Device for producing particles and method for producing particles

Abstract

A method of producing particles by bringing plural dissimilar materials A and B into contact with each other includes feeding a liquid into a reactor from a first end portion of the reactor such that the liquid flows along the inner peripheral surface of the reactor and generating a vortex flow toward a second end portion in the reactor by the feed of the liquid; disposing a flow-assisting blade capable of rotating around the central axis line in the reactor and rotating the flow-assisting blade; and injecting materials to be contacted A and B into the reactor, discharging a contacted liquid from the second end portion of the reactor, and generating the particles in the contacted liquid.

Claims

1. A method of producing particles by bringing plural dissimilar materials into contact with each other, the method comprising: feeding a liquid into a reactor from a first end portion of the reactor such that the liquid flows along an inner peripheral surface of the reactor and generating a vortex flow toward a second end portion in the reactor by the feeding of the liquid; disposing a flow-assisting blade capable of rotating around a central axis line of the reactor and rotating the flow-assisting blade; and injecting materials to be contacted into the reactor, discharging a contacted liquid from the second end portion of the reactor, and generating particles in the contacted liquid; wherein the flow-assisting blade has a radius r and wherein the reactor has an inner radius R, and wherein a ratio r/R of the radius r of the flow-assisting blade to the inner radius R of the reactor is to ; wherein an inlet for the liquid into the reactor has a cross-sectional area of A, and the liquid has an inflow rate Q into the reactor of 0.5 A to 10 A6010.sup.3; and wherein an average flow rate of the liquid at the inlet is Vv, and the flow-assisting blade is rotated at a speed that is Vv or more.

2. The method of producing particles according to claim 1, wherein all or part of the contacted liquid discharged from the second end portion of the reactor is fed into the reactor from the first end portion of the reactor such that the liquid flows along the inner peripheral surface of the reactor.

3. The method of producing particles according to claim 2, wherein part of the contacted liquid is extracted from a circulation system that transfers the contacted liquid discharged from the second end portion of the reactor to the first end portion of the reactor, and the particles are recovered by solid-liquid separation.

4. The method of producing particles according to claim 1, wherein the liquid is fed into the reactor from the first end portion at an inflow velocity of 0.5 m/sec or more.

5. The method of producing particles according to claim 1, wherein the reactor has a ratio L/D of 2 or more of the longitudinal length L to the diameter D of an internal space of the reactor.

6. The method of producing particles according to claim 1, wherein the flow-assisting blade has a disk shape intersecting with the central axis line of the reactor.

7. The method of producing particles according to claim 1, wherein the flow-assisting blade has a disk shape having a concave-convex portion in a periphery thereof.

8. The method of producing particles according to claim 1, wherein the flow-assisting blade has a disk-shaped body intersecting the central axis line of the reactor and a protrusion protruding to the second side at least in a periphery of the disk-shaped body and intersecting a circle having a center on the central axis line.

9. The method of producing particles according to claim 1, wherein the flow-assisting blade is located closer to the first end portion of the reactor than where the liquid is fed in the first end portion of the reactor.

10. The method of producing particles according to claim 1, wherein a position at which the materials to be contacted is injected, is disposed outboard from the flow-assisting blade in the direction of the radius around the central axis line in the reactor.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 a schematic diagram of a first example of the present invention.

(2) FIG. 2 is a lateral cross-sectional view of the example.

(3) FIG. 3 is a schematic diagram of a second example.

(4) FIG. 4 includes schematic diagrams (a) and (b) explaining generation of vortex flows.

(5) FIG. 5 is an explanatory photograph of a device not including a flow-assisting blade.

(6) FIG. 6 is an explanatory photograph of a device including a flow-assisting blade.

(7) FIG. 7 is a schematic diagram of another example of the present invention.

(8) FIG. 8 is a schematic diagram of another example of the present invention.

(9) FIG. 9 is a schematic diagram illustrating a first example of the flow-assisting blade.

(10) FIG. 10 is a schematic diagram illustrating a second example of the flow-assisting blade.

(11) FIG. 11 is a schematic diagram illustrating a third example of the flow-assisting blade.

(12) FIG. 12 is a schematic diagram illustrating a fourth example of the flow-assisting blade.

(13) FIG. 13 is a schematic diagram illustrating a fifth example of the flow-assisting blade.

(14) FIG. 14 is a schematic diagram according to another embodiment.

(15) FIG. 15 is a schematic diagram according to another embodiment.

(16) FIG. 16 is a schematic diagram according to another embodiment.

(17) FIG. 17 is an optical photomicrograph of particles prepared in Example 1.

(18) FIG. 18 is an optical photomicrograph of particles prepared in Comparative Example 1.

(19) FIG. 19 is an optical photomicrograph of particles prepared in Example 2.

(20) FIG. 20 is an optical photomicrograph of particles prepared in Comparative Example 2.

(21) FIG. 21 is an optical photomicrograph of particles prepared in Example 5.

(22) FIG. 22 is an optical photomicrograph of particles prepared in Comparative Example 5.

(23) FIG. 23 is an optical photomicrograph of particles prepared in Example 6.

(24) FIG. 24 is an optical photomicrograph of particles prepared in Comparative Example 6.

(25) FIG. 25 is a pH curve in Example 6.

(26) FIG. 26 is a pH curve in Comparative Example 6.

(27) FIG. 27 is an optical photomicrograph of particles prepared in Comparative Example 7.

(28) FIG. 28 is a pH curve in Comparative Example 7.

DESCRIPTION OF EMBODIMENTS

(29) The present invention provides a method and a device for producing particles, in particular, microparticles by bringing plural dissimilar materials into contact with each other in the industrial fields of cosmetics, catalysts, electronic materials, battery materials, fine ceramics, pharmaceuticals, and foods.

(30) In the method of preparing microparticles of the present invention, the solubility of the materials in a solution is controlled. More specifically, the microparticles are generated by varying some parameters of the solution, such as concentration, temperature, pH, and redox potential while a supersaturation state of the dissolved materials is transformed to a stable or metastable state of the dissolved materials.

(31) In order to generate uniform microparticles, it is significantly important to control the flow field in the reaction field to achieve a uniform supersaturation distribution in the reaction field.

(32) In the present invention, plural dissimilar materials are brought into contact with each other. The invention includes the following embodiments:

(33) (1) The supersaturation is controlled by bringing plural dissimilar materials into contact with each other (by causing the materials to react with each other in the case where the dissimilar materials are reactive);

(34) (2) The supersaturation is controlled by addition of a poor solvent such as alcohol (referred as poor solvent process); and

(35) (3) The supersaturation is controlled by injection of a cooling liquid or cooling gas.

(36) In these embodiments, the number of materials to be contacted (reactants) is not limited.

(37) The details of the present invention will now be described by a typical case that the plural dissimilar materials are two reactants (reactive materials) A and B reacting with each other.

(38) FIGS. 1 and 2 illustrate a first example of the present invention. The liquid flow in a reactor 10 is set to be a vortex flow, and an additional liquid containing reactants (reactive materials) to be added A and B is injected into the reaction field in the reactor 10 for performing contact processing (for performing reaction processing in this example), while a contacted liquid is discharged to the exterior of the system.

(39) In the example illustrated in the drawings, as the additional liquid containing materials to be added, the additional liquid containing the materials A and B, a gas (an inert gas such as a nitrogen gas or a carbon dioxide gas, or an active gas such as hydrogen or ammonia) may be injected together in parallel with the materials A and B.

(40) In the first example, the additional liquid is injected toward the reaction field of the additional liquid in the downstream direction of the vortex flow of the liquid.

(41) Although the reactor 10 illustrated in the drawings is vertically installed, the reactor 10 may be horizontally installed since there is no effect on the vortex flow in principle by the install direction of the reactor 10.

(42) The depicted reactor 10 has a cylindrical shape (with a circular-shaped inner circumference). Although a vortex flow can be generated even when the reactor 10 has an elliptical-shaped or polygonal-shaped inner circumference, the inner circumference is desirably circular-shaped or polygonal-shaped with many sides, at least five sides, to generate smoothly the vortex flow. Since it is necessary for the vortex flow just to be generated inside the reactor 10, as for the outer shape of the reactor 10, there is no limitation.

(43) A liquid 14 is fed into the reactor 10 from an inlet 10X disposed at a first end portion (the upper end portion in the drawings). The liquid 14 may be a fresh liquid to be added (the reactants may be contained or may not be contained in the fresh liquid) or a returned liquid sent back in a circulation system as the reaction liquid (contacted liquid) after the reaction between the materials A and B, as described in an example below.

(44) In order to generate a vortex flow by feeding the liquid 14 into the reactor 10 from the inlet 10X, it is desirable to feed the liquid 14 substantially along the tangential direction to the inner peripheral surface as shown in FIG. 2.

(45) In the present invention, a flow-assisting blade 12 rotatable around the central axis line is disposed in the reactor 10, and the flow-assisting blade 12 is rotated with a rotary driving means, for example, a motor 12A. The vortex flow velocity is increased by the rotation of the flow-assisting blade 12.

(46) The reactants (additional liquid containing materials A and B) are injected into the reactor 10. In such a case, injection nozzles 15a and 15b are desirably disposed outboard from the flow-assisting blade 12 in planar view (in the case where the injection nozzles 15a and 15b are inboard from the flow-assisting blade 12, for example, the flow-assisting blade 12 is divided into a fixed central portion and a rotating outer portion and the injection nozzles 15a and 15b extend through the central portion).

(47) The open ends of the injection nozzles 15a and 15b may be above the under surface of the flow-assisting blade 12 or may be below the under surface.

(48) The open ends of the injection nozzles 15a and 15b are desirably disposed in the vortex flow.

(49) The reaction liquid is discharged from an outlet 10Y of the second end portion of the reactor 10 (the lower end portion in the drawings).

(50) FIG. 3 illustrates a second example wherein a circulation system is formed. In detail, the reaction liquid is discharged from the outlet 10Y at the lower end portion of the reactor 10 and is circulated with a circulation pump 13 through circulation paths 17 and 18, and the contacted liquid is fed into the reactor 10 to generate a vortex flow. A regulator 16, which is for cooling, heating or the like of the liquid, may be provided if required.

(51) In the circulation system, the contacted liquid may be transferred from the midway of the circulation path 17 or the circulation path 18 to a subsequent facility or may be transferred from an overflow port 10Z of the reactor 10 to the subsequent facility as shown in the second example of FIG. 3.

(52) In the second example of FIG. 3, the final (reaction) contacted liquid is discharged from the overflow port 10Z and is introduced to a storage vessel 20 through an extraction path 19. At appropriate timing, an extraction valve 21 is opened to introduce a particle liquid to a final production step, for example, a solid-liquid separation step 24 with an extraction pump 22. A stirrer 23 may be disposed inside the storage vessel 20.

(53) In the process described above, a liquid is fed from the inlet 10X in the first end portion of the reactor 10 such that the liquid flows along the inner peripheral surface of the reactor 10. Since the liquid is fed in this way, the vortex flow is generated which directs toward the second end portion within the reactor 10.

(54) In the present invention, as shown in FIG. 1, a flow-assisting blade 12 rotatable around the central axis line is disposed in the reactor 10, and the vortex flow velocity is increased by such rotation of the flow-assisting blade 12.

(55) This will be schematically described. As shown in FIG. 4(a), in the case that any flow-assisting blade 12 is not provided, the pitches of the vortex flow SF are rough. In contrast, as shown in FIG. 4(b), in the case that a flow-assisting blade 12 is provided according to the present invention, the pitches of the vortex flow SF are fine. This indicates that the flow-assisting blade 12 can increase the energy of the vortex flow.

(56) FIG. 4 is merely conceptual. Since an actual liquid flow is continuous in the vertical direction, pitches of the vortex flow are not actually present. FIG. 4 conceptually illustrates, for example, the trace of the movement flow of a material added to the vortex flow.

(57) An experiment for verifying this conception was carried out. The following two states of the vortex flow were visually observed. In the first state, a liquid is fed from an inlet at the upper end portion of a cylindrical shaped reactor such that the liquid flows along the inner peripheral surface of the reactor as shown in FIG. 5. In the second case, a reactor is provided with a flow-assisting blade as shown in FIG. 6. In both cases, air was injected from the top into each reactor for clarification of visual verification.

(58) Close observation of FIG. 5 reveals that a high-speed flow field (the whitened portion) around the central axis of the reactor due to the vortex flow has a slightly larger diameter and that the flow has a fluctuation in the upper portion. In contrast, close observation of FIG. 6 including the flow-assisting blade reveals that a high-speed flow field (the whitened portion) around the central axis of the reactor has a smaller diameter and that the flow is approximately straight from the lower portion to the upper portion. The comparison of FIG. 5 with FIG. 6 also demonstrates the fact described above.

(59) The reactants A and B are injected into the reactor 10 under the large energy of the vortex flow. The reaction liquid is discharged from the outlet 10Y on the second end portion of the reactor 10.

(60) The reactants are injected into the vortex flow SF generated in the reactor 10 and are brought into contact with the vortex flow to cause powerful diffusion and mixing (contact), progress of a reaction, and generation of microparticles.

(61) Based on extensive studies involving various experiments, the mechanism generated by rotation of the flow-assisting blade according to the invention is presumed as follows:

(62) Materials to be contacted (e.g., reactants) injected into the reactor are brought into contact with a vortex flow having the large energy to start diffusion and mixing. Subsequently, the materials to be contacted (e.g., reactants) are caught into the vortex flow to cause powerful mixing and diffusion, resulting in a high-speed reaction.

(63) Since the vortex flow velocity is increased, the pitches of the vortex flow of the reactants are shorten until the materials reach the outlet of the reactor. In other words, the rotation distance in the vortex flow is elongated like a screw thread with a fine pitch.

(64) Accordingly, the reactants have a prolonged retention time in the reactor. In addition to the prolonged retention time of the reactants, the vortex flow velocity is increased, thus the materials to be contacted (e.g., reactants) sufficiently react with the liquid (e.g., contacted liquid), resulting in formation of microparticles at a high rate.

(65) In such a mechanism according to the present invention, the resulting particles (e.g., precipitated particles, crystal particles, or agglomerated particles) can have uniform sizes and shapes. Alternatively, aggregation of particles is accelerated to grow agglomerated particles.

(66) The flow-assisting blade can be downsized. Further, the liquid is not stirred by the flow-assisting blade alone and the motive power for the rotation of the flow-assisting blade thus should be enough to rotate itself for assisting the vortex flow, hence, the power expense is not costly.

(67) The reactants may be injected from any position closer to the center of the reactor 10 than the inner wall surface in the reaction field in the reactor 10, and the injection position is preferably located within of the radius r as the distance in the radial direction from the center.

(68) When the reactants are injected from the top as shown in FIG. 1, the injection position may be on the slightly outer side in relation to the position of the flow-assisting blade 12.

(69) As shown in FIG. 7, the reactants may be injected into the reactor 10 through the side wall from the exterior. The position of the flow-assisting blade 12 in the height direction may be lower than the inlet 10X, as shown in FIG. 7. As shown in FIG. 8, the injection position of the reactants may be higher than the inlet 10X. The injection position may be lower than the under surface of the flow-assisting blade 12 and may be higher than the lower surface. The types, positions, and number of injection materials can be appropriately selected.

(70) Although a single reactor 10 may be used, plural reactors 10 may be disposed in series. Alternatively, plural reactors 10 may be disposed in parallel according to circumstances.

(71) In these embodiments, any circulation system may be appropriately selected.

(72) The shape of the flow-assisting blade according to the present invention can be appropriately selected, in addition to the disk shape. FIGS. 9 to 13 show other examples.

(73) In the example shown in FIG. 9, a gear-shaped concave-convex portion 12b is formed in the periphery of a disk-shaped assisting blade 121. The concave-convex portion 12b increases the area in contact with a liquid to enhance the flowing effect. The reference sign 12a indicates the hole of engagement coupling with the rotary drive shaft.

(74) In the example shown in FIG. 10, plural straight blades 12c are disposed in the periphery of a disk-shaped assisting blade 122. The blades 12c cause a liquid scraping stirring effect to enhance the flowing effect.

(75) In the example shown in FIG. 11, a plurality of curved blades 12d is disposed in the periphery of a disk-shaped assisting blade 123. The blades 12d cause a liquid scraping stirring effect to enhance the flowing effect.

(76) In the example shown in FIG. 12, sawtooth protrusions and plural oblique blades 12e are disposed in the periphery of a disk-shaped assisting blade 124. The blades 12e cause a liquid scraping stirring effect to enhance the flowing effect.

(77) In the example shown in FIG. 13, a concave-convex portion composed of alternately formed involute curved protrusions 12f and recesses 12g is provided on the under surface of a disk-shaped assisting blade 125. The concave-convex portion causes a stirring effect to enhance the flowing effect.

(78) Other examples of the flow-assisting blade include Fan Blades, Propeller Blades, Soft Cross Blades, Square Cross Blades, Butterfly Blades, Turbine Blades, and Helicopter Blades.

(79) The ratio r/R of the radius r of the flow-assisting blade according to the present invention to the inner radius R of the reactor 10 is preferably to .

(80) The inflow rate Q [liter (L)/min] of a liquid into the reactor 10 is desirably 0.5 A to 10 A6010.sup.3 [L/min] where the average flow rate is Vv [m/sec] and the cross-sectional area of the inlet 10X is A [m.sup.2]. The rotation speed of the flow-assisting blade is preferably Vv or more, more preferably Vv or more in the tip speed.

(81) Such a rotation speed of the assisting blade can cause necessarily and sufficiently strong circulation in a flow field formed by inflow of a liquid into the reactor 10 in the tangential direction and the randomly fluctuated vortex flow can be controlled stably along the tangential direction in the reactor 10 as shown by the observation photograph of FIG. 6. Consequently, the material liquid can be uniformly diffused in the flow field.

(82) The flow-assisting blade exemplified above can accelerate the vortex flow without disordering the flow field.

(83) Several embodiments other than the embodiment described above will be described.

(84) In the embodiment shown in FIG. 14, the regulator 16 performs not only control of the temperature but also addition of a material Z for pH adjustment, gas injection, or addition of a material to be contacted. In such a case, a diffusion-accelerating means, such as a stirring means, may be provided in the regulator 16. A regulator 16 having a large capacity may also be used as a container for retaining a liquid.

(85) In the embodiment shown in FIG. 15, the liquid in the storage vessel 20 is partially sent back to the reactor 10 with a return pump 25 through a return path 26.

(86) The contacted liquid discharged from the reactor 10 may be partially sent into the storage vessel 20 with a feed pump 27 through a feed path 28 as needed.

(87) In the embodiment shown in FIG. 16, the liquid in the storage vessel 20 is partially sent back into the circulation system, for example, the inlet side of the regulator 16, with return pump 25 through a return path 26A.

(88) The present invention can be applied to producing of particles, in particular, fine particles necessary in the industrial fields of cosmetics, catalysts, electronic materials, battery materials, fine ceramics, pharmaceuticals, and foods, as described above.

(89) In particular, the present invention can be suitably applied to crystallization of two or more reactants, in addition to a poor solvent process.

(90) Several examples will now be shown. The inventors have verified that the tendencies shown in the examples are similar for other materials.

EXAMPLES

(91) Advantageous effects of the present invention will be clarified by the following examples and comparative examples.

(92) (Production of Zinc Hydroxide)

(93) In this example, zinc sulfate adjusted to 1 mol/L and 25% sodium hydroxide were injected into a reactor for the following reaction to produce zinc hydroxide:
ZnSO.sub.4+2NaOH.fwdarw.Zn(OH).sub.2+Na.sub.2SO.sub.4

(94) Table 1 shows the results of comparative evaluation after 180 minutes of an operation under conditions of 20 C., a pH of 12.5, an installed capacity of 5 L, and an average retention time of 30 min. The inlet diameter of the reactor was 13 mm.

(95) The term average retention time is synonymous with the liquid injection time necessary for filling the operational capacity of the reactor and is that when zinc sulfate and sodium hydroxide were injected at 167 mL/min in total.

(96) TABLE-US-00001 TABLE 1 Run No. 1 2 3 4 5 6 Exam- Comparative Exam- Comparative Exam- Comparative ple 1 Example 1 ple 2 Example 2 ple 3 Example 3 Target particles Zn(OH).sub.2 Zn(OH).sub.2 Zn(OH).sub.2 Zn(OH).sub.2 Al.sub.2(OH).sub.3 Al.sub.2(OH).sub.3 Inflow rate L/min 34 34 8 8 34 34 Assisting blade tip 4.3 0 4.3 0 4.3 0 speed m/sec Average particle 17 13 38 30 2.5 3 diameter m Evaluation of particle 0.8 1.3 0.56 0.58 1.2 1.7 size distribution Run No. 7 8 9 10 11 12 Exam- Comparative Exam- Comparative Exam- Comparative ple 4 Example 4 ple 5 Example 5 ple 6 Example 6 Target particles Al.sub.2(OH).sub.3 Al.sub.2(OH).sub.3 H.sub.2NCH.sub.2COOH H.sub.2NCH.sub.2COOH CaCO.sub.3 CaCO.sub.3 Inflow rate L/min 15 15 24 24 34 34 Assisting blade tip 4.3 0 4.3 0 4.3 0 speed m/sec Average particle 5 2 43.7 45 1.5 0.8 diameter m Evaluation of particle 1.2 1.0 1.9 2.6 1.2 1.6 size distribution

(97) (1) Low Inflow Rate (8 L/Min)

(98) A sharp particle size distribution is obtained substantially regardless of presence or absence of an assisting blade.

(99) The assisting blade can keep a sharp particle size distribution.

(100) (2) High Inflow Rate (34 L/Min)

(101) The presence of an assisting blade does not cause a substantial difference in the particle diameter but results in a sharp particle size distribution.

(102) The particle size distribution was evaluated based on the accumulated value (D90D10)/D50.

(103) FIGS. 17 to 20 are optical photomicrographs of particles prepared in Example 1, Comparative Example 1, Example 2, and Comparative Example 2.

(104) (Production of Aluminum Hydroxide)

(105) Aluminum hydroxide was prepared under the same conditions, and the effects by installation of a flow-assisting blade were investigated. Table 1 shows the results.

(106) Table 1 demonstrates that the particle size distribution in Example 3 in which a flow-assisting blade was installed was sharper than that in Comparative Example 3 in which the flow-assisting blade was not installed, although no substantial difference was observed in the particle diameter.

(107) In Example 4 and Comparative Example 4 at a low inflow rate under the same conditions, the particle size in Example 4 was larger than that in Comparative Example 4. In Example 4, aggregation of particles was accelerated by the effect of assisting the growth of agglomerated particles.

(108) (Production of Glycine)

(109) A saturated glycine liquid [(20 g+)/100 g] at 20 C. was used as a starting mother liquor and was circulated at 34 L/min. A 99.5% ethanol liquid was injected into the reactor to recrystallize glycine. The volume of the starting mother liquor was 2 L, and the ethanol liquid was injected into the reactor at 1.5 L/min for 80 seconds. The experiment was terminated at the time when the liquid volume in the device reached 4 L.

(110) The results are shown in Table 1. FIGS. 21 and 22 are optical photomicrographs of the particles prepared in Example 5 and Comparative Example 5.

(111) Table 1 demonstrates that the particle size distribution in Example 5 in which a flow-assisting blade was installed was sharper than that in Comparative Example 5 in which the flow-assisting blade was not installed. It was also demonstrated that the aspect ratios of the particles in FIG. 21 (Example 5) are almost constant, whereas the aspect ratios of the particles in FIG. 22 (Example 5) are somewhat irregular.

(112) (Production of Calcium Carbonate)

(113) A 10 wt % calcium hydroxide liquid (3 L) at 20 C. was used as a starting mother liquor and was circulated at 34 L/min. CO.sub.2 gas was injected into the reactor at 600 mL/min, and the experiment was terminated at the time when the pH reached 7 or less.

(114) The results are shown in Table 1. FIGS. 23 and 24 are optical photomicrographs of the particles prepared in Example 6 and Comparative Example 6. FIGS. 25 and 26 show the pH curved obtained in Example 6 and Comparative Example 6.

(115) In Comparative Example 7, a stirred reactor equipped with a two-stage stirring blade and a draft tube was used. A 10 wt % calcium hydroxide liquid (3 L) at 20 C. was used as a starting mother liquor, and CO.sub.2 gas was injected in the vicinity of the stirring blade to perform stirring with the CO.sub.2 gas and reaction with calcium hydroxide, and the experiment was terminated at the time when the pH reached 7 or less.

(116) The results are shown in Table 2. FIG. 27 is an optical photomicrograph of the particles prepared in Comparative Example 7. FIG. 28 shows a pH curve obtained in Comparative Example 7.

(117) TABLE-US-00002 TABLE 2 Run No. 13 Comparative Example 7 Target particles CaCO.sub.3 Rotation speed of stirring blade r.p.m 1000 Stirring blade tip speed 2.1 m/sec Average particle diameter 2 m Evaluation of particle size distribution 1.6

(118) Tables 1 and 2 demonstrate that Example 6, provided with a flow-assisting blade, accelerated aggregation of particles by the effect of assisting and an increase in the diameter of agglomerated particles compared to Comparative Example 6, and prepared particles with a sharp particle size distribution compared to those in Comparative Examples 6 and 7. Comparison of the pH curves of Example 6 and Comparative Example 6 demonstrates no substantial difference in the time required for the reaction. Example 6 demonstrates that the time required for the reaction was considerably shortened compared with Comparative Example 7.

REFERENCE SIGNS LIST

(119) 10 reactor 10X inlet 10Y outlet 10Z overflow port 12 flow-assisting blade 14 liquid 15A, 15B injection nozzle 16 regulator 17, 18 circulation path A, B reactant