Process for producing polyester resins using regenerated aqueous bis(2-hydroxyethyl) terephthalate solution

Abstract

The regenerated bis(2-hydroxyethyl) terephthalate obtained by depolymerization of waste polyester is mixed with water to prepare an aqueous solution under specific temperature and concentration conditions, thereby ensuring storage stability. By introducing such an aqueous solution of regenerated bis(2-hydroxyethyl) terephthalate into the polymerization of polyester resin, the uniformity of the raw materials and the reaction efficiency can be improved, thereby improving the quality of the final polyester resin.

Description

[Technical field]

[0001] The present invention relates to an aqueous solution of recycled bis(2-hydroxyethyl) terephthalate and a method for using same to prepare polyester resins. [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 around the world as an industrial material for medical fibers, tire cords, etc. In particular, polyester sheets or polyester plates have good transparency and excellent mechanical strength, and are therefore widely used as raw materials for cases, boxes, partitions, shelves, panels, packaging materials, building materials, interior and exterior materials, etc.

[0003] As a result, plastic waste such as polyester is generated at an uncontrollable level worldwide every year. In recent years, various countries around the world have formulated regulations and plans for recycling waste plastic resources, including waste polyester. For example, there are attempts to use a certain percentage or more of recycled resin in packaging materials used in various fields. Physical and chemical methods are used to recycle waste polyester, but physical recycling methods cannot guarantee purity and are not widely used.

[0004] In the chemical recycling process, the ester bonds of the waste polyester are broken down to depolymerize it. Reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis are used. Among these, glycolysis is the decomposition of the waste polyester by adding glycols such as ethylene glycol or diethylene glycol at high temperature. The reaction product obtained mainly contains bis(2-hydroxyethyl) terephthalate (BHET). After crystallization or purification, bis(2-hydroxyethyl) terephthalate can be used as a raw material for preparing unsaturated polyester or ester polyols. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Korean Patent No. 1386683 [Patent Document 2] U.S. Patent No. 7,211,193 [Non-patent literature]

[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] Recycled bis(2-hydroxyethyl) terephthalate obtained by depolymerization of waste polyester may be stored for a certain period of time after depolymerization before being used for polymerization of polyester resin. The quality of the recycled BHET may deteriorate depending on the storage conditions during this period, which may affect the quality of the final polyester resin.

[0008] As a result of research conducted by the present inventors, it was found that when recycled bis(2-hydroxyethyl) terephthalate is mixed with water to prepare an aqueous solution under specific temperature and concentration conditions, storage stability can be guaranteed, and the introduction of an aqueous solution of recycled BHET into the polymerization of polyester resin can improve the uniformity of raw materials and reaction efficiency.

[0009] Therefore, an object of the present invention is to provide a method for preparing an aqueous solution of regenerated bis(2-hydroxyethyl) terephthalate having excellent storage stability, and a method for preparing a high-quality polyester resin using the same. [Means for solving the problem]

[0010] According to the present invention, there is provided a method for preparing a polyester resin, comprising the steps of: (1) depolymerizing waste polyester to prepare recycled bis(2-hydroxyethyl) terephthalate; (2) mixing the recycled bis(2-hydroxyethyl) terephthalate with water at 60°C to 110°C to prepare an aqueous solution of recycled bis(2-hydroxyethyl) terephthalate having a concentration of 50% by weight to 95% by weight; and (3) using the aqueous solution of recycled bis(2-hydroxyethyl) terephthalate to prepare a polyester resin through an esterification reaction and a polycondensation reaction.

[0011] Further, according to the present invention, there is provided a method for preparing an aqueous solution of regenerated bis(2-hydroxyethyl) terephthalate, comprising the steps of (1) depolymerizing waste polyester to prepare regenerated bis(2-hydroxyethyl) terephthalate, and (2) mixing the regenerated bis(2-hydroxyethyl) terephthalate with water at 60°C to 110°C to prepare an aqueous solution of regenerated bis(2-hydroxyethyl) terephthalate having a concentration of 50% by weight to 95% by weight. Effect of the Invention

[0012] According to the present invention, when the recycled bis(2-hydroxyethyl) terephthalate obtained by depolymerization of waste polyester is mixed with water under specific temperature and concentration conditions to prepare an aqueous solution, storage stability can be guaranteed, and the aqueous solution of recycled BHET can be introduced into the polymerization of polyester resin to improve the uniformity of raw materials and reaction efficiency.

[0013] Specifically, the aqueous solution of recycled BHET shows little change in purity and color even after a period of storage, and the polyester resin polymerized using the aqueous solution of recycled BHET also has excellent color quality. Therefore, the polyester resin of the present invention can be used in various fields to manufacture articles made of environmentally friendly materials. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 illustrates a method for preparing an aqueous solution of recycled bis(2-hydroxyethyl) terephthalate and a method for using it to prepare a polyester resin according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [Best Mode for Carrying Out the Invention] The invention will now be described in more detail.

[0016] In this specification, the terms referring to each component are used to distinguish them from one another and are not intended to limit the scope of the embodiments. Furthermore, in this specification, the singular expressions are to be interpreted as including the plural as well, unless otherwise indicated by the context.

[0017] 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 element.

[0018] As used herein, the term "comprising" is intended to specify certain features, regions, steps, methods, elements, and / or components, and does not exclude the presence or addition of any other features, regions, steps, methods, elements, and / or components, unless specifically stated to the contrary.

[0019] According to one aspect of the present invention, there is provided a method for preparing a polyester resin, the method including the steps of: (1) depolymerizing waste polyester to prepare recycled bis(2-hydroxyethyl) terephthalate; (2) mixing the recycled bis(2-hydroxyethyl) terephthalate with water at 60°C to 110°C to prepare an aqueous solution of recycled bis(2-hydroxyethyl) terephthalate having a concentration of 50% by weight to 95% by weight; and (3) using the aqueous solution of recycled bis(2-hydroxyethyl) terephthalate to prepare a polyester resin through an esterification reaction and a polycondensation reaction.

[0020] According to another aspect of the present invention, there is provided a method for preparing an aqueous solution of regenerated bis(2-hydroxyethyl) terephthalate, the method comprising the steps of: (1) depolymerizing waste polyester to prepare regenerated bis(2-hydroxyethyl) terephthalate; and (2) mixing the regenerated bis(2-hydroxyethyl) terephthalate with water at 60°C to 110°C to prepare an aqueous solution of regenerated bis(2-hydroxyethyl) terephthalate having a concentration of 50% to 95% by weight.

[0021] FIG. 1 illustrates a method for preparing a polyester resin using an aqueous solution of recycled bis(2-hydroxyethyl) terephthalate according to one embodiment.

[0022] Referring to FIG. 1, first, a depolymerization step (S100) is performed to obtain high-purity regenerated BHET, in which waste polyester is crushed into flakes and subjected to a two-stage glycolysis reaction (180-200°C and 150-170°C), followed by purification by ion exchange and distillation. The regenerated BHET is then mixed with water at 60-110°C, and water is added thereto or evaporated therefrom to prepare an aqueous solution having a concentration of 50-95% by weight (S210). The aqueous solution of regenerated BHET is stored until it is introduced into the polymerization of polyester resin (S220). Then, in the polymerization of polyester resin, the aqueous solution of regenerated BHET is fed to a reactor together with additives, and an esterification reaction is carried out by optionally further adding additional glycol components and additional diacid components thereto (S310). The esterification product thus obtained is subjected to a polycondensation reaction to obtain a molten polyester resin, and the by-products formed during the reaction are discharged (S500). Thereafter, solid-state polymerization is further carried out as necessary, followed by further treatment to finally obtain a polyester resin (S400).

[0023] Each step will now be described in detail.

[0024] Regenerated Bis(2-hydroxyethyl) terephthalate Bis(2-hydroxyethyl)terephthalate is an ester of two ethylene glycols and one terephthalic acid. For example, bis(2-hydroxyethyl)terephthalate is a compound formed as an intermediate in the preparation of polyesters such as polyethylene terephthalate (PET) via the polymerization of ethylene glycol with terephthalic acid or its esters.

[0025] Bis(2-hydroxyethyl) terephthalate (BHET) used as a polymerization raw material for the polyester resin according to the present invention is obtained from waste polyesters having repeating units of ethylene glycol and terephthalic acid, such as polyethylene terephthalate (PET) or glycol-modified polyethylene terephthalate (PETG), by well-known depolymerization methods, such as glycolysis, hydrolysis, and methanolysis.

[0026] In this specification, bis(2-hydroxyethyl) terephthalate (BHET) obtained by depolymerization of waste polyester as described above will be referred to as "regenerated bis(2-hydroxyethyl) terephthalate (regenerated BHET)" or abbreviated as r-BHET or rBHET, but it should be understood as being different from the pure BHET compound.

[0027] Specifically, recycled BHET may contain by-products formed by side reactions with reagents or solvents used in various chemical steps during the depolymerization of waste polyester. These impurities may remain in trace amounts even after several purification steps. Thus, recycled BHET generally contains trace amounts of organic and inorganic impurities in addition to the main component BHET. For this reason, recycled BHET can also be considered as a type of composition containing two or more components, i.e., BHET composition. Recycled BHET may be used as a polymerization raw material for producing polyester resins.

[0028] Specifically, in addition to the main component BHET, the recycled BHET may contain trace amounts of different types of organic components, such as BHET analogues, e.g., mono(2-hydroxyethyl)terephthalic acid (MHET), by-products, e.g., BHET dimer, BHET trimer, and diethylene glycol ester, inorganic components, metal ions, and residual solvent components.

[0029] In the present invention, a regenerated BHET in which the content of such heterogeneous organic components is adjusted to a certain range is used. The content of each component in the regenerated BHET can be derived by measuring the peak area fraction (%) relative to the total peak area in a spectrum obtained using high performance liquid chromatography (HPLC).

[0030] Specifically, when measured by high performance liquid chromatography (HPLC), the recycled bis(2-hydroxyethyl) terephthalate (BHET) used as the raw material in the present invention has a peak area fraction of BHET of 96% or more. More specifically, the peak area fraction of BHET measured by HPLC may be 96.5% or more, 97% or more, 97.5% or more, or 98% or more.

[0031] Furthermore, the recycled bis(2-hydroxyethyl) terephthalate may have a peak area fraction of organic impurities of less than 5% in total as measured by HPLC, specifically less than 4%, less than 3%, less than 2%, less than 1%, or less than 0.7%.

[0032] In particular, the polyester resin according to the present invention includes recycled BHET in which the content of diethylene glycol ester (DEG ester) is adjusted to a certain level or less. For example, the recycled bis(2-hydroxyethyl) terephthalate may have a total peak area fraction of diethylene glycol ester compounds of less than 2% when measured by HPLC. Specifically, the total peak area fraction of diethylene glycol ester compounds may be less than 1.5%, less than 1%, less than 0.8%, or less than 0.7%.

[0033] As one example, the diethylene glycol ester compound can be a condensation product between an aromatic dicarboxylic acid, such as terephthalic acid, and diethylene glycol. As another example, the diethylene glycol ester compound can be a condensation product between an aromatic dicarboxylic acid, such as terephthalic acid, and a glycol (e.g., ethylene glycol) in addition to diethylene glycol.

[0034] According to one embodiment, the recycled BHET may contain 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate (CAS number 65133-69-9) of the following formula 1 as the first diethylene glycol ester. According to another embodiment, the recycled BHET may contain bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate (CAS number 26850-76-0) of the following formula 2 as the second diethylene glycol ester. When a polyester resin is prepared from recycled BHET in which the contents of the first diethylene glycol ester and the second diethylene glycol ester are adjusted to a certain level or less, the quality of the polyester resin is hardly deteriorated compared to that of a virgin resin, even though it is a recycled polyester resin obtained by chemical recycling.

[0035] [ka] [ka]

[0036] According to one embodiment, the peak area fraction of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate (first diethylene glycol ester) in the recycled bis(2-hydroxyethyl)terephthalate (BHET) is 2.5% or less when measured by high performance liquid chromatography (HPLC). Specifically, the peak area fraction of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate measured by HPLC can be 2.0% or less, 1.5% or less, 1.0% or less, or 0.5% or less.

[0037] According to another embodiment, the peak area fraction of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate (second diethylene glycol ester) in the recycled bis(2-hydroxyethyl)terephthalate (BHET) is 0.5% or less when measured by high performance liquid chromatography (HPLC). Specifically, the peak area fraction of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate measured by HPLC can be 0.2% or less, more specifically, 1.5% or less, 1.0% or less, or 0.5% or less.

[0038] Furthermore, the recycled bis(2-hydroxyethyl) terephthalate may have a total oligomer peak area fraction of 3% or less as measured by HPLC.

[0039] Specifically, the regenerated bis(2-hydroxyethyl)terephthalate may have a peak area fraction of BHET dimer of less than 3%, less than 2%, less than 1%, or less than 0.7% as measured by HPLC. Furthermore, the bis(2-hydroxyethyl)terephthalate produced by the above method may have a peak area fraction of BHET trimer of less than 1%, less than 0.5%, less than 0.3%, less than 0.1%, or 0% as measured by HPLC.

[0040] In addition, the recycled bis(2-hydroxyethyl) terephthalate may further contain impurities having a structure similar to that of bis(2-hydroxyethyl) terephthalate. For example, it may contain at least one selected from the group consisting of monohydroxyethyl terephthalate (MHET), bis(2-hydroxypropyl) terephthalate, and monohydroxyethyl ethoxy terephthalate. When measured by HPLC, the peak area fraction of the impurities having a structure similar to that of bis(2-hydroxyethyl) terephthalate may be less than 3%, less than 2%, less than 1%, or less than 0.5%.

[0041] Furthermore, the total content of residual solvents (e.g., ethylene glycol) in the recycled bis(2-hydroxyethyl) terephthalate may be less than 1 wt % when calculated based on the weight ratio detected by gas chromatography analysis. Specifically, the total content of residual solvents may be less than 0.5 wt %, less than 0.3 wt %, less than 0.2 wt %, less than 0.1 wt %, or less than 0.9 wt %.

[0042] Additionally, the recycled bis(2-hydroxyethyl) terephthalate may have a yellowness index (YID) of 3.0 or less as measured by a spectrophotometer in a 25% by weight solution. Specifically, the yellowness index may be 2.5 or less, 2.0 or less, 1.5 or less, or 1.0 or less.

[0043] Furthermore, the recycled bis(2-hydroxyethyl) terephthalate may have a total inorganic matter content of less than 5 ppm as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Specifically, the total inorganic matter content may be less than 3 ppm, less than 1 ppm, or nearly 0 ppm.

[0044] Preparation of regenerated bis(2-hydroxyethyl) terephthalate The bis(2-hydroxyethyl) terephthalate used in the preparation of the polyester resin according to the present invention is a recycled monomer obtained by depolymerization of waste polyester, and yet has a high purity and a low content of impurities such as diethylene glycol esters.

[0045] Such bis(2-hydroxyethyl) terephthalate can be obtained by carrying out a depolymerization reaction in multiple stages, with the temperature in the latter stages being significantly reduced, followed by post-depolymerization ion exchange and distillation of unreacted glycol.

[0046] A method for preparing regenerated bis(2-hydroxyethyl) terephthalate according to one embodiment may include: (1a) subjecting waste polyester to depolymerization by a first glycolysis reaction at a temperature of 180° C. to 200° C. to obtain a first reactant; (1b) subjecting the first reactant to depolymerization by a second glycolysis reaction at a temperature of 150° C. to 170° C. to obtain a second reactant; (1c) subjecting the second reactant to ion exchange by an ion exchange resin to obtain a third reactant; (1d) removing unreacted glycol from the third reactant by distillation at a temperature of 150° C. or less to obtain a fourth reactant; and (1e) subjecting the fourth reactant to distillation to obtain crude bis(2-hydroxyethyl) terephthalate.

[0047] According to the above method, bis(2-hydroxyethyl)terephthalate (BHET) can be produced in high purity by carrying out the depolymerization reaction in multiple stages while significantly reducing the temperature in the latter stages, thereby reducing the formation of diethylene glycol and impurities derived therefrom. Furthermore, according to the above method, bis(2-hydroxyethyl)terephthalate with improved quality in terms of color can be prepared by further carrying out ion exchange and distillation of unreacted glycol after the depolymerization reaction to reduce the formation of oligomers and remove chromophores.

[0048] According to another embodiment, before step (1a), a step of pulverizing the waste polyester to a size below a certain level may be further carried out. The waste polyester may have a particulate or fibrous form with a particle size of 4 mm or less. By adjusting the particle size or diameter of the waste polyester to within a specific range and carrying out the depolymerization, solvation can be promoted even under conditions of a relatively low temperature and a short reaction time.

[0049] According to another embodiment, the first glycolysis reaction in step (1a) is carried out in the presence of a catalyst. The catalyst includes a metal acetate or an anhydride or hydride thereof. More specifically, the catalyst may be at least one selected from the group consisting of zinc acetate, sodium acetate, cobalt acetate, manganese acetate, or a hydrate or anhydride thereof. Furthermore, the catalyst may be used in an amount of 0.2 parts by weight to 0.4 parts by weight based on 100 parts by weight of the waste polyester.

[0050] According to another embodiment, a further step of cooling the second reactant obtained in step (1b) to a temperature below a certain temperature may be carried out.

[0051] According to another embodiment, before the ion exchange in step (1c), a step of removing insoluble contaminants from the second reactant by filtration may be further carried out. Specifically, the second reactant may be cooled to 120° C. or less, and filtered after adding a filter aid.

[0052] According to another embodiment, prior to the ion exchange in step (1c), a further step of removing insoluble contaminants from the second reactant by filtration may be carried out.

[0053] According to another embodiment, the ion exchange resin in step (1c) is used in an amount of 1 to 20 parts by weight based on 100 parts by weight of the waste polyester, and includes at least one selected from the group consisting of a strong acid cation exchange resin, a weak acid cation exchange resin, and a chelating resin.

[0054] According to another embodiment, the distillation to remove the unreacted glycol in step (1d) may be carried out at a temperature between 100°C and 130°C.

[0055] According to another embodiment, the distillation to obtain crude bis(2-hydroxyethyl)terephthalate in step (1e) may be carried out by thin film evaporation under a pressure of 0.05 Torr to 0.4 Torr.

[0056] According to another embodiment, the method may further comprise the step of adsorption-crystallizing the crude bis(2-hydroxyethyl) terephthalate after the distillation of step (1e). The adsorption-crystallization may be carried out by adding an adsorbent using water as a solvent, filtering and crystallizing.

[0057] According to a specific embodiment, first, the waste polyester is crushed to a size of 4 mm or less, ethylene glycol is added thereto, and then subjected to a first glycolysis reaction at a temperature of 180°C to 200°C in the presence of a zinc acetate catalyst for about 2 hours, ethylene glycol is further added thereto, and then a second glycolysis reaction is carried out at a temperature of 150°C to 170°C for about 2 hours. Then, the mixture is cooled to below 120°C using a vacuum flash, a small amount of a filter aid is added, and then insoluble impurities are filtered and separated by solid-liquid separation, and ion-exchanged through a column filled with an ion-exchange resin. Next, unreacted glycol is recovered at a temperature of 100°C to 130°C, and purification is carried out by thin-film distillation at 190°C to 250°C, and finally an adsorption-crystallization step is carried out to obtain high-purity and high-quality bis(2-hydroxyethyl) terephthalate.

[0058] The above method involves two-stage glycolysis (i.e., the first glycolysis and the second glycolysis). When solvation is promoted in the first glycolysis, the second glycolysis can carry out the transesterification of the waste polyester under conditions of lower temperature and shorter reaction time. Therefore, the concentration of diethylene glycol (DEG) naturally formed at the general glycolysis temperature can be significantly reduced, and the content of diethylene glycol ester in the finally prepared bis(2-hydroxyethyl) terephthalate can be significantly reduced.

[0059] Preparation of aqueous solutions of regenerated bis(2-hydroxyethyl) terephthalate The quality of the recycled BHET may deteriorate depending on the storage conditions during this period, which may affect the quality of the final polyester resin.

[0060] According to the present invention, when recycled bis(2-hydroxyethyl) terephthalate is mixed with water under specific temperature and concentration conditions to prepare an aqueous solution, storage stability can be guaranteed, and the aqueous solution of recycled BHET can be introduced into the polymerization of polyester resin to improve the uniformity of raw materials and reaction efficiency.

[0061] The temperature (dissolution temperature) for preparing the aqueous solution of regenerated BHET of the present invention is 60° C. to 110° C., and within this range, the purity and color of the regenerated BHET can be maintained at an excellent level. For example, the temperature for preparing the aqueous solution of regenerated BHET may be 60° C. or higher, 70° C. or higher, 75° C. or higher, or 85° C. or higher, and may be 110° C. or lower, 100° C. or lower, 95° C. or lower, or 90° C. or lower.

[0062] Furthermore, the temperature at which the aqueous solution of regenerated BHET is stored may be the same as the temperature (dissolution temperature) at which the aqueous solution of regenerated BHET is prepared. That is, the aqueous solution of regenerated BHET can be prepared at a temperature of 60° C. to 110° C., and can be stored while maintaining the temperature conditions.

[0063] The concentration of the aqueous solution of regenerated BHET of the present invention is 50% to 95% by weight, and within this range, the specific heat of water as a solvent is high, so that the temperature change is small, resulting in excellent storage stability and reducing the amount of heat required to evaporate water from the aqueous solution. For example, the concentration of the aqueous solution of regenerated BHET may be 50% by weight or more, 55% by weight or more, 65% by weight or more, or 75% by weight or more, or may be 95% by weight or less, 90% by weight or less, 85% by weight or less, or 80% by weight or less.

[0064] As a specific example, a method for preparing an aqueous solution of regenerated BHET includes (2a) mixing regenerated bis(2-hydroxyethyl) terephthalate with water at 60°C to 110°C, and (2b) adjusting the concentration to 50% to 95% by weight after mixing by adding more water or by evaporating it.

[0065] The storage stability of the aqueous solution of regenerated BHET can be evaluated by measuring the purity and yellowness index of the aqueous solution of regenerated BHET after storage for a certain period of time at the preparation temperature of the aqueous solution of regenerated BHET (i.e., 60 to 110°C).

[0066] According to the present invention, the regenerated BHET is prepared and stored as an aqueous solution under specific temperature and concentration conditions, so that the purity and color decrease only slightly even after a certain period of storage.

[0067] For example, when an aqueous solution of regenerated BHET is stored at 60°C to 110°C for 5 days, the purity of the regenerated BHET can be measured to be 5% or less different from the initial purity. Such a difference in purity can be confirmed by comparing the peak area fraction (%) of BHET obtained by analyzing the regenerated BHET by high performance liquid chromatography (HPLC). Specifically, when an aqueous solution of regenerated BHET is stored at 60°C to 110°C for 5 days and then the water is evaporated to obtain regenerated BHET, the peak area fraction of BHET can be 90% or more, 93% or more, or 95% or more.

[0068] Furthermore, when an aqueous solution of regenerated bis(2-hydroxyethyl) terephthalate is stored at 60°C to 110°C for 5 days and then the water is evaporated to obtain regenerated bis(2-hydroxyethyl) terephthalate, and the regenerated bis(2-hydroxyethyl) terephthalate is dissolved in ethylene glycol having a concentration of 25% by weight at 120°C for 1 hour, the yellowness index (YID) can be measured to be 5 or less. For example, the yellowness index (YID) after storage for 5 days can be 5 or less, 4.5 or less, 4 or less, 3.5 or less, 3 or less, or 2.5 or less.

[0069] Furthermore, the yellowness index (YID) after storage for 5 days may have a difference of within 6, within 4, or within 2 compared to the initial value. Here, the initial yellowness index is obtained by measuring the same method as that of the regenerated BHET obtained by depolymerization (i.e., the regenerated BHET before being mixed with water to prepare an aqueous solution) (i.e., by dissolving in 25 wt % ethylene glycol at 120° C. for 1 hour and measuring).

[0070] Process for preparing polyester resin The aqueous solution of regenerated bis(2-hydroxyethyl) terephthalate can be used in the polymerization of polyester resins.

[0071] As an example, the aqueous solution of recycled bis(2-hydroxyethyl) terephthalate can be directly introduced into the polymerization reaction of polyester, which can be advantageous in terms of uniform supply of raw materials and reaction efficiency. In particular, when it is introduced into the polymerization reaction as an aqueous solution, the recycled BHET can be continuously introduced, which enables a continuous process of uniform polymerization reaction.

[0072] As another example, water in an aqueous solution of regenerated bis(2-hydroxyethyl)terephthalate may be evaporated to obtain solid-phase regenerated bis(2-hydroxyethyl)terephthalate, which may then be introduced into the polymerization reaction of polyester resin. In such a case, there is an advantage that existing methods and equipment for introducing solid-phase regenerated BHET can be used as is by storing the regenerated BHET as an aqueous solution for thermal stability and then evaporating the water to introduce it into the polymerization reaction.

[0073] In the polymerization, an esterification reaction (first polymerization reaction step) and a polycondensation reaction (second polymerization reaction step) may be carried out in sequence.

[0074] The polyester resin according to the present invention can be prepared by further adding terephthalic acid or its derivatives and / or ethylene glycol in addition to the recycled bis(2-hydroxyethyl) terephthalate. Furthermore, the polyester resin can be prepared as a copolymer by further adding other diacid and / or glycol comonomers.

[0075] For example, at least one monomer selected from the group consisting of (a) a dicarboxylic acid or a derivative thereof, (b) ethylene glycol or diethylene glycol, and (c) a diol-based comonomer may be further introduced into the esterification reaction.

[0076] The dicarboxylic acid may include at least one selected from terephthalic acid and isophthalic acid. Furthermore, the diol-based comonomer may include at least one selected from the group consisting of cyclohexane dimethanol, cyclohexane dimethanol derivatives, and isosorbide. The cyclohexane dimethanol derivative may be 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol.

[0077] Diol-based comonomers may further include 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, and 1,4-cyclohexanediol.

[0078] The esterification reaction may be carried out in the presence of an esterification reaction catalyst. For example, a zinc-based compound may be used. Specific examples of the zinc-based catalyst include zinc acetate, zinc acetate hydrate, zinc chloride, zinc sulfate, zinc sulfide, zinc carbonate, zinc citrate, zinc gluconate, or a mixture thereof.

[0079] The esterification reaction can be carried out, for example, at 0 kgf / cm 2 ~10.0kgf / cm 2 The esterification reaction can be carried out at a pressure of 0 kg / cm and a temperature of 150°C to 300°C. The conditions of the esterification reaction may be appropriately adjusted depending on the inherent properties of the polyester to be produced, the ratio of each component, or the processing conditions. Specifically, the esterification reaction pressure is 0 kg / cm 2 ~5.0kg / cm 2 , more specifically 0.1 kg / cm 2 ~3.0kg / cm 2 Furthermore, the temperature of the esterification reaction may be from 200°C to 270°C, more specifically from 240°C to 260°C.

[0080] The esterification reaction may be carried out in a batch or continuous manner. Each raw material may be fed separately, but it is preferable to feed the diol component, the dicarboxylic acid component, and the regenerated BHET in the form of a mixed slurry. Furthermore, the diol component, such as isosorbide, which is solid at room temperature, may be dissolved in water or ethylene glycol, and then mixed with the dicarboxylic acid component, such as terephthalic acid, to prepare a slurry. Alternatively, isosorbide may be melted at 60° C. or higher, and then mixed with the dicarboxylic acid component, such as terephthalic acid, and other diol components to prepare a slurry. Furthermore, water may be added to the mixed slurry to promote an increase in the fluidity of the slurry. Furthermore, in a continuous method, a liquid raw material (e.g., an aqueous solution of regenerated BHET) may be continuously fed to the reactor using a pump or the like. The hourly feed rate of the raw material can be determined by dividing the total amount of the raw material fed by the time required to achieve the target production rate per day (e.g., 50 t / day).

[0081] The mixture of the aqueous solution of the recycled bis(2-hydroxyethyl) terephthalate and other added components is left in the esterification reactor for a certain period of time, for example, 1 hour to 24 hours, or 4 hours to 10 hours, and then transferred to a polycondensation reactor. The polycondensation reaction can produce a relatively low molecular weight polyester resin by melt polymerization. Furthermore, after the melt polymerization, a relatively high molecular weight polyester resin can be produced by solid-phase polymerization.

[0082] 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. Furthermore, the pressure in the polycondensation reaction may be 0.01mmHg to 600mmHg, specifically 0.05mmHg to 200mmHg, more specifically 0.1mmHg to 100mmHg. By adopting reduced pressure conditions in the polycondensation reaction, glycol, which is a by-product of the polycondensation reaction, can be removed from the system. If the pressure of the polycondensation reaction exceeds the range of 0.01mmHg to 400mmHg, the removal of the by-product may be insufficient. Furthermore, if the temperature of the polycondensation reaction is less than 150°C, glycol, which is a by-product of the reaction, cannot be effectively removed from the system, and therefore the intrinsic viscosity of the final reaction product will be low, and the physical properties of the final polyester resin will be deteriorated. If the temperature of the polycondensation reaction exceeds 300°C, the possibility of yellowing of the final polyester resin will increase. Furthermore, the polycondensation reaction may be carried out for as long as necessary until the intrinsic viscosity of the final reaction product reaches a suitable level, for example, for an average residence time of 1 hour to 24 hours.

[0083] Further, the polycondensation reaction may be carried out in the presence of a polycondensation catalyst. The polycondensation catalyst may be, for example, a titanium-based compound, a germanium-based compound, an antimony-based compound, an aluminum-based compound, a tin-based compound, or a mixture thereof. Examples of titanium compounds include tetraethyl titanate, acetyl tripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, lactate titanate, triethanolamine titanate, acetylacetonate titanate, ethylacetoacetate titanate, isostearyl titanate, titanium dioxide, and the like. Examples of germanium-based compounds include germanium dioxide, germanium tetrachloride, germanium ethylene glycol oxide, germanium acetate, or a mixture thereof. Preferably, germanium dioxide can be used. Both crystalline and amorphous germanium dioxide may be used, and glycol-soluble ones may be used. The amount of the polycondensation catalyst used may be such that the amount of titanium element relative to the weight of the polyester resin is about 1 to 100 ppm, and more preferably about 1 to 50 ppm.

[0084] In addition to the polycondensation catalyst, a stabilizer, a colorant, a crystallizing agent, an antioxidant, a branching agent, etc. may be further used. The timing of adding these additives is not particularly limited, and they may be added at any time during the preparation step of the polyester resin.

[0085] As the stabilizer, phosphorus compounds such as phosphoric acid, trimethyl phosphate, triethyl phosphate, and triethyl phosphonoacetate may be commonly used. The amount of stabilizer added may be 10 to 200 ppm based on the amount of element, based on the weight of the polyester resin. Furthermore, common colorants such as cobalt acetate and cobalt propionate may be exemplified as colorants added to improve the color of the polyester resin. The amount of colorant added may be 10 to 200 ppm based on the amount of cobalt element, based on the weight of the polyester resin. If necessary, anthraquinone compounds, perinone compounds, azo compounds, methine compounds, etc. may be used as organic colorants. Commercially available toners such as Polysynthren Blue RLS manufactured by Clarient or Solvaperm Red BB manufactured by Clarient may be used. The amount of organic compound colorant added may be adjusted to 0 to 50 ppm based on the weight of the polyester resin. Crystal nucleating agents, ultraviolet absorbers, polyolefin resins, polyamide resins, etc. may be exemplified as crystallizing agents. Examples of the antioxidant include hindered phenol antioxidants, phosphorous antioxidants, thioether antioxidants, and mixtures thereof. Examples of the branching agent include ordinary branching agents having three or more functional groups, such as trimellitic anhydride, trimethylolpropane, trimellitic acid, and mixtures thereof.

[0086] Composition and characteristics of polyester resin The polyester resin of the present invention is a polyester resin regenerated by chemical recycling of waste polyester.

[0087] Specifically, the polyester resins of the present invention are polymerized using recycled BHET and therefore contain repeat units derived from recycled BHET in the polymer chain.

[0088] The content of recycled BHET in the polyester resin of the present invention may be 1% by weight or more, 5% by weight or more, 10% by weight or more, 30% by weight or more, 50% by weight or more, 70% by weight or more, or 90% by weight or more. Furthermore, the content of recycled BHET may be 100% by weight or less, 99% by weight or less, 80% by weight or less, 60% by weight or less, 40% by weight or less, or 20% by weight or less.

[0089] As an example, recycled bis(2-hydroxyethyl) terephthalate may be used in an amount of 10% to 99% by weight based on the weight of the polyester resin.

[0090] On the other hand, since bis(2-hydroxyethyl) terephthalate has a structure in which two ethylene glycols and one terephthalic acid are bonded, the polyester resin of the present invention can essentially contain repeating units derived from ethylene glycol and terephthalic acid.

[0091] As described above, the polyester resin of the present invention includes a diacid component and a glycol component as monomers constituting the polyester resin. In addition, the polyester resin of the present invention may further include an additional diacid component and an additional glycol component for polymerization of the polyester.

[0092] In the polyester resins of the present invention, the diacid component may be a dicarboxylic acid or a derivative thereof, and the glycol component may be a diol.

[0093] In particular, the dicarboxylic acid includes terephthalic acid, which can improve the physical properties of the polyester resin, such as heat resistance, chemical resistance, and weather resistance. For example, the terephthalic acid may be used in an amount of 5 mol% to 100 mol% based on the mole number of the total dicarboxylic acid. Furthermore, the terephthalic acid component may be formed from a terephthalic acid alkyl ester, such as dimethyl terephthalic acid.

[0094] Further, the diol includes ethylene glycol or diethylene glycol, which can contribute to improving the transparency and impact resistance of the polyester resin. For example, ethylene glycol and / or diethylene glycol may be used in an amount of 5 mol% to 100 mol% based on the mole number of the total diol.

[0095] According to one embodiment, the polyester resin of the present invention may be a copolymer resin containing two or more dicarboxylic acid components and / or two or more diol components.

[0096] Specifically, the dicarboxylic acid component may further include an aromatic dicarboxylic acid component other than terephthalic acid, an aliphatic dicarboxylic acid component, or a mixture thereof. The dicarboxylic acid other than terephthalic acid may be used in an amount of 1 mol % to 30 mol % based on the weight of the total dicarboxylic acid component.

[0097] The aromatic dicarboxylic acid component may be an aromatic dicarboxylic acid having 8 to 20 carbon atoms, preferably 8 to 14 carbon atoms, or a mixture thereof. Examples of aromatic dicarboxylic acids include, but are not limited to, isophthalic acid, naphthalenedicarboxylic acids, such as 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, 4,4'-stilbene dicarboxylic acid, 2,5-furandicarboxylic acid, 2,5-thiophenedicarboxylic acid, and the like.

[0098] The aliphatic dicarboxylic acid component may be an aliphatic dicarboxylic acid having 4 to 20 carbon atoms, preferably 4 to 12 carbon atoms, or a mixture thereof. Examples of aliphatic dicarboxylic acids include, but are not limited to, linear, branched or cyclic aliphatic dicarboxylic acid components such as cyclohexanedicarboxylic acid, 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, and the like.

[0099] Furthermore, the diol component may further include a comonomer other than ethylene glycol or diethylene glycol. The comonomer may include, for example, at least one selected from the group consisting of cyclohexanedimethanol, cyclohexanedimethanol derivatives, and isosorbide.

[0100] Cyclohexanedimethanol (e.g., 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol) can contribute to improving the transparency and impact resistance of the polyester resin produced. For example, cyclohexanedimethanol may be used in an amount of 5 mol% to 90 mol% based on the moles of the total diol. The cyclohexanedimethanol derivative may be 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol. The cyclohexanedimethanol derivative may be used in an amount of 0.1 mol% to 25 mol% based on the moles of the total diol.

[0101] Isosorbide can improve the processability of the final polyester resin. The transparency and impact resistance of the polyester resin are improved by the diol components of cyclohexanedimethanol and ethylene glycol, but for processability, the shear flow properties should be improved and the crystallization rate should be delayed. However, it is difficult to achieve this effect with cyclohexanedimethanol and ethylene glycol alone. Therefore, when isosorbide is used as the diol component, the shear flow properties are improved and the crystallization rate is delayed while maintaining the transparency and impact resistance, thereby improving the processability of the polyester resin produced. Preferably, isosorbide may be used in an amount of 0.1 mol% to 50 mol% based on the moles of the total diol.

[0102] As a specific example, the polyester resin includes a diacid component and a glycol component, the diacid component may include at least one selected from the group consisting of terephthalic acid, isophthalic acid, dimethyl isophthalate, phthalic acid, dimethyl phthalate, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, dimethyl 2,6-naphthalenedicarboxylate, diphenyldicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, dimethyl 1,4-cyclohexanedicarboxylate, dimethyl 1,3-cyclohexanedicarboxylate, sebacic acid, succinic acid, isodecyl succinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid, and azelaic acid, and the glycol component may include isosorbide (ISB), ethylene glycol, 1,2-propanediol. , 1,3-propanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate, and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol may be included.

[0103] According to one embodiment, the polyester resin may further include at least one monomer selected from the group consisting of (a) a dicarboxylic acid or a derivative thereof, (b) ethylene glycol or diethylene glycol, and (c) a diol-based comonomer in addition to bis(2-hydroxyethyl)terephthalate. The dicarboxylic acid may include at least one selected from terephthalic acid and isophthalic acid. Furthermore, the diol-based comonomer may include at least one selected from the group consisting of cyclohexanedimethanol, cyclohexanedimethanol derivatives, and isosorbide. The cyclohexanedimethanol derivative may be 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol. Diol-based comonomers may further include 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, and 1,4-cyclohexanediol.

[0104] When the Hunter Lab color space of the polyester resin is measured, the value obtained by subtracting the b value from the L value may be 85 or more. For example, the Lb value may be 85 or more, 86 or more, 87 or more, 88 or more, 89 or more, 90 or more, or 91 or more. Furthermore, the upper limit of the Lb value is not particularly limited. However, it may be, for example, 100 or less, 99 or less, 98 or less, 97 or less, or 95 or less. The measurement of the Hunter Lab color space can be performed by preparing a test piece having a thickness of 6 mm from the polyester resin.

[0105] The intrinsic viscosity of the polyester resin according to the present invention 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. Specifically, the intrinsic viscosity of the polyester resin at 35° C. may be 0.5 dl / g to 0.9 dl / g.

[0106] The polyester resin according to the present invention can be used as a material for beverage containers, packaging films, audio and video films, etc., because of its excellent color, mechanical strength, heat resistance, transparency, and gas barrier properties. Furthermore, the polyester sheet or polyester plate prepared from the polyester resin according to the present invention has good transparency and excellent mechanical strength, and can therefore be used as a raw material for cases, boxes, partitions, shelves, panels, packaging materials, building materials, interior and exterior materials, etc. Furthermore, the polyester resin according to the present invention can also be used as an industrial material for medical fibers and tire cords, etc.

[0107] [Mode of the invention] The present invention will be described in more detail below with reference to embodiments. However, these examples are provided for illustrative purposes only and the present invention is not limited thereto.

[0108] <Preparation and evaluation of regenerated bis(2-hydroxyethyl) terephthalate> Preparation example: r-BHET_A1 (regenerated BHET) Into a first reactor made of stainless steel (SUS), 1,000 g of waste polyester resin pulverized to a particle size of 4 mm or less, 2,000 g of ethylene glycol (EG), and 3.5 g of anhydrous zinc acetate were charged. The temperature inside the reactor was raised to 180°C, and depolymerization (first glycolysis reaction) was carried out over 2 hours. The resulting reactant (first reactant) was transferred to a second reactor and cooled to 150°C. 2,000 g of ethylene glycol was further added thereto, and depolymerization (second glycolysis reaction) was carried out for 2 hours while maintaining the reactor temperature at 150°C. The resulting reactant (second reactant) was cooled to 120°C by vacuum flash, 16 g of filter aid was added thereto, and then pressure filtration was performed to separate the solid and liquid. The separated liquid reaction product was passed through a column filled with ion exchange resin (BC107(H) manufactured by Bonlite) to remove ionic impurities, and a mixture (third reaction product) containing bis(2-hydroxyethyl) terephthalate and ethylene glycol was obtained. This mixture (third reaction product) was transferred to a 10-liter distillation apparatus and vacuum distilled at 130°C to recover unreacted ethylene glycol. The reaction product (fourth reaction product) from which ethylene glycol had been removed was thin-film evaporated in a thin-film evaporator (VKL70-4S manufactured by VTA) at 220°C and 0.08 Torr to obtain 1,040 g of a product from which dimers and higher oligomers had been removed. Then, for adsorption-crystallization, 1,040 g of the above product and 3,120 g of distilled water were put into a 20-liter glass reactor and dissolved at a temperature of 70°C, and then 5.2 g of activated carbon was added thereto, followed by stirring for 30 minutes and filtration. The filtrate was cooled to room temperature for crystallization, filtered, and dried in a vacuum oven, resulting in 990 g of the final product containing bis(2-hydroxyethyl) terephthalate.

[0109] Preparation example: r-BHET_A2 (regenerated BHET) A final product (referred to as r-BHET_A2) of 980 g containing bis(2-hydroxyethyl) terephthalate was obtained through the same procedure as in the preparation example of r-BHET_A1, except that the first glycolysis reaction was carried out at 180° C. for 1 hour.

[0110] Preparation example: r-BHET_A3 (regenerated BHET) Except for using 1,000 g of waste fiber as the raw material of waste polyester, 985 g of a final product containing bis(2-hydroxyethyl) terephthalate (referred to as r-BHET_A3) was obtained through the same procedure as in the preparation example of r-BHET_A1.

[0111] Preparation example: r-BHET_A5 (regenerated BHET) A final product containing bis(2-hydroxyethyl) terephthalate (referred to as r-BHET_A5) of 1,050 g was obtained through the same procedure as in the preparation example of r-BHET_A1, except that the adsorption-crystallization step was not performed after the thin-film evaporation.

[0112] Preparation example: r-BHET_B2 (regenerated BHET) In a stainless steel (SUS) reactor, 1,000 g of waste polyester resin with a particle size of 4 mm or less, 4,000 g of ethylene glycol (EG), and 3.5 g of anhydrous zinc acetate were charged. The temperature inside the reactor was raised to 210°C, and depolymerization (glycolysis reaction) was carried out for 4 hours. The resulting 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 using a centrifuge. The bis(2-hydroxyethyl) terephthalate obtained by centrifugation was washed twice with a sufficient amount of distilled water, and the residual solvent was removed in an oven to obtain about 1,010 g of a final product containing bis(2-hydroxyethyl) terephthalate (referred to as r-BHET_B2).

[0113] Test Example 1: Analysis of r-BHET components - HPLC The components of the regenerated bis(2-hydroxyethyl) terephthalate (BHET) were analyzed by high performance liquid chromatography (HPLC). About 0.01 g of the sample was diluted in about 20 ml of methanol and then measured by HPLC. Model:Waters e2695 Column: C18 (4.6 x 250 mm), 5 μm UV detector: 242 nm Injection volume: 10μl Eluent (gradient) A: HO+H 3 PO 4 , B: acetonitrile

[0114] Test Example 2: Measurement of residual solvents - GC The content of residual ethylene glycol (EG) in the recycled bis(2-hydroxyethyl) terephthalate (BHET) was measured by gas chromatography (GC). Approximately 0.1 g of sample was dissolved in CHCl 3 It was diluted to about 10 ml, filtered through a 0.45 μm filter, and then measured by GC. Model: Agilent 7890B Column: DB-624 (30m x 0.25mm x 1.4μm) Oven temperature: 60℃(2min.)-10℃ / min.-200℃(0min.)-20℃ / min.-260℃(5min.) Injection temperature: 250℃ Detector temperature: 250℃ Flow rate: 1.5ml / min.(N 2 ), split ratio: 1 / 50

[0115] Test Example 3: Yellowness Index (YID) Regenerated bis(2-hydroxyethyl) terephthalate was mixed with ethylene glycol (EG) and dissolved at 120°C for 1 hour to obtain a solution with a concentration of 25% by weight. Transmission data for this solution was acquired using a Hunterlab Color Flex EZ with an observer angle of 2° using illuminant D65. Yellowness index (YID) values ​​were calculated using the software color analyzer.

[0116] The test results are shown in Table 1 below.

[0117] [Table 1]

[0118] As can be seen from the above table, r-BHET_A1 to r-BHET_A5 had a high BHET ratio, no inorganic impurities were observed, and the content of DEG-derived esters was very low. In contrast, r-BHET_B2 had the problem of containing a large amount of dimer or DEG-derived esters and some residual solvent (EG).

[0119] <Preparation of aqueous solution of recycled BHET and preparation of polyester resin> Example 1 Step A: Preparation and storage of aqueous solutions of r-BHET The regenerated bis(2-hydroxyethyl)terephthalate, r-BHET_A2, was dissolved in water at 87° C., and the aqueous solution was adjusted to a concentration of 85% by weight by adding or evaporating water therefrom. The aqueous solution of the regenerated bis(2-hydroxyethyl)terephthalate was stored at the same temperature (87° C.) for 5 days and used as is in the next step.

[0120] Step B: Polymerization of polyester resin The esterification reactor was charged with an aqueous solution of the regenerated bis(2-hydroxyethyl) terephthalate (r-BHET_A2, 64,677.1 kg) obtained in the previous step, ethylene glycol (EG, 263.1 kg), 1,4-cyclohexanedimethanol (CHDM, 1,833.4 kg), isosorbide (ISB, 495.7 kg), diethylene glycol (DEG, 539.8 kg), Ge catalyst (32.0 kg), blue toner (0.150 kg), and red toner (0.075 kg). Nitrogen was then injected into the esterification reactor, and the reactor was heated to 2.0 kgf / cm below standard pressure (absolute pressure: 2,231.1 mmHg). 2The mixture in the esterification reactor was then heated to 220°C over 90 minutes, held at 220°C for 2 hours, and then heated to 260°C again over 2 hours. The mixture in the esterification reactor was stored at 260°C for about 7 hours, and then transferred to the polycondensation reactor, and the by-products formed during the reaction were discharged through a column and a cooler. The pressure in the esterification reactor was then lowered from standard pressure to 5 Torr (absolute pressure: 5 mmHg) over 30 minutes. At the same time, the temperature of the polycondensation reactor was raised to 280°C over 1 hour, and the polycondensation reaction was then carried out while maintaining the pressure in the polycondensation reactor at 1 Torr (absolute pressure: 1 mmHg) or less. At the start of the polycondensation reaction, the stirring speed may be set high. If the viscosity of the reactants increases with the progress of the polycondensation reaction, the stirring power becomes weak, or the temperature of the reactants exceeds the set temperature, the stirring speed may be appropriately adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.70 dl / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged out of the reactor to form pellets, solidified with a cooling liquid, and then granulated to an average weight of about 12-14 mg to prepare about 50 tons of polyester resin (copolymer).

[0121] Example 2 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), except that in step A, r-BHET_A3 was used as the regenerated bis(2-hydroxyethyl) terephthalate, the dissolution temperature was 90°C, and the concentration was 80% by weight, and in step B, an aqueous solution of regenerated bis(2-hydroxyethyl) terephthalate (r-BHET_A3, 32,424.4 kg), terephthalic acid (TPA, 21,1 90.8 kg), ethylene glycol (EG, 8,389.5 kg), 1,4-cyclohexanedimethanol (CHDM, 735.3 kg), diethylene glycol (DEG, 1,353.1 kg), Ge catalyst (32.0 kg), Ti catalyst (4.5 kg), phosphoric acid (5.0 kg), blue toner (0.200 kg), and red toner (0.050 kg) were added, and the esterification reaction was carried out at a temperature of 260°C and a pressure of 0.5 kgf / cm from the standard pressure. 2Except that it was carried out at high pressure and the polycondensation reaction was carried out at a temperature of 275° C. until the intrinsic viscosity (IV) reached 0.78 dl / g.

[0122] Example 3 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), except that in step A, r-BHET_A5 was used as the regenerated bis(2-hydroxyethyl) terephthalate, the dissolution temperature was 110°C, and the concentration was 95% by weight, and in step B, the reactor was charged with an aqueous solution of regenerated bis(2-hydroxyethyl) terephthalate (r-BHET_A5, 49,265.2 kg), terephthalic acid (TPA, 5,681.8 kg), ethylene glycol (EG, 707.4 kg), 1,4-cyclohexanedimethanol (CHDM, 10, The esterification reaction was carried out at a temperature of 255°C and a pressure of 2.0 kgf / cm under standard pressure. 2 Except that it was carried out at high pressure and the polycondensation reaction was carried out at a temperature of 285° C. until the intrinsic viscosity (IV) reached 0.78 dl / g.

[0123] Example 4 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), except that in step A, r-BHET_A1 was used as the regenerated bis(2-hydroxyethyl) terephthalate, the dissolution temperature was 60°C, and the concentration was 70% by weight, and in step B, an aqueous solution of regenerated bis(2-hydroxyethyl) terephthalate (r-BHET_A1, 17,210.2 kg), terephthalic acid (TPA, 26,244. 5 kg), ethylene glycol (EG, 9,662.1 kg), 1,4-cyclohexanedimethanol (CHDM, 10,082.2 kg), diethylene glycol (DEG, 2,394.1 kg), Ti catalyst (0.9 kg), phosphoric acid (10.0 kg), cobalt acetate (13.7 kg), blue toner (0.030 kg), and red toner (0.010 kg) were added. The esterification reaction was carried out at a temperature of 250°C and a pressure of 1.5 kgf / cm from the standard pressure. 2 Except that it was carried out at high pressure and the polycondensation reaction was carried out at a temperature of 270° C. until the intrinsic viscosity (IV) reached 0.82 dl / g.

[0124] Example 5 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), except that in step A, r-BHET_A5 was used as the regenerated bis(2-hydroxyethyl) terephthalate, the dissolution temperature was 80°C, and the concentration was 50% by weight, and in step B, the reactor was charged with an aqueous solution of the regenerated bis(2-hydroxyethyl) terephthalate (r-BHET_A5, 13,403.4 kg) obtained in the previous step, terephthalate, and terephthalate. The esterification reaction was carried out at a temperature of 265°C and a pressure of 1.0 kgf / cm under standard pressure. 2 Except that it was carried out at high pressure and the polycondensation reaction was carried out at a temperature of 275° C. until the intrinsic viscosity (IV) reached 0.70 dl / g.

[0125] Example 6 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), except that in step A, r-BHET_A3 was used as the regenerated bis(2-hydroxyethyl) terephthalate, the dissolution temperature was 90°C, and the concentration was 60% by weight, and in step B, the reactor was charged with an aqueous solution of the regenerated bis(2-hydroxyethyl) terephthalate (r-BHET_A3, 5,438.2 kg) obtained in the previous step, terephthalic acid (TPA, 35,935.9 kg), ethylene glycol (EG, 9,882.0 kg), 1,4-cyclohexanedimethanol (CH DM, 2,740.5 kg), diethylene glycol (DEG, 2773.8 kg), CHDM derivatives (containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a molar ratio of 1:3, 2,083.9 kg), Ge catalyst (32.0 kg), phosphoric acid (5.0 kg), blue toner (0.250 kg), and red toner (0.100 kg) were added, and the esterification reaction was carried out at a temperature of 260°C and a pressure of 0.5 kgf / cm from the standard pressure. 2 Except that it was carried out at high pressure and the polycondensation reaction was carried out at a temperature of 275° C. until the intrinsic viscosity (IV) reached 0.75 dl / g.

[0126] Example 7 The same procedure as in Example 1 was repeated, except that in step A, r-BHET_A5 was used as the regenerated bis(2-hydroxyethyl) terephthalate, the dissolution temperature was 105° C., and the concentration was 90% by weight; and in step B, the reactor was charged with an aqueous solution of the regenerated bis(2-hydroxyethyl) terephthalate (r-BHET_A5, 45,274.0 kg) obtained in the previous step, terephthalic acid (TPA, 12,680.8 kg), isophthalic acid (IPA, 29,588.5 kg), ethylene glycol The esterification reaction was carried out at a temperature of 260°C and a pressure of 3.0 kgf / cm under standard pressure until the intrinsic viscosity (IV) reached 0.65 dl / g. ... 2 Except that it was carried out under high pressure and polycondensation reaction was carried out at a temperature of 280°C to obtain granules. The granules were left at 150°C for 1 hour to crystallize, and then fed into a solid-state polymerization reactor. While flowing nitrogen at a rate of 50 L / min, the temperature of the reactor was increased from room temperature to 190°C at a rate of 40°C / h. While maintaining this, solid-state polymerization was carried out until the intrinsic viscosity (IV) of the granules in the reactor reached 1.10 dl / g, and about 50 tons of polyester resin (copolymer) was obtained.

[0127] Comparative Example 1 The same procedure as in Example 7 was repeated, except that in step A, r-BHET_A5 was used as the regenerated bis(2-hydroxyethyl)terephthalate, the dissolution temperature was 120°C, and the concentration was 50% by weight; and in step B, the reactor was charged with the aqueous solution of the regenerated bis(2-hydroxyethyl)terephthalate (r-BHET_A5, 26,318.5 kg) obtained in the previous step, terephthalic acid (TPA, 25,800.4 kg), ethylene glycol (EG, 10,707.0 kg), 1,4-cyclohexanedimethanol (CHDM, 746.0 kg), isosorbide (ISB, 504.3 kg), Ge catalyst (64.0 kg), blue toner (0.150 kg), and red toner (0.050 kg); the esterification reaction was carried out at a temperature of 260°C and a pressure of 0.5 kgf / cm below standard pressure. 2 Except for the fact that it was carried out at high pressure, the polycondensation reaction was carried out at a temperature of 280°C until the intrinsic viscosity (IV) reached 0.50 dl / g, and the solid-state polymerization was carried out at a temperature of 200°C until the intrinsic viscosity (IV) reached 0.70 dl / g, to obtain about 50 tons of polyester resin (copolymer).

[0128] Comparative Example 2 The same procedure as in Example 7 was repeated, except that in step A, r-BHET_B2 was used as the regenerated bis(2-hydroxyethyl) terephthalate, which was melted at 130°C and not mixed with water to prepare liquid regenerated bis(2-hydroxyethyl) terephthalate (concentration: 100% by weight); and in step B, the liquid regenerated bis(2-hydroxyethyl) terephthalate (r-BHET_B2, 19,107.3 kg) obtained in the previous step, terephthalic acid (TP A, 29,137.4 kg), ethylene glycol (EG, 27,413.9 kg), 1,4-cyclohexanedimethanol (CHDM, 3,610.8 kg), isosorbide (ISB, 976.3 kg), diethylene glycol (DEG, 265.8 kg), Ti catalyst (1.8 kg), cobalt acetate (8.5 kg), blue toner (0.150 kg), and red toner (0.050 kg) were added, and the esterification reaction was carried out at a temperature of 260°C and a pressure of 1.0 kgf / cm from the standard pressure. 2Except for the fact that it was carried out at high pressure, the polycondensation reaction was carried out at a temperature of 280°C until the intrinsic viscosity (IV) reached 0.70 dl / g, and the solid-state polymerization was carried out at a temperature of 200°C until the intrinsic viscosity (IV) reached 0.95 dl / g, to obtain about 50 tons of polyester resin (copolymer).

[0129] Comparative Example 3 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), except that in step A, r-BHET_A1 was used as the recycled bis(2-hydroxyethyl) terephthalate, the dissolution temperature was 50°C, and the concentration was 40% by weight; and in step B, the aqueous solution of the recycled bis(2-hydroxyethyl) terephthalate (r-BHET_A1, 64,677.1 kg) obtained in the previous step, ethylene glycol (EG, 263.1 kg), 1,4-cyclohexanedimethanol (CHDM, 1,833.4 kg), isosorbide (ISB, 495.7 kg), diethylene glycol (DEG, 539.8 kg), Ge catalyst (320.2 kg), phosphoric acid (1.0 kg), blue toner (0.150 kg), and red toner (0.050 kg) were charged into the reactor; the esterification reaction was carried out at a temperature of 255°C and a pressure of 0.5 kgf / cm below standard pressure. 2 Except that it was carried out at high pressure and the polycondensation reaction was carried out at a temperature of 280° C. until the intrinsic viscosity (IV) reached 0.60 dl / g.

[0130] Test Example 4: Changes in r-BHET composition Aqueous solutions of regenerated BHET were prepared in the same manner as in step A of the Examples and Comparative Examples, and were stored for 5 days while maintaining the temperature. Thereafter, the solvent (water) in the aqueous solution was evaporated, and HPLC analysis was carried out in the same manner as in Test Example 1. The peak area fractions (%) of BHET and the dimer thus analyzed are shown in Tables 2 and 3 below. Furthermore, the difference from the initial peak area fraction (%) of BHET shown in Table 1 above was calculated to calculate the change in purity (ΔBHET) after storage as an aqueous solution for 5 days. ΔBHET = BHET (1st day) - BHET (5th day) In the formula, BHET (day 0) is the peak area fraction (%) of BHET in the HPLC result of the regenerated BHET obtained by depolymerization, and BHET (day 5) is the peak area fraction (%) after storage as an aqueous solution for 5 days.

[0131] Test Example 5: Change in Yellowness Index (YID) Aqueous solutions of regenerated BHET were prepared in the same manner as in step A of the examples and comparative examples, and were stored for 5 days while maintaining the temperature. Thereafter, the water in the aqueous solution was evaporated to obtain regenerated BHET powder, and the yellowness index (YID) of this powder was measured in the same manner as in Test Example 3. The results are shown in Tables 2 and 3 below. Furthermore, the change in yellowness index after storage for 5 days (ΔYID) was calculated by calculating the difference from the initial yellowness index shown in Table 1 above. ΔYID = YID(day 5) - YID(day 0) where YID(day 0) is the yellowness index measured on the regenerated BHET obtained by depolymerization, and YID(day 5) is the yellowness index measured on the regenerated BHET after storage for 5 days as an aqueous solution.

[0132] The test results are shown in the table below.

[0133] [Table 2]

[0134] [Table 3]

[0135] Test Example 6: Evaluation of resin color The chromaticity and brightness of the samples were measured using a Varian Cary 5 UV / Vis / NIR spectrophotometer equipped with a diffuse reflectance accessory. Polyester resin test pieces with a thickness of 6 mm were prepared, and the transmission data of illuminant D65 was acquired at an observer angle of 2°, and processed using a color analyzer in Grams / 32 software to calculate Hunter Lab values. The results of subtracting the b value from the L value (Lb) are shown in the table below.

[0136] The test results are shown in the following Tables 4 and 5, along with the compositions of the polyester resins prepared in each of the Examples and Comparative Examples.

[0137] [Table 4]

[0138] [Table 5]

[0139] With reference to the results of the Examples, Comparative Examples, and their Test Examples, when recycled bis(2-hydroxyethyl) terephthalate was prepared as an aqueous solution under the preferred ranges of dissolution temperature and concentration of the present invention and stored as in Examples 1 to 7, the change in purity and yellowness index was very small even after 5 days, and the color quality of the polyester resin prepared therefrom was also excellent.

[0140] On the other hand, in the cases of Comparative Examples 1 to 3 where the aqueous solutions were not stored or where the aqueous solutions were stored outside the preferred ranges of dissolution temperature and concentration, the changes in purity and yellowness index after 5 days were very large, or the color quality of the polyester resins prepared therefrom was poor.

Claims

1. 1. A process for preparing a polyester resin comprising the steps of: (1) depolymerizing waste polyester to prepare recycled bis(2-hydroxyethyl) terephthalate; (2) mixing the recycled bis(2-hydroxyethyl) terephthalate with water at 60°C to 110°C to prepare an aqueous solution of recycled bis(2-hydroxyethyl) terephthalate having a concentration of 50% by weight to 95% by weight; (3) preparing a polyester resin by esterification and polycondensation using the aqueous solution of recycled bis(2-hydroxyethyl) terephthalate; A method comprising:

2. Step (1) is (1a) subjecting waste polyester to depolymerization by a first glycolysis reaction at a temperature of 180° C. to 200° C. to obtain a first reactant; (1b) subjecting the first reactant to depolymerization by a second glycolysis reaction at a temperature of 150° C. to 170° C. to obtain a second reactant; (1c) subjecting the second reactant to ion exchange with an ion exchange resin to obtain a third reactant; (1d) removing unreacted glycol from the third reactant by distillation at a temperature of 150° C. or less to obtain a fourth reactant; (1e) subjecting the fourth reactant to distillation to obtain crude bis(2-hydroxyethyl) terephthalate; 2. A method for preparing the polyester resin of claim 1 comprising:

3. 2. The method for preparing the polyester resin according to claim 1, wherein the recycled bis(2-hydroxyethyl) terephthalate has a peak area fraction of bis(2-hydroxyethyl) terephthalate of 96% or more and a peak area fraction of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl] terephthalate of 2.5% or less, as measured by high performance liquid chromatography (HPLC).

4. Step (2) (2a) mixing the regenerated bis(2-hydroxyethyl) terephthalate with water at 60° C. to 110° C.; (2b) After mixing, the concentration is adjusted to 50% by weight to 95% by weight by adding more water or evaporating it.

2. A method for preparing the polyester resin of claim 1 comprising:

5. The method for preparing the polyester resin described in claim 1, wherein the aqueous solution of the regenerated bis(2-hydroxyethyl) terephthalate prepared in step (2) is stored at 60°C to 110°C for 5 days, and then the water is evaporated to obtain a regenerated bis(2-hydroxyethyl) terephthalate. When the regenerated bis(2-hydroxyethyl) terephthalate is dissolved in ethylene glycol having a concentration of 25% by weight at 120°C for 1 hour, the yellowness index (YID) is measured to be 5 or less.

6. 2. The method for preparing a polyester resin according to claim 1, wherein when the aqueous solution of the recycled bis(2-hydroxyethyl) terephthalate prepared in step (2) is stored at 60° C. to 110° C. for 5 days, the purity of the recycled BHET is measured to be 5% or less different from the initial purity.

7. 2. The method for preparing the polyester resin according to claim 1, further comprising introducing at least one monomer selected from the group consisting of (a) a dicarboxylic acid or a derivative thereof, (b) ethylene glycol or diethylene glycol, and (c) a diol-based comonomer into the esterification reaction.

8. 8. The method for preparing a polyester resin according to claim 7, wherein the dicarboxylic acid comprises at least one selected from terephthalic acid and isophthalic acid.

9. 8. The method for preparing a polyester resin according to claim 7, wherein the diol-based comonomer comprises at least one selected from the group consisting of cyclohexanedimethanol, cyclohexanedimethanol derivatives, and isosorbide.

10. 10. The method for preparing a polyester resin according to claim 9, wherein the cyclohexanedimethanol derivative is 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol.

11. 8. The method for preparing a polyester resin of claim 7, wherein the diol based comonomer further comprises 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, and 1,4-cyclohexanediol.

12. 2. The method for preparing a polyester resin according to claim 1, wherein the polyester resin has an L minus b value of 85 or greater when measured in the Hunter Lab color space.

13. 1. A method for preparing an aqueous solution of regenerated bis(2-hydroxyethyl) terephthalate, comprising: (1) depolymerizing waste polyester to prepare recycled bis(2-hydroxyethyl) terephthalate; (2) mixing the regenerated bis(2-hydroxyethyl) terephthalate with water at 60° C. to 110° C. to prepare an aqueous solution of regenerated bis(2-hydroxyethyl) terephthalate having a concentration of 50% by weight to 95% by weight; A method comprising:

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