Separation system and separation method

Abstract

According to the present invention, an impurity is appropriately separated. This separation system comprises: a storage part in which there is stored a dissolution liquid including a polyester solution obtained by dissolving polyester in a carboxylic-acid-derived monomer, and an impurity, which is a component other than the polyester; a gas supply part which supplies a gas into the storage part, and causes the impurity in the dissolution liquid to move upward; a discharge part which discharges the impurity in the storage part; and a reaction part into which the polyester solution from which the impurity has been separated, and a reaction solvent that reacts with polyester, are introduced, and which is for depolymerizing the polyester in the polyester solution.

Description

Separation System and Separation Method

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

[0002] For example, in order to recycle polyester, a technique for separating impurities from polyester is known. Patent Document 1 describes that polyethylene terephthalate (PET) waste is put into ethylene glycol (EG) for depolymerization to obtain bis(β-hydroxyethyl) terephthalate (BHET), and that foreign substances other than PET are removed by a filter during or after the depolymerization reaction.

[0003] Japanese Patent No. 4065659

[0004] In order to efficiently recover polyester, it is required to appropriately separate impurities.

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

[0006] In order to solve the above-described problems and achieve the object, the separation system according to the present disclosure includes a storage unit that stores a polyester solution in which polyester is dissolved in a monomer derived from a carboxylic acid, and an impurity that is a component other than the polyester; a gas supply unit that supplies gas into the storage unit to move the impurities in the solution upward; a discharge unit that discharges the impurities in the storage unit; and a reaction unit that is introduced with the polyester solution from which the impurities have been separated and a reaction solvent that reacts with the polyester to depolymerize the polyester in the polyester solution.

[0007] To solve the above-mentioned problems and achieve the objective, the separation method according to the present disclosure includes the steps of: storing a dissolution containing a polyester solution in which polyester is dissolved in a monomer derived from a carboxylic acid, and impurities which are components other than polyester, in a storage unit; supplying gas into the storage unit to move the impurities in the dissolution upward; discharging the impurities from the storage unit; and introducing the polyester solution from which the impurities have been separated and a reaction solvent that reacts with polyester to depolymerize the polyester in the polyester solution.

[0008] According to this disclosure, impurities can be properly separated.

[0009] Figure 1 is a schematic diagram of the polyester recycling process in an embodiment. Figure 2 is a schematic diagram of the separation system according to the embodiment. Figure 3 is an explanatory diagram illustrating the gas supply. Figure 4 is a flowchart illustrating the operation flow of the separation system.

[0010] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. However, the present invention is not limited to these embodiments, and if there are multiple embodiments, they may be constructed by combining these embodiments.

[0011] (Recycling Process) Figure 1 is a schematic diagram of the polyester recycling process in this embodiment. In this embodiment, the polyester raw material Pm is depolymerized to monomerize it, and the monomer is repolymerized to recycle (regenerate) the polyester raw material Pm. Specifically, as shown in Figure 1, the polyester raw material Pm is flakened (step S100), the flakened polyester raw material Pm is dissolved in monomer D derived from carboxylic acid to produce a polyester solution (step S101), foreign matter is removed from the solution (step S102), the solution from which foreign matter has been removed is mixed with reaction solvent M and depolymerized (step S103), the monomer of the depolymerized polyester is purified (separated) to produce monomer D derived from carboxylic acid and monomer E of the alcohol component (step S104), monomer D is hydrolyzed to separate the reaction solvent M (step S106), and monomer F produced by the hydrolysis of monomer D and monomer E are polymerized (step S108) to regenerate the polyester raw material Pm. In addition, the recycling process employing the separation system 1 of this embodiment may omit the flake formation in step S100, or it may only involve the recovery of monomers D and E shown in steps S102 and S104, and monomer F shown in step S106, without performing the repolymerization process as in step S108.

[0012] (Polyester Raw Material) In this embodiment, the polyester raw material Pm to be depolymerized is a substance containing polyester. The polyester raw material Pm is not particularly limited, but examples include waste materials such as polyethylene terephthalate (PET), polyethylene butylene terephthalate (PEBT), polybutylene terephthalate (PBT), polycyclohexanedimethyl terephthalate (PCT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and polycarbonate (PC). The polyester raw material Pm is not limited to containing only polyester components, but may also contain components other than polyester (impurities). 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, polymerization catalysts, and organofluorine compounds (e.g., PFAS (Per- and Polyfluorescent Substances)). As an example of polyester raw material Pm, clothing in which polyester and other components are woven into fibers is also provided. Hereinafter, components other than polyester contained in the polyester raw material Pm will be referred to as impurities R. If impurities R contain organofluorine compounds (PFAS), then the organofluorine compounds are present in at least one of the following states: solid, liquid, and oil droplets. The following explanation will use the case where the organofluorine compound is PFAS as an example.

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

[0014] (Carboxylic acid-derived monomer) Monomer D derived from a carboxylic acid is a monomer having a carboxyl group, produced by the depolymerization reaction of a polyester. Monomer D may be, for example, dimethyl carboxylate or diethyl carboxylate. More specifically, monomer D is preferably a monomer of terephthalic acid, for example, dimethyl terephthalate (DMT).

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

[0016] In the following explanation, we will use the case where the polyester is PET, the reaction solvent M is methanol, the monomer D is DMT, and the monomer E is EG as an example.

[0017] (Separation System) Figure 2 is a schematic diagram of the separation system according to this embodiment. The separation system 1 according to this embodiment is a system that monomerizes polyester contained in the polyester raw material Pm to produce monomers D and E. As shown in Figure 1, the separation system 1 has a raw material storage section 10, a dissolution section 12, a solid-liquid separation section 13, a reaction solvent storage section 14, a reaction section 16, a separation section 18, a storage section 20, a gas supply section 21, a discharge section 22, a removal section 26, and a control section 30.

[0018] (Raw Material Storage Section) The raw material storage section 10 is a tank into which polyester raw material Pm is introduced and stored. In this embodiment, flake-formed polyester raw material Pm is stored in the raw material storage section 10, but the shape and size of the polyester raw material Pm may be arbitrary. The raw material storage section 10 is connected to the dissolution section 12 via an introduction pipe 10a. The polyester raw material Pm in the raw material storage section 10 is supplied to the dissolution section 12 through the introduction pipe 10a. The introduction pipe 10a is provided with an adjustment section 10b that adjusts the amount of polyester raw material Pm supplied from the raw material storage section 10 to the dissolution section 12. The adjustment section 10b is, for example, an on / off valve, which, when open, allows the polyester raw material Pm in the raw material storage section 10 to be supplied to the dissolution section 12, and when closed, stops the supply of polyester raw material Pm from the raw material storage section 10 to the dissolution section 12. However, the adjustment unit 10b is not limited to an on / off valve, and may be any mechanism capable of adjusting the supply of polyester raw material Pm to the melting unit 12. Furthermore, the polyester raw material Pm may be supplied directly to the melting unit 12 without passing through the raw material storage unit 10, the introduction pipe 10a, and the adjustment unit 10b.

[0019] (Dissolution section) The dissolution section 12 is a tank in which the dissolution solution Pd is stored. The dissolution solution Pd is a solution produced by mixing polyester raw material Pm and monomer D. Here, the polyester contained in the polyester raw material Pm dissolves in monomer D, but impurities R, which are components other than polyester contained in the polyester raw material Pm, remain without dissolving in monomer D. Therefore, it can be said that the dissolution solution Pd contains polyester solution P, in which the polyester contained in the polyester raw material Pm is dissolved in monomer D, and impurities R contained in the polyester raw material Pm.

[0020] Monomer D and polyester raw material Pm are supplied to the dissolution section 12. Within the dissolution section 12, the polyester contained in the polyester raw material Pm dissolves in the monomer D, while the impurity R remains undissolved in the monomer D, thereby generating a polyester solution P and a dissolution solution Pd containing the impurity R. By dissolving the polyester in the monomer D in this way, 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 the entire amount of polyester dissolved in the monomer D; at least some of the polyester may remain undissolved in the monomer D. Furthermore, if there are components other than polyester contained in the polyester raw material Pm that are soluble in the monomer D, the polyester solution P may also contain those components dissolved in the monomer D.

[0021] In this embodiment, the dissolution section 12 is provided with a heating section 12A. The heating section 12A heats the inside of the dissolution section 12, thereby heating the monomer D and polyester raw material Pm supplied to the dissolution section 12 to a predetermined temperature. The predetermined temperature is the temperature at which polyester can dissolve in monomer D. By heating to this predetermined temperature, the polyester contained in the polyester raw material Pm can be appropriately dissolved in monomer D. The predetermined temperature is preferably 140°C to 300°C, more preferably 160°C to 280°C, and even more preferably 190°C to 250°C. Note that the impurities R also include components that melt when heated to the predetermined temperature (the temperature at which polyester can dissolve in monomer D). Therefore, if the impurities R include components that melt when heated to the predetermined temperature, a portion of them will be contained in the dissolution solution Pd in ​​a molten state. In this embodiment, the heating section 12A is provided in the dissolution section 12, but the location where the heating section 12A is provided is not limited to this and is arbitrary.

[0022] (Solid-Liquid Separation Section) The solid-liquid separation section 13 is located in the dissolution section 12. The solid-liquid separation section 13 collects solid impurities R contained in the dissolution liquid Pd stored in the dissolution section 12 and separates the solid impurities R from the dissolution liquid Pd. The solid-liquid separation section 13 is a mesh-shaped filter through which liquid passes and which collects solids. In this embodiment, the solid-liquid separation section 13 is a container shape with an open top and is located at a predetermined distance from the sides and bottom of the dissolution section 12. The solid-liquid separation section 13 is located downstream of the inlet pipe 10a and the supply pipe to which monomer D is supplied, and upstream of the inlet pipe 12a that supplies the dissolution liquid Pd from the dissolution section 12 to the storage section 20 downstream. The dissolution liquid Pd flowing from the dissolution section 12 into the inlet pipe 12a passes through the solid-liquid separation section 13. As a result, the solid-liquid separation section 13 collects solids larger than the opening diameter of the mesh. The solid-liquid separation section 13 preferably has a mesh opening diameter of 1 mm or more and 50 mm or less.

[0023] In this embodiment, the solid-liquid separation unit 13 uses a mesh-shaped filter for filtration, but is not limited to this. The solid-liquid separation unit 13 may also separate impurities R from the dissolving solution Pd by centrifugal separation, which stirs the inside of the dissolving unit 12 around a predetermined axis and moves the impurities radially outward from the axis of rotation. The solid-liquid separation unit 13 only needs to be able to separate solid impurities of a predetermined size or larger from the dissolving solution Pd, and is not limited to filtration or centrifugal separation.

[0024] The foreign matter recovery unit 50 recovers solid impurities collected by the solid-liquid separation unit 13. The foreign matter recovery unit 50 recovers impurities attached to the filter of the solid-liquid separation unit 13, for example. The solid-liquid separation unit 13 may also be equipped with a press device that presses impurities attached to a mesh-shaped filter against the filter and squeezes out the dissolving liquid Pd contained in the impurities. By squeezing out the dissolving liquid with the press device before the foreign matter recovery unit 50 recovers the impurities, more dissolving liquid Pd can be left in the separation system 1. When the solid-liquid separation unit 13 separates by centrifugal separation, the foreign matter recovery unit 50 recovers impurities from the region where impurities are stored by centrifugal separation.

[0025] (Storage section) The storage section 20 is a tank in which the dissolving solution Pd is stored. The storage section 20 is connected to the dissolving section 12 via an introduction pipe 12a. The dissolving solution Pd in ​​the dissolving section 12 is supplied to the storage section 20 through the introduction pipe 12a. The introduction pipe 12a is provided with an adjustment section 12a1 that adjusts the amount of dissolving solution Pd supplied from the dissolving section 12 to the storage section 20. The adjustment section 12a1 is, for example, an on-off valve, which, when open, allows the dissolving solution Pd in ​​the dissolving section 12 to be supplied to the storage section 20, and when closed, stops the supply of dissolving solution Pd from the dissolving section 12 to the storage section 20. However, the adjustment section 12a1 is not limited to an on-off valve, and may be any mechanism capable of adjusting the supply of dissolving solution Pd to the storage section 20. In this embodiment, the storage unit 20 is connected to the dissolution unit 12 via the introduction pipe 12a, but a temporary storage unit for temporarily storing the dissolving solution Pd can also be provided between the dissolution unit 12 and the storage unit 20.

[0026] A gas supply unit 21, described later, is connected to the storage unit 20 via a gas supply pipe 21b. Gas G is supplied to the storage unit 20 from the gas supply unit 21.

[0027] In the storage section 20, the dissolving solution Pd is separated by gravity into the polyester solution P and impurities R. Here, the impurities R separated in the storage section 20 are impurities that were not recovered in the solid-liquid separation section 13 and moved to the storage section 20 together with the dissolving solution Pd. In this embodiment, the dissolving solution Pd stored in the storage section 20 is allowed to stand, and is separated by gravity into the polyester solution P and impurities R.

[0028] In this embodiment, the dissolution Pd stored in the storage section 20 is separated by gravity into a layer of first impurity R1, a layer of polyester solution P, and a layer of second impurity R2. The layer of first impurity R1 is formed vertically below the layer of polyester solution P. That is, first impurity R1 is an impurity R that does not dissolve in monomer D and has a specific gravity greater than that of polyester solution P. First impurity R1 settles in the polyester solution P within the storage section 20 to form the layer of first impurity R1. On the other hand, the layer of second impurity R2 is formed vertically above the layer of polyester solution P. That is, second impurity R2 is an impurity R that does not dissolve in monomer D and has a specific gravity less than that of polyester solution P. Second impurity R2 floats in the polyester solution P within the storage section 20 to form the layer of second impurity R2.

[0029] Furthermore, the dissolving solution Pd in ​​the storage section 20 is maintained at a predetermined temperature (a temperature at which polyester can dissolve in monomer D). At least some components of the first impurity R1 and the second impurity R2 are components of impurity R that melt when heated to the predetermined temperature, and therefore exist in a molten state in the storage section 20. The first impurity R1 and the second impurity R2 are, for example, plastics other than polyester (such as polyethylene other than polyester, polystyrene, polypropylene, polyvinyl chloride, etc.).

[0030] In this embodiment, the polyester solution P layer contains a third impurity R3. At least a portion of the components of the third impurity R3 are components of impurity R that do not dissolve in monomer D and do not melt even at a predetermined temperature (the temperature at which polyester can dissolve in monomer D). That is, at least a portion of the components of the third impurity R3 are not separated from the polyester solution P by gravity separation and exist in the polyester solution P in an insoluble solid state. In this embodiment, the third impurity R3 is dispersed in the polyester solution P. The third impurity R3 is, for example, a dye, a pigment, a polymerization catalyst, etc.

[0031] Furthermore, since PFAS, one of the impurities R, has a lower specific gravity than the polyester solution P, it is included in at least one of the second impurity R2 and the third impurity R3, but it may also be included in the first impurity R1 without floating in the polyester solution P.

[0032] (Gas supply unit) The gas supply unit 21 supplies gas G to the storage unit 20, thereby moving impurities R in the dissolving solution Pd within the storage unit 20 upwards. The gas G supplied from the gas supply unit 21 becomes bubbles in the dissolving solution Pd and rises within the dissolving solution Pd. As the gas G bubbles rise, at least some of the impurities R in the dissolving solution Pd also rise within the dissolving solution Pd. This allows components of the impurities R, such as PFAS, which have a lower specific gravity than the polyester solution P, to float to the upper layer of the dissolving solution Pd and be properly separated from the polyester solution P. The impurities R that rise with the gas G bubbles and float to the upper layer of the dissolving solution Pd form a layer of second impurities R2.

[0033] Figure 3 is an explanatory diagram illustrating the gas supply. The gas supply unit 21 includes a main body 21a, a gas supply pipe 21b, a gas adjustment unit 21c, and a nozzle 21d (see Figure 3). The gas supply unit 21 is connected to the storage unit 20 via the gas supply pipe 21b. The gas supply unit 21 is connected to the lower part of the storage unit 20.

[0034] In this embodiment, gas G is, for example, an inert gas. Examples of inert gases include nitrogen and noble gases (e.g., helium and argon). The following explanation will use the case where gas G is nitrogen as an example.

[0035] The main body 21a stores gas G. The main body 21a supplies the stored gas G to the storage section 20.

[0036] The gas supply pipe 21b is connected to the storage section 20. The gas supply pipe 21b is a pipe through which the gas G supplied from the main body 21a passes. The gas supply pipe 21b has a gas supply port 21b1 formed on one end and a gas outlet port 21b2 formed on the other end. The gas supply port 21b1 is connected to the main body 21a, and the gas outlet port 21b2 is connected to the storage section 20. The gas G is supplied to the storage section 20 through the gas supply pipe 21b. The gas supply pipe 21b is provided with a gas adjustment section 21c that adjusts the amount of gas G supplied from the main body 21a to the storage section 20.

[0037] The gas adjustment unit 21c is, for example, an on-off valve, which, when open, supplies gas G from the main body 21a to the storage unit 20, and when closed, stops the supply of gas G from the main body 21a to the storage unit 20. However, the gas adjustment unit 21c is not limited to an on-off valve, and may be any mechanism capable of adjusting the supply of gas G to the storage unit 20.

[0038] The nozzle 21d discharges gas G into the storage section 20. The nozzle 21d is provided at the gas outlet 21b2. The nozzle 21d is provided such that its opening 21d1 faces into the storage section 20. The nozzle 21d has a shape that satisfies the diameter of the bubble described later. For example, the nozzle 21d is conical. The opening 21d1 is circular. Note that the shape of the nozzle 21d and the shape of the opening 21d1 may be any shape as long as they satisfy the diameter of the bubble.

[0039] A detailed explanation of the supply of gas G by the gas supply unit 21 will be given later.

[0040] (Discharge section) The discharge section 22 is a mechanism for discharging impurities R separated from the polyester solution P in the storage section 20 to the outside of the storage section 20. The configuration of the discharge section 22 may be arbitrary, but in this embodiment, the discharge section 22 has a first discharge section 22a and second discharge sections 22b1 and 22b2.

[0041] The first discharge section 22a discharges the first impurity R1 from the storage section 20. In this embodiment, the first discharge section 22a is provided on a discharge pipe 20a connected to the storage section 20. The discharge pipe 20a is a pipe for discharging the first impurity R1, which has been separated to a lower layer from the polyester solution P, from the storage section 20. The discharge pipe 20a is connected to a position in the storage section 20 where the layer of the first impurity R1 is formed, and in this embodiment, it is connected to the bottom of the storage section 20. The first discharge section 22a is a mechanism for discharging the first impurity R1 from the storage section 20, and in this embodiment, it is a pump.

[0042] The second discharge sections 22b1 and 22b2 discharge the second impurity R2 from the storage section 20. The storage section 20 is connected to a discharge pipe 20b, which is provided with the second discharge section 22b2. The discharge pipe 20b is a pipe for discharging the second impurity R2, which has been separated to the upper layer above the polyester solution P, from the storage section 20. The discharge pipe 20b is connected to the position where the layer of the second impurity R2 in the storage section 20 is formed, and is connected vertically above the discharge pipe 20a. In this embodiment, the second discharge section 22b1 is a skimmer provided at the liquid surface of the polyester solution P, which recovers (scrapes off) the second impurity R2 floating on the liquid surface of the polyester solution P. The second discharge section 22b2 is provided on the discharge pipe 20b and is a mechanism for discharging the second impurity R2 recovered in the second discharge section 22b1 via the discharge pipe 20b, and in this embodiment it is a pump. Thus, in this embodiment, second discharge sections 22b1 and 22b2 are provided as a mechanism for discharging the second impurity R2, but the configuration of the second discharge section for discharging the second impurity R2 is not limited to this and may be arbitrary.

[0043] The first impurity R1 and the second impurity R2 separated from the polyester solution P in the storage unit 20 are discharged to the outside of the storage unit 20 through the first discharge unit 22a and the second discharge units 22b1 and 22b2. Thereby, the first impurity R1 and the second impurity R2 are removed from the polyester solution P. In the above description, the impurity R includes the first impurity R1 with a specific gravity greater than that of the polyester solution P and the second impurity R2 with a specific gravity smaller than that of the polyester solution P. However, the impurity R is not limited thereto, and the impurity R may include only one of the first impurity R1 and the second impurity R2.

[0044] In the above description, the second impurity R2 is discharged from the storage unit 20 by the second discharge unit 22b1 which is a skimmer. However, for example, it may be discharged from the storage unit 20 by overflow. In this case, for example, the upper end surface of the wall of the tank constituting the storage unit 20 forms the second discharge unit 22b1, and when the second impurity R2 reaches a position higher than the second discharge unit 22b1 (the upper end surface of the wall) due to the rise of the liquid level of the polyester solution P or the accumulation of the second impurity R2, it is discharged to the outside from the second discharge unit 22b1. The second discharge unit 22b1 may have a lower height than, for example, the upper end surface of other parts of the wall of the storage unit 20. Thereby, the second impurity R2 is preferentially discharged from the portion where the second discharge unit 22b1 is formed. When the second impurity R2 is discharged from the storage unit 20 by overflow, the skimmer may not be provided. Further, the overflow is not limited to the method described above.

[0045] (Outlet section) An inlet pipe 20c is connected to the storage section 20. The inlet pipe 20c is a pipe for discharging the polyester solution P separated from impurities R from the storage section 20. The inlet pipe 20c is connected to a position in the storage section 20 where a layer of polyester solution P is formed, and in this embodiment, it is connected to a position between the discharge pipe 20a and the discharge pipe 20b in the vertical direction. An outlet section 24 is provided on the inlet pipe 20c. The outlet section 24 is a mechanism for discharging the polyester solution P from the storage section 20, and in this embodiment, it is a pump. In this embodiment, the inlet pipe 20c is provided as an inlet pipe 20c1 connecting the storage section 20 and the filter 26a described later, an inlet pipe 20c2 connecting the filter 26a and the adsorption tower 26b described later, and an inlet pipe 20c3 connecting the adsorption tower 26b and the reaction section 16.

[0046] (Removal section) The removal section 26 is a mechanism for removing the third impurity R3 contained in the polyester solution P from the polyester solution P. The removal section 26 is connected downstream of the storage section 20 and removes the third impurity R3 present in the polyester solution P discharged from the storage section 20 from the polyester solution P. In this embodiment, the removal section 26 is provided with a filter 26a and an adsorption tower 26b.

[0047] (Filter) The filter 26a is connected to the storage section 20 via an inlet pipe 20c1. The polyester solution P discharged from the storage section 20 is introduced into the filter 26a through the inlet pipe 20c1. The filter 26a uses a filter to capture solid components contained in the third impurity R3 of the polyester solution P. For example, if the third impurity R3 contains PFAS, the filter 26a also uses a filter to capture PFAS dispersed in the polyester solution P in a solid state. For example, the filter 26a also uses a filter to capture PFAS dispersed in the polyester solution P in the form of oil droplets. The filter is preferably, for example, a ceramic filter.

[0048] (Adsorption Tower) The adsorption tower 26b is connected to the filter 26a via the introduction pipe 20c2. The polyester solution P (the polyester solution P after the solid components are collected by the filter 26a) discharged from the filter 26a is introduced into the adsorption tower 26b through the introduction pipe 20c2. The adsorption tower 26b has a collecting section for collecting the third impurity R3 contained in the polyester solution P. The collecting section of the adsorption tower 26b may be an adsorbent that adsorbs the third impurity R3 contained in the polyester solution P, or may be a filtering section that collects the third impurity by filtration. That is, the adsorption tower 26b may collect the third impurity R3 by at least one of adsorption or filtration. The adsorbent stored in the adsorption tower 26b is preferably one that can adsorb the molecular skeletons (for example, quinone group, azo group, heterocyclic ring, benzene ring) of the third impurity R3. Further, the adsorbent is preferably one that can adsorb PFAS dispersed in the polyester solution P that has passed through the filter 26a. The adsorbent is preferably activated carbon, for example.

[0049] The adsorption tower 26b is connected to the reaction section 16 described below via the introduction pipe 20c3. That is, the polyester solution P after the third impurity is removed in the adsorption tower 26b is introduced into the reaction section 16 through the introduction pipe 20c3.

[0050] In this manner, the polyester solution P led from the storage section 20 to the introduction pipe 20c1 is introduced into the filter 26a, where at least a portion of the third impurity R3 contained in the polyester solution P is collected by the filter 26a. The third impurity R3 collected by the filter 26a is discharged to the outside through the discharge pipe 26a1 connected to the filter 26a. In the example of Figure 2, the discharge pipe 26a1 is connected to the discharge pipe 20a, but it is not necessary for it to be connected to the discharge pipe 20a. The polyester solution P from which at least a portion of the third impurity R3 has been removed by the filter 26a is led out of the filter 26a and introduced into the adsorption tower 26b. In the adsorption tower 26b, any remaining third impurity R3 in the polyester solution P is adsorbed or filtered by the adsorption tower 26b and removed from the polyester solution P. The third impurity R3 adsorbed or filtered by the adsorption tower 26b is, for example, a dye or a polymerization catalyst. The polyester solution P from which the third impurity R3 has been removed by the adsorption tower 26b is discharged from the adsorption tower 26b and introduced into the reaction section 16 through the introduction tube 20c.

[0051] Thus, in this embodiment, a filter 26a and an adsorption tower 26b are provided as a mechanism for removing the third impurity R3 from the polyester solution P. However, the configuration of the removal unit 26 that discharges the third impurity R3 is not limited to this and may be arbitrary.

[0052] (Reaction Solvent Storage Section) The reaction solvent storage section 14 is a tank into which the reaction solvent M is introduced and stored. The reaction solvent storage section 14 is connected to the reaction section 16 via an introduction pipe 14a. The reaction solvent M in the reaction solvent storage section 14 is supplied to the reaction section 16 through the introduction pipe 14a. More specifically, the introduction pipe 14a is provided with a heating and pressurizing section 14b that pressurizes and heats the reaction solvent M. The heating and pressurizing section 14b pressurizes and heats the reaction solvent M, thereby bringing the reaction solvent M to a supercritical or subcritical state (pressurized gas or pressurized liquid). The reaction section 16 is supplied with the reaction solvent M in a supercritical or subcritical state (pressurized gas or pressurized liquid).

[0053] (Reaction Section) The reaction section 16 is a mechanism that generates a reaction solvent in which the depolymerized polyester is dissolved. Specifically, the reaction section 16 is a container into which the polyester solution P, separated from impurities R in the storage section 20, and the reaction solvent M are introduced to depolymerize the polyester in the polyester solution P. The reaction section 16 includes a first reaction section 16A and a second reaction section 16B. Hereinafter, within the reaction section 16, the direction from the first reaction section 16A toward the second reaction section 16B will be referred to as direction Y1, and the opposite direction to direction Y1 (the direction from the second reaction section 16B toward the first reaction section 16A) will be referred to as direction Y2. In this embodiment, direction Y2 is the direction of gravity (downward vertically).

[0054] (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 described as a section within the reaction section 16 that is filled with a packing material. As the packing material for the first reaction section 16A, known materials used in gas-liquid or liquid-liquid contact devices can be used, and for example, materials similar to those used in contact devices that extract active ingredients by bringing heavy oil and water into contact can be used. Specific examples of packing materials include pipes made of SUS, etc., Raschig rings, Berl saddles, Terralets, balls, etc.

[0055] An introduction tube 20c is connected to the first reaction section 16A. More specifically, an inlet 16C of the introduction tube 20c, which is an opening into which the polyester solution P from the storage section 20 is introduced, is connected to the first reaction section 16A. The inlet 16C is connected to the surface 16A1 of the first reaction section 16A on the first direction Y1 side. The introduction tube 20c is connected to the surface 16A1 such that the inlet 16C opens facing the second direction Y2 side, opposite to the first direction Y1. Thus, in this embodiment, the inlet 16C that opens facing the second direction Y2 side is connected to the surface 16A1 of the first reaction section 16A, but it is not limited to this. For example, the inlet 16C does not have to be directly connected to the first reaction section 16A, and the inlet 16C that opens facing the second direction Y2 side may be connected to the first direction Y1 side of the surface 16A1 of the first reaction section 16A within the reaction section 16.

[0056] An inlet tube 14a is connected to the reaction section 16. More specifically, an inlet port 16D of the inlet tube 14a, into which the reaction solvent M from the reaction solvent storage section 14 is introduced, is connected to the reaction section 16. The inlet port 16D is connected to the second direction Y2 side of the surface 16A2 of the first reaction section 16A on the second direction D2 side. The inlet tube 14a is connected to the second direction Y2 side of the surface 16A2 such that the inlet port 16D opens facing the first direction Y1 side or facing from the side toward the center. Thus, in this embodiment, the inlet port 16D, which opens facing the first direction Y1 side or facing from the side toward the center, is connected to the second direction Y2 side of the surface 16A2 of the first reaction section 16A, but is not limited to this. For example, the inlet port 16D may be directly connected to the first reaction section 16A, or it may be connected to the surface 16A2 of the first reaction section 16A.

[0057] Thus, in this embodiment, the inlet 16C into which the polyester solution P is introduced opens facing the second direction Y2, and the inlet 16D into which the reaction solvent M is introduced opens facing the first direction Y1, or facing from the side toward the center. Therefore, the polyester solution P and the reaction solvent M are introduced into the first reaction section 16A in directions facing each other.

[0058] The polyester solution P introduced into the first reaction section 16A from the inlet 16C moves along the surface of the packing material in the first reaction section 16A in the second direction Y2. Meanwhile, the reaction solvent M in a supercritical or subcritical state (pressurized gas or pressurized liquid) introduced from the inlet 16D moves within the first reaction section 16A in the first direction Y1. In the first reaction section 16A, the reaction solvent M in a supercritical or subcritical state (pressurized gas or pressurized liquid) comes into contact with the polyester solution P. The polyester in the polyester solution P is depolymerized (reduced to a lower molecular weight) by the reaction solvent M, and the depolymerized polyester is extracted into the reaction solvent M in a supercritical or subcritical state (pressurized gas or pressurized liquid). Hereinafter, the polyester depolymerized in the first reaction section 16A will be referred to as the 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 was extracted) will be referred to as the first solvent M1. The first solvent M1 containing the first depolymerized polyester P1 proceeds through the first reaction section 16A toward the first direction Y1 and is led out toward the first direction Y1 of the first reaction section 16A.

[0059] The first depolymerized polyester P1 includes monomers D and E produced by the depolymerization of polyester in polyester solution P, monomer D which was originally mixed in polyester solution P, and oligomers produced by the depolymerization of polyester. Here, oligomers are oligomers of carboxylic acid-derived or alcohol components that have not been monomerized but have been depolymerized from polyester (oligomers of carboxylic acid-derived or alcohol components with a smaller molecular weight than polyester).

[0060] (Second reaction section) The second reaction section 16B is formed within the reaction section 16, and is located where the first solvent M1 is discharged from the first reaction section 16A. In this embodiment, since the first solvent M1 is discharged in the first direction Y1, the second reaction section 16B can be described as a space formed in the first direction Y1 on the side of the first reaction section 16A.

[0061] In the second reaction section 16B, the first depolymerized polyester P1 contained in the first solvent M1 is further depolymerized (reduced to a lower molecular weight) by the reaction solvent M contained in the first solvent M1. Hereinafter, the first depolymerized polyester P1 further depolymerized in the second reaction section 16B will be referred to as the second depolymerized polyester P2, and the mixture of the second depolymerized polyester P2 and the reaction solvent M (the reaction solvent M in which the second depolymerized polyester P2 is dissolved) will be referred to as the second solvent M2. A discharge tube 16a is connected to the second reaction section 16B. More specifically, an outlet 16E of the discharge tube 16a, which is an opening from which the second solvent M2 from the second reaction section 16B is discharged, is connected to the second reaction section 16B. The second solvent M2 containing the second depolymerized polyester P2 in the second reaction section 16B is discharged from the outlet 16E through the discharge tube 16a to the outside of the second reaction section 16B.

[0062] The second depolymerized polyester P2 includes monomers D and E from the first depolymerized polyester P1, monomers D and E produced by the depolymerization of the oligomer in the first depolymerized polyester P1, and oligomers produced by the depolymerization of the first depolymerized polyester P1.

[0063] A discharge pipe 16b is connected to the bottom of the reaction section 16. More specifically, an outlet 16F of the discharge pipe 16b is connected to the bottom of the reaction section 16, which is an opening from which non-extracted substances (described later) from the reaction section 16 are discharged. Non-extracted substances, including impurities such as metal compounds that were not extracted by the reaction solvent M, and residues of undecomposed polyester that were not extracted by the reaction solvent M, are discharged from the outlet 16F. In other words, the non-extracted substances at the bottom of the reaction section 16 are discharged to the outside of the reaction section 16 through the outlet 16F and the discharge pipe 16b. The non-extracted substances discharged from the outlet 16F can be said to be components of the polyester solution P that remained in the first reaction section 16A and the second reaction section 16B without being led to the separation section 18 as the second solvent M2 (reaction solvent M in which the second depolymerized polyester P2 is dissolved).

[0064] Furthermore, the reaction section 16 may be provided with a heating section for heating the inside of the reaction section 16 and a pressurizing section for maintaining the internal pressure of the reaction section 16 above a predetermined value. The internal temperature of the reaction section 16 is preferably 250°C to 400°C, and more preferably 250°C to 350°C. The internal pressure of the reaction section 16 is preferably 1 MPa to 30 MPa, and more preferably 6 MPa to 25 MPa. The pressurizing section and the heating section may be controlled by the control unit 30.

[0065] (Separation section) The separation section 18 is introduced with a second solvent M2 containing the second depolymerized polyester P2, and separates the second solvent M2 into reaction solvent M, monomer D derived from carboxylic acid contained in the second depolymerized polyester P2, monomer E of the alcohol component contained in the second depolymerized polyester P2, and residual substances. The separation section 18 separates the second solvent M2 into monomer D, monomer E, and residual substances by distillation. The residual substances are components of the second solvent M2 other than reaction solvent M, monomer D, and monomer E, and include oligomers.

[0066] In this embodiment, the separation unit 18 has a first separation unit 18A, a second separation unit 18B, and a third separation unit 18C.

[0067] The first separation section 18A is a separation tower connected to the outlet pipe 16a. The 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 point component and a high-boiling point component with a higher boiling point than the low-boiling point 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 point component and the liquid component being the high-boiling point component. Outlet pipes 18Aa and 18Ab are connected to the first separation section 18A. The low-boiling point component is discharged from outlet pipe 18Aa, and the high-boiling point component is discharged from outlet pipe 18Ab.

[0068] The second separation section 18B is a separation column connected to the first separation section 18A via a discharge tube 18Aa. Low-boiling point components are introduced into the second separation section 18B via the discharge tube 18Aa. The second separation section 18B separates the low-boiling point components into a reaction solvent M and monomer E. Discharge tubes 18Ba and 18Bb are connected to the second separation section 18B. The reaction solvent M is discharged from discharge tube 18Ba, and monomer E is discharged from discharge tube 18Bb. Discharge tube 18Ba is connected to both the second separation section 18B and the reaction solvent storage section 14. Therefore, the reaction solvent M discharged from the second separation section 18B is returned to the reaction solvent storage section 14 and reused for polyester depolymerization.

[0069] The third separation section 18C is a separation column connected to the first separation section 18A via a discharge tube 18Ab. High-boiling-point components are introduced into the third separation section 18C via the discharge tube 18Ab. The third separation section 18C further separates the high-boiling-point components into residual high-boiling-point substances, low-boiling-point components containing the reaction solvent M and monomer E, and monomer D. Discharge tubes 18Ca, 18Cb, and 18Cc are connected to the third separation section 18C. Discharge tube 18Ca is connected to the second separation section 18B. The low-boiling-point components separated in the third separation section 18C are discharged to the second separation section 18B via the discharge tube 18Ca. The monomer D separated in the third separation section 18C is discharged from the discharge tube 18Cb, and the residual substances separated in the third separation section 18C are discharged from the discharge tube 18Cc.

[0070] An introduction pipe 18Cd is connected to the third separation section 18C. The introduction pipe 18Cd is also connected to the dissolution section 12, and introduces the monomer D discharged from the third separation section 18C into the dissolution section 12. In the example shown in Figure 2, the introduction pipe 18Cd branches off from the outlet pipe 18Cb. The introduction 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 dissolution section 12. The adjustment section 18Ce is, for example, an on-off valve, which, when open, allows the supply of monomer D to the dissolution section 12, and when closed, stops the supply of monomer D to the dissolution 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 dissolution section 12. In this embodiment, the adjustment section 18Ce is provided at the branching point of the introduction pipe 18Cd from the outlet pipe 18Cb, but it is not limited to that position and may be provided at any location. 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 18C. Alternatively, for example, the outlet pipe 18Cb may be provided with a storage section (tank) for storing monomer D, and the inlet pipe 18Cd may be connected to the storage section.

[0071] Furthermore, by connecting the outlet tube 18Cc to the dissolution section 12, at least a portion of the residual substance may be introduced into the dissolution section 12. By introducing the residual substance into the dissolution section 12, it becomes possible to depolymerize the oligomers contained in the residual substance again in the reaction section 16, thereby improving the monomer yield.

[0072] Furthermore, when the second solvent M2 containing the second depolymerized polyester P2 is separated in the separation unit 18, if PFAS is present in the remaining substance, the remaining PFAS is separated by distillation.

[0073] (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. The control unit 30 controls the foreign matter recovery unit 50 to recover impurities collected in the solid-liquid separation unit 13. Also, 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 adjustment unit 12a1 to control the amount of dissolving solution Pd supplied from the dissolution unit 12 to the storage unit 20. The control unit 30 controls the discharge unit 22 to discharge the impurities R separated from the polyester solution P in the storage unit 20 from the storage unit 20. The control unit 30 controls the discharge unit 24 to discharge the polyester solution P separated from the impurities R in the storage unit 20 from the storage unit 20 and control the amount of polyester solution P introduced into the reaction unit 16. The control unit 30 controls the heating and pressurizing unit 14b to bring the reaction solvent M into a supercritical or subcritical state (pressurized gas or pressurized liquid), and controls the amount of the supercritical or subcritical (pressurized gas or pressurized liquid) reaction solvent M 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.

[0074] In this embodiment, the control unit 30 is a computer and includes a processor, such as a CPU (Central Processing Unit), which is an arithmetic circuit, and a storage unit that stores various information such as the calculations performed by the processor and programs. The control unit 30 controls the isolated system 1 by reading the program from the storage unit.

[0075] However, the separation system 1 is not limited to being automatically controlled by the control unit 30; for example, at least some of the processes may be controlled by human operators.

[0076] (Operation of the Separation System) Next, the operation of the separation system 1 will be described. The control unit 30 controls the adjustment units 10b and 18Ce to introduce the polyester raw material Pm and monomer D into the dissolution unit 12, and mixes the polyester raw material Pm and monomer D in the dissolution unit 12 to generate a solution Pd. The control unit 30 controls the adjustment unit 12a1 to introduce the solution Pd generated in the dissolution unit 12 into the storage unit 20. In the solid-liquid separation unit 13, the separation system 1 removes impurities R from the solution Pd supplied from the dissolution unit 12 to the storage unit 20. The solution Pd introduced into the storage unit 20 is left to stand for a predetermined time, and by gravity it is separated into a layer of first impurity R1, a layer of polyester solution P, and a layer of second impurity R2. The method of letting the solution Pd stand can be arbitrary. Furthermore, the control unit 30 controls the gas supply unit 21 to supply gas G to the storage unit 20, thereby moving the impurities R contained in the dissolving solution Pd upward and causing them to float to the top of the polyester solution P layer as second impurities R2.

[0077] The control unit 30 controls the discharge unit 22 to discharge the first impurity R1 and the second impurity R2 from the storage unit 20, and controls the outlet unit 24 to release the polyester solution P from the storage unit 20. The polyester solution P released from the storage unit 20 has the third impurity R3 removed by the removal unit 26 and is introduced into the first reaction unit 16A. The control unit 30 controls the heating and pressurizing unit 14b to supply the reaction solvent M, which is in a supercritical or subcritical state (pressurized gas or pressurized liquid), to the reaction unit 16. The control unit 30 prefers that the reaction solvent M be between 250°C and 400°C, and more preferably between 250°C and 350°C. The control unit 30 prefers that the reaction solvent M be between 1 MPa and 30 MPa, and more preferably between 6 MPa and 25 MPa.

[0078] In this manner, when the polyester solution P and the reaction solvent M are supplied to the reaction section 16, the polyester contained in the polyester solution P is depolymerized in the first reaction section 16A to produce the first depolymerized polyester P1. Then, in the second reaction section 16B, the first depolymerized polyester P1 is further depolymerized to produce the second solvent M2, which is a mixture of the second depolymerized polyester P2 and the reaction solvent M. The second solvent M2 is separated into the reaction solvent M, monomer D, monomer E, and residual substances in the first separation section 18A, the second separation section 18B, and the third separation section 18C. As a result, monomers D and E are recovered from the polyester raw material Pm, and polyester can be regenerated by polymerizing them.

[0079] (Gas Supply) Next, the supply of gas G by the gas supply unit 21 will be explained using Figure 3.

[0080] As shown in Figure 3, the control unit 30 opens the gas adjustment unit 21c, and the gas supply unit 21 supplies gas G (nitrogen in this embodiment) from the main body 21a to the lower part of the storage unit 20. The gas G flows from the main body 21a through the gas supply pipe 21b and is supplied into the storage unit 20 via the nozzle 21d, where it forms bubbles in the polyester solution P (dissolved liquid Pd). The gas G, now in bubble form, moves through the polyester solution P in the storage unit 20 from the lower part (Y2 direction) to the upper part (Y1 direction). The bubbles moving through the polyester solution P in the storage unit 20 from the lower part to the upper part float to the surface of the polyester solution P. At this time, the impurities R move towards the surface of the polyester solution P along with the flow of the bubbles in the Y1 direction. For example, the impurities R flow in the Y1 direction through the polyester solution P between the bubbles. Also, the impurities R come into contact with the bubbles. Impurities R that come into contact with bubbles adhere to the bubbles and float to the surface of the polyester solution P along with the bubbles.

[0081] For example, the main body 21a of the gas supply unit 21 preferably supplies gas G to the storage unit 20 via the gas supply pipe 21b such that the diameter of the bubbles in the gas storage unit 20 is 10 μm or more and 200 μm or less. The diameter of the bubbles in the gas storage unit 20 is more preferably 20 μm or more and 160 μm or less, and even more preferably 30 μm or more and 130 μm or less. By having bubbles of this size, impurities R can be appropriately floated to the surface. The diameter of the bubbles can be adjusted by the gas supply conditions, such as the flow velocity of gas G, the area of ​​the opening 21d1 of the nozzle 21d, and the amount of gas G supplied.

[0082] In this embodiment, the diameter of the bubble may be determined by particle trajectory analysis. More specifically, particle trajectory analysis involves irradiating the bubble with laser light, visualizing the particle's movement using scattered light, and measuring the bubble's diameter from the Brownian motion velocity of the irradiated bubble using the Stokes-Einstein equation. However, the measurement of the bubble's diameter is not limited to this.

[0083] The second discharge section 22b1 has a rotating shaft that scrapes off impurities R (second impurity R2) that have floated to the surface of the dissolving liquid Pd (polyester solution P), and discharges them into the discharge pipe 20b.

[0084] According to this embodiment, as described above, impurities R are made to float to the surface by gas bubbles G. For example, impurities R with a specific gravity lower than that of the polyester solution P can be separated more appropriately than in the case of gravity separation alone. For example, according to this embodiment, organofluorine compounds (PFAS) can be appropriately separated and discharged. Impurities with a low specific gravity, such as PFAS, can be separated by gravity separation because their specific gravity is lower than that of the polyester solution P. However, they may be dispersed in the polyester solution P and not float to the surface appropriately. In contrast, according to this embodiment, PFAS and other impurities dispersed in the polyester solution P can be made to float to the surface of the polyester solution P by gas G and can be appropriately discharged from the storage section 20. Furthermore, by sufficiently discharging impurities with a low specific gravity, such as PFAS, in the storage section 20, the amount of impurities R (third impurity R3) that need to be removed in the subsequent removal section 26 can be reduced, and the frequency of replacing the filter and activated carbon in the removal section 26 can be reduced.

[0085] (Operation Flow) The operation flow of the separation system 1 described above will now be explained based on a flowchart. Figure 4 is a flowchart illustrating the operation flow of the separation system. As shown in Figure 4, the control unit 30 causes polyester to dissolve in monomer D, generating a solution Pd containing impurities R, which are components other than polyester, and introduces the solution Pd into the storage unit 20 (step S10). Then, the control unit 30 supplies gas G to the storage unit 20, causing the impurities R to float to the surface and be discharged (step S12). The control unit 30 introduces the polyester solution P and the reaction solvent into the reaction unit 16, and depolymerizes the polyester in the polyester solution P in the reaction unit 16 (step S14). Specifically, the control unit 30 introduces the polyester solution P and the reaction solvent into the reaction unit 16, depolymerizes the polyester in the polyester solution P, and generates a reaction solvent in which the depolymerized polyester is dissolved. The control unit 30 separates the reaction solvent into the reaction solvent and monomer in the separation unit 18 (step S16).

[0086] (Effects of the present disclosure) The separation system 1 according to the first aspect of the present disclosure includes a storage unit 20 in which a dissolution Pd containing a polyester solution P in which polyester is dissolved in a monomer derived from a carboxylic acid and impurities R which are components other than polyester is stored; a gas supply unit 21 that supplies gas G into the storage unit 20 to move the impurities R in the dissolution Pd upward; a discharge unit 22 that discharges the impurities R from the storage unit 20; and a reaction unit 16 into which the polyester solution P from which the impurities R have been separated and a reaction solvent M that reacts with polyester are introduced to depolymerize the polyester in the polyester solution P.

[0087] According to this disclosure, impurities can be properly separated.

[0088] A separation system 1 according to a second aspect of this disclosure is a separation system according to the first aspect, further comprising a removal unit 26 connected downstream of the storage unit 20, which removes impurities present in the polyester solution P from the polyester solution P. This allows for the proper separation of impurities.

[0089] A separation system 1 according to a third aspect of this disclosure is a separation system according to the first or second aspect, wherein the gas supply unit 21 supplies gas G in the storage unit 20 such that the diameter of the gas bubbles G is 30 μm or more and 130 μm or less. As a result, impurities R are lifted by the gas bubbles G, so that impurities with a specific gravity lower than, for example, the polyester solution P can be separated more appropriately than in the case of gravity separation alone. In other words, impurities can be efficiently discharged from the storage unit.

[0090] The separation system 1 according to the fourth aspect of this disclosure is a separation system according to any one of the first to third aspects, wherein gas G is an inert gas. This makes it possible to separate impurities while suppressing the oxidation of the polyester to be recovered.

[0091] The separation system 1 according to the fifth aspect of this disclosure is a separation system according to any one of the first to fourth aspects, wherein the impurities include organofluorine compounds. Therefore, the organofluorine compounds can also be made to float to the surface of the polyester solution P by gas G and can be appropriately discharged from the storage section 20.

[0092] A separation method according to a sixth aspect of the present disclosure includes the steps of: storing a dissolution Pd containing a polyester solution P in which polyester is dissolved in a monomer derived from a carboxylic acid and an impurity R which is a component other than polyester in a storage unit 20; supplying gas G into the storage unit 20 to move the impurity R in the dissolution Pd upward; discharging the impurity R from the storage unit 20; and introducing the polyester solution P from which the impurity R has been separated and a reaction solvent M that reacts with polyester to depolymerize the polyester in the polyester solution P.

[0093] According to this disclosure, impurities can be properly separated.

[0094] Although embodiments of the present invention have been described above, the embodiments are not limited to those described herein. Furthermore, the aforementioned components include those that can be easily conceived by those skilled in the art, those that are substantially the same, and those that fall within the so-called equivalent range. Moreover, the aforementioned 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 embodiments described above.

[0095] 1 Separation system 12 Dissolution section 13 Solid-liquid separation section 14 Reaction solvent storage section 16 Reaction section 18 Separation section 20 Storage section 21 Gas supply section 22 Discharge section 26 Removal section 26a Filtration machine 26b Adsorption tower 30 Control section D, E Monomer G Gas M Reaction solvent P Polyester solution Pd Dissolving solution Pm Polyester raw material R Impurities R1 First impurity R2 Second impurity R3 Third impurity

Claims

1. A separation system comprising: a storage section in which a dissolution containing a polyester solution in which polyester is dissolved in a monomer derived from a carboxylic acid, and impurities which are components other than polyester is stored; a gas supply section that supplies gas into the storage section to move the impurities in the dissolution upward; a discharge section that discharges the impurities from the storage section; and a reaction section into which the polyester solution from which the impurities have been separated and a reaction solvent that reacts with polyester are introduced to depolymerize the polyester in the polyester solution.

2. The separation system according to claim 1, further comprising a removal unit connected downstream of the storage unit for removing impurities present in the polyester solution from the polyester solution.

3. The separation system according to claim 1 or claim 2, wherein the gas supply unit supplies the gas in the storage unit such that the diameter of the gas bubbles is 30 μm or more and 130 μm or less.

4. The separation system according to claim 1 or claim 2, wherein the gas is an inert gas.

5. The separation system according to claim 1 or claim 2, wherein the impurity includes an organofluorine compound.

6. A separation method comprising: storing in a storage unit a solution containing a polyester solution in which polyester is dissolved in a monomer derived from a carboxylic acid, and impurities which are components other than the polyester; supplying gas into the storage unit to move the impurities in the solution upward; discharging the impurities from the storage unit; and introducing the polyester solution from which the impurities have been separated and a reaction solvent that reacts with the polyester to depolymerize the polyester in the polyester solution.

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