JP2005255963A - Method for recovering ester monomer from fibrous polyester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently recovering a refined ester monomer from dyed fibrous polyester wastes through ameliorating the problems involved in conventional methods for chemically recycling such fibrous wastes. <P>SOLUTION: The method comprises (1) a step of contacting a colored fibrous polyester with ethylene glycol to extract a color component in the fibrous polyester to obtain a fibrous polyester ≥60 in color L-value, (2) a step of separating the resultant fibrous polyester from its mixture with the ethylene glycol, (3) a step of depolymerizing the ester component constituting the fibrous polyester with a glycol to obtain a glycol solution containing an ester monomer, and (4) a step of obtaining the objective refined ester monomer by refining the glycol solution. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for recovering ester monomers from fibrous polyester. More specifically, the present invention relates to a method of extracting a colored component from a colored fibrous polyester not granulated into pellets, chips, etc., decomposing the ester component into glycol, and recovering the ester monomer.

  Polyester, such as polyethylene terephthalate, is widely used as a fiber, film, resin molded product, etc. due to its excellent properties, but it is effective for polyester waste such as fiber waste, film waste, resin molded product waste generated in these manufacturing processes. Use is a problem to be solved in terms of cost reduction. Moreover, although the fiber, film, and resin molded product used as polyester products are usually discarded after use, this disposal is problematic as it deteriorates the environment. Therefore, as these treatment methods, material recycling, thermal recycling, chemical recycling, and the like have been studied, and various proposals have been made.

  Among these, as material recycling, plastic bottle waste collected mainly by local governments is subjected to pulverization, separation, and purification treatment to form beautiful pet flakes, and then the flakes are reused as pet molding materials. However, it is difficult to ensure uniform quality for fiber scraps, and it is extremely difficult to adopt this recycling method, and there are no examples.

  Thermal recycling, which converts polyester waste into fuel, has the advantage of reusing polyester combustion heat, but there are problems of loss of polyester raw material and generation of carbon dioxide, which is not preferable from the viewpoint of resource saving and environmental conservation. .

  Chemical recycling, on the other hand, returns polyester waste to the raw material monomer, which is then subjected to a polycondensation reaction again to produce new polyester, so there is little deterioration in quality associated with the recovery process, and it is suitable for closed-loop recycling. .

  As a recycling method of polyester waste by this chemical recycling, for example, in Patent Document 1, resin-like, fiber-like, or film-like polyester waste generated in a polyester production process is treated with ethylene glycol (hereinafter referred to as EG) with a specific amount ratio. Proposal of a method for obtaining a regenerated polyester by subjecting the resulting aromatic dicarboxylic acid bisglycol ester and its low polymer (BHT) to an unpurified polycondensation reaction again after depolymerization. Has been. However, this method has the advantage that the depolymerization time can be shortened and BHT with less impurities such as diethylene glycol can be obtained. As a result, a polymer having a high quality, particularly a high softening point, can be obtained. In addition, it is not possible to prevent the coloring caused by the ink, and there is a disadvantage that only a special case where the composition of the polyester waste and the recycled polyester is the same can be adopted.

  In addition, when fibers outside the polyester manufacturing process are to be collected, it may be unavoidable to mix fibers different from polyesters such as polyethylene, polypropylene, nylon, and cotton. Furthermore, even if the material is polyester, the one containing a dye is decomposed during a series of reactions such as depolymerization and dispersed in the recovered ester monomer as a coloring component, and the quality is remarkably deteriorated.

  Therefore, in Patent Document 2, when recovering terephthalic acid from polyester fiber waste, a polyester fiber waste separated from other fibers is pulverized and granulated into a crude polyester, and in the pretreatment step, The resulting crude polyester is treated by the glycolysis-transesterification method, and the resulting dimethyl terephthalate is hydrolyzed to form terephthalic acid. Further, alkylene glycol is added to and mixed with this terephthalic acid, which is suitable for the polymerization reaction. A method for recovering the slurry as a slurry of terephthalic acid / alkylene glycol ratio has been proposed.

  Further, in Patent Document 2, when the crude polyester contains a dye, the crude polyester is treated with a solvent having a temperature of 100 to 190 ° C. (for example, water, alkylene glycol, dimethylformamide, paraxylene, 2-heptanone, etc. It is described that the product is transported to the reaction step after passing through a discharging step in which the dye is extracted by being put in the inside.

  However, according to the study of the present inventor, the dye contained in the granulated crude polyester cannot be substantially extracted and removed with water or alkylene glycol, the efficiency is low even with other extractants, and the subsequent processing steps It has become clear that the problem is that the product quality is degraded when the extractant is loaded and the extractant remains.

  In addition, as a method of chemically recycling PET bottle waste, the present inventors depolymerized the PET bottle waste with excess ethylene glycol (EG), and the resulting mixed solution of bis-β-hydroxyethyl terephthalate and EG is activated carbon. A method of obtaining high-purity bis-β-hydroxyethyl terephthalate by subjecting it to a purification treatment combining treatment, ion exchange treatment, crystallization treatment, etc., and further subjecting it to molecular distillation treatment (for example, Patent Document 3, Patent Document 4, etc.) ).

However, when trying to apply this method to chemical recycling of colored fibrous polyester waste, coloring components such as dyes contained in the fibrous polyester waste overload the purification process, and the method can be applied as it is. It became clear that it was not possible.
JP-A-48-61447 JP 2003-128626 A JP 2000-169623 A JP 2000-255839 A

  As a result of diligent research to develop a method for chemically recycling fibrous polyester, particularly colored fibrous polyester, the present inventor brought the colored fibrous polyester into contact with the extractant ethylene glycol without granulating. And found that the coloring component can be easily removed. Then, the ester component of the fibrous polyester subjected to this treatment is depolymerized with glycol to obtain a glycol solution containing an ester monomer, and the glycol solution is further purified (filtration treatment, adsorption treatment, ion exchange treatment, crystallization treatment, distillation treatment). It has also been found that a high-purity ester monomer can be efficiently obtained by attaching to these).

  Accordingly, an object of the present invention is to improve the problems of the conventional method of chemically recycling fibrous polyester, particularly colored fibrous polyester waste, and to efficiently recover ester monomers purified from the fibrous polyester. It is to provide.

  Another object of the present invention is to bring colored fibrous polyethylene terephthalate into contact with ethylene glycol to extract colored components contained in the fiber, and then subject to glycol decomposition and monomer purification to obtain colored fibrous polyethylene terephthalate. Is to provide a method for efficiently recovering ester monomers such as high purity bis (2-hydroxyethyl) terephthalate (hereinafter sometimes abbreviated as BHET).

  Still other objects and advantages of the present invention will become apparent from the following description.

An object of the present invention is a method for recovering an ester monomer from a fibrous polyester,
(1) An extraction step of bringing a colored fibrous polyester into contact with ethylene glycol, extracting a colored component in the fibrous polyester, and obtaining a fibrous polyester having a color L value of 60 or more,
(2) A separation step of separating the fibrous polyester from the mixture of the fibrous polyester and ethylene glycol after the extraction,
(3) A glycol decomposition step in which an ester component constituting the obtained fibrous polyester is depolymerized with glycol to obtain a glycol solution containing an ester monomer, and (4) a monomer that purifies the glycol solution to obtain a purified ester monomer. Purification process,
This is achieved by a method for recovering an ester monomer from a fibrous polyester comprising:

  In the extraction step, 5 to 50 parts by weight of ethylene glycol is used with respect to 1 part by weight of the fibrous polyester, the extraction temperature is 100 to 200 ° C., and the change value (ΔL) of the color L value of the fibrous polyester due to the extraction. (Value) is preferably 5 or more.

  In the glycol decomposition step, it is preferable to perform depolymerization with glycol after preliminarily decomposing the ester component constituting the fibrous polyester separated in the separation step using the ester monomer and / or oligomer.

  The monomer purification step is preferably performed by filtration, adsorption, ion exchange, crystallization, distillation, or a combination of these.

  Furthermore, the fibrous polyester is preferably made of polyethylene terephthalate, and the glycol used for depolymerization is preferably ethylene glycol.

  According to the present invention, there is provided a method for efficiently recovering an ester monomer purified from a fibrous polyester by improving the problems of a conventional method for chemically recycling a fibrous polyester, particularly a colored fibrous polyester. Can do.

<Fibrous polyester>
Examples of the fibrous polyester in the present invention include scraps generated in the production process of fibers such as short fibers and long fibers. Moreover, the waste which generate | occur | produced in processing processes, dyeing processes, sewing processes, etc., such as woven fabrics, knitted fabrics, nonwoven fabrics and the like using these fibers, and stuffed cotton can be mentioned. In addition, textile products such as trainers, jerseys, fleeces and umbrellas collected after being shipped to the market can be listed. Among these, it is clear and preferable that the scrap is generated from the fiber manufacturing process, the processing process using the fiber, the dyeing process, and the sewing process.

  Fibrous polyester is often discarded in the form of fibrous polyester alone or in the form of blended fibers with other fibers (for example, natural fibers), but when other fibers are mixed, recovery processing is performed. In order to increase the efficiency, it is preferable that the proportion of the fibrous polyester is 50% or more, further 70%, particularly 90% or more. It is preferable to use the UV discrimination method for determining whether or not the fiber waste is mainly made of fibrous polyester, or for determining the mixing ratio, but other methods may be used. It is preferable not to use the thing with a small ratio of fibrous polyester for this invention. In the present invention, the fibrous polyester is colored (dyed) with a dye, but an uncolored one may be mixed therein. In addition, there is no restriction | limiting in particular in the dye used for coloring of polyester, For example, direct dye, acid dye, basic dye, mordant dye, acid mordant dye, vat dye, disperse dye, reactive dye, fluorescent whitening dye, etc. Can be mentioned. Of these, disperse dyes are preferred.

  The fibrous polyester is not particularly limited in size as long as it does not interfere with extraction (discharging) in the extraction process, but in order to increase the extraction efficiency, the fiber length is 1 to 20 cm, It is preferable that it is 2-10 cm. Moreover, it is preferable that the length of one side of the fabric-like thing is 1-20 cm of the length near the said fiber length, Furthermore, it is 2-10 cm.

  As a polymer constituting the fibrous polyester, polyethylene terephthalate is particularly preferable. The polyethylene terephthalate is preferably a homopolymer, but may be a copolymer obtained by copolymerizing the third component in a small proportion (for example, 20 mol% or less with respect to the total acid component). Moreover, the blend polymer which mixed the other condensed resin in a small ratio (for example, 20 weight% or less with respect to the total weight) may be sufficient. These polymers usually contain modifiers (for example, pigments, dyes, stabilizers, etc.) for imparting the properties required for fibers.

<Extraction process>
The extraction step is a step of bringing a colored fibrous polyester into contact with ethylene glycol and extracting a colored component from the fibrous polyester. In the extraction process, the fibrous polyester is separated from other fibers as desired, and then cut into pieces to a predetermined size by cutting, cutting, pulverizing, etc., and then remaining in the fibrous form without granulation. A coloring component such as a dye contained in the fiber is extracted by contacting with glycol. At that time, the extraction treatment needs to be performed under the condition that the fibrous polyester is not substantially decomposed (depolymerized) by ethylene glycol. The method is not particularly limited, and for example, a batch extraction method, a multistage extraction method (multistage extraction method), a continuous countercurrent extraction method, or the like can be used. Also, a heated flow extraction method can be used. This batch extraction is a method in which the fibrous polyester is mixed and contacted with the whole amount of ethylene glycol as the extractant in one mixing tank, and is effective when the color value of the raw fibrous polyester is large. The multistage extraction method is a method in which the extraction method ethylene glycol is divided and the batch extraction method is repeated. At that time, both a parallel flow multistage extraction method and a countercurrent multistage extraction method can be used. As this multistage extraction method, for example, the Shanks method is useful. The continuous counter-current extraction method is a method in which the fibrous polyester and the ethylene glycol of the extractant are transferred to the counter-current, and the raw fibrous polyester to be supplied to the extraction device is an ethylene glycol containing a large amount of coloring components in the previous extraction process. The fibrous polyester before being brought into contact with and removed from the apparatus is brought into contact with newly supplied ethylene glycol. Examples of the heating flow extraction method include a method of spraying or flowing the ethylene glycol as the extractant onto the fibrous polyester. For example, there is a method in which ethylene glycol near the boiling point is caused to flow down and contact the fibrous polyester using a Soxhlet extraction apparatus. Examples of the extraction device include a Rotocel extraction device, a Kennedy extraction device, a Mig extraction device, a Bollman extraction device, a Hilbrandandt extraction device, a Bonoto extraction device, an Allis-Chalmers extraction device, a DeSmet extraction device, and a Chiyoda L-type extraction device. Can be mentioned.

  The amount of ethylene glycol required for extraction is preferably 5 to 50 parts by weight, more preferably 7 to 45 parts by weight, based on 1 part by weight of the fibrous polyester. This amount of ethylene glycol is the total amount of ethylene glycol used regardless of batch extraction or continuous extraction. Therefore, when extracting 1 weight part / hour fibrous polyester by a continuous extraction method, it is preferable to use 5-50 weight part / hour, Furthermore, 7-45 weight part / hour ethylene glycol. When batch extraction is performed in the batch extraction method, the total amount of ethylene glycol used in each extraction stage is 5 to 50 parts by weight, more preferably 7 to 45 parts by weight, based on 1 part by weight of the fibrous polyester. Part.

  The extraction temperature is preferably 100 to 200 ° C, more preferably 120 to 200 ° C, and particularly preferably 130 to 200 ° C. The higher this temperature, the higher the extraction efficiency and the processing time can be shortened. For example, when the temperature exceeds 190 ° C., the processing time can be shortened.

  This extraction (discharge) is performed until the color L value of the fibrous polyester is 60 or more, preferably 65 or more. At that time, the change value (ΔL value) of the color L value of the fibrous polyester is preferably 5 or more, more preferably 10 or more.

  Extraction with ethylene glycol depends on the color (L value) of the raw material polyester, but when the L value is 50 or less and further 40 or less in the first extraction, it is repeated twice or more to obtain the polyester color L. It is preferable to carry out until the value reaches 60 or more, and further 65 or more. This extraction time is preferably set to 10 minutes or more for one processing time in the multistage extraction method. The total extraction time is preferably 0.5 to 3.0 hours, more preferably 1.0 to 2.5 hours. Further, the extraction time (total extraction time) in the batch extraction method, the continuous alternating current extraction method, the heated flow extraction method and the like is preferably 0.5 to 3.0 hours, more preferably 1.0 to 2.5 hours. .

  As described above, the extraction in the present invention does not decompose (depolymerize) the fibrous polyester, and therefore it can be understood that the fiber shape does not substantially change before and after the extraction treatment. For this reason, it is preferable that the compound which exhibits a depolymerization effect does not exist in ethylene glycol of an extractant.

<Separation process>
In the separation step, the fibrous polyester is separated from the mixture of the fibrous polyester and ethylene glycol after the extraction. As this separation means, a known solid-liquid separation method (for example, pressing method, blow method, etc.) can be used.

  By this separation, the ethylene glycol remaining in the fibrous polyester is preferably 30% by weight or less, more preferably 1 to 25% by weight.

<Glycol decomposition process>
The glycol decomposing step is a step of obtaining a glycol solution containing an ester monomer by depolymerizing an ester component constituting the fibrous polyester separated in the separating step using glycol. In this glycol decomposition treatment, the fibrous polyester is usually subjected to glycol decomposition as it is, but depending on the case, the amount of free ethylene glycol may be reduced, or it may be subjected to glycol decomposition after other shapes are used. Is possible. For example, when the handling property at the time of decomposition treatment is increased or the glycol decomposition apparatus has structural limitations, it is preferable to granulate and then subject to the glycol decomposition reaction. In the case of granulating and subjecting to a glycol decomposition reaction, the granulating method is such that the fibrous polyester wetted with ethylene glycol is washed with water and dried, then melted and treated with a pelletizer, washed with water, and dried fibrous polyester. Preferred examples include a method of melting only a part of the surface and granulating, a method of compressing and granulating the fibrous polyester, and the like. The shape of the granulated product is preferably a cylindrical solid, and the diameter of the solid is 1 to 20 mm, more preferably 2 to 10 mm, and the length is 1 to 60 mm, further 2 to 50 mm. Is preferred.

  The ester component constituting the polyester is a unit in which a dicarboxylic acid and a diol component are bonded via an ester bond, and includes a polymer having a polymerization degree of 90 to 200 to an oligomer having a polymerization degree of 2 to 10. Therefore, according to the present invention, the ester component is depolymerized and decomposed to ester monomers exemplified by BHET having one dicarboxylic acid unit.

  As glycol, C2-C8 alkylene glycol, especially ethylene glycol are preferable. The depolymerization temperature is preferably 180 to 230 ° C, more preferably 190 to 220 ° C. The amount ratio of polyester and glycol during depolymerization is preferably 1: 9 to 3: 7 by weight. Preferred examples of the depolymerization catalyst include sodium hydroxide, sodium carbonate, sodium methylate, and zinc acetate. The amount of the catalyst is preferably 0.05 to 0.50% by weight, more preferably 0.15 to 0.40% by weight, based on the polyester. The depolymerization reaction time is preferably 0.5 to 7.0 hours, more preferably 0.5 to 5.0 hours.

  The concentration of the solid content in the resulting glycol solution is preferably 10 to 30% by weight, more preferably 15 to 25% by weight. This solid content is mainly composed of an ester monomer, and the ratio of the oligomer in the solid content is 1 to 30% by weight, and further 2 to 20% by weight.

  When the ester component constituting the fibrous polyester is an ethylene terephthalate unit and the decomposing agent is ethylene glycol, bis (2-hydroxyethyl) terephthalate (BHET) is obtained as an ester monomer by depolymerization.

  In this case, if the amount of polyester is too small relative to ethylene glycol, the amount of BHET produced will be less than the saturated solubility of ethylene glycol, which is greater than the maximum yield obtained for the total liquid volume subjected to deionization treatment. Since BHET can be obtained only with a small amount, it is not economical. On the other hand, if the amount of polyester is too large relative to ethylene glycol, BHET oligomers increase and the yield of BHET decreases. Further, if BHET is present in excess of the saturated solubility of ethylene glycol, BHET is precipitated, so that deionization treatment cannot be performed.

  The depolymerization is preferably carried out while providing a rectifying column in the reaction apparatus and distilling water from the reaction solution out of the system. At that time, the evaporated ethylene glycol is preferably returned to the system. Since the water content in the glycol solution obtained by performing the depolymerization reaction in this manner can be reduced, the hydrolysis reaction of the ester monomer can be suppressed. It is preferable to adjust so that the amount of water contained in the glycol solution is 0.5% by weight or less. The amount of moisture can be obtained by measuring the solution with an MK-SS Karl Fischer moisture meter manufactured by Kyoto Electronics Industry Co., Ltd.

(Preliminary disassembly)
In the glycol decomposition step, before the depolymerization with glycol, an ester component constituting the fibrous polyester is preliminarily decomposed using a polyester monomer and / or oligomer, and then the predecomposition product is depolymerized with glycol. preferable. When the polyester is polyethylene terephthalate, the polyester monomer is preferably BHET, and the oligomer is preferably BHET oligomer.

  The preliminary decomposition is preferably carried out by kneading the polyester with its monomers and / or oligomers (degree of polymerization 2 to 10) at a temperature of 200 to 300 ° C, preferably 230 to 280 ° C. The preliminary decomposition time is preferably 1.0 minute to 5.0 hours, more preferably 1.0 minute to 1.5 hours. At that time, the amount of the monomer and / or oligomer (degree of polymerization 2 to 10) with respect to the polyester is 0.1 to 1.0 part by weight, and further 0.2 to 0.8 part by weight per 1 part by weight of the polyester. It is preferable. The predegraded product obtained is composed of an ester component. The molecular weight is preferably 2 to 20, more preferably 3 to 10 in terms of polymerization degree.

  The preliminary decomposition is usually carried out under normal pressure. In this case, the low boiling point such as 30% by weight or less of 1 to 25% by weight of free ethylene glycol or water supplied into the system together with the fibrous polyester is used. It is preferable to carry out the components while evaporating and removing them out of the system. Moreover, you may implement under reduced pressure of the grade which the evaporate from a reaction system does not inhibit progress of reaction. In some cases, the evaporation can be carried out under pressure, preferably not more than the vapor pressure of ethylene glycol (for example, 1.3 MPa or less) while preventing the evaporated product from returning to the system.

  Next, the predecomposed product is preferably depolymerized at a temperature of 160 to 260 ° C., preferably 180 to 230 ° C. in the presence of a depolymerization catalyst using glycol which is a constituent component of polyester. Preferred examples of the depolymerization catalyst include sodium hydroxide, sodium carbonate, sodium methylate, and zinc acetate. Further, the amount of the catalyst is preferably 0.05 to 0.50% by weight, more preferably 0.15 to 0.40% by weight, based on the value obtained by converting the preliminarily decomposed product into polyester. The depolymerization reaction time is preferably 0.5 to 5.0 hours, more preferably 0.5 to 4.0 hours. At that time, the amount of glycol is preferably 2 to 10 parts by weight, more preferably 3 to 7 parts by weight per 1 part by weight of the predegraded product. The solid content of the resulting glycol solution (depolymerization solution) is mainly composed of polyester monomers (ester monomers), and the proportion of oligomers is reduced to 1 to 30% by weight, and further to 2 to 20% by weight. The concentration of the solid content is preferably 10 to 30% by weight, more preferably 15 to 25% by weight.

<Monomer purification process>
The monomer purification step is a step of obtaining a purified ester monomer by purifying the glycol solution obtained in the glycol decomposition step. The monomer purification step includes a filtration process, an adsorption process, an ion exchange process, a crystallization process, a distillation process, or a combination of these processes.

  In order to remove impurities, side reaction promoting components and the like contained in the glycol solution, it is preferable to remove them by filtration treatment, adsorption treatment, ion exchange treatment, or a combination thereof. That is, the glycol solution usually contains insoluble substances, but among these, relatively large coarse substances such as natural fiber waste that is not decomposed by glycol decomposition are removed by a first-stage filtration treatment with a filter such as a strainer, Next, relatively large solid particles such as titanium oxide are removed by a second-stage filtration process using a filter such as a fiber filter medium, and a minute amount of fine particles such as pigments that could not be filtered are removed by an adsorption process using activated carbon, and further a catalyst. It is preferable to remove and purify ionic substances such as residues by ion exchange treatment.

  Moreover, it is preferable to remove glycol-soluble impurities and side reaction products by crystallization treatment. Further, it is preferable to remove high-boiling impurities such as residual low-boiling substances and oligomers that cannot be removed by crystallization treatment by distillation treatment.

  Therefore, in the monomer purification step of the present invention, it is preferable to perform filtration, adsorption, ion exchange, crystallization and distillation in this order.

(First stage filtration)
The first-stage filtration treatment is a treatment for removing a relatively large coarse substance by filtering the glycol solution. In this filtration treatment, it is preferable to filter the glycol solution at 160 to 260 ° C., preferably 180 to 230 ° C., and remove coarse substances that have not been decomposed by the glycol decomposition reaction, for example, solid foreign matters such as natural fiber waste. For example, the glycol solution is preferably passed through a metal strainer having a pore diameter of 0.1 to 2 mm.

(Second stage filtration)
The second stage filtration process is a process for filtering the glycol solution to remove relatively large solid particles. In this filtration treatment, the glycol solution is cooled to 60 to 95 ° C., preferably 70 to 90 ° C. and filtered, and solid particles that have not been decomposed by the glycol decomposition reaction, for example, solid foreign matters having an average particle diameter of about 1 to 500 μm ( (Titanium oxide, carbon black, etc.) are preferably removed. For example, it is preferable to pass the glycol solution through a filtration device filled with a filter medium made of 3 to 20 dtex fibers (fibrous polyester, polypropylene fibers, etc.) with a porosity of 70 to 98%.

(Adsorption treatment)
The adsorption treatment is a treatment for adsorbing impurities in the glycol solution with an adsorbent such as activated carbon. The adsorption treatment is performed by maintaining the glycol solution at a temperature of 60 to 95 ° C., preferably 70 to 90 ° C., and passing the solution through an adsorption tower packed with activated carbon at a space velocity of 0.1 to 5.0 hr ^−1. preferable. This adsorption treatment also removes a colorant such as a pigment and can be called a decolorization treatment. Examples of the activated carbon include “Dia Hope 006” and “Dia Hope 008” manufactured by Mitsubishi Chemical Corporation.

(Ion exchange treatment)
The ion exchange treatment is a treatment for removing ionic substances such as catalyst residues in the glycol solution. As the ion exchange treatment, cation exchange is performed by maintaining the glycol solution at a temperature of 60 to 95 ° C., preferably 70 to 90 ° C., and passing the solution through a decation tower packed with a cation exchanger at a space velocity of ¹ to 12 hr ^−1. It is preferable that the anion exchange treatment be performed after passing through the connecting pipe for 3 seconds to 10 minutes and then passing through the deanion tower filled with the anion exchanger at a space velocity of 0.5 to 10 hr ^−1. . Preferable examples of the cation exchanger include cation exchange resin “Amberlite IR-120B” manufactured by Rohm and Haas. Moreover, as an anion exchanger, the mixture etc. of anion exchange resin "Amberlite IRA96SB" by Rohm and Haas company and a cation exchange resin "Amberlite IR-120B" etc. can be mentioned preferably, for example. The mixing ratio (volume ratio) of the anion exchange resin and cation exchange resin is preferably 1: 3 to 5: 1.

(Crystal treatment)
The crystallization process is a process in which the glycol solution is cooled, the ester monomer is precipitated, and solid-liquid separation is performed. In the crystallization treatment, the solution after the deionization treatment (deionization treatment solution) is cooled in the crystallization tank from a temperature equal to or higher than the saturation solubility to a temperature in the range of 15 to 30 ° C. It is preferable to deposit the ester monomer so that the average particle size of the precipitate is 40 to 200 μm (measured by diluting 10 times with EG using a Shimadzu SALD-200VER) while maintaining for 12 hours. When the deionized solution is cooled from a temperature equal to or higher than the saturation solubility, it is preferably slowly cooled, for example, at a rate of 0.1 to 0.5 ° C./min.

The obtained precipitate is separated into solid components by solid-liquid separation. Solid-liquid separation is preferably performed while maintaining the temperature during the crystallization treatment, that is, the temperature in the range of 15 to 30 ° C. The method for solid-liquid separation is not particularly limited, and preferred examples include pressure filtration, suction filtration, and centrifugation. For example, in the case of pressure filtration, the precipitate is preferably filtered by a filter press using a filter cloth having an air permeability of ^{3 to 30} cm ³ / min · cm ² . It is preferable to filter using 30 μm filter paper.

  Furthermore, recrystallization purification treatment may be performed using an organic solvent such as isopropyl alcohol.

  By performing crystallization treatment, components of synthetic fibers such as nylon that are decomposed by glycol decomposition and dissolved in glycol solution (for example, 5-aminocaproic acid glycol ester, adipic acid glycol ester, etc.) Since it is in a dissolved state, it is separated from the solid content.

(Distillation process)
The distillation treatment is a treatment for purifying the ester monomer obtained by the crystallization treatment by distillation. In the distillation treatment, the ester monomer filter cake obtained by the crystallization treatment is dissolved at 70 to 120 ° C., the melt is introduced into the first evaporator, and the temperature is 130 to 170 ° C. and the pressure is 300 to 1,000 Pa. Then, the low boiling point component is evaporated (first evaporation), and then the melt that has undergone the first evaporation is introduced into the second evaporation apparatus, and the low boiling point component is evaporated under the conditions of a temperature of 130 to 170 ° C. and a pressure of 50 to 250 Pa ( Second evaporation) is preferred. Next, it is preferable to introduce the melt obtained through the second evaporation into a falling film molecular distillation apparatus, and perform distillation (molecular distillation) under conditions of a temperature of 180 to 220 ° C. and a pressure of 25 Pa or less to obtain an ester monomer as a fraction.

  By purifying the ester monomer by the above-described operation, a high-quality ester monomer, preferably bis (2-hydroxyethyl) terephthalate (BHET) can be obtained efficiently. This purified BHET can be produced in the presence of a polymerization catalyst to produce high-quality (for example, excellent color tone) polyethylene terephthalate.

  Hereinafter, the present invention will be described more specifically with reference to examples. Needless to say, the present invention is not limited to this embodiment. The characteristics in the examples were measured by the following methods.

<UV discrimination method>
1 g of sample fiber was dissolved in 500 ml of a mixed solution of phenol / tetrachloroethane = 3/2. The insoluble matter remaining after suction filtration with 5A filter paper was washed with methanol and dried to determine the insoluble matter contamination rate. Subsequently, the absorbance at 310 nm of the filtrate was measured with an ultraviolet-visible spectrophotometer “UVmini-1240” (manufactured by Shimadzu Corporation), and the height of the peak corresponding to the waveform of polyethylene terephthalate as a standard substance was compared. The concentration of dissolved polyethylene terephthalate was calculated. From the mixing ratio and the concentration, the polyester content in the sample fiber was measured.

<Optical density measurement method (OD380)>
Dissolve 5 g of sample in methanol to make a 10 wt% methanol solution, UVmini-1240 (manufactured by Shimadzu Corporation) with a cell length of 10 mm, blank is zero-point corrected using methanol, and the absorbance of this solution at 380 nm is measured. It was measured.
<Color value (L value)>
The L value of the fiber or pellet was measured with a color measuring instrument ZE-2000 manufactured by Nippon Denshoku Industries Co., Ltd.

<Example 1>
(Extraction process)
100 g of fabric (L value: 22) made of polyethylene terephthalate fiber (determined by UV discrimination method) colored deep red was cut into a size of about 5 cm square using a cutting machine. The cut fabric was put into an autoclave having a capacity of 2 liters without any melt molding (granulation molding) and having a wire mesh attached to the bottom so that the liquid could be extracted from the bottom. The autoclave was charged with 1 liter of ethylene glycol (EG) and heated to 150 ° C. Thereafter, while maintaining the temperature at 150 ° C., about 5 milliliters of EG was extracted from the lower portion every 5 minutes, received in a test tube, and observed. As a result, the extraction of the dye started immediately and reached an equilibrium by visual observation after 15 minutes. It was recognized that After 30 minutes, the colored EG was extracted, and nitrogen gas was blown to drive out the remaining EG. When new EG was added again and heating extraction was repeated in the above procedure, it was confirmed that the equilibrium was reached at a coloring level lower than the previous time in about 15 minutes. After 30 minutes, the colored EG was extracted and the fabric was visually observed. As a result, discharging was performed to a very thin coloring level. Then, when heating EG extraction was performed once again in the same manner as described above, coloring of EG was extremely reduced, and thus slightly colored EG was extracted after 30 minutes.

(Separation process)
The temperature of the fabric was lowered to room temperature, the fabric was taken out and squeezed with a press roll to squeeze out the EG. The resulting fabric contained 20% by weight EG. A part of this fabric was taken out, washed with water and dried, and the color value was measured. The L value was 72.

(Glycol decomposition process)
123 g of the extracted fabric containing 20% by weight of EG was put into an autoclave equipped with a 2 liter reflux apparatus and a stirrer, and further 525 g of heated EG and 0.25 g of sodium hydroxide (NaOH) were added. Under normal pressure, the boiling point of EG was heated under reflux for 2 hours for depolymerization to obtain a glycol solution.

(Monomer purification process)
"First stage filtration"
The resulting glycol solution was passed through a basket strainer having a pore diameter of 1 mm to remove coarse solids that were not decomposed (depolymerized).

"Second stage filtration"
After the temperature of the glycol solution is lowered to 85 ° C., while maintaining this temperature, the solution is passed through a column packed with 6 dtex polypropylene fiber at a porosity of 85% to remove solids (particles) containing titanium oxide. As a result, an almost transparent liquid was obtained with the naked eye.

"Adsorption treatment"
The temperature of the glycol solution is maintained at 85 ° C., and the solution is passed through an 85 ° C. warm water jacketed glass column (decolorization column) filled with 50 ml of activated carbon Diahop 006 manufactured by Mitsubishi Chemical Co., Ltd. at a space velocity of 3 hr ^−1. And minute foreign matters were removed by adsorption treatment.

"Ion exchange process"
Next, while maintaining 85 ° C., the solution was passed through a 85 ° C. warm water jacketed glass column (cation exchange column) packed with 20 ml of a cation exchange resin (Rohm and Haas, Amberlite IR120B) at a space velocity of 7 hr ^−1. The cation exchange resin 6.7 ml and the anion exchange resin (Rohm and Haas, Amberlite IRA96SB) 13.3 ml were passed through a 85 ° C. hot water jacketed glass column (anion exchange column) at a space velocity of 7 hr ^−1. And deionized. The resulting glycol solution had an optical density (OD380) of 0.035.

"Crystal processing"
The temperature of the glycol solution was lowered to 25 ° C. with stirring for 5 hours to crystallize the ester monomer (BHET). Solid-liquid separation was performed by filtering with 5A filter paper.

"Distillation process"
The resulting crystallized product of the crude ester monomer (crude BHET) is melted at 110 ° C., and the low-boiling product mainly composed of EG is distilled off at a temperature of 150 ° C. and a pressure of 600 Pa, and the remaining low-boiling product. Was distilled at a temperature of 150 ° C. and a pressure of 106 Pa, and then subjected to molecular distillation with a glass laboratory molecular distiller under the conditions of 7.98 Pa and 185 ° C., and the fraction had a purity of 99.36% by weight and an optical density. (OD380) 0.005 high-purity BHET was obtained.

  When Example 1 was repeated using the same decolorization column, the decolorization column broke through when 5,600 ml of the glycol solution was flowed. The processing amount until this breakthrough was unstained polyethylene terephthalate as a raw material. When the fiber was used, the processing amount until breakthrough was close to about 6,000 ml.

<Comparative Example 1>
(Glycol decomposition process)
In Example 1, without extracting with EG, 100 g of the fabric was put into an autoclave equipped with a reflux heater and a stirrer having a capacity of 2 liters, and 550 g of heated EG and 0.25 g of NaOH were added thereto, under normal pressure. The solution was heated at reflux for 2 hours at the boiling point of EG for depolymerization to obtain a glycol solution.

(Monomer purification process)
"First stage filtration"
The resulting glycol solution was passed through a basket strainer having a pore diameter of 1 mm to remove coarse solids that were not decomposed (depolymerized).

"Second stage filtration"
After the obtained glycol solution was cooled to 85 ° C., the solid solution (particles) containing titanium oxide was passed through a column packed with 6 dtex polypropylene fiber at a porosity of 85% while maintaining this temperature. When removed, a red liquid having a hue almost the same as that of the fabric as seen with the naked eye was obtained.

"Adsorption treatment"
The temperature of the glycol solution was lowered to 85 ° C. and passed through the decolorization column in the same manner as in Example 1. The optical density (OD380) of the glycol solution immediately after the start of filtration was 0.035, but after 5 minutes, the activated carbon broke through, and decolorization was impossible.

<Example 2>
(Extraction process, separation process)
When extraction was performed in the same procedure as in Example 1 using 100 g of black polyethylene terephthalate fiber fabric (L value 19) used for straw umbrella, a fabric with L value 65 was obtained.

(Glycol decomposition process, monomer purification process)
Subsequently, when the fabric was subjected to glycol decomposition and monomer purification from the glycol solution in the same procedure as in Example 1, the purity of the obtained BHET was 98.9% by weight, and the optical density (OD380) was 0.003.

<Comparative example 2>
Except not performing extraction by EG, when it implemented like Example 2, breakthrough occurred in the stage which flowed 50 ml of glycol solutions to the activated carbon treatment column, and adsorption processing became impossible.

<Example 3>
When 100 g of scarlet polyethylene terephthalate fiber fabric (L value 22) used for straw umbrellas was extracted in the same procedure as in Example 1, a fabric having an L value of 66 was obtained. Subsequently, the fabric was subjected to glycol decomposition by the same procedure as in Example 1, and then the monomer was purified from the glycol solution. As a result, the purity of the obtained BHET was 99.0% by weight and the optical density (OD380) was 0.002. It was.

<Comparative Example 3>
The same red polyethylene terephthalate fiber fabric as used in Example 1 was cut into about 2 cm square, pelletized by applying to a melt extruder having a diameter of 20 mm at a melting temperature of 275 ° C., and having an average size of 3 mm in diameter and 5 mm in length. Manufactured. The L value of the obtained chip was 8. Using this chip, the extraction process with EG was repeated three times under the conditions of Example 1, but the L value of the chip remained at 8, and the dye was not substantially extracted.

<Comparative example 4>
The same red polyethylene terephthalate fiber fabric as used in Example 1 was cut into approximately 3 cm square, and then applied to a pellet mill (I-HC manufactured by Sato Iron Works) at 220 ° C., and the cylindrical solid in a state where only the surface was melted. It was molded into a product (8 mmφ × 20 mm). Using the obtained cylindrical solid material, extraction was performed by EG according to the procedure of Example 1. As a result, even when the extraction process was repeated three times, the extraction and removal of the dye in the melted portion was not visually confirmed. . Subsequently, the solid was used to decompose the glycol by the procedure of Example 1 and then the monomer purification from the glycol solution was advanced. When 210 ml of the glycol solution was passed through the 50 ml decolorization column, the activated carbon was broken through. Happened.

<Comparative Example 5>
In Example 1, when extraction with EG before depolymerization was performed once, the L value of the fabric was 41. Using this fabric, the glycol was decomposed by the procedure of Example 1 and then the monomer purification from the glycol solution was advanced. As a result, 80% glycol solution was passed through the 50 ml decolorization column, and activated carbon breakthrough occurred. It was.

<Example 4>
(Extraction process)
15 g of fabric (L value: 22) made of polyethylene terephthalate fiber (determined by UV discrimination method) colored in deep red was cut into a size of about 5 cm square using a cutting machine. The cut fabric is introduced into a Soxhlet extractor that combines an extraction glass tube (inner diameter 25 mm, height 150 mm) with a reflux condenser and an evaporation flask containing 100 g of EG. The discharging process was performed for 90 minutes while boiling. During this time, the total amount of EG that contacted the fabric was 345 g.

(Separation process)
The temperature of the fabric was lowered to room temperature, the fabric was taken out and squeezed with a press roll to squeeze out the EG. The resulting fabric contained 20% by weight EG. A part of this fabric was taken out, washed with water and dried, and the color value was measured. The L value was 75.

(Glycol decomposition process)
19 g of the extracted fabric containing 20% by weight of EG was put into a 2 liter autoclave equipped with a reflux device and a stirrer, and further 100 g of heated EG and 0.04 g of sodium hydroxide (NaOH) were added. A glycol solution was obtained by depolymerization by heating under reflux for 2 hours at the boiling point of EG at normal pressure.

(Monomer purification process)
When this glycol solution was subjected to monomer purification treatment in the same manner as in Example 1, high purity BHET having a purity of 99.4% by weight and an optical density (OD380) of 0.003 was obtained.

<Example 5>
(Extraction process)
40 g of fabric (L value: 22) made of polyethylene terephthalate fiber (determined by UV discrimination method) colored in deep red was cut into a size of about 3 cm square using a cutting machine. The cut fabric was fixed on a conveyor so that the cut pieces were arranged in series, and continuously extracted by a countercurrent extraction device (continuous countercurrent extraction). Extraction is performed by inserting fabric at 60 g / hr from one side of the extractor at the side of the extractor, and by injecting ethylene glycol at 195 ° C. at 1,200 g / hr from the other ethylene glycol inlet, The fabric is discharged from the ethylene glycol discharge port near the fabric insertion port, and the colored component extracted fabric is extracted from the fabric outlet near the ethylene glycol injection port. The contact time (extraction time) between the fabric and ethylene glycol is 40. Minutes.

(Separation process)
The temperature of the fabric was lowered to room temperature, the fabric was taken out and squeezed with a press roll to squeeze out the EG. The resulting fabric contained 20% by weight EG. A part of this fabric was taken out, washed with water and dried, and the color value was measured. The L value was 75.

(Glycol decomposition process)
50 g of the extracted fabric containing 20% by weight of EG was put into a 2 liter autoclave equipped with a reflux apparatus and a stirrer, and further 200 g of heated EG and 0.1 g of sodium hydroxide (NaOH) were added. A glycol solution was obtained by depolymerization by heating under reflux for 2 hours at the boiling point of EG at normal pressure.

(Monomer purification process)
When this glycol solution was subjected to monomer purification treatment in the same manner as in Example 1, high purity BHET having a purity of 99.4% by weight and an optical density (OD380) of 0.003 was obtained.

<Example 6>
(Extraction process, separation process)
When 60 g of dark blue polyethylene terephthalate fiber was used and the same method as in Example 5 was performed, the color L value was 73.

(Glycol decomposition process)
75 g of extracted fabric containing 20% by weight of EG and 30 g of BHET were put into a 2 liter separable flask, and the evaporated EG was distilled out of the system at a reaction temperature of 250 ° C. for 10 minutes. Pre-disassembled. 440 g of heated EG and 0.15 g of sodium hydroxide (NaOH) were added to the obtained predegraded product, and depolymerization was performed by heating at the boiling point of EG at normal pressure for 30 minutes under reflux to obtain a glycol solution. Obtained.

(Monomer purification process)
The same method as in Example 1 was used. As a result, a high purity BHET having a purity of 99.4% by weight and an optical density (OD380) of 0.004 was obtained.

  Since the method of the present invention can efficiently recover high-purity ester monomers by chemical recycling from fibrous polyesters, particularly colored fibrous polyesters, it can be expected to contribute to the recycling industry.

Claims (7)

A method for recovering ester monomers from fibrous polyester,
(1) An extraction step of bringing a colored fibrous polyester into contact with ethylene glycol, extracting a colored component in the fibrous polyester, and obtaining a fibrous polyester having a color L value of 60 or more,
(2) A separation step of separating the fibrous polyester from the mixture of the fibrous polyester and ethylene glycol after the extraction,
(3) A glycol decomposition step in which an ester component constituting the obtained fibrous polyester is depolymerized with glycol to obtain a glycol solution containing an ester monomer, and (4) a monomer that purifies the glycol solution to obtain a purified ester monomer. Purification process,
A method for recovering an ester monomer from a fibrous polyester comprising: The method of Claim 1 which uses 5-50 weight part of ethylene glycol with respect to 1 weight part of fibrous polyester. The method of Claim 1 or 2 whose extraction temperature is 100-200 degreeC. The method according to any one of claims 1 to 3, wherein a change value (ΔL value) of the color L value of the fibrous polyester by extraction is 5 or more. The glycol decomposition step performs depolymerization with glycol after predecomposing the ester component constituting the fibrous polyester separated in the separation step using the ester monomer and / or oligomer. 2. The method according to item 1. The method according to any one of claims 1 to 5, wherein the fibrous polyester is made of polyethylene terephthalate and the glycol used for depolymerization is ethylene glycol. The method according to any one of claims 1 to 6, wherein the monomer purification step comprises filtration, adsorption, ion exchange, crystallization, distillation or a combination thereof.