DE1246697B - Process for the production of aluminum oxide monohydrate with the boehmite crystal lattice - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

COIf

German class: 12 ro - 7

? A

Number: 1246697

File number: P 34667IV a / 12 m

Filing date: July 10, 1964

Opened on: August 10, 1967

The crystalline aluminum oxide hydrates have long been used for various purposes which depends on the very fine distribution of the crystals. These crystalline hydrates, like the hydrargillite or the boehmite, either form when aluminum compounds precipitate or more slowly by conversion from more or less amorphous sols or gels of aluminum hydroxide.

Depending on the various modifications, these crystalline hydrates are found as film-forming agents, as Carriers or fillers, as pigments, as binders or polishing agents and for the production of very finely calcined ones Products for ceramic purposes use, especially wherever a homogeneous Product of high fineness, which can be easily dispersed in aqueous media, may be of use can.

It is known that aluminum oxide monohydrate with the boehmite crystal lattice can be obtained by precipitation from a sodium aluminate solution with acid, prolonged heating of the separated gel, washing out and drying. However, this gives (for example according to the method described in "Angewandte Chemie", 65, p. 549 ff.) A pseudo as boehmite with an active surface area of 200 m ² / g, the behavior of which is substantially different from that obtainable according to the invention real, evenly and very finely crystallized boehmite.

From British Patent 893 852, a method has also become known in which a relatively fine monohydrate with boehmite crystal structure by heating an acidic aqueous dispersion is obtained from aluminum hydroxide in an autoclave at 120 to 250 ° C. The procedure that works in a highly diluted medium and is therefore cumbersome, leads to a sol that through Dialysis must be concentrated, so that the work-up of the products is quite complicated. here the method according to the invention provides a remedy in which there is no autoclave treatment with heating the desired fine crystalline product from the gel precipitated under very specific conditions is obtained.

The process according to the invention for the production of aluminum oxide monohydrate with the boehmite crystal lattice by precipitation from a sodium aluminate solution with acid, prolonged heating of the separated Gels as such or in aqueous suspension, washing out and gentle drying is thereby characterized in that the precipitation is carried out at a pH of 8 to 9 such that in

Process for the production of
Aluminum oxide monohydrate with the
Boehmite crystal lattice

Applicant:

Produits Chimiques Pechiney-Saint-Gobain,

Neuilly-sur-Seine (France)

Representative:

Dr.-Ing. F. Wuesthoff, Dipl.-Ing. G. Pulse
and Dr. E. Frhr. v. Pechmann, patent attorneys,
Munich 9, Schweigerstr. 2

Named as inventor:

Max Michel,

Sarcelles-les-Rosiers, Seine-et-Oise;
Denis Papee, Paris (France)

Claimed priority:

France of July 10, 1963 (940 954)

the gel containing up to 35 mole percent Al ₂ O ₈ still contains 0.05 to 0.5 equivalents of monovalent acid ions per mole of Al ₂ O and that the gel or its aqueous suspension is kept at 60 to 150 ° C. for 15 hours to days , washed out with ammonia and dried.

The washing is carried out with aqueous ammonia at a pH of 8 to 10, with most of the Foreign ions is removed. After drying in a drying cabinet or by spraying, one obtains compact masses or agglomerates of boehmite spheroids, which when redispersed in Water give colloidal solutions. If these masses or agglomerates are dispersed in an optionally organic liquid diluted with water, e.g. B. isopropanol, it remains after distilling off the liquid medium of the boehmite in powder form.

The presence of monovalent acid ions in the hydroxide is responsible for the conversion of the precipitated amorphous AJnmimumhydroxyds in boehmite necessary, however, on the other hand, by too high a concentration of these acid ions slows down the rate of conversion. Because of this, the

709 620/456

pH present during the precipitation and the way in which the precipitation takes place, of vital importance.

According to the invention, the continuous precipitation takes place of the sodium aluminate solution by acid with thorough stirring at a pH equal to during the precipitation remains in the range of 8 to 9. Then it is thrown off to remove it washed of practically all sodium ions with water and finally filtered. The thus obtained, Gel present as a filter cake is then further treated according to the invention as such or in aqueous suspension.

The temperature also has a decisive influence on the conversion of the amorphous aluminum hydroxides into boehmite. If the conversion process is carried out at too low a temperature, it is hardly possible to obtain crystallographically pure products, quite apart from the fact that the conversion time is much too long. , Up to 150 ° C, higher temperatures accelerate the process significantly, and as a particularly favorable temperatures have proven to about 100 ⁰ C, can be carried out without in which autoclave and the transition to the crystalline state relatively quickly.

example 1

By centrifuging, washing and filtering a suspension of aluminum hydroxide obtained by continuously precipitating a sodium aluminate solution containing 100 g of Al ₂ O ₃ equivalent per liter with a nitric acid solution of such a concentration and amount that this suspension was approximately 50 g Al ₂ O ₃ equivalent per liter and the molar ratio NO ₃ / A1 ₂ O _{S was} 0.16, a cake of a gel of aluminum hydroxide containing 20% of Al ₂ O. Equivalents was prepared. During the precipitation the pH was about 9. The resulting cake was heated to 110 ° C for 24 hours. After washing with ammonia and gentle drying, followed by dispersion in isopropanol, boehmite was obtained in the form of powder with an active surface area of 550 m ² / g.

Example 2

The same cake as in the previous example was subjected to treatment at 60 ° C for 170 hours. As in the previous example, it was washed out, dried and treated with isopropanol. An extremely fine boehmite in the form of powder with an active surface area of 580 m ² / g was obtained.

Example 3

Precipitation of aluminum hydroxide was carried out in the same general manner as in the previous examples, except that such an amount of nitric acid was used that the NO ₃ / Al ₂ O ₃ molar ratio was 0.29 and the pH during the precipitation was approximately 8. The cake was filtered so that the cake contained 25 percent by weight of Al ₂ O ₃ equivalent. This cake was treated at 110 ° C. for 90 hours. After washing, drying and dispersing in isopropanol as in the previous examples, boehmite was obtained in the form of powder with a specific surface area of 560 m ² / g.

Example 4

A cake of aluminum hydroxide gel was obtained in a similar general manner to the previous examples, _{except that the NO 3} / A1 ₂ O ₃ molar ratio was 0.25 and the pH during the continuous precipitation was approximately 8.5.

ίο This cake was diluted in water until a thick suspension of 15% Al ₂ O _{3 was} obtained. This dough was kept at a temperature of 110 ° C. for 80 hours with stirring, washed with aqueous ammonia and carefully dried, after which a mass of boehmite with an active surface area of 250 m ² / g was obtained.

Example 5

In the same general manner as in the previous example, a cake was made first and then a thick suspension of an aluminum hydroxide gel ^{with 15 0} _{AAl 2} O ₃ , but with the NO ₃ / Al ₂ O ₃ molar ratio being 0.20 and the pH during precipitation was about 8.5. This dough was kept at a temperature of 140 ° C. for 30 hours, then washed with aqueous ammonia and carefully dried, after which a mass of boehmite with an active surface area of 195 m ² / g was obtained.

Example6

The boehmite obtained in the previous examples was each at ordinary temperature redispersed in such an amount of water that in each case a suspension of 50 g / l was obtained. A glass film was immersed in each of these suspensions, the surface of which was completely cleaned had been. The sheet of glass was then allowed to drain for a few moments, leaving only one more thin layer of liquid remained on its surface. After gradual drying, each became a Adhering continuous and transparent film of aluminum hydroxide obtained.

Claims (1)

Claim: Process for the production of aluminum oxide monohydrate with the boehmite crystal lattice by precipitation from a sodium aluminate solution with acid, prolonged heating of the separated gel as such or in aqueous suspension, washing out and gentle drying, characterized in that the precipitation takes place at a pH of 8 to 9 is carried out in such a way that the _{gel containing up to 35 mol percent Al 2} O ₃ still contains 0.05 to 0.5 equivalents of monovalent acid ions per mole of Al ₂ O ₃ and that the gel or its aqueous suspension is 15 hours to 10 days kept at 60 to 150 ° C, washed with ammonia and dried. Considered publications:
British Patent No. 893,852;
"Kolloid-Zeitschrift", vol. 156, no. 1, p. 67/68;
"Angewandte Chemie", 65th year, 1953, No. 22, p. 549, right column. 709 620/456 7.67 © Bandesdruckerei Berlin