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

Abstract

Provided are: a polyester decomposition method capable of decomposing a polyester or a polyester contained in various polyester-containing materials into a monomer at a low temperature of 150 DEG C or lower in a simple step; and a polyester production method for producing a polyester from the monomer obtained by the decomposition method. And a polyester decomposition product recovery method for recovering a predetermined polyester decomposition product from the polyester decomposition product obtained by the polyester decomposition method. A polyester decomposition method for decomposing a polyester contained in a polyester-containing material, the polyester decomposition method comprising a decomposition step in which a base, a monohydric alcohol, and a diester carbonate are mixed and the polyester is decomposed.

Description

Technical Field

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

[0002] In recent years, due to concerns about environmental damage represented by marine pollution, the development of plastic recycling technology has become a top priority. Polyester is widely used as a material for bottles and fibers, especially polyethylene terephthalate (PET), which is produced in an annual amount of about 80 million tons worldwide. As recycling technologies for polyester, a material recycling method without depolymerization and a chemical recycling method after depolymerization and repolymerization are being developed. The polyester used in PET bottles and the like is easily applicable to the former method due to its high purity, but it is difficult to apply the former method to materials containing polyester (polyester-containing materials) such as polyester fibers and films containing polyester.

[0003] As a method for depolymerizing polyester, methods using water or supercritical alcohol are known (see Patent Document 1 and Patent Document 2). However, both require high temperature conditions of 300°C or above. On the other hand, in the transesterification method using an alkali catalyst and an alcohol, depolymerization can be achieved at a relatively low temperature. In the method using methanol, by using a halogenated solvent and potassium carbonate (see Non-Patent Document 1) or an alkali metal alkoxide (see Patent Document 3), depolymerization can be achieved at a low temperature of about room temperature (15 to 25°C) to 50°C. In addition, there is a known method for increasing the efficiency of depolymerization by using dimethyl carbonate as an ethylene glycol scavenger (Non-Patent Document 2). However, the depolymerization objects in these methods are limited to high-purity PET from PET bottles, etc., and other polyester-containing materials are not applicable to these methods. As a method for depolymerizing colored polyester fibers, there is known a method of excessively using an alkali catalyst and ethylene glycol, but in addition to requiring a high temperature of about 200°C, in order to obtain a high-purity monomer, it is also necessary to use a high-boiling point solvent to decolorize the fiber (see Patent Documents 4 to 6) or to use an oxidizing agent to decompose the dye (see Patent Document 7).

[0004] Prior art literature Patent Literature Patent Document 1: Japanese Patent No. 5099416 Patent Document 2: Japanese Patent Application Publication No. 2001-39908 Patent Document 3: U.S. Patent No. 10252976 Patent Document 4: Japanese Patent No. 4537288 Patent Document 5: Japanese Patent No. 5134563 Patent Document 6: Japanese Patent No. 6659919 Patent Document 7: Japanese Patent No. 6986813 Non-patent literature Non-patent literature 1: Green Chem. 2021, 23, 511. Non-patent literature 2: Green Chem. 2021, 23, 9412. Summary of the invention Problem that the invention aims to solve However, there is a problem that polyester or polyester contained in various polyester-containing materials cannot be decomposed into monomers at a low temperature of 150° C. or lower in a simple process.

[0005] An object of the present invention is to provide a polyester decomposition method capable of decomposing polyester or polyester contained in various polyester-containing materials into monomers at a low temperature of 150° C. or lower in a simple process, a polyester production method for producing polyester from the monomers obtained by the polyester decomposition method, and a polyester decomposition product recovery method for recovering a predetermined polyester decomposition product from the polyester decomposition product obtained by the polyester decomposition method.

[0006] Means used to solve problems The inventors of the present invention have conducted intensive studies on the above-mentioned problems and, as a result, have discovered the following revolutionary polyester decomposition method, polyester production method, and polyester decomposition product recovery method.

[0007] A first aspect of the present invention for solving the above-mentioned problems is a polyester decomposition method for decomposing polyester contained in a polyester-containing material, characterized by comprising a decomposition step of mixing an alkali, a monohydric alcohol and a carbonic acid diester to decompose the polyester.

[0008] Here, "decomposition" is a concept that includes deaggregation.

[0009] According to the first aspect, the polyester contained in the polyester-containing material can be decomposed into monomers in a simple process.

[0010] A second aspect of the present invention is the polyester decomposition method according to the first aspect, wherein the reaction temperature in the decomposition step is within a range of 20°C to 150°C.

[0011] 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 lower in a simple process.

[0012] A third aspect of the present invention is the polyester decomposition method according to the first or second aspect, wherein the base is an alkali metal carbonate, an alkali metal hydroxide or an alkali metal alkoxide.

[0013] According to the third aspect, the polyester contained in the polyester-containing material can be decomposed into monomers with higher purity.

[0014] A fourth aspect of the present invention is the polyester decomposition method according to the first or second aspect, wherein the monohydric alcohol is methanol.

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

[0016] A fifth aspect of the present invention is the polyester decomposition method according to the first or second aspect, wherein the carbonic acid diester is dimethyl carbonate.

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

[0018] A sixth aspect of the present invention is the polyester decomposition method according to the first or second aspect, wherein the polyester is decomposed by mixing the base, the monohydric alcohol and the carbonic acid diester using a mechanochemical reaction device in the decomposition step.

[0019] According to the sixth aspect, the polyester contained in the polyester-containing material can be decomposed without the need for a halogenated solvent, an excess organic solvent, and an excess base. Furthermore, after the decomposition, a monomeric dicarboxylic acid diester can be obtained as a main depolymerized product in good yield and high purity without the need for additional complicated steps.

[0020] A seventh aspect of the present invention is the polyester decomposition method according to the sixth aspect, wherein the reaction temperature of the decomposition step is within a range of 30°C to 100°C.

[0021] According to the seventh aspect, the polyester contained in the polyester-containing material can be decomposed at a reaction temperature of 100° C. or lower.

[0022] An eighth aspect of the present invention is the polyester decomposition method according to the sixth aspect, wherein the mechanochemical reaction device is a ball mill.

[0023] According to the eighth aspect, the polyester contained in the polyester-containing material can be decomposed with a smaller amount of the halogenated solvent, the organic solvent, and the alkali.

[0024] A ninth aspect of the present invention is the polyester decomposition method according to the first or second aspect, wherein the polyester-containing material includes at least one of polyester fibers and a film composed of polyester.

[0025] According to the ninth aspect, even in the polyester-containing material including at least one of polyester fiber and a film composed of polyester, the polyester contained therein can be decomposed.

[0026] A tenth aspect of the present invention is the polyester decomposition method according to the first or second aspect, wherein the polyester-containing material includes a substance other than polyester.

[0027] According to the tenth aspect, even if the polyester-containing material includes a substance other than polyester, the polyester contained therein can be decomposed.

[0028] An eleventh aspect of the present invention is a method for producing polyester, characterized in that polyester is produced using a polyester decomposition product obtained by the polyester decomposition method described in the first or second aspect.

[0029] According to the eleventh aspect, new polyester can be produced using the polyester decomposition product decomposed by the polyester decomposition method of the present invention as a raw material.

[0030] A twelfth aspect of the present invention is a polyester decomposition product recovery method, comprising recovering 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-naphthalene dicarboxylate or dimethyl 2,5-furan dicarboxylate, and comprising a distillation step of distilling the polyester decomposition product.

[0031] According to the twelfth embodiment, after obtaining a polyester decomposition product (solution) containing dimethyl terephthalate, dimethyl 2,6-naphthalene dicarboxylate or dimethyl 2,5-furan dicarboxylate, high-purity (99.0 to 99.9%) dimethyl terephthalate, dimethyl 2,6-naphthalene dicarboxylate or dimethyl 2,5-furan dicarboxylate can be obtained simply by distillation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The dimethyl terephthalate obtained in Example 1 is 1 Analytical results in H NMR.

[0033] Figure 2 This is the analysis result of dimethyl terephthalate obtained in Example 1 by gas chromatography.

[0034] Figure 3 The dimethyl terephthalate obtained in Example 3 is 1 Analytical results in H NMR.

[0035] Figure 4 This is the analysis result of dimethyl terephthalate obtained in Example 3 by gas chromatography.

[0036] Figure 5This is a table showing the results of Examples 1 to 6 and Comparative Examples 1 to 4.

[0037] Figure 6 This is a table showing the results of Examples 7 to 9.

[0038] Figure 7 This is a table showing the results of Example 10.

[0039] Figure 8 This is a table showing the results of Examples 11 to 17.

[0040] Fig. 9 This is a table showing the results of Examples 18 to 20.

[0041] Fig.10 This is a table showing the results of Examples 21 to 23.

[0042] Fig.11 This is a table showing the results of Examples 19, 24, and 25.

[0043] Fig.12 This is a table showing the results of Examples 26 to 32.

[0044] Fig.13 The dimethyl terephthalate obtained in Example 50 is 1 Analytical results in H NMR.

[0045] Fig.14 This is the analysis result of dimethyl terephthalate obtained in Example 50 by gas chromatography.

[0046] Fig.15 The dimethyl terephthalate obtained in Example 51 is 1 Analytical results in H NMR.

[0047] Fig.16 These are the results of gas chromatography analysis of dimethyl terephthalate obtained in Example 51.

[0048] Fig.17 The dimethyl terephthalate obtained in Example 52 is 1 Analytical results in H NMR.

[0049] Fig.18 This is the analysis result of dimethyl terephthalate obtained in Example 52 by gas chromatography.

[0050] Fig.19 The dimethyl terephthalate obtained in Example 53 is 1 Analytical results in H NMR.

[0051] Fig. 20This is the analysis result of dimethyl terephthalate obtained in Example 53 by gas chromatography.

[0052] Fig.21 This is a table showing the decomposition conditions in Examples 36 to 49.

[0053] Fig. 22 This is a table showing the decomposition conditions in Comparative Examples 5 to 7, Reference Example 1, and Examples 50 to 53.

[0054] Fig.23 This is a table showing the experimental results of Examples 36 to 53, Comparative Examples 5 to 7, and Reference Example 1. DETAILED DESCRIPTION

[0055] Hereinafter, embodiments of the polyester decomposition method and polyester production method of the present invention will be described. In addition, the present invention is not limited to the following embodiments.

[0056] (Implementation method 1) <<How to decompose polyester>> The polyester decomposition method according to one embodiment of the present invention comprises a decomposition step of decomposing the polyester in a polyester-containing material (polyester-containing material) using (mixing) an alkali, a monohydric alcohol, and a carbonic acid diester. In addition, the polyester-containing material may be one or more selected from the group consisting of a material containing polyester fibers (polyester fibers), a film containing polyester and components other than polyester, and polyester and components other than polyester.

[0057] According to the decomposition method of this embodiment, polyester can be decomposed at low temperature using a polyester-containing material which is different from PET film making and which is difficult to decompose at relatively low temperature in the past. Furthermore, there is no need to add complicated steps after decomposition, and the monomer, i.e., the dicarboxylic acid diester, can be obtained as a main decomposition product (depolymerization product) with high purity in a simple step.

[0058] Furthermore, in the conventional decomposition methods (methods described in Patent Documents 6 and 7), when decomposing colored fibers, only a dicarboxylic acid diester having a purity of about 99% can be obtained even by performing crystallization and distillation.

[0059] 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 operation alone, and a dicarboxylic acid diester having a purity of 99.9% or more can be obtained by distillation.

[0060] <Material containing polyester> In the present embodiment, the polyester-containing material is not particularly limited as long as it contains polyester. For example, it refers not only to polyester itself, such as a limited range of materials with an extremely high polyester content and a form suitable for reaction, such as polyethylene terephthalate (PET) film, but also to a wider range of materials having a low polyester content or a form not suitable for reaction.

[0061] More specifically, examples of the polyester-containing material include a material containing polyester fibers (polyester fibers), a film containing polyester and a component other than polyester, and a bulk material containing polyester and a component other than polyester.

[0062] Examples of the material containing polyester fibers include polyester fibers (fibers containing no component other than polyester), woven fabrics of polyester fibers, mixtures containing polyester fibers and components other than polyester fibers, and woven fabrics of the mixtures.

[0063] Examples of the mixture containing polyester fiber and a component other than polyester fiber include a mixed fiber of polyester fiber and a fiber other than polyester fiber and a woven fabric of the mixed fiber, a composite mixed fiber containing polyester fiber and a non-resin component (e.g., a colored fiber containing polyester fiber and a colorant) and a woven fabric of the composite mixed fiber, a composite mixed fiber containing polyester fiber, a fiber other than polyester fiber, and a non-resin component (e.g., a colored mixed fiber containing a mixed fiber and a colorant) and a woven fabric of the composite mixed fiber, etc. Here, in this specification, the "non-resin component" refers to a component that is neither polyester nor a resin other than polyester.

[0064] Examples of the film containing polyester and a component other than polyester include a single layer film containing polyester and a component other than polyester, and a laminated film which is a laminate of a film composed of polyester (polyester film) and a film containing a component other than polyester.

[0065] Examples of the single-layer film containing polyester and components other than polyester include a single-layer film containing both polyester and resins other than polyester and not containing non-resin components, a single-layer film containing both polyester and non-resin components and not containing resins other than polyester, and a single-layer film containing all of polyester, resins other than polyester, and non-resin components.

[0066] As a laminated film which is a laminate of a film composed of polyester and a film containing a component other than polyester, for example, there can be mentioned a laminated film which is a laminate of a film composed of polyester and a film containing a resin other than polyester and not containing polyester and non-resin components, a laminated film which is a laminate of a film composed of polyester and a film which contains a resin other than polyester and polyester and not containing non-resin components, a laminated film which is a laminate of a film composed of polyester and a film which contains a resin other than polyester and non-resin components and not containing polyester, a laminated film which is a laminate of a film composed of polyester and a film which contains all polyester, resin other than polyester and non-resin components, a multilayer film which is a laminate of any one or more of the above laminated films and any one or more of the above single-layer films, a multilayer film which is a laminate of any two or more of the above laminated films, a multilayer film which is a laminate of any two or more of the above single-layer films, etc.

[0067] Examples of the block containing polyester and components other than polyester include a block containing both polyester and resins other than polyester and not containing non-resin components, a block containing both polyester and non-resin components and not containing resins other than polyester, and a block containing all of polyester, resins other than polyester, and non-resin components.

[0068] Resins other than polyester can be selected arbitrarily according to the purpose without particular limitation. For example, in terms of high versatility and high applicability of the present invention, resins other than polyester include polyolefins such as polyethylene and polypropylene, polyamides such as cellulose and nylon, polyurethanes, and acrylic resins. These resins may be, for example, film-like (resin film) or fibrous (resin fiber).

[0069] Moreover, as a fiber other than polyester fiber, the fiber of the resin other than the above-mentioned polyester, cotton, rayon, etc. are mentioned.

[0070] In addition, the non-resin component can be arbitrarily selected according to the purpose without particular limitation. For example, in terms of high versatility and high applicability of the present invention, inorganic components (inorganic compounds) such as aluminum, colorants such as dyes and pigments, etc. can be cited as non-resin components.

[0071] The fiber diameters of the polyester fibers and fibers other than the polyester fibers in the polyester fiber-containing material are not particularly limited, and may be, for example, 0.1 μm to 200 μm, or 1 μm to 50 μm.

[0072] 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 refers to the thickness of the entire laminated film.

[0073] More specifically, the polyester fiber-containing material includes, for example, fabrics of various clothes, fibers as materials of the fabrics, etc. The fabrics may be, for example, cutouts generated when various clothes are manufactured, cutouts of various clothes after use, etc. The fibers as materials of the fabrics may be, for example, cutouts generated when fabrics are manufactured, cutouts generated from fabrics after use, etc.

[0074] More specifically, examples of the film containing polyester and components other than polyester include packaging films, scraps such as cut pieces generated during the production of packaging films, and scraps such as cut pieces of packaging films after use.

[0075] As the block containing polyester and components other than polyester, more specifically, for example, there can be cited particles and flakes containing polyester and components other than polyester. The maximum diameter of the block is not particularly limited, and can be, for example, 0.1 mm to 10 mm. Here, the "maximum diameter of the block" refers to the maximum value of the length of a line segment connecting two different points on the surface of the block.

[0076] The polyester-containing material used for polyester decomposition may be one or more than one kind. In the case of two or more kinds, their combination and ratio can be arbitrarily selected according to the purpose. That is, the polyester-containing material used for polyester decomposition is one or more kinds selected from the group consisting of a polyester fiber-containing material, a film containing polyester and a component other than polyester, and a block containing polyester and a component other than polyester.

[0077] When the polyester-containing material is a polyester fiber-containing material, the polyester fiber-containing material 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 the mixtures.

[0078] In the case where the polyester-containing material is a film containing polyester and components other than polyester, the film containing polyester and components other than polyester is preferably either or both of a single-layer film containing polyester and components other than polyester, and a laminated film which is a laminate of a film composed of polyester and a film containing components other than polyester.

[0079] In the polyester-containing material, the ratio of the content (mass parts) of polyester to the total mass (mass parts) of the polyester-containing material ([content (mass parts) of polyester contained in the polyester-containing material] / [total mass (mass parts) of the polyester-containing material]×100) (polyester content ratio) can be arbitrarily selected according to the purpose and is not particularly limited. Among them, the polyester content ratio may be 20% by mass or more and 100% by weight or less, preferably 40% by mass or more and 100% by mass or less or 40% by mass or more and less than 100% by mass, more preferably 55% by mass or more and 100% by mass or less or 55% by mass or more and less than 100% by mass, particularly preferably 70% by mass or more and 100% by mass or less or 70% by mass or less than 100% by mass. The higher the polyester content ratio, the greater the amount of monomer (dicarboxylic acid diester described below) generated per unit mass of the polyester-containing material by decomposition of the polyester.

[0080] [Polyester] The polyester in the polyester-containing material (polyester to be decomposed) is not particularly limited as long as it generates, by decomposition, an oligomer or polymer of a component having two functional groups capable of condensation reaction with a diol and a diol in one molecule.

[0081] The polyester may be an aromatic polyester having only an aromatic group (a divalent group having a structure in which one hydrogen atom is removed from each of two carbon atoms forming an aromatic ring skeleton in an aromatic compound) in the main chain having an ester bond, an aliphatic polyester having no aromatic group in the main chain (having an aliphatic group and no aromatic group), or a polyester having both an aromatic group and an aliphatic group in the main chain. The aromatic polyester may have only a divalent aromatic hydrocarbon group (arylene group) as the aromatic group, may have only a divalent aromatic heterocyclic group (heteroarylene group) as the aromatic group, or may have both a divalent aromatic hydrocarbon group and a divalent aromatic heterocyclic group as the aromatic group. Examples of heteroatoms possessed by the aromatic heterocyclic group include oxygen atoms and nitrogen atoms.

[0082] In addition, generally, the reactivity of the substrate in the transesterification reaction depends on the structure of the carboxylic acid side and the structure of the alcohol side. As described below, as the structure of the carboxylic acid side, since even polyesters (polyethylene terephthalate, polybutylene terephthalate, etc.) having a benzene ring or a naphthalene ring as an aromatic group can be well decomposed, it can be easily inferred that even polyesters having other aromatic structures such as furan can be similarly decomposed. Similarly, as the structure of the alcohol side, since even polyesters having a structure of ethylene glycol (polyethylene terephthalate, etc.) and 1,4-butanediol (polybutylene terephthalate, etc.) can be well decomposed, it can be easily inferred that even polyesters having a structure of other diols such as 1,3-propylene glycol can be similarly decomposed.

[0083] In terms of the higher effect and high versatility of the present invention, 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 furandicarboxylate (PEF, also known as polyethylene 2,5-furandicarboxylate).

[0084] By decomposing the polyester, a dicarboxylic acid diester determined according to the types of the polyester and the monohydric alcohol is generated from the polyester as a monomer.

[0085] For example, terephthalate diesters are produced from polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate; naphthalene dicarboxylic acid diesters (2,6-naphthalene dicarboxylic acid diesters) are produced from polyethylene naphthalate and polybutylene naphthalate; and furan dicarboxylic acid diesters (2,5-furan dicarboxylic acid diesters) are produced from polyethylene furan dicarboxylate.

[0086] For example, when methanol is used as the monohydric alcohol, dimethyl dicarboxylate is produced as the dicarboxylic acid diester.

[0087] The polyester used for decomposition may be one kind or two or more kinds. When there are two or more kinds, the combination and ratio thereof are not particularly limited and can be arbitrarily selected according to the purpose.

[0088] <Alkali> The base is not particularly limited and may be any of an inorganic base and an organic base, but is preferably an alkali metal carbonate or alkali metal hydroxide, or an alkali metal alkoxide, which reacts with a monohydric alcohol to form an alkali metal alkoxide.

[0089] Generally, in the transesterification reaction, the reaction proceeds as follows, that is, the alkoxide anion, which becomes a nucleophile, attacks the carbonyl group of the ester, and after passing through a quaternary carbon intermediate, the other alkoxide anion is liberated. Since the alkoxide anion is generated by the reaction of the corresponding alcohol and a base, any base that can deprotonate the alcohol can be used.

[0090] Examples of the inorganic base 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.

[0091] Examples of the organic base 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; alkaline earth metal alkoxides such as calcium methoxide, calcium ethoxide, calcium tert-butoxide, magnesium methoxide, magnesium ethoxide, and magnesium tert-butoxide; or nitrogen-containing organic bases (organic bases having a nitrogen atom) such as trimethylamine, triethylamine, tri-n-butylamine, trioctylamine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (abbreviation: TBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (abbreviation: DBU), 1,3-dimesitylimidazol-2-ylidene, and 1,3-dicyclohexylimidazol-2-ylidene.

[0092] The alkali metal alkoxide is preferably lithium methoxide, sodium methoxide or potassium methoxide, and more preferably sodium methoxide, in that decomposition of the polyester proceeds at a higher rate.

[0093] The nitrogen-containing organic base is preferably 1,5,7-triazabicyclo[4.4.0]dec-5-ene in that the decomposition of the polyester proceeds at a higher rate.

[0094] The base used for decomposing the polyester may be one kind or two or more kinds. When two or more kinds are used, the combination and ratio of the bases are not particularly limited and can be arbitrarily selected according to the purpose.

[0095] The base is particularly preferably an alkali metal alkoxide in terms of the decomposition of the polyester proceeding at a particularly high rate.

[0096] When decomposing polyester, the amount of the base used is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 6 parts by mass, for example, any one of 0.5 to 3 parts by mass and 3 to 6 parts by mass, relative to 100 parts by mass of the polyester in the polyester-containing material. When the amount of the base used is greater than the lower limit, the polyester is decomposed at a higher rate. When the amount of the base used is less than the upper limit, excessive use of the base is suppressed. That is, when decomposing polyester, the amount of the base used is preferably a catalytic amount (the base is a catalyst).

[0097] <Monohydric alcohol> When the monohydric alcohol is decomposed, an ester exchange reaction occurs with the polyester in the polyester-containing material. That is, when the polyester is decomposed, a diol corresponding to one monomer in the raw material used in the production of the polyester is produced by the reaction between the polyester and the monohydric alcohol, and a dicarboxylic acid diester corresponding to the other monomer or a derivative thereof is also produced.

[0098] Monohydric alcohol is not particularly limited. The reaction efficiency of the decomposition reaction of the present invention is controlled by the capture of the carbonic acid diester that exists in excess to free dihydric alcohol. Therefore, as described below, according to the fact that the reaction using methyl alcohol and dimethyl carbonate is effectively carried out, it can be easily inferred that even the combination of other monohydric alcohols and dialkyl carbonates is also effectively reacted.

[0099] For example, any of an aliphatic alcohol and an aromatic alcohol may be used, but an aliphatic alcohol (saturated aliphatic alcohol, unsaturated aliphatic alcohol) is preferred, and a saturated aliphatic alcohol is more preferred, since decomposition of the polyester proceeds at a higher rate.

[0100] Examples of the saturated aliphatic alcohol include alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, 1-propanol (n-propanol), 2-propanol (isopropanol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), and 2-methyl-2-propanol (tert-butanol).

[0101] The monohydric alcohol used for decomposing polyester may be only one or two or more. In the case of two or more, their combination and ratio are not particularly limited and can be arbitrarily selected according to the purpose. In addition, as the monohydric alcohol, methanol is particularly preferred in that the decomposition of polyester is carried out at a particularly high ratio.

[0102] When decomposing polyester, the amount of monohydric alcohol used is not particularly limited, but for example, when the polyester is polyethylene terephthalate (PET), it is preferably 30 to 200 parts by mass, and more preferably 50 to 160 parts by mass, relative to 100 parts by mass of PET in the polyester-containing material. In addition, when the polyester is polybutylene terephthalate (PBT), the amount of monohydric alcohol used is preferably 10 to 180 parts by mass, and more preferably 20 to 140 parts by mass, relative to 100 parts by mass of PBT in the polyester-containing material. By using a monohydric alcohol above these lower limits, the effect obtained by using a monohydric alcohol is higher. On the other hand, by using a monohydric alcohol below these upper limits, excessive use of a monohydric alcohol is suppressed.

[0103] <Carbonate diester> During the decomposition of polyester, the carbonate diester reacts with the diol produced by the polyester to generate a cyclic compound or a chain compound, which makes the reaction during the decomposition of the polyester, that is, the balance between the depolymerization reaction and the polymerization reaction of the polyester, incline to the depolymerization reaction being dominant, and has the effect of increasing the production rate of the target monomer. The carbonate diester functions as a diol scavenger.

[0104] As the reaction product of carbonic acid diester and diol, a cyclic compound (for example, the cyclic compound (61) described below) which is the reaction product of 1 molecule of carbonic acid diester and 1 molecule of diol, a chain compound (for example, the first chain compound (62) described below) which is the reaction product of 1 molecule of carbonic acid diester and 1 molecule of diol, and a chain compound (for example, the second chain compound (63) described below) which is the reaction product of 1 molecule of carbonic acid diester and 2 molecules of diol can be generated. Which of these cyclic compounds and chain compounds is generated is mainly determined by the type (for example, size) of diol. For example, the reaction product of carbonic acid diester and ethylene glycol is mainly a cyclic compound (more specifically, ethylene carbonate) which is the reaction product of 1 molecule of carbonic acid diester and 1 molecule of ethylene glycol.

[0105] As carbonic acid diester, for example, dialkyl carbonate, diaryl carbonate etc. can be enumerated. Two alkyl groups bonded with oxygen atom in dialkyl carbonate can be identical with each other, and also can be different from each other. In addition, two aryl groups bonded with oxygen atom in diaryl carbonate can be identical with each other, and also can be different from each other.

[0106] The alkyl group in the dialkyl carbonate may be linear, branched, or cyclic, and when cyclic, may be monocyclic or polycyclic.

[0107] The number of carbon atoms of the linear or branched alkyl group in the dialkyl carbonate is preferably 1 to 8. Examples of such alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, 1-methylbutyl, n-hexyl, 2-methylpentyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, n-heptyl, 2-methylhexyl, 3-methylhexyl, 2,2-dimethylpentyl, 2,3-dimethylpentyl, 2,4-dimethylpentyl, 3,3-dimethylpentyl, 3-ethylpentyl, 2,2,3-trimethylbutyl, n-octyl, and isooctyl.

[0108] Among them, the number of carbon atoms of the alkyl group is more preferably 1 to 4, and even more preferably 1 or 2. Such further preferred dialkyl carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0109] The aryl group in the diaryl carbonate may be any of a monocyclic or polycyclic group. The number of carbon atoms of the aryl group in the diaryl carbonate is preferably 6 to 10, and examples of such aryl groups include phenyl, 1-naphthyl, 2-naphthyl, o-tolyl, m-tolyl, p-tolyl, 2,3-xylyl (2,3-dimethylphenyl), 2,4-xylyl (2,4-dimethylphenyl), 2,5-xylyl (2,5-dimethylphenyl), 2,6-xylyl (2,6-dimethylphenyl), 3,4-xylyl (3,4-dimethylphenyl), 3,5-xylyl (3,5-dimethylphenyl), etc. As a more preferred diaryl carbonate, for example, diphenyl carbonate can be mentioned.

[0110] The carbonic acid diester used for decomposition of the polyester may be one kind or two or more kinds. When two or more kinds are used, the combination and ratio thereof are not particularly limited and can be arbitrarily selected according to the purpose.

[0111] The carbonic acid diester is more preferably one or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and diphenyl carbonate, and is particularly preferably dimethyl carbonate, in that the decomposition of the polyester proceeds at a higher rate.

[0112] When decomposing polyester, relative to 100 parts by mass of the polyester in the polyester-containing material, the usage of carbonic acid diester is preferably 100 to 5000 parts by mass, more preferably 100 to 1000 parts by mass, for example, 100 to 500 parts by mass. By the usage of carbonic acid diester being above the lower limit, the effect obtained by using carbonic acid diester becomes higher. By the usage of carbonic acid diester being below the upper limit, the excessive use of carbonic acid diester is suppressed.

[0113] <Solvent> When decomposing polyester, a solvent that is not an alkali, a monohydric alcohol, or a carbonic acid diester may be used. In the present embodiment, the decomposition of polyester is effectively performed even without using a solvent, but by using a solvent as needed, the handling properties of the formulation of each raw material such as the reaction solution may be improved, or the decomposition of polyester may be performed more effectively.

[0114] In this specification, unless otherwise specified, "solvent" is a concept including both a component that is liquid at room temperature for dissolving a solute and a component that is liquid at room temperature and functions as a dispersion medium for dispersing a dispersoid. In addition, "normal temperature" refers to a temperature that is not particularly cooled or heated, that is, a normal temperature, for example, a temperature of 15 to 25°C.

[0115] Here, the solvent is preferably an organic solvent. Examples of the organic solvent include aromatic hydrocarbons such as toluene, ethers such as tetrahydrofuran, alkanes such as n-hexane, halogenated hydrocarbons such as chloroform and dichloromethane, amides such as dimethylformamide, and sulfoxides such as dimethyl sulfoxide.

[0116] The solvent used for decomposing the polyester may be only one kind or two or more kinds. When there are two or more kinds, the combination and ratio of the solvents can be arbitrarily selected according to the purpose.

[0117] When a solvent is used, the amount of the solvent used is preferably 1 to 100,000 parts by mass, more preferably 1 to 10,000 parts by mass, relative to 100 parts by mass of the polyester-containing material during decomposition of the polyester. When the amount of the solvent used is greater than the lower limit, the effect obtained by using the solvent becomes higher. When the amount of the solvent used is less than the upper limit, excessive use of the solvent is suppressed.

[0118] <Other ingredients> In the decomposition of the polyester, other components which are not included in any of the polyester-containing material, the base, the monohydric alcohol, the carbonic acid diester, and the solvent may be used as long as the effects of the present invention are not impaired.

[0119] The other components used for polyester decomposition may be one or more than one. When there are two or more than two, their combination and ratio are not particularly limited and can be arbitrarily selected according to the purpose.

[0120] In the decomposition of polyester, the ratio of the total amount (mass parts) of the polyester-containing material, the base, the monohydric alcohol and the carbonic acid diester to the total amount (mass parts) of the components other than the solvent (([amount (mass parts) of the polyester-containing material] + [amount (mass parts) of the base] + [amount (mass parts) of the monohydric alcohol] + [amount (mass parts) of the carbonic acid diester]) / [total amount (mass parts) of the components other than the solvent] × 100) is preferably 80% to 100% by mass, more preferably 90% to 100% by mass, further preferably 95% to 100% by mass, for example, it may be any one of 97% to 100% by mass and 99% to 100% by mass. When the ratio is equal to or greater than the lower limit, the polyester can be more effectively decomposed.

[0121] Here, the total amount (parts by mass) of components other than the solvent used in decomposition of the polyester is synonymous with the total amount (parts by mass) of the polyester-containing material, the base, the monohydric alcohol, the carbonic acid diester and other components used in decomposition.

[0122] <Reaction conditions of decomposition process> The decomposition of the polyester in the polyester-containing material can be performed by blending (mixing) a base, a monohydric alcohol, a carbonic acid diester, the polyester-containing material, a solvent as required, and other components as required.

[0123] The mixing order of these raw materials is not particularly limited, but it is preferred to prepare a raw material composition as a mixture of a base, a monohydric alcohol, a carbonic acid diester, a solvent as required, and other components as required (for example, a mixture containing all raw materials other than the polyester material), and mix the raw material composition with the polyester-containing material. By adopting such a mixing order, the decomposition of the polyester proceeds at a higher rate.

[0124] In the raw material composition, when the amount of the base blended is a catalytic amount (the base is a catalyst), the raw material composition may be referred to as a "catalyst composition" in this specification.

[0125] The reaction temperature during the decomposition of the polyester (the reaction temperature of the decomposition step) can be appropriately adjusted in consideration of the type of raw materials used, etc., and the decomposition can be carried out at room temperature (normal temperature) or under heating conditions. In addition, the equipment used for heating is not particularly limited, and equipment such as a heater can be used.

[0126] The reaction temperature during decomposition of the polyester (reaction temperature of the decomposition step) is preferably 20° C. or higher, for example, 40° C. or higher and 60° C. or higher. The reaction temperature during decomposition of the polyester is preferably 150° C. or lower, for example, 100° C. or lower and 70° C. or lower.

[0127] 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., more preferably 50 to 120° C. For example, by adjusting reaction conditions other than the reaction temperature, the polyester can be decomposed at a sufficiently high rate even at a reaction temperature of 20 to 70° C.

[0128] According to the present embodiment, as described above, although not only PET film or the like is used but also polyester-containing materials which are difficult to decompose at relatively low temperatures are used, polyester can be decomposed at low temperatures such as 150° C. or lower. Thus, unlike the case where polyester is decomposed at high temperatures, the amount of by-products generated during decomposition can be reduced, and the coloring of the dicarboxylic acid diester (monomer) which is the main decomposition product can be reduced.

[0129] The decomposition of polyester may be carried out under any of normal pressure, reduced pressure, and increased pressure. The decomposition of polyester may be carried out under any of air and inert gas atmosphere.

[0130] Furthermore, the reaction time for decomposing the polyester can be appropriately adjusted in consideration of other reaction conditions such as reaction temperature and is not particularly limited. The reaction time for decomposing the polyester is not particularly limited as long as it is 0.5 to 24 hours, but is preferably 0.5 to 12 hours, and more preferably 1 to 8 hours.

[0131] In this embodiment, for example, the disappearance of polyester can be judged as the end of decomposition. Therefore, the time required until the polyester disappears can be used as the reaction time of decomposition. The time required until the polyester disappears can also be judged based on, for example, the time required until the mass reduction of the polyester-containing material stops.

[0132] In the mixture immediately after mixing the raw materials, the unreacted polyester-containing material does not dissolve and remains insoluble in other liquid components. Then, in the mixture (reactant) in which polyester decomposition is in progress, typically, both the unreacted polyester-containing material and the polyester-containing material during or after the reaction do not dissolve and remain insoluble in other liquid components. On the other hand, the diol and dicarboxylic acid diester, which are the reactants of polyester decomposition, typically dissolve in the liquid components.

[0133] During decomposition of the polyester, the mixture can be stirred by a known method, for example, a method of stirring by rotating a magnetic stirrer or a stirring blade, a method of stirring by using a ball mill, etc.

[0134] When decomposing polyester, for example, by using a reaction container whose bottom surface is flat as a reaction container, the contact area between the polyester-containing material insoluble in the liquid component and the liquid component can be increased. As a result, the amount of raw materials such as alkali, monohydric alcohol and carbonic acid diester used can be reduced compared to the case of using other reaction containers, and the polyester can be decomposed more efficiently.

[0135] <Post-processing conditions, removal conditions> After the above-mentioned step of decomposing the polyester is completed, the dicarboxylic acid diester, which is one of the main decomposition products, can be taken out at a high purity by post-treatment using a known method.

[0136] For example, after decomposing the polyester, the obtained reaction product is filtered, the volatile components are distilled off (concentrated), etc., and the obtained solid is washed with methanol and water to obtain a high-purity dicarboxylic acid diester. The obtained dicarboxylic acid diester can then be further purified by crystallization (crystallization), distillation, etc. as needed.

[0137] By appropriately adjusting the post-treatment conditions and the removal conditions, the reaction product of the diol and the carbonic acid diester, which is another main decomposition product, can also be removed in the same manner as in the case of the dicarboxylic acid diester.

[0138] According to the present embodiment, as described above, since decomposition can be performed at a low temperature such as 150°C or lower, the impurity content and coloration of the dicarboxylic acid diester can be reduced, unlike the case of decomposition at a high temperature. Therefore, without adding a complicated process, a dicarboxylic acid diester (monomer) with high purity and suppressed coloration can be obtained by a simplified process such as washing with methanol and water as described above. 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 a simplified process such as washing with methanol and water as described above.

[0139] On the other hand, when decomposition is performed at high temperature by conventional methods, a decolorization treatment using a high boiling point solvent or a decomposition treatment of the dye using an oxidizing agent is required to obtain a high-purity monomer, which requires complicated steps.

[0140] <<Production method of polyester>> The dicarboxylic acid diester in the polyester decomposition product obtained by the polyester decomposition method according to one embodiment of the present invention can be reused in the production of polyester. For example, Japanese Patent Application Laid-Open No. 2011-26437 discloses that dimethyl terephthalate (DMT), a decomposition product of polyethylene terephthalate, can be reused in the production of polyethylene terephthalate.

[0141] On the other hand, the reactant of the diol and carbonic acid diester in the polyester decomposition product can be converted into diol and carbonic acid diester by reaction with alcohol, and the regenerated carbonic acid diester can be reused in the decomposition of polyester, and the regenerated diol can be reused in the manufacture of polyester. For example, when a polyester having a structure that can be regarded as being derived from ethylene glycol is decomposed, ethylene carbonate is generated as a reactant of ethylene glycol and carbonic acid diester. In "Japanese Patent Gazette No. 4236208", it is disclosed that ethylene carbonate is converted into ethylene glycol and carbonic acid diester by reaction with alcohol.

[0142] Therefore, by utilizing the polyester decomposition method according to one embodiment of the present invention, polyester can be continuously produced in a closed-loop manner in the three chemical reactions of decomposing polyester, regenerating diol and carbonate diester from the reaction product of diol and carbonate diester, and producing polyester by reacting dicarboxylic acid diester with diol, without adding new production raw materials.

[0143] That is, the method for producing polyester according to the present embodiment includes a step of producing polyester using a polyester decomposition product (dicarboxylic acid diester, diol, etc.) obtained by the above-mentioned method for decomposing polyester according to the present embodiment.

[0144] The method for producing polyester according to the present embodiment has high adaptability to recycling of raw materials and can decompose polyester at low temperatures, and therefore has extremely high industrial applicability.

[0145] The continuous production of such a closed-ring polyester is shown by the following formula (chemical reaction formula). That is, according to the present embodiment, in the presence of a base, a polyester represented by the following general formula (1) (sometimes referred to as "polyester (1)" in this specification) and a monohydric alcohol represented by the following general formula (2) (sometimes referred to as "monohydric alcohol (2)" in this specification) react to produce a dicarboxylic acid diester represented by the following general formula (3) (sometimes referred to as "dicarboxylic acid diester (3)" in this specification) and a diol represented by the following general formula (4) (sometimes referred to as "diol (4)" in this specification). Then, by reacting the diol (4) with a carbonic acid diester represented by the following general formula (5) (sometimes referred to as “carbonic acid diester (5)” in the present specification), one or two or more selected from the group consisting of a cyclic compound represented by the following general formula (61) (sometimes referred to as “cyclic compound (61)” in the present specification), a first chain compound represented by the following general formula (62) (sometimes referred to as “first chain compound (62)” in the present specification), and a second chain compound represented by the following general formula (63) (sometimes referred to as “second chain compound (63)” in the present specification) are produced (these cyclic compounds and chain compounds are sometimes collectively referred to as “compound (6)” in the present specification).

[0146] By reacting these compounds (6) with an alcohol represented by the following general formula (7) (sometimes referred to as "alcohol (7)" in this specification), the diol (4) and the carbonic acid diester (5) are regenerated, and the polyester (1) is produced again by reacting the regenerated diol (4) with the dicarboxylic acid diester (3). The regenerated carbonic acid diester (5) can be reused during the depolymerization (decomposition) of the polyester (1).

[0147] [Chemical formula 1]

[0148] (Where X 1 , X 2 are each independently a divalent organic group, R 1 and R 2 Each is independently a monovalent organic group, and n is an integer greater than 2. Here, polyester (1) is the polyester in the polyester-containing material described above. Monohydric alcohol (2) is the monohydric alcohol used in the polyester depolymerization process described above. Dicarboxylic acid diester (3) is the dicarboxylic acid diester, which is one of the main depolymerization products described above. Diol (4) is the diol, which is another main depolymerization product described above. Carbonate diester (5) is the carbonate diester used in the polyester depolymerization process described above. Compound (6) (cyclic compound (61), first chain compound (62) and second chain compound (63)) is the reaction product of carbonate diester and diol generated in the polyester depolymerization process described above. Alcohol (7) is a raw material for regenerating carbonate diester and diol, and determines the structure of carbonate diester.

[0149] Where, X 1 It 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.

[0150] As the preferred X 1 Examples of the aromatic group include benzene-1,4-diyl (1,4-phenylene), naphthalene-2,6-diyl (2,6-naphthylene), furan-2,5-diyl (2,5-furanylene) and the like.

[0151] Where, X 2 It 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.

[0152] As the preferred X 2 Examples of the alkylene group include ethylene (-CH2CH2-), 1,3-propylene (trimethylene, -CH2CH2CH2-), 1,4-butylene (tetramethylene, -CH2CH2CH2CH2-), and the like, and an alkylene group having 2 to 4 carbon atoms is more preferred.

[0153] In the formula, R 1 It is a monovalent organic group and may be, for example, an aromatic group or an aliphatic group, but is preferably an aliphatic group (a saturated aliphatic group or an unsaturated aliphatic group).

[0154] As the preferred R 1 Examples include monovalent saturated aliphatic groups (i.e., alkyl groups) such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and tert-butyl. More preferred are monovalent saturated aliphatic groups (i.e., alkyl groups) having 1 to 4 carbon atoms.

[0155] In the formula, R 2 is a monovalent organic group, as R 2 , we can cite the 1In the formula, n is an integer greater than or equal to 2, and preferably an integer from 20 to 1,000.

[0156] The present invention will be described in more detail below by way of specific examples. However, the present invention is not limited to any of the examples shown below. In addition, the unit "ppm" shown below is all based on mass ratio.

[0157] <<Decomposition of polyester>> <Decomposition of polyester fiber> [Example 1] Sodium methoxide (NaOCH3) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., the same below, 0.58 g, 10.4 mmol, 2.9% by mass relative to the mass of the polyester fiber described below) was added to a 300 mL eggplant-shaped bottle. Methanol (manufactured by Kishida Chemical Co., Ltd., the same below, 13 mL, 51.4% by mass relative to the mass of the polyester fiber described below) and dimethyl carbonate (DMC) (manufactured by Tokyo Chemical Industry Co., Ltd., the same below, 100 mL, 535% by mass relative to the mass of the polyester fiber described below) were further added. The catalyst composition was prepared by uniformly dissolving these ingredients. A white coat for inspection (the proportion of polyester fiber in all fibers was 100% by mass) was cut into a size of about 2 cm × 2 cm, and a plurality of these cut pieces (20 g) were added to the catalyst composition in the eggplant-shaped bottle obtained above.

[0158] Here, the ratio (mass %) of polyester fibers in all fibers is synonymous with the ratio of the content (mass part) of polyester in the polyester-containing material to the total mass (mass part) of the polyester-containing material described above. This also applies to the other examples and comparative examples that follow.

[0159] Then, a magnetic stirrer and an oil bath were used to rotate the stirrer in the eggplant-shaped bottle, and the mixture of the catalyst composition and the cut material was stirred at 50°C for 3 hours to decompose the polyester fiber. Then, dimethyl carbonate (30 mL) was added to the reactant in the eggplant-shaped bottle to dissolve the precipitated target product, and the contents in the eggplant-shaped bottle were maintained at 50°C without cooling and hot filtration was performed. 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).

[0160] The obtained dimethyl terephthalate is treated with 1H NMR (apparatus: Bruker Avance III (registered trademark) 600 MHz manufactured by Bruker Corporation, the same shall apply hereinafter) and gas chromatography (apparatus: GC-2000 manufactured by Shimadzu Corporation, the same shall apply hereinafter) were used to analyze the obtained product, and it was confirmed that dimethyl terephthalate with a purity of 99% by mass or more was obtained. 1 The results of H NMR analysis were Figure 1 The gas chromatography analysis results are shown in Figure 2 Shown in.

[0161] <Decomposition of polyester fibers in mixed fibers containing polyester fibers and cotton> [Example 2] A white coat for chemical experiments (the proportion of polyester fiber in the total fiber is 65% by mass, and the proportion of cotton is 35% by mass) was cut into a size of about 2 cm×2 cm.

[0162] Here, the ratio of cotton in all fibers (mass %) refers to the ratio of the content (mass part) of cotton in the polyester-containing material to the total mass (mass part) of the polyester-containing material. This also applies to other fibers other than cotton in the following other examples.

[0163] Then, the polyester fibers in the cut materials (20 g) were decomposed in the same manner as in Example 1, except that the cut materials (20 g) of the chemical experiment white clothes that had been dried in advance were used instead of the cut materials (20 g) of the inspection white clothes, and the amount of sodium methoxide used was 0.38 g instead of 0.58 g, thereby obtaining dimethyl terephthalate (11.7 g). In this example, the amount of methanol used during the decomposition was 79.1% by mass relative to the amount of the polyester fibers in the mixed fiber.

[0164] The obtained dimethyl terephthalate was treated in the same manner as in Example 1. 1 As a result of H NMR and gas chromatography analysis, the same data as in Example 1 were obtained, and it was confirmed that dimethyl terephthalate having a purity of 99 mass % or more was obtained.

[0165] <Decomposition of polyester fiber in colored fiber containing polyester fiber and colorant> [Example 3] Colored clothing (the ratio of polyester fiber in all fibers is 100% by mass, and contains red, black, blue, etc. dyes) was cut into a size of about 2 cm × 2 cm. The polyester fiber in the cut material was decomposed in the same manner as in Example 1, except that multiple pieces of the colored clothing (20 g) were used instead of the multiple pieces of the white inspection clothing (20 g). Dimethyl terephthalate (18.4 g) was obtained. In this example, the amount of methanol used during the decomposition was 51.4% by mass relative to the amount of polyester fiber in the colored fibers.

[0166] The obtained dimethyl terephthalate was treated in the same manner as in Example 1. 1 H NMR and gas chromatography analysis confirmed that dimethyl terephthalate with a purity of 99% by mass or more was obtained. 1 The results of HNMR analysis were Figure 3 The gas chromatography analysis results are shown in Figure 4 Shown in.

[0167] <Decomposition of polyester fiber in colored fiber containing polyester fiber and colorant> [Example 4] Sodium methoxide (0.29 g, 5.2 mmol, 2.9% by mass relative to the mass of the polyester fiber described below) was added to a 100 mL screw-mouth sample bottle with a flat bottom. Methanol (4 mL, 31.6% by mass relative to the mass of the polyester fiber described below) and dimethyl carbonate (30 mL, 321% by mass relative to the mass of the polyester fiber described below) were further added, and the catalyst composition was prepared by uniformly dissolving these ingredients. Colored clothes (the proportion of polyester fibers in all fibers was 100% by mass, and dyes such as red, black, and blue were contained) were cut into a size of about 2 cm × 2 cm, and a plurality of these cut pieces (10 g) were added to the catalyst composition in the screw-mouth sample bottle obtained above. Using a magnetic stirrer and an oil bath, the stirrer was rotated in the screw-mouth sample bottle, and the mixture of the catalyst composition and the cut pieces was stirred at 70°C for 1 hour, thereby decomposing the polyester fiber. Then, the contents in the screw-mouth sample bottle were maintained at 70°C without cooling, and hot filtration was performed. Methanol (100 mL) was added to the filtrate, and the generated white crystals were filtered, washed with water (50 mL), and dried to obtain dimethyl terephthalate (7.4 g).

[0168] The obtained dimethyl terephthalate was treated in the same manner as in Example 1. 1As a result of H NMR and gas chromatography analysis, the same data as in Example 1 were obtained, and it was confirmed that dimethyl terephthalate having a purity of 99 mass % or more was obtained.

[0169] Furthermore, the total nitrogen content of the obtained dimethyl terephthalate was quantitatively measured by the same method as in Example 3. As a result, the nitrogen content of the dimethyl terephthalate was 19 ppm.

[0170] <Decomposition of polyester fibers in mixed fibers containing polyester fibers, rayon and polyurethane fibers> [Example 5] Mixed fibers (polyester fibers in the total fibers accounted for 54% by mass, rayon fibers accounted for 39% by mass, and polyurethane fibers accounted for 7% by mass) were cut into a size of about 2 cm x 2 cm. The polyester fibers in the cuts (10 g) were decomposed in the same manner as in Example 4, except that the polyester fibers in the cuts (10 g) were replaced with the colored clothing. Thus, dimethyl terephthalate (3.4 g) was obtained. In this example, the amount of methanol used during the decomposition was 58.6% by mass relative to the amount of polyester fibers in the mixed fibers.

[0171] The obtained dimethyl terephthalate was treated in the same manner as in Example 1. 1 As a result of H NMR and gas chromatography analysis, the same data as in Example 1 were obtained, and it was confirmed that dimethyl terephthalate having a purity of 99 mass % or more was obtained.

[0172] <Decomposition of polyester in a single-layer film containing polyester and components other than polyester> [Example 6] The dried composite film (single-layer film containing polyester and components other than polyester) was cut into a size of about 2 cm × 2 cm for the individual packaging film for washed snacks. The polyester in the cut material was decomposed in the same manner as in Example 4, except that multiple cut materials (10 g) of the single-layer film were used instead of the multiple cut materials (10 g) of the colored clothing. Thus, dimethyl terephthalate (3.4 g) was obtained.

[0173] The obtained dimethyl terephthalate was treated in the same manner as in Example 1. 1 As a result of H NMR and gas chromatography analysis, the same data as in Example 1 were obtained, and it was confirmed that dimethyl terephthalate having a purity of 99 mass % or more was obtained.

[0174] <Decomposition of polyester fiber in colored fiber containing polyester fiber and colorant> [Comparative Example 1] The polyester fiber was decomposed in the same manner as in Example 4, except that methanol (34 mL) was used instead of methanol (4 mL) and dimethyl carbonate (30 mL), thereby obtaining dimethyl terephthalate (2.1 g).

[0175] The obtained dimethyl terephthalate was treated in the same manner as in Example 4. 1 The results of H NMR analysis showed that, unlike the case of Example 4, a signal of an oligomer presumed to be an impurity was detected. That is, the obtained dimethyl terephthalate had a low purity.

[0176] [Comparative Example 2] The polyester fiber was decomposed 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), thereby obtaining dimethyl terephthalate (4.6 g).

[0177] The obtained dimethyl terephthalate was treated in the same manner as in Example 4. 1 The results of H NMR analysis showed that, unlike the case of Example 4, a signal of an oligomer presumed to be an impurity was detected. That is, the obtained dimethyl terephthalate had a low purity.

[0178] [Comparative Example 3] The polyester fiber was decomposed in the same manner as in Example 4, except that dimethyl sulfoxide (manufactured by Kishida Chemical Co., Ltd., 30 mL) was used instead of dimethyl carbonate (30 mL), thereby obtaining dimethyl terephthalate (4.0 g).

[0179] The obtained dimethyl terephthalate was treated in the same manner as in Example 4. 1 The results of H NMR analysis showed that, unlike the case of Example 4, a signal of an oligomer presumed to be an impurity was detected. That is, the obtained dimethyl terephthalate had a low purity.

[0180] [Comparative Example 4] Sodium hydroxide (NaOH) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 50 mg, 1.25 mmol, 0.25% by mass relative to the mass of the polyester fiber described below) was added to a 300 mL eggplant-shaped bottle. Ethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (100 mL) was further added, and the catalyst composition was prepared by uniformly dissolving these ingredients. Colored clothes (the proportion of polyester fibers in all fibers was 100% by mass, and dyes such as red, black, and blue were contained) were cut into a size of about 2 cm × 2 cm, and a plurality of these cut pieces (20 g) were added to the catalyst composition in the eggplant-shaped bottle obtained above. Using a magnetic stirrer and an oil bath, the stirrer was rotated in the eggplant-shaped bottle, and the polyester fiber was decomposed by stirring the mixture of the catalyst composition and the cut pieces at 195°C for 5 hours. Then, the reaction product in the eggplant-shaped flask was cooled to 100° C., and the precipitated solid was filtered by hot filtration, washed with water (100 mL), and dried to obtain bis(2-hydroxyethyl)terephthalate (20 g) as a decomposition product.

[0181] The total nitrogen content of the obtained bis(2-hydroxyethyl)terephthalate was quantitatively measured in the same manner as in Example 3. As a result, the nitrogen content of the bis(2-hydroxyethyl)terephthalate was 140 ppm.

[0182] The obtained bis(2-hydroxyethyl)terephthalate was significantly more strongly colored than the dimethyl terephthalate obtained in Examples 1 to 6.

[0183] The results of Examples 1 to 6 and Comparative Examples 1 to 4 were compared in Figure 5 In the figure, "alkali (usage amount (mass %))" means "the ratio of the usage amount (mass part) of the alkali to the amount (mass part) of the polyester in the polyester-containing material". Similarly, "carbonic acid diester (usage amount (mass %))" means "the ratio of the usage amount (mass part) of the carbonic acid diester to the amount (mass part) of the polyester in the polyester-containing material".

[0184] From these results, it is understood that in Examples 1 to 6, the polyester in the polyester-containing material can be decomposed at a low reaction temperature of 50 to 70° C. in a simple process without complicated steps, and a high-purity dicarboxylic acid diester (monomer) can be obtained.

[0185] On the other hand, in Comparative Examples 1 to 3, high-purity dicarboxylic acid diester (monomer) could not be obtained by decomposing the polyester in the polyester-containing material. In Comparative Examples 1 to 3, no carbonic acid diester was used in the decomposition.

[0186] In Comparative Example 4, polyester was decomposed by a typical conventional method, but the reaction temperature was too high and the content of nitrogen component in the dicarboxylic acid diester (monomer) was high, so a high-purity dicarboxylic acid diester could not be obtained.

[0187] From the comparison between Example 4 and Comparative Examples 1 to 3, it can be confirmed that the use of carbonic acid diester promotes the decomposition of polyester and significantly increases the amount of dicarboxylic acid diester produced.

[0188] [Examples 7-9] Using potassium methoxide (KOMe) as a base, methanol (MeOH) as a monohydric alcohol, and dimethyl carbonate (DMC) as a carbonic acid diester, the same operation as in Example 1 (reaction temperature: 50°C, reaction time: 5 hours) was performed to decompose the polyester-containing material, i.e., polybutylene terephthalate (PBT) powder (100 mg). The solution obtained after the reaction was filtered, biphenyl was added as an internal standard, and the product was quantified by analyzing it using gas chromatography ("GC-2000" manufactured by Shimadzu Corporation). The reaction is shown in the following chemical reaction formula. In addition, the amount of methanol added is different in each example.

[0189] [Chemical formula 2]

[0190] These results are Figure 6 As can be seen from the figure, according to the present invention, polybutylene terephthalate can be decomposed in the same manner as polyethylene terephthalate.

[0191] [Example 10] Using sodium methoxide (NaOMe) as a base, methanol (MeOH) as a monohydric alcohol, and dimethyl carbonate (DMC) as a carbonic acid diester, the same operation as in Example 1 (reaction temperature: 50°C, reaction time: 1 hour) was performed to decompose the polyester-containing material, namely polyethylene naphthalate (PEN) powder (100 mg). The solution obtained after the reaction was filtered, biphenyl was added as an internal standard, and the product was quantified by gas chromatography ("GC-2000" manufactured by Shimadzu Corporation). The reaction is shown in the following chemical reaction formula.

[0192] [Chemical formula 3]

[0193] These results are Figure 7 As can be seen from the figure, according to the present invention, polyethylene naphthalate can also be decomposed in the same manner as polyethylene terephthalate.

[0194] [Examples 11-17] The same operation as in Example 1 was performed by changing the type of catalyst (base), reaction temperature and reaction time to decompose the polyester-containing material, namely, polyethylene terephthalate powder. The solution obtained after the reaction was filtered, biphenyl was added as an internal standard, and the product was quantitatively analyzed by gas chromatography ("GC-2000" manufactured by Shimadzu Corporation). The reaction is shown in the following chemical reaction formula.

[0195] [Chemical formula 4]

[0196] These results are Figure 8 As shown in FIG. 1 , it can be seen that polyethylene terephthalate can be decomposed even if the type of base, reaction temperature and reaction time are changed.

[0197] [Examples 18-20] Using K2CO3 as a catalyst (base), the amount of the catalyst was changed, and the same operation as in Example 1 was performed (reaction temperature: 100°C, reaction time: 1 hour) to decompose polyethylene terephthalate powder (100 mg). The solution obtained after the reaction was filtered, biphenyl was added as an internal standard, and the product was quantitatively analyzed by gas chromatography ("GC-2000" manufactured by Shimadzu Corporation). The reaction is shown in the following chemical reaction formula.

[0198] [Chemical formula 5]

[0199] These results are Fig. 9 As shown in FIG. 1 , it can be seen that even when K2CO3 is used as a catalyst (base), polyethylene terephthalate powder can be fully decomposed.

[0200] [Examples 21-23] The same operation as in Example 1 (reaction temperature: 100°C, reaction time: 1 hour) was performed by changing the amount of the solvent, namely methanol and dimethyl carbonate, to decompose polyethylene terephthalate powder (100 mg). The solution obtained after the reaction was filtered, biphenyl was added as an internal standard, and the product was quantitatively analyzed by gas chromatography ("GC-2000" manufactured by Shimadzu Corporation). The reaction is shown in the following chemical reaction formula.

[0201] [Chemical formula 6]

[0202] These results are Fig.10 As shown in FIG. 1 , it can be seen that the polyethylene terephthalate powder can be sufficiently decomposed even when the amounts of methanol and dimethyl carbonate, which are solvents, are changed.

[0203] [Examples 24-25] Water was added and the same operation as in Example 1 was performed (reaction temperature: 100°C, reaction time: 1 hour) to decompose polyethylene terephthalate powder (100 mg). The solution obtained after the reaction was filtered, biphenyl was added as an internal standard, and the product was quantitatively analyzed by gas chromatography ("GC-2000" manufactured by Shimadzu Corporation). The reaction is shown in the following chemical reaction formula.

[0204] [Chemical formula 7]

[0205] These results are combined with those of Example 19. Fig.11 As shown in FIG. 1 , it can be seen that as the amount of water increases, polyethylene terephthalate becomes difficult to decompose.

[0206] [Examples 26-32] A solvent other than methanol and dimethyl carbonate was added, and the same operation as in Example 1 was performed (reaction temperature: 100° C., reaction time: 0.5 hours) to decompose polyethylene terephthalate powder (100 mg). The solution obtained after the reaction was filtered, biphenyl was added as an internal standard, and the product was quantitatively analyzed by gas chromatography (“GC-2000” manufactured by Shimadzu Corporation).

[0207] [Chemical formula 8]

[0208] The result will be Fig.12 As shown in FIG. 1 , it can be seen that the polyethylene terephthalate powder can be decomposed even when a solvent other than methanol and dimethyl carbonate is added.

[0209] [Example 33] K2CO3 was used as a catalyst (base), and the amount of the catalyst was changed to 7.4% by mass relative to the mass of the polyester. The same operation as in Example 1 (reaction temperature: 100°C, reaction time: 3 hours) was carried out to depolymerize a cut piece (1 g) of a white coat for inspection (the proportion of polyester fibers in all fibers was 100% by mass). After the reaction was completed, dimethyl carbonate and methanol were recovered by concentrating the reaction solution, and then the residue was subjected to reduced pressure distillation using a Kugelrohr distillation apparatus to obtain dimethyl terephthalate (0.90 g). According to 1 According to H NMR and gas chromatography, the purity of the obtained dimethyl terephthalate was 99% or more.

[0210] [Example 34] Under the conditions of Example 33, depolymerization of cutouts (1 g) of colored clothing (100% by mass of polyester fibers in all fibers, containing red, black, blue, and other dyes) was performed instead of white inspection clothing (100% by mass of polyester fibers in all fibers). After the reaction was completed, dimethyl carbonate and methanol were recovered by concentrating the reaction solution, and then the residue was subjected to reduced pressure distillation using a Kugelrohr distillation apparatus to obtain dimethyl terephthalate (0.87 g). 1 According to H NMR and gas chromatography, the purity of the obtained dimethyl terephthalate was 99% or more.

[0211] [Example 35] Under the conditions of Example 33, depolymerization of a cut material (1 g) of a white coat for chemical experiments (65% polyester and 35% cotton) was performed instead of a white coat for inspection (100% polyester in all fibers). After the reaction was completed, dimethyl carbonate and methanol were recovered by concentrating the reaction solution, and then the residue was subjected to reduced pressure distillation using a Kugelrohr distillation apparatus to obtain dimethyl terephthalate (0.52 g). 1 According to H NMR and gas chromatography, the purity of the obtained dimethyl terephthalate was 99% or more.

[0212] (Implementation method 2) In the first embodiment, there is no particular limitation on the device used when decomposing polyester. However, in the present embodiment, a method of decomposing polyester using a mechanochemical reaction device will be described.

[0213] <<How to decompose polyester>> The polyester decomposition method of the present embodiment comprises the steps of mixing (mixing) an alkali, 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 reaction device. 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 components other than polyester, and a block containing polyester and components other than polyester.

[0214] According to the decomposition method of the present embodiment, the polyester contained in the polyester-containing material can be decomposed without high temperature, halogenated solvent, excessive organic solvent, and excessive alkali. Moreover, after the decomposition, there is no need to add complicated steps, and the dicarboxylic acid diester as a monomer can be obtained with good yield and high purity as the main depolymerization product (decomposition product). That is, according to the decomposition method of the present embodiment, the polyester contained in the polyester-containing material can be effectively decomposed by a process with a small environmental load, and the dicarboxylic acid diester as a monomer can be obtained with good yield and high purity. Furthermore, at this time, as the polyester-containing material, a polyester-containing material that is different from PET film making and polyester is difficult to decompose at a relatively low temperature in the past can be used.

[0215] In addition, the polyester-containing material, base, monohydric alcohol, carbonic acid diester, solvent, and other components that can be used in this embodiment can be the same as those in the first embodiment.

[0216] <Mechanochemical reaction device> The mechanochemical reaction device used for decomposing polyester is a device for performing a well-known mechanochemical reaction, that is, a device for applying mechanical stress (external force) to a substance to cause a chemical change between the substance and the surrounding substances.

[0217] However, in the present embodiment, a mechanochemical reaction does not necessarily occur during the decomposition of polyester. In the present embodiment, a material in the above-mentioned specific range is used as the polyester-containing material, but by using a mechanochemical reaction device during the decomposition, the polyester can be easily decomposed even when the polyester-containing material as described above is used, which is generally difficult to decompose at a relatively low temperature.

[0218] The mechanochemical reaction device used for decomposing polyester is not particularly limited as long as it can carry out a mechanochemical reaction, and may be a known device. Examples of the mechanochemical reaction device include a container for containing an object to be subjected to a mechanochemical reaction and a stress applying unit (external force applying unit) for applying mechanical stress to the object, and a device having a stress applying unit.

[0219] Examples of the stress applying unit include solids made of hard materials such as metals, which can apply impact or shear to an object undergoing a mechanochemical reaction. Examples of the stress applying unit include spherical or bead-shaped units.

[0220] Examples of the material of the container and the stress applying unit constituting the mechanochemical reaction device include stainless steel (SUS), zirconium oxide (also known as zirconium dioxide), polytetrafluoroethylene, tungsten carbide, and agate.

[0221] In addition, the mechanochemical reaction device is not particularly limited, and may be, for example, any of a batch type device and a continuous type device. More specifically, as the mechanochemical reaction device, for example, a ball mill, a bead mill, a planetary mill, a twin-shaft kneading extruder, etc. may be cited. Among them, the mechanochemical reaction device is preferably a ball mill in terms of high versatility and easier decomposition of polyester.

[0222] <Reaction conditions> The decomposition of the polyester in the polyester-containing material can be performed by preparing a base, a monohydric alcohol, a carbonic acid diester, the polyester-containing material, a solvent as required, and other components as required, and reacting the obtained preparation using a mechanochemical reaction apparatus.

[0223] There is no particular restriction on the order of mixing these raw materials. For example, these raw materials can be mixed in any order. In addition, the raw material composition can be prepared as a mixture of a base, a monohydric alcohol, a carbonic acid diester, a solvent as required, and other components as required (for example, a mixture of all raw materials other than the polyester material), and the raw material composition and the polyester material can be mixed for mixing. In this case, as described below, the amount of the base mixed can be a catalytic amount (the base is a catalyst) (the raw material composition can be a catalyst composition).

[0224] The reaction temperature during the decomposition of polyester can be appropriately adjusted in consideration of the type of raw materials used, etc., and the decomposition can be performed at room temperature (normal temperature) or under heating conditions. In the present embodiment, the decomposition of polyester is fully performed even at room temperature, but it is performed more quickly under heating conditions. When the polyester is decomposed at room temperature (normal temperature), the reaction temperature can be any one of 15 to 25°C, 15 to 20°C, and 20 to 25°C.

[0225] In addition, when the polyester is decomposed under heating conditions, the reaction temperature (reaction temperature of the decomposition step) is not particularly limited as long as it is 30° C. to 150° C., but is more preferably 30° C. to 100° C. By setting the reaction temperature under heating conditions to be above these lower limits, the effect obtained by heating is higher. By setting the reaction temperature under heating conditions to be below these upper limits, excessive heating is suppressed.

[0226] According to the present embodiment, as described above, even when a polyester-containing material is used, which is different from PET film and the like and in which polyester is difficult to decompose at relatively low temperatures in the past, the polyester can be decomposed at a low temperature such as 100° C. or lower. Thus, unlike the case of decomposition at a high temperature (for example, 300° C. or higher), the amount of by-products generated during the decomposition of the polyester can be reduced, and the coloring of the dicarboxylic acid diester (monomer) as the main decomposition product can also be reduced.

[0227] The decomposition of polyester can be carried out under any of normal pressure, reduced pressure and increased pressure. The decomposition of polyester can be carried out under any of air and in an inert gas atmosphere.

[0228] The reaction time for decomposing the polyester can be appropriately adjusted in consideration of other reaction conditions such as reaction temperature, and is not particularly limited. 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.

[0229] In this embodiment, for example, the disappearance of polyester can be judged as the end of polyester decomposition. Therefore, the time required until the polyester disappears can be used as the reaction time of polyester decomposition. The time required until the polyester disappears can also be judged based on, for example, the time required until the mass reduction of the polyester-containing material stops.

[0230] In the mixture immediately after mixing the raw materials, the unreacted polyester-containing material does not dissolve and remains insoluble in other liquid components. Then, in the mixture (reactant) in which polyester decomposition is in progress, typically, both the unreacted polyester-containing material and the polyester-containing material during or after the reaction do not dissolve and remain insoluble in other liquid components. On the other hand, the reactants of polyester decomposition, i.e., diols and dicarboxylic acid diesters, typically dissolve in the liquid components.

[0231] The amount of the polyester-containing material is preferably 5 to 35 g per 1 L of the capacity of the container constituting the mechanochemical reaction device, for example, it may be any one of 5 to 25 g and 5 to 15 g, it may be any one of 8 to 35 g and 15 to 35 g, or it may be 8 to 25 g. By making the amount of the polyester-containing material within such a range, the polyester can be more effectively decomposed. Here, for example, when the mechanochemical reaction device is a ball mill, the container is a grinding tank.

[0232] The number of stress applying units constituting the mechanochemical reaction device is 1 or 2 or more, and can be arbitrarily selected according to the type of stress applying unit without particular limitation. For example, in the case where the mechanochemical reaction device is a ball mill and in the case where it is a planetary mill, the stress applying unit is a ball (crushing ball), and in the case where the mechanochemical reaction device is a bead mill, the stress applying unit is a bead, and the number of balls or beads can be appropriately adjusted according to the capacity of the container constituting the mechanochemical reaction device. For example, the number of balls or beads is preferably a number that makes the total volume of the balls or beads 3 to 30% relative to the capacity of the container, for example, it can be any number of 3 to 20% and 3 to 10%.

[0233] When the mechanochemical reaction device is a twin-screw kneading extruder, the stress applying unit is a screw, and the number of the screws is two.

[0234] In addition, when the mechanochemical reaction device is a ball mill or a planetary mill, the total volume of the stress applying units constituting the mechanochemical reaction device is preferably 1000 to 7000 mm2 per 1 g of the polyester-containing material. 3 , for example, it can be 1000~5500mm 3 and 1000~4000mm 3 Any one of them can be 3000~7000mm 3 and 5500~7000mm 3 Any one of the above can also be 3000~5500mm 3 Here, the total volume of the stress applying units refers to the total value of the volumes of all the stress applying units.

[0235] When the mechanochemical reaction device is a ball mill, the vibration frequency when it is operated to stir the preparation is preferably 15 to 40 Hz, for example, it can be any one of 15 to 27 Hz and 15 to 23 Hz, it can be any one of 23 to 40 Hz and 28 to 40 Hz, or it can be 23 to 27 Hz.

[0236] <Post-processing conditions, removal conditions> After the above-mentioned polyester decomposition process is completed, a post-treatment is performed by a known method to obtain a dicarboxylic acid diester, which is one of the main decomposition products, at a high purity. For example, after the polyester is decomposed, the obtained reaction product is filtered, the volatile components are distilled off (concentrated), etc., and the obtained solid is washed with water, methanol, or water and methanol, so that a high-purity dicarboxylic acid diester can be obtained. The obtained dicarboxylic acid diester can be further refined by crystallization (crystallization), distillation, etc. as needed.

[0237] The reaction product of the diol and the carbonic acid diester, which is another main decomposition product, can also be taken out in the same manner as in the case of the dicarboxylic acid diester by appropriately adjusting the post-treatment conditions and the taking-out conditions.

[0238] According to the present embodiment, as described above, since the polyester can be decomposed at a low temperature such as 100°C or lower, the impurity content and coloration of the dicarboxylic acid diester can be reduced, unlike the case where the polyester is decomposed at a high temperature. Therefore, it is not necessary to add a complicated process, and a dicarboxylic acid diester (monomer) with high purity and suppressed coloration can be obtained by a simplified process such as washing with water, methanol, etc. as described above. 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 a simplified process such as washing with water, methanol, etc. as described above.

[0239] On the other hand, when polyester is decomposed at high temperature by conventional methods, a decolorization treatment using a high boiling point solvent or a decomposition treatment of the dye using an oxidizing agent is required to obtain a high-purity monomer, which requires complicated steps.

[0240] Furthermore, by using the polyester production method of the first embodiment, it is of course possible to produce polyester using the polyester decomposition product (dicarboxylic acid diester, diol) obtained by the polyester decomposition method of the present embodiment.

[0241] Hereinafter, the invention of this embodiment will be described in more detail by using specific examples. In addition, polyethylene terephthalate (PET) is used as polyester. However, the invention of this embodiment is not limited to any of the examples shown below.

[0242] <<Decomposition of polyester>> <Decomposition of polyester fiber> [Example 36] A white test coat (the ratio of polyester fibers in all fibers was 100% by mass) was cut into a size of about 2 cm×2 cm, and a plurality of these cut pieces (0.1 g) were placed in a 10 mL stainless steel grinding pot.

[0243] Here, the ratio (mass %) of polyester fibers in all fibers is synonymous with the ratio of the content (mass part) of polyester in the polyester-containing material to the total mass (mass part) of the polyester-containing material described above. This also applies to the other examples and comparative examples that follow.

[0244] Furthermore, sodium methoxide (NaOCH3) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., the same below, 1.4 mg, 0.026 mmol, 1.4% by mass relative to the mass of the polyester fiber), methanol (CH3OH) (manufactured by Kishida Chemical Co., Ltd., the same below, 0.02 mL, 15.8% by mass relative to the mass of the polyester fiber), dimethyl carbonate (DMC) (manufactured by Tokyo Chemical Industry Co., Ltd., the same below, 0.2 mL, 214% by mass relative to the mass of the polyester fiber) and a stainless steel (SUS) grinding ball (10 mm in diameter, 1 piece) were put into the grinding pot and the lid was closed to seal the preparation. The grinding pot was set and fixed in a ball mill reaction device ("MM400" manufactured by Retsch, the same below), and the preparation was stirred at a vibration frequency of 25 Hz for 10 minutes at room temperature to decompose the polyester fiber. Then, dimethyl carbonate (10 mL) was added to the reaction product in the grinding tank to dissolve the precipitated target product, and the obtained liquid was filtered to obtain a dimethyl terephthalate solution.

[0245] Biphenyl was added to the obtained solution as an internal standard, and the solution was analyzed by gas chromatography ("GC-2000" manufactured by Shimadzu Corporation) to confirm that dimethyl terephthalate and ethylene carbonate were obtained, and the dimethyl terephthalate and ethylene carbonate were quantified. As a result, the yield of dimethyl terephthalate was 88%, and the yield of ethylene carbonate was 73%.

[0246] [Example 37] Dimethyl terephthalate (yield 88%) and ethylene carbonate (yield 72%) were obtained in the same manner as in Example 36, except that potassium methoxide (KOCH3) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 1.8 mg, 0.026 mmol, 1.8% by mass relative to the mass of the polyester fiber) was used instead of sodium methoxide.

[0247] [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 0.01 mL instead of 0.02 mL.

[0248] [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 0.03 mL instead of 0.02 mL.

[0249] [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 0.04 mL instead of 0.02 mL.

[0250] [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 decomposition was 0.1 mL instead of 0.2 mL.

[0251] [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 decomposition was 0.4 mL instead of 0.2 mL.

[0252] [Example 43] Dimethyl terephthalate (yield 87%) and ethylene carbonate (yield 72%) were obtained in the same manner as in Example 36, except that 10 stainless steel grinding balls with a diameter of 5 mm were used instead of one stainless steel grinding ball with a diameter of 10 mm.

[0253] [Example 44] Dimethyl terephthalate (yield 61%) and ethylene carbonate (yield 49%) were obtained by the same method as in Example 36, except that a 10 mL zirconium oxide (ZrO2) crushing jar was used instead of a 10 mL stainless steel crushing jar, and a 10 mm diameter zirconium oxide crushing ball was used instead of a 10 mm diameter stainless steel crushing ball.

[0254] [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 during stirring of the preparation was 20 Hz instead of 25 Hz.

[0255] [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 during stirring of the preparation was 30 Hz instead of 25 Hz.

[0256] [Example 47] Dimethyl terephthalate (yield 52%) and ethylene carbonate (yield 41%) were obtained in the same manner as in Example 36 except that the stirring time of the preparation was 5 minutes instead of 10 minutes.

[0257] [Example 48] Dimethyl terephthalate (yield 90%) and ethylene carbonate (yield 68%) were obtained in the same manner as in Example 36 except that the stirring time of the preparation was 15 minutes instead of 10 minutes.

[0258] [Example 49] Dimethyl terephthalate (yield 95%) and ethylene carbonate (yield 78%) were obtained in the same manner as in Example 36 except that the stirring time of the preparation was 20 minutes instead of 10 minutes.

[0259] [Comparative Example 5] The polyester fiber was attempted to be decomposed in the same manner as in Example 36 except that sodium methoxide was not used. However, the polyester fiber could not be decomposed and dimethyl terephthalate and ethylene carbonate were not generated (yield 0%).

[0260] [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 instead of methanol (0.02 mL) and dimethyl carbonate (0.2 mL).

[0261] [Comparative Example 7] Dimethyl terephthalate (yield 22%) was obtained in the same manner as in Example 36 except that toluene (manufactured by Kishida Chemical Co., Ltd., 0.2 mL) was used instead of dimethyl carbonate (0.2 mL). Ethylene carbonate was not obtained.

[0262] [Reference Example 1] A white test coat (polyester fiber ratio in all fibers: 100 mass %) was cut into pieces of approximately 2 cm×2 cm, and a plurality of these cut pieces (0.1 g) were placed in a 2 mL screw-top sample bottle with a flat bottom.

[0263] Furthermore, sodium methoxide (1.4 mg, 0.026 mmol, 1.4% by mass relative to the mass of the polyester fiber), methanol (0.02 mL, 15.8% by mass relative to the mass of the polyester fiber) and dimethyl carbonate (0.2 mL, 214% by mass relative to the mass of the polyester fiber) were added to the inside of the screw-mouth sample bottle. A magnetic stirrer and an aluminum block heater were used to rotate the stirrer inside the screw-mouth sample bottle, and the polyester fiber was decomposed by stirring the formulation at 50° C. for 10 minutes. Then, dimethyl carbonate (10 mL) was added to the reactant inside the screw-mouth sample bottle to dissolve the precipitated target, and the obtained liquid was filtered to obtain a solution of dimethyl terephthalate.

[0264] The obtained solution was analyzed by the same method as in Example 36. The results showed that the yield of dimethyl terephthalate was 23% and the yield of ethylene carbonate was 32%.

[0265] [Example 50] A white test coat (the ratio of polyester fiber in all fibers was 100 mass %) was cut into a size of about 2 cm×2 cm, and a plurality of these cut pieces (1 g) were placed in a 50 mL stainless steel grinding pot.

[0266] Furthermore, sodium methoxide (14 mg, 0.5 mmol, 1.4% by mass relative to the mass of the polyester fiber), methanol (0.2 mL, 15.8% by mass relative to the mass of the polyester fiber), dimethyl carbonate (1.5 mL, 160% by mass relative to the mass of the polyester fiber) and stainless steel crushing balls (10 mm in diameter, 5 pieces) were put into the crushing tank and the lid was closed to seal the formulation. The crushing tank was set and fixed in the ball mill reaction device, and the polyester fiber was decomposed by stirring the formulation at a vibration frequency of 25 Hz for 15 minutes at room temperature. Then, dimethyl carbonate (30 mL) was added to the reactant inside the crushing tank to dissolve the precipitated target, and the obtained liquid was filtered to obtain a solution of dimethyl terephthalate as a filtrate. The filtrate was concentrated under reduced pressure, and dimethyl terephthalate (yield 0.90 g, yield 86%) was obtained by washing the residue with water (20 mL) and methanol (10 mL) and drying.

[0267] The obtained dimethyl terephthalate is treated with 1 H NMR (apparatus: Bruker Avance III (registered trademark) 600 MHz manufactured by Bruker Corporation, the same shall apply hereinafter) and gas chromatography (apparatus: GC-2000 manufactured by Shimadzu Corporation, the same shall apply hereinafter) were used to analyze the product, and it was confirmed that dimethyl terephthalate with a purity of 99% by mass or more was obtained. 1 The results of H NMR analysis were Fig.13 The gas chromatography analysis results are shown in Fig.14 Shown in.

[0268] <Decomposition of polyester fibers in mixed fibers containing polyester fibers and cotton> [Example 51] A white coat for chemical experiments (the proportion of polyester fiber in the total fiber is 65% by mass, and the proportion of cotton is 35% by mass) was cut into a size of about 2 cm×2 cm.

[0269] Here, the ratio of cotton in all fibers (mass %) refers to the ratio of the content (mass part) of cotton in the polyester-containing material to the total mass (mass part) of the polyester-containing material. This also applies to other fibers other than cotton in the following other examples.

[0270] Next, except that multiple cut pieces (1 g) of the chemical experiment white coat were used instead of the multiple cut pieces (1 g) of the inspection white coat and the amount of sodium methoxide used was set to 30 mg instead of 14 mg, the polyester fiber in the cut pieces was decomposed in the same manner as in Example 50, thereby obtaining dimethyl terephthalate (yield 0.56 g, yield 86%).

[0271] The obtained dimethyl terephthalate was treated in the same manner as in Example 50. 1 H NMR and gas chromatography analysis confirmed that dimethyl terephthalate with a purity of 99% by mass or more was obtained. 1 The results of H NMR analysis were Fig.15 The gas chromatography analysis results are shown in Fig.16 Shown in.

[0272] <Decomposition of polyester fiber in colored fiber containing polyester fiber and colorant> [Example 52] Colored clothing (polyester fiber ratio in all fibers is 100% by mass, containing red, black, blue, etc. dyes) was cut into a size of about 2 cm×2 cm. The polyester fiber in the cut pieces (1 g) was decomposed in the same manner as in Example 43, except that the cut pieces (1 g) of the colored clothing were used instead of the cut pieces (1 g) of the above-mentioned white inspection clothing, thereby obtaining dimethyl terephthalate (yield 0.75 g, yield 73%).

[0273] The obtained dimethyl terephthalate was treated in the same manner as in Example 50. 1 H NMR and gas chromatography analysis confirmed that dimethyl terephthalate with a purity of 99% by mass or more was obtained. 1 The results of H NMR analysis were Fig.17 The gas chromatography analysis results are shown in Fig.18 Shown in.

[0274] <Decomposition of polyester fibers in mixed fibers containing polyester fibers and polyurethane fibers> [Example 53] Mixed fibers (87% by mass of polyester fibers and 13% by mass of polyurethane fibers in the total fibers) were cut into a size of about 2 cm×2 cm. The polyester fibers in the cut fibers were decomposed in the same manner as in Example 50, except that multiple cut fibers (1 g) of the mixed fibers were used instead of the multiple cut fibers (1 g) of the white inspection clothing and the amount of sodium methoxide used was 30 mg instead of 14 mg, thereby obtaining dimethyl terephthalate (yield 0.62 g, yield 70%).

[0275] The obtained dimethyl terephthalate was treated in the same manner as in Example 50. 1H NMR and gas chromatography analysis confirmed that dimethyl terephthalate with a purity of 99% by mass or more was obtained. 1 The results of H NMR analysis were Fig.19 The gas chromatography analysis results are shown in Fig. 20 Shown in.

[0276] The decomposition conditions in Examples 36 to 49 were Fig.21 It is shown that the decomposition conditions in Comparative Examples 5 to 7, Reference Example 1 and Examples 50 to 53 are Fig. 22 In addition, the results of Examples 36 to 53, Comparative Examples 5 to 7 and Reference Example 1 are shown in Fig.23 are shown together.

[0277] In addition, Fig.21 and Fig. 22 In the text, “alkali (usage amount (mass %))” means “the ratio of the usage amount (mass parts) of the alkali to the amount (mass parts) of the polyester in the polyester-containing material”. Similarly, “carbonic acid diester (usage amount (mass %))” means “the ratio of the usage amount (mass parts) of the carbonate diester to the amount (mass parts) of the polyester in the polyester-containing material”. Similarly, “monohydric alcohol (usage amount (mass %))” means “the ratio of the usage amount (mass parts) of the monohydric alcohol to the amount (mass parts) of the polyester in the polyester-containing material”.

[0278] As can be seen from these figures, in Examples 36 to 49, the polyester in the polyester-containing material can be obtained in good yield at room temperature through a process with low environmental load without using materials with high environmental load such as halogenated solvents, organic solvents and excessive bases.

[0279] In Examples 50 to 53, compared with Examples 36 to 49, the amount of polyester-containing material (polyester) used was increased, and the decomposition of polyester was carried out on a larger scale, but dicarboxylic acid diesters were obtained at a yield equal to or higher than that of Examples 36 to 49, and the purity of the obtained dicarboxylic acid diesters was a high purity of 99% by mass or more.

[0280] Therefore, although the dicarboxylic acid diester was not taken out in Examples 36 to 49, which made the decomposition of the polyester easier to proceed due to the smaller scale than in Examples 50 to 53, it can be seen that the dicarboxylic acid diester can be taken out with the same high purity as in Examples 50 to 53. Furthermore, in Examples 50 to 53, such a high-purity dicarboxylic acid diester can be obtained only by a simple process of concentrating the reaction solution under reduced pressure, washing with water, and drying, without complicated processes.

[0281] As described above, it was confirmed from Examples 36 to 53 that according to the present 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 load.

[0282] On the other hand, in Comparative Examples 5 to 7 and Reference Example 1, the dicarboxylic acid diester (monomer) could not be obtained at a good yield by decomposing the polyester in the polyester-containing material, and the polyester could not be effectively decomposed.

[0283] In Comparative Example 5, no alkali was used for decomposition of polyester. In Comparative Examples 6 and 7, no carbonate diester was used for decomposition of polyester. In Reference Example 1, no ball mill was used for decomposition of polyester.

[0284] (Other Implementation Methods) <Method for recovering polyester decomposition products> In the above-mentioned embodiment, the recovery method of dimethyl terephthalate (generated by decomposition of PET), dimethyl 2,6-naphthalene dicarboxylate (generated by decomposition of PEN), and dimethyl 2,5-furan dicarboxylate (generated by decomposition of PEF) as one of the polyester decomposition products is not particularly limited, but these substances obtained by the polyester decomposition method of the present invention can be easily separated by distillation (including sublimation refining). As a result, dimethyl terephthalate, dimethyl 2,6-naphthalene dicarboxylate, and dimethyl 2,5-furan dicarboxylate obtained by the polyester decomposition method of the present invention can be recovered with high purity (99.0 to 99.9%).

[0285] That is, after decomposing the polyester-containing material using the polyester decomposition method of the present invention, dimethyl terephthalate can be recovered with high purity (99.0 to 99.9%) by directly distilling (including sublimation refining) the obtained solution containing the polyester decomposition product (distillation step). In addition, the distillation (including sublimation refining) can use a commercially available general distiller or sublimator.

[0286] Here, 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, but may be atmospheric pressure, preferably 5 to 5000 Pa, and more preferably 8 to 4000 Pa.

[0287] [Examples 51 to 53] As shown in the following three chemical reaction formulas, after obtaining a polyester decomposition product (solution) containing dimethyl terephthalate using the above polyester decomposition method, the polyester decomposition product is directly distilled.

[0288] [Chemical formula 9]

[0289] [Chemical formula 10]

[0290] [Chemical formula 11]

[0291] As described above, it is understood that high-purity dimethyl terephthalate can be obtained simply by distilling the polyester decomposition product (solution) containing dimethyl terephthalate obtained by the polyester decomposition method of the present invention.

[0292] (Citation based on references of 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 herein by reference.

Claims

1. A polyester decomposition method for decomposing polyester contained in a polyester-containing material, characterized in that: The method comprises a decomposition step of mixing an alkali, a monohydric alcohol and a carbonic acid diester to decompose the polyester.

2. The polyester decomposition method according to claim 1, characterized in that: The reaction temperature of the decomposition step is in the range of 20°C to 150°C.

3. The polyester decomposition method according to claim 1 or 2, characterized in that: The base is an alkali metal carbonate, an alkali metal hydroxide or an alkali metal alkoxide.

4. The polyester decomposition method according to claim 1 or 2, characterized in that: The monohydric alcohol is methanol.

5. The polyester decomposition method according to claim 1 or 2, characterized in that: The carbonic acid diester is dimethyl carbonate.

6. The polyester decomposition method according to claim 1 or 2, characterized in that: In the decomposition step, the alkali, the monohydric alcohol, and the carbonic acid diester are mixed using a mechanochemical reaction device to decompose the polyester.

7. The polyester decomposition method according to claim 6, characterized in that: The reaction temperature of the decomposition step is in the range of 30°C to 100°C.

8. The polyester decomposition method according to claim 6, characterized in that: The mechanochemical reaction device is a ball mill.

9. The polyester decomposition method according to claim 1 or 2, characterized in that: The polyester-containing material includes at least one of polyester fibers and films composed of polyester.

10. The polyester decomposition method according to claim 1 or 2, characterized in that: The polyester-containing material includes substances other than polyester.

11. A method for producing polyester, characterized in that: The polyester is produced by using the polyester decomposition product obtained by the polyester decomposition method according to claim 1 or 2.

12. A method for recovering a polyester decomposition product, comprising recovering a predetermined polyester decomposition product from the polyester decomposition product obtained by the polyester decomposition method according to claim 1 or 2, characterized in that: The polyester decomposition product is dimethyl terephthalate, dimethyl 2,6-naphthalene dicarboxylate or dimethyl 2,5-furan dicarboxylate. The method comprises a distillation step of distilling the polyester decomposition product.

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