Recycled bis(4-hydroxybutyl) terephthalate, method for preparing same, and polyester resin using same

Abstract

The recycled bis(4-hydroxybutyl) terephthalate according to one embodiment has a low amount of residual ethylene glycol derivatives and can therefore be used as a polymerization raw material for high crystallinity engineering polyester products or biodegradable polyesters, offering superior qualities, for example, color.

Description

[Technical Field]

[0001] The present invention relates to the preparation of high purity bis(4-hydroxybutyl) terephthalate as a raw material for polyester resins using recycled monomers, and to polyester resins and articles obtained therefrom. [Background technology]

[0002] 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. In addition, 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 therefore they are widely used as raw materials for cases, boxes, partitions, shelves, panels, packaging materials, building materials, interior materials, exterior materials, etc.

[0003] As a result, plastic waste, such as polyester, is produced at uncontrollable levels worldwide every year. In recent years, countries around the world have created regulations and systems for recycling waste plastic resources, including waste polyester. Physical or chemical methods are used to recycle waste polyester, but physical recycling methods cannot guarantee purity and are therefore not widely used.

[0004] In chemical recycling methods, the ester bonds of waste polyester are cleaved and depolymerized. Reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis are used. Among them, glycolysis is the decomposition of waste polyester by adding glycols such as ethylene glycol or diethylene glycol at high temperatures. For example, bis(2-hydroxyethyl) terephthalate (BHET) can be obtained by glycolysis of waste polyethylene terephthalate (PET), and it is known to use it as a raw material to prepare polyester resins.

[0005] However, from the viewpoint of environmental consideration, it is more meaningful to convert waste PET products, which generally have a short lifespan, into long-life engineering polyester products or environmentally friendly biodegradable polyester products. In this regard, in recent years, attempts have been made to regenerate polyester resins other than PET by transesterification of waste PET and glycol. However, because an excessive amount of glycol is used in this reaction and the reaction time is long, there is a problem in that a large amount of by-products, such as cyclic ester compounds, are formed as a side reaction of the glycol. [Prior art document]

[0006] (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 [Problem to be solved by the invention]

[0007] The present inventors have attempted to develop a method for recycling BHET, obtained by depolymerization of waste PET-based products, into various engineering polyester products or environmentally friendly biodegradable polyester products, without using excessive amounts of glycols and minimizing the formation of by-products.

[0008] On the other hand, recycled BHET generally has low purity due to impurities formed from the reagents used in the depolymerization process and side reactions, so costly processes such as ion exchange or recrystallization are required to purify it, making it difficult to utilize commercially.

[0009] As a result of research conducted to solve this problem, it has become possible to obtain high-purity recycled bis(4-hydroxybutyl) terephthalate by using low-purity BHET or reducing the amount of 1,4-butanediol used by introducing BHET in portions or continuously into the transesterification reaction with 1,4-butanediol. As a result, it can be used as a raw material for preparing high-quality engineering polyester products or environmentally friendly biodegradable polyester products.

[0010] Therefore, an object of the present invention is to prepare high purity recycled bis(4-hydroxybutyl) terephthalate by using recycled BHET without using excessive amounts of 1,4-butanediol, to provide a raw material for the polymerization of various high quality polyester resins, and to provide various high quality polyester resins and articles therefrom. [Means for solving the problem]

[0011] According to an embodiment of the present invention, the total content of ethylene glycol, diethylene glycol, and derivatives thereof is: 1 There is provided recycled bis(4-hydroxybutyl) terephthalate having 20 mole % or less, based on the total moles of total glycols and their derivatives, as measured by H-NMR, and a color b value of 8 or less in the Hunter Lab color space when prepared into a test specimen having a thickness of 6 mm.

[0012] According to another aspect of the present invention, there is provided a method for producing a 1,4-butanediol-containing product, comprising: (1) supplying 1,4-butanediol to a reaction vessel; and (2) supplying bis(2-hydroxyethyl) terephthalate to the reaction vessel in portions or continuously to carry out a transesterification reaction, wherein the reaction satisfies the following formula (1): 1.5≦G / B≦3.5...(1) A method for preparing recycled bis(4-hydroxybutyl) terephthalate is provided, in which the above-mentioned conditions are met.

[0013] In relation (1), G is the total number of moles of 1,4-butanediol fed to the reaction vessel, and B is the total number of moles of bis(2-hydroxyethyl) terephthalate fed to the reaction vessel.

[0014] According to another aspect of the present invention, there is provided a raw material for the polymerization of polyester resins, comprising recycled bis(4-hydroxybutyl) terephthalate.

[0015] According to another aspect of the present invention, there is provided a method for preparing a polyester resin, the method comprising the steps of: (1) supplying 1,4-butanediol to a reaction vessel; (2) supplying bis(2-hydroxyethyl) terephthalate to the reaction vessel in portions or continuously to carry out a transesterification reaction; and (3) subjecting the product of the transesterification reaction to a polycondensation reaction, wherein the above-mentioned relationship (1) is satisfied.

[0016] According to another aspect of the present invention, there is provided a polyester resin prepared by the above-described process. [Effects of the Invention]

[0017] The recycled bis(4-hydroxybutyl) terephthalate of the present invention has a low content of ethylene glycol derivatives, which allows it to provide polyester resins with excellent crystallinity and purity.In addition, the recycled bis(4-hydroxybutyl) terephthalate of the present invention has excellent qualities such as color and can be easily crushed to produce flakes or powder, making it suitable for use as a raw material for various polymers.

[0018] Specifically, the present invention enables the preparation of high-purity 1,4-butanediol-derived polybutylene terephthalate-based polyester resins (such as PBT or TPEE), which can be used to produce high-value-added engineering polyester products or biodegradable polyester products (such as PBAT) with reduced ethylene glycol content, which can affect ecotoxicity from waste PET products.

[0019] In particular, according to the present invention, in the preparation of bis(4-hydroxybutyl) terephthalate by the transesterification of BHET and 1,4-butanediol, a certain amount of BHET relative to 1,4-butanediol is introduced into the reaction with 1,4-butanediol in portions or continuously, thereby enabling the use of low-purity BHET or increasing the purity while reducing the amount of 1,4-butanediol, which is advantageous from the standpoint of cost. [Brief explanation of the drawings]

[0020] [Figure 1] 1 shows the change in the residual percentage of ethylene glycol derivative over time for different feeding methods during the transesterification reaction. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will now be described in further detail.

[0022] In this specification, the terms referring to each component are used to distinguish them from each other and are not intended to limit the scope of the embodiments. In addition, in this specification, the singular forms "a," "an," and "the" are to be construed as including the plural unless the context clearly dictates otherwise.

[0023] 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 only to distinguish one element from another.

[0024] As used herein, the term "comprising" is intended to specify certain features, regions, steps, processes, elements, and / or components. This does not exclude the presence or addition of any other features, regions, steps, processes, elements, and / or components, unless specifically stated to the contrary.

[0025] The molecular weights of the compounds or polymers described herein, e.g., number average molecular weight or weight average molecular weight, are, as is well known, relative masses based on carbon 12. The units are not described, but may, if desired, be understood as molar masses (g / mol) of the same numerical value.

[0026] 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.

[0027] As used herein, a unit or group "derived from" a particular component refers to a portion of the component contained in the final product of a chemical reaction such as a polymerization reaction. This may be present in a form that has been modified during the reaction or that is combined with other components. For example, a unit or group derived from at least one monomer is contained in a chain that constitutes a polymer.

[0028] According to an aspect of the present invention, a method is provided for preparing recycled bis(4-hydroxybutyl) terephthalate, which can be used as a raw material for various polymers, by transesterification of bis(2-hydroxyethyl) terephthalate and 1,4-butanediol.

[0029] A method for preparing recycled bis(4-hydroxybutyl) terephthalate includes the steps of (1) supplying 1,4-butanediol to a reaction vessel, and (2) supplying bis(2-hydroxyethyl) terephthalate in portions or continuously to the reaction vessel to carry out a transesterification reaction.

[0030] Bis(2-hydroxyethyl) terephthalate In the bis(2-hydroxyethyl) terephthalate used in the present invention, the ethylene glycol residue is replaced with a 1,4-butanediol residue through a transesterification reaction. It may then be polymerized to form the polymer chain of the final polyester resin. Bis(2-hydroxyethyl) terephthalate is an ester of two ethylene glycols and one terephthalic acid. For example, it is a compound formed as an intermediate in the process of preparing polyesters such as polyethylene terephthalate (PET) by polymerization of ethylene glycol and terephthalic acid or its ester.

[0031] The bis(2-hydroxyethyl) terephthalate used in the present invention may be obtained by depolymerization of waste polyester. For example, bis(2-hydroxyethyl) terephthalate may be obtained from waste polyester having repeating units of ethylene glycol and terephthalic acid, such as polyethylene terephthalate (PET) or glycol-modified polyethylene terephthalate (PETG). Specifically, it may be obtained by well-known depolymerization methods such as glycolysis, hydrolysis, and methanolysis. In particular, bis(2-hydroxyethyl) terephthalate may be obtained by depolymerizing waste polyethylene terephthalate using ethylene glycol and then purifying it.

[0032] Because recycled bis(2-hydroxyethyl) terephthalate is subjected to several chemical steps in the process of preparing it from waste plastic, bis(2-hydroxyethyl) terephthalate with various purities is commercially available depending on the type of waste plastic and the depolymerization and purification methods.

[0033] The recycled bis(2-hydroxyethyl) terephthalate (referred to as recycled BHET or abbreviated as r-BHET or rBHET) obtained by depolymerization of waste polyester as described above may contain by-products formed by side reactions with reagents or solvents used in various chemical processes during the depolymerization of waste polyester. Therefore, recycled bis(2-hydroxyethyl) terephthalate obtained by depolymerization of waste polyester as described above should be understood to be different from a pure BHET compound. For this reason, recycled BHET can also be considered a type of composition containing two or more components, i.e., a BHET composition. Such recycled BHET may be used as a raw material for polymerization of polyester resins. Therefore, BHET recycled by a conventional depolymerization process contains organic and inorganic impurities in addition to BHET as the main component, and therefore its purity is low.

[0034] 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 1 wt. % or more, 3 wt. % or more, or 5 wt. % or more, and may be 30 wt. % or less, 25 wt. % or less, 20 wt. % or less, or 15 wt. % or less.

[0035] The purity of the recycled BHET may be measured using liquid chromatography, etc. Specifically, the purity of the recycled BHET may be calculated by measuring the percentage (%) of the peak area of ​​BHET relative to the total peak area in a spectrum obtained using high performance liquid chromatography (HPLC).

[0036] For example, the purity of the recycled BHET may be 99% or less, 97% or less, or 95% or less, or 70% or more, 75% or more, or 80% or more. Specifically, the purity of the BHET introduced into the transesterification reaction may be 70% to 99%, more specifically, 75% to 97% or 80% to 95%.

[0037] Transesterification 1,4-butanediol and bis(2-hydroxyethyl) terephthalate are subjected to a transesterification reaction.

[0038] [ka]

[0039] The 1,4-butanediol undergoes a transesterification reaction to form the residue of a reaction product, bis(4-hydroxybutyl) terephthalate, or an oligomer thereof, which may form the polymer chains of the final polyester resin.

[0040] The 1,4-butanediol introduced into the transesterification reaction has a boiling point more than 30° C. higher than that of ethylene glycol, which is advantageous with regard to purification by fractional distillation during the reaction.

[0041] The transesterification reaction may be carried out in the presence of a catalyst. Thus, when 1,4-butanediol or bis(2-hydroxyethyl) terephthalate is fed to the reaction vessel, the catalyst may be fed thereto.

[0042] As a catalyst for the transesterification reaction, for example, at least one selected from the group consisting of a titanium-based catalyst, a germanium-based catalyst, an antimony-based catalyst, an aluminum-based catalyst, and a tin-based catalyst may be used.

[0043] Examples of titanium-based catalysts include tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, triethanolamine titanate, acetylacetonate titanate, ethylacetoacetate titanate, isostearyl titanate, and titanium dioxide. Examples of germanium-based catalysts include germanium dioxide, germanium tetrachloride, germanium ethylene glycol oxide, germanium acetate, coprecipitates thereof, or mixtures thereof. Specifically, germanium dioxide can be used as the germanium-based catalyst. Both crystalline and amorphous germanium dioxides can be used as the germanium dioxide, and glycol-soluble germanium dioxides can also be used.

[0044] The amount of transesterification catalyst used may vary depending on the reaction conditions and catalyst used. For example, a metal-based catalyst (e.g., a titanium-based catalyst or a tin-based catalyst) may be used such that the weight of the metal-based catalyst is 10 ppm to 300 ppm based on the total weight of bis(2-hydroxyethyl) terephthalate fed to the reaction vessel. If it is less than 10 ppm, the transesterification reaction rate may be too slow, and therefore, it may be difficult to obtain recycled bis(4-hydroxybutyl) terephthalate with the desired high purity. If it is more than 300 ppm, the color b value of the resulting recycled bis(4-hydroxybutyl) terephthalate may be too high, and therefore, it may not be suitable as a raw material for the polymerization of polyester resins.

[0045] The transesterification reaction may be carried out in a batch or continuous manner.

[0046] As an example, 1,4-butanediol may be fed to a reaction vessel, the temperature may be increased, and when the temperature reaches a certain level, bis(2-hydroxyethyl) terephthalate may be fed.

[0047] Additionally, the transesterification reaction may be carried out under a nitrogen atmosphere.

[0048] For example, the bis(2-hydroxyethyl) terephthalate feed may be carried out at a temperature of 165° C. to 220° C. in a nitrogen atmosphere while ethylene glycol is removed as a by-product.

[0049] According to the invention, bis(2-hydroxyethyl) terephthalate is introduced in portions or continuously into the transesterification reaction with 1,4-butanediol.

[0050] According to one embodiment, bis(2-hydroxyethyl) terephthalate is introduced into the transesterification reaction with 1,4-butanediol in two or more portions.

[0051] The number of divided introductions may be 2 or more, 3 or more, 4 or more, or 5 or more, or may be 100 or less, 50 or less, 30 or less, 20 or less, 15 or less, or 10 or less. As a specific example, the number of divided introductions may be 2 to 30 or 3 to 15.

[0052] The time interval between the divided introductions may be determined by dividing the total introduction time period by the number of divided introductions, which may be, for example, 1 hour or more, or 2 hours or more, or 5 hours or less, or 4 hours or less.

[0053] Additionally, the amount to be introduced in one portion of the divided introduction may be determined by dividing the total amount of bis(2-hydroxyethyl) terephthalate to be introduced into the reaction by the number of divided introductions.

[0054] According to the present invention, the total amount of components introduced into the transesterification reaction satisfies the following relation (1): 1.5≦G / B≦3.5...(1)

[0055] In relation (1), G is the total number of moles of 1,4-butanediol fed to the reaction vessel, and B is the total number of moles of bis(2-hydroxyethyl) terephthalate fed to the reaction vessel.

[0056] If G / B is less than 1.5, a large amount of ethylene glycol residues derived from BHET will be present, which may reduce the purity of the recycled bis(4-hydroxybutyl) terephthalate. If G / B exceeds 3.5, an excessive amount of 1,4-butanediol will be supplied, which is undesirable. For example, G / B may be 1.5 or more, 1.8 or more, or 2.0 or more, or 3.5 or less, 3.0 or less, or 2.5 or less. As a specific example, G / B may be 1.5 to 3.0, or 1.5 to 2.5.

[0057] The number of divided introductions and the total introduction amount can be more efficiently controlled by the following relation (2).

[0058]

number

[0059] In relationship (2), G is the total number of moles of 1,4-butanediol fed to the reaction vessel, B is the total number of moles of bis(2-hydroxyethyl) terephthalate fed to the reaction vessel, and N is the number of divided introductions of bis(2-hydroxyethyl) terephthalate.

[0060] For example, the R value may be 5 or more, 6 or more, 8 or more, or 10 or more, or may be 100 or less, 50 or less, 30 or less, or 20 or less. As a specific example, it may be 4 to 50 or 6 to 30.

[0061] FIG. 1 shows the change in the residual percentage of ethylene glycol derivative over time during the transesterification reaction, with respect to the feeding method.

[0062] Referring to FIG. 1 , (a) when the ethylene glycol derivatives (mainly BHET) are introduced in a single portion with a G / B set at 2.5 (i.e., R=2.5), the amount of the ethylene glycol derivatives (mainly BHET) decreases from a maximum (100%) at the beginning of the introduction as the reaction proceeds; however, even at the time of reaction completion, the residual rate of the ethylene glycol derivatives remains at a high level (30%); (b) when the ethylene glycol derivatives are introduced in a single portion with a G / B set at 4.0 (i.e., R=4.0), the amount of the ethylene glycol derivatives decreases more rapidly and reaches a low level (10%) at the time of reaction completion; and (c) when the ethylene glycol derivatives are introduced in four portions with a G / B set at 2.5 (i.e., R=10.0), the amount of the ethylene glycol derivatives is maintained at a certain level (40%) or less throughout the reaction process, and in particular reaches a very low level (3%) at the time of reaction completion.

[0063] In the conventional processes (a) and (b) of Figure 1, an excess amount of 1,4-butanediol is required to reduce the residual percentage of the final ethylene glycol derivative, which increases costs. In contrast, in the process (c) of the present invention, the residual amount of ethylene glycol derivative in the final product can be made to a very low level without even increasing the amount of 1,4-butanediol.

[0064] According to another embodiment, bis(2-hydroxyethyl) terephthalate is introduced sequentially into a transesterification reaction with 1,4-butanediol.

[0065] The total time for continuous introduction may be, for example, 1 hour or more, or 2 hours or more, or 5 hours or less, or 4 hours or less.

[0066] For example, continuous introduction may be the introduction of a constant amount of bis(2-hydroxyethyl) terephthalate per hour. The amount of introduction per hour may be determined by dividing the total amount of bis(2-hydroxyethyl) terephthalate to be introduced into the reaction by the total introduction time.

[0067] Specifically, bis(2-hydroxyethyl) terephthalate may be dissolved in water at 80 to 100°C to prepare an aqueous BHET solution having a concentration of about 10 to 20% by weight, and the solution may be continuously introduced into the transesterification reaction. Continuous introduction may be carried out, for example, up to one hour before the end of the reaction. For continuous introduction of a fixed amount, a dropping funnel may be used in a laboratory setting, or a weighing feeder may be used in a commercial setting.

[0068] As a more specific example, a total of 577 g of bis(2-hydroxyethyl) terephthalate to be introduced may be dissolved in 3,861 g of purified water at 90° C. to prepare a slurry, and an aqueous BHET solution may be metered in at 18.5 g per minute for 4 hours out of the total 5 hours required for the transesterification reaction.

[0069] When the introduction of bis(2-hydroxyethyl) terephthalate in portions or continuously is completed, the reaction conditions may be maintained until the transesterification reaction is completed. In addition, the step of removing ethylene glycol as a by-product in a nitrogen atmosphere may be continued during the transesterification reaction. The removal of ethylene glycol may be carried out by a distillation process using the difference in boiling point between ethylene glycol and other components. For effective removal by distillation, nitrogen or an inert gas may be used. The ethylene glycol thus distilled off may be recovered by cooling and reused in other processes.

[0070] The end point of the transesterification reaction may 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 no more by-products are released.

[0071] The pressure in the reaction vessel for the transesterification reaction in a nitrogen atmosphere is, for example, 0.01 kg / cm 2 More than 0.05kg / cm 2 or more, or 0.1 kg / cm 2It may be more than 0.5 kg / cm 2 Below, 0.3kg / cm 2 Below 0.2kg / cm 2 or less than 1.5 kg / cm 2 The temperature during the transesterification reaction may be 165°C or higher, 170°C or higher, 180°C or higher, or 190°C or higher, and may be 225°C or lower, 220°C or lower, 215°C or lower, 210°C or lower, or 200°C or lower. Specifically, the transesterification reaction may be carried out at a temperature of 170°C or higher to facilitate the removal of ethylene glycol as a by-product. In addition, it may be carried out at a temperature 10°C lower than the boiling point of 1,4-butanediol to reduce the loss of 1,4-butanediol due to substitution. As a more specific example, the temperature during the transesterification reaction with 1,4-butanediol may be adjusted to 170°C to 220°C.

[0072] Recycled bis(4-hydroxybutyl) terephthalate The products of the transesterification reaction mainly include bis(4-hydroxybutyl) terephthalate and its derivatives, in which the ethylene glycol residue in bis(2-hydroxyethyl) terephthalate is replaced with other 1,4-butanediol residues. Recycled bis(4-hydroxybutyl) terephthalate includes components obtained by depolymerization of waste polyester.

[0073] Therefore, recycled bis(4-hydroxybutyl) terephthalate should be understood as something different from a pure bis(4-hydroxybutyl) terephthalate compound. For this reason, recycled bis(4-hydroxybutyl) terephthalate can be viewed as a type of composition containing two or more components. In other words, it can be understood as a bis(4-hydroxybutyl) terephthalate composition.

[0074] Specifically, recycled bis(4-hydroxybutyl) terephthalate (abbreviated as recycled BHBT, r-BHBT or rBHBT), obtained by transesterification with recycled BHET, can be represented by the following formula 1:

[0075] [ka] The compound includes a compound represented by

[0076] In formula 1, m is an integer of 1 to 4.

[0077] In other words, the recycled bis(4-hydroxybutyl) terephthalate may contain two or more derivatives of the compound represented by Formula 1, that is, monomers and oligomers such as dimers and trimers.

[0078] However, the product of the transesterification reaction may contain some unreacted materials or by-products in addition to the compound of Formula 1. Specifically, the product of the transesterification reaction may contain some impurities contained in the recycled BHET as its raw material, the reagents or solvents used in the transesterification reaction, or by-products formed by side reactions therewith.

[0079] As an example, the product of the transesterification reaction may include components derived from the unreacted 1,4-butanediol used as a starting material and the recycled bis(2-hydroxyethyl) terephthalate. Specifically, the product of the transesterification reaction may include ethylene glycol derivatives and diethylene glycol derivatives.

[0080] The ethylene glycol derivative and diethylene glycol derivative may be ethylene glycol or a compound having an ethylene glycol residue, such as ethylene glycol, diethylene glycol, or an ester thereof. Specifically, the ethylene glycol derivative and diethylene glycol derivative may include ethylene glycol, diethylene glycol, bis(2-hydroxyethyl) terephthalate, 2-hydroxyethyl terephthalate, 2-hydroxyethyl-4-hydroxybutyl terephthalate, bis(diethylene glycol) terephthalate, 2-hydroxydiethyl-diethylene glycol terephthalate, 4-hydroxybutyl-diethylene glycol terephthalate, and oligomers thereof.

[0081] As a specific example, the total content of ethylene glycol, diethylene glycol, and their derivatives present in the product of the transesterification reaction may be 20 mole % or less, based on the total moles of all glycols and their derivatives. As a more specific example, the total content of ethylene glycol, diethylene glycol, and their derivatives may be 15 mole % or less, based on the total moles of all glycols and their derivatives. The content is based on the amount of all glycols and their derivatives present in the product of the transesterification reaction.

[0082] In other words, the total content of ethylene glycol, diethylene glycol, and their derivatives in the recycled bis(4-hydroxybutyl) terephthalate according to the present invention is: 1The content of ethylene glycol residues is 20 mol% or less, based on the total moles of total glycols and their derivatives, as measured by H-NMR. For example, the total content of ethylene glycol, diethylene glycol, and their derivatives may be 15 mol% or less, 12 mol% or less, or 10 mol% or less. Meanwhile, the lower limit of the total content of ethylene glycol, diethylene glycol, and their derivatives is not particularly limited, and may be, for example, 0 mol% or more, more than 0 mol%, 0.01 mol% or more, 1 mol% or more, 3 mol% or more, or 5 mol% or more. The content of ethylene glycol residues is, for example, 0 mol% or more, more than 0 mol%, 0.01 mol% or more, 1 mol% or more, 3 mol% or more, or 5 mol% or more, with respect to the recycled BHBT. 1 By obtaining and analyzing H-NMR spectra, the total content of compounds containing ethylene glycol residues and diethylene glycol residues may be calculated based on the amount of all compounds.

[0083] Therefore, the recycled bis(4-hydroxybutyl) terephthalate of the present invention can be used as a raw material for preparing highly crystalline 1,4-butanediol-derived polyester resins, and the crystallinity of the polyester resins can be increased within the above-mentioned content range, resulting in better heat resistance and mechanical properties.

[0084] The recycled bis(4-hydroxybutyl) terephthalate prepared by the present invention may be crushed or pulverized at room temperature. Specifically, the recycled bis(4-hydroxybutyl) terephthalate may be crushed or pulverized into flakes of 0.2 g or less at room temperature. Therefore, the recycled bis(4-hydroxybutyl) terephthalate may be stored in a flake or powder state before being used as a polymerization raw material.

[0085] The recycled bis(4-hydroxybutyl) terephthalate according to the present invention, when prepared into a test piece having a thickness of 6 mm, has a color b value of 8 or less in the Hunter Lab color space. Specifically, the color b value may be 7 or less, 6 or less, 5 or less, 4 or less, or 3 or less. Meanwhile, the lower limit of the color b value is not particularly limited, and may be, for example, 0 or more, more than 0, 1 or more, or 2 or more.

[0086] According to a specific embodiment, the total content of ethylene glycol, diethylene glycol, and derivatives thereof may be 15 mole % or less, based on the total moles of total glycols and derivatives thereof, and the color b value may be 5 or less.

[0087] According to the present invention, the low amount of residual ethylene glycol derivatives in recycled bis(4-hydroxybutyl) terephthalate makes it possible to prepare high-purity 1,4-butanediol-derived polybutylene terephthalate-based polyester resins (e.g., PBT or TPEE) and to produce high-value engineering polyester or biodegradable polyester (e.g., PBAT) products with low content of ecotoxicologically toxic ethylene glycol from waste PET products. In addition, the recycled bis(4-hydroxybutyl) terephthalate products according to the present invention can be easily crushed to produce flakes or powder and have excellent color, making them suitable for use as polymerization raw materials.

[0088] According to another aspect of the present invention, there is provided a raw material for the polymerization of polyester resins, comprising recycled bis(4-hydroxybutyl) terephthalate.

[0089] Preparation of polyester resin (polycondensation reaction) The product of the transesterification reaction (ie, the mixture containing recycled bis(4-hydroxybutyl) terephthalate) may be subjected to a polycondensation reaction to prepare a polyester resin.

[0090] A method for preparing a polyester resin according to one embodiment of the present invention includes the steps of (1) supplying 1,4-butanediol to a reaction vessel, (2) supplying bis(2-hydroxyethyl) terephthalate to the reaction vessel in portions or continuously to carry out a transesterification reaction, and (3) subjecting the product of the transesterification reaction to a polycondensation reaction, wherein the components supplied to the reaction vessel satisfy the above-mentioned relational formula (1).

[0091] The polycondensation reaction may be carried out, for example, by reacting the transesterification reaction product at a temperature of 150°C to 300°C under reduced pressure conditions of 0.01 mmHg to 600 mmHg for 1 hour to 24 hours.

[0092] The temperature in the polycondensation reaction may be 150°C to 300°C, specifically 200°C to 290°C, and 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, and more specifically 0.1 mmHg to 100 mmHg. The temperature and pressure of the polycondensation reaction can advantageously remove glycol, a by-product of the polycondensation reaction, from the system. In addition, 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 an appropriate level.

[0093] The catalyst for the polycondensation reaction may be, for example, at least one selected from the group consisting of titanium-based catalysts, germanium-based catalysts, antimony-based catalysts, aluminum-based catalysts, and tin-based catalysts. Examples of titanium-based catalysts include tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, triethanolamine titanate, acetylacetonate titanate, ethylacetoacetic ester titanate, isostearyl titanate, and titanium dioxide. Examples of germanium-based catalysts include germanium dioxide, germanium tetrachloride, germanium ethylene glycol oxide, germanium acetate, or a combination thereof. Specifically, germanium dioxide can be used as the germanium-based catalyst. Both crystalline and amorphous germanium dioxides may be used, and glycol-soluble germanium dioxides may also be used.

[0094] Additionally, at least one of a glycol component and an acid component may be further introduced into the polycondensation reaction.

[0095] For example, the specific type of glycol component that may be further introduced into the polycondensation reaction may be a glycol monomer (eg, alkylene glycol) or a polymeric glycol (eg, polyether). Specifically, the glycol component may be selected from the group consisting of 1,3-propanediol, 1,4-cyclohexanedimethanol, 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, ethylene oxide-added polypropylene glycol, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, and poly-1,5-pentanediol.

[0096] In addition, the acid component that may be further introduced into the polycondensation reaction may be, for example, at least one selected from dicarboxylic acids and their esters. Specifically, the acid component may be selected from the group consisting of adipic acid, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, fumaric acid, glutaric acid, azelaic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, 4,4'-stilbenedicarboxylic acid, 2,5-furandicarboxylic acid, and 2,5-thiophenedicarboxylic acid.

[0097] Alternatively, ethylene glycol may be introduced as an additional glycol component and terephthalic acid may be introduced as an additional acid component in the polycondensation reaction, if desired.

[0098] Polyester resin According to another aspect of the present invention, there is provided a polyester resin prepared by the above-mentioned process. In other words, the polyester resin is prepared by polycondensation of recycled bis(4-hydroxybutyl) terephthalate obtained by transesterification, and therefore contains a polymer of recycled bis(4-hydroxybutyl) terephthalate. Therefore, the polyester resin contains units derived from components derived from recycled bis(4-hydroxybutyl) terephthalate.

[0099] In addition, since the recycled bis(4-hydroxybutyl) terephthalate contains unreacted glycol and acid components, or by-products such as ethylene glycol, in addition to bis(4-hydroxybutyl) terephthalate, units derived from these components may be incorporated into the polyester resin by subsequent polycondensation.

[0100] Specifically, the polyester resin may contain units derived from one or more glycol components and units derived from one or more acid components. The one or more glycol components may be the glycol monomers or polymer glycols exemplified above. The one or more acid components may be the aliphatic dicarboxylic acids and aromatic dicarboxylic acids exemplified above.

[0101] The glycol component and acid component constituting the polyester resin are derived from the bis(2-hydroxyethyl) terephthalate and glycol component initially introduced for preparing the polyester resin, or recycled bis(4-hydroxybutyl) terephthalate prepared therefrom, and an acid component additionally introduced.

[0102] The polyester resin may be a homopolymer or copolymer resin. For example, the polyester resin may be a homopolymer resin containing 1,4-butanediol as the glycol component and terephthalic acid as the acid component, in other words, a polybutylene terephthalate (PBT) resin. For another example, the polyester resin may be a copolymer resin containing 1,4-butanediol and an additional glycol as the glycol component, and terephthalic acid and an additional acid as the acid component. The additional glycol and acid components may be the glycol and acid components previously exemplified as those that can be additionally introduced into the polycondensation step in the method for preparing the polyester resin.

[0103] The polyester resin may have a total content of ethylene glycol residues and diethylene glycol residues below a certain level. For example, the total content of ethylene glycol residues and diethylene glycol residues of the polyester resin may be 20 mol% or less, 15 mol% or less, 10 mol% or less, 8 mol% or less, 7.5 mol% or less, 7 mol% or less, 6 mol% or less, 5 mol% or less, 4 mol% or less, or 3 mol% or less, based on the number of moles of total glycol residues. In addition, the total content of ethylene glycol residues and diethylene glycol residues may be 0 mol% or more, 0.01 mol% or more, 0.02 mol% or more, or 0.03 mol% or more. The total content of ethylene glycol residues and diethylene glycol residues may be: 1 The amount of the residues may be calculated by analyzing the spectrum of the resulting polyester resin by H-NMR. These residues may be derived from ethylene glycol, diethylene glycol, and their derivatives. As a specific example, the polyester resin may be 1When measured by H-NMR, the total content of ethylene glycol residues and diethylene glycol residues may be 0.01 mol % to 20 mol % based on the number of moles of all glycol residues. More specifically, the total content of ethylene glycol residues and diethylene glycol residues may be 0.01 mol % to 15 mol %, or 0.1 mol % to 10 mol %, based on the number of moles of all glycol residues. Within the above content ranges, the crystallinity of the polyester resin can be increased, thereby improving heat resistance and mechanical properties.

[0104] The polyester resin may have an intrinsic viscosity at 35°C of 0.5 dl / g to 1.5 dl / g. For example, the intrinsic viscosity at 35°C of the polyester resin may be 0.5 dl / g or more, 0.55 dl / g or more, 0.6 dl / g or more, 0.7 dl / g or more, 0.8 dl / g or more, 0.9 dl / g or more, or 1.0 dl / g or more, and may be 1.5 dl / g or less, 1.4 dl / g or less, 1.3 dl / g or less, 1.2 dl / g or less, 1.1 dl / g or less, 1.0 dl / g or less, or 0.7 dl / g or less. As a specific example, the polyester resin may have an intrinsic viscosity at 35°C of 0.55 to 1.1 dl / g or 0.6 to 0.7 dl / g.

[0105] The polyester resin may have a melting point (Tm) of 100° C. or more, 150° C. or more, or 200° C. or more, and 300° C. or less, 280° C. or less, 260° C. or less, or 240° C. or less. The polyester resin may have a heat of fusion (ΔH) of 10 J / g or more, 15 J / g or more, or 20 J / g or more, and 60 J / g or less, 50 J / g or less, or 40 J / g or less. f As a specific example, the polyester resin may have a melting point (Tm) of 100° C. or more and a heat of fusion (ΔH f As a more specific example, the polyester resin may have a melting point (Tm) of 200° C. or more and a heat of fusion (ΔH f ) may be included.

[0106] The polyester resin according to the present invention, when prepared into a test piece having a thickness of 6 mm, has a color b value of 18 or less in the Hunter Lab color space. Specifically, the color b value may be 15 or less, 13 or less, 11 or less, 10 or less, or 9 or less. On the other hand, the lower limit of the color b value is not particularly limited, and may be, for example, 0 or more, more than 0, 1 or more, or 2 or more.

[0107] The polyester resin prepared by the above process may have a state such as chip, pellet, or powder before molding. It may also have the shape of a molded article formed by a separate molding process such as extrusion or injection, for example, in the form of a film or sheet, or in the form of various injected parts for automotive, electrical, and industrial purposes.

[0108] Thus, the present invention also provides an article comprising a polyester resin.

[0109] In particular, the polyester resin of the present invention can be used as a high-value-added engineering polyester product or a biodegradable polyester product with a low content of ethylene glycol components that affect ecotoxicity.

[0110] Aspects of the invention Preferred embodiments are presented below for understanding the present invention. However, the following examples are provided only to facilitate understanding of the present invention, and are not intended to limit the scope of the present invention. [Example]

[0111] <Preparation of recycled bis(2-hydroxyethyl) terephthalate> Preparation example: rBHET1 A stainless steel (SUS) reactor was charged with 1,000 g of waste polyester resin, 4,000 g of ethylene glycol, and 3.5 g of zinc acetate anhydride. The temperature inside the reactor was raised to 196°C, and depolymerization by glycolysis reaction was carried out for 4 hours.

[0112] The reaction product was cooled to 30°C, and crystallization of bis(2-hydroxyethyl) terephthalate was carried out for 2 hours. The resulting slurry of bis(2-hydroxyethyl) terephthalate and ethylene glycol was subjected to solid-liquid separation in a centrifuge.

[0113] The bis(2-hydroxyethyl) terephthalate obtained by centrifugation was washed twice with sufficient distilled water, and the residual solvent was removed in an oven to obtain about 1,100 g of a final product containing bis(2-hydroxyethyl) terephthalate.

[0114] Preparation example: rBHET2 and rBHET3 Recycled bis(2-hydroxyethyl) terephthalate of various purities was prepared similarly to the preparation example of rBHET1, except that the purification process was adjusted.

[0115] To confirm the purity of the recycled bis(2-hydroxyethyl) terephthalate prepared in this manner, 0.01 g of each sample (rBHET1, rBHET2, or rBHET3) was diluted in 20 mL of methanol or chloroform and subjected to high-performance liquid chromatography (HPLC). In the HPLC spectrum, the areas of the BHET peak and the impurity peaks (other oligomers, DEG derivatives, and unreacted monomer) were summed and calculated as a percentage of the total peak area. The results are shown in the table below.

[0116] [Table 1]

[0117] <Preparation of recycled bis(4-hydroxybutyl) terephthalate and polyester resins> Example 1 Step (1): Preparation of recycled bis(4-hydroxybutyl) terephthalate by transesterification A 1-liter reactor for transesterification, equipped with a column and a condenser and capable of being cooled with water, was charged with 614 g of 1,4-butanediol (BD) as a glycol component and 58 mg of tetrabutyl titanate (TBT) as a reaction catalyst. The pressure in the reactor was then reduced to 0.1 kg / cm by flowing nitrogen. 2 The temperature was adjusted to 190°C, and the temperature was increased while maintaining the pressure and stirring. When the temperature in the reaction vessel reached approximately 190°C, 96.2 g of bis(2-hydroxyethyl) terephthalate (rBHET2) was added in six portions to carry out the transesterification reaction while maintaining the temperature at 190°C for 4 hours. During the reaction, glycol, a by-product, was discharged through a column and a condenser. Even after the addition of BHET was completed, the transesterification reaction was continued while maintaining 190°C until the glycol discharge stopped. Upon completion of the transesterification reaction, the nitrogen in the pressurized reaction vessel was released to the outside, and the pressure in the reaction vessel was reduced to atmospheric pressure. The resulting product (a mixture containing bis(4-hydroxybutyl) terephthalate) was then discharged to the outside and formed into a sheet. The product was allowed to solidify by natural cooling and then crushed to obtain 700 g of recycled bis(4-hydroxybutyl) terephthalate in the form of flakes with an average weight of approximately 0.5 to 1 g.

[0118] Step (2): Preparation of polyester resin by polycondensation reaction 300.7 g of recycled bis(4-hydroxybutyl) terephthalate (rBHBT) obtained in step (1) was fed to a polycondensation reaction vessel. The pressure in the reaction vessel was reduced from atmospheric pressure to 5.0 Torr (absolute pressure: 5 mmHg) over 30 minutes. Simultaneously, the temperature of the reaction vessel was increased to 245°C over 1 hour, and the polycondensation reaction was carried out while maintaining the pressure in the reaction vessel at 1 Torr (absolute pressure: 1 mmHg) or less. A high stirring speed was also possible at the start of the polycondensation reaction. As the polycondensation reaction progressed, the by-product glycol component was discharged from the reaction vessel. If the stirring force weakened due to an increase in the viscosity of the reaction mixture or if the temperature of the reaction mixture rose above the set temperature, the stirring speed was adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reaction vessel reached approximately 0.86 dL / g. When the intrinsic viscosity of the mixture in the reactor reached a desired level, the mixture was then discharged out of the reactor to form strands, which were solidified using a cooling liquid and then granulated to an average weight of approximately 12-14 mg, yielding 213.3 g of polyester resin.

[0119] Example 2 The same procedure as in Example 1 was repeated to obtain 196.2 g of a polyester resin, except that in step (1), 696 g of 1,4-butanediol (BD) was supplied, 577 g of recycled bis(2-hydroxyethyl) terephthalate (rBHET1) was dissolved in 3,861 g of purified water at 90°C to prepare a 13 wt% aqueous solution, and the aqueous solution of bis(2-hydroxyethyl) terephthalate was continuously supplied using a dropping funnel at a rate of 18.5 g per minute for 4 hours, and in step (2), 199.2 g of recycled bis(4-hydroxybutyl) terephthalate (rBHBT) and 62.6 g of adipic acid (AA) were supplied to the polycondensation reaction vessel, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reaction vessel reached about 1.23 dL / g.

[0120] Example 3 The same procedure as in Example 1 was repeated, except that in step (1), 368 g of 1,4-butanediol (BD) was supplied, 577 g of recycled bis(2-hydroxyethyl) terephthalate (rBHET1) was supplied in 12 portions, and the final temperature during the transesterification reaction was 220°C, and in step (2), 218.4 g of recycled bis(4-hydroxybutyl) terephthalate (rBHBT) and 77.4 g of polytetramethylene glycol (PTMG, Mn 1,000) were supplied to the polycondensation reaction vessel, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reaction vessel reached about 1.35 dL / g, thereby obtaining 232.4 g of a polyester resin.

[0121] Example 4 The same procedure as in Example 1 was repeated, except that in step (1), 577 g of recycled bis(2-hydroxyethyl) terephthalate (rBHET2) was divided into four portions and fed, and the final temperature during the transesterification reaction was 200°C, and in step (2), 220.2 g of recycled bis(4-hydroxybutyl) terephthalate (rBHBT) and 77.4 g of poly-1,3-propylene glycol (PO3G, Mn 1,000) were fed to the polycondensation reaction vessel, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reaction vessel reached about 1.25 dL / g, thereby obtaining 234.3 g of a polyester resin.

[0122] Example 5 The same procedure as in Example 1 was repeated, except that in step (1), 577 g of recycled bis(2-hydroxyethyl) terephthalate (rBHET1) was divided into eight portions and fed, and the final temperature during the transesterification reaction was 215°C, and in step (2), 220.2 g of recycled bis(4-hydroxybutyl) terephthalate (rBHBT) and 83.1 g of ethylene oxide-added polypropylene glycol (EO-PPG, Mn 2,400) were fed to the polycondensation reaction vessel, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reaction vessel reached about 1.23 dL / g, thereby obtaining 235.5 g of a polyester resin.

[0123] Example 6 The same procedure as in Example 1 was repeated, except that in step (1), the amount of 1,4-butanediol (BD) supplied was reduced to 491 g, 577 g of recycled bis(2-hydroxyethyl) terephthalate (rBHET1) was supplied in 10 portions, and the final temperature during the transesterification reaction was 170°C, and in step (2), 219.8 g of recycled bis(4-hydroxybutyl) terephthalate (rBHBT) and 78.0 g of polyethylene glycol (PEG, Mn 1,000) were supplied to the polycondensation reaction vessel, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reaction vessel reached about 1.29 dL / g, thereby obtaining 233.9 g of a polyester resin.

[0124] Comparative Example 1 The same procedure as in Example 1 was repeated, except that in step (1), recycled bis(2-hydroxyethyl) terephthalate (rBHET3) was fed all at once together with 1,4-butanediol (BD) at the start, and in step (2), 304.4 g of recycled bis(4-hydroxybutyl) terephthalate (rBHBT) was fed to the polycondensation reaction vessel, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reaction vessel reached about 0.62 dL / g, thereby obtaining 216.0 g of polyester resin.

[0125] Comparative Example 2 The same procedure as in Comparative Example 1 was repeated, except that in step (1), the amount of 1,4-butanediol (BD) supplied was reduced to 307 g, and recycled bis(2-hydroxyethyl) terephthalate (rBHET2) was supplied all at once at the start of the process, and in step (2), 190.5 g of recycled bis(4-hydroxybutyl) terephthalate (rBHBT) and 59.8 g of adipic acid (AA) were supplied to the polycondensation reaction vessel, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reaction vessel reached about 0.94 dL / g, thereby obtaining 187.7 g of a polyester resin.

[0126] Comparative Example 3 The same procedure as in Comparative Example 1 was repeated, except that in step (1), recycled bis(2-hydroxyethyl) terephthalate (rBHET2) was fed all at once together with 1,4-butanediol (BD) at the start of the transesterification reaction, and the final temperature during the transesterification reaction was 155°C, and in step (2), 231.6 g of recycled bis(4-hydroxybutyl) terephthalate (rBHBT) and 82.1 g of polytetramethylene glycol (PTMG, Mn 1,000) were fed to the polycondensation reaction vessel, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reaction vessel reached about 0.88 dL / g, thereby obtaining 246.4 g of a polyester resin.

[0127] Comparative Example 4 The same procedure as in Comparative Example 1 was repeated, except that in step (1), the amount of 1,4-butanediol (BD) supplied was reduced to 409 g, and recycled bis(2-hydroxyethyl) terephthalate (rBHET1) was supplied all at once at the start of the transesterification reaction, and the final temperature during the transesterification reaction was set to 230°C, and in step (2), 229.2 g of recycled bis(4-hydroxybutyl) terephthalate (rBHBT) and 81.3 g of poly-1,3-propylene glycol (PO3G, Mn 1,000) were supplied to the polycondensation reaction vessel, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reaction vessel reached about 1.08 dL / g, thereby obtaining 243.9 g of a polyester resin.

[0128] Comparative Example 5 The same procedure as in Comparative Example 1 was repeated, except that in step (1), the amount of 1,4-butanediol (BD) supplied was reduced to 409 g, and recycled bis(2-hydroxyethyl) terephthalate (rBHET2) was supplied all at once at the start of the transesterification reaction, and the final temperature during the transesterification reaction was set to 210°C, and in step (2), 229.2 g of recycled bis(4-hydroxybutyl) terephthalate (rBHBT) and 81.3 g of polyethylene glycol (PEG, Mn 1,000) were supplied to the polycondensation reaction vessel, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reaction vessel reached about 1.08 dL / g, thereby obtaining 243.9 g of a polyester resin.

[0129] Comparative Example 6 The same procedure as in Comparative Example 1 was repeated, except that in step (1), recycled bis(2-hydroxyethyl) terephthalate (rBHET3) was fed all at once together with 1,4-butanediol (BD) at the start, and recycled bis(4-hydroxybutyl) terephthalate was obtained without a nitrogen atmosphere, and in step (2), 307.2 g of recycled bis(4-hydroxybutyl) terephthalate (rBHBT) was fed to the polycondensation reaction vessel, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reaction vessel reached about 0.95 dL / g, thereby obtaining 218.0 g of a polyester resin.

[0130] Comparative Example 7 The same procedure as in Comparative Example 1 was repeated, except that in step (1), the amount of 1,4-butanediol (BD) supplied was increased to 1,023 g, and at the start, recycled bis(2-hydroxyethyl) terephthalate (rBHET2) was supplied all at once together with 1,4-butanediol (BD) to obtain recycled bis(4-hydroxybutyl) terephthalate without a nitrogen atmosphere, and in step (2), 303.6 g of recycled bis(4-hydroxybutyl) terephthalate (rBHBT) was supplied to the polycondensation reaction vessel, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reaction vessel reached about 0.95 dL / g, thereby obtaining 215.4 g of a polyester resin.

[0131] The ingredients used in the above examples and comparative examples, their amounts used, and other detailed process conditions are shown in Tables 2 and 3 below.

[0132] In addition, the 1,4-butanediol / rBHET ratio (G / B) of the following relational formula (1) and the rBHET introduction ratio (R) of the following relational formula (2) were calculated and are shown in Tables 2 and 3 below. 1.5≦G / B≦3.5...(1)

[0133] In the relational formula (1), G is the total number of moles of 1,4-butanediol, and B is the total number of moles of bis(2-hydroxyethyl) terephthalate.

[0134]

number

[0135] In the relationship (2), G is the total number of moles of 1,4-butanediol, B is the total number of moles of bis(2-hydroxyethyl) terephthalate, and N is the number of divided introductions of bis(2-hydroxyethyl) terephthalate.

[0136] Test Example 1: Crushability In the examples and comparative examples, recycled bis(4-hydroxybutyl) terephthalate sheets discharged from the transesterification reaction were broken into lumps of 50 g or more by hitting them with a rubber hammer or pressing them with a light load. If they were crushed into flakes of 0.2 g or less using a ball mill or pin mill at room temperature, they were rated as "brittle." If they were not crushed (i.e., sticky or waxy), they were rated as "waxy."

[0137] Test example 2: Color b The recycled bis(4-hydroxybutyl) terephthalate obtained in the examples and comparative examples was prepared into test specimens measuring 30 mm in width, 30 mm in length, and 6 mm in thickness by hot-press melting or extrusion, respectively. Transmittance data was obtained using illuminant D65 at a 2° observation angle, and the data was processed using a color analysis device in Grams / 32 software to measure the color b value in the Hunter Lab color space. Additionally, the polyester resins obtained in the examples and comparative examples were prepared into test specimens measuring 30 mm in width, 30 mm in length, and 6 mm in thickness by hot-press melting or extrusion, respectively, in the same manner as described above, and the color b value was measured in the same manner as described above.

[0138] Test example 3: 1 H-NMR (1) Analysis of recycled bis(4-hydroxybutyl) terephthalate The recycled bis(4-hydroxybutyl) terephthalate obtained in the examples and comparative examples was dissolved in CDCl3 solvent at a concentration of 3 mg / ml, and its FT-NMR was measured at 25°C using a nuclear magnetic resonance apparatus (JEOL, 600 MHz). 1 H-NMR spectra were obtained. The spectra were analyzed to calculate the total content of bis(4-hydroxybutyl) terephthalate (BHBT) and its oligomers, which was used as the content (mol%) of BHBT derivatives. In addition, the total content (mol%) of ethylene glycol (EG), diethylene glycol (DEG), and their derivatives was calculated based on the total number of moles of all glycols (EG, DEG, BD, etc.) and their derivatives. In addition, the content (mol%) of unreacted 1,4-butanediol was calculated based on the total number of moles of all glycols and their derivatives. The content was 1 The amounts of all compounds analyzed by H-NMR spectroscopy were used as a reference.

[0139] (2) Analysis of polyester resin Each polyester resin was dissolved in CDCl3 solvent at a concentration of 3 mg / ml, and its FT-NMR spectra were measured at 25°C using a nuclear magnetic resonance instrument (JEOL, 600 MHz). 1 H-NMR spectra were obtained, and the total content (mol%) of ethylene glycol and diethylene glycol residues was calculated based on the total moles of residues derived from all glycols (EG, DEG, BD, PEG, PTMG, PO3G, and EO-PPG, etc.) by analyzing the spectra.

[0140] Test Example 4: Intrinsic Viscosity The polyester resin was dissolved in orthochlorophenol (OCP) at 150° C. at a concentration of 0.12% to obtain a solution, and the intrinsic viscosity was measured using an Ubbelohde viscometer in a constant temperature bath at 35° C. Specifically, the temperature of the viscosity tube was maintained at 35° C., and the time required for the solvent to pass between specific inner sections of the viscosity tube (flow time) and the time required for the solution to pass through and obtain the specific viscosity were used to calculate the intrinsic viscosity.

[0141] Test Example 5: Tm and ΔHf Each polyester resin was dried under vacuum at 50°C for 15 hours to melt and quench, and then heated at 10°C / min in a differential scanning calorimeter (DSC, TA Instruments) for testing. The highest point of the endothermic peak due to resin melting was used as the melting point (Tm), and the heat of fusion (ΔH f ) was calculated as the area of ​​the endothermic peak.

[0142] The raw materials used, process conditions, and test results for the preparation of recycled bis(4-hydroxybutyl) terephthalate by transesterification are shown in Tables 2 and 3 below.

[0143] [Table 2]

[0144] [Table 3]

[0145] As can be seen from Tables 2 and 3 above, in Examples 1 to 6, the transesterification reaction was carried out in a nitrogen atmosphere while feeding recycled BHET continuously or in portions at an introduction ratio (R) of 5 or more, thereby effectively removing the reaction by-products ethylene glycol (EG) and unreacted 1,4-butanediol (BD). As a result, in Examples 1 to 6, the content of ethylene glycol (EG) derivatives in the final product (recycled BHBT) was low, at 20 wt% or less, and the purity was excellent. The final product was easily crushed into flakes or powder, had excellent color, and was suitable for use as a polymerization raw material.

[0146] In contrast, in Comparative Examples 1 to 7, where the transesterification reaction was carried out while feeding rBHET in one batch, the content of ethylene glycol (EG) derivatives in the final product (recycled BHBT) was high, exceeding 20 mol %. In particular, it was difficult to crush the final products in Comparative Examples 3, 6, and 7, and the color was poor in Comparative Examples 3 to 5, making them unsuitable as polymerization raw materials.

[0147] Additionally, the raw material feed amounts, process conditions, and test results for the preparation of polyester resins by polycondensation reaction are shown in Tables 4 and 5 below.

[0148] [Table 4]

[0149] [Table 5]

[0150] As can be seen from Tables 4 and 5 above, in Examples 1 to 6, high-quality recycled BHBT prepared by the process according to the present invention (transesterification was carried out in a nitrogen atmosphere while continuously or dividedly feeding recycled BHBT at an introduction ratio (R) of 5 or more) was used, and therefore the content of ethylene glycol (EG) residues in the final polyester resin was low, at 10 mol% or less.

[0151] In contrast, in Comparative Examples 1 to 7, which used low-quality recycled BHBT prepared by transesterification using a single feed of recycled BHET, the content of ethylene glycol (EG) residues in the final polyester resin was high, exceeding 20 mol%.

[0152] As a result, the polyester resins of the examples have higher melting points (T m ) and heat of fusion (ΔH f ) and showed excellent crystallinity.

Claims

1. The total content of ethylene glycol, diethylene glycol, and their derivatives is １ 1. A recycled bis(4-hydroxybutyl) terephthalate having 20 mole % or less, based on the total moles of total glycols and their derivatives, as measured by H-NMR, and a color b value of 8 or less in the Hunter Lab color space when prepared into a test specimen having a thickness of 6 mm.

2. 2. The recycled bis(4-hydroxybutyl) terephthalate of claim 1, comprising components obtained by depolymerization of waste polyester, wherein the total content of ethylene glycol, diethylene glycol, and derivatives thereof is 15 mol% or less, based on the total number of moles of total glycols and their derivatives, and wherein the color b value is 5 or less.

3. 2. The recycled bis(4-hydroxybutyl) terephthalate of claim 1, which can be crushed or ground into flakes of 0.2 g or less at room temperature.

4. (1) a step of supplying 1,4-butanediol to a reaction vessel; and (2) a step of supplying bis(2-hydroxyethyl) terephthalate to the reaction vessel in portions or continuously to carry out a transesterification reaction, The following relation (1): 1.5≦G / B≦3.5 ．．．（１） is fulfilled, A method for preparing recycled bis(4-hydroxybutyl) terephthalate, wherein in relation (1), G is the total number of moles of 1,4-butanediol fed to the reaction vessel, and B is the total number of moles of bis(2-hydroxyethyl) terephthalate fed to the reaction vessel.

5. 5. The method for preparing recycled bis(4-hydroxybutyl) terephthalate according to claim 4, wherein the purity of bis(2-hydroxyethyl) terephthalate is 70% to 99%.

6. The method for preparing recycled bis(4-hydroxybutyl) terephthalate according to claim 4, wherein the bis(2-hydroxyethyl) terephthalate is obtained by depolymerization of waste polyester.

7. In step (2), bis(2-hydroxyethyl) terephthalate is introduced into the transesterification reaction in two or more portions, and the reaction is carried out in accordance with the following relationship (2): [Equation 1] the introduction ratio (R) of bis(2-hydroxyethyl) terephthalate is 5 or more; In the formula (2), G is the total number of moles of at least one glycol component, B is the total number of moles of bis(2-hydroxyethyl) terephthalate, and N is the number of divided introductions of bis(2-hydroxyethyl) terephthalate.

5. A method for preparing the recycled bis(4-hydroxybutyl) terephthalate of claim 4.

8. 5. The method for preparing recycled bis(4-hydroxybutyl) terephthalate according to claim 4, wherein in step (2), the step of providing bis(2-hydroxyethyl) terephthalate is carried out at a temperature of 165°C to 220°C in a nitrogen atmosphere while ethylene glycol is removed as a by-product.

9. 5. The method for preparing recycled bis(4-hydroxybutyl) terephthalate according to claim 4, wherein in step (2), the total content of ethylene glycol, diethylene glycol, and derivatives thereof present in the product of the transesterification reaction is 20 mol % or less, based on the total moles of total glycols and their derivatives.

10. A raw material for polymerization of polyester resins comprising the recycled bis(4-hydroxybutyl) terephthalate of claim 1.

11. (1) feeding 1,4-butanediol to a reaction vessel; (2) supplying bis(2-hydroxyethyl) terephthalate in portions or continuously to a reaction vessel and carrying out a transesterification reaction; (3) subjecting the product of the transesterification reaction to a polycondensation reaction; Including, The following relation (1): 1.5≦G / B≦3.5 ．．．（１） is fulfilled, In the formula (1), G is the total number of moles of 1,4-butanediol fed to the reaction vessel, and B is the total number of moles of bis(2-hydroxyethyl) terephthalate fed to the reaction vessel. A method for preparing a polyester resin.

12. In step (3), at least one of a glycol component and an acid component is further provided; the glycol component is selected from the group consisting of 1,3-propanediol, 1,4-cyclohexanedimethanol, 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, ethylene oxide-added polypropylene glycol, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, and poly-1,5-pentanediol; the acid component is selected from the group consisting of adipic acid, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, fumaric acid, glutaric acid, azelaic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, 4,4'-stilbenedicarboxylic acid, 2,5-furandicarboxylic acid, and 2,5-thiophenedicarboxylic acid; A method for preparing the polyester resin of claim 11.

13. 13. A polyester resin prepared by the method of claim 11 or 12.

14. １ 14. The polyester resin of claim 13, having a total content of ethylene glycol and diethylene glycol residues of 0.01 mol % to 20 mol %, based on moles of total glycol residues, as measured by H-NMR.

15. 14. The polyester resin of claim 13, having a melting point (Tm) of 200°C or greater, a heat of fusion (ΔHf) of 20 J / g or greater, and a color b value of 18 or less in the Hunter Lab color space when prepared into test specimens having a thickness of 6 mm.

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