Method for separating polyester

Abstract

Provided is a method for separating a polyester from a polyester composite material containing said polyester and components other than the polyester. The method includes a decomposition step for bringing a base, a monohydric alcohol and a carbonic acid diester into contact with the polyester composite material so as to decompose the polyester. This method for separating a polyester enables a polyester to be separated from a polyester composite material containing said polyester and components other than the polyester while preventing degradation of the components other than the polyester.

Description

Polyester separation method

[0001] The present invention relates to a method for separating polyester.

[0002] In recent years, concerns about environmental destruction, such as marine pollution, have led to an urgent need for the development of plastic recycling technologies. Polyesters are widely used as materials for bottles and fibers, and polyethylene terephthalate (PET), in particular, is produced at approximately 80 million tons per year worldwide. Two recycling methods for polyester have been developed: a material recycling method that does not involve depolymerization, and a chemical recycling method that involves depolymerization and repolymerization. While the former method is easily applicable to polyesters used in PET bottles and the like due to their high purity, it is difficult to apply this method to materials containing polyester (polyester-containing materials), such as polyester fibers and films containing polyester.

[0003] Known methods for depolymerizing polyester include those using water or supercritical alcohol (see Patent Documents 1 and 2). However, both require high-temperature conditions of 300°C or higher. On the other hand, transesterification methods using a base catalyst and alcohol can achieve depolymerization at relatively low temperatures. Methods using methanol, including halogenated solvents and potassium carbonate (see Non-Patent Document 1) or alkali metal alkoxides (see Patent Document 3), can achieve depolymerization at low temperatures of room temperature to 50°C. Furthermore, a method is known in which depolymerization is made more efficient by using dimethyl carbonate as an ethylene glycol scavenger (see Non-Patent Document 2). However, these methods are limited to high-purity PET derived from PET bottles and the like, and other polyester-containing materials are not applicable to these methods. A method for depolymerizing colored polyester fibers using a base catalyst and excess ethylene glycol is known, but this requires high temperatures of around 200°C. Furthermore, to obtain high-purity monomers, it is necessary to decolorize the fibers with a high-boiling-point solvent (see Patent Documents 4 to 6) or decompose the dye with an oxidizing agent (see Patent Document 7).

[0004] From the viewpoint of solving these problems, Patent Document 8 discloses a catalyst composition containing a base catalyst, a monohydric alcohol, and a carbonate diester or a tetraalkoxysilane as a glycol scavenger, and a method for depolymerizing polyester using the same.

[0005] Japanese Patent No. 5099416, Japanese Patent Laid-Open No. 2001-39908, U.S. Patent No. 10252976, Japanese Patent No. 4537288, Japanese Patent No. 5134563, Japanese Patent No. 6659919, Japanese Patent No. 6986813, Japanese Patent Laid-Open No. 2022-126617

[0006] Green Chem. 2021,23,511. Green Chem. 2021,23,9412.

[0007] Here, polyester composite materials containing polyester and components other than polyester have been known for some time, and a typical example is a polyester blend product obtained by blending polyester with cotton. Even if attempts are made to separate the polyester from such polyester composite materials using the methods disclosed in Patent Documents 4 to 6, for example, the components other than polyester are also exposed to high temperatures, and deterioration is unavoidable.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a method for separating polyester from a polyester composite material containing polyester and components other than polyester while preventing deterioration of the components other than polyester.

[0009] As a result of extensive research, the inventors have found that the above-mentioned problems can be solved by a method for separating polyester, comprising a decomposition step of contacting a base, a monohydric alcohol, a carbonic acid diester, and a polyester composite material to decompose the polyester. Specifically, the present invention provides the following aspects [1] to

[10] . [1] A method for separating polyester from a polyester composite material containing a polyester and a component other than polyester, comprising a decomposition step of contacting a base, a monohydric alcohol, a carbonic acid diester, and the polyester composite material to decompose the polyester. [2] The method for separating polyester according to [1] above, wherein the base is one or more selected from alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, and nitrogen-containing organic bases. [3] The method for separating polyester according to [1] or [2] above, wherein the monohydric alcohol is an alcohol having 1 to 6 carbon atoms. [4] The method for separating polyester according to any one of [1] to [3] above, wherein the carbonic acid diester is a dialkyl carbonate having 1 to 12 carbon atoms. [5] The method for separating polyester according to any one of [1] to [4] above, wherein the polyester is one or more materials selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. [6] The method for separating polyester according to any one of [1] to [5] above, wherein the component other than polyester is one or more materials selected from the group consisting of cotton, rayon, polyurethane, nylon, acrylic, polyethylene, polypropylene, carbon-based materials, dyes, and pigments. [7] The method for separating polyester according to any one of [1] to [5] above, wherein the component other than polyester is one or more materials selected from the group consisting of cotton and polyurethane. [8] The method for separating polyester according to any one of [1] to [7] above, wherein the polyester composite material is a mixed fiber of polyester fibers and fibers other than polyester fibers. [9] The method for separating polyester according to any one of [1] to [7] above, wherein the polyester composite material is a film containing polyester and a component other than polyester.

[10] The method for separating polyester according to any one of [1] to [9] above, wherein the reaction temperature in the decomposition step is in the range of 20° C. or higher but lower than 180° C.

[11] A recovery method for recovering components other than polyester from a polyester composite material containing polyester and components other than polyester, by the separation method according to any one of [1] to

[10] above.

[0010] According to the present invention, it is possible to provide a method for separating polyester from a polyester composite material containing polyester and components other than polyester while preventing deterioration of the components other than polyester.

[0011] Solid cotton fibers recovered in Example 1 １３ 1 shows the results of C NMR analysis of the cotton fibers recovered in Example 1; 2 shows the results of Fourier transform infrared spectroscopy analysis of the cotton fibers recovered in Example 1; 3 shows the results of thermogravimetry analysis of the cotton fibers recovered in Example 1; 4 shows the results of differential scanning calorimetry analysis of the cotton fibers recovered in Example 1; and 5 shows the results of solid polyurethane fibers recovered in Example 2. １３ 1 shows the results of C NMR analysis of the polyurethane fiber recovered in Example 2. 2 shows the results of Fourier transform infrared spectroscopy analysis of the polyurethane fiber recovered in Example 2. 3 shows the results of thermogravimetry analysis of the polyurethane fiber recovered in Example 2. 4 shows the results of differential scanning calorimetry analysis of the polyurethane fiber recovered in Example 2.

[0012] Hereinafter, embodiments of the method for separating polyester and the method for recovering components other than polyester according to the present invention will be described, but the present invention is not limited to the following embodiments.

[0013] <<Polyester Separation Method>> A polyester separation method according to one embodiment of the present invention includes a decomposition step of contacting a base, a monohydric alcohol, and a carbonic acid diester with a polyester composite material containing a polyester and components other than the polyester, thereby decomposing the polyester in the polyester composite material. According to the separation method of this embodiment, the polyester can be separated under relatively low temperature conditions, thereby preventing deterioration of components other than the polyester contained in the polyester composite material. Furthermore, because the polyester is decomposed during polyester separation, the dicarboxylic acid diester monomer can be obtained with high purity.

[0014] <Polyester Composite Material> In the present embodiment, the polyester composite material is not particularly limited as long as it contains polyester and a component other than polyester, and examples thereof include a material containing a mixed fiber of polyester fibers and fibers other than polyester fibers, and a film, packaging container, bottle, lump, etc. containing polyester and a component other than polyester. The component other than polyester may be a resin other than polyester, or may be a non-resin component.

[0015] The mixed fibers may further contain non-resin components such as colorants. The film containing polyester and a component other than polyester may be, for example, a monolayer film containing polyester and a component other than polyester, or a laminate film that is a laminate of a film made of polyester and a film containing a component other than polyester. Examples of monolayer films containing polyester and a component other than polyester include monolayer films that contain both polyester and a resin other than polyester but no non-resin components, monolayer films that contain both polyester and a non-resin component but no resin other than polyester, and monolayer films that contain polyester, a resin other than polyester, and a non-resin component. Examples of laminate films that are laminates of a film made of polyester and a film containing a component other than polyester include a laminate film that is a laminate of a film made of polyester and a film that contains a resin other than polyester and that does not contain polyester or non-resin components, a laminate film that is a laminate of a film made of polyester and a film that contains both a resin other than polyester and polyester and that does not contain non-resin components, a laminate film that is a laminate of a film made of polyester and a film that contains both a resin other than polyester and non-resin components and that does not contain polyester, a laminate film that is a laminate of a film made of polyester and a film that contains both polyester and non-resin components and that does not contain resin other than polyester, a laminate film that is a laminate of a film made of polyester and a film that contains all of polyester, a resin other than polyester, and a non-resin component, a multilayer film that is a laminate of one or more of the above laminate films and one or more of the above monolayer films, a multilayer film that is a laminate of two or more of the above laminate films, and a multilayer film that is a laminate of two or more of the above monolayer films.

[0016] Examples of lumps containing polyester and components other than polyester include lumps containing both polyester and resins other than polyester but no non-resin components, lumps containing both polyester and non-resin components but no resins other than polyester, and lumps containing all of polyester, resins other than polyester, and non-resin components.

[0017] The resin other than polyester can be selected arbitrarily depending on the purpose and is not particularly limited. For example, in terms of high versatility and high applicability of the present invention, examples of resin other than polyester include polyolefins such as polyethylene and polypropylene, cellulose, polyamides such as nylon, polyurethane, and acrylic resins. These resins may be, for example, in the form of a film (resin film) or a fiber (resin fiber). Examples of fibers other than polyester fibers include fibers of resins other than the above polyesters, cotton, rayon, etc.

[0018] The non-resin component can be selected arbitrarily depending on the purpose and is not particularly limited. For example, in terms of high versatility and high applicability of the present invention, examples of the non-resin component include inorganic components (inorganic compounds) such as aluminum, and colorants such as dyes and pigments.

[0019] The fiber diameters of the polyester fibers and the fibers other than polyester fibers in the material containing the above-mentioned mixed fibers are not particularly limited and may be, for example, 0.1 μm to 200 μm or 1 μm to 50 μm. The thickness of the film containing polyester and a component other than polyester is not particularly limited and may be, for example, 0.5 μm to 1000 μm or 1 μm to 500 μm. Here, when the film is the above-mentioned laminate film, the film thickness means the thickness of the entire laminate film.

[0020] More specifically, examples of materials containing the above-mentioned mixed fibers include fabrics for various clothing, fibers that are materials for fabrics, etc. Fabrics may be unused or used, and may be uncut or cut pieces. Specific examples of uncut fabrics include unsold clothing and used clothing, and specific examples of cut pieces include cut pieces generated during the manufacture of various clothing, cut pieces from various clothing after use, etc. Fibers that are materials for fabrics may be, for example, small pieces of cut pieces generated during the manufacture of fabrics, cut pieces from used fabrics, etc.

[0021] The film containing polyester and components other than polyester may be unused or used, and may be uncut or cut. More specifically, examples include packaging film, small pieces of cut material generated during the production of packaging film, and small pieces of cut material from packaging film after use.

[0022] More specifically, examples of the aggregates containing polyester and components other than polyester include pellets and flakes containing polyester and components other than polyester. The maximum diameter of the aggregates is not particularly limited and may be, for example, 0.1 mm to 10 mm. Here, the "maximum diameter of the aggregate" refers to the maximum length of a line segment connecting two different points on the surface of the aggregate.

[0023] The polyester composite material may be one type or two or more types, and when two or more types are used, the combination and ratio thereof can be selected arbitrarily depending on the purpose. That is, the polyester composite material used for separating the polyester may be one or two or more types selected from the group consisting of a material containing polyester fibers, a film containing polyester and a component other than polyester, a packaging container containing polyester and a component other than polyester, a bottle containing polyester and a component other than polyester, and a lump containing polyester and a component other than polyester.

[0024] When the polyester composite material is a material containing a mixed fiber of polyester fibers and fibers other than polyester fibers, the material containing the mixed fiber is preferably one or more selected from the group consisting of mixed fibers, woven fabrics of mixed fibers, mixtures containing polyester fibers and components other than polyester fibers, and woven fabrics of such mixtures.When the polyester composite material is a film containing polyester and components other than polyester, the film containing polyester and components other than polyester is preferably either or both of a monolayer film containing polyester and components other than polyester, and a laminate film which is a laminate of a film made of polyester and a film containing components other than polyester.

[0025] In the polyester composite material, the ratio of the polyester content (parts by mass) to the total mass (parts by mass) of the polyester composite material ([content (parts by mass) of polyester contained in the polyester composite material] / [total mass (parts by mass) of the polyester composite material]×100) (polyester content) can be arbitrarily selected depending on the purpose and is not particularly limited. In particular, the polyester content is preferably 20% by mass or more and 90% by mass or less, more preferably 25% by mass or more and 90% by mass or less, even more preferably 30% by mass or more and 80% by mass or less, and particularly preferably 35% by mass or more and 75% by mass or less. The higher the polyester content, the greater the amount of monomer (dicarboxylic acid diester described below) generated per unit mass from the polyester composite material due to decomposition of the polyester. However, the lower the polyester content, the greater the amount of components other than polyester that can be recovered by separating the polyester.

[0026] [Polyester] The polyester in the polyester composite material (the polyester to be decomposed) is not particularly limited as long as it is an oligomer or polymer that, upon decomposition, produces a glycol and a component having two functional groups per molecule capable of condensation reacting with the glycol. The polyester may be an aromatic polyester having only aromatic groups (divalent groups having a structure in which one hydrogen atom is removed from each of two carbon atoms forming the aromatic ring skeleton of an aromatic compound) in its ester bond-containing main chain, an aliphatic polyester having no aromatic groups in its main chain (having both an aliphatic group and no aromatic group), or a polyester having both aromatic and aliphatic groups in its main chain. The aromatic polyester may have only divalent aromatic hydrocarbon groups (arylene groups) as aromatic groups, only divalent aromatic heterocyclic groups (heteroarylene groups), or both divalent aromatic hydrocarbon groups and divalent aromatic heterocyclic groups. Examples of heteroatoms in the aromatic heterocyclic groups include oxygen atoms and nitrogen atoms. In general, the reactivity of a substrate in a transesterification reaction depends on the structure on the carboxylic acid side and the structure on the alcohol side. As will be described later, polyesters (polyethylene terephthalate, polybutylene terephthalate, etc.) having an aromatic benzene ring or naphthalene ring as the carboxylic acid side structure can be decomposed well, and therefore it can be easily assumed that polyesters having other aromatic structures such as furan can be decomposed in a similar manner. Similarly, polyesters having an ethylene glycol (polyethylene terephthalate, etc.) or 1,4-butanediol (polybutylene terephthalate, etc.) structure as the alcohol side structure can be decomposed well, and therefore it can be easily assumed that polyesters having other dihydric alcohol structures such as 1,3-propanediol can be decomposed in a similar manner.In terms of enhancing the effects of the present invention and increasing versatility, the polyester is preferably an aromatic polyester, and more preferably polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), or polyethylene furanoate (PEF, also known as polyethylene furan dicarboxylate). Decomposition of the polyester produces, as a monomer, a dicarboxylic acid diester specific to the polyester and the type of monohydric alcohol.

[0027] For example, polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate produce terephthalic acid diesters, polyethylene naphthalate and polybutylene naphthalate produce naphthalenedicarboxylic acid diesters (2,6-naphthalenedicarboxylic acid diesters), and polyethylene furanoate produces furandicarboxylic acid diesters (2,5-furandicarboxylic acid diesters). For example, when methanol is used as the monohydric alcohol, dimethyl dicarboxylic acid esters are produced as dicarboxylic acid diesters. The polyester composite material may contain only one type of polyester, or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected as desired depending on the purpose.

[0028] <Base> The base is not particularly limited and may be either an inorganic base or an organic base, but is preferably an alkali metal carbonate or alkali metal hydroxide, or an alkali metal alkoxide, which reacts with a monohydric alcohol to produce an alkali metal alkoxide. Generally, in a transesterification reaction, an alkoxide anion serving as a nucleophile attacks the carbonyl group of an ester, passing through a quaternary carbon intermediate and then liberating the other alkoxide anion, thereby proceeding. Since an alkoxide anion is produced by the reaction of a corresponding alcohol with a base, any base capable of deprotonating an alcohol can be used.

[0029] Examples of inorganic bases include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide, alkali metal oxides such as lithium oxide, sodium oxide, and potassium oxide, alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide, and alkaline earth metal oxides such as calcium oxide and magnesium oxide. Examples of organic bases include alkali metal alkoxides such as lithium methoxide, lithium ethoxide, lithium tert-butoxide, sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium methoxide, potassium ethoxide, and potassium tert-butoxide, calcium dimethoxide, calcium diethoxide, calcium di-tert-butoxide, magnesium dimethoxide, magnesium diethoxide, and magnesium di-tert-butoxide. Examples of the alkali metal alkoxide include alkaline earth metal alkoxides such as 1,5,7-triazabicyclo[4.4.0]dec-5-ene (abbreviation: TBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (abbreviation: DBU), 1,3-dimesitylimidazol-2-ylidene, and 1,3-dicyclohexylimidazol-2-ylidene; and nitrogen-containing organic bases (organic bases having a nitrogen atom) such as lithium methoxide, sodium methoxide, or potassium methoxide, with sodium methoxide being more preferred, in terms of promoting polyester decomposition at a higher rate. The nitrogen-containing organic base is preferably 1,5,7-triazabicyclo[4.4.0]dec-5-ene, in terms of promoting polyester decomposition at a higher rate.

[0030] The base used in the decomposition step may be one type or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected arbitrarily depending on the purpose. The base is particularly preferably an alkali metal alkoxide, in that it allows the decomposition of the polyester to proceed at a particularly high rate. The amount of base used in the polyester decomposition step is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 6 parts by mass, even more preferably 0.5 to 3 parts by mass, and particularly preferably 3 to 6 parts by mass, per 100 parts by mass of the polyester in the polyester composite material. When the amount of base used is equal to or greater than the lower limit, the decomposition of the polyester proceeds at a higher rate. When the amount of base used is equal to or less than the upper limit, excessive use of the base is suppressed. That is, when decomposing the polyester, it is preferable that the amount of base used is a catalytic amount (the base is a catalyst).

[0031] <Monohydric Alcohol> In the decomposition process, the monohydric alcohol undergoes a transesterification reaction with the polyester in the polyester composite material. That is, during the decomposition of the polyester, the polyester reacts with the monohydric alcohol to produce a glycol corresponding to one of the monomers used in the production of the polyester, and a dicarboxylic acid diester corresponding to the other monomer or a derivative thereof. The monohydric alcohol is not particularly limited. The reaction efficiency of the decomposition reaction according to the present invention is controlled by the capture of the liberated dihydric alcohol by the excess diester carbonate. Therefore, as described below, based on the fact that the reaction using methanol and dimethyl carbonate proceeds efficiently, it can be easily assumed that the reaction will proceed efficiently with other combinations of monohydric alcohol and dialkyl carbonate. The monohydric alcohol may be, for example, either an aliphatic alcohol or an aromatic alcohol. However, in terms of proceeding with a higher rate of decomposition of the polyester, an aliphatic alcohol (saturated aliphatic alcohol, unsaturated aliphatic alcohol) is preferred, and a saturated aliphatic alcohol is more preferred.

[0032] Examples of saturated aliphatic alcohols include alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, 1-propanol (n-propyl alcohol), 2-propanol (isopropyl alcohol), 1-butanol (n-butyl alcohol), 2-methyl-1-propanol (isobutyl alcohol), 2-butanol (sec-butyl alcohol), and 2-methyl-2-propanol (tert-butyl alcohol). The monohydric alcohol used in the decomposition of polyester may be a single type or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected as desired depending on the purpose. Methanol is particularly preferred as the monohydric alcohol, as it allows polyester decomposition to proceed at a particularly high rate. The amount of monohydric alcohol used in the decomposition of polyester is not particularly limited. For example, when the polyester is polyethylene terephthalate (PET), the amount is preferably 30 to 200 parts by mass, more preferably 50 to 160 parts by mass, per 100 parts by mass of PET in the polyester composite material. Furthermore, when the polyester is polybutylene terephthalate (PBT), the amount of monohydric alcohol used is preferably 10 to 180 parts by mass, more preferably 20 to 140 parts by mass, per 100 parts by mass of PBT in the polyester composite material. When the amount of monohydric alcohol used is equal to or greater than these lower limits, the effects obtained by using the monohydric alcohol are enhanced. On the other hand, when the amount of monohydric alcohol used is equal to or less than these upper limits, excessive use of the monohydric alcohol is suppressed.

[0033] <Carbonate diester> Carbonate diester reacts with glycol generated from polyester during decomposition of polyester to produce a cyclic compound or a chain compound, which shifts the equilibrium between the depolymerization reaction and polymerization reaction of polyester during polyester decomposition in favor of the depolymerization reaction, thereby improving the production rate of the target monomer. Carbonate diester functions as a glycol scavenger. Reaction products of a carbonate diester and a glycol may include a cyclic compound (e.g., cyclic compound (1) below) that is a reaction product of one molecule of carbonate diester and one molecule of glycol, a chain compound (e.g., first chain compound (2) below) that is a reaction product of one molecule of carbonate diester and one molecule of glycol, a chain compound (e.g., second chain compound (3) below) that is a reaction product of one molecule of carbonate diester and two molecules of glycol, and a chain compound (e.g., third chain compound (4) below) that is a reaction product of two molecules of carbonate diester and one molecule of glycol. Whether a cyclic compound or a chain compound is produced is determined mainly by the type (e.g., size) of glycol. For example, the reaction product of a carbonic acid diester and ethylene glycol is mainly a cyclic compound (1) (more specifically, ethylene carbonate), which is a reaction product of one molecule of a carbonic acid diester and one molecule of ethylene glycol.

[0034] (In the formula, X １ ~X ５ are each independently a divalent organic group, and R １ ~R ３ are each independently a monovalent organic group.

[0035] Above X １ ~X ５ The divalent organic group represented by the formula (I) may be, for example, an aromatic group, an aliphatic group, or a group having both an aromatic group and an aliphatic group, and is preferably a divalent hydrocarbon group. Preferred divalent organic groups include, for example, an ethylene group (—CH ２ CH ２ -), 1,3-propylene group (trimethylene group, -CH ２ CH ２ CH２ -), 1,4-butylene group (tetramethylene group, -CH ２ CH ２ CH ２ CH ２ -), and alkylene groups having 2 to 4 carbon atoms are more preferred. １ ~R ３ The monovalent organic group represented by the formula (I) may be, for example, either an aromatic group or an aliphatic group, but is preferably an aliphatic group (a saturated aliphatic group or an unsaturated aliphatic group), and more preferably an aliphatic hydrocarbon group. Preferred monovalent organic groups include, for example, monovalent saturated aliphatic groups (i.e., alkyl groups) such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group, and is more preferably a monovalent saturated aliphatic group (i.e., alkyl group) having 1 to 4 carbon atoms.

[0036] Examples of carbonate diesters include dialkyl carbonates and diaryl carbonates. The two alkyl groups bonded to the oxygen atom in the dialkyl carbonate may be the same as or different from each other. Furthermore, the two aryl groups bonded to the oxygen atom in the diaryl carbonate may be the same as or different from each other. The alkyl group in the dialkyl carbonate may be linear, branched, or cyclic, and if cyclic, may be monocyclic or polycyclic. The number of carbon atoms in the linear or branched alkyl group in the dialkyl carbonate is preferably 1 to 8. Examples of such an alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a 1-methylbutyl group, an n-hexyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 2,2-dimethylbutyl group, a 2,3-dimethylbutyl group, an n-heptyl group, a 2-methylhexyl group, a 3-methylhexyl group, a 2,2-dimethylpentyl group, a 2,3-dimethylpentyl group, a 2,4-dimethylpentyl group, a 3,3-dimethylpentyl group, a 3-ethylpentyl group, a 2,2,3-trimethylbutyl group, an n-octyl group, and an isooctyl group. Among these, the number of carbon atoms in the alkyl group in the dialkyl carbonate is more preferably 1 to 4, and even more preferably 1 or 2. Such more preferred dialkyl carbonates include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0037] The aryl group in the diaryl carbonate may be either monocyclic or polycyclic. The aryl group in the diaryl carbonate preferably has 6 to 10 carbon atoms. Examples of such aryl groups include phenyl, 1-naphthyl, 2-naphthyl, o-tolyl, m-tolyl, p-tolyl, 2,3-xylyl (2,3-dimethylphenyl), 2,4-xylyl (2,4-dimethylphenyl), 2,5-xylyl (2,5-dimethylphenyl), 2,6-xylyl (2,6-dimethylphenyl), 3,4-xylyl (3,4-dimethylphenyl), and 3,5-xylyl (3,5-dimethylphenyl). A more preferred diaryl carbonate is diphenyl carbonate. The carbonate diester used in the decomposition of polyester may be one type or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected as desired depending on the purpose. In terms of proceeding with decomposition of the polyester at a higher rate, the carbonate diester is more preferably one or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and diphenyl carbonate, and is particularly preferably dimethyl carbonate.

[0038] In the polyester decomposition step, the amount of the carbonate diester used is preferably 100 to 5,000 parts by mass, more preferably 100 to 1,000 parts by mass, and may be, for example, 100 to 500 parts by mass, relative to 100 parts by mass of the polyester in the polyester composite material. When the amount of the carbonate diester used is equal to or greater than the lower limit, the effects obtained by using the carbonate diester are enhanced. When the amount of the carbonate diester used is equal to or less than the upper limit, excessive use of the carbonate diester is suppressed.

[0039] <Solvent> In the polyester decomposition step, a solvent that does not fall into any of the categories of base, monohydric alcohol, and carbonate diester may be used. In this embodiment, decomposition of the polyester proceeds efficiently even without the use of a solvent. However, using a solvent as needed may improve the handleability of the blend of raw materials, such as the reaction solution, and may result in more efficient decomposition of the polyester. In this specification, unless otherwise specified, the term "solvent" encompasses both a component that is liquid at room temperature and serves as a dispersant for dissolving a solute, and a component that is liquid at room temperature and serves as a dispersion medium for dispersing a dispersoid. Furthermore, "room temperature" refers to a temperature that is not particularly cooled or heated, i.e., an ordinary temperature, such as a temperature of 15 to 25°C. Here, the solvent is preferably an organic solvent. Examples of organic solvents include aromatic hydrocarbons such as toluene, ethers such as tetrahydrofuran, alkanes such as n-hexane, halogenated hydrocarbons such as chloroform and dichloromethane, amides such as dimethylformamide, and sulfoxides such as dimethyl sulfoxide. The solvent used for decomposing the polyester may be one kind or two or more kinds, and when two or more kinds are used, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0040] When a solvent is used during polyester decomposition, the amount used is preferably 1 to 100,000 parts by mass, and more preferably 1 to 10,000 parts by mass, per 100 parts by mass of the polyester composite material. When the amount of solvent used is equal to or greater than the lower limit, the effects obtained by using the solvent are enhanced. When the amount of solvent used is equal to or less than the upper limit, excessive use of the solvent is suppressed.

[0041] <Other Components> When decomposing the polyester, other components that do not fall under any of the polyester composite material, base, monohydric alcohol, carbonate diester, and solvent may be used as long as the effects of the present invention are not impaired. The other components can be selected arbitrarily depending on the purpose and are not particularly limited. The other components used in decomposing the polyester may be one type only or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected arbitrarily depending on the purpose. During decomposition of the polyester, the ratio of the total amount (parts by mass) of the polyester composite material, base, monohydric alcohol, and carbonate diester to the total amount (parts by mass) of components other than the solvent (([amount (parts by mass) of polyester composite material used] + [amount (parts by mass) of base used] + [amount (parts by mass) of monohydric alcohol used] + [amount (parts by mass) of carbonate diester used]) / [total amount (parts by mass) of components other than the solvent] × 100) is preferably 80% by mass to 100% by mass, more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass, and may be, for example, any one of 97% by mass to 100% by mass and 99% by mass to 100% by mass. When the ratio is equal to or greater than the lower limit, the polyester can be decomposed more efficiently. Here, the total amount (parts by mass) of components other than the solvent used during decomposition of the polyester is synonymous with the total amount (parts by mass) of the polyester composite material, base, monohydric alcohol, carbonic acid diester, and other components used during decomposition.

[0042] <Reaction Conditions> Decomposition of the polyester in the polyester composite material can be carried out by contacting a base, a monohydric alcohol, a carbonic acid diester, the polyester composite material, and optionally a solvent and other components. The order of contacting these raw materials is not particularly limited, but it is preferable to prepare a raw material composition that is a blend of a base, a monohydric alcohol, a carbonic acid diester, and optionally a solvent and other components (for example, a blend of all raw materials other than the polyester composite material), and then mix this raw material composition with the polyester composite material. This contact order allows for the decomposition of the polyester to proceed at a higher rate. When the amount of base blended in the raw material composition is catalytic (the base acts as a catalyst), the raw material composition may be referred to herein as a "catalyst composition."

[0043] The reaction temperature during decomposition of the polyester can be adjusted appropriately taking into account the type of raw material used, etc., and the decomposition may be carried out at room temperature (normal temperature) or under heated conditions. The equipment used for heating is not particularly limited, and equipment such as a heater can be used. The reaction temperature during decomposition of the polyester is preferably 20°C or higher, more preferably 40°C or higher, and even more preferably 60°C or higher. The reaction temperature during decomposition of the polyester is preferably less than 180°C, more preferably 150°C or lower, even more preferably 100°C or lower, and particularly preferably 70°C or lower. In one embodiment, the reaction temperature during decomposition of the polyester is, for example, preferably 20°C or higher and lower than 180°C, more preferably 40°C or higher and 150°C or lower, more preferably 50°C or higher and 120°C or lower, and particularly preferably 60°C or higher and 100°C or lower. For example, by adjusting reaction conditions other than the reaction temperature, it is possible to decompose the polyester at a sufficiently high rate even at a reaction temperature of 20°C or higher and 70°C or lower. As described above, according to the present embodiment, although it has been conventionally difficult to decompose polyester at relatively low temperatures, polyester can be decomposed at low temperatures, such as 150° C. or lower, and therefore it is possible to separate the polyester from the polyester composite material. As a result, unlike when polyester is decomposed at high temperatures, the amount of by-products produced during decomposition can be reduced, coloration of the dicarboxylic acid diester (monomer), which is the main decomposition product, can be reduced, and deterioration of components other than the polyester contained in the polyester composite material can be prevented.

[0044] The decomposition of the polyester may be carried out under normal pressure, reduced pressure, or increased pressure. The decomposition of the polyester may be carried out in air or in an inert gas atmosphere. The reaction time for decomposing the polyester is not particularly limited and can be adjusted appropriately taking into account other reaction conditions such as the reaction temperature. The reaction time for decomposing the polyester is not particularly limited as long as it is 0.5 to 24 hours, but is preferably 0.5 to 12 hours, and more preferably 1 to 8 hours. In this embodiment, the end of decomposition can be determined, for example, when the polyester disappears. Therefore, the time required for the polyester to disappear can be considered the decomposition reaction time. The time required for the polyester to disappear can also be determined, for example, by the time required for the mass loss of the polyester composite material to stop.

[0045] In a blend immediately after the contact of the raw materials, unreacted polyester composite material does not dissolve and remains insoluble in the other liquid components. In a blend during which polyester decomposition is in progress, typically, unreacted polyester composite material and polyester composite material during or after the polyester reaction do not dissolve and remain insoluble in the other liquid components. Meanwhile, glycols and dicarboxylic acid diesters, which are reaction products of polyester decomposition, typically dissolve in the liquid components. During polyester decomposition, such blends can be stirred by known methods, such as by rotating a magnetic stirrer or impeller, or by using a ball mill. During polyester decomposition, the polyester composite material, which has a low specific gravity, may float near the liquid surface. In such cases, the contact area between the insoluble polyester composite material and the liquid components can be increased by, for example, pushing the polyester composite material near the liquid surface to submerge it, or by using a narrow-mouthed reaction vessel. As a result, the amounts of raw materials such as base, monohydric alcohol, and carbonate diester used can be reduced compared to when other reaction vessels are used, and the polyester can be decomposed more efficiently. Furthermore, when a narrow-mouthed reaction vessel is used, if one with a wide bottom surface is used, the reaction vessel can be enlarged in capacity while ensuring a large contact area between the polyester composite material and the liquid component.

[0046] <Post-Treatment Conditions, Extraction Conditions> After the polyester decomposition process described above is completed, post-treatment can be performed using a known method, allowing one of the main decomposition products, the dicarboxylic acid diester, to be extracted with high purity. For example, after polyester decomposition, the resulting reaction product is subjected to solid-liquid separation procedures such as filtration, centrifugation, and decantation to recover components other than the polyester. The liquid obtained by the solid-liquid separation procedure is then subjected to distillation (concentration) of volatile components, and the resulting solid is washed with methanol and water to obtain a high-purity dicarboxylic acid diester. The resulting dicarboxylic acid diester may then be further purified by crystallization, distillation, or the like, as necessary. The other main decomposition product, the reaction product of glycol and carbonate diester, can also be extracted in the same manner as the dicarboxylic acid diester by appropriately adjusting the post-treatment and extraction conditions. According to this embodiment, as described above, decomposition is possible at low temperatures, such as below 180°C, and therefore, unlike decomposition at high temperatures, the impurity content and coloration of the dicarboxylic acid diester can be reduced. Therefore, a highly pure dicarboxylic acid diester (monomer) with reduced coloration can be obtained by the simplified process of washing with methanol and water as described above, without adding any complicated steps. Furthermore, even if the polyester composite material originally contains a colorant, the coloration of the dicarboxylic acid diester (monomer) derived from this colorant can also be reduced by the simplified process of washing with methanol and water as described above. In contrast, when decomposition is performed at high temperatures using conventional methods, obtaining a highly pure monomer requires complicated steps, such as a decolorization treatment using a high-boiling point solvent and a dye decomposition treatment using an oxidizing agent.

[0047] <<Method for Recovering Components Other Than Polyester>> According to the polyester separation method of one embodiment of the present invention, components other than polyester can be recovered from a polyester composite material. The recovered components other than polyester are not exposed to high temperatures, as described above, and are therefore less susceptible to deterioration and are therefore reusable. The components other than polyester can be recovered by solid-liquid separation from the reaction product after the polyester decomposition step, as described above. If necessary, they may be further washed with a solvent or dried. Details and specific examples of the components other than polyester recovered by the recovery method of this embodiment are the same as those of the components other than polyester contained in a polyester composite material in the polyester separation method described above. The use of the components other than polyester recovered by the recovery method of this embodiment (hereinafter sometimes referred to as "recovered material") is not particularly limited. When the recovered material is cotton or rayon, it can be reused as fibers or saccharified or converted into alcohol fuel by a bioprocess. When the recovered material is a carbon-based material such as polyurethane, nylon, acrylic, polyethylene, or polypropylene, it can be recycled as resin or fibers, for example.

[0048] The present invention will be described in more detail below with reference to specific examples. However, the present invention is not limited to the examples shown below. Note that the unit "ppm" shown below is always based on mass ratio.

[0049] <<Separation of Polyester>> <Separation of Polyester Fibers from a Fiber Blend Containing Polyester Fibers and Cotton> [Example 1] Sodium methoxide (NaOCH ３) (Fujifilm Wako Pure Chemical Industries, Ltd., hereinafter, 0.30 g, 5.5 mmol) was added, followed by methanol (Kishida Chemical Co., Ltd., hereinafter, 6.5 mL) and dimethyl carbonate (DMC) (Tokyo Chemical Industry Co., Ltd., hereinafter, 50 mL) and homogeneously dissolved to prepare a raw material composition. A lab coat (65% by mass of polyester fiber and 35% by mass of cotton in total fibers) was cut into approximately 2 cm x 2 cm pieces, and several pieces (10 g) were added to the raw material composition in the eggplant flask obtained above. Here, the percentage (mass%) of polyester fiber in total fibers is synonymous with the ratio of the polyester content (parts by mass) in the polyester composite material to the total mass (parts by mass) of the polyester composite material, as previously described. This also applies to the other examples and comparative examples that follow. Next, using a magnetic stirrer and an oil bath, the stirrer was rotated in the eggplant flask, and the mixture of the raw material composition and the cut material was stirred at 50°C for 2 hours to decompose the polyester fibers. Next, dimethyl carbonate (15 mL) was added to this mixture in the eggplant flask to dissolve the precipitated components, and the contents in the eggplant flask were filtered while still hot at 50°C without cooling, recovering cotton fibers (3.7 g) and a colorless solid (0.1 g) as solids. The filtrate was then distilled to recover dimethyl carbonate and methanol, and the residue was washed with methanol (25 mL) and water (25 mL) and dried to obtain dimethyl terephthalate (6.2 g). Regarding the cotton fibers, the cotton fibers recovered in Example 1, and the cuttings of the white coat, the solids were １３ Analysis by C NMR (apparatus: "Bruker AvanceNEO 400 MHz" manufactured by BRUKER, the same applies hereinafter), Fourier transform infrared spectroscopy (apparatus: "FT / IR-4100" manufactured by JASCO Corporation, the same applies hereinafter), thermogravimetry (apparatus: "STA7200RV" manufactured by Hitachi High-Tech Science Corporation, the same applies hereinafter), and differential scanning calorimetry (apparatus: "DSC7020" manufactured by Hitachi High-Tech Science Corporation, the same applies hereinafter) confirmed that cotton fibers were recovered in Example 1. １３The results of the C NMR analysis are shown in FIG. 1, the results of the Fourier transform infrared spectroscopy analysis are shown in FIG. 2, the results of the thermogravimetry analysis are shown in FIG. 3, and the results of the differential scanning calorimetry analysis are shown in FIG. 4.

[0050] <Separation of polyester fibers in a fiber mixture containing polyester fibers and polyurethane fibers> [Example 2] Sodium methoxide (NaOCH ３ ) (Fujifilm Wako Pure Chemical Industries, Ltd., hereinafter, 0.16 g, 3.0 mmol) was added, followed by methanol (Kishida Chemical Co., Ltd., hereinafter, 6.5 mL) and dimethyl carbonate (DMC) (Tokyo Chemical Industry Co., Ltd., hereinafter, 50 mL) and homogeneously dissolved to prepare a raw material composition. A white T-shirt (88% by mass of polyester fiber and 12% by mass of polyurethane fiber in total fibers) was cut into approximately 2 cm x 2 cm pieces, and several pieces (10 g) were added to the raw material composition in the eggplant flask obtained above. Next, using a magnetic stirrer and oil bath, the stirrer was rotated in the eggplant flask, and the mixture of raw material composition and cut material was stirred at 50 °C for 1 hour to decompose the polyester fiber. Next, dimethyl carbonate (15 mL) was added to this mixture in the recovery flask to dissolve the precipitated components, and the contents of the recovery flask were filtered while still hot at 50°C without cooling, recovering polyurethane fiber (0.98 g) and a colorless solid (0.3 g) as solids. The filtrate was then distilled to recover dimethyl carbonate and methanol, and the residue was washed with ethyl acetate (25 mL) and water (25 mL) and dried to obtain dimethyl terephthalate (7.2 g). Various analyses were performed on the polyurethane fiber, the polyurethane fiber recovered in Example 2, and the cut material of the white T-shirt in the same manner as in Example 1, and the results confirmed that polyurethane fiber was recovered in Example 2. １３ The results of the C NMR analysis are shown in FIG. 5, the results of the Fourier transform infrared spectroscopy analysis are shown in FIG. 6, the results of the thermogravimetry analysis are shown in FIG. 7, and the results of the differential scanning calorimetry analysis are shown in FIG. 8.

[0051] According to the separation method of the present invention, it is possible to separate polyester from a polyester composite material containing polyester and components other than polyester while preventing deterioration of the components other than polyester, and therefore the method can be suitably used as a method for recovering components other than polyester from a polyester composite material.

Claims

1. A method for separating a polyester from a polyester composite material containing a polyester and a component other than polyester, the method comprising a decomposition step of decomposing the polyester by contacting the polyester composite material with a base, a monohydric alcohol, a carbonic acid diester, and the polyester.

2. The method for separating polyester according to claim 1, wherein the base is at least one selected from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides and nitrogen-containing organic bases.

3. The method for separating polyester according to claim 1, wherein the monohydric alcohol is an alcohol having 1 to 6 carbon atoms.

4. The method for separating polyester according to claim 1, wherein the carbonic acid diester is a dialkyl carbonate having 1 to 12 carbon atoms.

5. The method for separating polyester according to claim 1, wherein the polyester is at least one selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate.

6. The method for separating polyester according to claim 1, wherein the component other than polyester is one or more materials selected from the group consisting of cotton, rayon, polyurethane, nylon, acrylic, polyethylene, polypropylene, carbon-based materials, dyes, and pigments.

7. The method for separating polyester according to claim 1, wherein the component other than polyester is one or more materials selected from the group consisting of cotton and polyurethane.

8. The method for separating polyester according to claim 1, wherein the polyester composite material is a mixture of polyester fibers and fibers other than polyester fibers.

9. The method for separating polyester according to claim 1, wherein the polyester composite material is a film containing polyester and a component other than polyester.

10. The method for separating polyester according to claim 1, wherein the reaction temperature in the decomposition step is in the range of 20°C or higher but lower than 180°C.

11. A recovery method for recovering components other than polyester from a polyester composite material containing polyester and components other than polyester, using the separation method according to claim 1.

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