Preparation method of bis (glycol) terephthalate oligomer and polyester resin

Abstract

According to the present invention, bis (glycol) terephthalate can be prepared by a transesterification reaction of a glycol and bis (2-hydroxyethyl) terephthalate, and then introduced into a polymerization reaction to increase the content of recovered raw materials in a polyester resin. Furthermore, impurities are removed by extracting a glycol byproduct during the transesterification reaction, thereby improving purity, and thus the quality of the final resin can be improved while reducing the amount of byproducts in the polymerization reaction.

Description

Technical Field

[0001] The present invention relates to a method for recovering terephthalate bis(glycol) ester oligomers and preparing polyester resins using the oligomers. Background Art

[0002] Polyester is widely used as a material for beverage filling containers, packaging films, audio and video films, etc. due to its excellent mechanical strength, heat resistance, transparency and gas barrier properties. In addition, polyester is widely produced 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, so they are widely used as raw materials for boxes, boxes, partitions, shelves, panels, packaging materials, construction materials, indoor and outdoor materials, etc.

[0003] As a result, the amount of waste plastics such as polyester generated worldwide each year has reached an uncontrollable level. Recently, countries around the world have formulated regulations and plans for the recycling of waste plastic resources, including waste polyester. For example, some people have tried to use recycled resins at a certain ratio or higher in packaging materials used in various fields. Although physical or chemical methods are used as methods for recycling waste polyester, physical recycling methods cannot guarantee purity and are therefore not widely used.

[0004] In the chemical recycling method, the ester bonds of the waste polyester are cleaved to depolymerize it. Reactions such as glycolysis, hydrolysis, methanolysis and aminolysis are used. Among them, glycolysis is the decomposition of waste polyester at high temperature by adding glycols such as ethylene glycol or diethylene glycol. The reaction products obtained mainly include bis(2-hydroxyethyl) terephthalate (BHET). Bis(2-hydroxyethyl) terephthalate can be used as a raw material for the preparation of unsaturated polyesters or ester polyols after crystallization or purification.

[0005] However, from the perspective of environmental friendliness, it is more meaningful to convert the waste PET products with a generally short service life into engineering polyester products or environmentally friendly biodegradable polyester products with a long service life. In this regard, recently, attempts have been made to regenerate polyester resins other than PET by transesterification of waste PET and diols. Since an excessive amount of diols is used in this reaction and the reaction time is long, there is a problem that a large amount of by-products such as cyclic ester compounds are formed as a side reaction of diols.

[0006] [Prior art literature]

[0007] (Non-patent document 1) Park, SH, Kim, SH, Poly (ethylene terephthalate) recycling for high value added textiles, Fashion and Textiles 1, 1 (2014). Summary of the invention

[0008] Technical issues

[0009] The present inventors attempted to develop a method that can improve the quality and economic benefits of the final product while increasing the content of recycled raw materials by recycling BHET obtained by depolymerizing waste PET products into various engineering polyester products or environmentally friendly biodegradable polyester products.

[0010] At the same time, due to the impurities formed by the reagents used in the depolymerization process and the side reactions, the recovered BHET usually has a low purity, so that a separate process such as ion exchange or recrystallization is required to purify it, resulting in the problem of increased cost. In addition, in addition to BHET, diol monomers (DEG, ISB, CHDM, etc.) must be used to produce copolyester resins, which makes it difficult to increase the content of recycled raw materials in the final resin. In the traditional method, if excessive BHET is added in the polymerization reaction in order to increase the content of recycled raw materials, the problem of increased diol byproducts will occur.

[0011] As a result of the research conducted by the present inventors, it has been found that when the diol used for copolymerization is previously subjected to an ester exchange reaction with BHET to prepare bis(glycol) terephthalate and then subjected to a polymerization reaction, the content of recycled raw materials in the polyester resin can be increased; and the purity is increased by collecting the diol by-product during the ester exchange reaction and removing impurities, thereby improving the quality of the final resin, while reducing the by-products during the polymerization reaction.

[0012] Therefore, an object of the present invention is to provide a method for preparing a polyester resin having a high content of recycled raw materials such as BHET, reducing by-products of the polymerization reaction, and having excellent final resin quality, and a polyester resin prepared thereby.

[0013] Solution to the problem

[0014] According to the present invention, a method for preparing a polyester resin is provided, which comprises subjecting bis(2-hydroxyethyl)terephthalate to an ester exchange reaction with a diol having 3 or more carbon atoms; collecting and removing ethylene glycol, a by-product formed during the ester exchange reaction; obtaining bis(diol)terephthalate oligomers as a product of the ester exchange reaction; and polymerizing using the bis(diol)terephthalate oligomers.

[0015] According to the present invention, a method for preparing bis(glycol) terephthalate oligomers is provided, which comprises subjecting bis(2-hydroxyethyl) terephthalate to an ester exchange reaction with a diol having 3 or more carbon atoms; and collecting and removing ethylene glycol, a byproduct formed during the ester exchange reaction.

[0016] Furthermore, according to the present invention, there are provided polyester resin and bis(glycol)terephthalate oligomer prepared by the above method.

[0017] Advantageous Effects of the Invention

[0018] According to the present invention, bis(2-hydroxyethyl) terephthalate as a recycled raw material obtained by depolymerization of waste polyester is previously subjected to an ester exchange reaction with a diol suitable for a desired copolymerization composition to prepare bis(diol) terephthalate oligomers, and then subjected to a polymerization reaction. Therefore, even if an excessive amount of bis(2-hydroxyethyl) terephthalate is not added in the polymerization reaction of the polyester resin, the content of the recycled raw material can be increased.

[0019] 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 reducing the cost of raw materials and processes. The purity can be improved by removing impurities, thereby obtaining a final resin with improved quality, which can be used to prepare an environmentally friendly polyester product. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A method for preparing a polyester resin according to an embodiment of the present invention is schematically described. DETAILED DESCRIPTION

[0021] Best Mode for Carrying Out the Invention

[0022] In the present specification, the terms relating to the respective components are used to distinguish them from each other, and are not intended to limit the scope of the embodiments. In addition, in the present specification, unless otherwise specified in the context, singular expressions are interpreted as also covering the plural.

[0023] In this specification, the terms first, second, etc. are used to describe various components. However, these components should not be limited by these terms. These terms are used to distinguish one element from another element.

[0024] In this specification, the term "includes / comprising" is intended to specify specific features, regions, steps, methods, elements and / or components. Unless explicitly stated to the contrary, the existence or addition of any other features, regions, steps, methods, elements and / or components is not excluded.

[0025] The molecular weight of the compound or polymer described in this specification, such as the number average molecular weight or weight average molecular weight, is a well-known relative mass based on carbon- 12. Although its unit is not described, it can be understood as the molar mass (g / mol) of the same numerical value if necessary.

[0026] In the present specification, a "derivative" of a specific compound means a compound obtained by converting part of the compound or combining it with other components through a chemical reaction, thereby containing a main part of the compound.

[0027] In this specification, a unit or group "derived" from a specific component refers to a part of the component included in the final product through a chemical reaction such as a polymerization reaction. It may exist in a form in which a part of it is modified during the reaction or combined with other components. For example, a unit or group derived from at least one monomer or oligomer is included in the chain constituting a polymer.

[0028] In the present specification, the recycled monomer or oligomer may refer to a monomer or oligomer obtained by decomposing, depolymerizing, reprocessing or repolymerizing waste plastics such as waste polyester by a physical or chemical method, or a polymer raw material containing them or derived therefrom.

[0029] As an example, bis(2-hydroxyethyl)terephthalate (BHET) used as a raw material in the process according to the present invention may be a recycled monomer obtained by depolymerization of waste polyester.

[0030] As another example, recycled monomers can also be used as diols having 3 or more carbon atoms for transesterification in the method of the present invention. As a specific example, at least one type of recycled diols can be used, such as recycled 1,4-cyclohexanedimethanol (r-CHDM), recycled diethylene glycol (r-DEG), and recycled isosorbide (r-ISB).

[0031] As another example, in the method of the present invention, the recycled monomer can also be used as a comonomer for the polymerization reaction of the polyester resin. As a specific example, at least one selected from the group consisting of recycled dicarboxylic acids and recycled diols can be used. As a more specific example, at least one type of recycled monomer can 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).

[0032] These recycled monomers can be obtained directly from waste plastics (such as waste polyester) by known methods, or can be purchased from the market and used.

[0033] In addition, the bis(glycol)terephthalate oligomers (e.g., BHDT oligomers, BHIT oligomers, BHCT oligomers, etc.) obtained as ester exchange reaction products according to the present invention can be recycled oligomers obtained by decomposing, depolymerizing, reprocessing or repolymerizing waste plastics (e.g., waste polyesters) by physical or chemical methods.

[0034] Such recycled raw materials such as recycled monomers or oligomers can be used to prepare the polyester resins of the present invention.

[0035] The invention provides a method for preparing a polyester resin, which comprises subjecting bis(2-hydroxyethyl) terephthalate to an ester exchange reaction with a diol having 3 or more carbon atoms; collecting and removing ethylene glycol, a by-product formed during the ester exchange reaction; obtaining bis(diol) terephthalate oligomers as the ester exchange reaction product; and performing polymerization using the bis(diol) terephthalate oligomers.

[0036] Figure 1 A method for preparing a polyester resin according to an embodiment of the present invention is schematically described. Figure 1 , the preparation method of the polyester resin according to one embodiment includes preparing the recovered bis(2-hydroxyethyl) terephthalate obtained by depolymerization of waste polyester (S100); carrying out transesterification reaction with a glycol having 3 or more carbon atoms (S200); collecting and removing the byproduct ethylene glycol (S500); and obtaining bis(glycol) terephthalate oligomer (S300). For subsequent polymerization, bis(2-hydroxyethyl) terephthalate, bis(glycol) terephthalate oligomer and other monomer mixtures are added to the esterification reaction, followed by a polycondensation reaction (S400) to obtain the polyester resin. The glycol byproduct (S500) can also be collected and removed during the esterification reaction and / or the polycondensation reaction. The glycol recovered in this way can be purified (S600) and then supplied to the transesterification reaction and / or polymerization step again.

[0037] According to the present invention, bis(2-hydroxyethyl) terephthalate as a recycled raw material obtained by depolymerization of waste polyester is previously subjected to an ester exchange reaction with a diol suitable for a desired copolymerization composition to prepare bis(diol) terephthalate oligomers, and then subjected to a polymerization reaction. Therefore, even if an excessive amount of bis(2-hydroxyethyl) terephthalate is not added in the polymerization reaction of the polyester resin, the content of the recycled raw material can be increased.

[0038] 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 reducing the cost of raw materials and processes. The purity can be improved by removing impurities, thereby obtaining a final resin with improved quality, which can be used to prepare an environmentally friendly polyester product.

[0039] Hereinafter, the present invention will be described in detail.

[0040] Bis(2-hydroxyethyl) terephthalate

[0041] Bis(2-hydroxyethyl)terephthalate is an ester formed from two ethylene glycols and one terephthalic acid. For example, it is a compound formed as an intermediate in a process for preparing polyesters such as polyethylene terephthalate (PET) by polymerization of ethylene glycol and terephthalic acid or its esters.

[0042] The bis(2-hydroxyethyl) terephthalate used in the present invention can be obtained by the depolymerization of waste polyester. For example, bis(2-hydroxyethyl) terephthalate can be obtained from waste polyesters such as polyethylene terephthalate (PET) or glycol-modified polyethylene terephthalate (PETG) having repeating units of ethylene glycol and terephthalic acid. 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 with ethylene glycol and then purifying it.

[0043] The bis(2-hydroxyethyl)terephthalate obtained by depolymerization of the waste polyester as described above is referred to as "recovered bis(2-hydroxyethyl)terephthalate (recovered BHET)", or simply r-BHET or rBHET, which needs to be understood as different from the pure BHET compound. Specifically, the recovered BHET may contain reagents or solvents used in various chemical steps during the depolymerization of the waste polyester, or by-products formed by side reactions with them. Therefore, the BHET recovered by the ordinary depolymerization method contains organic and inorganic impurities in addition to BHET as the main component; therefore, its purity is not high. Therefore, the recovered BHET can also be regarded as a composition including two or more components, that is, a BHET composition. This recovered BHET can be used as a polymerization raw material for producing polyester resins.

[0044] Impurities contained in the recycled BHET may include diethylene glycol derivatives and unreacted monomers, etc. The total content of impurities contained in the recycled BHET may be 10 wt % or more, 15 wt % or more, or 20 wt % or more, and may be 40 wt % or less, 35 wt % or less, 30 wt % or less, or 25 wt % or less.

[0045] The purity of recovered BHET can be measured using liquid chromatography, etc. Specifically, the purity of recovered BHET can be calculated by measuring the fraction (%) of the peak area of ​​BHET to the total peak area in a spectrum obtained using high performance liquid chromatography (HPLC).

[0046] For example, the purity of the recovered BHET can be 97% or less, 90% or less, 85% or less or 80% or less, and can be 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 can be 60% to 97%, more specifically, 65% to 90%, 65% to 85% or 70% to 80%.

[0047] Diol

[0048] The diol used in the transesterification reaction of the present invention undergoes a transesterification reaction with bis(2-hydroxyethyl)terephthalate to form a residue in a bis(diol)terephthalate oligomer as a product, which constitutes the polymer chain of the final polyester resin polymerized therefrom.

[0049] The diol used in the present invention may be a diol having 3 or more carbon atoms, which is used to replace the ethylene glycol residue in the transesterification reaction.

[0050] In particular, the boiling point of the diol is 10° C. or more higher than that of ethylene glycol, which facilitates purification by fractional distillation during the transesterification reaction.

[0051] Specifically, the diol used in the transesterification reaction of the present invention may be a diol monomer other than ethylene glycol (eg, an alkylene glycol having 3 or more carbon atoms) or a polymer diol (eg, polyether).

[0052] As a more specific example, the diol may be at least one selected from a diol monomer having 3 to 20 carbon atoms and a molecular weight of less than 500 and a polymeric diol having a number average molecular weight of 400 to 5,000.

[0053] The number of carbon atoms of the diol 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.

[0054] Specifically, the diol monomer may be an aliphatic diol having 3 to 20 carbon atoms. In addition, the aliphatic diol may be chain-shaped or cyclic.

[0055] As a specific example, the diol having 3 or more carbon atoms may include at least one selected from the group consisting of 1,3-propylene glycol, 1,4-butylene glycol, 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, 1,4-cyclohexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, copolymers of ethylene oxide and tetrahydrofuran, polypropylene glycol added with ethylene oxide, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, poly-1,5-pentanediol and their derivatives.

[0056] As a more specific example, the diol monomer may include at least one selected from the group consisting of diethylene glycol, isosorbide, 1,4-cyclohexanedimethanol and derivatives thereof. Such a diol monomer may be a raw diol.

[0057] As another example, the diol with 3 or more carbon atoms may include at least one recycled diol obtained by depolymerization of waste polyester. As a specific example, the recycled diol may be selected from the group consisting of recycled 1,4-cyclohexanedimethanol, recycled diethylene glycol, and recycled isosorbide. However, the type of recycled diol that can be used in the present invention is not limited thereto. Any recycled diol that can undergo an ester exchange reaction may be used. This recycled diol may be used in an ester exchange reaction to completely replace the original diol. Alternatively, the recycled diol and the original diol may be mixed in a certain ratio and used in an ester exchange reaction. The mixing ratio of the recovered 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, specifically, 1 mol% to 100 mol%, 1 mol% to 99 mol% or 30 mol% to 100 mol%, based on the moles of the total glycol.

[0058] 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, it may be a mixture comprising 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.

[0059] The diol monomer can have a molecular weight of less than 500, less than 400, less than 350, less than 300, or less than 250, for example.

[0060] The polymer diol may be, for example, selected from the group consisting of polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, copolymers of ethylene oxide and tetrahydrofuran, polypropylene glycol added with ethylene oxide, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, and poly-1,5-pentanediol. More specifically, the polymer diol may be at least one selected from the group consisting of polytetramethylene glycol, polycarbonate diol, polypropylene glycol, and polypropylene glycol added with ethylene oxide.

[0061] The number average molecular weight of the polymer diol may be, for example, 400 or more, 500 or more, 600 or more, 700 or more, or 800 or more, or 6000 or less, 5000 or less, 4000 or less, or 3000 or less. As a specific example, the number average molecular weight of the polymer diol may be 400 to 5000. More specifically, from the perspective of reducing phase separation, it may preferably be 1000 to 3000.

[0062] The polymer diol is used in an amount of 5 to 75 wt %, specifically 10 to 60 wt %, more specifically 15 to 50 wt %, based on the weight of the final polyester resin, which is beneficial to obtain a high molecular weight while improving the elasticity of the polyester resin.

[0063] Transesterification

[0064] The diol and bis(2-hydroxyethyl) terephthalate undergo an ester exchange reaction.

[0065] [Reaction Scheme 1]

[0066]

[0067] In Reaction Scheme 1, R is a diol group having 3 or more carbon atoms excluding OH groups at both ends. As an 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 linked by an ether group or a carbonate group. As another example, R may be a monocyclic or polycyclic group having 3 to 20 carbon atoms, wherein the ring may be aliphatic or aromatic, and may further contain one or more heteroatoms (e.g., O, N, and S).

[0068] In Reaction Scheme 1, m is a number ranging from 2 to 10, for example.

[0069] The transesterification reaction may be carried out in the presence of a catalyst. Thus, when the diol, acid or bis(2-hydroxyethyl)terephthalate is fed to the reactor, the catalyst may be fed together.

[0070] As a catalyst for the transesterification reaction, for example, at least one selected from the group consisting of a zinc-based catalyst, a titanium-based catalyst, a germanium-based catalyst, an antimony-based catalyst, an aluminum-based catalyst, and a tin-based catalyst may be used.

[0071] The example of zinc-based catalyst comprises zinc acetate, zinc acetate hydrate, zinc chloride, zinc sulfate, zinc sulfide, zinc carbonate, zinc citrate, zinc gluconate or its mixture. The example of titanium-based catalyst comprises tetraethyl titanate, acetyl tripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octanediol titanate, triethanolamine titanate, acetylacetonate titanate, ethyl acetoacetate titanate, isostearyl titanate, titanium dioxide etc. The example of germanium-based catalyst comprises germanium dioxide, germanium tetrachloride, ethylene glycol germanium oxide, germanium acetate or its combination. Specifically, germanium dioxide can be used as germanium-based catalyst. Both crystalline and amorphous germanium dioxide can be used as germanium dioxide, and germanium dioxide soluble in glycol can also be used.

[0072] The amount of the transesterification catalyst can vary according to the reaction conditions and the catalyst used. As an example, a metal-based catalyst (e.g., titanium-based catalyst, tin-based catalyst) can be used in an amount of 0.0001 to 0.05 parts by weight relative to 100 parts by weight of the diols and bis(2-hydroxyethyl)terephthalate fed into the reactor.

[0073] The transesterification reaction can be carried out batchwise or continuously.

[0074] As an example, when a diol or a diol and an acid are fed into a reactor and the temperature reaches a certain level while the temperature is increased, bis(2-hydroxyethyl) terephthalate may be fed. For example, the feeding of bis(2-hydroxyethyl) terephthalate may be carried out at a nitrogen atmosphere of 120° C. to 280° C., while collecting and removing the by-product ethylene glycol. 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 a pressure of 0.1 kgf / cm 2 Up to 2.0kgf / cm 2 The collected and removed ethylene glycol may be purified and then supplied again to at least one of the transesterification reaction and the polymerization reaction.

[0075] Bis(2-hydroxyethyl)terephthalate can be fed all at once to carry out transesterification with glycol. Alternatively, bis(2-hydroxyethyl)terephthalate can be introduced into the transesterification with glycol in a batch or continuous manner. In addition, bis(2-hydroxyethyl)terephthalate can be fed into the transesterification in the form of a powder or a solution. Bis(2-hydroxyethyl)terephthalate solution can be prepared by mixing bis(2-hydroxyethyl)terephthalate with at least one solvent of water and ethylene glycol at 60° C. to 190° C. and adjusting the concentration to 50% to 95% by weight.

[0076] According to one embodiment, terephthalic acid bis (2-hydroxyethyl) ester can be introduced into the transesterification reaction with diols in a mode of twice or more. The number of times introduced in batches can be 2 times or more, 3 times or more, 4 times or more or 5 times or more, or 100 times or less, 50 times or less, 30 times or less, 20 times or less, 15 times or less or 10 times or less. As a specific example, the number of times introduced in batches can be 2 to 30 times or 3 to 15 times. The time interval between batch introductions can be determined by dividing the total introduction time by the number of times introduced in batches. The total introduction time can be, for example, 1 hour or longer or 2 hours or longer, and can be 5 hours or shorter or 4 hours or shorter. In addition, an introduction amount during batch introduction can be determined by dividing the total amount of terephthalic acid bis (2-hydroxyethyl) ester to be introduced into the reaction by the number of times introduced in batches.

[0077] According to another embodiment, bis(2-hydroxyethyl) terephthalate is introduced into the transesterification reaction with diol in a continuous manner. The total time of continuous introduction can be, for example, 1 hour or longer or 2 hours or longer, and can be 5 hours or shorter or 4 hours or shorter. For example, continuous introduction can be to introduce a constant amount of bis(2-hydroxyethyl) terephthalate per hour. The amount introduced per hour can be determined 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 can be prepared in the form of a powder or a BHET aqueous solution, and the concentration of the BHET aqueous solution is about 10-20% by weight, dissolved in about 80-100°C water, which can be continuously fed. Continuous introduction can be carried out from the start of the transesterification reaction to 1 hour before the reaction is completed. A dripping funnel can be used at the laboratory level, or a metering feeder can be used at the commercial level to continuously introduce a constant amount per hour.

[0078] When the feeding of bis(2-hydroxyethyl)terephthalate is completed, reaction conditions can be maintained until the transesterification reaction is completed. In addition, the process of collecting and removing ethylene glycol as a by-product can be continued during the transesterification reaction. The collection and removal of ethylene glycol can be carried out by a distillation process, which utilizes the difference in boiling points with other components. The ethylene glycol distilled out like this can be recovered by cooling and reused in other processes.

[0079] The termination point of the transesterification reaction can be determined by considering the theoretical amount of ethylene glycol formed from bis(2-hydroxyethyl)terephthalate by the transesterification reaction, or as the point at which by-products are no longer released.

[0080] The pressure (absolute pressure) during the transesterification reaction may be, for example, 0.1 kgf / cm 2 or higher, 0.2kgf / cm 2 or higher or 0.5kgf / cm 2 or higher, and 2.5kgf / cm 2 or lower, 2.0kgf / cm 2 or lower or 1.5kgf / cm 2 or lower, specifically, 0.5kgf / cm 2 Up to 2.0kgf / cm 2 .

[0081] In addition, 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.

[0082] 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 Up to 2.0kgf / cm 2 under pressure.

[0083] In addition, the transesterification reaction can be performed under a nitrogen atmosphere.

[0084] The pressure and temperature conditions during the transesterification reaction can be appropriately adjusted according to the specific characteristics of the polyester to be produced, the ratio of each component or the process conditions. For example, the transesterification reaction can be carried out at a temperature of 180°C or higher to smoothly collect and remove the by-product ethylene glycol formed during the transesterification reaction. In addition, it can also be carried out at a temperature 10°C lower than the boiling point of the diol to reduce the loss of the diol used for substitution.

[0085] The products of the transesterification reaction mainly include bis(glycol)terephthalate oligomers and derivatives thereof, wherein the ethylene glycol residues in bis(2-hydroxyethyl)terephthalate are replaced by other glycol residues.

[0086] Therefore, the present invention provides a method for preparing bis(glycol)terephthalate oligomers, which comprises subjecting bis(2-hydroxyethyl)terephthalate to an ester exchange reaction with a diol having 3 or more carbon atoms; and collecting and removing ethylene glycol, a by-product formed during the ester exchange reaction.

[0087] In addition, the present invention provides terephthalic acid bis(glycol) ester oligomers prepared by the above method, that is, recycled terephthalic acid bis(glycol) ester oligomers.

[0088] According to one embodiment, the terephthalic acid bis(glycol) ester oligomer obtained by the transesterification reaction includes a compound represented by Formula 1 below.

[0089] [Formula 1]

[0090]

[0091] In Formula 1, —OR—OH is a group derived from a diol having 3 or more carbon atoms, and m is a number in the range of 2 to 10, for example.

[0092] As described above, the terephthalic acid bis(glycol) ester oligomer can have 2 to 10 repeating units. For example, the number of repeating units in the terephthalic acid bis(glycol) ester oligomer can be 2 or more or 3 or more, and 10 or less, 8 or less, 6 or less or 4 or less.

[0093] In Formula 1, R is a group derived from a diol having 3 or more carbon atoms. As an example, R can 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 by an ether group or a carbonate group. As another example, R can be a group of 3 to 20 carbon atoms comprising a monocyclic or polycyclic ring, wherein the ring can be aliphatic or aromatic, and can also contain one or more heteroatoms (e.g., O, N, and S).

[0094] As a specific example, Formula 1 may be a compound in which R is a group derived from diethylene glycol, i.e., bis(diethylene glycol) terephthalate oligomer (hereinafter referred to as BHDT oligomer). As another specific example, Formula 1 may be a compound in which R is a group derived from isosorbide, i.e., bis(isosorbide) terephthalate oligomer (hereinafter referred to 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., bis(1,4-cyclohexanedimethanol) terephthalate oligomer (hereinafter referred to as BHCT oligomer).

[0095] [Formula 1a]

[0096]

[0097] [Formula 1b]

[0098]

[0099] [Formula 1c]

[0100]

[0101] In Formulae 1a to 1c, m is a number in the range of 2 to 10, respectively.

[0102] The bis(glycol)terephthalate oligomer may include two or more compounds represented by Formula 1 or derivatives thereof.

[0103] Because the impurity in the terephthalic acid bis (glycol) ester oligomer is removed in the process of collecting and removing by-products such as the glycol formed in the transesterification reaction, its purity can be improved compared with the terephthalic acid bis (2-hydroxyethyl) ester as raw material.For example, the terephthalic acid bis (glycol) ester obtained by the transesterification reaction can have a purity of 80% or higher.More specifically, the purity of terephthalic acid bis (glycol) ester oligomer can be 85% or higher, 90% or higher or 95% or higher.As a specific example, it can be 80% to 99.9%.

[0104] Preparation of polyester resin

[0105] Thereafter, the polyester resin is prepared by performing polymerization using the bis(glycol)terephthalate oligomer.

[0106] In the polymerization step, an esterification reaction (first polymerization reaction step) and a polycondensation reaction (second polymerization reaction step) may be performed in sequence.

[0107] The polymerization step may be a step of preparing a copolymer. For example, the polymerization step may include subjecting a terephthalic acid bis(glycol) ester oligomer and at least one comonomer to an esterification reaction; and subjecting the esterification reaction product to polycondensation to obtain a copolymer.

[0108] Reaction Scheme 2 below schematically shows a copolymerization reaction using BHET as a comonomer, during which diols may be formed as by-products.

[0109] [Reaction Scheme 2]

[0110]

[0111] In Reaction Scheme 2, R is a group derived from a diol having 3 or more carbon atoms.

[0112] According to the present invention, during at least one of the esterification reaction and the polycondensation reaction, a step of collecting and removing ethylene glycol may be further performed. The collected and removed ethylene glycol may be purified and then supplied again to at least one of the transesterification reaction and the polymerization step.

[0113] As described above, in addition to the terephthalic acid bis(glycol) ester oligomer, additional recycled monomers may be added to the esterification reaction, and monomers other than recycled raw materials may also be added. For example, at least one comonomer selected from the group consisting of terephthalic acid bis(2-hydroxyethyl) ester, dicarboxylic acids, dicarboxylic acid derivatives, diols, and diol derivatives may be further introduced into the esterification reaction.

[0114] As a specific example, the dicarboxylic acid may include terephthalic acid or isophthalic acid; the dicarboxylic acid derivative may include dimethyl terephthalate or dimethyl isophthalate; the diol may include diethylene glycol, 1,4-cyclohexanedimethanol, isosorbide, 1,2-propylene glycol, 1,3-propylene glycol, 2-methyl-1,3-propylene glycol, 2-methylene-1,3-propylene glycol, 2-ethyl-1,3-propylene glycol, 2-isopropyl ... diol, 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; diol derivatives may include 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol. Such comonomers may be original monomers.

[0115] As another example, at least one comonomer may include a recycled monomer obtained by depolymerization of waste polyester. As a specific example, the at least one comonomer may include at least one recycled monomer selected from the group consisting of: recycled dicarboxylic acid, recycled dicarboxylic acid derivatives, recycled glycols, and recycled glycol derivatives. As a more specific example, 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 type of recycled monomer that can be used as a comonomer in the present invention is not limited thereto. Any recycled monomer that can be used to prepare a polyester resin can be used. This recycled monomer can be used for the polymerization of a polyester resin by completely replacing the original monomer. Alternatively, the recycled monomer and the original monomer can also be mixed in a certain proportion for the polymerization of a polyester resin. The mixing ratio of the recycled monomers can 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, specifically, 1 mol % to 100 mol %, 1 mol % to 99 mol % or 30 mol % to 100 mol %, based on the moles of the total monomers.

[0116] The esterification reaction can be carried out in the presence of an esterification catalyst. For example, a zinc-based compound can 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.

[0117] The esterification reaction can be carried out at, for example, 0 kgf / cm 2 Up to 10.0kgf / cm 2 The esterification reaction conditions can be appropriately adjusted according to the specific characteristics of the prepared polyester, the ratio of each component, the process conditions, etc. Specifically, the pressure in the esterification reaction can be 0 kg / cm 2 Up to 5.0kg / cm 2 , more specifically, 0.1 kg / cm 2 Up to 3.0kg / cm 2 In addition, the temperature of the esterification reaction may be 200°C to 270°C, more specifically, 240°C to 260°C.

[0118] Esterification can be carried out in batches or continuously. In addition, the recovery BHET, dicarboxylic acid and glycol as raw materials can be introduced into the reactor respectively, or two or more raw materials can be introduced in a mixed state. They can be introduced in solid, liquid or slurry form. As an example, dicarboxylic acid, glycol and recovery BHET can be introduced alone or in combination, and can be mixed with pre-prepared terephthalic acid oligomers. Terephthalic acid oligomers can be prepared by reacting glycols such as terephthalic acid and ethylene glycol, cyclohexanedimethanol, isosorbide. As another example, they can be introduced in the form of slurry, in which dicarboxylic acid and recovery BHET are mixed with glycol.

[0119] More specifically, a glycol (e.g., isosorbide) that is solid at room temperature can be dissolved in water or ethylene glycol and then mixed with a dicarboxylic acid (e.g., terephthalic acid) to prepare a slurry. Alternatively, isosorbide can be melted at 60°C or higher and then mixed with a dicarboxylic acid (e.g., terephthalic acid) and other glycols to prepare a slurry. In addition, additional water can be added to the mixed slurry to help increase the fluidity of the slurry. In addition, in a continuous process, a pump or the like can be used to continuously feed a liquid raw material (e.g., a solution of recovered BHET) into a reactor. The feed rate per hour can be determined by dividing the total amount of feed by time to achieve a target output per day.

[0120] The mixture of terephthalic acid bis (glycol) ester oligomer, other monomers and additive components is placed in an esterification reactor for a period of time, for example 1 hour to 24 hours or 4 hours to 10 hours, and then transferred to a polycondensation reactor. Polycondensation can produce a polyester resin with a relatively low molecular weight by melt polymerization. In addition, it is also possible to produce a polyester resin with a relatively high molecular weight by solid state polymerization after melt polymerization.

[0121] The temperature in the polycondensation reaction may be 150°C to 300°C, specifically, 200°C to 290°C, more specifically, 260°C to 280°C. In addition, the pressure in the polycondensation reaction may be 0.01 mmHg to 600 mmHg, specifically, 0.05 mmHg to 200 mmHg, more specifically, 0.1 mmHg to 100 mmHg. Since the polycondensation reaction adopts reduced pressure conditions, ethylene 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, the removal of the by-product may be insufficient. In addition, if the polycondensation reaction temperature is lower than 150°C, the reaction by-product glycol cannot be effectively collected and removed from the system; therefore, the intrinsic viscosity of the final reaction product is low, resulting in a decrease in the physical properties of the final polyester resin. If the temperature of 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 period of time, for example, an average residence time of 1 hour to 24 hours, until the intrinsic viscosity of the final reaction product reaches an appropriate level.

[0122] In addition, the polycondensation reaction can be carried out in the presence of a polycondensation catalyst. The polycondensation catalyst can 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, acetyl tripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octanediol titanate, lactic acid titanate, triethanolamine titanate, acetylacetonate titanate, ethyl acetoacetate titanate, isostearyl titanate, titanium dioxide, etc. Examples of germanium-based compounds include germanium dioxide, germanium tetrachloride, ethylene glycol germanium oxide, germanium acetate or a mixture thereof. Preferably, germanium dioxide can be used. Crystalline germanium dioxide and amorphous germanium dioxide can be used, and germanium dioxide soluble in glycol can also be used. The amount of the polycondensation catalyst can be such that the amount of titanium element is about 1 to 100 ppm relative to the weight of the polyester resin, more preferably about 1 to 50 ppm.

[0123] In addition to the polycondensation catalyst, stabilizers, colorants, crystallizing agents, antioxidants, branching agents, etc. may be used. The timing of adding these additives is not particularly limited, and they may be added at any time during the preparation of the polyester resin.

[0124] As a stabilizer, phosphorus-based compounds such as phosphoric acid, trimethyl phosphate, triethyl phosphate and triethyl phosphonoacetate can generally be used. Based on the amount of the element, relative to the weight of the polyester resin, its addition amount can be 10 to 200ppm. In addition, common colorants, such as cobalt acetate and cobalt propionate, can also be used as colorants to increase the color of the polyester resin. Based on the amount of the cobalt element, relative to the weight of the polyester resin, its addition amount can be 10 to 200ppm. If necessary, anthraquinone compounds, perinone compounds, azo compounds, methine compounds, etc. can be used as organic colorants. Commercially available toners can be used, such as Polysynthren Blue RLS from Clariant or Solvaperm Red BB from Clariant. Based on the weight of the polyester resin, the addition amount of the organic compound colorant can be adjusted to 0 to 50ppm. The crystallizer can be a crystal nucleating agent, an ultraviolet absorber, a polyolefin resin, a polyamide resin, etc. The antioxidant may be a hindered phenol antioxidant, a phosphite antioxidant, a thioether antioxidant or a mixture thereof. The branching agent may be a conventional branching agent having three or more functional groups, such as trimellitic anhydride, trimethylolpropane, trimellitic acid or a mixture thereof.

[0125] Polyester resin

[0126] According to another aspect of the present invention, a polyester resin prepared by the above method is provided.

[0127] The polyester resin of the present invention is a polyester resin regenerated by chemically recovering waste polyester.

[0128] That is, the polyester resin is prepared by polymerizing a raw material containing a bis(glycol)terephthalate oligomer. In addition, the polyester resin may contain bis(2-hydroxyethyl)terephthalate as a comonomer.

[0129] As described above, the bis(glycol)terephthalate oligomer may be a transesterification product between bis(2-hydroxyethyl)terephthalate and a glycol having 3 or more carbon atoms.

[0130] Here, the diol has 3 or more carbon atoms, and its specific types are as described above.

[0131] 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.

[0132] The total content of recycled raw materials in the polyester resin of the present invention can 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. In addition, the total content of recycled raw materials can 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, based on the weight of the polyester resin, the polyester resin can contain a total amount of 25% by weight or more of bis(2-hydroxyethyl) terephthalate and bis(glycol) terephthalate oligomers.

[0133] In the preparation of the polyester resin, in addition to the recycled raw materials, monomers commonly used for the polymerization of polyester resins (i.e., original monomers) are used, for example, at least one selected from the group consisting of dicarboxylic acids, dicarboxylic acid derivatives, diols and diol derivatives as described above, and thus the polyester resin may further contain these comonomers.

[0134] In addition, the polyester resin may further include at least one recovered monomer obtained by depolymerization of waste polyester. As a specific example, the at least one recovered monomer may be selected from the group consisting of recovered dicarboxylic acids, recovered dicarboxylic acid derivatives, recovered glycols, and recovered glycol derivatives. As a more specific example, the recovered monomer may be selected from the group consisting of recovered ethylene glycol, recovered 1,4-cyclohexanedimethanol, recovered diethylene glycol, recovered isosorbide, recovered terephthalic acid, recovered dimethyl terephthalate, recovered isophthalic acid, and recovered dimethyl isophthalate. However, the types of recovered monomers that can be used in the present invention are not limited thereto. Any recovered monomer that can be used to prepare polyester resins can be used. This recovered monomer can completely replace the original monomer and thus be included in the polyester resin. Alternatively, the recovered monomer and the original monomer can also be included in the polyester resin in a certain ratio. The mixing ratio of the recovered monomers is the same as the example in the above-mentioned method for preparing the polyester resin.

[0135] Since bis(2-hydroxyethyl)terephthalate used for preparing polyester resin has a structure in which two ethylene glycols and one terephthalic acid are bonded, the polyester resin of the present invention may include a repeating unit derived from ethylene glycol and terephthalic acid. In addition, since the structure of bis(glycol)terephthalate oligomer is formed by bonding two ethylene glycols each having 3 or more carbon atoms and one terephthalic acid, the polyester resin of the present invention may further include a repeating unit derived from a glycol having 3 or more carbon atoms.

[0136] As described above, the polyester resin of the present invention contains a dicarboxylic acid component and a diol component as monomer components (polymer constituent units) constituting it. These may be derived from bis(2-hydroxyethyl)terephthalate and a diol having 3 or more carbon atoms initially introduced for the preparation of the polyester resin, or a recycled bis(diol)terephthalate oligomer prepared therefrom and a comonomer additionally introduced.

[0137] Therefore, the polyester resin of the present invention may be a copolymerized resin comprising two or more dicarboxylic acid components and / or two or more diol components.

[0138] According to one embodiment, the diol component may further include a diol component other than ethylene glycol as a comonomer. The comonomer may include, for example, at least one selected from the group consisting of diethylene glycol, cyclohexanedimethanol, cyclohexanedimethanol derivatives, and isosorbide.

[0139] Diethylene glycol can help enhance the transparency and impact resistance of the polyester resin. For example, diethylene glycol can be used in an amount of 0.1 mol % to 50 mol % based on the moles of all diols.

[0140] Cyclohexanedimethanol (e.g., 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol) can help improve the transparency and impact resistance of the produced polyester resin. For example, cyclohexanedimethanol can be used in an amount of 5 mol % to 90 mol % based on the moles of all diol components. The cyclohexanedimethanol derivative can be 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol. The cyclohexanedimethanol derivative can be used in an amount of 0.1 mol % to 25 mol % based on the moles of all diol components.

[0141] Isosorbide can improve the processing properties of the final polyester resin. Although the diol components in cyclohexanedimethanol and ethylene glycol can improve the transparency and impact resistance of the polyester resin, the shear fluidization characteristics should also be improved and the crystallization rate should be delayed to improve the processing properties; however, it is difficult to achieve this effect by relying solely on cyclohexanedimethanol and ethylene glycol. Therefore, if isosorbide is used as a diol component, the shear fluidization characteristics can be improved, the crystallization rate can be delayed, and the transparency and impact resistance can be maintained, thereby improving the processing properties of the polyester resin. Preferably, isosorbide can be used in an amount of 0.1 mol% to 70 mol% based on the molar number of all diol components.

[0142] 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 moles of all dicarboxylic acids. In addition, the terephthalic acid component may be formed from an alkyl terephthalate (such as dimethyl terephthalate).

[0143] In addition, the dicarboxylic acid component may include an aromatic dicarboxylic acid component, an aliphatic dicarboxylic acid component or a mixed component thereof in addition to terephthalic acid. The dicarboxylic acid in addition to terephthalic acid may be used in an amount of 1 mol% to 30 mol% based on the weight of all dicarboxylic acid components.

[0144] The aromatic dicarboxylic acid component may be an aromatic dicarboxylic acid or a mixture thereof having 8 to 20 carbon atoms, preferably 8 to 14 carbon atoms. Examples of aromatic dicarboxylic acids include isophthalic acid, naphthalene dicarboxylic acid (e.g., 2,6-naphthalene dicarboxylic acid), diphenyl dicarboxylic acid, 4,4'-stilbene dicarboxylic acid, 2,5-furan dicarboxylic acid, 2,5-thiophene dicarboxylic acid, etc., but are not limited thereto.

[0145] The aliphatic dicarboxylic acid component may be an aliphatic dicarboxylic acid or mixture thereof having 4 to 20 carbon atoms, preferably 4 to 12 carbon atoms. Examples of aliphatic dicarboxylic acids include linear, branched or cyclic aliphatic dicarboxylic acid components such as cyclohexanedicarboxylic acids (e.g., 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., but are not limited thereto.

[0146] The polyester resin may also contain a catalyst for the polymerization reaction used in 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).

[0147] When the Hunter Lab color space is measured, the value obtained by subtracting the b value from the L value of the polyester resin may be 88 or greater, 89 or greater, 90 or greater, 91 or greater, 92 or greater, or 93 or greater. In addition, the upper limit of the L-b value is not particularly limited. However, it may also be, for example, 100 or less, 99 or less, 98 or less, 97 or less, or 95 or less. The measurement of the HunterLab color space can be performed by making a sample with a thickness of 6 mm using a polyester resin. As a specific example, when the Hunter Lab color space is measured, under the condition of a thickness of 6 mm, the value obtained by subtracting the b value from the L value of the polyester resin may be 88 or greater.

[0148] 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 intrinsic viscosity of the polyester resin at 35° C. may be 0.5 dl / g to 1.2 dl / g.

[0149] The polyester resin according to the present invention can be used as materials such as beverage filling containers, packaging films, audio and video films, etc. due to its excellent color, mechanical strength, heat resistance, transparency and gas barrier properties. In addition, the polyester sheet or plate prepared from the polyester resin according to the present invention has good transparency and excellent mechanical strength, and can be used as a raw material for boxes, boxes, partitions, shelves, panels, packaging materials, building materials, indoor and outdoor materials, etc. In addition, the polyester resin according to the present invention can be used as an industrial material such as medical fiber and tire cord.

[0150] Therefore, the present invention provides a product comprising the polyester resin. As an example, the product can be a film, a sheet or a profile. Specific examples of films include heat shrinkable films and blown films. Profiles refer to plastic products formed by continuous extrusion, excluding sheets and films. It can be manufactured by conventional extrusion molding methods, for example, it can be tubular or grooved.

[0151] Invention Mode

[0152] A preferred embodiment is given below to facilitate understanding of the present invention. However, the following examples are provided only to help easily understand the present invention, and the scope of the present invention is not limited thereby.

[0153] In the following examples, in the diols used in the transesterification reaction and the dicarboxylic acids or diols used as comonomers in the polymerization of the polyester resin, unless recycled monomers (e.g., terephthalic acid, ethylene glycol, etc.) are indicated, it should be understood that virgin monomers are used.

[0154] Preparation of recycled bis(2-hydroxyethyl) terephthalate

[0155] Recycled BHET of various purities was prepared by depolymerization of waste polyester resins purchased by known methods or commercially. The following Tables 1 and 2 show the purity of the recycled BHET used in each Preparation Example or Example analyzed using HPLC.

[0156] <Preparation of terephthalic acid bis(glycol) ester oligomer by transesterification>

[0157] Each of the various terephthalate bis(glycol) ester oligomers is prepared by transesterification of a glycol (CHDM, DEG or ISB) with bis(2-hydroxyethyl) terephthalate.

[0158] Preparation Example: BHCT#1

[0159] Prepare a transesterification reactor equipped with a tower and a condenser which can be cooled with water. Adjust the pressure in the reactor to 2 kg / cm by flowing nitrogen. 2 , and the temperature is increased while maintaining the pressure. When the temperature in the reactor reaches about 250°C, 1,4-cyclohexanedimethanol (CHDM, 511kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 361kg / h) and zinc acetate (0.0178kg / h) are continuously fed at the same time to carry out an ester exchange reaction. During the reaction, the by-product ethylene glycol is collected and removed by the tower and the condenser. Even after the addition of the raw materials is completed, the ester exchange reaction continues at 250°C for 7 hours until the ethylene glycol stops being discharged. After the ester exchange reaction is completed, the nitrogen in the pressurized reactor is released to the outside, the pressure in the reactor is reduced to normal pressure, and the product is obtained. As a result, a total amount of 14.2 tons of bis(1,4-cyclohexanedimethanol) terephthalate oligomers is obtained.

[0160] Preparation Example: BHCT#2

[0161] The same steps as in Preparation Example BHCT#1 were repeated to obtain a total of 28.0 tons of terephthalic acid bis(1,4-cyclohexanedimethanol) ester oligomers, except that 1,4-cyclohexanedimethanol (r-CHDM, 1208 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 710 kg / h) and zinc acetate (0.1168 kg / h) were continuously fed to the reactor for recovery. The transesterification reaction was carried out at a temperature of 150°C and a pressure of 0.1 kgf / cm 2 The reaction is carried out under a pressure of 1000 ℃ and 2000 ℃, and ethylene glycol is collected and removed as a by-product.

[0162] Preparation Example: BHCT#3

[0163] The same steps as in Preparation Example BHCT#1 were repeated to obtain a total of 7.0 tons of terephthalic acid bis(1,4-cyclohexanedimethanol) ester oligomers, except that 1,4-cyclohexanedimethanol (CHDM, 400 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 176 kg / h) and zinc acetate (0.0145 kg / h) were continuously fed into the reactor. The transesterification reaction was carried out at a temperature of 220°C and a pressure of 1 kgf / cm 2 The reaction was carried out under a pressure of 1000 ℃ for 2 hours, and ethylene glycol was collected and removed as a by-product.

[0164] Preparation Example: BHCT#4

[0165] The same steps as in Preparation Example BHCT#1 were repeated to obtain a total of 2.7 tons of terephthalic acid bis(1,4-cyclohexanedimethanol) ester oligomers, except that 1,4-cyclohexanedimethanol (CHDM, 191 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 67 kg / h) and zinc acetate (0.0011 kg / h) were continuously fed into the reactor. The transesterification reaction was carried out at a temperature of 190° C. and a pressure of 1 kgf / cm 2 The reaction was carried out under a pressure of 1000 ℃ and 800 ℃ for 6 hours, and ethylene glycol was collected and removed as a by-product.

[0166] Preparation Example: BHDT#1

[0167] The same steps as in Preparation Example BHCT#1 were repeated to obtain a total of 2.2 tons of terephthalic acid bis(diethylene glycol) ester oligomers, except that diethylene glycol (DEG, 42 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 67 kg / h) and zinc acetate (0.0063 kg / h) were continuously fed into the reactor. The transesterification reaction was carried out at a temperature of 190° C. and a pressure of 1 kgf / cm 2 The reaction was carried out under a pressure of 1000 ℃ and 800 ℃ for 6 hours, and ethylene glycol was collected and removed as a by-product.

[0168] Preparation Example: BHDT#2

[0169] The same steps as in Preparation Example BHCT#1 were repeated to obtain a total of 4.5 tons of terephthalic acid bis(diethylene glycol) ester oligomers, except that diethylene glycol (r-DEG, 173 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 139 kg / h) and zinc acetate (0.0112 kg / h) were continuously fed into the reactor. The transesterification reaction was carried out at a temperature of 170° C. and a flow rate of 2 kgf / cm 2 The reaction was carried out under a pressure of 1000 ℃ for 4 hours, and ethylene glycol was collected and removed as a by-product.

[0170] Preparation Example: BHIT#1

[0171] The same steps as in Preparation Example BHCT#1 were repeated to obtain a total of 7.8 tons of bis(isosorbide) terephthalate oligomers, except that isosorbide (ISB, 344 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 200 kg / h) and zinc acetate (0.0033 kg / h) were continuously fed to the reactor. The transesterification reaction was carried out at a temperature of 160° C. and a pressure of 0.5 kgf / cm 2 The reaction was carried out under a pressure of 1000 ℃ for 2 hours, and ethylene glycol was collected and removed as a by-product.

[0172] Preparation Example: BHIT#2

[0173] The same steps as in Preparation Example BHCT#1 were repeated to obtain a total of 7.5 tons of bis(isosorbide) terephthalate oligomers, except that isosorbide (r-ISB, 440 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 192 kg / h) and zinc acetate (0.0156 kg / h) were continuously fed to the reactor. The transesterification reaction was carried out at a temperature of 190° C. and a flow rate of 0.5 kgf / cm 2 The reaction was carried out under a pressure of 1000 ℃ for 2 hours, and ethylene glycol was collected and removed as a by-product.

[0174] The methods of the preparation examples are summarized in the following Table 1. In addition, the molecular weight of each terephthalic acid bis(glycol) ester obtained in the preparation examples was measured by gel permeation chromatography (GPC). The number of repeating units (units of condensation of terephthalic acid and glycol) was calculated and shown in the following table.

[0175]

Table 1

[0176]

[0177]

[0178] <Preparation of polyester resin>

[0179] The polyester resin was prepared using the bis(glycol)terephthalate prepared above.

[0180] Example 1

[0181] Each terephthalic acid bis (glycol) ester oligomer obtained in the preparation example was transferred to an esterification reactor, and other polymerization raw materials and catalysts were added. Nitrogen was injected into the reactor to make the pressure in the reactor 0.5 kgf / cm higher than the normal pressure. 2 The temperature of the esterification reactor was raised to 260°C, and then bis(diethylene glycol) terephthalate oligomer (BHDT#1, 90.5 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 1345.0 kg / h), terephthalic acid (TPA, 835.0 kg / h), ethylene glycol (EG, 72.2 kg / h), 1,4-cyclohexanedimethanol (CHDM, 30.5 kg / h), diethylene glycol (DEG, 22.5 kg / h), Ge catalyst (1.3 kg / h), Ti catalyst (0.19 kg / h), phosphoric acid (0.208 kg / h), blue toner (0.008 kg / h) and red toner (0.002 kg / h) 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 through a column and a condenser.

[0182] Then, the pressure of the polycondensation reactor is reduced from normal pressure to 5Torr (absolute pressure: 5mmHg) within 30 minutes. At the same time, the temperature of the polycondensation reactor is raised to 275°C within 1 hour, and then the polycondensation reaction is carried out, while the pressure of the polycondensation reactor is maintained at 1Torr (absolute pressure: 1mmHg) or lower. At the beginning of the polycondensation reaction, the stirring speed is set very high. As the polycondensation reaction proceeds, when the stirring ability weakens due to the increase in the viscosity of the reactants or the temperature of the reactants rises to above the set temperature, the stirring speed is appropriately adjusted accordingly. The polycondensation reaction is carried out for 7 hours until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reaches 0.70dl / g. Thereafter, the mixture is discharged to the outside of the reactor to form pellets, solidified with a coolant, and then granulated to an average weight of about 12 to 14mg.

[0183] The pellets were placed at 150° C. for 1 hour for crystallization 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. / hour. While maintaining this state, solid state polymerization was performed until the intrinsic viscosity (IV) of the pellets in the reactor reached 0.90 dl / g, obtaining about 50 tons of a polyester resin (copolymer).

[0184] Example 2

[0185] The same steps as in Example 1 were repeated to obtain about 50 tons of polyester resin (copolymer), except that bis(1,4-cyclohexanedimethanol) terephthalate oligomer (BHCT#1, 592.9 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 1801.4 kg / h), terephthalic acid (TPA, 157.0 kg / h), 1,4-cyclohexanedimethanol (CHDM, 54.5 kg / h), diethylene glycol (DEG, 10.3 kg / h), and terephthalic acid (TPA, 157.0 kg / h) were continuously fed. 22.5kg / h), CHDM derivative (containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol, molar ratio of 1:3, 41.4kg / h), Ge catalyst (2.7kg / h), Ti catalyst (0.19kg / h), phosphoric acid (0.208kg / h), blue toner (0.005kg / h) and red toner (0.001kg / h). The esterification reaction was carried out at a pressure 2.0kgf / cm higher than normal pressure. 2 The polycondensation reaction was carried out at a pressure of 255° C. for 5 hours, and at a temperature of 285° C. for 10 hours until the intrinsic viscosity (IV) reached 0.78 dl / g, and solid phase polymerization was not carried out.

[0186] Example 3

[0187] The same steps as in Example 1 were repeated to obtain about 50 tons of polyester resin (copolymer), except that bis(isosorbide) terephthalate oligomer (BHIT#1, 325.2 kg / h), bis(1,4-cyclohexanedimethanol) terephthalate oligomer (BHCT#2, 1167.5 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 554.3 kg / h), terephthalic acid (TPA, 492.6 kg / h), 1,4-cyclohexanedimethanol (CHDM, 75.4 kg / h), isosorbide (ISB, 76.5 kg / h), diethylene glycol (DEG, 9.3 kg / h), Ge catalyst (13.3 kg / h), phosphoric acid (0.042 kg / h), blue toner (0.006 kg / h) and red toner (0.002 kg / h) were continuously fed. The esterification reaction is carried out at a pressure 1.0 kgf / cm higher than normal pressure. 2 The polycondensation reaction was carried out at a pressure of 200° C. and a temperature of 265° C. for 4 hours, and at a temperature of 275° C. for 6 hours until the intrinsic viscosity (IV) reached 0.70 dl / g, and solid phase polymerization was not carried out.

[0188] Example 4

[0189] The same steps as in Example 1 were repeated to obtain about 50 tons of polyester resin (copolymer), except that bis(diethylene glycol) terephthalate oligomer (BHDT#2, 186.4 kg / h), bis(1,4-cyclohexanedimethanol) terephthalate oligomer (BHCT#3, 290.0 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 251.8 kg / h), terephthalic acid (TPA, 1275.2 kg / h), ethylene glycol (EG, 347.2 kg / h), 1,4-cyclohexanedimethanol (CHDM, 28.5 kg / h), diethylene glycol (DEG, 5.3 kg / h), CHDM derivatives (including 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol, molar ratio of 1:3, 86.8 kg / h), Ge catalyst (1.3 kg / h), phosphoric acid (0.208 kg / h), blue toner (0.010 kg / h) and red toner (0.004 kg / h). The esterification reaction was carried out at 0.5 kgf / cm higher than normal pressure. 2 The polycondensation reaction was carried out at a pressure of 200° C. and a temperature of 260° C. for 8 hours, and at a temperature of 275° C. for 9 hours until the intrinsic viscosity (IV) reached 0.75 dl / g, and solid phase polymerization was not carried out.

[0190] Example 5

[0191] The same steps as in Example 1 were repeated to obtain about 50 tons of polyester resin (copolymer), except that bis(1,4-cyclohexanedimethanol) terephthalate oligomer (BHCT#4, 110.9 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 1886.4 kg / h), terephthalic acid (TPA, 484.3 kg / h), isophthalic acid (IPA, 1276.9 kg / h), ethylene glycol (EG, 11.0 kg / h), isosorbide (ISB, 20.7 kg / h), diethylene glycol (DEG, 22.5 kg / h), Ti catalyst (0.19 kg / h), phosphoric acid (4.167 kg / h), cobalt acetate (0.4 kg / h), blue toner (0.010 kg / h) and red toner (0.004 kg / h) were continuously fed. The esterification reaction is 3.0kgf / cm higher than the normal pressure. 2 The reaction was carried out at a pressure 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 phase polymerization reaction was carried out until the intrinsic viscosity (IV) reached 1.10 dl / g.

[0192] Example 6

[0193] The same steps as in Example 1 were repeated to obtain about 50 tons of polyester resin (copolymer), except that bis(isosorbide) terephthalate oligomer (BHIT#2, 312.2 kg / h), bis(2-hydroxyethyl) terephthalate (BHET, 765.8 kg / h), terephthalic acid (TPA, 1042.7 kg / h), ethylene glycol (EG, 249.2 kg / h), 1,4-cyclohexanedimethanol (CHDM, 434.2 kg / h), isosorbide (ISB, 73.4 kg / h), Ti catalyst (0.19 kg / h), phosphoric acid (2.083 kg / h), cobalt acetate (0.1 kg / h), blue toner (0.004 kg / h) and red toner (0.002 kg / h) were continuously fed. The esterification reaction was carried out at a pressure 3.0 kgf / cm higher than normal pressure. 2 The polycondensation reaction was carried out at a pressure of 200° C. and a temperature of 260° C. for 5 hours, and at a temperature of 280° C. for 3 hours until the intrinsic viscosity (IV) reached 0.55 dl / g, and solid phase polymerization was not carried out.

[0194] Comparative Example 1

[0195] The same steps as in Example 1 were repeated to obtain about 50 tons of polyester resin (copolymer), except that bis(2-hydroxyethyl)terephthalate (BHET, 1441.1 kg / h), ethylene glycol (EG, 10.6 kg / h), 1,4-cyclohexanedimethanol (CHDM, 277.8 kg / h), CHDM derivatives (containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol, in a molar ratio of 1:3, 24.9 kg / h), Ge catalyst (1.6 kg / h), Ti catalyst (0.11 kg / h), phosphoric acid (0.125 kg / h), blue toner (0.003 kg / h) and red toner (0.001 kg / h) were continuously fed. The esterification reaction was carried out at a pressure 2.0 kgf / cm higher than normal pressure. 2 The polycondensation reaction was carried out at a pressure of 255° C. for 7 hours, and at a temperature of 285° C. for 12 hours until the intrinsic viscosity (IV) reached 0.78 dl / g, and solid phase polymerization was not carried out.

[0196] Comparative Example 2

[0197] The same steps as in Example 1 were repeated to obtain about 50 tons of polyester resin (copolymer), except that bis(2-hydroxyethyl)terephthalate (BHET, 335.1 kg / h), terephthalic acid (TPA, 657.0 kg / h), ethylene glycol (EG, 26.2 kg / h), 1,4-cyclohexanedimethanol (CHDM, 493.9 kg / h), CHDM derivatives (containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol, molar ratio of 1:3, 24.9 kg / h), Ge catalyst (8.0 kg / h), phosphoric acid (0.025 kg / h), blue toner (0.004 kg / h) and red toner (0.001 kg / h) were continuously fed. The esterification reaction was carried out at a pressure 1.0 kgf / cm higher than normal pressure. 2 The polycondensation reaction was carried out at a pressure of 200° C. and a temperature of 265° C. for 5 hours, and at a temperature of 275° C. for 5 hours until the intrinsic viscosity (IV) reached 0.70 dl / g, and solid phase polymerization was not carried out.

[0198] The raw materials used in the Examples and Comparative Examples are summarized in Table 2 below.

[0199]

Table 2

[0200]

[0201]

[0202] Test Case

[0203] The raw materials and the tests of the final resins used in the Examples and Comparative Examples are as follows.

[0204] (1) Addition amount of recycled BHET

[0205] The mole number of bis(2-hydroxyethyl)terephthalate (BHET) added is calculated as a percentage (mol %) based on the total mole number of dicarboxylic acids and their derivatives (TPA, BHET, BHDT, BHIT and BHCT) added to prepare the polyester resin.

[0206] (2) The content of recycled materials in the resin

[0207] 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.), the total weight percentage (wt%) of recycled monomers and oligomers (BHET, BHDT, BHIT, and BHCT) was calculated.

[0208] (3) Diol recovery analysis (relationship between by-products and yield)

[0209] The total amount of by-products (diols) collected and removed during the polymerization reaction (esterification reaction and polycondensation reaction) of the polyester resin is measured. The total amount of by-products (diols) collected and removed (kg) is divided by the total time (h) required for the polymerization reaction (esterification reaction and polycondensation reaction) of the polyester resin to calculate the by-products relative to the output (kg / h).

[0210] The test results are shown in Table 3 below.

[0211]

Table 3

[0212]

[0213]

[0214] As can be seen from Table 3 above, the amount of diol that needs to be collected and removed in Comparative Examples 1 and 2 increases significantly compared to Examples 1 to 6. In addition, in Comparative Example 1, the total content of recycled raw materials in the resin is lower, although the amount of BHET used is larger than that of Example 2. In Comparative Example 2, even if the same amount of BHET as that of Example 2 is used, the total content of recycled raw materials in the resin is lower.

Claims

1. A method for preparing a polyester resin, comprising: Transesterifying bis(2-hydroxyethyl) terephthalate with a diol having 3 or more carbon atoms; collecting and removing by-product ethylene glycol formed during the transesterification reaction; Obtaining terephthalic acid bis(glycol) ester oligomer as a transesterification reaction product; as well as The polymerization was carried out using bis(glycol) terephthalate oligomers.

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

4. The method for preparing a polyester resin according to claim 1, wherein the diol having 3 or more carbon atoms comprises at least one selected from the group consisting of 1,3-propylene glycol, 1,4-butylene glycol, 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, diol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, copolymers of ethylene oxide and tetrahydrofuran, polypropylene glycol added with ethylene oxide, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, poly-1,5-pentanediol and their derivatives. 5 . The method for preparing a polyester resin according to claim 1 , wherein the diol having 3 or more carbon atoms comprises at least one recycled diol obtained by depolymerization of waste polyester. 6 . 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 method for preparing a polyester resin according to claim 1, The polymerization steps include: esterifying a bis(glycol)terephthalate oligomer and at least one comonomer; and The esterification reaction product is subjected to a condensation polymerization reaction to obtain a copolymer.

8. The method for preparing a polyester resin according to 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 method for preparing a polyester resin according to claim 8, wherein the dicarboxylic acid comprises terephthalic acid or isophthalic acid; The dicarboxylic acid derivatives include dimethyl terephthalate or dimethyl isophthalate; The diol includes diethylene glycol, 1,4-cyclohexanedimethanol, isosorbide, 1,2-propylene glycol, 1,3-propylene glycol, 2-methyl-1,3-propylene glycol, 2-methylene-1,3-propylene glycol, 2-ethyl-1,3-propylene glycol, 2-isopropyl-1,3-propylene glycol, 2,2-dimethyl-1,3-propylene glycol, 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; and The diol derivatives include 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol.

10. 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. The method for preparing a polyester resin according to claim 7, further comprising collecting and removing ethylene glycol in at least one of the esterification reaction and the polycondensation reaction. 12 . The method for producing a polyester resin according to claim 1 , wherein the collected and removed ethylene glycol is purified and then supplied again to at least one of the transesterification reaction and the polymerization step.

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

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. A method for preparing a terephthalic acid bis(glycol) ester oligomer, comprising: Transesterifying bis(2-hydroxyethyl) terephthalate with a diol having 3 or more carbon atoms; as well as The by-product ethylene glycol formed during the transesterification reaction is collected and removed.

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

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

18. The method for preparing terephthalic acid bis(glycol) ester oligomer according to claim 15, wherein the transesterification reaction and the collection and removal of ethylene glycol are carried out at a temperature of 120°C to 260°C and a pressure of 0.1 kgf / cm 2 Up to 2.0kgf / cm 2 under pressure.

19. A polyester resin prepared by the method according to claim 1.

20. A terephthalic acid bis(glycol) ester oligomer prepared by the method according to claim 15.

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