JP2022134979A - Method for producing inorganic oxide particles - Google Patents

Abstract

To provide a method for producing inorganic oxide particles that enables the particles to maintain a constant quality by suppressing variations with time in particle density and average particle diameter.SOLUTION: A method for producing inorganic oxide particles comprises a step of thermally decomposing droplets of a raw material solution sprayed into a pyrolysis furnace of a spray pyrolysis device equipped with one or more combustion burners by combustion gas of the combustion burners. When a gas flow rate in the pyrolysis furnace is measured and the measured value of the gas flow rate exceeds an allowable range of a control value, the gas flow rate is adjusted by supplying the gas into the pyrolysis furnace so as to fall within the allowable range of the control value.SELECTED DRAWING: None

Description

The present invention relates to a method for producing inorganic oxide particles.

A spray pyrolysis method using a spray pyrolysis apparatus is known as a method for producing inorganic oxide particles. In the spray pyrolysis method using a spray pyrolysis apparatus, for example, in the pyrolysis furnace of the spray pyrolysis apparatus equipped with a spray device for spraying droplets of the raw material solution and a combustion burner for generating combustion gas Inorganic oxide particles are produced by spraying droplets of a raw material solution from an atomizing device and thermally decomposing the droplets using combustion gas from a combustion burner as a heat source (Patent Documents 1 and 2).

JP 2007-84355 A Japanese Patent Publication No. 2020-514223

However, according to studies by the present inventors, when inorganic oxide particles are continuously produced by a spray pyrolysis method using a spray pyrolysis apparatus, the number of produced inorganic oxide particles decreases as time passes from the start of spraying. It has been found that there is a problem of increased variability in particle density and average particle size.
An object of the present invention is to provide a method for producing inorganic oxide particles capable of suppressing temporal fluctuations in particle density and average particle size and maintaining constant quality.

The inventors of the present invention conducted various studies to clarify the factors behind the temporal variations in particle density and average particle size, and obtained the following findings. That is, when inorganic oxide particles are continuously produced by a spray pyrolysis method using a spray pyrolysis apparatus, heat is accumulated in the pyrolysis furnace over time and the temperature inside the furnace rises, so the temperature inside the furnace is kept constant. Combustion burners are controlled to maintain and the amount of firing of the stoking burners is reduced. As a result, the amount of combustion gas from the combustion burner decreases and the gas flow rate in the furnace decreases, which increases the retention time of droplets in the furnace and causes temperature variations in the furnace. Variation in particle density and average particle size of the produced inorganic oxide particles increases. Based on these findings, the inventors of the present invention examined the production conditions in the spray pyrolysis method in detail, and found that a control value was set for the gas flow rate in the pyrolysis furnace, and there was a discrepancy between the control value and the measured value. In the case, by supplying gas into the pyrolysis furnace so that it is within the allowable range of the control value and controlling the gas flow rate to be substantially constant, changes in the particle density and average particle size over time are suppressed, and a constant It was found that inorganic oxide particles with maintained quality can be stably produced.

That is, the present invention provides the following [1] to [4].
[1] A method for producing inorganic oxide particles, which includes a step of thermally decomposing droplets of a raw material solution sprayed into a pyrolysis furnace of a spray pyrolysis apparatus equipped with one or more combustion burners with combustion gas of a combustion burner. There is
Measure the gas flow rate in the pyrolysis furnace, and if the actual measured value of the acquired gas flow rate exceeds the allowable range of the control value, supply gas to the pyrolysis furnace so that it is within the allowable range of the control value. to adjust the gas flow rate,
A method for producing inorganic oxide particles.
[2] The method for producing inorganic oxide particles according to [1] above, wherein the control value is the gas flow rate in the pyrolysis furnace 1 hour after the start of spraying.
[3] The method for producing inorganic oxide particles according to [1] or [2] above, wherein the supplied gas is one or more selected from air, an inert gas, and a gas discharged outside the pyrolysis furnace. .
[4] The inorganic oxide particles according to any one of [1] to [3], wherein the temperature of the supplied gas is adjusted so that the temperature difference from the gas in the pyrolysis furnace is within 900 ° C. Production method.

EFFECTS OF THE INVENTION According to the present invention, it is possible to stably produce inorganic oxide particles in which the particle density and average particle size are suppressed from fluctuating over time and a constant quality is maintained.

It is a schematic diagram showing an example of a spray pyrolysis apparatus applicable to the production method of the present invention. It is a schematic diagram showing an example of a spray pyrolysis apparatus applicable to the production method of the present invention. It is a schematic diagram showing an example of a spray pyrolysis apparatus applicable to the production method of the present invention. It is a schematic diagram showing an example of a spray pyrolysis apparatus applicable to the production method of the present invention.

The method for producing inorganic oxide particles of the present invention will be described below.
In the method for producing inorganic oxide particles of the present invention, droplets (mist) of a raw material solution sprayed into a pyrolysis furnace of a spray pyrolysis apparatus equipped with one or more combustion burners are thermally decomposed by combustion gas of the combustion burner. It includes the step of Then, in the present invention, the gas flow rate in the pyrolysis furnace is measured, and when the obtained measured value of the gas flow rate exceeds the allowable range of the control value, the pyrolysis is performed so that it is within the allowable range of the control value. It is characterized by supplying gas into the furnace and adjusting the gas flow rate. Here, in this specification, "within the allowable range of the control value" means that the fluctuation range with respect to the control value is within a range of ± 15%, and the fluctuation range is preferably within a range of ± 10% be.

When continuously producing inorganic oxide particles by a spray pyrolysis method using a spray pyrolysis apparatus, it is necessary to ensure a certain level of quality. For this purpose, it is essential to maintain the thermal decomposition reaction under constant conditions. However, when inorganic oxide particles are continuously produced, heat is accumulated in the pyrolysis furnace over time and the temperature inside the furnace rises, so the combustion burner is controlled and the burning amount of the combustion burner decreases. The amount of combustion gas in the combustion burner is reduced, and the gas flow velocity in the furnace is lowered. As a result, the residence time of the droplets in the furnace becomes longer than in the initial stage of production, and temperature variations occur in the furnace, resulting in large variations in particle density and average particle diameter.
Therefore, in the present invention, the gas flow rate in the pyrolysis furnace is controlled so that it is always substantially constant. That is, a control value is set in advance for the gas flow rate in the pyrolysis furnace, and when the measured value of the gas flow rate exceeds the allowable range of the control value, the gas is supplied into the furnace so that it is within the allowable range of the control value. to keep the gas flow velocity substantially constant. As a result, the residence time of the droplets in the furnace is kept almost constant, and the temperature unevenness in the furnace can be suppressed. It is possible to stably produce the inorganic oxide particles that have been processed.

The control value is not particularly limited as long as the quality of the particle density and average particle size of the inorganic oxide particles to be produced can be maintained. can be set.

Preferred embodiments of the method for producing inorganic oxide particles of the present invention are described below with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions are omitted. Also, for convenience of illustration, the dimensional ratios in the drawings do not necessarily match those in the description.

1 to 4 show an example of a spray pyrolysis apparatus applicable to the method for producing inorganic oxide particles of the present invention.
The spray pyrolysis apparatuses 10 and 20 include, below the pyrolysis furnace 1, a spray device 3 for spraying droplets 2 of the raw material solution into the pyrolysis furnace 1, and a spray device 3 for thermally decomposing the droplets 2 with combustion gas. of combustion burner 4 is installed.
The spray pyrolysis apparatuses 30 and 40 are configured by connecting a pyrolysis furnace 1 consisting of a vertical tube and a combustion furnace consisting of a horizontal tube. A spraying device 3 for spraying droplets 2 is installed, and a combustion burner 4 for pyrolyzing the droplets 2 with combustion gas is installed in the horizontal tube. The horizontal pipe and the vertical pipe are connected with their base axes shifted so that the hot air flowing from the combustion burner 4 to the pyrolysis furnace 1 generates a swirling flow at the connecting portion.

Any material can be used for the pyrolysis furnace as long as it is made of a material that is used as a furnace material. Moreover, it is common to use refractory bricks, heat-insulating bricks, castables, etc. singly, in layers, or in combination for the inner wall of the metal shell.
The shape of the pyrolysis furnace is preferably a rigid cylindrical shape in that a swirling flow can be generated in the pyrolysis furnace.
The size of the pyrolysis furnace can be appropriately selected according to the production scale. 10000 mm.

The spraying device may include, for example, a fluid nozzle. Fluid nozzles include, for example, one-fluid nozzles, two-fluid nozzles, three-fluid nozzles, and four-fluid nozzles. Among them, a two-fluid nozzle, a three-fluid nozzle, and a four-fluid nozzle are preferable.

Fluid nozzle systems include an internal mixing system in which the gas and the raw material solution are mixed inside the nozzle and an external mixing system in which the gas and the raw material solution are mixed outside the nozzle, and both can be employed. As the gas supplied to the nozzle, for example, air, inert gas such as nitrogen or argon, or the like can be used. Among them, air is preferable from the viewpoint of economy.

The flow rate of the gas supplied to the nozzle is preferably 1000 times or more by volume the amount of the raw material solution sent to the nozzle. The upper limit of the gas flow rate is preferably 3,000 times or less, more preferably 2,500 times or less, from the viewpoints of preventing solidification at the tip of the nozzle, evaporating the solvent of droplets, and promoting inorganic salt precipitation.

The temperature of the gas supplied to the nozzle is preferably equal to or lower than the droplet temperature immediately after ejection, and more preferably normal temperature (20±15° C.) or lower. The lower limit of the gas temperature is preferably 1° C. or higher, more preferably 5° C. or higher, and even more preferably 10° C. or higher, in terms of ease of temperature control.

The installation position of the spray device may be in the center or at the end of the pyrolysis furnace, and may be either above or below the pyrolysis furnace. From the viewpoint of allowing the thermal decomposition reaction to proceed sufficiently, it is preferable to install the thermal decomposition furnace approximately in the center below the thermal decomposition furnace, as shown in FIGS. One or two or more spray devices can be installed. When two or more spray devices are installed, the intervals may be substantially the same or different.

Any commercially available combustion burner can be used. Considering the volume, specifications, etc. of the pyrolysis furnace, a combustion burner of the appropriate type should be selected. Also, it may be manufactured according to the specifications of the pyrolysis furnace.

The fuel used in the combustion burner is not particularly limited, and examples thereof include gaseous fuel, liquid fuel, and solid fuel, and two or more of these fuels may be co-fired. Gaseous fuels include, for example, LPG, city gas, and vaporized organic matter. Examples of liquid fuels include liquefied organic substances such as kerosene, light oil, heavy oil, and recycled oil. Examples of solid fuels include powdered coal, charcoal, wood, and the like.

1 and 2, the combustion burner can be set so that droplets ride on the flow of combustion gas and advance in the direction of the outlet of the pyrolysis furnace. It may be installed offset from the central axis of the cracking furnace. When the combustion burner is installed offset from the central axis of the pyrolysis furnace, the swirl flow advances upward from the bottom of the pyrolysis furnace, so the droplets can be swirled and lifted by the swirl flow.

Also, the combustion burner is preferably installed so that the flame of the combustion burner does not come into direct contact with the droplets. In order to do this, it is sufficient to install the combustion burner so that the flame of the combustion burner does not enter the pyrolysis furnace.

In this embodiment, first, the raw material solution is sprayed from the spray device into the pyrolysis furnace.
The raw material solution is a solution of a compound (hereinafter also referred to as "raw material compound") containing an element that constitutes an oxide.
The raw material compound is not particularly limited as long as it contains an element that constitutes an oxide and is soluble in a solvent such as water. Examples include inorganic salts, organic salts, and alkoxides. can do. Inorganic salts include, for example, nitrates, sulfates, carbonates, hydroxides, and halides. Organic salts include, for example, formates, acetates, propionates, oxalates, and citrates.

Specific examples of raw material compounds include aluminum salts, titanium salts, magnesium salts, calcium salts, borate salts, zinc salts, zirconium salts, barium salts, cesium salts, yttrium salts, aluminosilicates, aluminum alkoxides, and silicic acid. Alkoxide etc. are mentioned. Examples of aluminum salts include inorganic salts such as aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum phosphate, aluminum hydroxide, aluminum acetate and aluminum oxalate. Examples of aluminum alkoxides include aluminum sec-butyrate, aluminum isopropylate. Silicic acid alkoxides include tetraethoxysilane, tetramethoxysilane, 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. One or two or more raw material compounds can be used. Among them, one or two or more selected from aluminum salts, titanium salts, magnesium salts, aluminosilicates, aluminum alkoxides and silicate alkoxides are preferable as the raw material compound.

Inorganic oxides obtained from raw material compounds include, for example, oxides composed of metal oxides, alumina, silica, aluminum and silicon. More specifically, alumina, silica, oxides composed of aluminum and silicon, titanium oxides, magnesium oxides, zinc oxides, zirconium oxides, barium oxides, cerium oxides, yttrium oxides, etc. Composite oxides obtained by combining these oxides are also included.

A raw material solution may be prepared by mixing a raw material compound and a solvent. Solvents include water and organic solvents. Among them, water is preferable from the viewpoint of environmental impact and production cost.
The method of mixing the raw material compound and the solvent is not particularly limited, and the two may be added at the same time and mixed, or the other may be added to the other and mixed.

The concentration of the raw material compound in the raw material solution is preferably 0.01 mol/L to saturated concentration, and more preferably 0.1 to 1.0 mol/L, in consideration of the particle size distribution, density, strength, etc. of the resulting inorganic oxide particles. preferable.

The droplet temperature immediately after spraying is a temperature not higher than 1/2 of the boiling point of the solvent in the raw material solution, and can be appropriately set according to the type of solvent in the raw material solution. For example, when the raw material solution is an aqueous solution, the temperature is preferably 1 to 50°C, more preferably 5 to 40°C, and still more preferably 10 to 40°C. Note that the temperature control of the droplets immediately after being ejected can be performed by installing a thermocouple at the tip of the nozzle so as to come into contact with the droplets ejected from the nozzle. It is preferable that the thermocouple is installed within 5 cm from the tip of the nozzle. Moreover, in order to adjust the temperature of the raw material solution in the nozzle, the outer circumference of the nozzle may be covered with a heat insulating material. Examples of heat insulating materials include ceramic fibers, glass fibers, castables, and the like.

The average particle size of the droplets is preferably 0.5 to 60 μm, more preferably 1.0 to 20 μm, even more preferably 1.0 to 15 μm. It should be noted that the average particle size of the droplets can be adjusted by adjusting the shape of the nozzle spray port and the air pressure.

The temperature in the pyrolysis furnace is preferably 400-1800°C, more preferably 600-1500°C, even more preferably 700-1400°C, and even more preferably 900-1200°C. When it is less than 400°C, the thermal decomposition reaction tends to be insufficient, and when it exceeds 1800°C, it is difficult to sufficiently cool the particles when discharged from the thermal decomposition furnace, and the particles tend to agglomerate.

The droplets of the raw material solution sprayed from the spraying device are caught in the flow of the combustion gas generated by the combustion burner, the solvent evaporates from the droplets, the droplets quickly dry, the inorganic salt precipitates, and the inorganic salt is heated. It decomposes to produce inorganic oxide particles. However, when inorganic oxide particles are continuously produced, heat is accumulated in the pyrolysis furnace over time and the temperature inside the furnace rises. As a result, the liquid droplets remain in the furnace for a longer time, and the temperature becomes uneven in the furnace. Therefore, it is difficult to keep the quality of the inorganic oxide particles constant over a long period of time.
Therefore, in the present embodiment, in order to suppress the decrease in the gas flow rate in the furnace, to keep the residence time of droplets in the furnace constant, and to suppress the temperature unevenness in the furnace, Measure the gas flow velocity, and if the actual measured value of the acquired gas flow velocity exceeds the allowable range of the control value, adjust the gas flow velocity by supplying gas into the pyrolysis furnace so that it is within the allowable range of the control value. I do.

The spray pyrolysis apparatuses 10, 20, 30, and 40 are provided above the pyrolysis furnace 1 with a gas flow meter probe insertion port 6 for measuring the gas flow rate of the pyrolysis furnace 1 and the temperature inside the pyrolysis furnace 1. A thermometer 7 is installed for the measurement. A gas analyzer may be installed in place of the gas flow rate meter, and the gas flow rate may be calculated from the amount of oxygen in the exhaust gas to determine the gas flow rate.

The gas flow velocity in the pyrolysis furnace varies depending on the size of the pyrolysis furnace, but is usually 4 to 20 m/s, preferably 6 to 18 m/s, more preferably 6 to 15 m/s. be. If the gas flow rate is less than 4 m/s, it is difficult to generate a sufficient swirl flow in the furnace, and if it exceeds 20 m/s, the residence time of droplets in the pyrolysis furnace becomes short, resulting in insufficient pyrolysis reaction. In addition, droplets are fanned and easily adhere to the wall surface of the pyrolysis furnace.

The gas to be supplied is not particularly limited as long as it does not inhibit the thermal decomposition reaction. can. It is preferable that the gas discharged out of the pyrolysis furnace has an oxygen content of 5% by volume or more.

The spray pyrolysis apparatus 10 is provided with a gas supply pipe 5a for supplying gas into the pyrolysis furnace 1, and the gas is supplied from a gas discharge port 5b at the tip of the pipe toward the tip of the flame of the combustion burner 4. be done. As a result, the gas discharged from the tip of the gas supply pipe rises in the furnace together with the combustion gas of the combustion burner while being heated by the flame of the combustion burner, so that the gas flow velocity can be controlled to be substantially constant. A blower, a compressor, or the like may be appropriately selected according to the amount of gas to be supplied.

The spray pyrolysis apparatuses 20, 30, and 40 are embedded in the refractory material of the pyrolysis furnace 1 with the gas supply pipe 5a concentrically wound around the combustion burner 4. The gas supply pipe Four gas discharge ports 5b are provided at the tip of 5a. By winding the gas supply pipe 5a concentrically around the combustion burner 4 in this way, not only can the gas flow velocity be controlled to be substantially constant, but also the heat of the pyrolysis furnace 1 accumulated by the combustion burner 4 can be used to supply the gas. Since the gas inside the tube is heated and the temperature difference with the gas inside the pyrolysis furnace can be reduced, the thermal shock to the pyrolysis furnace can be suppressed. As a result, cracking or the like of the refractory material of the pyrolysis furnace can be suppressed. From this point of view, the temperature difference between the gas in the pyrolysis furnace and the gas to be supplied is preferably within 900° C., more preferably 500 to 900° C., from the viewpoint of suppressing thermal shock to the combustion tube. The spray pyrolysis apparatus 40 is provided above the pyrolysis furnace 1 with an exhaust gas circulation line 9 for circulating the exhaust gas discharged from the pyrolysis furnace 1 into the pyrolysis furnace 1. The circulation line 9 is Since it is connected to the gas supply pipe 5a through the blower 10, high-temperature exhaust gas can be supplied into the pyrolysis furnace 1 from the gas outlet 5b. As a result, not only can the temperature difference from the gas in the pyrolysis furnace be further suppressed, but also the amount of burning of the combustion burner can be suppressed, so that the running cost can be reduced.

It is preferable to provide two or more gas discharge ports 5b at the tip of the gas supply pipe 5a. As a result, the gas can be dispersedly introduced into the pyrolysis furnace, so that the thermal shock to the pyrolysis furnace can be suppressed and the temperature distribution in the pyrolysis furnace can be made uniform.
Moreover, it is preferable that the gas discharge port 5b at the tip of the gas supply pipe 5a is directed perpendicularly to the flame of the combustion burner. As a result, the discharged gas collides with the flame of the combustion burner and is sufficiently diffused, so that thermal shock to the pyrolysis furnace can be suppressed.

In this embodiment, the control value is the gas flow rate in the furnace one hour after the start of spraying. The allowable range of the control value is within ±15% of the control value, and preferably within ±10% of the control value.
After 1 hour from the start of spraying, the pyrolysis furnace does not accumulate excessive heat, and the quality of the inorganic oxide particles produced is kept constant. is set as a control value and used as an index, it is possible to suppress variations in the quality of the inorganic oxide particles that are subsequently produced.

After setting the control value, the gas flow rate in the furnace is measured at regular intervals.
With the passage of time, the firing rate of the combustion burner changes in conjunction with the furnace temperature, and the gas flow rate in the furnace decreases. When the actual measured value of exceeds the allowable range of the control value, gas may be supplied from a gas supply pipe provided in the furnace to adjust the value so that it falls within the allowable range of the control value. The gas supply may be controlled manually or automatically.

The gas flow rate in the furnace one hour after the start of spraying can be calculated by the following formula (1).

Gas flow velocity (m/s) = X/Y (1)

[In formula (1), X indicates the gas volume (m ³ /s) in the furnace, and Y indicates the cross-sectional area (m ² ) of the furnace. ]

Incidentally, the gas amount X in the furnace can be calculated by the following formula (2).

Amount of gas in furnace = P x Q x R x S (2)

[In the formula (2), P indicates a burning amount (m ³ /s), Q indicates an air ratio, R indicates a theoretical combustion gas amount (m ³ /s), and S indicates a volumetric expansion rate. ]

Here, the "heating amount (m ³ /s)" is the amount of gaseous fuel, and the "air ratio" is the ratio of the theoretical air amount to the actually supplied air amount, which is normally 1.4. The "theoretical combustion gas amount (m ³ /s)" is the amount of gas produced when the fuel is completely combusted with the theoretical amount of air, and can be calculated from the fuel composition. Furthermore, the “volumetric expansion coefficient” is the ratio between the target gas temperature and the gas temperature in the standard state, and can be obtained from the furnace temperature (K) measured by a thermocouple installed in the furnace.

Further, since the gas flow rate in the pyrolysis furnace depends on the firing rate of the combustion burner, the amount of gas supplied to the pyrolysis furnace may be adjusted in accordance with the decrease in the firing rate.
Gas is supplied into the pyrolysis furnace so that the ratio (B/A) of the two is 0.5 or less, where A is the combustion gas amount of the combustion burner and B is the gas supply amount. is preferred, more preferably 0.4 or less, and still more preferably 0.3 or less.

In this embodiment, since the gas flow rate in the pyrolysis furnace is kept substantially constant in this way, the residence time of droplets in the furnace is maintained substantially constant, and the temperature unevenness in the furnace is suppressed. be able to. As a result, temporal fluctuations in particle density and average particle size are suppressed, and inorganic oxide particles with constant quality and stable quality can be obtained.

The inorganic oxide particles produced by the pyrolysis reaction are recovered by a powder recovery device installed after the spray pyrolysis device. The inorganic oxide particles produced by the thermal decomposition reaction may be recovered by a powder recovery device after performing a melting step of further heating to melt the particle surfaces, if necessary.
Examples of the powder recovery device include a cyclone powder recovery machine and a bag filter. In recovering the oxide hollow particles, the particle size can be adjusted by passing through a filter. Further, dust removal and purification equipment such as a scrubber may be arranged downstream of the powder recovery device, if necessary.

The inorganic oxide particles produced by the method of the present invention may be solid particles, porous particles, hollow particles, or a mixture of two or more of these. Here, the term "solid particle" as used herein refers to a particle having a structure that does not have a cavity inside, for example, a particle consisting of a single layer, and a core (also referred to as an inner core) and a shell layer. Particles having a (also called shell) can be mentioned. A "hollow particle" is a particle having a structure having a cavity (hollow portion) inside and having a cavity surrounded by an outer shell. The number of cavities may be singular or plural. Furthermore, the term “porous particles” refers to particles having a large number of through holes connected from the particle surface to the inside. The size and shape of the through-hole are not particularly limited. Also, the particles may have closed pores inside.

Inorganic oxide particles can be produced in this way, and the inorganic oxide particles produced by the method of the present invention can have, for example, the following properties.
The average particle size of the inorganic oxide hollow particles is usually 0.5 to 50 μm, preferably 0.5 to 20 μm, more preferably 0.5 to 10 μm. The average particle diameter can be adjusted by adjusting the outlet shape of the fluid nozzle used for spraying and the pressure of the compressed air. Here, the "average particle size" as used herein means a particle size (d50) corresponding to 50% of the cumulative distribution curve when the particle size distribution of the sample is created on a volume basis in accordance with JIS R 1629. do. As a particle size distribution measuring device, for example, Microtrac (manufactured by Nikkiso Co., Ltd.) can be used.

The particle density of the inorganic oxide particles is usually 0.1-2.5 g/cm ³ , preferably 0.2-1.0 g/cm ³ , more preferably 0.3-0.6 g/cm 3 . is ³ . In addition, the particle density can be measured by a gas replacement method in accordance with JIS R 1620. As a particle density measuring device, for example, a dry automatic density meter “Accupic (manufactured by Shimadzu Corporation)” can be used.

EXAMPLES The embodiments of the present invention will now be described more specifically with reference to Examples. However, the present invention is not limited to the following examples.

1. Measurement of Particle Density Measured by the constant volume expansion method using a dry automatic densitometer (Accupic 1340, manufactured by Shimadzu Corporation). That is, after putting a sample into the cell, the cell was filled with an inert gas, the volume of the sample was measured, and the particle density was obtained from this volume and the sample mass previously measured.

2. Measurement of average particle size Microtrac (manufactured by Nikkiso Co., Ltd.) is used as a particle size distribution measuring device to create a volume-based particle size distribution in accordance with JIS R 1629, and the particle size corresponding to 50% of the cumulative distribution curve. ( _d50 ) was determined.

Example 1
Using the spray pyrolysis apparatus shown in FIG. 3, magnesium oxide hollow particles were produced by the following method.
A magnesium acetate aqueous solution was prepared by dissolving 5955 g of magnesium acetate in 300 liters of ion-exchanged water. This aqueous solution is sprayed using a three-fluid nozzle into a pyrolysis furnace whose internal temperature is controlled at 1150 ° C. by the combustion gas of the combustion burner, and the droplets are swirled and raised by the swirling flow of the combustion gas. and thermally decomposed, and magnesium oxide hollow particles were recovered using a bag filter. One hour after the start of spraying, the amount of combustion gas in the combustion burner and the gas flow rate at the outlet of the pyrolysis furnace were measured, and the gas flow rate at this time was set as a control value.
After 2 hours from the start of spraying, measure the combustion gas amount of the combustion burner and the gas flow rate at the outlet of the pyrolysis furnace, and adjust the gas supply pipe so that the gas flow rate at the outlet of the pyrolysis furnace is within ± 10% of the control value. 170° C. air was supplied at 20 m ³ N/h into the pyrolysis furnace from the gas outlet of .
The amount of combustion gas from the combustion burner and the gas flow rate at the outlet of the pyrolysis furnace are measured every hour until 6 hours have elapsed since the start of spraying, and the gas flow rate at the outlet of the pyrolysis furnace is within ±10% of the control value. The amount of air shown in Table 1 was supplied into the pyrolysis furnace as described above. In order to keep the thermal decomposition temperature constant at 1150° C. every hour from the start of spraying until 6 hours have passed, the combustion burner was controlled at the heating rate shown in Table 2.
The particle density and average particle diameter of the collected hollow particles were analyzed every hour from the start of spraying until 6 hours had passed. Table 1 shows the results. Table 3 shows the maximum variation in the gas flow velocity at the outlet of the pyrolysis furnace measured up to 6 hours after the start of spraying and the maximum variation in the physical properties of the particles up to 6 hours after the start of spraying.

Example 2
Using the spray pyrolysis apparatus shown in FIG. 4, magnesium oxide hollow particles were produced by the same operation as in Example 1, except that air at 500 ° C. was supplied into the pyrolysis furnace from the gas outlet of the gas supply pipe. did. In order to keep the thermal decomposition temperature constant at 1150° C. every hour from the start of spraying until 6 hours have passed, the combustion burner was controlled at the heating rate shown in Table 2. Then, the maximum fluctuation value of the gas flow velocity at the outlet of the pyrolysis furnace measured up to 6 hours after the start of spraying and the maximum fluctuation value of the particle physical properties up to 6 hours after the start of spraying were analyzed in the same manner as in Example 1. did. Table 3 shows the results.

Comparative example 1
Magnesium oxide hollow particles were produced in the same manner as in Example 1, except that air was not supplied into the pyrolysis furnace. Then, the maximum fluctuation value of the gas flow velocity at the outlet of the pyrolysis furnace measured up to 6 hours after the start of spraying and the maximum fluctuation value of the particle physical properties up to 6 hours after the start of spraying were analyzed in the same manner as in Example 1. did. Table 3 shows the results.

In Comparative Example 1, since the gas flow rate in the pyrolysis furnace was not adjusted, the gas flow rate fluctuated greatly over time from the start of spraying, and inorganic oxide hollow particles with large variations in particle density and average particle size were produced. was done.
On the other hand, in Examples 1 and 2, the gas flow rate in the pyrolysis furnace was controlled to be within the allowable range of the control value from the start of spraying, so the particle density and average particle size were small, and the quality was uniform. of inorganic oxide particles were produced.

1 pyrolysis furnace 2 droplets (mist)
3 spray device 4 combustion burner 5a gas supply pipe 5b gas discharge port 6 gas current meter probe insertion port 7 thermometer 8 exhaust gas circulation line 9 blower 10 spray pyrolysis device 20 spray pyrolysis device 30 spray pyrolysis device 40 spray pyrolysis Device

Claims (4)

A method for producing inorganic oxide particles, comprising the step of thermally decomposing droplets of a raw material solution sprayed into a pyrolysis furnace of a spray pyrolysis apparatus equipped with one or more combustion burners with combustion gas of a combustion burner,
Measure the gas flow rate in the pyrolysis furnace, and if the actual measured value of the acquired gas flow rate exceeds the allowable range of the control value, supply gas to the pyrolysis furnace so that it is within the allowable range of the control value. to adjust the gas flow rate,
A method for producing inorganic oxide particles. 2. The method for producing inorganic oxide particles according to claim 1, wherein the control value is the gas flow rate in the pyrolysis furnace after 1 hour from the start of spraying. 3. The method for producing inorganic oxide particles according to claim 1, wherein the supplied gas is one or more selected from air, an inert gas and a gas discharged outside the pyrolysis furnace. The method for producing inorganic oxide particles according to any one of claims 1 to 3, wherein the temperature of the supplied gas is adjusted so that the temperature difference from the gas in the pyrolysis furnace is within 900°C.

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