Method for producing polyester decomposition products, and method for producing polyester

Abstract

To provide a method for producing polyester decomposition products that can decompose polyester under mild conditions without requiring high temperature or high pressure, and that yields excellent amounts of dicarboxylic acid diesters, glycols, and cyclic carbonate esters. [Solution] The method for producing polyester decomposition products of this embodiment comprises: a decomposition step of contacting a polyester-containing material with a polyester-decomposition composition containing a base, a monohydric alcohol, and a diester carbonate to decompose the polyester in the polyester-containing material to obtain polyester decomposition products; a base reduction step of reducing the base content in the polyester decomposition products; a dehydration step of dehydrating the polyester decomposition products after the base reduction step; and a purification step of separating cyclic carbonate esters from the polyester decomposition products after the dehydration step.

Description

Technical Field

[0004] , , , ,

[0005] , , , ,

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

Background Art

[0002] <000D009>As methods for decomposing polyester, there are disclosed a method using water or supercritical alcohol (see, for example, Patent Documents 1 and Patent Documents 2), a method using a base catalyst and alcohol in a halogenated solvent (see, for example, Non-Patent Document 1 and Patent Document 3), a method using a basic catalyst and tetraalkoxysilane in an alcohol solvent (see, for example, Patent Document 4), and a method using a base catalyst in a mixed solvent of dimethyl carbonate and alcohol (see, for example, Patent Document 5).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Non-Patent Documents

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the methods described in Patent Documents 1 to 4 have slow reaction rates and the reaction equilibrium is biased towards the original system, requiring the input of large amounts of energy such as high temperature and pressure. Furthermore, the methods described in Patent Document 5 and Non-Patent Document 1, which address these issues, use diester carbonate as a raw material, thereby shifting the polyester decomposition reaction equilibrium towards the product side, allowing the reaction to proceed under mild conditions. In the methods described in these documents, dialkyl terephthalate, cyclic carbonate, and alkylene glycol are obtained by the polyester decomposition reaction.

[0006] While dialkyl terephthalate and alkylene glycol can be reused as raw materials for polyester, cyclic carbonate esters are thermally decomposable, and their yield tends to decrease due to thermal decomposition. This thermal decomposition reaction tends to be accelerated in the presence of metal components, and the same is true when catalysts containing alkali metal atoms as constituent elements are used. The inventors have investigated and found that in the separation and recovery process of cyclic carbonate esters, heating in the presence of metal components as a catalyst tends to accelerate the decomposition of cyclic carbonate esters, and that it is necessary to increase the recovery rate.

[0007] Therefore, the present invention aims to provide a method for producing polyester decomposition products that can decompose polyester under mild conditions without requiring high temperature or high pressure conditions, and that yields excellent amounts of dicarboxylic acid diesters, glycols, and cyclic carbonate esters. [Means for solving the problem]

[0008] The present invention has been made in view of the above problems, and as a result of the inventors of the present invention diligently studied to solve the aforementioned problems, they found that in a method for producing polyester decomposition products by contacting a polyester decomposition composition containing a base, a monohydric alcohol, and a diester carbonate with a polyester-containing material and decomposing the polyester in the polyester-containing material, catalysts such as bases can be efficiently reduced from the organic phase by using a predetermined extractant, and glycols that can be reused as raw materials for polyester and cyclic carbonates can be recovered in good yield, thus completing the present invention. That is, the present invention is as follows. [1] A decomposition step involves contacting a polyester-containing material with a polyester-decomposing composition comprising a base, a monohydric alcohol, and a diester carbonate to decompose the polyester in the polyester-containing material and obtain a polyester decomposition product. A base reduction step for reducing the amount of base contained in the polyester decomposition product, Following the base reduction step, a dehydration step is performed to dehydrate the polyester decomposition product, The process includes a purification step, which follows the dehydration step, in which cyclic carbonate esters are separated from the polyester decomposition product. A method for producing polyester decomposition products. [2] The purification step separates the cyclic carbonate ester and glycol from the polyester decomposition product containing the dicarboxylic acid diester. A method for producing polyester decomposition products as described in [1]. [3] The base reduction step includes liquid-liquid extraction. A method for producing polyester decomposition products as described in [1] or [2]. [4] The extractant for the aforementioned liquid-liquid extraction is water. A method for producing a polyester decomposition product as described in any of [1] to [3]. [5] Synthesis step 1 involves reacting carbon dioxide with a cyclic ether to synthesize a cyclic carbonate ester, React the cyclic carbonate obtained by the synthesis step 1 with a monohydric alcohol to synthesize a carbonic acid diester and a glycol, which is a synthesis step 2, Use the carbonic acid diester obtained in the synthesis step 2 in the decomposition step, [1]~[4] The method for producing a polyester decomposition product according to any one of the above. [6] Use the cyclic carbonate and / or the carbonic acid diester obtained in the purification step in the synthesis step 2, [5] The method for producing a polyester decomposition product according to the above. [7] The monohydric alcohol used in the step 1 and / or the decomposition step contains an alcohol having a carbon number of 1 or 2, The base contains at least one of an alkali metal and an alkaline earth metal, [5] or [6] The method for producing a polyester decomposition product according to the above. [8] Include a polymerization step of polymerizing using a polyester decomposition product obtained by the method according to any one of [1]~[7] as a monomer, The method for producing a polyester.

Effect of the Invention

[0009] According to the present invention, it is possible to provide a method for producing a polyester decomposition product that can decompose polyester under mild conditions without requiring high temperature and high pressure conditions, and has excellent yields of dicarboxylic acid diester, glycol, and cyclic carbonate.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described in detail. The present embodiment is an example for explaining the present invention, and the present invention is not limited to only this embodiment, and the present invention can be appropriately modified and implemented within the scope of its gist.

[0011] <Method for Producing Polyester Decomposition Product> The method for producing a polyester decomposition product according to this embodiment includes a decomposition step of bringing a polyester decomposition composition containing a base, a monohydric alcohol, and a diester carbonate into contact with a polyester-containing material to decompose the polyester in the polyester-containing material to obtain a polyester decomposition product, a base reduction step of reducing the content of the base contained in the polyester decomposition product, a dehydration step of dehydrating the polyester decomposition product after the base reduction step, and a purification step of separating a cyclic carbonate from the polyester decomposition product after the dehydration step, and may include other steps as necessary.

[0012] <Decomposition step> The decomposition step of this embodiment is a step of bringing a polyester decomposition composition containing a base, a monohydric alcohol, and a diester carbonate into contact with a polyester-containing material to decompose the polyester in the polyester-containing material to obtain a polyester decomposition product.

[0013] <Object to be decomposed> The polyester-containing material is not limited to a single polyester, and is a concept including materials containing polyester and materials other than polyester. Therefore, as long as the material contains polyester, it is not particularly limited as the object of decomposition.

[0014] The polyester-containing material of this embodiment is not particularly limited. For example, it includes a single polyester, a material having an extremely high polyester content and a form suitable for performing a decomposition reaction, such as a film made of polyethylene terephthalate (PET); materials having a low polyester content or not suitable for performing a decomposition reaction. The materials not suitable for performing the decomposition reaction are not particularly limited. For example, materials in which the surface of the polyester is coated with another substance so that the polyester decomposition composition and the polyester cannot physically contact each other can be mentioned. That is, a wide range of materials can be used as the polyester-containing material of this embodiment.

[0015] More specifically, the polyester-containing material of this embodiment is not particularly limited, but examples include a material containing polyester fibers, a film containing polyester and components other than polyester, and a mass containing polyester and components other than polyester.

[0016] Materials containing polyester fibers are not particularly limited, but examples include polyester fibers (fibers that do not contain components other than polyester), polyester fiber fabrics, mixtures containing polyester fibers and components other than polyester fibers, and fabrics of such mixtures.

[0017] The mixture containing polyester fibers and components other than polyester fibers is not particularly limited, but examples include mixed fibers of polyester fibers and fibers other than polyester fibers and fabrics of the mixed fibers, composite mixtures containing polyester fibers and non-resin components (for example, colored fibers containing polyester fibers and colorants) and fabrics of the composite mixture, and composite mixed fibers containing polyester fibers, fibers other than polyester fibers and non-resin components (for example, colored mixed fibers containing mixed fibers and colorants) and fabrics of the composite mixture. Here, in this embodiment, "non-resin component" means a component that does not fall under either polyester or resins other than polyester.

[0018] Furthermore, while there are no particular limitations on the films containing polyester and other components, examples include single-layer films containing polyester and other components, and laminated films which are laminates of a polyester film and a film containing other components.

[0019] The single-layer film containing polyester and non-polyester components is not particularly limited, but examples include a single-layer film containing both polyester and non-polyester resins and no non-resin components, a single-layer film containing both polyester and non-resin components and no non-polyester resins, and a single-layer film containing polyester, non-polyester resins, and non-resin components.

[0020] Laminated films, which are laminates of a polyester film and a film containing components other than polyester, are not particularly limited, but examples include: a laminated film made of a polyester film and a film containing a resin other than polyester and not containing either polyester or non-resin components; a laminated film made of a polyester film and a film containing both a resin other than polyester and polyester and not containing any non-resin components; a laminated film made of a polyester film and a film containing both a resin other than polyester and non-resin components and not containing polyester; a laminated film made of a polyester film and a film containing both polyester and non-resin components and not containing any resin other than polyester; a laminated film made of a polyester film and a film containing polyester, a resin other than polyester, and non-resin components; a multilayer film made of one or more of the above laminated films and one or more of the above single-layer films; a multilayer film made of two or more of the above laminated films; and a multilayer film made of two or more of the above single-layer films.

[0021] The bulk material containing polyester and non-polyester components is not particularly limited, but examples include bulk material containing both polyester and non-polyester resins and no non-resin components; bulk material containing both polyester and non-resin components and no non-polyester resins; and bulk material containing polyester, non-polyester resins, and non-resin components.

[0022] Resins other than polyester can be arbitrarily selected depending on the purpose and are not particularly limited. Examples of resins other than polyester that are highly versatile and have high applicability to the present invention include polyolefins such as polyethylene and polypropylene; polyamides such as cellulose and nylon; polyurethane; and acrylic resins. These resins are not particularly limited, but may be in the form of films (resin films) or fibers (resin fibers).

[0023] Other fibers besides polyester include fibers made from resins other than polyester, cotton, rayon, polyurethane, nylon, and olefins.

[0024] Furthermore, the non-resin components can be arbitrarily selected depending on the purpose and are not particularly limited. While the non-resin components are not particularly limited, examples of highly versatile and valuable applications of the present invention include inorganic components (inorganic compounds) such as aluminum, colorants such as dyes and pigments, stabilizers, antistatic agents, flame retardants, desiccants, and gas barrier agents.

[0025] In materials containing polyester fibers, the fiber diameters of the polyester fibers and the fibers other than polyester fibers are not particularly limited, but may be, for example, 0.1 μm to 200 μm or 1 μm to 50 μm.

[0026] The thickness of the film containing polyester and other components is not particularly limited, but may be, for example, 0.5 μm to 1000 μm, or 1 μm to 500 μm. Here, if the film is the laminated film described above, the film thickness refers to the total thickness of the laminated film.

[0027] More specifically, materials containing polyester fibers include, but are not limited to, fabrics for various garments, fibers that are the material for fabrics, etc. The fabric is not limited to, but may be, for example, small pieces such as cut pieces generated during the manufacture of various garments, or cut pieces of various garments after use. The fibers that are the material for fabrics are not limited to, but may be, for example, small pieces such as cut pieces generated during the manufacture of fabrics, or cut pieces generated from used fabrics.

[0028] More specifically, films containing polyester and other components, without any particular limitations, include packaging films, small pieces such as cut materials generated during the manufacture of packaging films, and small pieces such as cut materials of used packaging films.

[0029] More specifically, the aggregate containing polyester and non-polyester components can include, but are not limited to, pellets, flakes, scraps generated during PET bottle manufacturing, and crushed recycled PET bottles containing polyester and non-polyester components. The maximum diameter of the aggregate is not particularly limited, but may be, for example, 0.01 mm to 10 mm. Here, "maximum diameter of the aggregate" means the maximum length of the line segment connecting two different points on the surface of the aggregate. Specifically, for example, commercially available PET powder with a particle size of 106 μm or less can be used.

[0030] The polyester-containing material of this embodiment may be used alone or in combination of two or more types. When two or more types are used in combination, their combination and ratio can be arbitrarily selected according to the purpose. That is, the polyester-containing material of this embodiment is one or more types selected from the group consisting of materials containing polyester fibers, films containing polyester and non-polyester components, and lumps containing polyester and non-polyester components.

[0031] In this embodiment, if the polyester-containing material is a material containing polyester fibers, it is preferable that the material containing polyester fibers is one or more selected from the group consisting of polyester fibers, fabrics of polyester fibers, mixtures containing polyester fibers and components other than polyester fibers, and fabrics of the mixture.

[0032] In this embodiment, if the polyester-containing material is a film containing polyester and components other than polyester, it is preferable that the film containing polyester and components other than polyester is either a single-layer film containing polyester and components other than polyester, or a laminated film which is a laminate of a film made of polyester and a film containing components other than polyester, or both.

[0033] In the polyester-containing material of this embodiment, the ratio of the polyester content (parts by mass) to the total mass (parts by mass) of the polyester-containing material ([polyester content (parts by mass) in the polyester-containing material] / [total mass (parts by mass) of the polyester-containing material] × 100) (polyester content ratio) can be arbitrarily selected according to the purpose and is not particularly limited. Among these, the polyester content ratio is preferably 20% by mass or more and 100% by mass or less, more preferably 40% by mass or more and 100% by mass or less, even more preferably 55% by mass or more and 100% by mass or less, and most preferably 70% by mass or more and 100% by mass or less. The higher the polyester content ratio, the greater the amount of monomer (dicarboxylic acid diester described later) produced from the polyester-containing material per unit mass due to the decomposition of polyester tends to be.

[0034] <Polyester> In this embodiment, the polyester to be decomposed can be any conventionally known polyester, and is not particularly limited as long as it is an oligomer or polymer that produces glycol and dicarboxylic acid diester upon decomposition. The polyester used for decomposition may be used alone or in combination of two or more types. When using two or more types in combination, the combination and ratio can be arbitrarily selected according to the purpose and are not particularly limited.

[0035] The polyester in this embodiment may be an aromatic polyester or an aliphatic polyester. An aromatic polyester refers to a polymer consisting of any combination of an aromatic dicarboxylic acid and an aliphatic diol, an aliphatic dicarboxylic acid and an aromatic diol, or an aromatic dicarboxylic acid and an aromatic diol. An aliphatic polyester refers to a polymer consisting of an aliphatic dicarboxylic acid and an aliphatic diol. The aromatic groups in the aromatic polyester may be divalent aromatic hydrocarbon groups (arylene groups), divalent aromatic heterocyclic groups (heteroarylene groups), or may be composed of both divalent aromatic hydrocarbon groups and divalent aromatic heterocyclic groups. The heteroatoms in the above aromatic heterocyclic groups are not particularly limited, but examples include oxygen atoms and nitrogen atoms.

[0036] The reactivity of polyester depolymerization can be improved by altering the structures of the carboxylic acid side and the alcohol side. As will be discussed later, considering that polyesters having aromatic rings such as benzene rings or naphthalene rings as the carboxylic acid side structure (e.g., polyethylene terephthalate, polybutylene terephthalate), it can be seen that polyesters having other aromatic structures such as furan can be similarly decomposed. Similarly, considering that polyesters having ethylene glycol (e.g., polyethylene terephthalate) or 1,4-butanediol (e.g., polybutylene terephthalate) as the alcohol side structure can be similarly decomposed, it can be seen that polyesters having other dihydric alcohol structures such as 1,3-propanediol can also be similarly decomposed.

[0037] From the viewpoint of shortening the reaction time for decomposition, the polyester of this embodiment preferably contains aromatic polyesters, more preferably contains at least one selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and polyethylene furanoate (PEF, also known as polyethylene furanoate), and even more preferably contains at least one selected from the group consisting of polyalkylene terephthalate, polyalkylene naphthalate, and polyalkylene furanate.

[0038] As described above, the decomposition of polyester produces dicarboxylic acid diesters and other monomers, which are determined depending on the type of polyester and monohydric alcohol.

[0039] Examples of products that can be produced are not limited to these, but for example, terephthalic acid diesters can be produced from polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate; naphthalenedicarboxylic acid diesters (2,6-naphthalenedicarboxylic acid diesters) can be produced from polyethylene naphthalate and polybutylene naphthalate; and francicarboxylic acid diesters (2,5-francicarboxylic acid diesters) can be produced from polyethylene furanoate.

[0040] Furthermore, although not particularly limited, if methanol is used as the monohydric alcohol, for example, dimethyl dicarboxylic acid ester will be produced as the dicarboxylic acid diester.

[0041] <base> The base in this embodiment is not particularly limited, but for example, conventionally known bases can be used. The base may be either an inorganic base or an organic base, and it is preferable that it contains at least one alkali metal and an alkaline earth metal that reacts with a monohydric alcohol (described later) to produce an alkali metal alkoxide or an alkaline earth metal alkoxide.

[0042] Generally, in transesterification reactions, an alkoxy anion acting as a nucleophile attacks the carbonyl carbon of the ester, and after passing through a quaternary carbon intermediate, the reaction proceeds by liberating the alkoxy anion derived from the original structure that formed the ester bond. Since alkoxy anions are generated by the reaction of an alcohol with a base, the base in this embodiment is not particularly limited as long as it can deprotonate the alcohol.

[0043] Inorganic bases are not particularly limited, but examples include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; alkali metal oxides such as lithium oxide, sodium oxide, and potassium oxide; alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide; and alkaline earth metal oxides such as calcium oxide and magnesium oxide.

[0044] The organic bases are not particularly limited, but examples include alkali metal alkoxides such as lithium methoxide, lithium ethoxide, lithium tert-butoxide, sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium methoxide, potassium ethoxide, potassium tert-butoxide; calcium dimethoxide, calcium diethoxide, calcium ditert-butoxide, magnesium dimethoxide, magnesium diethoxide, magnesium Examples include alkaline earth metal alkoxides such as nesium ditert-butoxide; and nitrogen-containing organic bases (organic bases having a nitrogen atom) such as trimethylamine, triethylamine, tributylamine, trioctylamine, 1,5,7-triazabicyclo[4.4.0]deca-5-ene (TBD), 1,8-diazabicyclo[5.4.0]undeca-7-ene (DBU), 1,3-dimethylymidazole-2-ylidene, and 1,3-dicyclohexylimidazole-2-ylidene.

[0045] From the viewpoint of shortening the reaction time for decomposition of polyester, the alkali metal alkoxide is preferably an alkali metal alkoxide, more preferably lithium methoxide, sodium methoxide, or potassium methoxide, and particularly preferably sodium methoxide.

[0046] From the viewpoint of shortening the reaction time for polyester decomposition, the nitrogen-containing organic base is preferably 1,5,7-triazabicyclo[4.4.0]deca-5-ene.

[0047] The bases of this embodiment may be used individually or in combination of two or more. When using two or more bases, their combinations and ratios are not particularly limited and can be arbitrarily selected according to the purpose.

[0048] In this embodiment, the amount of base used is preferably 0.1 to 10 parts by mass, and more preferably 0.5 to 6 parts by mass, per 100 parts by mass of polyester in the polyester-containing material. Using 0.1 parts by mass or more of base per 100 parts by mass of polyester in the polyester-containing material tends to shorten the reaction time for decomposition of polyester. Using 10 parts by mass or less of base per 100 parts by mass of polyester in the polyester-containing material tends to prevent excessive use of base and is more economical. In other words, in the decomposition of polyester, it is preferable that the amount of base used is equivalent to the amount of catalyst.

[0049] <1K alcohol> During decomposition, monohydric alcohols undergo transesterification reactions with polyester in polyester-containing materials. Specifically, during the decomposition of polyester, the reaction between polyester and monohydric alcohol produces glycols corresponding to one monomer and dicarboxylic acid diesters corresponding to the other monomer or its derivative, which are among the raw materials used in polyester production.

[0050] The monohydric alcohol is not particularly limited, but for example, conventionally known alcohols can be used. The reaction efficiency of the decomposition reaction in this embodiment is controlled by the capture of the liberated dihydric alcohol by the excess diester carbonate. Therefore, any monohydric alcohol and diester carbonate can be used in combination, and it can be understood that the transesterification reaction proceeds efficiently regardless of the type of monohydric alcohol.

[0051] The monohydric alcohol is not particularly limited, but may be either an aliphatic alcohol or an aromatic alcohol. From the viewpoint of shortening the reaction time for decomposition of the polyester, it is preferable to use an aliphatic alcohol (saturated aliphatic alcohol or unsaturated aliphatic alcohol), and more preferably a saturated aliphatic alcohol.

[0052] The saturated aliphatic alcohol is not particularly limited, but examples include 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), 1-pentanol (n-pentanol), 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol (isoamyl alcohol), 2-methyl-2-butanol, 3-methyl-2-butanol, and 2,2-dimethyl-1-propanol, which are C1 to C5 alcohols. Here, from the viewpoint of shortening the reaction time for decomposition, the monohydric alcohol in this embodiment preferably contains a C1 to C5 monohydric alcohol, and more preferably contains a C1 or C2 monohydric alcohol. Examples of C1 or C2 monohydric alcohols include methanol and ethanol.

[0053] The monohydric alcohol used for decomposing polyester may be used alone or in combination of two or more types. When using two or more types in combination, the combination and ratio are not particularly limited and can be arbitrarily selected according to the purpose. From the viewpoint of shortening the reaction time for decomposing polyester, methanol is particularly preferred as the monohydric alcohol.

[0054] The amount of monohydric alcohol used during the decomposition of polyester varies depending on the structure of the polyester. Specifically, although not particularly limited, for example, when the polyester is polyethylene terephthalate (PET), 30 to 200 parts by mass, and more preferably 50 to 160 parts by mass, are preferred per 100 parts by mass of PET in the polyester-containing material. When the polyester is polybutylene terephthalate (PBT), 10 to 180 parts by mass, and more preferably 20 to 140 parts by mass, are preferred per 100 parts by mass of PBT in the polyester-containing material. Using 30 parts by mass or more of monohydric alcohol per 100 parts by mass of PET in the polyester-containing material tends to shorten the reaction time for decomposition of polyester. On the other hand, using 200 parts by mass or less of monohydric alcohol per 100 parts by mass of PET in the polyester-containing material tends to suppress the excessive use of monohydric alcohol, resulting in better economic performance.

[0055] <Diester carbonate> In this embodiment, the diester carbonate has a structure in which both hydrogen atoms of the carbonic acid are replaced by an organic group. During the decomposition of polyester, the diester carbonate reacts with the glycol produced from the polyester to generate a cyclic or chain-like compound, shifting the equilibrium between the depolymerization and polymerization reactions of the polyester so that the depolymerization reaction is dominant, thereby improving the production rate of the target monomer, which is a polyester decomposition product. In addition, the diester carbonate functions as a glycol scavenger.

[0056] The reaction products of diester carbonate and glycol can include cyclic compounds formed from the reaction of one molecule of diester carbonate and one molecule of glycol, chain compounds formed from the reaction of one molecule of diester carbonate and one molecule of glycol, and chain compounds formed from the reaction of one molecule of diester carbonate and two molecules of glycol. Which of these cyclic and chain compounds is formed is mainly determined by the type of glycol used. Specifically, although not particularly limited, for example, the reaction product of diester carbonate and ethylene glycol is mainly a cyclic compound formed from the reaction of one molecule of diester carbonate and one molecule of ethylene glycol.

[0057] Examples of diester carbonates include dialkyl carbonates and diaryl carbonates. The two alkyl or aryl groups bonded to the oxygen atom in a dialkyl carbonate or diaryl carbonate may be the same or different.

[0058] The alkyl group in the dialkyl carbonate is not particularly limited, but may be linear, branched, or cyclic, for example, and if cyclic, it may be monocyclic or polycyclic.

[0059] In dialkyl carbonates, the number of carbon atoms in the linear or branched alkyl group is preferably 1 to 5. Examples of such alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, and tert-pentyl groups.

[0060] In particular, the number of carbon atoms in the alkyl group is more preferably 1 to 4, and even more preferably 1 to 2.

[0061] The aryl group in diaryl carbonate may be monocyclic or polycyclic. The number of carbon atoms in the aryl group in diaryl carbonate is preferably 6 to 10, and such aryl groups are not particularly limited, but examples include phenyl group, 1-naphthyl group, 2-naphthyl group, o-tolyl group, m-tolyl group, p-tolyl group, 2,3-xylyl group (2,3-dimethylphenyl group), 2,4-xylyl group (2,4-dimethylphenyl group), 2,5-xylyl group (2,5-dimethylphenyl group), 2,6-xylyl group (2,6-dimethylphenyl group), 3,4-xylyl group (3,4-dimethylphenyl group), and 3,5-xylyl group (3,5-dimethylphenyl group). Among these, diphenyl carbonate is preferred from the viewpoint of shortening the reaction time in the decomposition of polyester.

[0062] The diester carbonate used for decomposing polyester may be used alone or in combination of two or more types. When using two or more diester carbonates in combination, the combination and ratio are not particularly limited and can be arbitrarily selected according to the purpose.

[0063] From the viewpoint of improving the decomposition rate of polyester, it is more preferable that the diester carbonate is one or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, and diphenyl carbonate, and dimethyl carbonate is particularly preferred.

[0064] When decomposing polyester, the amount of diester carbonate used is preferably 100 to 5000 parts by mass, more preferably 100 to 1000 parts by mass, and even more preferably 100 to 500 parts by mass, per 100 parts by mass of polyester in the polyester-containing material. Using 100 parts by mass or more of diester carbonate per 100 parts by mass of polyester in the polyester-containing material tends to shorten the reaction time in decomposing polyester. Using 5000 parts by mass or less of diester carbonate per 100 parts by mass of polyester in the polyester-containing material tends to suppress the overuse of diester carbonate and is more economical.

[0065] <Method for producing diester carbonates> The method for producing the diester carbonate used in the decomposition process is not particularly limited, but conventionally known methods can be applied, and specifically, it can be produced by the method described in the following literature. Patent Document 6: International Publication No. 2004 / 108696 Patent Document 7: International Publication No. 2005 / 123638 Non-patent document 2: Green Chemistry (2007), 9(6), 566-571 Among these, applying a method to produce diester carbonate using CO2 and cyclic carbonate esters as raw materials is a preferred embodiment because it allows for the recovery of cyclic carbonate esters, which are by-products in the polyester decomposition process within the invention, and their reuse as raw materials for diester carbonate, while also reducing the raw material cost in the production of diester carbonate. Furthermore, it can be cited as a suitable raw material from the perspective of increasing environmental awareness and CO2 fixation, making it a more green raw material in light of the growing concern for reducing environmental impact.

[0066] <Solvent> In the decomposition process, a solvent other than a base, monohydric alcohol, or diester carbonate may be used, as long as it does not hinder the effects of the present invention. In this embodiment, even without using a solvent, the decomposition of polyester can be carried out efficiently. However, by using a solvent as needed, the handling of the raw material mixture, such as the reaction solution, tends to be improved, and the reaction time in the decomposition of polyester can be shortened.

[0067] In this specification, the term "solvent" is a concept that encompasses both a component that is liquid at room temperature and used to dissolve a solute, and a component that is liquid at room temperature and functions as a dispersion medium for dispersing a dispersed phase. In this embodiment, "room temperature" means the temperature under normal conditions without cooling or heating, i.e., the normal temperature, such as 15 to 25°C.

[0068] When a polyester decomposition composition contains a solvent, the solvent is preferably an organic solvent. While not particularly limited, 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.

[0069] The solvent may be used alone or in combination of two or more. When using two or more solvents, their combination and ratio can be arbitrarily selected according to the purpose.

[0070] When a solvent is used, the amount of solvent used during the decomposition of polyester 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 polyester-containing material. While it is preferable not to use a solvent in that it eliminates the need for a solvent removal step during the purification of the target product, if using a solvent has the effect of allowing the reaction to proceed in a homogeneous system, it is preferable that the amount of solvent used be 1 part by mass or more per 100 parts by mass of polyester-containing material. From the viewpoint of reducing the burden of the solvent removal step, it is preferable that the amount used be 100,000 parts by mass or less per 100 parts by mass of polyester-containing material.

[0071] <Other ingredients> During the decomposition of polyester, other components that do not fall under the categories of base, monohydric alcohol, diester carbonate, or solvent may be used, as long as they do not impair the effects of the present invention.

[0072] Other components can be arbitrarily selected according to the purpose and are not particularly limited. Other components used for decomposing polyester may be used alone or in combination of two or more. When using two or more in combination, the combination and ratio are not particularly limited and can be arbitrarily selected according to the purpose.

[0073] During the decomposition of polyester, the ratio of the total amount (parts by mass) of polyester-containing material, base, monohydric alcohol, and diester carbonate used to the total amount (parts by mass) of components other than the solvent (([Amount of polyester-containing material used (parts by mass)] + [Amount of base used (parts by mass)] + [Amount of monohydric alcohol used (parts by mass)] + [Amount of diester carbonate used (parts by mass)]) / [Total amount of components other than the solvent used (parts by mass)] × 100) is preferably 80% to 100% by mass, more preferably 95% to 100% by mass, and even more preferably 97% to 100% by mass. When this ratio is 80% by mass or higher, polyester tends to be decomposed more efficiently.

[0074] Here, the total amount (parts by mass) of components other than the solvent used during the decomposition of polyester refers to the total amount (parts by mass) of the polyester-containing material, base, monohydric alcohol, diester carbonate, and other components used during the decomposition.

[0075] <Reaction conditions for the decomposition process> This process involves contacting a polyester-decomposing composition containing a base, a monohydric alcohol, and a diester carbonate with a polyester-containing material to decompose the polyester in the polyester-containing material and obtain a polyester decomposition product.

[0076] The method for bringing the polyester decomposition composition into contact with polyester is not particularly limited, but for example, from the viewpoint of ensuring a contact area, it is preferable to add fibrous, granular, or powdered polyester to the mixture and stir it.

[0077] The order in which these raw materials are blended is not particularly limited, but it is preferable to prepare a mixture of a base, a monohydric alcohol, a diester carbonate, a solvent if necessary, and other components if necessary (for example, a mixture of all raw materials except the polyester-containing material), and then mix this mixture with the polyester-containing material. This blending order tends to allow the decomposition of the polyester to proceed more efficiently.

[0078] The reaction temperature in the decomposition process can be adjusted as appropriate, taking into account the type of materials used, and the decomposition may be carried out at room temperature or under heated conditions. The equipment used for heating is not particularly limited, and equipment such as jackets and heaters can be used. Furthermore, in addition to heating the decomposition reactor itself, preheating is also a preferred method.

[0079] The reaction temperature for the decomposition step is preferably 20°C to 150°C, more preferably 30°C to 130°C, and even more preferably 40°C to 110°C.

[0080] According to this embodiment, polyester can be decomposed with a high decomposition rate, and the amount of oligomers and other by-products generated during the decomposition reaction can be reduced.

[0081] The decomposition process may be carried out under atmospheric pressure, reduced pressure, or pressurized pressure, and may be carried out under air or an inert gas atmosphere. To avoid conditions unfavorable to the decomposition reaction, such as catalyst deactivation, it is preferable to carry out the process under conditions free of moisture.

[0082] Furthermore, the reaction time in the decomposition process can be adjusted as appropriate considering other reaction conditions such as the reaction temperature, and is not particularly limited. The reaction time for the decomposition of polyester is not particularly limited as long as it is between 0.5 and 24 hours, but is preferably between 0.5 and 12 hours, and more preferably between 1 and 8 hours.

[0083] In this embodiment, the decomposition rate of polyester can be determined by the decomposition rate after 0.5 to 1 hour. Furthermore, the final decomposition rate of polyester can be determined by the decomposition rate after 2 to 8 hours.

[0084] Immediately after mixing the materials, the unreacted polyester-containing material remains insoluble in the polyester decomposition composition. During the decomposition of polyester, both the unreacted polyester-containing material and the polyester-containing material during or after the reaction generally remain insoluble in the other liquid components. On the other hand, the polyester decomposition products—dicarboxylic acid diesters, cyclic carbonates, and glycols—generally dissolve in the solution.

[0085] In the decomposition step, it is preferable to carry out the reaction while stirring by a known method. Such methods are not particularly limited, but examples include stirring by rotating a magnetic stirring bar or impeller, or stirring using a ball mill. Among these, from the viewpoint of carrying out the reaction efficiently, that is, efficiently dispersing the reaction substrate and completing the reaction, it is preferable to use the method of stirring by rotating a magnetic stirring bar or impeller.

[0086] <Base reduction process> The method for producing polyester decomposition products according to this embodiment includes a base reduction step for reducing the base content contained in the polyester decomposition products obtained by the above-described decomposition step. In the decomposition process, the polyester is decomposed, and the resulting solution containing dicarboxylic acid diesters, as well as by-products such as cyclic carbonate esters and dicarbonate diesters, contains bases that promote the decomposition of cyclic carbonate esters and other components. Therefore, the bases can be efficiently reduced through a base reduction process.

[0087] The base reduction step is not particularly limited, but conventionally known methods can be used. Among these, extraction is preferred, and liquid-liquid extraction is more preferred, as will be described later.

[0088] Here, extraction is one of the operations for separating components soluble in a particular solvent from components that are insoluble. While extraction is not particularly limited, examples include liquid-liquid extraction, solid-liquid extraction, and acid-base extraction. By adjusting the conditions for each, a suitable method can be applied. Considering that the polyester decomposition product manufacturing method in this embodiment is a continuous manufacturing process that does not involve handling solids, liquid-liquid extraction is preferred, and acid-base extraction is more preferred.

[0089] Liquid-liquid extraction, also known as solvent extraction, uses an extraction solvent (hereinafter simply referred to as "extractant") that is either immiscible or poorly immiscible with the phase in which the component to be separated is dissolved, and in which the component to be separated is easily dissolved. The extractant that can be used in this embodiment is not particularly limited, but for example, it is preferable to use water as an extractant that is immiscible with the organic phase in which the polyester is decomposed and which contains dicarboxylic acid diesters, by-product cyclic carbonate esters, and carbonate diesters, and in which the above products are poorly dissolved or eluted, and in which the base is efficiently dissolved.

[0090] When water is used as an extractant, the ratio A(wt / wt) of water to the organic phase containing the substance to be extracted is not particularly limited, but is preferably 0.01 to 2, more preferably 0.02 to 1.5, even more preferably 0.03 to 1, and particularly preferably 0.04 to 0.75 relative to the weight of the organic phase. From the viewpoint of efficiently reducing bases and improving the yield of dicarboxylic acid diesters, cyclic carbonate esters, and carbonate diesters, the above ratio A(wt / wt) is preferably 0.01 or higher, and from the viewpoint of preventing loss due to trace amounts of cyclic carbonate esters and carbonate diesters dissolving in water, the above ratio A(wt / wt) is preferably 2 or lower.

[0091] Furthermore, the temperature of the base reduction process is preferably 10°C to 95°C, more preferably 20°C to 80°C, even more preferably 25°C to 70°C, and particularly preferably 30°C to 70°C.

[0092] <Additives> Furthermore, in the base reduction step, it is also preferable to add an additive during extraction to further improve extraction efficiency. While there are no particular limitations on such additives, for example, since the catalyst is basic, adding an acidic additive can efficiently advance the extraction. The acidic additive can be an inorganic or organic compound, without any particular limitations.

[0093] Inorganic acids are not particularly limited, but examples include hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boric acid, hydrofluoric acid, fluorosulfonic acid, and hexafluorophosphate. Organic acids are not particularly limited, but examples include formic acid, acetic acid, propionic acid, oxalic acid, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, citric acid, tartaric acid, and lactic acid. The additives used may be used individually or in combination of two or more. When using two or more, the combination and ratio are not particularly limited and can be arbitrarily selected according to the purpose.

[0094] When using an acidic component as an additive, the amount added is preferably such that the calculated value of [Ma × α] / [Mb × n] is 0.1 or more and 2 or less, more preferably 0.1 or more and 1.5 or less, even more preferably 0.1 or more and 1.2 or less, and particularly preferably 0.1 or more and 1.1 or less. The degree of ionization used here indicates the dissociation ratio of an ionic compound in a solution, and represents the ratio of the number of ionized molecules to the number of molecules of the electrolyte or ionic compound. Generally, strong acids with a high degree of dissociation have a degree of dissociation close to 1 and ionize quantitatively, so they function as acids even with a smaller amount added than weak acids. In addition, when an acid is added, a neutralization operation of the organic phase may be performed by adding a base in a subsequent treatment. In this case, it is preferable that the base used is a weak base in order to suppress the denaturation of components contained in the organic phase.

[0095] Furthermore, the extraction method is not particularly limited and can be selected as appropriate. Specific examples of extraction methods are not particularly limited, but include, for example, batch stirring tanks, continuous stirring tanks, reactors with internal supports, forced circulation reactors, stationary mixers (line mixers or static mixers), ball rings, regularly packed columns, irregularly packed columns, mixer-packed columns with rotary stirrers, and tray columns.

[0096] When a packed column is used, the solid packing material of the packed column is not particularly limited, and packing materials commonly used in distillation columns and absorption columns can be used as appropriate. Preferred packing materials include, but are not particularly limited, Raschig rings, cascade mini rings, lessing rings, spiral rings, pole rings, interlock saddles, Stedman packing, McMahon packing, Dixon packing, Helix packing, coil packing, heat pipe packing, etc. When the distillation column is a tray column, but is not particularly limited, various tray columns having sieve trays, cascade trays, turbo grid trays, ripple trays, and dual trays can be used as appropriate. The material of the solid packing material can be appropriately selected from porcelain, metal, etc., and is not particularly limited. Among these, preferred materials for the solid filler include SUS304, SUS316, and SUS316L, as well as generally silicon dioxide (composition formula: SiO2), aluminum oxide (composition formula: Al2O3), a composite of silicon dioxide and aluminum oxide, a mixture of silicon dioxide and aluminum oxide, and carbon fluoride (a compound having repeating units of -CHF- or CF2-). While not particularly limited, fluororesins include, for example, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, perfluoroalkoxy fluororesins, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, and ethylene-chlorotrifluoroethylene copolymer. The preferred fillers described above may contain other metal atoms to the extent that they do not impair the effects of this embodiment.

[0097] Furthermore, in order to achieve a predetermined base reduction, the base reduction process of this embodiment may consist of a single extraction process or multiple extraction processes. In the configuration with multiple extraction processes, the processes may be arranged in parallel, in series, or as a combination thereof. The configuration of the process can also be a batch process, a continuous process, or any other preferred configuration.

[0098] Furthermore, in the base reduction step of this embodiment, from the viewpoint of improving liquid-liquid separation, some and / or all of the substances that function as amphiphilic substances may be reduced in advance from the polyester decomposition product. Such reduction operations are not particularly limited, but conventionally known methods such as distillation, crystallization, extraction, and adsorption can be used.

[0099] <Dehydration process> The method for producing polyester decomposition products of this embodiment includes a dehydration step after the base reduction step, in which the polyester decomposition products are dehydrated. After the base reduction step, although not particularly limited, the organic phase solution containing the dicarboxylic acid diester after the base used in the decomposition step has been extracted and reduced by, for example, liquid-liquid extraction using water as an extractant, may contain water at or close to its saturation solubility. The inclusion of a dehydration step in the method for producing polyester decomposition products of this embodiment is preferable from the viewpoint of suppressing the hydrolysis of components contained in the solution and improving the yield of each component. Generally, for dehydration, there are no particular limitations, but for example, an adsorbent (dehydrating agent) can be used or distillation can be performed. Such adsorbents are not particularly limited, but may be inorganic or organic dehydrating agents, with inorganic dehydrating agents being preferred. Examples of inorganic dehydrating agents are not particularly limited, but include calcium oxide, calcium chloride, calcium sulfate, barium oxide, magnesium sulfate, sodium sulfate, sodium carbonate, silica gel, aluminum oxide, amorphous silica alumina, and zeolites. Examples of zeolites are not particularly limited, but include molecular sieve 3A and molecular sieve 4A. Among these, from the viewpoint of improving dehydration efficiency, it is preferable to use one or more selected from the group consisting of molecular sieves, sodium sulfate, and magnesium sulfate, and it is more preferable to use molecular sieves. The dehydrating agent is not particularly limited, but for example, a preparation prepared by a conventionally known method may be used, or a commercially available product may be used.

[0100] Furthermore, while not particularly limited, packing materials commonly used in distillation columns and absorption columns can be used as appropriate. Preferred packing materials include, but are not particularly limited, Raschig rings, cascade mini rings, lessing rings, spiral rings, ball rings, interlock saddles, Stedman packing, McMahon packing, Dixon packing, Helix packing, coil packing, and heat pipe packing. If the distillation column is a tray column, while not particularly limited, various tray columns having sieve trays, cascade trays, turbo grid trays, ripple trays, dual trays, etc., can be used as appropriate. The material of the solid packing material can be appropriately selected from porcelain, metal, etc., and is not particularly limited. Among these, preferred materials for the solid filler include SUS304, SUS316, and SUS316L, as well as generally silicon dioxide (composition formula: SiO2), aluminum oxide (composition formula: Al2O3), a composite of silicon dioxide and aluminum oxide, a mixture of silicon dioxide and aluminum oxide, and carbon fluoride (a compound having repeating units of -CHF- or CF2-). While not particularly limited, fluororesins include, for example, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, perfluoroalkoxy fluororesins, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, and ethylene-chlorotrifluoroethylene copolymer. The preferred fillers described above may contain other metal atoms to the extent that they do not impair the effects of this embodiment.

[0101] Furthermore, in the dehydration process, it is preferable to reduce the pressure as appropriate in a temperature range where dicarboxylic acid diesters and cyclic carbonate esters do not undergo hydrolysis. Specifically, the pressure in the dehydration process is preferably 0.1 kPa or more and 101 kPa or less, more preferably 0.5 kPa or more and 50 kPa or less, even more preferably 1 kPa or more and 25 kPa or less, and particularly preferably 1 kPa or more and 10 kPa or less. Note that the pressure expressed here refers to absolute pressure, and unless otherwise specified, the same meaning applies hereafter. It is also a preferred embodiment to adjust the pressure of the distillation column so that the target component is distilled out, and to change the temperature so that each component is extracted. In addition, the target component may be recovered from the top, side cut, or bottom of the distillation column as needed.

[0102] Furthermore, in the dehydration process, it is preferable to have a component that forms an azeotrope with water. An azeotrope is a phenomenon in which the liquid phase and gas phase have the same composition when a mixture boils, and from the viewpoint of removing water under mild conditions and easily, it is preferable to have a component that forms the minimum azeotrope with water. Compounds that form an azeotrope are called azeotropic agents. Such components may be components already present in the system or added as third components. As components that function as azeotropes in a solution of polyester decomposition products containing the target components dicarboxylic acid diesters, cyclic carbonate esters, and glycols, it is preferable to use diester carbonates and monohydric alcohols as dehydrating agents, and it is more preferable from the viewpoint of dehydration efficiency to combine one or more from the group consisting of dimethyl carbonate, diethyl carbonate, methanol, and ethanol and subject them to distillation.

[0103] <Purification process> The purification step involves separating cyclic carbonate esters from the polyester decomposition product after the base reduction step. This purification step allows for the isolation of dicarboxylic acid diesters, which are the main polyester decomposition products, in high purity.

[0104] The purification step preferably further includes a step of separating the cyclic carbonate ester and glycol from the polyester decomposition product from the polyester decomposition product containing the dicarboxylic acid diester.

[0105] The purification method is not particularly limited, but examples include filtering, distillation (concentration) of volatile components off the reaction product after decomposition of the polyester, and the resulting solution containing the dicarboxylic acid diester may be further purified by crystallization, distillation, etc., as needed.

[0106] The other main decomposition product, cyclic carbonate ester, which is a reaction product of glycol and diester carbonate, can also be isolated in the same way as dicarboxylic acid diester by appropriately adjusting the processing conditions and isolation conditions in the purification process.

[0107] According to this embodiment, as described above, the polyester contained in the polyester-containing material can be decomposed with a high decomposition rate, thus reducing the amount of oligomers and other by-products generated during the decomposition reaction compared to conventional methods. Furthermore, even if the polyester-containing material originally contains a coloring agent, the coloring of dicarboxylic acid diesters (monomers) derived from this coloring agent tends to be reduced.

[0108] When distillation is performed in the purification process, conventionally known purification apparatus can be used in appropriate combinations, and are not particularly limited, but examples include ordered-packed columns, irregular-packed columns, thin-film distillers, and liquid-flow-under-film evaporators.

[0109] <Other processes> The method for producing polyester decomposition products according to this embodiment may include a synthesis step 1 of synthesizing a cyclic carbonate ester by reacting carbon dioxide with a cyclic ether, and a synthesis step 2 of synthesizing a dicarbonate and a glycol by reacting the cyclic carbonate ester obtained in synthesis step 1 with a monohydric alcohol. The dicarbonate obtained in synthesis step 2 can be used in the decomposition step.

[0110] Furthermore, the cyclic carbonate ester and / or diester carbonate obtained in the purification step can be used in the synthesis step 2.

[0111] <Method for manufacturing polyester> The polyester manufacturing method of this embodiment includes a polymerization step in which the polyester decomposition product obtained by the above-described method for manufacturing polyester decomposition products is polymerized using the polyester decomposition product as a monomer, and may include other steps as needed.

[0112] Of the polyester decomposition products obtained by the polyester decomposition product manufacturing method of this embodiment, the dicarboxylic acid diester can be reused in the production of polyester by conventionally known methods. Furthermore, the dialkyl terephthalate obtained above can be converted to a polyester precursor such as bis-(2-hydroxyethyl) terephthalate (hereinafter referred to as "BHET") or terephthalic acid (hereinafter referred to as "TPA") by conventionally known methods and reused in the production of polyester.

[0113] The reaction product of glycol and diester carbonate among the polyester decomposition products obtained by the polyester decomposition product manufacturing method of this embodiment can be converted back to glycol and diester carbonate by reaction with alcohol. This regenerated diester carbonate can be reused for decomposition of polyester, and the regenerated glycol can be reused in the manufacture of polyester. For example, when a polyester having a structure that can be considered to be derived from ethylene glycol is decomposed, ethylene carbonate is produced as a reaction product of ethylene glycol and ester carbonate. Japanese Patent No. 4236208 discloses the conversion of ethylene carbonate to ethylene glycol and ester carbonate by reaction with alcohol.

[0114] Therefore, by using the polyester decomposition product method and polyester method of this embodiment, polyester can be continuously produced through three chemical reactions: decomposition of polyester, regeneration of glycol carbonate from the reaction product of glycol and carbonate ester, and production of polyester precursors such as dicarboxylic acid diester or BHET synthesized from the obtained dicarboxylic acid diester, or polyester by reaction of TPA with glycol.

[0115] In other words, the method for producing polyester according to this embodiment includes a step of producing polyester using polyester decomposition products (dicarboxylic acid diester, alkylene glycol, etc.) obtained by the polyester decomposition method according to this embodiment described above. [Examples]

[0116] Next, the present invention will be specifically described based on examples, but the present invention is not particularly limited by the following examples. Furthermore, the yields of dialkyl terephthalate, dialkyl carbonate, and glycol described in the examples were calculated based on the molecular weight corresponding to the structure of the polyester. For example, when polyethylene terephthalate was used as the polyester, the yield of each product was calculated based on the number of moles corresponding to the repeating unit skeleton consisting of a terephthalic acid skeleton and an ethylene glycol skeleton (equivalent to a molecular weight of 192), which was used as the reference.

[0117] [Example 1] [Process 1: Production of ethylene carbonate] Using the same method as in Example 1 described in International Publication Number WO2004 / 108696, 136 g of ethylene carbonate (hereinafter also referred to as EC) was obtained from CO2 and ethylene oxide as raw materials.

[0118] [Step 2: Production of Dimethyl Carbonate] Using the same method as in Example 1 described in International Publication No. WO2005 / 123638, the EC synthesized in the aforementioned process and methanol were subjected to a process for producing dimethyl carbonate (hereinafter also referred to as DMC) as raw materials, yielding an EC conversion rate of 99%, a DMC yield of 99.8%, and an ethylene glycol (hereinafter also referred to as EG) yield of 99.8%.

[0119] [Step 3: Decomposition of polyester fibers] Polyester depolymerization was performed using the same method as for international publication number WO2024 / 34609. 0.58 g and 1.0 g of sodium methoxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were placed in a 300 mL round-bottom flask as base catalysts. 7.9 g of methanol (manufactured by Kishida Chemical Co., Ltd.) and 107 g of DMC were added to the flask, and the catalyst composition was prepared by uniformly dissolving these components. 20 g of 1 cm square 100% PET white fibers were added to the catalyst composition obtained above. Next, using a magnetic stirrer and an oil bath, the stirring bar was rotated in the round-bottom flask, and the mixture of the catalyst composition and PET fibers was stirred at 50°C for 2 hours to decompose the PET fibers. Then, 32g of DMC was added to the reaction mixture in the round-bottom flask to dissolve the precipitate, and the contents of the round-bottom flask were thermally filtered while maintaining the temperature at 50°C without cooling.

[0120] [Step 4: Base Reduction Process] 20 g of deionized water at 50°C was added to the filtrate obtained in the above process, and batch water extraction was performed. The mixture was kept completely mixed for 1 minute while maintaining the temperature at 50°C, and after standing separation, the two liquid phases were separated, and the organic phase was recovered. The concentration of the base catalyst in the organic phase was 18 wt ppm.

[0121] [Step 5: Dehydration step] From the obtained organic phase containing dimethyl terephthalate, methanol and an azeotropic mixture of dicarbonate and water were removed as the low-boiling component. After distillation, the organic phase yielded dimethyl terephthalate (hereinafter referred to as DMT) in 92% yield, EC in 84% yield, and ethylene glycol (EG) in 3% yield. The sodium methoxide content in the obtained DMT-containing phase was 18 wt ppm.

[0122] [Step 6: Purification step] The composition obtained in step 5 was subjected to a packed column with side cut lines (Helipak No. 1, equivalent to 15 theoretical stages), operated at a column base temperature of 150°C and a column top pressure of 2 kPa. The EG recovery rate was 97%, the EC recovery rate was 95%, and the DMT recovery rate was 95%.

[0123] [Examples 2 and 3] Examples 2 and 3 were operated under the same conditions as Example 1, except that the amount of water used in step 4 of Example 1 was 10g and 30g, respectively. The sodium methoxide contained in the obtained DMT-containing organic phase was 27 wtppm and 5 wtppm, respectively. When subjected to the subsequent steps from step 5 onwards, the results are shown in Table 1.

[0124] [Examples 4 and 5] Examples 4 and 5 were operated under the same conditions as Example 1, except that the extraction temperature in step 4 of Example 1 was set to 30°C and 70°C, respectively. The sodium methoxide contained in the obtained DMT-containing organic phase was 13 wt ppm and 11 wt ppm, respectively. After being subjected to the subsequent steps from step 5 onward, the results are shown in Table 1.

[0125] [Examples 6 and 7] Examples 6 and 7 were operated under the same conditions as in Example 1, except that the extraction time in step 4 of Example 1 was set to 0.5 minutes and 2 minutes, respectively. The sodium methoxide contained in the obtained DMT-containing organic phase was 23 wt ppm and 9 wt ppm, respectively. When subjected to subsequent steps from step 5 onward, the results are shown in Table 1.

[0126] [Table 1]

[0127] [Example 8] For Example 8, the steps up to step 3 of Example 1 were repeated 10 times, and the recovered crude reaction solution was subjected to step 4. The liquid-liquid extraction method used in step 4 was modified as follows. A continuous extraction column (1 inch inner diameter, packed with 3mm diameter SUS316 Helipak No. 1 packing beds, 120cm packed bed height) was kept warm at 50°C with a jacket. Water was supplied from the bottom of the extraction column at a rate of 10 mL / min. The filtrate obtained in step 3 was then supplied from the top of the extraction column at a rate of 50 mL / min, resulting in countercurrent contact. The organic phase was recovered from the bottom of the column after contact with water. After oil-water separation using a decanter, the amount of base catalyst component in the recovered organic phase was 11 wt ppm. The same procedure as in Example 1 was then performed, and the results are shown in Table 2.

[0128] [Examples 9-12] Examples 9 to 12 were operated under the same conditions as Example 1, except that the conditions for the base reduction step in step 4 of Example 8 were as shown in Table 2. The results are shown in Table 2.

[0129] [Table 2]

[0130] [Example 13] [Step 7: Recovery of carbonate esters] In Example 13, the DMC used in step 3 of Example 1 and the EC isolated in step 6 were recovered, and the EC was used as a raw material for DMC production. The EC recovery rate at this time was 99.5%, and the DMC recovery rate was 99.5%. When depolymerizing the same amount of PET (20g) as described above, the amount of EC needed as a remaining raw material was 0.7g. This was used as a raw material for DMC along with the recovered EC, and subjected to the same reaction as described above to obtain 8.5g of DMC. This DMC was combined with 131g of recovered DMC and subjected to the PET depolymerization reaction and post-treatment, and similar to Example 1, DMT was obtained in a yield of 92% (based on the terephthalic acid skeleton), EC in a yield of 84% (based on the ethylene glycol skeleton), and EG in a yield of 3%. By repeatedly operating steps 1 through 7, the PET depolymerization reaction process was able to operate continuously without any raw material shortages.

[0131] [Examples 14-19] Examples 14-16 were operated as described in Example 1, except that the conditions for step 3 of Example 1 were as shown in Table 4. Examples 17-19 were operated as described in Example 8, except that the conditions for step 4 of Example 8 were as shown in Table 5, resulting in the results shown in Table 5. Here, in Tables 4 and 5, DRT means dialkyl terephthalate, DET means diethyl terephthalate, and DMT means dimethyl terephthalate. DMC means dimethyl carbonate, and DEC means diethyl carbonate. The raw materials for Examples 14 and 17 were adjusted to the same molar amounts as those described in Example 1. As a result, DET was obtained in 90% yield, EC in 84% yield, and EG in 3% yield for Examples 14 and 17. DMT was obtained in 90% yield, EC in 84% yield, and EG in 3% yield for Examples 15 and 18. Furthermore, DMT was obtained in 90% yield, EC in 84% yield, and EG in 3% yield in Examples 16 and 19.

[0132] [Comparative Example 1] Except for not performing steps 4 and 5 in Example 1, when the method described in Example 1 was applied to step 6, EC underwent thermal decomposition, making it difficult to recover EC and EG. In addition, carbonate esters could not be recovered in step 7, and the EC and DMC unit consumption increased. The results for Comparative Example 1 are shown in Table 3.

[0133] [Comparative Example 2] Except for not performing step 5 in Example 1, when step 6 was applied using the method described in Example 1, some of the recovered EC underwent thermal decomposition, and it was not possible to recover EC and EG. In addition, carbonate esters could not be recovered in step 7, and the EC and DMC unit consumption increased. The results for Comparative Example 2 are shown in Table 3.

[0134] [Comparative Example 3] After obtaining the polyester decomposition reaction solution by step 3 of Example 1, the solution was evaporated and concentrated to remove the solvents, leaving a residue containing dimethyl terephthalate. The residue was recovered and washed with a mixture of 40 g water and 40 g methanol. DMT remained on the filter cloth, but EC and EG were not present and dissolved in the washing solution. When this washing solution was recovered and subjected to distillation separation, the EC found in the crude reaction solution underwent thermal decomposition or hydrolysis, making it difficult to recover EC. In addition, some of the terminal hydroxyl groups of EG were converted to sodium salts. Various other high-boiling point components were also observed, resulting in a low recovery rate of 3%, as shown in Table 3.

[0135] [Table 3]

[0136] [Table 4]

[0137] [Table 5] [Industrial applicability]

[0138] The method for producing polyester decomposition products according to this embodiment can suppress the modification of the recovered diester carbonate and the by-product cyclic ester carbonate, and furthermore, it is possible to continuously operate the method for producing dicarboxylic acid diesters and the like by polyester decomposition with high yield and stability.

Claims

1. A decomposition step involves contacting a polyester-containing material with a polyester-decomposing composition comprising a base, a monohydric alcohol, and a diester carbonate to decompose the polyester in the polyester-containing material and obtain a polyester decomposition product. A base reduction step for reducing the amount of base contained in the polyester decomposition product, Following the base reduction step, a dehydration step is performed to dehydrate the polyester decomposition product, The process includes a purification step, which follows the dehydration step, in which cyclic carbonate esters are separated from the polyester decomposition product. A method for producing polyester decomposition products.

2. The purification step separates the cyclic carbonate ester and glycol from the polyester decomposition product containing the dicarboxylic acid diester. A method for producing a polyester decomposition product according to claim 1.

3. The base reduction step includes liquid-liquid extraction. A method for producing a polyester decomposition product according to claim 1.

4. The extractant for the aforementioned liquid-liquid extraction is water. A method for producing polyester decomposition products according to claim 3.

5. Synthesis step 1 involves reacting carbon dioxide with a cyclic ether to synthesize a cyclic carbonate ester, Synthesis step 2 involves reacting the cyclic carbonate ester obtained in synthesis step 1 with a monohydric alcohol to synthesize a dicarbonate and a glycol. The diester carbonate obtained in the synthesis step 2 is used in the decomposition step. A method for producing a polyester decomposition product according to claim 1.

6. The cyclic carbonate ester and / or dicarbonate obtained in the purification step is used in the synthesis step 2. A method for producing polyester decomposition products according to claim 5.

7. The monohydric alcohol used in step 1 and / or the decomposition step includes an alcohol having 1 or 2 carbon atoms. The base comprises at least one of alkali metals and alkaline earth metals. A method for producing polyester decomposition products according to claim 5.

8. The process includes a polymerization step in which a polyester decomposition product obtained by any one of claims 1 to 7 is used as a monomer for polymerization, A method for manufacturing polyester.

Images