WO2026010092A1 - Method for treating waste polyester textile - Google Patents

Abstract

The present invention relates to a method for treating waste polyester textile, a polyester textile obtained thereby, and an apparatus for treating same. According to the present invention, dye-containing impurities in waste polyester textiles can be efficiently removed using a small amount of solvent.

Description

Method for processing waste polyester textiles

The present invention relates to a method for treating waste polyester textile (specifically, discarded polyester textile) and a polyester textile (regenerated polyester textile) obtained from the method.

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.

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.

Accordingly, various attempts are being made to recycle waste polyester products by decomposing (depolymerizing) them through chemical or physical methods. Examples of these chemical methods include hydrolysis, alcoholysis, and glycolysis, which are classified based on the type of solvent used for depolymerization.

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 decomposition (depolymerization).

Conventionally, methods such as solvent immersion treatment or adsorption treatment using activated carbon have been used to remove dyes contained in waste polyester textiles. However, solvent immersion treatment requires multiple decolorization treatments using large amounts of solvent, which reduces process efficiency and incurs high costs. Furthermore, when toxic solvents (e.g., toluene, xylene, etc.) are used, process stability and environmental friendliness are also reduced. In addition, the lifespan of activated carbon in adsorption treatment decreases rapidly as the dye content increases, and the amount of waste polyester textile that can be decolorized in a single treatment is limited.

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

In order to solve the above-described conventional problems, the inventors of the present invention have conducted various studies, and as a result, they have confirmed that the pretreatment process (decolorization process) for removing components such as dyes contained in waste polyester textiles by contacting the waste polyester textiles with vaporized solvents and/or condensed solvents is improved, thereby significantly improving the depolymerization efficiency and recyclability of the waste polyester textiles.

Accordingly, the object of the present invention is to provide a method for treating waste polyester textiles with improved process efficiency, process stability, and environmental friendliness, and a polyester textile obtained from the method.

In addition, another object of the present invention is to provide a device for treating the waste polyester textile.

In addition, another object of the present invention is to provide a method for depolymerizing the waste polyester textile.

In order to solve the above problem, the present invention provides a method for treating waste polyester textile, comprising the steps of: (1) introducing waste polyester textile into a first container and introducing a solvent into a second container; (2) forming a vaporized solvent from the solvent; and (3) contacting a liquefied solvent formed through condensation of the vaporized solvent with the waste polyester textile, wherein the ratio of the amount of waste polyester textile introduced into the first container to the amount of solvent introduced into the second container is 1:3 to 20.

In addition, the present invention provides a polyester textile obtained from the above processing method.

In addition, the present invention provides a device for treating waste polyester textile, comprising: a container section including a first container into which waste polyester textile is introduced and a second container into which a solvent is introduced; a heating section for heating the solvent to form a vaporized solvent; a condensation section for condensing the vaporized solvent to form a liquefied solvent; and a connection section for connecting the first container and the condensation section so that the liquefied solvent is supplied to the waste polyester textile, wherein the ratio of the amount of waste polyester textile introduced into the first container to the amount of solvent introduced into the second container is 1:3 to 20.

In addition, the present invention provides a method for depolymerizing waste polyester textile, comprising the steps of (A) depolymerizing waste polyester textile pretreated by the above treatment method to obtain a product; and (B) purifying the product to obtain a purified product containing recycled bis(2-hydroxyethyl)terephthalate.

The present invention separates dye-containing impurities contained in waste polyester textile by contact with a vaporized solvent and/or a liquefied solvent (e.g., a liquefied solvent falls on the waste polyester textile) without requiring the waste polyester textile to be completely immersed in the solvent, so that pretreatment such as decolorization can be performed well with a small amount of solvent, unlike solvent immersion treatment (immersion method) in which a large amount of solvent is used to perform multiple decolorization treatments, thereby achieving a reduction in process costs.

In addition, the present invention can have excellent removal efficiency (decolorization efficiency) of dye-containing impurities because a relatively high-temperature solvent (e.g., an initial condensation solvent, or a condensation solvent formed (purified) through re-vaporization and re-condensation after contact with the textile) is continuously supplied to the waste polyester textile.

Furthermore, the present invention can increase the surface area of waste polyester textiles. When waste polyester textiles with such a large surface area are used, the separation of dye-containing impurities can be effectively achieved. Therefore, the present invention can achieve the desired removal of dye-containing impurities in just one cycle, thereby shortening the treatment (pretreatment) process time of waste polyester textiles.

In addition, the present invention can have excellent process stability and environmental friendliness because it uses a non-toxic solvent.

FIG. 1 is a schematic diagram showing a device for processing waste polyester textile according to one embodiment of the present invention.

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.

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.

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

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.

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.

The sizes of each component in this drawing may be exaggerated for illustration purposes and may differ from the sizes actually applied.

The present invention relates to a method for treating waste polyester textile, which can increase the efficiency of the pretreatment and depolymerization processes by treating waste polyester textile through a vapor method for vaporizing and liquefying a solvent, a polyester textile obtained thereby, a treatment device therefor, and a depolymerization method therefor.

Specifically, the present invention provides a method for producing a recycled polyester textile by contacting a vaporized solvent and/or a liquefied solvent with waste polyester textile, wherein the solvents separate (dissolve and separate) dye-containing impurities contained in the waste polyester textile, thereby providing a recycled polyester textile that exhibits properties equivalent to those of virgin polyester textile while ensuring that characteristics such as color are maintained at a desired level.

The present invention is described in detail as follows.

Method for processing waste polyester textiles

The method for treating waste polyester textile of the present invention comprises the steps of: (1) introducing waste polyester textile into a first container and introducing a solvent into a second container; (2) forming a vaporized solvent from the solvent; and (3) contacting a liquefied solvent formed through condensation of the vaporized solvent with the waste polyester textile, wherein the ratio of the amount of waste polyester textile introduced into the first container to the amount of solvent introduced into the second container is 1:3 to 20.

Step (1): Input of waste polyester textile and solvent respectively

According to the present invention, step (1) is a step of introducing waste polyester textile into a first container and introducing a solvent into a second container to start a treatment process (pretreatment process) of waste polyester textile.

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. Before being put into the first container, the waste polyester textile may go through a process of removing metal components (e.g., accessories, zippers, etc.) or other foreign substances (e.g., textile parts with different components from polyester, dust, etc.) in order to increase the efficiency of the treatment process using a solvent (decolorization efficiency in the pretreatment process).

The above-mentioned waste polyester textile can be introduced into the first container in a conventional manner, and at this time, can be placed in the first container in an evenly spread state to increase the surface area. As the waste polyester textile is placed in this manner to increase the surface area, the removal efficiency of dye-containing impurities can be increased.

The above solvent is not particularly limited as long as it is a solvent capable of separating (dissolving) dye-containing impurities contained in the waste polyester textile.

According to the present invention, the solvent may be a solvent having a boiling point (B.P) of 110 to 250°C. Specifically, the boiling point of the solvent may be 111 to 245°C, 112 to 240°C, 113 to 235°C, 114 to 230°C, 115 to 225°C, 116 to 220°C, 117 to 215°C, 120 to 210°C, 124 to 205°C, 125 to 200°C, 127 to 195°C, 130 to 190°C, 133 to 185°C, 135 to 180°C, 137 to 175°C, 140 to 170°C, 145 to 165°C, or 150 to 160°C. If the boiling point of the above solvent is less than 110°C, the efficiency of removing dye-containing impurities may decrease, and if it exceeds 250°C, the cost of the treatment process may increase excessively or the polyester textile may decompose (decomposition due to melting) and the treatment process may become difficult to proceed.

According to the present invention, the solvent may be a solvent having a latent heat of 70 cal/g or more. Specifically, the latent heat of the solvent may be 71 cal/g or more, 73 cal/g or more, 76 cal/g or more, 78 cal/g or more, 83 cal/g or more, 86 cal/g or more, 89 cal/g or more, or 95 cal/g or more, and may be 110 cal/g or less, 108 cal/g or less, 106 cal/g or less, 105 cal/g or less, 103 cal/g or less, 102 cal/g or less, 100 cal/g or less, 98 cal/g or less, 96 cal/g or less, 94 cal/g or less, or 92 cal/g or less. For example, the latent heat of the solvent may be 70 to 110 cal/g, 72 to 109 cal/g, 75 to 107 cal/g, 77 to 104 cal/g, 80 to 101 cal/g, 85 to 99 cal/g, 88 to 97 cal/g, 90 to 93 cal/g, or 91 to 92 cal/g. As the latent heat of the solvent is within the above range, the removal efficiency of dye-containing impurities can be secured while preventing excessive costs from being consumed in the treatment process.

According to the present invention, the solvent may be a solvent having a solubility parameter (∂ _t ) of 17 to 23. Specifically, the solubility parameter of the solvent may be 17 to 22.9, 17.2 to 22.8, 17.4 to 22.7, 17.5 to 22.6, 18 to 22.5, 18.5 to 22.4, 19 to 22.3, 19.2 to 22.2, or 19.4 to 22.1. As the solubility parameter of the solvent is within the above range, the removal efficiency of dye-containing impurities can be maximized.

The above dissolution parameter may refer to the Hansen Solubility Parameter (HSP).

The above Hansen solubility parameter (HSP) is an index representing solubility characteristics proposed by Dr. C. Hansen in 1967. In the above HSP, the degree of bonding within a substance is considered by dividing it into the following three factors.

(1) Solubility factor (δ _d ) resulting from nonpolar dispersion bonding

(2) Solubility factor (δ _p ) caused by polar bonding due to permanent dipoles

(3) Solubility factor (δ _h ) caused by hydrogen bonding

These HSPs provide more detailed information on the bonding within a substance than other solubility factors, allowing for accurate and systematic determination of the solubility of a solvent.

HSP = (δ _d , δ _p , δ _h ), (J/cm3) ^½

δTot =(4δ _d ² + δ _p ² + δ _h ² ) ^½ , (J/㎤) ^½

The above HSP is a vector having a size and direction in the space composed of the above three elements, and the above δTot represents the magnitude of the HSP vector or the distance between factors. The basic unit representing the above HSP is (J/㎤) ^½ or (MPa) ^½ . This HSP value can be calculated using a program called HSPiP (Hansen Solubility Parameters in Practice) of Dr. Hansen.

According to the present invention, the solvent may include a ketone solvent. The ketone solvent may be an aliphatic ketone solvent, an alicyclic ketone solvent, or an aromatic ketone solvent. Specifically, the ketone solvent may include at least one selected from the group consisting of cyclopentanone, cyclohexanone, and methyl isobutyl ketone (MIBK). Preferably, the ketone solvent may be cyclopentanone or cyclohexanone. The solvent can efficiently remove dye-containing impurities contained in waste polyester textile without being toxic, thereby improving treatment process efficiency, process stability, and environmental friendliness.

Meanwhile, according to the present invention, the ratio (a:b) of the amount (a) of waste polyester textile introduced into the first container and the amount (b) of solvent introduced into the second container may be 1:3 to 20. Specifically, the ratio (a:b) may be a volume ratio of 1:4 to 20, 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. The ratio (a:b) may be a weight:volume ratio, and may mean that the amount (b) introduced per 1 g of the amount (a) introduced is 3 to 20 ml. As the above ratio (a:b) is within the above range, the removal of dye-containing impurities contained in waste polyester textile is efficiently performed, and an excessive amount of solvent is prevented from being used, thereby preventing an increase in the cost of the treatment process.

Step (2): Formation of vaporized solvent

According to the present invention, step (2) is a step of forming a vaporized solvent from the solvent introduced into the second container. The method for forming the vaporized solvent from the solvent may not be particularly limited as long as it is a commonly known vaporization method. For example, a depressurization method for lowering the internal pressure of the second container into which the solvent is introduced, or a method for heating the solvent may be applied.

When forming the vaporized solvent by heating the solvent, the temperature for heating the solvent may be applied starting from a temperature higher than the boiling point of the solvent to a temperature capable of maintaining the properties of the waste polyester textile while ensuring the durability of the second container, or until the temperature at which decomposition of the waste polyester textile occurs (e.g., a temperature lower than the melting point of the waste polyester textile).

The vaporized solvent formed from the above solvent moves toward the waste polyester textile, and the moved vaporized solvent removes dye-containing impurities contained in the waste polyester textile as it passes through the waste polyester textile, which will be described later.

Step (3): Contact with liquefied solvent

According to the present invention, step (3) is a step in which a liquefied solvent formed through condensation of the vaporized solvent comes into contact with the waste polyester textile.

Specifically, step (3) may include: (3-1) a step of first contacting the waste polyester textile with the vaporized solvent while passing through the waste polyester textile; and (3-2) a step of second contacting the waste polyester textile with the liquefied solvent formed through condensation of the vaporized solvent passing through the waste polyester textile. For example, the vaporized solvent moves upward toward the waste polyester textile and first contacts the waste polyester textile while passing through the waste polyester textile, and when the vaporized solvent that made the first contact continues to move upward and reaches a region where condensation of the vaporized solvent occurs, condensation of the vaporized solvent occurs to form a liquefied solvent, and then the formed liquefied solvent moves downward toward the waste polyester textile and secondarily contacts the waste polyester textile. In the present invention, the steps (3-1) and (3-2) are performed continuously and continuously, so that even if only one cycle is performed within a set period of time using a small amount of solvent, dye-containing impurities contained in waste polyester textile can be efficiently removed. For example, the one cycle may mean that the treatment process is performed using only the solvent introduced into the second container until the dye-containing impurities in the waste polyester textile introduced into the first container are completely removed.

That is, according to the present invention, in step (3), the dye-containing impurities contained in the waste polyester textile can be removed (separated) by bringing the vaporized solvent and/or the liquefied solvent into contact with the waste polyester textile. The removal (separation) can be achieved by physically/chemically bonding or dissolving the dye-containing impurities in the vaporized solvent and/or the liquefied solvent.

Meanwhile, the liquefied solvent that has made a second contact with the waste polyester textile can be collected in the second container by passing through the waste polyester textile and falling into a second container. The liquefied solvent collected in the second container includes a solvent and dye-containing impurities, which undergo a re-vaporization process again during a single cycle, and are separated into a vaporized solvent (purified vaporized solvent) and a solidified dye-containing impurities. Subsequently, the separated vaporized solvent (purified vaporized solvent) is again subjected to a first contact with the waste polyester textile, and then undergoes a re-liquefaction process again, and is converted into a liquefied solvent (purified liquefied solvent), which can then fall onto the waste polyester textile and come into second contact with the waste polyester textile. In this way, during one cycle, the solvent undergoes a phase transition from vaporization -> liquefaction -> vaporization -> liquefaction, and as the solvent formed in each phase transition process comes into contact with waste polyester textile, the present invention can more efficiently remove dye-containing impurities while reusing the solvent.

Specifically, in the present invention, the above steps (2) and (3) can be performed repeatedly at least once during one cycle.

The time for performing the above step (3) is not particularly limited, and can be appropriately adjusted depending on the amount of waste polyester textile input, its surface area, or the amount of solvent input.

The method for treating waste polyester textile of the present invention may further include a step of washing waste polyester textile from which dye-containing impurities have been removed through steps (1) to (3) with a washing solvent (e.g., purified water, acetone, etc.); and a step of drying the washed waste polyester textile by a conventional method.

polyester textile

The polyester textile of the present invention is a regenerated polyester textile obtained through the aforementioned processing method. Because the polyester textile is obtained through the aforementioned processing method, it exhibits properties equivalent to those of virgin polyester textile while also exhibiting superior characteristics, such as color.

Specifically, according to the present invention, the polyester textile may have an L(hunter) of 70 or more. More specifically, the 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 89.5, 75 to 89, or 83.5 to 88.8). When the L(hunter) of the polyester textile exhibits the above values, the removal of dye-containing impurities is maximized, and thus the polyester textile may exhibit excellent color characteristics. Therefore, when an additional decomposition (depolymerization) step is performed using the polyester textile of the present invention, a high-quality polymerization raw material or polymer can be obtained.

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.

Treatment device for waste polyester textiles

The device for treating waste polyester textile of the present invention comprises a container section including a first container into which waste polyester textile is introduced and a second container into which a solvent is introduced; a heating section for heating the solvent to form a vaporized solvent; a condensing section for condensing the vaporized solvent to form a liquefied solvent; and a connecting section for connecting the first container and the condensing section to supply the liquefied solvent to the waste polyester textile, which will be described in detail with reference to FIG. 1 as follows.

According to the present invention, the container part (10) includes a first container (11) and a second container (12).

The first container (11) is a container into which waste polyester textile (P) is introduced, and may have various shapes. For example, the shape of the first container (11) may be appropriately modified in consideration of the surface area, volume, weight, etc. of the waste polyester textile (P) and the structure connected to the condenser (30). In addition, the material of the first container (11) is not particularly limited as long as it is durable, and may be made of glass, ceramic, metal, etc., for example.

This first container (11) may include a structure (F) having pores formed therein to allow movement of the vaporized solvent while fixing the position of the waste polyester textile (P). For example, the structure (F) may be a metal mesh.

The second container (12) is a container into which the solvent (S) is introduced, and may have various shapes. For example, the shape of the second container (12) may be appropriately modified in consideration of the capacity of the solvent (S) and the transport efficiency of the vaporized solvent. In addition, the material of the second container (12) is not particularly limited as long as it has chemical resistance to the solvent (S) and durability against heat, and may be made of glass, ceramic, metal, etc., specifically.

The position of the second container (12) is not particularly limited, but may be positioned below the first container (11). As the second container (12) is positioned below the first container (11), the vaporized solvent formed from the solvent in the second container (12) can smoothly move to the first container (11) and efficiently contact the waste polyester textile (P).

Meanwhile, the first container (11) and the second container (12) may be integral or individually separated. Specifically, the integral container may be divided into upper and lower compartments, such that the upper portion is applied as the first container (11) and the lower portion is applied as the second container (12). In addition, the individual, independent first containers (11) and second containers (12) may be connected to each other.

According to the present invention, the heating unit (20) heats the solvent (S) in the second container (12) to form a vaporized solvent, and may have a commonly known structure (e.g., a heating mantle).

According to the present invention, the condensing unit (30) condenses the vaporized solvent formed from the solvent (S) in the second container (12) to form a liquefied solvent. This condensing unit (30) may have a commonly known structure (e.g., a reflux condenser equipped with a valve and a vacuum means). The condensing unit (30) may be positioned at the upper portion of the first container (11) so that the liquefied solvent can efficiently contact the waste polyester textile (so that the liquefied solvent can efficiently fall on the waste polyester textile).

According to the present invention, the connecting portion (40) connects the first container (11) and the condensing portion (30) so that the liquefied solvent is supplied to the waste polyester textile (P). Specifically, the connecting portion (40) may serve as a path (passage) through which the liquefied solvent formed in the condensing portion (30) moves toward the waste polyester textile (P). This connecting portion (40) may have a sealed structure that prevents external air from entering the connecting portion between the first container (11) and the condensing portion (30).

Meanwhile, according to the present invention, the ratio (a:b) of the amount (a) of waste polyester textile (P) introduced into the first container (11) and the amount (b) of solvent (S) introduced into the second container (12) may be 1:3 to 20. Specifically, the ratio (a:b) may be, in terms of volume, 1:4 to 20, 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 of dye-containing impurities included in the waste polyester textile (P) is efficiently performed, while preventing the use of an excessive amount of solvent, thereby preventing an increase in the cost of the treatment process of the waste polyester textile.

Depolymerization method of waste polyester textile

The method for depolymerizing waste polyester textile (or recycling method) of the present invention comprises: (A) a step of depolymerizing waste polyester textile pretreated by the above method for treating waste polyester textile to obtain a product; and (B) a step of purifying the product to obtain a purified product containing recycled bis(2-hydroxyethyl)terephthalate.

Step (A): Pretreatment and depolymerization of waste polyester textiles

According to the present invention, step (A) is a step of pretreating waste polyester textile using the aforementioned method for treating waste polyester textile and then depolymerizing the waste polyester textile. By pretreating waste polyester textile using the aforementioned method, waste polyester textile from which dye-containing impurities have been efficiently removed can be economically obtained. Furthermore, by performing the depolymerization process using the pretreated waste polyester textile, a polymerization raw material (recycled raw material) with high purity and excellent color characteristics can be obtained in high yield.

The above depolymerization can be performed using a conventionally known depolymerization process for waste polyester. Specifically, the depolymerization can be performed using a conventionally known reaction such as glycolysis, hydrolysis, methanolysis, or aminolysis.

For example, the depolymerization may be achieved through a glycolysis reaction in which the polymer chains of pretreated waste polyester textile are decomposed by a glycol-based compound. The glycol-based compound is not particularly limited, but may be ethylene glycol, propylene glycol, diethylene glycol, or a combination thereof.

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 waste polyester textile.

The temperature at which the above depolymerization 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 depolymerization 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 temperature required for depolymerization is reached. As the depolymerization is performed at the above temperature and time, the glycolysis reaction can be performed smoothly while minimizing the production of by-products.

Specifically, the depolymerization may include (A-1) a step of first depolymerizing the pretreated waste polyester textile through a glycolysis reaction at a temperature of 180 to 200°C to obtain a first product; and (A-2) a step of secondly depolymerizing the first product through a glycolysis reaction at a temperature of 150 to 170°C to obtain a second product.

Meanwhile, the depolymerization may be performed in the presence of a catalyst that activates the glycolysis reaction. 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.

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.

By performing these steps (A), a product containing crude bis(2-hydroxyethyl)terephthalate (crude-BHET) can be obtained.

Step (B): Purification

According to the present invention, step (B) is a step of purifying the product to obtain a purified product containing regenerated bis(2-hydroxyethyl)terephthalate (r-BHET). The purification may be performed using a conventionally known purification process. Specifically, the purification may be performed by undergoing one or more of crystallization (cooling), filtration, ion exchange, distillation, and adsorption.

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.

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.

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 (-SO ₃ H) 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.

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.

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.

The product obtained through the above step (B) may include recycled bis(2-hydroxyethyl) terephthalate having high purity and excellent color characteristics. Specifically, the recycled bis(2-hydroxyethyl) terephthalate may exhibit a yellowness index (YID) of 6 or less, 5.5 or less, 5 or less, 4.5 or less, 4 or less, 3.5 or less, or 3 or less (e.g., 1 to 6, 1.5 to 5.5, 2 to 5, or 2.5 to 4.5), thereby exhibiting excellent color characteristics. Such recycled bis(2-hydroxyethyl) terephthalate may be usefully used as a polymerization raw material (recycled raw material) for producing a polymer (e.g., polyester) due to its high purity and excellent color characteristics.

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.

[Example 1]

A glass container (first container), a glass flask (second container), a heating mantle (heating unit), a reflux condenser (condensing unit), and a glass connector (connection unit) were installed as shown in Fig. 1, and a treatment process (pretreatment process) of waste polyester textile was performed.

Specifically, 100 ml of cyclohexanone was added to a 500 ml glass flask. Then, 10 g of waste polyester textile (specifically, waste polyethylene terephthalate textile) was added to the glass container (waste polyester textile input amount: cyclohexanone input amount = 1:10).

The above glass flask and the glass container were connected, and the glass flask was fixed to a heating mantle. Next, the temperature of the heating mantle was increased to 160°C, which is higher than the boiling point of cyclohexanone (150°C), so that cyclohexanone was vaporized. The vaporized cyclohexanone formed through the vaporization moved upward in the glass flask and made primary contact with the waste polyester textile in the glass container (some moved to the reflux condenser without making contact), and the vaporized cyclohexanone that passed through the waste polyester textile moved to the reflux condenser located above the waste polyester textile. Subsequently, the vaporized cyclohexanone was converted into liquefied cyclohexanone through the reflux condenser, and the converted liquefied cyclohexanone fell downward and made secondary contact with the waste polyester textile. The dye-containing impurities contained in the waste polyester textile were removed by the first and second contacts described above, and the liquefied cyclohexanone after the second contact fell into the glass flask and settled.

The vaporization and liquefaction of the cyclohexanone were continuously performed until the dye-containing impurities contained in the waste polyester textile were completely removed. Thereafter, the waste polyester textile was removed from the glass container, washed with water, and dried in a vacuum oven to obtain polyester textile from which the dye-containing impurities were removed (completely decolorized).

[Examples 2 to 5]

A polyester textile from which dye-containing impurities were removed (bleached) was obtained through the same process as Example 1, except that the amount of solvent added, the vaporization conditions of the solvent, or the type of solvent were changed as shown in Table 1 below.

[Comparative Example 1]

10 g of waste polyester textile and 70 ml of cyclohexanone were placed together in a 500 ml flask (waste polyester textile input amount: cyclohexanone input amount = 1:7). Then, the flask was fixed to a heating mantle, the temperature of the heating mantle was increased to 120°C, and the mixture was stirred for 2 hours to remove dye-containing impurities contained in the waste polyester textile. The above removal process was considered one cycle, and three cycles were performed by replacing the cyclohexanone with new ones.

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

[Comparative Example 2]

A polyester textile from which dye-containing impurities were removed (bleached) was obtained through the same process as in Comparative Example 1, except that the amount of solvent added was changed as shown in Table 2 below.

[Comparative Examples 3 to 8]

A polyester textile from which dye-containing impurities were removed (bleached) was obtained through the same process as Example 1, except that the amount of solvent added, the vaporization conditions of the solvent, or the type of solvent were changed as shown in Table 2 below.

[Manufacturing Example 1]

1000 g of the polyester textile obtained in Example 1, 2000 g of ethylene glycol, and 5.0 g of zinc acetate anhydride were charged into a first stainless steel (SUS) reactor, and the internal temperature of the first reactor was raised to 180°C to perform primary depolymerization 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 charged, and secondary depolymerization 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 16 g of filter aid (Celite ^TM 545) was charged 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.

The above mixture was cooled to room temperature under stirring in a 10 L jacket-type cooling water circulation crystallizer for 2 hours, and the obtained crystallized product was separated into solid and liquid under a pressure of 3 bar using a pressurized Nutsche filter (jacket-type, filtration area 0.2 m ² ) 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, thereby obtaining 1040 g of the product.

Afterwards, 1040 g of the above-mentioned resultant and 3120 g of distilled water were placed in a 10 L glass reactor for adsorption-crystallization and dissolved at a temperature of 70°C. 5.2 g of activated carbon was added, stirred for 30 minutes, and filtered. The filtrate obtained through the 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).

[Manufacturing Examples 2 to 5]

A purified product containing regenerated bis(2-hydroxyethyl)terephthalate was obtained through the same process as in Manufacturing Example 1, except that the polyester textile obtained through Examples 2 to 5 was used instead of the polyester textile obtained through Example 1.

[Comparative Manufacturing Examples 1 to 8]

A purified product containing regenerated bis(2-hydroxyethyl)terephthalate was obtained through the same process as in Manufacturing Example 1, except that the polyester textile obtained through Comparative Examples 1 to 8 was used instead of the polyester textile obtained through Example 1.

[Experimental Example 1] Recovery rate (%)

The ratio of the weight of the obtained (processed) polyester textile to the weight of the initially injected waste polyester textile was calculated as a percentage, and the results are shown in Tables 1 and 2 below.

[Example 2] Color L

Color L(hunter) (L(hunter) of pretreated polyester textile), one of the color systems established by the international standard color measurement organization (CIE (Commission International d'Eclairage)), was measured using Colorimeter CM-3600A (manufactured by Konica Minolta), and the results are shown in Tables 1 and 2 below.

[Example 3] YID

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 and 2 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.

division Example 1
(Manufacturing Example 1) Example 2
(Manufacturing Example 2) Example 3
(Manufacturing Example 3) Example 4
(Manufacturing Example 4) Example 5
(Manufacturing Example 5) Solvent Cyclohexanone Cyclohexanone Cyclopentanone MIBK Cyclohexanone S/L ratio 1/10 1/15 1/10 1/10 1/3 B.P(℃) 156 156 130.6 116.5 156 Latent heat 91 91 96.3 82.5 91 S.P(∂t) 19.6 19.6 22.1 17 19.6 Safety - - - - - Recovery rate (%) 98 95.1 96 99.8 99.2 treatment
In the process
Used
Total solvent
Amount used (ml) 100 150 100 100 50 Color
L(hunter) 88.5 83.2 80.1 75.9 70.2 r-BHET YID 2.9 3.8 4.1 5.6 5.9

division Comparative Example 1
(comparison
Manufacturing example
1) Comparative Example 2
(comparison
Manufacturing example
2) Comparative Example 3
(comparison
Manufacturing example
3) Comparative Example 4
(comparison
Manufacturing example
4) Comparative Example 5
(comparison
Manufacturing example
5) Comparative Example 6
(comparison
Manufacturing example
6) Comparative Example 7
(comparison
Manufacturing example
7) Comparative Example 8
(comparison
Manufacturing example
8) Solvent Cyclohexanone Cyclohexanone Cyclohexanone Acetone Ethyl acetoacetate EG Toluene NMP S/L ratio 1/7
(immersion method) 1/15
(immersion method) 1/2 1/10 1/10 1/10 1/10 1/10 B.P(℃) 156 156 156 56 180.8 197.3 110.6 203 Latent heat 91 91 91 122 91 191 86.1 62.5 S.P(∂t) 19.6 19.6 19.6 19.9 19.9 33 18.2 23.0 Safety - - - - - - toxic substances
(Crown method) toxic substances
(Crown method) Recovery rate (%) 95 95 98 97 96 under 50 99 under 50 Processing process
at
Used
Total solvent
amount used
(ml) 210
(3 cycles) 450
(3 cycles) 20 100 100 100 100 100 Color L(hunter) 80.3 83.4 50.5 41.6 67.3 59.3 78.0 - r-BHET
YID 4.5 3.4 35 30 15 - 4.8 -

Referring to Tables 1 and 2 above, it can be confirmed that Examples 1 to 5, to which the treatment process of the present invention was applied, produced polyester textiles with high recovery rates and excellent color characteristics. Furthermore, it can be confirmed that when polyester textiles pretreated through Examples 1 to 5 are depolymerized, r-BHET with excellent color characteristics is produced.

On the other hand, Comparative Examples 1 and 2 show poor color characteristics of polyester textile even after 3 cycles using a large amount of solvent, and Comparative Examples 3 to 6 show poor color characteristics of polyester textile as the amount of solvent input, boiling point, latent heat, or dissolution parameter goes beyond the range specified in the present invention. In particular, Comparative Example 6 shows that decomposition (depolymerization) of waste polyester textile occurs during the treatment process, and the recovery rate is also significantly reduced. On the other hand, Comparative Examples 7 and 8 are not suitable for use as a treatment process because they use toxic solvents, and Comparative Example 8 shows that decomposition (depolymerization) of waste polyester textile occurs like Comparative Example 6, and the recovery rate is reduced.

[Explanation of symbols]

10: Courage

11: First container

12: Second container

20: Heating section

30: Condenser

40: Connection

Claims (13)

(1) A step of putting waste polyester textile into a first container and putting a solvent into a second container; (2) a step of forming a vaporized solvent from the solvent; and (3) a step of contacting the liquefied solvent formed through condensation of the vaporized solvent with the waste polyester textile; A method for treating waste polyester textile, wherein the ratio of the amount of waste polyester textile introduced into the first container to the amount of solvent introduced into the second container is 1:3 to 20. In the first paragraph, A method for treating waste polyester textile, wherein the solvent has a boiling point (B.P) of 110 to 250°C. In the first paragraph, A method for treating waste polyester textile, wherein the solvent has a latent heat of 70 cal/g or more. In the first paragraph, A method for treating waste polyester textile, wherein the solvent has a solubility parameter (∂ _t ) of 17 to 23. In the first paragraph, A method for treating waste polyester textile, wherein the solvent comprises a ketone solvent. In paragraph 5, A method for treating waste polyester textile, wherein the ketone solvent comprises at least one selected from the group consisting of cyclopentanone, cyclohexanone, and methyl isobutyl ketone. In the first paragraph, A method for treating waste polyester textile, wherein dye-containing impurities contained in the waste polyester textile are removed by contact in the above step (3). In the first paragraph, The above step (3) is, (3-1) A step in which the vaporized solvent first comes into contact with the waste polyester textile while passing through the waste polyester textile; and (3-2) A method for treating waste polyester textile, comprising a step of secondarily contacting the waste polyester textile with a liquefied solvent formed through condensation of the vaporized solvent that has passed through the waste polyester textile. Polyester textile obtained by the treatment method of claim 1. In paragraph 9, Polyester textile with L(hunter) of 70 or higher. A container section including a first container into which waste polyester textile is introduced and a second container into which a solvent is introduced; A heating unit that heats the solvent to form a vaporized solvent; A condenser for condensing the vaporized solvent to form a liquefied solvent; and A connecting portion is included to connect the first container and the condenser so that the liquefied solvent is supplied to the waste polyester textile, A device for treating waste polyester textile, wherein the ratio of the amount of waste polyester textile introduced into the first container to the amount of solvent introduced into the second container is 1:3 to 20. (A) a step of depolymerizing waste polyester textile pretreated by the treatment method of paragraph 1 to obtain a product; and (B) A method for depolymerizing waste polyester textile, comprising a step of purifying the above product to obtain a purified product containing recycled bis(2-hydroxyethyl)terephthalate. In paragraph 12, A method for depolymerizing waste polyester textile, wherein the yellowness index (YID) of the above-mentioned recycled bis(2-hydroxyethyl) terephthalate is 6 or less.