JP5565833B2 - Method for producing aggregate particles - Google Patents

Description

  The present invention relates to a method for producing aggregate particles having an average particle diameter of micrometer order and a narrow particle size distribution, which are formed by aggregation of metal oxide, metal hydroxide or metal hydroxide nanoparticles. About. More specifically, the metal oxide, metal hydroxide, or metal hydroxide nanoparticles that can be used for ceramic raw materials and pigments, catalyst carriers and adsorbents, photocatalysts, energy device electrode materials, and the like are formed in an aggregate. The present invention relates to a method for producing aggregate particles, which can produce aggregate particles having an average particle diameter on the order of micrometers and having a narrow particle size distribution at a high speed and with little influence on the environment.

Conventionally, spray drying, ultrasonic spray drying, and the like have been used as methods for producing aggregate particles formed by aggregation of metal oxides, metal hydroxides, or metal hydroxide nanoparticles. Yes.
The spray drying method is a method in which a metal oxide, a metal hydroxide oxide, a metal hydroxide slurry, or the like is sprayed and dried in a high-temperature air stream, and the resulting aggregated particles are collected by a cyclone or a filter. In addition, the ultrasonic spray drying method atomizes (aerosols) a metal oxide, metal hydroxide or metal hydroxide slurry by ultrasonic irradiation, and then introduces this into a high-temperature air stream to dry. In this method, the resulting spherical aggregate particles are collected by a cyclone or a filter. Such a method for producing aggregate particles is simple and highly productive, and has a small influence on the environment, and is therefore used as a general industrial production technique.

On the other hand, as a method for producing aggregate particles having a narrow particle size distribution, a method is known in which droplets are generated by an ink jet nozzle and then dried (see Patent Documents 1 and 2). In this method, the particle size distribution of the droplets ejected from the inkjet nozzle is narrow and highly uniform, so the droplets are deposited on a substrate with a large water contact angle close to the nozzle, dried and collected, and the particle size is distributed. Aggregate particles with a narrow distribution can be obtained.
However, in such a method, not only the productivity is very bad, but depending on the distance between the inkjet nozzle and the substrate and the state of the airflow in the vicinity of the nozzle, the droplets come into contact with each other, and contact growth of the droplet particles occurs. In some cases, it is difficult to control the particle size distribution.

Furthermore, as a method for producing aggregate particles, a metal alkoxide is dissolved in a solvent composed of water and alcohol together with a cationic or nonionic surfactant, and an acid or the like is added in an emulsion such as water-alcohol to form the metal alkoxide. There is a method of producing nanoporous porous aggregate particles by hydrolyzing and volatilizing the solvent, and then baking to remove organic substances (see Patent Documents 3 and 4). According to such a method, it is possible to obtain porous aggregate particles having a narrow particle size distribution, but there is a problem in that it is necessary to remove the surfactant by baking or the like, which adversely affects the environment.
Therefore, the liquid mixture of the metal alkoxide and the organic solvent is hydrolyzed with water, and the reaction product is subjected to extraction treatment of organic components such as alcohol in the reaction product with subcritical or supercritical carbon dioxide. A manufacturing method has been proposed (see Patent Document 5). In this method, it is not necessary to burn off and remove the surfactant, but it is necessary to burn away the organic component such as alcohol derived from the metal alkoxide or the mixed solvent with the metal alkoxide, or to recover and treat the waste liquid. The problem of adversely affecting the environment remained.

JP 2005-213626 A JP 2008-15346 A JP 2003-335515 A JP 2003-335506 A JP 2006-290680 A

  In view of the above problems, the present inventors have formed a metal oxide, metal hydrated oxide, or metal hydroxide nanoparticles aggregated, have a narrow particle size distribution, excellent productivity, and environmental friendliness. As a result of diligent investigations on a new method for producing aggregate particles having a small influence, it is generally used on an industrial scale without using an emulsion using a surfactant and an organic solvent, and without using a metal alkoxide and an organic solvent. The present invention has found a method capable of producing aggregate particles that are as simple and excellent in productivity as those of conventional spray spray drying methods and have a narrow particle size distribution at a high speed and with little influence on the environment. It came to complete.

  Therefore, the present invention has an average particle size of micrometer order formed by aggregation of metal oxide, metal hydrated oxide or metal hydroxide nanoparticles, and has a narrow particle size distribution (particle size is uniform). It is an object of the present invention to provide a method for producing aggregate particles at high speed and with less environmental impact.

That is, the present invention
(1) A step of mixing a high density carbon dioxide and a metal oxide, a metal hydroxide, or an aqueous dispersion of metal hydroxide nanoparticles to form a mixture, and jetting the mixture from a nozzle A method for producing aggregate particles having an average particle diameter of 0.1 to 5 μm formed by aggregation of nanoparticles, the method comprising: obtaining ice droplet particles; and removing moisture from the ice droplet particles by drying ,
(2) Aggregate particles according to (1) above, wherein the high density carbon dioxide and the aqueous dispersion are put into a mixer and a high shear field having a Reynolds number of 8000 or more is formed to form the mixture. Manufacturing method,
(3) The method for producing aggregate particles according to (1) or (2), wherein the mixture is a mixture in which the aqueous dispersion is dispersed in an emulsion state in the high-density carbon dioxide,
(4) The above ice droplet particles are recovered in a solvent solution that is incompatible with water set to a temperature equal to or higher than the boiling point of water, and moisture is removed from the ice droplet particles by drying. A method for producing an aggregate particle according to any one of the above,
Is to provide.

  According to the present invention, metal oxide, metal hydrated oxide, or metal hydroxide nanoparticles are formed to have an average particle size on the order of micrometers and a narrow particle size distribution (the particle size is uniform). A) Aggregate particles can be produced at high speed and with less environmental impact.

It is a conceptual diagram of the apparatus for demonstrating the manufacturing method of the aggregate particle | grains of this invention.

  The method for producing aggregated particles of nanoparticles according to the present invention includes high-density carbon dioxide and metal oxide, metal hydroxide or metal hydroxide nanoparticles (hereinafter, simply referred to as “nanoparticles”). A step of forming a mixture by mixing with an aqueous dispersion of the above, a step of spraying the mixture from a nozzle to obtain ice droplet particles, and a step of removing moisture from the ice droplet particles by drying. This is a method for producing aggregate particles having an average particle diameter of 0.1 to 5 μm formed by aggregation of nanoparticles.

Hereinafter, the present invention will be described in more detail with reference to FIG.
FIG. 1 is a conceptual diagram of an apparatus for explaining a method for producing aggregate particles. In FIG. 1, 1 is carbon dioxide in a cylinder. 2 is a gas pressurizing pump for pressurizing carbon dioxide. 3 is a carbon dioxide temperature controller (heat exchanger). 4 is an aqueous dispersion of nanoparticles. 5 is a liquid pressurizing pump for pressurizing the aqueous dispersion of nanoparticles. 6 is an aqueous dispersion temperature controller (heat exchanger). 7 is a mixer for mixing carbon dioxide (high density carbon dioxide) and an aqueous dispersion. Reference numeral 8 denotes a pipe connected to the mixer 7, and the mixer 9 is constituted by the mixer 7 and the pipe 8. Reference numeral 10 denotes an injection nozzle, and a pipe 8 is connected to the opposite side of the nozzle injection port. Reference numeral 11 denotes ice droplet particles ejected from the ejection nozzle 10. Reference numeral 12 denotes an oil bath for collecting and drying the ice droplet particles 11. Moreover, PI and TI arrange | positioned at each place of FIG. 1 are a pressure gauge and a thermometer, respectively.

[First step]
The first step of the present invention is a step of forming a mixture by mixing high density carbon dioxide and an aqueous dispersion of metal oxide, metal hydroxide or metal hydroxide nanoparticles.
The high density carbon dioxide used in the present invention is supercritical carbon dioxide (carbon dioxide having a temperature and pressure condition of 31.1 ° C. or higher, 7.4 MPa or higher) and liquefied carbon dioxide (−56.6 ° C. or higher, It means a liquid phase generated under temperature and pressure conditions equal to or higher than the saturated vapor pressure at that temperature.
The density of the high-density carbon dioxide is preferably 0.85 to 0.98 g / cm ^{3, and} is preferably as high as the pressure resistance performance and temperature adjustment width of the apparatus allow.
The method for producing high-density carbon dioxide used in the present invention is not particularly limited, and known supercritical carbon dioxide and liquefied carbon dioxide production methods can be employed. For example, as shown in FIG. 1, carbon dioxide 1 in a cylinder is increased to a high pressure using a gas pressurizing pump 2, and further set to a target temperature using a temperature controller (heat exchanger (heating / cooling device) 3. Thus, high density carbon dioxide (liquefied carbon dioxide) can be obtained.

Further, the metal oxide, metal hydrated oxide or metal hydroxide nanoparticles used in the present invention are not particularly limited, and examples thereof include silicon oxide, aluminum oxide, zirconium oxide, titanium oxide, tin oxide, Metals containing amorphous or crystalline metal oxide nanoparticles such as iron oxide, yttrium oxide, zinc oxide, magnesium oxide, nickel oxide, or structural water such as hydrous silicon oxide, hydrous titanium oxide, hydrous zirconium oxide Hydrous oxide nanoparticles or metal hydroxide nanoparticles such as zirconium hydroxide, tin hydroxide, and aluminum hydroxide can be used.
In addition, since the present invention produces aggregated particles having an average particle size of the order of micrometers, the average particle size of the metal oxide, metal hydroxide or metal hydroxide nanoparticles is 100 nm or less. It is preferably 1 to 50 nm, more preferably 1 to 20 nm.
The method for producing nanoparticles is not particularly limited, and a known method for producing nanoparticles can be employed (see, for example, JP-A-2006-16236 and JP-A-4112250).

Moreover, the method for producing the aqueous dispersion of nanoparticles is not particularly limited, and an aqueous dispersion in which nanoparticles are dispersed can be produced by an ordinary method. For example, it can be prepared by adding nanoparticles to water and stirring. In addition, it is preferable to employ | adopt the well-known method for disperse | distributing a nanoparticle uniformly in an aqueous dispersion liquid, such as using an ultrasonic wave at the time of stirring.
Further, the water in which the nanoparticles are dispersed is separated from the isoelectric point of the nanoparticles by about ± 1 or more so that the state in which the nanoparticles are dispersed in water by the electrostatic repulsion between the nanoparticles can be maintained. It is preferable to adjust the pH. As the pH adjuster, acids such as hydrochloric acid, sulfuric acid and nitric acid which are usually used for pH adjustment, ammonia and the like can be used.
In order to prevent aggregation of the nanoparticles, the ratio of nanoparticles in the aqueous dispersion (solid content ratio) is preferably about 1 to 20% by mass. By adjusting the ratio of the nanoparticles (solid content ratio) and the pH of water within this range, precipitation due to aggregation of the nanoparticles is unlikely to occur, and an aqueous dispersion in which the nanoparticles are uniformly dispersed in the aqueous dispersion can be obtained.

In this first step, it is particularly important to form a mixture by mixing high density carbon dioxide and an aqueous dispersion of nanoparticles (hereinafter sometimes simply referred to as “aqueous dispersion”). Usually, high-density carbon dioxide and water are incompatible with each other, and since the difference in surface tension between the two is large, it is difficult to mix them. Therefore, high density carbon dioxide and aqueous dispersion are put in a mixer and mixed at high speed, and mixed in high density carbon dioxide as a W / C (Water in Carbon dioxide) emulsion in which the aqueous dispersion is dispersed in an emulsion state. It is preferable to form a body.
However, even in the emulsion formed in this way, as described above, carbon dioxide and water are not compatible with each other, and since the difference in surface tension between the two is large, the stability of the emulsion is low and the life is short. Become. Therefore, it is preferable to make the formed emulsion into a highly turbulent state to improve the stability of the emulsion and to prolong the life of the emulsion.

As a method for stabilizing the emulsion in a highly turbulent state, a method in which high-density carbon dioxide and an aqueous dispersion are put into a mixer and a high shear field having a Reynolds number of 8000 or more can be formed in the mixer. . In order to form a high shear field having a Reynolds number of 8000 or more in the mixer, the Reynolds number in the mixer is preferably 14,000 or more.
Specifically, using a T-shaped joint (for example, SS-1F0-3GC manufactured by Suediloc Co.) having a tube having an inner diameter of 0.3 to 0.5 mm as the mixer 7, the gas pressurizing pump 2 and the carbon dioxide temperature controller 3 are used. The high-density carbon dioxide produced by the above-described method flows into one inlet of the T-shaped joint of the mixer 7 at a predetermined amount and pressure, and the aqueous dispersion 4 is dispersed by the liquid pressurizing pump 5 and the dispersion liquid temperature controller 6. Into the other inlet of the T-joint of the mixer 7 with a predetermined amount and pressure, so that the high-density carbon dioxide and the aqueous dispersion collide and mix with each other. It is possible to adopt a method of forming an emulsion in the outflow pipe by introducing the high density carbon dioxide and the aqueous dispersion into the pipe) while mixing them.
For example, a T-shaped joint (SS-1F0-3GC manufactured by Suediloc Co., Ltd.) having a channel diameter of 0.3 mm is used for the mixer 7, and the supply temperature and supply pressure of the high-density carbon dioxide and the aqueous dispersion are 20 ° C. and 10 MPa, respectively. If the blending ratio (weight basis) of the high density carbon dioxide and the aqueous dispersion is 8: 2, the flow rate of the high density carbon dioxide is 60 to 100 ml / min, and the flow rate of the aqueous dispersion is 13 to 35 ml / min. It can be.

As shown in FIG. 1, a pipe 8 is connected to the mixer (T-shaped joint) 7, and the inner diameter of the pipe 8 and the volume flow rate of the mixture of high-density carbon dioxide and aqueous dispersion are adjusted. Thus, the Reynolds number in the mixer can be adjusted.
If the Reynolds number in the mixer is 8000 or more, a high shear field can be formed, whereby a turbulent state can be formed and maintained to stabilize the emulsion. The Reynolds number is preferably 10,000 or more, more preferably 12,000 or more. For example, when the Reynolds number is 8000 or more, the inner diameter of the pipe 8 is 0.5 mm, a T-shaped joint (mixer 7) having a flow path diameter of 0.3 mm is used, and the supply temperature of the high-density carbon dioxide and the aqueous dispersion is used. And a supply pressure of 20 ° C. and 10 MPa, respectively, and a mixing ratio (weight basis) of the high density carbon dioxide and the aqueous dispersion is 8: 2, the volume of the mixture of the high density carbon dioxide and the aqueous dispersion The flow rate may be 55 ml / min or more. When the Reynolds number is 10,000 or more, the volume flow rate of the mixture may be 65 ml / min or more. When the Reynolds number is 12000 or more, the volume flow rate of the mixture is What is necessary is just to be 70 ml / min or more.
Any mixer other than a T-shaped joint may be used as long as it can form a high shear field with a Reynolds number of 14,000 or more, and an industrial general-purpose mixer such as a static mixer, a micromixer (for example, manufactured by IMM) or the like is used. You can also

[Second step]
The second step of the present invention is a step of obtaining ice droplet particles by jetting a mixture of high-density carbon dioxide and an aqueous dispersion from a nozzle.
In this second step, a mixture (emulsion) of high-density carbon dioxide and an aqueous dispersion is jetted from a nozzle and rapidly decompressed and expanded to obtain ice droplet particles. When the mixture is ejected from the nozzle, the temperature of the decompressed and expanded mixture decreases due to the Joule-Thomson effect of carbon dioxide and adiabatic expansion, so that the water in the mixture freezes. On the other hand, carbon dioxide is vaporized and separated from the mixture. As a result, small ice droplet particles containing a plurality of nanoparticles are formed alone.

It is preferable that the blending ratio of the high density carbon dioxide and the aqueous dispersion for forming the ice droplet particles satisfies the relationship of the following formula (1) by calculation of the Joule-Thomson effect.
Weight of water in water dispersion / (mass of water in water dispersion + weight of high density carbon dioxide) × 100 ≦ 30 wt% (mass%) (1)

In addition, the particle diameter of the formed ice droplet particles is not particularly limited, but the particle diameter of the aggregate particles finally obtained (0.1 to 5 μm) because it shrinks to about 1/2 to 1/3 due to drying shrinkage. ), The average particle diameter is preferably in the range of 0.2 to 15 μm.
Ice droplet particles having such an average particle diameter can be adjusted by the spray pressure of the mixture. The injection pressure can be controlled by pressure loss due to the pressure of high-density carbon dioxide, the pressure of the aqueous dispersion, and the shape of the injection nozzle (injection nozzle length).
Although FIG. 1 shows the case where the injection pressure is adjusted by the pressure of high-density carbon dioxide, the pressure of the aqueous dispersion, and the shape of the injection nozzle, mixing is performed by providing a pressure adjustment valve in front of the injection nozzle 10. It is also possible to adjust the injection pressure of the body.

Moreover, the mixture injected from the nozzle becomes ice droplet particles due to a decrease in temperature and separation of carbon dioxide, but the ice droplet particles may collide with each other during spatial flow. In general, it is considered that the growth of droplet particles due to the collision of droplets is caused by the liquid crosslinking force between the droplets, and the liquid crosslinking force is expressed by the following equation (2).
^{_{Fc = [πr 2 2 σ (}} 1 / r 1 -1 / r 2) + 2πr 2 σ] (Dp / 2) ··· (2)
Where Fc is the liquid crosslinking force (N), σ is the surface tension (mN / m), Dp is the droplet diameter (μm), and r ₁ and r ₂ are the radius of curvature between droplets (μm).

That is, in the case of droplet particles, the surface tension is small, and when the diameter of the droplet particles is reduced, the liquid crosslinking force is reduced and the particle growth due to collision between the droplets is reduced, but when the solvent is water The surface tension is large, the growth of droplet particles is unavoidable, and the obtained aggregate particles have a wide particle size distribution.
On the other hand, in the case of ice droplet particles, there are aggregation or growth due to re-freezing due to inter-particle pressure melting at the time of collision and aggregation due to rearrangement of a water-like film on the surface of the ice droplet particles. Regarding the possibility of particle growth by pressure melting of ice droplet particles, for example, the melting pressure of ice at −5 ° C. is 560 atm, and it is considered that there is no growth by pressure melting under normal conditions. In other words, in the case of ice droplet particles, the aggregation of ice droplet particles occurs, but the particle growth like droplets hardly occurs.
Therefore, the ice droplet particles ejected from the nozzle flow spatially without growing, and are guided to the drying section.

The environment in which the mixture is injected may be in the atmosphere, but in consideration of the ease of vaporization of carbon dioxide, it is preferable to inject under reduced pressure.
Moreover, it is preferable to inject a mixture into a predetermined container from the ease of collection | recovery of ice droplet particle | grains. In FIG. 1, in order to collect the ice droplet particles 11 with the oil bath 12, a mixture (emulsion) of high-density carbon dioxide and an aqueous dispersion is jetted from the spray nozzle 10 toward the oil bath 12 to thereby drop the ice droplet particles 11. The state which forms is shown.

[Third step]
The third step of the present invention is a step of removing moisture from the ice droplet particles by drying.
In this step, it is necessary to remove moisture so that the ice droplet particles do not come into contact with each other during the drying. This is because, when the ice droplet particles come into contact with each other, the particle diameter of the obtained aggregate particles becomes large or the particle size distribution is widened, making it difficult to obtain highly uniform aggregate particles.
As a drying method, a solvent liquid in which ice droplet particles are not compatible with water is set to a temperature equal to or higher than the boiling point of water in advance, and the ice droplet particles are collected with this solvent solution to remove moisture from the ice droplet particles. As a method, it is possible to employ a method in which ice droplet particles are collected in an atmosphere of 0 ° C. or less and moisture is removed by lyophilization as it is. Furthermore, known drying methods such as vacuum drying, room temperature drying, heating drying with a heater set to a temperature equal to or higher than the boiling point of water, and heating airflow can also be employed.
In FIG. 1, the ice droplet particles 11 are collected by an oil bath 12 of a silicone oil (solvent liquid that is incompatible with water and water droplets) set at a temperature equal to or higher than the boiling point of water. The water is removed from 11.

Then, by passing through the first to third steps, the average particle diameter formed by aggregation of metal oxide, metal hydroxide or metal hydroxide nanoparticles is 0.1 to 5 μm, and the particle size distribution Aggregate particles having a narrow particle diameter (with uniform particle diameter) can be obtained.
The average particle size and particle size distribution of the aggregate particles can be measured with a laser diffraction particle size distribution measuring apparatus (for example, SALD-300V manufactured by Shimadzu Corporation).
For example, the average particle diameter is the particle diameter (D50) at the 50% particle number, and the particle size distribution is the ratio of the particle diameter (D60) at the 60% particle number to the particle diameter (D10) at the 10% particle number (D60 / D10) can be evaluated.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
In addition, the various characteristics in each example were measured according to the method shown below.
(1) Appearance shape of aggregate particles The appearance shape of the obtained aggregate particles was observed using a scanning electron microscope (JSM-6510, manufactured by JEOL Ltd.).
(2) Average particle diameter of aggregate particles The average particle diameter of aggregate particles was measured with a laser diffraction particle size distribution analyzer (SALD-300V manufactured by Shimadzu Corporation), and the particle diameter (D50) at 50% particle number did.
(3) Particle size distribution of aggregate particles The particle size distribution of aggregate particles was measured by a laser diffraction type particle size distribution measuring device (SALD-300V, manufactured by Shimadzu Corporation) in the same manner as in the case of the average particle size. The particle size (D60) at 10% and the particle size (D10) ratio at 10% number of particles (D60 / D10) were evaluated.

Example 1
Aggregate particles were produced using a production apparatus as shown in FIG.
A T-shaped joint (SS-1F0-3GC manufactured by Suedilock Co., Ltd.) having an inner diameter of φ0.3 mm is prepared as the mixer 7, and the pipe 8 is made of stainless steel having an inner diameter of 0.5 mm, an outer diameter of φ1.57 mm, and a length of 6 m (SUS316). Was prepared (GL Science Co., Ltd.), and the pipe 8 was connected to the outflow pipe of the T-shaped joint to obtain a mixer 9. Further, the pipe 8 of the mixer 9 and the injection nozzle 10 were connected.
In addition, a plunger pump (NP-KX-500 manufactured by Nippon Seimitsu Kagaku Co., Ltd.) with a maximum flow rate of 100 ml / min and a maximum pressure of 35 MPa is used as the gas pressurization pump 2, and a maximum flow rate of 50 ml / min, A plunger pump (100 syringe manufactured by ISCO) with a maximum pressure of 50 MPa was used.

As an aqueous dispersion, a nano zirconia particle dispersion (manufactured by Sumitomo Osaka Cement Co., Ltd., average primary particle diameter 3 nm, average dispersion particle diameter 9 nm, zirconia solid content ratio 10% by mass, pH 4) is used. did. This aqueous dispersion 4 was immersed in a thermostatic bath to a temperature of 20 ° C.
Furthermore, high-density carbon dioxide (liquefied carbon dioxide) was obtained by increasing the pressure of carbon dioxide 1 in the cylinder using a gas pressurizing pump 2 and a carbon dioxide temperature controller 3.
Then, the pressure of the high density carbon dioxide is adjusted by the gas pressurizing pump 2 and the carbon dioxide temperature controller 3 to a predetermined pressure (P2), and the pressure of the aqueous dispersion is adjusted to the liquid pressurizing pump 5 and the aqueous dispersion temperature. The high pressure carbon dioxide and the aqueous dispersion are respectively introduced from the inlets on both sides of the T-shaped joint of the mixer 7 by adjusting with the vessel 6 to a predetermined pressure (P3). The high density carbon dioxide and the aqueous dispersion were allowed to flow into the outflow pipe (the remaining pipe of the T-shaped joint) and mixed to produce a mixture (emulsion).
At this time, the mixing ratio of the high-density carbon dioxide and the aqueous dispersion (water mixing ratio) [weight of water in the aqueous dispersion / (mass of water in the aqueous dispersion + weight of high-density carbon dioxide) × 100 (mass%) )] Was 17% by mass.

Further, the pressure (injection pressure) (P1) of the injection nozzle 10 was adjusted to be a predetermined pressure depending on the pressure of high density carbon dioxide (P2), the pressure of the aqueous dispersion (P3), and the shape of the injection nozzle 10. .
Then, the ice droplet particles 11 formed by spraying from the spray nozzle 10 were collected in a silicone oil oil bath 12 set at 150 ° C., and moisture was removed in the silicone oil. The aggregate particles formed in the silicone oil were separated from the aggregate oil and the silicone oil using filter paper, and the separated aggregate particles were washed with acetone. After washing, the aggregate particles were collected and dried for 24 hours with a dryer at 120 ° C. to produce aggregate particles formed by aggregation of nanoparticles.

About the obtained aggregate particle, observation of an external shape, measurement of an average particle diameter, and evaluation of particle size distribution were performed.
Solid ratio of nano zirconia particles in aqueous dispersion, aqueous dispersion flow rate, aqueous dispersion pressure P3, high density carbon dioxide flow rate (CO ₂ flow rate), high density carbon dioxide pressure (CO ₂ pressure P2), high Density of carbon dioxide (CO ₂ density), injection nozzle pressure (nozzle pressure P1), water blending ratio, Reynolds number (Re number) in the mixer, appearance shape of the obtained aggregate particles, average particle diameter ( D50) and particle size distribution (D60 / D10) are shown in Table 1.

Examples 2-8
Same as Example 1, except that the water dispersion pressure P3, CO ₂ flow rate, CO ₂ pressure P2, CO ₂ density, nozzle pressure P1, water blending ratio and Re number of Example 1 were changed to the values shown in Table 1. As a result, aggregated particles formed by the aggregation of nanoparticles were produced.
Table 1 shows the appearance shape, average particle diameter (D50), and particle size distribution (D60 / D10) of the obtained aggregate particles.

Example 9
Table 1 shows the solid content ratio of the nano-zirconia particles in the aqueous dispersion of Example 1, the aqueous dispersion pressure P3, the CO ₂ flow rate, the CO ₂ pressure P2, the CO ₂ density, the nozzle pressure P1, the water mixing ratio, and the Re number. Except for changing to the indicated values, aggregate particles formed by aggregation of nanoparticles were produced in the same manner as in Example 1.
Table 1 shows the appearance shape, average particle diameter (D50), and particle size distribution (D60 / D10) of the obtained aggregate particles.

Example 10
TiO ₂ sol (manufactured by Taki Chemical Co., Ltd., Tynock M-6, average primary particle size 5 nm, average dispersed particle size 20 nm, TiO ₂ solid content ratio 6% by mass, pH 3) was used as the aqueous dispersion. Example 1 was the same as Example 1 except that the water dispersion pressure P3, the CO ₂ flow rate, the CO ₂ pressure P2, the CO ₂ density, the nozzle pressure P1, the water mixing ratio, and the Re number were changed to the values shown in Table 1. As a result, aggregated particles formed by the aggregation of nanoparticles were produced.
Table 1 shows the appearance shape, average particle diameter (D50), and particle size distribution (D60 / D10) of the obtained aggregate particles.

Example 11
As an aqueous dispersion, an ZnO nanoparticle dispersion (manufactured by Sumitomo Osaka Cement Co., Ltd., ultrafine zinc oxide dispersion, average primary particle size 15 nm, average dispersed particle size 60 nm, zinc oxide solid content ratio 10 mass% PH 8) was used, and the water dispersion pressure P3, CO ₂ flow rate, CO ₂ pressure P2, CO ₂ density, nozzle pressure P1, water mixing ratio, and Re number of Example 1 were changed to the values shown in Table 1. In the same manner as in Example 1, aggregate particles formed by aggregation of nanoparticles were produced.
Table 1 shows the appearance shape, average particle diameter (D50), and particle size distribution (D60 / D10) of the obtained aggregate particles.

Example 12
As an aqueous dispersion, an CeO ₂ sol (manufactured by Taki Chemical Co., Ltd., Nidral B-10, average primary particle size 10 nm, average dispersed particle size 20 nm, CeO ₂ solid content ratio 10 mass%, pH 8) is used. Example 1 except that the water dispersion pressure P3, CO ₂ flow rate, CO ₂ pressure P2, CO ₂ density, nozzle pressure P1, water mixing ratio and Re number of Example 1 were changed to the values shown in Table 1. In the same manner as in No. 1, aggregate particles formed by aggregation of nanoparticles were produced.
Table 1 shows the appearance shape, average particle diameter (D50), and particle size distribution (D60 / D10) of the obtained aggregate particles.

Comparative Example 1
The same nanoparticle aqueous dispersion as in Example 1 was sprayed at a flow rate of 5 g / min to be atomized (aerosol), and this was introduced into a high-temperature air stream and dried. Recovered with a filter (conventional spray method).
Table 1 shows the appearance shape, average particle diameter (D50), and particle size distribution (D60 / D10) of the aggregate particles obtained by this method.

As can be seen from Table 1, the aggregate particles produced in Examples 1 to 12 had a spherical appearance and an average particle diameter (D50) of 0.5 to 4.6 μm. Moreover, the particle size distribution (D60 / D10) of the aggregate particles was 2.0 to 4.1, the particle size distribution was narrow, the particle diameter was uniform, and the uniformity was high.
On the other hand, the aggregate particles produced by Comparative Example 1 had both external and spherical spherical shapes, and the average particle diameter (D50) was 7.0 μm. Moreover, the particle size distribution (D60 / D10) of the aggregate particles was 11.3, the particle size distribution was wide, and the uniformity was low compared to Examples 1-12.
Therefore, according to the present invention, aggregate particles can be produced simply by drying the sprayed ice droplet particles without using a metal alkoxide or an organic solvent. It has been found that aggregate particles can be produced with less.

  According to the method for producing aggregate particles of the present invention, metal oxide, metal hydrated oxide, or metal hydroxide nanoparticles are formed by aggregation, have an average particle size on the order of micrometers, and a particle size distribution Can be produced at a high speed and with less impact on the environment, and is suitably used as a raw material for ceramic raw materials and pigments, catalyst carriers and adsorbents, photocatalysts, energy device electrode materials, etc. It is done.

1 Carbon dioxide 2 Gas pressure pump 3 Carbon dioxide temperature controller (heat exchanger)
4 Aqueous dispersion 5 Liquid pressurizing pump 6 Aqueous dispersion temperature controller (heat exchanger)
7 Mixer 8 Piping 9 Mixer 10 Injection nozzle 11 Ice droplet particle 12 Oil bath

Claims (4)

Mixing high density carbon dioxide selected from supercritical carbon dioxide and liquefied carbon dioxide with an aqueous dispersion of metal oxide, metal hydroxide or metal hydroxide nanoparticles to form a mixture; and And an average particle diameter of the nanoparticles formed by aggregating the particles including a step of spraying the mixture from the nozzle to obtain ice droplet particles and a step of removing moisture from the ice droplet particles by drying. Method for producing aggregate particles of ˜5 μm.   The method for producing aggregate particles according to claim 1, wherein the high density carbon dioxide and the aqueous dispersion are put in a mixer and a high shear field having a Reynolds number of 8000 or more is formed to form the mixture.   The method for producing aggregate particles according to claim 1 or 2, wherein the mixture is a mixture in which the aqueous dispersion is dispersed in an emulsion state in the high-density carbon dioxide.   The assembly according to any one of claims 1 to 3, wherein the ice droplet particles are collected in a solvent solution that is incompatible with water set to a temperature equal to or higher than the boiling point of water, and moisture is removed from the ice droplet particles by drying. A method for producing body particles.

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