Recycled raw material composition comprising bis(2-hydroxyethyl) terephthalate, and preparation method therefor

Abstract

This method for preparing a recycled raw material composition, comprising a step of adding an adsorbent in portions according to the composition of chromophores remaining in a bis(2-hydroxyethyl) terephthalate solution obtained by depolymerizing waste polyester, maximizes adsorption efficiency, and thus enables removal of chromophores to a level that is difficult to achieve through removal with a single adsorption.

Description

Recycled raw material composition containing bis(2-hydroxyethyl)terephthalate and method for manufacturing the same

[0001] The present invention relates to a recycled raw material composition comprising bis(2-hydroxyethyl)terephthalate obtained by depolymerization of waste polyester and a method for manufacturing the same.

[0002] Among the types of polymers closely utilized in modern life, polyester is widely used as a material for beverage or food containers, various packaging films, and interior and exterior materials such as panels, shelves, and partitions, due to its excellent mechanical strength, heat resistance, transparency, and gas barrier properties. As a result of this extensive use, the annual generation of plastic waste, including polyester, is becoming unmanageable; consequently, countries around the world have recently been establishing regulations and measures regarding the recycling of waste plastic resources, including waste polyester.

[0003] There are physical or chemical methods for recycling the waste polyester mentioned above, but physical recycling methods are not widely applied because they cannot guarantee purity. Meanwhile, chemical recycling methods involve depolymerizing waste polyester by breaking the ester bonds, utilizing reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis. Among these, glycolysis involves decomposing waste polyester by adding a glycol, such as ethylene glycol or diethylene glycol, to it, and a composition containing mainly bis(2-hydroxyethyl)terephthalate (BHET) is obtained. The bis(2-hydroxyethyl)terephthalate contained in the composition can be used as a raw material for manufacturing unsaturated polyester or ester polyol after purification.

[0004] Compositions containing bis(2-hydroxyethyl)terephthalate recycled in this manner may contain reagents or solvents used in various chemical steps during the depolymerization of waste polyester, or byproducts generated by side reactions with them; these impurities may remain in trace amounts even after multiple purifications. In particular, the additives used during the initial production of polyester are rich in colorants with molecular structures that exhibit strong color development, and these colorants may also be generated or incorporated after the polyester production process. Consequently, compositions containing bis(2-hydroxyethyl)terephthalate recycled from contaminated waste polyester exhibit poor color quality, making them difficult to use in the production of high-quality polyester resins.

[0005] As such, compositions with a high content of by-products, which are impurities, along with recycled bis(2-hydroxyethyl)terephthalate, have poor color characteristics, and recycled polyester resins manufactured using this as a polymerization raw material have the problem of being difficult to achieve the required quality (e.g., high transparency and low yellowness).

[0006] [Prior Art Literature]

[0007] [Patent Literature]

[0008] (Patent Document 1) Republic of Korea Published Patent Application No. 2022-0068991

[0009] Raw materials recycled from colored waste polyester or mixed with heterogeneous materials present a problem in that it is difficult to obtain high-quality products polymerized from them due to the presence of residual colorants that are difficult to remove by conventional purification methods. In particular, raw materials recycled from polyester fibers and films are highly likely to contain residual chromophores, which significantly reduces their value as polymerization materials.

[0010] Accordingly, the inventors recognized that simply increasing the amount of adsorbent used for the removal of chromophores has limitations, and by maximizing adsorption efficiency through the divided input of the adsorbent according to the characteristics of the chromophores, they were able to remove chromophores to a level that is difficult to achieve with single adsorption.

[0011] Therefore, the objective of the present invention is to provide a recycled raw material composition with improved color that enables the production of high-quality and transparent polyester products by maximizing the removal of residual chromophores in a bis(2-hydroxyethyl)terephthalate solution obtained by depolymerizing waste polyester.

[0012] According to one aspect of the present invention, a method for preparing a recycled raw material composition is provided, comprising the steps of: depolymerizing waste polyester to obtain crude bis(2-hydroxyethyl)terephthalate; adding a solvent to the crude bis(2-hydroxyethyl)terephthalate to obtain a solution; and adding an adsorbent to the solution to adsorb impurities, wherein the adsorption step is performed two or more times, and each adsorption step is selected from (a) an adsorption step using an adsorbent having a relative micropore ratio (MPR) of 30% or less; and (b) an adsorption step using an adsorbent having a relative micropore ratio (MPR) of more than 30%, wherein the relative micropore ratio (MPR) is calculated by the following formula by BET analysis of the adsorbent:

[0013] MPR (%) = (P A / (P B + P C )) x 100

[0014] Here, P A is the sum of the volumes (cc / g) of pores A with a size of less than 2 nm, and P B is the sum of the volumes (cc / g) of pores B with a size of 2 nm to 50 nm, and P C is the sum of the volumes of pores C with a size greater than 50 nm (cc / g).

[0015] According to another aspect of the present invention, a recycled raw material composition is provided, which is prepared by the above method, comprises bis(2-hydroxyethyl)terephthalate, is dissolved in ethylene glycol at a concentration of 50% by weight, and has a yellowness (YID) of 20 or less measured after heat treatment in an oven at 170°C for 1 hour.

[0016] According to another aspect of the present invention, a recycled raw material composition is provided, which is manufactured by the above method and has a content of bis(2-hydroxyethyl)terephthalate of 95 weight% or more and a metal content of less than 20 ppm.

[0017] According to the present invention, by maximizing the removal of residual chromophores in a bis(2-hydroxyethyl)terephthalate solution obtained by depolymerizing waste polyester, a recycled raw material composition with improved color can be provided, which enables the production of high-quality and transparent polyester products.

[0018] Specifically, according to the present invention, rather than simply increasing the amount of adsorbent used to remove chromophores, the adsorbent is divided and added according to the composition of the chromophores to maximize adsorption efficiency, thereby enabling the removal of chromophores to a level that is difficult to achieve with single adsorption.

[0019] Therefore, the present invention can be applied to the recycling of waste polyester in which coloring agents that are difficult to remove by conventional purification methods, such as those mixed with heterogeneous materials or colored fibers and films, remain, thereby providing high-quality recycled raw materials with high value as polymerization raw materials.

[0020] FIG. 1 shows the internal pore structure of an adsorbent according to one embodiment (A: micropore, B: mesopore, C: macropore).

[0021] Figure 2 shows UV-Vis spectra obtained from various BHET-containing regenerated raw material compositions.

[0022] In this specification, terms referring to each component are used to distinguish them from other components and are not intended to limit the embodiments. Additionally, in this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0023] In this specification, terms such as "first," "second," etc. are used to describe various components, and said components should not be limited by said terms. These terms are used for the purpose of distinguishing one component from another.

[0024] In this specification, the use of the word “comprising” is intended to specify certain characteristics, regions, steps, processes, elements, and / or components, and unless specifically stated otherwise, it does not exclude the presence or addition of other characteristics, regions, steps, processes, elements, and / or components.

[0025] In the numerical ranges defining the size, physical properties, etc., of components described in this specification, if a numerical range in which only the upper limit is defined and a numerical range in which only the lower limit is defined are separately exemplified, it should be understood that a numerical range combining these upper and lower limits is also included within the exemplary scope of the present invention.

[0026] A method for preparing a recycled raw material composition according to one aspect of the present invention comprises the steps of: depolymerizing waste polyester to obtain crude bis(2-hydroxyethyl)terephthalate; adding a solvent to the crude bis(2-hydroxyethyl)terephthalate to obtain a solution; and adding an adsorbent to the solution to adsorb impurities.

[0027]

[0028] Depolymerization of waste polyester

[0029] First, waste polyester is depolymerized to obtain crude bis(2-hydroxyethyl)terephthalate.

[0030] The above waste polyester can be obtained from polyester material products discarded after use. Specifically, the waste polyester may include waste materials such as beverage bottles, fabrics, films, cases, boxes, partitions, shelves, protective panels, packaging, construction materials, and interior and exterior materials made of various polyester materials (e.g., polyethylene terephthalate (PET) materials) that are discarded by users after use.

[0031] The aforementioned waste polyester may be contaminated waste polyester. The contaminants present in the waste polyester are quite diverse. Examples of such contaminants include additives used during the initial manufacturing of the polyester and substances generated during the usage process or incorporated due to contamination. In particular, the additives used during the initial manufacturing process are rich in substances with molecular structures that exhibit strong color development, and these color-developing structural substances may be generated or incorporated after the polyester is manufactured.

[0032] The above waste polyester has a purity of 80% or more and may contain 5% by weight or less of dyes and pigments.

[0033] The waste polyester may undergo pretreatment prior to depolymerization. This pretreatment may consist of removing other plastics, metals, and other foreign substances mixed in the waste, washing it, and then crushing it using a crusher. Through this pretreatment process, the waste polyester may take on a flake form. Additionally, the waste polyester may have a microstructure similar to fibers.

[0034] The waste polyester pretreated in this manner is subsequently fed into a depolymerization process. The depolymerization can be carried out by chemical methods using reactions such as glycolysis, hydrolysis, methanolysis, or aminolysis.

[0035] In one embodiment, the depolymerization process may include a glycolysis reaction. As is well known, the glycolysis reaction refers to a chemical reaction that decomposes polymer chains, etc., by glycol. The glycol may be, for example, ethylene glycol, propylene glycol, diethylene glycol, or a combination thereof. The total input weight of the glycol may be 1 to 2 times, 2 to 3 times, or 3 times or more relative to the weight of the waste polyester resin, and may also be 7 times or less, 5 times or less, or 4 times or less. For example, the input weight of the glycol may be 1 to 7 times relative to the weight of the waste polyester resin, specifically 2 to 5 times, and more specifically 3 to 4 times.

[0036] A catalyst may be used in the glycolysis reaction described above. The catalyst may be a metal catalyst, for example, a metal salt catalyst or a metallic organic catalyst. Specifically, the catalyst may be an acetate, carbonate, oxide, hydroxide, etc. of a metal. In one embodiment, the depolymerization is carried out in the presence of a catalyst, and the catalyst comprises an acetate of a metal, an anhydride, or a hydrate thereof, and the metal may be an alkali metal, an alkaline earth metal, or a transition metal. More specifically, the catalyst may be one or more selected from the group consisting of zinc acetate, sodium acetate, cobalt acetate, and manganese acetate, or in the form of a hydrate or anhydride thereof. In addition, the input weight of the catalyst 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 relative to 100 parts by weight of the waste polyester resin, and may also be 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. For example, the input weight of the catalyst may be 0.1 to 1 part by weight relative to 100 parts by weight of the waste polyester resin, and specifically, 0.2 to 0.7 parts by weight. More specifically, the catalyst may be used in an amount of 0.2 to 0.4 parts by weight relative to 100 parts by weight of the waste polyester.

[0037] As a specific example, the glycolysis of step (a) above may include the reaction of waste polyester and ethylene glycol in the presence of an acetate-based catalyst.

[0038] The temperature at which the above depolymerization is performed is not particularly limited, but may be 180°C to 220°C, specifically 180°C to 210°C, 185°C to 200°C, 185°C to 195°C, or 190°C to 195°C. Additionally, the time at which the above depolymerization is performed is not particularly limited, but may be 1 hour to 30 hours from the point at which the temperature required for depolymerization is reached, specifically 1.5 hours to 15 hours, 2 hours to 10 hours, 2 hours to 8 hours, 2.5 hours to 6 hours, or 3 hours to 5 hours. As depolymerization is performed at the above temperatures and times, the glycolysis reaction proceeds smoothly, and the formation of by-products can be minimized.

[0039] The above depolymerization may include, for example, a multi-stage depolymerization reaction at a low temperature. According to one embodiment, the depolymerization comprises the step of depolymerizing waste polyester by a first glycolysis reaction at a high temperature; and the step of depolymerizing by a second glycolysis reaction at a low temperature.

[0040] The temperature during the first glycolysis reaction may be 170 ℃ or higher, 180 ℃ or higher, or 190 ℃ or higher, and may also be 205 ℃ or lower, 200 ℃ or lower, 195 ℃ or lower, or 190 ℃ or lower. For example, the temperature during the first glycolysis reaction may be 180 ℃ to 200 ℃, specifically 180 ℃ to 195 ℃, more specifically 180 ℃ to 190 ℃.

[0041] In addition, the temperature during the second glycolysis reaction may be 140 ℃ or higher, 150 ℃ or higher, or 160 ℃ or higher, and may also be 170 ℃ or lower, or 160 ℃ or lower. For example, the temperature during the second glycolysis reaction may be 150 ℃ to 170 ℃, specifically 150 ℃ to 160 ℃, and more specifically 150 ℃ to 155 ℃.

[0042] As a specific example, the depolymerization may include (1) a step of obtaining a first reaction product by depolymerizing waste polyester by a first glycolysis reaction at a temperature of 180°C to 200°C; and (2) a step of obtaining a second reaction product by depolymerizing the first reaction product by a second glycolysis reaction at a temperature of 150°C to 170°C.

[0043] The time required for the first and second glycolysis reactions may be at least 1 hour or at least 2 hours from the time the appropriate temperature is reached, and may also be 4 hours or less or 3 hours or less. For example, the time required for the first and second glycolysis reactions may be 1 to 4 hours from the time the appropriate temperature is reached, specifically 1 to 3 hours, and more specifically 1 to 2 hours.

[0044] As a more specific example, the first glycolysis reaction may be carried out at a temperature of 180°C to 190°C for 1 to 3 hours. Additionally, the second glycolysis reaction may be carried out at a temperature of 150°C to 160°C for 1 to 3 hours.

[0045] As an example, the first glycolysis reaction may be carried out under a zinc anhydride catalyst. As a specific example, the first glycolysis reaction may be carried out under a zinc anhydride catalyst at a temperature of 180°C to 200°C for 1 hour to 3 hours. The zinc anhydride may be used in an amount of 0.2 to 0.4 parts by weight per 100 parts by weight of the waste polyester. Additionally, the second glycolysis reaction may be carried out at a temperature of 140°C to 160°C for 1 hour to 3 hours after the additional addition of ethylene glycol without the addition of an additional catalyst.

[0046] As such, unpurified bis(2-hydroxyethyl)terephthalate, i.e., crude BHET, after depolymerization may not have sufficient color quality. For example, the yellowness (YID) measured in the solid phase of the waste polyester crude BHET may be 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 15 or more, or 20 or more, and as a specific example, may be 5 to 100, or 10 to 100.

[0047]

[0048] Post-depolymerization process

[0049] In one embodiment, the method of the present invention may further include a step of purifying the depolymer (zobis(2-hydroxyethyl)terephthalate) obtained by the glycolysis. The purification may be at least one selected from the group consisting of, for example, cooling, filtration, distillation, and solvent recovery.

[0050] In one embodiment, the depolymer may undergo cooling. 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.

[0051] Subsequently, insoluble foreign substances can be removed from the cooled depolymer through filtration. As a specific example, the step of cooling the depolymer to 120°C or lower and filtering by introducing a filter aid may be additionally included. As a result, fine particles and insoluble organic substances present in the depolymer can be filtered by solid-liquid separation.

[0052] Since bis(2-hydroxyethyl)terephthalate (BHET) or oligomer substances obtained through depolymerization exist in a solid form at room temperature, it is difficult to separate foreign substances at room temperature; therefore, it is preferable to separate them under temperature conditions of 90°C to 150°C, more specifically 110°C to 150°C. In addition, maintaining the above temperature range improves flowability, making it easier to remove insoluble foreign substances.

[0053] The removal of insoluble foreign substances through solid-liquid separation can be achieved using various methods and devices, such as pressurized filters, centrifuges, filter presses, belt presses, etc., but is not limited to any method capable of separating foreign substances.

[0054] In addition, the above depolymer may undergo further ion exchange through an ion exchange resin. By undergoing the above ion exchange, ionic impurities present in the depolymer, specifically catalysts and metallic foreign substances, can be removed.

[0055] In addition, the above-mentioned depolymer may undergo an additional step of removing moisture and residual solvent by distillation.

[0056] Since unreacted glycol still remains in the depolymerized product filtered through the previous step, it is necessary to remove it from the reactant before the subsequent step.

[0057] In addition, it is necessary to perform a process to recover unreacted glycols for an economical depolymerization process. That is, among the glycols such as ethylene glycol, propylene glycol, and diethylene glycol that were previously introduced into the depolymerization, it is possible to recover the glycols that remain without participating in the glycolysis reaction and reuse them in the glycolysis reaction.

[0058] Distillation to remove the above unreacted glycol can be carried out, for example, by vacuum distillation, and for this purpose, a glass distillation apparatus or a rotary evaporator may be used.

[0059] By performing the vacuum distillation for removing unreacted glycol at a temperature of 150°C or lower, the generation of diethylene glycol and impurities derived therefrom can be further reduced, thereby improving the purity of BHET. For example, the vacuum distillation for removing unreacted glycol may be at a temperature of 150°C or lower, 130°C or lower, or 120°C or lower, and may also be at a temperature of 80°C or higher, 90°C or higher, 100°C or higher, or 110°C or higher. Specifically, the temperature during the distillation for removing unreacted glycol may be 80°C to 190°C, or 90°C to 150°C. As a more specific example, the distillation for removing unreacted glycol may be performed at a temperature of 100°C to 130°C.

[0060] The pressure during vacuum distillation for removing the 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, and more specifically, vacuum distillation may be performed under stepwise vacuum conditions from 760 torr to 0.8 torr.

[0061] In addition, the above-mentioned depolymer can be manufactured by further undergoing a thin-film distillation step under reduced pressure.

[0062] The above thin-film distillation is a distillation method that increases the surface area in contact with a heat source by forming a thin film of the mixture to be separated. Specifically, a mixture introduced into the evaporator of a thin-film distiller forms a thin film on the inner wall of the thin-film distiller by a wiper rotor, and subsequently, distillation is carried out under appropriate temperature conditions by heating. In addition, a condenser for recovering the evaporated material may be provided inside the thin-film distiller.

[0063] The above thin-film distillation can be performed by short-path evaporation. Since such short-path thin-film distillation allows for a short residence time of the substance and enables vacuum distillation using a high vacuum, it is possible to separate high-boiling point or high-molecular-weight substances that are difficult to separate by other distillation methods while minimizing changes in reactants due to heat. In addition, lowering the pressure inside the thin-film distiller lowers the vapor pressure of the substance, which has the advantage of causing evaporation to occur at a temperature lower than its original boiling point.

[0064] As a specific example, the depolymerization product is fed into a short-path thin film distiller, and a wiper forming a thin film rotates at 300 rpm or more, thereby separating the vaporized material and the non-vaporized material. During the thin film distillation, the internal thin film temperature of the upper thin film distillation device may be, for example, 150 ℃ to 250 ℃, 190 ℃ to 250 ℃, or 180 ℃ to 220 ℃. Additionally, during the thin film distillation, the internal pressure of the upper thin film distillation device 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.

[0065]

[0066] Adsorption process

[0067] A solvent is added to the previously obtained zobis(2-hydroxyethyl)terephthalate to obtain a solution.

[0068] The solvent may be one or more selected from the group consisting of, for example, water, alcohols, ketones, amines, toluene, benzene, heptane, xylene, and glycol. Specifically, the solvent may be at least one of water and glycol. More specifically, the solvent may be at least one of water and ethylene glycol.

[0069] In one embodiment, the solvent may be added in an amount of 0.1 to 20 times the weight of the zobis(2-hydroxyethyl)terephthalate. Specifically, the amount of the solvent may be 0.1 to 10 times, 0.5 to 20 times, 1 to 20 times, 1 to 10 times, 0.5 to 10 times, or 0.5 to 5 times the weight of the zobis(2-hydroxyethyl)terephthalate.

[0070] Subsequently, an adsorbent is added to the obtained solution (i.e., the solution containing BHET) to adsorb impurities.

[0071] According to one embodiment of the present invention, the adsorption step is performed two or more times. Or, the adsorption step may be performed three or more times. For example, the adsorption step may be performed 2 to 5 times, 2 to 4 times, 3 to 5 times, 3 to 4 times, or 2 to 3 times.

[0072] Each adsorption step is selected from (a) an adsorption step using an adsorbent with a micropore relative ratio (MPR) of 30% or less; and (b) an adsorption step using an adsorbent with a micropore relative ratio (MPR) of more than 30%.

[0073] The above relative micropore ratio (MPR) is calculated by the following formula based on BET analysis of the adsorbent.

[0074] MPR(%) = (P A / (P B + PC )) x 100

[0075] Here, P A is the sum of the volumes (cc / g) of pore A with a size of less than 2 nm, and P B is the sum of the volumes (cc / g) of pores B with a size of 2 nm to 50 nm, and P C is the sum of the volumes (cc / g) of pores C with a size greater than 50 nm.

[0076] The relative micropore ratio (MPR) of the adsorbent used in step (a) above is 30% or less, and may be, for example, 5% to 30%, 10% to 30%, 15% to 30%, 20% to 30%, or 25% to 30%. In addition, the relative micropore ratio (MPR) of the adsorbent used in step (b) above is greater than 30% and may be, for example, 31% or more, 32% or more, 35% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 100% or more; and may also be 500% or less, 450% or less, 400% or less, 350% or less, or 300% or less. Specifically, it may be greater than 30% and less than or equal to 500%, greater than 30% and less than or equal to 450%, greater than 30% and less than or equal to 400%, greater than 30% and less than or equal to 350%, greater than 30% and less than or equal to 300%, 31% to 500%, 31% to 450%, 31% to 400%, 31% to 350%, or 31% to It may be 300%, 32% to 500%, 32% to 450%, 32% to 400%, 32% to 350%, or 32% to 300%.

[0077] FIG. 1 shows the internal pore structure of an adsorbent according to one embodiment. The pores inside the adsorbent can be divided into three types according to their diameter. For example, a pore (A) with a diameter of less than about 2 nm can be referred to as a micropore, a pore (B) with a diameter of about 2 nm to 50 nm can be referred to as a mesopore, and a pore (C) with a diameter exceeding about 50 nm can be referred to as a macropore. As such, the adsorbent can have pores of various diameters inside, and pores with smaller diameters can be located inside the adsorbent.

[0078] Therefore, a higher value of the above relative micropore ratio (MPR) indicates a larger proportion of micropores (A), and a lower value of the above relative micropore ratio (MPR) indicates a larger proportion of mesopores (B) and macropores (C).

[0079] Carbon-based inorganic adsorbents may be used as the adsorbents used in the above adsorption step. For example, the carbon-based inorganic adsorbents may be activated carbon, carbon black, graphite, clay, etc., and the shape of the adsorbent is not particularly limited.

[0080] In one embodiment, the adsorbent used in the adsorption step comprises at least one selected from the group consisting of activated carbon, carbon black, graphite, and clay, and 50 m 2 / g to 1800 m 2 It can have a specific surface area of ​​ / g. The specific surface area of ​​the adsorbent is, for example, 50 m² 2 / g or more, 100 m 2 / g or more, 300 m 2 / g or more, 500 m 2 / g or more or 800 m 2 It can be more than / g, and also 1800 m 2 / g or less, 1750 m 2 / g or less or 1700 m2 It may be less than / g. Specifically, the specific surface area of ​​the adsorbent is 50 m² 2 / g to 1800 m 2 / g, 100 m 2 / g to 1800 m 2 / g, 300 m 2 / g to 1800 m 2 / g, 500 m 2 / g to 1800 m 2 / g, 800 m 2 / g to 1800 m 2 / g, 50 m 2 / g to 1750 m 2 / g, 100 m 2 / g to 1750 m 2 / g, 300 m 2 / g to 1750 m 2 / g, 500 m 2 / g to 1750 m 2 / g, 800 m 2 / g to 1750 m 2 / g, 50 m 2 / g to 1700 m 2 / g, 100 m 2 / g to 1700 m 2 / g, 300 m 2 / g to 1700 m 2 / g, 500 m 2 / g to 1700 m 2 / g, or 800 m 2 / g to 1700 m 2 / g. When such an adsorbent is introduced into a solution containing bis(2-hydroxyethyl)terephthalate, the chromophores of the impurities can be adsorbed into the pores of the adsorbent and removed.

[0081] In the present invention, each adsorption step can be performed using a batch-type adsorption reactor or a continuous-type adsorption reactor. For example, if the adsorption step is performed twice, a batch-type adsorption reactor and a batch-type adsorption reactor may be used in succession, a continuous-type adsorption reactor and a continuous-type adsorption reactor may be used in succession, or a batch-type adsorption reactor and a continuous-type adsorption reactor may be used in succession.

[0082] In the present invention, the temperature at which each adsorption step is performed may be, for example, 50°C or higher, 60°C or higher, 70°C or higher, and may also be 120°C or lower, 110°C or lower, or 100°C or lower. In addition, the time at which each adsorption step is performed may be, for example, 10 minutes or more, 20 minutes or more, or 30 minutes or more, and may also be 5 hours or less, 3 hours or less, or 1 hour or less.

[0083] In one embodiment, each of the adsorption steps may be performed at a temperature of 50°C to 120°C for 10 minutes to 5 hours. Within the preferred range, the adsorption efficiency can be increased by more effectively removing residual chromophores in the solution.

[0084] In addition, the weight of the adsorbent used in each of the above adsorption steps may be, for example, 0.1 parts by weight or more, 0.5 parts by weight or more, or 1 part by weight or more relative to 100 parts by weight of the above-mentioned zobis(2-hydroxyethyl)terephthalate, and may also be 10 parts by weight or less, 5 parts by weight or less, or 3 parts by weight or less.

[0085] In addition, the weight of the adsorbent used in each of the above adsorption steps may all be the same, or the weight of the adsorbent used in one adsorption step may be 1 to 2 times the weight of the adsorbent used in another adsorption step.

[0086] In one embodiment, the weight of the adsorbent used in each of the adsorption steps may be 0.1 to 5 parts by weight relative to 100 parts by weight of the zobis(2-hydroxyethyl)terephthalate. Within the preferred range, the adsorption efficiency can be increased by more effectively removing the chromophore remaining in the solution.

[0087] In one embodiment, the adsorption step may include the repeated performance of the adsorption step (a) or (b). Specifically, the adsorption step may perform the adsorption step (a) in succession or the adsorption step (b) in succession.

[0088] In another embodiment, the adsorption step may include the adsorption steps (a) and (b). Specifically, the adsorption step may include the adsorption step (a) and the adsorption step (b) sequentially. Alternatively, the adsorption step may include the adsorption step (b) and the adsorption step (a) sequentially.

[0089] In another embodiment, the adsorption step may include alternating performance of the adsorption steps (a) and (b), specifically including the adsorption step (a), the adsorption step (b), and the adsorption step (a) sequentially, or including the adsorption step (b), the adsorption step (a), and the adsorption step (b) sequentially.

[0090] In another embodiment, the adsorption step comprises the adsorption steps (a) and (b), wherein each adsorption step (a) and / or (b) may be repeated two or more times. For example, the adsorption step (a) may be repeated two or more times after the adsorption step (b), or the adsorption step (b) may be repeated two or more times after the adsorption step (a). Alternatively, the adsorption step (b) may be performed after the adsorption step (a) is repeated two or more times, and the adsorption step (a) may be performed after the adsorption step (b) is repeated two or more times.

[0091] When the adsorption step (b) is repeated multiple times in the above adsorption step, the relative micropore ratio (MPR) used in each step may differ. For example, the above adsorption step (b) may include an adsorption step (b1) using an adsorbent with an MPR greater than 30% and less than 40%, and an adsorption step (b2) using an adsorbent with an MPR of 40% or more. Specifically, when the above adsorption step (b) is repeated multiple times in the above adsorption step, the adsorption step (b1) and the adsorption step (b2) may be included sequentially, or the adsorption step (b2) and the adsorption step (b1) may be included sequentially. Alternatively, the adsorption step (b1), the adsorption step (b2), and the adsorption step (b1) may be included sequentially, or the adsorption step (b2), the adsorption step (b1), and the adsorption step (b2) may be included sequentially.

[0092] Figure 2 shows UV-Vis spectra obtained from various BHET-containing recycled raw material compositions. As shown in Figure 2, after depolymerizing colored waste polyester, various types of chromophores remain in the unrefined BHET-containing composition (crude BHET).

[0093] Therefore, it is effective to use an adsorbent having pores corresponding to the size of each chromophore. Meanwhile, competition for adsorption occurs depending on the difference in chromophore concentration, and chromophores with a relatively higher concentration reach the adsorbent first. Thus, when adding an adsorbent to a solution containing chromophores of various particle sizes, the type of adsorbent to be added can be determined based on the relative concentration of the chromophores. If the concentration of large-particle chromophores among the impurities is relatively high, adding an adsorbent with small pores may reduce adsorption efficiency because the pore openings of the adsorbent may be blocked by the large-particle chromophores. Conversely, if the concentration of small-particle chromophores among the impurities is relatively high, an adsorbent with large pores may be disadvantageous for rapidly adsorbing small-particle chromophores due to its small surface area. Therefore, the type and order of adsorbent addition can be controlled according to the proportion of chromophores contained in the solution.

[0094] As in the present invention, when the adsorbent is divided and added in two or more stages, chromophores can be removed to a level that is difficult to achieve with single adsorption, and the total amount of adsorbent used can be reduced by maximizing adsorption efficiency, making it economical. In particular, when adding two or more types of adsorbents in divided stages, it is advisable to adjust the order of the adsorbents according to the relative ratio of chromophores contained in the solution. For example, when adsorbing impurities mixed with dyes of various particle sizes (i.e., impurities mixed with large and small dyes), effective adsorption can be achieved by using two types of adsorbents with different relative micropore ratios (MPR) (i.e., an adsorbent with a high MPR and an adsorbent with a low MPR). First, if the concentration of large dyes among the impurities is relatively high, the large dyes can be effectively adsorbed by performing a primary adsorption using an adsorbent with a low MPR. Consequently, after the primary adsorption, the concentration of small dyes becomes relatively high, and then the small dyes can be effectively adsorbed by performing a secondary adsorption using an adsorbent with a high MPR. After the second adsorption, the concentration of large-sized dyes becomes relatively high again, and accordingly, a third adsorption can be performed using an adsorbent with a small MPR to effectively adsorb the remaining large-sized dyes.

[0095] The chromophore remaining in this step may be, for example, an organic dye and / or an inorganic pigment. Specifically, the decomposing chromophore may include at least one selected from the group consisting of quinone dyes, azo dyes, and inorganic pigments. More specifically, the chromophore may be reactive blue 4, acid blue 3, methylene blue, red 19, yellow 18, beta-naphthol, etc.

[0096] In one embodiment, the adsorption step (a) removes a chromophore that peaks in the wavelength band of 200 nm to 500 nm of the UV-Vis spectrum, and the adsorption step (b) removes a chromophore that peaks in the wavelength band of 500 nm to 800 nm of the UV-Vis spectrum.

[0097] The chromophore removed in the above adsorption step (a), that is, the chromophore exhibiting a peak in the wavelength range of 200 nm to 500 nm, may be, for example, Red 19, Yellow 18, beta-naphthol, etc.

[0098] The chromophore removed in the above adsorption step (b), that is, the chromophore exhibiting a peak in the wavelength range of 500 nm to 800 nm, may be, for example, reactive blue 4, acid blue 3, methylene blue, etc.

[0099] After the above adsorption step, a step of removing the adsorbent using a filtration device may be additionally included.

[0100]

[0101] Crystallization and washing

[0102] In one embodiment, the method for preparing a recycled raw material composition of the present invention further includes a step of crystallizing the solution that has undergone the adsorption of impurities, thereby enabling uniform crystallinity.

[0103] The device for the crystallization described above is not particularly limited, but can be performed using an evaporation-type crystallizer or a jacket-type crystallizer. As the crystallization is performed through the crystallizer, the removal of low-molecular-weight compounds, which are impurities, is efficiently achieved, thereby obtaining a recycled raw material composition having uniform crystallinity.

[0104] The above-described evaporative crystallizer (vacuum depressurization crystallizer) enables the crystallization of solids contained in a product by evaporating the solvent contained in the product through a reduced pressure under a vacuum state, and can have a generally known structure. When crystallizing a product using the above-described evaporative crystallizer, localized or non-uniform crystallization can be prevented by ensuring a uniform temperature change throughout the product (crystallization occurs while maintaining a uniform temperature throughout). The effectiveness of such an evaporative crystallizer can be enhanced by optimally controlling the temperature and pressure or by proceeding with the process in stages.

[0105] The jacket-type crystallizer described above directly cools the product using a cooling medium to cause crystallization of solids contained in the product, and may have a structure that is generally known. The stirring speed of such a jacket-type crystallizer may be 10 rpm to 300 rpm, 30 rpm to 250 rpm, 50 rpm to 230 rpm, 70 rpm to 200 rpm, 80 rpm to 150 rpm, or 90 rpm to 120 rpm. As the stirring speed is within the above range, uniform crystallization of the product is achieved, and the removal of low molecular weight compounds can be efficiently achieved. Meanwhile, the cooling medium is not particularly limited as long as it is a commonly known medium, and specifically, water, an organic solvent (e.g., ethylene glycol), or a mixture thereof may be used.

[0106] According to the present invention, the crystallization of the product can be performed at a cooling rate of 0.1 ℃ / min to 2.0 ℃ / min, taking into account the crystallinity of the product. Specifically, the cooling rate may be 0.1 ℃ / min to 1.5 ℃ / min, 0.1 ℃ / min to 1.0 ℃ / min, or 0.1 ℃ / min to 0.7 ℃ / min.

[0107] Crystallization of the above product can be performed by lowering the temperature of the product to 40°C or lower, for example, to room temperature, at the above cooling rate. In one embodiment, after the adsorption step, a step of precipitating crystals of bis(2-hydroxyethyl)terephthalate in a solvent by cooling to 20°C to 40°C may be included.

[0108] In one embodiment, the method according to the present invention may further include a washing step after the adsorption step. More specifically, the method according to the present invention may further include a washing step after the preceding adsorption and crystallization steps. The washing may be performed using a solvent, for example, water. The amount of solvent used for the washing may be 0.1 to 2 times the weight of bis(2-hydroxyethyl)terephthalate, or 0.2 to 1.5 times.

[0109]

[0110] Recycled raw material composition

[0111] The present invention provides a recycled raw material composition manufactured by the method described above.

[0112] The above recycled raw material composition includes bis(2-hydroxyethyl)terephthalate (BHET) obtained by depolymerization of waste polyester.

[0113] Meanwhile, the above-mentioned recycled raw material composition may contain reagents or solvents used in various chemical steps during the depolymerization of waste polyester, or by-products generated by side reactions with them. Specifically, the recycled raw material composition may contain trace amounts of organic and inorganic impurities in addition to the main component, BHET.

[0114] The recycled raw material composition according to the present invention contains bis(2-hydroxyethyl)terephthalate obtained by the depolymerization of waste polyester, while having excellent color and quality. Therefore, the recycled raw material composition can be used as a polymerization raw material for the manufacture of polyester resin. As such, the recycled raw material composition of the present invention may also be referred to as a polymerization raw material composition or a recycled BHET composition.

[0115] In one embodiment, the recycled raw material composition may be dissolved in ethylene glycol at a concentration of 50% by weight, and the yellowness (YID) measured after heat treatment in a 170°C oven for 1 hour may be 20 or less. For example, the yellowness after heat treatment in a 170°C oven for 1 hour may be 20 or less, 15 or less, 10 or less, or 5 or less. Specifically, the yellowness may be 0 to 20, 0 to 15, 0 to 10, or 0 to 5.

[0116] The above yellowness may be measured as Illuminant D65 using a colorimeter at an observer's angle of 2° for a solution obtained by dissolving a recycled raw material composition and ethylene glycol in a weight ratio of 1:1 in an oven at 170°C and heat-treating it for 1 hour.

[0117] The content of BHET in the above-mentioned recycled raw material composition can be measured using liquid chromatography or the like. Specifically, the content of BHET in the above-mentioned recycled raw material composition can be derived by measuring the fraction (%) of the BHET peak area among the total peak areas in a spectrum obtained using high-performance liquid chromatography (HPLC).

[0118] In one embodiment, the content of BHET in the recycled raw material composition is 95 weight% or more. For example, the content of BHET in the recycled raw material composition may be 97 weight% or more, 98 weight% or more, 99 weight% or more, or 99.5 weight% or more, and specifically may be 95 weight% to 100 weight%, or 97 weight% to 100 weight%.

[0119] The recycled raw material composition according to one embodiment may have a peak area ratio of bis(2-hydroxyethyl)terephthalate of 97% or more when analyzed by high-performance liquid chromatography (HPLC), and more specifically, 98% or more, 99% or more, or 99.5% or more.

[0120] Meanwhile, the above-mentioned recycled raw material composition may include compounds other than BHET, specifically BHET analogs, BHET oligomers (e.g., dimers, trimers), esters (e.g., DEG esters), etc.

[0121] In addition, when the above-described recycled raw material composition is analyzed by high-performance liquid chromatography (HPLC), the peak area ratio of monohydroxyethyl terephthalate (MHET) may be 5% or less, 3% or less, 2% or less, 1.5% or less, 1% or less, or 0.5% or less, and may also be 0% or more, or 0.001% or more. As a specific example, when the above-described recycled raw material composition is analyzed by high-performance liquid chromatography (HPLC), the peak area ratio of monohydroxyethyl terephthalate (MHET) may be 2% or less, and specifically, may be 0.001% to 2%.

[0122] In addition, when the above-mentioned recycled raw material composition is analyzed by high-performance liquid chromatography (HPLC), the peak area ratio of BHET oligomers of dimer or higher may be 5% or less, 3% or less, 2% or less, 1.5% or less, 1% or less, or 0.5% or less, and may be 0% or more, or 0.001% or more, and specifically may be 0.001% to 1%.

[0123] In addition, when the above-described recycled raw material composition is analyzed by high-performance liquid chromatography (HPLC), the peak area ratio of diethylene glycol (DEG) ester may be 2% or less, 1.5% or less, 1% or less, 0.7% or less, 0.6% or less, or 0.5% or less, and may also be 0% or more, or 0.001% or more. As a specific example, when the above-described recycled raw material composition is analyzed by high-performance liquid chromatography (HPLC), the peak area ratio of diethylene glycol (DEG) ester may be 0.5% or less in total, and specifically, may be 0.001% to 0.5%. The above-described diethylene glycol ester compound may include 2-hydroxyethyl [2-(2-hydroxyethoxy)ethyl]terephthalate and bis [2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate.

[0124] In one embodiment, the recycled raw material composition has a metal content of less than 20 ppm. For example, the metal content may be less than 20 ppm, less than 15 ppm, less than 10 ppm, or less than 5 ppm. Specifically, the metal content may be 0 ppm or more to less than 20 ppm, 0 ppm or more to less than 15 ppm, 0 ppm or more to less than 10 ppm, or 0 ppm or more to less than 5 ppm.

[0125] Preferred embodiments are presented below to aid in understanding the present invention. However, the following embodiments are provided merely to facilitate a better understanding of the invention and do not limit the scope of the invention.

[0126]

[0127] Example 1

[0128] 1000 g of waste polyester fiber, 4000 g of ethylene glycol, and 0.42 g of zinc acetate dihydrate were all fed together into a stainless steel (SUS) reactor, and the internal temperature of the reactor was raised to 195°C and depolymerization was carried out for 4 hours.

[0129] Insoluble solid impurities remaining in the obtained reaction product were removed through a mesh filter, and the mixture from which the insoluble components had been removed was transferred to a 10L distillation apparatus and vacuum distillation was performed at 130°C to recover unreacted ethylene glycol. The reaction product from which the ethylene glycol had been removed was thin-film distilled in a thin-film distiller (VTA’s VKL70-4S) at 220°C and 0.08 Torr to obtain crude BHET from which oligomers of dimer or higher were removed.

[0130] Subsequently, the above BHET and distilled water (weight ratio 1:3) were introduced into a 20 L adsorption tank and dissolved at a temperature of 70°C. Then, 1 part by weight of activated carbon (AC1) was added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes. The filtrate was reintroduced into a 20 L adsorption tank and dissolved again at a temperature of 70°C. Then, 1 part by weight of activated carbon (AC4) was added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes. The filtrate was reintroduced into a 20 L adsorption tank and dissolved again at a temperature of 70°C. Then, 1 part by weight of activated carbon (AC1) was added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes.

[0131] After transferring the filtered solution to an evaporation-type crystallizer, crystallization was carried out by cooling it to room temperature while adjusting the evaporation conditions (pressure conditions) to maintain a uniform temperature throughout. The crystals and mother liquor obtained at the end were separated by pressure filtration to obtain 1025 g of a recycled raw material composition from which chromophores and impurities were well removed.

[0132]

[0133] Example 2

[0134] 100 g of waste polyester fiber, 400 g of ethylene glycol, and 0.042 g of zinc acetate dihydrate were all fed together into a stainless steel (SUS) reactor, and the internal temperature of the reactor was raised to 195°C and depolymerization was carried out for 4 hours.

[0135] Insoluble solid impurities remaining in the obtained reaction product were removed through a mesh filter, and the mixture from which the insoluble components were removed was transferred to a 10L distillation apparatus and vacuum distillation was performed at 130°C to recover unreacted ethylene glycol. The reaction product from which the ethylene glycol had been removed was thin-film distilled in a thin-film distiller (VTA VKL70-4S) at 220°C and 0.08 Torr to obtain crude BHET from which oligomers of dimer or higher were removed.

[0136] Subsequently, before being introduced into the continuous adsorption reactor, crude BHET and distilled water (weight ratio 1:3) were introduced and preheated at 100°C. Then, the crude BHET and distilled water were introduced at a temperature of 90°C using a liquid pump into a reactor (parr 54, tubular reactor, 10 mm inner diameter and 400 mm length) in which the upper part was fixed with glass beads and the middle part was fixed with activated carbon (AC1) (1 part by weight per 100 parts by weight of BHET) and glass beads. Using a valve at the bottom of the reactor, the solution after reaction was introduced using a liquid pump into a second reactor fixed with activated carbon (AC4) (1 part by weight per 100 parts by weight of BHET). The solution obtained at the bottom was introduced into a third reactor fixed with activated carbon (AC1) (1 part by weight per 100 parts by weight of BHET) to be adsorbed, and the solution after adsorption was obtained from the bottom of the reactor.

[0137] After transferring the filtered solution to an evaporation-type crystallizer, crystallization was carried out by cooling it to room temperature while adjusting the evaporation conditions (pressure conditions) to maintain a uniform temperature throughout. The crystals and mother liquor obtained at the end were separated by pressure filtration to obtain 100 g of a recycled raw material composition from which chromophores and impurities were well removed.

[0138]

[0139] Example 3

[0140] 1000 g of waste polyester film, 4000 g of ethylene glycol, and 0.42 g of zinc acetate dihydrate were all fed together into a stainless steel (SUS) reactor, and the internal temperature of the reactor was raised to 195°C and depolymerization was carried out for 4 hours.

[0141] Insoluble solid impurities remaining in the obtained reaction product were removed through a mesh filter, and the mixture from which the insoluble components were removed was transferred to a 10L distillation apparatus and vacuum distillation was performed at 130°C to recover unreacted ethylene glycol. The reaction product from which the ethylene glycol had been removed was thin-film distilled in a thin-film distiller (VTA VKL70-4S) at 220°C and 0.08 Torr to obtain crude BHET from which oligomers of dimer or higher were removed.

[0142] Subsequently, the above BHET and distilled water (weight ratio 1:3) were introduced into a 20 L adsorption tank and dissolved at a temperature of 85°C. Then, 1 part by weight of activated carbon (AC1) was added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes. The filtrate was reintroduced into a 20 L adsorption tank and dissolved again at a temperature of 85°C. Then, 1 part by weight of activated carbon (AC4) was added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes. The filtrate was reintroduced into a 20 L adsorption tank and dissolved again at a temperature of 85°C. Then, 1 part by weight of activated carbon (AC1) was added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes.

[0143] After transferring the filtered solution to an evaporation-type crystallizer, crystallization was carried out by cooling it to room temperature while adjusting the evaporation conditions (pressure conditions) to maintain a uniform temperature throughout. The crystals and mother liquor obtained at the end were separated by pressure filtration to obtain 1025 g of a recycled raw material composition from which chromophores and impurities were well removed.

[0144]

[0145] Example 4

[0146] 1000 g of waste polyester fiber, 4000 g of ethylene glycol, and 0.42 g of zinc acetate dihydrate were all fed together into a stainless steel (SUS) reactor, and the internal temperature of the reactor was raised to 195°C and depolymerization was carried out for 4 hours.

[0147] Insoluble solid impurities remaining in the obtained reaction product were removed through a mesh filter, and the mixture from which the insoluble components were removed was transferred to a 10L distillation apparatus and vacuum distillation was performed at 130°C to recover unreacted ethylene glycol. The reaction product from which the ethylene glycol had been removed was thin-film distilled in a thin-film distiller (VTA VKL70-4S) at 220°C and 0.08 Torr to obtain crude BHET from which oligomers of dimer or higher were removed.

[0148] Subsequently, the above BHET and distilled water (weight ratio 1:3) were introduced into a 20 L adsorption tank and dissolved at a temperature of 65°C. Then, 1 part by weight of activated carbon (AC1) was added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes. The filtrate was reintroduced into a 20 L adsorption tank and dissolved again at a temperature of 65°C. Then, 1 part by weight of activated carbon (AC2) was added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes. The filtrate was reintroduced into a 20 L adsorption tank and dissolved again at a temperature of 65°C. Then, 1 part by weight of activated carbon (AC1) was added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes.

[0149] After transferring the filtered solution to an evaporation-type crystallizer, crystallization was carried out by cooling it to room temperature while adjusting the evaporation conditions (pressure conditions) to maintain a uniform temperature throughout. The crystals and mother liquor obtained at the end were separated by pressure filtration to obtain 1025 g of a recycled raw material composition from which chromophores and impurities were well removed.

[0150]

[0151] Example 5

[0152] 1000 g of waste polyester fiber, 4000 g of ethylene glycol, and 0.42 g of zinc acetate dihydrate were all fed together into a stainless steel (SUS) reactor, and the internal temperature of the reactor was raised to 195°C and depolymerization was carried out for 4 hours.

[0153] Insoluble solid impurities remaining in the obtained reaction product were removed through a mesh filter, and the mixture from which the insoluble components were removed was transferred to a 10L distillation apparatus and vacuum distillation was performed at 130°C to recover unreacted ethylene glycol. The reaction product from which the ethylene glycol had been removed was thin-film distilled in a thin-film distiller (VTA VKL70-4S) at 220°C and 0.08 Torr to obtain crude BHET from which oligomers of dimer or higher were removed.

[0154] Subsequently, the above BHET and distilled water (weight ratio 1:3) were introduced into a 20 L adsorption tank and dissolved at a temperature of 90°C. Then, 1 part by weight of activated carbon (AC3) was added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes. The filtrate was reintroduced into a 20 L adsorption tank and dissolved again at a temperature of 90°C. Then, 1 part by weight of activated carbon (AC4) was added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes. The filtrate was reintroduced into a 20 L adsorption tank and dissolved again at a temperature of 90°C. Then, 1 part by weight of activated carbon (AC1) was added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes.

[0155] After transferring the filtered solution to an evaporation-type crystallizer, crystallization was carried out by cooling it to room temperature while adjusting the evaporation conditions (pressure conditions) to maintain a uniform temperature throughout. The crystals and mother liquor obtained at the end were separated by pressure filtration to obtain 1025 g of a recycled raw material composition from which chromophores and impurities were well removed.

[0156]

[0157] Example 6

[0158] 1000 g of waste polyester fiber, 4000 g of ethylene glycol, and 0.42 g of zinc acetate dihydrate were all fed together into a stainless steel (SUS) reactor, and the internal temperature of the reactor was raised to 195°C and depolymerization was carried out for 4 hours.

[0159] Insoluble solid impurities remaining in the obtained reaction product were removed through a mesh filter, and the mixture from which the insoluble components were removed was transferred to a 10L distillation apparatus and vacuum distillation was performed at 130°C to recover unreacted ethylene glycol. The reaction product from which the ethylene glycol had been removed was thin-film distilled in a thin-film distiller (VTA VKL70-4S) at 220°C and 0.08 Torr to obtain crude BHET from which oligomers of dimer or higher were removed.

[0160] Subsequently, the above BHET and distilled water (weight ratio 1:3) were added to a 20 L adsorption tank and dissolved at a temperature of 70°C, after which 1.5 parts by weight of activated carbon (AC1) were added per 100 parts by weight of BHET and stirred and filtered for 30 minutes. The filtrate was reintroduced into a 20 L adsorption tank and dissolved again at a temperature of 70°C, after which 1.5 parts by weight of activated carbon (AC4) were added per 100 parts by weight of BHET and stirred and filtered for 30 minutes.

[0161] After transferring the filtered solution to an evaporation-type crystallizer, crystallization was carried out by cooling it to room temperature while adjusting the evaporation conditions (pressure conditions) to maintain a uniform temperature throughout. The crystals and mother liquor obtained at the end were separated by pressure filtration to obtain 1025 g of a recycled raw material composition from which chromophores and impurities were well removed.

[0162]

[0163] Example 7

[0164] 1000 g of waste polyester fiber, 4000 g of ethylene glycol, and 0.42 g of zinc acetate dihydrate were all fed together into a stainless steel (SUS) reactor, and the internal temperature of the reactor was raised to 195°C and depolymerization was carried out for 4 hours.

[0165] Insoluble solid impurities remaining in the obtained reaction product were removed through a mesh filter, and the mixture from which the insoluble components were removed was transferred to a 10L distillation apparatus and vacuum distillation was performed at 130°C to recover unreacted ethylene glycol. The reaction product from which the ethylene glycol had been removed was thin-film distilled in a thin-film distiller (VTA VKL70-4S) at 220°C and 0.08 Torr to obtain crude BHET from which oligomers of dimer or higher were removed.

[0166] Subsequently, the above BHET and distilled water (weight ratio 1:3) were added to a 20 L adsorption tank and dissolved at a temperature of 65°C, then 2 parts by weight of activated carbon (AC1) were added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes. The filtrate was reintroduced into a 20 L adsorption tank and dissolved again at a temperature of 65°C, then 1 part by weight of activated carbon (AC4) was added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes.

[0167] After transferring the filtered solution to an evaporation-type crystallizer, crystallization was carried out by cooling it to room temperature while adjusting the evaporation conditions (pressure conditions) to maintain a uniform temperature throughout. The crystals and mother liquor obtained at the end were separated by pressure filtration to obtain 1025 g of a recycled raw material composition from which chromophores and impurities were well removed.

[0168]

[0169] Comparative Example 1

[0170] 1000 g of waste polyester fiber, 4000 g of ethylene glycol, and 0.42 g of zinc acetate dihydrate were all fed together into a stainless steel (SUS) reactor, and the internal temperature of the reactor was raised to 195°C and depolymerization was carried out for 4 hours.

[0171] Insoluble solid impurities remaining in the obtained reaction product were removed through a mesh filter, and the mixture from which the insoluble components were removed was transferred to a 10L distillation apparatus and vacuum distillation was performed at 130°C to recover unreacted ethylene glycol. The reaction product from which the ethylene glycol had been removed was thin-film distilled in a thin-film distiller (VTA VKL70-4S) at 220°C and 0.08 Torr to obtain crude BHET from which oligomers of dimer or higher were removed.

[0172] Afterwards, the above BHET and distilled water (weight ratio 1:3) were added to a 20 L adsorption tank and dissolved at a temperature of 80°C, then 3 parts by weight of activated carbon (AC1) were added per 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes.

[0173] After transferring the filtered solution to an evaporation-type crystallizer, crystallization was carried out by cooling it to room temperature while adjusting the evaporation conditions (pressure conditions) to maintain a uniform temperature throughout. The crystals and mother liquor obtained at the end were separated by pressure filtration to obtain 1025 g of a recycled raw material composition from which chromophores and impurities were well removed.

[0174]

[0175] Comparative Example 2

[0176] 1000 g of waste polyester fiber, 4000 g of ethylene glycol, and 0.42 g of zinc acetate dihydrate were all fed together into a stainless steel (SUS) reactor, and the internal temperature of the reactor was raised to 195°C and depolymerization was carried out for 4 hours.

[0177] Insoluble solid impurities remaining in the obtained reaction product were removed through a mesh filter, and the mixture from which the insoluble components were removed was transferred to a 10L distillation apparatus and vacuum distillation was performed at 130°C to recover unreacted ethylene glycol. The reaction product from which the ethylene glycol had been removed was thin-film distilled in a thin-film distiller (VTA VKL70-4S) at 220°C and 0.08 Torr to obtain crude BHET from which oligomers of dimer or higher were removed.

[0178] Afterwards, the above BHET and distilled water (weight ratio 1:3) were added to a 20 L adsorption tank and dissolved at a temperature of 90°C, then 1.5 parts by weight of activated carbon (AC1) and 1.5 parts by weight of activated carbon (AC4) were added simultaneously relative to 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes.

[0179] After transferring the filtered solution to an evaporation-type crystallizer, crystallization was carried out by cooling it to room temperature while adjusting the evaporation conditions (pressure conditions) to maintain a uniform temperature throughout. The crystals and mother liquor obtained at the end were separated by pressure filtration to obtain 1025 g of a recycled raw material composition from which chromophores and impurities were well removed.

[0180]

[0181] Comparative Example 3

[0182] 1000 g of waste polyester fiber, 4000 g of ethylene glycol, and 0.42 g of zinc acetate dihydrate were all fed together into a stainless steel (SUS) reactor, and the internal temperature of the reactor was raised to 195°C and depolymerization was carried out for 4 hours.

[0183] Insoluble solid impurities remaining in the obtained reaction product were removed through a mesh filter, and the mixture from which the insoluble components were removed was transferred to a 10L distillation apparatus and vacuum distillation was performed at 130°C to recover unreacted ethylene glycol. The reaction product from which the ethylene glycol had been removed was thin-film distilled in a thin-film distiller (VTA VKL70-4S) at 220°C and 0.08 Torr to obtain crude BHET from which oligomers of dimer or higher were removed.

[0184] Afterwards, the above BHET and distilled water (weight ratio 1:3) were added to a 20 L adsorption tank and dissolved at a temperature of 80°C, then 2 parts by weight of activated carbon (AC1) and 1 part by weight of activated carbon (AC4) were added simultaneously relative to 100 parts by weight of BHET, and the mixture was stirred and filtered for 30 minutes.

[0185] After transferring the filtered solution to an evaporation-type crystallizer, crystallization was carried out by cooling it to room temperature while adjusting the evaporation conditions (pressure conditions) to maintain a uniform temperature throughout. The crystals and mother liquor obtained at the end were separated by pressure filtration to obtain 1025 g of a recycled raw material composition from which chromophores and impurities were well removed.

[0186]

[0187] Test example

[0188] The compositions obtained in the above examples and comparative examples were tested as follows.

[0189]

[0190] (1) HPLC

[0191] Approximately 0.01 g of the recycled raw material composition was diluted in approximately 20 mL of methanol and analyzed by high-performance liquid chromatography (HPLC) (Model: Waters e2695, Column: C18 (4.6 x 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 out of the total peak area of ​​the HPLC was obtained.

[0192] - MHET: Monohydroxyethyl terephthalate

[0193] - BHET: Bis(2-hydroxyethyl)terephthalate

[0194] - BHEI: Bis(2-hydroxyethyl)isophthalate

[0195] - DEG-ester-1: 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate

[0196] - DEG-ester-2: Bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate

[0197] - Me-ester-1 : 2-hydroxyethyl methyl terephthalate

[0198] - HA-ester: 2-hydroxyethyl(2-acetoxyethyl)terephthalate

[0199] - Dimer: BHET dimer

[0200] - Trimer: BHET trimer

[0201] The results are shown in Table 1 below.

[0202] MHETBHETDEG-ester1DEG-ester2HA-esterMe-ESTERDEG-dimer1DimerDEG-dimer2TrimerUnknown Example 11.0598.50.180.010.020.0200.14000.08 Example 20.9698.210.240.040.060.0300.240.010.040.17 Example 31.6295.51.460.040.030.050.010.620.050.190.43 Example 42.0497.520.110.010.010.0300.1200.010.15 Example 52.1297.210.20.010.010.0300.1800.050.19 Example 60.8998.330.240.040.010.0600.180.010.030.21 Example 72.0997.230.270.030.020.0200.150.0100.18 Comparative Example 11.5597.060.610.110.030.0400.130.0100.46 Comparative Example 21.1298.010.30.060.040.0200.190.010.050.2 Comparative Example 32.197.180.250.020.02000.130.010.010.28

[0203]

[0204] (2) YID (Accelerated YID measurement)

[0205] 20 g of ethylene glycol and 20 g of a recycled raw material composition were mixed, melted in an oven at 170°C, and heat-treated for 1 hour. Transmission data was obtained for the obtained solution using Illuminant D65 with Hunterlab's Color Flex EZ at an observer angle of 2°, and the Yellowness Identification (YID) value was calculated using a color analysis device within the software. The results are shown in Table 2 below.

[0206] LabYID Activated Carbon Example 1 59.21-0.9 1.8 24.31 Adsorption: AC1 - AC4 - AC1 (Batch, Waste Fiber) Example 2 58.64-0.9 7 2.2 75.63 Adsorption: AC1 - AC4 - AC1 (Continuous, Waste Fiber) Example 3 58.93-1.2 83.2 28.11 Adsorption: AC1 - AC4 - AC1 (Batch, Waste Film) Example 4 58.68-0.8 7 2.2 35.65 Adsorption: AC1 - AC2 - AC1 (Batch, Waste Fiber) Example 5 54.31-1.2 13.2 8.84 Adsorption: AC3 - AC4 - AC1 (Batch, Waste Fiber) Example 6 53.92-1.2 33.65 10.39 Adsorption: AC1 - AC4 (Batch type, waste fiber) Example 7 5 8.57-1.39 3.58.9 Adsorption: AC1 - AC4 (2:1) (Batch type, waste fiber) Comparative Example 1 5 2.23 3.77 10.6 5 41.52 Adsorption: AC1 added at once (Batch type, waste fiber) Comparative Example 2 5 0.53-0.061 3.06 46 Adsorption: AC1-AC4 added at once (Batch type, waste fiber) Comparative Example 3 5 4.28-2.16 10.8 13 2.68 Adsorption: AC1-AC4-AC1 added simultaneously

[0207]

[0208] As shown in Table 2 above, the recycled raw material compositions obtained in Examples 1 to 7 had a low yellowness (YID) and excellent color.

[0209]

[0210] (3) UV

[0211] 0.5 g of the recycled raw material composition was diluted in 9.5 g of DMSO and analyzed using a UV spectrophotometer (Shimadzu Model UV-1800). The results are shown in Figure 2.

[0212] As shown in Figure 2, the UV-Vis spectrum of the recycled raw material composition of Example 1 can be seen to have several chromophores removed from the UV-Vis spectrum of crude BHET.

[0213]

[0214] (4) ICP-AES

[0215] 0.3 g of the recycled raw material composition was treated with ultrasound and diluted with ultrapure water, and then the mineral content (ppm) was measured using ICP-AES (Agilent Model 5100) (detection limit 5 ppm). The results are shown in Table 3 below.

[0216] (ppm) ZnMgFeSbPBaTi Total Example 10.36 -0.25 1.9 0.24 --2.14 Example 20.37 -0.11 20.24 --2.24 Example 30.9 7 0.5 0.2 10.6 9 0.7 10.39 -1.79 Example 40.3 4 0.6 3 0.4 8 0.1 29.8 0.34 -10.26 Example 50.7 9 0.1 20.1 0.23 ---0.23 Example 61 -0.26 1.6 ---1.6 Example 7 1.7 -0.6 20.5 2 ---2.84 Comparative Example 10.29 --0.28 3.5 -0.13 4.2 Comparative Example 20.36-10.34 1.2--2.9 Comparative Example 30.52-0.79 1.3---2.61

[0217]

[0218] (5) BET

[0219] The ratio of micropore and mesopore volumes was measured for the adsorbent using a BET surface area / pore size analyzer (Autosorb IQ from Quantachrome). The results are shown in Table 4 below.

[0220] Activated Carbon P A (cc / g)P B (cc / g)P C (cc / g)P B +P C (cc / g)(P A / (P B +P C )) x100 (%) Fraction of pores A (%) Fraction of pores B (%) Fraction of pores C (%) Surface area (m² 2 / g)AC10.1590.5350.0260.56128.3422.08274.2573.661859.3AC20.3550.112540.00980.1224290.174.423.62.1107 5.6AC30.2560.5790.0210.642.6529.90267.6842.4141125.5AC40.3850.930.091.02137.7227.3966.0506.5591664- P A : Sum of the volumes (cc / g) of pores A with a size of less than 2 nm - P B : Sum of the volumes (cc / g) of pores B with a size of 2 nm to 50 nm - P C : Sum of the volumes (cc / g) of pores C larger than 50 nm

Claims

1. A step of obtaining zobis(2-hydroxyethyl)terephthalate by depolymerizing waste polyester; A step of obtaining a solution by adding a solvent to the above-mentioned zobis(2-hydroxyethyl)terephthalate; and The method includes the step of adding an adsorbent to the above solution to adsorb impurities, and The above adsorption step is performed two or more times, and each adsorption step (a) an adsorption step using an adsorbent having a relative micropore ratio (MPR) of 30% or less; and (b) Selected from among adsorption steps using an adsorbent with a relative micropore ratio (MPR) of more than 30%, and A method for preparing a recycled raw material composition, wherein the above-mentioned relative micropore ratio (MPR) is calculated by the following formula based on BET analysis of the above-mentioned adsorbent: MPR (%)= (P A / (P B + P C )) x 100 Here, P A is the sum of the volumes (cc / g) of pores A with a size of less than 2 nm, and P B is the sum of the volumes (cc / g) of pores B with a size of 2 nm to 50 nm, and P C is the sum of the volumes of pores C with a size greater than 50 nm (cc / g).

2. In Paragraph 1, The above waste polyester has a purity of 80% or more, and A method for preparing a recycled raw material composition comprising 5 weight% or less of dyes and pigments.

3. In Paragraph 1, A method for producing a recycled raw material composition, wherein each of the above adsorption steps is performed using a batch adsorption reactor or a continuous adsorption reactor.

4. In Paragraph 1, A method for preparing a recycled raw material composition, wherein each of the above adsorption steps is performed at a temperature of 50°C to 120°C for 10 minutes to 5 hours.

5. In Paragraph 1, The adsorbent used in the above adsorption step is It comprises at least one selected from the group consisting of activated carbon, carbon black, graphite, and clay, and 50 m 2 / g to 1800 m 2 Method for manufacturing a recycled raw material composition having a specific surface area of ​​ / g.

6. In Paragraph 1, The weight of the adsorbent used in each of the above adsorption steps is A method for preparing a recycled raw material composition comprising 0.1 to 5 parts by weight per 100 parts by weight of the above-mentioned zobis(2-hydroxyethyl)terephthalate.

7. In Paragraph 1, The above adsorption step A method for preparing a recycled raw material composition, comprising repeating the adsorption step (a) or (b) above.

8. In Paragraph 1, The above adsorption step A method for preparing a recycled raw material composition comprising the above adsorption steps (a) and (b).

9. In Paragraph 1, After the above adsorption step, A method for preparing a recycled raw material composition, further comprising the step of removing an adsorbent using a filtration device.

10. In Paragraph 1, After the above adsorption step, A method for preparing a recycled raw material composition, comprising the step of cooling to 20℃ to 40℃ to precipitate crystals of bis(2-hydroxyethyl)terephthalate in a solvent.

11. In Paragraph 1, A method for preparing a recycled raw material composition, wherein the solvent is one or more selected from the group consisting of water, alcohols, ketones, amines, toluene, benzene, heptane, xylene, and glycol.

12. In Paragraph 1, A method for preparing a recycled raw material composition, wherein the above solvent is added in an amount of 0.1 to 20 times the weight of the above-mentioned zobis(2-hydroxyethyl)terephthalate.

13. In Paragraph 1, The above adsorption step (a) removes a chromophore that exhibits a peak in the wavelength band of 200 nm to 500 nm of the UV-Vis spectrum, and The above adsorption step (b) is a method for preparing a recycled raw material composition, which removes a chromophore that exhibits a peak in the wavelength band of 500 nm to 800 nm of the UV-Vis spectrum.

14. Manufactured by the method of any one of claims 1 to 13, and A recycled raw material composition containing bis(2-hydroxyethyl)terephthalate, dissolved in ethylene glycol at a concentration of 50 wt%, and having a yellowness (YID) of 20 or less measured after heat treatment in an oven at 170°C for 1 hour.

15. Manufactured by the method of any one of claims 1 to 13, and A recycled raw material composition having a bis(2-hydroxyethyl)terephthalate content of 95 weight% or more and a metal content of less than 20 ppm.

Images