JP7266361B2 - Manufacturing method of hollow particles - Google Patents

Description

The present invention relates to a method for producing hollow particles by spray pyrolysis.

As a method for producing fine particles by the spray pyrolysis method, a ceramic or metal pyrolysis furnace is used because of the ease of temperature control, and an externally heated spray pyrolysis apparatus is used for heating with an external electric heater or the like. Alternatively, a common method is to use an internal combustion spray pyrolysis apparatus in which a combustion burner is arranged inside the pyrolysis furnace and the particles are directly heated by combustion of fuel. Among them, as an internal combustion spray decomposition apparatus, a method of directly contacting the spray mist with the flame of the burner in the pyrolysis furnace (Patent Document 1), a method of installing a burner around the spray nozzle and thermally decomposing (Patent Document 2), A method of generating a reaction gas flow using a main flame hole and auxiliary flame holes arranged around the main flame hole, and spraying the raw material solution in the meantime (Patent Document 3), Raw material liquid mist and spray control A method of forming a flame by a burner in a gas mixing portion (Patent Document 4) and the like have been reported.

JP-A-2001-17857 JP-A-2001-137699 JP 2008-194637 A JP 2013-17957 A

However, in the methods described in Patent Documents 1, 2 and 4, since the spray mist undergoes a thermal decomposition reaction within the flame, the reaction itself is efficient and rapid, but the obtained particles are dense and hollow particles cannot be obtained. . Further, in the method described in Patent Document 3, the melted particles are welded to each other, so uniform hollow particles cannot be obtained.
Accordingly, an object of the present invention is to provide a spray pyrolysis method capable of producing hollow particles of constant quality at a high yield.

Therefore, the present inventors have studied various conditions in which the sprayed mist does not become solid, is kept hollow, and does not fuse with other particles in the pyrolysis furnace. The inventors have found that hollow particles can be obtained efficiently and at a high yield by thermal decomposition of the raw material if the raw material is not brought into direct contact with the flame but passed through the vicinity of the flame without contact, and the present invention was completed.

That is, the present invention provides the following [1] to [4].

[1] A method for producing hollow particles by spraying a raw material solution into a pyrolysis furnace and thermally decomposing it with a combustion burner provided in the pyrolysis furnace, wherein the spray mist does not come into direct contact with the flame of the combustion burner. A method for producing hollow particles, characterized by passing through.
[2] The method for producing hollow particles according to [1], wherein the raw material solution is sprayed so as to form an air shield around at least the sprayed mist that contacts the flame.
[3] The method for producing hollow particles according to [1] or [2], wherein the obtained hollow particles have a particle density of 0.1 to 1.0 g/cm ³ .
[4] The method for producing hollow particles according to any one of [1] to [3], wherein the obtained hollow particles have an average particle size of 1 to 100 μm.

According to the method of the present invention, the particles are not condensed, and hollow microparticles of uniform quality can be obtained in a high yield. Since the hollow particles obtained by the method of the present invention are hollow fine particles, they are useful as heat-insulating materials, heat-shielding materials, catalyst carriers, building materials, plastic fillers, and the like.

4 shows the positional relationship between the flame and spray mist in Example 1. FIG. 1 shows an SEM image of particles obtained in Example 1. FIG. 4 shows the positional relationship between the flame and spray mist in Example 2. FIG. 4 shows an SEM image of the particles obtained in Example 2. FIG. 3 shows the positional relationship between flame and spray mist in Comparative Example 1. FIG. 1 shows an SEM image of particles obtained in Comparative Example 1. FIG. 3 shows the positional relationship between flame and spray mist in Comparative Example 2. FIG. An SEM image of the particles obtained in Comparative Example 2 is shown. The image which looked at the spray nozzle used in Example 2 from the front is shown.

The method for producing hollow particles of the present invention is a method for producing hollow particles in which a raw material solution is sprayed into a pyrolysis furnace and thermally decomposed by a combustion burner provided in the pyrolysis furnace. It is characterized by passing through a vicinity that does not come into direct contact with the flame.

In the production method of the present invention, a raw material compound-containing solution (also referred to as a raw material solution), which is a raw material for hollow particles, is sprayed from a spray nozzle into the firing atmosphere of a combustion burner.

Any general firing furnace equipped with a combustion burner, such as an internal combustion rotary kiln or a vertical furnace that directly burns gas and / or liquid fuel with a burner as a heat source, can be used as the manufacturing equipment. be able to. When a rotary kiln is used, coarse particles adhered or agglomerated are discharged from the front of the kiln by rolling, so stable operation can be maintained. Further, the vertical furnace can be installed in a small space, is excellent in equipment cost, and can be easily operated and managed because a thermometer can be arranged in the furnace.

Any of gaseous fuels such as LPG, city gas, ammonia gas, and vaporized organic matter, and liquid fuels such as kerosene, light oil, heavy oil, and recycled oil can be used as the fuel.

The solution to be sprayed may be a raw material containing hollow particles, that is, an element that constitutes an oxide. For example, it is a compound that dissolves in a solvent such as water, and examples thereof include inorganic salts and metal alkoxides. More specifically, aluminum salts, titanium salts, magnesium salts, calcium salts, sodium salts, potassium salts, lithium salts, borates, phosphates, aluminosilicates, aluminum alkoxides, tetraethoxysilane, tetramethoxysilane, etc. silicic acid alkoxide and the like.
A solution of aluminum oxide or silicon oxide dispersed in a solvent, or a sol solution of aluminum oxide or silicon oxide can also be used as the raw material solution. Furthermore, raw materials of other elements can be added in order to adjust the melting temperature, heat resistance and particle strength.

Further, the oxides obtained from these raw material compounds include inorganic oxides such as metal oxides, alumina, silica, calcia, magnesia, oxides composed of aluminum and silicon, and more specifically, alumina , silica, oxides composed of aluminum and silicon, titanium oxide, magnesium oxide, calcium oxide, sodium oxide, potassium oxide, lithium oxide, boron oxide, phosphorus oxide, zirconium oxide, barium oxide , cerium oxide, yttrium oxide, etc., and composite oxides in which these oxides are combined.
Solvents for dissolving or dispersing the raw materials of the elements constituting these oxides include water and organic solvents, but water is preferable from the viewpoint of environmental impact and production costs. or alkali may be added. Examples of acids that can be used include hydrochloric acid, nitric acid, sulfuric acid, and organic acids. Examples of alkalis that can be used include sodium hydroxide, calcium hydroxide, potassium hydroxide, and the like.

The solution is supplied to the spray nozzle via a general pump such as a mono pump, tube pump, diaphragm pump, etc., and sprayed into the pyrolysis furnace.
A two-fluid nozzle or a four-fluid nozzle is used to atomize the solution into droplets with compressed air.
Two-fluid and four-fluid nozzle systems include an internal mixing system in which air and the solution are mixed inside the nozzle and an external mixing system in which air and the solution are mixed outside the nozzle. Available.
In addition to the spray nozzle for the solution, for the purpose of protecting the solution atomized from the spray nozzle from the flame of the fuel burner, compressed air or compressed water is used as a carrier to wrap the mist sprayed from the outer periphery of the spray nozzle. , and it is convenient to use compressed air of 0.1 to 1.0 MPa for these. Furthermore, it is preferable to insert them as a swirling flow because the effect is high.
As for the amount of carrier to be inserted, it is preferable to use the same amount of compressed air as the amount of primary air for the two-fluid nozzle or four-fluid nozzle, and the amount of compressed water to be the same as the amount of solution inserted, but the present invention is not limited to this.

In the present invention, the atomized mist is passed through the vicinity of the combustion burner where it does not come into direct contact with the flame. Means for preventing the spray mist from coming into direct contact with the flame of the combustion burner include, for example, means for passing the spray mist over the flame of the combustion burner as shown in FIG. At this time, the outer edge of the spray mist and the outer edge of the flame should be kept from contact, and the distance between the outer edge of the spray mist and the outer edge of the flame is preferably 1 mm or more and 500 mm or less, and 5 mm or more and 300 mm or less. and more preferably 10 mm or more and 200 mm or less.

As a means for preventing the spray mist from directly contacting the flame of the combustion burner, it is also preferable to spray the raw material solution so that an air shield is formed at least around the spray mist that contacts the flame (Fig. 3). Specifically, it is preferable to double the spray nozzles as shown in FIG. 9, and to spray compressed air or compressed water so as to wrap the mist sprayed from the periphery of the spray nozzles as shown in FIG. At this time, as shown in FIG. 9, the spray nozzle is preferably a double nozzle in which the compressed air forms a swirling flow. At this time, the thickness of the air shield layer formed around the spray mist is preferably 0.1 mm or more and 300 mm or less, more preferably 0.5 mm or more and 100 mm or less, and even more preferably 1.0 mm or more and 50 mm or less.

According to the method of the present invention, since the spray mist does not come into direct contact with the flame of the combustion burner, the spray droplets are thermally decomposed after drying. That is, the sprayed droplets are dried to form a film of the inorganic compound, and the internal liquid is dried starting from the film, so that the particles become hollow. Then, a thermal decomposition reaction occurs at a high temperature, so that by strengthening the hollow structure, hollow particles having a shell defining a hollow chamber and having a uniform shell thickness can be obtained.

Since the hollow particles obtained by the present invention have a hollow shape, the particle density is as small as 0.1 to 1.0 g/cm ³ , preferably 0.3 to 0.8 g/cm ³ . The particle density can be measured by the gas replacement method of JIS R 1620 "Method for measuring particle density of fine ceramic powder".

The hollow particles obtained by the present invention have an average particle diameter of 1 to 100 μm, and can be fine particles having an average particle diameter of 1 to 50 μm, and can also be fine particles having an average particle diameter of 1 to 30 μm. can.

Hollow particles obtained by the present invention may be subjected to particle size adjustment by sieving, gravity, inertia, centrifugation, wind classifiers, and the like, and dry or wet classifiers can be used. Also, the specific gravity may be adjusted using a specific gravity separator or the like.

EXAMPLES Next, the present invention will be described in more detail with reference to examples. In the examples, the temperature inside the furnace was measured with a K thermocouple. Also, the particle density was measured with an Accupic. The particle size distribution was measured by Microtrac (laser diffraction scattering method).
(1) Production conditions To 100 L of ion-exchanged water, 1992 g of tetraethyl orthosilicate, 131 g of aluminum nitrate nonahydrate, 455 g of magnesium nitrate hexahydrate, 516 g of calcium nitrate tetrahydrate, 1666 g of sodium tetraborate decahydrate, 1 L of concentrated nitric acid was put into a rotary kiln or a solution tank of a vertical gas furnace and stirred. The injected aqueous solution is sprayed into a rotary kiln (Φ350 x 4000) or a vertical gas furnace (Φ1000 x 3000) in a mist form through a two-fluid nozzle by a liquid feed pump, and the amount of fuel burned is adjusted to reach the target temperature. Hollow particles prepared and synthesized were recovered with a bag filter.

(2) Conditions of Examples and Comparative Examples Example 1
The furnace temperature was set to 900° C., and the spray mist was adjusted to pass over the flame as shown in FIG. A SEM image of the hollow particles obtained in Example 1 is shown in FIG.

Example 2
The temperature inside the furnace was set to 950°C, and as shown in Fig. 3, two spray nozzles (the double nozzles in Fig. 9 form a swirl flow shield of compressed air around the mist), and the mist was sprayed over the top of the flame. sprayed.

A SEM image of the hollow particles obtained in Example 2 is shown in FIG.

Comparative example 1
The furnace temperature was set to 900° C., and atomized mist was sprayed to the center of the flame as shown in FIG. A SEM image of the particles obtained in Comparative Example 1 is shown in FIG.

Comparative example 2
The temperature inside the furnace was set to 950° C., and the spray mist was sprayed so that it was in direct contact with the upper part of the flame as shown in FIG. A SEM image of the particles obtained in Comparative Example 2 is shown in FIG.

Table 1 shows the properties of the particles obtained in Examples 1 and 2 and Comparative Examples 1 and 2.

The particle density of Comparative Example 1 is 2.50 g/cm ³ , which is equivalent to the theoretical density. Therefore, considering the SEM image of FIG. 6, all the particles are considered to be solid particles.
Further, in order to determine the proportion of solid particles in Comparative Example 2, gravity separation was performed with water to determine the proportion. As a result, the mixing rate of solid particles in Comparative Example 2 was 25%. Also, the SEM image in FIG. 8 indicates a mixture of solid particles and hollow particles.

The particles obtained in Examples 1 and 2 were uniform and fine hollow particles, as shown in FIGS. 2 and 4 and Table 1.

Claims (4)

A method for producing hollow particles in which a raw material solution is sprayed into a pyrolysis furnace and thermally decomposed by a combustion burner provided in the pyrolysis furnace, wherein the spray mist is passed through the vicinity of the combustion burner where it does not come into direct contact with the flame. A method for producing hollow particles characterized by
A means for preventing the spray mist from directly contacting the flame of the combustion burner is a double nozzle having an inner two-fluid nozzle and an outer nozzle, and sprays compressed air from the outer nozzle and from the inner two-fluid nozzle. A method for producing hollow particles, which is a means for forming an air shield with a thickness of 1.0 mm or more and 50 mm or less around the atomized mist by enveloping the atomized mist with compressed air. 2. The method for producing hollow particles according to claim 1, wherein the spray nozzle is a double nozzle in which the compressed air forms a swirling flow . 3. The method for producing hollow particles according to claim 1, wherein the resulting hollow particles have a particle density of 0.1 to 1.0 g/cm ³ . The method for producing hollow particles according to any one of claims 1 to 3, wherein the resulting hollow particles have an average particle size of 1 to 100 µm.

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