PROCESS FOR IMPROVING THE ABRASION RESISTANCE OF ZEOLITE MOULDED BODIES

METHODE POUR AMELIORER LA RESISTANCE DE CORPS MOULES A BASE DE ZEOLITE CONTRE L'USURE

English Abstract

The abrasion resistance of zeolite moulded bodies is improved by spraying the zeolite moulded bodies with an aqueous silica sol solution and then optionally drying and calcining them.

French Abstract

La résistance à l'usure de corps moulés à base de zéolithe est améliorée en pulvérisant les corps moulés à base de zéolithe d'une sol de silice aqueuse, puis éventuellement en les séchant et en les calcinant.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A process for improving the abrasion resistance
of zeolite moulded bodies, in which zeolite moulded bodies
are sprayed with an aqueous solution of silica sol, and in
which, after spraying with said silica sol, the zeolite
moulded bodies are dried at temperatures of between 20°C
and 200°C and calcined between 200°C and 1000°C.
2. A process according to claim 1, in which the
silica sol used contains up to 40 per cent of silicon
dioxide.
3. A process according to claim 1 or 2, in which a
silica sol which is stabilized with alkali metal ions or
ammonium ions is used.
4. A process according to claim 1, 2 or 3, in which
the proportion by weight of the silicon dioxide resulting
from the silica sol, referred to the dry weight of the
zeolite moulded bodies used, is between 0.1 and 20 per
cent.
5. A process according to any one of claims 1 to 4,
in which finished, calcined zeolite moulded bodies are
sprayed.
6. A process according to any one of claims 1 to 4,
in which non-calcined zeolite moulded bodies are sprayed.

Description

CA 02219604 1997-10-29
Process For Improving The Abrasion Resistance Of Zeolite
Moulded Bodies
Zeolites are used in the fields of adsorption and catalysis
mainly as moulded bodies, for example as extrudates or
granules, whose mean diameter can range from approx. 30 Eun
to approx. 10 mm.
Of great importance, in addition to the actual function of
the zeolite granules, are their mechanical properties, for
example breaking resistance and abrasion resistance. Of
particular importance is the resistance of these moulded
bodies in processes in which gases or liquids flow through
zeolite fixed beds. A high abrasion resistance is also
required for zeolite granules which are used in so-called
static adsorption, since otherwise their handling leads to
the production of dust. Such granules are, for example,
the zeolites that are used to dry the air in the gap
between panes of insulating glass.
It is known to manufacture zeolite moulded bodies, depend-
ing on the desired particle size and shape, by means of
spray, fluidized bed and plate granulation, as well as by
extrusion, in which ceramic binders are often used. Drying
and calcining steps are also added for the consolidation of
the granules or extrudates where necessary.
In some cases the abrasion resistance of the zeolite gran-
ules such as are obtained directly in the granulation pro-
cess is not sufficient for the requirements of the particu-
lar application.
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CA 02219604 1997-10-29
An object therefor exists in improving the abrasion resist-
ance of zeolite moulded bodies.
The invention provides a process for improving the abrasion
resistance of zeolite moulded bodies, in which the zeolite
moulded bodies are sprayed with an aqueous solution of
silica sol.
This measure can be applied at various points in the granu-
lation process: for example, the spraying of the silica sol
onto finished, calcined zeolite moulded bodies is possible.
Alternatively the spraying can also be carried out on non-
calcined zeolite moulded bodies, so-called "green
compacts", which have not yet undergone a heat treatment.
The spraying can also be carried out on non-calcined zeo-
lite moulded bodies in the fluidized bed during the drying.
In a particular embodiment the zeolite moulded bodies are
placed on a rotating plate and sprayed with silica sol
solution. A procedure of this kind can be either continu-
ous or discontinuous.
The silica sol can be used in amounts such that the propor-
tion by weight of the silicon dioxide resulting from it,
referred to the dry weight of the zeolite moulded bodies
used, comes to between 0.1 and 20 per cent. In individual
cases the silica sol can be used in an amount that suf-
fices, on the one hand, to improve the abrasion resistance
of the zeolite moulded bodies, but, on the other, does not
impair the function of the zeolite moulded bodies.
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CA 02219604 1997-10-29
The silicon dioxide content of the silica sol can lie be-
tween 1 and 40 per cent. The silica sol can be stabilized
with ammonium ions or with alkali metal ions. Suitable
silica sols are for example the products sold under the
tradenames LUDOX AS 40 and HS 40 of the company DuPont, and
solutions produced from the latter by dilution with water.
After the spraying of the zeolite moulded bodies with
silica sol, a drying and a calcining can be added, in which
the drying temperature can come to between 20°C and 200°C,
and the calcining temperature to between 200°C and 1000°C.
The process according to the invention has the advantage
that the abrasion resistance of zeolite moulded bodies can
be significantly improved.
Features and advantages of the invention will be more read-
ily apparent by reference to the following examples, which
are not to be construed as limiting the scope of the inven-
tion as defined in the following claims.
Examples
The zeolite moulded bodies used have a diameter of between
0.5 and 0.9 mm. They were manufactured according to the
method of DE 31 32 379.
To check the abrasion resistance, the following test
utilizing fluidized bed apparatus as schematically shown in
FIGURE 1 is used:
Some 100 g (dry weight, determined after calcining at
450°C) are weighed out on a precision balance (tolerance
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CA 02219604 1997-10-29
+/- 0.1 g) and placed on the fritted glass bottom of the
apparatus. A cone filled tightly with glass wool, which
serves as a filter for fine dust, is placed in position.
The weight of the cone filled with glass wool is determined
with an analytical balance (tolerance: +/- 0.002 g). An
air current of 1500 1/h is passed through the apparatus for
a period of 3 h. After this the cone is carefully removed
and weighed once again with the analytical balance. This
produces the fine dust proportion in per cent as a measure
of the abrasion resistance according to dust portion in per
cent = (fine dust x 100) / weighed portion.
Example 1
146.8 g of dried zeolite moulded bodies (green compacts)
(dry weight after calcining at 1000°C: 114.0 g) were placed
on a laboratory granulating plate. During the rotation of
the plate 1.28 g of Ludox AS 40, diluted with 1.28 g of
water, were sprayed onto the zeolite moulded bodies within
120 sec. A two-fluid nozzle (inner diameter: 0.5 mm,
admission pressure 0.25 bar) was used for this. The amount
of silicon dioxide contained in the silica sol, referred to
the dry weight of the zeolite moulded bodies used, came to
0.45 per cent. The sprayed zeolite moulded bodies were
dried in a drying cabinet for 1 h at 50°C and then calcined
in a muffle kiln at 480°C (heating from room temperature: 2
h, residence time: 1 h). Non-sprayed zeo-lite moulded
bodies were subjected to the same drying and
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CA 02219604 1997-10-29
calcining procedure for comparison purposes. The abrasion
resistance was then determined on the two samples. The
zeolite moulded bodies sprayed with silica sol led to
0.0367 per cent of fine dust, while the non-sprayed zeolite
moulded bodies showed 0.0679 per cent.
The zeolite moulded bodies sprayed according to the
invention therefore exhibited an improved abrasion
resistance.
Example 2
200.0 g of calcined zeolite moulded bodies (dry weight
after calcining.at 1000 °C: 197.0 g) were placed on a
laboratory granulating plate. During the rotation of the
plate 2.5 g of Ludox AS 40, diluted with 7.5 g of water,
were sprayed onto the zeolite moulded bodies within 120
sec. A two-fluid nozzle (inner diameter: 0.5 mm, admission
pressure 0.25 bar) was used for this. The amount of silicon
dioxide contained in the silica sol, referred to the dry
weight of the zeolite moulded bodies used, came to 0.51 per
cent. The sprayed zeolite moulded bodies were dried in
parallel with non-sprayed zeolite moulded bodies in a
drying cabinet for 1 h at 50 °C and then calcined in a
muffle kiln at 480 °C (heating from room temperature: 2 h,
residence time: 1 h). The abrasion resistance was then
determined on the two samples. The zeolite moulded bodies
sprayed with silica sol led to 0.0069 per cent of fine
dust, while the non-sprayed zeolite moulded bodies showed
0.0330 per cent.
The zeolite moulded bodies sprayed according to the
invention therefore exhibited an improved abrasion
resistance.
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CA 02219604 1997-10-29
Example 3
The test according to Example 2 was repeated with 400.0 g
of calcined zeolite moulded bodies from another batch,
during which 2.5 g of Ludox AS 40, diluted with 17.5 g of
water, were sprayed on within 150 sec. The amount of
silicon dioxide contained in the silica sol, referred to
the dry weight of the zeolite moulded bodies used, thus
came to 0.25 per cent. The zeolite moulded bodies sprayed
with silica sol led to 0.0164 per cent of fine dust, the
non-sprayed zeolite moulded bodies to 0.0428 per cent.
Example 4
The test according to Example 3 was repeated, in which
8.0 g of Ludox AS 40, diluted with 12.0 g of water; were
sprayed on within 240 sec. The amount of silicon dioxide
contained in the silica sol, referred to the dry weight of
the zeolite moulded bodies used, thus came to 0.81 per
cent. The zeolite moulded bodies sprayed with silica sol
led to 0.0137 per cent of fine dust, the zeolite moulded
bodies not sprayed with silica sol to 0.0428 per cent.
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Representative Drawing