Ester monomer composition and method for obtaining an ester monomer composition

Abstract

The object of the present invention is to solve the problems of the prior art described above and to provide a technology that enables the maximum effective utilization of waste polyester resources with the minimum necessary process, and to obtain a high-quality ester monomer composition with controlled composition. [Solution] An ester monomer composition mainly composed of bis-(2-hydroxyethyl) terephthalate (BHET), wherein the heat of fusion is 31 J / g or more and less than 160 J / g.

Description

[Technical Field]

[0001] The present invention relates to an ester monomer composition obtained from a polyester molded article and a method for obtaining the same ester monomer composition. [Background technology]

[0002] Modern economic and social systems have been sustained by a mass production, mass consumption, and mass disposal model. However, this has led to various negative environmental impacts, including the depletion of natural resources, environmental destruction associated with resource extraction, global warming due to greenhouse gas emissions, and rising sea levels. Therefore, in order to efficiently utilize limited resources and continue sustainable growth, it has become essential to build a circular economy system that minimizes waste generation and reuses or recycles the waste that is generated in a way that does not burden the environment.

[0003] Realizing a circular economy requires the establishment of recycling systems such as thermal recycling, material recycling, and chemical recycling. Among these, chemical recycling technology, which decomposes and purifies waste plastics down to their raw monomer units and obtains recycled resin materials of the same quality as before disposal from the resulting monomers, is attracting attention.

[0004] Polyester fibers, which are inexpensive and exhibit suitable properties for clothing and industrial nonwoven fabrics, are also expected to be recycled through chemical recycling. Technologies for recycling them down to the raw material monomer unit through hydrolysis and glycol decomposition have been explored. For example, by adding ethylene glycol (EG) to polyester fibers recovered as waste and depolymerizing them through glycol decomposition, the ester monomer bis-(2-hydroxyethyl) terephthalate (BHET) can be obtained. Using this BHET as a monomer raw material, recycled polyethylene terephthalate (PET) resin can be manufactured.

[0005] On the other hand, modifying polyester fibers by copolymerizing them with various monomers to improve their properties for specific applications is a widely used technique, and it is easy to assume that recovered polyester fibers will contain copolymer components. Therefore, in order to produce PET resin free of copolymer components from recovered polyester fibers containing copolymer components, a purification process for monomers obtained by depolymerization is necessary, and various methods have been proposed to date.

[0006] For example, Patent Document 1 discloses a method for obtaining high-purity DMT by carrying out a depolymerization reaction of polyester waste containing isophthalic acid as a copolymer component using EG, then converting it to dimethyl terephthalate (DMT) using methanol, and separating and removing the isophthalic acid component by recrystallization and washing with an organic solvent. Patent Document 2 also discloses a method for obtaining ester monomers and recycled polyester resins from which the isophthalic acid component has been separated and removed by carrying out a depolymerization reaction of copolymer polyester containing isophthalic acid using alkylene glycol, then cooling the temperature to crystallize and performing solid-liquid separation. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2001-294553 [Patent Document 2] Japanese Patent Publication No. 2023-146176 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The method disclosed in Patent Document 1 is undesirable because it requires depolymerizing polyester waste using EG and then converting the ester monomer from BHET to DMT using methanol, which leads to increased manufacturing costs and environmental burden. Furthermore, since the recrystallized DMT is washed with an organic solvent, the copolymer components are discarded without being reused, making it difficult to say that limited resources are being used effectively.

[0009] Furthermore, the method disclosed in Patent Document 2 separates and removes copolymer components by depolymerizing the copolymerized polyester using an alkylene glycol such as EG, and then cooling it down to separate the solid and liquid components. This method is an improvement over Patent Document 1 in terms of process reduction. On the other hand, because the alkylene glycol solution obtained from the depolymerization reaction is cooled down as is, if the copolymerized polyester contains impurities such as coloring components, these impurities are easily incorporated into the ester monomer, leading to a decrease in the quality of recycled PET. Also, while ester monomers show good solubility with alkylene glycol, making it easy to separate and remove copolymer components, this reduces the recovery rate of the target recovered product, the ester monomer, and worsens the recycling efficiency. Furthermore, since copolymer components are separated and removed in the same way as in Patent Document 1, there is room for technological improvement to effectively utilize resources. When waste polyester contains copolymer components, if the amount of such copolymer components in the recovered ester monomer can be controlled, the desired recycled copolymerized polyester can be obtained by directly repolymerizing the recovered ester monomer.

[0010] The object of the present invention is to solve the problems of the prior art described above and to provide a technology that enables the maximum effective utilization of waste polyester as a resource using the minimum necessary process, and to obtain a high-quality ester monomer composition with controlled composition. [Means for solving the problem]

[0011] The above problems are solved by the following [1] to

[10] . [1] An ester monomer composition mainly composed of bis-(2-hydroxyethyl) terephthalate (BHET), wherein the heat of fusion of the ester monomer composition is 31 J / g or more and less than 160 J / g. [2] The ester monomer composition according to [1] above, wherein the molar ratio of BHET is 0.700 or more and less than 1.000 when the total molar amount of the dicarboxylic acid ester compounds contained in the ester monomer composition is set to 1.000. [3] The ester monomer composition according to any one of [1] or [2] above, wherein the ester monomer composition contains an isophthalic acid ester compound. [4] The ester monomer composition according to any one of [1] to [3] above, wherein the molar ratio of the isophthalic acid ester compound is greater than 0.003 and 0.300 or less when the total molar amount of the dicarboxylic acid ester compounds contained in the ester monomer composition is set to 1.000. [5] A method for obtaining an ester monomer composition mainly composed of BHET from a polyester molded article mainly composed of polyethylene terephthalate (PET) along the following steps. <000007�> (1) A step of depolymerizing a polyester molded article mainly composed of PET using ethylene glycol (EG) to obtain an EG solution of a mixture containing BHET. (2) A step of recovering a mixture containing BHET from the EG solution of the mixture containing BHET obtained in the step (1). (3) A step of dissolving the mixture containing BHET obtained in the step (2) in water at 60°C or higher and 100°C or lower to obtain an aqueous solution. (4) A step of cooling the aqueous solution obtained in the step (3) to the crystallization temperature Tc represented by Formulas 1 to 3 and precipitating the ester monomer composition as a solid.

[0012] [Number]

[0013] [Number] <[

[0014]

Number

[0015] (x is the molar ratio of BHET (0.000 < x ≤ 1.000)) when the total molar amount of the dicarboxylic acid ester compound contained in the mixture containing BHET is taken as 1.000) (5) Step of separating the solid ester monomer composition precipitated in the step (4) from water and recovering it from the aqueous solution [6] The method according to [5] above, wherein in the aqueous solution obtained in step (3), the weight ratio of water to the mixture containing BHET is 4 or more and 39 or less [7] The method according to [5] or [6] above, wherein in step (4), after cooling to the crystallization temperature Tc, it is held for 0 hours or more and 21 hours or less [8] The method according to any one of [5] to [7] above, wherein in steps (1) to (4), the mixture containing BHET contains an isophthalic acid ester compound [9] A recycled polyester resin obtained by polycondensing the ester monomer composition according to [1] above

[10] A recycled polyester molded article made of the recycled polyester resin according to [9] above

Advantages of the Invention

[0016] According to the present invention, it is possible to maximize the effective utilization of waste polyester as a resource with a minimum necessary process and obtain an ester monomer composition of high quality and controlled composition

Brief Description of the Drawings

[0017] [[ID= / / ID=36]] [Figure 1] It is a correlation diagram of the molar ratio x of BHET in the mixture and the temperature for explaining the crystallization temperature Tc in step (4) [Figure 2] It is a correlation diagram of the molar ratio x of BHET in the mixture and the temperature for explaining the preferable crystallization temperature Tc in step (4) [Figure 3]This figure shows the range of crystallization temperature Tc settings when, in step (4), the molar ratio y of BHET is controlled to 0.980 ≤ y < 0.990 (upward-sloping shaded area) and when it is controlled to 0.997 ≤ y ≤ 1.000 (downward-sloping shaded area), with the total molar amount of dicarboxylic acid ester compound in the ester monomer composition being 1.000. [Modes for carrying out the invention]

[0018] The present invention will be described in detail below.

[0019] In the present invention, the ester monomer composition mainly composed of BHET is a composition containing 50% by weight or more of BHET, and can be prepared for the purpose of making the most effective use of waste polyester as a resource. For example, it can be prepared by recovering BHET from an EG solution of a mixture obtained by depolymerizing a polyester molded product containing 50% by weight or more of PET using EG. The heat of fusion of the ester monomer composition mainly composed of BHET is 31 J / g or more and less than 160 J / g. For example, it can be calculated as the area value of the endothermic peak observed when the composition is held at 180°C for 5 minutes, rapidly cooled to 25°C at a rate of 100°C / min or more, and then heated from 25°C to 180°C at a heating rate of 16°C / min using a differential scanning calorimeter. If the heat of fusion is less than 31 J / g, the ester monomer composition becomes less crystalline and glassy, ​​resulting in high stickiness, which makes it prone to remaining in pipes or causing blockages when introduced into reaction vessels, and thus has extremely poor handling properties. Conversely, if the heat of fusion is 160 J / g or more, the melting process takes too long when repolymerizing with ester monomers, resulting in reduced production efficiency. For excellent handling, the heat of fusion is preferably 31 J / g or more, more preferably 79 J / g or more, and even more preferably 112 J / g or more. Furthermore, for efficient melting, it is preferably less than 160 J / g, more preferably less than 154 J / g, even more preferably less than 152 J / g, particularly preferably less than 138 J / g, and most preferably less than 131 J / g.

[0020] Furthermore, the ester monomer composition mainly composed of BHET in the present invention may contain any other components as long as they do not hinder the objectives of the present invention. For example, it may contain dicarboxylic acid ester compounds other than BHET, in which polymerization of the recycled copolymer polyester resin can be carried out directly without adding different monomer components to the ester monomer composition, thus enabling process reduction. In this case, it is preferable that the molar ratio of BHET, when the total molar amount of dicarboxylic acid ester compounds contained in the ester monomer composition is set to 1.000, is 0.700 or more and less than 1.000, in which the ester monomer composition has excellent handling properties and it is easy to obtain a recycled copolymer polyester resin with good physical properties.

[0021] Examples of dicarboxylic acid ester compounds other than BHET include monoester compounds, diester compounds, or 2-5 ester oligomer compounds having a chemical structure formed by the condensation of 2-5 of these monoester or diester compounds, all consisting of a dicarboxylic acid residue and an alkylene glycol residue. More specifically, dicarboxylic acid residues include aromatic dicarboxylic acid residues such as terephthalic acid residue, isophthalic acid residue, 5-sulfoisophthalic acid residue, sodium 5-sulfoisophthalate residue, naphthalenedicarboxylic acid residue, and 4,4'-diphenyldicarboxylic acid residue, as well as aliphatic dicarboxylic acid residues such as adipic acid residue, sebaciic acid residue, and cyclohexanedicarboxylic acid residue. Examples of alkylene glycol residues include ethylene glycol residue, propylene glycol residue, tetramethylene glycol residue, hexamethylene glycol residue, diethylene glycol residue, triethylene glycol residue, cyclohexanedimethanol residue, neopentyl glycol residue, polyethylene glycol residue, polypropylene glycol residue, and polytetramethylene glycol residue. As a diester compound of dicarboxylic acid consisting of these dicarboxylic acid residues and alkylene glycol residues, it is preferable to include at least one of an isophthalic acid ester compound having an isophthalic acid residue or a 5-sulfoisophthalic acid ester compound having a 5-sulfoisophthalic acid residue, in order to improve the handling properties of the ester monomer composition and to easily control the composition of the ester monomer composition by the method described later, and it is more preferable to include an isophthalic acid ester compound having an isophthalic acid residue, and it is particularly preferable that the isophthalic acid ester compound having an isophthalic acid residue is bis(2-hydroxyethyl) isophthalate, which consists of an isophthalic acid residue and an ethylene glycol residue.

[0022] The molar ratio of isophthalic acid ester compounds in the ester monomer composition is preferably greater than 0.003 and less than or equal to 0.300, in terms of the molar ratio of isophthalic acid ester compounds when the total molar amount of dicarboxylic acid ester compounds contained in the ester monomer composition is set to 1.000, in terms of excellent handling properties of the ester monomer composition and the ability to lower the melting point of the regenerated copolymer polyester resin obtained by polymerizing the ester monomer composition. If the molar ratio is 0.003 or less, the heat of fusion of the ester monomer composition tends to be high, and it takes a long time for the ester monomer composition to melt when repolymerized. In addition, when polymerizing a regenerated copolymer polyester resin copolymerized with isophthalic acid residues using this ester monomer composition, it becomes necessary to add isophthalic acid monomer separately afterwards, which is inefficient. On the other hand, if the molar ratio is greater than 0.300, the handling properties of the ester monomer composition deteriorate significantly. Therefore, in terms of excellent handling properties, the molar ratio of isophthalic acid ester compounds is preferably 0.300 or less, more preferably 0.120 or less, and even more preferably 0.050 or less. Furthermore, in terms of enabling the lower melting point of the copolymerized polyester obtained by repolymerizing the ester monomer composition, it is preferable that the melting point be greater than 0.003, more preferably greater than 0.010, and even more preferably greater than 0.020.

[0023] Furthermore, in order to obtain a high-quality color tone for the recycled polyester resin obtained by polycondensation of the ester monomer composition in the present invention, the color tone L* value of the ester monomer composition is preferably 85.0 or higher, more preferably 90.0 or higher, even more preferably 93.0 or higher, and particularly preferably 95.0 or higher, with an upper limit of 100.0. The color tone a* value is preferably -2.0 or higher and 2.0 or lower, more preferably -1.0 or higher and 1.0 or lower, and even more preferably -0.5 or higher and 0.5 or lower. The color tone b* value is preferably -5.0 or higher and 5.0 or lower, more preferably -4.0 or higher and 4.0 or lower, even more preferably -3.0 or higher and 3.0 or lower, particularly preferably -2.0 or higher and 2.0 or lower, and most preferably -1.5 or higher and 1.5 or lower.

[0024] In the present invention, the ester monomer composition mainly composed of BHET may be prepared in any way, but in order to make the most effective use of waste polyester as a resource, a method for obtaining an ester monomer composition mainly composed of BHET from a polyester molded product mainly composed of polyethylene terephthalate (PET) may be used, which is the method described in [5] above, that is, a method following the steps (1) to (5) below. (1) A process of depolymerizing a polyester molded product mainly composed of PET using ethylene glycol (EG) to obtain an EG solution of a mixture containing BHET. (2) A step of recovering the mixture containing BHET from the EG solution of the mixture containing BHET obtained in step (1) above. (3) Dissolve the mixture containing BHET obtained in step (2) in water at a temperature of 60°C to 100°C to obtain an aqueous solution. (4) A step of cooling the aqueous solution obtained in step (3) to a crystallization temperature Tc represented by formulas 1 to 3, thereby precipitating the ester monomer composition as a solid.

[0025]

number

[0026]

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[0027]

number

[0028] (x is the molar ratio of BHET (0.000) when the total molar amount of dicarboxylic acid ester compounds contained in the mixture containing BHET is set to 1.000) <x≦1.000)) (5) A step of separating the solid ester monomer composition precipitated in step (4) from water and recovering it from the aqueous solution. In step (1) described above, the polyester molded product mainly composed of PET is a PET resin molded product containing 50% by weight or more of PET, and its shape is not particularly limited, such as chips, bottles, fibers such as clothing or nonwoven fabrics, films, etc., and it may also be crushed and cut, and may be used products that have been sold and used, or process waste generated in the manufacturing process. Regarding the shape, it is preferable, and more preferable, to be fibers or films, as they have a large surface area and allow for a reduction in reaction time when depolymerizing with EG in the same step. Furthermore, the polyester molded product mainly composed of PET may also contain copolymerized polyester containing copolymer components other than terephthalic acid residues and ethylene glycol residues, and copolymerized polyester molded products with the same composition may be used individually, or for example, multiple polyester molded products with different copolymer compositions may be mixed, and the content of dicarboxylic acid ester compounds derived from the copolymer components in the mixture containing BHET obtained after depolymerization may be controlled.

[0029] When a polyester molded product mainly composed of PET is a used product from marine operations or the marine environment, for example, a PET bottle recovered from the ocean or a nonwoven fabric substrate recovered from a seawater treatment membrane, it may contain at least one alkali metal or alkaline earth metal as an impurity, at a rate of 0.0 mmol / g to 10.0 mmol / g per gram of the polyester molded product. If such metal ions remain in the ester monomer composition obtained from the PET-based polyester molded product, or in the recycled polyester resin obtained by polymerizing the ester monomer composition, the color tone deteriorates and the quality is reduced. Therefore, in order to facilitate purification after depolymerization, the upper limit of the content is preferably 10.0 mmol / g or less, more preferably 5.0 mmol / g or less, and even more preferably 1.0 mmol / g or less. Note that the PET bottle recovered from the ocean or the nonwoven fabric substrate recovered from a seawater treatment membrane may have sand, mud, mold, and microorganisms that have grown during storage attached to them, so washing with water or the like and drying may be performed as necessary before depolymerization in step (1) above.

[0030] Furthermore, in step (1) above, when depolymerizing a polyester molded product mainly composed of PET using EG, the depolymerization conditions are not particularly limited, but for example, it is preferable that the amount of EG added is 1.5 parts by weight or more per 1.0 part by weight of the polyester molded product. If it is less than 1.5 parts by weight, the depolymerization reaction will not proceed sufficiently, and the recovery rate of BHET will decrease. On the other hand, adding more than 10.0 parts by weight yields the same effect, so it is undesirable from a cost standpoint. The temperature for depolymerization is preferably 190°C to 210°C. In addition, from the viewpoint of efficient depolymerization, it is preferable to add sodium hydroxide or sodium carbonate to the polyester molded product in an amount of 0.1% by weight or more and 2.0% by weight or less.

[0031] In step (2) described above, the method for recovering the mixture containing BHET from the EG solution of the mixture containing BHET obtained in step (1) is not particularly limited. For example, a distillation method in which EG is removed by heating under reduced pressure, or a reprecipitation method in which the EG solution of the mixture containing BHET is added to water, then cooled and solid-liquid separated may be used.

[0032] In step (3) described above, the mixture containing BHET obtained in step (2) is dissolved in water at a temperature of 60°C to 100°C. The solubility of BHET and other dicarboxylic acid ester compounds in water is moderately low, making it suitable for controlling the recovery rate and composition of the ester monomer composition in step (4) described below. When using EG as a solvent in known methods, the solubility of dicarboxylic acid ester compounds such as BHET in EG is high, and in order to increase the recovery rate, excessive cooling is required, or dicarboxylic acid ester compounds other than BHET are removed from the ester monomer composition, making it difficult to effectively utilize them as copolymer components.

[0033] Furthermore, in step (3), when obtaining the aqueous solution, the weight ratio of water to the mixture containing BHET is preferably 4 or more and 39 or less. If the weight ratio is less than 4, when the aqueous solution is cooled, the water and the precipitated ester monomer composition solidify together, making it difficult to separate the ester monomer composition from the water in step (5). When the weight ratio is 4 or more, the larger the weight ratio, the easier it is for water-soluble impurities in the mixture containing BHET to be removed during the cooling process, but at the same time, the recovery rate of the ester monomer composition decreases. In order to achieve both the effect of removing impurities and the recovery rate, the weight ratio is preferably 4 or more, and more preferably 9 or more. It is also preferably 39 or less, and more preferably 19 or less. Furthermore, if it is desired to improve the purity of the resulting ester monomer composition, step (3) is more preferably a method that includes the following steps (3a) to (3c). (3a) Dissolve the mixture containing BHET obtained in step (2) above in water at a temperature of 60°C to 100°C and perform thermal filtration. (3b) A step of performing an adsorption treatment on the filtrate obtained in step (3a) at a temperature of 60°C to 100°C, which is either an ion exchange treatment or an activated carbon treatment. (3c) Adding water at 60°C to 100°C to the filtrate after adsorption treatment obtained in step (3b) above to obtain an aqueous solution of a mixture containing BHET. In the aforementioned step (3a), impurities insoluble in water at temperatures between 60°C and 100°C can be removed by thermal filtration. Examples of such impurities include metal compounds such as titanium dioxide, inorganic compounds such as silica gel, sand and mud adhering to the polyester molded product, and resin components other than polyester that were compounded and used in the polyester molded product.

[0034] Furthermore, when dissolving the mixture containing BHET in water at 60°C to 100°C in step (3a) above, the weight ratio of water to the mixture containing BHET is preferably 0.5 to 39.0. If the weight ratio of water to the mixture containing BHET is less than 0.5, dicarboxylic acid ester compounds such as BHET are likely to precipitate, and these dicarboxylic acid ester compounds will also be removed during hot filtration, resulting in a decrease in yield. Also, if the weight ratio of water to the mixture containing BHET is high, the amount of energy required for heating and maintaining the temperature of the aqueous solution increases, which is disadvantageous in terms of cost. For this reason, the upper limit of the weight ratio is preferably 39.0 or less, more preferably 19.0 or less, even more preferably 9.0 or less, particularly preferably 4.0 or less, and most preferably 2.0 or less.

[0035] In step (3b) described above, the filtrate obtained in step (3a) can be subjected to at least one of ion exchange treatment and activated carbon treatment at a temperature of 60°C to 100°C to remove impurities other than dicarboxylic acid ester compounds dissolved in the filtrate. The adsorption treatment may be carried out by directly adding and stirring the adsorbent to the filtrate, or by pre-filling a column or the like with the adsorbent and passing the filtrate through it. Ion exchange treatment can use ion exchange resins or ion exchange membranes as adsorbents, but from a cost perspective, it is preferable to use ion exchange resins. There are no particular restrictions on the ionic form of the ion exchange resin, but in the case of cation exchange resins, H is preferred because of their superior ion exchange capacity. + Type, Na + In the case of type anion exchange resin, Cl -Various types of resins can be used, such as free base type. Since both cationic and anionic ionic impurities can be removed, both cation exchange resins and anion exchange resins may be used. However, when using PET bottles recovered from the ocean or nonwoven fabric substrates recovered from seawater treatment membranes for polyester molded products mainly composed of PET, alkali metal ions and alkaline earth metal ions may be present, which can cause discoloration of the resulting ester monomer composition or recycled polyester resin. Therefore, it is preferable to use cation exchange resins. The amount of adsorbent used in the ion exchange treatment must be such that the amount of ion exchange groups in the adsorbent is at least 1 equivalent relative to the amount of ionic impurities. Furthermore, while there are no particular restrictions on the activated carbon used for activated carbon treatment, its average pore size is preferably between 0.5 nm and 200 nm, because if it is smaller than the impurity molecules, it will not adsorb impurities well, and if it is larger than the impurity molecules, the interaction with the pore wall weakens and the adsorption performance decreases. Also, the specific surface area of ​​the activated carbon is preferably between 300 m² / g and 5000 m² / g, from the viewpoint that if it is too small, the amount of impurities adsorbed decreases, and if it is too large, the activated carbon particles become small and handling deteriorates. In addition, the pore volume of the activated carbon is preferably between 0.2 mL / g and 2.5 mL / g, from the viewpoint that if it is too small, the amount of impurities adsorbed decreases, and if it is too large, the density of activated carbon particles decreases, resulting in a smaller packing amount when packing the column and a decrease in adsorption efficiency.

[0036] In step (3c), water at 60°C to 100°C is added to the filtrate after adsorption treatment obtained in steps (3a) and (3b) to adjust the concentration of the resulting aqueous solution. Specifically, if steps (3a) and (3b) are carried out under conditions where the weight ratio of water to the mixture containing BHET is less than 4, from the viewpoint of increasing the amount of energy required to heat and maintain the temperature of the aqueous solution, then if step (4) is carried out as is, when the aqueous solution is cooled, the water and the precipitated ester monomer composition will solidify together, making it difficult to separate the ester monomer composition from the water in step (5), which is undesirable. In such cases, by adding water at 60°C to 100°C to the filtrate after adsorption treatment obtained in steps (3a) and (3b) to make the weight ratio of water to the mixture containing BHET 4 to 39, it becomes possible to carry out the subsequent steps (4) and (5) in the preferred form of the present invention. If the weight ratio of water to the mixture containing BHET in the filtrate after step (3b) is appropriate, step (3c) can be omitted.

[0037] In step (4) described above, the aqueous solution of the mixture containing BHET obtained in step (3) is cooled to a crystallization temperature Tc (°C) represented by formulas 1 to 3. This makes it possible to control the composition of the ester monomer composition and recover it with high efficiency, while simultaneously removing thermally degraded products generated during depolymerization and improving the quality of the ester monomer composition. In this invention, the crystallization temperature Tc is greater than 0°C and less than 60°C. Formulas 1 to 3 are empirical formulas based on experimental results obtained through the inventors' diligent research, where x is the molar ratio of BHET when the total molar amount of dicarboxylic acid ester compounds contained in the mixture containing BHET is set to 1.000. The setting range of the crystallization temperature Tc according to formula 1 is shown in Figure 1. When x is 1.000, the only dicarboxylic acid ester compound contained in the mixture containing BHET is BHET, and the heat of fusion of the ester monomer composition obtained after step (5) tends to be high. Therefore, it is preferable that x is less than 1.000. Furthermore, when x is 0.990 or more and less than 1.000, the molar ratio of BHET in the ester monomer composition obtained after step (5) becomes 0.997 or more and 1.000 or less in a temperature range that can be substantially controlled in a system using water as a solvent under atmospheric pressure. In this case as well, the heat of fusion of the ester monomer composition tends to be high. Therefore, it is more preferable that x is less than 0.990.

[0038] Equation 2 shows the lower limit of the crystallization temperature Tc in step (4). By cooling to a temperature range of L1 or higher, the molar ratio y of BHET can be controlled to 0.950 or higher, when the total molar amount of dicarboxylic acid ester compounds in the ester monomer composition is 1.000. More detailed control is also possible. In equations 4 to 10 below, if the crystallization temperature Tc is to be between 0.950 and less than 0.980, the crystallization temperature Tc should be within the temperature range satisfied by equation 4. If the crystallization temperature Tc is to be between 0.980 and less than 0.990, the crystallization temperature Tc should be within the temperature range satisfied by equation 5. If the crystallization temperature Tc is to be between 0.990 and less than 0.997, the crystallization temperature Tc should be within the temperature range satisfied by equation 6. If the crystallization temperature Tc is to be between 0.997 and 1.000, the crystallization temperature Tc should be within the temperature range satisfied by equation 7.

[0039]

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[0040] (However, this is assuming that 0.950 ≤ y < 0.980 is the case.)

[0041]

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[0042] (However, this is assuming that 0.980 ≤ y < 0.990 is controlled.)

[0043]

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[0044] (However, this is assuming that 0.990 ≤ y < 0.997 is the case.)

[0045]

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[0046] (However, this is assuming that the value is controlled to be 0.997 ≤ y ≤ 1.000)

[0047]

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[0048]

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[0049]

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[0050] Furthermore, Equation 3 indicates the upper limit of the crystallization temperature Tc in step (4), and by cooling to a temperature range below this temperature R1, the ester monomer composition can be recovered with high efficiency. In order to further increase the recovery rate, it is more preferable to set the crystallization temperature Tc to the temperature range satisfied by Equation 11 in the following Equations 11 to 14, and even more preferable to set the temperature Tc to the temperature range satisfied by Equation 12.

[0051]

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[0052]

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[0053]

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[0054]

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[0055] Figure 2 is a modified version of Figure 1 with L2-L4, R2, and R3 added, and Figure 3 shows examples of the setting range for the crystallization temperature Tc when y is controlled to 0.980 ≤ y < 0.990 using equations 5 and 11 (upward-sloping shaded area), and when y is controlled to 0.997 ≤ y ≤ 1.000 using equations 7 and 12 (downward-sloping shaded area).

[0056] Furthermore, in step (4), after cooling to the crystallization temperature Tc, the ester monomer composition may be immediately separated from water and recovered from the aqueous solution without holding, or the cooled state may be maintained at the crystallization temperature Tc, after which the ester monomer composition may be separated from water and recovered from the aqueous solution. Maintaining the cooled state increases the amount of precipitated ester monomer composition and improves the recovery rate. In terms of improving the recovery rate of the ester monomer composition, the holding time is preferably 0 hours or more, more preferably 3 hours or more, even more preferably 6 hours or more, and particularly preferably 21 hours. The recovery rate plateaus even if held for longer than 21 hours, so there is no point in extending it further.

[0057] In steps (1) to (4) of the method of the present invention, the mixture containing BHET preferably contains at least one of an isophthalic acid ester compound having an isophthalic acid residue or a 5-sulfoisophthalic acid ester compound having a 5-sulfoisophthalic acid residue, more preferably an isophthalic acid ester compound having an isophthalic acid residue, and among isophthalic acid ester compounds having an isophthalic acid residue, it is particularly preferable to use bis(2-hydroxyethyl) isophthalate, which consists of an isophthalic acid residue and an ethylene glycol residue, because it is easy to control the composition of the ester monomer composition. This is because bis(2-hydroxyethyl) isophthalate, which consists of an isophthalic acid residue and an ethylene glycol residue, is an isomer of BHET and has similar solubility, and the handling properties of the obtained ester monomer composition are also easily improved. In step (5) above, the method for separating the solid ester monomer composition precipitated in step (4) with water and recovering it from the aqueous solution is not particularly limited, and for example, solid-liquid separation by filtration or centrifugation can be used.

[0058] In the present invention, in order to make the most effective use of waste polyester as a resource, recycled polyester resin can be obtained by using the above-mentioned ester monomer composition in polymerization. The polymerization method is not particularly limited, but for example, after melting at 250°C, 0.005% by weight of cobalt acetate tetrahydrate and phosphoric acid, 0.03% by weight of antimony trioxide and 0.3% by weight of titanium dioxide particles can be added, and by heating and stirring at 290°C and removing EG under reduced pressure, a repolymerized polyester resin suitable for fiber applications can be obtained. If the ester monomer composition contains dicarboxylic acid ester compounds other than BHET, polymerization of the recycled copolymerized polyester resin can be carried out directly without adding different monomer components to the ester monomer composition afterwards.

[0059] The recycled polyester resin obtained by polymerizing the ester monomer composition of the present invention preferably has a melting point of 196°C or higher and less than 255°C, observed when heated from 20°C to 280°C at a heating rate of 16°C / min using a differential scanning calorimeter after isothermal holding at 280°C for 5 minutes and rapid cooling to room temperature at a rate of 100°C / min or higher. Below 196°C, the crystallinity of the recycled polyester resin decreases significantly, leading to a decrease in strength, making it unsuitable for industrial material applications. Therefore, in terms of excellent material strength, a melting point of 196°C or higher is preferred, more preferably 232°C or higher, and even more preferably 245°C or higher. On the other hand, above 255°C, the melting point is equivalent to that of non-copolymerized PET resin, reducing the significance of applying the present invention; therefore, a melting point of less than 255°C is preferred. Furthermore, in terms of lowering the melting point and improving moldability, a melting point of less than 253°C is preferred, and even more preferably less than 251°C.

[0060] Furthermore, the recycled polyester resin of the present invention preferably has a diethylene glycol residue content of 0.1% by weight or more and less than 0.7% by weight, in order to have excellent colorfastness when, for example, it is formed into fibers, knitted and woven, and then dyed with dyes. Moreover, in order to further improve colorfastness, it is more preferable that the content be 0.6% by weight or less, even more preferable that be 0.4% by weight or less, and particularly preferable that be 0.2% by weight or less. However, since diethylene glycol residues in recycled polyester resin are always produced as a by-product in the process of obtaining recycled polyester resin by polycondensation of ester monomers, it is difficult to reduce the content to less than 0.1% by weight.

[0061] Furthermore, the recycled polyester resin of the present invention is preferable to have a Hunter tone L value of 70.0 or higher, more preferably 73.0 or higher, even more preferably 76.0 or higher, and particularly preferable 79.0 or higher, as it is easier to control the desired color tone when the recycled polyester resin is formed into fibers, knitted, and dyed with dyes. Furthermore, since it is possible to make the Hunter tone L value less than 85.0 even without adding fluorescent whitening agents, a Hunter tone L value of less than 85.0 is preferable. The Hunter tone a value is preferable to be between -2.0 and 2.0, more preferably -1.5 and 1.5, and even more preferably -1.0 and 1.0. The Hunter tone b value is preferable to be between -5.0 and 5.0, more preferably -4.5 and 4.5, even more preferably -4.0 and 4.0, particularly preferable -3.5 and 3.5, and most preferably -3.0 and 3.0.

[0062] The recycled polyester resin of the present invention is preferably used as a molded recycled polyester product such as bottles, films, or fibers by melt molding. In particular, since waste polyester collected as waste is directly recycled as a resource into clothing or industrial nonwoven fabrics, and then collected again after being used by consumers, it is possible to reduce the amount of petroleum used in polyester production and the environmental burden of incinerating waste plastics, its use as a textile product such as clothing or industrial nonwoven fabrics is particularly preferred and exemplifies this. However, the use is not limited to molded products. [Examples]

[0063] <A. Composition Analysis of Polyester Molded Products, Mixtures Containing BHET, and Ester Monomer Compositions> The composition analysis and calculation of the molar ratio of polyester molded products, mixtures containing BHET, and ester monomer compositions were carried out as follows.

[0064] As a sample for evaluation, a solution containing 5.0% by weight of a polyester molded product, a mixture containing BHET, or an ester monomer composition in deuterated 1,1,1,3,3,3 - hexafluoroisopropanol was prepared. For this solution, using a nuclear magnetic resonance apparatus, JNM - ECZ500R manufactured by JEOL Ltd. 1 1H - NMR measurement was performed, and from the obtained spectrum, the molar ratios of Formulas 15 to 17 were calculated from the integral values of the peaks derived from terephthalic acid and the peaks derived from other copolymerization components, for example, isophthalic acid. (Formula 15) Molar ratio of the target dicarboxylic acid residue when the total molar amount of dicarboxylic acid residues in the polyester molded product is 1.000 = Integral value of the target dicarboxylic acid residue / Total integral value of all dicarboxylic acid residues in the polyester molded product (Formula 16) Molar ratio of the target dicarboxylic acid ester compound when the total molar amount of dicarboxylic acid ester compounds in the mixture containing BHET is 1.000 = Integral value of the target dicarboxylic acid ester compound / Total integral value of all dicarboxylic acid ester compounds in the mixture containing BHET (Formula 17) Molar ratio of the target dicarboxylic acid ester compound when the total molar amount of dicarboxylic acid ester compounds in the ester monomer composition is 1.000 = Integral value of the target dicarboxylic acid ester compound / Total integral value of all dicarboxylic acid ester compounds in the ester monomer composition.

[0065] <B. Calculation of the Recovery Rate of the Ester Monomer Composition> The recovery rate of the ester monomer composition was calculated by Equation 18 and evaluated as follows. The recovered ester monomer composition was dried to remove EG and water, and then its weight was measured.

[0066] (Equation 18) Recovery rate of ester monomer (%) = Weight of recovered ester monomer composition / Theoretical weight of ester monomer composition obtained from the polyester molded product charged into the depolymerization reaction × 100 SS: 85% or more and 100% or less S: 80% or more and less than 85% A: 70% or more and less than 80% B: 60% or more and less than 70% C: 0% or more and less than 60%.

[0067] <C. Measurement of Heat of Fusion of Ester Monomer Composition> The heat of fusion of the ester monomer composition was measured as follows using a TA Instruments differential scanning calorimeter (DSC) Q2000 type after weighing approximately 5 mg of the ester monomer composition. After holding isothermally at 180°C for 5 minutes and immediately taking out the sample onto an iron plate cooled to 25°C to rapidly cool it to 25°C at a rate of 100°C / min or more, the heat of fusion was measured as the area value of the endothermic peak observed when heating from 25°C to 180°C at a heating rate of 16°C / min using the above differential scanning calorimeter. The measurement was performed 3 times for each sample, and the average value was taken as the measured value.

[0068] <D. Estimation of Melting Time of Ester Monomer Composition> The melting time of the ester monomer composition was estimated by Equation 19 assuming that 100 kg of the ester monomer composition was heated with a 4 kW heater with an efficiency of 95%. (Equation 19) Melting time of ester monomer composition (min) = Heat of fusion of ester monomer composition (J / g) × 100 (kg) × 0.95 / 4 (kW) / 60 (sec / min) <E. Evaluation of Handling Property of Ester Monomer Composition> The handling property of the ester monomer composition was evaluated as follows. After pulverizing about 100 g of the ester monomer composition into about 1 mm cubes using a pestle and mortar, when introducing it into a test tube using a funnel with an inner diameter of 7 mm, the states of the test tube and the funnel were visually confirmed. S: There was no adhesion at all on both the inner wall of the funnel and the test tube. A: A little adhesion remained only on the funnel. B: A little adhesion remained on both the inner wall of the funnel and the test tube. C: It was blocked inside the funnel.

[0069] <F. Measurement of the color tone of the ester monomer composition> Using a Minolta spectrophotometer CM - 3700d type, the sample was placed with a black calibration plate as the background, and the color tone L* value, a* value, and b* value were measured and evaluated as follows. S: L* value is 93 or more and 100 or less, a* value is -0.5 or more and 0.5 or less, b* value is -3.0 or more and 3.0 or less. A: L* value is 90 or more and less than 93, a* value is -1.0 or more and less than -0.5 or greater than 0.5 and 1.0 or less, b* value is -4.0 or more and less than -3.0 or greater than 3.0 and 4.0 or less. B: L* value is 85 or more and less than 90, a* value is -2.0 or more and less than -1.0 or greater than 1.0 and 2.0 or less, b* value is -5.0 or more and less than -4.0 or greater than 4.0 and 5.0 or less. C: L* value is 0 or more and less than 85, a* value is less than -2.0 or greater than 2.0, b* value is less than -5.0 or greater than 5.0.

[0070] <G. Measurement of the melting point of the recycled polyester resin> The melting point of the recycled polyester resin was measured as follows: approximately 5 mg of the recycled polyester resin was weighed, and a TA Instruments differential scanning calorimeter (DSC) Q2000 was used. The sample was isothermally held at 280°C for 5 minutes, and then immediately taken out and quenched to 25°C at a rate of 100°C / min or more on an iron plate cooled to 25°C. After that, using the above differential scanning calorimeter, the peak position of the endothermic peak observed when heating from 25°C to 280°C at a heating rate of 16°C / min was measured as the melting point. The measurement was performed 3 times for each sample, and the average value was taken as the measured value.

[0071] Also, when the melting point of non-copolymerized PET was measured by the above method, it was 255°C. Therefore, the melting point difference from PET was calculated using Equation 20. (Equation 20) Melting point difference from PET (°C) = 255 (°C) - Melting point of recycled polyester resin (°C) <H. Measurement of content ratio of diethylene glycol residues> The content ratio of diethylene glycol residues was measured as follows. The recycled polyester resin was decomposed at 260°C using 2-aminoethanol as a solvent and adding 1,6-hexanediol as an internal standard substance. After cooling, methanol was added, followed by neutralization with an acid, and the precipitate was filtered. The filtrate was measured using a Shimadzu Corporation gas chromatograph GC-14B.

[0072] <I. Measurement of color tone of recycled polyester resin> The pellets of the recycled polyester resin were filled into a quartz cell with a height of 20 mm, and the Hunter color tones: L value, a value, and b value were measured in transmission mode using a Suga Test Instruments color difference meter SM Color Computer model SM-T45, and evaluated as follows. S: L value 76 or more and less than 85, a value -1.0 or more and 1.0 or less, b value -4.0 or more and 4.0 or less A: L value 73 or more and less than 76, a value -1.5 or more and less than -1.0 or more than 1.0 and 1.5 or less, b value -4.5 or more and less than -4.0 or more than 4.0 and 4.5 or less B: L value is 70 or more and less than 73, a value is -2.0 or more and less than -1.5 or greater than 1.5 and 2.0 or less, b value is -5.0 or more and less than -4.5 or greater than 4.5 and 5.0 or less C: L value is 0 or more and less than 70, a value is less than -2.0 or greater than 2.0, b value is less than -5.0 or greater than 5.0.

[0073] <Measurement of Intrinsic Viscosity of J. Polyester Molded Products and Recycled Polyester Resins> The polyester molded product or recycled polyester resin was dissolved in an o-chlorophenol solvent to prepare solutions with concentrations of 0.5 g / dL, 0.2 g / dL, and 0.1 g / dL. Then, the relative viscosity (ηr) of the obtained solution with concentration C at 25°C was measured using an Ubbelohde viscometer, and (ηr - 1) / C was plotted against C. The intrinsic viscosity was determined by extrapolating the obtained results to a concentration of 0.

[0074] <K. Average Single Fiber Diameter of Polyester Non-Woven Fabric> For the average single fiber diameter, 10 small piece samples were randomly collected from the polyester non-woven fabric, and photos were taken at 500 - 3000 times magnification using a scanning electron microscope (「VHX-2000」manufactured by Keyence Corporation). The diameters of 10 single fibers were measured from each sample, for a total of 100 single fibers, and the average value was rounded to the first decimal place.

[0075] <L. Thickness of Polyester Non-Woven Fabric> For the thickness of the polyester non-woven fabric, 10 small piece samples were randomly collected. Using a micrometer manufactured by Mitutoyo Corporation, the non-woven fabric was sandwiched between an anvil with a diameter of 6 mm and a spindle, and two points were measured at equal intervals within the small piece sample in 0.01 mm units. The average value of a total of 20 points was rounded to the third decimal place.

[0076] <M. Areal Density of Polyester Non-Woven Fabric> Three samples of 30 cm × 50 cm polyester non-woven fabric were collected, and the weight of each sample was measured. The average value of the obtained values was converted per unit area and rounded to the first decimal place.

[0077] <Measurement of metal content> The metal content of the polyester molded product mainly composed of PET was calculated as the total molar amount (mmol / g) of alkali metals and alkaline earth metals contained per 1 g of the polyester molded product. Specifically, using a scanning electron microscope SU1510 manufactured by Hitachi High-Tech Corporation, it was calculated by the following method from the atomic fraction of carbon atoms, alkali metal atoms, and alkaline earth metal atoms obtained by Energy Dispersive X-ray Spectroscopy (EDX) measurement under the condition of an acceleration voltage of 15 kV. (Equation 21) Molar ratio of metal atoms to carbon atoms = Total atomic fraction of metal atoms of alkali metals and alkaline earth metals (At%) / Atomic fraction of carbon atoms (At%) (Equation 22) Metal content (mmol / g) = Molar ratio of metal atoms to carbon atoms × 10 / 192 (g / mol) × 1000 Note that the following (Equation 22) is a calculation taking into account that the number of carbon atoms per repeating unit structure of PET is 10 and the molar molecular weight of the repeating unit structure of PET is 192.

[0078] [Example 1] As a polyester molded product mainly composed of PET, a chip-shaped PET resin (intrinsic viscosity: 0.65) and a chip-shaped copolymerized PET resin (intrinsic viscosity: 0.60) in which isophthalic acid was copolymerized at 40% with respect to all acid components were mixed, and when the total molar amount of dicarboxylic acid residues in the whole mixture was 1.000, a mixture was prepared in which the molar ratio of terephthalic acid residues was 0.700 and the molar ratio of isophthalic acid residues was 0.300.

[0079] 200.0 g of a polyester molded product mainly composed of PET with the molar ratio prepared as above was placed in a 2 L four-neck flask, and further 1000.0 g of EG and 2.0 g of sodium hydroxide were added, followed by stirring. Depolymerization was carried out at an EG temperature of 200 °C for 4 hours to obtain an EG solution of a mixture containing BHET.

[0080] From an EG solution of a mixture containing BHET, EG was removed by distillation under reduced pressure of 500 Pa at 120°C to obtain an ester monomer composition from the precipitated mixture containing BHET. The recovery rate and physical properties of the ester monomer composition are shown in Table 1.

[0081] Using 100 g of the obtained ester monomer composition as a raw material, after melting at 250°C, 0.005% by weight of cobalt acetate tetrahydrate and phosphoric acid, 0.03% by weight of antimony trioxide, and 0.3% by weight of titanium dioxide particles were added. Repolymerization was carried out by heating and stirring at 290°C while removing EG under reduced pressure, yielding a recycled polyester resin with an intrinsic viscosity of 0.65. The physical properties of the recycled polyester resin are shown in Table 1.

[0082] [Example 2] The procedure was carried out in the same manner as in Example 1, except that a polyester molded product mainly composed of PET was prepared by mixing chip-shaped PET resin (intrinsic viscosity: 0.65) and chip-shaped copolymerized PET resin (intrinsic viscosity: 0.60) in which isophthalic acid was copolymerized at 40% of the total acid component, and the molar ratio of terephthalic acid residues was adjusted to 0.880 and the molar ratio of isophthalic acid residues was 0.120, with the total molar amount of dicarboxylic acid residues in the entire mixture being 1.000.

[0083] [Example 3] As a polyester molded product mainly composed of PET, a mixture was prepared by mixing chip-shaped PET resin (intrinsic viscosity: 0.65) and chip-shaped copolymerized PET resin (intrinsic viscosity: 0.60) in which isophthalic acid copolymerized to 40% of the total acid components. The mixture was prepared so that the molar ratio of terephthalic acid residues was 0.700 and the molar ratio of isophthalic acid residues was 0.300, with the total molar amount of dicarboxylic acid residues in the entire mixture set to 1.000.

[0084] 200.0 g of a polyester molded product mainly composed of PET, prepared according to the molar ratio described above, was placed in a 2.0 L four-necked flask. 1000.0 g of EG and 2.0 g of sodium hydroxide were then added, and the mixture was stirred. Depolymerization was carried out at an EG temperature of 200°C for 4 hours to obtain an EG solution of a mixture containing BHET.

[0085] From an EG solution of a mixture containing BHET, EG was removed by distillation at 120°C under reduced pressure of 500 Pa to obtain a mixture containing BHET. Water was added to the mixture containing BHET in a weight ratio of 9, and the mixture was heated to 90°C to obtain an aqueous solution of the mixture containing BHET. The mixture was then cooled to a crystallization temperature Tc = 4°C and held for 3 hours to precipitate the ester monomer composition as a solid. The ester monomer composition was separated from water by filtration and dried at 50°C to obtain the ester monomer composition. The recovery rate and physical properties of the ester monomer composition are shown in Table 1.

[0086] Using 100 g of the obtained ester monomer composition as a raw material, after melting at 250°C, 0.005% by weight of cobalt acetate tetrahydrate and phosphoric acid, 0.03% by weight of antimony trioxide, and 0.3% by weight of titanium dioxide particles were added. Repolymerization was carried out by heating and stirring at 290°C while removing EG under reduced pressure, yielding a recycled polyester resin with an intrinsic viscosity of 0.65. The physical properties of the recycled polyester resin are shown in Table 1.

[0087] [Examples 4-22] As the polyester resin constituting the PET-based polyester molded product, chip-shaped PET resin (intrinsic viscosity: 0.65) and chip-shaped copolymerized PET resin (intrinsic viscosity: 0.60) in which isophthalic acid copolymerized to 40% of the total acid component were mixed. The molar ratios of terephthalic acid residues and isophthalic acid residues were prepared as shown in Tables 1 and 2, with the total molar amount of dicarboxylic acid residues in the mixture set to 1.000. Furthermore, the procedure was carried out in the same manner as in Example 3, except that the crystallization temperature Tc when crystallizing the mixture containing BHET after depolymerization and distillation removal was set to the temperatures shown in Tables 1 and 2.

[0088] [Table 1]

[0089] [Table 2]

[0090] [Table 3]

[0091] [Examples 23-25] The procedure was carried out in the same manner as in Example 4, except that after depolymerization and removal of EG, the weight ratio of water added to the mixture containing BHET was as shown in Table 3.

[0092] [Examples 26-29] The procedure was carried out in the same manner as in Example 4, except that the holding time at the crystallization temperature Tc during the crystallization of the mixture containing BHET after depolymerization and distillation removal was set to the temperatures shown in Table 3.

[0093] [Examples 30, 31] As the polyester resin constituting a polyester molded product mainly composed of PET, chip-shaped PET resin (intrinsic viscosity: 0.65) and chip-shaped copolymerized PET resin in which isophthalic acid copolymerized at 40% of the total acid component (intrinsic viscosity: 0.60) were mixed, and the molar ratios of terephthalic acid residues and isophthalic acid residues were prepared as shown in Table 3, with the total molar amount of dicarboxylic acid residues in the entire mixture set to 1.000.

[0094] 200.0 g of a polyester molded product mainly composed of PET, prepared according to the molar ratio described above, was placed in a 2 L four-necked flask. 1000.0 g of EG and 2.0 g of sodium hydroxide were then added, and the mixture was stirred. Depolymerization was carried out at an EG temperature of 200 °C for 4 hours to obtain an EG solution of a mixture containing BHET.

[0095] The EG solution of the BHET-containing mixture obtained was slowly cooled to 70°C, then cooled to 15°C and held for 3 hours to precipitate the ester monomer composition as a solid. The ester monomer composition was separated from the EG and dried at 50°C using a vacuum dryer to obtain the ester monomer composition. The recovery rate and physical properties of the ester monomer composition are shown in Table 3.

[0096] Using 100 g of the obtained ester monomer composition as a raw material, after melting at 250°C, 0.005% by weight of cobalt acetate tetrahydrate and phosphoric acid, 0.03% by weight of antimony trioxide, and 0.3% by weight of titanium dioxide particles were added. Repolymerization was carried out by heating and stirring at 290°C while removing EG under reduced pressure, yielding a recycled polyester resin with an intrinsic viscosity of 0.65. The physical properties of the recycled polyester resin are shown in Table 3.

[0097] [Example 32] A polyester nonwoven fabric, primarily composed of PET, used as a base material for water treatment membranes, before assembly into the water treatment membrane (average single fiber diameter: 14 μm, thickness: 0.09 mm, basis weight: 70 g / m²). 2 The nonwoven fabric used was 0.980 molar ratio of terephthalic acid residues and 0.020 molar ratio of isophthalic acid residues, and the metal content was 0.00 mmol / g.

[0098] 200.0 g of a polyester molded product mainly composed of PET was placed in a 2.0 L four-necked flask, and 1000.0 g of EG and 2.0 g of sodium hydroxide were added. The mixture was stirred, and depolymerization was carried out at an EG temperature of 200 °C for 4 hours to obtain an EG solution of a mixture containing BHET.

[0099] From an EG solution of a mixture containing BHET, EG was removed by distillation at 120°C under reduced pressure of 500 Pa to obtain a mixture containing BHET. Water was added to the mixture containing BHET in a weight ratio of 9, and the mixture was heated to 90°C to obtain an aqueous solution of the mixture containing BHET. Solid matter was then removed by hot filtration using a 1.6 μm filter to obtain an aqueous solution of the mixture containing BHET. Subsequently, the mixture was cooled to a crystallization temperature Tc = 2°C and held for 3 hours to precipitate the ester monomer composition as a solid. The ester monomer composition was separated from water by filtration and dried at 50°C to obtain the ester monomer composition. The recovery rate and physical properties of the ester monomer composition are shown in Table 3.

[0100] Using 100 g of the obtained ester monomer composition as a raw material, after melting at 250°C, 0.005% by weight of cobalt acetate tetrahydrate and phosphoric acid, 0.03% by weight of antimony trioxide, and 0.3% by weight of titanium dioxide particles were added. Repolymerization was carried out by heating and stirring at 290°C while removing EG under reduced pressure, yielding a recycled polyester resin with an intrinsic viscosity of 0.65. The physical properties of the recycled polyester resin are shown in Table 3.

[0101] [Example 33] As a polyester molded product with PET as the main component, the nonwoven fabric is made from a base material recovered from water treatment membranes used in seawater desalination (average single fiber diameter: 14 μm, thickness: 0.09 mm, basis weight: 70 g / m²). 2 The nonwoven fabric was used. The molar ratio of terephthalic acid residues in this nonwoven fabric was 0.980, the molar ratio of isophthalic acid residues was 0.020, and the metal content was 0.29 mmol / g. Note that the surface of the nonwoven fabric was soiled with mud, so the above evaluation was performed after washing and drying.

[0102] Except as described above, the procedure was carried out in the same manner as in Example 32.

[0103] [Example 34] As a polyester molded product with PET as the main component, the nonwoven fabric is made from a base material recovered from water treatment membranes used in seawater desalination (average single fiber diameter: 14 μm, thickness: 0.09 mm, basis weight: 70 g / m²). 2It was used. The molar ratio of terephthalic acid residues in this non-woven fabric was 0.980, the molar ratio of isophthalic acid residues was 0.020, and the metal content was 0.29 mmol / g. Since the surface of the non-woven fabric was soiled with mud, the above evaluations were performed after washing with water and drying.

[0104] 200.0 g of a polyester molded product mainly composed of PET was placed in a 2.0 L four-necked flask, and further 1000.0 g of EG and 2.0 g of sodium hydroxide were added, followed by stirring. Depolymerization was carried out at an EG temperature of 200 °C for 4 hours to obtain an EG solution of a mixture containing BHET.

[0105] From the EG solution of the mixture containing BHET, EG was distilled off at 120 °C under a reduced pressure of 500 Pa to obtain a mixture containing BHET. Water was added so that the weight ratio became 9 with respect to the weight of the mixture containing BHET, and it was heated to 90 °C to obtain an aqueous solution of the mixture containing BHET. Then, solids were removed by hot filtration using a 1.6 μm filter. Thereafter, 26.5 g of activated carbon (10% by weight of the theoretical amount of the ester monomer composition to be produced) having an average pore diameter of 0.9 nm, a specific surface area of 1000 m 2 / g, and a pore volume of 0.5 mL / g was added, and it was stirred for 1 hour while heating to 90 °C, and the activated carbon was removed using a 1.6 μm filter to obtain an aqueous solution of the mixture containing BHET.

[0106] Other than the above, it was carried out in the same manner as in Example 32.

[0107] [Example 35] As a polyester molded product mainly composed of PET, a non-woven fabric of the base material recovered from the water treatment membrane used for seawater desalination treatment (average single fiber diameter: 14 μm, thickness: 0.09 mm, basis weight: 70 g / m 2 ) was used. The molar ratio of terephthalic acid residues in this non-woven fabric was 0.980, the molar ratio of isophthalic acid residues was 0.020, and the metal content was 0.29 mmol / g. Since the surface of the non-woven fabric was soiled with mud, the above evaluations were performed after washing with water and drying.

[0108] 200.0 g of a polyester molded product mainly composed of PET was placed in a 2.0 L four-necked flask, and 1000.0 g of EG and 2.0 g of sodium hydroxide were added. The mixture was stirred, and depolymerization was carried out at an EG temperature of 200 °C for 4 hours to obtain an EG solution of a mixture containing BHET.

[0109] From an EG solution of a mixture containing BHET, EG was removed by distillation at 120°C under reduced pressure of 500 Pa to obtain a mixture containing BHET. Water was added to the mixture containing BHET in a weight ratio of 9, and the mixture was heated to 90°C to obtain an aqueous solution of the mixture containing BHET. Solid matter was then removed by hot filtration using a 1.6 μm filter. Subsequently, Amberlite™ cation exchange resin IR120B(H) manufactured by Organo Corporation was added to the filtrate. + 300 g (12 equivalents of cation exchange resin capable of adsorbing metal ions) of a specific type (type, apparent density: 790 g / LR, cation exchange group amount: ≥1.80 mol / LR) was added, stirred for 1 hour while heating at 90°C, and the ion exchange resin was removed using a 1.6 μm filter. Subsequently, an average pore size of 0.9 nm and a specific surface area of ​​1000 m² was used. 2 26.5 g of activated carbon (10% by weight of the theoretical amount of the ester monomer composition to be produced) with a pore volume of 0.5 mL / g was added and stirred for 1 hour. The activated carbon was then removed using a 1.6 μm filter to obtain an aqueous solution of the mixture containing BHET.

[0110] Except for the above, the procedure was carried out in the same manner as in Example 32.

[0111] [Comparative Example 1] The procedure was carried out in the same manner as in Example 1, except that a chip-shaped copolymerized PET resin (intrinsic viscosity: 0.60) in which isophthalic acid was copolymerized at 40% of the total acid component was used as the polyester molded product with PET as the main component.

[0112] Comparative Example 1 had a low heat of fusion for the ester monomer composition and was significantly inferior in terms of handling properties. [Industrial applicability]

[0113] According to the present invention, by making maximum effective use of waste polyester as a resource with the minimum necessary process, it is possible to obtain a high-quality ester monomer composition and a recycled polyester resin obtained by repolymerizing the ester monomer composition, making it useful in the chemical recycling of textile products such as clothing and industrial nonwoven fabrics. [Explanation of symbols]

[0114] 1: Curve showing R1 (R1 = {-24.485 / (x-1.261)} - 38.934 (Equation 3)) 2: Curve showing L1 (L1 = 200.358x 3 -496.588x 2 +392.101x-95.871(Formula 2)) 3: Range of crystallization temperature Tc (°C) 4: Curve showing L2 (L2 = 5457.598x 3 -14831.163x 2 +13289.532x-3915.967(Formula 8)) 5: Curve showing L3 (L3 = 17883.981x 3 -49374.856x 2 +45097.769x-13606.894(Formula 9)) 6: Curve showing L4 (L4 = 27416.355x 3 -75766.941x 2 +69284.818x-20934.232 (Equation 10)) 7: Curve showing R² (R² = {-25.027 / (x-1.238)} - 51.957 (Equation 13)) 8: Curve showing R3 (R3 = {-4.997 / (x-1.090)} - 15.234 (Equation 14)) 9: Setting range of crystallization temperature Tc when y is controlled to 0.980 ≤ y < 0.990 using equations 5 and 11 (upward-sloping shaded area) 10: Setting range of crystallization temperature Tc when y is controlled to 0.997 ≤ y ≤ 1.000 using equations 7 and 12 (downward-sloping shaded area)

Claims

1. An ester monomer composition mainly composed of bis-(2-hydroxyethyl) terephthalate (BHET), wherein the heat of fusion is 31 J / g or more and less than 160 J / g.

2. The ester monomer composition according to claim 1, wherein the molar ratio of BHET is 0.700 or more and less than 1.000 when the total molar amount of dicarboxylic acid ester compounds contained in the ester monomer composition is taken as 1.

000.

3. The ester monomer composition according to claim 1 or 2, wherein the ester monomer composition contains an isophthalate ester compound.

4. The ester monomer composition according to claim 3, wherein the molar ratio of isophthalic acid ester compounds is greater than 0.003 and less than or equal to 0.300, when the total molar amount of dicarboxylic acid ester compounds contained in the ester monomer composition is taken as 1.

000.

5. A method for obtaining an ester monomer composition mainly composed of polyethylene terephthalate (PET) from a polyester molded product mainly composed of polyethylene terephthalate (PET), following the steps described below. (1) A process of depolymerizing a polyester molded product mainly composed of PET using ethylene glycol (EG) to obtain an EG solution of a mixture containing BHET. (2) A step of recovering the mixture containing BHET from the EG solution of the mixture containing BHET obtained in step (1) above. (3) A step of dissolving the mixture containing BHET obtained in step (2) in water at a temperature of 60°C to 100°C to obtain an aqueous solution. (4) A step of cooling the aqueous solution obtained in step (3) to a crystallization temperature Tc represented by formulas 1 to 3, thereby precipitating the ester monomer composition as a solid. [Math 1] [Math 2] [Math 3] (x is the molar ratio of BHET to the total molar amount of dicarboxylic acid ester compounds contained in the mixture containing BHET, with 1.000 being the molar ratio (0.000 < x ≤ 1.000)) (5) A step of separating the solid ester monomer composition precipitated in step (4) from water and recovering it from the aqueous solution.

6. The method according to claim 5, wherein in the aqueous solution obtained in step (3), the weight ratio of water to the mixture containing BHET is 4 or more and 39 or less.

7. The method according to claim 5, wherein in step (4), after cooling to the crystallization temperature Tc, the mixture is held for 0 hours or more and 21 hours or less.

8. The method according to any one of claims 5 to 7, wherein the mixture containing BHET contains an isophthalate ester compound.

9. A recycled polyester resin obtained by polycondensing the ester monomer composition described in claim 1.

10. A recycled polyester molded article made from the recycled polyester resin described in claim 9.

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