Method for preparing bis(glycol) terephthalate oligomers and polyester resins

Abstract

According to the present invention, bis(glycol) terephthalate can be prepared by the transesterification reaction of glycol with bis(2-hydroxyethyl) terephthalate and then introduced into the polymerization reaction to increase the content of recycled raw materials in the polyester resin. Furthermore, purity can be improved by removing impurities through extraction of glycol by-products during the transesterification reaction, thus improving the quality of the final resin while reducing the amount of by-products from the polymerization reaction.

Description

Detailed Description of the Invention

[0001] [Technical field] The present invention relates to recycled bis(glycol) terephthalate oligomers and methods for using same to prepare polyester resins.

[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 containers, packaging films, audio and video films, etc. Furthermore, polyester is widely produced worldwide as an industrial material for medical fibers, tire cords, etc. In particular, polyester sheets or plates have good transparency and excellent mechanical strength, and as a result, are widely used as raw materials for cases, boxes, partitions, shelves, panels, packaging materials, building materials, interior and exterior materials, etc.

[0003] As a result, plastic waste, including polyester, is generated at an uncontrollable rate on a global scale every year. Recently, countries around the world have been creating regulations and plans for the reuse of waste plastic resources, including waste polyester. For example, there are attempts to use recycled resins in packaging materials used in various fields above a certain percentage. While physical and chemical methods are used to reuse waste polyester, physical recycling methods cannot guarantee purity and are not widely used.

[0004] In chemical recycling processes, the ester bonds of waste polyesters are broken to depolymerize them. Reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis are used. Among them, glycolysis is the decomposition of waste polyesters by adding glycols such as ethylene glycol or diethylene glycol at high temperatures. The resulting reaction product contains primarily bis(2-hydroxyethyl) terephthalate (BHET). Bis(2-hydroxyethyl) terephthalate may be used as a raw material for preparing unsaturated polyester or ester polyols after their crystallization or purification.

[0005] However, from the viewpoint of environmental friendliness, it is more meaningful to convert waste PET products, which generally have a short lifespan, into engineering polyester products with a long lifespan or environmentally friendly biodegradable polyester products. In this regard, attempts have recently been made to regenerate polyester resins other than PET by transesterification of waste PET and glycol. This reaction has problems in that an excessive amount of glycol is used and the reaction time is long, resulting in the formation of large amounts of by-products such as cyclic ester compounds as a side reaction of glycol.

[0006] [Prior art document] [Non-Patent Document 1] Park, SH, Kim, SH, Poly(ethylene terephthalate) recycling for high value added textiles, Fashion and Textiles 1, 1 (2014)

[0007] [DISCLOSURE OF THE INVENTION] [Technical issues] The present inventors have attempted to develop a technology for recycling BHET obtained by depolymerization of waste PET-based products into various engineering polyester products or environmentally friendly biodegradable polyester products, which can increase the content of recycled raw materials while improving the quality and economic efficiency of the final products.

[0008] However, recycled BHET generally has low purity due to impurities formed from the reagents used in the depolymerization process and side reactions, and therefore requires a separate process, such as ion exchange or recrystallization, to purify it, thereby increasing costs. Furthermore, glycol monomers (DEG, ISB, CHDM, etc.) must be used in addition to BHET to produce copolyester resins, making it difficult to increase the recycled raw material content in the final resin. When excessive amounts of BHET are added to the polymerization reaction to increase the recycled raw material content in conventional processes, an increase in glycol by-products occurs.

[0009] As a result of research conducted by the present inventors, it was discovered that if the glycol for copolymerization is first subjected to a transesterification reaction with BHET to prepare bis(glycol) terephthalate, which is then subjected to a polymerization reaction, the content of recycled raw materials in the polyester resin can be increased; the purity can be improved by collecting the glycol by-product during the transesterification reaction and removing impurities, thereby enhancing the quality of the final resin along with the reduction of by-products during the polymerization reaction.

[0010] Therefore, it is an object of the present invention to provide a method for preparing a polyester resin having a high content of recycled raw materials such as BHET, reduced by-products of the polymerization reaction, and excellent quality of the final resin and polyester resin prepared thereby.

[0011] [Solution to the problem] According to the present invention, there is provided a method for preparing a polyester resin, the method comprising the steps of: subjecting bis(2-hydroxyethyl) terephthalate to a transesterification reaction with a glycol having three or more carbon atoms; collecting and removing ethylene glycol as a by-product formed during the transesterification reaction; obtaining bis(glycol) terephthalate oligomers as products of the transesterification reaction; and conducting polymerization using the bis(glycol) terephthalate oligomers.

[0012] According to the present invention, there is provided a method for preparing bis(glycol) terephthalate oligomers, the method comprising the steps of subjecting bis(2-hydroxyethyl) terephthalate to a transesterification reaction with a glycol having three or more carbon atoms; and collecting and removing ethylene glycol as a by-product formed during the transesterification reaction.

[0013] Further provided in accordance with the subject invention are polyester resins and bis(glycol) terephthalate oligomers prepared by the above methods.

[0014] [Advantageous effects of the invention] According to the present invention, bis(2-hydroxyethyl) terephthalate, a recycled raw material obtained by depolymerization of waste polyester, is first subjected to a transesterification reaction with a glycol appropriate for the desired copolymerization composition to prepare a bis(glycol) terephthalate oligomer, which is then subjected to a polymerization reaction. As a result, the content of the recycled raw material can be increased without adding an excessive amount of bis(2-hydroxyethyl) terephthalate to the polymerization reaction of the polyester resin.

[0015] According to the present invention, in particular, since the glycol by-product (ethylene glycol) is collected and removed during the transesterification reaction, the glycol by-product formed in the subsequent polymerization reaction of the polyester resin can be reduced, and the recovered glycol can be reused in the polymerization reaction, thereby also reducing raw material and process costs. The removal of impurities can improve purity, resulting in a final resin with enhanced quality, which can be applied to the preparation of environmentally friendly polyester products. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic representation of a method for preparing a polyester resin according to one embodiment of the present invention.

[0017] [Best Mode for Carrying Out the Invention] As used herein, the terms referring to each component are used to distinguish one from the other and are not intended to limit the scope of the embodiments. Furthermore, as used herein, the singular "a," "an," or "the" is to be construed as including the plural as well, unless the context clearly dictates otherwise.

[0018] In this specification, terms such as first, second, etc. are used to describe various components. However, the components should not be limited by the terms. The terms are used to distinguish one element from another.

[0019] As used herein, the term "comprise" is intended to specify certain properties, regions, steps, processes, elements and / or components. It does not exclude the presence or addition of any other properties, regions, steps, processes, elements and / or components, unless specifically stated to the contrary.

[0020] The molecular weight of the compounds or polymers described herein, e.g., number average molecular weight or weight average molecular weight, is, as is well known, a relative mass based on carbon 12. Although the units are not given, if necessary, it may be understood as the molecular weight (g / mol) of the same numerical value.

[0021] As used herein, a "derivative" of a particular compound refers to a compound obtained by partially converting the compound by chemical reaction or by combining it with other components, thereby containing the major portion of the compound.

[0022] As used herein, a unit or group "derived from" a particular component refers to a portion of the component that is contained in the final product through a chemical reaction, such as a polymerization reaction. It may be that the portion is modified during the reaction, or it may exist in a form that is combined with other components. For example, a unit or group derived from at least one monomer or oligomer is contained in the chain that constitutes the polymer.

[0023] As used herein, recycled monomers or oligomers may refer to monomers or oligomers obtained by decomposing, depolymerizing, reprocessing, or repolymerizing waste plastics, such as waste polyester, by physical or chemical methods, or by polymerizing raw materials containing or derived therefrom.

[0024] By way of example, the bis(2-hydroxyethyl) terephthalate (BHET) used as starting material for the process according to the invention may be a recycled monomer obtained by depolymerization of waste polyester.

[0025] As another example, recycled monomers may also be used as glycols having three or more carbon atoms that are subjected to transesterification in the process of the present invention. As a specific example, at least one type of recycled glycol may be used, such as recycled 1,4-cyclohexanedimethanol (r-CHDM), recycled diethylene glycol (r-DEG), and recycled isosorbide (r-ISB).

[0026] As another example, recycled monomers may also be used as comonomers in the polymerization reaction of polyester resins in the method of the present invention. As a specific example, at least one type selected from recycled dicarboxylic acids and recycled diols may be used. As a more specific example, at least one type of recycled monomer may be used, such as recycled ethylene glycol (r-EG), recycled 1,4-cyclohexanedimethanol (r-CHDM), recycled diethylene glycol (r-DEG), recycled isosorbide (r-ISB), recycled terephthalic acid (r-TPA), recycled isophthalic acid (r-IPA), and recycled dimethyl terephthalate (r-DMT).

[0027] Such recycled monomers may be obtained directly from waste plastics, such as waste polyester, by known methods, or may be purchased and used commercially.

[0028] Furthermore, the bis(glycol) terephthalate oligomer (e.g., BHDT oligomer, BHIT oligomer, BHCT oligomer, etc.) obtained as the product of the transesterification reaction according to the present invention may be a recycled oligomer obtained by decomposing, depolymerizing, reprocessing, and repolymerizing waste plastics such as waste polyesters by physical or chemical methods.

[0029] Such recycled raw materials, such as recycled monomers or oligomers, can be used in the preparation of polyester resins in the present invention.

[0030] The present invention provides a method for preparing a polyester resin, the method comprising the steps of: subjecting bis(2-hydroxyethyl) terephthalate to a transesterification reaction with a glycol having three or more carbon atoms; collecting and removing ethylene glycol as a by-product formed during the transesterification reaction; obtaining bis(glycol) terephthalate oligomers as products of the transesterification reaction; and conducting polymerization using the bis(glycol) terephthalate oligomers.

[0031] FIG. 1 is a schematic diagram illustrating a method for preparing a polyester resin according to one embodiment of the present invention. Referring to FIG. 1, the method for preparing a polyester resin according to one embodiment includes the steps of preparing recycled bis(2-hydroxyethyl) terephthalate (S100) obtained by depolymerization of waste polyester, subjecting it to a transesterification reaction with a glycol having three or more carbon atoms (S200), collecting and removing the by-product ethylene glycol (S500), and obtaining bis(glycol) terephthalate oligomers (S300). For subsequent polymerization, bis(2-hydroxyethyl) terephthalate, bis(glycol) terephthalate oligomers, and other monomer mixtures are added to an esterification reaction, followed by a polycondensation reaction (S400) to obtain a polyester resin. Glycol by-products may also be collected and removed during the esterification and / or polycondensation reactions (S500). The glycol thus recovered may be purified (S600) and then re-fed to the transesterification and / or polymerization steps.

[0032] According to the present invention, bis(2-hydroxyethyl) terephthalate, a recycled raw material obtained by depolymerization of waste polyester, is first subjected to a transesterification reaction with a glycol appropriate for the desired copolymer composition to prepare a bis(glycol) terephthalate oligomer, which is then subjected to a polymerization reaction. As a result, the content of the recycled raw material can be increased without adding an excessive amount of bis(2-hydroxyethyl) terephthalate to the polymerization reaction of the polyester resin.

[0033] In particular, according to the present invention, since the glycol by-product (ethylene glycol) is collected and removed during the transesterification reaction, the glycol by-product formed in the subsequent polymerization reaction of the polyester resin can be reduced, and the recovered glycol can be reused in the polymerization reaction, thereby also reducing raw material and process costs. Purity can be improved by removing impurities, resulting in a final resin with enhanced quality, which can be applied to the preparation of environmentally friendly polyester products.

[0034] The invention is described in more detail below.

[0035] (bis(2-hydroxyethyl) terephthalate) Bis(2-hydroxyethyl) terephthalate is an ester of two ethylene glycols and one terephthalic acid. It is a compound formed as an intermediate in the process of preparing polyesters, such as polyethylene terephthalate (PET), by the polymerization of ethylene glycol and terephthalic acid or its esters.

[0036] The bis(2-hydroxyethyl) terephthalate used in the present invention can be obtained by depolymerization of waste polyester. For example, bis(2-hydroxyethyl) terephthalate can be obtained from waste polyesters having repeating units of ethylene glycol and terephthalic acid, such as polyethylene terephthalate (PET) or glycol-modified polyethylene terephthalate (PETG). Specifically, it can be obtained by well-known depolymerization methods such as glycolysis, hydrolysis, and methanolysis. In particular, bis(2-hydroxyethyl) terephthalate can be obtained by depolymerizing waste polyethylene terephthalate using ethylene glycol and then purifying it.

[0037] The bis(2-hydroxyethyl) terephthalate obtained by the depolymerization of the above-mentioned waste polyester is referred to as "regenerated bis(2-hydroxyethyl) terephthalate (regenerated BHET)" or abbreviated as r-BHET or rBHET, and should be understood as being distinct from the pure BHET compound. Specifically, regenerated BHET may contain by-products formed by side reactions with reagents or solvents used in various chemical steps during the depolymerization of waste polyester. Thus, BHET regenerated by a conventional depolymerization process contains organic and inorganic impurities in addition to BHET as the main component; therefore, its purity is low. For this reason, regenerated BHET can also be considered a type of composition containing two or more components, i.e., a BHET composition. Such regenerated BHET may be used as a polymerization raw material for producing polyester resins.

[0038] The impurities contained in the recycled BHET may include, for example, diethylene glycol derivatives and unreacted monomers. The total content of impurities contained in the recycled BHET may be 10% by weight or more, 15% by weight or more, or 20% by weight or more, and may be 40% by weight or less, 35% by weight or less, 30% by weight or less, or 25% by weight or less.

[0039] The purity of the regenerated BHET may be evaluated using liquid chromatography, etc. Specifically, the purity of the regenerated BHET may be calculated by measuring the fraction (%) of the peak area of BHET from the total peak area in a spectrum obtained using high-performance liquid chromatography (HPLC).

[0040] For example, the purity of the recycled BHET may be 97% or less, 90% or less, 85% or less, or 80% or less, or 60% or more, 65% or more, or 70% or more. Specifically, the purity of the BHET introduced into the transesterification reaction of the present invention may be 60% to 97%, particularly 65% to 90%, 65% to 85%, or 70% to 80%.

[0041] (glycol) The glycols used in the transesterification reaction of the present invention are used in a transesterification reaction with bis(2-hydroxyethyl) terephthalate to form the residues in the bis(glycol) terephthalate oligomers as products, which then constitute the polymer chains of the final polymerized polyester resin.

[0042] The glycols used in the present invention may be glycols having 3 or more carbon atoms that replace the ethylene glycol residue in the transesterification reaction.

[0043] In particular, glycol has a boiling point 10° C. or more higher than that of ethylene glycol, which is advantageous for purification by fractional distillation during the transesterification reaction.

[0044] Specifically, the glycol used in the transesterification reaction of the present invention may be a glycol monomer other than ethylene glycol (eg, an alkylene glycol having 3 or more carbon atoms) or a polymeric glycol (eg, a polyether).

[0045] As a more specific example, the glycol may be at least one selected from glycol monomers having 3 to 20 carbon atoms and a molecular weight of less than 500, and polymeric glycols having a number average molecular weight of 400 to 5,000.

[0046] The number of carbon atoms in the glycol monomer may be, for example, 3 or more, or 4 or more, and may be 20 or less, 15 or less, 12 or less, 10 or less, or 8 or less.

[0047] Specifically, the glycol monomer may be an aliphatic diol having 3 to 20 carbon atoms. Furthermore, the aliphatic diol may be a chain or a cyclic type.

[0048] Specific examples of glycols having 3 or more carbon atoms include 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, isosorbide, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, The polyisoprene may contain at least one selected from the group consisting of 1,2-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, a copolymer of ethylene oxide and tetrahydrofuran, an ethylene oxide-added polypropylene glycol, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, poly-1,5-pentanediol, and derivatives thereof.

[0049] As a more specific example, the glycol monomer may include at least one selected from the group consisting of diethylene glycol, isosorbide, 1,4-cyclohexanedimethanol, and derivatives thereof. Such glycol monomer may be virgin glycol.

[0050] As another example, the glycol having three or more carbon atoms may include at least one type of recycled glycol obtained by depolymerization of waste polyester. As a specific example, the recycled glycol may be selected from the group consisting of recycled 1,4-cyclohexanedimethanol, recycled diethylene glycol, and recycled isosorbide. However, the types of recycled glycols that can be used in the present invention are not limited thereto. Any recycled glycol that can be subjected to a transesterification reaction may be used. Such recycled glycol may be used in the transesterification reaction to completely replace virgin glycol. Alternatively, recycled glycol and virgin glycol may be mixed in a specific ratio and used in the transesterification reaction. The mixing ratio of recycled glycol may be, for example, 0 mol% or more, 1 mol% or more, 10 mol% or more, 20 mol% or more, 30 mol% or more, 50 mol% or more, or 60 mol% or more, and 100 mol% or less, 99 mol% or less, 90 mol% or less, 50 mol% or less, or 40 mol% or less, particularly 1 mol% to 100 mol%, 1 mol% to 99 mol%, or 30 mol% to 100 mol%, based on the number of moles of total glycol.

[0051] Specific examples of the derivative of 1,4-cyclohexanedimethanol may include 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate, 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol, or a mixture thereof. More specifically, the derivative may be a mixture containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a molar ratio of 1:1 to 1:5 or 1:2 to 1:4.

[0052] The glycol monomer may have a molecular weight of less than 500, less than 400, less than 350, less than 300, less than 250, for example.

[0053] The polymer glycol may be selected from the group consisting of, for example, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, a copolymer of ethylene oxide and tetrahydrofuran, ethylene oxide-added polypropylene glycol, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, and poly-1,5-pentanediol. More specifically, the polymer glycol may include at least one selected from the group consisting of polytetramethylene glycol, polycarbonate diol, polypropylene glycol, and ethylene oxide-added polypropylene glycol.

[0054] The polymer glycol may have a number average molecular weight of, for example, 400 or more, 500 or more, 600 or more, 700 or more, or 800 or more, and 6,000 or less, 5,000 or less, 4,000 or less, or 3,000 or less. As a specific example, the number average molecular weight of the polymer glycol may be 400 to 5,000. More specifically, it may be preferably 1,000 to 3,000 from the viewpoint of reducing phase separation.

[0055] The polymer glycol is used in an amount of 5% to 75% by weight, preferably 10% to 60% by weight, and especially 15% to 50% by weight, based on the weight of the final polyester resin, which is advantageous for achieving a high molecular weight while improving the elastic modulus of the polyester resin.

[0056] (Transesterification reaction) Glycol and bis(2-hydroxyethyl) terephthalate are subjected to a transesterification reaction. [ka]

[0057] In Reaction Scheme 1, R is a glycol group having 3 or more carbon atoms, excluding the OH groups at both ends. For example, R may be an alkylene group having 3 to 20 carbon atoms, or a group in which two or more identical or different alkylene groups having 2 to 10 carbon atoms are connected via an ether group or a carbonate group. As another example, R may be a group of 3 to 20 carbon atoms containing one or more rings, which may be aliphatic or aromatic and may contain one or more heteroatoms (e.g., O, N, and S).

[0058] In Reaction Scheme 1, m is a number ranging from 2 to 10, for example.

[0059] The transesterification reaction may be carried out in the presence of a catalyst, so when glycol, acid, or bis(2-hydroxyethyl) terephthalate is fed to the reactor, the catalyst may be fed along with it.

[0060] As a catalyst for the transesterification reaction, for example, at least one selected from the group consisting of zinc-based catalysts, titanium-based catalysts, germanium-based catalysts, antimony-based catalysts, aluminum-based catalysts, and tin-based catalysts may be used.

[0061] Examples of zinc-based catalysts include zinc acetate, zinc acetate hydrate, zinc chloride, zinc sulfate, zinc sulfide, zinc carbonate, zinc citrate, zinc gluconate, or mixtures thereof. Examples of titanium-based catalysts include tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, triethanolamine titanate, acetylacetonato titanate, ethyl acetoacetate titanate, isostearyl titanate, titanium dioxide, etc. Examples of germanium-based catalysts include germanium dioxide, germanium tetrachloride, germanium ethylene glycol oxide, germanium acetate, or combinations thereof. Specifically, germanium dioxide can be used as the germanium-based catalyst. Both crystalline and amorphous germanium dioxide can be used, and glycol-soluble germanium dioxide can also be used.

[0062] The amount of transesterification catalyst used can vary depending on the reaction conditions and the catalyst used. For example, a metal-based catalyst (e.g., a titanium-based catalyst, a tin-based catalyst) may be used in an amount of 0.0001 to 0.05 parts by weight per 100 parts by weight of glycol and bis(2-hydroxyethyl) terephthalate fed to the reactor.

[0063] The transesterification reaction may be carried out batchwise or continuously.

[0064] For example, glycol, or glycol together with acid, may be fed to a reactor, and the temperature may be increased until the temperature reaches a specific level, at which point bis(2-hydroxyethyl) terephthalate may be fed. The feeding of bis(2-hydroxyethyl) terephthalate may be carried out, for example, while the by-product ethylene glycol is collected and removed in a nitrogen atmosphere at a temperature of 120°C to 280°C. As a specific example, the collection and removal of ethylene glycol may be carried out at a temperature of 120°C to 260°C and under a pressure of 0.1 kgf / cm. 2 ~2.0kgf / cm 2The collected and removed ethylene glycol may be purified and then fed back to at least one of the transesterification reaction and the polymerization reaction.

[0065] The bis(2-hydroxyethyl) terephthalate may be fed all together and subjected to the transesterification reaction with glycol. Alternatively, the bis(2-hydroxyethyl) terephthalate may be introduced in portions or continuously into the transesterification reaction with glycol. Furthermore, the bis(2-hydroxyethyl) terephthalate may be fed to the transesterification reaction in the form of a powder or a solution. A solution of bis(2-hydroxyethyl) terephthalate may be prepared by mixing bis(2-hydroxyethyl) terephthalate with at least one solvent selected from water and ethylene glycol at 60°C to 190°C and adjusting the concentration to 50% to 95% by weight.

[0066] According to one embodiment, bis(2-hydroxyethyl) terephthalate may be introduced into the transesterification reaction with glycol in two or more separate introductions. The number of separate introductions may be two or more, three or more, four or more, or five or more, and may be 100 or less, 50 or less, 30 or less, 20 or less, 15 or less, or 10 or less. Specific examples include 2 to 30 or 3 to 15 separate introductions. The time interval between separate introductions may be determined by dividing the total introduction time by the number of separate introductions. The total introduction time may be, for example, one hour or more, two hours or more, or five hours or less, or four hours or less. Furthermore, the amount introduced at one time during separate introductions may be determined by dividing the total amount of bis(2-hydroxyethyl) terephthalate introduced into the reaction by the number of separate introductions.

[0067] According to another embodiment, bis(2-hydroxyethyl) terephthalate is continuously introduced into the transesterification reaction with glycol. The total time for continuous introduction may be, for example, 1 hour or more, or 2 hours or more, and 5 hours or less, or 4 hours or less. For example, continuous introduction may involve introducing a fixed amount of bis(2-hydroxyethyl) terephthalate per hour. The amount introduced per hour may be calculated by dividing the total amount of bis(2-hydroxyethyl) terephthalate introduced into the reaction by the total introduction time. As a specific example, bis(2-hydroxyethyl) terephthalate may be prepared in powder form or dissolved in water at about 80 to 100°C to form an aqueous BHET solution having a concentration of about 10 to 20% by weight, and may be continuously introduced. Continuous introduction may be carried out from the beginning of the transesterification reaction until 1 hour before the completion of the reaction. A dropping funnel may be used at the laboratory level, or at a commercial level, a metered feeder may be used for continuous introduction of a fixed amount per hour.

[0068] Once the supply of bis(2-hydroxyethyl) terephthalate is complete, the reaction conditions may be maintained until the transesterification reaction is complete. Furthermore, the process of collecting and removing ethylene glycol as a by-product may be continued during the transesterification reaction. The collection and removal of ethylene glycol may be carried out by a distillation process using the difference in boiling point from the other components. The distilled ethylene glycol may be recovered by cooling and reused in other processes.

[0069] The end point of the transesterification reaction may be determined by taking into account the theoretical amount of ethylene glycol formed from bis(2-hydroxyethyl) terephthalate by the transesterification reaction, or as the point at which no more by-products are released.

[0070] The pressure (absolute pressure) during the transesterification reaction is, for example, 0.1 kgf / cm 2 More than 0.2kgf / cm 2 or more, or 0.5kgf / cm 2 or more, and 2.5kgf / cm2 Below, 2.0kgf / cm 2 or less, or 1.5kgf / cm 2 Below, especially 0.5kgf / cm 2 ~2.0kgf / cm 2 may be.

[0071] Furthermore, the temperature during the transesterification reaction may be 120°C or higher, 140°C or higher, 160°C or higher, 180°C or higher, or 200°C or higher, and may be 300°C or lower, 280°C or lower, 260°C or lower, 250°C or lower, or 220°C or lower.

[0072] As a specific example, the transesterification reaction can be carried out at a temperature of 120°C to 260°C and a pressure of 0.1 kgf / cm 2 ~2.0kgf / cm 2 The pressure may be

[0073] Additionally, the transesterification reaction may be carried out under a nitrogen atmosphere.

[0074] The pressure and temperature conditions during the transesterification reaction may be appropriately adjusted depending on the specific properties of the polyester to be produced, the ratio of each component, or process conditions. For example, the transesterification reaction may be carried out at a temperature of 180°C or higher to facilitate the collection and removal of ethylene glycol, a by-product formed during the transesterification reaction. Furthermore, it may be carried out at a temperature 10°C lower than the boiling point of glycol to reduce the loss of glycol during the transesterification reaction.

[0075] The products of the transesterification reaction primarily comprise bis(glycol) terephthalate oligomers and their derivatives, in which the ethylene glycol residues in bis(2-hydroxyethyl) terephthalate are replaced with other glycol residues.

[0076] Accordingly, the present invention provides a method for preparing bis(glycol) terephthalate oligomers, the method comprising the steps of subjecting bis(2-hydroxyethyl) terephthalate to a transesterification reaction with a glycol having three or more carbon atoms; and collecting and removing ethylene glycol as a by-product formed during the transesterification reaction.

[0077] Furthermore, the present invention provides a bis(glycol) terephthalate oligomer, i.e., a recycled bis(glycol) terephthalate oligomer prepared by the above-described method.

[0078] According to one embodiment, the bis(glycol) terephthalate oligomer obtained by the transesterification reaction comprises a compound represented by the following formula 1: [ka]

[0079] In formula 1, —OR—OH is a group derived from a glycol having 3 or more carbon atoms, and m is a number ranging from 2 to 10, for example.

[0080] As described above, the bis(glycol) terephthalate oligomer may have 2 to 10 repeating units. For example, the number of repeating units in the bis(glycol) terephthalate oligomer may be 2 or more, or 3 or more, and 10 or less, 8 or less, 6 or less, or 4 or less.

[0081] In Formula 1, R is a group derived from a glycol having three or more carbon atoms. For example, R may be an alkylene group having 3 to 20 carbon atoms, or a group in which two or more identical or different alkylene groups having 2 to 10 carbon atoms are connected via an ether group or a carbonate group. As another example, R may be a group of 3 to 20 carbon atoms containing a single or multiple rings, where the rings may be aliphatic or aromatic and may contain one or more heteroatoms (e.g., O, N, and S).

[0082] As a specific example, Formula 1 may be a compound in which R is a group derived from diethylene glycol, i.e., a bis(diethylene glycol) terephthalate oligomer (hereinafter abbreviated as BHDT oligomer). As another specific example, Formula 1 may be a compound in which R is a group derived from isosorbide, i.e., a bis(isosorbide) terephthalate oligomer (hereinafter abbreviated as BHIT oligomer). As another specific example, Formula 1 may be a compound in which R is a group derived from 1,4-cyclohexanedimethanol, i.e., a bis(1,4-cyclohexanedimethanol) terephthalate oligomer (hereinafter abbreviated as BHCT oligomer). [ka]

[0083] In the formulae 1a to 1c, m is a number ranging from 2 to 10.

[0084] The bis(glycol) terephthalate oligomer may comprise two or more compounds represented by Formula 1 or derivatives thereof.

[0085] Since impurities in the bis(glycol) terephthalate oligomer are removed in the process of collecting and removing by-products such as glycol formed during the transesterification reaction, its purity can be increased compared to that of the starting material, bis(2-hydroxyethyl) terephthalate. For example, the bis(glycol) terephthalate obtained by the transesterification reaction may have a purity of 80% or more. More specifically, the purity of the bis(glycol) terephthalate oligomer may be 85% or more, 90% or more, or 95% or more. Specifically, the purity may be 80% to 99.9%.

[0086] (Preparation of Polyester Resin) A polyester resin is then prepared by polymerization using bis(glycol) terephthalate oligomer.

[0087] In the polymerization step, the esterification reaction (first polymerization reaction step) and the polycondensation reaction (second polymerization reaction step) may be carried out sequentially.

[0088] The polymerizing step may be a step of preparing a copolymer, for example, the polymerizing step may include the steps of subjecting a bis(glycol) terephthalate oligomer and at least one comonomer to an esterification reaction; and subjecting the esterification reaction product to polycondensation to obtain a copolymer.

[0089] Reaction Scheme 2 below schematically illustrates a copolymerization reaction using BHET as a comonomer, in which glycol may be formed as a by-product. [ka]

[0090] In Reaction Scheme 2, R is a group derived from a glycol having 3 or more carbon atoms.

[0091] According to the present invention, the step of collecting and removing ethylene glycol may further be carried out during at least one of the esterification reaction and the polycondensation reaction, and the collected and removed ethylene glycol may be purified and then re-fed to at least one of the transesterification step and the polymerization step.

[0092] As described above, additional recycled monomers may be added to the esterification reaction in addition to the bis(glycol) terephthalate oligomer, or monomers other than the recycled raw material may also be added. For example, at least one comonomer selected from the group consisting of bis(2-hydroxyethyl) terephthalate, dicarboxylic acids, dicarboxylic acid derivatives, diols, and diol derivatives may be further introduced into the esterification reaction.

[0093] As specific examples, the dicarboxylic acid may include terephthalic acid or isophthalic acid; the dicarboxylic acid derivative may include dimethyl terephthalate or dimethyl isophthalate; the glycol may include diethylene glycol, 1,4-cyclohexanedimethanol, isosorbide, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3 The diol derivative may include 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol. Such comonomers may be virgin monomers.

[0094] In another example, the at least one comonomer may include recycled monomers obtained by depolymerization of waste polyester. Specifically, the at least one comonomer may include at least one recycled monomer selected from the group consisting of recycled dicarboxylic acids, recycled dicarboxylic acid derivatives, recycled diols, and recycled diol derivatives. More specifically, the recycled monomer may be selected from the group consisting of recycled ethylene glycol, recycled 1,4-cyclohexanedimethanol, recycled diethylene glycol, recycled isosorbide, recycled terephthalic acid, recycled dimethyl terephthalate, recycled isophthalic acid, and recycled dimethyl isophthalate. However, the types of recycled monomers that can be used as comonomers in the present invention are not limited thereto. Any recycled monomers that can be used in the preparation of polyester resins can also be used. Such recycled monomers may be used in the polymerization of polyester resins by completely replacing virgin monomers. Alternatively, recycled and virgin monomers may be mixed in a specific ratio and used in the polymerization of polyester resins. The mixing ratio of the recycled monomer may be, for example, 0 mol% or more, 1 mol% or more, 10 mol% or more, 20 mol% or more, 30 mol% or more, 50 mol% or more, or 60 mol% or more, and 100 mol% or less, 99 mol% or less, 90 mol% or less, 50 mol% or less, or 40 mol% or less, particularly 1 mol% to 100 mol%, 1 mol% to 99 mol%, or 30 mol% to 100 mol%, based on the number of moles of the total monomers.

[0095] The esterification reaction may be carried out in the presence of an esterification catalyst. For example, a zinc-based compound may be used. Specific examples of zinc-based catalysts include zinc acetate, zinc acetate hydrate, zinc chloride, zinc sulfate, zinc sulfide, zinc carbonate, zinc citrate, zinc gluconate, or a mixture thereof.

[0096] The esterification reaction can be carried out at a pressure of, for example, 0 kgf / cm 2 ~10.0kgf / cm 2The esterification reaction may be carried out at a pressure of 0.01 to 0.15 kg / cm and a temperature of 150 to 300°C. The esterification reaction conditions may be suitably adjusted depending on the specific properties of the polyester to be produced, the ratio of each component, or the process conditions. Specifically, the pressure in the esterification reaction may be adjusted to 0.01 to 0.15 kg / cm. 2 ~5.0kg / cm 2 , especially 0.1 kg / cm 2 ~3.0kg / cm 2 Furthermore, the temperature in the esterification reaction may be 200°C to 270°C, particularly 240°C to 260°C.

[0097] The esterification reaction may be carried out batchwise or continuously. Furthermore, the raw materials, recycled BHET, dicarboxylic acid, and diol, may be introduced into the reactor separately, or two or more raw materials may be introduced in a mixed state. They may be introduced in solid, liquid, or slurry form. For example, the dicarboxylic acid, diol, and recycled BHET may be added individually or in combination, or may be mixed with pre-prepared terephthalic acid oligomers. Terephthalic acid oligomers may be prepared, for example, by reacting terephthalic acid with a diol such as ethylene glycol, cyclohexanedimethanol, and isosorbide. In another example, they may be introduced in the form of a slurry in which the dicarboxylic acid and recycled BHET are mixed with the diol.

[0098] More specifically, a diol such as isosorbide, which is solid at room temperature, may be dissolved in water or ethylene glycol and then mixed with a dicarboxylic acid such as terephthalic acid to prepare a slurry. Alternatively, isosorbide may be melted at 60°C or higher and then mixed with a dicarboxylic acid such as terephthalic acid and another diol to prepare a slurry. Furthermore, water may be added to the mixed slurry to help increase the fluidity of the slurry. Furthermore, in a continuous system, a liquid feedstock (e.g., a solution of recycled BHET) may be continuously fed to the reactor using a pump or the like. To achieve a target daily production volume, the hourly feed rate of the feedstock can be calculated by dividing the total amount of the feedstock by the time.

[0099] The mixture of bis(glycol) terephthalate oligomer, other monomers, and additive components is left in the esterification reactor for a certain period of time, for example, 1 to 24 hours or 4 to 10 hours, and then transferred to a polycondensation reactor. The polycondensation reaction can produce a polyester resin having a relatively low molecular weight by melt polymerization. Furthermore, a polyester resin having a relatively high molecular weight can be produced by solid-state polymerization after melt polymerization.

[0100] The temperature in the polycondensation reaction may be 150°C to 300°C, preferably 200°C to 290°C, and especially 260°C to 280°C. Furthermore, the pressure in the polycondensation reaction may be 0.01 mmHg to 600 mmHg, preferably 0.05 mmHg to 200 mmHg, and especially 0.1 mmHg to 100 mmHg. When reduced pressure conditions are used in the polycondensation reaction, glycol, a by-product of the polycondensation reaction, can be collected and removed from the system. If the pressure in the polycondensation reaction exceeds the range of 0.01 mmHg to 400 mmHg, removal of the by-product may be insufficient. Furthermore, if the temperature in the polycondensation reaction is lower than 150°C, glycol, a by-product of the reaction, cannot be effectively collected and removed from the system; therefore, the intrinsic viscosity of the final reaction product is low, resulting in reduced physical properties of the final polyester resin. If the temperature in the polycondensation reaction exceeds 300° C., the possibility of yellowing of the final polyester resin increases. Furthermore, the polycondensation reaction may be carried out for a required time, for example, an average residence time of 1 hour to 24 hours, until the intrinsic viscosity of the final reaction product reaches a suitable level.

[0101] Furthermore, the polycondensation reaction may be carried out in the presence of a polycondensation catalyst. The polycondensation catalyst may be, for example, a titanium-based compound, a germanium-based compound, an antimony-based compound, an aluminum-based compound, a tin-based compound, or a mixture thereof. Examples of titanium-based compounds include tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, lactate titanate, triethanolamine titanate, acetylacetonato titanate, ethyl acetoacetate titanate, isostearyl titanate, and titanium dioxide. Examples of germanium-based compounds include germanium dioxide, germanium tetrachloride, germanium ethylene glycol oxide, germanium acetate, or a mixture thereof. Preferably, germanium dioxide is used. Both crystalline and amorphous germanium dioxide may be used, and glycol-soluble germanium dioxide may also be used. The amount of polycondensation catalyst used may be such that the amount of elemental titanium is about 1 ppm to 100 ppm, more preferably about 1 ppm to 50 ppm, based on the weight of the polyester resin.

[0102] In addition to the polycondensation catalyst, a stabilizer, a pigment, a crystallizing agent, an antioxidant, a branching agent, etc. may also be used. The timing of adding these additives is not particularly limited, and they may be added at any time during the preparation step of the polyester resin.

[0103] Phosphorus-based compounds, such as phosphoric acid, trimethyl phosphate, triethyl phosphate, and triethyl phosphonoacetate, are commonly used as stabilizers. Their added amount may be about 10 ppm to 200 ppm based on the amount of elemental cobalt relative to the weight of the polyester resin. Furthermore, common pigments such as cobalt acetate and cobalt propionate may be added to enhance the color of the polyester resin. Their added amount may be about 10 ppm to 200 ppm based on the amount of elemental cobalt relative to the weight of the polyester resin. If necessary, anthraquinone-based compounds, perinone-based compounds, azo-based compounds, methine-based compounds, and the like may be used as organic pigments. Commercially available toners, such as Polysynthren Blue RLS from Clarient or Solvaperm Red BB from Clarient, may also be used. The amount of organic pigment added may be adjusted to 0 to 50 ppm based on the weight of the polyester resin. Crystal nucleating agents, ultraviolet absorbers, polyolefin resins, polyamide resins, and the like may also be used as crystallization agents. 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 conventional branching agent having three or more functional groups, such as trimellitic anhydride, trimethylolpropane, trimellitic acid, or a mixture thereof.

[0104] (polyester resin) According to another aspect of the present invention, there is provided a polyester resin prepared by the above process.

[0105] The polyester resin of the present invention is a polyester resin regenerated by chemical recycling of waste polyester.

[0106] That is, the polyester resin is prepared by polymerization of raw materials including bis(glycol) terephthalate oligomer. Additionally, the polyester resin may contain bis(2-hydroxyethyl) terephthalate as a comonomer.

[0107] As mentioned above, the bis(glycol) terephthalate oligomer may be a transesterification reaction product between bis(2-hydroxyethyl) terephthalate and a glycol having three or more carbon atoms.

[0108] Here, the glycol has 3 or more carbon atoms, and specific types thereof are as exemplified above.

[0109] As a specific example, the bis(glycol) terephthalate may be selected from the group consisting of bis(diethylene glycol) terephthalate, bis(isosorbide) terephthalate, bis(1,4-cyclohexanedimethanol) terephthalate, and derivatives thereof.

[0110] The total recycled content of the polyester resin of the present invention may be 1% by weight or more, 5% by weight or more, 10% by weight or more, 25% by weight or more, 30% by weight or more, 50% by weight or more, 70% by weight or more, or 90% by weight or more. Furthermore, the total recycled content may be 100% by weight or less, 99% by weight or less, 80% by weight or less, 60% by weight or less, 40% by weight or less, or 20% by weight or less. As a specific example, the polyester resin may contain bis(2-hydroxyethyl) terephthalate and bis(glycol) terephthalate oligomer in a combined amount of 25% by weight or more based on the weight of the polyester resin.

[0111] Generally, the monomers (i.e., unused monomers) used in the polymerization of polyester resins, such as at least one selected from the group consisting of the above-mentioned dicarboxylic acids, dicarboxylic acid derivatives, diols, and diol derivatives, are used in addition to recycled raw materials in the preparation of polyester resins, and therefore the polyester resins may further contain these comonomers.

[0112] Furthermore, the polyester resin may further contain at least one recycled monomer obtained by depolymerization of waste polyester. Specifically, the at least one recycled monomer may be selected from the group consisting of recycled dicarboxylic acids, recycled dicarboxylic acid derivatives, recycled diols, and recycled diol derivatives. More specifically, the recycled monomer may be selected from the group consisting of recycled ethylene glycol, recycled 1,4-cyclohexanedimethanol, recycled diethylene glycol, recycled isosorbide, recycled terephthalic acid, recycled dimethyl terephthalate, recycled isophthalic acid, and recycled dimethyl isophthalate. However, the types of recycled monomers that can be used in the present invention are not limited thereto. Any recycled monomer that can be used in preparing polyester resins may be used. Such recycled monomers may be incorporated into the polyester resin by completely replacing virgin monomers. Alternatively, recycled and virgin monomers may be incorporated into the polyester resin together in a specific ratio. The mixing ratio of the recycled monomers is as exemplified above in the process for preparing the polyester resin.

[0113] Since bis(2-hydroxyethyl) terephthalate used in preparing the polyester resin has a structure in which two ethylene glycols and one terephthalic acid are bonded, the polyester resin of the present invention can contain repeating units derived from ethylene glycol and terephthalic acid. Furthermore, since bis(glycol) terephthalate oligomer has a structure in which two ethylene glycols and one terephthalic acid, each having three or more carbon atoms, are bonded, the polyester resin of the present invention can further contain repeating units derived from a glycol having three or more carbon atoms.

[0114] As described above, the polyester resin of the present invention contains a dicarboxylic acid component and a glycol component as monomer components (polymer building block units) that constitute the polyester resin. These components may be derived from bis(2-hydroxyethyl) terephthalate and a glycol having 3 or more carbon atoms that were initially introduced for the preparation of the polyester resin, or from a recycled bis(glycol) terephthalate oligomer prepared therefrom, and further comonomers that were introduced.

[0115] Thus, the polyester resin of the present invention may be a copolymerized resin containing two or more dicarboxylic acid components and / or two or more diol components.

[0116] According to one embodiment, the diol component may further include a diol component other than ethylene glycol as a comonomer, such as at least one selected from the group consisting of diethylene glycol, cyclohexanedimethanol, cyclohexanedimethanol derivatives, and isosorbide.

[0117] Diethylene glycol can contribute to enhancing the transparency and impact resistance of the polyester resin. For example, diethylene glycol may be used in an amount of 0.1 mol % to 50 mol % based on the total number of moles of diols.

[0118] Cyclohexanedimethanol (e.g., 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol) can contribute to enhancing the transparency and impact resistance of the resulting polyester resin. For example, cyclohexanedimethanol may be used in an amount of 5 mol % to 90 mol % based on the total number of moles of the diol component. The cyclohexanedimethanol derivative may be 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol. The cyclohexanedimethanol derivative may be used in an amount of 0.1 mol % to 25 mol % based on the total number of moles of the diol component.

[0119] Isosorbide can improve the processability of the final polyester resin. The transparency and impact resistance of polyester resins are enhanced by the diol components cyclohexanedimethanol and ethylene glycol, but the shear thinning properties must be improved and the crystallization rate must be slowed for processability; however, it is difficult to achieve this effect with cyclohexanedimethanol and ethylene glycol alone. Therefore, when isosorbide is used as the diol component, the shear thinning properties are improved and the crystallization rate is slowed, while the transparency and impact resistance are maintained, thereby improving the processability of the resulting polyester resin. Preferably, isosorbide may be used in an amount of 0.1 mol% to 70 mol% based on the total moles of the diol component.

[0120] The polyester resin may contain terephthalic acid as a dicarboxylic acid component. For example, terephthalic acid may be used in an amount of 5 mol % to 100 mol % based on the total number of moles of dicarboxylic acids. Furthermore, the terephthalic acid component may be formed from a terephthalic acid alkyl ester such as dimethyl terephthalate.

[0121] Furthermore, the dicarboxylic acid component may further contain an aromatic dicarboxylic acid component other than terephthalic acid, an aliphatic dicarboxylic acid component, or a mixture thereof. The dicarboxylic acid other than terephthalic acid may be used in an amount of 1 mol % to 30 mol % based on the total weight of the dicarboxylic acid component.

[0122] The aromatic dicarboxylic acid component may be an aromatic dicarboxylic acid having 8 to 20 carbon atoms, preferably 8 to 14 carbon atoms, or a mixture thereof. Examples of aromatic dicarboxylic acids include, but are not limited to, isophthalic acid, naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, 4,4'-stilbene dicarboxylic acid, 2,5-furandicarboxylic acid, 2,5-thiophenedicarboxylic acid, and the like.

[0123] The aliphatic dicarboxylic acid component may be an aliphatic dicarboxylic acid having 4 to 20 carbon atoms, preferably 4 to 12 carbon atoms, or a mixture thereof. Examples of aliphatic dicarboxylic acids include, but are not limited to, linear, branched, or cyclic aliphatic dicarboxylic acid components, for example, cyclohexanedicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and 1,3-cyclohexanedicarboxylic acid, phthalic acid, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, fumaric acid, adipic acid, glutaric acid, azelaic acid, etc.

[0124] The polyester resin may also contain a catalyst used in the polymerization reaction for its preparation. For example, the polyester resin may contain at least one catalyst selected from metal oxides and acetates. The metal contained in the catalyst may be selected from the group consisting of antimony (Sb), titanium (Ti), germanium (Ge), manganese (Mn), cobalt (Co), tin (Sn), and calcium (Ca).

[0125] When the Hunter Lab color space is measured, the polyester resin may have a value obtained by subtracting the b value from the L value of 88 or more, 89 or more, 90 or more, 91 or more, 92 or more, or 93 or more. Furthermore, the upper limit of the Lb value is not particularly limited. However, it may be, for example, 100 or less, 99 or less, 98 or less, 97 or less, or 95 or less. Measurement of the Hunter Lab color space may be performed by making a test piece having a thickness of 6 mm using the polyester resin. As a specific example, when the Hunter Lab color space is measured, the polyester resin may have a value obtained by subtracting the b value from the L value of 88 or more under a thickness condition of 6 mm.

[0126] The intrinsic viscosity of the polyester resin at 35° C. may be 0.5 dl / g or more, 0.6 dl / g or more, or 0.7 dl / g or more, and may 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. For example, the polyester resin may have an intrinsic viscosity of 0.5 dl / g to 1.2 dl / g at 35° C.

[0127] Due to its excellent color, mechanical strength, heat resistance, transparency, and gas barrier properties, the polyester resin according to the present invention can be used as a material for beverage containers, packaging films, audio and video films, etc. Furthermore, polyester sheets or plates prepared from the polyester resin according to the present invention have good transparency and excellent mechanical strength, and as a result, can be used as raw materials for cases, boxes, partitions, shelves, panels, packaging materials, building materials, interior and exterior materials, etc. Furthermore, the polyester resin according to the present invention can be used as industrial materials, for example, medical fibers and tire cords.

[0128] Thus, the present invention provides an article comprising a polyester resin. For example, the article may be a film, a sheet, or a profile. Specific examples of films include heat-shrinkable films and blown films. A profile refers to a continuously extruded plastic article, excluding sheets and films. It may be fabricated by a typical extrusion method and may have the shape of, for example, a tube or a conduit.

[0129] [Embodiments of the present invention] A preferred embodiment is presented below for understanding the present invention. However, the following examples are provided only to facilitate understanding of the present invention, and the scope of the present invention is not limited thereby.

[0130] In the examples below, it should be understood that for glycols used in transesterification reactions and dicarboxylic acids or diols used as comonomers in the polymerization of polyester resins, virgin monomer was used unless it is indicated as recycled monomer (e.g., terephthalic acid, ethylene glycol, etc.).

[0131] (Preparation of Regenerated Bis(2-hydroxyethyl) Terephthalate) Recycled BHET of various purities was prepared by depolymerization of waste polyester resin by known methods or purchased commercially. Tables 1 and 2 below show the purity, as analyzed using HPLC, of the recycled BHET used in each of the preparations or examples.

[0132] <Preparation of bis(glycol) terephthalate oligomers by transesterification> Various bis(glycol) terephthalate oligomers were prepared by transesterification of glycol (CHDM, DEG, or ISB) and bis(2-hydroxyethyl) terephthalate, respectively.

[0133] [Preparation example: BHCT #1] The transesterification reactor was equipped with a column and a condenser that could be cooled with water. Flowing nitrogen was used to cool the reactor at a rate of 2 kg / cm. 2 The pressure in the reactor was adjusted and the temperature was increased while maintaining the pressure. When the temperature in the reactor reached approximately 250°C, the transesterification reaction was carried out while continuously feeding 1,4-cyclohexanedimethanol (CHDM, 511 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 361 kg / h), and zinc acetate (0.0178 kg / h). During the reaction, the by-product ethylene glycol was collected and removed using a column and condenser. Even after the addition of the raw materials was completed, the transesterification reaction continued for a total of 7 hours while maintaining the temperature at 250°C until ethylene glycol discharge stopped. Upon completion of the transesterification reaction, the nitrogen in the pressurized reactor was released to the outside, and the pressure in the reactor was reduced to standard pressure to obtain the product. As a result, a total of 14.2 tons of bis(1,4-cyclohexanedimethanol) terephthalate oligomer was obtained.

[0134] [Preparation example: BHCT #2] Recycled 1,4-cyclohexanedimethanol (r-CHDM, 1,208 kg / hr), bis(2-hydroxyethyl) terephthalate (BHET, 710 kg / hr), and zinc acetate (0.1168 kg / hr) were continuously fed to the reactor, and the transesterification reaction with ethylene glycol as a by-product, which was collected and removed, was carried out at a temperature of 150°C and 0.1 kgf / cm. 2 The same procedure as in Preparative Example BHCT #1 was repeated except that it was carried out at a pressure of 1000 kJ / min to give a total amount of 28.0 tons of bis(1,4-cyclohexanedimethanol) terephthalate oligomer.

[0135] [Preparation example: BHCT #3] 1,4-Cyclohexanedimethanol (CHDM, 400 kg / hr), bis(2-hydroxyethyl) terephthalate (BHET, 176 kg / hr), and zinc acetate (0.0145 kg / hr) were continuously fed to the reactor and transesterification reaction with ethylene glycol as a by-product was carried out at a temperature of 220°C and 1 kgf / cm with the by-product collected and removed. 2The same procedure as in Preparative Example BHCT #1 was repeated except that the reaction was carried out at a pressure of 1000 kJ / min for 2 hours to obtain a total amount of 7.0 tons of bis(1,4-cyclohexanedimethanol) terephthalate oligomer.

[0136] [Preparation example: BHCT #4] 1,4-Cyclohexanedimethanol (CHDM, 191 kg / hr), bis(2-hydroxyethyl) terephthalate (BHET, 67 kg / hr), and zinc acetate (0.0011 kg / hr) were continuously fed to the reactor and transesterification reaction was carried out at a temperature of 190°C and 1 kgf / cm with ethylene glycol as a by-product, which was collected and removed. 2 The same procedure as in Preparative Example BHCT #1 was repeated except that the reaction was carried out at a pressure of 1000 kJ / min for 6 hours to obtain a total amount of 2.7 tons of bis(1,4-cyclohexanedimethanol) terephthalate oligomer.

[0137] [Preparation Example: BHDT #1] Diethylene glycol (DEG, 42 kg / hr), bis(2-hydroxyethyl) terephthalate (BHET, 67 kg / hr), and zinc acetate (0.0063 kg / hr) were continuously fed to the reactor and transesterification reaction was carried out at a temperature of 190°C and 1 kgf / cm with ethylene glycol as a by-product collected and removed. 2 The same procedure as in Preparative Example BHCT #1 was repeated except that the reaction was carried out at a pressure of 1000 kJ / min for 6 hours to obtain a total amount of 2.2 tons of bis(diethylene glycol) terephthalate oligomer.

[0138] [Preparation Example: BHDT #2] Recycled diethylene glycol (r-DEG, 173 kg / hr), bis(2-hydroxyethyl) terephthalate (BHET, 139 kg / hr), and zinc acetate (0.0112 kg / hr) were continuously fed to the reactor, and the transesterification reaction with ethylene glycol as a by-product, which was collected and removed, was carried out at a temperature of 170°C and 2 kgf / cm. 2The same procedure as in Preparative Example BHCT #1 was repeated except that the reaction was carried out at a pressure of 1000 kJ / min for 4 hours to obtain a total amount of 4.5 tons of bis(diethylene glycol) terephthalate oligomer.

[0139] [Preparation example: BHIT #1] Isosorbide (ISB, 344 kg / hr), bis(2-hydroxyethyl) terephthalate (BHET, 200 kg / hr), and zinc acetate (0.0033 kg / hr) were continuously fed to the reactor and transesterification with ethylene glycol as a by-product, which was collected and removed, was carried out at a temperature of 160°C and 0.5 kgf / cm 2 The same procedure as in Preparative Example BHCT #1 was repeated except that the reaction was carried out at a pressure of 1000 kJ / min for 2 hours to obtain a total amount of 7.8 tons of bis(isosorbide) terephthalate oligomer.

[0140] [Preparation example: BHIT #2] Regenerated isosorbide (r-ISB, 440 kg / hr), bis(2-hydroxyethyl) terephthalate (BHET, 192 kg / hr), and zinc acetate (0.0156 kg / hr) were continuously fed to the reactor, and the transesterification reaction with ethylene glycol as a by-product, which was collected and removed, was carried out at a temperature of 190°C and 0.5 kgf / cm. 2 The same procedure as in Preparative Example BHCT #1 was repeated except that the reaction was carried out at a pressure of 1000 kJ / min for 2 hours to obtain a total amount of 7.5 tons of bis(isosorbide) terephthalate oligomer.

[0141] The processes of the preparation examples are summarized in Table 1 below. Furthermore, the molecular weight of each bis(glycol) terephthalate obtained in the preparation examples was measured by gel permeation chromatography (GPC). The number of repeating units (units formed by condensation of terephthalic acid and diol) was calculated from the molecular weight and is shown in the table below. [Table 1]

[0142] <Preparation of Polyester Resin> A polyester resin was prepared using the bis(glycol) terephthalate prepared above.

[0143] Example 1 Each bis(glycol) terephthalate oligomer obtained in each Preparation Example was transferred to an esterification reactor, and other polymerization raw materials and a catalyst were added. Nitrogen was injected into the reactor, and the pressure was increased by 0.5 kgf / cm from the standard pressure. 2 The reactor was pressurized to a high temperature. The temperature of the esterification reactor was increased to 260°C, and bis(diethylene glycol) terephthalate oligomer (BHDT #1, 90.5 kg / hr), bis(2-hydroxyethyl) terephthalate (BHET, 1,345 kg / hr), terephthalic acid (TPA, 835 kg / hr), ethylene glycol (EG, 72.2 kg / hr), 1,4-cyclohexanedimethanol (CHDM, 30.5 kg / hr), diethylene glycol (DEG, 22.5 kg / hr), Ge catalyst (1.3 kg / hr), Ti catalyst (0.19 kg / hr), phosphoric acid (0.208 kg / hr), blue toner (0.008 kg / hr), and red toner (0.002 kg / hr) were continuously fed into the esterification reactor. The esterification reaction was carried out at 260°C for about 7 hours, and then the product was transferred to a polycondensation reactor, and the by-products formed during the reaction were collected and removed by a column and a condenser.

[0144] The pressure in the polycondensation reactor was then reduced from standard pressure to 5 Torr (absolute pressure: 5 mmHg) over 30 minutes. Simultaneously, the temperature of the polycondensation reactor was increased to 275°C over 1 hour, and the polycondensation reaction was then carried out while maintaining the pressure in the polycondensation reactor at 1 Torr (absolute pressure: 1 mmHg) or less. At the beginning of the polycondensation reaction, the stirring speed was set high. As the polycondensation reaction progressed, if the stirring power weakened due to an increase in the viscosity of the reactants or if the temperature of the reactants exceeded the set temperature, the stirring speed was adjusted accordingly. The polycondensation reaction was carried out for 7 hours until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.70 dL / g. The mixture was then discharged outside the reactor to form pellets, solidified using a cooling liquid, and then granulated to an average weight of approximately 12-14 mg.

[0145] The granules were left to stand at 150°C for 1 hour to crystallize, and then fed into a solid-state polymerization reactor. While nitrogen was flowing at a rate of 50 L / min, the temperature of the reactor was raised from room temperature to 200°C at a rate of 40°C / hr. While maintaining this temperature, solid-state polymerization was carried out until the intrinsic viscosity (IV) of the granules in the reactor reached 0.90 dL / g, yielding approximately 50 tons of polyester resin (copolymer).

[0146] Example 2 Bis(1,4-cyclohexanedimethanol) terephthalate oligomer (BHCT The following substances were continuously fed: #1,592.9 kg / hr), bis(2-hydroxyethyl) terephthalate (BHET, 1,801.4 kg / hr), terephthalic acid (TPA, 157.0 kg / hr), 1,4-cyclohexanedimethanol (CHDM, 54.5 kg / hr), diethylene glycol (DEG, 22.5 kg / hr), CHDM derivative (4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a molar ratio of 1:3, 41.4 kg / hr), Ge catalyst (2.7 kg / hr), Ti catalyst (0.19 kg / hr), phosphoric acid (0.208 kg / hr), blue toner (0.005 kg / hr), and red toner (0.001 kg / hr), at a pressure of 2.0 kgf / cm above standard pressure. 2 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), except that the esterification reaction was carried out at high pressure and a temperature of 255°C for 5 hours, and the polycondensation reaction was carried out at a temperature of 285°C for 10 hours until the intrinsic viscosity (IV) reached 0.78 dL / g, and no solid-state polymerization was carried out.

[0147] Example 3 Bis(isosorbide) terephthalate oligomer (BHIT #1, 325.2 kg / hr), bis(1,4-cyclohexanedimethanol) terephthalate ester oligomer (BHCT #2, 1,167.5 kg / hr), bis(2-hydroxyethyl) terephthalate (BHET, 554.3 kg / hr), terephthalic acid (TPA, 492.6 kg / hr), 1,4-cyclohexanedimethanol (CHDM, 75.4 kg / hr), isosorbide (ISB, 76.5 kg / hr), diethylene glycol (DEG, 9.3 kg / hr), Ge catalyst (13.3 kg / hr), phosphoric acid (0.042 kg / hr), blue toner (0.006 kg / hr), and red toner (0.002 kg / hr) were continuously fed at a pressure of 1.0 kgf / cm above standard pressure. 2 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), except that the esterification reaction was carried out at high pressure and a temperature of 265°C for 4 hours, and the polycondensation reaction was carried out at a temperature of 275°C for 6 hours until the intrinsic viscosity (IV) reached 0.70 dL / g, and no solid-state polymerization was carried out.

[0148] Example 4 Bis(diethylene glycol) terephthalate oligomer (BHDT #2, 186.4 kg / hr), bis(1,4-cyclohexanedimethanol) terephthalate oligomer (BHCT #3, 290.0 kg / hr), bis(2-hydroxyethyl) terephthalate (BHET, 251.8 kg / hr), terephthalic acid (TPA, 1,275.2 kg / hr), ethylene glycol (EG, 347.2 kg / hr), 1,4-cyclohexanedimethanol (CHDM, 28.5 kg / hr), diethylene glycol (DEG, 5.3 kg / hr), CHDM derivative (4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a 1:3 molar ratio, 86.8 kg / hr) , Ge catalyst (1.3 kg / hour), phosphoric acid (0.208 kg / hour), blue toner (0.010 kg / hour), and red toner (0.004 kg / hour) were continuously supplied, and the pressure was 0.5 kgf / cm from the standard pressure. 2 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), except that the esterification reaction was carried out under high pressure and at a temperature of 260°C for 8 hours, and the polycondensation reaction was carried out at a temperature of 275°C for 9 hours until the intrinsic viscosity (IV) reached 0.75 dL / g, and no solid-state polymerization was carried out.

[0149] Example 5 Bis(1,4-cyclohexanedimethanol) terephthalate oligomer (BHCT #4, 110.9 kg / hr), bis(2-hydroxyethyl) terephthalate (BHET, 1,886.4 kg / hr), terephthalic acid (TPA, 484.3 kg / hr), isophthalic acid (IPA, 1,276.9 kg / hr), ethylene glycol (EG, 11.0 kg / hr), isosorbide (ISB, 20.7 kg / hr), diethylene glycol (DEG, 22.5 kg / hr), Ti catalyst (0.19 kg / hr), phosphoric acid (4.167 kg / hr), cobalt acetate (0.4 kg / hr), blue toner (0.010 kg / hr), and red toner (0.004 kg / hr) were continuously fed at a pressure of 3.0 kgf / cm above standard pressure.2 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), except that the esterification reaction was carried out under high pressure at a temperature of 260°C for 5 hours, the polycondensation reaction was carried out at a temperature of 280°C for 4 hours until the intrinsic viscosity (IV) reached 0.60 dL / g, and the solid-state polymerization was carried out until the intrinsic viscosity (IV) reached 1.10 dL / g.

[0150] Example 6 Bis(isosorbide) terephthalate oligomer (BHIT #2, 312.2 kg / hr), bis(2-hydroxyethyl) terephthalate (BHET, 765.8 kg / hr), terephthalic acid (TPA, 1,042.7 kg / hr), ethylene glycol (EG, 249.2 kg / hr), 1,4-cyclohexanedimethanol (CHDM, 434.2 kg / hr), isosorbide (ISB, 73.4 kg / hr), Ti catalyst (0.19 kg / hr), phosphoric acid (2.083 kg / hr), cobalt acetate (0.1 kg / hr), blue toner (0.004 kg / hr), and red toner (0.002 kg / hr) were continuously fed into the reactor at a pressure of 3.0 kgf / cm above standard pressure. 2 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), except that the esterification reaction was carried out under high pressure at a temperature of 260°C for 5 hours, and the polycondensation reaction was carried out at a temperature of 280°C for 3 hours until the intrinsic viscosity (IV) reached 0.55 dL / g, and no solid-state polymerization was carried out.

[0151] Comparative Example 1 Bis(2-hydroxyethyl) terephthalate (BHET, 1,441.1 kg / hour), ethylene glycol (EG, 10.6 kg / hour), 1,4-cyclohexanedimethanol (CHDM, 277.8 kg / hour), CHDM derivative (4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a molar ratio of 1:3, 24.9 kg / hour), Ge catalyst (1.6 kg / hour), Ti catalyst (0.11 kg / hour), phosphoric acid (0.125 kg / hour), blue toner (0.003 kg / hour), and red toner (0.001 kg / hour) were continuously fed, and the pressure was 2.0 kgf / cm above standard pressure. 2 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), except that the esterification reaction was carried out at high pressure and a temperature of 255°C for 7 hours, and the polycondensation reaction was carried out at a temperature of 285°C for 12 hours until the intrinsic viscosity (IV) reached 0.78 dL / g, and no solid-state polymerization was carried out.

[0152] Comparative Example 2 Bis(2-hydroxyethyl) terephthalate (BHET, 335.1 kg / hr), terephthalic acid (TPA, 657.0 kg / hr), ethylene glycol (EG, 26.2 kg / hr), 1,4-cyclohexanedimethanol (CHDM, 493.9 kg / hr), CHDM derivative (4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a 1:3 molar ratio, 24.9 kg / hr), Ge catalyst (8.0 kg / hr), phosphoric acid (0.025 kg / hr), blue toner (0.004 kg / hr), and red toner (0.001 kg / hr) were continuously fed at a pressure of 1.0 kgf / cm above standard pressure. 2The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), except that the esterification reaction was carried out at high pressure and a temperature of 265°C for 5 hours, and the polycondensation reaction was carried out at a temperature of 275°C for 5 hours until the intrinsic viscosity (IV) reached 0.70 dL / g, and no solid-state polymerization was carried out.

[0153] Table 2 below summarizes the raw materials used in the examples and comparative examples. [Table 2]

[0154] [Test example] The raw materials and final resins used in the examples and comparative examples were tested as follows.

[0155] (1) Amount of recycled BHET added The number of moles of bis(2-hydroxyethyl) terephthalate (BHET) added was calculated as a percentage (mol%) based on the total number of moles of dicarboxylic acid and its derivatives (TPA, BHET, BHDT, BHIT, and BHCT) added to prepare the polyester resin.

[0156] (2) Recycled material content in resin The total weight percent (wt%) of recycled monomers and oligomers (BHET, BHDT, BHIT, and BHCT) was calculated based on the total weight of monomers and oligomers used to prepare the polyester resins (BHET, BHDT, BHIT, BHCT, TPA, IPA, EG, CHDM, ISB, DEG, etc.).

[0157] (3) Analysis of glycol recovery (by-products relative to production volume) The total amount of by-products (glycols) collected and removed during the polyester resin polymerization reaction (esterification reaction and polycondensation reaction) was measured. The total amount (kg) of by-products (glycols) collected and removed was divided by the total time (hours) required for the polyester resin polymerization reaction (esterification reaction and polycondensation reaction) to calculate the by-products relative to the production amount (kg / hour).

[0158] The test results are shown in Table 3 below. [Table 3]

[0159] As can be seen from Table 3 above, the amount of glycol required to be collected and removed increased significantly in Comparative Examples 1 and 2 compared to Examples 1 to 6. Furthermore, the total recycled content in the resin was lower in Comparative Example 1, even though a larger amount of BHET was used than in Example 2. The total recycled content in the resin was lower in Comparative Example 2, even though the same amount of BHET was used as in Example 2.

Claims

1. subjecting bis(2-hydroxyethyl) terephthalate to a transesterification reaction with a glycol having three or more carbon atoms; collecting and removing ethylene glycol as a by-product formed during the transesterification reaction; obtaining a bis(glycol) terephthalate oligomer as a product of the transesterification reaction; conducting a polymerization using the bis(glycol) terephthalate oligomer; 1. A method for preparing a polyester resin, comprising:

2. 2. The method for preparing a polyester resin according to claim 1, wherein the bis(2-hydroxyethyl) terephthalate is obtained by depolymerization of waste polyester.

3. 2. The method for preparing a polyester resin according to claim 1, wherein the bis(2-hydroxyethyl) terephthalate has a purity of 60% to 97%.

4. The glycol having three or more carbon atoms is preferably 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, isosorbide, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 2. The method for preparing the polyester resin according to claim 1, wherein the polyester resin comprises at least one selected from the group consisting of olefins, 1,4-cyclohexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, copolymers of ethylene oxide and tetrahydrofuran, ethylene oxide-added polypropylene glycol, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, poly-1,5-pentanediol, and derivatives thereof.

5. 10. The method for preparing a polyester resin according to claim 1, wherein the glycol having three or more carbon atoms comprises at least one type of recycled glycol obtained by depolymerization of waste polyester.

6. 10. The method for preparing a polyester resin according to claim 1, wherein the bis(glycol) terephthalate oligomer has 2 to 10 repeating units.

7. the polymerization step subjecting the bis(glycol) terephthalate oligomer and at least one comonomer to an esterification reaction; subjecting the esterification reaction product to a polycondensation reaction to obtain a copolymer; 10. A method for preparing the polyester resin of claim 1, comprising:

8. 8. The method for preparing the polyester resin of claim 7, wherein at least one comonomer selected from the group consisting of dicarboxylic acids, dicarboxylic acid derivatives, diols, and diol derivatives is further introduced into the esterification reaction.

9. the dicarboxylic acid comprises terephthalic acid or isophthalic acid; the dicarboxylic acid derivative comprises dimethyl terephthalate or dimethyl isophthalate; the glycol comprises diethylene glycol, 1,4-cyclohexanedimethanol, isosorbide, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, or 1,4-cyclohexanediol; the diol derivative comprises 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol; A method for preparing the polyester resin of claim 8.

10. 9. The method for preparing a polyester resin according to claim 8, wherein the at least one comonomer comprises a recycled monomer obtained by depolymerization of waste polyester.

11. 8. The method for preparing the polyester resin of claim 7, further comprising the step of collecting and removing ethylene glycol during at least one of the esterification reaction and the polycondensation reaction.

12. 2. The method for preparing a polyester resin according to claim 1, wherein the collected and removed ethylene glycol is purified and then fed again for at least one of the transesterification reaction and the polymerization step.

13. 2. The method for preparing a polyester resin according to claim 1, wherein the polyester resin comprises the bis(2-hydroxyethyl) terephthalate and the bis(glycol) terephthalate in a combined amount of 25% by weight or more, based on the weight of the polyester resin.

14. 14. The method for preparing a polyester resin according to claim 13, wherein the polyester resin further comprises at least one recycled monomer obtained by depolymerization of waste polyester.

15. subjecting bis(2-hydroxyethyl) terephthalate to a transesterification reaction with a glycol having three or more carbon atoms; collecting and removing the by-product ethylene glycol formed during the transesterification reaction; 1. A method for preparing a bis(glycol) terephthalate oligomer, comprising:

16. 16. The method for preparing bis(glycol) terephthalate oligomer according to claim 15, wherein the bis(2-hydroxyethyl) terephthalate is supplied to the transesterification reaction in the form of a powder or a solution.

17. 16. The method for preparing bis(glycol) terephthalate oligomer according to claim 15, wherein a solution of bis(2-hydroxyethyl) terephthalate is prepared by mixing the bis(2-hydroxyethyl) terephthalate with at least one solvent selected from water and ethylene glycol at 60°C to 190°C, and adjusting the concentration to 50% to 95% by weight.

18. The transesterification reaction and the collection and removal of the ethylene glycol are carried out at a temperature of 120°C to 260°C and a pressure of 0.1 kgf / cm ２ ~2.0kgf / cm ２ 16. The method for preparing bis(glycol) terephthalate oligomers of claim 15, wherein the method is carried out at a pressure of

19. A polyester resin prepared by the method of claim 1.

20. 16. A bis(glycol) terephthalate oligomer prepared by the method of claim 15.

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