JPH0645453B2 - Method for producing spherical silica gel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing spherical silica gel. Silica gel is widely used as a desiccant, a column packing material for liquid chromatography and gas chromatography, and is also used as a catalyst for various reactions.

[Prior art]

Conventionally, spherical silica gel and crushed silica gel are known as silica gel. Spherical silica gel is superior to crushed silica gel in its performance and use characteristics. However, the production of spherical silica gel is not easy and expensive.

The following methods are known as conventional methods for obtaining spherical silica gel.

(1) Japanese Patent Laid-Open No. 60-71515 discloses a method in which a water glass sol is emulsified in an organic solvent containing a first surfactant and then a second surfactant is added to cause gelation. Have been described. This method requires a distillation step to separate the organic solvent used for emulsification and silica gel, and is economically disadvantageous.

(2) Japanese Patent Publication No. 54-9588 describes a method of forming spherical particles by using colloidal silica as a binder a polymerizable organic material having miscibility with water. The product obtained by this method is a mixture of silica sol particles and an organic material, and in order to obtain silica gel, a step of removing the polymerized organic material by sintering at 500 ° C. or higher for 4 hours or more is required.

A spray drying method is known as a method for obtaining spherical silica gel without using the above-mentioned organic solvent or organic material.

(3) JP-A-53-65293 describes a method of spray drying silica sol.

However, when the present inventors carried out this method, it was found that the product was likely to be a silica gel having a hollow or a large depression although the product was spherical. Silica gel having such hollows or large dents is not preferable as a catalyst carrier, a packing material for liquid chromatography, etc., because it has insufficient mechanical strength and is damaged, and the packing density is lowered.

(4) Japanese Patent Publication No. 47-3446 discloses that an aqueous solution of an alkali metal silicate and a mineral acid are reacted to obtain pH = 9.
A method is described in which a silica hydrosol of 6 to 10.9 is prepared, gelled, further reacted with a mineral residue to form an acidic silica gel slurry, and spray-dried.

However, when the present inventors carried out this method, it was found that the product was likely to be irregularly shaped particles or a mixture of silica gel having many irregularities on the surface. Such silica gel is not preferable because it causes a decrease in packing efficiency as compared with spherical silica gel.

[Problems to be solved by the invention]

An object of the present invention is to provide a method for producing extremely spherical silica gel in which hollow and irregular particles are not mixed in a simpler method without using an organic solvent or an organic material as in the above-mentioned prior art. It is in.

[Means for solving problems]

The gist of the present invention is a method for producing silica gel by spray drying silica sol, in a method for producing spherical silica gel characterized by spray drying after mixing silica sol with an aqueous alkali metal silicate solution. The details will be described.

The silica sol used in the present invention may be a commercially available silica sol, or may be a silica sol produced by an acid decomposition method of an alkali metal silicate, an ion exchange method, electrodialysis or the like. Alternatively, it may be a silica sol produced by peptization of hydrated silica gel, or may be a silica sol obtained from a hydrolyzable silicon compound.

Such silica sol is mixed with an aqueous alkali metal silicate solution. Examples of alkali metal silicates include sodium silicate and potassium silicate, but sodium silicate is common.

Although it is unknown about the action of alkali metal silicate on silica sol, it was difficult to obtain it by spray-drying silica sol alone by spray drying after mixing silica sol with alkali metal silicate aqueous solution. Alternatively, spherical silica gel without large depressions can be easily obtained.

As a method of mixing the silica sol with the alkali metal silicate aqueous solution, in addition to the method of adding the alkali metal silicate aqueous solution to the silica sol under stirring, a method of adding the silica sol to the alkali metal silicate aqueous solution under stirring, or Alternatively, a method of continuously mixing silica sol and an aqueous solution of an alkali metal silicate is also possible.

However, at this time, it is necessary to adjust each concentration and mixing ratio of the silica sol and the alkali metal silicate aqueous solution. Here, the mixing ratio and concentration of the silica sol and the alkali metal silicate aqueous solution have a significant influence on the shape of the finally obtained silica gel. That is, the SiO ₂ concentration of the mixed solution is 5
The respective concentrations of the silica sol and the alkali metal silicate aqueous solution may be adjusted so as to be -30 wt%, preferably 10-25 wt%. If it is less than 5 wt%, hollow particles are likely to be mixed,
If it exceeds 30 wt%, the mixed solution may gel and spray drying may be difficult.

As a mixing ratio of the silica sol and the aqueous solution of alkali metal silicate, it is preferable to adjust the mixed solution such that SiO ₂ in the aqueous solution of alkali metal silicate is 0.8 to 27.1 parts by weight per 1 part by weight of SiO _{2 in} the silica sol. . Below 0.8 parts by weight,
The effect of the alkali metal silicate aqueous solution is small, and although it is spherical like the product obtained by spray-drying the silica sol alone, it is easy to obtain a mixture of particles having large depressions. On the other hand, when the amount is 27.1 parts by weight or more, the product obtained by spray drying tends to form particles having large depressions.

The mixing temperature is not particularly limited, but may be about room temperature and may be heated.

Spherical particles can be obtained by spray-drying the mixed solution of the silica sol thus obtained and the alkali metal silicate. As a spray dryer, nozzle type,
Disk type, two-fluid type, etc. are generally used, and either method can be used. Hot air temperature for drying is 100
About 300 ° C is acceptable.

Next, the obtained spherical particles are washed and dried to obtain spherical silica gel. Here, as a washing method, a method of neutralizing the obtained spherical particles with an acid and then washing with water, or a method of simply washing with water until it becomes neutral can be used.

By the above method, it is possible to obtain spherical silica gel having a smooth surface and free of hollow and irregular shaped particles.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, without using an organic solvent or an organic material, without requiring complicated operations, the surface is smooth by a simple method, and hollow, irregular-shaped particles It is possible to obtain spherical silica gel that is not mixed.

EXAMPLES Next, the present invention will be described more specifically by way of examples.

[Example 1] Silica sol adjusted to a SiO ₂ concentration of 15 wt% (manufactured by Nissan Chemical Industries, Ltd., trade name Snowtex S, (hereinafter, silica sol is manufactured by the same company)) 664 g, SiO ₂ concentration of 15 wt% No. 3 sodium silicate aqueous solution 336 adjusted to
g at room temperature with stirring for 10 minutes. The resulting mixed liquid was spray-dried at a feed rate of 720 ml / hr with a lab spray dryer set at a disk rotation speed of 15,000 rpm, an inlet hot air temperature of 100 ° C. and an outlet hot air temperature of 70 ° C. to obtain spherical particles. Subsequently, the obtained spherical particle slurry was washed with water until the pH became neutral, and dried at 110 ° C. overnight.

The silica gel thus obtained had a spherical shape and a smooth surface as shown in FIG. 1, and almost no hollow or irregularly shaped particles were mixed.

In Example 2 SiO ₂ concentration 10 wt% to adjust the No. 3 sodium silicate aqueous solution 860 g, was added silica sol (Snowtex S) 140 g which had been adjusted to SiO ₂ concentration of 10 wt%, Example 1
Spray-dried, washed with water and dried in the same manner as in.

The surface of the obtained silica gel was smooth as in Example 1, and there was almost no mixture of hollow and irregularly shaped particles.

In Example 3 SiO ₂ concentration 15 wt% to adjust the No. 3 sodium silicate aqueous solution 115 g, was added SiO ₂ concentration 15 wt% to adjust the silica sol (Snowtex 30) 385 g, likewise spray-dried as in Example 1 , Washed with water and dried.

The surface of the obtained silica gel was smooth as in Example 1, and there was almost no mixture of hollow and irregularly shaped particles.

[Comparative Example 1] Silica sol having a SiO ₂ concentration of 25 wt% (Snowtex S) 5
00 g was spray dried, washed with water and dried in the same manner as in Example 1.

The resulting silica gel was almost hollow and irregularly shaped particles as shown in FIG.

[Brief description of drawings]

FIG. 1 is a micrograph (magnification: 200 times) showing the particle structure of silica gel obtained by the method of Example 1. FIG. 2 is a micrograph (magnification: 200) showing the particle structure of silica gel obtained by the method of Comparative Example 1.

Claims (1)

[Claims] 1. A method for producing silica gel by spray-drying silica sol, which comprises mixing silica sol with an aqueous alkali metal silicate solution and then spray-drying.