Chemistry of inorganic compounds – Zeolite
Patent
1996-12-19
1998-06-30
Bell, Mark L.
Chemistry of inorganic compounds
Zeolite
423709, 423710, 423711, 4233282, 4233301, 423333, C01B 3902
Patent
active
057729794
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/EP95/00103, filed Jan. 11, 1995.
FIELD OF THE INVENTION
The invention describes the preparation of alkali metal aluminosilicates, in particular crystalline aluminosilicates having the P-structure. These materials are of value as a component in detergent formulations in which they remove calcium and magnesium hardness ions by ion exchange. They also have other properties which provide additional benefits when used in detergent formulations. These aluminosilicates will be referred to as zeolite P in this description.
BACKGROUND OF THE INVENTION
While the utility of zeolite P in detergent formulations has been acknowledged, for example in European Patent Application 0384070 (Unilever), they must be manufactured by a commercially effective process in order to become available on the market place. Thus, while the properties of a material may make it a useful commercial commodity, its manufacture has to be optimised for large scale production. The zeolite P class includes a series of synthetic zeolite phases which may be in cubic configuration (also termed B or P.sub.c) or tetragonal configuration (also termed P.sub.1) but is not limited to these forms. The structure and characteristics of the zeolite P class are given in "Zeolite Molecular Sieves" of Donald W Breck (published 1974 and 1984 by Robert E Krieger of Florida USA). The zeolite P class has the typical oxide formula: is lithium, potassium, sodium, cesium or rubidium with sodium and potassium being preferred and sodium being the cation normally used in commercial processes.
Thus sodium may be present as the major cation with another alkali metal present in a minor proportion to provide a specific benefit.
In EP-A-384,070 is disclosed a process for manufacturing zeolite P having a silicon to aluminium molar ratio not exceeding 1.33 wherein a sodium aluminate solution, having a Na.sub.2 O:Al.sub.2 O.sub.3 molar ratio from 1.4 to 2.0, is mixed with a sodium silicate solution, having a SiO.sub.2 :Na.sub.2 O molar ratio from 0.8 to 3.4, at a temperature from 25.degree. C. to boiling point and with vigorous stirring to give a gel having the following composition: H.sub.2 O.
The gel is then aged for 0.5 to 10 hours at a temperature above 70.degree. C., the crystalline sodium aluminosilicate thus formed being then washed and dried.
This process, with such a gel composition, even though being suitable for producing zeolite P on a bench scale, can't always be directly transposed to industrial scale.
Any industrial process must satisfy a series of requirements. First of all, the dilution must be as low as possible to keep the size of the reactors within satisfactory limits. Therefore the water content of the gel must be as low as possible. Secondly, the gel composition must be as stoichiometric as possible in order to limit reactants consumption. Thirdly, the process must be as simple as possible, i.e the different reactants must be as few as possible and they also must be easy to manipulate.
GENERAL DESCRIPTION OF THE INVENTION
It is an object of the present invention to provide a process for manufacturing an alkali metal aluminosilicate of zeolite P type having the oxide formula sodium hydroxide are mixed together to produce a first reacting gel having the general formula: zeolite P nuclei are formed, while its degree of crystallinity is below 25%, in a sufficient amount so as to produce a second reacting gel having the general formula: product being filtered washed and dried.
By doing so, zeolite P seeds are produced in-situ in a first reacting gel with a SiO.sub.2 /Al.sub.2 O, ratio of above 2.2 and it is only after the formation of zeolite P seeds, but before said seeds have the time to fully grow, that sodium aluminate solution is added in order to get a gel which can have a SiO.sub.2 /Al.sub.2 O.sub.3 ratio of about 2 which therefore enables producing a zeolite P having also a SiO.sub.2 /Al.sub.2 O.sub.3 ratio of about 2.
Preferably, the first reacting gel has the general formula:
Pre
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Bell Mark L.
Crossfield Limited
Troilo Louis M.
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