Method for producing carbonate diester

Abstract

This method for producing a carbonate diester comprises: a step for obtaining a carbonate diester from a composition (A) containing a raw material carbonate ester derived from a polyester, a monohydric alcohol, and 1.0% by mass or less of at least one selected from dicarboxylic acids and dicarboxylic acid esters. According to said method, a carbonate diester serving as a raw material for a polyester can be efficiently produced from a raw material carbonate ester derived from a polyester, and it is possible to enable closed-loop polyester recycling.

Description

Carbonate diester manufacturing method

[0001] The present invention relates to a method for producing a carbonic acid diester.

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

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

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

[0005] According to the polyester decomposition method disclosed in the aforementioned Patent Document 2, it is disclosed that 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. However, from the viewpoint of performing polyester regeneration in a closed loop system, it is considered preferable to recover and reuse substances other than the monomer.

[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.

[0007] As a result of extensive research, the inventors have found that the above-mentioned problems can be solved by a method for producing a carbonate diester, the method comprising the step of obtaining a carbonate diester from composition (A) containing a starting carbonate ester, a monohydric alcohol, and 1.0 mass% or less of at least one selected from dicarboxylic acids and dicarboxylic acid esters. Specifically, the present invention provides the following aspects [1] to

[17] . [1] A method for producing a carbonate diester, the method comprising the step of obtaining a carbonate diester from composition (A) containing a starting 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, the method comprising the step of obtaining a carbonate diester from composition (A) containing a starting 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 carbonate diester according to the above [1] or [2], wherein the total content of dicarboxylic acids and dicarboxylic acid esters in composition (A) is 500 mass ppm 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 a low-boiling component containing the carbonate diester is withdrawn from an upper portion of the distillation column. [5] The method for producing a carbonate diester according to [4] above, further comprising withdrawing a high-boiling component containing the produced glycol from a lower portion of the multi-stage distillation column. [6] The method for producing a carbonate diester according to any one of [1] to [5] above, wherein the content of the starting carbonate ester in 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 carbonate diester according to any one of [1] to [6] above, wherein the produced glycol is removed in the step of obtaining the carbonate diester. [8] The method for producing a carbonate diester according to any one of [1] to [7] above, wherein the starting carbonate ester is a cyclic carbonate 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 [1] to [9] above, 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 and obtain a decomposition product containing the starting carbonate ester.

[11] The method for producing a carbonate diester according to

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

[12] The method for producing a carbonate diester according to

[10] or

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

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

[10] to

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

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

[10] to

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

[15] The method for producing a carbonate diester according to

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

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

[10] to

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

[17] The method for producing a carbonate diester 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.

[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.

[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 dicarboxylate esters. According to the production method of this embodiment, a carbonate diester that can be used for decomposing polyesters can be produced using the raw material carbonate ester derived from a polyester, thereby realizing closed-loop polyester decomposition.

[0011] <<Step of Obtaining Carbonic Acid Diester>> Composition (A) used in the step of obtaining the carbonic acid diester contains a polyester-derived starting material carbonic acid ester and a monohydric alcohol, as described above, and has a dicarboxylic acid and dicarboxylic acid ester content (when composition (A) contains both a dicarboxylic acid and a dicarboxylic acid ester, the total content of these; the same applies hereinafter) of 1.0 mass% or less. More specifically, the content of dicarboxylic acid and dicarboxylic acid ester in 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%, polymerization of the polyester will proceed, which may result in clogging of a reactive distillation apparatus or the like, making it impossible to efficiently obtain the target carbonic acid 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 Carbonate> The raw carbonate is derived from a polyester and is preferably obtained by decomposing a polyester. The raw carbonate may be a cyclic carbonate, a chain carbonate, or a mixture thereof, but a cyclic carbonate is preferred. The cyclic carbonate is preferably one represented by the following general formula (1), and more preferably ethylene carbonate:

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

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

[0016] 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 above 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 above upper limit, excessive use of the starting carbonate ester is suppressed.

[0018] <Monohydric Alcohol> In the step of obtaining a carbonate diester, the monohydric alcohol undergoes a transesterification reaction with the raw material carbonate ester. That is, in the step of obtaining a carbonate diester, the raw material carbonate ester reacts with the monohydric alcohol to produce a carbonate diester as well as glycol 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 carbonate diester 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 as desired depending on the purpose. Note that, as the monohydric alcohol, alcohols having 1 to 6 carbon atoms are preferred, and methanol is particularly preferred in that the step of obtaining a carbonate diester proceeds at a particularly high rate. The amount of monohydric alcohol used in the step of obtaining a 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 equal to or greater than the above lower limit, the reaction efficiency in producing the carbonate diester is improved, and when the amount of monohydric alcohol used is equal to or less than the above upper limit, excessive use of the monohydric alcohol is suppressed.

[0020] <Carbonate diester> Examples of the carbonate diester obtained by the step of obtaining the carbonate diester include dialkyl carbonate and diaryl carbonate. The two alkyl groups bonded to the oxygen atom in the dialkyl carbonate may be the same as or different from each other. Furthermore, the two aryl groups bonded to the oxygen atom in the diaryl carbonate may be the same as or different from each other. The alkyl group in the dialkyl carbonate may be linear, branched, or cyclic, and if cyclic, may be monocyclic or polycyclic. The number of carbon atoms in the linear or branched alkyl group in the dialkyl carbonate is preferably 1 to 8. Examples of such an alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a 1-methylbutyl group, an n-hexyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 2,2-dimethylbutyl group, a 2,3-dimethylbutyl group, an n-heptyl group, a 2-methylhexyl group, a 3-methylhexyl group, a 2,2-dimethylpentyl group, a 2,3-dimethylpentyl group, a 2,4-dimethylpentyl group, a 3,3-dimethylpentyl group, a 3-ethylpentyl group, a 2,2,3-trimethylbutyl group, an n-octyl group, and an isooctyl group. Among these, the number of carbon atoms in the alkyl group in the dialkyl carbonate is more preferably 1 to 4, and even more preferably 1 or 2. Such more preferred dialkyl carbonates include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[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. 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 will vary depending on the starting carbonate ester and monohydric alcohol used, and one type or two or more types may be obtained.

[0022] <Removal of Glycol> In the method for producing a carbonate diester according to this embodiment, in the step of obtaining the carbonate diester, glycol is produced by the transesterification reaction between the 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 the glycol is not particularly limited, and it can be performed by distillation, for example. The distillation may be performed batchwise or continuously, and may be simple distillation or multi-stage distillation. More specifically, as described below, a multi-stage distillation column can be used to efficiently remove glycol from the bottom of the distillation column while the transesterification reaction is being carried out. Furthermore, when the boiling points of the raw material carbonate ester and glycol are close to each other, the glycol can also 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 carbonate diester is preferably one or more selected from alkali metal carbonates, phosphates, and hydroxides, and alkaline earth metal carbonates, phosphates, and hydroxides, and more preferably one or more 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 a dicarboxylic acid and a dicarboxylic acid ester, and optionally further containing a catalyst. Details of each of these components are as described above. Furthermore, the composition (A) may further contain a solvent. Details of the solvent that can be used in the step of obtaining a carbonate diester are the same as those used in the polyester decomposition step described below.

[0025] The reaction temperature in the step of obtaining a carbonate diester can be adjusted appropriately 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 a 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 a carbonate diester is preferably less than 180°C, more preferably 150°C or lower, even more preferably 100°C or lower, and particularly preferably 70°C or lower. In one embodiment, the reaction temperature in the step of obtaining a 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, a carbonate diester can be obtained at a sufficiently high yield even at a reaction temperature of 20°C or higher and 70°C or lower.

[0026] The step of obtaining a carbonate diester may be carried out under normal pressure, reduced pressure, or increased pressure. The step of obtaining a carbonate diester may be carried out under air or an inert gas atmosphere. 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. 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, with low-boiling components, including the produced carbonate diester, being 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 from the viewpoint of promoting the reaction of the unreacted starting carbonate ester. The reaction can also be promoted by withdrawing the high-boiling components, including the produced glycol, from the bottom of the multi-stage distillation column. Although this varies depending on the temperature and pressure conditions of the distillation column, the glycol concentration increases in the lower part of the distillation column.

[0028] The temperature at the bottom of the multi-stage distillation column is usually −20 to 350° C., preferably 10 to 250° C., and more preferably 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 x 10 ６ Pa, more preferably 1.0 x 10 ４ ~5.0 x 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] <<Step of Obtaining Decomposition Product>> The raw material carbonate ester described above is derived from a polyester, and specifically includes one obtained by decomposing a polyester-containing material. Preferably, the raw material carbonate ester is obtained by a step of contacting a polyester-containing material containing a polyester with a base, a monohydric alcohol, and a carbonate diester to decompose the polyester and obtain a decomposition product containing the raw material carbonate ester (hereinafter also referred to as a “polyester decomposition step”).

[0031] <Polyester-Containing Material> In the present embodiment, the polyester-containing material is not particularly limited as long as it contains polyester, and may contain a component other than polyester, and examples thereof include materials containing polyester fibers, and polyester-containing films, packaging containers, bottles, lumps, etc. The component other than polyester may be a resin other than polyester, or may be a non-resin component.

[0032] Specific examples of the polyester-containing material include materials containing polyester fibers (polyester fibers), films containing polyester and components other than polyester, and lumps containing polyester and components other than polyester. Materials containing polyester fibers include, for example, polyester fibers (fibers containing no components other than polyester), woven polyester fibers, mixtures containing polyester fibers and components other than polyester fibers, and woven fabrics of such mixtures. Mixtures containing polyester fibers and components other than polyester fibers include, for example, mixed fibers of polyester fibers and fibers other than polyester fibers and woven fabrics of such mixed fibers, composite mixtures containing polyester fibers and non-resin components (e.g., colored fibers containing polyester fibers and colorants) and woven fabrics of such composite mixtures, and composite mixed fibers containing polyester fibers, fibers other than polyester fibers, and non-resin components (e.g., colored mixed fibers containing mixed fibers and colorants) and woven fabrics of such composite mixtures. Here, in this specification, "non-resin components" refers to components that do not fall into either polyester or resins other than polyester.

[0033] Examples of films containing polyester and components other than polyester include a monolayer film containing polyester and a component other than polyester, and a laminate film that is a laminate of a film made of polyester (polyester film) and a film containing a component other than polyester. Examples of monolayer films containing polyester and a component other than polyester include a monolayer film that contains both polyester and a resin other than polyester and does not contain a non-resin component, a monolayer film that contains both polyester and a non-resin component and does not contain a resin other than polyester, and a monolayer film that contains all of polyester, a resin other than polyester, and a non-resin component.

[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 all of polyester, a resin other than polyester, and a non-resin component, a multilayer film that is a laminate of one or more of the above laminate films and one or more of the above monolayer films, a multilayer film that is a laminate of two or more of the above laminate films, and a multilayer film that is a laminate of two or more of the above monolayer films.

[0035] Examples of aggregates containing polyester and components other than polyester include aggregates containing both polyester and resins other than polyester but no non-resin components, aggregates containing both polyester and non-resin components but no resins other than polyester, and aggregates containing polyester, resins other than polyester, and non-resin components. The resin other than polyester can be selected arbitrarily depending on the purpose and is not particularly limited. For example, resins other than polyester that are highly versatile and highly applicable to the present invention include polyolefins such as polyethylene and polypropylene, cellulose, polyamides such as nylon, polyurethane, and acrylic resins. These resins may be, for example, in the form of a film (resin film) or a fiber (resin fiber). Examples of fibers other than polyester fibers include fibers of resins other than the above-mentioned polyesters, cotton, rayon, etc.

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

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

[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. However, 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 capable of condensation with the glycol. The polyester may be an aromatic polyester having only aromatic groups (divalent groups having a structure in which one hydrogen atom is removed from each of two carbon atoms forming the aromatic ring skeleton of an aromatic compound) in its ester bond-containing main chain, an aliphatic polyester having no aromatic groups in its main chain (having both an aliphatic group and no aromatic group), or a polyester having both aromatic and aliphatic groups in its main chain. The aromatic polyester may have only divalent aromatic hydrocarbon groups (arylene groups) as aromatic groups, only divalent aromatic heterocyclic groups (heteroarylene groups), or both divalent aromatic hydrocarbon groups and divalent aromatic heterocyclic groups. Examples of heteroatoms in the aromatic heterocyclic groups include oxygen atoms and nitrogen atoms. In general, the reactivity of a substrate in a transesterification reaction depends on the structure on the carboxylic acid side and the structure on the alcohol side. As will be described later, polyesters (polyethylene terephthalate, polybutylene terephthalate, etc.) having an aromatic benzene ring or naphthalene ring as the carboxylic acid side structure can be decomposed well, and therefore it can be easily assumed that polyesters having other aromatic structures such as furan can be decomposed in a similar manner. Similarly, polyesters having an ethylene glycol (polyethylene terephthalate, etc.) or 1,4-butanediol (polybutylene terephthalate, etc.) structure as the alcohol side structure can be decomposed well, and therefore it can be easily assumed that polyesters having other dihydric alcohol structures such as 1,3-propanediol can be decomposed in a similar manner.In terms of enhancing the effects of the present invention and increasing versatility, the polyester is preferably an aromatic polyester, and more preferably polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), or polyethylene furanoate (PEF, also known as polyethylene furan dicarboxylate). Decomposition of the polyester produces, as a monomer, a dicarboxylic acid diester specific to the polyester and the type of monohydric alcohol.

[0045] For example, polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate produce terephthalic acid diesters, polyethylene naphthalate and polybutylene naphthalate produce naphthalenedicarboxylic acid diesters (2,6-naphthalenedicarboxylic acid diesters), and polyethylene furanoate produces furandicarboxylic acid diesters (2,5-furandicarboxylic acid diesters). For example, when methanol is used as the monohydric alcohol, dimethyl dicarboxylic acid esters are produced as dicarboxylic acid diesters. The polyester-containing material may contain only one type of polyester, or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected as desired depending on the purpose.

[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, or an alkali metal alkoxide, which reacts with a monohydric alcohol to produce an alkali metal alkoxide. Generally, in a transesterification reaction, an alkoxide anion serving as a nucleophile attacks the carbonyl group of an ester, passing through a quaternary carbon intermediate and then liberating the other alkoxide anion, thereby proceeding. Since an alkoxide anion is produced by the reaction of a corresponding alcohol with a base, any base capable of deprotonating an alcohol can be used.

[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; Examples of the alkali metal alkoxide include alkaline earth metal alkoxides such as 1,5,7-triazabicyclo[4.4.0]dec-5-ene (abbreviation: TBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (abbreviation: DBU), 1,3-dimesitylimidazol-2-ylidene, and 1,3-dicyclohexylimidazol-2-ylidene; and nitrogen-containing organic bases (organic bases having a nitrogen atom) such as lithium methoxide, sodium methoxide, or potassium methoxide, with sodium methoxide being more preferred, in terms of promoting polyester decomposition at a higher rate. The nitrogen-containing organic base is preferably 1,5,7-triazabicyclo[4.4.0]dec-5-ene, in terms of promoting polyester decomposition at a higher rate.

[0048] The base used in the decomposition step may be one type or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected arbitrarily depending on the purpose. As the base, in order to achieve particularly high rates of polyester decomposition, it is preferable to use one or more types selected from alkali metal carbonates, phosphates, and hydroxides, and alkaline earth metal carbonates, phosphates, and hydroxides, 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 at least the lower limit, polyester decomposition proceeds at a higher rate. When the amount of base used is at most the upper limit, excessive use of base is suppressed. That is, when decomposing polyester, it is preferable to use a catalytic amount of base (the base is a catalyst).

[0049] <Monohydric Alcohol> In the decomposition process, the monohydric alcohol undergoes a transesterification reaction with the polyester in the polyester-containing material. That is, during the decomposition of the polyester, the reaction between the polyester and the monohydric alcohol produces a glycol corresponding to one of the monomers used in the production of the polyester, and a dicarboxylic acid diester corresponding to the other monomer or 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 free dihydric alcohol by the excess diester carbonate. Therefore, as described below, based on the fact that the reaction using methanol and dimethyl carbonate proceeds efficiently, it can be easily assumed that the reaction will proceed efficiently with other combinations of monohydric alcohol and dialkyl carbonate. The monohydric alcohol may be, for example, either an aliphatic alcohol or an aromatic alcohol. However, in terms of proceeding with a higher rate of decomposition of the polyester, an aliphatic alcohol (saturated aliphatic alcohol, unsaturated aliphatic alcohol) is preferred, and a saturated aliphatic alcohol is more preferred.

[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 in the decomposition of polyester may be a single type or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected as desired depending on the purpose. Methanol is particularly preferred as the monohydric alcohol, as it promotes particularly high rates of polyester decomposition. The amount of monohydric alcohol used in the decomposition of polyester is not particularly limited. For example, when the polyester is polyethylene terephthalate (PET), the amount is preferably 30 to 200 parts by mass, and more preferably 50 to 160 parts by mass, per 100 parts by mass of PET in the polyester-containing material. Furthermore, when the polyester is polybutylene terephthalate (PBT), the amount of monohydric alcohol used is preferably 10 to 180 parts by mass, more preferably 20 to 140 parts by mass, per 100 parts by mass of PBT in the polyester-containing material. When the amount of monohydric alcohol used is equal to or greater than these lower limits, the effects obtained by using the monohydric alcohol are enhanced. On the other hand, when the amount of monohydric alcohol used is equal to or less than these upper limits, excessive use of the monohydric alcohol is suppressed.

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

[0052] (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, for example, an ethylene group (—CH ２ CH ２ -), 1,3-propylene group (trimethylene group, -CH ２ CH ２ CH２ -), 1,4-butylene group (tetramethylene group, -CH ２ CH ２ CH ２ CH ２ -), and alkylene groups having 2 to 4 carbon atoms are more preferred. １ ~R ３ The monovalent organic group represented by the formula (I) may be, for example, either an aromatic group or an aliphatic group, but is preferably an aliphatic group (a saturated aliphatic group or an unsaturated aliphatic group), and more preferably an aliphatic hydrocarbon group. Preferred monovalent organic groups include, for example, monovalent saturated aliphatic groups (i.e., alkyl groups) such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group, and is more preferably a monovalent saturated aliphatic group (i.e., alkyl group) having 1 to 4 carbon atoms.

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

[0055] The aryl group in the diaryl carbonate may be either monocyclic or polycyclic. The aryl group in the diaryl carbonate preferably has 6 to 10 carbon atoms. Examples of such aryl groups include phenyl, 1-naphthyl, 2-naphthyl, o-tolyl, m-tolyl, p-tolyl, 2,3-xylyl (2,3-dimethylphenyl), 2,4-xylyl (2,4-dimethylphenyl), 2,5-xylyl (2,5-dimethylphenyl), 2,6-xylyl (2,6-dimethylphenyl), 3,4-xylyl (3,4-dimethylphenyl), and 3,5-xylyl (3,5-dimethylphenyl). A more preferred diaryl carbonate is diphenyl carbonate. The carbonate diester used in the decomposition of polyester may be one type or two or more types. When two or more types are used, the combination and ratio thereof are not particularly limited and can be selected as desired depending on the purpose. In terms of proceeding with decomposition of the polyester at a higher rate, the carbonate diester is more preferably one or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and diphenyl carbonate, and is particularly preferably dimethyl carbonate.

[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 base, monohydric alcohol, and carbonate diester may be used. In this embodiment, decomposition of the polyester proceeds efficiently even without the use of a solvent. However, using a solvent as needed may improve the handleability of the blend of raw materials, such as the reaction solution, and may result in more efficient decomposition of the polyester. In this specification, unless otherwise specified, the term "solvent" encompasses both a component that is liquid at room temperature and serves as a dispersant for dissolving a solute, and a component that is liquid at room temperature and serves as a dispersion medium for dispersing a dispersoid. Furthermore, "room temperature" refers to a temperature that is not particularly cooled or heated, i.e., an ordinary temperature, such as a temperature of 15 to 25°C. Here, the solvent is preferably an organic solvent. Examples of organic solvents include aromatic hydrocarbons such as toluene, ethers such as tetrahydrofuran, alkanes such as n-hexane, halogenated hydrocarbons such as chloroform and dichloromethane, amides such as dimethylformamide, and sulfoxides such as dimethyl sulfoxide. The solvent used for decomposing the polyester may be one kind or two or more kinds, 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 decomposition of the polyester, 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 Components> When decomposing the polyester, other components that do not fall under any of the polyester-containing material, base, monohydric alcohol, carbonate diester, and solvent may be used as long as the effects of the present invention are not impaired. 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 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. During decomposition of the polyester, the ratio of the total amount (parts by mass) of the polyester-containing material, base, monohydric alcohol, and carbonate diester to the total amount (parts by mass) of components other than the solvent (([amount (parts by mass) of polyester-containing material] + [amount (parts by mass) of base] + [amount (parts by mass) of monohydric alcohol] + [amount (parts by mass) of carbonate diester]) / [total amount (parts by mass) of components other than the solvent] × 100) is preferably 80% by mass to 100% by mass, more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass, and may be, for example, any one of 97% by mass to 100% by mass and 99% by mass to 100% by mass. When the ratio is equal to or greater than the lower limit, the polyester can be decomposed more efficiently. 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> Decomposition of the polyester in the polyester-containing material can be carried out by contacting a base, a monohydric alcohol, a carbonic acid diester, the polyester-containing material, and optionally a solvent and optionally other components. Details of each of these components are as described above.

[0061] The reaction temperature during decomposition of the polyester can be adjusted appropriately taking into account the type of raw material used, etc., and the decomposition may be carried out at room temperature (normal temperature) or under heated conditions. The equipment used for heating is not particularly limited, and equipment such as a heater can be used. The reaction temperature 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 less than 180°C, more preferably 150°C or lower, even more preferably 100°C or lower, and particularly preferably 70°C or lower. In one embodiment, the reaction temperature 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, more preferably 50°C or higher and 120°C or lower, and particularly preferably 60°C or higher and 100°C or lower. For example, by adjusting reaction conditions other than the reaction temperature, it is possible to decompose the polyester at a sufficiently high rate even at a reaction temperature of 20°C or higher and 70°C or lower. According to the present embodiment, as described above, while it has been conventionally difficult to decompose polyesters at relatively low temperatures, it is now possible to decompose polyesters at low temperatures, such as 150° C. or lower, and thus it is possible to separate polyesters from polyester-containing materials. As a result, unlike when polyesters are decomposed at high temperatures, the amount of by-products produced during decomposition can be reduced, discoloration of the dicarboxylic acid diester (monomer), which is the main decomposition product, can be reduced, and deterioration of components other than polyester contained in the polyester-containing material can be prevented.

[0062] The decomposition of the polyester may be carried out under normal pressure, reduced pressure, or increased pressure. The decomposition of the polyester may be carried out under atmospheric pressure or an inert gas atmosphere. The reaction time during the decomposition of the polyester is not particularly limited and can be adjusted appropriately taking into account other reaction conditions such as the reaction temperature. The reaction time during the decomposition of the polyester is not particularly limited as long as it is 0.5 to 24 hours, but is preferably 0.5 to 12 hours, and more preferably 1 to 8 hours. In this embodiment, the end of decomposition can be determined, for example, when the polyester disappears. Therefore, the time required for the polyester to disappear can be considered the decomposition reaction time. The time required for the polyester to disappear can also be determined, for example, by the time required for the mass loss of the polyester-containing material to stop.

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

[0064] <Post-Treatment Conditions, Extraction Conditions> After the polyester decomposition process described above is completed, the resulting decomposition product can be post-treated by a known method, allowing the raw material carbonate ester and dicarboxylic acid diester to be extracted with high purity. For example, after decomposition of the polyester, the resulting decomposition product can be subjected to solid-liquid separation procedures such as filtration, centrifugation, and decantation at a temperature equal to or higher than the melting point of the raw material carbonate ester to recover components other than the polyester. The liquid obtained by the solid-liquid separation procedure is then subjected to distillation (concentration) of volatile components, and the resulting solid is washed with alcohol or water to remove the raw material carbonate ester, thereby obtaining a high-purity dicarboxylic acid diester. If necessary, the resulting dicarboxylic acid diester may be further purified by crystallization, distillation, or the like. Meanwhile, the raw material carbonate ester obtained in a dissolved state in methanol and water can be recovered by crystallization, distillation, or the like. According to this embodiment, as described above, decomposition is possible at low temperatures, such as below 180°C, and therefore, unlike decomposition at high temperatures, the impurity content and coloration of the dicarboxylic acid diester can be reduced. Therefore, a highly pure dicarboxylic acid diester having reduced coloration can be obtained by the simplified process of washing with methanol and water as described above, without adding any complicated steps. Furthermore, even if the polyester-containing material originally contains a colorant, the coloration of the dicarboxylic acid diester derived from the colorant can also be reduced by the simplified process of washing with methanol and water as described above.

[0065] <Removal of Dicarboxylic Acid Ester> This embodiment preferably includes a step of removing the dicarboxylic acid ester from the decomposition product obtained as described above. By removing the dicarboxylic acid ester 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) to be 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, the starting carbonate ester may be recovered as a solution by performing a solid-liquid separation operation such as filtration, centrifugation, or decantation at a temperature equal to or higher than the melting point of the starting carbonate ester, followed by distilling off the volatile components and washing the precipitated solid with a solvent selected from alcohol and water. Alternatively, the dicarboxylic acid ester may be removed by crystallizing it directly from the decomposition product under appropriate conditions.

[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. Note that the unit "ppm" shown below is always based on mass ratio.

[0067] [Production Example 1] (Decomposition of Polyester) Potassium phosphate (K ３ P.O. ４) (Fujifilm Wako Pure Chemical Industries, Ltd.) was added, followed by 6.5 L of methanol (Kishida Chemical Co., Ltd.) and 50 L of dimethyl carbonate (DMC) (Tokyo Chemical Industry Co., Ltd.), and the mixture was uniformly dispersed to prepare a raw material composition. A white coat (100% by mass of polyester fiber in total fibers) was cut into approximately 2 cm x 2 cm pieces, and several pieces (10 kg) were added to the raw material composition in the 200 L reactor obtained above. Here, the proportion (by mass%) of polyester fiber in total fibers is synonymous with the ratio of the polyester content (parts by mass) to the total mass (parts by mass) of the polyester-containing material, as described above. Next, the mixture of the raw material composition and the cut material was stirred at 50°C for 2 hours to decompose the polyester fiber. Next, dimethyl carbonate (15 L) was added to the mixture in the reactor to dissolve the precipitated components, and the contents were hot-filtered at 50°C without cooling, and the filtrate was recovered.

[0068] Example 1 (Removal of Dicarboxylic Acid Ester) 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 Carbonate Diester) 9.7 kg of methanol was added to 300 g of the ethylene carbonate obtained as described above, and 20 g of an 18 mass % ethylene glycol solution of potassium hydroxide (KOH) was added to obtain a composition. This composition contains a dicarboxylic acid and a carboxylic acid ester in a total amount of 1.0 mass % or less. The composition was supplied to a multi-stage distillation column, and the reaction was carried out while the low-boiling components, including dimethyl carbonate, produced were withdrawn from the top of the distillation column and the high-boiling components, including ethylene glycol, produced were withdrawn from the bottom of the column, and dimethyl carbonate was recovered.

[0070] Comparative Example 1 An ethylene carbonate composition containing 2 mass% of dimethyl terephthalate was obtained from the filtrate obtained in Production Example 1 without sufficient removal of the dicarboxylic acid ester, dimethyl terephthalate. 9.7 kg of methanol was added to 300 g of the obtained ethylene carbonate composition, and 20 g of an 18 mass% ethylene glycol solution of potassium hydroxide (KOH) was added to obtain a composition. When the composition was supplied to a multi-stage distillation column and heated in the same manner as in Example 1, polymerization of the polyester proceeded partially, producing solids and clogging the multi-stage distillation column, making it impossible to recover dimethyl carbonate.

[0071] According to the production method of the present invention, a carbonic acid diester that accelerates polyester decomposition 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 dicarboxylic acids and dicarboxylic acid esters.

3. A method for producing a carbonic acid diester according to claim 1 or 2, wherein the total content of dicarboxylic acid and dicarboxylic acid ester in composition (A) is 500 mass ppm or less.

4. A method for producing a carbonic acid diester according to claim 1 or 2, wherein the step of obtaining the carbonic acid diester is carried out continuously in a multi-stage distillation column, and low-boiling components containing the carbonic acid diester are extracted from the top of the distillation column.

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

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

8. A method for producing a carbonic acid diester according to claim 1 or 2, wherein the raw material carbonic acid ester is a cyclic carbonic acid ester.

9. A method for producing a carbonic acid diester according to claim 1 or 2, 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. A method for producing a carbonic acid diester according to claim 1 or 2, further comprising the step of contacting a polyester-containing material containing a polyester with a base, a monohydric alcohol, and a carbonic acid diester to decompose the polyester and obtain a decomposition product containing the raw material carbonic acid 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 carbonic acid 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 carbonic acid diester according to claim 10, wherein the monohydric alcohol in the step of obtaining the decomposition product is methanol.

14. A 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 carbonic acid 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. 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.