Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – And additional al or si containing component
Reexamination Certificate
2000-06-20
2004-01-20
Nguyen, Cam N. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
And additional al or si containing component
C502S063000, C502S085000, C502S086000
Reexamination Certificate
active
06680271
ABSTRACT:
INTRODUCTION AND BACKGROUND
The present invention relates to a process of making and treating solid zeolite granulates in order to enhance their abrasion resistance. In another aspect, the present invention relates to the improved solid zeolite granulates obtained thereby.
Zeolites are well known and find use in the fields of application of adsorption and catalysis mainly as molded bodies, extrudates or granulates, whose mean diameter can range from approximately 30 &mgr;m to approximately 10 mm.
Zeolites were first recognized as a new type of mineral in 1756. The word zeolite was derived from two Greek words meaning to boil and a stone. Several properties of zeolite minerals have been studied, including adsorption and ion exchange. These studies led to the preparation of amorphous aluminosilicate ion exchangers for use in water softening. Studies of the gas-adsorption properties of dehydrated natural-zeolite crystals more than 60 years ago led to the discovery of their molecular-sieve behavior. As microporous solids with uniform pore sizes that range from 0.3 to 0.8 nm, these materials can selectively adsorb or reject molecules based on their molecular size. This effect, with obvious commercial overtones leading to novel processes for separation of materials, inspired attempts to duplicate the natural materials by synthesis. Many new crystalline zeolites have been synthesized and several fulfill important functions in the chemical and petroleum industries and consumer products such as detergents.
More than 150 synthetic zeolite types and 40 zeolite minerals are known. The nomenclature of zeolite minerals follows established procedures. No practical system of nomenclature for the synthetic materials and their many modifications has yet been devised. Consequently, a system based on trivial symbols is used to denote the synthetic zeolites in terms of their composition and structure.
Of great importance, in addition to the actual function of the zeolite granulates, are their mechanical properties, for example the breaking resistance and the abrasion resistance. Of particular importance is the abrasion resistance of such granulates in processes in which gases or liquids flow through the 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 solid zeolite granulates are used, for example, to dry the air in the space between panes of insulating glass, which makes dust formation from the granulates a particularly undesirable trait.
Molecular-sieve zeolites are crystalline aluminosilicates of group IA and group IIA elements such as sodium, potassium, magnesium, and calcium. Chemically, they are represented by the empirical formula:
M
2
O.Al
2
O
3
.ySiO
2
.wH
2
O
whereby y is 2 or greater, n is the cation valence, and w represents the water contained in the voids of the zeolite. Structurally, zeolites are complex, crystalline inorganic polymers based on an infinitely extending framework of AlO
4
and SiO
4
tetrahedra linked to each other by the sharing of oxygen atoms. This framework structure contains channels or interconnected voids that are occupied by the cations and water molecules. The cations are mobile and ordinarily undergo ion exchange. The water may be removed reversibly, generally by the application of heat, which leaves intact a crystalline host structure permeated by the micropores which may amount to 50% of the crystals by volume. In some zeolites, dehydration may produce some perturbation of the structure such as cation movement and some degree of framework distortion.
The structural formula of a zeolite is based on the crystal unit cell, the smallest unit of structure being represented by
M
x
[(AlO
2
)
x
(SiO
2
)
y
].wH
2
O
where n is the valence of cation M, w is the number of water molecules per unit cell, x and y are the total number of tetrahedra per unit cell, and y/x usually has values of 1-5. Recently, however, high silica zeolites have been prepared in which y/x is 10 to 100, or even higher.
It is known to manufacture zeolite granulates, depending on the desired particle size and shape, by means of spray, fluidized bed and pan granulation, as well as extrusion, in which ceramic binders are often used. Drying and calcining steps are also added for the consolidation of the granulates or extrudates where necessary.
However, in some cases, the abrasion resistance of the zeolite granulates such as are obtained directly in the granulation process is not sufficient for the requirements of the particular application. It is desired, therefore, that a simple, cost-effective way of improving the abrasion resistance of such zeolite granulates be provided.
SUMMARY OF THE INVENTION
An object of the present invention is to improve the abrasion resistance of solid zeolite granulates. Another aspect of the present invention is to overcome problems relating to the manufacture of solid zeolite granulates that have been encountered in the past.
In achieving the above and other objects, one feature of the present invention is a process for improving the abrasion resistance of such zeolite solids, which is characterized in that the zeolite granulates are sprayed with an aqueous solution of silica sol. It was unexpectedly discovered that this single step provides an inexpensive yet effective way to improve abrasion resistance in zeolite granulates when such abrasion resistance is required, for example, to prevent the unwanted formation of dust particles from the solids.
In carrying out the process of the invention, the spraying of the zeolite can be applied at various points in the granulation process: for example, the spraying of the silica sol can be conducted by spraying finished, calcined zeolite granulates. Alternatively, the spraying can be carried out on non-calcined zeolite granulates, so-called “green compacts”, which have not yet undergone a heat treatment. The spraying can also be carried out on non-calcined zeolite granulates in the fluidized bed during the drying of the formed zeolite solids.
In a particular embodiment, the zeolite granulates are placed on a rotating pan and sprayed with silica sol solution. A procedure of this kind can be either continuous or discontinuous.
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Patent Abstracts of Japan, vol. 011, No. 132 (C-417), Apr. 24, 1987 & JP 61 266306 dated Nov. 26, 1986.
Feuer Oliver
Heindl Frank
Kossel Elke
Roland Eckehart
Bunch William D.
Cross Charles A.
Grace GmbH & Co. KG
Nguyen Cam N.
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