Method for extracting coloring component from colored polyester fiber, and method for obtaining ester monomer and further regenerated polyester from colored-component-extracted polyester fiber

Abstract

To provide a high-efficiency method for extracting a coloring component from a colored polyester fiber, the method being capable of suppressing re-attachment of the coloring component to the fiber due to retention of the extract solution, and being capable of processing in a short time even when the colored polyester fiber is packed such that a load of 10 kg / m2 or more is applied to some portion of a bottom surface of a polyester-fiber-packed section in an extraction apparatus.SOLUTION: A method for extracting a coloring component from a colored polyester fiber comprises passing a heated liquid and a heated vapor of a glycol or monoalkyl ether alcohol through the colored polyester fiber to extract the coloring component, where the passage of the heated liquid and the passage of the heated vapor are performed in the same direction and in the same flow sense.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates mainly to a method for extracting colored components from colored polyester fibers. [Background technology]

[0002] As a result of maintaining a social system based on mass production, mass consumption, and mass waste up until now, various adverse effects on the environment have been confirmed, such as the depletion of natural resources and the destruction of nature caused by resource extraction. Therefore, in order to continue sustainable growth through the efficient use of limited resources, it has become essential to reduce the amount of waste generated and to build a recycling-oriented social system that reuses and recycles waste so as not to burden the environment.

[0003] To realize such a recycling-oriented social system, it is necessary to establish recycling systems such as thermal recycling, material recycling, and chemical recycling. With regard to plastic products, attention is being focused on material recycling technology that can be recycled into products at low cost, and chemical recycling technology that can be recycled without compromising quality.

[0004] Polyester fiber, which is used in a wide range of applications due to its low cost, excellent mechanical properties, and dry feel, is also being considered for regeneration through material recycling and chemical recycling, and the key to this is technology for the prior removal of coloring components such as disperse dyes and cationic dyes. By carrying out material recycling and chemical recycling processes using polyester fiber from which coloring components have been removed in advance as raw material, the quality of the recycled polyester can be easily improved.

[0005] Various methods have been proposed so far as techniques for removing coloring components from polyester fibers. For example, Patent Documents 1 and 2 propose techniques for extracting coloring components from polyester using ethylene glycol liquid or alcohol ether liquid.

[0006] Patent Document 3 proposes a technology in which an alcohol ether liquid and steam are brought into contact with polyester in a countercurrent (reverse) flow manner by reflux operation to extract colored components, while Patent Document 4 proposes a technology in which ethylene glycol liquid and steam are brought into contact with polyester in a countercurrent (reverse) flow manner by reflux operation to extract a certain amount of colored components, and then the extracted components are refined in a chemical recycling process to obtain high-purity ester monomers. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-330444 [Patent Document 2] Japanese Patent Publication No. 2020-176258 [Patent Document 3] Japanese Patent Application Publication No. 2020-133089 [Patent Document 4] International Publication No. 2023 / 176649 Summary of the Invention [Problem to be solved by the invention]

[0008] The coloring component extraction techniques described in Patent Documents 1 and 2 employ a simple extraction method in which a liquid having excellent solubility for the coloring component is brought into contact with polyester at a temperature equal to or higher than the glass transition point of the polyester, but have the problem of low extraction efficiency of the coloring component. Extracting most of the coloring component contained in polyester fibers requires long-term treatment, which also reduces the yield of polyester fiber, making the method unsuitable for commercialization.

[0009] Therefore, the above technology was improved, and in the coloring component extraction technology described in Patent Document 3, an alcohol ether liquid and steam are brought into countercurrent (reverse) contact with the polyester by reflux operation, which succeeds in increasing the extraction efficiency of the coloring components. However, as described in this technology, after the coloring component extraction, the polyester fiber is taken out and placed in deionized water at 25°C to remove excess solvent on the surface, and then baked and dried at 100°C, which means that an extra step of removing the alcohol ether liquid adhering to the polyester fiber is required before carrying out the chemical recycling process, and in addition, despite the improvement, a more efficient technology for removing coloring components was desired.

[0010] The coloring component extraction technology described in Patent Document 4 solves the above problem by combining a technology in which ethylene glycol liquid and vapor are brought into countercurrent (reverse) contact with polyester through a reflux operation to extract a certain amount of coloring components, and then in a chemical recycling process, the ester monomer aqueous solution is subjected to impurity filtration and adsorption treatment, followed by crystallization purification.

[0011] However, in the method of bringing the extraction liquid and its vapor into contact with the polyester in a countercurrent manner as described in Patent Document 3 or 4, it was found that when a large amount of colored polyester fibers is put into the extractor and extraction treatment is carried out simultaneously with the liquid and the vapor, the extraction of the colored components does not proceed uniformly and the extraction efficiency drops significantly. After extensive investigation, it was found that when the filling height or packing density of the polyester fibers in the extractor increases, specifically when the load applied to any point on the bottom of the polyester fiber filling section in the extractor exceeds 10 kg / m 2 It was confirmed that when colored polyester fibers are packed in the above manner, the permeability and breathability of the extraction liquid and its vapor deteriorate, causing uneven flow, and as a result, the extraction liquid accumulates from the bottom to the middle layers of the polyester fiber packing. When the extraction liquid contaminated with coloring components accumulates from the bottom to the middle layers of the polyester fiber packing, not only does the extraction rate of the coloring components decrease, but the coloring components also reattach to the polyester fibers, resulting in a significant decrease in the efficiency of coloring component extraction for the polyester fibers packed in the middle layer and below.

[0012] The object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a method for reducing the load applied to any point on the bottom surface of the polyester fiber filling section of an extraction device to 10 kg / m 2 The present invention provides a highly efficient method for extracting colored components, which can process the material in a short time even when colored polyester fibers are packed in the above amount. [Means for solving the problem]

[0013] The above-mentioned problems can be solved by a method for extracting colored components by passing a heated liquid of glycol or monoalkyl ether alcohol through colored polyester fibers and passing heated steam through the fibers, in which the passing of the heated liquid and the passing of the heated steam are carried out in the same direction and in the same orientation. [Effects of the Invention]

[0014] According to the present invention, in the method for extracting colored components from colored polyester fibers, it is possible to suppress the redeposition of colored components on the fibers due to the retention of the extraction liquid, and it is possible to prevent the load applied to any point on the bottom surface of the polyester fiber filling section of the extraction device from being 10 kg / m 2 Even when the colored polyester fibers are packed in the above amount, a highly efficient method for extracting colored components can be provided, which allows processing in a short time. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention relates to a method for extracting colored components by passing a heated liquid or heated vapor of glycol or monoalkyl ether alcohol through colored polyester fibers, and the method involves passing the heated liquid and the heated vapor through the fibers in the same direction. The present invention will be described in detail below.

[0016] The polyester described in this invention refers to polyesters in general that can be molded, such as polyethylene terephthalate (PET), polypropylene terephthalate (polytrimethylene terephthalate), polybutylene terephthalate, polyethylene naphthalate, polylactic acid, etc. Examples of molded polyester products include textile products, film products, and resin products, and the present invention is suitable for removing colored components from dye-containing textile products and removing coating layers containing heat-degraded colorants from coating layer-containing film products, but is most suitable for removing dyes from PET fibers, which are widely distributed as clothing fibers.

[0017] The polyester described in the present invention may also be a copolymer polyester mainly composed of the above polyester, and examples of copolymerizable dicarboxylic acid units contained in the copolymer polyester include aromatic dicarboxylic acids such as isophthalic acid and sulfoisophthalic acid salts, and aliphatic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and adipic acid, and examples of diol units include, but are not limited to, ether diols such as diethylene glycol, polyethylene glycol, and polytetramethylene ether glycol. Examples of copolymer polyesters suitable for the present invention include isophthalic acid-copolymerized PET, sulfoisophthalic acid-copolymerized PET, and polyethylene glycol-copolymerized PET, which are widely distributed as clothing fibers.

[0018] The polyester fiber described in the present invention refers to fibers and structures made thereof in general, and may be a monofilament yarn, a multifilament yarn, a spun staple yarn, or a twisted yarn made by combining these. It may also be a fabric (woven fabric) made by knitting or weaving these fibers or yarns, or a cut piece of fabric, or a garment made by processing and sewing these. In particular, in the present invention, from the viewpoint of excellent handleability during extraction of coloring components, the polyester fiber is preferably in the form of a yarn and / or fabric (hereinafter referred to as a yarn and / or fabric containing polyester fiber), and particularly preferably a garment or a piece of fabric (woven fabric) cut into several centimeters square.

[0019] The yarn and / or fabric containing the polyester fiber described in the present invention may contain fibers other than polyester fibers. Examples of fibers other than polyester include, but are not limited to, cotton, regenerated cellulose, nylon, acrylic, polyurethane, and polypropylene. This method is particularly suitable for polyester / cotton blended yarns, which are widely available on the market. To efficiently obtain coloring component-extracted polyester fibers and ensure high quality of the purified ester monomers obtained as a result, the polyester fiber content in the yarn and / or fabric is preferably 35% by weight or more, more preferably 50% by weight or more, and most preferably 65% ​​by weight or more.

[0020] The origin of the colored polyester fiber described in the present invention is not limited, and it may be fabric, cloth, or cloth fragments before product processing, or may be derived from clothing, interior fabrics such as curtains, sofa fabrics, carpets, etc., or industrial textile materials such as airbags, seat belts, car seat fabrics, etc. From the viewpoint of product recycling, offcuts generated in the clothing manufacturing process after dyeing of fabrics (cloths) or clothing discarded without being worn are preferred, and worn clothing collected from consumers, used interior fabrics, industrial textile materials, and cut pieces thereof are particularly preferred.

[0021] The coloring component in the present invention refers to a substance that absorbs light having a wavelength of 400 nm or more and 800 nm or less, and is mainly a dye compound for fibers and its modified products. The dye types include, but are not limited to, disperse dyes and cationic dyes, which are dyes for polyester.

[0022] Since the present invention relates to a technology for extracting the coloring component in a colored polyester fiber and decolorizing the polyester fiber, there is no point in applying the technology of the present invention when the colored polyester fiber contains an extremely small amount of the coloring component. In the present invention, a colored polyester fiber is defined as one whose integrated value of visible light absorbance intensity calculated by the following method is 5 or more. Note that when fabric pieces with an integrated value of visible light absorbance intensity of 5 or more and fabric pieces with an integrated value of less than 5 are mixed and are difficult to separate, there is no problem in applying the present invention to such mixed fabric pieces.

[0023] The integrated value of visible light absorbance is calculated as follows. First, a mixed solvent of water and hexafluoroisopropanol (HFIP) (2 mL water: 8 mL HFIP) is prepared, and the polyester is dissolved in this mixed solvent to form a 1.0 wt % polyester solution. If the polyester is difficult to dissolve, it is dissolved in HFIP before preparing the mixed solvent, and then water is added. The polyester solution is filtered through a 0.2 μm filter, and the absorbance intensity of the filtered polyester solution is measured at 1 nm intervals using a spectrophotometer (e.g., Hitachi High-Tech Science Corporation, U3010 spectrophotometer) in wavelength scan mode from 400 nm to 800 nm. The sum of the obtained absorbance intensities is calculated as the integrated value. If the absorbance intensity of the polyester is at the upper limit of the measured intensity, a 0.25 wt % polyester solution is prepared and its absorbance is measured in the same manner. The integrated value is calculated as four times the sum of the obtained absorbance intensities.

[0024] In the coloring component extraction method of the present invention, it is essential to use glycol or a monoalkyl ether alcohol as the extraction solvent because of its excellent ability to extract polyester dyes from polyester fibers. Ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monobutyl ether are particularly preferred because of their excellent polyester dye extraction efficiency. Ethylene glycol is the most preferred extraction solvent because it not only provides the best polyester dye extraction efficiency but also eliminates the need for a step of removing the extraction solvent before chemically recycling the polyester fibers by depolymerizing them in ethylene glycol after coloring component extraction, making it the most advantageous in terms of operation.

[0025] In the coloring component extraction method of the present invention, it is essential to pass and aerate a heated liquid and heated steam of glycol or monoalkyl ether alcohol through the colored polyester fiber filling section (colored polyester fibers filled in an extraction vessel), respectively. Passing the heated liquid serves to extract and discharge the coloring components. Since the extracted coloring components reattach to the polyester fibers and contact with the heated steam becomes impossible, it is preferable that the contact form between the colored polyester fibers and the heated liquid be liquid passing rather than immersion. The heated steam serves to improve the coloring component extraction rate by scission of the polyester molecular chain and relaxation of the crystalline structure. Since the dye extraction rate is significantly reduced without contact with the heated steam, it is preferable to simultaneously pass heated steam through.

[0026] In the coloring component extraction method of the present invention, when passing a heated liquid of glycol or monoalkyl ether alcohol and passing heated steam, the compound species of the heated liquid and the heated steam do not need to be the same, but it is preferable that the compound species of the heated liquid and the heated steam are the same in order to facilitate reuse of glycol or monoalkyl ether alcohol contaminated with coloring components by distillation purification.

[0027] In the coloring component extraction method of the present invention, when passing a heated liquid of glycol or monoalkyl ether alcohol and aerating heated steam, the intervals between passing the heated liquid and aerating heated steam are not particularly specified. In the dye extraction step, only the heated liquid may be continuously supplied and the heated steam may be intermittently supplied, or only the heated steam may be continuously supplied and the heated liquid may be intermittently supplied. However, from the viewpoint of obtaining the best coloring component extraction rate, it is preferable to always simultaneously and continuously supply both the heated liquid and the heated steam from the start to the end of the coloring component extraction treatment. When alternately supplying heated liquid and heated steam, a shorter supply switching interval is preferable. Longer supply switching intervals tend to cause the added heated liquid to cool at the bottom of the device, reducing the extraction efficiency of colored components. For this reason, the supply switching interval is preferably shorter than 10 minutes (referring to a repeated cycle of adding heated liquid for 10 minutes, stopping the supply of heated liquid, adding heated steam for 10 minutes, and then stopping the liquid supply of heated steam). It is more preferable to set the supply switching interval to 5 minutes or less, more preferably 1 minute or less, and most preferably 0.25 minutes. Although the method of alternately supplying heated liquid and heated steam intermittently is inferior in extraction efficiency compared to simultaneous supply, it has the advantage of reducing the total amount of liquid and steam used per unit time for heated glycol or heated monoalkyl ether alcohol, thereby enabling the downsizing of the glycol or monoalkyl ether alcohol heating and vaporization equipment.

[0028] In the colored component extraction method of the present invention, when passing a heated glycol or monoalkyl ether alcohol liquid and aerating heated steam through the polyester fiber-packed section, the direction of the liquid and aeration is not limited, and colored components can be extracted. However, it is most preferable to pass the liquid and aerate in the same direction in the extraction vessel, i.e., in a parallel flow manner. By passing the heated liquid and aerating heated steam in a parallel flow manner, the flow of heated steam can prevent the heated liquid from drifting or stagnating, and the heated liquid can be quickly discharged from the polyester fiber-packed section. This prevents the load applied to any point on the bottom of the polyester fiber-packed section in the extraction device from exceeding 10 kg / m. 2Even when the colored polyester fibers are packed so that the flow rate is equal to or greater than the above, it is possible to extract most of the colored components in a short time. When the flow of the heated glycol or monoalkyl ether alcohol liquid and the flow of the heated steam are carried out in opposite directions, i.e., in a countercurrent manner, the load applied to any point on the bottom of the polyester fiber packed section in the extraction device is 10 kg / m 2 If the colored polyester fibers are packed so as to satisfy the above conditions, the heated liquid contaminated with the coloring component will stagnate from the lower to middle layers of the colored polyester fiber packed section, reducing the coloring component extraction rate and causing the coloring component to reattach to the polyester fibers, significantly reducing the efficiency of coloring component extraction from the polyester fibers packed in the middle layer and below. Note that the lower layer of the colored polyester fiber packed section described here means the lower part of the packed section of polyester fiber charged into the extractor, divided into three equal parts in the vertical height direction, and the middle layer means the central part of the packed section of polyester fiber charged into the extractor, divided into three equal parts in the vertical height direction.

[0029] In the coloring component extraction method of the present invention, in order to ensure the extraction time and sufficiently extract the coloring components, the contact times of the colored polyester fiber with the heated liquid and heated steam are each preferably 15 minutes or longer, more preferably 30 minutes or longer, and even more preferably 60 minutes or longer. On the other hand, in order to suppress decomposition of the polyester fiber and maintain the yield, the contact times are each preferably 120 minutes or shorter, more preferably 90 minutes or shorter, and even more preferably 60 minutes or shorter.

[0030] In the coloring component extraction method of the present invention, the temperature at which the heated liquid is introduced is preferably at least "(the boiling point of the heated liquid) -40°C," more preferably at least "(the boiling point of the heated liquid) -20°C," and even more preferably at least "(the boiling point of the heated liquid) -5°C," in order to improve the molecular mobility of the polyester and the coloring component and extract the coloring component more efficiently. Specifically, when ethylene glycol is selected as the heated liquid and heated steam to be introduced, the temperature at which the heated liquid is introduced is preferably at least 158°C, more preferably at least 178°C, and even more preferably at least 193°C, in order to improve the molecular mobility of the polyester and the coloring component and extract the coloring component more efficiently. On the other hand, the temperature at which the heated liquid is introduced is preferably at most 220°C, more preferably at most 193°C, in order to prevent decomposition of the polyester fiber due to excessive heating and maintain the yield.

[0031] In the coloring component extraction method of the present invention, from the viewpoint of improving the extraction efficiency of the coloring component, the temperature at which the heated steam is introduced is preferably equal to or higher than the boiling point of the heated steam, more preferably "(the boiling point of the heated steam) + 5°C," even more preferably "(the boiling point of the heated steam) + 10°C," and particularly preferably "(the boiling point of the heated steam) + 20°C." Specifically, when ethylene glycol is selected as the heated liquid and heated steam to be introduced, from the viewpoint of appropriately decomposing the polyester fiber, relaxing the crystalline structure, and improving the extraction efficiency of the coloring component, the temperature at which the heated steam is introduced is preferably 198°C or higher, more preferably 203°C or higher, even more preferably 208°C or higher, and particularly preferably 218°C or higher. On the other hand, from the viewpoint of suppressing excessive decomposition of the polyester fiber and maintaining the yield, the temperature at which the heated steam is introduced is preferably 230°C or lower, more preferably 218°C or lower.

[0032] In the coloring component extraction method of the present invention, it is preferable to extract the coloring component from the colored polyester fiber under a pressure of 0.1 MPa or more in terms of excellent operating costs. Operation at a pressure of less than 0.1 MPa not only requires the preparation of a pressure reducing facility but also makes it difficult to control the temperature of the heated liquid to be added in the high-temperature range where the coloring component extraction efficiency is excellent. On the other hand, it is preferable to extract the coloring component from the colored polyester fiber under a pressure of 0.2 MPa or less in terms of excellent operability in the extraction operation. Operation at a pressure higher than atmospheric pressure can raise the upper limit of the temperature of the heated liquid to be added, thereby promoting the extraction of the coloring component. However, this causes the decomposition of the polyester fiber to proceed, significantly reducing the yield, and raising the temperature to near the melting point of the polyester causes the polyester fiber to melt, significantly worsening operability. Therefore, a pressure of 0.2 MPa or less is preferable.

[0033] In the coloring component extraction method of the present invention, in order to more quickly discharge the heated ethylene glycol liquid contaminated with the coloring component from the colored polyester fiber packed section and improve the efficiency of coloring component extraction, the heated steam passing through the colored polyester fiber packed section is preferably introduced so that the linear velocity is 0.01 m / s or more, more preferably 0.02 m / s or more, and even more preferably 0.04 m / s or more. On the other hand, in order to suppress decomposition of the polyester fiber due to contact with excessive heated steam, the heated steam is preferably introduced so that the linear velocity is 0.06 m / s or less, more preferably 0.04 m / s or less.

[0034] In the coloring component extraction method of the present invention, from the viewpoint of efficiently extracting and discharging the coloring component, the heated liquid is preferably charged so that the linear velocity is 0.00001 m / s, more preferably 0.00005 m / s, even more preferably 0.0001 m / s, particularly preferably 0.0005 m / s or more, extremely preferably 0.0010 m / s or more, and most preferably 0.0020 m / s or more. On the other hand, if the amount of heated liquid charged is excessive, not only will the heated liquid contaminated with the coloring component remain, reducing the efficiency of coloring component extraction and causing a decrease in yield due to the progress of polyester fiber decomposition, but also steam will be difficult to pass through within the extraction apparatus, causing a dangerous increase in the internal pressure of the apparatus, so it is preferable to charge the heated ethylene glycol liquid passing through the colored polyester fiber packed section so that the linear velocity is 0.0030 m / s or less.

[0035] In the coloring component extraction method of the present invention, the device configuration is not limited, but an example is shown below. The coloring component extraction operation is carried out in an extraction vessel, which is the main body of the device. The extraction vessel may be equipped with at least one raw material (colored polyester fiber) inlet, heated liquid inlet, heated steam inlet, and liquid and steam outlets. The liquid and steam outlets may be integrated into one location. The extraction vessel preferably has a jacket-type heating structure or a covering structure made of heat-retaining and heat-insulating material.

[0036] As the extraction vessel, a typical cylindrical or rectangular tubular extraction vessel can be used, and a cylindrical extraction vessel is preferred because it is easy to keep warm, has few edges, and allows the heated liquid or heated steam to pass through uniformly. If the vessel is approximating a cylindrical or rectangular tubular shape, it may have a shape such as a truncated cone or truncated pyramid whose cross-sectional area varies in the axial direction of the cylinder or rectangular tubular. Furthermore, the bottom of the cylinder or rectangular tubular vessel may be flat, or may be spherical, conical, or the like.

[0037] In the colored component extraction method of the present invention, the heated liquid and heated steam are passed through and ventilated in the same direction. Therefore, the heated liquid inlet and heated steam inlet are located on the upper bottom (top surface) or a side surface near the upper bottom of a cylindrical or rectangular tubular extraction vessel, and the liquid and steam outlets are located on the lower bottom (bottom surface) or a side surface near the lower bottom on the opposite side of the colored polyester fiber-filled section, but are not limited thereto. The installation angles of the inlets and outlets are also not limited. Furthermore, when a typical cylindrical or rectangular tubular extraction vessel is used as the extraction vessel, the extraction vessel is preferably installed so that the axis of the cylinder or rectangular tubular is at an angle of 0° to 90° relative to the vertical height direction, with the vertical height direction being 0°, to allow the heated liquid to be rapidly discharged by gravity. Since a shallower angle is more advantageous for discharge, an angle of 0° to 45° is more preferable, with 0° being the most preferred. Furthermore, when the angle is greater than 45° and less than 90°, it is preferable to provide a rotation mechanism in the extraction vessel to ensure uniform contact with the heated liquid and heated steam. When the angle is more than 45° and not more than 90°, it is preferable to provide the outlet with a screw structure or the like that assists in discharging the liquid.

[0038] The colorant-extracted polyester fiber obtained by the colorant extraction method of the present invention may be used as a raw material to obtain a recycled polyester resin by material recycling. The colorant-extracted polyester fiber can be remelted in an extruder and pelletized to obtain a recycled polyester resin. Since the colorant-extracted polyester fiber obtained by the method described in the present invention has a lower molecular weight than general molding polyesters, it is preferable to increase the molecular weight of the recycled polyester resin by solid-state polymerization before processing it into a product. Furthermore, the colorant-extracted polyester fiber obtained by the colorant extraction method of the present invention may be used as a raw material to obtain a high-purity ester monomer by chemical recycling, and further, the high-purity ester monomer may be repolymerized to obtain a recycled polyester resin. An example of a method for obtaining a high-purity ester monomer is described below.

[0039] According to the color component extraction method of the present invention, colored polyester fibers are extracted using heated ethylene glycol liquid and heated steam from colored polyester fibers. The extracted polyester fibers are recovered with ethylene glycol still attached. Chemical recycling of ethylene glycol-attached colored polyester fibers is not required. The ethylene glycol-attached colored polyester fibers are transferred to a depolymerization device, where a metal hydroxide and / or transesterification catalyst is added as a depolymerization catalyst. The fibers are heated at 185°C to 210°C, preferably 195°C to 210°C, under atmospheric pressure for 1 hour to 6 hours. An ethylene glycol solution containing ester monomers can be obtained by depolymerizing the fibers for 1 hour to 6 hours. To control the amount of ethylene glycol attached and the molar ratio (molar amount of ethylene glycol units in the solution / molar amount of terephthalic acid units in the solution) of the ethylene glycol solution containing ester monomers obtained after depolymerization, the colored polyester fibers may be squeezed to remove some of the attached ethylene glycol, or additional ethylene glycol may be added. The ester monomer obtained by the described method is an ester monomer having two 2-hydroxyethyl groups, in which a dicarboxylic acid and ethylene glycol are condensed via an ester bond.

[0040] If the amount of ethylene glycol attached to the coloring component-extracted polyester fiber is too small, it becomes difficult to uniformly proceed with depolymerization and the yield of ester monomer decreases. Therefore, the amount of ethylene glycol attached per 1.0 part by weight of polyester fiber is preferably 1.0 part by weight or more, more preferably 1.6 parts by weight or more, even more preferably 2.3 parts by weight or more, and particularly preferably 2.5 parts by weight or more. Even if more than 10.0 parts by weight of ethylene glycol is attached, the yield of ester monomer remains the same, but the cost required for heating increases, which is undesirable. From the viewpoint of cost, the amount is preferably 9.0 parts by weight or less, more preferably 8.0 parts by weight or less, and even more preferably 6.0 parts by weight or less.

[0041] Examples of depolymerization catalysts for coloring component-extracted polyester fibers generally include metal hydroxides and transesterification catalysts. Metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide are preferred, while transesterification catalysts such as lithium acetate, sodium acetate, magnesium acetate, cobalt acetate, manganese acetate, and calcium acetate are preferred, but are not limited to these. From the standpoint of low cost and excellent depolymerization rate, it is more preferred to use sodium hydroxide in an amount ranging from 0.1% by weight to 2.0% by weight based on the coloring component-extracted polyester fibers.

[0042] When ester monomers are obtained by chemical recycling using the coloring component-extracted polyester fibers obtained by the coloring component extraction method of the present invention as raw materials, in order to improve the purity of the ester monomers, a method for purifying ester monomers, in which the step of obtaining purified ester monomers from an ethylene glycol solution containing ester monomers obtained by depolymerizing the coloring component-extracted polyester fibers, is preferably performed by a method for purifying ester monomers comprising only the following steps (A) to (D): (A) A step of removing ethylene glycol from the ethylene glycol solution containing the ester monomer after depolymerization until the ethylene glycol is in the range of 0 mass % or more and 20 mass % or less to recover the ester monomer. (B) A process of dissolving the recovered ester monomer in hot water at 85°C to 100°C and filtering it while hot. (C) A step of subjecting the filtered solution at a temperature of 85°C to 100°C to activated carbon treatment and / or ion exchange treatment. (D) A step of cooling the filtered solution at 85°C to 100°C to 30°C or less to crystallize and recover the ester monomer. The ion exchange treatment means exposing the target solution to an ion exchange membrane or an ion exchange resin.

[0043] In the method for obtaining ester monomers from coloring component-extracted polyester fibers according to the present invention, it is preferable to carry out a step of removing ethylene glycol from the ester monomers after depolymerization until the ethylene glycol content is in the range of 0 to 20% by weight. If the ethylene glycol content in the ester monomer is high, the yield will decrease in the subsequent hot filtration and crystallization steps, so the ethylene glycol content is more preferably 15% by weight or less, even more preferably 10% by weight or less, and most preferably 5% by weight or less.

[0044] Any of the following methods may be used as a step for removing ethylene glycol from the ester monomer after depolymerization. The first is a reprecipitation step in which an ethylene glycol solution of the ester monomer obtained by depolymerization is added dropwise to water adjusted to 30°C or less to obtain a cloudy solution, and then the ester monomer containing impurities is recovered using a filter. The water temperature is preferably 25°C or less, and more preferably 20°C or less, in terms of increasing the yield. The second is a distillation step in which ethylene glycol contained in the solution obtained by depolymerization is distilled off to increase the concentration. Note that, in terms of excellent color tone of the resulting ester monomer, it is preferable to employ the reprecipitation step or to use both steps in combination.

[0045] In the method of obtaining ester monomers from coloring component-extracted polyester fibers described in the present invention, a hot water dissolution step and a hot filtration step are preferably employed to remove impurities (such as metal compounds such as titanium oxide and inorganic compounds such as silica gel) contained in the colored PET fibers. Water is added dropwise in an amount of 1.0 to 40.0 parts by weight to 1.0 part by weight of the recovered ester monomer obtained in the ethylene glycol removal step, and the mixture is heated to 85°C or higher, more preferably 90°C or higher, and even more preferably 95°C or higher, and the mixture is passed through a filter to obtain a transparent high-temperature aqueous solution in which the ester monomers are dissolved.

[0046] The method for obtaining ester monomers from coloring component-extracted polyester fibers according to the present invention preferably includes an adsorption step in which an adsorbent such as activated carbon or an ion exchange membrane or ion exchange resin is added to the clear high-temperature aqueous solution after the filtration step to remove impurities from the aqueous solution. An activated carbon treatment step is more preferred because it is possible to adsorb impurities regardless of their structure, and an ion exchange resin can also be suitably used when it is clear that a cationic dye, which is a coloring component, remains.

[0047] When exposing to activated carbon or the like, it is preferable to pass the solution through a column packed with activated carbon or to add activated carbon directly to the solution. When using a column, for example, when passing a 2.5 wt% ester monomer aqueous solution, if the space velocity is low, the ester monomer is adsorbed and the yield decreases. Therefore, from the viewpoint of ensuring the yield of the ester monomer, the space velocity is set to 2.1 h -1 More than 8.0 hours is preferable. -1 More than 13.0 hours is more preferable. -1 More than 20.0 hours is more preferable. -1 More than 50 hours is particularly preferable. -1 On the other hand, 300.0 hours or more is most preferable. -1 If the space velocity is higher, colored components and impurities will not be sufficiently removed, so the space velocity should be set to 300.0 h -1 It is preferable to pass the liquid through the filter at a speed of 200.0 hours or less. -1 It is more preferable that it is less than 100.0 hours. -1 It is even more preferable that:

[0048] Furthermore, when activated carbon or the like is added directly to the solution and the adsorption treatment is carried out for 60 to 90 minutes, the amount added is preferably in the range of 1% by weight or more and 65% by weight or less relative to BHET. From the viewpoint of improving the impurity removal rate, the amount of activated carbon or the like added is more preferably 3% by weight or more, even more preferably 5% by weight or more, and most preferably 10% by weight or more. From the viewpoint of suppressing the amount of ester monomer adhesion to the activated carbon and improving the yield, the amount of activated carbon or the like added is more preferably 40% by weight or less, even more preferably 30% by weight or less, and most preferably 20% by weight or less. 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 is not essential depending on the properties of the adsorbent.

[0049] The method for obtaining ester monomers from coloring component-extracted polyester fibers according to the present invention preferably includes a crystallization step in which the clear, high-temperature aqueous solution after the adsorption treatment is cooled to precipitate the solid content of the ester monomers and perform solid-liquid separation. The cooling temperature is preferably 30°C or lower, more preferably 25°C or lower, and even more preferably 20°C or lower, in order to increase the crystallization yield. On the other hand, since freezing makes it impossible to recover the crystallized product, the cooling temperature is preferably 2°C or higher, more preferably 5°C or higher.

[0050] In the method of obtaining a high-purity ester monomer from a coloring component-extracted polyester fiber according to the present invention, a high-quality ester monomer having excellent color tone can be obtained by carrying out the purification step described above. The obtained high-quality ester monomer can be polymerized in the presence of a polymerization catalyst according to a known polyester polymerization method to produce a high-quality recycled polyester resin having excellent color tone, heat resistance, and drying properties.

[0051] Furthermore, recycled polyester fibers can be produced by melt-spinning the produced recycled polyester resin as a raw material according to a known polyester melt-spinning process. Furthermore, knitted and woven fabrics can be produced from the produced recycled polyester fibers according to a conventional method. Furthermore, recycled polyester nonwoven fabrics can be produced according to a known polyester melt-blowing process or spunbonding process.

[0052] The coloring component extraction method of the present invention can produce yarns and / or fabrics containing polyester fibers, particularly yarns and / or fabrics containing 35% by weight to 100% by weight of polyester fibers, in which the polyester fiber portion has a weight-average molecular weight of 2000 to 6500 and a sum of absorbance intensities in the range of 400 to 800 nm, measured at 1 nm intervals using a spectrophotometer, of 20 to 220 (hereinafter referred to as "extracted yarns and / or fabrics"). The polyester fibers in the polyester fiber portion of the extracted yarns and / or fabrics are coloring component-extracted polyester fibers from which coloring components have been extracted using the coloring component extraction method of the present invention. The extracted yarns and / or fabrics of the present invention are suitable for chemical recycling of polyester, and the polyester fiber content is 35% by weight or more, more preferably 50% by weight or more, and most preferably 65% ​​by weight or more, due to the excellent yield and quality of the ester monomer obtained by chemical recycling.

[0053] In the extracted yarn and / or fabric of the present invention, the weight-average molecular weight of the polyester fiber (coloring component-extracted polyester fiber) in the polyester fiber portion is 2000 or more and 6500 or less. When the weight-average molecular weight of the polyester fiber is 6500 or less, preferably 6000 or less, more preferably 5500 or less, even more preferably 5000 or less, particularly preferably 4500 or less, and most preferably 4000 or less, the time for solid polyester to disappear during depolymerization, i.e., the time for depolymerization to be completed, can be set to 30 minutes or less, thereby reducing the energy consumption required for chemical recycling. On the other hand, a weight-average molecular weight of 2000 or more is necessary for the polyester fiber to maintain its fibrous shape.

[0054] The extracted yarn and / or fabric of the present invention has a sum of absorbance intensities in the range of 400 nm to 800 nm when a 1 wt % solution of polyester fiber (coloring component-extracted polyester fiber) in polyester fiber is measured at 1 nm intervals using a spectrophotometer, of 20 to 220. When the sum of absorbance intensities is 220 or less, more preferably 160 or less, even more preferably 120 or less, particularly preferably 80 or less, and most preferably 40 or less, the quality of the ester monomer obtained by chemical recycling is good. On the other hand, when the sum of absorbance intensities is 20 or more, the coloring components derived from the recovered product can be retained in the ester monomer obtained by chemical recycling without significantly deteriorating the quality, and this can serve as a mark (traceable) that the product is recycled. [Example]

[0055] A. Color analysis of fiber and BHET The sample was placed against a black calibration plate using a Minolta CM-3700d spectrophotometer, and the color tone L*, a*, and b* values ​​were measured. When analyzing the color tone of a BHET sample, the sample may be enclosed in a colorless sample bag to a thickness of 1 mm. If the sample bag exhibits a slight hue, the values ​​should be corrected.

[0056] B. Integrated absorbance values ​​of colored polyester fiber and ester monomer A mixed solvent of water and hexafluoroisopropanol (HFIP) (2 mL water: 8 mL HFIP) was prepared, and polyester was dissolved in this mixed solvent to a solution concentration of 1.0 wt %. When polyester was difficult to dissolve, it was dissolved in HFIP before preparing the mixed solvent, and then water was added.

[0057] The polyester solution was filtered through a 0.2 μm filter, and the absorbance intensity of the filtered polyester solution was measured at 1 nm intervals from 400 nm to 800 nm in wavelength scan mode using a Hitachi High-Tech Science U3010 spectrophotometer, and the sum of the obtained absorbance intensities was calculated as an integral value. When the absorbance intensity of the polyester reached the upper limit of the measured intensity, a 0.25 wt % polyester solution was prepared and its absorbance was measured in the same way, and the integral value was calculated as four times the sum of the obtained absorbance intensities.

[0058] C. Integrated absorbance values ​​of colored components extracted from polyester fiber (top / middle / bottom rows) The integral value of the absorbance intensity was calculated essentially according to the method described in Example B. The polyester fiber after coloring component extraction was removed from the coloring component extraction device by dividing the polyester fiber packing section into three equal parts in the vertical direction: upper, middle, and lower. These were designated as coloring component-extracted polyester fiber (upper row), coloring component-extracted polyester fiber (middle row), and coloring component-extracted polyester fiber (lower row). Ten randomly selected pieces of cloth or fiber were taken from each of the polyester fiber samples taken from the upper, middle, and lower rows, and the adhering ethylene glycol was removed by vacuum drying at 80°C. 0.15 g of each piece was cut out. The integral value of the absorbance intensity of the cut fibers was calculated according to the method described in Example B., and the median (median of n = 10) was used as the integral value of the absorbance intensity of the coloring component-extracted polyester fiber (upper row, middle row, and lower row).

[0059] D. Linear velocity of heated liquid The volume of heated liquid V1 (m) injected per second was measured using a flow meter installed in the liquid injection section. 3 / s) was measured. Also, the vertical cross section of the cylindrical coloring component extraction device in the polyester fiber filling section with respect to the axial direction of the device was measured. 2 ) and the value obtained by dividing the vertical cross section S of the device by the volume V1 of the heated liquid introduced was determined as the linear velocity of the heated liquid passing through.

[0060] E. Linear velocity of heating steam The volume of heating steam V2 (m) injected per second was measured using a flow meter installed at the steam injection point.3 / s) was measured. Also, the vertical cross section of the cylindrical coloring component extraction device in the polyester fiber filling section with respect to the axial direction of the device was measured. 2 ) and the value obtained by dividing the vertical cross section S of the device by the volume V2 of the heated liquid introduced was taken as the linear aeration velocity of the heated liquid.

[0061] F. Stable operation The determination of whether stable operation was possible during the colored component extraction operation was carried out in three stages: S, A, and B, as follows.

[0062] (S) The liquid level of the heated liquid added to the polyester fiber filling section of the coloring component extraction device is not observed at all.

[0063] (A) The liquid surface of the heated liquid added was observed in the lower layer of the polyester fiber packed section of the coloring component extraction device, and there was a slight accumulation of the heated liquid.

[0064] (B) The liquid surface of the heated liquid introduced was observed in the middle layer of the polyester fiber filling section of the coloring component extraction device, and the stagnation of the heated liquid was noticeable.

[0065] G. Fiber Yield The fiber yield was calculated using the following formula: M2 / M1 x 100, where M1 (kg) is the weight of polyester fiber fed into the coloring component extraction device and M2 (kg) is the weight of polyester fiber recovered from the device after extraction. Note that M2 (kg) is the weight of polyester fiber recovered from the device after extraction, after adhering ethylene glycol has been removed by washing or vacuum drying.

[0066] H. Ester Monomer Quality Evaluation The quality of the ester monomer was evaluated based on the color tone and rated on a four-point scale of S, A, B, and C as follows.

[0067] (S) The color tone b* value of the ester monomer is -1.5 or more and less than 1.5.

[0068] (A) The color tone b* value of the ester monomer is 1.5 or more and less than 2.5.

[0069] (B) The color tone b* value of the ester monomer is 2.5 or more and less than 3.0. (C) The color tone b* value of the ester monomer is less than -1.5 or 3.0 or more. I. Evaluation of weight average molecular weight of polyester fiber The weight average molecular weight of the polyester fiber was measured by gel permeation chromatography under the following conditions: After the coloring component extraction, the polyester fiber filling portion of the coloring component extraction device was divided into three equal parts in the vertical height direction: upper, middle, and lower portions, and the polyester fiber was removed from the device, and the same weight was measured from each portion for measurement. Apparatus: Gel permeation chromatograph (GPC) (Waters-e2695) Detector: Differential refractive index detector RI (Waters-2414, sensitivity 128x) Column: Showa Denko Shodex HFIP806M (two columns connected) Solvent: hexafluoroisopropanol (0.01N sodium trifluoroacetate added) Flow rate: 1.0mL / min Column temperature: 30℃ Sample concentration: 0.8 mg / 1.0 mL Injection volume: 0.10mL Standard sample: Standard polymethyl methacrylate. J. Depolymerization completion time of polyester fiber The time to complete depolymerization of polyester fiber was defined as the time when the internal temperature reached 195°C during the depolymerization operation and immediately after the addition of sodium hydroxide, and the time when it was confirmed by visual observation that the polyester fiber had completely dissolved and a homogeneous depolymerized solution had been formed. Note that if the polyester fiber was completely dissolved before the addition of sodium hydroxide, the time was defined as "0 minutes."

[0070] [Example 1] 0.2 kg of fabric composed of PET fibers dyed with a black disperse dye containing 0.3 parts by weight of titanium dioxide was cut into 2 cm squares. A cylindrical glass device (covered with heat-insulating material) with an inner diameter of 12 cm and a height of 30 cm was prepared as the extraction vessel. It had a raw material inlet, heated liquid inlet, and heated steam inlet at the top, and a liquid and steam outlet at the bottom. The cylinder was set up so that its axis was aligned vertically. A metal filter was placed at the exhaust port of the extraction vessel to prevent the PET cloth pieces from falling, and 0.2 kg of PET cloth pieces were then loaded into the extraction vessel.

[0071] Ethylene glycol liquid at 195°C was sprayed from the heated liquid inlet at a rate of 11.3 mL per second (corresponding to a linear velocity of 0.0010 m / s). The ethylene glycol liquid passed through the PET fiber packed section along the axial direction of the cylindrical extraction vessel, and the ethylene glycol liquid contaminated with coloring components was quickly discharged from the outlet. Simultaneously with the start of the heated liquid injection, ethylene glycol steam at 210°C was injected from the heated steam inlet at a rate of 226.1 cm per second. 3 The ethylene glycol vapor was introduced at a volume equivalent to a linear velocity of 0.02 m / s. The introduced ethylene glycol vapor was partially condensed while passing through the PET fiber packed section along the axial direction of the cylindrical extraction vessel and was quickly discharged from the outlet.

[0072] The heated liquid and heated steam were continuously supplied for 30 minutes to extract the coloring components, after which the flow of heated liquid and heated steam was stopped and the device was air-cooled until the internal temperature reached 50°C or below. The coloring component-extracted PET fiber in the extraction device was packed to a width of 18 cm vertically from the bottom of the device. The cloth pieces packed in the upper part (0-6 cm from the top of the packing, divided into three equal layers vertically) were collected as the coloring component-extracted PET fiber (upper layer), the cloth pieces packed in the middle part (6-12 cm from the top of the packing, divided into three equal layers vertically) were collected as the coloring component-extracted PET fiber (middle layer), and the cloth pieces packed in the lower part (12-18 cm from the top of the packing, divided into three equal layers vertically) were collected as the coloring component-extracted PET fiber (lower layer).

[0073] The color component extracted PET fibers (top row), (middle row), and (bottom row) were each squeezed to adjust the amount of ethylene glycol attached to 1.6 parts by weight per part by weight of PET fiber, and 260 g of each was placed in a 2 L three-neck flask and mixed. The flask was heated to 195°C, and 1.5 g of sodium hydroxide was added. Depolymerization was carried out for 2 hours with stirring at a heating temperature of 210°C. After depolymerization, the flask was cooled to 120°C and the internal pressure was reduced to a minimum of 80 Pa while distilling off the ethylene glycol, yielding bis(2-hydroxyethyl) terephthalate (BHET, ester monomer) containing 15 wt% ethylene glycol.

[0074] 0.4 parts by weight of water was added to 1.0 part by weight of BHET containing 15% by weight of ethylene glycol, and the mixture was heated to 95°C, after which it was added dropwise to 2.8 L of water whose temperature had been adjusted to 30°C or less to obtain a cloudy white solution. The liquid from the resulting cloudy white solution was centrifuged to obtain crude BHET containing impurities as a solid content.

[0075] To 1 part by weight of the crude BHET obtained, 3 parts by weight of hot water heated to 98°C was added, and the mixture was filtered using a 1.6 μm filter. To the resulting clear filtrate, 0.1 parts by weight of activated carbon from Osaka Gas Chemicals and 0.1 parts by weight of ion exchange resin AMBERLITE IR120BH manufactured by Organo Corporation were added per 1.0 part by weight of crude BHET, and the mixture was stirred while maintaining the liquid temperature at 98°C. After 1 hour, the mixture was filtered using a 1.6 μm filter to remove the activated carbon. The resulting clear filtrate was cooled to below 30°C to crystallize BHET, and solid-liquid separation was performed by centrifugation to obtain purified BHET as a solid.

[0076] [Examples 2 to 7] The procedure of Example 1 was repeated except that the coloring component extraction time, i.e., the heated liquid introduction time and heated steam introduction time, were changed as shown in Table 1, to obtain coloring component-extracted polyester fibers and ester monomers.

[0077] [Examples 8 to 10] The same procedures as in Example 1 were carried out except that the temperature at which the heated liquid was introduced was changed as shown in Table 1, and colored component-extracted polyester fibers and ester monomers were obtained.

[0078] [Table 1]

[0079] [Examples 11 to 13] The same procedures as in Example 1 were carried out except that the temperature at which heated steam was introduced was changed as shown in Table 2, and colored component-extracted polyester fibers and ester monomers were obtained.

[0080] [Example 14] The procedure was carried out as in Example 1, except that the heated liquid introduction temperature, heated steam introduction temperature, and internal pressure in the extraction apparatus were changed as shown in Table 2, to obtain colored component-extracted polyester fibers and ester monomers.

[0081] [Examples 15 to 19] The same procedures as in Example 1 were carried out except that the amount of heated steam introduced was changed so that the linear velocity of the heated steam would be as shown in Table 2, thereby obtaining colored component-extracted polyester fibers and ester monomers.

[0082] [Table 2]

[0083] [Examples 20 to 24] The same procedures as in Example 1 were carried out except that the amount of heated liquid added was changed so that the linear velocity of the heated liquid was as shown in Table 3, and colored component-extracted polyester fibers and ester monomers were obtained.

[0084] [Example 25] The same procedure as in Example 1 was carried out except that the extraction apparatus was installed at an angle of 45° in the vertical direction, and colored component-extracted polyester fibers and ester monomers were obtained.

[0085] [Example 26] The extraction apparatus was changed to a cylindrical metal apparatus covered with heat insulating material, with a diameter of 31 cm and a height of 60 cm, and the amount of colored polyester fiber added was changed to 1.2 kg, but the same procedure as in Example 1 was carried out to obtain colored component-extracted polyester fiber and ester monomer. Note that in Example 26, since it was impossible to observe the polyester fiber filling portion, a determination of whether stable operation was possible was not made.

[0086] [Example 27] The procedure was carried out as in Example 1, except that the extraction apparatus was changed to a cylindrical metal apparatus covered with heat insulating material, with a diameter of 31 cm and a height of 60 cm, the amount of colored polyester fiber charged was changed to 1.2 kg, and the heating liquid charging temperature, heating steam charging temperature, and internal pressure in the extraction apparatus were changed as shown in Table 3, thereby obtaining colored component-extracted polyester fiber and ester monomer. Note that in Example 27, since it was impossible to observe the polyester fiber-filled portion, a determination of whether stable operation was possible was not made.

[0087] [Example 28] The procedure of Example 1 was repeated except that the heated liquid and heated steam to be fed were both changed to ethylene glycol monomethyl ether, the heating liquid feeding temperature and the heated steam feeding temperature were changed as shown in Table 3, and the coloring component-extracted polyester fiber was washed with water and dried before depolymerization, thereby obtaining a coloring component-extracted polyester fiber and an ester monomer.

[0088] [Comparative Example 1] The procedure of Example 1 was repeated except that the heated steam inlet in the extraction apparatus was positioned at the bottom instead of the top, the liquid outlet at the bottom was a sealed system to prevent steam from leaking from the liquid outlet at the bottom, an open steam outlet was newly installed at the top, and the heated steam was vented in a vertically upward direction, opposite to that in Example 1, to obtain colored component-extracted polyester fiber and ester monomer.

[0089] In Comparative Example 1, the heated liquid and heated steam were passed in opposite directions, i.e., countercurrent flow was used. Therefore, the heated steam acted as an obstacle, slowing the discharge rate of the heated liquid, and it was confirmed that the heated liquid contaminated with coloring components remained up to the middle layer of the polyester fiber packed section. As a result, the extraction rate of the coloring components from the polyester fibers packed in the middle and lower layers decreased, and the extracted coloring components reattached to the polyester fibers, resulting in insufficient extraction of the coloring components from the polyester fibers. Therefore, despite undergoing purification procedures such as activated carbon treatment and crystallization in the chemical recycling process, the absorbance integral value of the ester monomer exceeded 6, resulting in poor color tone.

[0090] Comparative Example 2 The same procedure as in Comparative Example 1 was carried out except that the extraction apparatus was installed at an angle of 45° in the vertical direction, and colored component-extracted polyester fibers and ester monomers were obtained.

[0091] In Comparative Example 2, as in Comparative Example 1, it was confirmed that the heated liquid contaminated with the coloring components remained up to the middle layer of the polyester fiber filling section. As a result, the extraction rate of the coloring components from the polyester fibers filled in the middle and lower layers decreased, and the extracted coloring components reattached to the polyester fibers, resulting in insufficient extraction of the coloring components from the polyester fibers. Therefore, as in Comparative Example 1, despite undergoing purification operations such as activated carbon treatment and crystallization in the chemical recycling process, the absorbance integrated value of the ester monomer exceeded 6, resulting in poor color tone.

[0092] Comparative Example 3 The same procedure as in Example 1 was carried out except that no heated steam was added, to obtain colored component-extracted polyester fibers and ester monomers.

[0093] In Comparative Example 3, the heated steam was not passed through, so the molecular chain scission and crystalline structure relaxation of the colored polyester fiber were insufficient, and the extraction rate of the coloring component was significantly reduced. Because the extraction of the coloring component from the polyester fiber was insufficient, the absorbance integrated value of the ester monomer exceeded 6, resulting in a poor color tone, despite undergoing purification procedures such as activated carbon treatment and crystallization in the chemical recycling process.

[0094] Comparative Example 4 The procedure was carried out as in Comparative Example 1, except that the time for adding the heated liquid and heated steam was 135 minutes, to obtain colored component-extracted polyester fibers and ester monomers.

[0095] In Comparative Example 4, the extraction treatment was carried out for a long time, and although the flow of the heated liquid and the flow of the heated steam were countercurrent, the extraction of the coloring components progressed to a minimum. However, the polyester fiber was immersed in the stagnant high-temperature liquid for a long time, which progressed the decomposition of the polyester fiber, resulting in a significantly low fiber yield of less than 50%.

[0096] [Table 3]

[0097] [Examples 29 to 31] The same procedure as in Example 1 was carried out except that the fabric to be added was a PET / cotton blended yarn as shown in Table 4, and a fabric containing coloring component-extracted polyester fiber and an ester monomer were obtained.

[0098] [Examples 32 to 35] The extraction apparatus was installed at a 45° inclination in the vertical direction, heated steam and heated liquid were alternately introduced at intervals shown in Table 4, and the total extraction treatment time was 60 minutes (separate contact with heated steam for a total of 30 minutes at intervals shown in Table 4, and with heated liquid for a total of 30 minutes at intervals shown in Table 4), but the same procedures as in Example 1 were carried out, thereby obtaining colored component-extracted polyester fibers and ester monomers.

[0099] [Examples 36 and 37] The same procedure as in Example 1 was repeated, except that the amounts of heated steam and heated liquid added were changed so that the linear velocities of the heated steam and heated liquid would be the values ​​shown in Table 4, to obtain colored component-extracted polyester fibers and ester monomers.

[0100] [Table 4] [Industrial Applicability]

[0101] According to the present invention, it is possible to suppress the redeposition of coloring components on the fibers due to the retention of the extraction liquid, and the load applied to any point on the bottom surface of the polyester fiber filling section of the extraction device is 10 kg / m 2 Even when colored polyester fibers are loaded as described above, by providing a highly efficient method for extracting colored components that can be processed in a short time, it is possible to simultaneously secure a large amount of polyester raw material for material recycling or chemical recycling and achieve high quality recycled polyester.

Claims

1. This is a method for extracting colored components by passing a heated liquid and a heated vapor of glycol or monoalkyl ether alcohol through colored polyester fiber, respectively, in which the passing of the heated liquid and the passing of the heated vapor are carried out in the same direction and in the same orientation.

2. 2. The method for extracting coloring components according to claim 1, wherein the colored polyester fibers are supplied as yarn and / or fabric containing colored polyester fibers.

3. 3. The method for extracting colored components according to claim 2, wherein the yarn and / or fabric contains 35% or more of colored polyester fibers.

4. 3. The method for extracting colored components according to claim 2, wherein the passing of the heated liquid of glycol or monoalkyl ether alcohol and the passing of the heated steam are carried out simultaneously.

5. 3. The method for extracting colored components according to claim 2, wherein the passing of the heated liquid of glycol or monoalkyl ether alcohol and the passing of the heated vapor are alternately carried out at intervals of 0.25 minutes to 10.0 minutes.

6. 6. The method for extracting colored components according to claim 4, wherein the heated liquid and the heated vapor are ethylene glycol.

7. 6. The method for extracting colored components according to claim 5, wherein the contact time between the colored polyester fiber and the heated liquid and heated steam of ethylene glycol is 15 minutes or more and 120 minutes or less, respectively, the introduction temperature of the heated liquid is 158°C or more and 220°C or less, and the introduction temperature of the heated steam is 198°C or more and 230°C or less.

8. 7. The method for extracting colored components according to claim 6, wherein the heated ethylene glycol steam is introduced so that the linear velocity of the heated ethylene glycol steam passing through the colored polyester fiber is 0.01 m / s or more and 0.06 m / s or less.

9. 7. The method for extracting colored components according to claim 6, wherein the heated ethylene glycol liquid is introduced so that the linear velocity of the heated ethylene glycol liquid passing through the colored polyester fiber is 0.0005 m / s or more and 0.0030 m / s or less.

10. 7. The method for extracting colored components according to claim 6, wherein the heated ethylene glycol liquid is introduced so that the linear velocity of the heated ethylene glycol liquid passing through the colored polyester fiber is 0.00001 m / s or more and 0.00300 m / s or less.

11. A method for obtaining an ethylene glycol solution containing an ester monomer, comprising heating a coloring component-extracted polyester fiber having 1.0 part by weight or more and 9.0 parts by weight or less of ethylene glycol liquid attached to 1.0 part by weight of polyester fiber, obtained by the method according to claim 6, in the presence of a metal hydroxide and / or an ester exchange catalyst to depolymerize the polyester fiber.

12. A method for obtaining a purified ester monomer, comprising sequentially carrying out the following steps (A) to (D) on an ethylene glycol solution containing an ester monomer obtained by the method according to claim 11: (A) A step of removing ethylene glycol from the ethylene glycol solution containing the ester monomer after depolymerization until the ethylene glycol concentration is in the range of 0 mass % or more and 15 mass % or less to recover the ester monomer. (B) A step of dissolving the recovered ester monomer in hot water at 85°C or higher and 100°C or lower and filtering the hot water (C) A step of subjecting the filtered solution at 85°C to 100°C to activated carbon treatment and / or ion exchange treatment. (D) A step of cooling the filtered solution at 85°C or higher and 100°C or lower to 30°C or lower to crystallize and recover the ester monomer.

13. A method for obtaining a recycled polyester resin, comprising the steps of: distilling off ethylene glycol from the purified ester monomer obtained by the method according to claim 12 under heating and reduced pressure, and polycondensing the resulting ester monomer.

14. A method for obtaining recycled polyester fibers, comprising melt-spinning the recycled polyester resin obtained by the method according to claim 13.

15. A method for producing a knitted or woven fabric or a nonwoven fabric from the recycled polyester fibers obtained by the method according to claim 14.

16. A yarn and / or fabric containing 35% by weight or more of polyester fiber, wherein the polyester has a weight average molecular weight of 2,000 or more and 6,500 or less, and when a 1% by weight solution of the polyester fiber portion is measured at 1 nm intervals using a spectrophotometer, the sum of the absorbance intensities in the range of 400 nm to 800 nm is 20 or more and 220 or less.

Images