Method for producing carbonic acid diester

Abstract

To provide a method for producing a carbonic acid diester, by which the carbonic acid diester becoming a raw material for a polyester can efficiently be produced from a raw material carbonic acid ester derived from the polyester to enable the closed-loop type regeneration of the polyester.SOLUTION: A method for producing a carbonic acid diester includes a step of obtaining a carbonic acid diester from a composition (A) containing a raw material carbonic acid ester derived from a polyester, a monohydric alcohol, and 1.0 mass% or less of at least one selected from a dicarboxylic acid and a dicarboxylic acid ester.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a carbonic acid diester. [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, a dicarboxylic acid diester monomer can be obtained with high purity by decomposing a polyester using a base, a monohydric alcohol, and a carbonate diester. From the viewpoint of regenerating polyester in a closed loop, it is considered preferable to recover and reuse substances other than the monomers.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to enable closed-loop polyester decomposition by a method for efficiently producing a carbonate diester that promotes polyester decomposition from a raw material carbonate ester derived from 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 carbonate diester, which includes a step of obtaining a carbonate diester from composition (A) containing a raw material carbonate ester, a monohydric alcohol, and 1.0 mass% or less of at least one selected from dicarboxylic acids and dicarboxylic acid esters. That is, the present invention provides the following aspects [1] to

[17] . [1] A method for producing a carbonate diester, comprising a step of obtaining a carbonate diester from a composition (A) containing a raw material carbonate ester derived from a polyester, a monohydric alcohol, and 1.0 mass% or less of at least one selected from dicarboxylic acids and dicarboxylic acid esters. [2] A method for producing a carbonate diester, comprising a step of obtaining a carbonate diester from a composition (A) containing a raw material carbonate ester, a monohydric alcohol, and 1.0 mass% or less of at least one selected from dicarboxylic acids and dicarboxylic acid esters. [3] The method for producing a carbonic acid diester according to the above [1] or [2], wherein the total content of the dicarboxylic acid and the dicarboxylic acid ester in the composition (A) is 500 ppm by mass or less. [4] The method for producing a carbonate diester according to [1] or [2] above, wherein the step of obtaining the carbonate diester is continuously carried out in a multi-stage distillation column, and low-boiling components containing the carbonate diester are withdrawn from the top of the distillation column. [5] The method for producing a carbonate diester according to the above [4], further comprising withdrawing the produced high-boiling components, including glycol, from the bottom of the multi-stage distillation column. [6] The method for producing a carbonic acid diester according to any one of [1] to [5] above, wherein the content of the raw material carbonic acid ester in the composition (A) is 0.5 to 50 mass % and the content of the monohydric alcohol is 40 to 99.5 mass %. [7] The method for producing a carbonic acid diester according to any one of the above [1] to [6], wherein the produced glycol is removed in the step of obtaining the carbonic acid diester. [8] The method for producing a carbonic acid diester according to any one of the above [1] to [7], wherein the starting carbonic acid ester is a cyclic carbonic acid ester. [9] The method for producing a carbonic acid diester according to any one of the above [1] to [8], wherein the raw material carbonic acid ester is ethylene carbonate, the monohydric alcohol is an alcohol having 1 to 6 carbon atoms, and the carbonic acid diester is a dialkyl carbonate having 1 to 12 carbon atoms.

[10] The method for producing a carbonate diester 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 carbonate diester to decompose the polyester, thereby obtaining a decomposition product containing the starting carbonate ester.

[11] The method for producing a carbonic acid diester according to

[10] above, further comprising a step of removing the dicarboxylic acid ester from the decomposition product.

[12] The method for producing a carbonate diester 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 carbonic acid diester 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 carbonate diester 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 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 carbonate diester according to the above

[10] , wherein the base is potassium phosphate.

[16] The method for producing a carbonic acid diester 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 a carbonate diester according to any one of

[10] to

[16] , 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. [Effects of the Invention]

[0008] According to the present invention, a method for efficiently producing a carbonate diester that promotes the decomposition of polyester from a raw material carbonate ester derived from polyester makes it possible to decompose polyester in a closed-loop manner. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the method for producing a carbonic acid diester 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 carbonate diester according to one embodiment of the present invention includes a step of obtaining a carbonate diester from composition (A) containing a raw material carbonate ester derived from a polyester, a monohydric alcohol, and 1.0 mass% or less of at least one selected from dicarboxylic acids and dicarboxylic acid esters. According to the production method of this embodiment, a carbonate diester that can be used for decomposing polyesters can be produced using a raw material carbonate ester derived from polyesters as a raw material, thereby realizing closed-loop polyester decomposition.

[0011] <<Process for obtaining carbonic acid diester>> The composition (A) used in the step of obtaining the carbonic acid diester contains a raw material carbonic acid ester derived from a polyester as described above and a monohydric alcohol, and has a dicarboxylic acid and dicarboxylic acid ester content (when the composition (A) contains both a dicarboxylic acid and a dicarboxylic acid ester, the total content of these; the same applies below) of 1.0 mass% or less. More specifically, the content of dicarboxylic acid and dicarboxylic acid ester in the composition (A) is preferably 500 mass ppm or less, more preferably 10 mass ppm or less, and even more preferably 1.0 mass ppm or less. If the total content of dicarboxylic acid and carboxylic acid ester in composition (A) exceeds 1.0 mass%, the polymerization of polyester will proceed, which may result in clogging of a reactive distillation apparatus or the like, making it impossible to efficiently obtain the target carbonate diester.

[0012] 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.

[0013] <Raw material carbonate ester> The raw material carbonate ester is derived from polyester, and is preferably obtained by decomposing polyester. The raw material 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] The chain carbonate ester may be a monoester or a diester, or a mixture thereof, and is preferably a hydrocarbyl carbonate monoester, a hydrocarbyl carbonate diester, or a mixture thereof. The chain carbonate ester preferably has 3 to 15 carbon atoms, more preferably 5 to 13 carbon atoms, and even more preferably 7 to 11 carbon atoms.

[0017] The amount of the starting carbonate ester used in the step of obtaining the carbonate diester is preferably 0.5 to 50 mass %, more preferably 0.8 to 30 mass %, and even more preferably 1.0 to 15 mass %, based on the total amount of the composition (A). When the amount of the starting carbonate ester used is equal to or greater than the lower limit, the reaction efficiency in the production of the carbonate diester is improved, and when the amount of the starting carbonate ester used is equal to or less than the upper limit, excessive use of the starting carbonate ester is suppressed.

[0018] <Monohydric alcohol> In the step of obtaining a carbonic acid diester, the monohydric alcohol undergoes a transesterification reaction with the raw material carbonic acid ester. That is, in the step of obtaining a carbonic acid diester, the raw material carbonic acid ester reacts with the monohydric alcohol to produce a carbonic acid diester as well as glycols and the like. The monohydric alcohol is not particularly limited and may be, for example, either an aliphatic alcohol or an aromatic alcohol. However, in terms of the transesterification reaction proceeding at a higher rate, an aliphatic alcohol (saturated aliphatic alcohol, unsaturated aliphatic alcohol) is preferred, and a saturated aliphatic alcohol is more preferred.

[0019] Examples of saturated aliphatic alcohols include alcohols having 1 to 6 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), 2-methyl-2-propanol (tert-butyl alcohol), various pentanols, and various hexanols. The monohydric alcohol used in the step of obtaining a carbonic acid diester 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. As the monohydric alcohol, an alcohol having 1 to 6 carbon atoms is preferred, and methanol is particularly preferred in that the step of obtaining a carbonic acid diester proceeds at a particularly high efficiency. The amount of monohydric alcohol used in the step of obtaining the carbonate diester is not particularly limited, but is preferably 40 to 99.5 mass %, more preferably 60 to 99.2 mass %, and even more preferably 80 to 99.0 mass %, based on the total amount of composition (A). When the amount of monohydric alcohol used is at least the above lower limit, the reaction efficiency in producing the carbonate diester is improved, and when the amount of monohydric alcohol used is at most the above upper limit, excessive use of the monohydric alcohol is suppressed.

[0020] <Carbonate diester> Examples of carbonate diesters obtained by the step of obtaining a carbonate diester 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 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.

[0021] 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 obtained in the step of obtaining the carbonate diester varies depending on the raw material carbonate ester and monohydric alcohol used, but only one type may be obtained, or two or more types may be obtained.

[0022] <Glycol removal> In the method for producing a carbonate diester according to the present embodiment, in the step of obtaining the carbonate diester, a glycol is produced by a transesterification reaction between a raw material ester and a monohydric alcohol. By removing this glycol, the equilibrium reaction can be shifted, and the carbonate diester can be produced more efficiently. The specific method for removing glycol is not particularly limited, and can be, for example, distillation. The distillation may be performed batchwise or continuously, and may be simple distillation or multi-stage distillation. More specifically, as will be described later, a multi-stage distillation column may be used, and glycol can be efficiently removed from the bottom of the distillation column while the above-mentioned transesterification reaction is being carried out. Furthermore, when the boiling points of the starting carbonate ester and glycol are close to each other, the glycol can be removed by separate precision distillation.

[0023] <Catalyst> The catalyst used in the step of obtaining the carbonate diester is not particularly limited, and can be selected from, for example, existing transesterification catalysts and bases used in the step of obtaining the decomposition product described below. Furthermore, metal-organic frameworks (MOFs) and ion exchange resins can also be used as the catalyst. The catalyst used in the step of obtaining the carbonic acid diester is preferably at least one selected from the group consisting of alkali metal carbonates, phosphates, and hydroxides, and alkaline earth metal carbonates, phosphates, and hydroxides, and more preferably at least one selected from potassium carbonate, potassium hydroxide, and potassium phosphate.

[0024] <Reaction conditions> The step of obtaining a carbonate diester can be carried out using a composition (A) containing a raw material carbonate ester derived from a polyester, a monohydric alcohol, and 1.0 mass % or less of at least one selected from dicarboxylic acids and dicarboxylic acid esters, and optionally further containing a catalyst. Details of each of these components are as described above. The composition (A) may further contain a solvent. Details of the solvent that can be used in the step of obtaining the carbonic acid diester are the same as those of the solvent used in the polyester decomposition step described below.

[0025] The reaction temperature in the step of obtaining a carbonate diester 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 step of obtaining the carbonate diester 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 step of obtaining the carbonate diester 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 step of obtaining the carbonate diester 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 obtain the carbonate diester in a sufficiently high yield even at a reaction temperature of 20° C. or higher and 70° C. or lower.

[0026] The step of obtaining the carbonic acid diester 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 in the step of obtaining a carbonate diester is not particularly limited and can be appropriately adjusted in consideration of other reaction conditions such as the reaction temperature, etc. The reaction time in the step of obtaining a carbonate diester is preferably 0.5 to 24 hours, more preferably 0.5 to 12 hours, and even more preferably 1 to 8 hours.

[0027] The step of obtaining the carbonate diester is preferably carried out by reactive distillation using a multi-stage distillation column, and is preferably carried out while continuously supplying the composition (A) to the multi-stage distillation column. More specifically, the step of obtaining the carbonate diester is preferably carried out continuously in a multi-stage distillation column, and low-boiling components including the produced carbonate diester are preferably withdrawn from the top of the distillation column. This allows the target carbonate diester to be recovered from the top of the distillation column, but high-boiling components, such as the unreacted starting carbonate ester and the produced glycol, remain in the distillation column. Therefore, it is preferable to separately supply a monohydric alcohol to the distillation column in order to promote the reaction of the unreacted starting carbonate ester. The reaction can also be accelerated by withdrawing the high-boiling components, including glycol, produced from the bottom of the multi-stage distillation column. Although this varies depending on the temperature and pressure conditions of the distillation column, the concentration of glycol increases in the bottom of the distillation column.

[0028] The temperature at the bottom of the multi-stage distillation column is usually from -20 to 350°C, preferably from 10 to 250°C, and more preferably from 50 to 220°C. The operating pressure of the multi-stage distillation column may be reduced pressure, normal pressure, or increased pressure, but is usually 1.0 to 2.0 × 10 absolute pressure. 6 Pa, preferably 1.0 x 10 3 ~1.0×10 6 Pa, more preferably 1.0 × 10 4 ~5.0×10 5 It is Pa.

[0029] The multi-stage distillation column is preferably a continuous multi-stage tray distillation column, and any column typically used as a continuous multi-stage tray distillation column, such as a column using bubble cap trays, perforated trays, valve trays, or countercurrent trays, can be used.

[0030] <<Process for obtaining decomposition products>> The raw material carbonate ester is derived from a polyester, and specifically includes a material obtained by decomposing a polyester-containing material. Preferably, the raw material carbonate ester is obtained by a process (hereinafter also referred to as a "polyester decomposition process") in which a polyester-containing material containing a polyester is contacted with a base, a monohydric alcohol, and a carbonic acid diester to decompose the polyester and obtain a decomposition product containing the raw material carbonate ester.

[0031] <Polyester-containing materials> In the present embodiment, 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] [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 that are 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 a dicarboxylic acid diester as a monomer, which is specific depending on the type of polyester and monohydric alcohol.

[0045] 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.

[0046] <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.

[0047] 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, alkaline earth metal phosphates, etc. Examples of the alkali metal hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide, etc. Examples of the alkali metal oxides include lithium oxide, sodium oxide, potassium oxide, etc. Examples of the alkali metal carbonates include potassium carbonate, etc. Examples of the alkali metal phosphates include potassium phosphate, etc. Examples of the alkaline earth metal hydroxides include calcium hydroxide, magnesium hydroxide, etc. Examples of the alkaline earth metal oxides include calcium oxide, magnesium oxide, etc. 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.

[0048] 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, 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, in terms of particularly high rate of decomposition of polyester, and it is particularly preferable to use at least one of potassium phosphate and potassium carbonate. 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).

[0049] <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 reaction in this embodiment is controlled by the capture of the liberated dihydric alcohol by the diester carbonate present in excess. Therefore, as will be described later, from the fact that the reaction using methanol and dimethyl carbonate proceeds efficiently, it can be easily assumed that the reaction will proceed efficiently in the same way with other combinations of monohydric alcohol and dialkyl carbonate. 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.

[0050] 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 during decomposition of polyester 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.

[0051] <Carbonate diester> The carbonate diester reacts with glycols generated from the polyester during decomposition of the polyester to produce cyclic compounds or chain compounds, thereby shifting the equilibrium between the depolymerization reaction and polymerization reaction of the polyester during decomposition in favor of the depolymerization reaction, thereby improving the production rate of the target monomer. The carbonate diester functions as a glycol scavenger. The reaction product of a carbonate diester and a glycol may be a cyclic compound (e.g., cyclic compound (1) described below) which is a reaction product of one molecule of carbonate diester and one molecule of glycol, a chain compound (e.g., first chain compound (2) described below) which is a reaction product of one molecule of carbonate diester and one molecule of glycol, a chain compound (e.g., second chain compound (3) described below) which is a reaction product of one molecule of carbonate diester and two molecules of glycol, or a chain compound (e.g., third chain compound (4) described below) which is a reaction product of two molecules of carbonate diester and one molecule of glycol. Whether a cyclic compound or a chain compound is produced is determined primarily by the type (e.g., size) of the glycol. For example, the reaction product of a carbonate diester and ethylene glycol is primarily a cyclic compound (1) (more specifically, ethylene carbonate) which is a reaction product of one molecule of carbonate diester and one molecule of ethylene glycol.

[0052] [ka] (In the formula, X 1 ~X 5 are each independently a divalent organic group, and R 1 ~R 3 are each independently a monovalent organic group.

[0053] Above X 1 ~X 5 The divalent organic group represented by the formula (I) may be, for example, an aromatic group, an aliphatic group, or a group having both an aromatic group and an aliphatic group, and is preferably a divalent hydrocarbon group. Preferred divalent organic groups include 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 3The 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] <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.

[0058] When a solvent is used during polyester decomposition, the amount used is preferably 1 to 100,000 parts by mass, and more preferably 1 to 10,000 parts by mass, per 100 parts by mass of the polyester-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.

[0059] <Other ingredients> When decomposing the polyester, other components that do not fall under any of the polyester-containing material, base, monohydric alcohol, carbonic acid diester, and solvent may be used as long as they do not impair the effects of the present invention. 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. During decomposition of the polyester, the ratio of the total amount (parts by mass) of the polyester-containing material, base, monohydric alcohol, and carbonate diester to the total amount (parts by mass) of components other than the solvent (([amount (parts by mass) of polyester-containing material 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 during decomposition of the polyester is synonymous with the total amount (parts by mass) of the polyester-containing material, base, monohydric alcohol, carbonic acid diester, and other components used during decomposition.

[0060] <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.

[0061] The reaction temperature during decomposition of the polyester can be appropriately adjusted taking into consideration the type of raw material used, etc., and the decomposition may be carried out at room temperature (normal temperature) or under heated conditions. The equipment used for heating is not particularly limited, and equipment such as a heater can be used. The reaction temperature during decomposition of the polyester is preferably 20° C. or higher, more preferably 40° C. or higher, and even more preferably 60° C. or higher. The reaction temperature during decomposition of the polyester is preferably 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 during decomposition of the polyester is, for example, preferably 20° C. or higher and lower than 180° C., more preferably 40° C. or higher and 150° C. or lower, 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.

[0062] 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.

[0063] 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.

[0064] <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 raw material 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 solid-liquid separation procedures such as filtration, centrifugation, decantation, etc. at a temperature equal to or higher than the melting point of the raw material carbonate ester to recover components other than the polyester, and then volatile components are distilled off (concentrated) from the liquid obtained by the solid-liquid separation procedure. The resulting solid is washed with alcohol or water to remove the raw material 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 raw material 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.

[0065] <Removal of dicarboxylic acid esters> In this embodiment, it is preferable to include a step of removing dicarboxylic acid esters from the decomposition product obtained as described above. By removing the dicarboxylic acid esters from the decomposition product, the decomposition product after the removal treatment contains 1.0 mass % or less of at least one selected from dicarboxylic acids and dicarboxylic acid esters, and can be used as composition (A) used in the step of obtaining the carbonate diester described above. Methods for removing the dicarboxylic acid ester from the decomposition product include purification by distillation or crystallization. As described above, a solid-liquid separation operation such as filtration, centrifugation, or decantation may be performed at a temperature equal to or higher than the melting point of the starting carbonate ester, and the volatile components may be distilled off to precipitate a solid, which may then be washed with a solvent selected from alcohol and water to recover the starting carbonate ester as a solution. Alternatively, the conditions may be appropriately adjusted to allow the dicarboxylic acid ester to crystallize directly from the decomposition product and be removed. [Example]

[0066] 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.

[0067] [Manufacturing Example 1] (Decomposition of polyester) 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.

[0068] [Example 1] (Removal of dicarboxylic acid esters) The filtrate obtained in Production Example 1 is distilled to recover dimethyl carbonate and methanol, and the residue is purified by distillation to remove dimethyl terephthalate from ethylene carbonate.

[0069] (Production of carbonic acid diesters) To 3 g of the ethylene carbonate obtained as described above, 97 g of methanol was added, and 0.2 g of an 18% by mass solution of potassium hydroxide (KOH) in ethylene glycol was added to obtain a composition containing 1.0% by mass or less of dicarboxylic acids and carboxylic acid esters in total. The above composition is supplied to a multi-stage distillation column, and the reaction is carried out while the produced low-boiling components, including dimethyl carbonate, are withdrawn from the top of the distillation column and the produced high-boiling components, including ethylene glycol, are withdrawn from the bottom of the column, thereby allowing dimethyl carbonate to be recovered.

[0070] [Comparative Example 1] An ethylene carbonate composition containing 2 mass% of dimethyl terephthalate is obtained from the filtrate obtained in Production Example 1 without sufficient removal of the dicarboxylic acid ester dimethyl terephthalate. 97 g of methanol is added to 3 g of the obtained ethylene carbonate composition, and 0.2 g of an 18 mass% ethylene glycol solution of potassium hydroxide (KOH) is added to obtain a composition. When the above composition was supplied to a multi-stage distillation column and heated in the same manner as in Example 1, polymerization of the polyester partially progressed, solids were produced, and the multi-stage distillation column was clogged, making it impossible to recover dimethyl carbonate. [Industrial Applicability]

[0071] According to the production method of the present invention, a carbonic acid diester that accelerates the decomposition of polyester can be efficiently produced.

Claims

1. A method for producing a carbonate diester, comprising a step of obtaining a carbonate diester from composition (A) containing a raw material carbonate ester derived from a polyester, a monohydric alcohol, and 1.0 mass% or less of at least one member selected from dicarboxylic acids and dicarboxylic acid esters.

2. A method for producing a carbonate diester, comprising a step of obtaining a carbonate diester from composition (A) containing a raw material carbonate ester, a monohydric alcohol, and 1.0 mass% or less of at least one member selected from a dicarboxylic acid and a dicarboxylic acid ester.

3. 3. The method for producing a carbonic acid diester according to claim 1, wherein the total content of the dicarboxylic acid and the dicarboxylic acid ester in the composition (A) is 500 ppm by mass or less.

4. 3. The method for producing a carbonic acid diester according to claim 1, wherein the step of obtaining the carbonic acid diester is carried out continuously in a multi-stage distillation column, and the low-boiling components containing the carbonic acid diester are withdrawn from an upper portion of the distillation column.

5. The method for producing a carbonate diester according to claim 4, further comprising withdrawing high-boiling components containing glycol produced from the bottom of the multi-stage distillation column.

6. 3. The method for producing a carbonate diester according to claim 1, wherein the content of the raw material carbonate ester in the composition (A) is 0.5 to 50 mass% and the content of the monohydric alcohol in the composition (A) is 40 to 99.5 mass%.

7. The method for producing a carbonic acid diester according to claim 1 or 2, wherein the glycol produced in the step of obtaining the carbonic acid diester is removed.

8. 3. The method for producing a carbonic acid diester according to claim 1, wherein the raw material carbonic acid ester is a cyclic carbonic acid ester.

9. 3. The method for producing a carbonic acid diester according to claim 1, wherein the raw material carbonic acid ester is ethylene carbonate, the monohydric alcohol is an alcohol having 1 to 6 carbon atoms, and the carbonic acid diester is a dialkyl carbonate having 1 to 12 carbon atoms.

10. 3. The method for producing a carbonate diester according to claim 1 or 2, further comprising 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 starting carbonate ester.

11. The method for producing a carbonic acid diester according to claim 10, further comprising a step of removing the dicarboxylic acid ester from the decomposition product.

12. The method for producing a carbonate diester 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 carbonate diester 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 carbonic acid diester 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 carbonate diester according to claim 10, wherein the base is potassium phosphate.

16. The method for producing a carbonic acid diester 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 carbonic acid diester 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.

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