JPH07257919A - Production of spherical silica particle - Google Patents

Abstract

PURPOSE:To produce solid spherical silica particles contg. no hollow or deformed particles and having good shape when spherical silica particles having 1-200mum particle diameter range are formed. CONSTITUTION:A suspension contg. silica hydrogel and at least one of ammonium nitrate and urea is spray-dried to form spherical particles and these particles are burnt at >=400 deg.C.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing spherical silica particles. The spherical silica particles obtained by the present invention are spherical silica particles having a high degree of solidity, have high mechanical and physical strengths, and are excellent in powder fluidity, and are used as catalysts, catalyst carriers, inert substances and the like. It is useful.

[0002]

2. Description of the Related Art When silica particles are used as a catalyst or catalyst carrier, various physical properties such as shape, particle strength, average particle size, surface area, average pore size, and pore volume are usually strictly controlled. Is required. In particular, regarding the shape, a solid spherical shape is generally desired. This is because the particles themselves have large mechanical and physical strengths, and when they are used in a fluidized state, they have excellent fluidity.

Various methods for producing such spherical silica particles have been proposed. For example, Japanese Patent Laid-Open No. 2-2
21112, after wet pulverizing a silica hydrogel obtained by reacting an alkali metal silicate with a mineral acid, the amount of water present is 0.2 to 1.5 with respect to the silica hydrogel.
A method in which the weight is adjusted to twice the weight and spray drying is performed.
No. 713, the amorphous silica obtained by extruding an aqueous solution of an alkali metal silicate into a water-miscible organic medium or an acid solution through pores, treating the coagulated product with an acid-containing solution, and then washing with water, Is wet pulverized to obtain a fine particle silica suspension having a weight average particle diameter of 10 μm or less, and a method of spray-drying this is disclosed in JP-A-3-170318. Silica silica gel slurry, and then p
A method of aging while maintaining H at 9.0 or more, washing and drying, in JP-A-63-16049, is obtained by spraying activated silica gel obtained by mixing an aqueous alkali silicate solution with an acid. A method of drying a spherical silica hydrogel and the like are disclosed.

However, conventional manufacturing methods such as these are
It is good when forming fine spherical particles, but when forming spherical particles having a particle size of 20 to 200 μm, which are used in a fluidized bed reaction, hollow and irregular particles are mixed to form a solid spherical particle having a good shape. It was difficult to manufacture, and the strength of the particles was not always satisfactory.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of producing spherical silica particles having a good shape and high solidity even when spherical particles having a large particle size are formed. is there.

[0006]

According to the present invention, a suspension containing silica hydrogel and at least one selected from the group consisting of ammonium nitrate and urea is subjected to a spray drying operation to produce spherical particles, and the particles are heated to 400 ° C. The present invention relates to a method for producing spherical silica particles, which comprises firing at the above temperature.

The present invention will be specifically described below. The silica hydrogel that is the starting material in the present invention can be prepared by any method known in the technical field of this type. For example, it can be obtained by hydrolysis of silicate ester, silicate or the like, reaction of alkali metal silicate with mineral acid, and the like. When a silica hydrogel having a low alkali metal content is used, it is disclosed in JP-A-62-3011.
No. 62-3012 is recommended, but the production method is not particularly limited. The silica hydrogel has an average particle size of 10 μm or less, preferably 5 μm or less, and more preferably 1 μm or less.

In the present invention, such a silica hydrogel is mixed with ammonium nitrate or urea, or both ammonium nitrate and urea to prepare a suspension. Commercially available ammonium nitrate and urea can be used. As ammonium nitrate, a method of adding nitric acid and aqueous ammonia may be used. A silica sol can be mixed with this suspension. This can increase the strength of the particles.

The mixing ratio of ammonium nitrate and / or urea is 10% by weight based on the silica solid content in the suspension.
Above, it is desirable to mix in the range of preferably 30 to 70% by weight. When the mixing ratio is less than 10% by weight, the effect of obtaining spherical silica particles having a good shape is small, and hollow particles and irregularly shaped particles may be mixed in the particles obtained by spray drying. Further, if mixed excessively, ammonium nitrate or urea may be violently decomposed during spray drying or subsequent drying, and some silica particles may be crushed. The suspension does not affect the shape of the spherical silica particles obtained by its PH value. When the PH value is in the range of 5 to 7, the fluidity of the suspension tends to decrease, and in that case, it is preferable to dilute with water. The silica concentration in the prepared suspension is preferably in the range of 10 to 50% by weight.

Next, this suspension is subjected to spray drying operation to be granulated into spherical particles and dried to produce spherical silica particles.
The spray drying can be performed using an arbitrary device such as a centrifugal type, a pressure nozzle type, or a two-fluid nozzle type. Although the atmosphere for spray drying is not limited, it is preferably performed in an air stream for economic reasons. The spherical silica particles obtained by spray drying are dried at a temperature of about 150 to 300 ° C. and then 400 ° C. or higher, preferably 450 to 130.
The final product is baked at a temperature in the range of 0 ° C. The firing time may be about 0.5 to 50 hours.

The calcination may be carried out separately in the calcination and the final calcination, or may be carried out at a single temperature without separation. The firing method is also not particularly limited, and any method such as static firing or fluidized firing may be used. The firing atmosphere is not limited, and an inert gas atmosphere such as argon or helium, an oxidizing atmosphere such as air, or a reducing atmosphere such as hydrogen can be used, but in an air stream for economic reasons. It is preferable to carry out. The heating source is arbitrary, and electric heat or combustion gas is an economical heat source. The added ammonium nitrate or urea is completely decomposed and removed in the process of drying and baking. According to the method of the present invention, the particle size is 1 to 20.
It is possible to obtain spherical silica particles having an average particle size in the range of 0 μm and in the range of 5 to 150 μm.

[0012]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 Silica hydrogel obtained by reacting sodium silicate with nitric acid was wet pulverized to have a concentration of 30 wt% and an average particle size of 0.5 μ.
m silica hydrogel was prepared. Ammonium nitrate (purity 98%) 765 was added to 5000 g of this silica hydrogel.
g was added with stirring, and 2 g of 61 wt% nitric acid was further added to adjust the pH to 2. The amount of ammonium nitrate added corresponds to 50 wt% with respect to the total silica. The suspension was spray-dried to obtain spherical particles, which were then heat-treated at 250 ° C. for 3 hours, calcined at 400 ° C. for 2 hours, and finally calcined at 500 ° C. or 1000 ° C. for 4 hours, respectively. . The obtained calcined silica particles have an average particle size of 4 in both cases of calcining at 500 ° C. or 1000 ° C.
The particle size was 2 μm, and the shape was solid spherical particles.

Example 2 Silica hydrogel 50 prepared in the same manner as in Example 1.
To OO g, 987 g of 61 wt% nitric acid was added with stirring, 1083 g of 15 wt% aqueous ammonia was added, and 2 g of 61 wt% nitric acid was added to adjust pH to 2.
The added nitric acid and aqueous ammonia correspond to 50 wt% as the amount of ammonium nitrate based on the total silica. The suspension was spray dried to give spherical particles, which were then washed at 250 ° C for 3
After heat treatment for 2 hours, it was further calcined at 400 ° C. for 2 hours and finally calcined at 1000 ° C. for 4 hours to produce spherical silica particles.

Example 3 Spherical silica particles were produced in the same manner as in Example 1 except that the amount of ammonium nitrate was 459 g or 1531 g. The amounts of ammonium nitrate added correspond to 30 wt% and 100 wt% of the total silica, respectively.

Example 4 Silica sol [Cataloid S-2, manufactured by Catalyst Kasei Kogyo Co., Ltd.]
0 L, concentration 20 wt%] 750 g, 61 wt% nitric acid 3 g was added to adjust the pH to about 2, and 1167 g of silica hydrogel prepared in the same manner as in Example 1 and 255 g of ammonium nitrate were added with stirring. 6 in this suspension
The pH was adjusted to 2 by adding 1 g of 1 wt% nitric acid. The amount of ammonium nitrate added corresponds to 50 wt% with respect to the total silica. The suspension was spray-dried to obtain spherical particles, which were then heat treated at 250 ° C. for 3 hours and then further 40
Pre-baked at 0 ℃ for 2 hours, and finally 1000 ℃, 1100 ℃
Alternatively, spherical silica particles were produced by firing at 1200 ° C. for 4 hours each.

Example 5 The pH of the suspension was adjusted by using 17 g of 15 wt% ammonia water.
The same method as in Example 4 except that the pH was adjusted to 5.0 and 500 g of water was added to dilute it, or the pH of the suspension was adjusted to 10.6 using 812 g of 15 wt% ammonia water. To produce spherical silica particles.

EXAMPLE 6 Urea (purity 98%) 255 instead of ammonium nitrate 255
Spherical silica particles were produced in the same manner as in Example 4 except that g was used.

Comparative Example 1 Example 4 except that ammonium nitrate was not added.
Silica particles were produced in the same manner as in.

The silica particles obtained in Examples 2 to 6 have an average particle size in the range of 42 to 51 μm,
All the particles were solid spherical particles. On the other hand, the silica particles obtained in Comparative Example 1 have an average particle size of 43 μm.
And its shape was hollow particles.

The properties and shapes of the silica particles produced in Examples 1 to 6 and Comparative Example 1 are summarized in Table 1. Further, the simplest method for directly and sensuously determining the quality of the produced silica particles is to directly observe the silica particles with an electron microscope. The silica particles produced in Examples and Comparative Examples were all observed with an electron microscope and photographed. 1 and 2 of the drawings respectively show an electron micrograph of the silica particles of Example 3 and Example 6, and FIG. 3 shows an electron micrograph of the silica particles of Comparative Example 1.

[0022]

[Table 1]

[0023]

According to the present invention, the particle size is 1 to 200 μm.
When forming spherical silica particles in the range of m, it was possible to produce solid spherical silica particles having a good shape without mixing hollow and irregularly shaped particles.

[Brief description of drawings]

FIG. 1 is an electron micrograph of spherical silica particles produced in Example 3.

FIG. 2 is an electron micrograph of spherical silica particles produced in Example 6.

3 is an electron micrograph of silica particles produced in Comparative Example 1. FIG.

Claims (2)

[Claims] 1. A method comprising subjecting a suspension containing silica hydrogel and at least one selected from the group consisting of ammonium nitrate and urea to a spray drying operation to form spherical particles, and calcining the particles at a temperature of 400 ° C. or higher. A method for producing spherical silica particles, which is characterized. 2. The method according to claim 1, wherein the suspension contains silica sol.