JPH0733427A - Production of spherical silica fine powder controlled in pore structure - Google Patents

Abstract

PURPOSE:To obtain spherical silica fine powder controlled in a pore structure by controlling the viscosity of silicate ion-containing aq. soln. as the indication of the polymerization degree of the silicate ion and thermal decomposition temp. in a atomized combustion method. CONSTITUTION:In the production method for the atmized combustion method spherical silica in which the aq. soln. containing the silicate ion consisting of alkoxy-silicon, water and small amount of acid is changed into misty state by an ultrasonic vibrator, then the mist is introduced to a high temp. heating combustion device together with air or gaseous oxygen to decompose by heat, the objective spherical silica powder is obtained by controlling the viscosity of silicate ion-containing aq. soln. as the indication of the polymerization degree of the silicate ion and thermal decomposition temp. The concn. of silicate ion in the silicate ion aq. soln. is within the range of 0.05-2.0mol/l. When the concn. is <=0.05mol/l, the efficiency of an oxide powder production is low, and the concn. is >=2.0mol/l, the gelation of the silicate ion is liable to occur according to the progress of an aging, and it becomes difficult to maintain a solution state, on the other hand, the acid amount to be added is required to be 0.01-0.03 times per the concn. of the silicate ion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to produce a spherical silica powder by thermally decomposing an alkoxy silicon. The silica powder produced by this method is an adsorbent,
It can be used as a catalyst carrier or a chromatographic carrier for separation and analysis.

[0002]

Silica generally has a high surface area and a high pore volume, and is widely used as a dehydrating agent, a desiccant, a chromatographic adsorbent, a catalyst carrier, etc. In particular, silica gel is an industrial material. Besides, it is used in large quantities as a moisture absorption inhibitor to maintain the quality of various daily necessities in general households, and the application of silica products is wide-ranging, and it is indispensable as one of the basic materials supporting industrial activities. It is a substance that does not become.

[0003] Normally used silica is formed by precipitating as a precipitate by neutralizing an aqueous solution of sodium silicate (water glass) with a mineral acid such as hydrochloric acid, washing it with water, drying it, and firing it if necessary. , There are several other manufacturing methods, for example, a method of gelling by spray-pressing silica sol into a heated non-polar solvent,
It can be produced by a method of emulsifying an aqueous solution of silicate and then performing interfacial polymerization, a method of hydrolyzing alkoxy silicon in an organic solvent, a method of thermally decomposing a silicon compound under heating, and the like.

These production methods can be classified into a wet method and a dry method, and each has a characteristic silica powder. For example, in the case of a silica powder by a wet method, alkoxy silicon is hydrolyzed in an organic solvent. The silica powder produced by the method is said to be a method of obtaining a powder having a narrow particle size distribution and excellent dispersibility, but since the fine primary particles are usually obtained as complicatedly agglomerated particles, their shape Is likely to be non-uniform and has a high surface area and a high pore volume, but its particle size distribution is broad and it is difficult to obtain a powder having good dispersibility.

On the other hand, in the case of the dry method, those having physical properties different from those of ordinary silica can be obtained. For example, silicon is made into a chloride having volatility in advance, and then vaporized and then mixed gas flow of oxygen and hydrogen is obtained. Silica obtained by introducing it into a flame and thermally decomposing it is called ultrafine anhydrous silica, and it is possible to obtain a powder of almost perfect spherical fine particles with a uniform particle size, low cohesiveness, and small bulk specific gravity. It is also possible to obtain silica fine particles commonly referred to as "Aerosil" having excellent dispersibility.

In the production of silica fine particles, silicon is converted into a volatile substance such as silicon chloride in advance, and then vaporized and then thermally decomposed, whereas recently, an inorganic compound aqueous solution or a mixed aqueous solution thereof, or a silicon compound-containing aqueous solution is used. Etc. are atomized by an ultrasonic vibrator, entrained in air or oxygen gas and fed into a high temperature heating / calcining device, and thermally decomposed to produce metal oxide or metal composite oxide fine particles, or silica powder, etc. Manufacturing methods have been proposed.

This method is called a spray pyrolysis method or a spray combustion method and is a raw material for highly functional sintered ceramics in which the fine structure of the powder such as shape, particle size distribution and average particle diameter is controlled. Is a method for producing fine powders that has been devised in order to meet the demands of, for example, ceramics association magazine, Vol. 94, No. 8 (1986), pages 813 to 817 by ultrasonic spray pyrolysis of metal alkoxide. A method of producing spherical particles of strontium titanate is described in Journal of Ceramic Society of Japan, Vol. 97, No. 4, (1989), 407-41.
On page 2, the production method of lead titanate or lead zirconate by spray pyrolysis is shown, respectively.

On the other hand, Chemical Industry, Vol. 40, No. 12 (19
(1989), pages 1030 to 1034 show a method for producing spherical silica by the spray combustion method. As the method, nitric acid is added to an aqueous solution of methyl silicate, and then atomized by an ultrasonic vibrator and then pyrolyzed. However, there is a method of making the particle diameters of the silica fine particles produced therein uniform, in which the aqueous solution of methyl silicate is pre-heated to cause hydrolysis or polycondensation of silicate ions and to increase the polymerization. It is promoted or by adding methanol to the silicate ion-containing aqueous solution and then thermally decomposing it.

In industrial use of fine particle powders, it is important that the particle diameters are uniform when ceramics are produced by sintering, but it is high in use as an adsorbent or a catalyst carrier. It is generally important that the powder has a surface area and a high pore volume, and in order to be highly applicable to these applications as an even better material, in addition to the surface area and the pore volume, the average pore diameter Alternatively, it is preferable that the powder has a controlled pore size distribution and the like. For example, in the case of alumina, which is commonly used as a catalyst carrier along with silica, many studies have been made on methods for controlling these physical properties. On the other hand, in the case of silica, there have been few studies on physical property control, and in particular, in the case of spherical silica produced by the spray combustion method, the production method itself is new, and the silica particle size Knowledge of Minori is not only to have been shown slightly in academic journals.

[0010]

In using a porous inorganic oxide such as silica, in order to form an adsorbent or a catalyst carrier having excellent performance, a powder having a controlled particle size is required. It is preferable, however, that the physical properties such as surface area, pore volume, pore size distribution, or average pore size are preferably adjusted within a predetermined range, and in the silica production method in the spray combustion method, these physical properties control The technical method is unknown, and it is necessary to establish a physical property control method that can be easily applied in order to effectively use it.

[0011]

In the spray combustion method, an aqueous solution of raw material is atomized using an ultrasonic vibrator, and this is introduced into a high temperature heating combustor together with air or oxygen gas, and is oxidized by thermal decomposition. It is a method for producing fine particles of fine particles, and fine particles can be obtained because combustion of atomized raw material fine droplets is carried out in a short time, and its composition reflects the metal ion composition of the raw material aqueous solution as it is. It is a method that can obtain an oxide powder characterized in that the shape of particles is spherical and the particle size distribution is relatively narrow.

The inventors of the present invention have long conducted research on a method for producing spherical silica by the spray combustion method, and have mainly studied the method for producing an aqueous metal solution as a raw material, the shape of silica or its physical properties. Then, nitric acid was added to the aqueous solution of methyl silicate, and then heat treatment was performed to cause hydrolysis of the silicate ion and its polycondensation, and methanol was added to the aqueous solution in which its polymerization was promoted or the solution containing methyl silicate. It was clarified that spherical silica with uniform particle size can be obtained from highly concentrated silicate ion aqueous solution by pyrolyzing the aqueous solution.

In order to effectively utilize spherical silica by the spray combustion method, it is preferable to obtain an oxide having a uniform particle diameter, but the surface area, pore volume, and pore diameter of silica as a porous oxide are preferable. If the pore structure such as distribution and average pore diameter can be controlled to physical properties suitable for the purpose, its application range will be expanded, and it is possible to meet the demand for securing excellent selectivity in adsorbents, catalyst carriers, etc. In view of the fact that it can be produced and can be used at a high level, a method for producing spherical silica by the spray combustion method was further investigated.

In the production of spherical silica by the spray combustion method, an aqueous solution of alkoxysilicon is used. However, if the aqueous solution is atomized as it is for thermal decomposition, it disappears due to combustion of carbon components during the reaction process. In addition, since scattering of silicon occurs and the generated silica particles become non-uniform, as a preventive measure, the aqueous solution is pre-treated to hydrolyze and polycondense the silicate ions to polymerize them. As a pretreatment method, the silicate ion-containing aqueous solution is maintained at a specific temperature set in the range of 70 to 90 ° C., and aging is carried out for a specific time to accelerate the polymerization thereof, which is acceptable. After it is made into an aqueous solution containing silicate ions having a viscosity within the range of viscosity, it is atomized by an ultrasonic vibrator and then introduced into a high temperature heating combustor for thermal decomposition. It was produced spherical silica by.

When the physical properties of the obtained spherical silica were measured, surprisingly, an oxide powder having a very large surface area was obtained, and silicic acid for the purpose of making the particle diameters of the spherical silica particle powder uniform. Spherical silica powder obtained by thermal decomposition after mere heat treatment as a pretreatment for an ion-containing aqueous solution is 2
While the surface area was 0 to 30 m ² / g, the silica powder obtained by subjecting this pretreatment method to thermal decomposition had a much larger surface area of ²⁰⁰ to 400 m ² / g.
Had a surface area of.

The silicate ion aqueous solution in the present invention is an aqueous solution obtained by adding a small amount of acid to an alkoxysilicon aqueous solution,
Silicic acid esters such as methyl silicate, ethyl silicate, propyl silicate and butyl silicate can be used as the alkoxy silicon compound, and mineral acids such as nitric acid and hydrochloric acid, or formic acid, acetic acid and propionic acid can be used as the added acid. Organic acids such as oxalic acid and tartaric acid can be used.

The silicate ion concentration in the aqueous silicate ion solution is 0.05 to 2.0 mol / liter, preferably 0.1.
The range is from 1.0 to 1.0 mol / liter, and the concentration is 0.1.
If the amount is less than 05 mol / liter, the efficiency of oxide powder production is poor, and if the concentration is more than 2.0 mol / liter, gelation of silicate ions is likely to occur as aging proceeds, making it difficult to maintain a solution state. On the other hand, it is necessary that the amount of acid added is 0.01 to 0.03 times the molar amount of the silicate ion concentration.

After adding a small amount of acid, the aqueous solution of silicate ion is aged at 70 to 90 ° C. to accelerate the polymerization by hydrolyzing the silicate ion and its polycondensation. Viscosity gradually increases,
Since a sharp increase in viscosity is seen from a certain point in time, it is necessary that the viscosity be in the range of 1.0 to 3.0 centipoise in consideration of atomization of the raw material aqueous solution. It is preferable to complete the aging just before the rapid increase in viscosity observed after the lapse of time, and for aging at 80 ° C., it is 6 to 10 hours.

The aging of the aqueous solution of silicate ion is a controlling factor for increasing the surface area of the spherical silica powder obtained by the spray combustion method. Since a silica powder having a surface area and a pore volume can be obtained, a silica powder whose physical properties are controlled can be produced by arbitrarily adjusting the degree of aging within a range in which the viscosity does not exceed a predetermined value. You can do it.

The silicate ion aqueous solution that has been aged at 70 to 90 ° C. is then atomized by an ultrasonic atomizer, introduced into a combustor heated at high temperature by being entrained in air or an oxygen-containing gas, and thermally decomposed. However, the decomposition temperature is 400-1,
It is necessary to be in the range of 000 ° C. At a temperature of 400 ° C or lower, combustion removal of carbon components becomes insufficient, and carbon remains in the silica particles, and at a temperature of 1,000 ° C or higher, the silica skeleton Siloxane bond (-Si-O-Si-
O) is affected and a part of the silica powder is melted, so that a powder having preferable physical properties cannot be obtained.

In the method for producing spherical silica fine particles according to the present invention, the thermal decomposition temperature affects the average pore diameter of the produced silica, and powders having a small average pore diameter can be obtained in low temperature thermal decomposition, whereas high temperature thermal decomposition is required. In the decomposition, a silica powder having a large average pore diameter is obtained, and the average pore diameter of the produced silica can be controlled by adjusting the decomposition temperature, and the temperature applied in the present invention is 400 to 1,000 ° C. In, the average pore diameter can be controlled in the range of 6 to 50Å, and the pore distribution is sharp.

[0022]

EXAMPLES Next, the contents of the present invention will be specifically described by way of examples. The thermal decomposition method of the silicate ion-containing aqueous solution by the spray combustion device described therein is as follows, and the physical properties thereof are as follows. The measurement was performed by a method utilizing ordinary nitrogen adsorption. The thermal decomposition by the spray combustion method device will be described below. The spray combustion apparatus used in the present invention is as in the conceptual diagram shown in FIG. 1, and is composed of a spray generator (ultrasonic vibrator) and a tubular electric furnace with a reaction tube for thermal decomposition, and the frequency of the ultrasonic vibrator. Is 1.5 megahertz, and the flow rate of fine droplets of the silicate ion aqueous solution atomized by the vibrator is 1
5 liter / min. It is supplied to the pyrolysis reaction tube along with the oxygen gas of the powder, and is thermally decomposed instantaneously to form spherical fine-particle silica powder. To be done.

The reaction tube for thermal decomposition has an inner diameter of 3.2 cm and a length of 6
It is a quartz tube of 0 cm, and the fine droplets of the atomized silicate ion solution are 15 l / min. Since the oxygen gas is supplied together with the oxygen gas into the reaction tube, the residence time in the reaction zone is 3 seconds or less, and the heat for decomposing the fine droplets is supplied by the tubular electric furnace, but the heater is It is divided into three parts, an upper part, a middle part, and a lower part, and the temperature of each part is independently controlled, so that the thermal decomposition of fine droplets can be performed at any temperature.

Example 1-1 25 g of ethyl silicate was weighed in a 500 cc beaker, 200 cc of pure water was gradually added and dissolved by stirring, and then 1 cc of dilute nitric acid (3N) was added and mixed to obtain a silicate ion-containing aqueous solution. Was prepared and then this aqueous solution was heated at 80 ° C. for 8 hours.
After the aging, the viscosity of the silicate ion-containing aqueous solution after the aging was 2.7 centipoise.

In parallel with this, the reaction tube for thermal decomposition is prepared by heating to a predetermined temperature (850 ° C.), the aged silicate ion-containing aqueous solution is atomized by a spray generator, and oxygen gas ( 15 liters / min.) To form a spherical silica fine particle by supplying it to a reaction tube for thermal decomposition, further collecting by collecting in water and then drying,
Silica fine powder was obtained by the spray combustion method by firing at 500 ° C. for 4 hours in an electric furnace. The specific surface area, pore volume, and average pore diameter measurement results of this powder are shown in Table 1, and the pore distribution measurement The results are shown in Table 2.

Example 1-2 and Example 1-3 By the same treatment method as in Example 1-1, except that the aging time of the silicate ion-containing aqueous solution was changed to 4 and 6 hours in Example 1-1. Spherical silica fine particles of Examples 1-2 and 1-3 were prepared, and the specific surface area of the obtained silica powder,
Table 1 shows the measurement results of the pore volume and the average pore diameter.

Example 2 In Example 1-1, the temperature of the reaction tube for thermal decomposition was set to 500.
The spherical silica powder of Example 2 was prepared by the same treatment method as in Example 1-1, except that the temperature was set to 0 ° C. and the fine droplet decomposition temperature of the atomized silicate ion solution was lowered. Table 1 shows the measurement results of the specific surface area, pore volume, and average pore diameter of the silica powder.

Comparative Example 1 In Example 1-1, the silicate ion-containing aqueous solution was heated to 80 ° C.
Example 1-1, except that no aging in Example 1 was performed.
A spherical silica powder of Comparative Example 1 was prepared by the same treatment method as in Example 1. The measurement results of the specific surface area, pore volume and average pore diameter of the obtained powder are shown in Table 1.

Comparative Example 2 In Example 1-1, the temperature of the reaction tube for thermal decomposition was set to 1, 2
A spherical silica powder of Comparative Example 2 was prepared by the same treatment method as that of Example 1-1, except that the temperature was set to 00 ° C. and the fine droplet decomposition temperature of the atomized silicate ion solution was increased.
Table 1 shows the measurement results of the specific surface area, pore volume, and average pore diameter of the obtained silica powder.

[0030]

[Table 1]

[0031]

[Table 2] Table 2 Pore distribution measurement results of spherical silica powder (Example 1-1) ───────────────────────── Diameter (Å) 10 20 30 50 100 ───────────────────────── Differential pore volume (cc / g ・ Å) 0.14 0.35 0.08 0.02 0.00 ─────────────────────────

[0032]

In the method for producing spherical silica by atomizing silicate ions and then thermally decomposing them, the silicate ions in the aqueous solution are hydrolyzed and polycondensed to accelerate their polymerization to 70 to 90. According to the method of aging at 0 ° C, the specific surface area and pore volume of the produced silica can be controlled by changing the aging time, and the average pore diameter can be arbitrarily controlled by changing the decomposition temperature.

[0033]

[Brief description of drawings]

FIG. 1 shows an overall view of a spray combustion device.

[Explanation of symbols]

 1; Quartz tube 2; Glass tube 3; Electric furnace 4; Collector 5; Oxygen flow meter 6; Ultrasonic vibrator 7; Ultrasonic controller 8; Raw material solution

Claims (3)

[Claims] 1. A spray combustion method in which a silicate ion-containing aqueous solution consisting of alkoxysilicon, water and a small amount of acid is atomized by an ultrasonic vibrator and then introduced into a high temperature heating combustor together with air or oxygen gas for thermal decomposition. In the method for producing spherical silica, a method for producing spherical silica powder in which the pore structure is controlled by adjusting the viscosity of a silicate ion-containing aqueous solution as an index of the degree of polymerization of silicate ion and the thermal decomposition temperature. 2. A silicate ion-containing aqueous solution consisting of alkoxy silicon, water and a small amount of acid is aged at 70 to 90 ° C. to have a viscosity of 1 to 3 centipoise, and then atomized by an ultrasonic vibrator, The method for producing spherical silica powder having a controlled pore structure according to claim 1, which is introduced into a high temperature heating combustor together with air or oxygen gas. 3. The silicate ion concentration in the silicate ion-containing aqueous solution is 0.05 to 2.0 mol / liter, and the decomposition temperature of the atomized aqueous solution fine droplets in the combustor is 400 to 100.
The method for producing spherical silica powder having a controlled pore structure according to claim 1, which is 0 ° C.