Recycled raw material composition and its preparation method

Abstract

This invention relates to a recycled raw material composition and its preparation method. The recycled raw material composition comprises recycled bis(2-hydroxyethyl) terephthalate formed by the depolymerization of waste polyester, wherein the peak area ratio of acetate compounds is 1.0% or less when analyzed by high performance liquid chromatography (HPLC). Due to the reduced impurity content, this recycled raw material composition can exhibit high purity and high quality.

Description

Technical Field

[0001] This invention relates to a recycled raw material composition obtained through a waste polyester recycling process, which has high purity, high quality and minimal impurities, and a method for preparing the recycled raw material composition. Background Technology

[0002] 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 decorative materials such as panels, shelves, and partitions due to its excellent mechanical strength, heat resistance, transparency, and gas barrier properties.

[0003] Therefore, uncontrollable plastic waste, such as polyester, is generated every year. Currently, countries around the world have formulated regulations and plans for the recycling and utilization of waste plastic resources, including waste polyester.

[0004] Although methods for recycling waste polyester include physical and chemical methods, physical recycling methods cannot guarantee purity and are therefore not widely used. In chemical recycling methods, the ester bonds of waste polyester are broken, causing it to depolymerize. For example, reactions can be carried out through glycololysis, hydrolysis, methanololysis, and ammonolysis. Glycololysis involves adding glycols such as ethylene glycol or diethylene glycol to decompose waste polyester. The main reaction product obtained is bis(2-hydroxyethyl) terephthalate (BHET). The bis(2-hydroxyethyl) terephthalate contained in the product can be used as a raw material for preparing unsaturated polyesters or ester polyols after crystallization or purification.

[0005] However, products containing bis(2-hydroxyethyl) terephthalate (BHET) have relatively high impurity content, making it difficult to obtain high purity and high quality bis(2-hydroxyethyl) terephthalate (BHET). Summary of the Invention

[0006] Technical issues

[0007] Typically, the recycled raw material composition obtained through the depolymerization reaction of waste polyester contains, in addition to bis(2-hydroxyethyl) terephthalate, a useful recycled raw material, oligomers such as dimers and trimers; diethylene glycol esters derived from diethylene glycol (DEG); acetate esters obtained by using acetate catalysts; or bis(2-hydroxyethyl) terephthalate analogs as impurities, which is a factor that reduces the purity and quality of the recycled raw material composition.

[0008] In particular, the inventors have demonstrated that, among the aforementioned impurities, diethylene glycol esters, acetate esters, and BHET analogs reduce the purity and quality of bis(2-hydroxyethyl) terephthalate in the recycled raw material composition; therefore, when polymers are prepared using recycled bis(2-hydroxyethyl) terephthalate, the degree of polymerization and heat resistance of the polymer will deteriorate.

[0009] To address this problem, the inventors have demonstrated that by controlling the polarity of the solvent and carrying out the crystallization process during the depolymerization of waste polyester, the content of impurities such as diethylene glycol esters, acetate esters, and BHET analogs in the recycled raw material composition can be adjusted to a specific range; thereby obtaining a polymer with improved polymerization degree and heat resistance, thus completing the present invention.

[0010] Therefore, one object of the present invention is to provide a recycled raw material composition with minimized impurity content and a method for preparing the same, wherein the recycled raw material composition can ensure that the degree of polymerization and heat resistance of the polymer material are at target levels.

[0011] Solution to the problem

[0012] To achieve the above objectives, the present invention provides a recycled raw material composition comprising bis(2-hydroxyethyl) terephthalate formed by depolymerization of waste polyester, wherein the peak area fraction of acetate compounds is 1.0% or lower when the recycled raw material composition is analyzed by high performance liquid chromatography (HPLC).

[0013] Furthermore, the present invention provides a method for preparing a recycled raw material composition, comprising: (1) depolymerizing waste polyester by diol hydrolysis 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 ion exchange resin treatment to adjust the polarity of the solvent contained in the reactant; (4) cooling the reactant with added water to crystallize it; and (5) pressurizing and filtering the crystals obtained by crystallization to obtain a product containing recycled bis(2-hydroxyethyl) terephthalate.

[0014] Beneficial effects of the invention

[0015] In this invention, the separation and purification of impurities (e.g., acetate compounds, diethylene glycol compounds, BHET analogs, BHET oligomers, etc.) are optimized by controlling the polarity of the solvent used in the depolymerization process of waste polyester. As a result, a recycled raw material composition with minimized 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.

[0016] Since the present invention provides high-purity and high-quality bis(2-hydroxyethyl) terephthalate by depolymerizing the waste polyester, it not only recycles resources, but also helps to use bis(2-hydroxyethyl) terephthalate as a recycled raw material (polymerization raw material) to prepare polymers with excellent heat resistance and color properties (e.g., recycled polyester resins).

[0017] The best embodiment of the present invention

[0018] The present invention will be described in detail below. The present invention is not limited to the contents disclosed below; it can be modified in various forms as long as the spirit of the invention remains unchanged.

[0019] In this specification, the term "comprising" is intended to specify a particular feature, region, step, method, element, and / or component. Unless otherwise expressly stated, the presence or addition of any other feature, region, step, method, element, and / or component is not excluded.

[0020] In this specification, the terms first, second, etc., are used to describe various components. However, these components should not be limited by these terms. These terms are only used to distinguish one element from another.

[0021] Unless otherwise stated, all numbers and expressions relating to the quantities of components, reaction conditions, etc., used herein should be understood to be modified by the term “about”.

[0022] In this specification, unless the context otherwise indicates, singular expressions are to be interpreted as also encompassing plural expressions.

[0023] Recycled raw material composition

[0024] The recycled raw material composition of the present invention comprises bis(2-hydroxyethyl) terephthalate formed from the depolymerization of waste polyester, and when the recycled raw material composition is analyzed by high performance liquid chromatography (HPLC), the peak area fraction of acetate compounds is 1.0% or less. The recycled raw material composition of the present invention allows control over the content of acetate compounds as impurities to a specific range of 1.0% or less; therefore, the resulting recycled raw material, i.e., recycled bis(2-hydroxyethyl) terephthalate, has high purity. When used to prepare polymers (e.g., recycled polyester resins), it prevents a decrease in heat resistance (Tm, Tg) due to the increase of diethylene glycol units (DEG units) or a decrease in the degree of polymerization due to the effect of end-capping groups. Therefore, polymers with excellent heat resistance, color characteristics, etc., can be provided.

[0025] Acetate compounds included in the recycled feedstock composition can be byproducts of acetates, which act as catalysts in the depolymerization of waste polyester via glycololysis. Specifically, referring to reaction formula 1 below, acetate-derived acetic acid (AA) used as a catalyst can react with ethylene glycol (EG) to produce acetate compounds, such as 2-hydroxyethyl acetate (HA) and water (H2O). In this case, since 2-hydroxyethyl acetate (HA) has a similar boiling point to ethylene glycol (EG), it is not easily filtered out as an impurity during the recovery and reuse of ethylene glycol (EG). As a result, byproducts such as acetate compounds accumulate as the process continues. That is, referring to reaction formula 2 below, 2-hydroxyethyl acetate (HA) can undergo transesterification with bis(2-hydroxyethyl) terephthalate (BHET) to produce ester compounds, such as 2-hydroxyethyl(2-acetoxyethyl) terephthalate (HAET) and ethylene glycol (EG).

[0026] [Reaction Formula 1]

[0027] [Reaction 2]

[0028] The resulting acetate compounds (e.g., 2-hydroxyethyl (2-acetoxyethyl) terephthalate (HAET)) can act as impurities (e.g., reducing BHET purity, generating HA, and functioning as end-capping groups). The recycled feedstock composition of the present invention has a minimized content of acetate compounds. As a result, high-purity recycled bis(2-hydroxyethyl) terephthalate (BHET) can be provided.

[0029] Specifically, in this invention, when the regenerated raw material composition is analyzed by high-performance liquid chromatography (HPLC), the peak area fraction of the acetate compound (HA-ester) can be 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, 0.1% or less, 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. For example, the peak area fraction of the acetate compound (HA-ester) can be 0 to 1.0%, greater than 0 to 0.9%, greater than 0 to 0.5%, greater than 0 to 0.3%, greater than 0 to 0.1%, greater than 0 to 0.09%, or 0.01 to 0.09%.

[0030] In addition to acetate compounds, the recycled raw material composition of the present invention may also contain impurities such as bis(2-hydroxyethyl) terephthalate (BHET) analogs (isomers), bis(2-hydroxyethyl) terephthalate (BHET) oligomers (dimers, trimers, etc.) and diethylene glycol esters. In the present invention, the content of these impurities is also controlled within a specific range.

[0031] Specifically, in this invention, when the recycled raw material composition is analyzed by high performance liquid chromatography (HPLC), the peak area fraction of the compound containing bis(2-hydroxyethyl) isophthalate (BHET analogue) can be 1.0% or less. The compound containing bis(2-hydroxyethyl) isophthalate can be a compound consisting solely of bis(2-hydroxyethyl) isophthalate. Bis(2-hydroxyethyl) isophthalate can be an impurity formed during the depolymerization of waste polyester containing isophthalic acid units (IPA units) via a diol hydrolysis reaction (see reaction formula 3 below).

[0032] [Reaction 3]

[0033] The bis(2-hydroxyethyl) isophthalate thus generated may act as an impurity. When polymers are prepared using recycled feedstock compositions containing this substance, the melting point (Tm) of the polymers prepared therefrom is significantly reduced, thereby significantly decreasing the heat resistance of the polymers. The recycled feedstock compositions of the present invention contain a minimized amount of bis(2-hydroxyethyl) isophthalate. Therefore, polymers with excellent heat resistance can be provided.

[0034] Specifically, in this invention, when the recycled raw material composition is analyzed by high performance liquid chromatography (HPLC), the peak area fraction of the compound bis(2-hydroxyethyl) isophthalate (BHEI) is 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. For example, the peak area fraction of bis(2-hydroxyethyl) isophthalate (BHEI) compounds can be 0 to 1.0%, greater than 0 to 0.99%, greater than 0 to 0.97%, greater than 0 to 0.92%, greater than 0 to 0.6%, greater than 0 to 0.55%, or 0.01 to 0.35%.

[0035] In this invention, when the recycled raw material composition is analyzed by high performance liquid chromatography (HPLC), the total peak area fraction of diethylene glycol ester compounds can be 2.0% or less (the sum of the peak area fractions of diethylene glycol ester compounds is 2.0% or less). Diethylene glycol ester compounds can be generated during the depolymerization of waste polyester via a diol hydrolysis reaction, through a transesterification reaction between diethylene glycol and bis(2-hydroxyethyl) terephthalate (BHET). Specifically, the diethylene glycol ester compounds may include 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl] terephthalate (DEG-ester-1) represented by Formula 1 and bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylic acid ester (DEG-ester-2) represented by Formula 2.

[0036] [Formula 1]

[0037] [Equation 2]

[0038] Specifically, in this invention, when the regenerated raw material composition is analyzed by high performance liquid chromatography (HPLC), the peak area fraction of diethylene glycol ester compounds (DEG-esters) (e.g., the peak area fraction of DEG-ester-1 and the peak area fraction of DEG-ester-2) can be 1.99% or lower, 1.95% or lower, 1.93% or lower, 1.9% or lower, 1.88% or lower, 1.85% or lower, 1.83% or lower, 1.83% or lower, 1.8% or lower, 1.78% or lower, 1.77% or lower, 1.75% or lower, 1.73% or lower, 1.7% or lower, 1.65% or lower, 1.63% or lower, or 1.6% or lower. For example, the total peak area fraction of diethylene glycol esters (DEG-esters) can be 0 to 1.99%, greater than 0 to 1.95%, greater than 0 to 1.85%, greater than 0 to 1.8%, 0 to 1.7%, greater than 0 to 1.6%, or 0.01 to 1.5%.

[0039] In this invention, when the recycled raw material composition is analyzed by high-performance liquid chromatography (HPLC), the total peak area fraction of the dimer or higher degree of polymerization oligomers can be 2.0% or lower (the sum of the peak area fractions of the dimer or higher degree of polymerization oligomers is 2.0% or lower). Specifically, the dimer or higher degree of polymerization oligomers can be dimers of bis(2-hydroxyethyl) terephthalate (BHET), trimers of bis(2-hydroxyethyl) terephthalate (BHET), or combinations thereof. The oligomers can have a molecular weight of 2000 g / mol or lower (e.g., 1000 to 2000 g / mol).

[0040] Specifically, in this invention, when the recycled raw material composition is analyzed by high performance liquid chromatography (HPLC), the total peak area fraction of dimer or higher degree of polymerization oligomers (e.g., the peak area fraction of dimer and the peak area fraction of trimer) can be 1.5% or lower, 1.3% or lower, 1.0% or lower, less than 1.0%, 0.95% or lower, 0.9% or lower, 0.85% or lower, 0.8% or lower, 0.75% or lower, 0.7% or lower, 0.6% or lower, 0.55% or lower, 0.5% or lower, 0.45% or lower, 0.4% or lower, 0.39% or lower, 0.35% or lower, or 0.3% or lower. For example, the total peak area fraction of dimers or oligomers with higher degrees of polymerization can be 0 to 1.0%, greater than 0 to 0.9%, greater than 0 to 0.6%, 0.01 to 0.55%, 0.05 to 0.53%, 0.1 to 0.5%, or 0.15 to 0.4%.

[0041] Meanwhile, the recycled bis(2-hydroxyethyl) terephthalate (r-BHET) in the recycled raw material composition of the present invention is formed through the depolymerization of waste polyester. It can be a compound formed as an intermediate during the preparation of polyester by polymerization of ethylene glycol and terephthalic acid or its esters. The recycled bis(2-hydroxyethyl) terephthalate (r-BHET) can have high purity because the impurity content is controlled at or below the specific levels described above. Therefore, it can have physical properties equivalent to pure bis(2-hydroxyethyl) terephthalate (pure BHET). Furthermore, the recycled bis(2-hydroxyethyl) terephthalate (r-BHET) has excellent crystallinity, resulting in a high melting point, and can also possess excellent qualities such as color.

[0042] Specifically, the purity of regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) can be calculated by the percentage (%) of the peak area of ​​BHET in the spectrum of the regenerated feedstock composition obtained by high performance liquid chromatography (HPLC).

[0043] For example, in this invention, when the recycled raw material composition is analyzed by high performance liquid chromatography (HPLC), the peak area fraction of bis(2-hydroxyethyl) terephthalate can be 92% or higher. Specifically, the peak area fraction of bis(2-hydroxyethyl) terephthalate can be 93% or higher, 93.5% or higher, 94% or higher, 94.3% or higher, 94.5% or higher, 94.8% or higher, 95.3% or higher, 95.5% or higher, 95.8% or higher, 96% or higher, 98% or higher, 99% or higher, or 100%. Therefore, the recycled bis(2-hydroxyethyl) terephthalate contained in the recycled raw material composition can have high purity.

[0044] Furthermore, in this invention, when the recycled raw material composition is analyzed by high-performance liquid chromatography (HPLC), the peak area fraction of monohydroxyethyl terephthalate (MHET) can be 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 fraction of monohydroxyethyl terephthalate (MHET) can be 0 to 2%, greater than 0 to 1.9%, 0.5 to 1.5%, or 0.8 to 1.1%.

[0045] Simultaneously, with increasing content of bis(2-hydroxyethyl) terephthalate and / or diethylene glycol esters in the recycled feedstock composition, the heat resistance of the final polymer, such as melting point (Tm), decreases linearly. Acetate compounds can act as end-capping agents that inhibit polymer chain growth. With increasing content of these compounds, the heat resistance of the final polymer decreases exponentially. Based on this relationship, a correlation can be derived to predict the heat resistance of polymers prepared using the recycled feedstock composition (specifically, recycled bis(2-hydroxyethyl) terephthalate).

[0046] For example, in this invention, when the recycled raw material composition is analyzed by high performance liquid chromatography (HPLC), it can have a thermal performance degradation index (TDI) of 6.0 or less, as defined in Equation 1 below.

[0047] [Equation 1]

[0048] TDI = [DEG-ester-1] + ([DEG-ester-2] × 2) + exp^[HA-ester] + exp^[BHEI]

[0049] In Equation 1, DEG-ester-1 is the peak area fraction (%) of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl] terephthalate, DEG-ester-2 is the peak area fraction (%) of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylic acid ester, HA-ester is the peak area fraction (%) of 2-hydroxyethyl(2-acetoxyethyl) terephthalate, and BHEI is the peak area fraction (%) of bis(2-hydroxyethyl) isophthalate.

[0050] In Equation 1, only the numerical values ​​of each parameter are used for calculation, i.e., units are not considered.

[0051] Specifically, if the thermal performance degradation index (TDI) defined by Equation 1 is 5.8 or less, the degradation of the polymer's heat resistance due to DEG-ester-1, DEG-ester-2, HA-ester, and BHEI during the preparation of the polymer (e.g., recycled polyester resin) can be more effectively prevented. For example, the thermal performance degradation index (TDI) can 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).

[0052] When analyzed in a solution (sample recovery feed solution) dissolved in dimethylformamide at a concentration of 25% by weight, the recycled feed composition of the present invention can have a yellow index (YID) of 5.0 or less. Specifically, the yellow index (YID) can 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. Due to having such a yellow index (YID), the recycled feed composition of the present invention can facilitate the preparation of polymers (recycled polyester resins) with excellent color properties (e.g., transparency).

[0053] Preparation method of recycled raw material composition

[0054] The method for preparing the recycled raw material composition of the present invention is a method for preparing a recycled raw material composition with minimized impurity content as described above, including adjusting the polarity of the solvent used in the depolymerization process and then carrying out a cooling crystallization process. Specifically, the method for preparing the recycled raw material composition of the present invention includes: (1) depolymerizing waste polyester by diol hydrolysis 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 after ion exchange resin treatment to adjust the polarity of the solvent contained in the reactant; (4) cooling the reactant with added water to crystallize it; and (5) pressurizing and filtering the crystallized product to obtain a product containing recycled bis(2-hydroxyethyl) terephthalate. This will be described in detail below.

[0055] In this invention, reactants can refer to the products obtained through each step.

[0056] Step (1): Depolymerization of waste polyester

[0057] In this invention, step (1) is a step of depolymerizing waste polyester by diol hydrolysis to obtain reactant (a) containing crude bis(2-hydroxyethyl) terephthalate (crude BHET).

[0058] Depolymerized waste polyester can be obtained by pretreating consumer waste. This waste can include beverage bottles, fabrics, films, boxes, containers, partitions, shelves, protective panels, packaging materials, building materials, and interior and exterior finishing materials containing polyester.

[0059] Polyesters contained in various waste products can be obtained by (co)polymerization of one or more acid components and one or more alcohol components known in the art. The acid component may specifically include at least one selected from the group consisting of terephthalic acid, isophthalic acid, dimethyl terephthalate, dimethyl terephthalate, naphthalic acid, phthalic acid, adipic acid, azelaic acid, sebacic acid, and sebacic 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, neopentanediol, 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-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, isosorbide dimethyl, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol.

[0060] Pretreatment can be carried out by removing other plastics, metals, and foreign matter mixed in with various wastes, washing, and then crushing them using a shredder. As a result of pretreatment, waste polyester may be in flake form. Furthermore, waste polyester may have a fine, fiber-like structure.

[0061] Step (1) of depolymerizing waste polyester may include: (1-1) depolymerizing (first depolymerization) waste polyester by a first diol depolymerization reaction to obtain a first reactant (a-1); and (1-2) depolymerizing (second depolymerization) the first reactant (a-1) by a second diol depolymerization reaction to obtain a second reactant (a-2).

[0062] Specifically, step (1-1) may include a process of primarily cleaving the polymer chain of the waste polyester with a first diol compound to obtain the first reactant (a-1).

[0063] There are no particular limitations on the first diol compound used in the first depolymerization in step (1-1), but it may specifically include at least one selected from the group consisting of ethylene glycol (monoethylene glycol), propylene glycol and diethylene glycol.

[0064] There is no particular limitation on the amount of the first diol compound fed in step (1-1). Specifically, it can be 1 or more, 2 or more, or 3 or more, and 7 or less, 5 or less, or 4 or less (e.g., 1 to 7, 2 to 5, or 3 to 4 times) the weight of the waste polyester.

[0065] The first depolymerization temperature in step (1-1) is not particularly limited, but it can be between 180 and 200°C, specifically 180 to 195°C, 180 to 193°C, 180 to 190°C, 180 to 188°C, or 180 to 185°C. Furthermore, the first depolymerization time is not particularly limited, but it can be 1 to 4 hours, 1 to 3 hours, or 1 to 2 hours from reaching the required first depolymerization temperature. Because the temperature and time of the first depolymerization are within the above ranges, the first diglycolysis reaction of the waste polyester can proceed smoothly, while minimizing the formation of byproducts such as diethylene glycol esters.

[0066] The first depolymerization in step (1-1) can be carried out in the presence of a catalyst that activates the first diollysis reaction. There are no particular limitations on the catalyst; generally known catalysts are suitable, but it 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.

[0067] There is no particular limitation on the amount of catalyst fed in step (1-1), but it can 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 relative to 100 parts by weight of waste polyester.

[0068] For example, the first diol hydrolysis reaction carried out in step (1-1) can be a reaction between waste polyester and ethylene glycol in the presence of zinc acetate hydrate.

[0069] Step (1-2) may include a process of subjecting the first reactant (a-1) obtained in step (1-1) to a secondary cleavage chemical reaction using a second diol compound to obtain a second reactant (a-2). The second reactant (a-2) may refer to reactant (a) obtained through step (1).

[0070] The second diol compound used in the second depolymerization in step (1-2) is not particularly limited, but it may specifically include at least one selected from the group consisting of ethylene glycol (monoethylene glycol), propylene glycol, and diethylene glycol. The second diol compound may be derived from the first depolymerization process in step (1-1), or may be further added in the second depolymerization process in step (1-2).

[0071] There are no particular limitations on the amount of the second diol compound fed in steps (1-2) (the additional amount used in the second depolymerization). Specifically, it can be 1 or more, 2 or more, or 3 or more, and 7 or less, 5 or less, or 4 or less (e.g., 1 to 7 times, 2 to 5 times, or 3 to 4 times) of the weight of the waste polyester.

[0072] The second depolymerization temperature in step (1-2) is not particularly limited, but it can be between 150 and 170°C. Specifically, it can be 150 to 165°C, 150 to 163°C, 150 to 160°C, 150 to 158°C, or 150 to 155°C. Furthermore, the second depolymerization time is not particularly limited, but it can be 1 to 4 hours, 1 to 3 hours, or 1 to 2 hours from reaching the required second depolymerization temperature. Because the temperature and time of the second depolymerization are both within the above ranges, the second depolymerization of the first reactant (a-1) can proceed smoothly, while minimizing the formation of impurities such as diethylene glycol esters.

[0073] The second depolymerization in step (1-2) can be carried out in the presence of a catalyst that activates the second diollysis reaction. The catalyst can be derived from the first depolymerization process in step (1-1), or it can be further added during the second depolymerization process in step (1-2). The catalyst is described in the same way as the catalyst in step (1-1) above; therefore, a detailed description is omitted.

[0074] By performing depolymerization in steps (1-1) and (1-2), reactant (a) containing crude bis(2-hydroxyethyl) terephthalate (crude BHET) can be obtained in high yield.

[0075] Meanwhile, the method for preparing the recycled raw material composition of the present invention may further include cooling the reactant (a) obtained in step (1) and performing solid-liquid separation before performing step (2) below, so as to improve the efficiency of removing impurities.

[0076] Specifically, in the cooling and solid-liquid separation process, reactant (a) is cooled by vacuum flash evaporation, and then subjected to solid-liquid separation using a filter aid through a pressure filtration process. Accordingly, reactant (a) can be converted into liquid reactant (b). As the cooling and solid-liquid separation steps proceed further, solid impurities such as particles and insoluble organic matter contained in the first reactant (a) are removed, thereby improving the yield and purity of the final product (recycled feedstock composition).

[0077] There is no particular limitation on the temperature at which the first reactant (a) is cooled by flash evaporation under reduced pressure, but it can specifically 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 (e.g., 100 to 135°C, 105 to 125°C, or 110 to 120°C).

[0078] There is no particular limitation on the pressure for vacuum flash evaporation, but it can be 200 tor or less, 150 tor or less, 100 tor or less, 50 tor or less, or 30 tor or less, and 5 tor or more, 8 tor or more, 10 tor or more, or 15 tor or more (e.g., 5 to 200 tor, 10 to 100 tor, or 15 to 50 tor).

[0079] There are no particular limitations on the filter aids used for solid-liquid separation; any filter aid known in the art may be used, but it may specifically include at least one selected from the group consisting of diatomaceous earth, perlite, and asbestos powder.

[0080] Step (2): Treatment with ion exchange resin

[0081] In this invention, step (2) is the process of treating reactant (a) with an ion exchange resin (if cooling and solid-liquid separation are performed, reactant (a) becomes liquid reactant (b)). Specifically, this can be achieved by passing reactant (a) through an ion exchange resin or by adding ion exchange resin to reactant (a). As the above process proceeds, ionic impurities contained in reactant (a) can be removed to obtain reactant (c) of high purity.

[0082] The ion exchange resin can be a cation exchange resin, anion exchange resin, amphoteric ion exchange resin, chelating resin, or a combination thereof, which are known in the art.

[0083] Cation exchange resins may specifically include strongly acidic cation exchange resins having sulfonic acid groups (-SO3H) or weakly acidic cation exchange resins having carboxyl groups (-COOH). Anion exchange resins may include strongly basic anion exchange resins in the form of quaternary ammonium salts or weakly basic anion exchange resins having primary to tertiary amino groups. Chelating resins may be polymeric resins with reactive functional groups, such as acetates or phosphates that chelate metal ions such as sodium, copper, nickel, zinc, and manganese.

[0084] When treatment is carried out by adding ion exchange resin to reactant (a), there is no particular limitation on the amount of ion exchange resin fed (dosage), but it can be specifically one or more, two or more, three or more, or five or more, and 20 or less, 15 or less, 10 or less, or eight or less (e.g., 1 to 20 times, 2 to 15 times, 3 to 10 times, or 5 to 8 times) the weight of the catalyst used in depolymerization. Furthermore, relative to 100 parts by weight of the waste polyester from step (1), the amount of ion exchange resin fed (dosage) can be one or more, two or more, three or more, or five or more, and 50 or less, 20 or less, 15 or less, 10 or less, or 7 or less (e.g., 1 to 50 parts by weight, 3 to 20 parts by weight, or 5 to 10 parts by weight).

[0085] When reactant (a) is treated with an ion exchange resin, the ion exchange resin may be in the form of particles of a predetermined size. Specifically, the step of removing ionic impurities can be carried out by passing liquid reactant (b) through a column packed with ion exchange resin particles having a particle size of 0.3 to 1.5 mm, 0.5 to 1.3 mm, or 0.7 to 1.0 mm.

[0086] In the reactant (c) obtained by treatment with ion exchange resin, the polarity of the solvent can be controlled by the following step (3).

[0087] Step (3): Control of solvent polarity

[0088] In this invention, step (3) involves adding water to the reactant (c) obtained in step (2) via ion exchange resin treatment to adjust the polarity of the solvent contained in the reactant (c). When such step (3) is performed, the crystal growth of regenerated bis(2-hydroxyethyl) terephthalate is successfully achieved during the cooling crystallization process in step (4) below. This significantly increases the pressure filtration efficiency in step (5) below and allows for the separation of BHET analogs (e.g., BHEI) that 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.

[0089] Specifically, if the crystal growth of bis(2-hydroxyethyl) terephthalate (BHET) is successfully achieved during the cooling crystallization process in step (4), the separation efficiency of low-melting-point compounds and impurities such as chromophore molecules can be improved. Therefore, it is necessary to ensure good crystal growth of bis(2-hydroxyethyl) terephthalate (BHET). In this invention, the crystal growth (crystal formation) of bis(2-hydroxyethyl) terephthalate (BHET) varies significantly depending on the polarity of the solvent contained in the reactant (c) after cooling crystallization. Therefore, it is very important to control the polarity of the solvent contained in the reactant (c) obtained by ion exchange resin treatment before the cooling crystallization step.

[0090] Therefore, in this invention, water is added to the reactant (c) obtained by step (2) to optimally control the polarity of the solvent contained in the reactant (c), thereby ensuring good growth of bis(2-hydroxyethyl) terephthalate (BHET) crystals during the cooling crystallization process in step (4) below.

[0091] In this invention, the amount of water added to the reactant (c) obtained by ion exchange resin treatment is not particularly limited, but it can be from 25% to 80% by weight (specifically, the solvent contained in the components of reactant (d) excluding crude BHET), based on the total weight of the solvent in the reactant (d) with added water. That is, water can be added to the reactant (c) obtained by ion exchange resin treatment such that the weight of the water is 25% to 80% by weight of the total weight of the solvent in the reactant (d) with added water. Specifically, based on the total weight of the solvent (polarity-controlled solvent), the amount of water added can 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. When the amount of water added is within the above range, the pressure filtration efficiency can be improved, while accelerating the crystal growth of bis(2-hydroxyethyl) terephthalate (BHET).

[0092] In this invention, the solvent contained in reactant (c) may include glycol solvents. For example, reactant (c) may contain a first glycol compound and / or a second glycol compound used in the first and / or second glycololysis reactions as a glycol solvent. When water is added to reactant (c), the polarity of the solvent contained in reactant (c) can be controlled. Specifically, the polarity-controlled solvent may include water and glycol solvents (e.g., ethylene glycol (monoethylene glycol), propylene glycol, diethylene glycol, or combinations thereof). The blending ratio of water and glycol solvent contained in the polarity-controlled solvent is not particularly limited, but it 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. When the blending ratio is within the above range, the polarity of the solvent contained in reactant (c) can be optimized to the desired level.

[0093] When water is added as described above, a reactant (d) containing a solvent with controlled polarity can be obtained.

[0094] Step (4): Cooling and crystallization

[0095] In this invention, step (4) is the step of cooling the reactant (d) in which water was added in step (3) to crystallize it. Specifically, when the temperature of the reactant (d) containing a polarity-controlled solvent is lowered to carry out crystallization, a crystalline product (e) containing bis(2-hydroxyethyl) terephthalate (BHET) with crystalline properties can be obtained.

[0096] There are no particular restrictions on the crystallization temperature of reactant (d), but it can 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 it can 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 crystallization temperature of reactant (d) can be room temperature (20±5°C).

[0097] When cooling crystallization is performed, acetate esters and diethylene glycol esters, which are impurities, can be effectively removed.

[0098] Step (5): Pressure filtration

[0099] In this invention, step (5) is to pressurize and filter the crystals (e) obtained in step (4) to obtain a product (f) containing regenerated bis(2-hydroxyethyl) terephthalate. Specifically, product (f) may be a filter cake containing regenerated bis(2-hydroxyethyl) terephthalate.

[0100] There are no particular restrictions on the pressure for pressurizing the crystalline material (e), but it can be from 0.1 to 21 bar, 0.5 to 10 bar, or 1 to 5 bar. Furthermore, there are no particular restrictions on the temperature for pressurizing the filtration, but it can be from 5 to 35°C, 10 to 30°C, or 15 to 25°C.

[0101] There are no particular restrictions on the filters used for pressure filtration, but they can specifically be Nutsche filters or filter presses.

[0102] Pressure filtration using a Nutsche filter may include the steps of placing the crystalline material into the Nutsche filter, injecting an inert gas such as nitrogen, and pressurizing it to initially separate the solvent and solids (filter cake). Furthermore, it may include the steps of injecting water into the Nutsche filter to wash away residual solvent remaining in the solids (filter cake), followed by injecting an inert gas and pressurizing it to a secondary separation of the solids (filter cake) and water. The resulting solids (filter cake) may then be subjected to drying and cooling steps.

[0103] Pressure filtration using a filter press may include steps such as forming a filter chamber with a filter plate having a filter surface, filter cloth and cover plate, and pressurizing the crystals (e) between the filter cloth and cover plate under high pressure to achieve solid-liquid separation.

[0104] When pressure filtration is performed, acetate compounds, diethylene glycol compounds, and BHET oligomers, which are impurities, can be effectively removed.

[0105] Meanwhile, since the crystals (e) are obtained through step (3) of controlling solvent polarity and step (4) of cooling crystallization, they can have excellent pressure filtration performance. For example, the pressure filtration rate of the crystals (e) can be 100 L / min or higher, specifically, 105 L / min or higher, 115 L / min or higher, 120 L / min or higher, 140 L / min or higher, 150 L / min or higher, 160 L / min or higher, 170 L / min or higher, 180 L / min or higher, 200 L / min or higher, 220 L / min or higher, 250 L / min or higher, or 270 L / min or higher (e.g., 100 to 300 L / min, 120 to 290 L / min, 170 to 280 L / min, or 220 to 280 L / min).

[0106] In this invention, when analyzed by high performance liquid chromatography (HPLC), the total peak area fraction of the product (f) obtained by pressure filtration containing dimers or oligomers with a higher degree of polymerization can be 10.0% or less (the sum of the peak area fractions of dimers or oligomers with a higher degree of polymerization is 10.0% or less). Specifically, the total peak area fraction of dimers or oligomers with a higher degree of polymerization (the peak area fraction of the dimer of BHET and the peak area fraction of the trimer of BHET) can be 9% or less, 8.5% or less, 8% or less, 7.5% 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 (e.g., 0 to 10%, greater than 0 to 8%, 0.1 to 6.5%, or 0.2 to 5.2%).

[0107] Specifically, the product (f) obtained by pressure filtration may have 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 to 9%, greater than 0 to 7.5%, 0.1 to 6.5%, or 0.2 to 5%).

[0108] Furthermore, when analyzed by high performance liquid chromatography (HPLC), the peak area fraction of the trimer oligomer (e.g., the trimer of BHET) contained in the product (f) obtained by pressure filtration can be 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 to 9%, greater than 0 to 7.5%, 0.1 to 6.5%, or 0.2 to 5%).

[0109] Step (6): Distillation

[0110] The method for preparing the recycled raw material composition of the present invention may further include distilling the product (f) obtained in step (5) for further purification. Specifically, step (6) of distilling the product (f) may include: (6-1) vacuum distilling the product; and (6-2) thin-film evaporation of the product obtained by vacuum distillation in step (6-1).

[0111] In this invention, step (6-1) is to perform vacuum distillation on the product (f) obtained by step (5) to remove unreacted diol compounds (e.g., ethylene glycol and diethylene glycol) contained in the product (f).

[0112] A glass distillation apparatus or a rotary evaporator can be used for vacuum distillation in step (6-1).

[0113] There are no particular limitations on the vacuum distillation conditions in step (6-1), but they can be carried out at a temperature of 150°C or lower and a pressure of 0.1-200 Torr. More specifically, the pressure for vacuum distillation can be 0.1 to 150 Torr, 0.2 to 100 Torr, 0.3 to 50 Torr, or 0.5 to 30 Torr. Furthermore, the temperature for vacuum distillation can 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 (e.g., 90 to 150°C, 100 to 145°C, 120 to 135°C, or 100 to 130°C).

[0114] Unreacted diols removed by vacuum distillation can be recovered and reused in the depolymerization process of step (1), thereby improving the economic efficiency of the depolymerization process.

[0115] In this invention, step (6-2) is to perform thin-film evaporation on the product (g) obtained by vacuum distillation to remove dimers or oligomers with higher degree of polymerization (e.g., BHET dimers and BHET trimers) contained in the product (f).

[0116] A thin-film evaporator, including an evaporator, a wiper rotor, and a condenser, can be used for thin-film evaporation in step (6-2).

[0117] There are no particular restrictions on the conditions for thin-film evaporation in step (6-2), but it can be carried out at a temperature of 150 to 250°C and a pressure of 0.005 to 5 Torr. More specifically, the pressure for thin-film evaporation can be 0.005 to 4.5 Torr, 0.01 to 4 Torr, 0.05 to 3 Torr, or 0.07 to 1.5 Torr. Furthermore, the temperature for thin-film evaporation (the internal film temperature of the thin-film evaporator) can be 180 to 240°C, 185 to 230°C, 190 to 225°C, 195 to 220°C, or 200 to 220°C.

[0118] The final product (h) obtained through this distillation process, namely the recycled feedstock composition, may contain high-purity recycled bis(2-hydroxyethyl) terephthalate. Detailed Implementation

[0119] Invention Model

[0120] The present invention will now be described in more detail with reference to embodiments. However, these embodiments are provided for illustrative purposes only, and the present invention is not limited thereto.

[0121] [Example 1]

[0122] 1000g of waste polyester resin, 2000g of ethylene glycol, and 10g of anhydrous zinc acetate were charged into a first reactor made of stainless steel (SUS). The temperature inside the first reactor was raised to 180°C, and a first depolymerization (first diollysis reaction) was carried out for 2 hours to obtain a first reactant (a-1). Subsequently, the obtained first reactant (a-1) was transferred to a second reactor and cooled to 150°C. Then, 2000g of ethylene glycol was further charged into the second reactor, and a second depolymerization (second diollysis reaction) was carried out for 2 hours, while the temperature of the second reactor was maintained at 150°C to obtain a second reactant (a-2) containing crude bis(2-hydroxyethyl) terephthalate (crude BHET).

[0123] The second reactant (a-2) obtained was cooled to 120°C by vacuum flash evaporation, and 16g of filter aid (Celite) was added to it. TM 545), then pressure filtration was applied to separate the solid and liquid components, yielding liquid reactants (b).

[0124] Subsequently, the liquid reactant (b) is passed through a column packed with ion exchange resin (Bonlite BC107(H)) to remove ionic impurities contained in the liquid reactant (b), thereby obtaining a mixture (reactant (c)) containing crude bis(2-hydroxyethyl) terephthalate (crude BHET) and ethylene glycol.

[0125] Subsequently, water (DIW) was added to the mixture (reactant (c)) to adjust the polarity of the solvent contained in the mixture (reactant (c)). The mixture (reactant (d)) with added water was cooled to room temperature in a 10-liter cooling crystallizer to allow crystallization. In this case, water (feed) was added to the mixture (reactant (c)) so that the water (DIW) content in the solvent component of the mixture (reactant (d)) excluding crude BHET was 40% by weight.

[0126] The crystalline material (e) obtained by crystallization was subjected to solid-liquid separation by pressurized Nutsche filtration to obtain a filter cake containing regenerated bis(2-hydroxyethyl) terephthalate (r-BHET), as product (f).

[0127] The product (f) thus obtained is transferred to a 10-liter distillation apparatus and subjected to vacuum distillation at 130°C to remove (recover) unreacted ethylene glycol. Subsequently, the product (g) from which ethylene glycol has been removed is subjected to thin-film evaporation in a thin-film evaporator (VTA VKL70-4S) at 220°C and 0.08 Torr to remove dimers or oligomers with higher degrees of polymerization, thereby obtaining a recycled feedstock composition as the final product (h).

[0128] [Example 2]

[0129] The final product (h) was obtained by the same steps as in Example 1, except that water was added to the mixture (reactant (c)) so that the water content in the solvent component of the mixture (reactant (d)) other than crude BHET was 30% by weight.

[0130] [Example 3]

[0131] The final product (h) was obtained by the same steps as in Example 1, except that water was added to the mixture (reactant (c)) so that the water content in the solvent component of the mixture (reactant (d)) other than crude BHET was 50% by weight.

[0132] [Example 4]

[0133] The final product (h) was obtained by the same steps as in Example 1, except that water was added to the mixture (reactant (c)) such that the water content in the solvent component of the mixture (reactant (d)) other than crude BHET was 75% by weight.

[0134] [Example 5]

[0135] The final product (h) was obtained by the same steps as in Example 1, except that water was added to the mixture (reactant (c)) such that the water content in the solvent component of the mixture (reactant (d)) other than crude BHET was 88% by weight.

[0136] [Comparative Example 1]

[0137] The final product (h) is obtained by the same steps as in Example 1, except that water is not added to the mixture (reactant (c)).

[0138] [Comparative Example 2]

[0139] The final product (h) was obtained by the same steps as in Example 1, except that water was added to the mixture (reactant (c)) so that the water content in the solvent component of the mixture (reactant (d)) other than crude BHET was 20% by weight.

[0140] [Comparative Example 3]

[0141] The final product (h) is obtained by the same steps as in Example 1, except that ethanol is added to the mixture (reactant (c)) instead of water.

[0142] [Test Example]

[0143] The materials obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were tested using the following methods. The results are shown in Table 1 below.

[0144] (1) High Performance Liquid Chromatography

[0145] 0.01 g of sample (final product (h)) was diluted in 20 mL of methanol and subjected to 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). The peak area fraction (%) of the following components in the total peak area of ​​HPLC was then obtained.

[0146] -MHET: Monohydroxyethyl terephthalate

[0147] -BHET: Bis(2-hydroxyethyl) terephthalate

[0148] -BHEI: Bis(2-hydroxyethyl) isophthalate

[0149] -DEG-Ester-1: 2-Hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate

[0150] -DEG-Ester-2: Bis[2-(2-hydroxyethoxy)ethyl]phenyl-1,4-dicarboxylic acid ester

[0151] -HA- ester: 2-hydroxyethyl (2-acetoxyethyl) terephthalate

[0152] - Dimer: BHET dimer

[0153] - Trimer: BHET trimer

[0154] (2) TDI

[0155] The sample (final product (h)) was analyzed by HPLC using the test method in section (1) above, and the thermal performance degradation index (TDI) was calculated as expressed by Equation 1 below.

[0156] [Equation 1]

[0157] TDI = [DEG-ester-1] + ([DEG-ester-2] × 2) + exp^[HA-ester] + exp^[BHEI]

[0158] In Equation 1, DEG-ester-1 is the peak area fraction (%) of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl] terephthalate, DEG-ester-2 is the peak area fraction (%) of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylic acid ester, HA-ester is the peak area fraction (%) of 2-hydroxyethyl(2-acetoxyethyl) terephthalate, and BHEI is the peak area fraction (%) of bis(2-hydroxyethyl) isophthalate. Only the numerical values ​​of each parameter are used, i.e., units are disregarded. Here, exp^ represents the exponential function (e^).

[0159] (3) Yellow Index (YID)

[0160] The sample (final product (h)) was dissolved in dimethylformamide at a concentration of 25% by weight at room temperature to prepare a solution. The prepared solution was allowed to stand for 30 minutes, after which its yellow index was measured. Specifically, transmittance data were obtained using HunterLab's Color Flex EZ with a D65 standard light source at an observation angle of 2°. The yellow index (YID) value was calculated using the color analyzer in the software.

[0161] (4) Pressure filtration rate

[0162] Use a filter press (filtration area 0.4m²) 2 (e) 4 filter plates were used to filter crystalline material under a pressure of 18 bar to measure the pressure filtration rate.

[0163] ◎: Filtration rate of 250 liters / minute or higher

[0164] ○: Filtration rate is 100 liters / minute to less than 250 liters / minute

[0165] ×: Filtration rate of 100 liters / minute or lower

[0166] [Table 1]

[0167] As shown in Table 1 above, the degree of BHET crystal growth varies depending on the composition and polarity of the solvent in the cooling crystallization step (4), which in turn leads to changes in the removal (separation) performance of low-melting-point impurities and chromophore molecules. Specifically, in the embodiments of the present invention, the polarity of the solvent can be controlled to accelerate the crystal growth of BHET, while increasing the solubility of dimers or oligomers with higher polymerization degrees, thereby obtaining high-purity BHET and minimizing the content of impurities such as HA-ester, DEG-ester-1, DEG-ester-2, dimers, trimers, etc.

[0168] In this situation, if excessive water is added, the solubility of dimers or oligomers with higher degrees of polymerization decreases, and the undissolved oligomers hinder the growth of BHET crystals, which may increase the amount of microcrystals formed, thereby reducing the pressure filtration performance (the sedimentation effect becomes dominant). Therefore, the amount of water added must be controlled to avoid excessive addition (see Example 5).

[0169] Furthermore, if no water is added (see Comparative Example 1), or if the amount of water added is insufficient to control the solvent polarity (see Comparative Example 2), the purity of BHET is significantly reduced because the solvent polarity is insufficient to accelerate the crystal growth of BHET. Moreover, even when the solvent polarity is adjusted by using ethanol instead of water (see Comparative Example 3), the purity of BHET is still significantly reduced because the change in solvent polarity is minimal.

Claims

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

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

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

4. The recycled raw material composition according to claim 1, wherein when the recycled raw material composition is analyzed by high performance liquid chromatography (HPLC), the total peak area fraction of dimers or oligomers with higher degree of polymerization is 2.0% or less.

5. The recycled material composition according to claim 1, wherein when analyzed in a dimethylformamide solution at a concentration of 25% by weight, the yellow index (YID) of the recycled material composition is 5.0 or less.

6. The recycled raw material composition according to claim 1, wherein the peak area fraction of bis(2-hydroxyethyl) terephthalate is 92% or higher when the recycled raw material composition is analyzed by high performance liquid chromatography (HPLC).

7. The recycled feedstock composition according to claim 1, wherein the thermal performance degradation index (TDI) of the recycled feedstock composition, as analyzed by high performance liquid chromatography (HPLC), is 6.0 or less, said TDI as defined by the following Equation 1: [Equation 1]: TDI = [DEG-ester-1] + ([DEG-ester-2] × 2) + exp^[HA-ester] + exp^[BHEI]; In Equation 1, DEG-ester-1 is the peak area fraction (%) of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl] terephthalate, DEG-ester-2 is the peak area fraction (%) of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylic acid ester, HA-ester is the peak area fraction (%) of 2-hydroxyethyl(2-acetoxyethyl) terephthalate, and BHEI is the peak area fraction (%) of bis(2-hydroxyethyl) isophthalate. The TDI is calculated only by the numerical values ​​of each parameter, i.e., units are not considered.

8. A method for preparing a recycled raw material composition, comprising: (1) The waste polyester was depolymerized by diol hydrolysis to obtain a reactant containing crude bis(2-hydroxyethyl) terephthalate (crude BHET); (2) Treat the reactants with an ion exchange resin; (3) Add water to the reactants obtained by ion exchange resin treatment to adjust the polarity of the solvent contained in the reactants; (4) Cool the reactants with added water to allow them to crystallize; and, (5) The crystals obtained by crystallization are subjected to pressure filtration to obtain a product containing regenerated bis(2-hydroxyethyl) terephthalate.

9. The method for preparing the recycled raw material composition according to claim 8, wherein step (1) comprises: (1-1) The waste polyester was depolymerized by a first diol hydrolysis reaction at 180 to 200 °C to obtain the first reactant; and, (1-2) The first reactant is depolymerized by a second diol hydrolysis reaction at 150 to 170 °C to obtain the second reactant.

10. The method for preparing the recycled raw material composition according to claim 8, wherein in step (3), the amount of water added is 25% to 80% by weight based on the total weight of the solvent other than crude BHET in the reactants in which water has been added.

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

20.

12. The method for preparing the recycled raw material composition according to claim 8, wherein the pressure filtration rate of the crystals in step (5) is 100 liters / minute or higher.

13. The method for preparing the recycled raw material composition according to claim 8, wherein, when analyzed by high performance liquid chromatography (HPLC), the product obtained in step (5) has a total peak area fraction of dimers or oligomers with higher degree of polymerization of 10.0% or less.

14. The method for preparing the recycled raw material composition according to claim 8, further comprising (6) distilling the product obtained in step (5).

15. The method for preparing the recycled raw material composition according to claim 14, wherein step (6) comprises: (6-1) Vacuum distillation of the product; and, (6-2) The product obtained by vacuum distillation in step (6-1) is subjected to thin film evaporation.

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