JP4054183B2 - Alumina production equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an alumina production method and production apparatus, and more particularly to a method and apparatus for producing alumina by continuously preparing a raw aluminum salt aqueous solution and a neutralizing agent aqueous solution.
[0002]
[Prior art]
Porous alumina is currently widely used industrially as a catalyst carrier, adsorbent, etc., but the range of pore volume, pore diameter, surface area, etc. of porous alumina required according to the intended use However, there is a need for adjustment of these pore distributions. In addition, 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 pore volume distribution and the pore diameter distribution, a method such as aging is performed on alumina hydrate obtained by neutralization reaction, etc. Methods have been proposed for adjusting the conditions for the formation of hydrate precipitates.
[0003]
As an example of the former, for example, amorphous alumina hydrate is heated and stirred at a temperature of 50 ° C. or higher under weakly alkaline conditions of pH 8 to 12, and the alumina particle size of pseudoboehmite is grown to grow alumina. Japanese Patent Publication No. 53-19000 discloses a method in which the pore volume having a pore diameter smaller than 600 mm of the product is larger than 0.6 mg / g.
[0004]
As an example of the latter, Japanese Patent Publication No. 57-44605 discloses that an aluminum salt is added to an aluminum hydroxide-containing slurry adjusted to pH 6 to 10 and maintained at a temperature of 50 ° C. or higher, and the pH of the slurry is 5 or lower. Alternatively, a method for adjusting the pore distribution of the alumina product, for example, the pore volume distribution, by repeating the operation of adding a neutralizing agent and returning the pH to 6 to 10 after a plurality of times after setting to 11 or more is described. Japanese Patent Laid-Open No. 58-190823 discloses that the hydrogen ion concentration and temperature of an aluminum hydroxide-containing slurry are maintained at pH 6 to 11 and 50 ° C. or higher, respectively, while the hydroxide contained in the slurry at an aluminum molar ratio. A step of forming an alumina gel by adding an aluminum salt and a pH control agent to the slurry at a rate of 20 to 500% / hr when the amount of aluminum is 100%, and a step of converting the alumina gel into alumina There is disclosed a method for producing an alumina support, wherein at least one of the aluminum salt and the pH control agent substantially contains a sulfate group.
In the conventional methods for producing porous alumina described in JP-B-57-44605, JP-A-58-190823, etc., an aluminum salt and a neutralizing agent are added to an alumina hydrate-containing slurry. These are added and reacted in order or simultaneously to produce porous alumina in a batch mode.
[0005]
However, when the porous alumina is produced by such a method, the alumina hydrate is mixed in the slurry containing a large amount of the alumina hydrate, so that the mixing of the alumina hydrate becomes uneven. As a result, alumina hydrate fine particles were newly formed, resulting in a distribution in the size of the finally obtained alumina hydrate particles, and there was a possibility that the pore distribution of porous alumina could not be adjusted sufficiently. .
In addition, in the production of porous alumina as described above, since the production conditions and the production operation of the alumina product are complicated, the preparation of the raw aluminum salt aqueous solution and the neutralizing agent aqueous solution is batch-processed, and the work efficiency However, there were problems such as requiring low skill of workers.
[0006]
[Problems to be solved by the invention]
As a result of intensive studies in order to solve such problems of the prior art, the present inventor can continuously carry out the preparation of the raw material aluminum salt aqueous solution and the neutralizing agent aqueous solution, and an industrial production method. As a result, a production method and a production apparatus for alumina, which are satisfactory, are completed.
[0007]
[Means for Solving the Problems]
The method for producing alumina according to the present invention continuously supplies an aqueous solution of an aluminum salt and an aqueous solution of a neutralizing agent under conditions of pH 6 to 9, room temperature to 95 ° C., and contact residence time of 1 minute to 60 minutes. Are mixed to produce an aqueous slurry containing alumina hydrate.
The aluminum salt and the neutralizing agent are preferably composed of a combination of aluminum sulfate and sodium aluminate.
The alumina production apparatus according to the present invention is partitioned into a mixing part equipped with a stirrer and a staying part equipped with a pH meter by a partition plate provided in the tank, and a raw material aluminum salt aqueous solution and a neutralizing agent in the mixing part Each of the introduction lines of the aqueous solution is connected, and the retention tank has a preparation tank in which a discharge line of the produced alumina hydrate-containing aqueous slurry is connected.
The introduction line of the raw material aluminum salt aqueous solution and / or the neutralizing agent aqueous solution preferably has a line mixer.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of the method and apparatus for producing alumina according to the present invention will be described below with reference to the flowchart shown in FIG.
[0009]
The mixing tank 10 that forms the main part of the present invention is partitioned into a mixing unit 12 and a staying unit 13 by a partition plate 11. The number of partition plates 11 is not limited to one, but may be a plurality.
The mixing unit 12 includes a stirrer 14 and is connected to an introduction line 16 for a raw material aluminum salt aqueous solution and an introduction line 17 for a neutralizing agent aqueous solution. On the other hand, the retention unit 13 is provided with a pH meter 15 and connected to a discharge line 18 for the aqueous slurry containing the produced alumina hydrate.
A line mixer (static mixer) 20 is provided in the introduction line 16 of the raw aluminum salt aqueous solution. In a sodium aluminate aqueous solution diluted to a concentration used for alumina preparation, sodium aluminate hydrolyzes with time and precipitates. Therefore, in the conventional method, it was necessary to prepare a dilute sodium aluminate aqueous solution for each alumina preparation, but in the present invention, by adjusting the flow rate of the raw sodium aluminate aqueous solution and the dilute water flow, Thus, a dilute sodium aluminate aqueous solution that is automatically used for preparation can be prepared. Moreover, the temperature of the diluted sodium aluminate aqueous solution is also adjusted by adjusting the temperature of the diluted water.
[0010]
The other end of the discharge line 18 of the produced alumina hydrate-containing aqueous slurry is connected to an aging tank 30, where alumina hydrate is obtained in which particles are uniformly grown to a desired size.
The bottom of the aging tank 30 and the Oliver drum filter as the filter 40 are connected by an aging slurry discharge line 32. After the impurities are removed by washing with hot water in the filter 40, the dehydrated alumina cake is introduced into the high-temperature aging tank 50 through the line 42, and then sent to the next process (not shown). The process description is the same as that of a conventional alumina production apparatus. Reference numeral 34 denotes a circulation line for returning the overflow from the filter 40 to the aging tank 30.
[0011]
The aluminum salt used in the present invention may be water-soluble, such as acidic aluminum salts such as aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum acetate, basic aluminum sulfate, basic aluminum nitrate, basic aluminum chloride, basic acetic acid. Examples include basic aluminum salts such as aluminum, sodium aluminate, and potassium aluminate. Such an aluminum salt is desirably used in an aqueous solution of 0.5 to 20% by weight, preferably 2 to 10% by weight in terms of Al ₂ O ₃ .
[0012]
In the present invention, the neutralizing agent refers to a water-soluble substance having a property of reacting with an aluminum salt to form a precipitate of alumina hydrate. For example, an acidic aluminum salt such as aluminum sulfate is used as the aluminum salt. The basic substance such as sodium aluminate, potassium aluminate, caustic soda, ammonia, etc. is used as the neutralizing agent, and the basic aluminum salt such as sodium aluminate is used as the aluminum salt. If so, an acidic substance such as aluminum sulfate, aluminum nitrate, aluminum chloride, sulfuric acid, hydrochloric acid, acetic acid or the like is used as a neutralizing agent. As such a neutralizing agent, an aqueous solution which is dissolved and contained in such an amount that it reacts with the aluminum salt to form an alumina hydrate having a concentration range of 1 to 10% by weight in terms of Al ₂ O ₃ is used. desirable.
[0013]
In this embodiment, an aqueous solution of sodium aluminate is supplied from the raw material aluminum salt aqueous solution introduction line 16, and an aqueous solution of aluminum sulfate is supplied from the neutralizer aqueous solution introduction line 17. (Static mixer) 20 is provided, and by supplying warm water to the line mixer 20, the diluted sodium aluminate aqueous solution is prevented from being hydrolyzed. The aqueous solution of aluminum sulfate is stable, and a large amount of diluted aqueous aluminum sulfate solution can be prepared and stored at a time.
Both the sodium aluminate aqueous solution and the aluminum sulfate aqueous solution are continuously introduced into the preparation tank 10 at a predetermined flow rate. Accordingly, the concentration, pH, and temperature conditions of the mixed solution in the preparation tank 10 are adjusted and maintained within a range suitable for the growth of the alumina hydrate particles.
[0014]
The contact residence time of the liquid mixture in the mixing tank 10 needs to 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 an alumina hydrate having a different crystal form is formed, and the contact residence time is more than 1 minute. If it is short, the neutralization reaction does not proceed sufficiently, so that the 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 liquid in the mixing tank 10, and the like are determined based on the contact residence time.
[0015]
The pH of the mixed solution in the preparation tank 10 is adjusted to a specific value in the range of 6 to 9 by the pH meter 15 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 hardly occurs. Conversely, 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. Furthermore, the range of 50 ° C. or higher, particularly 60 ° C. to 95 ° C. is preferable.
[0016]
The alumina hydrate thus generated by staying in the preparation tank 10 for a predetermined time overflows from the discharge line 18 and enters the aging tank 30. Since the treatment process after the aging tank 30 is the same as the known process as described above, the description thereof is omitted.
[0017]
【The invention's effect】
According to the method and apparatus for producing alumina according to the present invention, porous alumina, which has heretofore been difficult to produce only in batch mode, can be produced continuously on an industrial scale.
Moreover, according to the alumina manufacturing method and apparatus of the present invention, since the raw material aluminum salt aqueous solution and the neutralizing agent aqueous solution are continuously prepared, the productivity is excellent even though the manufacturing operation is simple. Furthermore, it has a remarkable effect that control of various physical properties such as pore volume, pore diameter, specific surface area and the like is extremely easy and reliable.
The porous alumina obtained by the present invention is used in industrial fields where porous alumina has been conventionally used, such as various catalyst carriers, adsorbents, and desiccants.
[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 put in a stainless steel mixing tank 10 having a capacity of 1 m ³ to about 30%, and this is heated and held at 65 ° C.
Next, about 300 liters of an aluminum sulfate aqueous solution containing 2.5% by weight of alumina heated to 65 ° C. was introduced into the preparation tank 10 in about 10 minutes, and the pH of the mixed solution was maintained at 7.2.
[0019]
2. Continuous operation of the compounding tank 10 A sodium aluminate aqueous solution and an aluminum sulfate aqueous solution are continuously supplied to the compounding tank 10, and the mixed solution is stirred at a low speed to generate small gel balls.
A sodium aluminate aqueous solution having an alumina concentration of 22% by weight is mixed with 260 liters / hour together with warm water 1500 liters / hour by the line mixer 20 and supplied from the introduction line 16. An aqueous aluminum sulfate solution having an alumina concentration of 2.5% by weight is supplied from the introduction line 17 at 1553 liters / hour.
The mixed solution in the preparation tank 10 is maintained at a temperature of 65 ° C. and pH 7.2 ± 0.2, and the residence time in the tank is set to 10 minutes, and the produced alumina hydrate slurry is extracted from the discharge line 18 to the aging tank 30. . In addition, 2 weight% of sodium aluminate 50 weight% sodium gluconate aqueous solution was added as a crystal growth inhibitor.
[0020]
3. Operating conditions of the aging tank 30 In the aging tank 30, the alumina hydrate slurry is retained at 65 ° C for 90 minutes, stirred and aged, and then sent to the filter 40.
4). In the cleaning filtration running conditions <br/> filtration machine 40 (10 m ³ Oliver drum filters), washing the slurry with 0.1 wt% of ammonia water 60 to 65 ° C.. The amount of washing water was 35 times that of dry alumina, and the remaining Na ₂ O amount: 0.05% by weight or less and the remaining SO ₄ amount: 1.5% by weight or less were set as washing target values.
5. In operating conditions <br/> steam jacketed hot aging tank 50 of the hot aging tank 50, a de-Na · de SO ₄ alumina hydrate slurry sent, by adding 15 wt% aqueous ammonia pH 10. 5 and aged at 95 ° C. for 20 hours.
[0021]
6). Final process After completion of the ripening, the slurry was sent to a drying / firing process (not shown), dried at 130C for 13 hours, and then calcined at 500C for 1 hour to obtain an alumina support. The main physical properties of this alumina support were as follows.
Na ₂ O content: 0.02% by weight
SO ₄ content: 0.84% by weight
Specific surface area: 270 m ² / g
Pore volume: 0.71 ml / g
[Brief description of the drawings]
FIG. 1 is a flow diagram of an alumina production apparatus of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Preparation tank 11 Partition plate 12 Mixing part 13 Retention part 14 Stirrer 15 pH meter 16 Raw material aluminum salt aqueous solution introduction line 17 Neutralizing agent aqueous solution introduction line 18 Product alumina hydrate containing aqueous slurry discharge line 20 Line mixer

Claims (2)

  It is divided into a mixing part equipped with a stirrer and a staying part equipped with a pH meter by a partition plate provided in the tank, and each introduction line of the raw material aluminum salt aqueous solution and the neutralizing agent aqueous solution is connected to the mixing part, It has a blending tank in which the discharge line of the produced alumina hydrate-containing aqueous slurry is connected to the staying part, and an aging tank for aging the aqueous slurry that is connected to the discharge line and overflows. Alumina production equipment. The raw material sodium aluminate aqueous solution from inlet line of aluminum salt aqueous solution or neutralizing agent solution is introduced, alumina production apparatus according to claim 1, further comprising a line mixer for supplying dilution water to the inlet line of the sodium aluminate solution.

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