Process for increasing the rupture resistence of granules.

The present invention relates to a method for increasing the breaking strength of zeolite granules, in particular SiO₂-bound moldings.

Zeolites are framework silicates with the general formula:<chemistry id="chem0001" num="0001"><img file="EP0170026A2_D0001.tif" /></chemistry>where M^I. = monovalent cations such as Li, Na, K and M.^II = Divalent cations such as Mg, Ca, Sr, Ba can be.

Synthesized zeolites are widely used in adsorption technology. Examples include: Zeolite A, Zeolite X, Zeolite Y, Zeolite L, Zeolite T, Zeolite S, Zeolite F, Zeolite H, Mordenite, Erionite, Ofretite, Ferrierite, ZSM5, ZSM11, Chabasite and others

Type A zeolites, those of oxidic composition<chemistry id="chem0002" num="0002"><img file="EP0170026A2_D0002.tif" /></chemistry>and type X zeolites, those of the oxidic composition<chemistry id="chem0003" num="0003"><img file="EP0170026A2_D0003.tif" /></chemistry>correspond, where M is a metal and n is pure valence, are used after drying with binders into pellets, spheres and granules for drying or fine cleaning of gas and liquid streams. Binder-free moldings of zeolite A are also used.

In the drying and fine cleaning processes, the fluid turns into relatively small amounts of water or other impurities, such as C0₂, H₂S, acetylene, NH₃ removed among other things. If, on the other hand, it is about the adsorptive separation of components which are contained in the fluid in higher concentrations, one speaks of material separations.

Examples of industrial absorption processes are: separation of hydrocarbons, production of ultra-pure hydrogen by pressure swing adsorption (DWA); Separation of oxygen and nitrogen by DWA, drying and cleaning of natural gas, drying of cracked gases, etc.

In terms of the process, a distinction is made between static adsorption and dynamic adsorption of zeolites.

Examples of static adsorption are the use of molecular sieve moldings for multi-pane insulating glass, the drying of refrigerant circuits and the removal of water from solvent-free polyurethane systems for zeolite powder and in the case of moisture-sensitive coating systems.

The industrial adsorption processes listed above are all based on the so-called dynamic adsorption. In all adsorption processes, zeolites of types A and X are used in their synthesis form, ie with Na as the cation or in the form modified by ion exchange.

In the case of zeolite A, the pore size can be influenced by the cations. In synthesis, zeolite A is generally obtained in the Na form, which has a pore size of approximately 4 Å (see DW Breck, Zeolithe Molecular Sieves J. Wiley, New York 1974). By ion exchange, instead of Na⁺-Ions the more voluminous R⁺- Introduce ions, which narrows the pores to approx. 3 R. On the other hand, when the Na^+-Ions against divalent approx²⁺-Ions the pores expanded to 5 Å, because instead of two Na ions only approx. Approx²⁺-Ion enters the lattice with approximately the same ion radius. This change in the pore size naturally affects the selectivity of the zeolites due to the sieving action.

The adsorption properties of the zeolites are based on two completely different principles. Firstly, molecules of different cross-sectional projections can be separated from each other by only allowing the smaller ones to pass through the zeolite pores of uniform size and thus access to the actual ones_Adsorption cavities. This behavior is known as the so-called sieve effect during adsorption. Second, thanks to the polar structure of the inner surface of the zeolite crystals, more polar molecules are preferentially adsorbed over less polar ones. The existing electrostatic field also causes an increased adsorption of more polarizable molecules compared to less polarizable (polarity effect). It is always assumed that the molecular geometry allows penetration into the zeolite crystal through the pores.

In adsorption technology, the zeolitic molecular sieves are generally used as granules. Suitable binders are, for example, kaolins, attapulgites, bentonites, sepiolites and the like. as well as water glasses, gellable silica sols and aluminum oxides.

Clay-bound granules are widely used in absorption technology. However, they have the disadvantage of a high calcining temperature (&gt; 600 ° C.) in order to obtain hard, unbreakable and water-stable granules. Depending on the clay binder and the production process, the adsorption performance is influenced. Due to their self-adsorption and catalytic properties, aluminum oxides can lead to disturbances in many adsorptions based on the zeolitic molecular sieve effect.

A porous zeolite granulate with a macroporous structure which is well suited for adsorption purposes is obtained if silica gel which can be gelled is used as a binder. According to German Patent 1,165,562, powdery molecular sieve zeolites can be stirred with an aqueous, stable silica sol to form a flowable suspension, the suspension can be distributed into drops of the desired size in a water-immiscible liquid after addition of a gelling catalyst, and finally the sol-gel conversion Pearl granules are removed from the liquid. This creates an Si0₂- Bound pearl-shaped granules, the proportion of binder by suitable measures, as described in the German patent. can be converted into a so-called binder-free granulate. This measure naturally increases the adsorption capacity, since 100% zeolite is now present, the breaking strength and the abrasion resistance are significantly improved. However, this affects the previously existing macroporous structure.

For certain areas of application in the adsorption sector, it is desirable that rapid adsorption or rapid desorption be present in the molecular sieve granulate, for example in what is known as pressure swing adsorption. These adsorption properties are at Sio₂-bound molecular sieve granules are available to the desired extent due to their macroporous structure. For technical use, however, the Si0₂-bound granules less suitable due to their insufficient abrasion resistance and hardness.

The object of the present invention was therefore to develop a method which, while increasing the breaking strength and improving the abrasion values, the macroporous structure of Si0 which is favorable for the adsorption₂- maintains bound granules.

The present invention relates to a method for increasing the breaking strength of Si0₂-bound zeolitic molecular sieve granules, which is characterized in that the granules are treated with aqueous solutions of divalent metals.

Surprisingly, it was found that treatment of the SiO₂-containing granules with solutions of the salts of alkaline earth metal cations such as Mg²⁺, Approx²⁺, Sr²⁺ or also salts of transition cations such as Mn²⁺, Ni²⁺, Zn etc. there is a significant increase in breaking strength (see table 1 below).

<tables id="tabl0001" num="0001"><img file="EP0170026A2_D0004.tif" /></tables>

As can be seen from the table, when the polyvalent cations are exchanged there is an increase in the breaking strength, while when the monovalent cations are exchanged there is a constant or a significant drop in the breaking strength.

Calcium is particularly suitable for the treatment of the granules for obvious reasons. When the granules are treated with aqueous salt solutions, an ion exchange naturally takes place on the zeolite. Table 2 below shows that a certain amount of divalent ions must therefore be introduced into the granules in order to achieve the desired increase in breaking strength.<tables id="tabl0002" num="0002"><img file="EP0170026A2_D0005.tif" /></tables>

The granules are treated at room temperature or at elevated temperatures, preferably 30-100 ° C. The treatment time can be selected between a few hours and several days, a time between 1.0 and 10 hours is preferred. Repetition can be repeated to intensify the treatment. For economic reasons, the minimum necessary duration of treatment or Number of treatments determined, which depends on the different areas of application of the granulate.

When using alkaline earth metal salts, the ion exchange on the zeolite required for certain applications can be combined with the treatment according to the invention of the Sio2-bound granules.

The so-called pressure swing adsorption can be mentioned as an example of the use of the granules hardened by the treatment according to the invention. The superiority of Si0₂-bound molecular sieve granules compared to the prior art, clay-bound molecular granules, is expressed in a 30% higher performance in oxygen enrichment from air.

As another example of the superiority Si0₂-bound and hardened granules the air purification is given here, with Si0₂-bound granules a significant 28% higher performance compared to clay-bound molecular sieve granules is achieved.

The preparation of the granules according to the invention is described in the examples below.

example 1

2000 g Si0₂-containing Na zeolite granules of the sieve fraction 2 - 3 mm are filled into a glass column and with 1.6 liters of one molar MgCl₂Solution treated at 80 ° C. The MgC1₂Solution continuously circulated through the column for 4 hours. After two treatments, the granules were then washed chloride-free, dried and activated at 500 ° C. The fracture hardness of the treated material increased from 3.1 to 3.4 kg and the abrasion decreased by 50%.

Example 2

2000 g SiO₂-containing Na zeolite A granules of the sieve fraction 2 - 3 mm are filled into a glass column and with 1.6 liters of one molar CaCl₂Solution treated at 80 ° C. The CaCl solution is continuously circulated through the column for 4 hours. After two treatments, the granules were washed free of chloride, dried and activated at 500 ° C.

The hardness of the treated material increased from 3.1 to 3.5 kg and the abrasion decreased by 60%.

Examples 3 to 6

The treatment conditions for the SiO₂-bound granules with the metal salt solutions correspond to Example 1.

The fracture hardness is increased by treatment with saline divalent ions.

Examples 7 and 8

The treatment conditions for the Si0₂-bound granules with the metal salt solutions correspond to Example 1.

The fracture hardness is reduced by treatment with salt solutions of monovalent ions or remains the same.

Examples 9 to 13

Here the treatment conditions were chosen so that increasing amounts of CaO remain in the granulate. An SiO₂-bound Na zeolite granules with a grain size of 3-4 mm. The initial hardness of 4.0 kg increases with increasing CaO content in the granulate up to 8.0 kg.

Example 14

3000 g SiO₂-containing Na zeolite granules of the sieve fraction 2-4 mm are filled into a glass column and with 2.4 liters of one molar CaCl₂Solution treated at 80 ° C. The CaCl₂Solution continuously circulated through the column for 4 hours. After a single treatment, the granules were washed free of chloride, dried and activated at 500 ° C.

The fracture hardness of the treated granules increased from 3.3 kg to 4.4 kg mean fracture hardness.

Example 15

1000 g Sio₂-containing Na zeolite X granules of the sieve fraction 2-4 mm are filled into a glass column and with 0.8 liters of one molar CaCl₂Solution treated at 80 ° C. The CaCl₂Solution continuously circulated through the column for 4 hours. After two treatments, the granules were washed free of chloride, dried and activated at 500 ° C.

The fracture hardness of the treated material increased from 3.3 kg to 4.8 kg mean fracture hardness.