DE1467250C - Process for the production of precipitated aluminum oxide trihydrate with a soda content of at most 0.10 liters - Google Patents

Description

1 2

In contrast, it is the aim of the invention to provide a counterfeit and in the petrochemical industry as a catalysis process with the aid of a catalyst, catalyst support and as a process-controlling aluminum oxide trihydrate with a soda content, for example as a dehydrating agent . below about 0.10 ° / ₀ can be produced. This task, activated aluminum oxide, which is intended to be activated as a catalyst or catalyst carrier, dissolves a slight amount of soda by the method of the invention.

content (below about 0.10%). The soda content of the invention is therefore a method

is usually used in percent by weight of sodium oxide for the production of precipitated aluminum _{oxide tri-}

(Na ₂ O), based on the weight of the hydrate as starting with a soda content of at most 0.10 ° / _0th

product used aluminum oxide trihydrate based on Na ₂ O, by inoculating a supersaturated

Aluminum oxide solution in aqueous caustic soda with

(Al ₂ O ₃ -3H ₂ O), finely divided aluminum oxide trihydrate, which is characterized in that during the precipitation of the

expressed. The activated aluminum oxide will. Aluminum oxide trihydrates by regulating the temperature

by calcining aluminum oxide trihydrate at 15 temperature of the solution, the concentration of the dissolved

an average temperature below 900 ° C, preferably Al ₂ O ₃ is adjusted so that the ratio of the

at about 500 ^° C. Alumi-

Due to the fact that aluminum oxide niumoxide amount, calculated as Al ₂ O ₃ , and the amount

at calcination temperatures above about 900 ⁰ C in the dissolved sodium hydroxide, calculated as Na ₂ CO ₃ ,

is converted into a passive form, the soda ao per precipitation step can on average not be greater than

content of aluminum oxide is not as usual by 0.13: 1.

Calcining at high temperature can be reduced. The method of the invention can, like the examples

For the production of aluminum oxide with little show during a precipitation step both at

So far it has therefore been necessary to keep the metallic content of the soda more constant as well as gradually decreasing

Aluminum, which is usually only carried out at a low Na- 35 temperature,

The invention is based on the following facts,

to convert soda-free aluminum oxide hydrate and from:

this activated by moderate calcining alumi- It was found that an aluminum oxide tri-

to produce nium oxide. . Low soda hydrate from a supersaturated

In the aluminum industry, large amounts of 3 ° sodium aluminate solution are obtained by inoculating with aluminum

Aluminum oxide trihydrate precipitated by the Bayer process oxide trihydrate and the precipitate under

manufactured. In this process, an aluminum can be run that only has one conditions

Oxyder ore, like bauxite, with an aqueous caustic soda - low aluminum oxide supersaturation in the solution

solution (maintained under pressure and at a temperature of. This can be over a wide temperature

above 100 ⁰ C) leached or digested, which means that the temperature range can only be carried out if the

the aluminum oxide converted to sodium aluminate during the aluminum oxide concentration in the solution

will. The accompanying impurities of the ore of the precipitation lies so that bsi the precipitation temperature only

are separated off as insoluble residues. a slight degree of alumina supersaturation

At the closing temperature is in the. aqueous is maintained.

Caustic soda solution dissolved enough aluminum oxide to 40 The solubility of aluminum oxide trihydrate in

to produce a not fully saturated aluminate solution. aqueous caustic soda solution increases with increasing temperature

This is then increased by relaxation to around temperature and with the basicity. A caustic soda

100 ° C cooled and to remove insoluble content of about 120 g NaOH per liter with a Tern-

Filtered off residues. By cooling the temperature from 7O ⁰ C, an equilibrium solution corresponds to

Sodium aluminate solution is approximately its supersaturation of aluminum oxide trihydrate

with respect to the aluminum oxide trihydrate. The 43 g per liter, based on Al ₂ O ₃ . The solubility of

Solution is then further to a temperature in the aluminum oxide trihydrate in the same etching

Cooled range from 60 to 75 ⁰ C, at which they strongly sodium solution at a temperature of about 150 ° C

is oversaturated with aluminum oxide trihydrate. approximately 117 grams of Al ₈ O ₃ per liter. Hence is a

This supersaturated solution is with a vaccine 50 aqueous Ätznätronlösung, which at 150 ⁰ C with aluminum

batch of previously precipitated, finely divided aluminum oxide trihydrate is saturated at one temperature

added sodium oxide trihydrate. The resulting increase of 70 ° C is strongly oversaturated.

The slurry is stirred for about 24 hours in order to effect the greater the degree of supersaturation of the sodium the precipitation of the aluminum oxide trihydrate on the aluminate solution, the faster the inoculation takes place. Here fall about 50 ° / ₀ 55 precipitation of alumina trihydrate. The temperature of the aluminum oxide of the solution as aluminum oxide of the precipitation solution also influences the velocity trihydrate. ability of precipitation ". The higher the temperature of the

The aluminum oxide tri-aqueous aluminum oxide-containing caustic soda solution obtained in this way is

hydrate, however, has a soda content of about 0.35 to the greater the speed of the aluminum

0.50% that for the production of activated 60 oxide trihydrate precipitation. However, in the case of a

Aluminum oxide for use as a catalyst or gave the initial aluminum oxide concentration

Catalyst support is too high. the higher temperature partly due to the

With the usual methods, such as those taking aluminum oxide supersaturation, for example, the French patent specification 1029 096 and in the An increase in the Alumi- ■ used as an inoculation batch US Pat. No. 2,478,675, is the amount of sodium oxide trihydrate used to create Niederher after the precipitation, a second stage, suggested germination for the aluminum oxide to be precipitated, in which the soda content of the aluminum oxide trihydrate also increases the overall speed trihydrate is lowered. the aluminum oxide trihydrate precipitation by

enlargement of the surface or multiplication of the germs on which aluminum oxide trihydrate is deposited.

Since the precipitation at a constant temperature of a slightly supersaturated solution is slow and the yield of precipitated Aluminiumoxydtri ¹ · hydrate per unit volume of the solution within a given time is low, and although the resulting precipitated alumina trihydrate tends under such conditions, the desired low soda content below about Having 0.10%, it is convenient and desirable to carry out the precipitation at the highest allowable temperature. In order to increase the yield of aluminum oxide trihydrate with a low soda content, it is also advisable to initiate the precipitation at practically the highest possible temperature, preferably at about 100 ° C or at least in the temperature range of 80 to 100 ° C, and to cool the precipitation solution to the extent that that a controlled, low and preferably constant aluminum oxide supersaturation is maintained to the same extent as the aluminum oxide content of the solution decreases. If necessary, the precipitation can be carried out at a constant temperature in the range of 50 to 100 ° C more or less. ·

The solubilities and concentrations of alumina trihydrate in aqueous caustic soda solutions are often expressed as the ratio of alumina to caustic soda, alumina being expressed in grams of Al ₂ O ₃ per liter and caustic soda (NaOH) in grams per liter of equivalent Na ₂ CO ₃ . If the extent of aluminum oxide supersaturation in aqueous caustic soda solutions is expressed in units of the ratio just defined, then fluctuations in the caustic soda content can be taken into account.

In the precipitation of alumina trihydrate with little. Soda content from aqueous caustic soda solutions according to the practices of the invention, the supersaturation of alumina in the aqueous caustic soda solution is maintained at a relatively low level during the precipitation process, which on average should not be greater than about 0.13 ratio units; That is, the ratio of the amount of aluminum oxide beyond the amount dissolved in equilibrium solubility to the amount of caustic soda in the solution is no greater than about 0.13: 1, with aluminum oxide being assumed _{as Al 2} O ₃ and caustic soda as Na ₂ CO _{3 for the calculation.} The aluminum oxide supersaturation is preferably maintained during the precipitation process, with adaptation to the above-mentioned ratio, at a value which is not greater than 20 g of aluminum oxide per liter of aqueous caustic soda solution, e.g. B. in the range 5 to

ίο 20 g of aluminum oxide per liter. .

Furthermore, when carrying out the invention Process the aqueous, aluminum oxide-containing caustic soda solution preferably substantially be free of organic compounds or contain only a small amount of organic matter since it has been determined that the presence of Organic compounds in the precipitation solution tend to reduce the soda content of the precipitated aluminum oxide trihydrate to increase. .

The principles of the invention result from the following series of experiments:

. Test series 1

Aqueous sodium aluminate solutions were prepared whose soda content was 119 g per liter, based on NaOH (corresponding to 158 g Na ₂ CO ₃ per liter) and contained varying amounts of aluminum oxide.

A small amount of each solution was finely divided with Alumina trihydrate inoculated at an amount of 60 g per liter. The alumina trihydrate precipitation was rotated for a period of approximately 23 hours at a temperature of 65 ° C Nickel bottles carried out. Subsequent to the precipitation, the aluminum oxide trihydrate was separated off, dried, weighed and analyzed and the average alumina supersaturation in the Precipitation solution (based on that of A. S. Russell,

J. D. Edwards and CS. Taylor under the Title "Solubility and density of aluminum oxides hydrogenated in NaOH solutions" in the "Journal of Metals", Edition 7, 1955, pp. 1123 to 1138, published values). The results of these trials are shown in Table I.

Table I.

Initial alumina content Ratio g / l Al ₂ O ₃ to
g / l caustic soda as Na ₂ CO ₃
(Ratio units) g / l
Al ₁ O, Average aluminum oxide supersaturation
during precipitation % Na ₁ O in the precipitated
Alumina trihydrate g / l
Al ₂ O,. 0.60 35.6 . Ratio g / l Al ₂ O ₃ TO
g / l caustic soda as Na ₂ CO ₃
: (Ratio units) 0.30 94.6 0.55 32.1 ί 0.23 0.25 86.7 0.50 29.0 0.20 0.20 78.8 0.45 24.1 ¹ 0.18 0.13 71.0 0.40 20.0 '■ 0.15 0.07 ■ · ■; 63.1 0.35 16.4 0.13 0.03 55.2 ! 0.10

Test series 2

A second series of experiments similar to those described in connection with series 1 was carried out. In this second series of experiments, the alumina trihydrate precipitation was carried out at a temperature of 82 ° C. The results of this second series of tests are ^; summarized in Table II.

Ratio g / l Al ₁ O, to
g / l caustic soda as Na ₁ CO ₃
(Ratio units) 1,467 250 6th Il % Na _: O in the precipitated
Alumina trihydrate 0.57 0.09 0.55 table 0.07 0.50 0.05 5 0.45 g / l
Al ₁ O ₁ Average alumina supersaturation
during precipitation 0.02 21.8 Ratio g / l AIjO ₃ to
. g / l caustic soda as Na ₁ CO, ■
I (ratio units) i Initial aluminum oxide coating 20.2 0.14 gl
Al ₁ O, 16.3 0.13 89.9 . 12.5 0.10 86.7 0.05 78.8 71.0

The experiments indicated above show that by maintaining the aluminum oxide supersaturation, d. H. Amount of aluminum oxide over equilibrium solubility in addition, with an average value no greater than about 0.13 ratio units while the precipitation is, essentially soda-free alumina trihydrate is precipitated. These attempts also show the dependence of the soda content of the precipitated aluminum oxide trihydrate on the average supersaturation of aluminum oxide in the aqueous, basic precipitation solution during the precipitation.

Carrying out the method of the invention is explained in more detail in Examples I to III below. These describe embodiments of the Process of the invention in which a) batchwise at constant temperature and gradually decreasing Supersaturation, b) intermittently with cooling and gradually reduced (supersaturation and c) continuously work is carried out at constant temperature and constant supersaturation.

B c i s ρ i c 1 I

84 g of bauxite were treated in an autoclave at a temperature of about 150 ° C. under a pressure of 3 to 4 atmospheres with a basic aluminate solution of 156 g of Na.CO ₃ and 48 g of 1 Al ₂ O _{3 for} 45 minutes, to dissolve the aluminum oxide. At the end of this time the caustic soda and aluminum oxide containing solution was removed from the autoclave and analyzed to determine its aluminum oxide concentration. An aluminum oxide concentration of 9IgI Al ₁ O _{3 was} found. The solution containing caustic soda and aluminum oxide was then filtered and cooled to 93.degree. C. in the process. At this temperature 66 g of aluminum oxide are soluble in the caustic soda solution of the concentration mentioned (as can be seen from the literature on the solubility of aluminum oxide trihydrate in NaOH solutions listed in test series 1). At this temperature, the amount of aluminum oxide per liter in the solution is 25 g / l above the amount necessary to saturate the solution, and the ratio of this amount to the amount of caustic soda per liter, expressed as NajCOj. is 0.16: 1.00.

The solution was then seeded with a 30 g'l containing Aluminiumoxydhydratlösung (crystallization nuclei) having a soda content of 0.10 ° / _{0 1} O Na. Precipitation was allowed to proceed for 24 hours. During the entire duration of the precipitation the temperature was kept at 93 ° C. At the end of this time the precipitated aluminum oxide trihydrate was filtered off, weighed and analyzed. The weight of the filtered aluminum oxide trihydrate was 54.5 g / l of the starting solution and the soda content was 0.09 ° / ₀ Na ₁ O. From this, the weight of the precipitated aluminum oxide trihydrate per liter is calculated to be 24.5 g and the sodagchalt of this precipitated aluminum oxide trihydrate to 0.08 ⁰ Z ₀ Na ₂ O. The filtrate was analyzed and gave an aluminum

»O nium oxide concentration of 75 g / l. As a result of the temperature of 93 ^C C where the precipitation was performed, a Aliiminiumoxydrnenge over that required to saturate the amount of solution to the caustic Sodäkonzentration. calculated as

* 5 Sodium carbonate, from 0.0 (S: 1.00. During this precipitation step, the mean ratio of aluminum oxide oversaturation to caustic soda concentration was 0.11: 1.00. At this temperature, the caustic soda solution used in this example dissolves at the saturation point 52 gl oxide. The ratio of the aluminum oxide supersaturation to the caustic soda concentration of the solution when cooled to this temperature was 0.147: 1 (K). 54.5 gl aluminum oxide trihydrate (crystallization nucleus) were then added a soda content 0.09 ° _'o Na ₂ O (which is the same concentration as in the product from the previous precipitation stage!) was added. the precipitate was for 24 hours carried out at a constant temperature of 80 C. Thereafter, the precipitated alumina trihydrate was filtered off, weighed The weight of the filtered alumina trihydrate was 72.5 g of the starting solution, and de The soda content was 0.09 ° ₀ Na ₂ O.

The filtered solution was analyzed and showed an aluminum oxide concentration of 63 g. This results in an amount of aluminum oxide at 80 "C above the amount necessary for the saturation of the solution for the caustic soda concentration, calculated as Na ₂ CO ₃ , of 0.06: 1.00. The mean ratio of the aluminum oxide overacidification to the caustic soda concentration was therefore 0.103: during this second precipitation stage: 1.00..

B e i s ρ i e 1 II

Process carried out in sections without additional cooling.

In this example, a liquid with an alkali concentration of 156 g'l was calculated as

. Na _x CO ₃ . proceeded from a plant for the bauxite digestion working according to the Bayer process. After the bauxite digestion and removal (for example by means of filtration) of the red mud, the liquid contained 96 g of 1 AUO ₃ . After it had passed through the pipes to the separators, its temperature was 95 ^: C. One of the separators was used for

Making a hydrate with a low soda content. All separators had a capacity of 900 m ³ . For this purpose, so-called Pachucha tanks with an open top, cylindrical cross-section and a height of 2 to 3 times the diameter with conical bottoms were used, the cone angle being 45 to 60 °. These tanks contained a central standpipe, at the lower end of which air was introduced into the tank, which, as it rose, moved both liquid and solid particles from the bottom of the cone upwards, which overflowed at the upper edge of the cylindrical wall, so that the entire contents of the tank were stirred .

At the end of a 24-hour deposition, a concentration of 75 g / l Al ₂ O ₃ with 55 g / l solids (aluminum oxide trihydrate) in suspension in the liquid obtained ^{resulted at 87 ° C.} The air supply was then turned off so that the solids could settle. The sludge settling at the bottom of the cone contained 50% solids (1 l contained 795 g hydrate). 30 g / l solids were retained as seed for the next cycle. For this purpose, 28.3 m ³

Sludge 'withdrawn. This sludge

contained the desired product. It was washed, filtered and dried. It is important to keep them vigorous Wash out to remove adsorbed soda.

For the beginning of the next run there should be an Al ₂ O ₃ concentration of 91 g / l in the tank. This could be transit mixing of 685 m ^s

Starting liquid with 215 m ^{3 of} the

(96_ 75 ')

used liquid already in the tank. For this purpose, 657 m ³ (685-28.3) of the clear liquid was withdrawn from the top of the separator (leaving 215 m ^{3 of} used liquid and the crystallization nuclei on the bottom of the tank). The decanted liquid can be fed to the tank for the used liquid for return to the digestion device, but it can also be mixed with the starting liquid in another separator in order to separate more of the aluminum oxide dissolved in it (while cooling to 65 to 70 ° C and a large batch of crystallization nuclei, the aluminum oxide concentrations can be reduced to 51 to 52 g / l Al ₂ O ₃ ). 685 m ^{3 of} the starting liquid (96 g / _{l Al 2} O ₃ , 95 ° C.) were then added. When mixing with the 215 m ^{3 of} the consumed liquid at 87 ° C. and 75 g / l Al ₂ O ₃ , a total volume of 900 m ^a and a mixing temperature of 93 ° C. were obtained, the aluminum oxide concentration being 91 g / l Al ₂ O ₃ was. The air supply was then switched on again and the precipitation continued for 24 hours by means of the crystallization nuclei present in a concentration of 30 g'l. During this time the liquid cooled to 87 ° C. The precipitation increased the solids content to 55 g, while the concentration of dissolved aluminum oxide fell to 75 g / l Al ₂ O _3. The cycle was then repeated.

During the deposition, the mean AIu

. ■ 91 - 7 ^

concentration of minium oxide 83 g of 1 Al ₂ O ₃ -, V, the

mean temperature was 90'C. At this temperature and an alkali concentration of 156 g'l, calculated as Na ₂ CO ₃ , the saturation is 65 g / l Al ₂ O ₃ . This gave an average supersaturation of 18 g / l Al ₂ O ₃ or a ratio of } - ~ - 0.12. The

Product has a Na ₂ O content of about 0.09 ° / _0th

As in the normal Bayer process, the seedling batch can be adjusted in a given time to achieve the desired yield.
Note: This procedure does not require any

»O special equipment. It can be the existing one Bayer plant can be used for bauxite digestion. The method uses the principle that the with deposited and not washable amount of soda depends on the aluminum oxide supersaturation. One Yield of 25 g / l in 24 hours corresponds to about half the yield of the normal process sequence; the However, making this particular product does not involve any loss of aluminum oxide or any. other by-product,

Example III
Continuous work with a separator:

A separator (900 m ³ ) contained a Bayer

* s sludge - a temperature of 65 ° C. 67 g / l solids and 50.8 g / l A1 ₂ O _{S were} dissolved in the slurry. The hydration was carried out at a temperature of 9O ⁰ C, it contained 94.6 g / l Al ₂ O ₃ and a caustic concentration of 158 g / l, calculated as Na ₂ O _3. The liquid feed was 0.167 m * / min. At the same time, the take-off at the overflow of the standpipe was 0.167 m / min. The overflow contained 67 g / l of solids Al ₂ O ₃ · 3 H ₂ O. The hydrate was then washed, filtered and dried at a rate of 11.2 kg / min. To obtain A1 O ₃ · 3H ₂ O 0.07 up to 0,09 ° / ₀ Na ₂ O.

The natural rate of cooling of the tank is such that the 90 ° C temperature of the inlet just covers the heat loss. Any tendency

* o the tank temperature deviating from 65 "C can be corrected by correcting the temperature of the inflowing liquid. Over time the seedling batch can become coarser. In this case, the yield is lower and the aluminum oxide concentration rises to over 51 g / l Al ₂ O _3. To solve this problem, productivity can be increased by wet grinding part of the seedling batch in order to ensure sufficient fineness.

Degree of saturation was here

158

Claims (1)

Claim: Process for the production of precipitated aluminum oxide trihydrate with a soda content not exceeding 0.10%. based on Na ₂ O, by inoculating a supersaturated aluminum oxide solution in aqueous caustic soda with finely divided aluminum oxide trihydrate, characterized in that during the precipitation of the aluminum oxide trihydrate by regulating the temperature of the solution, the concentration of the dissolved Al ₂ O ₃ is adjusted so that the ratio of the Amount of aluminum oxide present via the solution equilibrium, calculated as Al ₂ O ₃ , and the 6s amount of dissolved sodium hydroxide, calculated as Na ₂ CO ₃ , per precipitation step is on average not greater than 0.13: 1. 009 639/87