Method for producing polyester

Abstract

Provided is a novel method for producing a polyester, comprising the step of condensation polymerization of a starting material containing a carbonic acid ester and at least one compound selected from a dicarboxylic acid ester and a dicarboxylic acid.

Description

Polyester manufacturing method

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

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

[0003] As a method for depolymerizing polyester, Patent Document 1 discloses a catalyst composition containing a base catalyst, a monohydric alcohol, and a carbonate diester or a tetraalkoxysilane as a glycol scavenger, and a method for depolymerizing polyester using the catalyst composition, while Patent Document 2 discloses a method for decomposing polyester using a base, a monohydric alcohol, and a carbonate diester.

[0004] JP 2022-126617 A International Publication No. 2024 / 034609

[0005] According to the polyester decomposition method disclosed in the above-mentioned Patent Document 2, it is disclosed that a dicarboxylic acid diester and a glycol carbonate ester, which are monomers, can be obtained by decomposing a polyester using a base, a monohydric alcohol, and a carbonate diester. Meanwhile, a method of producing a polyester by dehydration condensation of a dicarboxylic acid and a diol is generally known.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a novel method for producing polyester.

[0007] As a result of extensive research, the inventors have found that the above-mentioned problems can be solved by a method for producing a polyester, comprising a step of condensation polymerizing a raw material containing a glycol carbonate ester and one or more selected from a dicarboxylic acid ester and a dicarboxylic acid. Specifically, the present invention provides the following aspects [1] to

[20] . [1] A method for producing a polyester, comprising a step of condensation polymerizing a raw material containing a glycol carbonate ester and one or more selected from a dicarboxylic acid ester and a dicarboxylic acid. [2] A method for producing a polyester according to the above [1], wherein at least a portion of the glycol carbonate ester is derived from a polyester. [3] A method for producing a polyester according to the above [1] or [2], wherein at least a portion of the one or more selected from a dicarboxylic acid ester and a dicarboxylic acid is a dicarboxylic acid ester derived from a polyester. [4] A method for producing a polyester according to any one of the above [1] to [3], wherein the molar ratio of the glycol carbonate ester to the one or more selected from a dicarboxylic acid ester and a dicarboxylic acid is 0.90 to 1.10. [5] A method for producing a polyester according to any one of the above [1] to [4], wherein the glycol carbonate ester includes a cyclic carbonate ester. [6] The method for producing a polyester according to any one of [1] to [5] above, wherein the glycol carbonate ester is ethylene carbonate, and the one or more selected from dicarboxylic acid esters and dicarboxylic acids are one or more selected from monoesters and diesters of dicarboxylic acids selected from phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, and furandicarboxylic acid. [7] The method for producing a polyester according to any one of [1] to [6] above, further comprising removing at least a portion of the resulting dicarboxylic acid carbonate. [8] The method for producing a polyester according to any one of [1] to [7] above, wherein the reaction temperature in the condensation polymerization step is in the range of 50°C to 350°C. [9] The method for producing a polyester according to any one of [1] to [8] above, wherein the condensation polymerization step is carried out in a reduced pressure environment of -10 kPaG or less.

[10] The method for producing a polyester according to any one of [1] to [9] above, further comprising the step of contacting a polyester-containing material containing a polyester with a base, a monohydric alcohol, and a carbonate diester to decompose the polyester and obtain a decomposition product containing the glycol carbonate ester and the dicarboxylate ester.

[11] The method for producing a polyester according to

[10] above, further comprising purifying the decomposition product by at least one of distillation and crystallization and using the purified product as the glycol carbonate ester and dicarboxylate ester in the condensation polymerization step.

[12] The method for producing a polyester according to

[10] or

[11] above, wherein the reaction temperature in the step of obtaining the decomposition product is in the range of 20°C to 150°C.

[13] The method for producing a polyester according to any one of

[10] to

[12] above, wherein the monohydric alcohol in the step of obtaining the decomposition product is methanol.

[14] The method for producing a polyester according to any one of

[10] to

[13] above, wherein the base in the step of obtaining the decomposition product is one or more selected from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, nitrogen-containing organic bases, and alkali metal phosphates.

[15] The method for producing a polyester according to any one of

[10] to

[14] above, wherein the base is potassium phosphate.

[16] The method for producing a polyester according to any one of

[10] to

[15] above, wherein the polyester is one or more selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and polyethylene furanoate.

[17] The method for producing a polyester according to any one of

[10] to

[16] above, wherein the polyester-containing material further contains one or more selected from the group consisting of cotton, rayon, polyurethane, nylon, acrylic, polyethylene, polypropylene, carbon-based materials, dyes, and pigments.

[18] A method for producing a polyester, comprising the steps of contacting a polyester-containing material containing a polyester with a base, a monohydric alcohol, and a carbonate diester to decompose the polyester and obtain a decomposition product containing a glycol carbonate ester and a dicarboxylic acid ester, and condensation polymerizing a raw material containing the glycol carbonate ester and the dicarboxylic acid ester while removing at least a portion of the resulting carbonate diester, wherein the carbonate diester removed in the condensation polymerization step is used as the carbonate diester in the step of obtaining the decomposition product.

[19] A method for producing a carbonate diester, comprising condensation polymerizing a raw material containing a glycol carbonate ester and a dicarboxylic acid ester.

[20] A method for producing a carbonate diester according to

[19] above, further comprising the step of contacting a polyester-containing material containing a polyester with a base, a monohydric alcohol, and a carbonate diester to decompose the polyester and obtain a decomposition product containing the glycol carbonate ester and the dicarboxylic acid ester.

[0008] According to the present invention, a novel method for producing polyester can be provided.

[0009] [Method for Producing Polyester] Hereinafter, an embodiment of the method for producing polyester according to the present invention will be described, but the present invention is not limited to the following embodiment.

[0010] A method for producing a polyester according to one embodiment of the present invention includes a step of condensation polymerizing a raw material containing a carbonate ester of a glycol and one or more selected from a dicarboxylic acid ester and a dicarboxylic acid. The production method according to this embodiment can provide a novel method for producing a polyester.

[0011] <<Condensation Polymerization Step>> The polyester of this embodiment can be produced by a conventionally known transesterification or esterification method using a raw material containing a glycol carbonate ester and one or more selected from a dicarboxylic acid ester and a dicarboxylic acid. For example, a production method (transesterification method) can be used in which a raw material containing a glycol carbonate ester and one or more selected from a dicarboxylic acid ester and a dicarboxylic acid is subjected to a transesterification reaction in the presence of a transesterification catalyst, and the resulting reaction product is further polycondensed at high temperature, in a high vacuum (reduced pressure), and under melting conditions. Alternatively, a production method (esterification method) can be used in which a raw material containing a glycol carbonate ester and one or more selected from a dicarboxylic acid ester and a dicarboxylic acid is subjected to an esterification reaction, and the resulting reaction product is further polycondensed at high temperature, in a high vacuum (reduced pressure), and under melting conditions. Furthermore, the poly(alkylene dicarboxylate ester) obtained by the melt polymerization reaction in the condensation polymerization step is pelletized, and then, if necessary, the production method of the polyester of this embodiment may include a step of performing a solid-state polymerization reaction to further increase the molecular weight or reduce impurities such as oligomers. As for the method for carrying out the condensation polymerization reaction in the step of carrying out the solid-state polymerization reaction, any known method for solid-state polymerization reaction may be adopted.

[0012] <Dicarboxylic Acid Esters and Dicarboxylic Acids> Specific examples of the dicarboxylic acids include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, and furandicarboxylic acid, as well as various aliphatic dicarboxylic acids. Examples of the dicarboxylic acid esters include monoesters and diesters of the dicarboxylic acids described above. Furthermore, dicarboxylic acid esters having 10 to 20 carbon atoms are preferably used. It is preferable that at least a portion of the dicarboxylic acid esters and dicarboxylic acids be dicarboxylic acid esters derived from polyesters, and more preferably dicarboxylic acid esters obtained by decomposing polyesters.

[0013] <Glycol Carbonate> The glycol carbonate may be a cyclic carbonate, a chain carbonate, or a mixture thereof, but a cyclic carbonate is preferred. As the cyclic carbonate, one represented by the following general formula (1) is preferred, and ethylene carbonate is more preferred.

[0014] (In the formula, X １ is a divalent organic group.

[0015] Above X １ The divalent organic group represented by the formula (I) may be, for example, an aromatic group, an aliphatic group, or a group having both an aromatic group and an aliphatic group, and is preferably a divalent hydrocarbon group. Preferred divalent organic groups include, for example, an ethylene group (—CH ２ CH ２ -), 1,2-propylene group, 1,3-propylene group (trimethylene group, -CH ２ CH ２ CH ２ -), 1,2-butylene group, 1,3-butylene group, 1,4-butylene group (tetramethylene group, -CH ２ CH ２ CH ２ CH ２ -), and alkylene groups having 2 to 4 carbon atoms are more preferred.

[0016] Examples of the chain carbonate ester include glycol alkyl carbonate esters represented by the following general formula (2), diglycol carbonate esters represented by the following general formula (3), and glycol dicarbonate esters represented by the following general formula (4). Mixtures of these may also be used.

[0017] (In the formula, X ２ ~X ５ are each independently a divalent organic group, and R １ ~R ３ are each independently a monovalent organic group. ２ ~X ５The divalent organic group represented by the formula (I) may be, for example, an aromatic group, an aliphatic group, or a group having both an aromatic group and an aliphatic group, and is preferably a divalent hydrocarbon group. Preferred divalent organic groups include, for example, an ethylene group (—CH ２ CH ２ -), 1,3-propylene group (trimethylene group, -CH ２ CH ２ CH ２ -), 1,4-butylene group (tetramethylene group, -CH ２ CH ２ CH ２ CH ２ -), and alkylene groups having 2 to 4 carbon atoms are more preferred. １ ~R ３ The monovalent organic group represented by the formula (I) may be, for example, either an aromatic group or an aliphatic group, but is preferably an aliphatic group (a saturated aliphatic group or an unsaturated aliphatic group), and more preferably an aliphatic hydrocarbon group. Preferred monovalent organic groups include, for example, monovalent saturated aliphatic groups (i.e., alkyl groups) such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group, and is more preferably a monovalent saturated aliphatic group (i.e., alkyl group) having 1 to 4 carbon atoms.

[0018] The glycol carbonate ester is preferably derived from polyester, and more preferably obtained by decomposing polyester.

[0019] The molar ratio of the amounts of glycol carbonate ester and one or more selected from dicarboxylic acid esters and dicarboxylic acids used in the raw materials for the condensation polymerization step can be appropriately selected depending on the target molecular weight of the polyester obtained by condensation polymerization. Typically, the ratio of the amounts of glycol carbonate ester and one or more selected from dicarboxylic acid esters and dicarboxylic acids used is preferably 0.90 to 1.10, more preferably 0.95 to 1.05, in terms of molar ratio. By keeping the molar ratio of the amounts of carbonate ester and one or more selected from dicarboxylic acid esters and dicarboxylic acids used within the above range, the molecular weight of the polyester obtained by condensation polymerization can be controlled within an appropriate range, and excessive use of raw materials can be suppressed.

[0020] Furthermore, in the polyester production method of this embodiment, the raw material may further contain a glycol compound. When the raw material contains the glycol compound, the molar ratio of the total amount of one or more selected from dicarboxylic acid esters and dicarboxylic acids to the total amount of glycol carbonate ester and glycol is 0.50 to 2.0, preferably 0.90 to 1.10, and more preferably 0.95 to 1.05. In this case, the content of the glycol compound per 100 parts by mass of glycol carbonate ester in the raw material is preferably 0.01 to 100,000 parts by mass, more preferably 1 to 10,000 parts by mass. Examples of the glycol compound include alkylene glycols, such as ethylene glycol, 1,3-propanediol (1,3-propylene glycol, trimethylene glycol), 1,2-propanediol, 1,4-butanediol (tetramethylene glycol), neopentylene glycol, and hexamethylene glycol. Among these, it is particularly preferred when ethylene glycol is the main target, and in this case, for example, alkylene glycols such as 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, hexamethylene glycol, decamethylene glycol, cyclohexanedimethanol, diethylene glycol, triethylene glycol, poly(oxy)ethylene glycol, polytetramethylene glycol, polymethylene glycol, etc. may be used alone or in combination, and can be selected arbitrarily depending on the purpose. Furthermore, as long as the polymer chain constituting the obtained polyester is substantially linear, the raw material may further contain a polyfunctional compound having a valence of three or more, such as glycerin, trimethylolpropane, pentaerythritol, etc., and may also contain a monofunctional compound, such as decyl alcohol, dodecyl alcohol, 2-phenylethanol, etc., as necessary.

[0021] <Removal of Carbonate Diester> In the condensation polymerization step, a carbonate diester is produced during the condensation polymerization. By removing this, the equilibrium reaction can be shifted, allowing for more efficient production of polyester. That is, the condensation polymerization step is preferably carried out while removing at least a portion of the produced carbonate diester. The specific method for removing the carbonate diester is not particularly limited, but it can be carried out, for example, by reducing the pressure in the condensation polymerization reaction step. More specifically, the condensation polymerization can be carried out while removing the carbonate diester from the reactor of the condensation polymerization step. Furthermore, in the present invention, it is preferable to utilize the carbonate diester removed from the reactor of the condensation polymerization step in the step of obtaining a decomposition product, which will be described later. Furthermore, in the present invention, the carbonate diester removed from the reactor of the condensation polymerization step can be purified as needed to produce a product.

[0022] The reaction temperature in the condensation polymerization step can be adjusted appropriately taking into account the types of raw materials used, etc., and is preferably carried out under heated conditions. The equipment used for heating is not particularly limited, and equipment such as a heater can be used. The reaction temperature in the condensation polymerization step is preferably within the range of 50°C to 350°C, more preferably within the range of 70 to 300°C, and even more preferably within the range of 90 to 250°C.

[0023] The condensation polymerization step may be carried out under normal pressure, reduced pressure, or increased pressure. From the viewpoint of removing at least a portion of the carbonate diester produced as described above, the step is preferably carried out under a reduced pressure environment of -10 kPaG or less, more preferably under a reduced pressure environment of -30 kPaG or less, and even more preferably under a reduced pressure environment of -50 kPaG or less.

[0024] The reaction time of the condensation polymerization step can be appropriately adjusted in consideration of other reaction conditions such as the reaction temperature, and is not particularly limited. However, it is preferably 0.5 to 24 hours, more preferably 0.5 to 12 hours, and even more preferably 1 to 8 hours.

[0025] <Catalysts, etc.> In the condensation polymerization step, it is preferable to use a condensation polymerization catalyst and, if necessary, a stabilizer. These catalysts and stabilizers can be those known for use in the condensation polymerization of polybutylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, etc. Examples of suitable transesterification catalysts include titanium compounds and common alkali metal and / or alkaline earth metal catalysts containing lithium, sodium, potassium, rubidium, magnesium, calcium, strontium, barium, etc. Manganese compounds and tin compounds can also be used. These transesterification catalysts can be used alone or in combination. However, when synthesizing polyesters for bottles, it is preferable to use titanium compounds. Using alkali metal and / or alkaline earth metal catalysts as transesterification catalysts requires a larger amount than titanium compounds, which undesirably increases the crystallinity of the bottle body when molded into a bottle, causing whitening. In contrast, titanium compounds are highly active, so only a small amount is required, preventing whitening of the bottle body.

[0026] As the condensation polymerization catalyst, a germanium compound, an antimony compound, a titanium compound, or the like can be used. Examples of the germanium compound include germanium monoxide, germanium dioxide, germanium tetraethoxide, and germanium tetra-n-butoxide. Examples of the antimony compound include antimony trioxide and antimony acetate. These compounds may be used alone or in combination of two or more. In the production method of this embodiment, a titanium compound can also be used as the condensation polymerization catalyst. From the viewpoint of reducing foreign matters caused by the catalyst, it is more preferable to use a titanium compound that is soluble in the polymer as the titanium compound. Titanium compounds commonly used as polyester polycondensation catalysts, such as titanium acetate, titanium tetrabutoxide and condensates thereof, titanium tetraisopropoxide, titanium tetranormalpropoxide, titanium tetraethoxide, titanium tetramethoxide, titanium tetrakisacetylacetonate complex, titanium tetrakis(2,4-hexanedionato) complex, titanium tetrakis(3,5-heptanedionato) complex, titanium dimethoxybisacetylacetonate complex, titanium diethoxybisacetylacetonate complex, titanium diisopropoxybisacetylacetonate complex, titanium dinormalpropoxybisacetylacetonate complex, titanium dibutoxybisacetylacetonate complex, titanium tetraisopropoxybisacetylacetonate complex, titanium tetrabutoxide ... Examples of the titanium bis(acetylacetonate) complex include titanium dihydroxybisglycolate, titanium dihydroxybislactate, titanium dihydroxybis(2-hydroxypropionate), titanium lactate, titanium octanediolate, titanium dimethoxybistriethanolaminate, titanium diethoxybistriethanolaminate, titanium dibutoxybistriethanolaminate, hexamethyl dititanate, hexaethyl dititanate, hexapropyl dititanate, hexabutyl dititanate, hexaphenyl dititanate, octamethyl trititanate, octaethyl trititanate, octapropyl trititanate, octabutyl trititanate, octaphenyl trititanate, hexaalkoxy dititanate, and octaalkyl trititanate.The titanium compound is more preferably selected from tetramethyl titanate, tetraethyl titanate, tetra-n-propyl titanate, tetraisopropyl titanate, tetrabutyl titanate, tetrahexyl titanate, hexamethyl dititanate, hexaethyl dititanate, hexa-n-propyl dititanate, hexaisopropyl dititanate, hexabutyl dititanate, and hexahexyl dititanate.

[0027] Furthermore, a reaction product of a titanium compound and a phosphorus compound is also a preferred embodiment of the polycondensation catalyst. Examples of the phosphorus compound include monomethyl acid phosphate (monomethyl phosphate), monoethyl acid phosphate (monoethyl phosphate), mono-n-propyl acid phosphate, monoisopropyl acid phosphate (monoisopropyl phosphate), monobutyl acid phosphate (monobutyl phosphate), monopentyl acid phosphate, monohexyl acid phosphate, monoheptyl acid phosphate, monooctyl acid phosphate (monoctyl phosphate), dimethyl phosphate, diethyl phosphate, di-n-propyl phosphate, diisopropyl phosphate, dibutyl phosphate, dihexyl phosphate, diheptyl phosphate, and dioctyl phosphate. These phosphorus compounds may be used alone or in combination of two or more. As the combination of the titanium compound and the phosphorus compound, a combination of a titanium compound selected from tetra-n-propyl titanate, tetraisopropyl titanate, and tetrabutyl titanate with a phosphorus compound selected from monobutyl phosphate, dibutyl phosphate, monooctyl phosphate, and dioctyl phosphate is particularly preferred.

[0028] Examples of other polymerization catalysts containing titanium element include reaction products of aryl titanates, alkyl titanates or aryl titanates with phosphite esters, reaction products of reaction products of alkyl titanates or aryl titanates with trimellitic acid and phosphite ester compounds, titanium hydroxide, and α-titanic acid.

[0029] In the production method of this embodiment, the catalyst can be incorporated so that the content of the alkali metal compound or alkaline earth metal compound in the polyester after the condensation polymerization reaction is 0.1 to 100 ppm by mass. More preferably, the alkali metal compound or alkaline earth metal compound is incorporated so that the content of the alkali metal atom or alkaline earth metal atom contained in the alkali metal compound or alkaline earth metal compound in the polyester is 0.1 to 100 ppm by mass. The content of the alkali metal atom or alkaline earth metal atom is more preferably in the range of 0.5 to 20 ppm by mass, even more preferably 1.0 to 10 ppm by mass, and most preferably 1.5 to 5 ppm by mass. By incorporating a certain amount of such a compound in the polyester, it is possible to perform a deactivation treatment of the polycondensation catalyst during condensation polymerization and solid-state polymerization. When a germanium compound, an antimony compound, a titanium compound, or the like is used as the condensation polymerization catalyst, the amount used is preferably 1.0 to 2000 ppm by mass, more preferably 20 to 1000 ppm by mass, and even more preferably 50 to 600 ppm by mass, based on the total amount of the raw materials.

[0030] Furthermore, in the production method of this embodiment, 1.0 to 100 ppm by mass of polyhexamethylene terephthalate (hereinafter sometimes referred to as modified polyester) having a hydrophilic group can be blended with the polyester obtained by the above method. This compound acts as a crystallization accelerator for the polyester, and by blending this compound, it is possible to promote thermal crystallization and increase productivity during neck crystallization. Various polymers such as vinyl chloride, polystyrene, and Teflon (registered trademark) can be used as the crystallization accelerator. However, from the viewpoint of ensuring hygiene and transparency, particularly when applied to food containers, compounds with a similar composition are preferred, and specifically modified polyesters as described below are preferred. Increasing the productivity of the neck crystallization step is important for increasing productivity when producing heat-resistant bottles using the polyester obtained by the production method of this embodiment.

[0031] The condensation polymerization can be carried out in the presence of a stabilizer, if necessary. Examples of stabilizers that are preferred include phosphoric acid esters such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, triphenyl phosphate, and tricresyl phosphate; phosphorous acid esters such as triphenyl phosphite, tris-dodecyl phosphite, and tris-nonylphenyl phosphite; acidic phosphoric acid esters such as methyl acid phosphate, isopropyl acid phosphate, butyl acid phosphate, dibutyl phosphate, monobutyl phosphate, and dioctyl phosphate; and phosphoric acid and polyphosphoric acid phosphoric acid compounds. The amount of stabilizer added is typically 5.0 to 1,000 ppm by mass, preferably 10 to 500 ppm by mass, in terms of the mass of phosphorus element in the stabilizer relative to all raw materials. Addition of 5.0 ppm by mass or more of stabilizer results in excellent thermal stability during remelting and molding, a reduced amount of by-products, and improved color. When the content is 1000 ppm by mass or less, the decomposition reaction caused by the phosphorus element is unlikely to occur, and the thermal stability is improved.

[0032] In the condensation polymerization, other additives such as at least one selected from a tinting agent, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, an alkali metal, an alkaline earth metal, and a compound thereof may be used as needed.

[0033] <<Step of Obtaining Decomposition Product>> The production method of this embodiment preferably further includes a step of contacting a polyester-containing material containing a polyester with a base, a monohydric alcohol, and a carbonate diester to decompose the polyester and obtain a decomposition product containing the glycol carbonate ester and the dicarboxylic acid ester. The glycol carbonate ester used in the condensation polymerization step is preferably derived from a polyester, and more specifically, includes one obtained by decomposing a polyester-containing material. More preferably, it is one obtained by a step of contacting a polyester-containing material containing a polyester with a base, a monohydric alcohol, and a carbonate diester to decompose the polyester and obtain a decomposition product containing the carbonate ester and the dicarboxylic acid ester (hereinafter also referred to as a "polyester decomposition step" or simply a "decomposition step").

[0034] <Polyester-containing material> The polyester-containing material is not particularly limited as long as it contains polyester, and may contain components other than polyester, and examples thereof include materials containing polyester fibers, and polyester-containing films, packaging containers, bottles, lumps, etc. The components other than polyester may be resins other than polyester, or may be non-resin components.

[0035] Specific examples of the polyester-containing material include materials containing polyester fibers (polyester fibers), films containing polyester and components other than polyester, and lumps containing polyester and components other than polyester. Materials containing polyester fibers include, for example, polyester fibers (fibers containing no components other than polyester), woven polyester fibers, mixtures containing polyester fibers and components other than polyester fibers, and woven fabrics of such mixtures. Mixtures containing polyester fibers and components other than polyester fibers include, for example, mixed fibers of polyester fibers and fibers other than polyester fibers and woven fabrics of such mixed fibers, composite mixtures containing polyester fibers and non-resin components (e.g., colored fibers containing polyester fibers and colorants) and woven fabrics of such composite mixtures, and composite mixed fibers containing polyester fibers, fibers other than polyester fibers, and non-resin components (e.g., colored mixed fibers containing mixed fibers and colorants) and woven fabrics of such composite mixtures. Here, in this specification, "non-resin components" refers to components that do not fall into either polyester or resins other than polyester.

[0036] Examples of films containing polyester and components other than polyester include a monolayer film containing polyester and a component other than polyester, and a laminate film that is a laminate of a film made of polyester (polyester film) and a film containing a component other than polyester. Examples of monolayer films containing polyester and a component other than polyester include a monolayer film that contains both polyester and a resin other than polyester and does not contain a non-resin component, a monolayer film that contains both polyester and a non-resin component and does not contain a resin other than polyester, and a monolayer film that contains all of polyester, a resin other than polyester, and a non-resin component.

[0037] Examples of laminate films that are laminates of a film made of polyester and a film containing a component other than polyester include a laminate film that is a laminate of a film made of polyester and a film that contains a resin other than polyester and that does not contain polyester or non-resin components, a laminate film that is a laminate of a film made of polyester and a film that contains both a resin other than polyester and polyester and that does not contain non-resin components, a laminate film that is a laminate of a film made of polyester and a film that contains both a resin other than polyester and non-resin components and that does not contain polyester, a laminate film that is a laminate of a film made of polyester and a film that contains both polyester and non-resin components and that does not contain resin other than polyester, a laminate film that is a laminate of a film made of polyester and a film that contains all of polyester, a resin other than polyester, and a non-resin component, a multilayer film that is a laminate of one or more of the above laminate films and one or more of the above monolayer films, a multilayer film that is a laminate of two or more of the above laminate films, and a multilayer film that is a laminate of two or more of the above monolayer films.

[0038] Examples of aggregates containing polyester and components other than polyester include aggregates containing both polyester and resins other than polyester but no non-resin components, aggregates containing both polyester and non-resin components but no resins other than polyester, and aggregates containing polyester, resins other than polyester, and non-resin components. The resin other than polyester can be selected arbitrarily depending on the purpose and is not particularly limited. For example, resins other than polyester that are highly versatile and highly applicable to the present invention include polyolefins such as polyethylene and polypropylene, cellulose, polyamides such as nylon, polyurethane, and acrylic resins. These resins may be, for example, in the form of a film (resin film) or a fiber (resin fiber). Examples of fibers other than polyester fibers include fibers of resins other than the above-mentioned polyesters, cotton, rayon, etc.

[0039] The non-resin component can be selected arbitrarily depending on the purpose and is not particularly limited. For example, in terms of high versatility and high applicability of the present invention, examples of the non-resin component include inorganic components (inorganic compounds) such as aluminum, and colorants such as dyes and pigments.

[0040] The fiber diameters of the polyester fibers and the fibers other than polyester fibers in the material containing polyester fibers are not particularly limited and may be, for example, 0.1 μm to 200 μm or 1 μm to 50 μm. The thickness of the film containing polyester and a component other than polyester is not particularly limited and may be, for example, 0.5 μm to 1000 μm or 1 μm to 500 μm. Here, when the film is the above-mentioned laminate film, the film thickness refers to the thickness of the entire laminate film.

[0041] More specifically, examples of materials containing the above-mentioned mixed fibers include fabrics for various clothing, fibers that are materials for fabrics, etc. Fabrics may be unused or used, and may be uncut or cut pieces. Specific examples of uncut fabrics include unsold clothing and used clothing, and specific examples of cut pieces include cut pieces generated during the manufacture of various clothing, cut pieces from various clothing after use, etc. Fibers that are materials for fabrics may be, for example, small pieces of cut pieces generated during the manufacture of fabrics, cut pieces from used fabrics, etc.

[0042] The film containing polyester and components other than polyester may be unused or used, and may be uncut or cut. More specifically, examples include packaging film, small pieces of cut material generated during the production of packaging film, and small pieces of cut material from packaging film after use.

[0043] More specifically, examples of the aggregates containing polyester and components other than polyester include pellets and flakes containing polyester and components other than polyester. The maximum diameter of the aggregates is not particularly limited and may be, for example, 0.1 mm to 10 mm. Here, the "maximum diameter of the aggregate" refers to the maximum length of a line segment connecting two different points on the surface of the aggregate.

[0044] The polyester-containing material may be one kind or two or more kinds, and when two or more kinds are used, the combination and ratio thereof can be selected arbitrarily depending on the purpose. That is, the polyester-containing material used for decomposing polyester may be one or two or more kinds selected from the group consisting of materials containing polyester fibers and films, packaging containers, bottles, and lumps containing polyester.

[0045] When the polyester-containing material is a material containing polyester fibers, the material containing mixed fibers is preferably one or more selected from the group consisting of polyester fibers, woven polyester fiber fabrics, polyester mixed fibers, woven polyester mixed fiber fabrics, mixtures containing polyester fibers and components other than polyester fibers, and woven fabrics of such mixtures.When 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 monolayer film containing polyester and components other than polyester, and a laminate film which is a laminate of a film made of polyester and a film containing components other than polyester.

[0046] In the polyester-containing material, the ratio of the polyester content (parts by mass) to the total mass (parts by mass) of the polyester-containing material ([content (parts by mass) of polyester contained in polyester-containing material] / [total mass (parts by mass) of polyester-containing material] × 100) (polyester content) can be selected arbitrarily depending on the purpose and is not particularly limited. In particular, the polyester content is preferably 20% by mass or more and 90% by mass or less, more preferably 25% by mass or more and 90% by mass or less, even more preferably 30% by mass or more and 80% by mass or less, and particularly preferably 35% by mass or more and 75% by mass or less. The higher the polyester content, the greater the amount of monomer (dicarboxylic acid diester described below) generated per unit mass from the polyester-containing material due to decomposition of the polyester. However, the lower the polyester content, the greater the amount of components other than polyester that can be recovered by separating the polyester.

[0047] <Polyester> The polyester in the polyester-containing material (the polyester to be decomposed) is not particularly limited as long as it is an oligomer or polymer that, upon decomposition, produces a glycol and a component having two functional groups per molecule capable of condensation reacting with the glycol. The polyester may be an aromatic polyester having only aromatic groups (divalent groups having a structure in which one hydrogen atom is removed from each of two carbon atoms forming the aromatic ring skeleton of an aromatic compound) in its ester bond-containing main chain, an aliphatic polyester having no aromatic groups in its main chain (having both an aliphatic group and no aromatic group), or a polyester having both aromatic and aliphatic groups in its main chain. The aromatic polyester may have only divalent aromatic hydrocarbon groups (arylene groups) as aromatic groups, only divalent aromatic heterocyclic groups (heteroarylene groups), or both divalent aromatic hydrocarbon groups and divalent aromatic heterocyclic groups. Examples of heteroatoms in the aromatic heterocyclic groups include oxygen atoms and nitrogen atoms. In general, the reactivity of a substrate in a transesterification reaction depends on the structure on the carboxylic acid side and the structure on the alcohol side. As will be described later, polyesters (polyethylene terephthalate, polybutylene terephthalate, etc.) having an aromatic benzene ring or naphthalene ring as the carboxylic acid side structure can be decomposed well, and therefore it can be easily assumed that polyesters having other aromatic structures such as furan can be decomposed in a similar manner. Similarly, polyesters having an ethylene glycol (polyethylene terephthalate, etc.) or 1,4-butanediol (polybutylene terephthalate, etc.) structure as the alcohol side structure can be decomposed well, and therefore it can be easily assumed that polyesters having other dihydric alcohol structures such as 1,3-propanediol can be decomposed in a similar manner.In terms of enhancing the effects of the present invention and increasing versatility, the polyester is preferably an aromatic polyester, and more preferably polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), or polyethylene furanoate (PEF, also known as polyethylene furan dicarboxylate). Decomposition of the polyester produces, as a monomer, a dicarboxylic acid diester specific to the polyester and the type of monohydric alcohol.

[0048] For example, polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate produce terephthalic acid diesters, polyethylene naphthalate and polybutylene naphthalate produce naphthalenedicarboxylic acid diesters (2,6-naphthalenedicarboxylic acid diesters), and polyethylene furanoate produces furandicarboxylic acid diesters (2,5-furandicarboxylic acid diesters). For example, when methanol is used as the monohydric alcohol, dimethyl dicarboxylic acid esters are produced as dicarboxylic acid diesters. The polyester-containing material may contain only one type of polyester, or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected as desired depending on the purpose.

[0049] <Base> The base is not particularly limited and may be either an inorganic base or an organic base, but is preferably an alkali metal carbonate or alkali metal hydroxide, or an alkali metal alkoxide, which reacts with a monohydric alcohol to produce an alkali metal alkoxide. Generally, in a transesterification reaction, an alkoxide anion serving as a nucleophile attacks the carbonyl group of an ester, passing through a quaternary carbon intermediate and then liberating the other alkoxide anion, thereby proceeding. Since an alkoxide anion is produced by the reaction of a corresponding alcohol with a base, any base capable of deprotonating an alcohol can be used.

[0050] Examples of inorganic bases include alkali metal hydroxides, alkali metal oxides, alkali metal carbonates, alkali metal phosphates, alkaline earth metal hydroxides, alkaline earth metal oxides, alkaline earth metal carbonates, and alkaline earth metal phosphates. It is preferable to use one or more selected from alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, nitrogen-containing organic bases, and alkali metal phosphates. Examples of the alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of the alkali metal oxides include lithium oxide, sodium oxide, and potassium oxide. Examples of the alkali metal carbonates include potassium carbonate. Examples of the alkali metal phosphates include potassium phosphate. Examples of the alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Examples of the alkaline earth metal oxides include calcium oxide and magnesium oxide. Examples of organic bases include alkali metal alkoxides such as lithium methoxide, lithium ethoxide, lithium tert-butoxide, sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium methoxide, potassium ethoxide, and potassium tert-butoxide; calcium dimethoxide, calcium diethoxide, calcium di-tert-butoxide, magnesium dimethoxide, magnesium diethoxide, and magnesium di-tert-butoxide; and alkaline earth metal alkoxides such as lithium methoxide, lithium methoxide, lithium iodide ...The nitrogen-containing organic base is preferably 1,5,7-triazabicyclo[4.4.0]dec-5-ene, since this allows the decomposition of the polyester to proceed at a higher rate.

[0051] The base used in the decomposition step may be one type or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected arbitrarily depending on the purpose. As the base, in order to achieve particularly high rates of polyester decomposition, it is preferable to use one or more types selected from alkali metal carbonates, phosphates, and hydroxides, and alkaline earth metal carbonates, phosphates, and hydroxides. It is particularly preferable to use at least one of potassium phosphate and potassium carbonate, and it is most preferable to use potassium phosphate. The amount of base used in the polyester decomposition step is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 6 parts by mass, even more preferably 0.5 to 3 parts by mass, and particularly preferably 3 to 6 parts by mass, per 100 parts by mass of polyester in the polyester-containing material. When the amount of base used is at least the lower limit, polyester decomposition proceeds at a higher rate. When the amount of base used is at most the upper limit, excessive use of base is suppressed. That is, when decomposing polyester, it is preferable to use a catalytic amount of base (the base is a catalyst).

[0052] <Monohydric Alcohol> In the decomposition step, the monohydric alcohol undergoes a transesterification reaction with the polyester in the polyester-containing material. That is, during the decomposition of the polyester, the reaction between the polyester and the monohydric alcohol produces a glycol corresponding to one of the monomers used in the production of the polyester, and a dicarboxylic acid diester corresponding to the other monomer or its derivative. The monohydric alcohol is not particularly limited. The reaction efficiency of the decomposition step is controlled by the capture of the free dihydric alcohol by the excess diester carbonate. Therefore, as described below, based on the fact that the reaction using methanol and dimethyl carbonate proceeds efficiently, it can be easily assumed that the reaction will proceed efficiently with other combinations of monohydric alcohol and dialkyl carbonate. The monohydric alcohol may be, for example, either an aliphatic alcohol or an aromatic alcohol. However, in terms of proceeding with a higher rate of decomposition of the polyester, an aliphatic alcohol (saturated aliphatic alcohol, unsaturated aliphatic alcohol) is preferred, and a saturated aliphatic alcohol is more preferred.

[0053] Examples of saturated aliphatic alcohols include alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, 1-propanol (n-propyl alcohol), 2-propanol (isopropyl alcohol), 1-butanol (n-butyl alcohol), 2-methyl-1-propanol (isobutyl alcohol), 2-butanol (sec-butyl alcohol), and 2-methyl-2-propanol (tert-butyl alcohol). The monohydric alcohol used in the decomposition of polyester may be a single type or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected as desired depending on the purpose. Methanol is particularly preferred as the monohydric alcohol, as it allows polyester decomposition to proceed at a particularly high rate. The amount of monohydric alcohol used in the polyester decomposition step is not particularly limited. For example, when the polyester is polyethylene terephthalate (PET), the amount is preferably 30 to 200 parts by mass, and more preferably 50 to 160 parts by mass, per 100 parts by mass of PET in the polyester-containing material. Furthermore, when the polyester is polybutylene terephthalate (PBT), the amount of monohydric alcohol used is preferably 10 to 180 parts by mass, more preferably 20 to 140 parts by mass, per 100 parts by mass of PBT in the polyester-containing material. When the amount of monohydric alcohol used is equal to or greater than these lower limits, the effects obtained by using the monohydric alcohol are enhanced. On the other hand, when the amount of monohydric alcohol used is equal to or less than these upper limits, excessive use of the monohydric alcohol is suppressed.

[0054] <Carbonate diester> In the polyester decomposition process, the carbonate diester reacts with glycol generated from the polyester to produce a cyclic compound or a chain compound, and has the effect of shifting the equilibrium between the reactions during polyester decomposition, i.e., the depolymerization reaction and the polymerization reaction of the polyester, in favor of the depolymerization reaction, thereby improving the production rate of the target monomer. The carbonate diester functions as a glycol scavenger.

[0055] Examples of carbonate diesters include dialkyl carbonates and diaryl carbonates. The two alkyl groups bonded to the oxygen atom in the dialkyl carbonate may be the same as or different from each other. Furthermore, the two aryl groups bonded to the oxygen atom in the diaryl carbonate may be the same as or different from each other. The alkyl group in the dialkyl carbonate may be linear, branched, or cyclic, and if cyclic, may be monocyclic or polycyclic. The number of carbon atoms in the linear or branched alkyl group in the dialkyl carbonate is preferably 1 to 8. Examples of such an alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a 1-methylbutyl group, an n-hexyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 2,2-dimethylbutyl group, a 2,3-dimethylbutyl group, an n-heptyl group, a 2-methylhexyl group, a 3-methylhexyl group, a 2,2-dimethylpentyl group, a 2,3-dimethylpentyl group, a 2,4-dimethylpentyl group, a 3,3-dimethylpentyl group, a 3-ethylpentyl group, a 2,2,3-trimethylbutyl group, an n-octyl group, and an isooctyl group. Among these, the number of carbon atoms in the alkyl group in the dialkyl carbonate is more preferably 1 to 4, and even more preferably 1 or 2. Such more preferred dialkyl carbonates include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0056] The aryl group in the diaryl carbonate may be either monocyclic or polycyclic. The aryl group in the diaryl carbonate preferably has 6 to 10 carbon atoms. Examples of such aryl groups include phenyl, 1-naphthyl, 2-naphthyl, o-tolyl, m-tolyl, p-tolyl, 2,3-xylyl (2,3-dimethylphenyl), 2,4-xylyl (2,4-dimethylphenyl), 2,5-xylyl (2,5-dimethylphenyl), 2,6-xylyl (2,6-dimethylphenyl), 3,4-xylyl (3,4-dimethylphenyl), and 3,5-xylyl (3,5-dimethylphenyl). A more preferred diaryl carbonate is diphenyl carbonate. The carbonate diester used in the decomposition of polyester may be one type or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected as desired depending on the purpose. In terms of proceeding with decomposition of the polyester at a higher rate, the carbonate diester is more preferably one or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and diphenyl carbonate, and is particularly preferably dimethyl carbonate.

[0057] In the polyester decomposition step, the amount of carbonate diester used is preferably 100 to 5,000 parts by mass, more preferably 100 to 1,000 parts by mass, and may be, for example, 100 to 500 parts by mass, relative to 100 parts by mass of the polyester in the polyester-containing material. When the amount of carbonate diester used is equal to or greater than the lower limit, the effects obtained by using the carbonate diester are enhanced. When the amount of carbonate diester used is equal to or less than the upper limit, excessive use of the carbonate diester is suppressed.

[0058] As the carbonate diester used in the polyester decomposition step, it is preferable to use the one produced and removed in the above-mentioned condensation polymerization step, since this enables closed-loop polyester regeneration.

[0059] <Solvent> In the polyester decomposition step, a solvent that does not fall into any of the categories of base, monohydric alcohol, and carbonate diester may be used. In this embodiment, decomposition of the polyester proceeds efficiently even without the use of a solvent. However, using a solvent as needed may improve the handleability of the blend of raw materials, such as the reaction solution, and may result in more efficient decomposition of the polyester. In this specification, unless otherwise specified, the term "solvent" encompasses both a component that is liquid at room temperature and serves as a dispersant for dissolving a solute, and a component that is liquid at room temperature and serves as a dispersion medium for dispersing a dispersoid. Furthermore, "room temperature" refers to a temperature that is not particularly cooled or heated, i.e., an ordinary temperature, such as a temperature of 15 to 25°C. Here, the solvent is preferably an organic solvent. Examples of organic solvents include aromatic hydrocarbons such as toluene, ethers such as tetrahydrofuran, alkanes such as n-hexane, halogenated hydrocarbons such as chloroform and dichloromethane, amides such as dimethylformamide, and sulfoxides such as dimethyl sulfoxide. The solvent used for decomposing the polyester may be one kind or two or more kinds. When two or more kinds are used, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0060] When a solvent is used in the polyester decomposition step, the amount used is preferably 1 to 100,000 parts by mass, and more preferably 1 to 10,000 parts by mass, per 100 parts by mass of the polyester-containing material. When the amount of solvent used is equal to or greater than the lower limit, the effects obtained by using the solvent are enhanced. When the amount of solvent used is equal to or less than the upper limit, excessive use of the solvent is suppressed.

[0061] <Other Components> In the polyester decomposition step, other components that do not fall under any of the polyester-containing material, base, monohydric alcohol, carbonate diester, and solvent may be used as long as the effects of the present invention are not impaired. The other components can be selected arbitrarily depending on the purpose and are not particularly limited. The other components used in the polyester decomposition may be one type only or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected arbitrarily depending on the purpose. In the polyester decomposition step, the ratio of the total amount (parts by mass) of the polyester-containing material, base, monohydric alcohol, and carbonate diester to the total amount (parts by mass) of components other than the solvent (([amount (parts by mass) of polyester-containing material used] + [amount (parts by mass) of base used] + [amount (parts by mass) of monohydric alcohol used] + [amount (parts by mass) of carbonate diester used]) / [total amount (parts by mass) of components other than the solvent] × 100) is preferably 80% by mass to 100% by mass, more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass, and may be, for example, any one of 97% by mass to 100% by mass and 99% by mass to 100% by mass. When the ratio is equal to or greater than the lower limit, the polyester can be decomposed more efficiently. Here, the total amount (parts by mass) of components other than the solvent used in the polyester decomposition step is synonymous with the total amount (parts by mass) of the polyester-containing material, base, monohydric alcohol, carbonic acid diester, and other components used during decomposition.

[0062] <Reaction Conditions> Decomposition of the polyester in the polyester-containing material can be carried out by contacting a base, a monohydric alcohol, a carbonic acid diester, the polyester-containing material, and optionally a solvent and optionally other components. Details of each of these components are as described above.

[0063] The reaction temperature in the polyester decomposition step can be adjusted appropriately taking into account the type of raw material used, etc., and the decomposition may be carried out at room temperature (normal temperature) or under heated conditions. The equipment used for heating is not particularly limited, and equipment such as a heater can be used. The reaction temperature in the polyester decomposition step is preferably 20°C or higher, more preferably 40°C or higher, and even more preferably 60°C or higher. The reaction temperature in the polyester decomposition step is preferably less than 180°C, more preferably 150°C or lower, even more preferably 100°C or lower, and particularly preferably 70°C or lower. In one embodiment, the reaction temperature in the polyester decomposition step is, for example, preferably 20°C or higher and lower than 180°C, more preferably 40°C or higher and 150°C or lower, even more preferably 50°C or higher and 120°C or lower, and particularly preferably 60°C or higher and 100°C or lower. For example, by adjusting reaction conditions other than the reaction temperature, it is possible to decompose the polyester at a sufficiently high rate even at a reaction temperature of 20°C or higher and 70°C or lower. According to the present embodiment, as described above, while it has been conventionally difficult to decompose polyesters at relatively low temperatures, it is now possible to decompose polyesters at low temperatures, such as 150° C. or lower, and thus it is possible to separate polyesters from polyester-containing materials. As a result, unlike when polyesters are decomposed at high temperatures, the amount of by-products produced during decomposition can be reduced, discoloration of the dicarboxylic acid diester (monomer), which is the main decomposition product, can be reduced, and deterioration of components other than polyester contained in the polyester-containing material can be prevented.

[0064] The decomposition of the polyester may be carried out under normal pressure, reduced pressure, or increased pressure. The decomposition of the polyester may be carried out under atmospheric pressure or an inert gas atmosphere. The reaction time during the decomposition of the polyester is not particularly limited and can be adjusted appropriately taking into account other reaction conditions such as the reaction temperature. The reaction time during the decomposition of the polyester is not particularly limited as long as it is 0.5 to 24 hours, but is preferably 0.5 to 12 hours, and more preferably 1 to 8 hours. In this embodiment, the end of decomposition can be determined, for example, when the polyester disappears. Therefore, the time required for the polyester to disappear can be considered the decomposition reaction time. The time required for the polyester to disappear can also be determined, for example, by the time required for the mass loss of the polyester-containing material to stop.

[0065] In the blend immediately after the contact of the raw materials, the unreacted polyester-containing material does not dissolve and remains insoluble in the other liquid components. In the blend during which the decomposition of the polyester is in progress, typically, the unreacted polyester-containing material and the polyester-containing material during or after the polyester reaction do not dissolve and remain insoluble in the other liquid components. Meanwhile, the reaction products of the polyester decomposition, glycol and cyclic carbonate, are typically dissolved in the liquid components. During the decomposition of the polyester, such blends can be stirred by known methods, such as by rotating a magnetic stirrer or impeller, or by using a ball mill. During the decomposition of the polyester, the polyester-containing material, which has a low specific gravity, may float to the surface of the liquid. In such cases, the contact area between the insoluble polyester-containing material and the liquid components can be increased by, for example, pushing the polyester-containing material near the surface to submerge it, or by using a narrow-mouthed reaction vessel. As a result, the amounts of raw materials such as base, monohydric alcohol, and carbonate diester used can be reduced compared to when other reaction vessels are used, and polyesters can be decomposed more efficiently. Furthermore, when a narrow-mouthed reaction vessel is used, if one with a wide bottom surface is used, the reaction vessel can be enlarged in capacity while ensuring a sufficient contact area between the polyester-containing material and the liquid component.

[0066] <Post-Treatment Conditions, Extraction Conditions> After the polyester decomposition process described above is completed, the resulting decomposition product can be post-treated by a known method, allowing the carbonate ester and dicarboxylic acid diester to be extracted with high purity. For example, after decomposition of the polyester, the resulting decomposition product can be subjected to solid-liquid separation procedures such as filtration, centrifugation, and decantation at a temperature equal to or higher than the melting point of the carbonate ester to recover components other than the polyester. The liquid obtained by the solid-liquid separation procedure is then subjected to distillation (concentration) of volatile components, and the resulting solid is washed with alcohol or water to remove the carbonate ester, thereby obtaining a high-purity dicarboxylic acid diester. If necessary, the resulting dicarboxylic acid diester may be further purified by crystallization, distillation, or the like. Meanwhile, the carbonate ester obtained in a state dissolved in methanol and water can be recovered by crystallization, distillation, or the like. According to this embodiment, as described above, decomposition is possible at low temperatures, such as below 180°C. Therefore, unlike decomposition at high temperatures, the impurity content and coloration of the dicarboxylic acid diester can be reduced. Therefore, a highly pure dicarboxylic acid diester with reduced coloration can be obtained by the simplified process of washing with methanol and water, as described above, without adding any complicated steps. Furthermore, even if the polyester-containing material originally contains a colorant, the coloring of the dicarboxylic acid diester derived from this colorant can also be reduced by the simplified process of washing with methanol and water as described above.

[0067] The polyester production method of this embodiment may be a closed-loop production method in which the glycol carbonate ester and dicarboxylate ester obtained in the polyester decomposition step are used in the condensation polymerization step, and the carbonate diester removed in the condensation polymerization step is used in the decomposition product obtaining step. Such a closed-loop production method is extremely useful for polyester regeneration because the carbonate diester can be repeatedly used. More specifically, it is preferable to perform both the decomposition product obtaining step and the condensation polymerization step continuously, and use the carbonate diester recovered in the condensation polymerization step in the decomposition product obtaining step, thereby enabling polyester regeneration in a closed-loop system in which the carbonate diester is recycled. That is, the method for producing a polyester according to the present embodiment preferably includes the steps of: bringing a polyester-containing material containing a polyester into contact with a base, a monohydric alcohol, and a carbonic acid diester to decompose the polyester and obtain a decomposition product containing a glycol carbonic acid ester and a dicarboxylic acid ester; and condensation polymerizing a raw material containing the glycol carbonic acid ester and the dicarboxylic acid ester while removing at least a portion of the resulting carbonic acid diester, and using the carbonic acid diester removed in the condensation polymerization step as the carbonic acid diester in the step of obtaining the decomposition product.

[0068] [Method for producing a carbonate diester] The method for producing a polyester of this embodiment can also be considered as a method for obtaining a carbonate diester by a step of condensation polymerization of raw materials containing a carbonate ester of a glycol and a dicarboxylic acid ester. Details and preferred aspects of the condensation polymerization step are the same as those of the condensation polymerization step in the above-mentioned method for producing a polyester. However, in order to obtain the target carbonate diester, it is necessary to use a dicarboxylic acid ester rather than a dicarboxylic acid.

[0069] The method for producing a carbonate diester of this embodiment preferably further includes a step of contacting a polyester-containing material containing a polyester with a base, a monohydric alcohol, and a carbonate diester to decompose the polyester, thereby obtaining a decomposition product containing the glycol carbonate ester and the dicarboxylic acid ester. Details and preferred aspects of the step of obtaining the decomposition product are the same as those of the step of obtaining the decomposition product in the above-mentioned method for producing a polyester.

[0070] The method for producing a carbonate diester according to the present embodiment is a method for producing a polyester by condensation polymerization of raw materials containing a carbonate ester of a glycol and a dicarboxylic acid ester. According to the production method according to the present embodiment, a novel method for producing a polyester can be provided. Hereinafter, embodiments of the method for producing a polyester according to the present invention will be described. However, the present invention is not limited to the following embodiments.

[0071] The present invention will be described in more detail below with reference to specific examples. However, the present invention is not limited to the examples shown below. Note that the unit "ppm" shown below is always based on mass ratio.

[0072] Example 1: 300 g of dimethyl terephthalate (manufactured by Tokyo Chemical Industry Co., Ltd.), 154 g of ethylene glycol (manufactured by Tokyo Chemical Industry Co., Ltd.), and 55 g of ethylene carbonate (manufactured by Tokyo Chemical Industry Co., Ltd.) were added to a 1-liter round-bottom flask equipped with a mechanical stirrer and mixed. The mixture was heated and stirred until the dimethyl terephthalate was dissolved. Next, 0.11 g of calcium acetate monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added, and bishydroxyethyl terephthalate (BHET) was synthesized by transesterification. The reaction was continued until the amount of methanol produced reached 99% of the theoretical value. Subsequently, 0.087 g of trimethyl phosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added and stirred. Then, 0.11 g of antimony trioxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added and the mixture was heated under reduced pressure. The condensation polymerization reaction was carried out for 4 hours at a reactor pressure of 140 Pa and a heat medium temperature of 280°C. The molecular weight of the resulting polymer was calculated by gel permeation chromatography, and it was found to be a polyester having a number average molecular weight (Mn) of 16,800 g / mol and a weight average molecular weight (Mw) of 53,200 g / mol.

[0073] [Example 2] Transesterification and condensation polymerization were carried out in the same manner as in Example 1, except that the amount of ethylene glycol used was changed to 115 g and the amount of ethylene carbonate used was changed to 110 g under the conditions of Example 1. The molecular weight of the resulting polymer was calculated by gel permeation chromatography, and it was found to be a polyester with a number average molecular weight (Mn) of 17,700 g / mol and a weight average molecular weight (Mw) of 52,000 g / mol.

[0074] [Example 3] (Step of obtaining decomposition product) Potassium phosphate (K ３ P.O. ４11 g of ethanol (Fujifilm Wako Pure Chemical Industries, Ltd.) was added, followed by 65 mL of methanol (Kishida Chemical Co., Ltd.) and 500 mL of dimethyl carbonate (DMC) (Tokyo Chemical Industry Co., Ltd.), and the mixture was uniformly dispersed to prepare a raw material composition. A white coat (100% by mass of polyester fiber in total fibers) was cut into approximately 2 cm x 2 cm pieces, and several pieces (100 g) were added to the raw material composition in the three-neck flask obtained above. Here, the percentage (mass%) of polyester fiber in total fibers is synonymous with the ratio of the polyester content (parts by mass) to the total mass (parts by mass) of the polyester-containing material, as described above. The mixture of raw material composition and cut material was then stirred at 50°C for 2 hours in an oil bath to decompose the polyester fiber. Dimethyl carbonate (150 mL) was then added to the mixture in the eggplant flask to dissolve the precipitated components. The contents were then hot-filtered at 50°C without cooling, and the filtrate was collected.

[0075] (Removal of Dimethyl Carbonate and Methanol) The recovered filtrate is distilled to recover dimethyl carbonate and methanol. The resulting filtrate (residual liquid) after distillation contains ethylene carbonate and terephthalic acid esters such as dimethyl terephthalate.

[0076] (Production of Polyester) The residual liquid obtained as described above is heated under reduced pressure, and the dimethyl carbonate produced is removed by evaporation while condensation polymerization of ethylene carbonate contained in the residual liquid with a terephthalic acid ester is allowed to proceed, thereby producing a polyester. (Production of Carbonate Diester) Dimethyl carbonate removed by evaporation in the above-described production of polyester can be produced by recovering and purifying it.

[0077] The production method of the present invention is a novel method capable of producing useful polyesters.

Claims

1. A method for producing a polyester, comprising a step of condensation polymerizing a raw material containing a carbonate ester of a glycol and one or more selected from a dicarboxylic acid ester and a dicarboxylic acid.

2. The method for producing a polyester according to claim 1, wherein at least a portion of the glycol carbonate ester is derived from a polyester.

3. The method for producing a polyester according to claim 1 or 2, wherein at least a portion of the one or more selected from the group consisting of dicarboxylic acid esters and dicarboxylic acids is a dicarboxylic acid ester derived from a polyester.

4. The method for producing a polyester according to any one of claims 1 to 3, wherein the molar ratio of the glycol carbonate ester to the one or more selected from the dicarboxylic acid ester and the dicarboxylic acid is 0.90 to 1.

10.

5. The method for producing a polyester according to any one of claims 1 to 4, wherein the glycol carbonate ester includes a cyclic carbonate ester.

6. A method for producing a polyester according to any one of claims 1 to 5, wherein the glycol carbonate ester is ethylene carbonate, and the one or more selected from the dicarboxylic acid ester and dicarboxylic acid are one or more selected from monoesters and diesters of a dicarboxylic acid selected from phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, and furandicarboxylic acid.

7. The method for producing a polyester according to any one of claims 1 to 6, further comprising the step of carrying out the condensation polymerization while removing at least a portion of the resulting carbonate diester.

8. The method for producing a polyester according to any one of claims 1 to 7, wherein the reaction temperature in the condensation polymerization step is in the range of 50°C to 350°C.

9. The method for producing a polyester according to any one of claims 1 to 8, wherein the condensation polymerization step is carried out in a reduced pressure environment of -10 kPaG or less.

10. A method for producing a polyester according to any one of claims 1 to 9, further comprising the step of contacting a polyester-containing material containing a polyester with a base, a monohydric alcohol, and a carbonic acid diester to decompose the polyester, thereby obtaining a decomposition product containing the glycol carbonic acid ester and the dicarboxylic acid ester.

11. The method for producing polyester according to claim 10, further comprising purifying the decomposition product by at least one of distillation and crystallization and using the purified product as glycol carbonate ester and dicarboxylic acid ester in the condensation polymerization step.

12. The method for producing a polyester according to claim 10 or 11, wherein the reaction temperature in the step of obtaining the decomposition product is in the range of 20°C to 150°C.

13. The method for producing a polyester according to any one of claims 10 to 12, wherein the monohydric alcohol used in the step of obtaining the decomposition product is methanol.

14. The method for producing a polyester according to any one of claims 10 to 13, wherein the base used in the step of obtaining the decomposition product is at least one selected from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, nitrogen-containing organic bases, and alkali metal phosphates.

15. The method for producing a polyester according to any one of claims 10 to 14, wherein the base is potassium phosphate.

16. The method for producing a polyester according to any one of claims 10 to 15, wherein the polyester is at least one selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and polyethylene furanoate.

17. The method for producing polyester according to any one of claims 10 to 16, wherein the polyester-containing material further contains one or more materials selected from the group consisting of cotton, rayon, polyurethane, nylon, acrylic, polyethylene, polypropylene, carbon-based materials, dyes, and pigments.

18. A method for producing polyester, comprising: a step of contacting a polyester-containing material containing a polyester with a base, a monohydric alcohol, and a carbonic acid diester to decompose the polyester and obtain a decomposition product containing a glycol carbonic acid ester and a dicarboxylic acid ester; and a step of condensation polymerizing a raw material containing the glycol carbonic acid ester and the dicarboxylic acid ester while removing at least a portion of the carbonic acid diester produced, wherein the carbonic acid diester removed in the condensation polymerization step is used as the carbonic acid diester in the step of obtaining the decomposition product.

19. A method for producing a carbonate diester, comprising condensation polymerizing a raw material containing a glycol carbonate ester and a dicarboxylic acid ester to obtain the carbonate diester.

20. A method for producing a carbonic acid diester according to claim 19, further comprising the step of contacting a polyester-containing material containing a polyester with a base, a monohydric alcohol, and a carbonic acid diester to decompose the polyester and obtain a decomposition product containing the glycol carbonic acid ester and the dicarboxylic acid ester.

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