Recovery method and recovery device for thermoplastic polymer-derived component, depolymerization intermediate composition, depolymerization reaction composition, and production method and production device for recycled monomer

Abstract

In recovery of a thermoplastic polymer-derived component, a flow path etc. of a device are problematically blocked by a water-insoluble solid component of a different material. In order to highly efficiently and stably recover a thermoplastic polymer-derived component from a thermoplastic polymer composition which contains a thermoplastic polymer and a water-insoluble solid component, the present invention provides a method for recovering a thermoplastic polymer-derived component, said method comprising a step for obtaining a thermoplastic polymer-derived component by separating a water-insoluble solid component at 110-350°C and 0.14-30 MPa from a mixture of water and a thermoplastic polymer composition which contains a thermoplastic polymer and the water-insoluble solid component.

Description

Method and apparatus for recovering components derived from thermoplastic polymers, depolymerized intermediate composition, depolymerization reaction composition, and method and apparatus for producing recycled monomers

[0001] The present invention relates to a method and apparatus for recovering components derived from thermoplastic polymers, a method and apparatus for producing recycled monomers, a method for producing a depolymerized intermediate composition, a method for producing a depolymerization reaction composition, a polyamide monomer or a polyester monomer, polyamide or polyester, methods for producing these, and molded articles, fibers, films, or sheets obtained using these.

[0002] In recent years, interest in global environmental issues has increased, triggered by the problem of marine plastic pollution, and there is a growing demand for the creation of a sustainable society. Global environmental issues include global warming, resource depletion, and water shortages. Many of these issues are caused by the rapid increase in resource consumption and greenhouse gas emissions due to human activities since the Industrial Revolution. To create a sustainable society, it is important to develop technologies that recycle fossil resources such as plastics and reduce greenhouse gas emissions.

[0003] Plastics are processed into various shapes depending on their intended use. Plastics can be used alone or in combination with other materials. Examples of the latter include blended materials spun with different fibers to exhibit various properties, laminated products in which different polymer layers are formed by coating, film lamination, or two-color molding, resin molded products made from polymer alloys containing different polymers, and fiber-reinforced composite materials containing fibrous fillers. To recycle composite materials that contain these mixed materials, it is necessary to remove the dissimilar materials.

[0004] As a plastic recycling technology, for example, an apparatus and method have been disclosed in which waste polyethylene terephthalate (PET) is brought into contact with high-temperature, high-pressure water in a molten state to continuously decompose it and recover raw material monomers (Patent Document 1).

[0005] As a recycling technology for plastic composite materials, for example, an apparatus and method are disclosed in which a plastic molded product containing inorganic substances is treated with a subcritical fluid in a batch reaction tank, the inorganic substances are crushed in an extraction section, and the inorganic substances are separated from the monomers (Patent Document 2).Furthermore, a separation and recovery apparatus is disclosed in which the hydrolyzable polymer is continuously separated and recovered as its raw material compound and the non-hydrolyzable polymer is continuously separated and recovered as a high-purity polymer in which the inclusion of the hydrolyzable polymer is suppressed from a resin mixture containing a resin containing a hydrolyzable polymer and a resin containing a non-hydrolyzable polymer (Patent Document 3).

[0006] Furthermore, as a technology for peeling heterogeneous polymers from a laminate and separating and recycling polyamide or polyester (Patent Document 4), a method has been disclosed in which an airbag base fabric made of silicone-coated polyamide fibers is immersed in an alkali-isopropanol solution to remove the silicone coating on the airbag base fabric and recover polyamide 66. Also disclosed is a method in which polyamide is dissolved by heating it together with ethylene glycol at a temperature of 180°C or higher and silicone that is insoluble in ethylene glycol is removed (Patent Document 5).

[0007] Also, a method (Patent Document 6) for recovering raw material monomers after depolymerizing polyamide or polyester and separating it from other materials has been disclosed, in which a glass fiber-reinforced polyamide 66 composition is reacted in ethylene glycol at 180°C in the presence of calcium chloride for 30 minutes, followed by separation and purification to obtain 86% by mass of hexamethylenediamine, adipic acid, and their derivatives in total, relative to 100% by mass of polyamide 66. Furthermore, a method (Patent Document 7) has been disclosed in which a multilayer film consisting of a polyamide or polyester layer and a polyethylene layer is subjected to a hydrothermal reaction at a high temperature of 250 to 380°C, and the polyamide or polyester is recycled as a raw material monomer and the polyethylene is recycled as is.

[0008] JP 9-77905 A JP 2009-7417 A JP 2023-1084 A JP 2009-269475 A JP 2018-172618 A International Publication No. 2023 / 120427 JP 2023-1085 A

[0009] The device and method for recovering raw material monomers from PET disclosed in Patent Document 1 are capable of continuous processing, but there is a concern that the throttle valve may be clogged when processing composite materials containing inorganic substances, etc. This limits the amount of raw material that can be recycled.

[0010] The apparatus and method for recovering inorganic substances from plastics disclosed in Patent Document 2 are intended to recover inorganic substances contained in plastics, and since the plastics are treated in a batch-type reaction vessel and then cooled to separate the solid inorganic substances, there is a problem in that insufficiently decomposed plastics that precipitate during cooling are also recovered together with the inorganic substances. The separation and recovery apparatus disclosed in Patent Document 3 assumes a state in which the non-hydrolyzable polymer is dissolved, and therefore cannot be operated stably when the non-hydrolyzable polymer is solid.

[0011] The method of stripping and removing silicone using an alkali-isopropanol solution disclosed in Patent Document 4 maintains the shape of the polyamide, leaving the silicone coating between the fibers, making complete removal difficult. The method of recovering high-quality polyamide by dissolving polyamide disclosed in Patent Document 5 produces by-products resulting from an esterification reaction between the carboxyl groups of the polyamide and the hydroxyl groups of ethylene glycol, making separation from the monomer difficult. Patent Document 6, which decomposes polyamide or polyester to recover raw material monomers, does not disclose a method for separating different materials. Patent Document 7 describes a method for removing solid components from the melt in advance when polyamide or polyester contains solid components that do not melt under hydrothermal reaction conditions. However, heating above the melting point of the polymer raises concerns about thermal degradation of the polymer and other components. As described above, conventional techniques require the treatment method to be tailored depending on the shape and properties of the different components, making them less versatile for treating plastic waste with diverse shapes and compositions.

[0012] In light of the above, an object of the present invention is to provide a method and apparatus for recovering thermoplastic polymer-derived components, as well as a method and apparatus for producing recycled monomers, which solve the problem of clogging of the device's flow channels by water-insoluble solid components from a thermoplastic polymer composition containing a thermoplastic polymer and a water-insoluble solid component, and enable highly efficient and stable recovery of thermoplastic polymer-derived components. Furthermore, plastic waste can be fed into a depolymerization apparatus in the same form regardless of its shape or composition and depolymerized. In particular, an object of the present invention is to provide a method for obtaining a depolymerized intermediate composition from which inorganic substances, crosslinked polymers, etc. can be easily separated by partially depolymerizing polyamide or polyester from a product made of a polyamide composition or polyester composition containing water-insoluble components such as inorganic substances and crosslinked polymers. Another object of the present invention is to provide a method for efficiently producing monomers from a depolymerized intermediate composition by separating inorganic substances, crosslinked polymers, etc.

[0013] In order to solve the above problems, the present invention has the following features. 1. A method for recovering a component derived from a thermoplastic polymer, comprising the step of separating the water-insoluble solid component S from a mixture containing a thermoplastic polymer composition containing a thermoplastic polymer P and a water-insoluble solid component S under conditions of 110°C to 350°C and 0.14 MPa to 30 MPa, to obtain a component derived from the thermoplastic polymer P. 2. The method for recovering a component derived from a thermoplastic polymer as described in 1, in which the mass of the thermoplastic polymer composition is a (kg), the mass of water is b (kg), and the mixture is mixed so that the ratio b / a is 1 to 100. 3. The method for recovering a component derived from a thermoplastic polymer as described in 1 or 2, in which the step of separating the water-insoluble solid component S is carried out at a temperature equal to or higher than the melting point of the thermoplastic polymer P in water. 4. The method for recovering a component derived from a thermoplastic polymer as described in any one of 1 to 3, in which the water-insoluble solid component S includes a crosslinked silicone polymer and / or a fibrous filler. 5. 5. The method for recovering a component derived from a thermoplastic polymer according to any one of 1 to 4, wherein the thermoplastic polymer P comprises polyamide and / or polyester. 6. The method for recovering a component derived from a thermoplastic polymer according to any one of 1 to 5, wherein the thermoplastic polymer composition constitutes an article, and the article is an airbag fabric. 7. A method for producing a recycled monomer, comprising a step of depolymerizing a component derived from a thermoplastic polymer recovered by the method for recovering a component derived from a thermoplastic polymer according to any one of 1 to 6.

[0014] 8. An apparatus for recovering a thermoplastic polymer-derived component, comprising: a pressure vessel (D) for obtaining a solution obtained by mixing a thermoplastic polymer composition containing a thermoplastic polymer P and a water-insoluble solid component S with water; means (F) for separating the water-insoluble solid component S from the mixture discharged from the pressure vessel (D) at 110°C or higher and 350°C or lower and 0.14 MPa or higher and 30 MPa or lower; and a thermoplastic polymer-derived component tank (H) for recovering a thermoplastic polymer-derived component, with a filter provided between the pressure vessel (D) and the thermoplastic polymer-derived component tank (H) as the means for separating the water-insoluble solid component S. 10. An apparatus for recovering a thermoplastic polymer-derived component, comprising: means (A) for supplying a thermoplastic polymer composition containing a thermoplastic polymer P and a water-insoluble solid component S; means (B) for supplying water; and means (C) for obtaining a thermoplastic polymer-derived component by separating the water-insoluble solid component S from a mixture of the thermoplastic polymer composition supplied from means (A) and the water supplied from means (B) at 110°C to 350°C and 0.14 MPa to 30 MPa, wherein the water-insoluble solid component S is obtained, the means (C) comprising at least a filter. 10. The apparatus for recovering a thermoplastic polymer-derived component according to claim 8 or 9, wherein the water-insoluble solid component S comprises a crosslinked silicone polymer and / or a fibrous filler. 11. The apparatus for recovering a thermoplastic polymer-derived component according to any of claims 8 to 10, wherein the thermoplastic polymer P comprises a thermoplastic polyamide and / or a thermoplastic polyester. 12. The apparatus for recovering a thermoplastic polymer-derived component according to any of claims 8 to 11, wherein the thermoplastic polymer composition is an airbag fabric. 13. A recycled monomer production apparatus having a reactor (G) into which the thermoplastic polymer-derived component discharged from the means (F) in claim 8 or the means (C) in claim 9 is introduced and which depolymerizes the thermoplastic polymer-derived component.

[0015] 14. A method for producing a depolymerized intermediate composition, comprising a step of depolymerizing a polyamide composition in the presence of water at a temperature greater than 200°C and less than 270°C to obtain a depolymerized intermediate composition, wherein the depolymerized intermediate composition contains 10% by mass or more and 70% by mass or less of a monomer of the polyamide and / or a derivative thereof relative to 100% by mass of polyamide-derived components. 15. A method for producing a depolymerized intermediate composition, comprising a step of depolymerizing a polyester composition in the presence of water at a temperature greater than 150°C and less than 240°C to obtain a depolymerized intermediate composition, wherein the depolymerized intermediate composition contains 10% by mass or more and 70% by mass or less of a monomer of the polyester and / or a derivative thereof relative to 100% by mass of polyester-derived components. 16. 17. The method for producing a depolymerized intermediate composition according to any one of 14 to 16, wherein the depolymerized intermediate composition contains a polyamide- or polyester-derived component insoluble in water at 25°C and a polyamide- or polyester-derived component soluble in water at 25°C, and the volume average particle size of the component insoluble in water at 25°C measured with a particle size distribution analyzer is less than 100 μm. 17. The method for producing a depolymerized intermediate composition according to any one of 14 to 16, wherein an alkali metal compound and / or an alkaline earth metal compound is further allowed to coexist in the step of obtaining the depolymerized intermediate composition. 18. The method for producing a depolymerized intermediate composition according to any one of 14 to 16, wherein the polyamide or polyester contains dicarboxylic acid residues, and X mol of the dicarboxylic acid residues and Y mol of alkali metal ions are mixed in a reaction system. １ mol and / or alkaline earth metal ions are ２ 18. The method for producing a depolymerized intermediate composition according to any one of 14 to 17, wherein a hydroxide, an oxide, a carbonate, or a mixture containing two or more of these is allowed to coexist so as to satisfy (Formula 1). １ +2 x Y ２) / X≦1.5 (Equation 1) 19. The method for producing a depolymerized intermediate composition according to any one of 14 to 18, wherein the polyamide composition or polyester composition contains 0.01% by mass or more and 60% by mass or less of a component other than polyamide or polyester that is insoluble in water at 25°C, based on 100% by mass of the polyamide composition or polyester composition. 20. The method for producing a depolymerized intermediate composition according to any one of 14 to 19, wherein the polyamide composition or polyester composition contains a component containing silicon. 21. The method for producing a depolymerized intermediate composition according to any one of 14 to 19, wherein the step of obtaining a depolymerized intermediate composition further comprises, after depolymerization, a step of removing, with a filter, components insoluble in water at 25°C, other than polyamide-derived components or polyester-derived components.

[0016] 22. A method for producing a depolymerization reaction composition, comprising: a monomer-containing composition containing 10% by mass or more and 70% by mass or less of polyamide monomers and / or derivatives thereof, or polyester monomers and / or derivatives thereof, and 30% by mass or more and 90% by mass or less of components derived from polyamide or polyester other than the monomers and / or derivatives thereof, relative to 100% by mass of polyamide-derived components or polyester-derived components; and a step of depolymerizing the polyamide composition or polyester composition in the presence of water at 225°C or more and 350°C or less to obtain a depolymerization reaction composition, wherein the depolymerization reaction composition contains 75% by mass or more of polyamide monomers and / or derivatives thereof, or polyester monomers and / or derivatives thereof, relative to 100% by mass of polyamide-derived components or polyester-derived components. 23. The method for producing a depolymerization reaction composition according to claim 22, wherein the monomer-containing composition is a depolymerized intermediate composition obtained by the method for producing a depolymerized intermediate composition according to any one of claims 14 to 21.

[0017] 24. A method for producing a depolymerized reaction composition of a polyamide composition or a polyester composition, comprising the following steps 1 and 2, in this order: (Step 1) depolymerizing a polyamide composition or a polyester composition in the presence of water at 150°C or higher and 300°C or lower to obtain an aqueous slurry solution or an aqueous solution containing a monomer-containing composition, wherein the monomer-containing composition contains 10% by mass or higher and 70% by mass or lower of polyamide monomers and / or derivatives thereof, or polyester monomers and / or derivatives thereof, relative to 100% by mass of polyamide-derived components or polyester-derived components; and (Step 2) further depolymerizing the aqueous slurry solution or aqueous solution at 225°C or higher and 350°C or lower to obtain a depolymerized reaction composition, wherein the depolymerized reaction composition contains 75% by mass or higher of polyamide monomers and / or derivatives thereof, or polyester monomers and / or derivatives thereof, relative to 100% by mass of polyamide-derived components or polyester-derived components. 25. The method for producing a depolymerization reaction composition according to 24, wherein an alkali metal compound and / or an alkaline earth metal compound is further present in the first step and / or the second step.

[0018] 26. A polyamide monomer or polyester monomer obtained by purifying a depolymerization reaction composition obtained by the method for producing a depolymerization reaction composition according to any one of 22 to 25. 27. A method for producing a polyamide or a method for producing a polyester, comprising a step of polycondensing a raw material containing the polyamide monomer or polyester monomer according to 26. 28. A polyamide or polyester obtained by polycondensing a raw material containing the polyamide monomer or polyester monomer according to 27. 29. A molded article, fiber, film, or sheet obtained using the polyamide or polyester according to 28.

[0019] According to the present invention, the problem of blockage of process flow paths due to water-insoluble solid components during recovery of thermoplastic polymer-derived components is solved, and thermoplastic polymer-derived components can be recovered with high efficiency and stability. Also provided are a method and apparatus for producing recycled monomers by depolymerizing the obtained thermoplastic polymer-derived components. According to another aspect of the present invention, plastic waste of various shapes and compositions can be fed into the depolymerization apparatus in the same form, thereby providing a versatile method for producing recycled monomers. In particular, by partially depolymerizing polyamide or polyester from a product made of a polyamide composition or polyester composition containing water-insoluble components such as inorganic substances and crosslinked polymers, a depolymerized intermediate composition can be obtained from which the inorganic substances, crosslinked polymers, etc. can be easily separated, and monomers can be produced from the depolymerized intermediate composition with high efficiency.

[0020] Schematic diagram of an apparatus for recovering components derived from a thermoplastic polymer, showing one embodiment of the present invention. Schematic diagram of an apparatus for producing recycled monomer, showing one embodiment of the present invention. Schematic diagram of an apparatus for producing recycled monomer, showing another embodiment of the present invention. Schematic diagram of an apparatus for producing recycled monomer, showing another embodiment of the present invention. Schematic diagram of an apparatus for producing recycled monomer, showing another embodiment of the present invention.

[0021] The present invention is described in further detail below, but is not limited to these embodiments. [First Aspect of the Present Invention] The first aspect of the present invention is a recovery method and recovery apparatus for obtaining a thermoplastic polymer-derived component by converting a thermoplastic polymer-derived component into a water-soluble state without removing water-insoluble solid components S contained in a thermoplastic polymer composition, such as inorganic substances, crosslinked polymers, silicones, and other materials, and separating the water-insoluble solid components S using a filter or the like. This prevents inorganic substances, crosslinked polymers, silicones, and other materials from adhering to the device's flow channels and piping, causing blockages. By depolymerizing the obtained thermoplastic polymer-derived component, recycled monomers can be produced with high efficiency. In the present invention, the term "thermoplastic polymer-derived component" is defined as a general term for thermoplastic polymers and / or oligomers, as well as monomers and / or derivatives thereof that are raw materials for thermoplastic polymers.

[0022] The apparatus for recovering a thermoplastic polymer-derived component of the present invention can be broadly divided into those that perform continuous treatment and those that perform batch treatment. In the case of continuous treatment, the apparatus for recovering a thermoplastic polymer-derived component of the present invention has a means (A) for supplying a thermoplastic polymer composition containing a thermoplastic polymer P and a water-insoluble solid component S, a means (B) for supplying water, and a means (C) for separating the water-insoluble solid component S from a mixture of the thermoplastic polymer composition supplied from means (A) and water supplied from means (B) at 110°C to 350°C and 0.14 MPa to 30 MPa to obtain a thermoplastic polymer-derived component, wherein means (C) is equipped with at least a filter.

[0023] In the case of batch processing, the apparatus for recovering a thermoplastic polymer-derived component of the present invention comprises a pressure vessel (D) for obtaining a solution obtained by mixing a thermoplastic polymer composition containing a thermoplastic polymer P and a water-insoluble solid component S with water, a means (F) for separating the water-insoluble solid component S from the mixture discharged from the pressure vessel (D) at 110°C to 350°C and 0.14 MPa to 30 MPa, and a thermoplastic polymer-derived component tank (H) for recovering the thermoplastic polymer-derived component, and a filter is provided between the water-insoluble pressure vessel (D) and the thermoplastic polymer-derived component tank (H) as the means for separating the solid component (F). Each component will be described below, but first, the effect of water in the first embodiment of the present invention will be described.

[0024] When water is heated to a pressure of 22.1 MPa and a temperature of 374.2°C, it is in a state that is neither liquid nor gas. Water in this state is called supercritical water. Hot water at a temperature and pressure slightly lower than the critical point of water, near the critical point, is called subcritical water. Despite being water, subcritical water has the following characteristics: (i) a low dielectric constant and (ii) a high ionic product. The dielectric constant and ionic product of subcritical water depend on the temperature and the partial pressure of water and can be controlled. The low dielectric constant makes it an excellent solvent for organic compounds, despite being water. Furthermore, the high ionic product increases the concentrations of hydrogen ions and hydroxide ions. Therefore, subcritical water has excellent hydrolysis properties. In the present invention, subcritical water is defined as water at a temperature of 110°C to 350°C and a pressure of 0.14 MPa to 30 MPa. In a first aspect of the present invention, a thermoplastic polymer P can be melted or dissolved in subcritical water. This contributes to the separation of the thermoplastic polymer-derived component soluble in subcritical water from the solid component S, which is a different material insoluble in water, from a thermoplastic polymer composition containing a thermoplastic polymer P and a water-insoluble solid component S.

[0025] The water used in the present invention is not particularly limited, and any type of water may be used, such as tap water, deionized water, distilled water, or well water. Deionized water or distilled water is preferred from the viewpoint of suppressing side reactions due to the influence of coexisting salts. Other solvents, such as alcohol, may be added to the water used in the present invention. Examples of alcohols include aliphatic monohydric alcohols having 1 to 10 carbon atoms, such as methanol, ethanol, 1-propanol, 2-propanol, isobutanol, and tert-butyl alcohol; aliphatic or alicyclic dihydric alcohols having 2 to 20 carbon atoms, such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, decamethylene glycol, cyclohexanedimethanol, cyclohexanediol, and dimer diol; and aliphatic trihydric alcohols having 3 to 10 carbon atoms, such as glycerol. The alcohols may be used alone or in combination of two or more in any desired content.

[0026] Depending on the type of thermoplastic polymer composition, an alkali (earth) metal salt may be added to water to promote hydrolysis of the thermoplastic polymer. The term "alkali (earth) metal salt" refers to both alkali metal salts and alkaline earth metal salts. As used herein, the term "alkali (earth) metal salt" refers to both salts containing alkali metal atoms, such as lithium, sodium, and potassium, and salts containing alkaline earth atoms, such as magnesium, calcium, and barium, and mixtures thereof.

[0027] Next, the thermoplastic polymer composition of the present invention containing the thermoplastic polymer P and the water-insoluble solid component S (sometimes simply referred to as the "thermoplastic polymer composition" in the present invention) may be of any type as long as it contains a hydrolyzable thermoplastic polymer. The bone-dry melting point of the thermoplastic polymer P in the thermoplastic polymer composition of the present invention is preferably 200°C or higher. The bone-dry state herein is defined as a water content in the thermoplastic polymer of 0.5% by mass or less. The water content can be measured by the Karl Fischer method in accordance with Japanese Industrial Standard JIS K 7251. The upper limit of the bone-dry melting point is not particularly limited, but is generally about 350°C. The bone-dry melting point of the thermoplastic polymer P in the thermoplastic polymer composition is the temperature of the endothermic peak that appears when, using a differential scanning calorimeter, a bone-dry thermoplastic polymer composition is cooled from a molten state to 30°C at a rate of 10°C / min under a nitrogen gas atmosphere, and then heated at a rate of 10°C / min. However, when two or more endothermic peaks are detected, the temperature of the endothermic peak with the greatest peak intensity is taken as the melting point in the bone-dry state. Thermoplastic polymers with a melting point of 200°C or higher in the bone-dry state have a wide range of applications and are in high demand, so are preferred from the perspective of resource recovery.

[0028] Furthermore, the melting point of the thermoplastic polymer may decrease in water. The melting point of the thermoplastic polymer P in water can be determined by sealed container thermal analysis (SC-DSC). Specifically, the thermoplastic polymer P and an equal amount of distilled water are sealed in a stainless steel pressure-resistant sealed container for DSC, and the temperature is increased from 30°C to 350°C at a heating rate of 10°C / min under nitrogen flow using a differential thermal analyzer (Hitachi High-Tech Science DSC7000X). The melting point in water is determined as the temperature of the endothermic peak that appears when the temperature is increased from 30°C to 350°C at a heating rate of 10°C / min under nitrogen flow. However, if two or more endothermic peaks are detected, the temperature of the endothermic peak with the greatest peak intensity is determined as the melting point in water. In the present invention, it is preferable to separate the water-insoluble solid component S by reducing the viscosity of the thermoplastic polymer P at a temperature equal to or higher than the melting point of the thermoplastic polymer P in water. In the above method, for example, the melting point of polyamide 66 in water is 179°C, 86°C lower than its melting point in an oven-dry state (265°C).

[0029] In the present invention, the thermoplastic polymer P preferably contains a thermoplastic polyamide and / or a thermoplastic polyester. Examples of thermoplastic polyamides include polyamide 6 and polyamide 66. Examples of thermoplastic polyesters include polyethylene terephthalate, polybutylene terephthalate, and polycarbonate. Thermoplastic polyamides are widely used as engineering plastics, films, and textile products. Thermoplastic polyesters are also widely used as engineering plastics, bottles, films, and textile products. Therefore, thermoplastic polyamides and thermoplastic polyesters are preferred in terms of ease of resource recovery and ease of hydrolysis. The content of thermoplastic polyamide or thermoplastic polyester in the thermoplastic polymer composition of the present invention is preferably 30% or more by mass, more preferably 50% or more, and even more preferably 70% or more.

[0030] The water-insoluble solid component S in the present invention can be defined by sealed container thermal analysis (SC-DSC). Specifically, the water-insoluble solid component S and an equal amount of distilled water to the water-insoluble solid component S are sealed in a stainless steel pressure-resistant sealed container for DSC, and the temperature is increased from 30°C to 350°C at a heating rate of 10°C / min under a nitrogen flow using a differential thermal analyzer (DSC7000X manufactured by Hitachi High-Tech Science). The water-insoluble solid component S indicates a material that exhibits an endothermic peak of 5 J / g or less, a material that does not exhibit an endothermic peak, or a material that exhibits an endothermic peak of 5 J / g or more and whose peak temperature is equal to or higher than the operating temperature of the solid component separation step. Here, the operating temperature of the solid component separation step refers to the temperature in the step of separating the water-insoluble solid component S.

[0031] Examples of the water-insoluble solid component S include inorganic materials such as glass and metals, and organic materials such as cross-linked polymers, natural fibers, and recycled fibers. Examples of inorganic materials among the water-insoluble solid components S include fibrous fillers and non-fibrous fillers. Fibrous fillers are fillers having a fibrous shape, and specific examples include glass fibers, polyacrylonitrile (PAN)-based and pitch-based carbon fibers, metal fibers such as stainless steel fibers, aluminum fibers, and brass fibers, gypsum fibers, ceramic fibers, asbestos fibers, zirconia fibers, alumina fibers, silica fibers, titanium oxide fibers, silicon carbide fibers, rock wool, potassium titanate whiskers, silicon nitride whiskers, wollastonite, and alumina silicate fibrous and whisker-like fillers, as well as glass fibers and carbon fibers coated with one or more metals selected from the group consisting of nickel, copper, cobalt, silver, aluminum, iron, and alloys thereof.

[0032] Specific examples of non-fibrous fillers include talc, wollastonite, zeolite, sericite, mica, kaolin, clay, pyrophyllite, bentonite, asbestos, non-swelling silicates such as alumina silicate and calcium silicate, swellable layered silicates such as Li-type fluorine taeniolite, Na-type fluorine taeniolite, Na-type tetrasilicic fluorine mica and Li-type tetrasilicic fluorine mica, metal oxides such as silicon oxide, magnesium oxide, alumina, silica, diatomaceous earth, zirconium oxide, titanium oxide, iron oxide, zinc oxide, calcium oxide, tin oxide and antimony oxide, calcium carbonate, magnesium carbonate, zinc carbonate and barium carbonate. Examples of suitable clay minerals include metal carbonates such as dolomite and hydrotalcite, metal sulfates such as calcium sulfate and barium sulfate, metal hydroxides such as magnesium hydroxide, calcium hydroxide, aluminum hydroxide and basic magnesium carbonate, smectite clay minerals such as montmorillonite, beidellite, nontronite, saponite, hectorite and sauconite, various clay minerals such as vermiculite, halloysite, kanemite, Kenyaite, zirconium phosphate and titanium phosphate, glass beads, glass flakes, ceramic beads, boron nitride, aluminum nitride, silicon carbide, calcium phosphate, carbon black and graphite. The swellable layered silicate may have exchangeable cations present between layers exchanged with organic onium ions. Examples of organic onium ions include ammonium ions, phosphonium ions and sulfonium ions.

[0033] Examples of crosslinked polymers include acrylic polymers, silicone polymers, and urethane polymers crosslinked using a crosslinking agent. For example, crosslinked silicone polymers are often coated on fibers or films processed from thermoplastic polymers. Natural fibers include cotton, silk, linen, and wool, while regenerated fibers include cellulose fibers such as rayon, Ponosic, cupra, and lyocell. For example, cellulose fibers are often blended with thermoplastic polymer fibers. The thermoplastic polymer composition of the present invention may contain two or more water-insoluble solid components S. The content of the water-insoluble solid component S is preferably 1 to 200 parts by mass per 100 parts by mass of the thermoplastic polymer. In the present invention, the water-insoluble solid component S preferably contains a crosslinked silicone polymer and / or a fibrous filler. Thermoplastic polymers containing crosslinked silicone polymers are widely used as base fabrics for airbags (articles), i.e., airbag base fabrics. Furthermore, thermoplastic polymers containing fibrous fillers are widely used as glass fiber reinforced resins, making resource recovery easier.

[0034] The thermoplastic polymer composition of the present invention may contain various additives within the scope of the present invention. Specific examples of the various additives include antioxidants and heat stabilizers (hindered phenols, hydroquinones, phosphites and their substituted derivatives, copper halides, iodine compounds, etc.), weathering agents (resorcinols, salicylates, benzotriazoles, benzophenones, hindered amines, etc.), release agents and lubricants (aliphatic alcohols, aliphatic amides, aliphatic bisamides, bisureas, polyethylene wax, etc.), pigments (cadmium sulfide, phthalocyanine, carbon black, etc.), dyes (nigrosine, aniline black, etc.), plasticizers (octyl p-oxybenzoate, N-butylbenzenesulfonamide, etc.), and band-forming agents. Examples of suitable additives include antistatic agents (anionic alkyl sulfate antistatic agents, cationic quaternary ammonium salt antistatic agents, nonionic antistatic agents such as polyoxyethylene sorbitan monostearate, and betaine amphoteric antistatic agents), flame retardants (hydroxides such as melamine cyanurate, magnesium hydroxide, and aluminum hydroxide, phosphorus-based flame retardants such as ammonium polyphosphate, melamine polyphosphate, and metal phosphinates, brominated polystyrene, brominated polyphenylene oxide, brominated polycarbonate, brominated epoxy resin, and combinations of these brominated flame retardants with antimony trioxide). When these additives are contained, the content is preferably 10 parts by mass or less, and more preferably 1 part by mass or less, per 100 parts by mass of the thermoplastic polymer P component.

[0035] In the present invention, the thermoplastic polymer composition may be a waste product of a resin molding. When the thermoplastic polymer composition is a waste product of a resin molding, the amount of resources available for recovery of thermoplastic polymer-derived components increases. When the thermoplastic polymer is a thermoplastic polyamide, waste products of a resin molding containing the thermoplastic polyamide include polyamide products, industrial waste (process offcuts) generated during the production of polyamide products, and post-consumer waste of polyamide products. Examples of polyamide products include textile fabrics for clothing such as used clothing, uniforms, sportswear, and underwear; industrial textile fabrics such as curtains, carpets, ropes, nets, belts, seats, seatbelts, and airbags; automobile parts; molded parts for housing construction materials; molded electrical and electronic parts; aircraft parts; industrial machinery parts; film products; extrusion molded products; in-situ polymerization molded products; and RIM molded products. Furthermore, waste products include product scraps, pellet scraps, lump scraps, and cutting chips generated during these production processes.

[0036] When the thermoplastic polymer P is a thermoplastic polyester, waste resin molded articles containing the thermoplastic polyester include thermoplastic polyester products, industrial waste (process offcuts) generated during the manufacturing process of thermoplastic polyester products, and post-consumer waste of thermoplastic polyester products. Examples of thermoplastic polyester products include containers such as beverage bottles and seasoning bottles; sheet products such as food trays, blister packs, food dividers, and industrial trays; film products such as packaging films, optical functional films, magnetic tapes, release films, and insulating materials; textile structures for clothing such as used clothing, uniforms, sportswear, and underwear; industrial textile structures such as curtains, carpets, nets, belts, seats, seatbelts, and airbags; molded articles such as automobile parts, electrical and electronic components, building materials, daily necessities, household goods, and sanitary products. Furthermore, waste also includes product scraps, pellet scraps, and agglomerate scraps generated during the production process. The thermoplastic polymer composition is preferably an airbag. Using an airbag as the thermoplastic polymer composition facilitates resource recovery.

[0037] Next, each means of the recovery device for components derived from thermoplastic polymers and the production method and production device for recycled monomers will be described.

[0038] The recovery device for thermoplastic polymer-derived components of the present invention may be either a device that performs continuous treatment or a device that performs batch treatment. The device that performs continuous treatment has a means (A) for supplying a thermoplastic polymer composition (sometimes simply referred to as "means (A)" in the present invention). Examples of the means (A) include a device that heats and melts the composition using an electric heater and applies pressure using a gear pump, a device that simultaneously heats and pressurizes the composition using an extruder, a device that combines an extruder and a gear pump, and a device that further heats the thermoplastic polymer discharged from the extruder using an electric heater. Among these, a device that uses an extruder is preferred as the means (A). When the means (A) is a device that uses an extruder, the pressure at which the thermoplastic polymer composition is extruded is more likely to be stable. The temperature at which the thermoplastic polymer composition is heated is preferably to a temperature at which the thermoplastic polymer P melts. By heating to a temperature at which the thermoplastic polymer P melts, the composition can be efficiently mixed with water. Here, the means (B) for supplying water (sometimes simply referred to as "means (B)" in the present invention) may be, for example, a device that introduces water under pressure into high-pressure equipment using a diaphragm pump, gear pump, plunger pump, or the like, and then heats it to a predetermined temperature using a heat exchanger, electric heater, heating furnace, or the like, although devices not exemplified here may also be used.

[0039] [Means (C) for Separating Water-Insoluble Solid Component S to Obtain Thermoplastic Polymer-Derived Component] The continuous system of the apparatus for recovering a thermoplastic polymer-derived component of the present invention includes means (C) (sometimes simply referred to as "means (C)" in the present invention) for separating water-insoluble solid component S from a mixture of the thermoplastic polymer composition supplied from means (A) and water supplied from means (B) at 110°C or higher and 350°C or lower and 0.14 MPa or higher and 30 MPa or lower to obtain a thermoplastic polymer-derived component.

[0040] In method (C), the water-insoluble solid component S is separated to obtain a thermoplastic polymer-derived component at 110°C to 350°C and 0.14 MPa to 30 MPa. By setting the temperature to 110°C to 350°C and 0.14 MPa to 30 MPa, dissolution, melting, and hydrolysis of the thermoplastic polymer P are promoted, making it easier to separate the water-insoluble solid component S, and excessive decomposition of the thermoplastic polymer-derived component is also suppressed. The temperature condition is preferably 130°C to 350°C. The pressure is preferably 1.0 MPa or more, more preferably 2.0 MPa or more, and even more preferably equal to or greater than the saturated vapor pressure at the temperature when separating the water-insoluble solid component S from the solution containing the thermoplastic polymer-derived component. On the other hand, 10 MPa or less is preferred, and 4 MPa or less is more preferred.

[0041] In the present invention, it is preferable to supply the mass a (kg) of the thermoplastic polymer composition and the mass b (kg) of water to means (C) so that b / a is 1 or more and 100 or less. b / a is more preferably 2 or more, and even more preferably 3 or more. By making b / a 1 or more, the viscosity of the mixture of the thermoplastic polymer composition and water decreases, making it easier to separate the water-insoluble solid component S. On the other hand, by making b / a 100 or less, it is possible to reduce the energy required to heat the water and the energy required to purify the recycled monomer. b / a is more preferably 10 or less, even more preferably 8 or less, and most preferably 6 or less.

[0042] In means (C), the temperature is preferably set to a temperature equal to or higher than the temperature at which the thermoplastic polymer-derived component melts or dissolves in water. Maintaining this temperature allows the thermoplastic polymer-derived component to flow, enabling efficient separation of the water-insoluble solid component S. Means (C) is equipped with a filter. In addition to conventional filters, devices such as screen changers, laser filters, and drum filters can also be used as filters, as long as they can be used at temperatures between 110°C and 350°C and between 0.14 MPa and 30 MPa. By providing means (C) with a filter, the removal rate of the water-insoluble solid component S can be increased. Here, the removal rate is defined as (the amount of water-insoluble solid component S captured by the filter) / (the amount of water-insoluble solid component S present in the thermoplastic polymer composition).

[0043] Furthermore, in order to prevent clogging of the filter, reduce the frequency of cleaning, and ensure a retention area for the water-insoluble solid components S captured by the filter, the filter is preferably combined with a separation tank described below and installed in the separation tank. The water-insoluble solid components S captured by the filter in the separation tank can be appropriately intermittently extracted and recovered. The filter aperture and filter area are appropriately selected depending on the type, amount, and size of the water-insoluble solid components S.

[0044] In addition to the filter, means (C) may also include a separation method utilizing the difference in specific gravity between the water-insoluble solid component S and the thermoplastic polymer-derived component. Separation methods utilizing the difference in specific gravity include a separation tank using gravity, and a centrifuge or hydrocyclone using centrifugal force. Regarding the separation tank, if the specific gravity of the water-insoluble solid component S is greater than that of the thermoplastic polymer-derived component, the water-insoluble solid component S will accumulate at the bottom of the separation tank, so a method in which the thermoplastic polymer-derived component is extracted from the top of the separation tank is preferred. On the other hand, if the specific gravity of the water-insoluble solid component S is less than that of the thermoplastic polymer-derived component, the water-insoluble solid component S will accumulate at the top of the separation tank, so a method in which the thermoplastic polymer-derived component is extracted from the bottom of the separation tank is preferred. The water-insoluble solid component S accumulated in the separation tank can also be extracted intermittently and recovered as appropriate. The extracted water-insoluble solid component S may be further separated offline using solid-liquid separation means such as filters. Any type of centrifuge or hydrocyclone may be used as long as it can be used at a temperature of 110° C. or higher and 350° C. or lower and at a pressure of 0.14 MPa or higher and 30 MPa or lower.

[0045] [Pressure Vessel (D) and Feed Gas for Obtaining a Solution Comprising a Mixture of Thermoplastic Polymer Composition and Water] When the apparatus for recovering a thermoplastic polymer-derived component of the present invention is used in a batchwise process, it has a pressure vessel (D) (sometimes simply referred to as "pressure vessel (D)" in the present invention) for obtaining a solution comprising a mixture of a thermoplastic polymer composition and water. In the present invention, it is preferable to mix thermoplastic polymer composition a (kg) and water b (kg) in the pressure vessel (D) so that b / a is 1 or more and 100 or less. b / a is more preferably 2 or more, and even more preferably 3 or more. By setting b / a to 1 or more, the viscosity of the mixture of thermoplastic polymer composition and water is reduced, making it easier to separate the water-insoluble solid component S. On the other hand, by setting b / a to 100 or less, the energy required for heating the water and the energy required for purifying the recycled monomer can be reduced. b / a is more preferably 10 or less, more preferably 8 or less, and most preferably 6 or less. The temperature inside the pressure vessel (D) is preferably set to a temperature at or above the temperature at which the thermoplastic polymer-derived component melts or dissolves in water. By maintaining the temperature within the above range, the thermoplastic polymer-derived component can be fluidized, and the water-insoluble solid component S can be efficiently separated.

[0046] When the thermoplastic polymer-derived component recovery apparatus of the present invention is used in a batchwise process, it may include a means (E) (sometimes simply referred to as "means (E)" in the present invention) for supplying an inert gas or steam into the pressure vessel (D). By including the means (E), the pressure vessel (D) can be filled with an inert gas or steam, thereby suppressing side reactions such as oxidation of the thermoplastic polymer P within the pressure vessel. Furthermore, in the present invention, when discharging the thermoplastic polymer-derived component from the pressure vessel (D), it is necessary to maintain a temperature of 110°C to 350°C and a pressure of 0.14 MPa to 30 MPa. Therefore, by supplying an inert gas or steam from the means (E) or adjusting the vapor pressure difference with the downstream thermoplastic polymer-derived component tank (H), the thermoplastic polymer-derived component can be discharged from the pressure vessel (D) together with water while maintaining the pressure. The pressure is preferably 1.0 MPa or higher, more preferably 2.0 MPa or higher, and even more preferably equal to or higher than the saturated vapor pressure at the temperature at which the water-insoluble solid component S is separated from the solution containing the thermoplastic polymer-derived component. On the other hand, it is preferably 10 MPa or less, and more preferably 4 MPa or less.

[0047] Examples of the inert gas in means (E) include nitrogen, rare gases such as argon, etc., but nitrogen is preferred in consideration of ease of availability and handling. Examples of means (E) include direct supply from a high-pressure gas tank, supply of gas pressurized by a compressor, supply of steam from a boiler, or a combination of these. Compressors include positive displacement and turbo types, but any type is acceptable as long as the desired pressure can be obtained.

[0048] [Means (F) for Separating Water-Insoluble Solid Component S] The apparatus for recovering a thermoplastic polymer-derived component of the present invention includes means (F) (sometimes simply referred to as "means (F)" in the present invention) for separating water-insoluble solid components from the mixture discharged from the pressure vessel (D) at 110°C or higher and 350°C or lower and 0.14 MPa or higher and 30 MPa or lower. In the apparatus for recovering a thermoplastic polymer-derived component of the present invention, means (F) includes a filter. By including means (F) in a filter, the removal rate of water-insoluble solid component S can be increased. Here, the removal rate is defined as (the amount of water-insoluble solid component S captured by the filter) / (the amount of water-insoluble solid component S present in the thermoplastic polymer composition). The filter aperture and filter area are appropriately selected depending on the type, shape, and amount of water-insoluble solid component S. Means (F) may be installed inside the pressure vessel (D). When means (F) is installed inside the pressure vessel (D), separation can be performed while maintaining a temperature of 110°C to 350°C and a pressure of 0.14 MPa to 30 MPa by supplying an inert gas or steam from means (E) as described above, moving the filter inside the pressure vessel (D), or adjusting the vapor pressure difference with the downstream thermoplastic polymer-derived component tank (H). If separation is possible at a temperature of 110°C to 350°C and a pressure of 0.14 MPa to 30 MPa, means (F) may be installed outside the pressure vessel (D). Means (A) and (B) can also be connected to means (F) (or means (D) if means (F) is inside means (D)). In this case, means (C) and means (F) have the same function.

[0049] [Thermoplastic polymer-derived component tank (H)] The device for recovering a thermoplastic polymer-derived component of the present invention has a thermoplastic polymer-derived component tank (H) for recovering a thermoplastic polymer-derived component, and is provided with a filter between the pressure vessel (D) and the thermoplastic polymer-derived component tank (H) as means (F) for separating the water-insoluble solid component S. By providing an arbitrary pressure difference between the thermoplastic polymer-derived component tank (H) and the pressure vessel (D), the thermoplastic polymer-derived component can pass through the filter.

[0050] The thermoplastic polymer-derived component recovery device of the present invention preferably includes a heat exchanger in which heat is exchanged between the mixture of thermoplastic polymer-derived components and water discharged from the means (C) or the means (F) and the water supplied by the means (B) or the pressure vessel (D). Heat exchange can improve the thermal efficiency of the entire process, which is preferable from the perspective of reducing energy consumption. Heat exchangers have complex flow paths to ensure a sufficient heat transfer area, which raises concerns about problems such as accumulation of water-insoluble solid components and blockage. By removing the water-insoluble solid components at 110°C or higher and 350°C or lower and 0.14 MPa or higher and 30 MPa or lower, as in the present invention, after mixing water and a thermoplastic polymer composition, the risk of blockage of the flow path is reduced, making it easier to install heat exchangers with complex shapes.

[0051] [Reactor (G) for Depolymerizing Thermoplastic Polymer-Derived Components] The recycled monomer production apparatus of the present invention has a reactor (G) (sometimes simply referred to as "reactor (G)" in the present invention) into which the thermoplastic polymer-derived components discharged from means (C) or means (F) of the thermoplastic polymer-derived component recovery apparatus of the present invention are introduced and which depolymerizes the thermoplastic polymer-derived components. By having the reactor (G), recycled monomer can be produced. In the present invention, by removing water-insoluble solid components using means (C) or means (F), problems such as accumulation and blockage of water-insoluble solid components in the reactor (G) or piping can be prevented. The reactor (G) may be either a batch or continuous reactor, but a continuous reactor is preferred. By using the reactor (G) as a continuous reactor, the time required for charging and discharging the batch reactor can be shortened, thereby improving productivity per unit volume. The continuous reactor may be a tubular reactor or a continuous tank reactor. When the reactor (G) is of a batch type, the thermoplastic polymer-derived component tank (H) can also be used as the reactor (G).

[0052] The temperature and pressure in reactor (G) may be different from those in means (C), (D), and (F). Since reactor (G) is intended to depolymerize the thermoplastic polymer-derived component to obtain a monomer, it is preferable to set the temperature and pressure higher than those in means (C), (D), and (F). It is also possible to improve the amount of monomer produced by adding additives such as water, alkali, and other organic solvents such as alcohol to the thermoplastic polymer-derived component and water supplied to reactor (G). Examples of alkali include the aforementioned alkaline (earth) metal salts.

[0053] The depolymerized product of the thermoplastic polymer-derived component and water discharged from reactor (G) are preferably introduced into a cooling device for terminating the depolymerization reaction by lowering the temperature. Examples of cooling devices for terminating the depolymerization reaction include a cooler and a flash tank. Among these, it is preferable that the cooling device for terminating the depolymerization reaction includes the above-mentioned heat exchanger for heating the water. Since the depolymerized product of the thermoplastic polymer-derived component and water after cooling are usually under high pressure, a back pressure valve or the like can be used as a known method. In the present invention, since solid components insoluble in water are removed, the risk of clogging of the back pressure valve can be reduced.

[0054] Regarding the monomer purification apparatus and the repolymerization apparatus, the recycled monomer obtained after the depolymerization reaction is preferably purified by a known method such as distillation or crystallization. The purified monomer is preferably repolymerized and reused as a composition containing the thermoplastic polymer P. As the repolymerization method, a known polymerization method can be used.

[0055] [Method for recovering thermoplastic polymer-derived components and method for producing recycled monomers] The method for recovering thermoplastic polymer-derived components of the present invention includes a step of separating water-insoluble solid components from a mixture of a thermoplastic polymer composition and water at 110°C to 350°C and 0.14 MPa to 30 MPa to obtain a thermoplastic polymer-derived component (hereinafter referred to as a solid component separation step). The operating temperature of the solid component separation step is preferably 130°C to 350°C. Furthermore, in the method for recovering thermoplastic polymer-derived components of the present invention, it is preferable to mix the mass a (kg) of the thermoplastic polymer composition and the mass b (kg) of water so that b / a is 1 to 100. By setting b / a to 1 or more, the viscosity of the mixture of the thermoplastic polymer composition and water is reduced, making it easier to separate the water-insoluble solid components. b / a is more preferably 2 or more, and even more preferably 3 or more. On the other hand, by setting b / a to 100 or less, the energy required for heating the water and the energy required for purifying the recycled monomer can be reduced. The ratio b / a is more preferably equal to or less than 10, even more preferably equal to or less than 8, and most preferably equal to or less than 6. The definitions, examples, and preferred embodiments of the thermoplastic polymer composition, the water-insoluble solid component S, the temperature and the pressure conditions are as described above.

[0056] The water-insoluble solid component separation step is preferably carried out at a temperature equal to or higher than the melting point of the thermoplastic polymer P in water. The method for measuring the melting point of the thermoplastic polymer P in water is as described above. By carrying out the water-insoluble solid component separation step at a temperature equal to or higher than the melting point of the thermoplastic polymer P in water, the viscosity of the thermoplastic polymer P is reduced, making it easier to separate the water-insoluble solid component S. In the method for recovering a thermoplastic polymer-derived component of the present invention, the water-insoluble solid component S and the thermoplastic polymer-derived component can be separated by utilizing a difference in specific gravity. Examples and preferred embodiments of separation by utilizing a difference in specific gravity are as described above. In the method for recovering a thermoplastic polymer-derived component of the present invention, it is preferable to include a step of separating the water-insoluble solid component S using a filter. Examples and preferred embodiments of the filter are as described above.

[0057] In the method for recovering a thermoplastic polymer-derived component of the present invention, it is preferable to perform heat exchange between the mixture of the thermoplastic polymer-derived component and water and the water supplied to the thermoplastic polymer composition. By performing heat exchange, thermal efficiency can be improved, which is preferable from the viewpoint of reducing energy consumption.

[0058] The method for producing a recycled monomer of the present invention includes a step of depolymerizing the thermoplastic polymer-derived component recovered by the above-mentioned method for recovering a thermoplastic polymer-derived component. The produced recycled monomer is preferably purified and then repolymerized to be reused as a thermoplastic polymer composition.

[0059] [Example of a production apparatus for thermoplastic polymer-derived components and recycled monomers] The following description will be made with reference to the drawings. FIG. 1 shows an example of a batch-type recovery apparatus for thermoplastic polymer-derived components. A pressure vessel 16 equipped with an agitator 20 is used as the pressure vessel (D) for obtaining a solution obtained by mixing a thermoplastic polymer composition with water. A compressor 15 is used as a means (E) for supplying an inert gas or steam into the pressure vessel (D). A filter 7 installed in the pressure vessel (D) is used as a means (F) for separating water-insoluble solid components 19 from the mixture discharged from the pressure vessel (D) at 110°C to 350°C and 0.14 MPa to 30 MPa. The pressure vessel (D) is purged with an inert gas using a valve 21 and a gas back pressure valve 18. Similarly, the thermoplastic polymer-derived component tank 22 is purged with an inert gas using a valve 21 and a gas back pressure valve 18. The thermoplastic polymer composition and water are then sealed in a pressure vessel 16 and heated to a temperature of 110°C to 350°C and a pressure of 0.14 MPa to 30 MPa. Under these temperature and pressure conditions, the thermoplastic polymer melts, dissolves, and hydrolyzes, separating from the water-insoluble solid component 19. While maintaining the above temperature and pressure conditions, a valve 21 between the pressure vessel 16 and a thermoplastic polymer-derived component tank 22 is opened, and the thermoplastic polymer-derived component and water are introduced into the thermoplastic polymer-derived component tank 22. The thermoplastic polymer-derived component and water can be recovered from the valve 21 below the thermoplastic polymer-derived component tank.

[0060] Figure 2 shows an example of a recycled monomer production apparatus having a reactor (G) for depolymerizing a thermoplastic polymer-derived component, located further downstream from the batch-type thermoplastic polymer-derived component recovery apparatus shown in Figure 1. A tubular reactor 10 is used as the reactor (G) for depolymerizing the thermoplastic polymer-derived component. Additional depolymerization reaction water stored in a depolymerization reaction additional water tank 27 is pressurized by a pump 8 and heated by a heater 9. A valve 21 at the bottom of a thermoplastic polymer-derived component tank 22 is opened, and the additional depolymerization reaction water and the thermoplastic polymer-derived component are mixed, pressurized by a pump 8, heated by a heater 9, and introduced into the tubular reactor 10. The depolymerized thermoplastic polymer-derived component discharged from the tubular reactor 10 is cooled by a cooler 12, depressurized by a backpressure valve 13, and stored in a depolymerized product tank 14.

[0061] FIG. 3 shows an example of a recycled monomer production apparatus having a reactor (G) for depolymerizing thermoplastic polymer-derived components downstream of a continuous thermoplastic polymer-derived component recovery apparatus. A raw material hopper 1 and an extruder 2 are used as the means for supplying the thermoplastic polymer composition (A). A water tank 3, a water pump 4, and a water heater 5 are used as the means for supplying water (B). Filters 7 installed in multiple separation tanks 6 are used as the means for obtaining thermoplastic polymer-derived components by separating water-insoluble solid components from a mixture of the thermoplastic polymer composition supplied from the means (A) and water supplied from the means (B) at 110°C to 350°C and 0.14 MPa to 30 MPa. In the apparatus shown in FIG. 3, the filter 7 is positioned so that the liquid phase flows from bottom to top to separate the water-insoluble solid components 19, which have a higher specific gravity than the thermoplastic polymer-derived components. A tubular reactor 10 is used as the reactor (G) for depolymerizing the thermoplastic polymer-derived components. The thermoplastic polymer composition stored in the raw material hopper 1 is heated and pressurized in the extruder 2. The water stored in the water tank 3 is pressurized by the water pump 4 and heated by the water heater 5, and then merged with the thermoplastic polymer composition. The merged solution is maintained at 110°C to 350°C and 0.14 MPa to 30 MPa, and then separated into thermoplastic polymer-derived components and water-insoluble solid components 19 in the separation tank 6 and the filter 7. If the system is operated for a long period of time, the water-insoluble solid components 19 will accumulate in the separation tank 6, and the water-insoluble solid components can be removed intermittently as needed. Note that in Figure 3, multiple separation tanks 6 and filters 7 are present, and by operating them sequentially, the water-insoluble solid components 19 are removed from the idle separation tanks. Although not shown in Figure 3, each of the multiple separation tanks 6 is equipped with a flow path and a valve. The additional water for depolymerization reaction stored in the additional water tank 27 for depolymerization reaction is pressurized by the pump 8, heated by the heater 9, mixed with the component derived from a thermoplastic polymer discharged from the separation tank 6, pressurized by the pump 8, heated by the heater 9, and introduced into the tubular reactor 10. The depolymerized product of the component derived from a thermoplastic polymer discharged from the tubular reactor 10 is cooled by the cooler 12, has its pressure released by the back pressure valve 13, and is stored in the depolymerized product tank 14.

[0062] Figure 4 shows an example of an apparatus in which, in addition to the apparatus of Figure 3, a heat exchanger 11 is installed that performs heat exchange between the depolymerized product of thermoplastic polymer-derived components discharged from the tubular reactor and water to be supplied to the separation tank 6. By installing the heat exchanger 11, it is possible to reuse the heat discharged from the tubular reactor 10 in which depolymerization is performed, thereby improving the thermal efficiency of the entire process.

[0063] Figure 5 shows an example of an apparatus in which the filter 7 in the separation tank 6 of the apparatus in Figure 4 has been modified so that the thermoplastic polymer-derived components flow from top to bottom. When the specific gravity of the water-insoluble solid components 19 is lighter than that of the thermoplastic polymer-derived components, clogging of the filter 7 can be prevented by modifying the filter 7 so that the thermoplastic polymer-derived components flow from top to bottom. Figure 6 shows the apparatus in Figure 2 with a buffer tank 30 added. Adding a buffer tank at the boundary between the batch-type pressure vessel and the continuous reactor makes it easier to control the amount of water added to the depolymerization reaction, which contains additives such as alkali.

[0064] [Second Aspect of the Invention] The second aspect of the present invention is a production method for obtaining a depolymerized intermediate composition by performing a first-stage depolymerization reaction under conditions that suppress the degradation of foreign materials, such as silicone, in order to separate inorganic substances and crosslinked polymers contained in a polyamide composition or a polyester composition. This also includes a production method for obtaining a depolymerized intermediate composition by partially depolymerizing a polyamide or polyester monomer in the first stage so that the depolymerized intermediate composition can be fed into a depolymerization apparatus in the same form when performing the second-stage depolymerization reaction described below. Therefore, the polyamide composition or polyester composition may contain components other than polyamide or polyester, or may be polyamide or polyester monomer alone, regardless of its shape or composition. In the presence of water, the polyamide composition or polyester composition is partially decomposed to obtain an aqueous slurry or aqueous solution of the depolymerized intermediate composition, which is then subjected to a second-stage depolymerization reaction to produce an aqueous slurry or aqueous solution of the depolymerized reaction composition. The depolymerized intermediate composition also includes oligomers and monomers. However, the components contained in the aqueous slurry or aqueous solution are limited to those derived from the polyamide or derivative obtained in the first-stage depolymerization. Meanwhile, a monomer-containing composition is a collective term for a composition containing a polymer and / or oligomer, a monomer, and / or its derivatives. By subjecting a monomer-containing composition to second-stage depolymerization, a depolymerization reaction composition, i.e., a monomer and its derivatives, can be produced with high yield. That is, by using a two-stage method in which depolymerization is stopped midway, unnecessary components are separated, and then further depolymerization is performed, the polyamide or polyester composition containing the foreign material can be separated regardless of its form or composition. The polyamide or polyester-derived components can be fed to the second-stage depolymerization device in the same form, thereby enabling highly efficient production of recycled monomers of the monomer and / or its derivatives. In the present invention, a polyamide or polyester composition is defined as a composition containing 5 to 100% by mass of polyamide or polyester per 100% by mass of the polyamide or polyester composition.

[0065] A second aspect of the present invention will be described below. In a preferred method for producing a polyamide-derived depolymerized intermediate composition according to the present invention, the step of obtaining the depolymerized intermediate composition involves depolymerizing a polyamide composition in the presence of water at a temperature greater than 200°C and less than 270°C to obtain the depolymerized intermediate composition. Hereinafter, a depolymerized intermediate composition obtained by depolymerizing a polyamide may be referred to as a polyamide-derived depolymerized intermediate composition. The polyamide in the polyamide composition used in the present invention is primarily composed of residues of amino acids, lactams, or diamines and dicarboxylic acids. Herein, "primarily composed of" refers to the presence of 50 mol% or more of residues selected from amino acids, lactams, diamines, and dicarboxylic acids in all structural units, and preferably 80 mol% or more of these residues.

[0066] Representative examples of raw materials for polyamides include amino acids such as 6-aminocaproic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, and para-aminomethylbenzoic acid; lactams such as ε-caprolactam and ω-laurolactam; aliphatic diamines such as tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 2-methylpentamethylenediamine, nonamethylenediamine, 2-methyloctamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4- / 2,4,4-trimethylhexamethylenediamine, and 5-methylnonamethylenediamine; aromatic diamines such as metaxylylenediamine and paraxylylenediamine; 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, and 1-amino-3-aminomethyl-3-methyl-3-methyl-2 ... Alicyclic diamines such as 5,5-trimethylcyclohexane, bis(4-aminocyclohexyl)methane, bis(3-methyl-4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminopropyl)piperazine, and aminoethylpiperazine; aliphatic dicarboxylic acids such as adipic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, 5-sodiumsulfoisophthalic acid, and 2,6-naphthalenedicarboxylic acid; and alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, and 1,3-cyclopentanedicarboxylic acid. In the present invention, two or more polyamide homopolymers or copolymers derived from these raw materials may be blended. The polyamide is not particularly limited, but from the viewpoint of recycling the polyamide and facilitating the promotion of cyclical use of fossil resources, homopolymers of polycaproamide (polyamide 6) and polyhexamethylene adipamide (polyamide 66), which are produced in large quantities and consumed in large quantities, and copolymers thereof are particularly preferred.

[0067] A preferred method for producing a polyamide-derived depolymerized intermediate composition includes depolymerizing 100 parts by mass of polyamide in a polyamide composition in the presence of 100 to 1,000 parts by mass of water to obtain a depolymerized intermediate composition. If the amount of water is less than 100 parts by mass, the dispersibility and solubility of the polyamide composition in water tend to decrease, resulting in reduced reaction efficiency. The amount of water is more preferably 120 parts by mass or more, and even more preferably 150 parts by mass or more. On the other hand, the amount of water is more preferably 800 parts by mass or less, even more preferably 500 parts by mass or less, and particularly preferably 300 parts by mass or less. The present invention relates to a method for producing a raw material monomer by depolymerizing polyamide, with the aim of achieving both the recycling of fossil resources and the reduction of greenhouse gas emissions. Water has a specific heat capacity of 4.3 kJ / kg·K and a heat of vaporization of 2,250 kJ / kg, which are very high compared to other organic solvents. Therefore, it is important to reduce the amount of water used. By keeping the amount of water within these ranges, both production efficiency and energy savings for the depolymerized intermediate composition can be achieved. There are no particular restrictions on the water used, as in the first embodiment, but from the viewpoint of suppressing side reactions due to the influence of coexisting salts, deionized water or distilled water is preferably used as water.

[0068] A suitable method for producing a polyamide-derived depolymerized intermediate composition preferably includes a step of depolymerizing a polyamide composition at a temperature greater than 200°C and less than 270°C to obtain a depolymerized intermediate composition. The depolymerization temperature is the temperature at which the polyamide composition is depolymerized in the presence of water in a temperature-controlled reaction vessel, and may be a constant temperature or a temperature that varies over time. By setting the depolymerization temperature to greater than 200°C and less than 270°C, the viscosity of the polyamide in the presence of water can be reduced, increasing its solubility and dispersibility, accelerating the reaction, and suppressing overreaction of the polyamide monomer produced by depolymerization. The depolymerization temperature is preferably 205°C or higher, more preferably 210°C or higher. On the other hand, the depolymerization temperature is preferably less than 260°C, more preferably less than 250°C, and even more preferably less than 240°C. The depolymerization temperature may temporarily become 270°C or higher within a range that does not impair the effects of the present invention. However, by keeping the depolymerization temperature below 270°C, over-reaction of the polyamide monomer can be suppressed. Therefore, it is preferable to keep the depolymerization temperature below 270°C throughout the step of obtaining a depolymerized intermediate composition.

[0069] The polyamide-derived depolymerized intermediate composition contains 10% by mass or more and 70% by mass or less of polyamide monomers and / or derivatives thereof, out of a total of 100% by mass of polyamide-derived components constituting the depolymerized intermediate composition. By setting the content within this range, the polyamide can be reduced in molecular weight and converted into a water slurry or water-soluble form while suppressing side reactions during the production of the depolymerized intermediate composition, thereby facilitating subsequent introduction into a depolymerization step. Furthermore, even when water-insoluble components other than polyamide are contained, separation of the water-insoluble components other than polyamide is facilitated. The content is preferably 12% by mass or more, more preferably 15% by mass or more. Meanwhile, the content is preferably 65% ​​by mass or less, more preferably 60% by mass or less.

[0070] Here, the content of the monomer and / or its derivative in the depolymerized intermediate composition can be calculated by quantitative analysis using gas chromatography (GC), ion chromatography (IC), liquid chromatography (LC), etc. as described in the Examples. Meanwhile, the content of components derived from polyamide in the depolymerized intermediate composition other than the monomer and / or its derivative is defined as the content of polyamide oligomer.

[0071] A suitable method for producing the polyester-derived depolymerized intermediate composition of the present invention is a step of obtaining a depolymerized intermediate composition by depolymerizing a polyester in a polyester composition at a temperature of 150° C. or higher and lower than 240° C. Hereinafter, a depolymerized intermediate composition obtained by depolymerizing a polyester may be referred to as a polyester-derived depolymerized intermediate composition.

[0072] The polyester in the polyester composition used in the present invention has as its main constituents residues of dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative, or has as its main constituent a structure in which a diol residue is bonded to a carbonyl group (carbonate ester bond). Here, "main constituent" means that, among all structural units, residues of dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative account for 50 mol% or more, and preferably 80 mol% or more of these residues. Here, the carbonyl group of the carbonate ester bond is not included in all structural units. Examples of the dicarboxylic acid or an ester-forming derivative thereof include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, bis(p-carboxyphenyl)methane, 1,4-anthracenedicarboxylic acid, 1,5-anthracenedicarboxylic acid, 1,8-anthracenedicarboxylic acid, 2,6-anthracenedicarboxylic acid, 9,10-anthracenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-tetrabutylphosphoniumisophthalic acid, and 5-sodiumsulfoisophthalic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, malonic acid, glutaric acid, and dimer acid; and alicyclic dicarboxylic acids such as 1,3-cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid, and ester-forming derivatives thereof. Two or more of these may be used.

[0073] The ester-forming derivatives referred to here include the alkyl esters, acid anhydrides, acid halides, etc. of the dicarboxylic acids mentioned above. Preferred examples of alkyl esters of dicarboxylic acids include methyl esters, ethyl esters, hydroxyethyl esters, and hydroxybutyl esters. Preferred examples of acid anhydrides of dicarboxylic acids include anhydrides of dicarboxylic acids and anhydrides of dicarboxylic acids and acetic acid. Preferred examples of halides of dicarboxylic acids include acid chlorides, acid bromides, and acid iodides. Examples of the diol or its ester-forming derivative include aliphatic or alicyclic glycols having 2 to 20 carbon atoms, such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, decamethylene glycol, cyclohexanedimethanol, cyclohexanediol, dimer diol, and isosorbide; long-chain glycols having a molecular weight of 200 to 100,000, such as polyethylene glycol, poly-1,3-propylene glycol, and polytetramethylene glycol; aromatic dioxy compounds, such as 4,4'-dihydroxybiphenyl, hydroquinone, t-butylhydroquinone, bisphenol A, bisphenol S, and bisphenol F; and ester-forming derivatives thereof. Two or more of these may be used. Examples of the ester-forming derivative include compounds in which the hydrogen atoms of the hydroxy groups of a diol are substituted with acetyl groups.

[0074] The polyester may be an aliphatic polyester, an aromatic polyester, or a copolymer thereof. However, aromatic polyesters or copolymers thereof are preferred due to their wider range of applications. Aromatic polyesters or copolymers thereof may be used alone or in combination of two or more at any content. Among these, polyesters with high production and consumption volumes are preferred, as they facilitate the recycling of polyesters and the promotion of fossil resource recycling. Examples of polyesters with high production and consumption volumes include polyesters obtained by polycondensation of at least one selected from terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, and their ester-forming derivatives with at least one selected from ethylene glycol, 1,3-propylene glycol, and 1,4-butanediol or their ester-forming derivatives. Among these, at least one selected from the group consisting of polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and copolymers thereof is particularly preferred.

[0075] A suitable method for producing a polyester-derived depolymerized intermediate composition preferably includes a step of depolymerizing 100 parts by mass of polyester in a polyester composition in the presence of 100 parts by mass or more and 1,000 parts by mass or less of water to obtain a depolymerized intermediate composition. If the amount of water is less than 100 parts by mass, the dispersibility and solubility of the polyester composition in water tend to decrease, resulting in a decrease in reaction efficiency. The amount of water is preferably 120 parts by mass or more, more preferably 150 parts by mass or more. On the other hand, the amount of water is preferably 800 parts by mass or less, more preferably 500 parts by mass or less, and even more preferably 300 parts by mass or less. In a method for producing a raw material monomer by depolymerizing a polyester, it is important to reduce the amount of water used, as described above. By keeping the amount of water within these ranges, both production efficiency and energy savings for the depolymerized intermediate composition can be achieved.

[0076] A suitable method for producing a polyester-derived depolymerized intermediate composition includes a step of depolymerizing the polyester in the polyester composition at a temperature of 150°C or higher and lower than 240°C to obtain a depolymerized intermediate composition. The depolymerization temperature is the temperature at which the polyester composition is depolymerized in the presence of water in a temperature-controlled reaction vessel, and may be a constant temperature or a temperature that varies over time. By setting the depolymerization temperature to 150°C or higher and lower than 240°C, the viscosity of the polyester in the presence of water can be reduced, increasing its solubility and dispersibility, accelerating the reaction, and suppressing overreaction of the polyester monomer produced by depolymerization. The depolymerization temperature is preferably 180°C or higher, more preferably 190°C or higher. On the other hand, the depolymerization temperature is preferably lower than 235°C, more preferably lower than 232°C. The depolymerization temperature may temporarily exceed 240°C as long as the effects of the present invention are not impaired. However, by setting the depolymerization temperature to lower than 240°C, overreaction of the polyester monomer can be suppressed, and therefore it is preferable to always maintain the depolymerization temperature below 240°C during the step of obtaining the depolymerized intermediate composition.

[0077] The polyester-derived depolymerized intermediate composition contains 10% by mass or more and 70% by mass or less of polyester monomers and / or derivatives thereof, based on 100 parts by mass of polyester-derived components constituting the depolymerized intermediate composition. By setting the content within this range, the polyester can be reduced in molecular weight and converted into a water slurry or water-soluble form while suppressing side reactions during the production of the depolymerized intermediate composition, thereby facilitating subsequent introduction into a depolymerization process. Furthermore, even when water-insoluble components other than polyesters are contained, separation of the water-insoluble components other than polyesters is facilitated. The content is preferably 12% by mass or more, more preferably 15% by mass or more. Meanwhile, the content is preferably 65% ​​by mass or less, more preferably 60% by mass or less. The content of the monomers and / or derivatives thereof in the depolymerized intermediate composition can be calculated by quantitative analysis using gas chromatography (GC) or liquid chromatography (LC). Meanwhile, the content of polyester-derived components other than the monomers and / or derivatives thereof in the depolymerized intermediate composition is referred to as the polyester oligomer content.

[0078] In the present invention, the depolymerization time during the production of the depolymerized intermediate composition is not particularly limited, but a preferred example is 0.1 to 60 minutes. The depolymerization time during the production of the depolymerized intermediate composition refers to the total time maintained in the presence of water at a temperature above 200°C in the case of a polyamide composition and at 150°C or higher in the case of a polyester composition. The depolymerization time also includes the time during which the polymer composition and water are maintained in the reaction vessel at a temperature within the above range in the coexistence of the polymer composition and water, including the temperature increase process until the depolymerization temperature is reached and the cooling process after the reaction at the depolymerization temperature. A depolymerization time of 60 minutes or less facilitates the suppression of yield reduction due to overreaction of the monomer. Furthermore, when the polyamide composition or polyester composition contains a different material that is insoluble in water, the different material is less likely to corrode or pulverize, facilitating separation from the depolymerized intermediate composition. A depolymerization time of 45 minutes or less is preferred, with 40 minutes or less being more preferred, and 35 minutes or less being even more preferred. On the other hand, a depolymerization time of 0.1 minutes or more allows the depolymerization reaction to proceed sufficiently, which tends to improve the yield of the monomer and / or its derivatives. The depolymerization time is preferably 0.1 minutes or more, more preferably 1 minute or more, and even more preferably 3 minutes or more.

[0079] Furthermore, the depolymerization pressure when reacting at the depolymerization temperature is preferably 0.48 MPa or higher. By setting the depolymerization pressure to 0.48 MPa or higher, depolymerization can be promoted. A depolymerization pressure of 1.0 MPa or higher is more preferable, and 1.5 MPa or higher is even more preferable. There is no particular upper limit to the depolymerization pressure, but an example is 22.1 MPa or lower. Setting the depolymerization pressure to 0.48 MPa or higher and 22.1 MPa or lower increases the ionic product of water, tending to promote the hydrolysis reaction of polyamide or polyester. One method for setting the depolymerization pressure within this pressure range is to pressurize the inside of a pressure vessel and then seal it. To pressurize the inside of the pressure vessel, a gas may be sealed in addition to the polyamide composition or polyester composition and water. Examples of the gas to be sealed include air, argon, and nitrogen. From the viewpoint of suppressing side reactions such as oxidation reactions, nitrogen or argon is preferably used as the sealed gas. The inside of the pressure vessel can also be pressurized by introducing high-pressure water. When high-pressure water is used, the pressure vessel can be kept gas-free. The degree of gas pressure is not particularly limited as long as it is set to the desired pressure, but may be 0.3 MPa or more.

[0080] The depolymerized intermediate composition may be a water-soluble or water-insoluble component at 25°C, or may contain both. To promote the recycling of fossil resources, a means of recycling waste plastics processed into various shapes, such as textile products, films, and molded resin products, is desired. In particular, used waste plastics are not limited to components other than the composite polyamide or polyester, and are expected to contain foreign matter introduced during use and recovery. In consideration of the above-mentioned issues specific to waste plastics, the depolymerized intermediate composition of the present invention is preferably in the form of an aqueous slurry solution or an aqueous solution when mixed with water, as this provides excellent handling. Here, "in the form of an aqueous slurry solution or an aqueous solution" means that the mixture of the depolymerized intermediate composition and water is in the form of an aqueous slurry solution or an aqueous solution at a temperature range from 0°C (the melting point of water) or higher to below the upper limit of the depolymerization temperature. By converting a polyamide composition or a polyester composition into an aqueous slurry solution or solution of a depolymerized intermediate composition, it becomes possible to supply the depolymerized intermediate composition to a depolymerization apparatus in a state dispersed or dissolved in water, regardless of the shape of the waste plastic used. Furthermore, the aqueous slurry solution or solution has excellent fluidity, making it easy to separate the composition from other materials that are insoluble in water.

[0081] In the method for producing a depolymerized intermediate composition, the depolymerized intermediate composition preferably contains a polyamide- or polyester-derived component insoluble in water at 25°C and a polyamide- or polyester-derived component soluble in water at 25°C, and the volume-average particle size of the water-insoluble component at 25°C measured using a particle size distribution analyzer is less than 100 μm. In the present invention, the term "component insoluble in water at 25°C" refers to a component that dissolves in an amount of less than 0.1 g per 100 g of water at 25°C. The "component insoluble in water at 25°C" may also be simply referred to as the "water-insoluble component." The volume-average particle size can be calculated using the method using a particle size distribution analyzer described in the Examples. The depolymerized intermediate composition thus obtained can be obtained as a water slurry solution or aqueous solution of the depolymerized intermediate composition regardless of the form of the waste plastic, and can be similarly supplied to a depolymerization apparatus. The volume-average particle size is more preferably 80 μm or less, even more preferably 60 μm or less, and particularly preferably 40 μm or less. The lower limit of the volume average particle size is not particularly limited, but it is most preferably 0 μm (indicating a state in which the particle is dissolved in water).

[0082] Methods for adjusting the volume average particle size within the above range include, for example, methods that increase the solubility or dispersibility of the polyamide-derived component or polyester-derived component in water. Specific examples include increasing the depolymerization temperature during the production of the depolymerized intermediate composition, increasing the amount of water relative to the polyamide composition or polyester composition, adding a compound to promote depolymerization, increasing the stirring speed, and adding a dispersing aid. In the present invention, the term "polyamide-derived component" refers collectively to polyamide, polyamide oligomers obtained by depolymerizing polyamide, and polyamide monomers. The polyamide oligomers and polyamide monomers may be derivatized. The polyamide-derived component does not necessarily contain all three of the above components. For example, a polyamide-derived component may be referred to as a polyamide-derived component even if it contains only one or two of polyamide, polyamide oligomer, and polyamide monomer. The same applies to polyester-derived components.

[0083] An alkali (earth) metal compound may be further present during the production of the depolymerized intermediate composition. The presence of an alkali (earth) metal compound can convert dicarboxylic acid, a type of polyamide or polyester monomer, into an alkali (earth) metal dicarboxylate salt, thereby increasing its solubility in water and improving the efficiency of separation from other materials. The term "alkali (earth) metal compound" refers to both alkali metal compounds and alkaline earth metal compounds. The term "alkali (earth) metal compound" refers to either a compound containing an alkali metal atom such as lithium, sodium, potassium, or cesium, or a compound containing an alkaline earth atom such as magnesium, calcium, or barium, or a mixture thereof.

[0084] Examples of the alkali metal compound include alkali metal hydroxides, alkali metal oxides, alkali metal carbonates, alkali metal phosphates, and alkali metal borates. From the viewpoint of increasing the yield of monomers and their derivatives, the alkali metal compound is preferably at least one selected from the group consisting of alkali metal hydroxides and alkali metal carbonates, and more preferably at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, cesium hydrogen carbonate, lithium carbonate, sodium carbonate, potassium carbonate, and cesium carbonate. Examples of the alkaline earth metal compound include alkaline earth metal hydroxides, alkaline earth metal oxides, alkaline earth metal carbonates, alkaline earth metal phosphates, and alkaline earth metal borates. In particular, from the viewpoint of increasing the yield of monomers and their derivatives, the alkaline earth metal compound is preferably at least one selected from the group consisting of alkaline earth metal hydroxides and alkaline earth metal carbonates, and more preferably at least one selected from the group consisting of magnesium hydroxide, calcium hydroxide, barium hydroxide, magnesium carbonate, calcium carbonate, and barium carbonate. The amount of the compound selected from the above-mentioned alkaline (earth) metal hydroxides, oxides, carbonates, phosphates, borates, and mixtures containing two or more of these is preferably set depending on the content of dicarboxylic acid residues in the polyamide and / or polyester in the polyamide composition and / or polyester composition.

[0085] In the method for producing a depolymerized intermediate composition, in the step of obtaining the depolymerized intermediate composition, a polyamide or polyester contains dicarboxylic acid residues, and X mol of the dicarboxylic acid residues and alkali metal ions are reacted with Y １ mol and / or alkaline earth metal ions are ２ It is preferable that hydroxides, oxides, carbonates, and mixtures containing two or more of these metals coexist so as to satisfy the formula (1). １ +2 x Y ２) / X≦1.5 (Formula 1) By setting the value within this range, over-reaction of the depolymerized monomer can be suppressed, and an aqueous slurry solution or solution of the depolymerized intermediate composition can be easily obtained. By obtaining the depolymerized intermediate composition as an aqueous slurry solution or solution of the depolymerized intermediate composition, the fluidity is excellent, and separation from components insoluble in water at 25°C other than the polyamide-derived components or polyester-derived components contained in the polyamide composition or polyester composition described below is facilitated. Furthermore, when the polyamide composition or polyester composition contains an inorganic component described below, the depolymerization of the polyamide or polyester can be promoted while suppressing elution of decomposed inorganic components into water. (Y １ +2 x Y ２ ) / X is more preferably 0.6 or more, even more preferably 0.8 or more, and particularly preferably 0.9 or more. １ +2 x Y ２ ) / X is more preferably 1.3 or less, and even more preferably 1.1 or less. The amount of dicarboxylic acid residues contained in the polyamide composition and polyester composition can be measured by proton nuclear magnetic resonance spectroscopy ( １ Quantitation can be achieved from the spectrum obtained by 1 H-NMR.

[0086] There are no particular limitations on the method for allowing the alkaline (earth) metal compound to coexist. For example, an aqueous solution may be prepared in advance by mixing the alkaline (earth) metal compound with water; the polyamide composition and / or polyester composition may be mixed with the alkaline (earth) metal compound and then brought into contact with water; or the polyamide composition may be contacted with water and then further mixed with the alkaline (earth) metal compound.

[0087] In the present invention, a polyamide composition or a polyester composition is depolymerized, and then components other than polyamide-derived components or polyester-derived components that are insoluble in water at 25°C are separated from the polyamide composition or polyester composition by the method described below, thereby obtaining a depolymerized intermediate composition. Examples of components other than polyamide- or polyester-derived components that are insoluble in water at 25°C include organic components such as other polymers and organic fibers other than polyamides and polyesters, and inorganic components such as inorganic fibers and non-fibrous inorganic fillers. In the method for producing a depolymerized intermediate composition of the present invention, the polyamide composition or polyester composition preferably contains an inorganic component. Until now, polyamide compositions or polyester compositions containing inorganic components have been difficult to recycle due to the inclusion of foreign matter or deterioration of the inorganic components during reprocessing, resulting in the majority of compositions being incinerated or landfilled after use. According to the present invention, polyamide compositions or polyester compositions containing inorganic components, which have been difficult to chemically recycle using conventional methods, can be utilized as a chemical recycling resource and can be regenerated into products equivalent to petrochemicals.

[0088] Examples of the other polymers include polyolefin, modified polyphenylene ether, polysulfone, polyketone, polyetherimide, polyarylate, polyethersulfone, polyetherketone, polythioetherketone, polyetheretherketone, polyimide, polyamideimide, polyethylene tetrafluoride, polyphenylene sulfide, polyurethane, silicone, polyacrylic acid, etc. Two or more of these may be contained, and they may be crosslinked.

[0089] Examples of the organic fibers include natural fibers such as cotton, hemp, and silk, and synthetic fibers such as aramid, acrylic, and rayon. Examples of the inorganic fibers include fibrous or whisker-like fillers such as glass fibers, carbon fibers, metal fibers, gypsum fibers, ceramic fibers, asbestos fibers, zirconia fibers, alumina fibers, silica fibers, titanium oxide fibers, silicon carbide fibers, aramid fibers, rock wool, potassium titanate whiskers, silicon nitride whiskers, wollastonite, and alumina silicate. Two or more of these may be contained. Examples of the non-fibrous inorganic fillers include non-swelling silicates, swellable layered silicates, metal hydroxides, smectite clay minerals, various clay minerals, glass beads, glass flakes, ceramic beads, boron nitride, aluminum nitride, silicon carbide, calcium phosphate, carbon black, and graphite. Two or more of these may be contained.

[0090] The form or article of the polyamide composition or polyester composition may include, but is not limited to, fibers, films, and resin molded products. When a material other than polyamide or polyester is used, examples of the fiber include blended fibers with fibers of different materials (natural fibers, synthetic fibers), fabrics combined with different materials by sewing, impregnation, bonding, coating, etc.; examples of the film include films coated with different materials, laminated films with different materials, and examples of the resin molded product include resin molded products obtained by melt-kneading different materials, two-color molded products with different materials, and resin molded products combined with different materials by fastening, welding, bonding, etc. In particular, silicone-coated polyamide 66 compositions used in airbags and glass fiber-blended polyamide compositions and polyester compositions used in automotive parts are used in large quantities. From the perspective of resource recycling, in the method for producing a depolymerized intermediate composition of the present invention, it is preferable that the polyamide composition or polyester composition contains a silicon-containing component. Examples of the silicon-containing component include silicone and glass fiber.

[0091] The polyamide composition or polyester composition used in the present invention may contain various additives within the scope of the present invention, such as antioxidants, heat stabilizers, weathering agents, mold release agents and lubricants, pigments, dyes, plasticizers, antistatic agents, and flame retardants.

[0092] Specific examples of products using the polyamide composition in the present invention include engine peripheral parts such as radiator tanks and oil pans, automobile parts such as gears, electric and electronic parts such as connectors and switches, parts for industrial machinery such as fasteners and binding bands, industrial fiber structures such as airbag fabrics and tire cords, fiber structures for clothing, sheets, films, molded products, etc. Furthermore, product scraps, pellet scraps, lump scraps, etc. generated in the production process of these products may also be used.

[0093] Specific examples of products using the polyester composition include sheet products such as beverage bottles, seasoning bottles, food trays, blister packs, food dividers, and industrial trays, film products such as packaging films, optical functional films, release films, magnetic tapes, and insulating materials, textile structures for clothing such as used clothing, uniforms, sportswear, and underwear, industrial textile structures such as curtains, carpets, nets, belts, and sheets, molded articles such as automobile parts, electrical and electronic parts, building materials, daily necessities, household goods, and sanitary products, etc. Furthermore, product scraps, pellet scraps, lump scraps, etc. generated in the production processes of these products may also be used.

[0094] Since the object of the present invention is to chemically recycle polyamide or polyester, it is preferable that the polyamide composition or polyester composition contain fewer components other than components derived from polyamide or polyester. From the viewpoint of ensuring the fluidity of a solution containing a depolymerized intermediate composition, the method for producing a depolymerized intermediate composition of the present invention preferably contains 0.01% by mass or more and 60% by mass or less of components insoluble in water at 25°C other than components derived from polyamide or polyester, per 100% by mass of the polyamide composition or polyester composition. The content of components insoluble in water at 25°C other than components derived from polyamide or polyester is more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0095] The present invention preferably further includes a step of removing, using a filter, components insoluble in water at 25°C other than components derived from the polyamide or polyester after depolymerization of the polyamide composition or polyester composition. By including the step of removing the water-insoluble components, the depolymerized intermediate composition has the same form as a depolymerized intermediate composition produced from a polyamide composition or polyester composition that does not contain components insoluble in water at 25°C other than components derived from the polyamide or polyester. The method for removing the water-insoluble components using a filter is not particularly limited, and any commonly known method can be selected depending on the properties and size of the water-insoluble components obtained after depolymerization of the polyamide composition or polyester composition. The temperature for removing the water-insoluble components using a filter is not particularly limited, but is preferably 25°C or higher and the depolymerization temperature or lower. To increase the fluidity of an aqueous slurry solution of the depolymerized intermediate composition or to dissolve the depolymerized intermediate composition in water, a temperature of 50°C or higher is more preferred, 100°C or higher is even more preferred, and 130°C or higher is particularly preferred. The depolymerized intermediate composition thus obtained is in the form of a water slurry solution or an aqueous solution regardless of the shape and composition of the polyamide composition or polyester composition, and can therefore be supplied in the same form to a subsequent depolymerization apparatus, and is particularly suitable for use in the production of recycled monomers.

[0096] In the present invention, after depolymerization of a polyamide composition or polyester composition, the weight-average major axis of components other than polyamide-derived components or polyester-derived components that are insoluble in water at 25°C and do not pass through a 40-mesh filter, as observed with an optical microscope at 25°C, is preferably 100 μm or more. A weight-average major axis of 100 μm or more increases the difference in particle size between the polyamide-derived components or polyester-derived components and the water-insoluble components, allowing the polyamide-derived components or polyester-derived components to be efficiently recovered by removal through a filter. The weight-average major axis can be calculated using the optical microscope observation method described in the Examples. To improve separability from the polyamide-derived components or polyester-derived components, the weight-average major axis is preferably 120 μm or more, more preferably 200 μm or more, and even more preferably 250 μm or more. Preferred methods for achieving a weight-average major axis within the above range include lowering the depolymerization temperature to suppress deterioration of components other than polyamide-derived or polyester-derived components, and increasing the amount of water to reduce viscosity and prevent particle size reduction due to shear forces during liquid delivery. On the other hand, excessively large particle sizes of water-insoluble components other than polyamide-derived or polyester-derived components clog the flow path, making separation from the polyamide-derived or polyester-derived components difficult. Therefore, the minor axis of the water-insoluble components other than polyamide- or polyester-derived components is preferably less than 10 cm. The minor axis is more preferably less than 5 cm, and even more preferably less than 1 cm. Preferred methods for achieving a weight-average major axis within the above range include roughly chopping or crushing the polyamide or polyester composition in advance, attaching blades to a stirring blade to chop the composition simultaneously with depolymerization, suppressing aggregation and coalescence by stirring, and adding a dispersing aid.

[0097] In the present invention, after depolymerization of a polyamide composition or polyester composition, the composition preferably contains polyamide-derived or polyester-derived components and other components insoluble in water at 25°C, and polyamide- or polyester-derived components soluble in water at 25°C, and the volume average particle size of the components insoluble in water at 25°C that pass through a 40-mesh filter is less than 100 μm as determined with a particle size distribution analyzer. Here, "polyamide-derived or polyester-derived components and other components insoluble in water at 25°C" refers to both polyamide-derived or polyester-derived components insoluble in water at 25°C and components other than polyamide-derived or polyester-derived components that are insoluble in water at 25°C. The same applies to the "component insoluble in water at 25°C" in "components insoluble in water at 25°C that pass through a 40-mesh filter." The volume average particle size can be calculated using the method using a particle size distribution analyzer described in the Examples. The depolymerized intermediate composition thus obtained can be obtained as a water slurry solution or aqueous solution of the depolymerized intermediate composition, making it easy to supply the plastic waste in the same form to the depolymerization apparatus regardless of the shape or composition. The volume average particle size is more preferably 80 μm or less, even more preferably 60 μm or less, and particularly preferably 40 μm or less. There is no particular restriction on the lower limit of the volume average particle size, but 0 μm (indicating a state dissolved in water) is most preferable. Here, when all components other than polyamide-derived components or polyester-derived components have been removed by a filter, the volume average particle size will be that of only the water-insoluble components of the polyamide-derived components or polyester-derived components.

[0098] In the present invention, after depolymerizing the polyamide composition or polyester composition, it is preferable to remove 20% by mass or more of 100% by mass of components insoluble in water at 25°C other than polyamide-derived components or polyester-derived components from the polyamide composition or polyester composition using a filter. The higher the removal rate of water-insoluble components, the more improved the separation and recovery of the polyamide composition-derived components or polyester composition-derived components. Filter removal can be performed using various known removal methods, such as filters, strainers, and screens. Specific examples of fixed filters include cartridge filters, leaf filters, filter presses, and Nutsche filters. Fixed strainers include basket strainers, cartridge strainers, T-type strainers, and Y-type strainers. Moving filters include belt filters, centrifugal filters, screen changers, and drum filters. Screens include fixed screens such as bar screens, vibrating screens, in-plane screens, rotary screens, and conveyor screens. Preferred examples of methods for achieving the removal rate within the above range include reducing the mesh size of the filter medium and performing removal using a filter multiple times.The removal rate is more preferably 50% by mass or more, even more preferably 55% by mass or more, and particularly preferably 65% ​​by mass or more.The upper limit of the removal rate is not particularly limited, but 100% by mass is most preferred.The removal rate of water-insoluble components can be calculated by a washing extraction method using a solvent that dissolves only polyamide-derived components or polyester-derived components as described in the examples.

[0099] The method for producing a depolymerized intermediate composition can employ various known reaction methods, such as batch and continuous methods. Examples of batch methods include autoclaves equipped with a stirrer and a heating function, vertical or horizontal reactors, and vertical or horizontal reactors equipped with a compression mechanism such as a cylinder in addition to a stirrer and a heating function. Examples of continuous methods include extruders equipped with a heating function, tubular reactors, tubular reactors equipped with a mixing mechanism such as a baffle, line mixers, vertical or horizontal reactors, vertical or horizontal reactors equipped with a stirrer, and towers. The production atmosphere is preferably a non-oxidizing atmosphere, more preferably an inert atmosphere such as nitrogen, helium, or argon, and even more preferably a nitrogen atmosphere from the standpoints of economy and ease of handling.

[0100] One embodiment of the method for producing a depolymerization reaction composition of the present invention includes a step of depolymerizing a monomer-containing composition containing 10% by mass or more and 70% by mass or less of polyamide monomers and / or polyester monomers and / or derivatives, and 30% by mass or more and 90% by mass or less of components derived from polyamides or polyesters other than the monomers and / or derivatives, in the presence of water at 225°C or more and 350°C or less, to obtain a depolymerization reaction composition, wherein the depolymerization reaction composition contains 75% by mass or more of polyamide monomers and / or derivatives, or polyester monomers and / or derivatives, in 100% by mass of the polyamide-derived or polyester-derived components. Here, the polyamide-derived or polyester-derived components in the depolymerization reaction composition refer to the monomers and / or derivatives thereof and components derived from polyamides or polyesters other than the monomers and / or derivatives, the total content of which is 100% by mass. The components derived from polyamides or polyesters other than the monomers and / or derivatives thereof include polyamide oligomers and / or derivatives thereof. Examples of methods for adjusting the content of the monomer and / or its derivative within the above range include a method in which the depolymerization temperature is adjusted to the above preferred range, and a method in which an alkaline (earth) metal compound or the like is further added.

[0101] In the method for producing a depolymerization reaction composition of the present invention, the monomer-containing composition is preferably the above-mentioned polyamide-derived depolymerized intermediate composition or polyester-derived depolymerized intermediate composition. The above-mentioned depolymerized intermediate composition has the same form regardless of the shape or composition of the polyamide composition or polyester composition, and therefore can be suitably supplied to a depolymerization apparatus in the step of obtaining a depolymerization reaction composition. Furthermore, a depolymerized intermediate composition produced from a polyamide composition or polyester composition containing foreign materials is particularly preferred because the foreign materials can be removed in advance by the above-mentioned method, facilitating the separation and purification of the monomer from the depolymerization reaction composition.

[0102] Another embodiment of the method for producing a depolymerization reaction composition of the present invention includes the following first and second steps. Step 1 is a first-stage depolymerization step, and Step 2 is a second-stage depolymerization step. Steps 1 and 2 are performed in this order: (Step 1) A step of depolymerizing a polyamide or polyester in a polyamide composition or a polyester composition in the presence of water at 150°C or higher and 300°C or lower to obtain an aqueous slurry solution or solution containing a monomer-containing composition, wherein 100% by mass of the polyamide-derived component or polyester-derived component in the monomer-containing composition contains 10% by mass or higher and 70% by mass or lower of polyamide monomers and / or derivatives thereof, or polyester monomers and / or derivatives thereof; and (Step 2) A step of further depolymerizing the aqueous slurry solution or solution at 225°C or higher and 350°C or lower to obtain a depolymerization reaction composition, wherein 100% by mass of the polyamide-derived component or polyester-derived component in the depolymerization reaction composition contains 75% by mass or higher of polyamide monomers or polyester monomers and / or derivatives thereof.

[0103] By including the first and second steps, it is possible to obtain a depolymerization reaction composition containing 75 mass % or more of polyamide monomers and / or derivatives thereof, or polyester monomers and / or derivatives thereof.

[0104] The depolymerization temperature in the first step is 150°C or higher and 300°C or lower. By setting the depolymerization temperature in the first step to 150°C or higher, the polyamide or polyester softens and the contact area with water can be increased, thereby improving depolymerization efficiency. The depolymerization temperature in the first step is preferably higher than 160°C, more preferably higher than 175°C, even more preferably higher than 190°C, and particularly preferably higher than 200°C. On the other hand, by setting the depolymerization temperature in the first step to 300°C or lower, undesirable reactions such as thermal decomposition and overreactions accompanied by elimination of monomer end groups can be suppressed. The depolymerization temperature in the first step is preferably lower than 290°C, more preferably lower than 280°C, and even more preferably lower than 270°C. In particular, the depolymerization temperature of the polyester composition is particularly preferably lower than 240°C, since this makes it easier to suppress discoloration.

[0105] The depolymerization temperature in the second step is 225°C or higher and 350°C or lower. Setting the depolymerization temperature in the second step to 225°C or higher facilitates dispersion and dissolution of the monomer-containing composition in water, thereby improving depolymerization efficiency. Subcritical water, which is a temperature and pressure range slightly lower than the critical point of water (pressure 22.1 MPa, temperature 374.2°C), is characterized by (i) a low dielectric constant and (ii) a high ionic product. Despite being water, it dissolves organic compounds and exhibits excellent hydrolysis properties. Setting the depolymerization temperature in the second step to 350°C or lower further promotes depolymerization of the monomer-containing composition while suppressing undesirable reactions such as thermal decomposition, thereby producing a depolymerization reaction composition containing 75% by mass or more of polyamide monomers and / or derivatives thereof, or polyester monomers and / or derivatives thereof. In particular, when a monomer-containing composition containing a diol or a diamine is depolymerized, the depolymerization temperature in the second step is preferably 320°C or lower, and more preferably 300°C or lower, since this makes it easier to suppress side reactions involving elimination of hydroxyl groups or amino groups.

[0106] The depolymerization reaction composition in the second step preferably contains 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, of polyamide monomers and / or derivatives thereof, or polyester monomers and / or derivatives thereof. Water can be further added in the second step. Adding water in the second step can accelerate the depolymerization of the monomer-containing composition. However, from the viewpoint of energy conservation, it is preferable to use less water with a high specific heat capacity. Therefore, the amount of water added in the second step, together with the water used in the first step, is preferably adjusted to 1,000 parts by mass or less. The total amount of water used in the first and second steps is more preferably 800 parts by mass or less, even more preferably 500 parts by mass or less, and particularly preferably 300 parts by mass or less. Furthermore, an alkaline (earth) metal compound can be further present in the first step and / or the second step. Examples of the alkaline (earth) metal compound include the compounds that can be used in the production of the depolymerized intermediate composition described above.

[0107] In the method for producing a depolymerization reaction composition of the present invention, the depolymerization time in the second step during production of the depolymerization reaction composition is not particularly limited, but a preferred example is 0.1 to 60 minutes. The depolymerization time in the method for producing a depolymerization reaction composition of the present invention refers to the total time maintained at the depolymerization temperature of 225°C or higher in the presence of water. The depolymerization time also includes the time during which the monomer-containing composition and water are maintained at the temperature range in the reaction vessel in the coexistence of the monomer. A depolymerization time of 60 minutes or less tends to suppress yield reduction due to overreaction of the monomer. A depolymerization time of 45 minutes or less is preferred, more preferably 40 minutes or less, and even more preferably 35 minutes or less. On the other hand, a depolymerization time of 0.1 minutes or more allows the depolymerization reaction to proceed sufficiently, which tends to improve the yield of the monomer and / or its derivatives. A depolymerization time of 0.1 minutes or more is preferred, more preferably 1 minute or more, and even more preferably 3 minutes or more. In the production of the depolymerization reaction composition, the depolymerization pressure in the first step and the second step may be the same as the conditions applied in the production of the depolymerized intermediate composition described above.

[0108] There are no particular limitations on the method for recovering the depolymerization reaction composition produced by the method for producing a depolymerization reaction composition of the present invention, and any method can be used. Monomers from the obtained depolymerization reaction composition can be recovered by known methods such as extraction, distillation, and solid-liquid separation. Furthermore, to obtain monomers of even higher purity, the depolymerization reaction composition may be further purified by known methods. The polyamide monomer or polyester monomer of the present invention can be obtained by purifying the depolymerization reaction composition obtained by the method for producing a depolymerization reaction composition of the present invention. The polyamide monomer or polyester monomer of the present invention can be used as a polymerization raw material for polyamide or polyester, similar to monomers produced from petroleum-derived raw materials.

[0109] The polyamide or polyester production method of the present invention includes a step of polycondensing raw materials containing the polyamide or polyester monomers of the present invention. Examples of polyamide production methods include thermal polycondensation of amino acids, lactams, diamines, and dicarboxylic acids, either directly or with their salts. Examples of polyester production methods include esterification of dicarboxylic acids with diols, followed by polycondensation, or transesterification of diols with dialkyl dicarboxylates obtained by chemically converting dicarboxylic acids, followed by polycondensation. The polyamide or polyester production method of the present invention allows polyamide or polyester to be regenerated by depolymerizing the polyamide composition and / or polyester composition and repolymerizing the resulting monomers. This allows for the production of environmentally friendly recycled materials that contribute to resource recycling and reduced greenhouse gas emissions.

[0110] The polyamide or polyester of the present invention is obtained by polycondensation of raw materials containing the polyamide monomer or polyester monomer of the present invention. The polyamide or polyester of the present invention can be processed into various products such as injection-molded products, extrusion-molded products, fiber structures, films, and sheets, just like polyamides or polyesters produced from petroleum-derived raw materials. These products are useful for automobile parts, electrical and electronic parts, industrial machinery parts, industrial fiber structures, fiber structures for clothing, sheets, films, and the like. The molded products, fibers, films, or sheets of the present invention are made using the polyamide or polyester of the present invention.

[0111] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The following raw materials were used in the examples of the first and second aspects of the present invention. Deionized water was used as the water.

[0112] (A-1) Polyamide 66 waste: 30% glass fiber (GF) reinforced polyamide 66 molding waste (crushed sprue and runners, passing through an 8 mm mesh), melting point in a bone-dry state: 265°C, melting point in water: 179°C, melting point of GF: 500°C or higher. The thermoplastic polymer is polyamide 66, and the water-insoluble solid component is GF. (A-2) Polyamide 66 waste: Silicone-coated airbag fabric made from polyamide 66 recovered from scrapped vehicles, with 12.0% by mass of components other than polyamide, melting point in a bone-dry state: 265°C, melting point in water: 179°C, and no melting point of the silicone coating. The thermoplastic polymer is polyamide 66, and the water-insoluble solid component is the silicone coating. (B-1) Polyamide 6 waste: 30% glass fiber (GF) reinforced polyamide 6 molding scraps (crushed sprues and runners, passing through an 8 mm mesh), melting point in a bone-dry state: 225°C, melting point in water: 160°C, melting point of GF: 500°C or higher. The thermoplastic polymer is polyamide 6, and the water-insoluble solid component is GF. (C-1) Polyethylene terephthalate waste: Blended fiber consisting of 82% by mass of polyethylene terephthalate (PET) and 18% by mass of cotton, melting point in a bone-dry state: 250°C, melting point in water: 220°C, no melting point of cotton. The thermoplastic polymer is PET, and the water-insoluble solid component is cotton. (C-2) Polybutylene terephthalate waste: glass fiber (GF) 30% reinforced polybutylene terephthalate (PBT) molding waste (crushed sprue and runners, passing through an 8 mm mesh), melting point in an oven-dry state: 224°C, melting point in water: 196°C, melting point of GF: 500°C or higher. The thermoplastic polymer is PBT, and the water-insoluble solid component is GF. (D-1) Polyamide 66: "Amilan" (registered trademark), CM3001-N manufactured by Toray Industries, Inc. (D-2) Polyamide 66 waste: silicone-coated airbag fabric made of polyamide 66 recovered from scrapped vehicles, amount of components other than polyamide: 12.0% by mass (D-3) Polyamide 66 waste: GF-reinforced polyamide 66 molding scrap (crushed sprue and runners, passed through an 8 mm mesh), amount of components other than polyamide (glass fiber): 31.2% by mass (E-1) Polyamide 6 waste: GF-reinforced polyamide 6 molding scrap (crushed sprue and runners, passed through an 8 mm mesh), amount of components other than polyamide (glass fiber): 31.0% by mass.

[0113] The evaluation methods for the first and second aspects of the present invention are as follows. <Yield of hexamethylenediamine (GC)> The yield of hexamethylenediamine is calculated from the amount of hexamethylenediamine quantified by gas chromatography (GC). Hexamethylenediamine is quantified by the absolute calibration method (calibration reagent: first-class, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Apparatus: GC-2010 manufactured by Shimadzu Corporation Column: DB-5 0.32 mm x 30 m (0.25 μm) manufactured by Agilent Technologies Carrier gas: Helium Detector: Flame ionization detector (FID) Sample: In the first aspect, an aqueous solution or aqueous slurry of the depolymerized product of a thermoplastic polymer-derived component containing recycled monomers after termination of the depolymerization reaction is used. In the second aspect, an aqueous slurry or aqueous solution of a depolymerized intermediate composition or a depolymerization reaction composition is used. Approximately 0.15 g of the water slurry or aqueous solution is taken, diluted with approximately 10 g of deionized water, and components insoluble in the deionized water are separated and removed by filtration to prepare a sample for gas chromatography measurement.

[0114] <Yield (IC) of Adipic Acid (Disodium Adipate)> The yield of adipic acid is calculated from the amount of adipic acid quantified by ion chromatography (IC). Adipic acid is quantified by the absolute calibration method (calibration reagent: adipic acid: special grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Apparatus: HIC-20Asuper, manufactured by Shimadzu Corporation; Column: Shim-pack IC-SA2 (250 mm x 4.6 mm ID), manufactured by Shimadzu Corporation; Detector: Electrical conductivity detector (suppressor); Eluent: 4.0 mM sodium bicarbonate / 1.0 mM sodium carbonate aqueous solution; Flow rate: 1.0 ml / min; Injection volume: 50 microliters; Column temperature: 30°C; Sample: In the first embodiment, an aqueous solution or aqueous slurry of the depolymerized product of a thermoplastic polymer-derived component containing recycled monomers after termination of the depolymerization reaction is used. In the second embodiment, a water slurry or aqueous solution of the depolymerized intermediate composition or the depolymerization reaction composition is used. About 0.02 g of the water slurry or aqueous solution is taken, diluted with about 10 g of deionized water, and filtered to separate and remove components insoluble in deionized water, thereby preparing a sample for ion chromatography measurement.

[0115] <Yield of Terephthalic Acid (HPLC)> The yield of terephthalic acid is calculated from the amount of terephthalic acid quantified by high-performance liquid chromatography (HPLC). The amount of terephthalic acid is quantified using the absolute calibration curve method (calibration curve reagent: special grade, manufactured by Kanto Chemical Co., Ltd.). In this example, although a metal terephthalate salt is produced after the reaction, it is converted to terephthalic acid by the acid contained in the mobile phase. Apparatus: LC-10Avp series manufactured by Shimadzu Corporation; Column: Mightysil RP-18GP150-4.6; Detector: Photodiode array detector (UV, wavelength 254 nm); Flow rate: 1 mL / min; Column temperature: 40°C; Mobile phase: 0.1% by volume aqueous acetic acid solution / acetonitrile; Sample: Approximately 0.1 g of an aqueous slurry or solution of the depolymerized product of a thermoplastic polymer-derived component containing recycled monomers after the depolymerization reaction was stopped was weighed and diluted with approximately 10 g of water. Insoluble components are separated and removed by filtration to prepare a sample for high performance liquid chromatography.

[0116] <ε-Caprolactam Yield (HPLC)> The yield of ε-caprolactam is calculated from the amount of ε-caprolactam quantified by high-performance liquid chromatography (HPLC). The amount of ε-caprolactam is quantified by the absolute calibration method (calibration reagent: special grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Apparatus: LC-10Avp series manufactured by Shimadzu Corporation; Column: Mightysil RP-18GP150-4.6; Detector: Photodiode array detector (UV = 205 nm); Flow rate: 1 mL / min; Column temperature: 40°C; Mobile phase: 0.1% aqueous acetic acid / acetonitrile; Sample: In a first embodiment, an aqueous solution or aqueous slurry of a depolymerized product of a thermoplastic polymer-derived component containing recycled monomers after termination of the depolymerization reaction is used. In a second embodiment, an aqueous slurry or aqueous solution of a depolymerized intermediate composition or a depolymerization reaction composition is used. Approximately 0.15 g of the aqueous slurry or solution is taken, diluted with approximately 10 g of deionized water, and filtered to separate and remove components insoluble in the deionized water, thereby preparing a sample for high performance liquid chromatography measurement.

[0117] <Melting Point of Thermoplastic Polymer in Absolute Dry State and Melting Point of Polyamide> The melting point of the thermoplastic polymer in the thermoplastic polymer composition is the temperature of the endothermic peak that appears when the thermoplastic polymer is cooled from a molten state to 30°C at a rate of 10°C / min under a nitrogen flow using a differential thermal analyzer (TG / DTA7200, manufactured by Hitachi High-Tech Science), and then heated to 350°C at a rate of 10°C / min. The melting point of the polyamide is the temperature of the endothermic peak that appears when approximately 5.0 mg of polyamide is heated from 40°C to 300°C at a rate of 10°C / min under a nitrogen flow using a differential thermal analyzer (TG / DTA7200, manufactured by Hitachi High-Tech Science). However, if two or more endothermic peaks are detected, the temperature of the endothermic peak with the greatest peak intensity is taken as the melting point in the absolute dry state.

[0118] <Melting Point of Thermoplastic Polymer in Water> A thermoplastic polymer and an equal amount of distilled water are sealed in a stainless steel pressure-resistant sealed container for DSC, and the temperature is increased from 40°C to 350°C at a rate of 10°C / min under a nitrogen flow using a differential thermal analyzer (DSC7000X manufactured by Hitachi High-Tech Science). The temperature of the endothermic peak that appears when this is measured is the melting point in water. However, if two or more endothermic peaks are detected, the temperature of the endothermic peak with the greatest peak intensity is taken as the melting point in water.

[0119] <Analysis of Water-Insoluble Solid Component> The water-insoluble solid component and an equal amount of distilled water to the water-insoluble solid component were sealed in a stainless steel pressure-resistant sealed container for DSC, and the sample was heated from 30°C to 350°C at a heating rate of 10°C / min under a nitrogen flow using a differential thermal analyzer (DSC7000X manufactured by Hitachi High-Tech Science). It was confirmed that the sample showed an endothermic peak of 5 J / g or less, no endothermic peak, or an endothermic peak exceeding 5 J / g and having a peak temperature equal to or higher than the operating temperature of the solid component separation step. Here, the operating temperature of the solid component separation step refers to the temperature of the step of separating the water-insoluble solid component described in the first aspect of the present invention.

[0120] <Volume Average Particle Size (Particle Size Distribution Meter)> In a second aspect of the present invention, a depolymerized intermediate composition was added to a medium (water) in a laser diffraction particle size distribution measuring device (Microtrac MT3300EXII) manufactured by Nikkiso Co., Ltd. until a measurable concentration was reached, and ultrasonic dispersion was performed at 30 W for 60 seconds. The volume average particle size was calculated from the particle size distribution measured over a measurement time of 10 seconds. However, when polyamide waste was used as the raw material, the depolymerized intermediate composition passed through a 40-mesh cylindrical filter after completion of the reaction was used for measurement. The refractive index during measurement was 1.52, and the refractive index of the medium (water) was 1.333.

[0121] <Removal rate of foreign materials> In the second aspect of the present invention, the removal rate of components insoluble in water at 25°C other than polyamide-derived components or polyester-derived components in a polyamide composition or polyester composition, i.e., foreign material, is determined as follows. The polyamide waste and the components remaining in the cylindrical filter were dried for 12 hours in a vacuum oven set at 80°C and the masses were weighed. Each was washed three times with hexafluoroisopropanol, and the remaining foreign material was dried for 12 hours in a vacuum oven set at 80°C and the mass was weighed. The content of foreign materials was calculated as the ratio of the dry mass after washing to the dry mass before washing, and the removal rate was calculated from the ratio of the content rates of foreign materials.

[0122] <Weight-average major diameter of foreign materials> In the second aspect of the present invention, the foreign materials after solvent washing obtained in the removal rate measurement are observed under an optical microscope at a magnification of 50 to 100 times, and the major diameter of each of 1,000 randomly selected foreign materials is measured. The measured values ​​(μm) are used to calculate the weight-average major diameter (Lw) according to the following formula. However, if there are fewer than 1,000 foreign materials, all foreign materials are included. Weight-average major diameter (Lw) = Σ(Li ２ × ni) / Σ(Li × ni) Li: major diameter of different material ni: number of different materials with major diameter Li.

[0123] <Concentration of Depolymerized Intermediate Composition in Aqueous Slurry Solution or Aqueous Solution> In a second aspect of the present invention, approximately 10 g of an aqueous slurry solution or aqueous solution containing a depolymerized intermediate composition was precisely weighed out, and the resulting solid was concentrated and dried using an evaporator. To this solid was added hexafluoroisopropanol to dissolve the polyamide-derived component, and solvent-insoluble components were removed by vacuum filtration to obtain a filtrate in which the polyamide-derived component was dissolved. The filtrate was concentrated using an evaporator and then dried in a freeze dryer for 12 hours, and the mass of the resulting dried depolymerized intermediate was weighed. The concentration of the depolymerized intermediate composition in the aqueous slurry solution or aqueous solution was calculated from the mass of the aqueous slurry solution or aqueous solution and the mass of the resulting dried depolymerized intermediate.

[0124] <Molecular Weight of Polyamide (GPC)> Approximately 2.5 mg of polyamide was dissolved in 4 ml of hexafluoroisopropanol (0.005 N sodium trifluoroacetate added), and the resulting solution was filtered through a 0.45 μm filter. The weight average molecular weight (Mw) was measured by GPC using the resulting solution. The measurement conditions were as follows: Pump: e-Alliance GPC system (Waters); Detector: Waters 2414 differential refractometer (Waters); Column: Shodex HFIP-806M (2 columns) + HFIP-LG; Solvent: hexafluoroisopropanol (0.005 N sodium trifluoroacetate added); Flow rate: 1 ml / min; Sample injection volume: 0.1 ml; Temperature: 30°C; Molecular weight reference material: polymethyl methacrylate.

[0125] [Example 1] Examples 1 to 6 represent a first embodiment of the present invention, using the recycled monomer production apparatus shown in Figure 2. (A-1) 2.0 kg of polyamide 66 waste, 3.5 kg of deionized water, and 0.24 kg of sodium hydroxide were prepared and sealed in a pressure vessel 16 equipped with a filter 7 and an agitator 20. Nitrogen, an inert gas, was supplied from the compressor 15 to fill the pressure vessel 16. The pressure vessel 16 was then heated to 230°C while stirring with the agitator 20, and the pressure vessel 16 was pressurized (2.6 MPaG). The pressure vessel 16 was then cooled to 160°C, and a small amount of water and nitrogen were sealed in the thermoplastic polymer-derived component tank 22, which was then preheated to 160°C. The valve 21 at the bottom of the pressure vessel 16 was opened, and nitrogen gas at a pressure of 0.62 MPaG or more was introduced into the pressure vessel 16 from the compressor 15, thereby sealing the thermoplastic polymer-derived component in the thermoplastic polymer-derived component tank 22. (A-1) GF in the polyamide 66 waste is captured and removed by filter 7. Next, a solution of 18 parts by mass of sodium hydroxide per 100 parts by mass of deionized water is prepared in depolymerization reaction additional water tank 27. Valve 21 at the bottom of thermoplastic polymer-derived component tank 22 is opened, and thermoplastic polymer-derived components are discharged from thermoplastic polymer-derived component tank 22 at a flow rate of 6.0 L / h. This is mixed with the additional depolymerization reaction water discharged from depolymerization reaction additional water tank 27 at a flow rate of 1.1 L / h. The mixed solution is heated and pressurized to 230°C and 3.0 MPaG and introduced into tubular reactor 10, which uses two tubes with an inner diameter of 2.3 cm and a length of 250 cm. The depolymerized product containing recycled monomers discharged from tubular reactor 10 is returned to room temperature and pressure by cooler 12 and backpressure valve 13 and stored in depolymerized product tank 14. The hexamethylenediamine yield calculated by gas chromatography measurement of the produced depolymerized product shows a high yield. Furthermore, the yield of adipic acid calculated by ion chromatography is high. By using this device, even when treating polyamide 66 waste containing GF, it is possible to separate the polyamide 66-derived components dissolved in water, and it is possible to produce hexamethylenediamine and adipic acid with high yields without causing pipe clogging by GF.

[0126] Example 2 The recycled monomer production apparatus shown in FIG. 2 was used. The same amount of raw material as in Example 1 was sealed in a pressure vessel 16 equipped with a filter 7 and an agitator 20. As in Example 1, the pressure vessel 16 was pressurized (2.6 MPaG). Next, a small amount of water and nitrogen was sealed in the thermoplastic polymer-derived component tank 22 and preheated to 210°C. At this time, the thermoplastic polymer-derived component tank 22 was pressurized to 1.9 MPaG, creating a pressure difference between the pressure vessel 16 and the thermoplastic polymer-derived component tank 22. The valve 21 at the bottom of the pressure vessel 16 was opened, and the thermoplastic polymer-derived component was sealed in the thermoplastic polymer-derived component tank 22. (A-1) The GF in the polyamide 66 waste was captured and removed by the filter 7. By utilizing the vapor pressure difference of water, the thermoplastic polymer-derived component could be sealed in the thermoplastic polymer-derived component tank 22 while maintaining the temperature and pressure conditions without introducing high-pressure nitrogen gas into the pressure vessel 16. Subsequent operations were carried out in the same manner as in Example 1 to produce a depolymerized product containing recycled monomer. The yield of hexamethylenediamine calculated by gas chromatography measurement of the produced depolymerized product is high, and the yield of adipic acid calculated by ion chromatography measurement is also high.

[0127] Example 3: The recycled monomer production apparatus shown in Figure 2 was used. (A-2) 2.0 kg of polyamide 66 waste, 4.3 kg of deionized water, and 0.30 kg of sodium hydroxide were prepared and sealed in a pressure vessel 16 equipped with a filter 7 and an agitator 20. Nitrogen, an inert gas, was supplied from a compressor 15 to fill the pressure vessel 16. The pressure vessel 16 was then heated to 230°C while stirring with the agitator 20, creating a pressurized state (2.6 MPaG) inside the pressure vessel 16. Next, a small amount of water and nitrogen were sealed in the thermoplastic polymer-derived component tank 22 and preheated to 210°C. At this time, the thermoplastic polymer-derived component tank 22 was pressurized to 1.9 MPaG, creating a pressure difference between the pressure vessel 16 and the tank 22. The valve 21 at the bottom of the pressure vessel 16 was opened, and the thermoplastic polymer-derived component was sealed in the thermoplastic polymer-derived component tank 22. (A-2) The silicone coating in the polyamide 66 waste was captured by the filter 7 and removed. Subsequent operations were carried out in the same manner as in Example 1 to produce a depolymerized product containing recycled monomers. The hexamethylenediamine yield calculated by gas chromatography measurement of the produced depolymerized product showed a high yield. Furthermore, the adipic acid yield calculated by ion chromatography measurement also showed a high yield. By using this apparatus, even in the treatment of polyamide 66 waste containing a silicone coating, the silicone coating can be separated from polyamide 66-derived components dissolved in water, and diamines and dicarboxylic acids can be produced in high yields without causing pipe clogging due to the silicone coating.

[0128] Example 4: The recycled monomer production apparatus shown in Figure 2 was used. (B-1) 2.0 kg of polyamide 6 waste and 4.2 kg of deionized water were prepared and sealed in a pressure vessel 16 equipped with a filter 7 and an agitator 20. Nitrogen, an inert gas, was supplied from a compressor 15 to fill the pressure vessel 16 with nitrogen. The pressure vessel 16 was then heated to 250°C while stirring with the agitator 20, creating a pressurized state (3.8 MPaG) inside the pressure vessel 16. A small amount of water and nitrogen was then sealed in the thermoplastic polymer-derived component tank 22 and preheated to 240°C. At this time, the thermoplastic polymer-derived component tank 22 was pressurized to 3.3 MPaG, creating a pressure difference between the tank and the pressure vessel 16. The valve 21 at the bottom of the pressure vessel 16 was opened, and the thermoplastic polymer-derived component was sealed in the thermoplastic polymer-derived component tank 22. (B-1) The GF in the polyamide 6 waste was captured and removed by the filter 7. Next, the valve 21 at the bottom of the thermoplastic polymer-derived component tank 22 is opened, and the thermoplastic polymer-derived component is discharged from the thermoplastic polymer-derived component tank 22 at a flow rate of 6.0 L / h. (B-1) When treating polyamide 6 waste, no additional water is supplied before the depolymerization reactor. The thermoplastic polymer-derived component is heated and pressurized to 320°C and 15 MPaG and introduced into a tubular reactor 10 using two tubes with an inner diameter of 2.3 cm and a length of 250 cm. The depolymerized product containing recycled monomers discharged from the tubular reactor is returned to room temperature and pressure by a cooler 12 and a back-pressure valve 13 and stored in a depolymerized product tank 14. The ε-caprolactam yield calculated by high-performance liquid chromatography measurement of the produced depolymerized product shows a high yield.

[0129] Example 5: The thermoplastic polymer-derived component recovery device shown in Figure 1 was used. (C-1) 2.0 kg of polyethylene terephthalate waste, 9.8 kg of deionized water, and 0.72 kg of sodium hydroxide were prepared and sealed in a pressure vessel 16 equipped with a filter 7. The agitator 20 was not used. Nitrogen, an inert gas, was supplied from the compressor 15 to fill the pressure vessel 16. The pressure vessel 16 was then heated to 180°C, and the pressure vessel 16 was pressurized (1.0 MPaG). Next, a small amount of water and nitrogen were sealed in the thermoplastic polymer-derived component tank 22, which was then preheated to 150°C. At this time, the thermoplastic polymer-derived component tank 22 was at 0.5 MPaG, creating a pressure difference between it and the pressure vessel 16. 15 minutes after the pressure vessel 16 reached 180°C, the valve 21 at the bottom of the pressure vessel 16 was opened, and the thermoplastic polymer-derived component was sealed in the thermoplastic polymer-derived component tank 22. (C-1) Cotton in the polyethylene terephthalate waste is captured and removed by filter 7. A depolymerized product containing recycled monomers is obtained from valve 21 at the bottom of thermoplastic polymer-derived component tank 22. The yield of terephthalic acid calculated by high-performance liquid chromatography measurement of the produced depolymerized product shows a high yield. By using this device, even when treating polyethylene terephthalate waste containing cotton, it is possible to separate the cotton from polyethylene terephthalate-derived components dissolved in water, and to produce terephthalic acid at a high yield without causing pipe clogging by the cotton.

[0130] Example 6: The thermoplastic polymer-derived component recovery device shown in Figure 1 was used. 2.0 kg of (C-2) polybutylene terephthalate waste and 8.4 kg of deionized water were prepared and sealed in a pressure vessel 16 equipped with a filter 7 and an agitator 20. Nitrogen, an inert gas, was supplied from a compressor 15 to fill the pressure vessel 16. The pressure vessel 16 was then heated to 290°C, and the pressure vessel 16 was pressurized (7.4 MPaG). Next, a small amount of water and nitrogen were sealed in a thermoplastic polymer-derived component tank 22, which was then preheated to 280°C. At this time, the thermoplastic polymer-derived component tank 22 was at 6.4 MPaG, creating a pressure difference between the pressure vessel 16 and the tank 22. 15 minutes after the pressure vessel 16 reached 290°C, the valve 21 at the bottom of the pressure vessel 16 was opened, and the thermoplastic polymer-derived component was sealed in the thermoplastic polymer-derived component tank 22. (C-2) GF in the polybutylene terephthalate waste is captured and removed by filter 7. A depolymerized product containing recycled monomers is obtained from valve 21 at the bottom of thermoplastic polymer-derived component tank 22. The terephthalic acid yield calculated by high-performance liquid chromatography measurement of the recovered depolymerized product shows a high yield. By using this device, even when treating polybutylene terephthalate waste containing GF, it is possible to separate GF from polybutylene terephthalate-derived components dissolved in water, and terephthalic acid can be produced stably and with a high yield without causing pipe clogging by GF.

[0131] [Example 7] The following are examples, comparative examples, and reference examples of the second aspect of the present invention. In Examples 7 to 13, the first-stage depolymerization reaction of the second aspect was carried out to obtain a solution or slurry of a depolymerized intermediate composition. Polyamide 66 (D-1), water, and sodium hydroxide were charged into an autoclave made of SUS316L and equipped with a stirrer in the amounts shown in Table 1. The amount of water blended per 100 parts by mass of polyamide was 201 parts by mass. The amount of alkali metal ions Y calculated from the amount of polyamide blended X moles and the amount of sodium hydroxide blended was １ Molar ratio Y expressed in moles １The ratio of 1 / X to 1 was 1.00. The reaction vessel was purged with nitrogen and sealed under a nitrogen pressure of 0.5 MPa. The reaction was then heated to 230°C while stirring at 200 rpm. The pressure inside the system was 2.6 MPa during the reaction. After completion of the reaction, the system was cooled to room temperature and a liquid slurry of the depolymerized intermediate composition was recovered. The total time during which the polyamide and water were kept coexisting in the reaction vessel at temperatures above 200°C was 25 minutes. The hexamethylenediamine yield calculated by gas chromatography measurement of the recovered depolymerized intermediate composition was 30 mol%, and the sodium adipate yield calculated by ion chromatography measurement was 38 mol%. The amount of monomer and its derivatives obtained from 100% by mass of polyamide was 42% by mass. The volume average particle diameter measured with a particle size distribution analyzer was 6.7 μm.

[0132] Examples 8 to 10, Comparative Examples 1 to 3 Polyamides were depolymerized in the same manner as in Example 7, except that the amount of water, the amount and concentration of the aqueous sodium hydroxide solution, the depolymerization temperature, and the reaction time were appropriately changed, to obtain depolymerized intermediate compositions. In Comparative Example 1, the reaction was carried out at a temperature lower than 200°C, and therefore the reaction time was set to the time (20 minutes) for treatment at 120°C.

[0133]

[0134] In Examples 7 to 10, the polyamide composition was depolymerized by appropriately adjusting the amount of water and the reaction temperature, thereby obtaining an aqueous slurry solution of a depolymerized intermediate composition containing a predetermined content of monomer and monomer derivative. On the other hand, in Comparative Example 1, in which the depolymerization temperature was set low, the polyamide remained in pellet form, and a depolymerized intermediate composition containing the predetermined content of monomer and monomer derivative was not obtained. Furthermore, in Comparative Example 2, in which the amount of water was reduced, the polyamide became lumpy, and a depolymerized intermediate composition containing the predetermined content of monomer and monomer derivative was not obtained. In Comparative Example 3, in which the amount of alkali metal hydroxide was reduced, the particle size of the water-insoluble components increased, forming a paste at room temperature, and a depolymerized intermediate composition containing the predetermined content of monomer and monomer derivative was not obtained. Thus, in the solution of a depolymerized intermediate composition obtained by depolymerizing a polyamide composition by appropriately adjusting the amount of water and the depolymerization temperature, the polyamide was converted into a homogeneous liquid mixture, which makes it easy to supply to a depolymerization apparatus and is suitable for use in producing polyamide monomers.

[0135] Examples 11 and 12, Comparative Example 4 (D-2) Polyamide 66 waste (silicone-coated airbag fabric made of polyamide 66 recovered from scrapped vehicles) was cut into approximately 10 cm square pieces and depolymerized in the same manner as in Example 7, with appropriate changes to the amount of water, the amount and concentration of aqueous sodium hydroxide, the depolymerization temperature, and the reaction time, to obtain a depolymerized intermediate composition. After completion of the depolymerization reaction, the floating silicone-coated residue was recovered by solid-liquid separation using a 40-mesh cylindrical filter. The silicone-coated residue was washed three times with hexafluoroisopropanol and then dried for 12 hours in a vacuum oven set at 80°C, and the resulting dried product was weighed. Furthermore, the removal rate of the water-insoluble component (silicone coating) and the weight-average major axis were calculated using the dried product. In Example 12, the polyamide-derived depolymerized intermediate composition that passed through the cylindrical filter was obtained as an aqueous slurry solution with a polyamide-derived depolymerized intermediate composition concentration of 27% by mass.

[0136] Example 13, Comparative Example 5 (D-3) Polyamide 66 waste (30% GF reinforced polyamide 66 molding scraps) was depolymerized in the same manner as in Example 7, with appropriate changes to the amount of water, the amount and concentration of aqueous sodium hydroxide, the depolymerization temperature, and the reaction time, to obtain a depolymerized intermediate composition. After completion of the depolymerization reaction, the settled glass fibers were subjected to solid-liquid separation using a 40-mesh cylindrical filter to recover the glass fiber residue. The glass fiber residue was washed three times with hexafluoroisopropanol and then pre-dried for 12 hours in a vacuum oven set at 80°C, and the obtained dried product was weighed. Furthermore, the removal rate of water-insoluble components (glass fibers) and the weight-average major axis were measured using the dried product. In Example 13, the polyamide-derived depolymerized intermediate composition that passed through the cylindrical filter was obtained as an aqueous slurry solution with a polyamide-derived depolymerized intermediate composition concentration of 25% by mass.

[0137]

[0138] In Examples 11 and 12, an aqueous slurry solution of a depolymerized intermediate composition was obtained in which silicone coating residue floated to the surface. In Example 13, in which molding waste containing glass fibers was depolymerized, an aqueous slurry solution of a depolymerized intermediate composition in which the glass fibers settled was obtained. In this way, the solution of a depolymerized intermediate composition obtained by depolymerizing polyamide 66 waste by appropriately adjusting the amount of water and depolymerization temperature converts the polyamide into a homogeneous liquid mixture. Therefore, even if the polyamide composition has a different form or contains various other materials, it can be supplied to a depolymerization apparatus in the same manner and be suitably used for producing polyamide monomers. Furthermore, by depolymerizing the content of monomers and monomer derivatives in the depolymerized intermediate composition to a predetermined range, decomposition of the other materials can be suppressed and separated, making it possible to recover polyamide-derived components.

[0139] On the other hand, in Comparative Example 4, which was obtained by depolymerizing airbags recovered from scrapped vehicles under conditions with a high alkali addition amount, an aqueous solution of depolymerized and dissolved polyamide was obtained, but some of the silicone coating decomposed to sizes that were not visible to the naked eye, and the amount that passed through the cylindrical filter and became mixed into the depolymerized intermediate composition increased, resulting in a low removal rate. Comparative Example 5, which was obtained by depolymerizing molding waste containing glass fibers at 280°C, also obtained an aqueous solution of depolymerized and dissolved polyamide, but the glass fibers were pulverized, resulting in a low removal rate for the same reason as above. Thus, when depolymerization conditions are set such that the content of monomers and monomer derivatives in the depolymerized intermediate composition exceeds the specified range, other materials decompose, making separation from polyamide-derived components complicated.

[0140] Example 14 An SUS316L autoclave equipped with a stirrer was charged with the aqueous slurry solution of the polyamide-derived depolymerized intermediate composition obtained in the same manner as in Example 8, water, and sodium hydroxide in the amounts shown in Table 3. A second-stage depolymerization reaction was carried out from the depolymerized intermediate composition obtained in the first-stage depolymerization reaction step to obtain a depolymerized reaction composition. The reaction vessel was purged with nitrogen, sealed under a nitrogen pressure of 0.5 MPa, and then heated to 230°C while stirring at 200 rpm to carry out the reaction. During the reaction, the pressure in the system was 2.5 MPa. After completion of the reaction, the system was cooled to room temperature, and the aqueous solution of the depolymerized reaction composition was recovered. The polyamide-derived depolymerized intermediate composition was maintained at temperatures above 225°C in the reaction vessel for a total of 25 minutes.

[0141] [Example 15] A depolymerization reaction composition was obtained in the same manner as in Example 14, except that an aqueous slurry solution of a polyamide-derived depolymerized intermediate composition having a concentration of 27 mass%, which was obtained by depolymerizing in the same manner as in Example 12 and then separating and removing the silicone coating residue, as well as water and sodium hydroxide were charged in the amounts shown in Table 3.

[0142] Example 16 A depolymerization reaction composition was obtained in the same manner as in Example 14, except that an aqueous slurry solution of a polyamide-derived depolymerized intermediate composition having a concentration of 25% by mass, obtained by depolymerizing in the same manner as in Example 13 and then separating and removing glass fibers, was charged with water and sodium hydroxide in the amounts shown in Table 3. The reaction conditions, yields of the reaction products, quantitative results, and analytical results of Examples 14 to 16 are shown in Table 3.

[0143]

[0144] In Examples 14 to 16, water and an alkali hydroxide were added to a depolymerized intermediate composition having a polyamide monomer and / or a derivative thereof content within a predetermined range, and the mixture was maintained at a preferred temperature range to depolymerize the composition, thereby obtaining a polyamide monomer and / or a derivative thereof in high yield.

[0145] Example 17: 28.50 g of (E-1) polyamide 6 waste and 58.25 g of water were charged into a SUS316L autoclave equipped with a stirrer. The amount of water was 296 parts by mass per 100 parts by mass of polyamide. The reaction vessel was purged with nitrogen and sealed under a nitrogen pressure of 0.5 MPa. The temperature was raised to 280°C while stirring at 200 rpm and maintained for 15 minutes to carry out the reaction. The pressure in the system during the reaction was 6.5 MPa. After completion of the reaction, the mixture was cooled to room temperature and subjected to solid-liquid separation using a 40-mesh cylindrical filter to recover an aqueous slurry solution of a depolymerized intermediate composition (the volume average particle size of the depolymerized intermediate composition was 9.2 μm). The total time during which the polyamide and water were allowed to coexist and maintained at above 200°C in the reaction vessel was 60 minutes. The caprolactam yield calculated by liquid chromatography measurement of the recovered depolymerized intermediate composition was 47 mol%, and the amount of monomer obtained from 100 parts by mass of polyamide was 47 parts by mass. The removal rate of water-insoluble components (glass fibers) was 98%, and the weight average glass fiber length was 282 μm. The polyamide-derived depolymerized intermediate composition that passed through the cylindrical filter was obtained as an aqueous slurry solution with a depolymerized intermediate composition concentration of 24% by mass.

[0146] 60.03 g of an aqueous slurry solution of a 24% by mass polyamide-derived depolymerized intermediate composition obtained by separating and removing the glass fibers was charged into an SUS316L autoclave equipped with a stirrer. The atmosphere in the reaction vessel was replaced with nitrogen, and the vessel was sealed under a nitrogen pressure of 0.5 MPa. The temperature was raised to 320°C while stirring at 200 rpm, and the reaction was carried out by maintaining the temperature for 15 minutes. During the reaction, the pressure in the system was 11.9 MPa. After completion of the reaction, the system was cooled to room temperature, and a transparent liquid depolymerized intermediate composition was recovered. The total time the temperature was maintained above 225°C in the reaction vessel was 40 minutes. The ε-caprolactam yield calculated by liquid chromatography measurement of the recovered depolymerized reaction composition was 76 mol%. The amount of monomer obtained from 100% by mass of the polyamide-derived component in the depolymerized intermediate composition was 76% by mass. In Example 17, the glass fibers were removed from a depolymerized intermediate composition having a polyamide monomer content within a preferred range, and then the depolymerized intermediate composition was maintained at a preferred temperature range for further depolymerization, thereby obtaining polyamide monomers in a high yield.

[0147] Reference Example 1 5.52 g of hexamethylenediamine (Fujifilm Wako Pure Chemical Industries, Ltd., first grade) and 6.94 g of adipic acid (Fujifilm Wako Pure Chemical Industries, Ltd., special grade) were dissolved in 12.7 g of water to prepare a salt solution. This salt solution was placed in a reaction vessel, sealed, and purged with nitrogen. The heater on the outer periphery of the reaction vessel was set to 290°C and heating was initiated. After the internal pressure reached 1.75 MPa, the internal pressure was maintained at 1.75 MPa while releasing moisture to the outside of the system, and the temperature was raised to 237°C. After the internal temperature reached 237°C, the internal pressure was adjusted to normal pressure over 1 hour (internal temperature at normal pressure: 257°C). Subsequently, the reaction vessel was maintained for 60 minutes while nitrogen was flowing through it (nitrogen flow), yielding polyamide 66 (maximum temperature reached: 274°C). The weight average molecular weight of the resulting polyamide 66 was 56,900 g / mol and the melting point was 261°C.

[0148] Example 18 Hexamethylenediamine was extracted with isobutanol from the depolymerization reaction composition obtained in the same manner as in Example 14, concentrated using an evaporator, and then distilled at 84-90°C and 3±1 hPa to obtain crude hexamethylenediamine. The crude hexamethylenediamine was again distilled at 84-90°C and 3±1 hPa to obtain purified hexamethylenediamine. 15 mL of 35% aqueous hydrochloric acid was added to the aqueous sodium adipate solution from which hexamethylenediamine had been removed by extraction, yielding a slurry solution from which adipic acid had precipitated. The slurry solution was heated in an 80°C oil bath to form a homogeneous solution, and then allowed to stand at room temperature for 12 hours to precipitate crude adipic acid. To the crude adipic acid recovered by vacuum filtration, water was added in an amount twice the mass of the crude adipic acid, and the mixture was heated again in an 80°C oil bath to form a homogeneous solution. The mixture was then left to stand at room temperature for 12 hours, and the precipitated adipic acid was recovered by vacuum filtration and dried for 12 hours in a vacuum oven set at 110°C to obtain purified adipic acid. Polyamide 66 was produced in the same manner as in Reference Example 1, except that 5.50 g of the resulting hexamethylenediamine and 6.87 g of adipic acid were used as polymerization raw materials. The resulting recycled polyamide 66 had a weight average molecular weight of 58,700 g / mol and a melting point of 260°C.

[0149] [Example 19] Hexamethylenediamine, adipic acid, and polyamide 66 were produced in the same manner as in Example 18 from the depolymerization reaction composition obtained in the same manner as in Example 15. The weight-average molecular weight of the resulting recycled polyamide 66 was 59,000 g / mol, and the melting point was 260°C.

[0150] Example 20 Hexamethylenediamine, adipic acid, and polyamide 66 were produced from the depolymerization reaction composition obtained in the same manner as in Example 16, in the same manner as in Example 18. The weight-average molecular weight of the resulting recycled polyamide 66 was 58,100 g / mol, and the melting point was 261°C. From the above results, it was found that, from Reference Example 1 and Examples 18 to 20, polyamides obtained by repolymerizing hexamethylenediamine and adipic acid obtained by depolymerizing polyamide exhibited weight-average molecular weights and melting points equivalent to those of polyamides polymerized from reagent diamines and reagent dicarboxylic acids.

[0151] The present invention can be suitably used for chemical recycling of thermoplastic polymer compositions containing a thermoplastic polymer and a water-insoluble solid component. Furthermore, plastic waste of various compositions and forms can be recycled. For example, the present invention can be suitably used for separating water-insoluble solid components such as glass fibers from thermoplastic polyamide products and thermoplastic polyester products, and recovering the raw material monomers. When used in chemical recycling, the present invention can achieve both resource recycling and reduced greenhouse gas emissions.

[0152] REFERENCE SIGNS LIST 1 raw material hopper 2 extruder 3 water tank 4 water pump 5 water heater 6 separation tank 7 filter 8 pump 9 heater 10 tubular reactor 11 heat exchanger 12 cooler 13 back pressure valve 14 depolymerized product tank 15 compressor 16 pressure vessel 18 gas back pressure valve 19 water-insoluble solid component 20 agitator 21 valve 22 thermoplastic polymer-derived component tank 27 depolymerization reaction additional water tank 30 buffer tank

Claims

1. A method for producing a depolymerization reaction composition of a polyamide composition or a polyester composition, comprising the following first and second steps in this order: (Step 1) A step of depolymerizing a polyamide composition or a polyester composition in the presence of water at 150°C or higher and 300°C or lower to obtain a water slurry solution or an aqueous solution containing a monomer-containing composition, wherein the monomer-containing composition contains 10% by mass or higher but 70% by mass or lower of polyamide monomers and / or derivatives thereof, or polyester monomers and / or derivatives thereof, relative to 100% by mass of polyamide-derived components or polyester-derived components. (Second step) A step of further depolymerizing the water slurry solution or aqueous solution at 225°C or higher and 350°C or lower to obtain a depolymerization reaction composition, in which the depolymerization reaction composition contains 75% by mass or more of polyamide monomers and / or derivatives thereof, or polyester monomers and / or derivatives thereof, relative to 100% by mass of polyamide-derived components or polyester-derived components.

2. The method for producing a depolymerization reaction composition according to claim 1 , wherein an alkali metal compound and / or an alkaline earth metal compound is further present in the first step and / or the second step.

3. A polyamide monomer or a polyester monomer obtained by purifying a depolymerization reaction composition obtained by the method for producing a depolymerization reaction composition according to claim 1 or 2.

4. A method for producing a polyamide or a method for producing a polyester, comprising a step of polycondensing a raw material containing the polyamide monomer or the polyester monomer according to claim 3.

5. A polyamide or polyester obtained by polycondensation of raw materials containing the polyamide monomer or polyester monomer according to claim 4.

6. A molded article, fiber, film, or sheet made using the polyamide or polyester according to claim 5.