JPH0262490B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an improvement in a process for producing alumina with a low sodium content using a sodium compound as at least part of the raw material.

[Prior art]

Conventionally, in order to produce alumina, there have been methods that utilize the reaction of strong aluminum salts such as aluminum sulfate and aluminum nitrate with sodium compounds such as sodium hydroxide and sodium carbonate, and methods that utilize the reaction of sodium aluminate with an acid or the strong acid of aluminum. Methods using reactions with salt are known. Furthermore, a method for producing alumina is also known, which includes a step of alternately adding sodium aluminate and a strong aluminum salt to an aqueous solution containing seed alumina hydrogel particles to cause crystal growth of alumina hydrogel particles.

In such a method for producing alumina, the generated precipitate (alumina hydrogel) is washed with water, filtered, and then dried and fired to obtain alumina. In this case, the water washing process is
If this is insufficient, the sodium content derived from the raw materials will remain in the alumina produced, so in order to obtain alumina with a low sodium content, it is necessary to carry out the washing sufficiently until the pH of the washing waste becomes neutral. is necessary. On the other hand, the filterability of alumina hydrogel depends on its pH, and as it approaches neutrality, the filterability deteriorates significantly. Moreover, this tendency becomes particularly noticeable in the production of alumina with a high surface area. Therefore, in conventional alumina production techniques, in order to obtain high surface area alumina with a low sodium content, significant difficulties have arisen in filtering the alumina hydrogel after washing with water.

〔the purpose〕

The present invention aims to overcome the aforementioned drawbacks found in the prior art.

〔composition〕

As a result of various studies to achieve the above object, the present inventors have found that after filtering an aqueous solution containing an alkaline alumina hydrogel containing sodium while keeping its alkalinity, and drying and baking the obtained alkaline alumina hydrogel, discovered that alumina with a reduced sodium content could be easily produced when brought into contact with an aqueous ammonium salt solution without the difficulties of filtration seen in the prior art, and thus completed the present invention. .

That is, according to the present invention, an alkaline aqueous liquid containing a sodium-containing alkaline alumina hydrogel formed using a sodium compound as at least a part of a raw material is filtered while remaining alkaline, and the obtained alkaline alumina hydrogel is dried. A method for producing low sodium-containing alumina is provided, which comprises contacting the alumina with an aqueous ammonium salt solution after calcination.

In the production of alumina in the present invention, the step of forming an alumina hydrogel can be performed by a conventionally known method. For example, methods for producing high surface area alumina include methods for obtaining crystal-grown alumina hydrogel by holding precipitates produced by neutralization reaction of aluminum salts in hydrothermal conditions for a long time, and methods for producing alumina hydrogels that have grown crystals. A method for obtaining a crystal-grown alumina hydrogel by adding the hydrogel particles to a hydrogel while alternating the PH range between an undissolved PH region and a soluble PH region, and a method for obtaining a crystal-grown alumina hydrogel, and a method for obtaining a crystal-grown alumina hydrogel by alternating the PH range between the non-dissolving PH region and the soluble PH region of the hydrogel particles. A method of adding aluminum sulfate and sodium aluminate while keeping the pH constant is known, and the present invention can be advantageously used for alumina hydrogel obtained by such a method.

Additionally, the present inventors proposed that aluminum sulfate and sodium aluminate be alternately added to the seed alumina hydrogel within the non-dissolving PH range of the alumina hydrogel particles as an industrially advantageous method for producing high surface area porous alumina. We have previously developed a method to obtain crystal-grown alumina hydrogel by adding alumina and causing pH fluctuations in response to the addition. The present invention can be particularly advantageously applied to alumina hydrogel obtained by such a method.

In the present invention, the alumina hydrogel containing sodium and exhibiting alkalinity obtained as described above is subjected to a filtration treatment while remaining alkaline. Of course, prior to this filtration process, the alumina hydrogel may be subjected to a suitable washing process with water, but as with conventional washing processes, it is necessary to wash the alumina hydrogel sufficiently with water to obtain a neutral alumina hydrogel. There isn't. The pH of the alumina hydrogel subjected to filtration is in the range of 7-12, preferably 8-10. This filtration treatment can be performed much more easily than conventional methods because alumina hydrogel exhibits alkalinity and has excellent filterability.

Next, the thus separated alumina hydrogel (aluminum hydroxide precipitate) is dried and calcined, and brought into contact with an aqueous ammonium salt solution in the form of alumina. In this case, drying and firing of the alumina hydrogel can be performed according to conventionally known methods. For example, drying at 100-200℃
Calcination can be carried out at a temperature of 400 to 700 °C. Further, in drying and firing the alumina hydrogel, alumina can be handled in the form of a molded or non-molded product.
When drying and baking in the form of a molded product, the alumina hydrogel filter cake obtained by filtration is used as a molding material, molded using an extruder, etc. in the presence of a molding aid if necessary, and then dried. , is advantageously calcined.

Removal of sodium from alumina using an aqueous ammonium salt solution in the present invention is carried out by bringing calcined alumina into contact with an aqueous ammonium salt solution. In this case, the contact temperature may be room temperature, but it is more advantageous to carry out the contact at a high temperature. for example,
Desodium treatment of alumina can be advantageously carried out by bringing it into contact with a boiling aqueous ammonium salt solution. The ammonium salt concentration in the ammonium salt aqueous solution is not particularly limited, but is generally 0.1 to 5 mol/, preferably 0.5 to 3 mol/
It is. As the ammonium salt, ammonium chloride, ammonium sulfate, ammonium nitrate, etc. are used. By this ammonium salt aqueous solution treatment, the sodium content in alumina reacts with the ammonium salt and is eluted into the aqueous solution. Prior to this ammonium salt aqueous solution treatment, sodium components that are easily eluted with water or an acidic aqueous solution may be removed, if necessary.

The alumina treated with the ammonium salt aqueous solution can be made into alumina with a reduced sodium content by washing with water, drying and firing. Alumina treated with an aqueous ammonium salt solution contains ammonium ions, but these ammonium ions can be decomposed and removed in the subsequent firing step. The firing step in this case is preferably carried out at a temperature of 200 to 800°C, preferably 300 to 700°C.

〔effect〕

According to the invention, alumina with low sodium content, especially high surface area porous alumina (specific surface area
150 m ² /g or more, preferably 200 m ² /g or more, pore volume 0.4 ml / g or more, preferably 0.5 ml / g or more)
In the method for manufacturing alumina hydrogel, the alumina hydrogel is filtered while remaining alkaline without any special water washing treatment, so the operation is similar to the conventional method of thoroughly washing the alumina hydrogel with water and filtering the neutral alumina hydrogel. It is very simple compared to .
In particular, neutral alumina hydrogel has poor filtration properties and its filtration process is extremely difficult and takes a long time, but this does not occur in the present invention. Furthermore, in the present invention, since the sodium content removal treatment is performed on calcined alumina which is easy to handle, it is easy to carry out and can be carried out until the sodium content becomes extremely small.

According to the invention, the sodium content is 0.2% by weight
Hereinafter, particularly 0.1% by weight or less of high surface area porous alumina can be obtained. Since such alumina has many acidic points that are not neutralized, it can be advantageously used as a catalyst carrier, an adsorbent, a solid acid catalyst, and the like.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Comparative example Aluminum sulfate aqueous solution with Al ₂ O ₃ concentration of 80 g/
0.2 and deionized water 40°C in an enameled container, heated to 90°C, and stirred vigorously.
Sodium aluminate aqueous solution with Al ₂ O ₃ concentration 69 g/1.8
When added instantly, it became cloudy and an alumina hydrogel aqueous solution with a pH of 10 was obtained.

This was used as a seed alumina hydrogel aqueous solution, and when 0.4 of an aluminum sulfate aqueous solution with an Al ₂ O ₃ concentration of 80 g/was instantly added thereto, the pH became 6.5. Next, when 1.2 of a sodium aluminate aqueous solution with an Al ₂ O ₃ concentration of 69 g was added instantly, the PH
An alumina hydrogel aqueous solution of 10.5 was obtained. The temperature during the addition operation was maintained at about 90°C.

Next, this alumina hydrogel aqueous solution was filtered, redispersed in deionized water 2, and washed by filtering three times to obtain a cake. This filtration operation takes time each time, totaling 7 times.
It took days. The resulting cake was molded into a cylindrical shape using an extruder having a die with a hole of 1.6 mmφ, and the temperature
It was dried at 120°C for 3 hours. After that, it was placed in an electric furnace and fired at 550°C for 3 hours while blowing air.
The physical properties of the alumina molded product obtained in this way are: BET surface area (m ² /g) 240, pore diameter (Å)
110, and the pore volume (cc/g) was 0.740. Also,
The Na content of this product was 0.18 (wt%).

Example 1 Aluminum sulfate aqueous solution with Al ₂ O ₃ concentration of 80 g/
0.2 and deionized water 40°C in an enameled container, heated to 90°C, and stirred vigorously.
Sodium aluminate aqueous solution with Al ₂ O ₃ concentration 69 g/1.8
When added instantly, it became cloudy and an alumina hydrogel aqueous solution with a pH of 10 was obtained.

This was used as a seed alumina hydrogel aqueous solution, and when 0.4 of an aluminum sulfate aqueous solution with an Al ₂ O ₃ concentration of 80 g/was instantly added thereto, the pH became 6.5. Next, when 1.2 of an aqueous solution of sodium aluminate with an Al ₂ O ₃ concentration of 69 g was added instantly, the PH
An alumina hydrogel aqueous solution of 10.5 was obtained. The temperature during the addition operation was maintained at about 90°C.

Next, this alumina hydrogel was directly filtered to obtain a cake. The obtained product was molded into a cylindrical shape using an extruder having a die with a hole of 1.6 mmφ, and the temperature was
It was dried at 120°C for 3 hours. After that, it was placed in an electric furnace and fired at 550°C for 3 hours while blowing air.
The Na content of this product was 6.19wt%.

Next, 5 times the amount of 2.2N ammonium chloride water was added to this baked product, heated until it boiled, cooled, and then the supernatant was removed. This operation was repeated two more times, and then washed with warm water and then dried and fired. The Na content in the alumina thus obtained was 0.11 (wt%).

Further, the physical properties of this alumina showed a BET surface area (m ² /g) of 245, a pore diameter (Å) of 113, and a pore volume (cc/g) of 0.745.

Example 2 When the alumina with a Na content of 0.18 wt% obtained in the comparative example was treated in place of the alumina with a Na content of 6.19 wt% in Example 1, the Na content was
It was reduced to 0.013wt%.

Example 3 When the alumina with a Na content of 0.11 wt% obtained in Example 1 was replaced with the alumina with a Na content of 0.18 wt% of Example 2, the Na content was reduced to 0.012%.

Claims (1)

[Claims] 1. An aqueous solution containing an alkaline alumina hydrogel containing sodium formed using a sodium compound as at least a part of the raw material is filtered while remaining alkaline, and the resulting alkaline alumina hydrogel is dried and calcined, and then mixed with an aqueous ammonium salt solution. A method for producing low-sodium-containing alumina, the method comprising contacting the alumina.