Monomer production system and monomer production method

Abstract

To improve the yield of monomer.SOLUTION: A monomer production system includes: a dissolution unit in which a polyester solution is stored; a first reaction unit to which the polyester solution and a reaction solvent are introduced, and which depolymerizes the polyester in the polyester solution and extracts a first depolymerized polyester, which contains the depolymerized polyester, to the reaction solvent; a second reaction unit which further depolymerizes the first depolymerized polyester, and generates a second depolymerized polyester, which is the further depolymerized first depolymerized polyester; a separation unit for separating the reaction solvent in which the second depolymerized polyester is dissolved into the reaction solvent, a monomer derived from carboxylic acid, a monomer of an alcohol component, and a residual substance containing an oligomer, which is a component other than the reaction solvent, the monomer derived from carboxylic acid or the monomer of an alcohol component; and an introduction pipe through which the monomer derived from carboxylic acid and the residual substance are introduced to the dissolution unit.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a monomer production system and a monomer production method. [Background technology]

[0002] In the recycling of polyester, attempts have been made to depolymerize polyester to form monomers and then polymerize them again. Patent Document 1 describes a technology in which polyethylene terephthalate (PET) and dimethyl terephthalate (DMT) are mixed and dissolved, and in a first reaction section, supercritical methanol is applied to depolymerize the PET, and in a second reaction section, the depolymerized PET is further reacted with methanol to monomerize the PET into DMT and ethylene glycol (EG). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4008214 Summary of the Invention [Problem to be solved by the invention]

[0004] When recycling polyester, it is necessary to improve the yield of the monomer.

[0005] The present disclosure is intended to solve the above-mentioned problems, and has an object to provide a monomer production system and a monomer production method that can improve the monomer yield. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the monomer production system according to the present disclosure includes a dissolution section in which a polyester solution in which a polyester is dissolved in a carboxylic acid monomer is stored, a first reaction section to which the polyester solution and a reaction solvent that reacts with the polyester are introduced and the polyester solution is brought into contact with the reaction solvent to depolymerize the polyester in the polyester solution and extract a first depolymerized polyester, which is the depolymerized polyester, into the reaction solvent, and a reaction section to which the reaction solvent into which the first depolymerized polyester has been extracted is introduced and the first depolymerized polyester is further reacted with the reaction solvent to extract the first depolymerized polyester. The dissolution apparatus includes a second reaction section that further depolymerizes the first depolymerized polyester to produce a second depolymerized polyester, which is the further depolymerized first depolymerized polyester; a separation section that receives the reaction solvent in which the second depolymerized polyester has been dissolved and separates the reaction solvent in which the second depolymerized polyester has been dissolved into the reaction solvent, a monomer derived from a carboxylic acid contained in the second depolymerized polyester, a monomer of an alcohol component contained in the second depolymerized polyester, and residual substances that are components other than the reaction solvent, the monomer derived from a carboxylic acid, and the monomer of an alcohol component and include oligomers; and an introduction pipe that introduces the monomer derived from a carboxylic acid and the residual substances into the dissolution section.

[0007] In order to solve the above-mentioned problems and achieve the object, the monomer production method according to the present disclosure includes the steps of: producing a polyester solution in a dissolution section, in which a polyester is dissolved in a carboxylic acid-derived monomer; bringing the polyester solution into contact with the reaction solvent to depolymerize the polyester in the polyester solution and extracting a first depolymerized polyester, which is the depolymerized polyester, into the reaction solvent; further reacting the first depolymerized polyester with the reaction solvent to further depolymerize the first depolymerized polyester and produce a second depolymerized polyester, which is the further depolymerized first depolymerized polyester; separating the reaction solvent in which the second depolymerized polyester is dissolved into the reaction solvent, the carboxylic acid-derived monomer contained in the second depolymerized polyester, the alcohol component monomer contained in the second depolymerized polyester, and a residual substance that is a component other than the reaction solvent, the carboxylic acid-derived monomer, and the alcohol component monomer and includes an oligomer; and introducing the carboxylic acid-derived monomer and the residual substance into the dissolution section. [Effects of the Invention]

[0008] According to the present disclosure, the yield of monomer can be improved. [Brief explanation of the drawings]

[0009] [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 a monomer production system according to the first embodiment. [Figure 3] FIG. 3 is a flowchart illustrating the operation flow of the monomer production system. [Figure 4] FIG. 4 is a schematic diagram showing another example of the reaction section. [Figure 5] FIG. 5 is a schematic diagram of a melting part according to the second embodiment. [Figure 6] FIG. 6 is a schematic diagram of a dissolving part according to another example of the second embodiment. [Figure 7] FIG. 7 is a schematic diagram of a monomer production system according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] (First embodiment) (Recycling process) FIG. 1 is a schematic diagram of a polyester recycling process according to this embodiment. In this embodiment, polyester raw material Pm is depolymerized to form monomers, and the monomers are then repolymerized to recycle (recycle) the polyester raw material Pm. Specifically, as shown in FIG. 1, polyester raw material Pm is flaked (step S100), mixed with reaction solvent M to depolymerize the polyester raw material Pm (step S102), the depolymerized polyester monomers are purified (separated) to produce carboxylic acid-derived monomer D and alcohol component monomer E (step S104), monomer D is hydrolyzed to separate the by-product reaction solvent M (step S106), and monomer F and monomer E, produced by hydrolysis of monomer D, are polymerized (step S108), thereby regenerating the polyester raw material Pm. Note that the monomer production system 1 according to this embodiment may only perform the processes of producing monomers D and E shown in steps S102 and S104, without performing the repolymerization process as in step S108. In this embodiment, during depolymerization, the monomer D produced in the depolymerization reaction and the residual substance R are also added to the polyester raw material Pm, as will be described in detail later.

[0012] (polyester) In this embodiment, the polyester raw material Pm to be depolymerized is a substance containing polyester. However, it is not limited to materials containing only polyester components and may also contain components other than polyester components (such as impurities). 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 most typical application is the recycling of PET bottles. Other materials that can be processed include PET film, such as photographic film; PET tape, such as magnetic tape; PET fiber used as polyester fiber; and PET sheet used for cups, trays, and transparent packaging.

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

[0014] (Carboxylic acid-derived monomers) The carboxylic acid-derived monomer D is a monomer having a carboxylic acid 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).

[0015] (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).

[0016] 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.

[0017] (Monomer production system) FIG. 2 is a schematic diagram of a monomer production system according to the first embodiment. The monomer production system 1 according to the first embodiment is a system that converts polyester contained in a polyester raw material Pm into monomers to produce monomers D and E. 2 As shown in FIG. 1, the monomer production system 1 includes a storage section 10, a dissolution section 12, a solvent storage section 14, a reaction section 16 including a first reaction section 16A and a second reaction section 16B, a separation section 18, and a control section 20.

[0018] (Storage section) The storage section 10 is a tank (hopper) into which the polyester raw material Pm is introduced and in which the polyester raw material Pm is stored. In this embodiment, the storage section 10 stores the flaked polyester raw material Pm, but the shape and size of the polyester raw material Pm may be arbitrary. The storage section 10 is connected to the dissolving section 12 via an inlet pipe 10a. The polyester raw material Pm in the 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 storage section 10 to the dissolving section 12. The adjustment section 10b is, for example, an on-off valve. When in an open state, the adjustment section 10b allows the polyester raw material Pm in the storage section 10 to be supplied to the dissolving section 12, and when in a closed state, the adjustment section 10b stops the supply of the polyester raw material Pm in the 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.

[0019] (melting part) The dissolution section 12 is a tank that stores a polyester solution P in which the polyester contained in the polyester raw material Pm is dissolved in the monomer D. Monomer D and the polyester raw material Pm are supplied to the dissolution section 12, and the polyester contained in the polyester raw material Pm dissolves in the monomer D in the dissolution section 12 to produce a polyester solution P. Dissolving the polyester in the monomer D in this manner reduces the viscosity and improves the fluidity, allowing the polyester to be easily introduced into the reaction section 16. Furthermore, the residual substance R, which will be described later, is also supplied to the dissolution section 12, and the polyester contained in the polyester raw material Pm dissolves in the monomer D and the oligomer contained in the residual substance R in the dissolution section 12 to produce a polyester solution P. In other words, the polyester solution P can be said to be a solution in which the polyester is dissolved in the monomer D and the residual substance R. However, the polyester solution P does not necessarily have to be entirely dissolved in the monomer D and the residual substance R; at least a portion of the polyester may be in a state in which it is not dissolved in the monomer D and the residual substance R.

[0020] The dissolving section 12 is connected to a first reaction section 16A, which will be described later, via an inlet pipe 12a. The polyester solution P 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 12b and a heating section 12c. The supply section 12b 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. The heating section 12c is a mechanism for heating the polyester solution P.

[0021] (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).

[0022] (Reaction section) The reaction section 16 is a container into which the polyester solution P and the reaction solvent M are supplied. The reaction section 16 includes a first reaction section 16A and a second reaction section 16B.

[0023] (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. A known filler used in gas-liquid or liquid-liquid contactors can be used for the first reaction section 16A, such as a filler similar to that 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, and Terralets.

[0024] An inlet pipe 12a is connected to the first reaction section 16A. More specifically, an inlet 16C, which is an opening of the inlet pipe 12a through which the polyester solution P from the dissolving section 12 is introduced, is connected to the first reaction section 16A. The inlet 16C is connected to a surface 16A1 on the first direction D1 side of the first reaction section 16A. The inlet pipe 12a is connected to the surface 16A1 so that the inlet 16C opens toward the second direction D2, which is the opposite direction 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 section 16A, but this is not limiting. For example, the inlet 16C does not have to be directly connected to the first reaction section 16A, and the inlet 16C opening toward the second direction D2 may be connected to the first direction D1 side of the surface 16A1 of the first reaction section 16A within the reaction section 16.

[0025] 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.

[0026] In this embodiment, the inlet 16C through which the polyester solution P is introduced opens facing the second direction D2, and the inlet 16D through which the reaction solvent M is introduced opens facing the first direction D1 or from the side toward the center. Therefore, the polyester solution P and the reaction solvent M are introduced into the first reaction section 16A in directions facing each other.

[0027] The polyester solution P 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 polyester solution P. The polyester in the polyester solution P 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.

[0028] The first depolymerized polyester P1 includes monomers D and E produced by depolymerizing the polyester in the polyester solution P, monomer D that was originally mixed in the polyester solution P, and oligomers produced by depolymerizing the polyester. The oligomers referred to here are carboxylic acid or alcohol oligomers that have not been monomerized but have been depolymerized from the polyester (carboxylic acid or alcohol oligomers with a smaller molecular weight than 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 R that have been depolymerized, as well as monomers D and E produced by depolymerizing the oligomers contained in the residual substance R.

[0029] (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.

[0030] 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 containing the second depolymerized polyester PE) 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.

[0031] The second depolymerized polyester P2 contains monomers D and E produced by depolymerizing the oligomers in the first depolymerized polyester P1, and oligomers produced by depolymerizing the first depolymerized polyester P1.

[0032] 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 pipe 16b 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 (reaction solvent M containing the second depolymerized polyester P2) and remained in the first reaction section 16A and the second reaction section 16B.

[0033] 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 20.

[0034] (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 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 an oligomer.

[0035] In this embodiment, the separation section 18 has a first separation section 18A, a second separation section 18B, and a third separation section 18C.

[0036] 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.

[0037] 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 the monomerization of polyester.

[0038] 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 the residual substances R separated in the third separation section 18C is discharged from the outlet pipe 18Cc.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 2, the introduction pipe 10a, the introduction pipe 18Cd, and the introduction pipe 18Cf connected to the dissolving section 12 are not connected to each other but are directly connected to the dissolving section 12. However, at least two of the introduction pipe 10a, the introduction pipe 18Cd, and the introduction pipe 18Cf may be connected (merged) and the connected pipe may be connected to the dissolving section 12.

[0043] (Control unit) The control unit 20 is a control device that controls the monomer production system 1. The control unit 20 controls the adjustment unit 10b to control the amount of polyester raw material Pm supplied from the storage unit 10 to the dissolution unit 12. The control unit 20 controls the supply unit 12b to control the amount of polyester solution P supplied from the dissolution unit 12 to the first reaction unit 16A. The control unit 20 controls the heating unit 12c to control the heating degree of the polyester solution P. The control unit 20 controls the heating and pressurization unit 14b to bring the reaction solvent M to a supercritical state or a subcritical state (pressurized gas or pressurized liquid) and controls the amount of reaction solvent M in the supercritical state or subcritical state (pressurized gas or pressurized liquid) supplied to the reaction unit 16. The control unit 20 controls the adjustment unit 18Ce to control the amount of monomer D supplied to the dissolution unit 12. The control unit 20 controls the adjustment unit 18Cg to control the amount of residual material R supplied to the dissolution unit 12.

[0044] In this embodiment, the control unit 20 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 contents of calculations performed by the processor and programs. The control unit 20 executes control of the monomer production system 1 by reading out the programs from the storage unit.

[0045] However, the monomer production system 1 is not limited to being automatically controlled by the control unit 20, and for example, at least a part of the processing may be controlled by the operation of an operator.

[0046] (Operation of the Monomer Production System) Next, the operation of the monomer production system 1 will be described. The control unit 20 controls the adjustment units 10b, 18Ce, and 18Cg to introduce the polyester raw material Pm, the monomer D, and the residual substance R into the dissolution unit 12, and mixes the polyester raw material Pm, the monomer D, and the residual substance R in the dissolution unit 12 to produce the polyester solution P. It is preferable that the control unit 20 introduces the polyester raw material Pm into the dissolution unit 12 after introducing the monomer D and the residual substance R into the dissolution unit 12. Introducing the polyester raw material Pm later makes it possible to properly dissolve the polyester raw material Pm.

[0047] The control unit 20 preferably controls the weight ratio of the total amount of monomer D and residual substance R supplied to the dissolution unit 12 relative to the amount of polyester raw material Pm supplied to the dissolution unit 12 to be 0.05 or more and 5 or less, more preferably 0.1 or more and 2 or less, and even more preferably 0.2 or more and 1 or less. By controlling the supply amount ratio within this range, it is possible to sufficiently recover the monomers D and E from the polyester raw material Pm while suppressing a decrease in fluidity due to an excessive amount of polyester raw material Pm. Furthermore, the control unit 20 controls the weight ratio of the amount of residual substance R supplied to the dissolution unit 12 relative to the amount of monomer D supplied to the dissolution unit 12 to be 0 or more and 5 or less, more preferably 0 or more and 3 or less, and even more preferably 0.5 or more and 2 or less. By controlling the supply amount ratio within this range, it is possible to sufficiently recover the monomers D and E from the residual substance R while suppressing a decrease in fluidity due to an excessive amount of monomer D.

[0048] In this embodiment, the control unit 20 introduces a portion of the monomer D extracted from the third separation unit 18C into the dissolving unit 12, and introduces a portion of the residual substance R extracted from the third separation unit 18C into the dissolving unit 12. The ratio of the amount of residual substance R introduced into the dissolving unit 12 to the amount of residual substance R extracted from the third separation unit 18C is preferably 30% to 99% by weight, and more preferably 60% to 98% by weight. By returning the residual substance R at such a ratio, the oligomers contained in the residual substance R are depolymerized to improve the yield of the monomer, while preventing the concentration of impurities other than oligomers in the residual substance R from becoming too high.

[0049] The control unit 20 controls the supply unit 12b and the heating unit 12c to heat the polyester solution P in the dissolving unit 12 and supply the polyester solution P to the first reaction unit 16A. The control unit 20 preferably sets the temperature of the polyester solution P to 250°C or higher and 400°C or lower, and more preferably to 250°C or higher and 350°C or lower.

[0050] The control unit 20 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 control unit 20 preferably sets the reaction solvent M at a temperature of 250°C or higher and 400°C or lower, and more preferably at a temperature of 250°C or higher and 350°C or lower. The control unit 20 preferably sets the reaction solvent M at a pressure of 1 MPa or higher and 30 MPa or lower, and more preferably at a pressure of 6 MPa or higher and 25 MPa or lower.

[0051] In this manner, by supplying the polyester solution P and the reaction solvent M to the reaction section 16, the polyester and oligomers contained in the polyester raw material Pm are 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 substance R in the first separation section 18A, second separation section 18B, and third separation section 18C. In this manner, the monomers D and E are recovered from the polyester raw material Pm, and by polymerizing them, the polyester raw material Pm can be regenerated.

[0052] The operation flow of the monomer production system 1 described above will be described with reference to a flowchart. FIG. 3 is a flowchart illustrating the operation flow of the monomer production system. As shown in FIG. 3, the control unit 20 introduces the polyester raw material Pm, the monomer D, and the residual substance R into the dissolution unit 12 to produce a polyester solution P (step S10). The control unit 20 then introduces the polyester solution P and the reaction solvent M into the first reaction unit 16A to depolymerize them, extracting the first depolymerized polyester P1 into the reaction solvent M (step S12). The first solvent M1 from which the first depolymerized polyester P1 has been extracted is then introduced into the second reaction unit 16B, where the first depolymerized polyester P1 is further depolymerized to produce the second depolymerized polyester P2 (step S14). The separation unit 18 then separates the second solvent M2 in which the second depolymerized polyester P2 has been dissolved into the reaction solvent M, the monomer D, the monomer E, and the residual substance R (step S16). Thereafter, if the process is to be terminated (Step S18; Yes), the process is terminated; if the process is not to be terminated (Step S18; No), the process returns to Step S10, and the monomer D and a portion of the remaining substance R separated in the separation section 18 are introduced into the dissolution section 12, and the process is continued.

[0053] (effect) When the polyester raw material Pm is depolymerized to produce the monomers D and E, it is necessary to improve the yield of the monomers D and E. In this embodiment, the residual substance R, which is a substance other than the reaction solvent M, the monomer D, and the monomer E separated in the separation section 18, is returned to the dissolution section 12. The residual substance R contains oligomers that have not been depolymerized into monomers. Therefore, by returning the residual substance R to the dissolution section 12, the oligomers contained in the residual substance R can be depolymerized again, thereby improving the yield of the monomers D and E.

[0054] Since the polyester solution P contains residual substances R, it is thought that the flowability will be lower than when the polyester solution P contains only monomer D and polyester raw material Pm. This may result in a decrease in the flowability of the polyester solution P in the first reaction section 16A, which may result in a decrease in reactivity. In contrast, in this embodiment, the ratio of the amount of residual substances R supplied to the dissolution section 12 to the amount of monomer D supplied to the dissolution section 12 is specified. Therefore, this embodiment can suppress a decrease in reactivity (depolymerization) when residual substances R are added.

[0055] However, the polyester solution P and the reaction solvent M do not necessarily need to be supplied in directions facing each other, and may be supplied in the same direction. FIG. 4 is a schematic diagram showing another example of the reaction section. In this case, for example, as shown in FIG. 4, the reaction section 16 may have a double-tube structure, with the inner tube portion being the first reaction section 16Ab and the outer tube portion being the second reaction section 16Bb. In this case, the inlet 16Cb for the polyester solution P and the inlet 16Db for the reaction solvent M open toward the second direction D2 and are connected to the surface of the first reaction section 16Ab facing the first direction D1. Therefore, the polyester solution P and the reaction solvent M are supplied toward the second direction D2, i.e., in the same direction. The polyester solution P and reaction solvent M react in the first reaction section 16Ab while proceeding in the second direction D2, flowing into the second reaction section 16Bb at the tip of the first reaction section 16Ab as first solvent M1 (reaction solvent M from which the first depolymerized polyester P1 has been extracted), where the reaction continues, and are discharged from an outlet 16Eb opening at the side of the second reaction section 16Bb as second solvent M2 (reaction solvent M containing the second depolymerized polyester P2). In addition, non-extracts are discharged from an outlet 16Fb opening at the bottom of the reaction section 16.

[0056] (Second embodiment) Next, a second embodiment will be described. The second embodiment differs from the first embodiment in that a plurality of dissolving sections 12 are provided. In the second embodiment, a description of the parts that are common to the first embodiment will be omitted.

[0057] Fig. 5 is a schematic diagram of a dissolving portion according to the second embodiment. As shown in Fig. 5, in the second embodiment, a first dissolving portion 12A and a second dissolving portion 12B are provided as the plurality of dissolving portions 12. In the example of Fig. 5, two dissolving portions, the first dissolving portion 12A and the second dissolving portion 12B, are provided, but the number of dissolving portions 12 is not limited to two and may be three or more.

[0058] The first dissolution section 12A is a tank into which the polyester raw material Pm, monomer D, and residual substances R are introduced to produce the polyester solution P. The first dissolution section 12A is connected to the reservoir 10 via an inlet pipe 10a, and the polyester raw material Pm is introduced from the reservoir 10. The first dissolution section 12A is connected to the third separation section 18C via an inlet pipe 18Cd, and the monomer D is introduced from the third separation section 18C. The first dissolution section 12A is connected to the third separation section 18C via an inlet pipe 18Cf, and the residual substances R are introduced from the third separation section 18C.

[0059] The second dissolution section 12B is connected to the first dissolution section 12A via a pipe 12Aa, and the polyester solution P produced in the first dissolution section 12A is introduced therein. The second dissolution section 12B is connected to the first reaction section 16A via an inlet pipe 12a. The polyester solution P introduced into the second dissolution section 12B is then discharged to the first reaction section 16A through the inlet pipe 12a. In this manner, in the example of FIG. 5, the second dissolution section 12B is provided between the first dissolution section 12A and the first reaction section 16A, and the first dissolution section 12A and the second dissolution section 12B are connected in series. Note that when there are three or more dissolution sections 12, the other dissolution sections 12 are connected in series between the second dissolution section 12B and the first reaction section 16A. In other words, the dissolution sections 12 are connected in series. In this way, by providing multiple dissolution sections 12 and connecting them in series, it is possible to temporarily store the polyester solution P produced in the first dissolution section 12A in the second dissolution section 12B, which serves as a buffer tank, so that the polyester raw material Pm can be reliably dissolved and introduced into the first reaction section 16A.

[0060] However, the dissolution sections 12 are not limited to being connected in series and may be connected in parallel. Fig. 6 is a schematic diagram of another example of the dissolution section of the second embodiment. When the dissolution sections 12 are connected in parallel as shown in Fig. 6, the polyester raw material Pm, the monomer D, and the residual substance R are introduced into the first dissolution section 12A and the second dissolution section 12B, and the polyester solution P is produced in the first dissolution section 12A and the second dissolution section 12B. The first dissolution section 12A and the second dissolution section 12B are connected to the first reaction section 16A via the inlet pipe 12a, and the polyester solution P in the first dissolution section 12A and the second dissolution section 12B is introduced into the first reaction section 16A through the inlet pipe 12a.

[0061] 6, it is preferable to alternately switch between producing the polyester solution P and supplying the polyester solution P to the first reaction section 16A for each dissolution section 12. That is, for example, during the period when the polyester raw material Pm, monomer D, and residual substances R are being introduced into the first dissolution section 12A, the polyester solution P is already stored in the second dissolution section 12B, and the polyester solution P is discharged from the second dissolution section 12B to the first reaction section 16A. During the period when the polyester raw material Pm, monomer D, and residual substances R are being introduced into the second dissolution section 12B, the polyester solution P is already stored in the first dissolution section 12A, and the polyester solution P is discharged from the first dissolution section 12A to the first reaction section 16A.

[0062] Specifically, in the example of Fig. 6, first dissolving section 12A is connected to inlet pipe 10a1 branching off from inlet pipe 10a, and second dissolving section 12B is connected to inlet pipe 10a2 branching off from inlet pipe 10a. In the example of Fig. 6, adjustment section 10b is provided at the point where inlet pipes 10a1 and 10a2 branch off, and adjusts the amount of polyester raw material Pm supplied from reservoir 10 to first dissolving section 12A and the amount of polyester raw material Pm supplied from reservoir 10 to second dissolving section 12B. Furthermore, first dissolving section 12A is connected to inlet pipe 18Cd1 branching off from inlet pipe 18Cd, and second dissolving section 12B is connected to inlet pipe 18Cd2 branching off from inlet pipe 18Cd. In the example of Fig. 6, adjustment section V1 is provided at the point where inlet pipes 18Cd1 and 18Cd2 branch off. The adjustment unit V1 adjusts the amount of monomer D supplied from the third separation unit 18C to the first dissolving unit 12A and the amount of monomer D supplied from the third separation unit 18C to the second dissolving unit 12B. The first dissolving unit 12A is connected to an inlet pipe 18Cf1 branching off from the inlet pipe 18Cf, and the second dissolving unit 12B is connected to an inlet pipe 18Cf2 branching off from the inlet pipe 18Cf. In the example of FIG. 6, the adjustment unit V2 is provided at the point where the inlet pipes 18Cf1 and 18Cf2 branch off. The adjustment unit V2 adjusts the amount of residual material R supplied from the third separation unit 18C to the first dissolving unit 12A and the amount of residual material R supplied from the third separation unit 18C to the second dissolving unit 12B. Furthermore, first dissolution section 12A is connected to inlet pipe 12a1 which joins with inlet pipe 12a, and second dissolution section 12B is connected to inlet pipe 12a2 which joins with inlet pipe 12a. Inlet pipe 12a1 is provided with supply section 12b1 which controls the supply of polyester solution P from first dissolution section 12A, and inlet pipe 12a2 is provided with supply section 12b2 which controls the supply of polyester solution P from second dissolution section 12B.

[0063] During the period in which polyester solution P is produced in first dissolution section 12A, control section 20 controls adjustment sections 10b, V1, and V2 to supply polyester raw material Pm, monomer D, and residual substances R to first dissolution section 12A to produce polyester solution P in first dissolution section 12A, while controlling supply sections 12b1 and 12b2 to supply polyester solution P from second dissolution section 12B to first reaction section 16A. During this period, control section 20 does not supply polyester raw material Pm, monomer D, or residual substances R to second dissolution section 12B, and does not supply polyester solution P from first dissolution section 12A to first reaction section 16A. Meanwhile, during the period in which the polyester solution P is produced in the second dissolving unit 12B, the control unit 20 controls the adjusting units 10b, V1, and V2 to supply the polyester raw material Pm, monomer D, and residual substances R to the second dissolving unit 12B, thereby producing the polyester solution P in the second dissolving unit 12B, while controlling the supply units 12b1 and 12b2 to supply the polyester solution P from the first dissolving unit 12A to the first reaction unit 16A. During this period, the control unit 20 does not supply the polyester raw material Pm, monomer D, and residual substances R to the first dissolving unit 12A, and does not supply the polyester solution P from the second dissolving unit 12B to the first reaction unit 16A. Note that the configuration shown in FIG. 6 is merely an example, and layouts other than that shown in FIG. 6 may be used as long as multiple dissolving units 12 are connected in parallel. Furthermore, even when the dissolving units 12 are connected in parallel, the number of dissolving units 12 may be three or more.

[0064] As described above, in the second embodiment, the multiple dissolving units 12 are connected in series or in parallel, but a combination of series and parallel connections may also be used. For example, for multiple dissolving units 12 connected in parallel, another dissolving unit 12 may be connected in series.

[0065] (Third embodiment) Next, a third embodiment will be described. The third embodiment differs from the first embodiment in that the non-extract discharged from the reaction section 16 is also mixed with the polyester solution P. In the third embodiment, explanations of parts that are common to the first embodiment will be omitted. Note that the third embodiment can also be applied to the second embodiment.

[0066] FIG. 7 is a schematic diagram of a monomer production system according to a third embodiment. As shown in FIG. 7, in the monomer production system 1A according to the third embodiment, a discharge pipe 16b connected to the bottom of the reaction section 16 is connected to the dissolution section 12. The non-extracted matter in the reaction section 16 is supplied to the dissolution section 12 through the discharge pipe 16b. More specifically, the discharge pipe 16b is provided with an adjustment section 16b1 that adjusts the amount of non-extracted matter supplied to the dissolution section 12. The adjustment section 16b1 is, for example, an on-off valve. When open, the adjustment section 16b1 allows the non-extracted matter in the reaction section 16 to be supplied to the dissolution section 12, and when closed, the adjustment section 16b1 stops the supply of the non-extracted matter in the reaction section 16 to the dissolution section 12. In the third embodiment, the control section 20 controls the adjustment section 16b1 to control the supply of the non-extracted matter in the reaction section 16 to the dissolution section 12. The timing of discharging the non-extract from the reaction unit 16 may be arbitrary. For example, a level meter provided at the bottom of the reaction unit 16 may be used to control the level of the non-extract so that it falls within a predetermined range, or the non-extract may be discharged periodically at regular intervals. The level meter may detect the difference in density between the reaction solvent M and the non-extract. The adjustment unit 16b1 is not limited to an on-off valve and may be any mechanism capable of adjusting the supply of the non-extract to the dissolution unit 12.

[0067] As in the third embodiment, by returning the non-extract to the dissolving section 12, the oligomers contained in the non-extract can be converted into monomers, and the yield of the monomers can be further improved.

[0068] (Effects of the present disclosure) As described above, the monomer production system 1 according to the present disclosure includes the dissolution section 12, the first reaction section 16A, the second reaction section 16B, the separation section 18, and the inlet pipes 18Cd and 18Cf. The dissolution section 12 stores a polyester solution P in which a polyester is dissolved in a carboxylic acid-derived monomer D. The first reaction section 16A receives the polyester solution P and a reaction solvent M that reacts with the polyester. The polyester solution P is brought into contact with the reaction solvent M to depolymerize the polyester in the polyester solution P, and a first depolymerized polyester P1 containing the depolymerized polyester is extracted into the reaction solvent M. The second reaction section 16B receives the reaction solvent M (first solvent M1) from which the first depolymerized polyester P1 has been extracted. The first depolymerized polyester P1 is further reacted with the reaction solvent M to further depolymerize the first depolymerized polyester P1, thereby producing a second depolymerized polyester P2, which is the depolymerized first depolymerized polyester P1. The separation unit 18 introduces the reaction solvent M (second solvent M2) in which the second depolymerized polyester P2 has been dissolved, and separates the reaction solvent M in which the second depolymerized polyester P2 has been dissolved 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 which is a component other than the reaction solvent M, the monomer D derived from a carboxylic acid, and the monomer E of an alcohol component and which includes an oligomer. The inlet pipes 18Cd and 18Cf introduce the monomer D derived from a carboxylic acid and the residual substance R into the dissolution unit 12.

[0069] When the polyester raw material Pm is depolymerized to produce the monomers D and E, it is necessary to improve the yield of the monomers D and E. In this embodiment, the residual substance R separated in the separation section 18 is returned to the dissolution section 12. The residual substance R contains oligomers that have not been depolymerized into monomers. Therefore, by returning the residual substance R to the dissolution section 12, the oligomers contained in the residual substance R can be depolymerized again, thereby improving the yield of the monomers D and E.

[0070] Preferably, the inlet pipes 18Cd and 18Cf introduce a portion of the carboxylic acid-derived monomer D separated in the separation section 18 and a portion of the residual substance R separated in the separation section 18 into the dissolving section 12. According to the monomer production system 1, since a portion of the monomer D is returned to the dissolving section 12, it is possible to improve the fluidity of the polyester raw material Pm by the monomer D while suppressing a decrease in the yield of the monomer D. Furthermore, according to the monomer production system 1, since a portion of the residual substance R is returned to the dissolving section 12, it is possible to improve the yield of the monomers D and E while suppressing an increase in the concentration of impurities contained in the residual substance R.

[0071] The monomer production system 1 further includes a control unit 20 that controls the supply of the polyester raw material Pm, the carboxylic acid-derived monomer D, and the residual substance R to the dissolution section 12. The control unit 20 preferably introduces the polyester raw material Pm into the dissolution section 12 after the carboxylic acid-derived monomer D and the residual substance R have been introduced into the dissolution section 12. According to the monomer production system 1, introducing the polyester raw material Pm later can prevent insufficient dissolution of the polyester raw material Pm.

[0072] The monomer production system 1 further includes a control unit 20 that controls the supply of polyester raw material Pm, carboxylic acid-derived monomer D, and residual substance R to the dissolution unit 12. The control unit 20 preferably sets the weight ratio of the total supply amount of carboxylic acid-derived monomer D and residual substance R to the supply amount of polyester raw material Pm to be 0.05 or more and 5 or less. By setting the mixing ratio of polyester raw material Pm, monomer D, and residual substance R within this range, it is possible to suppress a decrease in fluidity caused by an excessive amount of polyester raw material Pm, while sufficiently recovering monomers D and E from the polyester raw material Pm.

[0073] The control unit 20 preferably sets the weight ratio of the supply amount of the residual substance R to the carboxylic acid-derived monomer D to be equal to or greater than 0 and equal to or less than 5. By setting the ratio of the supply amount of the residual substance R to be within this range, it is possible to sufficiently recover the monomers D and E from the residual substance R while suppressing a decrease in fluidity caused by an excessively small amount of monomer D. It is possible to sufficiently recover the monomers D and E from the residual substance R while suppressing a decrease in fluidity caused by an excessively small amount of monomer D.

[0074] The monomer production system 1 is preferably provided with a plurality of dissolving sections 12. Providing a plurality of dissolving sections 12 makes it possible to separate the dissolving section that dissolves the polyester raw material Pm from the dissolving section that supplies the polyester solution P to the first reaction section 16A, so it is not necessary to charge the raw materials for the polyester solution P while controlling them to achieve a desired mixing ratio; it is sufficient to finally achieve the desired mixing ratio. Furthermore, since the time required for dissolving the polyester raw material Pm can be secured, problems caused by undissolved polyester raw material Pm (such as pipe blockage) can be suppressed.

[0075] The monomer production system 1 preferably includes a first dissolving section 12A into which the polyester, the carboxylic acid-derived monomer D, and the residual substance R are introduced to produce a polyester solution P, and a second dissolving section 12B into which the polyester solution P produced in the first dissolving section 12A is introduced and which discharges the introduced polyester solution P to the first reaction section 16A. By connecting a plurality of dissolving sections 12 in series in this manner, the polyester raw material Pm can be reliably dissolved and introduced into the first reaction section 16A.

[0076] The monomer production system 1 preferably includes a first dissolution section 12A and a second dissolution section 12B into which polyester, carboxylic acid-derived monomer D, and residual substances R are introduced to produce a polyester solution P. During the period in which polyester, carboxylic acid-derived monomer D, and residual substances R are introduced into the first dissolution section 12A, the polyester solution P is discharged from the second dissolution section 12B to the first reaction section 16A. During the period in which polyester, carboxylic acid-derived monomer D, and residual substances R are introduced into the second dissolution section 12B, the polyester solution P is discharged from the first dissolution section 12A to the first reaction section 16A. By connecting multiple dissolution sections 12 in parallel in this manner and switching between the dissolution section that dissolves the polyester raw material Pm and the dissolution section that supplies the polyester solution P to the first reaction section 16A, the polyester raw material Pm can be reliably dissolved and introduced into the first reaction section 16A.

[0077] It is preferable that the polyester solution P and the reaction solvent M are introduced into the first reaction section 16A in directions facing each other.

[0078] The monomer production system 1A preferably has a discharge pipe 16b that introduces the non-extractables into the dissolving section 12. The non-extractables are components that remain in the first reaction section 16A and the second reaction section 16B without being led to the separation section 18. By returning the non-extractables to the dissolving section 12, the yields of the monomers D and E can be further improved.

[0079] Preferably, the polyester raw material Pm contains polyethylene terephthalate, the reaction solvent M is methanol, the carboxylic acid-derived monomer D is dimethyl terephthalate, and the alcohol component monomer E is ethylene glycol. The monomer production system 1 can appropriately improve the yields of dimethyl terephthalate and ethylene glycol.

[0080] The monomer production method of the present disclosure includes the steps of: producing a polyester solution P in a dissolution section 12, in which a polyester is dissolved in a carboxylic acid-derived monomer D; bringing the polyester solution P into contact with a reaction solvent M to depolymerize the polyester in the polyester solution P and extracting a first depolymerized polyester P1 containing the depolymerized polyester into the reaction solvent M; further reacting the first depolymerized polyester P1 with the reaction solvent M to further depolymerize the first depolymerized polyester P1 and produce a second depolymerized polyester P2 that is the further depolymerized first depolymerized polyester P1; separating the reaction solvent M in which the second depolymerized polyester P2 has been dissolved into the reaction solvent M, the carboxylic acid-derived monomer D contained in the second depolymerized polyester P2, the alcohol component monomer E contained in the second depolymerized polyester P2, and a residual substance R that is a component other than the reaction solvent M, the carboxylic acid-derived monomer D, and the alcohol component monomer E and includes oligomers; and introducing the carboxylic acid-derived monomer D and the residual substance R into the dissolution section 12. According to this method, the residual substance R is returned to the dissolution section 12, thereby improving the yield of the monomer.

[0081] 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]

[0082] 10 Reservoir 12 Melting part 14 Solvent reservoir 16A First reaction section 16B Second reaction section 18 Separation section 18A 1st separation section 18B 2nd separation section 18C 3rd separation section 18Cd, 18Cf introduction tube 20 Control Unit D and E monomers M reaction solvent P Polyester solution Pm polyester raw material P1 First depolymerized polyester P2 Second Depolymerized Polyester R Residual substances

Claims

1. a dissolving section in which a polyester solution in which a polyester is dissolved in a carboxylic acid-derived monomer is stored; a first reaction section into which the polyester solution and a reaction solvent that reacts with the polyester are introduced and the polyester solution is brought into contact with the reaction solvent to depolymerize the polyester in the polyester solution and extract a first depolymerized polyester containing the depolymerized polyester into the reaction solvent; a second reaction section into which the reaction solvent from which the first depolymerized polyester has been extracted is introduced, and the first depolymerized polyester is further reacted with the reaction solvent to further depolymerize the first depolymerized polyester and produce a second depolymerized polyester, which is the further depolymerized first depolymerized polyester; a separation unit to which the reaction solvent in which the second depolymerized polyester has been dissolved is introduced and which separates the reaction solvent in which the second depolymerized polyester has been dissolved into the reaction solvent, a monomer derived from a carboxylic acid contained in the second depolymerized polyester, a monomer of an alcohol component contained in the second depolymerized polyester, and a residual substance which is a component other than the reaction solvent, the monomer derived from a carboxylic acid, and the monomer of an alcohol component and which includes an oligomer; a first inlet pipe connected to the separation section and configured to introduce the carboxylic acid-derived monomer separated in the separation section into the dissolution section; a second introduction pipe connected to the separation section and introducing the residual substance separated in the separation section into the dissolution section; having Monomer production system.

2. 2. The monomer production system according to claim 1, wherein the first inlet pipe introduces a portion of the carboxylic acid-derived monomer separated in the separation section into the dissolution section, and the second inlet pipe introduces a portion of the remaining substance separated in the separation section into the dissolution section.

3. a control unit that controls the supply of polyester raw materials containing the polyester, the carboxylic acid-derived monomer, and residual substances to the dissolution unit; 3. The monomer production system according to claim 1, wherein the control unit introduces the polyester raw material into the dissolution section after the carboxylic acid-derived monomer and residual substances have been introduced into the dissolution section.

4. a control unit that controls the supply of polyester raw materials containing the polyester, the carboxylic acid-derived monomer, and residual substances to the dissolution unit; 4. The monomer production system according to claim 1, wherein the control unit controls a weight ratio of the total supply amount of the carboxylic acid-derived monomer and residual substances to the supply amount of the polyester raw material to be 0.05 or more and 5 or less.

5. The monomer production system according to claim 4 , wherein the control unit controls a weight ratio of the amount of the remaining substance supplied to the amount of the carboxylic acid-derived monomer to be 0 or more and 5 or less.

6. The monomer production system according to claim 1 , wherein a plurality of the dissolving sections are provided.

7. a first dissolution zone into which the polyester, the carboxylic acid-derived monomer, and residual materials are introduced to produce the polyester solution; 7. The monomer production system according to claim 6, further comprising: a second dissolution section into which the polyester solution produced in the first dissolution section is introduced and which discharges the introduced polyester solution into the first reaction section.

8. a first dissolution zone and a second dissolution zone into which the polyester, the carboxylic acid-derived monomer, and residual materials are introduced to produce the polyester solution; During a period in which the polyester, the carboxylic acid-derived monomer, and residual substances are introduced into the first dissolution zone, the polyester solution is discharged from the second dissolution zone to the first reaction zone; 7. The monomer production system according to claim 6, wherein the polyester solution is discharged from the first dissolution zone to the first reaction zone during a period in which the polyester, the carboxylic acid-derived monomer, and residual substances are introduced into the second dissolution zone.

9. 9. The monomer production system according to claim 1, wherein the polyester solution and the reaction solvent are introduced into the first reaction zone in directions facing each other.

10. 10. The monomer production system according to claim 1, further comprising a pipe for introducing non-extractable components, which are not delivered to the separation section as the reaction solvent in which the second depolymerized polyester is dissolved, but remain in the first reaction section and the second reaction section, into the dissolution section.

11. 11. The monomer production system according to claim 1, wherein the polyester is polyethylene terephthalate, the reaction solvent is methanol, the carboxylic acid-derived monomer is dimethyl terephthalate, and the alcohol component monomer is ethylene glycol.

12. producing a polyester solution in a dissolution section, in which the polyester is dissolved in a carboxylic acid-derived monomer; a step of depolymerizing the polyester in the polyester solution by contacting the polyester solution with a reaction solvent, and extracting a first depolymerized polyester containing the depolymerized polyester into the reaction solvent; further reacting the first depolymerized polyester with the reaction solvent to further depolymerize the first depolymerized polyester and produce a second depolymerized polyester, which is the further depolymerized first depolymerized polyester; separating, by a separation unit, the reaction solvent in which the second depolymerized polyester is dissolved into the reaction solvent, a monomer derived from a carboxylic acid contained in the second depolymerized polyester, a monomer of an alcohol component contained in the second depolymerized polyester, and a remaining substance which is a component other than the reaction solvent, the monomer derived from a carboxylic acid, and the monomer of an alcohol component and which includes an oligomer; introducing the carboxylic acid-derived monomer separated in the separation section into the dissolution section through a first introduction pipe connected to the separation section; introducing the residual substance separated in the separation section into the dissolution section through a second introduction pipe connected to the separation section; having Monomer production method.

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