DD273824A1 - PROCESS FOR THE PRODUCTION OF TONERDE - Google Patents

Abstract

The invention relates to a process for producing alumina by thermal decomposition of aluminum chloride hexahydrate. Field of application of the invention is the production of special clay. The inventive method is characterized in that AlCl36 H2O is partially decomposed in the temperature range of 130-200C to a molar ratio nAl nCl 0.8-2.0, this decomposition product is reacted with up to five times the amount of water to a basic Aluminiumchloridsol, by dehydration a gel is prepared, which is calcined at 400-700C with constant removal of the fission gases by an inert gas stream to a-alumina. This ensures that the thermally decomposable aluminum compound (gel) has a diasporanaloge Nahordnung showing a transition to a-Al2O3 at 400C in the thermal decomposition under conditions according to the invention.

Description

Field of application of the invention

The invention relates to a process for the preparation of alumina by thermal decomposition of aluminum compounds. Field of application of the invention is the production of special clay.

Characteristic of the known state of the art

The production of α-alumina by thermal decomposition of aluminum compounds is generally known. Thus, the bulk of the industrially produced 0-Al ₂ O ₃ for aluminum extraction from the aluminum obtained according to the BAYER-Verf aluminum trihydroxide [Al (OH) ₃ ] is prepared. As further precursors for the recovery of alumina by thermal decomposition Aluminiumöxidhydroxide, -saue, complex compounds and organic aluminum compounds are known. For example, British Patent GB 2,184,715 describes a process for producing alumina by thermal calcination of basic aluminum chlorides. The thermal cleavage proceeds at low temperatures with the formation of metastable transitional toners, which change into the thermodynamically stable α-form at> 950 ° C. A disadvantage dabai are the high temperatures required to produce the α-alumina.

In this context, it is also known that in diaspore the transition into the a-alumina soil occurs without the formation of metastable transitional alumina at temperatures of about 42O ⁰ C (Tokar, K .; Krischner, H .; Monatshefte für Chemie 91 [1960] 757 -763). This behavior is attributed to structural analogies between diaspore and corundum. However, this peculiarity is technically not usable because on the one hand the bauxites present a toner-rich mixture of hydroxides and oxide hydroxides of aluminum, including diaspore, are not separable and on the other diaspore with great effort by rehydration of H-Al ₂ O ₃ in its active form (0 .'Al ₂ O ₃ ) or by reacting aluminum with water vapor at temperatures above 340 ⁰ C and pressures above 100 bar can be prepared. It is also known that Ci-Al ₂ O ₃ by treatment of aluminum hydroxides or oxides with steam at temperatures above 43O ⁰ C and pressures above 30 bar can be produced. It is also known, 0-AI ₂ O ₃ by hydrolysis of ₃ AIF in moist air at 700 ⁰ C, or by intensive grinding of bayerite and boehmite above 25O ⁰ C to produce (Petzold, A .; Ulbricht, J .: clay and Tonerdewerkstoffe, VEB German publishing house for raw materials industry, Leipzig 1984, Ullmanns Encyklopadie of the technical chemistry, publishing house chemistry, Weinheim Bergstrasse, 4.Aufl., Volume 7).

From the Auslegeschrift DE-AS 1954138 a process for the preparation of highly pure 0-Al ₂ O _{3 is} known in which an Al-containing starting material in a jet mill at 315-815 ° C milled and leaving the mill product at a temperature of 700 is calcined to 1000 ⁰ C. Starting materials are a solid, molten or dissolved aluminum nitrate, chloride, chlorate or bromide, a sol, suspension, gel or paste obtained by ammonia precipitation from an Al salt solution at pH values less than 6, finally a hydrated alumina mixture with ammonium nitrate or nitric acid. It is stated that the product leaving the mill contains 10-20% of O-Al ₂ O ₃ . The intermediate obtained from aluminum chloride bai is 750-85O ⁰ C completely converted to Al ₂ O _3.

Although all of these known process proposals for the production of α-alumina allow their formation at least partially at lower temperatures, but tecnnisch be realized only with considerable effort.

Object of the invention

The aim of the invention is an economical process for the preparation of α-Al ₂ O ₃ at considerably lower temperatures than hitherto technically common.

Explanation of the nature of the invention

The invention has for its object to produce a thermally decomposable aluminum compound having the same Nahordnuniisverhältnisse as diaspore.

Erfindungsgomäß the object is achieved in that Aluminiumchloridhexahydrat in the temperature range of

130-200 ^c C to a molar ratio - = 0.8-2.0, this decomposition product with up to five times the amount

n _C i

dehydration to produce a gel which is calcined at 400-700 ° C. with constant removal of the fission gases by an inert gas stream to form α-alumina. The aluminum chloride hexahydrate dried in the temperature range <100 ° C. is reduced to particle sizes crushed from 0.1 to 1 mm and advantageously thermally decomposed to achieve a uniform state of degradation in a fluidized bed at 130-200 ° C. The subsequent dissolution process of the resulting decomposition product can be accelerated by heating and the solutions can be concentrated by evaporation of the liquid. Depending on the concentration, low viscous to viscous basic solutions (brine) are obtained. Further depletion of the liquid produces crystal clear, brittle gels. Advantageously, further processing of the gel takes place in a powdery state.

For this purpose, either the sol can be dispersed and the sol droplets can be converted into the gel state, or it is produced by drying a larger amount of sol a compact gel body, which can be easily ground due to its Sprödigkeh. In the first case, it is advisable to start with low-viscosity sols and to carry out the sol-gel transition by spray-drying or by emulsifying or spraying the sol into a water-removing liquid. In the second approach, a highly viscous sol is dried to form an airgel, with respect to the drying time is a function of the layer thickness. The drying time can be considerably shortened by higher temperatures. IR spectrometric studies of the X-ray amorphous gels revealed spectra with diasporic absorption bands, i. h., that in them a Diasporanaloge Nahordnung exists.

For the formation of 0.-Al ₂ O ₃ by calcination of the gels at the indicated low temperatures and the calcination conditions are erfindungsweseilich. It has been found that the desired success occurs only when provided by an inert gas stream such as nitrogen or air for a rapid removal of HCI and H ₂ O-rich fission gases. In the diffractogram of such calcined samples, the maxima of the 0-Al ₂ O _{3 are found} as the only crystalline phase after calcination at 400 ⁰ C.

Ausführungsbelsplal

The invention is explained in more detail in the following exemplary embodiments:

example 1

Dried and K jrngrößen of 0.1-1 mm crushed aluminum chloride is decomposed in a Wirbelsohichtripparatur jai a temperature of 170 ⁰ C to a molar ratio n _A / n _C i of 1.3. The decomposition product is dissolved in water at a mass ratio solid: water of 1: 1.5 in the heat. The resulting sol can be emulsified by means of a high-speed paddle stirrer (1 000 rpm " ¹ ) in sec-butanol, ratio of 1:10 carbon black.

The Soltröpfchen transform by dehydration in gel balls, it spherical particles were obtained with a diameter of 1-10pm. The gel powder was filtered off, washed with butanol and dried.

When dried, it shows the IR absorption bands of the diaspore, but is X-ray amorphous.

The gel powder thus prepared was calcined in air in a tube furnace after gradual heating at 6f O ⁰ C with continuous removal of the fission gases. The calcinate showed in the diffractogram only the maxima of α · Α! ₂ Ο ₃ . The specific surface of the Prodi. ? 3 was determined to be 22m ² g ~ '. The spherical particles are largely retained during calcination. They adopt e η single-grained, porous structure. The residual content of volatile substances is 1.2%.

Example 2

As in exemplary embodiment 1. Finally, aluminum hexahydrate was thermally decomposed to a molecular weight of 1.3. The decomposition product was dissolved in the heat and the sol evaporated to a viscous consistency. The viscous sol was air dried. The resulting crystal clear, brittle gel was then crushed. The gel shows an IR spectrum corresponding to the diaspore, it is X-ray amorphous.

The milled gel was calcined analogously to Example 1. In the X-ray diffractogram of the calcinate, only the diffraction maxima of the Ci-Al ₂ O _{3 are} observed. The specific surface area is 8m ² g "'and has a residual content of 0.7% volatiles, which is finely divided and easily comminuted Under the electron microscope primary particles are around 0.1 μΓη, often also well-formed hexagonal sheets with The advantage of the solution according to the invention is the production of α-alumina at lower temperatures than hitherto technically customary, so that a considerable saving in energy results Crystallites with grain sizes <1 pm are formed in comparison with known Verfahron.

Claims (3)

1. A process for the preparation of alumina by thermal decomposition of aluminum compounds, characterized in that aluminum chloride hexahydrate in the temperature range of 130-200 ⁰ C to a molar ratio - ^ i = 0.8-2.0 is partially decomposed, this decomposition product nci is reacted with up to five times Ivenge of water to a basic Aluminiumchloridsol, by dehydration eh gel is prepared, which is calcined at 400-700 ⁰ C with constant removal of the cracking gases by an inert gas stream to α-alumina. 2. The method according to claim 1, characterized in that the decomposition of aluminum chloride hexahydrate after prior drying and grinding to particle sizes of 0.1 to 1 mm in a Wii belschicht. 3. The method according to claim 1 and 2, characterized in that the gel is prepared as a powder by dispersing the sol and the sol droplets are transferred to the gel state or by drying a larger amount of sol generates a gel body and then ground.