Method for recovering polyester component and method for producing recycled polyester

Abstract

To provide a method for recovering a polyester component from a fiber product mainly containing a polyester fiber and a crosslinked acrylic resin, and a method for producing recycled polyester which uses the recovered polyester component and shows little coloration.SOLUTION: A method for recovering a polyester component treats a fiber product containing a polyester fiber and a crosslinked acrylic resin at a temperature of 100°C to 185°C in lower alcohol containing a catalyst, and recovers a polyester component. Preferably, the polyester fiber is composed of polyester containing alkylene terephthalate as a main repeating unit, the acrylic resin is a crosslinked acrylic resin, and the lower alcohol is alkylene glycol. A method for producing recycled polyester repolymerizes the polyester component obtained by the recovery method.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for recovering polyester components from textile products that mainly contain polyester fibers and crosslinked acrylic resins, and a method for producing recycled polyester using the recovered polyester. [Background technology]

[0002] Polyester is widely used in textile products due to its excellent properties, but the effective utilization of polyester textile products after use is a major issue, including environmental concerns. In particular, textile products in which acrylic resin printing is applied to the surface of a polyester fiber sheet are widely used due to the variety of colors they offer, but there is a problem in that it is difficult to separate the polyester fiber from the acrylic resin that is strongly bonded to it.

[0003] Typically, material recycling, thermal recycling, and chemical recycling are considered as the main methods for treating used polyester fiber products. Among these, chemical recycling, in which polyester polymers are depolymerized to raw materials and then repolymerized, is superior as a closed-loop recycling method from the viewpoint of minimizing the deterioration of quality associated with recycling. Among these, chemical recycling, which is characterized by depolymerizing polyester to an intermediate that can be directly subjected to a polycondensation reaction to produce recycled polyester, is also an excellent method in terms of energy consumption in chemical recycling.

[0004] However, recycled polyester polymers obtained from polyester fiber products printed with acrylic resin have problems such as extremely low yields and inability to suppress discoloration.

[0005] In order to suppress discoloration of the recovered polymer, for example, Patent Document 1 has attempted, as a step of removing discoloration-causing substances, an adsorption treatment in which the discoloration-causing substances are brought into contact with an adsorbent after the depolymerization intermediate, a decomposition treatment in which the discoloration-causing substances are decomposed with a decomposing agent, or a reduction treatment in which the discoloration-causing substances are reduced with a reducing agent. However, although these methods remove discoloration-causing substances such as dyes to a certain extent, there is a problem in that it is not possible to obtain a polyester polymer with reduced discoloration at the same level as that of a polyester polymer produced by a normal production method that does not use recycled raw materials. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-88096 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 textile products containing mainly polyester fibers and crosslinked acrylic resins, and a method for producing recycled polyester with little coloration 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 treating a textile product containing polyester fibers and a crosslinked acrylic resin in a lower alcohol containing a catalyst at a temperature of 100°C to 185°C, and recovering the polyester component. (2) The method for recovering a polyester component according to (1) above, wherein the polyester fiber is made of a polyester having alkylenebenzene dicarboxylate as the main repeating unit. (3) The method for recovering a polyester component according to (1) or (2) above, wherein the acrylic resin is a crosslinked acrylic resin. (4) The method for recovering a polyester component according to any one of (1) to (3) above, wherein the lower alcohol is alkylene glycol. (5) The method for recovering a polyester component according to any one of (1) to (4) above, wherein the catalyst is a zinc-based catalyst. (6) A method for recovering a polyester component according to any one of (1) to (5) above, wherein the catalyst is sodium methoxide or titanium tetraoxide. (7) The method for recovering a polyester component according to any one of (1) to (6) above, further comprising treating with an adsorbent. (8) The method for recovering a polyester component according to any one of (1) to (7) above, wherein the polyester component to be recovered is a bis(hydroxyalkyl) benzenedicarboxylate. (9) A method for producing recycled polyester, which comprises repolymerizing the polyester component obtained by the recovery method according to any one of (1) to (8) above. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for recovering polyester components from textile products containing mainly polyester fibers and crosslinked acrylic resins, and a method for producing recycled polyester with little coloration using the recovered polyester. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below. The method for recovering a polyester component of the present invention essentially involves treating a textile product containing a polyester fiber and a crosslinked acrylic resin in a lower alcohol containing a catalyst at a temperature of 100°C to 185°C to recover the polyester component.

[0011] [Textile products] The textile product used in the present invention contains polyester fibers and a crosslinked acrylic resin. Furthermore, it is preferable that the textile product be primarily composed of polyester fibers. Here, "primarily composed of polyester fibers" means that polyester fibers make up the majority of the fibers constituting the textile product. The polyester fibers preferably account for 50% by weight or more, more preferably 75% by weight or more, and particularly preferably 90% by weight or more, of the weight of the textile product.

[0012] Examples of textile products made of such polyester fibers and cross-linked acrylic resin include T-shirts with acrylic prints on the surface, clothing with acrylic prints on logos, and flags and banners with acrylic resin printed all over. Since such textile products are produced and consumed in large quantities and a large amount is discarded, there is also a great demand for recycling. The amount of cross-linked acrylic resin attached to the textile product is preferably less than 50% by weight, particularly in the range of 10 to 25% by weight.

[0013] [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.

[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 polyester obtained by combining such a polycarboxylic acid and a polyalcohol is used as one of the starting materials for forming a textile 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.

[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, 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.

[0019] [Acrylic resin] The textile products used in the present invention contain crosslinked acrylic resin in addition to the polyester fibers described above. Here, acrylic resin refers to a combination of acrylic esters and / or methacrylic esters, typically polymethyl methacrylate (PMMA) resin. In the textile products used in the present invention, the acrylic resin is crosslinked. Examples of crosslinking agents that can be used include epoxy and isocyanate-based agents, which are commonly used as curing agents or fixers for acrylic resins to improve the fastness and washing durability of resin prints. The degree of crosslinking is preferably 0.1% to 10%, and more preferably 1% to 5%.

[0020] The crosslinked acrylic resin used simultaneously with the textile product in the present invention includes acrylic prints used on the surface of clothing such as T-shirts, acrylic prints as logos on the surface of clothing, acrylic resins printed all over flags, banners, etc. Such textile products are produced and consumed in large quantities, and a large amount is also discarded, so there is a great demand for recycling them.

[0021] [Polyester component recovery process] In the present invention, a textile product containing the above-mentioned polyester fiber and crosslinked acrylic resin is used as a starting material to recover the polyester component, and the textile product is treated in a lower alcohol containing a catalyst at a temperature of 100°C to 185°C to recover the polyester component.

[0022] The treatment conditions are more preferably in the temperature range of 125° C. to 185° C., particularly 130° C. to 180° C. The treatment time is preferably 6 hours or less, more preferably in the range of 0.5 to 4 hours. The pressure during the treatment is preferably normal pressure, but when a solvent with a low boiling point is used, it is preferable to treat under pressure.

[0023] The amount of lower alcohol solution used during treatment is preferably 2 to 20 times the weight of the textile product, which is the structure to be treated. The amount is more preferably 3 to 10 times. During treatment with the solution, in addition to immersion and standing, it is preferable to agitate the solution with a liquid circulation system or a rotating blade.

[0024] In the recovery method of the present invention, the textile product is treated in a lower alcohol containing a high temperature catalyst, whereby the polyester fiber is depolymerized to form bis(hydroxyalkyl) benzenedicarboxylate, which is then dissolved in the lower alcohol, while the cross-linked acrylic resin remains mostly in a solid state. Therefore, it is possible to separate the polyester component in the solution from the solid cross-linked acrylic resin by solid-liquid separation.

[0025] The recovered polyester component can be used as is after purification and drying, or it can be further depolymerized to bis(hydroxyalkyl) benzenedicarboxylate to produce an intermediate for polyester polymer, which can then be used for repolymerization of polyester polymer.

[0026] Furthermore, in the recovery method of the present invention, it is more preferable to select alkylene glycol as the lower alcohol and use a polyester depolymerization catalyst as the catalyst. In this case, in the recovery process, the polyester component is depolymerized to bis(hydroxyalkyl) benzenedicarboxylate, and at the same time, the acrylic resin having a crosslinked structure is partially dissolved but remains mostly in a solid state. Therefore, it is possible to separate the bis(hydroxyalkyl) benzenedicarboxylate, which is the polyester component in the solution, from the solid crosslinked acrylic resin by solid-liquid separation.

[0027] Furthermore, trace amounts of acrylic resin contained in the recovered polyester component can be easily removed by treating them in the subsequent crystallization step or adsorption step.

[0028] [Lower alcohols] Examples of lower alcohols used in the recovery method of the present invention include monohydric alcohols having a linear hydrocarbon group with 5 or less carbon atoms, dihydric alcohols (also called diols or glycols), trihydric alcohols, and benzyl alcohol having an aromatic ring. These alcohols have a relatively low viscosity even at room temperature and easily penetrate into resins, making them ideal for the present invention.

[0029] More specifically, examples of the lower alcohol include methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, diethylene glycol, glycerin, and benzyl alcohol. Among these, ethylene glycol, diethylene glycol, propanediol, and benzyl alcohol are more preferred, and ethylene glycol (EG) is particularly preferred. By using such lower alcohols, boiling, evaporation, decomposition, and side reactions are less likely to occur in the treatment temperature range described below, and their moderate viscosity allows for good permeability into the resin, enabling more efficient recovery.

[0030] [Alkylene glycol] In addition, it is preferable to select alkylene glycol as the lower alcohol used in the recovery method of the present invention, and this makes it possible to simultaneously obtain bis(hydroxyalkyl) benzenedicarboxylate, which is an intermediate for polyester polymer, in the above recovery step.

[0031] The alkylene glycol (hereinafter sometimes abbreviated as AG) used in the depolymerization reaction in this step is the same as the polyalcohol that forms the backbone structure of the polyester used in the textile product, or the same as the polyalcohol that constitutes the polyester obtained by repolymerizing the intermediate bis(hydroxyalkyl) aromatic dicarboxylate.

[0032] 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.

[0033] [catalyst] Specific examples of the first transition metal preferably used in the present invention include titanium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, of which zinc and titanium are preferred, and zinc-based catalysts that can be used at low temperatures are particularly preferred. These catalysts are preferably those used in the depolymerization and transesterification of polyesters.

[0034] In addition to utilizing the polyester components recovered in this invention as they are, one of the goals is to further depolymerize and repolymerize them to produce chemically recycled polyester. Even if manganese or zinc remains in the process of separating and recovering the acrylic resin and polyester, it is unlikely to have a negative effect on the quality (particularly the color) of the chemically recycled polyester in the subsequent depolymerization and repolymerization processes.

[0035] In the present invention, acetates of first transition metals, sodium methoxide, or titanium tetraoxide are preferred. Zinc acetate is particularly preferred. Although the mechanism behind this is unclear, it is thought that this is because it is active at relatively low temperatures and can selectively depolymerize only polyester.

[0036] The amount of catalyst used during depolymerization varies depending on the catalyst used. In the case of zinc acetate or titanium tetraoxide, the amount is preferably 20 to 1000 mmol%, more preferably 30 to 750 mmol%, and particularly preferably 50 to 500 mmol% relative to the polyester. In the case of sodium methoxide, the amount is preferably 25 to 300 mol%, more preferably 50 to 200 mol%, and particularly preferably 100 to 150 mol%. Here, "mol%" refers to the ratio of the number of catalyst molecules to the structural units of the polyester. In the case of "mmol%", the ratio is 1 / 1000 of that "mol%". 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 be reduced, which is undesirable.

[0037] [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-described steps. The purification step includes crystallization or adsorption treatment, and it is more preferable to perform both of them.

[0038] [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. 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.

[0039] When solid-liquid separation is performed after crystallization, it is preferable to wash the crystallized product with water or alkylene glycol. The washing is preferably performed by treating the product in a Nutsche filter while spraying a washing liquid. By performing these treatments, 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.

[0040] 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.

[0041] 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.

[0042] [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.

[0043] 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 step can be carried out by dissolving the polyester component 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.

[0044] [Polyester component: bis(hydroxyalkyl) benzenedicarboxylate] When the polyester component contained in a textile product is recovered as a bis(hydroxyalkyl) aromatic dicarboxylate as an intermediate substance for polyester through the above-mentioned recovery process (depolymerization), it can be used as an intermediate substance for the production of recycled polyester polymers.

[0045] The aromatic bis(hydroxyalkyl) dicarboxylates vary depending on the type of polyester and alkylene glycol (lower alcohol) contained in the starting textile product. When the polyester is made from a polyester (polyalkylene terephthalate) that primarily uses terephthalic acid as the polycarboxylic acid, bis(hydroxyalkyl) benzenedicarboxylate (hereinafter referred to as BHAT; bishydroxyalkyl terephthalate) is obtained.

[0046] 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.

[0047] [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.

[0048] As a catalyst for repolymerization to obtain a recycled polyester polymer, known catalysts such as antimony, germanium or titanium catalysts can be used, specifically diantimony trioxide.

[0049] 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).

[0050] 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.

[0051] [Physical properties of recycled polymers] The recycled polyester polymer obtained in this manner is a polymer with little yellowness, which is considered to be of inferior quality. According to the method for recovering polyester of the present invention, colored by-products caused by components other than polyester are less likely to be produced.

[0052] In the recycled polyester polymer obtained by the present invention, the crosslinked acrylic resin has been removed, and if the crosslinked acrylic resin has been colored with a pigment, the pigment has also been removed. [Example]

[0053] The present invention will be described in more detail below with reference to examples, in which the values ​​were determined by the following methods.

[0054] 1) Intrinsic viscosity (IV) The recovered polyester was dissolved in 10 mL of a tetrachloroethane / phenol mixed solvent (volume ratio 1 / 1), and the intrinsic viscosity (dL / g) at 35°C was measured.

[0055] 2) Glass transition temperature (Tg), crystallization temperature (Tc), melting point (Tm) A 10 mg sample was cut and placed in an aluminum pan, and the melting point was measured using a differential scanning calorimeter (DSC Q10) manufactured by TA Instruments-Waters LLC. The measurement conditions were as follows: the sample was first heated from 25°C to 300°C at a heating rate of 20°C / min, then rapidly cooled and quenched. The quenched sample was then heated from 25°C to 300°C at a heating rate of 20°C / min, and the crystalline melting point was determined.

[0056] 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 measurement device ("SE7700" manufactured by Nippon Denshoku Industries Co., Ltd.). * , a * , b * The values ​​were measured.

[0057] [Example 1] (Polyester component recovery process) As a textile product made of polyester fiber and cross-linked acrylic resin, an acrylic-printed polyester fabric (hereinafter referred to as "fabric") was prepared as a sample, in which acrylic rubber containing pigment ink was printed on a polyester fiber fabric (2 / 2 twill structure, 100% polyethylene terephthalate (PET) fiber).

[0058] 300 g of this fabric was placed in a 2 L separable flask together with 1500 g of ethylene glycol (EG) in which 1.13 g of zinc acetate as a depolymerization catalyst had been dissolved (total 1501.13 g), and the flask was filled with nitrogen. The separable flask containing the sample was then heated to an internal temperature of 175°C using a mantle heater, and depolymerization treatment was carried out at normal pressure for 1 hour while stirring. Insoluble matter, which appeared to be the printed part, was confirmed in the BHET (bis(hydroxyethyl)benzenedicarboxylate) solution after depolymerization. Therefore, the depolymerized solution was filtered through a 200 μm mesh, and the printed part remaining inside was removed by solid-liquid separation. The recovered printed part retained its original shape and had not been decomposed during the above process.

[0059] The BHET solution obtained by solid-liquid separation at 175°C was cooled to 90°C and filtered through a cartridge filter with a mesh size of 0.20 μm to remove impurities. After gradually cooling to 70°C, the temperature was lowered to 15°C while stirring and cooling. After that, stirring was continued for 60 minutes while maintaining the internal temperature at 15°C, and the internal temperature was lowered to precipitate BHET crystals, yielding a BHET / EG slurry. This BHET / EG slurry at 15°C was subjected to a compression treatment using a filter press manufactured by Nippon Filter Equipment Co., Ltd., to carry out solid-liquid separation of BHET and EG. The separated BHET contained 35% by mass of EG based on the weight of the cake recovered after the filter press.

[0060] 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 5°C 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 254 g of dried BHET. The obtained BHET was white and free of any foreign matter.

[0061] (repolymerization of polyester) Then, 254 g of the obtained dried BHET was placed in a reaction vessel under normal pressure and nitrogen atmosphere, along with 0.007 g of a phosphorus-based stabilizer and 0.07 g 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.

[0062] 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. The physical properties of the recycled polyester after repolymerization, such as hue L*, a*, and b* values, are shown in Table 1.

[0063] [Example 2] The polyester component as an intermediate was recovered by vacuum drying in the same manner as in Example 1, and further repolymerized to obtain a recycled polyester.

[0064] In the BHET solution immediately after depolymerization at 130°C, insoluble matter that appeared to be the printed part was confirmed, as in Example 1. Furthermore, the printed part recovered by filtering the solution through a 200 μm mesh retained its original shape and was not decomposed during the above process. The final recycled polyester polymer also had a high degree of whiteness, and no foreign matter was found to be mixed in. The physical properties of the recycled polyester after repolymerization, such as hue L*, a*, and b* values, are also shown in Table 1.

[0065] [Example 3] The polyester component BHET was recovered and further repolymerized in the same manner as in Example 1, to obtain recycled polyester, except that the depolymerization catalyst in Example 1 was changed from 1.13 g of zinc acetate to 1.57 g of titanium tetraoxide and the internal temperature was changed from 175°C to 130°C.

[0066] In the BHET solution immediately after depolymerization at 130°C, insoluble matter that appeared to be the printed part was confirmed, as in Example 1. Furthermore, the printed part recovered by filtering the solution through a 200 μm mesh retained its original shape and was not decomposed during the above process. The final recycled polyester polymer also had high whiteness and was free of any visible foreign matter. The physical properties of the recycled polyester after repolymerization, such as hue L*, a*, and b* values, are shown in Table 1.

[0067] [Comparative Example 1] An attempt was made to recover BHET, a polyester component, in the same manner as in Example 1, except that the internal temperature of the EG containing the depolymerization catalyst of Example 1 was changed from 175°C to 220°C. However, immediately after the depolymerization treatment, the insoluble matter in the BHET solution had partially decomposed and no longer maintained its original shape, and the EG solution contained not only BHET but also the acrylic print and the black pigment contained in the print, making it impossible to separate them. Furthermore, when the depolymerization treatment time was changed from 1 hour to 4 hours, the dissolution of the acrylic print progressed further.

[0068] Comparative Example 2 An attempt was made to recover BHET, a polyester component, in the same manner as in Example 1, except that the internal temperature of the EG containing the depolymerization catalyst of Example 1 was changed from 175°C to 70°C and the depolymerization treatment time was changed from 1 hour to 4 hours. However, it was confirmed that the printed portion and the fabric portion did not change and could not be separated.

[0069] Comparative Example 3 The polyester component BHET was recovered and further repolymerized to obtain a recycled polyester in the same manner as in Example 1, except that the depolymerization catalyst in Example 1 was changed from 1.13 g of zinc acetate to 0.38 g of manganese acetate, the internal temperature was increased from 175°C to 220°C, and the depolymerization treatment time was changed from 1 hour to 4 hours. However, just after depolymerization at 220°C, insoluble matter that appeared to be the printed part was confirmed in the BHET solution, as in Example 1. However, unlike Example 1, the acrylic printed part did not maintain its original shape and was partially decomposed, and some of the acrylic printed part was mixed into the EG solution.

[0070] Furthermore, coloration was observed in the recycled polyester recovered in the same manner as in Example 1. The physical properties of the recycled polyester after repolymerization, such as hue L*, a*, and b* values, are shown in Table 1.

[0071] [Table 1] [Industrial Applicability]

[0072] The present invention provides a method for recovering polyester components from textile products containing polyester fibers and crosslinked acrylic resins. The method involves depolymerizing the polyester, separating and adsorbing organic matter other than polyester, and then repolymerizing the depolymerized polyester. The resulting recycled polyester polymer has the same color and physical properties as virgin polyester polymer obtained by polymerization of petroleum-derived raw materials, and can therefore be used as a raw material for textile products. This 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 polyester components, characterized by treating a textile product containing polyester fibers and crosslinked acrylic resin in a lower alcohol containing a catalyst at a temperature of 100°C to 185°C, wherein the lower alcohol is alkylene glycol.

2. A method for recovering polyester components, characterized by treating a textile product containing polyester fibers and crosslinked acrylic resin in a lower alcohol containing a catalyst at a temperature of 100°C to 185°C, wherein the catalyst is a zinc-based catalyst.

3. A method for recovering polyester components, characterized by treating a textile product containing polyester fibers and crosslinked acrylic resin in a lower alcohol containing a catalyst at a temperature of 100°C to 185°C, wherein the catalyst is sodium methoxide or titanium tetrabucite.

4. A method for recovering polyester components, characterized in that a textile product containing polyester fibers and crosslinked acrylic resin is treated in a lower alcohol containing a catalyst at a temperature of 100°C to 185°C, wherein alkylene glycol is selected as the lower alcohol, the catalyst is a polyester depolymerization catalyst, and the recovered polyester component is bis(hydroxyalkyl) benzenedicarboxylate.

5. A method for recovering polyester components according to any one of claims 1 to 4, wherein the polyester fiber is made of polyester having alkylenebenzene dicarboxylate as the main repeating unit.

6. A method for recovering polyester components according to any one of claims 1 to 4, further comprising treating with an adsorbent.