DK151219B - PROCEDURE FOR PREPARING A POWDER-SHEET CRYSTALLIC ZEOLITIC MOLECULAR SIGHT OF TYPE A - Google Patents

Description

151219

The invention relates to a process for producing a powdery crystalline zeolite molecular sieve of type A having a particle diameter of less than 2 µm, preferably less than 1 µm, by hydrothermal crystallization of an alumosilicate / water synthesis mixture.

Zeolite molecular year views with their special properties in ion exchange and adsorption have long been known. Their synthesis is due to the fact that a synthesis mixture with the components a Na 2 O x b A ^ O ^ x c S 10 O Depending on the composition, reaction temperature and reaction time of the starting mixture, compounds of the general formula Na ^ Al ^ Si ^ are obtained. n 1 ^ 0, which can be distinguished from each other on the basis of their X-ray spectra. In these syntheses, sodium can be replaced by other mono- or di-valent ions. Thus, e.g. German Patent No. 1,038,017 discloses a process for preparing a molecular sieve A with the gross formula 1.0 - 0.2: αΪ · 2 ° 3:: H2 H2 ° * where M represents a metal cation, n its valence and Y a value up to 6. Common to this and all other known methods is that in the synthesis crystals having an average diameter of more than 2JA are obtained.

For use as an adsorbent, catalyst support or ion exchanger, the molecular sieves are transferred with a suitable binder into molds. The production of mold bodies requires a great deal of technical effort, while at the same time reducing the effect due to the binder content. In addition, the reaction rate greatly decreased as a result of the long diffusion paths, making drying of organic liquids difficult. Furthermore, e.g. by removal of metals including radioactive metals from feed water and wastewater ion exchange and precipitation are separated. Therefore, it is advisable to use powdery molecular sieves for such applications. Also in lacquers, only molecular sieve powders are used.

However, the molecular yearly views that can be prepared by the present methods are generally not suitable. The crystals contained in the powders cause the molecular sieves to be deposited in wires and lead to constipation. Furthermore, these crystals appear abrasive and destroy pumps and bearings. When used in lacquers, a rough lacquer surface is obtained. By comminuting these molecular sieves by grinding, their activity is clearly diminished.

The object of the invention is to synthesize a molecular sieve powder which provides a quasi-stable suspension and only settles slowly, reduces the risk of wear on appliances and can be incorporated into varnishes without further treatment.

It has now surprisingly been found that a powdery crystalline zeolite molecular sieve having the desired properties and, above all, exhibiting undiminished activity can be obtained by the process according to the invention, which is characterized by preparing the synthesis mixture by adding 816 parts by volume. sodium aluminate solution having a content of 8.1% by weight ° S

4.8 wt.% Al 2 O 2 to 110 parts by volume of water glass consisting of 8 wt.% Na 2 O, 26 wt.% SiO 2 and 66 wt.% Water, and during and / or after preparing the synthesis mixture at temperatures between 25 and 80 °. C and / or during crystallization at temperatures between 80 and 240 ° C allow shear forces to act.

U.S. Patent No. 3,310,373 discloses a process for preparing synthetic crystalline aluminum silicates from an amorphous reaction mixture. In order to accelerate the growth of the crystalline aluminum silicates, the reaction mixture is subjected to crystallization in aqueous suspension during milling in a grinding apparatus to obtain a particle size of less than 5 microns. According to patent specification column 2, lines 18-19, the particle size should preferably be less than 1 micron, but it is clear from line 19-22 3 151219 in the same column that these small particles should serve as seed crystals to accelerate crystal growth and thus not may be the desired end result. Thus, from the aforementioned patent, nothing can be deduced that the process of the present invention is directed to the production of molecular sieves having a particle size of less than 2 microns, and preferably below 1 microns, as is the case with the process of the present invention. Furthermore, it is noted that said grinding apparatus e.g. can be a ball mill.

In the method of the present method, on the other hand, shear forces must be used to obtain a particle size of the crystals of less than 2 microns, preferably below 1 microns.

From Chemical Abstracts, Vol. 77, 1972, Abstract No. 77363 t, which relates to the preparation of synthetic zeolites of, inter alia, type A, it appears that the particle size can be adjusted between 0.3 and 5 microns depending on the intensity of the mechanical stirring. However, it is not recognized, however, that the technical effect obtained by the method according to the invention is conditional on the application of shear forces, all while stirring and shear are not identical concepts.

What is surprising about the method according to the invention is that a particle reduction can be obtained even by a very gentle actuation mechanism, cf. Example 2.

Apparatus such as "Ultra Turrax" and "Dispax Reactor" from Jahnke & Kunkel or the blending siren from Kotthoff can be used to generate shear forces. Also special stirrer types (turbochargers and the like) or circulation pumps are suitable. In the case of these devices, only those with high shear effect are involved.

The most advantageous is to let the shear forces act already in the preparation of the synthesis mixture, ie. by the joining of aqueous sodium-alumina top solution and water glass. As a result, it is irrelevant whether the aluminate solution is added to the water glass, whether the water glass is added to the aluminate solution, or whether both reactants are introduced simultaneously into the reaction vessel.

However, it is also very beneficial if the shear forces are allowed to work after the preparation of the synthesis mixture.

Furthermore, it is necessary that during or after the preparation of the synthesis mixture, something is heated during the shear effect. As mentioned, temperatures between 25 and 80 ° C, preferably 30 to 60 ° C, are used.

Finally, shear stress during crystallization can also lead to improved powdery molecular sieves. In this way, the shear forces act on the crystals under wading. As mentioned, the crystallization is carried out at temperatures between 80 and 240 ° C, so that the shear stress 4 occurs at these temperatures.

Thus, by suitable selection of reaction parameters such as temperature, time and mixture composition, crystals having an average diameter of less than 2 µx are obtained.

The process of the invention is particularly directed to the preparation of a type A molecular sieve which can be used as ion exchanger, i.e. as a phosphate substitute in detergents, and whose effect in softening water exceeds the known phosphate softeners and which allows the formation of quasi-stable suspensions and hardly causes wear on apparatus, e.g. washing machines. Furthermore, since an amorphous alkali aluminum silicate cannot be used in detergents, the process of the invention is directed to the preparation of a pure crystalline alkali aluminum silicate having a particle size of at most 2 microns, preferably 1 microns. A larger particle size of the zeolite is not practically usable for its intended purpose, since the alkali aluminum silicate particles would then settle significantly faster than desired and deposit on the laundry, thereby causing dusting in the dry laundry.

The process according to the invention is further elucidated by the following examples.

Example 1

To 110 l of water glass consisting of 8 wt% Na 2 O, 26 wt% SiO 2 and 66 wt% water, 816 l sodium aluminate solution containing 8.1 wt% Na 2 O and 4.8 wt% is added over 1 hour. al ^. During this time, the present solution is vigorously stirred with an "Ultra-Turrax" from the company Jahnke & Kunkel (about 3000 rpm). The mixture is then heated to 95 ° C for 10 hours, filtered and washed to a pH of 10.5. The type A molecular sieve obtained, determined electronically, has an average crystal diameter of less than 1, 1 Kg of this molecular sieve powder dispersed in 10 ml of water in a test tube. After 20 minutes of standing, 117 of this amount have settled on the bottom.

If you prepare a synthesis mixture of the same composition without stirring with an "Ultra-ftirraxHog", otherwise treating it in the same way, you obtain a molecular sieve, which according to the above time and method has already been deposited in an amount of 53%.

Example 2

From the components and quantities mentioned in Example 1, a synthesis mixture is prepared under gentle agitation with a paddle stirrer. Then this .3 mixture is re-pumped with a circulation pump with a capacity of 10 m / hour. Then the mixture is heated to 95 ° C for 6 hours, filtered and dried. The sedimentation volume determined by the method of Example 1 in this case amounts to 9% of the starting amount.

Claims (1)

Process for preparing a powdery crystalline zeolite molecular sieve of type A having a particle diameter of less than 2 µm, preferably below 1 gm, by hydrothermal crystallization of an alumosilicate / water synthesis mixture, characterized by preparing the synthesis mixture by adding 816 parts by volume sodium aluminate solution having a content of 8.1 wt% Na 2 O and 4.8 wt% A 2 O 2 to 110 parts by volume of water glass consisting of 8 wt% 2 O, 26 wt% SiO 2 and 66 wt% water, and and / or after the preparation of the synthesis mixture at temperatures between 25 and 80 ° C and / or during crystallization at temperatures between 80 and 240 ° C, shear forces act.