Method for producing recycled material compositions

Abstract

The present invention relates to a method for preparing a recycled raw material composition using the depolymerization of waste polyester. This preparation method includes (1) pre-treating waste polyester having an apparent density of 0.1 kg / L or less until it has an apparent density of 0.5 kg / L or more; (2) depolymerizing the pre-treated waste polyester; and (3) purifying the reaction product obtained through depolymerization.

Description

Detailed Description of the Invention

[0001] [Technical Field] The present invention relates to a method for preparing a recycled raw material composition capable of preparing a high-yield, high-purity recycled raw material composition through a waste polyester recycling process (pretreatment and depolymerization), and to a recycled raw material composition prepared therefrom.

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

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

[0004] Physical recycling methods or chemical recycling methods are used as methods for recycling waste polyester, but physical recycling methods cannot guarantee purity and therefore have not been widely popularized. On the other hand, in chemical recycling methods, the ester bonds of waste polyester facilitate the depolymerization of waste polyester. Reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis are used. Among them, glycolysis decomposes waste polyester by adding a glycol such as ethylene glycol or diethylene glycol, thereby obtaining recycled raw materials such as bis(2-hydroxyethyl) terephthalate (BHET).

[0005] However, the degree of contamination, shape, and apparent density of waste polyester vary depending on the environment in which it is recovered. Waste polyester may contain different components rather than a single component, and therefore the amount that can be depolymerized using chemical recycling methods is limited. For this reason, there is a limit to increasing the yield of recycled raw materials to a required level.

[0006] [Disclosure of the Invention] [Technical issues] To solve the above-mentioned conventional problems, the object of the present invention is to provide a method for preparing a recycled raw material composition that can be prepared economically and in high yield, even when waste polyester having various degrees of contamination, shapes, apparent densities, etc., and having heterogeneous components as well as single components, is used as a raw material for depolymerization.

[0007] Furthermore, another object of the present invention is to provide a high-purity recycled raw material composition prepared by the above preparation method.

[0008] [Means of solving the problem] To solve the above problems, the present invention provides a method for preparing a recycled raw material composition, comprising the steps of (1) pre-treating waste polyester having an apparent density of 0.1 kg / L or less until it has an apparent density of 0.5 kg / L or more, (2) depolymerizing the pre-treated waste polyester, and (3) purifying the reaction material obtained through depolymerization.

[0009] Furthermore, the present invention provides a recycled raw material composition prepared by the above preparation method.

[0010] [Advantageous effects of the invention] In this invention, waste polyester is subjected to a pretreatment operation to adjust its apparent density to a certain range or higher, and the waste polyester with the adjusted apparent density is depolymerized to prepare a recycled raw material composition. Therefore, even when waste polyester having various degrees of contamination, shapes, and apparent densities, and containing heterogeneous components as well as single components, is used as a raw material for depolymerization, it is possible to prepare a recycled raw material composition of high purity with high yield.

[0011] Therefore, the present invention enables the economical and effective recycling of waste polyester.

[0012] [Best mode for carrying out the invention] The present invention will now be described in detail. In this specification, the present invention is not limited to the present disclosure given below, but can be modified in various ways as long as the essential elements of the invention are not changed.

[0013] In this specification, the term “including” is intended to specify certain features, areas, steps, methods, elements, and / or components. Unless otherwise stated, this does not preclude the presence or addition of any other features, areas, steps, methods, elements, and / or components.

[0014] Throughout this specification, terms such as "first," "second," etc., are used to describe various components. However, components should not be limited by these terms. These terms are used for the purpose of distinguishing one element from another.

[0015] All numbers and expressions relating to the quantities of components, reaction conditions, etc., used herein should be understood to be modified by the term “approximately” unless otherwise indicated.

[0016] In this specification, singular expressions are interpreted as also covering plurals unless otherwise specified in the context.

[0017] Polyester is used in many fields and is therefore commercialized in various forms. Articles containing polyester are composed of polyester as a single component, or, if necessary, composed of other components, in which case polyester is mixed with other components. Consequently, waste polyester derived from used products comes in a variety of shapes, sizes, and compositions.

[0018] To facilitate recycling, such waste polyester is typically subjected to processes such as removal of foreign substances and crushing. In such processes, the degree of crushing of the waste polyester can be expressed as apparent density (kg / L). A higher apparent density is more favorable for the chemical recycling process of waste polyester.

[0019] In particular, the inventors have found that when a chemical recycling process is carried out using waste polyester as a raw material for depolymerization, and when waste polyester with a low apparent density is used, the amount of waste polyester and reactants (e.g., glycol compounds) that can be used in the depolymerization process is limited, and as a result, the production capacity of recycled raw material compositions through the chemical recycling process of waste polyester is reduced. Furthermore, waste polyester that has heterogeneous components rather than a single component (e.g., polyester mixed with polyolefins, polyamides, polytetrafluoroethylenes, etc.) and has a lower apparent density makes it difficult to separate heterogeneous components and remove impurities during the purification operation after the depolymerization operation. Consequently, the purity and yield of recycled raw material compositions derived from waste polyester are also significantly reduced.

[0020] As described above, the inventors have found that the apparent density of waste polyester, which is the raw material for depolymerization, is a factor that greatly affects the efficiency of the chemical recycling process, the purity and yield of the recycled raw material composition. Based on this, the inventors have adopted a pretreatment operation to control the apparent density of waste polyester in order to improve the overall process efficiency and prepare a high-purity recycled raw material composition with high yield.

[0021] In other words, in the present invention, the apparent density of waste polyester is increased to a certain range or beyond through a specific pretreatment operation, and then a chemical recycling process is carried out, which includes a depolymerization operation as described in detail below.

[0022] (Method for preparing recycled raw material compositions) A method for preparing a recycled raw material composition according to the present invention comprises: (1) pre-treating waste polyester having an apparent density of 0.1 kg / L or less until it has an apparent density of 0.5 kg / L or more; (2) depolymerizing the pre-treated waste polyester; and (3) purifying the reaction product obtained through depolymerization.

[0023] Step (1): Preprocessing to control apparent density According to the present invention, step (1) is a step of pre-treating waste polyester having an apparent density of 0.1 kg / L or less until it has an apparent density of 0.5 kg / L or more.

[0024] If the apparent density of the waste polyester is 0.1 kg / L or less, the amount of waste polyester and glycol compounds that can be used in the depolymerization operation is limited, which may reduce the efficiency of the depolymerization reaction. Therefore, the apparent density of the waste polyester is adjusted to 0.5 kg / L or more through the pretreatment in step (1). When the apparent density of the waste polyester is adjusted to 0.5 kg / L or more, the surface area of ​​the waste polyester increases, thereby significantly increasing the efficiency of the depolymerization reaction using glycol compounds. Insoluble components (foreign matter derived from other components) in the reactant obtained through the depolymerization operation may exist in the form of uniform fine particles, making the purification of insoluble components easier. Therefore, in the present invention, the overall process efficiency is increased while the loss of recycled raw materials (e.g., bis(2-hydroxyethyl) terephthalate (BHET)) containing insoluble components is minimized, thereby making it possible to prepare a recycled raw material composition of high purity and high yield.

[0025] The apparent density of the waste polyester subjected to pretreatment is specifically 0.53 kg / L or more, 0.55 kg / L or more, 0.58 kg / L or more, 0.6 kg / L or more, 0.63 kg / L or more, 0.65 kg / L or more, 0.67 kg / L or more, 0.69 kg / L or more, 0.7 kg / L or more, 0.72 kg / L or more, 0.73 kg / L or more, 0.75 kg / L or more, 0.77 kg / L or more, or 0.8 kg / L or more in consideration of the purity and yield of the recycled raw material composition (for example, it may be 0.52 to 0.8 kg / L, 0.56 to 0.79 kg / L, 0.61 to 0.78 kg / L, 0.64 to 0.78 kg / L, or 0.68 to 0.77 kg / L).

[0026] The pretreatment of waste polyester is not particularly limited, but can be performed through melt extrusion using an extruder. When waste polyester is pretreated through melt extrusion, the apparent density of the waste polyester can be easily adjusted to 0.5 kg / L or more, which is a desirable level in the present invention. In such cases, it is desirable to optimally control the melt extrusion conditions in order to adjust the apparent density of the waste polyester to 0.5 kg / L or more.

[0027] Specifically, according to the present invention, melt extrusion can be performed at a temperature of 250 to 300°C and an extrusion speed of 100 to 350 rpm for 2 to 15 minutes. When the melt extrusion conditions are out of the above range, the waste polyester may be decomposed (deformed or lost) due to overheating, or standardization that enables control of the apparent density may become impossible.

[0028] The melt extrusion temperature refers to the barrel temperature of the extruder. Specifically, the melt extrusion temperature may be 250 to 295°C, 250 to 290°C, 250 to 285°C, 250 to 280°C, 250 to 275°C, 255 to 275°C, or 260 to 270°C.

[0029] The melt extrusion speed refers to the screw rotation speed of the extrusion molding machine. Specifically, the melt extrusion speed can be 110-330 rpm, 115-300 rpm, 120-280 rpm, 125-250 rpm, 130-230 rpm, 135-220 rpm, 140-210 rpm, or 145-205 rpm.

[0030] The melt extrusion time refers to the time that waste polyester remains in the screw of the extruder. Specifically, the melt extrusion time can be 2 to 13 minutes, 2 to 10 minutes, 2.5 to 8 minutes, 2.5 to 7 minutes, 3 to 6 minutes, 3 to 5 minutes, or 2 to 5 minutes.

[0031] The extruder used for melt extrusion is not particularly limited, as long as it is a generally known extruder. Specifically, the extruder may be a single-screw extruder or a twin-screw extruder.

[0032] According to the present invention, no other additives (organic or inorganic additives) can be added to the melt extrusion. In other words, in the present invention, the apparent density of the waste polyester is adjusted physically, rather than chemically, through melt extrusion.

[0033] According to the present invention, waste polyester whose apparent density has been adjusted to 0.5 kg / L or more through pretreatment may have various shapes. Specifically, the shape of the pretreated waste polyester may be spherical, elliptical, cylindrical, or prism-shaped, and preferably cylindrical. Furthermore, the size (longest) of the pretreated waste polyester is not particularly limited, but may be 5 mm or less, 4 mm or less, 3 mm or less, 2 mm or less, or 1 mm or less (for example, 0.5 to 5 mm, 1.5 mm to 4.5 mm, 2 to 4 mm, 2.5 to 3.5 mm, or 2 to 3 mm). As a result, the efficiency of the depolymerization reaction of waste polyester can be increased while the convenience of handling the waste polyester is ensured.

[0034] On the other hand, according to the present invention, the waste polyester to be pretreated is not particularly limited as long as it is waste containing polyester. Specifically, the waste polyester may include waste polyester fabric (fibers), waste polyester film, waste polyester flakes, waste polyester powder, or a combination thereof.

[0035] Step (2): Depolymerization According to the present invention, step (2) is a step of depolymerizing waste polyester whose apparent density has been adjusted to 0.5 kg / L or more through the pretreatment in step (1). The depolymerization step may include (2-1) subjecting the waste polyester with the adjusted apparent density to depolymerization through a first glycolysis reaction at a temperature of 180 to 200°C to obtain a first reactant; and (2-2) subjecting the first reactant to depolymerization through a second glycolysis reaction at a temperature of 150 to 170°C to obtain a second reactant.

[0036] Specifically, step (2-1) may include an operation to perform a glycolysis reaction to obtain a first reactant (first product) by cleaving the polymer chains of waste polyester mainly with a first glycol compound.

[0037] The first glycol compound used in the depolymerization of step (2-1) is not particularly limited, but may specifically include at least one selected from the group consisting of ethylene glycol, propylene glycol, and diethylene glycol.

[0038] The amount supplied for the first glycol compound is not particularly limited. Specifically, the amount supplied may be 1 or more times, 2 or more times, or 3 or more times the weight of the pre-treated waste polyester, and 7 or less times, 5 or less times, or 4 or less times (for example, 1 to 7 times, 2 to 5 times, or 3 to 4 times).

[0039] The depolymerization temperature in step (2-1) may be 180-200°C, specifically 180-195°C, 180-193°C, 180-190°C, 180-188°C, or 180-185°C. Furthermore, the depolymerization time in step (2-1) is not particularly limited, but may be 1-4 hours, 1-3 hours, or 1-2 hours from the time required to reach the temperature necessary for the first depolymerization. When the depolymerization in step (2-1) is carried out within the above range in terms of temperature and time, the first glycolysis reaction of the waste polyester can proceed smoothly while minimizing the formation of by-reactants such as diethylene glycol ester compounds.

[0040] The depolymerization in step (2-1) may be carried out in the presence of a catalyst that activates the first glycolysis reaction. The catalyst is not particularly limited as long as it is a generally known catalyst, but may specifically include metal acetates, their anhydrides, or their hydrates. More specifically, the catalyst may be at least one selected from the group consisting of zinc acetate, sodium acetate, cobalt acetate, and manganese acetate, its hydrate, or its anhydride.

[0041] The amount of catalyst supplied (used) in step (2-1) is not particularly limited, but may be 0.01 to 5 parts by weight, 0.05 to 3 parts by weight, 0.1 to 2 parts by weight, 0.15 to 1 part by weight, 0.2 to 0.6 parts by weight, or 0.2 to 0.4 parts by weight per 100 parts by weight of waste polyester.

[0042] For example, the first glycolysis reaction in step (2-1) could be the reaction of waste polyester with ethylene glycol in the presence of zinc acetate hydrate.

[0043] Step (2-2) may include a glycolysis reaction to obtain a second reactant (second product) by secondarily cleaving the first reactant obtained in step (2-1) with a second glycol compound. The second reactant may refer to the reactant obtained through step (2).

[0044] The second glycol compound used in the depolymerization of step (2-2) is not particularly limited, but may specifically include at least one selected from the group consisting of ethylene glycol, propylene glycol, and diethylene glycol. The second glycol compound may be derived from the depolymerization operation of step (2-1) or may be further supplied during the depolymerization operation of step (2-2).

[0045] The amount supplied by the second glycol compound (the additional amount used in the second depolymerization) is not particularly limited and may be 1 or more, 2 or more, or 3 or more times the weight of the pre-treated waste polyester, and 7 or less, 5 or less, or 4 or less (for example, 1 to 7 times, 2 to 5 times, or 3 to 4 times).

[0046] The depolymerization temperature in step (2-2) may be 150-170°C. Specifically, the depolymerization temperature may be 150-165°C, 150-163°C, 150-160°C, 150-158°C, or 150-155°C. Furthermore, the depolymerization time in step (2-2) is not particularly limited, but may be 1-4 hours, 1-3 hours, or 1-2 hours from the time required to reach the temperature necessary for the second depolymerization. When the depolymerization in step (2-2) is carried out within the above range in terms of temperature and time, the second glycolysis reaction of the first reactant can proceed smoothly while minimizing the formation of impurities such as diethylene glycol ester compounds.

[0047] The depolymerization in step (2-2) may be carried out in the presence of a catalyst that activates the second glycolysis reaction. The catalyst may be derived from the depolymerization operation in step (2-1) or may be further supplied during the depolymerization operation in step (2-2). The description of the catalyst is the same as the description of the catalyst in step (2-1) above, and therefore a detailed description is omitted.

[0048] When depolymerization is carried out through steps (2-1) and (2-2), the reactant containing crude bis(2-hydroxyethyl) terephthalate (crude BHET) can be obtained in high yield.

[0049] Step (3): Purification According to the present invention, step (3) is a step of purifying the reactant (depolymerized reactant) obtained through depolymerization in step (2). The purification of the reactant can be carried out through various steps.

[0050] For example, according to the present invention, the purification in step (3) may include cooling the reactant to a temperature of 100 to 150°C and then pressure filtering the reactant at a pressure of 0.01 to 0.5 MPa. Specifically, in the pressure filtration, the reactant is cooled through a reduced-pressure flash and then subjected to solid-liquid separation through a pressure filtration operation using a filter aid. As a result, the reactant can be converted into a liquid reactant. When pressure filtration is performed, solid impurities such as fine particles and insoluble organic substances contained in the reactant are removed, thereby increasing the purity and yield of the recycled raw material composition.

[0051] The temperature at which the reactants are cooled through a depressurized flash may be specifically 100-135°C, 105-125°C, or 110-120°C. Furthermore, the pressure for performing the depressurized flash is not particularly limited, but may be 20 Torr or less, 150 Torr or less, 100 Torr or less, 50 Torr or less, or 30 Torr or less, and may be 5 Torr or more, 8 Torr or more, 10 Torr or more, or 15 Torr or more (e.g., 5-200 Torr, 10-100 Torr, or 15-50 Torr).

[0052] The reactants cooled through a reduced-pressure flash may have a pressure filtration rate of 1.5 L / min or more. Specifically, the pressure filtration rate of the reactants may be 2 L / min or more, 2.5 L / min or more, 3 L / min or more, 3.5 L / min or more, 4 L / min or more, 4.5 L / min or more, 5 L / min or more, or 5.5 L / min or more (for example, 1.5-6 L / min, 3-5.7 L / min, 4-5.6 L / min, or 4.5-5.5 L / min). As described above, the high pressure filtration rate of the reactants in the present invention may result in high overall process efficiency. This improvement in pressure filtration rate is possible by adjusting the apparent density of the waste polyester to 0.5 kg / L or more to ensure good separation between different components in the waste polyester.

[0053] On the other hand, the filter aid is not particularly limited as long as it is generally known, but may specifically include at least one selected from the group consisting of diatomaceous earth, perlite, and asbestos powder.

[0054] According to the present invention, the purification in step (3) may include treating the reactant with an ion exchange resin. Specifically, the treatment may be carried out by passing the reactant through an ion exchange resin or by adding the ion exchange resin to the reactant. When the above operation is performed, ionic impurities contained in the reactant may be removed in order to obtain the reactant in high purity.

[0055] Ion exchange resins can be commonly known cation exchange resins, anion exchange resins, amphoteric ion exchange resins, chelate resins, or combinations thereof.

[0056] 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. Chelate resins may be polymer resins having reactive functional groups such as acetates or phosphates that chelate metal ions such as sodium, copper, nickel, zinc, and manganese.

[0057] When the treatment is carried out by adding an ion exchange resin to the reactant, the amount of ion exchange resin supplied (used) is not particularly limited, but may be 1 or more times, 2 or more times, 3 or more times, or 5 or more times the weight of the catalyst used in the depolymerization of step (2), and 20 or less times, 15 or less times, 10 or less times, or 8 or less times (for example, 1 to 20 times, 2 to 15 times, 3 to 10 times, or 5 to 8 times). Furthermore, the amount of ion exchange resin supplied (used) may be 1 or more parts by weight, 2 or more parts by weight, 3 or more parts by weight, or 5 or more parts by weight per 100 parts by weight of waste polyester from step (2), and 50 or less parts by weight, 20 or less parts by weight, 15 or less parts by weight, 10 or less parts by weight, or 7 or less parts by weight (for example, 1 to 50 parts by weight, 3 to 20 parts by weight, or 5 to 10 parts by weight).

[0058] When the treatment is carried out by passing the reactant through an ion exchange resin, the ion exchange resin may be in the form of particles having a predetermined size. Specifically, the treatment for removing ionic impurities may be carried out by passing the reactant (e.g., a liquid reactant) through a column packed with ion exchange resin particles having particle sizes of 0.3–1.5 mm, 0.5–1.3 mm, or 0.7–1.0 mm.

[0059] According to the present invention, the purification in step (3) may include cooling and crystallizing the reactants. Specifically, cooling crystallization can be carried out by lowering the temperature of the reactants. The temperature for cooling the reactants for crystallization is not particularly limited, but may be 70°C or lower, 60°C or lower, 50°C or lower, 40°C or lower, 30°C or lower, or 25°C or lower, and may be 0°C or higher, 5°C or higher, 10°C or higher, 15°C or higher, or 20°C or higher. Once cooling crystallization is carried out, acetic acid ester compounds and diethylene glycol ester compounds as impurities can be effectively removed.

[0060] According to the present invention, the purification in step (3) may include distillation of the reactants. Specifically, the distillation may be carried out by subjecting the reactants to vacuum distillation to obtain a product, and then subjecting the product thus obtained to thin-film evaporation.

[0061] Glass distillation apparatus or rotary evaporators may be used for vacuum distillation of reactants.

[0062] Vacuum distillation conditions are not particularly limited, but can be carried out at a temperature of 150°C or lower and a pressure of 0.1 to 200 Torr. More specifically, the pressure for carrying out vacuum distillation may be 0.1 to 150 Torr, 0.2 to 100 Torr, 0.3 to 50 Torr, or 0.5 to 30 Torr. Furthermore, the temperature for carrying out vacuum distillation may be 90°C or higher, 100°C or higher, or 110°C or higher, and 145°C or lower, 140°C or lower, or 135°C or lower (e.g., 90 to 150°C, 100 to 145°C, 120 to 135°C, or 100 to 130°C).

[0063] Unreacted glycol compounds (e.g., ethylene glycol and diethylene glycol) contained in the reactants can be removed and recovered by vacuum distillation, and the recovered glycol compounds can be reused in the depolymerization operation of step (2).

[0064] Thin-film evaporators, including an evaporator, wiper rotor, and condenser, can be used for thin-film evaporation of reactants.

[0065] The thin-film evaporation conditions are not particularly limited, but specifically they can be carried out at a pressure of 0.005 to 5 Torr and a temperature of 150 to 250°C. More specifically, the pressure for carrying out thin-film evaporation may 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 carrying out thin-film evaporation (internal thin-film temperature of the thin-film evaporator) may be 180 to 240°C, 185 to 230°C, 190 to 225°C, 195 to 220°C, or 200 to 220°C.

[0066] Oligomers such as dimers or higher-order oligomers (e.g., BHET dimers and BHET trimers) contained in the reactants can be effectively removed by thin-film evaporation.

[0067] On the other hand, pressurized filtration, ion exchange resin treatment, cold crystallization, vacuum distillation, and thin-film evaporation for the purification of reactants may be performed depending on the type of impurity, and the order in which each step is performed may also be appropriately selected.

[0068] In the present invention, a high-purity recycled raw material composition can be prepared in high yield through purification in step (3). In particular, in the present invention, it is possible to prepare a recycled raw material composition in which the content of specific impurities is controlled to be within or below a certain range, and the content of bis(2-hydroxyethyl) terephthalate (BHET) as a desirable component is significantly high.

[0069] In particular, the composition of a recycled raw material composition obtained by the depolymerization of waste polyester can be confirmed by measuring the peak area fraction (%) of the analyzed component out of the total peak area in the spectrum obtained by analyzing the recycled raw material composition by high-performance liquid chromatography (HPLC). In such cases, if the peak area fraction of components considered to be impurities is low, and the peak area fraction of BHET, a desirable component, is high, the purity of the recycled raw material composition may be high.

[0070] For example, according to the present invention, when the recycled raw material composition obtained through steps (1) to (3) is analyzed by high-performance liquid chromatography (HPLC), the sum of the peak area fractions (x) of the diethylene glycol ester (DEG-ester) compound and the peak area fraction (y) of monohydroxyethyl terephthalate (MHET) (x+y) may be less than 4.0%. Specifically, the sum of the peak area fractions (x+y) may be 3.8% or less, 3.5% or less, 3.3% or less, 3.0% or less, 2.8% or less, 2.5% or less, 2.3% or less, 2.0% or less, 1.9% or less, 1.5% or less, 1.3% or less, 1.0% or less, or 0.8% or less (for example, 0-3.5%, 0.3-3.0%, 0.5-2.5%, or 0.8-2.0%). If diethylene glycol ester (DEG-ester) compounds remain in the recycled raw material composition, the melting point of the recycled polyester resin prepared using the recycled raw material composition decreases, thereby degrading the thermal resistance of the recycled polyester resin. However, since the content of diethylene glycol ester (DEG-ester) compounds in the recycled raw material composition of the present invention is controlled to a minimum, it can be advantageously used as a polymerization raw material for preparing recycled polyester resins with excellent thermal resistance.

[0071] Diethylene glycol ester (DEG-ester) compounds may specifically include 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate (DEG-ester-1), bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate (DEG-ester-2), or combinations thereof.

[0072] According to the present invention, when the recycled raw material composition obtained through steps (1) to (3) is analyzed by high-performance liquid chromatography (HPLC), the peak area fraction of acetate ester (HA-ester) compounds may be less than 0.4%. Specifically, the peak area fraction of acetate ester (HA-ester) compounds may be 0.35% or less, 0.3% or less, 0.25% or less, 0.23% or less, 0.2% or less, 0.18% or less, 0.15% or less, 0.13% or less, 0.1% or less, 0.09% or less, 0.07% or less, 0.05% or less, or 0.03% or less (for example, 0 to 0.35%, greater than 0 to 0.3%, 0.01 to 0.25%, 0.03 to 0.2%, or 0.05 to 0.15%). If acetate ester (HA-ester) compounds remain in the recycled raw material composition, they may act as terminators that inhibit polymer chain growth when recycled polyester resin is prepared using the recycled raw material composition, resulting in a deterioration of the thermal resistance of the recycled polyester resin. However, since the content of acetate ester (HA-ester) compounds in the recycled raw material composition of the present invention is controlled to a minimum, it can be advantageously used as a polymerization raw material for preparing recycled polyester resin with excellent thermal resistance.

[0073] Acetate ester (HA-ester) compounds may include 2-hydroxyethyl (2-acetoxyethyl) terephthalate.

[0074] According to the present invention, when the recycled raw material composition obtained through steps (1) to (3) is analyzed by high-performance liquid chromatography (HPLC), the peak area fraction of bis(2-hydroxyethyl) terephthalate (BHET) may be 95% or higher. Specifically, the peak area fraction of bis(2-hydroxyethyl) terephthalate (BHET) may be 95.5% or higher, 96% or higher, 96.5% or higher, 97% or higher, 97.5% or higher, 98% or higher, 98.5% or higher, 99% or higher, 99.5% or higher, or 100% (for example, 95-100%, 96-99%, 96-98%, or 96.5-98%). As described above, since the recycled raw material composition of the present invention has a significantly high peak area fraction of bis(2-hydroxyethyl) terephthalate (BHET) as a desirable component, it is possible to achieve high purity and high yield.

[0075] According to the present invention, when a recycled raw material composition is prepared through steps (1) to (3), the process yield (Y) according to the following equation 1 may be 80% or more. Specifically, the process yield (Y) may be 81% or more, 81.5% or more, 82% or more, 82.5% or more, 83% or more, 83.5% or more, 84% or more, 84.5% or more, 85% or more, 85.5% or more, 86% or more, 86.5% or more, 87% or more, 88% or more, or 90% or more (for example, 80-99%, 81-95%, 82-90%, or 84-88%). [Equation 1] Y(%) = (W1 / W2) × 100

[0076] In Equation 1, W1 is the weight of the recycled raw material composition obtained through steps (1) to (3) (the actual weight of the recycled raw material composition obtained through the chemical recycling process), and W2 is the theoretical weight of the recycled raw material composition prepared from the waste polyester used in step (1) (the theoretical weight of the recycled raw material composition that can be obtained through the chemical recycling process of waste polyester).

[0077] (Recycled raw material composition) The recycled raw material composition according to the present invention is prepared by the method for preparing the recycled raw material composition described above. In particular, the recycled raw material composition may contain a high content of recycled bis(2-hydroxyethyl) terephthalate (r-BHET) formed by the depolymerization of waste polyester.

[0078] According to the present invention, the recycled raw material composition contains a high content of recycled bis(2-hydroxyethyl) terephthalate (r-BHET), while the content of impurities (e.g., MHET, DEG-ester, HA-ester, BHET dimer, BHET trimer, etc.) is controlled to be within a specific range or less, making it advantageous for use in the preparation of recycled polyester resins. In particular, since the recycled bis(2-hydroxyethyl) terephthalate (r-BHET) contained in the recycled raw material composition has crystalline properties and high purity, it may have physical properties equivalent to those of unused bis(2-hydroxyethyl) terephthalate (unused BHET). Therefore, when recycled polyester resin is prepared using recycled bis(2-hydroxyethyl) terephthalate (r-BHET), it is possible to provide recycled polyester resin with excellent thermal resistance, weather resistance, color characteristics, etc.

[0079] [Mode of the invention] The present invention will be described in further detail below with reference to embodiments. However, these embodiments are provided for illustrative purposes only, and the present invention is not limited thereto.

[0080] [Example 1] Step (1): Pretreatment A waste polyester fabric with an apparent density of 0.1 kg / L or less was supplied to a twin-screw extruder and subjected to a pretreatment operation by melt extrusion for 3 minutes at a barrel temperature of 250°C and an extrusion speed of 200 rpm to obtain 1,000 g of waste polyester fabric with a controlled apparent density.

[0081] Step (2): Depolymerization 1,000 g of the waste polyester fabric obtained above, 2,000 g of ethylene glycol, and 15.0 g of anhydrous zinc acetate were placed in a first reactor made of stainless steel (SUS). The temperature inside the first reactor was raised to 180°C, and the first depolymerization (first glycolysis reaction) was carried out for 2 hours to obtain the first reactant. Subsequently, the first reactant obtained in this way was transferred to a second reactor and cooled to 150°C. Then, another 2,000 g of ethylene glycol was supplied to the second reactor, and the second depolymerization (second glycolysis reaction) was carried out for 2 hours, during which the reactor temperature was maintained at 150°C to obtain the second reactant.

[0082] Step (3): Purification The second reactant obtained above was cooled to 120°C by passing it through a reduced-pressure flash, and then subjected to high-temperature pressurized filtration (solid-liquid separation) to obtain a liquid reactant.

[0083] The resulting liquid reactant was passed through a column packed with ion exchange resin (Bonlite BC107(H)) to remove ionic impurities, yielding a mixture containing regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) and ethylene glycol.

[0084] The mixture was transferred to a 10-liter distillation apparatus, and vacuum distillation was performed at 130°C to remove (recover) unreacted ethylene glycol. Subsequently, the third reactant, from which ethylene glycol had been removed, was subjected to thin-film evaporation in a thin-film evaporator (VTA VKL70-4S) at 220°C and 0.08 Torr to obtain a fourth reactant from which dimers or higher-order oligomers had been removed.

[0085] Subsequently, for adsorption and crystallization, the fourth reactant and distilled water were placed in a 20-liter glass reactor and dissolved at a temperature of 70°C. Activated carbon was then added to the reactor, followed by stirring for 30 minutes, and the mixture was filtered. Next, the filtrate obtained by filtration was cooled to room temperature and crystallized, filtered again, and dried in a vacuum oven to prepare a recycled raw material composition containing recycled bis(2-hydroxyethyl) terephthalate.

[0086] [Example 2] A recycled raw material composition was prepared through the same procedure as in Example 1, except that a waste polyester banner was used instead of waste polyester fabric, and the pretreatment conditions were adjusted as shown in Table 1 below.

[0087] [Example 3] A recycled raw material composition was prepared through the same procedure as in Example 1, except that waste polyester film scraps were used instead of waste polyester fabric, and the pretreatment conditions were adjusted as shown in Table 1 below.

[0088] [Example 4] The recycled raw material composition was prepared through the same procedure as in Example 1, except that the pretreatment conditions for the waste polyester fabric were adjusted as shown in Table 1 below.

[0089] [Example 5] The recycled raw material composition was prepared through the same procedure as in Example 1, except that the pretreatment conditions for the waste polyester fabric were adjusted as shown in Table 1 below.

[0090] [Example 6] The recycled raw material composition was prepared through the same procedure as in Example 1, except that the pretreatment conditions for the waste polyester fabric were adjusted as shown in Table 1 below.

[0091] [Comparative Example 1] A recycled raw material composition was prepared through the same procedure as in Example 1, except that the pretreatment of the waste polyester fabric was omitted.

[0092] [Comparative Example 2] The recycled raw material composition was prepared through the same procedure as in Example 2, except that the pretreatment of the waste polyester banner was omitted.

[0093] [Comparative Example 3] The recycled raw material composition was prepared through the same procedure as in Example 3, except that the pretreatment of waste polyester film scraps was omitted.

[0094] [Comparative Example 4] A recycled raw material composition was prepared through the same procedure as in Example 1, except that waste polyester fabric having an apparent density of 0.1 kg / L or less was supplied to a reactor capable of crushing and crystallizing, and instead of subjecting it to pretreatment by melt extrusion, it was subjected to a pretreatment operation (heat setting) by heating at 220°C for 60 minutes to obtain waste polyester fabric with an adjusted apparent density.

[0095] [Comparative Example 5] A recycled raw material composition was prepared through the same procedure as in Comparative Example 4, except that a waste polyester banner was used instead of waste polyester fabric.

[0096] [Comparative Example 6] A recycled raw material composition was prepared through the same procedure as in Comparative Example 4, except that waste polyester film scraps were used instead of waste polyester fabric.

[0097] [Example Test] The substances obtained in Examples 1-6 and Comparative Examples 1-6 were tested by the following methods. The results are shown in Tables 1 and 2 below.

[0098] (1) High-performance liquid chromatography (HPLC) 0.01 g of the sample (recycled raw material composition) was diluted with 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 fraction (%) of the following components was confirmed from the total peak area of ​​the HPLC. 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

[0099] (2) Apparent density (kg / L) Each waste polyester was filled into a 2-liter flask of known capacity without applying pressure, its weight was measured, and the apparent density was calculated using the relationship between the measured weight and the flask volume. The results are shown in Tables 1 and 2 below.

[0100] (3) Pressure filtration rate (L / min) The pressure filtration rate of the depolymerization reactant (second reactant) was measured under the following conditions. The results are shown in Tables 1 and 2 below. Pressure filter area: 700 cm² 2 Pressure filter mesh size: 1 μm; Pressure: 0.01~0.5 MPa

[0101] (4) Process yield (%) The process yield of the recycled raw material composition was calculated according to Equation 1 below. [Equation 1] Y(%) = (W1 / W2) × 100

[0102] In Equation 1, W1 is the weight of the recycled raw material composition obtained through steps (1) to (3), and W2 is the theoretical weight of the recycled raw material composition prepared from the waste polyester used in step (1).

[0103] [Table 1]

[0104] [Table 2]

[0105] Referring to Tables 1 and 2 above, when the apparent density of the waste polyester, which was the raw material for depolymerization, was adjusted to 0.5 kg / L or higher through a pretreatment operation by melt extrusion, the depolymerization reaction proceeded smoothly, and even when the waste polyester contained heterogeneous components as well as a single component, the separation efficiency of insoluble components was improved, thereby enabling the preparation of high-purity recycled raw material compositions in high yield (see Examples 1-3).

[0106] However, if pretreatment is performed without optimal control of the temperature, extrusion rate, and time under which melt extrusion is carried out, the waste polyester may be excessively decomposed or not dissolved at all, making standardization impossible. Therefore, it is sometimes desirable to optimally control the conditions under which melt extrusion is carried out (see Examples 4-6).

[0107] On the other hand, when the recycled raw material composition was prepared without pretreatment, a recycled raw material composition containing many impurities was prepared in a significantly lower yield (see Comparative Examples 1-3). Furthermore, when pretreatment was performed using a method other than melt extrusion, the apparent density of the waste polyester could not be adjusted to 0.5 kg / L or higher, resulting in a decrease in the purity and yield of the recycled raw material composition (see Comparative Examples 4-6).

Claims

1. (1) A step of pre-treating waste polyester having an apparent density of 0.1 kg / L or less until it has an apparent density of 0.5 kg / L or more, (2) The step of depolymerizing the pretreated waste polyester, (3) A step of purifying the reaction product obtained through the depolymerization, A method for preparing a recycled raw material composition containing [a specific substance].

2. A method for preparing the recycled raw material composition according to claim 1, wherein the pretreatment in step (1) is carried out by melt extrusion.

3. A method for preparing the recycled raw material composition according to claim 2, wherein the melt extrusion is carried out at a temperature of 250 to 300°C and an extrusion speed of 100 to 350 rpm for 2 to 15 minutes.

4. A method for preparing the recycled raw material composition according to claim 2, wherein the melt extrusion is performed without the addition of additives.

5. A method for preparing the recycled raw material composition according to claim 1, wherein the waste polyester, whose apparent density has been adjusted to 0.5 kg / L or more in step (1), has a size of 5 mm or less and has a cylindrical shape.

6. A method for preparing the recycled raw material composition according to claim 1, wherein the waste polyester pretreated in step (1) comprises waste polyester fabric, waste polyester film, waste polyester flakes, waste polyester powder, or a combination thereof.

7. Step (2) is, (2-1) The waste polyester, whose apparent density has been adjusted, is subjected to depolymerization through a first glycolysis reaction at a temperature of 180 to 200°C to obtain a first reactant; and (2-2) The first reactant is subjected to depolymerization at a temperature of 150 to 170°C via a second glycolysis reaction to obtain a second reactant. A method for preparing the recycled raw material composition according to claim 1, comprising:

8. A method for preparing the recycled raw material composition according to claim 1, wherein step (3) comprises cooling the reactant to a temperature of 100 to 150°C and pressure filtering the reactant at a pressure of 0.01 to 0.5 MPa, wherein the rate of pressure filtering of the cooled reactant is 1.5 L / min or more.

9. A method for preparing the recycled raw material composition according to claim 1, wherein step (3) comprises cooling and crystallizing the reactant.

10. A method for preparing the recycled raw material composition according to claim 1, wherein step (3) comprises distilling the reactant.

11. A method for preparing the recycled raw material composition according to claim 1, wherein when the recycled raw material composition obtained through steps (1) to (3) is analyzed by high-performance liquid chromatography (HPLC), the sum of the peak area fractions of the diethylene glycol ester compound and the monohydroxyethyl terephthalate is less than 4.0%.

12. A method for preparing the recycled raw material composition according to claim 1, wherein when the recycled raw material composition obtained through steps (1) to (3) is analyzed by high-performance liquid chromatography (HPLC), the peak area fraction of the acetate ester compound is less than 0.4%.

13. A method for preparing the recycled raw material composition according to claim 1, wherein when the recycled raw material composition obtained through steps (1) to (3) is analyzed by high-performance liquid chromatography (HPLC), the peak area fraction of bis(2-hydroxyethyl) terephthalate is 95% or more.

14. A method for preparing the recycled raw material composition according to claim 1, wherein the process yield (Y) according to the following equation 1 is 80% or more: [Equation 1] Y(%)=(W １ / W ２ )×100 (In equation 1, W １ W is the weight of the recycled raw material composition obtained through steps (1) to (3), ２ (wherein this is the theoretical weight of the recycled raw material composition prepared from the waste polyester used in step (1)).

15. A recycled raw material composition prepared by the preparation method described in any one of claims 1 to 14.

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