Recycled bhet having low yellow index and manufacturing method of polyester resin

Abstract

This method comprising the steps of reacting waste polyester with a chromophore decomposing agent after depolymerization and separating and removing bis(2-hydroxyethyl)terephthalate can provide regenerated bis(2-hydroxyethyl)terephthalate having a low yellow index from highly contaminated waste polyester.

Description

Method for producing recycled BHET and polyester resins with low yellowness

[0001] The present invention relates to a method for producing recycled BHET having low yellowness and a method for producing a polyester resin using the same.

[0002]

[0003] Polyester boasts excellent mechanical strength, heat resistance, transparency, and gas barrier properties, making it widely used in beverage containers, packaging films, and audio and video films. Polyester is also widely produced worldwide as industrial materials, including medical fibers and tire cords. In particular, polyester sheets and boards, with their excellent transparency and mechanical strength, are widely used in cases, boxes, partitions, shelves, panels, packaging, building materials, and interior and exterior finishes.

[0004] Accordingly, plastic waste, such as polyester, is generated globally annually at a rate that is difficult to manage. Recently, countries around the world are developing regulations and measures for recycling waste plastic resources, including waste polyester. Physical and chemical methods are used to recycle waste polyester, but physical recycling methods are not widely used due to their inability to guarantee purity.

[0005] Meanwhile, chemical recycling methods depolymerize waste polyester by breaking the ester bonds, specifically using reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis. Among these, glycolysis decomposes waste polyester by adding a glycol such as ethylene glycol or diethylene glycol at high temperatures, and the reaction product mainly containing bis(2-hydroxyethyl) terephthalate (BHET) is obtained. Bis(2-hydroxyethyl) terephthalate contained in the reaction product can be used as a raw material for manufacturing unsaturated polyester or ester polyol after crystallization or purification.

[0006] However, bis(2-hydroxyethyl)terephthalate regenerated in this way may contain byproducts generated by reagents or solvents used in various chemical steps during depolymerization from waste polyester, or by side reactions with them, and these impurities may remain in trace amounts even after multiple purifications. In particular, additives used in the initial production of polyester are rich in substances with molecular structures that have strong structural coloring, and these coloring structural substances may also be generated or mixed in after the production of polyester. Bis(2-hydroxyethyl)terephthalate regenerated from contaminated waste polyester in this way has poor color, making it difficult to use it in the production of high-quality polyester resin.

[0007] [Prior Art Literature]

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

[0009]

[0010] If the color of recycled bis(2-hydroxyethyl)terephthalate is poor, it directly affects the color of the polyester resin manufactured using it. However, improving the color of recycled bis(2-hydroxyethyl)terephthalate has not been easy using conventional techniques.

[0011] Accordingly, as a result of research conducted by the inventors of the present invention, the yellowness of recycled bis(2-hydroxyethyl)terephthalate could be significantly reduced through a process of reacting highly polluted waste polyester with a chromophore decomposing agent after depolymerization and separating and removing the chromophore decomposing agent from BHET.

[0012] Therefore, the task of the present invention is to produce a recycled bis(2-hydroxyethyl)terephthalate having a low yellowness from contaminated waste polyester, and to produce a recycled polyester resin having a high whiteness using the same.

[0013]

[0014] According to one aspect of the present invention, a method for producing recycled bis(2-hydroxyethyl)terephthalate is provided, comprising the steps of: (1) obtaining a depolymerized product from waste polyester by glycolysis; (2) reacting the depolymerized product with a chromophore decomposing agent to obtain a decomposed product in which the chromophore is decomposed; (3) adsorbing and removing the chromophore in the decomposed product with an ion exchange resin to obtain a purified product; and (4) crystallizing the purified product.

[0015] According to another aspect of the present invention, there is provided a regenerated bis(2-hydroxyethyl) terephthalate manufactured by the above method and having a yellowness index (YI) of 7 or less measured for a solution dissolved in ethylene glycol at a concentration of 50 wt%.

[0016] According to another aspect of the present invention, a method for producing a polyester resin is provided, comprising the steps of: (1) obtaining a depolymerized product from waste polyester by glycolysis; (2) reacting the depolymerized product with a chromophore decomposing agent to obtain a decomposed product in which the chromophore is decomposed; (3) adsorbing and removing the chromophore in the decomposed product with an ion exchange resin to obtain a purified product; (4) crystallizing the purified product to obtain regenerated bis(2-hydroxyethyl)terephthalate; and (5) polymerizing the polyester resin using the regenerated bis(2-hydroxyethyl)terephthalate.

[0017] According to another aspect of the present invention, a polyester resin manufactured by the above method is provided.

[0018]

[0019] According to the method of the present invention, by reacting waste polyester with a chromophore decomposing agent after depolymerization and separating and removing the resulting decomposed chromophore and byproducts, even if the waste polyester has a high contamination level, the yellowness of bis(2-hydroxyethyl) terephthalate regenerated therefrom can be significantly reduced and the impurity content can be minimized. Therefore, a polyester resin manufactured using the regenerated bis(2-hydroxyethyl) terephthalate obtained according to the above method has high whiteness and excellent quality.

[0020]

[0021] FIG. 1 shows the UV-Vis absorbance spectrum of an aqueous solution of bis(2-hydroxyethyl)terephthalate according to one embodiment of the present invention.

[0022]

[0023] The terms used to refer to each component in this specification are used to distinguish it from other components and are not intended to limit the implementation examples. Furthermore, the singular expressions used in this specification include the plural expressions unless the context clearly dictates otherwise.

[0024] In this specification, the terms "first," "second," etc. are used to describe various components, and the components should not be limited by the terms. The terms are used for the purpose of distinguishing one component from another.

[0025] The word "comprising" or "including" in this specification is intended to specify particular features, regions, steps, processes, elements and / or components, and does not exclude the presence or addition of other features, regions, steps, processes, elements and / or components, unless specifically stated to the contrary.

[0026] The molecular weight of the compound described in this specification or the molecular weight of the polymer, for example, the number average molecular weight or the weight average molecular weight, is a relative mass based on carbon-12, as is well known, and does not specify a unit, but may be understood as a molar mass (g / mol) of the same numerical value, if necessary.

[0027] In the numerical ranges that limit the size, physical properties, etc. of the components described in this specification, if a numerical range limited only to the upper limit and a numerical range limited only to the lower limit are separately exemplified, it should be understood that a numerical range in which these upper and lower limits are combined is also included in the exemplary range of the present invention.

[0028] According to one aspect of the present invention, a method for producing a recycled bis(2-hydroxyethyl)terephthalate having a low yellowness is provided by depolymerizing contaminated waste polyester and decomposing and removing a chromophore.

[0029] A method for producing recycled bis(2-hydroxyethyl)terephthalate according to one embodiment comprises the steps of (1) obtaining a depolymerized product from waste polyester by glycolysis; (2) reacting the depolymerized product with a chromophore decomposing agent to obtain a decomposed product in which the chromophore is decomposed; (3) adsorbing and removing the chromophore in the decomposed product with an ion exchange resin to obtain a purified product; and (4) crystallizing the purified product.

[0030] In addition, a step of distilling moisture and residual solvent within the depolymerized product may be additionally included prior to the above step (2).

[0031] In addition, a step of adding an adsorbent to the purified material and adsorbing it prior to crystallization in the above step (4) may be additionally included.

[0032] According to the method of the present invention, by reacting waste polyester with a chromophore decomposing agent after depolymerization and separating and removing the resulting decomposed chromophore and byproducts, even if the waste polyester has a high contamination level, the yellowness of bis(2-hydroxyethyl) terephthalate regenerated therefrom can be significantly reduced and the impurity content can be minimized. Therefore, a polyester resin manufactured using the regenerated bis(2-hydroxyethyl) terephthalate obtained according to the above method has high whiteness and excellent quality.

[0033] Hereinafter, the above-mentioned regenerated bis(2-hydroxyethyl)terephthalate and its manufacturing method are described in detail.

[0034]

[0035] Depolymerization of waste polyester

[0036] First, a depolymerized product is obtained from waste polyester by glycolysis.

[0037] Waste polyester can be obtained from polyester products discarded after use. Specifically, waste polyester can include various types of polyester materials (e.g., polyethylene terephthalate (PET)) discarded by users, such as beverage bottles, fabrics, films, cases, boxes, partitions, shelves, protective panels, packaging, building materials, and interior and exterior materials.

[0038] The above-mentioned waste polyester may be contaminated waste polyester. The contaminants present within the waste polyester are quite diverse. These contaminants include, for example, additives used during the initial polyester manufacturing process, substances generated during use, or substances incorporated through contamination. In particular, additives used during the initial manufacturing process are rich in substances with structurally strong color-producing molecular structures, and these color-producing structural substances may be generated or incorporated after the polyester is manufactured.

[0039] For example, the yellowness index (YI) measured in the solid state of the waste polyester 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 specific examples, may be 5 to 100, or 10 to 100. In one embodiment, the waste polyester may have a yellowness index (YI) measured in the solid state of 10 or more.

[0040] The waste polyester may undergo pretreatment prior to depolymerization. This pretreatment may involve removing other plastics, metals, and other foreign substances contained in the waste, washing the waste, and then crushing it using a crusher. After undergoing this pretreatment process, the waste polyester may take the form of flakes. Furthermore, the waste polyester may also have a fine fiber-like structure.

[0041] The waste polyester pretreated in this manner is then fed into a depolymerization process. The depolymerization process may include, for example, a glycolysis reaction. As is well known, the glycolysis reaction refers to a chemical reaction that decomposes polymer chains and the like using a glycol such as ethylene glycol. The total input weight of the glycol may be 1 time or more, 2 times or more, or 3 times or more, and may also be 7 times or less, 5 times or less, or 4 times or less, relative to the weight of the waste polyester resin. For example, the input weight of the glycol may be 1 to 7 times, specifically 2 to 5 times, and more specifically 3 to 4 times, relative to the weight of the waste polyester resin.

[0042] A catalyst may be used in the above glycolysis reaction. The catalyst may be a metal catalyst, for example, a metal salt catalyst or a metallic organic catalyst. Specifically, the catalyst may be a metal acetate, carbonate, oxide, hydroxide, etc., and the metal may be an alkali metal, an alkaline earth metal, a transition metal, etc. As a specific example, the catalyst includes a metal acetate, an anhydride, or a hydrate thereof, and more specifically, it may be at least one selected from the group consisting of zinc acetate, sodium acetate, cobalt acetate, and manganese acetate, or a hydrate or anhydride thereof. In addition, the input weight of the catalyst may be 0.01 part by weight or more, 0.1 part by weight or more, 0.2 part by weight or more, or 0.3 part by weight or more, and may also be 5 parts by weight or less, 1 part by weight or less, 0.7 part by weight or less, 0.5 part by weight or less, or 0.4 part by weight or less, relative to 100 parts by weight of the waste polyester resin. For example, the input weight of the catalyst may be 0.1 part by weight to 1 part by weight, and specifically, 0.2 part by weight to 0.7 part by weight. More specifically, the catalyst may be used in an amount of 0.2 part by weight to 0.4 part by weight relative to 100 parts by weight of the waste polyester.

[0043] As a specific example, the glycolysis of step (a) may comprise the reaction of waste polyester with ethylene glycol in the presence of an acetate-based catalyst.

[0044] The above depolymerization may include, for example, a multi-stage depolymerization reaction at low temperatures. In one embodiment, the depolymerization comprises a step of depolymerizing the waste polyester by a first glycolysis reaction at high temperatures; and a step of depolymerizing the waste polyester by a second glycolysis reaction at low temperatures.

[0045] The temperature during the first glycolysis reaction may be 170°C or higher, 180°C or higher, or 190°C or higher, and may also be 220°C or lower, 210°C or lower, 200°C or lower, 195°C or lower, or 190°C or lower. For example, the temperature during the first glycolysis reaction may be 180°C to 210°C, specifically 180°C to 200°C, and more specifically 180°C to 190°C.

[0046] In addition, the temperature during the second glycolysis reaction may be 140°C or higher, 150°C or higher, or 160°C or higher, and may also be 180°C or lower, 170°C or lower, or 160°C or lower. For example, the temperature during the second glycolysis reaction may be 150°C to 170°C, specifically 150°C to 160°C, and more specifically 150°C to 155°C.

[0047] As a specific example, the step of obtaining the depolymerization product may include the step of obtaining a first depolymerization product by a first glycolysis reaction of waste polyester at a temperature of 180°C to 210°C; and the step of obtaining a second depolymerization product by a second glycolysis reaction of the first depolymerization product at a temperature of 150°C to 170°C.

[0048] The time required for the first and second glycolysis reactions may be 1 hour or more or 2 hours or more 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 hour to 4 hours, specifically 1 hour to 3 hours, and more specifically 1 hour to 2 hours from the time the appropriate temperature is reached.

[0049] As a more specific example, the first glycolysis reaction may be performed at a temperature of 180°C to 190°C for 1 to 3 hours. Additionally, the second glycolysis reaction may be performed at a temperature of 150°C to 160°C for 1 to 3 hours.

[0050] As an example, the first glycolysis reaction may be performed under a zinc acetate anhydride catalyst. As a specific example, the first glycolysis reaction may be performed under a zinc acetate anhydride catalyst at a temperature of 180°C to 200°C for 1 to 3 hours. The zinc acetate anhydride may be used in an amount of 0.2 to 0.4 parts by weight based on 100 parts by weight of the waste polyester. In addition, the second glycolysis reaction may be performed at a temperature of 140°C to 160°C for 1 to 3 hours after additional addition of ethylene glycol without additional addition of a catalyst.

[0051]

[0052] Post-depolymerization process

[0053] The depolymerized product (crude bis(2-hydroxyethyl)terephthalate solution) obtained by the above glycolysis can undergo post-processes such as cooling, filtration, adsorption, distillation, and solvent recovery.

[0054] In one embodiment, the depolymerization product may be cooled. The cooling temperature may be, for example, 150°C or lower, 140°C or lower, 130°C or lower, 120°C or lower, 110°C or lower, or 100°C or lower, and may also be 50°C or higher, 60°C or higher, 70°C or higher, 80°C or higher, or 90°C or higher.

[0055] Thereafter, insoluble foreign substances can be removed from the cooled depolymerized product through filtration. As a specific example, the process may further include cooling the depolymerized product to 120°C or below and filtering it using a filter aid. As a result, fine particles and insoluble organic substances present within the depolymerized product can be filtered out through solid-liquid separation.

[0056] Since bis(2-hydroxyethyl) terephthalate (BHET) or oligomers obtained through a depolymerization reaction exist in a solid form at room temperature, it is difficult to separate foreign substances at room temperature. Therefore, it is recommended to separate them under temperature conditions of 90°C to 150°C, more specifically, 110°C to 150°C. In addition, if the above temperature range is maintained, the fluidity is good, making it easy to remove insoluble foreign substances.

[0057] Removal of insoluble foreign substances through solid-liquid separation can be accomplished using various methods and devices. For example, equipment such as pressure filters, centrifuges, filter presses, and belt presses can be used. However, the method is not limited to these as long as it can separate foreign substances.

[0058] Additionally, the depolymerized product may undergo further ion exchange using an ion exchange resin. By undergoing the ion exchange, ionic impurities, specifically catalysts and metal foreign substances, present in the depolymerized product can be removed.

[0059] Additionally, the above-mentioned polymer may undergo a further step of removing moisture and residual solvent by distillation.

[0060] 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.

[0061] Additionally, for an economical depolymerization process, it is necessary to perform a process for recovering unreacted glycols. That is, among the glycols previously introduced into the depolymerization process, such as ethylene glycol, propylene glycol, and diethylene glycol, it is possible to recover the remaining glycols that are not involved in the glycolysis reaction and reuse them in the glycolysis reaction.

[0062] Distillation to remove the unreacted glycol can be performed, for example, by vacuum distillation, and a glass distillation apparatus or a rotary evaporator can be used for this purpose.

[0063] The reduced pressure distillation for removing the unreacted glycol can be performed at a temperature of 150°C or lower, thereby further reducing the generation of diethylene glycol and impurities derived therefrom, thereby improving the purity of BHET. For example, the reduced pressure distillation for removing the unreacted glycol can be performed at 150°C or lower, 130°C or lower, or 120°C or lower, and can also be performed at 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 the unreacted glycol can be 80°C to 190°C, or 90°C to 150°C. As a more specific example, the distillation for removing the unreacted glycol can be performed at a temperature of 100°C to 130°C.

[0064] The pressure during the reduced pressure 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, the reduced pressure distillation may be performed under stepwise reduced pressure conditions from 760 torr to 0.8 torr.

[0065] Additionally, the above polymer can be manufactured by further performing a thin film distillation step under reduced pressure.

[0066] Thin-film distillation is a distillation method that forms a thin film of a mixture to be separated, thereby increasing the surface area in contact with a heat source. Specifically, a mixture introduced into the evaporator of a thin-film distiller is formed as a thin film on the inner wall of the thin-film distiller by a wiper rotor, and then distillation is performed under appropriate temperature conditions through heating. Furthermore, a condenser may be provided within the thin-film distiller to recover the evaporated material.

[0067] The above-described thin-film distillation can be performed using short-path evaporation. This short-path thin-film distillation method, with its short residence time and the ability to perform reduced-pressure distillation using high vacuum, minimizes heat-induced changes in reactants while allowing the separation of high-boiling-point or high-molecular-weight substances that are difficult to separate using other distillation methods. Furthermore, lowering the pressure within the thin-film distillation chamber lowers the vapor pressure of the substance, allowing evaporation to occur at a temperature lower than its original boiling point.

[0068] As a specific example, the depolymerization result is fed into a short-path thin-film distiller, and a wiper that forms a thin-film rotates at 300 rpm or more, so that vaporized substances and non-vaporized substances can be separated and obtained. The internal thin-film temperature of the upper thin-film distillation device during the thin-film distillation may be, for example, 150°C to 250°C, 190°C to 250°C, or 180°C to 220°C. In addition, the internal pressure of the upper thin-film distillation device during the thin-film distillation 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.

[0069]

[0070] Chromophore decomposition

[0071] Afterwards, the above-mentioned depolymerization product is reacted with a chromophore decomposing agent to obtain a decomposed product in which the chromophore is decomposed.

[0072] For example, the chromophore decomposing agent may include an oxidizing agent, and specifically, may include at least one selected from the group consisting of a chlorine-based oxidizing agent, an oxygen-based oxidizing agent, and hydrogen peroxide. Examples of the chlorine-based oxidizing agent include chloramines, chlorates, chloric acids, chlorinated isocyanuric acids, and chlorine dioxide. Examples of the oxygen-based oxidizing agent include hydrogen persulfates, persulfates, percarbonates, and perborates.

[0073] Specific examples of the above chloramines include chloramine T (sodium N-chloro-p-toluenesulfonamide), dichloramine T (N,N'-dichloro-p-toluenesulfonamide), chloramine B (sodium N-chlorobenzenesulfonamide), and dichloramine B (N,N'-dichlorobenzenesulfonamide).

[0074] Specific examples of the above chlorate salts include sodium chlorate, potassium chlorate, lithium chlorate, ammonium chlorate, calcium chlorate, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, sodium chlorite, disodium chlorite, potassium perchlorate, rubidium perchlorate, cesium perchlorate, ammonium perchlorate, potassium perchlorate, calcium perchlorate, silver perchlorate, sodium perchlorate, magnesium perchlorate, etc.

[0075] Specific examples of the above chloric acids include perchloric acid (HClO4), chloric acid (HClO3), and hypochloric acid (HClO).

[0076] Specific examples of the above chlorinated isocyanuric acids include chlorinated isocyanuric acid, sodium chlorinated isocyanurate, potassium chlorinated isocyanurate, dichloroisocyanuric acid, sodium dichloroisocyanurate, potassium dichloroisocyanurate, trichloroisocyanuric acid, sodium trichloroisocyanurate, potassium trichloroisocyanurate, etc.

[0077] In the above decomposition reaction, one type of chromophore decomposition agent may be used alone, or two or more types of chromophore decomposition agents may be used in combination. When two or more types of chromophore decomposition agents are used, they may be introduced into the depolymerization product simultaneously or sequentially.

[0078] In one embodiment, the chromophore decomposing agent may include a chlorine-based oxidizing agent.

[0079] As a specific example, the chromophore decomposing agent may include chloramines. As a more specific example, the chromophore decomposing agent may include chloramine-T, and the chromophore decomposing effect may be more effective than other chloramines.

[0080] As another specific example, the chromophore decomposing agent may further include, in addition to chloramines, at least one selected from chlorates, chloric acids, and hydrogen peroxide. As a more specific example, the chromophore decomposing agent may further include, in addition to chloramines, at least one selected from the group consisting of NaClO, NaClO4, HClO4, HClO, and H2O2. When two or more chromophore decomposing agents are used in combination in this way, the chromophore decomposition effect may be more effective.

[0081] The chromophore decomposed in this step may be, for example, an organic dye and / or an inorganic pigment. Specifically, the chromophore decomposed may include at least one selected from the group consisting of a quinone dye, an azo dye, and an inorganic pigment.

[0082] More specifically, the chromophore may be at least one selected from the group consisting of alizarin, purpurin, munjistin, laccaic, Disperse blue 79, Disperse blue 167, Disperse blue 183, Red 2G, Acid Orange 5, Direct Blue, methyl orange, methyl red, and methyl yellow.

[0083]

[0084] Ion exchange resin adsorption

[0085] Next, the chromophore in the above-mentioned decomposition product is adsorbed and removed using an ion exchange resin to obtain a purified product.

[0086] By passing through the above ion exchange resin adsorption, the chromophore and by-products present in the decomposition product can be removed.

[0087] As is well known, an ion-exchange resin refers to a resin or polymer that acts as a medium for ion exchange. The ion-exchange resin may include a cation exchange resin, an anion exchange resin, an amphoteric ion exchange resin, a chelating resin, etc.

[0088] The cation exchange resin may include a strongly acidic cation exchange resin having a sulfonic acid group (-SO3H) and a weakly acidic cation exchange resin having a carboxyl group (-COOH), and the anion exchange resin may include a strongly basic anion exchange resin in the form of a quaternary ammonium salt and a weakly basic anion exchange resin having a primary to tertiary amino group.

[0089] In a specific example, the ion exchange resin adsorption may include an adsorption step using a strongly acidic cation exchange resin and an adsorption step using a strongly basic anion exchange resin. When these two steps are performed, the ionic substance removal efficiency is significantly improved compared to a single adsorption step using a cation or anion exchange resin, thereby improving the yellowness and color of the final product.

[0090] According to one embodiment, the ion exchange is performed by introducing an ion exchange resin into the decomposition product (the product of the depolymerization product reacting with the chromophore decomposing agent).

[0091] The weight of the ion exchange resin added may be 1 to 20 times, 3 to 15 times, 10 to 15 times, or 8 to 10 times the weight of the catalyst added in the depolymerization reaction, and may also be 10 to 15 times, 10 to 15 times, or 10 to 15 times the weight of the catalyst added in the depolymerization reaction. For example, the weight of the ion exchange resin added may be 1 to 20 times, specifically 3 to 15 times, and more specifically 5 to 8 times the weight of the catalyst added in the depolymerization reaction.

[0092] In addition, the weight of the ion exchange resin may be 1 part by weight or more, 3 parts by weight or more, or 5 parts by weight or more, and may also be 50 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, or 7 parts by weight or less, relative to 100 parts by weight of the waste polyester introduced in the previous depolymerization reaction.

[0093] As a specific example, the ion exchange resin may be used in an amount of 1 to 20 parts by weight based on 100 parts by weight of the waste polyester.

[0094] According to another embodiment, the ion exchange is performed using a column comprising an ion exchange resin.

[0095] Specifically, the column may be filled with particles of an ion exchange resin, and ion exchange may be performed while the decomposition product (a product of the depolymerization product reacting with a chromophore decomposing agent) passes through the column.

[0096] The particle size of the ion exchange resin particles may be, for example, 0.3 mm to 1.5 mm, and more specifically, 0.6 mm to 0.9 mm.

[0097] The temperature during the above ion exchange may be, for example, 140°C or less, 130°C or less, 120°C or less, 110°C or less, 100°C or less, and may also be 50°C or more, 60°C or more, 70°C or more, 80°C or more, or 90°C or more.

[0098] The above ion exchange resin can adsorb a chromophore contained in the decomposition product, and the specific types of the chromophores are as exemplified above.

[0099] In addition, the ion exchange resin can adsorb, in addition to the chromophore, at least one selected from the group consisting of halide ions, metal ions, charged particulates, and their conjugate acid or base ions.

[0100] In addition, the ion exchange resin can adsorb the chromophore decomposing agent added to the depolymerization product in the previous step.

[0101]

[0102] crystallization

[0103] The purified product obtained by adsorption using an ion exchange resin undergoes crystallization.

[0104] A manufacturing method according to one embodiment may further include, prior to the crystallization, a step of adding an adsorbent to the purified material and adsorbing it.

[0105] The above adsorbent may be a carbon-based inorganic adsorbent, and specifically, activated carbon, activated clay, etc. may be used. The shape of the adsorbent is not particularly limited. As a specific example, the adsorbent may include activated carbon.

[0106] Sub-micron sized particles, undissolved organic matter, etc. in the purified product can be adsorbed and removed by the adsorbent.

[0107] Adsorption by the above adsorbent can be performed in an aqueous solution, and specifically, activated carbon can be added to the purified product in an aqueous solution state.

[0108] The amount of the activated carbon may be, for example, 0.01 parts by weight or more, 0.1 parts by weight or more, 0.3 parts by weight or more, 0.5 parts by weight or more, 0.7 parts by weight or more, or 1 part by weight or more, and may also be 10 parts by weight or less, 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, or 1.5 parts by weight or less, relative to 100 parts by weight of bis(2-hydroxyethyl)terephthalate contained in the purified product.

[0109] As a specific example, the activated carbon may be used in an amount of 0.5 to 2 parts by weight relative to 100 parts by weight of bis(2-hydroxyethyl)terephthalate contained in the purified product. Within the above preferred range, the adsorption effect may be further improved, and more specifically, the activated carbon may be used in an amount of 1 to 2 parts by weight relative to 100 parts by weight of bis(2-hydroxyethyl)terephthalate contained in the purified product.

[0110] The filtrate obtained through the above adsorbent may undergo crystallization.

[0111] Various solvents can be used for the above crystallization, but a solvent that can dissolve bis(2-hydroxyethyl)terephthalate well is preferably used. As a specific example, to obtain the final reactant, water is added as a solvent to regenerated bis(2-hydroxyethyl)terephthalate, heated to dissolve, an adsorbent is added, filtering is performed, and crystallization is performed from the resulting solution, and finally filtering is performed to obtain high-purity bis(2-hydroxyethyl)terephthalate.

[0112] The water to be added may be added in an amount of 100 to 500 parts by weight, specifically 200 to 400 parts by weight, and more specifically 300 to 350 parts by weight, based on 100 parts by weight of the recycled bis(2-hydroxyethyl)terephthalate.

[0113] Additionally, the melting temperature may be 50°C to 95°C, specifically 60°C to 85°C, and more specifically 70°C to 75°C.

[0114] The initial temperature of the crystallization reaction may be, for example, 40°C or higher, 50°C or higher, or 60°C or higher, and may also be 90°C or lower, 80°C or lower, or 70°C or lower. In addition, the end temperature of the crystallization reaction may be, for example, 0°C or higher, 10°C or higher, 15°C or higher, or 20°C or higher, and may also be 35°C or lower, 30°C or lower, or 25°C or lower. The crystallization reaction may be carried out by cooling in stages.

[0115] In one specific example, the crystallization is performed in an aqueous solution, and can be performed by stepwise cooling the aqueous solution from 40°C to 70°C to 15°C to 35°C.

[0116]

[0117] Regenerated bis(2-hydroxyethyl)terephthalate

[0118] The present invention provides a regenerated bis(2-hydroxyethyl)terephthalate obtained by the method described above.

[0119] In this specification, bis(2-hydroxyethyl) terephthalate (BHET) obtained by depolymerization of waste polyester is conveniently referred to as “recycled BHET” or abbreviated as r-BHET or rBHET, and it is necessary to understand it as distinct from a pure BHET compound.

[0120] Meanwhile, recycled bis(2-hydroxyethyl) terephthalate may contain byproducts generated by side reactions with reagents or solvents used in the various chemical steps during depolymerization from waste polyester, and these impurities may remain in trace amounts even after multiple purifications. Therefore, recycled BHET generally contains trace amounts of organic and inorganic impurities in addition to the main component, BHET. For this reason, recycled BHET can be viewed as a type of composition containing two or more components, or in other words, a BHET composition. Such recycled BHET can be used as a polymerization raw material for the production of polyester resin.

[0121] Another recycled bis(2-hydroxyethyl)terephthalate according to the present invention is obtained by depolymerization of waste polyester, and has excellent color and quality.

[0122] In one embodiment, the regenerated bis(2-hydroxyethyl)terephthalate may have a yellowness index (YI) of 7 or less, measured for a solution dissolved in ethylene glycol at a concentration of 50 wt%. For example, the yellowness index may be 7 or less, 6 or less, 5 or less, 4.5 or less, 4 or less, 3.5 or less, 3 or less, 2.5 or less, 2 or less, 1.5 or less, or 1 or less. As specific examples, the yellowness index may be 0 to 7, 0 to 6, 0 to 5, 0 to 4, 0 to 3, 1 to 7, 1 to 6, 1 to 5, 1 to 4, 1 to 3, 2 to 7, 2 to 6, 2 to 5, 2 to 4, or 0 to 3.

[0123] The above yellowness may be measured, for example, using a colorimeter at an observer's angle of 2° with Illuminant D65 for a solution in which recycled bis(2-hydroxyethyl) terephthalate and ethylene glycol are dissolved in a weight ratio of 1:1 in an oven at 170°C and heat-treated for 1 hour.

[0124] The purity of the above-mentioned regenerated BHET can be measured using liquid chromatography, etc. Specifically, the purity of the above-mentioned regenerated BHET can be derived by measuring the fraction (%) of the BHET peak area among the total peak area in a spectrum obtained using high-performance liquid chromatography (HPLC).

[0125] For example, the purity of the above-described regenerated BHET may be 95% or greater, 97% or greater, 98% or greater, 99% or greater, or 99.5% or greater, and specifically 95% to 100%, or 97% to 100%.

[0126] According to one embodiment, the regenerated bis(2-hydroxyethyl)terephthalate may have a peak area ratio of bis(2-hydroxyethyl)terephthalate of 97% or more, and more specifically, 98% or more, 99% or more, or 99.5% or more, when analyzed by high-performance liquid chromatography (HPLC).

[0127] Meanwhile, the above-mentioned regenerated bis(2-hydroxyethyl)terephthalate may include compounds other than BHET, specifically, BHET analogs, BHET oligomers (e.g., dimers, trimers), esters (e.g., DEG esters), etc.

[0128] In addition, the recycled bis(2-hydroxyethyl)terephthalate may have a peak area ratio of monohydroxyethyl terephthalate (MHET) of 5% or less, 3% or less, 2% or less, 1.5% or less, 1% or less, or 0.5% or less when analyzed by high-performance liquid chromatography (HPLC), and may also have a peak area ratio of 0% or more, or 0.001% or more. As a specific example, the recycled bis(2-hydroxyethyl)terephthalate may have a peak area ratio of monohydroxyethyl terephthalate (MHET) of 2% or less when analyzed by high-performance liquid chromatography (HPLC), and specifically, may have a peak area ratio of 0.001% to 2%.

[0129] In addition, the regenerated bis(2-hydroxyethyl)terephthalate may have a peak area ratio of dimer or higher BHET oligomers of a total of 5% or less, 3% or less, 2% or less, 1.5% or less, 1% or less, or 0.5% or less when analyzed by high-performance liquid chromatography (HPLC), and may also have a peak area ratio of 0% or more, or 0.001% or more. As a specific example, the regenerated bis(2-hydroxyethyl)terephthalate may have a peak area ratio of dimer or higher BHET oligomers of a total of 1% or less when analyzed by high-performance liquid chromatography (HPLC), and may specifically have a peak area ratio of 0.001% to 1%.

[0130] In addition, the recycled bis(2-hydroxyethyl)terephthalate may have a peak area ratio of diethylene glycol (DEG) ester of 2% or less, 1.5% or less, 1% or less, 0.7% or less, 0.6% or less, or 0.5% or less when analyzed by high-performance liquid chromatography (HPLC), and may also have a peak area ratio of 0% or more, or 0.001% or more. As a specific example, the recycled bis(2-hydroxyethyl)terephthalate may have a peak area ratio of diethylene glycol (DEG) ester of 0.5% or less when analyzed by high-performance liquid chromatography (HPLC), and may specifically have a peak area ratio of 0.001% to 0.5%. The above diethylene glycol ester compound may include 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate and bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate.

[0131]

[0132] Manufacturing of polyester resin

[0133] According to another aspect of the present invention, a method for producing a polyester resin is provided, comprising the steps of: (1) obtaining a depolymerized product from waste polyester by glycolysis; (2) reacting the depolymerized product with a chromophore decomposing agent to obtain a decomposed product in which the chromophore is decomposed; (3) adsorbing and removing the chromophore in the decomposed product with an ion exchange resin to obtain a purified product; (4) crystallizing the purified product to obtain regenerated bis(2-hydroxyethyl)terephthalate; and (5) polymerizing the polyester resin using the regenerated bis(2-hydroxyethyl)terephthalate.

[0134] In the method for manufacturing the above polyester resin, the specific process conditions of steps (1) to (4) can be applied to the contents described above in the method for manufacturing recycled bis(2-hydroxyethyl)terephthalate.

[0135] Polyester resin is polymerized using the regenerated bis(2-hydroxyethyl)terephthalate manufactured in this manner.

[0136] The polymerization of the above polyester resin may include a step of producing a low molecular weight oligomer by performing a polycondensation reaction (first polycondensation reaction) under low vacuum; and a step of producing a polyester resin by performing a polycondensation reaction (second polycondensation reaction) on the oligomer under high vacuum.

[0137] The above first polycondensation reaction and the above second polycondensation reaction can be carried out by applying reduced pressure conditions to remove the solvent contained in the regenerated bis(2-hydroxyethyl) terephthalate and the by-products of the polycondensation reaction (glycol, etc.) by discharging them to the outside of the system.

[0138] The pressure during the first polycondensation reaction may be, for example, 700 mmHg or less, 600 mmHg or less, 500 mmHg or less, 400 mmHg or less, 350 mmHg or less, 300 mmHg or less, or 250 mmHg or less, and may also be 160 mmHg or more, 180 mmHg or more, 200 mmHg or more, 220 mmHg or more, or 240 mmHg or more. According to one embodiment, the pressure during the first polycondensation reaction is 200 mmHg to 600 mmHg, and when it is within the preferred range, it may be more advantageous to sufficiently remove by-products of the low-vacuum polycondensation reaction while maintaining the degree of vacuum during the polycondensation reaction.

[0139] In addition, the temperature during the first polycondensation reaction may be, for example, 100°C or higher, 130°C or higher, 160°C or higher, 180°C or higher, or 200°C or higher, and may also be 300°C or lower, 280°C or lower, 250°C or lower, or 230°C or lower. As a specific example, the first polycondensation reaction may be performed at a temperature of 180°C to 250°C and a pressure of 200 mmHg to 400 mmHg.

[0140] In addition, the first polycondensation reaction may be performed until the number average molecular weight of the low molecular weight oligomer reaches an appropriate level. The time required for the first polycondensation reaction is not particularly limited, but may be, for example, 30 minutes or more, 1 hour or more, 2 hours or more, or 3 hours or more, and may also be 15 hours or less, 10 hours or less, 5 hours or less, or 4 hours or less, and specifically, may be 1 hour to 5 hours.

[0141] The pressure during the second polycondensation reaction may be, for example, less than 200 mmHg, less than 150 mmHg, less than 100 mmHg, less than 50 mmHg, less than 10 mmHg, or less than 1 mmHg, and may also be 0.001 mmHg or more, 0.01 mmHg or more, 0.1 mmHg or more, or 0.5 mmHg or more. According to one embodiment, the pressure during the second polycondensation reaction is less than 200 mmHg, and when it is within the preferred range, it may be more advantageous to sufficiently remove by-products of the polycondensation reaction while maintaining the degree of vacuum during the polycondensation reaction.

[0142] In addition, the temperature during the second polycondensation reaction may be, for example, 230°C or higher, 240°C or higher, 250°C or higher, or 260°C or higher, and may also be 300°C or lower, 290°C or lower, 280°C or lower, or 270°C or lower. As a specific example, the second polycondensation reaction may be performed at a temperature of 250°C to 300°C and a pressure of 0.01 mmHg to 150 mmHg. Within the above preferred range, the vacuum degree during the polycondensation reaction is maintained while sufficiently removing byproducts of the polycondensation reaction, which may be more advantageous in suppressing yellowing of the final resin.

[0143] In addition, the second polycondensation reaction may be performed until the number average molecular weight of the polyester resin reaches an appropriate level. The time required for the second polycondensation reaction is not particularly limited, but may be, for example, 30 minutes or more, 1 hour or more, 2 hours or more, or 5 hours or more, and may also be 60 hours or less, 48 ​​hours or less, 24 hours or less, or 15 hours or less, and specifically, may be 1 hour to 24 hours.

[0144] The method for producing a polyester resin of the present invention may additionally include a process commonly employed in this field in addition to the process described above.

[0145] As an example, the method for producing the polyester resin may additionally include a process of forming pellets by molding the polyester resin after the polycondensation reaction.

[0146] As another example, the method for producing the polyester resin may further include a step of solid-state polymerizing the polyester resin after the condensation polymerization reaction. The temperature during the solid-state polymerization may be, for example, 180°C or higher, 190°C or higher, 200°C or higher, or 205°C or higher, and may also be 260°C or lower, 240°C or lower, 220°C or lower, or 215°C or lower. As a specific example, the solid-state polymerization may be performed at a temperature of 200°C to 220°C. In addition, the pressure during the solid-state polymerization may be, for example, 10.0 torr or lower, 5.0 torr or lower, 2.0 torr or lower, or 1.0 torr or lower, and may be 0.01 torr or higher, 0.1 torr or higher, 0.2 torr or higher, or 0.5 torr or higher, and specifically, may be 0.2 torr to 2.0 torr. Additionally, the above solid-state polymerization can be performed in an atmosphere of an inert gas such as nitrogen.

[0147] The polyester resin according to the present invention can be manufactured as a copolymerized polyester resin by further adding an additional diacid component in addition to the regenerated bis(2-hydroxyethyl)terephthalate. The additional diacid component may be a dicarboxylic acid or a derivative thereof, and the dicarboxylic acid may include at least one selected from terephthalic acid and isophthalic acid. For example, the dicarboxylic acid or a derivative thereof may be additionally added during the first polycondensation reaction.

[0148] In addition, the polycondensation reaction may be carried out in the presence of a polycondensation catalyst, and the polycondensation catalyst may be selected from the group consisting of a titanium-based compound, a germanium-based compound, an antimony-based compound, and an aluminum-based compound. The amount of the polycondensation catalyst used is preferably 0.1 ppm to 500 ppm based on the amount of metal elements relative to the weight of the final polyester resin, but since the amount used affects the color of the final polyester resin, the amount used may vary depending on the desired color and the stabilizer and coloring agent used.

[0149] In addition to the above-mentioned polycondensation catalyst, stabilizers, coloring agents, crystallizers, antioxidants, branching agents, etc. may be further used, and the timing of adding these additives is not particularly limited and may be added at any time during the manufacturing stage of the polyester resin.

[0150] As the above stabilizer, phosphorus compounds such as phosphoric acid, trimethyl phosphate, triethyl phosphate, and triethylphosphonoacetate can be generally used, and the amount added can be 10 to 200 ppm based on the amount of phosphorus element relative to the weight of the polyester resin. In addition, as a coloring agent added to improve the color of the polyester resin, typical coloring agents such as cobalt acetate and cobalt propionate can be exemplified, and the amount added can be 10 to 200 ppm based on the amount of cobalt element relative to the weight of the polyester resin. If necessary, anthraquinone compounds, perinone compounds, azo compounds, methine compounds, etc. can be used as an organic compound coloring agent, and commercially available products include toners such as Polysynthren Blue RLS from Clarient or Solvaperm Red BB from Clarient. The amount of the organic compound coloring agent added can be adjusted to 0 to 50 ppm based on the weight of the polyester resin. Examples of the crystallizer include a crystal nucleating agent, an ultraviolet absorber, a polyolefin resin, a polyamide resin, and the like. Examples of the antioxidant include a hindered phenol antioxidant, a phosphite antioxidant, a thioether antioxidant, or a mixture thereof. Examples of the branching agent include a typical branching agent having three or more functional groups, such as trimellitic anhydride, trimethylol propane, trimellitic acid, or a mixture thereof.

[0151]

[0152] Composition and properties of polyester resin

[0153] According to another aspect of the present invention, a polyester resin manufactured by the above method is provided.

[0154] The polyester resin manufactured in this way is a regenerated polyester resin through chemical recycling of waste polyester.

[0155] Specifically, since the polyester resin of the present invention is polymerized using recycled BHET, it includes repeating units derived from recycled BHET in the polymer chain.

[0156] The content of recycled BHET in the polyester resin of the present invention may be 90 wt% or more, or 95 wt% or more. In addition, the content of the recycled BHET may be 100 wt% or less, 99 wt% or less, or 95 wt% or less.

[0157] As an example, the recycled bis(2-hydroxyethyl)terephthalate may be included in an amount of 90 wt% to 100 wt% based on the weight of the polyester resin.

[0158] Meanwhile, since bis(2-hydroxyethyl)terephthalate has a structure in which two ethylene glycols and one terephthalic acid are combined, the polyester resin of the present invention may essentially include repeating units derived from ethylene glycol and terephthalic acid.

[0159] In addition, the polyester resin of the present invention may be a copolymerized polyester resin, and may further include, for example, an additional diacid component as a copolymer monomer. The additional diacid component may be a dicarboxylic acid or a derivative thereof, and the dicarboxylic acid includes at least one selected from terephthalic acid and isophthalic acid, and these may improve the physical properties of the polyester resin, such as heat resistance, chemical resistance, and weather resistance.

[0160] In this way, the polyester resin of the present invention contains high-purity and high-quality recycled bis(2-hydroxyethyl)terephthalate, and thus has few impurities and excellent heat resistance even though it is a recycled resin.

[0161] Accordingly, the present invention provides a polyester resin manufactured by the method described above. That is, the polyester resin of the present invention includes recycled bis(2-hydroxyethyl)terephthalate, wherein the peak area fraction of bis(2-hydroxyethyl)terephthalate measured by high-performance liquid chromatography (HPLC) is 96% or more, and the peak area fraction of diethylene glycol (DEG) ester compound is less than 2% in total.

[0162] Additionally, the polyester resin may have a concentration of diethylene glycol of, for example, 2.5 wt% or less, 1.5 wt% or less, 1.2 wt% or less, 1.0 wt% or less, or 0.9 wt% or less, as measured by gas chromatography. As a specific example, the polyester resin may have a concentration of diethylene glycol of 0.8 wt% or less, as measured by gas chromatography.

[0163] The intrinsic viscosity (IV) of the polyester resin of the present invention may be, for example, 0.5 dl / g or more, 0.6 dl / g or more, 0.7 dl / g or more, 0.75 dl / g or more, 0.76 dl / g or more, or 0.8 dl / g or more at 35°C, and may also be 1.2 dl / g or less, 1.1 dl / g or less, 1.0 dl / g or less, or 0.9 dl / g or less. According to one embodiment, the intrinsic viscosity of the polyester resin is 0.6 dl / g to 1.2 dl / g at 35°C. The intrinsic viscosity may be obtained, for example, by dissolving the polyester resin in a solvent such as orthochlorophenol and then using an Ubbelohde viscosity meter to obtain a specific viscosity therefrom.

[0164] In addition, the glass transition temperature (Tg) of the polyester resin of the present invention may be, for example, 65°C or higher, 70°C or higher, 75°C or higher, or 79.5°C or higher, and may also be 100°C or lower, 95°C or lower, 90°C or lower, or 85°C or lower. As a specific example, the glass transition temperature (Tg) of the polyester resin may be 75°C to 95°C, or 79.5°C to 90°C. The melting point may be measured, for example, by a method including a step of placing the polyester resin in a differential scanning calorimeter (DSC) and heating it at a constant rate from room temperature to 280°C.

[0165] In addition, the melting point (Tm) of the polyester resin of the present invention may be, for example, 240°C or higher, 250°C or higher, 254.5°C or higher, or 255°C or higher, and may also be 290°C or lower, 280°C or lower, 270°C or lower, or 260°C or lower. As a specific example, the melting point of the polyester resin may be 240°C to 290°C, or 254.5°C to 280°C.

[0166] The glass transition temperature (Tg) and melting point (Tm) of a polyester resin can be calculated from the heat flow obtained when a sample is filled into an aluminum pan using a differential scanning calorimeter (DSC), the temperature is increased to 280°C at 10°C / min, maintained at 280°C for 5 minutes, then cooled to 30°C at -300°C / min, and then the temperature is increased to 280°C at 10°C / min.

[0167] In addition, the polyester resin may have an L* value of 60 or more, 70 or more, 80 or more, 85 or more, 86 or more, or 87 or more, and may also have an L* value of 90 or less when measured in the CIE LAB color space. As a specific example, the polyester resin may have an L* value of 60 to 90, 70 to 90, 80 to 90, 86 to 90, or 87 to 90 when measured in the CIE LAB color space.

[0168] In addition, the polyester resin may have a b* value of 10 or less, 8 or less, 6 or less, 5 or less, 4 or less, 3 or less, 2 or less, or 1 or less when measured in the CIE LAB color space, and may also be 0 or more. As a specific example, the polyester resin may have a b* value of 0 to 10, 0 to 6, 0 to 5, 0 to 4, or 0 to 3 when measured in the CIE LAB color space.

[0169] In addition, the polyester resin may have a value (L*-b*) obtained by subtracting the b* value from the L* value when measuring the CIE LAB color space of 50 or more, 60 or more, 70 or more, 80 or more, 86 or more, or 87 or more. In addition, the upper limit of the L*-b* value is not particularly limited, but may be, for example, 100 or less, 97 or less, 95 or less, 93 or less, or 90 or less. As a specific example, the L*-b* value may be 70 to 100, 80 to 100, 70 to 90, or 80 to 90.

[0170]

[0171] Hereinafter, preferred examples are presented to aid in understanding the present invention. However, the following examples are provided solely to facilitate a better understanding of the present invention and are not intended to limit the scope of the present invention.

[0172]

[0173] <Example of manufacturing recycled bis(2-hydroxyethyl)terephthalate>

[0174]

[0175] Example A1

[0176] 1000 g of waste polyester resin, 2000 g of ethylene glycol, and 5.0 g of zinc acetate anhydride were charged into a first stainless steel (SUS) reactor, and the internal temperature of the reactor was raised to 180°C to conduct depolymerization (first glycolysis reaction) for 2 hours. The obtained reactant was transferred to a second reactor and cooled to 150°C, and then 2000 g of ethylene glycol was additionally charged, and depolymerization (second glycolysis reaction) was conducted for 2 hours while maintaining the reactor temperature at 150°C.

[0177] The obtained reactant was cooled to 110°C and then pressure-filtered to separate the solid and liquid. The separated liquid reactant was passed through a column packed with an ion exchange resin (BC107(H) from Bonlite) to remove ionic impurities, thereby obtaining a mixture containing bis(2-hydroxyethyl)terephthalate and ethylene glycol. The mixture was transferred to a 10 L distillation device and distilled under reduced pressure at 130°C to recover unreacted ethylene glycol. The reactant from which ethylene glycol had been removed was subjected to thin-film distillation at 220°C and 0.08 Torr in a thin-film distillation unit (VKL70-4S from VTA) to remove oligomers higher than dimers, thereby obtaining 1040 g of the product. The obtained product and 3120 g of distilled water were then mixed in a 20 L glass reactor and heated to 70°C to obtain a crude BHET aqueous solution.

[0178] Chloramine-T (CAT) 2.6 g and NaClO 2.6 g were added to the above BHET aqueous solution, and the chromophore decomposition reaction was performed for 1 hour. The obtained decomposition product (product of the decomposition reaction) was separated into a cation exchange resin (BC107(H) from Bonlite) and an anion exchange resin (TRILITE from Samyang) ®The purified solution was sequentially passed through a column filled with SAR10MBOH. 5.2 g of activated carbon was additionally added to the purified solution, stirred for 30 minutes, and filtered. The filtrate was cooled to room temperature to crystallize, filtered, and dried in a vacuum oven. As a result, regenerated bis-2-hydroxyethyl terephthalate with excellent color and purity was obtained.

[0179]

[0180] Example A2

[0181] The procedure of Example A1 was repeated, but the amount of chloramine-T added was changed to 1.3 g, thereby obtaining regenerated bis(2-hydroxyethyl)terephthalate.

[0182]

[0183] Example A3

[0184] The procedure of Example A1 was repeated, but using the same amount of HClO4 instead of NaClO, to obtain regenerated bis(2-hydroxyethyl)terephthalate.

[0185]

[0186] Example A4

[0187] The procedure of Example A1 was repeated, but using the same amount of H2O2 solution instead of NaClO, to obtain regenerated bis(2-hydroxyethyl)terephthalate.

[0188]

[0189] Example A5

[0190] The procedure of Example A1 was repeated, but without adding NaClO, to obtain regenerated bis(2-hydroxyethyl)terephthalate.

[0191]

[0192] Example A6

[0193] The procedure of Example A1 was repeated, but the amount of activated carbon added was changed to 10.4 g, and regenerated bis(2-hydroxyethyl)terephthalate was obtained.

[0194]

[0195] Comparative Example A1

[0196] The procedure of Example A1 was repeated, but without adding both chloramine-T and NaClO, and regenerated bis(2-hydroxyethyl)terephthalate was obtained.

[0197]

[0198] Comparative Example A2

[0199] The procedure of Example A1 was repeated, but neither chloramine-T nor NaClO was added, and the amount of activated carbon added was changed to 10.4 g, thereby obtaining regenerated bis(2-hydroxyethyl)terephthalate.

[0200]

[0201] Comparative Example A4

[0202] The procedure of Example A1 was repeated, but after the removal reaction of the chromogenic molecule, a cation exchange resin (BC107) and an anion exchange resin (Samyang Corporation's TRILITE) were used. ® The regenerated bis(2-hydroxyethyl)terephthalate was obtained without passing it through the column filled with SAR10MBOH.

[0203]

[0204] The manufacturing process of regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) of the above examples and comparative examples is summarized in the table below.

[0205] Classification Information Example A1 Example A2 Example A3 Example A4 Example A5 Example A6 rBHET Process Decomposer 1 CATCATCATCATCATCAT Decomposer 2 NaClONaClOHClO4H2O2--Ion exchange Cathode ion / Yin ...

[0206] Classification Information Comparison Example A1 Comparison Example A2 Comparison Example A4 rBHET Process Decomposer 1--CAT Decomposer 2--NaClO Ion exchange Cathode / Yin / Yin - Adsorbent Activated carbon Activated carbon Activated carbon

[0207]

[0208] <Example of manufacturing recycled polyester resin>

[0209]

[0210] Example B1

[0211] In Example A1, 990 g of the regenerated bis(2-hydroxyethyl) terephthalate (r-BHET), 156 g of water, and 242 g of ethylene glycol (EG) were uniformly mixed at 70°C to prepare an r-BHET solution (concentration 71.4 wt%). 1388 g of the regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) solution prepared above, 0.4 g of antimony oxide as a catalyst, 0.3 g of triethyl phosphate as a stabilizer, and 0.2 g of cobalt acetate as a coloring agent were charged into a 7 L reactor capable of vacuum reaction. The temperature of the reactor was increased to 190°C over 2 hours, and after reaching 190°C, the pressure of the reactor was decreased from normal pressure to 200 Torr (absolute pressure: 200 mmHg) over 30 minutes. Maintaining the pressure of the reactor at 200 Torr (absolute pressure: 200 mmHg), a low-vacuum polycondensation reaction was performed for 1 hour. The pressure of the reactor was decreased from 200 Torr (absolute pressure: 200 mmHg) to 5 Torr (absolute pressure: 5 mmHg) over 30 minutes, and at the same time, the temperature of the reactor was increased to 280°C over 1 hour. Maintaining the pressure of the reactor at 1 Torr (absolute pressure: 1 mmHg) or less, a high-vacuum polycondensation reaction was performed. The mixture inside the reactor was discharged outside the reactor to form strands, which were solidified with a cooling liquid and granulated to an average weight of approximately 12 to 14 mg. The particles were allowed to crystallize at 150°C for 1 hour and then placed in a 20 L solid-state polymerization reactor. Thereafter, nitrogen was flowed into the reactor at a rate of 50 L / min. At this time, the temperature of the reactor was increased from room temperature to 140°C at a rate of 40°C / hour and maintained at 140°C for 3 hours, thereby obtaining a regenerated polyester resin.

[0212]

[0213] Example B2

[0214] The procedure of Example B1 was repeated, but using the recycled bis(2-hydroxyethyl)terephthalate (r-BHET) prepared in Example A2, to obtain a recycled polyester resin.

[0215]

[0216] Example B3

[0217] The procedure of Example B1 was repeated, but using the recycled bis(2-hydroxyethyl)terephthalate (r-BHET) prepared in Example A3, to obtain a recycled polyester resin.

[0218]

[0219] Example B4

[0220] The procedure of Example B1 was repeated, but using the recycled bis(2-hydroxyethyl)terephthalate (r-BHET) prepared in Example A4, to obtain a recycled polyester resin.

[0221]

[0222] Example B5

[0223] The procedure of Example B1 was repeated, but using the recycled bis(2-hydroxyethyl)terephthalate (r-BHET) prepared in Example A5, to obtain a recycled polyester resin.

[0224]

[0225] Example B6

[0226] The procedure of Example B1 was repeated, but using the recycled bis(2-hydroxyethyl)terephthalate (r-BHET) prepared in Example A6, to obtain a recycled polyester resin.

[0227]

[0228] Comparative Example B1

[0229] The procedure of Example B1 was repeated, but using the recycled bis(2-hydroxyethyl)terephthalate (r-BHET) prepared in Comparative Example A1, to obtain a recycled polyester resin.

[0230]

[0231] Comparative Example B2

[0232] The procedure of Example B1 was repeated, but using the recycled bis(2-hydroxyethyl)terephthalate (r-BHET) prepared in Comparative Example A2, to obtain a recycled polyester resin.

[0233]

[0234] Comparative Example B4

[0235] The procedure of Example B1 was repeated, but using the recycled bis(2-hydroxyethyl)terephthalate (r-BHET) prepared in Comparative Example A4, to obtain a recycled polyester resin.

[0236]

[0237] Test Example 1

[0238] The regenerated bis(2-hydroxyethyl)terephthalate obtained in the above examples and comparative examples was tested for the following items.

[0239]

[0240] (1) HPLC

[0241] Approximately 0.01 g of regenerated BHET 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). Afterwards, the peak area fraction (%) of the following components among the total peak area of ​​HPLC was obtained.

[0242] - MHET: Monohydroxyethyl terephthalate

[0243] - BHET: bis(2-hydroxyethyl) terephthalate

[0244] - DEG-ester-1: 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate

[0245] - DEG-ester-2: Bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate

[0246] - Dimer / trimer: BHET dimer / trimer

[0247]

[0248] (2) Absorbance

[0249] The UV-Vis absorbance of the crude BHET aqueous solution (after thin-film distillation) that underwent the chromophore decomposition reaction in the above examples and comparative examples was measured in transmission mode together with a reference sample using an Agilent model (Cary 4000). The absorbance (in arbitrary units) at a wavelength of 400 nm is shown in Table 3 below. In addition, the absorbance spectra of some examples are shown in Fig. 1.

[0250]

[0251] (3) Yellowness (accelerated YI measurement method)

[0252] 20 g of ethylene glycol and 20 g of recycled BHET were mixed and dissolved in an oven at 170°C, followed by heat treatment for 1 hour. Transmittance data for the resulting solution was obtained using Hunterlab's Color Flex EZ with Illuminant D65 at an observer angle of 2°, and the yellowness index (YI) value was calculated using the color analysis device within the software.

[0253]

[0254] The results are shown in the table below.

[0255] Category Item Information Example A1 Example A2 Example A3 Example A4 Example A5 Example A6 r-BHET Composition HPLCMHET 1.78 0.89 3.12 1.3 21.0 21.0 5 BHET 97.2 0.9 8.10 96.0 197.4 4 97.6 4 97.5 8 DEG-ester-10.4 10.4 10.3 70.5 20.4 6 0.4 3 DEG-ester-20.0 40.0 40.0 20.0 40.0 5 0.0 3 Dimer 0 .210.350.290.350.650.54Trimer0.010.010.010.010.010.01Other0.350.200.180.320.170.36Absorbance@400nm0.0560.0790.0670.0660.0860.063ColorYI2.304.803.904.206.604.50

[0256] Category Item Information Comparison Example A1 Comparison Example A2 Comparison Example A4 r-BHET Composition HPLC MHET 0.89 1.81 2.55 BHET 98.10 96.88 96.43 DEG-ester-10.4 10.56 0.65 DEG-ester-20.04 0.04 0.04 Dimer 0.35 0.34 0.22 Trimer 0.01 0.02 0.01 Other 0.20 0.35 0.10 Absorbance @ 400 nm 0.21 10.16 40.116 Color YI 6 1.00 29.5 0 8.60

[0257]

[0258] As shown in the table above, the regenerated BHET obtained in Examples A1 to A6 had lower impurity content and lower absorbance and yellowness than the regenerated BHET obtained in Comparative Examples A1 to A4, and thus had superior quality and color.

[0259]

[0260] Test Example 2

[0261] The polyester resins obtained in the above examples and comparative examples were tested for the following items.

[0262]

[0263] (1) DSC

[0264] Using a differential scanning calorimeter (DSC, Q20 model, TA instrument), the sample was filled into an aluminum pan, heated to 280°C at 10°C / min, maintained at 280°C for 5 minutes, then cooled to 30°C at -300°C / min, and then heated to 280°C at 10°C / min. The glass transition temperature (T) was determined from the heat flow obtained. g ), melting temperature (T m ) was obtained.

[0265]

[0266] (2) Intrinsic viscosity (IV)

[0267] After obtaining a solution by dissolving polyester resin in orthochlorophenol (OCP) at a concentration of 1.2 g / dL at 150℃, the intrinsic viscosity was measured using an Ubbelohde viscosity tube.

[0268] Specifically, the temperature of the viscosity tube was maintained at 35°C, and the time it took for the solvent to pass through a specific internal section of the viscosity tube (efflux time) and the time it took for the solution to pass through were measured to obtain the specific viscosity, which was then used to calculate the intrinsic viscosity.

[0269]

[0270] (3) Color (for PET chip)

[0271] The manufactured polyester resin (PET chip) was used as a sample, and its color was measured using a colorimeter (CHROMA METER CR-410, Konica Minolta). The color was measured using the CIE LAB color space L*, a*, and b* values. The CIE LAB color space is a color space coordinate defined by the CIE (International Commission on Illumination) based on the opposite colors such as yellow-blue and green-red that humans perceive colors. The L* value represents brightness (0~100; 0 is black, 100 is white), the a* value represents green-red (based on 0, + is red, - is green), and the b* value represents yellow-blue color (based on 0, + is yellow, - is blue).

[0272]

[0273] The results of the above test are shown in the table below.

[0274] Example B1 Example B2 Example B3 Example B4 Example B5 Example B6 Recycled PET resin r-BHET Example A1 Example A2 Example A3 Example A4 Example A5 Example A6 Tg(℃) 80.279.980.080.180.380.0 Tm(℃) 256.2257.1256.2255.3256.4255.4 IV(g / dL) 0.810.810.790.800.810.82 Color L*90.088.689.489.087.989.2b*0.92.11.21.92.91.4L*-b*89.186.588.287.185.087.8

[0275] Comparison of the old secretion B1 Comparison of the old secretion B2 Comparison of the old secretion B4 Recycled PET resin r-BHET Comparison of the old secretion A1 Comparison of the old secretion A2 Comparison of the old secretion A4 Tg(℃) 78.3 79.0 77.8 Tm(℃) 253.2 253.7 252.4 IV(g / dL) 0.75 0.8 10.73 Color L*58.1 64.5 85.8 b*9.1 8.5 6.8 L*-b*49.0 56.0 79.0

[0276]

[0277] As can be seen in the table above, the recycled polyester resins obtained in Examples B1 to B6 not only had superior thermal properties compared to the recycled polyester resins obtained in Comparative Examples B1 to B4, but also had high whiteness and thus excellent color.

[0278] In particular, when synthesizing the results of the previous tests, it can be seen that the color of the recycled BHET directly affects the color of the final polyester resin, and that small quality differences in the recycled BHET result in large quality differences in the final polyester resin.

Claims

1. (1) A step of obtaining a depolymerized product from waste polyester by glycolysis; (2) A step of reacting the above polymer with a chromophore decomposing agent to obtain a decomposed product in which the chromophore is decomposed; (3) A step of obtaining a purified product by adsorbing and removing the chromophore in the above decomposition product with an ion exchange resin; and (4) A method for producing regenerated bis(2-hydroxyethyl)terephthalate, comprising a step of crystallizing the purified product.

2. In paragraph 1, A method for producing recycled bis(2-hydroxyethyl)terephthalate, wherein the waste polyester of the above step (1) has a yellowness index (YI) measured in a solid state of 10 or more.

3. In paragraph 1, The step of obtaining the depolymer in the above step (1) is A step of obtaining a first depolymerized product by a first glycolysis reaction at a temperature of 180°C to 210°C from the above waste polyester; and A method for producing regenerated bis(2-hydroxyethyl)terephthalate, comprising a step of obtaining a second depolymer by a second glycolysis reaction of the first depolymer at a temperature of 150°C to 170°C.

4. In paragraph 1, Before the above step (2) A method for producing regenerated bis(2-hydroxyethyl)terephthalate, further comprising a step of distilling moisture and residual solvent within the depolymerized product.

5. In paragraph 1, A method for producing regenerated bis(2-hydroxyethyl)terephthalate, wherein the chromophore decomposing agent of the above step (2) includes chloramines.

6. In paragraph 5, A method for producing regenerated bis(2-hydroxyethyl)terephthalate, wherein the chromophore decomposing agent of the above step (2) additionally includes at least one of chlorates, chloric acid, and hydrogen peroxide.

7. In paragraph 1, The chromophore decomposed in the above step (2) is A method for producing regenerated bis(2-hydroxyethyl)terephthalate, comprising at least one selected from the group consisting of quinone dyes, azo dyes and inorganic pigments.

8. In paragraph 1, The ion exchange resin of the above step (3) contains, in addition to the above chromophore, A method for producing regenerated bis(2-hydroxyethyl)terephthalate, which adsorbs at least one selected from the group consisting of halide ions, metal ions, charged particulates, and their conjugate acid or base ions.

9. In paragraph 1, The adsorption of the above step (3) is Adsorption step by a strong acid cation exchange resin; and A method for producing regenerated bis(2-hydroxyethyl)terephthalate, comprising an adsorption step using a strongly basic anion exchange resin.

10. In paragraph 1, Before crystallization in the above step (4) It further includes a step of adding an adsorbent to the purified water and performing adsorption, A method for producing regenerated bis(2-hydroxyethyl)terephthalate, wherein the adsorbent comprises activated carbon.

11. In paragraph 10, A method for producing regenerated bis(2-hydroxyethyl) terephthalate, wherein the adsorbent is used in an amount of 0.5 to 2 parts by weight relative to 100 parts by weight of bis(2-hydroxyethyl) terephthalate contained in the purified product.

12. In paragraph 1, The crystallization of the above step (4) is performed in an aqueous solution, A method for producing regenerated bis(2-hydroxyethyl)terephthalate, which is performed by gradually cooling an aqueous solution of 40°C to 70°C to 15°C to 35°C.

13. Manufactured by the method of paragraph 1, Regenerated bis(2-hydroxyethyl) terephthalate having a yellowness index (YI) of 7 or less measured for a solution dissolved in ethylene glycol at a concentration of 50 wt%. 14.(1) A step of obtaining a depolymerized product from waste polyester by glycolysis; (2) A step of reacting the above polymer with a chromophore decomposing agent to obtain a decomposed product in which the chromophore is decomposed; (3) A step of obtaining a purified product by adsorbing and removing the chromophore in the above decomposition product using an ion exchange resin; (4) a step of crystallizing the purified product to obtain regenerated bis(2-hydroxyethyl)terephthalate; and (5) A method for producing a polyester resin, comprising a step of polymerizing a polyester resin using the above-mentioned regenerated bis(2-hydroxyethyl)terephthalate.

15. Polyester resin manufactured by the method of Article 14.

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