Method for depolymerizing waste polyester textile

Abstract

The present invention relates to a method for depolymerizing a waste polyester textile and a recycled polymerization raw material obtained thereby. According to the present invention, impurities contained in the waste polyester textile can be efficiently removed through a simple pretreatment process, and thus a high-quality recycled polymerization raw material can be obtained.

Description

Depolymerization method of waste polyester textile

[0001] The present invention relates to a method for depolymerizing waste polyester textile (specifically, polyester textile discarded after use) and a regenerated polymerization raw material obtained through the method.

[0002] Polyester is a type of polymer containing ester groups within its molecular structure. It is primarily manufactured by reacting compounds containing carboxyl groups with compounds containing hydroxyl groups. These polyesters boast excellent mechanical properties, heat resistance, chemical resistance, and moldability, and are widely used in the manufacture of various products, including films, bottles, containers, and clothing.

[0003] Products containing the above polyester are disposed of by incineration or landfill after use. However, incineration of waste polyester products generates harmful gases during combustion. Landfill disposal also causes the products to remain in the soil permanently, preventing them from decomposing, potentially contributing to soil acidification.

[0004] Accordingly, various attempts are being made to recycle waste polyester products by depolymerizing them using chemical or physical methods. Examples of such chemical methods include hydrolysis, alcoholysis, and glycolysis.

[0005] To depolymerize waste polyester products using the above chemical methods to obtain high-quality polymerization raw materials or polymer products, a pretreatment process is crucial. This process removes dyes, metal components, and other foreign substances contained in the waste polyester products. In particular, waste polyester textiles such as clothing and cloth often contain dyes, and thus, a pretreatment process (bleaching process) to remove the dyes may be essential for their depolymerization.

[0006] Conventionally, methods such as adsorption treatment using activated carbon have been used to remove dyes contained in waste polyester textiles. However, the lifespan of the activated carbon decreases rapidly as the dye content increases, and the amount of waste polyester textile that can be decolorized in a single treatment is limited.

[0007] Therefore, there is a need for a depolymerization technology that improves the pretreatment process of waste polyester textiles to enhance process efficiency, process stability, and environmental friendliness.

[0008] In order to solve the above-mentioned conventional problems, the inventors of the present invention have conducted various studies, and as a result, it has been confirmed that by treating waste polyester textiles with a specific immersion process using a solvent, the pretreatment process for removing impurities such as dyes and foreign materials contained in waste polyester textiles is improved, and thus the depolymerization efficiency and recyclability of waste polyester textiles are significantly improved.

[0009] Accordingly, the object of the present invention is to provide a method for depolymerizing waste polyester textiles with improved depolymerization efficiency, recyclability, process stability, and environmental friendliness.

[0010] In addition, another object of the present invention is to provide a regenerated polymerization raw material obtained from the depolymerization method of the waste polyester textile.

[0011] To solve the above problem, the present invention provides a method for depolymerizing waste polyester textile, which comprises a step of depolymerizing pretreated waste polyester textile by immersing it in an organic solvent at a temperature of more than 60 to 180°C.

[0012] In addition, the present invention provides a regenerated polymerization raw material obtained from the above depolymerization method.

[0013] The present invention efficiently removes (separates) impurities such as dyes and foreign materials contained in waste polyester textile by pretreating waste polyester textile through a simple process of immersing the waste polyester textile in a specific solvent, and then performs a depolymerization process on the waste polyester textile from which the impurities have been removed, thereby achieving an improvement in overall process efficiency.

[0014] Specifically, by immersing waste polyester textile in a specific solvent, a pretreatment process can be performed at a relatively low temperature, and removal of not only dyes but also heterogeneous materials (e.g., PU) contained in the waste polyester textile can be efficiently achieved, thereby reducing the cost consumed in the pretreatment process of the waste polyester textile, and as a result of the depolymerization process, a recycled polymerization raw material (e.g., r-BHET) with excellent purity and physical properties (e.g., color) can be obtained in high yield.

[0015] Hereinafter, the present invention will be described in detail. Herein, the present invention is not limited to the contents described below, and may be modified in various forms as long as the gist of the invention is not changed.

[0016] The word "comprising" or "including" in this specification is intended to specify particular features, regions, steps, processes, elements and / or components, and does not exclude the presence or addition of other features, regions, steps, processes, elements and / or components, unless specifically stated to the contrary.

[0017] In this specification, singular expressions may be interpreted to include the singular or plural as interpreted in the context, unless otherwise specified.

[0018] All numbers and expressions indicating the amounts of components, reaction conditions, etc. described in this specification can be understood to be modified by the term “about” in all cases unless otherwise specified.

[0019] The terms first, second, etc. described in this specification are used to describe various components, and the components should not be limited by the terms, and the terms are used only for the purpose of distinguishing one component from another.

[0020]

[0021] The present invention relates to a method for depolymerizing waste polyester textile, which can increase the overall process efficiency by carrying out a depolymerization process after a simple pretreatment process of immersing waste polyester textile in a specific solvent at a controlled temperature, and to a regenerated polymerization raw material obtained thereby.

[0022] The present invention is described in detail as follows.

[0023]

[0024] Depolymerization method of waste polyester textile

[0025] The method for depolymerizing waste polyester textile of the present invention comprises a step of depolymerizing waste polyester textile that has been pretreated by immersing it in an organic solvent at a temperature of more than 60 to 180°C.

[0026]

[0027] Pretreatment of waste polyester textiles

[0028] According to the present invention, the depolymerization method includes a process of pretreating waste polyester textile by immersing the waste polyester textile in an organic solvent at a temperature of more than 60 to 180°C.

[0029] The above waste polyester textile is a polyester textile that has been discarded after use, and may be a woven fabric, knitted fabric, non-woven fabric, or a combination thereof containing polyester. For example, the waste polyester textile may include, but is not limited to, waste clothing, waste curtains, waste cloth, waste quilt, waste towel, waste banner, etc. containing polyester. Such waste polyester textile may go through a process of removing metal components (e.g., jewelry, zippers, etc.) or other foreign substances before being immersed in the organic solvent in order to increase the efficiency of the pretreatment process using a solvent (e.g., the decolorization efficiency in the pretreatment process).

[0030] The organic solvent is not particularly limited as long as it is an organic solvent capable of removing (dissolving) impurities contained in the waste polyester textile at a temperature range of from 60 to 180°C. Specifically, according to the present invention, the organic solvent may include at least one selected from the group consisting of a ketone solvent, an ester solvent, and a sulfur compound solvent. Since the organic solvent includes the solvent(s), the solubility of impurities such as dyes and different materials (e.g., PU) contained in the waste polyester textile is improved, thereby increasing the efficiency of the pretreatment process. In particular, by using the solvent(s), the removal of impurities efficiently occurs even at a relatively low temperature of from 60 to 180°C, thereby reducing the cost consumed in the pretreatment process and increasing the recovery rate of the waste polyester textile.

[0031] According to the present invention, the ketone solvent may include cyclopentanone, cyclohexanone, acetophenone, or a combination thereof. In addition, the ester solvent may include ethyl acetoacetate, dimethyl adipate, or a combination thereof. In addition, the sulfur compound solvent may include dimethyl sulfoxide.

[0032] The organic solvent may be heated to a temperature of 60 to 180°C, which is a temperature for pretreatment of waste polyester textile. When the temperature of the organic solvent is 60°C or lower, the decolorization efficiency of the dye contained in the waste polyester textile may decrease or the solubility of different materials may decrease, and when the temperature of the organic solvent exceeds 180°C, depolymerization may occur, which may decrease the recovery rate of the waste polyester textile. Specifically, the temperature of the organic solvent may be 70 to 180°C, 80 to 175°C, 90 to 175°C, 100 to 170°C, 105 to 170°C, 110 to 165°C, 115 to 160°C, 120 to 160°C, 120 to 155°C, or 120 to 145°C.

[0033] According to the present invention, in the pretreatment process, the ratio (a:b) of the amount (a) of the organic solvent to the amount (b) of the waste polyester textile may be less than 1:3 to 25. Specifically, the ratio (a:b) may be, in terms of volume, 1:4 to 24, 1:5 to 22, 1:5 to 20, 1:6 to 19, 1:7 to 18, 1:8 to 17, 1:9 to 16, or 1:10 to 15. When the ratio (a:b) is within the above range, the removal efficiency of impurities contained in the waste polyester textile (e.g., decolorization efficiency of dye) is excellent, while the use of an excessive amount of solvent is prevented, thereby preventing an increase in the cost of the pretreatment process.

[0034] The pretreatment of waste polyester textile using the organic solvent may be performed one or more times. Specifically, according to the present invention, the pretreatment may be repeated two or more times. For example, the pretreatment may be repeated two to three times. By repeating the pretreatment two to three times, the removal efficiency of impurities is increased while the excessive use of organic solvent is prevented, thereby preventing an increase in costs in the pretreatment process.

[0035] According to the present invention, when the pretreatment is repeated two or more times, the organic solvents used in each repetition may be the same or different. For example, the organic solvents used in each repetition may be different, thereby increasing the efficiency of removing impurities contained in waste polyester textiles. Thus, when subjected to the depolymerization process described below, a recycled polymerization raw material having high quality (e.g., color characteristics) can be obtained.

[0036] Specifically, the pretreatment may include a first pretreatment in which waste polyester textile is immersed in a first organic solvent at a temperature exceeding 60 to 180°C and reacted for 1 to 3 hours; a second pretreatment in which the first pretreated waste polyester textile is immersed in a second organic solvent at a temperature exceeding 60 to 180°C and reacted for 1 to 3 hours; and a third pretreatment in which the second pretreated waste polyester textile is immersed in a third organic solvent at a temperature exceeding 60 to 180°C and reacted for 1 to 3 hours, through which the pretreatments may be repeatedly performed.

[0037] The first organic solvent, the second organic solvent, and the third organic solvent used in the first, second, and third pretreatments, respectively, are the organic solvents described above, and these organic solvents may be the same or different from each other. In addition, the first organic solvent, the second organic solvent, and the third organic solvent may be organic solvents newly prepared for each pretreatment process or organic solvents used before each pretreatment process. For example, the first organic solvent used in the first pretreatment and the third organic solvent used in the third pretreatment may be the same, and the second organic solvent used in the second pretreatment may be different from the first organic solvent and the third organic solvent. Specifically, the first organic solvent and the third organic solvent may be the ketone-based solvent or the ester-based solvent, and the second organic solvent may be the sulfur compound-based solvent.

[0038] In addition, the temperature of the first to third organic solvents used in the first to third pretreatments can be controlled within the temperature range of the organic solvents described above.

[0039] By performing this pretreatment, impurities contained in the waste polyester textile can be efficiently removed. Specifically, according to the present invention, the pretreatment can remove dyes contained in the waste polyester textile. Furthermore, the pretreatment can remove polyurethane (PU) contained in the waste polyester textile.

[0040] According to the present invention, the waste polyester textile that has undergone the above pretreatment may exhibit an L(hunter) of 70 or more. Specifically, the waste polyester textile may have an L(hunter) of 72 or more, 74 or more, 76 or more, 78 or more, 80 or more, 82 or more, 84 or more, 86 or more, or 88 or more (e.g., 70 to 90, 71 to 85, 72 to 83, or 73 to 82). When the L(hunter) of the pretreated waste polyester textile exhibits the above value, the removal of impurities such as dyes is maximized, and thus, when subjected to a depolymerization process described below, a high-quality recycled polymer raw material can be obtained.

[0041] The above L(hunter) is a color system established by the International Standard Color Measurement Organization (CIE (Commission International d'Eclairage)) and can be measured using the Colorimeter CM-3600A (manufacturer: Konica Minolta). Specifically, the above L(hunter) represents brightness (brightness), and the closer its value is to 100, the whiter it is.

[0042]

[0043] Meanwhile, the method for depolymerizing waste polyester textile according to the present invention may further include a step of washing and drying the waste polyester textile from which impurities have been removed through the above-described pretreatment. Specifically, prior to the depolymerization process described below, the method may further include a step of washing the pretreated waste polyester textile with a washing solvent (e.g., purified water, acetone, etc.); and a step of drying the washed waste polyester textile using a conventional method.

[0044]

[0045] Depolymerization of pretreated waste polyester textiles

[0046] According to the present invention, the depolymerization method comprises a process for depolymerizing the pretreated waste polyester textile. The depolymerization may be performed using any conventionally known process for depolymerizing waste polyester. Specifically, the depolymerization may be performed using conventionally known reactions such as glycolysis, hydrolysis, methanolysis, or aminolysis.

[0047] For example, the depolymerization can be achieved through a glycolysis reaction in which the polymer chains of the pretreated waste polyester textile are decomposed by a glycol compound.

[0048] Specifically, according to the present invention, the depolymerizing step may include a step of decomposing the pretreated waste polyester textile through a glycolysis reaction to obtain a product; and a step of purifying the product to obtain a purified product containing a recycled polymerization raw material.

[0049] The step of obtaining the above product is a step of performing a glycolysis reaction that decomposes the polymer chain of waste polyester textile by a glycol compound. At this time, the glycol compound used is not particularly limited, but may be ethylene glycol, propylene glycol, diethylene glycol, or a combination thereof.

[0050] The amount of the glycol compound to be added (used) is not particularly limited, but may be 1 time or more, 1.5 times or more, 2 times or more, 3 times or more, 4 times or more, or 5 times or more, and 7 times or less, 6 times or less, 5 times or less, or 4.5 times or less (e.g., 1.5 to 7 times, 2 to 5 times, or 3 to 4 times) relative to the weight of the pretreated waste polyester textile.

[0051] The temperature at which the glycolysis reaction is performed is not particularly limited, but may be 140 to 220°C, 145 to 210°C, 150 to 200°C, 155 to 195°C, 170 to 190°C, or 180 to 190°C. In addition, the time at which the glycolysis reaction is performed is not particularly limited, but may be 1 to 30 hours, 1.5 to 15 hours, 2 to 10 hours, 2 to 8 hours, 2.5 to 6 hours, or 3 to 5 hours from the time at which the required temperature is reached. As the glycolysis reaction is performed at the above temperature and time, depolymerization can be smoothly performed, while minimizing the production of by-products.

[0052] Specifically, the step of obtaining the product through the glycolysis reaction may include a step of decomposing the pretreated waste polyester textile through a first glycolysis reaction at a temperature of 180 to 200°C to obtain a first product; and a step of decomposing the first product through a second glycolysis reaction at a temperature of 150 to 170°C to obtain a second product.

[0053] Meanwhile, the glycolysis reaction may be performed in the presence of a catalyst. The catalyst is not particularly limited as long as it is a commonly known catalyst, but may specifically include a metal acetate, an anhydride thereof, or a hydrate thereof. More specifically, the catalyst may be one or more compounds selected from the group consisting of zinc acetate, sodium acetate, cobalt acetate, and manganese acetate, a hydrate thereof, or anhydride thereof.

[0054] The amount of the catalyst to be added (used) is not particularly limited, but may be 0.001 to 3 parts by weight, 0.005 to 2 parts by weight, 0.01 to 1 part by weight, or 0.03 to 0.5 parts by weight, based on 100 parts by weight of the pretreated waste polyester textile.

[0055] By performing this glycolysis reaction, a product containing crude bis(2-hydroxyethyl)terephthalate (crude-BHET) can be obtained.

[0056] The step of obtaining the above-mentioned purified product is a step of purifying the product obtained through the above-mentioned glycolysis reaction to obtain a purified product containing a regenerated polymerization raw material, and a conventionally known purification process may be applied. Specifically, the purification may be performed by undergoing one or more of the following processes: crystallization (cooling), filtration, ion exchange, distillation, and adsorption.

[0057] The above crystallization (cooling) process may include a conventionally known crystallization process. By performing this crystallization process, by-products and the like generated by side reactions in the depolymerization process can be removed.

[0058] The above filtration process may include membrane filtration, filterate filtration, reduced pressure flash (cooling), solid-liquid separation, centrifugation, etc. By performing such filtration processes, fine particles and / or insoluble solid impurities contained in the obtained product can be removed.

[0059] The above ion exchange is a process that is typically performed using a known ion exchange resin. Specifically, the ion exchange resin may include a cation exchange resin, an anion exchange resin, an amphoteric ion exchange resin, a chelating resin, etc. The cation exchange resin may specifically be a strongly acidic cation exchange resin having a sulfonic acid group (-SO3H), or a weakly acidic cation exchange resin having a carboxyl group (-COOH). The anion exchange resin may be a strongly basic anion exchange resin in the form of a quaternary ammonium salt, or a weakly basic anion exchange resin having an amino group. By performing this ion exchange process, catalysts and / or metal foreign substances, etc. can be removed.

[0060] The above distillation may include processes such as vacuum distillation, thin film evaporation, falling film evaporation, and short path evaporation. By going through these distillation processes, unreacted glycol compounds, etc. can be removed.

[0061] The above adsorption is a process typically performed using a known adsorbent (e.g., activated carbon). By performing this adsorption process, other foreign substances can be removed.

[0062] The purified product obtained through this purification process includes a regenerated polymerization raw material, wherein the regenerated polymerization raw material may have high purity and excellent color characteristics. Specifically, according to the present invention, the regenerated polymerization raw material may be regenerated bis(2-hydroxyethyl)terephthalate.

[0063]

[0064] Regenerated polymer raw materials

[0065] The regenerated polymerization raw material of the present invention is obtained through the depolymerization method described above. Since the regenerated polymerization raw material is obtained through the depolymerization method described above, it can exhibit properties equivalent to those of virgin polymerization raw materials while also exhibiting superior characteristics such as color.

[0066] Specifically, according to the present invention, the regenerated polymerization raw material may be regenerated bis(2-hydroxyethyl)terephthalate.

[0067] Such recycled bis(2-hydroxyethyl) terephthalate may exhibit excellent color characteristics, such as a yellowness index (YID) of 6 or less, 5.8 or less, 5.6 or less, 5.5 or less, 5.3 or less, 5.0 or less, 4.8 or less, 4.5 or less, 4.3 or less, or 4 or less (e.g., 1 to 6, 3 to 5.5, 3.5 to 5, or 4 to 4.5). The recycled bis(2-hydroxyethyl) terephthalate has high purity and excellent color characteristics, and thus can be usefully used as a raw material for producing a polymer (e.g., polyester).

[0068] The present invention is described in more detail through the following examples. However, the following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention.

[0069]

[0070] [Example 1]

[0071] Pretreatment of waste polyester textiles

[0072] 30 g of waste polyester textile (specifically, waste polyethylene terephthalate textile) and 450 ml of cyclohexanone were charged together into a 500 ml flask (waste polyester textile input amount: cyclohexanone input amount = 1:15). Next, the flask was fixed to a heating mantle, the temperature of the heating mantle was increased to 120°C, and the reaction was carried out with stirring for 2 hours. Next, cyclohexanone was removed from the flask to obtain waste polyester textile. The process of treating the waste polyester textile with the cyclohexanone was considered one cycle, and a total of three cycles were performed by replacing the cyclohexanone (pretreatment was repeated three times).

[0073] Afterwards, the waste polyester textile was taken out of the flask, washed with water, and dried in a vacuum oven to obtain a pretreated polyester textile.

[0074] Depolymerization of waste polyester textiles

[0075] 1000 g of waste polyester textile, 2000 g of ethylene glycol, and 5.0 g of zinc acetate anhydride obtained through the above pretreatment were introduced into a first reactor made of stainless steel (SUS), and the internal temperature of the first reactor was raised to 180°C to perform the first glycolysis reaction for 2 hours. The obtained product (first product) was transferred to a second reactor and cooled to 150°C, and then 2000 g of ethylene glycol was additionally introduced, and the second glycolysis reaction was performed for 2 hours while maintaining the temperature of the second reactor at 150°C. The obtained product (second product) was cooled to 120°C through a reduced pressure flash, and then filtered using Celite TM545) 16 g was added and pressure filtration was performed to perform solid-liquid separation. The separated liquid product was passed through a column packed with ion exchange resin (BC107(H) from Bonlite) to remove ionic impurities, thereby obtaining a mixture containing crude bis(2-hydroxyethyl)terephthalate and ethylene glycol.

[0076] The above mixture was cooled to room temperature over 2 hours under stirring in a 10 L jacket-type cooling water circulation crystallizer, and the obtained crystal product was filtered through a pressurized Nutsche filter (jacket-type, filtration area 0.2 m 2 ) was used to separate solid and liquid under a pressure of 3 bar to obtain a BHET cake. The BHET cake was transferred to a 10 L distillation device, reheated to 130 ℃, and stepwise reduced pressure distillation was performed under reduced pressure conditions from 760 torr to 0.8 torr to remove (recover) unreacted ethylene glycol. The obtained product from which unreacted ethylene glycol was removed was subjected to thin-film distillation at 220 ℃ and 0.08 Torr in a thin-film distiller (VKL70-4S from VTA) to remove oligomers higher than dimers, and 1040 g of the product was obtained. Afterwards, 1040 g of the above product and 3120 g of distilled water were placed in a 10 L glass reactor for adsorption-crystallization, dissolved at a temperature of 70 ℃, and 5.2 g of activated carbon was added, stirred for 30 minutes, and then filtered. The filtrate obtained through the above filtration was cooled to room temperature to crystallize, filtered again, and dried in a vacuum oven to obtain 1980 g of a purified product containing regenerated bis(2-hydroxyethyl) terephthalate (r-BHET).

[0077]

[0078] [Examples 2 to 10]

[0079] A purified product containing regenerated bis(2-hydroxyethyl)terephthalate (r-BHET) was obtained through the same process as Example 1, except that the type of solvent, the amount of solvent added, or the number of pretreatment cycles were changed as shown in Tables 1 and 2 below. In this case, Example 7 performed the pretreatment by performing a total of three cycles using cyclohexanone in the first pretreatment, dimethyl sulfoxide (DMSO) in the second pretreatment, and cyclohexanone in the third pretreatment.

[0080]

[0081] [Comparative Examples 1 to 3]

[0082] A purified product containing regenerated bis(2-hydroxyethyl)terephthalate (r-BHET) was obtained through the same process as Example 1, except that the reaction temperature or type of solvent in the pretreatment was changed as shown in Table 3 below.

[0083]

[0084] [Experimental Example 1] Recovery rate (%)

[0085] The ratio of the weight of the waste polyester textile obtained after pretreatment to the weight of the initially introduced waste polyester textile was calculated as a percentage, and the results are shown in Tables 1 to 3 below.

[0086]

[0087] [Example 2] Color L (hunter)

[0088] Color L(hunter) (L(hunter) of pretreated waste polyester textile), one of the color systems established by the international standard color measurement organization (CIE (Commission International d'Eclairage)), was measured using a Colorimeter CM-3600A (manufactured by Konica Minolta), and the results are shown in Tables 1 to 3 below.

[0089]

[0090] [Experimental Example 3] r-BHET YID

[0091] The purified product containing regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) was dissolved in dimethylformamide at room temperature at a concentration of 25 wt%, and the yellowness index (YID) was measured after 30 minutes, and the results are shown in Tables 1 to 3 below. Specifically, transmission data was obtained with Illuminant D65 using Hunterlab's Color Flex EZ at an observer angle of 2°, and the yellowness index (YID) of r-BHET was calculated using the color analysis device in the software.

[0092]

[0093] [Test Example 4] Polyurethane (PU) residue rate (%)

[0094] The residual percentage of polyurethane (PU) was confirmed by analyzing each waste polyester textile before and after pretreatment using Proton NMR (Nuclear Magnetic Resonance), and the results are shown in Tables 1 to 3 below. Specifically, the mol% of polytetraethylene ether glycol (PTMEG), a raw material for polyurethane (PU), was calculated based on the mol% of terephthalic acid (TPA), a raw material for polyethylene terephthalate (PET), and the ratio of the value calculated before pretreatment to the value calculated after pretreatment was calculated as a percentage to confirm the residual percentage of polyurethane (PU).

[0095]

[0096] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Organic solvent Cyclohexanone Cyclopentanone Acetophenone Ethyl acetoacetate Dimethyl adipate DMSO Organic solvent amount (ml) 450 450 450 450 450 450 S / L ratio 1 / 151 / 151 / 151 / 151 / 151 / 15 Reaction temperature (℃) 120 120 120 120 120 Number of cycles 333333 Recovery rate (%) 95.1 91.4 98.7 99.7 99.5 95.1 Color L 81.6 80.87 7.88 1.97 5.78 1.6 r-BHET YID 4.3 4.14 94.15 44.3 PU Residual rate (%) 0 0 0 0 0 0 0

[0097] Example 7 Example 8 Example 9 Example 10 Organic solvent Cyclohexanone+DMSOCyclohexanoneCyclohexanoneCyclohexanoneOrganic solventAmount used (ml)45030090750S / L ratio1 / 151 / 151 / 31 / 25Reaction temperature (℃)100120120120Number of cycles3233Recovery rate (%)99999994.1Color L75.173.270.485.8r-BHET YID2.84.85.63.2PU Residue rate (%)0000

[0098] Comparative Example 1 Comparative Example 2 Comparative Example 3 Organic solvent Cyclohexanone EGAcetone Organic solvent Amount used (ml) 450 450 450 S / L ratio 1 / 15 1 / 15 1 / 15 Reaction temperature (℃) 60 190 50 Number of cycles 333 Recovery rate (%) 99.7 61.2 97.1 Color L 35.9 7.6 41.7 r-BHET YID 425.4 30.5 PU Residue rate (%) 4.8 4.3 4.7

[0099] Referring to Tables 1 to 3 above, it can be confirmed that Examples 1 to 10, in which waste polyester textiles were pretreated using the pretreatment process of the present invention, have high L values ​​of the pretreated waste polyester textiles and that most of the polyurethane (PU) remains in the pretreated waste polyester textiles. Furthermore, it can be confirmed that r-BHET with excellent color characteristics was obtained by depolymerizing the pretreated waste polyester textiles.

[0100] On the other hand, in Comparative Examples 1 to 3, it can be confirmed that impurities in the waste polyester textile are not sufficiently removed or decomposition of the waste polyester textile occurs due to the temperature of the organic solvent being too low or too high in the pretreatment process, so that the color characteristics of the pretreated waste polyester textile and r-BHET are significantly reduced and the recovery rate of the waste polyester textile is also low.

[0101] Additionally, although a high amount of organic solvent is used to obtain waste polyester textile with a high L value, the cost of the pretreatment process increases, so it is desirable to apply a ratio of the amount of waste polyester textile to the amount of organic solvent used to be less than 25 (e.g., S / L ratio = 1 / 3 to less than 25) (see Example 10).

Claims

A method for depolymerizing waste polyester textile, comprising a step of depolymerizing pretreated waste polyester textile by immersing it in an organic solvent at a temperature exceeding 1.60 to 180°C.

2. In paragraph 1, A method for depolymerizing waste polyester textile, wherein the ratio of the amount of the organic solvent used in the pretreatment to the amount of the waste polyester textile used is less than 1:3 to 25.

3. In paragraph 1, A method for depolymerizing waste polyester textile, wherein the organic solvent comprises at least one selected from the group consisting of ketone solvents, ester solvents, and sulfur compound solvents.

4. In paragraph 3, A method for depolymerizing waste polyester textile, wherein the ketone solvent comprises cyclopentanone, cyclohexanone, acetophenone, or a combination thereof.

5. In paragraph 3, A method for depolymerizing waste polyester textile, wherein the ester solvent comprises ethyl acetoacetate, dimethyl adipate, or a combination thereof.

6. In paragraph 3, A method for depolymerizing waste polyester textile, wherein the sulfur compound solvent comprises dimethyl sulfoxide.

7. In paragraph 1, A method for depolymerizing waste polyester textile, wherein the temperature of the organic solvent is 120 to 160°C.

8. In paragraph 1, A method for depolymerizing waste polyester textile, wherein the above pretreatment is repeated two or more times.

9. In paragraph 8, A method for depolymerizing waste polyester textile, wherein the above pretreatment is performed twice or more repeatedly, and the organic solvent used in each time is the same or different.

10. In paragraph 1, The above preprocessing, Primary pretreatment of waste polyester textile by immersing it in a first organic solvent at a temperature of 60 to 180°C and reacting it for 1 to 3 hours; Secondary pretreatment of immersing the first pretreated waste polyester textile in a second organic solvent at a temperature of 60 to 180°C and reacting for 1 to 3 hours; and A method for depolymerizing waste polyester textile, comprising a third pretreatment comprising immersing the second pretreated waste polyester textile in a third organic solvent at a temperature of 60 to 180°C and reacting the second pretreated waste polyester textile for 1 to 3 hours.

11. In paragraph 10, A method for depolymerizing waste polyester textile, wherein the first organic solvent, the second organic solvent and the third organic solvent are the same or different from each other.

12. In paragraph 1, A method for depolymerizing waste polyester textile, wherein the dye contained in the waste polyester textile is removed through the above pretreatment.

13. In paragraph 1, A method for depolymerizing waste polyester textile, wherein polyurethane (PU) contained in the waste polyester textile is removed through the above pretreatment.

14. In paragraph 1, A method for depolymerizing waste polyester textile, wherein the waste polyester textile that has undergone the above pretreatment has an L(hunter) of 70 or more.

15. In paragraph 1, The above depolymerizing step is, A step of obtaining a product by decomposing the above-mentioned pretreated waste polyester textile through a glycolysis reaction; and A method for depolymerizing waste polyester textile, comprising a step of purifying the above product to obtain a purified product containing a regenerated polymerization raw material.

16. A regenerated polymerization raw material obtained from the depolymerization method of waste polyester textile of Article 1.

17. In paragraph 16, The above regenerated polymerization raw material is regenerated bis(2-hydroxyethyl)terephthalate, A recycled polymerization raw material having a yellowness index (YID) of 6 or less of the above-mentioned recycled bis(2-hydroxyethyl) terephthalate.