JP2025009679A - Method for obtaining bis-2-hydroxyethyl terephthalate from polyester fabric - Google Patents

Abstract

To provide a technique for sufficiently removing a coloring component from a polyester fabric containing an ionic-bonding dye and efficiently obtaining bis-2-hydroxyethyl terephthalate excellent in color tone to thereby enable recycling the bis-2-hydroxyethyl terephthalate before disposal to a recycled polyester resin having the same quality as a virgin polyester resin used as a raw material of a dyed fiber.SOLUTION: Provided is a method for obtaining bis-2-hydroxyethyl terephthalate from a colored polyester fabric containing more than 0.0 wt.% and 10.0 wt.% or less of an ionic-bonding dye as a coloring component, comprising the following steps: (1) a step of simultaneously bringing the colored polyester fabric containing an ionic-bonding dye into contact with ethylene glycol vapor of 195°C to 205°C and an ethylene glycol liquid of 150°C to 195°C for 5 minutes or more and less than 150 minutes to extract the coloring component; (2) a step of depolymerizing the polyester fabric after extraction, obtained by executing the step (1), with ethylene glycol to recover crude bis-2-hydroxyethyl terephthalate; and (3) a step of dissolving the crude bis-2-hydroxyethyl terephthalate, obtained by executing the step (2), in a solvent and purifying the material to obtain bis-2-hydroxyethyl terephthalate.SELECTED DRAWING: None

Description

The present invention relates to a method for obtaining bis-2-hydroxyethyl terephthalate from a polyester fabric containing an ion-bonding dye.

Modern economic society has been sustained by a social system of mass production, mass consumption, and mass waste, but various adverse effects on the environment have been confirmed, such as the depletion of natural resources, destruction of the environment due to resource extraction, global warming caused by greenhouse gas emissions, and rising sea levels. Therefore, in order to continue sustainable growth by efficiently using limited resources, it has become essential to build a recycling-oriented social system that minimizes waste generation and reuses and recycles generated waste in a way that does not burden the environment.

To realize a recycling-oriented society, it is necessary to establish recycling systems such as thermal recycling, material recycling, and chemical recycling. In particular, attention is being paid to chemical recycling technology, which breaks down and refines waste plastics down to their raw monomer units, and then uses the resulting monomers to produce recycled resin materials of the same quality as those before disposal.

Polyester fibers, which are inexpensive and have suitable physical properties for clothing, are also expected to be regenerated through chemical recycling, and the application of technologies to regenerate them down to the raw material monomer unit through hydrolysis and glycol decomposition has been considered. For example, when ethylene glycol (EG) is added to polyester fabric recovered from waste clothing and depolymerized through glycol decomposition, the ester monomer bis-2-hydroxyethyl terephthalate (BHET) can be obtained. By using this BHET as a monomer raw material, polyethylene terephthalate (PET) resin regenerated through chemical recycling can be manufactured.

However, if the recovered polyester fabric is colored, applying the chemical recycling process to it as is will result in the resulting monomer raw material and recycled polyester resin being colored, making it impossible to obtain recycled polyester resin of the same quality as the virgin polyester resin used as the raw material for the dyed fibers. Therefore, an extraction process is required to remove the colored components from the recovered fabric as a pretreatment before applying the chemical recycling process, and various methods have been proposed to date.

For example, Patent Document 1 discloses a method in which a liquid glycol extractant is brought into contact with fibrous polyester to extract a colorant, followed by an extraction step in which depolymerization is performed with ethylene glycol, and the ethylene glycol solution of the resulting ester monomer is purified to obtain the ester monomer.

Patent Document 2 also discloses a method of extracting dyes and the like from polyester fabric using an extraction solvent, as well as a method of decolorizing the dyes using an oxidizing agent or reducing agent to remove their color-developing properties, followed by chemical depolymerization of the polyester fabric and purifying the resulting depolymerized product to obtain BHET.

JP 2005-255963 A JP 2023-41599 A

The extraction process disclosed in Patent Document 1 is a method of contacting fibrous polyester with liquid ethylene glycol. Specifically, the method disclosed includes immersing a piece of cloth in ethylene glycol and heating it at 150°C, filling a piece of cloth in a Soxhlet extraction apparatus and contacting the piece of cloth with liquid ethylene glycol while refluxing the ethylene glycol, and contacting the piece of cloth with liquid ethylene glycol at 195°C by continuous countercurrent extraction using a conveyor. These methods are expected to have a certain extraction effect for coloring components such as disperse dyes that do not form chemical bonds with the polymer molecules that make up the fiber. On the other hand, for coloring components such as cationic dyes that are firmly bonded to the polymer molecules that make up the fiber by molecular-level ionic bonds, simply contacting the coloring components with liquid ethylene glycol as an extractant is not able to cut the strong bonds between the dye molecules and the polymer molecules, and therefore no extraction effect can be obtained. The ester monomer obtained by the subsequent depolymerization and purification processes is colored, and it is not possible to obtain a recycled polyester resin of the same quality as the virgin polyester resin used as the raw material for dyed fibers.

In addition, the decolorization process disclosed in Patent Document 2 uses an oxidizing agent or reducing agent to cause the dye molecules to lose their coloring regardless of the type of dye molecule, and is therefore expected to be effective in suppressing coloration of the resulting BHET. However, since oxidizing agent molecules, reducing agent molecules, and modified dye molecules remain in the BHET and may inhibit the repolymerization reaction or become foreign matter, additional removal operations are required in the subsequent purification process to obtain recycled polyester resin of the same quality as the virgin polyester resin used as the raw material for dyed fibers, which leads to increased energy consumption and costs and is not efficient.

The object of the present invention is to provide a technology that overcomes the problems of the above-mentioned conventional technology, sufficiently removes coloring components from polyester fabrics containing ion-bonding dyes, and efficiently obtains BHET with excellent color tone, thereby making it possible to obtain recycled polyester resin of the same quality as the virgin polyester resin used as a raw material for dyed fibers.

The above problems are solved by the following [1] to [5].
[1] A method for obtaining bis-2-hydroxyethyl terephthalate from a polyester fabric containing more than 0.0% by weight and not more than 10.0% by weight of an ion-bonding dye, comprising the steps of:
(1) A step of contacting a colored polyester fabric containing an ion-bonding dye with ethylene glycol vapor at 195° C. or higher and 205° C. or lower and ethylene glycol liquid at 150° C. or higher and 195° C. or lower simultaneously for 5 minutes or higher and less than 150 minutes to extract a colored component; (2) A step of depolymerizing the extracted polyester fabric obtained by carrying out the step (1) with ethylene glycol to recover crude bis-2-hydroxyethyl terephthalate; (3) A step of dissolving the crude bis-2-hydroxyethyl terephthalate obtained by carrying out the step (2) in a solvent and purifying it to obtain bis-2-hydroxyethyl terephthalate. [2] The method for obtaining bis-2-hydroxyethyl terephthalate according to [1], wherein the main component of the solvent used in the step (3) is water.
[3] The method for obtaining bis-2-hydroxyethyl terephthalate according to [2], wherein the step (3) consists of only the following steps (3a) to (3c):
(3a) A step of dissolving the crude bis-2-hydroxyethyl terephthalate obtained by carrying out the step (2) in hot water at 60°C to 100°C and filtering the mixture while it is hot; (3b) A step of subjecting the aqueous solution obtained by carrying out the step (3a) to both an activated carbon treatment and an ion exchange treatment at 60°C to 100°C; and (3c) A step of cooling the aqueous solution obtained by carrying out the step (3b) to 30°C or less to crystallize and recover bis-2-hydroxyethyl terephthalate. [4] In the step (3b), the volume ratio of the adsorbents used in the activated carbon treatment and the ion exchange treatment, respectively, represented by the following formula 1, is 0.10 or more and 100.00 or less.
(Formula 1) Volume ratio = Volume of adsorbent used in ion exchange treatment (mL) / Volume of adsorbent used in activated carbon treatment (mL)
[5] The method for obtaining bis-2-hydroxyethyl terephthalate according to [3], wherein in the step (3b), the activated carbon treatment and the ion exchange treatment are carried out by passing the liquid through columns packed with the respective adsorbents, and the space velocity is 2.1 hr ^-1 or more and 300.0 hr ^-1 or less.

According to the present invention, by thoroughly removing coloring components from polyester fabric containing ion-bonding dyes and efficiently obtaining BHET with excellent color tone, it is possible to regenerate the fabric into PET resin of the same quality as virgin PET resin.

The present invention is described in detail below.

In this invention, polyester fabric refers to recovered polyester fabric for chemical recycling, and is not limited to clothing-shaped or fabric-shaped fabrics, but also includes cut pieces. In addition, recovery does not only refer to used fabrics, but also includes manufacturing and process waste from the manufacturing process.

In the present invention, the polyester fabric contains an ionic dye as a coloring component. The ionic dye contained in the polyester fabric as a coloring component is called a cationic dye (basic dye) or an anionic dye (acid dye), and is a dye that dyes the fabric in a form in which the dye molecule and the polymer molecule constituting the fiber are firmly bonded by ionic bonds at the molecular level. Cationic dyes are preferably used as the ionic dye because they are easy to color polyester fibers. In the present invention, it is essential that the polyester fabric contains an ionic dye as a coloring component, but other coloring components may also be contained. There are no particular limitations on the other coloring components, and examples of such components include disperse dyes, direct dyes, reactive dyes, vat dyes, organic pigments, and inorganic pigments.

In the present invention, the content of the ionic bond dye is more than 0.0% by weight and 10.0% by weight based on the polyester fiber. If the ionic bond dye is not present or the content is extremely low, there is no point in applying the present invention, so the ionic bond dye is preferably present in an amount of 0.01% by weight or more, more preferably 0.05% by weight or more, and particularly preferably 0.1% by weight or more. In addition, in terms of being able to perform a more efficient extraction process of the coloring components, the content of the ionic bond dye is preferably 9.0% by weight or less, more preferably 8.5% by weight or less, and particularly preferably 8.0% by weight or less.

The polyester fabric is mainly composed of polyester fibers such as polyethylene terephthalate fibers, polypropylene terephthalate fibers, and polybutylene terephthalate fibers, but polyethylene terephthalate fibers are preferable because ethylene glycol is used in the process of extracting the dye. The monomers constituting the polyester fibers are dicarboxylic acids and diols, and the polyester fibers may be copolymerized polyester fibers in which two or more types of monomers are copolymerized. There are no particular limitations on the monomers constituting the polyester fibers, but examples of the dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, 4,4'-diphenyldicarboxylic acid, cyclohexane dicarboxylic acid, 5-sulfoisophthalic acid, and sodium 5-sulfoisophthalate, and aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and examples of the diols include ethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol, cyclohexane dimethanol, neopentyl glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

The polyester fabric may contain fibers other than polyester fibers. There are no particular limitations on the fibers other than polyester fibers, but examples include cellulose fibers, polyolefin fibers, acrylic fibers, nylon fibers, and polyurethane fibers. The content is preferably 10% or less, more preferably 5% or less, and particularly preferably 0.5% or less. If the content of fibers other than polyester fibers is within this range, a BHET with excellent color tone can be obtained by the method described in the present invention.

In the present invention, as the extraction process of the coloring components of the polyester fabric (process (1)), it is necessary to carry out a process of contacting the polyester fabric with ethylene glycol vapor at 195°C to 205°C and ethylene glycol liquid at 150°C to 195°C simultaneously for 5 minutes to less than 150 minutes. By contacting with ethylene glycol vapor, the polymer fiber structure of the polyester fabric is relaxed, and even if the coloring components are ionic, in which the dye molecules and polymer molecules are strongly bonded, extraction proceeds quickly. When the temperature of the ethylene glycol liquid is 150°C or higher, more preferably 185°C or higher, the extraction efficiency of the coloring components is particularly improved. On the other hand, when the ethylene glycol vapor is 205°C or lower, the extraction of the coloring components can be promoted while suppressing the decomposition of the polyester fibers that constitute the polyester fabric. When the polyester fabric is contacted with ethylene glycol vapor or a pressurized ethylene glycol solution at a temperature higher than 205°C, the decomposition of the polyester fibers that constitute the polyester fabric also proceeds quickly, and the yield of the polyester fabric is deteriorated. The solvent used in the extraction step is most preferably ethylene glycol, since it has a low boiling point and can be brought into contact with the polyester fiber while suppressing decomposition of the polyester fiber, but other glycol-based solvents may be used in some cases. Examples include propylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol, cyclohexanedimethanol, neopentyl glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. However, because the glycol-based solvent has a higher boiling point than ethylene glycol, the temperature of the glycol-based solvent in contact with the polyester fiber increases, causing the decomposition of the polyester fiber to proceed rapidly, resulting in a poor yield of polyester fabric, or the boiling point of the glycol-based solvent is higher than the decomposition temperature, making it impossible to generate the glycol-based solvent vapor at normal pressure.

It is essential that the time for contacting the polyester fabric with ethylene glycol is 5 minutes or more and less than 150 minutes. By making the contact time with ethylene glycol 5 minutes or more, the coloring components are sufficiently extracted, and a BHET with excellent color tone can be obtained. It is preferably 10 minutes or more, more preferably 30 minutes or more. On the other hand, if the contact time is less than 150 minutes, the decomposition of the polyester fibers constituting the polyester fabric does not progress, and the yield of the polyester fabric is improved. If the contact time is longer than 150 minutes, the decomposition of the polyester fibers constituting the polyester fabric progresses, and the yield of the polyester fabric deteriorates. It is preferably less than 120 minutes, more preferably less than 60 minutes.

The yield of polyester fabric in the extraction process is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and most preferably 90% or more.

In the present invention, the polyester fabric after extraction is depolymerized with ethylene glycol in a depolymerization step (step (2)) and recovered as crude BHET. Step (2) is further divided into a step of adding ethylene glycol to the polyester fabric obtained in step (1) to depolymerize it, and a step of recovering crude BHET from the ethylene glycol solution containing BHET obtained by depolymerization.

The amount of ethylene glycol added during depolymerization is preferably 2.0 parts by weight or more per 1.0 part by weight of polyester fabric. If it is less than 2.0 parts by weight per 1.0 part by weight of polyester fabric, the molecular weight of the resulting BHET will be large, resulting in a decrease in yield in the subsequent purification process and a decrease in efficiency. In addition, adding more than 10.0 parts by weight of EG will produce the same effect, so it is not preferable from the standpoint of cost. The temperature during depolymerization is preferably 190°C or higher and 210°C or lower. In addition, from the viewpoint of efficient depolymerization, it is preferable to add sodium hydroxide or sodium carbonate to ethylene glycol in a range of 0.5% by weight or higher and 2.0% by weight or lower with respect to BHET.

In the process of recovering crude BHET from the ethylene glycol solution containing BHET obtained by depolymerization, it is particularly preferable that the ethylene glycol content in the crude BHET is removed to 0% by weight or more and 5% by weight or less. If the ethylene glycol content in the crude BHET is more than 5% by weight, it is not preferable because the yield will deteriorate in the hot filtration process and crystallization process performed thereafter. In order to remove ethylene glycol from the ethylene glycol solution containing BHET after depolymerization, any of the following methods may be used. The first method is a reprecipitation method in which the ethylene glycol solution containing BHET obtained by depolymerization is dropped into water adjusted to 20°C or less to obtain a cloudy solution, and then the crude BHET containing impurities is recovered using a filter. The water temperature is preferably 15°C or less in terms of increasing the yield, and more preferably 10°C or less. The second method is a high-concentration method in which the ethylene glycol contained in the ethylene glycol solution containing BHET obtained by depolymerization is distilled off and removed; specifically, EG can be quickly removed by heating to 80-150°C and reducing the pressure to a range of 200-1000 Pa. The reprecipitation method is preferable for removing ethylene glycol because when the ethylene glycol solution containing BHET is dropped into water, the colored components migrate to the aqueous phase, making it easy to improve the purity of BHET.

The crude BHET recovered by depolymerization of the polyester fabric after extraction preferably has a polydispersity of 1.20 or less, more preferably 1.10 or less, and particularly preferably 1.05 or less, since the yield will deteriorate in the subsequent purification step, particularly in the hot filtration step. The polydispersity evaluation of the crude BHET refers to a value measured and calculated by the following method using a differential refractive index detector RI (e.g., Waters'"Waters-2414" with a sensitivity of 128x) and gel permeation chromatography (GPC, e.g., Waters'"Waters-e2695").
[1] Take 2.5 mg of crude BHET, add 3 mL of hexafluoroisopropanol (containing 0.01 N sodium trifluoroacetate), and filter through a 0.45 μm filter.
[2] The filtrate is measured using a differential refractive index detector RI (for example, Waters'"Waters-2414" with a sensitivity of 128x) as a detector and GPC (for example, Waters'"Waters-e2695" etc.) under the following conditions.
Column: Showa Denko Co., Ltd., Shodex HFIP806M (2 columns connected)
Solvent: Hexafluoroisopropanol (0.01N sodium trifluoroacetate added)
Flow rate: 1.0 mL/min Column temperature: 30° C.
・Injection volume: 0.10mL
Standard sample: Standard polymethyl methacrylate, standard BHET (manufactured by Tokyo Chemical Industry Co., Ltd.)
In addition, in order to efficiently improve the purity of the crude BHET in the purification step carried out thereafter, it is preferable that the amount of coloring components contained in the crude BHET is less than 200.0 in terms of the absorbance intensity area observed in the range of 400 nm to 800 nm using a spectrophotometer. If the amount of coloring components contained in the crude BHET is 200.0 or more, the life of the adsorbent used in the purification step will be shortened and it will not be efficient. In terms of being able to efficiently perform purification and obtaining BHET with excellent color tone, the absorbance intensity area is more preferably less than 150.0, even more preferably less than 125.0, and particularly preferably less than 100.0. The absorbance intensity evaluation using a spectrophotometer is carried out as follows. The sample used for evaluation is prepared by preparing a mixed solvent of water and hexafluoroisopropanol (1:4), preparing a solution containing 1 wt % crude BHET in this mixed solvent, and calculating the integrated value of the absorbance intensity from 400 to 800 nm in wavelength scan mode using a spectrophotometer, for example a U3010 spectrophotometer manufactured by Hitachi High-Tech Science Corporation.

In the present invention, the crude BHET recovered by depolymerization of the polyester fabric after extraction is dissolved in a solvent and purified (step (3)) to obtain BHET with improved purity. There are no particular restrictions on the solvent used for purification as long as it dissolves BHET, but it is preferable that the main component is water or ethylene glycol, as this is less likely to become a foreign matter when producing recycled PET resin. In particular, the use of water is more preferable, as it tends to improve the yield in the crystallization step. Note that a substance that occupies 50% or more by weight of the solvent used for purification is considered to be the main component.

The process for dissolving crude BHET in a solvent and purifying it to obtain BHET includes the following hot filtration (step (3a)), adsorption treatment (step (3b)), crystallization (step (3c)), as well as liquid phase chromatography, centrifugation, molecular distillation, and the like. However, it is preferable that the process consists of only steps (3a) to (3c) in terms of reducing energy consumption and carbon dioxide emissions.
(3a) A step of dissolving crude bis-2-hydroxyethyl terephthalate in hot water at 60°C to 100°C and filtering it while hot; (3b) A step of subjecting the aqueous solution obtained by carrying out the step (3a) to both activated carbon treatment and ion exchange treatment at 60°C to 100°C; (3c) A step of cooling the aqueous solution obtained by carrying out the step (3b) to 30°C or less to crystallize and recover bis-2-hydroxyethyl terephthalate. As the step (3a), it is preferable to dissolve the crude BHET recovered in the depolymerization step in hot water at 60°C to 100°C and filter it while hot. In order to remove impurities (metal compounds typified by titanium oxide, inorganic compounds typified by silica gel, etc.) contained in the polyester fiber, it is particularly preferable to employ a hot water dissolution step and a hot filtration step. By dissolving the crude BHET recovered in the depolymerization step in hot water at 60°C or more and passing it through a filter, a transparent high-temperature aqueous solution in which BHET is dissolved can be obtained. If the temperature of the hot water is lower than 60° C., BHET will precipitate during filtration, resulting in a decrease in yield. In terms of preventing BHET from precipitating, the temperature of the hot water is more preferably 70° C. or higher, even more preferably 80° C. or higher, and most preferably 85° C. or higher. The higher the hot water temperature, the better, but if the temperature exceeds 100° C., the water will boil at normal pressure, so the temperature is preferably 100° C. or lower.

In step (3b), the 60°C to 100°C aqueous BHET solution after hot filtration in step (3a) is preferably subjected to activated carbon treatment and ion exchange treatment to adsorb and remove colored components and impurities in the aqueous solution. If the temperature of the hot water is lower than 60°C, BHET will precipitate during the activated carbon treatment and ion exchange treatment, resulting in a decrease in yield. In terms of preventing BHET from precipitating, the hot water temperature is more preferably 70°C or higher, even more preferably 80°C or higher, and most preferably 85°C or higher. The higher the hot water temperature, the better, but if it exceeds 100°C, it will boil at normal pressure, so it is preferably 100°C or lower.

Activated carbon treatment can remove coloring components or impurities, whether ionic or nonionic, but BHET is also adsorbed, and therefore the yield will decrease if BHET comes into contact with an excessive amount of activated carbon. For example, when activated carbon is added directly to the solution and adsorption treatment is performed for 30 to 90 minutes, the lower limit of the amount added is preferably 1% by weight or more of BHET in order to sufficiently remove coloring components, more preferably 4% by weight or more, and even more preferably 10% by weight or more. The upper limit of the amount added is preferably 100% by weight or less in order to prevent a decrease in yield, more preferably 84% by weight or less, even more preferably 21% by weight or less, particularly preferably 16% by weight or less, and most preferably 12% by weight or less.

In the ion exchange treatment, ionic coloring components and impurities in BHET can be efficiently removed without deteriorating the yield of BHET. In particular, when the polyester fabric contains an ion-bonding dye as a coloring component, the ion-bonding dye can be easily removed by the ion exchange treatment. In the ion exchange treatment, an ion exchange resin or an ion exchange membrane can be used as an adsorbent, but it is preferable to use an ion exchange resin from the viewpoint of cost. As the ion exchange resin, for example, IR120B, IR124, IRC76 as a cation exchange resin, and IRA96SB, IRA402BL, IRA410, etc. as an anion exchange resin, which are Amberlite TM manufactured by Organo Corporation, can be used. There is no particular restriction on the ion type of the ion exchange resin, but since it has excellent ion exchange capacity, H ⁺ type and Na ⁺ type can be used in the case of a cation exchange resin, and Cl ^- type and free base type can be used in the case of an anion exchange resin. The ion exchange group of the ion exchange resin is not particularly limited, but in the case of a cation exchange resin, a sulfonic acid group, a carboxylic acid group, etc. can be used because of their excellent ion exchange capacity, and in the case of an anion exchange resin, a trimethylammonium group, a dimethylethanolammonium group, a dimethylammonium group, etc. can be used.

When it is clear that most of the coloring components are derived from cationic dyes, cation exchange resins can be suitably used, and when it is clear that they are derived from anionic dyes, anion exchange resins can be suitably used. However, since ionic impurities other than coloring components can be removed, it is particularly preferable to use both cation exchange resins and anion exchange resins. The amount of adsorbent used in the ion exchange treatment must be prepared so that the ion exchange group of the adsorbent is 1 equivalent or more relative to the mole number of the ion-binding dye contained in the crude BHET. The amount of ion exchange groups of the ion exchange resin may be calculated by any method, but for example, in the case of a cation exchange resin, the ion exchange resin is filled in a column, an aqueous hydrochloric acid solution is passed through to convert the ion exchange group to the H ⁺ type, pure water is passed through, and then an aqueous sodium chloride solution is passed through, and the resulting treatment liquid is subjected to neutralization titration. In the case of an anion exchange resin, the aqueous hydrochloric acid solution may be replaced with a sodium chloride solution by the above-mentioned operation. The number of moles of the ion-bonding dye in the crude BHET may be calculated by any method, but for example, it can be calculated by preparing a crude BHET with a known dye content and a crude BHET with an unknown dye content, and comparing the absorption intensity area observed in the range of 400 nm to 800 nm using a spectrophotometer. If the molecular weight of the dye contained is unknown, 400 g/mol may be used as a representative value. If the amount is less than 1 equivalent, the dye cannot be completely removed theoretically. In terms of being able to shorten the treatment time and to sufficiently remove the dye, the amount of the ion exchange group is preferably 10 equivalents or more, more preferably 51 equivalents or more, particularly preferably 90 equivalents or more, and most preferably 109 equivalents or more. The absorbance intensity evaluation using a spectrophotometer is performed as follows. The sample used for evaluation is prepared by preparing a mixed solvent of water and hexafluoroisopropanol (1:4), preparing a solution containing 1 wt % BHET in this mixed solvent, and calculating the integrated value of the absorbance intensity from 400 to 800 nm in wavelength scan mode using a spectrophotometer, for example a U3010 spectrophotometer manufactured by Hitachi High-Tech Science Corporation.

For the activated carbon treatment and ion exchange treatment, a method of passing the solution through a column filled with each adsorbent or adding the adsorbent directly to the solution is preferably used. When using a column, for example, when passing a 2.5 wt% BHET aqueous solution, it is preferable to pass the solution at a spatial velocity of more than 0.1 hr ^-1 and less than 100.0 hr -1 in order to improve the removal rate of coloring components and impurities. If it is 0.1 hr ^-1 or less, the treatment time becomes too long, and if it is 100.0 hr ^-1 or more, the liquid passing is too fast and coloring components and impurities are not sufficiently removed. Since the treatment can be performed efficiently ^, the lower limit of the liquid passing rate is more preferably 2.1 hr ^-1 or more, and the upper limit of the liquid passing rate is more preferably 50.0 hr ^-1 or less, and even more preferably 20.0 hr ^-1 or less.

In the activated carbon treatment, if the space velocity is low, BHET is adsorbed and the yield is reduced. Therefore, from the viewpoint of ensuring the yield of BHET, the lower limit of the space velocity is preferably 2.1 hr ^-1 or more, more preferably 8.0 hr ^-1 or more, even more preferably 13.0 hr ^-1 or more, particularly preferably 20.0 hr ^-1 or more, and most preferably 50.0 hr ^-1 or more, while the upper limit of the space velocity is preferably 300.0 hr ^-1 or less. If it is less than 2.1 hr ^-1 , the yield of BHET is significantly reduced, but if it is higher than 300.0 hr ^-1 , the reduction in the yield of BHET is suppressed.

Therefore, the column flow conditions need to consider the balance between the removal of coloring components and impurities and the yield of BHET, and taking the above contents into consideration, the spatial velocity is preferably 2.1 hr ^-1 or more and 300.0 hr ^-1 or less. If it is less than 2.1 hr ^-1 , the yield of BHET drops significantly, and if it is higher than 300.0 hr ^-1 , the coloring components and impurities are not sufficiently removed. From the viewpoint of recovering BHET with a high yield and sufficiently removing coloring components and impurities, the lower limit of the spatial velocity of BHET is more preferably 8.0 hr ^-1 or more, even more preferably 13.0 hr ^-1 or more, particularly preferably 20.0 hr ^-1 or more, and most preferably 50.0 hr ^-1 or more. The upper limit of the spatial velocity is more preferably 200.0 hr ^-1 or less, and even more preferably 100.0 hr ^-1 or less.

The method of packing the adsorbent into the column is not particularly limited, and a method of mixing multiple types of adsorbents and packing them into a single column may be selected, but a method of packing one type of adsorbent into one column or a method of packing into a multi-layer column with separate layers for each type of adsorbent is preferred, in that the liquid flow conditions can be controlled for each type of adsorbent.

The order of the activated carbon treatment and the ion exchange treatment can be either first or second, but if there is clearly residual ion-bonding dye in the crude BHET, it is preferable to carry out the ion exchange treatment first and then the activated carbon treatment in order to purify it efficiently.

In order not to deteriorate the yield of BHET, the volume ratio of the adsorbents used in the activated carbon treatment and the ion exchange treatment, respectively, represented by the following formula 1, is preferably 0.10 or more and 100.00 or less.
(Formula 1) Volume ratio = Volume of adsorbent used in ion exchange treatment (mL) / Volume of adsorbent used in activated carbon treatment (mL)
If the volume ratio is less than 0.10, the amount of adsorbent used in the activated carbon treatment is excessive or the amount of adsorbent used in the ion exchange treatment is insufficient, which may result in a poor yield of BHET or insufficient removal of ion-bonding dyes. If the volume ratio is greater than 100.00, the amount of adsorbent used in the activated carbon treatment is insufficient or the amount of adsorbent used in the ion exchange treatment is excessive, which may result in insufficient removal of ion-bonding dyes and other impurities or may be disadvantageous in terms of cost. Since the treatment can be performed without deteriorating the yield, the lower limit of the volume ratio is more preferably 0.40 or more, even more preferably 0.55 or more, particularly preferably 0.70 or more, and most preferably 0.85 or more. After the adsorption treatment, a transparent high-temperature aqueous solution from which impurities and adsorbents such as activated carbon have been removed can be obtained by passing the solution through a filter, but this may not be necessary depending on the type of adsorbent and the treatment method.

Finally, in step (3c), it is preferable to cool the 60-100°C aqueous solution that has been treated with activated carbon and ion exchange to 30°C or less to crystallize and recover bis-2-hydroxyethyl terephthalate. In order to obtain BHET in high yield, the cooling temperature is preferably 30°C or less, more preferably 15°C or less, even more preferably 10°C or less, and most preferably in the range of 2-5°C. After crystallization, the BHET is separated into solid and liquid by filtration or centrifugation, and then preferably dried with air or hot air at 40-90°C to reduce the moisture content, which allows subsequent repolymerization to be carried out quickly.

The yield of BHET in the purification step (step (3)) is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and most preferably 90% or more.

In the method of the present invention, when chemically recycling polyester fabric, the above-mentioned purification process is carried out, thereby making it possible to obtain high-quality BHET with excellent color tone. The obtained high-quality BHET can be polymerized in the presence of a polymerization catalyst according to a known PET polymerization method to produce high-quality recycled PET equivalent to virgin PET.

The color tone L* value of the BHET obtained by the method of the present invention is preferably in the range of 80.0 to 100.0, more preferably in the range of 90.0 to 100.0, and particularly preferably in the range of 95.0 to 100.0. The color tone a* value is preferably in the range of -5.0 to 5.0, more preferably in the range of -2.0 to 2.0, and particularly preferably in the range of -1.5 to 1.5. The color tone b* value is preferably in the range of -5 to 5, more preferably in the range of -2.0 to 2.0, and particularly preferably in the range of -1.5 to 1.5. When the color tone L* value, a* value, and b* value are in these ranges, the color tone of the recycled polyester resin obtained by polycondensation of BHET is equivalent to that of virgin polyester resin.

Furthermore, the amount of coloring components contained in BHET is preferably such that the absorbance area observed in the range of 400 nm to 800 nm using a spectrophotometer is less than 20.0. In terms of obtaining high-quality BHET and PET resin with a small amount of absorbance, it is more preferable that the absorbance area is less than 10.0, even more preferable that the absorbance area is less than 2.0, particularly preferable that the absorbance area is less than 0.5, and most preferable that the absorbance area is less than 0.3. The lower detection limit is 0.1. The absorbance intensity evaluation using a spectrophotometer is performed as follows. The sample used for the evaluation is prepared by preparing a mixed solvent of water and hexafluoroisopropanol (1:4), and then preparing a solution containing 1% by weight of BHET using this mixed solvent. A spectrophotometer, for example a U3010 spectrophotometer manufactured by Hitachi High-Tech Science Corporation, is used to calculate the integral value of the absorbance intensity from 400 to 800 nm in wavelength scan mode.

In addition, it is preferable that the BHET obtained by the method of the present invention has been removed from the copolymerization components contained in the polyester fabric. There are various compounds as copolymerization components remaining in the purified BHET. For example, dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, 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, and diols include ethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol, cyclohexanedimethanol, neopentyl glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. In particular, it is preferable that sodium 5-sulfoisophthalate, which is often used in polyester fibers dyed with cationic dyes, has been removed. If the copolymerization components are contained, the crystallinity of the recycled polyethylene terephthalate resin obtained by polycondensing BHET is reduced, and the processability and physical properties are deteriorated. The detection of the copolymerization components remaining in BHET can be carried out, for example, as follows. The sample used for evaluation is prepared by preparing a solution containing 1.5% by weight of BHET in deuterated deuterated hexafluoroisopropanol, and performing ¹ H-NMR measurement using a nuclear magnetic resonance apparatus, for example, a nuclear magnetic resonance apparatus JNM-ECZ500R manufactured by JEOL Ltd., to confirm whether peaks derived from copolymerization components other than BHET are observed in the obtained spectrum. The peak derived from the benzene ring of BHET is observed near 7.5 ppm, and the peaks derived from the ethylene group are observed near 3.3 ppm and 3.8 ppm, and the ratio of the integral value of the peak derived from the benzene ring to the integral value of the peak derived from the ethylene group is approximately 1:2. If a peak other than the peak derived from BHET is observed in the obtained spectrum, it can be determined that copolymerization components and other impurities remain. For example, if sodium 5-sulfoisophthalate remains, a peak is observed near 8.2 ppm to 8.3 ppm.

By polycondensing the BHET obtained by chemically recycling polyester fabric using the method of the present invention, polyethylene terephthalate resin of the same quality as before recycling can be obtained.

A. Calculation of the extraction yield
The yield in the extraction step was calculated using Equation 2 and evaluated as follows. After the extraction treatment, the fabric was dried to remove the extraction solvent, and then the weight was measured.

(Formula 2) Extraction process yield (%) = weight of fabric after extraction treatment / weight of fabric before extraction treatment × 100
S: 90% or more and 100% or less; A: 80% or more and less than 90%; B: 70% or more and less than 80%; C: 60% or more and less than 70%; D: 0% or more and less than 60%.

<B. Absorbance area measurement of crude BHET and purified BHET>
The absorbance area using a spectrophotometer was measured as follows. For the sample used in the evaluation, a mixed solvent (1:4) of water and hexafluoroisopropanol was prepared, and then a solution of 1 wt % BHET was prepared in this mixed solvent. Using a spectrophotometer (Hitachi High-Tech Science U3010 spectrophotometer) in wavelength scan mode, the integrated value of the absorbance from 400 to 800 nm (absorbance area) was calculated.

<C. Calculation of the number of moles of ion-binding dye contained in crude BHET>
A sample with a known dye content was prepared by mixing crude BHET with 200% Nichilon Black TR, which is classified as a cationic dye, at a concentration of 4% by weight, and the absorbance area was measured by the method described in Section A above. The absorbance areas of the sample with a known dye content and the samples described in the Examples and Comparative Examples were compared to calculate the number of moles of the ionic dye contained in 2 g of crude BHET. Note that 400 g/mol was used as a representative molecular weight of the ionic dye.

D. Polydispersity Measurement of Crude BHET
The polydispersity of crude BHET was measured by gel permeation chromatography under the following conditions:
Apparatus: Gel permeation chromatograph (GPC) (Waters-e2695)
Detector: Differential refractive index detector RI (Waters-2414, sensitivity 128x)
Column: Showa Denko Co., Ltd., Shodex HFIP806M (2 columns connected)
Solvent: Hexafluoroisopropanol (0.01N sodium trifluoroacetate added)
Flow rate: 1.0mL/min
Column temperature: 30°C
Injection volume: 0.10mL
Standard samples: standard polymethyl methacrylate, standard BHET (manufactured by Tokyo Chemical Industry Co., Ltd.).

E. Calculation of purification step yield
The yield in the purification step was calculated using Equation 3 and evaluated as follows.

(Equation 3) Yield (%) of purification step = weight of purified BHET / weight of crude BHET x 100
S: 90% or more and 100% or less; A: 80% or more and less than 90%; B: 70% or more and less than 80%; C: 60% or more and less than 70%; D: 0% or more and less than 60%.

F. Calculation of Total Yield
The total yield of purified BHET obtained from the fabric before the extraction treatment was calculated using Equation 4, and was evaluated as follows. When the extraction step was not performed, the yield was calculated as 100%.

(Formula 4) Total yield (%) = Yield of extraction step x Yield of purification step / 100
S: 80% or more and 100% or less; A: 70% or more and less than 80%; B: 60% or more and less than 70%; C: 50% or more and less than 60%; D: 0% or more and less than 50%.

<G. Color Analysis of BHET>
A Minolta CM-3700d spectrophotometer was used to analyze the color tone of the fabric and BHET. The samples were placed against a black calibration plate, and the L*, a*, and b* values of the color tone were measured.

H. Detection of Copolymer Components Remaining in BHET Detection of copolymer components remaining in BHET was carried out as follows.

As a sample for evaluation, a solution containing 1.5% by weight of BHET was prepared using deuterated deuterated hexafluoroisopropanol. This solution was subjected to ^1H -NMR measurement using a nuclear magnetic resonance apparatus, JNM-ECZ500R manufactured by JEOL Ltd., and it was confirmed whether a peak derived from sodium 5-sulfoisophthalate was observed in the obtained spectrum. If a peak was observed, it was judged that the copolymerization component was "present," and if not, it was judged that the copolymerization component was "absent."

[Example 1]
As a polyester fabric containing an ion-bonding dye, a black polyester fabric was prepared by dyeing (120°C, 60 minutes) with Nichilon Black TR200%, which is classified as a cationic dye, at a concentration of 4% owf and cutting it into 1 cm squares. The fabric was a polyester fabric in which polyethylene terephthalate was copolymerized with sodium 5-sulfoisophthalate.

(Extraction process) 1000 g of ethylene glycol and 0.1 g of sodium hydroxide were placed in a 2 L four-neck flask and placed in a mantle heater, after which 15 g of cut black polyester fabric was filled into a glass tube 25 mm in diameter and 300 mm in length and connected to the 2 L four-neck flask. A Dimroth condenser was then connected to the top of the connected glass tube. The mantle heater was set to a temperature of 210°C and heating was started. The mantle heater was exposed to EG reflux for 30 minutes to bring the fabric into contact with EG vapor and high-temperature EG liquid, and the colored components were extracted. The temperature of the vapor passing through the bottom of the glass tube was 195-205°C, and the temperature of the liquid EG refluxed through the Dimroth condenser was 185-195°C. The extracted fabric was washed with water, dried, and collected. The yield of polyester fabric in the extraction process is shown in Table 1.

(Depolymerization process) After extraction, the fabric was washed with water and dried, and 10.0 g was placed in a 1 L four-neck flask. 55 g of ethylene glycol and 0.1 g of sodium hydroxide were added, and the mixture was stirred and depolymerized for 2 hours at an ethylene glycol temperature of 200°C. After depolymerization, heating was stopped, and when the depolymerized solution had dropped to 100°C or less, it was dropped into 500 mL of water adjusted to 10°C or less to obtain a cloudy solution. The resulting cloudy solution was filtered through a 4 μm filter to obtain crude BHET as a solid. The absorbance intensity area, moles of ion-bonding dye, and polydispersity of crude BHET are shown in Table 1.

(Purification step) 2.0 g of the obtained crude BHET was dissolved in 80 mL of 95 ° C. hot water to prepare a 2.5 wt % crude BHET aqueous solution, and filtered using a 1.6 μ filter. 0.30 mL of cation exchange resin IR120B (H ⁺ type, apparent density: 790 g / L-R, amount of cation exchange group: ≧ 1.80 mol / L-R) of Amberlite TM manufactured by Organo Corporation was added to the obtained transparent filtrate and stirred while heating to 95 ° C., and after 1 hour, the ion exchange resin was removed using a 1.0 μ filter. Next, 0.36 mL (10 wt %) of activated carbon (bulk density 0.56 g / mL) from Osaka Gas Chemicals was added to the obtained transparent filtrate with respect to the crude BHET, and stirred while heating to 95 ° C., and after 1 hour, the activated carbon was removed using a 1.0 μ filter. The obtained transparent filtrate was cooled to 20° C. or lower, and BHET was crystallized to perform solid-liquid separation, and the solid content was air-dried at 50° C. to obtain purified BHET. The yield of the purification process, the total yield, the color tone of BHET, the absorbance area, and the presence or absence of 5-sulfoisophthalic acid remaining as a copolymerization component in BHET are shown in Table 1.

[Example 2]
The same procedure as in Example 1 was carried out, except that the dye concentration during dyeing of the polyester fabric containing the ion-bonding dye was 10% owf.

[Examples 3 to 6]
The same procedure as in Example 1 was repeated except that in the extraction step, the contact time with ethylene glycol was as shown in Table 1.

[Example 7]
The same procedures as in Example 1 were carried out except that sodium hydroxide was not added in the depolymerization step.

[Example 8]
The same procedure as in Example 1 was repeated except that in the purification step, hot ethylene glycol at 95° C. was used instead of hot water.

[Examples 9 to 12]
The purification step was carried out in the same manner as in Example 1, except that the temperature of the hot water was as shown in Table 2.

[Example 13]
The purification step was carried out in the same manner as in Example 1, except that the amount of adsorbent added and the stirring time were as shown in Table 2.

[Examples 14 to 17]
In the purification step, the ion exchange treatment and activated carbon treatment of the transparent solution after filtration were carried out in the same manner as in Example 1, except that two glass columns were filled with an ion exchange resin and activated carbon, respectively, and the solution was passed through the column filled with the ion exchange resin and the column filled with the activated carbon in that order, and then crystallization was carried out. The loading amount and passing rate of each adsorbent are as shown in Table 2. In addition, in each example, the time from when the solution entered each column until it came out (contact time with the adsorbent) was 6 minutes, 36 seconds, 15 seconds, and 7 seconds.

[Examples 18 to 25]
The same procedure as in Example 1 was repeated except that the amounts of activated carbon and ion exchange resin used in the purification step were changed as shown in Table 3.

[Examples 26 to 30]
In the purification step, the ion exchange treatment and activated carbon treatment of the transparent solution after filtration were carried out in the same manner as in Example 1, except that two glass columns were filled with an ion exchange resin and activated carbon, respectively, and the solution was passed through the column filled with the ion exchange resin and the column filled with the activated carbon in that order, and then crystallization was carried out. The loading amount and passing rate of each adsorbent are as shown in Table 4. In addition, in each example, the time from when the solution entered each column until it came out (contact time with the adsorbent) was 12 minutes 19 seconds, 1 minute 32 seconds, 57 seconds, 4 seconds, and 3 seconds.

[Comparative Example 1]
The same procedure as in Example 1 was carried out, except that the extraction step was not carried out.

[Comparative Example 2]
The same operations as in Example 1 were carried out except that the extraction step was not carried out, and further, in the depolymerization step, the obtained depolymerized solution was not subjected to reprecipitation, and ethylene glycol was removed by distillation under reduced pressure to obtain crude BHET (high concentration method), and then hot ethylene glycol at 95° C. was used instead of hot water in the purification step.

[Comparative Example 3]
The extraction step was not carried out, and further, in the depolymerization step, depolymerization was carried out under the conditions of 18 wt% fabric, 81 wt% ethylene glycol, and 1 wt% water. The ethylene glycol solution containing the crude BHET after depolymerization was not subjected to reprecipitation, but was directly transferred to the purification step. At this time, the ethylene glycol solution containing the crude BHET had a crude BHET content of 23 wt%, 76 wt% ethylene glycol, and 1 wt% water. The crude BHET for characteristic evaluation was obtained by extracting a portion from the ethylene glycol solution containing the crude BHET after depolymerization, and collecting it by a high concentration method in which ethylene glycol is removed by distillation under reduced pressure.

In the purification step, the temperature of the ethylene glycol solution containing the crude BHET after depolymerization was kept at 80° C., and filtration was carried out using a 1.6 μm filter. The obtained solution was passed through a column packed with 100 mL of activated carbon (Taikyo SGA, manufactured by Futamura Chemical Co., Ltd.) at a flow rate of 250 mL/h (space velocity 2.5 hr ^-1 ), and then passed through a multi-layer column packed with 25 mL of a cation exchange resin (Amberlite TM IR120B, manufactured by Organo Corporation, H ⁺ type, apparent density: 790 g/L-R, amount of cation exchange group: ≧1.80 mol/L-R) and 25 mL of anion exchange resin (Amberlite TM IRA96SB, manufactured by Organo Corporation, free base type, apparent density: 670 g/L-R, amount of anion exchange group: ≧1.25 mol/L-R) (space velocity 5.0 hr ^-1 ), and then crystallization was carried out. The procedure was carried out in the same manner as in Example 1 except for the above operations.

In Comparative Examples 1 to 3, the extraction process was not performed, so the removal of ionic dyes was insufficient even after the purification process, and the color tone and absorbance intensity measurements of crude BHET and purified BHET were poor.

[Comparative Examples 4 to 6]
The extraction step was carried out in the same manner as in Example 1, except that the contact time with ethylene glycol was as shown in Table 5. In Comparative Example 4, no ion exchange resin was added, and in Comparative Example 5, no activated carbon was added.

In Comparative Examples 4 to 6, the contact time with ethylene glycol in the extraction process was too long, which led to the progress of decomposition of the polyester fibers, resulting in a significantly poor yield in the extraction process.

[Comparative Example 7]
In the extraction step, the glass tube in which the recovered fabric was packed was changed to a Soxhlet extractor equipped with a reflux condenser, and the contact time with ethylene glycol was changed to 90 minutes, but the same procedure was followed as in Example 1. Note that, at this time, the ethylene glycol vapor reached the cooling tube without coming into contact with the packed fabric.

[Comparative Example 8]
In the extraction step, the cut fabric was not packed in a glass tube but directly placed in a 2 L four-neck flask and immersed in EG, a Dimroth condenser was directly connected to the 2 L four-neck flask instead of a glass tube, and the temperature setting of the mantle heater was changed to 150° C., but the same procedures as in Example 1 were carried out.

[Comparative Example 9]
In the extraction step, as described in Example 1 of Patent Document 1, the cut fabric was not filled in a glass tube but directly placed in a 2L four-neck flask and immersed in ethylene glycol, and a Dimroth condenser was directly connected to the 2L four-neck flask without connecting the glass tube, and the set temperature of the mantle heater was changed to 150°C. After contacting the fabric with ethylene glycol for 30 minutes, the ethylene glycol in the four-neck flask was replaced with fresh ethylene glycol and the same operation was carried out. This was repeated three times in total so that the total contact time was 90 minutes. Thereafter, the temperature of the fabric was lowered to room temperature, and the fabric was squeezed with a press roll to squeeze out the ethylene glycol.

In the depolymerization step, 52.5 g of ethylene glycol and 0.025 g of sodium hydroxide were added to 12.3 g of the extracted fabric containing 20% by weight of ethylene glycol to carry out depolymerization. The ethylene glycol solution containing the crude BHET after depolymerization was not reprecipitated and was directly transferred to the purification step. Crude BHET for characteristic evaluation was obtained by extracting a portion of the ethylene glycol solution containing the crude BHET after depolymerization and collecting it by a high concentration method in which ethylene glycol was removed by distillation under reduced pressure.

In the purification step, as described in Example 1 of Patent Document 1, the temperature of the ethylene glycol solution was kept at 85 ° C., and filtration was performed using a 1.6 μ filter. The obtained solution was passed through a column packed with 50 mL of activated carbon (Mitsubishi Chemical Corporation, Diahope 006) at a spatial velocity of 3.0 hr ^-1 , then passed through a column packed with 20 mL of cation exchange resin (Organo Corporation, Amberlite TM IR120B, H ⁺ type, apparent density: 790 g / L-R, amount of cation exchange group: ≧ 1.80 mol / L-R) at a spatial velocity ^of 7 hr -1, and further passed through a column packed with 6.7 mL of the cation exchange resin and 13.3 mL of anion exchange resin (Organo Corporation, Amberlite TM IRA96SB, free base type, apparent density: 670 g / L-R, amount of anion exchange group: ≧ 1.25 mol / L-R), and then crystallization was performed. The rest of the procedure was the same as in Example 1.

[Comparative Example 10]
In the extraction step, as described in Example 5 of Patent Document 1, the cut fabric was fixed to a conveyor so as to be arranged in series, and was continuously extracted by a countercurrent extraction device. The extraction was performed by inserting the fabric from one side of the fabric inlet of the extractor at 60 g/hr, injecting 195°C ethylene glycol from the other ethylene glycol inlet at 1,200 g/hr, discharging the ethylene glycol after extraction from the ethylene glycol outlet near the fabric inlet, and discharging the fabric from which the coloring components had been extracted from the fabric outlet near the ethylene glycol inlet, and the contact time between the fabric and ethylene glycol was 40 minutes. After that, the fabric was cooled to room temperature, and squeezed with a press roll to squeeze out the ethylene glycol.
The procedure was the same as in Comparative Example 9 except for the above-mentioned operations.

In Comparative Examples 7 to 10, the temperature of the ethylene glycol liquid that came into contact with the fabric during the extraction process was low, and there was no contact with ethylene glycol vapor, so the ionic dye was not sufficiently removed even after the purification process, and the color tone and absorbance intensity measurements of the purified BHET were poor.

According to the present invention, coloring components can be sufficiently removed from polyester fabric containing ion-bonding dyes, and BHET having excellent color tone can be efficiently obtained. Since the fabric can be regenerated into PET resin of the same quality as that before disposal, the present invention is useful in the chemical recycling of fibers and textile products.

Claims (5)

A method for obtaining bis-2-hydroxyethyl terephthalate from a polyester fabric containing more than 0.0% by weight and not more than 10.0% by weight of an ion-bonding dye, comprising the steps of:
(1) A step of contacting a polyester fabric containing an ion-bonding dye with ethylene glycol vapor at 195° C. or more and 205° C. or less and ethylene glycol liquid at 150° C. or more and 195° C. or less simultaneously for 5 minutes or more and less than 150 minutes to extract a coloring component; (2) A step of depolymerizing the polyester fabric obtained after extraction by carrying out the step (1) with ethylene glycol to recover crude bis-2-hydroxyethyl terephthalate; (3) A step of dissolving the crude bis-2-hydroxyethyl terephthalate obtained by carrying out the step (2) in a solvent and purifying it to obtain bis-2-hydroxyethyl terephthalate. The method for obtaining bis-2-hydroxyethyl terephthalate according to claim 1, wherein the main component of the solvent used in step (3) is water. The method for obtaining bis-2-hydroxyethyl terephthalate according to claim 2, wherein the step (3) consists of the following steps (3a) to (3c) only:
(3a) A step of dissolving the crude bis-2-hydroxyethyl terephthalate obtained by carrying out the step (2) in hot water at 60°C to 100°C and filtering the solution while hot; (3b) A step of subjecting the aqueous solution obtained by carrying out the step (3a) to both activated carbon treatment and ion exchange treatment at 60°C to 100°C; (3c) A step of cooling the aqueous solution obtained by carrying out the step (3b) to 30°C or less to crystallize and recover bis-2-hydroxyethyl terephthalate. The method for obtaining bis-2-hydroxyethyl terephthalate according to claim 3, wherein in the step (3b), the volume ratio of the adsorbents used in the activated carbon treatment and the ion exchange treatment, respectively, represented by the following formula 1, is 0.10 or more and 100.00 or less.
(Formula 1) Volume ratio = Volume of adsorbent used in ion exchange treatment (mL) / Volume of adsorbent used in activated carbon treatment (mL) The method for obtaining bis-2-hydroxyethyl terephthalate according to claim 3, wherein in the step (3b), the activated carbon treatment and the ion exchange treatment are carried out by passing the liquid through columns packed with the respective adsorbents, and the space velocity is from 2.1 hr ^-1 to 300.0 hr ^-1 , respectively.