Method for recovering polyester component and method for producing recycled polyester

Abstract

To provide a method for recovering a polyester component from a polyester-containing material, and a method for producing recycled polyester using the recovered polyester.SOLUTION: A recovery method treats a polyester-containing material in high-temperature dimethyl terephthalate, and recovers a polyester component. Preferably, polyester contains alkylene benzene dicarboxylate as a main repeating unit and contains a polyester fiber, and the dimethyl terephthalate is a recycled product, and is recovered from a system together with polyester. A method for producing recycled polyester repolymerizes the polyester component obtained by the recovery method.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for recovering polyester components from textile products containing various types of fibers, and a method for producing recycled polyester using the recovered polyester components. [Background technology]

[0002] Various textile products have been widely used, particularly in the field of clothing. Among these fibers, natural fibers such as cotton and silk have gradually been replaced by synthetic fibers, and among these synthetic fibers, the production of polyester fibers has been increasing rapidly in recent years. (According to data from 2020, polyester fibers accounted for approximately 52% of total textile production (Non-Patent Document 1, page 9).) In other words, recycling polyester fibers is highly effective as a measure to promote sustainability.

[0003] On the other hand, the materials used to make textile products have become increasingly diverse, particularly in the clothing industry, and polyester fibers are increasingly being used as composite materials containing other materials rather than as a standalone material. However, it is not easy to recover and recycle polyester components from composite materials containing such various fibers, etc. Polyester recovered from composite materials composed of multiple materials is likely to contain impurities, and the recycled polyester polymer is also prone to coloration and difficult to whiten. In particular, when attempting chemical recycling by depolymerizing and repolymerizing polyester, the color of the polyester obtained after repolymerization from such composite materials tends to be brown, and only products of poor quality are obtained.

[0004] As a solution to such problems, for example, Patent Document 1 discloses a method for chemically recycling waste polyester products, in which the discoloration-causing substances are removed by various methods, such as an adsorption treatment in which the discoloration-causing substances are brought into contact with an adsorbent after depolymerization of the polyester, a decomposition treatment in which the discoloration-causing substances are decomposed with a decomposing agent, and a reduction treatment in which the discoloration-causing substances are reduced with a reducing agent. However, even with this method, it has been difficult to recover the polyester component with high purity from a composite material containing polyester fibers and other fibers. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-88096 [Non-patent literature]

[0006] [Non-Patent Document 1] Preferred Fiber & Materials Market Report 2021 (Textile Exchange, 2021) [Retrieved May 31, 2024], Internet, <URL: https: / / textileexchange.org / app / uploads / 2021 / 08 / Textile-Exchange_Preferred-Fiber-and-Materials-Market-Report_2021.pdf> , p.9 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a method for recovering polyester components from polyester-containing materials, and a method for producing recycled polyester using the recovered polyester. [Means for solving the problem]

[0008] The method for recovering a polyester component of the present invention includes the following inventions. (1) A method for recovering a polyester component, comprising the steps of treating a polyester-containing material in dimethyl terephthalate (DMT) at 140°C or higher and 155°C or lower, and recovering the polyester component. (2) A method for recovering a polyester component according to (1) above, wherein DMT is recovered from the process in addition to the polyester component. (3) The method for recovering a polyester component according to (1) or (2) above, wherein the polyester comprises a polyester having alkylenebenzene dicarboxylate as a main repeating unit. (4) The method for recovering a polyester component according to any one of (1) to (3) above, wherein the polyester-containing material contains polyester fibers. (5) A method for recovering polyester components according to (4) above, wherein the polyester-containing material contains, in addition to polyester fibers, one or more of cellulose-based natural fibers, cellulose-based regenerated fibers, cellulose-based semi-synthetic fibers, protein fibers, nylon fibers, polyurethane fibers, acrylic fibers, and modacrylic fibers. (6) The method for recovering a polyester component according to any one of (1) to (5) above, wherein the DMT is recycled DMT. (7) A method for producing recycled polyester, which comprises repolymerizing the polyester component obtained by the recovery method according to any one of (1) to (6) above. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for recovering polyester components from polyester-containing materials and a method for producing recycled polyester using the recovered polyester. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an IR chart of the recycled polyester polymer recovered in Example 1. [Figure 2] 1 is an IR chart of the polyester component recovered in Example 2 after the second treatment. [Figure 3] 1 is an IR chart of the polyester component recovered in Example 3 after the second treatment. [Figure 4] 1 is an IR chart of the recycled polyester polymer recovered in Example 4. [Figure 5]1 is an IR chart of the polyester component recovered in Example 5 after the second treatment. [Figure 6] 1 is an IR chart of the polyester component recovered in Example 6 after the second treatment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below. The method for recovering a polyester component of the present invention essentially includes a step of treating a polyester-containing material in dimethyl terephthalate (DMT) at 140° C. or higher and 155° C. or lower to recover the polyester component.

[0012] [Polyester content] The polyester-containing material, which is the starting material of the present invention, contains a polyester polymer in various forms such as fibers, films, and molded articles, and also includes polyester-containing materials that are subject to recycling as industrial waste, etc. These polyester-containing materials include not only polyesters contained in various wastes such as used clothing and plastic products, but also various forms such as scraps generated in manufacturing processes and packaging containers such as PET bottles.

[0013] [polyester] Here, polyester refers to a polymer composed of a polycondensate synthesized by dehydration condensation of a polycarboxylic acid and a polyalcohol to form an ester bond. Such polyesters are polymers having ester bonds and are generally classified into aliphatic polyesters, semi-aromatic polyesters, and wholly aromatic polyesters.

[0014] The polycarboxylic acid constituting the polyester is preferably a dicarboxylic acid or an ester-forming derivative thereof, and more preferably an aromatic dicarboxylic acid such as terephthalic acid or 2,6-naphthalenedicarboxylic acid.

[0015] The polyalcohol, the other component constituting the polyester, is preferably a diol or an ester-forming derivative thereof. The diol is preferably an aliphatic glycol having 2 to 20 carbon atoms. Examples of the aliphatic glycol include ethylene glycol (hereinafter sometimes abbreviated as EG), 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. The aliphatic glycol may be an alicyclic glycol having 3 to 30 carbon atoms, and a specific example is 1,4-cyclohexanedimethanol.

[0016] In the present invention, a material containing a polyester in which such a polycarboxylic acid and a polyalcohol are combined is used as one of the starting materials. Among these, it is preferable that the polyester is an aromatic polyester, more specifically, a polyester having alkylenebenzene dicarboxylate as the main repeating unit, and furthermore, it is preferable that the polyester is a polyester having polyalkylene terephthalate, particularly polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, or the like as the main component.

[0017] Furthermore, when the aromatic polyester is polyalkylene terephthalate (terephthalic acid: para position), it is also preferable that the polymer contains this as the main polymer component and other minor polymer components. Here, the main polyester component means 60 mass % or more of the weight of the polymer. The minor polymer component is preferably, for example, polyalkylene isophthalate (isophthalic acid: meta position).

[0018] In particular, when the polyester is a polyalkylene terephthalate, which is an aromatic polyester, polyesters obtained by copolymerizing terephthalic acid as a dicarboxylic acid component with isophthalic acid or a sulfoisophthalic acid cation salt such as 5-sodium sulfoisophthalic acid as a copolymerization component have been used as a preferred embodiment because of their excellent dyeability and resulting physical properties, particularly when used as fibers. Additionally, depending on the purpose of imparting functionality, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, hydroxycarboxylic acids, organic phosphate esters, ethers (diethylene glycol, polyethylene glycol, polytetramethylene glycol, etc.), etc. may also be copolymerized.

[0019] [Dimethyl terephthalate (DMT)] The dimethyl terephthalate (hereinafter sometimes referred to as "DMT") used in the present invention is preferably regenerated DMT obtained by recycling polyester fabric or polyester fiber as a raw material. By using such regenerated DMT, it is possible to maintain a high recycling rate in the final polyester.

[0020] More specifically, the DMT used in the present invention is preferably DMT obtained by adding methanol to bishydroxyethyl terephthalate (hereinafter sometimes referred to as "BHET"), which is obtained by adding ethylene glycol to polyester fabric or polyester fiber obtained during processing or as a recycled product, and then depolymerizing the resulting product.

[0021] Furthermore, it is preferable that the DMT used in the recovery method of the present invention is subsequently recovered in addition to the polyester component, in the same manner as the polyester component. Regarding the recycled DMT obtained from outside the system and the DMT recovered in addition to the polyester component in the system, the DMT itself is preferably recovered by evaporation, preferably under reduced pressure, or by solvent washing.

[0022] [Method for recovering polyester component (1); First treatment] In the present invention, the polyester component is recovered using the polyester-containing material as a starting material by treating the polyester-containing material in dimethyl terephthalate (DMT) at 140°C or higher and 155°C or lower, and then recovering the polyester component.

[0023] Treatment in DMT at such a temperature swells the polyester polymer, allowing for effective removal of foreign matter such as disperse dyes, as well as processing agents added to the surface of textile products and acetate fibers blended with polyester fibers.

[0024] The treatment temperature during this first treatment is more preferably in the range of 148°C to 152°C. The treatment time is preferably 5 minutes to 2 hours, more preferably 10 minutes to 1 hour, and particularly preferably 20 minutes to 40 minutes. Furthermore, the amount of DMT used during the first treatment is preferably 3 to 1000 times the weight of the polyester-containing material to be treated. A liquid volume of 5 to 500 times, and particularly 8 to 50 times, is more preferred. During treatment with DMT, in addition to immersion and standing, the solution is preferably agitated by liquid circulation or by a rotating blade or the like.

[0025] Then, after the immersion in DMT, it is preferable to repeat the immersion and drainage multiple times. As the drainage treatment, various methods can be used, such as squeezing, centrifugal separation, and Soxhlet extraction. It is also effective to repeat the immersion and drainage multiple times, and it is more preferable to repeat the immersion and drainage treatment five or more times, and particularly 6 to 10 times.

[0026] [Method for recovering polyester component (2); Second treatment] When the polyester-containing material contains only a small amount of foreign matter, such as dyes, the polyester component can be recovered by the first treatment alone. However, when the polyester-containing material contains a large amount of other fibers, it is preferable to subsequently carry out the second treatment described below. The second treatment is a method for recovering polyester components in which polyester-containing materials are dissolved in DMT at a temperature higher than that in the first treatment.

[0027] Dissolving polyester-containing materials in such high-temperature DMT can effectively remove foreign matter that is insoluble in DMT. Unlike polyester polymers and polyester fibers, other fiber components, such as cotton, rayon, wool, silk, acrylic, and nylon, as well as metal parts such as zippers contained in clothing, do not dissolve even in such high-temperature DMT solutions.

[0028] The treatment temperature for the second treatment is preferably in the range of 160°C to 280°C, more preferably 180°C to 250°C, and particularly preferably 185°C to 220°C. The treatment time is preferably 5 minutes to 2 hours, more preferably 10 minutes to 1 hour, and particularly preferably 20 to 40 minutes. The amount of DMT used during treatment is preferably 0.3 to 10 times the weight of the textile product to be treated, more preferably 0.5 to 5 times, and particularly preferably 0.5 to 3 times. During this second treatment with DMT, in addition to immersion and standing, it is also preferable to agitate the solution using a liquid circulation system or a rotating blade.

[0029] The polyester-containing material after the second treatment was filtered through a metal mesh to remove undissolved materials such as zippers, buttons, and other fiber components such as cotton. The DMT solution after this filtration contained a large amount of polyester components.

[0030] [Polyester component recovery method (3); 3rd treatment (depolymerization)] Furthermore, the polyester component obtained by the above-mentioned method for recovering a polyester component (first treatment, or first treatment and second treatment) is preferably further subjected to depolymerization as a third treatment. That is, it is preferable to further depolymerize the polyester component obtained by the above-mentioned polyester component recovery into a bis(hydroxyalkyl) aromatic dicarboxylate in alkylene glycol containing a depolymerization catalyst.

[0031] The treatment conditions for depolymerization are preferably a temperature range of 180°C to 250°C for 2 to 8 hours, and more preferably a temperature range of 190°C to 240°C for 3 to 6 hours while stirring.

[0032] If the second treatment is performed, the solution can be dried to leave only the polyester component before depolymerization, but it is more efficient to subject the resulting polyester component and the solvent, DMT, to a transesterification reaction in alkylene glycol containing a depolymerization catalyst to convert them into aromatic bis(hydroxyalkyl) dicarboxylate. Although DMT is used as a solvent, it is commonly used as a raw material for polyester and does not adversely affect the quality of the final recycled polyester.

[0033] During this process, DMT reacts with alkylene glycol (hereinafter sometimes referred to as "AG") such as ethylene glycol (hereinafter sometimes referred to as "EG") to form a bis(hydroxyalkyl) aromatic dicarboxylate such as BHET. In this process, alcohols such as methanol (MeOH) are generated, and it is preferable to recover these by refluxing them outside the system.

[0034] [catalyst] The catalyst used in the depolymerization reaction of the third treatment, the depolymerization step, is preferably a catalyst based on a first transition metal. Specific examples include fatty acid salts, carbonates, sulfates, phosphates, oxides, hydroxides, halides, and alcoholates of first transition metals. Manganese and zinc are preferably used as the first transition metal.

[0035] As the catalyst, manganese oxide, manganese acetate, zinc oxide, or zinc acetate is preferably used, with manganese acetate being particularly preferred. One or more types of catalyst may be used in combination. In particular, when manganese acetate is used as the catalyst, it has high solubility in alkylene glycol, making it possible to reduce the amount of catalyst remaining in the subsequent process. The catalyst is preferably dissolved or suspended in alkylene glycol before use.

[0036] Generally, depolymerized polyester products often gradually become discolored due to long-term storage, etc. However, the products obtained by the recovery method and production method of the present invention clearly show little discoloration. In particular, when a manganese-based catalyst is used during depolymerization, a polyester polymer with little discoloration can be obtained.

[0037] The amount of catalyst used during depolymerization is preferably 20 to 500 mmol%, more preferably 30 to 300 mmol%, and particularly preferably 50 to 150 mmol% relative to the polyester. Here, "mol%" refers to the ratio of the number of catalyst molecules to the constituent units of the polyester. "mmol%" is 1 / 1000 of that. If the amount of catalyst used is less than the above range, the catalytic activity will be insufficient, and if it is more, the effect of inhibiting discoloration will decrease, which is not preferable. If a manganese-based catalyst is used as the catalyst, depolymerization can be carried out with a small amount used.

[0038] [Alkylene glycol] The alkylene glycol (AG) used in the depolymerization reaction in the depolymerization step is the same as the polyalcohol forming the skeletal structure of the polyester used in the polyester-containing material, or the same as the polyalcohol constituting the polyester obtained by repolymerizing the intermediate bis(hydroxyalkyl) aromatic dicarboxylate.

[0039] Examples of alkylene glycols that are the same as the polyalcohols that form the backbone structure of the polyester include ethylene glycol (EG) when the polyester is polyethylene terephthalate (PET), 1,3-propanediol (trimethylene glycol, C3G) when the polyester is polytrimethylene terephthalate, and 1,4-butanediol (C4G) when the polyester is polybutylene terephthalate. The alkylene glycol may be a mixture of the alkylene glycols.

[0040] The amount of alkylene glycol is preferably 2 to 20 times, and more preferably 3 to 10 times, the weight of the recovered polyester. By using a large amount of alkylene glycol during depolymerization in this way, and removing the solids and insolubles remaining inside the organic matter containing the bis(hydroxyalkyl) aromatic dicarboxylate by filtration, followed by further crystallization and solid-liquid separation, the amount of the depolymerization catalyst and other foreign matter mixed in can be reduced.

[0041] [Refining process] The method for recovering a polyester component of the present invention preferably includes a purification step of further purifying the obtained polyester component after the above steps. The purification step includes crystallization or adsorption treatment, and it is more preferable to perform both. In particular, it is preferable to purify the depolymerization reaction product.

[0042] [Crystallization] When the recovered polyester component is a depolymerization reaction product, the purification step is carried out by lowering the temperature in alkylene glycol to crystallize it. The temperature lowering conditions for crystallization are preferably from a temperature of 60°C or higher to 25°C or lower, and more preferably to 15°C or lower.

[0043] After the crystallization, solid-liquid separation is preferably carried out. The alkylene glycol content in the cake after the solid-liquid separation is preferably 100% by weight or less, more preferably 55% by weight or less, still more preferably 1 to 30% by weight, and particularly preferably 5 to 25% by weight.

[0044] The recovered product obtained after solid-liquid separation is preferably washed with water or alkylene glycol. By carrying out such treatment, the depolymerization catalyst dissolved in the alkylene glycol and other substances that cause coloration can be washed away, and a more highly purified bis(hydroxyalkyl) aromatic dicarboxylate can be obtained.

[0045] The solution used for washing is preferably one with low viscosity, and from this viewpoint, water is preferably used. The amount of washing liquid is preferably 1 to 100 times, more preferably 1.5 to 10 times the weight of the cake. The liquid temperature during washing is 0 to 40°C. If the liquid temperature is higher than this, the cake itself will be more likely to dissolve, resulting in a lower yield, which is not preferred.

[0046] After washing, the product is dried in a vacuum dryer or the like to obtain the aromatic dicarboxylic acid bis(hydroxyalkyl). When the alkylene glycol used in the production method of the present invention is the same as the diol component of the polyester after repolymerization, it is also preferable to repolymerize it without drying.

[0047] [Adsorption treatment] It is also preferred to further subject the obtained polyester component to a treatment for adsorbing foreign matter using an adsorbent such as activated carbon. Other adsorbents include those made of styrene or acrylic cross-linked copolymers, and more preferably, synthetic adsorbents made of styrene or acrylic cross-linked copolymers having a macroporous structure without functional groups.

[0048] This adsorption treatment is a process in which the polyester component is brought into contact with an adsorbent, and organic substances derived from, for example, decomposition products of fibers and resins other than polyester contained in the aromatic dicarboxylate bis(hydroxyalkyl) composition, as well as additives such as dyes and pigments, are adsorbed onto the adsorbent, thereby obtaining a more purified polyester component. This adsorption process can be carried out by dissolving a polyester component such as an aromatic dicarboxylate bis(hydroxyalkyl) composition in water or an organic solvent to form an aqueous solution or solution, and then adding an adsorbent thereto, thereby bringing the two into contact in water or an organic solvent.

[0049] [Polyester component: bis(hydroxyalkyl) benzenedicarboxylate] The polyester component in the original polyester content can be recovered as a bis(hydroxyalkyl) aromatic dicarboxylate as a polyester intermediate by the depolymerization process. This bis(hydroxyalkyl) aromatic dicarboxylate, which is also a polyester component, can be used as an intermediate in the production of recycled polyester polymers.

[0050] The aromatic bis(hydroxyalkyl) dicarboxylates obtained vary depending on the polyester and alkylene glycol used in the depolymerization. When the polyester is a polyester (polyalkylene terephthalate) that primarily uses terephthalic acid as the polycarboxylic acid, bis(hydroxyalkyl) benzenedicarboxylates (hereinafter sometimes referred to as BHATs; bishydroxyalkyl terephthalates) are obtained.

[0051] Specifically, when C3G (1,3-propanediol (trimethylene glycol)) is used as the alkylene glycol for depolymerization, BHPT (bishydroxypropyl terephthalate) is obtained. When C4G (1,4-butanediol) is used as the alkylene glycol for depolymerization, BHBT (bishydroxybutyl terephthalate) is obtained. When ethylene glycol is used as the alkylene glycol for depolymerization, BHET (bishydroxyethyl terephthalate) is obtained.

[0052] [Production of recycled polymers (repolymerization)] The polyester component obtained by the recovery method of the present invention can be further repolymerized to produce recycled polyester. In particular, when the obtained polyester component is a bis(hydroxyalkyl) aromatic dicarboxylate, a recycled polyester polymer can be more efficiently produced by polycondensation reaction. The recycled polyester polymer obtained by the present invention has a low content of foreign matter, is less colored, and has excellent hue.

[0053] As the catalyst for repolymerization to obtain the recycled polyester polymer, known catalysts such as antimony, germanium or titanium catalysts can be used, and specific examples thereof include diantimony trioxide.

[0054] It is preferable to carry out the polycondensation reaction while discharging alkylene glycol and the like generated in the repolymerization reaction outside the reactor. The amount of catalyst used is in the range of 10 to 1000 ppm based on the weight of the aromatic dicarboxylic acid bis(hydroxyalkyl). After polycondensation, it is preferable to add a conventionally known phosphorus-based stabilizer such as orthophosphoric acid or phosphorous acid. The amount of the phosphorus-based stabilizer used is preferably in the range of 1 to 100 ppm based on the weight of the aromatic bis(hydroxyalkyl) dicarboxylate.

[0055] [Physical properties of recycled polymers] The recycled polyester polymer obtained in this manner has little yellowing, which is considered to be inferior in quality. The polyester component recovery method of the present invention is less likely to produce residual foreign matter or by-products derived from materials other than polyester that cause discoloration. This is thought to be because the catalyst is easily dissociated from the bis(hydroxyalkyl) aromatic dicarboxylate even in subsequent processes such as crystallization, making it less likely to remain as an impurity. This effect is particularly pronounced when depolymerization is performed using a low concentration of a manganese-based catalyst.

[0056] In the recycled polyester polymer obtained by the present invention, other components contained in the original polyester content have been removed, and even if the original polyester content contained dyed polyester fibers, the dyes have also been removed in the recovery process.

[0057] The resulting recycled polyester polymer preferably exhibits the following properties: The resulting recycled polyester polymer meets the L certification of the International Commission on Illumination (CIE). * , a * , b * As the hue in the color space colorimeter, b * The value is preferably not more than 8. L* is preferably not less than 75, and more preferably from 80 to 100. The resulting recycled polyester polymer has an intrinsic viscosity (IV) of the polymer of preferably 0.30 to 1.50 dL / g, more preferably 0.40 to 1.30 dL / g, and particularly preferably 0.50 to 1.20 dL / g. [Example]

[0058] The present invention will be described in more detail below with reference to examples, in which the values ​​were determined by the following methods.

[0059] (1)Measurement method 1) Intrinsic viscosity (IV) The recovered polyester was dissolved in 10 mL of a mixed solvent of tetrachloroethane and phenol (volume ratio 1 / 1), and the intrinsic viscosity (dL / g) at 35°C was measured.

[0060] 2) IR measurement (infrared spectroscopy) Infrared spectroscopy was performed on the target sample using the "IRSprint" manufactured by Shimadzu Corporation. The measurement conditions were wavelength range: 400-4000 cm -1 , resolution is 4cm -1 The number of integrations was 20. The waveform obtained was 1715 cm, which is a characteristic of PET. -1 : Ester C=O stretching, 1505 cm -1Benzene ring stretching, 1240 cm -1 Aromatic ester CO stretching, 1095 cm -1 : Ester CO stretch, 725cm -1 : The peak of the CH out-of-plane bending angle of the benzene ring was confirmed.

[0061] 3) Polymer color The dissolved recovered material (5 g) was pressed between two metal plates to form a plate, which was then heated at 140°C for 2 hours to crystallize the sample and prepare a measurement sample. The measurement sample was measured for hue L according to JIS Z8781-4:2013 using a measuring device ("SE-7700" manufactured by Nippon Denshoku Industries Co., Ltd.). * , a * , b * The values ​​were measured.

[0062] [Example 1] (Textile products) Recycled polyester clothing (used clothing) was cut into approximately 3 cm square pieces using a shredder, and 200 g of these pieces were used as textile product samples for testing. However, the polyester clothing included only used clothing with a tag indicating that it was 100% polyester.

[0063] (Polyester Component Recovery Method (1) First Treatment) The treatment solution was 10 times the amount of DMT as the textile product, and placed in a 5 L separable flask. The internal temperature was set to 150°C using a mantle heater, and the mixture was stirred for 30 minutes. At this point, the dye in the fabric had been decolorized by the liquid components. The mixture was then filtered through a metal mesh with a mesh size of 200 μm to obtain a decolorized fabric on the mesh. However, since the recovered fabric still had some coloring, the above process was repeated five times, and the white fabric (textile product) was recovered as a polyester component.

[0064] (Polyester Component Recovery Method (2) Second Treatment) 402 g of the recovered textile product was added to a 5 L separable flask with one volume of DMT as a treatment liquid, and the flask was heated to 190°C using a mantle heater and stirred for 30 minutes. At this point, the components believed to be PET from the fabric had dissolved in the liquid, but some undissolved material was still present. The mixture was then filtered using a metal mesh with 200 μm openings, and undissolved materials such as zippers, buttons, and fiber components thought to be cotton were removed, resulting in the recovery of polyester components with fewer impurities.

[0065] (Polyester Component Recovery Method (3); Third Treatment (Depolymerization)) After removing the foreign matter, five times the amount of ethylene glycol and 0.125 wt% manganese acetate were added to the liquid component, and the internal temperature was set to 220°C and stirred for four hours. During the process, DMT reacted with EG to form BHET, and MeOH was generated, so this was refluxed outside the system and recovered. The liquid component was then gradually cooled to 70°C, and the temperature was then lowered to 15°C while stirring and cooling. Thereafter, stirring was carried out for 60 minutes while the internal temperature was kept at 15°C, and the internal temperature was lowered to precipitate BHET crystals, thereby obtaining a BHET / EG slurry.

[0066] The BHET / EG slurry was pressed using a filter press manufactured by Nippon Filter Equipment Co., Ltd., and solid-liquid separation of BHET and EG was carried out. The separated BHET contained 35% by mass of EG based on the weight of the cake recovered after the filter press. The cake after EG separation was placed in 25°C pure water in an amount twice the mass of the cake and stirred, and then washed with water using a Nutsche filter.

[0067] After the solid-liquid separation was completed, the BHET was dissolved in 20 times its mass of hot water (90°C), and then 0.25 times its mass of activated carbon was added and stirred for 1 hour. Nutsche filtration was then performed, and the aqueous solution from which the activated carbon had been removed was cooled to precipitate BHET. Nutsche filtration was then performed again, and BHET was recovered as a polyester component. The recovered BHET was dried in a vacuum dryer at 50°C for 8 hours to obtain dried BHET. The obtained BHET was white and free of any foreign matter.

[0068] (repolymerization of polyester) Then, 254 parts by mass of the obtained dried BHET was placed in a reaction vessel under normal pressure and nitrogen atmosphere, together with 0.007 parts by mass of a phosphorus-based stabilizer and 0.07 parts by mass of diantimony trioxide as a repolymerization catalyst. The temperature inside the reactor was then raised to 285°C, and the pressure was gradually reduced under the following conditions: normal pressure for 10 minutes, 4 kPa for 10 minutes, and 0.4 kPa for 40 minutes. A polycondensation reaction was carried out while distilling off ethylene glycol and other substances generated during the reaction outside the reactor, to obtain a recycled polyester polymer.

[0069] The recycled polyester polymer was then continuously extruded from the discharge port in the form of strands, which were then cooled and cut into pellets of approximately 3 mm in size. The pellets had a high whiteness and were free of any visible foreign matter. Hue L after first processing * , a * , b * The IV value and color L of the sample after repolymerization are shown in Table 1. * , a * , b * The values ​​are shown in Table 2, and the IR chart of the recycled polymer is shown in Figure 1.

[0070] [Table 1]

[0071] [Table 2]

[0072] [Example 2] The textile product, the first treatment, and the second treatment were carried out in the same manner as in Example 1.

[0073] (Polyester component recovery process) Thereafter, treatment with benzyl alcohol was carried out instead of the catalyst-containing ethylene glycol used in Example 1. That is, after the foreign matter was removed, a five-fold amount of benzyl alcohol at 160°C was added to the liquid component mainly composed of DMT, and the internal temperature was set to 160°C for 30 minutes, followed by filtration, and the polyester was recovered as a solid component without depolymerization as a polyester component recovery step.

[0074] The collected solid matter was washed, dried, and subjected to IR analysis, which confirmed that the waveform was characteristic of PET. * , a * , b * The IV value and color L of the sample after the second treatment are shown in Table 1. * , a * , b * The values ​​are shown in Table 2, and the IR chart of the sample after the second treatment is shown in FIG.

[0075] [Example 3] The textile product, the first treatment, and the second treatment were carried out in the same manner as in Example 1.

[0076] (Polyester component recovery process) After removing the foreign matter, the liquid component, mainly consisting of DMT, was heated to a set temperature of 200°C under vacuum (8 kPa), the DMT component was evaporated and removed from the system, and the polyester was recovered as a solid component.

[0077] The collected solid matter was washed, dried, and subjected to IR analysis, which confirmed that the waveform was characteristic of PET. * , a * , b * The IV value and color L of the sample after the second treatment are shown in Table 1. * , a * , b * The values ​​are shown in Table 2, and the IR chart of the sample after the second treatment is shown in FIG.

[0078] [Example 4] (Textile products) 100 g of polyester fabric dyed with a disperse dye and 100 g of uncolored multi-fiber woven fabric were prepared. These textile products were cut with scissors into approximately 3 cm squares, totaling 200 g, and used as textile product samples for testing.

[0079] Here, the multi-fiber mixed woven fabric is defined in (JISL0803:2011 Mixed Weave No. 1), and has a basis weight of 200 g / m, with cotton yarn, nylon filament yarn, acetate filament yarn, worsted (wool) yarn, rayon filament yarn (bright), acrylic spun yarn, silk yarn, and polyester spun yarn each constituting a certain area of ​​warp yarn, and polyester spun yarn as weft yarn. 2 It is a woven fabric.

[0080] (Polyester Component Recovery Method (1) First Treatment) As in Example 1, the treatment with DMT at 150°C was repeated five times. As a result, the colored polyester fabric was bleached, and the acetate fiber warp yarns in the multi-fiber mixed woven fabric were replaced by polyester fiber weft yarns, and the acetate fiber dissolved in the DMT solution.

[0081] (Polyester Component Recovery Method (2) Second Treatment) As a preliminary experiment, multi-fiber mixed woven fabrics were treated with DMT at 190°C in the same manner as in Example 1. Only fabrics with polyester and acetate fiber wefts dissolved in DMT, while fabrics with cotton, rayon, wool, silk, acrylic, or nylon wefts dissolved only the polyester fiber warp, and the wefts remained insoluble.

[0082] The textile product after the first treatment was treated with DMT at 190°C in the same manner as in Example 1, and then filtered using a metal mesh with a mesh size of 200 μm to remove insoluble cotton, rayon, wool, silk, acrylic, and nylon fiber components, thereby obtaining a DMT solution in which polyester fibers were dissolved.

[0083] (Polyester Component Recovery Method (3); Third Treatment (Depolymerization)) Thereafter, the DMT solution in which the polyester fibers were mainly dissolved was treated in the same manner as in Example 1 to recover BHET, which is a polyester component.

[0084] (repolymerization of polyester) Thereafter, the obtained dried BHET was used to repolymerize polyester in the same manner as in Example 1 to obtain a recycled polyester polymer. The whiteness was high and no foreign matter was found to be present.

[0085] Hue L after first processing * , a * , b * The IV value and color L of the sample after repolymerization are shown in Table 1. * , a * , b * The values ​​are shown in Table 2, and the IR chart of the recycled polymer is shown in Figure 4.

[0086] [Example 5] DMT was prepared by adding ethylene glycol to polyester fabric, depolymerizing it, and then adding methanol to the resulting BHET. The crude dimethyl terephthalate was further purified by distillation at a pressure of 6.7 kPa and a column bottom temperature of 180-200°C.

[0087] Using this DMT, the same first and second treatments as in Example 1 were carried out. Hue L after first processing * , a * , b * The values, the weight of the recovered material and the weight of the removed foreign matter after the second treatment are shown in Table 1, and the IR chart of the sample after the second treatment is shown in Figure 5.

[0088] [Example 6] The same experiment as in Example 3 was carried out except that the DMT obtained in Example 5 was used. The recovered solid component was confirmed to be PET by IR. Color after the first treatment: L * , a * , b * The IV value and color L of the sample after the second treatment are shown in Table 1.* , a * , b * The values ​​are shown in Table 2, and the IR chart of the sample after the second treatment is shown in FIG. [Industrial Applicability]

[0089] The method for recovering polyester components from composite materials containing polyester fibers and various other fibers of the present invention involves depolymerizing the polyester, separating and adsorbing and removing components other than polyester, and then repolymerizing the resulting recycled polyester polymer. Because the recycled polyester polymer has the same color and physical properties as virgin polyester polymer obtained by polymerization of petroleum-derived raw materials, it can be used as a raw material for textile products. As a result, this method promotes the reuse of discarded textile products that would otherwise not be recycled into fibers, thereby contributing to reducing environmental impact.

Claims

1. A method for recovering a polyester component, comprising the steps of treating a polyester-containing material in dimethyl terephthalate (DMT) at 140°C or higher and 155°C or lower, and recovering the polyester component.

2. 2. The method for recovering a polyester component according to claim 1, wherein DMT is recovered from the process in addition to the polyester component.

3. 2. The method for recovering a polyester component according to claim 1, wherein the polyester comprises a polyester having alkylenebenzene dicarboxylate as a main repeating unit.

4. 2. The method for recovering a polyester component according to claim 1, wherein the polyester-containing material contains polyester fibers.

5. 5. The method for recovering polyester components according to claim 4, wherein the polyester-containing material contains, in addition to polyester fibers, one or more of cellulose-based natural fibers, cellulose-based regenerated fibers, cellulose-based semi-synthetic fibers, protein fibers, nylon fibers, polyurethane fibers, acrylic fibers, and modacrylic fibers.

6. 2. The method for recovering a polyester component according to claim 1, wherein the DMT is recycled DMT.

7. A method for producing recycled polyester, which comprises reusing the polyester component obtained by the recovery method according to any one of claims 1 to 6.

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