Methods for producing recycled BHET and polyester resin with a low yellow index

Abstract

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

Description

Detailed description of the invention

[0001] [Technical field] The present invention relates to a method for preparing recycled BHET with a low yellow index and a method for preparing a polyester resin using the same.

[0002] [Background technology] Due to its excellent mechanical strength, heat resistance, transparency, and gas barrier properties, polyester is widely used as a material for beverage filling containers, packaging films, audio and video films, and other applications. Furthermore, polyester is widely manufactured worldwide as an industrial material such as medical fibers and tire cords. In particular, polyester sheets or plates have good transparency and excellent mechanical strength, and are therefore widely used as raw materials for cases, boxes, partitions, shelves, panels, packaging materials, building materials, and interior and exterior materials.

[0003] As a result, plastic waste, including polyester, is generated globally at an unmanageable level every year. In recent years, regulations and plans for the recycling of waste plastic resources, including waste polyester, have been developed in countries around the world. Physical and chemical methods are used to recycle waste polyester, but physical recycling methods cannot guarantee purity and are therefore not widely used.

[0004] On the other hand, in the chemical recycling method, the ester bonds of waste polyester are cleaved and then depolymerized. Specifically, reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis are used. Among these, glycolysis involves decomposing waste polyester by adding glycols such as ethylene glycol or diethylene glycol at high temperatures. The reaction product mainly contains bis(2-hydroxyethyl) terephthalate (BHET). The bis(2-hydroxyethyl) terephthalate contained in the reaction product can be used as a raw material for preparing unsaturated polyester or ester polyol after crystallization or purification.

[0005] However, the 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 by-products formed by side reactions with them. These impurities may remain in trace amounts even after several purifications. In particular, additives used in the initial production of polyester are rich in substances with molecular structures that produce strong coloration. Furthermore, these substances with colored structures may be formed or incorporated after the preparation of the polyester. Bis(2-hydroxyethyl) terephthalate recovered from such contaminated waste polyester has poor color quality and is unsuitable for use in the production of high-quality polyester resins.

[0006] [Prior art document] [Patent] [Patent Document 1] Korean Patent Application Publication No. 2022-0068991

[0007] [Overview of the prefecture] [Problems the invention aims to solve] Poor color quality of recycled bis(2-hydroxyethyl) terephthalate directly affects the color of the polyester resin prepared using it. However, improving the color of such recycled bis(2-hydroxyethyl) terephthalate using conventional techniques has not been easy.

[0008] Based on research conducted by the present inventors, the yellow index of recycled bis(2-hydroxyethyl) terephthalate can be significantly reduced by depolymerizing highly contaminated waste polyester, reacting it with a chromophore decomposer, and then separating and removing the chromophore decomposer from BHET.

[0009] Therefore, the object of the present invention is to prepare recycled bis(2-hydroxyethyl) terephthalate with a low yellow index from contaminated waste polyester, and to use it to prepare recycled polyester resin with a high white index.

[0010] [Means for solving the problem] According to an aspect of the present invention, a method for preparing recycled bis(2-hydroxyethyl) terephthalate is provided, comprising: (1) obtaining a depolymerization product by glycolysis of waste polyester; (2) reacting the depolymerization product with a chromophore decomposing agent to obtain a decomposition product in which the chromophore has been decomposed; (3) adsorbing and removing the chromophore from the decomposition product using an ion exchange resin to obtain a purified product; and (4) crystallizing the purified product.

[0011] According to another aspect of the present invention, a regenerated bis(2-hydroxyethyl) terephthalate prepared by the above method is provided, wherein the yellow index (YI) is 7 or less when measured for a solution dissolved in ethylene glycol at a concentration of 50% by weight.

[0012] According to another aspect of the present invention, a method for preparing a polyester resin is provided, comprising: (1) obtaining a depolymerization product by glycolysis of waste polyester; (2) reacting the depolymerization product with a chromophore decomposing agent to obtain a decomposition product in which the chromophore has been decomposed; (3) adsorbing and removing the chromophore from the decomposition product using an ion exchange resin to obtain a purified product; (4) crystallizing the purified product to obtain regenerated bis(2-hydroxyethyl) terephthalate; and (5) polymerizing a polyester resin using the regenerated bis(2-hydroxyethyl) terephthalate.

[0013] According to another aspect of the present invention, a polyester resin prepared by the above method is provided.

[0014] [Effects of the invention] According to the method of the present invention, when waste polyester is depolymerized, it reacts with a chromophore decomposing agent, and the resulting decomposed chromophore and by-products are separated and removed. As a result, even if the contamination level of the waste polyester is high, the yellow index of the bis(2-hydroxyethyl) terephthalate recovered therefrom can be significantly reduced, and the impurity content can be reduced to the lowest level. Therefore, polyester resins prepared using recycled bis(2-hydroxyethyl) terephthalate obtained by the above method have a high white index and excellent quality. [Brief explanation of the drawing]

[0015] [Figure 1] This figure shows the UV-Vis absorbance spectra of a crude aqueous solution of bis(2-hydroxyethyl) terephthalate according to an embodiment of the present invention.

[0016] [Modes for carrying out the invention] In this specification, terms used to refer to each component are used to distinguish them from one another and are not intended to limit the scope of the embodiments. Furthermore, unless otherwise specified in the context, singular expressions are interpreted as encompassing plurals as well.

[0017] In this specification, terms such as "first," "second," etc., are used to describe various components. However, components should not be limited by these terms. The terms are used for the purpose of distinguishing one component from another.

[0018] In this specification, the term “including” is intended to specify certain characteristics, areas, steps, methods, elements, and / or components. Unless otherwise stated, this does not preclude the presence or addition of any other characteristics, areas, steps, methods, elements, and / or components.

[0019] The molecular weight of the compounds or polymers described in this specification, such as the number average molecular weight or the weight average molecular weight, is the relative mass based on carbon 12 as is well known. Although the unit is not described, it can be understood as the molar mass (g / mol) of the same numerical value as needed.

[0020] In the numerical ranges limiting the sizes and physical properties, etc. of the components described in this specification, when separately exemplifying the numerical range limited only by the upper limit value and the numerical range limited only by the lower limit value, it should be understood that the numerical range combining these upper limit values and lower limit values is also included in the exemplary range of the present invention.

[0021] According to an aspect of the present invention, there is provided a method for preparing bis(2-hydroxyethyl) terephthalate with a low yellowness index, in which waste polyester is depolymerized and the chromophore is decomposed and removed.

[0022] The method for preparing recycled bis(2-hydroxyethyl) terephthalate according to an embodiment of the present invention includes: (1) a step of obtaining a depolymerization product by glycolysis of waste polyester; (2) a step of reacting the depolymerization product with a chromophore decomposing agent to obtain a decomposition product in which the chromophore is decomposed; (3) a step of adsorbing and removing the chromophore in the decomposition product using an ion exchange resin to obtain a purified product; and (4) a step of crystallizing the purified product.

[0023] Furthermore, this method may further include a step of distilling the water and residual solvent in the depolymerization product before step (2).

[0024] Furthermore, this method may further include a step of adding an adsorbent to the purified product and adsorbing it before the crystallization in step (4).

[0025] According to the method of the present invention, when waste polyester is depolymerized, it reacts with a chromophore decomposing agent, and the resulting decomposed chromophore and by-products are separated and removed. As a result, even if the contamination level of the waste polyester is high, the yellow index of the bis(2-hydroxyethyl) terephthalate recovered therefrom can be significantly reduced, and the impurity content can be reduced to the lowest level. Therefore, polyester resins prepared using recycled bis(2-hydroxyethyl) terephthalate obtained by the above method have a high white index and excellent quality.

[0026] The following describes in detail recycled bis(2-hydroxyethyl) terephthalate and the method for preparing it. Depolymerization of waste polyester First, the depolymerization product is obtained by glycolysis of waste polyester.

[0027] Waste polyester can be obtained from polyester material products that have been discarded after use. In particular, waste polyester may include waste such as beverage bottles, cloth, film, cases, boxes, partitions, shelves, protective panels, packaging materials, building materials, and interior and exterior materials, including various polyester materials (e.g., polyethylene terephthalate (PET) materials) that have been discarded after use by consumers.

[0028] Waste polyester may be contaminated waste polyester. The contaminants present in waste polyester are highly diverse. These contaminants include, for example, additives used in the initial production of polyester and substances formed during use or incorporated through contamination. In particular, additives used in the initial production of polyester are rich in substances with molecular structures that exhibit strong coloration. These substances with colored structures can be formed or incorporated after the preparation of polyester.

[0029] For example, when measured in solid phase, waste polyester may have a yellow index (YI) of 5 or higher, 6 or higher, 7 or higher, 8 or higher, 9 or higher, 10 or higher, 15 or higher, or 20 or higher, specifically 5 to 100 or 10 to 100. In one embodiment, the yellow index (YI) of waste polyester when measured in solid phase may be 10 or higher.

[0030] Waste polyester may be pre-treated before being subjected to depolymerization. Pre-treatment can be carried out by removing other plastics, metals, and impurities mixed in the waste, washing it, and then crushing it in a pulverizer. As a result of pre-treatment, the waste polyester may be in flake form. Furthermore, the waste polyester may have a fine structure such as fibers.

[0031] Next, the waste polyester pretreated in this manner is subjected to a depolymerization process. The depolymerization process may include, for example, a glycolysis reaction. As is well known, glycolysis is a chemical reaction in which polymer chains, etc., are cleaved by glycols such as ethylene glycol. The total weight of the added glycol may be 1, 2, or 3 times or more the weight of the waste polyester resin, or it may be 7, 5, or 4 times or less. For example, the weight of the added glycol may be 1 to 7 times, specifically 2 to 5 times, or more specifically 3 to 4 times, the weight of the waste polyester resin.

[0032] A catalyst may be used in the glycolysis reaction. The catalyst may be a metal catalyst, for example, a metal salt catalyst or a metal organocatalyst. Specifically, the catalyst may be a metal acetate, carbonate, oxide, or hydroxide, and the metal may be an alkali metal, an alkaline earth metal, or a transition metal. Specifically, the catalyst may include a metal acetate or its anhydride or hydride. More specifically, it may be at least one selected from the group consisting of zinc acetate, sodium acetate, cobalt acetate, manganese acetate, or their hydrates or anhydrides. Furthermore, the weight of the added 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, or 5 parts by weight or less, 1 part by weight or less, 0.7 parts by weight or less, 0.5 parts by weight or less, or 0.4 parts by weight or less, per 100 parts by weight of waste polyester resin. For example, the amount of catalyst to be added may be 0.1 to 1 part by weight, specifically 0.2 to 0.7 parts by weight, per 100 parts by weight of waste polyester resin. More specifically, the catalyst may be used in an amount of 0.2 to 0.4 parts by weight per 100 parts by weight of waste polyester.

[0033] As a specific example, the glycolysis in step (a) may include the reaction of waste polyester with ethylene glycol in the presence of an acetate-based catalyst.

[0034] Depolymerization may include, for example, a multi-step depolymerization reaction at low temperatures. According to one embodiment, depolymerization includes subjecting waste polyester to depolymerization by a first glycolysis reaction at high temperatures, and subjecting the product to depolymerization at low temperatures by a second glycolysis reaction.

[0035] The temperature during the first glycolysis reaction may be 170°C or higher, 180°C or higher, or 190°C or higher, and may 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, more specifically 180°C to 200°C, and more specifically 180°C to 190°C.

[0036] Furthermore, the temperature during the second glycolysis reaction may be 140°C or higher, 150°C or higher, or 160°C or higher, and may 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.

[0037] As a specific example, the step of obtaining a depolymerization product may include (1) obtaining a first depolymerization product by a first glycolysis reaction of waste polyester at a temperature of 180 to 210°C, and (2) obtaining a second depolymerization product by a second glycolysis reaction of the first depolymerization product at a temperature of 150 to 170°C.

[0038] The time required for the first and second glycolysis reactions may be 1 hour or more, 2 hours or more, or 4 hours or less, or 3 hours or less, from the time the appropriate temperature is reached. For example, the time required for the first and second glycolysis reactions may be 1 to 4 hours, specifically 1 to 3 hours, or more specifically 1 to 2 hours, from the time the appropriate temperature is reached.

[0039] 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. Furthermore, the second glycolysis reaction may be carried out at a temperature of 150°C to 160°C for 1 to 3 hours.

[0040] For example, the first glycolysis reaction may be carried out in the presence of a zinc acetate anhydride catalyst. Specifically, the first glycolysis reaction may be carried out in the presence of a zinc acetate anhydride catalyst at a temperature of 180°C to 200°C for 1 to 3 hours. The zinc acetate anhydride catalyst may be used in an amount of 0.2 to 0.4 parts by weight per 100 parts by weight of waste polyester. Furthermore, the second glycolysis reaction may be carried out at a temperature of 140°C to 160°C for 1 to 3 hours by adding ethylene glycol without adding the catalyst.

[0041] Process after depolymerization The depolymerization product obtained by glycolysis (crude bis(2-hydroxyethyl) terephthalate solution) may be subjected to subsequent processes such as cooling, filtration, adsorption, distillation, and solvent recovery.

[0042] In one embodiment, the depolymerization product may be subjected to 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, 100°C or lower, or 50°C or higher, 60°C or higher, 70°C or higher, 80°C or higher, or 90°C or higher.

[0043] Subsequently, insoluble impurities can be removed from the cooled depolymerization product by filtration. Specifically, the depolymerization product may be cooled to 120°C or below, and a filter aid may be added before further filtration. As a result, fine particles and insoluble organic matter present in the depolymerization product can be removed by solid-liquid separation.

[0044] Since bis(2-hydroxyethyl) terephthalate (BHET) or oligomers obtained by the depolymerization reaction exist as solids at room temperature, it is difficult to separate impurities at room temperature. Therefore, it is preferable to separate impurities at a temperature of 90°C to 150°C, more specifically 110°C to 150°C. Furthermore, if the above temperature range is maintained, the fluidity is good, which may facilitate the removal of insoluble impurities.

[0045] Various methods and devices can be used to remove insoluble impurities by solid-liquid separation. For example, devices such as pressure filters, centrifuges, filter presses, and belt presses may be used. However, the method is not limited to these, as long as any method capable of separating impurities is used.

[0046] Furthermore, the depolymerization product may be subjected to further ion exchange using an ion exchange resin. When the depolymerization product is subjected to ion exchange, ionic impurities present in the depolymerization product, specifically catalysts and metallic contaminants, can be removed.

[0047] Furthermore, the depolymerization product may be subjected to further removal of water and residual solvent by distillation.

[0048] Even after filtration in the previous step, unreacted glycol remains in the depolymerization product; therefore, it is necessary to remove the unreacted glycol from the product before proceeding to the next step.

[0049] Furthermore, in order to carry out the depolymerization method economically, it is necessary to perform a step to recover unreacted glycol. Specifically, glycols that were used in the depolymerization process beforehand and remain without participating in the glycolysis reaction, such as ethylene glycol, propylene glycol, and diethylene glycol, can be recovered and reused.

[0050] Distillation to remove unreacted glycol can be carried out, for example, by vacuum distillation. A glass distillation apparatus or a rotary evaporator may be used for this purpose.

[0051] Since vacuum distillation to remove unreacted glycol is performed at temperatures below 150°C, the purity of BHET can be increased by further reducing the formation of diethylene glycol and impurities derived from diethylene glycol. For example, vacuum distillation to remove unreacted glycol may be performed at temperatures below 150°C, below 130°C, or below 120°C, and above 80°C, above 90°C, above 100°C, or above 110°C. Specifically, the temperature during distillation to remove unreacted glycol may be between 80°C and 190°C, or between 90°C and 150°C. As a more specific example, distillation to remove unreacted glycol may be performed at temperatures between 100°C and 130°C.

[0052] The pressure during vacuum distillation to remove unreacted glycol may be, for example, 0.1 Torr to 760 Torr, 0.1 Torr to 200 Torr, or 0.5 Torr to 30 Torr. More specifically, vacuum distillation can be carried out under stepwise reduced pressure conditions from 760 Torr to 0.8 Torr.

[0053] Furthermore, the depolymerization product can be prepared by a further step of thin-film distillation under reduced pressure.

[0054] Thin-film distillation is a distillation method that separates a mixture into a thin film in order to increase the surface area of ​​the mixture in contact with the heat source. Specifically, the mixture supplied to the evaporator of a thin-film evaporator forms a thin film on the inner wall of the evaporator by a wiper rotor. Then, distillation is carried out under appropriate temperature conditions by heating. Furthermore, a cooler for recovering the evaporated material may be provided inside the thin-film evaporator.

[0055] Thin-film evaporation may also be performed by short-pass evaporation. Such short-pass and thin-film evaporation have short residence times and allow for reduced-pressure distillation under high vacuum, making it possible to separate high-boiling-point or high-molecular-weight substances that are difficult to separate by other distillation methods, while minimizing thermal changes to the reactants. Furthermore, lowering the pressure inside the thin-film evaporator lowers the vapor pressure of the substance, which has the advantage of allowing evaporation to be performed at a temperature lower than the original boiling point.

[0056] As a specific example, the depolymerization product is supplied to a short pass and a thin-film evaporator, and a wiper for forming a thin film is rotated at 300 rpm or more. As a result, evaporated and non-evaporated substances can be separated from each other. The internal thin-film temperature at the top of the thin-film evaporator during thin-film evaporation may be, for example, 150°C to 250°C, 190°C to 250°C, or 180°C to 220°C. Furthermore, the internal pressure at the top of the thin-film evaporator during thin-film evaporation may be, for example, 0.005 Torr to 5.0 Torr, 0.05 Torr to 5.0 Torr, 0.05 Torr to 1.5 Torr, or 0.05 Torr to 1 Torr.

[0057] Decomposition of chromophore Subsequently, the depolymerization product is reacted with a chromophore decomposition agent to obtain a decomposition product in which the chromophore has been decomposed.

[0058] For example, the chromophore decomposing agent may contain an oxidizing agent. Specifically, the chromophore decomposing agent may contain at least one selected from the group consisting of chlorine-based oxidizing agents, oxygen-based oxidizing agents, and hydrogen peroxide. Examples of chlorine-based oxidizing agents include chloramine, chlorate salts, chloric acid, chloroisocyanuric acid, and chlorine dioxide. Examples of oxygen-based oxidizing agents include hydrogen persulfate, persulfate salts, percarbonate salts, and perborate salts.

[0059] Specific examples of chloroamines 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).

[0060] Specific examples of chlorates 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, and magnesium perchlorate.

[0061] Specific examples of chloric acid include perchloric acid (HClO4), chloric acid (HClO3), and hypochlorous acid (HClO).

[0062] Specific examples of chloroisocyanuric acid include chloroisocyanuric acid, sodium chloroisocyanurate, potassium chloroisocyanurate, dichloroisocyanuric acid, sodium dichloroisocyanurate, potassium dichloroisocyanurate, trichloroisocyanuric acid, sodium trichloroisocyanurate, and potassium trichloroisocyanurate.

[0063] In the decomposition reaction, one type of chromophore decomposer may be used alone, or two or more types of chromophore decomposers may be used in combination. When two or more chromophore decomposers are used, they can be added to the depolymerization simultaneously or sequentially.

[0064] In one embodiment, the chromophore decomposing agent may include a chlorine-based oxidizing agent.

[0065] As a specific example, the chromophore decomposing agent may contain chloroamine. As a more specific example, the chromophore decomposing agent may contain chloramine-T, which may be more effective in producing a chromophore decomposing effect than other chloramines.

[0066] As another specific example, the chromophore decomposing agent may further contain at least one of chlorates, chloric acid, and hydrogen peroxide in addition to chloroamine. As a more specific example, the chromophore decomposing agent may further contain at least one selected from the group consisting of NaClO, NaClO4, HClO4, HClO, and H2O2 in addition to chloroamine. When two or more chromophore decomposing agents are used in combination as described above, the chromophore decomposing effect may be more effective.

[0067] The chromophore decomposed in this step may be, for example, an organic dye and / or an inorganic pigment. Specifically, the chromophore decomposed may be at least one selected from the group consisting of quinone dyes, azo dyes, and inorganic pigments.

[0068] More specifically, the chromophore may be at least one selected from the group consisting of alizarin, purpurin, mundistine, laccaic, disperse blue 79, disperse blue 167, disperse blue 183, red 2G, acid orange 5, direct blue, methyl orange, methyl red, and methyl yellow.

[0069] Adsorption by ion exchange resin Next, the chromophore in the decomposition product is adsorbed and removed by an ion exchange resin to obtain a purified product.

[0070] When decomposition products are subjected to ion exchange, chromophores and by-products present in the decomposition products can be removed.

[0071] As is well known, ion exchange resins refer to resins or polymers that function as a medium for ion exchange. Ion exchange resins may include cation exchange resins, anion exchange resins, amphoteric ion exchange resins, chelate resins, and the like.

[0072] Cation exchange resins may include strongly acidic cation exchange resins having sulfonic acid groups (-SO3H) and weakly acidic cation exchange resins having carboxyl groups (-COOH). Anion exchange resins may include strongly basic anion exchange resins in the form of quaternary ammonium salts and weakly basic anion exchange resins having primary to tertiary amino groups.

[0073] In specific examples, adsorption using ion exchange resins 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 efficiency of removing ionic substances is significantly improved compared to when only one adsorption step is performed using a cation or anion exchange resin, thereby improving the yellow index and color of the final product.

[0074] According to one embodiment, ion exchange is performed by adding an ion exchange resin to the decomposition product (the result of the reaction between the depolymerization product and the chromophore decomposition agent).

[0075] The weight of the ion exchange resin added may be 1, 3, or 5 times or more the weight of the catalyst added in the depolymerization reaction, and may also be 20, 15, 10, or 8 times or less. For example, the weight of the ion exchange resin added may be 1 to 20 times, specifically 3 to 15 times, or more specifically 5 to 8 times, the weight of the catalyst added in the depolymerization reaction.

[0076] Furthermore, the weight of the ion exchange resin to be added may be 1 part by weight or more, 3 parts by weight or more, or 5 parts by weight or more, per 100 parts by weight of the waste polyester resin used in the depolymerization reaction, and may also be 50 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, or 7 parts by weight or less.

[0077] For example, the ion exchange resin may be used in an amount of 1 to 20 parts by weight per 100 parts by weight of waste polyester.

[0078] According to another embodiment, ion exchange is performed using a column containing an ion exchange resin.

[0079] Specifically, the column can be packed with ion exchange resin particles, and ion exchange can be performed while the decomposition products (the reaction result between depolymerization products and a chromophore decomposing agent) pass through the column.

[0080] The particle size of the ion exchange resin particles may be, for example, 0.3 mm to 1.5 mm, or more specifically, 0.6 mm to 0.9 mm.

[0081] The ion exchange temperature may be, for example, 140°C or lower, 130°C or lower, 120°C or lower, 110°C or lower, or 100°C or lower, or it may be 50°C or higher, 60°C or higher, 70°C or higher, 80°C or higher, or 90°C or higher.

[0082] Ion exchange resins can adsorb chromophores contained in decomposition products. Specific types of chromophores are as described above.

[0083] Furthermore, in addition to chromophores, the ion exchange resin can adsorb at least one selected from the group consisting of halide ions, metal ions, charged fine particles, and their conjugate acid or conjugate base ions.

[0084] Furthermore, the ion exchange resin can adsorb the chromophore decomposing agent added to the depolymerization product in the previous step.

[0085] crystallization The purified product obtained by adsorption using an ion exchange resin is subjected to crystallization.

[0086] The method according to one embodiment may further include adding an adsorbent to the purified product and performing adsorption before crystallization.

[0087] Carbon-based inorganic adsorbents can be used as adsorbents. Specifically, activated carbon, activated clay, etc., can be used. The shape of the adsorbent is not particularly limited. For example, the adsorbent may include activated carbon.

[0088] Submicron-sized particles, undissolved organic matter, and other elements in the purified product can be adsorbed and removed by the adsorbent.

[0089] Adsorption using adsorbents can be carried out in an aqueous solution. Specifically, activated carbon can be added to the purified product in an aqueous solution.

[0090] The amount of activated carbon used may be 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, per 100 parts by weight of bis(2-hydroxyethyl) terephthalate contained in the purified product, or 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.

[0091] As a specific example, activated carbon may be used in an amount of 0.5 to 2 parts by weight per 100 parts by weight of bis(2-hydroxyethyl) terephthalate contained in the purified product. Within the above preferred range, the adsorption effect may be better. More specifically, activated carbon may be used in an amount of 1 to 2 parts by weight per 100 parts by weight of bis(2-hydroxyethyl) terephthalate contained in the purified product.

[0092] The filtrate obtained by passing it through the adsorbent may be subjected to crystallization.

[0093] Various solvents may be used for crystallization, but preferably a solvent capable of dissolving bis(2-hydroxyethyl) terephthalate is used. Specifically, to obtain the final reaction product, water is added as a solvent to the regenerated bis(2-hydroxyethyl) terephthalate dissolved by heating, an adsorbent is added to this, and the solution obtained by filtration is subjected to crystallization and final filtration. As a result, high-purity bis(2-hydroxyethyl) terephthalate can be obtained.

[0094] Water may be added in an amount of 100 to 500 parts by weight, specifically 200 to 400 parts by weight, or more specifically 300 to 350 parts by weight, per 100 parts by weight of recycled bis(2-hydroxyethyl) terephthalate.

[0095] Furthermore, the dissolution temperature may be 50°C to 95°C, specifically 60°C to 85°C, or more specifically 70°C to 75°C.

[0096] The initial temperature of the crystallization reaction may be, for example, 40°C or higher, 50°C or higher, or 60°C or higher, or 90°C or lower, 80°C or lower, or 70°C or lower. Furthermore, the termination 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, or 35°C or lower, 30°C or lower, or 25°C or lower. The crystallization reaction can be carried out by stepwise cooling.

[0097] In one embodiment, crystallization is carried out in an aqueous solution. Crystallization can be achieved by slowly cooling the aqueous solution from 40°C to 70°C to 15°C to 35°C. Regenerated bis(2-hydroxyethyl) terephthalate The present invention provides regenerated bis(2-hydroxyethyl) terephthalate obtained by the above method.

[0098] In this specification, bis(2-hydroxyethyl) terephthalate (BHET) obtained by the depolymerization of the waste polyester described above will be referred to as "recycled bis(2-hydroxyethyl) terephthalate (recycled BHET)," or abbreviated as r-BHET or rBHET, but it should be understood that it is different from pure BHET compounds.

[0099] On the other hand, recycled bis(2-hydroxyethyl) terephthalate may contain reagents or solvents used in various chemical steps during the depolymerization of waste polyester, or by-products formed by side reactions with them. These impurities may remain in trace amounts even after several 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 considered a type of composition containing two or more components, i.e., a BHET composition. Such recycled BHET can be used as a polymerization raw material for preparing polyester resins.

[0100] The recycled bis(2-hydroxyethyl) terephthalate according to the present invention is obtained by the depolymerization of waste polyester and has excellent color and quality.

[0101] In one embodiment, recycled bis(2-hydroxyethyl) terephthalate may have a yellow index (YI) of 7 or less when measured in a solution dissolved in ethylene glycol at a concentration of 50% by weight. Specifically, the yellow 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. For example, the yellow index may be 0-7, 0-6, 0-5, 0-4, 0-3, 1-7, 1-6, 1-5, 1-4, 1-3, 2-7, 2-6, 2-5, 2-4, or 0-3.

[0102] For example, the yellow index can be measured using an Illuminant D65 colorimeter at an observation angle of 2° on a solution obtained by dissolving recycled bis(2-hydroxyethyl) terephthalate and ethylene glycol in a 1:1 weight ratio in an oven at 170°C and heat-treating it for 1 hour.

[0103] The purity of regenerated BHET can be measured using liquid chromatography or other methods. Specifically, the purity of regenerated BHET can be calculated by measuring the peak area fraction (%) of BHET relative to the total peak area in the spectrum obtained using high-performance liquid chromatography (HPLC).

[0104] For example, the purity of recycled BHET can be 95% or higher, 97% or higher, 98% or higher, 99% or higher, or 99.5% or higher, specifically 95% to 100% or 97% to 100%.

[0105] According to one embodiment, when measured by high-performance liquid chromatography (HPLC), the regenerated bis(2-hydroxyethyl) terephthalate may have a peak area fraction of 97% or more, more specifically, 98% or more, 99% or more, or 99.5% or more.

[0106] On the other hand, recycled bis(2-hydroxyethyl) terephthalate may include compounds other than BHET, specifically BHET analogs, BHET oligomers (e.g., dimers, trimers), and esters (e.g., DEG esters).

[0107] Furthermore, when regenerated bis(2-hydroxyethyl) terephthalate is measured by high-performance liquid chromatography (HPLC), the peak area fraction 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 0% or more or 0.001% or more. Specifically, when regenerated bis(2-hydroxyethyl) terephthalate is measured by high-performance liquid chromatography (HPLC), the peak area fraction of monohydroxyethyl terephthalate (MHET) may be 2% or less, specifically 0.001% to 2%.

[0108] Furthermore, when regenerated bis(2-hydroxyethyl) terephthalate is measured by high-performance liquid chromatography (HPLC), the total peak area fraction of dimers or more of BHET oligomers may be 5% or less, 3% or less, 2% or less, 1.5% or less, 1% or less, or 0.5% or less, and 0% or more or 0.001% or more. Specifically, when regenerated bis(2-hydroxyethyl) terephthalate is measured by high-performance liquid chromatography (HPLC), the total peak area fraction of dimers or more of BHET oligomers may be 1% or less, specifically 0.001% to 1%.

[0109] Furthermore, when regenerated bis(2-hydroxyethyl) terephthalate is measured by high-performance liquid chromatography (HPLC), the total peak area fraction 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 0% or more or 0.001% or more. Specifically, when regenerated bis(2-hydroxyethyl) terephthalate is measured by high-performance liquid chromatography (HPLC), the total peak area fraction of diethylene glycol (DEG) ester may be 0.5% or less, specifically 0.001% to 0.5%. Diethylene glycol ester compounds may include 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl] terephthalate and bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate.

[0110] Preparation of polyester resin According to another aspect of the present invention, a method for preparing a polyester resin is provided, comprising: (1) obtaining a depolymerization product by glycolysis of waste polyester; (2) reacting the depolymerization product with a chromophore decomposing agent to obtain a decomposition product in which the chromophore has been decomposed; (3) adsorbing and removing the chromophore from the decomposition product using an ion exchange resin to obtain a purified product; (4) crystallizing the purified product to obtain regenerated bis(2-hydroxyethyl) terephthalate; and (5) polymerizing a polyester resin using the regenerated bis(2-hydroxyethyl) terephthalate.

[0111] In a method for preparing polyester resin, the specific process conditions of steps (1) to (4) can be used as those described above in a method for preparing recycled bis(2-hydroxyethyl) terephthalate.

[0112] The recycled bis(2-hydroxyethyl) terephthalate prepared in this way is used to polymerize polyester resins.

[0113] Polymerization of polyester resin involves preparing a low molecular weight oligomer by performing a polycondensation reaction (first polycondensation reaction) under low vacuum, and then preparing a polyester resin by subjecting this oligomer to a polycondensation reaction (second polycondensation reaction) under high vacuum.

[0114] The first and second polycondensation reactions can be carried out under reduced pressure, allowing the solvent contained in the regenerated bis(2-hydroxyethyl) terephthalate and the by-products of the polycondensation reaction (such as glycols) to be discharged from the system.

[0115] 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, or 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. Within the above preferred range, it may be even more advantageous to sufficiently remove by-products of the polycondensation reaction under low vacuum while maintaining the vacuum level during the polycondensation reaction.

[0116] Furthermore, 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. Specifically, the first polycondensation reaction may be carried out at a temperature of 180°C to 250°C and a pressure of 200 mmHg to 400 mmHg.

[0117] Furthermore, the first polycondensation reaction may be carried out 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, or 15 hours or less, 10 hours or less, 5 hours or less, or 4 hours or less. Specifically, it may be between 1 and 5 hours.

[0118] The pressure during the second polycondensation reaction may be, for example, less than 200 mmHg, 150 mmHg or less, 100 mmHg or less, 50 mmHg or less, 10 mmHg or less, or 1 mmHg or less, or 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. Within the above preferred range, it may be even more advantageous to sufficiently remove by-products of the polycondensation reaction while maintaining the vacuum level during the polycondensation reaction.

[0119] Furthermore, 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 be 300°C or lower, 290°C or lower, 280°C or lower, or 270°C or lower. Specifically, the second polycondensation reaction may be carried out at a temperature of 250°C to 300°C and a pressure of 0.01 mmHg to 150 mmHg. Within the above preferred range, it may be even more advantageous to sufficiently remove by-products of the polycondensation reaction while maintaining the vacuum level during the polycondensation reaction, thereby suppressing yellowing of the final resin.

[0120] Furthermore, the second polycondensation reaction may be carried out 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, or 60 hours or less, 48 ​​hours or less, 24 hours or less, or 15 hours or less. Specifically, it may be between 1 and 24 hours.

[0121] The method for preparing the polyester resin of the present invention may further include steps commonly used in the art, in addition to the steps described above.

[0122] As an example, a method for preparing a polyester resin may further include the step of molding the polyester resin after a polycondensation reaction to form pellets.

[0123] As another example, a method for preparing a polyester resin may further include a step of subjecting the polyester resin to solid-phase polymerization after a polycondensation reaction. The temperature during solid-phase polymerization may be, for example, 180°C or higher, 190°C or higher, 200°C or higher, or 205°C or higher, and may be 260°C or lower, 240°C or lower, 220°C or lower, or 215°C or lower. Specifically, solid-phase polymerization may be carried out at a temperature of 200°C to 220°C. Furthermore, the pressure during solid-phase 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. Specifically, it may be 0.2 Torr to 2.0 Torr. Furthermore, solid-phase polymerization may be carried out in an inert gas atmosphere such as nitrogen.

[0124] The polyester resin according to the present invention can be prepared as a copolymerized polyester resin by further adding an additional diacid component to recycled bis(2-hydroxyethyl) terephthalate. The additional diacid component may be a dicarboxylic acid or a derivative thereof. The dicarboxylic acid may include at least one selected from terephthalic acid and isophthalic acid. For example, a dicarboxylic acid or a derivative thereof may be further added during the first polycondensation reaction.

[0125] Furthermore, the polycondensation reaction may be carried out in the presence of a polycondensation catalyst. The polycondensation catalyst may be selected from the group consisting of titanium-based compounds, germanium-based compounds, antimony-based compounds, and aluminum-based compounds. The amount of 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. The amount used may vary depending on the desired color and the stabilizers and colorants used, as it affects the color of the final polyester resin.

[0126] In addition to the polycondensation catalyst, stabilizers, colorants, crystallizers, antioxidants, branching agents, etc., may also be used. The timing of adding these additives is not particularly limited and they may be added at any point during the polyester resin preparation step.

[0127] As stabilizers, phosphorus compounds, such as phosphoric acid, trimethyl phosphate, triethyl phosphate, and triethylphosphonoacetate, can generally be used. The amount of stabilizer added can be 10 to 200 ppm relative to the weight of the polyester resin, based on the amount of the element. Furthermore, as colorants added to improve the color of the polyester resin, common colorants such as cobalt acetate and cobalt propionate can be exemplified. The amount of colorant added can be 10 to 200 ppm relative to the weight of the polyester resin, based on the amount of cobalt element. If necessary, organic colorants such as anthraquinone compounds, perinone compounds, azo compounds, and methine compounds may be used. Commercial toners such as Clarient's Polysynthren Blue RLS or Clarient's Solvaperm Red BB may be used. The amount of organic compound colorant added can be adjusted to 0 to 50 ppm, based on the weight of the polyester resin. Examples of crystallizing agents include crystal nucleating agents, ultraviolet absorbers, polyolefin resins, polyamide resins, etc. Examples of antioxidants include hindered phenol antioxidants, phosphite antioxidants, thioether antioxidants, or mixtures thereof. Examples of branching agents include conventional branching agents having three or more functional groups, such as trimellitic anhydride, trimethylolpropane, trimellitic acid, or mixtures thereof.

[0128] Composition and properties of polyester resins According to another aspect of the present invention, a polyester resin prepared by the above method is provided.

[0129] The polyester resin prepared in this way is a polyester resin recycled through the chemical recycling of waste polyester.

[0130] Specifically, the polyester resin of the present invention is polymerized using recycled BHET, and therefore contains repeating units derived from recycled BHET in its polymer chains.

[0131] The recycled BHET content in the polyester resin of the present invention may be 90% by weight or more, or 95% by weight or more. Furthermore, the recycled BHET content may be 100% by weight or less, 99% by weight or less, or 95% by weight or less.

[0132] For example, recycled bis(2-hydroxyethyl) terephthalate may be used in an amount of 90% to 100% by weight based on the weight of the polyester resin.

[0133] On the other hand, since bis(2-hydroxyethyl) terephthalate has a structure in which two ethylene glycol molecules and one terephthalic acid molecule are bonded together, the polyester resin of the present invention may essentially contain repeating units derived from ethylene glycol and terephthalic acid.

[0134] Furthermore, the polyester resin of the present invention may be a copolymerized polyester resin. For example, it may further contain additional diacid components as copolymer monomers. The additional diacid components may be dicarboxylic acids or their derivatives. The dicarboxylic acids may include at least one selected from terephthalic acid and isophthalic acid. Dicarboxylic acids can improve the physical properties of the polyester resin, such as heat resistance, chemical resistance, and weather resistance.

[0135] As described above, the polyester resin of the present invention contains high-purity, high-quality recycled bis(2-hydroxyethyl) terephthalate, and therefore, despite being a recycled resin, it has few impurities and excellent heat resistance.

[0136] Therefore, the present invention provides a polyester resin prepared by the method described above. In other words, in the polyester resin of the present invention, when measured by high-performance liquid chromatography (HPLC), the total peak area fraction of bis(2-hydroxyethyl) terephthalate is 96% or more, and the peak area fraction of diethylene glycol (DEG) ester compounds is less than 2%.

[0137] Furthermore, when measured by gas chromatography, the polyester resin may have a diethylene glycol concentration of, for example, 2.5% by weight or less, 1.5% by weight or less, 1.2% by weight or less, 1.0% by weight or less, or 0.9% by weight or less. Specifically, when measured by gas chromatography, the polyester resin may have a diethylene glycol concentration of 0.8% by weight or less.

[0138] The intrinsic viscosity of the polyester resin of the present invention at 35°C 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, 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 at 35°C may be between 0.6 dl / g and 1.2 dl / g. The intrinsic viscosity can be calculated, for example, by dissolving the polyester resin in a solvent such as orthochlorophenol and determining the specific viscosity using an Ubbelohde viscometer or the like.

[0139] Furthermore, 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, or it may be 100°C or lower, 95°C or lower, 90°C or lower, or 85°C or lower. Specifically, 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 that includes placing the polyester resin in a differential scanning calorimeter (DSC) and raising the temperature from room temperature to 280°C at a constant rate.

[0140] Furthermore, 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, or it may be 290°C or lower, 280°C or lower, 270°C or lower, or 260°C or lower. Specifically, the melting point (Tm) of the polyester resin may be 240°C to 290°C or 254.5°C to 280°C.

[0141] The glass transition temperature (Tg) and melting point (Tm) of polyester resin can be measured using differential scanning calorimetry (DSC). This involves filling an aluminum pan with the sample, heating it to 280°C at 10°C / min, maintaining it at 280°C for 5 minutes, then cooling it to 30°C at -300°C / min, and finally raising the temperature to 280°C at 10°C / min, and measuring the heat flow rate obtained.

[0142] Furthermore, polyester resin is used when measuring the CIE Lab color space, L * The value may be 60 or higher, 70 or higher, 80 or higher, 85 or higher, 86 or higher, or 87 or higher, and 90 or lower. For example, when measuring polyester resin in the CIE Lab color space, L * The value could be 60-90, 70-90, 80-90, 86-90, or 87-90.

[0143] Furthermore, when measuring the CIE Lab color space, polyester resin is b * The value may be 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, and 0 or greater. For example, when measuring polyester resin in the CIE Lab color space, b * The value can be 0-10, 0-6, 0-5, 0-4, or 0-3.

[0144] Polyester resin is used when measuring in the Hunter Lab color space, L * From the value b * (L) * -b * The value may be 50 or higher, 60 or higher, 70 or higher, 80 or higher, 86 or higher, or 87 or higher. Furthermore, (L* -b * ) The upper limit of the value is not particularly limited. However, the upper limit can be, for example, 100 or less, 97 or less, 95 or less, 93 or less, or 90 or less. As a specific example, (L * -b * ) The value can be 70 to 100, 80 to 100, 70 to 90, or 80 to 90.

[0145] [Aspects of the Invention] Hereinafter, preferred embodiments are shown for the understanding of the present invention. However, the following examples are provided for facilitating the understanding of the present invention, and the scope of the present invention is not limited thereby.

[0146] [Preparation Example of Bis(2-hydroxyethyl) terephthalate] Example A1 Into a first reactor made of stainless steel (SUS), 1,000 g of waste polyester resin, 2,000 g of ethylene glycol, and 5.0 g of zinc acetate anhydride were charged. The temperature inside the reactor was raised to 180 °C, and depolymerization (the first glycolysis reaction) was carried out over 2 hours. The obtained reaction product was transferred to a second reactor and cooled to 150 °C. Then, 2,000 g of ethylene glycol was further added thereto, and depolymerization (the second glycolysis reaction) was carried out for 2 hours while maintaining the reactor temperature at 150 °C.

[0147] The obtained reaction product was cooled to 110 °C and subsequently subjected to pressure filtration for solid-liquid separation. The separated liquid reaction product was passed through a column filled with an ion exchange resin (BC107(H) made by Bonlite) to remove ionic impurities, and a mixture containing bis(2-hydroxyethyl) terephthalate and ethylene glycol was obtained. This mixture was transferred to a 10-liter distillation apparatus, and vacuum distillation was carried out at 130 °C to recover unreacted ethylene glycol. The reaction product from which ethylene glycol was removed was subjected to thin-film evaporation in a thin-film evaporator (VKL70-4S made by VTA) at 220 °C and 0.08 Torr to obtain 1,040 g of a product from which oligomers of dimer or higher were removed. Thereafter, the obtained result and 3,120 g of distilled water were mixed in a 20-liter glass reactor and heated to 70 °C to obtain a crude BHET aqueous solution.

[0148] 2.6 g of chloramine-T(CAT) and 2.6 g of NaClO were added to a crude BHET aqueous solution, and a chromophore decomposition reaction was carried out for 1 hour. The resulting decomposition products (results of the decomposition reaction) were sequentially passed through a column packed with cation exchange resin (Bonlite BC107(H)) and anion exchange resin (Samyang TRILITE® SAR10MBOH) to obtain a purified solution. 5.2 g of activated carbon was further added to the purified solution, and it was stirred for 30 minutes and then 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.

[0149] Example A2 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as in Example A1, except that the amount of chloramine-T was changed to 1.3 g.

[0150] Example A3 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as in Example A1, except that the same amount of HClO4 was used instead of NaClO.

[0151] Example A4 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as in Example A1, except that the same amount of H2O2 solution was used instead of NaClO.

[0152] Example A5 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as in Example A1, except that NaClO was not used.

[0153] Example A6 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as in Example A1, except that the amount of activated carbon was changed to 10.4 g.

[0154] Comparative Example A1 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as in Example A1, except that neither chloramine-T nor NaClO was used.

[0155] Comparative example A2 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as in Example A1, except that neither chloramine-T nor NaClO was used, and the amount of activated carbon was changed to 10.4 g.

[0156] Comparative example A4 After the chromophore removal reaction, the same procedure as in Example A1 was repeated, except that the sample was not passed through a column packed with cation exchange resin (Bonlite BC107(H)) and anion exchange resin (Samyang TRILITE® SAR10MBOH), to obtain regenerated bis(2-hydroxyethyl) terephthalate.

[0157] The methods for preparing recycled bis(2-hydroxyethyl) terephthalate in the examples and comparative examples are summarized in the table below.

[0158] [Table 1]

[0159] [Table 2]

[0160] <Examples of preparation of recycled polyester resin> Example B1 990 g of regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) prepared in Example A1, 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% by weight). 1,388 g of the regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) solution prepared above, 0.4 g of antimony trioxide as a catalyst, 0.3 g of triethyl phosphate as a stabilizer, and 0.2 g of cobalt acetate as a coloring agent were added to a 7-liter reactor capable of reacting under vacuum. The reactor temperature was raised to 190°C over 2 hours. Once the temperature reached 190°C, the reactor pressure was reduced from standard pressure to 200 Torr (absolute pressure: 200 mmHg) over 30 minutes. The polycondensation reaction was carried out under low vacuum for 1 hour while maintaining the reactor pressure at 200 Torr (absolute pressure: 200 mmHg). The reactor pressure was then reduced from 200 Torr (absolute pressure: 200 mmHg) to 5 Torr (absolute pressure: 5 mmHg) over 30 minutes. Simultaneously, the reactor temperature was raised to 280°C over 1 hour, and the polycondensation reaction was carried out under high vacuum while maintaining the reactor pressure below 1 Torr (absolute pressure: 1 mmHg). The mixture in the reactor was discharged to form strands, which were solidified with a coolant and then granulated to an average weight of approximately 12-14 mg. These granules were left at 150°C for 1 hour to crystallize and then supplied to a 20-liter reactor for solid-phase polymerization. Subsequently, nitrogen was introduced into the reactor at a rate of 50 liters / minute. In this process, the reactor temperature was raised from room temperature to 140°C at a rate of 40°C / hour, and maintained at 140°C for 3 hours to obtain recycled polyester resin.

[0161] Example B2 A recycled polyester resin was obtained by repeating the same procedure as in Example B1, except that the recycled bis(2-hydroxyethyl) terephthalate (r-BHET) prepared in Example A2 was used.

[0162] Example B3 A recycled polyester resin was obtained by repeating the same procedure as in Example B1, except that recycled bis(2-hydroxyethyl) terephthalate (r-BHET) prepared in Example A3 was used.

[0163] Example B4 A recycled polyester resin was obtained by repeating the same procedure as in Example B1, except that recycled bis(2-hydroxyethyl) terephthalate (r-BHET) prepared in Example A4 was used.

[0164] Example B5 A recycled polyester resin was obtained by repeating the same procedure as in Example B1, except that the recycled bis(2-hydroxyethyl) terephthalate (r-BHET) prepared in Example A5 was used.

[0165] Example B6 A recycled polyester resin was obtained by repeating the same procedure as in Example B1, except that the recycled bis(2-hydroxyethyl) terephthalate (r-BHET) prepared in Example A6 was used.

[0166] Comparative Example B1 A recycled polyester resin was obtained by repeating the same procedure as in Example B1, except that recycled bis(2-hydroxyethyl) terephthalate (r-BHET) prepared in Comparative Example A1 was used.

[0167] Comparative example B2 A recycled polyester resin was obtained by repeating the same procedure as in Example B1, except that recycled bis(2-hydroxyethyl) terephthalate (r-BHET) prepared in Comparative Example A2 was used.

[0168] Comparative example B4 A recycled polyester resin was obtained by repeating the same procedure as in Example B1, except that recycled bis(2-hydroxyethyl) terephthalate (r-BHET) prepared in Comparative Example A4 was used.

[0169] Test Example 1 The regenerated bis(2-hydroxyethyl) terephthalate prepared in each example and comparative example was tested as follows. (1) HPLC Approximately 0.01 g of regenerated BHET was diluted with approximately 20 ml of methanol and analyzed by high-performance liquid chromatography (HPLC) (model: Waters e2695, column: C18 (4.6 × 250 mm), 5 μm, UV detector: 242 nm, injection volume: 10 μl, eluent (gradient) A: H2O + H3PO4, B: acetonitrile). Subsequently, the peak area fraction (%) of the following components was obtained from the total peak area of ​​the HPLC. MHET: Monohydroxyethyl terephthalate BHET: Bis(2-hydroxyethyl) terephthalate, DEG-Ester-1:2-Hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate DEG-Ester-2: Bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate Dimer / trimer: BHET dimer / trimer (2) Absorbance For each crude BHET aqueous solution (after thin film evaporation) subjected to the chromophore decomposition reaction in the examples and comparative examples, the UV-Vis absorbance was measured in transmission mode together with a standard sample using an Agilent model (Cary 4000). The absorbance (in arbitrary units) at a wavelength of 400 nm is shown in Table 3 below. Furthermore, the absorbance spectra of several examples are shown in Figure 1. (3) Yellow index (promoted YI measurement) 20 g of ethylene glycol and 20 g of recycled BHET were mixed and dissolved in an oven at 170°C for 1 hour. Transmittance data of the solution was obtained using a Hunterlab Color Flex EZ with an Illuminant D65 at an observation angle of 2°. The yellow index (YI) value was calculated using the color analyzer in the software.

[0170] The results are shown in the table below.

[0171] [Table 3]

[0172] [Table 4]

[0173] As can be seen from the table above, the recycled BHET obtained in Examples A1 to A6 had a lower impurity content, lower absorbance and yellow index than the recycled BHET obtained in Comparative Examples A1 to A4, and exhibited superior quality and color.

[0174] Test Example 2 The polyester resins used in the examples and comparative examples were tested as follows. (1) DSC A differential scanning calorimeter (DSC, Q20 model, TA Instrument) was used. Each sample was placed in an aluminum pan and heated to 280°C at 10°C / min, maintained at 280°C for 5 minutes, and then cooled to 30°C at -300°C / min. Subsequently, the glass transition temperature (Tg) and melting temperature (Tm) were determined from the heat flow rate obtained when the temperature was raised to 280°C at 10°C / min. (2) Intrinsic viscosity (IV) Each polyester resin was dissolved in orthochlorophenol (OCP) at 150°C at a concentration of 1.2 g / dl to obtain a solution, and its intrinsic viscosity was measured using an Ubbelohde viscometer.

[0175] Specifically, the viscosity tube temperature was maintained at 35°C, and the time required for the solvent to pass through a specific part of the tube (flow time), as well as the time required for the solution to pass through to obtain the specific viscosity, were used to calculate the intrinsic viscosity. (3) Color (for PET chips) Each prepared 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 in the CIE LAB color space L. * a * , and b * It was measured as a value. The CIE LAB color space is a color space coordinate defined by the CIE (International Commission on Illumination) based on complementary colors perceived by humans, such as yellow-blue and green-red. *The value represents brightness (0 to 100; 0 is black, 100 is white), a * The value represents green-red (with 0 as the base, + is red and - is green), b * The value represents yellow-blue (0 is the base value; + means yellow, and - means blue).

[0176] The test results are shown in the table below.

[0177] [Table 5]

[0178] [Table 6]

[0179] As can be seen from 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 exhibited a higher whiteness index and superior color.

[0180] In particular, based on the above test results, it will be understood that the color of recycled BHET directly affects the color of the final polyester resin. Even slight differences in the quality of recycled BHET can result in significant differences in the quality of the final polyester resin.

Claims

1. A method for preparing regenerated bis(2-hydroxyethyl) terephthalate, (1) A step of obtaining a depolymerization product by glycolysis of waste polyester, (2) The step of reacting the depolymerization product with a chromophore decomposing agent to obtain a decomposition product in which the chromophore has been decomposed, (3) A step of adsorbing and removing the chromophore from the decomposition product using an ion exchange resin to obtain a purified product, (4) A step of crystallizing the purified product Methods that include...

2. A method for preparing recycled bis(2-hydroxyethyl) terephthalate according to claim 1, wherein the waste polyester has a yellow index (YI) of 10 or more when measured in solid phase.

3. The step of obtaining the depolymerization product is, The steps include obtaining a first depolymerization product by a first glycolysis reaction of the waste polyester at a temperature of 180 to 210°C, The steps include obtaining a second depolymerization product by a second glycolysis reaction of the first depolymerization product at a temperature of 150 to 170°C, and A method for preparing the regenerated bis(2-hydroxyethyl) terephthalate according to claim 1, comprising:

4. A method for preparing regenerated bis(2-hydroxyethyl) terephthalate according to claim 1, further comprising the step of distilling the water and residual solvent in the depolymerization product before step (2).

5. A method for preparing regenerated bis(2-hydroxyethyl) terephthalate according to claim 1, wherein the chromophore decomposing agent in step (2) comprises chloroamine.

6. A method for preparing regenerated bis(2-hydroxyethyl) terephthalate according to claim 5, wherein the chromophore decomposing agent in step (2) further comprises at least one of chlorates, chloric acid, and hydrogen peroxide.

7. A method for preparing recycled bis(2-hydroxyethyl) terephthalate according to claim 1, wherein the chromophore decomposed in step (2) comprises at least one selected from the group consisting of quinone dyes, azo dyes, and inorganic pigments.

8. A method for preparing regenerated bis(2-hydroxyethyl) terephthalate according to claim 1, wherein the ion exchange resin in step (3) adsorbs, in addition to the chromophore, at least one selected from the group consisting of halide ions, metal ions, charged fine particles, and their conjugate acid or conjugate base ions.

9. A method for preparing regenerated bis(2-hydroxyethyl) terephthalate according to claim 1, wherein the adsorption in step (3) includes an adsorption step using a strongly acidic cation exchange resin and an adsorption step using a strongly basic anion exchange resin.

10. A method for preparing regenerated bis(2-hydroxyethyl) terephthalate according to claim 1, further comprising the step of adding an adsorbent to the purified product and adsorbing it, wherein the adsorbent comprises activated carbon, prior to the crystallization in step (4).

11. A method for preparing regenerated bis(2-hydroxyethyl) terephthalate according to claim 10, wherein the activated carbon is used in an amount of 0.5 to 2 parts by weight per 100 parts by weight of bis(2-hydroxyethyl) terephthalate contained in the purified product.

12. A method for preparing regenerated bis(2-hydroxyethyl) terephthalate according to claim 1, wherein the crystallization is carried out in an aqueous solution, and the aqueous solution is slowly cooled from 40°C to 70°C to 15°C to 35°C.

13. A regenerated bis(2-hydroxyethyl) terephthalate prepared by the method described in claim 1, wherein the yellow index (YI) is 7 or less when measured for a solution dissolved in ethylene glycol at a concentration of 50% by weight.

14. A method for preparing polyester resin, (1) A step of obtaining a depolymerization product by glycolysis of waste polyester, (2) The step of reacting the depolymerization product with a chromophore decomposing agent to obtain a decomposition product in which the chromophore has been decomposed, (3) A step of adsorbing and removing the chromophore from the decomposition product using an ion exchange resin to obtain a purified product, (4) The step of crystallizing the purified product to obtain regenerated bis(2-hydroxyethyl) terephthalate, (5) The step of polymerizing the polyester resin using the recycled bis(2-hydroxyethyl) terephthalate. Methods that include...

15. A polyester resin prepared by the method described in claim 14.

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