JPH0645452B2 - Method for producing silica gel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing silica gel, and more particularly to a method for producing silica gel using tetraalkoxysilane as a raw material.

[Prior Art] Conventionally, as a method for producing silica gel, a tetraalkoxysilane such as tetramethoxysilane or tetraethoxysilane is hydrolyzed in the presence of an acid under a reaction condition of a water / alkoxysilane molar ratio of 5 or more. There is known a method in which silica gel is obtained by passing through silanol to give a sol-like silica, which is then kept in a standing state to give a gel-like substance, which is then dried at room temperature for several days to obtain silica gel.

[Problems to be Solved by the Invention] However, in this conventional method, it takes a long time for the gel structure to be completed by hydrolysis and polymerization, and if the gel aging time is omitted, the produced silica gel is Unreacted alkoxy groups remain, and when this gel is dried and sintered, the organic residue is carbonized and black particles are mixed into silica gel.

[Means for Solving Problems] The present invention has been conceived in view of such a viewpoint, and in a method for producing silica gel by hydrolyzing tetraalkoxysilane, the reaction molar ratio of water / tetraalkoxysilane is It is a method for producing silica gel in which the hydrolysis reaction and the sol-gel reaction are carried out under reflux conditions of 3 or more.

The tetraalkoxysilane used in the method of the present invention is represented by the general formula Si (OR) ₄ (wherein R represents an alkyl group).
And examples thereof include tetramethoxysilane, tetraethoxysilane, and tetraisopropoxysilane. This tetraalkoxysilane is produced by any method such as a method of directly contacting silicon and alcohol with mercury chloride or sodium alcoholate as a catalyst, a method of synthesizing by reaction of silicon chloride and alcohol, and the like. May be

Further, in order to accelerate the hydrolysis of the tetraalkoxysilane, it is desirable to use a hydrolysis catalyst, and examples of such a catalyst include hydrochloric acid, sulfuric acid, carbon dioxide gas, ammonia and the like.

Next, the hydrolysis reaction of tetraalkoxysilane in the present invention will be described. The hydrolysis reaction of tetraalkoxysilane has long been known as a sol-gel reaction. The reaction process is extremely complicated because it proceeds by polymerizing while repeating hydrolysis and dehydration condensation, which makes it very complicated and it is difficult to describe it completely by a reaction formula.
Therefore, it is appropriate to calculate the required water content based on the reaction formula shown below.

Si (OR) ₄ + 4H ₂ O → Si (OH) ₄ + 4ROH (1) Si (OH) ₄ → SiO ₂ + 2H ₂ O (2) Si (OR) ₄ + 2H ₂ O → SiO ₂ + 4ROH (3) That is, tetra In order to promote the hydrolysis of alkoxysilane quantitatively, it is necessary to add 4 mol of water to 1 mol of tetraalkoxysilane based on the above reaction formula (1), but dehydration is performed based on the reaction formula (2). Considering the amount of water produced by the condensation, it is sufficient to add twice the molar amount of water to the tetraalkoxysilane as shown in the reaction formula (33).

The hydrolysis reaction is generally carried out at room temperature or under slight heating, but the present invention is carried out under reflux conditions in order to efficiently produce good silica gel. Therefore, the hydrolysis reaction and the completion of the gel structure proceed extremely quickly.

The amount of water added is theoretically required to be 2 mol per 1 mol of tetraalkoxysilane, as is clear from the above reaction formula (3), but if the added amount is too small, the hydrolysis reaction becomes insufficient, After the gel is fired, carbide is formed in silica. Also, if the addition amount is large, the hydrolysis reaction proceeds well,
A large amount of water has to be removed during gel firing, which is not industrially advantageous. Therefore, the amount of water added is an amount sufficient to carry out the hydrolysis reaction, and it is desirable that the amount is as small as possible. It is enough. If it is less than 3 mol, a very long reaction time is required.

The water may be added all at once when performing the hydrolysis reaction, by dividing a predetermined amount into several portions and adding them at appropriate intervals, or by continuously adding them with a metering pump. Although there is no problem, the method of adding all at once is superior in order to efficiently obtain the gel-like material.

By carrying out the hydrolysis reaction under reflux conditions, the time required to obtain a gel-like substance is shortened, and if 3 mol or more of water is added to 1 mol of tetraalkoxysilane, it is possible to obtain good charcoal-free materials after firing. Silica is obtained. In addition, the time required to obtain a gel-like substance is shortened as the amount of water added increases. Further, it is advantageous to add an alcohol as a solvent to the hydrolysis reaction. In this case, the amount of the alcohol to be added is usually 0.5 to 1 mol with respect to 1 mol of the tetraalkoxysilane. It doesn't have to be. If the amount of alcohol used is increased, the time until a gel is obtained becomes longer, and conversely, if the amount of alcohol used is decreased, it becomes cloudy during the hydrolysis reaction, but the time to obtain a gel is shortened. Therefore, there is no particular influence on the physical properties of the produced silica. Therefore, alcohol may not be added at all, but it is desirable to add an appropriate amount in order to carry out the reaction efficiently.

A sol is produced by the hydrolysis reaction and then gelation proceeds. In the present invention, this sol-gel reaction is also carried out under reflux conditions to complete the reaction promptly. By keeping the sol or gel as it is under reflux conditions, hydrolysis is promoted and alcohol is released. As a result, silica gel having a small amount of residual alkoxy groups can be obtained in a short time. Further, since the water required for the hydrolysis step can be effectively secured by carrying out the reflux, it is possible to obtain silica gel having no carbide after the drying / sintering step at a water / tetraalkoxysilane molar ratio of 3 or more. it can.

[Examples] Hereinafter, the method of the present invention will be specifically described based on Examples and Comparative Examples.

Example 1 A glass reaction vessel was charged with 100 parts by weight of tetramethoxysilane and 16.7 parts by weight of methanol, and pure water 3
5.7 parts by weight were added all at once, and then carbon dioxide gas was blown in. Then, the mixture was heated at 200 rpm while stirring, and a hydrolysis reaction was performed under reflux conditions to obtain a gel-like product in about 100 minutes. Further, the gel structure was completed by maintaining it under reflux conditions for 3 hours. The obtained gel-like substance is dried and further 1,10
Upon sintering at 0 ° C., good white silica free of carbides was obtained.

Example 2 Using a reaction vessel similar to that of Example 1, 100 parts by weight of tetramethoxysilane and 17 parts by weight of methanol were charged,
Further, 47.3 parts by weight of pure water was added all at once, and then carbon dioxide gas was blown in. When the hydrolysis reaction was carried out in the same manner as in Example 1, a gel-like substance was obtained in about 30 minutes. Further, the mixture was maintained under reflux conditions for about 1 hour, and white favorable silica was obtained in the same manner as in Example 1.

Example 3 100 parts by weight of tetramethoxysilane and 66.
7 parts by weight were charged, 58.7 parts by weight of pure water was further added all at once, and then carbon dioxide gas was blown in. A hydrolysis reaction was carried out in the same manner as in Example 1 to obtain a gel-like product in about 90 minutes. Further, the mixture was maintained under reflux conditions for 1 hour, and white favorable silica was obtained in the same manner as in Example 1.

Example 4 100 parts by weight of tetramethoxysilane and memethanol 8.
3 parts by weight were charged, 58.7 parts by weight of pure water was further added all at once, and then carbon dioxide gas was blown in. The hydrolysis reaction was performed in the same manner as in Example 1 to obtain a cloudy gel-like substance in about 20 minutes. Further, the mixture was maintained under reflux conditions for 1 hour, and white favorable silica was obtained in the same manner as in Example 1.

Example 5 100 parts by weight of tetramethoxysilane and methanol 16.
With 7 parts by weight, while blowing carbon dioxide gas, 200
Stir at rpm and add 48.7 parts by weight of pure water under reflux conditions.
The mixture was divided and added every hour to carry out a hydrolysis reaction. A gel-like substance was obtained in about 260 minutes. Further, the mixture was maintained under reflux conditions for 1 hour, and white favorable silica was obtained in the same manner as in Example 1.

Example 6 100 parts by weight of tetramethoxysilane and methanol 16.
With 7 parts by weight, while blowing carbon dioxide gas, 200
It was stirred at rpm and kept under reflux conditions. Pure water 58.
The hydrolysis reaction was carried out by continuously adding 7 parts by weight with a metering pump at a rate of 5.2 ml / min. A gel was obtained in about 30 minutes. Example 1 was kept under reflux conditions for 1 hour.
A good white silica was obtained in the same manner as in.

Comparative Example 1 A glass reaction vessel was charged with 100 parts by weight of tetramethoxysilane and 16.7 parts by weight of methanol, and further purified water 3
3.0 parts by weight was added all at once, and then carbon dioxide gas was blown in. Then, the hydrolysis reaction was performed in the same manner as in Example 1. A gel was obtained in about 150 minutes. Further, it was kept under reflux condition for 3 hours and dried and sintered in the same manner as in Example 1. As a result, a different color carbide was generated in silica.

Comparative Example 2 100 parts by weight of tetramethoxysilane and 17 parts by weight of methanol were charged, 58.7 parts by weight of pure water was added all at once, and then carbon dioxide gas was blown in. The hydrolysis reaction was carried out while stirring at room temperature. It took about 250 minutes to obtain a gel. The obtained gel-like material was further kept at room temperature for 1 day, dried and further sintered at 1,100 ° C. to obtain silica containing a small amount of carbide. In order to obtain good silica by this method, it was necessary to keep the gel at room temperature for 3 days or more.

[Effects of the Invention] According to the present invention, the amount of water added during the hydrolysis reaction is smaller than in the prior art, and silica gel having a completed gel structure can be obtained in an extremely short time. Therefore, silica gel can be produced industrially efficiently. In addition, the silica gel obtained by the method of the present invention does not generate carbides after sintering, and becomes white silica having good physical properties.

Claims (2)

[Claims] 1. A method for producing silica gel by hydrolyzing tetraalkoxysilane, wherein the hydrolysis reaction and the sol-gel reaction are carried out under a reflux condition under a water / tetraalkoxysilane molar ratio of 3 or more. And a method for producing silica gel. 2. The method for producing silica gel according to claim 1, wherein the hydrolysis reaction is carried out in the presence of alcohol.