Crystallization method and crystallization apparatus

Abstract

To provide a crystallization method and a crystallization apparatus capable of suppressing the range of a particle size distribution and stably operating the apparatus even when implementing concentration operation during reaction crystallization.SOLUTION: In a crystallization method that a circulation path 12 is formed between a main reaction part 11 and a concentration reaction vessel 13 and reaction crystallization is implemented,: the circulation path 12 has an inflow path 12a from the main reaction part 11 to the concentration reaction vessel 13 and an outflow path 12b from the concentration reaction vessel 13 to the main reaction part 11 ; the inflow path 12a and the outflow path 12b are connected at the lower part of the concentration reaction vessel 13 and an agitation zone 14 is formed; a clarification zone 18 to generate a supernatant liquid is formed at the upper part of the concentration reaction vessel 13; and a concentration zone 17 to precipitate particulates is formed between the agitation zone 14 and the clarification zone 18.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a crystallization method and a crystallizer. [Background technology]

[0002] Micron-sized spherical particles, obtained by the aggregation and growth of nanometer- to submicron-sized primary particles, are often used in applications such as battery materials, catalysts, pharmaceutical raw materials, and cosmetic materials, where they are used as fillers for functional materials and raw materials. When addressing packing and packing density, the sphericity and particle size distribution of the resulting particles are particularly important. Many applications require the optimal combination of large and small particle sizes to increase packing density, and broad particle size distributions are often sought. Meanwhile, many applications require uniform particle size to achieve uniform particle functionality, and many applications require materials with narrow particle size distributions to ensure uniform particle distribution within the material. One example is the cathode material for all-solid-state batteries, a promising technology for the future. Various methods have been devised to obtain uniform particle sizes, including classification, crystallization while separating large and small particle sizes, and the addition of seed particles (seed crystals) in advance. Furthermore, methods for controlling particle size during crystallization by increasing the number of particles in the solution or the suspension density have also been devised. There is also a method of increasing the raw material concentration in advance, but this increases the amount of by-products produced, so there is a limit to how much the raw material concentration can be increased.

[0003] Patent Document 1 describes a method for increasing the productivity of a product by concentrating discharged particles and returning them to a crystallization tank, thereby increasing the slurry concentration and maintaining a constant particle size distribution. However, the concentration operation increases the residence time, which can lead to particle enlargement and a change in particle size distribution. Therefore, the invention described in Patent Document 1 describes a method for operating the crystallization system so that the feed rate and slurry concentration set under the reference conditions for continuously overflowing the reaction solution satisfy a certain relationship with the feed rate and slurry concentration set under the operating conditions for concentrating the reaction solution removed from the reaction vessel and then returning it to the reaction vessel. However, the operating conditions for concentrating the slurry require the feed rate and slurry concentration to be set relative to the reference conditions for not concentrating the slurry, which complicates operational management. Furthermore, the feed rate of the feed rate must be changed as the slurry concentration progresses, further complicating operational management.

[0004] Patent Document 2 describes connecting a reactor to a concentrator and setting the circulation flow rate so as not to change the agitation state of the reactor when circulating the reaction slurry produced in the reactor between the reactor and the concentrator. However, suppressing the circulation flow rate of the slurry in the concentration operation results in an insufficient concentration time, making it difficult to increase the concentration achieved. In the concentration operation, when the concentration area, such as a filter cloth, a separation medium (e.g., membrane), or a settling area, is fixed, this affects the achievable concentration. Furthermore, suppressing the circulation flow rate of the slurry in the concentration operation is difficult when the concentration area is fixed. Depending on the target substance, it may be necessary to operate the circulation flow rate higher, making it difficult to avoid affecting the agitation state.

[0005] Patent Document 3 proposes that crystal growth can be achieved using already crystallized crystals as seed crystals while suppressing the precipitation of new crystals during the concentration operation, and that the seed crystals can be grown to the desired particle size by continuing to supply and circulate the raw material compound. Furthermore, when using a separation membrane in the concentration operation, problems such as clogging can make continuous operation difficult. Therefore, a system has been proposed that includes a classification process prior to the concentration operation, thereby stabilizing the concentration operation by removing large particles that cause membrane clogging. However, in practice, classification on the order of a few microns is difficult, and as a result, the target particle size is a product of 10 microns or more. Furthermore, the classification operation itself is difficult to stabilize, making operational management complicated. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6493082 [Patent Document 2] Patent No. 5206948 [Patent Document 3] Japanese Patent Publication No. 2020-99841 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made under such circumstances, and aims to provide a crystallization method and a crystallization apparatus that can suppress the range of particle size distribution and enable stable operation of the apparatus even when a concentration operation is carried out during reactive crystallization. [Means for solving the problem]

[0008] In order to solve the above problems and achieve the above object, the present invention proposes the following aspects.

[0009] A first aspect of the present invention is a crystallization method for performing reactive crystallization by forming a circulation path between a main reaction section and a concentration reaction tank, wherein the circulation path has an inlet path from the main reaction section to the concentration reaction tank and an outlet path from the concentration reaction tank to the main reaction section, the inlet path and the outlet path are connected to form a stirring zone at the bottom of the concentration reaction tank, a clarified zone in which a supernatant liquid is produced is formed at the top of the concentration reaction tank, and a concentration zone in which particles settle is formed between the stirring zone and the clarified zone.

[0010] According to the first aspect, the internal state of the main reaction section is determined primarily by the flow rate of the circulation path between the main reaction section and the concentration reaction tank. Furthermore, the concentration reaction tank has a concentration zone and a clarification zone above the stirring zone. This minimizes the effect of the concentration operation on the reaction and reduces the impact on the product particles. This makes it easier to adjust the concentration operation. Furthermore, by increasing the particle concentration in the concentration reaction tank through concentration, it becomes possible to reduce the amount of product slurry stored and also reduce the load on subsequent solid-liquid separation operations such as filtration and drying.

[0011] A second aspect of the present invention is characterized in that, in the first aspect, the ratio L / D of the height L from the lower end of the concentration reaction tank to the overflow level to the diameter D of the concentration reaction tank is within the range of 2 to 20.

[0012] According to the second aspect, the shape of the concentration reaction vessel has an appropriate aspect ratio, which makes it easier to optimize the mutual influences between the stirring zone, the concentration zone, and the clarification zone.

[0013] A third aspect of the present invention is characterized in that, in the first or second aspect, the liquid level in the concentration reaction tank is gradually increased during reactive crystallization, and the concentration zone and the clarification zone are formed during the reactive crystallization process.

[0014] According to the third aspect, particles contained in the reaction liquid supplied from the main reaction section can be retained mainly in the stirring zone. As the reaction liquid accumulates in the concentration reaction tank, the reaction liquid is concentrated, and the supernatant liquid can reach the clarification zone. The reaction liquid can be efficiently concentrated and separated by the settling of the particles and the rising of the supernatant liquid.

[0015] A fourth aspect of the present invention is characterized in that, in the third aspect, a ratio Vt / Vs of the volume Vt in the concentration reaction tank increased after the start of reactive crystallization to the volume Vs in the concentration reaction tank at the start of reactive crystallization is greater than 1.

[0016] According to the fourth embodiment, the supernatant liquid rises to the concentration zone and the clarification zone in response to the increased volume Vt during the reactive crystallization operation, and the particles remaining in the stirring zone can be concentrated.

[0017] A fifth aspect of the present invention is characterized in that, in any one of the first to fourth aspects, the ratio H / L of the height H from the lower end of the concentration reaction tank to the height L from the lower end of the concentration reaction tank to the overflow level is less than 20% as a percentage.

[0018] According to the fifth aspect, the range of the stirring zone is relatively low relative to the height of the concentration reaction tank, so that the particles retained in the stirring zone can be concentrated more effectively.

[0019] A sixth aspect of the present invention is a crystallization apparatus for performing reactive crystallization by forming a circulation path between a main reaction section and a concentration reaction tank, wherein the circulation path has an inlet path from the main reaction section to the concentration reaction tank and an outlet path from the concentration reaction tank to the main reaction section, the inlet path and the outlet path are connected to form a stirring zone at the bottom of the concentration reaction tank, a clarified zone in which a supernatant liquid is produced is formed at the top of the concentration reaction tank, and a concentration zone in which particles settle is formed between the stirring zone and the clarified zone.

[0020] According to the sixth aspect, the internal state of the main reaction section is determined mainly by the flow rate of the circulation path between the main reaction section and the concentration reaction tank. Furthermore, the concentration reaction tank has a concentration zone and a clarification zone above the stirring zone. This makes it difficult for the concentration operation to affect the reaction, and also reduces the impact on the product particles. This makes it easier to adjust the concentration operation.

[0021] A seventh aspect of the present invention is characterized in that, in the sixth aspect, the ratio L / D of the height L from the lower end of the concentration reaction tank to the overflow level to the diameter D of the concentration reaction tank is within the range of 2 to 20.

[0022] According to the seventh aspect, the shape of the concentration reaction vessel has an appropriate aspect ratio, which makes it easier to optimize the mutual influences between the stirring zone, the concentration zone, and the clarification zone.

[0023] The eighth aspect of the present invention is characterized in that, in the sixth or seventh aspect, the ratio H / L of the height H from the lower end of the concentration reaction tank to the height L from the lower end of the concentration reaction tank to the overflow level is less than 20% as a percentage.

[0024] According to the eighth aspect, the range of the stirring zone is relatively low relative to the height of the concentration reaction tank, so that the particles retained in the stirring zone can be concentrated more effectively. [Effects of the Invention]

[0025] According to the present invention, it is possible to provide a crystallization method and a crystallization apparatus that can suppress the range of particle size distribution and ensure stable operation of the apparatus even when a concentration operation is carried out during reactive crystallization. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a crystallization apparatus according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram illustrating the operation of a concentration reaction tank. [Figure 3]FIG. 1 is a schematic diagram showing an example of a crystallization apparatus provided with a concentration operation section. [Figure 4] FIG. 1 is a schematic diagram showing a crystallizer of Comparative Example 1. [Figure 5] 1 is a graph showing the change in SS concentration over time in Example 1. [Figure 6] 1 is a graph showing the particle size distribution of the product of Example 1. [Figure 7] 1 is a graph showing the particle size distribution of the supernatant liquid in Example 1. [Figure 8] 1 is a graph showing the change in SS concentration of the product. [Figure 9] 1 is a graph showing the change in D50 of the product. [Figure 10] 1 is a graph showing the transition of the (D90-D10) / D50 value of the product. [Figure 11] 1 is a graph showing the transition of the SS concentration in the supernatant. [Figure 12] 1 is a graph showing the transition of the (D90-D10) / D50 value of the supernatant. [Figure 13] 1 is a photograph, substituted for a drawing, showing SEM data of the product of Comparative Example 1. [Figure 14] 1 is a photograph, substituted for a drawing, showing SEM data of the product of Example 2. [Figure 15] 1 is a photograph, substituted for a drawing, showing SEM data of particle groups in the supernatant liquid of Example 2. [Figure 16] FIG. 1 is a schematic diagram showing a crystallizer of Reference Example 1. [Figure 17] FIG. 1 is a schematic diagram showing a crystallizer of Reference Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be described below based on preferred embodiments with reference to the drawings. As shown in Figure 1, a crystallizer 10 of this embodiment forms a circulation path 12 between a main reaction section 11 and a concentration reaction tank 13, and performs reactive crystallization.

[0028] The reaction process in the main reaction section 11 is carried out, for example, by supplying one or more raw material liquids 10a, 10b into the main reaction section 11. In the main reaction section 11, the raw material liquids 10a, 10b may come into contact with the reaction liquid 11a circulating through the circulation path 12 to carry out the reaction process. The raw material liquids 10a, 10b are liquids containing substances to be added to the reaction field. The raw material liquids 10a, 10b may be solutions or dispersions. A portion of the substances to be added to the reaction field may be supplied to the concentration reaction tank 13 as one or more raw material liquids 10c or substances other than raw materials 10d, 10e. A portion of the raw material liquids 10a, 10b may be supplied to the concentration reaction tank 13.

[0029] The starting mother liquor used in the crystallizer 10 from the start of the reaction may be a solution that does not contain the raw material liquids 10a and 10b. The starting mother liquor may also contain components of the raw material liquid 10c. The reaction liquid 11a may be used as the starting mother liquor. As the reaction crystallization progresses, the reaction liquid 11a becomes a slurry containing suspended solids. Although not shown, a gas may be supplied to the main reaction section 11 or the concentration reaction tank 13 together with the raw material liquids 10a, 10b, and 10c. The gas may be an inert gas such as nitrogen gas or carbon dioxide gas, or a reactive gas such as air, oxygen, ozone, ammonia, chlorine, or hydrogen that undergoes a chemical reaction during the reaction process.

[0030] Although not specifically shown, the crystallizer 10 may include equipment for preparing the raw material solutions 10a, 10b, and 10c. Examples of such equipment include containers for dissolving raw materials in a solvent such as water to produce the raw material solutions 10a, 10b, and 10c, containers for storing the raw material solutions 10a, 10b, and 10c, and paths and pumps for supplying the raw material solutions 10a, 10b, and 10c.

[0031] A reaction liquid 11a obtained by mixing the raw material liquids 10a, 10b, and 10c is circulated between the main reaction section 11 and the concentration reaction tank 13 via a circulation path 12 by the power of a circulation pump 15. The circulation path 12 has an inflow path 12a from the main reaction section 11 to the concentration reaction tank 13 and an outflow path 12b from the concentration reaction tank 13 to the main reaction section 11.

[0032] The main reaction section 11 provides a reaction field by contacting the raw material liquids 10a and 10b, or by contacting the raw material liquids 10a and 10b with the reaction liquid 11a. To promote a uniform reaction, the main reaction section 11 may be provided with a device or structure (not shown) for forming a swirling flow, stirring flow, or other flow. To control particle growth, shear force can be obtained by a circulating flow, rotational energy, or the like. The main reaction section 11 shown is oriented horizontally, but it may also be oriented vertically.

[0033] Although not particularly shown, two or more main reaction sections 11 may be arranged in series or in parallel. When the main reaction sections 11 are arranged in series, the reaction liquid 11a passes through two or more main reaction sections 11 in the process of being sent from the concentration reaction tank 13 to the circulation path 12 and then returned to the concentration reaction tank 13. When the main reaction sections 11 are arranged in parallel, the inflow path 12a and the outflow path 12b branch into two or more paths in the process of being sent from the concentration reaction tank 13 to the circulation path 12 and then returned to the concentration reaction tank 13, and the reaction liquid 11a passes through the main reaction section 11 in each of the branched paths.

[0034] The concentration reaction tank 13 ensures a residence time for the reaction liquid 11a, thereby stabilizing the reaction liquid 11a, growing particles, concentrating by sedimentation, etc. For example, by making the capacity of the concentration reaction tank 13 larger than the internal volumes of the main reaction section 11 and the circulation path 12, the residence time of the reaction liquid 11a in the concentration reaction tank 13 can be extended.

[0035] The concentration reaction tank 13 is formed in a tubular shape such as a cylindrical or rectangular tube. At the bottom of the concentration reaction tank 13, the inlet path 12a and outlet path 12b of the circulation path 12 are connected to form a stirring zone 14. In the stirring zone 14, the reaction liquid 11a may be stirred by the flow of the reaction liquid 11a from the inlet path 12a toward the outlet path 12b. The inlet path 12a may be branched into multiple paths to allow the reaction liquid 11a to flow into the concentration reaction tank 13. Depending on the size of the concentration reaction tank 13, outlets may be provided at multiple locations and merge with the outlet path 12b.

[0036] In order to suppress turbulence in the concentration reaction tank 13 due to the inflow energy of the reaction liquid 11a flowing from the main reaction unit 11 into the concentration reaction tank 13, it is preferable to provide a structure for adjusting the flow at the outlet of the main reaction unit 11, the inside of the inflow path 12a, the inlet of the concentration reaction tank 13, etc. For example, a diffuser may be installed to weaken the liquid flow, or a structure may be provided that makes it possible to adjust the outflow direction from the main reaction unit 11 or the inflow direction into the concentration reaction tank 13.

[0037] Although not shown, a stirring device for stirring the reaction liquid 11a, a structure for controlling the flow of the reaction liquid 11a, etc. may be placed inside the concentration reaction tank 13. This can promote mixing of the reaction liquid 11a or mixing of the reaction liquid 11a with the raw material liquid 10c. For example, a rotating shaft may be installed from the bottom to the top of the concentration reaction tank 13, and stirring blades or the like (not shown) may be attached to the rotating shaft.

[0038] By adjusting the positions and directions at which inflow path 12a and outflow path 12b are connected to concentration reaction tank 13, it is possible to suppress particle deposition without providing a stirring device.

[0039] The connection position of the outflow path 12b to the concentration reaction tank 13 is preferably the lower end of the concentration reaction tank 13. This can facilitate the delivery of particles. The lower end of the concentration reaction tank 13 is preferably funnel-shaped. The flow velocity at the outlet of the concentration reaction tank 13 may be, for example, within a range of 0.3 to 10 m / s.

[0040] The concentration reaction tank 13 has an overflow discharge channel 16 for discharging overflow. The overflow discharge channel 16 may be always open to the concentration reaction tank 13. The overflow discharge channel 16 may be closed except when sampling or other such operations are required. A plurality of collecting basins may be installed around the circumference of the concentration reaction tank 13. A ring-shaped opening may be provided around the entire circumference to connect the concentration reaction tank 13 and the overflow discharge channel 16. The overflow discharge channel 16 may also be located at the top end of the concentration reaction tank 13.

[0041] A clarification zone 18, in which a supernatant liquid is produced, is formed above the concentration reaction tank 13. A concentration zone 17, in which particles settle, is formed between the stirring zone 14 and the clarification zone 18. As shown in FIG. 2, the overflow level Lt may be set depending on the location of the overflow discharge channel 16. The cross-sectional shapes of the concentration zone 17 and the clarification zone 18 may be continuous cylindrical shapes with the same shape above and below. The inner surfaces of the concentration reaction tank 13 in the concentration zone 17 and the clarification zone 18 may be tapered, flat, or may have irregularities.

[0042] To improve settling performance, a settling device such as an inclined pipe or inclined plate may be provided in the thickening zone 17 or the clarification zone 18. If the slurry contains gas, the particles may rise due to the growth of bubbles. To suppress the growth of bubbles, the settling device may be installed above the thickening zone 17 or on the clarification zone 18 side, and no settling device may be provided below the thickening zone 17. The location where bubbles are generated may be controlled by irradiating a specific zone with ultrasound.

[0043] In the crystallizer 10 of this embodiment, the interior of the concentration reaction tank 13 is vertically divided into a plurality of zones, namely, a stirring zone 14, a concentration zone 17, and a clarification zone 18. The reaction liquid 11a circulating between the main reaction unit 11 and the concentration reaction tank 13 is distributed mainly in the stirring zone 14. The internal state of the main reaction unit 11 is determined mainly by the flow rate of the circulation path 12 between the main reaction unit 11 and the concentration reaction tank 13.

[0044] Because the concentration reaction tank 13 has a concentration zone 17 and a clarification zone 18 above the stirring zone 14, the concentration operation is less likely to affect the reaction, and the impact on the product particles can also be reduced. This makes it easier to adjust the concentration operation. Furthermore, concentration increases the particle concentration in the concentration reaction tank 13, making it possible to reduce the amount of product slurry stored and also reduce the load on subsequent solid-liquid separation operations such as filtration and drying.

[0045] Since no partition wall, diaphragm, or the like is provided between stirring zone 14 and clarification zone 18 to separate only the dispersion medium of the slurry into clarification zone 18, some particles may rise from stirring zone 14 to concentration zone 17. However, because the flow is restricted in concentration zone 17 so that the particles settle, the amount of particles rising to clarification zone 18 can be restricted. Compared to concentration operations using membrane separation, this method can avoid reduced operational stability and increased operating costs due to membrane fouling, etc.

[0046] The ratio L / D of the height L from the lower end of the concentration reaction tank 13 to the overflow level Lt to the diameter D of the concentration reaction tank 13 is preferably within the range of 1 to 20, more preferably within the range of 2 to 20, even more preferably within the range of 2 to 10, and even more preferably within the range of 3 to 8. When the shape of the concentration reaction tank 13 has an appropriate aspect ratio, it becomes easier to optimize the mutual influences between the stirring zone 14, the concentration zone 17, and the clarification zone 18.

[0047] If the concentration reaction tank 13 is not cylindrical, the equivalent diameter may be diameter D. The equivalent diameter is calculated by 4A / B, where A is the cross-sectional area and B is the perimeter of the cross section. The equivalent diameter of a circle is equal to the diameter, and the equivalent diameter of a square is equal to the length of one side. The cross-sectional shape of the concentration reaction tank 13 in a horizontal plane is not particularly limited, but if it is a polygon, the corners may be rounded. The cross-sectional shapes of the stirring zone 14, concentration zone 17, and clarification zone 18 may be the same or similar, and the cross-sectional shapes of the different zones may also be different.

[0048] When reactive crystallization is started, the liquid level Ls at the start may be set at a position lower than the overflow level Lt. When the reaction liquid 11a is supplied from the main reaction section 11, the liquid level in the concentration reaction tank 13 gradually rises. As a result, the concentration zone 17 and the clarification zone 18 are formed midway through the reactive crystallization process. The height difference between the liquid level Ls at the start and the overflow level Lt is not particularly limited, but is, for example, about 1 m to 10 m, and preferably less than 7 m.

[0049] The particles contained in the reaction liquid 11a supplied from the main reaction section 11 can be retained mainly in the stirring zone 14. As the supply of the reaction liquid 11a accumulates, the reaction liquid 11a is concentrated, and the supernatant liquid is separated from the particles and reaches the clarification zone 18. The sedimentation of the particles and the rising of the supernatant liquid allow the reaction liquid 11a to be efficiently concentrated and separated.

[0050] The rate at which the liquid level rises until it reaches the overflow level Lt may be constant or may fluctuate slightly. If there is no sudden rise in the liquid level, the particles can have time to settle while the liquid level rises, and the rise of the particles can be suppressed. It is preferable that the rate at which the liquid level rises is not excessively large compared to the settling rate of the particles. Since the settling rate decreases as the particle diameter decreases, the inflow amount of the reaction liquid 11a may be set so that larger particles settle and smaller particles rise relative to the desired particle diameter.

[0051] The liquid level Ls at the start may be at a position higher than the position where inflow path 12a is connected to concentration reaction tank 13. Although it depends on the size of concentration reaction tank 13, the liquid level Ls at the start may be set at a height of, for example, less than 1 m, more preferably less than 0.5 m, from inflow path 12a.

[0052] The ratio H / L of the height H from the lower end of the concentration reaction tank 13 to the inflow path 12a to the height L from the lower end of the concentration reaction tank 13 to the overflow level Lt is preferably less than 50%, more preferably less than 30%, and even more preferably less than 20%. By making the range of the stirring zone 14 relatively narrow compared to the height of the concentration reaction tank 13, the particles retained in the stirring zone 14 can be concentrated more effectively.

[0053] The ratio Vt / Vs of the volume Vt increased in the concentration reaction tank 13 after the start to the volume Vs in the concentration reaction tank 13 at the start is preferably greater than 0.5, more preferably greater than 0.8, and even more preferably greater than 1. The volume Vs at the start is the volume contained from the lower end of the concentration reaction tank 13 to the liquid level Ls at the start. The volume Vt increased after the start is the volume contained from the liquid level Ls at the start to the overflow level Lt. In response to the increased volume Vt, the supernatant liquid rises to the concentration zone 17 and clarification zone 18, allowing the particles remaining in the stirring zone 14 to be concentrated.

[0054] Obstacles 19 such as cones and baffles may be installed inside the concentration reaction tank 13 for the purpose of suppressing the rise of particles due to the momentum of the reaction liquid 11a flowing from the inflow path 12a into the concentration reaction tank 13. The obstacles 19 are preferably installed at the boundary between the stirring zone 14 and the concentration zone 17. The position of the obstacles 19 is preferably above the initial liquid level Ls or the connection position of the inflow path 12a. The obstacles 19 may also be installed below the initial liquid level Ls or the connection position of the inflow path 12a. If the flow velocity at the time of inflow is less than 1 m / s, for example, the obstacles 19 may not be necessary.

[0055] The total volume V of the concentration reaction tank 13, which is the sum of the initial volume Vs and the volume increase Vt after the start of the reaction, is preferably set within an appropriate range depending on the amount of raw material supplied. When the amount of raw material supplied from the outside per hour to the entire crystallization apparatus 10 is q, V / q is preferably within the range of 1 to 24 hours, and more preferably within the range of 1 to 5 hours.

[0056] The supernatant liquid discharged from the overflow discharge channel 16 may be concentrated and recovered. For example, as shown in Figure 3, a concentration operation unit 20 for concentrating the supernatant liquid 26 may be provided. The concentration operation unit 20 has a concentration tank 24 connected to the overflow discharge channel 16.

[0057] A portion of the supernatant liquid 26 stored in the thickening tank 24 is circulated between the thickening tank 24 and the solid-liquid separator 21 via the second circulation path 22 by the power of the second circulation pump 23. The second circulation path 22 has a delivery path 22a from the thickening tank 24 to the solid-liquid separator 21 and a return path 22b from the solid-liquid separator 21 to the thickening tank 24.

[0058] The method of solid-liquid separation in the solid-liquid separator 21 is not particularly limited, and examples include a filter material such as a filter cloth, a solid-liquid separation membrane, centrifugation, sedimentation, a liquid cyclone, etc. It is preferable to select an appropriate solid-liquid separator 21 depending on the viscosity of the supernatant liquid 26, the concentration and particle size of the suspended matter contained in the supernatant liquid 26, etc. The particle size distribution can be measured, for example, by a laser light diffraction scattering method, etc.

[0059] By the solid-liquid separation operation, a separated liquid 31 such as a filtrate or a membrane filtrate is separated from the supernatant liquid 26. The separated liquid 31 may be a liquid that does not contain suspended matter, or may be a liquid that has a lower concentration of suspended matter than the supernatant liquid 26.

[0060] In particular, when the solid-liquid separator 21 has a solid-liquid separation membrane, solid-liquid separation is easy even if the suspended matter contained in the slurry-like supernatant liquid 26 is minute. Furthermore, the use of a solid-liquid separation membrane can reduce the amount of suspended matter contained in the separated liquid 31. This makes it possible to more efficiently concentrate and recover the suspended matter, and more stable solid-liquid separation is possible.

[0061] The shape of the solid-liquid separation membrane is not particularly limited, and examples thereof include a filamentous hollow fiber membrane, a flat membrane, and a tubular membrane. A hollow fiber membrane may be used by bundling a large number of hollow fibers into the form of a sheet or the like. Separation methods for solid-liquid separation membranes include reverse osmosis (RO), ultrafiltration (UF), and microfiltration (MF). The solid-liquid separation membrane in the solid-liquid separation device 21 may be fixed or may be capable of rotation or other movement. Furthermore, the fixed membrane may have a rotating blade that fluidizes the solid layer on the membrane surface.

[0062] A hollow fiber membrane is preferred as the solid-liquid separation membrane, since it allows a large-area solid-liquid separation membrane to be housed compactly, making it easy to reduce the installation area. Furthermore, when the concentration of suspended solids in the supernatant liquid 26 is low, for example, about 0.1 to 50% by weight, it is preferred to use a solid-liquid separation membrane, particularly a hollow fiber membrane.

[0063] The separated liquid 31 from the solid-liquid separator 21 can be stored in a separated liquid container 32. The solid-liquid separator 21 and the separated liquid container 32 are connected by a separated liquid path 33. The separated liquid path 33 can be opened and closed by a valve 34. The separated liquid 31 that is no longer needed in the separated liquid container 32 can be discharged from a separated liquid discharge path 35.

[0064] If the amount of suspended matter adhering to the inside of the solid-liquid separator 21 increases, the performance of solid-liquid separation may deteriorate. In particular, if the solid-liquid separator 21 has a filter medium, a solid-liquid separation membrane, etc., the suspended matter may adhere to the filter medium, the solid-liquid separation membrane, etc. In order to maintain or restore the performance of solid-liquid separation, it is preferable to clean the solid-liquid separator 21.

[0065] The cleaning operation of the solid-liquid separator 21 may be a backwashing operation. In the backwashing operation, a liquid is supplied in the opposite direction to that in the solid-liquid separation operation. It is preferable to perform the backwashing operation by supplying a liquid to the filter medium, solid-liquid separation membrane, etc. from the outlet side. Even when the liquid is supplied to the inlet side in the cleaning operation, the floating matter adhering to the filter medium, etc. is separated and returned to a fluid slurry state, which makes it possible to perform the cleaning operation of the filter medium, etc.

[0066] The washing liquid used in the washing operation may be any liquid having a lower concentration of suspended solids than the supernatant liquid 26, and may also be a liquid containing no suspended solids. Separation liquid 31 can also be used as the washing liquid. In this case, even if separation liquid 31 gets mixed into the supernatant liquid 26, the effect on the operation can be suppressed. Separation liquid 31 in separation liquid container 32 can be supplied to solid-liquid separator 21 via separation liquid return line 37 by the power of return pump 36. During the washing operation using separation liquid 31, valve 34 of separation liquid path 33 is closed.

[0067] While the separation liquid 31 is stored in the separation liquid container 32, the suspended matter in the separation liquid 31 may be allowed to settle. The liquid with a reduced concentration of suspended matter may be discharged from the separation liquid discharge channel 35, and the liquid with an increased concentration of suspended matter due to settling may be used for cleaning. Conversely, the liquid with an increased concentration of suspended matter due to settling may be discharged from the separation liquid discharge channel 35, and the liquid with an increased concentration of suspended matter may be used for cleaning.

[0068] The cleaning operation of the solid-liquid separator 21 is preferably carried out as appropriate when the separated liquid 31 decreases or when the differential pressure between the inlet and outlet sides of the solid-liquid separator 21 increases. This restores the functionality of the solid-liquid separator 21 and allows the concentration operation to be continued effectively. By temporarily carrying out a cleaning operation in contrast to the concentration operation that is carried out continuously, fluctuations in the slurry concentration due to the cleaning operation can be suppressed.

[0069] Concentrated slurry 25 can be obtained by removing separated liquid 31 from supernatant liquid 26. Although not specifically shown, concentrated slurry 25 concentrated in concentration operation section 20 may be supplied to crystallizer 10. For example, a line 27 may be provided to return a portion of concentrated slurry 25 to the lower part of concentration reaction tank 13 or to outflow line 12b.

[0070] For example, if a line 27 for returning concentrated slurry 25 is installed, as indicated by the two-dot chain line in Figure 3, long-term continuous operation is possible as a batch continuous method without discharging particle waste liquid. If line 27 for returning concentrated slurry 25 is omitted, the slurry concentrated in the concentration operation unit 20 before particle growth has progressed sufficiently becomes waste liquid. If line 27 for returning concentrated slurry 25 is installed, low-concentration suspended solids (SS) discharged from the overflow discharge line 16 can be concentrated in the concentration operation unit 20, allowing particles to grow and be recovered as high-concentration slurry. This reduces the load on the filtration device in the subsequent solid-liquid separation device 21, making it possible to recover a cleaner separated liquid 31.

[0071] Examples of membrane concentrators used in the solid-liquid separator 21 include rotary flat membranes, devices with rotating blades relative to fixed flat membranes, hollow fiber membranes, etc. In addition to membranes, SS can also be directly recovered using concentration using filter cloths, centrifugation, sedimentation, or dehydrators such as belt presses and filter presses.

[0072] The present invention has been described above based on preferred embodiments, but the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention. The particles produced by reactive crystallization are not particularly limited and may be inorganic or organic. For example, the method can be applied to the production of cathode active materials for lithium-ion batteries and various other applications. The dispersion medium for the slurry may be water or an organic solvent. [Example]

[0073] Next, examples and comparative examples will be shown to clarify the effects of the present invention, but the present invention is not limited to these examples.

[0074] Example 1 A crystallizer 10 having the general configuration shown in Figure 1 was constructed. The initial capacity of the crystallizer was 4 L, and after overflow discharge it was 15 L. The total feed rate of all raw materials was adjusted to 67 mL / min, so that the residence time would be 60 min at the initial capacity of the crystallizer. The raw material liquids were as follows:

[0075] Nickel sulfate, cobalt sulfate, and manganese sulfate were used as metal sources, and the concentration of each was adjusted to 1.5 mol / L using ion exchange liquid (pure water). The molar ratio of the metals supplied to the device was determined by allocating the amount of raw material supplied according to the molar ratio required for the product. The metal sources were supplied with caustic soda at a concentration of 20 wt% and an ammonia source at a concentration of approximately 10 wt%, and the specified pH and temperature were then maintained. The operating pH was set to 11.0, and the operating temperature to 50°C.

[0076] The reaction liquid (slurry) obtained by mixing the raw material liquids was circulated at 11 L / min, and reaction liquid 11a was mixed with raw material liquids 10a, 10b, and 10c in main reaction section 11 and concentration reaction tank 13, reacted, and then circulated within the system. This circulation flow agitates stirring zone 14 of concentration reaction tank 13. Here, nitrogen gas is supplied to main reaction section 11 through the bottom of concentration reaction tank 13 at a rate of less than 5 mL / min to produce divalent metal hydroxide from the metal source and alkali.

[0077] The concentration reaction tank 13 is cylindrical, with a diameter D of 200 mm, excluding the funnel-shaped lower part, and is equipped with an overflow discharge channel 16 at a height L of 1000 mm from the bottom. The overflow occurred when 3θ, the elapsed time coefficient, had elapsed since the start of operation. After that, the operation continued until 11θ (660 min), the elapsed time coefficient, had elapsed, and the supernatant liquid was discharged at 67 mL / min, the same amount as the raw material supply rate. The elapsed time coefficient is a value obtained by dividing the actual elapsed time by the residence time.

[0078] During operation, a small amount of approximately 100 mL was discharged from the bottom of the concentration reaction tank 13 every 60 minutes only during sampling. The product slurry was collected from the bottom of the concentration reaction tank 13. The supernatant slurry was collected from the overflow discharge path 16. The analysis results of the slurry will be described later.

[0079] Example 2 As shown in Figure 3, the crystallizer 10 was equipped with a concentration operation section 20, and the operation was the same as in Example 1, except that the nitrogen gas supply rate was 10 mL / min. The operation was continued until 28θ (1680 min) had elapsed as an elapsed time coefficient. As in Example 1, product slurry was collected from the bottom of the concentration reaction tank 13 only during sampling. The supernatant slurry discharged by overflow after 3θ had elapsed was entirely recovered via the membrane concentration unit of the concentration operation section 20. The analysis results of the slurry will be described later.

[0080] Example 3 The dimensions of the apparatus used in Example 2 were slightly changed. Specifically, the apparatus capacity was 1 L at the start and 6.2 L at the time of overflow discharge. The total feed rate of all raw materials was adjusted to 25 mL / min so that the residence time was 40 min at the initial apparatus capacity. The concentration reaction tank 13 was cylindrical with a diameter D of 80 mm, excluding the funnel-shaped lower part, and an overflow discharge channel 16 was provided at a height L of 1000 mm from the bottom. Other than that, the operation was carried out in the same manner as in Example 2.

[0081] In Example 3, the operation was continued until an elapsed time coefficient of 20θ (1200 min) had elapsed. As in Example 1, the product slurry was collected from the bottom of the concentration reaction tank 13 only during sampling. The supernatant slurry discharged by overflow after 3θ had elapsed was entirely recovered via the membrane concentration unit of the concentration operation section 20. The analysis results of the slurry will be described later.

[0082] (Comparative Example 1) A crystallizer 100 was produced having a configuration generally shown in Figure 4. A reaction liquid 11a is supplied from the main reaction section 11 to the retention tank 40 through an inlet line 12a and returned to the main reaction section 11 through an outlet line 12b using a circulation pump 15.

[0083] The total supply rate of all raw materials was adjusted to 25 mL / min, with an apparatus capacity of 1 L and a residence time of 40 min. The raw material solutions 10a, 10b, 10c, etc. were the same as those in Example 1, and the operating pH and operating temperature were also set to the same as those in Example 1. A supply path 41 for the raw material solution 10c, etc. was installed along the central axis of the residence tank 40.

[0084] The slurry of reaction liquid 11a obtained by mixing the raw material liquids was circulated at 8 L / min, and reaction liquid 11a was mixed with raw material liquids 10a, 10b, and 10c in main reaction section 11 and retention tank 40, reacted, and circulated within the system. This circulation flow agitates the inside of retention tank 40. Here, nitrogen gas was supplied to the bottom of retention tank 40 at 20 mL / min to produce divalent metal hydroxide from the metal source and alkali.

[0085] Slurry was discharged at a rate of 25 mL / min, the same amount as the raw material supply rate, from overflow discharge channel 16 provided on the outer periphery of retention tank 40. The slurry discharged as overflow was used for sampling. The analysis results of the slurry will be described later.

[0086] (Slurry analysis results) The results of analyzing the slurries obtained using the devices of Examples 1 to 3 and Comparative Example 1 will be described. FIG. 5 is a graph showing the change in the SS concentration of the slurry collected in Example 1. The SS concentration of the product collected from the bottom of the concentration reaction tank 13 is designated "Example 1," and the SS concentration of the supernatant liquid collected as the overflow is designated "Example 1 (OF)." The particle size distribution was measured by a laser light diffraction scattering method.

[0087] The particle size distribution of the product obtained after 11θ in Example 1 is shown in Figure 6. From this particle size distribution, it can be seen that the median diameter is 4.213 μm, the mean diameter is 4.109 μm, the mode diameter is 4.562 μm, the standard deviation is 0.124 μm, the 10% diameter is 2.913 μm, the 20% diameter is 3.345 μm, the 30% diameter is 3.622 μm, the 40% diameter is 3.922 μm, the 50% diameter is 4.213 μm, the 60% diameter is 4.501 μm, the 70% diameter is 4.089 μm, the 80% diameter is 5.138 μm, and the 90% diameter is 5.843 μm.

[0088] The particle size distribution of the supernatant obtained after 11θ in Example 1 is shown in Figure 7. From this particle size distribution, it can be seen that the 10% diameter is 2.628 μm, the 20% diameter is 3.307 μm, the 30% diameter is 3.355 μm, the 40% diameter is 3.618 μm, the 50% diameter is 3.901 μm, the 60% diameter is 4.210 μm, the 70% diameter is 4.546 μm, the 80% diameter is 4.909 μm, and the 90% diameter is 5.530 μm.

[0089] 8, 9, and 10 show the changes in SS concentration, D50 value (median diameter), and particle size distribution evaluation index (D90-D10) / D50 value over time for the products obtained in Examples 1 to 3 and Comparative Example 1. The products in Examples 1 to 3 are slurries collected from the bottom of the concentration reaction tank 13. In these products, the SS concentration increases over time, while the particle size also grows. Furthermore, the (D90-D10) / D50 value is small, less than 1, indicating that the particles grow more uniformly.

[0090] In Comparative Example 1, the slurry discharged as overflow was used as the product. After the elapsed time factor reached 5, the SS concentration and particle size remained approximately constant, and no further concentration or particle growth was observed. In addition, the (D90-D10) / D50 value was large at approximately 1.2, indicating a broad particle size distribution.

[0091] 11 and 12 show the changes in the SS concentration of the supernatant collected as overflow in Examples 1 to 3 and the particle size distribution evaluation index (D90-D10) / D50 value. As mentioned above, sampling of the supernatant began after the elapsed time index reached 3. The results for the supernatant are labeled "Example 1 (OF)," "Example 2 (OF)," and "Example 3 (OF)," respectively, to distinguish them from the product. While the SS concentration of the supernatant shown in FIG. 11 is lower than the SS concentration of the product shown in FIG. 8, the (D90-D10) / D50 value of the supernatant shown in FIG. 12 is approximately the same as the (D90-D10) / D50 value of the product shown in FIG. 10.

[0092] 13, 14, and 15 show SEM data of particles in the product of Comparative Example 1, the product of Example 2, and the supernatant of Example 2. It can be seen that the particle size of the product of Comparative Example 1 is relatively variable. In Example 2, it can be seen that the particle size of both the product and the supernatant is relatively uniform.

[0093] In Examples 2 and 3, the particle size distribution evaluation index (D90-D10) / D50 value and D50 value (median diameter) obtained by recovering all of the slurry discharged by overflow in a membrane concentration unit were as follows.

[0094] Example 2: (D90-D10) / D50=0.64, D50=4.7 μm Example 3: (D90-D10) / D50=0.94, D50=4.1 μm

[0095] The recovery rate of SS recovered via overflow relative to the total solid content of the product was as follows:

[0096] Example 2: SS recovery rate 21% Example 3: SS recovery rate 1.8%

[0097] The higher the separation performance in the sedimentation concentration operation, the more particles are recovered from the bottom of the concentration reaction tank, and the fewer particles are recovered from the overflow. The higher the separation performance, the smaller the particle size tends to be. When the separation performance is relatively low, the amount of particles contained in the overflow increases, and particles with a particle distribution similar to that of the particle group in the slurry circulating in the crystallizer are recovered from the overflow by the membrane concentration unit. Production management, such as whether to increase or decrease the separation performance, can be appropriately determined depending on the operating procedures, the intended use of the target product, etc.

[0098] According to the analysis results of Examples 1 to 3, it was found that although the concentration of particle groups differs between the upper and lower parts of the concentration reaction tank, the particle size distribution itself that constitutes the particle groups does not change. The reason why the particle groups of the product obtained by sedimentation concentration and the particle groups contained in the supernatant liquid have a similar particle size distribution is not clear, but possible reasons include the formation of particle groups by electrostatic aggregation of particles, or the movement and uniformization of particle groups at the lower part to the upper part due to gas floating in the liquid or thermal convection.

[0099] When the experiment was repeated under conditions other than those of Examples 1 to 3, the same phenomenon was observed even when the particle size distribution was broader, and the particle size distribution in the lower part (high concentration) and the particle size distribution in the upper part (low concentration) were identical.

[0100] The following reference 1, available through J-STAGE, operated by the Japan Science and Technology Agency (JST), suggests that the apparent particle size distribution changes very little with depth from the liquid surface, and that as the solid concentration increases, interference between particle groups slows down settling and narrows the spread of the distribution.

[0101] Reference 1: Itsuma Sekiguchi et al., "Settling Behavior of Suspended Particles in the Interfered Settling Region (1st Report)," Journal of the Mining Industry of Japan, Vol. 91, No. 1053, 1975, pp. 721-726. https: / / www.jstage.jst.go.jp / article / shigentosozai1953 / 91 / 1053 / 91_1053_721 / _article / -char / ja

[0102] A settling thickener tank can be designed by taking into account the settling velocity of particles, the ascending velocity of the supernatant liquid, and the upward flow of gas. The ascending velocity of the supernatant liquid can be set by the area relative to the raw material supply rate. If the settling velocity of stationary slurry particles (v) (m / s), the raw material inflow rate (q) (ml / min), the area (A), and the allowance for the upward gas flow (α (a constant greater than 1)), the required area (A) can be calculated as A > α·q / v. While a sufficiently large area (A) is desirable from the perspective of particle separation, the planar size of the settling thickener tank, including area (A), is determined by taking into account equipment installation constraints. The height of the settling thickener tank also takes into account building height constraints. Particle group concentration is possible even if sufficient area for particle separation is not available. In this case, adding a particle recovery process such as membrane separation in the downstream stage can improve the SS recovery rate while still achieving the effect of settling thickener.

[0103] (Reference example 1) 16, it is also conceivable to supply raw material liquids 10a, 10b, and 10c from the upper part of retention tank 40, and then send the resulting reaction liquid 11a from the lower part of retention tank 40 to settling separation and discharge mechanism 43 via delivery path 42a by the power of circulation pump 15. In lower part 44 of settling separation and discharge mechanism 43, concentrated slurry whose solid concentration has increased to, for example, 8 wt% through settling separation can be discharged via discharge path 45. In upper part 46 of settling separation and discharge mechanism 43, slurry whose solid concentration is, for example, about 2 wt% can be returned to retention tank 40 via return path 42b.

[0104] (Reference example 2) It is also possible to omit the main reaction section 11 and circulation path 12 of the crystallizer 10. For example, as shown in FIG. 17, raw material liquids 10a, 10b, and 10c may be supplied from the top of the concentration reaction tank 13. By installing an agitator 51 below the concentration reaction tank 13, a stirring zone 14 can be formed. The agitator 51 is not limited to a type having a bearing at the bottom, and may be a type suspended from above.

[0105] Like the crystallizer 10 shown in Figure 1, the crystallizer 50 shown in Figure 17 has an overflow discharge path 16 for discharging overflow. As a result, a clarified zone 18 in which a supernatant liquid is produced is formed in the upper part of the concentration reaction tank 13. A concentration zone 17 in which particles settle is formed between the stirring zone 14 and the clarified zone 18. The interior of the concentration reaction tank 13 is divided into an upper and lower zone: the stirring zone 14, the concentration zone 17, and the clarified zone 18. The reaction takes place only in the stirring zone 14.

[0106] A discharge line 52 is connected to the bottom of the concentration reaction tank 13, and discharges the slurry using the power of a discharge pump 53. The lower end of the concentration reaction tank 13 may be funnel-shaped. The cross-sectional shapes of the concentration zone 17 and the clarification zone 18 may be continuous cylinders with the same shape above and below. The inner surfaces of the concentration reaction tank 13 in the concentration zone 17 and the clarification zone 18 may be tapered, flat, or may have irregularities. To improve settling performance, a settling device such as an inclined pipe or an inclined plate may be provided in the concentration zone 17 or the clarification zone 18. [Explanation of symbols]

[0107] H: Height from the bottom of the concentration reactor to the inflow path L Height from the bottom of the concentration reactor to the overflow level Ls Starting liquid level Lt Overflow Level Vs Volume in the concentration reactor at the start of reaction crystallization Vt The volume of the concentration reactor that increased after the start of reaction crystallization 10 Crystallizer 11 Main reaction section 11a Reaction solution 12 Circulation Route 12a Inflow route 12b Outflow route 13 Concentration reaction tank 14 Mixing Zone 15 Circulation Pump 16 Overflow discharge channel 17 Enrichment Zone 18 Clear Zone

Claims

1. A crystallization method for performing reactive crystallization by forming a circulation path between a main reaction section and a concentration reaction tank, the circulation path has an inflow path from the main reaction section to the concentration reaction tank and an outflow path from the concentration reaction tank to the main reaction section, A raw material solution in which a raw material substance is dissolved in a solvent is supplied to the main reaction section, and a reaction solution obtained by mixing the raw material solutions is circulated between the main reaction section and the concentration reaction tank to form a reaction field, a stirring zone is formed in the lower part of the concentration reaction tank by connecting the inflow path and the outflow path; a clarified zone in which a supernatant liquid is produced is formed in the upper part of the concentration reaction tank; and a concentration zone in which particles settle is formed between the stirring zone and the clarified zone.

2. The crystallization method described in claim 1, characterized in that a circulation pump is provided between the concentration reaction tank and the main reaction section, and the reaction field is formed by the circulation pump returning the reaction liquid from the concentration reaction tank to the main reaction section.

3. A crystallization method as described in claim 1 or 2, characterized in that the stirring zone promotes stirring of the reaction liquid by the flow of the reaction liquid from the inlet path toward the outlet path.

4. 4. The crystallization method according to claim 1, wherein a ratio L / D of a height L from a lower end of the concentration reaction tank to an overflow level to a diameter D of the concentration reaction tank is within a range of 2 to 20.

5. The crystallization method according to any one of claims 1 to 4, wherein the liquid level in the concentration reaction tank is gradually increased during reactive crystallization, and the concentration zone and the clarification zone are formed during the reactive crystallization process.

6. 6. The crystallization method according to claim 5, wherein a ratio Vt / Vs of an increase in the volume Vt in the concentration reaction tank after the start of the reactive crystallization to a volume Vs in the concentration reaction tank at the start of the reactive crystallization is greater than 1.

7. The crystallization method according to any one of claims 1 to 6, wherein a ratio H / L of a height H from a lower end of the concentration reaction tank to a height L from a lower end of the concentration reaction tank to an overflow level is less than 20% as a percentage.

8. A crystallization apparatus that forms a circulation path between a main reaction section and a concentration reaction tank and performs reactive crystallization, the circulation path has an inflow path from the main reaction section to the concentration reaction tank and an outflow path from the concentration reaction tank to the main reaction section, A raw material solution in which a raw material substance is dissolved in a solvent is supplied to the main reaction section, and a reaction solution obtained by mixing the raw material solutions is circulated between the main reaction section and the concentration reaction tank to form a reaction field, a stirring zone formed at a lower part of the concentration reaction tank by connecting the inflow path and the outflow path; a clarified zone in which a supernatant liquid is produced formed at an upper part of the concentration reaction tank; and a concentration zone in which particles settle is formed between the stirring zone and the clarified zone.

9. A crystallization apparatus as described in Claim 8, characterized in that a circulation pump is provided between the concentration reaction tank and the main reaction section, and the reaction field is formed by the circulation pump returning the reaction liquid from the concentration reaction tank to the main reaction section.

10. A crystallization apparatus as described in claim 8 or 9, characterized in that the stirring zone promotes stirring of the reaction liquid by the flow of the reaction liquid from the inlet path toward the outlet path.

11. The crystallization apparatus according to any one of claims 8 to 10, wherein a ratio L / D of a height L from a lower end of the concentration reaction tank to an overflow level to a diameter D of the concentration reaction tank is within a range of 2 to 20.

12. The crystallization apparatus according to any one of claims 8 to 11, characterized in that a ratio H / L of a height H from a lower end of the concentration reaction tank to a height L from a lower end of the concentration reaction tank to an overflow level is less than 20% as a percentage.

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