Recycled raw material composition and method for producing the same

Abstract

The present invention relates to a recycled raw material composition and a method for producing the recycled raw material composition, wherein the recycled raw material composition contains recycled bis(2-hydroxyethyl) terephthalate formed by the depolymerization of waste polyester, and the peak area ratio of acetate ester compounds determined by high-performance liquid chromatography (HPLC) analysis is 1.0% or less. Due to the reduced impurity content, the recycled raw material composition can exhibit high purity and high quality.

Description

Detailed Description of the Invention

[0001] [Technical Field] The present invention relates to a recycled raw material composition obtained through a recycling process of waste polyester, which can have high purity and high quality with minimal impurities, and a process for preparing the recycled raw material composition.

[0002] [Background Art] Among the polymers commonly used in modern life, polyester is widely used as a material for beverage and food containers, various packaging films, and interior and exterior materials such as panels, shelves, and partitions due to its excellent mechanical strength, heat resistance, transparency, and gas barrier properties.

[0003] As a result, plastic waste such as polyester is generated at an unmanageable level every year. In recent years, countries around the world have formulated regulations and plans for recycling waste plastic resources including waste polyester.

[0004] As a method for recycling waste polyester, a physical recycling method or a chemical recycling method is used. However, the physical recycling method cannot guarantee purity and is therefore not widely adopted. On the other hand, in the chemical recycling method, the ester bond of waste polyester is cleaved to perform depolymerization. Reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis are used. Among the above, glycolysis is to decompose waste polyester by adding glycol such as ethylene glycol or diethylene glycol. A product mainly containing bis(2-hydroxyethyl) terephthalate (BHET) is obtained. The bis(2-hydroxyethyl) terephthalate contained in the product can be used as a raw material for preparing unsaturated polyester or ester polyol after its crystallization or purification.[[ID=ZI]]

[0005] However, products containing bis(2-hydroxyethyl) terephthalate (BHET) have relatively high levels of impurities, which limits the ability to obtain high-purity, high-quality bis(2-hydroxyethyl) terephthalate (BHET) from them.

[0006] [Disclosure of the Invention] [Technical challenges] Generally, recycled raw material compositions obtained as a result of the depolymerization reaction of waste polyester contain, in addition to bis(2-hydroxyethyl) terephthalate as a useful recycled raw material, impurities such as oligomers including dimers and trimers, diethylene glycol ester compounds derived from diethylene glycol (DEG), acetate ester compounds obtained using acetate catalysts, or bis(2-hydroxyethyl) terephthalate (BHET) analogs, which are factors that reduce the purity and quality of the recycled raw material composition.

[0007] In particular, the inventors have confirmed that among the above-mentioned impurities, diethylene glycol ester compounds, acetate ester compounds, and BHET analogs degrade the purity and quality of bis(2-hydroxyethyl) terephthalate contained in the recycled raw material composition, and as a result, when polymers are prepared using recycled bis(2-hydroxyethyl) terephthalate, the degree of polymerization and heat resistance properties of the polymer deteriorate.

[0008] To solve this problem, the present inventors have confirmed that when the crystallization process is carried out by controlling the polarity of the solvent during the depolymerization process of waste polyester, the content of impurities such as diethylene glycol ester compounds, acetate ester compounds, and BHET analogs in the recycled raw material composition can be adjusted to a specific range, and as a result, a polymer with improved degree of polymerization and heat resistance can be obtained, thus leading to the present invention.

[0009] Therefore, the object of the present invention is to provide a recycled raw material composition that minimizes the impurity content and ensures the degree of polymerization and heat resistance properties of the polymer material are at target levels, as well as a process for preparing the same.

[0010] [Solutions to the problem] To achieve the above objective, the present invention provides a recycled raw material composition comprising bis(2-hydroxyethyl) terephthalate formed by the depolymerization of waste polyester, and having a peak area ratio of 1.0% or less of acetate ester compounds when analyzed by high-performance liquid chromatography (HPLC).

[0011] In addition, the present invention provides a process for preparing a recycled raw material composition, comprising the steps of: (1) depolymerizing waste polyester by a glycol decomposition reaction to obtain a reaction product containing crude bis(2-hydroxyethyl) terephthalate (crude BHET); (2) treating the reaction product with an ion exchange resin; (3) adding water to the reaction product obtained by treatment with the ion exchange resin to adjust the polarity of the solvent contained in the reaction product; (4) cooling the reaction product to which water has been added to perform crystallization; and (5) performing pressure filtration of the crystallized product obtained through crystallization to obtain a product containing recycled bis(2-hydroxyethyl) terephthalate.

[0012] [Beneficial effects of the invention] In this invention, the polarity of the solvent used in the depolymerization process of waste polyester is controlled, thereby optimizing the separation and purification of impurities (e.g., acetate ester compounds, diethylene glycol ester compounds, BHET analogs, BHET oligomers, etc.). As a result, a recycled raw material composition with minimal impurity content can be obtained. Therefore, this invention can provide high-purity and high-quality bis(2-hydroxyethyl) terephthalate as a recycled raw material (polymerization raw material) from the recycled raw material composition.

[0013] As described above, the present invention not only enables resource recycling by providing high-purity and high-quality bis(2-hydroxyethyl) terephthalate through depolymerization of waste polyester, but also contributes to the preparation of polymers (e.g., recycled polyester resins) with excellent heat resistance and color characteristics using bis(2-hydroxyethyl) terephthalate as a recycled raw material (polymerization raw material).

[0014] [Best embodiment for carrying out the invention] The present invention will be described in detail below. The present invention as described herein is not limited to the disclosure below and can be modified in various forms without altering the spirit of the invention.

[0015] In this specification, the term “comprising” is intended to identify specific features, areas, steps, processes, elements, and / or components. Unless otherwise stated, this does not preclude the presence or addition of any other features, areas, steps, processes, elements, and / or components.

[0016] Throughout this specification, terms such as "first," "second," etc., are used to describe various components. However, these terms should not limit the components. These terms are used for the purpose of distinguishing one component from another.

[0017] All numerical values ​​and expressions used herein regarding the quantities of components, reaction conditions, etc., should be understood to be modified by the term "approximately" unless otherwise indicated.

[0018] In this specification, singular expressions are interpreted as encompassing plural numbers unless otherwise specified in the context.

[0019] [Recycled raw material composition] The recycled raw material composition according to the present invention contains bis(2-hydroxyethyl) terephthalate formed by the depolymerization of waste polyester, and has a peak area percentage of acetate ester compounds of 1.0% or less when analyzed by high-performance liquid chromatography (HPLC). The recycled raw material composition according to the present invention has an acetate ester compound as an impurity in a controlled content within a specific range of 1.0% or less, and therefore the recycled raw material obtained therefrom, i.e., recycled bis(2-hydroxyethyl) terephthalate, has high purity. When a polymer (e.g., recycled polyester resin) is prepared using this, it is possible to prevent a decrease in heat resistance properties (Tm, Tg) caused by an increase in diethylene glycol units (DEG units) or a decrease in the degree of polymerization due to the action of terminal groups. As a result, it is possible to provide a polymer with excellent heat resistance properties, color characteristics, etc.

[0020] Acetate ester compounds contained in recycled raw material compositions may be byproducts of acetate salts used as catalysts during the depolymerization of waste polyester by glycol decomposition reactions. Specifically, referring to reaction scheme 1 below, acetic acid (AA) derived from the acetate salt used as a catalyst may react with ethylene glycol (EG) to produce acetate compounds such as 2-hydroxyethyl acetate (HA) and water (H2O). In such cases, since 2-hydroxyethyl acetate (HA) has a boiling point close to that of ethylene glycol (EG), it is not easy to filter it out as an impurity during the recovery and reuse of ethylene glycol (EG). As a result, byproducts such as acetate ester compounds accumulate as the process continues. That is, referring to reaction scheme 2 below, 2-hydroxyethyl acetate (HA) may undergo a transesterification reaction with bis(2-hydroxyethyl) terephthalate (BHET) to produce ester compounds such as 2-hydroxyethyl (2-acetoxyethyl) terephthalate (HAET) and ethylene glycol (EG).

[0021] [ka]

[0022]

Chem.

[0023] The acetate ester compounds (e.g., 2-hydroxyethyl (2-acetoxyethyl) terephthalate (HAET)) thus produced may act as impurities (e.g., reduction of BHET purity, generation of HA, and acting as end groups). The recycled raw material composition according to the present invention has a very low content of acetate ester compounds. As a result, high-purity recycled bis(2-hydroxyethyl) terephthalate (BHET) can be provided.

[0024] Specifically, the recycled raw material composition according to the present invention may have a peak area ratio of acetate ester compounds (HA ester) of 0.9% or less, 0.8% or less, 0.7% or less, 0.6% or less, 0.5% or less, 0.4% or less, 0.3% or less, 0.2% or less, 0.1% or less, less than 0.1%, 0.09% or less, 0.08% or less, 0.07% or less, 0.05% or less, 0.04% or less, or 0.03% or less when analyzed by high performance liquid chromatography (HPLC). For example, the peak area ratio of acetate ester compounds (HA ester) may be 0 to 1.0%, more than 0 to 0.9%, more than 0 to 0.5%, more than 0 to 0.3%, more than 0 to 0.1%, more than 0 to 0.09%, or 0.01 to 0.09%.

[0025] On the other hand, the recycled raw material composition according to the present invention may contain impurities such as bis(2-hydroxyethyl) terephthalate (BHET) analogs (isomers), bis(2-hydroxyethyl) terephthalate (BHET) oligomers (dimers, trimers, etc.), and diethylene glycol ester compounds in addition to acetate ester compounds. In the present invention, the contents of these impurities are also controlled within a specific range.

[0026] Specifically, according to the present invention, when analyzing a recycled raw material composition by high performance liquid chromatography (HPLC), the peak area ratio of the compound containing bis(2-hydroxyethyl) isophthalate, which is a BHET analog, may be 1.0% or less. The compound containing bis(2-hydroxyethyl) isophthalate may be a compound composed only of bis(2-hydroxyethyl) isophthalate. Bis(2-hydroxyethyl) isophthalate may be an impurity formed when waste polyester containing isophthalic acid units (IPA units) is depolymerized by a glycolysis reaction (see the following Reaction Scheme 3).

Chemical formula

[0027] The bis(2-hydroxyethyl) isophthalate thus produced may act as an impurity. When a polymer is prepared using a recycled raw material composition containing this, the melting point (Tm) of the polymer prepared therefrom is significantly reduced, thereby significantly reducing the heat resistance characteristics of the polymer. The recycled raw material composition according to the present invention has a very low content of bis(2-hydroxyethyl) isophthalate. As a result, a polymer having excellent heat resistance characteristics can be provided.

[0028] Specifically, the recycled raw material composition according to the present invention may have a peak area ratio of a compound containing bis(2-hydroxyethyl) isophthalate (BHEI) of 0.98% or less, 0.95% or less, 0.93% or less, 0.92% or less, 0.9% or less, 0.7% or less, 0.6% or less, 0.5% or less, 0.48% or less, 0.46% or less, 0.43% or less, 0.4% or less, 0.38% or less, 0.35% or less, 0.33% or less, or 0.3% or less when analyzed by high performance liquid chromatography (HPLC). For example, the peak area ratio of the compound containing bis(2-hydroxyethyl) isophthalate (BHEI) may be 0 to 1.0%, more than 0 to 0.99%, more than 0 to 0.97%, more than 0 to 0.92%, more than 0 to 0.6%, more than 0 to 0.55%, or 0.01 to 0.35%.

[0029] According to the present invention, the recycled raw material composition may have a total peak area percentage of 2.0% or less of diethylene glycol ester compounds when analyzed by high-performance liquid chromatography (HPLC) (the total peak area percentage of diethylene glycol ester compounds is 2.0% or less). Diethylene glycol ester compounds may be produced by a transesterification reaction between diethylene glycol and bis(2-hydroxyethyl) terephthalate (BHET) during the depolymerization process of waste polyester by glycol decomposition reaction. Specifically, the diethylene glycol ester compounds may include 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate (DEG ester 1) represented by the following chemical formula 1, and bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate (DEG ester 2) represented by the following chemical formula 2.

[0030] [ka]

[0031] [ka]

[0032] Specifically, when analyzed by high-performance liquid chromatography (HPLC), the recycled raw material composition according to the present invention may have a total peak area percentage of diethylene glycol ester compounds (DEG esters) of 1.99% or less, 1.95% or less, 1.93% or less, 1.9% or less, 1.88% or less, 1.85% or less, 1.83% or less, 1.8% or less, 1.78% or less, 1.77% or less, 1.75% or less, 1.73% or less, 1.7% or less, 1.65% or less, 1.63% or less, or 1.6% or less (for example, the peak area percentage of DEG ester 1 and the peak area percentage of DEG ester 2). For example, the peak area percentage for diethylene glycol ester compounds (DEG esters) may be 0-1.99%, greater than 0-1.95%, greater than 0-1.85%, greater than 0-1.8%, greater than 0-1.7%, greater than 0-1.6%, or 0.01-1.5% in total.

[0033] According to the present invention, when analyzed by high-performance liquid chromatography (HPLC), the recycled raw material composition may have a total peak area percentage of 2.0% or less for dimers or higher-order oligomers (the sum of the peak area percentages of dimers or higher-order oligomers is 2.0% or less). Specifically, the dimers or higher-order oligomers may be dimers of bis(2-hydroxyethyl) terephthalate (BHET), trimers of bis(2-hydroxyethyl) terephthalate (BHET), or combinations thereof. The oligomers may have a molecular weight of 2,000 g / mol or less (for example, 1,000 to 2,000 g / mol).

[0034] Specifically, when analyzed by high-performance liquid chromatography (HPLC), the recycled raw material composition according to the present invention may have a total peak area percentage of dimers or higher-order oligomers (e.g., peak area percentage of dimers and peak area percentage of trimers) of 1.5% or less, 1.3% or less, 1.0% or less, less than 1.0%, 0.95% or less, 0.9% or less, 0.85% or less, 0.8% or less, 0.75% or less, 0.7% or less, 0.65% or less, 0.6% or less, 0.55% or less, 0.5% or less, 0.45% or less, 0.4% or less, 0.39% or less, 0.35% or less, or 0.3% or less. For example, the peak area percentage of dimers or higher-order oligomers may be 0-1.0%, greater than 0-0.9%, greater than 0-0.6%, 0.01-0.55%, 0.05-0.53%, 0.1-0.5%, or 0.15-0.4% in total.

[0035] On the other hand, the recycled bis(2-hydroxyethyl) terephthalate (r-BHET) contained in the recycled raw material composition according to the present invention is formed by the depolymerization of waste polyester. r-BHET may also be a compound formed as an intermediate in the process of preparing polyester by polymerization of ethylene glycol with terephthalic acid or its ester. As described above, since the impurity content is controlled to be below a specific level, recycled bis(2-hydroxyethyl) terephthalate (r-BHET) can have high purity. Therefore, r-BHET can have physical properties equivalent to virgin bis(2-hydroxyethyl) terephthalate (virgin BHET). In addition, recycled bis(2-hydroxyethyl) terephthalate (r-BHET) has excellent crystallinity, which gives it a high melting point, and it can also have excellent qualities such as color.

[0036] Specifically, the purity of recycled bis(2-hydroxyethyl) terephthalate (r-BHET) may be calculated by measuring the ratio (%) of the peak area of ​​BHET to the total peak area in the spectrum of the recycled raw material composition obtained using high-performance liquid chromatography (HPLC).

[0037] For example, when analyzed by high-performance liquid chromatography (HPLC), the recycled raw material composition according to the present invention may have a peak area percentage of 92% or more of bis(2-hydroxyethyl) terephthalate. Specifically, the peak area percentage of bis(2-hydroxyethyl) terephthalate may be 93% or more, 93.5% or more, 94% or more, 94.3% or more, 94.5% or more, 94.8% or more, 95% or more, 95.3% or more, 95.5% or more, 95.8% or more, 96% or more, 98% or more, 99% or more, or even 100%. Therefore, the recycled bis(2-hydroxyethyl) terephthalate contained in the recycled raw material composition can have high purity.

[0038] In addition, when analyzed by high-performance liquid chromatography (HPLC), the recycled raw material composition may have a peak area percentage of monohydroxyethyl terephthalate (MHET) of 2% or less, 1.8% or less, 1.5% or less, 1.4% or less, 1.2% or less, 1% or less, 0.99% or less, or 0.95% or less. Specifically, the peak area percentage of monohydroxyethyl terephthalate (MHET) may be 0-2%, greater than 0-1.9%, 0.5-1.5%, or 0.8-1.1%.

[0039] On the other hand, as the content of bis(2-hydroxyethyl) isophthalate and / or diethylene glycol ester compounds in the recycled raw material composition increases, the heat resistance properties of the final polymer, such as the melting point (Tm), decrease linearly. Acetate ester compounds act as inhibitors of polymer chain growth. As the content of acetate ester compounds increases, the heat resistance properties of the final polymer decrease exponentially. This relationship can be used to derive correlations and predict the heat resistance properties of polymers prepared using recycled raw material compositions (specifically, recycled bis(2-hydroxyethyl) terephthalate).

[0040] For example, the recycled raw material composition according to the present invention may have a thermal degradation index (TDI) of 6.0 or less, as defined by the following formula 1, when analyzed by high-performance liquid chromatography (HPLC). [Formula 1] TDI = [DEG ester 1] + ([DEG ester 2] × 2) + exp^[HA ester] + exp^[BHEI] In Formula 1, DEG ester 1 is the peak area percentage (%) of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate, DEG ester 2 is the peak area percentage (%) of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate, HA ester is the peak area percentage (%) of 2-hydroxyethyl(2-acetoxyethyl)terephthalate, and BHEI is the peak area percentage (%) of bis(2-hydroxyethyl)isophthalate.

[0041] In Equation 1, calculations are performed using only the numerical values ​​of these parameters, excluding their units.

[0042] Specifically, when the thermal degradation index (TDI) defined by Equation 1 is 5.8 or less, it is possible to more effectively prevent the degradation of the polymer's heat resistance properties by DEG ester 1, DEG ester 2, HA ester, and BHEI during the preparation of the polymer (e.g., recycled polyester resin). For example, the thermal degradation index (TDI) may be 5.5 or less, 5.4 or less, 5.2 or less, 5.0 or less, 4.9 or less, 4.8 or less, 4.5 or less, 4.3 or less, or 4.0 or less (specifically, 0 to 5.5, 0.5 to 5.0, or 1.0 to 4.0).

[0043] The recycled raw material composition according to the present invention may have a yellowness index (YID) of 5.0 or less when analyzed as a solution (sample recycled raw material solution) obtained by dissolving it in dimethylformamide at a concentration of 25% by weight. Specifically, the yellowness index (YID) may be 4.9 or less, 4.5 or less, 4.3 or less, 4.0 or less, 3.8 or less, 3.5 or less, 3.3 or less, 3.0 or less, 2.5 or less, or 2.3 or less. Having such a yellowness index (YID), the recycled raw material composition according to the present invention can contribute to the preparation of polymers (recycled polyester resins) having excellent color characteristics (e.g., transparency).

[0044] [Process for preparing recycled raw material compositions] The process for preparing the recycled raw material composition according to the present invention is a process for preparing a recycled raw material composition in which the polarity of the solvent used in the depolymerization step is adjusted, followed by a cooling and crystallization step, thereby minimizing the impurity content as described above. Specifically, the process for preparing the recycled raw material composition according to the present invention includes: (1) depolymerizing waste polyester by a glycol decomposition reaction to obtain a reactant containing crude bis(2-hydroxyethyl) terephthalate (crude BHET); (2) treating the reactant with an ion exchange resin; (3) adding water to the reactant obtained by treatment with the ion exchange resin to adjust the polarity of the solvent contained in the reactant; (4) cooling the reactant to which water has been added to perform crystallization; and (5) performing pressure filtration of the crystallized product obtained through crystallization to obtain a product containing recycled bis(2-hydroxyethyl) terephthalate. This will be described in detail below.

[0045] In this invention, the term "reactant" may refer to the product obtained through each step. Step (1): Depolymerization of waste polyester According to the present invention, step (1) is the step of depolymerizing waste polyester by a glycol decomposition reaction to obtain a reaction product (a) containing crude bis(2-hydroxyethyl) terephthalate (crude BHET).

[0046] The waste polyester used for depolymerization may be obtained by pre-treating waste products that have been discarded after use by consumers. The waste products may include beverage bottles, fabrics, films, cases, boxes, partitions, shelves, protective panels, packaging materials, building materials, and interior and exterior materials, all of which contain polyester.

[0047] Polyesters contained in various waste products may be obtained through a (co)polymerization reaction of one or more commonly known acid components with one or more commonly known alcohol components. Specifically, the acid components may include at least one selected from the group consisting of terephthalic acid, isophthalic acid, dimethyl terephthalic acid, dimethyl terephthalate, naphthalenedicarboxylic acid, orthophthalic acid, adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid. The alcohol component may specifically include at least one selected from the group consisting of ethylene glycol, 1,3-propanediol, 1,2-octanediol, 1,3-octanediol, 2,3-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,1-dimethyl-1,5-pentanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, isosorbide, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol.

[0048] Pretreatment may be carried out by removing other plastics, metals, and foreign matter mixed in with the various wastes, washing them, and then crushing them in a crusher. As a result of pretreatment, the waste polyester may have a flake form. In addition, the waste polyester may have a fibrous microstructure.

[0049] Step (1) of depolymerizing the waste polyester may include (1-1) depolymerizing the waste polyester by a first glycol decomposition reaction (first depolymerization) to obtain a first reactant (a-1), and (1-2) depolymerizing the first reactant (a-1) by a second glycol decomposition reaction (second depolymerization) to obtain a second reactant (a-2).

[0050] Specifically, step (1-1) may include carrying out a chemical reaction to obtain a first reactant (a-1) by first cleaving the polymer chains of waste polyester with a first glycol-based compound.

[0051] The first glycol compound used in the first depolymerization of step (1-1) is not particularly limited, but may specifically include at least one selected from the group consisting of ethylene glycol (monoethylene glycol), propylene glycol, and diethylene glycol.

[0052] The amount of the first glycol compound supplied in step (1-1) is not particularly limited. Specifically, the amount supplied may be 1 or more times, 2 or more times, or 3 or more times the weight of the waste polyester, and 7 or less times, 5 or less times, or 4 or less times (for example, 1 to 7 times, 2 to 5 times, or 3 to 4 times).

[0053] The first depolymerization temperature in step (1-1) is not particularly limited, but may be 180-200°C, specifically 180-195°C, 180-193°C, 180-190°C, 180-188°C, or 180-185°C. In addition, the first depolymerization time is not particularly limited, but may be 1-4 hours, 1-3 hours, or 1-2 hours from the time the temperature required for the first depolymerization is reached. Since the first depolymerization temperature and time are within the above ranges, the first glycol decomposition reaction of waste polyester can be carried out smoothly while minimizing the formation of by-reactants such as diethylene glycol ester compounds.

[0054] The first depolymerization in step (1-1) may be carried out in the presence of a catalyst that activates the first glycol decomposition reaction. The catalyst is not particularly limited as long as it is a generally known catalyst, but may specifically include metal acetates, their anhydrides, or their hydrides. More specifically, the catalyst may be at least one selected from the group consisting of zinc acetate, sodium acetate, cobalt acetate, and manganese acetate, their hydrates, or their anhydrides.

[0055] The amount of catalyst supplied (used) in step (1-1) is not particularly limited, but specifically, it may be 0.01 to 5 parts by weight, 0.05 to 3 parts by weight, 0.1 to 2 parts by weight, 0.15 to 1 part by weight, 0.2 to 0.6 parts by weight, or 0.2 to 0.4 parts by weight per 100 parts by weight of waste polyester.

[0056] For example, the first glycol decomposition reaction carried out in step (1-1) may be a reaction of waste polyester with ethylene glycol in the presence of zinc acetate hydrate.

[0057] Step (1-2) may include carrying out a chemical reaction to obtain a second reactant (a-2) by secondarily cleaving the first reactant (a-1) obtained in step (1-1) with a second glycol compound. The second reactant (a-2) may refer to reactant (a) obtained through step (1).

[0058] The second glycol compound used in the second depolymerization step (1-2) is not particularly limited, but may specifically include at least one selected from the group consisting of ethylene glycol (monoethylene glycol), propylene glycol, and diethylene glycol. The second glycol compound may originate from the first depolymerization step (1-1) or may be further added during the second depolymerization step (1-2).

[0059] The amount of the second glycol compound supplied in step (1-2) (the additional amount used in the second depolymerization) is not particularly limited. Specifically, the amount supplied may be 1 or more times, 2 or more times, or 3 or more times the weight of the waste polyester, and 7 or less times, 5 or less times, or 4 or less times (for example, 1 to 7 times, 2 to 5 times, or 3 to 4 times).

[0060] The second depolymerization temperature in step (1-2) is not particularly limited, but may be 150-170°C. Specifically, it may be 150-165°C, 150-163°C, 150-160°C, 150-158°C, or 150-155°C. In addition, the second depolymerization time is not particularly limited, but may be 1-4 hours, 1-3 hours, or 1-2 hours from the time the temperature required for the second depolymerization is reached. Since the temperature and time of the second depolymerization are within the above ranges, the second depolymerization of the first reactant (a-1) is carried out smoothly while minimizing the formation of impurities such as diethylene glycol ester compounds.

[0061] The second depolymerization in step (1-2) may be carried out in the presence of a catalyst that activates the second glycol decomposition reaction. The catalyst may be derived from the first depolymerization step in step (1-1) or may be further added during the second depolymerization step in step (1-2). The description of the catalyst is the same as the description of the catalyst in step (1-1) above, so a detailed description is omitted.

[0062] Since depolymerization is carried out through steps (1-1) and (1-2), a reaction product (a) containing crude bis(2-hydroxyethyl) terephthalate (crude BHET) can be obtained in high yield.

[0063] On the other hand, the process for preparing the recycled raw material composition according to the present invention may further include, before performing step (2) below, a step of cooling the reactant (a) obtained through step (1), and a step of performing solid-liquid separation thereof to improve the efficiency of impurity removal.

[0064] Specifically, in the cooling and solid-liquid separation, reactant (a) is cooled by a reduced-pressure flash and then subjected to solid-liquid separation through a pressurized filtration process using a filter aid. As a result, reactant (a) can be converted into liquid reactant (b). Further cooling and solid-liquid separation steps remove solid impurities such as particulate matter and insoluble organic substances contained in the first reactant (a), thereby increasing the yield and purity of the final product (recycled raw material composition).

[0065] The temperature at which the first reactant (a) is cooled by the reduced-pressure flash is not particularly limited, but may be 150°C or lower, 140°C or lower, 135°C or lower, 130°C or lower, 125°C or lower, 120°C or lower, or 115°C or lower, and 50°C or higher, 70°C or higher, 80°C or higher, 100°C or higher, 105°C or higher, or 110°C or higher (for example, 100-135°C, 105-125°C, or 110-120°C).

[0066] The pressure required to perform a depressurization flush is not particularly limited, but may be 200 Torr or less, 150 Torr or less, 100 Torr or less, 50 Torr or less, or 30 Torr or less, and 5 Torr or more, 8 Torr or more, 10 Torr or more, or 15 Torr or more (for example, 5 to 200 Torr, 10 to 100 Torr, or 15 to 50 Torr).

[0067] The filter aids used for solid-liquid separation are not particularly limited as far as is generally known, but may specifically include at least one selected from the group consisting of diatomaceous earth, perlite, and asbestos powder.

[0068] Step (2): Treatment with ion exchange resin According to the present invention, step (2) is a step of treating reactant (a) (if cooling and solid-liquid separation are performed, reactant (a) becomes liquid reactant (b)) with an ion exchange resin. Specifically, this treatment may be carried out by passing reactant (a) through an ion exchange resin or by adding the ion exchange resin to reactant (a). By performing the above steps, ionic impurities contained in reactant (a) are removed, and a high-purity reactant (c) can be obtained.

[0069] The ion exchange resin may be a commonly known cation exchange resin, anion exchange resin, amphoteric ion exchange resin, chelate resin, or a combination thereof.

[0070] The cation exchange resin may specifically include 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 include a strongly basic anion exchange resin in the form of a quaternary ammonium salt or a weakly basic anion exchange resin having primary to tertiary amino groups. The chelating resin may be a polymer resin having reactive functional groups such as acetates or phosphates that chelate metal ions such as sodium, copper, nickel, zinc, and manganese.

[0071] When the treatment is carried out by adding an ion exchange resin to the reactant (a), the amount of ion exchange resin supplied (used) is not particularly limited, but specifically it may be 1 or more, 2 or more, 3 or more, or 5 or more times the weight of the catalyst used in the depolymerization of step (1), and 20 or less, 15 or less, 10 or less, or 8 or less (for example, 1 to 20 times, 2 to 15 times, 3 to 10 times, or 5 to 8 times). In addition, the amount of ion exchange resin supplied (used) may be 1 or more parts by weight, 2 or more parts by weight, 3 or more parts by weight, or 5 or more parts by weight, and 50 or less parts by weight, 20 or less parts by weight, 15 or less, 10 or less, or 7 or less parts by weight (for example, 1 to 50 parts by weight, 3 to 20 parts by weight, or 5 to 10 parts by weight) per 100 parts by weight of the waste polyester from step (1).

[0072] When the treatment is carried out by passing the reactant (a) through an ion exchange resin, the ion exchange resin may be in the form of particles having a predetermined size. Specifically, the treatment for removing ionic impurities can be carried out by passing the liquid reactant (b) through a column packed with ion exchange resin particles having particle sizes of 0.3 to 1.5 mm, 0.5 to 1.3 mm, or 0.7 to 1.0 mm.

[0073] In the reactant (c) obtained by treatment with an ion exchange resin, the polarity of the solvent can be controlled through the following step (3).

[0074] Step (3): Control of solvent polarity According to the present invention, step (3) is a step of adding water to the reactant (c) obtained by treatment with an ion exchange resin in step (2) to adjust the polarity of the solvent contained in the reactant (c). When such a step (3) is performed, the crystal growth of regenerated bis(2-hydroxyethyl) terephthalate is smoothly achieved in the cooling crystallization step of step (4) below, which significantly increases the efficiency of pressurized filtration in step (5) below, enabling the separation of BHET analogs (e.g., BHEI) which are difficult to separate due to their structural similarity to bis(2-hydroxyethyl) terephthalate (BHET). As a result, a high-purity regenerated raw material composition (i.e., regenerated bis(2-hydroxyethyl) terephthalate) can be prepared.

[0075] Specifically, if the crystal growth of bis(2-hydroxyethyl) terephthalate (BHET) is successfully achieved in the cooling crystallization step (4), the separation efficiency of impurities such as low-melting-point compounds and chromophore molecules can be improved. Therefore, it is necessary to ensure that the crystals of bis(2-hydroxyethyl) terephthalate (BHET) grow well. Here, the crystal growth (crystal formation) of bis(2-hydroxyethyl) terephthalate (BHET) changes significantly depending on the polarity of the solvent contained in the reactant (c) subjected to cooling crystallization. Therefore, it is very important to control the polarity of the solvent contained in the reactant (c) obtained through treatment with ion exchange resin before the cooling crystallization step.

[0076] Therefore, in the present invention, water is added to the reactant (c) obtained through step (2) to optimally control the polarity of the solvent contained in the reactant (c), thereby enabling good growth of bis(2-hydroxyethyl) terephthalate (BHET) crystals in the cooling crystallization step of step (4) below.

[0077] According to the present invention, the amount of water added to the reactant (c) obtained by treatment with an ion exchange resin is not particularly limited, but may be 25 to 80% by weight of the total weight of the solvent (specifically, the solvent contained in the component obtained by removing crude BHET from the reactant (d) to which water has been added. That is, water may be added to the reactant (c) obtained by treatment with an ion exchange resin such that the weight of water is 25 to 80% by weight of the total weight of the solvent contained in the reactant (d) to which water has been added. Specifically, the amount of water added may be 26 to 79% by weight, 27 to 78% by weight, 28 to 77% by weight, 29 to 76% by weight, 30 to 75% by weight, 35 to 75% by weight, 40 to 75% by weight, or 45 to 75% by weight of the total weight of the solvent (solvent with controlled polarity). Since the amount of water added is within the above range, the crystal growth of bis(2-hydroxyethyl) terephthalate (BHET) is promoted, and at the same time, the efficiency of pressurized filtration can be increased.

[0078] According to the present invention, the solvent contained in reactant (c) may include a glycol-based solvent. For example, reactant (c) may include a first glycol compound and / or a second glycol compound used as a glycol solvent for a first glycol decomposition reaction and / or a second glycol decomposition reaction. By adding water to reactant (c), the polarity of the solvent contained in reactant (c) can be controlled. Specifically, a polarity-controlled solvent may include water and a glycol-based solvent (e.g., ethylene glycol (monoethylene glycol), propylene glycol, diethylene glycol, or a combination thereof). The mixing ratio of water and glycol-based solvent contained in the polarity-controlled solvent is not particularly limited, but may be a weight ratio of 25:75 to 80:20, specifically 28:72 to 80:20, 29:71 to 80:20, 30:70 to 80:20, 30:70 to 78:22, or 30:70 to 75:25. Since the mixing ratio is within the above range, the polarity of the solvent contained in reactant (c) can be optimized to the desired level.

[0079] By adding water as described above, a reactant (d) containing a solvent with controlled polarity can be obtained.

[0080] Step (4): Cooling crystallization According to the present invention, step (4) is a step of cooling the reactant (d) to which water was added in step (3) to perform crystallization. Specifically, by lowering the temperature of the reactant (d) to which the polarity of the solvent is controlled and performing crystallization, a crystallized product (e) containing crystalline bis(2-hydroxyethyl) terephthalate (BHET) can be obtained.

[0081] The temperature for crystallization of reactant (d) is not particularly limited, but may be 70°C or lower, 60°C or lower, 50°C or lower, 40°C or lower, 30°C or lower, or 25°C or lower, and may also be 0°C or higher, 5°C or higher, 10°C or higher, 15°C or higher, or 20°C or higher. For example, the temperature for crystallization of reactant (d) may be room temperature (20±5°C).

[0082] By performing cooling crystallization, acetate-based ester compounds and diethylene glycol ester compounds can be efficiently removed as impurities.

[0083] Step (5): Pressure filtration According to the present invention, step (5) is a step of performing pressure filtration of the crystallized product (e) obtained in step (4) to obtain a product (f) containing regenerated bis(2-hydroxyethyl) terephthalate. Specifically, product (f) may be a cake containing regenerated bis(2-hydroxyethyl) terephthalate.

[0084] The pressure for pressurized filtration of the precipitate (e) is not particularly limited, but may be 0.1 to 21 bar, 0.5 to 10 bar, or 1 to 5 bar. In addition, the temperature for pressurized filtration is not particularly limited, but may be 5 to 35°C, 10 to 30°C, or 15 to 25°C.

[0085] The filter used for pressurized filtration is not particularly limited, but may specifically be a Nutsche filter or a filter press.

[0086] Pressure filtration using a Nutsche filter may include a step of placing the crystallized material in the Nutsche filter, injecting an inert gas such as nitrogen to pressurize it, and primarily separating the solvent from the solid (cake). In addition, pressure filtration using a Nutsche filter may further include a step of injecting water into the Nutsche filter to wash away any residual solvent remaining in the solid (cake), injecting an inert gas to pressurize it, and primarily separating the solid (cake) from the water. The solid (cake) thus obtained can then be subjected to drying and cooling steps.

[0087] Pressure filtration using a filter press may include a step of forming a filtration chamber with a filter plate having a filtration surface, a filter cloth, and a cover, and performing solid-liquid separation by pressurizing the precipitate (e) at high pressure between the filter cloth and the cover.

[0088] By performing pressurized filtration, impurities such as acetate ester compounds, diethylene glycol ester compounds, and BHET oligomers can be efficiently removed.

[0089] On the other hand, since the precipitate (e) is obtained through the step of controlling the polarity of the solvent (3) and the step of cooling crystallization (4), it can have excellent pressurized filtration performance. For example, the pressurized filtration rate of the precipitate (e) may be 100 L / min or more, specifically 105 L / min or more, 115 L / min or more, 120 L / min or more, 125 L / min or more, 140 L / min or more, 150 L / min or more, 160 L / min or more, 170 L / min or more, 180 L / min or more, 200 L / min or more, 220 L / min or more, 250 L / min or more, or 270 L / min or more (for example, 100-300 L / min, 120-290 L / min, 170-280 L / min, or 220-280 L / min).

[0090] According to the present invention, the product (f) obtained by pressure filtration may have a total peak area percentage of dimers or higher-order oligomers of 10.0% or less when analyzed by high-performance liquid chromatography (HPLC) (the sum of the peak area percentages of dimers or higher-order oligomers is 10.0% or less). Specifically, the total peak area percentage of dimers or higher-order oligomers (peak area percentage of dimers and peak area percentage of trimers of BHET) may be 9% or less, 8.5% or less, 8% or less, 7.5% or less, 7% or less, 6.5% or less, 6% or less, 5.5% or less, 5.1% or less, 4.5% or less, 4% or less, 3.7% or less, 3.4% or less, or 3% or less (for example, 0-10%, greater than 0-8%, 0.1-6.5%, or 0.2-5.2%).

[0091] Specifically, product (f) obtained by pressure filtration may have peak area percentages of dimer oligomers (e.g., BHET dimers) of 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4.5% or less, 4.4% or less, 4% or less, 3.8% or less, 3.5% or less, 3% or less, 2.9% or less, or 2.7% or less (e.g., 0-9%, greater than 0-7.5%, 0.1-6.5%, or 0.2-5%) when analyzed by high-performance liquid chromatography (HPLC).

[0092] In addition, product (f) obtained by pressure filtration may have peak area percentages of trimer oligomers (e.g., trimers of BHET) of 1% or less, 0.99% or less, 0.95% or less, 0.9% or less, 0.8% or less, 0.7% or less, 0.65% or less, 0.6% or less, 0.55% or less, 0.5% or less, 0.4% or less, 0.3% or less, or 0.2% or less (e.g., 0-9%, greater than 0-7.5%, 0.1-6.5%, or 0.2-5%) when analyzed by high-performance liquid chromatography (HPLC).

[0093] Step (6): Distillation The process for preparing the recycled raw material composition according to the present invention may further include a step of distilling the product (f) obtained through step (5) for further purification. Specifically, step (6) of distilling the product (f) may include (6-1) subjecting the product to vacuum distillation and (6-2) subjecting the product obtained by vacuum distillation in step (6-1) to thin-film evaporation.

[0094] According to the present invention, step (6-1) is to subject the product (f) obtained through step (5) to vacuum distillation to remove unreacted glycol compounds (e.g., ethylene glycol and diethylene glycol) contained in product (f).

[0095] A glass distillation apparatus or rotary evaporator may be used for vacuum distillation in step (6-1).

[0096] The vacuum distillation conditions in step (6-1) are not particularly limited, but specifically, they can be carried out at a temperature of 150°C or lower and a pressure of 0.1 to 200 Torr. More specifically, the pressure for carrying out vacuum distillation may be 0.1 to 150 Torr, 0.2 to 100 Torr, 0.3 to 50 Torr, or 0.5 to 30 Torr. In addition, the temperature for carrying out vacuum distillation may be 90°C or higher, 100°C or higher, or 110°C or higher, and 145°C or lower, 140°C or lower, or 135°C or lower (for example, 90 to 150°C, 100 to 145°C, 120 to 135°C, or 100 to 130°C).

[0097] Unreacted glycol compounds removed through vacuum distillation can be recovered and reused in the depolymerization step (1), thereby increasing the economic efficiency of the depolymerization process.

[0098] According to the present invention, step (6-2) is to subject the product (g) obtained by vacuum distillation to thin-film evaporation to remove dimers or higher-order oligomers (e.g., BHET dimers and BHET trimers) contained in product (f).

[0099] A thin-film evaporator equipped with an evaporator, a wiper rotor, and a condenser may be used for thin-film evaporation in step (6-2).

[0100] The conditions for thin film evaporation in step (6-2) are not particularly limited, but specifically, they can be carried out at a temperature of 150-250°C and a pressure of 0.005-5 Torr. More specifically, the pressure for carrying out thin film evaporation may be 0.005-4.5 Torr, 0.01-4 Torr, 0.05-3 Torr, or 0.07-1.5 Torr. In addition, the temperature for carrying out thin film evaporation (internal thin film temperature of the thin film evaporator) may be 180-240°C, 185-230°C, 190-225°C, 195-220°C, or 200-220°C.

[0101] The final product (h) obtained through this distillation process, i.e., the recycled raw material composition, may contain high-purity recycled bis(2-hydroxyethyl) terephthalate.

[0102] [Embodiments of the Invention] The present invention will be described in more detail below with reference to embodiments. However, these embodiments are provided for illustrative purposes only, and the present invention is not limited thereto.

[0103] [Example 1] 1,000 g of waste polyester resin, 2,000 g of ethylene glycol, and 10 g of anhydrous zinc acetate were charged into a first reactor made of stainless steel (SUS). The temperature in the first reactor was raised to 180°C, and the first depolymerization (first glycol decomposition reaction) was carried out for 2 hours to obtain the first reactant (a-1). Subsequently, the first reactant (a-1) obtained in this manner was transferred to a second reactor and cooled to 150°C. Then, 2,000 g of ethylene glycol was further charged into the second reactor, and while maintaining the temperature of the second reactor at 150°C, the second depolymerization (second glycol decomposition reaction) was carried out for 2 hours to obtain the second reactant (a-2) containing crude bis(2-hydroxyethyl) terephthalate (crude BHET).

[0104] The second reactant (a-2) obtained in this manner was cooled to 120°C by vacuum flashing, 16 g of a filter aid (Celite® 545) was added thereto, and then solid-liquid separation was performed by pressurized filtration to obtain the liquid reactant (b).

[0105] Next, the liquid reactant (b) was passed through a column packed with ion exchange resin (Bonlite BC107(H)) to remove ionic impurities contained in the liquid reactant (b) to obtain a mixture containing crude bis(2-hydroxyethyl) terephthalate (crude BHET) and ethylene glycol (reactant (c)).

[0106] Next, water (DIW) was added to the mixture (reactant (c)) to adjust the polarity of the solvent contained in the mixture (reactant (c)). The temperature of the mixture (reactant (d)) to which water had been added was cooled to room temperature in a 10-liter refrigerated crystallizer, and crystallization was performed. In this case, water was added (supplied) to the mixture (reactant (c)) so that the water (DIW) content in the solvent components other than crude BHET in the mixture (reactant (d)) was 40% by weight.

[0107] The precipitate (e) obtained through crystallization was subjected to solid-liquid separation by pressurized Nutsche filtration to obtain a cake containing regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) as product (f).

[0108] The product (f) obtained in this manner was transferred to a 10-liter distillation apparatus, and vacuum distillation was performed at 130°C to remove (recover) unreacted ethylene glycol. Subsequently, the product (g), from which ethylene glycol had been removed, was subjected to thin-film evaporation in a thin-film evaporator (VTA VKL70-4S) at 220°C and 0.08 Torr to remove dimers or higher-order oligomers, thereby obtaining a recycled raw material composition as the final product (h).

[0109] [Example 2] The final product (h) was obtained through the same procedure as in Example 1, except that water was added to the mixture (reactant (c)) so that the water content in the solvent components other than crude BHET in the mixture (reactant (d)) was 30% by weight.

[0110] [Example 3] The final product (h) was obtained through the same procedure as in Example 1, except that water was added to the mixture (reactant (c)) so that the water content in the solvent components other than crude BHET in the mixture (reactant (d)) was 50% by weight.

[0111] [Example 4] The final product (h) was obtained through the same procedure as in Example 1, except that water was added to the mixture (reactant (c)) so that the water content in the solvent components other than crude BHET in the mixture (reactant (d)) was 75% by weight.

[0112] [Example 5] The final product (h) was obtained through the same procedure as in Example 1, except that water was added to the mixture (reactant (c)) so that the water content in the solvent components other than crude BHET in the mixture (reactant (d)) was 88% by weight.

[0113] [Comparative Example 1] The final product (h) was obtained through the same procedure as in Example 1, except that water was not added to the mixture (reactant (c)).

[0114] [Comparative Example 2] The final product (h) was obtained through the same procedure as in Example 1, except that water was added to the mixture (reactant (c)) so that the water content in the solvent components other than crude BHET in the mixture (reactant (d)) was 20% by weight.

[0115] [Comparative Example 3] The final product (h) was obtained through the same procedure as in Example 1, except that ethanol was added to the mixture (reactant (c)) instead of water.

[0116] [Example Test] The materials obtained in Examples 1-5 and Comparative Examples 1-3 were tested by the following methods. The results are shown in Table 1 below.

[0117] (1) High-performance liquid chromatography (HPLC) 0.01 g of the sample (final product (h)) was diluted in 20 ml of methanol and analyzed by high-performance liquid chromatography (HPLC) (model: Waters e2695, column: C18 (4.6 × 250 mm), 5 μm, UV detector: 242 nm, injection volume: 10 μl, eluent (gradient) A: H2O + H3PO4, B: acetonitrile). Subsequently, the peak area percentage (%) of the following components in the total peak area of ​​the HPLC was obtained. MHET: Monohydroxyethyl terephthalate BHET: Bis(2-hydroxyethyl) terephthalate, BHEI: Bis(2-hydroxyethyl) isophthalate DEG ester 1:2-hydroxyethyl [2-(2-hydroxyethoxy)ethyl]terephthalate DEG Ester 2: Bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate HA ester: 2-hydroxyethyl (2-acetoxyethyl) terephthalate Dimer: BHET Dimer Trimmer: BHET Trimmer

[0118] (2) TDI Using the test method described in Section (1) above, HPLC analysis was performed on the sample (final product (h)), and the thermal degradation index (TDI) expressed by Equation 1 below was calculated. [Formula 1] TDI = [DEG ester 1] + ([DEG ester 2] × 2) + exp^[HA ester] + exp^[BHEI] In Equation 1, DEG ester 1 is the peak area percentage (%) of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate, DEG ester 2 is the peak area percentage (%) of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate, HA ester is the peak area percentage (%) of 2-hydroxyethyl(2-acetoxyethyl)terephthalate, and BHEI is the peak area percentage (%) of bis(2-hydroxyethyl)isophthalate. Calculations are performed using only the numerical values ​​of these parameters with their units removed. Here, exp^ represents the exponential function (e^).

[0119] (3) Yellowness index (YID) The sample (final product (h)) was dissolved in dimethylformamide at room temperature to a concentration of 25% by weight to prepare a solution. The solution thus prepared was left to stand for 30 minutes, and then its yellowness index was measured. Specifically, a HunterLab Color Flex EZ was used, and transmittance data was obtained at an observation angle of 2° using a light source (Illuminuteant) D65. The yellowness index (YID) value was calculated using the color analyzer in the software.

[0120] (4) Pressure filtration rate The crystallized material (e) is filtered using a filter press (filtration area 0.4 m²). 2 The sample was filtered using four filter plates under a pressure of 18 bar, and the pressure filtration rate was measured. ◎: Filtration speed of 250 L / min or more ○: Filtration speed 100L / min to less than 250L / min ×: Filtration speed less than 100 L / min

[0121] [Table 1]

[0122] Referring to Table 1 above, the degree of BHET crystal growth varied depending on the solvent composition and polarity in the cooling crystallization step (4), thereby altering the removal (separation) performance of low-melting-point impurities and chromophore molecules. Specifically, in the examples of the present invention, high-purity BHET was obtained while minimizing the content of impurities such as HA ester, DEG ester 1, DEG ester 2, dimers, and trimers, by increasing the solubility of dimers or higher-order oligomers and simultaneously controlling the polarity of the solvent to promote BHET crystal growth.

[0123] In such cases, if an excess of water is added, the solubility of dimers or higher-order oligomers decreases, and the undissolved oligomers act as obstacles to the crystal growth of BHET, which can increase the amount of microcrystals formed and thereby reduce the pressure filtration performance (the settling effect becomes dominant). Therefore, it is desirable to control the amount of water added to prevent the addition of an excess of water (see Example 5).

[0124] In addition, when no water was added (see Comparative Example 1), or when water was added at a level that could not control the polarity of the solvent (see Comparative Example 2), the solvent polarity was insufficient to promote BHET crystal growth, resulting in a significant decrease in the purity of BHET. Furthermore, even when ethanol was used instead of water to adjust the solvent polarity (see Comparative Example 3), the change in solvent polarity was not significant, resulting in a significant decrease in the purity of BHET.

Claims

1. A recycled raw material composition comprising bis(2-hydroxyethyl) terephthalate formed by the depolymerization of waste polyester, and having a peak area percentage of acetate ester compounds of 1.0% or less when analyzed by high-performance liquid chromatography (HPLC).

2. The recycled raw material composition according to claim 1, wherein, when analyzed by high-performance liquid chromatography (HPLC), it has a peak area percentage of 1.0% or less of a compound containing bis(2-hydroxyethyl) isophthalate.

3. The recycled raw material composition according to claim 1, wherein, when analyzed by high-performance liquid chromatography (HPLC), it has a total peak area ratio of 2.0% or less of diethylene glycol ester compounds.

4. The recycled raw material composition according to claim 1, wherein, when analyzed by high-performance liquid chromatography (HPLC), it has a total peak area ratio of 2.0% or less for dimers or higher-order oligomers.

5. The recycled raw material composition according to claim 1, wherein a solution obtained by dissolving the recycled raw material composition in dimethylformamide at a concentration of 25% by weight has a yellowness index (YID) of 5.0 or less.

6. The recycled raw material composition according to claim 1, wherein, when analyzed by high-performance liquid chromatography (HPLC), it has a peak area ratio of 92% or more of bis(2-hydroxyethyl) terephthalate.

7. The recycled raw material composition according to claim 1, having a thermal degradation index (TDI) of 6.0 or less, as defined by the following formula 1, when analyzed by high-performance liquid chromatography (HPLC): [Formula 1] TDI = [DEG ester 1] + ([DEG ester 2] × 2) + exp^[HA ester] + exp^[BHEI] (In Formula 1, DEG ester 1 is the peak area percentage (%) of 2-hydroxyethyl [2-(2-hydroxyethoxy)ethyl]terephthalate, DEG ester 2 is the peak area percentage (%) of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate, HA ester is the peak area percentage (%) of 2-hydroxyethyl (2-acetoxyethyl)terephthalate, and BHEI is the peak area percentage (%) of bis(2-hydroxyethyl)isophthalate. Calculations are performed using only the numerical values ​​of these parameters with their units removed.)

8. (1) A step of depolymerizing waste polyester by glycol decomposition reaction to obtain a reaction product containing crude bis(2-hydroxyethyl) terephthalate (crude BHET), (2) A step of treating the reaction product with an ion exchange resin, (3) A step of adding water to the reactant obtained by treatment with the ion exchange resin to adjust the polarity of the solvent contained in the reactant, (4) The step of cooling the reaction product to which water has been added and performing crystallization, (5) A process for preparing a recycled raw material composition, comprising the step of performing pressure filtration of the crystallized product obtained through the crystallization to obtain a product containing recycled bis(2-hydroxyethyl) terephthalate.

9. Step (1) is, (1-1) A step of depolymerizing the waste polyester by a first glycol decomposition reaction at 180 to 200°C to obtain a first reactant, A process for preparing the recycled raw material composition according to claim 8, comprising the steps of (1-2) depolymerizing the first reactant by a second glycol decomposition reaction at 150 to 170°C to obtain a second reactant.

10. A process for preparing the recycled raw material composition according to claim 8, wherein the amount of water added in step (3) is 25 to 80% by weight of the total weight of the solvent obtained by removing the crude BHET from the reactant to which water has been added.

11. The solvent contained in the reaction product obtained by treatment with the ion exchange resin includes a glycol-based solvent, A process for preparing the recycled raw material composition according to claim 8, wherein the polarity-controlled solvent comprises water and the glycol-based solvent in a weight ratio of 25:75 to 80:

20.

12. A process for preparing the recycled raw material composition according to claim 8, wherein the pressurized filtration rate of the crystallized material in step (5) is 100 L / min or more.

13. A process for preparing the recycled raw material composition according to claim 8, wherein the product obtained in step (5) has a total peak area ratio of 10.0% or less of dimers or higher-order oligomers when analyzed by high-performance liquid chromatography (HPLC).

14. A process for preparing the regenerative raw material composition according to claim 8, further comprising the step of (6) distilling the product obtained through step (5).

15. Step (6) is, (6-1) The step of subjecting the product to vacuum distillation, A process for preparing the recycled raw material composition according to claim 14, comprising the step of (6-2) subjecting the product obtained by vacuum distillation in step (6-1) to thin-film evaporation.

Images