WO2025205744A1 - 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 - Google Patents

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

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, polyamide monomers or polyester monomers, polyamides or polyesters, methods for producing these, and molded articles, fibers, films, or sheets made using these.

In recent years, interest in global environmental issues has grown in the wake of the marine plastic pollution problem, and there are calls 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 recycle fossil resources such as plastics, and to develop technologies for reducing greenhouse gas emissions.

Plastics are processed into a variety of shapes depending on the application. Plastics may be used alone or in combination with other materials. Examples of the latter include blended materials spun with different types of 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. In order to recycle composite materials that are mixed with these different materials, it is necessary to remove the different materials.

As a plastic recycling technology, for example, a device 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, continuously decomposed, and the raw material monomers are recovered (Patent Document 1).

Recycling technologies for plastic composite materials include, for example, an apparatus and method that treats plastic molded products containing inorganic substances with a subcritical fluid in a batch reactor, crushes the inorganic substances in the discharge section, and separates the inorganic substances from monomers (Patent Document 2). Furthermore, a separation and recovery apparatus has been disclosed that continuously separates and recovers the hydrolyzable polymer as its raw material compound and the non-hydrolyzable polymer as a high-purity polymer with reduced contamination from a resin mixture containing a resin containing a hydrolyzable polymer and a resin containing a non-hydrolyzable polymer (Patent Document 3).

Furthermore, as a technology for peeling heterogeneous polymers from a laminate and separating and recycling the polyamide or polyester (Patent Document 4), a method is 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 from the airbag base fabric and recover polyamide 66. Also disclosed is a method in which the polyamide is dissolved by heating it together with ethylene glycol at a temperature of 180°C or higher, and the silicone that is insoluble in ethylene glycol is removed (Patent Document 5).

Furthermore, a method (Patent Document 6) for recovering raw material monomers after depolymerizing polyamide or polyester and separating it from other materials is 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 a total of 86% by mass of hexamethylenediamine, adipic acid, and their respective derivatives, relative to 100% by mass of polyamide 66. Furthermore, a method is disclosed in which a multilayer film consisting of a polyamide or polyester layer and a polyethylene layer is hydrothermally treated at a high temperature of 250-380°C, and the polyamide or polyester is recycled as raw material monomers, while the polyethylene remains intact (Patent Document 7).

Japanese Patent Application Publication No. 9-77905 Japanese Patent Application Laid-Open No. 2009-7417 JP 2023-1084 A JP 2009-269475 A Japanese Patent Application Laid-Open No. 2018-172618 International Publication No. 2023/120427 Japanese Patent Application Laid-Open No. 2023-1085

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

The device and method for recovering inorganic matter from plastics disclosed in Patent Document 2 targets the inorganic matter contained in plastics, and since the plastic is treated in a batch-type reaction vessel and then cooled to separate the solid inorganic matter, there is a problem in that insufficiently decomposed plastic that precipitates during cooling is also recovered along with the inorganic matter. The separation and recovery device disclosed in Patent Document 3 assumes that the non-hydrolyzable polymer is in a dissolved state, and therefore cannot be operated stably if the non-hydrolyzable polymer is solid.

The method of stripping and removing silicone using an alkali-isopropanol solution, as disclosed in Patent Document 4, maintains the shape of the polyamide, leaving the silicone coating between the fibers, making complete removal difficult. Patent Document 5, a method of recovering high-quality polyamide by dissolving polyamide, 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, a method of decomposing polyamide or polyester to recover raw material monomers, does not disclose a method for separating the different materials. Patent Document 7 describes a method for removing solid components from the melt in advance when the polyamide or polyester contains solid components that do not melt under hydrothermal reaction conditions. However, heating above the polymer's melting point raises concerns about thermal degradation of the polymer and other components. As described above, conventional technologies require treatment methods to be tailored to the shape and properties of the different components, making them less versatile for treating plastic waste with diverse shapes and compositions.

In light of the above, the present invention aims to provide a method and apparatus for recovering thermoplastic polymer-derived components, as well as a method and apparatus for producing recycled monomers, that solve the problem of clogging of the device's flow paths 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, the present invention aims 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. A further object is to separate inorganic substances, crosslinked polymers, etc., and produce monomers from the depolymerized intermediate composition with high efficiency.

In order to solve the above problems, the present invention has the following configuration.
1. A method for recovering a component derived from a thermoplastic polymer, comprising a step of separating the water-insoluble solid component S from a mixture containing water and a thermoplastic polymer composition containing a thermoplastic polymer P and a water-insoluble solid component S under conditions of 110°C or higher and 350°C or lower and 0.14 MPa or higher and 30 MPa or lower, to obtain a component derived from the thermoplastic polymer P.
2. The method for recovering a component derived from a thermoplastic polymer according to 1, wherein 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 or more and 100 or less.
3. The method for recovering a component derived from a thermoplastic polymer according to 1 or 2, wherein 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 according to any one of 1 to 3, wherein the water-insoluble solid component S comprises a crosslinked silicone polymer and/or a fibrous filler.
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 base fabric.
7. A method for producing a recycled monomer, comprising a step of depolymerizing a thermoplastic polymer-derived component recovered by the method for recovering a thermoplastic polymer-derived component according to any one of 1 to 6.

8. An apparatus for recovering a thermoplastic polymer-derived component, comprising: a pressure vessel (D) for obtaining a solution 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 at 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, wherein a filter is 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.
9. 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 or higher and 350°C or lower and 0.14 MPa or higher and 30 MPa or lower, wherein the means (C) is equipped with at least a filter.
10. The device for recovering a component derived from a thermoplastic polymer according to 8 or 9, wherein the water-insoluble solid component S includes a crosslinked silicone polymer and/or a fibrous filler.
11. The device for recovering a component derived from a thermoplastic polymer according to any one of 8 to 10, wherein the thermoplastic polymer P comprises a thermoplastic polyamide and/or a thermoplastic polyester.
12. The device for recovering a component derived from a thermoplastic polymer according to any one of 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.

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 higher than 200°C and lower 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 of 150°C or higher and lower than 240°C to obtain a depolymerized intermediate composition, wherein the depolymerized intermediate composition contains 10% by mass or higher and 70% by mass or lower of a monomer of the polyester and/or a derivative thereof relative to 100% by mass of polyester-derived components.
16. The method for producing a composition of depolymerized intermediates according to 14 or 15, wherein the composition of depolymerized intermediates 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 17, wherein in the step of obtaining the depolymerized intermediate composition, the polyamide or polyester contains a dicarboxylic acid residue, and X mol of the dicarboxylic acid residue and a hydroxide, oxide, carbonate containing Y ₁ mol of alkali metal ions and/or Y ₂ mol of alkaline earth metal ions, or a mixture containing two or more of these, are allowed to coexist so as to satisfy (Formula 1).
0.5≦(Y ₁ + 2×Y ₂ )/X≦1.5 (Formula 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 from 0.01% by mass to 60% by mass of a component other than polyamide or polyester that is insoluble in water at 25°C, per 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 a step of removing, after depolymerization, components insoluble in water at 25°C other than polyamide-derived components or polyester-derived components using a filter.

22. A monomer-containing composition, in which 100% by mass of a polyamide-derived component or a polyester-derived component is present, contains 10% by mass or more and 70% by mass or less of a polyamide monomer and/or a polyester monomer and/or a derivative thereof, and 30% by mass or more and 90% by mass or less of a polyamide- or polyester-derived component other than the monomer and/or a derivative thereof;
The method for producing a depolymerization reaction composition includes a step of depolymerizing the polyamide composition or the polyester composition in the presence of water at 225°C or higher and 350°C or lower 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.

24. 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:
25. The method for producing a depolymerization reaction composition according to claim 24, wherein an alkali metal compound and/or an alkaline earth metal compound is further added in the first and/or second steps.

26. 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 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 a polyamide monomer or a polyester monomer according to 26.
28. A polyamide or polyester obtained by polycondensation of a raw material containing a polyamide monomer or a polyester monomer as described in 27.
29. A molded article, fiber, film, or sheet made using the polyamide or polyester according to 28.

The present invention solves the problem of blockage of process flow paths, etc., due to water-insoluble solid components when recovering thermoplastic polymer-derived components, enabling highly efficient and stable recovery of thermoplastic polymer-derived components. It also provides 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, providing a highly 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.

Schematic diagram of a recovery device for components derived from thermoplastic polymers, showing one embodiment of the present invention. Schematic diagram of a recycled monomer production apparatus showing one embodiment of the present invention. 1 is a schematic diagram of a recycled monomer production apparatus according to another embodiment of the present invention. 1 is a schematic diagram of a recycled monomer production apparatus according to another embodiment of the present invention. 1 is a schematic diagram of a recycled monomer production apparatus according to another embodiment of the present invention. 1 is a schematic diagram of a recycled monomer production apparatus according to another embodiment of the present invention.

The present invention will be described in more detail below, but the present invention is not limited to these embodiments.
[First aspect of the present invention]
A first aspect of the present invention is a recovery method and recovery apparatus for obtaining components derived from thermoplastic polymers by converting thermoplastic polymer-derived components 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 paths and piping, causing blockages. By depolymerizing the obtained thermoplastic polymer-derived components, recycled monomers can be produced with high efficiency. In the present invention, the term "thermoplastic polymer-derived components" 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.

The thermoplastic polymer-derived component recovery device of the present invention can be broadly divided into those that process continuously and those that process batchwise. In the case of continuous processing, the thermoplastic polymer-derived component recovery device of the present invention has 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 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, with means (C) including at least a filter.

In the case of batch processing, the thermoplastic polymer-derived component recovery device 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, with a filter 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 explained below, but first, the effect of water in the first embodiment of the present invention will be explained.

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 this invention, subcritical water is defined as water 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. In a first aspect of the present invention, 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 water-insoluble solid component S, which is a different material, from a thermoplastic polymer composition containing a thermoplastic polymer P and a water-insoluble solid component S.

There are no particular limitations on the water used in the present invention, and any type of water may be used, including tap water, deionized water, distilled water, and well water. Deionized water and distilled water are preferred to prevent side reactions caused by coexisting salts. Other solvents, such as alcohol, may also 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. Alcohols may be used alone or in combination of two or more in any desired proportions.

Depending on the type of thermoplastic polymer composition, an alkali (earth) metal salt may be added to the 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. In this specification, alkali (earth) metal salts refer 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, as well as mixtures thereof.

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) can 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. In this specification, the bone-dry state is defined as a water content of 0.5% by mass or less in the thermoplastic polymer. 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 around 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, the bone-dry thermoplastic polymer composition is cooled from a molten state to 30°C at a rate of 10°C/min in a nitrogen gas atmosphere, and then heated at a rate of 10°C/min. 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 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 they are preferred from the perspective of resource recovery.

Furthermore, the melting point of a thermoplastic polymer may decrease in water. The melting point of a thermoplastic polymer P in water can be determined by sealed container thermal analysis (SC-DSC). Specifically, thermoplastic polymer P and an equal amount of distilled water are sealed in a stainless steel pressure-resistant sealed container for DSC. Using a differential thermal analyzer (Hitachi High-Tech Science DSC7000X), the mixture is heated from 30°C to 350°C at a rate of 10°C/min under a nitrogen flow. The temperature of the endothermic peak that appears when this occurs is taken as the melting point in water. However, if two or more endothermic peaks are detected, the temperature of the endothermic peak with the greatest intensity is taken 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).

In the present invention, the thermoplastic polymer P preferably comprises 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 thermoplastic polyamide or thermoplastic polyester is preferably contained in the thermoplastic polymer composition of the present invention in a mass ratio of 30% or more, more preferably 50% or more, and even more preferably 70% or more.

The water-insoluble solid component S in this invention can be defined by sealed container thermal analysis (SC-DSC). Specifically, when the water-insoluble solid component S and an equal amount of distilled water are sealed in a stainless steel pressure-resistant sealed container for DSC and heated from 30°C to 350°C at a heating rate of 10°C/min under a nitrogen flow using a differential thermal analyzer (Hitachi High-Tech Science DSC7000X), the water-insoluble solid component S exhibits an endothermic peak of 5 J/g or less, no endothermic peak, or an endothermic peak of 5 J/g or more with 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 during the step of separating the water-insoluble solid component S.

Examples of water-insoluble solid components 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 with a fibrous shape, and specific examples include glass fiber, polyacrylonitrile (PAN)-based and pitch-based carbon fiber, stainless steel fiber, metal fibers such as aluminum fiber and brass fiber, gypsum fiber, ceramic fiber, asbestos fiber, zirconia fiber, alumina fiber, silica fiber, titanium oxide fiber, silicon carbide fiber, rock wool, potassium titanate whiskers, silicon nitride whiskers, wollastonite, alumina silicate, and other fibrous and whisker-like fillers; and glass fiber or carbon fiber coated with one or more metals selected from the group consisting of nickel, copper, cobalt, silver, aluminum, iron, and alloys thereof.

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, swelling 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 silicate, 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 silicates may have exchangeable cations between layers exchanged with organic onium ions. Examples of organic onium ions include ammonium ions, phosphonium ions, and sulfonium ions.

Examples of cross-linked polymers include acrylic polymers, silicone polymers, and urethane polymers cross-linked using a cross-linking agent. For example, cross-linked silicone polymers are often coated on fibers or films made from processed 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 cross-linked silicone polymer and/or a fibrous filler. Thermoplastic polymers containing cross-linked silicone polymers are widely used as base fabrics for airbags (articles), i.e., airbag base fabrics. Thermoplastic polymers containing fibrous fillers are widely used as glass fiber reinforced resins, making their original resources easily recoverable.

The thermoplastic polymer composition of the present invention may contain various additives, etc., as long as they do not impair the objectives of the present invention. Specific examples of 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 (such as alkyl sulfate-type anionic antistatic agents, quaternary ammonium salt-type cationic antistatic agents, nonionic antistatic agents such as polyoxyethylene sorbitan monostearate, and betaine-type amphoteric antistatic agents), flame retardants (such as 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 included, their content is preferably 10 parts by weight or less, and more preferably 1 part by weight or less, per 100 parts by weight of the thermoplastic polymer component P.

In the present invention, the thermoplastic polymer composition may be a waste resin molded product. When the thermoplastic polymer composition is a waste resin molded product, the amount of raw materials available for recovering thermoplastic polymer-derived components increases. When the thermoplastic polymer is a thermoplastic polyamide, waste resin molded products containing the thermoplastic polyamide include polyamide products, industrial waste (process offcuts) generated during the polyamide product manufacturing process, and post-consumer polyamide product waste. 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, sheets, seatbelts, and airbags; automobile parts; molded parts for housing construction materials; electrical and electronic molded parts; aircraft parts; industrial machinery parts; film products; extrusion molded products; in-situ polymerization molded products; and RIM molded products. Furthermore, waste also includes product scraps, pellet scraps, lump scraps, and cutting scraps generated during these production processes.

When the thermoplastic polymer P is a thermoplastic polyester, waste resin moldings 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 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 tape, release films, and insulating materials; textile structures for clothing such as used clothing, uniforms, sportswear, and underwear; industrial textile structures such as curtains, carpets, netting, belts, seats, seatbelts, and airbags; molded products 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 chunk 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.

Next, we will explain each of the means involved in the recovery device for thermoplastic polymer-derived components and the manufacturing method and equipment for recycled monomers.

The thermoplastic polymer-derived component recovery device of the present invention may be either a continuous treatment device or a batch treatment device. Continuous treatment devices have a means (A) for supplying a thermoplastic polymer composition (sometimes simply referred to as "means (A)" in the present invention). Examples of 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 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. Of these, it is preferable that means (A) be a device that uses an extruder. Using an extruder as means (A) makes it easier to stabilize the pressure at which the thermoplastic polymer composition is extruded. It is preferable to heat the thermoplastic polymer composition to a temperature at which the thermoplastic polymer P melts. Heating the thermoplastic polymer P to a temperature at which the thermoplastic polymer P melts allows it to 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 into high-pressure equipment using a diaphragm pump, gear pump, plunger pump, etc., and then heats it to a predetermined temperature using a heat exchanger, electric heater, heating furnace, etc., although devices not exemplified here may also be used.

[Means (C) for separating the water-insoluble solid component S to obtain a thermoplastic polymer-derived component]
The continuous system of the device 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 a water-insoluble solid component S from a mixture of the thermoplastic polymer composition supplied from the means (A) and water supplied from the 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.

In method (C), the water-insoluble solid component S is separated to obtain a thermoplastic polymer-derived component at a temperature of 110°C to 350°C and a pressure of 0.14 MPa to 30 MPa. By setting the temperature to 110°C to 350°C and a pressure of 0.14 MPa to 30 MPa, the dissolution, melting, and hydrolysis of the thermoplastic polymer P is promoted, making it easier to separate the water-insoluble solid component S and preventing excessive decomposition of the thermoplastic polymer-derived component. The temperature condition is preferably 130°C to 350°C. 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 when separating the water-insoluble solid component S from the solution containing the thermoplastic polymer-derived component. On the other hand, a pressure of 10 MPa or lower is preferred, and a pressure of 4 MPa or lower is more preferred.

In the present invention, it is preferable to supply means (C) with a mass a (kg) of the thermoplastic polymer composition and a mass b (kg) of water 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.

In means (C), it is preferable to set the temperature at or above 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 ordinary 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 in the filter) / (the amount of water-insoluble solid component S present in the thermoplastic polymer composition).

Furthermore, in order to prevent clogging of the filter, reduce cleaning frequency, and ensure a retention area for the water-insoluble solid components S captured by the filter, it is preferable to combine the filter with the separation tank described below and install it inside the separation tank. The water-insoluble solid components S captured by the filter inside the separation tank can be extracted and recovered intermittently as appropriate. The filter openings and filter area are selected appropriately depending on the type, amount, and size of the water-insoluble solid components S.

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. Examples of 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 it is preferable to extract the thermoplastic polymer-derived component from the top of the separation tank. 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 it is preferable to extract the thermoplastic polymer-derived component from the bottom of the separation tank. The water-insoluble solid component S that accumulates 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. As for centrifuges and hydrocyclones, any type is acceptable as long as they can be used at temperatures between 110°C and 350°C and at pressures between 0.14 MPa and 30 MPa.

[Pressure vessel (D) and supply gas for obtaining a solution of a 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 obtained by mixing the thermoplastic polymer composition and water. In the present invention, it is preferable to mix the 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 the 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, it is possible to reduce the energy required to heat the water and the energy required for purifying the recycled monomer. b/a is more preferably 10 or less, even 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.

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 between 110°C and 350°C and a pressure between 0.14 MPa and 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 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 preferable, and 4 MPa or less is more preferable.

The inert gas in means (E) can be nitrogen, argon, or other rare gases, but nitrogen is preferred due to its ease of availability and ease of handling. Means (E) can be, for example, a direct supply from a high-pressure gas tank, a supply of gas pressurized by a compressor, a steam supply from a boiler, or a combination of these. Compressors include positive displacement and turbo types, but any type is acceptable as long as the required pressure can be obtained.

[Means for separating water-insoluble solid component S (F)]
The thermoplastic polymer-derived component recovery device of the present invention includes a 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 thermoplastic polymer-derived component recovery device of the present invention, the means (F) includes a filter. By including the means (F) in 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). The filter aperture and filter area are appropriately selected depending on the type, shape, and amount of the water-insoluble solid component S. The 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.

[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 the 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.

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

[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) that receives the thermoplastic polymer-derived component discharged from means (C) or means (F) of the thermoplastic polymer-derived component recovery apparatus of the present invention and depolymerizes the thermoplastic polymer-derived component. The reactor (G) enables the production of recycled monomer. In the present invention, removing water-insoluble solid components using means (C) or means (F) can prevent problems such as accumulation and blockage of water-insoluble solid components in the reactor (G) or piping. The reactor (G) may be either a batch or continuous reactor, but a continuous reactor is preferred. Using a continuous reactor for the reactor (G) can shorten the time required for charging and discharging from a batch reactor, thereby improving productivity per unit volume. The continuous reactor may be a tubular reactor or a continuous tank reactor. When the reactor (G) is a batch reactor, the thermoplastic polymer-derived component tank (H) can also be used as the reactor (G).

The temperature and pressure inside reactor (G) may be different from those in means (C), (D), and (F). Because the purpose of reactor (G) is to depolymerize the thermoplastic polymer-derived component to obtain monomers, 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 alkalis include the alkaline (earth) metal salts mentioned above.

The depolymerized thermoplastic polymer-derived component and water discharged from reactor (G) are preferably fed into a cooling device to stop the depolymerization reaction by lowering the temperature. Examples of cooling devices for stopping the depolymerization reaction include a cooler and a flash tank. In particular, it is preferable that the cooling device for stopping the depolymerization reaction includes a heat exchanger for heating the water described above. Since the depolymerized thermoplastic polymer-derived component and water after cooling are usually under high pressure, a back pressure valve or other known method can be used. In the present invention, solid components insoluble in water are removed, thereby reducing the risk of clogging of the back pressure valve.

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

[Method for recovering components derived from thermoplastic polymers and method for producing recycled monomers]
The method for recovering a thermoplastic polymer-derived component of the present invention includes a step of separating a water-insoluble solid component 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 a thermoplastic polymer-derived component 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 component. 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. b/a is more preferably 10 or less, even more preferably 8 or less, and most preferably 6 or less. 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.

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.

In the method of the present invention for recovering components derived from thermoplastic polymers, it is preferable to carry out heat exchange between the mixture of the components derived from thermoplastic polymers and water and the water supplied to the thermoplastic polymer composition. By carrying out heat exchange, thermal efficiency can be improved, which is preferable from the perspective of reducing energy consumption.

The method for producing recycled monomers of the present invention includes a step of depolymerizing the thermoplastic polymer-derived components recovered by the above-mentioned method for recovering thermoplastic polymer-derived components. The produced recycled monomer is preferably purified and then repolymerized, and reused as a thermoplastic polymer composition.

[Examples of production equipment 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 device 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 and 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 the pressure vessel 16 and heated to 110°C to 350°C and 0.14 MPa to 30 MPa. Under the above temperature and pressure conditions, the thermoplastic polymer melts, dissolves, and hydrolyzes, and separates from the water-insoluble solid component 19. While maintaining the above temperature and pressure conditions, valve 21 between pressure vessel 16 and thermoplastic polymer-derived component tank 22 is opened, and the thermoplastic polymer-derived component and water are charged into thermoplastic polymer-derived component tank 22. The thermoplastic polymer-derived component and water can be recovered from valve 21 below the thermoplastic polymer-derived component tank.

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

Figure 3 shows an example of a recycled monomer production system that has a reactor (G) for depolymerizing thermoplastic polymer-derived components, located downstream of a continuous thermoplastic polymer-derived component recovery system. 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 the water supplied from the means (B) at 110°C to 350°C and 0.14 MPa to 30 MPa. In the system shown in Figure 3, the filter 7 is installed 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 depolymerization reaction water stored in the additional depolymerization reaction water tank 27 is pressurized by pump 8 and heated by heater 9, mixed with the thermoplastic polymer-derived component discharged from the separation tank 6, pressurized by pump 8, heated by heater 9, and introduced into the tubular reactor 10. The depolymerized thermoplastic polymer-derived component discharged from the tubular reactor 10 is cooled by the cooler 12, the pressure is released by the back pressure valve 13, and the depolymerized product is stored in the depolymerized product tank 14.

Figure 4 shows an example of an apparatus that, in addition to the apparatus shown in Figure 3, is equipped with a heat exchanger 11 that exchanges heat between the depolymerized thermoplastic polymer-derived component discharged from the tubular reactor and the water 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 where depolymerization occurs, thereby improving the thermal efficiency of the entire process.

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. If the specific gravity of the water-insoluble solid components 19 is lighter than that of the thermoplastic polymer-derived components, changing the flow of the thermoplastic polymer-derived components from top to bottom through the filter 7 can prevent blockage of the filter 7. Figure 6 shows the apparatus in Figure 2 with the addition of a buffer tank 30. By adding a buffer tank at the boundary between the batch pressure vessel and the continuous reactor, it becomes easier to control the amount of additional water for the depolymerization reaction, which contains additives such as alkali.

[Second Aspect of the Present Invention]
A 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 other materials, such as silicone, in order to separate inorganic substances and crosslinked polymers contained in a polyamide composition or a polyester composition. The present invention 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.

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 primarily comprises residues of amino acids, lactams, or diamines and dicarboxylic acids. Herein, "primarily comprising" 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.

Typical 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- Examples of suitable polyamides include alicyclic diamines such as 3,5,5-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. There are no particular restrictions on the polyamide, but from the perspective of recycling polyamide and facilitating the promotion of fossil resource recycling, homopolymers of polycaproamide (polyamide 6) and polyhexamethylene adipamide (polyamide 66), which are produced and consumed in large quantities, and copolymers thereof are particularly preferred.

A preferred method for producing a polyamide-derived depolymerized intermediate composition includes depolymerizing 100 parts by weight of polyamide in a polyamide composition in the presence of 100 to 1,000 parts by weight of water to obtain a depolymerized intermediate composition. If the amount of water is less than 100 parts by weight, the dispersibility and solubility of the polyamide composition in water tend to decrease, resulting in reduced reaction efficiency. The amount of water is preferably 120 parts by weight or more, and even more preferably 150 parts by weight or more. On the other hand, the amount of water is more preferably 800 parts by weight or less, even more preferably 500 parts by weight or less, and particularly preferably 300 parts by weight or less. The present invention relates to a method for producing raw material monomers by depolymerizing polyamide, with the aim of both recycling fossil resources and reducing 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 significantly higher than those of 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 perspective of suppressing side reactions due to the influence of coexisting salts, deionized water or distilled water is preferably used.

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 is 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 rise to 270°C or higher as long as the effects of the present invention are not impaired; however, by keeping the depolymerization temperature below 270°C, over-reaction of the polyamide monomer can be suppressed, and therefore it is preferable to keep the temperature below 270°C throughout the process of obtaining the depolymerized intermediate composition.

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, it is possible to suppress side reactions during the production of the depolymerized intermediate composition while lowering the molecular weight of the polyamide and making it into a water slurry or water-soluble, making it easier to subsequently introduce into the depolymerization process. Furthermore, even when water-insoluble components other than polyamide are contained, the 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. On the other hand, the content is preferably 65% by mass or less, more preferably 60% by mass or less.

Here, the content of monomers and/or derivatives thereof 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 monomers and/or derivatives thereof is referred to as the content of polyamide oligomers.

A suitable method for producing the polyester-derived depolymerized intermediate composition of the present invention is 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 the depolymerized intermediate composition. Hereinafter, the depolymerized intermediate composition obtained by depolymerizing the polyester may be referred to as the polyester-derived depolymerized intermediate composition.

The polyester in the polyester composition used in the present invention has as its main constituents residues of dicarboxylic acid or its ester-forming derivatives and diol or its ester-forming derivatives, or has as its main constituent a structure in which a diol residue is bonded to a carbonyl group (carbonate ester bond). Here, "having as the main constituent" means that, of all structural units, residues of dicarboxylic acid or its ester-forming derivatives and diol or its ester-forming derivatives account for 50 mol% or more, and it is preferable that these residues account for 80 mol% or more. Here, carbonyl groups in carbonate ester bonds are 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, as well as ester-forming derivatives thereof. Two or more of these may be used.

The ester-forming derivatives referred to here are the alkyl esters, acid anhydrides, acid halides, etc. of the dicarboxylic acids mentioned above. As alkyl esters of dicarboxylic acids, methyl esters, ethyl esters, hydroxyethyl esters, hydroxybutyl esters, etc. are preferably used. As acid anhydrides of dicarboxylic acids, anhydrides of dicarboxylic acids with each other, anhydrides of dicarboxylic acids with acetic acid, etc. are preferably used. As halides of dicarboxylic acids, acid chlorides, acid bromides, acid iodides, etc. are preferably used. Examples of the diols or their ester-forming derivatives 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 derivatives include compounds in which the hydrogen atoms of the hydroxy groups of diols are substituted with acetyl groups.

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 polyester 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. Of these, at least one selected from the group consisting of polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and copolymers thereof is particularly preferred.

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 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 polyester composition in water tend to decrease, and the reaction efficiency tends to decrease. 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 polyester, it is important to reduce the amount of water used, as mentioned above. By keeping the amount of water within these ranges, both production efficiency of the depolymerized intermediate composition and energy conservation can be achieved.

A preferred method for producing a polyester-derived depolymerized intermediate composition includes depolymerizing the polyester in the polyester composition at a temperature of 150°C or higher but 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 constant or varied over time. Setting the depolymerization temperature to 150°C or higher but lower than 240°C reduces the viscosity of the polyester in the presence of water, increasing its solubility and dispersibility and accelerating the reaction, while also preventing overreaction of the polyester monomers 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, maintaining the depolymerization temperature below 240°C prevents overreaction of the polyester monomers, and therefore it is preferable to maintain the temperature below 240°C throughout the process of obtaining the depolymerized intermediate composition.

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 out of 100 parts by mass of polyester-derived components constituting the depolymerized intermediate composition. By setting the content within this range, side reactions during the production of the depolymerized intermediate composition can be suppressed while the polyester is reduced in molecular weight and made into a water slurry or water-soluble, facilitating subsequent introduction into the depolymerization process. Furthermore, even when water-insoluble components other than polyester are contained, separation of the water-insoluble components other than polyester 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.

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 for polyamide compositions and at 150°C or higher for polyester compositions. The depolymerization time also includes the time during which the polymer composition and water are maintained at the same temperature range in the reaction vessel while coexisting in the depolymerization temperature, 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 helps to prevent yield reduction due to overreaction of the monomer. Furthermore, if 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.

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 accelerated. 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 accelerate 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. Nitrogen or argon is preferably used as the sealed gas to suppress side reactions such as oxidation reactions. The inside of the pressure vessel can also be pressurized by introducing high-pressure water. When using high-pressure water, the pressure vessel can be kept gas-free. The degree of gas pressure is not particularly limited as it can be set to the desired pressure, but examples include 0.3 MPa or higher.

The depolymerized intermediate composition may be composed of components that are soluble in water at 25°C, components that are insoluble in water, or both. To promote the recycling of fossil fuel resources, a means of recycling waste plastics that have been processed into various forms, such as textile products, films, and molded resin products, is desirable. In particular, used waste plastics are expected to contain not only components other than the composite polyamide or polyester, but also foreign matter that has been 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 aqueous solution when mixed with water, as this provides excellent handling. Here, "in the form of an aqueous slurry solution or aqueous solution" means that the mixture of the depolymerized intermediate composition and water is in the form of an aqueous slurry solution or aqueous solution at a temperature range above 0°C, the melting point of water, and below the upper limit of the depolymerization temperature. By converting a polyamide composition or polyester composition into an aqueous slurry solution or solution of a depolymerized intermediate composition, it becomes possible to supply the depolymerized intermediate composition to the depolymerization apparatus in a water-dispersed or water-dissolved state, regardless of the form of waste plastic used. Furthermore, because the composition is an aqueous slurry solution or solution, it has excellent fluidity, making it easy to separate from other materials that are insoluble in water.

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, as determined using a particle size distribution analyzer, is less than 100 μm. In this specification, "components insoluble in water at 25°C" refers to components that dissolve in an amount of less than 0.1 g per 100 g of water at 25°C. The "components insoluble in water at 25°C" may also be simply referred to as "water-insoluble components." 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 supplied to the depolymerization apparatus in the same manner. 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 lower limit to the volume average particle size, but it is most preferably 0 μm (indicating a state dissolved in water).

Methods for adjusting the volume average particle size to 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 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 this 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 component containing only one or two of polyamide, polyamide oligomer, and polyamide monomer may still be referred to as a polyamide-derived component. The same applies to polyester-derived components.

When producing the depolymerized intermediate composition, an alkali (earth) metal compound may also be present. The presence of an alkali (earth) metal compound converts dicarboxylic acid, a type of polyamide or polyester monomer, into an alkali (earth) metal dicarboxylic acid salt, which increases its solubility in water and therefore improves the efficiency of separation from other materials. "Alkaline (earth) metal compounds" refers to alkali metal compounds and alkaline earth metal compounds. The term "alkali (earth) metal compounds" refers to either compounds containing alkali metal atoms such as lithium, sodium, potassium, or cesium, or compounds containing alkaline earth atoms such as magnesium, calcium, or barium, or a mixture of these.

Examples of alkali metal compounds include alkali metal hydroxides, alkali metal oxides, alkali metal carbonates, alkali metal phosphates, and alkali metal borates. In particular, from the viewpoint of increasing the production rate of monomers and their derivatives, it is preferable that the alkali metal compound be at least one selected from the group consisting of alkali metal hydroxides and alkali metal carbonates, and it is more preferable that the alkali metal compound be at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, cesium bicarbonate, lithium carbonate, sodium carbonate, potassium carbonate, and cesium carbonate. Examples of alkaline earth metal compounds 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 production rate 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 dicarboxylic acid residue content of the polyamide and/or polyester in the polyamide composition and/or polyester composition.

In the method for producing a depolymerized intermediate composition, in the step of obtaining a depolymerized intermediate composition, it is preferable that the polyamide or polyester contains a dicarboxylic acid residue, and that X mol of the dicarboxylic acid residue and a hydroxide, oxide, carbonate containing Y ₁ mol of alkali metal ions and/or Y ₂ mol of alkaline earth metal ions, or a mixture containing two or more of these, coexist so as to satisfy (Formula 1).
0.5≦(Y ₁ + 2×Y ₂ )/X≦1.5 (Formula 1)
By setting the ratio within this range, overreaction of the depolymerized monomer is suppressed and an aqueous slurry solution or aqueous solution of the depolymerized intermediate composition can be easily obtained. Obtaining the depolymerized intermediate composition as an aqueous slurry solution or aqueous solution of the depolymerized intermediate composition provides excellent fluidity, facilitating 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. Furthermore, when the polyamide composition or polyester composition contains an inorganic component described below, depolymerization of the polyamide or polyester can be promoted while suppressing elution of decomposed inorganic components into water. ( _Y1 + 2× _Y2 )/X is more preferably 0.6 or more, even more preferably 0.8 or more, and particularly preferably 0.9 or more. Meanwhile, ( _Y1 + 2× _Y2 )/X is more preferably 1.3 or less, even more preferably 1.1 or less. The amount of dicarboxylic acid residues contained in the polyamide composition and polyester composition can be quantified from a spectrum obtained by proton nuclear magnetic resonance spectroscopy ( ¹ H-NMR) using sulfuric acid, chloroform, or hexafluoroisopropanol as a heavy solvent.

There are no particular restrictions on the method for allowing the alkaline (earth) metal compound to coexist. An aqueous solution may be prepared by mixing the alkaline (earth) metal compound with water in advance; 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 brought into contact with water and then further mixed with the alkaline (earth) metal compound.

In the present invention, a polyamide composition or 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 physical properties caused by degradation of the inorganic components during reprocessing, and most have been incinerated or landfilled after use. According to the present invention, polyamide compositions or polyester compositions containing inorganic components, which were difficult to chemically recycle using conventional methods, can be utilized as a chemical recycling resource and can be regenerated into products equivalent to petrochemicals.

Examples of the other polymers include polyolefins, modified polyphenylene ethers, polysulfones, polyketones, polyetherimides, polyarylates, polyethersulfones, polyetherketones, polythioetherketones, polyetheretherketones, polyimides, polyamideimides, polyethylene tetrafluoride, polyphenylene sulfide, polyurethanes, silicones, and polyacrylic acids. These may contain two or more types, and may be crosslinked.

The organic fibers include natural fibers such as cotton, linen, and silk, and synthetic fibers such as aramid, acrylic, and rayon. The inorganic fibers include fibrous and whisker-like fillers such as glass fiber, carbon fiber, metal fiber, gypsum fiber, ceramic fiber, asbestos fiber, zirconia fiber, alumina fiber, silica fiber, titanium oxide fiber, silicon carbide fiber, aramid fiber, rock wool, potassium titanate whiskers, silicon nitride whiskers, wollastonite, and alumina silicate. Two or more of these may be contained. 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.

The forms or articles of polyamide or polyester compositions include, but are not limited to, fibers, films, and molded resin products. When materials other than polyamide or polyester are used, examples of fibers include blends of fibers with different materials (natural fibers, synthetic fibers), fabrics combined with different materials by sewing, impregnation, bonding, coating, etc.; films include films coated with different materials, laminated films with different materials; and molded resin products include resin molded products made 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. Silicone-coated polyamide 66 compositions used in airbags and glass fiber-blended polyamide and polyester compositions used in automotive parts are particularly widely used. 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 or polyester composition contain a silicon-containing component. Examples of silicon-containing components include silicone and glass fiber.

The polyamide composition or polyester composition used in the present invention may contain various additives, provided that the purpose of the present invention is not impaired. Specific examples of various additives include antioxidants, heat stabilizers, weathering agents, mold release agents and lubricants, pigments, dyes, plasticizers, antistatic agents, and flame retardants.

Specific examples of products that can be used as polyamide compositions in the present invention include engine peripheral parts such as radiator tanks and oil pans, automotive parts such as gears, electrical and electronic parts such as connectors and switches, industrial machinery parts such as fasteners and cable ties, 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 during the production process of these products may also be used.

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, netting, belts, and sheets; molded products such as automobile parts, electrical and electronic parts, building materials, daily necessities, household goods, and sanitary products. Furthermore, product scraps, pellet scraps, and lump scraps generated during the production processes of these products may also be used.

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

The present invention preferably further includes a step of filtering out components insoluble in water at 25°C other than components derived from the polyamide or polyester after depolymerizing the polyamide composition or polyester composition. Including the step of filtering out the water-insoluble components results in a depolymerized intermediate composition in the same form as a depolymerized intermediate composition produced from a polyamide 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 filtering out the water-insoluble components is not particularly limited, but any commonly known method can be selected depending on the properties and size of the water-insoluble components remaining after depolymerization of the polyamide or polyester composition. The temperature for filtering out the components is not particularly limited, but is preferably 25°C or higher and the depolymerization temperature or lower. To increase the fluidity of the 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 obtained in this manner is an aqueous slurry solution or an aqueous solution, regardless of the shape or composition of the polyamide composition or polyester composition, and can therefore be supplied to the subsequent depolymerization apparatus in the same form, making it particularly suitable for use in producing recycled monomers.

In the present invention, after depolymerization of a polyamide composition or polyester composition, it is preferable that the weight-average major axis, as observed with an optical microscope at 25°C, 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 is 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 transport. On the other hand, excessively large particle sizes of water-insoluble components other than polyamide-derived or polyester-derived components can clog the flow path, making separation from the polyamide-derived or polyester-derived components difficult. Therefore, the minor axis of water-insoluble components other than polyamide- or polyester-derived components is preferably less than 10 cm. A minor axis of less than 5 cm is more preferred, and less than 1 cm is even more preferred. 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.

In the present invention, after depolymerization of a polyamide composition or polyester composition, the resulting composition preferably contains polyamide-derived or polyester-derived components and other components insoluble in water at 25°C, as well as polyamide- or polyester-derived components soluble in water at 25°C. The volume average particle size of the components insoluble in water at 25°C that pass through a 40-mesh filter, as determined using a particle size distribution analyzer, is less than 100 μm. 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 "components 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 lower limit to the volume average particle size, but 0 μm (indicating a state dissolved in water) is most preferable. Here, if all components other than polyamide-derived components or polyester-derived components can be removed using 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.

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 better 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 methods for achieving a removal rate within the above range include reducing the mesh size of the filter medium or performing removal using a filter multiple times. A removal rate of 50% by mass or more is more preferred, 55% by mass or more is even more preferred, and 65% by mass or more is particularly preferred. There is no particular upper limit to the removal rate, but 100% by mass is most preferred. The removal rate of water-insoluble components can be calculated by a washing and extraction method using a solvent that dissolves only polyamide-derived components or polyester-derived components, as described in the examples.

A variety of well-known reaction methods, including batch and continuous methods, can be used to produce the depolymerized intermediate composition. For example, batch methods include autoclaves equipped with a stirrer and 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 heating function. 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. Furthermore, a non-oxidizing atmosphere is preferred for production, and an inert atmosphere such as nitrogen, helium, or argon is more preferred. From the standpoints of economy and ease of handling, a nitrogen atmosphere is even more preferred.

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 to 70% by mass of polyamide monomers and/or derivatives thereof, or polyester monomers and/or derivatives thereof, and 30% by mass to 90% by mass of components derived from polyamides or polyesters other than the monomers and/or derivatives thereof, in the presence of water at 225°C to 350°C 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, in 100% by mass of polyamide-derived components or polyester-derived components. Here, the polyamide-derived components or polyester-derived components in the depolymerization reaction composition refer to monomers and/or derivatives thereof and components derived from polyamides or polyesters other than monomers and/or derivatives, the total content of which is 100% by mass. Examples of 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 preferred range described above, and a method in which an alkaline (earth) metal compound or the like is further added.

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, making it easy to separate and purify the monomer from the depolymerization reaction composition.

Another embodiment of the method for producing a depolymerized 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 polyamide-derived components or polyester-derived components in the monomer-containing composition contain 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 depolymerized reaction composition, wherein 100% by mass of polyamide-derived components or polyester-derived components in the depolymerized reaction composition contain 75% by mass or higher of polyamide monomers or polyester monomers and/or derivatives thereof.

By including the first and second steps, a depolymerization reaction composition containing 75% by mass or more of polyamide monomers and/or derivatives thereof, or polyester monomers and/or derivatives thereof can be obtained.

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 increases, thereby improving depolymerization efficiency. The depolymerization temperature in the first step is preferably above 160°C, more preferably above 175°C, even more preferably above 190°C, and particularly preferably above 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 involving elimination of monomer end groups can be suppressed. The depolymerization temperature in the first step is preferably below 290°C, more preferably below 280°C, and even more preferably below 270°C. In particular, a depolymerization temperature of less than 240°C for the polyester composition is particularly preferred, as this makes it easier to suppress discoloration.

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 makes it easier for the monomer-containing composition to disperse and dissolve in water, improving depolymerization efficiency. Subcritical water, which has 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 has 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, resulting in a depolymerization reaction composition containing 75% by mass or more of polyamide monomers and/or their derivatives, or polyester monomers and/or their derivatives. In particular, when depolymerizing a monomer-containing composition containing a diol or diamine, the depolymerization temperature in the second step is preferably 320°C or less, and more preferably 300°C or less, because this makes it easier to suppress side reactions involving the elimination of hydroxyl groups or amino groups.

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 their derivatives, or polyester monomers and/or their derivatives. Water can be further added in the second step. Adding water in the second step can promote depolymerization of the monomer-containing composition. However, from the perspective of energy conservation, it is preferable to use less water, which has 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, and particularly preferably 300 parts by mass or less. Furthermore, an alkaline (earth) metal compound can be further present in the first and/or second steps. Examples of alkaline (earth) metal compounds include the compounds that can be used in producing the depolymerized intermediate composition described above.

In the method for producing a depolymerization reaction composition of the present invention, the depolymerization time in the second step of producing 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 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 helps to suppress yield reduction due to overreaction of the monomer. 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. A depolymerization time of 0.1 minutes or more is preferred, with 1 minute or more being more preferred, and 3 minutes or more being even more preferred. Furthermore, in the production of the depolymerization reaction composition, the depolymerization pressure in the first and second steps can be the same as the conditions applied when producing the depolymerized intermediate composition described above.

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 can be recovered from the obtained depolymerization reaction composition by known methods such as extraction, distillation, and solid-liquid separation. Furthermore, to obtain monomers of even higher purity, the 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.

The polyamide production method or polyester production method of the present invention includes a step of polycondensing raw materials containing the polyamide monomer or polyester monomer of the present invention. Examples of polyamide production methods include a method of thermally polycondensing amino acids, lactams, diamines, and dicarboxylic acids directly or their salts. Examples of polyester production methods include a method of subjecting dicarboxylic acids and diols to an esterification reaction, followed by a polycondensation reaction, and a method of subjecting dicarboxylic acids to a chemical conversion dialkyl dicarboxylate, obtained by chemically converting the dicarboxylic acid, to a transesterification reaction with a diol, followed by a polycondensation reaction. In the polyamide production method or polyester production method of the present invention, polyamide or polyester can be regenerated by repolymerizing the monomer obtained by depolymerizing the polyamide composition and/or polyester composition. This allows for the production of environmentally friendly recycled materials that contribute to resource recycling and the reduction of greenhouse gas emissions.

The polyamide or polyester of the present invention is obtained by polycondensation of raw materials containing a polyamide monomer or polyester monomer of the present invention. Like polyamides or polyesters produced from petroleum-derived raw materials, the polyamide or polyester of the present invention can be processed and used into various products such as injection-molded articles, extrusion-molded articles, fiber structures, films, and sheets. 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 articles, fibers, films, or sheets of the present invention are made using the polyamide or polyester of the present invention.

The present invention will be explained below using examples, but the present invention is not limited to these examples. The following raw materials were used in each example of the first and second aspects of the present invention. Note that deionized water was used.

(A-1) Polyamide 66 waste: glass fiber (GF) 30% reinforced polyamide 66 molding waste (crushed sprue and runners, passing through an 8 mm mesh), melting point in an oven-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: a silicone-coated airbag fabric made of polyamide 66 recovered from scrapped vehicles, with 12.0% by mass of components other than polyamide, a bone-dry melting point of 265°C, a melting point in water of 179°C, and no melting point for the silicone coating. The thermoplastic polymer is polyamide 66, and the water-insoluble solid component is the silicone coating.
(B-1) Polyamide 6 waste: glass fiber (GF) 30% reinforced polyamide 6 molding scraps (crushed sprue and runners, passing through an 8 mm mesh), with a bone-dry melting point of 225°C, a melting point in water of 160°C, and a melting point of GF of 500°C or higher. The thermoplastic polymer is polyamide 6, and the water-insoluble solid component is GF.
(C-1) Polyethylene terephthalate waste: a blended fiber consisting of 82% by mass of polyethylene terephthalate (PET) and 18% by mass of cotton, with a bone-dry melting point of 250°C, a melting point of 220°C in water, and no melting point for 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 base fabric made of polyamide 66 recovered from scrapped vehicles, content of components other than polyamide: 12.0% by mass
(D-3) Polyamide 66 waste: GF reinforced polyamide 66 molding scraps (crushed sprue and runners, passed through an 8 mm mesh), content of components other than polyamide (glass fiber) 31.2% by mass
(E-1) Polyamide 6 waste: GF-reinforced polyamide 6 molding scraps (crushed sprues and runners, passed through an 8 mm mesh), 31.0 mass% of components other than polyamide (glass fibers).

The evaluation methods for the first and second aspects of the present invention are as follows.
<Hexamethylenediamine Yield (GC)>
The yield of hexamethylenediamine is calculated from the amount of hexamethylenediamine determined by gas chromatography (GC). Hexamethylenediamine is determined by the absolute calibration method (calibration reagent: Fujifilm Wako Pure Chemical Industries, Ltd., first-grade).
Equipment: Shimadzu GC-2010
Column: Agilent Technologies DB-5 0.32 mm x 30 m (0.25 μm)
Carrier gas: Helium Detector: Flame ionization detector (FID)
Sample: In a first embodiment, an aqueous solution or aqueous slurry of a depolymerized product of a component derived from a thermoplastic polymer 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 aqueous solution is taken and diluted with approximately 10 g of deionized water, and components insoluble in deionized water are separated and removed by filtration to prepare a sample for gas chromatography measurement.

<Yield (IC) of adipic acid (disodium adipate)>
The yield of adipic acid is calculated from the amount of adipic acid determined by ion chromatography (IC). Adipic acid is determined by the absolute calibration method (calibration reagent: adipic acid: Fujifilm Wako Pure Chemical Industries, Ltd., special grade).
Equipment: Shimadzu HIC-20Asuper
Column: Shimadzu Shim-pack IC-SA2 (250 mm x 4.6 mm ID)
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 a first embodiment, an aqueous solution or aqueous slurry of a depolymerized product of a component derived from a thermoplastic polymer 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 0.02 g of the aqueous slurry or aqueous solution is taken, diluted with approximately 10 g of deionized water, and filtered to separate and remove components insoluble in deionized water, thereby preparing a sample for ion chromatography measurement.

<Yield of terephthalic acid (HPLC)>
The yield of terephthalic acid is calculated from the amount of terephthalic acid determined by high performance liquid chromatography (HPLC). The amount of terephthalic acid is determined by the absolute calibration method (calibration 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: Shimadzu LC-10Avp series 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 vol% aqueous acetic acid solution/acetonitrile Sample: Approximately 0.1 g of a water slurry or aqueous solution of the depolymerized product of the thermoplastic polymer-derived component containing the recycled monomer after the depolymerization reaction was terminated was weighed out and diluted with approximately 10 g of water. Insoluble components were separated and removed by filtration to prepare a sample for high-performance liquid chromatography measurement.

<ε-Caprolactam Yield (HPLC)>
The yield of ε-caprolactam is calculated from the amount of ε-caprolactam determined by high performance liquid chromatography (HPLC). The amount of ε-caprolactam is determined by the absolute calibration curve method (calibration curve reagent: special grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).
Apparatus: Shimadzu LC-10Avp series 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 component derived from a thermoplastic polymer 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 aqueous 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.

<Bone-dry Melting Point of Thermoplastic Polymer and Melting Point of Polyamide>
The melting point of the thermoplastic polymer in the thermoplastic polymer composition was determined by measuring the endothermic peak temperature when the thermoplastic polymer was 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 was determined by measuring the endothermic peak temperature when approximately 5.0 mg of polyamide was 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 were detected, the temperature of the endothermic peak with the greatest peak intensity was determined as the melting point in the bone-dry state.

<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.

<Analysis of water-insoluble solid components>
The water-insoluble solid component and an equal amount of distilled water to the water-insoluble solid component are placed in a stainless steel pressure-resistant sealed vessel for DSC, and the mixture is 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 is confirmed that the mixture exhibits 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.

<Volume average particle size (particle size distribution meter)>
In a second aspect of the present invention, a depolymerized intermediate composition is added to a medium (water) in a laser diffraction particle size distribution analyzer (Microtrac MT3300EXII) manufactured by Nikkiso Co., Ltd. until a measurable concentration is reached, and ultrasonic dispersion is performed at 30 W for 60 seconds. The volume average particle size is then 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.

<Removal rate of different materials>
In a 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 materials, 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 materials were dried for 12 hours in a vacuum oven set at 80°C, and the masses were 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 of foreign materials.

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

<Concentration of Depolymerized Intermediate Composition in Water Slurry Solution or Aqueous Solution>
In a second aspect of the present invention, approximately 10 g of an aqueous slurry solution or 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 components, and solvent-insoluble components were removed by vacuum filtration to obtain a filtrate in which the polyamide-derived components were 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 solution was calculated from the mass of the aqueous slurry solution or solution and the mass of the resulting dried depolymerized intermediate.

<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) of the resulting solution was measured by GPC measurement under the following conditions:
Pump: e-Alliance GPC system (manufactured by Waters)
Detector: Differential refractometer Waters 2414 (manufactured by Waters)
Column: Shodex HFIP-806M (2 columns) + HFIP-LG
Solvent: hexafluoroisopropanol (0.005N sodium trifluoroacetate added)
Flow rate: 1 ml/min Sample injection amount: 0.1 ml Temperature: 30°C
Molecular weight standards: polymethyl methacrylate.

[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.

[Example 2]
The recycled monomer production apparatus shown in Figure 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). Subsequently, a small amount of water and nitrogen was sealed in a 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 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. (A-1) 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 depolymerized product thus produced exhibits a high yield of hexamethylenediamine as calculated by gas chromatography, and a high yield of adipic acid as calculated by ion chromatography.

[Example 3]
The recycled monomer production equipment 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 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 it 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. (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.

[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. Next, a small amount of water and nitrogen was sealed in a 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.

[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.

[Example 6]
The thermoplastic polymer-derived component recovery device shown in Figure 1 was used. (C-2) 2.0 kg of 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 it and the pressure vessel 16. 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.

[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. (D-1) Polyamide 66, water, and sodium hydroxide were charged into an SUS316L autoclave equipped with a stirrer in the amounts shown in Table 1. The amount of water was 201 parts by mass per 100 parts by mass of polyamide. The molar ratio Y ₁ /X, expressed as ₁ mole of alkali metal ion Y, calculated from the amount of polyamide (X moles) and the amount of sodium hydroxide, 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 to carry out the reaction. The pressure inside the system during the reaction was 2.6 MPa. After completion of the reaction, the system was cooled to room temperature, and a liquid slurry of a depolymerized intermediate composition was recovered. The total time for which the polyamide and water were kept together in the reaction vessel at a temperature 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.

[Examples 8 to 10, Comparative Examples 1 to 3]
A depolymerized intermediate composition was obtained by depolymerizing a polyamide 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. 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.

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 suitable for use in producing polyamide monomers.

[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.

[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 solution, 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.

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 is suitable for use in producing polyamide monomers. Furthermore, by depolymerizing the content of monomers and monomer derivatives in the depolymerized intermediate composition so that it falls within a specified range, decomposition of the other materials can be suppressed and separated, making it possible to recover polyamide-derived components.

On the other hand, in Comparative Example 4, which was obtained by depolymerizing airbags recovered from scrapped vehicles under conditions with a high amount of added alkali, 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 an increased amount passed through the cylindrical filter and became mixed into the depolymerized intermediate composition, resulting in a low removal rate. In Comparative Example 5, which was obtained by depolymerizing molding waste containing glass fibers at 280°C, an aqueous solution of depolymerized and dissolved polyamide was also obtained, 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 more difficult.

[Example 14]
An aqueous slurry solution of the polyamide-derived depolymerized intermediate composition obtained in the same manner as in Example 8, water, and sodium hydroxide were charged in the amounts shown in Table 3 into an SUS316L autoclave equipped with a stirrer. 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.

[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 the polyamide in the same manner as in Example 12 and then separating and removing the silicone coating residue, water, and sodium hydroxide were charged in the amounts shown in Table 3.

[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 mass%, obtained by depolymerizing in the same manner as in Example 13 and then separating and removing the 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.

In Examples 14 to 16, a depolymerized intermediate composition containing a polyamide monomer and/or its derivative within a specified range was further depolymerized by adding water and an alkali hydroxide and maintaining the mixture at a preferred temperature range, thereby obtaining a high yield of polyamide monomer and/or its derivative.

[Example 17]
An SUS316L autoclave equipped with a stirrer was charged with 28.50 g of (E-1) polyamide 6 waste and 58.25 g of water. The amount of water per 100 parts by mass of polyamide was 296 parts by mass. 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 the 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.

60.03 g of an aqueous slurry solution containing a 24% by weight polyamide-derived depolymerized intermediate composition, obtained by separating and removing the glass fibers, was placed in an SUS316L autoclave equipped with a stirrer. The reactor was purged with nitrogen and sealed under a nitrogen pressure of 0.5 MPa. The temperature was raised to 320°C while stirring at 200 rpm and maintained for 15 minutes to allow the reaction to proceed. The pressure inside the system was 11.9 MPa during the reaction. After completion of the reaction, the system was cooled to room temperature and the clear liquid depolymerized intermediate composition was recovered. The total time the reaction vessel was maintained above 225°C was 40 minutes. The ε-caprolactam yield calculated by liquid chromatography of the recovered depolymerized reaction composition was 76 mol%. The amount of monomer obtained from 100% by weight of the polyamide-derived components in the depolymerized intermediate composition was 76% by weight. In Example 17, a depolymerized intermediate composition having a polyamide monomer content within a preferred range was subjected to removal of the glass fibers, and then further depolymerization was carried out at a preferred temperature range, thereby obtaining polyamide monomer in high yield.

[Reference example 1]
A salt solution was prepared by dissolving 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) in 12.7 g of water. 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.

[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.

[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.

[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 exhibit weight-average molecular weights and melting points equivalent to those of polyamides polymerized from reagent diamines and reagent dicarboxylic acids.

The present invention can be suitably used for the chemical recycling of thermoplastic polymer compositions containing thermoplastic polymers and water-insoluble solid components. It can also recycle plastic waste of a variety of compositions and forms. For example, it can be suitably used to separate water-insoluble solid components such as glass fibers from thermoplastic polyamide products and thermoplastic polyester products, and recover the raw material monomers. When used in chemical recycling, the present invention can achieve both resource recycling and a reduction in greenhouse gas emissions.

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 (29)

A method for recovering a component derived from a thermoplastic polymer, comprising the steps of separating the water-insoluble solid component S from a mixture containing water and 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, thereby obtaining a component derived from the thermoplastic polymer P. The method for recovering components derived from a thermoplastic polymer according to claim 1, wherein the amount 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 or more and 100 or less. The method for recovering components derived from a thermoplastic polymer according to claim 1 or 2, wherein 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. The method for recovering components derived from thermoplastic polymers according to any one of claims 1 to 3, wherein the water-insoluble solid component S comprises a crosslinked silicone polymer and/or a fibrous filler. The method for recovering components derived from thermoplastic polymers according to any one of claims 1 to 4, wherein the thermoplastic polymer P comprises polyamide and/or polyester. The method for recovering components derived from thermoplastic polymers according to any one of claims 1 to 5, wherein the thermoplastic polymer composition constitutes an article, the article being an airbag fabric. A method for producing recycled monomers, comprising a step of depolymerizing thermoplastic polymer-derived components recovered by the method for recovering thermoplastic polymer-derived components described in any one of claims 1 to 6. An apparatus for recovering thermoplastic polymer-derived components, comprising: a pressure vessel (D) for obtaining a solution 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 thermoplastic polymer-derived components, 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. An apparatus for recovering thermoplastic polymer-derived components, 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 a temperature of 110°C to 350°C and a pressure of 0.14 MPa to 30 MPa, wherein means (C) is equipped with at least a filter. The device for recovering components derived from thermoplastic polymers described in claim 8 or 9, wherein the water-insoluble solid component S includes a crosslinked silicone polymer and/or a fibrous filler. The device for recovering components derived from thermoplastic polymers described in any one of claims 8 to 10, wherein the thermoplastic polymer P includes a thermoplastic polyamide and/or a thermoplastic polyester. The device for recovering components derived from thermoplastic polymers described in any one of claims 8 to 11, wherein the thermoplastic polymer composition is an airbag fabric. A recycled monomer production apparatus having a reactor (G) into which the thermoplastic polymer-derived components discharged from means (F) of claim 8 or means (C) of claim 9 are input and which depolymerizes the thermoplastic polymer-derived components. A method for producing a depolymerized intermediate composition, comprising the 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 polyamide monomers and/or derivatives thereof per 100% by mass of polyamide-derived components. A method for producing a depolymerized intermediate composition, comprising the step of depolymerizing a polyester composition in the presence of water at a temperature of 150°C or higher and lower than 240°C to obtain a depolymerized intermediate composition, wherein the depolymerized intermediate composition contains 10% by mass or higher and 70% by mass or lower of polyester monomers and/or derivatives thereof per 100% by mass of polyester-derived components. The method for producing a depolymerized intermediate composition according to claim 14 or 15, wherein the depolymerized intermediate composition contains a polyamide- or polyester-derived component that is insoluble in water at 25°C and a polyamide- or polyester-derived component that is soluble in water at 25°C, and the volume average particle size of the component that is insoluble in water at 25°C as determined with a particle size distribution analyzer is less than 100 μm. The method for producing a depolymerized intermediate composition according to any one of claims 14 to 16, wherein an alkali metal compound and/or an alkaline earth metal compound is further present in the step of obtaining the depolymerized intermediate composition. 18. The method for producing a depolymerized intermediate composition according to any one of claims 14 to 17, wherein in the step of obtaining the depolymerized intermediate composition, the polyamide or polyester contains a dicarboxylic acid residue, and _X mol of the dicarboxylic acid residue and a hydroxide, oxide, carbonate, or a mixture containing two or more of these, each containing Y ₁ mol of alkali metal ions and/or Y 2 mol of alkaline earth metal ions, are allowed to coexist so as to satisfy (Formula 1).
0.5≦(Y ₁ + 2×Y ₂ )/X≦1.5 (Formula 1) The method for producing a depolymerized intermediate composition according to any one of claims 14 to 18, wherein the polyamide composition or the 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, per 100% by mass of the polyamide composition or the polyester composition. The method for producing a depolymerized intermediate composition according to any one of claims 14 to 19, wherein the polyamide composition or polyester composition contains a silicon-containing component. The method for producing a depolymerized intermediate composition according to any one of claims 14 to 19, wherein the step of obtaining the depolymerized intermediate composition further comprises, after depolymerization, a step of removing components insoluble in water at 25°C other than polyamide-derived components or polyester-derived components using a filter. The monomer-containing composition contains, relative to 100% by mass of polyamide-derived components or polyester-derived components, 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,
A method for producing a depolymerization reaction composition, comprising a step of depolymerizing a polyamide composition or a polyester composition in the presence of water at 225°C or higher and 350°C or lower 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. The method for producing a depolymerization reaction composition according to claim 22, wherein the monomer-containing composition is a depolymerization intermediate composition obtained by the method for producing a depolymerization intermediate composition according to any one of claims 14 to 21. 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 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; (Step 2) A step of further depolymerizing the aqueous slurry solution or the 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. The method for producing a depolymerization reaction composition according to claim 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. A polyamide monomer or polyester monomer obtained by purifying a depolymerization reaction composition obtained by the method for producing a depolymerization reaction composition described in any one of claims 22 to 25. A method for producing a polyamide or a polyester, comprising a step of polycondensing raw materials containing the polyamide monomer or polyester monomer according to claim 26. A polyamide or polyester obtained by polycondensation of raw materials containing the polyamide monomer or polyester monomer described in claim 26. A molded article, fiber, film, or sheet made using the polyamide or polyester described in claim 28.