DE2525929A1 - PROCESS FOR PRODUCING PURE ALUMINUM OXYDE - Google Patents

Description

DlPL-IMa R. MSRTENS ⁶ Sranxfurt / M, 9.6.1975

DIPL-PiIVS. Dl.R. KEL K 83 P 52

6 Frankfurt, '?! I, Ar.:., Ei urgsir. 34? ζ 9 ζ Q O Q

, vUTHNEi'i Industrieanlagen-Aktiengesellschaft in, vien

Aichholzgasse 51-53

Process for the production of pure aluminum oxide

Jis is known for the purpose of producing pure alpha or Gamma alumina non-alumina in hydrochloric acid particular Dissolve purity and thermally decompose this solution · This manufacturing process is correspondingly complex and expensive.

shows, however, that it is quite possible to produce from a waste solution, such as is obtained in the etching of aluminum foil / aluminum oxide with a hydrochloric acid Genalt of at least 99.5, preferably 99.8% AIPO, by thermal decomposition, when one proceeds according to the invention :

Accordingly, the present invention relates to a method for the production of aluminum oxide by producing an aluminum chloride solution, thermal decomposition of the same and using the hydrogen chloride obtained in the cleavage to produce the aluminum chloride solution, thereby marked that

a) a solution is assumed which is obtained when aluminum foils are treated with a purity of at least 99.9, preferably 99.99 % Al with regenerated hydrochloric acid;

b) the solution mentioned - preferably after contacting the furnace exhaust gases - in direct contact with 7üO to 1300, preferably 750 to 950 ⁰ C hot, by burning

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- '2. -

Finally, gaseous heating medium with a maximum of 0.01 wt.> o S gases created in the form of S-compounds, evaporated and pyrohydrolytically to one in one operation Hydrogen chloride-containing gas phase and aluminum oxide decomposed;

c) the aluminum oxide with a content of at least 99 »5, preferably 99.8 % AlpO ^, is separated from the gas phase above its dew point;

d) the hydrogen chloride from the gas phase in water with an electrical conductivity of max. 10, preferably 2 microSiemens per centimeter or a solution of max. 5 J & aluminum chloride and max. 5 % hydrogen chloride in this same water, as is obtained during rinsing, preferably adiabatic, absorbed, and

e) the regenerated hydrochloric acid obtained in this way in stage a) is returned.

This process makes it possible to produce high-purity aluminum oxide without having to buy and use very pure aluminum. Rather, aluminum foil is refined into a product with a large surface area with a special structure, as is required, for example, for the production of electrical capacitors. Even the expensive, practically mercury-free hydrochloric acid, which is suitable for etching the foil, only has to be topped up in accordance with the low losses. In the solution preparation plant, these are only about 0.5 % of the throughput of chloride ions. Even if the entire circuit including the foil etching system is included, the additional losses of chloride ions or circuit hydrochloric acid can be kept below 8, preferably 3 % , if the rinsing water that occurs during etching is kept as low as possible with economical countercurrent flow , that he

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they can fully incorporate into the circulatory process as an absorbent for the hydrogen chloride. In this case it is Another advantage of the process is that the laborious work-up, which complies with the strict waste water laws the wastewater can not only be reduced considerably, but also completely avoided,

It goes without saying that the parts of the apparatus that come into contact with the material flows must not only be corrosion-resistant in the usual sense, but also be selected in such a way that, as a result of corrosion and erosion, large proportions of impurities that cannot be tolerated get into the aluminum oKyd produced. Ceramic linings were therefore used which contained less than k% TiO ₂ , 2% Fe ₂ O-, and 1 ft CaO or Na ₂ O + KpO each. Where the temperature allowed it, acid-proof rubber linings were chosen. An acid-proof porcelain proved itself as the material for the packing of the hydrogen chloride absorption column.

According to the method described, it is possible to produce aluminum oxide that has less than the following maximum amounts of impurities contains: 50 ppm each of Fe, Si and Ca; 20 ppm Zn; 10 ppm Ti, Mn and Mg; 5 ppm Cu and B; 3 ppm Mo, Ga and Co. Most methods fail when it comes to the detection of Na, K and V. You have it, mainly through the choice of the decomposition temperature in the furnace, in the nand, the proportions of alpha and Adjust gamma aluminum oxide to a ratio that can be freely selected in the range from about 15:85 to 85:15. Ever The longer the dwell time and the higher the temperature in the furnace, the greater the proportion of alpha oxide.

It is also not difficult to determine the residual content as chloride to reduce the presence of chlorine below 0.2% in the oxide. By a thermal aftertreatment, it is also possible to remove this residual content and, in parallel, that part of the Oxyds, which is present in gamma-u'orm, to reduce even further.

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It is not difficult to find> 0 ppm residual chlorine as chloride and underneath, or to practically one hundred percent alpha aluminum oxide.

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Claims (1)

Claim: Process for the production of aluminum oxide by manufacturing an aluminum chloride solution, thermal decomposition of the same and use of the, cleavage obtained hydrogen chloride for the preparation of aluminum chloride solution, characterized in that a) a solution is assumed which is obtained when treating aluminum foils with a purity of at least 99.9, preferably 99.99 % Al with regenerated hydrochloric acid; b) said solution - preferably after ivontaktierung with the kiln exhaust gases - in direct contact with 7üO to 1300, preferably 750 to 95O ⁰ G mean exclusively gaseous by burning heating means max u, u1 Gew.ft s in the form of o compounds. resulting gases, evaporated in one operation and pyrohydrolytically decomposed to a gas phase containing hydrogen chloride and aluminum oxide; c) the aluminum oxide with a content of at least 99.5, preferably 99.8 / o AlpO, from the gas phase through the latter Dew point separated; d) the hydrogen chloride from the gas phase in water with an electrical conductivity of max. 10, preferably 2 MikrοSiemens per centimeter or a solution of max. 5 / ό aluminum chloride and max. 5> ό hydrogen chloride in flat this water, as it arises during rinsing, preferably adiabatically, absorbed, and 509883/0852 e) the regenerated hydrochloric acid obtained in this way in atuie a) is returned. 509883/0852