Method for recovering polyester component and method for producing recycled polyester

Abstract

To provide a method for recovering a polyester component from a composite material fiber product including polyester fibers, and a method for producing recycled polyester using the recovered polyester component.SOLUTION: A method for recovering a polyester component is provided, the method sequentially performing, on a composite material fiber product containing polyester fibers, at least two selected from: (a) a reducing solvent contact step; (b) an aprotic polar solvent contact step; (c) a zinc chloride aqueous solution contact step; (d) a high-temperature aromatic alcohol solution contact step, (e) a high-temperature alkylene glycol solvent contact step; and (f) a high-temperature dimethyl terephthalate solvent contact step. The method further includes a method for producing recycled polyester by repolymerizing the obtained polyester component.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for recovering polyester components from products containing various 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 Among these fibers, natural fibers such as cotton and silk have gradually been replaced by synthetic fibers, and among these synthetic fibers, the production of polyester fibers has been increasing rapidly in recent years.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. For example, in recent years, acrylic fibers or polyurethane fibers are often used together with polyester fibers as moisture absorbing and heat generating materials for winter clothing and bedding.

[0004] 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.

[0005] 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]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-88096 [Non-patent literature]

[0007] [Non-Patent Document 1] “Preferred Fiber & Materials Market Report 2021”, 2021, Textile Exchange, [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]

[0008] An object of the present invention is to provide a method for recovering polyester components from composite fiber products containing polyester fibers, and a method for producing recycled polyester using the recovered polyester components. [Means for solving the problem]

[0009] The method for recovering a polyester component of the present invention includes the following inventions. (1) A method for recovering polyester components, comprising subjecting a composite fiber product containing polyester fibers to at least two of the following treatments (a) to (f) in the following order: (a) a solvent contact step in which the textile product is brought into contact with an aqueous solution containing a reducing agent at a temperature of 50 to 100°C; (b) a solvent contacting step in which the textile product is brought into contact with an aprotic polar solvent at a temperature of 30 to 160°C; (c) a solvent contact step in which the textile product is brought into contact with an aqueous zinc chloride solution at a temperature of 30 to 100°C. (d) a solvent contact step in which the textile product is brought into contact with a solution of an aromatic alcohol or its derivative in a temperature range of 70 to 170°C. (e) a solvent contact step in which the textile product is brought into contact with alkylene glycol in a temperature range of 140 to 200°C. (f) a solvent contacting step of contacting the textile product with dimethyl terephthalate (DMT) at a temperature in the range of 150 to 300°C. (2) The method for recovering polyester components according to (1) above, wherein the composite fiber product contains, in addition to polyester fiber, two or more types of fiber selected from the group consisting of cellulose-based natural fiber, cellulose-based regenerated fiber, cellulose-based semi-synthetic fiber, protein fiber, silk, nylon fiber, polyurethane elastic fiber, acrylic fiber (PAN), and modacrylic fiber. (3) The method for recovering a polyester component according to (1) or (2) above, wherein the polyester fiber is made of a polyester having alkylenebenzene dicarboxylate as the main repeating unit. (4) A method for producing recycled polyester, which comprises repolymerizing the polyester component obtained by the recovery method according to any one of (1) to (3) above. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for recovering a polyester component from a composite fiber product containing polyester fiber, and a method for producing recycled polyester using the recovered polyester component. [Brief explanation of the drawings]

[0011] [Figure 1] 1 shows an IR waveform of the solid content recovered in Example 1. [Figure 2] 1 shows an IR waveform of the solid content recovered in Example 2. [Figure 3] 1 shows an IR waveform of the solid content recovered in Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below. The method for recovering a polyester component of the present invention requires that a composite material fiber product containing polyester fibers be subjected to at least two of the following treatment steps (a) to (f) in the following order: (a) a solvent contact step in which the textile product is brought into contact with an aqueous solution containing a reducing agent at a temperature of 50 to 100°C; (b) a solvent contacting step in which the textile product is brought into contact with an aprotic polar solvent at a temperature of 30 to 160°C; (c) a solvent contact step in which the textile product is brought into contact with an aqueous zinc chloride solution at a temperature of 30 to 100°C. (d) a solvent contact step in which the textile product is brought into contact with a solution of an aromatic alcohol or its derivative in a temperature range of 70 to 170°C. (e) a solvent contact step in which the textile product is brought into contact with alkylene glycol in a temperature range of 140 to 200°C. (f) a solvent contacting step of contacting the textile product with dimethyl terephthalate (DMT) at a temperature in the range of 150 to 300°C.

[0013] [Composite fiber products] The composite fiber product used in the present invention contains polyester fibers. Furthermore, the composite fiber product used in the present invention preferably contains, in addition to polyester fibers, two or more fibers selected from the group consisting of cellulose-based natural fibers, cellulose-based regenerated fibers, cellulose-based semi-synthetic fibers, protein fibers, silk, nylon fibers, polyurethane elastic fibers, acrylic fibers (PAN), and modacrylic fibers, and the method for recovering polyester components of the present invention is effective. Furthermore, the composite fiber product is useful when it is a fiber product using a moisture-absorbing and heat-generating fiber containing polyester fibers and acrylic fibers (PAN) or modacrylic fibers. More specifically, the method is particularly effective for fiber products using stretchable moisture-absorbing and heat-generating fibers made of polyester (PET), rayon, acrylic, or polyurethane.

[0014] [Polyester fiber] Here, polyester fiber refers to a fiber made of a polycondensate synthesized by dehydration condensation of a polycarboxylic acid and a polyalcohol to form an ester bond. The polyester forming the fiber is a polymer having an ester bond and is generally classified into aliphatic polyester, semi-aromatic polyester, and wholly aromatic polyester.

[0015] 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.

[0016] 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.

[0017] In the present invention, a polyester obtained by combining such a polycarboxylic acid and a polyalcohol is used as one of the starting materials for forming a composite fiber product. 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.

[0018] 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).

[0019] In particular, when the polyester is a polyalkylene terephthalate, which is an aromatic polyester, a polyester 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 is one preferred embodiment in terms of high dyeability and the resulting physical properties. 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.

[0020] [Other fibers] The textile products used in the present invention are best suited to those containing, in addition to the above-mentioned polyester fibers, cellulose-based natural fibers, cellulose-based regenerated fibers, cellulose-based semi-synthetic fibers, protein fibers, silk, nylon fibers, polyurethane elastic fibers, acrylic fibers (PAN), modacrylic fibers, etc. Furthermore, it is preferable that the textile products contain two or more types of fibers selected from the above groups.

[0021] Furthermore, for example, cellulosic natural fibers are fibers obtained primarily from plants, particularly cotton, linen, and jute. Cellulosic regenerated fibers include rayon and lyocell, which are produced by chemically processing wood pulp or cotton linters. Cellulosic semi-synthetic fibers include acetate fibers such as diacetate and triacetate, which are fibers produced from cellulose and then chemically modified. Preferred nylon fibers include nylon 6 synthesized from caprolactam and nylon 66 synthesized from adipic acid and hexamethylenediamine. Protein fibers are preferably fibers having cystine bonds (SS), so-called animal hair fibers made from mammalian body hair, and more specifically, animal hair fibers such as wool, cashmere, mohair, alpaca, camel, and angora are preferred.

[0022] Polyurethane elastic fibers are polyurethane fibers with urethane bonds (-NHCOO-) in the molecular chain, composed of a flexible soft segment with a low melting point and a hard segment with a high melting point, and have excellent elasticity. Examples of polyurethane elastic fibers include polyether-based polyurethane fibers and polyester-based polyurethane fibers with different soft segments. An example of polyether-based polyurethane fibers is "Leica" (registered trademark) manufactured by Asahi Kasei Fibers Corporation. Acrylic fibers are preferably fibers made from a polymer or copolymer of 85 to 100% by weight of acrylonitrile and 0 to 15% by weight or less of an unsaturated vinyl monomer. Modacrylic fibers are fibers made from a copolymer of 35 to 85% by weight of acrylonitrile and 15 to 65% by weight of an unsaturated vinyl monomer.

[0023] [Recovery of polyester components (1)] In the present invention, a composite fiber product containing the above-described polyester fiber is used as a starting material to recover the polyester component. That is, the composite fiber product is subjected to at least two of the following treatments (a) to (f) in order to recover the polyester component. (a) a solvent contact step in which the textile product is brought into contact with an aqueous solution containing a reducing agent at a temperature of 50 to 100°C; (b) a solvent contacting step in which the textile product is brought into contact with an aprotic polar solvent at a temperature of 30 to 160°C; (c) a solvent contact step in which the textile product is brought into contact with an aqueous zinc chloride solution at a temperature of 30 to 100°C. (d) a solvent contact step in which the textile product is brought into contact with a solution of an aromatic alcohol or its derivative in a temperature range of 70 to 170°C. (e) a solvent contact step in which the textile product is brought into contact with alkylene glycol in a temperature range of 140 to 200°C. (f) a solvent contacting step of contacting the textile product with dimethyl terephthalate (DMT) at a temperature in the range of 150 to 300°C.

[0024] In the present invention, the order of these treatments is important, and by carrying out the treatments (a) to (f) in this order, it becomes possible to recover the polyester component more effectively and efficiently. Each treatment will be described in detail below.

[0025] [(a) Reduction Treatment] This method involves treating a composite material fiber product containing polyester fiber as described above in an aqueous solution containing a reducing agent at a temperature of 50 to 100°C, and then recovering the polyester component. This method is particularly effective when the composite material fiber product contains protein fibers such as wool.

[0026] Protein fibers such as wool are polymers cross-linked by cystine bonds (SS). Here, by treating them with a high-temperature aqueous solution containing a reducing agent, the cystine bonds are broken, eliminating the hardly soluble parts and separating the protein fibers from the composite fiber product, making it easier to recover the polyester component.

[0027] The reducing agent is not particularly limited, but preferred examples include known reducing agents having a thiol group, such as thioglycolic acid, thioglycolic acid salts (ammonium thioglycolate, monoethanolamine thioglycolate, etc.), cysteamine, cysteamine salts (cysteamine hydrochloride, etc.), cysteine ​​(L-cysteine, DL-cysteine, etc.), cysteine ​​salts (L-cysteine ​​hydrochloride, DL-cysteine ​​hydrochloride, etc.), acetylcysteine ​​(N-acetyl-L-cysteine, etc.), glyceryl thioglycolate, thiolactic acid, thiolactate salts, and butyrolactone thiol. Other known reducing agents, such as sulfites (sodium sulfite, etc.), can also be used. Sodium disulfite, sodium sulfite, sodium thioglycolate, cysteine, etc. are particularly preferred.

[0028] In this step, the reaction is preferably carried out in an aqueous solution at a temperature of 70 to 100°C, more preferably 90 to 100°C. The treatment time is preferably in the range of 0.5 to 10 hours, more preferably 1 to 3 hours. Furthermore, the treatment is preferably carried out while stirring.

[0029] In order to ensure that the reducing agent is thoroughly impregnated into the textile product, it is preferable that the aqueous treatment solution contains a surfactant such as urea or sodium dodecyl sulfate. Thereafter, the material is washed, the water is evaporated in a dryer, and the material is sent to the next step to recover the polyester component.

[0030] This reduction treatment (a) allows protein fibers such as wool to be separated and removed from composite fiber products, thereby significantly reducing reaction inhibition during the depolymerization of polyester into its reaction intermediate, bis(hydroxyalkyl) benzenedicarboxylate. The treated textile product can be filtered through a metal mesh, washed, dried and then sent to the next process.

[0031] [(b) Aprotic polar solvent treatment] This method involves contacting a composite material fiber product containing the above-mentioned polyester fiber with an aprotic polar solvent at a temperature of 90 to 160°C, and then recovering the polyester component. This method is particularly effective when the composite material fiber product also contains acrylic fiber, acetate fiber, etc.

[0032] Examples of aprotic polar solvents used in this step include dimethyl sulfoxide, dimethylacetamide, dimethylformamide, acetone, acetonitrile, and diethyl ether. The boiling point of the aprotic polar solvent and the solubility of the acrylic fiber in the aprotic polar solvent should be high, and from this perspective, dimethyl sulfoxide, dimethylacetamide, and dimethylformamide are preferably used as the aprotic polar solvent, and dimethyl sulfoxide (DMSO) is particularly preferred.

[0033] The amount of the aprotic polar solvent used in the solvent contact step is preferably 3 to 1000 times, more preferably 5 to 500 times, and particularly preferably 8 to 50 times the weight of the textile product to be treated by solvent contact.

[0034] In the solvent contacting step, the textile product is preferably brought into contact with the aprotic polar solvent by immersing the textile product in the aprotic polar solvent. This immersion treatment may be carried out by leaving the textile product stationary in the aprotic polar solvent, or is preferably carried out by immersing the textile product in the aprotic polar solvent and then stirring the resulting mixture with a liquid circulation system or a rotary blade.

[0035] This process is also useful for removing coloring substances such as pigments from the fibers. In this solvent contact treatment process, the aprotic polar solvent is removed from the fibers of the textile product or from the textile product in which the aprotic polar solvent has been absorbed between the fibers or between the fibers and the resin. The removal of the solvent can be performed by squeezing, centrifugal separation, or Soxhlet extraction.

[0036] The solvent contact step and the solvent removal step may be performed once, but are preferably repeated multiple times. That is, it is preferable to alternately repeat the immersion and drainage treatments two or more times. Specifically, it is preferable to alternately repeat the immersion and drainage treatments preferably five or more times, and particularly preferably six to ten times.

[0037] The draining step is carried out so that the weight of the textile product containing the aprotic polar solvent after the removal step is preferably 300% by weight or less, more preferably 150 to 250% by weight, and particularly preferably 180 to 220% by weight, based on 100% by weight of the dry weight of the textile product.

[0038] According to the above-described method, polyester can be recovered from a textile product containing polyester fibers and acrylic or acetate fibers by dissolving the acrylic or acetate fibers, dye components, pigment components, etc. in an aprotic polar solvent and removing the solution.

[0039] This method makes it possible to effectively remove foreign matter from the polyester recovered, such as acrylic fibers, acetate fibers, dyes, and pigments. The treated textile product can be filtered through a metal mesh, washed, dried and then sent to the next process.

[0040] [(c) Zinc chloride treatment] This method involves contacting a composite fiber product containing the above-mentioned polyester fiber with an aqueous zinc chloride solution at a temperature of 30 to 100°C, and then recovering the polyester component. This method is particularly effective when the composite fiber product also contains rayon fiber, acrylic fiber, and silk.

[0041] The concentration of the aqueous zinc chloride solution is preferably 60 to 80%, and the amount of solution is preferably 3 to 50 times, and more preferably 5 to 20 times, the weight of the textile product. The temperature of the treatment solution is preferably in the range of 60 to 95°C, and the treatment time is preferably in the range of 10 to 60 minutes. The treated textile product can be filtered through a metal mesh, washed, dried and then sent to the next process.

[0042] [(d) Aromatic alcohol treatment] This method involves contacting a composite material fiber product containing the above-mentioned polyester fiber with a solution of an aromatic alcohol or its derivative at a temperature in the range of 70 to 170°C, and then recovering the polyester component. This method is particularly effective when the composite material fiber product also contains urethane fiber.

[0043] Examples of aromatic alcohols or derivatives thereof include benzyl alcohol, benzaldehyde, and benzoic acid, and preferably benzyl alcohol (hereinafter sometimes referred to as "BA") is used. The aromatic alcohol or its derivative is used in the form of a heated solution. The aromatic alcohol or its derivative may be used by mixing it with another solvent. The boiling point of each solvent is preferably 100°C or higher, more preferably 150 to 250°C.

[0044] In the recovery method of the present invention, the polyester is treated by contacting it with a solution of such an aromatic alcohol or a derivative thereof at a temperature in the range of 70 to 170° C. Furthermore, the treatment temperature is preferably in the range of from the glass transition temperature of the polyester or higher to the glass transition temperature of the polyester +100° C. More preferably, the treatment temperature is in the range of from +10° C. to +80° C. above the glass transition temperature of the polyester, and particularly preferably in the range of from +15° C. to +60° C. above the glass transition temperature of the polyester.

[0045] The amount of the solution used during treatment is preferably 3 to 1000 times, more preferably 5 to 500 times, and particularly preferably 8 to 50 times the weight of the textile product to be treated. The treatment is carried out by immersing the textile in a solution. This treatment may be carried out by leaving the textile in the solution, but is preferably carried out by agitating the solution in which the textile is immersed using a liquid circulation system or a rotating blade.

[0046] After immersion, the textile product is dehydrated. As a dehydration treatment after immersion, methods such as squeezing, dehydration by centrifugation, and Soxhlet extraction can be applied. It is preferable to repeat the immersion and drainage several times, preferably 5 or more times, and particularly preferably 6 to 10 times.

[0047] The dewatering treatment is carried out under conditions such that the weight of the textile product containing the solution after dewatering is preferably 300% by weight or less, more preferably 150 to 250% by weight, and particularly preferably 180 to 220% by weight, based on the dry weight of the textile product. The treated textile product can be filtered through a metal mesh or the like, washed, dried, and then sent to the next step.

[0048] [(e) Alkylene glycol treatment] This method involves contacting a composite material fiber product containing the above-mentioned polyester fiber with alkylene glycol at a temperature in the range of 140 to 200°C, and then recovering the polyester component. This method is particularly effective when the composite material fiber product also contains nylon fiber.

[0049] The alkylene glycol is particularly preferably ethylene glycol (EG). The treatment temperature is more preferably in the range of 150°C to 180°C, and the amount of liquid is preferably 3 to 50 times, more preferably 5 to 20 times, the weight of the textile product. The treatment time is preferably in the range of 10 to 60 minutes. The treated textile product can be filtered through a metal mesh, washed, dried and then sent to the next process.

[0050] [(f) Dimethyl terephthalate (DMT) treatment] This method involves contacting a composite material fiber product containing the above-mentioned polyester fiber with dimethyl terephthalate (DMT) at a temperature range of 150°C to 300°C, and then recovering the polyester component. This method is particularly effective when the composite material fiber product contains fibers other than polyester.

[0051] By dissolving a composite textile product containing polyester fiber in such high-temperature DMT, foreign substances that are insoluble in DMT can be effectively removed. Unlike polyester fiber, other fiber components such as cotton, rayon, wool, silk, acrylic, and nylon do not dissolve even in such high-temperature DMT solutions.

[0052] The treatment temperature is preferably in the range of 150°C to 280°C, and more preferably 250°C or lower, particularly 220°C or lower. 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, and more preferably 0.5 times or more. During this treatment, in addition to immersion and standing, it is also preferable to agitate the solution using a liquid circulation system or a rotating blade.

[0053] The treated polyester-containing material is filtered through a metal mesh or other solution to remove undissolved materials such as other fiber components. Since the DMT solution after filtration contains a large amount of polyester components, it is preferable to remove the DMT by evaporation, washing, or other means and recover the polyester components.

[0054] [Recovery of polyester components (2); depolymerization treatment] Furthermore, it is preferable that the polyester component obtained through the polyester component recovery treatment in which at least two of the above treatments (a) to (f) are carried out in order is further subjected to a depolymerization treatment.

[0055] That is, it is preferable to further depolymerize the polyester component obtained in the above-mentioned polyester component recovery (1) into a bis(hydroxyalkyl) aromatic dicarboxylate in alkylene glycol containing a depolymerization catalyst. 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.

[0056] [catalyst] The catalyst used in the depolymerization reaction of the depolymerization step is preferably a first transition metal catalyst. Specific examples include first transition metal fatty acid salts, carbonates, sulfates, phosphates, oxides, hydroxides, halides, and alcoholates. Manganese and zinc are preferably used as the first transition metal.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] [Alkylene glycol] The alkylene glycol (hereinafter sometimes abbreviated as 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 textile product, or the same as the polyalcohol constituting the polyester obtained by repolymerizing the intermediate bis(hydroxyalkyl) aromatic dicarboxylate.

[0061] 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.

[0062] 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.

[0063] [Refining process] In the method for recovering a polyester component of the present invention, it is preferable to further carry out a purification step after the polyester component recovery step. In particular, when the depolymerization treatment of recovery (2) is carried out, it is preferable to include a purification step of purifying the depolymerization reaction product. The purification step includes crystallization and adsorption treatment, and it is more preferable to carry out both of them.

[0064] [Crystallization] The purification step is carried out by crystallizing the polyester components such as the depolymerization reaction product in alkylene glycol by lowering the temperature. 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. 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] [Adsorption treatment] It is also preferable to further subject the obtained polyester component such as aromatic dicarboxylate bis(hydroxyalkyl) to an adsorption treatment for 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.

[0069] This adsorption treatment is a process in which a bis(hydroxyalkyl) aromatic dicarboxylate composition is brought into contact with an adsorbent, and nitrogen-containing organic compounds and the like contained in the bis(hydroxyalkyl) aromatic dicarboxylate composition are adsorbed onto the adsorbent, thereby obtaining a more purified bis(hydroxyalkyl) aromatic dicarboxylate. This adsorption step can be carried out by dissolving the aromatic dicarboxylate bis(hydroxyalkyl) composition in water or an organic solvent to prepare an aqueous solution or solution, and then adding the adsorbent thereto, thereby bringing the two into contact in water or an organic solvent.

[0070] [Polyester component: bis(hydroxyalkyl) benzenedicarboxylate] The polyester component contained in the composite fiber product can be recovered as a bis(hydroxyalkyl) aromatic dicarboxylate as a polyester intermediate through the depolymerization process. This bis(hydroxyalkyl) aromatic dicarboxylate, which is also a polyester component, can then be used as an intermediate in the production of recycled polyester polymers.

[0071] 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.

[0072] 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.

[0073] [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.

[0074] 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.

[0075] 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.

[0076] [Physical properties of recycled polymers] The recycled polyester polymer obtained in this manner has little yellowish tinge, which is considered to be inferior in quality. According to the method for recovering polyester of the present invention, it is difficult to produce residual foreign matter or by-products derived from materials other than polyester, which may cause discoloration due to the influence of components other than polyester. The recycled polyester polymer obtained by the present invention has been freed from other fiber components contained in the composite fiber product, and if the polyester fiber in the composite fiber product is dyed, the dye is also removed.

[0077] 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 8 or less, more preferably 6.5 to -20, and particularly preferably 5.0 to -15. * However, it is preferably 75 or more, and more preferably 80 to 100. The nitrogen content derived from the acrylic fiber, polyurethane elastic yarn, and dye contained in the obtained recycled polyester polymer is preferably 15 ppm or less, more preferably 12 ppm or less. 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]

[0078] The present invention will be described in more detail below with reference to examples, in which the values ​​were determined by the following methods.

[0079] (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.

[0080] 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 -1 Benzene 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.

[0081] 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.

[0082] 4) Nitrogen (N) content Measurements were made using a total nitrogen and protein analyzer (Nitto Seiko Analytech DTN-300V).

[0083] [Example 1] (Textile products) 400 g of multi-fiber woven fabric and 12 g of polyurethane elastic fiber (Asahi Kasei Leica®) were prepared, and the multi-fiber woven fabric was cut with scissors to a length of approximately 3 cm to prepare a mixture as a textile product sample for testing. This textile product sample contained various fibers, including cotton, nylon, acetate, wool, rayon, acrylic, silk, polyester, and polyurethane.

[0084] 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 constituting the warp yarns in a certain area, and polyester spun yarn as the weft. 2 It is a woven fabric.

[0085] The following treatments were carried out in order: [Recovery of polyester components (1)] (a) Reducing agent treatment First, a reduction treatment solution was prepared by adjusting the mixed aqueous solution to 100 ml of water, 10 g of sodium disulfite, 48 g of urea, and 5 g of sodium dodecyl sulfate. Next, 412 g of the above textile product sample and 4120 g of the reduction treatment solution (10 times the amount) were placed in a 5 L separable flask, and the flask was heated to 90°C using a mantle heater and heated for 30 minutes with stirring. The mixture was then filtered through a metal mesh with 200 μm openings, and the residue on the mesh was washed and dried. In the multi-fiber woven fabric, the worsted warp yarn was removed from the weft yarn only, and it was confirmed that the worsted wool had been removed. Other fibers remained.

[0086] (b) Aprotic polar solvent treatment 4120 g of DMSO, 10 times the amount of the original sample, was used as the aprotic polar solvent. (a) The textile product sample after the reducing agent treatment was placed in a 5 L separable flask together with DMSO and stirred at room temperature for 30 minutes. After that, it was filtered using a metal mesh with 200 μm openings, and the residue on the mesh was washed and dried. In the multi-fiber woven fabric, the warp yarns of the fabric were replaced with weft yarns only, and it was confirmed that the acrylic spun yarns and acetate filament yarns had been removed in addition to the worsted (wool) yarns. Other fibers remained.

[0087] (c) Zinc chloride treatment A 70% aqueous zinc chloride solution was prepared as the treatment solution. 4120 g of treatment solution, 10 times the amount of the original sample, was used. The textile product samples after (a) and (b) treatments were placed in a 5 L separable flask together with the zinc chloride solution, and the internal temperature was set to 90°C using a mantle heater, followed by stirring for 30 minutes. The mixture was then filtered through a metal mesh with 200 μm openings, and the residue on the mesh was washed and dried. In the multi-fiber woven fabric, silk and rayon filament yarns were used in the warp yarns, but were now used only in the weft yarns, and it was confirmed that in addition to worsted (wool), acrylic spun yarns, and acetate filament yarns, silk and rayon filament yarns had been removed. Other fibers remained.

[0088] (d) Aromatic alcohol treatment 4120 g of BA, which is 10 times the amount of the original sample, was used as the aromatic alcohol, and the textile product sample after (a) to (c) treatments was placed in a 5 L separable flask together with BA, and the internal temperature was set to 105°C using a mantle heater and stirred for 30 minutes. After that, the mixture was filtered using a metal mesh with 200 μm openings, and the residue on the mesh was washed and dried. Although there was no change in the multi-fiber mixed woven fabric, no polyurethane elastic fibers remained on the wire mesh.

[0089] (e) Alkylene glycol treatment The alkylene glycol used was 4120 g of ethylene glycol, which was 10 times the amount of the original sample, and the textile product sample after treatments (a) to (d) was placed in a 5 L separable flask together with ethylene glycol, and the internal temperature was set to 160°C using a mantle heater and stirred for 30 minutes.The flask was then filtered using a metal mesh with 200 μm openings, and the residue on the mesh was washed and dried. It was confirmed that in the multi-fiber woven fabric, nylon filament yarns were used in the warp only in the weft, and that in addition to worsted (wool), acrylic spun yarn, acetate filament yarn, silk yarn and rayon filament yarn, nylon filament yarn had also been removed.

[0090] By carrying out the above treatments (a) to (e) in order, only the polyester spun yarn as the weft and the polyester spun yarn and cotton yarn as the warp remained.

[0091] [Recovery of polyester components (2)] For 100 parts by mass of the recovered material, 500 parts by mass of ethylene glycol (EG) and 0.12 parts by mass of manganese acetate as a depolymerization catalyst were prepared, and three times the amount was charged into a 2 L separable flask and sealed with nitrogen. Note that the manganese acetate was dissolved in EG before charging.

[0092] The separable flask containing the sample was then heated to an internal temperature of 220°C using a mantle heater, and depolymerization treatment was carried out at normal pressure for 4 hours while stirring. Insoluble matter, likely cotton, was confirmed in the BHET (bis(hydroxyethyl) benzenedicarboxylate) solution after depolymerization. The depolymerized solution was filtered through a 200 μm mesh, and the solid matter remaining inside was separately recovered. This was then filtered through a cartridge filter with a 0.20 μm mesh to obtain a BHET / EG solution from which impurities had been removed. The recovered solid matter was washed and dried, and then subjected to component analysis by FT-IR, with a peak intensity of 3300 cm. -1 The OH group peak in the vicinity and the 1200-800cm -1There were bands where glucose rings and glycosidic bonds overlapped nearby, and the peak characteristics confirmed that it was cotton. The IR measurement chart is shown in Figure 1.

[0093] The liquid components were gradually cooled to 70°C, and then the temperature was 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.

[0094] The BHET / EG slurry was then pressed using a filter press manufactured by Nippon Filter Equipment Co., Ltd., to separate the BHET from the EG. The separated BHET contained 35% by mass of EG based on the weight of the cake recovered from 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.

[0095] 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 to recover the BHET, which was 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.

[0096] (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 then 0.4 kPa for 40 minutes. The polycondensation reaction was carried out while distilling off ethylene glycol and other products generated during the reaction outside the reactor, yielding a recycled polyester polymer.

[0097] 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 whiteness was high and no foreign matter was found to be present. The color of the recovered BHET was L. * , a * , b * value and the color of the repolymerized polymer L * , a * , b * The values, IV values ​​and N contents are shown in Table 1.

[0098] [Example 2] In the same manner as in Example 1, the treatments of steps (a) to (e) were carried out. Then, the following treatments were carried out on the obtained textile product samples after treatments (a) to (e).

[0099] (f) DMT treatment Ten times the amount of DMT used as a treatment agent for the textile product sample was added to a 5 L separable flask, and the mixture was stirred for 30 minutes at a set temperature of 150°C using a mantle heater. After that, filtration was carried out using a metal mesh with a mesh size of 200 μm, and the residue on the mesh was washed and dried. The residue after drying was collected and analyzed for components by FT-IR. -1 The OH group peak in the vicinity and the 1200-800cm -1 There were bands where nearby glucose rings and glycosidic bonds overlapped, and the peak characteristics confirmed that it was cotton. The IR measurement chart is shown in Figure 2.

[0100] On the other hand, the liquid after filtration was washed with methanol and then dried, and a white solid was recovered as a polyester component. The residue after drying was subjected to component analysis by FT-IR and confirmed to be a PET polymer. The color of the recovered polyester component was L * , a * , b * The values, IV values ​​and N contents are also shown in Table 1.

[0101] [Example 3] A moisture-absorbing and heat-generating material was prepared as a textile sample for testing. This moisture-absorbing and heat-generating material consisted of 34% rayon, 33% polyester (PET), 28% acrylic, and 5% polyurethane.

[0102] After steps (c) and (d) of Example 1 were carried out in order, the polyester component recovery process was carried out in the same manner as in Example 1 to recover the polyester component BHET, followed by the same repolymerization process as in Example 1 to obtain recycled polyester. Both the polyester component BHET and the repolymerized polyester had high whiteness and no foreign matter was found to be mixed in. * , a * , b * Value and color of repolymerized polymer L * , a * , b * The values, IV values ​​and N contents are also shown in Table 1.

[0103] [Example 4] A moisture-absorbing and heat-generating material was prepared as a textile product sample for testing in the same manner as in Example 3. This moisture-absorbing and heat-generating material was composed of 34% rayon, 33% polyester (PET), 28% acrylic, and 5% polyurethane. After the steps (b) and (d) of Example 1 were carried out in this order, the polyester component recovery treatment was carried out in the same manner as in Example 1.

[0104] That is, 500 parts by mass of ethylene glycol (EG) and 0.12 parts by mass of manganese acetate as a depolymerization catalyst were prepared for 100 parts by mass of the recovered material, and three times the amount was charged into a 2 L separable flask and sealed with nitrogen. Note that the manganese acetate was dissolved in EG before charging.

[0105] The separable flask containing the sample was then heated to an internal temperature of 220°C using a mantle heater, and depolymerization treatment was carried out at normal pressure for 4 hours while stirring. Cotton-like insoluble matter was confirmed in the BHET (benzenedicarboxylate bis(hydroxyethyl)) solution after depolymerization. The depolymerized solution was filtered through a 200 μm mesh to recover the solid matter remaining inside, which was then filtered through a cartridge filter with a 0.20 μm mesh to remove impurities. The recovered solid matter was washed and dried, and then its components were analyzed by FT-IR. The 3300 cm peaks, derived from cellulose, were observed. -1 The OH stretching vibration peak in the vicinity was broad, confirming that it was rayon. The IR measurement chart is shown in Figure 3.

[0106] The liquid component was gradually cooled to 70°C, and then cooled to 15°C while stirring and cooling. Thereafter, stirring was continued 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.

[0107] 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.

[0108] After the solid-liquid separation, 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 to recover the BHET, which was 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.

[0109] Subsequently, the polyester was repolymerized in the same manner as in Example 1 to obtain recycled polyester polymer in the form of granular pellets of approximately 3 mm. The whiteness was high and no foreign matter was found to be present. * , a * , b * Value and color of repolymerized polymer L * , a * , b * The values, IV values ​​and N contents are also shown in Table 1.

[0110] [Comparative Example 1] 100g of multi-fiber woven fabric and 200g of polyester fabric were prepared, and both the multi-fiber woven fabric and the polyester fabric were cut with scissors to a length of approximately 3cm to prepare a mixture of textile samples for testing. This textile sample contained various fibers, including cotton, nylon, acetate, wool, rayon, acrylic, silk, polyester, and polyurethane. The multi-fiber mixed woven fabric here was the same white fabric as that in Example 1 (JISL0803:2011 Mixed Weave No. 1). The polyester fabric was made of undyed PET fiber yarns.

[0111] Unlike Example 1, the treatments (a) to (e) were not carried out, and the polyester component recovery treatment was then carried out in the same manner as in Example 1. Specifically, 500 parts by mass of ethylene glycol (EG) and 0.12 parts by mass of manganese acetate as a depolymerization catalyst were added to 100 parts by mass of the above-mentioned textile product sample, and three times the amount was added to a 2 L separable flask and sealed with nitrogen. Note that the manganese acetate was dissolved in EG before addition.

[0112] The separable flask containing the sample was then heated to an internal temperature of 220°C using a mantle heater, and depolymerization treatment was carried out at normal pressure for 4 hours while stirring. During this process, the liquid in the flask gradually turned brown. Insoluble matter that appeared to be fibrous was confirmed in the depolymerized solution. The depolymerized solution was filtered through a 200 μm mesh to recover the solids remaining inside, and then filtered through a cartridge filter with 0.20 μm openings to remove impurities. The recovered solids included cotton-like fibrous material and carbonized fibrous material.

[0113] The liquid component was gradually cooled to 70°C, and then cooled to 15°C while stirring and cooling. Thereafter, stirring was continued 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.

[0114] The BHET / EG slurry was pressed using a filter press manufactured by Nippon Filter Equipment Co., Ltd., to separate the BHET from the EG. The separated BHET contained 35% by mass of EG based on the weight of the cake recovered from 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. The brown color of the resulting cake was visually confirmed.

[0115] 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 to recover the BHET. The recovered BHET was dried in a vacuum dryer at 50°C for 8 hours to obtain dried BHET. Although the color of the BHET had lightened, it still retained color and contained impurities.

[0116] 254 parts by weight of the resulting dried BHET was then placed in a reaction vessel under nitrogen atmosphere at atmospheric pressure, along with 0.007 parts by weight of a phosphorus-based stabilizer and 0.07 parts by weight of diantimony trioxide as a repolymerization catalyst. The temperature inside the reactor was then raised to 285°C, and the pressure was gradually reduced for 10 minutes at atmospheric pressure, 10 minutes at 4 kPa, and 40 minutes at 0.4 kPa. The polycondensation reaction was carried out while distilling off ethylene glycol and other products generated during the reaction. The reaction product was then continuously extruded in strand form from the discharge port, cooled, and cut to obtain granular pellets approximately 3 mm in size. The resulting pellets were brown, indicating that only recycled PET with a high impurity content was obtained. The color of the recovered BHET was L. * , a * , b * Value and color of repolymerized polymer L * , a * , b * The values, IV values ​​and N contents are also shown in Table 1.

[0117] [Table 1] [Industrial Applicability]

[0118] 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 subjecting a composite fiber product containing polyester fibers to at least two of the following treatments (a) to (f) in the following order: (a) a solvent contact step in which the textile product is brought into contact with an aqueous solution containing a reducing agent at a temperature of 50 to 100°C; (b) a solvent contacting step in which the textile product is brought into contact with an aprotic polar solvent at a temperature of 30 to 160°C. (c) a solvent contact step in which the textile product is brought into contact with an aqueous zinc chloride solution at a temperature of 30 to 100°C. (d) a solvent contact step in which the textile product is brought into contact with a solution of an aromatic alcohol or its derivative in the temperature range of 70 to 170°C. (e) a solvent contact step in which the textile product is contacted with alkylene glycol at a temperature in the range of 140 to 200°C. (f) a solvent contact step in which the textile product is contacted with dimethyl terephthalate (DMT) at a temperature in the range of 150 to 300°C.

2. 2. The method for recovering a polyester component according to claim 1, wherein the composite fiber product contains, in addition to polyester fibers, two or more types of fibers selected from the group consisting of cellulose-based natural fibers, cellulose-based regenerated fibers, cellulose-based semi-synthetic fibers, protein fibers, silk, nylon fibers, polyurethane elastic fibers, acrylic fibers (PAN), and modacrylic fibers.

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

4. 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 3.

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