Polyester decomposition method, polyester production method, and polyester decomposition product recovery method

Abstract

[Problem] To provide: a polyester decomposition method capable of decomposing polyester and polyester contained in various polyester-containing materials into monomers by a simple process at a low temperature of 150°C or less; a polyester production method that produces polyester from monomers obtained by this decomposition method; and a polyester decomposition product recovery method that recovers a predetermined polyester decomposition product from the polyester decomposition product obtained by this polyester decomposition method. [Solution] A polyester decomposition method for polyester contained in a polyester-containing material, the polyester decomposition method having a decomposition step that mixes a base, a monohydric alcohol, and a carbonic acid diester to decompose the polyester.

Description

Polyester decomposition method, polyester production method, and polyester decomposition product recovery method

[0001] The present invention relates to a polyester decomposition method for decomposing polyester, a polyester production method for producing polyester from monomers obtained by this polyester decomposition method, and a polyester decomposition product recovery method for recovering a predetermined polyester decomposition product from the polyester decomposition product obtained by this polyester decomposition method.

[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 involve the use of a halogenated solvent, potassium carbonate (see Non-Patent Document 1), or an alkali metal alkoxide (see Patent Document 3), which can achieve depolymerization at low temperatures between room temperature (15-25°C) and approximately 50°C. Another method is known that uses dimethyl carbonate as an ethylene glycol scavenger to improve depolymerization efficiency (see Non-Patent Document 2). However, these methods are limited to high-purity PET derived from PET bottles and other materials, and other polyester-containing materials have not been successfully applied. A method using a base catalyst and excess ethylene glycol for depolymerizing colored polyester fibers is known, but this requires high temperatures of approximately 200°C. Furthermore, to obtain high-purity monomers, it is necessary to decolorize the fibers with a high-boiling-point solvent (see Patent Documents 4-6) or decompose the dye with an oxidizing agent (see Patent Document 7).

[0004] Japanese Patent No. 5099416 Japanese Patent Publication No. 2001-39908 U.S. Patent No. 10252976 Specification Japanese Patent No. 4537288 Japanese Patent No. 5134563 Japanese Patent No. 6659919 Japanese Patent No. 6986813

[0005] Green Chem. 2021,23,511. Green Chem. 2021,23,9412.

[0006] However, there is a problem in that polyesters and polyesters contained in various polyester-containing materials cannot be decomposed into monomers at a low temperature of 150° C. or less in a simple process.

[0007] The present invention aims to provide a polyester decomposition method capable of decomposing polyesters and polyesters contained in various polyester-containing materials into monomers at a low temperature of 150°C or less and in a simple process; a polyester production method for producing polyesters from the monomers obtained by this polyester decomposition method; and a polyester decomposition product recovery method for recovering a predetermined polyester decomposition product from the polyester decomposition product obtained by this polyester decomposition method.

[0008] The inventors of the present invention have conducted extensive research into the above-mentioned problems and have discovered the following revolutionary polyester decomposition method, polyester production method, and polyester decomposition product recovery method.

[0009] A first aspect of the present invention for solving the above-mentioned problems is a polyester decomposition method for polyester contained in a polyester-containing material, characterized in that the method includes a decomposition step of mixing a base, a monohydric alcohol, and a carbonic acid diester to decompose the polyester.

[0010] Here, the term "decomposition" is a concept that includes depolymerization.

[0011] According to the first aspect, the polyester contained in the polyester-containing material can be decomposed into monomers in a simple process.

[0012] A second aspect of the present invention is the polyester decomposition method according to the first aspect, characterized in that the reaction temperature in the decomposition step is in the range of 20°C to 150°C.

[0013] According to the second aspect, the polyester contained in the polyester-containing material can be decomposed into monomers at a low temperature of 150° C. or less and in a simple process.

[0014] A third aspect of the present invention is the method for decomposing a polyester according to the first or second aspect, characterized in that the base is an alkali metal carbonate, an alkali metal hydroxide or an alkali metal alkoxide.

[0015] According to the third aspect, the polyester contained in the polyester-containing material can be decomposed into monomers with higher purity.

[0016] A fourth aspect of the present invention is the polyester decomposition method according to the first or second aspect, characterized in that the monohydric alcohol is methanol.

[0017] According to the fourth aspect, the polyester contained in the polyester-containing material can be decomposed into monomers with higher purity.

[0018] A fifth aspect of the present invention is the method for decomposing a polyester according to the first or second aspect, characterized in that the carbonate diester is dimethyl carbonate.

[0019] According to the fifth aspect, the polyester contained in the polyester-containing material can be decomposed into monomers with higher purity.

[0020] A sixth aspect of the present invention is the method for decomposing a polyester according to the first or second aspect, wherein the decomposition step comprises mixing a base, a monohydric alcohol, and a carbonate diester using a mechanochemical reaction apparatus to decompose the polyester.

[0021] According to the sixth aspect, the polyester contained in the polyester-containing material can be decomposed without the need for a halogenated solvent, an excessive amount of an organic solvent, or an excessive amount of a base. Moreover, the dicarboxylic acid diester monomer can be obtained as the main depolymerized product in good yield and with high purity without adding any complicated steps after the decomposition.

[0022] A seventh aspect of the present invention is the method for decomposing a polyester according to the sixth aspect, characterized in that the reaction temperature in the decomposition step is in the range of 30°C to 100°C.

[0023] According to the seventh aspect, the polyester contained in the polyester-containing material can be decomposed at a reaction temperature of 100° C. or less.

[0024] An eighth aspect of the present invention is the polyester decomposition method according to the sixth aspect, characterized in that the mechanochemical reaction apparatus is a ball mill.

[0025] According to the eighth aspect, the polyester contained in the polyester-containing material can be decomposed with smaller amounts of halogenated solvent, organic solvent, and base.

[0026] A ninth aspect of the present invention is the method for decomposing polyester according to the first or second aspect, characterized in that the polyester-containing material contains at least one of polyester fibers and a film made of polyester.

[0027] According to the ninth aspect, even if the polyester-containing material contains at least one of polyester fibers and a film made of polyester, the polyester contained therein can be decomposed.

[0028] A tenth aspect of the present invention is the method for decomposing polyester according to the first or second aspect, wherein the polyester-containing material contains substances other than polyester.

[0029] According to the tenth aspect, even if a polyester-containing material contains substances other than polyester, the polyester contained therein can be decomposed.

[0030] An eleventh aspect of the present invention is a polyester production method, which comprises producing a polyester using a polyester decomposition product obtained by the polyester decomposition method according to the first or second aspect.

[0031] According to the eleventh aspect, a new polyester can be produced using a polyester decomposition product obtained by the polyester decomposition method according to the present invention as a raw material.

[0032] A twelfth aspect of the present invention is a method for recovering a polyester decomposition product, which recovers a predetermined polyester decomposition product from a polyester decomposition product obtained by the polyester decomposition method according to the first or second aspect, wherein the predetermined polyester decomposition product is dimethyl terephthalate, dimethyl 2,6-naphthalenedicarboxylate, or dimethyl 2,5-furandicarboxylate, and the method for recovering a polyester decomposition product is characterized by having a distillation step of distilling the polyester decomposition product.

[0033] According to the twelfth aspect, after obtaining a polyester decomposition product (solution) containing dimethyl terephthalate, dimethyl 2,6-naphthalenedicarboxylate, or dimethyl 2,5-furandicarboxylate, high-purity (99.0 to 99.9%) dimethyl terephthalate, dimethyl 2,6-naphthalenedicarboxylate, or dimethyl 2,5-furandicarboxylate can be obtained simply by distillation.

[0034] Dimethyl terephthalate obtained in Example 1 １ 1H NMR analysis results of dimethyl terephthalate obtained in Example 1. 1H NMR analysis results of dimethyl terephthalate obtained in Example 3. １ 1H NMR analysis results. ... １ 1H NMR analysis results of dimethyl terephthalate obtained in Example 50. 1H NMR analysis results of dimethyl terephthalate obtained in Example 51. １ 1H NMR analysis results of dimethyl terephthalate obtained in Example 51. 1H NMR analysis results of dimethyl terephthalate obtained in Example 52. １1H NMR analysis results of dimethyl terephthalate obtained in Example 52. 1H NMR analysis results of dimethyl terephthalate obtained in Example 53. １ 1 is a table showing the decomposition conditions in Examples 36 to 49. 2 is a table showing the decomposition conditions in Comparative Examples 5 to 7, Reference Example 1, and Examples 50 to 53. 3 is a table showing the experimental results of Examples 36 to 53, Comparative Examples 5 to 7, and Reference Example 1. 4 is a table showing the experimental results of Examples 36 to 53, Comparative Examples 5 to 7, and Reference Example 1.

[0035] Hereinafter, embodiments of the polyester decomposition method and polyester production method according to the present invention will be described, but the present invention is not limited to the following embodiments.

[0036] (Embodiment 1) <<Method for Decomposing Polyester>> A method for decomposing polyester according to one embodiment of the present invention includes a decomposition step of decomposing polyester in a material containing polyester (a polyester-containing material) using (a mixture of) a base, a monohydric alcohol, and a carbonic acid diester. The polyester-containing material may be one or more materials selected from the group consisting of a material containing polyester fibers (polyester fibers), a film containing polyester and a component other than polyester, and a polyester and a component other than polyester.

[0037] According to the decomposition method of the present embodiment, unlike PET films, polyesters can be decomposed at low temperatures using polyester-containing materials, which have traditionally been difficult to decompose at relatively low temperatures. Moreover, the method does not require additional complicated steps after decomposition, and a dicarboxylic acid diester monomer can be obtained with high purity as the main decomposition product (depolymerized product) through a simplified process.

[0038] In the conventional decomposition methods (methods described in Patent Documents 6 and 7), when colored fibers are decomposed, even if crystallization and distillation are carried out, only a dicarboxylic acid diester with a purity of about 99% can be obtained.

[0039] On the other hand, in the present invention, for example, a dicarboxylic acid diester having a purity of 99% or more can be obtained by a simple washing procedure alone, and further, a dicarboxylic acid diester having a purity of 99.9% or more can be obtained by distillation.

[0040] <Polyester-Containing Material> In the present embodiment, the polyester-containing material is not particularly limited as long as it contains polyester, and refers to not only a limited range of materials that have an extremely high polyester content and a morphology suitable for carrying out a reaction, such as polyester itself or a polyethylene terephthalate (PET) film, but also a broader range of materials in general that have a low polyester content or a morphology unsuitable for carrying out a reaction.

[0041] More specifically, examples of polyester-containing materials include materials containing polyester fibers (polyester fibers), films containing polyester and components other than polyester, and lumps containing polyester and components other than polyester.

[0042] Examples of materials containing polyester fibers include polyester fibers (fibers that do not contain any components other than polyester), woven polyester fibers, mixtures containing polyester fibers and components other than polyester fibers, and woven polyester mixtures.

[0043] Examples of mixtures containing polyester fibers and components other than polyester fibers include mixed fibers of polyester fibers and fibers other than polyester fibers and woven fabrics of such mixed fibers, composite mixtures containing polyester fibers and non-resin components (e.g., colored fibers containing polyester fibers and a colorant) and woven fabrics of such composite mixtures, composite mixed fibers containing polyester fibers, fibers other than polyester fibers, and non-resin components (e.g., colored mixed fibers containing mixed fibers and a colorant) and woven fabrics of such composite mixtures, etc. Here, in this specification, "non-resin components" refers to components that do not fall into either polyester or resins other than polyester.

[0044] Examples of films containing polyester and a component other than polyester include a monolayer film containing polyester and a component other than polyester, and a laminate film that is a laminate of a film made of polyester (polyester film) and a film containing a component other than polyester.

[0045] Examples of monolayer films containing polyester and components other than polyester include monolayer films that contain both polyester and resins other than polyester but do not contain non-resin components, monolayer films that contain both polyester and non-resin components but do not contain resins other than polyester, and monolayer films that contain all of polyester, resins other than polyester, and non-resin components.

[0046] 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.

[0047] 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.

[0048] The resin other than polyester can be arbitrarily selected 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).

[0049] Examples of fibers other than polyester fibers include fibers of resins other than the above polyesters, cotton, rayon, and the like.

[0050] The non-resin component can be selected arbitrarily depending on the purpose and is not particularly limited. For example, inorganic components (inorganic compounds) such as aluminum, colorants such as dyes and pigments, and the like can be used as the non-resin component, as they are highly versatile and highly applicable to the present invention.

[0051] In a material containing polyester fibers, the fiber diameters of the polyester fibers and the fibers other than polyester fibers are not particularly limited, and may be, for example, 0.1 μm to 200 μm or 1 μm to 50 μm.

[0052] The thickness of the film containing polyester and components 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 laminated film, the thickness of the film means the thickness of the entire laminated film.

[0053] More specifically, examples of materials containing polyester fibers include fabrics for various clothing, fibers that are materials for fabrics, etc. Fabrics may be, for example, small pieces such as cut pieces generated during the manufacture of various clothing, or cut pieces of various clothing after use. Fibers that are materials for fabrics may be, for example, small pieces such as cut pieces generated during the manufacture of fabrics, or cut pieces generated from fabrics after use.

[0054] More specifically, examples of films containing polyester and components other than polyester include packaging films, small pieces such as cut pieces generated during the production of packaging films, and small pieces such as cut pieces of packaging films after use.

[0055] 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.

[0056] The polyester-containing material used for decomposing 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. That is, the polyester-containing material used for decomposing polyester is one or more kinds selected from the group consisting of a material containing polyester fiber, a film containing polyester and a component other than polyester, and a lump containing polyester and a component other than polyester.

[0057] When the polyester-containing material is a material containing polyester fibers, the material containing polyester fibers is preferably one or more selected from the group consisting of polyester fibers, woven fabrics of polyester fibers, mixtures containing polyester fibers and components other than polyester fibers, and woven fabrics of such mixtures.

[0058] When the polyester-containing material is a film containing polyester and a component other than polyester, the film containing polyester and a component other than polyester is preferably either or both of a monolayer film containing polyester and a component other than polyester, and a laminate film which is a laminate of a film made of polyester and a film containing a component other than polyester.

[0059] In a polyester-containing material, the ratio of the polyester content (parts by mass) to the total mass (parts by mass) of the polyester-containing material ([polyester content (parts by mass) contained in the polyester-containing material] / [total mass (parts by mass) of the polyester-containing material] × 100) (polyester content) can be arbitrarily selected depending on the purpose and is not particularly limited. In particular, the polyester content may be 20% by mass or more and 100% by weight or less, and is preferably 40% by mass or more and 100% by weight or less, or 40% by mass or more and less than 100% by weight, more preferably 55% by mass or more and 100% by weight or less, or 55% by mass or more and less than 100% by weight, and particularly preferably 70% by mass or more and 100% by weight or less, or 70% by mass or more and less than 100% by weight. The higher the polyester content, the greater the amount of monomer (dicarboxylic acid diester described below) generated per unit mass from the polyester-containing material due to decomposition of the polyester.

[0060] [Polyester] The polyester in the polyester-containing 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, in one molecule, two functional groups capable of condensation reacting with the glycol.

[0061] 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 the two carbon atoms forming the aromatic ring skeleton in an aromatic compound) in its main chain having an ester bond, an aliphatic polyester having no aromatic groups in its main chain (having an aliphatic group but not an 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.

[0062] 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.

[0063] In terms of achieving a higher effect of the present invention and having high 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).

[0064] By decomposition of the polyester, a dicarboxylic acid diester specific to the type of polyester and monohydric alcohol is produced from the polyester as a monomer.

[0065] For example, terephthalic acid diesters are produced from polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate, naphthalenedicarboxylic acid diesters (2,6-naphthalenedicarboxylic acid diesters) are produced from polyethylene naphthalate and polybutylene naphthalate, and furandicarboxylic acid diesters (2,5-furandicarboxylic acid diesters) are produced from polyethylene furanoate.

[0066] For example, when methanol is used as the monohydric alcohol, a dicarboxylic acid dimethyl ester is produced as the dicarboxylic acid diester.

[0067] The polyester used for the decomposition 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.

[0068] <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 that reacts with a monohydric alcohol to produce an alkali metal alkoxide, or an alkali metal alkoxide.

[0069] Generally, transesterification proceeds by the reaction of a nucleophilic alkoxide anion with the carbonyl group of an ester, resulting in the liberation of the other alkoxide anion via a quaternary carbon intermediate. Since the alkoxide anion is generated by the reaction of the corresponding alcohol with a base, any base capable of deprotonating the alcohol can be used.

[0070] 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.

[0071] 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; and alkaline earth metal alkoxides such as 1,2,3,4-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, 1,3-dicyclohexylimidazol-2-ylidene, and the like.

[0072] The alkali metal alkoxide is preferably lithium methoxide, sodium methoxide or potassium methoxide, and more preferably sodium methoxide, in that the decomposition of the polyester proceeds at a higher rate.

[0073] The nitrogen-containing organic base is preferably 1,5,7-triazabicyclo[4.4.0]dec-5-ene, since this allows the decomposition of the polyester to proceed at a higher rate.

[0074] The base used for decomposing the polyester may be one type only, or two or more types may be used. 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.

[0075] The base is particularly preferably an alkali metal alkoxide, in that the decomposition of the polyester proceeds at a particularly high rate.

[0076] When decomposing the polyester, the amount of base used is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 6 parts by mass, per 100 parts by mass of the polyester in the polyester-containing material, and may be, for example, either 0.5 to 3 parts by mass or 3 to 6 parts by mass. 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. In other words, when decomposing the polyester, the amount of base used is preferably a catalytic amount (the base is a catalyst).

[0077] <Monohydric Alcohol> When the monohydric alcohol is decomposed, it undergoes a transesterification reaction with the polyester in the polyester-containing material. That is, when the polyester is decomposed, 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.

[0078] 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 diester carbonate present in excess. Therefore, as will be described later, from the fact that the reaction using methanol and dimethyl carbonate proceeds efficiently, it can be easily assumed that the reaction will proceed efficiently in the same way with other combinations of monohydric alcohol and dialkyl carbonate.

[0079] For example, either an aliphatic alcohol or an aromatic alcohol may be used, but in terms of the rate at which decomposition of the polyester proceeds, an aliphatic alcohol (saturated aliphatic alcohol, unsaturated aliphatic alcohol) is preferred, and a saturated aliphatic alcohol is more preferred.

[0080] 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).

[0081] The monohydric alcohol 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 are not particularly limited and can be arbitrarily selected depending on the purpose. Note that, as the monohydric alcohol, methanol is particularly preferred in that the decomposition of the polyester proceeds at a particularly high rate.

[0082] The amount of monohydric alcohol used during polyester decomposition is not particularly limited, but 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-containing 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-containing 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.

[0083] <Carbonate diester> During the decomposition of polyester, the carbonate diester reacts with glycol generated from the polyester to produce a cyclic compound or a chain compound, and has the effect of shifting the equilibrium between the reactions during polyester decomposition, i.e., the depolymerization reaction and the polymerization reaction of the polyester, in favor of the depolymerization reaction, thereby improving the production rate of the target monomer. The carbonate diester functions as a glycol scavenger.

[0084] The reaction product of a carbonate diester and a glycol may be a cyclic compound which is a reaction product of one molecule of a carbonate diester and one molecule of a glycol (for example, a cyclic compound (61) described below), a chain compound which is a reaction product of one molecule of a carbonate diester and one molecule of a glycol (for example, a first chain compound (62) described below), or a chain compound which is a reaction product of one molecule of a carbonate diester and two molecules of a glycol (for example, a second chain compound (63) described below). Whether a cyclic compound or a chain compound is produced is determined mainly by the type (for example, size) of the glycol. For example, the reaction product of a carbonate diester and ethylene glycol mainly becomes a cyclic compound (more specifically, ethylene carbonate) which is a reaction product of one molecule of a carbonate diester and one molecule of ethylene glycol.

[0085] 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 or different. Furthermore, the two aryl groups bonded to the oxygen atom in the diaryl carbonate may be the same or different.

[0086] The alkyl group in the dialkyl carbonate may be linear, branched, or cyclic, and when cyclic, it may be monocyclic or polycyclic.

[0087] 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.

[0088] Among these, the number of carbon atoms in the alkyl group 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.

[0089] The aryl group in the diaryl carbonate may be either monocyclic or polycyclic. The number of carbon atoms in the aryl group in the diaryl carbonate is preferably 6 to 10, and examples of such aryl groups include phenyl group, 1-naphthyl group, 2-naphthyl group, o-tolyl group, m-tolyl group, p-tolyl group, 2,3-xylyl group (2,3-dimethylphenyl group), 2,4-xylyl group (2,4-dimethylphenyl group), 2,5-xylyl group (2,5-dimethylphenyl group), 2,6-xylyl group (2,6-dimethylphenyl group), 3,4-xylyl group (3,4-dimethylphenyl group), and 3,5-xylyl group (3,5-dimethylphenyl group). A more preferred diaryl carbonate is, for example, diphenyl carbonate.

[0090] The carbonate diester used for decomposing the polyester may be one type only, or two or more types may be used. 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.

[0091] 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.

[0092] During decomposition of the polyester, 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-containing 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.

[0093] <Solvent> When decomposing the polyester, a solvent that does not fall into any of the categories of a base, a monohydric alcohol, and a carbonic acid diester may be used. In the present embodiment, the decomposition of the polyester proceeds efficiently even without using a solvent, but by using a solvent as necessary, the handleability of a mixture of raw materials such as a reaction liquid may be improved, and the decomposition of the polyester may proceed more efficiently.

[0094] In this specification, unless otherwise specified, the term "solvent" is a concept that encompasses both a component that is liquid at room temperature and that dissolves a solute, and a component that is liquid at room temperature and that functions as a dispersion medium for dispersing a dispersoid. Furthermore, "room temperature" means a temperature that is not particularly cooled or heated, i.e., an ordinary temperature, and examples thereof include a temperature of 15 to 25°C.

[0095] Here, the solvent is preferably an organic solvent, for example, 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, sulfoxides such as dimethyl sulfoxide, etc.

[0096] 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.

[0097] When a solvent is used, the amount of solvent used during decomposition of the polyester 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-containing 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.

[0098] <Other Components> When decomposing the polyester, other components that do not fall under any of the polyester-containing material, base, monohydric alcohol, carbonate diester, and solvent may be used as long as the effects of the present invention are not impaired.

[0099] The other components can be arbitrarily selected depending on the purpose and are not particularly limited. The other components 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 are not particularly limited and can be arbitrarily selected depending on the purpose.

[0100] During decomposition of the polyester, the ratio of the total amount (parts by mass) of the polyester-containing 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-containing material] + [amount (parts by mass) of base] + [amount (parts by mass) of monohydric alcohol] + [amount (parts by mass) of carbonate diester]) / [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.

[0101] 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-containing material, base, monohydric alcohol, carbonic acid diester, and other components used during decomposition.

[0102] <Reaction conditions for the decomposition step> The decomposition of the polyester in the polyester-containing material can be carried out by blending (mixing) a base, a monohydric alcohol, a carbonic acid diester, the polyester-containing material, and, if necessary, a solvent and, if necessary, other components.

[0103] The order in which these raw materials are mixed 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 optionally other components (for example, a blend of all raw materials other than the polyester-containing material), and then mix this raw material composition with the polyester-containing material. By using such a blending order, the decomposition of the polyester proceeds at a higher rate.

[0104] In the raw material composition, when the amount of base blended is a catalytic amount (the base acts as a catalyst), the raw material composition may be referred to as a "catalyst composition" in this specification.

[0105] The reaction temperature during decomposition of the polyester (the reaction temperature in the decomposition step) can be appropriately adjusted in consideration of 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.

[0106] The reaction temperature during decomposition of the polyester (reaction temperature in the decomposition step) is preferably 20° C. or higher, and may be, for example, either 40° C. or higher or 60° C. or higher. The reaction temperature during decomposition of the polyester is preferably 150° C. or lower, and may be, for example, either 100° C. or lower or 70° C. or lower.

[0107] In one embodiment, the reaction temperature during decomposition of the polyester (reaction temperature in the decomposition step) is, for example, preferably 20 to 150° C., and more preferably 50 to 120° C. 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 to 70° C.

[0108] As described above, according to this embodiment, not only PET films and the like but also polyester-containing materials, which have conventionally been difficult to decompose at relatively low temperatures, are used, but the polyester can be decomposed at low temperatures, such as 150° C. or less. This makes it possible to reduce the amount of by-products produced during decomposition, unlike when polyester is decomposed at high temperatures, and also reduces the coloration of dicarboxylic acid diesters (monomers), which are the main decomposition products.

[0109] The decomposition of the polyester may be carried out under normal pressure, reduced pressure, or increased pressure, and may be carried out in air or in an inert gas atmosphere.

[0110] Furthermore, the reaction time during decomposition of the polyester is not particularly limited and can be appropriately adjusted in consideration of other reaction conditions such as the reaction temperature, etc. The reaction time during decomposition of 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.

[0111] In this embodiment, for example, the end of decomposition can be determined when the polyester disappears. Therefore, the time required for the polyester to disappear can be used as 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-containing material to stop.

[0112] In a blend immediately after blending the raw materials, unreacted polyester-containing materials do not dissolve and remain insoluble in the other liquid components. In a blend (reactant) in which decomposition of the polyester is in progress, typically, unreacted polyester-containing materials and polyester-containing materials during or after the polyester reaction do not dissolve and remain insoluble in the other liquid components. On the other hand, glycols and dicarboxylic acid diesters, which are the reactants of the polyester decomposition, typically dissolve in the liquid components.

[0113] Such a compound can be stirred during the decomposition of the polyester by a known method, for example, by rotating a magnetic stirrer or stirring blade, or by using a ball mill.

[0114] When decomposing a polyester, for example, by using a reaction vessel having a flat bottom, the contact area between the liquid component and the polyester-containing material that is insoluble in the liquid component can be increased, and as a result, the amounts of raw materials such as the 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.

[0115] <Post-Treatment Conditions, Extraction Conditions> After the polyester decomposition step is completed, post-treatment is carried out by a known method, and one of the main decomposition products, the dicarboxylic acid diester, can be extracted with high purity.

[0116] For example, after decomposition of the polyester, the resulting reaction product is filtered, volatile components are removed by distillation (concentration), and the resulting solid is washed with methanol and water to obtain a highly pure dicarboxylic acid diester. The resulting dicarboxylic acid diester may then be further purified by crystallization (crystallization), distillation, or the like, as necessary.

[0117] The other major decomposition product, the reaction product of glycol and carbonic acid diester, can also be isolated in the same manner as the dicarboxylic acid diester by appropriately adjusting the post-treatment conditions and isolation conditions.

[0118] According to this embodiment, as explained above, decomposition is possible at low temperatures, such as 150°C or lower. Therefore, unlike decomposition at high temperatures, the impurity content and discoloration of the dicarboxylic acid diester can be reduced. Therefore, a highly pure dicarboxylic acid diester (monomer) with reduced discoloration 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-containing material originally contains a colorant, the coloration of the dicarboxylic acid diester (monomer) derived from the colorant can be reduced by the simplified process of washing with methanol and water as described above.

[0119] In contrast, when decomposition is carried out at high temperatures using conventional methods, in order to obtain a highly pure monomer, it is necessary to carry out a decolorization treatment using a high-boiling point solvent and a dye decomposition treatment using an oxidizing agent, which require complicated processes.

[0120] <<Method for Producing Polyester>> Of the polyester decomposition products obtained by the polyester decomposition method according to one embodiment of the present invention, dicarboxylic acid diesters can be reused for the production of polyesters. For example, Japanese Patent Application Laid-Open No. 2011-26437 discloses that dimethyl terephthalate (DMT), a decomposition product of polyethylene terephthalate, is reused for the production of polyethylene terephthalate.

[0121] On the other hand, among the polyester decomposition products, the reaction product of glycol and carbonate diester can be converted into glycol and carbonate diester by reaction with alcohol, and this regenerated carbonate diester can be reused for the decomposition of polyester, and the regenerated glycol can be reused for the production of polyester. For example, when a polyester having a structure considered to be derived from ethylene glycol is decomposed, ethylene carbonate is produced as a reaction product of ethylene glycol and carbonate diester. "Japanese Patent No. 4236208" discloses the conversion of ethylene carbonate into ethylene glycol and carbonate diester by reaction with alcohol.

[0122] Therefore, by utilizing the polyester decomposition method according to one embodiment of the present invention, polyester can be continuously produced in a closed-loop system without inputting new raw materials for the three chemical reactions: decomposition of polyester, regeneration of glycol and carbonate diester from the reaction product of glycol and carbonate diester, and production of polyester by reaction of dicarboxylic acid diester with glycol.

[0123] That is, the method for producing a polyester according to this embodiment includes a step of producing a polyester using polyester decomposition products (dicarboxylic acid diesters, glycols, etc.) obtained by the method for decomposing a polyester according to this embodiment described above.

[0124] The method for producing a polyester according to the present embodiment has high suitability for recycling raw materials and enables decomposition of polyester at low temperatures, and therefore has extremely high industrial utility value.

[0125] Such continuous production of a polyester in a closed-loop system is shown by the following formula (chemical reaction formula): That is, according to this embodiment, a polyester represented by the following general formula (1) (sometimes referred to herein as "polyester (1)") reacts with a monohydric alcohol represented by the following general formula (2) (sometimes referred to herein as "monohydric alcohol (2)") in the presence of a base to produce a dicarboxylic acid diester represented by the following general formula (3) (sometimes referred to herein as "dicarboxylic acid diester (3)") and a glycol represented by the following general formula (4) (sometimes referred to herein as "glycol (4)"). Then, a reaction between glycol (4) and a carbonate diester represented by the following general formula (5) (sometimes referred to herein as "carbonate diester (5)") produces one or more compounds selected from the group consisting of a cyclic compound represented by the following general formula (61) (sometimes referred to herein as "cyclic compound (61)"), a first chain compound represented by the following general formula (62) (sometimes referred to herein as "first chain compound (62)"), and a second chain compound represented by the following general formula (63) (sometimes referred to herein as "second chain compound (63)") (these cyclic compounds and chain compounds are sometimes collectively referred to herein as "compound (6)").

[0126] The reaction of these compounds (6) with an alcohol represented by the following general formula (7) (sometimes referred to as "alcohol (7)" in this specification) regenerates glycol (4) and carbonate diester (5), and the regenerated glycol (4) reacts with dicarboxylic acid diester (3) to produce polyester (1) again. The regenerated carbonate diester (5) can be reused during depolymerization (decomposition) of polyester (1).

[0127]

[0128] (In the formula, X １ , X ２ are each independently a divalent organic group, and R １ and R ２are each independently a monovalent organic group, and n is an integer of 2 or more.

[0129] Here, polyester (1) is the polyester in the polyester-containing material, as described above. Monohydric alcohol (2) is the monohydric alcohol used in the polyester depolymerization process, as described above. Dicarboxylic acid diester (3) is the dicarboxylic acid diester, which is one of the main depolymerization products, as described above. Glycol (4) is the glycol, which is the other main depolymerization product, as described above. Carbonic acid diester (5) is the carbonate diester used in the polyester depolymerization process, as described above. Compound (6) (cyclic compound (61), first chain compound (62), and second chain compound (63)) is the reaction product of the carbonate diester and glycol, which is produced in the polyester depolymerization process, as described above. Alcohol (7) is a raw material used to regenerate the carbonate diester and glycol, and determines the structure of the carbonate diester.

[0130] In the formula, X １ is a divalent organic group, and may be, for example, an aromatic group, an aliphatic group, or a group having both an aromatic group and an aliphatic group.

[0131] Preferred X １ Examples of the alkyl group include aromatic groups such as benzene-1,4-diyl group (1,4-phenylene group), naphthalene-2,6-diyl group (2,6-naphthylene group), and furan-2,5-diyl group (2,5-furanylene group).

[0132] In the formula, X ２ is a divalent organic group, and may be, for example, an aromatic group, an aliphatic group, or a group having both an aromatic group and an aliphatic group.

[0133] Preferred X ２ Examples of the ethylene group include: ２ CH ２ -), 1,3-propylene group (trimethylene group, -CH ２ CH ２ CH ２ -), 1,4-butylene group (tetramethylene group, -CH ２ CH ２ CH２ CH ２ -), and alkylene groups having 2 to 4 carbon atoms are more preferred.

[0134] In the formula, R １ is a monovalent organic group, which 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).

[0135] Preferred R １ Examples of the alkyl group include 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 a monovalent saturated aliphatic group (i.e., alkyl group) having 1 to 4 carbon atoms is more preferred.

[0136] In the formula, R ２ is a monovalent organic group, and R ２ As for R １ In the formula, n is an integer of 2 or more, and preferably an integer of 20 to 1,000.

[0137] 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.

[0138] <<Decomposition of Polyester>> <Decomposition of Polyester Fiber> [Example 1] Sodium methoxide (NaOCH ３) (Fujifilm Wako Pure Chemical Industries, Ltd., the same applies hereinafter, 0.58 g, 10.4 mmol, 2.9 mass% relative to the mass of the polyester fiber described below), and then methanol (Kishida Chemical Co., Ltd., the same applies hereinafter, 13 mL, 51.4 mass% relative to the mass of the polyester fiber described below) and dimethyl carbonate (DMC) (Tokyo Chemical Industry Co., Ltd., the same applies hereinafter, 100 mL, 535 mass% relative to the mass of the polyester fiber described below) were added to uniformly dissolve these blended components, thereby preparing a catalyst composition. A laboratory lab coat (100 mass% polyester fiber in total fibers) was cut into pieces approximately 2 cm x 2 cm in size, and several of these cut pieces (20 g) were added to the catalyst composition obtained above in the eggplant flask.

[0139] Here, the proportion (mass %) of polyester fibers in all fibers is synonymous with the proportion of the polyester content (parts by mass) in the polyester-containing material relative to the total mass (parts by mass) of the polyester-containing material, as explained above. This also applies to the other examples and comparative examples that follow.

[0140] Next, using a magnetic stirrer and an oil bath, the stirrer was rotated in the recovery flask, and the mixture of the catalyst composition and the cut material was stirred at 50°C for 3 hours, thereby decomposing the polyester fibers. Next, dimethyl carbonate (30 mL) was added to the reaction mixture in the recovery flask to dissolve the precipitated target product, and the contents in the recovery flask were filtered while still hot at 50°C without cooling. The filtrate was concentrated to recover dimethyl carbonate and methanol, and the residue was washed with methanol (50 mL) and water (50 mL) and dried to obtain dimethyl terephthalate (18.5 g).

[0141] The obtained dimethyl terephthalate is １ Analysis by H NMR (apparatus: Bruker Avance III (registered trademark) 600 MHz, hereinafter the same) and gas chromatography (apparatus: Shimadzu Corporation GC-2000, hereinafter the same) confirmed that dimethyl terephthalate with a purity of 99% by mass or more was obtained. １The results of the H NMR analysis are shown in Figure 1, and the results of the gas chromatography analysis are shown in Figure 2. <Decomposition of polyester fiber in a blend of polyester fiber and cotton>

[0142] Example 2 A white coat for chemical experiments (65% by mass of polyester fiber and 35% by mass of cotton in total fibers) was cut into a size of approximately 2 cm x 2 cm.

[0143] Here, the percentage of cotton in all fibers (% by mass) refers to the percentage of cotton content (parts by mass) in the polyester-containing material relative to the total mass (parts by mass) of the polyester-containing material. This also applies to fibers other than cotton in the other examples below.

[0144] Next, the polyester fibers in the cut pieces were decomposed in the same manner as in Example 1, except that multiple pre-dried cut pieces (20 g) of the lab coat were used instead of the multiple cut pieces (20 g) of the laboratory coat described above, and the amount of sodium methoxide used was changed from 0.58 g to 0.38 g, thereby obtaining dimethyl terephthalate (11.7 g). In this example, the amount of methanol used during the decomposition was 79.1 mass % relative to the amount of polyester fibers in the mixed fibers.

[0145] The obtained dimethyl terephthalate was subjected to the same procedure as in Example 1. １ As a result of analysis by H NMR and gas chromatography, data similar to those in Example 1 were obtained, and it was confirmed that dimethyl terephthalate having a purity of 99% by mass or more was obtained.

[0146] <Decomposition of polyester fibers in colored fibers containing polyester fibers and colorants>

[0147] Example 3: A colored garment (100% by mass of polyester fiber in the total fiber, containing dyes such as red, black, and blue) was cut into pieces approximately 2 cm x 2 cm in size. The polyester fibers in the cut pieces were decomposed to obtain dimethyl terephthalate (18.4 g) in the same manner as in Example 1, except that multiple cut pieces (20 g) of this colored garment were used instead of the multiple cut pieces (20 g) of the above-mentioned white examination gown. In this example, the amount of methanol used during decomposition was 51.4% by mass relative to the amount of polyester fiber in the colored garment.

[0148] The obtained dimethyl terephthalate was subjected to the same procedure as in Example 1. １ As a result of analysis by H NMR and gas chromatography, it was confirmed that dimethyl terephthalate having a purity of 99% by mass or more was obtained. １ The results of the H NMR analysis are shown in FIG. 3, and the results of the gas chromatography analysis are shown in FIG. 4.

[0149] Decomposition of Polyester Fibers in Colored Fibers Containing Polyester Fibers and Colorants Example 4 Sodium methoxide (0.29 g, 5.2 mmol, 2.9 mass % relative to the mass of the polyester fiber described below) was added to a 100 mL screw vial with a flat bottom. Methanol (4 mL, 31.6 mass % relative to the mass of the polyester fiber described below) and dimethyl carbonate (30 mL, 321 mass % relative to the mass of the polyester fiber described below) were then added to uniformly dissolve these components to prepare a catalyst composition. Colored clothing (100 mass % polyester fiber relative to the total fiber, containing dyes such as red, black, and blue) was cut into pieces approximately 2 cm x 2 cm in size, and several pieces (10 g) of these cut pieces were added to the catalyst composition in the screw vial obtained above. Using a magnetic stirrer and an oil bath, the stirrer was rotated within the screw vial, and the mixture of the catalyst composition and cut pieces was stirred at 70°C for 1 hour to decompose the polyester fibers. Next, the contents in the screw vial were filtered while still hot at 70° C. without cooling. Methanol (100 mL) was added to the filtrate, and the resulting white crystals were filtered off, washed with water (50 mL), and dried to obtain dimethyl terephthalate (7.4 g).

[0150] The obtained dimethyl terephthalate was subjected to the same procedure as in Example 1. １ As a result of analysis by H NMR and gas chromatography, data similar to those in Example 1 were obtained, and it was confirmed that dimethyl terephthalate having a purity of 99% by mass or more was obtained.

[0151] Furthermore, the total nitrogen content of the obtained dimethyl terephthalate was quantitatively measured in the same manner as in Example 3, and the nitrogen content of the dimethyl terephthalate was found to be 19 ppm.

[0152] <Decomposition of polyester fibers in a blend of polyester fibers, rayon, and polyurethane fibers>

[0153] Example 5: A fiber blend (54% by mass of polyester fiber, 39% by mass of rayon, and 7% by mass of polyurethane fiber in the total fiber) was cut into pieces approximately 2 cm x 2 cm in size. The polyester fibers in the cut pieces were decomposed to obtain dimethyl terephthalate (3.4 g) in the same manner as in Example 4, except that multiple cut pieces (10 g) of this fiber blend were used instead of the multiple cut pieces (10 g) of the colored clothing described above. In this example, the amount of methanol used during decomposition was 58.6% by mass relative to the amount of polyester fiber in the fiber blend.

[0154] The obtained dimethyl terephthalate was subjected to the same procedure as in Example 1. １ As a result of analysis by H NMR and gas chromatography, data similar to those in Example 1 were obtained, and it was confirmed that dimethyl terephthalate having a purity of 99% by mass or more was obtained.

[0155] Decomposition of Polyester in a Monolayer Film Containing Polyester and Components Other Than Polyester Example 6 Individual packaging film for confectionery was washed with water and dried to obtain a composite film (a monolayer film containing polyester and components other than polyester). The polyester in the cut pieces was decomposed to obtain dimethyl terephthalate (3.4 g) in the same manner as in Example 4, except that multiple cut pieces (10 g) of this monolayer film were used instead of the multiple cut pieces (10 g) of the colored clothing described above.

[0156] The obtained dimethyl terephthalate was subjected to the same procedure as in Example 1. １ As a result of analysis by H NMR and gas chromatography, data similar to those in Example 1 were obtained, and it was confirmed that dimethyl terephthalate having a purity of 99% by mass or more was obtained.

[0157] <Decomposition of polyester fibers in colored fibers containing polyester fibers and colorant> [Comparative Example 1] Dimethyl terephthalate (2.1 g) was obtained by decomposing polyester fibers in the same manner as in Example 4, except that methanol (34 mL) was used without using dimethyl carbonate instead of using methanol (4 mL) and dimethyl carbonate (30 mL).

[0158] The obtained dimethyl terephthalate was subjected to the same procedure as in Example 4. １ As a result of the H NMR analysis, signals presumably due to oligomer impurities were detected, unlike in Example 4. That is, the obtained dimethyl terephthalate was of low purity.

[0159] [Comparative Example 2] Dimethyl terephthalate (4.6 g) was obtained by decomposing polyester fibers in the same manner as in Example 4, except that toluene (manufactured by Kishida Chemical Co., Ltd., 30 mL) was used instead of dimethyl carbonate (30 mL).

[0160] The obtained dimethyl terephthalate was subjected to the same procedure as in Example 4. １ As a result of the H NMR analysis, signals presumably due to oligomer impurities were detected, unlike in Example 4. That is, the obtained dimethyl terephthalate was of low purity.

[0161] [Comparative Example 3] Dimethyl terephthalate (4.0 g) was obtained by decomposing polyester fibers in the same manner as in Example 4, except that dimethyl sulfoxide (Kishida Chemical Co., Ltd., 30 mL) was used instead of dimethyl carbonate (30 mL).

[0162] The obtained dimethyl terephthalate was subjected to the same procedure as in Example 4. １ As a result of the H NMR analysis, signals presumably due to oligomer impurities were detected, unlike in Example 4. That is, the obtained dimethyl terephthalate was of low purity.

[0163] Comparative Example 4: Sodium hydroxide (NaOH) (50 mg, 1.25 mmol, 0.25% by mass relative to the mass of polyester fiber described below) was added to a 300 mL recovery flask, followed by ethylene glycol (Fujifilm Wako Pure Chemical Industries, Ltd.) (100 mL). These components were uniformly dissolved to prepare a catalyst composition. Colored clothing (100% by mass of polyester fiber in total fibers, containing dyes such as red, black, and blue) was cut into approximately 2 cm x 2 cm pieces, and several pieces (20 g) were added to the catalyst composition in the recovery flask obtained above. Using a magnetic stirrer and an oil bath, the stirrer was rotated in the recovery flask, and the mixture of catalyst composition and cut material was stirred at 195°C for 5 hours to decompose the polyester fiber. Next, the reaction product in the recovery flask was allowed to cool to 100°C, and the precipitated solid was separated by hot filtration, washed with water (100 mL), and dried to obtain bis(2-hydroxyethyl) terephthalate (20 g) as a decomposition product.

[0164] The total nitrogen content of the resulting bis(2-hydroxyethyl) terephthalate was quantitatively measured in the same manner as in Example 3. The nitrogen content of the bis(2-hydroxyethyl) terephthalate was found to be 140 ppm.

[0165] The resulting bis(2-hydroxyethyl) terephthalate was clearly more colored than the dimethyl terephthalate obtained in Examples 1 to 6. The results of Examples 1 to 6 and Comparative Examples 1 to 4 are summarized in FIG. 5. In this figure, "base (usage amount (% by mass))" means "the ratio of the amount of base used (parts by mass) to the amount of polyester (parts by mass) in the polyester-containing material." Similarly, "carbonate diester (usage amount (% by mass))" means "the ratio of the amount of carbonate diester used (parts by mass) to the amount of polyester (parts by mass) in the polyester-containing material."

[0166] As is clear from these results, in Examples 1 to 6, the polyester in the polyester-containing material was decomposed at a low reaction temperature of 50 to 70°C in a simple process without requiring any complicated steps, and a high-purity dicarboxylic acid diester (monomer) was obtained.

[0167] In contrast, in Comparative Examples 1 to 3, a high-purity dicarboxylic acid diester (monomer) was not obtained due to the decomposition of the polyester in the polyester-containing material. In Comparative Examples 1 to 3, no carbonic acid diester was used during the decomposition.

[0168] In Comparative Example 4, polyester was decomposed by a typical conventional method, but the reaction temperature was too high and the nitrogen content of the dicarboxylic acid diester (monomer) was high, so that a high-purity dicarboxylic acid diester could not be obtained.

[0169] From a comparison between Example 4 and Comparative Examples 1 to 3, it was confirmed that the use of a carbonic acid diester accelerates the decomposition of the polyester and significantly increases the amount of dicarboxylic acid diester produced.

[0170] Examples 7-9: Using potassium methoxide (KOMe) as the base, methanol (MeOH) as the monohydric alcohol, and dimethyl carbonate (DMC) as the carbonate diester, the same procedure as in Example 1 (reaction temperature: 50°C, reaction time: 5 hours) was carried out to decompose 100 mg of a polyester-containing material, polybutylene terephthalate (PBT) powder. After the reaction, the solution obtained was filtered, biphenyl was added as an internal standard, and the product was analyzed using gas chromatography (Shimadzu Corporation, "GC-2000") to quantify the amount of product. This reaction is represented by the following chemical reaction formula. The amount of methanol added varied for each example.

[0171] These results are shown in Figure 6. From this figure, it was found that the present invention can decompose polybutylene terephthalate in the same way as polyethylene terephthalate.

[0172] Example 10: Using sodium methoxide (NaOMe) as the base, methanol (MeOH) as the monohydric alcohol, and dimethyl carbonate (DMC) as the carbonate diester, the same procedure as in Example 1 (reaction temperature: 50°C, reaction time: 1 hour) was carried out to decompose polyethylene naphthalate (PEN) powder (100 mg), a polyester-containing material. The solution obtained after the reaction was filtered, and biphenyl was added as an internal standard. The product was analyzed using gas chromatography (Shimadzu Corporation, "GC-2000") to quantify the amount of the product. This reaction is represented by the following chemical reaction formula:

[0173] These results are shown in Figure 7. From this figure, it was found that the present invention can decompose polyethylene naphthalenedicarboxylate in the same way as polyethylene terephthalate.

[0174] Examples 11-17: The same procedure as in Example 1 was carried out to decompose a polyester-containing material, polyethylene terephthalate powder, by varying the type of catalyst (base), reaction temperature, and reaction time. After the reaction, the solution obtained was filtered, biphenyl was added as an internal standard, and the product was analyzed using gas chromatography (Shimadzu Corporation, "GC-2000") to quantify the amount of the product. This reaction is represented by the following chemical reaction formula:

[0175] These results are shown in Figure 8. This figure shows that polyethylene terephthalate can be decomposed even when the type of base, reaction temperature, and reaction time are changed.

[0176] [Examples 18-20] K as a catalyst (base) ２ CO ３ Using the above and varying the amount of catalyst, the same procedure as in Example 1 (reaction temperature: 100°C, reaction time: 1 hour) was carried out to decompose polyethylene terephthalate powder (100 mg). After the reaction, the solution obtained was filtered, biphenyl was added as an internal standard, and the product was analyzed using gas chromatography (Shimadzu Corporation, "GC-2000") to quantify the amount of the product. This reaction is represented by the following chemical reaction formula:

[0177]

[0178] These results are shown in Figure 9. From this figure, it can be seen that K ２ CO ３ It was found that polyethylene terephthalate powder can be sufficiently decomposed even when using

[0179] Examples 21-23 Polyethylene terephthalate powder (100 mg) was decomposed by the same procedure as in Example 1 (reaction temperature: 100°C, reaction time: 1 hour) except for varying the amounts of methanol and dimethyl carbonate used as solvents. The solution obtained after the reaction was filtered, and biphenyl was added as an internal standard. The product was analyzed using gas chromatography (Shimadzu Corporation, "GC-2000") to quantify the amount of the product. This reaction is represented by the following chemical reaction formula:

[0180] These results are shown in Figure 10. This figure shows that polyethylene terephthalate powder can be sufficiently decomposed even when the amounts of methanol and dimethyl carbonate used as solvents are changed.

[0181] Examples 24-25 Water was added, and the same procedure as in Example 1 (reaction temperature: 100°C, reaction time: 1 hour) was carried out to decompose polyethylene terephthalate powder (100 mg). After the reaction, the solution obtained was filtered, and biphenyl was added as an internal standard. The product was analyzed using gas chromatography (Shimadzu Corporation, "GC-2000") to quantify the amount of the product. This reaction is represented by the following chemical reaction formula:

[0182]

[0183] These results are shown in Figure 11 together with the results of Example 19. From this figure, it was found that polyethylene terephthalate became more difficult to decompose as the water content increased.

[0184] Examples 26-32 Solvents other than methanol and dimethyl carbonate were added, and polyethylene terephthalate powder (100 mg) was decomposed by the same procedure as in Example 1 (reaction temperature: 100°C, reaction time: 0.5 hours). After the reaction, the solution obtained was filtered, biphenyl was added as an internal standard, and the product was analyzed using gas chromatography (Shimadzu Corporation, "GC-2000") to quantify the amount of the product.

[0185] The results are shown in Figure 12. As can be seen from this figure, it was found that polyethylene terephthalate powder could be decomposed even if a solvent other than methanol and dimethyl carbonate was added.

[0186] [Example 33] K as a catalyst (base) ２ CO ３ The same procedure as in Example 1 (reaction temperature: 100°C, reaction time: 3 hours) was carried out to depolymerize cut pieces (1 g) of a white examination gown (100% by mass of polyester fibers in total fibers) using the catalyst of Example 1, except that the amount of the catalyst was changed to 7.4% by mass relative to the mass of polyester. After completion of the reaction, the reaction solution was concentrated to recover dimethyl carbonate and methanol, and the residue was distilled under reduced pressure using a Kugelrohr distillation apparatus to obtain dimethyl terephthalate (0.90 g). The obtained dimethyl terephthalate was １ The purity was 99% or more based on H NMR and gas chromatography.

[0187] [Example 34] Under the conditions of Example 33, depolymerization was carried out on cut pieces (1 g) of colored clothing (100% by mass of polyester fibers in total fibers, containing red, black, blue, etc. dyes) instead of white examination gowns (100% by mass of polyester fibers in total fibers). After the reaction was completed, the reaction solution was concentrated to recover dimethyl carbonate and methanol, and the residue was distilled under reduced pressure using a Kugelrohr distillation apparatus to obtain dimethyl terephthalate (0.87 g). The obtained dimethyl terephthalate was １ The purity was 99% or more based on H NMR and gas chromatography.

[0188] [Example 35] Under the conditions of Example 33, depolymerization was carried out on a cut piece (1 g) of a white coat for chemical experiments (65% by mass of polyester fiber in the total fibers, 35% by mass of cotton) instead of a white coat for examination (100% by mass of polyester fiber in the total fibers). After the reaction was completed, the reaction solution was concentrated to recover dimethyl carbonate and methanol, and the residue was distilled under reduced pressure using a Kugelrohr distillation apparatus to obtain dimethyl terephthalate (0.52 g). The obtained dimethyl terephthalate was １ The purity was 99% or more based on H NMR and gas chromatography.

[0189] (Embodiment 2) In Embodiment 1, the device used for decomposing polyester is not particularly limited, but in this embodiment, a method for decomposing polyester using a mechanochemical reaction device will be described.

[0190] <<Polyester Decomposition Method>> The polyester decomposition method according to this embodiment includes a step of blending a base, a monohydric alcohol, a carbonic acid diester, and a polyester-containing material, and depolymerizing (decomposing) the polyester contained in the polyester-containing material (polyester-containing material) using a mechanochemical reactor. The polyester-containing material may be, for example, one or more selected from the group consisting of a material containing polyester fibers (polyester fibers), a film containing polyester and a component other than polyester, and a lump containing polyester and a component other than polyester.

[0191] According to the decomposition method of this embodiment, the polyester contained in the polyester-containing material can be decomposed without the need for high temperatures, a halogenated solvent, an excessive amount of organic solvent, or an excessive amount of base. Furthermore, without the need for additional complicated processes after decomposition, the dicarboxylic acid diester monomer can be obtained in high yield and high purity as the main depolymerization product (decomposition product). That is, according to the decomposition method of this embodiment, the polyester contained in the polyester-containing material can be decomposed efficiently using a process with a low environmental impact, and the dicarboxylic acid diester monomer can be obtained in high yield and high purity. Furthermore, unlike PET films and the like, polyester-containing materials can be used, which have traditionally been difficult to decompose at relatively low temperatures.

[0192] The polyester-containing material, base, monohydric alcohol, carbonic acid diester, solvent, and other components that can be used in this embodiment are the same as those in the first embodiment.

[0193] <Mechanochemical Reaction Apparatus> The mechanochemical reaction apparatus used in the decomposition of polyester is an apparatus for carrying out a well-known mechanochemical reaction, i.e., a chemical change that occurs between a substance and a surrounding substance by applying mechanical stress (external force) to the substance.

[0194] However, in this embodiment, it is not essential to cause a mechanochemical reaction during the decomposition of the polyester. In this embodiment, a material within the specific range described above is used as the polyester-containing material, but by using a mechanochemical reaction device during the decomposition, it is possible to easily decompose the polyester even when using the polyester-containing material described above, which is usually difficult to decompose at relatively low temperatures.

[0195] The mechanochemical reaction apparatus used for decomposing polyester is not particularly limited as long as it can perform a mechanochemical reaction, and may be any known apparatus. Examples of the mechanochemical reaction apparatus include a container for storing an object to be subjected to a mechanochemical reaction and a stress-applying means (external force-applying means) for applying mechanical stress to the object, and an apparatus equipped with the stress-applying means.

[0196] The stress applying means may be, for example, a solid made of a hard material such as metal, which can apply impact or shear to the object undergoing the mechanochemical reaction. The stress applying means may be, for example, ball-shaped or bead-shaped.

[0197] Examples of materials for the vessel and stress applying means constituting the mechanochemical reaction device include stainless steel (SUS), zirconium oxide (also known as zirconia), polytetrafluoroethylene, tungsten carbide, and agate.

[0198] The mechanochemical reactor is not particularly limited and may be, for example, a batch reactor or a continuous reactor. More specific examples of the mechanochemical reactor include a ball mill, a bead mill, a planetary mill, and a twin-screw kneading extruder. Among these, a ball mill is preferred as the mechanochemical reactor because it is highly versatile and allows polyester decomposition to proceed more easily.

[0199] <Reaction Conditions> The decomposition of the polyester in the polyester-containing material can be carried out by blending a base, a monohydric alcohol, a carbonic acid diester, the polyester-containing material, and optionally a solvent and optionally other components, and reacting the resulting blend using a mechanochemical reactor.

[0200] The order in which these raw materials are mixed is not particularly limited. For example, these raw materials may be mixed separately in any order. Alternatively, a raw material composition that is a blend of a base, a monohydric alcohol, a carbonic acid diester, and optionally a solvent and optionally other components (for example, a blend of all raw materials other than the polyester-containing material) may be prepared, and then this raw material composition and the polyester-containing material may be mixed to mix them. In this case, as described below, the amount of base mixed may be a catalytic amount (the base is a catalyst) (the raw material composition may be a catalytic composition).

[0201] The reaction temperature during decomposition of the polyester can be appropriately adjusted taking into consideration the type of raw material used, etc., and the decomposition may be carried out at room temperature (normal temperature) or under heated conditions. In this embodiment, the decomposition of the polyester proceeds sufficiently even at room temperature, but may proceed more rapidly under heated conditions. When the decomposition of the polyester is carried out at room temperature (normal temperature), the reaction temperature may be any of 15 to 25°C, 15 to 20°C, and 20 to 25°C.

[0202] Furthermore, when decomposition of a polyester is carried out under heating conditions, the reaction temperature (reaction temperature in the decomposition step) is not particularly limited as long as it is 30°C to 150°C, but 30°C to 100°C is more preferable. When the reaction temperature under heating conditions is equal to or higher than these lower limit values, the effect obtained by heating is enhanced. When the reaction temperature under heating conditions is equal to or lower than these upper limit values, excessive heating is suppressed.

[0203] As described above, according to the present embodiment, unlike PET films and the like, polyester-containing materials are used, which have conventionally been difficult to decompose at relatively low temperatures, but the polyester can be decomposed at low temperatures, such as 100° C. or lower. This makes it possible to reduce the amount of by-products produced during polyester decomposition, unlike decomposition at high temperatures (e.g., 300° C. or higher), and also reduces the coloration of dicarboxylic acid diesters (monomers), which are the main decomposition products.

[0204] The decomposition of the polyester may be carried out under normal pressure, reduced pressure, or increased pressure, and may be carried out in air or in an inert gas atmosphere.

[0205] The reaction time for decomposing the polyester is not particularly limited and can be appropriately adjusted in consideration of other reaction conditions such as the reaction temperature, etc. The reaction time for decomposing the polyester is preferably 3 to 60 minutes, more preferably 3 to 40 minutes, and even more preferably 3 to 25 minutes.

[0206] In this embodiment, for example, the time when the polyester disappears can be determined as the end of decomposition of the polyester. Therefore, the time required for the polyester to disappear can be determined as the reaction time of the polyester decomposition. 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-containing material to stop.

[0207] In a blend immediately after blending the raw materials, unreacted polyester-containing materials do not dissolve and remain insoluble in the other liquid components. In a blend (reactant) in which decomposition of the polyester is in progress, typically, unreacted polyester-containing materials and polyester-containing materials during or after the polyester reaction do not dissolve and remain insoluble in the other liquid components. On the other hand, glycols and dicarboxylic acid diesters, which are the reactants of the polyester decomposition, typically dissolve in the liquid components.

[0208] The amount of polyester-containing material blended is preferably 5 to 35 g per 1 L of the volume of the container constituting the mechanochemical reactor, and may be, for example, 5 to 25 g, 5 to 15 g, 8 to 35 g, 15 to 35 g, or 8 to 25 g. Having the amount of polyester-containing material blended in this range allows for more efficient decomposition of polyester. Here, for example, when the mechanochemical reactor is a ball mill, the container is a grinding jar.

[0209] The number of stress-applying means constituting the mechanochemical reaction apparatus is one or two or more, and can be selected arbitrarily depending on the type of stress-applying means, without any particular limitation. For example, when the mechanochemical reaction apparatus is a ball mill or a planetary mill, the stress-applying means is balls (grinding balls), and when the mechanochemical reaction apparatus is a bead mill, the stress-applying means is beads, and the number of balls or beads can be appropriately adjusted depending on the capacity of the container constituting the mechanochemical reaction apparatus. For example, the number of balls or beads is preferably such that the total volume of the balls or beads is 3 to 30% of the capacity of the container, and may be, for example, 3 to 20% or 3 to 10%.

[0210] When the mechanochemical reactor is a twin-screw kneading extruder, the stress-applying means are screws, the number of which is two.

[0211] In addition, when the mechanochemical reaction device is a ball mill or a planetary mill, the total volume of the stress applying means constituting the mechanochemical reaction device is 1000 to 7000 mm per 1 g of the blended amount of the polyester-containing material. ３ For example, it is preferably 1000 to 5500 mm ３ , and 1000 to 4000 mm ３ or 3000 to 7000 mm ３ , and 5500 to 7000 mm ３ or 3000 to 5500 mm ３ Here, the total volume of the stress-applying means is the total volume of all the stress-applying means.

[0212] When the mechanochemical reactor is a ball mill, the vibration frequency when operating it to stir the compound is preferably 15 to 40 Hz, and may be, for example, any one of 15 to 27 Hz, 15 to 23 Hz, 23 to 40 Hz, and 28 to 40 Hz, or 23 to 27 Hz.

[0213] <Post-treatment conditions, extraction conditions> After the completion of the polyester decomposition step, post-treatment is carried out by a known method, and one of the main decomposition products, a dicarboxylic acid diester, can be extracted with high purity. For example, after polyester decomposition, the resulting reaction product is filtered, volatile components are distilled off (concentrated), etc., and the resulting solid is washed with water, methanol, or water and methanol to obtain a high-purity dicarboxylic acid diester. The obtained dicarboxylic acid diester may be further purified by crystallization (crystallization), distillation, etc., as necessary.

[0214] The other major decomposition product, the reaction product of glycol and carbonic acid diester, can also be isolated in the same manner as the dicarboxylic acid diester by appropriately adjusting the post-treatment conditions and isolation conditions.

[0215] According to this embodiment, as explained above, polyester can be decomposed at low temperatures, such as 100°C or below. Therefore, unlike polyester decomposition at high temperatures, the impurity content and discoloration of the dicarboxylic acid diester can be reduced. Therefore, a highly pure dicarboxylic acid diester (monomer) with reduced discoloration can be obtained by the simplified process of washing with water, methanol, etc., as described above, without adding any complicated steps. Furthermore, even if the polyester-containing material originally contains a colorant, the coloration of the dicarboxylic acid diester (monomer) derived from this colorant can be reduced by the simplified process of washing with water, methanol, etc., as described above.

[0216] In contrast, when polyester is decomposed at high temperatures using conventional methods, in order to obtain highly pure monomers, it is necessary to perform a decolorization treatment using a high-boiling point solvent and a dye decomposition treatment using an oxidizing agent, which require complicated processes.

[0217] It goes without saying that by using the polyester production method of embodiment 1, polyester decomposition products (dicarboxylic acid diesters, glycols) obtained by the polyester decomposition method of this embodiment can be used to produce polyesters.

[0218] The present invention will be described in more detail below with reference to specific examples. Polyethylene terephthalate (PET) was used as the polyester. However, the present invention is not limited to the examples shown below.

[0219] <<Decomposition of Polyester>> <Decomposition of Polyester Fiber> [Example 36] A white examination gown (proportion of polyester fibers in all fibers: 100% by mass) was cut into pieces of approximately 2 cm x 2 cm, and a plurality of these cut pieces (0.1 g) were placed inside a 10 mL stainless steel crushing jar.

[0220] Here, the proportion (mass %) of polyester fibers in all fibers is synonymous with the proportion of the polyester content (parts by mass) in the polyester-containing material relative to the total mass (parts by mass) of the polyester-containing material, as explained above. This also applies to the other examples and comparative examples that follow.

[0221] Furthermore, sodium methoxide (NaOCH ３ ) (Fujifilm Wako Pure Chemical Industries, Ltd., the same applies hereinafter, 1.4 mg, 0.026 mmol, 1.4 mass% relative to the mass of the polyester fibers), methanol (CHOH) (Kishida Chemical Co., Ltd., the same applies hereinafter, 0.02 mL, 15.8 mass% relative to the mass of the polyester fibers), dimethyl carbonate (DMC) (Tokyo Chemical Industry Co., Ltd., the same applies hereinafter, 0.2 mL, 214 mass% relative to the mass of the polyester fibers), and a stainless steel (SUS) grinding ball (10 mm diameter, 1 ball) were placed into a grinding jar, and the lid was closed to seal the blend. This grinding jar was placed and fixed in a ball mill reaction apparatus (Retsch "MM400", the same applies hereinafter), and the blend was stirred at room temperature at a frequency of 25 Hz for 10 minutes to decompose the polyester fibers. Next, dimethyl carbonate (10 mL) was added to the reaction mixture inside the grinding jar to dissolve the precipitated target product, and the resulting liquid was filtered to obtain a solution of dimethyl terephthalate.

[0222] Biphenyl was added to the obtained solution as an internal standard, and the solution was analyzed using gas chromatography ("GC-2000" manufactured by Shimadzu Corporation). This confirmed that the obtained products were dimethyl terephthalate and ethylene carbonate, and when the amounts of dimethyl terephthalate and ethylene carbonate were quantified, the yield of dimethyl terephthalate was 88%, and the yield of ethylene carbonate was 73%.

[0223] [Example 37] Potassium methoxide (KOCH) was used instead of sodium methoxide. ３ Dimethyl terephthalate (yield 88%) and ethylene carbonate (yield 72%) were obtained in the same manner as in Example 36, except that 1.8 mg of ethylene carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 0.026 mmol, 1.8 mass% relative to the mass of the polyester fibers) was used.

[0224] Example 38 Dimethyl terephthalate (yield 54%) and ethylene carbonate (yield 42%) were obtained in the same manner as in Example 36, except that the amount of methanol used was changed from 0.02 mL to 0.01 mL.

[0225] Example 39 Dimethyl terephthalate (yield 62%) and ethylene carbonate (yield 49%) were obtained in the same manner as in Example 36, except that the amount of methanol used was changed from 0.02 mL to 0.03 mL.

[0226] Example 40 Dimethyl terephthalate (yield 62%) and ethylene carbonate (yield 47%) were obtained in the same manner as in Example 36, except that the amount of methanol used was changed from 0.02 mL to 0.04 mL.

[0227] Example 41 Dimethyl terephthalate (yield 77%) and ethylene carbonate (yield 64%) were obtained in the same manner as in Example 36, except that the amount of dimethyl carbonate used during the decomposition was changed from 0.2 mL to 0.1 mL.

[0228] Example 42 Dimethyl terephthalate (yield 79%) and ethylene carbonate (yield 62%) were obtained in the same manner as in Example 36, except that the amount of dimethyl carbonate used during the decomposition was changed from 0.2 mL to 0.4 mL.

[0229] Example 43 Dimethyl terephthalate (yield 87%) and ethylene carbonate (yield 72%) were obtained in the same manner as in Example 36, except that ten 5 mm diameter stainless steel milling balls were used instead of one 10 mm diameter stainless steel milling ball.

[0230] Example 44 Dimethyl terephthalate (yield 61%) and ethylene carbonate (yield 49%) were obtained in the same manner as in Example 36, except that a 10 mL zirconium oxide (ZrO) grinding jar was used instead of the 10 mL stainless steel grinding jar, and one 10 mm diameter zirconium oxide grinding ball was used instead of one 10 mm diameter stainless steel grinding ball.

[0231] Example 45 Dimethyl terephthalate (yield 64%) and ethylene carbonate (yield 51%) were obtained in the same manner as in Example 36, except that the vibration frequency when stirring the blend was changed from 25 Hz to 20 Hz.

[0232] Example 46 Dimethyl terephthalate (yield 76%) and ethylene carbonate (yield 62%) were obtained in the same manner as in Example 36, except that the vibration frequency when stirring the blend was changed from 25 Hz to 30 Hz.

[0233] Example 47 Dimethyl terephthalate (yield 52%) and ethylene carbonate (yield 41%) were obtained in the same manner as in Example 36, except that the blend was stirred for 5 minutes instead of 10 minutes.

[0234] Example 48 Dimethyl terephthalate (yield 90%) and ethylene carbonate (yield 68%) were obtained in the same manner as in Example 36, except that the mixing time of the blend was changed from 10 minutes to 15 minutes.

[0235] Example 49 Dimethyl terephthalate (yield 95%) and ethylene carbonate (yield 78%) were obtained in the same manner as in Example 36, except that the mixing time of the blend was changed from 10 minutes to 20 minutes.

[0236] [Comparative Example 5] Decomposition of polyester fibers was attempted in the same manner as in Example 36, except that sodium methoxide was not used. However, the polyester fibers could not be decomposed, and dimethyl terephthalate and ethylene carbonate were not produced (yield 0%).

[0237] Comparative Example 6 Dimethyl terephthalate (yield 10%) and ethylene carbonate (yield 7%) were obtained in the same manner as in Example 36, except that methanol (0.2 mL) was used without dimethyl carbonate instead of using methanol (0.02 mL) and dimethyl carbonate (0.2 mL).

[0238] Comparative Example 7 Dimethyl terephthalate (yield 22%) was obtained in the same manner as in Example 36, except that toluene (Kishida Chemical Co., Ltd., 0.2 mL) was used instead of dimethyl carbonate (0.2 mL). In this case, ethylene carbonate was not obtained.

[0239] Reference Example 1 A laboratory gown (100% by mass of polyester fibers in total fibers) was cut into pieces of approximately 2 cm x 2 cm, and several pieces (0.1 g) of the cut pieces were placed inside a 2 mL screw vial with a flat bottom.

[0240] Furthermore, sodium methoxide (1.4 mg, 0.026 mmol, 1.4 mass% relative to the mass of the polyester fibers), methanol (0.02 mL, 15.8 mass% relative to the mass of the polyester fibers), and dimethyl carbonate (0.2 mL, 214 mass% relative to the mass of the polyester fibers) were added to the inside of the screw vial. Using a magnetic stirrer and an aluminum block heater, the stirrer was rotated inside the screw vial, and the blend was stirred at 50°C for 10 minutes to decompose the polyester fibers. Next, dimethyl carbonate (10 mL) was added to the reaction mixture inside the screw vial to dissolve the precipitated target product, and the resulting liquid was filtered to obtain a solution of dimethyl terephthalate.

[0241] The resulting solution was analyzed in the same manner as in Example 36, and the yield of dimethyl terephthalate was found to be 23% and the yield of ethylene carbonate was found to be 32%.

[0242] Example 50 A white examination gown (proportion of polyester fibers in total fibers: 100% by mass) was cut into pieces of approximately 2 cm x 2 cm, and several pieces (1 g) of the cut pieces were placed in a 50 mL stainless steel crushing jar.

[0243] Furthermore, sodium methoxide (14 mg, 0.5 mmol, 1.4 mass% relative to the mass of the polyester fibers), methanol (0.2 mL, 15.8 mass% relative to the mass of the polyester fibers), dimethyl carbonate (1.5 mL, 160 mass% relative to the mass of the polyester fibers), and stainless steel grinding balls (10 mm diameter, 5 balls) were charged into the grinding jar, and the lid was closed to seal the blend. The grinding jar was placed and fixed in a ball mill reaction apparatus, and the blend was stirred at room temperature at a frequency of 25 Hz for 15 minutes to decompose the polyester fibers. Next, dimethyl carbonate (30 mL) was added to the reaction mixture in the grinding jar to dissolve the precipitated target product, and the resulting liquid was filtered to obtain a solution of dimethyl terephthalate as a filtrate. The filtrate was concentrated under reduced pressure, and the residue was washed with water (20 mL) and methanol (10 mL), and dried to obtain dimethyl terephthalate (yield: 0.90 g, 86%).

[0244] The obtained dimethyl terephthalate is １ Analysis by H NMR (apparatus: Bruker Avance III (registered trademark) 600 MHz, hereinafter the same) and gas chromatography (apparatus: Shimadzu Corporation GC-2000, hereinafter the same) confirmed that dimethyl terephthalate with a purity of 99% by mass or more was obtained. １ The results of the H NMR analysis are shown in FIG. 13, and the results of the gas chromatography analysis are shown in FIG.

[0245] <Decomposition of Polyester Fiber in a Fiber Blend Containing Polyester Fiber and Cotton> [Example 51] A white coat for chemical experiments (65% by mass of polyester fiber and 35% by mass of cotton in the total fibers) was cut into a size of approximately 2 cm x 2 cm.

[0246] Here, the percentage of cotton in all fibers (% by mass) refers to the percentage of cotton content (parts by mass) in the polyester-containing material relative to the total mass (parts by mass) of the polyester-containing material. This also applies to fibers other than cotton in the other examples below.

[0247] Next, the polyester fibers in this cut material were decomposed in the same manner as in Example 50, except that multiple cut pieces (1 g) of this chemical laboratory white coat were used instead of the multiple cut pieces (1 g) of the above-mentioned laboratory white coat, and the amount of sodium methoxide used was changed from 14 mg to 30 mg, thereby obtaining dimethyl terephthalate (yield 0.56 g, 86%).

[0248] The obtained dimethyl terephthalate was subjected to the same procedure as in Example 50. １ As a result of analysis by H NMR and gas chromatography, it was confirmed that dimethyl terephthalate having a purity of 99% by mass or more was obtained. １ The results of the H NMR analysis are shown in FIG. 15, and the results of the gas chromatography analysis are shown in FIG.

[0249] Decomposition of Polyester Fibers in Colored Fibers Containing Polyester Fibers and Colorant Example 52 A colored garment (100% by mass of polyester fibers in all fibers, containing dyes such as red, black, and blue) was cut into pieces of approximately 2 cm x 2 cm. The polyester fibers in the cut pieces were decomposed in the same manner as in Example 43, to obtain dimethyl terephthalate (yield: 0.75 g, 73%), except that multiple cut pieces (1 g) of this colored garment were used instead of the multiple cut pieces (1 g) of the above-mentioned white examination gown.

[0250] The obtained dimethyl terephthalate was subjected to the same procedure as in Example 50. １ As a result of analysis by H NMR and gas chromatography, it was confirmed that dimethyl terephthalate having a purity of 99% by mass or more was obtained. １ The results of the H NMR analysis are shown in FIG. 17, and the results of the gas chromatography analysis are shown in FIG.

[0251] Decomposition of Polyester Fibers in a Fiber Blend Comprising Polyester and Polyurethane Fibers Example 53 A fiber blend (87% by mass of polyester fiber and 13% by mass of polyurethane fiber in the total fiber) was cut into pieces of approximately 2 cm x 2 cm. The polyester fibers in the cut pieces were decomposed in the same manner as in Example 50, except that multiple pieces (1 g) of this fiber blend cut into pieces were used instead of the multiple pieces (1 g) of the above-mentioned white examination coat cut into pieces, and the amount of sodium methoxide used was changed from 14 mg to 30 mg, to obtain dimethyl terephthalate (yield 0.62 g, 70%).

[0252] The obtained dimethyl terephthalate was subjected to the same procedure as in Example 50. １ As a result of analysis by H NMR and gas chromatography, it was confirmed that dimethyl terephthalate having a purity of 99% by mass or more was obtained. １ The results of the H NMR analysis are shown in FIG. 19, and the results of the gas chromatography analysis are shown in FIG. 20.

[0253] The decomposition conditions in Examples 36 to 49 are shown in Figure 21, and the decomposition conditions in Comparative Examples 5 to 7, Reference Example 1, and Examples 50 to 53 are shown in Figure 22. The results of Examples 36 to 53, Comparative Examples 5 to 7, and Reference Example 1 are summarized in Figure 23.

[0254] 21 and 22, "base (amount used (mass %))" means "the ratio of the amount of base used (parts by mass) to the amount of polyester (parts by mass) in the polyester-containing material." Similarly, "carbonate diester (amount used (mass %))" means "the ratio of the amount of carbonate diester used (parts by mass) to the amount of polyester (parts by mass) in the polyester-containing material." Similarly, "monohydric alcohol (amount used (mass %))" means "the ratio of the amount of monohydric alcohol used (parts by mass) to the amount of polyester (parts by mass) in the polyester-containing material."

[0255] As is clear from these figures, in Examples 36 to 49, dicarboxylic acid diesters (monomers) were obtained in good yields from the polyester in the polyester-containing material at room temperature using processes with a low environmental impact, without using materials with a high environmental impact such as halogenated solvents, organic solvents, or an excess amount of base.

[0256] In Examples 50 to 53, the amount of polyester-containing material (polyester) used was increased compared to Examples 36 to 49, and the decomposition of the polyester was carried out on an upscaled scale. However, the dicarboxylic acid diester was obtained in a yield equal to or greater than that of Examples 36 to 49, and the purity of the obtained dicarboxylic acid diester was high, being 99% by mass or more in all cases.

[0257] Therefore, although dicarboxylic acid diesters were not isolated in Examples 36 to 49, which were carried out on a smaller scale than in Examples 50 to 53 and thus facilitated the progress of polyester decomposition, it was determined that dicarboxylic acid diesters of a high purity equivalent to those in Examples 50 to 53 could be isolated. Furthermore, in Examples 50 to 53, such high-purity dicarboxylic acid diesters were obtained by a simple process in which the reaction solution was concentrated under reduced pressure, washed with water, and dried, without requiring any complicated steps.

[0258] As described above, from Examples 36 to 53, it was confirmed that, according to this embodiment, by using a ball mill, the polyester in the polyester-containing material can be efficiently decomposed into high-purity monomers in a process with a small environmental impact.

[0259] In contrast to this, in Comparative Examples 5 to 7 and Reference Example 1, the dicarboxylic acid diester (monomer) could not be obtained in good yield due to the decomposition of the polyester in the polyester-containing material, and the polyester could not be decomposed efficiently.

[0260] In Comparative Example 5, no base was used during the decomposition of the polyester. In Comparative Examples 6 and 7, no carbonic acid diester was used during the decomposition of the polyester. In Reference Example 1, no ball mill was used during the decomposition of the polyester.

[0261] Other Embodiments <Method for Recovering Polyester Decomposition Products> In the above-described embodiment, the method for recovering dimethyl terephthalate (produced by the decomposition of PET), dimethyl 2,6-naphthalenedicarboxylate (produced by the decomposition of PEN), and dimethyl 2,5-furandicarboxylate (produced by the decomposition of PEF), which are polyester decomposition products, was not particularly limited. However, these substances obtained by the polyester decomposition method of the present invention can be easily isolated by distillation (including sublimation purification). As a result, dimethyl terephthalate, dimethyl 2,6-naphthalenedicarboxylate, and dimethyl 2,5-furandicarboxylate obtained by the polyester decomposition method of the present invention can be recovered with high purity (99.0 to 99.9%).

[0262] That is, after decomposing a polyester-containing material using the polyester decomposition method of the present invention, the resulting solution containing the polyester decomposition product can be directly distilled (including sublimation purification) (distillation step) to recover dimethyl terephthalate with high purity (99.0 to 99.9%). Note that, for distillation (including sublimation purification), a commercially available general distiller, sublimator, or the like can be used.

[0263] The temperature during distillation (including sublimation) is not particularly limited as long as it is 100 to 300° C., but is preferably 120 to 200° C. The pressure during distillation (including sublimation) is not particularly limited and may be atmospheric pressure, but is preferably 5 to 5000 Pa, and more preferably 8 to 4000 Pa.

[0264] [Examples 51 to 53] As shown by the following three chemical reaction formulas, a polyester decomposition product (solution) containing dimethyl terephthalate was obtained using the polyester decomposition method described above, and then the polyester decomposition product was directly distilled.

[0265]

[0266]

[0267]

[0268] As described above, it was found that high-purity dimethyl terephthalate can be obtained by simply distilling a polyester decomposition product (solution) containing dimethyl terephthalate obtained by using the polyester decomposition method of the present invention.

[0269] (Incorporation by reference to basic application) This application claims priority based on Japanese Patent Application No. 2022-126948 filed on August 9, 2023, and Japanese Patent Application No. 2022-126949 filed on August 9, 2023, and the entire contents of Japanese Patent Application No. 2022-126948 and Japanese Patent Application No. 2022-126949 are incorporated by reference into this application.

Claims

1. A method for decomposing a polyester contained in a polyester-containing material, the method comprising a decomposition step of mixing a base, a monohydric alcohol, and a carbonic acid diester to decompose the polyester.

2. A polyester production method for producing polyester using a polyester decomposition product obtained by decomposing polyester contained in a polyester-containing material, characterized in that the polyester production method includes a decomposition step in which a base, a monohydric alcohol, and a carbonic acid diester are mixed to decompose the polyester.

3. A method for recovering a specified polyester decomposition product from a polyester decomposition product obtained by decomposing a polyester contained in a polyester-containing material, the method comprising a decomposition step of mixing a base, a monohydric alcohol, and a carbonic acid diester to decompose the polyester.

4. 2. The polyester decomposition method according to claim 1, wherein the reaction temperature in the decomposition step is in the range of 20°C to 100°C.

5. 5. The method for decomposing a polyester according to claim 1, wherein the base is an alkali metal carbonate, an alkali metal hydroxide, or an alkali metal alkoxide.

6. The polyester decomposition method according to claim 1 or 4, wherein the monohydric alcohol is methanol.

7. 5. The polyester decomposition method according to claim 1, wherein the carbonic acid diester is dimethyl carbonate.

8. 5. The polyester decomposition method according to claim 1, wherein the decomposition step comprises mixing the base, the monohydric alcohol, and the carbonate diester using a mechanochemical reaction apparatus to decompose the polyester.

9. The polyester decomposition method according to claim 8, wherein the reaction temperature in the decomposition step is in the range of 30°C to 100°C.

10. The polyester decomposition method according to claim 8, wherein the mechanochemical reaction device is a ball mill.

11. 5. The method for decomposing polyester according to claim 1, wherein the polyester-containing material includes at least one of polyester fibers and a film made of polyester.

12. 10. The polyester decomposition method according to claim 1, wherein the polyester-containing material contains substances other than polyester.

13. A polyester decomposition method, characterized in that, among the polyester decomposition products obtained by the polyester decomposition method described in claim 1 or 4, a reaction product of glycol and carbonic acid diester is regenerated into glycol and carbonic acid diester by reaction with alcohol, and the regenerated carbonic acid diester is reused for the decomposition of polyester.

14. A method for producing polyester as described in claim 2, characterized in that, among the obtained polyester decomposition products, a reaction product of glycol and carbonic acid diester is regenerated into glycol and carbonic acid diester by reaction with alcohol, and the regenerated glycol is reused in the production of polyester.

15. A method for recovering polyester decomposition products, characterized in that the specified polyester decomposition product described in claim 3 is dimethyl terephthalate, dimethyl 2,6-naphthalenedicarboxylate, or dimethyl 2,5-furandicarboxylate.

16. The method for recovering polyester decomposition products described in claim 3, characterized in that it includes a distillation process for distilling the polyester decomposition products.