Crystallization system, crystallization method, and program

Abstract

To stably recover a separation target.SOLUTION: A crystallization system includes: a crystallization tank into which dissolution liquid is supplied, and in which, a separation target is crystallized from the dissolution liquid, and the separation-target-crystallized dissolution liquid is stored as slurry; a solid-liquid separation unit into which the slurry is introduced from the crystallization tank and which separates the separation target being a solid component from the slurry by using the filter; and a control unit that controls supply of the slurry from the crystallization tank to the solid-liquid separation unit. While the supply of the slurry from the crystallization tank to the solid-liquid separation unit is performed by flow rate constant control in which a constant amount of the slurry is supplied per unit time, when a filtration layer being a layer of the separation target is formed on the filter, the control unit switches the supply of the slurry from the crystallization tank to the solid-liquid separation unit from the flow rate constant control to a liquid level constant control in which a liquid level of the dissolution liquid of the crystallization tank is constant.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a crystallization system, a crystallization method, and a program. [Background technology]

[0002] For example, crystallization may be carried out to recycle polyester. Patent Document 1 describes that dimethyl aromatic dicarboxylic acid and dihydric alcohol can be recovered with high purity by carrying out crystallization. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-249597 Summary of the Invention [Problem to be solved by the invention]

[0004] Here, when recovering the separation target by crystallization, it is required to recover the separation target stably.

[0005] The present disclosure is intended to solve the above-mentioned problems, and aims to provide a crystallization system and a crystallization method that can stably recover a separation target. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the crystallization system according to the present disclosure comprises: a crystallization tank into which a solution is supplied, a substance to be separated is crystallized from the solution, and the solution from which the substance to be separated has been crystallized is stored as a slurry; a solid-liquid separation unit into which the slurry is introduced from the crystallization tank and which separates the substance to be separated, that is, a solid component, from the slurry using a filter; and a control unit that controls the supply of the slurry from the crystallization tank to the solid-liquid separation unit, wherein while the supply of the slurry from the crystallization tank to the solid-liquid separation unit is controlled by constant flow rate control in which a constant amount of the slurry is supplied per unit time, when a filtration layer, which is the layer to be separated, is formed on the filter, the control unit switches the supply of the slurry from the crystallization tank to the solid-liquid separation unit from the constant flow rate control to constant liquid level control in which the liquid level of the solution in the crystallization tank is kept constant.

[0007] In order to solve the above-mentioned problems and achieve the object, a crystallization method according to the present disclosure includes the steps of: supplying a solution to a crystallization tank; crystallizing a separation target from the solution in the crystallization tank to obtain a slurry; supplying the slurry from the crystallization tank to a solid-liquid separation section and separating the separation target, which is a solid component, from the slurry using a filter provided in the solid-liquid separation section; and controlling the supply of the slurry from the crystallization tank to the solid-liquid separation section, wherein in the step of controlling the supply of the slurry, while the supply of the slurry from the crystallization tank to the solid-liquid separation section is under constant flow rate control in which a constant amount of the slurry is supplied per unit time, when a filtration layer, which is the layer to be separated, is formed on the filter, the supply of the slurry from the crystallization tank to the solid-liquid separation section is switched from the constant flow rate control to constant liquid level control in which the liquid level of the solution in the crystallization tank is kept constant.

[0008] In order to solve the above-mentioned problems and achieve the object, the program according to the present disclosure causes a computer to execute the following steps: supplying a solution to a crystallization tank; crystallizing a separation target from the solution in the crystallization tank to obtain a slurry; supplying the slurry from the crystallization tank to a solid-liquid separation section and separating the separation target, which is a solid component, from the slurry using a filter provided in the solid-liquid separation section; and controlling the supply of the slurry from the crystallization tank to the solid-liquid separation section, wherein in the step of controlling the supply of the slurry, while the supply of the slurry from the crystallization tank to the solid-liquid separation section is under constant flow rate control so that a constant amount of the slurry is supplied per unit time, if a filtration layer, which is the layer to be separated, is formed on the filter, the supply of the slurry from the crystallization tank to the solid-liquid separation section is switched from the constant flow rate control to constant liquid level control so that the liquid level of the solution in the crystallization tank is constant. [Effects of the Invention]

[0009] According to the present disclosure, the separation target can be stably recovered. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a polyester recycling process according to the present embodiment. [Figure 2] FIG. 2 is a schematic diagram of the separation system according to the first embodiment. [Figure 3] FIG. 3 is a schematic side view of the crystallization system. [Figure 4] FIG. 4 is a schematic cross-sectional view showing a part of the solid-liquid separation section. [Figure 5] FIG. 5 is a schematic diagram showing the separation mechanism of the solid-liquid separation section. [Figure 6] FIG. 6 is a schematic block diagram of the control unit. [Figure 7] FIG. 7 is a flowchart illustrating the control flow of the control unit. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments, and when there are multiple embodiments, the present invention also includes configurations in which the respective embodiments are combined.

[0012] (First embodiment) (Recycling process) FIG. 1 is a schematic diagram of a polyester recycling process according to this embodiment. In this embodiment, the polyester raw material Pm is depolymerized to form monomers, and the monomers are then polymerized again to recycle (regenerate) the polyester raw material Pm. Specifically, as shown in FIG. 1, the polyester raw material Pm is flaked (step S100), the solution is mixed with a reaction solvent M for depolymerization (step S102), the depolymerized polyester monomers are purified (separated) to produce a carboxylic acid-derived monomer D and an alcohol component monomer E (step S104), the monomer D is hydrolyzed, and the reaction solvent M is separated (step S106), and the monomer F produced by hydrolysis of the monomer D is polymerized with the monomer E (step S108), thereby regenerating the polyester raw material Pm. In addition, in the recycling process employing the separation system 1 of this embodiment, the flaking step S100 may be omitted, or only the process of recovering monomers D and E shown in step S104 and monomer F shown in step S106 may be performed without performing the repolymerization process as in step S108.

[0013] (Polyester raw material) In this embodiment, the polyester raw material Pm to be depolymerized is a substance containing polyester. The polyester raw material Pm is not particularly limited, but examples include waste products such as polyethylene terephthalate (PET), polyethylene butylene terephthalate (PEBT), polybutylene terephthalate (PBT), polycyclohexane dimethyl terephthalate (PCT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and polycarbonate (PC). The polyester raw material Pm is not limited to those containing only polyester components, but also includes components other than polyester components. Examples of components other than polyester contained in the polyester raw material Pm include plastics other than polyester, such as polyethylene, polystyrene, polypropylene, and polyvinyl chloride, metals, dyes, pigments, and polymerization catalysts. Examples of the polyester raw material Pm include clothing in which polyester and other components are knitted into fibers. Hereinafter, components other than polyester contained in the polyester raw material Pm are referred to as impurities.

[0014] (Reaction solvent) The reaction solvent M is a solvent that reacts with the polyester to depolymerize the polyester, and may be, for example, at least one of methanol, ethanol, water, and ethylene glycol.

[0015] (Carboxylic acid-derived monomers) The carboxylic acid-derived monomer D is a monomer having a carboxyl group produced by depolymerization of a polyester. Monomer D may be, for example, dimethyl carboxylate or diethyl carboxylate. Furthermore, monomer D is preferably a terephthalic acid monomer, such as dimethyl terephthalate (DMT).

[0016] (Alcohol component monomer) The alcohol component monomer E is an alcohol component monomer produced by the depolymerization reaction of the polyester. The alcohol component monomer E may be, for example, a dihydroxy compound (dihydric alcohol), or more specifically, ethylene glycol (EG).

[0017] In the following, an example will be described in which the polyester is PET, the reaction solvent M is methanol, the monomer D is DMT, and the monomer E is EG.

[0018] (separate system) Fig. 2 is a schematic diagram of a separation system according to the first embodiment. The separation system 1 according to the first embodiment is a system that monomerizes polyester contained in a polyester raw material Pm to produce monomers D and E. As shown in Fig. 2, the separation system 1 includes a raw material storage section 10, a dissolving section 12, a solid-liquid separation section 13, a solvent storage section 14, a reaction section 16, a separation section 18, a control section 30, a temporary storage section 70, and a crystallization system 80.

[0019] Hereinafter, the Z direction is the vertical direction (up and down direction). The vertically upward direction of the Z direction is referred to as the Z1 direction, and the vertically downward direction is referred to as the Z2 direction.

[0020] (Raw material storage section) The raw material storage section 10 is a tank into which the polyester raw material Pm is introduced and stored. In this embodiment, the raw material storage section 10 stores flaked polyester raw material Pm, but the shape and size of the polyester raw material Pm may be arbitrary. The raw material storage section 10 is connected to the dissolving section 12 via an inlet pipe 10a. The polyester raw material Pm in the raw material storage section 10 is supplied to the dissolving section 12 through the inlet pipe 10a. The inlet pipe 10a is provided with an adjustment section 10b that adjusts the amount of polyester raw material Pm supplied from the raw material storage section 10 to the dissolving section 12. The adjustment section 10b is, for example, an on-off valve. When open, the adjustment section 10b allows the polyester raw material Pm in the raw material storage section 10 to be supplied to the dissolving section 12, and when closed, the adjustment section 10b stops the supply of the polyester raw material Pm in the raw material storage section 10 to the dissolving section 12. However, the adjustment section 10b is not limited to an on-off valve and may be any mechanism that can adjust the supply of the polyester raw material Pm to the dissolving section 12. The polyester raw material Pm may be supplied directly to the dissolving section 12 without passing through the raw material reservoir 10, the introduction pipe 10a, and the adjusting section 10b.

[0021] (melting part) The dissolving unit 12 is a tank that stores a solution Pd. The solution Pd is a solution produced by mixing a polyester raw material Pm and a monomer D. Here, the polyester component contained in the polyester raw material Pm dissolves in the monomer D, but impurities, which are components other than the polyester contained in the polyester raw material Pm, remain without dissolving in the monomer D. Therefore, it can be said that the solution Pd contains a polyester solution P in which the polyester contained in the polyester raw material Pm is dissolved in the monomer D, and the impurities contained in the polyester raw material Pm.

[0022] Monomer D and polyester raw material Pm are supplied to dissolution section 12. In dissolution section 12, the polyester contained in polyester raw material Pm dissolves in monomer D, while impurities remain undissolved in monomer D, producing polyester solution P and impurity-containing solution Pd. Dissolving polyester in monomer D in this manner reduces viscosity and improves fluidity, allowing polyester to be easily introduced into reaction section 16. Note that the polyester solution P does not necessarily have to be one in which all of the polyester is dissolved in monomer D; at least a portion of the polyester may be insoluble in monomer D. Furthermore, if there is a component soluble in monomer D among the components other than polyester contained in polyester raw material Pm, the polyester solution P may also contain that component dissolved in monomer D.

[0023] The dissolving section 12 is connected to a first reaction section 16A, which will be described later, via an inlet pipe 12a. The solution Pd in ​​the dissolving section 12 is supplied to the first reaction section 16A through the inlet pipe 12a. The inlet pipe 12a is also provided with a supply section 12a1. The supply section 12a1 is a mechanism for supplying the polyester solution P in the dissolving section 12 to the first reaction section 16A, and is a pump in this embodiment.

[0024] In this embodiment, the melting section 12 is provided with a heating section 12A. The heating section 12A heats the interior of the melting section 12, thereby heating the monomer D and polyester raw material Pm supplied to the melting section 12 to a predetermined temperature. The predetermined temperature is a temperature at which the polyester can be dissolved in the monomer D. Heating at this predetermined temperature allows the polyester contained in the polyester raw material Pm to be properly dissolved in the monomer D. The predetermined temperature is preferably 140°C or higher and 300°C or lower, more preferably 160°C or higher and 280°C or lower, and even more preferably 190°C or higher and 250°C or lower. Note that the impurities also contain components that melt when heated to a predetermined temperature (a temperature at which the polyester can be dissolved in the monomer D). Therefore, if the impurities contain a component that melts when heated to a predetermined temperature, the impurities will be contained in the solution Pd in ​​a partially melted state. In this embodiment, the heating section 12A is provided in the melting section 12, but the location at which the heating section 12A is provided is not limited thereto and may be any location.

[0025] (Solvent reservoir) The solvent reservoir 14 is a tank into which the reaction solvent M is introduced and where the reaction solvent M is stored. The solvent reservoir 14 is connected to the reaction section 16 via an inlet pipe 14a. The reaction solvent M in the solvent reservoir 14 is supplied to the reaction section 16 through the inlet pipe 14a. More specifically, the inlet pipe 14a is provided with a heating and pressurizing section 14b that pressurizes and heats the reaction solvent M. The heating and pressurizing section 14b pressurizes and heats the reaction solvent M, thereby bringing the reaction solvent M into a supercritical state or a subcritical state (pressurized gas or pressurized liquid). The reaction section 16 is supplied with the reaction solvent M in a supercritical state or a subcritical state (pressurized gas or pressurized liquid).

[0026] (Reaction section) The reaction section 16 is a container into which the solution Pd and the reaction solvent M are introduced to depolymerize the polyester in the solution Pd. The reaction section 16 includes a first reaction section 16A and a second reaction section 16B.

[0027] (First reaction section) The first reaction section 16A is formed within the reaction section 16. In this embodiment, the first reaction section 16A can be said to be a portion of the reaction section 16 that is filled with a filler. The first reaction section 16A can use a known filler used in gas-liquid or liquid-liquid contactors, such as fillers similar to those used in contactors that bring heavy oil and water into contact to extract active ingredients. Specific examples of fillers include pipes made of stainless steel or the like, Raschig rings, Berl saddles, terrarettes, balls, and the like.

[0028] An inlet pipe 12a is connected to the first reaction unit 16A. More specifically, an inlet 16C, which is an opening of the inlet pipe 12a through which the dissolving solution Pd from the dissolving unit 12 is introduced, is connected to the first reaction unit 16A. The inlet 16C is connected to a surface 16A1 on the first direction D1 side of the first reaction unit 16A. The inlet pipe 12a is connected to the surface 16A1 so that the inlet 16C opens toward a second direction D2, which is opposite to the first direction D1. In this embodiment, the inlet 16C opening toward the second direction D2 is connected to the surface 16A1 of the first reaction unit 16A, but this is not limiting. For example, the inlet 16C does not have to be directly connected to the first reaction unit 16A. The inlet 16C opening toward the second direction D2 may be connected to a position closer to the first direction D1 than the surface 16A1 of the first reaction unit 16A within the reaction unit 16.

[0029] An inlet pipe 14a is connected to the reaction section 16. More specifically, an inlet 16D, which is an opening of the inlet pipe 14a through which the reaction solvent M is introduced from the solvent reservoir 14, is connected to the reaction section 16. The inlet 16D is connected closer to the second direction D2 than the surface 16A2 on the second direction D2 side of the first reaction section 16A. The inlet pipe 14a is connected closer to the second direction D2 than the surface 16A2 so that the inlet 16D opens toward the first direction D1 or from a side toward the center. In this embodiment, the inlet 16D, which opens toward the first direction D1 or from a side toward the center, is connected closer to the second direction D2 than the surface 16A2 of the first reaction section 16A. However, this is not limiting. For example, the inlet 16D may be directly connected to the first reaction section 16A or may be connected to the surface 16A2 of the first reaction section 16A.

[0030] In this embodiment, the inlet 16C through which the solution Pd is introduced opens in the second direction D2, and the inlet 16D through which the reaction solvent M is introduced opens in the first direction D1 or from the side toward the center. Therefore, the solution Pd and the reaction solvent M are introduced into the first reaction section 16A in directions facing each other.

[0031] The solution Pd introduced into the first reaction section 16A through the inlet 16C moves in the second direction D2 on the surface of the filler in the first reaction section 16A. Meanwhile, the reaction solvent M in a supercritical or subcritical state (pressurized gas or pressurized liquid) introduced through the inlet 16D moves in the first reaction section 16A in the first direction D1. In the first reaction section 16A, the reaction solvent M in a supercritical or subcritical state (pressurized gas or pressurized liquid) comes into contact with the solution Pd. The polyester in the solution Pd is depolymerized (reduced in molecular weight) by the reaction solvent M, and the depolymerized polyester is extracted into the reaction solvent M in a supercritical or subcritical state (pressurized gas or pressurized liquid). Hereinafter, the polyester depolymerized in the first reaction section 16A will be referred to as a first depolymerized polyester P1, and the mixture of the first depolymerized polyester P1 and the reaction solvent M (the reaction solvent M from which the first depolymerized polyester P1 has been extracted) will be referred to as a first solvent M1. The first solvent M1 containing the first depolymerized polyester P1 proceeds in the first direction D1 through the first reaction section 16A and is discharged to the first direction D1 side of the first reaction section 16A.

[0032] The first depolymerized polyester P1 includes monomers D and E produced by depolymerizing the polyester in the solution Pd, monomer D originally mixed in the solution Pd, and oligomers produced by depolymerizing the polyester. The oligomers referred to here are carboxylic acid- or alcohol-derived oligomers (carboxylic acid- or alcohol-derived oligomers with smaller molecular weights than polyester) that are not monomerized but are depolymerized from the polyester. The oligomers contained in the residual substance R in the polyester solution P are also depolymerized by the reaction solvent M. Therefore, the first depolymerized polyester P1 also includes the depolymerized residual substance R. The depolymerized residual substance R includes oligomers contained in the residual substance that have been depolymerized, as well as monomers D and E that are formed by depolymerizing the oligomers contained in the residual substance.

[0033] (Second reaction section) The second reaction section 16B is formed in the reaction section 16, and is formed at a location where the first solvent M1 is discharged from the first reaction section 16A. In this embodiment, the first solvent M1 is discharged in the first direction D1, and therefore the second reaction section 16B can be said to be a space formed on the first direction D1 side of the first reaction section 16A.

[0034] In the second reaction section 16B, the first depolymerized polyester P1 contained in the first solvent M1 is further depolymerized (reduced in molecular weight) by the reaction solvent M contained in the first solvent M1. Hereinafter, the first depolymerized polyester P1 further depolymerized in the second reaction section 16B will be referred to as the second depolymerized polyester P2, and the mixture of the second depolymerized polyester P2 and the reaction solvent M (the reaction solvent M in which the second depolymerized polyester P2 is dissolved) will be referred to as the second solvent M2. An outlet pipe 16a is connected to the second reaction section 16B. More specifically, an outlet 16E, which is an opening of the outlet pipe 16a through which the second solvent M2 is discharged from the second reaction section 16B, is connected to the second reaction section 16B. The second solvent M2 containing the second depolymerized polyester P2 in the second reaction section 16B is discharged from the outlet 16E through the outlet pipe 16a to the outside of the second reaction section 16B.

[0035] The second depolymerized polyester P2 contains the monomers D and E in the first depolymerized polyester P1, the monomers D and E produced by depolymerizing the oligomers in the first depolymerized polyester P1, and the oligomers produced by depolymerizing the first depolymerized polyester P1.

[0036] A discharge pipe 16b is connected to the bottom of the reaction section 16. More specifically, a discharge port 16F, which is an opening of the discharge pipe 16b through which non-extractable materials (described below) in the reaction section 16 are discharged, is connected to the bottom of the reaction section 16. The non-extractable materials include impurities such as metal compounds that were not extracted into the reaction solvent M and residues of undecomposed polyester that were not extracted into the reaction solvent M. That is, the non-extractable materials at the bottom of the reaction section 16 are discharged from the discharge port 16F through the discharge pipe 16b to the outside of the reaction section 16. The non-extractable materials discharged from the discharge port 16F can be considered to be components of the polyester solution P that were not introduced into the separation section 18 as the second solvent M2 (the reaction solvent M in which the second depolymerized polyester P2 is dissolved) and remained in the first reaction section 16A and the second reaction section 16B.

[0037] The reaction section 16 may also be provided with a heating section that heats the interior of the reaction section 16 and a pressurizing section that maintains the pressure inside the reaction section 16 at a predetermined value or higher. The temperature inside the reaction section 16 is preferably 250°C or higher and 400°C or lower, and more preferably 250°C or higher and 350°C or lower. The pressure inside the reaction section 16 is preferably 1 MPa or higher and 30 MPa or lower, and more preferably 6 MPa or higher and 25 MPa or lower. The pressurizing section and the heating section may be controlled by the control section 30.

[0038] (separation part) The separation unit 18 receives the second solvent M2 containing the second depolymerized polyester P2 and separates the second solvent M2 into the reaction solvent M, a monomer D derived from a carboxylic acid contained in the second depolymerized polyester P2, a monomer E of an alcohol component contained in the second depolymerized polyester P2, and a residual substance R. The separation unit 18 distills the second solvent M2 to separate it into the monomer D, the monomer E, and the residual substance R. The residual substance R is a component of the second solvent M2 other than the reaction solvent M, the monomer D, and the monomer E, and includes oligomers.

[0039] In this embodiment, the separation section 18 has a first separation section 18A, a second separation section 18B, and a third separation section 18C.

[0040] The first separation section 18A is a separation column connected to the outlet pipe 16a. A second solvent M2 containing a second depolymerized polyester P2 is introduced into the first separation section 18A via the outlet pipe 16a. The first separation section 18A separates the second solvent M2 into a low-boiling component and a high-boiling component having a higher boiling point than the low-boiling component. For example, in the first separation section 18A, the second solvent M2 may be heated to a predetermined temperature, and the gaseous component may be the low-boiling component and the liquid component may be the high-boiling component. The first separation section 18A is connected to outlet pipes 18Aa and 18Ab. The low-boiling component is discharged from the outlet pipe 18Aa, and the high-boiling component is discharged from the outlet pipe 18Ab.

[0041] The second separation section 18B is a separation column connected to the first separation section 18A via an outlet pipe 18Aa. Low-boiling point components are introduced into the second separation section 18B via the outlet pipe 18Aa. The second separation section 18B separates the low-boiling point components into a reaction solvent M and a monomer E. Outlet pipes 18Ba and 18Bb are connected to the second separation section 18B. The reaction solvent M is discharged from the outlet pipe 18Ba, and the monomer E is discharged from the outlet pipe 18Bb. The outlet pipe 18Ba is connected to the second separation section 18B and the solvent reservoir 14. Therefore, the reaction solvent M discharged from the second separation section 18B is returned to the solvent reservoir 14 and reused for depolymerization of polyester.

[0042] The third separation section 18C is a separation column connected to the first separation section 18A via the outlet pipe 18Ab. High-boiling components are introduced into the third separation section 18C via the outlet pipe 18Ab. The third separation section 18C further separates the high-boiling components into high-boiling residual substances R, low-boiling components containing reaction solvent M and monomer E, and monomer D. The third separation section 18C is connected to the outlet pipes 18Ca, 18Cb, and 18Cc. The outlet pipe 18Ca is connected to the second separation section 18B. The low-boiling components separated in the third separation section 18C are discharged to the second separation section 18B via the outlet pipe 18Ca. The monomer D separated in the third separation section 18C is discharged from the outlet pipe 18Cb and introduced into the temporary storage section 70. The residual substances R separated in the third separation section 18C are discharged from the outlet pipe 18Cc.

[0043] An inlet pipe 18Cd is connected to the third separation section 18C. The inlet pipe 18Cd is also connected to the dissolving section 12 and introduces the monomer D discharged from the third separation section 18C into the dissolving section 12. In the example shown in FIG. 2, the inlet pipe 18Cd branches off from the outlet pipe 18Cb. The inlet pipe 18Cd is provided with an adjustment section 18Ce that adjusts the amount of monomer D supplied from the third separation section 18C to the dissolving section 12. The adjustment section 18Ce is, for example, an on-off valve that, when open, allows the monomer D to be supplied to the dissolving section 12 and, when closed, stops the supply of the monomer D to the dissolving section 12. However, the adjustment section 18Ce is not limited to an on-off valve and may be any mechanism capable of adjusting the supply of monomer D to the dissolving section 12. In this embodiment, the adjustment section 18Ce is provided at the point where the inlet pipe 18Cd branches off from the outlet pipe 18Cb, but the adjustment section 18Ce may be provided at any position. Furthermore, the inlet pipe 18Cd does not have to be connected to the outlet pipe 18Cb, and may be directly connected to the third separation section 18 C. Furthermore, for example, the outlet pipe 18Cb may be provided with a reservoir (tank) for storing the monomer D, and the inlet pipe 18Cd may be connected to the reservoir.

[0044] An inlet pipe 18Cf is connected to the third separation section 18C. The inlet pipe 18Cf is also connected to the dissolving section 12 and introduces the remaining material R discharged from the third separation section 18C into the dissolving section 12. In the example of FIG. 2, the inlet pipe 18Cf branches off from the outlet pipe 18Cc. The inlet pipe 18Cf is provided with an adjustment section 18Cg that adjusts the amount of remaining material R supplied from the third separation section 18C to the dissolving section 12. The adjustment section 18Cg is, for example, an on-off valve that, when open, allows the remaining material R to be supplied to the dissolving section 12 and, when closed, stops the supply of the remaining material R to the dissolving section 12. However, the adjustment section 18Cg is not limited to an on-off valve and may be any mechanism capable of adjusting the supply of the remaining material R to the dissolving section 12. In this embodiment, the adjustment section 18Cg is provided at the point where the inlet pipe 18Cf branches off from the outlet pipe 18Cc, but the adjustment section 18Cg may be provided at any location. Furthermore, the inlet pipe 18Cf does not have to be connected to the outlet pipe 18Cc, and may be directly connected to the third separation section 18C.

[0045] For example, the discharge pipe 18Cc may be provided with a reservoir (tank) for storing the residual substance R, and the introduction pipe 18Cf may be connected to the reservoir. The introduction pipe 18Cf may be provided with a filter that allows oligomers in the residual substance R to pass through while collecting foreign matter in the residual substance R.

[0046] (Temporary storage section) The temporary storage section 70 is, for example, a tank, and temporarily stores the monomer D supplied from the third separation section 18C. The temporary storage section 70 is connected to the third separation section 18C via an outlet pipe 18Cb. The temporary storage section 70 is connected to the dissolution tank 82 via an outlet pipe 72. The temporary storage section 70 supplies the temporarily stored monomer D to the dissolution tank 82 of the crystallization system 80.

[0047] (Crystallization System) The crystallization system 80 crystallizes the monomer D from the solution containing the monomer D separated in the separation unit 18. The monomer D separated in the separation unit 18 may contain impurities. The crystallization system 80 crystallizes the highly pure monomer D from the solution containing the monomer D, removing the impurities. Examples of impurities include isomers of the monomer D that were not completely separated by distillation in the third separation unit 18C. For example, when the monomer D is DMT, the isomer of DMT is DMI (dimethyl isophthalate), which is derived from the copolymerized isophthalic acid (IPA). DMI has a boiling point close to that of DMT, making it difficult to separate by distillation. However, it can be separated by crystallization. That is, in this embodiment, highly pure monomer D can be extracted by crystallizing the monomer D (DMT) without crystallizing DMI. Hereinafter, the highly pure monomer D extracted by crystallization will be referred to as "monomer HD" as appropriate.

[0048] Furthermore, in this embodiment, the crystallization system 80 hydrolyzes the crystallized monomer HD to produce PTA (high-purity terephthalic acid). However, the crystallization system 80 is not limited to performing the process of obtaining PTA from the crystallized monomer HD, and may perform only the process of crystallizing the monomer HD.

[0049] Furthermore, although the crystallization system 80 of this embodiment is provided in the separation system 1 and used to crystallize the monomer HD, the use of the crystallization system 80 is not limited thereto. The crystallization system 80 may be a system that separates, by crystallization, from a solution of any component, a separation target of any component dissolved in the solution.

[0050] The crystallization system 80 according to this embodiment will be specifically described below. Figure 3 is a schematic side view of the crystallization system.

[0051] The crystallization system 80 includes a dissolution tank 82, an adjustment section 86, a crystallization tank 90, an agitation section 100, a solid-liquid separation section 120, a melting tank 150, a temporary melt storage tank 160, and a hydrolysis separation reaction section 170. In this embodiment, the crystallization system 80 is connected downstream of the discharge pipe 72, and extracts, by crystallization, monomers HD from a solution L containing dissolved monomers D that flows through the discharge pipe 72.

[0052] (dissolving tank) The dissolution tank 82 is a tank that stores a solution L in which the monomer D is dissolved. The dissolution tank 82 is connected to the temporary storage section 70 via an outlet pipe 72. The monomer D containing impurities separated in the third separation section 18C is introduced from the temporary storage section 70 into the dissolution tank 82. A solvent that dissolves the monomer D is also introduced into the dissolution tank 82. As a result, the monomer D is dissolved in the solvent in the dissolution tank 82 and stored as a solution L. Note that any liquid may be used as the solvent, but methanol is used in this embodiment.

[0053] The dissolution tank 82 is connected to an adjustment unit 86 and a crystallization tank 90 via an inlet pipe 84. The solution L stored in the dissolution tank 82 is introduced into the crystallization tank 90 via the inlet pipe 84 and the adjustment unit 86. The dissolution tank 82 is located in the Z1 direction (vertically above) the crystallization tank 90, which will be described later. However, the positional relationship between the dissolution tank 82 and the crystallization tank 90 in the Z direction is not limited to this and may be arbitrary.

[0054] (Introduction tube) The inlet pipe 84 extends in the Z2 direction (vertically downward) from the dissolution tank 82 toward the crystallization tank 90. ​​The inlet pipe 84 connects the dissolution tank 82 with an opening 90c of the crystallization tank 90. ​​The solution L in the dissolution tank 82 flows through the inlet pipe 84 and the adjustment unit 86 into the crystallization tank 90.

[0055] (adjustment section) The adjustment unit 86 is a device that reduces the pressure of the solution L. The adjustment unit 86 is connected to the inlet pipe 84 and the crystallization tank 90. ​​In this embodiment, the adjustment unit 86 is directly connected to the crystallization tank 90. ​​The adjustment unit 86 adjusts the flow rate of the solution L using a valve provided therein. The adjustment unit 86 reduces the pressure of the solution L by opening and closing the valve. The adjustment unit 86 reduces the pressure of the solution L introduced from the dissolution tank 82 via the inlet pipe 84, and introduces the reduced-pressure solution L into the crystallization tank 90.

[0056] In this embodiment, the adjustment unit 86 is a pressure-reducing valve. The adjustment unit 86 may have any structure as long as it is a pressure-reducing valve, but in this embodiment, it is an angle valve. The solution L introduced into the adjustment unit 86 is introduced into the crystallization tank 90 in a state where it has been reduced in pressure by the adjustment unit 86. Because the temperature of the reduced-pressure solution L decreases, the monomer HD to be separated is crystallized from the reduced-pressure solution L. Note that in this embodiment, the adjustment unit 86 is directly connected to the crystallization tank 90, but this is not limiting, and a pipe connecting the adjustment unit 86 and the opening 90c of the crystallization tank 90 may be provided between the adjustment unit 86 and the opening 90c.

[0057] (Crystallization tank) The crystallization tank 90 is a tank into which the solution L depressurized by the adjustment unit 86 is introduced and in which the object to be separated (monomer HD in this case) is crystallized from the solution L. The solution L depressurized by the adjustment unit 86 is introduced into the crystallization tank 90. ​​In this way, the depressurized solution L is introduced into the crystallization tank 90 and the solution L is stored in a depressurized state. In other words, the crystallization tank 90 can be said to be a flash-type crystallization tank in which the internal pressure is reduced below the external pressure.

[0058] A discharge pipe 114 for discharging the slurry S is connected to the crystallization tank 90. ​​The discharge pipe 114 is provided with an adjustment unit 116 for adjusting the amount of slurry S supplied from the crystallization tank 90 to the solid-liquid separation unit 120. The adjustment unit 116 is, for example, an on-off valve, which, when open, allows the slurry S to be supplied to the solid-liquid separation unit 120 and, when closed, stops the supply of the slurry S to the solid-liquid separation unit 120. However, the adjustment unit 116 is not limited to an on-off valve and may be any mechanism capable of adjusting the supply of the slurry S to the solid-liquid separation unit 120. The slurry S is a slurry containing crystallized monomer HD and a solution L in which the monomer HD has been crystallized.

[0059] Baffles 110 are provided inside the crystallization tank 90 to rectify the flow of the solution L in the crystallization tank 90. ​​The shape, installation position, and number of the baffles 110 are arbitrary, but in this embodiment, the baffles 110 are provided on the inner wall surface of the crystallization tank 90, and more specifically, are plate-shaped members extending in the Z direction on the inner wall surface of the side wall. However, the baffles 110 are not an essential component and do not necessarily have to be provided in the crystallization tank 90.

[0060] (stirring section) The stirring unit 100 is provided in the crystallization tank 90, and is a device that rotates and stirs the inside of the crystallization tank 90 when a drive unit 102 (e.g., a motor) is driven. In this embodiment, the stirring blade 106 is located on the Z2 side of the adjustment unit 86. The stirring blade 106 is also located on the Z1 side of the bottom surface 90a of the crystallization tank 90, and is provided in a position facing the bottom surface 90a (i.e., a position overlapping the bottom surface 90a when viewed from the Z direction). The stirring unit 100 is also preferably provided at the center of the crystallization tank 90 when viewed from the Z direction. That is, it is preferable that the central axis of the stirring unit 100 and the central axis of the crystallization tank 90 coincide with each other.

[0061] (Crystallization of Monomer HD) With the above-described configuration, the crystallization system 80 crystallizes the monomer HD from the solution L in the crystallization tank 90. ​​That is, when the solution L in the dissolution tank 82 is supplied to the adjustment unit 86 via the inlet pipe 84, the solution L is depressurized by the adjustment unit 86. The solution L depressurized by the adjustment unit 86 is introduced into the crystallization tank 90 through the opening 90c. As the temperature of the depressurized solution L decreases, the monomer HD is crystallized in the crystallization tank 90 and stored as a slurry S. Furthermore, the inside of the crystallization tank 90 is stirred by the stirring unit 100, which promotes the crystallization of the monomer HD in the crystallization tank 90.

[0062] (PTA manufacturing) Next, the solid-liquid separation section 120, melting tank 150, temporary melt storage tank 160, and hydrolysis separation reaction section 170 in the crystallization system 80, which produce PTA from monomer HD, will be described.

[0063] (Solid-liquid separation section) Fig. 4 is a cross-sectional view showing a part of the solid-liquid separation unit, and Fig. 5 is a schematic view showing the separation mechanism of the solid-liquid separation unit.

[0064] The solid-liquid separation section 120 is connected to the crystallization tank 90 via a discharge pipe 114. The slurry S produced in the crystallization tank 90 is introduced into the solid-liquid separation section 120 from the crystallization tank 90 via the discharge pipe 114. As shown in FIG. 4, the solid-liquid separation section 120 separates the solid components to be separated from the slurry S using a filter 130. In this embodiment, the solid-liquid separation section 120 separates the slurry S into the monomers HD to be separated and a filtrate FL, which is the monomers HD separated from the slurry S. The filtrate FL is discharged from a discharge pipe 144 connected to the solid-liquid separation section 120 and treated. The filtrate FL is a liquid component obtained by separating the monomers HD from the slurry S, but may contain the monomers HD, which are solid components not separated (collected) by the filter 130.

[0065] The solid-liquid separation section 120 may have any structure capable of separating the separation target (monomer HD) from the slurry S using the filter 130. In this embodiment, the solid-liquid separation section 120 may be a centrifuge. In this case, for example, the interior of the solid-liquid separation section 120 rotates around a predetermined axis, and the slurry S is moved radially outward by the centrifugal force caused by this rotation, and the solid component (separation target) in the slurry S is collected by the filter 130 provided radially outward, while the liquid component in the slurry S passes through, thereby separating the separation target from the slurry S.

[0066] The following describes a specific configuration of the solid-liquid separation unit 120 according to this embodiment. The solid-liquid separation unit 120 according to this embodiment has a main body 121 and a separation mechanism 126.

[0067] The main body 121 is a casing having an opening at an inlet 124 and an internal space formed therein. The inlet 124 is an opening that connects the outer surface of the main body 121 with the internal space. A separation mechanism 126 is housed in the internal space of the main body 121. The main body 121 is connected to the crystallization tank 90 (discharge pipe 114 in this example) via the inlet 124. The slurry S in the crystallization tank 90 flows into the internal space of the main body 121 through the inlet 124. As shown in FIG. 4 , in this embodiment, the inlet 124 is provided at the top (vertically upper end) of the main body 121 and opens vertically upward, but this is not limiting.

[0068] The separating mechanism 126 includes a scraper 128 , a filter (screen) 130 , and a basket 132 .

[0069] The scraper 128 is a rotating body and is a mechanism for moving the slurry S radially outward by rotating. The scraper 128 is rotated by being driven by a motor (not shown). In this embodiment, the scraper 128 rotates around a rotation axis extending in the vertical direction and has a shape such that its outer diameter increases, for example, in a direction away from the inlet 124 (vertically downward in this example). A scraping portion 128a is formed on the outer surface of the scraper 128. The scraping portion 128a has a shape in which, for example, multiple protrusions are formed along the direction of rotation of the scraper 128. By providing the scraping portion 128a, the solid components collected by the filter 130 can be appropriately scraped off. The scraping portion 128a scrapes off the solid components collected by the filter 130, thereby making the thickness of the solid components collected by the filter 130 uniform.

[0070] The filter 130 is a filtering mechanism that passes liquid components and collects solid components. It separates the monomers HD (to be separated) from the slurry S by collecting the monomers HD (to be separated). In this embodiment, the filter 130 separates the slurry S, which has been moved radially outward by the scraper 128, into the monomers HD (to be separated) and filtrate FL. The filter 130 may have any structure that allows the liquid components to pass through and collects the solid components, but in this embodiment, it may have a structure with multiple small holes. The filter 130 has a shape such that its outer diameter increases in the direction away from the inlet 124 (vertically downward in this example). The filter 130 is located between the scraper 128 and the inlet 124. The filter 130 is not fixed to the scraper 128 and therefore does not rotate. The gap between the filter 130 and the scraper 128 is adjustable.

[0071] The basket 132 is provided between the filter 130 and the inlet 124, and is a cover member that prevents the centrifuged monomer HD and filtrate FL from scattering into the main body 121. The basket 132 is, for example, a mesh-like member provided with a plurality of openings that are larger than those of the filter 130, and is shaped such that its outer diameter increases in the direction away from the inlet 124 (in this example, the vertically downward direction). The basket 132 is provided so as to cover the filter 130. The basket 132 is not fixed to the scraper 128, and therefore does not rotate.

[0072] In this embodiment, the solid-liquid separation unit 120 having the above-described structure separates the slurry S into monomers HD (to be separated) and filtrate FL. That is, the slurry S supplied from the inlet 124 into the main body 121 moves radially outward within the main body 121 due to centrifugal force caused by the rotation of the scraper 128, and comes into contact with the surface of the filter 130 on the scraper 128 side. The monomers HD (to be separated), which are solid components of the slurry S, are collected by the filter 130, and the filtrate FL, which is a liquid component of the slurry S, passes through the filter 130, moves radially outward from the filter 130, and is discharged to the outside of the solid-liquid separation unit 120.

[0073] As solid-liquid separation continues in the solid-liquid separation section 120, the collected monomers HD (to be separated) accumulate on the filter 130, and a filtration layer F, which is a layer of the collected monomers HD, is formed on the filter 130. In this embodiment, the monomers HD (to be separated) are collected on the filter 130 (the surface of the filter 130 facing the scraper 128), and therefore the filtration layer F is formed on the filter 130. The filtration layer F provides the filter 130 with an even denser filtering mechanism, and the formation of the filtration layer F enables the monomers HD to be collected more stably.

[0074] Thus, the separation mechanism 126 has a structure including the basket 132, the filter 130, and the scraper 128, but it is sufficient that the separation mechanism 126 includes the filter 130, and the scraper 128 and the basket 132 may not be provided. In this embodiment, the separation mechanism 126 has a substantially conical shape, but may have any shape.

[0075] (Melting tank, temporary melt storage tank, hydrolysis and separation reaction section) The highly pure monomer HD obtained by solid-liquid separation from the slurry S is introduced into a melting tank 150 through an outlet pipe 146 connected to the solid-liquid separation section 120. The melting tank 150 is a tank that heats and melts the introduced monomer HD. The monomer HD melted in the melting tank 150 is introduced into a temporary melt storage tank 160 where it is temporarily stored, and then introduced from the temporary melt storage tank 160 into a hydrolysis separation reaction section 170. The hydrolysis separation reaction section 170 is a tank that adds water to the introduced monomer HD to hydrolyze the monomer HD. The hydrolysis separation reaction section 170 hydrolyzes the monomer HD to produce PTA. The PTA then undergoes a crystallization process and a drying process (not shown) before being stored in a hopper.

[0076] (Detection unit) In this embodiment, the crystallization system 80 includes a detection unit 140. The detection unit 140 is a sensor that detects parameters (operation information) related to the operation of the solid-liquid separation unit 120. In this embodiment, the parameters include the operating noise of the solid-liquid separation unit 120, the current value of the motor of the solid-liquid separation unit 120, the vibration of the solid-liquid separation unit 120, the concentration of monomer HD contained in the filtrate FL separated in the solid-liquid separation unit 120, the color of the filtrate FL separated in the solid-liquid separation unit 120, and the water content of the monomer HD separated in the solid-liquid separation unit 120 (the proportion of water contained in the monomer HD). The parameters are not limited to these and may be determined arbitrarily. The detection unit 140 is provided at a position where the parameters can be detected. For example, the detection unit 140 is connected to the solid-liquid separation unit 120. The detection unit 140 may be any sensor capable of detecting parameters related to the operation of the solid-liquid separation unit 120. For example, the detector 140 may actually be a sound level meter, an ammeter, a vibration sensor, a turbidity meter, a clock, or the like.

[0077] (Control unit) Next, the control unit 30 shown in Fig. 2 will be described. Fig. 6 is a schematic block diagram of the control unit. The control unit 30 is a control device that controls the separation system 1, and is a computer in this embodiment. As shown in Fig. 6, the control unit 30 includes an input unit 32, an output unit 34, a communication unit 36, a storage unit 38, and a processing unit 40.

[0078] The input unit 32 is a device that accepts user operations and may be, for example, a mouse, keyboard, or touch panel. The output unit 34 is a device that outputs information and may be, for example, a display that displays images. The input unit 32 and the output unit 34 do not necessarily have to be provided. The communication unit 36 ​​is a module that communicates with external devices and may include, for example, an antenna. In this embodiment, the communication method used by the communication unit 36 ​​is wireless communication, but any communication method may be used. The control unit 30 may be configured as a standalone device, may be configured integrally with other devices, or may be configured as a system combining various devices such as a computing device and a data server, and is not particularly limited.

[0079] The storage unit 38 is a memory that stores various information such as the calculation contents and programs of the processing unit 40, and includes at least one of a main storage device such as a RAM (Random Access Memory), a ROM (Read Only Memory), and an external storage device such as an HDD (Hard Disk Drive). The programs for the processing unit 40 saved in the storage unit 38 may be stored in a recording medium that can be read by the control unit 30.

[0080] The processing unit 40 is an arithmetic device and includes an arithmetic circuit such as a CPU (Central Processing Unit). The processing unit 40 includes a detection control unit 42, an information acquisition unit 44, and a system control unit 46. The processing unit 40 implements the detection control unit 42, the information acquisition unit 44, and the system control unit 46 and executes the processes thereof by reading and executing a program (software) from the storage unit 38. The processing unit 40 may execute these processes using a single CPU, or may be provided with multiple CPUs and execute the processes using the multiple CPUs. Furthermore, at least a portion of the detection control unit 42, the information acquisition unit 44, and the system control unit 46 may be implemented using hardware.

[0081] The detection control unit 42 controls the detection unit 140 to cause the detection unit 140 to detect parameters related to the operation of the solid-liquid separation unit 120, the information acquisition unit 44 acquires information on the parameters detected by the detection unit 140 as operation information of the solid-liquid separation unit 120, and the system control unit 46 controls each mechanism of the separation system 1. The detailed processing contents of these will be described later.

[0082] (Separation system control) Next, we will explain the control of the separation system 1 by the control unit 30. Note that the separation system 1 is not limited to being automatically controlled by the control unit 30 as described below, and for example, at least a part of the processing may be controlled by the operation of an operator.

[0083] (Depolymerization of polyester) The control unit 30 controls the adjusting units 10b and 18Ce via the system control unit 46 to introduce the polyester raw material Pm and the monomer D into the dissolving unit 12 and mix the polyester raw material Pm and the monomer D in the dissolving unit 12 to generate a solution Pd. The system control unit 46 controls the supply unit 12a1 to introduce the solution Pd generated in the dissolving unit 12 into the first reaction unit 16A.

[0084] The system control unit 46 controls the heating and pressurizing unit 14b to supply the reaction solvent M in a supercritical state or a subcritical state (pressurized gas or pressurized liquid) to the reaction unit 16. The system control unit 46 preferably sets the reaction solvent M at 250°C or higher and 400°C or lower, and more preferably at 250°C or higher and 350°C or lower. The system control unit 46 preferably sets the reaction solvent M at 1 MPa or higher and 30 MPa or lower, and more preferably at 6 MPa or higher and 25 MPa or lower.

[0085] In this manner, by supplying the solution Pd and the reaction solvent M to the reaction section 16, the polyester contained in the solution Pd is depolymerized in the first reaction section 16A to produce a first depolymerized polyester P1. Then, in the second reaction section 16B, the first depolymerized polyester P1 is further depolymerized to produce a second solvent M2, which is a mixture of the second depolymerized polyester P2 and the reaction solvent M. The second solvent M2 is separated into the reaction solvent M, monomer D, monomer E, and residual substances in the first separation section 18A, the second separation section 18B, and the third separation section 18C.

[0086] (Monomer HD crystallization treatment) The system control unit 46 controls the adjustment unit 86 to supply the solution L to the adjustment unit 86, depressurize the solution L using the adjustment unit 86, and introduce the depressurized solution L through the opening 90c into the crystallization tank 90. ​​Because the solution L introduced into the crystallization tank 90 has been depressurized, the monomer HD to be separated is crystallized from the solution L in the crystallization tank 90. ​​The system control unit 46 also controls the rotation of the agitation unit 100. This agitates the inside of the crystallization tank 90, making it possible to prevent the monomer HD from accumulating around the opening 90c in the crystallization tank 90.

[0087] (Solid-liquid separation of monomer HD) The system control unit 46 causes the slurry S to be supplied from the crystallization tank 90 to the solid-liquid separation unit 120. The system control unit 46 controls the adjustment unit 116 to cause the slurry S to be supplied from the crystallization tank 90 to the solid-liquid separation unit 120. The system control unit 46 also controls the amount of slurry S supplied from the crystallization tank 90 to the solid-liquid separation unit 120. The supply process of the slurry S from the crystallization tank 90 to the solid-liquid separation unit 120 will be described in detail below.

[0088] (Constant flow rate control) At the time when the supply of the slurry S to the solid-liquid separation section 120 is started, the system control section 46 causes the slurry S to be supplied from the crystallization tank 90 to the solid-liquid separation section 120 by a constant flow rate control method. The time when the supply of the slurry S is started here refers to, for example, the time when the slurry S is first supplied to the solid-liquid separation section 120 after the filter 130 is replaced, or the time when the slurry S is first supplied to the solid-liquid separation section 120 after the filter 130 is cleaned by backwashing or the like.

[0089] Constant flow rate control refers to control in which the amount of slurry S supplied from the crystallization tank 90 to the solid-liquid separation section 120 per unit time is constant. However, in constant flow rate control, the amount of slurry S supplied from the crystallization tank 90 to the solid-liquid separation section 120 per unit time is not necessarily strictly constant and may deviate by a predetermined amount. That is, for example, constant flow rate control refers to control in which the amount of slurry S supplied from the crystallization tank 90 to the solid-liquid separation section 120 per unit time approaches a target value. The system control unit 46 controls the slurry S from the crystallization tank 90 to the solid-liquid separation section 120 so as to achieve constant flow rate control, for example, by adjusting the aperture of the adjustment unit 116. In this case, for example, a flow meter is provided to measure the amount of slurry S supplied from the crystallization tank 90 to the solid-liquid separation section 120, and the system control unit 46 may control the slurry S from the crystallization tank 90 to the solid-liquid separation section 120 so that the flow rate measured by this flow meter is constant (approaching the target value). Furthermore, for example, the system control unit 46 may control the slurry S from the crystallization tank 90 to the solid-liquid separation unit 120 so that the opening degree of the adjustment unit 116 is kept constant.

[0090] (Constant liquid level control) When a filtration layer F (a layer of monomer HD) is formed on the filter 130 during constant flow rate control, the system control unit 46 switches the supply of the slurry S from the crystallization tank 90 to the solid-liquid separation unit 120 from constant flow rate control to constant liquid level control. After switching to constant liquid level control, the system control unit 46 maintains the constant liquid level control until the next time the supply of the slurry S to the solid-liquid separation unit 120 is started.

[0091] Constant liquid level control refers to control of adjusting the supply amount of slurry S from the crystallization tank 90 to the solid-liquid separation section 120 so that the liquid level of the solution L in the crystallization tank 90 is maintained at a constant height. However, constant liquid level control does not necessarily require that the liquid level of the solution L in the crystallization tank 90 be strictly constant, and may deviate by a predetermined amount. That is, for example, constant liquid level control refers to control of bringing the liquid level of the solution L in the crystallization tank 90 closer to a target value. The system control unit 46 controls the slurry S from the crystallization tank 90 to the solid-liquid separation section 120 so as to achieve constant liquid level control, for example, by adjusting the aperture of the adjustment unit 116. In this case, for example, a sensor that measures the liquid level of the solution L in the crystallization tank 90 may be provided, and the system control unit 46 may control the slurry S from the crystallization tank 90 to the solid-liquid separation section 120 so that the liquid level is the height measured by this sensor (close to the target value).

[0092] By controlling the liquid level at a constant level, the residence time of the solution L in the crystallization tank 90 can be kept constant, thereby maintaining the amount and quality of the crystallized monomer HD at a constant level, thereby enabling stable recovery of the monomer HD. However, the present inventors have found through extensive research that constant liquid level control can sometimes cause fluctuations in the amount of slurry S supplied from the crystallization tank 90 to the solid-liquid separation section 120, making it impossible to stably recover the monomer HD. For example, the crystallization tank 90 receives solution L in a state close to a saturated solution from the dissolution tank 82. However, pressure regulation by the pressure regulator 86 can cause fluctuations in the pressure within the crystallization tank 90, which can lead to fluctuations in the amount of solution L flowing into the crystallization tank 90. ​​If constant liquid level control is performed in such a case, fluctuations in the amount of solution L flowing into the crystallization tank 90 can cause fluctuations in the amount of slurry S supplied to the solid-liquid separation section 120. This can lead to unstable operation of the solid-liquid separation section 120 and result in unstable recovery of the monomer HD.

[0093] In contrast, in this embodiment, constant flow rate control is initially performed to suppress fluctuations in the supply rate of the slurry S to the solid-liquid separation section 120, thereby suppressing instability in the operation of the solid-liquid separation section 120. Furthermore, once the filtration layer F is formed on the filter 130, the control is switched to constant liquid level control. This constant liquid level control makes it possible to maintain the residence time of the solution L in the crystallization tank 90 close to constant. Furthermore, the filtration layer F enables stable collection of solid components in the filter 130 and stable passage of liquid components, thereby suppressing instability in the operation of the solid-liquid separation section 120 even if the supply rate of the slurry S to the solid-liquid separation section 120 fluctuates. As such, this embodiment makes it possible to stably recover the monomer HD.

[0094] (Determining whether a filtration layer has been formed) As described above, the control unit 30 switches from constant flow rate control to constant liquid level control when the filtration layer F is formed on the filter 130. At this time, the criterion for determining whether the filtration layer F is formed on the filter 130 may be arbitrary. In this embodiment, the control unit 30 automatically determines whether the filtration layer F is formed on the filter 130 based on the detection results of the detection unit 140, which detects parameters related to the operation of the solid-liquid separation unit 120. This determination method will be specifically described below.

[0095] As described above, the detection control unit 42 of the control unit 30 controls the detection unit 140 to detect parameters related to the operation of the solid-liquid separation unit 120. The information acquisition unit 44 of the control unit 30 acquires information on the parameters detected by the detection unit 140 as operation information of the solid-liquid separation unit 120. The system control unit 46 of the control unit 30 determines whether a filtration layer F has been formed on the filter 130 based on the operation information of the solid-liquid separation unit 120. If the operation information of the solid-liquid separation unit 120 satisfies a predetermined condition, the system control unit 46 determines that a filtration layer F has been formed on the filter 130. If the operation information of the solid-liquid separation unit 120 does not satisfy the predetermined condition, the system control unit 46 determines that a filtration layer F has not been formed on the filter 130. Then, if the system control unit 46 determines that a filtration layer F has been formed on the filter 130 during constant flow rate control, it switches from constant flow rate control to constant liquid level control. Note that the above switching determination process may be executed sequentially. That is, while constant flow rate control is being performed, the detection control unit 42 causes the detection unit 140 to sequentially detect parameters, the information acquisition unit 44 sequentially acquires the parameters, and the system control unit 46 sequentially determines whether a filtration layer F has been formed on the filter 130. Then, when it is determined that a filtration layer F has been formed on the filter 130, the switching determination process is terminated and the control is switched from constant flow rate control to constant liquid level control. The predetermined conditions that are the criteria for determining whether a filtration layer F has been formed may be set arbitrarily.

[0096] The determination of whether the filtration layer F has been formed does not necessarily have to be performed automatically based on the parameters (operation information) detected by the detection unit 140 as described above. For example, an operator may determine whether the filtration layer F has been formed on the filter 130 by checking parameters related to the operation of the solid-liquid separation unit 120. In this case, if the operator determines that the filtration layer F has been formed on the filter 130, the operator may input a command to switch control to the input unit 32. When the command to switch control is input to the input unit 32, the control unit 30 may determine that the filtration layer F has been formed on the filter 130 and switch from constant flow rate control to constant liquid level control. That is, in this case, the control unit 30 acquires the command from the operator as operation information that satisfies a predetermined condition, and when the operation information that satisfies the predetermined condition is acquired, the control unit 30 may determine that the filtration layer F has been formed on the filter 130 and switch from constant flow rate control to constant liquid level control.

[0097] (Specific examples of judgment) The following describes specific processing details of the method performed by the control unit 30 to determine whether a filtration layer F has been formed on the filter 130. The control unit 30 may perform at least one of the controls described below. However, the control unit 30 preferably performs a combination of two or more of the controls described below, and may perform all of the controls described below. In other words, it is preferable that the control unit 30 perform a combination of any two, any three, any four, any five, any six, or all seven of the first to seventh controls described below.

[0098] Furthermore, at least some of the following controls may be performed by an operator. That is, the operator checks the parameters for each of the following controls, and when it is determined that a filtration layer F has been formed on the filter 130, the operator inputs a command to switch the control to the input unit 32. When the command to switch the control is input to the input unit 32, the control unit 30 determines that a filtration layer F has been formed on the filter 130 and switches from constant flow rate control to constant liquid level control.

[0099] (First control) In the first control, the operating noise of the solid-liquid separation unit 120 is used as a parameter related to the operation of the solid-liquid separation unit 120. That is, the detection control unit 42 causes the detection unit 140 to detect the operating noise of the solid-liquid separation unit 120. The information acquisition unit 44 acquires information about the operating noise of the solid-liquid separation unit 120 detected by the detection unit 140 as operation information. For example, the detection control unit 42 causes the detection unit 140 to detect the volume of the operating noise of the solid-liquid separation unit 120, and the information acquisition unit 44 acquires the volume of the operating noise of the solid-liquid separation unit 120 as operation information. The system control unit 46 determines whether the operating noise acquired by the information acquisition unit 44 satisfies a predetermined condition. If the operating noise satisfies the predetermined condition, the system control unit 46 determines that the filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. The predetermined condition here may be set arbitrarily, but refers to a fluctuation in the operating noise (a fluctuation in the volume of the operating noise) being equal to or less than a predetermined threshold. That is, if the amount of fluctuation in the loudness of the operation noise within a predetermined period is equal to or less than a predetermined threshold, the system control unit 46 determines that the filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. In other words, the system control unit 46 determines that the amount of fluctuation in the loudness of the operation noise is equal to or less than the predetermined threshold and determines that the filtration layer F has been formed if the amount of fluctuation in the loudness of the operation noise within a predetermined period is greater than the predetermined threshold, and maintains constant flow rate control.

[0100] In addition, in the first control, if the operator makes the judgment, for example, the operator may check the volume of the operating noise of the solid-liquid separation section 120, and if the operator determines that the fluctuation in the volume of the operating noise is below a predetermined threshold, input a command to switch control to the input section 32, thereby switching from constant flow rate control to constant liquid level control.

[0101] (Second control) In the second control, the current value of the motor of the solid-liquid separation unit 120 is used as a parameter related to the operation of the solid-liquid separation unit 120. That is, the detection control unit 42 causes the detection unit 140 to detect the current value of the motor of the solid-liquid separation unit 120. The information acquisition unit 44 acquires information on the current value of the motor of the solid-liquid separation unit 120 detected by the detection unit 140 as operation information. The system control unit 46 determines whether the current value acquired by the information acquisition unit 44 satisfies a predetermined condition. If the current value satisfies the predetermined condition, the system control unit 46 determines that the filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. The predetermined condition here may be set arbitrarily, but refers to the amount of fluctuation in the current value being equal to or less than a predetermined threshold. That is, if the amount of fluctuation in the current value within a predetermined period is equal to or less than a predetermined threshold, the system control unit 46 determines that the filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. In other words, the system control unit 46 determines that a filtration layer F has been formed if the current value of the solid-liquid separation unit 120 detected by the detection unit 140 for a predetermined period of time falls within the predetermined range, and determines that the fluctuation in the current value is equal to or less than a predetermined threshold. On the other hand, if the fluctuation in the current value is greater than the predetermined threshold, the system control unit 46 determines that a filtration layer F has not been formed, and maintains constant flow rate control.

[0102] In addition, in the second control, if the operator makes the judgment, for example, the operator may check the motor current value detected by the detection unit 140, and if the operator determines that the fluctuation in the motor current value is below a predetermined threshold, input a command to switch control to the input unit 32, thereby switching from constant flow rate control to constant liquid level control.

[0103] (Third control) In the third control, the vibration of the solid-liquid separation unit 120 is used as a parameter related to the operation of the solid-liquid separation unit 120. That is, the detection control unit 42 causes the detection unit 140 to detect the vibration of the solid-liquid separation unit 120. The information acquisition unit 44 acquires information about the vibration of the solid-liquid separation unit 120 detected by the detection unit 140 as operation information. For example, the detection control unit 42 causes the detection unit 140 to detect the vibration of the solid-liquid separation unit 120, and the information acquisition unit 44 acquires the vibration of the solid-liquid separation unit 120 as operation information. The system control unit 46 determines whether the vibration acquired by the information acquisition unit 44 satisfies a predetermined condition. If the vibration satisfies the predetermined condition, the system control unit 46 determines that a filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. The predetermined condition here may be set arbitrarily, but refers to the amount of vibration fluctuation being equal to or less than a predetermined threshold. That is, if the amount of vibration fluctuation within a predetermined period is equal to or less than a predetermined threshold, the system control unit 46 determines that the filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. In other words, the system control unit 46 sets a vibration range for the solid-liquid separation unit 120 in advance, and if the vibration detected by the detection unit 140 for a predetermined period is within the set vibration range, the system control unit 46 determines that the filtration layer F has been formed. On the other hand, if the amount of vibration fluctuation within the predetermined period is greater than a predetermined threshold, the system control unit 46 determines that the filtration layer F has not been formed and maintains constant flow rate control. Note that the information about the vibration of the solid-liquid separation unit 120 used for this determination may be the frequency of the vibration or the magnitude (amplitude) of the vibration.

[0104] In addition, in the third control, if the operator makes the judgment, for example, the operator may check the vibration of the solid-liquid separation section 120 and, if the operator determines that the amount of vibration fluctuation is below a predetermined threshold, input a command to switch control to the input section 32, thereby switching from constant flow rate control to constant liquid level control.

[0105] (4th control) In the fourth control, the operating time, which is the time during which the solid-liquid separation unit 120 is controlled under constant flow rate control, is used as a parameter related to the operation of the solid-liquid separation unit 120. That is, the detection control unit 42 causes the detection unit 140 to measure the time (operating time) during which the solid-liquid separation unit 120 is controlled under constant flow rate control. In this case, it is preferable that the detection unit 140 starts measuring the operating time once the solid-liquid separation unit 120 starts operating. The information acquisition unit 44 acquires information on the operating time of the solid-liquid separation unit 120 detected by the detection unit 140 as operation information. The system control unit 46 determines whether the operating time acquired by the information acquisition unit 44 satisfies a predetermined condition. If the operating time satisfies the predetermined condition, it determines that the filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. Here, the predetermined condition may be set arbitrarily, but refers to the operating time being equal to or greater than a predetermined threshold. That is, if the operating time is equal to or greater than the predetermined threshold, the system control unit 46 determines that the filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. In other words, the system control unit 46 sets in advance the operating time of the solid-liquid separation unit 120 until the filtration layer F is formed, and if the operating time of the solid-liquid separation unit 120 is equal to or longer than the set operating time, it determines that the operating time is equal to or longer than a predetermined threshold value and that the filtration layer F has been formed.

[0106] In addition, in the fourth control, if the operator makes the judgment, for example, the operator may check the operating time of the solid-liquid separation section 120 and, if the operator determines that the operating time of the solid-liquid separation section 120 is equal to or greater than a predetermined threshold, input a command to switch control to the input section 32, thereby switching from constant flow rate control to constant liquid level control.

[0107] (5th control) In the fifth control, the concentration of the target substance to be separated contained in the filtrate FL is used as a parameter for the operation of the solid-liquid separation unit 120. That is, in the fifth control, the concentration of the monomer HD contained in the filtrate FL is used as a parameter for the operation of the solid-liquid separation unit 120. That is, the detection control unit 42 causes the detection unit 140 to detect the concentration of the monomer HD contained in the filtrate FL filtered by the filter of the solid-liquid separation unit 120. The information acquisition unit 44 acquires information on the concentration of the monomer HD contained in the filtrate FL detected by the detection unit 140 as operation information. The system control unit 46 determines whether the concentration of the monomer HD contained in the filtrate FL acquired by the information acquisition unit 44 satisfies a predetermined condition. If the concentration satisfies the predetermined condition, the system control unit 46 determines that a filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. The predetermined condition here may be set arbitrarily, but it refers to the amount of fluctuation in the concentration of the monomer HD contained in the filtrate FL being equal to or less than a predetermined threshold. That is, if the amount of fluctuation in the concentration of the monomer HD contained in the filtrate FL within a predetermined period is equal to or less than a predetermined threshold, the system control unit 46 determines that a filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. In other words, the system control unit 46 sets a range for the concentration of the monomer HD contained in the filtrate FL in advance, and if the detected concentration of the monomer HD contained in the filtrate FL is within the set concentration range, the system control unit 46 determines that the concentration is constant and that a filtration layer F has been formed. On the other hand, if the amount of fluctuation in the concentration of the monomer HD contained in the filtrate FL is greater than the predetermined threshold, the system control unit 46 determines that a filtration layer F has not been formed and maintains constant flow rate control.

[0108] In the fifth control, if an operator makes the judgment, for example, the operator may determine whether the concentration of monomer HD contained in the filtrate FL is constant by looking through a sight glass (sight window, not shown) provided in the solid-liquid separation section 120. If the operator determines that the fluctuation amount of the monomer HD concentration contained in the filtrate FL is below a predetermined threshold, the operator may input a command to switch control to the input unit 32, thereby switching from constant flow rate control to constant liquid level control. The operator may also extract a predetermined amount of filtrate FL from the solid-liquid separation section 120, measure the concentration of monomer HD contained in the filtrate FL, and determine that the concentration is constant. Alternatively, for example, the operator may extract a predetermined amount of filtrate FL from the solid-liquid separation section 120 and determine that the concentration of monomer HD contained in the filtrate FL is constant based on the stickiness of the filtrate FL when touched. The predetermined amount of filtrate FL extracted by the operator may be any amount.

[0109] (6th control) In the sixth control, the color of the filtrate FL is used as a parameter related to the operation of the solid-liquid separation unit 120. That is, the detection control unit 42 causes the detection unit 140 to detect the color of the filtrate FL. The information acquisition unit 44 acquires information on the color of the filtrate FL of the solid-liquid separation unit 120 detected by the detection unit 140 as operation information. The system control unit 46 determines whether the color of the filtrate FL acquired by the information acquisition unit 44 satisfies a predetermined condition. If the color of the filtrate FL satisfies the predetermined condition, the system control unit 46 determines that a filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. The predetermined condition here may be set arbitrarily, but refers to the amount of change in the color of the filtrate FL being equal to or less than a predetermined threshold. That is, if the amount of change in the color of the filtrate FL within a predetermined period is equal to or less than a predetermined threshold, the system control unit 46 determines that a filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. In other words, the system control unit 46 sets a predetermined color range for the filtrate FL, and if the color of the filtrate FL detected by the detection unit 140 is within the set color range, the system control unit 46 determines that the color is constant and that a filtration layer F has been formed. On the other hand, if the amount of change in the color of the filtrate FL is greater than a predetermined threshold, the system control unit 46 determines that a filtration layer F has not been formed and maintains constant flow rate control.

[0110] In the sixth control, if the operator makes the judgment, for example, the operator may look through a sight glass provided in the solid-liquid separation section 120 to determine whether the amount of color fluctuation of the filtrate FL is constant or below a predetermined value. If the operator determines that the color of the filtrate FL is constant, the operator may input a command to switch control to the input unit 32, switching from constant flow rate control to constant liquid level control. The operator may also extract a predetermined amount of filtrate FL from the solid-liquid separation section 120, measure the color, and determine that the color is constant. Alternatively, for example, the operator may extract a predetermined amount of filtrate FL from the solid-liquid separation section 120 and determine that the color is constant based on the stickiness when touched.

[0111] (7th control) In the seventh control, the moisture content of the separation target (monomer HD) separated by the filter 130 is used as a parameter related to the operation of the solid-liquid separation unit 120. That is, the detection control unit 42 causes the detection unit 140 to detect the moisture content of the separation target separated by the filter 130 of the solid-liquid separation unit 120. The information acquisition unit 44 acquires information on the moisture content of the separation target detected by the detection unit 140 as operation information. The system control unit 46 determines whether the moisture content of the separation target acquired by the information acquisition unit 44 satisfies a predetermined condition. If the moisture content satisfies the predetermined condition, the system control unit 46 determines that a filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. The predetermined condition here may be set arbitrarily, but refers to the amount of fluctuation in the moisture content of the separation target being equal to or less than a predetermined threshold. That is, if the amount of fluctuation in the moisture content of the separation target within a predetermined period is equal to or less than a predetermined threshold, the system control unit 46 determines that a filtration layer F has been formed and switches from constant flow rate control to constant liquid level control. In other words, the system control unit 46 sets a range of moisture content of the separation target in advance, and if the moisture content of the separation target detected by the detection unit 140 is within the set moisture content range, the system control unit 46 determines that the moisture content is constant and that a filtration layer F has been formed. On the other hand, if the amount of fluctuation in the moisture content of the separation target is greater than a predetermined threshold, the system control unit 46 determines that a filtration layer F has not been formed and maintains constant flow rate control.

[0112] In the seventh control, if the operator makes the judgment, for example, the operator may take out a predetermined amount of the separation target, measure the moisture content of the taken out separation target, and determine that the moisture content is constant. Alternatively, for example, the operator may take out the separation target and determine that the moisture content is constant based on the stickiness when touched. If the operator determines that the moisture content of the separation target is constant, the operator may input a command to switch control to the input unit 32 from constant flow rate control to constant liquid level control. In the seventh control, the operator may also determine that the moisture content of the separation target is constant by looking through a sight glass provided in the solid-liquid separation unit 120.

[0113] As described above, the control unit 30 only needs to perform at least one of the first to seventh controls described above. In this embodiment, the control unit 30 performs the first to fourth controls. An operator then determines whether the parameters in the fifth to seventh controls satisfy predetermined conditions. The operator may also perform all of the determinations made by the control unit 30 in the first to seventh controls. That is, in all of the first to seventh controls, the operator may input a command to switch control to the input unit 32, thereby switching from constant flow rate control to constant liquid level control.

[0114] (Control Flow) The control flow of the control unit 30 described above will now be described. FIG. 7 is a flowchart illustrating the control flow of the control unit. As shown in FIG. 7, the control unit 30 causes the system control unit 46 to supply the slurry S from the crystallization tank 90 to the solid-liquid separation unit 120 under constant flow rate control (step S10), and determines whether a filtration layer F has been formed in the solid-liquid separation unit 120 (step S12). If the system control unit 46 determines that a filtration layer F has been formed (step S12; Yes), it switches from constant flow rate control to constant liquid level control (step S14). That is, the system control unit 46 switches to control to maintain a constant liquid level of the solution L in the crystallization tank 90. ​​If the system control unit 46 determines that a filtration layer F has not been formed (step S12; No), it continues the processing of step S10 until it determines that a filtration layer F has been formed. The control details by the system control unit 46 have been described above, so a description thereof will be omitted.

[0115] (Effects of the present disclosure) The crystallization system according to the first embodiment of the present disclosure includes a crystallization tank 90 into which a solution L is supplied, a substance to be separated is crystallized from the solution L, and the solution L resulting from the crystallization of the substance to be separated is stored as a slurry S; a solid-liquid separation section 120 into which the slurry S is introduced from the crystallization tank 90 and which separates the solid component to be separated from the slurry S using a filter 130; and a control unit 30 which controls the supply of the slurry S from the crystallization tank 90 to the solid-liquid separation section 120. While the supply of the slurry S from the crystallization tank 90 to the solid-liquid separation section 120 is controlled by constant flow rate control, in which a constant amount of slurry is supplied per unit time, when a filtration layer F, which is a layer to be separated, is formed on the filter 130, the control unit 30 switches the supply of the slurry S from the crystallization tank 90 to the solid-liquid separation section 120 from constant flow rate control to constant liquid level control, in which the liquid level of the solution L in the crystallization tank 90 is kept constant.

[0116] This allows the constant flow rate control to suppress fluctuations in the amount of slurry supplied to the solid-liquid separation section. Furthermore, once the filtration layer is formed, the constant flow rate control is switched to constant control, which keeps the liquid level of the solution in the crystallization tank constant, making it possible to keep the residence time of the solution in the crystallization tank close to constant. By performing constant flow rate control to form the filtration layer before performing constant liquid level control, it becomes possible to stably operate the solid-liquid separation section even if the amount of slurry supplied to the solid-liquid separation section fluctuates. Therefore, the material to be separated can be stably recovered.

[0117] A crystallization system according to a second aspect of the present disclosure is the crystallization system according to the first aspect, further comprising a detection unit 140 that detects parameters related to the operation of the solid-liquid separation unit 120. The control unit 30 acquires the parameters detected by the detection unit 140 as operation information for the solid-liquid separation unit 120 and determines whether a filtration layer F has been formed based on the operation information. By forming a filtration layer, the solid-liquid separation unit can be operated stably even if the amount of slurry supplied to the solid-liquid separation unit fluctuates. Therefore, the material to be separated can be recovered stably.

[0118] A crystallization system according to a third aspect of the present disclosure is the crystallization system according to the first or second aspect, in which the control unit 30 acquires information on the operating sound of the solid-liquid separation unit 120 as operation information of the solid-liquid separation unit 120, and determines that a filtration layer F has been formed when the fluctuation amount of the operating sound is equal to or less than a predetermined threshold. By forming a filtration layer, the solid-liquid separation unit can be stably operated even if the amount of slurry supplied to the solid-liquid separation unit fluctuates. Therefore, the material to be separated can be stably recovered.

[0119] A crystallization system according to a fourth aspect of the present disclosure is the crystallization system according to any one of the first to third aspects, in which the control unit 30 acquires information on the current value of the motor of the solid-liquid separation unit 120 as operation information of the solid-liquid separation unit 120, and determines that a filtration layer F has been formed when the amount of fluctuation in the current value is equal to or less than a predetermined threshold. By forming a filtration layer, the solid-liquid separation unit can be stably operated even if the amount of slurry supplied to the solid-liquid separation unit fluctuates. Therefore, the material to be separated can be stably recovered.

[0120] A crystallization system according to a fifth aspect of the present disclosure is the crystallization system according to any one of the first to fourth aspects, in which the control unit 30 acquires information on the vibration of the solid-liquid separation unit 120 as operation information of the solid-liquid separation unit 120, and determines that a filtration layer F has been formed when the amount of fluctuation in the vibration is equal to or less than a predetermined threshold. By forming a filtration layer, the solid-liquid separation unit can be stably operated even if the amount of slurry supplied to the solid-liquid separation unit fluctuates. Therefore, the material to be separated can be stably recovered.

[0121] A crystallization system according to a sixth aspect of the present disclosure is the crystallization system according to any one of the first to fifth aspects, in which the control unit 30 acquires information on the operation time, which is the time during which constant flow rate control is performed, as operation information of the solid-liquid separation unit 120, and determines that a filtration layer F has been formed when the operation time reaches a predetermined threshold value. By forming a filtration layer, the solid-liquid separation unit can be stably operated even if the amount of slurry supplied to the solid-liquid separation unit fluctuates. Therefore, the material to be separated can be stably recovered.

[0122] A crystallization system according to a seventh aspect of the present disclosure is the crystallization system according to any one of the first to sixth aspects, in which the control unit 30 acquires information on the concentration of the separation target contained in the slurry S from which the separation target has been separated by the filter 130 as operation information for the solid-liquid separation unit 120, and determines that a filtration layer F has been formed when the amount of fluctuation in the concentration is equal to or less than a predetermined threshold. By forming a filtration layer, the solid-liquid separation unit can be stably operated even if the amount of slurry supplied to the solid-liquid separation unit fluctuates. Therefore, the separation target can be stably recovered.

[0123] A crystallization system according to an eighth aspect of the present disclosure is the crystallization system according to any one of the first to seventh aspects, in which the control unit 30 acquires color information of the slurry S from which the separation target has been separated by the filter 130 as operation information of the solid-liquid separation unit 120, and determines that a filtration layer F has been formed when the amount of color change is equal to or less than a predetermined threshold. By forming a filtration layer, the solid-liquid separation unit can be stably operated even if the amount of slurry supplied to the solid-liquid separation unit fluctuates. Therefore, the separation target can be stably recovered.

[0124] A crystallization system according to a ninth aspect of the present disclosure is the crystallization system according to any one of the first to eighth aspects, in which the control unit 30 acquires information on the moisture content of the separation target separated by the filter 130 as operation information of the solid-liquid separation unit 120, and determines that a filtration layer F has been formed when the amount of moisture content fluctuation is equal to or less than a predetermined threshold. By forming a filtration layer, the solid-liquid separation unit can be stably operated even if the amount of slurry supplied to the solid-liquid separation unit fluctuates. Therefore, the separation target can be stably recovered.

[0125] A crystallization method according to a tenth aspect of the present disclosure includes the steps of supplying a solution L to a crystallization tank 90, crystallizing a material to be separated from the solution L in the crystallization tank 90 to obtain a slurry S, supplying the slurry S from the crystallization tank 90 to a solid-liquid separation section 120 and separating the solid component to be separated from the slurry using a filter 130 provided in the solid-liquid separation section 120, and controlling the supply of the slurry S from the crystallization tank 90 to the solid-liquid separation section 120. In the step of controlling the supply of the slurry S, the supply of the slurry S from the crystallization tank 90 to the solid-liquid separation section 120 is controlled under constant flow rate control, in which a constant amount of slurry is supplied per unit time. When a filtration layer F, which is a layer to be separated, is formed on the filter, the supply of the slurry S from the crystallization tank 90 to the solid-liquid separation section 120 is switched from constant flow rate control to constant liquid level control, in which the liquid level of the solution L in the crystallization tank 90 is kept constant.

[0126] This allows the constant flow rate control to suppress fluctuations in the amount of slurry supplied to the solid-liquid separation section. Furthermore, once the filtration layer is formed, the constant flow rate control is switched to constant liquid level control, which keeps the liquid level of the solution in the crystallization tank constant, making it possible to keep the residence time of the solution in the crystallization tank close to constant. By performing constant flow rate control to form the filtration layer before performing constant liquid level control, it becomes possible to stably operate the solid-liquid separation section even if the amount of slurry supplied to the solid-liquid separation section fluctuates. Therefore, the material to be separated can be stably recovered.

[0127] A program according to an eleventh aspect of the present disclosure causes a computer to execute the following steps: supplying a solution L to a crystallization tank 90; crystallizing a material to be separated from the solution L in the crystallization tank 90 to obtain a slurry S; supplying the slurry S from the crystallization tank 90 to a solid-liquid separation section 120 and separating the solid component to be separated from the slurry S using a filter 130 provided in the solid-liquid separation section 120; and controlling the supply of the slurry S from the crystallization tank 90 to the solid-liquid separation section 120. In the step of controlling the supply of the slurry S, while the supply of the slurry S from the crystallization tank 90 to the solid-liquid separation section 120 is being controlled under constant flow rate control, which supplies a constant amount of slurry S per unit time, if a filtration layer F, which is a layer to be separated, is formed on the filter 130, the supply of the slurry S from the crystallization tank 90 to the solid-liquid separation section 120 is switched from constant flow rate control to constant liquid level control, which maintains a constant liquid level of the solution L in the crystallization tank 90.

[0128] This allows the constant flow rate control to suppress fluctuations in the amount of slurry supplied to the solid-liquid separation section. Furthermore, once the filtration layer is formed, the constant flow rate control is switched to constant control, which keeps the liquid level of the solution in the crystallization tank constant, making it possible to keep the residence time of the solution in the crystallization tank close to constant. By performing constant flow rate control to form the filtration layer before performing constant liquid level control, it becomes possible to stably operate the solid-liquid separation section even if the amount of slurry supplied to the solid-liquid separation section fluctuates. Therefore, the material to be separated can be stably recovered.

[0129] Although the embodiments of the present invention have been described above, the embodiments are not limited to the contents of these embodiments. Furthermore, the above-described components include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the scope of what is called equivalents. Furthermore, the above-described components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the above-described embodiments. [Explanation of symbols]

[0130] 1 Separation System 12 Melting part 13, 120 Solid-liquid separation section 14 Solvent reservoir 16 Reaction section 18 Separation part 30 Control Unit 80 Crystallization System 82 Dissolution tank 86 Adjustment section 90 Crystallization tank 100 Stirring section 110 Baffle 126 Separation mechanism 128 Scraper 130 filters 132 Basket 140 Detector D, HD, E monomers F filtration layer FL filtrate M reaction solvent P Polyester solution Pd, L solution Pm polyester raw material R Residual substances S Slurry

Claims

1. a crystallization tank into which a solution is supplied, a separation target is crystallized from the solution, and the solution from which the separation target has been crystallized is stored as a slurry; a solid-liquid separation section into which the slurry is introduced from the crystallization tank and which separates the solid component to be separated from the slurry by a filter; a control unit that controls the supply of the slurry from the crystallization tank to the solid-liquid separation unit, when a filtration layer, which is the layer to be separated, is formed on the filter while the supply of the slurry from the crystallization tank to the solid-liquid separation unit is being controlled under constant flow rate control in which a constant amount of the slurry is supplied per unit time, the control unit switches the supply of the slurry from the crystallization tank to the solid-liquid separation unit from the constant flow rate control to constant liquid level control in which the liquid level of the solution in the crystallization tank is kept constant. Crystallization systems.

2. The method further includes a detection unit that detects parameters related to the operation of the solid-liquid separation unit, and the control unit acquires the parameters detected by the detection unit as operation information of the solid-liquid separation unit and determines whether the filtration layer has been formed based on the operation information. The crystallization system of claim 1 .

3. The control unit acquires information about the operation sound of the solid-liquid separation unit as operation information of the solid-liquid separation unit, and determines that the filtration layer has been formed when a fluctuation amount of the operation sound is equal to or less than a predetermined threshold value. The crystallization system according to claim 1 or claim 2.

4. The control unit acquires information on a current value of a motor of the solid-liquid separation unit as operation information of the solid-liquid separation unit, and determines that the filtration layer has been formed when a fluctuation amount of the current value is equal to or less than a predetermined threshold. The crystallization system according to claim 1 or claim 2.

5. The control unit acquires information about the vibration of the solid-liquid separation unit as operation information of the solid-liquid separation unit, and determines that the filtration layer has been formed when a fluctuation amount of the vibration is equal to or less than a predetermined threshold. The crystallization system according to claim 1 or claim 2.

6. The control unit acquires information on the operation time, which is the time during which control is performed under the constant flow rate control, as operation information of the solid-liquid separation unit, and determines that the filtration layer has been formed when the operation time is equal to or greater than a predetermined threshold. The crystallization system according to claim 1 or claim 2.

7. The control unit acquires information on the concentration of the separation target contained in the slurry from which the separation target has been separated by the filter as operation information of the solid-liquid separation unit, and determines that the filtration layer has been formed when the amount of change in the concentration is equal to or less than a predetermined threshold. The crystallization system according to claim 1 or claim 2.

8. The control unit acquires color information of the slurry from which the separation target has been separated by the filter as operation information of the solid-liquid separation unit, and determines that the filtration layer has been formed when the amount of change in color is equal to or less than a predetermined threshold. The crystallization system according to claim 1 or claim 2.

9. The control unit acquires information on the moisture content of the separation target separated by the filter as operation information of the solid-liquid separation unit, and determines that the filtration layer has been formed when a fluctuation amount of the moisture content is equal to or less than a predetermined threshold. The crystallization system according to claim 1 or claim 2.

10. supplying a solution to a crystallizer; crystallizing the object to be separated from the solution in the crystallization tank to obtain a slurry; supplying the slurry from the crystallization tank to a solid-liquid separation section, and separating the solid component to be separated from the slurry by a filter provided in the solid-liquid separation section; and controlling the supply of the slurry from the crystallization tank to the solid-liquid separation section, In the step of controlling the supply of the slurry, when a filtration layer, which is the layer to be separated, is formed on the filter while the supply of the slurry from the crystallization tank to the solid-liquid separation section is being controlled under constant flow rate control in which a constant amount of the slurry is supplied per unit time, the supply of the slurry from the crystallization tank to the solid-liquid separation section is switched from the constant flow rate control to constant liquid level control in which the liquid level of the solution in the crystallization tank is kept constant. Crystallization method.

11. supplying a solution to a crystallizer; crystallizing the object to be separated from the solution in the crystallization tank to obtain a slurry; supplying the slurry from the crystallization tank to a solid-liquid separation section, and separating the solid component to be separated from the slurry by a filter provided in the solid-liquid separation section; and controlling the supply of the slurry from the crystallization tank to the solid-liquid separation section, In the step of controlling the supply of the slurry, when a filtration layer, which is the layer to be separated, is formed on the filter while the supply of the slurry from the crystallization tank to the solid-liquid separation section is being controlled under constant flow rate control in which a constant amount of the slurry is supplied per unit time, the supply of the slurry from the crystallization tank to the solid-liquid separation section is switched from the constant flow rate control to constant liquid level control in which the liquid level of the solution in the crystallization tank is kept constant. program.

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