Bis(2-hydroxyethyl)terephthalate composition and method for producing same

Abstract

The present invention pertains to a bis(2-hydroxyethyl)terephthalate (BHET) composition obtained by decomposing a polyester, the BHET composition being characterized in that the peak area at 360-800 nm as measured with a spectrophotometer is 0-10. When the BHET composition is mixed with 40 times the amount of water as the BHET composition at 95°C, the mass of insoluble fraction is preferably 1% or more relative to the mass of the BHET composition. When the BHET composition is mixed with 40 times the amount of water as the BHET composition at 95°C, the insoluble fraction is preferably a polyethylene terephthalate (PET) oligomer.

Description

Bis(2-hydroxyethyl) terephthalate composition and method for producing the same

[0001] The present invention relates to a bis(2-hydroxyethyl) terephthalate composition and a method for producing the same.

[0002] Until now, a social system based on mass production, mass consumption, and mass disposal has been maintained, but various negative environmental impacts such as the depletion of natural resources and the destruction of nature due to resource extraction have been confirmed. Therefore, in order to efficiently utilize limited resources and continue sustainable growth, it has become essential to build a circular social system that minimizes waste generation and reuses or recycles the waste that is generated so as not to burden the environment.

[0003] To realize such a circular social system, it is necessary to establish recycling systems such as thermal recycling, material recycling, and chemical recycling. Among these, chemical recycling technology, which can decompose waste plastics into low molecular weight materials, purify them, and then regenerate plastic materials of equivalent quality from the purified low molecular weight materials, is attracting attention.

[0004] Polyester, being inexpensive and used in a wide range of applications, also has a growing need for recycling, and various methods have been proposed as chemical recycling technologies.

[0005] For example, Patent Documents 1 and 2 propose a chemical recycling technology that uses polyethylene terephthalate (PET) containing impurities, performs depolymerization, and purifies the monomer bis(2-hydroxyethyl) terephthalate (BHET) obtained after depolymerization using activated carbon.

[0006] Patent Document 3 proposes a chemical recycling technology that uses colored PET waste and performs depolymerization and evaporation purification of the BHET after depolymerization.

[0007] Japanese Patent Publication No. 2023-41608, Japanese Patent Publication No. 2022-544275, Japanese Patent Publication No. 2022-13942

[0008] However, the chemical recycling technologies described in Patent Documents 1 to 3 above do not adequately remove colorants contained in the obtained BHET. For example, Patent Documents 1 and 2 perform purification such as activated carbon treatment in the "adsorption step" or "decolorization step" disclosed in the examples, and Patent Document 3 performs purification such as thin film evaporation in the "recovery step" disclosed in the examples. However, depending on the recycled raw material, there was a problem that the color tone of the obtained BHET was inferior even after these purifications.

[0009] The object of the present invention is to solve the problems of the above-mentioned prior art by using activated carbon with excellent adsorption performance for colorants contained in the BHET composition, thereby enabling both the adsorption removal of colorants by activated carbon and the recovery of the BHET composition, and providing a BHET composition with better color tone compared to a BHET composition obtained by conventional purification methods.

[0010] The above problems are solved by the following [1] to

[15] . [1] A bis(2-hydroxyethyl) terephthalate (BHET) composition obtained by decomposing polyester, characterized in that the peak area in the 360 ​​to 800 nm range measured by a spectrophotometer is 0 or more and 10 or less. [2] The BHET composition according to [1], characterized in that when the BHET composition is mixed with 40 times the amount of water relative to the BHET composition at 95°C, the mass of the insoluble matter is 1% or more relative to the mass of the BHET composition. [3] The BHET composition according to [1] or [2], characterized in that when the BHET composition is mixed with 40 times the amount of water relative to the BHET composition at 95°C, the insoluble matter is polyethylene terephthalate (PET) oligomer.

[0011] [4] A recycled polyethylene terephthalate (PET) composition obtained by polycondensing a BHET composition according to any one of [1] to [3]. [5] The recycled PET composition according to [4], characterized in that the peak area in the 360 ​​to 800 nm range measured by a spectrophotometer is 0 or more and 10 or less.

[0012] [6] A method for producing a bis(2-hydroxyethyl) terephthalate (BHET) composition comprising the following steps (1) to (4), wherein step (3) satisfies conditions (a) and (b): (1) A step of depolymerizing a polyethylene terephthalate (PET) composition with ethylene glycol to obtain a crude BHET composition; (2) A step of dissolving the crude BHET composition in hot water to obtain an aqueous solution of the crude BHET composition; (3) A step of treating the aqueous solution of the crude BHET composition with activated carbon to obtain an aqueous solution of the BHET composition; (4) A step of extracting the BHET composition from the aqueous solution of the BHET composition; (a) The mass ratio of the crude BHET composition to water constituting the aqueous solution of the crude BHET composition is 1:0.5 to 1:40; (b) The pH of the activated carbon is less than 9. [7] The method for producing a BHET composition according to [6], characterized in that the PET composition is a yarn and / or fabric containing dyed PET fibers. [8] A method for producing a BHET composition according to [6] or [7], characterized in that the PET composition is a yarn and / or fabric containing a material other than PET. [9] A method for producing a BHET composition according to any one of [6] to [8], characterized in that the activated carbon has the following characteristics: (a) a 25 ppm aqueous dye solution and 0.25% by mass of the activated carbon relative to the aqueous dye solution are stirred for 1 hour, and the dye concentration of the aqueous solution after removing the activated carbon is 5 ppm or less.

[10] A method for producing a BHET composition according to any one of [6] to [9], characterized in that the average pore size of the activated carbon is 0.5 nm or more and 200 nm or less.

[11] A method for producing a BHET composition according to any one of [6] to

[10] , characterized in that the total volume of pores in the activated carbon with a pore size of 1.0 nm or more and 10 nm or less is 50% or more of the total pore volume.

[12] The specific surface area of ​​the activated carbon is 300 m². ２ / g or more, 5000m ２A method for producing a BHET composition according to any one of [6] to

[11] , characterized in that the amount is less than or equal to / g.

[13] A method for producing a BHET composition according to any one of [6] to

[12] , characterized in that the pore volume of the activated carbon is 0.2 mL / g or more and 2.5 mL / g or less.

[14] A method for producing a BHET composition according to any one of [6] to

[13] , characterized in that in step (3), the temperature of the crude BHET composition aqueous solution during processing is 60°C to 105°C.

[15] A method for producing a BHET composition according to any one of [6] to

[14] , characterized in that in step (3), the crude BHET composition aqueous solution is passed through the column at a space velocity of 0.5 to 1000 / h with the activated carbon packed in the column.

[0013] The BHET composition in this invention may also contain a PET oligomer. A PET oligomer is a compound represented by the following chemical formula, consisting of terephthalic acid residues and ethylene glycol residues, with n being 2 to 5.

[0014]

[0015] According to the present invention, it is possible to provide a BHET composition with a low colorant content and excellent color tone.

[0016] The present invention will be described in detail below.

[0017] In this invention, a BHET composition refers to a composition containing BHET and other compounds that do not hinder repolymerization. A crude BHET composition refers to a BHET composition containing impurities (substances that may become impurities during repolymerization), such as dyes and other materials (including their decomposition products).

[0018] The BHET composition of the present invention is a BHET composition obtained by decomposing polyester, characterized in that the peak area in the 360-800 nm range, as measured by a spectrophotometer, is 0 or more and 10 or less.

[0019] The present invention aims to provide a BHET composition with excellent color tone for synthesizing recycled PET compositions that have a color tone equivalent to that of virgin polymers in the chemical recycling of PET. Therefore, from the viewpoint of good color tone, the BHET composition has a peak area of ​​0 or more and 10 or less in the 360-800 nm range as measured by a spectrophotometer. The absorbance observed in the 360-800 nm wavelength range correlates with the amount and type of coloring component.

[0020] From the viewpoint of a BHET composition with superior color tone, the peak area measured by a spectrophotometer is preferably 5 or less, more preferably 3 or less, and most preferably 1 or less.

[0021] In the BHET composition of the present invention, the peak area is evaluated using a spectrophotometer as follows. First, a mixed solvent of water and hexafluoroisopropanol (HFIP) (2 mL water: 8 mL HFIP) is prepared, and the BHET composition is dissolved in the mixed solvent at a concentration of 1.0 mass / vol. To promote the dissolution of the BHET composition, the BHET composition may be dissolved in HFIP before preparing the mixed solvent, and then water may be added. The obtained solution is filtered through a 0.2 μm filter, and the absorbance intensity of the filtered solution at 360 nm to 800 nm intervals is measured at 1 nm intervals using a spectrophotometer (for example, a U3010 spectrophotometer manufactured by Hitachi High-Tech Science Co., Ltd.) in wavelength scan mode, and the sum of the obtained absorbance intensities is calculated as the integral value (peak area). If the absorbance intensity exceeds the upper limit of measurement, a 0.25 mass / vol.% solution is prepared and the absorbance intensity is measured in the same manner, and four times the sum of the obtained absorbance intensities is calculated as the integral value (peak area).

[0022] The color tone of the BHET composition is set to be equivalent to that of virgin polymers, with color tone: b * The value is preferably -10 or greater and 10 or less, more preferably -6 or greater and 6 or less, even more preferably -2 or greater and 2 or less, and most preferably 0 or greater and 1 or less.

[0023] Color tone of BHET composition (L * Value, a * value, b *The value can be measured using a spectrophotometer, for example, a Minolta CM-3700d spectrophotometer, with the sample placed against a black calibration plate.

[0024] The process for purifying BHET compositions generally involves mixing them with hot water to create an aqueous solution, followed by filtration or adsorption of insoluble matter. A common method for extracting the purified BHET composition from the aqueous solution is crystallization, where the ratio of BHET composition to hot water is adjusted, and the BHET composition is recovered by precipitation due to differences in solubility caused by temperature changes in the aqueous solution. In crystallization, the presence of insoluble matter in the system initiates the precipitation of dissolved BHET using the insoluble matter as a nucleation site, thus shortening the crystallization initiation time. This reduces the time required for BHET composition production and improves the productivity of BHET composition. Therefore, it is preferable that insoluble matter is present when the BHET composition is mixed with 40 times the amount of water at 95°C, which is the aqueous solution condition at the start of the crystallization process. In addition, since PET oligomers, which are generally insoluble in hot water, can be used as raw materials for recycled PET, similar to BHET, it is preferable that the insoluble component is a PET oligomer from the viewpoint of not becoming an impurity in the BHET composition. Furthermore, among PET oligomers, PET dimers dissolve when the BHET concentration in the aqueous solution is increased, so it is preferable that the PET oligomer is a PET dimer from the viewpoint of improving the yield of the BHET composition by increasing the BHET concentration while using a small amount of hot water in the insoluble component filtration. The mass of the insoluble component is preferably 1% or more, more preferably 3% or more, even more preferably 7% or more, and most preferably 10% or more, relative to the mass of the BHET composition, from the viewpoint of shortening the crystallization start time and improving the productivity of the BHET composition.

[0025] A recycled PET composition can be obtained by polycondensation of the BHET composition of the present invention. From the viewpoint of good color tone, it is preferable that the peak area of ​​the recycled PET composition in the 360 ​​to 800 nm range, as measured by a spectrophotometer, is 0 or more and 10 or less. From the viewpoint of a recycled PET composition with even better color tone, it is preferable that the peak area measured by a spectrophotometer is 5 or less, more preferably 3 or less, and most preferably 1 or less.

[0026] The recycled PET composition of the present invention may contain, in addition to PET, dicarboxylic acid components and / or diol components as copolymerization components. There are no particular restrictions on the copolymerization components constituting the recycled PET composition, but for example, dicarboxylic acid components include, in addition to terephthalic acid, aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, cyclohexanedicarboxylic acid, 5-sulfoisophthalic acid, and sodium 5-sulfoisophthalate, as well as aliphatic dicarboxylic acids such as adipic acid and sebacic acid. Diol components include, in addition to ethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol, cyclohexanedimethanol, neopentyl glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0027] As a method for producing the BHET composition of the present invention, the following method consisting of steps (1) to (4) can be suitably used, in order to provide a BHET composition with excellent color tone. (1) A step of depolymerizing the PET composition with ethylene glycol to obtain a crude BHET composition. (2) A step of dissolving the crude BHET composition in hot water to obtain an aqueous solution of the crude BHET composition. (3) A step of treating the aqueous solution of the crude BHET composition with activated carbon to obtain an aqueous solution of the BHET composition. (4) A step of extracting the BHET composition from the aqueous solution of the BHET composition obtained in step (3). An example of a method for producing the BHET composition will be described below.

[0028] As step (1), first, a PET composition and ethylene glycol are introduced into a depolymerization apparatus, a depolymerization catalyst is added, and the mixture is heated to 185°C or higher and 210°C or lower under normal pressure for depolymerization to obtain an ethylene glycol solution as a depolymerized solution containing a BHET composition. Subsequently, as a method for removing ethylene glycol to obtain a crude BHET composition, any of the following methods may be used. The first is a reprecipitation step in which the depolymerized solution is dropped into water and the temperature is adjusted to 30°C or lower to precipitate the crude BHET composition, and the crude BHET composition is recovered using a filter. The second is a distillation step in which ethylene glycol contained in the depolymerized solution is removed by distillation to increase the concentration. In view of the excellent color tone of the obtained crude BHET composition, it is preferable to adopt the reprecipitation step or use both steps in combination.

[0029] In obtaining the BHET composition of the present invention, the PET composition used as a recycled raw material includes a step (step (3)) of being treated with activated carbon in the process of producing the BHET composition, and it is possible to obtain a BHET composition with a good color tone. Therefore, it may be a yarn and / or fabric containing dyed PET fibers and / or a yarn and / or fabric containing materials other than PET.

[0030] In the yarn and / or fabric containing dyed PET fibers, disperse dyes are preferable as the dyeing component because adsorption onto activated carbon easily proceeds, but there is no particular limitation, and examples include ionic bond dyes, direct dyes, reactive dyes, vat dyes, organic pigments, inorganic pigments, and the like.

[0031] In yarns and / or fabrics containing materials other than PET, thermal decomposition products of the materials other than PET may appear as coloring components (thermal decomposition coloring components) during the depolymerization process. However, since these can be removed by adsorption using activated carbon, similar to dyes, the color tone of the BHET composition obtained in step (4) is good. There are no particular restrictions on the materials other than PET, but examples include cotton, polyurethane, nylon, acrylic, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, polyolefin, wool, silk, and rayon. From the viewpoint of efficiently adsorbing and removing thermal decomposition coloring components and providing a BHET composition with excellent color tone, cellulose compositions such as cotton and rayon, polyurethane, nylon, acrylic, and polyolefin are preferred, and cellulose compositions such as cotton and rayon are more preferred. Furthermore, while there are no particular restrictions regarding the content of materials other than PET in yarns and / or fabrics containing materials other than PET, from the viewpoint of providing a BHET composition with excellent color tone by removing thermal decomposition coloring components derived from materials other than PET, it is preferable that the materials other than PET are contained in a proportion of 50% or less, more preferably 35% or less, even more preferably 15% or less, even more preferably 20% or less, and particularly preferably 10% or less, from the viewpoint of improving yield by preventing absorption of the depolymerization solution into the materials other than PET.

[0032] Also, the monomers constituting the PET composition used as the recycling raw material are terephthalic acid as the dicarboxylic acid component and ethylene glycol as the diol component, and the PET composition may be a copolymerized polyester composition copolymerized with other monomers. There is no particular limitation on the monomers constituting the copolymerized polyester composition. For example, in addition to terephthalic acid, the dicarboxylic acid includes aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, cyclohexanedicarboxylic acid, 5-sulfoisophthalic acid, and sodium 5-sulfoisophthalate, and aliphatic dicarboxylic acids such as adipic acid and sebacic acid. The diol includes, in addition to ethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol, cyclohexanedimethanol, neopentyl glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like.

[0033] In obtaining the BHET composition of the present invention, the depolymerization time is preferably 0.5 hours or more, more preferably 1.0 hours or more, in terms of sufficiently promoting the reaction and improving the yield of the BHET composition. Also, in terms of reducing the heating energy, it is preferably 6.0 hours or less, more preferably 3.0 hours or less, and most preferably 2.0 hours or less.

[0034] In obtaining the BHET composition of the present invention, the addition rate of ethylene glycol with respect to the number of moles of the repeating unit of PET is preferably 100 mol% or more, since when the mass of ethylene glycol with respect to PET becomes too small, it becomes difficult for the depolymerization to proceed uniformly and the yield of the BHET composition deteriorates. Also, even if more than 3000 mol% of ethylene glycol is added, the total yield of BHET and PET oligomers is the same, and the cost required for heating increases, so it is preferably 3000 mol% or less.

[0035] Common depolymerization catalysts for PET include metal hydroxides and transesterification catalysts. Suitable metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide, while suitable transesterification catalysts include lithium acetate, sodium acetate, magnesium acetate, cobalt acetate, manganese acetate, and calcium acetate, but are not limited to these. Sodium hydroxide is preferably used in an amount of 0.1% to 2.0% by mass relative to PET due to its low cost and excellent depolymerization rate.

[0036] In step (2), the crude BHET composition is dissolved in hot water to remove insoluble impurities contained in the PET (such as metal compounds represented by titanium dioxide and inorganic compounds represented by silica gel) and insoluble materials other than PET. Water is added to the crude BHET composition obtained in step (1) and heated (dissolved in hot water), and the mixture is passed through a filter to obtain an aqueous solution of the crude BHET composition.

[0037] As step (3), a crude BHET composition aqueous solution containing coloring components that satisfies the following conditions (a) and (b) is purified with activated carbon to obtain a BHET composition aqueous solution from which the coloring components have been removed. (a) The mass ratio of crude BHET composition to water constituting the crude BHET composition aqueous solution is 1:0.5 to 1:40. (b) The pH of the activated carbon is less than 9.

[0038] In condition (a), the mass ratio of water to crude BHET composition (with the crude BHET composition set to 1) is preferably 40 or less, more preferably 20 or less, even more preferably 10 or less, even more preferably 6.0 or less, and most preferably 3.0 or less, because a lower proportion of water increases the solubility of PET oligomers, allowing for dissolution and recovery, and improving the yield of the total amount of BHET and PET oligomers that become raw materials for recycled PET. Furthermore, if the impurity concentration in the BHET composition is excessively high, the aqueous BHET composition solution will distill off without sufficient adsorption treatment being completed on a certain amount of activated carbon, resulting in a deterioration of the color tone of the resulting BHET composition. Therefore, a mass ratio of 0.5 or more, and more preferably 1.0 or more, is preferable.

[0039] In condition (b), when the activated carbon used in the purification of the crude BHET composition aqueous solution (step (3)) has a high pH and is strongly alkaline, oxygen-containing functional groups such as carboxyl groups, phenol groups, and lactone groups on the surface of the activated carbon dissociate, generating a negative charge. On the other hand, for example, disperse dyes and thermal decomposition coloring components of cotton remaining in the BHET composition are also negatively charged in water, and the negatively charged activated carbon causes electrostatic repulsion with these adsorbed objects, reducing the adsorption efficiency and worsening the color tone of the resulting BHET composition. For this reason, a pH of less than 9 is preferable. Furthermore, when the pH is low and acidic, oxygen-containing functional groups on the surface of the activated carbon accept protons and become protonated, so the negative charge on the surface of the activated carbon changes to a positive charge, causing electrostatic attraction with the adsorbed objects and improving the adsorption efficiency, thus providing a BHET composition with excellent color tone. For this reason, a pH of 7 or less is preferable, more preferably 6 or less, more preferably 5 or less, more preferably 4 or less, more preferably 3.5 or less, even more preferably 3 or less, and most preferably 2.5 or less. Furthermore, from the viewpoint of preventing corrosion and deterioration of the adsorption treatment equipment, a value of 0 or greater is preferable.

[0040] The pH of activated carbon can be adjusted as follows: Activated carbon and an acidic aqueous solution are placed in a container and stirred. The filtered activated carbon is washed with water to remove excess acid and then dried. Examples of acidic aqueous solutions used for adjustment include hydrochloric acid, nitric acid, and sulfuric acid. The pH of the adjusted activated carbon is measured according to JIS K 1474:2014. The pH of the activated carbon can be controlled by adjusting the concentration of the acidic aqueous solution and the stirring time.

[0041] Generally, the coloring components contained in the crude BHET aqueous solution obtained by decomposing polyester are mainly PET decomposition products, dyes, and dye decomposition products. Therefore, the activated carbon used for purifying the crude BHET aqueous solution preferably has the following characteristics regarding dye adsorption performance.

[0042] (a) A 25 ppm aqueous dye solution and 0.25% by mass of activated carbon relative to the aqueous dye solution are stirred for 1 hour, and the dye concentration of the aqueous solution after removing the activated carbon becomes 5 ppm or less.

[0043] The dye used in the measurement of characteristic (a) is Nichilon Black TR 200% as a cationic dye. As mentioned above, disperse dyes are preferred for the raw material PET composition, but since disperse dyes are not water-soluble and do not disperse in aqueous solutions, a water-soluble cationic dye is used to evaluate the performance of the activated carbon in an aqueous solution. The dye concentration can be measured specifically by the method described in the examples.

[0044] From the viewpoint of obtaining a BHET composition with excellent color tone using activated carbon having high adsorption performance, activated carbon is more preferable if the dye concentration of the aqueous solution after removal of the activated carbon is 3 ppm or less, and activated carbon is even more preferable if the dye concentration is 1 ppm or less.

[0045] In obtaining the BHET composition of the present invention, the average pore size of the activated carbon used to purify the crude BHET composition aqueous solution is preferably 0.5 nm or larger, more preferably 0.7 nm or larger, and even more preferably 0.9 nm or larger, because adsorption is difficult in pores smaller than the molecular size of coloring components such as dyes and thermal decomposition coloring components contained in the crude BHET composition aqueous solution. This is from the viewpoint of appropriately adsorbing coloring components and improving the color tone of the obtained BHET composition. Furthermore, adsorption by activated carbon is due to the interaction between the activated carbon surface and the adsorbed substance. The strength of the interaction becomes stronger as the distance between the activated carbon surface and the adsorbed substance decreases. Therefore, when the pore size of the activated carbon is large, the space in which the adsorbed substance can move freely within the pores becomes larger, and the variation in the distance between the activated carbon surface and the adsorbed substance becomes larger. As a result, the sum of the interaction strengths between the activated carbon surface and the adsorbed material decreases, reducing adsorption efficiency. Additionally, PET oligomers with larger molecular sizes than BHET are adsorbed, leading to a decrease in yield. Therefore, an average pore diameter of 200 nm or less is preferable, more preferably 20 nm or less, even more preferably 5.0 nm or less, even more preferably 3.0 nm or less, and most preferably 1.5 nm or less. However, forming micropores (pores of 2 nm or less) in the production of activated carbon is difficult, and it is not necessary to excessively reduce the average pore diameter when the adsorption efficiency is not high. The average pore diameter of activated carbon can be obtained by analyzing the nitrogen adsorption / desorption isotherm obtained by nitrogen adsorption measurement using the GCMC method.

[0046] Also, generally, it is difficult to control the pores of activated carbon to the same size, and the size varies depending on the raw material of the activated carbon and the activation treatment conditions, resulting in variations in the pore diameter. If the variation in the pore diameter is large, the proportion of pores for adsorbing specific molecules is small, leading to inefficient treatment. Therefore, it is preferable to use activated carbon having pores of an appropriate size at a certain ratio or more. In the activated carbon used for purifying the aqueous solution of the crude BHEt composition, from the viewpoint of increasing the proportion of pores suitable for the molecular size of the coloring component and improving the color tone of the resulting BHEt composition, the total volume of pores having a pore diameter of 1.0 nm or more and 10 nm or less is preferably 50% or more of the total pore volume, more preferably the total volume of pores having a pore diameter of 1.0 nm or more and 7.0 nm or less is 50% or more of the total pore volume, still more preferably the total volume of pores having a pore diameter of 1.0 nm or more and 5.0 nm or less is 50% or more of the total pore volume, and even more preferably the total volume of pores having a pore diameter of 1.0 nm or more and 4.0 nm or less is 50% or more of the total pore volume. In addition, from the viewpoint of adsorbing more coloring components and extending the life of the activated carbon, the total volume of pores having a pore diameter of 1.0 nm or more and 4.0 nm or less is more preferably 60% or more of the total pore volume, and most preferably 65% or more of the total pore volume. The pore volume distribution of the activated carbon is obtained by analyzing the nitrogen adsorption and desorption isotherm obtained by nitrogen adsorption measurement by the GCMC method.

[0047] In obtaining the BHEt composition of the present invention, the specific surface area of the activated carbon used for purifying the aqueous solution of the crude BHEt composition is such that if the specific surface area is small, the area available for the adsorption target to adsorb becomes small, and the amount of the coloring component contained in the aqueous solution of the crude BHEt composition adsorbed and removed decreases. Therefore, from the viewpoint of adsorbing a large amount of the coloring component contained in the aqueous solution of the crude BHEt composition and improving the color tone of the resulting BHEt composition, 300 m ２ / g or more is preferable, 1000 m ２ / g or more is more preferable, 1500 m ２A specific surface area of ​​5000 m² is even more preferable, as a larger specific surface area results in smaller activated carbon particle sizes, allowing fine black activated carbon particles to pass through the filter and be mixed into the BHET composition during activated carbon removal. In addition, the specific surface area depends on the number and diameter of pores, and a smaller diameter tends to result in a larger specific surface area. Therefore, if the diameter of the pores is smaller than the molecular size of the coloring component, which is the adsorbed substance, it becomes difficult to capture the coloring component within the pores, and the amount of adsorption and removal decreases. Consequently, a larger specific surface area results in a lower color tone of the resulting BHET composition. ２ Preferably less than / g, and 4000m ２ More preferably less than / g, and 3000m ２ More preferably less than / g, and 2500m ２ A value of less than / g is most preferable. The specific surface area of ​​activated carbon is obtained by analyzing the nitrogen adsorption / desorption isotherm obtained by nitrogen adsorption measurement using the BET method.

[0048] In obtaining the BHET composition of the present invention, the pore volume of the activated carbon used to purify the crude BHET composition aqueous solution is preferably 0.2 mL / g or more, more preferably 0.5 mL / g or more, and even more preferably 1.0 mL / g or more, because a smaller pore volume reduces the space available for adsorption of the adsorbed material, thus decreasing the amount of coloring components adsorbed and removed from the crude BHET composition aqueous solution. This is because a larger pore volume reduces the space available for adsorption of the adsorbed material, thus decreasing the amount of adsorption of coloring components contained in the crude BHET composition aqueous solution and improving the color tone of the resulting BHET composition. Furthermore, a larger pore volume reduces the density of the activated carbon, resulting in a smaller amount of activated carbon that can be packed into the container, thus decreasing the adsorption efficiency. In addition, a larger space allows the adsorbed material to move freely within the pores, increasing the variation in the distance between the adsorbed material and the activated carbon surface, which reduces the sum of the interaction strengths and decreases the adsorption efficiency. Therefore, a pore volume of 2.5 mL / g or less is preferable, more preferably 2.0 mL / g or less, more preferably 1.8 mL / g or less, and most preferably 1.5 mL / g or less, as a larger pore volume results in a lower color tone of the resulting BHET composition. The pore volume of the activated carbon is obtained by analyzing the nitrogen adsorption / desorption isotherm obtained by nitrogen adsorption measurement using the GCMC method.

[0049] In obtaining the BHET composition of the present invention, the temperature of the aqueous solution of the crude BHET composition during processing is preferably 60°C or higher, in that it increases the solubility of BHET, thereby preventing precipitation during processing and increasing the yield. Furthermore, a temperature of 80°C or higher is preferred, more preferably 90°C or higher, and most preferably 95°C or higher, in that higher temperatures increase the solubility of the PET oligomer and improve the yield. In addition, since the heat exchange when molecules adsorb to activated carbon is exothermic, a temperature of 105°C or lower is preferred, and most preferably 100°C or lower, in that higher temperatures lead to more active desorption of adsorbed material and a decrease in the adsorption performance of the activated carbon. Note that when the BHET composition is a highly concentrated aqueous solution, the boiling point of the aqueous solution may exceed the boiling point of water, which is 100°C.

[0050] In obtaining the BHET composition of the present invention, the method of treating the crude BHET composition aqueous solution with activated carbon in step (3) is preferably one in which activated carbon is packed into a column and the crude BHET composition aqueous solution is passed through, from the viewpoint of enabling continuous processing of large quantities and improving productivity. The space velocity during column passage is preferably 0.5 / h or more, more preferably 1.0 / h or more, and even more preferably 10 / h or more, in order to shorten the passage time and improve productivity. Furthermore, if the space velocity is too high, the BHET composition aqueous solution distills out before sufficient adsorption treatment is completed on a certain amount of activated carbon, and the color tone of the obtained BHET composition deteriorates. Therefore, the space velocity is preferably 1000 / h or less, more preferably 300 / h or less, even more preferably 100 / h or less, and most preferably 50 / h or less.

[0051] Finally, as step (4), the method for extracting the BHET composition from the BHET composition aqueous solution treated in step (3) is preferably crystallization, in which water is added to the BHET composition aqueous solution as needed, the BHET composition aqueous solution is cooled, and the solid components of the BHET composition precipitate and solid-liquid separation is performed. Before cooling, the BHET composition aqueous solution preferably contains 6.0 times or more the mass of water relative to the BHET composition, in order to improve the rate of impurity removal. Furthermore, the cooling temperature is preferably 30°C or lower in order to increase the crystallization yield, and preferably 0°C or higher, as freezing would make it impossible to recover the crystallized material.

[0052] As described above, the BHET composition with a low colorant content of the present invention can be recovered as a BHET composition with good color tone, and the recovered BHET composition can be used as a raw material for repolymerization to provide a recycled PET composition with good color tone.

[0053] The present invention will be further described below with reference to examples and comparative examples, but is not limited to these examples and comparative examples.

[0054] A. Analysis of Coloring Component Content The integral value of visible light absorbance intensity was calculated as follows. First, a mixed solvent of water and hexafluoroisopropanol (HFIP) (2 mL water: 8 mL HFIP) was prepared, and the sample was dissolved in the mixed solvent at a concentration of 1.0 mass / vol. To promote the dissolution of the sample, the sample was dissolved in HFIP before preparing the mixed solvent, and then water was added as needed. The obtained solution was filtered through a 0.2 μm filter, and the absorbance intensity of the filtered solution at 1 nm intervals from 360 nm to 800 nm was measured using a spectrophotometer (Hitachi High-Tech Science Co., Ltd. U3010) in wavelength scan mode, and the sum of the obtained absorbance intensities was calculated as the integral value (peak area). If the absorbance intensity exceeded the upper limit of measurement, a 0.25 mass / vol.% solution was prepared and the absorbance intensity was measured in the same manner, and four times the sum of the obtained absorbance intensities was calculated as the integral value (peak area).

[0055] B. Analysis of the Dye Adsorption Performance of Activated Carbon The dye adsorption performance of activated carbon was analyzed according to the following method. A 25 ppm aqueous solution of Nichilon Black TR 200%, a cationic dye, was prepared. 0.25% by mass of activated carbon was added to the aqueous solution and stirred for 1 hour. The dye concentration was measured in the aqueous solution after the activated carbon was removed by filtration. The dye concentration was calculated by using a spectrophotometer (Hitachi High-Tech Science Co., Ltd., Spectrophotometer U3010) in wavelength scan mode to measure the absorbance of the filtered solution at 1 nm intervals from 360 nm to 800 nm, and converting the sum (integral value) of the obtained absorbance intensities to the dye concentration. To convert the integral values ​​to dye concentrations, the integral values ​​were similarly calculated using 200% aqueous solutions of the cationic dye Nichilon Black TR (1, 2.5, 5, 10, 25 ppm) with known concentrations, and a linear calibration curve based on the relationship between dye concentration and integral value was used.

[0056] C. Analysis of the pH of activated carbon. The pH was measured according to JIS K 1474:2014. The method is shown below.

[0057] Weighed out 1.0 g of activated carbon (based on dry weight) if it was in powder form, or 3.0 g if it was in granular form, and transferred it to a 100-200 mL beaker. Add 100 mL of water and heat gently for 5 minutes, maintaining a steady boil. After that, it was cooled to room temperature, water was added to make a total volume of 100 mL, and it was stirred well. The pH of the suspension was then measured using a pH meter.

[0058] D. Analysis of Average Pore Diameter, Pore Volume Distribution, Specific Surface Area, and Pore Volume of Activated Carbon Nitrogen adsorption measurements were performed on activated carbon at 77 K (liquid nitrogen temperature), and nitrogen adsorption / desorption isotherms were determined. The pore characteristics of the activated carbon were calculated from the obtained nitrogen adsorption / desorption isotherms. The nitrogen adsorption / desorption isotherms were measured using a BELSORP18PLUS-HT manufactured by Nippon Bell. Specific surface area was analyzed using the BET method, and pore volume distribution, pore volume, and average pore diameter were analyzed using the GCMC method. The volume ratio of pores within a specific pore diameter range was calculated from the integrated curve of the pore volume distribution.

[0059] E. Color Analysis Using a Minolta CM-3700d spectrophotometer, the sample was placed with a black calibration plate in the background, and the color L * Value and a* value, b * The value was measured.

[0060] F. Measurement of the mass of insoluble matter in the BHET composition. 5.0 g of BHET composition and 200 g of water were mixed and held at 95°C for 10 minutes. Then, while maintaining a constant temperature, filtration was performed using a 4 μm filter, and the amount of residue was measured as the mass of insoluble matter. The ratio of the mass of insoluble matter to the mass of BHET composition was calculated.

[0061] G. Analysis of insoluble matter (identification of PET-derived components) The insoluble matter of the BHET composition obtained in section F above was analyzed using a Nicolet iS10 FT-IR manufactured by Thermo Fisher Scientific Inc. at 400 cm². －１ From 4000cm －１ Measurements were taken within the wavenumber range up to 700 cm. －１ Nearby, 1100 cm －１ Nearby, 1240 cm －１ Nearby, 1700 cm －１ Nearby, 3400 cm －１ By checking for the presence of peaks in the vicinity, we determined whether the insoluble components were PET-derived components (BHET, PET oligomer, PET).

[0062] H. Analysis of Insoluble Matter (Identification of PET Oligomers) If the insoluble matter of the BHET composition obtained in section F was identified as a PET-derived component in section G, this analysis was performed further. Approximately 5 mg of the insoluble matter was weighed, and using a TA Instruments differential scanning calorimeter (DSC) Q2000, the temperature at the peak of the endothermic peak observed when the material was heated from 20°C to 280°C at a heating rate of 16°C / min was used as the melting point. The melting point was then determined by checking whether one or more of the measured melting points fell within the range of 150°C to 230°C. This determined whether the PET-derived component was a PET oligomer.

[0063] I. Measurement of Crystallization Initiation Time A BHET aqueous solution was prepared by mixing 5 g of BHET composition with 200 g of water. After holding the solution at 95°C for 10 minutes, it was filtered, and the amount of residue was measured. Next, the BHET aqueous solution prepared and held at the same temperature was allowed to cool at room temperature. After a predetermined time had elapsed from the start of cooling, it was filtered, and the amount of residue was measured. The increase in residue was calculated using Equation 1, and the time at which the increase in residue reached 0.5 g or more (10% by mass of the BHET composition at the time of aqueous solution preparation) was defined as the crystallization initiation time. (Equation 1) Increase in residue (g) = Amount of residue after cooling (g) - Amount of residue before cooling (g)

[0064] J. Calculation of Yield The yield of the BHET composition was calculated using Formula 2 and evaluated as follows: (Formula 2) Yield (%) = Mass of BHET composition after crystallization / Mass of crude BHET composition × 100 S: 75% or more and 100% or less A: 70% or more and less than 75% B: 65% or more and less than 70% C: 60% or more and less than 65% D: 0% or more and less than 60%.

[0065] (Example 1) 100 g of cut fabric made of dyed PET fibers was placed in a four-necked flask, and 1100 mol% ethylene glycol relative to the number of moles of repeating units of PET and 1 mass% sodium hydroxide relative to the fabric were added, the mixture was stirred, and depolymerization was carried out at a set temperature of 210°C for 2 hours.

[0066] The depolymerization solution was cooled, and once the temperature dropped to below 130°C, it was added dropwise to six times the volume of water relative to the depolymerization solution. The temperature was then adjusted to below 30°C to precipitate the crude BHET composition, which was then filtered using a 4 μm filter to obtain the crude BHET composition as solid content. When the coloring component concentration of the crude BHET composition was measured, the peak area was 90.

[0067] Ten g of the obtained crude BHET composition was mixed with 30 g of water to obtain a ratio of water mass / crude BHET composition mass = 3.0. The mixture was then filtered using a 1.6 μm filter while maintaining a temperature of 95°C.

[0068] The following steps constitute the purification process of the BHET composition (steps (3) to (4)), and the BHET composition obtained after the purification process was evaluated based on its color, yield, and crystallization initiation time.

[0069] The filtered crude BHET composition aqueous solution was kept at the same temperature as the filtration temperature, and then mixed with 5.0 mL of activated carbon (pH 2.0, average pore size 1.5 nm, specific surface area 2500 m²). ２ A column packed with (BHET / g, pore volume 1.5 mL / g) was passed through at a flow rate of 250 mL / h (space velocity 50 / h), and the dropwise solution was collected. Then, hot water was added to the dropwise solution so that the mass ratio of crude BHET composition to water was 1:40, and the solution was cooled from 95°C to 4°C. Solid-liquid separation was performed to obtain the BHET composition as solid content.

[0070] (Examples 2-7) The process was carried out in the same manner as in Example 1, except that the activated carbon used in the purification process was changed to activated carbon with pH values ​​of 3.5, 4.0, 5.0, 6.0, 7.0, and 8.0, respectively.

[0071]

[0072] (Examples 8-13) The activated carbon used in the purification process of Example 1 had average pore sizes of 0.5 nm, 0.7 nm, 0.9 nm, 3.0 nm, 5.0 nm, and 20 nm, respectively, and specific surface area of ​​300 m² each. ２ / g, 1000m ２ / g, 1500m ２ / g, 3000m ２ / g, 4000m ２ / g, 5000m ２ The procedure was carried out in the same manner as in Example 1, except that the activated carbon was changed to one with a pore volume of 0.2 mL / g, 0.5 mL / g, 1.0 mL / g, 1.8 mL / g, 2.0 mL / g, and 2.5 mL / g, respectively.

[0073]

[0074] (Examples 14-19) The same procedure as in Example 1 was followed, except that the amount of water per 10 g of the crude BHET composition was changed to 5.0 g, 10 g, 60 g, 100 g, 200 g, and 400 g, respectively.

[0075]

[0076] (Examples 20-24) The same procedure as in Example 1 was followed, except that the filtration temperature and liquid flow temperature were changed to 50°C, 60°C, 80°C, 90°C, and 100°C, respectively.

[0077] (Example 25) The procedure was carried out in the same manner as in Example 1, except that the amount of water per 10 g of crude BHET composition was changed to 10 g, and the filtration temperature and liquid flow temperature were changed to 105°C.

[0078] In Example 25, the amount of water was reduced from Example 1 to create a high-concentration aqueous solution of the BHET composition, which can greatly utilize the boiling point elevation effect so that the filtration temperature and the liquid temperature passing through the solution are above the boiling point of water, 100°C.

[0079]

[0080] (Examples 26-32) The process was carried out in the same manner as in Example 1, except that the flow rate (space velocity) in the purification step was changed to 0.5 mL / h (0.1 / h), 2.5 mL / h (0.5 / h), 5.0 mL / h (1.0 / h), 50 mL / h (10 / h), 500 mL / h (100 / h), 1500 mL / h (300 / h), and 5000 mL / h (1000 / h), respectively.

[0081] (Examples 33-35) The same procedure as in Example 1 was followed, except that the cut fabric made of dyed PET fibers in Example 1 was replaced with a cut fabric made of undyed blended fibers with PET:cotton ratios of 85:15, 65:35, and 50:50, respectively.

[0082] Furthermore, even with undyed blended fibers, for example, if the material other than PET is cotton, the decomposition products of cotton will appear as coloring components due to heating in the depolymerization process. However, since the decomposition products of cotton are mainly water-soluble, the coloring components can be removed by the process of dropping the depolymerization solution into water to obtain solid components and by the process of treating with activated carbon. Furthermore, even if the coloring components are not water-soluble, they can generally be removed in the filtration process of the crude BHET composition aqueous solution.

[0083] (Example 36) The procedure was carried out in the same manner as in Example 34, except that the cut fabric made of undyed blended fibers with a PET:cotton ratio of 65:35 was changed to a cut fabric made of dyed blended fibers with the same PET:cotton ratio as in Example 34.

[0084] Even if the crude BHET composition contained dyes and cotton decomposition products, a BHET composition with excellent color tone was obtained by treating it with activated carbon.

[0085]

[0086] (Comparative Example 1) The procedure was carried out in the same manner as in Example 1, except that the activated carbon used in the purification process of Example 1 was changed to activated carbon with a pH of 9.0.

[0087] In Comparative Example 1, the color tone of the resulting BHET composition was poor because a large amount of the coloring component was not sufficiently adsorbed and removed.

[0088] (Comparative Example 2) The procedure was carried out in the same manner as in Example 1, except that the activated carbon treatment in the purification step was omitted, hot water was added to the filtered crude BHET composition aqueous solution so that the mass ratio of crude BHET composition to water was 1:40, the mixture was cooled from 95°C to 4°C, solid-liquid separation was performed, and the BHET composition was obtained as solid content.

[0089] In Comparative Example 2, the color of the resulting BHET composition was poor because a large amount of coloring components remained due to the lack of adsorption and purification of the coloring components.

[0090] (Comparative Example 3) The procedure was carried out in the same manner as in Example 1, except that the amount of water per 10 g of crude BHET composition was changed to 1.0 g.

[0091] In Comparative Example 3, the color tone of the resulting BHET composition was poor because the coloring components were not sufficiently adsorbed and remained in large quantities.

[0092] (Comparative Example 4) The procedure was carried out in the same manner as in Example 34, except that the activated carbon treatment in the purification step of Example 34 was omitted, hot water was added to the filtered crude BHET composition aqueous solution so that the mass ratio of crude BHET composition to water was 1:40, the temperature was cooled from 95°C to 4°C, solid-liquid separation was performed, and the BHET composition was obtained as solid content.

[0093] Comparative Example 4 did not undergo adsorption purification of cotton decomposition products, which are the coloring components, and a large amount of cotton decomposition products remained, resulting in a poor color tone for the obtained BHET composition.

[0094]

[0095] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications are possible without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2024-219533, filed on 16 December 2024, which is incorporated herein by reference in its entirety.

[0096] The present invention provides a BHET composition with good color tone, which is superior in color tone compared to a BHET composition manufactured and purified according to conventional methods, and can be repolymerized to provide a recycled PET composition with good color tone.

Claims

1. A bis(2-hydroxyethyl) terephthalate (BHET) composition obtained by decomposing polyester, characterized in that the peak area in the 360-800 nm range, as measured by a spectrophotometer, is 0 or more and 10 or less.

2. The BHET composition according to claim 1, characterized in that when the BHET composition is mixed with 40 times the amount of water relative to the BHET composition at 95°C, the mass of the insoluble portion is 1% or more relative to the mass of the BHET composition.

3. The BHET composition according to claim 1 or 2, characterized in that the insoluble portion when the BHET composition is mixed with 40 times the amount of water relative to the BHET composition at 95°C is polyethylene terephthalate (PET) oligomer.

4. A recycled polyethylene terephthalate (PET) composition obtained by polycondensing the BHET composition described in claim 1 or 2.

5. The recycled PET composition according to claim 4, characterized in that the peak area in the 360-800 nm range, as measured by a spectrophotometer, is 0 or more and 10 or less.

6. A method for producing a bis(2-hydroxyethyl) terephthalate (BHET) composition, comprising the following steps (1) to (4), wherein step (3) satisfies conditions (a) and (b): (1) A step of depolymerizing a polyethylene terephthalate (PET) composition with ethylene glycol to obtain a crude BHET composition. (2) A step of dissolving the crude BHET composition in hot water to obtain an aqueous solution of the crude BHET composition. (3) A step of treating the aqueous solution of the crude BHET composition with activated carbon to obtain an aqueous solution of the BHET composition. (4) A step of extracting the BHET composition from the aqueous solution of the BHET composition. (a) The mass ratio of the crude BHET composition to water constituting the aqueous solution of the crude BHET composition is 1:0.5 to 1:

40. (b) The pH of the activated carbon is less than 9.

7. The method for producing the BHET composition according to claim 6, characterized in that the PET composition is a yarn and / or fabric containing dyed PET fibers.

8. A method for producing a BHET composition according to claim 6 or 7, characterized in that the PET composition is a yarn and / or fabric containing a material other than PET.

9. A method for producing the BHET composition according to claim 6 or 7, wherein the activated carbon has the following characteristics: (a) a 25 ppm aqueous dye solution and 0.25% by mass of the activated carbon relative to the aqueous dye solution are stirred for 1 hour, and the dye concentration of the aqueous solution after the activated carbon is removed is 5 ppm or less.

10. A method for producing the BHET composition according to claim 6 or 7, characterized in that the average pore size of the activated carbon is 0.5 nm or more and 200 nm or less.

11. A method for producing a BHET composition according to claim 6 or 7, characterized in that the total volume of pores with a pore diameter of 1.0 nm or more and 10 nm or less in the activated carbon is 50% or more of the total pore volume.

12. The specific surface area of ​​the activated carbon is 300 m². ２ / g or more, 5000m ２ A method for producing the BHET composition according to claim 6 or 7, characterized in that the amount is less than or equal to / g.

13. A method for producing the BHET composition according to claim 6 or 7, characterized in that the pore volume of the activated carbon is 0.2 mL / g or more and 2.5 mL / g or less.

14. The method for producing a BHET composition according to claim 6 or 7, characterized in that, in step (3), the temperature of the aqueous solution of the crude BHET composition being processed is 60°C to 105°C.

15. The method for producing a BHET composition according to claim 6 or 7, characterized in that, in step (3) above, the crude BHET composition aqueous solution is passed through the column at a space velocity of 0.5 to 1000 / h while the activated carbon is packed into the column.

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