Method for recovering polyester and method for manufacturing recycled polyester polymer

Abstract

Provided is a method for recovering polyester from a fiber product containing dye-colored polyester fibers and acrylic fibers, the method being characterized by comprising: a solvent contact step in which the fiber product is brought into contact with an aprotic polar solvent at a temperature of 30-160°C; and an acrylic fiber and dye removal step in which the solvent, along with the acrylic fibers and the dye dissolved therein, is removed from the fiber product to obtain polyester. Provided is a method for manufacturing a recycled polyester polymer with reduced coloration using the method for recovering polyester.

Description

Method for recovering polyester and method for producing recycled polyester polymer

[0001] The present invention relates to a method for recovering polyester from a textile product containing polyester fibers and acrylic fibers colored with dyes, and to a method for producing a recycled polyester polymer by depolymerizing the polyester and then repolymerizing it to produce a polyester polymer.

[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.

[0003] Material recycling, thermal recycling, and chemical recycling are the main methods being considered for the effective reuse of post-use materials. Of these, chemical recycling, in which polyester polymers are depolymerized to their raw materials and then repolymerized, is superior as a closed-loop recycling method in terms of minimizing the loss of quality that accompanies recycling. Among these, the method of using intermediates that can be directly subjected to polycondensation reactions to produce recycled polyester is also an excellent method from the viewpoint of energy consumption.

[0004] However, the recycled polyester polymer obtained in this manner has the problem that coloration cannot be sufficiently suppressed.

[0005] In particular, when polyester fiber products contain different polymers such as acrylic fibers or are dyed products, it has been difficult to recover polyester efficiently while suppressing discoloration.

[0006] For example, in Patent Document 1, attempts are made to remove color-causing substances by carrying out an adsorption treatment in which the color-causing substances are brought into contact with an adsorbent after depolymerization into an intermediate, a decomposition treatment in which the color-causing substances are decomposed with a decomposing agent, and a reduction treatment in which the color-causing substances are reduced with a reducing agent. However, although these methods remove color-causing substances such as dyes that are clearly mixed into the polymer to some extent, they are unable to obtain a polyester polymer with reduced coloring at the same level as polyester polymers produced by conventional production methods that do not use recycled raw materials.

[0007] According to the investigations of the present inventors, in textile products that are mainly composed of polyester fibers and also contain acrylic fibers, separation before and after depolymerization is particularly difficult, and the color of the chemically recycled polyester after repolymerization often becomes brownish.

[0008] An object of the present invention is to provide a method for recovering polyester from a textile product containing polyester fibers colored with a dye and acrylic fibers, and a method for producing a recycled polyester polymer with little coloration by depolymerizing the polyester and then repolymerizing it.

[0009] The present invention is a method for recovering polyester from a textile product containing polyester fibers and acrylic fibers colored with a dye, the method comprising: a solvent contacting step of contacting the textile product with an aprotic polar solvent at a temperature of 30 to 160°C; and an acrylic fiber and dye removing step of removing the solvent and the acrylic fibers and dye dissolved therein from the polyester fibers to obtain polyester.

[0010] The present invention also relates to a method for producing a recycled polyester polymer from a textile product containing polyester fibers colored with a dye and acrylic fibers, the method comprising: a depolymerization step of depolymerizing the polyester recovered by the above-described recovery method in alkylene glycol to obtain a depolymerized reaction product; and a repolymerization step of polycondensing the depolymerized reaction product to obtain a polyester polymer.

[0011] According to the present invention, it is possible to provide a method for recovering polyester from a textile product containing polyester fibers colored with a dye and acrylic fibers, and a method for producing a recycled polyester polymer with little coloration by depolymerizing the polyester and further repolymerizing it.

[0012] The present invention will be described in detail below.

[0013] [Textile Product] In the present invention, the textile product is a textile product containing polyester fibers colored with a dye and acrylic fibers. This textile product is mainly composed of fibers made of polyester. Here, "mainly composed of fibers made of polyester" means that polyester fibers make up the largest proportion of the fibers making up the textile product. The polyester fibers preferably account for 50% by weight or more, more preferably 80% by weight or more, based on the weight of the textile product.

[0014] Examples of textile products include knitted clothing such as sweaters, outdoor wear, and sportswear, batting for clothing and bedding, blankets, yarn, and carpets. Intermediate products such as woven and knitted fabrics, nonwoven fabrics, and wadding that constitute these products, as well as scraps generated in the manufacturing process and products discarded after use or in inventory, also fall under the category of textile products of the present invention.

[0015] [Polyester Fiber] The polyester in polyester fiber is a polycondensate synthesized by dehydration condensation of a polycarboxylic acid and a polyalcohol to form an ester bond. Polyester is a polymer having an ester bond and is generally classified into aliphatic polyester, semi-aromatic polyester, and wholly aromatic polyester.

[0016] The polycarboxylic acid constituting this polyester is preferably a dicarboxylic acid or an ester-forming derivative thereof, and the dicarboxylic acid is preferably an aromatic dicarboxylic acid such as terephthalic acid or 2,6-naphthalenedicarboxylic acid.

[0017] As the polyalcohol, a diol is preferably used. Specifically, an aliphatic glycol having 2 to 20 carbon atoms is used. Examples of this aliphatic glycol include ethylene glycol (hereinafter sometimes abbreviated as EG), 1,3-propanediol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. The aliphatic glycol may also be an alicyclic glycol having 3 to 30 carbon atoms, specifically, 1,4-cyclohexanedimethanol.

[0018] The polyester is preferably polyalkylene terephthalate, and more preferably polyethylene terephthalate, polytrimethylene terephthalate, or polybutylene terephthalate.

[0019] In the present invention, all or at least a part of the polyester fiber is colored with a dye. The dye is preferably a disperse dye, and among disperse dyes, a disperse dye containing a nitrogen atom is preferred. Particularly preferred dyes are azo-based disperse dyes.

[0020] [Acrylic Fiber] Acrylic fiber is a fiber made of a polymer whose main component is acrylonitrile. Examples of the fiber made of a polymer whose main component is acrylonitrile include the acrylic fiber and acrylic-based fiber described below.

[0021] The acrylic fiber is preferably a fiber produced from a polymer or copolymer of 85 to 100% by weight of acrylonitrile and 0 to 15% by weight of an unsaturated vinyl monomer.

[0022] Acrylic fibers, also known as 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] Examples of unsaturated vinyl monomers copolymerizable with acrylonitrile include acrylic acid esters (methyl acrylate, ethyl acrylate, etc.), methacrylic acid esters (methyl methacrylate, ethyl methacrylate, etc.), vinyl acetate, vinyl chloride, vinylidene chloride, styrene, acrylic acid and its salts, methacrylic acid and its salts, styrene sulfonic acid and its salts, and methacrylic sulfonic acid and its salts. Hereinafter, acrylic fibers and acrylic-based fibers will be collectively referred to as acrylic fibers.

[0024] The acrylic fiber may be composed of a single component yarn, or may be a blended fiber, blended yarn, or composite yarn with polyester fiber or the like.

[0025] The amount of acrylic fiber contained in the textile product is preferably 50% by weight or less, more preferably 30% by weight or less, and particularly preferably in the range of 5 to 20% by weight, based on the total weight of the textile product.

[0026] [Method for recovering polyester] The method for recovering polyester of the present invention includes a solvent contacting step of contacting the above-mentioned textile product with an aprotic polar solvent at a temperature of 30 to 160°C, and an acrylic fiber and dye removing step of removing the solvent and the acrylic fiber and dye dissolved therein from the textile product to obtain polyester.

[0027] Examples of aprotic polar solvents 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 are preferably high, and from this viewpoint, dimethyl sulfoxide, dimethylacetamide, and dimethylformamide are preferably used as the aprotic polar solvent, and dimethyl sulfoxide is particularly preferably used.

[0028] 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.

[0029] 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.

[0030] The acrylic fiber and dye removal process is carried out by removing the aprotic polar solvent from the textile product that has been absorbed between the fibers in the solvent contact treatment process. The removal of the aprotic polar solvent can be carried out by squeezing, centrifugal separation, or Soxhlet extraction.

[0031] The solvent contact step and the solvent removal step are preferably repeated. That is, the immersion and drainage treatments are preferably repeated alternately multiple times. Specifically, the immersion and drainage treatments are preferably repeated alternately five or more times, and particularly preferably six to ten times.

[0032] 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.

[0033] According to the above-mentioned method, the acrylic fiber component and the dye component are dissolved in an aprotic polar solvent from a textile product containing polyester fibers and acrylic fibers, and the solution is then removed, thereby recovering the polyester.

[0034] The polyester recovered by this method preferably has a nitrogen content derived from acrylic fibers and dyes of 15 ppm or less, more preferably 10 ppm or less, and therefore can remove most of the acrylic fibers and dyes from textile products containing polyester fibers and acrylic fibers colored with dyes.

[0035] [Method for producing recycled polyester polymer] Another aspect of the present invention is a method for producing recycled polyester polymer, which includes a depolymerization step of depolymerizing polyester, recovered from a textile product containing polyester fibers colored with a dye and acrylic fibers, in alkylene glycol by the above-described method to obtain a depolymerization reaction product, and a repolymerization step of polycondensing the depolymerization reaction product to obtain a polyester polymer.

[0036] This method makes it possible to obtain recycled polyester polymers with reduced coloring, low yellowness, and high whiteness, comparable to that of conventionally produced polyester polymers.

[0037] [Depolymerization Step] A catalyst is used in the depolymerization reaction of the depolymerization step. As the catalyst, a first transition metal catalyst is preferably used. Specific examples include first transition metal fatty acid salts, carbonates, sulfates, phosphates, oxides, hydroxides, halides, and alcoholates. As the first transition metal, manganese and zinc are preferably used.

[0038] As the catalyst, manganese oxide, manganese acetate, zinc oxide, or zinc acetate is preferably used, and manganese acetate is particularly preferably used. 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 step. The catalyst is preferably dissolved or suspended in alkylene glycol before use.

[0039] [Alkylene Glycol] The alkylene glycol (hereinafter sometimes abbreviated as AG) used 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.

[0040] 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.

[0041] 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 manner and subsequently carrying out crystallization and solid-liquid separation, the amounts of contaminating depolymerization catalysts and other foreign substances can be reduced.

[0042] 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.

[0043] 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 suppressing discoloration will decrease, which is not preferable. If a manganese-based catalyst is used as the catalyst, depolymerization can be performed with a small amount used.

[0044] [Purification Step] The method for producing a recycled polyester polymer of the present invention preferably includes a purification step of purifying the depolymerization reaction product after the depolymerization step and before the repolymerization step.

[0045] The purification step is carried out by lowering the temperature of the depolymerization reaction product in alkylene glycol to cause crystallization. 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.

[0046] After the crystallization, it is preferable to carry out solid-liquid separation. 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.

[0047] 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 color-causing substances can be washed away, and a more highly purified bis(hydroxyalkyl) aromatic dicarboxylate can be obtained.

[0048] 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 range, the cake itself will be easily dissolved, which is undesirable as it reduces the yield.

[0049] After washing, the product is dried in a vacuum dryer or the like to obtain a bis(hydroxyalkyl) aromatic dicarboxylate.

[0050] 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.

[0051] The resulting aromatic bis(hydroxyalkyl) dicarboxylate may be subjected to adsorption treatment to remove foreign matter using an adsorbent such as activated carbon.

[0052] [Intermediate Material] The polyester contained in the textile product is converted into an aromatic dicarboxylate bis(hydroxyalkyl) as an intermediate material through the above-mentioned depolymerization step, and this is used to produce a recycled polyester polymer.

[0053] The aromatic bis(hydroxyalkyl) dicarboxylate varies depending on the polyester and alkylene glycol subjected to depolymerization. When the polyester is a polyester (polyalkylene terephthalate) using terephthalic acid as the polycarboxylic acid as the raw material, bis(hydroxyalkyl) benzenedicarboxylate (hereinafter sometimes referred to as BHAT; bishydroxyalkyl terephthalate) is obtained.

[0054] 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.

[0055] [Repolymerization Step] The resulting bis(hydroxyalkyl) aromatic dicarboxylate is subjected to a polycondensation reaction by a conventional method to produce a recycled polyester polymer. The recycled polyester polymer obtained by the present invention is resistant to coloration and has excellent hue.

[0056] As a catalyst for repolymerization to obtain a recycled polyester polymer, known catalysts such as antimony, germanium or titanium catalysts can be used, and diantimony trioxide is preferably used.

[0057] 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 dicarboxylate bis(hydroxyalkyl).

[0058] After polycondensation, it is preferable to add a conventionally known phosphorus-based stabilizer such as orthophosphoric acid or phosphorous acid, and 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.

[0059] [Physical Properties of Recycled Polyester Polymer] The recycled polyester polymer obtained in this manner exhibits little discoloration, such as yellowing. This is thought to be because the polyester recovery method of the present invention is less likely to produce colored by-products, and the catalyst is more likely to dissociate from the aromatic dicarboxylate bis(hydroxyalkyl) in subsequent crystallization and other processes, making it less likely to remain as an impurity. This effect is particularly pronounced when depolymerization is performed using a low concentration of a manganese-based catalyst.

[0060] In the recycled polyester polymer obtained by the present invention, the acrylic fibers have been removed, and if the polyester fibers in the textile product are dyed, the dyes have also been removed.

[0061] The resulting recycled polyester polymer preferably exhibits the following properties: ＊ , a ＊ , b ＊ As the hue in the color space colorimeter, b ＊ The value is preferably 8 or less, more preferably 1 to −20, and particularly preferably 0.5 to −15.

[0062] The resulting recycled polyester polymer has a yellowness index (YI) of preferably 15 or less, more preferably 5 to -50, and even more preferably 0 to -20. The resulting recycled polyester polymer has a whiteness index (W) of preferably 75 or more, and even more preferably 80 to 100.

[0063] The nitrogen content of the resulting recycled polyester polymer derived from the acrylic fiber or dye is preferably 15 ppm or less, more preferably 10 ppm or less. The resulting recycled polyester polymer has an intrinsic viscosity (IV) 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.

[0064] The present invention will be described in more detail below with reference to the following examples. The values ​​in the examples were determined by the following methods: "% owf" is an abbreviation for "% on the weight of fiber."

[0065] 1) Hue (L ＊ a ＊ b ＊ , YI, W) A sample (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 to obtain a measurement sample. The measurement sample was measured for hue L according to JIS Z8781-4:2013 using a measurement device ("ZE-6000" manufactured by Nippon Denshoku Industries Co., Ltd.). ＊ , a ＊ , b ＊ The yellowness index (YI) was calculated using the following formula (1), and the whiteness index (W) was calculated using the following formula (2). Yellowness index (YI): 0.34-71.7×a ＊ / L ＊ +178.78 x b ＊ / L ＊ (1) Whiteness (W): 100-√{(100-L ＊ ) ２ +a ＊２ +b ＊２} (2) The higher the yellowness index (YI) value, the stronger the yellowness, and the higher the whiteness index (W) value, the stronger the whiteness.

[0066] 2) Nitrogen (N) content: Measured using a total nitrogen / protein analyzer (Nitto Seiko Analytech DTN-300V).

[0067] 3) Intrinsic Viscosity (IV) 0.12 g of a fiber (polymer) sample 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.

[0068] 4) Glass transition point (Tg) and melting point (Tm) were measured in accordance with ISO 11357-3 and ASTM D3418 using a differential scanning calorimeter (DSC) manufactured by Seiko Instruments Inc. In the measurement, the temperature was raised from room temperature to 350°C at a heating rate of 20°C / min to completely melt the polymer of the fiber, then the temperature was lowered to 50°C at a heating rate of 10°C / min, and further raised to 350°C at a heating rate of 20°C / min. The apex of the endothermic peak obtained when the temperature was raised to 350°C was taken as the melting point. The glass transition point was also taken as the temperature at the center of the endothermic curve that did not show a peak-shaped or valley-shaped endothermic peak like the melting point, but instead showed a shoulder-shaped step in the endothermic direction.

[0069] 5) Fineness, strength, elongation, and fiber length For long fibers, the fineness, strength, elongation, and fiber length were measured according to the methods described in JIS L 1015:2021 8.3 and 8.5, and for short fibers, the fineness, strength, elongation, and fiber length were measured according to the methods described in JIS L 1015:2021 8.4, 8.5, and 8.7.

[0070] [Example 1] (Polyester recovery process) As a textile product, a fabric consisting of 380 g of dyed polyethylene terephthalate (hereinafter referred to as "PET") fiber and 20 g of acrylic fiber (hereinafter sometimes referred to as "PAN") was prepared.

[0071] The PET fiber colored (dyed) with the dye was a long fiber having an IV of 0.60 dL / g, a Tg of 70°C, a Tm of 255°C, a fineness of 24 dtex, a strength of 3.9 cN / dtex, and an elongation of 41%, and was dyed using 0.87% owf of an azo orange dye, 0.4% owf of an azo red dye, and 4.7% owf of an azo black dye as disperse dyes, and contained 0.38 wt% of nitrogen (N).

[0072] The PAN fiber was manufactured by Nippon Exlan Kogyo Co., Ltd. and had a fineness of 0.9 dtex, a fiber length of 38 mm, a strength of 3.3 cN / dtex, an elongation of 34%, and a nitrogen (N) content of 24% by weight.

[0073] 400 g of this textile product was placed in a 5-liter separable flask, and 4,000 g of dimethyl sulfoxide (DMSO) that had been heated in a separate beaker until the internal temperature reached 105° C. was added to the separable flask. With the textile product immersed in dimethyl sulfoxide, the mixture was stirred for 30 minutes while adjusting the internal temperature to 105° C. (immersion treatment).

[0074] The textile was removed from the separable flask and squeezed to remove excess treatment liquid (a liquid in which the dye and acrylic fiber were dissolved in dimethyl sulfoxide). Coloration was observed in the treatment liquid, and the weight of the lightly decolorized textile after squeezing was 970 g.

[0075] After squeezing, the textile product was again placed in the separable flask, and the same immersion in dimethyl sulfoxide (DMSO) and squeezing treatment were alternately repeated six times. Visual observation showed that the textile product had turned white by the third immersion and squeezing treatment, but even after the fourth and subsequent treatments, the treatment liquid after squeezing was slightly colored, and it was only after the sixth treatment that the treatment liquid after squeezing finally became transparent.

[0076] The treated textile product was dried in a vacuum dryer at 80° C. for 8 hours, and polyester with high whiteness was recovered.

[0077] (Polyester Recycling Step) 300 parts by weight of the polyester recovered by the above method, 1500 parts by weight of ethylene glycol (EG), and 0.38 parts by weight (100 mmol% based on the polyester) of manganese acetate as a depolymerization catalyst were charged into a 2-liter separable flask and nitrogen was sealed in. At this time, the manganese acetate was dissolved in EG before charging.

[0078] Thereafter, the separable flask containing the sample was heated with a mantle heater to an internal temperature of 220°C, and depolymerization treatment was carried out for 4 hours at normal pressure while stirring. The BHET (bis(hydroxyethyl)benzenedicarboxylate) solution after this depolymerization was colorless and transparent, with no coloring observed.

[0079] The depolymerized solution was further filtered through a 200 μm mesh to remove any solids remaining inside. After gradual cooling to 70°C, the solution was cooled with stirring by lowering the temperature from 70°C to 40°C over a period of 0 to 10 minutes, from 40°C to 30°C over a period of 10 to 60 minutes, and from 30°C to 15°C over a period of 60 to 180 minutes. Thereafter, the solution was stirred for 60 minutes while maintaining the internal temperature at 15°C, and the internal temperature was lowered to precipitate BHET crystals (for a total of 4 hours), thereby obtaining a BHET / EG slurry.

[0080] 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 weight of EG based on the weight of the cake recovered from the filter press. After EG separation, the cake was washed with water using a Nutsche filter while spraying it with 25°C pure water in an amount twice its weight. The BHET after solid-liquid separation was then dried in a vacuum dryer at 50°C for 8 hours to obtain dried BHET. The resulting BHET was white and free of any visible foreign matter.

[0081] Thereafter, 254 parts by weight of the obtained dried BHET was placed in a reaction vessel under normal pressure and under a nitrogen atmosphere, together with 0.007 parts by weight of a phosphorus-based stabilizer and 0.07 parts by weight of diantimony trioxide as a repolymerization catalyst. Next, the temperature inside the reactor was set to 285°C, and the pressure was gradually reduced under the following conditions: normal pressure for 10 minutes, a pressure of 4 kPa for 10 minutes, and a pressure of 0.4 kPa for 40 minutes. While distilling off ethylene glycol and other substances generated during the reaction outside the reactor, a polycondensation reaction was carried out, yielding a recycled polyester polymer.

[0082] Before recovery (textile products), polyester recovered and dried, recycled polyester after repolymerization ＊ a ＊ b ＊ The physical properties such as the value and nitrogen content are shown in Table 1.

[0083] Example 2 The same procedure as in Example 1 was carried out, except that the temperature of the immersion treatment of the textile product in dimethyl sulfoxide (DMSO) was changed from 105°C to 130°C. The color of the treatment liquid after squeezing in the recovery step was darker than in Example 1, and a precipitate that appeared to be a dissolved PET was confirmed in the treatment liquid. The textile product itself was a polyester fabric with high whiteness. The physical properties of the textile product before recovery treatment, the polyester that had been dried after polyester recovery treatment, and the recycled polyester after repolymerization are shown in Table 1.

[0084] Example 3 The same procedure as in Example 1 was carried out, except that the temperature of the immersion treatment in dimethyl sulfoxide (DMSO) was changed from 105°C to 160°C. The weight of the recovered polyester was reduced, but the color of the residual liquid after squeezing in the recovery step was darker than in Example 1, and a precipitate that appeared to be a dissolved PET was confirmed in the residual liquid. The textile product itself was a polyester fabric with high whiteness. The physical properties of the textile product before recovery treatment, the polyester dried after polyester recovery treatment, and the recycled polyester after repolymerization are shown in Table 1.

[0085] [Example 4] Except for using an undyed white fabric, the same procedure as in Example 1 was carried out. Table 1 shows the physical properties of the recycled polyester before the recovery treatment (textile product), the polyester that had been recovered and dried, and the recycled polyester after repolymerization.

[0086]

[0087] Comparative Example 1 A recovery treatment was carried out in the same manner as in Example 1, except that the treatment temperature of dimethyl sulfoxide (DMSO) was changed from 105°C to 25°C. No coloration was observed in the textile product in the recovery step or in the residual liquid after squeezing. The physical properties of the polyester before the recovery treatment (textile product) and the polyester after the polyester recovery treatment and drying are shown in Table 2.

[0088] Comparative Example 2 A recovery process was carried out in the same manner as in Example 1, except that the treatment temperature of dimethyl sulfoxide (DMSO) was changed from 105°C to 180°C. During the treatment process at 180°C, the entire amount of the textile product containing PET was dissolved in DMSO, making it impossible to recover the product after the squeezing process. The physical properties of the textile product before the recovery process are shown in Table 2.

[0089] Comparative Example 3 A recovery treatment was carried out in the same manner as in Example 1, except that dimethyl sulfoxide (DMSO) was changed to benzyl alcohol (BA). It was confirmed that the PAN turned brown during the recovery process, and that most of the PAN solid content remained even after the sixth treatment. Table 2 shows the physical properties of the recycled polyester before the recovery treatment (textile product), the polyester that had been recovered and dried, and the recycled polyester after repolymerization.

[0090]

[0091] The recycled polyester polymer obtained by the present invention can be used as a raw material for textile products, as well as for films and resins, and contributes to reducing the environmental impact caused by waste incineration and dumping into oceans and rivers.

Claims

1. A method for recovering polyester from a textile product containing polyester fibers colored with dyes and acrylic fibers, comprising a solvent contacting step of contacting the textile product with an aprotic polar solvent at a temperature of 30 to 160°C, and an acrylic fiber and dye removing step of removing the solvent and the acrylic fibers and dye dissolved therein from the polyester fibers to obtain polyester.

2. The method for recovering polyester according to claim 1, wherein the aprotic polar solvent is at least one selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, and dimethylformamide.

3. A method for producing a recycled polyester polymer from a textile product containing polyester fibers colored with a dye and acrylic fibers, comprising a depolymerization step of depolymerizing the polyester recovered by the recovery method described in claim 1 in alkylene glycol to obtain a depolymerized reaction product, and a repolymerization step of polycondensing the depolymerized reaction product to obtain a polyester polymer.

4. The method for producing the recycled polyester polymer according to claim 3, further comprising a purification step of purifying the depolymerization reaction product after the depolymerization step and before the repolymerization step.

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