JP2003095647A - Equipment and method for producing alumina - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide equipment and a method for industrial production of alumina which enables continuous blending of an aqueous solution of a raw material aluminum salt and an aqueous solution of a neutralizer. SOLUTION: A blending vessel 10 is partitioned into a mixing part 12 and a waiting part 13 with a partition plate 11. A mixing part 12 is provided with a stirrer machine and besides connected to an introduction line 16 of the aqueous solution of the raw material aluminum salt and an introduction line 17 of the aqueous solution of the neutralizer. On the other hand, the waiting part 13 is provided with a pH meter 15 and besides connected to an discharging line 18 of an aqueous slurry containing a formed aluminum hydrate. The introduction line 16 of the aqueous solution of the raw material aluminum salt is provided with a line mixer (a static mixer) 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing alumina, and more particularly to a method and an apparatus for producing alumina by continuously mixing raw material aluminum salt aqueous solution and neutralizing agent aqueous solution. Is.

[0002]

2. Description of the Related Art At present, porous alumina is widely used industrially as a catalyst carrier, an adsorbent, etc., but the pore volume and pore diameter of the porous alumina required depending on the purpose of use thereof. , The surface area and the like are different, and it is necessary to control the pore distribution. Further, the porous alumina molded body is required to have excellent properties such as mechanical strength. Conventionally, as a method of adjusting the pore distribution of porous alumina, for example, the distribution of pore volume or the distribution of pore diameter, a method of subjecting alumina hydrate obtained by a neutralization reaction to treatment such as aging, or alumina. Methods have been proposed to control the conditions under which hydrate precipitates are formed.

As an example of the former, for example, amorphous alumina hydrate is heated and stirred at a temperature of 50 ° C. or higher under a weak alkaline condition of pH 8 to 12 for aging to grow the alumina particle size of pseudo-boehmite. , Alumina product 600
Å Pore volume smaller than 0.6mg / g
A method of increasing the size is described in Japanese Patent Publication No. 53-19000.

As an example of the latter, Japanese Examined Patent Publication No. 57-44605
Japanese Patent Laid-Open Publication No. 10-96242 discloses a neutralizing agent after adding an aluminum salt to an aluminum hydroxide-containing slurry adjusted to a pH of 6 to 10 and maintained at a temperature of 50 ° C. or higher to adjust the pH of the slurry to 5 or lower or 11 or higher. The method of adjusting the pore distribution of the alumina product, for example, the distribution of the pore volume, by repeating the operation of adding pH and returning to pH 6 to 10 a plurality of times is described. Further, JP-A-58-190823 discloses that the hydrogen ion concentration and the temperature of the aluminum hydroxide-containing slurry are maintained at pH 6 to 11 and 50 ° C. or higher, respectively, while the hydroxide contained in the slurry is contained at the aluminum molar ratio. 20 when the amount of aluminum is 100%
The step of adding an aluminum salt and a pH control agent into the slurry at a rate of ˜500% / hr to form an alumina gel, and the step of converting the alumina gel into alumina, wherein the aluminum salt and the pH control agent are added. Out of
Disclosed is a method for producing an alumina carrier, at least one of which substantially contains a sulfate group.
JP-B-57-44605 and JP-A-58-19.
In each of the conventional methods for producing porous alumina described in Japanese Patent Publication No. 0823, etc., an aluminum hydrate and a neutralizing agent are added to and reacted with an alumina hydrate-containing slurry in order or at the same time, and the porosity is batchwise. Manufactures alumina.

However, when the porous alumina is produced by such a method, the alumina hydrate is mixed in a slurry containing a large amount of the alumina hydrate, so that the mixing of the alumina hydrate becomes uneven. In addition, alumina hydrate fine particles are newly generated, resulting in a distribution in the size of the finally obtained alumina hydrate particles, and the pore distribution of the porous alumina may not be adjusted sufficiently. was there. Further, in the production of porous alumina as described above, since the production conditions and the production operation of the alumina product are complicated, the mixing of the raw material aluminum salt aqueous solution and the neutralizing agent aqueous solution is batch-processed, and the working efficiency is However, there was a problem in that the worker's skill was required.

[0006]

DISCLOSURE OF THE INVENTION As a result of intensive studies to solve the problems of the prior art, the inventors of the present invention have continuously prepared a raw material aluminum salt aqueous solution and a neutralizing agent aqueous solution. The alumina manufacturing method and manufacturing apparatus have been completed that can be implemented and are satisfactory as an industrial manufacturing method.

[0007]

In the method for producing alumina according to the present invention, an aqueous solution of an aluminum salt and an aqueous solution of a neutralizing agent are continuously supplied, pH 6 to 9, room temperature to 95 ° C., contact residence time 1 The method is characterized in that both are mixed under a condition of minutes to 60 minutes to form an alumina hydrate-containing aqueous slurry. The aluminum salt and the neutralizing agent preferably consist of a combination of aluminum sulfate and sodium aluminate. The alumina manufacturing apparatus according to the present invention is divided into a mixing section equipped with a stirrer and a retention section equipped with a pH meter by a partition plate provided in the tank, and the raw material aluminum salt aqueous solution and the neutralizing agent are contained in the mixing section. It is characterized in that it has a mixing tank in which each introduction line of the aqueous solution is connected and a discharge line of the produced alumina hydrate-containing aqueous slurry is connected to the retention part. A line mixer is preferably provided in the introduction line of the raw material aluminum salt aqueous solution and / or the neutralizing agent aqueous solution.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the method and apparatus for producing alumina according to the present invention will be described below with reference to the flow chart shown in FIG.

The mixing tank 10 which is an essential part of the present invention is divided into a mixing section 12 and a retention section 13 by a partition plate 11. The number of partition plates 11 is not limited to one and may be multiple. The mixing unit 12 is provided with a stirrer 14, and an introduction line 16 for the raw material aluminum salt aqueous solution and an introduction line 17 for the neutralizing agent aqueous solution are connected. On the other hand, the retention part 1
3 is equipped with a pH meter 15 and is connected to a discharge line 18 for the produced alumina hydrate-containing aqueous slurry. In the introduction line 16 of the raw material aluminum salt aqueous solution,
A line mixer (static mixer) 20 is provided. An aqueous solution of sodium aluminate diluted to the concentration used for alumina preparation causes hydrolysis of sodium aluminate over time and precipitates. Therefore, in the conventional method, it was necessary to prepare a diluted sodium aluminate aqueous solution for each alumina preparation, but in the present invention, by adjusting the flow rate of the raw material sodium aluminate aqueous solution and the flow rate of the dilution water, continuous Then, the diluted sodium aluminate aqueous solution used for the preparation can be automatically prepared. In addition, by adjusting the temperature of the diluting water, the temperature of the dilute aqueous solution of sodium aluminate is also adjusted.

The other end of the discharge line 18 for the produced alumina hydrate-containing aqueous slurry is connected to a maturing tank 30.
Here, an alumina hydrate in which particles are uniformly grown to a desired size is obtained. The bottom of the aging tank 30 and the oliver drum filter as the filter 40 are connected by a discharge line 32 for the aging slurry. Impurities are removed by washing with hot water in the filter 40, and the dehydrated alumina cake is introduced into the high temperature aging tank 50 through the line 42 and then sent to the next step (not shown). And the process description is the same as the conventional alumina manufacturing apparatus. Reference numeral 34 is a circulation line for returning the overflow from the filter 40 to the aging tank 30.

The aluminum salt used in the present invention may be any water-soluble one, such as acidic aluminum salts such as aluminum sulfate, aluminum nitrate, aluminum chloride and aluminum acetate, basic aluminum sulfate, basic aluminum nitrate, basic aluminum chloride, Examples thereof include basic aluminum salts such as basic aluminum acetate, sodium aluminate, and potassium aluminate. It is desirable to use an aqueous solution of such an aluminum salt in an amount of 0.5 to 20% by weight, preferably 2 to 10% by weight in terms of Al ₂ O ₃ .

In the present invention, the neutralizing agent is aluminum
It has the property of reacting with salt to form a precipitate of alumina hydrate.
A water-soluble substance, such as an aluminum salt
For use with acidic aluminum salts such as aluminum sulfate
Sodium aluminate, aluminate
Basic substances such as potash, caustic soda, ammonia, etc.
Is used as a neutralizing agent, and aluminum is used as an aluminum salt.
If a basic aluminum salt such as sodium acid sodium salt is used,
Aluminum sulfate or glass as a neutralizing agent,
Aluminum acid, aluminum chloride, sulfuric acid, hydrochloric acid, acetic acid
An acidic substance such as is used. Such a neutralizer
Reacts with the aluminum salt to form Al ₂O₃1 in conversion
Alumina hydrate is produced in the concentration range of 10% by weight.
It is desirable to use an aqueous solution containing such a solution.

In the present embodiment, the aqueous solution of sodium aluminate is supplied from the introduction line 16 of the raw material aluminum salt aqueous solution, and the aqueous solution of aluminum sulfate is supplied from the introduction line 17 of the neutralizing agent aqueous solution. A line mixer (static mixer) 20 is provided, and hot water is supplied to the line mixer 20 to prevent hydrolysis of the diluted sodium aluminate aqueous solution. The aqueous solution of aluminum sulfate is stable, and it is possible to prepare and store a large amount of dilute aqueous solution of aluminum sulfate at one time. Both the sodium aluminate aqueous solution and the aluminum sulfate aqueous solution are continuously introduced into the mixing tank 10 at a predetermined flow rate. Therefore, the conditions of the concentration, pH, and temperature of the mixed solution in the mixing tank 10 are adjusted and maintained within the range suitable for the growth of alumina hydrate particles.

The contact residence time of the mixed solution in the mixing tank 10 must be 1 minute to 60 minutes. When the contact residence time is longer than 60 minutes, the previously precipitated alumina hydrate becomes seeds and crystal growth occurs, so that alumina hydrate having a different crystal form is produced, and the contact residence time is longer than 1 minute. If it is short, the neutralization reaction will not proceed sufficiently,
Precipitation of alumina hydrate is insufficient. The preferred contact residence time is in the range of 2 minutes to 20 minutes. The size of the mixing tank 10, the number of partition plates 11, the flow path of the mixed solution in the mixing tank 10, and the like are determined based on the contact residence time.

The pH of the mixed solution in the mixing tank 10 is measured by a pH meter 1
5 is adjusted to a specific value in the range of 6 to 9 according to the characteristics of the alumina to be obtained. When the pH of the mixed solution is lower than 6, the growth of alumina hydrate particles is unlikely to occur. On the contrary, when the pH is higher than 9, the produced alumina hydrate is dissolved again, which is not preferable. The temperature of the mixed solution in the mixing tank 10 is preferably in the range of room temperature to 95 ° C from the viewpoint of the particle growth rate of the alumina hydrate. Further, it is preferably 50 ° C. or higher, particularly preferably in the range of 60 ° C. to 95 ° C.

The alumina hydrate thus produced by staying in the mixing tank 10 for a predetermined time overflows from the discharge line 18 and enters the aging tank 30. Aging tank 30
Since the subsequent processing steps are the same as the known processes as described above, the description thereof will be omitted.

[0017]

According to the method and apparatus for producing alumina of the present invention, it is possible to continuously produce porous alumina on an industrial scale, which has hitherto been difficult to produce only by a batch method. Further, according to the method and apparatus for producing alumina of the present invention, since the raw material aluminum salt aqueous solution and the neutralizing agent aqueous solution are continuously mixed, the productivity is excellent despite the simple manufacturing operation. Further, it has a remarkable effect that various physical properties such as pore volume, pore diameter and specific surface area can be controlled very easily and surely. The porous alumina obtained by the present invention is used in various industrial fields such as various catalyst carriers, adsorbents, and desiccants, in which porous alumina has been conventionally used.

[0018]

EXAMPLE Alumina was continuously produced according to the flow shown in FIG. The production capacity of this device is 3 tons / day. 1. At the start of operation (startup ) A sodium aluminate aqueous solution containing 5.0% by weight of alumina is poured into a stainless steel mixing tank 10 having a volume of 1 m ³ up to about 30%, and this is heated to 65 ° C. and kept. Then, about 300 liters of an aluminum sulfate aqueous solution containing 2.5 wt% alumina heated to 65 ° C. was introduced into the mixing tank 10 for about 10 minutes to maintain the pH of the mixed solution at 7.2.

2. Continuous Operation of Mixing Tank 10 Sodium aluminate aqueous solution and aluminum sulfate aqueous solution are continuously supplied to mixing tank 10, and the mixed solution is stirred at a low speed to generate small gel beads. An aqueous solution of sodium aluminate having an alumina concentration of 22% by weight is mixed with 260 liters / hour of warm water and 1500 liters / hour of water in the line mixer 20 and supplied from the introduction line 16. Also, the aluminum sulfate aqueous solution having an alumina concentration of 2.5 wt% is 1553
Liters / hour are supplied from the inlet line 17. The mixed liquid in the mixing tank 10 has a temperature of 65 ° C. and a pH of 7.2 ± 0.2.
And the residence time in the tank was set to 10 minutes, and the generated alumina hydrate slurry was discharged from the discharge line 18 to the aging tank 30.
Pull out. As a crystal growth inhibitor, 50% by weight of sodium gluconate aqueous solution was added to the sodium aluminate in an amount of 2% by weight.

3. Operating Conditions of Aging Tank 30 In the aging tank 30, the alumina hydrate slurry was heated to 65 ° C.
The mixture is retained for 90 minutes, stirred and aged, and then sent to the filter 40. 4. Washing / Filtration Operating Conditions In the filter 40 (10 m ³ Oliver drum filter), the slurry is washed with 0.1 wt% ammonia water at 60 to 65 ° C. The amount of washing water was 35 times that of dry alumina, the amount of residual Na ₂ O: 0.05% by weight or less, the amount of residual SO ₄
Amount: 1.5% by weight or less was set as the cleaning target value. 5. Operating Conditions of the High Temperature Aging Tank 50 In the steam jacketed high temperature aging tank 50, 15 wt% ammonia water was added to the sent alumina hydrate slurry that had been Na / SO ₄ removed to adjust the pH to 10.5. Aged at 95 ° C for 20 hours.

6. Final step After completion of the above aging, the slurry is sent to a drying / firing step (not shown) and dried at 130 ° C for 13 hours, and then 500 ° C.
After firing for 1 hour, an alumina carrier was obtained. The main physical properties of this alumina carrier were as follows. Na ₂ O content: 0.02 wt% SO ₄ content: 0.84 wt% Specific surface area: 270 m ² / g Pore volume: 0.71 ml / g

[Brief description of drawings]

FIG. 1 is a flow chart of an alumina production apparatus of the present invention.

[Explanation of symbols]

10 Mixing tank 11 partition boards 12 Mixing section 13 Retention area 14 Stirrer 15 pH meter 16 Raw material aluminum salt aqueous solution introduction line 17 Neutralizer aqueous solution introduction line 18 Aqueous slurry discharge line containing produced alumina hydrate 20 line mixer

Claims (4)

[Claims] 1. Alumina is prepared by continuously supplying an aqueous solution of an aluminum salt and an aqueous solution of a neutralizing agent, and mixing both under conditions of pH 6 to 9, room temperature to 95 ° C., and contact residence time of 1 minute to 60 minutes. A method for producing alumina, which comprises producing a hydrate-containing aqueous slurry. 2. The method for producing alumina according to claim 1, wherein the aluminum salt and the neutralizing agent are a combination of aluminum sulfate and sodium aluminate. 3. A partition plate provided in the tank divides a mixing section equipped with a stirrer and a retention section equipped with a pH meter, and each of the raw material aluminum salt aqueous solution and the neutralizing agent aqueous solution is introduced into the mixing section. An alumina production apparatus comprising: a mixing tank, which is connected to a line and to which a discharge line for the produced alumina hydrate-containing aqueous slurry is connected to the retention part. 4. The alumina production apparatus according to claim 3, further comprising a line mixer in a line for introducing the raw material aluminum salt aqueous solution and / or the neutralizing agent aqueous solution.