Polymerizable raw material containing recycled bis(2-hydroxyethyl) terephthalate and method for preparing the same

Abstract

The present invention provides a polymerization raw material that is excellent in purity and quality, and does not suffer from the problem of reduced heat resistance when polymers are polymerized from recycled monomers. [Solution] A polymerization raw material is provided which contains recycled bis(2-hydroxyethyl) terephthalate, in which the content of acetic acid ester compounds and diethylene glycol ester compounds is adjusted to specific levels.

Description

Technical Field

[0001] The present invention relates to a polymerization raw material containing bis(2-hydroxyethyl) terephthalate (BHET) regenerated from waste polyester and a method for preparing the same.

Background Art

[0002] Since polyester is excellent in mechanical strength, heat resistance, transparency, and gas barrier properties, it is widely used as a material for beverage filling containers, packaging films, audio films, video films, etc. Furthermore, polyester is also widely manufactured worldwide as industrial materials such as medical fibers and tire cords. In particular, polyester sheets or plates have good transparency and excellent mechanical strength, and thus are widely used as raw materials for cases, boxes, partitions, shelves, panels, packaging materials, building materials, interior and exterior materials, etc.

[0003] As a result, plastic wastes such as polyester are generated worldwide at an unmanageable level every year. In recent years, regulations and plans regarding the recycling of waste plastic resources including waste polyester have been created in countries around the world. Although physical or chemical methods are used as methods for recycling waste polyester, the physical recycling method is not widely used because purity cannot be guaranteed.

[0004] On the other hand, in the chemical recycling method, the ester bond of waste polyester is cleaved and depolymerized. Specifically, reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis are used. In particular, glycolysis is the decomposition of waste polyester by adding a glycol such as ethylene glycol or diethylene glycol at a high temperature. A reaction product mainly containing bis(2-hydroxyethyl) terephthalate (BHET) is obtained. The bis(2-hydroxyethyl) terephthalate contained in the reaction product can be used as a raw material for preparing unsaturated polyester or ester polyol after crystallization or purification.

[0005] However, in order to use bis(2-hydroxyethyl) terephthalate as the above raw material, it is necessary to increase the purity of bis(2-hydroxyethyl) terephthalate by minimizing the formation of by-products such as diethylene glycol esters during the depolymerization process. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Korean Patent Application Publication No. 2022-0068991 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Generally, bis(2-hydroxyethyl) terephthalate, regenerated from the depolymerization of waste polyester resins, contains oligomeric substances such as dimers and trimers, in addition to by-products derived from diethylene glycol (DEG), which are formed at high depolymerization temperatures. These oligomers contribute to the deterioration of product quality. Furthermore, the acetate, which is primarily used as a catalyst in glycolysis, has a boiling point close to that of ethylene glycol, which is primarily used as a solvent. Therefore, it is not easy to filter it out as an impurity during the recovery and reuse of ethylene glycol. As a result, it accumulates as the process is repeated, forming by-products.

[0008] In particular, the inventors noted that among these by-products, acetic acid ester compounds and diethylene glycol ester compounds impair the purity and quality of recycled bis(2-hydroxyethyl) terephthalate, thereby impairing the degree of polymerization and heat resistance when preparing polymers from it. To solve this problem, the inventors were able to control the content of acetic acid ester compounds and diethylene glycol ester compounds in the final product to a specific level by removing these low-weight organic substances during the purification process. As a result, it became possible to prevent a decrease in heat resistance during polymer preparation.

[0009] Therefore, an object of the present invention is to provide a polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate that does not reduce heat resistance in the preparation of the polymer, and a method for preparing the same. [Means for solving the problem]

[0010] According to one embodiment of the present invention, a polymerization raw material obtained by depolymerization of waste polyester is provided, wherein, when measured by high-performance liquid chromatography (HPLC), the peak area portion of bis(2-hydroxyethyl) terephthalate is 95% or more, the total peak area portion of acetate-based ester compounds is 0.001% to 1.0%, and the total peak area portion of diethylene glycol ester compounds is 0.001% to 2.0%.

[0011] According to another aspect of the present invention, a method for preparing a polymerization raw material is provided, comprising: (a) depolymerizing waste polyester by glycolysis to obtain a crude bis(2-hydroxyethyl) terephthalate solution; (b) cooling the crude bis(2-hydroxyethyl) terephthalate solution to crystallize it; and (c) separating the crystallized product into solid and liquid using a pressure filter. [Effects of the Invention]

[0012] In this invention, the content of acetic acid ester compounds and diethylene glycol ester compounds in the polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate is adjusted to a specific level. In this way, it is possible to prevent a decrease in heat resistance properties caused by these compounds during the polymerization of recycled polyester resin.

[0013] To prepare such polymerization raw materials containing recycled bis(2-hydroxyethyl) terephthalate, low-weight organic substances, including acetic acid, are removed during the purification process by cold crystallization and pressure filtration, in order to effectively suppress the content of by-products such as acetic acid ester compounds or diethylene glycol ester compounds.

[0014] Therefore, the present invention not only allows for the depolymerization of waste polyester to prepare polymerization raw materials, but also enables the production of polyester resins and products with excellent quality, such as heat resistance, using these materials as raw materials. [Modes for carrying out the invention]

[0015] In this specification, terms used to refer to each component are for the purpose of distinguishing them from one another and are not intended to limit the scope of the embodiments. Furthermore, unless otherwise specified in the context, singular expressions are interpreted as including plural forms.

[0016] In this specification, terms such as "First," "Second," etc., are used to describe various components. However, these terms should not be used to limit the components. The terms are used to distinguish one element from another.

[0017] In this specification, the term “comprising” is intended to specify certain characteristics, areas, steps, processes, elements, and / or components. Unless otherwise stated, this does not preclude the presence or addition of any other characteristics, areas, steps, processes, elements, and / or components.

[0018] In the numerical ranges that limit the contents, physical properties, etc. of the components described in this specification, when the numerical ranges limited only by the upper limit value and the numerical ranges limited only by the lower limit value are separately exemplified, it should be understood that the numerical ranges combining these upper limit values and lower limit values are also included in the exemplary ranges of the present invention.

[0019] The molecular weight of the compound or polymer described in this specification, for example, the number average molecular weight or the weight average molecular weight, is a relative mass based on carbon 12 as is well known. Although the unit is not described, if necessary, it can be understood as the molar mass (g / mol) of the same numerical value.

[0020] The polymerization raw material of the present invention containing recycled bis(2-hydroxyethyl) terephthalate is obtained by depolymerization of waste polyester. When measured by high performance liquid chromatography (HPLC), the total peak area portion of acetic acid ester compounds is 1.0% or less, and the total peak area portion of diethylene glycol ester compounds is 2.0% or less.

[0021] The polymerization raw material according to one embodiment is obtained by depolymerization of waste polyester. When measured by high performance liquid chromatography (HPLC), the peak area portion of bis(2-hydroxyethyl) terephthalate is 95% or more, the total peak area portion of acetic acid ester compounds is 0.001% to 1.0%, and the total peak area portion of diethylene glycol ester compounds is 0.001% to 2.0%.

[0022] In order to adjust the contents of acetic acid ester compounds and diethylene glycol ester compounds in the polymerization raw material to specific levels, it is possible to prevent the reduction of heat resistance characteristics by these compounds in the polymerization of recycled polyester resin.

[0023] Hereinafter, the polymerization raw material according to the present invention will be described in detail.

[0024] Polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate Bis(2-hydroxyethyl) terephthalate (BHET) is an ester of two ethylene glycols and one terephthalic acid. For example, BHET is a compound formed as an intermediate in the process of preparing polyesters such as polyethylene terephthalate (PET) by polymerization of ethylene glycol and terephthalic acid or its ester.

[0025] On the other hand, a polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate (recycled BHET) obtained by depolymerization of waste polyester may contain reagents or solvents used in various chemical steps during the depolymerization of waste polyester, or by-products formed by side reactions with them. Therefore, the polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate obtained by depolymerization of the above waste polyester can be regarded as a type of composition containing two or more components. Therefore, in the present invention, the polymerization raw material containing recycled BHET may be referred to as a "recycled BHET composition" or a "polymerization raw material composition".

[0026] A polymerization raw material containing BHET recycled by a general depolymerization process contains organic and inorganic impurities in addition to BHET as a main component, and thus the purity is not high. However, the polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate according to the present invention is excellent in purity and quality despite being obtained by depolymerization of waste polyester.

[0027] The purity of the polymerization raw material containing recycled BHET can be measured using, for example, liquid chromatography. Specifically, the purity of the polymerization raw material containing recycled BHET can be calculated by measuring the portion (%) of the peak area of BHET in the total peak area in the spectrum obtained using high performance liquid chromatography (HPLC).

[0028] When measured by high-performance liquid chromatography (HPLC), the polymerization raw material may have a peak area portion of 95% or more of bis(2-hydroxyethyl) terephthalate. For example, the peak area portion of bis(2-hydroxyethyl) terephthalate may be 95% or more, 97% or more, 98% or more, 99% or more, or 99.5% or more, and may also be 99.998% or less, 99.99% or less, 99.9% or less, or 99% or less, and more specifically, it may be 95% to 99.998% or 97% to 99.998%. According to one embodiment, the polymerization raw material may have a peak area portion of bis(2-hydroxyethyl) terephthalate of 95% to 99.998%, more specifically, 97% to 99.998%, 98% to 99.998%, 99% to 99.998%, or 99.5% to 99.998%, when measured by high-performance liquid chromatography (HPLC).

[0029] On the other hand, polymerization raw materials may include compounds other than BHET, specifically BHET analogs, BHET oligomers (e.g., dimers, trimers), esters, and acetate-based compounds.

[0030] More specifically, when measured by high-performance liquid chromatography (HPLC), the polymerization raw material may have a total peak area portion of oligomers, such as dimers or more, of 2.0% or less. More specifically, the total peak area portion of oligomers, such as dimers or more, may be 1.5% or less, 1.0% or less, or 0.5% or less. On the other hand, the lower limit of the peak area portion of oligomers, such as dimers or more, may be 0% or more, 0.001% or more, 0.01% or more, or 0.1% or more.

[0031] Generally, polymerization raw materials recycled from the depolymerization of waste polyester resins contain oligomeric substances such as dimers and trimers, in addition to by-products derived from diethylene glycol (DEG) formed at high depolymerization temperatures. These substances can impair the quality of the product.

[0032] Furthermore, acetate salts (e.g., zinc acetate), which are primarily used as catalysts in glycolysis, react with ethylene glycol during the depolymerization reaction to convert to hydroxyethyl acetate (HA). HA has a boiling point close to that of ethylene glycol, which is primarily used as the solvent, and therefore is not easily filtered out as an impurity during the recovery and reuse of ethylene glycol. As a result, it accumulates as the process is repeated, forming by-products.

[0033] As shown in the reaction scheme 1 below, acetic acid (AA) derived from metal acetates, which is mainly used as a catalyst, may react with ethylene glycol (EG) to produce acetic acid compounds such as 2-hydroxyethyl acetate (HA) and water (H2O).

[0034] [ka]

[0035] Furthermore, as shown in the reaction scheme 2 below, 2-hydroxyethyl acetate (HA) can be converted to ester compounds such as 2-hydroxyethyl (2-acetoxyethyl) terephthalate (HAET) and ethylene glycol (EG) by transesterification with bis(2-hydroxyethyl) terephthalate (BHET).

[0036] [ka]

[0037] The polymerization raw materials according to the embodiment, when measured by high-performance liquid chromatography (HPLC), have a total peak area portion of acetic acid-based ester compounds of 1.0% or less. More specifically, the polymerization raw materials may have a total peak area portion of acetic acid-based ester compounds of 0.7% or less, 0.5% or less, 0.3% or less, or 0.2% or less when measured by high-performance liquid chromatography (HPLC). On the other hand, the lower limit of the peak area portion of acetic acid-based ester compounds may be 0.001% or more, 0.01% or more, or 0.1% or more in total. According to one embodiment, the polymerization raw materials, when measured by high-performance liquid chromatography (HPLC), may have a total peak area portion of acetic acid-based ester compounds of 0.001% to 1.0%, more specifically, 0.001% to 0.7%, 0.001% to 0.5%, 0.001% to 0.3%, or 0.001% to 0.2%. The acetic acid-based ester compound may be a 2-hydroxyethyl acetate compound. More specifically, the acetate ester compound may include at least one selected from the group consisting of 2-hydroxyethyl (2-acetoxyethyl) terephthalate (HAET), 2-acetoxyethyl [2-(2-hydroxyethoxy)ethyl] terephthalate, and 2-hydroxyethyl [2-[2-(2-hydroxyethoxy)ethoxy]ethyl] terephthalate. As a more detailed example, the acetate ester compound may include 2-hydroxyethyl (2-acetoxyethyl) terephthalate.

[0038] Furthermore, when measured by high-performance liquid chromatography (HPLC), the polymerization raw material has a total peak area portion of 2.0% or less of diethylene glycol (DEG) ester compounds. For example, the total peak area portion of diethylene glycol (DEG) ester compounds may be 1.5% or less, 1% or less, or 0.5% or less. On the other hand, the lower limit of the peak area portion of diethylene glycol (DEG) ester compounds may be 0.001% or more, 0.01% or more, or 0.1% or more. According to one embodiment, when measured by high-performance liquid chromatography (HPLC), the polymerization raw material may have a total peak area portion of 0.001% to 2.0%, more specifically, 0.001% to 1.5%, 0.001% to 1%, or 0.001% to 0.5% of diethylene glycol (DEG) ester compounds. The diethylene glycol ester compound may include 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate and bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate. These are represented by the following formulas 1 and 2, respectively.

[0039] [ka] [ka]

[0040] In this invention, by adjusting the content of acetic acid-based ester compounds and diethylene glycol ester compounds in the polymerization raw materials to specific levels, it is possible to prevent a decrease in heat resistance properties caused by these compounds during the polymerization of recycled polyester resin.

[0041] As the content of diethylene glycol ester compounds in the polymerization raw materials increases, the heat resistance properties of the final polymer resin, such as the melting point, decrease linearly. Acetate ester compounds act as polymerization inhibitors, suppressing the growth of polymer chains. As their content increases, the heat resistance properties of the final polymer resin decrease exponentially. Using these relationships, an equation can be derived to predict the heat resistance properties of polymer resins prepared from polymerization raw materials.

[0042] For example, when measured by high-performance liquid chromatography (HPLC), the polymerization raw material may have a thermal property drop index (TDI) of 6.0 or less, 5.0 or less, 4.0 or less, or 3.0 or less, as defined by the following formula. TDI = [DEG-ester-1] + [DEG-ester-2] × 2 + exp^[HA-ester]

[0043] Here, DEG-ester-1 is the peak area portion (%) of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate, DEG-ester-2 is the peak area portion (%) of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate, and HA-ester is the peak area portion (%) of 2-hydroxyethyl(2-acetoxyethyl)terephthalate. This formula is calculated using only the numerical values ​​of these parameters, excluding their units.

[0044] More specifically, when the thermal degradation index (TDI) defined by the above formula is 3.0 or less, it is possible to more effectively prevent the deterioration of heat resistance properties due to these compounds during the polymerization of recycled polyester resin. More specifically, the thermal degradation index (TDI) may be 2.5 or less, or 2.0 or less. Alternatively, the thermal degradation index (TDI) may be 0 to 3.0, 0 to 2.5, 0.5 to 3.0, 1.0 to 3.0, or 0.5 to 2.5.

[0045] Furthermore, the polymerization raw material may have a peak area portion of monohydroxyethyl terephthalate (MHET) at a concentration of 2% or less, 1.5% or less, 1% or less, or 0.5% or less, when measured by high-performance liquid chromatography (HPLC).

[0046] The polymerization raw material of the present invention has excellent crystallinity, resulting in a high melting point and superior quality such as color.

[0047] For example, the polymerization raw material may have a melting point (mp) of 100°C or higher, 105°C or higher, or 110°C or higher, and 125°C or lower, 120°C or lower, or 115°C or lower. In particular, the polymerization raw material may have a melting point of 110°C to 115°C.

[0048] The polymerization raw material may have a yellowness index (YID) of 5.0 or less when measured in a solution dissolved in dimethylformamide at a concentration of 25% by weight. More specifically, the yellowness index may be 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, 2.5 or less, 2.0 or less, 1.5 or less, or 1.0 or less.

[0049] Furthermore, the total content of residual ethylene glycol in the polymerization raw material may be 1% by weight or less, 0.9% by weight or less, 0.5% by weight or less, or 0.3% by weight or less, based on the weight ratio detected by gas chromatography analysis. More specifically, the content of residual ethylene glycol in the polymerization raw material may be 0.5% by weight or less. More specifically, the content of residual ethylene glycol in the polymerization raw material may be 0.2% by weight or less, 0.15% by weight or less, or 0.1% by weight or less.

[0050] A method for preparing a polymerization raw material according to the present invention comprises: (a) depolymerizing waste polyester by glycolysis to obtain a crude bis(2-hydroxyethyl) terephthalate solution; (b) cooling the crude bis(2-hydroxyethyl) terephthalate solution to crystallize it; and (c) separating the crystallized product into solid and liquid using a pressure filter.

[0051] By removing low-weight organic substances, including acetic acid, during the purification process through cold crystallization and pressure filtration, the content of by-products such as acetic acid-based ester compounds or diethylene glycol ester compounds can be effectively suppressed.

[0052] The following describes in detail each step of the method for preparing the polymerization raw material according to the present invention.

[0053] Depolymerization of waste polyester First, waste polyester is depolymerized by glycolysis to obtain a crude bis(2-hydroxyethyl) terephthalate solution.

[0054] Waste polyester raw materials can be obtained from polyester material products that have been discarded after use. More specifically, waste polyester can be obtained by pre-treating waste containing various polyester materials (e.g., polyethylene terephthalate (PET) materials) that have been discarded after consumer use, such as beverage bottles, fabrics, films, cases, boxes, partitions, shelves, protective panels, packaging materials, building materials, and interior and exterior materials.

[0055] Pretreatment can be carried out by removing other plastics, metals, and foreign matter mixed in the waste, washing it, and then crushing it in a crusher. As a result of pretreatment, the waste polyester raw material may have a flake shape. Furthermore, the waste polyester raw material may have a fibrous microstructure.

[0056] Next, the waste polyester pretreated in this manner is subjected to a depolymerization process. The depolymerization process may include, for example, a glycolysis reaction. As is well known, glycolysis is a chemical reaction that cleaves polymer chains or other similar substances with a glycol such as ethylene glycol. The total weight of the added glycol may be 1, 2, 3 or more times the weight of the waste polyester resin, and may also be 7, 5, 4 or less times. For example, the weight of the added glycol may be 1 to 7 times, more specifically 2 to 5 times, and more specifically 3 to 4 times, the weight of the waste polyester resin.

[0057] A catalyst can be used in the glycolysis reaction. The catalyst may be a metal catalyst, for example, a metal salt catalyst or a metal organocatalyst. More specifically, the catalyst may be a metal acetate, carbonate, oxide, or hydroxide, and the metal may be an alkali metal, an alkaline earth metal, or a transition metal. As a detailed example, the catalyst includes a metal acetate, or its anhydride or hydride. More specifically, it may be at least one selected from the group consisting of zinc acetate, sodium acetate, cobalt acetate, and manganese acetate, or in the form of their hydrates or anhydrides. Furthermore, the weight of the catalyst added may be 0.01 parts by weight or more, 0.1 parts by weight or more, 0.2 parts by weight or more, or 0.3 parts by weight or more, and 5 parts by weight or less, 1 part by weight or less, 0.7 parts by weight or less, 0.5 parts by weight or less, or 0.4 parts by weight or less, per 100 parts by weight of waste polyester resin. For example, the amount of catalyst to be added may be 0.1 to 1 part by weight, more specifically 0.2 to 0.7 parts by weight, per 100 parts by weight of waste polyester resin. More specifically, the catalyst may be used in an amount of 0.2 to 0.4 parts by weight per 100 parts by weight of waste polyester.

[0058] As a detailed example, the glycolysis in step (a) may include the reaction of waste polyester with ethylene glycol in the presence of an acetic acid catalyst.

[0059] Depolymerization may include, for example, a multi-step depolymerization reaction at low temperatures. According to one embodiment, depolymerization includes depolymerizing waste polyester by a first glycolysis reaction at high temperatures; and depolymerizing the product by a second glycolysis reaction at low temperatures.

[0060] The temperature during the first glycolysis reaction may be 170°C or higher, 180°C or higher, or 190°C or higher, and may also be 205°C or lower, 200°C or lower, 195°C or lower, or 190°C or lower. For example, the temperature during the first glycolysis reaction may be 180°C to 200°C, more specifically 180°C to 195°C, and more specifically 180°C to 190°C.

[0061] Furthermore, the temperature during the second glycolysis reaction may be 140°C or higher, 150°C or higher, or 160°C or higher, and may also be 170°C or lower, or 160°C or lower. For example, the temperature during the second glycolysis reaction may be 150°C to 170°C, more specifically 150°C to 160°C, and more specifically 150°C to 155°C.

[0062] As a detailed example, depolymerization may include (1) depolymerizing waste polyester by a first glycolysis reaction at a temperature of 180 to 200°C to obtain a first reactant; and (2) depolymerizing the first reactant by a second glycolysis reaction at a temperature of 150 to 170°C to obtain a second reactant.

[0063] The time required for the first and second glycolysis reactions may be 1 hour or more, 2 hours or more, and 4 hours or less, or 3 hours or less, from the time the optimal temperature is reached. For example, the time required for the first and second glycolysis reactions may be 1 to 4 hours, more specifically 1 to 3 hours, and more specifically 1 to 2 hours, from the time the optimal temperature is reached.

[0064] As a more detailed example, the first glycolysis reaction can be carried out at a temperature of 180°C to 190°C for 1 to 3 hours. Furthermore, the second glycolysis reaction can be carried out at a temperature of 150°C to 160°C for 1 to 3 hours.

[0065] For example, the first glycolysis reaction can be carried out in the presence of a zinc acetate anhydride catalyst. In more detail, the first glycolysis reaction can be carried out at a temperature of 180°C to 200°C for 1 to 3 hours in the presence of a zinc acetate anhydride catalyst. The zinc acetate anhydride may be used in an amount of 0.2 to 0.4 parts by weight per 100 parts by weight of waste polyester. Furthermore, the second glycolysis reaction can be carried out at a temperature of 140°C to 160°C for 1 to 3 hours, after adding ethylene glycol without adding a catalyst.

[0066] Cooling and filtration Next, the crude bis(2-hydroxyethyl) terephthalate solution obtained by depolymerization can be cooled. The cooling temperature may be, for example, 150°C or lower, 140°C or lower, 130°C or lower, 120°C or lower, 110°C or lower, or 100°C or lower, and may also be 50°C or higher, 60°C or higher, 70°C or higher, 80°C or higher, or 90°C or higher.

[0067] As an example, cooling can be performed by a vacuum flash process. More specifically, the temperature of the crude bis(2-hydroxyethyl) terephthalate solution can be reduced by evaporating ethylene glycol under vacuum using a vacuum flash process. For example, the crude bis(2-hydroxyethyl) terephthalate solution may be further cooled to below 120°C by vacuum flash prior to subsequent steps. More specifically, the temperature of the crude bis(2-hydroxyethyl) terephthalate solution can be reduced to below 110°C or below 100°C by a vacuum flash process. The pressure conditions for the vacuum flash process may be, for example, below 200 Torr, below 100 Torr, or below 50 Torr, and more specifically, between 10 Torr and 200 Torr, between 10 Torr and 100 Torr, or between 10 Torr and 50 Torr.

[0068] Subsequently, insoluble impurities can be removed from the cooled crude bis(2-hydroxyethyl) terephthalate solution by filtration. In a detailed example, the crude bis(2-hydroxyethyl) terephthalate solution can be cooled to below 120°C, and a filter aid can be added before filtration. As a result, particulate matter and insoluble organic matter present in the crude bis(2-hydroxyethyl) terephthalate solution can be filtered by solid-liquid separation.

[0069] As filter aids, known components such as diatomaceous earth, perlite, and asbestos powder can be used. For example, 0.1 to 2.0 parts by weight of a filter aid may be added to 100 parts by weight of crude bis(2-hydroxyethyl) terephthalate solution.

[0070] Since bis(2-hydroxyethyl) terephthalate (BHET) or oligomers obtained by the depolymerization reaction exist in solid form at room temperature, separation of foreign substances at room temperature is difficult. Therefore, it is preferable to separate them under temperature conditions of 90°C to 150°C, more specifically 110°C to 150°C. Furthermore, maintaining the above temperature range improves fluidity, which may facilitate the removal of insoluble foreign substances.

[0071] Various methods and apparatuses can be used to remove insoluble foreign matter by solid-liquid separation. For example, pressure filters, centrifuges, pressure filters, and belt presses can be used. However, the method is not limited to these, as long as it can be used to separate foreign matter.

[0072] According to one embodiment, a solid-liquid separation step is performed on a crude bis(2-hydroxyethyl) terephthalate solution by filtering out the low-weight organic substances contained therein, thereby allowing most acetic acid ester compounds and diethylene glycol ester compounds to be discharged in liquid form.

[0073] A process according to one embodiment includes cooling a crude bis(2-hydroxyethyl) terephthalate solution to crystallize it; and separating the crystallized product into solid and liquid using a pressure filter.

[0074] The cooling crystallization temperature may be, for example, 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, 5°C or higher, or 20°C or higher. In particular, room temperature may be used.

[0075] Acetic acid compounds and diethylene glycol compounds can be removed by cooling crystallization.

[0076] The operating pressure of the pressure filter may be 0.1 bar to 21 bar, or more specifically, 1 bar to 5 bar. Furthermore, the operating temperature of the pressure filter may be 5°C to 35°C, or more specifically, 15°C to 25°C.

[0077] The pressure filter may also be a Nutsche filter or a pressure filter.

[0078] Before using the Nütsche filter, it is desirable to inactivate the container by purging with nitrogen or similar means. First, the mixture is placed in the Nütsche filter, an inert gas such as nitrogen is injected, and pressurized to separate the solvent from the filter cake. Then, water is injected into the Nütsche filter to wash away any residual solvent remaining in the filter cake, an inert gas is injected, and pressurized to separate the filter cake from the water. The resulting filter cake may be dried and cooled.

[0079] A pressure filter is a device that separates solids and liquids by forming a filtration chamber with a filter plate having a filter surface, a filter cloth, and a lid, and injecting the reactants under high pressure between the filter cloth and the lid. Compared to a vacuum filter, a pressure filter allows for more effective solid-liquid separation because the pressure difference across the filter material acting as the solid-liquid separation surface is larger.

[0080] Acetic acid compounds and diethylene glycol compounds may be removed by a pressure filter.

[0081] Ion exchange Furthermore, the crude bis(2-hydroxyethyl) terephthalate solution can be subjected to further ion exchange using an ion exchange resin. Ion exchange can remove ionic impurities, specifically catalysts and foreign substances, present in the crude bis(2-hydroxyethyl) terephthalate solution.

[0082] As is well known, ion exchange resins refer to resins or polymers that act as a medium for ion exchange. Ion exchange resins may include cation exchange resins, anion exchange resins, amphoteric ion exchange resins, chelate resins, and the like.

[0083] The cation exchange resin may include a strongly acidic cation exchange resin having a sulfonic acid group (SO3H) and 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 and a weakly basic anion exchange resin having primary to tertiary amino groups.

[0084] As a detailed example, the ion exchange resin may include at least one selected from the group consisting of strongly acidic cation exchange resins, weakly acidic cation exchange resins, and chelate resins.

[0085] According to one embodiment, ion exchange is performed by adding an ion exchange resin to a crude bis(2-hydroxyethyl) terephthalate solution.

[0086] The weight of the ion exchange resin added may be 1, 3, or 5 times the weight of the catalyst added in the depolymerization reaction, or more, and may also be 20, 15, 10, 8 times, or less. For example, the weight of the ion exchange resin added may be 1 to 20 times, more specifically 3 to 15 times, and more specifically 5 to 8 times, the weight of the catalyst added in the depolymerization reaction.

[0087] Furthermore, the weight of the ion exchange resin to be added may be 1 part by weight or more, 3 parts by weight or more, or 5 parts by weight or more, per 100 parts by weight of waste polyester resin used in the depolymerization reaction, and may also be 50 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, or 7 parts by weight or less.

[0088] As a detailed example, ion exchange resin can be used in an amount of 1 to 20 parts by weight per 100 parts by weight of waste polyester.

[0089] In another embodiment, ion exchange is performed by using a column containing an ion exchange resin.

[0090] In detail, ion exchange can be performed by packing the column with ion exchange resin particles and passing a crude bis(2-hydroxyethyl) terephthalate solution through the column.

[0091] The particle diameter of the ion exchange resin particles may be, for example, 0.3 mm to 1.5 mm, or more specifically, 0.6 mm to 0.9 mm.

[0092] The ion exchange temperature may be, for example, 140°C or lower, 130°C or lower, 120°C or lower, 110°C or lower, or 100°C or lower, and may also be 50°C or higher, 60°C or higher, 70°C or higher, 80°C or higher, or 90°C or higher.

[0093] Further purification steps The polymerization raw material containing the recycled bis(2-hydroxyethyl) terephthalate described above may be further purified as needed. For example, the polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate may be prepared by further removing unreacted glycol by distillation.

[0094] Since unreacted glycol remains in the depolymerization product after filtering in the previous step, it is necessary to remove the glycol from the product before proceeding to the next step.

[0095] Furthermore, in order to carry out an economical depolymerization process, it is necessary to implement a step to recover unreacted glycols. That is, glycols such as ethylene glycol, propylene glycol, and diethylene glycol that were used in the previous depolymerization and did not participate in the glycolysis reaction can be recovered and reused.

[0096] Distillation to remove unreacted glycol can be carried out, for example, by vacuum distillation. A glass distillation apparatus or a rotary evaporator may be used for this purpose.

[0097] Performing vacuum distillation to remove unreacted glycol at temperatures below 150°C further reduces the formation of diethylene glycol and its derived impurities, thereby improving the purity of BHET. For example, vacuum distillation to remove unreacted glycol can be performed at temperatures below 150°C, below 130°C, or below 120°C, and above 80°C, above 90°C, above 100°C, or above 110°C. More specifically, the temperature during distillation to remove unreacted glycol may be between 80°C and 190°C or between 90°C and 150°C. As a more detailed example, distillation to remove unreacted glycol may be performed at temperatures between 100°C and 130°C.

[0098] The pressure during vacuum distillation to remove unreacted glycol may be, for example, 0.1 Torr to 760 Torr, 0.1 Torr to 200 Torr, or 0.5 Torr to 30 Torr. More specifically, vacuum distillation can be carried out under progressively reduced pressure from 760 Torr to 0.8 Torr.

[0099] According to another example, a polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate can be prepared by further performing at least one of thin-film distillation under reduced pressure and adsorption crystallization following dissolution in water.

[0100] Thin-film distillation is a distillation method that forms a thin film of the mixture to be separated in order to increase the surface area in contact with the heat source. Specifically, the mixture supplied to the evaporator of a thin-film evaporator forms a thin film on the inner wall of the evaporator by a wiper rotor. Distillation is then carried out under appropriate temperature conditions by heating. Furthermore, a condenser may be provided inside the thin-film evaporator to recover the evaporated material.

[0101] Thin-film evaporation can be performed by short-pass evaporation. Such short-pass and thin-film evaporation methods have short residence times and allow for vacuum distillation using high vacuum. Therefore, they minimize thermal changes to reactants while enabling the separation of high-boiling-point or high-molecular-weight materials that are difficult to separate by other distillation methods. Furthermore, reducing the pressure inside the thin-film evaporator lowers the vapor pressure of the material, allowing evaporation at a temperature lower than its original boiling point.

[0102] As a detailed example, the depolymerization product is supplied to a short pass and a thin film evaporator, and a thin film forming wiper is rotated at 300 rpm or more. As a result, the vaporized material and the non-vaporized material can be separated from each other. The internal thin film temperature of the upper thin film evaporator during thin film evaporation may be, for example, 150°C to 250°C, 190°C to 250°C, or 180°C to 220°C. Furthermore, the internal pressure of the upper thin film evaporator during thin film evaporation may be, for example, 0.005 Torr to 5.0 Torr, 0.05 Torr to 5.0 Torr, 0.05 Torr to 1.5 Torr, or 0.05 Torr to 1 Torr.

[0103] Adsorption crystallization can be carried out, for example, by adding an adsorbent using water as a solvent, filtering, and then crystallizing the mixture.

[0104] Various solvents can be used for adsorption crystallization, but preferably, a solvent capable of dissolving bis(2-hydroxyethyl) terephthalate is used. In a detailed example, to obtain the final reaction product, water is added as a solvent to a polymerization raw material containing regenerated bis(2-hydroxyethyl) terephthalate, dissolved by heating, an adsorbent is added to this, the solution obtained by filtration is crystallized, and finally filtered. As a result, a polymerization raw material of high purity can be obtained.

[0105] Water may be added in an amount of 100 to 500 parts by weight, more specifically 200 to 400 parts by weight, or more specifically 300 to 350 parts by weight, per 100 parts by weight of polymerization raw material.

[0106] Furthermore, the dissolution temperature may be 50°C to 95°C, more specifically 60°C to 85°C, and even more specifically 70°C to 75°C.

[0107] The adsorbent added can adsorb and remove other foreign substances. It may be added in an amount of 0.1 to 3 parts by weight per 100 parts by weight of polymerization raw material. The type and form of the adsorbent are not particularly limited. For example, activated carbon may be used.

[0108] [Mode of the invention] The following are preferred embodiments for understanding the present invention. However, these embodiments are provided to facilitate understanding the present invention and do not limit the scope of the invention.

[0109] Example 1 1,000 g of waste polyester resin, 2,000 g of ethylene glycol, and 5.0 g of anhydrous zinc acetate were charged into a first reactor made of stainless steel (SUS). The temperature inside the reactor was raised to 180°C, and depolymerization (first glycolysis reaction) was carried out for 2 hours. The resulting reaction product (first reaction product) was transferred to a second reactor and cooled to 150°C. Another 2,000 g of ethylene glycol was added, and depolymerization (second glycolysis reaction) was carried out for 2 hours while maintaining the reactor temperature at 150°C.

[0110] The reaction product obtained in this manner (second reaction product) was cooled to 120°C by vacuum flashing, 16 g of a filter aid (Celite® 545) was added, and then solid-liquid separation was performed by pressurized filtration. The separated liquid reaction product was passed through a column packed with ion exchange resin (Bonlite BC107(H)) to remove ionic impurities and obtained a mixture containing bis(2-hydroxyethyl) terephthalate and ethylene glycol (third reaction product).

[0111] This mixture (third reaction product) was cooled to room temperature over 2 hours while being stirred at 100 rpm in a 10-liter crystallization apparatus equipped with a cooling water circulation jacket. The resulting crystallized product was filtered under a pressure of 3 bar using a pressurized Nutsch filter (jacket type, filtration area 0.2 m²). 2 The solid and liquid were separated using ) to obtain the BHET cake (fourth reaction product).

[0112] The BHET cake was transferred to a 10-liter distillation apparatus and heated again to 130°C. Unreacted ethylene glycol was recovered by vacuum distillation under stepwise reduced pressure from 760 Torr to 0.8 Torr. The reaction product from which ethylene glycol had been removed (reactant #5) was subjected to thin-film evaporation in a thin-film evaporator (VTA VKL70-4S) at 220°C and 0.08 Torr to obtain 1,040 g of product from which dimers and oligomers had been removed. Subsequently, for adsorption crystallization, 1,040 g of the above product and 3,120 g of distilled water were charged into a 10-liter glass reactor, dissolved at a temperature of 70°C, then 5.2 g of activated carbon was added, followed by stirring for 30 minutes, and the mixture was filtered. The filtrate was cooled to room temperature, filtered, and dried in a vacuum oven to crystallize it. As a result, 1,980 g of polymerization raw material containing regenerated bis(2-hydroxyethyl) terephthalate was obtained.

[0113] Example 2 Except for adjusting the reaction time of the first glycolysis reaction to 1 hour, the same procedure as in Example 1 was repeated to obtain a polymerization raw material containing regenerated bis(2-hydroxyethyl) terephthalate.

[0114] Example 3 Instead of a pressurized Nutsch filter, filtration is performed using a pressure filter under 18 bar pressure (filtration area 0.4 m²). 2 The same procedure as in Example 1 was repeated, except that a filter plate (4ea) was used, to obtain a polymerization raw material containing regenerated bis(2-hydroxyethyl) terephthalate.

[0115] Example 4 Except for using waste polyester fibers as the waste polyester resin, the same procedure as in Example 1 was repeated to obtain a polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate.

[0116] Example 5 Except for not performing adsorption crystallization after thin-film distillation, the same procedure as in Example 1 was repeated to obtain a polymerization raw material containing regenerated bis(2-hydroxyethyl) terephthalate.

[0117] Comparative Example 1 Except for adjusting the temperature of the first glycolysis reaction to 210°C and the temperature of the second glycolysis reaction to 250°C, the same procedure as in Example 1 was repeated to obtain a polymerization raw material containing regenerated bis(2-hydroxyethyl) terephthalate.

[0118] Comparative Example 2 Except for omitting the cooling crystallization and pressurized Nütsch filter steps, the same procedure as in Example 1 was repeated to obtain a polymerization raw material containing regenerated bis(2-hydroxyethyl) terephthalate.

[0119] Test example The polymerization raw materials containing recycled bis(2-hydroxyethyl) terephthalate in the examples and comparative examples were tested as follows.

[0120] (1) High-performance liquid chromatography (HPLC) Approximately 0.01 g of each polymerization raw material, including recycled bis(2-hydroxyethyl) terephthalate, was diluted with approximately 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 portion (%) of the total peak area of ​​the HPLC was obtained for the following components. MHET: Monohydroxyethyl terephthalate BHET: Bis(2-hydroxyethyl) terephthalate 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 Trimer: BHET trimer

[0121] (2) Gas chromatography (GC) 0.1 g of each polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate was dissolved in 310 ml of CHCl3, filtered through a 0.45 μm filter, and measured by GC. Model: Agilent 7890B Column: DB-624 (30m x 0.25mm x 1.4μm) Oven temperature: 60°C (2 minutes) - 10°C / minute - 200°C (0 minutes) - 20°C / minute - 260°C (5 minutes) Injector temperature: 250℃ Detector temperature: 250℃ Flow rate: 1.5 ml / min (N2), Split ratio: 1 / 50

[0122] (3) TDI Each polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate was subjected to HPLC analysis using the same method as in Section (1) above. The thermal degradation index (TDI), defined by the following formula, was then calculated. TDI = [DEG-ester-1] + [DEG-ester-2] × 2 + exp^[HA-ester] Here, DEG-ester-1 represents the peak area portion (%) of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate, DEG-ester-2 represents the peak area portion (%) of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate, and HA-ester represents the peak area portion (%) of 2-hydroxyethyl(2-acetoxyethyl)terephthalate. This index was calculated by taking only the numerical values ​​of these parameters without their units.

[0123] (4) Differential scanning calorimetry (DSC) For each polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate, the melting point (mp) was measured using a differential scanning calorimeter (DSC, TA Instruments Q20) while heating from 30°C to 280°C at a rate of 20°C / min.

[0124] (5) Inductively coupled plasma atomic emission spectrometry (ICP-AES) 0.3 g of each polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate was sonicated and diluted with ultrapure water. The inorganic content (ppm) was measured using ICP-AES (Agilent Model 5100) (detection limit 5 ppm).

[0125] (6) Yellowness index (YID) Each polymerization raw material containing recycled bis(2-hydroxyethyl) terephthalate was dissolved in dimethylformamide at a concentration of 25% by weight at room temperature, and the yellowness index was measured after 30 minutes. Transmission data was obtained using a Hunterlab Color Flex EZ with a D65 light source at an observer angle of 2°. The yellowness index (YID) value was calculated using a software color analyzer.

[0126] The results of the test examples are shown in the table below.

[0127] [Table 1]

[0128] As can be seen from the table above, the polymerization raw materials containing recycled BHET obtained in Examples 1 to 5 had a total HPLC peak area portion of 2.0% or less of diethylene glycol ester compounds (DEG-ester-1, DEG-ester-2) and a total HPLC peak area portion of 1.0% or less of acetic acid ester compounds (HA-ester), but were excellent in terms of the content of other impurities (MHET, dimers, trimers) or residual EG, melting point (mp), inorganic content, and yellowness index (YID). In particular, the polymerization raw materials containing recycled BHET obtained in Examples 1 to 5 had a thermal degradation index (TDI) of 3.0 or less. Therefore, it is expected that polymerizing recycled polyester resin from these raw materials will result in excellent heat resistance.

[0129] In contrast, the polymerization raw materials containing recycled BHET obtained in Comparative Examples 1 and 2 had a total HPLC peak area portion of more than 2.0% of diethylene glycol ester compounds (DEG-ester-1, DEG-ester-2) and a total HPLC peak area portion of more than 1.0% of acetic acid ester compounds (HA-ester), but were inferior in terms of the content of other impurities (MHET, dimers, trimers) or residual EG, melting point (mp), inorganic content, and yellowness index (YID). In particular, the polymerization raw materials containing recycled BHET obtained in Comparative Examples 1 and 2 reached a maximum thermal degradation index (TDI) of 9.23. Therefore, it is expected that the heat resistance properties will be inferior when recycled polyester resin is polymerized from these materials.

Claims

1. A polymerization raw material obtained by depolymerization of waste polyester, wherein, when measured by high-performance liquid chromatography (HPLC), the peak area portion of bis(2-hydroxyethyl) terephthalate is 95% or more, the total peak area portion of acetic acid ester compounds is 0.001% to 1.0%, and the total peak area portion of diethylene glycol ester compounds is 0.001% to 2.0%.

2. The polymerization raw material according to claim 1, wherein the acetic acid-based ester compound comprises 2-hydroxyethyl (2-acetoxyethyl) terephthalate.

3. The polymerization raw material according to claim 1, wherein the diethylene glycol ester compound comprises 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate and bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate.

4. When measured by high-performance liquid chromatography (HPLC), the following formula applies: TDI = [DEG-ester-1] + [DEG-ester-2] × 2 + exp^[HA-ester] Having a thermal property degradation index of 3.0 or less as defined by, The polymerization raw material according to claim 1, wherein DEG-ester-1 is the peak area portion (%) of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate, DEG-ester-2 is the peak area portion (%) of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate, and HA-ester is the peak area portion (%) of 2-hydroxyethyl(2-acetoxyethyl)terephthalate, and the index is calculated by taking only the numerical values ​​of these parameters excluding their units.

5. The polymerization raw material according to claim 1, which, when measured by high-performance liquid chromatography (HPLC), has a total peak area portion of 2.0% or less of dimers or oligomers.

6. The polymerization raw material according to claim 1, wherein the content of residual ethylene glycol in the polymerization raw material is 0.5% by weight or less.

7. The polymerization raw material according to claim 1, wherein, when measured in a solution dissolved in dimethylformamide at a concentration of 25% by weight, it has a yellowness index (YID) of 5.0 or less.

8. The polymerization raw material according to claim 1, having a melting point of 110°C to 115°C.

9. A method for preparing polymerization raw materials according to claim 1, (a) The step of depolymerizing waste polyester by glycolysis to obtain a crude bis(2-hydroxyethyl) terephthalate solution; (b) The step of cooling the crude bis(2-hydroxyethyl) terephthalate solution to crystallize it; (c) A method comprising the step of separating the crystallized product into a solid and a liquid using a pressure filter.

10. The depolymerization in step (a) is (1) The waste polyester is subjected to depolymerization by a first glycolysis reaction at a temperature of 180°C to 200°C to obtain a first reaction product; (2) The first reactant is subjected to depolymerization by a second glycolysis reaction at a temperature of 150 to 170°C to obtain a second reactant. The method according to claim 9, including the method described in claim 9.

11. The method according to claim 9, wherein the pressure filter in step (c) is a Nütsch filter or a pressure filter.

12. The method according to claim 9, wherein the acetic acid compound and the diethylene glycol compound are removed by the pressurized filter of step (c).

13. The method according to claim 9, wherein the polymerization raw material is prepared by further performing the step of removing unreacted glycol by distillation.

14. The method according to claim 9, wherein the polymerization raw material is prepared by further performing at least one of thin-film distillation under reduced pressure and adsorption crystallization following dissolution in water.

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