Process for producing aromatic dicarboxylic acid bis(hydroxyalkyl) and process for producing recycled aromatic polyester

Abstract

Provided is a method for producing an aromatic bis(hydroxyalkyl) dicarboxylate by depolymerizing a polyester in the presence of a catalyst. This method for producing an aromatic bis(hydroxyalkyl) dicarboxylate by depolymerizing a polyester in the presence of a catalyst is characterized in that the catalyst is a manganese-based catalyst and the used amount of the catalyst with respect to the polyester is 20-500 mmol%. Also provided is a method for producing a polyester polymer and an intermediate thereof, wherein the polyester polymer is produced by performing re-polymerization using the aromatic bis(hydroxyalkyl) dicarboxylate as a raw material, and the polyester polymer has less coloration like a virgin product (product which is produced by polymerizing monomers without performing depolymerization).

Description

Technical Field

[0001] The present invention relates to a method for depolymerizing polyester to produce aromatic dicarboxylic acid bis(hydroxyalkyl) and a method for producing aromatic polyester using the same. Specifically, the present invention relates to a method for producing recycled aromatic polyester by depolymerizing aromatic polyester contained in polyester scraps and product recyclates containing aromatic polyester, and then repolymerizing it.

Background Art

[0002] Aromatic polyesters, such as polyethylene terephthalate, are widely used as fibers, films, and resin molded products due to their excellent properties. In these manufacturing and processing steps, unused polyester raw materials, as well as fibrous, film-like, and other shaped scraps and end materials are generated. In addition, fibers, films, and resin molded products used as polyester products are discarded after use or in an unused state, and such waste has become a problem as it deteriorates the environment.

[0003] As methods for recycling these process scraps, end materials, unused raw materials, and product wastes, there are material recycling, chemical recycling, and thermal recycling. Among chemical recycling methods, chemical recycling in which a monomer in a form where one molecule of aromatic dicarboxylic acid and two molecules of diol are bonded by an ester group, or an intermediate obtained by further depolymerizing an oligomer in which they are ester-bonded is repolymerized and used is an excellent method because recycled aromatic polyester can be produced by a direct polycondensation reaction, requiring less energy.

[0004] As this method, for example, there is a method in which polyethylene terephthalate is depolymerized in ethylene glycol to obtain bis(2-hydroxyethyl) terephthalate, which is then polycondensed to obtain recycled aromatic polyester.

[0005] However, there was a problem that the recycled aromatic polyester polymer obtained in this way was colored. Furthermore, aromatic polyesters may contain sulfophthalic acid-based components such as metal salts of sulfophthalic acid such as sodium sulfophthalate, tetraalkylphosphonium salts of sulfophthalic acid, and tetraalkylammonium salts of sulfophthalic acid as dicarboxylic acid components for the purpose of improving the dyeability of polyester fibers. In this case, the recycled aromatic polyester obtained simply by depolymerization and then repolymerization has problems other than the coloring problem, such as a decrease in molecular weight (intrinsic viscosity), melting point, and crystallinity, or an increase in by-products (such as diethylene glycol), resulting in inferior heat resistance.

[0006] Among these, in Patent Document 1, as a step for removing coloring factor substances, adsorption treatment in which the coloring factor substances are brought into contact with an adsorbent, decomposition treatment in which the coloring factor substances are decomposed with a decomposing agent, reduction treatment in which the coloring factor substances are reduced with a reducing agent, etc. have been attempted. However, although the coloring factor substances such as dyes clearly mixed in the polymer are removed to some extent, a production method for obtaining a polyester polymer with coloring suppressed to the same level as that of a normal production polyester polymer has not yet been obtained.

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made in view of the above background. The object of the present invention is, firstly, to provide a method for producing aromatic dicarboxylic acid bis(hydroxyalkyl) by depolymerizing polyester and a method for producing a polyester polymer therefrom, and a method for producing an aromatic polyester polymer and an intermediate thereof with coloring suppressed to the same level as that of virgin products (products produced by polymerizing monomers without undergoing depolymerization).

[0008] A second object of the present invention is to provide a method for producing a recycled aromatic polyester by depolymerizing and then repolymerizing an aromatic polyester contained in polyester fiber scraps containing an aromatic polyester or recycled polyester products, etc., while providing a method for producing a recycled aromatic polyester having heat resistance comparable to that of virgin aromatic polyester. In particular, even when a sulfoisophthalic acid component is contained in an aromatic polyester as a dicarboxylic acid component, a method for producing a recycled aromatic polyester having heat resistance comparable to that of virgin aromatic polyester is provided.

Means for Solving the Problems

[0009] That is, a first invention of the present invention is a method for producing an aromatic dicarboxylic acid bis(hydroxyalkyl) by depolymerizing a polyester in the presence of a catalyst, wherein the catalyst is a manganese-based catalyst and the amount of catalyst used is 20 to 500 mmol% based on the polyester.

[0010] The method for producing an aromatic dicarboxylic acid bis(hydroxyalkyl) of the present invention is a method for producing an aromatic dicarboxylic acid bis(hydroxyalkyl) by depolymerizing a polyester in the presence of a catalyst, wherein the catalyst is a manganese-based catalyst and the amount of catalyst used is 20 to 500 mmol% based on the polyester.

[0011] Furthermore, it is preferable that the polyester is mainly composed of polyalkylene terephthalate, and the polyalkylene terephthalate is any one of polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate.

[0012] Further, it is preferable that the aromatic dicarboxylic acid bis(hydroxyalkyl) is benzene dicarboxylic acid bis(hydroxyalkyl), the manganese-based catalyst is manganese acetate, the catalyst is used as a solution previously dissolved in an alkylene glycol, the temperature is lowered in the alkylene glycol for crystallization after depolymerization, and it is preferable to wash with water after crystallization.

[0013] The first invention of the present invention also includes a method for producing a polyester resin characterized by repolymerizing the aromatic dicarboxylic acid bis(hydroxyalkyl) obtained by any of the above production methods. And it includes the polyester resin obtained by this production method.

[0014] In a preferred embodiment, the present invention is a method for producing a recycled aromatic polyester in which a polyester containing an aromatic polyester is depolymerized and then the components obtained by depolymerization are polycondensed to obtain a recycled aromatic polyester. The depolymerization is carried out by depolymerizing the polyester in the presence of a catalyst to obtain aromatic dicarboxylic acid bis(hydroxyalkyl). The catalyst used for the depolymerization is a manganese-based catalyst, and the amount of catalyst used is 20 to 500 mmol% based on the polyester.

[0015] In this preferred embodiment, more preferably, the aromatic dicarboxylic acid bis(hydroxyalkyl) is purified after depolymerization and before polycondensation.

[0016] And particularly preferably, the polycondensation is carried out by polycondensing the purified aromatic dicarboxylic acid bis(hydroxyalkyl) in the presence of an alkali metal and / or an alkaline earth metal.

[0017] The present invention also relates to a method for producing a recycled aromatic polyester by depolymerizing a polyester containing an aromatic polyester and then polycondensing the components obtained by the depolymerization to obtain a recycled aromatic polyester. The method comprises depolymerizing a polyester containing an aromatic polyester in an alkylene glycol to obtain an aromatic dicarboxylic acid bis(hydroxyalkyl), purifying the aromatic dicarboxylic acid bis(hydroxyalkyl), and polycondensing the purified aromatic dicarboxylic acid bis(hydroxyalkyl) in the presence of an alkali metal and / or an alkaline earth metal to obtain a recycled aromatic polyester. This is the second invention of the present invention and will be described in detail later.

Advantages of the Invention

[0018] According to the present invention, firstly, in a method for producing an aromatic dicarboxylic acid bis(hydroxyalkyl) by depolymerizing a polyester and a method for producing a polyester polymer therefrom, it is possible to provide a method for producing a virgin product (produced by polymerizing monomers without undergoing depolymerization), a polyester polymer with suppressed coloring, and an intermediate thereof.

[0019] According to the present invention, secondly, there is provided a method for producing a recycled aromatic polyester by depolymerizing an aromatic polyester contained in polyester fiber scraps or recycled polyester products containing an aromatic polyester and then polymerizing it again, and a method for producing a recycled aromatic polyester having excellent heat resistance comparable to that of a virgin aromatic polyester. In particular, even when a sulfoisophthalic acid component is contained in the aromatic polyester as a dicarboxylic acid component, it is possible to provide a method for producing a recycled aromatic polyester having excellent heat resistance comparable to that of a virgin aromatic polyester.

Best Mode for Carrying Out the Invention

[0020] 〔First Invention〕 Hereinafter, the first invention of the present invention will be described in detail.

[0021] The present invention relates to a method for producing aromatic dicarboxylic acid bis(hydroxyalkyl) by depolymerizing polyester in the presence of a catalyst. Here, the polyester is a polycondensate synthesized by dehydrative condensation of a polyvalent carboxylic acid and a polyalcohol to form an ester bond. Or the polyester is a polymer having an ester bond. As the polyester, a semi-aromatic polyester is preferable.

[0022] As the polyvalent carboxylic acid constituting such a polyester, it is preferable to use a dicarboxylic acid or its ester-forming derivative. Specifically, aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, bis(p-carboxyphenyl)methane, anthracenedicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-tetrabutylphosphonium isophthalic acid, 5-sodium sulfoisophthalic acid, etc. can be mentioned. Also, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, malonic acid, glutaric acid, dimer acid, and alicyclic dicarboxylic acids such as 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid can be mentioned. It is also possible to use the ester-forming derivatives of the above dicarboxylic acids.

[0023] Among them, as the polyvalent carboxylic acid constituting the polyester used in the present invention, it is more preferable to mainly use terephthalic acid or 2,6-naphthalenedicarboxylic acid. It is also preferably applied to the case of mainly using terephthalic acid and using an isophthalic acid component as a copolymerization component, more specifically, a polyester copolymerized with isophthalic acid or 5-sodium sulfoisophthalic acid.

[0024] Also, as the polyalcohol which is the other component constituting the polyester, it is preferable to use a diol or its ester-forming derivative. Specifically, aliphatic glycols having 2 to 20 carbon atoms, namely, ethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, decamethylene glycol, cyclohexanedimethanol, cyclohexanediol, dimer diol, etc. can be mentioned.

[0025] Alternatively, as the polyalcohol, long-chain glycols having a molecular weight of 200 to 100,000, namely, polyethylene glycol, poly-1,3-propylene glycol, poly-1,2-propylene glycol, polytetramethylene glycol, etc. can be used. Also, aromatic dioxy compounds, namely, 4,4'-dihydroxybiphenyl, hydroquinone, tert-butyl hydroquinone, bisphenol A, bisphenol S, bisphenol F, etc. can also be used. Further, it is also preferable to use ester-forming derivatives of these polyalcohols and diols.

[0026] Among them, as the alcohol constituting the polyester used in the present invention, it is preferable to use ethylene glycol (hereinafter sometimes abbreviated as EG), 1,3-propanediol, or 1,4-butanediol.

[0027] The polyester obtained by combining the above polyvalent carboxylic acid and polyalcohol can be used as a starting material in the present invention, but it is preferable that the polyester is a semi-aromatic polyester, and more preferably a polyalkylene terephthalate. In particular, it is particularly preferable that the polyalkylene terephthalate is any one of polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate.

[0028] The method for producing the aromatic dicarboxylic acid bis(hydroxyalkyl) of the present invention depolymerizes the above polyester in the presence of a catalyst. In the present invention, it is important to select a manganese-based catalyst as the catalyst here.

[0029] Examples of the manganese-based catalyst include fatty acid salts, carbonates, sulfates, phosphates, oxides, hydroxides, halides, alcoholates, etc. of manganese (Mn), and it is also preferable to combine one or more of them. In the present invention, manganese oxide or manganese acetate can be used, and particularly manganese acetate is preferably used.

[0030] Further, the catalyst to be used is preferably used as a solution previously dissolved in an alkylene glycol. As the alkylene glycol (hereinafter sometimes abbreviated as AG), the same one as the diol component forming the skeletal structure of the above polyester as the starting material can be used. Also, it is possible to use the diol constituting the polyester finally obtained as the product obtained by repolymerizing the aromatic dicarboxylic acid bis(hydroxyalkyl) obtained by the production method of the present invention.

[0031] Examples of the alkylene glycol forming or capable of forming the skeletal structure of the polyester include ethylene glycol (EG) when the polyester is polyethylene terephthalate (PET), 1,3-propanediol (trimethylene glycol, C3G) when it is polytrimethylene terephthalate, and 1,4-butanediol (C4G) when it is polybutylene terephthalate. Also, as this alkylene glycol, it is also preferable to use a mixture of the above alkylene glycols according to the purpose.

[0032] The reason is not arbitrary, but the effects of the present invention are remarkably manifested only when a manganese-based catalyst is selected from various catalysts. The effects of the present invention are particularly evident when there is no other coloring substance, rather than when depolymerizing recycled polyester containing other coloring substances. For example, the depolymerized product of polyester often gradually becomes more discolored over time due to long-term storage, etc., but the product obtained by the production method of the present invention is clearly less discolored.

[0033] Also, in the production method of the present invention, the amount of catalyst used needs to be 20 to 500 mmol% based on the polyester. Furthermore, it is preferably 30 to 300 mmol%, particularly preferably 50 to 150 mmol%. Here, mol% indicates the ratio of the number of catalyst molecules to the structural units of the polyester, and mmol% is 1000 times that. With ordinary other catalysts, sufficient depolymerization cannot be achieved with such a low addition amount, but by using a manganese-based catalyst, it becomes possible to suppress the amount used to a low level. If the amount of catalyst used is too less than this range, the catalytic activity is not sufficient, and if it is too much, the effect of suppressing discoloration decreases.

[0034] The production method of the aromatic dicarboxylic acid bis(hydroxyalkyl) of the present invention is a production method that essentially requires depolymerizing the above polyester in the presence of a manganese-based catalyst, and the amount of catalyst used at that time is 20 to 500 mmol% based on the polyester.

[0035] Furthermore, in the production method of the present invention, after depolymerization using the above catalyst, it is preferable to lower the temperature and crystallize in alkylene glycol. As the temperature-lowering conditions during crystallization, it is more preferable to lower the temperature from a temperature of 60°C or higher to 25°C or lower, and further preferably by a method of cooling to 15°C or lower. Further, it is preferable to perform solid-liquid separation after crystallization, and the alkylene glycol content in the cake after solid-liquid separation is preferably 100% by mass or less. Further, it is preferable that the alkylene glycol content is 55% by mass or less, or adjusted to a range of 1 to 30% by mass, particularly preferably in a range of 5 to 25% by mass. Also, the amount of alkylene glycol used during the initial depolymerization is preferably 2 to 20 times, and further preferably 3 to 10 times the amount of the raw material polyester. By using a large amount of alkylene glycol during depolymerization and performing crystallization and solid-liquid separation in this way, it has become possible to further reduce the amount of the depolymerization catalyst and other foreign substances mixed in the production method of the present invention.

[0036] Since the manganese-based catalyst used in the present invention is used in a small amount, it is possible to further reduce it by such treatment in alkylene glycol. In particular, when manganese acetate is used as the catalyst, the solubility in alkylene glycol is high, and it has become possible to more effectively reduce the amount of the catalyst remaining in the subsequent process.

[0037] Furthermore, in the production method of the present invention, it is preferable to wash the cake after depolymerization with water or alkylene glycol after crystallization as described above. More preferably, it is treated with a Nutsche filter while spraying the cleaning liquid. By performing these treatments, the depolymerization catalyst dissolved in the alkylene glycol and other coloring causative substances can be washed away, and it becomes possible to obtain an aromatic dicarboxylic acid bis(hydroxyalkyl) with a higher degree of purification. As the solution used for washing, it is preferable that the viscosity is low, and from this viewpoint, it is preferable to use water. The amount of the cleaning liquid is preferably 1 to 100 times the weight of the cake, and more preferably 1.5 to 10 times the weight. The liquid temperature during washing is preferably in the range of 0 to 40 °C. If the temperature is too high, the cake itself is likely to dissolve and the yield decreases. Thereafter, an aromatic dicarboxylic acid bis(hydroxyalkyl) can be obtained by drying with a vacuum dryer or the like. In addition, when the alkylene glycol used in the production method of the present invention is the same as the diol component of the polyester resin after repolymerization, it is also a preferable method for producing polyester to perform repolymerization without drying it as it is.

[0038] The aromatic dicarboxylic acid bis(hydroxyalkyl) obtained by the production method of the present invention as described above depends on the types of polyester and alkylene glycol used. However, when mainly using a polyester (polyalkylene terephthalate) with terephthalic acid as the polycarboxylic acid as the raw material, it is preferably a method for producing benzenedicarboxylic acid bis(hydroxyalkyl) (hereinafter, BHAT; sometimes referred to as bis(hydroxyalkyl) terephthalate). More specifically, when using C3G (1,3-propanediol (trimethylene glycol)) as the alkylene glycol, BHPT (bis(hydroxypropyl) terephthalate) is produced, and when using C4G (1,4-butanediol), BHBT (bis(hydroxybutyl) terephthalate) is produced. In particular, when using polyethylene terephthalate mainly composed of terephthalic acid and ethylene glycol as a component constituting the polyester, it becomes possible to produce benzenedicarboxylic acid bis(hydroxyethyl) (BHET; bis(hydroxyethyl) terephthalate).

[0039] Furthermore, the aromatic dicarboxylic acid bis(hydroxyalkyl) obtained by the production method of the present invention as described above can be repolymerized by a conventionally known method to obtain a polyester resin having an excellent hue that is difficult to be colored.

[0040] That is, another production method of the polyester resin of the present invention is a production method for repolymerizing the aromatic dicarboxylic acid bis(hydroxyalkyl) obtained by the above production method. Furthermore, the polyester resin of another invention of the present invention is obtained by this production method of the polyester resin.

[0041] As the catalyst during repolymerization for obtaining the polyester resin, known catalysts such as Sb-based, Ge-based, or titanium-based catalysts can be used, and in particular, antimony trioxide is preferably used. It is preferable to carry out the polycondensation reaction while flowing away alkylene glycol and the like generated by the reaction outside the reactor during repolymerization. The amount of the catalyst used is preferably in the range of 10 to 1000 ppm based on the weight of the aromatic dicarboxylic acid bis(hydroxyalkyl) used.

[0042] Furthermore, in the method for producing the polyester resin of the present invention, after polycondensation using a catalyst, a conventionally known phosphorus-based stabilizer is preferably used. The amount of the phosphorus-based stabilizer used is preferably in the range of 1 to 100 ppm respectively based on the weight of the aromatic dicarboxylic acid bis(hydroxyalkyl) used.

[0043] Unlike the case where Mg hydroxide, Na hydroxide, etc. conventionally widely used are used as the depolymerization catalyst, the polyester resin thus obtained is a resin with less discoloration such as yellowing. This was visible to the naked eye even at the stage of the aromatic dicarboxylic acid bis(hydroxyalkyl) obtained in the middle, but after repolymerization into the resin, the hue L * , a * , b * When the values were measured with a colorimeter, it was particularly remarkable for the value of b * . The polyester produced under the conditions of the present invention is only -3 or less, more preferably -3.5 or less, while those produced with other catalysts have higher values, and some of them have positive values (strong yellowing). The reason is not clear, but it is considered that the manganese-based catalyst can depolymerize at a low concentration, not only hardly produces colored by-products, but also is easily dissociated from the aromatic dicarboxylic acid bis(hydroxyalkyl) even in subsequent processes such as crystallization, and hardly remains as impurities, which is effectively working.

[0044] Furthermore, the obtained polyester resin can be suitably used for applications such as fibers, films, and resins.

[0045] 〔Second Invention〕 Next, the second invention of the present invention will be described in detail. The second invention of the present invention is a method for producing a recycled aromatic polyester by depolymerizing a polyester containing an aromatic polyester and then polycondensing the components obtained by the depolymerization to obtain a recycled aromatic polyester. The method is characterized in that a polyester containing an aromatic polyester is depolymerized in an alkylene glycol to obtain an aromatic dicarboxylic acid bis(hydroxyalkyl), the aromatic dicarboxylic acid bis(hydroxyalkyl) is purified, and the purified aromatic dicarboxylic acid bis(hydroxyalkyl) is polycondensed in the presence of an alkali metal and / or an alkaline earth metal to obtain a recycled aromatic polyester.

[0046] Hereinafter, the second invention and its preferred embodiments will be described in detail.

[0047] 〔Polyester〕 In the second invention of the present invention, as the polyester which is a raw material for obtaining a recycled aromatic polyester, a polyester recovered from a shaped article of polyester (hereinafter referred to as "recovered polyester") containing an aromatic polyester is used. Examples of the shaped article of polyester include those formed into fibers, films, sheets, and other forms.

[0048] When the recovered polyester is a fiber, it may be in the form of a fiber processed product. When it is a film or a sheet, it may be a tray or a bag. As other forms, a bottle is exemplified.

[0049] The recovered polyester may be recovered from the offcuts and non-conforming products generated in the process of manufacturing these. Examples of the offcuts and non-conforming products include raw material pellets that do not meet the required standards, materials and cut fragments that become unnecessary during molding or processing, generated scraps, transition products and prototypes generated during brand change, defective products, and their cuttings.

[0050] In a preferred embodiment of the second invention of the present invention, polyester fiber scraps are used as the recycled polyester. In the recycled polyester, the polyester fiber scraps preferably account for 50% by mass or more, more preferably 51% by mass or more, and even more preferably 70% by mass or more.

[0051] This polyester fiber scrap includes those recovered as waste materials during the manufacturing process, processing process, distribution, etc. before being put on the market as fiber products or processed fiber products, as well as fiber products and processed fiber products recovered after being put on the market. This processed fiber product may or may not have been used. It may also be something that has been discarded.

[0052] The polyester fiber scraps only need to be constituent fibers of polyester fibers, and may additionally contain natural fibers such as cotton, wool, and silk, chemical fibers derived from natural materials such as rayon, cupra, acetate, and lyocell, and synthetic fibers other than polyester fibers such as polyamide fibers, acrylic fibers, and urethane fibers.

[0053] The polyester fiber scraps may be colored, and may be cation-dyeable polyester fibers that can be dyed with cationic dyes having excellent color-developing properties and vividness. This cation-dyeable polyester fiber is composed of an aromatic polyester copolymerized with an aromatic dicarboxylic acid having a sulfonate group as a substituent on the aromatic ring, to which a cationic dye can form an ionic bond.

[0054] 〔Aromatic polyester〕 An aromatic polyester is a polymer obtained by polycondensing an aromatic dicarboxylic acid component and a diol component. The aromatic polyester may be a homopolymer, a copolymer, or a mixture thereof.

[0055] Examples of the aromatic dicarboxylic acid component constituting the aromatic polyester include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, bis(p-carboxyphenyl)methane, anthracenedicarboxylic acid, and 4,4'-diphenyletherdicarboxylic acid. Preferably, terephthalic acid and 2,6-naphthalenedicarboxylic acid are used, and particularly preferably, terephthalic acid is used.

[0056] In addition to the above aromatic dicarboxylic components, aromatic dicarboxylic acids having a sulfonate group as a substituent on the aromatic ring, such as 5-sodium sulfoisophthalic acid, 5-tetrabutylphosphonium sulfoisophthalic acid, and 5-tetrabutylammonium sulfoisophthalic acid, may be copolymerized.

[0057] As the diol component constituting the aromatic polyester, an aliphatic glycol having 2 to 20 carbon atoms or an alicyclic diol can be used. Specifically, ethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, decamethylene glycol, cyclohexanedimethanol, cyclohexanediol, and dimer diol can be exemplified. Preferably, ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,4-cyclohexanedimethanol are used.

[0058] Preferred aromatic polyesters are polyalkylene terephthalates using terephthalic acid as the dicarboxylic acid component and alkylene glycol as the diol. At this time, preferred alkylene glycols are ethylene glycol, 1,3-propanediol, and 1,4-butanediol. Preferred aromatic polyesters are polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate. These aromatic polyesters may be copolymers.

[0059] A copolyester aromatic polyester containing an aromatic dicarboxylic acid having a sulfonate group has good dyeability with cationic dyes, and thus this component is often contained in the aromatic polyester of fibers.

[0060] In the second invention of the present invention, the aromatic polyester may be a copolyester aromatic polyester in which an isophthalic acid component having a sulfonate group, particularly a metal sulfonate group, is contained as a dicarboxylic acid component. As the isophthalic acid having a metal sulfonate group, 5-sodium sulfoisophthalic acid can be exemplified. In this case, the aromatic dicarboxylic acid bis(hydroxyalkyl) obtained by depolymerization described later becomes 5-sodium sulfoisophthalic acid bis(2-hydroxyethyl).

[0061] The copolymerization amount of the sulfoisophthalate component in the aromatic polyester with respect to all the dicarboxylic acid components is 0.5 to 15 mol%, preferably 1 to 10 mol%.

[0062] According to the second invention of the present invention, even if a copolyester aromatic polyester copolymerized with a sulfoisophthalate component is mixed in the aromatic polyester as a raw material for depolymerization, a recycled aromatic polyester having high heat resistance can be obtained.

[0063] A preferred example of the aromatic polyester targeted by the second invention of the present invention is an aromatic polyester in which the main dicarboxylic acid component is terephthalic acid, the secondary dicarboxylic acid component contains 5-sodium sulfoisophthalic acid, and the diol component is ethylene glycol. Here, "main" means 80 mol% or more, preferably 90 mol% or more per all the dicarboxylic acid components.

[0064] 〔Depolymerization〕 In the second invention of the present invention, the aromatic polyester is depolymerized in an alkylene glycol. This depolymerization reaction is carried out in the presence of a catalyst, and as the catalyst, preferably a manganese-based catalyst or a zinc-based catalyst, particularly preferably a manganese-based catalyst is used.

[0065] Examples of the manganese-based catalyst include manganese fatty acid salts, carbonates, sulfates, phosphates, oxides (manganese oxide), hydroxides, halides, and alcoholates. As the manganese fatty acid salt, manganese acetate can be exemplified.

[0066] As the manganese-based catalyst, from the viewpoint of the polymer hue after repolymerization, manganese oxide, manganese acetate are preferably used, and manganese acetate is particularly preferably used. These may be used alone or in combination of a plurality. The catalyst is preliminarily dissolved or suspended in an alkylene glycol and used as a solution or suspension.

[0067] When manganese acetate is used as the catalyst, its solubility in alkylene glycol is high, and the amount of the remaining catalyst can be reduced. The amount of the alkylene glycol used in the depolymerization reaction is preferably 2 to 20 times, more preferably 3 to 10 times the mass of the aromatic polyester. Using the alkylene glycol within this range is preferable because the amount of contamination of the catalyst and other foreign substances can be reduced.

[0068] The amount of the manganese-based catalyst used in the depolymerization reaction is preferably 20 to 500 mmol%, more preferably 30 to 300 mmol%, and particularly preferably 50 to 150 mmol% based on the total dicarboxylic acid content constituting the aromatic polyester. When the manganese-based catalyst is not used, sufficient depolymerization cannot be performed with such a low concentration of catalyst addition. If the amount of the catalyst used is less than 20 mmol%, the catalyst activity is not sufficient and it is not preferable. If it exceeds 500 mmol%, the effect of suppressing discoloration is reduced and it is not preferable.

[0069] The temperature of the depolymerization reaction is, for example, 180 to 250°C, preferably 185 to 210°C, and the time is, for example, 0.5 to 10 hours, preferably 1 to 4 hours. The pressure may be normal pressure or, for example, 760 to 2000 mmHg.

[0070] [Alkylene Glycol] As the alkylene glycol, it is preferable to use the same one as the diol component constituting the above aromatic polyester, or the same one as the diol component constituting the recycled aromatic polyester obtained by the production method of the second invention of the present invention.

[0071] That is, depending on the aromatic polyester or recycled aromatic polyester, it is preferable to use the following as the alkylene glycol.

[0072] When the aromatic polyester and / or recycled aromatic polyester is polyethylene terephthalate, it is preferable to use ethylene glycol as the alkylene glycol.

[0073] When the aromatic polyester and / or recycled aromatic polyester is polytrimethylene terephthalate, it is preferable to use 1,3-propanediol (trimethylene glycol) as the alkylene glycol.

[0074] When the aromatic polyester and / or recycled aromatic polyester is polybutylene terephthalate, it is preferable to use 1,4-butanediol as the alkylene glycol.

[0075] In any case, the alkylene glycol may be a mixture of alkylene glycols constituting the aromatic polyester and / or recycled aromatic polyester.

[0076] 〔Purification〕 In the second invention of the present invention, it is important to purify the aromatic dicarboxylic acid bis(hydroxyalkyl) obtained by depolymerizing the aromatic polyester.

[0077] The purification of the aromatic dicarboxylic acid bis(hydroxyalkyl) is preferably carried out by crystallization in an alkylene glycol solution of the aromatic dicarboxylic acid bis(hydroxyalkyl).

[0078] Crystallization is preferably carried out by cooling a solution obtained by depolymerizing an aromatic polyester from a temperature of 60 °C or higher to a temperature of 25 °C or lower, and more preferably by further cooling to a temperature of 15 °C or lower.

[0079] By cooling, the solid of the crystallized aromatic dicarboxylic acid bis(hydroxyalkyl) will be separated from the liquid solution. The solid of the crystallized aromatic dicarboxylic acid bis(hydroxyalkyl) is referred to as "cake". The cake is separated from the liquid and then subjected to a polycondensation reaction.

[0080] As one of the aspects of the second invention of the present invention, there is an aspect where the aromatic polyester is an aromatic polyester containing an isophthalic acid component having a metal sulfonate group as a copolymerization component, that is, the main dicarboxylic acid component is terephthalic acid, the secondary dicarboxylic acid component is 5-sodium sulfoisophthalic acid, and the diol component is ethylene glycol. In this case, what is obtained by depolymerizing this is that the main depolymerization product is terephthalic acid bis(2-hydroxyethyl), the secondary depolymerization product is 5-sodium sulfoisophthalic acid bis(2-hydroxyethyl), and the obtained depolymerization product is a mixture containing these. When this is purified, terephthalic acid bis(2-hydroxyethyl) (sometimes referred to as bis-2-hydroxyethyl terephthalate or BHET) crystallizes as a cake, while the secondary depolymerization product, 5-sodium sulfoisophthalic acid bis(2-hydroxyethyl) (sometimes referred to as BHESI), does not crystallize and remains in a liquid state. Therefore, BHET that crystallizes can be obtained in a solid state by solid-liquid separation and separated from the liquid BHESI that does not crystallize, and only BHET can be taken out with high purity.

[0081] Therefore, in the second invention of the present invention, even if an aromatic polyester contains an aromatic polyester containing an isophthalic acid component having a metal sulfonate group as a copolymerization component, it is depolymerized to separate the copolymerization component and then polycondensed again, whereby a recycled aromatic polyester excellent in heat resistance can be produced. At this time, the amount of the isophthalic acid component having a metal sulfonate group contained in the aromatic polyester is, for example, 2 mol% or less, preferably 0.5 mol% or less, based on the amount of all dicarboxylic acid components of the aromatic polyester.

[0082] 〔Washing〕 The cake of aromatic dicarboxylic acid bis(hydroxyalkyl) is preferably washed. That is, it is preferable that washing is performed after crystallization of the aromatic dicarboxylic acid bis(hydroxyalkyl).

[0083] The washing of the cake is preferably performed using water or alkylene glycol as the washing liquid. The washing liquid preferably has a low viscosity, and water is preferable from this viewpoint. The washing is preferably performed by treating with a Nutsche filter while spraying the washing liquid onto the cake.

[0084] By washing, the depolymerization catalyst dissolved in the alkylene glycol solution after depolymerization and the coloring causative substances contained in the aromatic polyester subjected to depolymerization are washed away, and high-purity aromatic dicarboxylic acid bis(hydroxyalkyl) can be obtained.

[0085] The amount of the washing liquid used for washing is preferably 1 to 100 times, more preferably 1.5 to 10 times the mass of the cake of aromatic dicarboxylic acid bis(hydroxyalkyl). The temperature of the washing liquid is preferably 0 to 40°C. If the temperature exceeds 40°C, the cake itself is likely to dissolve and the yield decreases, which is not preferable.

[0086] After washing, the cake is dried to obtain high-purity aromatic dicarboxylic acid bis(hydroxyalkyl) having no sulfo group. Drying can be performed, for example, using a vacuum dryer.

[0087] When an alkylene glycol is used in the cleaning liquid and the alkylene glycol used is the same as the diol component of the recycled aromatic polyester, it may be subjected to polycondensation without drying.

[0088] The mode of drying the bis(hydroxyalkyl) aromatic dicarboxylate after washing and then subjecting it to a polycondensation reaction is a preferred mode.

[0089] 〔Polycondensation〕 Polycondensation is carried out to obtain a recycled aromatic polyester from bis(hydroxyalkyl) aromatic dicarboxylate. This polycondensation reaction is carried out in the presence of a polymerization catalyst and an alkali metal and / or an alkaline earth metal. The polycondensation reaction itself can be carried out by a method commonly used in the art using a polymerization catalyst commonly used in the art. The polycondensation reaction is preferably carried out while distilling off the alkylene glycol generated during the polycondensation reaction outside the reaction vessel.

[0090] Examples of the polymerization catalyst include antimony-based, germanium-based, and titanium-based catalysts, and preferably an antimony-based catalyst is used. As the antimony-based catalyst, for example, antimony trioxide is used. The amount of the polymerization catalyst used is preferably 10 to 1000 ppm based on the mass of bis(hydroxyalkyl) aromatic dicarboxylate.

[0091] The alkylene glycol content of the cake of the purified bis(hydroxyalkyl) aromatic dicarboxylate when subjected to the polycondensation reaction is preferably 100% by mass or less, more preferably 55% by mass or less, still more preferably 30% by mass or less, and particularly preferably 25% by mass or less based on the mass of bis(hydroxyalkyl) aromatic dicarboxylate.

[0092] The temperature of the polycondensation reaction is, for example, 230 to 330 °C, preferably 250 to 310 °C, and the reaction time is, for example, 240 minutes or less, preferably 180 minutes or less. The reaction is carried out under reduced pressure, for example, 100 Pa or less, preferably 50 Pa or less.

[0093] Alkali metal and / or alkaline earth metal Examples of the alkali metal include lithium, sodium, potassium, rubidium, and cesium, and preferably sodium and potassium are used.

[0094] Examples of the alkaline earth metal include calcium, barium, beryllium, and magnesium, and preferably calcium and magnesium are used.

[0095] Particularly preferred as the alkali metal and / or alkaline earth metal is sodium.

[0096] From the viewpoint of the polymer hue after repolymerization, the usage amount of the alkali metal and / or alkaline earth metal is preferably 5 to 1000 ppm, more preferably 10 to 500 ppm, based on the mass of the aromatic dicarboxylic acid bis(hydroxyalkyl).

[0097] The alkali metal and / or alkaline earth metal is preferably used in the form of its respective salt. That is, it is preferably used as an alkali metal salt and / or an alkaline earth metal salt.

[0098] Examples of the acid component constituting the alkali metal salt and / or alkaline earth metal salt include propionic acid, acetic acid, oxalic acid, formic acid, carbonic acid, etc., and preferably acetic acid is used.

[0099] As the alkali metal salt and / or alkaline earth metal salt, preferably lithium acetate, sodium acetate, potassium acetate, calcium acetate, barium acetate, magnesium acetate, and more preferably sodium acetate are used.

[0100] Stabilizer During the polycondensation reaction, it is preferable to add a phosphorus-based stabilizer. Known phosphorus-based stabilizers can be used, and for example, it is 1 to 100 ppm based on the mass of the aromatic dicarboxylic acid bis(hydroxyalkyl). Examples of the phosphorus-based stabilizer include phosphorous acid, orthophosphoric acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, diethyl benzenephosphonate, dimethyl (2-hydroxyethyl)phosphonate, and / or phenylphosphonic acid, and preferably orthophosphoric acid, trimethyl phosphate, triethyl phosphate, and triphenyl phosphate.

Examples

[0101] Hereinafter, the present invention will be described more specifically by way of examples. Each value in the examples was determined by the following measurement methods.

[0102] In the description of the addition amount of the catalyst, "mol%" of the catalyst with respect to the polyester indicates the ratio of the number of catalyst molecules to the structural units of the polyester. (1) Measurement method 1) Hue (L * a * b * ) It was measured by the following method. The polymer (5 g) was pressed between two metal plates to form a plate shape, and then heated at 140 °C for 2 hours to crystallize the sample. The measurement sample was used with a measuring device ("ZE-6000" manufactured by Nippon Denshoku Industries Co., Ltd.) to measure the values of hue L * , a * , b * in accordance with JIS Z8781-4:2013. 2) Metal content The amounts of various metal elements in the polymer were measured by melting the polymer to form a circular disk and using a fluorescent X-ray measuring device "ZSXPrimus II" manufactured by Rigaku Corporation to measure the amount of the metal corresponding to the catalyst used. In the table, "ND" means below the detection limit (5 ppm or less). 3) Intrinsic viscosity (IV) 0.6 g of polyester was dissolved by heating in 50 cc of o-chlorophenol, and after once cooling, it was calculated from the solution viscosity of the solution measured at a temperature of 35 °C using an Ubbelohde viscometer, using a calibration curve prepared separately. 4) Glass transition point (Tg), melting point (Tm), crystallization temperature (Tc) 10 mg of the sample was cut out and filled into an aluminum pan, and the melting point was measured using a "DSC apparatus Q10" manufactured by TA Instruments-Waters LLC. As the measurement conditions, first, after once heating from 25 °C to 300 °C at a heating rate of 20 °C / min, it was rapidly cooled and quenched. Then, for this quenched sample, it was heated from 25 °C to 300 °C at 20 °C / min, and the crystal melting point was determined. 5) Content of 5-sodium sulfoisophthalic acid The sample was molded into a plate shape, and the sulfur content derived from the sulfo group was measured using a fluorescence X-ray apparatus "ZSXPrimus II" manufactured by Rigaku Corporation, and the content of 5-sodium sulfoisophthalic acid was calculated. In the table, "ND" means below the detection limit (5 ppm or less). 6) Diethylene glycol (DEG) content The polyester was decomposed using water-hydrazine, and the content of diethylene glycol in this decomposition product was measured using gas chromatography (HP6850 manufactured by Hewlett-Packard). (2) Polyester resin As the polyester resin to be subjected to depolymerization, generally distributed polyethylene terephthalate (PET) pellets were obtained. The physical properties and color tone of this polyester resin were as described in Table 1.

[0103] In Examples 1 to 3 and Comparative Examples 1 to 12, this polyethylene terephthalate (PET) pellet was used as the polyester resin to be subjected to depolymerization.

[0104]

Table 1

[0105] 〔Example 1〕 To 300 parts by mass of a polyester resin, 1500 parts by mass of ethylene glycol (EG) and 0.38 part by mass of manganese acetate (100 mmol% based on the polyester) as a depolymerization catalyst were charged into a 2 L separable flask and sealed with nitrogen. At this time, manganese acetate was dissolved in EG in advance and then charged. The polyester resin used was an uncolored polyethylene terephthalate resin and contained 297 ppm of Sb as a polymerization catalyst.

[0106] Thereafter, the separable flask containing the sample was heated by a mantle heater to an internal temperature of 220 °C and depolymerization treatment was carried out at normal pressure for 4 hours while stirring. The BHET (bis(hydroxyethyl) benzene dicarboxylate) solution after this depolymerization was colorless and transparent and no coloring was observed. Further, this solution after depolymerization was filtered through a 200 μm mesh to remove the solid content remaining inside, and after gradually cooling to 70 °C, while stirring and cooling, the temperature drop from 70 °C to 40 °C was carried out over an elapsed time of 0 to 10 minutes, the temperature drop from 40 °C to 30 °C was carried out over an elapsed time of 10 to 60 minutes, and the temperature drop from 30 °C to 15 °C was carried out over an elapsed time of 60 to 180 minutes. Thereafter, stirring was carried out for 60 minutes while maintaining the internal temperature at 15 °C to lower the internal temperature and precipitate crystals of BHET (total 4 hours) to obtain a BHET / EG slurry.

[0107] The BHET / EG slurry was subjected to a pressing treatment with a filter press manufactured by Nippon Filtration K.K. to perform solid-liquid separation of BHET and EG. The BHET separated at this time contained 35% by mass of EG based on the cake weight recovered after the filter press. While spraying 2 weight times of pure water at 25 °C on the cake after this EG separation, a water washing treatment was carried out with a Nutsche filter. Thereafter, the BHET for which solid-liquid separation was completed was subjected to a drying treatment at 50 °C for 8 hours in a vacuum dryer to obtain dried BHET. The obtained BHET was white and no foreign matter was observed to be mixed in.

[0108] Subsequently, 254 parts by mass of the obtained dried BHET was charged into a reaction vessel at normal pressure under a nitrogen atmosphere together with 0.007 parts by mass of a phosphorus-based stabilizer and 0.07 parts by mass of antimony trioxide as a repolymerization catalyst. Next, the temperature inside the reactor was set to 285°C, and the pressure was gradually reduced step by step under the conditions of normal pressure for 10 minutes, 4 kPa for 10 minutes, and further 0.4 kPa for 40 minutes, while distilling off ethylene glycol and the like generated by the reaction outside the reactor, and a polycondensation reaction was carried out.

[0109] Finally, the quality of the produced polyethylene terephthalate was shown in Table 2 and Table 3.

[0110]

Table 2

[0111]

Table 3

[0112] 〔Example 2〕 The same treatment was carried out except that the depolymerization catalyst used in Example 1 was changed to manganese oxide instead of manganese acetate, and the BHET obtained by depolymerization and the repolymerized polyethylene terephthalate resin were collected. At this time, the BHET solution after depolymerization was colorless and transparent, and no coloring was observed. The quality is shown in Table 2 and Table 3 together.

[0113] 〔Example 3〕 The same treatment was carried out except that the addition amount of manganese acetate used in Example 1 was changed from 0.38 parts by mass (100 mmol% based on the polyester) to 0.30 parts by mass (80 mmol% based on the polyester). Although some undissolved substances were confirmed in the BHET solution after depolymerization, the BHET obtained by depolymerization and the repolymerized polyethylene terephthalate resin could be collected. The quality is shown in Table 2 and Table 3 together.

[0114] Regarding the manganese acetate used in Example 1, the same treatment as in Example 1 was carried out except that the addition amount was further reduced to 0.038 parts by mass (10 mmol% based on the polyester). As a result, depolymerization did not proceed sufficiently, and a large amount of undegraded polyester remained in the flask. The amount of BHET obtained was small, and repolymerization could not be carried out.

[0115] [Comparative Examples 1 to 4] The depolymerization catalyst used in Example 1 was replaced with calcium acetate (Comparative Example 1), magnesium acetate (Comparative Example 2), cerium acetate (Comparative Example 3), and cobalt acetate (Comparative Example 4), respectively. The same treatment was carried out, and the BHET obtained by depolymerization and the repolymerized polyethylene terephthalate resin were collected. When calcium acetate (Comparative Example 1) and magnesium acetate (Comparative Example 2) were used, relatively many undegraded substances were observed after depolymerization. In addition, the BHET solution after depolymerization obtained in Comparative Examples 1 to 4 was colored, unlike in the examples. Although the physical properties such as the melting point of the finally obtained polyester were equivalent to those of the examples, coloring was also observed in the intermediate-stage BHET. In addition, the metal content derived from each catalyst component showed a higher residual metal amount compared to manganese. The quality is shown in Tables 2 and 3 together.

[0116] [Comparative Example 5] The depolymerization catalyst was changed to titanium tetrabutoxide instead of the manganese acetate used in Example 1. Since this catalyst is also a polymerization catalyst, the same treatment was carried out except that 0.07 g of antimony trioxide, which is a polymerization catalyst, was not added. The BHET obtained by depolymerization and the repolymerized polyethylene terephthalate resin were collected. The obtained BHET solution after depolymerization was significantly colored. Although the amount of antimony in the finally obtained polyester resin was suppressed, the residual metal amount of titanium was higher than that of manganese, and coloring of BHET and the resin could not be suppressed. The quality is shown in Tables 2 and 3 together.

[0117] [Comparative Example 6] Instead of using manganese acetate as in Example 1, the same treatment was carried out except that the depolymerization catalyst was sodium hydroxide. However, the depolymerization did not proceed sufficiently, and a large amount of undegraded polyester remained in the flask. The amount of BHET was small, and repolymerization could not be carried out.

[0118] 〔Comparative Examples 7 - 9〕 Instead of using manganese acetate as in Example 1, the depolymerization catalysts were the same sodium hydroxide (Comparative Example 7), sodium carbonate (Comparative Example 8), and sodium acetate (Comparative Example 9) as in Comparative Example 6. Further, the same treatment was carried out except that the input amount was changed from 0.38 parts by mass in Example 1 to 9.0 parts by mass, and the BHET obtained by depolymerization and the repolymerized polyethylene terephthalate resin were collected. The obtained BHET solution after depolymerization was colored. However, as a result, the residual metal content in the repolymerized polyester was more than that in the examples, and coloring was also observed. The quality is shown in Tables 2 and 3 together.

[0119] 〔Comparative Example 10〕 Instead of using manganese acetate as in Example 1, the same treatment was carried out except that the depolymerization catalyst was potassium carbonate. However, the depolymerization did not proceed sufficiently, and a large amount of undegraded polyester remained in the flask. The amount of BHET was small, and repolymerization could not be carried out.

[0120] 〔Comparative Examples 11 and 12〕 Instead of using manganese acetate as in Example 1, the depolymerization catalysts were the same potassium carbonate (Comparative Example 11) and potassium acetate (Comparative Example 12) as in Comparative Example 10. Further, the same treatment was carried out except that the input amount was changed from 0.38 parts by mass in Example 1 to 9.0 parts by mass, and the BHET obtained by depolymerization and the repolymerized polyethylene terephthalate resin were collected. The obtained BHET solution after depolymerization was colored. However, as a result, the residual metal content in the repolymerized polyester was more than that in the examples, and coloring was also observed. The quality is shown in Tables 2 and 3 together.

[0121] 〔Reference Example〕 The production of the copolyester aromatic polyester and aromatic polyester used in Example 21, Example 22, Reference Example 21 and Comparative Example 21 will be described in Reference Examples 1 to 3 below.

[0122] 〔Reference Example 1〕 (Production of 5-Sodium Sulfophthalic Acid Copolyester Aromatic Polyester 1) In a reaction vessel under normal pressure in a nitrogen atmosphere, 191.3 parts by mass of dimethyl terephthalate (DMT), 124.2 parts by mass of ethylene glycol (EG), and 4.4 parts by mass of sodium dimethyl 5-sulfophthalate manufactured by Takemoto Yushi Co., Ltd. were added. 0.07 parts by mass of manganese acetate and 0.22 parts by mass of sodium acetate were added as catalysts, the reaction temperature was set to 240 ° C, and a transesterification reaction was carried out while removing methanol.

[0123] Next, 0.07 parts by mass of antimony trioxide and 0.03 parts by mass of orthophosphoric acid were charged into the reaction product after the transesterification reaction was completed. The temperature in the reaction vessel was set to 285 ° C, and the pressure was gradually reduced step by step under normal pressure for 10 minutes, 4 kPa for 10 minutes, and 0.4 kPa for 40 minutes, and a polycondensation reaction was carried out while distilling off ethylene glycol and the like generated by the reaction outside the reaction vessel. There was no oligomer blockage in the distillation part. The quality of the produced copolyester aromatic polyester is shown in Table 4.

[0124] 〔Reference Example 2〕 (Production of 5-Sodium Sulfophthalic Acid Copolyester Aromatic Polyester 2) In Reference Example 1, a copolyester aromatic polyester was obtained under the same conditions as in Reference Example 1 except that 185.7 parts by mass of dimethyl terephthalate (DMT) and 13.0 parts by mass of dimethyl 5-sodium sulfophthalate were used. The quality is shown in Table 4.

[0125] 〔Reference Example 3〕 (Production of Aromatic Polyester) In a reaction vessel under normal pressure in a nitrogen atmosphere, 194.2 parts by mass of dimethyl terephthalate (DMT), 124.2 parts by mass of ethylene glycol (EG), and 0.07 parts by mass of manganese acetate were added, the reaction temperature was set to 240 ° C, and a transesterification reaction was carried out while distilling off methanol.

[0126] Next, 0.07 parts by mass of antimony trioxide and 0.03 parts by mass of orthophosphoric acid were charged into the reactant in which the transesterification reaction was completed. The temperature in the reaction vessel was set to 285 °C, and the pressure was gradually reduced stepwise under normal pressure for 10 minutes, at 4 kPa for 10 minutes, and at 0.4 kPa for 40 minutes. While distilling off ethylene glycol and the like generated by the reaction outside the reaction vessel, a polycondensation reaction was carried out. No oligomer blockage occurred in the distillation part. The quality of the produced aromatic polyester is shown in Table 4.

[0127] [Example 21] To 300 parts by mass of the copolyester aromatic polyester obtained in Reference Example 1, 1500 parts by mass of ethylene glycol (EG) and 0.38 parts by mass of manganese acetate (100 mmol% based on all dicarboxylic acid components of the copolyester aromatic polyester) were charged into a 2 L separable flask.

[0128] At this time, manganese acetate was dissolved in EG in advance to form a solution before use. Then, under nitrogen enclosure, a depolymerization reaction was carried out at 202 °C for 4 hours while stirring to obtain a depolymerization sample.

[0129] The obtained depolymerization sample was gradually cooled to 70 °C, and then stirred and cooled in a constant temperature bath at 15 °C while lowering the internal temperature to precipitate crystals of bis-2-hydroxyethyl terephthalate (BHET) to obtain a BHET / EG slurry.

[0130] The BHET / EG slurry was subjected to a pressing treatment with a filter press manufactured by Nippon Filtration K.K. to perform solid-liquid separation of BHET and EG, and a cake of BHET was obtained. At this time, the BHET contained 34% by mass of EG with respect to the cake recovered after the filter press.

[0131] While spraying 2 times the mass of pure water with respect to the cake of BHET subjected to this EG separation, a water washing treatment was carried out with a Nutsche filter. The cake of BHET after the solid-liquid separation was dried in a vacuum dryer at 50 °C for 8 hours to obtain Depolymerization Sample 1.

[0132] Subsequently, 254 parts by mass of this depolymerized sample 1, 0.07 parts by mass of antimony trioxide, 0.005 parts by mass of orthophosphoric acid, and 0.22 parts by mass of sodium acetate were charged into a reaction vessel under normal pressure in a nitrogen atmosphere.

[0133] Next, the temperature inside the reaction vessel was set to 285°C, and the pressure was gradually reduced stepwise under normal pressure for 10 minutes, at 4 kPa for 10 minutes, and at 0.4 kPa for 40 minutes. While distilling off ethylene glycol and the like generated by the reaction outside the reaction vessel, a polycondensation reaction was carried out to obtain a recycled aromatic polyester.

[0134] This recycled aromatic polyester had a higher IV and melting point than the raw material aromatic polyester despite having undergone depolymerization and polycondensation, and was also white and of high quality. Its quality is shown in Table 5.

[0135] [Example 22] A depolymerization reaction was carried out in the same manner as in Example 21, except that the copolymerized aromatic polyester of Reference Example 1 used in Example 21 was changed to the copolymerized aromatic polyester of Reference Example 2, to obtain a depolymerized sample 2.

[0136] 254 parts by mass of this depolymerized sample 2, 0.07 parts by mass of antimony trioxide, 0.005 parts by mass of orthophosphoric acid, and 0.22 parts by mass of sodium acetate were charged into a reaction vessel under normal pressure in a nitrogen atmosphere.

[0137] Next, the temperature inside the reaction vessel was set to 285°C, and the pressure was gradually reduced stepwise under normal pressure for 10 minutes, at 4 kPa for 10 minutes, and at 0.4 kPa for 40 minutes. While distilling off ethylene glycol and the like generated by the reaction outside the reaction vessel, a polycondensation reaction was carried out to obtain a recycled aromatic polyester.

[0138] The obtained recycled aromatic polyester had a higher IV and melting point than the raw material aromatic polyester despite having undergone depolymerization and polycondensation, and was also white and of high quality. Its quality was shown in Table 5.

[0139] 〔Reference Example 21〕 To 300 parts by mass of the copolyaromatic polyester obtained in Reference Example 1, 1500 parts by mass of ethylene glycol (EG) and 0.38 parts by mass of manganese acetate were charged into a separable flask with a capacity of 2 L, and depolymerization reaction was carried out at 202 °C for 4 hours while stirring under nitrogen enclosure to obtain a depolymerized sample.

[0140] Under a nitrogen atmosphere, into a reaction vessel under normal pressure, 508 parts by mass of the depolymerized sample obtained above, 0.07 parts by mass of antimony trioxide, 0.005 parts by mass of orthophosphoric acid and 0.22 parts by mass of sodium acetate were charged.

[0141] Next, the temperature in the reaction vessel was set to 285 °C, and the pressure was gradually reduced stepwise under the conditions of normal pressure for 10 minutes, 4 kPa for 10 minutes, and 0.4 kPa for 40 minutes, and polycondensation reaction was carried out while distilling off ethylene glycol and the like generated by the reaction outside the reaction vessel to obtain a regenerated aromatic polyester.

[0142] The obtained regenerated aromatic polyester had a large residual content of Na sulfoisophthalate, and its IV value and melting point were inferior to those of Examples 21 and 22. The quality is shown in Table 5.

[0143] 〔Comparative Example 21〕 Under a nitrogen atmosphere, into a reaction vessel under normal pressure, 254 parts by mass of the depolymerized sample 2 obtained in Example 22, 0.07 parts by mass of antimony trioxide and 0.005 parts by mass of orthophosphoric acid were charged.

[0144] Next, the temperature in the reaction vessel was set to 285 °C, and the pressure was gradually reduced stepwise under the conditions of normal pressure for 10 minutes, 4 kPa for 10 minutes, and 0.4 kPa for 40 minutes, and polycondensation reaction was carried out while distilling off ethylene glycol and the like generated by the reaction outside the reaction vessel to obtain a regenerated aromatic polyester.

[0145] The obtained regenerated aromatic polyester had a low content of 5-sodium sulfoisophthalate, but its melting point was low. The quality is shown in Table 5.

[0146]

Table 4

[0147]

Table 5

Industrial Applicability

[0148] The regenerated aromatic polyester obtained by depolymerizing and then repolymerizing the aromatic dicarboxylic acid bis(hydroxyalkyl) obtained by the production method of the present invention, the aromatic polyester obtained using at least one of them as a raw material, and further the aromatic polyester component contained in polyester scraps and product recyclables has less yellowness and excellent hue, and also can suppress the deterioration of physical properties due to the presence of the copolymer component before depolymerization. Therefore, it can be suitably used, for example, as a material for fibers, films, and resins.

Claims

1. A method for producing aromatic dicarboxylic acid bis(hydroxyalkyl) by depolymerizing polyester in the presence of a catalyst, wherein the catalyst is manganese acetate and the amount of the catalyst used is 20 to 300 mmol% based on the polyester. A method for producing aromatic dicarboxylic acid bis(hydroxyalkyl).

2. The method for producing aromatic dicarboxylic acid bis(hydroxyalkyl) according to claim 1, wherein the polyester contains polyalkylene terephthalate as a main component.

3. The method for producing aromatic dicarboxylic acid bis(hydroxyalkyl) according to claim 2, wherein the polyalkylene terephthalate is any one of polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate.

4. The method for producing aromatic dicarboxylic acid bis(hydroxyalkyl) according to claim 1, wherein the aromatic dicarboxylic acid bis(hydroxyalkyl) is benzene dicarboxylic acid bis(hydroxyalkyl).

5. The method for producing aromatic dicarboxylic acid bis(hydroxyalkyl) according to claim 1, wherein the catalyst is used as a solution previously dissolved in alkylene glycol.

6. The method for producing aromatic dicarboxylic acid bis(hydroxyalkyl) according to claim 1, wherein after depolymerization, the temperature is lowered in alkylene glycol for crystallization.

7. The method for producing aromatic dicarboxylic acid bis(hydroxyalkyl) according to claim 6, wherein after crystallization, it is washed with water.

8. A method for producing a polyester resin, characterized by repolymerizing the aromatic dicarboxylic acid bis(hydroxyalkyl) obtained by the production method according to any one of claims 1 to 7.

9. A method for producing a recycled aromatic polyester, wherein a polyester containing an aromatic polyester is depolymerized and then the components obtained by depolymerization are polycondensed to obtain a recycled aromatic polyester. The depolymerization is carried out by depolymerizing the polyester in the presence of a catalyst to obtain aromatic dicarboxylic acid bis(hydroxyalkyl), and the catalyst used in the depolymerization is manganese acetate, and the amount of the catalyst used is 20 to 300 mmol% based on the polyester. A method for producing a recycled aromatic polyester.

10. The method for producing a recycled aromatic polyester according to claim 9, wherein the aromatic dicarboxylic acid bis(hydroxyalkyl) is purified after depolymerization and before polycondensation.

11. The method for producing a recycled aromatic polyester according to claim 10, wherein the polycondensation is carried out by polycondensing a purified aromatic dicarboxylic acid bis(hydroxyalkyl) in the presence of an alkali metal and / or an alkaline earth metal.

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