Chemistry of inorganic compounds – Zeolite
Patent
1995-09-22
1997-07-08
Group, Karl
Chemistry of inorganic compounds
Zeolite
423711, 423DIG21, 423DIG24, C01B 3916, C01B 3920
Patent
active
056458118
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for the production of very fine-particle alkali metal aluminium silicates, more particularly zeolites of the A type, of the P type and of the faujasite type (X and Y).
2. Statement of Related Art
Alkali metal aluminium silicates of the type in question are used, for example, as builders for laundry detergents, dishwashing detergents and cleaning formulations, as molecular sieves, catalysts and absorbents and as additives in ceramic frits and glazes.
Two important criteria for the use of zeolites in laundry detergents, dishwashing detergents and cleaning compositions and as additives in ceramic frits and glazes are the mean particle size (expressed as the d.sub.50 value) and the width of the particle size distribution spectrum. The d.sub.50 value indicates that 50% by weight of the measured sample consists of particles which are smaller than the indicated value. There are various methods for measuring the d.sub.50 value. The measured values obtained by the various methods cannot readily be compared with one another. In the context of the present invention, the d.sub.50 value is measured by light diffraction and light scattering methods. This procedure is described, for example, in H. Wachernig, Sprechsaal, Vol. 121, No. 3, 1988, pages 213 to 215.
Another important criterion for the use of zeolites in laundry detergents, dishwashing detergents and cleaning compositions is their cation exchange capacity, more particularly their exchange capacity with respect to calcium ions. The corresponding values were determined by adding the corresponding zeolite to a calcium chloride solution and, after filtration, subjecting the remaining calcium ions present in the solution to complexometric titration.
There are various known processes for the production of very fine-particle zeolites of the zeolite A type.
DE-A-29 51 192 describes a process for the production of zeolite A with a small and uniform particle size. The particle size is controlled on the basis of the following parameters: temperature,
The particle size of the zeolite formed after crystallization is reduced by increasing the solids concentration on the one hand and by increasing the Na.sub.2 O/Al.sub.2 O.sub.3 ratio in the reaction mixture on the other hand, i.e. in the solutions which, after they have been combined, form an amorphous alumosilicate gel. This process has its natural limits: if, for example, the solids concentration is excessively increased, the particle size spectrum expands. If the Na.sub.2 O/Al.sub.2 O.sub.3 ratio is too high, the time between complete reaction to zeolite 4A and the following conversion into hydroxysodalite is very short so that there is not enough time for subsequent processing of the zeolite suspension.
It is known from DE-A-27 04 310 that, after the reaction components involved in the production of alkali metal aluminium silicates have been mixed with intensive stirring, the intensive stirring can be continued at least until the viscosity maximum is exceeded or, optionally, the viscosity maximum is not fully reached, after which the suspensions are recycled at least once through a size-reducing unit and are then optionally kept at elevated temperature pending crystallization.
It is known from DE-A-27 34 296 that, in the production of fine-particle sodium aluminium silicates, the suspension obtained after the aqueous sodium aluminate solution has been rapidly mixed with the aqueous sodium silicate solution can be briefly stirred at the same temperature before the crystallization step is carried out at elevated temperature.
DE-A-30 11 834 describes a process for the production of very fine-particle zeolitic sodium aluminium silicates, in which steam is introduced during discontinuous crystallization and, at the same time, the suspension is stirred with multiple-stage high-shear stirrers.
DE-A-29 41 636 also relates to a process for the continuous production of very fine-particle zeolitic sodium aluminium silicates, in which suspensi
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Blasey Gerhard
Kuhm Peter
Salz Rainer
Group Karl
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
Millson Jr. Henry E.
Sample David
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