Hydrolysis reaction system and control method

Abstract

In the present invention, terephthalic acid is appropriately obtained from DMT while lowering energy consumption. This hydrolysis reaction system comprises: a reaction tank to which dimethyl terephthalate and water are supplied and in which the dimethyl terephthalate is hydrolyzed by the water to generate terephthalic acid and methanol; a discharge device for discharging a mixture of methanol and water from the reaction tank; and a control device for controlling the discharge system. The control device: does not discharge the mixture to the discharge device in a first period up to a first timing point after the dimethyl terephthalate and water are supplied to the reaction tank; discharges the mixture to the discharge device in a second period after the first timing point up to a second timing point that is after the first timing point; and does not discharge the mixture to the discharge device in a third period after the second timing point up to a point where terephthalic acid is derived from the reaction tank. The first period is shorter than the third period.

Description

Hydrolysis reaction system and control method

[0001] The present disclosure relates to a hydrolysis reaction system and a control method.

[0002] It is known that when producing terephthalic acid from dimethyl terephthalate (DMT), DMT is hydrolyzed. Patent Document 1 discloses a method in which heated steam and heated DMT are introduced into a hydrolysis reactor, the reactants are removed from the bottom of the hydrolysis reactor, a mixture of methanol and water is removed from the top of the hydrolysis reactor, the mixture is condensed, and water, which is part of the condensate, is supplied from the top of the hydrolysis reactor.

[0003] Japanese Unexamined Patent Publication No. 57-95925

[0004] However, when methanol and water are extracted from a hydrolysis reactor and the water is refluxed to the hydrolysis reactor as described in Patent Document 1, the water needs to be refluxed at a high temperature and pressure, which requires excessive energy. Therefore, there is a need for a method for appropriately obtaining terephthalic acid from DMT while suppressing energy consumption.

[0005] An object of the present disclosure is to provide a hydrolysis reaction system and control method that can appropriately obtain terephthalic acid from DMT while suppressing energy consumption.

[0006] In order to solve the above-described problems and achieve the objects, the hydrolysis reaction system according to the present disclosure includes a reaction tank to which dimethyl terephthalate and water are supplied and in which the dimethyl terephthalate is hydrolyzed by the water to produce terephthalic acid and methanol; a discharge device that discharges a mixture of methanol and water from the reaction tank; and a control device that controls the discharge system, wherein the control device does not cause the discharge device to discharge the mixture during a first period from when the dimethyl terephthalate and the water are supplied to the reaction tank to a first timing, causes the discharge device to discharge the mixture during a second period from the first timing to a second timing that is later than the first timing, and does not cause the discharge device to discharge the mixture during a third period from the second timing to when terephthalic acid is discharged from the reaction tank, and the first period is shorter than the third period.

[0007] In order to solve the above-described problems and achieve the objects, the hydrolysis reaction system according to the present disclosure includes: a supply tank to which dimethyl terephthalate and water are supplied; a reaction tank connected to the supply tank, to which dimethyl terephthalate and water are supplied from the supply tank and in which the dimethyl terephthalate is hydrolyzed by the water to produce terephthalic acid and methanol; and a discharge device that discharges a mixture of methanol and water from the reaction tank.

[0008] In order to solve the above-mentioned problems and achieve the objects, a control method according to the present disclosure is a control method for controlling a hydrolysis reaction system including a reaction tank to which dimethyl terephthalate and water are supplied and in which the dimethyl terephthalate is hydrolyzed by the water to produce terephthalic acid and methanol, and a discharge device that discharges a mixture of methanol and water from the reaction tank, the control method including the steps of: supplying the dimethyl terephthalate and water to the reaction tank; not causing the discharge device to discharge the mixture during a first period from when the dimethyl terephthalate and the water are supplied to the reaction tank to a first timing; causing the discharge device to discharge the mixture during a second period from the first timing to a second timing that is later than the first timing; and causing the discharge device to discharge the mixture during a third period from the second timing to when terephthalic acid is discharged from the reaction tank, wherein the first period is shorter than the third period.

[0009] In order to solve the above-mentioned problems and achieve the objects, the present disclosure provides a control method for controlling a hydrolysis reaction system including: a supply tank to which dimethyl terephthalate and water are supplied; a reaction tank connected to the supply tank, to which dimethyl terephthalate and water are supplied from the supply tank and in which the dimethyl terephthalate is hydrolyzed by the water to produce terephthalic acid and methanol; and a discharge device that discharges a mixture of methanol and water from the reaction tank, the control method including the steps of: supplying the dimethyl terephthalate and water to the supply tank; and discharging the mixture from the reaction tank using the discharge device.

[0010] According to the present disclosure, terephthalic acid can be appropriately obtained from DMT while suppressing energy consumption.

[0011] Fig. 1 is a schematic diagram of a polyester recycling process according to this embodiment. Fig. 2 is a schematic diagram of a separation system according to this embodiment. Fig. 3 is a schematic diagram illustrating a hydrolysis reaction system according to a first embodiment. Fig. 4 is a diagram illustrating control of a discharge device according to the first embodiment. Fig. 5 is a flowchart illustrating a processing flow of a control unit. Fig. 6 is a schematic diagram illustrating a hydrolysis reaction system according to a second embodiment.

[0012] 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.

[0013] (Recycling Process) FIG. 1 is a schematic diagram of a polyester recycling process according to this embodiment. In this embodiment, a polyester raw material Pm is depolymerized to form monomers, and the monomers are then repolymerized to recycle (regenerate) the polyester raw material Pm. Specifically, as shown in FIG. 1 , the polyester raw material Pm is flaked (step S100), the solution is mixed with a reaction solvent M for depolymerization (step S102), the depolymerized polyester monomers are purified (separated) to produce a carboxylic acid-derived monomer D and an alcohol component monomer E (step S104), the monomer D is hydrolyzed to separate the reaction solvent M (step S106), and the monomer F produced by hydrolysis of the monomer D is polymerized with the monomer E (step S108), thereby regenerating the polyester raw material Pm. In addition, in the recycling process employing the separation system 1 of this embodiment, the flaking step S100 may be omitted, or only the process of recovering monomers D and E shown in step S104 and monomer F shown in step S106 may be performed without performing the repolymerization process as in step S108.

[0014] (Polyester Raw Material) In this embodiment, the polyester raw material Pm to be depolymerized is a substance containing polyester. The polyester raw material Pm is not particularly limited, but examples include waste products such as polyethylene terephthalate (PET), polyethylene butylene terephthalate (PEBT), polybutylene terephthalate (PBT), polycyclohexane dimethyl terephthalate (PCT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and polycarbonate (PC). The polyester raw material Pm is not limited to those containing only polyester components, but also includes components other than polyester components. Examples of components other than polyester contained in the polyester raw material Pm include plastics other than polyester, such as polyethylene, polystyrene, polypropylene, and polyvinyl chloride, metals, dyes, pigments, and polymerization catalysts. Examples of polyester raw material Pm include clothing in which polyester and other components are knitted into fibers. Hereinafter, components other than polyester contained in the polyester raw material Pm are referred to as impurities.

[0015] (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, water, and ethylene glycol.

[0016] (Carboxylic acid-derived monomer) The carboxylic acid-derived monomer D is a monomer having a carboxyl group produced by depolymerization of a polyester. The monomer D may be, for example, dimethyl carboxylate or diethyl carboxylate. Furthermore, the monomer D is preferably a terephthalic acid monomer, for example, dimethyl terephthalate (DMT).

[0017] (Alcohol Component Monomer) The alcohol component monomer E is an alcohol component monomer produced by a depolymerization reaction of the polyester. The monomer E may be, for example, a dihydroxy compound (dihydric alcohol), or more specifically, ethylene glycol (EG).

[0018] 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.

[0019] (First embodiment) (Separation system) Fig. 2 is a schematic diagram of a separation system according to the first embodiment. Fig. 3 is a schematic diagram illustrating a hydrolysis reaction system according to the first embodiment. The separation system 1 according to the first embodiment is a system that monomerizes polyester contained in a polyester raw material Pm to produce monomers D and E. As shown in Fig. 2, the separation system 1 has a raw material storage section 10, a dissolving section 12, a solid-liquid separation section 13, a solvent storage section 14, a reaction section 16, a separation section 18, a control section 30, a temporary storage section 70, a crystallization system 80, and a hydrolysis reaction system 200.

[0020] Hereinafter, the Z direction is the vertical direction (up-down direction). The vertically upward direction of the Z direction is referred to as the Z1 direction, and the vertically downward direction of the Z direction is referred to as the Z2 direction.

[0021] (Raw Material Storage Section) The raw material storage section 10 is a tank into which the polyester raw material Pm is introduced and stored. In this embodiment, the raw material storage section 10 stores flaked polyester raw material Pm, but the shape and size of the polyester raw material Pm may be arbitrary. The raw material storage section 10 is connected to the dissolving section 12 via an inlet pipe 10a. The polyester raw material Pm in the raw material storage section 10 is supplied to the dissolving section 12 through the inlet pipe 10a. The inlet pipe 10a is provided with an adjustment section 10b that adjusts the amount of polyester raw material Pm supplied from the raw material storage section 10 to the dissolving section 12. The adjustment section 10b is, for example, an on-off valve. When in an open state, the adjustment section 10b allows the polyester raw material Pm in the raw material storage section 10 to be supplied to the dissolving section 12, and when in a closed state, it stops the supply of the polyester raw material Pm in the raw material storage section 10 to the dissolving section 12. However, the adjusting 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 dissolving section 12. Furthermore, the polyester raw material Pm may be supplied directly to the dissolving section 12 without passing through the raw material storage section 10, the introduction pipe 10a, and the adjusting section 10b.

[0022] (Dissolving section) The dissolving section 12 is a tank in which the dissolving liquid Pd is stored. The dissolving liquid Pd is a solution produced by mixing the polyester raw material Pm with 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 the polyester contained in the polyester raw material Pm, remain without dissolving in the monomer D. Therefore, it can be said that the dissolving liquid Pd contains a polyester solution P in which the polyester contained in the polyester raw material Pm is dissolved in the monomer D, and impurities contained in the polyester raw material Pm.

[0023] Monomer D and 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 undissolved in the monomer D, thereby producing a polyester solution P and a solution Pd containing impurities. By dissolving the polyester in the monomer D in this manner, the viscosity can be reduced and the fluidity can be improved, allowing the polyester to be easily introduced into the reaction section 16. Note that the polyester solution P is not limited to one in which the entire amount of polyester is dissolved in the monomer D; at least a portion of the polyester may be insoluble in the monomer D. Furthermore, if there is a component soluble in the monomer D among the components other than the polyester contained in the polyester raw material Pm, the polyester solution P may also contain that component dissolved in the monomer D.

[0024] The dissolving section 12 is connected to a first reaction section 16A (described later) via an inlet pipe 12a. The dissolving solution Pd in ​​the dissolving section 12 is supplied to the first reaction section 16A through the inlet pipe 12a. The inlet pipe 12a is also provided with a supply section 12a1. The supply section 12a1 is a mechanism for supplying the polyester solution P in the dissolving section 12 to the first reaction section 16A, and is a pump in this embodiment.

[0025] In this embodiment, the dissolving section 12 is provided with a heating section 12A. The heating section 12A heats the interior of the dissolving section 12, thereby heating the monomer D and polyester raw material Pm supplied to the dissolving 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 this predetermined temperature, the polyester contained in the polyester raw material Pm can be properly dissolved in the monomer D. The predetermined temperature is preferably 140°C or higher and 300°C or lower, more preferably 160°C or higher and 280°C or lower, and even more preferably 190°C or higher and 250°C or lower. Note that the impurities also include components that melt when heated to a predetermined temperature (a temperature at which the polyester can be dissolved in the monomer D). Therefore, if the impurities include a component that melts when heated to a predetermined temperature, the impurities will be contained in the solution Pd in ​​a partially melted state. In this embodiment, the heating section 12A is provided in the dissolving section 12, but the location of the heating section 12A is not limited thereto and may be any location.

[0026] (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).

[0027] (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.

[0028] (First Reaction Section) The first reaction section 16A is formed within the reaction section 16. In this embodiment, the first reaction section 16A can be said to be a portion of the reaction section 16 that is filled with a filler. The first reaction section 16A can be made of a known filler used in gas-liquid or liquid-liquid contactors, such as fillers similar to those used in contactors that bring heavy oil and water into contact to extract active ingredients. Specific examples of fillers include pipes made of stainless steel or the like, Raschig rings, Berl saddles, terrarettes, balls, and the like.

[0029] An inlet pipe 12a is connected to the first reaction unit 16A. More specifically, an inlet 16C, which is an opening of the inlet pipe 12a through which the dissolution liquid Pd from the dissolution unit 12 is introduced, is connected to the first reaction unit 16A. The inlet 16C is connected to a surface 16A1 in the Z1 direction (vertically upward) of the first reaction unit 16A. The inlet pipe 12a is connected to the surface 16A1 so that the inlet 16C opens toward the Z2 direction, which is the opposite direction to the Z1 direction. In this embodiment, the inlet 16C opening toward the Z2 direction is connected to the surface 16A1 of the first reaction unit 16A, but this is not limiting. For example, the inlet 16C does not have to be directly connected to the first reaction unit 16A, and the inlet 16C opening toward the Z2 direction may be connected to the Z1 direction side of the surface 16A1 of the first reaction unit 16A within the reaction unit 16.

[0030] 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 Z2 direction than the surface 16A2 on the Z2 direction side of the first reaction section 16A. The inlet pipe 14a is connected closer to the Z2 direction than the surface 16A2 so that the inlet 16D opens toward the Z1 direction or from the side toward the center. In this embodiment, the inlet 16D, which opens toward the Z1 direction or from the side toward the center, is connected closer to the Z2 direction than the surface 16A2 of the first reaction section 16A. However, this 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.

[0031] In this embodiment, the inlet 16C through which the solution Pd is introduced opens in the Z2 direction, and the inlet 16D through which the reaction solvent M is introduced opens in the Z1 direction or from the side toward the center. Therefore, the solution Pd and the reaction solvent M are introduced into the first reaction section 16A in directions facing each other.

[0032] The solution Pd introduced into the first reaction section 16A from the inlet 16C moves in the Z2 direction on the surface of the filler of the first reaction section 16A. Meanwhile, the reaction solvent M in a supercritical or subcritical state (pressurized gas or pressurized liquid) introduced from the inlet 16D moves in the Z1 direction within the first reaction section 16A. In the first reaction section 16A, the reaction solvent M in a supercritical or subcritical state (pressurized gas or pressurized liquid) comes into contact with the solution Pd. The polyester in the solution Pd is depolymerized (reduced in molecular weight) by the reaction solvent M, and the depolymerized polyester is extracted into the reaction solvent M in a supercritical or subcritical state (pressurized gas or pressurized liquid). Hereinafter, the polyester depolymerized in the first reaction zone 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 Z1 direction through the first reaction zone 16A and is discharged to the Z1 direction side of the first reaction zone 16A.

[0033] The first depolymerized polyester P1 includes monomers D and E produced by depolymerizing the polyester in the solution Pd, monomer D originally mixed in the solution Pd, and oligomers produced by depolymerizing the polyester. The oligomers referred to here refer to carboxylic acid-derived or alcohol-derived oligomers (carboxylic acid-derived or alcohol-derived oligomers with smaller molecular weights than polyester) that are not monomerized but are depolymerized from the polyester. Furthermore, oligomers contained in the residual substance R in the polyester solution P are also depolymerized by the reaction solvent M. Therefore, the first depolymerized polyester P1 also includes the depolymerized residual substance R. The depolymerized residual substance R includes oligomers contained in the residual substance that have been depolymerized, as well as monomers D and E formed by depolymerizing the oligomers contained in the residual substance.

[0034] (Second Reaction Unit) The second reaction unit 16B is formed within the reaction unit 16, and is formed at a location where the first solvent M1 is discharged from the first reaction unit 16A. In this embodiment, since the first solvent M1 is discharged in the Z1 direction, the second reaction unit 16B can be said to be a space formed on the Z1 direction side of the first reaction unit 16A.

[0035] In the second reaction zone 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 zone 16B will be referred to as the second depolymerized polyester P2, and the mixture of the second depolymerized polyester P2 and the reaction solvent M (the reaction solvent M in which the second depolymerized polyester P2 is dissolved) will be referred to as the second solvent M2. An outlet pipe 16a is connected to the second reaction zone 16B. More specifically, an outlet 16E, which is an opening of the outlet pipe 16a through which the second solvent M2 from the second reaction zone 16B is discharged, is connected to the second reaction zone 16B. The second solvent M2 containing the second depolymerized polyester P2 in the second reaction zone 16B is discharged from the outlet 16E through the outlet pipe 16a to the outside of the second reaction zone 16B.

[0036] The second depolymerized polyester P2 contains the monomers D and E in the first depolymerized polyester P1, the monomers D and E produced by depolymerizing the oligomers in the first depolymerized polyester P1, and the oligomers produced by depolymerizing the first depolymerized polyester P1.

[0037] A discharge pipe 16b is connected to the bottom of the reaction zone 16. More specifically, a discharge port 16F, which is an opening of the discharge pipe 16b through which non-extractable matter (described below) in the reaction zone 16 is discharged, is connected to the bottom of the reaction zone 16. The non-extractable matter includes 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 matter at the bottom of the reaction zone 16 is discharged from the discharge port 16F through the discharge pipe 16b to the outside of the reaction zone 16. The non-extractable matter discharged from the discharge port 16F can be said to be components of the polyester solution P that were not led to the separation zone 18 as the second solvent M2 (reaction solvent M in which the second depolymerized polyester P2 is dissolved) but remained in the first reaction zone 16A and the second reaction zone 16B.

[0038] The reaction section 16 may also be provided with a heating section that heats the interior of the reaction section 16 and a pressurizing section that maintains the pressure inside the reaction section 16 at a predetermined value or higher. The temperature inside the reaction section 16 is preferably 250°C or higher and 400°C or lower, and more preferably 250°C or higher and 350°C or lower. The pressure inside the reaction section 16 is preferably 1 MPa or higher and 30 MPa or lower, and more preferably 6 MPa or higher and 25 MPa or lower. The pressurizing section and the heating section may be controlled by the control section 30.

[0039] (Separation Section) The separation section 18 is introduced with a second solvent M2 containing a second depolymerized polyester P2, and separates the second solvent M2 into a reaction solvent M, a monomer D derived from a carboxylic acid contained in the second depolymerized polyester P2, a monomer E of an alcohol component contained in the second depolymerized polyester P2, and a residual substance R. The separation section 18 distills the second solvent M2 to separate it into the monomer D, the monomer E, and the residual substance R. The residual substance R is a component of the second solvent M2 other than the reaction solvent M, the monomer D, and the monomer E, and includes oligomers.

[0040] In this embodiment, the separation section 18 has a first separation section 18A, a second separation section 18B, and a third separation section 18C.

[0041] The first separation section 18A is a separation column connected to the outlet pipe 16a. A second solvent M2 containing the 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, with the gaseous component being the low-boiling component and the liquid component being 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.

[0042] 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 reaction solvent M and monomer E. Outlet pipes 18Ba and 18Bb are connected to the second separation section 18B. The reaction solvent M is discharged from the outlet pipe 18Ba, and the monomer E is discharged from the outlet pipe 18Bb. The outlet pipe 18Ba is connected to the second separation section 18B and the solvent reservoir 14. Therefore, the reaction solvent M discharged from the second separation section 18B is returned to the solvent reservoir 14 and reused for depolymerization of polyester.

[0043] 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, low-boiling components containing the 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. Furthermore, the monomer D separated in the third separation section 18C is discharged from the outlet pipe 18Cb and introduced into the temporary storage section 70. The residual substances separated in the third separation section 18C are discharged from the outlet pipe 18Cc.

[0044] 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. Alternatively, 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.

[0045] 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 residual material R discharged from the third separation section 18C into the dissolving section 12. In the example shown in 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 residual 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. When open, the adjustment section 18Cg allows the residual material R to be supplied to the dissolving section 12, and when closed, the adjustment section 18Cg stops the supply of the residual 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 residual 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.

[0046] 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 also 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.

[0047] (Temporary Storage Section) The temporary storage section 70 is, for example, a tank, and temporarily stores the monomer D supplied from the third separation section 18C. The temporary storage section 70 is connected to the third separation section 18C via an outlet pipe 18Cb. The temporary storage section 70 is connected to a dissolution tank 82, which will be described later, via an outlet pipe 72. The temporary storage section 70 supplies the temporarily stored monomer D to the dissolution tank 82.

[0048] (Crystallization System) The crystallization system 80 crystallizes the monomer D from a solution containing the monomer D dissolved in the separation unit 18. The monomer D separated in the separation unit 18 may contain impurities. The crystallization system 80 crystallizes the highly pure monomer D from the solution containing the monomer D, removing the impurities. Examples of impurities include isomers of the monomer D that were not completely separated by distillation in the third separation unit 18C. For example, when the monomer D is DMT, the isomer of DMT is DMI (dimethyl isophthalate) derived from the copolymer IPA (isophthalic acid). DMI has a boiling point close to that of DMT, making it difficult to separate by distillation, but it can be separated by crystallization. That is, in this embodiment, highly pure monomer D can be extracted by crystallizing the monomer D (DMT) without crystallizing the DMI. Hereinafter, the highly pure monomer D extracted by crystallization will be referred to as monomer HD, as appropriate.

[0049] 2, the crystallization system 80 includes a dissolution tank 82, an adjustment section 86, a crystallization tank 90, an agitation section 100, a solid-liquid separation section 120, a melting tank 130, and a temporary melt storage tank 140. In this embodiment, the crystallization system 80 is connected downstream of the discharge pipe 72, and extracts, by crystallization, a monomer HD from a solution containing dissolved monomer D flowing through the discharge pipe 72.

[0050] (Dissolution Tank) The dissolution tank 82 is a tank that stores a solution L in which the monomer D is dissolved. The dissolution tank 82 is connected to the temporary storage section 70 via the outlet pipe 72. The monomer D containing impurities separated in the third separation section 18C is introduced from the temporary storage section 70 into the dissolution tank 82. A solvent that dissolves the monomer D is also introduced into the dissolution tank 82. As a result, the monomer D is dissolved in the solvent in the dissolution tank 82 and stored as a solution L. Note that any liquid may be used as the solvent, but methanol is used in this embodiment.

[0051] The dissolution tank 82 is connected to an adjustment unit 86 and a crystallization tank 90 via an inlet pipe 84. The solution L stored in the dissolution tank 82 is introduced into the crystallization tank 90 via the inlet pipe 84 and the adjustment unit 86. The dissolution tank 82 is located in the Z1 direction (vertically higher) than the crystallization tank 90, which will be described later. Furthermore, the bottom surface of the dissolution tank 82 on the Z2 direction side is located in the Z1 direction above an opening 90c formed in the crystallization tank 90. ​​However, the positional relationship between the dissolution tank 82 and the crystallization tank 90 in the Z direction is not limited to this and may be arbitrary.

[0052] (Inlet Pipe) The inlet pipe 84 is a pipe that connects the dissolution tank 82 and the crystallization tank 90. ​​The inlet pipe 84 extends in the Z2 direction from the point where it is connected to the dissolution tank 82 to the point where it is connected to the crystallization tank 90 (the adjustment unit 86 in this example). In other words, in the section from the point where it is connected to the dissolution tank 82 to the point where it is connected to the crystallization tank 90 (the adjustment unit 86 in this example), the inlet pipe 84 extends in the Z2 direction rather than in the Z1 direction as it approaches the point where it is connected to the crystallization tank 90 (the adjustment unit 86 in this example).

[0053] The solution L in the dissolution tank 82 flows through the inlet pipe 84 and the adjustment section 86 into the crystallization tank 90 .

[0054] (Adjustment Unit) The adjustment unit 86 is a device that reduces the pressure of the solution L. The adjustment unit 86 is connected to the inlet pipe 84 and the crystallization tank 90. ​​The adjustment unit 86 reduces the pressure of the solution L introduced from the dissolution tank 82 via the inlet pipe 84, and introduces the solution L in a reduced pressure state into the crystallization tank 90.

[0055] In this embodiment, the adjusting unit 86 is a pressure reducing valve. The adjusting unit 86 may have any structure as long as it is a pressure reducing valve, but in this embodiment, it is an angle valve. In this embodiment, the adjusting unit 86 is directly connected to the crystallization tank 90.

[0056] The solution L introduced into the adjusting section 86 is introduced into the crystallization tank 90 in a state where the pressure of the solution L has been reduced by the adjusting section 86. Since the temperature of the reduced-pressure solution L is reduced, the monomer HD to be separated is crystallized from the reduced-pressure solution L.

[0057] In this embodiment, the adjustment unit 86 is directly connected to the crystallization tank 90, but this is not limited thereto, and a pipe connecting the adjustment unit 86 and the crystallization tank 90 may be provided between the adjustment unit 86 and the crystallization tank 90.

[0058] (Crystallization Tank) The crystallization tank 90 is a tank into which the solution L depressurized by the adjustment unit 86 is introduced and in which the object to be separated (monomer HD in this case) is crystallized from the solution L. The solution L depressurized by the adjustment unit 86 is introduced into the crystallization tank 90. ​​In this way, the depressurized solution L is introduced into the crystallization tank 90 and the solution L is stored in a depressurized state. In other words, the crystallization tank 90 can be said to be a flash-type crystallization tank in which the internal pressure is reduced below the external pressure.

[0059] The crystallization tank 90 is connected to a discharge pipe 121 for discharging the slurry S. The slurry S is a slurry containing the crystallized monomer HD and the solution L from which the monomer HD has been removed.

[0060] A baffle 110 is provided inside the crystallization tank 90 to rectify the flow of the solution L in the crystallization tank 90. ​​The shape, mounting position, and number of the baffle 110 are arbitrary, but in this embodiment, the baffle 110 is provided on the inner wall surface of the crystallization tank 90, and more specifically, is a plate-shaped member extending in the Z direction on the inner wall surface of the side wall 90b. However, the baffle 110 is not an essential component and does not have to be provided in the crystallization tank 90.

[0061] (Agitation Unit) The agitation unit 100 is provided in the crystallization tank 90 and rotates when a drive unit (e.g., a motor) is driven, thereby agitating the inside of the crystallization tank 90. ​​In this embodiment, the agitation blade is located on the Z2 side of the adjustment unit 86. The agitation blade is also located on the Z1 side of the bottom surface of the crystallization tank 90, facing the bottom surface (i.e., overlapping the bottom surface as viewed from the Z direction). The agitation unit 100 is preferably provided at the center of the crystallization tank 90 as viewed from the Z direction. That is, it is preferable that the central axis of the agitation unit 100 and the central axis of the crystallization tank 90 coincide with each other.

[0062] (Crystallization of Monomer HD) With the above-described configuration, the crystallization system 80 crystallizes the monomer HD from the solution L in the crystallization tank 90. ​​That is, when the solution L in the dissolution tank 82 is supplied to the adjustment unit 86 via the inlet pipe 84, the solution L is depressurized by the adjustment unit 86. The solution L depressurized by the adjustment unit 86 is introduced into the crystallization tank 90 through the opening 90c. Because the temperature of the depressurized solution L decreases, the monomer HD is crystallized in the crystallization tank 90 and stored as a slurry S. Furthermore, the inside of the crystallization tank 90 is stirred by the stirring unit 100, which promotes the crystallization of the monomer HD in the crystallization tank 90.

[0063] (Solid-Liquid Separation Section) The solid-liquid separation section 120 is connected to the crystallization tank 90 via a discharge pipe 121. The slurry S (solution L in which the monomer HD has been crystallized) produced in the crystallization tank 90 is introduced into the solid-liquid separation section 120 from the crystallization tank 90 via the discharge pipe 121. The solid-liquid separation section 120 separates the introduced slurry S into solid and liquid components. The solid-liquid separation section 120 separates the slurry S into solid components to be separated and liquid components. In this embodiment, the solid-liquid separation section 120 separates the slurry S into the monomer HD and the solution L from which the monomer HD has been removed. The solution L from which the monomer HD has been removed is discharged from a discharge pipe 123 connected to the solid-liquid separation section 120 and treated. The solid-liquid separation unit 120 may be, for example, a centrifuge, which separates the separation target from the solution L by centrifuging, stirring the interior of the solid-liquid separation unit 120 around a predetermined axis and moving the separation target radially outward from the rotating shaft. The solid-liquid separation unit 120 is not limited to centrifugal separation as long as it can separate the separation target from the solution L. For example, the solid-liquid separation unit 120 may separate the separation target from the solution L using a filter.

[0064] (Melting Tank) The melting tank 130 is connected to the solid-liquid separation section 120 via an outlet pipe 122. The melting tank 130 is also connected to a temporary melt storage tank 140 via a supply pipe 132. The melting tank 130 melts (melts) the highly pure monomer HD obtained through solid-liquid separation from the slurry S. The melting tank 130 melts the monomer HD to form a liquid, and supplies the liquid to the temporary melt storage tank 140 via the supply pipe 132.

[0065] (Temporary melt storage tank) The temporary melt storage tank 140 is connected to the hydrolysis reaction system 200 (described later) via an outlet pipe 214. The temporary melt storage tank 140 is a tank that temporarily stores the monomer HD that has been melt-treated in the melting tank 130. The temporary melt storage tank 140 supplies the stored monomer HD to the hydrolysis reaction system 200.

[0066] (Hydrolysis Reaction System) The hydrolysis reaction system 200 is a system that is supplied with DMT and water and hydrolyzes the DMT to produce PTA (high-purity terephthalic acid). In this embodiment, the hydrolysis reaction system 200 is connected to the crystallization system 80 and hydrolyzes the monomer HD (DMT) produced in the crystallization system 80 to produce PTA, but is not limited to being connected to the crystallization system 80. In other words, the hydrolysis reaction system 200 may be a system that is provided in any facility that is supplied with DMT and water and hydrolyzes the DMT to produce PTA.

[0067] The hydrolysis reaction system 200 includes a reaction vessel 210 , a first treatment device 212 , a second treatment device 218 , and a discharge system 240 .

[0068] (First Treatment Apparatus) The first treatment apparatus 212 is an apparatus that heats the monomer HD to a predetermined temperature and pressurizes the monomer HD to a predetermined pressure. In this embodiment, the first treatment apparatus 212 is connected to the temporary melt storage tank 140, and the monomer HD is supplied from the temporary melt storage tank 140. The first treatment apparatus 212 heats the monomer HD supplied from the temporary melt storage tank 140 to a predetermined temperature and pressurizes the monomer HD to a predetermined pressure. The predetermined temperature and pressure may be any values, but are preferably values ​​suitable for the hydrolysis reaction of the monomer HD, and may be, for example, 270°C and 6.4 MPa.

[0069] The first treatment device 212 is connected to the reaction tank 210 via an outlet pipe 214, and the monomer HD whose temperature and pressure have been increased in the first treatment device 212 is supplied to the reaction tank 210 through the outlet pipe 214. In this embodiment, a valve unit 216 is provided in the outlet pipe 214. The valve unit 216 is, for example, an on-off valve, and the supply of the monomer HD from the first treatment device 212 to the reaction tank 210 is controlled by opening and closing the valve. For example, when the valve unit 216 is in an open state, the monomer HD in the first treatment device 212 flows through the outlet pipe 214 and is introduced into the reaction tank 210.

[0070] (Second Treatment Device) The second treatment device 218 is a device that treats water for hydrolyzing the monomer HD. Water is supplied to the second treatment device 218 from any device or tank, and the second treatment device 218 heats the supplied water to a predetermined temperature and pressurizes the water to a predetermined pressure. The predetermined temperature and pressure may be any values, but are preferably values ​​suitable for the hydrolysis reaction of the monomer HD, and may be, for example, 270°C and 6.4 MPa.

[0071] The second treatment device 218 is connected to the reaction tank 210 via a supply pipe 220, and water whose temperature and pressure have been increased in the second treatment device 218 is supplied to the reaction tank 210 through the supply pipe 220. In this embodiment, a valve unit 222 is provided in the supply pipe 220. The valve unit 222 is, for example, an on-off valve, and controls the supply of water from the second treatment device 218 to the reaction tank 210 by opening and closing the valve. For example, when the valve unit 222 is in an open state, the water in the second treatment device 218 flows through the supply pipe 220 and is introduced into the reaction tank 210.

[0072] It is not necessary to provide the first treatment device 212 and the second treatment device 218. When the first treatment device 212 and the second treatment device 218 are not provided, the temperature and pressure of the monomer HD and water may be increased in the reaction tank 210.

[0073] (Reaction Tank) The reaction tank 210 is a tank to which the monomer HD and water are supplied. The monomer HD and water are supplied to the reaction tank 210 separately (in a separated state), rather than in a mixed state. In this embodiment, the reaction tank 210 is connected to a first treatment device 212 via an outlet pipe 214, and to a second treatment device 218 via a supply pipe 220. The reaction tank 210 is supplied with heated and pressurized monomer HD from the first treatment device 212, and with heated and pressurized water from the second treatment device 218. However, the monomer HD may be supplied to the reaction tank 210 in a mixed state with water. In this case, it is preferable that the mixture of monomer HD and water is heated and pressurized to a predetermined temperature and a predetermined pressure in the reaction tank 210.

[0074] In the reaction tank 210, PTA and methanol are produced by hydrolyzing DMT, which is the monomer HD, with water. More specifically, in the reaction tank 210, the hydrolysis proceeds as a first reaction shown in the following formula (1) and a second reaction shown in the following formula (2).

[0075] DMT+H ２ O→MMT+MeOH...(1) MMT+H ２ O⇔PTA+MeOH...(2)

[0076] DMT in formula (1) is dimethyl terephthalate, and H in formulas (1) and (2) ２ O is water, MMT in formulas (1) and (2) is monomethyl terephthalate, MeOH in formulas (1) and (2) is methanol, and PTA in formula (2) is high-purity terephthalic acid. That is, in reaction vessel 210, DMT is hydrolyzed to produce the intermediate products MMT and methanol, and MMT is hydrolyzed to produce PTA and methanol. The first reaction is an irreversible reaction in which MMT and methanol are produced from DMT and water. On the other hand, the second reaction is a reversible reaction (equilibrium reaction) in which both a reaction in which PTA and methanol are produced from MMT and water and a reaction in which MMT and water are produced from PTA and methanol occur.

[0077] An outlet pipe 230 is connected to the reaction tank 210. PTA and water produced in the reaction tank 210 flow through the outlet pipe 230. A discharge unit 232 is provided in the outlet pipe 230. The discharge unit 232 is a device that discharges PTA and water from the reaction tank 210. The discharge unit 232 is, for example, an on-off valve, and controls the inflow and outflow of PTA and water produced in the reaction tank 210 by opening and closing the valve. When the discharge unit 232 is open, the PTA and water in the reaction tank 210 are discharged from the reaction tank 210 via the outlet pipe 230. The PTA discharged from the reaction tank 210 may be treated in a subsequent process. For example, the PTA and water may be stored in a hopper after undergoing a crystallization process, a dehydration process, and a drying process (not shown).

[0078] (Discharge System) The discharge system 240 is connected to the reaction tank 210 and discharges a mixture of methanol and water from the reaction tank 210 and supplies water to the reaction tank 210. By discharging methanol from the reaction tank 210 using the discharge system 240, the reaction in the second reaction in which MMT and water are produced from PTA and methanol (the leftward reaction in formula (2)) is suppressed, thereby enabling the appropriate production of PTA. Furthermore, by supplying water to the reaction tank 210 using the discharge system 240, the reaction in which PTA is produced and the operation of achieving the required particle size distribution in the subsequent crystallization step are prevented from being hindered, thereby enabling the appropriate production of PTA. Note that in this embodiment, the discharge system 240 performs the process of discharging methanol and water from the reaction tank 210 and the process of supplying water to the reaction tank 210, but is not limited thereto. For example, the discharge system 240 may perform only the process of discharging methanol and water from the reaction tank 210 without performing the process of supplying water to the reaction tank 210.

[0079] In this embodiment, the discharge system 240 includes a discharge device 244 , a separation device 260 , and a water treatment device 270 .

[0080] (Discharge Device) The discharge device 244 is connected to the reaction tank 210 and discharges a mixture of methanol and water from the reaction tank 210. In this embodiment, a discharge pipe 242 is connected to the reaction tank 210, and the discharge device 244 is a valve provided on the discharge pipe 242. For example, when the discharge device 244 is open, it discharges the methanol and water in the reaction tank 210 from the reaction tank 210 via the discharge pipe 242.

[0081] (Separation Device) The separation device 260 is a device into which a mixture of methanol and water is introduced and which separates water from the mixture of methanol and water. The separation device 260 is connected to the discharge device 244 and separates water from the mixture of methanol and water discharged from the reaction tank 210 by the discharge device 244. More specifically, the separation device 260 is connected to the discharge pipe 242 at a position downstream of the position where the discharge device 244 is provided in the flow direction of the mixture of methanol and water. The separation device 260 receives the mixture of methanol and water from the discharge pipe 242 and separates water from the mixture introduced therein. The separation device 260 may be a device that separates water from the mixture of methanol and water by any method, but may, for example, separate water by evaporating methanol by heating.

[0082] The separator 260 is connected to a water treatment device 270 via a water discharge pipe 262 , and the water separated in the separator 260 is supplied to the water treatment device 270 through the water discharge pipe 262 .

[0083] (Water Treatment Apparatus) The water treatment apparatus 270 is an apparatus that receives the water separated in the separation apparatus 260 and treats the received water. The water treatment apparatus 270 is connected to the separation apparatus 260 via a water discharge pipe 262, and the water separated in the separation apparatus 260 is received from the water discharge pipe 262. The water treatment apparatus 270 heats the received water to a predetermined temperature and pressurizes it to a predetermined pressure. The predetermined temperature and pressure may be any values, but are preferably values ​​suitable for the hydrolysis reaction of the monomer HD, and may be, for example, 270°C and 6.4 MPa.

[0084] The water treatment device 270 is connected to the reaction tank 210 via a treated water discharge pipe 272. Water that has been subjected to temperature and pressure increase treatment in the water treatment device 270 is returned to the reaction tank 210 through the treated water discharge pipe 272. In this embodiment, a supply device 274 is provided in the treated water discharge pipe 272. The supply device 274 is a device that supplies water treated in the water treatment device 270 from the water treatment device 270 to the reaction tank 210. The supply device 274 is, for example, an on-off valve, and controls the supply of water from the water treatment device 270 to the reaction tank 210 by opening and closing the valve. When the valve of the supply device 274 is in an open state, the water from the water treatment device 270 flows through the treated water discharge pipe 272 and is returned to the reaction tank 210.

[0085] The water treatment device 270 may or may not be integrated with the second treatment device 218. When the water treatment device 270 is not provided, a larger amount of water is supplied to the reaction tank 210 than when the water treatment device 270 is provided. This allows the hydrolysis reaction system 200 to perform the hydrolysis treatment without running out of water. This also prevents precipitation of PTA in the reaction tank 210, allowing it to be appropriately treated in steps after hydrolysis.

[0086] (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 polyester raw material Pm supplied from the raw material storage unit 10 to the dissolution unit 12. Furthermore, if the solid-liquid separation unit 13 is equipped 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 solution Pd supplied from the dissolution unit 12 to the reaction unit 16. The control unit 30 controls the heating and pressurization unit 14b to bring the reaction solvent M to a supercritical state or 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 30 controls the adjustment unit 18Ce to control the amount of monomer D supplied to the dissolution unit 12. The control unit 30 controls the adjustment unit 18Cg to control the amount of residual material R supplied to the dissolution unit 12. The control unit 30 adjusts the adjustment unit 86 of the crystallization system 80 to reduce the pressure of the solution L and control the flow rate of the solution L into the crystallization tank 90. ​​The control unit 30 controls the rotation of the stirring unit 100. The control unit 30 controls the operation of the hydrolysis reaction system 200.

[0087] 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 contents of calculations performed by the processor and programs. The control unit 30 executes control of the separation system 1 by reading out programs from the storage unit.

[0088] 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.

[0089] (Operation of 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, and mixes the polyester raw material Pm and the monomer D in the dissolution unit 12 to generate a solution Pd. The control unit 30 controls the supply unit 12a1 to introduce the solution Pd generated in the dissolution unit 12 into the first reaction unit 16A.

[0090] The control unit 30 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 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.

[0091] In this manner, by supplying the solution Pd and the reaction solvent M to the reaction section 16, the polyester contained in the solution Pd is depolymerized in the first reaction section 16A to produce a first depolymerized polyester P1. Then, in the second reaction section 16B, the first depolymerized polyester P1 is further depolymerized to produce a second solvent M2, which is a mixture of a second depolymerized polyester P2 and the reaction solvent M. The second solvent M2 is separated into the reaction solvent M, monomer D, monomer E, and residual substances in the first separation section 18A, the second separation section 18B, and the third separation section 18C.

[0092] The control unit 30 controls the adjustment unit 86 to supply the solution L to the adjustment unit 86, depressurize the solution L using the adjustment unit 86, and introduce the depressurized solution L into the crystallization tank 90. ​​Since the solution L introduced into the crystallization tank 90 has been depressurized, the target monomer HD is crystallized from the solution L in the crystallization tank 90.

[0093] The control unit 30 also controls the hydrolysis reaction system 200 to hydrolyze the monomer HD to produce PTA. Specifically, the control unit 30 controls the first treatment device 212 to increase the temperature and pressure of the monomer HD and supply the heated and pressurized monomer HD to the reaction tank 210. The control unit 30 also controls the second treatment device 218 to increase the temperature and pressure of water and supply the heated and pressurized water to the reaction tank 210. The control unit 30 also controls the discharge device 244 to discharge the mixture of water and methanol from the reaction tank 210. The control unit 30 also controls the separation device 260 to separate water from the mixture of water and methanol. The control unit 30 also controls the water treatment device 270 to increase the temperature and pressure of water and supply the heated and pressurized water to the reaction tank 210. As a result, the monomer HD is hydrolyzed in the reaction tank 210 to produce PTA. Furthermore, the control unit 30 controls the discharge unit 232 to discharge PTA from the reaction tank 210 .

[0094] (Control of Hydrolysis System) As described above, the control unit 30 introduces the monomer HD (DMT) and water into the reaction tank 210 and controls the discharge device 244 to discharge a mixture of water and methanol from the reaction tank 210. By discharging methanol from the reaction tank 210 in this manner, the reaction of producing MMT and water from PTA and methanol (the leftward reaction in Equation (2)) is suppressed, as described above, enabling the appropriate production of PTA. Furthermore, the control unit 30 controls the water treatment device 270 to return heated and pressurized water to the reaction tank 210 to replenish the water discharged together with methanol from the reaction tank 210. This prevents the reaction of producing PTA and the subsequent crystallization step from being hindered, enabling the appropriate production of PTA. However, the water returned to the reaction tank 210 must be heated and pressurized to promote hydrolysis, and this heating and pressurization requires energy. In response to this problem, the inventors of the present invention have conducted extensive research and found that by appropriately controlling the discharge of the water and methanol mixture, it is possible to discharge enough methanol to adequately produce PTA while suppressing the amount of water discharged. This allows for the appropriate production of PTA while suppressing the amount of water discharged, thereby reducing the energy required to raise the temperature and pressure of the return water. Specific details of this control are described below.

[0095] FIG. 4 is a diagram illustrating control of the discharge device according to the first embodiment. The horizontal axis of FIG. 4 represents time, the vertical axis on the right represents the state of the discharge device 244, and line L represents the operation of the discharge device 244. That is, when the discharge device 244 is OFF on line L, the discharge device 244 is not discharging the mixture of water and methanol from the reaction tank 210 (discharge is stopped). Also, when the discharge device 244 is ON on line L, the discharge device 244 is discharging the mixture of water and methanol from the reaction tank 210. Also, timing T0 on the horizontal axis of FIG. 4 indicates the timing at which hydrolysis of DMT starts in the reaction tank 210. That is, timing T0 refers to the timing when heated and pressurized DMT (monomer HD) and heated and pressurized water are supplied to the reaction tank 210 (the timing when the supply of DMT and water is completed), and in this embodiment, refers to the timing when the supply of DMT and water from the first treatment device 212 and the second treatment device 218 to the reaction tank 210 is completed. That is, in this embodiment, DMT and water are supplied to the reaction tank 210 for a predetermined period, and the supply of DMT and water is stopped at timing T0. Furthermore, timing T3 refers to the timing when discharge of PTA from the reaction tank 210 begins, and in this embodiment, refers to the timing when PTA production is completed and PTA is discharged from the reaction tank 210 by the discharge unit 232.

[0096] As shown by line L in FIG. 4 , the control unit 30 stops the discharge device 244 from discharging the mixture from the reaction vessel 210 during a first period from time T0 to a first time T1. Furthermore, the control unit 30 causes the discharge device 244 to discharge the mixture from the reaction vessel 210 during a second period from the first time T1 to a second time T2 that follows the first time T1. Furthermore, the control unit 30 stops the discharge device 244 from discharging the mixture from the reaction vessel 210 during a third period from the second time T2 to time T3. That is, the control unit 30 starts the discharge device 244 at the first time T1 and stops the discharge at the second time T2. Here, the first period from time T0 to the first time T1 is shorter than the third period from the second time T2 to time T3. That is, the control unit 30 discharges methanol and water only during the initial period from the start of hydrolysis during the entire period from the start of hydrolysis T0 to the end of hydrolysis T3. This allows the amount of water discharged to be reduced while discharging methanol to an extent that allows hydrolysis to be promoted, thereby enabling appropriate production of PTA while reducing energy consumption.

[0097] More specifically, the inventors, through extensive research, have identified the reaction rates of Equations (1) and (2) within the reaction vessel 210. Specifically, they have found that the reaction of Equation (1) (the MMT production reaction) proceeds rapidly in the initial stage, while the reaction of Equation (2) (the equilibrium reaction for the production of MMT and PTA) proceeds relatively slowly thereafter. Therefore, as in this embodiment, by discharging methanol and water from the first timing T1, it is possible to discharge methanol only after sufficient MMT has been produced, thereby promoting the PTA production reaction. Furthermore, by stopping the discharge of methanol and water at the relatively early second timing T2, the amount of water discharged can be reduced, thereby suppressing energy consumption. For example, line L1 in FIG. 4 indicates an example of the DMT concentration within the reaction vessel 210, line L2 in FIG. 4 indicates an example of the MMT concentration within the reaction vessel 210, and line L3 in FIG. 4 indicates an example of the PTA concentration within the reaction vessel 210. As shown in FIG. 4, by controlling the discharge device 244 as shown by line L, methanol can be discharged only after sufficient MMT has been produced, and the amount of water discharged can be reduced, thereby making it possible to produce PTA at a high concentration while suppressing energy consumption.

[0098] The concentration of DMT in reaction vessel 210 refers to the ratio of the mass of DMT to the total mass of DMT, MMT, and PTA. Similarly, the concentration of MMT in reaction vessel 210 refers to the ratio of the mass of MMT to the total mass of DMT, MMT, and PTA, and the concentration of PTA in reaction vessel 210 refers to the ratio of the mass of PTA to the total mass of DMT, MMT, and PTA.

[0099] The first timing T1 and the second timing T2 may be set to any timing at which the first period is shorter than the third period. However, in this embodiment, the first timing T1 is preferably set to a timing at which the MMT concentration in the reaction vessel 210 is 20% or more and 60% or less, more preferably a timing at which it is 30% or more and 50% or less, and even more preferably a timing at which it is 35% or more and 45% or less. The second timing T2 is preferably set to a timing at which the MMT concentration in the reaction vessel 210 is 0% or more and 50% or less, more preferably a timing at which it is 0% or more and 40% or less, and even more preferably a timing at which it is 0% or more and 30% or less. The MMT concentration at each timing does not need to be actually measured; it can be calculated based on the amount, pressure, and temperature of the DMT and water supplied. Furthermore, the first timing T1 may be set to a timing at which the reaction to PTA reaches equilibrium, calculated from the reaction equilibrium equation (2).

[0100] Furthermore, the ratio of the length of the first period from timing T0 to the first timing T1 to the period (total period) from timing T0 to timing T3 is preferably 1% to 20%, more preferably 5% to 20%, and even more preferably 10% to 20%. Furthermore, the ratio of the length of the second period from the first timing T1 to the second timing T2 to the period (total period) from timing T0 to timing T3 is preferably 1% to 30%, more preferably 5% to 20%, and even more preferably 10% to 20%. Furthermore, each time length may be calculated using the reaction equilibrium equation (2). By setting each period in this manner, PTA can be produced at a high concentration while suppressing energy consumption.

[0101] The control unit 30 may arbitrarily control the timing at which the heated and pressurized water is returned from the water treatment device 270 to the reaction tank 210. For example, the control unit 30 may return the water to the reaction tank 210 immediately after the water treatment device 270 has completed raising the temperature and pressure of the water.

[0102] The flow of the hydrolysis reaction system 200 processing by the control unit described above will now be described. FIG. 5 is a flowchart illustrating the processing flow of the control unit. As shown in FIG. 5, the control unit 30 controls the first treatment device 212 and the second treatment device 218 to supply heated and pressurized DMT and water to the reaction tank 210 (step S10). This initiates the DMT hydrolysis reaction. When the first time T1 is reached (step S12; Yes), i.e., when a first period has elapsed since time T0, when the supply of DMT and water to the reaction tank 210 was completed, the control unit 30 controls the discharge device 244 to discharge the methanol and water mixture from the reaction tank 210 (step S14). On the other hand, if the first time T1 has not been reached (step S12; No), the process returns to step S12, stops discharge from the discharge device 244, and waits for the first time T1 to be reached.

[0103] After step S14, if the second timing T2 is reached (step S16; Yes), the control unit 30 stops the discharge of the methanol and water mixture from the reaction tank 210 by the discharge device 244 (step S18). Thereafter, if timing T3 is reached, the control unit 30 controls the discharge unit 232 to discharge PTA from the reaction tank 210, and ends this process. On the other hand, if the second timing T2 is not reached (step S16; No), the process returns to step S16, and the discharge device 244 continues discharging while waiting for the second timing T2 to be reached.

[0104] Effect of First Embodiment As described above, in this embodiment, during a first period from timing T0 to a first timing T1, the discharge device 244 stops discharging the mixture from the reaction tank 210, during a second period from the first timing T1 to a second timing T2, the discharge device 244 discharges the mixture from the reaction tank 210, and during a third period from the second timing T2 to a timing T3, the discharge of the mixture from the reaction tank 210 is stopped. This makes it possible to suppress the amount of water discharged while discharging methanol to an extent that allows hydrolysis to be promoted, thereby enabling PTA to be appropriately produced while suppressing energy consumption.

[0105] Second Embodiment Next, a second embodiment will be described. The second embodiment differs from the first embodiment in that a plurality of tanks to which DMT and water are supplied are provided in series. Components having the same functions as those in the first embodiment are designated by the same reference numerals, and detailed descriptions thereof will be omitted.

[0106] FIG. 6 is a schematic diagram illustrating a hydrolysis reaction system according to the second embodiment.

[0107] As shown in Fig. 6, a hydrolysis reaction system 200A according to the second embodiment includes a first treatment device 212, a second treatment device 218, a supply tank 300, and a reaction tank 310. The hydrolysis reaction system 200A according to the second embodiment may include any number of reaction tanks 310, but preferably includes multiple reaction tanks 310. Fig. 6 shows an example in which three reaction tanks 310, namely, reaction tanks 310a, 310b, and 310c, are provided.

[0108] (Supply Tank) The supply tank 300 is a tank to which DMT and water are supplied. The supply tank 300 is supplied with the monomer HD and water separately (separated), rather than with the monomer HD and water mixed together. In this embodiment, the supply tank 300 is connected to a first treatment device 212 via an outlet pipe 214 and to a second treatment device 218 via a supply pipe 220. The supply tank 300 is supplied with the monomer HD whose temperature and pressure have been increased from the first treatment device 212, and with the water whose temperature and pressure have been increased from the second treatment device 218. However, the monomer HD may be supplied to the supply tank 300 in a mixed state with the water. In this case, it is preferable that the mixture of the monomer HD and water is heated and pressurized to a predetermined temperature and a predetermined pressure in the supply tank 300.

[0109] The discharge system 240 is not connected to the supply tank 300. That is, the mixture of water and methanol is not discharged from the supply tank 300 via the discharge device 244, and water is not supplied to the supply tank 300 from the water treatment device 270.

[0110] The supply tank 300 preferably has a different shape from the reaction tank 310 described below. For example, the supply tank 300 is preferably a tubular (plug flow) type. That is, the area of ​​the flow path through which the fluid in the supply tank 300 flows is preferably smaller than the area of ​​the flow path through which the fluid in the reaction tank 310 flows. The supply tank 300 may also be provided with a rectifier 302 therein. The rectifier 302 is a mechanism for rectifying the flow of the fluid in the supply tank 300, and may be, for example, a plurality of tubes arranged in parallel. In this way, by being tubular or having a rectifier, the supply tank 300 can prevent the hydrolysis reaction from proceeding too quickly, and the hydrolysis reaction can be appropriately carried out in the downstream reaction tank 310 while the methanol is discharged by the discharge system 240.

[0111] The supply tank 300 is connected to the reaction tank 310 via an outlet pipe 304. When a plurality of reaction tanks 310 are provided, the supply tank 300 is connected to the reaction tank 310 that is the most upstream of the plurality of reaction tanks 310 in the direction of fluid flow. In the example of FIG. 6 , the supply tank 300 is connected to the reaction tank 310a. The DMT and water supplied into the supply tank 300 are supplied to the reaction tank 310 via the outlet pipe 304. Note that a portion of the supplied DMT may be hydrolyzed in the supply tank 300. In this case, products (e.g., MMT, methanol, PTA) produced by the hydrolysis of DMT are also supplied to the reaction tank 310. In other words, the DMT and water supplied from the supply tank 300 to the reaction tank 310 are not limited to DMT and water, but also include products produced by the hydrolysis of DMT. Furthermore, when the above-described first reaction is completed in the supply tank 300 and all of the DMT has been converted to MMT, the DMT and water supplied from the supply tank 300 to the reaction tank 310 may refer to MMT and methanol.

[0112] (Reaction Tank) The reaction tank 310 is a tank to which DMT and water are supplied from the supply tank 300. In the reaction tank 310, the DMT supplied from the supply tank 300 is hydrolyzed to produce PTA. Note that, when MMT is supplied from the supply tank 300 as a product produced by hydrolysis of DMT, the MMT may also be hydrolyzed to produce PTA. That is, in the reaction tank 310, the first reaction and the second reaction described in the first embodiment are carried out. Note that, when the first reaction is completed in the supply tank 300, only the second reaction may be carried out in the reaction tank 310.

[0113] A discharge system 240a is connected to the reaction tank 310. Therefore, a mixture of methanol and water is discharged from the reaction tank 310 by the discharge device 244, water is separated from the mixture by the separation device 260, and the water separated by the separation device 260 is heated and pressurized by the water treatment device 270. The water heated and pressurized by the water treatment device 270 is returned to the reaction tank 310 through a treated water discharge pipe 272. In this embodiment, a supply device 274 is provided in the treated water discharge pipe 272. The supply device 274 supplies water treated by the water treatment device 270 from the water treatment device 270 to the reaction tank 310. The supply device 274 is, for example, an on-off valve, and controls the supply of water from the water treatment device 270 to the reaction tank 310 by opening and closing the valve. When the valve of the supply device 274 is open, the water from the water treatment device 270 flows through the treated water discharge pipe 272 and is returned to the reaction tank 310.

[0114] In addition, an outlet pipe 344 is connected to the reaction tank 310. The PTA and water produced in the reaction tank 310 flow through the outlet pipe 344. The outlet pipe 344 is provided with a discharge unit 232. The discharge unit 232 is a device that discharges the PTA and water from inside the reaction tank 310.

[0115] When a plurality of reaction vessels 310 are provided, the reaction vessels 310 are connected in series in the fluid flow direction. The reaction vessel 310 furthest upstream in the fluid flow direction is connected to the supply vessel 300, and the reaction vessel 310 furthest downstream in the fluid flow direction is connected to the outlet pipe 344. The discharge system 240a may be connected to all of the reaction vessels 310, or to only some of the reaction vessels 310. That is, when a plurality of reaction vessels 310 are provided, the discharge system 240a may be connected to at least some of the reaction vessels 310. However, in this case, it is preferable that the discharge system 240a be connected to at least the most upstream reaction vessel 310 (the reaction vessel 310 connected to the supply vessel 300). The discharge system 240a does not need to be connected to the reaction vessel 310 furthest downstream in the fluid flow direction. 6, the reaction tank 310a is connected to the supply tank 300, the reaction tank 310b is connected to the reaction tank 310a, and the reaction tank 310c is connected to the reaction tank 310b. The reaction tank 310a is connected to a discharge system 240a, but the reaction tanks 310b and 310c are not connected to the discharge system 240a. However, the discharge system 240a may also be connected to at least one of the reaction tanks 310b and 310c.

[0116] (Control of Hydrolysis System) Next, control of the hydrolysis reaction system 200 in the second embodiment will be described. In the second embodiment, the control unit 30 controls the first treatment device 212 to increase the temperature and pressure of DMT and supply the heated and pressurized DMT to the supply tank 300. The control unit 30 also controls the second treatment device 218 to increase the temperature and pressure of water and supply the heated and pressurized water to the supply tank 300. The DMT supplied to the supply tank 300 is supplied to the reaction tank 310 while being hydrolyzed. The control unit 30 controls the discharge device 244 to discharge the mixture of water and methanol from the reaction tank 310. The control unit 30 controls the separation device 260 to separate water from the mixture of water and methanol. The control unit 30 controls the water treatment device 270 to increase the temperature and pressure of water and supply the heated and pressurized water to the reaction tank 310. This promotes the reaction of producing PTA from MMT in the reaction vessel 310, thereby properly producing PTA. The control unit 30 also controls the discharge unit 232 to discharge PTA from the reaction vessel 310.

[0117] As described above, in the second embodiment, a supply tank 300 and a reaction tank 310 are provided, and a discharge system 240 is connected to the reaction tank 310. This allows methanol to be discharged from the reaction tank 310, where MMT has been sufficiently produced, thereby promoting the reaction that produces PTA and enabling appropriate PTA production. Furthermore, by not providing the discharge system 240 (discharge device 244) in the supply tank 300, excessive discharge of water can be suppressed. Therefore, in the second embodiment, too, it is possible to suppress the amount of water discharged while discharging methanol to an extent that allows hydrolysis to be promoted, thereby enabling appropriate PTA production while suppressing energy consumption.

[0118] In the second embodiment, unlike the first embodiment, it is not necessary to adjust the timing of operating the discharge device 244. For example, in the second embodiment, the discharge device 244 may be constantly operated to constantly discharge water and methanol from the reaction tank 310.

[0119] Effect of the Present Disclosure A hydrolysis reaction system according to a first aspect of the present disclosure includes a reaction vessel 210 to which dimethyl terephthalate and water are supplied and in which the dimethyl terephthalate is hydrolyzed by the water to produce terephthalic acid and methanol; a discharge device 244 that discharges a mixture of methanol and water from the reaction vessel 210; and a control device that controls the discharge device 244, wherein the control device does not cause the discharge device 244 to discharge the mixture during a first period from when dimethyl terephthalate and water are supplied to the reaction vessel 210 to a first time T1, causes the discharge device 244 to discharge the mixture during a second period from the first time T1 to a second time T2 that is later than the first time T1, and does not cause the discharge device 244 to discharge the mixture during a third period from the second time T2 to when terephthalic acid is extracted from the reaction vessel 210, wherein the first period is shorter than the third period.

[0120] This allows the amount of methanol discharged to be sufficient to promote hydrolysis while suppressing the amount of water discharged, thereby enabling PTA to be appropriately produced while reducing energy consumption, i.e., terephthalic acid to be appropriately obtained from DMT while reducing energy consumption.

[0121] In the hydrolysis reaction system according to the second aspect of the present disclosure, the first timing T1 is the timing at which the concentration of monomethyl terephthalate, an intermediate product of hydrolysis, in the reaction tank 210 reaches 20% or more and 50% or less. This makes it possible to reduce the amount of water discharged while discharging methanol to an extent that allows hydrolysis to be promoted, thereby enabling appropriate production of PTA while reducing energy consumption.

[0122] A hydrolysis reaction system according to a third aspect of the present disclosure is the hydrolysis reaction system according to the first or second aspect, wherein the second timing T2 is the timing at which the concentration of monomethyl terephthalate, an intermediate product of hydrolysis, in the reaction tank 210 falls to 0% or more and 30% or less. This makes it possible to reduce the amount of water discharged while discharging methanol to an extent that allows hydrolysis to be promoted, thereby enabling appropriate production of PTA while reducing energy consumption.

[0123] A hydrolysis reaction system according to a fourth aspect of the present disclosure is the hydrolysis reaction system according to any one of the first to third aspects, further comprising a separation device 260 that separates water from the mixture discharged by the discharge device 244, a water treatment device that increases the temperature and pressure of the water separated by the separation device 260, and a supply device 274 that supplies the water heated and pressurized by the water treatment device 270 to the reaction tank 210. This allows the hydrolysis treatment to be performed without a shortage of water. This also leads to the prevention of precipitation of PTA in the reaction tank 210, allowing appropriate treatment in steps after hydrolysis.

[0124] A hydrolysis reaction system according to a fifth aspect of the present disclosure includes a supply tank 300 to which dimethyl terephthalate and water are supplied, a reaction tank 310 connected to the supply tank 300, to which dimethyl terephthalate and water are supplied from the supply tank 300 and in which the dimethyl terephthalate is hydrolyzed by the water to produce terephthalic acid and methanol, and a discharge device that discharges a mixture of methanol and water from the reaction tank 310. This allows the amount of water discharged to be reduced while discharging methanol to an extent that allows hydrolysis to be promoted, thereby enabling appropriate production of PTA while reducing energy consumption.

[0125] A hydrolysis reaction system according to a sixth aspect of the present disclosure is the hydrolysis reaction system according to the fifth aspect, wherein a plurality of reaction tanks 310 are provided in series, and the discharge device is connected to at least one of the reaction tanks 310. Therefore, it is possible to reduce the amount of water discharged while discharging methanol to an extent that allows hydrolysis to be promoted, and therefore it is possible to appropriately produce PTA while reducing energy consumption.

[0126] A hydrolysis reaction system according to a seventh aspect of the present disclosure is the hydrolysis reaction system according to the fifth or sixth aspect, further comprising a separation device 260 that separates water from the mixture discharged by the discharge device 244, and a water treatment device 270 that increases the temperature and pressure of the water separated by the separation device 260 and supplies the heated and pressurized water to the reaction tank 310.

[0127] This allows the hydrolysis treatment to be carried out without a shortage of water. Furthermore, the reaction of producing PTA from MMT in the reaction tank 310 is promoted, and PTA is produced appropriately.

[0128] A control method according to an eighth aspect of the present disclosure is a control method for controlling a hydrolysis reaction system including a reaction tank 210 to which dimethyl terephthalate and water are supplied and in which the dimethyl terephthalate is hydrolyzed by the water to produce terephthalic acid and methanol, and a discharge device 244 that discharges a mixture of methanol and water from the reaction tank 210, the control method including the steps of: supplying dimethyl terephthalate and water to the reaction tank 210; not causing the discharge device 244 to discharge the mixture during a first period from when the dimethyl terephthalate and water are supplied to the reaction tank 210 to a first time T1; causing the discharge device 244 to discharge the mixture during a second period from the first time T1 to a second time T2 that is later than the first time T1; and causing the discharge device 244 to discharge the mixture during a third period from the second time T2 to when terephthalic acid is extracted from the reaction tank 210, wherein the first period is shorter than the third period.

[0129] This allows the amount of methanol discharged to be sufficient to promote hydrolysis while suppressing the amount of water discharged, thereby enabling PTA to be appropriately produced while reducing energy consumption, i.e., terephthalic acid to be appropriately obtained from DMT while reducing energy consumption.

[0130] A control method according to a ninth aspect of the present disclosure is a control method for controlling a hydrolysis reaction system including: a supply tank 300 to which dimethyl terephthalate and water are supplied; a reaction tank 310 connected to the supply tank 300, to which dimethyl terephthalate and water are supplied from the supply tank 300 and in which the dimethyl terephthalate is hydrolyzed by the water to produce terephthalic acid and methanol; and a discharge device 244 that discharges a mixture of methanol and water from the reaction tank 310, the control method including the steps of supplying dimethyl terephthalate and water to the supply tank 300; and causing the discharge device 244 to discharge the mixture from the reaction tank 310.

[0131] This allows the amount of water discharged to be reduced while allowing methanol to be discharged to an extent that allows hydrolysis to be promoted, thereby enabling PTA to be appropriately produced while reducing energy consumption.

[0132] 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.

[0133] 1 Separation system 12 Dissolution section 13 Solid-liquid separation section 14 Solvent storage section 16 Reaction section 18 Separation section 30 Control section 82 Dissolution tank 86 Adjustment section 90 Crystallization tank 100 Stirring section 200, 200A Hydrolysis reaction system 210, 310, 310a, 310b, 310c Reaction tank 212 First treatment device 218 Second treatment device 240, 240a Discharge system 260 Separation device 270 Water treatment device 300 Supply tank D, E, HD Monomer M Reaction solvent P Polyester solution Pd, L Dissolved solution Pm Polyester raw material R Residual substance

Claims

1. A hydrolysis reaction system comprising: a reaction vessel to which dimethyl terephthalate and water are supplied and which hydrolyzes the dimethyl terephthalate with the water to produce terephthalic acid and methanol; a discharge device that discharges a mixture of methanol and water from the reaction vessel; and a control device that controls the discharge device, wherein the control device: does not cause the discharge device to discharge the mixture during a first period from when the dimethyl terephthalate and the water are supplied to the reaction vessel to a first timing; causes the discharge device to discharge the mixture during a second period from the first timing to a second timing that is later than the first timing; and does not cause the discharge device to discharge the mixture during a third period from the second timing to when terephthalic acid is discharged from the reaction vessel; and the first period is shorter than the third period.

2. The hydrolysis reaction system according to claim 1, wherein the first timing is the timing at which the concentration of monomethyl terephthalate, an intermediate product of hydrolysis in the reaction tank, falls to 20% or more and 50% or less.

3. The hydrolysis reaction system according to claim 1 or 2, wherein the second timing is the timing at which the concentration of monomethyl terephthalate, an intermediate product of hydrolysis in the reaction tank, falls to between 0% and 30%.

4. The hydrolysis reaction system according to claim 1 or 2, further comprising: a separation device that separates water from the mixture discharged by the discharge device; a water treatment device that increases the temperature and pressure of the water separated by the separation device; and a supply device that supplies the water heated and pressurized by the water treatment device to the reaction tank.

5. A hydrolysis reaction system comprising: a supply tank to which dimethyl terephthalate and water are supplied; a reaction tank connected to the supply tank, to which dimethyl terephthalate and water are supplied from the supply tank and in which the dimethyl terephthalate is hydrolyzed by the water to produce terephthalic acid and methanol; and a discharge device that discharges a mixture of methanol and water from the reaction tank.

6. The hydrolysis reaction system according to claim 5, wherein a plurality of the reaction vessels are provided in series, and the discharge device is connected to at least one of the reaction vessels.

7. The hydrolysis reaction system according to claim 5 or 6, further comprising: a separation device that separates water from the mixture discharged by the discharge device; a water treatment device that increases the temperature and pressure of the water separated by the separation device; and a supply device that supplies the water heated and pressurized by the water treatment device to the reaction tank.

8. A method for controlling a hydrolysis reaction system including a reaction tank to which dimethyl terephthalate and water are supplied and which hydrolyzes the dimethyl terephthalate with the water to produce terephthalic acid and methanol, and a discharge device which discharges a mixture of methanol and water from the reaction tank, the method comprising: a step of supplying the dimethyl terephthalate and water to the reaction tank; a step of not causing the discharge device to discharge the mixture during a first period from when the dimethyl terephthalate and the water are supplied to the reaction tank to a first timing; a step of causing the discharge device to discharge the mixture during a second period from the first timing to a second timing that is later than the first timing; and a step of causing the discharge device to discharge the mixture during a third period from the second timing to when terephthalic acid is discharged from the reaction tank, wherein the first period is shorter than the third period.

9. A method for controlling a hydrolysis reaction system comprising: a supply tank to which dimethyl terephthalate and water are supplied; a reaction tank connected to the supply tank, to which dimethyl terephthalate and water are supplied from the supply tank and in which the dimethyl terephthalate is hydrolyzed by the water to produce terephthalic acid and methanol; and a discharge device that discharges a mixture of methanol and water from the reaction tank, the method comprising: a step of supplying the dimethyl terephthalate and water to the supply tank; and a step of causing the discharge device to discharge the mixture from the reaction tank.

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