Crystallization system and crystallization method

Abstract

To provide a crystallization system and a crystallization method where a separation object is suitably crystallized.SOLUTION: A crystallization system comprises: an adjusting part to reduce the pressure of a dissolved solution dissolved with a separation object; a crystallization tank where an opening part is connected to the adjusting part, a pressure-reduced dissolved solution is introduced from the opening by the adjusting part, and the separation object is crystallized from the dissolved solution at the inside; and an agitation part which is set in the crystallization tank and which generates the downward flow of the dissolved liquid by agitating the inside of the crystallization tank. The agitation blade to agitate the dissolved solution in the agitation part is positioned at the lower side from the opening in the vertical direction.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a crystallization system and a crystallization method.

Background Art

[0002] For example, when recycling polyester, a crystallization operation may be performed. Patent Document 1 describes that in a crystallization tank to which a pressure reducing valve is connected, the pressure reducing valve is directly connected to the crystallization tank.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technique of Patent Document 1, crystals precipitated by crystallization may accumulate at the outlet of the pressure reducing valve, and there is a possibility that the pressure reducing valve may be blocked, making it impossible to appropriately crystallize the separation target.

[0005] The present disclosure solves the above-described problems and aims to provide a crystallization system and a crystallization method capable of appropriately crystallizing a separation target.

Means for Solving the Problems

[0006] In order to solve the above-described problems and achieve the object, a crystallization system according to the present disclosure includes an adjustment unit that reduces the pressure of a solution in which a separation target is dissolved, a crystallization tank in which an opening connected to the adjustment unit is formed, and the solution depressurized by the adjustment unit is introduced from the opening, and the separation target is crystallized from the solution inside, and a stirring unit provided in the crystallization tank that stirs the inside of the crystallization tank to generate a downward flow of the solution, and a stirring blade of the stirring unit that stirs the solution is located vertically below the opening.

[0007] In order to solve the above problems and achieve the object, a crystallization method according to the present disclosure includes an adjustment unit that reduces the pressure of a liquid, a crystallization tank in which an opening connected to the adjustment unit is formed, and a stirring unit provided in the crystallization tank and having a stirring blade that stirs the liquid and is located below the opening in the vertical direction. The crystallization method of the crystallization system includes: supplying a solution in which a separation target is dissolved to the adjustment unit, reducing the pressure of the solution by the adjustment unit, and introducing the solution from the opening into the crystallization tank; and crystallizing the separation target from the solution in the crystallization tank. And a step of rotating the stirring unit in a state where the depressurized solution is introduced into the crystallization tank to stir the inside of the crystallization tank to generate a downward flow of the solution.

Effect of the Invention

[0008] According to the present disclosure, the separation target can be appropriately crystallized.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0010] Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail. Note that the present invention is not limited by this embodiment, and when there are a plurality of embodiments, those configured by combining each embodiment are also included.

[0011] (First Embodiment) (Recycling Process) FIG. 1 is a schematic diagram of the polyester recycling process in this embodiment. In this embodiment, a process of recycling (regenerating) the polyester raw material Pm is performed by depolymerizing the polyester raw material Pm into monomers and then repolymerizing the monomers. Specifically, as shown in FIG. 1, the polyester raw material Pm is flaked (step S100), the solution is mixed with the reaction solvent M and depolymerized (step S102), the monomers of the depolymerized polyester are purified (separated) to produce the monomer D derived from carboxylic acid and the monomer E of the alcohol component (step S104), the monomer D is hydrolyzed to separate the reaction solvent M (step S106), and the monomer F generated by the hydrolysis of the monomer D and the monomer E are polymerized (step S108) to regenerate the polyester raw material Pm. Note that the recycling process employing the separation system 1 of this embodiment may omit the flaking in step S100, or may only perform the process of recovering the monomers D, E shown in step S104 and the monomer F shown in step S106 without performing the repolymerization process as in step S108.

[0012] (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. For example, it may be 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 the polyester component. Examples of components other than polyester contained in the polyester raw material Pm include plastics such as polyethylene, polystyrene, polypropylene, and polyvinyl chloride other than polyester, metals, dyes, pigments, and polymerization catalysts. Examples of the polyester raw material Pm also include clothes in which polyester and other components are woven in a fibrous form. Hereinafter, components other than polyester contained in the polyester raw material Pm are regarded as impurities.

[0013] (Reaction solvent) The reaction solvent M is a solvent that reacts with polyester to depolymerize the polyester. The reaction solvent M may be, for example, at least one of methanol, ethanol, water, and ethylene glycol.

[0014] (Monomer derived from carboxylic acid) The monomer D derived from carboxylic acid is a monomer having a carboxyl group generated by the depolymerization reaction of polyester. The monomer D may be, for example, dimethyl carboxylate or diethyl carboxylate. Furthermore, it is preferable that the monomer D is a monomer of terephthalic acid, and it may be, for example, dimethyl terephthalate (DMT).

[0015] (Monomer of alcohol component) Monomer E of the alcohol component is a monomer of the alcohol component produced by the depolymerization reaction of the polyester. Monomer E may be, for example, a dihydroxy compound (dihydric alcohol), and more specifically, it may be ethylene glycol (EG).

[0016] Hereinafter, a case where the polyester is PET, the reaction solvent M is methanol, monomer D is DMT, and monomer E is EG will be described as an example.

[0017] (Separation system) Figure 2 is a schematic diagram of the separation system according to the first embodiment. The separation system 1 according to the first embodiment is a system that monomerizes the polyester contained in the polyester raw material Pm to generate monomers D and E. As shown in Figure 2, the separation system 1 includes a raw material storage unit 10, a dissolution unit 12, a solid-liquid separation unit 13, a solvent storage unit 14, a reaction unit 16, a separation unit 18, a control unit 30, a temporary storage unit 70, and a crystallization system 80.

[0018] Hereinafter, the Z direction is the vertical direction (up and down direction). The upward direction in the vertical direction of the Z direction is defined as the Z1 direction, and the downward direction in the vertical direction is defined as the Z2 direction.

[0019] (Raw material storage unit) The raw material storage section 10 is a tank into which the polyester raw material Pm is introduced and where the polyester raw material Pm is stored. In the present embodiment, the flaked polyester raw material Pm is stored in the raw material storage section 10, but the shape and size of the polyester raw material Pm may be arbitrary. The raw material storage section 10 is connected to the dissolution section 12 via the introduction pipe 10a. The polyester raw material Pm in the raw material storage section 10 is supplied to the dissolution section 12 through the introduction pipe 10a. The introduction pipe 10a is provided with an adjustment section 10b for adjusting the amount of the polyester raw material Pm supplied from the raw material storage section 10 to the dissolution section 12. The adjustment section 10b is, for example, an on-off valve. In the open state, the polyester raw material Pm in the raw material storage section 10 is supplied to the dissolution section 12, and in the closed state, the supply of the polyester raw material Pm in the raw material storage section 10 to the dissolution section 12 is stopped. However, the adjustment section 10b is not limited to being an on-off valve and may be any mechanism capable of adjusting the supply of the polyester raw material Pm to the dissolution section 12. Also, the polyester raw material Pm may be supplied directly to the dissolution section 12 without passing through the raw material storage section 10, the introduction pipe 10a, and the adjustment section 10b.

[0020] (Dissolution section) The dissolution section 12 is a tank in which the dissolved liquid Pd is stored. The dissolved liquid Pd is a solution formed by mixing the polyester raw material Pm and the 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 polyester contained in the polyester raw material Pm, remain without dissolving in the monomer D. Therefore, it can be said that the dissolved liquid Pd contains the 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.

[0021] The monomer D and the polyester raw material Pm are supplied to the dissolution section 12. In the dissolution section 12, the polyester contained in the polyester raw material Pm dissolves in the monomer D, while impurities remain without dissolving in the monomer D, and a polyester solution P and a dissolution liquid Pd containing impurities are generated. By dissolving the polyester in the monomer D in this way, the viscosity can be reduced and the fluidity can be improved, and the polyester can be easily led out to the reaction section 16. Note that the polyester solution P is not limited to the case where the entire amount of the polyester is dissolved in the monomer D, and at least a part of the polyester may be in a state of not being dissolved in the monomer D. Further, among the components other than the polyester contained in the polyester raw material Pm, if there is a component that can be dissolved in the monomer D, the polyester solution P may also contain that component dissolved in the monomer D.

[0022] The dissolution section 12 is connected to a first reaction section 16A, which will be described later, via an introduction pipe 12a. The dissolution liquid Pd in the dissolution section 12 is supplied to the first reaction section 16A through the introduction pipe 12a. Further, a supply section 12a1 is provided in the introduction pipe 12a. The supply section 12a1 is a mechanism for supplying the polyester solution P in the dissolution section 12 to the first reaction section 16A, and is a pump in this embodiment.

[0023] In this embodiment, the melting section 12 is provided with a heating section 12A. By heating the inside of the melting section 12, the heating section 12A heats the monomer D and the 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. By heating at such a predetermined temperature, the polyester contained in the polyester raw material Pm can be appropriately 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 include components that melt when heated to the predetermined temperature (the temperature at which the polyester can be dissolved in the monomer D). Therefore, when the impurities contain components that melt when heated to the predetermined temperature, a part of them is in a molten state and is contained in the solution Pd. In this embodiment, the heating section 12A is provided in the melting section 12, but the position where the heating section 12A is provided is not limited thereto and is arbitrary.

[0024] (Solvent storage section) The solvent storage section 14 is a tank into which the reaction solvent M is introduced and stored. The solvent storage section 14 is connected to the reaction section 16 via an introduction pipe 14a. The reaction solvent M in the solvent storage section 14 is supplied to the reaction section 16 through the introduction pipe 14a. More specifically, the introduction 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 makes the reaction solvent M into a supercritical state or a subcritical state (pressurized gas or pressurized liquid) by pressurizing and heating the reaction solvent M. The reaction section 16 is supplied with the reaction solvent M in a supercritical state or a subcritical state (pressurized gas or pressurized liquid).

[0025] (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.

[0026] (First reaction section) The first reaction section 16A is formed within the reaction section 16. In the present embodiment, the first reaction section 16A can be said to be the location within the reaction section 16 filled with a filler. As the filler for the first reaction section 16A, known materials used in gas-liquid or liquid-liquid contact devices can be used. For example, the same filler as that used in a contact device for extracting active ingredients by bringing heavy oil into contact with water can be used. Specific examples of the filler include pipes made of SUS or the like, Raschig rings, Berl saddles, Telarets, balls, and the like.

[0027] An introduction pipe 12a is connected to the first reaction section 16A. More specifically, an inlet 16C, which is an opening through which the dissolved liquid Pd from the dissolution section 12 in the introduction pipe 12a is introduced, is connected to the first reaction section 16A. The inlet 16C is connected to the surface 16A1 on the first direction D1 side of the first reaction section 16A. The introduction pipe 12a is connected to the surface 16A1 such that the inlet 16C opens facing the second direction D2 side opposite to the first direction D1. Thus, in the present embodiment, the inlet 16C opening facing the second direction D2 side is connected to the surface 16A1 of the first reaction section 16A, but it is not limited thereto. For example, the inlet 16C may not be directly connected to the first reaction section 16A, and the inlet 16C opening facing the second direction D2 side may be connected to the first direction D1 side of the surface 16A1 of the first reaction section 16A within the reaction section 16.

[0028] The introduction pipe 14a is connected to the reaction section 16. More specifically, an inlet 16D, which is an opening through which the reaction solvent M from the solvent storage section 14 is introduced into the introduction pipe 14a, is connected to the reaction section 16. The inlet 16D is connected to the second direction D2 side of the surface 16A2 of the first reaction section 16A. The introduction pipe 14a is connected to the second direction D2 side of the surface 16A2 such that the inlet 16D faces the first direction D1 side or opens from the side surface toward the center side. Thus, in the present embodiment, the inlet 16D that faces the first direction D1 side or opens from the side surface toward the center side is connected to the second direction D2 side of the surface 16A2 of the first reaction section 16A, but it is not limited thereto. 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.

[0029] Thus, in the present embodiment, the inlet 16C through which the dissolved solution Pd is introduced opens facing the second direction D2, and the inlet 16D through which the reaction solvent M is introduced faces the first direction D1 or opens from the side surface toward the center side. Therefore, in the first reaction section 16A, the dissolved solution Pd and the reaction solvent M are introduced in directions facing each other.

[0030] The dissolved solution Pd introduced from the inlet 16C into the first reaction section 16A moves on the surface of the packing material in the first reaction section 16A in the second direction D2. On the other hand, the reaction solvent M in the supercritical state or subcritical state (pressurized gas or pressurized liquid) introduced from 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 the supercritical state or subcritical state (pressurized gas or pressurized liquid) comes into contact with the dissolved solution Pd. The polyester in the dissolved solution Pd is depolymerized (molecular weight reduced) by the reaction solvent M, and the depolymerized polyester is extracted by the reaction solvent M in the supercritical state or subcritical state (pressurized gas or pressurized liquid). Hereinafter, the polyester depolymerized in the first reaction section 16A is referred to as the first depolymerized polyester P1, and a 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) is referred to as the first solvent M1. The first solvent M1 containing the first depolymerized polyester P1 proceeds through the first reaction section 16A to the first direction D1 side and is led out to the first direction D1 side of the first reaction section 16A.

[0031] Note that the first depolymerized polyester P1 includes monomers D and E generated by depolymerizing the polyester in the dissolved solution Pd, monomer D originally mixed in the dissolved solution Pd, and oligomers generated by depolymerizing the polyester. The oligomers here refer to oligomers derived from carboxylic acids or alcohol components that have not been monomerized but have been depolymerized from polyester (oligomers derived from carboxylic acids or alcohol components with a molecular weight smaller than that of polyester). Also, 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 is oligomers contained in the residual substance that have been depolymerized, monomers D and E obtained by depolymerizing the oligomers contained in the residual substance, and the like.

[0032] (Second reaction section) The second reaction section 16B is formed within the reaction section 16, and the second reaction section 16B is formed at a location where the first solvent M1 is derived from the first reaction section 16A. In the present embodiment, since the first solvent M1 is derived toward the first direction D1, 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.

[0033] 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 is referred to as a second depolymerized polyester P2, and a 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) is referred to as a second solvent M2. A lead-out pipe 16a is connected to the second reaction section 16B. More specifically, a lead-out port 16E, which is an opening from which the second solvent M2 from the second reaction section 16B is led out, of the lead-out pipe 16a 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 led out to the outside of the second reaction section 16B through the lead-out pipe 16a from the lead-out port 16E.

[0034] Note that the second depolymerized polyester P2 includes monomers D and E in the first depolymerized polyester P1, monomers D and E generated by depolymerizing oligomers in the first depolymerized polyester P1, and oligomers generated by depolymerizing the first depolymerized polyester P1.

[0035] At the bottom of the reaction section 16, a discharge pipe 16b is connected. More specifically, at the bottom of the reaction section 16, a discharge port 16F, which is an opening of the discharge pipe 16b through which non-extracts (described later) inside the reaction section 16 are discharged, is connected. From the discharge port 16F, non-extracts are discharged, including impurities such as metal compounds not extracted into the reaction solvent M and residues of undecomposed polyester not extracted into the reaction solvent M. That is, the non-extracts 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-extracts discharged from the discharge port 16F can be said to be the components remaining in the first reaction section 16A and the second reaction section 16B without being led to the separation section 18 as the second solvent M2 (the reaction solvent M in which the second depolymerized polyester P2 is dissolved) in the polyester solution P.

[0036] Also, the reaction section 16 may be provided with a heating section for heating the inside of the reaction section 16 and a pressurizing section for maintaining the pressure inside the reaction section 16 at a predetermined value or more. The temperature inside the reaction section 16 is preferably set to 250°C or more and 400°C or less, and more preferably 250°C or more and 350°C or less. Also, the pressure inside the reaction section 16 is preferably 1 MPa or more and 30 MPa or less, and more preferably 6 MPa or more and 25 MPa or less. The pressurizing section and the heating section may be controlled by the control section 30.

[0037] (Separation section) The separation section 18 is introduced with the second solvent M2 containing the second depolymerized polyester P2, and separates the second solvent M2 into the reaction solvent M, the monomer D derived from the carboxylic acid contained in the second depolymerized polyester P2, the monomer E of the alcohol component contained in the second depolymerized polyester P2, and the residual substance R. The separation section 18 separates the second solvent M2 into the monomer D, the monomer E, and the residual substance R by distilling the second solvent M2. The residual substance R is a component other than the reaction solvent M, the monomer D, and the monomer E in the second solvent M2 and contains oligomers.

[0038] In the present embodiment, the separation section 18 includes a first separation section 18A, a second separation section 18B, and a third separation section 18C.

[0039] The first separation unit 18A is a separation tower connected to the lead-out pipe 16a. The second solvent M2 containing the second depolymerized polyester P2 is introduced into the first separation unit 18A through the lead-out pipe 16a. The first separation unit 18A separates the second solvent M2 into a low-boiling component and a high-boiling component having a boiling point higher than that of the low-boiling component. For example, in the first separation unit 18A, the second solvent M2 may be set at a predetermined temperature, and the component that has become a gas may be regarded as the low-boiling component, and the liquid component may be regarded as the high-boiling component. The lead-out pipes 18Aa and 18Ab are connected to the first separation unit 18A. The low-boiling component is led out from the lead-out pipe 18Aa, and the high-boiling component is led out from the lead-out pipe 18Ab.

[0040] The second separation unit 18B is a separation tower connected to the first separation unit 18A through the lead-out pipe 18Aa. The low-boiling component is introduced into the second separation unit 18B through the lead-out pipe 18Aa. The second separation unit 18B separates the low-boiling component into the reaction solvent M and the monomer E. The lead-out pipes 18Ba and 18Bb are connected to the second separation unit 18B. The reaction solvent M is led out from the lead-out pipe 18Ba, and the monomer E is led out from the lead-out pipe 18Bb. Note that the lead-out pipe 18Ba is connected to the second separation unit 18B and the solvent storage unit 14. Therefore, the reaction solvent M led out from the second separation unit 18B is returned to the solvent storage unit 14 and reused for the depolymerization of the polyester.

[0041] The third separation unit 18C is a separation tower connected to the first separation unit 18A through the lead-out pipe 18Ab. The high-boiling component is introduced into the third separation unit 18C through the lead-out pipe 18Ab. The third separation unit 18C separates the high-boiling component into a residue R having an even higher boiling point, a low-boiling component containing the reaction solvent M and the monomer E, and the monomer D. The lead-out pipes 18Ca, 18Cb, and 18Cc are connected to the third separation unit 18C. The lead-out pipe 18Ca is connected to the second separation unit 18B. The low-boiling component separated within the third separation unit 18C is led out to the second separation unit 18B through the lead-out pipe 18Ca. Also, the monomer D separated within the third separation unit 18C is led out from the lead-out pipe 18Cb and introduced into the temporary storage unit 70. The residue R separated within the third separation unit 18C is led out from the lead-out pipe 18Cc.

[0042] A introducing pipe 18Cd is connected to the third separation section 18C. The introducing pipe 18Cd is also connected to the dissolution section 12, and introduces the monomer D derived from the third separation section 18C into the dissolution section 12. In the example of FIG. 2, the introducing pipe 18Cd branches from the leading pipe 18Cb. The introducing pipe 18Cd is provided with an adjusting section 18Ce for adjusting the amount of the monomer D supplied from the third separation section 18C to the dissolution section 12. The adjusting section 18Ce is, for example, an on-off valve. In the open state, the monomer D is supplied to the dissolution section 12, and in the closed state, the supply of the monomer D to the dissolution section 12 is stopped. However, the adjusting section 18Ce is not limited to being an on-off valve, and may be any mechanism capable of adjusting the supply of the monomer D to the dissolution section 12. In the present embodiment, the adjusting section 18Ce is provided at the branching position of the introducing pipe 18Cd from the leading pipe 18Cb, but the position where it is provided is not limited thereto and may be arbitrary. Further, the introducing pipe 18Cd may not be connected to the leading pipe 18Cb and may be directly connected to the third separation section 18C. Further, for example, a storage section (tank) for storing the monomer D may be provided in the leading pipe 18Cb, and the introducing pipe 18Cd may be connected to the storage section.

[0043] A introducing pipe 18Cf is connected to the third separation part 18C. The introducing pipe 18Cf is also connected to the dissolving part 12, and introduces the residual substance R derived from the third separation part 18C into the dissolving part 12. In the example of FIG. 2, the introducing pipe 18Cf branches from the leading-out pipe 18Cc. The introducing pipe 18Cf is provided with an adjusting part 18Cg for adjusting the amount of the residual substance R supplied from the third separation part 18C to the dissolving part 12. The adjusting part 18Cg is, for example, an on-off valve. When it is in the open state, it supplies the residual substance R to the dissolving part 12, and when it is in the closed state, it stops the supply of the residual substance R to the dissolving part 12. However, the adjusting part 18Cg is not limited to being an on-off valve, and may be any mechanism capable of adjusting the supply of the residual substance R to the dissolving part 12. In the present embodiment, the adjusting part 18Cg is provided at the branching position of the introducing pipe 18Cf from the leading-out pipe 18Cc, but the position where it is provided is not limited thereto and may be arbitrary. Further, the introducing pipe 18Cf may not be connected to the leading-out pipe 18Cc and may be directly connected to the third separation part 18C.

[0044] For example, a storage part (tank) for storing the residual substance R may be provided in the leading-out pipe 18Cc, and the introducing pipe 18Cf may be connected to the storage part. Further, a filter for collecting foreign substances in the residual substance R while allowing oligomers in the residual substance R to pass through may be provided in the introducing pipe 18Cf.

[0045] (Temporary storage part) The temporary storage part 70 is, for example, a tank, and temporarily stores the monomer D supplied from the third separation part 18C. The temporary storage part 70 is connected to the third separation part 18C via the leading-out pipe 18Cb. The temporary storage part 70 is connected to the dissolving tank 82 via the leading-out pipe 72. The temporary storage part 70 supplies the temporarily stored monomer D to the dissolving tank 82 of the crystallization system 80.

[0046] (Crystallization system) The crystallization system 80 is a system that crystallizes monomer D from a solution in which monomer D separated by the separation unit 18 is dissolved. The monomer D separated by the separation unit 18 may contain impurities, and the crystallization system 80 crystallizes highly pure monomer D from which impurities have been removed from the solution in which monomer D is dissolved. Examples of the impurities here include isomers of monomer D that could not be completely separated by distillation in the third separation unit 18C. For example, when monomer D is DMT, the isomer of DMT is DMI (dimethyl isophthalate) derived from IPA (isophthalic acid) of the copolymer. DMI has a boiling point close to that of DMT and is difficult to separate by distillation, but can be separated by crystallization. That is, in the present embodiment, highly pure monomer D can be extracted by crystallizing monomer D (DMT) without crystallizing DMI. Hereinafter, the highly pure monomer D extracted by crystallization is appropriately referred to as monomer HD.

[0047] Furthermore, in the present 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 up to obtaining PTA from the crystallized monomer HD, and may only perform the process of crystallizing monomer HD.

[0048] Also, the crystallization system 80 of the present embodiment is provided in the separation system 1 and used for the purpose of crystallizing monomer HD, but the use of the crystallization system 80 is not limited thereto. The crystallization system 80 may be a system that separates a separation target of an arbitrary component dissolved in a solution of an arbitrary component by crystallization from the solution.

[0049] Hereinafter, the crystallization system 80 according to the present embodiment will be specifically described. FIG. 3 is a schematic side view of the crystallization system. FIG. 4 is a schematic top view of the crystallization system. FIG. 5 is a schematic top view showing the internal structure of the crystallization unit. FIG. 6 is a schematic top view of the crystallization unit showing the arrangement when the number of baffles is different.

[0050] The crystallization system 80 includes a dissolution tank 82, an adjustment unit 86, a crystallization tank 90, a stirring unit 100, a solid-liquid separation unit 120, a melting tank 130, a melting temporary storage tank 140, and a water addition separation reaction unit 150. In the present embodiment, the crystallization system 80 is connected downstream of the lead-out pipe 72 and extracts monomer HD by crystallization from the solution in which monomer D flowing through the lead-out pipe 72 is dissolved.

[0051] (Dissolution tank) The dissolution tank 82 is a tank that stores the solution L in which monomer D is dissolved. The dissolution tank 82 is connected to the temporary storage unit 70 via the lead-out pipe 72. Monomer D containing impurities, which has been separated by the third separation unit 18C, is introduced into the dissolution tank 82 from the temporary storage unit 70. Further, a solvent for dissolving monomer D is introduced into the dissolution tank 82. As a result, in the dissolution tank 82, monomer D is dissolved in the solvent and stored as the solution L. Although any liquid may be used as the solvent, methanol is used in the present embodiment.

[0052] The dissolution tank 82 is connected to the adjustment unit 86 and the crystallization tank 90 via the introduction pipe 84. The solution L stored in the dissolution tank 82 is introduced into the crystallization tank 90 via the introduction pipe 84 and the adjustment unit 86. Note that the dissolution tank 82 is located in the Z1 direction (vertically upward) relative to the crystallization tank 90 described later. More specifically, the bottom surface on the Z2 direction side of the dissolution tank 82 is located in the Z1 direction relative to the opening 90c formed in the crystallization tank 90. However, the positional relationship in the Z direction between the dissolution tank 82 and the crystallization tank 90 is not limited to this and may be arbitrary.

[0053] (Introduction pipe) The introduction pipe 84 is a pipe that connects the dissolution tank 82 and the crystallization tank 90. In the present embodiment, as will be described later, since the introduction pipe 84 is connected to the adjustment part 86 connected to the opening 90c of the crystallization tank 90, it can be said that it is connected to the crystallization tank 90 (opening 90c) via the adjustment part 86. The introduction pipe 84 extends in the Z2 direction from the location where it is connected to the dissolution tank 82 to the location where it is connected to the crystallization tank 90 (in this example, the adjustment part 86). In other words, in the section from the location where the introduction pipe 84 is connected to the dissolution tank 82 to the location where it is connected to the crystallization tank 90 (in this example, the adjustment part 86), it can be said that it extends in the Z2 direction without going toward the Z1 direction side as it goes toward the location where it is connected to the crystallization tank 90 (in this example, the adjustment part 86). In the example of FIG. 3, the introduction pipe 84 extends along the Z2 direction, but it is not limited thereto, and it may extend obliquely with respect to the Z2 direction.

[0054] The dissolved liquid L in the dissolution tank 82 flows through the introduction pipe 84 and the adjustment part 86 into the crystallization tank 90.

[0055] (Adjustment part) The adjustment part 86 is a device that reduces the pressure of the dissolved liquid L. The adjustment part 86 is connected to the introduction pipe 84 and the crystallization tank 90. The adjustment part 86 reduces the pressure of the dissolved liquid L introduced from the dissolution tank 82 via the introduction pipe 84 and introduces the dissolved liquid L in the depressurized state into the crystallization tank 90.

[0056] The adjustment part 86 is a pressure reducing valve in the present embodiment. The adjustment part 86 may have any structure as long as it is a pressure reducing valve, but it is an angle valve in the present embodiment. By being an angle valve, the adjustment part 86 can reduce the pressure efficiently. As shown in FIG. 4, the adjustment part 86 of the present embodiment includes a valve part 86a, an adjustment handle 86b, and a pipe part 86c.

[0057] The pipe section 86c is a tubular member with a flow path formed inside, and one end 86d is connected to the introduction pipe 84. In this embodiment, the end 86d has a shape with a flange formed around the opening, and the end 84a on the side connected to the adjustment section 86 of the introduction pipe 84 also has a shape with a flange formed around the opening. In this embodiment, a plurality of fastening holes (not shown) penetrate through the flanges of the ends 86d and 84a, and the end 86d and the end 84a are connected by being fastened with a fastening member 85 inserted into the fastening holes.

[0058] Also, for the pipe section 86c, the other end 86e is connected to the crystallization tank 90. In this embodiment, the end 86e has a shape with a flange formed around the opening. Further, on the wall surface of the crystallization tank 90, a recessed portion 90a and an opening portion 90c that communicates the inside and the outside of the crystallization tank 90 and is formed at a position overlapping the recessed portion 90a are formed. In this embodiment, the pipe section 86c is directly connected to the crystallization tank 90 by being fastened with a fastening member 87 in a state where the end 86e of the pipe section 86c is inserted into the recessed portion 90a of the crystallization tank 90.

[0059] As described above, since the adjustment section 86 in this embodiment is an angle valve, the flow path on the end 86d side of the pipe section 86c and the flow path on the end 86e side of the pipe section 86c intersect. In this embodiment, the flow path on the end 86d side of the pipe section 86c and the flow path on the end 86e side intersect in the horizontal direction. The horizontal direction is a direction orthogonal to the Z direction (vertical direction).

[0060] The valve section 86a is a valve provided in the flow path inside the pipe section 86c. The adjustment handle 86b is attached to the valve section 86a and is a mechanism for adjusting the opening degree of the flow path inside the pipe section 86c by the valve section 86a. The adjustment section 86 adjusts the opening and closing of the valve inside the valve section 86a by rotating the adjustment handle 86b, thereby adjusting the flow rate and pressure of the dissolution liquid L.

[0061] The solution L introduced into the adjustment unit 86 is introduced into the crystallization tank 90 in a state of reduced pressure by the adjustment unit 86. Since the temperature of the solution L under reduced pressure decreases, the monomer HD to be separated crystallizes from the solution L under reduced pressure.

[0062] In this embodiment, the adjustment unit 86 is directly connected to the crystallization tank 90. However, the present invention is not limited thereto, 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.

[0063] (Crystallization tank) The crystallization tank 90 is a tank into which the solution L decompressed by the adjustment unit 86 is introduced, and in which the target to be separated (here, the monomer HD) crystallizes from the solution L inside. As described above, the crystallization tank 90 is formed with an opening 90c connected to the adjustment unit 86, and the solution L decompressed by the adjustment unit 86 is introduced from the opening 90c. In this way, the crystallization tank 90 is introduced with the solution L under reduced pressure and stores the solution L in a state of reduced pressure. That is, the crystallization tank 90 can be said to be a flash-type crystallization tank in which the internal pressure is reduced compared to the external pressure.

[0064] The crystallization tank 90 is, for example, a tank, and its shape may be arbitrary. In this embodiment, it has an upper surface portion 90a1, a bottom surface portion 90a2, and side walls 90b.

[0065] The side wall 90b is the wall surface of the crystallization tank 90. The upper surface portion 90a1 is a member that covers the end portion of the side wall 90b on the Z1 direction side, and the bottom surface portion 90a2 is a member that covers the end portion of the side wall 90b on the Z2 direction side. In the present embodiment, the side wall 90b is cylindrical, and the upper surface portion 90a1 and the bottom surface portion 90a2 are hemispherical, but their shapes are not limited to this and may be arbitrary. In the present embodiment, the recessed portion 90a and the opening 90c are formed in the side wall 90b. Further, in the present embodiment, a through hole through which the stirring portion 100 described later passes is opened in the upper surface portion 90a1. Further, a discharge pipe 121 for discharging the slurry S is connected to the bottom surface portion 90a2. Note that the slurry S is a slurry containing the crystallized monomer HD and the dissolution liquid L from which the monomer HD has been removed. However, the positions where the recessed portion 90a and the opening 90c, the through hole through which the stirring portion 100 passes, and the discharge pipe 121 are provided are not limited to this and may be arbitrary. For example, the discharge pipe 121 may be provided on the side wall 90b.

[0066] Inside the crystallization tank 90, a baffle 110 is provided. The baffle 110 is a member that rectifies the flow of the dissolution liquid L in the crystallization tank 90. The shape, attachment position, and number of the baffle 110 are arbitrary. In the present embodiment, the baffle 110 is provided on the inner wall surface of the crystallization tank 90 (side wall 90b). Further, more specifically, it is a plate-like member extending in the Z direction on the inner wall surface of the side wall 90b.

[0067] In this embodiment, a plurality of baffles 110 are provided on the inner wall surface of the side wall 90b in the circumferential direction when the central axis along the Z direction of the crystallization tank 90 is taken as the axial direction. In this embodiment, each baffle 110 is provided so as to be arranged at equal intervals in the circumferential direction when viewed from the Z direction. For example, as shown in FIG. 5, when there are three baffles 110, the three baffles 110 are provided at intervals of 120°. Further, as shown in FIG. 6, when there are two baffles 110, the two baffles 110 are provided facing each other, that is, at intervals of 180°. Further, when a plurality of baffles 110 are provided, the opening 90c is provided at the central position between two adjacent baffles 110 in the circumferential direction. That is, for example, in the example of FIG. 7, since the baffles 110 are adjacent to each other at intervals of 180°, the opening 90c is provided at a position adjacent to each baffle 110 at intervals of 90°.

[0068] However, the baffle 110 is not an essential component and may not be provided in the crystallization tank 90.

[0069] (Stirring section) The stirring section 100 is a device provided in the crystallization tank 90 for stirring the inside of the crystallization tank 90. The stirring section 100 has a rotating shaft 104 and stirring blades 106.

[0070] The rotating shaft 104 is a shaft-shaped member rotatably inserted into the inside of the crystallization tank 90. The stirring blade 106 is a blade provided at the tip of the rotating shaft 104 on the Z2 direction side. The stirring blade 106 may have, for example, a shape in which a plurality of blades are arranged in the circumferential direction. The stirring blade 106 is located on the Z2 direction side of the opening 90c inside the crystallization tank 90. Further, in this embodiment, the stirring blade 106 is located on the Z2 direction side of the adjustment section 86. Further, the stirring blade 106 is located on the Z1 direction side of the bottom surface portion 90a2 of the crystallization tank 90 and is provided at a position facing the bottom surface portion 90a2 (that is, a position overlapping the bottom surface portion 90a2 when viewed from the Z direction). Further, it is preferable that the stirring section 100 is provided at the central position of the crystallization tank 90 when viewed from the Z direction. That is, it is preferable that the central axis of the stirring section 100 coincides with the central axis of the crystallization tank 90.

[0071] The stirring unit 100 rotates by driving the drive unit 102 (for example, a motor) and stirs the inside of the crystallization tank 90. Here, the stirring unit 100 is configured to generate a downward flow Df in the crystallization tank 90 by rotating. The downward flow Df refers to the water flow directed from the tip of the stirring blade 106 in the Z2 direction. For example, the rotation direction of the stirring unit 100 and the direction of the blade of the stirring blade 106 are set to be able to generate the downward flow Df. Therefore, when the stirring unit 100 rotates in the crystallization tank 90 in which the depressurized dissolved liquid L is stored, as shown in FIG. 3, the dissolved liquid L flows from the tip of the stirring blade 106 along the downward flow Df to the Z2 direction side and reaches the bottom surface portion 90a2. The dissolved liquid L that has reached the bottom surface portion 90a2 flows radially outward along the bottom surface portion 90a2 and flows as an upward flow Uf along the side wall 90b to the Z1 direction side. That is, in the present embodiment, the dissolved liquid L in the crystallization tank 90 flows in the Z2 direction along the downward flow Df in the region on the Z2 direction side of the stirring blade 106, and flows in the Z1 direction along the upward flow Uf in the region on the Z1 direction side of the stirring blade 106 closer to the side wall 90b.

[0072] (Crystallization of Monomer HD) The crystallization system 80 crystallizes the monomer HD from the dissolved liquid L in the crystallization tank 90 with the above configuration. That is, when the dissolved liquid L in the dissolution tank 82 is supplied to the adjustment unit 86 via the introduction pipe 84, the dissolved liquid L is depressurized by the adjustment unit 86. The dissolved liquid L depressurized by the adjustment unit 86 is introduced into the crystallization tank 90 through the opening 90c. Since the temperature of the depressurized dissolved liquid L decreases, the monomer HD is crystallized in the crystallization tank 90 and stored as a slurry S. Further, by stirring the inside of the crystallization tank 90 with the stirring unit 100, the crystallization of the monomer HD in the crystallization tank 90 is promoted.

[0073] Here, since the dissolution liquid L is depressurized immediately after passing through the adjustment unit 86, monomer HD may crystallize at the opening 90c which is the inlet introduced into the crystallization tank 90. In this case, the solid component monomer HD may accumulate at the opening 90c and block at least a part of the opening 90c. As a result, the dissolution liquid L may not be properly introduced into the crystallization tank 90, and there is a possibility that the monomer HD to be separated cannot be properly obtained.

[0074] On the other hand, in the present embodiment, while the stirring unit 100 is configured to generate a downward flow Df, the stirring blade 106 is arranged on the Z2 direction side of the opening 90c. Thereby, an upward flow Uf is generated in the region where the opening 90c is formed, and the monomer HD deposited in the opening 90c or flowing through the opening 90c can be introduced into the crystallization tank 90 by the upward flow Uf, and the blockage of the opening 90c can be suppressed. Furthermore, since the monomer HD accumulates on the edge of the opening 90c on the Z2 direction side, the monomer HD deposited on the opening 90c can be lifted upward by the upward flow Uf in the Z1 direction and removed appropriately. In addition, in the present embodiment, since the adjustment unit 86 is directly connected to the opening 90c, the flow path from the adjustment unit 86 to the crystallization tank 90 can be shortened, and the blockage by the monomer HD can be more appropriately suppressed. Furthermore, in the present embodiment, since the baffle 110 is provided inside the crystallization tank 90, the upward flow Uf can be rectified, and the monomer HD can be removed more appropriately.

[0075] Also, in the introduction pipe 84 connecting the dissolution tank 82 and the crystallization tank 90, when the pressure loss of the dissolution liquid L becomes high due to the head pressure, there is a possibility that bubbles are generated from the dissolution liquid L due to the decompression. When bubbles are generated, vapor lock occurs in the adjustment unit 86, and the dissolution liquid L cannot be properly introduced into the crystallization tank 90, and there is a possibility that the monomer HD cannot be properly crystallized. On the other hand, in the present embodiment, the dissolution tank 82 is arranged on the Z1 direction side of the crystallization tank 90. Thereby, the pressure loss of the dissolution liquid L due to the head pressure is suppressed, the generation of vapor lock due to bubbles is suppressed, and the monomer HD can be properly crystallized.

[0076] (Production of PTA) Next, a method for producing PTA from monomer HD by the crystallization system 80 will be described. The crystallization system 80 produces PTA by means of a solid-liquid separation unit 120, a melting tank 130, a temporary melting storage tank 140, and a hydrolysis separation reaction unit 150.

[0077] The solid-liquid separation unit 120 is connected to the crystallization tank 90 via a discharge pipe 121. The solid-liquid separation unit 120 is introduced with a slurry S (a solution L in which monomer HD has crystallized) generated in the crystallization tank 90 from the crystallization tank 90 via the discharge pipe 121. The solid-liquid separation unit 120 separates the introduced slurry S into a solid component to be separated and a liquid component. In the present embodiment, the solid-liquid separation unit 120 separates the slurry S into monomer HD and the solution L from which monomer HD has been removed. The solution L from which monomer HD has been removed is discharged from a discharge pipe 123 connected to the solid-liquid separation unit 120 and processed. The solid-liquid separation unit 120 is, for example, a centrifuge, and may separate the separation target from the solution L by centrifugation that stirs the inside of the solid-liquid separation unit 120 around a predetermined axis and moves the separation target to the outside in the radial direction of the rotating shaft. The solid-liquid separation unit 120 only needs to be able to separate the separation target from the solution L, and is not limited to centrifugation. For example, the solid-liquid separation unit 120 may separate the separation target from the solution L by a filter.

[0078] The highly pure monomer HD separated from the slurry S by solid-liquid separation is introduced into the melting tank 130 from a discharge pipe 122 connected to the solid-liquid separation unit 120. The melting tank 130 is a tank that heats and melts the introduced monomer HD. The monomer HD melted in the melting tank 130 is introduced into the temporary melting storage tank 140 for temporary storage, and then introduced from the temporary melting storage tank 140 into the hydrolysis separation reaction unit 150. The hydrolysis separation reaction unit 150 is a tank that adds water to the introduced monomer HD and hydrolyzes the monomer HD. The hydrolysis separation reaction unit 150 produces PTA by hydrolyzing the monomer HD. Thereafter, although not shown, PTA is stored in a hopper through a crystallization step and a drying step.

[0079] (Control unit) The control unit 30 is a control device that controls the separation system 1. The control unit 30 controls the adjustment unit 10b to control the amount of the polyester raw material Pm supplied from the raw material storage unit 10 to the dissolution unit 12. Further, when the solid-liquid separation unit 13 is provided with a drive unit, the control unit 30 controls the operation of the solid-liquid separation unit 13. The control unit 30 controls the supply unit 12a1 to control the amount of the dissolution liquid Pd supplied from the dissolution unit 12 to the reaction unit 16. The control unit 30 controls the heating and pressurizing unit 14b to make the reaction solvent M in a supercritical state or a subcritical state (pressurized gas or pressurized liquid), and controls the supply amount of the reaction solvent M in the supercritical state or the subcritical state (pressurized gas or pressurized liquid) to the reaction unit 16. The control unit 30 controls the adjustment unit 18Ce to control the supply amount of the monomer D to the dissolution unit 12. The control unit 30 controls the adjustment unit 18Cg to control the supply amount of the residual substance R to the dissolution unit 12. The control unit 30 adjusts the adjustment unit 86 to control the flow rate of the dissolution liquid L to the crystallization tank 90 while depressurizing the dissolution liquid L. The control unit 30 controls the drive unit 102 to control the rotation of the stirring unit 100.

[0080] In this embodiment, the control unit 30 is a computer and includes a processor including an arithmetic circuit such as a CPU (Central Processing Unit), and a storage unit that stores various information such as the arithmetic content and programs by the processor. The control unit 30 executes the control of the separation system 1 by reading a program from the storage unit.

[0081] However, the separation system 1 is not limited to being automatically controlled by the control unit 30, and for example, at least a part of the processing may be controlled by the operation of an operator.

[0082] (Operation of the separation system) Next, the operation of the separation system 1 will be described. The control unit 30 controls the adjustment units 10b and 18Ce to introduce the polyester raw material Pm and the monomer D into the dissolution unit 12, mix the polyester raw material Pm and the monomer D in the dissolution unit 12, and generate a dissolution liquid Pd. The control unit 30 controls the supply unit 12a1 to introduce the dissolution liquid Pd generated in the dissolution unit 12 into the first reaction unit 16A.

[0083] The control unit 30 controls the heating and boosting 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 control unit 30 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 control unit 30 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.

[0084] In this way, by supplying the dissolved solution Pd and the reaction solvent M to the reaction unit 16, in the first reaction unit 16A, the polyester contained in the dissolved solution Pd is depolymerized to produce the first depolymerized polyester P1. Then, in the second reaction unit 16B, the first depolymerized polyester P1 is further depolymerized to produce the 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, the monomer D, the monomer E, and the residual substances in the first separation unit 18A, the second separation unit 18B, and the third separation unit 18C.

[0085] The control unit 30 controls the adjustment unit 86 to supply the dissolved solution L to the adjustment unit 86, and the adjustment unit 86 depressurizes the dissolved solution L and introduces the depressurized dissolved solution L into the crystallization tank 90 from the opening 90c. Since the dissolved solution L introduced into the crystallization tank 90 is depressurized, in the crystallization tank 90, the monomer HD to be separated is crystallized from the dissolved solution L. Further, the control unit 30 controls the rotation of the stirring unit 100. Thereby, the inside of the crystallization tank 90 is stirred to generate a downward flow Df of the dissolved solution L in the crystallization tank 90. As a result, an upward flow Uf is generated near the opening 90c, and it is possible to suppress the deposition of the monomer HD on the opening 90c.

[0086] (Effect of the present disclosure) The crystallization system according to the first aspect of the present disclosure includes an adjustment unit 86 that reduces the pressure of a solution L in which a separation target is dissolved, and an opening 90c connected to the adjustment unit 86 is formed. The solution L decompressed by the adjustment unit 86 is introduced from the opening 90c, and a separation target is crystallized from the solution L inside. It has a crystallization tank 90 and a stirring unit 100 provided in the crystallization tank 90 for stirring the inside of the crystallization tank 90 to generate a downward flow Df of the solution L. The stirring blade 106 of the stirring unit 100 that stirs the solution L is located below the opening 90c in the vertical direction.

[0087] Therefore, an upward flow can be generated by the stirring blade. The upward flow removes the monomer crystals deposited at the opening so as to make them float. Therefore, the separation target can be appropriately crystallized.

[0088] The crystallization system according to the second aspect of the present disclosure is the crystallization system according to the first aspect, and the adjustment unit 86 is directly connected to the opening 90c. Therefore, the flow path between the adjustment unit and the crystallization tank can be shortened, and blockage of the opening by the monomer can be suppressed.

[0089] The crystallization system according to the third aspect of the present disclosure is the crystallization system according to the first aspect or the second aspect, and further includes a baffle 110 provided inside the crystallization tank 90 for rectifying the flow of the solution L in the crystallization tank 90. Thereby, the flow of the solution can be assisted, and the separation target can be appropriately crystallized.

[0090] The crystallization system according to the fourth aspect of the present disclosure is the crystallization system according to the third aspect, and the baffle 110 is a plate member extending in the vertical direction on the wall surface without the crystallization tank 90. Thereby, the flow of the solution can be assisted, and the separation target can be appropriately crystallized.

[0091] The crystallization system according to the fifth aspect of the present disclosure is the crystallization system according to any one of the first aspect to the fourth aspect, and the adjustment unit 86 is an angle valve. As a result, the solution is decompressed by the valve itself and by flowing through the angled flow path, so that decompression can be efficiently performed.

[0092] The crystallization system according to the sixth aspect of the present disclosure is the crystallization system according to any one of the first aspect to the fifth aspect, further comprising a dissolution tank 82 for storing the dissolution liquid L and an introduction pipe 84 connecting the dissolution tank 82 and the opening 90c. The dissolution tank 82 is located above the crystallization tank 90 in the vertical direction. Thereby, the dissolution liquid L flows from the dissolution tank to the crystallization tank without going against gravity. Therefore, it is possible to suppress an increase in pressure loss due to head pressure. In addition, vapor lock caused by bubbles generated in the adjustment unit can be eliminated, leading to appropriate crystallization of the separation target.

[0093] The crystallization system according to the seventh aspect of the present disclosure is the crystallization system according to any one of the first aspect to the sixth aspect, wherein the separation target is dimethyl terephthalate. Therefore, dimethyl terephthalate (DMT) can be crystallized.

[0094] The crystallization method according to the eighth aspect of the present disclosure is a crystallization method of a crystallization system having an adjustment unit 86 for reducing the pressure of a liquid, a crystallization tank 90 in which an opening 90c connected to the adjustment unit 86 is formed, and a stirring unit 100 provided in the crystallization tank 90 and having a stirring blade 106 for stirring the liquid and located below the opening 90c in the vertical direction. The method includes: supplying a dissolution liquid L in which the separation target is dissolved to the adjustment unit 86, reducing the pressure of the dissolution liquid L by the adjustment unit 86 and introducing it from the opening 90c into the crystallization tank 90, and crystallizing the separation target from the dissolution liquid L in the crystallization tank 90; and rotating the stirring unit 100 with the reduced-pressure dissolution liquid L introduced into the crystallization tank 90 to stir the inside of the crystallization tank 90 and generate a downward flow Df of the dissolution liquid L.

[0095] Therefore, an upward flow can be generated by the stirring blade. The upward flow removes the crystals of the monomer deposited at the opening so as to make them rise. Therefore, the separation target can be appropriately crystallized.

[0096] The embodiments of the present invention have been described above, but the embodiments are not limited by the contents of these embodiments. Further, the components described above include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those within the so-called equivalent range. Furthermore, the above-described components can be combined as appropriate. Moreover, various omissions, substitutions, or changes of the components can be made without departing from the gist of the above-described embodiments.

Explanation of Reference Numerals

[0097] 1 Separation system 12 Dissolution section 13 Solid-liquid separation section 14 Solvent storage section 16 Reaction section 18 Separation section 30 Control section 80 Crystallization system 82 Dissolution tank 86 Adjustment section 90 Crystallization tank 100 Stirring section 110 Baffle D, HD, E monomers M Reaction solvent P Polyester solution Pd, L Solution Pm Polyester raw material R Residual substance

Claims

1. An adjustment unit that reduces the pressure of a solution in which a separation target is dissolved, An opening is formed that is connected to the adjustment unit, and the solution reduced in pressure by the adjustment unit is introduced from the opening, and a crystallization tank in which the separation target is crystallized from the solution inside, A stirring unit provided in the crystallization tank, stirring the inside of the crystallization tank to generate a downward flow of the solution, The stirring blade of the stirring unit that stirs the solution is located below the opening in the vertical direction, Crystallization system.

2. The adjustment unit is directly connected to the opening, The crystallization system according to claim 1.

3. It is further provided inside the crystallization tank with a baffle that rectifies the flow of the solution in the crystallization tank, The crystallization system according to claim 1 or claim 2.

4. The baffle is a plate member extending in the vertical direction on the inner wall surface of the crystallization tank, The crystallization system according to claim 3.

5. The adjustment unit is an angle valve, The crystallization system according to claim 1 or claim 2.

6. It further includes a dissolution tank in which the solution is stored and an introduction pipe connecting the dissolution tank and the opening, The dissolution tank is located above the crystallization tank in the vertical direction, The crystallization system according to claim 1 or claim 2.

7. The separation target is dimethyl terephthalate, The crystallization system according to claim 1 or claim 2.

8. An adjustment unit that reduces the pressure of a liquid, A crystallization tank in which an opening connected to the adjustment unit is formed, A crystallization method of a crystallization system having a stirring unit provided in the crystallization tank, in which a stirring blade that stirs the liquid is located below the opening in the vertical direction, Supplying a solution in which a separation target is dissolved to the adjustment unit, reducing the pressure of the solution by the adjustment unit and introducing it into the crystallization tank from the opening, and crystallizing the separation target from the solution in the crystallization tank, In a state where the decompressed solution is introduced into the crystallization tank, rotating the stirring unit to stir the inside of the crystallization tank to generate a downward flow of the solution, Including, Crystallization method.

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