Polyester manufacturing method

Abstract

A novel method for producing polyester is provided. The method for producing a polyester includes a step of condensation polymerizing raw materials containing a carbonate ester and at least one selected from a dicarboxylic acid ester and a dicarboxylic acid.

Description

[Technical Field]

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

[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. Polyester is widely used as a material 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 polyester used in PET bottles and other products due to its 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-126617 [Patent Document 2] International Publication No. 2024 / 034609 Summary of the Invention [Problem to be solved by the invention]

[0005] According to the polyester decomposition method disclosed in the above-mentioned Patent Document 2, it is disclosed that polyester is decomposed using a base, a monohydric alcohol, and a carbonate diester to obtain a dicarboxylic acid diester and a glycol carbonate ester, which are monomers. As a method for producing polyester, a method based on dehydration condensation of dicarboxylic acid and 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. [Means for solving the problem]

[0007] As a result of intensive research conducted by the present inventors, it has been found that the above-mentioned problems can be solved by a method for producing a polyester, which includes a step of condensation polymerization of a raw material containing a carbonate ester of a glycol and one or more selected from a dicarboxylic acid ester and a dicarboxylic acid. That is, 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 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 the above [1], wherein at least a part of the glycol carbonate ester is derived from a polyester. [3] The method for producing a polyester according to the above [1] or [2], wherein at least a part of the one or more selected from the dicarboxylic acid ester and the dicarboxylic acid is a dicarboxylic acid ester derived from a polyester. [4] The 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 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 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 at least one selected from dicarboxylic acid esters and dicarboxylic acids is at least one 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 the above [1] to [6], wherein the condensation polymerization step is carried out while removing at least a portion of the resulting carbonate diester. [8] The method for producing a polyester according to any one of the above [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 the above [1] to [8], wherein the condensation polymerization step is carried out in a reduced pressure environment of -10 kPaG or less.

[10] The method for producing the polyester according to any one of the above [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 a polyester according to the above

[10] , 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 dicarboxylic acid ester in the condensation polymerization step.

[12] The method for producing a polyester according to the above

[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 the above

[10] to

[12] , 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 the above

[10] to

[13] , wherein the base used in the step of obtaining the decomposition product is at least one selected from 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 the above

[10] to

[14] , 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 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 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 process 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 a glycol carbonate ester and a dicarboxylic acid ester; and a step of condensation-polymerizing a raw material containing the carbonate ester of the glycol and the dicarboxylic acid ester while removing at least a portion of the resulting carbonate diester; The method for producing a polyester, 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 to obtain the carbonate diester.

[20] A method for producing a carbonate diester 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, thereby obtaining a decomposition product containing the carbonate ester of the glycol and the dicarboxylic acid ester. [Effects of the Invention]

[0008] According to the present invention, a novel method for producing polyester can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Polyester manufacturing method] Hereinafter, an embodiment of the method for producing a 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 at least one selected from a dicarboxylic acid ester and a dicarboxylic acid. According to the production method of this embodiment, a novel method for producing polyester can be provided.

[0011] <<Condensation polymerization process>> The polyester in 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. Examples of such a method include a production method (transesterification method) 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 under high vacuum (reduced pressure) and in a melt, and a production method (esterification method) 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 under high vacuum (reduced pressure) and in a melt. Furthermore, the poly(alkylene dicarboxylate ester) obtained by the melt polymerization reaction in the condensation polymerization step may be pelletized, and then, if necessary, a step of performing a solid-state polymerization reaction may be included in the production method of the polyester according to this embodiment in order to further increase the molecular weight or reduce impurities such as oligomers. Regarding the method for performing the condensation polymerization reaction in the solid-state polymerization reaction step, any known method for solid-state polymerization may be used.

[0012] <Dicarboxylic acid esters and dicarboxylic acids> Specific examples of the dicarboxylic acid 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 ester include monoesters and diesters of the above-mentioned dicarboxylic acids. Furthermore, dicarboxylic acid esters having 10 to 20 carbon atoms are preferably used. At least a part of the dicarboxylic acid ester and dicarboxylic acid is preferably a dicarboxylic acid ester derived from a polyester, and more preferably a dicarboxylic acid ester obtained by decomposing a polyester.

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

[0014] [ka] (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 alkylene groups such as ethylene (-CH2CH2-), 1,2-propylene, 1,3-propylene (trimethylene, -CH2CH2CH2-), 1,2-butylene, 1,3-butylene, and 1,4-butylene (tetramethylene, -CH2CH2CH2CH2-), 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. [ka]

[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. Above X 2 ~X 5 The divalent organic group represented by the formula (I) may be, for example, an aromatic group, an aliphatic group, or a group having both an aromatic group and an aliphatic group, and is preferably a divalent hydrocarbon group. Preferred divalent organic groups include alkylene groups such as an ethylene group (-CH2CH2-), a 1,3-propylene group (trimethylene group, -CH2CH2CH2-), and a 1,4-butylene group (tetramethylene group, -CH2CH2CH2CH2-), and alkylene groups having 2 to 4 carbon atoms are more preferred. Above R 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 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 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 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 prevented.

[0020] In the polyester production method of this embodiment, the raw materials may further contain a glycol compound. When the raw materials contain 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 materials 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, specifically 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, ethylene glycol is particularly preferred when it is the main target. In this case, 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, and polymethylene glycol may be used alone or in combination, and can be selected arbitrarily depending on the purpose. Furthermore, as long as the polymer chains constituting the resulting polyester are substantially linear, the raw material may further contain a trivalent or higher polyfunctional compound such as glycerin, trimethylolpropane, or pentaerythritol, and may also contain a monofunctional compound such as decyl alcohol, dodecyl alcohol, or 2-phenylethanol, as necessary.

[0021] <Removal of carbonic acid diesters> In the condensation polymerization step, a carbonic acid diester is produced as the condensation polymerization proceeds, but removing this diester can shift the equilibrium reaction, allowing for more efficient production of the polyester. That is, the condensation polymerization step is preferably carried out while removing at least a portion of the produced carbonic acid diester. The specific method for removing the carbonate diester is not particularly limited, but for example, it can be performed by reducing pressure in the condensation polymerization reaction step. More specifically, the condensation polymerization can be performed while removing the carbonate diester from the reactor of the condensation polymerization step. 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. In the present invention, the carbonate diester removed from the reactor of the condensation polymerization step can be purified as needed to produce a final product.

[0022] The reaction temperature in the condensation polymerization step can be appropriately adjusted taking into consideration 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 a range of 50 to 350°C, more preferably within a range of 70 to 300°C, and even more preferably within a 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 for the condensation polymerization step can be adjusted appropriately in consideration of other reaction conditions such as the reaction temperature, and is not particularly limited, but is preferably 0.5 to 24 hours, more preferably 0.5 to 12 hours, and even more preferably 1 to 8 hours.

[0025] <Catalyst etc.> In the condensation polymerization step, it is preferable to use a condensation polymerization catalyst and, if necessary, a stabilizer, etc. As these catalysts, stabilizers, etc., those known as catalysts, stabilizers, etc. used in the condensation polymerization of polybutylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, etc. can be used. Examples of 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, but titanium compounds are preferred for synthesizing polyesters for bottles. Using alkali metal and / or alkaline earth metal catalysts as transesterification catalysts requires adding a larger amount than titanium compounds. However, this undesirably increases the crystallinity of the bottle body when molded into a bottle, causing whitening. In contrast, titanium compounds are highly active, so only small amounts are 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 a condensation polymerization catalyst. It is more preferable to use a titanium compound that is soluble in the polymer in order to reduce catalyst-induced foreign matter. Titanium compounds commonly used as polyester polycondensation catalysts include, for example, 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 titanium bis(acetylacetonate) complexes 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] In addition, 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 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, the polycondensation catalyst can be deactivated during condensation polymerization and solid-state polymerization. When a germanium compound, antimony compound, 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, thermal crystallization can be promoted and productivity during neck crystallization can be increased. 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 productivity in 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. Preferred stabilizers 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. The amount of stabilizer added is usually 5.0 to 1000 ppm by mass, preferably 10 to 500 ppm by mass, in terms of the mass of phosphorus in the stabilizer relative to all raw materials. When the amount of stabilizer added is 5.0 ppm by mass or more, for example, the thermal stability effect during remelting and molding is excellent, the amount of by-products generated is reduced, and the color is improved. When the amount is 1000 ppm by mass or less, decomposition reactions due to phosphorus element are less likely to occur, and 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] <<Process for obtaining decomposition products>> The production method of the present embodiment preferably further includes 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, thereby obtaining a decomposition product containing the glycol carbonic acid ester and the dicarboxylic acid ester. The glycol carbonate ester used in the above-mentioned condensation polymerization process is preferably derived from a polyester, and more specifically, can be one obtained by decomposing a polyester-containing material. More preferably, it is one obtained by a process in which a polyester-containing material containing a polyester is contacted 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 process" or simply "decomposition process").

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

[0035] Specific 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 lump containing polyester and a component other than polyester. Examples of materials containing polyester fibers include polyester fibers (fibers that do not contain any components other than polyester), woven polyester fibers, mixtures containing polyester fibers and components other than polyester fibers, and woven polyester mixtures. Examples of mixtures containing polyester fibers and components other than polyester fibers include mixed fibers of polyester fibers and fibers other than polyester fibers and woven fabrics of such mixed fibers, composite mixtures containing polyester fibers and non-resin components (e.g., colored fibers containing polyester fibers and a colorant) and woven fabrics of such composite mixtures, composite mixed fibers containing polyester fibers, fibers other than polyester fibers, and non-resin components (e.g., colored mixed fibers containing mixed fibers and a colorant) and woven fabrics of such composite mixtures, etc. Here, in this specification, "non-resin components" refers to components that do not fall into either polyester or resins other than polyester.

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

[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 polyester, a resin other than polyester, and non-resin components, a multilayer film that is a laminate of one or more of the above laminate films and one or more of the above single-layer 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 single-layer films.

[0038] Examples of lumps containing polyester and components other than polyester include lumps containing both polyester and resins other than polyester but no non-resin components, lumps containing both polyester and non-resin components but no resins other than polyester, and lumps containing all of polyester, resins other than polyester, and non-resin components. The resin other than polyester can be arbitrarily selected depending on the purpose and is not particularly limited. For example, in terms of high versatility and high applicability of the present invention, examples of resin other than polyester include polyolefins such as polyethylene and polypropylene, cellulose, polyamides such as nylon, polyurethane, and acrylic resins. These resins may be, for example, in the form of a film (resin film) or a fiber (resin fiber). Examples of fibers other than polyester fibers include fibers of resins other than the above polyesters, cotton, rayon, and the like.

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

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

[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, but 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 the two carbon atoms forming the aromatic ring skeleton of an aromatic compound) in its main chain having an ester bond, an aliphatic polyester having no aromatic groups in its main chain (having an aliphatic group but 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 described below, polyesters (polyethylene terephthalate, polybutylene terephthalate, etc.) having an aromatic benzene ring or naphthalene ring as the carboxylic acid side structure can be decomposed well, so it can be easily assumed that polyesters having other aromatic structures such as furan can also 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, so it can be easily assumed that polyesters having other dihydric alcohol structures such as 1,3-propanediol can also be decomposed in a similar manner. In terms of achieving a higher effect of the present invention and having high versatility, the polyester is preferably an aromatic polyester, and more preferably polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), or polyethylene furanoate (PEF, also known as polyethylene furan dicarboxylate). Decomposition of polyester produces dicarboxylic acid diesters as monomers, which are specific depending on the type of polyester and monohydric alcohol.

[0048] For example, terephthalic acid diesters are produced from polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate, naphthalenedicarboxylic acid diesters (2,6-naphthalenedicarboxylic acid diesters) are produced from polyethylene naphthalate and polybutylene naphthalate, and furandicarboxylic acid diesters (2,5-furandicarboxylic acid diesters) are produced from polyethylene furanoate. For example, when methanol is used as the monohydric alcohol, a dicarboxylic acid dimethyl ester is produced as the dicarboxylic acid diester. The type of polyester contained in the polyester-containing material may be only one type, or two or more types. When there are two or more types, the combination and ratio thereof are not particularly limited and can be selected arbitrarily 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 that reacts with a monohydric alcohol to produce an alkali metal alkoxide, or an alkali metal alkoxide. Generally, transesterification proceeds by the reaction of a nucleophilic alkoxide anion with the carbonyl group of an ester, resulting in the liberation of the other alkoxide anion via a quaternary carbon intermediate. Since the alkoxide anion is generated by the reaction of the corresponding alcohol with a base, any base capable of deprotonating the alcohol can be used.

[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 at least one 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 1,2,3-dimethyl-2,4-triazabicyclo[4.4.0]dec-5-ene (abbreviation: TBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (abbreviation: DBU), 1,3-dimesitylimidazol-2-ylidene, 1,3-dicyclohexylimidazol-2-ylidene, and the like. The alkali metal alkoxide is preferably lithium methoxide, sodium methoxide or potassium methoxide, and more preferably sodium methoxide, in that the decomposition of the polyester proceeds at a higher rate. The nitrogen-containing organic base is preferably 1,5,7-triazabicyclo[4.4.0]dec-5-ene, in that decomposition of the polyester proceeds at a higher rate.

[0051] The base used in the decomposition step 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. As the base, in terms of proceeding with the decomposition of the polyester at a particularly high rate, it is preferable to use one or more selected from carbonates, phosphates and hydroxides of alkali metals, and carbonates, phosphates and hydroxides of alkaline earth metals, and 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 equal to or greater than the lower limit, the decomposition of the polyester proceeds at a higher rate. When the amount of base used is equal to or less than the upper limit, excessive use of base is suppressed. That is, when decomposing the polyester, the amount of base used is preferably a catalytic amount (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 polyester reacts with the monohydric alcohol to produce a glycol corresponding to one of the monomers used in the production of the polyester, and a dicarboxylic acid diester corresponding to the other monomer or a derivative thereof. The monohydric alcohol is not particularly limited. The reaction efficiency of the decomposition step is controlled by the capture of the liberated dihydric alcohol by the diester carbonate present in excess. Therefore, as will be described later, the fact that the reaction using methanol and dimethyl carbonate proceeds efficiently means that the reaction will also 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, but in terms of the rate at which the decomposition of the polyester proceeds, 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 for decomposing the polyester may be one kind or two or more kinds, and when two or more kinds are used, the combination and ratio thereof are not particularly limited and can be arbitrarily selected depending on the purpose. Note that, as the monohydric alcohol, methanol is particularly preferred in that the decomposition of the polyester proceeds at a particularly high rate. The amount of monohydric alcohol used in the polyester decomposition step is not particularly limited, but for example, when the polyester is polyethylene terephthalate (PET), the amount is preferably 30 to 200 parts by mass, more preferably 50 to 160 parts by mass, per 100 parts by mass of PET in the polyester-containing material. Furthermore, when the polyester is polybutylene terephthalate (PBT), the amount of monohydric alcohol used is preferably 10 to 180 parts by mass, more preferably 20 to 140 parts by mass, per 100 parts by mass of PBT in the polyester-containing material. When the amount of monohydric alcohol used is equal to or greater than these lower limits, the effects obtained by using the monohydric alcohol are enhanced. On the other hand, when the amount of monohydric alcohol used is equal to or less than these upper limits, excessive use of the monohydric alcohol is suppressed.

[0054] <Carbonate diester> The carbonate diester reacts with glycols generated from the polyester during the polyester decomposition process to produce cyclic compounds or chain compounds, thereby shifting the equilibrium between the depolymerization reaction and polymerization reaction of the polyester during polyester decomposition 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 or different. Furthermore, the two aryl groups bonded to the oxygen atom in the diaryl carbonate may be the same or different. The alkyl group in the dialkyl carbonate may be linear, branched, or cyclic, and when cyclic, it 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 number of carbon atoms in the aryl group in the diaryl carbonate is preferably 6 to 10, and examples of such aryl groups include phenyl, 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, for example, diphenyl carbonate. The carbonate diester used for decomposing the polyester may be one type only, or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected arbitrarily depending on the purpose. 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 allows for closed-loop polyester regeneration.

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

[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 ingredients> In the polyester decomposition step, other components that do not fall into any of the polyester-containing material, base, monohydric alcohol, carbonic acid 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 for decomposing the polyester may be one kind or two or more kinds, and when two or more kinds are used, the combination and ratio thereof are not particularly limited and can be 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 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 process 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> The polyester in the polyester-containing material can be decomposed by contacting a base, a monohydric alcohol, a carbonic acid diester, the polyester-containing material, and optionally a solvent and optionally other components, as described above in detail.

[0063] The reaction temperature in the polyester decomposition step can be appropriately adjusted taking into consideration the type of raw material used, etc., and the decomposition may be carried out at room temperature (normal temperature) or under heated conditions. 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 lower 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. As described above, according to the present embodiment, while it has been difficult to decompose polyester at relatively low temperatures in the past, polyester can be decomposed at low temperatures, such as 150°C or lower, making it possible to separate polyester from a polyester-containing material. This makes it possible to reduce the amount of by-products produced during decomposition, reduce the coloring of the dicarboxylic acid diester (monomer), which is the main decomposition product, and prevent deterioration of components other than polyester contained in the polyester-containing material, unlike when polyester is decomposed at high temperatures.

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

[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, neither the unreacted polyester-containing material nor the polyester-containing material during or after the polyester reaction dissolves and remains insoluble in the other liquid components. Meanwhile, the glycol and cyclic carbonate, which are reaction products of the decomposition of the polyester, typically dissolve in the liquid components. Such a compound can be stirred during the decomposition of the polyester by a known method, for example, by rotating a magnetic stirrer or stirring blade, or by using a ball mill. During the decomposition of polyester, polyester-containing materials with low specific gravity may rise to the surface of the liquid. In such cases, for example, the polyester-containing material near the surface of the liquid can be pushed down to sink, or a narrow-mouthed reaction vessel can be used to increase the contact area between the insoluble polyester-containing material and the liquid component. As a result, the amounts of raw materials such as base, monohydric alcohol, and carbonate diester can be reduced compared to when other reaction vessels are used, and polyester can be decomposed more efficiently. Furthermore, when using a narrow-mouthed reaction vessel, using one with a wide bottom surface allows the reaction vessel to have a large capacity while ensuring the contact area between the polyester-containing material and the liquid component.

[0066] <Post-processing conditions, removal conditions> After the step of decomposing the polyester is completed, the resulting decomposition product is subjected to post-treatment by a known method, and the carbonate ester and dicarboxylic acid diester can be isolated with high purity. For example, after decomposition of the polyester, the resulting decomposition product is subjected to a solid-liquid separation procedure such as filtration, centrifugation, decantation, etc. at a temperature equal to or higher than the melting point of the carbonate ester to recover components other than the polyester, and then the liquid obtained by the solid-liquid separation procedure is subjected to distillation (concentration) of volatile components, etc., and the resulting solid is washed with alcohol or water to remove the carbonate ester, thereby obtaining a high-purity dicarboxylic acid diester, which may be further purified by crystallization (crystallization), distillation, etc., as necessary. On the other hand, the carbonate ester obtained in a state of being dissolved in methanol and water can be recovered by crystallization (crystallization), distillation, or the like. According to this embodiment, as explained above, decomposition is possible at low temperatures, such as below 180°C, and therefore, unlike decomposition at high temperatures, the impurity content and discoloration of the dicarboxylic acid diester can be reduced. Therefore, a highly pure dicarboxylic acid diester with reduced discoloration can be obtained by the simplified process of washing with methanol and water as described above, without adding any complicated steps. Furthermore, even if the polyester-containing material originally contains a colorant, the coloration of the dicarboxylic acid diester 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 production 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 carry out both the step of obtaining the decomposition product and the step of condensation polymerization continuously, and use the carbonate diester recovered in the condensation polymerization step in the step of obtaining the decomposition product, since this allows polyester to be regenerated 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 includes the steps of: bringing a polyester-containing material containing a polyester into contact with a base, a monohydric alcohol, and a carbonate diester to decompose the polyester, thereby obtaining a decomposition product containing a glycol carbonate ester and a dicarboxylate ester; and a step of condensation-polymerizing a raw material containing the carbonate ester of the glycol and the dicarboxylic acid ester while removing at least a portion of the resulting carbonate diester; In the method for producing a polyester, the carbonate diester removed in the condensation polymerization step is preferably used as the carbonate diester in the step of obtaining the decomposition product.

[0068] [Method of producing carbonate diester] The method for producing a polyester according to the present embodiment can also be understood as a method for obtaining a carbonate diester by a step of condensation polymerization of raw materials containing a glycol carbonate ester and a dicarboxylic acid ester. The details and preferred embodiments of the condensation polymerization step are the same as those of the condensation polymerization step in the polyester production method described above, except that in order to obtain the target carbonate diester, it is necessary to use a dicarboxylic acid ester instead of a dicarboxylic acid.

[0069] The method for producing a carbonate diester of the present 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 carbonate ester of the glycol and the dicarboxylic acid ester. The details and preferred embodiments 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 polyester. Hereinafter, an embodiment of the method for producing a polyester according to the present invention will be described, but the present invention is not limited to the following embodiment.

[0070] The method for producing a carbonate diester according to the present embodiment is a method for obtaining 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 of this embodiment, a novel method for producing polyester can be provided. Hereinafter, an embodiment of the method for producing a polyester according to the present invention will be described, but the present invention is not limited to the following embodiment. [Example]

[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. The unit "ppm" shown below is always based on mass ratio.

[0072] [Example 1] 300 g of dimethyl terephthalate (Tokyo Chemical Industry Co., Ltd.), 154 g of ethylene glycol (Tokyo Chemical Industry Co., Ltd.), and 55 g of ethylene carbonate (Tokyo Chemical Industry Co., Ltd.) were mixed in a 1-liter round-bottom flask equipped with a mechanical stirrer and heated and stirred until the dimethyl terephthalate dissolved. Next, 0.11 g of calcium acetate monohydrate (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. Next, 0.087 g of trimethyl phosphate (Fujifilm Wako Pure Chemical Industries, Ltd.) was added and stirred. Then, 0.11 g of antimony trioxide (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 transfer 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 with 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 under the same conditions 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. 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) A raw material composition was prepared by adding 11 g of potassium phosphate (K3PO4) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to a 3 L three-neck flask equipped with a stirrer and reflux condenser, followed by 65 mL of methanol (manufactured by Kishida Chemical Co., Ltd.) and 500 mL of dimethyl carbonate (DMC) (manufactured by Tokyo Chemical Industry Co., Ltd.) and uniformly dispersing them. White coat (100% by mass of polyester fiber in total fibers) was cut into pieces approximately 2 cm x 2 cm in size, and several pieces (100 g) of these cut pieces were added to the raw material composition in the three-neck flask obtained above. Here, the proportion (mass %) of polyester fibers in all fibers is synonymous with the proportion of polyester content (parts by mass) in the polyester-containing material relative to the total mass (parts by mass) of the polyester-containing material, as explained above. Next, the mixture of the raw material composition and the cut material was stirred in an oil bath at 50°C for 2 hours to decompose the polyester fibers. Next, dimethyl carbonate (150 mL) was added to this mixture in the recovery flask to dissolve the precipitated components, and the contents were filtered while still hot at 50°C without being cooled, 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 distillation filtrate (residue) contains ethylene carbonate and terephthalic acid esters such as dimethyl terephthalate.

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

[0077] The production method of the present invention is a novel method by which useful polyesters can be produced.

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 at least one selected from a dicarboxylic acid ester and a dicarboxylic acid.

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

3. 2. The method for producing a polyester according to claim 1, wherein at least a part 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. 2. The method for producing a polyester according to claim 1, wherein a 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 claim 1 , wherein the glycol carbonate ester comprises a cyclic carbonate ester.

6. 2. The method for producing a polyester according to claim 1, wherein the glycol carbonate ester is ethylene carbonate, and the at least one selected from the group consisting of a dicarboxylic acid ester and a dicarboxylic acid is at least one selected from the group consisting of a monoester and a diester 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 claim 1 , further comprising the step of performing the condensation polymerization while removing at least a portion of the resulting carbonate diester.

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

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

10. 2. The method for producing a polyester according to claim 1, further 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, thereby obtaining a decomposition product containing the glycol carbonic acid ester and the dicarboxylic acid ester.

11. The method for producing a 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 the glycol carbonate ester and dicarboxylic acid ester in the condensation polymerization step.

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

14. 11. The method for producing a polyester according to claim 10, 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 claim 10, wherein the base is potassium phosphate.

16. 11. The method for producing a polyester according to claim 10, 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. 11. The method for producing a polyester according to claim 10, 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 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 a glycol carbonate ester and a dicarboxylate ester; and a step of condensation-polymerizing a raw material containing the carbonate ester of the glycol and the dicarboxylic acid ester while removing at least a portion of the resulting carbonate diester; The method for producing a polyester, 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 to obtain the carbonate diester.

20. The method for producing a carbonic acid diester further includes 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, thereby obtaining a decomposition product containing the glycol carbonic acid ester and the dicarboxylic acid ester.

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