Method for producing inorganic oxide particles

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

[Technical field]

[0001] The present invention relates to a method for producing inorganic oxide particles. [Background technology]

[0002] A spray pyrolysis method using a spray pyrolysis device is known as a method for producing inorganic oxide particles. In the spray pyrolysis method using a spray pyrolysis device, for example, droplets of a raw material solution are sprayed from the spray device into a pyrolysis furnace of the spray pyrolysis device equipped with a spray device for spraying droplets of a raw material solution and a combustion burner for generating combustion gas, and the droplets are thermally decomposed using the combustion gas from the combustion burner as a heat source to produce inorganic oxide particles (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-84355 A [Patent Document 2] Special Publication No. 2020-514223 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the inventors have found through their investigations that when inorganic oxide particles are continuously produced by the spray pyrolysis method using a spray pyrolysis apparatus, there is a problem in that the variation in particle density and average particle size of the inorganic oxide particles produced increases as time passes from the start of spraying. An object of the present invention is to provide a method for producing inorganic oxide particles that can suppress fluctuations over time in particle density and average particle size and maintain a constant quality. [Means for solving the problem]

[0005] The present inventors have conducted various studies to determine the causes of such fluctuations in particle density and average particle size over time, and have found the following: When inorganic oxide particles are continuously produced by the spray pyrolysis method using a spray pyrolysis device, the pyrolysis furnace accumulates heat over time and the temperature inside the furnace rises, so the combustion burner is controlled to maintain the temperature inside the furnace constant, and the amount of burning of the combustion burner is reduced. As a result, the amount of combustion gas from the combustion burner decreases, and the gas flow rate inside the furnace decreases, so the residence time of the droplets in the furnace becomes longer and temperature unevenness occurs inside the furnace, so that the particle density and average particle size of the inorganic oxide particles produced over time vary more. Based on this knowledge, the inventors have examined in detail the production conditions in the spray pyrolysis method and found that by setting a control value for the gas flow rate in the pyrolysis furnace and, if a discrepancy occurs between this control value and the actual measured value, supplying gas into the pyrolysis furnace so that the gas flow rate is within the allowable range of the control value to control it to be approximately constant, thereby suppressing fluctuations in particle density and average particle size over time and enabling the stable production of inorganic oxide particles with a consistent quality.

[0006] That is, the present invention provides the following [1] to [4]. [1] A method for producing inorganic oxide particles, comprising a step of pyrolyzing droplets of a raw material solution sprayed into a pyrolysis furnace of a spray pyrolysis apparatus equipped with one or more combustion burners by a combustion gas of the combustion burner, measuring a gas flow rate in the pyrolysis furnace, and when the actual measured value of the gas flow rate exceeds a tolerance range of the control value, supplying gas into the pyrolysis furnace to adjust the gas flow rate so that the gas flow rate falls within the tolerance range of the control value; 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 a pyrolysis furnace one hour after the start of spraying. [3] The method for producing inorganic oxide particles according to [1] or [2] above, wherein the supply gas is one or more selected from air, an inert gas, and a gas discharged outside a pyrolysis furnace. [4] The method for producing inorganic oxide particles according to any one of the above [1] to [3], wherein the temperature of the supply gas is adjusted so that the temperature difference with the gas in the pyrolysis furnace is within 900°C. Effect of the Invention

[0007] According to the present invention, it is possible to stably produce inorganic oxide particles with a constant quality, in which the fluctuation over time of the particle density and the average particle size is suppressed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an example of a spray pyrolysis apparatus applicable to the production method of the present invention. [Diagram 2] FIG. 1 is a schematic diagram showing an example of a spray pyrolysis apparatus applicable to the production method of the present invention. [Diagram 3] FIG. 1 is a schematic diagram showing an example of a spray pyrolysis apparatus applicable to the production method of the present invention. [Figure 4] FIG. 1 is a schematic diagram showing an example of a spray pyrolysis apparatus applicable to the production method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The method for producing inorganic oxide particles of the present invention will be described below. The method for producing inorganic oxide particles of the present invention includes a step of pyrolyzing droplets (mist) of a raw material solution sprayed into a pyrolysis furnace of a spray pyrolysis apparatus equipped with one or more combustion burners by combustion gas from the combustion burner. The present invention is characterized in that the gas flow rate in the pyrolysis furnace is measured, and when the actual value of the gas flow rate obtained exceeds the allowable range of the control value, gas is supplied into the pyrolysis furnace to adjust the gas flow rate so that it falls within the allowable range of the control value. Here, in this specification, "within the allowable range of the control value" means that the fluctuation range of the control value is within ±15%, and the fluctuation range is preferably within ±10%.

[0010] In the continuous production of inorganic oxide particles by the spray pyrolysis method using a spray pyrolysis device, it is necessary to ensure a certain level of quality. To achieve this, it is essential to maintain the pyrolysis reaction under constant conditions. However, when inorganic oxide particles are continuously produced, the pyrolysis furnace accumulates heat over time, causing the temperature inside the furnace to rise, and the combustion burner is controlled to reduce the amount of combustion gas fired by the combustion burner, which in turn reduces the amount of combustion gas in the combustion burner and decreases the gas flow rate inside the furnace. As a result, the residence time of the droplets in the furnace becomes longer than at the beginning of production, and temperature unevenness occurs inside the furnace, resulting in greater variation in particle density and average particle size. Therefore, in the present invention, the gas flow rate in the pyrolysis furnace is controlled so that it is always approximately constant. That is, a control value is set in advance for the gas flow rate in the pyrolysis furnace, and when the actual value of the gas flow rate exceeds the allowable range of the control value, gas is supplied into the furnace so that the gas flow rate is within the allowable range of the control value to maintain the gas flow rate approximately constant. This keeps the residence time of the droplets in the furnace approximately constant and also suppresses temperature unevenness in the furnace, thereby suppressing fluctuations in particle density and average particle size over time and enabling the stable production of inorganic oxide particles with a constant quality.

[0011] The control value is not particularly limited as long as it can maintain the quality of the particle density and average particle size of the inorganic oxide particles produced, but can be set, for example, based on the gas flow rate in the furnace one hour after the start of spraying of the raw material solution.

[0012] Hereinafter, preferred embodiments of the method for producing inorganic oxide particles of the present invention will be described with reference to the drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated descriptions will be omitted. In addition, for convenience of illustration, the dimensional ratios of the drawings do not necessarily match those in the description.

[0013] 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 are provided below the pyrolysis furnace 1 with a spray device 3 for spraying droplets 2 of the raw material solution into the pyrolysis furnace 1, and a combustion burner 4 for pyrolyzing the droplets 2 with combustion gas. The spray pyrolysis devices 30, 40 are constructed by connecting a pyrolysis furnace 1 consisting of a vertical tube and a combustion furnace consisting of a horizontal tube, and the vertical tube is equipped with a spray device 3 for spraying droplets 2 of the raw material solution into the pyrolysis furnace 1, and the horizontal tube is equipped with a combustion burner 4 for pyrolyzing the droplets 2 with combustion gas. The horizontal and vertical tubes are connected with their base axes offset so that the hot air flowing from the combustion burner 4 to the pyrolysis furnace 1 generates a swirling flow at the connecting part.

[0014] The pyrolysis furnace may be made of any material that is used as a furnace material, and may be selected taking into consideration the heating temperature, etc. Generally, firebricks, insulating bricks, castables, etc. are used on the inner wall of the metal shell, either alone or in layers, or in combination. The pyrolysis furnace is preferably in the shape of a vertical cylinder, since this allows a swirling flow to be generated within the pyrolysis furnace. The size of the pyrolysis furnace can be appropriately selected depending on the production scale. For example, when it is a vertical cylindrical furnace, the inner diameter is preferably 600 to 1600 mm, and the height is preferably 3000 to 10000 mm.

[0015] The spray device may be, for example, a fluid nozzle. Examples of the fluid nozzle include a one-fluid nozzle, a two-fluid nozzle, a three-fluid nozzle, and a four-fluid nozzle. Among these, the two-fluid nozzle, the three-fluid nozzle, and the four-fluid nozzle are preferred.

[0016] The fluid nozzle type includes an internal mixing type in which the gas and the raw material solution are mixed inside the nozzle, and an external mixing type in which the gas and the raw material solution are mixed outside the nozzle, and either type can be adopted. The gas supplied to the nozzle can be, for example, air, or an inert gas such as nitrogen or argon. Among them, air is preferable from the viewpoint of economy.

[0017] The flow rate of the gas supplied to the nozzle is preferably 1000 times or more by volume relative to the amount of the raw material solution fed to the nozzle. The upper limit of the gas flow rate is preferably 3000 times or less, more preferably 2500 times or less, from the viewpoints of preventing solidification at the nozzle tip and promoting solvent evaporation from the droplets and deposition of inorganic salts.

[0018] The temperature of the gas supplied to the nozzle is preferably equal to or lower than the temperature of the droplets immediately after ejection, and more preferably equal to or lower than room temperature (20±15° C.). From the viewpoint of ease of temperature control, the lower limit of the gas temperature is preferably equal to or higher than 1° C., more preferably equal to or higher than 5° C., and even more preferably equal to or higher than 10° C.

[0019] The spray device may be installed at the center or end of the pyrolysis furnace, or above or below the pyrolysis furnace. However, from the viewpoint of preventing the occurrence of materials adhering to the pyrolysis furnace wall and allowing the pyrolysis reaction to proceed sufficiently, it is preferable to install the spray device at approximately the center below the pyrolysis furnace, as shown in Figures 1 to 4. One or more spray devices may be installed. When two or more spray devices are installed, they may be spaced at approximately the same interval or at different intervals.

[0020] Any combustion burner that is commercially available can be used. The appropriate type of combustion burner should be selected taking into consideration the volume and specifications of the pyrolysis furnace. It is also possible to manufacture a burner according to the specifications of the pyrolysis furnace.

[0021] 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 mixed and burned. Examples of gaseous fuels include LPG, city gas, and vaporized organic matter. Examples of liquid fuels include liquefied organic matter such as kerosene, light oil, heavy oil, and recycled oil. Examples of solid fuels include powdered coal, charcoal, and wood.

[0022] The combustion burner may be installed so that the droplets ride on the flow of the combustion gas toward the outlet of the pyrolysis furnace as shown in Figures 1 and 2, or may be installed offset from the central axis of the pyrolysis furnace as shown in Figure 3. When the combustion burner is installed offset from the central axis of the pyrolysis furnace, a swirling flow advances from the bottom to the top of the pyrolysis furnace, so that the droplets can be raised while swirling due to the swirling flow.

[0023] In addition, it is preferable to install the combustion burner so that the flame of the combustion burner does not directly contact the droplets. To achieve this, the combustion burner is installed so that the flame does not enter the pyrolysis furnace, for example, by providing a mechanism for moving the combustion burner in the forward and backward directions and adjusting it as necessary.

[0024] 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 a "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 constituting an oxide and dissolves in a solvent such as water, and may contain one or more of inorganic salts, organic salts, and alkoxides. Examples of inorganic salts include nitrates, sulfates, carbonates, hydroxides, and halides. Examples of organic salts include formates, acetates, propionates, oxalates, and citrates.

[0025] Specific examples of the raw material compounds include aluminum salts, titanium salts, magnesium salts, calcium salts, borates, zinc salts, zirconium salts, barium salts, cesium salts, yttrium salts, aluminosilicates, aluminum alkoxides, and silicate alkoxides. 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-butylate and aluminum isopropylate. Examples of silicate alkoxides include tetraethoxysilane and tetramethoxysilane. In addition, a solution in which aluminum oxide or silicon oxide is dispersed in a solvent, or a sol solution of aluminum oxide or silicon oxide can also be used as the raw material solution. Furthermore, in order to adjust the melting temperature, heat resistance, and particle strength, raw materials of other elements can also be added. Note that one or more raw material compounds can be used. Among them, one or more raw material compounds selected from aluminum salts, titanium salts, magnesium salts, aluminosilicates, aluminum alkoxides, and silicate alkoxides are preferable.

[0026] Examples of inorganic oxides obtained from raw material compounds include metal oxides, oxides of alumina, silica, aluminum, and silicon. More specifically, examples include oxides of alumina, silica, aluminum, and silicon, titanium oxide, magnesium oxide, zinc oxide, zirconium oxide, barium oxide, cerium oxide, yttrium oxide, etc., and also include composite oxides that combine these oxides.

[0027] The raw material solution may be prepared by mixing the raw material compounds with a solvent. Examples of the solvent include water and organic solvents. Among them, water is preferred from the viewpoints of environmental impact and production costs. The method for mixing the raw material compound and the solvent is not particularly limited; both may be added at the same time and mixed, or one may be added to the other and mixed.

[0028] The concentration of the raw material compound in the raw material solution is preferably from 0.01 mol / L to the saturated concentration, more preferably from 0.1 to 1.0 mol / L, taking into consideration the particle size distribution, density, strength, etc. of the resulting inorganic oxide particles.

[0029] The temperature of the droplets immediately after spraying is 1 / 2 or less of the boiling point of the solvent in the raw solution, and can be appropriately set depending on the type of solvent in the raw solution. For example, when the raw solution is an aqueous solution, the temperature is preferably 1 to 50°C, more preferably 5 to 40°C, and even more preferably 10 to 40°C. The temperature of the droplets immediately after spraying can be controlled by installing a thermocouple at the tip of the nozzle so that it comes into contact with the droplets sprayed from the nozzle. The thermocouple is preferably installed within 5 cm from the tip of the nozzle. In order to adjust the temperature of the raw solution in the nozzle, the outer periphery of the nozzle may be covered with a heat insulating material. Examples of the heat insulating material include ceramic fiber, glass fiber, and castable.

[0030] The average particle size of the droplets is preferably 0.5 to 60 μm, more preferably 1.0 to 20 μm, and even more preferably 1.0 to 15 μm. The average particle size of the droplets can be adjusted by the shape of the nozzle spray opening and the air pressure.

[0031] The temperature in the pyrolysis furnace is preferably 400 to 1800° C., more preferably 600 to 1500° C., further preferably 700 to 1400° C., and even further preferably 900 to 1200° C. If the temperature is less than 400° C., the pyrolysis reaction is likely to be insufficient, and if the temperature exceeds 1800° C., the particles are difficult to cool sufficiently when discharged out of the pyrolysis furnace, and the particles are likely to aggregate with each other.

[0032] The droplets of the raw material solution sprayed from the spraying device are caught in the flow of combustion gas generated by the combustion burner, and the solvent evaporates from the droplets, quickly drying them, and inorganic salts are precipitated. The inorganic salts are then thermally decomposed to produce inorganic oxide particles. However, when inorganic oxide particles are continuously produced, the pyrolysis furnace accumulates heat over time, the temperature inside the furnace rises, the amount of heat of the combustion burner is controlled, and the amount of combustion gas decreases. As a result, the gas flow rate inside the furnace decreases, the residence time of the droplets in the furnace increases, and temperature unevenness occurs inside the furnace. Therefore, it is difficult to maintain a constant quality of the inorganic oxide particles over a long period of time. Therefore, in this embodiment, in order to suppress a decrease in the gas flow rate inside the furnace, keep the residence time of the droplets inside the furnace constant, and suppress temperature unevenness inside the furnace, the gas flow rate inside the pyrolysis furnace is measured, and if the actual measured value of the gas flow rate obtained exceeds the allowable range of the control value, gas is supplied into the pyrolysis furnace to adjust the gas flow rate so that it falls within the allowable range of the control value.

[0033] In the spray pyrolysis devices 10, 20, 30, and 40, a gas flow meter probe insertion port 6 for measuring the gas flow velocity in the pyrolysis furnace 1 and a thermometer 7 for measuring the temperature inside the pyrolysis furnace 1 are installed above the pyrolysis furnace 1. Note that a gas analyzer may be installed instead of the gas flow meter, and the gas flow velocity may be obtained by calculating the gas flow rate from the oxygen amount in the exhaust gas.

[0034] 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, and more preferably 6 to 15 m / s. If the gas flow velocity is less than 4 m / s, it is difficult to generate a sufficient swirling flow in the furnace, and if it exceeds 20 m / s, the residence time of the droplets in the pyrolysis furnace is shortened, so that not only is the pyrolysis reaction insufficient, but the droplets are also agitated and tend to adhere to the wall of the pyrolysis furnace.

[0035] The gas to be supplied is not particularly limited as long as it does not inhibit the pyrolysis reaction, and examples thereof include air, inert gas, and gas discharged outside the pyrolysis furnace, and one or more of these may be used. Note that the gas discharged outside the pyrolysis furnace preferably has an oxygen ratio of 5 volume % or more.

[0036] The spray pyrolysis device 10 is provided with a gas supply pipe 5a for supplying gas into the pyrolysis furnace 1, and gas is supplied from a gas discharge port 5b at the end of the pipe toward the tip of the flame of the combustion burner 4. As a result, the gas discharged from the end 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 rate can be controlled to be approximately constant. Note that a blower, compressor, etc. may be appropriately selected depending on the amount of gas to be supplied.

[0037] In addition, the spray pyrolysis devices 20, 30, and 40 are embedded in the refractory material of the pyrolysis furnace 1 with the gas supply pipe 5a wound concentrically around the combustion burner 4, and four gas outlets 5b are provided at the tip of the gas supply pipe 5a. By winding the gas supply pipe 5a concentrically around the combustion burner 4 in this way, not only can the gas flow rate be controlled to be approximately constant, but the gas in the gas supply pipe is heated by the heat of the pyrolysis furnace 1 stored by the combustion burner 4, and the temperature difference with the gas in the pyrolysis furnace can be reduced, so that the thermal shock to the pyrolysis furnace is suppressed. As a result, cracking of the refractory material of the pyrolysis furnace can be suppressed. From this viewpoint, 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 the thermal shock to the combustion tube. In addition, the spray pyrolysis device 40 is provided with an exhaust gas circulation line 9 above the pyrolysis furnace 1 for circulating the exhaust gas discharged from the pyrolysis furnace 1 into the pyrolysis furnace 1, and the circulation line 9 is connected to the gas supply pipe 5a via a blower 10, so that high-temperature exhaust gas can be supplied from the gas outlet 5b into the pyrolysis furnace 1. This not only further reduces the temperature difference with the gas inside the pyrolysis furnace, but also reduces the amount of fuel used by the combustion burner, thereby reducing running costs.

[0038] It is preferable to provide two or more gas discharge ports 5b at the tip of the gas supply pipe 5a, so that the gas can be dispersed and introduced into the pyrolysis furnace, which reduces thermal shock to the pyrolysis furnace and makes the temperature distribution in the pyrolysis furnace uniform. In addition, it is preferable that the gas discharge port 5b at the tip of the gas supply pipe 5a is oriented perpendicular to the flame of the combustion burner, so that the discharged gas collides with the flame of the combustion burner and is sufficiently diffused, thereby suppressing thermal shock to the pyrolysis furnace.

[0039] In this embodiment, the gas flow rate in the furnace one hour after the start of spraying is set as the control value. The allowable range of the control value is within a fluctuation range of ±15%, and preferably within a fluctuation range of ±10%. One hour after the start of spraying, the pyrolysis furnace does not accumulate excessive heat and the quality of the inorganic oxide particles produced is maintained constant. Therefore, by setting the gas flow rate inside the furnace one hour after the start of spraying as a control value and using this as an indicator, it is possible to suppress variation in the quality of the inorganic oxide particles produced thereafter.

[0040] After the control value is set, the gas flow rate inside the furnace is measured at regular intervals. As time passes, the amount of combustion burner heating changes in conjunction with the temperature inside the furnace, and the gas flow rate inside the furnace decreases, so for example, the gas flow rate inside the furnace is measured every hour from the start of spraying, and when the actual gas flow rate exceeds the allowable range of the control value, gas is supplied from a gas supply pipe installed inside the furnace to adjust it so that it falls within the allowable range of the control value. The gas supply may be controlled manually or automatically.

[0041] The gas flow rate in the furnace one hour after the start of spraying can be calculated by the following formula (1).

[0042] Gas flow rate (m / s) = X / Y (1)

[0043] [In formula (1), X is the amount of gas in the furnace (m 3 / s), and Y is the cross-sectional area of ​​the furnace (m 2 ) is shown.

[0044] The amount of gas X in the furnace can be calculated by the following formula (2).

[0045] Amount of gas in the furnace = P × Q × R × S (2)

[0046] In formula (2), P is the amount of fuel (m 3 / s), Q is the air ratio, and R is the theoretical combustion gas volume. [ (m 3 / s) / (m 3 / s)] and S represents the volume expansion coefficient.

[0047] Here, "fuel volume (m 3 / s) is the amount of gaseous fuel, and the "air ratio" is the ratio between the theoretical amount of air and the amount of air actually supplied, which is usually 1.4. [ (m 3 / s) / (m 3 / s)] " is the amount of gas that is generated when the fuel is given a theoretical amount of air and completely combusted, and can be calculated from the fuel composition. Furthermore, "volume expansion coefficient" is the ratio between the target gas temperature and the gas temperature under standard conditions, and can be calculated from the furnace temperature (K) measured by a thermocouple installed in the furnace.

[0048] In addition, since the gas flow rate in the pyrolysis furnace depends on the amount of fuel burned by the combustion burner, the amount of gas supplied to the pyrolysis furnace may be adjusted in accordance with the amount of reduction in the amount of fuel burned. The gas is preferably supplied into the pyrolysis furnace so that the ratio (B / A) of the amount of combustion gas from the combustion burner, A, and the amount of gas supplied, B, is 0.5 or less, more preferably 0.4 or less, and even more preferably 0.3 or less.

[0049] In this embodiment, the gas flow rate in the pyrolysis furnace is maintained substantially constant in this manner, so that the residence time of the droplets in the furnace is maintained substantially constant, and temperature unevenness in the furnace can be suppressed. As a result, the fluctuation of the particle density and the average particle size over time is suppressed, and inorganic oxide particles of stable quality can be obtained.

[0050] The inorganic oxide particles produced by the pyrolysis reaction are collected by a powder recovery device installed downstream of the spray pyrolysis device. The inorganic oxide particles produced by the pyrolysis reaction may be further heated as necessary to melt the particle surfaces, and then collected by the powder recovery device. Examples of the powder recovery device include a cyclone powder recovery machine and a bag filter. When recovering the oxide hollow particles, the particle size can be adjusted by passing the particles through a filter. In addition, a dust removal and purification device such as a scrubber may be installed downstream of the powder recovery device as necessary.

[0051] 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, in this specification, "solid particles" refers to particles with a structure that does not have a cavity inside, and examples thereof include particles consisting of a single layer and particles having a core (also called an inner core) and a shell layer (also called an outer shell). Furthermore, "hollow particles" refers to particles with a structure having a cavity (hollow part) inside and having a cavity surrounded by an outer shell. The number of cavities may be single or multiple. Furthermore, "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 holes are not particularly limited. Furthermore, the particles may have closed pores inside.

[0052] Inorganic oxide particles can be produced in this manner. 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, and more preferably 0.5 to 10 μm. The average particle size can be adjusted by adjusting the shape of the outlet of the fluid nozzle used for spraying and the pressure of the compressed air. Here, in this specification, the "average particle size" means the particle size (d50) corresponding to 50% of the cumulative distribution curve when the particle size distribution of the sample is prepared on a volume basis in accordance with JIS R 1629. For example, a Microtrac (manufactured by Nikkiso Co., Ltd.) can be used as a particle size distribution measuring device.

[0053] The particle density of inorganic oxide particles is usually 0.1 to 2.5 g / cm 3 and preferably 0.2 to 1.0 g / cm 3 and more preferably 0.3 to 0.6 g / cm 3 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

[0054] The embodiments of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0055] 1. Measurement of Particle Density The density was measured by a constant volume expansion method using a dry automatic density meter (AccuPic 1340, manufactured by Shimadzu Corporation). That is, after placing the sample in a cell, the cell was filled with an inert gas and the volume of the sample was measured, and the particle density was calculated from this volume and the sample mass measured in advance.

[0056] 2. Measurement of average particle size A Microtrac (manufactured by Nikkiso Co., Ltd.) was used as a particle size distribution measuring device to create a volumetric particle size distribution in accordance with JIS R 1629, and the particle diameter (d 50 ) was sought.

[0057] 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 5955g of magnesium acetate in 300L of ion-exchanged water. This aqueous solution was sprayed using a three-fluid nozzle into a pyrolysis furnace whose internal temperature was controlled at 1150°C by the combustion gas from a combustion burner, and the droplets were raised while being swirled by the swirling flow of the combustion gas, passed through the pyrolysis furnace and pyrolyzed, and magnesium oxide hollow particles were collected using a bag filter. One hour after the start of spraying, the amount of combustion gas from the combustion burner and the gas flow rate at the pyrolysis furnace outlet were measured, and the gas flow rate at this time was set to a control value. Two hours after the start of spraying, the amount of combustion gas from the combustion burner and the gas flow rate at the pyrolysis furnace outlet were measured, and 170°C air was blown into the pyrolysis furnace from the gas outlet of the gas supply pipe for 20 m so that the gas flow rate at the pyrolysis furnace outlet was within the range of ±10% of the control value. 3 It was supplied at N / h. The amount of combustion gas from the combustion burner and the gas flow rate at the pyrolysis furnace outlet were measured every hour from the start of spraying until 6 hours had elapsed, and the amount of air shown in Table 1 was supplied into the pyrolysis furnace so that the gas flow rate at the pyrolysis furnace outlet was within the range of ±10% of the control value. Note that the combustion burner was controlled to the amount of combustion shown in Table 2 in order to maintain the pyrolysis temperature at a constant 1150°C every hour from the start of spraying until 6 hours had elapsed. The particle density and average particle size of the collected hollow particles were analyzed every hour from the start of spraying until 6 hours had elapsed. The results are shown in Table 1. In addition, the maximum fluctuation value of the gas flow velocity at the pyrolysis furnace outlet measured from the start of spraying until 6 hours had elapsed, and the maximum fluctuation value of the particle properties from the start of spraying until 6 hours had elapsed are shown in Table 3.

[0058] [Table 1]

[0059] Example 2 Magnesium oxide hollow particles were produced in the same manner 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 using the spray pyrolysis apparatus shown in Fig. 4. Note that in order to maintain the pyrolysis temperature constant at 1150°C every hour for 6 hours after the start of spraying, the combustion burner was controlled to the amount of heat shown in Table 2. Then, the maximum fluctuation value of the gas flow velocity at the pyrolysis furnace outlet measured for 6 hours after the start of spraying and the maximum fluctuation value of the particle properties for 6 hours after the start of spraying were analyzed in the same manner as in Example 1. The results are shown in Table 3.

[0060] Comparative Example 1 Except for not supplying air into the pyrolysis furnace, magnesium oxide hollow particles were produced in the same manner as in Example 1. 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 properties up to 6 hours after the start of spraying were analyzed in the same manner as in Example 1. The results are shown in Table 3.

[0061] [Table 2]

[0062] [Table 3]

[0063] In Comparative Example 1, the gas flow rate in the pyrolysis furnace was not adjusted, so the gas flow rate fluctuated significantly over time from the start of spraying, and inorganic oxide hollow particles with large variations in particle density and average particle size were produced. In contrast, in Examples 1 and 2, the gas flow rate in the pyrolysis furnace was controlled so as to be within the allowable range of the control value from the start of spraying, so that inorganic oxide particles of consistent quality were produced with small variations in particle density and average particle size. [Explanation of symbols]

[0064] 1 Pyrolysis furnace 2. Droplets (mist) 3 Spray device 4 Combustion burner 5a Gas supply pipe 5b Gas outlet 6 Gas flow meter probe insertion port 7 Thermometer 8 Exhaust gas recirculation line 9 Blower 10 Spray pyrolysis equipment 20 Spray pyrolysis equipment 30 Spray pyrolysis equipment 40 Spray pyrolysis equipment

Claims

1. A method for producing inorganic oxide particles, comprising a step of pyrolyzing droplets of a raw material solution sprayed into a pyrolysis furnace of a spray pyrolysis apparatus equipped with one or more combustion burners, by a combustion gas of the combustion burner, a gas flow rate at the outlet of the pyrolysis furnace is measured, and when the actual measured value of the gas flow rate exceeds a tolerance range of a control value set based on the gas flow rate at the outlet of the pyrolysis furnace one hour after the start of spraying, a gas is supplied into the pyrolysis furnace to adjust the gas flow rate so that the gas flow rate falls within the tolerance range of the control value; A method for producing inorganic oxide particles.

2. A method for producing inorganic oxide particles as described in claim 1, wherein the gas supplied when adjusting the gas flow rate is one or more selected from air, an inert gas, and a gas discharged outside the pyrolysis furnace.

3. A method for producing inorganic oxide particles as described in claim 1 or 2, wherein the temperature of the gas supplied when adjusting the gas flow rate is adjusted so that the temperature difference with the gas in the pyrolysis furnace is within 900°C.

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