DE1008722B - Process for granulating alumina - Google Patents

Description

GERMAN

The multiple technical application possibilities for granulated alumina led to different ones Suggestions for their preparation. For example, an earlier procedure is followed from aluminum alcoholates, from which, by hydrolysis, a relatively pure, pasty aluminum hydroxide (Hydrogel) is obtained, which by subsequent dehydration and tempering in the known, horn-like modification of aluminum oxide is transferred. The expensive starting product and the properties of the obtained alumina moldings (low porosity, small surface area) made this process appear to be in need of improvement. The invention shows a way from an easily and cheaply available raw product to a particularly stable one To get clay with significantly increased porosity or surface. The invention relates to a Process for granulating alumina, comprising the following individual steps:

A) Dehydration of technical grade α-alumina trihydrate by heating to a temperature between 150 and 500 °, the conditions so chosen are that the water vapor is continuously removed as it forms. To make it happen These conditions can be used to maintain a vacuum in the heater or to remove the alumina keep a stream of hot and dry gases moving (fluidizing), which at the same time serves to keep the To heat the product and to dissipate the water vapor.

B) If necessary, grinding or grinding the dehydrated product, such that the for the particular type of granulation and the grain size favorable for the intended use.

C) Shaping granules in any way, for example by pressing, extrusion, granulating in a coating pan, etc., using a limited amount of water as a binder. That Water, in suspension or solution, can contain one or more chemicals, if intended is to incorporate these into the alumina granules, for example to make the latter more catalytic! To use reactions. A partial transfer of the previously dehydrated clay already takes place here in / J-trihydrate (rehydration).

D) hardening of the granules by setting with water with further rehydration to the trihydrate.

E) Heat treatment of the granules, those previously or because the excess, chemically unbound water is also withdrawn. This "tempering" is used for the renewed transfer of the trihydrate into active oxide and is tailored to the use, to which the active alumina is intended in each case.

Applicant:

Pechiney, Company de Produits
Chimiques et Electrometallurgiques, Paris

Representative: Dr.-Ing. F. Wuesthoff, patent attorney,
Munich 9, Schweigerstr. 2

Claimed priority:
France of March 25, 1953 and January 27, 1954

Lucien Pingard, Salindres, Gard (France),
has been named as the inventor

The hardening of the granules mentioned under D) is based on the ability of the dehydrated clay as it is obtained in the process stage described under A), at least partially through Setting «with water to convert it into bayerite. This recrystallization is rather slow and takes a long time l> at normal temperature several days until it is complete, but it can be increased by increasing the temperature be accelerated. "" '■■■ · "".

On rehydration, only a small part of the water used for granulating involved, so that the Hauptänteildes water can be removed during the course of Reäktivierung ¹ at a moderate temperature. To remove the last part, a higher temperature is necessary. The opposite of hydration then takes place: the bayerite crystals dehydrate and weak, crystalline clay with reactive properties is formed again. In doing so, however, the granules retain the cohesion that was given to them through hydration. They have a remarkable mechanical resistance and can be subjected to heat treatment at very high temperatures without losing their resistance.

Considering that the recrystallization of the original alumina to bayerite is a slow one Process, it is necessary to leave the clay in contact with the water for a long enough time, so that this transformation is complete, or at least sufficiently advanced.

The degree of rehydration reached at the point in time when you go to activation affects the degree of rehydration very strong the results.

. ■ '709 510/400

If reactivation takes place immediately after granulation, the single grains practically "retain" their original structure and show no mechanical resistance whatsoever.

A treatment in a humid atmosphere at 100 ° after granulation leads within a few hours, to harden the grains. After activation, they have a relatively little extended surface, however, a very remarkable porous volume: new intergranular adsorption ίο series occur; in fact, the grains close together closely as a result of rehydration together.

Subjecting the grains or the granules to a treatment in a closed vessel at moderate If the temperature is below 75 °, the rehydration takes place slower, but the grains are sufficiently hard. After reactivating that is porous volume less large than before, albeit noticeably larger than that of the original activated one Clay. The specific surface area is quite significant, usually greater than that of the dem Product subjected to granulation. An analogous result is obtained if you simply add the granules kept at normal temperature for a few days before reactivating.

Examples

1. The powdery clay (surface 240 m ² / g, porous volume 0.19 cm ³ / g) is ground in a ball mill and converted into granules with a grain size of 2 to 5 mm by adding water. The granules are stored in barrels for 8 days, then dried for 8 hours at 100 ° and finally reactivated for 2 hours at 300 ° while blowing dry air through them.

A product is obtained with the composition Al ₂ O ₃ · 0.62H ₂ O with a surface area of 260 m ² / g and a porous volume of 0.29 cm ³ / g.

2. The granulate is produced under the same conditions as in Example 1, but then for 8 hours kept at 100 ° in non-hermetically sealed containers, dried at 100 ° and finally Reactivated for 2 hours at 400 °.

The grains then have a composition corresponding to Al ₂ O ₃ · 0.36 H ₂ O, a surface area of 200 m ² / g and a porous volume of 0.33 cm ³ / g.

3. The procedure is the same as in Example 2, but the reactivation is carried out at 560 °.

The product corresponds to the composition Al ₂ O ₃ -O ₅ IoH ₂ O and has a surface area of m ² / g and a porous volume of 0.36 cm ³ / g.

In comparison, the hydrargillite activated directly at 560 °, of the same composition as the above product, has a maximum porous volume obtained by direct activation of. 0.28 cm ³ / g and a surface area of 130 m ² / g.

Among the numerous possible uses for the granulated, activated clays, the following are mentioned: Adsorption, drying of gases, chromatography, catalysis, use as a catalyst carrier, Manufacture of aluminum fluoride by dry means, manufacture of refractory insulating pieces etc.

Claims (3)

Patent claims: 1. Process for the production of activated alumina in the form of mechanically resistant Granules with a high microporous volume and / or large surface, characterized in that that technical a-alumina trihydrate in a vacuum or in a stream drier, inert gases dehydrated at 160 to 500 °, whereupon it is made by means of a limited Amount of water with gentle heating to less than 100 ° forms a paste, this and that Granules for the purpose of hardening the individual grains under the action of further moisture at 20 to 150 ° completely hydrated to /? - alumina hydrate, whereupon the hardened grains are known Way after driving off the excess water by tempering at 250 to 600 ° in active again Transferred to clay. 2. The method according to claim 1, characterized in that that the granules in order to achieve an increased microporous volume in a humid atmosphere at about 100 ° for 8 to 10 hours cures and then heat-treats them at 400 to 600 ° while blowing dry air through them (annealed). 3. The method according to claim 1 or 2, characterized in that the granules for the purpose Achieving a particularly large surface in a moist atmosphere at 25 to 75 ° hardens and they then heat-treated (annealed) for a few hours at 250 to 400 °. Publications considered: German Patent No. 801 154. © 709 510/400 5.57