Method for pretreating blended fiber, depolymerization method comprising same, and method for producing terephthalic acid

Abstract

The present invention relates to a method for pretreating a blended fiber, a depolymerization method comprising same, and a method for producing terephthalic acid. Specifically, according to an embodiment of the present invention, by comprising a step of contacting a blended fiber, in which a polyester fiber and a polyurethane fiber are mixed, with an organic solvent, the amount of change (ΔCT) in the content of the polyurethane fiber included in the blended fiber according to specific expression 1 before and after the contact with the organic solvent is 0.7 or greater, and thus the polyurethane fiber in the pretreated blended fiber can be effectively removed, thereby improving the purity of the polyester fiber in the blended fiber.

Description

Method for pretreatment of blended fibers, and a depolymerization method including the same and a method for producing terephthalic acid

[0001] The present invention relates to a pretreatment method for blended fibers capable of effectively removing polyurethane fibers from waste blended fibers comprising polyester fibers and polyurethane fibers, a depolymerization method comprising the same, and a method for producing terephthalic acid.

[0002] Due to its excellent mechanical strength, heat resistance, transparency, and gas barrier properties, polyester is widely used as a material for beverage filling containers, packaging, audio or video films, as well as for industrial materials such as medical fibers and tire cords. In particular, polyester sheets and panels are used for cases, boxes, partitions, shelves, panels, packaging, construction materials, and interior and exterior finishing materials because of their good transparency and excellent mechanical strength.

[0003] As the annual global volume of polyester-based plastic waste reaches unmanageable levels, interest in recycling waste polyester or regeneration processes utilizing it is growing. Furthermore, countries around the world have recently been establishing regulations and measures regarding the recycling of waste plastic resources, including waste polyester. For instance, regulations are being discussed that require the use of recycled resins in packaging materials across various sectors at a certain percentage or higher.

[0004] For example, polyethylene terephthalate (PET) is widely used to manufacture a wide range of products such as films, fibers, bottles, and containers due to its excellent properties such as heat resistance, processability, transparency, and non-toxicity. However, most of it is landfilled or incinerated after use, so research on recycling or regeneration processes using it is ongoing.

[0005] Unlike films, bottles, and containers, fibers containing PET additionally include fibers such as polyurethane, cotton, nylon, polypropylene, polyethylene, and polystyrene to improve the physical properties of the fibers. In particular, since polyurethane fibers can be depolymerized together with PET during chemical recycling processes such as PET depolymerization, this can make the purification process of the depolymerized PET components difficult or generate oligomers such as carbamates and polyols, thereby lowering the purity of the PET. Furthermore, in the case of carbamates, there is a problem in that isocyanates, amines, and their secondary decomposition products may be generated when the PET depolymerization products are exposed to high temperatures of over 200°C during the distillation process. Moreover, these impurities can lead to quality issues, such as reduced purity of the recycled PET and deterioration of color characteristics. Accordingly, research is continuing on methods to effectively remove polyurethane fibers from blended fibers containing polyester fibers and polyurethane fibers.

[0006] [Prior Art Literature]

[0007] [Patent Literature]

[0008] (Patent Document 1) Korean Published Patent Application No. 2003-0041949

[0009] Accordingly, the present invention aims to provide a pretreatment method for a blended fiber capable of selectively removing polyurethane fibers from a blended fiber in which polyester fibers and polyurethane fibers are mixed, a depolymerization method comprising the same, and a method for producing terephthalic acid.

[0010] A pretreatment method for a blended fiber according to one embodiment of the present invention includes the step of contacting a blended fiber, in which polyester fiber and polyurethane fiber are mixed, with an organic solvent, and the change in the content of polyurethane fiber contained in the blended fiber according to Formula 1 below before and after contact with the organic solvent (ΔCT) is 0.7 or more.

[0011] [Equation 1] ΔCT = (CT1- CT2) / CT1

[0012] In the above Equation 1,

[0013] CT1 is the content of polyurethane fibers in the blended fibers before contacting the blended fibers with the organic solvent (unit: weight%), and CT2 is the content of polyurethane fibers in the blended fibers after contacting the blended fibers with the organic solvent (unit: weight%).

[0014] A method for depolymerizing a blended fiber according to another embodiment of the present invention comprises the step of depolymerizing a pretreated blended fiber by contacting a blended fiber, in which polyester fiber and polyurethane fiber are mixed, with an organic solvent, wherein the change in the content of polyurethane fiber contained in the blended fiber according to Formula 1 before and after contact with the organic solvent in the pretreatment of the blended fiber (ΔCT) is 0.7 or more.

[0015] A method for producing terephthalic acid according to another embodiment of the present invention comprises: (1) a step of pretreating a blended fiber by contacting a blended fiber, in which polyester fiber and polyurethane fiber are mixed, with an organic solvent; (2) a step of depolymerizing the pretreated blended fiber; and (3) a step of hydrolyzing the depolymerization reaction product obtained through the depolymerization, wherein the change in the content of polyurethane fiber contained in the blended fiber according to Formula 1 before and after contact with the organic solvent in the pretreatment step (ΔCT) is 0.7 or more.

[0016] Regenerated terephthalic acid according to another embodiment of the present invention is prepared according to the method for preparing terephthalic acid, and the color-b measured by a colorimeter is less than 2.

[0017] A polyester resin according to another embodiment of the present invention is prepared from a polymerization raw material containing the regenerated terephthalic acid.

[0018] A pretreatment method for a blended fiber according to one embodiment of the present invention includes the step of contacting a blended fiber, in which polyester fibers and polyurethane fibers are mixed, with an organic solvent. Since the change in the content of polyurethane fibers contained in the blended fiber according to a specific formula 1 before and after contact with the organic solvent (ΔCT) is controlled to be 0.7 or higher, the polyurethane fibers are effectively removed from the blended fiber, thereby improving the purity of the polyester fibers within the blended fiber.

[0019] The present invention will be described in detail below. The present invention is not limited to the contents disclosed below, but can be modified in various forms as long as the essence of the invention is not altered.

[0020] In this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0021] All numbers and expressions indicating the amounts of components, reaction conditions, etc. described in this specification should be understood as being modified by the term "about" in all cases unless otherwise specified.

[0022] In this specification, terms such as "first," "second," etc. are used to describe various components, and said components are not limited by said terms. These terms are used solely for the purpose of distinguishing one component from another.

[0023]

[0024] [Pretreatment Method for Blended Fibers]

[0025] A pretreatment method for a blended fiber according to one embodiment of the present invention includes the step of contacting a blended fiber, in which polyester fiber and polyurethane fiber are mixed, with an organic solvent, and the change in the content of polyurethane fiber contained in the blended fiber according to Formula 1 below before and after contact with the organic solvent (ΔCT) is 0.7 or more.

[0026] [Equation 1] ΔCT = (CT1- CT2) / CT1

[0027] In the above Equation 1,

[0028] CT1 is the content of polyurethane fibers (unit: weight%) in the blended fibers before contacting the blended fibers with the organic solvent (blended fibers before contact with the organic solvent), and CT2 is the content of polyurethane fibers (unit: weight%) in the blended fibers after contacting the blended fibers with the organic solvent (blended fibers after contact with the organic solvent).

[0029] For example, the change in the content of polyurethane fibers included in the blended fiber according to Formula 1 above (ΔCT) may be 0.7 or more, 0.8 or more, 0.9 or more, or 0.99 or more, and specifically, 0.7 to 1.0, 0.8 to 1.0, or 0.9 to 1.0. By satisfying the above range, the purity of the polyester fibers in the pretreated blended fiber can be improved, and thereby, when manufacturing terephthalic acid, the quality of the terephthalic acid can be improved.

[0030] Prior to the step of contacting with the organic solvent, the blended fiber may comprise 70% to 99% by weight of polyester fiber and 1% to 30% by weight of polyurethane fiber. For example, prior to the step of contacting with the organic solvent, the blended fiber may comprise 75% to 98% by weight, 80% to 97% by weight, or 85% to 95% by weight of polyester fiber, and 2% to 25% by weight, 3% to 20% by weight, or 5% to 15% by weight of polyurethane fiber.

[0031] The above organic solvent may have a boiling point of 80°C or higher. For example, the boiling point of the above organic solvent may be 85°C or higher, 100°C or higher, 150°C or higher, 180°C or higher, or 200°C or higher. Specifically, the above organic solvent may have a boiling point of 80°C to 230°C, 85°C to 210°C, 90°C to 200°C, or 95°C to 195°C.

[0032] The organic solvent may comprise a monoalcohol having 3 to 14 carbon atoms or 3 to 8 carbon atoms; or a diol selected from the group consisting of ethylene glycol, diethylene glycol, propanediol, and butanediol. Additionally, the organic solvent may comprise one or more selected from the group consisting of acetonitrile, 1,2-dichloroethane, methyl ethyl ketone, dioxane, ethyl acetate, and butyl acetate.

[0033] For example, the organic solvent may include one or more selected from the group consisting of monoalcohols having 3 to 5 carbon atoms, 1,2-dichloroethane, butyl acetate, and ethylene glycol. When the blended fiber is pretreated using the organic solvent, the depolymerization and hydrolysis processes described later can be easily performed, thereby simultaneously improving the yield and color characteristics (color-b) of the finally produced terephthalic acid.

[0034] The step of contacting with the organic solvent may be performed at 80°C to 160°C for 1 hour to 20 hours. For example, the step of contacting with the organic solvent may be performed at 85°C to 160°C, 90°C to 158°C, or 100°C to 155°C for 2 hours to 18 hours, 2.5 hours to 16 hours, 3 hours to 14 hours, or 4 hours to 12 hours.

[0035] When the organic solvent is contacted with the blended fibers at a temperature below the above range, it is difficult for the organic solvent to penetrate into the blended fibers, which limits the selective removal of polyurethane fibers; and when the organic solvent is contacted with the blended fibers at a temperature higher than the above range, there is a concern that the recovery rate of the polyester fibers will decrease as depolymerization of the polyester fibers occurs during the pretreatment process.

[0036] Additionally, the step of contacting the blended fiber with the organic solvent may be performed by immersing the blended fiber in the organic solvent or by refluxing the organic solvent. Refluxing may mean that the liquid organic solvent is heated to convert into a gaseous state, and then converted back into a liquid state by a cooling means to come into contact with the blended fiber.

[0037] In the step of contacting with the organic solvent, the organic solvent may be introduced in an amount of 5 to 100 times the weight of the blended fiber. For example, in the step of contacting with the organic solvent, the amount of the organic solvent introduced may be 10 to 80 times, 20 to 60 times, or 25 to 50 times the weight of the blended fiber.

[0038] After the step of contacting with the organic solvent, the blended fiber may comprise 98% to 100% by weight of polyester fiber and 0% to 2% by weight of polyurethane fiber. For example, after the step of contacting with the organic solvent, the blended fiber may comprise 98.5% to 100% by weight, 99% to 99.9% by weight, or 99.5% to 99.8% by weight of polyester fiber, and 0% to 1.5% by weight, 0.1% to 1% by weight, or 0.2% to 0.5% by weight of polyurethane fiber.

[0039] A pretreatment method for blended fibers according to one embodiment of the present invention may further include one or more steps selected from the group consisting of a filtration step, a washing step, and a drying step after the step of contacting with the organic solvent.

[0040] As a specific example, after the step of contacting with the organic solvent, a filtration step, a washing step, and a drying step may be performed sequentially.

[0041] The washing step described above may be performed using the organic solvent. As a specific example, the washing step may be performed using the same organic solvent as the organic solvent used in the step of contacting with the organic solvent.

[0042]

[0043] [Depolymerization Method of Blended Fibers]

[0044] A method for depolymerizing a blended fiber according to another embodiment of the present invention includes the step of depolymerizing a pretreated blended fiber by contacting a blended fiber, in which polyester fiber and polyurethane fiber are mixed, with an organic solvent, wherein the change in the content of polyurethane fiber contained in the blended fiber according to Formula 1 below before and after contact with the organic solvent in the pretreatment of the blended fiber (ΔCT) is 0.7 or more.

[0045] [Equation 1] ΔCT = (CT1- CT2) / CT1

[0046] In the above Equation 1,

[0047] CT1 is the content of polyurethane fibers in the blended fibers before contacting the blended fibers with the organic solvent (unit: weight%), and

[0048] CT2 is the content of polyurethane fibers in the blended fibers after contacting the blended fibers with the organic solvent (unit: weight%).

[0049] The description of the process for pre-treating the above-mentioned blended fibers is the same as previously stated.

[0050] The above depolymerization may be performed by introducing a depolymerization solvent comprising a monoalcohol having 3 to 14 carbon atoms; or a diol selected from the group consisting of ethylene glycol, diethylene glycol, propanediol, and butanediol, into the pretreated blended fiber.

[0051] The weight ratio of the pretreated blended fiber and the depolymerization solvent may be 1:1 to 10. For example, the weight ratio of the pretreated blended fiber and the depolymerization solvent may be 1:1 to 8, 1:1 to 6, 1:1 to 4, 1:1 to 3.5, 1:1.1 to 3.3, 1:2 to 4, or 1:2 to 3.5.

[0052] As a specific example, the depolymerization solvent may be the same as the organic solvent. Specifically, the depolymerization solvent used for the depolymerization may be the same as the organic solvent used in the pretreatment process of the blended fiber. Since the organic solvent and the depolymerization solvent are the same, depolymerization can be carried out immediately without undergoing a drying process even if some organic solvent remains in the blended fiber after pretreatment, and separate equipment for recovering the organic solvent is not required, thereby simplifying the process and providing a very advantageous effect in terms of investment costs.

[0053] The depolymerization reaction product obtained through the above depolymerization may include a compound represented by the following chemical formula 1.

[0054] [Chemical Formula 1]

[0055]

[0056] In the above chemical formula 1,

[0057] R1 is a linear or branched alkyl having 3 to 14 carbon atoms; or a hydroxyalkyl having 2 to 14 carbon atoms.

[0058] For example, the above compound may be dibutyl terephthalate, dipentyl terephthalate, dihexyl terephthalate, di(2-ethyl-1-hexyl) terephthalate, or bis(2-hydroxyethyl) terephthalate.

[0059] Meanwhile, the above depolymerization may include alcohololysis.

[0060] The above alcohol decomposition reaction can be carried out by introducing an alcohol decomposition catalyst into the pretreated blended fiber, thereby obtaining the above depolymerization reaction product.

[0061] The above-mentioned alcohol decomposition catalyst may be a metal acetate salt, an alkali metal salt, or a hydroxy salt.

[0062] Specifically, the above alcohol decomposition catalyst is Li + , Na + , K + or Cs + alkali metal ions, Be 2+ , Mg 2+ , Ca 2+ or Ba 2+ alkaline earth metal ions, NH4 + or NR4 + Ammonium ions of (R is alkyl), and Zn 2+ One or more cations selected from the group consisting of; and OH - , OR - (R is alkyl), HCO3- , CO3 2- , benzoate ion (C7H5O2 - It may include one or more anions selected from the group consisting of ), 4-alkoxycarbonylbenzoate ions, acetate ions, and terephthalate ions. R may be an alkyl having 1 to 10 carbon atoms or an alkyl having 1 to 5 carbon atoms.

[0063] For example, the above alcohol decomposition catalyst may include one or more selected from the group consisting of Zn(OAC)2, Co(OAc)2, Mn(OAc)2, Mg(OAc)2, Ca(OAc)2, Ba(OAc)2, LiOAc, NaOAc, KOAc, Zn(OAC)2·2H2O, Co(OAc)2·4H2O, Pb(OAc)2, Mn(OAc)2·4H2O, Mg(OAc)2·4H2O, Pd(OAc)2, Ti(OBu)4, Ti(OiPr)4, GeO2, Al(OiPr)3, Na2CO3, K2CO3, dibutyltin(IV) oxide, tin octosate, titanium phosphate, and terephthalic acid.

[0064] In addition, the amount of the alcohol decomposition catalyst added may be 10 ppm to 10,000 ppm relative to the total weight of the pretreated blended fiber. For example, the amount of the alcohol decomposition catalyst added may be 10 ppm to 9,000 ppm, 15 ppm to 8,000 ppm, 20 ppm to 6,000 ppm, 50 ppm to 3,500 ppm, 100 ppm to 1,500 ppm, 150 ppm to 1,000 ppm, 180 ppm to 500 ppm, or 200 ppm to 450 ppm relative to the total weight of the pretreated blended fiber.

[0065] The above alcohol decomposition reaction can be carried out for 0.5 to 24 hours at a temperature of 160°C to 280°C and a pressure of 1 bar to 40 bar. For example, the above alcohol decomposition reaction may be carried out at a temperature of 165°C to 280°C, 165°C to 270°C, 180°C to 270°C, 190°C to 250°C, 200°C to 265°C, 220°C to 265°C, 240°C to 260°C, or 245°C to 260°C, and at a pressure of 1 bar to 38 bar, 1 bar to 33 bar, 1 bar to 28 bar, 1 bar to 24 bar, 2 bar to 40 bar, 3 bar to 35 bar, or 5 bar to 30 bar for 0.5 hours to 22 hours, 1 hour to 15 hours, 1.5 hours to 10 hours, 2 hours to 8 hours, or 2 hours to 6 hours.

[0066] A method for depolymerizing a blended fiber according to another embodiment of the present invention may further include a step of purifying the depolymerization reaction product after the depolymerization step.

[0067] The purification step described above may include a step of adsorbing using one or more adsorbents selected from the group consisting of activated carbon, silica gel, alumina, zeolite, and activated clay, or adsorbing through bed adsorption. The adsorbent may be activated carbon or a mixture of activated carbon and silica gel. Specifically, the adsorbent may be a mixture of activated carbon and silica gel mixed in a weight ratio of 1:0.5 to 1.5 or 1:0.8 to 1.2.

[0068] The amount of the adsorbent added may be 0.1% to 20% by weight based on the total weight of the depolymerization reaction product. For example, the amount of the adsorbent added may be 0.1% to 18% by weight, 0.1% to 15% by weight, 0.1% to 10% by weight, 0.1% to 5% by weight, or 0.1% to 2% by weight based on the total weight of the depolymerization reaction product.

[0069] Purity and yield can be further improved by additionally performing a step of purifying the depolymerization reaction product using a specific adsorbent that satisfies the input amount of the above numerical range. Specifically, by performing the step of purifying the depolymerization reaction product with the specific adsorbent, insoluble impurities such as metals or additives such as coloring agents and pigments derived from waste polyester that may be contained in the depolymerization reaction product can be more effectively removed; thus, when manufacturing terephthalic acid, the purity and yield of terephthalic acid can be further improved.

[0070] A method for depolymerizing blended fibers according to another embodiment of the present invention may further include a concentration step after the purification step.

[0071] The above concentration may be performed at a temperature of 50°C to 120°C for 0.5 hours to 6 hours. For example, the above concentration may be performed by stirring the purified depolymerization reaction product at a temperature of 55°C to 115°C, 60°C to 110°C, 65°C to 105°C, or 75°C to 100°C for 1 hour to 5 hours, 1.5 hours to 4 hours, or 2 hours to 4 hours.

[0072] A method for depolymerizing blended fibers according to another embodiment of the present invention may further include a step of fractionally distilling the purified depolymerization reaction product after the purification step. For example, the fractional distillation may be performed under vacuum and at a temperature of 150°C to 300°C, 180°C to 270°C, 200°C to 250°C, or 220°C to 240°C.

[0073] The purified depolymerization reaction product may have a low content of insoluble impurities such as metals. Specifically, the total content of metals measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) in the purified depolymerization reaction product may be less than 100 ppm relative to the total weight of the purified depolymerization reaction product.

[0074] For example, the total content of metals measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) in the purified depolymerization reaction product may be 80 ppm or less, 70 ppm or less, 60 ppm or less, 50 ppm or less, 40 ppm or less, or less than 30 ppm relative to the total weight of the purified depolymerization reaction product. In particular, the total content of Sb, Ti, and Zn in the purified depolymerization reaction product may be less than 30 ppm, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, 5 ppm or less, 3 ppm or less, or 1 ppm or less.

[0075] The aforementioned Sb is known as a widely used catalyst in general polyester polymerization due to its excellent stability, reaction rate, and cost-effectiveness; however, as regulations regarding Sb are becoming stricter due to its impact on the human body and the environment, it is a substance that must be removed during the chemical regeneration process.

[0076] The above Ti is used as a polyester polymerization catalyst or as an additive in the polyester processing process in the form of TiO2; however, if it is contained in an amount exceeding a certain limit, it can degrade the quality of recycled terephthalic acid produced therefrom or polyester resins made using it, thereby limiting its applications.

[0077] The aforementioned Zn is also used as a polyester polymerization catalyst; however, since its residue can affect the control of reactivity in the manufacturing process of recycled terephthalic acid or polyester resins using it, it is desirable to remove it.

[0078] According to the present invention, by further performing the purification, the total content of metals, particularly Sb, Ti, and Zn as described above, in the purified depolymerization reaction product is very low, less than 30 ppm.

[0079] For example, the content of Sb measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) in the purified depolymerization reaction product may be less than 30 ppm, 20 ppm or less, 10 ppm or less, or 1 ppm or less relative to the total weight of the purified depolymerization reaction product.

[0080] In addition, the content of Ti measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) in the purified depolymerization reaction product may be less than 30 ppm, 20 ppm or less, 10 ppm or less, or 1 ppm or less relative to the total weight of the purified depolymerization reaction product.

[0081] In addition, the content of Zn measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) in the purified depolymerization reaction product may be less than 30 ppm, 20 ppm or less, 10 ppm or less, or 1 ppm or less relative to the total weight of the purified depolymerization reaction product.

[0082]

[0083] [Method for manufacturing terephthalic acid]

[0084] A method for producing terephthalic acid according to another embodiment of the present invention comprises: (1) a step of pretreating a blended fiber, in which polyester fiber and polyurethane fiber are mixed, by contacting the blended fiber with an organic solvent; (2) a step of depolymerizing the pretreated blended fiber; and (3) a step of hydrolyzing the depolymerization reaction product obtained through the depolymerization, wherein the change in the content of polyurethane fiber contained in the blended fiber according to Formula 1 below before and after contact with the organic solvent in the pretreatment step (ΔCT) is 0.7 or more.

[0085] [Equation 1] ΔCT = (CT1- CT2) / CT1

[0086] In the above Equation 1,

[0087] CT1 is the content of polyurethane fibers in the blended fibers before contacting the blended fibers with the organic solvent (unit: weight%), and

[0088] CT2 is the content of polyurethane fibers in the blended fibers after contacting the blended fibers with the organic solvent (unit: weight%).

[0089] Step (1): Preprocessing step

[0090] The description of the above preprocessing step (1) is the same as previously described.

[0091] Step (2): Depolymerization step

[0092] The description of the above depolymerization step (2) is the same as previously described.

[0093] Step (3): Hydrolysis step

[0094] The hydrolysis step may be performed by adding water to the depolymerization reaction product. For example, the hydrolysis reaction may be performed by adding water to the depolymerization reaction product and at a temperature of 180°C to 280°C, 185°C to 280°C, 200°C to 275°C, 220°C to 270°C, or 240°C to 265°C for 0.5 to 24 hours, 1 to 20 hours, 2.5 to 12 hours, or 3 to 8 hours.

[0095] The above water may be added in an amount of 1 to 500 times the weight of the depolymerization reaction product. For example, in the hydrolysis step, the amount of water added may be 1 to 500 times, 1 to 450 times, 1 to 400 times, 1 to 250 times, 1 to 100 times, 1 to 50 times, 1.2 to 20 times, or 1.5 to 10 times the weight of the depolymerization reaction product.

[0096] In addition, a hydrolysis catalyst may be introduced in the above hydrolysis step. Specifically, hydrolysis may be performed by introducing a hydrolysis catalyst into a mixture of the depolymerization reaction product and water.

[0097] The above-mentioned hydrolysis catalyst may be a metal acetate salt, an alkali metal salt, or a hydroxy salt.

[0098] Specifically, the hydrolysis catalyst is Li + , Na + , K + or Cs + alkali metal ions, Be 2+ , Mg 2+ , Ca 2+ or Ba 2+ alkaline earth metal ions, NH4 + or NR4 + Ammonium ions of (R is alkyl), and Zn 2+ One or more cations selected from the group consisting of; and OH -, OR - (R is alkyl), HCO3 - , CO3 2- , benzoate ion (C7H5O2 - It may include one or more anions selected from the group consisting of ), 4-alkoxycarbonylbenzoate ions, acetate ions, and terephthalate ions. R may be an alkyl having 1 to 10 carbon atoms or an alkyl having 1 to 5 carbon atoms.

[0099] For example, the hydrolysis catalyst may include one or more selected from the group consisting of Zn(OAC)2, Co(OAc)2, Mn(OAc)2, Mg(OAc)2, Ca(OAc)2, Ba(OAc)2, LiOAc, NaOAc, KOAc, Zn(OAC)2·2H2O, Co(OAc)2·4H2O, Pb(OAc)2, Mn(OAc)2·4H2O, Mg(OAc)2·4H2O, Pd(OAc)2, Ti(OBu)4, Ti(OiPr)4, GeO2, Al(OiPr)3, Na2CO3, K2CO3, dibutyltin(IV) oxide, tin octosate, titanium phosphate, and terephthalic acid.

[0100] The amount of the hydrolysis catalyst added may be 10 ppm to 10,000 ppm relative to the total weight of the depolymerization reaction product. For example, the amount of the hydrolysis catalyst added may be 15 ppm to 8,000 ppm, 20 ppm to 5,500 ppm, 30 ppm to 3,000 ppm, 50 ppm to 1,600 ppm, 100 ppm to 1,200 ppm, 150 ppm to 1,100 ppm, 300 ppm to 1,000 ppm, 350 ppm to 950 ppm, 400 ppm to 850 ppm, 420 ppm to 700 ppm, or 450 ppm to 650 ppm relative to the total weight of the depolymerization reaction product.

[0101] According to the present invention, terephthalic acid can be produced through the hydrolysis step. Specifically, solid terephthalic acid can be produced by additionally undergoing the steps of filtration, washing, and drying the hydrolysis reaction product obtained through the hydrolysis step (reaction).

[0102] More specifically, the hydrolysis reaction product can be cooled to an appropriate temperature, such as room temperature to less than 100°C, to obtain a solution in the form of a slurry, and the solid obtained by filtering can be washed and then vacuum dried to obtain solid terephthalic acid.

[0103] Through the above washing, residual pigments or yellow impurities generated from pigment decomposition during hydrolysis can be effectively removed, thereby improving the yellowness or color characteristics of terephthalic acid. In addition, by using water for the washing, inorganic salts can be removed, thus improving the quality of terephthalic acid.

[0104]

[0105] [Regenerated Terephthalic Acid]

[0106] Regenerated terephthalic acid according to another embodiment of the present invention is produced according to the method for producing terephthalic acid described above, and the color-b measured by a colorimeter is less than 2.

[0107] Specifically, the regenerated terephthalic acid may have a color-b value of 1.6 or less, 1.4 or less, 1.3 or less, or 1 or less as measured by a colorimeter. Since the numerical range of color-b is equivalent to that of general new terephthalic acid produced in a petrochemical process, the color-b of the regenerated terephthalic acid satisfies the above range, resulting in low yellowness and good purification, thus the quality of the regenerated terephthalic acid is excellent.

[0108] The above color-b is a color system established by the International Commission on Color Measurement (CIE (Commission International d'Eclairage)), expresses color by denoted as L (lightness), a (complementary color from green to red), and b (complementary color from yellow to blue), and can be measured using a colorimeter.

[0109] The regenerated terephthalic acid may have a total metal content of less than 100 ppm as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). For example, the regenerated terephthalic acid may have a total metal content of 90 ppm or less, 80 ppm or less, 65 ppm or less, 50 ppm or less, 35 ppm or less, less than 30 ppm, 15 ppm or less, 9 ppm or less, 7 ppm or less, 5 ppm or less, or 1 ppm or less.

[0110] In addition, the regenerated terephthalic acid may have a total content of Sb, Ti, and Zn measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) of less than 30 ppm. For example, the regenerated terephthalic acid may have a total content of Sb, Ti, and Zn that is harmful to the human body or potentially used as a reaction or by-reaction catalyst in future polymerization processes of 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, 5 ppm or less, 3 ppm or less, or 1 ppm or less.

[0111] Specifically, the content of Sb measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) in the regenerated terephthalic acid may be less than 30 ppm, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, 5 ppm or less, 3 ppm or less, or 1 ppm or less relative to the total weight of the regenerated terephthalic acid.

[0112] In addition, the content of Ti measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) in the regenerated terephthalic acid may be less than 30 ppm, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, 5 ppm or less, 3 ppm or less, or 1 ppm or less relative to the total weight of the regenerated terephthalic acid.

[0113] In addition, the content of Zn measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) in the regenerated terephthalic acid may be less than 30 ppm, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, 5 ppm or less, 3 ppm or less, or 1 ppm or less relative to the total weight of the regenerated terephthalic acid.

[0114]

[0115] [Polyester resin and method of manufacturing the same]

[0116] A polyester resin according to another embodiment of the present invention is prepared from a polymerization raw material containing the regenerated terephthalic acid.

[0117] Specifically, the polyester resin can be obtained through a polymerization reaction of a polymerization raw material comprising the regenerated terephthalic acid, a diol compound or a derivative thereof, and optionally a dicarboxylic acid compound or a derivative thereof.

[0118] The above diol compound or derivative thereof may include one or more selected from the group consisting of ethylene glycol, diethylene glycol, 1,4-butanediol, 1,3-propanediol, 1,4-cyclohexanedimethanol, isosorbide, and neopentyl glycol, and the above dicarboxylic acid compound or derivative thereof may include one or more selected from the group consisting of terephthalic acid (TPA), isophthalic acid (IPA), 2,6-naphthalenedicarboxylic acid (2,6-NDA), dimethyl terephthalate (DMT), dimethylisophthalic acid (DMI), and 2,6-dimethylnaphthalenedicarboxylic acid (2,6-NDC).

[0119] A method for manufacturing a polyester resin according to another embodiment of the present invention comprises the steps of: esterifying a polymerization raw material containing the regenerated terephthalic acid; and polycondensing the esterification reaction product obtained through the esterification reaction.

[0120] The above esterification reaction may be carried out at a temperature of 200°C to 350°C, 220°C to 320°C, or 250°C to 290°C. Additionally, the above esterification reaction is carried out at 0 kg / cm² relative to atmospheric pressure. 2 Up to 10 kg / cm² 2 (0 mmHg to 7355.6 mmHg), 0 kg / cm² 2 Up to 5 kg / cm² 2 (0 mmHg to 3677.8 mmHg) or 0 kg / cm² 2 Up to 2.0 kg / cm² 2 It can be performed under high pressure conditions of (0 mmHg to 1471.1 mmHg). Additionally, the esterification reaction can be performed for 1 hour to 24 hours, 1 hour to 10 hours, or 1 hour to 6 hours.

[0121] The above polycondensation reaction may be carried out at a temperature of 150°C to 400°C, 200°C to 370°C, 250°C to 350°C, or 270°C to 300°C. Additionally, the above polycondensation reaction may be carried out under reduced pressure conditions of 0.01 mmHg to 400 mmHg, 0.05 mmHg to 100 mmHg, or 0.1 mmHg to 100 mmHg. Furthermore, the above polycondensation reaction may be carried out for the time required to reach a desired intrinsic viscosity, for example, for 1 hour to 24 hours, 1 hour to 10 hours, or 1 hour to 4 hours.

[0122] Meanwhile, a catalyst and / or stabilizer may be additionally added to the above esterification reaction and the above polycondensation reaction.

[0123] The above catalyst may be a methylate of sodium or magnesium; an acetate, borate, fatty acid salt, or carbonate of Zn, Cd, Mn, Co, Ca, Ba, etc.; or an oxide or hydrate of Mg, Pb, Mn, Ti, Si, Sb, Sn, Al, etc. For example, the above catalyst may be tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, triethanolamine titanate, ethyl acetoacetic ester titanate, isostearyl titanate, titanium dioxide, germanium dioxide, germanium tetrachloride, germanium ethylene glycoside, germanium acetate, or a combination thereof.

[0124] Phosphorus-based compounds such as phosphoric acid, trimethyl phosphate, and triethyl phosphate may be used as the above stabilizer.

[0125] A method for manufacturing a polyester resin according to another embodiment of the present invention may further include a step of solid-state polymerization. For example, the solid-state polymerization may be performed after the step of polycondensation. The solid-state polymerization may be performed at a temperature of 190°C to 230°C, under pressure conditions of 0.2 torr to 2.0 torr, or under a nitrogen atmosphere.

[0126] The above contents will be explained in more detail by the following examples. However, the following examples are merely for illustrating the present invention, and the scope of the examples is not limited to these.

[0127]

[0128] [Example]

[0129] Pretreatment of Blended Fibers

[0130] Example 1-1

[0131] 30 g of waste blended fiber (polyethylene terephthalate (PET) fabric containing 5 wt% polyurethane (PU)) cut to a size of 1 cm by 1 cm was added to a 2 L flask, along with 900 mL of 1,2-dichloroethane as an organic solvent. The mixture was stirred under reflux at 84°C for 12 hours, then cooled to room temperature, filtered using a 0.45 µm PTFE membrane filter (Aldrich Zap-cap), and washed with 1,2-dichloroethane. Subsequently, it was dried in a vacuum oven at 80°C for 8 hours.

[0132]

[0133] Examples 1-2

[0134] The blended fiber was pretreated in the same manner as in Example 1-1, except that butyl acetate was used instead of 1,2-dichloroethane and the fiber was pretreated under reflux at 126°C.

[0135]

[0136] Examples 1-3

[0137] The blended fiber was pretreated in the same manner as in Example 1-1 above, except that 1-butanol was used instead of 1,2-dichloroethane and the fiber was pretreated under reflux at 118°C.

[0138]

[0139] Examples 1-4

[0140] The blended fibers were pretreated in the same manner as in Examples 1-3 above, except that the pretreatment was performed for 8 hours.

[0141]

[0142] Examples 1-5

[0143] The blended fibers were pretreated in the same manner as in Examples 1-3 above, except that the pretreatment was performed for 4 hours.

[0144]

[0145] Examples 1-6

[0146] The blended fibers were pretreated in the same manner as in Examples 1-3 above, except that 300 ml of 1-butanol was used.

[0147]

[0148] Examples 1-7

[0149] The blended fiber was pretreated in the same manner as in Examples 1-3, except that 30 g of waste blended fiber (polyethylene terephthalate (PET) fabric containing 20 wt% polyurethane (PU)) cut into a size of 1 cm in width and 1 cm in length was used.

[0150]

[0151] Examples 1-8

[0152] The blended fiber was pretreated in the same manner as in Examples 1-3, except that 30 g of waste blended fiber (polyethylene terephthalate (PET) fabric containing 30 wt% polyurethane (PU)) cut into a size of 1 cm in width and 1 cm in length was used.

[0153]

[0154] Examples 1-9

[0155] 30 g of waste blended fiber (polyethylene terephthalate (PET) fabric containing 5 wt% polyurethane (PU)) cut to a size of 1 cm by 1 cm was added to a 2 L flask, along with 900 mL of 1-hexanol as an organic solvent. After stirring in an immersion state at 150°C for 12 hours, the mixture was cooled to room temperature, filtered using a 0.45 µm PTFE membrane filter (Aldrich Zap-cap), and then washed with 1-hexanol. Subsequently, it was dried in a vacuum oven at 130°C for 8 hours.

[0156]

[0157] Examples 1-10

[0158] The blended fibers were pretreated in the same manner as in Examples 1-9 above, except that 2-ethyl-1-hexanol was used instead of 1-hexanol.

[0159]

[0160] Example 1-11

[0161] The blended fibers were pretreated in the same manner as in Examples 1-9 above, except that ethylene glycol was used instead of 1-hexanol.

[0162]

[0163] Comparative Example 1-1

[0164] The blended fiber was pretreated in the same manner as in Example 1-1 above, except that methanol was used instead of 1,2-dichloroethane and the pretreatment was performed under reflux at 65°C.

[0165]

[0166] Comparative Example 1-2

[0167] The blended fiber was pretreated in the same manner as in Example 1-1 above, except that acetone was used instead of 1,2-dichloroethane and the pretreatment was performed under reflux at 50°C.

[0168]

[0169] Comparative Examples 1-3

[0170] The blended fiber was pretreated in the same manner as in Example 1-1 above, except that dichloromethane was used instead of 1,2-dichloroethane and the fiber was pretreated under reflux at 40°C.

[0171]

[0172] Comparative Examples 1-4

[0173] 30 g of waste blended fiber (polyethylene terephthalate (PET) fabric containing 5 wt% polyurethane (PU)) cut to a size of 1 cm by 1 cm was added to a 2 L flask, along with 900 mL of 2-ethyl-1-hexanol as an organic solvent. After stirring in an immersion state at 190°C for 12 hours, the mixture was cooled to room temperature, filtered using a 0.45 μm PTFE membrane filter (Aldrich Zap-cap), and then washed with 2-ethyl-1-hexanol. Subsequently, it was dried in a vacuum oven at 130°C for 8 hours.

[0174]

[0175] Comparative Examples 1-5

[0176] The blended fibers were pretreated in the same manner as Comparative Examples 1-4, except that ethylene glycol was used instead of 2-ethyl-1-hexanol.

[0177]

[0178] Comparative Examples 1-6

[0179] The blended fibers were pretreated in the same manner as in Examples 1-3 above, except that they were pretreated under reflux conditions at 60℃.

[0180]

[0181] Experimental Example 1: PET and PU content in blended fibers

[0182] For the blended fibers pretreated in Examples 1-1 to 1-11 and Comparative Examples 1-1 to 1-5, the content of PET and PU in the blended fibers before and after pretreatment was measured. Specifically, the weight of the blended fibers before and after pretreatment was measured, and the content of PET and PU in the fibers was analyzed using NMR (JEOL, OXFORD 600). Subsequently, the change in the content of polyurethane fibers (ΔCT) according to Equation 1 below was calculated, and the results are shown in Table 1 below.

[0183] [Equation 1] ΔCT = (CT1- CT2) / CT1

[0184] In Formula 1 above,

[0185] CT1 is the content (unit: wt%) of the polyurethane fiber in the blended fiber before contacting the blended fiber with the organic solvent, and CT2 is the content (unit: wt%) of the polyurethane fiber in the blended fiber after contacting the blended fiber with the organic solvent.

[0186]

[0187] Before Separation PretreatmentAfter PretreatmentFormula 1Content of PET (wt%)Content of PU (wt%)Recovery Rate (wt%)Content of PET (wt%)Content of PU (wt%)Example 1-195.05.096.099.01.00.80Example 1-295.05.095.499.60.40.92Example 1-395.05.095.299.80.20.96Example 1-495.05.095.999.10.90.82Example 1-595.05.095.899.20.80.84Example 1-695.05.095.899.20.80.84Example 1-780.020.081.698.41.60.92Example 1-870.030.071.898.21.80.94Example 1-995.05.095.199.90.10.98Example 1-1095.05.095.010001Example 1-1195.05.095.010001Comparative Example 1-195.05.010095.05.00Comparative Example 1-295.05.010095.05.00Comparative Example 1-395.05.010095.05.00Comparative Example 1-495.05.0<2010001>Comparative Example 1-595.05.0<2010001>Comparative Example 1-695.05.099.795.34.70.06* Recovery Rate = (Weight (g) of the dried fiber after pretreatment / Weight (g) of the blended fiber before pretreatment) × 100

[0188] Referring to Table 1 above, it was confirmed that the waste blended fibers of Examples 1-1 to 1-11, pretreated according to the present invention, had PU effectively removed, resulting in high PET purity and recovery rates. On the other hand, in Comparative Examples 1-1 to 1-3, there was almost no PU removal effect, and in Comparative Examples 1-4 and 1-5, although there was a PU removal effect due to the high pretreatment temperature (contact temperature), depolymerization of PET also occurred simultaneously, resulting in a very low PET recovery rate. In the case of Comparative Example 1-6, even though 1-butanol was used as the organic solvent in the same way as in Example 1-3, the PU removal effect was negligible due to the low pretreatment temperature.

[0189] Sea merger

[0190] Example 2-1

[0191] 1.00 kg of waste blended fibers pretreated in Example 1-1 and 3.24 kg of 1-butanol were introduced into a first high-pressure reactor with a capacity of 7 L, and 200 mg of Zn(OAC)2·2H2O (200 ppm relative to the total weight of the waste blended fibers) was added as a hydroxylaseation catalyst.

[0192] Subsequently, all connections of the first high-pressure reactor were tightened to maintain a seal, and the temperature was raised to 250°C over a period of 1 hour. The alcohololysis reaction was carried out by stirring for 4 hours while maintaining the temperature at 250°C, and after the alcohololysis reaction was completed, it was cooled to room temperature. Afterward, the product of the alcohololysis reaction was filtered using a Buchner funnel, and the excess 1-butanol was concentrated and fractionally distilled to obtain 1.17 kg of liquid dibutyl terephthalate as a compound of Formula 1.

[0193]

[0194] Examples 2-2 to 2-8

[0195] Depolymerization was carried out in the same manner as in Example 2-1, except that the waste blended fibers pretreated in Examples 1-2 to 1-8 were used instead of the waste blended fibers pretreated in Example 1-1.

[0196]

[0197] Examples 2-9

[0198] 1.00 kg of waste blended fibers pretreated in Examples 1-9 and 3.26 kg of 1-hexanol were introduced into a first high-pressure reactor with a capacity of 7 L, and 200 mg of Zn(OAC)2·2H2O (200 ppm relative to the total weight of the waste blended fibers) was added as a hydroxylaseation catalyst.

[0199] Subsequently, all connections of the first high-pressure reactor were tightened to maintain a seal, and the temperature was raised to 250°C over a period of 1 hour. The alcohololysis reaction was carried out by stirring for 4 hours while maintaining the temperature at 250°C, and after the alcohololysis reaction was completed, it was cooled to room temperature. Afterward, the product of the alcohololysis reaction was filtered using a Buchner funnel, and the excess 1-hexanol was concentrated and fractionally distilled to obtain 1.36 kg of liquid dihexyl terephthalate as a compound of Formula 1.

[0200]

[0201] Example 2-10

[0202] 1.00 kg of waste blended fibers pretreated in Examples 1-10 and 3.33 kg of 2-ethyl-1-hexanol were introduced into a first high-pressure reactor with a capacity of 7 L, and 200 mg of Zn(OAC)2·2H2O (200 ppm relative to the total weight of the waste blended fibers) was added as a hydroxylase catalyst.

[0203] Subsequently, all connections of the first high-pressure reactor were tightened to maintain a seal, and the temperature was raised to 250°C over a period of 1 hour. The alcohololysis reaction was carried out by stirring for 4 hours while maintaining the temperature at 250°C, and after the alcohololysis reaction was completed, it was cooled to room temperature. Afterward, the product of the alcohololysis reaction was filtered using a Buchner funnel, and the excess 2-ethyl-1-hexanol was concentrated and fractionally distilled to obtain 1.48 kg of liquid di(2-ethyl-1-hexyl)terephthalate as a compound of Formula 1.

[0204]

[0205] Example 2-11

[0206] 1.00 kg of waste blended fibers pretreated in Examples 1-11 and 4.44 kg of ethylene glycol were introduced into a first high-pressure reactor with a capacity of 7 L, and 200 mg of Zn(OAC)2·2H2O (200 ppm relative to the total weight of the waste blended fibers) was added as a hydroxylaseation catalyst.

[0207] Subsequently, all connections of the first high-pressure reactor were tightened to maintain a seal, and the temperature was raised to 200°C over a period of 1 hour. The alcohololysis reaction was carried out by stirring for 4 hours while maintaining the temperature at 200°C, and after the alcohololysis reaction was completed, it was cooled to 80°C. Afterward, the product of the alcohololysis reaction was filtered using a Buchner funnel, and the excess ethylene glycol was concentrated and recrystallized to obtain 0.99 kg of solid bis(2-hydroxyethyl)terephthalate as a compound of Formula 1.

[0208]

[0209] Comparative Examples 2-1 to 2-3

[0210] Depolymerization was carried out in the same manner as in Example 2-1, except that waste blended fibers pretreated in Comparative Examples 1-1 to 1-3 were used instead of waste blended fibers pretreated in Example 1-1.

[0211]

[0212] Experimental Example 2: Yield and Purity of Depolymerization Reaction Product

[0213] The purity of each depolymerization reaction product (compound of Formula 1) obtained in Examples 2-1 to 2-11 and Comparative Examples 2-1 to 2-3 was analyzed using conventionally known high-performance liquid chromatography (HPLC). In addition, the yield of the depolymerization reaction product was calculated according to the following formula, and the results are shown in Table 2 below.

[0214] Yield (%) = (Number of moles of compound of Formula 1 obtained / Number of moles of PET in blended fibers added after pretreatment) × 100

[0215]

[0216] Classification Depolymerization Solvent Alcohol Decomposition Reaction Conditions Yield (%) Purity (%) of Purified Depolymerization Reaction Product Example 2-11-Butanol 250℃ / 4h 81.199.5 Example 2-21-Butanol 250℃ / 4h 80.899.2 Example 2-31-Butanol 250℃ / 4h 83.399.0 Example 2-41-Butanol 250℃ / 4h 82.599.3 Example 2-51-Butanol 250℃ / 4h 82.199.1 Example 2-61-Butanol 250℃ / 4h 83.899.0 Example 2-71-Butanol 250℃ / 4h 83.999.4 Example 2-81-Butanol 250℃ / 4h 81.498.9 Example 2-91-Hexanol 250℃ / 4h 85.199.0 Example 2-102-Ethyl-1-Hexanol 250℃ / 4h 83.299.4 Example 2-11-Ethylene Glycol 200℃ / 4h 85.298.8 Comparative Example 2-11-Butanol 250℃ / 4h 79.495.5 Comparative Example 2-21-Butanol 250℃ / 4h 83.895.9 Comparative Example 2-31-Butanol 250℃ / 4h 80.496.2

[0217] Referring to Table 2 above, it was confirmed that the waste blended fibers of Examples 2-1 to 2-11, pretreated according to the present invention, had PU effectively removed and the purity of the depolymerization reaction product was high at 98.5% or higher, whereas the waste blended fibers of Comparative Examples 2-1 to 2-3 had PU components remaining even after pretreatment, so the purity of the depolymerization reaction product was relatively low.

[0218] Hydrolysis

[0219] Example 3-1

[0220] 100 g of the depolymerization reaction product prepared in Example 2-1 and 400 g of water were introduced into a second high-pressure reactor with a capacity of 1 L, and 50 mg of Zn(OAC)2·2H2O (500 ppm relative to the total weight of the depolymerization reaction product) was added as a hydrolysis catalyst.

[0221] Subsequently, all connections of the second high-pressure reactor were closed to maintain a seal, and the temperature was raised to 230°C. The hydrolysis reaction was carried out for 5 hours while maintaining the temperature at 230°C, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. The solid obtained by filtering the hydrolysis reaction product was washed with 1-butanol at 90°C and water at 90°C and vacuum dried to obtain 54.3 g of solid regenerated terephthalic acid (r-TPA).

[0222]

[0223] Examples 3-2 to 3-11 and Comparative Examples 3-1 to 3-3

[0224] Hydrolysis was carried out in the same manner as in Example 3-1, except that the depolymerization reaction products prepared in Examples 2-2 to 2-11 and Comparative Examples 2-1 to 2-3 were used.

[0225]

[0226] Experimental Example 3: Hydrolysis reaction product yield and Color b

[0227] The Color b values ​​of each hydrolysis reaction product obtained in Examples 3-1 to 3-11 and Comparative Examples 3-1 to 3-3 were measured using a Colorimeter CM-3600A (Manufacturer: Konica Minolta). In addition, the yield of the hydrolysis reaction product (r-TPA) was calculated according to the following formula, and the results are shown in Table 3 below.

[0228] Yield (%) = (Number of moles of obtained r-TPA / Number of moles of compound of Formula 1 added) × 100

[0229] Classification Hydrolysis Reaction Conditions Yield of r-TPA (%) Color b Example 3-1 230℃ / 5h 911.5 Example 3-2 230℃ / 5h 891.7 Example 3-3 230℃ / 5h 921.5 Example 3-4 230℃ / 5h 881.4 Example 3-5 230℃ / 5h 911.7 Example 3-6 230℃ / 5h 881.6 Example 3-7 230℃ / 5h 901.6 Example 3-8 230℃ / 5h 891.5 Example 3-9 200℃ / 5h 821.3 Example 3-10 230℃ / 5h 811.5 Example 3-11 200℃ / 5h 921.3 Comparative Example 3-1230℃ / 5h 9125.3 Comparative Example 3-2230℃ / 5h 8931.6 Comparative Example 3-3230℃ / 5h 8829.9

[0230] Referring to Table 3 above, in Examples 3-1 to 3-11 to which the depolymerization reaction products of Examples 2-1 to 2-11 pretreated according to the present invention were applied, a hydrolysis reaction product (r-TPA) with a color b value of less than 2 was obtained, whereas in Comparative Examples 3-1 to 3-3 to which the depolymerization reaction products of Comparative Examples 2-1 to 2-3 with low purity were applied, the color b value of the hydrolysis reaction product (r-TPA) was very high, and it was confirmed that the color was significantly reduced.

Claims

1. A step comprising contacting a blended fiber, in which polyester fibers and polyurethane fibers are mixed, with an organic solvent, and A pretreatment method for a blended fiber, wherein the change in the content of polyurethane fibers contained in the blended fiber according to Formula 1 below before and after contact with the organic solvent (ΔCT) is 0.7 or more: [Equation 1] ΔCT = (CT1- CT2) / CT1 In the above Equation 1, CT1 is the content of polyurethane fibers in the blended fibers before contacting the blended fibers with the organic solvent (unit: weight%), and CT2 is the content of polyurethane fibers in the blended fibers after contacting the blended fibers with the organic solvent (unit: weight%).

2. In Paragraph 1, The above organic solvent is a pretreatment method for blended fibers having a boiling point of 80°C or higher.

3. In Paragraph 1, A method for pretreating blended fibers, wherein the organic solvent comprises a monoalcohol having 3 to 14 carbon atoms; or a diol selected from the group consisting of ethylene glycol, diethylene glycol, propanediol, and butanediol.

4. In Paragraph 1, A method for pretreating blended fibers, wherein the organic solvent comprises one or more selected from the group consisting of acetonitrile, 1,2-dichloroethane, methyl ethyl ketone, dioxane, ethyl acetate, and butyl acetate.

5. In Paragraph 1, Prior to the step of contacting the above organic solvent, A method for pretreating a blended fiber, wherein the blended fiber comprises 70% to 99% by weight of polyester fiber and 1% to 30% by weight of polyurethane fiber.

6. In Paragraph 1, After the step of contacting the above organic solvent, A method for pretreating a blended fiber, wherein the blended fiber comprises 98% to 100% by weight of polyester fiber and 0% to 2% by weight of polyurethane fiber.

7. In Paragraph 1, A pretreatment method for blended fibers, wherein the step of contacting with the organic solvent is performed at 80°C to 160°C for 1 hour to 20 hours.

8. In Paragraph 1, A pretreatment method for blended fibers, wherein the step of contacting with the organic solvent is performed by immersing the blended fibers in the organic solvent or by refluxing.

9. In Paragraph 1, A pretreatment method for blended fibers, wherein in the step of contacting with the organic solvent, the organic solvent is introduced in an amount of 5 to 100 times the weight of the blended fiber.

10. In Paragraph 1, After the step of contacting with the organic solvent, one or more steps selected from the group consisting of a filtration step, a washing step, and a drying step are additionally included. A pretreatment method for blended fibers, wherein the washing step is performed using the organic solvent.

11. A step of depolymerizing a pretreated blended fiber by contacting a blended fiber, in which polyester fibers and polyurethane fibers are mixed, with an organic solvent, and A method for depolymerizing a blended fiber, wherein the change in the content of polyurethane fibers contained in the blended fiber according to Formula 1 below (ΔCT) before and after contact with the organic solvent in the pretreatment of the blended fiber is 0.7 or more: [Equation 1] ΔCT = (CT1- CT2) / CT1 In the above Equation 1, CT1 is the content of polyurethane fibers in the blended fibers before contacting the blended fibers with the organic solvent (unit: weight%), and CT2 is the content of polyurethane fibers in the blended fibers after contacting the blended fibers with the organic solvent (unit: weight%).

12. In Paragraph 11, A method for depolymerizing a blended fiber, wherein the depolymerization is performed by introducing a depolymerization solvent comprising a monoalcohol having 3 to 14 carbon atoms; or a diol selected from the group consisting of ethylene glycol, diethylene glycol, propanediol, and butanediol, into the pretreated blended fiber.

13. In Paragraph 12, A method for depolymerizing blended fibers, wherein the weight ratio of the pretreated blended fibers and the depolymerization solvent is 1:1 to 10.

14. In Paragraph 12, The above depolymerization solvent is the same as the above organic solvent, a method for depolymerizing blended fibers.

15. In Paragraph 11, A method for depolymerizing blended fibers, wherein the depolymerization reaction product obtained through the above depolymerization comprises a compound represented by the following chemical formula 1: [Chemical Formula 1] In the above chemical formula 1, R1 is a linear or branched alkyl having 3 to 14 carbon atoms; or a hydroxyalkyl having 2 to 14 carbon atoms.

16. In Paragraph 11, The above depolymerization includes alcohololysis, and A method for depolymerizing blended fibers, wherein the above alcohol decomposition is performed at a temperature of 160°C to 280°C and a pressure of 1 bar to 40 bar for 0.5 hours to 24 hours. 17.(1) A step of pre-treating the blended fibers by contacting the blended fibers, which are a mixture of polyester fibers and polyurethane fibers, with an organic solvent; (2) a step of depolymerizing the above-mentioned pretreated blended fibers; and (3) A step of hydrolyzing the depolymerization reaction product obtained through the above depolymerization, and A method for producing terephthalic acid, wherein the change in the content of polyurethane fibers contained in the blended fibers according to Formula 1 below (ΔCT) is 0.7 or more before and after contact with the organic solvent in the above pretreatment step: [Equation 1] ΔCT = (CT1- CT2) / CT1 In the above Equation 1, CT1 is the content of polyurethane fibers in the blended fibers before contacting the blended fibers with the organic solvent (unit: weight%), and CT2 is the content of polyurethane fibers in the blended fibers after contacting the blended fibers with the organic solvent (unit: weight%).

18. In Paragraph 17, A method for producing terephthalic acid, wherein the above hydrolysis is performed at 180°C to 280°C for 0.5 hours to 24 hours.

19. In Paragraph 17, Water is introduced into the above hydrolysis step, and A method for producing terephthalic acid, wherein the water is added in an amount of 1 to 500 times the weight of the depolymerization reaction product.

20. Manufactured according to the method for manufacturing terephthalic acid of claim 17, Regenerated terephthalic acid with a color-b of less than 2 as measured by a colorimeter.

21. In Paragraph 20, The above-mentioned regenerated terephthalic acid is a regenerated terephthalic acid having a total metal content of less than 100 ppm as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

22. In Paragraph 20, The above-mentioned regenerated terephthalic acid is a regenerated terephthalic acid having a total content of Sb, Ti, and Zn of less than 30 ppm as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

23. A polyester resin manufactured from a polymerization raw material containing the recycled terephthalic acid of claim 20.

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