DE1767724A1 - Process for the production of finely divided aluminum oxide - Google Patents

Description

W, R. Grace & Co (iJü 6 ^ 5 2J51 - prio 12.6.6?

New York , N.Y./V. 5t .A. ^{A ll81} ^ "55 ² H)

Hamburg, γ. June 1968

Process for the production of finely divided aluminum oxide

The invention relates to a method for producing pulverulent Alumina with a particle size in the range of 0.02 to 2 microns. After this process, a finely divided Aluminum oxide can be obtained, which has an internal surface area of over 5 m / g and is practically sodium-free.

Aluminum oxide powders with these properties are used as catalyst bases, Pigments, used in ceramic products and as additives to various other systems.

Kerarnikwaren v / ground generally at temperatures over 1200 ⁰ C. At these temperatures all phases of the aluminum oxide are converted into tf-aluminum oxide. Since this conversion is undesirable,-aluminum oxide is normally used in the manufacture of ceramic goods. With the method according to the invention, it is now possible to produce finely divided (K -aluminum oxide powder, which, due to its fine particle size, has further advantages for the

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Manufacture of ceramic goods offers. So it is known that the strength of the finished ceramic products depends on the particle size of the alumina used; through the at the method according to the invention achieved particular fineness of the It is possible for particles to apply lower firing temperatures and manufacture products of greater strength.

Most catalytic reactions are carried out at temperatures which are below the temperature at which V aluminum oxide is converted into X aluminum oxide. However, the temperatures in these reactions are generally so high that amorphous aluminum oxide crystallizes. According to the process according to the invention, aluminum oxides can be used with

produce inner surfaces of over 200 m / g, which have a

Form particularly good catalyst base.

The inventive method can be applied to the production of (y - or / - aluminum oxide can be turned off. The particle size of the products obtained by the process according to the invention is usually in the submicron range. Because of this property, they are particularly suitable as pigments and Additives, as this requires products with a particularly fine particle size.

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A conventional process for making alumina consists in the neutralization of an aluminum salt. For example, the readily available one is used as the starting material for this Alum (aluminum sulfate) is used. In this manufacturing process an alum solution is neutralized with ammonia, an A] kaliba.se or an alkaline earth base. The precipitated one Aluminum oxide is then used to remove unwanted Washed impurities. Above all, it is very important that the finished aluminum oxide is sodium-free, because even small amounts of sodium cause the sintering of aluminum oxide promote and thereby lead to a loss of internal surface and pore volume.

With the present invention, a process for the production of particulate aluminum oxide with a particle size of about 0.02 to 2 microns is proposed, in which a precursor for aluminum oxide is introduced into a comminution device operated at a temperature of about 26o C and there with heating crushed to the desired particulate product.

An air jet mill is preferred as the comminuting device. The task of the shredding device at This method consists in increasing the speed of translation. It is well known that small particles

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react faster than larger ones. For example · in the production of aluminum oxide from aluminum nitrate a faster reaction takes place when the aluminum nitrate is in a finely divided state. Mine too can only be alumina produced by thermal decomposition of aluminum nitrate, but the product then does not have the desired particle size.

For the production of fine particles, for obtaining the desired Aluminum oxide phase and - if this is appropriate or necessary - to avoid washing stages is one rapid dehydration and / or decomposition with the lowest possible temperature gradients required.

The normal jet mills available on the market are modified in such a way that that they can be operated at the temperatures required for the decomposition or dehydration of the precursor to aluminum oxide with the desired inner surface, the desired pore volume and the desired crystal phase required are.

Suitable precursors or starting materials for manufacture of aluminum oxide are aluminum nitrate, aluminum sulfate and aluminum oxide hydrate in a slurry. An aluminum nitrate solution is expediently with before being introduced into the grinder

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Nitric acid to a pH of 1 to 2 or with ammonium hydroxide or ammonia gas adjusted to a pH of 2 to 1.5. The neutralization product of an aluminum nitrate solution, with ammonium hydroxide or Ammonia gas or the acidification product of aluminum nitrate with nitric acid or the aluminum nitrate or an aluminum nitrate solution to be introduced.

The properties of the finished product change with the working conditions the mill and the pH ranges at which the starting material decomposes or dehydrates in the jet mill will. The starting material can be milled as a solution, slurry, slurry, or partially dehydrated solid. The mill is operated at a temperature above 260 ° G. If ammonium nitrate is added or formed in the process the concentration may be less than, the same as, or greater than the amount that would normally come from the above production results.

The starting material introduced into the mill can also consist of Aluminum nitrate nonahydrate exist, which can be combined with any Amount of ammonia gas has been treated. The product treated in this way is introduced into a mill operated at temperatures above 260 ° C.

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The starting material can also be produced on the wines described above using aluminum sulfate or aluminum ammonium sulfate instead of the nitrate. During milling at 566 ⁰ C the sulfates remain below sets .. The milled Frodukt is then heated to a temperature above 78o C ^0, where f is one-piece Ϋ- -Aluminiumoxyd is obtained.

Any aluminum oxide hydrate can also be used as the starting material, which may optionally be mixed with solid Ammonium nitrate mixed or in an ammonium nitrate solution can be sliced up. By grinding mixtures with ammonium nitrate, aluminum oxides become physical with others Properties retained than when grinding without ammonium nitrate.

In the processes described above, in which ammonium nitrate is added or formed, the solids, pastes, slurries or solutions are introduced into a jet mill, which ™ is operated at a temperature above 26o ° C, which means that the Dehydrated precursor to the desired aluminum oxide and / or thermally decomposed. The physical state in which the starting material is used depends on the im The finished product depends on the desired physical and chemical properties and the desired crystal phase.

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BATH

In certain processes for the production of the starting material, for example when neutralizing with ammonia: the salts are precipitated with ammonia, whereby the oxide hydrate and ammonium nitrate are formed. The ammonium nitrate is decomposed in the mill and the oxide hydrate is dehydrated to aluminum oxide. The precipitation can take place in a satisfactory manner in a device which is referred to as an oxide hydrate reactor and in which homogeneous, finely divided precipitates can be produced directly and continuously. This reactor is equipped with W metering pumps, which deliver the starting materials in precisely measured quantities into a mixing chamber. The mixing chamber is surrounded by a heating and cooling jacket and equipped with a high-speed stirrer. The liquid starting materials are injected into the chamber through nozzles so that they are mixed extremely quickly in a very short time.

The concentration of the aluminum salt solution depends on the desired finished product. Good results have been achieved with solutions using. M salt concentrations (calculated as aluminum oxide) of about $ 2 to $ 10, and preferably about $ 5 to $ 7.

The adjustment of a certain pH value is also an important feature of the method according to the invention, since the physical properties and crystal structure of the

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Product depend on the pH of the material fed into the mill. Good products are obtained when the pH value swa starting material is adjusted to about 1.0-10.

The solutions, slurries or gels produced by precipitation are introduced into the mill at a rate that will give the desired end product. When using a 20 cm jet mill operated with steam, a feed rate of 50 to 300 ml is for example per minute and preferably about 120 to 220 ml per minute. Pest substances can be processed at speeds from 50 to j500 g per minute and preferably about ^ 100 to 200 g per minute fed will.

'J C

One of the essential advantages of the process according to the invention is that the aluminum oxide produced in this way can be sintered to a high density at temperatures which are several hundred degrees lower than with aluminum oxides produced by other processes. The calcination temperature depends, of course, on whether one wants to produce j * - or (X -aluminum oxide. However, it is also considerably lower than the temperatures required in conventional production processes to form the same product.

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The invention is illustrated in more detail by the following examples, however, it is not limited to the same.

Example 1

An aluminum nitrate solution with an aluminum nitrate content of 80% by weight was prepared. This solution was mixed with so much 4% ammonium hydroxide solution in the mentioned oxide hydrate reactor that the resulting slurry had a pH value of 1 Had value of about 9. The water was filtered off from the slurry and the wet filter cake was dried at room temperature to give a product containing 1% aluminum oxide and 1% ammonium nitrate. This solid product was introduced into a jet mill which was operated at a temperature of about 427 ° C. An amorphous aluminum in ium OXa ^7- d was obtained which contained 16% water and 0.8% ammonium nitrate.

Example 2 -Yy

An aluminum nitrate solution with an aluminum nitrate content of 28% by weight was prepared and, while heating, neutralized with so much 15% ammonia solution that some aluminum oxide was precipitated and a slurry with a pH of 5-6 was obtained. The reaction was carried out in the oxide hydrate reactor at a temperature of "about 60 ° C. The slurry withdrawn from the oxide hydrate reactor, which Κ, Ί% aluminum oxide

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and 22 $ ammonia was aged for about 8 hours at 40 to 60 ° C. It was then introduced into a jet mill operated at 427 ° C. at such a rate that 454 g of product per hour were obtained. The experiment was continued until 22.680 kg of product had been obtained. The product consisted of Of aluminum oxide, which still contained 15 $ water and 0.9 $ ammonium nitrate.

example

In the same manner as in Examples 1 and 2, they were felling an aluminum nitrate solution with ammonia to produce a series of slurries produced and ground at different temperatures. The pH value, the aging and the concentration were varied along with the feed rate, the exit temperature and the grinding pressure in the mill. The products were examined for total volatility, electrolyte content, internal surface and crystal phase. The results of some these experiments are shown in Table 1 below.

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Table 1 _: ■

Production of aluminum oxide from aluminum nitrate neutralized with ammonia solution L ε ε I / 6 ε 8 D

Attempt precipitation after 1 hour at 427 ^° C. ,

pH in the $ A1 _P Q, X-ray analysis in the interior of the total weight Volatile # NELNO, output Ar ^ fiWs- surface (Oewji) to _{lm Prod} u _k t material matirrial m ² / g for 8 hours. oei 900 C

In this series of experiments the starting material was aged for 2 hours at 60 ° C and the slurry introduced at a rate of I50 ml / min in an operated with an exit temperature of 427 ⁰ C mill.

1, 5.7 3.1 '<* 90 13.0 0.8

2 '9.3 2.8 OC and £ 195 12.0 2.6

3 5.6 4.5 amorphous 220 28.4 ..7.0

4 9.2 5.5 CX and / _ 250 31.6 20.0

In this series of experiments, the starting material for longer than 20 hours at 6O ⁰ C was aged and introduced the slurry at a rate of I50 ml / min in an operated with an exit temperature of 427 ° C mill.

9.5 '1.5

- 19.3 x 7.0
15.4 1.6

18.8 5 -a

5 ■ 5.7 3.1 C? V 105 β 9.3 2.8 Oc and V * - 230 03 7th 5.6 4.5 OC . 125 D.
O 8th 9.2 5.5 ΐ 285 δ >

The determination of the inner surface and the X-ray analysis were carried out after the product had been activated ^{at 427 ° C. for 1 hour.}

The values given in Table 1 show the variability of the physical properties of the product during manufacture by the process according to the invention. The results show that amorphous aluminum oxide or a mixture of (/ - and V · aluminum oxide can be obtained by appropriate adjustment of the pH value and the aluminum salt concentration in the starting material.

Example 4

A series of tests was carried out to determine the effect of ammonia gas concentration on manufacturing processes in which aluminum nitrate is neutralized with ammonia gas. In all experiments, the slurry was fed into a mill operating at 427 ° C at a rate of 150 ml / min. Aluminum nitrate solutions with an aluminum content (calculated as Al ₂ O.) of $ 5 to $ 7.2 were prepared. The ammonia gas was passed through the vigorously stirred aluminum nitrate solution in a stream of air. The stoichiometric neutralization was reached after about 5 hours. The results of this series of tests are given in Table 2 below:

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L. ε ε ι / 6 ε 8 6 0 L * Α1 ₂ ο _: Manufacturing Table 2 inner surface
2
in m / g total
fleeting
after Erhit
zen on
90 ° C in the product Roentgen-
analysis
- after 1-
constant
Heat
to 427 ⁰ C 7.2 of aluminum oxide from ι 55 15.1 1.0 attempt conditions 5.2 41 13.6 0.7 (<x) + (u) No. PH with ammonia gas 1 1.4 5.2 . ■ neutralized aluminum nitrate 14.1 0.8 amorphous \ · 2 1.1 5.1 when felling 75 15.5 1.6 5.5 5 5
Molver
ratio 235 55.7 19th (uC) + C H ) 5 2.0 5.2 0 75 9.6 1.4 Oi 4th 2.6 5.2 0 ENT, 85 10.0 o, 6 (X 5 4th 5.0 added 364 25.5 • 4.8 OC 6th , 5.0 0 7th 6.5
7.0 1.5 8th 9
9.5 5 5 5 6th

() β very small maxima

No ammonia was added in experiments 1, 2 and j5. In experiment 2, the pH was adjusted with nitric acid. From the products of the experiments ^! to 8 shows that the
inner surface of the product passes through a maximum at a pH value of 4 to 4.5. This rather steep curve drops rapidly at pHi values of 5 to 6.5 and then increases again. The largest internal surface was preserved if that much
Ammonia gas was added so that the slurry fed into the mill had a pH of 9 to 9.5. These fourths are shown graphically in FIG.

Ex iel 5

In this example, the influence of temperature on the
X-ray diagram and the amount of ammonium nitrate remaining in the product shown. Each test was carried out at three different operating temperatures of the mill, ie at yj \ ° C, 427 ° C and 482 ° C. The pH was varied between J5.7 and 9.2. The influence of these process conditions on the X-ray diagram is shown in table j5:

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Table 3

pH value of the Rön tg cndiagr am m at a mill temp . of starting materials = '

371 C '427 ⁰ C 482 ° C

3.7 amorphous (X -f- Y- O

5.3 amorphous Oi o (

7.3 OC " (K '

From these fourths it is evident that with a starting material neutralized to pH 3.7 by increasing the operating temperature of the jet mill from 371 ° C to 482 ° C, the product changes from amorphous aluminum oxide to aluminum oxide. On neutralization from to a pH four of 9.2, at least some J ^A alumina was obtained in all cases.

In these tests it was also investigated to what extent the ammonium nitrate content of the residue depends on the operating temperature depends on the jet mill. The results are given in Table 4:

Table 4

pH value of the weight NHj.NO 'in the residue at a

Starting material * mill temperature of

3.7 5.3 7.3 9.2

371 ° C 427 ⁰ C 482 ° c 10 5 0.3 4th 1.5 0.5 2 1.5 0.2 30 * 1 1

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As was to be expected, the amount of ammonium nitrate in the product at pH values from 3.7 to 7.3 decreases with increasing mill temperature. If, however, so much ammonia is added that the pH. Value rises to 9 * 2, then even after grinding at a temperature of 482 ° C., \% ammonium nitrate remains in the product.

The results of these experiments are shown graphically in FIG shown.

Example 6

Two experiments were carried out in which aluminum nitrate (Al (NO,) -, 9H ₂ O) was ground directly at 427 ° C. The mill was operated at a speed at which 1134 g of product per hour were obtained. The product was analyzed and showed the X-ray diagram of p ( -aluminum oxide. It contained 12 $ water and 0.5 $ unreacted aluminum nitrate. This shows the advantages of the process according to the invention for the production of -aluminum oxide. This result is unexpected, since one Heating aluminum nitrate (Al (NO,), 9HgO) in a crucible gives J * aluminum oxide.

In a second series of tests, the same aluminum

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nitrate hydrate treated as in the above experimental grater with three times the stoichlometric amount of ammonia gas. The product of this neutralization was introduced into a jet mill operated at a temperature of 427 ° C. at a rate of 150 g / min. The product was W aluminum oxide

2 with an inner surface area of 300 m / g.

Example 7

In order to illustrate the flexibility of the process according to the invention, the aluminum nitrate was replaced by aluminum sulfate during production. First, 6.8 kg of aluminum sulfate AIg (SOh) V. Dissolve 18HgO in 2.5 gallons of water in the oxide hydrate reactor with stirring. The resulting slurry had a pH of 7 * 5 and contained ~ $, 8% by weight of aluminum oxide; it was introduced into a jet mill operated ^{at a temperature of 482 °} C. at a rate of 120 ml / min. The product consisted of a mixture of aluminum and ammonium sulfate. This mixture was calcined for 3 hours at a temperature of 900 ° C. and gave ** -aluminum oxide with an internal surface area of 180 m / g. From this it can be seen that the process according to the invention can be used to produce vf -aluminum oxide with an internal surface area of about 200 m 2 / g from an aluminum sulfate solution.

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BATH ORIGINAL

- μί-

Example]. 8th

A dried aluminum oxide hydrate containing ammonium nitrate and water was prepared, which corresponded to the dehydrated product prepared in Example 1. In order to investigate the effect of washing, the sample was divided into parts, one of which was washed free of ammonium nitrate and dried and the other was stirred into a jet mill without further treatment. Both portions were introduced into the jet mill operated at a temperature of 471 ° C. at a rate of 150 g / min. The unwashed material gave OC -Aluminium oxide and the washed. YES - aluminum oxide.

From these results it can be seen that the process according to the invention is extremely flexible and that either (X - or JA - aluminum oxide can be produced by appropriate selection of the process conditions.

Example 9

In order to show the effect of adding ammonium nitrate, a commercially available aluminum oxide trihydrate (Al ₂ O -, 2H ^ O) with and without the addition of ammonium nitrate was ground at 443 ° C.

In the first experiment the aluminum oxide trihydrate was stored at 44 ° C

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JS

Grind to a product, which after slurrying in water and standing for 15 hours at room temperature gave a clear mother solution.

-,

In the second experiment, the aluminum oxide trihydrate was treated with 20 Mix by weight ammonium nitrate and grind the mixture at 44-5 ° C. The ground product was slurried with water and left to stand at room temperature for 15 hours. After that, the mother solution was still cloudy, but could by adding φ Ammonium nitrate to be clarified.

This shows that when aluminum oxide trihydrate is ground smaller particles with ammonium nitrate than with grinding can be obtained without ammonium nitrate.

In the jet mill so either ejne solution of a precursor for alumina or a slurry of AIuminiumoxydhydrat, which was prepared by precipitation of an alumina m resulting salt prepared to be introduced.

hb: ma: ni

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Claims (11)

Claims 1. Process for the preparation of particulate! Aluminum oxide having a particle size of about 0.02 to 2 microns, characterized in that a precursor for aluminum oxide is converted into one with a temperature of over about 26o ° C operated comminution device such as a jet mill and there with heating to the desired particulate Crushed product. 2. The method according to claim 1, characterized in that aluminum nitrate is used as a preliminary product for aluminum oxide and it is decomposed in the mill. 3. The method according to claim 2, characterized in that the aluminum nitrate is introduced into the mill as an aqueous solution with an aluminum nitrate content of 5 to 35 $ and the mill operates at a temperature of 570 to 57O ° C. 4. The method according to claim 2 or j5, characterized in that that the pH of the aluminum nitrate solution is adjusted to about 1 to 2 by adding dilute nitric acid. 109839/1331 BATH 5. The method according to claim 2 or 3, characterized in that the pH of the aluminum nitrate solution by adding of ammonium hydroxide solution adjusts to about 2 to 3.5. 6. The method according to claim 3, characterized in that one uses a ,, containing about 20 L to about 30 wt $ aluminum nitrate solution and the jet mill operates at a temperature of about 425-510 ⁰ C. ' 7. The method according to claim 6, characterized in that the pH of the aluminum nitrate solution is adjusted to about 2.5 to 9.5 with gaseous ammonia. 8. The method according to claim 1, characterized in that there is a slurry of as a preliminary product for aluminum oxide Alumina hydrate with a pH in the range of about 3.5 to 10 used. 9. The method according to claim 8, characterized in that a ^{jet mill operated at a temperature of 425 to 50 0} C is used as the comminuting device and the aluminum oxide hydrate is introduced into the mill as a mixture with about 5 to 50% ammonium nitrate. BATH 109839/1331 10. Process according to claim 1 for the production of aluminum oxide with an inner surface of 150 to 200 m / g, characterized in that one a) an aluminum sulfate solution containing 1 wt while stirring vigorously with an amount sufficient to adjust its pH to about 4.0 to 10 Ammonia added b) the resulting slurry at a speed introducing from about 100 to 300 ml / min into a jet mill operated at a temperature of about 482 ° C; c) subjecting the slurry to heating and grinding in the mill d) the product is calcined at a temperature above 770 ° C. 11. The method according to claim 1 for the production of Q ( aluminum oxide with an inner surface of about 20 to 100 m / g, characterized in that one a) an aluminum nitrate solution containing 1% by weight excess salt while stirring vigorously with a sufficient to adjust its pH value to about 5 * 0 to 5 * 6 Amount of ammonia added; b) the resulting slurry into one having a temperature at a rate of about 100 to 300 ml per minute at about 482 ° C operated jet mill introduces and c) the nitrate is crushed in the mill and thermally decomposed. hb: ma: ni 109839/1331 BATH Blank page