowered to
' below 0.025% by this process. Since the silicon dioxide is
obtained with a bulk density of only approx. 15 g/1 at the
end of this process, vacuum compaction follows, with which
tamped densities of approx. 50 g/1 and more can be
established.
The particle sizes of the silicon dioxides can be varied
with the aid of the reaction conditions, such as, for
example, flame temperature, hydrogen or oxygen content,
amount of silicon tetrachloride, residence time in the
flame or length of the coagulation zone.
The BET surface area is determined with nitrogen in
accordance with DIN 66 131.

The pore volume is determined via the Hg forcing-in method.
For this, the sample is dried for 15 h at 100°C in a drying
cabinet and degassed at room temperature in vacuo.
The micropores are determined by plotting an N isotherm and
evaluating this by the method of BET, de Boer and Barret,
Joyner, Halenda. For this the sample is dried for 15 h at
100°C in a drying cabinet and degassed for 1 h at 200°C in
vacuo.
The particle size distribution is determined by means of
the Cilas Granulameter 715 laser-optical particle size
analyzer.
The tamped density is determined in accordance with ASTM D
4164-88.
The content of particles which have tucks is determined by
counting on an SEM photograph of suitable magnification. An
uncertainty of an estimated +/- 10% arises due to particles
in which the tuck is covered. Section images can be
prepared to detect inner hollow spaces. An opening in the
particle, the size of which makes up 5-90% of the particle
diameter and which opens wider inwards at least a minimal
amount is to be evaluated as a tuck. To rule out a
numerical over-representation of very fine particles, only
some of the particles of which the diameter is above the
D10 value of the particle size distribution weighted
according to volume are taken into account.
Preparation of the granules according to the invention in
example 18
The pyrogenically prepared silicon dioxide is dispersed in
completely demineralized water, the particular auxiliary
substance being admixed. A dispersing unit which operates
by the rotor/stator principle is used here. The suspensions
formed are spray dried. The finished product is separated
off via a filter or cyclone.

The heat treatment of the spray granules is carried out in
muffle ovens.
The spray-dried and optionally heat-treated and/or sifted
granules are initially introduced into a mixer for the
silanization, and are sprayed optionally first with water
and then with the silane Si 108 (trimethoxyoctylsilane) or
HMDS (hexamethyldisilazane) with intensive mixing. When the
spraying has ended, after-mixing is carried out for a
further 15 to 30 min, and then heat treatment for 1 to 4 h
at 100 to 400°C.
The water employed can be acidified with an acid, for
example hydrochloric acid, down to a pH of 7 to 1. The
silanizing agent employed can be dissolved in a solvent,
such as, for example, ethanol.
Detailed information on the preparation and the properties
of individual granule examples are to be found in table 2 .
For comparison, granules were prepared in accordance with
US 5776240.
As the SEM photographs of fig. 1-3 demonstrate
impressively, the content of particles with tucks is
reduced significantly compared with the prior art. Fig. 4
shows that also no noticeable content of inner hollow
spaces is present.

We Claim:
1. Granules based on pyrogenically prepared silicon dioxide with the
following physico-chemical characteristic data:
Average particle diameter: 10 to 120 am
BET surface area: 40 to 400 m2/g
Pore volume: 0.5 to 2.5 ml/g
Pore distribution: content of pores of
pore diameter < 5 nm in the total pore volume of less than 5%,
remainder meso- and macropores
Tamped density: 220 to 1,000 g/1
Numerical content of particles in the particle size range above the
D10 value of the particle size distribution weighted according to
volume which have tucks or closed off inner hollow spaces: <
35%.
2. Process for the preparation of granules as claimed in claim 1,
wherein pyrogenically prepared silicon dioxide is dispersed in a
liquid, preferably water, with one or more auxiliary substances, it
being possible for the components of the dispersion to be added in
any desired sequence, the dispersion is spray dried, the granules
obtained are optionally heat-treated at a temperature of 150 to
1,100°C, the granules are optionally silanized and/or the granules

are optionally subjected to a sifting or sieving, it being possible for
the particle size fractions separated off optionally to be recycled.
The optional process steps of heat treatment, silanization and
sieving or sifting can be carried out in any desired sequence.
3. Process as claimed in claim 2, wherein one or more components
from the following substances are used as auxiliary substances:
polymers, e.g. cellulose derivatives, polyethylene glycol, waxes,
polyolefins, polyvinyl alcohols or polyacrylates, acids, e.g. formic,
acetic, lactic, oxalic, nitric, hydrochloric or citric acid, bases, e.g.
ammonia, amines or alkali metal, alkylammonium or alkaline earth
metal hydroxides, sols, e.g. silica sols, aluminium oxide sols or
sols of other oxides, water-glass or silicic acid esters, e.g. tetraethyl
orthosilicate.
4. Process as claimed in claim 2, wherein one or more components
from the following substances are used as auxiliary substances:
carboxymethylcelluloses, methylcelluloses or celluloses etherified
with other alcohols, water-glass or silica sol.

Granules based on pyrogenically prepared silicon dioxide with the following physico-chemical characteristic data: Average particle diameter: 10 to 120 μm BET surface area: 40 to 400 m2/g
Pore volume: 0.5 to 2.5 ml/g
Pore distribution: content of pores of pore
diameter < 5 nm in the total pore volume of less than 5%, remainder meso- and macropores
Tamped density: 220 to 1,000 g/1
Numerical content of particles in the particle size range above the D10 value of the particle size distribution weighted according to volume which have tucks or closed off
inner hollow spaces: < 35 %
They are prepared by a procedure in which silicon dioxide is dispersed in a liquid, preferably water, together with
one or more auxiliaries, the dispersion is spray dried and the granules are optionally heat-treated and/or silanized. The granules are employed as a catalyst support.